Biventricular pacing decreases the inducibility of ventricular tachycardia in patients with ischemic cardiomyopathy

Advances in Cardiac Pacing: Arrhythmia Prediction, Prevention and Control Strategies

Cardiac arrhythmias constitute a tremendous burden on healthcare and are the leading cause of mortality worldwide. An alarming number of people have been reported to manifest sudden cardiac death as the first symptom of cardiac arrhythmias, accounting for about 20% of all deaths annually. Furthermore, patients prone to atrial tachyarrhythmias such as atrial flutter and fibrillation often have associated comorbidities including hypertension, ischemic heart disease, valvular cardiomyopathy and increased risk of stroke. Technological advances in electrical stimulation and sensing modalities have led to the proliferation of medical devices including pacemakers and implantable defibrillators, aiming to restore normal cardiac rhythm. However, given the complex spatiotemporal dynamics and non-linearity of the human heart, predicting the onset of arrhythmias and preventing the transition from steady state to unstable rhythms has been an extremely challenging task. Defibrillatory shocks still remain the primary clinical intervention for lethal ventricular arrhythmias, yet patients with implantable cardioverter defibrillators often suffer from inappropriate shocks due to false positives and reduced quality of life. Here, we aim to present a comprehensive review of the current advances in cardiac arrhythmia prediction, prevention and control strategies. We provide an overview of traditional clinical arrhythmia management methods and describe promising potential pacing techniques for predicting the onset of abnormal rhythms and effectively suppressing cardiac arrhythmias. We also offer a clinical perspective on bridging the gap between basic and clinical science that would aid in the assimilation of promising anti-arrhythmic pacing strategies.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Immediate electrical storm of Torsades de Pointes after CRT-D implantation in an ischemic cardiomyopathy patient

Cardiac resynchronization therapy with an implantable cardioverter-defibrillator (CRT-D) is the preferred treatment for patients with severe heart failure, dyssynchrony, and an increased risk of sudden cardiac death or for primary ventricular arrhythmia survivors. Rarely, left ventricular epicardial pacing can induce ventricular tachyarrhythmia rather than a beneficial effect. We describe an ischemic cardiomyopathy patient who underwent CRT-D therapy and developed sustained torsades de pointes (TdP) immediately after switching to biventricular pacing (BVP) mode. Here, TdP possibly developed owing to the change in the dispersion of repolarization of the left ventricle myocardium. The diagnosis and management of BVP-induced ventricular arrhythmia is discussed.

Management of ventricular arrhythmias in structural heart disease

Ventricular arrhythmias (VA) are a source of significant morbidity and mortality in patients with structural heart disease (SHD). The advent of the implantable cardiac defibrillator (ICD) has had a positive effect on mortality, but the associated morbidity remains a significant problem. Modern treatment of VA has advanced far beyond medical therapy and includes strategies as simple as intelligent ICD programming and as complex as catheter ablation (CA). In these pages, the spectrum of management strategies will be discussed; from anti-arrhythmic drugs and ICD implantation and programming to CA and autonomic modulation. The focus of this review will be on strategies for secondary prevention of VA in patients with SHD, supported by clinical evidence for their utilization.

A new method of building permanent A-V block model: ablating his-bundle potential through femoral artery with pre-implanted biventricular pacemaker

Background

To explore the feasibility of a new method of achieving a permanent A-V block animal model.

Methods

16 beagles were randomly divided into two groups based on the method of their pre-implanted biventricular pacemakers. (1) In the first group (8 beagles), the A-V block model was achieved by ablating his-bundle potential at the site of the left ventricular superior-septum, under the aortic sinus, through femoral artery. (2) In the second group (8 beagles), the A-V block model was achieved by ablating his-bundle potential at the triangle of Koch, through femoral vein. A complete A-V block model was achieved as a standard in this study. The success rates, intraoperative arrhythmias, operative and X-ray exposure time, intraoperative bleeding amount were assessed in this two groups, both animal models were followed up for four weeks and then fasted to monitor myocardial pathological changes.

Results

The success rate of the first group, which with fewer intraoperative arrhythmias, and less operative and X-ray exposure time, was significantly higher than the second group.

Conclusions

Compared with traditional animal method, our new method of ablating his-bundle potential at the left ventricle from the femoral artery has a higher success rate, fewer occurrence of malignant arrhythmias, and less operation and X-ray time. Thus, our new method should be preferred in the building of Permanent A-V Block Model.

Is CRT pro-arrhythmic? A comparative analysis of the occurrence of ventricular arrhythmias between patients implanted with CRTs and ICDs

Aim and Hypothesis: Despite the proven symptomatic and mortality benefit of cardiac resynchronization therapy (CRT), there is anecdotal evidence it may be pro-arrhythmic in some patients. We aimed to identify if there were significant differences in the incidence of ventricular arrhythmias (VAs) in patients undergoing CRT-D and implantable cardioverter-defibrillators (ICD) implantation for primary prevention indication. We hypothesized that CRT is unlikely to be pro-arrhythmic based on the positive mortality and morbidity data from large randomized trials.

Methods and Results: A retrospective analysis of device therapies for VA in a primary prevention device cohort was performed. Patients with ischemic (IHD) and non-ischemic (DCM) cardiomyopathy and ICD or CRT+ICD devices (CRT-D) implanted between 2005 and 2007 without prior history of sustained VA were included for analysis. VA episodes were identified from stored electrograms and defined as sustained (VT/VF) if therapy [anti-tachycardia pacing (ATP) or shocks] was delivered or non-sustained (NSVT) if not. Of a total of 180 patients, 117 (68% male) were in the CRT-D group, 42% IHD, ejection fraction (EF) 24.5 ± 8.2% and mean follow-up 23.9 ± 9.8 months. 63 patients (84% male) were in the ICD group, 60% IHD, EF 27.7 ± 7.2% and mean follow-up 24.6 ± 10.8 months. Overall, there was no significant difference in the incidence of VA (35.0 vs. 38.1%, p = 0.74), sustained VT (21.3 vs. 28.5%, p = 0.36) or NSVT (12.8 vs. 9.5%, p = 0.63) and no significant difference in type of therapy received for VT/VF: ATP (68 vs. 66.6%, p = 0.73) and shocks (32 vs. 33.3%, p = 0.71) between the CRT-D and ICD groups, respectively.

Conclusion: In patients with cardiomyopathy receiving CRT-D and ICDs for primary prophylaxis, there was no significant difference in the incidence of VA. From this single center retrospective analysis, there is no evidence to support cardiac resynchronization causing pro-arrhythmia.

The proarrhythmic effect of cardiac resynchronization therapy: an issue that should be borne in mind

The demonstrated benefits of cardiac resynchronization therapy (CRT) in reducing mortality and hospitalizations for heart failure, improving NYHA functional class and inducing reverse remodeling have led to its increasing use in clinical practice. However, its potential contribution to complex ventricular arrhythmias is controversial.We present the case of a female patient with valvular heart failure and severe systolic dysfunction, in NYHA class III and under optimal medical therapy, without previous documented ventricular arrhythmias. After implantation of a CRT defibrillator, she suffered an arrhythmic storm with multiple episodes of monomorphic ventricular tachycardia (VT), requiring 12 shocks. Subsequently, a pattern of ventricular bigeminy was observed, as well as reproducible VT runs induced by biventricular pacing. Since no other vein of the coronary sinus system was accessible, it was decided to implant an epicardial lead to stimulate the left ventricle, positioned in the left ventricular mid-lateral wall. No arrhythmias were detected in the following six months. This case highlights the possible proarrhythmic effect of biventricular pacing with a left ventricular lead positioned in the coronary sinus venous system.

Global and regional ventricular repolarization study by body surface potential mapping in patients with left bundle-branch block and heart failure undergoing cardiac resynchronization therapy

BACKGROUND

The controversial effects promoted by cardiac resynchronization therapy (CRT) on the ventricular repolarization (VR) have motivated VR evaluation by body surface potential mapping (BSPM) in CRT patients.

METHODS

Fifty-two CRT patients, mean age 58.8 ± 12.3 years, 31 male, LVEF 27.5 ± 9.2, NYHA III-IV heart failure with QRS181.5 ± 14.2 ms, underwent 87-lead BSPM in sinus rhythm (BASELINE) and biventricular pacing (BIV). Measurements of mean and corrected QT intervals and dispersion, mean and corrected T peak end intervals and their dispersion, and JT intervals characterized global and regional (RV, Intermediate, and LV regions) ventricular repolarization response.

RESULTS

Global QTm (P < 0.001) and QTc(m) (P < 0.05) were decreased in BIV; QTm was similar across regions in both modes (P = ns); QTc(m) values were lower in RV/LV than in Intermediate region in BASELINE and BIV (P < 0.001); only RV/Septum showed a significant difference (P < 0.01) in the BIV mode. QTD values both of BASELINE (P < 0.01) and BIV (P < 0.001) were greater in the Intermediate than in the LV region. CRT effect significantly reduced global/regional QTm and QTc(m) values. QTD was globally decreased in RV/LV (Intermediate: P = ns). BIV mode significantly reduced global T peak end mean and corrected intervals and their dispersion. JT values were not significant.

CONCLUSIONS

Ventricular repolarization parameters QTm, QTc(m), and QTD global/regional values, as assessed by BSPM, were reduced in patients under CRT with severe HF and LBBB. Greater recovery impairment in the Intermediate region was detected by the smaller variation of its dispersion.

Ventricular tachycardia or ventricular fibrillation occurs less often in patients with left bundle branch block and combined resynchronization and defibrillators than in patients with narrow QRS and conventional defibrillators

AIMS

Mortality in chronic heart failure (CHF) patients with left bundle branch block (LBBB) is high. Cardiac resynchronization therapy (CRT) reduces symptoms and mortality in CHF patients with LBBB. Whether CRT promotes or prevents ventricular tachycardia (VT)/ventricular fibrillation (VF) remains controversial, however. Therefore, we aimed to analyse arrhythmia-related CRT effects and characterized the VT/VF incidence in CRT-defibrillator patients and matched controls with conventional implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden cardiac death.

METHODS AND RESULTS

We enrolled 134 patients [110 men, left ventricular ejection fraction (LVEF) 24 ± 8%, 71 coronary artery disease, CRT-ICD 67, conventional ICD matched controls 67, follow-up 31 ± 17 months] and monitored overall survival and the time to a first VT/VF episode. Controls did not have LBBB. They were otherwise matched for age, LVEF, and follow-up duration. Gender and underlying disease did not differ between the groups. Kaplan-Meier analysis revealed more favourable arrhythmia-free survival in CRT-ICD vs. conventional ICD patients [hazard ratio (HR) 2.26, confidence interval (CI) 1.09-4.67, log rank P = 0.023]. The difference persisted in the multivariate Cox regression analysis (HR 3.25, CI 1.18-8.93, P= 0.022). Overall survival was similar in both groups (HR 1.45, CI 0.55-3.82, P = 0.45).

CONCLUSIONS

Chronic heart failure patients with LBBB treated with CRT-ICD, experience less and delayed VT/VF episodes compared with matched controls without LBBB receiving conventional ICD. In the long-term, CRT appears to exert antiarrhythmic effects and to attenuate the particularly high arrhythmia-related risk of CHF patients with LBBB. The incremental benefit of adding the ICD option to CRT pacing in LBBB patients appears questionable.

Prediction of appropriate defibrillator therapy in heart failure patients treated with cardiac resynchronization therapy

The necessity of implantable cardioverter-defibrillator (ICD) implantation in patients with systolic heart failure (HF) who undergo cardiac resynchronization therapy (CRT) may be questioned. The aim of this study was to identify patients at low risk for sustained ventricular arrhythmia. One hundred sixty-nine consecutive patients with HF (mean age 60 +/- 12 years, 125 men, 73% in New York Heart Association class III) referred for CRT and prophylactic, primary prevention ICD implantation underwent baseline clinical and echocardiographic assessment and regular device follow-up. The primary study end point was appropriate ICD therapy. During a mean follow-up period of 654 +/- 394 days, 35 patients (21%) had sustained ventricular arrhythmias requiring appropriate ICD therapy. Of the 3 patients who experienced sudden cardiac death, 2 had been treated with appropriate ICD therapy before sudden cardiac death. In a multivariate model, only history of nonsustained ventricular tachycardia (p = 0.001), a severely (<20%) decreased left ventricular ejection fraction (p = 0.001), and digitalis therapy (p = 0.08) independently predicted appropriate ICD therapy. Patients with 0 (n = 46), 1 (n = 36), 2 (n = 73), and 3 (n = 14) risk factors for appropriate ICD therapy had a 7%, 14%, 27%, and 64% and 0%, 6%, 10%, and 43% incidence of appropriate ICD therapy for ventricular arrhythmias and for rapid ventricular tachycardia or ventricular fibrillation, respectively. In conclusion, apart from commonsense considerations (age and significant co-morbidities), ICD addition seems ineffective in CRT patients without nonsustained ventricular tachycardia, digoxin therapy, and severely reduced left ventricular systolic function.

Effect of cardiac resynchronization therapy on the incidence of electrical storm

BACKGROUND

Hemodynamic improvement from biventricular pacing is well documented; however, its electrophysiologic effects have not been systematically studied. In this study, incidence and risk factors for electrical storm (ES) were investigated in 729 ICD and biventricular defibrillator (CRT-D) heart failure patients.

METHODS

168 consecutive CRT-D and 561 ICD patients were retrospectively analyzed for the occurrence of VT/VF and predisposing factors. Electrical storm was defined as ventricular tachycardia or fibrillation ≥3 times during 24 h. Mean follow-up was 41 months.

RESULTS

In 168 CRT-D patients only one patient experienced electrical storm compared to 39 patients out of 561 ICD patients (0.6% vs. 7%, p<0.01). 33% of the patients with electrical storm died within one year. In the CRT-D group 81 patients (48%) developed VT or VF and received at least one appropriate therapy, compared to 281 patients (50%) in the ICD group. Mean ejection fraction was 21.7% in the CRT-D group and 34.7% (p<0.01) in the ICD group. Stratifying the patients according to primary or secondary prevention and ejection fraction demonstrated that VT/VF clusters were significantly associated with ICD indication for secondary prevention, previous myocardial infarction and LVEF<30%.

CONCLUSION

The development of electrical storm is accompanied with a highly increased mortality risk even if an ICD/CRT-D is implanted. In CRT-D patients electrical storm is much less common than in ICD patients. Secondary prevention and ejection fraction<30% are predictors of electrical storm. Beside hemodynamic improvements cardiac resynchronization therapy may reduce the arrhythmia burden in heart failure patients.

The beneficial effect of biventricular pacing on ventricular tachycardia in a patient with non-ischemic cardiomyopathy

The effect of cardiac resynchronisation therapy on ventricular tachycardias (VT) has not been well established. This case-report demonstrates the favourable impact of biventricular pacing on ventricular arrhythmias. In 2004, a patient with dilated cardiomyopathy and ICD since 1999 was admitted to our Division for multiple VT. While left ventricular function was markedly reduced and mitral regurgitation was severe, he was asymptomatic for heart failure. Amiodarone was not administered on account of a documented proarrhythmic effect. The patient's ICD was upgraded to an ICD-biventricular system. After upgrading, a significant reduction in the number of VT was noted.

Anti- and pro-arrhythmic effects of cardiac resynchronization therapy: point of view

Cardiac resynchronization therapy (CRT) in patients with heart failure and bundle branch block (BBB) improves regional muscle mechanics and mechanical pump function of the heart. In addition, modulation of wall motion timing and contraction can exert an antiarrhythmic effect, reducing the potential of sudden cardiac death. This effect of CRT could also be attributed to the improvement in excitation-contraction coupling, mechanical synchronization, and improved myocardial perfusion. However, it can be hypothesized that the BBB results in a concealed reentry, in which a delayed depolarization wave re-enters during phase two of the action potential. This concealed phase 2 reentry can lead to early after depolarizations and cardiac arrhythmias. By synchronizing the two ventricles, CRT eliminates the reentry substrate and the resulting arrhythmias. This hypothesis and the potential arrhythmogenic effects of CRT are discussed with regard to ventricular remodeling and mechano-electrical feedback in this setting.

Cardiac resynchronization therapy and its potential proarrhythmic effect

Cardiac resynchronization therapy (CRT) has become an established adjunctive treatment to optimal pharmacologic therapy in patients with advanced chronic heart failure (CHF), diminished left ventricular (LV) function and intraventricular conduction delay. Although CRT has been shown to improve ventricular hemodynamics, quality of life and exercise capacity, there is some evidence that it may rarely potentiate ventricular arrhythmias. As CRT is considered for an expanded population of CHF patients, and left-sided pacing is considered as an option for pacemaker-indicated patients (potentially without defibrillator backup), the effect of these pacing modalities on the incidence of ventricular tachyarrhythmia must be systematically studied and mechanistically understood. Strategies to prospectively predict the proarrhythmic potential of LV epicardial pacing need to be developed, and therapy accordingly individualized. This review attempts to summarize the current information on proarrhythmia in resynchronization therapy.

Surgery for ventricular tachycardia in patients undergoing surgical ventricular restoration: The Karolinska approach

This article presents a review on the efficacy of surgical ventricular restoration and direct surgery for ventricular tachycardia in patients with left ventricular aneurysm or dilated ischemic cardiomyopathy. The procedure includes a non-electrophysiologically guided subtotal endocardiectomy and cryoablation in addition to endoventricular patch plasty of the left ventricle. Coronary artery bypass surgery and mitral valve repair are performed concomitantly as needed. In our experience, this procedure yielded a 90% success rate in terms of freedom from spontaneous ventricular tachycardia, with an early mortality rate of 3.8%. A practical guide to the pre- and postoperative management of these patients is provided.

Transvenous dual site left ventricular pacing plus biventricular pacing for the management of refractory ventricular tachycardia

This is a case report of a male patient with nonischemic cardiomyopathy who had severely depressed left ventricular systolic function and functional class III congestive heart failure (CHF). He also had left bundle branch block (LBBB) and recurrent ventricular tachycardia (VT). Though the patient's CFH functional class improved after implantation of a transvenous biventricular ICD system, recurrent VT episodes required the initiation of amiodarone. After an improved condition for 28 months, recurrent VT episodes led to multiple consecutive ICD shocks, which constituted an electrical storm and a battery status of elective replacement indicator (ERI). The recurrent VT episodes were suppressed with intravenous amiodarone and lidocaine. As Radiofrequency ablation was declined by the patient, a new left ventricular (LV) lead was transvenously added, providing biventricular and dual site LV pacing. After this intervention the arrhythmia subsided and the intravenous antiarrhythmic medications were stopped. No episodes of sustained VT leading to ICD shocks were observed for the following 9 months. The events in this case suggest that dual site LV pacing with biventricular pacing could be an alternative strategy for the management of refractory VT.

Cardiac Resynchronization Therapy: A Review of Proarrhythmic and Antiarrhythmic Mechanisms

Available evidence supports the hypothesis that cardiac resynchronization therapy (CRT) results in favorable structural as well as electrical remodeling. Electrical remodeling seems to be related, to a large extent, to structural remodeling, usually referred to as reverse remodeling of left ventricular (LV) dysfunction. This can lead to amelioration of the arrhythmogenic substrate associated with depressed LV systolic function and heart failure. However, a direct electrophysiological effect due to favorable remodeling of repolarization with reduction of the dispersion of repolarization cannot be ruled out. On the other hand, in a small subgroup of patients, CRT could increase the dispersion of repolarization and induce malignant ventricular tachyarrhythmias. Clinical trials have consistently shown improved outcome with CRT-defibrillators (CRT-D) and more trials have demonstrated the benefits of the defibrillator in the population with depressed LV function. However, some physicians argue that implanting the less expensive and less complicated CRT-pacemaker (CRT-P) may be appropriate in certain groups of patients. Before this position is accepted, it is imperative that criteria for the selection of this group of patients with presumably low risk for sudden arrhythmic death as well as the proarrhythmic effect of CRT be clearly defined.

Benefit of Combined Resynchronization and Defibrillator Therapy in Heart Failure Patients With and Without Ventricular Arrhythmias

OBJECTIVES

We attempted to assess the efficacy of combined cardiac resynchronization therapy-implantable cardioverter-defibrillator (CRT-ICD) in heart failure patients with and without ventricular arrhythmias.

BACKGROUND

Because CRT and ICDs both lower all-cause mortality in patients with advanced heart failure, combination of both therapies in a single device is challenging.

METHODS

A total of 191 consecutive patients with advanced heart failure, left ventricular ejection fraction <35%, and a QRS duration >120 ms received CRT-ICD. Seventy-one patients had a history of ventricular arrhythmias (secondary prevention); 120 patients did not have prior ventricular arrhythmias (primary prevention). During follow-up, ICD therapy rate, clinical improvement after 6 months, and mortality rate were evaluated.

RESULTS

During follow-up (18 +/- 4 months), primary prevention patients experienced less appropriate ICD therapies than secondary prevention patients (21% vs. 35%, p < 0.05). Multivariate analysis revealed, however, no predictors of ICD therapy. Furthermore, a similar, significant, improvement in clinical parameters was observed at 6 months in both groups. Also, the mortality rate in the primary prevention group was lower than in the secondary prevention group (3% vs. 18%, p < 0.05).

CONCLUSIONS

As 21% of the primary prevention patients and 35% of the secondary prevention patients experienced appropriate ICD therapy within 2 years after implant, and no predictors of ICD therapy could be identified, implantation of a CRT-ICD device should be considered in all patients eligible for CRT.

Potential proarrhythmic effect of biventricular pacing: fact or myth?

BACKGROUND

Hemodynamic improvement from biventricular pacing is well documented; however, its electrophysiologic effects have not been systematically studied. Sporadic case reports suggest a proarrhythmic effect of biventricular pacing resulting primarily in polymorphic ventricular tachycardia/ventricular fibrillation (VT/VF).

OBJECTIVES

The purpose of this study was to report a series of patients in whom implantation of a biventricular system resulted in VT/VF storm with predominance of monomorphic VT.

METHODS

In a retrospective analysis of all biventricular implants over a 4-year period at a single medical center, we identified 5 of 145 patients (3.4%) who developed VT/VF after they were upgraded to a biventricular system. All patients were male, age 71 +/- 8 years, with ejection fraction of 0.25 +/- 0.1. Four of five patients had ischemic cardiomyopathy.

RESULTS

All patients developed incessant VT/VF within 1 week of implantation. Monomorphic VT of single morphology was noted in 3 of 5 patients, monomorphic VT of multiple morphologies in 1, and polymorphic VT/VF in 1. VT was managed by temporary discontinuation of biventricular pacing in all patients, amiodarone in 3 of 5, sotalol in 1, and beta-blocker in 1. During 11 +/- 7 months of follow-up, 4 of 5 patients remain alive and are arrhythmia-free.

CONCLUSION

Biventricular pacing may result in precipitation of VT/VF storm in a minority of patients with prior history of VT/VF. This may be the first case series reporting both monomorphic and polymorphic VT after an upgrade to a system with biventricular pacing capabilities. The arrhythmias can be managed by conventional therapy and may require temporary discontinuation of left ventricular pacing. This observation is relevant to patients receiving a biventricular pacemaker without an implantable cardioverter-defibrillator backup.

Effect of cardiac resynchronization therapy on the incidence of ventricular arrhythmias in patients with an implantable cardioverter-defibrillator

BACKGROUND

Cardiac resynchronization therapy (CRT) reduces mortality in selected patients with heart failure. However, this result may not be entirely related to the beneficial hemodynamic effects of CRT.

OBJECTIVES

The purpose of this study was to assess retrospectively the effect of CRT on the incidence of appropriate therapy in patients with an implantable cardioverter-defibrillator (ICD).

METHODS

Sixty-five patients (48 men and 17 women; mean age 58 +/- 13 years) with an ICD (31 biventricular, 34 dual-chamber) were included in the study. Clinical, ECG, and ICD stored data and electrograms were collected.

RESULTS

Biventricular and dual-chamber ICDs were implanted in 31 and 34 patients, respectively, who had either ischemic (n = 36) or dilated cardiomyopathy (n = 29). Thirty-two (49%) patients received > or =1 appropriate ICD therapy during follow-up of 11 +/- 8 months. Thirty-five percent and 62% of patients with biventricular (n = 11) and dual-chamber ICDs (n = 21), respectively, received appropriate ICD therapy during the follow-up period (odds ratio = 0.340, P = .048). Stratifying the patients according to underlying heart disease and ejection fraction resulted in an adjusted odds ratio = 0.239 (P = .029). Comparing the rate of > or =1 appropriate ICD therapy between the two groups by Kaplan-Meier analysis and the log rank test resulted in P = .027.

CONCLUSION

In this retrospective analysis, biventricular pacing was associated with a decreased incidence of sustained ventricular arrhythmias requiring ICD therapy. The antiarrhythmic effect of biventricular pacing could contribute to the reduction in mortality reported in recent large-scale clinical trials on CRT. However, further prospective studies are warranted to clarify this issue.

Surgery for Ventricular Tachycardia in Patients Undergoing Left Ventricular Reconstruction by the Dor Procedure

BACKGROUND

Surgical ventricular restoration (the Dor procedure) is an option in patients with coronary artery disease and postinfarction left ventricular aneurysm. The procedure can be extended to treat ventricular tachycardia (VT). The aim of this study was to evaluate the Dor procedure including VT surgery in our institution.

METHODS

From July 1997 to December 2003, 53 consecutive patients with left ventricular aneurysm and VT underwent surgical ventricular restoration including nonguided endocardiectomy and cryoablation. Twenty-four patients had at least one preoperative episode of spontaneous VT, of which 8 were survivors of sudden cardiac death. Twenty-nine patients had inducible-only VT. In 45 patients, who underwent preoperative programmed stimulation, sustained uniform VT could be initiated. Arrhythmia control was evaluated by programmed stimulation or analysis of events registered by implanted defibrillators and by review of patient's records.

RESULTS

Early mortality was 2 of 53 (3.8%). Mean follow-up was 3.7 years. At 1, 3, and 5 years overall actuarial survival was 94%, 80%, and 59%, respectively. Surgical success rate in patients with preoperative spontaneous VT was 91%. Inducible VT was found in 5 of 35 patients who underwent postoperative programmed stimulation. There was no arrhythmia-related late death and there was no loss to follow-up.

CONCLUSIONS

The Dor procedure including VT surgery is an effective treatment for postinfarction left ventricular aneurysm and VT and eliminates the need for an implantable defibrillator in most patients. Early and long-term results are good in terms of survival and arrhythmia control.

Impact of Upgrade to Cardiac Resynchronization Therapy on Ventricular Arrhythmia Frequency in Patients With Implantable Cardioverter-Defibrillators

OBJECTIVES

This study compared cardiac resynchronization therapy's (CRT) impact on ventricular tachyarrhythmia susceptibility in patients who, due to worsening heart failure (HF) symptoms, underwent a replacement of a conventional implantable cardioverter-defibrillator (ICD) with a CRT-ICD.

BACKGROUND

Cardiac resynchronization therapy is an effective addition to conventional treatment of HF in many patients with left ventricular systolic dysfunction. However, whether CRT-induced improvements in HF status also reduce susceptibility to life-threatening arrhythmias is less certain.

METHODS

Clinical and ICD electrogram data were evaluated in 18 consecutive ICD patients who underwent an upgrade to CRT-ICD. Pharmacologic HF therapy was not altered during follow-up. The definition of ventricular tachycardia (VT) and ventricular fibrillation (VF) for each patient was as determined by device programming. Statistical comparisons used paired t tests.

RESULTS

Findings were recorded during two time periods: 47 +/- 21 months (range 24 to 70 months) before and 14 +/- 2 months (range 9 to 18 months) after CRT upgrade. At time of upgrade, patient age was 69 +/- 11 years and ejection fraction was 21 +/- 8%. Before CRT the frequency of VT, VF, and appropriate ICD shocks was 0.31 +/- 1.23, 0.047 +/- 0.083, and 0.048 +/- 0.085 episodes/month/patient, respectively. After CRT-ICD, VT and VF arrhythmia burdens and frequency of shocks were respectively 0.13 +/- 0.56, 0.001 +/- 0.004, and 0.003 +/- 0.016 episodes/month/patient (p = 0.59, 0.03, and 0.05 vs. pre-CRT).

CONCLUSIONS

Arrhythmia frequency and number of appropriate ICD treatments were reduced after upgrade to CRT-ICD for HF treatment. Thus, apart from hemodynamic benefits, CRT may also ameliorate ventricular tachyarrhythmia susceptibility in HF patients.

Effect of cardiac resynchronization therapy on inducibility of ventricular tachyarrhythmias in cardiac arrest survivors with either ischemic or idiopathic dilated cardiomyopathy

We evaluated whether long-term cardiac resynchronization therapy affects the inducibility of ventricular tachyarrhythmias in relation to reverse remodeling in cardiac arrest survivors with either ischemic or idiopathic dilated cardiomyopathy. Clinical, electrophysiologic, and echocardiographic data of 18 patients were obtained before and after 6 months of cardiac resynchronization.

Effects of Cardiac Resynchronization Therapy on Ventricular Repolarization in Patients with Congestive Heart Failure

INTRODUCTION

Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure.

METHODS AND RESULTS

Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms).

CONCLUSIONS

Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.

Comparison of conventional and biventricular antitachycardia pacing in a geometrically realistic model of the rabbit ventricle

INTRODUCTION

ICDs often are programmed with antitachycardia pacing (ATP) as the first response to ventricular tachycardia (VT). Many ICDs have an additional lead available for ventricular pacing. We hypothesized that using the additional lead for ATP would improve therapy by advancing the orthodromic wavefront, thereby reducing the size of the excitable gap and inducing block of all reentrant activity.

METHODS AND RESULTS

Monomorphic VT was initiated in a thin-walled model of rabbit ventricular myocardium that included an apical infarct and anatomically realistic dimensions. ATP with up to eight pulses was delivered at 90% of VT cycle length to one (conventional) or two (biventricular) stimulation areas. Stimulation areas were adjusted from 0.017 cm2 to 0.169 cm2 to modulate interactions between the antidromic and VT wavefronts, and between the orthodromic wavefront and the VT's refractory region. During conventional ATP, we found that larger stimulation areas terminated the VT in three pulses. Continued pacing after termination caused VT reinitiation in the reversed direction in some instances. With smaller stimulation areas, conventional ATP simply reset the circuit. During biventricular ATP, larger stimulation areas terminated VT in one pulse. There were no instances of reinitiation with reversal. However, with smaller stimulation areas, prolongation of refractoriness near the additional stimulation area facilitated induction of functional reentry with pathways modified by continued pacing.

CONCLUSION

Our modeling suggests that biventricular ATP is superior to conventional ATP under conditions where the additional ventricular lead effectively advances the orthodromic wavefront. Failure to achieve this advancement poses a risk of VT acceleration.

Cardiac pacing: the state of the art

Permanent cardiac pacing remains the only effective treatment for chronic, symptomatic bradycardia. In recent years, the role of implantable pacing devices has expanded substantially. At the beginning of the 21st century, exciting developments in technology seem to happen at an exponential rate. Major advances have extended the use of pacing beyond the arrhythmia horizon. Such developments include dual-chamber pacers, rate-response algorithms, improved functionality of implantable cardioverter defibrillators, combinations of sensors for optimum physiological response, and advances in lead placement and extraction. Cardiac pacing is poised to help millions of patients worldwide to live better electrically. We review pacing studies of sick-sinus syndrome, neurocardiogenic syncope, hypertrophic obstructive cardiomyopathy, and cardiac resynchronisation therapy, which are common or controversial indications for cardiac pacing. We also look at the benefits and complications of implantation in specific arrhythmias, suitability of different pacing modes, and the role of permanent pacing in the management of patients with heart failure.

Effects of Cardiac Resynchronization on Disease Progression in Patients With Left Ventricular Systolic Dysfunction, an Indication for an Implantable Cardioverter-Defibrillator, and Mildly Symptomatic Chronic Heart Failure

Background— The effects of cardiac resynchronization therapy (CRT) in patients with mildly symptomatic heart failure have not been fully elucidated.

Methods and Results— The Multicenter InSync ICD Randomized Clinical Evaluation II (MIRACLE ICD II) was a randomized, double-blind, parallel-controlled clinical trial of CRT in NYHA class II heart failure patients on optimal medical therapy with a left ventricular (LV) ejection fraction ≤35%, a QRS ≥130 ms, and a class I indication for an ICD. One hundred eighty-six patients were randomized: 101 to the control group (ICD activated, CRT off) and 85 to the CRT group (ICD activated, CRT on). End points included peak V̇ o 2 , V̇ e /V̇ co 2 , NYHA class, quality of life, 6-minute walk distance, LV volumes and ejection fraction, and composite clinical response. Compared with the control group at 6 months, no significant improvement was noted in peak V̇ o 2 , yet there were significant improvements in ventricular remodeling indexes, specifically LV diastolic and systolic volumes ( P =0.04 and P =0.01, respectively), and LV ejection fraction ( P =0.02). CRT patients showed statistically significant improvement in V̇ e /V̇ co 2 ( P =0.01), NYHA class ( P =0.05), and clinical composite response ( P =0.01). No significant differences were noted in 6-minute walk distance or quality of life scores.

Conclusions— In patients with mild heart failure symptoms on optimal medical therapy with a wide QRS complex and an ICD indication, CRT did not alter exercise capacity but did result in significant improvement in cardiac structure and function and composite clinical response over 6 months.

Biventricular pacing reduces the induction of monomorphic ventricular tachycardia: A potential mechanism for arrhythmia suppression

OBJECTIVES

The aim of the present study was to evaluate in a prospective randomized fashion the electrophysiologic effects of acute biventricular (BV) pacing. We hypothesized that (1) the local coupling interval in the left ventricle in response to right-sided ventricular premature beats is prolonged when BV pacing is applied during the drive train compared with right ventricular (RV) pacing, and (2) BV programmed electrical stimulation (PES) decreases the induction of ventricular arrhythmias compared with standard RV-PES, regardless of the presence of intraventricular conduction delay.

BACKGROUND

Previous studies have suggested that BV pacing might decrease the frequency of ventricular arrhythmias; however, the mechanism of arrhythmia suppression remains unclear.

METHODS

Eighteen patients with coronary artery disease were randomized to RV-PES or BV-PES with a repeat study using the other pacing mode. The RV effective refractory periods were measured during RV-PES and BV-PES. In addition, the local LV S(1)-S(2) coupling interval was measured at 600/450 ms and 400/350 ms during RV-PES and BV-PES.

RESULTS

BV-PES had no effect on RV effective refractory periods. On the other hand, the local LV S(1)-S(2) coupling intervals increased significantly during BV-PES compared with RV-PES (P < .0001). Ventricular tachycardia was induced in six patients using RV-PES but in only one patient with BV-PES (RR = 83%, P = .01). No difference was observed in the induction of ventricular fibrillation.

CONCLUSIONS

BV-PES significantly reduced the induction of ventricular tachycardia compared to RV-PES, with no significant effect on ventricular fibrillation induction. Our findings may help explain the reduced incidence of ventricular arrhythmias noted with chronic BV pacing.

Effect of left ventricular remodeling after cardiac resynchronization therapy on frequency of ventricular arrhythmias

We evaluated whether cardiac resynchronization therapy affects the prevalence of ventricular tachycardia in relation to reverse remodeling in patients with end-stage heart failure. Clinical, echocardiographic, and implantable cardioverter-defibrillator (ICD) data of 17 patients with ICDs were obtained before and after they had received an upgrade to an ICD-cardiac resynchronization therapy device.

Structural pathways and prevention of heart failure and sudden death

We review the macroscopic and microscopic anatomy of myocardial disease associated with heart failure (HF) and sudden cardiac death (SCD) and focus on the prevention of SCD in light of its structural pathways. Compared to patients without SCD, patients with SCD exhibit 5- to 6-fold increases in the risks of ventricular arrhythmias and SCD. Epidemiologically, left ventricular hypertrophy by ECG or echocardiography acts as a potent dose-dependent SCD predictor. Dyslipidemia, a coronary disease risk factor, independently predicts echocardiographic hypertrophy. In adult SCD autopsy studies, increases in heart weight and severe coronary disease are constant findings, whereas rates of acute coronary thrombi vary remarkably. The microscopic myocardial anatomy of SCD is incompletely defined but may include prevalent changes of advanced myocardial disease, including cardiomyocyte hypertrophy, cardiomyocyte apoptosis, fibroblast hyperplasia, diffuse and focal matrix protein accumulation, and recruitment of inflammatory cells. Hypertrophied cardiomyocytes express "fetospecific" genetic programs that can account for acquired long QT physiology with risk for polymorphic ventricular arrhythmias. Structural heart disease associated with HF and high SCD risk is causally related to an up-regulation of the adrenergic renin-angiotensin-aldosterone pathway. In outcome trials, suppression of this pathway with combinations of beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin-II receptor blockers, and mineralocorticoid receptor blockers have achieved substantial total mortality and SCD reductions. Contrarily, trials with ion channel-active agents that are not known to reduce structural heart disease have failed to reduce these risks. Device therapy effectively prevents SCD, but whether biventricular pacing-induced remodeling decreases left ventricular mass remains uncertain.

Combining electrical therapies for advanced heart failure: the Milan experience with biventricular pacing-defibrillation backup combination for primary prevention of sudden cardiac death

Biventricular pacing (BVP) improves hemodynamics and symptoms in patients with heart failure with bundle branch block. Patients with a left ventricular ejection fraction <0.35 and ventricular tachyarrhythmias are at risk of sudden cardiac death, and they benefit most from implantable cardioverter defibrillators (ICDs). No study has evaluated the efficacy of the BVP-ICD combination in patients with heart failure with no history of syncope or sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Our prospective, observational study was performed on 135 consecutive patients with heart failure (aged, 64 +/- 11 years; 76% male; New York Heart Association functional class, 3.1 +/- 0.8; ejection fraction 0.28 +/- 0.06; ischemic heart failure, 43%; QRS interval duration, 153 +/- 11 msec) treated at our cardiac pacing unit between January 1999 and April 2001. In the first year (control phase), BVP alone was implanted. After that, BVP with ICD backup was used (prophylactic phase). Follow-up data were obtained by outpatient visits with electrocardiographic and echocardiographic examinations done at 3-month intervals. For patients who died, we examined hospital records, death certificates, and autopsy reports. Follow-up time averaged 840 days. The first 47 patients received BVP alone. During follow-up study, 19% of these patients died suddenly, and 11% died of worsening heart failure. None of the patients who died suddenly had hemodynamic deterioration or BVP malfunction before the event. The BVP-ICD group comprised 88 patients (18% with VT/VF inducibility on electrophysiologic testing). During follow-up study, 32% of these patients (18% with positive electrophysiologic testing) had VT/VF episodes successfully treated by ICD; 5% received inappropriate discharges on atrial fibrillation; and 6% died of heart failure with 1 sudden cardiac death. Cox proportional hazards model in the BVP-ICD group compared with BVP alone revealed hazard ratios for all-cause mortality and sudden cardiac death of 0.76 (95% confidence interval [CI], 0.58 to 0.96; p = 0.01) and 0.08 (95% CI, 0.05 to 0.42; p <0.01), respectively, adjusting for baseline characteristics and follow-up duration. Mortality in patients with heart failure remains high after BVP implantation, mainly because of sudden cardiac death. Although there are limitations with an observational study, our experience suggests that ICD backup grants increased security in BVP patients without conventional class I ICD indications.

Effect of biventricular pacing on heart rate variability in patients with chronic heart failure

BACKGROUND

Biventricular pacing is emerging as a long-term therapy for symptomatic heart failure. Analysis of heart rate variability (HRV) has become an important predictive tool in this syndrome.

AIM OF THE STUDY

To assess whether chronic resynchronization therapy can affect HRV in patients with heart failure.

METHODS AND RESULTS

Thirteen patients with heart failure were studied (mean age+/-1 S.E. 65+/-2.2 years, QRS 195+/-5.3 ms, NYHA class 3.2+/-0.1, LVEF 21+/-1.7%). The protocol included a preliminary no pacing period for 1 month following device implantation. Twenty-four hour Holter ECG recordings were performed at the end of this period (baseline) and after 3 months of biventricular stimulation (VDD mode). Prior to and following pacing patients underwent NYHA class evaluation, 6-min walk test, Quality of Life Assessment and a cardiopulmonary exercise test. Biventricular pacing improved functional class (P<0.0001) and Quality of life (P<0.0001), increased 6-min walk distance, (P=0.008) and exercise duration (P<0.0001) but had no significant effect on peak exercise VO(2). Resynchronization therapy increased mean 24-h RR (922+/-58 vs. 809+/-41 ms at baseline, P=0.006), SDNN (111+/-11 vs. 83+/-8 ms, P=0.003), SDNN-I (56+/-10 vs. 40+/-5 ms, P=0.02), rMSSD (66+/-14 vs. 41+/-8 ms, P=0.003), Total Power (5724+/-1875 vs. 2074+/-553 ms(2), P=0.03), Ultra Low Frequency Power (1969+/-789 vs. 653+/-405 ms(2), P=0.03) and Very Low Frequency Power (2407+/-561 vs. 902+/-155 ms(2), P=0.004).

CONCLUSION

Biventricular pacing in heart failure improves autonomic function by increasing HRV. This may have important prognostic implications.

Cardiac resynchronization and death from progressive heart failure: a meta-analysis of randomized controlled trials

CONTEXT

Progressive heart failure is the most common mechanism of death among patients with advanced heart failure. Cardiac resynchronization, a pacemaker-based therapy for heart failure, enhances cardiac performance and quality of life, but its effect on mortality is uncertain.

OBJECTIVE

To determine whether cardiac resynchronization reduces mortality from progressive heart failure.

DATA SOURCES

MEDLINE (1966-2002), EMBASE (1980-2002), the Cochrane Controlled Trials Register (Second Quarter, 2002), The National Institutes of Health ClinicalTrials.gov database, the US Food and Drug Administration Web site, and reports presented at scientific meetings (1994-2002). Search terms included pacemaker, pacing, heart failure, dual-site, multisite, biventricular, resynchronization, and left ventricular preexcitation.

STUDY SELECTION

Eligible studies were randomized controlled trials of cardiac resynchronization for the treatment of chronic symptomatic left ventricular dysfunction. Eligible studies reported death, hospitalization for heart failure, or ventricular arrhythmia as outcomes. Of the 6883 potentially relevant reports initially identified, 11 reports of 4 randomized trials with 1634 total patients were included in the meta-analysis.

DATA EXTRACTION

Trial reports were reviewed independently by 2 investigators in an unblinded standardized manner.

DATA SYNTHESIS

Follow-up in the included trials ranged from 3 to 6 months. Pooled data from the 4 selected studies showed that cardiac resynchronization reduced death from progressive heart failure by 51% relative to controls (odds ratio [OR], 0.49; 95% confidence interval [CI], 0.25-0.93). Progressive heart failure mortality was 1.7% for cardiac resynchronization patients and 3.5% for controls. Cardiac resynchronization also reduced heart failure hospitalization by 29% (OR, 0.71; 95% CI, 0.53-0.96) and showed a trend toward reducing all-cause mortality (OR, 0.77; 95% CI, 0.51-1.18). Cardiac resynchronization was not associated with a statistically significant effect on non-heart failure mortality (OR, 1.15; 95% CI, 0.65-2.02). Among patients with implantable cardioverter defibrillators, cardiac resynchronization had no clear impact on ventricular tachycardia or ventricular fibrillation (OR, 0.92; 95% CI, 0.67-1.27).

CONCLUSIONS

Cardiac resynchronization reduces mortality from progressive heart failure in patients with symptomatic left ventricular dysfunction. This finding suggests that cardiac resynchronization may have a substantial impact on the most common mechanism of death among patients with advanced heart failure. Cardiac resynchronization also reduces heart failure hospitalization and shows a trend toward reducing all-cause mortality.

Effect of epicardial or biventricular pacing to prolong QT interval and increase transmural dispersion of repolarization: does resynchronization therapy pose a risk for patients predisposed to long QT or torsade de pointes?

BACKGROUND

The present study examined pacing site-dependent changes in QT interval and transmural dispersion of repolarization (TDR) and their potential role in the development of torsade de pointes (TdP).

METHODS AND RESULTS

In humans, the QT interval, JT interval, and TDR were measured in 29 patients with heart failure during right ventricular endocardial pacing (RVEndoP), biventricular pacing (BiVP), and left ventricular epicardial pacing (LVEpiP). In animal experiments, pacing site--dependent changes in ventricular repolarization were examined with a rabbit left ventricular wedge preparation in which action potentials from endocardium and epicardium could be simultaneously recorded with a transmural ECG. In humans, LVEpiP and BiVP led to significant QT and JT prolongation. LVEpiP also enhanced TDR. Frequent R-on-T extrasystoles generated by BiVP and LVEpiP but completely inhibited by RVEndoP occurred in 4 patients, of whom 1 developed multiple episodes of nonsustained polymorphic ventricular tachycardia and another suffered incessant TdP. In rabbit experiments, switching from endocardial to epicardial pacing produced a net increase in QT interval and TDR by 17+/-5 and 22+/-5 ms, respectively (n=6, P<0.01), without parallel increases in ventricular transmembrane action potential durations. Epicardial pacing facilitated transmural propagation of early afterdepolarization, leading to the development of R-on-T extrasystoles and TdP in the presence of action potential duration-prolonging agents.

CONCLUSIONS

LVEpiP and BiVP increase QT, JT, and TDR by altering the transmural sequence of activation of the intrinsically heterogeneous ventricular myocardium. Our data suggest that the resultant exaggeration of arrhythmic substrates can lead to the development of TdP in a subset of patients.

Biventricular pacing for congestive heart failure

Resynchronization with biventricular pacing is a relatively new and important nonpharmacological therapy for patients with heart failure. A prolonged PR interval, a wide QRS, and left bundle branch block are typical conduction disturbances associated with left ventricular dysfunction. The intraventricular conduction delays often lead to loss of synchronization of ventricular contraction, thus contributing to additional problems for the heart failure patient. Biventricular pacing offers (surgically implanted leads implies a thoracotomy or mini-thoracotomy for an epicardial lead and not the preferred transvenous approach) for an endocardial lead, considerable promise for improving the quality of life, exercise tolerance, as well as for decreasing hospitalization for patients with Class III or Class IV heart failure.