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

Study Overview

• Status: Not yet recruiting
• Conditions: Heart Failure; Cardiomyopathies; Atrial Fibrillation (AF)
• Intervention / Treatment: Device: Left Bundle Branch Area Pacing (LBBAP) for CRT; Device: Coronary Sinus (CS) Lead-Based Biventricular CRT

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 44
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Tae-Hoon Kim, Professor; Phone Number: +82-2-2228-8467; Email: thkimcardio@yuhs.ac

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

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)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: LBBAP Group; Participants undergo CRT device implantation (CRT-P or CRT-D) with Left Bundle Branch Area Pacing (LBBAP) as the left ventricular lead strategy. LBBAP is attempted first; if not feasible, crossover to CS lead is permitted. AVJ ablation is performed per clinical indication.	Device: Left Bundle Branch Area Pacing (LBBAP) for CRT; CRT device (CRT-P or CRT-D) implantation using LBBAP as the left ventricular pacing lead. A pacing lead is advanced through the interventricular septum to achieve left bundle branch area capture, confirmed by pacing parameters and electrocardiographic criteria (RBBB-like pattern with short R-peak latency in V5/V6). RV lead is implanted in standard fashion. AVJ ablation may be performed per clinical indication.
Active Comparator: CS Pacing Group; Participants undergo CRT device implantation (CRT-P or CRT-D) with conventional Coronary Sinus (CS) lead-based pacing as the left ventricular lead strategy. AVJ ablation is performed per clinical indication.	Device: Coronary Sinus (CS) Lead-Based Biventricular CRT; CRT device (CRT-P or CRT-D) implantation using a conventional coronary sinus (CS) lead as the left ventricular pacing lead. The CS lead is advanced via the coronary sinus into a lateral or posterolateral cardiac vein to achieve biventricular pacing. RV lead is implanted in standard fashion. AVJ ablation may be performed per clinical indication.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change from Baseline Left Ventricular Ejection Fraction (LVEF) at 12 Months	Change in left ventricular ejection fraction (LVEF) from baseline to 12 months post-implantation, as measured by transthoracic echocardiography performed and interpreted by a blinded independent central core laboratory. LVEF is assessed using the biplane Simpson method.	Baseline (at the time of device implantation) and 12 months post-implantation

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Proportion of patients with absolute LVEF increase ≥5% at 12 months	Echocardiographic CRT response defined as absolute improvement in LVEF of ≥5% or ≥10% from baseline at 12 months, assessed by blinded core lab.	12 months post-implantation
Proportion of patients with absolute LVEF increase ≥10% at 12 months	Echocardiographic CRT response defined as absolute improvement in LVEF of ≥5% or ≥10% from baseline at 12 months, assessed by blinded core lab.	12 months post-implantation
Change in QRS Duration From Baseline	QRS duration measured from surface ECG in milliseconds.	Immediately post-implant and at 12 months
Time to First Treated Ventricular Arrhythmia	Time from randomization to first detection of treated ventricular arrhythmia (VT/VF) recorded by the implanted device within 12 months.	Up to 12 months
Composite of All-Cause Death and Heart Failure Hospitalization	Clinical events adjudicated by an independent committee. Heart failure hospitalization defined as unplanned outpatient/ED visit or inpatient admission with HF signs/symptoms requiring intravenous therapy.	Up to 12 months (first occurrence)
All-cause mortality	Clinical events adjudicated by an independent committee. Heart failure hospitalization defined as unplanned outpatient/ED visit or inpatient admission with HF signs/symptoms requiring intravenous therapy.	Up to 12 months (first occurrence)
Heart failure hospitalization	Clinical events adjudicated by an independent committee. Heart failure hospitalization defined as unplanned outpatient/ED visit or inpatient admission with HF signs/symptoms requiring intravenous therapy.	Up to 12 months (first occurrence)
Cardiovascular death	Clinical events adjudicated by an independent committee. Heart failure hospitalization defined as unplanned outpatient/ED visit or inpatient admission with HF signs/symptoms requiring intravenous therapy.	Up to 12 months (first occurrence)
Immediate procedural success rate of LBBAP lead implantation	Successful LBBAP lead placement defined by achievement of left bundle branch capture with acceptable pacing threshold (≤1.5V/0.5ms), impedance (300-1200Ω), and electrocardiographic criteria (RBBB pattern, short R-peak latency in V5/V6).	Immediately after the implantation procedure
Lead capture loss rate at 12 months	Loss of left bundle branch capture or inability to maintain pacing threshold <2.5V/0.5ms at 12 months.	12 months post-implantation
Composite Rate of Worsening Heart Failure by Echocardiographic Criteria	Composite endpoint defined as ≥5% absolute decrease in LVEF from baseline or ≥15% increase in LVESV from baseline during follow-up.	Up to 12 months
Device and Procedure-Related Complications	All device/procedure-related complications and reinterventions occurring up to 12 months, adjudicated by an independent events committee.	Up to 12 months (device/procedure-related complications within 7 days for acute; up to 12 months for chronic)
Reintervention Rate	All device/procedure-related complications and reinterventions occurring up to 12 months, adjudicated by an independent events committee.	Up to 12 months

Collaborators and Investigators

• Sponsor: Yonsei University

Study record dates

Study Major Dates

• Study Start (Estimated): June 30, 2026
• Primary Completion (Estimated): June 30, 2029
• Study Completion (Estimated): December 31, 2029

Study Registration Dates

• First Submitted: April 23, 2026
• First Submitted That Met QC Criteria: April 23, 2026
• First Posted (Actual): May 1, 2026

Study Record Updates

• Last Update Posted (Actual): May 1, 2026
• Last Update Submitted That Met QC Criteria: April 23, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Heart Failure; Cardiac Resynchronization Therapy; CRT; Left Bundle Branch Area Pacing; Permanent Atrial Fibrillation; LBBAP; Conduction System Pacing; AVJ Ablation
• Additional Relevant MeSH Terms: Cardiovascular Diseases; Pathologic Processes; Heart Diseases; Arrhythmias, Cardiac; Pathological Conditions, Signs and Symptoms; Heart Failure; Atrial Fibrillation; Cardiomyopathies
• Other Study ID Numbers: 4-2025-1786

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No