We describe an atypical case of an atrioventricular septal defect with a common atrioventricular junction in which the right-sided component of the common atrioventricular valve was imperforate, producing tricuspid atresia with a severely hypoplastic right ventricle and an ostium primum defect. We discuss the implications of the anatomic findings with regard to concepts of cardiac development, drawing a comparison with similar cases previously reported.

We describe two infants having an atrioventricular septal defect in the setting of a double inlet atrioventricular connection, but with patency of the left-sided valvar orifice and an imperforate right-sided valvar component, and a further case with atrioventricular septal defect and an imperforate Ebstein's malformation, all producing the haemodynamic effect of tricuspid atresia. We make comparisons with the arrangement in trisomy 16 mice, in whom deficient atrioventricular septation is seen at times with the common atrioventricular junction exclusively connected to the left ventricle, a situation similar to that seen in two of our infants. We also review previous reports emphasising the important theoretical implication of the findings despite their rarity.