All patients will receive an implantable cardioverter defibrillator OVATIO™ DR model 6550 or a later Sorin Group device offering the same functions. After Enrolment visit but before implant, patients will be randomized in two arms according to the parallel study design. Whenever possible before implant there will be the first Holter recording for the Tvar risk stratification procedure. In case Tvar recording could not be performed before implant it has to be performed before patient leaves the hospital post implant in unpaced rhythm.