TOVA was begun in FY 1999 to identify activities (such as heavy exertion) that trigger ICD discharge, assess factors (such as beta-blockade) that modify the susceptibility to triggering, determine if ICD discharges occurred more frequently in certain periods (i.e., the 3 hours after awakening, on Monday, and in winter), and utilize electrograms recorded prior to ICD discharge to identify sympathetic activation during triggering. TOVA used a cohort design with a nested case-crossover analysis. TOVA characterized triggering in episodes of ICD discharge in 1,140 patients treated in 31 centers nationwide over four years.