Differentiating discrete subaortic stenosis (DSAS) from aortic valve stenosis (AVS) may be difficult, even at cardiac catheterization. Twenty-two patients with DSAS were studied echocardiographically and compared with 41 patients with AVS and 234 normal subjects. A ratio of left ventricular outflow tract to aortic root (LVOT: AO) < 0.80 determined LVOT narrowing in 19 of 22 DSAS patients. The aortic valve echogram was abnormal in 19 of 20 patients with DSAS and complete aortic valve echograms. Abnormalities included marked fluttering and early systolic partial closure ranging from 13-88% of total aortic valve systolic excursion. AVS patients did not have comparable changes. Neither LVOT narrowing nor degree of aortic valve partial closure (AVPC) correlated with pressure gradients determined by catheterization. A subaortic membrane was visualized in three patients. Asymmetric septal hypertrophy was noted in five patients with DSAS.
DSAS is characterized by LVOT narrowing, early systolic AVPC, marked aortic valve flutter, and, in some cases, by a subaortic membrane. Cardiac catheterization is necessary to quantitate the degree of LVOT obstruction.