Anatomic and functional "obstruction" of the outflow tract in atrioventricular septal defects with separate valve orifices ("ostium primum atrial septal defect"): an echocardiographic study.

Left ventricular (LV) outflow tract (OT) obstruction can be treacherous in any form of atrioventricular (AV) septal defect. The properties of the LVOT were investigated echocardiographically in 64 patients with separate valve orifices ("ostium primum atrial septal defect") who had survived corrective surgery. M-mode and cross-sectional echocardiographic (echo) images were made of the LVOT. The degree of malalignment of the aorta with the ventricular septum, the left atrium-aortic ratio, the fractional LV shortening and the diameter of the LVOT were recorded. Fixed anatomical obstruction was found in 3 patients, consisting of muscular bands or abnormal attachment of tension apparatus. Malalignment of the aorta with the ventricular septum was found in 62% of the patients. The diameter of the LVOT was smaller than that of the aortic root in 71% of the cases. The mean diameter of the LVOT was 92 +/- 27% (range 35 to 143%) of the aortic root diameter. Because its walls are mainly muscular, the LVOT constricts during systole. The mean end-systolic diameter of the LVOT was 77 +/- 22% (range 23 to 129%) of the aortic root diameter. Sequential measurements showed that the LVOT constricted gradually, but the velocity of constriction in patients with the most severe narrowing showed a distinct maximum in the first fifth of systole. In conclusion, a series of elements contribute to a potentially perilous arrangement of the LVOT in patients with AV septal defect. This intrinsically narrow tunnel was constricted during systole by its muscular walls.(ABSTRACT TRUNCATED AT 250 WORDS)