SyncAV Post-Market Trial

Inclusion Criteria: 1. Scheduled to receive a new CRT implant or an upgrade (Abbott CRT device and Abbott Quadripolar LV lead) from an existing implantable cardioverter defibrillator/pacemaker implant with no more than 10% RV pacing at the last device interrogation, no prior LV lead placement, AND meet the following additional criteria: 1. Mild to severe heart failure despite optimal medical therapy for at least 3 months prior to signing consent. Optimal medical therapy is defined as maximal tolerated dose of beta-blockers and a therapeutic dose of angiotensin-converting enzyme inhibitor, angiotensin receptor blocker, or aldosterone antagonist 2. LVEF ≤ 35% based on a prior standard of care echocardiogram 3. Left bundle branch block (LBBB) as documented on an ECG. Criteria for complete LBBB should include, i. QRS duration ≥ 120 ms ii. QS or rS pattern in leads V1 iii. mid-QRS notching or slurring in leads I, aVL, V5, and V6 iv. Absence of Q-wave in leads V5 and V6 d. Intact AV conduction (PR interval ≤ 280 ms on surface ECG) 2. At least 18 years old, or of legal age and willing and capable to give informed consent specific to each country and national laws 3. Willing and able to comply with the prescribed follow-up tests and schedule of evaluations Exclusion Criteria: 1. Recent myocardial infarction or unstable angina within 40 days prior to signing consent 2. Recent cardiac revascularization (angioplasty, stent or bypass graft) in the 4 weeks prior to signing consent or planned within 3 months following consent 3. Cerebrovascular accident or transient ischemic attack in the 3 months prior to signing consent 4. Any other therapeutic cardiovascular procedure (transcatheter aortic valve replacement, MitraClip, cardiac surgery, left atrial appendage closure, patent foramen ovale closure, or any ablation procedures) in the 3 months prior to signing consent 5. Permanent or persistent AF at the time of signing consent 6. Paroxysmal AF with at least one cardioversion within 60 days prior to signing consent 7. Prior CRT device implant 8. Prior His Bundle pacing implant or plan to have His Bundle pacing implant 9. Pregnant or breastfeeding at the time of signing consent 10. Incapacitated or unable to read or write 11. Undergone cardiac transplantation or have a classification of Status 1 for cardiac transplantation or consideration for transplantation during the study follow-up period 12. Life expectancy \< 12 months due to any condition 13. Unavailable for at least 12 months of follow-up visits 14. Enrolled in or intend to participate in a clinical drug and/or device study during this clinical trial which could confound the results of this trial as determined by Abbott