Idiopathic hypertrophic subaortic stenosis viewed by wide-angle, phased-array echocardiography.

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Abstract
A wide-angle, phased array ultrasonic sector scanner was used to view the heart in 18 patients with idiopathic hypertrophic subaortic stenosis (IHSS). The rapid systolic anterior motion (SAM) of the mitral apparatus appeared quite separate from movement of either the left ventricular posterior wall or prominent papillary muscles. The SAM always occurred in a location judged to be the chordal end of the mitral leaflets. The SAM involved the whole mitral apparatus more extensively in patients with high outflow tract gradients at rest (> 60 mmHg) and in all patients during Valsalva maneuver of amyl nitrite inhalation. The mitral apparatus, including the papillary muscles, was anteriorly displaced in short-axis images of these patients'' hearts. True end-systolic cavity obliteration was not seen at rest in any patient, since a small space persisted posteriorly between the papillary muscles in short-axis images. These data support some and negate other previously proposed mechanisms for the mitral valve SAM and abnormal left ventricular dynamic geometry in patients with IHSS. Localized subaortic thick septal myocardium was seen in each case. An unusual echo pattern within the myocardium and especially in portions of the thick septum was noted. This pattern was present along 20-100% (mean 50%) of the septal length, and 16-40% (mean 25%) of the left ventricular circumference and in the posterobasal myocardium in 2 patients. This echo pattern within the thick septal myocardium may be related to abnormal myocardial structure or myocardial fibrosis noted previously by histologic methods.