This is a multi-center, prospective, single-blind, randomized controlled clinical trial to evaluate the efficacy and safety of Bachmann bundle pacing (BBP) in preventing new-onset atrial fibrillation (AF) in patients with chronic cardiac insufficiency who have indications for cardiac resynchronization therapy with left bundle branch pacing (CRT/LBBP) or implantable cardioverter defibrillator (ICD) implantation.

A total of 110 eligible patients will be randomly assigned 1:1 to the BBP group or the traditional right atrial appendage (RAA) pacing group. All patients will receive guideline-directed medical therapy (GDMT) for at least 3 months and standardized follow-up for 12 months after device implantation. The primary endpoint is the incidence of new-onset AF within 12 months after implantation. Secondary endpoints include time to first new-onset AF, procedural success rate, changes in cardiac function parameters, and incidence of adverse events. This study aims to provide high-level evidence-based medical evidence for BBP as a new atrial pacing strategy to prevent AF in heart failure patients.

Background Chronic heart failure (HF) is a prevalent and prognostically poor cardiovascular disorder, with atrial fibrillation (AF) being the most common arrhythmia comorbid with HF. The bidirectional interaction between HF and AF forms a vicious cycle, significantly elevating the risks of mortality, hospitalization, and stroke in affected patients. Epidemiological data indicate that the cumulative incidence of AF following pacemaker implantation reaches 30-40%, a rate markedly higher than that in the general population without pacemaker implantation.

Traditional right atrial appendage (RAA) pacing, the most widely used clinical atrial pacing approach, induces prolonged interatrial conduction, asynchronous atrial contraction, and hemodynamic perturbations, which predispose patients to AF. The Bachmann bundle represents the most physiological atrial pacing site; pacing in this region achieves synchronous activation of the left and right atria, producing a narrower P wave compared with sinus rhythm and traditional RAA pacing. While prior studies have suggested that Bachmann bundle pacing (BBP) may reduce the recurrence and progression of atrial arrhythmias, there remains a paucity of prospective randomized controlled trials investigating the efficacy of BBP in preventing new-onset AF in HF patients undergoing cardiac resynchronization therapy with left bundle branch pacing (CRT/LBBP) or implantable cardioverter defibrillator (ICD) implantation.

Study Objectives The primary objective of this study is to determine whether BBP reduces the incidence of new-onset AF within 12 months of device implantation, compared with traditional RAA pacing, in HF patients with indications for CRT/LBBP or ICD implantation. Secondary objectives include evaluating the impact of BBP on the time to first new-onset AF, procedural safety, cardiac function parameters, electrophysiological indices, and clinical adverse events (including HF rehospitalization, all-cause death, and stroke) during the 12-month follow-up period.

Study Procedures

1. Screening and Baseline Assessment Eligible patients are identified per predefined inclusion and exclusion criteria. Following written informed consent, baseline data are collected, including demographic characteristics, medical history, 12-lead electrocardiogram (ECG), 24-hour Holter monitoring, transthoracic echocardiography, New York Heart Association (NYHA) functional classification, 6-minute walk test results, and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels.
2. Randomization Patients are stratified by implant device type (CRT/LBBP or ICD) and randomized in a 1:1 ratio to the BBP group or the RAA pacing group via a central randomization system.
3. Intervention Patients in the BBP group undergo atrial lead implantation at the Bachmann bundle region, identified via anatomical localization and intracardiac electrogram recording. Successful BBP is defined by characteristic ECG changes: a positive P wave in leads I, II, III, and aVF; a biphasic or negative P wave in lead V1; a P wave duration narrowed by >10 ms compared with baseline (in patients with pre-existing interatrial block); and documentation of the Bachmann bundle potential. If BBP implantation fails, the patient is immediately converted to RAA pacing, with the cause of failure recorded in detail. Intraoperative pacing parameters (threshold, sensing, impedance) are monitored in both groups.
4. Follow-up All patients undergo follow-up assessments at 1 week, 3 months, 6 months, 9 months, and 12 months post-implantation. Follow-up evaluations include ECG, 24-hour Holter monitoring, pacemaker programming, echocardiography, NYHA classification reassessment, 6-minute walk test, NT-proBNP measurement, medication adjustment tracking, and adverse event reporting.
5. Statistical Analysis All data are analyzed in accordance with the intention-to-treat (ITT) principle. The primary endpoint is compared using analysis of covariance, and the time to first new-onset AF is evaluated via the Kaplan-Meier method with log-rank testing. Continuous variables are compared using the t-test or Wilcoxon rank-sum test, while categorical variables are analyzed with the chi-square test or Fisher's exact test. A two-sided P value < 0.05 is considered statistically significant.

Inclusion Criteria:

1. Aged between 18 and 70 years old;
2. Diagnosis of chronic cardiac insufficiency according to current guidelines, and received guideline-directed medical therapy (GDMT) for at least 3 months;
3. Have indications for CRT/LBBP or ICD implantation, and expected atrial pacing ratio > 20%, including: Sinus rhythm, QRS duration > 120ms, LBBB, LVEF ≤ 35% with symptomatic heart failure; Sinus rhythm, QRS duration ≥ 150ms, non-LBBB, LVEF ≤ 35% with symptomatic heart failure; Sinus rhythm, QRS duration > 120ms, LBBB, LVEF 36%-50% with symptomatic heart failure; Symptomatic heart failure with LVEF ≤ 50% and expected ventricular pacing ratio > 20%; Symptomatic heart failure with LVEF ≤ 50% requiring ICD implantation for primary or secondary sudden death prevention, with atrial pacing indication due to sinus bradycardia or expected atrial pacing ratio > 20%;
4. Patients with pacing-induced cardiomyopathy requiring upgrade therapy, in sinus rhythm, and requiring reimplantation of atrial lead;
5. Signed written informed consent form approved by the ethics committee.

Exclusion Criteria:

1. Expected survival time less than 12 months;
2. Status after mechanical tricuspid valve replacement, or congenital heart disease (including dextrocardia, transposition of great arteries, single left persistent superior vena cava);
3. Previous history of atrial fibrillation;
4. Previous cardiac surgery, or requiring surgical treatment for severe structural heart disease within 1 year;
5. Pregnancy, planned pregnancy, or heart transplantation;
6. Patient refusal to participate in the study.

The decision to share individual participant data (IPD) is currently undecided and will be reassessed upon completion of the study. Considerations will include compliance with Chinese regulations on medical data privacy, ethical approval requirements for data sharing, and the need to protect participants' confidential health information. A formal IPD sharing plan will be developed if deemed appropriate post-study, in accordance with international clinical research standards.

This trial uses a single-blind design masking outcomes assessors, plus statistical analysts, echocardiographers, and adverse event adjudicators (not listed in standard options). These personnel receive de-identified data without group assignment (Bachmann bundle pacing vs. RAA pacing) for outcome evaluation, echocardiography interpretation, and adverse event adjudication.

Participants, care providers, and investigators are not masked due to the procedural nature of the pacing intervention-they must know the assigned group for implantation, pacemaker adjustment, and study oversight. No other parties are masked.