Initial Chronic Human Validation Study: Subcutaneous Implantable Cardioverter Defibrillator (S-ICD) System

Inclusion Criteria: * replacement of an existing transvenous implantable cardioverter defibrillator (ICD) system * American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) Class I or II indications for ICD implantation * Age \>= 18 years * Appropriate pre-operative Electrocardiogram (ECG) as measured with a specially developed template Exclusion Criteria: * Subjects unable or unwilling to provide informed consent * Any condition which precludes the subject's ability to comply with the study requirements * Females who are pregnant or lactating and pre-menopausal women who are unwilling to use adequate birth control for the duration of the study * Participation in another investigational device trial at any time during the conduct of the S-ICD system trial without written consent from the sponsor. * Patients with a serious medical condition and life expectancy of less than one year. * Patients with documented spontaneous and frequently recurring ventricular tachyarrhythmias (VT) that is reliably terminated with anti-tachycardia pacing * Patients with existing epicardial patches or subcutaneous electrodes in the left thoracic quadrant * Patients with chronic renal failure, i.e. with a creatinine level of \>2.5 mg/dl unless prescribed drug therapy known to increase creatinine levels in which case the value should be \<= 3mg/dl