Percutaneous transluminal balloon dilatation for discrete subaortic stenosis.

Seven patients, mean age 8 +/- 3.6 years, with clinical and hemodynamic diagnoses of discrete subaortic stenosis were treated by percutaneous transluminal balloon dilatation (PTBD) of the membrane during cardiac catheterization. One patient had an associated aortic coarctation that was first dilated. After PTBD left ventricular (LV) systolic pressure decreased significantly, from 181 +/- 25 to 139 +/- 11 mm Hg (p less than 0.005); peak gradient diminished from 65 +/- 18 to 12 +/- 9 mm Hg (p less than 0.001). Mild aortic regurgitation was present in 6 patients during basal conditions. After PTBD, the same degree of regurgitation was observed in all but 1 patient, in whom it disappeared. There were no major complications. Clinical observations after PTBD were consistent with hemodynamic findings. Precordial thrill always disappeared and the peak murmur became earlier in systole. In 2 patients the discrete subaortic stenosis was clearly visualized at 2-dimensional echocardiography as a fixed subvalvular structure throughout the cardiac cycle. After dilatation this was only identifiable at its implantation base; during contraction there was no fixed structure at the LV outflow tract. Four patients were hemodynamically reevaluated 6.7 +/- 1.7 months later and were found to have LV pressure relief and a degree of aortic regurgitation similar to those observed immediately after PTBD.