Morphometric analysis of atrioventricular septal defect with common valve orifice

Objectives. We sought to analyze morphometric features of atrioventricular septal defect (AVSD) in autopsy specimens and to consider the developmental implications of obstruction in either ventricular outflow tract. Background. Left ventricular outlet obstruction (LVO) is more prevalent in patients with Rastelli type A morphology. When tetralogy of Fallot (ToF) complicates this malformation, there is usually a free floating superior bridging leaflet. The reasons for these associations are uncertain. Methods. In 133 hearts with AVSD and common atrioventricular (AV) valve orifice, we measured the degrees of horizontal and anterior deviation of the great arteries from the AV valve, the diameters of the ventricular outlets and the great arteries and the degree of deficiency of the ventricular septum. Results. In Rastelli type A morphology, the great arteries were deviated more leftward than in type C morphology (p < 0.01). Type A hearts also had a relatively small aorta, with a long and narrow subaortic tract. The presence of obstruction in either ventricular outlet was associated with a more oblique arrangement of the great arteries, with the pulmonary trunk being more leftward than in hearts without LVO (p < 0.01). In combination with ToF, the aorta was dextroposed and the pulmonary trunk was located more posteriorly (p < 0.01). No heart with type A morphology showed ToF (p < 0.01). Conclusions. The geometric arrangement of the great arteries correlated significantly with obstruction in either ventricular outflow tract and with the Rastelli subtypes. Malrotation of the developing outlet septum may be an embryologic factor producing obstruction, with horizontal deviation of the outlets also influencing the morphology of the superior bridging leaflet. (C) 1998 by the American College of Cardiology.