An implantable cardioverter defibrillator (ICD) is a permanent device in which a lead (wire) inserts into the right ventricle and monitors the heart rhythm. It is implanted similar to a pacemaker and the generator lays in the upper chest area. Therapies are delivered in the form of anti-tachycardia pacing (ATP) or shocks to convert to sinus rhythm from sustained ventricular tachycardia or ventricular fibrillation, both of which are life-threatening rhythms.

For primary prevention of sudden cardiac death, ICDs are indicated:

1. Patients with a prior myocardial infarction and a left ventricular ejection fraction of < 30% (MI must have been at least 40 days prior in order to allow time for recovery of LV systolic function)

2. Patients with systolic heart failure (New York Heart Association functional class II or III) and an ejection fraction < 35%. Optimal medical therapy must be present and at least 3 months must have elapsed in case the systolic function recovers to an ejection fraction > 35% in both non-ischemic cardiomyopathy patients and ischemic cardiomyopathy patients who underwent bypass surgery.

For secondary prevention of sudden cardiac death, ICDs are indicated:

1. Patients with documented cardiac arrest from sustained ventricular tachycardia or ventricular fibrillation or documented hemodynamically stable sustained ventricular tachycardia even if the left ventricular ejection fraction is > 35%, as long as no reversible cause is identified. The above must not be within 48 hours of an acute coronary syndrome.