LBBAP vs. CS Pacing for CRT in Permanent Atrial Fibrillation and Heart Failure (SYNC-AF)

Left Bundle Branch Area Pacing Versus Coronary Sinus Pacing for Cardiac Resynchronization Therapy for Patients With Permanent Atrial Fibrillation and Heart Failure: The SYNC-AF Trial

This is a prospective, multicenter, randomized controlled trial comparing Left Bundle Branch Area Pacing (LBBAP)-based cardiac resynchronization therapy (CRT) with conventional coronary sinus (CS) lead-based CRT in patients with permanent atrial fibrillation (AF) and heart failure (HF) who meet indications for CRT device implantation.

Atrial fibrillation and heart failure frequently coexist, and both rapid heart rate and its irregularity contribute to worsening cardiac function. Atrioventricular junction (AVJ) ablation combined with CRT (biventricular pacing) has been established as an effective strategy for rate control and cardiac resynchronization in this population, supported by Class I recommendation in the 2021 ESC guidelines. However, conventional biventricular CRT via the CS lead can induce artificial electrical dyssynchrony, particularly in patients with a narrow QRS complex, potentially limiting its benefit.

Conduction system pacing (CSP), including LBBAP, has emerged as a physiologic alternative that directly stimulates the native conduction system, preserving synchronous ventricular activation. Recent evidence (ALTERNATIVE-AF trial) suggests CSP may be superior to biventricular CRT in permanent AF patients undergoing AVJ ablation. However, no randomized controlled trial has directly compared LBBAP-based CRT with CS lead-based CRT in this specific population.

The SYNC-AF trial will randomize 44 patients (22 per arm) to either LBBAP or CS pacing for CRT. The primary endpoint is change in left ventricular ejection fraction (LVEF) at 12 months as assessed by echocardiography in a blinded core laboratory. Secondary endpoints include changes in QRS duration, major adverse clinical events, device/procedure-related complications, and ventricular arrhythmia burden.

ECHOCARDIOGRAPHIC CORE LAB:

All echocardiographic assessments (LVEF, LVESV, LVEDV, etc.) are performed and interpreted by a blinded independent core laboratory at Severance Hospital to ensure objective and consistent measurement.

FOLLOW-UP SCHEDULE:

Screening (implant day) → Visit 1 (2 weeks-1 month) → Visit 2 (3 months ±3 months) → Visit 3 (6 months ±3 months) → Visit 4 (12 months ±3 months).

STATISTICAL ANALYSIS:

Primary analysis follows the Intention-To-Treat (ITT) principle. Per-Protocol (PP) analysis will be performed as sensitivity analysis. The primary endpoint (LVEF change at 12 months) will be compared using Student's t-test or Wilcoxon rank-sum test. Time-to-event analyses will use Kaplan-Meier survival curves with log-rank test and Cox proportional hazards model.

SAMPLE SIZE:

44 patients total (22 per arm). Based on the assumption of an absolute 10% greater improvement in LVEF with LBBAP-CRT vs. BiV-CRT, with 80% power and 5% two-sided alpha, with 10% dropout allowance.

PARTICIPATING CENTERS:

Multiple centers in the Republic of Korea (at least 4 centers), led by Severance Hospital, Yonsei University College of Medicine.

Inclusion Criteria:

1. Age ≥19 years
2. Indication for CRT (CRT-P or CRT-D) device implantation per current guidelines
3. Permanent atrial fibrillation (with or without planned AVJ ablation)
4. Ability to understand the purpose of the study and provide written informed consent

Exclusion Criteria:

1. Prosthetic tricuspid valve
2. Prior myocardial infarction involving the interventricular septal area
3. Life expectancy less than 12 months
4. Unable to comply with planned 12-month follow-up for any reason
5. Pregnancy
6. History of heart transplantation
7. Persistent left superior vena cava (PLSVC)