Lesions of the Atrioventricular Conduction System after Repair of Ventricular Septal Defect Relation to

DURING the repair of congenital defects of the venitricular septum, various dis-turbances 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 teeh-nies are based on the assumption that trauma to the AV conduction system occurring dur-ing 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 te-tralogy of Fallot, and one of common AV canal. There is general agreement that permanent complete heart block is almost always asso-ciated with a lesion in the proximal portion of the AV conduction system.7 ' 8 There is not such general agreement concerning the mor-phology 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 no