Electrophysiological delineation of the specialized A-V conduction system in patients with corrected transposition of the great vessels and ventricular septal defect.

The specialized atrioventricular (A-V) conduction system was electrophysiologically delineated during open-heart surgery in four patients with congenitally corrected transposition of the great vessels and associated ventricular septal defect and one patient with single ventricle. Two consistent observations were made: 1) In no case was the specialized A-V conduction system found in the right atrium, whether or not there was a coronary sinus ostium present. 2) Specialized A-V conduction system electrograms were never delineated posterior to the ventricular septal defect, in contradistinction to this usual location in hearts having ventricular septal defects associated with other congenital lesions. In three of five patients, the initial course of the A-V conduction system of the ventricles was delineated between the anterior aspect of the ventricular septal defect and the pulmonary artery. In one patient the proximal portion of the A-V conduction system was delineated on the anterior aspect of the pulmonary conus. The course and extent of the A-V conduction system delineated in the morphological left ventricle suggests it is a left bundle branch. The surgical implications of the ectopic location of the A-V conduction system anterior to the ventricular septal defect, and the variability of the more proximal portion of the A-V conduction system are discussed.