Left-sided obstructive lesions in atrioventricular septal defects: an anatomic study.

Actual and potential factors that create an obstruction to the flow within the systemic side of the heart have been analyzed in 114 specimens with atrioventricular septal defects. Hearts with separate right and left atrioventricular orifices and with common atrioventricular orifice were included. Potential inlet obstruction was due to tethering of the "cleft" of the left atrioventricular valve to the septum in 17.5%, incomplete "cleft" in 8%, and deformed valve leaflets in 70% of cases. Potential factors predisposing to left ventricular outflow tract obstruction were seen in 70% of cases, 21% being due to abnormal position of the papillary muscle and the remainder due to intrinsic hypoplasia of the outflow tract. Anatomic factors producing unequivocal obstruction were seen in 29% of cases. Twenty-two percent had obstructions at the inlet level, of which 13% were due to malformations of the left atrioventricular valve or the left component of a common valve. The other 9% had overall inlet obstruction due to severe hypoplasia of the left ventricle itself. Unequivocal outlet obstruction was observed in 7% of cases, 5% due to abnormal disposition of papillary muscles in the outflow tract and 2% to aneurysm of the interventricular septal remnant. Although anatomic obstruction occurs in the minority of cases (29%), this report shows that potential obstruction must be taken into account when considering surgical repairs.