Anatomy of the ventricular septal defect in outflow tract defects: similarities and differences

The study objective was to analyze the anatomy of the ventricular septal defect found in various phenotypes of outflow tract defects.

We reviewed 277 heart specimens with isolated outlet ventricular septal defect without subpulmonary stenosis (isolated outlet ventricular septal defect, 19); tetralogy of Fallot (71); tetralogy of Fallot with pulmonary atresia (51); common arterial trunk (54); double outlet right ventricle (65) with subaortic, doubly committed, or subpulmonary ventricular septal defect; and interrupted aortic arch type B (17). Special attention was paid to the rims of the ventricular septal defect viewed from the right ventricular side and the relationships between the tricuspid and aortic valves.

The ventricular septal defect was always located in the outlet of the right ventricle, between the 2 limbs of the septal band. There was a fibrous continuity between the tricuspid and aortic valves in 74% of specimens with isolated outlet ventricular septal defect, 66% of specimens with tetralogy of Fallot, 39% of specimens with tetralogy of Fallot with pulmonary atresia, 4.6% of specimens with double outlet right ventricle, 1.8% of specimens with common arterial trunk, and zero of specimens with interrupted aortic arch type B (P < .005). When present, this continuity always involved the anterior tricuspid leaflet.

The ventricular septal defect in outflow tract defects is always an outlet ventricular septal defect, cradled between the 2 limbs of the septal band. However, there are some differences regarding the posteroinferior and superior rims of the ventricular septal defect. These differences suggest an anatomic continuum from the isolated outlet ventricular septal defect to the interrupted aortic arch type B rather than distinct physiologic phenotypes, related to various degrees of abnormal rotation of the outflow tract during heart development: minimal in isolated outlet ventricular septal defect; incomplete in tetralogy of Fallot, tetralogy of Fallot with pulmonary atresia, and double outlet right ventricle; absent in common arterial trunk; and excessive in interrupted aortic arch type B.