Surgical anatomy of the atrioventricular conduction bundle in anomalous muscle bundle of the right ventricle with subarterial ventricular septal defect.

A stillborn baby girl was found to have an anomalous muscle bundle of the right ventricle, associated with a doubly committed subarterial ventricular septal defect. The latter was separated from the area of the atrioventricular conduction bundle by muscle. Serial histologic sectioning of the specialized atrioventricular junctional area revealed that the final bifurcation of the branching bundle came astride the septum in the inferior angle of the defect. The right bundle branch bifurcated and one of its branches continued along the anomalous muscle bundle in subendocardial position. This anatomy supports the concept that the bundle, in this heart, represented an early takeoff of the moderator band. The surgical anatomy suggests that resection of the anomalous muscle bundle and closure of the ventricular septal defect might well have produced heart block. The generally accepted rule that resection of anomalous muscle bundles in the right ventricle is surgically safe should be reconsidered.