The purpose of this study is to evaluate the safety and efficacy of conduction system pacing (CSP) using left bundle branch pacing (LBBP) and atrioventricular junction (AVJ) ablation in patients with end-stage heart failure and permanent atrial fibrillation (AF). Participants who are candidates for heart transplantation or left ventricular assist device (LVAD) implantation will be randomized to either the SYNC group (ICD implantation combined with LBBP and AVJ ablation) or the control group (ICD implantation only). The investigators will compare clinical outcomes, including mortality and heart failure hospitalization, between the two strategies over a 1-year follow-up period.

End-stage heart failure patients often face a poor prognosis due to comorbid permanent AF, which leads to irregular heart rates and worsens ventricular function. While implantable cardioverter-defibrillators (ICDs) are standard for preventing sudden cardiac death, they may not sufficiently prevent heart failure progression in patients with narrow QRS complexes. This study explores a "SYNC" strategy using LBBP and AVJ ablation to achieve ventricular synchronization and heart rate regularization. This is a multicenter, prospective, randomized (1:1), single-blind trial involving 120 participants.

Inclusion Criteria: Participants must have LVEF≤35%, permanent AF for >6 months, and be eligible for ICD implantation while awaiting heart transplantation or LVAD.

Intervention (SYNC Group): Participants receive an ICD with an LBBP lead (Medtronic SelectSecure™ 3830) and undergo AVJ ablation.

Control Group: Participants receive standard ICD implantation with a minimal ventricular pacing setting.

Follow-up: Clinical assessments, echocardiography, and device profiles will be monitored at baseline, 1, 3, 6, and 12 months post-procedure.

Inclusion Criteria:

Candidates for ICD implantation (primary or secondary prevention). Permanent AF (>6 months) unsuitable for or failed catheter ablation. End-stage heart failure considering heart transplant or LVAD. LVEF ≤ 35 within 6 weeks before enrollment. NYHA functional class ≥ II. On GDMT for at least 3 months. Age ≥ 19 years.

Exclusion Criteria:

Existing LVAD or prior heart transplantation. Indications for cardiac resynchronization therapy (CRT). History of mechanical tricuspid valve replacement. Expected survival≤ 12 months. Inability to comply with the study protocol.