 1. Data collection will include patient information kept in a database with name kept confidential. Patients will only be identified by number in keeping with privacy laws and practice. In addition to usual patient characteristics, data variables to be collected in both configurations will include: R wave amplitude in sinus rhythm, time to detection in VF, total episode duration time to Vfib detection and charge delivered, number of drop outs undersensing in VF, and follow up R wave amplitude in one month. 