INTRODUCTION — Life-threatening ventricular arrhythmias, including sustained ventricular tachycardia (VT) and ventricular fibrillation (VF), are common in patients with systolic heart failure (HF) and dilated cardiomyopathy and may lead to sudden cardiac death (SCD). Primary prevention of SCD refers to medical or interventional therapy undertaken to prevent SCD in patients who have not experienced symptomatic life-threatening sustained VT/VF or sudden cardiac arrest (SCA) but who are felt to be at an increased risk for such an event. The primary prevention of SCD in patients with HF and cardiomyopathy with reduced ejection fraction, either due to coronary heart disease or a dilated nonischemic etiology, will be reviewed here with emphasis on the role of implantable cardioverter-defibrillators (ICDs). The different types of ventricular arrhythmias, the effects of HF therapy on ventricular arrhythmias, the role of electrophysiologic testing, and the secondary prevention of SCD are discussed separately. (See "Ventricular arrhythmias: Overview in patients with heart failure and cardiomyopathy" and "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy".)
The approaches to the treatment of ventricular arrhythmias related to specific heart muscle diseases or primary electrical system diseases such as hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, isolated left ventricular noncompaction, Chagas disease, Brugada syndrome, long QT syndrome, and other channelopathies are discussed elsewhere.
CAUSES OF DEATH IN HEART FAILURE — Causes of death in patients with heart failure include:
●Progressive pump failure.
●Unexpected SCD (usually from a ventricular tachyarrhythmia, but asystole and pulseless electrical activity [PEA] are also seen less frequently).
●SCD in the setting of worsening heart failure.
The mode of death in patients with HF is more likely to be "sudden" in patients with class II or III HF, while the mode of death is more likely to be related to "pump" failure in patients with class IV HF (figure 1) . Therefore, primary prevention implantable cardioverter-defibrillator (ICD) trials (in the absence of cardiac resynchronization therapy [CRT]) have excluded patients with NYHA class IV HF. In fact, the 2017 American Heart Association/American College of Cardiology/Heart Rhythm Society (AHA/ACC/HRS) Guidelines state that "ICD therapy is not indicated for NYHA Class IV patients with medication-refractory HF who are not also candidates for cardiac transplantation, an LVAD (left ventricular assist device), or CRT-D," listing this as a class III indication . (See 'Class IV heart failure' below and "Heart transplantation in adults: Indications and contraindications" and "Cardiac resynchronization therapy in heart failure: Indications and choice of system".)
RISK STRATIFICATION STRATEGIES — While implantable cardioverter-defibrillators (ICDs) are highly efficacious in the treatment of ventricular tachyarrhythmias and prevention of SCD, they are costly, require ongoing follow-up, and have numerous risks at the time of implantation (eg, bleeding, pneumothorax, perforation, etc) as well as over the lifetime of the device (eg, infection, device and lead malfunction, etc). In addition, only a subset of patients with cardiomyopathy develop sustained ventricular tachyarrhythmias or SCD. As such, the risk stratification of patients prior to ICD therapy is important for providing therapy to patients at highest risk of SCD and minimizing the number of ICD implantations in patients who are unlikely to benefit.
Numerous patient-related clinical markers as well as data derived from testing have been associated with increased risk of sudden death, and a variety of attempts have been made to develop risk stratification schema to more specifically identify an individual patient's risk of SCD. To date, however, the optimal approach to SCD risk stratification for placement of a primary prevention ICD continues to rely primarily upon the following:
●Etiology of left ventricular dysfunction
●Left ventricular ejection fraction
●Heart failure symptom classification
●Life expectancy greater than one year
●Inducible sustained ventricular tachycardia
●Nonsustained ventricular tachycardia on electrocardiogram (ECG) monitoring
LVEF and risk — Patients with significant reductions in left ventricular ejection fraction (LVEF) appear to be at greatest risk, and derive the greatest benefit, from primary prevention ICD implantation. (See 'Trials of primary prevention ICDs in ischemic cardiomyopathy' below and 'Trials of primary prevention ICDs in nonischemic dilated cardiomyopathy' below.)
Though most studies of prophylactic ICD implantation have included patients with an LVEF ≤35 percent, the large majority of patients included in most trials have had ejection fractions under 30 percent, resulting in some uncertainty regarding the potential benefit of prophylactic ICD insertion for patients with LVEF between 30 and 35 percent. This issue was addressed in a retrospective cohort study using registry data from the NCDR ICD registry of patients who underwent ICD implantation in 2006 or 2007 (median follow-up 4.4 years) and Get With The Guidelines-Heart Failure (GWTG-HF) patients without an ICD (enrolled between 2005 and 2009 with median follow-up of 2.9 years), in which the benefits of ICD implantation were separately evaluated among patients with LVEF <30 percent and those with LVEF 30 to 35 percent . All-cause mortality was significantly lower in patients with an ICD and any level of LVEF, compared with those without an ICD:
●LVEF 30 to 35 percent – hazard ratio (HR) 0.83, 95% CI 0.69-0.99
●LVEF <30 percent – HR 0.72, 95% CI 0.65-0.81
While this study is nonrandomized, the data suggest that patients with LVEF between 30 and 35 percent do appear to benefit from prophylactic ICD insertion.
SCD risk prediction post-MI — A number of clinical features have been evaluated as a means for identifying patients at the greatest risk of SCD following an acute myocardial infarction (MI). These include:
●Left ventricular (LV) dysfunction or reduced LVEF
●HF symptoms and the degree of heart failure
●Q-waves on the surface ECG
●Intraventricular conduction delay
●Spontaneous ventricular premature beats (VPBs) and nonsustained ventricular tachycardia (NSVT)
●Late potentials on a signal-averaged ECG (SAECG)
●VT induced by electrophysiologic study (EPS)
●Reduced heart rate variability (HRV)
●Microvolt T-wave (repolarization) alternans (TWA)
A detailed discussion of the utility of these clinical predictors is presented separately. (See "Incidence of and risk stratification for sudden cardiac death after myocardial infarction".)
Clinical risk markers — A variety of novel risk stratification schemes derived from retrospective studies have shown the ability to predict SCD risk, but none have been prospectively validated in independent populations or have become part of the routine practice for primary prevention ICD placement [4-13]. Therefore, traditional risk stratification based on etiology of cardiomyopathy, LVEF, HF class, and select other risk markers (eg, inducible sustained ventricular arrhythmias) continues to form the basis for recommendations regarding ICD use.
Initial studies evaluating the role of ICD therapy in reducing mortality focused on patients with reduced LV systolic function and class II-III heart failure. As the mode of death in patients with class II-III heart failure was more likely sudden (in 59 to 64 percent of cases ), and enrollment criteria for ICD trials often included patients with class II-III HF symptoms. In contrast, patients with class IV heart failure were more likely to die from heart failure (56 percent) than from sudden death (33 percent). Studies examining the relationship between one-year mortality and LV function after MI in the pre- and post-thrombolytic era demonstrated a much higher cardiac mortality rate in patients with LVEF <40 percent [14,15]. The presence of NSVT or frequent ventricular ectopy was also associated with increased mortality post-MI, so NSVT was also used as a risk factor for inclusion in some of the randomized ICD trials. Earlier studies also demonstrated that inducible sustained monomorphic VT was associated with an increased risk of sudden death or sustained ventricular arrhythmias .
Myocardial fibrosis on CMR — The presence of myocardial fibrosis, identified by late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) imaging appears to be a robust predictor of ventricular arrhythmias or SCD across a wide spectrum of patients with non-ischemic cardiomyopathy, including those with a mean LVEF >35 percent.
●A 2017 systematic review and meta-analysis, which included 2948 patients from 29 observational studies, assessed the relationship between LGE and ventricular arrhythmias in patients with non-ischemic dilated cardiomyopathy . Over a mean follow-up of three years, the primary endpoint (sustained ventricular arrhythmia, appropriate ICD intervention, or SCD) occurred in 350 patients, including 21 percent of patients with LGE (compared with 4.7 percent of patients without LGE; pooled odds ratio [OR] 4.3, 95% CI 3.3-5.8). LGE was able to risk stratify patients at all levels of LVEF (both above and below 35 percent) and was most powerful among patients with ICDs previously placed for primary prevention (OR 7.8, 95% CI 1.7-35.8).
●In a 2019 Australian prospective, nonrandomized study of 452 patients with non-ischemic cardiomyopathy (LVEF ≤35 percent) who had all undergone CMR imaging and who met ESC/AHA criteria for primary prevention ICD placement, half received a primary prevention ICD according to the judgment of the treating physician and prevailing local practice . Patients with myocardial fibrosis (manifest by LGE on CMR imaging) who received an ICD had lower mortality than those who did not get an ICD (HR 0.45, 95% CI 0.26-0.77). However, there was no difference in survival with or without an ICD for the 175 patients without myocardial fibrosis.
The MARVEN (Clinical, Electrocardiographic, and Cardiac Magnetic Resonance Imaging Risk Factors Associated with Ventricular Tachyarrhythmias in Nonischemic Cardiomyopathy) Study is an NHLBI-sponsored prospective, observational study aimed at developing optimal risk stratification strategies to predict ventricular tachyarrhythmias in patients with nonischemic cardiomyopathy undergoing CRT-D implantation to determine whether LGE-CMR will further improve risk stratification in patients with nonischemic cardiomyopathy, LVEF ≤35 percent, and QRS ≥120 milliseconds . While not currently utilized in SCD risk stratification guidelines, if these data are confirmed in additional prospective studies, then LGE on CMR may become a criterion used in future risk stratification schemes.
USE OF AN ICD — Malignant ventricular arrhythmias potentially leading to SCD are more frequently seen in patients with certain cardiomyopathies (compared with the general population), particularly in association with heart failure (HF) symptoms. As in secondary prevention, randomized clinical trials have established a clear role for primary prevention implantable cardioverter-defibrillators (ICDs) in selected patients (table 1). In contrast, antiarrhythmic drugs other than beta blockers do not appear to improve outcomes. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy".)
The role of an ICD in the primary prevention of SCD among patients with HF and cardiomyopathy depends upon several factors:
●The severity of left ventricular (LV) systolic dysfunction.
●The severity of clinical HF (table 2).
●The etiology of LV dysfunction (ie, ischemic or nonischemic cardiomyopathy).
●Competing co-morbidities that affect longevity and risk of ICD complications (eg, chronic kidney disease, chronic obstructive pulmonary disease, etc).
The risk of SCD increases with the severity of both LV systolic dysfunction and clinical HF . However, the risk of death due to other causes (eg, progressive HF) also increases with worsening HF and LV systolic dysfunction, reinforcing the importance of appropriate patient selection prior to primary prevention ICD placement. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Epidemiology'.)
Cardiac resynchronization therapy (CRT) may be appropriate treatment for selected HF patients with ischemic or non-ischemic cardiomyopathy and reduced left ventricular ejection fraction (LVEF) (≤35 percent) with a wide QRS complex (especially if left bundle branch block QRS morphology), if left ventricular function does not improve with guideline-directed medical therapy. Ventricular dyssynchrony refers to the loss of coordinated contraction across the left ventricle. Dyssynchrony can further impair the pump function of a failing ventricle and exacerbate HF symptoms. CRT can improve pump performance, reverse the deleterious process of ventricular remodeling, and improve survival in appropriately selected patients. CRT can be achieved with a device designed for pacing only (CRT-P) or can be incorporated into a combination device with an ICD (CRT-D) (figure 2) . (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system".)
Our approach for patients with ischemic cardiomyopathy — We recommend ICD therapy for primary prevention of SCD in the following groups of patients with ischemic cardiomyopathy:
●For patients with cardiomyopathy due to ischemic heart disease, left ventricular ejection fraction (LVEF) ≤35 percent, and associated HF with New York Heart Association (NYHA) functional class II or III status .
●For patients with cardiomyopathy due to ischemic heart disease, LVEF ≤30 percent, and NYHA functional class I status .
•In both instances, patients should be at least 40 days post-myocardial infarction (MI) and more than three months following revascularization and taking guideline-directed medical therapy. These restrictions recognize that revascularization and medical therapy may result in significant improvement in LVEF and/or HF class.
●For patients with nonsustained ventricular tachycardia (NSVT) associated with prior MI, LVEF ≤40 percent, and inducible sustained VT or ventricular fibrillation at electrophysiology study [2,22,23]. Patients should be past the acute phase of MI, on guideline-directed medical therapy, and have reasonable expectation for survival for at least one year.
Patients who have had an MI resulting in reduced LVEF are at increased risk of SCD, most often due to a ventricular tachyarrhythmia. Prophylactic ICD implantation for the primary prevention of SCD reduces mortality in selected patients with ischemic cardiomyopathy. Coronary revascularization itself may also reduce the future risk of malignant arrhythmias and SCD, as shown in the early versus late ICD implantation strategies and differing results in various randomized trials. The best approach to selecting patients with ischemic cardiomyopathy for ICD therapy for primary prevention has been explored in several major randomized trials, with the indications for ICD implantation derived largely from the inclusion criteria of these trials. One caveat, however, is that these trials took place prior to the contemporary guideline-based approaches to optimal medical therapy for patients with heart failure and cardiomyopathy.
Trials of primary prevention ICDs in ischemic cardiomyopathy
MADIT-I trial — The Multicenter Automatic Defibrillator Implantation Trial (MADIT, now called MADIT-I) was the first trial to demonstrate that the ICD has a role in primary prevention of SCD in certain high-risk, asymptomatic patients . Patients had a prior MI with reduced LVEF (≤35 percent), NSVT on ECG monitoring, and inducible sustained monomorphic VT during electrophysiology study (EPS) that was also inducible after administration of intravenous procainamide. Among 196 patients who were randomly assigned to pharmacologic therapy (including an antiarrhythmic drug at the discretion of the clinician, with amiodarone administered to most patients) or an ICD and followed for an average of 27 months, patients assigned to ICD therapy had significant reductions in overall mortality, cardiac mortality, and arrhythmic deaths compared with patients assigned to medical therapy (figure 3). While the MADIT-I trial remains an important landmark study in the utilization of ICDs for primary prevention, it has largely been supplanted by subsequent studies with larger numbers of patients, better methodologies, and simpler risk stratification schemes for study entry.
MUSTT trial — The Multicenter Unsustained Tachycardia Trial (MUSTT trial), which was not primarily designed as a randomized ICD clinical trial but rather to study the management of high-risk patients using the results of electrophysiology study (EPS), enrolled patients with prior MI, reduced LVEF (≤40 percent), asymptomatic NSVT on ECG monitoring, inducible sustained VT during EPS, and no history of VT or syncope . A total of 704 patients were randomly assigned to either standard medical therapy (353 patients) or EPS-guided antiarrhythmic therapy, which included either an antiarrhythmic agent (154 patients received a class IA drug with or without mexiletine, propafenone, sotalol, or amiodarone) or an ICD (161 patients) if at least one antiarrhythmic agent was ineffective. After a median follow-up of 39 months, the five-year (25 versus 32 percent, relative risk [RR] 0.73, 95% CI 0.53-0.99) rates for the primary endpoint (arrhythmic death or resuscitated SCD) were significantly lower for EPS-guided therapy compared with standard medical therapy. The reduction in the primary endpoint in the EPS-guided group was largely attributable to ICD therapy; at five years, the primary endpoint occurred in 9 percent of those receiving an ICD, compared with 37 percent of those receiving an antiarrhythmic drug (RR 0.24, 95% CI 0.13-0.45) (figure 4).
Whether inducible arrhythmia might be prognostically important in patients with an LVEF of 30 to 40 percent was addressed in another analysis from MUSTT . The rate of arrhythmic death at five years was significantly increased for patients with inducible VT and LVEF between 30 and 40 percent, suggesting that for patients with LVEF ≥30 percent only, electrophysiology testing may have useful predictive value.
CABG Patch trial — The Coronary Artery Bypass Graft (CABG) Patch trial evaluated the efficacy of an epicardial ICD implanted at the time of coronary artery bypass graft surgery among 900 patients with severe coronary artery disease (CAD), reduced LVEF <36 percent, abnormal signal averaged ECG, and no prior sustained VT or syncope . Epicardial ICD systems were predominantly used. Compared with standard medical therapy over an average of 32 months, there was no significant difference in overall or cardiovascular mortality among patients with an ICD (hazard ratio [HR] 1.07 for overall mortality compared with standard medical therapy, 95% CI 0.81-1.42) (figure 5). This negative trial is a primary reason why current guidelines recommend against primary prevention ICD implantation for patients who have recently undergone coronary revascularization, as revascularization itself may reduce the future risk of malignant arrhythmias and SCD.
MADT-II trial — The Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II) enrolled 1232 patients with a prior MI more than 30 days prior to enrollment (and more than three months if bypass surgery was performed) and reduced LVEF (≤30 percent); NSVT and inducible VT during EPS were not required . The study, which randomly assigned patients to a prophylactic ICD or conventional medical therapy, was stopped early due to benefit of ICD therapy after an average follow-up of 20 months. Patients in the ICD group had reduced all-cause mortality (14.2 versus 19.8 percent for conventional therapy; HR 0.65, 95% CI 0.51-0.93) (figure 6).
SCD-HeFT trial — The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), which evaluated ICD and amiodarone therapies in patients with both ischemic (52 percent) or nonischemic (48 percent) cardiomyopathy, enrolled patients with NYHA class II or III heart failure (CHF) for at least three months prior to randomization, reduced LVEF (≤35 percent), and treated with angiotensin converting enzyme (ACE) inhibitor and beta-blocker, if tolerated :
●NYHA class II or III HF.
●Congestive heart failure (CHF) present for at least three months prior to randomization and treated with ACE inhibitor and beta blocker, if tolerated.
Among 2521 patients who were randomly assigned to ICD implantation, amiodarone, or placebo, and followed for a median of 46 months, total mortality at five years was significantly reduced with ICD therapy (29 versus 36 percent with placebo; HR 0.77, 95% CI 0.62-0.96). The benefit of an ICD was comparable among patients with either an ischemic or nonischemic cardiomyopathy. A long-term analysis of SCD-HeFT participants, published in July 2020, showed continued survival benefit in the ICD arm over placebo arm at a median follow-up of 11 years (HR 0.87, 95% CI 0.76-0.98) . Long-term benefit was most evident for patients with ischemic cardiomyopathy and those with NYHA functional class II symptoms at enrollment.
These results suggest that an ICD is beneficial in patients with chronic HF and a diminished LVEF (≤35 percent), despite appropriate medical therapy for at least three months. In contrast, amiodarone provided no benefit over placebo.
DINAMIT trial — The Defibrillator in Acute Myocardial Infarction Trial (DINAMIT), which evaluated the role of prophylactic ICD implantation compared with standard medical therapy, enrolled 674 patients with MI in the preceding 6 to 40 days (mean of 18 days), reduced LVEF (≤35 percent), and reduced heart rate variability or elevated resting heart rate (≥80 beats/minute) . Patients with sustained VT >48 hours post-MI, NYHA class IV HF, or CABG or three-vessel percutaneous coronary intervention post-MI were excluded. After a mean follow-up of 30 months, there was no significant difference in annual all-cause mortality between the patients with and without an ICD (7.5 versus 6.9 percent annual mortality; HR 1.08, 95% CI 0.76-1.55). This negative trial provides an important rationale for the current guideline recommendation that ICD implantation should be deferred until at least 40 days after an MI.
IRIS trial — The Immediate Risk Stratification Improves Survival (IRIS) trial also evaluated the efficacy of ICD therapy versus standard therapy early post-MI and enrolled patients with an MI in the preceding 5 to 31 days and at least one of the following: reduced LVEF (≤40 percent) with a resting heart rate ≥90 beats/minute or NSVT at a rate of ≥150 beats/minute or both . Among 898 randomized patients who were followed for an average of 37 months, there was no difference in all-cause mortality between patients randomly assigned to ICD therapy and those assigned to medical therapy (HR 1.04 for ICD therapy, 95% CI 0.81-1.35).
Nonischemic dilated cardiomyopathy
Our approach for patients with nonischemic dilated cardiomyopathy — We recommend ICD therapy for primary prevention of SCD in the following groups of patients with nonischemic dilated cardiomyopathy:
●For patients meeting SCD-HeFT criteria, including an LVEF ≤35 percent and NYHA class II to III (table 2) HF, we suggest ICD implantation rather than guideline-directed optimal medical therapy alone .
●For most patients with LVEF ≤35 percent, class III or IV HF, and a QRS duration ≥120 milliseconds (especially if left bundle branch block [LBBB] QRS morphology), we recommend implantation of a combined CRT-D device (biventricular pacing combined with an ICD).
●Additionally, many patients with specific non-ischemic cardiomyopathies (eg, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, cardiac amyloidosis, etc) may be candidates for primary prevention ICD based on disease-specific risk markers. The approaches to selection of appropriate patients in a variety of conditions are discussed in the individual UpToDate topics.
Ventricular arrhythmias are common in patients with HF and a nonischemic cardiomyopathy. While some small early trials suggested no benefit of ICD therapy in patients with nonischemic cardiomyopathy, subsequent larger trials and a 2004 meta-analysis have demonstrated greater overall survival following prophylactic ICD implantation in selected patients. While ICDs effectively reduce mortality from SCD, the benefit on total mortality appears diminished in the setting of optimal guideline-directed medical therapy and CRT. (See "Ventricular arrhythmias: Overview in patients with heart failure and cardiomyopathy".)
Trials of primary prevention ICDs in nonischemic dilated cardiomyopathy
DEFINITE trial — The Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial evaluated the efficacy of an ICD versus standard medical therapy, in 458 patients with nonischemic dilated cardiomyopathy, reduced LVEF (≤35 percent), and premature ventricular beats or NSVT . After mean follow-up of 29 months, there was a trend toward reduction in the primary endpoint of all-cause mortality in patients treated with an ICD (7.9 versus 14.1 percent with medical therapy alone; HR 0.65, 95% CI 0.40-1.06). Fewer sudden deaths occurred in the ICD arm, although the numbers were very small (3 deaths versus 14 deaths in the medical therapy arm; HR 0.20, 95% CI 0.06-0.71). The all-cause mortality rate in the "medical therapy only" arm of DEFINITE (14.1 percent at two years) was lower than had been anticipated when the study was designed, potentially contributing to the trial being underpowered for its primary endpoint.
SCD-HeFT trial — The Sudden Cardiac Death in Heart Failure trial (SCD-HeFT), which evaluated ICD and amiodarone therapies in patients with both ischemic (52 percent) or nonischemic (48 percent) cardiomyopathy, identified a significant reduction in overall mortality with ICD therapy (29 versus 36 percent with placebo; HR 0.77, 95% CI 0.62-0.96) . The benefit of an ICD was comparable among patients with either an ischemic or nonischemic cardiomyopathy. (See 'Trials of primary prevention ICDs in ischemic cardiomyopathy' above.)
COMPANION trial of ICD combined with CRT — For most patients with LVEF ≤35 percent, class III or IV HF, and a QRS duration ≥120 milliseconds, we recommend implantation of a combined CRT-D device (biventricular pacing combined with an ICD) [32,33]. The benefit appears to be greatest in patients with a left bundle branch block and QRS duration ≥150 milliseconds [34-36]. Patients with right bundle branch block and a QRS duration <150 ms are much less likely to benefit from CRT.
The Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) trial evaluated optimal medical therapy versus CRT with or without an ICD among 682 patients with nonischemic dilated cardiomyopathy, reduced LVEF (≤35 percent), and NYHA class III or IV HF symptoms requiring hospitalization within the prior year . After median follow-up of 16 months, there was a significant reduction in the incidence of the combined endpoint of all-cause mortality and all-cause hospitalization in the two arms receiving CRT compared with the medical therapy only arm (56 versus 68 percent). The CRT-D arm, but not the CRT-P arm, experienced a significant improvement in the secondary endpoint of all-cause mortality alone.
DANISH trial — The Danish Study to Assess the Efficacy of ICDs in Patients with Non-Ischemic Systolic Heart Failure on Mortality (DANISH) randomly assigned 1116 patients with symptomatic systolic HF (LVEF ≤35 percent) not caused by ischemic heart disease to an ICD with guideline-directed optimal medical therapy or medical therapy alone . Over a median follow-up of 5.6 years, no significant difference was noted in the primary outcome of total mortality (120 deaths [21.6 percent] in the ICD group compared with 131 deaths [23.4 percent] in the group without an ICD; HR 0.87, 95% CI 0.68-1.12). A significant reduction was noted in the prespecified secondary outcome of SCD in the group receiving ICDs (24 deaths [4.3 percent] compared with 46 sudden deaths [8.2 percent] in the no ICD group; HR 0.50, 95% CI 0.31-0.82), as well as nonsignificant trends toward reduction in total cardiovascular mortality and increased device infections in the ICD group.
Compared with prior primary prevention ICD trials, the overall mortality rate of patients in the DANISH trial was low, likely due to improved medical therapy for HF (notably a much higher utilization of ACE-I/ARB and beta blockers than in the older trials) and the use of CRT, which was not available during the older primary prevention trials. Because of this, the DANISH trial may have been underpowered to show a mortality benefit of ICD therapy. Finally, as there are competing causes of death with increasing age, one might not expect the same benefit of ICD therapy in older patients, who may have greater comorbidities which could contribute to nonarrhythmic causes of death. Our experts feel that it would be premature to use data from the DANISH study as the sole basis to withhold potentially life-saving ICD therapy from all patients with nonischemic cardiomyopathy. Instead, the results actually support the use of ICDs in younger patients who have a cardiomyopathy not caused by ischemic heart disease. For those patients who are likely to have a strong response to CRT or who are not considered good candidates for ICD therapy, a CRT-P device may be more suitable and compatible with therapeutic goals.
Meta-analyses of ICD trials in nonischemic cardiomyopathy — Several updated meta-analyses have been published that include patients with nonischemic cardiomyopathy receiving an ICD for primary prevention from the same original five ICD trials (CAT, AMIOVIRT, DEFINITE, SCD-HeFT, and COMPANION) as well as patients from the DANISH trial [38-46]. When considering all six trials collectively, each of the meta-analyses demonstrated a significant benefit of the ICD on all-cause mortality in patients with nonischemic cardiomyopathy (19 to 24 percent hazard reduction compared with medical therapy alone). When only patients who also received CRT in the COMPANION and DANISH trials were analyzed, there was a nonsignificant trend toward reduction in all-cause mortality among patients with an ICD (approximately 25 to 30 percent hazard reduction with nonsignificant confidence intervals) [38,40,43]. Despite the lack of a significant incremental benefit of the ICD in the two trials that included CRT, it is currently premature to withhold ICD therapy in all patients with nonischemic cardiomyopathy who require concomitant CRT. Adequately powered randomized studies are needed before recommending a change in current practice guidelines.
GUIDELINE-DIRECTED MEDICAL THERAPY — For patients who meet criteria for insertion of an implantable cardioverter-defibrillator (ICD) for the primary prevention of SCD, in the absence of a contraindication, we recommend optimizing guideline-directed medical therapy prior to ICD implantation.
Heart failure therapy — Several of the components of appropriate medical therapy after a myocardial infarction (MI) reduce SCD as well as overall mortality. While these data are derived from trials in patients with ischemic heart disease, we can infer that many of the same benefits should apply to SCD risk reduction in patients with nonischemic cardiomyopathy. (See "Overview of the acute management of ST-elevation myocardial infarction" and "Overview of the acute management of non-ST-elevation acute coronary syndromes" and "Overview of the management of heart failure with reduced ejection fraction in adults".)
●Beta blockers – In addition to reducing overall mortality in patients with an acute MI, beta blockers also reduced the risk of SCD [47,48]. The SCD benefit is better established in patients with chronic HF. (See "Acute myocardial infarction: Role of beta blocker therapy" and "Ventricular arrhythmias: Overview in patients with heart failure and cardiomyopathy", section on 'Heart failure therapy'.)
Post-MI patients with an ICD also appear to derive a benefit from beta blockers. In a cohort of 691 patients with ischemic cardiomyopathy who received an ICD in the MADIT-II trial, the 433 patients treated with a beta blocker had significantly lower mortality (hazard ratio [HR] 0.43) compared with those not taking beta blockers; additionally, patients in the highest quartile of beta blocker dose had a significant reduction in the risk of ventricular tachyarrhythmias requiring ICD discharge (HR 0.48) .
●ACE inhibitors – A meta-analysis of 15,104 patients in 15 trials of acute MI found that angiotensin-converting enzyme (ACE) inhibitor therapy reduced the risk of SCD (odds ratio 0.80, 95% CI 0.70-0.92, absolute benefit approximately 1.4 percent) as well as overall and cardiovascular mortality . (See "Angiotensin converting enzyme inhibitors and receptor blockers in acute myocardial infarction: Clinical trials".)
●Angiotensin II receptor blockers – Angiotensin II receptor blockers (ARBs) are often used for patients who cannot tolerate ACE inhibitors. At appropriate doses, it is likely that ARBs reduce the risk of SCD to the same degree as ACE inhibitors . (See "Angiotensin converting enzyme inhibitors and receptor blockers in acute myocardial infarction: Recommendations for use".)
●Angiotensin receptor-neprilysin inhibitor – The combination of an ARB and neprilysin inhibitor, known as angiotensin receptor-neprilysin inhibitor or ARNI, is another therapy for use in patients with HF and reduced LVEF (HFrEF). A randomized double-blind trial (PARADIGM-HF) in patients with HFrEF found that sacubitril-valsartan reduced cardiovascular mortality and hospitalization for HF as well as all-cause mortality compared with a standard dose of the ACE inhibitor enalapril . The ARNI combination is administered in conjunction with other HF therapies, in place of an ACE inhibitor or ARB. (See "Primary pharmacologic therapy for heart failure with reduced ejection fraction", section on 'Primary components of therapy'.)
●Statins – Statins given to patients who have had an acute MI improve overall mortality. Although data are limited and inconclusive, part of the benefit may result from a lower rate of SCD, which may reflect a direct effect of statin therapy [53-55]. (See "Low density lipoprotein-cholesterol (LDL-C) lowering after an acute coronary syndrome".)
●Mineralocorticoid receptor antagonists – Among post-MI patients who have left ventricular (LV) dysfunction and HF and/or diabetes, eplerenone significantly reduced both overall mortality and SCD (relative risk for SCD 0.79, 95% CI 0.64-0.97) . (See "Primary pharmacologic therapy for heart failure with reduced ejection fraction", section on 'Mineralocorticoid receptor antagonist'.)
Sodium–glucose co-transporter 2 inhibitors (SGLT-2 inhibitors) – Evidence as to whether SGLT-2 inhibitors reduced SCD and/or ventricular arrhythmias in patients with HF is mixed and has not been directly studied. In a post-hoc analysis of the DAPA-HF trial of persons with New York Heart Association (NYHA) class II to IV HF and LVEF <40 percent, the SGLT-2 inhibitor dapagliflozin reduced occurrence of the composite outcome of any serious ventricular arrhythmia, resuscitated cardiac arrest, or sudden death compared with placebo . Among participants randomized to dapagliflozin, 140 of 2373 patients (5.9 percent) experienced the composite outcome compared with 175 of 2371 patients (7.4 percent) in the placebo group (HR 0.79, 95% CI 0.63-0.99). The effect was consistent across each of the composite outcome components. While a prior meta-analysis of 34 randomly controlled trials in participants with type 2 diabetes mellitus or HF also showed that SGLT-2 inhibitors reduced SCD compared with placebo or active control (OR 0.72 95% CI 0.54-0.97), this result just achieved statistical significance, and there was no significant difference in incident ventricular arrhythmia or cardiac arrest . (See "Primary pharmacologic therapy for heart failure with reduced ejection fraction", section on 'Sodium-glucose co-transporter 2 inhibitors'.)
Despite the proven benefits, some patients are not receiving guideline-directed medical therapy at the time of ICD implantation. In a 2011 study analyzing 175,757 first-time ICD recipients, using data from the National Cardiovascular Data Registry, 25.7 percent of ICD recipients without a documented contraindication were reported as not receiving optimal medical therapy at the time of ICD implantation, including 18.7 percent who were reported as not receiving an ACE inhibitor or ARB and 10.7 percent who were reported as not receiving a beta blocker . While some of these gaps may reflect issues of coding and documentation, these data suggest an opportunity for significant improvement in the treatment of patients with evidence-based, cost-effective therapies that could potentially result in improvement in cardiomyopathy and avoidance of an ICD. Although current guidelines suggest at least three months of guideline-directed medical therapy in patients with symptomatic HF and left ventricular ejection fraction (LVEF) ≤35 percent, the ideal duration of guideline-directed medical therapy prior to prophylactic ICD implantation remains uncertain. However, data demonstrate that a relevant proportion of patients with newly diagnosed HF may show recovery of LVEF >35 percent beyond three months after initiation of HF therapy, allowing left ventricular reverse remodeling to occur during intensified treatment .
Antiarrhythmic drugs — Randomized clinical trials do not support the routine use of prophylactic antiarrhythmic drug therapy, other than beta blockers, to prevent SCD in patients with HF [1,61-64]. The lack of overall benefit from prophylactic antiarrhythmic drug therapy is due to both incomplete suppression of ventricular arrhythmias and the risk of proarrhythmia [62,63,65-69]. Given the established superiority of an ICD in high-risk patients, class I and class III antiarrhythmic drugs no longer have an established role for the primary prevention of SCD.
Among the antiarrhythmic drugs, amiodarone has the advantage of a relatively low rate of proarrhythmia, less negative inotropic effect, and higher efficacy for suppression of tachyarrhythmias. While amiodarone is not approved for use in the primary prevention of arrhythmias, this was a common off-label use of the drug . In addition, amiodarone is frequently used for the treatment of atrial fibrillation as it is considered relatively "safe," from a cardiac standpoint, with low risk for proarrhythmia in the setting of HF . (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Antiarrhythmic drugs' and "Amiodarone: Clinical uses", section on 'Amiodarone for ventricular arrhythmias'.)
Class IV heart failure — Class IV HF is a state that may be transitory and therefore associated with heterogeneous prognosis. Once class IV HF is refractory (stage D HF), life expectancy is generally less than one year unless cardiac transplantation is performed or a left ventricular assist device is implanted. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Cardiac transplantation'.)
The role of implantable cardioverter-defibrillator (ICD) therapy for primary prevention of SCD in patients with New York Heart Association (NYHA) class IV HF with a narrow QRS complex has not been studied. NYHA class IV patients were generally excluded from randomized primary prevention ICD trials due to high expected mortality rate from pump failure, and only a small number were included in cardiac resynchronization therapy combined with ICD (CRT-D) trials. However, a nonrandomized series of patients awaiting cardiac transplantation suggested a higher likelihood of survival to transplantation with ICD therapy, regardless of whether the ICD indication was well established .
Given these considerations, for ambulatory patients with NYHA class IV HF, a left ventricular ejection fraction (LVEF) ≤35 percent and a narrow QRS complex (ie, no dyssynchrony), who are awaiting cardiac transplantation outside the hospital, ICD implantation may be considered as a bridge to transplantation. However, there are very limited data to support this recommendation [2,71]. According to the 2017 Guideline for the Management of Patients with Ventricular Arrhythmias, "in patients with HFrEF who are awaiting heart transplant and who otherwise would not qualify for an ICD (eg, NYHA class IV and/or use of inotropes) with a plan to discharge home, an ICD is reasonable (class IIa recommendation, B-NR)." A wearable defibrillator vest may be considered as an alternative in selected patients [72,73].
Older adults and patients with comorbidities — Because of the competing risks of arrhythmic and nonarrhythmic death, some investigators have expressed concern that older adults and those with multiple or severe comorbidities might be less likely to derive benefit from an ICD [74-77]. The mean age of patients in randomized primary prevention ICD trials ranged from 60 to 67 years, and patients over 75 to 80 years comprised a relatively small proportion of these cohorts. Because most older adult patients as well as those patients with severe comorbidities (such as advanced kidney disease) were excluded from most of the major ICD trials, the survival benefit from ICD implantation in such populations is less well defined. The decision to recommend an ICD should be made on a case-by-case basis based on shared decision making, taking into account patient values and preferences. Age or comorbidity alone should not be a sole exclusion for ICD implantation.
As part of the 2017 AHA/ACC/HRS guideline for management of ventricular arrhythmias and prevention of SCD, a systematic review was performed to specifically assess the impact of primary prevention ICD therapy among older patients and patients with significant morbidities . The following findings were noted:
●Older adults – While the systematic review identified 10 studies of primary prevention ICD use among older adults, because of concerns about overlapping patients between some of the studies, the final "minimal overlap" meta-analysis included four studies with unique patient populations. Compared with patients without ICD implantation, patients who received a primary prevention ICD had a 25 percent reduction in total mortality (hazard ratio [HR] 0.75, 95% CI 0.67-0.83).
●Patients with comorbidities – Among 10 studies of primary prevention ICD use in patients with a variety of comorbidities (including renal disease, chronic obstructive pulmonary disease, and diabetes, among others), ICD implantation for primary prevention was associated with a 28 percent reduction in total mortality (HR 0.72, 95% CI 0.65-0.79), with similar findings in the "minimal overlap" meta-analysis, which included only five studies (HR 0.71, 95% CI 0.61-0.82).
●Patients with renal disease – Patients with chronic kidney disease requiring dialysis have increased mortality and reported high rates of SCD. Among five studies (two post-hoc analyses of randomized trial data and three observational studies) specifically looking at patients with varying degrees of chronic renal disease, primary prevention ICD use was associated with a 29 percent reduction in total mortality (HR 0.71, 95% CI 0.60-0.85). (See "Evaluation of sudden cardiac arrest and sudden cardiac death in dialysis patients".)
Following the systematic review for the 2017 AHA/ACC/HRS guidelines, additional studies have been published evaluating the role of primary prevention ICDs in older patients and those with severe kidney disease. While randomized trial data are absent, clinicians have shown a preference for using the totally subcutaneous ICD (S-ICD) in patients with severe kidney disease (in particular among patients who undergo regular hemodialysis) in order to reduce the risk of intravascular infection in this population .
●In a retrospective multi-center cohort of 300 patients receiving a primary prevention ICD or CRT-D, which included 150 patients ≥80 years old (mean age 82 years, 76 percent with one or fewer comorbidities) and 150 patients <80 years old (mean age 62 years, matched for sex and type of heart disease), similar numbers of patients received an appropriate shock (19.4 percent of older patients versus 21.6 percent of younger patients) with no significant difference in complication rates over mean follow-up of three years . These data suggest that, compared with younger patients, primary prevention ICDs can be safely implanted in selected patients ≥80 years old with few or no comorbidities.
●In patients on dialysis who did not meet standard indications for ICD therapy, the ICD2 trial was published suggesting no benefit from primary prevention ICDs . In the ICD2 trial, 200 patients on dialysis who had an LVEF ≥35 percent without HF symptoms and no documented VT were randomized to ICD implantation with optimal medical therapy or to not receive an ICD. Following randomization of 188 patients, the trial was stopped prematurely due to futility, with no significant improvement among ICD recipients in five-year rates of SCD (9.7 versus 7.9 percent without ICD; HR 1.3, 95% CI 0.5-3.3) or overall survival (50.6 versus 54.4 percent without ICD; HR 1.0, 95% CI 0.7-1.5). While the results may be partially explained by the lower than expected observed rates of SCD in the study (annual rate of 2 percent versus expected rate of 5 to 6 percent), the data do not support extending primary prevention ICD use in dialysis beyond the standard indications. However, it should be noted that transvenous ICDs (often dual chamber systems) were utilized and significant complications occurred, including adverse events related to the ICD implantation procedure in 13 percent and ICD explantation (primarily due to bacteremia) in 7.5 percent. These results cannot necessarily be extrapolated to totally subcutaneous systems, which are frequently utilized in patients on dialysis as they appear to be associated with lower rates of bacteremia than transvenous systems. (See 'Our approach for patients with ischemic cardiomyopathy' above and 'Our approach for patients with nonischemic dilated cardiomyopathy' above and "Subcutaneous implantable cardioverter defibrillators".)
GAPS IN THE GUIDELINES
Possible indications not addressed by guidelines — The HRS/ACC/AHA Expert Consensus Statement on the Use of ICD Therapy in Patients Who Are Not Included or Not Represented in Clinical Trials evaluated important clinical situations for which implantable cardioverter-defibrillator (ICD) therapy might be beneficial in selected populations that were not consistently included in randomized clinical trials and may not be included in guideline documents . This document includes discussion related to the following topics:
●Use of an ICD in patients with an abnormal troponin that is not due to a myocardial infarction (MI).
●Use of an ICD within 40 days after a MI, such as patients with preexisting left ventricular (LV) dysfunction or those requiring non-elective permanent pacing.
●Use of an ICD within the first 90 days after revascularization, such as patients with preexisting LV dysfunction or those requiring non-elective permanent pacing.
●Use of an ICD within the first nine months after initial diagnosis of nonischemic cardiomyopathy.
Recommendations were made based on available evidence as well as consensus opinion. Many clinical scenarios where gaps in evidence exist for ICD therapy are also discussed in the 2013 Appropriate Use Criteria for Implantable Cardioverter-Defibrillators and Cardiac Resynchronization Therapy (CRT) .
Patients undergoing generator replacement with improved LVEF and/or no prior ICD therapies — An additional clinical scenario that is not fully covered in professional society guidelines and consensus documents is the management of patients who have received a primary prevention ICD who have improved or normalized LV function, have never received appropriate ICD therapy, and have either reached the point of elective replacement for their device or require reimplantation after system extraction (ie, due to infection) [74,84-89].
●Among a subset of 1273 patients from the SCD-HeFT trial (624 randomized to ICD, 649 randomized to placebo) who had repeat assessment of left ventricular ejection fraction (LVEF) at a mean of 13.5 months post-randomization, 371 patients (29 percent) showed improvement to LVEF >35 percent (186 [29.8 percent] in ICD group versus 185 [28.5 percent] in placebo group) . There was a similar reduction in all-cause mortality with the ICD in both the LVEF ≤35 percent group (adjusted hazard ratio [HR] 0.64, 95% CI 0.48-0.85) and the LVEF >35 percent group (adjusted HR 0.62, 95% CI 0.29-1.30).
●Among 752 patients from the MADIT-CRT study with mild HF symptoms, 7.3 percent had normalized LVEF to >50 percent after cardiac resynchronization therapy (CRT; so-called "super-responders"); these "super-responders" had a low rate of ventricular arrhythmias, with only 3 of 55 super-responders (5 percent) having treated VT (none requiring an ICD shock) at a mean follow-up of 2.2 years .
●Among 231 patients with an ICD placed for primary prevention, 26 percent had shown enough improvement in LVEF to no longer meet implant criteria at the time of elective generator replacement . Patients in whom LVEF improved had a lower rate of appropriate therapy after generator replacement (2.8 percent per year) than those whose LVEF remained ≤35 percent (10.7 percent per year).
●Among a prospective cohort of 538 patients from the PROSE-ICD study who received a primary prevention ICD and had subsequent reassessment of LVEF, 40 percent of patients had >5 percent improvement in LVEF (over 4.9 years of follow-up), of whom 25 percent had improvement in LVEF to >35 percent . Risk of an appropriate shock was significantly lower (but not completely eliminated) in patients with improved LVEF.
●Among a cohort of 1421 patients with an ICD (49 percent primary prevention, 51 percent secondary prevention) scheduled to undergo generator replacement an average of 3.5 years following initial implantation, 471 patients (33 percent) had received an appropriate shock prior to replacement . Following generator replacement, 435 patients (31 percent) received an appropriate ICD therapy during mean follow-up of 2.7 years. Patients with prior appropriate ICD therapy were significantly more likely to receive additional therapy following generator replacement (HR 3.0, 95% CI 2.4-3.7).
With limited observational data and no randomized trial data to guide decision making for patients with normalized LVEF, clinicians need to weigh a number of factors when planning generator replacement or system reimplantation in such patients, including original indication, possibility of relapse in LV dysfunction, overall prognosis, comorbidities, and patient preference. The 2013 ACC/HRS/AHA Appropriate Use Criteria suggest that replacement of CRT-D with CRT-P devices "may be appropriate" in selected patients who underwent initial ICD implantation for primary prevention indications if substantial improvement in LV function is noted (LVEF now >35 percent, and particularly if ≥50 percent), if no clinically relevant ventricular arrhythmias have occurred . However, due to the paucity of prospective data on this topic, it is also considered appropriate to replace a CRT-D device with a new CRT-D device in situations where LV function has improved .
PROGNOSTIC SIGNIFICANCE OF ICD SHOCKS AND DEVICE PROGRAMMING — Among patients with HF receiving implantable cardioverter-defibrillators (ICDs) for primary prevention in the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), an appropriate shock, as compared with no appropriate shock, was associated with substantially increased all-cause mortality (hazard ratio [HR] 5.7, 95% CI 4.0-8.1) . An inappropriate shock, as compared with no inappropriate shock, was also associated with a significant increase in mortality (HR 2.0, 95% CI 1.3-3.1). The most common cause of death among patients who received any ICD shock was progressive HF. Other studies have also shown that appropriate or inappropriate shocks are associated with increased mortality [92,93]. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy" and "Prognosis of heart failure".)
Several trials have underscored the importance of reducing both appropriate and inappropriate shocks through optimizing ICD programming. The Multicenter Automatic Defibrillator Implantation Trial-Reduce Inappropriate Therapy (MADIT-RIT) study found improved survival in ICD recipients who were randomly assigned to ICD programming with a high rate cutoff and/or long detection times, both of which were associated with fewer ICD shocks compared with conventional programming . The Avoiding Defibrillator Therapies For Non-sustained Arrhythmias In ICD Patients (ADVANCE) III trial found a similar benefit for extended detection time in reducing both appropriate and inappropriate ICD shocks . The 2015 HRS/EHRA/APHRS/SOLAECE Expert Consensus Statement on Optimal Implantable Cardioverter-Defibrillator Programming and Testing outlines the importance of proper ICD programming in reducing unnecessary therapy . (See "Implantable cardioverter-defibrillators: Optimal programming".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Heart failure in adults" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Cardiac implantable electronic devices".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Implantable cardioverter-defibrillators (The Basics)")
●Beyond the Basics topic (see "Patient education: Implantable cardioverter-defibrillators (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●While implantable cardioverter-defibrillators (ICDs) are highly efficacious in the treatment of ventricular tachyarrhythmias and prevention of sudden cardiac death (SCD), they are costly, require ongoing follow-up, and have acute procedural and long-term risks (eg, infection, device and lead malfunction, etc). In addition, only a subset of patients with cardiomyopathy develop sustained ventricular tachyarrhythmias or SCD. Therefore, risk stratification of patients prior to considering ICD therapy is important for targeting therapy to patients at highest risk of SCD and minimizing the number of ICD implantations in patients who are unlikely to benefit. (See 'Risk stratification strategies' above.)
●Recommendations for selecting the optimal patients for ICD therapy are based largely upon the entry criteria in the major trials. Prior to recommending ICD therapy for the primary prevention of SCD, there should be a reasonable expectation of survival with a good functional status for at least one year regardless of the indication for ICD therapy.
•For patients who meet criteria for insertion of an ICD for the primary prevention of SCD, in the absence of a contraindication, we recommend optimizing guideline-directed medical therapy with a beta blocker and either an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker prior to ICD implantation (Grade 1A). (See 'Guideline-directed medical therapy' above and "Overview of the management of heart failure with reduced ejection fraction in adults".)
•For patients with cardiomyopathy due to ischemic heart disease, left ventricular ejection fraction (LVEF) ≤35 percent, and associated heart failure (HF) with New York Heart Association (NYHA) functional class II or III status, we recommend ICD therapy for primary prevention of SCD (Grade 1A). Patients should be evaluated at least 40 days post-myocardial infarction (MI) and more than three months following revascularization. (See 'Ischemic cardiomyopathy' above.)
•For patients with cardiomyopathy due to ischemic heart disease, LVEF ≤30 percent, and NYHA functional class I status, we recommend ICD therapy for primary prevention of SCD (Grade 1B). Patients should be evaluated at least 40 days post-MI and more than three months following revascularization. (See 'Ischemic cardiomyopathy' above.)
•For patients with nonischemic dilated cardiomyopathy, LVEF ≤35 percent, and associated HF with NYHA functional class II or III symptoms, we suggest ICD therapy for primary prevention of SCD rather than optimal medical therapy alone (Grade 2B). ICDs are very effective at reducing total mortality and mortality from SCD, although the benefits of an ICD on total mortality may be diminished in the setting of guideline-directed optimal medical therapy and cardiac resynchronization therapy (CRT). All patients receiving an ICD for primary prevention of SCD should be treated with at least three months of guideline-directed medical therapy prior to ICD implantation. (See 'Nonischemic dilated cardiomyopathy' above.)
•For patients with an LVEF ≤35 percent, HF with NYHA functional class III or IV status, and a QRS duration ≥120 milliseconds, we recommend implantation of a combined CRT-D device (biventricular pacing combined with an ICD) rather than an ICD alone (Grade 1A). Strongest consideration for the CRT component should be given for those patients with left bundle branch block (LBBB) QRS morphology, those with QRS duration ≥150 milliseconds, and those dependent upon ventricular pacing due to atrioventricular block. (See 'Trials of primary prevention ICDs in nonischemic dilated cardiomyopathy' above and "Cardiac resynchronization therapy in heart failure: Indications and choice of system".)
•The role of ICD therapy for primary prevention of SCD in patients with HF and NYHA class IV status who have a narrow QRS complex has not been well-studied, as NYHA class IV patients have generally been excluded from randomized primary prevention ICD trials due to high expected mortality rate. For ambulatory patients with NYHA class IV HF, an LVEF ≤35 percent, and a narrow QRS complex (ie, no dyssynchrony) who are awaiting cardiac transplantation outside the hospital, it is reasonable to consider ICD implantation as a bridge to transplantation. (See 'Class IV heart failure' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, and Scott Manaker, MD, PhD, who contributed to an earlier version of this topic review.
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