 1. Procedures to be followed would include screening of all eligible patients undergoing implant of a Medtronic defibrillator for either primary or secondary prevention. If patients meet inclusion criteria they would then undergo informed consent and if willing be enrolled in the study. Defibrillator implant and testing would be performed as per usual practice of the implanting physician. The RV lead will be placed at the RV apex as is usual for regular implantation of devices. However, if a lead is placed elsewhere, the patient will need to be withdrawn from the study. 