Variations in the morphology of the ventricular septal defect and disposition of the atrioventricular conduction tissues in tetralogy of Fallot.

Seventeen heart specimens with tetralogy of Fallot were studied to assess the anatomy of the ventricular septal defect and the disposition and potential vulnerability to surgical trauma of the atrioventricular conduction tissue. Eleven had defects of the perimembranous type. In the majority of these cases the non-branching and branching atrioventricular bundle lay posterior to the defect in a position unlikely to be damaged during closure of the defect. However, in one case, the non-branching bundle extended onto the rim of the defect and in a further 4 cases, other major components of the atrioventricular conduction tissue appeared vulnerable. Six ventricular septal defects were of the muscular outlet type and the atrioventricular conduction tissue did not appear vulnerable in any case of this type. Conclusive differentiation between perimembranous and muscular outlet defects was not always possible on gross morphological examination. It is suggested that the crest of the muscular septum and fibrous tissue in the posterior corner of the ventricular septal defect should be avoided during closure of the defect.