Strategic MAnagement to Optimize Response To Cardiac Resynchronization Therapy

INTERVENTION: 1:1 randomization will occur in the electronic data capture (EDC) system. Subjects will be randomized between AV Delay programming schemes defined by SmartDelay or a Fixed AV Delay of 120ms in CRT. 1:1 randomization will occur in the electronic data capture (EDC) system. Subjects will be randomized between AV Delay programming schemes defined by SmartDelay or a Fixed AV Delay of 120ms in CRT. CONDITION: Heart Failure, Ventricular Tachycardia, Ventricular Fibrillation PRIMARY OUTCOME: Left Ventricular End Systolic Volume (LVESV) >= 15% at 6 months compared to pre‐implant baseline. SECONDARY OUTCOME: Clinical Composite Endpoint; All‐cause mortality; Heart failure events; NYHA Class; Quality of Life (patient Global Assessment instrument); Six‐minute walk distance; Kansas City Cardiomyopathy Questionnaire; Left‐ventricular ejection fraction (LVEF) INCLUSION CRITERIA: Subject must be indicated to receive a de novo quadripolar Boston Scientific Cardiac Resynchronization Therapy Defibrillator (CRT‐D) in conjunction with an ACUITY X4 LV lead. This includes subjects who are indicated to receive an upgrade to a BSC X4 CRT‐D from a previously implanted device. In order to achieve a homogenous population for the study, qualifying subjects are those with heart failure who meet indications for use defined as those subjects who receive stable optimal pharmacologic therapy (OPT) for heart failure and who meet any one of the following classifications: ‐ Moderate to severe heart failure (NYHA Class III‐IV) with EF <= 35% and QRS duration >=120 ms ‐ Left bundle branch block (LBBB) with QRS duration >=150 ms, EF <=30%, and mild (NYHA Class II) ischemic or nonischemic heart failure Subject is age 20 or above Subject is willing and capable of providing informed consent Subject is willing and capable of complying with