Clinical appraisal of his bundle electrocardiogram taken under cardiotomy in congenital heart disease.

The specialized conduction system in the heart was electrophysiologically delineated under cardiotomy in 74 patients with congenital heart disease primarily to determine the topographic relationship of the conduction system to intracardiac structures. Histological study was also done to evaluate the electrophysiological data. Differences were found between the ordinary ventricular septal defect (VSD), inlet-type perimembranous defect, and the ordinary tetralogy of Fallot (TOF), outlet-type perimembranous defect. A superficial run of the His bundle along the lower rim summit of defect was often demonstrated electrophysiologically in large VSD of types II or III, whereas the bundle took marked leftward course in TOF. The right bundle branch (RBB) ran beneath or slightly posterior to the Lancisi equivalent structure (LES) in VSD, while it ran under or slightly anterior to LES in TOF. This papillary muscle could be a rough landmark of the RBB. The course of the RBB in TOF, however, had to be histologically confirmed, since its deep location made electrophysiological delineation difficult. All the sites with a high deflection were the areas where the conduction system was histologically demonstrated beneath the endocardium.