CONDUCTION SYSTEM IN HYPOPLASIA OF THE AORTIC TRACT COMPLEX

The course of the conduction system in 2 cases of hypoplasia of the aortic tract complex, 1 with mitral stenosis and the other with mitral atresia was studied. In both a posterior atrioventricular (AV) node formed the AV bundle. In case 1, the bundle was short and bifurcated early. The branching bundle gave off a large left bundle branch (LBB), many Mahaim fibers to the septum and a small right bundle branch (RBB). In case 2, the AV node was divided into 2 parts which formed 2 posterior bundles which joined together to form a short branching bundle. Instead of a LBB, there were profuse Mahaim fiber passing from the branching bundle to the depths of the ventricular septum. The RBB was large. The embryology of abnormalities in the conduction system, particularly in the LBB, is discussed.