Electrophysiological delineation of the specialized conduction system during cardiotomy and its clinical appraisal.

The specialized conduction system was delineated electrophysiologically during cardiotomy, primarily to discover the topographic relations between the conduction system and the intracardiac structures. A series of 72 cases operated on for congenital cardiac anomalies was studied. A superficial location of the His bundle along the lower rim of the defect was often noticed in cases of large ventricular septal defect (VSD) of type II or III, whereas a marked leftward deviation was noted, in cases of tetralogy of Fallot (TOF). Significant deflections were commonly recorded on the tricuspid annulus a few mm below the defect, and frequently on the lower rim behind the muscle of Lancisi (ML) in both VSD and TOF (left ventricule side in TOF). Particular care should be taken in these areas, during closure of any defect. The ML was found to be a rough landmark for the right bundle branch, although topographic relations were slightly altered according to the type of disease. The change may also depend on whether the perimembranous defect is of the inlet- or outlet-type.