What is the indication for an Automated Internal Cardioverter Defibrillator (AICD)?

Indications for Automated Implantable Cardioverter Defibrillator (AICD)

An AICD is indicated for both secondary prevention (survivors of cardiac arrest or sustained ventricular arrhythmias) and primary prevention (high-risk patients with reduced ejection fraction who have not yet experienced life-threatening arrhythmias), with specific timing and clinical criteria that must be met to optimize mortality benefit. 1

Secondary Prevention Indications (Class I)

AICD implantation is recommended for patients who have survived a cardiac arrest or experienced hemodynamically unstable ventricular arrhythmias not due to reversible causes. 2, 1

• Survivors of cardiac arrest due to ventricular fibrillation (VF) or ventricular tachycardia (VT) when the event occurred more than 48 hours after acute myocardial infarction and no reversible cause is identified 2
• Patients with structural heart disease and spontaneous sustained VT, whether hemodynamically stable or unstable 1
• Patients with syncope of undetermined origin who have clinically relevant, hemodynamically significant sustained VT or VF induced at electrophysiological study 1
• Life expectancy must exceed 1 year with reasonable functional status 2, 1

The AVID trial demonstrated a 28% reduction in total mortality and 50% reduction in arrhythmic mortality with ICD therapy compared to antiarrhythmic drugs in secondary prevention patients. 2 The mortality benefit was most pronounced in patients with LVEF between 20-34%. 2

Primary Prevention Indications (Class I)

Post-Myocardial Infarction Patients

AICD is indicated for patients at least 40 days post-MI with LVEF ≤35% and NYHA Class II-III symptoms, or LVEF ≤30% with NYHA Class I symptoms. 1, 3

• Must be at least 40 days post-MI to avoid the early post-infarction period when ICD does not improve survival 2
• Must be at least 90 days post-revascularization (PCI or CABG) 3
• The MADIT-II trial established the LVEF ≤30% threshold with significant survival benefit 3

Non-Ischemic Cardiomyopathy

AICD is indicated for patients with non-ischemic dilated cardiomyopathy, LVEF ≤35%, and NYHA Class II-III symptoms after at least 3 months of optimal medical therapy. 1, 3

• For newly diagnosed non-ischemic cardiomyopathy (<9 months), defer ICD for 3 months unless sustained ventricular arrhythmias occur or permanent pacing is required 1
• The SCD-HeFT trial showed 23% mortality reduction for patients with LVEF ≤35% and NYHA Class II-III, regardless of ischemic versus non-ischemic etiology 3

High-Risk Patients with Preserved EF

AICD is indicated for patients with prior MI, LVEF ≤40%, nonsustained VT, and inducible VF or sustained VT at electrophysiological study. 1

• This indication stems from the MADIT trial, which established prophylactic ICD benefit in this specific population 2

Special Population Indications

Hypertrophic Cardiomyopathy

• AICD implantation is reasonable for patients with one or more major risk factors for sudden cardiac death 1

Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy

• AICD implantation is reasonable for patients with one or more risk factors for sudden cardiac death 1

Adult Congenital Heart Disease

• ICD decisions should not be based solely on ejection fraction but should incorporate multiple risk factors including prior palliative shunts, unexplained syncope, frequent PVCs, QRS duration ≥180 ms, and elevated BNP 2, 1

Neuromuscular Disorders

• Primary and secondary prevention ICDs are recommended for the same indications as for patients with non-ischemic cardiomyopathy if meaningful survival >1 year is expected 2
• AICD is reasonable for Emery-Dreifuss and limb-girdle type IB muscular dystrophies with progressive cardiac involvement 2

Left Ventricular Assist Device (LVAD)

• Patients with pre-existing ICD at time of LVAD placement showed 39% relative-risk reduction in all-cause mortality compared to those without ICD 2
• Patients with history of pre-LVAD ventricular arrhythmias have nearly 10-fold risk of post-LVAD arrhythmias 2

Heart Transplant Recipients

• AICD may be reasonable for patients with severe allograft vasculopathy with LV dysfunction if meaningful survival >1 year is expected 2

Critical Timing Exclusions (Class III)

Do not implant AICD within 40 days of acute MI or within 48 hours of acute ischemia, as early implantation has not shown survival benefit and may increase non-arrhythmic deaths. 2, 3

• The CABG Patch trial showed no survival benefit when ICDs were implanted immediately after coronary bypass surgery 2
• LVEF should be reassessed 6-12 weeks after MI in stable patients on optimized heart failure medication before making ICD decision 2

Device Selection Considerations

Subcutaneous ICD (Class I)

• Recommended for patients who meet ICD criteria but have inadequate vascular access or high infection risk, and do not need pacing for bradycardia, VT termination, or cardiac resynchronization therapy 2

Wearable Cardioverter-Defibrillator (Class IIa-IIb)

• Reasonable for patients with ICD and history of cardiac arrest or sustained VA when ICD removal is required due to infection 2
• May be reasonable for patients at increased SCD risk but temporarily ineligible for ICD, such as those within 40 days of MI, newly diagnosed non-ischemic cardiomyopathy, or awaiting cardiac transplant 2

Essential Prerequisites for All Indications

Before AICD implantation, patients must have all reversible causes excluded, be on optimal medical therapy, and have life expectancy >1 year with reasonable functional status. 2, 1, 3

• Patients with life expectancy ≤6 months are generally not appropriate candidates 2
• Patients ≥75 years still derive benefit, though absolute benefit may be lower due to competing causes of death 3
• Concomitant antiarrhythmic drug therapy is used in 69% of AICD patients to reduce shock frequency 4

Common Pitfalls to Avoid

• Do not implant too early post-MI: The 40-day waiting period is critical, as the DINAMIT trial showed no benefit and possible harm with early implantation 3
• Do not rely solely on EF in congenital heart disease: These patients require multifactorial risk assessment beyond ejection fraction 2, 1
• Do not implant subcutaneous ICD if pacing may be needed: Patients requiring bradycardia pacing, antitachycardia pacing, or CRT should receive transvenous systems 2
• Reassess LVEF after revascularization: Patients who undergo successful revascularization may have improved LVEF, though secondary prevention indications remain valid regardless of post-revascularization EF 2