The obstructive subaortic conus.

Eleven children are reported who had stenosis under a malposed aorta with gradients of 20 to 76 mm Hg between the right ventricle and aorta. The subaortic obstruction was caused by hypertrophy of the foreshortened infundibulum and malalignment of the infundibular septum relative to the remainder of the ventricular septum. Of these 11 patients, nine had a ventricular septal defect and seven had coarctation of the aorta. Rightward deviation of the infundibulum and aorta produced an unusually long left main coronary artery that was compressed by the stent of a bioprosthetic conduit valve in one patient. Serial cardiac catheterization studies in four patients showed progressive stenosis in each. Subaortic stenosis can develop in patients with malposition of the aorta and the frequency may be greater than 5% since milder forms are likely to occur. The obstruction can be progressive. The left coronary artery may be particularly vulnerable to compression after operative repair with an extracardiac conduit.