The purpose of this study is to determine the proportion of patients who are undergoing Biventricular (BiV) Implantable Cardioverter Defibrillator (ICD) implantation in whom optimization of atrioventricular (AV) delay is not possible due to prolonged inter-atrial/intra-atrial delay. These patients would benefit from left atrial pacing, and if a significant number of patients fall into this group, it may be beneficial to develop a left atrial lead.