Objective: Atrioventricular septal defect with only a ventricular component of septal deficiency is the least common of the various forms of this malformation. We reviewed its morphology in heart specimens and compared our findings with the other forms for a better understanding of its surgical morphology.
Methods: We examined 78 cardiac specimens with atrioventricular septal defect; 56 (72%) had common atrioventricular valve orifice with both atrial and ventricular components (so-called "complete" form), and 22 (28%) had separate valve orifices (so-called "partial" or "incomplete" form) with 17 having only an atrial component (so-called "ostium primum" form) and 5 having only a ventricular component.
Results: Among hearts with atrioventricular septal defect, the hearts with only ventricular component of the defect had the mildest deformity of the ventricular mass, characterized by less inlet-outlet disproportion, smaller "gap" between anterior and posterior parts of the atrioventricular junction, and the least extensive septal deficiency. However, these hearts still possessed the characteristic common atrioventricular junction and had 5-leaflet configuration of the atrioventricular valve with similar proportions of mural leaflets in both valve orifices, as in other forms. Furthermore, owing to the unique relationship of the bridging leaflets to the septum, the leaflets were always "upwardly" displaced as opposed to "downwardly" displaced leaflets in "ostium primum" form.
Conclusions: Our observations suggest this entity might represent the mildest end of the whole spectrum of hearts with atrioventricular septal defect. Since "upwardly" displaced leaflets are not modifiable and could be aggravated further after surgery, they might play a role in late valve dysfunction.