Clinical features that will be examined as potential AE predictors included: age at presentation to the NIH; family history of SD; pre-syncope or syncope; exercise-induced hypotension; ventricular septal thickness; LV outflow obstruction; elevated LV end diastolic pressure; QRS duration; QT interval; VT on ambulatory electrocardiographic monitoring; myocardial ischemia on stress nuclear perfusion imaging; inducible VT; intra-cardiac conduction intervals; and ventricular refractory periods. Statistical significance for the time-to-event analyses will be assessed using the logrank statistic for dichotomous variables and Cox's score statistic for continuous variables.