Intracardiac defibrillator (ICD) is useful in which of the following ?

Ref. AHA guidelines   ICD Indications (AHA Guidelines) Class I indications (ie, the benefit greatly outweighs the risk, and the treatment should be administered) are as follows: Structural heart disease, sustained VT Syncope of undetermined origin, inducible VT or VF at electrophysiologic study (EPS) Left ventricular ejection fraction (LVEF) ≤35% due to prior MI, at least 40 days post-MI, NYHA class II or III LVEF ≤35%, NYHA class II or III LVEF ≤30% due to prior MI, at least 40 days post-MI LVEF ≤40% due to prior MI, inducible VT or VF at EPS   Class IIa indications (ie, the benefit outweighs the risk and it is reasonable to administer the treatment) are as follows: Unexplained syncope, significant LV dysfunction, nonischemic cardiomyopathy Sustained VT, normal or near-normal ventricular function Hypertrophic cardiomyopathy with 1 or more major risk factors Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) with 1 or more risk factors for sudden cardiac death (SCD) Long QT syndrome, syncope or VT while receiving beta-blockers Nonhospitalized patients awaiting heart transplant Brugada syndrome, syncope or VT Catecholaminergic polymorphic VT, syncope or VT while receiving beta-blockers Cardiac sarcoidosis, giant cell myocarditis, or Chagas disease