ADVANCE-D: Antitachycardia Pacing (ATP) Delivery for Painless Implantable Cardioverter Defibrillator (ICD) Therapy

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.

Main objective: Compare \& quantify efficacy of two different sequences of burst ATP strategies for the termination of ventricular tachycardia (with Cycle Lenght (CL) of 240ms-320ms) from baseline to 12 months post randomisation in patients who are treated with ATP -8 pulses, 88% versus patients who are treated with ATP -15 pulses, 88% Secondary objectives: * Estimate the efficacy of ATP in successfully treating FVT episodes for patients in primary and secondary prevention * Estimate acceleration rate or degeneration of ATP therapy for treating spontaneous FVT episodes in the ATP 15 vs 8 arm * Compare the likelihood of syncopal events associated with spontaneous FVT episodes * Estimate the percent reduction in number of shocks delivered per patient for treating spontaneous FVT episodes * Evaluate different possible predictors of ATP success: VT rate, underlying disease, Anti-Arrhythmic Drugs (AAD), infarct zone, etc.