Anatomical variations in atrioventricular conduction system with reference to ventricular septal defects.

The course of the atrioventricular conducting tissues was studied in IO hearts having ventricular septal defects. Seven of the defects were in the membranous portion of the septum, and in these hearts the common atrioventricular bundle passed down the posterior edge of the defect and bifur- cated on its inferior border. In 3 of these specimens the bundle deviated to the left side of the sep- tum before bifurcating. The 3 remaining hearts possessed defects of the muscular septum. In 2 of these the common bundle bifurcated within the septum anterosuperiorly to the defect. The left branch descended to become intimately related to the anterior border of the defect. In the other heart with low anterior intramuscular defects the right bundle-branch traversed the septum and divided astride the defect. These results are discussed in relation to surgical repair of the defects and to the reports of previous investigators. The added risk of damaging the conducting tissue is emphasized in cases which deviate from the usually accepted pattern.