Echocardiographic Measurement of the Left Ventricular Outflow Gradient in Idiopathic Hypertrophic Subaortic Stenosis

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Abstract
The characteristic hemodynamic abnormality in idiopathic hypertrophic subaortic stenosis is a highly variable subaortic obstruction to left ventricular ejection. Previous studies have shown that during systole, the left ventricular outflow tract is narrowed by motion of the anterior mitral leaflet toward the ventricular septum. If this were responsible for the obstruction, we believed it would be possible to predict quantitatively the gradient in the disease from echocardiograms. We computed an obstruction index by dividing the duration of outflow narrowing by the mean septal-anterior mitral-leaflet distance and compared the result with the simultaneously measured peak left ventricular outflow pressure gradient in 56 beats from 11 patients with this form of subaortic stenosis. The correlation between the obstruction index and gradient was highly significant (gradient = 1.8 obstruction index - 35; r = 0.95). Echocardiography thus confirms that the pressure gradient in the disorder is caused by narrowing of the left ventricular outflow tract between the anterior mitral leaflet and ventricular septum, and the technic may be used to quantitate the gradient. (N Engl J Med 288: 989–993, 1973)