Discrete subaortic stenosis: the value of cross-sectional sector echocardiography in evaluating different types of obstruction.

The value of cross-sectional sector echocardiography in the visualization of discrete subaortic stenosis (DSS) was investigated using an 80 degrees phased-array sector scanner with simultaneously derived M-mode outputs. Thirty-three patients (including 22 postoperative patients) with proven DSS were investigated and divided into two groups: group I--discrete membranous type; and group II--diffuse fibromuscular type. In group I (15 patients), two isolated subaortic ridges were identified as discrete linear echoes in the long axis of the outflow tract in five patients. A single distinct and isolated linear echo was observed in three patients, whereas in another five the ridges appeared to be attached to the ventricular septum and/or to the base of the anterior mitral leaflet. In two patients with mild DSS, a false-negative diagnosis was made. Only 2 out of 12 patients in this group showed a short remnant of the ridge after surgical revision. In group II, a more generalized or long-segment narrowing was present in 18 patients; in 14 of them the ridges were continuous with the walls of the outflow tract. Eight out of ten patients reexamined following resection of fibromuscular tissue still had residual obstruction. Analysis of the simultaneous M-mode recordings revealed that the transient appearance of the ridge in the outflow tract depended on the normal movement of the heart within the chest, on the lengthening of the membrane itself, and on the angle between the ultrasound beam and the membrane during different cardiac cycles. Our study shows that a spectrum of one- and two-dimensional patterns exists depending on the nature of the obstructing lesion. Cross-sectional sector echocardiography provides more direct visualization and characterization of various types of DSS than M-mode echocardiography does.