 The SENSE-AF study aims to determine the performance of the OptiSense lead in sensing fine episodes of Atrial TachyarrhythmiaAtrial Fibrillation ATAF and rejecting Far-Field R Wave FFRW. The performance of the lead will be measured as a difference in device-determined time in ATAF and surface-ECG determined time in ATAF. This measurement will be compared to the control group which will be randomized to receive SJMs TendrilTM RA leads. 