The role of prophylactic implantable cardioverter defibrillators in heart failure: Recent trials usher in a new era of device therapy

Sudden cardiac death (SCD) manifested as ventricular fibrillation or sustained ventricular tachycardia has been a major focus of cardiovascular research for more than three decades. Although mortality in patients with heart failure (HF) caused by left ventricular systolic dysfunction has declined in recent years through effective pharmacotherapeutic strategies, SCD remains the major cause of death in symptomatic HF, with little improvement by drug therapy. Although it is clear that the implantable cardioverter defibrillator (ICD) is efficacious and should be used to prevent a recurrence of sustained ventricular arrhythmia (secondary prevention) in most patients, the guidelines for prophylactic use of ICDs (primary prevention) are less well defined. The results of recent clinical trials examining the efficacy of prophylactic ICD therapy in HF patients have clarified the role of ICD treatment in this population. This article reviews these trials and summarizes our current approach to the prevention of SCD in HF.     

A critical appraisal of indications for the implantable cardioverter defibrillator (ICD).

The implantable cardioverter defibrillator (ICD) is a remarkably effective therapy for reducing sudden cardiac death in patients with malignant ventricular arrhythmias. The indications for implantation of the ICD were approved in 1985 by the United States Food and Drug Administration; it could be implanted in patients who have experienced cardiac arrest or in those with recurrent ventricular arrhythmias which are not suppressed by anti-arrhythmic drugs in the electrophysiology laboratory. These established indications have not changed in the last seven years. In the near future, the release of third-generation ICDs (with antitachycardia pacing) will likely further expand indications for the device. Many patients with stable ventricular tachycardia who have not had syncope or cardiac arrest will receive a third-generation defibrillator. Also, three clinical trials now in progress--CABG-PATCH, Multicenter Automatic Defibrillator Implantation Trial (MADIT) and Multicenter Unsustained Tachycardia Trial (MUSTT)--are studying "pre-event" patients with low ejection fraction and electrical instability; some of the patients in each trial are being prospectively randomized to the ICD. Within the next five years we will have a better understanding of the role of ICD therapy in such patients. Until these studies are completed, it is important that the indications for the ICD not be expanded.     

Update on implantable cardioverter defibrillator trials

Many randomized trials of implantable cardioverter defibrillator (ICD) therapy versus medical treatment for the prevention of death in survivors of cardiac arrest or in patients at high risk of sudden cardiac death (SCD) have been reported. ICD therapy has been consistently efficacious in preventing SCD. ICD therapy has generally favorably impacted total mortality, but this has depended upon the control group's risk for arrhythmic and nonarrhythmic mortality. In these trials, predictors of sudden or total mortality better than ventricular dysfunction have not emerged. This review summarizes the randomized ICDs trials and the impact ICDs have on SCD prevention.     

Implantable device therapy

Sudden cardiac death (SCD) accounts for two-thirds of fatal events related to heart disease. Coronary heart disease and non-ischemic cardiomyopathy are the most common causes of SCD. Data from major randomized trials have consistently shown that therapy with an implantable cardioverter defibrillator (ICD) results in a significant and meaningful effect on survival through a reduction in the risk of SCD in these population. These data have resulted in a marked increase in the application of implantable device therapy in the past 2 decades from secondary prevention with an implantable cardioverter/defibrillator (ICD) in survivors of a cardiac arrest to primary prevention of SCD in asymptomatic patients with ischemic and non-ischemic left ventricular dysfunction, and prevention of symptomatic heart failure progression and death with cardiac resynchronization therapy (CRT), and devices that combine CRT and ICD therapies (CRT-D). However, there are still areas of uncertainty regarding device therapy that include inconsistent benefit in risk-subgroups of patients with low ejection fraction; increased risk of heart failure after life-prolonging ICD therapy, and a considerable rate of device malfunction despite increasing sophistication. In the present review we focus on current data regarding the clinical indications as well as the safety and efficacy of implantable device therapy, including ICD, CRT, and CRT-D.     

室性心律失常的治疗及进展

自从认识到心脏骤停作为心脏性猝死的机制具有很高的发生率以来,医学和临床医生一直在追求一种方法来预测及预防这些心血管事件。在室性心律失常患者中已经完成的一些安慰剂对照的抗心律失常药物试验并没有一致地认为抗心律失常药物治疗能够降低总病死率。近几年发表的临床随机试验证明,植入型心脏复律除颤器与传统的抗心律失常治疗相比,可降低高危亚组患者的病死率。然而,在患者中识别致死性室性心律失常的危险性及衡量使用植入型心脏复律除颤器治疗的价-效比已经成为当今的社会医学问题,尤其在美国。室性心律失常的治疗和心脏性猝死预防仍是将来需要关注的问题。     

Current role of device therapy to reduce sudden cardiac death in heart failure

Sudden cardiac death (SCD) continues to be a major contributor to mortality in patients with heart failure (HF) despite recent advances in medical therapy. Device therapy, including the implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy (CRT), serves as an adjunct in reducing HF mortality. Several clinical trials support the prophylactic use of the ICD in reducing mortality in certain HF populations and have established the clinical benefits of CRT in advanced HF. More recently, the Comparison of Medical Therapy Pacing and Defibrillation in Heart Failure trial was the first study to demonstrate a survival benefit of CRT alone or in conjunction with an ICD. This article reviews the most pertinent data regarding the role of device therapy in reducing SCD in HF and addresses future challenges faced by device manufacturers and clinicians.     

Pharmacological therapy for ventricular arrhythmias: evidence for current treatment strategies and perspectives for the future

This review summarizes the current status of pharmacological therapy for ventricular arrhythmias in symptomatic patients. The selection of specific drugs for this indication is highly dependent on the underlying heart disease. In primary prevention of sudden death, antiarrhythmic agents do not play a role--except betareceptor antagonists. Similarly, in patients treated for secondary prevention of cardiac arrest or hemodynamically symptomatic ventricular tachycardia, the implantable defibrillator constitutes the therapy of choice with hardly any role left for antiarrhythmic drugs. An emerging role for antiarrhythmic drug therapy is represented by the concomitant pharmacological treatment in ICD recipients who experience shocks from their devices (hybrid therapy). Several randomized clinical trials have recently evaluated this issue and permit an evidence-based treatment strategy. Currently, most patients receive sotalol or amiodarone for hybrid therapy with azimilide as a potential new class III antiarrhythmic drug for this treatment indication.     

The Optimal Timing of Primary Prevention Implantable Cardioverter-Defibrillator Referral in the Rapidly Changing Medical Landscape

The use of implantable cardioverter-defibrillators (ICDs) significantly reduces the risk of mortality in patients with heart failure with reduced ejection fraction (HFrEF). Current guidelines, which are based on seminal clinical trials published nearly 2 decades ago, recommend that patients be on optimal medical therapy for HF for a minimum of 3 months before referral for prophylactic ICD. This waiting period allows for left ventricular reverse remodelling and improvement in HF symptoms, which may render primary prevention ICD implantation unnecessary. However, medical therapy for HFrEF has significantly evolved since the publication of these landmark trials. Given the plethora of medical therapy options now available for HFrEF, it is appropriate to reassess the duration of this waiting period. In the present review, we examine the landmark randomised trials in primary prevention of sudden cardiac death in patients with HFrEF, summarise the novel medical therapies (sacubitril-valsartan, sodium-glucose cotransporter 2 inhibitors, ivabradine, vericiguat, and omecamtiv mecarbil) that have emerged since the publication of those trials, discuss the optimal timing of ICD referral, and review subtypes of nonischemic cardiomyopathy where timing of ICD insertion is guided by alternative criteria. With the steps now needed to optimise medical therapy for HFrEF, in terms of both classes of drugs and doses of each agent, it can easily take up to 6 months to achieve optimisation. Following that, waiting periods of 3 months for ischemic cardiomyopathy and 6 months for nonischemic cardiomyopathy may be required to allow adequate reverse remodelling before reevaluating for ICD implantation.     

Primary Prevention Implantable Cardioverter-Defibrillator Therapy in Heart Failure with Recovered Ejection Fraction

Given recent advances in both pharmacologic and nonpharmacologic strategies for improving outcomes related to chronic systolic heart failure, heart failure with recovered ejection fraction (HFrecEF) is now recognized as a distinct clinical entity with increasing prevalence. In many patients who once had an indication for active implantable cardioverter-defibrillator (ICD) therapy, questions remain regarding the usefulness of this primary prevention strategy to protect against syncope and cardiac arrest after they have achieved myocardial recovery. Early, small studies provide convincing evidence for continued guideline-directed medical therapy (GDMT) in segments of the HFrecEF population to promote persistent left ventricular myocardial recovery. Retrospective data suggest that the risk of sudden cardiac death is lower, but still present, in HFrecEF as compared with HF with reduced ejection fraction, with reports of up to 5 appropriate ICD therapies delivered per 100 patient-years. The usefulness of continued ICD therapy is weighed against the unfavorable effects of this strategy, which include a cumulative risk of infection, inappropriate discharge, and patient-level anxiety. Historically, many surrogate measures for risk stratification have been explored, but few have demonstrated efficacy and widespread availability. We found that the available data to inform decisions surrounding the continued use of active ICD therapies in this population are incomplete, and more advanced tools such as genetic testing, evaluation of high-risk structural cardiomyopathies (such as noncompaction), and cardiac magnetic resonance imaging have emerged as vital in risk stratification. Clinicians and patients should engage in shared decision-making to evaluate the appropriateness of active ICD therapy for any given individual. In this article, we explore the definition of HFrecEF, data underlying continuation of guideline-directed medical therapy in patients who have achieved left ventricular ejection fraction recovery, the benefits and risks of active ICD therapy, and surrogate measures that may have a role in risk stratification.     

Indications for implantable cardioverter defibrillator therapy

The implantable cardioverter defibrillator (ICD) is now an integral therapy for cardiac patient care. More than 20 years have passed since the first ICD implant. Sudden cardiac death from arrhythmia (ventricular tachycardia and fibrillation) has been significantly decreased because of the use of ICD therapy. Primary treatment trials have shown ICD therapy to be superior to drug therapy. Most of these trials compared ICD therapy with amiodarone or sotalol. Prevention trials have also been completed. Patients with nonsustained ventricular tachycardia, low left ventricular ejection fraction, and coronary artery disease were evaluated with electrophysiology studies. Patients with inducible ventricular arrhythmias were treated with ICD or drug suppression therapy. ICD therapy was superior to drug therapy for prevention of fatal arrhythmias. Ongoing trials include evaluation of ICD therapy for patients with high-risk substrates: congestive heart failure, dilated cardiomyopathy, hypertrophic cardiomyopathy, and repolarization syndromes. Factors such as medication inefficacy/side effects, transvenous ICD implantation and overwhelming mortality benefits have expanded ICD usage beyond the original restrictive guidelines.     

Role of wearable and automatic external defibrillators in improving survival in patients at risk for sudden cardiac death

Cardiac arrest is a vexing public health problem. Fortunately, implantable cardioverter-defibrillators (ICDs) have been proven to decrease overall mortality in several populations at high risk for cardiac arrest. However, it is still unclear how to treat patients who have an elevated risk of cardiac arrest but are not in one of the identified high-risk groups proven to benefit from an ICD. It also is uncertain how to manage high-risk patients who have an accepted indication for an ICD but are unable or unwilling to have an ICD. In these clinical situations, the wearable defibrillator and automatic external defibrillator are options that should be considered. Both devices have been shown in small series to be highly effective at restoring sinus rhythm in patients with a ventricular tachyarrhythmia. However, there is still a lack of large-scale trials proving that these devices should be employed routinely in specific high-risk patient populations.     

The current role of cardiac resynchronization therapy in reducing mortality and hospitalization in heart failure patients: a meta-analysis from clinical trials

Many diagnostic and therapeutic advances have been reached for congestive heart failure (HF). However, despite clinical improvement and longer survival conferred by new pharmacological options, this syndrome is associated with high morbidity and mortality. Atrial-synchronized biventricular pacing (cardiac resynchronization therapy, CRT) has proven to be effective treatment in symptomatic patients with reduced left ventricular ejection fraction and electromechanical dyssynchrony. To date, many papers have been published on the role of CRT in improving quality of life, functional and neurohormonal parameters and reducing mortality and hospitalization. Eligible studies were randomized controlled trials of CRT for the treatment of chronic, symptomatic left ventricular dysfunction. Our search began dating back to 1994 and was updated to October 2006. Pooled data from the 6 selected studies showed that CRT reduced all-cause mortality by 28% (hazard ration [HR] = 0.72; 95% confidence interval [CI]: 0.60-0.86) and new hospitalizations for worsening HF by 37% (HR = 0.63; 95% CI: 0.44-0.91). This meta-analysis showed that patients with implantable cardiac defibrillators (ICDs) alone and ICD+CRT had a significant reduction of worsening HF hospitalization rate compared to no CRT-no ICD patients. Among patients with ICDs, CRT showed a slight effect on all-cause mortality reduction but no clear impact on worsening HF rehospitalization.     

Use of traditional and biventricular implantable cardiac devices for primary and secondary prevention of sudden death

Sudden cardiac death is the leading cause of cardiac mortality, particularly among high-risk populations with known left ventricular systolic dysfunction. Multiple randomized clinical trials demonstrated a significant mortality benefit of the implantable cardioverter defibrillator (ICD) compared with antiarrhythmic drug therapy or standard medical care. Initial ICD trials showed a mortality improvement for patients who previously had experienced aborted sudden cardiac death or sustained ventricular tachycardia (secondary prevention). Primary prevention trials in selected high-risk patients who had both ischemic and nonischemic cardiomyopathy also demonstrated a mortality benefit associated with ICD treatment. More recently, cardiac resynchronization therapy with or without defibrillator capability has been shown to reduce morbidity and mortality among advanced heart failure patients with a prolonged QRS duration.     

Long-term outcome of implanted cardioverter defibrillators in survivors of out-of-hospital cardiac arrest of cardiac origin.

BACKGROUND: Little is known about the long-term outcome of implantable cardioverter defibrillator (ICD) therapy in survivors of out-of-hospital cardiac arrest (OHCA). METHODS AND RESULTS: The frequency of lethal ventricular arrhythmias and whether ICD implantation can prevent recurrence of cardiac arrest were examined. Long-term (24.4+/-11.9 months) outcome was examined in 23 patients with OHCA who were treated with an ICD (OHCA group) and 35 patients without OHCA (non-OHCA group) who were treated with an ICD. Patients in both groups had same clinical backgrounds; however, those in the OHCA group showed a significantly lower incidence of induced ventricular arrhythmias (71%) than the non-OHCA group (96%). In the follow-up period, patients in the OHCA group had almost the same incidence of ICD discharge (30%) as patients in the non-OHCA group (40%). The rate of recurrence of ventricular fibrillation in the OHCA patients was 13%, and it was difficult to estimate the rate by induced ventricular arrhythmia. CONCLUSION: The results suggest that ICD implantation for survivors of OHCA with favorable neurological recovery might be effective for preventing recurrence of cardiac arrest.     

Implantable cardioverter defibrillator therapy in postinfarction patients

PURPOSE OF REVIEW: In the past few years, new clinical trials were conducted to determine the effectiveness of implantable cardioverter defibrillators (ICDs) for prevention of mortality in patients with ischemic and nonischemic cardiomyopathies. This paper aims to provide an overview of the current state of knowledge regarding ICD therapy in postinfarction patients. RECENT FINDINGS: Postinfarction patients with severe left ventricular dysfunction are at high risk of sudden cardiac death. Antiarrhythmic therapy does not improve survival in such patients and, therefore, ICDs emerged as treatment of choice for both primary and secondary prevention of mortality after MI. The MADIT (Multicenter Automatic Defibrillator Implantation Trial) and MUSTT (Multicenter Unsustained Tachycardia Trial) trials were the first primary prevention ICD trials documenting a substantial reduction in mortality with an ICD in postinfarction patients with depressed ejection fraction, nonsustained ventricular tachycardia, and inducible sustained ventricular tachycardia. The recently completed MADIT II trial broadened indications for prophylactic use of ICD in postinfarction patients with ejection fraction of 30% or less without a requirement for additional risk stratifiers. The benefit from ICD therapy in patients with low ejection fraction was recently confirmed by results from the SCD-HeFT (Sudden Cardiac Death in Heart Failure) and COMPANION (Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure) trials. SUMMARY: Recent clinical trials established ICD as an important therapeutic modality for primary and secondary prevention of mortality in postinfarction patients.     

Device therapy in heart failure patients with chronic kidney disease

Heart failure (HF) and chronic kidney disease (CKD) both carry significant risk for sudden cardiac death, hospitalization, and mortality; when combined, however, they markedly increase the risk of morbidity and mortality. Device therapies such as implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy (CRT) are treatments proven to have significant benefit on clinical outcomes in select patients with HF. However, the majority of studies supporting the use of these devices have limited data on patients with CKD or end-stage renal disease. In this review, we discuss the intersection of HF and CKD as it relates to progressive HF and the risk of sudden death. Although these disorders are common and have a poor prognosis, the evidence available for guiding treatment decisions for the use of ICD and CRT devices in these patients is lacking. Given this lack of clear evidence, pragmatic clinical trials and comparative effectiveness studies are needed to help identify the appropriate use of ICD and CRT devices in this high-risk population of patients with HF and CKD.     

室性心律失常的治疗进展

Ventricular arrhythmias(VA)include premature ventricular contractions(PVC),ventricular tachycardia(VT),ventricular flutter or defibrillation(VFL/VF).Although commonly related to structural heart disease,a significant percentage of VA are idiopathic(occurring in patients with otherwise normal hearts).Classic antiarrhythmic drugs(AADs)for VA have limited effectiveness,and pose the risk of life-threatening VT/VF.Very few AADs have been successful in the last few decades,due to safety concerns or limited benefits in comparison to existing therapy.Amiodarone has emerged as the leading antiarrhythmic therapy for termination and prevention of VA in different clinical settings because of its proven efficacy and safety.For VT/VF,implantable cardioverter defibrillator(ICD)appear to be the unique,yet unsatisfactory,solution.Indications for ICD have evolved considerably from initial implantation exclusively in patients who had survived one or more cardiac arrests and failed pharmacological therapy.Multipie clinical trials have established that ICD use results in improved survival compared with antiarrhythmic agents for secondary prevention of sudden cardiac death(SCD).Large prospective,randomized,multicenter studies have also demonstrated that ICD therapy is effective for primary prevention of sudden death and improves total survival in selected patient populations who have not previously had a cardiac arrest or sustained VT.Catheter ablation is now an important option to control recurrent VT.The field has evolved rapidly and is a work in progress.Ablation is often a sole therapy of VT in patients without structural heart disease and is commonly combined with an ICD and/or antiarrhythmic therapy for scar-related VT associated with structural heart disense.     

Significance of QRS complex duration in patients with heart failure

Prolongation of QRS (> or =120 ms) occurs in 14% to 47% of heart failure (HF) patients. Left bundle branch block is far more common than right bundle branch block. Left-sided intraventricular conduction delay is associated with more advanced myocardial disease, worse left ventricular (LV) function, poorer prognosis, and a higher all-cause mortality rate compared with narrow QRS complex. It also predisposes heart failure patients to an increased risk of ventricular tachyarrhythmias, but the incidence of cardiac or sudden death remains unclear because of limited observations. A progressive increase in QRS duration worsens the prognosis. No electrocardiographic measure is specific enough to provide subgroup risk categorization for excluding or selecting HF patients for prophylactic implantable cardioverter-defibrillator (ICD) therapy. In ICD patients with HF, a wide underlying QRS complex more than doubles the cardiac mortality compared with a narrow QRS complex. There is a high incidence of an elevated defibrillation threshold at the time of ICD implantation in patients with QRS > or =200 ms. Mechanical LV dyssynchrony potentially treatable by ventricular resynchronization occurs in about 70% of HF patients with left-sided intraventricular conduction delay, a fact that would explain the lack of therapeutic response in about 30% of patients subjected to ventricular resynchronization according to standard criteria relying on QRS duration. The duration of the basal QRS complex does not reliably predict the clinical response to ventricular resynchronization, and QRS narrowing after cardiac resynchronization therapy does not correlate with hemodynamic and clinical improvement. Mechanical LV dyssynchrony is best shown by evolving echocardiographic techniques (predominantly tissue Doppler imaging) currently in the process of standardization.     

Significance of QRS complex duration in patients with heart failure.

Prolongation of QRS (> or =120 ms) occurs in 14% to 47% of heart failure (HF) patients. Left bundle branch block is far more common than right bundle branch block. Left-sided intraventricular conduction delay is associated with more advanced myocardial disease, worse left ventricular (LV) function, poorer prognosis, and a higher all-cause mortality rate compared with narrow QRS complex. It also predisposes heart failure patients to an increased risk of ventricular tachyarrhythmias, but the incidence of cardiac or sudden death remains unclear because of limited observations. A progressive increase in QRS duration worsens the prognosis. No electrocardiographic measure is specific enough to provide subgroup risk categorization for excluding or selecting HF patients for prophylactic implantable cardioverter-defibrillator (ICD) therapy. In ICD patients with HF, a wide underlying QRS complex more than doubles the cardiac mortality compared with a narrow QRS complex. There is a high incidence of an elevated defibrillation threshold at the time of ICD implantation in patients with QRS > or =200 ms. Mechanical LV dyssynchrony potentially treatable by ventricular resynchronization occurs in about 70% of HF patients with left-sided intraventricular conduction delay, a fact that would explain the lack of therapeutic response in about 30% of patients subjected to ventricular resynchronization according to standard criteria relying on QRS duration. The duration of the basal QRS complex does not reliably predict the clinical response to ventricular resynchronization, and QRS narrowing after cardiac resynchronization therapy does not correlate with hemodynamic and clinical improvement. Mechanical LV dyssynchrony is best shown by evolving echocardiographic techniques (predominantly tissue Doppler imaging) currently in the process of standardization.     

Appropriate ICD therapy in patients with idiopathic dilated cardiomyopathy: long term follow-up

The implantable cardioverter defibrillator (ICD) has proved effective in preventing sudden death and decreasing mortality in randomised secondary prevention trials. Some nonrandomized studies have reported different incidences and predictors of appropriate ICD therapy in patients with idiopathic dilated cardiomyopathy (DCM). The antiarrhythmic and other medical therapies were different between the published studies and it was reported that not using beta-blockers was a predictor of appropriate ICD therapy. In the present study, we report on our long-term experience with ICD therapy in patients with DCM, the majority of whom were treated with beta-blockers and amiodarone. The study population consisted of 25 patients with DCM who underwent initial transvenous ICD implantation between December 1995 and May 2005. Indications for ICD implantation were monomorphic sustained ventricular tachycardia (VT) in 16 patients (64%), cardiac arrest in 8 patients (32%), and syncope plus inducible VT in one patient. Twenty-four patients underwent an electrophysiologic study (EPS). In 18 patients, the ICDs were programmed to only shocks and in 7 patients an additional antitachycardia pacing program was performed. One patient was lost to follow-up and 24 patients were followed-up primarily in our ICD pacemaker outpatient clinic. Appropriate ICD therapy was defined as antitachycardia pacing therapy or shock for tachyarrhythmia determined by evaluation of the clinical information and by device diagnostics to be either ventricular fibrillation or ventricular tachycardia. The mean follow-up was 39.29 +/- 30.59 months after ICD implantation. At follow-up, 17 patients were using a beta-blocker and 16 patients amiodarone. Appropriate ICD therapy was observed in 14 patients (58%). The detected arrhythmias were VT in 12 patients, ventricular fibrillation (VF) in one, and VT and VF in one patient. The time to first ICD therapy was 15.93 +/- 18.45 (range, 1-74) months. Using the Kaplan-Meier method, the percent survival free of appropriate ICD therapy was 82%, 72%, 66%, and 55% at 1, 2, 3, and 4 years follow-up, respectively. The clinical, echocardiographic, and electrophysiologic characteristics did not differ between those who did and did not receive appropriate ICD therapy. However, the mean QRS duration was significantly longer in patients who received appropriate ICD therapies. Cox regression analysis did not reveal any factors that predicted appropriate ICD therapy. Five patients (21%) died during follow-up. Four deaths were classified as cardiac and one as noncardiac. The cumulative survival from total death was 94%, 82%, 82%, and 69%, and the cumulative survival from cardiac death was 94%, 82%, 82%, and 76% during 1, 2, 3, and 4 years of follow-up, respectively. In summary, in this selected patient population with DCM, the majority of patients were unresponsive to beta-blocker and antiarrhythmic therapy. Most of these patients received appropriate ICD therapy during follow-up. Cox regression analysis did not identify any factors that predicted appropriate ICD therapy. Additional trials with larger patient populations are needed to detect the predictors of appropriate ICD therapy in patients with DCM.