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3,400 | Brugada syndrome in a patient with accessory pathway. | Brugada syndrome in a patient with Wolff-Parkinson-White syndrome. We report a 32-year-old man with orthodromic atrioventricular (AV) reciprocating tachycardia using a right posterior accessory pathway. However, his ECG showed ST segment elevation in leads V1 to V3. After successful radiofrequency ablation of his accessory pathway a cardioverter defibrillator was implanted. |
3,401 | Programmed ventricular stimulation: influence of early versus late introduction of a third extrastimulus, a randomized, prospective study. | The aim of this prospective study was to analyze the yield of early vs late introduction of a third extra-stimulus during programmed ventricular stimulation.</AbstractText>Two randomized protocols of programmed ventricular stimulation were used in 94 consecutive patients with coronary artery disease who were studied because of non-sustained ventricular tachycardia (9.6%), sustained monomorphic ventricular tachycardia (46.8%), ventricular fibrillation (18.1) or syncope (25.5%). During protocol A, a third extrastimulus was introduced during a basic drive cycle length of 500 ms after completion of programmed ventricular stimulation with 1 and 2 extrastimuli during sinus rhythm and paced cycle lengths of 500, 430. 370 and 330 ms. During protocol B, the third extrastimulus was introduced early (after 1 and 2 extrastimuli during sinus rhythm and a paced cycle length of 500 ms). Both protocols began at the right ventricular apex. If sustained ventricular tachyarrhythmia had been induced, the same sequence of programmed ventricular stimulation was repeated at the right ventricular outflow tract.</AbstractText>The overall incidence of induced arrhythmias did not differ between the two protocols. However, the use of the third extrastimulus (both protocols) increased the yield of ventricular fibrillation induction significantly (P < 0.04) compared with ventricular tachycardia induction.</AbstractText>The introduction of the third extrastimulus should be considered only at the end of stimulation protocols (especially in those patients without previously documented sustained ventricular tachyarrhythmias) in order to prevent induction of polymorphic ventricular tachycardia or fibrillation.</AbstractText> |
3,402 | Catheter ablation using very high frequency current: effects on the atrioventricular junction and ventricular myocardium in sheep. | Radiofrequency ablation is currently used in the treatment of various cardiac arrhythmias. However, this technique is limited by impedance rise, leading to coagulum formation and desiccation of tissue. We developed a new generator, providing very high frequency (27 MHz) current, which is in the intermediate range between radiofrequency and microwave energy. The aim of this study was to evaluate the results for catheter ablation of the atrioventricular junction and characteristics of the lesions obtained at ventricular sites.</AbstractText>The generator was coupled to a specially designed 7-French coaxial catheter. The study included experiments performed on 10 sheep (Wt. 31- 42 kg). In seven sheep, the catheter was introduced into the femoral vein and advanced across the tricuspid annulus to record the largest possible His electrogram. VHF current was applied for 25 s, with increasing energies. The energy needed to obtain complete atrioventricular (AV) block ranged from 60 to 100 Watts. Six animals were observed for 6 to 21 days. Complete AV block was found to be persistent. In those seven sheep in whom AV junction was ablated and in three additional sheep, the ablation catheter was positioned toward the right ventricular apex using the same approach and into the left ventricle via the femoral artery, and 20 to 90 Watts energy was delivered in order to assess the size of the induced lesions. Side effects included ventricular tachycardia degenerating into ventricular fibrillation in six cases, but the same effect was observed in this animal model with radiofrequency energy. No cardiac perforation was noted. No thrombus was observed at the catheter tip. The size of the lesion ranged from 3 to 45 mm in width and 1 to 15 mm in depth.</AbstractText>Catheter ablation using VHF current is feasible and appears effective in producing stable AV block when applied at the AV junction and results in substantial myocardial lesions. Further studies are needed to define its clinical interest and side effects.</AbstractText> |
3,403 | Modification of the radial procedure in a patient with partial atrioventricular septal defect. | We successfully cured atrial fibrillation while preserving internodal conduction in a patient with a partial atrioventricular septal defect. Because the anterior and middle internodal tracts are interrupted by the defect, the lower right atrial incision of either the maze or the radial procedure may interrupt the remaining posterior tract, resulting in internodal conduction block. We deleted the posterior septal incision from the radial procedure and replaced it with a right-side left atriotomy. The patient resumed normal sinus rhythm with significant contraction of the right and left atria. The preserved internodal pathway through the posterior interatrial septum was confirmed by electrophysiologic study. |
3,404 | [Chronic simultaneous stimulation of both ventricles, a new treatment option for severe congestive heart failure]. | Dilated congestive heart failure due to systolic left ventricle dysfunction frequently leads to intraventricular conduction disturbances with a prolonged QRS complex (> 120 ms). The prolonged conduction time in the ventricles causes electrical asynchrony of the ventricles and contributes to a further reduction of systolic function, changes of filling and relaxation intervals, and promotes mitral valve insufficiency. Chronic simultaneous stimulation of both the right and left ventricle in patients with severe heart failure improves functional status, quality of life, and exertion tolerance. At present the implantation of a biventricular pacemaker is time consuming because the positioning of the lead in a left ventricular epicardial vein is difficult. As congestive heart failure is frequently associated with an increased risk of ventricular fibrillation, the combined implantation of a biventricular stimulator and an implantable automatic defibrillator is sometimes necessary. Preliminary calculations show that about 750 patients per year with severe congestive heart failure are eligible for a biventricular stimulator. |
3,405 | Postextrasystolic repolarization abnormalities in ST-U segment in patients with ventricular arrhythmias. | Changes in U-wave amplitude after premature ventricular contractions (PVC) are known as prognostic markers in the long QT syndrome dependent on bradycardia. The purpose of the study was to find correlation between postextrasystolic ST-U segment changes and a history of sustained ventricular tachycardia or ventricular fibrillation (VT/VF).</AbstractText>The ST-U segment configurations were taken from the 24-hour ambulatory ECG. The comparison of the morphology of these segments was performed between sinus beats preceding PVC's and first postextrasystolic beats.</AbstractText>Two groups of patients were evaluated: 1) 32 patients with VT/VF history (VT/VF group), and 2) 36 patients with potentially malignant arrhythmia (structural heart disease with frequent PVCs and/or nonsustained VT- nsVT) (non-VT/VF group).</AbstractText>We found T-wave changes in 8 patients (25%) from the VT/VF group and in 12 patients (33.3%) from the nonVT/VF group (P = NS) and U-wave changes in 13 patients (40.6%) and 3 patients (8.3%), respectively (P < 0.05). Other ECG indexes related to PVC's were also considered: RR interval, coupling interval (CI), prematurity index (PI), and postextrasystolic pause (PP). The analysis of these ECG indices revealed, when compared with patients without T-U-wave changes, that the occurrence of U-wave changes was significantly related to longer RR interval of the sinus rhythm preceding PVC: 1025 +/- 211 vs 918 +/- 200 ms (P < 0.05). The prematurity index was lowest in patients with U-wave changes: 0.54 +/- 0.12 vs 0.65 +/- 0.16 (P < 0.01) while postextrasystolic pauses leading to the postextrasystolic U-wave changes were significantly longer: 1383 +/- 223 vs 1130 +/- 247 ms (P < 0.001). CI did not differentiate patients: 556 +/- 108 vs 584 +/- 117 ms (P = NS).</AbstractText>Postextrasystolic changes in ST-U segment configuration are dependent on bradycardia, low prematurity index of the PVC, and the lengthening of the postextrasystolic pause. U-wave changes more frequently appeared in patients with malignant arrhythmias. Follow-up study is needed to assess if they might be predictive for the occurrence or reoccurrence of arrhythmic episodes.</AbstractText> |
3,406 | Use of an insertable loop recorder in a myotonic dystrophy patient. | The case of a 66-year-old woman with myotonic dystrophy is presented. This patient underwent implantation of an insertable loop recorder as a participant in a clinical trial. At 1-month follow-up, interrogation of the insertable loop recorder revealed multiple episodes of wide complex tachycardia. She underwent electrophysiologic study, which revealed moderate His-Purkinje disease, focal atrial tachycardia, monomorphic ventricular tachycardia, and ventricular fibrillation. Successful radiofrequency ablation of the focal atrial tachycardia and implantation of a dual-chamber implantable cardioverter defibrillator was performed. |
3,407 | Mind the model: effect of instrumentation on inducibility of atrial fibrillation in a sheep model. | Atrial electrical remodeling, shortening of the atrial effective refractory period (AERP) underlying atrial fibrillation (AF) has been described in different animal models. However, there remains some controversy regarding the time course of this electrical remodeling and the need for secondary factors in the development of AF. We investigated the effect of instrumentation on the inducibility of AF. We hypothesized that epicardial instrumentation could be a confounding factor that accelerates the development of AF.</AbstractText>Thirty sheep were rapidly atrially paced at 600 beats/min for 15 weeks: 15 were endocardially instrumented and paced (endo), and 15 were both endocardially and epicardially instrumented. Six of these animals were endocardially paced (sham) and 9 were epicardially paced (epi). The underlying rhythm was determined at regular intervals, and electrophysiologic study was performed. AF developed significantly faster in the epi group. After 3 weeks of pacing, the cumulative incidence of sustained AF (>1 hour) already was 70% in this group versus only 14% and 20% in the endo and sham groups, respectively. After 15 weeks of pacing, this difference was no longer evident. Baseline AERP and minimal AERP, reached before the development of AF, were not significantly different in the three groups. Epicardial instrumentation (epi and sham) increased baseline left and right atrial pressures, but only epicardial stimulation (epi) led to early development of AF.</AbstractText>In this sheep model of AF, the experimental setup is a major determinant of the inducibility of AF. Not epicardial instrumentation per se but epicardial stimulation accelerated the development of AF. Different animal models</AbstractText> |
3,408 | Implantable cardioverter defibrillator utilization based on discharge diagnoses from Medicare and managed care patients. | Implantable cardioverter defibrillators (ICDs) have become an accepted therapy for patients at high risk of sudden cardiac death. To assess the current utilization of this therapy, we estimated the number of patients at risk of sudden death using an historical claims-based study and compared these results to current ICD usage volumes.</AbstractText>Managed care and Medicare databases (claims related to 4.6 million covered U.S. lives during a 12-month period) were analyzed to identify patients who had either a primary or secondary diagnosis of ventricular tachycardia, ventricular fibrillation, ventricular flutter, or cardiac arrest. These patients were further required to have a diagnosis code indicating a previous myocardial infarction or congestive heart failure. Patients who died during the study period or did not have medical insurance were excluded. In the base case scenario, 1,226 patients per million population were identified as potential ICD candidates. Sensitivity analyses reduced that value to a range from 736 to 1,140 ICD candidates per million population. Sensitivity factors considered included acute myocardial infarction, comorbidities, age, secondary ventricular tachycardia/ventricular fibrillation diagnosis, and varying degrees of left ventricular dysfunction. These results contrast with an ICD usage rate of 416 per million population in the United States and lower rates in other countries.</AbstractText>This study suggests that, based on discharge diagnoses, many patients who could benefit from ICDs are not receiving this therapy. Diverse reasons for this underutilization should be addressed to improve access to, and appropriate use of, this therapy.</AbstractText> |
3,409 | Diagnostic performance of a dual-chamber cardioverter defibrillator programmed with nominal settings: a European prospective study. | Despite technologic developments, accurate discrimination of ventricular tachyarrhythmia from rapid rhythms of nonventricular origin remains a challenge. We sought to examine the sensitivity and specificity of a dual-chamber arrhythmia detection algorithm, the PARAD algorithm, incorporated in a dual-chamber implantable cardioverter defibrillator, the Defender (ELA Medical).</AbstractText>All detailed tachycardia episodes (i.e., with stored atrial and ventricular channel markers and electrograms) retrieved from the Holter memory of the device were analyzed from 95 patients (86 men and 9 women; age 62 +/- 12 years) implanted with the Defender with the algorithm programmed at nominal settings. Over a follow-up of 15 +/- 8 months, 559 detailed sustained tachycardia episodes detected in the tachycardia zone were gathered in 62 patients. Of the 300 ventricular tachycardia (VT) episodes, 298 were appropriately classified as VT by the algorithm. Of the 259 supraventricular tachycardia (SVT) episodes, 231 were appropriately classified as SVT. In 8 patients, 28 episodes of SVT were misclassified as VT: 25 atrial fibrillation episodes (6 patients), 2 sinus tachycardia (1 patient), and 1 atrial tachycardia. Calculated sensitivity and specificity were 99.3% and 89.2% on a per episode basis and 99.8% (95% confidence interval: 97.8 to 100) and 91.6% (95% confidence interval: 86.0 to 97.3) on a per patient basis, respectively.</AbstractText>In this selected population of patients, the PARAD algorithm was safe and reliable for detection of a wide spectrum of tachyarrhythmias. Its specificity was high, particularly with respect to sinus tachycardia detection, but it must be improved with respect to detection of atrial fibrillation.</AbstractText> |
3,410 | Evolution of implantable cardioverter defibrillator indications: comparison of guidelines in the United States and Europe. | The rate of implantation of implantable cardioverter defibrillators (ICD) is growing much faster in the United States than in western Europe. Among several factors, education and awareness of the problem of sudden cardiac death might account for this discrepancy.</AbstractText>Guidelines for ICD implantation developed in the United States and various European countries are compared, including the one recently published by the Working Groups on Arrhythmias and Cardiac Pacing of the European Society of Cardiology. Although all guidelines fully concur in their recommendations for patients after cardiac arrest due to ventricular fibrillation and ventricular tachycardia, small but noticeable differences in opinion can be traced for patients with sustained ventricular tachycardia or syncope, and for primary prevention. In general, European guidelines are more restrictive for the latter indications. Whereas U.S. guidelines were quickly updated over the years, this process took much longer in Europe, and several countries only recently adopted their first guidelines.</AbstractText>Although different in details, the recent release of ICD guidelines in major western European countries will undoubtedly lead to a pronounced increase of patients protected by this form of therapy in Europe in the coming years.</AbstractText> |
3,411 | Automatic external defibrillator: key link in the chain of survival. | Sudden cardiac death is a major health problem. Worldwide success of resuscitation from out-of-hospital cardiac arrest is modest, with 5% to 10% survival to hospital discharge.</AbstractText>In the chain of survival, early defibrillation (goal <5 min after collapse) is a major determinant of successful outcome of resuscitation. This goal is rarely achieved, but the automatic external defibrillator (AED) is a promising tool for lay defibrillation. The AED is a safe and effective device with nearly 100% accurate detection of ventricular fibrillation and nearly 100% accurate detection of a nonshockable rhythm. A large uncontrolled experience suggests improved outcome in nontraditional responders such as police. Controlled studies of community application of the AED are under way.</AbstractText>The AED is a promising tool in the fight against sudden cardiac death and should be studied and supported by all scientists involved, including electrophysiologists.</AbstractText> |
3,412 | Vasopressin and epinephrine are equally effective for CPR in a rat asphyxia model. | Epinephrine has been administered as a drug essential for cardiopulmonary resuscitation (CPR). Recently, vasopressin has been reported to be more effective than epinephrine for CPR in a ventricular fibrillation (VF) model. As a different myocardial pathology is speculated to exist between the VF model and the asphyxia model, we investigated whether vasopressin is also effective in a rat asphyxia model. Twenty-one Sprague-Dawley male rats were divided into three groups: vasopressin 0.8 U/kg (Vaso-Gr), epinephrine 0.05 mg/kg (Epi-Gr), and saline same volume as the other two drugs (Sal-Gr). Five minutes after suffocation induced by obstruction of the tracheal tube, CPR was performed using each drug. Although only one animal survived (17%) in the Sal-Gr, 6/7 (85%) survived in both Vaso-Gr and Epi-Gr (P<0.01). Vasopressin is as effective as epinephrine for CPR in asphyxia-induced rats. |
3,413 | Beneficial effects of vasopressin in prolonged pediatric cardiac arrest: a case series. | Children who suffer cardiac arrest have a poor prognosis. Based on laboratory animal studies and clinical data in adults, vasopressin is an exciting new vasopressor treatment modality during cardiopulmonary resuscitation (CPR). In particular, vasopressin has resulted in short term resuscitation benefits as a "rescue" pressor agent in the setting of prolonged out-of-hospital CPR for ventricular fibrillation in adults. This retrospective series presents the first evidence for resuscitation benefit of bolus vasopressin therapy in the specific setting of pediatric cardiac arrest. All episodes of CPR initiated in a 120-bed tertiary care children's hospital over a three-year period (1997-2000) were reviewed. Four children in the pediatric ICU received vasopressin boluses as rescue therapy during six cardiac arrest events, following failure of conventional CPR, advanced life support, and epinephrine vasopressor therapy. Return of spontaneous circulation for greater than 60 min occurred in three of four patients (75%) and in four of six CPR events (66%) following vasopressin administration. Two of four vasopressin recipients survived >24 h; one survived to hospital discharge and one had withdrawal of supportive therapies following family discussion. Our observations are AHA level 5 (retrospective case series) evidence that vasopressin administration may be beneficial during prolonged pediatric cardiac arrest. Such reports should pave the way for prospective clinical trials comparing vasopressor medications in the setting of pediatric cardiac arrest. |
3,414 | Gender differences in arrhythmias. | Electrocardiographic and electrophysiologic differences between men and women have long been noted. Women have a higher intrinsic heart rate than men, along with a longer corrected QT interval and a shorter sinus nodal recovery time. The incidence of and risk factors for a variety of arrhythmias differ between men and women. Atrioventricular nodal reentry tachycardia has a 2:1 female-to-male predominance, while accessory pathways are twice as frequent in men. Although atrial fibrillation is more prevalent in men of all age groups, the absolute numbers of men and women with atrial fibrillation are equal, and the associated morbidity and mortality experienced by women with atrial fibrillation appear to be worse. Women have a lower incidence of sudden cardiac death, and female survivors of sudden cardiac death have a lower frequency of spontaneous or inducible ventricular tachycardia. On the other hand, drug-induced torsade de pointes and symptomatic long QT syndrome have a female predominance. Therefore, greater caution should be used when prescribing QT-prolonging drugs in women. The incidence of arrhythmias is increased during pregnancy, and management of pregnant patients poses a significant challenge. The mechanisms of these gender differences are unclear but may be related to hormonal effects and the shorter QT interval in adult males. Pharmacologic and nonpharmacologic therapies are usually equally efficacious, but the risks of pharmacologic therapy are different in men and women. Atrial fibrillation may be more difficult to treat in women. |
3,415 | [Effect of emotional stress on the cardiac rhythm variability in rats]. | A degree of irregularities of the heart rhythm was studied by two methods: chaos-analysis and the HRV (heart rate variability) analysis. Our study shows an individual response in 3 groups of animals: 1--animals with low initial level of chaos (correlation dimension (PD2 < 2); 2--animals with high level of chaos (PD2 > 4); and animals with middle level of chaos (2 < PD2 < 4). The first two groups proved to be more sensitive to stress than the third group. Moreover we found that the electrical stability of the heart as measured by the fibrillation threshold, was higher for the chaos third group. The animals of the first two groups had low cardiac stability and high risk of stress-induced cardiac disturbances. |
3,416 | Electrical storms in an ICD-recipient with 429 delivered appropriate shocks: therapeutic management with antiarrhythmic drug combination. | The case of a 65 year old man with ischemic cardiomyopathy, an ICD device and recurrent electrical storms is presented. The patient had been implanted with an ICD device due to aborted sudden death. The first electrical storm occurred 12 months later. It was terminated by the administration of intravenous amiodarone and the patient was discharged on maintenance dose amiodarone and b-blocker. After a period of 3 months during which the patient remained asymptomatic, a second arrhythmic clustering occurred and it was controlled by the addition of mexiletine. A total number of 429 appropriate shocks had been delivered by the device. Thereafter and for a seven month follow-up period, the patient remains asymptomatic under this combination of antiarrhythmic drugs. |
3,417 | Innovative endovascular defibrillator lead use in superior vena cava obstruction. | We describe an unusual case of severe heart failure (HF) and rapid atrial fibrillation (AF) improved through ablation and pacemaker implant despite superior vena cava obstruction (SVCO).</AbstractText>SVCO precluded upper body venous access to the heart for procedural rate control. Both AV Junctional ablation and permanent endovascular lead placement were achieved through the inferior vena cava (IVC).</AbstractText>Clinical improvement from NYHA Class IV to Class II HF was observed with effective nonpharmacologic ventricular rate control.</AbstractText>HF patients with rapid AF and SVCO can achieve ventricular rate control through lower body venous access to the heart utilizing 100-cm endovascular defibrillator rate sensing leads.</AbstractText> |
3,418 | Precordial QT dispersion does not predict inducibility of ventricular tachyarrhythmias at post-revascularization electrophysiologic study. | We tested the hypothesis that revascularization would decrease QT interval dispersion and that QT interval dispersion would predict the outcome of the electrophysiologic study following revascularization.</AbstractText>QT interval dispersion may be a measure of the inhomogeneity of ventricular repolarization. The value of the QT interval dispersion for predicting inducibility of ventricular tachyarrhythmias (VT) during electrophysiologic studies after coronary artery revascularization in patients with hemodynamically significant VT is unknown.</AbstractText>QT interval dispersions were measured from electrocardiograms recorded before and after coronary artery revascularization, but before an electrophysiologic study during the same hospitalization. Fifty-six patients (93% male, 65.1 +/- 9.6 years) were studied. QT interval dispersion decreased significantly following revascularization from 69 +/- 31 ms to 53 +/- 23 ms (p=0.002). Inducibility of VT could not be predicted by the QT interval dispersion following revascularization (50 +/- 30 ms in patients with VT induced vs. 58 +/- 25 ms in patients without VT induced at electrophysiologic study; p=0.2). The change in QT interval dispersion with revascularization (-15 +/- 33 ms vs. -17 +/- 46 ms; p=0.9) could not predict VT inducibility. Actuarial survival after 80 months follow-up was similar in the patients in whom VT was induced (82%) and those patients in whom VT was not induced (83%; p=NS).</AbstractText>Coronary artery revascularization decreased QT interval dispersion in patients with hemodynamically significant VT, but QT interval dispersion was not predictive of inducibility of VT at follow-up electrophysiologic study. Actuarial survival was similar in patients in whom VT was induced and patients in whom VT was not induced.</AbstractText> |
3,419 | Clinical and molecular heterogeneity in the Brugada syndrome: a novel gene locus on chromosome 3. | Brugada syndrome is a form of idiopathic ventricular fibrillation characterized by a right bundle-branch block pattern and ST elevation (STE) in the right precordial leads of the ECG. Sodium channel blockers increase STE. Mutations of the cardiac sodium channel SCN5A cause the disorder, and an implantable cardioverter-defibrillator is often recommended for affected individuals. Mutations in other genes have not been identified, and it is not known if the efficacy of drug testing or the malignancy of arrhythmias correlates to the gene defect.</AbstractText>We performed histories, physical examinations, ECGs, and drug testing on a large multigenerational family with Brugada syndrome. DNA isolated from blood samples, polymorphic genomic markers, and polymorphisms within candidate sodium channels were used for a genome-wide screen, fine mapping, and linkage analysis. We identified 12 affected individuals (right bundle-branch block, > or =1-mm STE) with an autosomal dominant inheritance pattern characterized by incomplete penetrance that appeared to be dependent on age and sex. Four affected individuals had syncope and 2 had documented ventricular arrhythmias, but there was minimal family history of sudden death. Procainamide infusions did not identify additional affected individuals. Linkage was present to an approximately equal 15-cM region on chromosome 3p22-25 (maximum LOD score=4.00). The sodium channel genes SCN5A, SCN10A, and SCN12A on chromosome 3 were excluded as candidates (LOD scores < or =-2).</AbstractText>A Brugada syndrome locus distinct from SCN5A is associated with progressive conduction disease, a low sensitivity to procainamide testing, and a relatively good prognosis in a single large pedigree.</AbstractText> |
3,420 | [Indications and potential benefits of implantable automatic defibrillator endowed with biventricular pacing]. | Heart failure (HF) is associated with a poor long-term survival due to progressive refractory heart dysfunction and sudden cardiac death. Cardiac resynchronization through three-chambered atriobiventricular pacing has been introduced to treat patients with drug-refractory HF and unsynchronized ventricular activation due to left bundle branch block (LBBB). The technique is aimed to overcome inter- and intraventricular conduction delays leading to a ventricular dyssynchrony, characterized by paradoxical septal wall motion, presystolic mitral regurgitation, and reduction in diastolic filling times. Acute studies demonstrated that biventricular pacing (and maybe left ventricular pacing alone) may improve both systolic and diastolic function. First studies on chronically paced patients consistently showed that the QRS shortening was associated with a significant improvement in symptoms, NYHA functional class, left ventricular ejection fraction (LVEF), exercise tolerance, and quality of life. As far as sudden cardiac death prevention in HF is concerned, the implantable cardioverter-defibrillator (ICD) has been demonstrated to be the most effective therapy in patients with prior cardiac arrest due to ventricular fibrillation or poorly tolerated ventricular tachycardia. Low LVEF, unsustained ventricular tachycardia and inducibility at electrophysiological study also may identify high risk patients requiring ICD implantation. Further studies are needed in evaluating the impact of cardiac resynchronization on hard endpoints, such as survival and long-term clinical outcome, as well as in upgrading risk stratification criteria to be used in candidate selection to ICD implantation. However, HF patients with prior cardiac arrest and LBBB should be considered as the optimal candidates to the "ICD implantation combined with biventricular pacing". Conversely, HF patients with LBBB, but without cardiac arrest, could be considered for "biventricular pacing combined with an ICD". The selection criteria for this novel non-pharmacological therapy still have to be defined. The authors emphasize the main indication to ICD implantation combined with biventricular pacing, i.e. HF patients with prior cardiac arrest and LBBB; controversially, while they discuss the other indications to biventricular pacing combined with an ICD. |
3,421 | [Variables of arrhythmia risk in relation to pacemaker and implantable defibrillator]. | Patients suffering from heart failure are at high risk of arrhythmic death. Conventional pacemakers have not shown to affect mortality in patients with chronic heart failure and sick sinus syndrome, while this issue is established in patients with III degree or advanced atrioventricular block. Biventricular pacing has recently been introduced in clinical practice and the experience is limited; to date, only an improvement in symptoms and quality of life has been shown. Biventricular pacing with implantable cardioverter-defibrillator back-up is promising. The implantable cardioverter-defibrillator is able to reduce total and sudden mortality in high risk patients, as clearly demonstrated by several randomized clinical trials. |
3,422 | [Prognostic value of supraventricular arrhythmias in heart failure]. | Supraventricular tachyarrhythmias can be responsible for severe hemodynamic derangement which may contribute to the progression and worsening of heart failure. The resultant effect of these arrhythmias, however, is conditioned by several concomitant factors, such as age of the patients, left ventricular systolic function, and ventricular rate response. If the role of such arrhythmias in functional class, morbidity, and functional capacity is well accepted, controversial data are available on their role on mortality in patients with heart failure. |
3,423 | [Arrhythmia risk stratification in patients with heart failure: prognostic evaluation of arrhythmia risk]. | Sudden cardiac death is one of the more frequent causes of death in patients with heart failure. Thus, identification of patients at risk is a major clinical problem not only for the unpredictability of the event but also for the continuous growth of patients' number. The most widely used parameter for risk stratification is ejection fraction. Unfortunately, its predictive accuracy is limited and often it is impossible to distinguish patients with an increased arrhythmic mortality from those with an increased mortality due to pump failure. Heart rate variability and baroreflex sensitivity analysis has been largely utilized to obtain information on autonomic modulation of sinus node as well as to identify patients at risk. However, at variance with results observed in post-myocardial infarction patients, lower values of both parameters have been reported in patients with either an increased total or arrhythmic mortality. More recently, T wave alternans analysis has been found effective in identifying patients with an increased arrhythmic risk. Ongoing studies will provide evidence to support the use of this non-invasive technique in patients with cardiac insufficiency. Finally, the role of programmed electrical stimulation in heart failure patients appears limited. Inducibility of monomorphic sustained ventricular tachycardia seems to correlate better with the presenting clinical arrhythmia than with patient outcome. In conclusion, our capability of identifying heart failure patients at risk for arrhythmic death is far from being satisfactory. It is possible that the combination of results of multiple non-invasive tests such as reduction in ejection fraction and positivity for T wave alternans may not only provide general prognostic information but also facilitate the appropriate identification of patients at risk who may benefit from antiarrhythmic therapy. |
3,424 | [Arrhythmia risk stratification based on etiological and anatomo-structural factors]. | In patients with heart failure, sudden death is very common, particularly in subjects in NYHA functional class II and III (respectively 50-80% and 30-50% of all deaths). The mechanisms at the root of sudden death depend on whether heart failure is secondary to an ischemic or non-ischemic heart disease. In ischemic heart disease, sudden death is mainly arrhythmic (ventricular tachycardia/ventricular fibrillation caused by the reentry circuits in the infarct area or by acute ischemic episodes or bradyarrhythmia). In non-ischemic heart disease, the percentage of arrhythmic sudden deaths seems to be lower. Furthermore, a percentage of sudden death cases with heart failure can be linked to electromechanical dissociation and to pulmonary or systemic embolism. Moreover the risk stratification level differs depending on whether heart failure is caused by an ischemic or a non-ischemic heart disease. The various non-invasive studies mainly employed in patients with ischemic heart disease cannot be reliably used to study patients with non-ischemic heart disease. Even the programmed ventricular stimulation demonstrated prognostic reliability only in cases involving ischemic heart disease. The therapeutic approach may also be conditioned by the heart disease responsible for heart failure. To date, for example, all the studies published on primary prevention of sudden death with an implantable defibrillator have been carried out in patients with ischemic heart disease. |
3,425 | [Arrhythmia risk stratification in patients with heart failure. Foreword]. | The challenge of preventing arrhythmic sudden death is one of the major issues of today's treatment of heart failure. To pursue this aim, an accurate selection of candidates for sudden death has to be routinely carried out, while a maximized and individualized drug treatment has to be extensively administered in all high-risk selected patients. However, in clinical practice there is no agreement on the selection criteria of sudden death risk, particularly in patients with advanced heart failure. Furthermore, the real impact of each category of drugs in reducing the risk of sudden death in heart failure patients is still under debate. As far as non-pharmacological options are concerned, implantable cardioverter-defibrillators (ICD) have been demonstrated to be the most effective therapy in patients with prior cardiac arrest due to ventricular fibrillation or poorly tolerated ventricular tachycardia. Low left ventricular ejection fraction, unsustained ventricular tachycardia and inducibility at electrophysiological study also may identify high-risk patients requiring ICD implantation. However, such a stratification seems to be effective in ischemic more than in non-ischemic patients, while generally the primary prevention of sudden death is still restricted to a minority of patients. Biventricular pacing has been proven to be effective in optimizing left ventricular function in more than 50% of left bundle branch block and advanced heart failure patients, while further studies are needed to evaluate the real impact of cardiac resynchronization therapy on hard endpoints, such as survival and long-term clinical outcome. Therefore, the selection criteria of "responders" to this novel non-pharmacological therapy still have to be defined. There is convincing evidence in the literature that tailored drug therapy can be highly effective in preventing heart failure progression as well as in reducing total and sudden mortality. Nevertheless, prevention of sudden death is still a debated point in heart failure treatment. For this reason, we aimed to provide heart failure specialists with updated reviews on this topic, such as those published in this issue of the Italian Heart Journal Supplement. Therefore, we are proud to present all the authors who contributed with the high quality of their articles to this editorial effort. Obviously, we have to thank the authors, but we also have to address the readers, thanking them in advance for their interest in such an initiative. |
3,426 | Transferring patients for direct coronary angioplasty: a retrospective analysis of 135 unselected patients with acute myocardial infarction. | Direct coronary angioplasty (PTCA) represents the most effective treatment for acute myocardial infarction. However, only a minority of patients are initially admitted to hospitals with direct PTCA facilities available 24 hours daily. The safety and benefits of transfer direct PTCA are debated, and we have no data about the early return of patients to the admission hospital.</AbstractText>We report our experience with transfer direct PTCA in unselected patients with acute myocardial infarction, and the early post-procedural return to the referring hospitals.</AbstractText>One hundred and thirty-five unselected patients with acute myocardial infarction were referred to our center for direct PTCA during 1998. The majority of patients (n = 93, 69%, group T) were initially admitted to a primary hospital whereas the rest (n = 42, 31%, group NT) were directly admitted to our hospital. One hundred and thirty-four patients underwent coronary angiography, and direct PTCA was attempted in 126 patients. The median time interval between admission and direct PTCA was higher in group T (60 vs 40 min, p < 0.001). Only 3 patients (3.2%) had severe complications during transfer to our center: 1 patient with cardiogenic shock died, and 2 patients had ventricular fibrillation. The procedural and in-hospital outcomes of both groups were similar. The early post-procedural transfer to the referring hospital was possible in 88% of patients; no complications occurred during the transfer. The incidences of cardiac mortality at 6 months and at long-term follow-up were 3.4 and 5.1% respectively.</AbstractText>In our experience, interhospital transfer for direct PTCA in unselected patients with acute myocardial infarction is feasible and safe. The early return to the admission hospital is safe and does not negatively influence the in-hospital outcome.</AbstractText> |
3,427 | Mental stress as a trigger of acute cardiac events: the role of laboratory studies. | Mental stress has long been implicated as a potential trigger of myocardial infarction and sudden cardiac death. This article reviews research conducted in the past two decades utilizing laboratory studies to investigate behaviorally-induced pathophysiological effects (including increased cardiac demand, decreased myocardial supply, and impaired dilation of coronary resistance vessels), in patients with coronary artery disease. The clinical significance of mental stress-induced ischemia is supported by findings of a predictive relationship of mental stress-induced ischemia for ambulatory ischemia and subsequent cardiac events. Mental stress-induced ventricular fibrillation, ventricular tachycardia, and T-wave alternans are also being explored as possible markers of arrhythmic vulnerability in human and animal models. T-wave alternans comparable to exercise can be induced by an anger-like state in an animal model, and with mental stress in patients with implantable cardioverter-defibrillators. Future directions for research on mental stress and cardiac events are suggested, including further studies of mechanisms of mental stress-induced arrhythmia and ischemia, additional studies of the prognostic significance of stress-induced ischemia and T-wave alternans, and use of pharmacological and psychosocial treatments for preventing stress-induced cardiac events. |
3,428 | Myocardial membrane fatty acids and the antiarrhythmic actions of dietary fish oil in animal models. | Epidemiologic studies, animal studies, and more recently, clinical intervention trials all suggest a role for regular intake of dietary fish oil in reducing cardiovascular morbidity and mortality. Prevention of cardiac arrhythmias and sudden death is demonstrable at fish or fish oil intakes that have little or no effect on blood pressure or plasma lipids. In animals, dietary intake of fish oil [containing both eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3)] selectively increases myocardial membrane phospholipid content of DHA, whereas low dose consumption of purified fatty acids shows antiarrhythmic effects of DHA but not EPA. Ventricular fibrillation induced under many conditions, including ischemia, reperfusion, and electrical stimulation, and even arrhythmias induced in vitro with no circulating fatty acids are prevented by prior dietary consumption of fish oil. The preferential accumulation of DHA in myocardial cell membranes, its association with arrhythmia prevention, and the selective ability of pure DHA to prevent ventricular fibrillation all point to DHA as the active component of fish oil. The antiarrhythmic effect of dietary fish oil appears to depend on the accumulation of DHA in myocardial cell membranes. |
3,429 | A method to quantify the dynamics and complexity of re-entry in computational models of ventricular fibrillation. | Ventricular fibrillation is a deadly cardiac arrhythmia. There is evidence that electrical activity in cardiac tissue is sustained during fibrillation by re-entrant waves that rotate around filaments. In this paper we develop a method for identifying and tracking filaments in a computational model of ventricular fibrillation. This method identifies the birth, death, bifurcation and amalgamation of filaments and these events are summarized on a directed graph. The approach described in this study provides ways to quantify the complex patterns of electrical activity seen in computational models of fibrillation, to relate the behaviour of computational models to experimental data and thus to gain insights into the underlying mechanisms of this dangerous arrhythmia. |
3,430 | From the HOPE to the ONTARGET and the TRANSCEND studies: challenges in improving prognosis. | The Heart Outcomes Prevention Evaluation (HOPE) study conclusively demonstrated that ramipril, an angiotensin-converting enzyme (ACE) inhibitor, reduces the risk of cardiovascular death, myocardial infarction (MI), and death in patients at risk for cardiovascular events but without heart failure. The Study to Evaluate Carotid Ultrasound Changes in Patients Treated with Ramipril and Vitamin E (SECURE) substudy demonstrated that ramipril also reduced atherosclerosis. These results suggest that the renin-angiotensin system (RAS) has a more important role in the development and progression of atherosclerosis than previously believed, and they indicate the need for further clinical studies to define the range of benefits available from modifying the RAS. Achieving maximum benefit may require treatment with both an ACE inhibitor and an angiotensin II type-1 receptor blocker (ARB). The Randomized Evaluation of Strategies for Left Ventricular Dysfunction (RESOLVD) study indicated that combining an ACE inhibitor with an ARB decreased blood pressure and improved the ejection fraction more than treatment with either drug alone in patients with congestive heart failure. The Valsartan in Heart Failure Trial (Val-HeFT) showed that the combination of an ACE inhibitor and an ARB reduced hospitalization for heart failure in patients with congestive heart failure by 27.5%, although no decrease in all-cause mortality was observed. The Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial (ONTARGET) is a large, long-term study (23,400 patients, 5.5 years). It will compare the benefits of ACE inhibitor treatment, ARB treatment, and treatment with an ACE inhibitor and ARB together, in a study population with established coronary artery disease, stroke, peripheral vascular disease, or diabetes with end-organ damage. Patients with congestive heart failure will be excluded. In a parallel study, patients unable to tolerate an ACE inhibitor will be randomized to receive telmisartan or placebo (the Telmisartan Randomized Assessment Study in ACE-I Intolerant Patients with Cardiovascular Disease [TRANSCEND]). The primary endpoint for both trials is a composite of cardiovascular death, MI, stroke, and hospitalization for heart failure. Secondary endpoints will investigate reductions in the development of diabetes mellitus, nephropathy, dementia, and atrial fibrillation. These 2 trials are expected to provide new insights into the optimal treatment of patients at high risk of complications from atherosclerosis. |
3,431 | The Low Energy Safety Study (LESS): rationale, design, patient characteristics, and device utilization. | A 10-J energy safety margin has traditionally been used in programming implantable cardioverter defibrillators (ICDs). The Low Energy Safety Study (LESS) tests the hypothesis that programming shocks to lower energy margins is safe and effective.</AbstractText>Patients with standard ICD indications undergo defibrillation threshold testing (DFT) at the time of ICD implant, with reconfirmation of lowest successful energy twice (DFT++). Patients are randomized to 2 groups: the first has the initial 2 shocks for ventricular fibrillation conversion programmed at 2 energy steps above DFT++ (typically 4-6 J, maximum 10 J) with subsequent shocks at maximum energy, and the second has all shocks programmed at maximum energy. Patients are followed up every 3 months for 2 years to assess shock conversion efficacy of spontaneous arrhythmias. In a subgroup of patients, there is a second randomization to energy levels of 0, 1, 2, 3, or 4 steps above implant DFT++ for conversion testing of 3 induced ventricular fibrillation episodes at prehospital discharge, 3 months, and 12 months after implant.</AbstractText>Enrollment is complete (702 patients), but follow-up results are pending. There were no significant variations in implant indications and baseline antiarrhythmic drug use over the 3-year enrollment period, although an increase in the percentage of dual-chamber ICDs implanted occurred, with the majority (65%) of implanted ICDs being dual-chamber devices by the end of the enrollment period.</AbstractText>The results of LESS should facilitate the development of algorithms for programming ICD energy safety margins.</AbstractText> |
3,432 | Frequency analysis of ventricular fibrillation in Swine ventricles. | It has been suggested from frequency analysis that cardiac fibrillation is driven by stable intramural reentry, with wavebreak occurring due to failure of 1:1 propagation. We tested this hypothesis with a combined experimental and theoretical approach. Optical mapping was performed on epicardial, endocardial, and transmural cut surfaces of fibrillating swine ventricles. Wavelets were characterized, the frequency content of optical signals analyzed, and space-time plots (STPs) constructed to detect Wenckebach-like conduction. The findings were compared with simulations in 2D and 3D cardiac tissue using the Luo-Rudy action potential model. The incidence of reentry in the cut transmural surface (11.8% in right ventricle, 14.3% in left ventricle) was similar to that on the endocardial surface (13.1%, P=NS) but greater than on the epicardial surface (7.7%, P<0.01). Frequency spectra of optically recorded membrane voltage were organized into spatial domains with the same dominant frequency, but these domains were nonstationary. In STPs, pseudo-2:1 conduction block was caused by double potentials arising when reentry occurred on the recording site rather than true Wenckebach conduction. The latter was observed in 11 of 166 STPs but did not occur at borders of high-to-low frequency domains. In simulations, similar findings were obtained when action potential duration (APD) restitution slope was steep. Stationary dominant frequency domains with Wenckebach conduction patterns were observed only in the presence of shallow APD restitution slope and marked nonuniform tissue heterogeneity. In conclusion, stable intramural reentry as the engine of fibrillation was not observed. Our findings support the idea that dynamic wavebreak plays a fundamental role in the generation and maintenance of ventricular fibrillation. |
3,433 | Independent contribution of catecholamines to arrhythmogenesis during evolving infarction in the isolated rat heart. | Ventricular fibrillation (VF) in conscious rats with coronary artery ligation occurs in two phases, before (phase 1) and after (phase 2) 90 min of ischaemia respectively. The mechanisms of phase 2 VF are not established. Interestingly, phase 2 VF is absent in isolated (denervated) buffer-perfused rat hearts. We investigated whether catecholamine supplementation (to mimic sympathetic drive) was sufficient to restore phase 2 VF in such hearts. Isolated rat hearts (n=10 per group) underwent coronary ligation for 240 min. At 90 min, during a period of relative electrical stability, the perfusion solution was switched from standard (Krebs) to identical solution or Krebs containing catecholamines (313 nM noradrenaline and 75 nM adrenaline) with or without 10 microM trimazosin (an alpha(1)-adrenoceptor antagonist) or 10 microM atenolol (a beta(1)-adrenoceptor antagonist). Although in all groups the incidence of phase 1 VF was high (80 - 100%), the temporal distribution of VF was monophasic, i.e. only one heart in one group developed phase 2 VF (P=NS). Other ventricular arrhythmias (e.g., tachycardia; VT) exhibited a similar temporal distribution. Nevertheless, haemodynamic changes confirmed sympathomimetic effects of catecholamines, e.g., heart rate was increased from 278+/-7 beats min(-1) in controls to 335+/-8 beats min(-1) (P<0.05) by catecholamines, an effect that could be blocked by atenolol (285+/-7 beats min(-1)) but not by trimazosin (342+/-12 beats min(-1)). Coronary flow was correspondingly increased from 7.7+/-0.7 ml min(-1) g(-1) to 16.5+/-1.3 ml min(-1) g(-1) (P<0.05); this effect could be blocked by atenolol (8.1+/-0.6 ml min(-1) g(-1)) and was enhanced by trimazosin (20.7+/-2.4 ml min(-1) g(-1)). In conclusion, despite evidence of adequate alpha- and beta-adrenoceptor activation, catecholamine supplementation to isolated buffer-perfused rat hearts was insufficient to restore phase 2 VF. It therefore appears unlikely that catecholamines alone mediate phase 2 VF. |
3,434 | Optimal ventricular rate slowing during atrial fibrillation by feedback AV nodal-selective vagal stimulation. | Although the beneficial effects of ventricular rate (VR) slowing during atrial fibrillation (AF) are axiomatic, the precise relationship between VR and hemodynamics has not been determined. We hypothesized that selective atrioventricular node (AVN) vagal stimulation (AVN-VS) by varying the nerve stimulation intensity could achieve precise graded slowing and permit evaluation of an optimal VR during AF. The aims of the present study were the following: 1) to develop a method for computerized vagally controlled VR slowing during AF, 2) to determine the hemodynamic changes at each level of VR slowing, and 3) to establish the optimal anterograde VR during AF. AVN-VS was delivered to the epicardial fat pad that projects parasympathetic nerve fibers to the AVN in 14 dogs. Four target average VR levels, corresponding to 75%, 100%, 125%, and 150% of the sinus cycle length (SCL), were achieved by computer feedback algorithm. VR slowing resulted in improved hemodynamics and polynomial fit analysis found an optimum for the cardiac output at VR slowing of 87% SCL. We conclude that this novel method can be used to maintain slow anterograde conduction with best hemodynamics during AF. |
3,435 | Effects of amiodarone on wave front dynamics during ventricular fibrillation in isolated swine right ventricle. | The effects of acute amiodarone infusion on dynamics of ventricular fibrillation (VF) are unclear. Six isolated swine right ventricles (RVs) were studied in vitro. Activation patterns during VF were mapped optically, whereas action potentials were recorded with a glass microelectrode. At baseline, VF was associated with frequent spontaneous wave breaks. Amiodarone (2.5 microg/ml) reduced spontaneous wave breaks and increased the cycle length (CL) of VF from 83.3 +/- 17.8 ms at baseline to 118.4 +/- 25.8 ms during infusion (P < 0.05). Amiodarone increased the reentrant wave front CL (114.4 +/- 15.5 vs. 78.2 +/- 19.0 ms, P < 0.05) and central core area (4.1 +/- 3.8 vs. 0.9 +/- 0.3 mm2, P < 0.05). Within 30 min of infusion, VF terminated (n = 1), converted to ventricular tachycardia (VT) (n = 1) or continued at a slower rate (n = 4). Amiodarone flattened the APD restitution curves. We conclude that amiodarone reduced spontaneous wave breaks. It might terminate VF or convert VF to VT. These effects were associated with the flattening of APD restitution slope and increased core size of reentrant wave fronts. |
3,436 | Successful explantation of a ventricular assist device following fulminant influenza type A-associated myocarditis. | We report a case of fulminant myocarditis associated with refractory ventricular fibrillation following influenza A infection. Histologic examination was consistent with myocarditis and serology confirmed the viral etiology. The patient was supported with biventricular assist devices for 20 days during which her refractory ventricular fibrillation resolved spontaneously. This is the first documented case of resolution of prolonged ventricular fibrillation while on a ventricular assist device. This case suggests those patients with fulminant viral myocarditis and refractory ventricular arrhythmias may be supported successfully with ventricular assist devices until myocardial recovery takes place. |
3,437 | Coronary artery spasm and ventricular fibrillation after off-pump coronary surgery. | Native coronary artery or bypass graft spasm is a rare cause of acute myocardial infarction after coronary artery bypass grafting. This report presents angiographic documentation of native coronary artery spasm following successful multivessel off-pump coronary revascularization, which caused myocardial ischemia leading to inferior wall myocardial infarction and ventricular fibrillatory arrest. |
3,438 | Gatifloxacin-associated corrected QT interval prolongation, torsades de pointes, and ventricular fibrillation in patients with known risk factors. | Drugs not commonly considered to be cardioactive agents have been reported to cause prolongation of the corrected QT interval with resultant torsades de pointes or ventricular fibrillation. We report 4 cases of gatifloxacin-associated cardiac toxicity in patients with known risk factors for this adverse event. |
3,439 | [Biventicular pacing in patients with severe heart failure]. | According to initial clinical results biventricular pacing seems to be effective in the treatment of patients suffering from drug refractory severe heart failure combined with intraventricular conduction disturbance. Biventricular cardioverter defibrillators and biventricular pacemakers were implanted in patients suffering from drug refractory severe heart failure in 3 and in 2 cases, respectively (follow up > 6 months). NYHA III-IV functional class, low left ventricular ejection fraction (23.2 +/- 5.4%), wide QRS (> 150 ms) with left bundle branch block and lateral dyssynchrony were present in each case. The left ventricle was enlarged in each patient (end-diastolic/end-systolic diameter: 78.6 +/- 9.2/66.2 +/- 8.1 mm). The indications of cardioverter defibrillator implantations were both sustained ventricular tachycardia and ventricular fibrillation, nonsustained ventricular tachycardia combined with syncope in 2 and in 1 case, respectively. The duration of QRS decreased (190 +/- 36 vs. 134 +/- 17 ms, p = 0.012) and wall movement disorder disappeared. At the last follow up every patients were in NYHA II functional class and a decrease in left ventricular diameter could be observed (end-diastolic: 72 +/- 10.4 mm, p = 0.07; end-systolic: 62 +/- 10 mm, p = 0.09). During the follow up period (7.3 +/- 1.7 months) 18 episodes of ventricular arrhythmias could be detected in the same patient. Biventricular pacemakers and cardioverter defibrillators were implanted and applied successfully in the treatment of congestive heart failure for the first time in Hungary. The effect of biventricular pacing on morbidity and mortality, the cost-effectiveness, the exact indication and the combined use with cardioverter defibrillator have yet to be proven in future randomized trials. |
3,440 | Difficult cases in heart failure: reversible cardiomyopathy due to atrial fibrillation in a 46-year-old patient. | The authors describe the challenging case of a 46-year-old patient who presented with a 2-week history of exertional dyspnea, paroxysmal nocturnal dyspnea, and orthopnea. He was found to have left ventricular failure and atrial fibrillation with a rapid ventricular rate. Initial work-up revealed dilated cardiomyopathy with marked left ventricular dysfunction, without any obvious cause. He received standard medical therapy for left ventricular dysfunction and his symptoms improved. Electrical cardioversion to sinus rhythm and maintenance resulted in complete recovery of left ventricular function within 6 months. (c)2001 CHF, Inc. |
3,441 | Dofetilide in patients with congestive heart failure and left ventricular dysfunction: safety aspects and effect on atrial fibrillation. The Danish Investigators of Arrhythmia and Mortality on Dofetilide (DIAMOND) Study Group. | INTRODUCTION. Atrial fibrillation is a frequent cause of worsening of symptoms in patients with congestive heart failure. The drugs currently available for maintenance of sinus rhythm all have major side effects. METHODS. In 34 Danish coronary care units, 1518 patients with congestive heart failure and reduced left ventricular systolic function were randomized to receive either placebo or a new class III antiarrhythmic drug, dofetilide. The dose of dofetilide was adjusted according to the presence of atrial fibrillation, the length of the QT interval, and renal function. Patients were continuously monitored electrocardiographically for the first 3 days of the study. The primary end point was all-cause mortality and follow-up was for at least 1 year. RESULTS. In the dofetilide/placebo groups, 311/317 patients died (41%/42%). The hazard ratio for dofetilide treatment was 0.95 (95% confidence interval, 0.81-1.11). Treatment with dofetilide reduced worsening of heart failure significantly (hazard ratio, 0.75; 0.63-0.89). After 1 year, 61% of patients with atrial fibrillation at the start of the study had converted to sinus rhythm on dofetilide, vs. 33% in the placebo group. After conversion to sinus rhythm, 78%/43% of patients in the dofetilide/placebo groups remained in sinus rhythm for at least 1 year. There were 25 instances (3%) of torsade de pointes ventricular tachycardia in the dofetilide group and none in the placebo group. CONCLUSION. In patients with congestive heart failure, dofetilide can effectively convert atrial fibrillation to sinus rhythm and maintain sinus rhythm after conversion. Hospitalization for congestive heart failure is reduced. Dofetilide does not affect mortality. (c)2001 by CHF, Inc. |
3,442 | Atrial fibrillation in patients with heart failure: pharmacologic options. | Atrial fibrillation is a common arrhythmia in patients with heart failure. The presence of atrial fibrillation deteriorates cardiac function and increases the risk of thromboembolic events. The management of patients with atrial fibrillation in association with heart failure should consist of ventricular rate control, prevention of thromboembolic events, and conversion to normal sinus rhythm. Traditionally, digoxin has been widely used in patients with heart failure and atrial fibrillation; however, it does very little to restore sinus rhythm and requires the addition of another rate-limiting agent to control ventricular rate. The likelihood of successful cardioversion is dependent on the duration of heart failure and the degree of neurohormonal activation. The initiation of antiarrhythmic drug therapy in patients with heart failure should be guided by safety issues as well as consideration of potential benefits vs. risks associated with therapy. Amiodarone has been evaluated in numerous clinical trials and appears to be safe and effective when used in low dosage. Treatment with dofetilide is another option. Comparative studies with oral dofetilide vs. amiodarone are needed to evaluate their efficacy in restoration and maintenance of sinus rhythm in patients with heart failure. Such trials will clearly define the role of dofetilide in the treatment of atrial fibrillation. Routine prophylactic use of antiarrhythmic drug therapy for chronic atrial fibrillation in the setting of heart failure is not recommended due to a low efficacy rate and high proarrhythmic risk. Anticoagulation with warfarin and rate control remain the standard therapy. (c)2001 by CHF, Inc. |
3,443 | Importance of continuous chest compressions during cardiopulmonary resuscitation: improved outcome during a simulated single lay-rescuer scenario. | Interruptions to chest compression-generated blood flow during cardiopulmonary resuscitation (CPR) are detrimental. Data show that such interruptions for mouth-to-mouth ventilation require a period of "rebuilding" of coronary perfusion pressure to obtain the level achieved before the interruption. Whether such hemodynamic compromise from pausing to ventilate is enough to affect outcome is unknown.</AbstractText>Thirty swine (weight 35 +/- 2 kg) underwent 3 minutes of untreated ventricular fibrillation before 12 minutes of basic life support CPR. Animals were randomized to receive either standard airway (A), breathing (B), and compression (C) CPR with expired-gas ventilation in a 15:2 compression-to-ventilation ratio or continuous chest compression CPR. Those randomized to the standard 15:2 group had no chest compressions for a period of 16 seconds each time the 2 ventilations were delivered. Defibrillation was attempted at 15 minutes of cardiac arrest. All resuscitated animals were supported in an intensive care environment for 1 hour, then in a maintenance facility for 24 hours. The primary end point of neurologically normal 24-hour survival was significantly better in the experimental group receiving continuous chest compression CPR (12 of 15 versus 2 of 15; P<0.0001).</AbstractText>Mouth-to-mouth ventilation performed by single layperson rescuers produces substantial interruptions in chest compression-supported circulation. Continuous chest compression CPR produces greater neurologically normal 24-hour survival than standard ABC CPR when performed in a clinically realistic fashion. Any technique that minimizes lengthy interruptions of chest compressions during the first 10 to 15 minutes of basic life support should be given serious consideration in future efforts to improve outcome results from cardiac arrest.</AbstractText> |
3,444 | A mutant cardiac sodium channel with multiple biophysical defects associated with overlapping clinical features of Brugada syndrome and cardiac conduction disease. | Loss of Na(+) channel function has been implicated in idiopathic ventricular fibrillation (IVF) and Brugada syndrome. We have studied the biophysical properties of an IVF mutation (S1710L) that exhibited an unusual clinical phenotype: rate-dependent bundle branch block without manifestation of Brugada-type ECG pattern.</AbstractText>The mutant S1710L channels were expressed in mammalian cells and their gating properties, studied using whole-cell patch clamp techniques, were compared with wild-type (WT) and a Brugada syndrome mutant channel T1620M.</AbstractText>The S1710L channel exhibited significantly faster macroscopic current decay than WT or T1620M. In addition, S1710L showed a negative shift in the voltage-dependence of fast inactivation and slower recovery from fast inactivation than in WT or T1620M. In addition to the alterations in fast inactivation most commonly observed in Brugada syndrome mutations, S1710L exhibited marked enhancement in slow inactivation and a large positive shift of activation that potentially decreases conduction velocity.</AbstractText>These functional abnormalities may be responsible for the overlapping clinical phenotypes associated with Brugada syndrome and the cardiac conduction defect, a novel cardiac Na(+) channelopathy.</AbstractText> |
3,445 | Oral loading with propafenone for conversion of recent-onset atrial fibrillation: a review on in-hospital treatment. | Atrial fibrillation (AF) is a very common arrhythmia. In order to treat acute AF rapidly, effective drug regimens are required. Propafenone is a class IC antiarrhythmic agent that is suitable for oral loading as it reaches peak plasma concentrations within 2 to 4 hours of administration. The use of propafenone loading in patients with AF must be based on appropriate patient selection in view of the negative inotropic effect and the potential proarrhythmic effects of the drug. A series of controlled trials in patients with recent-onset AF without heart failure who were hospitalised with enforced bed rest has shown that orally loaded propafenone (450 to 600 mg as single dose) exerts a relatively quick effect (within 3 to 4 hours) and a high rate of efficacy (72 to 78% within 8 hours). A potentially harmful effect of class IC agents is the risk of transforming AF into atrial flutter (3.5 to 5% of patients). However, atrial flutter with 1 : 1 atrioventricular response was observed in only two of 709 patients receiving propafenone (0.3% incidence). Nevertheless, the potential negative inotropic effect of propafenone demands careful patient selection, with systematic exclusion of patients with left ventricular dysfunction or congestive heart failure. Oral loading with propafenone can be considered as an episodic treatment in patients with AF recurrences, as has been proposed for other drugs in the past. However, the safety of oral loading with propafenone as an outpatient treatment in appropriately selected patients has to be assessed by appropriately designed prospective studies. |
3,446 | [2 year follow-up of 321 patients with an implantable cardioverter/defibrillator: comparison of patients with and without atrial fibrillation]. | Atrial fibrillation is the most common cause of inappropriate therapy deliveries by implantable cardioverter/defibrillators (ICD). However, the importance of atrial fibrillation for the induction of ventricular arrhythmias and for the prognosis is controversial. We studied 321 ICD patients (pts) over the median follow-up of 25 months. In 92 pts, atrial fibrillation was found to be the underlying rhythm (in 49 pts chronic, in 43 pts paroxysmal), in 229 pts sinus rhythm. Pts with atrial fibrillation were older (67 +/- 9 vs. 63 +/- 9 years, p = 0.001) and were considered to suffer more often from a valvular (14 vs. 4%, p = 0.004) or a dilative cardiomyopathy (29 vs. 19%, p = 0.04). Both groups were similar regarding other baseline characteristics like gender, left ventricular ejection fraction, hypertension, diabetes and in the ICD system (single chamber, dual chamber) used. Pts with atrial fibrillation experienced more appropriate (ventricular fibrillation: 0.33 vs. 0.2/month, p = 0.0049, ventricular tachycardias: 0.05 vs 0/month, p = 0.0033) as well as inappropriate (34 vs. 8%, p < 0.001) therapy deliveries by the ICD. Pts with atrial fibrillation were found to suffer twice as much from a progression of their heart failure (43% vs. 22%, p < 0.001). After multivariate analysis, atrial fibrillation was significantly associated with progressive pump-failure mortality (relative risk (RR) 3.12, confidence interval (CI) 1.30 to 7.48, p = 0.01). There was no difference in the incidence of ICD therapies and mortality rates between the pts with chronic and paroxysmal atrial fibrillation.</AbstractText>The presence of atrial fibrillation in ICD patients is associated with a progression of heart failure and therefore is an unfavorable factor for pump-failure death. Also, atrial fibrillation is a marker for greater possibility to experience more appropriate as well as inappropriate therapy deliveries by the ICD.</AbstractText> |
3,447 | A prospective investigation into the epidemiology of in-hospital pediatric cardiopulmonary resuscitation using the international Utstein reporting style. | Data regarding pediatric in-hospital cardiopulmonary resuscitation (CPR) have been limited because of retrospective study designs, small sample sizes, and inconsistent definitions of cardiac arrest and CPR. The purpose of this study was to prospectively describe and evaluate pediatric in-hospital CPR with the international consensus-derived epidemiologic definitions from the Utstein guidelines.</AbstractText>All 129 in-hospital CPRs during 12 months at a 122-bed university children's hospital in Sao Paulo, Brazil, were described and evaluated using Utstein reporting guidelines. These guidelines include standardized descriptions of hospital variables, patient variables, arrest/event variables, and outcome variables. CPR was defined as chest compressions and assisted ventilation provided because of cardiac arrest or because of severe bradycardia with poor perfusion. Outcome variables included sustained return of spontaneous circulation, 24-hour survival, 30-day survival, 1-year survival, and neurologic status of survivors by the Pediatric Cerebral Performance Category Scale.</AbstractText>Of the 6024 children admitted to the hospital, 176 (3%) had an episode that met the criteria for provision of CPR and 129 (2%) received CPR, 86 for clinical cardiac arrest and 43 for bradycardia with poor perfusion. Most of the children (71%) had preexisting chronic diseases. The most common precipitating causes were respiratory failure (61%) and shock (29%). The initial cardiac rhythm was asystole in 71 children (55%), pulseless electrical activity in 12 (9%), ventricular fibrillation in 1, and bradycardia with pulses and poor perfusion in 43 (33%). Eighty-three children (64%) attained sustained return of spontaneous circulation (>20 minutes), 43 (33%) were alive at 24 hours, 24 (19%) were alive at 30 days, and 19 (15%) were alive at 1 year. Although many factors correlated with 24-hour survival, multivariate logistic regression analysis revealed independent association of 24-hour survival with respiratory failure as the precipitating cause (odds ratio [OR]: 4.92; 95% confidence interval [CI]: 1.73-14.0), bradycardia with pulses as the initial event (OR: 2.68; 95% CI: 1.01-7.1), and shorter duration of CPR (OR: 0.92; 95% CI: 0.89-0.96 for each elapsed minute). Similarly, 30-day survival was independently associated with respiratory failure as the precipitating cause and shorter duration of CPR. Thirty-day survival decreased by 5% with each elapsed minute of CPR. Nineteen (91%) of the 21 survivors to hospital discharge and 16 (83%) of the 19 1-year survivors had no demonstrable long-term change in neurologic function from their pre-CPR status.</AbstractText>During this study, CPR was uncommon but not rare. Respiratory failure was the most common precipitating cause, followed by shock. Preexisting chronic diseases were prevalent among these children. Asystole was the most common initial cardiac rhythm, and bradycardia with pulses and poor perfusion was the second most common. Ventricular fibrillation was rare, but children with acute cardiac diseases, such as cardiac surgery and acute cardiomyopathies, were not admitted to this children's hospital. CPR was effective: nearly two thirds of these children were initially successfully resuscitated, and one third were alive at 24 hours compared with imminent death without CPR and advanced life support. Nevertheless, survival progressively decreased over time, generally as a result of the underlying disease process. One-year survival was 15%. Importantly, most of these survivors had no demonstrable change in gross neurologic function from their pre-CPR status.</AbstractText> |
3,448 | Amiodarone -- waxed and waned and waxed again. | Amiodarone has been used as an anti-arrhythmic drug since the 1970s and has an established role in the treatment of ventricular tachyarrhythmias. Although considered to be a class III anti-arrhythmic, amiodarone also has class I, II and IV actions, which gives it a unique pharmacological and anti-arrhythmic profile. Amiodarone is a structural analogue of thyroid hormone and some of its anti-arrhythmic properties and toxicity may be attributable to interactions with nuclear thyroid hormone receptors. The lipid solubility of amiodarone gives it an exceptionally long half-life. Oral amiodarone takes days to work in ventricular tachyarrhythmias, but iv. amiodarone has immediate effect and can be used in life threatening ventricular arrhythmias. Intravenous amiodarone administered after out-of-hospital cardiac arrest due to ventricular fibrillation improves survival to hospital admission. Many survivors of myocardial infarction (MI) die during the subsequent year, probably due to ventricular arrhythmia. Amiodarone reduces sudden death after MI and this benefit is predominantly observed in patients with preserved cardiac function. Sudden cardiac death, predominantly due to ventricular arrhythmias, is also commonly seen in patients with heart failure. The Grupo de Estudio de la Sobrevida en lsuficiencia Cardiaca en Argentina (GESICA) and Estudio Piloto Argentino de Muerte Subita y Amiodarona (EPAMSA) trials showed survival benefit of amiodarone in heart failure, whereas Congestive Heart Failure-Survival Trial of Anti-arrhythmic Therapy (CHF-STAT) did not. Subsequent meta-analysis established a survival benefit of amiodarone in heart failure. Implanted Cardioverter Def ibrillators (ICDs) also give survival benefit to patients at risk of sudden death. In patients with a history of ventricular fibrillation or haemodynamically-compromising ventricular tachycardia, ICDs have been shown to be superior to anti-arrhythmic drugs, principally amiodarone. Further analysis has been undertaken to ascertain which patients are most likely to benefit from ICDs, as these are more expensive than treatment with amiodarone. Patients with severely depressed ejection fractions should be the first to be considered for ICDs. A new indication for amiodarone is atrial fibrillation or flutter. Amiodarone is effective in chronic and recent onset atrial fibrillation and orally or iv. for atrial fibrillation after heart surgery. In atrial fibrillation amiodarone is more than or equi-effective with flecainide, quinidine, racemic sotalol, propafenone and diltiazem and therefore should be considered for first line therapy. Amiodarone is also safe and effective in controlling refractory tachyarrhythmias in infants and is safe after cardiac surgery. |
3,449 | Genetic and biophysical basis of sudden unexplained nocturnal death syndrome (SUNDS), a disease allelic to Brugada syndrome. | Sudden unexplained nocturnal death syndrome (SUNDS), a disorder found in southeast Asia, is characterized by an abnormal electrocardiogram with ST-segment elevation in leads V1-V3 and sudden death due to ventricular fibrillation, identical to that seen in Brugada syndrome. We screened patients with SUNDS for mutations in SCN5A, the gene known to cause Brugada syndrome, as well as genes encoding ion channels associated with the long-QT syndrome. Ten families were enrolled, and screened for mutations using single-strand DNA conformation polymorphism analysis, denaturing high-performance liquid chromatography and DNA sequencing. Mutations were identified in SCN5A in three families. One mutation, R367H, lies in the first P segment of the pore-lining region between the DIS5 and DIS6 transmembrane segments of SCN5A. A second mutation, A735V, lies in the first transmembrane segment of domain II (DIIS1) close to the first extracellular loop between DIIS1 and DIIS2, whereas the third mutation, R1192Q, lies in domain III. Analysis of these mutations in Xenopus oocytes showed that the R367H mutant channel did not express any current and the likely effect of this mutation is to depress peak current due to the loss of one functional allele. The A735V mutant expressed currents with steady state activation voltage shifted to more positive potentials. The R1192Q mutation accelerated the inactivation of the sodium channel current. Both mutations resulted in reduced sodium channel current (I(Na)) at a time corresponding to the end of phase 1 of the action potential, as described previously in the Brugada syndrome. Based upon these observations we suggest that SUNDS and Brugada syndrome are phenotypically, genetically and functionally the same disorder. |
3,450 | Life situation of patients with an implantable cardioverter defibrillator: a descriptive longitudinal study. | The aim of this study was to describe changes in the life situation of patients with an implantable cardioverter defibrillator over a period of 1 year. A sample of 56 consecutive patients took part in the study. Life situation was measured through uncertainty in illness, satisfaction, and fear of the life situation. Descriptive statistics were used to present results, and analytical statistics were used to map out changes over time. Overall uncertainty showed a decrease over time. A statistically significant difference was found within the domain uncertainty related to information (P < 0.001). Satisfaction increased within the domains health-functioning, socio-economic, psychological-spiritual, and family. The ability to act within the domain health-functioning showed a statistical significance (P < 0.05). The domain life changes within fear in the life situation decreased and showed a statistical significance (P < 0.05). The overall life situation showed increased satisfaction as well as lower uncertainty and fear in the life situation. The research indicates that patients need more information about changes in the life situation after the implantable cardioverter defibrillator-implantation. The study encourages more humanistic, holistic research about patients' life situations as well as more education in teaching skills for health care personnel. |
3,451 | Streptozotocin diabetes protects against arrhythmias in rat isolated hearts: role of hypothyroidism. | We examined the contribution of hypothyroidism to streptozotocin diabetes-induced alterations in the arrhythmia susceptibility of ex vivo hearts to regional zero-flow ischaemia. Diabetic rats received either protamine zinc insulin (10 IU/kg/day, s.c.) or triiodothyronine (10 microg/kg/day, s.c.) for 8 weeks commencing 72 h after injection of streptozotocin (60 mg/kg, i.p.). Arrhythmias were determined in ex vivo Langendorff-perfused hearts, subjected to a 30-min main left coronary artery occlusion, followed by 30-min reperfusion. Serum free thyroxine concentrations, rectal temperature and ex vivo heart rate were significantly decreased in the 8-week diabetic group (P<0.001). These changes were prevented by administration of triiodothyronine or insulin. Ventricular fibrillation during reperfusion was abolished in hearts from diabetic rats. This protection was prevented by treatment with either triiodothyronine or insulin. Hearts from methimazole-hypothyroid rats also showed no ventricular fibrillation during reperfusion. The protection against ischaemia-reperfusion-arrhythmias observed in hearts from streptozotocin-diabetic rats may be due to diabetes-induced hypothyroidism. |
3,452 | Inappropriate use of digoxin in older hospitalized heart failure patients. | Older adults are more likely to suffer from the adverse effects of digoxin. Studies have described the inappropriate use of digoxin in various populations. The objective of this study was to determine the correlates of inappropriate digoxin use in older heart failure patients.</AbstractText>We studied older hospitalized heart failure patients with documented left ventricular (LV) function evaluation and electrocardiography. Digoxin use was considered inappropriate if patients had preserved LV systolic function (ejection fraction greater > or =40%) or if they had no atrial fibrillation (AF). We compared baseline patient characteristics by indication for digoxin and tested statistical significance using Pearson's chi-square analysis and Student's t tests. Using logistic regression, we determined the correlates of inappropriate use and initiation of digoxin.</AbstractText>Subjects (N = 603) had a mean age of 79 (+/-7) years; 59% were women, and 18% were African American. A total of 376 patients (62%) were discharged on digoxin, and 223 (37%) had no indication for its use. Half of the patients without an indication for digoxin received the drug. Of 132 patients without an indication and not already on digoxin, 38 (29%) were initiated on it. After adjustment for various patient and care characteristics, prior digoxin use (adjusted odds ratio [OR] 11.47, 95% confidence interval [CI] 5.72-23.02) and pulse > or =100/min (adjusted OR 2.33, 95% CI 1.10-4.94) were associated with inappropriate digoxin use. Pulse > or =100/min was also associated with inappropriate initiation of the drug (adjusted OR 2.95, 95% CI 1.28-6.78).</AbstractText>Inappropriate use of digoxin was common and was associated with prior use. Tachycardia was associated with inappropriate use and initiation. Electrocardiography and echocardiography should be performed in all older heart failure patients. Digoxin therapy should not be initiated or continued in patients without any evidence of LV systolic dysfunction or chronic AF.</AbstractText> |
3,453 | Passenger mortalities aboard cruise ships. | to study the epidemiology of passenger mortalities on cruise ships.</AbstractText><AbstractText Label="METHODS, MATERIAL AND RESULTS" NlmCategory="UNASSIGNED">during six years (April 1995 to April 2001) deaths aboard two similar cruise ships (A & B) were registered and studied. Each ship had an average of approximately 800 passengers with median age about 65 years. Twenty five passengers died: 9 men and 3 women on ship A and 10 men and 3 women on ship B. There was an average of one death every six months per ship. More men than women died, although there were more female passengers on both ships (P<0.05). Eleven passengers were found dead in their cabins. Five deaths outside the medical centers were witnessed; four of them had asystole and one ventricular fibrillation when medical staff arrived. Nine patients died after 1/2 to 52 hours of intensive care in the medical centers aboard.</AbstractText> |
3,454 | Electrical storm due to amiodarone induced thyrotoxicosis in a young adult with dilated cardiomyopathy: thyroidectomy as the treatment of choice. | For a patient with idiopathic dilated cardiomyopathy, an implantable defibrillator, and amiodarone induced thyrotoxicosis associated with ventricular fibrillation storm. Medical therapy was ineffective. Thyroidectomy resulted in immediate control of the arrhythmia and permitted reinitiation of amiodarone. At 18-month follow-up, the patient remained euthyroid on amiodarone and ventricular arrhythmia free. |
3,455 | Pacemaker-mediated tachycardia in a biventricular pacing system. | A 63-year-old man with chronic atrial fibrillation and heart failure had a biventricular pacing system implanted. The pulse generator was a standard DDDR pacemaker, using the atrial channel for the right ventricular lead and the ventricular channel for the left ventricular lead. During final adjustment of the pacing parameters, a pacemaker tachycardia triggered by T wave oversensing from the right ventricular lead was recorded. |
3,456 | Spontaneously terminating apparent ventricular fibrillation during transesophageal electrophysiological testing in infants with Wolff-Parkinson-White syndrome. | This article describes two infants with Wolff-Parkinson-White (WPW) syndrome in whom apparent VF occurred without antecedent AF or atrial flutter during routine transesophageal electrophysiological testing. Remarkably, this arrhythmia terminated spontaneously in both infants. The documentation of self-limited apparent VF, or polymorphic ventricular tachycardia close to VF, in transesophageal testing adds another dimension to the management of WPW. |
3,457 | Minimally invasive cardioverter defibrillator implantation for children: an animal model and pediatric case report. | The smaller venous capacitance in infants and small children may hamper transvenous ICD lead implantation, and epicardial approaches require thoracotomy and have associated complications. The study evaluated the feasibility and performance of subcutaneous arrays and active can ICDs without transvenous shocking coils or epicardial patches. An immature and mature pig were anesthetized and ventilated. A pacing lead was inserted in the right ventricle for fibrillation induction and rate sensing. Subcutaneous arrays were positioned in the right and left chest walls. An ICD emulator was placed in abdominal and prepectoral pockets. Fluoroscopic images were acquired for each electrical vector configuration (array --> can, can --> array, array --> array, array + array --> can). Ventricular fibrillation was induced and DFT testing performed. Defibrillation was achieved in all ten trials in the immature piglet, with DFT < or = 9 J, regardless of vector configuration. Using a single subcutaneous array and active can, the shock impedance ranged from 28-36 ohms. With two arrays, shocking impedance fell to 15-22 ohms. In the adult pig, defibrillation was not accomplished with maximum energy of 40 J, using all vector configurations. Using data garnered from these experiments, this technique was then successfully performed in a 2-year-old child with VT and repaired congenital heart disease, needing an ICD. This study demonstrates the feasibility of leadless ICD implantation in an immature animal and successful implementation in a small child. A single subcutaneous array and active can resulted in excellent implant characteristics and DFTs with a minimally invasive approach. Defibrillation was not possible in a larger animal, possibly due to maximal available energy. This may be of value for small children requiring ICD implantation. |
3,458 | Acute cardiovascular effects of diltiazem in anesthetized dogs with induced atrial fibrillation. | Atrial fibrillation (AF) is one of the most important arrhythmias of dogs. In a previous study, we determined the dosage of intravenously administered diltiazem necessary to reduce ventricular response (VR), cardiac output (CO), and mean systemic arterial pressure (P(Ao)) to values similar to those observed during sinus rhythm (SR) before induction of AF. The present study was conducted to establish an acute, effective dosage of diltiazem given PO. AF was produced by rapid atrial pacing in healthy, anesthetized Beagle Hounds. Dogs were instrumented to record hemodynamic and electrophysiological parameters. Four dogs were given 2.5 mg/kg diltiazem, and another 4 dogs were given 5 mg/kg diltiazem by stomach tube, whereas 4 other dogs received vehicle in equivalent volumes. Plasma concentrations of diltiazem were measured at various intervals after dosing. A dosage of 5 mg/kg diltiazem produced plasma concentrations of 32-100 ng/mL 3 hours after administration, concentrations within the published effective range for dogs with naturally occurring AF. Between 2 and 3 hours after this dosage, the rate pressure product (RPP) and an index of left ventricular efficiency returned to values similar to those observed during SR. Thus, we believe that diltiazem at anorally administered dosages of 5 mg/kg should be considered to produce therapeutic blood concentrations and favorable hemodynamic effects in dogs with naturally occurring AF. These data must be extrapolated with caution to dogs with long-standing AF produced by natural causes. |
3,459 | Implantable cardioverter defibrillator in a 4-month-old infant with cardiac arrest associated with a vascular heart tumor. | A previously healthy male infant was resuscitated after spontaneous ventricular fibrillation at 9 weeks of age. Echocardiography revealed three tumors in the left ventricle not amenable to complete resection. Despite treatment with antiarrhythmic agents the ventricular arrhythmias continued. When the child was 4 months old and weighed 7 kg an ICD system was implanted using epicardial sense-pacing leads and a superior vena caval lead as a subcutaneous defibrillator coil placed posterior on the left thorax. Shocks were delivered between the subcutaneous coil lead and the intraabdominally placed ICD can. This ICD array system has not been reported previously. |
3,460 | Absence of a morning peak in ventricular tachycardia and fibrillation events in nonischemic heart disease: analysis of therapies by implantable cardioverter defibrillators. | A growing number of Japanese patients are being treated with ICDs. Efforts are warranted to minimize the rates of ICD shocks that cause discomfort and anxiety. The circadian distribution of ICD discharges was investigated in 80 patients (57+/-10 years of age, 69 men) from ten Japanese medical centers. The underlying heart disease was ischemic in 27 versus nonischemic in 53 patients. All patients had refractory VT or VF, and received appropriate shocks confirmed by stored data retrieved from the memory of the ICD. In the analysis of 354 appropriate shocks delivered in the overall population, a morning peak in VT or VF episodes was observed. However, subgroup analyses of the circadian distribution of ICD shocks revealed that the morning peak in VT or VF episodes was confined to patients with ischemic heart disease and was blunted by treatment patients with beta-adrenergic blockers. The absence of a morning peak in appropriate ICD shocks among patients with nonischemic heart disease remains unexplained and was unrelated to the use of beta-adrenergic blockers. In conclusion, the circadian pattern of appropriate ICD discharges was related to the underlying heart disease. In patients with ischemic heart disease, recurrences of VT or VF peaked in the morning. In contrast, in patients without ischemic heart disease, the episodes of VT or VF were evenly distributed during waking hours. Beta-adrenergic blockers appeared to blunt the morning peak in VT or VF among patients with ischemic heart disease. |
3,461 | [Multichamber pacing--a new non-pharmacologic method for the treatment of severe heart failure]. | According to initial clinical results biventricular pacing seems to be effective in the treatment of patients suffering from drug refractory severe heart failure combined with intraventricular conduction disturbance. Biventricular cardioverter defibrillators and biventricular pacemakers were implanted in patients suffering from drug refractory severe heart failure in 10 and in 15 cases, respectively. NYHA III-IV functional class, low left ventricular ejection fraction (24.2 +/- 6%), wide QRS (> 150 ms) with left bundle branch block and lateral dyssynchrony were present in each case. The left ventricle was enlarged in each patient (endodiastolic/endsystolic diameter: 78.6 +/- 9.2/68.2 +/- 8.3). The indications of cardioverter defibrillator implantations were both sustained ventricular tachycardia and ventricular fibrillation, nonsustained ventricular tachycardia combined with syncope in 7 and in 3 case, respectively. The duration of QRS decreased (187 +/- 32 vs. 136 +/- 19 ms, p = 0.012) and wall movement disorder disappeared. At the last follow up every patients were in NYHA II functional class and a decrease in left ventricular diameter could be observed (endodiastolic: 70.3 +/- 9.1 mm, p = 0.04; endosystolic: 61.9 +/- 8.8 mm, p = 0.04). During the follow up period (8.8 +/- 5.1 months) 18 episodes of ventricular arrhythmias were detected in the same patient, 2 patients died (1 arrhythmia death, 1 sudden cardiac death). Biventricular pacemakers and cardioverter defibrillators were implanted and applied successfully in the treatment of congestive heart failure for the first time in Hungary. |
3,462 | Physiologic atrial cardiac pacing for the prevention of chronic atrial fibrillation associated with sick sinus syndrome. | Long-term results of physiologic atrial pacing have been analyzed for the possibility of avoiding the recurrence of paroxysmal atrial fibrillation and the progression to chronic permanent atrial fibrillation in patients with paroxysmal atrial fibrillation related to sick sinus syndrome. Seventy four patients were evaluated and divided into two groups; 39 patients underwent atrial pacing (AAI, 53%) and 35 had ventricular pacing by single-lead pacing (VVI, 47%). All patients had been evaluated periodically on an out-patient basis by 24 hour Holter monitoring. Basic rhythms in all AAI patients were based on atrial pacing, resulting from the suppression of paroxysmal atrial fibrillation. Basic rhythms in the VVI paced patients were variable, consisting of regular sinus rhythm, transient atrial fibrillation, and ventricular pacing in 30 of 35 patients in the VVI group. The remaining five patients progressed to chronic permanent atrial fibrillation (0% in AAI vs. 14% in VVI, p < 0.05). Thromboembolic complications were not observed in the AAI pacing group. Three patients demonstrated thromboembolic complications (0% in AAI vs. 8.6% in VVI, p < 0.05). The effect of preventing paroxysmal atrial fibrillation and the progression to chronic atrial fibrillation was evident in the AAI paced group, but VVI pacing cannot prevent paroxysmal atrial fibrillation and chronic atrial fibrillation. In addition, potential risks of thromboembolic complications caused by atrial fibrillation were not decreased in VVI paced patients. |
3,463 | The impact of postoperative atrial fibrillation on neurocognitive outcome after coronary artery bypass graft surgery. | Neurocognitive decline is a continuing source of morbidity after cardiac surgery. Atrial fibrillation occurs often after cardiac surgery and has been linked to adverse neurologic events. We sought to determine whether postoperative atrial fibrillation was associated with postoperative cognitive dysfunction. Four-hundred-eleven patients were enrolled to receive a battery of neurocognitive tests both preoperatively and 6 wk after elective coronary artery bypass graft surgery. Neurocognitive test scores were separated into four cognitive domains, with a composite cognitive index (the mean of the four domain scores) determined for each patient at every testing period. Multivariable analysis controlling for age, years of education, diabetes mellitus, left ventricular ejection fraction, and preoperative atrial fibrillation compared the presence of postoperative atrial fibrillation with change in cognitive function. Three-hundred-eight patients completed both pre- and postoperative cognitive testing; 69 patients (22%) had postoperative atrial fibrillation. Those who developed atrial fibrillation showed more cognitive decline than those who did not develop postoperative atrial fibrillation (P = 0.036). Atrial fibrillation was associated with poorer cognitive function 6 wk after surgery. Although the mechanism of this association is yet to be determined, prevention of atrial fibrillation may result in improved neurocognitive function.</AbstractText>Neurocognitive dysfunction is common after coronary artery bypass graft surgery. The relationship between atrial fibrillation and neurocognitive dysfunction has not been examined. Our study shows that postoperative atrial fibrillation is associated with neurocognitive decline.</AbstractText> |
3,464 | ACLS. | It must be emphasised that the published International Guidelines 2000 contain an in-depth presentation of the scientific evidence behind advanced life support. The exact interpretation of this evidence, and the algorithms adopted by a national resuscitation council will depend upon various factors such as local interpretation of the evidence, local practice and availability of drugs. The ERC is publishing its own summaries of the guideline changes and the sequences of action for both BLS and ALS and these papers are recommended for further reading. |
3,465 | Endothelin receptor blockade and in-stent restenosis. | The aim of the present study was to test whether oral dosing of an endothelin (ET) receptor antagonist was able to reduce restenosis in the model of stent-induced restenosis. After pigs underwent coronary artery catheterization they were randomly allocated either to controls or to treatment with the ET receptor antagonist BSF 208075. Thirty-seven pigs underwent percutaneous transluminal coronary angioplasty plus stent implantation; seven animals died of ventricular fibrillation due to procedure-related myocardial ischaemia. From the 30 surviving animals coronary arteries were sampled after 6 weeks of oral treatment with 10 mg/kg/day BSF 208075 or vehicle and histologically evaluated. Stent implantation had no effect on total coronary artery diameter, and media thickness was virtually identical in the two groups. However, neointimal thickness in the group treated with the ET receptor antagonist was significantly reduced, resulting in a significantly larger total coronary artery lumen in the treated group. As in the setting of stent implantation neither 'recoil' nor scar-related vascular remodelling can occur, this result allows the conclusion of a significant antiproliferative effect of ET receptor antagonism in pig coronary arteries. |
3,466 | [Sudden cardiac death]. | Sudden cardiac death describes the unexpected natural death from cardiac cause within a short time period from the onset of symptoms (usually one hour) in a person without any prior condition that would appear fatal. The mechanism is generally a malignant ventricular arrhythmia (ventricular tachycardia or fibrillation). Sudden death is a major public health problem as it accounts for 3 to 400,000 deaths annually in the United States. Risk factors, physiopathological mechanisms, disease states associated with sudden death, and primary and secondary prevention treatments are reviewed. |
3,467 | A stroke prediction score in the elderly: validation and Web-based application. | The objective of this study was to construct a prediction model for predicting stroke in an elderly U.S. population, and to assess the accuracy in this population of other previously published prediction models. The subjects were participants in the Cardiovascular Health Study: 2,495 men and 3,393 women age 65 years and older at baseline, and followed for 6.3 years. Among 5,711 participants free of baseline stroke, 399 strokes occurred. Sex-specific prediction equations were constructed using study variables that were most importantly related to incident stroke: age, systolic blood pressure, diabetes, ECG diagnosis of atrial fibrillation or left ventricular hypertrophy, confirmed history of cardiovascular disease, diabetes, time to walk 15 ft, and serum creatinine. The prediction rule was implemented as a risk score and in a Web-based interactive Java applet. Overall, the model predicted 5-year stroke risks ranging from less than 1 to 59%. The 20% of subjects in the highest predicted risk group had a 5-year actual stroke incidence rate of 15%, while the 20% lowest risk group had a 1% incidence. Risk scores from two other studies performed well in these study participants. Effective discrimination between low and high stroke risk in the elderly was possible in this cohort with data that are easy to obtain. Evaluation of the generalizability and clinical usefulness of this prediction model requires further research. |
3,468 | [Possibility of gene-specific treatment for hereditary arrhythmic diseases]. | Recent genetic and molecular technology have shown that genetic abnormalities related to the cardiac ion channels can be a cause of some hereditary arrhythmic diseases. Until now, advanced analysis has proceeded especially in congenital long QT syndrome, and six different subtypes have been identified in Romano-Ward syndrome and 2 subtypes in Jervell & Lange-Nielsen syndrome. Since the mechanism of QT interval prolongation in each subtype is based on the malfunction of different cardiac ion channels, the same pharmacological treatment may show different antiarrhythmic effects for each subtype. In this paper, we review some of the hereditary arrhythmic diseases and discuss the possibility of gene-specific treatment in such diseases. |
3,469 | A calcium sensor in the sodium channel modulates cardiac excitability. | Sodium channels are principal molecular determinants responsible for myocardial conduction and maintenance of the cardiac rhythm. Calcium ions (Ca2+) have a fundamental role in the coupling of cardiac myocyte excitation and contraction, yet mechanisms whereby intracellular Ca2+ may directly modulate Na channel function have yet to be identified. Here we show that calmodulin (CaM), a ubiquitous Ca2+-sensing protein, binds to the carboxy-terminal 'IQ' domain of the human cardiac Na channel (hH1) in a Ca2+-dependent manner. This binding interaction significantly enhances slow inactivation-a channel-gating process linked to life-threatening idiopathic ventricular arrhythmias. Mutations targeted to the IQ domain disrupted CaM binding and eliminated Ca2+/CaM-dependent slow inactivation, whereas the gating effects of Ca2+/CaM were restored by intracellular application of a peptide modelled after the IQ domain. A naturally occurring mutation (A1924T) in the IQ domain altered hH1 function in a manner characteristic of the Brugada arrhythmia syndrome, but at the same time inhibited slow inactivation induced by Ca2+/CaM, yielding a clinically benign (arrhythmia free) phenotype. |
3,470 | [Mid-ventricular obstructive hypertrophic cardiomyopathy associated with an apical aneurysm and sustained ventricular tachycardia: a case report]. | A 60-year-old woman presented with mid-ventricular obstructive hypertrophic cardiomyopathy associated with an apical aneurysm and sustained ventricular tachycardia. She was admitted because of drug refractory ventricular tachycardia. She had been treated with several antiarrhythmic agents, including amiodarone, but symptomatic episodes had continued. Echocardiography, magnetic resonance imaging, and left ventriculography showed mid-ventricular obstructive hypertrophic cardiomyopathy with an apical aneurysm. Electrophysiological study easily reproduced sustained pleomorphic ventricular tachycardia, polymorphic ventricular tachycardia, and ventricular fibrillation. The patient underwent implantation of a cardioverter-defibrillator. The relationship between mid-ventricular hypertrophic cardiomyopathy and apical aneurysm is unknown, but mid-ventricular hypertrophic cardiomyopathy is one of the causes of severe ventricular arrhythmias and sudden death. |
3,471 | Electrocardiogram and rhythm strip interpretation by final year medical students. | The pre-registration house officers (PRHO) is often called upon to interpret electrocardiograms ECG. We invited final-year medical students who had successfully completed their written final examinations, to interpret three rhythm-strip tracings, and three 12-lead ECG tracings. The rhythm-strips were of ventricular fibrillation (VF), ventricular tachycardia (VT), and complete heart block. Of the three 12-lead ECG tracings, one was an inferior myocardial infarction (MI), one was atrial fibrillation (AF), and one showed no abnormality. Forty-six medical students attended. Of these, 50% had received no formal training in ECG interpretation, although 89% had tried to learn ECG interpretation from books. Only 9% felt confident in their interpretation of ECG tracings. Of the rhythm-strips, 100% correctly identified VF, 96% recognised VT, and 67% identified complete heart block. Of the 12-lead ECG tracings, 61 % recognised the MI, 54% recognised AF, and only 46% successfully identified the normal ECG as such. The group were significantly worse at 12-lead ECG interpretation compared to rhythm-strips (p<0.01). The members of the group who had received formal training in ECG interpretation were significantly better at interpreting both rhythm-strips and 12-lead ECG tracings (p<0.05). It would appear that formal ECG training as an undergraduate improves PRHO interpretation of ECG tracings, and the PRHO should not interpret 12-lead ECG tracings without consulting more senior medical staff. |
3,472 | Early recovery of left ventricular function after stentless versus stented aortic valve replacement for pure aortic stenosis and severe cardiac dysfunction. | The aim of this study was to evaluate early recovery of systolic function after stentless aortic valve replacement (AVR) versus stented AVR.</AbstractText>Fifty-four consecutive patients with pure aortic stenosis and impaired left ventricular function (LVEF < or = 35%) were studied retrospectively. Aortic regurgitation, concomitant valvular or coronary artery surgery, atrial fibrillation, and a previous AVR were exclusion criteria. Twenty-two patients (mean age, 70.0 +/- 6.5 years) received a stentless bioprosthesis and 32 (mean age, 58.9 +/- 6.2 years, P =.031 between groups) a mechanical or stented biologic valve. Patients underwent echocardiography preoperatively, at discharge, at 6 months, and at 1 year after surgery.</AbstractText>At 6 months, analysis of variance demonstrated significant differences between groups in fractional shortening measured at the endocardium and midwall fractional shortening (<0.001), velocity of circumferential shortening (P <.001) ejection fraction (P =.02), left ventricular mass index (P <.001), systolic meridional wall stress, and circumferential wall stress (P <.001), One-year studies confirmed these findings.</AbstractText>LV function showed, after a stentless AVR, an early recovery greater than in patients receiving a stented valve.</AbstractText>Copyright 2001 by W.B. Saunders Company</CopyrightInformation> |
3,473 | Lengthening of intraatrial conduction time in atrial fibrillation and its relation with early recurrence of atrial fibrillation. | Intraatrial conduction delay in atrial fibrillation (AF) that is considered a component of atrial electrical remodeling has been demonstrated previously in experimental models and it is considered an important factor for the induction or stabilization of AF. However, it is not known if this phenomenon exists in human AF. The present study aimed to compare intraatrial conduction time (IACT) in patients with chronic atrial fibrillation who were converted to sinus rhythm and a matched control group, and to investigate its relation with early AF recurrence. Seventeen patients with chronic AF (mean duration of 20.71+/-16.35 months) were enrolled in the study (7 males, 10 females, 63+/-8 years). An age and sex matched control group (n=12) consisted of patients with sinus rhythm who underwent electrophysiological study (EPS). None of the patients were on any antiarrhythmic treatment during the procedures. Cardioversion was performed via external DC cardioversion. Eight patients in the control group were delivered a DC shock because of induced ventricular tachycardia during EPS. IACT was defined as the interval between the onset of P wave surface ECG and the beginning of A wave at high right atrium (IACT 1) and low right atrium (IACT 2). Additionally, the interval between A wave at high right atrium and low right atrium was measured (IACT 3). Patient characteristics such as age, sex and echocardiographic variables were not different between the AF group and the control group. Heart rate after cardioversion was found to be similar between the two groups. Total delivered energy was significantly higher in the AF group than in the control group (464.47+/-165.82 joules vs. 315.00+/-27.77 joules, p<0.001). IACT 1 (15.30+/-7.61 msec vs 8.50+/-5.29 msec, p<0.02 ), IACT 2 (45.25+/-836 msec vs 26.44+/-10.45 msec, p<0.001) and IACT 3 (26.9+/-8.26 msec vs. 18.67+/-10.05, p<0.05) significantly lengthened in the AF group after maintenance of sinus rhythm compared to the control group. There were 6 early AF recurrences during the 1 week follow-up period. Multivariate analysis, revealed IACT 2 and IACT 3 were significantly different between the control group, the patient with recurred AF and the patients with maintained sinus rhythm. Post-hoc analysis revealed that IACT 2 and IACT 3 significantly lengthened in the patients with recurred AF compared to both the control group and patients with maintained sinus rhythm. On the other hand, only IACT 2 patients with maintained sinus rhythm were found to be higher than those of the control group. The present study indicated that intraatrial conduction was disturbed in patients with AF, a finding which is consistent with those of previous experimental studies. Additionally, such a phenomenon may be a risk factor for the early recurrence of AF after cardioversion to sinus rhythm. |
3,474 | [Drug therapy in cardiopulmonary resuscitation]. | In the year 2000, new international guidelines for cardiopulmonary resuscitation (CPR) were published by the American Heart Association, and the European Resuscitation Council. These guidelines are evidence-based, indicating that these recommendations are based primarily on interpretation of data from clinical studies. Levels of recommendation range from class I (proven safe and useful), class IIa (intervention of choice), IIb (alternative intervention), indeterminate (research stage), and class III (unacceptable, no benefit). Administration of drugs during CPR should be performed intravenously or intraosseously (class IIa) or, as a second-line approach, endotracheally (class IIb). Due to lack of evidence, the standard dose of 1 mg epinephrine to treat ventricular fibrillation, pulseless electrical activity, or asystole was categorized as class indeterminate; while a single dose of 40 units vasopressin to treat adults with shock-refractory ventricular fibrillation received a IIb recommendation. Owing to a lack of clinical data, the use of vasopressin was neither recommended to treat adults with pulseless electrical activity or asystole, nor for the use in children. Both endothelin and calcium were not recommended for routine use (class indeterminate). Careful titration of acid-base status with 1 mL/kg 8.4% sodium bicarbonate should only be administered if indicated by blood gas analysis (class indeterminate). If 1 mg epinephrine fails to be effective in adult patients with pulseless electrical activity or asystole, 1 mg atropine can be administered (class indeterminate). Regarding antiarrhythmic drugs, 300 mg amiodarone (class IIb) showed the best results in shock-refractory ventricular fibrillation. The postresuscitation phase has the goal to achieve the best possible neurological performance after return of spontaneous circulation, which requires careful optimization of organ functions. |
3,475 | Outcome of out-of-hospital postcountershock asystole and pulseless electrical activity versus primary asystole and pulseless electrical activity. | In the prehospital setting, countershock terminates ventricular fibrillation (VF) in about 80% of cases. However, countershock is most commonly followed by asystole or pulseless electrical activity (PEA). The consequences of such a countershock outcome have not been well studied. The purpose of this investigation was to compare the outcome of prehospital VF victims shocked into asystole or PEA with that of patients whose first documented rhythm was asystole or PEA (primary asystole or PEA).</AbstractText>Observational, retrospective study conducted over 5 yrs (1995-1999).</AbstractText>A municipal hospital with a catchment area of >200,000.</AbstractText>Consecutive adult patients with out-of-hospital nontraumatic cardiopulmonary arrest of cardiac origin. Patients found in VF who developed asystole or PEA after countershocks (group 1) and patients found in asystole or PEA (primary asystole or PEA) (group 2) were included if the reported downtime was <10 min.</AbstractText>None.</AbstractText>Study end points included restoration of circulation (defined as a pulse for any duration), survival to hospital admission, and survival to hospital discharge. Ratios were determined, 95% confidence intervals were calculated, and observed differences were compared. For group 1 patients (n = 101), 61% of patients had a bystander-witnessed collapse and 34% received bystander cardiopulmonary resuscitation. For group 2 patients (n = 140), collapse was bystander witnessed in 71% and 45% received bystander cardiopulmonary resuscitation. These differences were not statistically significant. Restoration of circulation was significantly more frequent in group 2 than group 1 (42% vs. 16%, p <.001) as was survival to hospital admission (36% vs. 11%, p =.001). Survival to hospital discharge was greater in group 2 patients, but the difference failed to achieve statistical significance (10% vs. 3%, p =.062).</AbstractText>Countershock of prolonged VF followed by a nonperfusing rhythm has a worse prognosis than primary asystole or PEA and may be related to myocardial electrical injury.</AbstractText> |
3,476 | Optimizing timing of ventricular defibrillation. | Our intent was to evolve a prognosticator that would predict the likelihood that an electrical shock would restore a perfusing rhythm. Such a prognosticator was to be based on conventional electrocardiographic signals but without constraints caused by artifacts resulting from precordial compression. The adverse effects of "hands off" intervals for rhythm analyses would therefore be minimized. Such a prognosticator was further intended to reduce the number of electrical shocks and the total energy delivered and thereby minimize postresuscitation myocardial dysfunction.</AbstractText>Observational study.</AbstractText>Medical research laboratory of a university-affiliated research and educational institute.</AbstractText>Domestic pigs.</AbstractText>Ventricular fibrillation was induced in an established porcine model of cardiac arrest. Recordings of scalar lead 2 over the frequency range of 4-48 Hz were utilized. The area under the curve representing the amplitude and frequency was defined as the amplitude spectrum area (AMSA).</AbstractText>A derivation group of 55 animals yielded a threshold value of AMSA that uniformly predicted successful resuscitation. A separate group of 10 animals, a validation group, confirmed that an AMSA value of 21 mV.Hz predicted restoration of perfusing rhythm after 7 of 8 electrical shocks and failure of electrical conversion in 21 of 23 electrical shocks, yielding sensitivity and specificity of about 90%. The negative predictive value of AMSA was 95% and statistically equivalent to that of coronary perfusion pressure, mean amplitude, and median frequency. The positive predictive value that would prompt continuation of cardiopulmonary resuscitation without interruption for an unsuccessful defibrillation attempt was greatly improved with AMSA (78%) as compared with coronary perfusion pressure (42%), mean amplitude (32%), and median frequency (29%).</AbstractText>AMSA has the potential for guiding more optimal timing of defibrillation without adverse interruption of cardiopulmonary resuscitation or the delivery of unsuccessful high energy electrical shocks that contribute to postresuscitation myocardial injury.</AbstractText> |
3,477 | Involvement of the central nervous system in the protective effect of melanocortins in myocardial ischaemia/reperfusion injury. | Melanocortin peptides exert, in rats, a protective effect in myocardial ischaemia followed by reperfusion, or permanent occlusion of a coronary artery. Moreover, melanocortins have an anti-shock effect. Since the mechanism of the life-saving effect of these peptides in haemorrhagic shock includes an essential brain loop, we aimed to determine whether the central nervous system (CNS) is also involved in the protective effect against the outcome of short-term myocardial ischaemia followed by reperfusion. Ischaemia was produced in anaesthetized rats by ligature of the left anterior descending coronary artery for 5 min. Reperfusion-induced ventricular tachycardia (VT), ventricular fibrillation (VF) and lethality, and the time-course of arterial blood pressure over 5 min following reperfusion were evaluated. Groups of 8-14 rats were used. Intravenous (i.v.) injection of ACTH-(1-24) (0.16-0.48 mg/kg) during the ischaemic period dose dependently reduced the incidence of VT, VF and of lethality. In saline-treated rats, coronary reperfusion caused VT in 100% animals, VF in 86%, and death in 86%. The highest dose of ACTH-(1-24) (0.48 mg/kg) completely prevented the occurrence of VT, VF and death in all rats (P<0.005). Moreover, the melanocortin peptide prevented the fall in mean arterial pressure (MAP) occurring during reperfusion. Treatment with ACTH-(1-24) by the intracerebroventricular (i.c.v.) route also reduced the incidence of VT, VF and lethality, and prevented the fall in MAP in a dose dependent manner. Complete (100%) protection occurred with an i.c.v. dose (0.048 mg/kg) 10 times less than that needed by the i.v. route. The present data show that in the protective effect of melanocortin peptides against the injury after myocardial ischaemia/reperfusion, the i.c.v. route of administration is more effective than the i.v. route. They suggest that a CNS mechanism, not yet identified, may be involved. |
3,478 | Thrombolytic therapy after cardiac arrest and its effect on neurological outcome. | the aim of the study is to investigate the effect of thrombolytic therapy on neurological outcome in patients after cardiac arrest due to acute myocardial infarction. Laboratory investigations have demonstrated that thrombolytic therapy after cardiopulmonary resuscitation improves neurological function.</AbstractText>from July 1991 to June 1996, patients with witnessed ventricular fibrillation cardiac arrest due to acute MI and successful restoration of spontaneous circulation admitted to the emergency department were analyzed retrospectively. A logistic regression model was used to assess the association between thrombolytic therapy and neurological outcome [best cerebral performance category (CPC) within 6 months after cardiac arrest].</AbstractText>all 157 patients [median age 57 years (IQR 50-69)] were analyzed. Thrombolytic therapy was applied in 42 patients (27%). With thrombolytic therapy good functional neurological recovery (CPC 1 or 2) was achieved more frequently (69 vs. 50%, P=0.03). After controlling for age, prehospital dosage of epinephrine, and the duration of cardiac arrest we found a non significant trend towards good neurological recovery when thrombolytic therapy was given (OR 1.9, 95% CI 0.8-4.6).</AbstractText>thrombolytic therapy after cardiac arrest due to acute myocardial infarction is associated with improved neurological outcome.</AbstractText> |
3,479 | Inspiratory impedance threshold valve during CPR. | The use of an inspiratory impedance threshold valve (ITV) during cardiopulmonary resuscitation (CPR) should reduce intrathoracic pressure during natural chest recoil or active chest decompression. This might in turn improve venous return and thereby organ blood flow. The haemodynamic effects during both standard CPR and active compression-decompression (ACD)-CPR with and without the ITV, therefore, were studied in a well-established porcine model with cross-over design. Sixteen pigs were randomised to one of four methods initially, changing the method every fifth minute during mechanical chest compression at 100 min(-1). Myocardial blood flow was doubled when the valve was added to standard CPR, median (q25-q75) 14 (3-47) versus 27 (9-51) ml min(-1) 100 g(-1) (P=0.001). ACD-CPR caused a similar increase, while adding the ITV to ACD-CPR only tended to increase myocardial blood flow (P=0.077). Varying the technique had no effect on cerebral, kidney or carotid blood flow, coronary perfusion pressure, expired CO(2) concentrations or blood gases. The valve is a promising new tool in CPR, but more independent studies of the device are needed. |
3,480 | Should ward nurses be using automatic external defibrillators as first responders to improve the outcome from cardiac arrest? A systematic review of the primary research. | The outcome from in-hospital cardiac arrest has improved little since the implementation of cardiopulmonary resuscitation 40 years ago. Early defibrillation improves survival following ventricular fibrillation and pulseless ventricular tachycardia. The emergence of automatic external defibrillators and advisory defibrillators has been heralded as the answer to defibrillation delays in-hospital.</AbstractText>To locate and evaluate the evidence supporting automatic external defibrillator use in-hospital on general wards.</AbstractText>A systematic review of indexed and grey literature to identify primary research.</AbstractText>Fifteen in-hospital automatic external defibrillator studies were located, five met the inclusion criteria.</AbstractText>There is limited primary research evaluating automatic external defibrillators in-hospital. Manual defibrillators remain the most commonly used device for in-hospital defibrillation. Automated external defibrillators offer an alternative to manual defibrillation providing they have a screen and manual override capability, and the technology for pacing is close to hand. For in-hospital automatic external defibrillator programmes to be effective a change in nursing philosophy must occur, and defibrillation must become an expected rather than an extended nursing role.</AbstractText> |
3,481 | Exploding implantable cardioverter defibrillator. | A 79-year-old man with a pectoral implantable cardioverter defibrillator (ICD) system underwent periodic defibrillation threshold testing 18 months after implant. Attempted delivery of a 15-J shock caused a light flash above the pocket and a loud "pop." High-voltage lead impedance was <20 ohms. Pocket exploration revealed insulation abrasion of the high-voltage portion of the single-coil right ventricular lead. The outer shield of the active can pulse was perforated and scorched due to arcing. Device analysis confirmed a shorted transistor in the high-voltage output circuit. Unsuspected physical contact between high-voltage electrodes of opposite polarity within the pocket can cause catastrophic ICD system failure. |
3,482 | Paradoxic abbreviation of repolarization in epicardium of the right ventricular outflow tract during augmentation of Brugada-type ST segment elevation. | We report the case of a 53-year-old Japanese man with a typical Brugada-like ECG in whom epicardial and endocardial activation-recovery intervals (ARI) in the right ventricular outflow tract (RVOT) were simultaneously measured by recording unipolar electrograms from the Pathfinder catheter introduced in the great cardiac vein as well as from the multielectrode basket catheter deployed in the RVOT. Epicardial ARI in the RVOT was abbreviated paradoxically at the beat of augmented ST segment elevation in lead V2 after a long pause or after pilsicainide injection. Endocardial ARI in the RVOT and epicardial ARI in the left ventricle were prolonged or were not changed. Our data support the hypothesis that heterogenous response of repolarization across the ventricular wall in the RVOT is responsible for accentuation of ST segment elevation in the right precordial leads. |
3,483 | Electrical remodeling and atrial dilation during atrial tachycardia are influenced by ventricular rate: role of developing tachycardiomyopathy. | Atrial fibrillation (AF) and congestive heart failure (CHF) are two clinical entities that often coincide. Our aim was to establish the influence of concomitant high ventricular rate and consequent development of CHF on electrical remodeling and dilation during atrial tachycardia.</AbstractText>A total of 14 goats was studied. Five goats were subjected to 3:1 AV pacing (A-paced group, atrial rate 240 beats/min, ventricular rate 80 beats/min). Nine goats were subjected to rapid 1:1 AV pacing (AV-paced group, atrial and ventricular rates 240 beats/min). During 4 weeks, right atrial (RA) and left ventricular (LV) diameters were measured during sinus rhythm. Atrial effective refractory periods (AERP) and inducibility of AF were assessed at three basic cycle lengths (BCL). After 4 weeks of rapid AV pacing, RA and LV diameters had increased to 151% and 113% of baseline, whereas after rapid atrial pacing alone, these parameters were unchanged. Right AERP (157+/-10 msec vs 144+/-16 msec at baseline with BCL of 400 msec in the A-paced and AV-paced group, respectively) initially decreased in both groups, reaching minimum values within 1 week. Subsequently, AERP partially recovered in AV-paced goats, whereas AERP remained short in A-paced goats (79+/-7 msec vs 102+/-12 msec after 4 weeks; P < 0.05). Left AERP demonstrated a similar time course. Inducibility of AF increased in both groups and reached a maximum during the first week in both groups, being 20% and 48% in the A-paced and AV-paced group, respectively.</AbstractText>Nature and time course of atrial electrical remodeling and dilation during atrial tachycardia are influenced by concurrent high ventricular rate and consequent development of CHF.</AbstractText> |
3,484 | Electroporation in a model of cardiac defibrillation. | It is known that high-strength shock disrupts the lipid matrix of the myocardial cell membrane and forms reversible aqueous pores across the membrane. This process is known as "electroporation." However, it remains unclear whether electroporation contributes to the mechanism of ventricular defibrillation. The aim of this computer simulation study was to examine the possible role of electroporation in the success of defibrillation shock.</AbstractText>Using a modified Luo-Rudy-1 model, we simulated two-dimensional myocardial tissue with a homogeneous bidomain nature and unequal anisotropy ratios. Spiral waves were induced by the S1-S2 method. Next, monophasic defibrillation shocks were delivered externally via two line electrodes. For nonelectroporating tissue, termination of ongoing fibrillation succeeded; however, new spiral waves were initiated, even with high-strength shock (24 V/cm). For electroporating tissue, high-strength shock (24 V/cm) was sufficient to extinguish ongoing fibrillation and did not initiate any new spiral waves. Weak shock (16 to 20 V/cm) also extinguished ongoing fibrillation; however, in contrast to the high-strength shock, new spiral waves were initiated. Success in defibrillation depended on the occurrence of electroporation-mediated anodal-break excitation from the physical anode and the virtual anode. Some excitation wavefronts following electrical shock used a deexcited area with recovered excitability as a pass-through point; therefore, electroporation-mediated anodal-break excitation is necessary to block out the pass-through point, resulting in successful defibrillation.</AbstractText>The electroporation-mediated anodal-break excitation mechanism may play an important role in electrical defibrillation.</AbstractText> |
3,485 | Lidocaine increases the proarrhythmic effects of monophasic but not biphasic shocks. | Lidocaine increases monophasic shock defibrillation energy requirement (DER) values but does not alter biphasic shock DER values. However, the mechanism of this drug/shock waveform interaction is unknown. It may be that lidocaine increases the proarrhythmic actions of monophasic shocks but not biphasic shocks. Thus, lidocaine may increase monophasic shock DER values by increasing myocardial vulnerability to shock-induced ventricular fibrillation.</AbstractText>Area of myocardial vulnerability (AOV), defined by a two-dimensional grid according to shock strength (y-axis) and shock coupling interval (x-axis), was assessed for biphasic shocks (n = 11) and monophasic shocks (n = 13) in intact swine hearts. Shocks were randomly delivered during right ventricular pacing at 10 shock strengths (50 to 500 V) and five coupling intervals (160 to 240 msec). AOV was defined as the number of points within the test grid that induced ventricular fibrillation. AOV, upper limit of vulnerability (ULV), and DER values were determined at baseline and during systemic infusion of lidocaine (10 mg/kg/hour). Lidocaine increased AOV, ULV, and DER values by 35%, 23%, and 36%, respectively, for monophasic shocks. However, lidocaine did not alter AOV, ULV, or DER values for biphasic shocks.</AbstractText>Lidocaine increases the AOV to monophasic shocks, which is directly related to changes in ULV and DER values. This implies that lidocaine increases the proarrhythmic activity of monophasic shocks but not biphasic shocks. This may explain why lidocaine increases monophasic shock DER values.</AbstractText> |
3,486 | Modified moving average analysis of T-wave alternans to predict ventricular fibrillation with high accuracy. | T-wave alternans is a marker of cardiac electrical instability with the potential for arrhythmia risk stratification. The modified moving average method was developed to measure alternans in settings with artifacts, noise, and nonstationary data. Algorithms were developed and performance characteristics were validated with simulated electrocardiograms (ECGs). Experimental laboratory ECGs with dynamically changing alternans values were analyzed. Alternans values estimated by modified moving average analysis correlated strongly with input alternans values (r(2) = 0.9999). Rapidly changing alternans levels and phase reversals did not perturb the measurement. When heart rate was increased from 60 to 180 beats/min, with T-wave alternans apex moving from 237 to 103 ms after the R wave, the measured alternans peak varied <5% from input value. Simulated 50- to 1,000-microV motion artifact spikes typical of treadmill ECGs produced inaccuracies <2%. Alternans values in experimental laboratory study using standard electrodes tracked vulnerability to myocardial ischemia-induced ventricular fibrillation with 100% sensitivity and specificity at a cut point of 0.75 mV. Modified moving average analysis is a robust method that precisely measures T-wave alternans in settings with artifacts, noise, and nonstationary data typical of clinical ECGs and yields an accurate estimate of risk for ventricular fibrillation. |
3,487 | Aerobic exercise conditioning: a nonpharmacological antiarrhythmic intervention. | Sudden, unexpected cardiac death due to ventricular fibrillation is the leading cause of death in most industrially developed countries. Yet, despite the enormity of this problem, the development of safe and effective antiarrhythmic therapies has proven to be an elusive goal. In fact, many initially promising antiarrhythmic medications were subsequently found to increase rather than to decrease cardiac mortality. It is now known that cardiac disease alters cardiac autonomic balance and that the patients with the greatest changes in this cardiac neural regulation (i.e., decreased parasympathetic coupled with increased sympathetic activity) are also the patients at the greatest risk for sudden death. A growing body of experimental and epidemiological data demonstrates that aerobic exercise conditioning can dramatically reduce cardiac mortality, even in patients with preexisting cardiac disease. Conversely, the lack of exercise is strongly associated with an increased incidence of many chronic debilitating diseases, including coronary heart disease. Because it is well established that aerobic exercise conditioning can alter autonomic balance (increasing parasympathetic tone and decreasing sympathetic activity), a prudently designed exercise program could prove to be an effective and nonpharmacological way to enhance cardiac electrical stability, thereby protecting against sudden cardiac death. |
3,488 | Value of plasma B type natriuretic peptide measurement for heart disease screening in a Japanese population. | Conflict exists regarding the usefulness of measuring plasma B type natriuretic peptide (BNP) concentrations for identifying impaired left ventricular (LV) systolic function during mass screening. Various cardiac abnormalities, regardless of degree of LV dysfunction, are prone to carry a high risk of cardiovascular events.</AbstractText>To examine the validity of plasma BNP measurement for detection of various cardiac abnormalities in a population with a low prevalence of coronary heart disease and LV systolic dysfunction.</AbstractText>Participants in this cross sectional study attended a health screening programme in Iwate, northern Japan. Plasma BNP concentrations were determined in 1098 consecutive subjects (mean age 56 years) by direct radioimmunoassay. All subjects underwent multiphasic health checkups including physical examination, ECG, chest radiography, and transthoracic echocardiography.</AbstractText>Conventional diagnostic methods showed 39 subjects to have a wide range of cardiac abnormalities: lone atrial fibrillation or flutter in 11; previous myocardial infarction in seven; valvar heart disease in seven; hypertensive heart disease in six; cardiomyopathy in six; atrial septal defect in one; and cor pulmonale in one. No subjects had a low LV ejection fraction (< 40%). To assess the utility of plasma BNP measurement for identification of such patients, receiver operating characteristic analysis was performed. The optimal threshold for identification was a BNP concentration of 50 pg/ml with sensitivity of 89.7% and specificity of 95.7%. The area under the receiver operating characteristic curve was 0.970. The positive and negative predictive values at the cutoff level were 44.3% and 99.6%, respectively.</AbstractText>Measurement of plasma BNP concentration is a very efficient and cost effective mass screening technique for identifying patients with various cardiac abnormalities regardless of aetiology and degree of LV systolic dysfunction that can potentially develop into obvious heart failure and carry a high risk of a cardiovascular event.</AbstractText> |
3,489 | Terikalant and barium decrease the area of vulnerability to ventricular fibrillation induction by T-wave shocks. | The area of vulnerability (AOV) to ventricular fibrillation (VF) induction by high-voltage shocks has been proposed as a measure of vulnerability to VF. Biphasic shocks spanning the T wave and ranging between 50 V and the upper limit of vulnerability (ULV) to VF were delivered before and after terikalant (1 mg/kg) and barium (1.1 mg/kg load followed by 0.05-0.10 mg/kg/min maintenance) or vehicle in dogs. The AOV decreased by 34% and 28% (p < 0.01) after terikalant and barium (n = 8 dogs each), respectively. Mean ULV, defibrillation threshold (DFT), and ventricular vulnerability period (VVP) decreased by 16%, 23%, and 31% (p < 0.01), respectively, after terikalant, and by 25%, 17% (p < 0.01), and 13% (p = 0.08), respectively, after barium. Vehicle (n = 14) did not significantly alter any of these variables. The ULV was correlated with the DFT before and after terikalant (r = 0.78, p < 0.01) and barium (r = 0.83, p < 0.01). Potassium channel blockers of the current reduce the ability to induce VF; this effect may be related to the anti-fibrillatory action of class III anti-arrhythmic drugs and their ability to decrease DFT. |
3,490 | Implantable cardioverter defibrillator trials: what's new? | The implantable cardioverter defibrillator (ICD) has been in clinical use for 20 years and its clinical role is becoming increasingly clear. A number of well-designed trials demonstrated its effectiveness in high-risk patients who have already experienced a malignant arrhythmia. A more controversial role for the ICD is in patients who are at high risk but have not yet had an arrhythmic event. Randomized clinical trials published in the late 1990s demonstrated survival benefit with the ICD in narrowly defined high-risk populations. These populations are presently defined by a low ejection fraction and inducible ventricular tachyarrhythmia. Clinical trials still in progress will determine whether broader populations will benefit from prophylactic ICD implantation. These trials will have broad clinical importance. |
3,491 | The Brugada syndrome. | The Brugada syndrome describes a subgroup of patients at risk for the occurrence of ventricular fibrillation who have no definable structural heart disease associated with a right bundle branch block conduction pattern and ST-segment elevation in the right precordial leads. This syndrome is caused by genetic defects in the alpha subunit of the sodium channel. This defect causes a reduction in the sodium channel current, which accentuates the epicardial action potential notch leading to ST-segment elevation. Sodium channel blockers can potentiate these findings and screen for patients with intermittent baseline electrocardiographic findings. Because of the poor prognosis of such patients, symptomatic patients should be treated with an implantable cardioverter-defibrillator. |
3,492 | Consequences of atrial tachycardia-induced remodeling depend on the preexisting atrial substrate. | All animal studies of atrial tachycardia (AT) remodeling to date have been performed in normal hearts, but clinical atrial fibrillation (AF) often occurs in the setting of heart disease. This study evaluated the effects of a pathological AF substrate on AT-induced remodeling.</AbstractText>Fourteen control dogs, 12 AT-only dogs (400 bpm for 1 week), 14 congestive heart failure (CHF) dogs (CHF only, ventricular tachypacing, 220 to 240 bpm for 5 weeks), and 13 CHF+AT dogs (ventricular tachypacing-induced CHF, 1 week of AT superimposed on the last week of ventricular tachypacing) were studied for evaluation of AT effects in normal hearts (AT-only versus control dogs) and CHF hearts (CHF+AT versus CHF-only dogs). In normal hearts, AT strongly decreased the effective refractory period (ERP) and abolished ERP rate adaptation, whereas conduction velocity was unaltered. In CHF dogs, AT reduced ERP to a significantly lesser extent, did not alter ERP rate adaptation, and reduced conduction velocity. AT alone increased atrial vulnerability to extrastimuli and prolonged AF. In the presence of CHF, AT had no clear effect on atrial vulnerability but increased the prevalence of prolonged AF.</AbstractText>The electrophysiological effects of AT are different in hearts with a CHF-induced pathological substrate for AF than in normal hearts. These findings have potentially important implications for understanding how AF occurring in diseased hearts begets AF.</AbstractText> |
3,493 | Safety and efficacy of intraarterial thrombolysis for perioperative stroke after cardiac operation. | Acute ischemic stroke after cardiac operations is a devastating complication with limited therapeutic options. As clinical trials of thrombolysis for acute ischemic stroke exclude patients with recent major surgery, the safety of intraarterial thrombolysis in this setting is unknown.</AbstractText>Thirteen patients with acute ischemic stroke within 12 days of cardiac operation underwent intraarterial thrombolysis within 6 hours of stroke symptom onset. The National Institutes of Health Stroke Scale was used to assess neurologic recovery.</AbstractText>The mean age was 69 years (standard deviation +/-5 years) and 62% were men. Cardiac procedures included valve operations in 6 patients, coronary artery bypass grafting in 4, valve and coronary artery bypass grafting in 2, and left ventricular assist device in 1 patient. Atrial fibrillation occurred in 5 patients (38%). The mean time from operation to stroke was 4.3 days (standard deviation +/- 3 days). Thrombolysis was initiated within 3.6 hours (standard deviation +/-1.6 hours) of stroke symptom onset. Recanalization was complete in 1 patient, partial in 5, and 7 patients had low flow. Neurologic improvement occurred in 5 patients (38%). One patient needed a chest tube for hemothorax, 2 others were transfused for low hemoglobin. No operative intervention for bleeding was necessary.</AbstractText>In select patients with acute ischemic stroke after recent cardiac operation, intraarterial thrombolysis appears to be reasonably safe and may lead to neurologic recovery.</AbstractText> |
3,494 | Prehospital management of cardiac arrest: how useful are vasopressor and antiarrhythmic drugs? | Out-of-hospital resuscitation protocols for patients suffering cardiac arrest have historically included cardiopulmonary resuscitation, defibrillation, and rapid transport to a hospital. For many years, use of drugs to improve myocardial perfusion or to correct arrhythmias that occur during cardiac arrest has been part of prehospital efforts to revive patients in ventricular tachycardia or ventricular fibrillation. Use of some of these drugs, however, may be based more on tradition than on well-documented evidence of efficacy. The authors reviewed pertinent data on the vasopressors epinephrine and vasopressin and the antiarrhythmics amiodarone and lidocaine to evaluate the usefulness of these drugs in cardiac arrest. They found little clinical data supporting the prehospital use of lidocaine in cardiac arrest, and despite a great deal of laboratory and clinical data addressing the efficacy of epinephrine, there is no large, randomized, controlled clinical trial supporting its use. Data on amiodarone and vasopressin support the use of these drugs in out-of-hospital resuscitation efforts. |
3,495 | Automated external defibrillators appropriately recognize ventricular fibrillation in electromagnetic fields. | Automated external defibrillators (AEDs) are increasingly available in industrial settings, but many industries have high electromagnetic fields (EMFs), which can interfere with the function of electronic devices. This study evaluated the performance of several AEDs when exposed to high EMFs.</AbstractText>Three commercially available AEDs were evaluated in the setting of a public utility coal-fired electrical generation plant. Each AED was placed in three areas of high EMF ranging from 310 to 1,600 milligauss. A signal generator, used to simulate various cardiac rhythms, was connected to the AEDs. Rhythms simulated were ventricular fibrillation, asystole, and normal sinus rhythm. Each of the AED's interpretations of various rhythms were evaluated in the different EMF settings.</AbstractText>Rhythms of ventricular fibrillation, asystole, and normal sinus rhythm were correctly recognized by each AED in each of the three areas of high EMF. Each AED appropriately recommended defibrillation when presented with ventricular fibrillation. No misinterpretations or inappropriate defibrillations were observed.</AbstractText>Electromagnetic fields generated by an electrical power plant did not interfere with three commercial AEDs' abilities to correctly interpret simulated rhythms and recommend appropriate defibrillation.</AbstractText> |
3,496 | Successful treatment with an implantable cardioverter defibrillator for spontaneous ventricular fibrillation in dilated cardiomyopathy with very high defibrillation thresholds. | A 72-year-old male patient with idiopathic dilated cardiomyopathy who had shown recurrent episodes of drug refractory ventricular fibrillation underwent implantation of a transvenous implantable cardioverter defibrillator (ICD). Ventricular fibrillation (VF) was induced by a T wave shock at the implantation. However, the ICD device with a maximum energy of 30 J failed to terminate the VF. Reversing defibrillation polarity and/or adding a defibrillation electrode lead at the site of a high superior vena cava were also ineffective. The ICD was programmed to a maximum energy of 30 J when the device sensed spontaneous VF. During the follow-up period of 5 months, two episodes of spontaneous VF were recorded from ICD telemetry, and the ICD device terminated VF successfully with the first therapy shock in both episodes. No previous reports have shown failure to terminate induced VF at implantation of the ICD with successful termination of spontaneous VF during follow-up. Careful follow-up is needed in ICD patients, especially those with very high defibrillation thresholds. |
3,497 | Cardiac involvement in thyroid hormone resistance. | To analyze the cardiovascular alterations thought to occur in resistance to thyroid hormone (RTH), cardiac involvement in 54 patients with RTH was investigated with the help of two-dimensional and Doppler echocardiography. Data from 41 of 54 adult subjects with RTH were also compared with those of 24 and 20 cases with hyperthyroidism (H) and hypothyroidism (h), respectively, as well as 22 healthy euthyroid controls (C). With respect to the type of mutations, no correlation was found between cardiovascular features and genotype. Compared with affected adults, children with RTH showed markedly higher serum free T3 (FT3), free T4 (FT4), and baseline TSH concentrations. Compared with healthy children of comparable age, RTH children had significantly higher heart rate and lower left ventricular (LV) ejection fraction (P = 0.006). Also, higher heart rate and FT4 as well as shorter diastolic relaxation of the myocardium (all P = 0.001) between RTH subjects with and without thyrotoxic cardiovascular features were found. Cardiac symptoms (palpitations, 32% vs. 71%) and signs (sinus tachycardia, 26% vs. 79%; atrial fibrillation, 6% vs. 17%) were significantly less frequent in RTH vs. H (all P = 0.001). Compared with C and h, heart rate, cardiac output, stroke volume, and systolic aortic flow velocity were strongly increased in RTH (all P = 0.0001) and H, although ejection (P = 0.0012) and shortening (P = 0.0001) fractions of the LV were markedly lower in RTH vs. H. Diastolic parameters, such as isovolumic relaxation (P = 0.0001) and deceleration time (P = 0.013), were shorter in RTH vs. h and C. In RTH, positive correlations between FT3 and heart rate, and between FT4 and LV ejection fraction were observed, whereas negative correlations between both FT3 and FT4 and isovolumic relaxation were noted. In conclusion, these findings indicate a modulated hyperthyroid effect on cardiac systolic and diastolic function of the myocardium in RTH, whereas other parameters, such as ejection and shortening fractions of the LV, systolic diameter, and LV wall thickness, were comparable to C. Differences in term of cardiovascular changes were smaller between the RTH and C groups than the RTH and the H or h groups. Thus, an incomplete cardiac response to thyroid hormone is present in RTH. |
3,498 | Ionic mechanism of electrical alternans. | Although alternans of action potential duration (APD) is a robust feature of the rapidly paced canine ventricle, currently available ionic models of cardiac myocytes do not recreate this phenomenon. To address this problem, we developed a new ionic model using formulations of currents based on previous models and recent experimental data. Compared with existing models, the inward rectifier K(+) current (I(K1)) was decreased at depolarized potentials, the maximum conductance and rectification of the rapid component of the delayed rectifier K(+) current (I(Kr)) were increased, and I(Kr) activation kinetics were slowed. The slow component of the delayed rectifier K(+) current (I(Ks)) was increased in magnitude and activation shifted to less positive voltages, and the L-type Ca(2+) current (I(Ca)) was modified to produce a smaller, more rapidly inactivating current. Finally, a simplified form of intracellular calcium dynamics was adopted. In this model, APD alternans occurred at cycle lengths = 150-210 ms, with a maximum alternans amplitude of 39 ms. APD alternans was suppressed by decreasing I(Ca) magnitude or calcium-induced inactivation and by increasing the magnitude of I(K1), I(Kr), or I(Ks). These results establish an ionic basis for APD alternans, which should facilitate the development of pharmacological approaches to eliminating alternans. |
3,499 | Biphasic waveform external defibrillation thresholds for spontaneous ventricular fibrillation secondary to acute ischemia. | The goal of this study was to determine if the defibrillation threshold (DFT) after spontaneous ventricular fibrillation (VF) secondary to acute ischemia differs from the DFT for electrically induced VF in the absence of ischemia in anesthetized, closed-chest dogs and pigs.</AbstractText>The efficacy of external defibrillators has been tested mainly in animals and humans using E-VF, yet external defibrillators are often used in patients to halt S-VF.</AbstractText>Protocol 1: biphasic truncated exponential (BTE) waveform shocks were delivered through electrodes placed in an anterior-anterior (A-A) position (left and right lateral thorax) in nine dogs. After measuring the E-VF DFT, acute ischemia was induced with an angioplasty balloon in either the left anterior descending or left circumflex coronary artery, and the S-VF DFT was determined. Protocol 2: in a group of 12 pigs, the E-VF DFT and S-VF DFT were determined for electrodes in the A-A position and in the anterior-posterior position (A-P). Protocol 3: the E-VF DFT was determined in seven pigs. Then up to three shocks 1.5x the E-VF DFT were delivered to S-VF. If defibrillation did not occur, a step-up protocol was used until defibrillation occurred.</AbstractText>Protocol 1: the DFT for E-VF was 65 +/- 28 J (mean +/- SD) compared with 226 +/- 97 J for S-VF, p < 0.05. Protocol 2: the DFT was 152 +/- 58 J for E-VF and 315 +/- 123 J for S-VF for A-A electrodes. The DFT was 100 +/- 43 J for E-VF and 206 +/- 114 J for S-VF for A-P electrodes. Protocol 3: 11/37 shocks of strength 1.5x E-VF DFT (182 +/- 40 J) stopped the arrhythmia. The episodes of S-VF not halted by these shocks required energy levels of up to 400 J for defibrillation.</AbstractText>External defibrillation of S-VF induced by acute ischemia requires significantly more energy than VF induced by 60-Hz current in the absence of ischemia. A safety margin >1.5x the DFT for electrically induced VF may be necessary in BTE external defibrillators to defibrillate S-VF.</AbstractText> |
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