What are the indications for implantable cardioverter-defibrillator (ICD) in patients with low ejection fraction (EF)?

Indications for ICD in Patients with Low Ejection Fraction

ICD implantation is recommended for patients with LVEF ≤35% who are at least 40 days post-MI and 90 days post-revascularization with NYHA class II-III symptoms, or LVEF ≤30% with NYHA class I symptoms, provided they are on guideline-directed medical therapy and have expected survival >1 year with good functional status. 1

Primary Prevention Indications by Etiology

Ischemic Cardiomyopathy (Post-MI)

LVEF ≤30%:

• NYHA Class I, II, or III symptoms qualify for ICD at least 40 days post-MI and 90 days post-revascularization 1, 2
• This represents the strongest indication with Class I, Level A evidence 1

LVEF 31-35%:

• NYHA Class II or III symptoms meet criteria for ICD placement 1, 2
• Must be at least 40 days post-MI and 90 days post-revascularization 1

LVEF ≤40% with inducible VT:

• Patients with nonsustained VT, prior MI, and inducible sustained VT at electrophysiologic study qualify for ICD 1
• This indication applies even with higher EF when arrhythmia inducibility is demonstrated 1

Non-Ischemic Dilated Cardiomyopathy

LVEF ≤35%:

• NYHA Class II or III symptoms after at least 3 months of optimal medical therapy 1, 2
• Evidence is slightly less robust than for ischemic cardiomyopathy, but still represents a Class I indication 1

LVEF ≤30-35%:

• Primary prevention indication with NYHA Class II-III symptoms on chronic GDMT 1
• Reasonable expectation of survival with good functional status for >1 year required 1

Secondary Prevention Indications

Cardiac arrest survivors:

• ICD indicated for survivors of VF or hemodynamically unstable sustained VT after excluding reversible causes 1
• This applies regardless of ejection fraction 2

Spontaneous sustained VT:

• ICD indicated in patients with structural heart disease and spontaneous sustained VT, whether hemodynamically stable or unstable 1

Post-ACS ventricular arrhythmias:

• ICD implantation is reasonable for clinically relevant ventricular arrhythmias occurring >48 hours and within 40 days post-MI 1
• Sustained VT/VF >48 hours after STEMI (not due to transient/reversible causes) warrants ICD before discharge 1

Critical Timing Requirements

The 40-day rule:

• Do not implant ICD within 40 days of acute MI 1, 2
• Early implantation has not shown survival benefit and may increase non-arrhythmic deaths 1
• The DINAMIT trial demonstrated a 58% reduction in arrhythmic deaths but this was offset by increased non-arrhythmic mortality 1

The 90-day post-revascularization rule:

• Wait at least 90 days after revascularization (PCI or CABG) before ICD implantation 1
• This allows time for potential LVEF recovery with optimal medical therapy 1

Non-ischemic cardiomyopathy timing:

• Defer ICD for 3 months in newly diagnosed non-ischemic cardiomyopathy (<9 months) unless sustained ventricular arrhythmias occur 2
• This waiting period allows assessment of response to GDMT 2

Essential Prerequisites

Guideline-directed medical therapy optimization:

• GDMT must be optimized before ICD implantation to assess whether LVEF improves 1
• Contemporary GDMT includes beta-blockers, ACE inhibitors/ARBs/ARNIs, mineralocorticoid receptor antagonists, and SGLT2 inhibitors 3
• These medications themselves reduce sudden cardiac death risk, potentially altering the benefit-risk calculus for ICD 3

Life expectancy requirement:

• Expected survival must exceed 1 year with reasonable functional status 1, 2
• ICD and CRT-D are not indicated when comorbidities or frailty limit survival with good functional capacity to <1 year 1
• Projected life expectancy ≤6 months provides no mortality benefit from ICD 4

Special Populations and Considerations

Genetic arrhythmogenic cardiomyopathy:

• ICD is reasonable with high-risk features of sudden death and EF ≤45% 1
• Note the higher EF threshold compared to other indications 1

Patients ≥75 years:

• Still derive benefit from ICD implantation, though absolute benefit may be lower due to competing causes of death 2

Congenital heart disease:

• Do not apply LVEF cutoffs alone to these patients 2
• Requires multifactorial risk assessment beyond ejection fraction 2

Common Pitfalls and Caveats

The absence of syncope does not eliminate arrhythmia risk:

• Many patients with severe LV dysfunction experience their first arrhythmic event as sudden death 4
• Among non-ischemic cardiomyopathy patients with mean EF 21%, 40% received appropriate ICD shocks during follow-up despite no prior syncope 4

LVEF improvement after ICD implantation:

• Patients whose LVEF improves to >35% during follow-up have significantly lower rates of appropriate ICD therapy (3.3% vs 7.2% per year) 5
• However, they still receive appropriate therapies, and inappropriate shock rates remain similar 5
• Do not remove ICD based on LVEF improvement alone 5

Very low EF (<15-20%) considerations:

• When LVEF is severely depressed, the prevailing mode of cardiac death is often non-sudden or related to bradyarrhythmias/electromechanical dissociation rather than ventricular tachyarrhythmias 4
• This may reduce the relative benefit of ICD in extremely low EF populations 4

The early post-MI period:

• Risk of sudden cardiac death is highest in the first month post-MI 1
• However, routine early ICD implantation has not improved survival 1
• Manage early ventricular arrhythmias first with beta-blockers and/or antiarrhythmic therapy 1

Wearable cardioverter-defibrillator:

• Usefulness of temporary wearable cardioverter-defibrillator in patients with LVEF ≤35% early after MI is uncertain for improving survival 1

Disparities in ICD utilization:

• Black patients are less likely to receive ICD than White patients even when meeting criteria (OR 0.80) 6
• Only 16.9% of eligible Veterans with LVEF ≤35% post-MI actually received ICD placement 6
• Half of patients on optimal GDMT still did not receive indicated ICD 6