Inclusion Criteria:  Patients who have sustained VA (VA ≥ 30s or receiving appropriate ICD therapies) are presented to the clinic or admitted to the hospital within 7 days of episodes. The causes of VA are associated with structural heart diseases including ischemic or nonischemic cardiomyopathy (idiopathic cardiomyopathy, hypertrophic cardiomyopathy, cardiac sarcoidosis or amyloidosis, and arrhythmogentic right ventricular dysplasia). Subjects are 18 years of age and older.  Exclusion Criteria:  Advanced comorbid conditions with life expectancy < 1 year. Unwilling or unable to return for required follow-up visits. Female patients who is pregnant or of childbearing potential and not on a reliable form of birth control. Pacing artifacts prevents Skin Sympathetic Nerve Activity (SKNA) analyses. Allergic to skin patch electrodes. Vulnerable populations (fetuses, neonates, pregnant women, prisoners, institutionalized individuals).