Bundle Branch Pacing to Preserve Ejection Fraction in Atrial Fibrillation Trial

The BEAT Study is a prospective, multicenter, open-label, randomized controlled clinical trial designed to compare left bundle branch area pacing with conventional right ventricular pacing as the initial pacing strategy in adults with permanent atrial fibrillation, preserved left ventricular ejection fraction, and an indication for permanent ventricular pacing.

Conventional right ventricular pacing is the standard pacing strategy for patients with bradycardia. The ventricular lead is usually positioned at the right ventricular apex or septum. Although this approach is well established, prolonged right ventricular pacing produces a non-physiological pattern of ventricular electrical activation. The resulting electrical and mechanical dyssynchrony may progressively impair left ventricular function and lead to pacing-induced cardiomyopathy, heart failure, hospitalization, and the need for a subsequent procedure to upgrade the pacing system to biventricular pacing.

Patients with permanent atrial fibrillation who require a pacemaker may be particularly exposed to these complications because they generally have a high burden of ventricular pacing. This applies both to patients with slow atrial fibrillation and to those undergoing atrioventricular node ablation for rapid atrial fibrillation. Although these patients may have preserved left ventricular systolic function at the time of pacemaker implantation, repeated non-physiological ventricular activation could contribute to subsequent deterioration in cardiac function.

Left bundle branch area pacing is a conduction-system pacing technique in which the ventricular lead is advanced through the interventricular septum to stimulate the left bundle branch or the surrounding conduction tissue. By recruiting the heart's intrinsic conduction system, this approach is intended to produce more physiological and synchronous ventricular activation than conventional right ventricular pacing. It may therefore preserve left ventricular function and reduce the clinical consequences associated with long-term ventricular pacing.

Evidence supporting left bundle branch area pacing has increased, particularly in patients with impaired left ventricular function or an indication for cardiac resynchronization. However, long-term randomized evidence remains limited in patients with permanent atrial fibrillation, preserved left ventricular ejection fraction, and an expected high ventricular pacing burden. In particular, the effect of the initial pacing strategy on major clinical events in this population has not been adequately established.

The study hypothesis is that left bundle branch area pacing, compared with conventional right ventricular pacing, will reduce clinically important adverse events over 2 years by limiting pacing-related ventricular dyssynchrony and preventing deterioration in left ventricular function.

A total of 642 participants will be enrolled and randomly assigned in a 1:1 ratio to one of two pacing strategies:

Left bundle branch area pacing: implantation of a single-chamber pacemaker with the ventricular lead positioned within the left bundle branch area through the interventricular septum to capture the cardiac conduction system.

Conventional right ventricular pacing: implantation of a single-chamber pacemaker with the ventricular lead positioned at the right ventricular apex or right ventricular septum.

Randomization will be stratified by participating center and by the indication for pacing: rapid permanent atrial fibrillation requiring atrioventricular node ablation or slow permanent atrial fibrillation. Because the implantation techniques are different and identifiable to the treating clinicians, the study is open label.

Participants will be followed for 24 months after pacemaker implantation. Study assessments will include clinical evaluation, pacemaker interrogation, 12-lead electrocardiography, echocardiography, collection of hospitalizations and cardiac reinterventions, assessment of adverse events, and evaluation of health-related quality of life. Follow-up will include clinical visits approximately 2, 12, and 24 months after implantation and telephone contacts approximately 6 and 18 months after implantation.

Echocardiography will be performed at baseline and at the end of the 2-year follow-up to evaluate changes in left ventricular systolic function and ventricular volumes. Pacemaker interrogation will be used to document device function and the proportion of ventricular pacing. Quality of life will be assessed using the Short Form-36 Health Survey and the Kansas City Cardiomyopathy Questionnaire.

The principal comparison will assess whether left bundle branch area pacing improves the proportion of participants who remain free from all-cause death, unplanned hospitalization for heart failure, and upgrade to biventricular pacing at 2 years. Additional analyses will examine cardiac function, individual clinical events, cardiac reinterventions, device- and procedure-related complications, and changes in quality of life. Unplanned heart failure hospitalizations and upgrades to biventricular pacing will be reviewed by an independent adjudication committee.

The primary analysis will follow the intention-to-treat principle. The study is intended to determine whether a physiological pacing strategy should replace conventional right ventricular pacing as the preferred initial approach for patients with permanent atrial fibrillation, preserved left ventricular function, and a substantial anticipated requirement for ventricular pacing.