BUNDLE BRANCH BLOCK, HEMIBLOCK AND ATRIOVENTRICULAR (AV) BLOCK

The conducting system of the heart comprises the AV node and the bundle of His which divides into a right and a left bundle branch. The right bundle branch is a discrete structure from its origin to its termination, but the left bundle branch quickly divides into an anterior (superior) and a posterior (inferior) fascicle (Fig. 7.1). The infra-Hisian portion of the conducting system is therefore essentially trifascicular, consisting of the right bundle branch and the anterior and posterior fascicles of the left bundle branch.