Tricuspid atresia with overriding imperforate tricuspid membrane: an anatomic variant.

An anatomical study of 34 specimens presenting with tricuspid atresia, in which particular emphasis was devoted to the atrioventricular junctional area, revealed 5 cases with an imperforate valve. In 1 heart the valve was completely committed to the right ventricle. In the other 4, however, the membrane was related not only to the right ventricle but also to the left ventricle. A hypoplastic right ventricular inlet portion was found in these 4 specimens. In 2 cases the tricuspid membrane overrode an inconspicuous inlet septal defect. In the other 2 hearts, as studied macroscopically, no defect was present underneath the membrane, which was connected to both right and left ventricles. These 4 specimens also had other ventricular septal defects. In classical tricuspid atresia, characterized by absence of the inlet portion of the right ventricle, the inlet septum is absent. In contrast, these 4 hearts did have an hypoplastic inlet septum.