The morphologic nature of noncommitted ventricular septal defects in specimens with double-outlet right ventricle

Lev's contribution to the understanding of the morphology of hearts with double-outlet right ventricle and the surgical feasibility for correction is important and remains in current use. However, the term noncommitted ventricular septal defect remains enigmatic. The aim of this study was to elucidate the morphologic nature of the noncommitted ventricular septal defect in view of its surgical implications.

We examined 67 specimens with double-outlet right ventricle, focusing on the relationship of the ventricular septal defect to the semilunar orifices.

The defect was subaortic, subpulmonary, or doubly committed in 55 specimens. In a further 8 specimens, the defect opened into the outlet portion of the right ventricle, but the distance between the ventricular septal defect and the semilunar orifice was extensive, either because of extreme dextroposition of the aorta or a broad ventriculoinfundibular fold, which, in some cases, was associated with a long-outlet septum. A truly noncommitted ventricular septal defect was found in the inlet in the remaining 4 specimens. An atrioventricular septal defect without extension to the outlet was present in 3 cases, and a ventricular septal defect limited to the inlet was found in another case. The ventriculoinfundibular fold, part of the outlet septum and septal band or septomarginal trabeculation, had fused to form a crestlike structure. The septomarginal trabeculation is a useful landmark in the right ventricle to differentiate the inlet from the outlet in different forms of double-outlet right ventricle.

We do not suggest to discard the Lev terminology but rather to differentiate the noncommitted ventricular septal defect into 2 types: the truly noncommitted defect of the inlet type and the not-directly-committed defect, which does open into the outlet portion of the right ventricle. The implication for the surgeon is 2-fold. The tricuspid valve or right part of the atrioventricular valve is interposed between the noncommitted ventricular septal defect and the semilunar orifice. The not-directly-committed defect opens into the outlet portion of the right ventricle but is not directly subaortic or subpulmonary.