Evaluation of ACUITY™ X4 Quadripolar Coronary Venous Leads and RELIANCE™ 4-FRONT Defibrillation Leads

Inclusion Criteria: Subjects indicated for a CRT-D that fulfill one of the following 5 criteria\[1\]: 1. Subject with left ventricular ejection fraction (LVEF) less than or equal to 35%, sinus rhythm, left bundle branch block (LBBB) with a QRS duration greater than or equal to 150 ms, and a NYHA class II, III or ambulatory IV symptoms on Guideline-Directed Medical Therapy (GDMT)\* 2. Subject with LVEF less than or equal to 35%, sinus rhythm, LBBB with a QRS duration 120 to 149 ms, and NYHA class II, III, or ambulatory IV symptoms on GDMT\* 3. Subject with LVEF less than or equal to 35%, sinus rhythm, a non-LBBB pattern with a QRS duration greater than or equal to 150 ms, and NYHA class III/ ambulatory class IV symptoms on GDMT\* 4. Subject with atrial fibrillation and LVEF less than or equal to 35% on GDMT\* if a) the subject requires ventricular pacing or otherwise meets CRT criteria \[listed here\] and b) AV nodal ablation or pharmacologic rate control will allow near 100% ventricular pacing with CRT 5. Subject on GDMT\* who have LVEF less than or equal to 35% and are undergoing new device placement with anticipated requirement for significant (\>40%) ventricular pacing \*GDMT = Guideline-directed medical therapy (formerly known as optimal pharmaceutical therapy (OPT)), represents optimal medical therapy as defined by ACCF/ AHA guideline-recommended therapies (primarily Class I) * Subject is intended to receive the ACUITY X4 LV lead and RELIANCE 4-FRONT RV lead (optional in Study Phase 1) and BSC CRT-D with quadripolar header as their initial (de novo) cardiac implants * Subject is willing and capable of providing informed consent (which can include the use of a legally authorized representative \[LAR\] for documentation of informed consent) and participating in all testing associated with this investigation at an approved center and at the intervals defined by this protocol * Subject is age 18 or above, or of legal age to give informed consent specific to state and national law Exclusion Criteria: Subjects who meet any one of the following criteria will be excluded from this clinical study. * Subject has a known or suspected sensitivity to dexamethasone acetate (DXA) * Subject has a mechanical tricuspid heart valve * Subject is enrolled in any other concurrent study, with the exception of local mandatory governmental registries and observational studies/registries\* that are not in conflict and do not affect the following: * Schedule of procedures for the Study (i.e. should not cause additional or missed visits); * Study outcome (i.e. involve medications that could affect the heart rate of the subject); * Conduct of the Study per good clinical practice (GCP) / International Organization for Standardization (ISO) 14155:2011/ 21 Code of Federal Regulations (CFR) 812, local regulations * Subject is currently on the active heart transplant list * Subject has a documented life expectancy of less than twelve months * Women of childbearing potential who are or might be pregnant at the time of study enrollment or CRT-D System implant (method of assessment upon physician's discretion) * Subjects currently requiring chronic dialysis \*Sponsors of such studies/registries should be informed and Boston Scientific must be informed by the investigator about the parallel conduct of these projects in the subject and of the project's basic nature. The decision if a desired mandatory governmental registry or observational study/ registry is in conflict with this exclusion criterion is up to the enrolling investigator.