The Course of the Conduction

The conduction systems of three hearts with single ventricle and inverted (L-) loop and inverted (L-) transposition were studied by serial section. The course of the conduction system was similar in all three hearts. The regular (posterior) atrioventricular (A-V) node was rudimentary and did not form the bundle of His. An accessory (anterior) A-V node was present in the roof of the right atrium. This node pierced the connective tissue adjacent to the right side of the pulmonary annulus to form the bundle of His. The bundle proceeded into the main ventricular chamber lying on the septum between this chamber and the small outlet chamber. It bifurcated a varying distance from the defect in this septum. The right bundle branch proceeded through the septal wall to the trabeculae of the outlet chamber. The left bundle branch proceeded caudad on the anterior wall of the main ventricular chamber. An unusual feature in one case was the splitting of the anterior node into two parts, one forming the bundle of His, and the other giving off Mahaim fibers to the ventricular myocardium. The surgical importance of avoiding the right side of the pulmonary annulus and the region adjoining the defect is stressed.