ICD vs Amiodarone for Heart Failure: Which Prevents Sudden Death?

Research-informed explainer — last updated April 12, 2026

If you have heart failure with a weakened heart — an ejection fraction of 35% or below — and your symptoms are stable with optimal medical therapy, the evidence strongly favors an implantable cardioverter-defibrillator (ICD) over amiodarone to prevent sudden cardiac death. The landmark SCD-HeFT trial showed that ICD reduced all-cause mortality by 23% while amiodarone provided no survival benefit compared to placebo. Amiodarone still has a role in managing arrhythmia symptoms and as adjunctive therapy, but it should not be considered a substitute for an ICD in patients who meet the criteria for device therapy.

This explainer draws on peer-reviewed research from heart failure and electrophysiology specialists listed in the Convene directory. Their published work includes the SCD-HeFT trial, the COMPANION cardiac resynchronization trial, the ACC/AHA/HRS 2008 device therapy guidelines, and the 2021 ESC heart failure guidelines.

What is sudden cardiac death in heart failure?

Sudden cardiac death (SCD) is death from an unexpected cardiac cause — usually a chaotic, lethal heart rhythm called ventricular fibrillation — within an hour of the onset of symptoms. It accounts for roughly 50% of deaths in heart failure patients, making it the single most common way people with heart failure die.

The risk is highest in patients with significantly reduced ejection fraction. When the heart muscle is weak and dilated, the electrical system becomes unstable. Ventricular tachycardia (a rapid but organized rhythm) can degenerate into ventricular fibrillation, which is rapidly fatal without intervention. Both a device that can deliver an immediate shock (ICD) and drugs that suppress the abnormal electrical signals (antiarrhythmics like amiodarone) have been studied as prevention strategies.

What the two approaches do

An implantable cardioverter-defibrillator (ICD) is a small device implanted under the skin below the collarbone, with leads that run into the heart chambers. It continuously monitors the heart rhythm. If it detects ventricular fibrillation or dangerous ventricular tachycardia, it delivers a shock within seconds — terminating the lethal rhythm. ICD implantation is a minor surgical procedure done under local anesthesia with sedation, typically with one overnight stay. Modern ICDs also function as pacemakers and can record and store rhythm data for review.

Amiodarone is an antiarrhythmic drug taken by mouth or given intravenously in emergencies. It suppresses the abnormal electrical activity that triggers life-threatening rhythms. It is highly effective at terminating and preventing arrhythmias in the short term. The problem is its side effect profile over years of use: thyroid dysfunction (both overactive and underactive thyroid), pulmonary toxicity (lung scarring), liver abnormalities, peripheral neuropathy, and sensitivity to sunlight. These toxicities occur in a meaningful fraction of patients on long-term amiodarone and require regular monitoring.

At a glance

What SCD-HeFT found

The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) enrolled 2,521 patients with NYHA class II or III heart failure and ejection fraction of 35% or below. Patients were randomized to three groups: placebo, amiodarone, or a shock-only single-lead ICD. The trial followed patients for a median of 45.5 months.

The primary endpoint was all-cause mortality. At five years, mortality was 29% in the placebo group, 28% in the amiodarone group, and 22% in the ICD group. The ICD reduced mortality by 23% relative to placebo (hazard ratio 0.77, p=0.007). Amiodarone showed no significant survival benefit compared to placebo — and in patients with NYHA class III heart failure, amiodarone appeared to worsen outcomes compared to placebo [1].

This trial settled the debate about whether amiodarone could substitute for an ICD in eligible patients. It cannot. The device prevents sudden death by terminating the lethal rhythm when it occurs; amiodarone reduces the frequency of the rhythm but cannot reliably prevent all events or resuscitate the patient when a fatal rhythm does occur.

The CRT-D question: when to add resynchronization

Some heart failure patients have both a severely reduced ejection fraction and a conduction delay (widened QRS on EKG, particularly left bundle branch block). In this subgroup, cardiac resynchronization therapy — synchronized pacing of both ventricles — can improve heart function and symptoms. CRT can be added to an ICD (CRT-D) in eligible patients.

The COMPANION trial, led by William Abraham of Ohio State University, enrolled 1,520 patients with NYHA class III or IV heart failure, ejection fraction below 35%, and prolonged QRS duration. It randomized patients to optimal medical therapy alone, optimal therapy plus CRT without a defibrillator (CRT-P), or optimal therapy plus CRT with a defibrillator (CRT-D). CRT-D reduced the composite of all-cause mortality or hospitalization by 40% compared to optimal medical therapy alone [3].

For patients who meet both ICD criteria (EF ≤35%) and CRT criteria (QRS ≥130 ms with LBBB morphology), a CRT-D device combines the mortality benefit of the defibrillator with the functional benefit of resynchronization.

What the guidelines say

The ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities — co-authored by Kenneth Ellenbogen of VCU's Pauley Heart Center — established the framework for ICD indications that is still largely in use today [4]. A Class I indication (strongest recommendation) applies to:

• Patients with EF ≤35% due to ischemic heart disease who are at least 40 days post-myocardial infarction, on optimal medical therapy, and have NYHA class II or III symptoms
• Patients with nonischemic dilated cardiomyopathy and EF ≤35%, NYHA class II or III symptoms, on optimal medical therapy for at least three months
• Survivors of ventricular fibrillation or sustained ventricular tachycardia

The three-month waiting period for optimal medical therapy matters. Some patients whose ejection fraction is measured early after a heart attack or new diagnosis may recover function with beta-blockers, ACE inhibitors, and SGLT2 inhibitors. Repeat echocardiography after three to six months of guideline-directed therapy is standard before committing to ICD implantation, because an EF that recovers above 35% with treatment changes the risk-benefit calculus.

The 2021 ESC heart failure guidelines — referenced in research from Donna Mancini — continue to recommend ICD therapy for primary prevention of sudden death in patients with HFrEF who meet the above criteria, alongside a comprehensive framework for device therapy within the broader context of optimal medical management [5].

The problem of inappropriate shocks

ICDs save lives, but they also deliver shocks that are sometimes unnecessary. An inappropriate shock — triggered by a rapid but non-lethal rhythm like supraventricular tachycardia or atrial fibrillation with fast ventricular response — is physically painful and psychologically distressing.

In SCD-HeFT and subsequent registries, inappropriate shocks occurred in roughly 10–15% of patients over follow-up. Research from the SCD-HeFT investigators showed that patients who received any ICD shock — appropriate or inappropriate — had significantly higher subsequent mortality than those who never received a shock [2]. The shocks themselves may not cause harm, but they serve as markers for underlying disease progression.

This has led to refinement of ICD programming, with longer detection intervals before shocking to allow time for self-terminating rhythms to resolve. Modern programming has substantially reduced inappropriate shock rates without increasing the rate of untreated dangerous rhythms.

When amiodarone is still used

Despite the SCD-HeFT results, amiodarone remains an important drug in heart failure care — just in a different role.

As an adjunct to ICD therapy in patients with frequent shocks. Some ICD patients have ventricular storm — multiple episodes of ventricular tachycardia triggering repeated shocks. Amiodarone reduces the frequency of these episodes, improving quality of life while the device handles any rhythm that breaks through.

In patients who are not candidates for ICD. Some patients have advanced heart failure with limited life expectancy, significant comorbidities that make surgery too risky, or have chosen a more conservative management approach. In these patients, amiodarone can reduce symptomatic arrhythmia burden without the goal of mortality reduction.

For acute arrhythmia management. Intravenous amiodarone is a first-line drug for ventricular tachycardia or fibrillation in the acute setting — in the hospital or during resuscitation.

While awaiting reassessment of eligibility. If a patient's ejection fraction is newly reduced and they are starting guideline-directed therapy, short-term amiodarone can manage any arrhythmias during the waiting period before a repeat EF assessment.

Questions to ask your cardiologist

• What is my current ejection fraction, and has it been rechecked after at least three months of optimal medical therapy?
• Do I have ischemic or nonischemic cardiomyopathy, and does that affect my ICD eligibility timeline?
• Do I have a wide QRS on my EKG that might qualify me for CRT-D instead of ICD alone?
• If I already have an ICD, is my programming set to minimize inappropriate shocks?
• If I am on amiodarone long term, am I getting regular thyroid, liver, and pulmonary function testing?
• What is my life expectancy and overall functional status, and how should that inform the decision about device therapy?

The bottom line

For patients with stable heart failure and an ejection fraction at or below 35%, the SCD-HeFT trial established definitively that an ICD reduces all-cause mortality by 23% while amiodarone does not. This evidence is now the foundation of cardiology guidelines worldwide. If you have heart failure with reduced ejection fraction and have been on optimal medical therapy for at least three months, a conversation about ICD eligibility is warranted. Amiodarone remains a valuable drug — but as a complement to device therapy, not a substitute for it.