Anatomic, electrical, and hemodynamic characterization of Bachmann bundle in the swine heart.

Background: Bachmann bundle area (BBA) pacing is an attractive alternative to traditional right atrial appendage (RAA) pacing, but its hemodynamic benefits are poorly understood.

Objective: The purpose of this study was to evaluate hemodynamic effects of BBA pacing and structural characteristics of the aligned myocytes within BBA.

Methods: Five swine were subjected to volume overload by intravenous infusion of 3 L of 0.9% saline solution during 30 minutes. Medtronic 3830 pacing leads were placed in the RAA and BBA. Rates were alternated between the 2 sites at 110, 120, and 130 beats/min, with the acquisition of left ventricular pressure-volume loops. Anatomies were formalin-fixed and treated with a 7.5% iodine solution to delineate contractile myocardium. The specimens underwent a perfused contrast-enhanced micro-computed tomography protocol with iodine to identify soft tissue differences in the tissue.

Results: Our findings revealed atrial synchrony with BBA pacing compared with RAA pacing. BBA pacing reduced average P-wave duration by 27 ms, accompanied by increased left ventricular stroke volume across pacing speeds (23%, 17%, and 15% at 110, 120, and 130 beats/min, respectively). Micro-computed tomography scans depicted orientations of the Bachmann bundle.

Conclusions: Through this study, we have achieved a comprehensive hemodynamic characterization and anatomic reconstruction of Bachmann bundle in a swine model subjected to volume overload. The hemodynamic improvements of BBA pacing relative to RAA pacing underscore the potential of BBA pacing as an alternative site for atrial pacing. This understanding of atrial physiology may inform clinical interventions to optimize pacing strategies.