Right bundle branch in ventricular septal defects

This study aims to review the anatomical variations of the right bundle branch (RBB) in normal hearts and various ventricular septal defect (VSD) subtypes through a systematic literature review. Additionally, it seeks to propose hypotheses for optimizing surgical approaches to minimize conduction disturbances during VSD closure, based on anatomical evidence. We performed a systematic literature review of peer-reviewed articles published up to October 2024, focusing on the anatomy of the cardiac conduction system and its variations in association with VSD subtypes. The review encompassed 30 articles, analysing anatomical data from over 100 reported cases of normal and VSD hearts. In the normal heart, the RBB courses posterior to Lancisi's muscle, which originates at the junction of the anterior-basal and posterior-basal limbs of the trabecular septomarginalis (TSM). In perimembranous inlet VSDs, the medial papillary muscle (MPM) does not reliably indicate the RBB's course; instead, the RBB runs close to the membranous flap, positioning it on the edge of the VSD. In perimembranous outlet VSDs, the posterior limb of the TSM covers the branching and bifurcating bundles and the base of the RBB, causing these components to deviate towards the left ventricle beneath the defect's edge, maintaining a distance of 3-5 mm. The RBB then courses intramurally, emerging at the base of the MPM. In tetralogy of Fallot cases with perimembranous outlet VSDs, the RBB consistently courses approximately 2 mm anterior to the MPM in 63-86% of cases. In normal hearts, the RBB runs posterior to Lancisi's muscle; however, in perimembranous outlet VSDs (especially ToF), the RBB typically courses about 2 mm anterior to the MPM, a critical detail to consider during VSD repair to avoid conduction system injury.