The purpose of this study is to estimate and quantify the difference in efficacy of two sequences of ATP therapies (burst 15 pulses, 88% versus burst 8 pulses, 88%) during an episode of spontaneous rhythms classified as fast ventricular tachycardia (FVT) via ventricular fibrillation (VF) in patients who have a Class I or II A indication for ICD implantation, and thus to promote the "painless" therapy aspect of ICD treatment and improve quality of life outcomes for patients.