Lesions of the Atrioventricular Conduction

DURING the repair of congenital defects of the venitricular septum, various disturbances of cardiac function may occur.1'Permanent complete heart block has been the most serious of these disturbances. Right bundle-branch block seems benign. Inereased knowledge of the anatomic features of the atrioventricular (AV) conduction system has resulted in surgical technics that have nearly eliminated complete heart block.5 These teehnies are based on the assumption that trauma to the AV conduction system occurring during surgical repair of a ventricular septal defect is the cause of postoperative functional disturbances. However, studies documenting an anatomic cause for heart block are few; Reemtsma and associates6 investigated the lesions responsible for fatal postoperative complete heart block in three cases-one of isolated ventricular septal defect, one of tetralogy of Fallot, and one of common AV canal. There is general agreement that permanent complete heart block is almost always associated with a lesion in the proximal portion of the AV conduction system.7' 8 There is not such general agreement concerning the morphology of the conduction system of hearts with right bundle-branch block.7 The present study of cases operated upon during a period when heart block was not