Strategic Management to Optimize Response To Cardiac Resynchronization Therapy

• 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 BSC US 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 ≥ 130 ms, EF ≤ 30%, and mild (NYHA Class II) ischemic or nonischemic heart failure or asymptomatic (NYHA Class I) ischemic heart failure

• Subject is age 18 or above, or of legal age to give informed consent specific to each country and national laws

• Subject is willing and capable of providing informed consent

• Subject is willing and capable of complying with visits and procedures as defined by this protocol