6. Participants with a history of sustained ventricular tachycardia or aborted ventricular fibrillation or with a history of atrioventricular (AV) nodal or sinoatrial (SA) nodal dysfunction for which a pacemaker/implantable cardioverter-defibrillators [ICD] is indicated but not placed (participants who do have a pacemaker/ICD are allowed on study)