After informed consent, patients undergo an initial history and examination conducted by an attending electrophysiologist. Thereafter, patients are generally seen by an ICD nurse every 3 months and are evaluated for the purposes of the study every six months. The physician and/or nurse will record the variables shown in Table D1 on paper forms or directly into REDCap, web-based entry form. At each routine clinic visit (Q 3 month intervals) the ICD will be interrogated and any episodes of ventricular tachycardia lasting >10 beats with a cycle length < 400 ms, ventricular fibrillation, or any anti-tachycardia pacing or ICD therapies will be recorded. If a ventricular arrhythmia is detected blood will be drawn and a digital ECG will be performed as described for the 6 month follow up visits. Further evaluation and treatment of the arrhythmia will be managed independently by the clinical attending physician, who will be notified of the arrhythmia by telephone, with written confirmation and documentation. At alternate visits (every 6 months) the patient will be evaluated by an attending electrophysiologist, a 60cc blood sample will be obtained, a 5-minute digital ECG, and any additional laboratory and diagnostic testing will be performed as clinically indicated.