Its aims are fourfold: 1) To accurately risk stratify a large cohort of implantable cardioverter-defibrillator (ICD) patients for ICD shock risk and mortality using traditional risk markers as well as genetic markers 2) To find a link between repolarization biomarkers and genetic markers of calcium metabolism. 3) To compare invasive and noninvasive electrophysiologic (EP) testing systematically 4) To assess temporal changes of typical noninvasive risk stratifiers and their prognostic implication.