In this study, subjects will be randomized to receive a subcutaneous implantable cardioverter defibrillator or Conventional Medical Therapy (CMT). Randomization will be stratified by enrolling site, in a 2:1 (S-ICD:CMT) scheme. Length of follow-up for each subject will be dependent on the date of entry into the study, since all subjects will be followed to a common study termination date.