RESTING ECHOCARDIOGRAPHIC FEATURES OF LATENT LEFT-VENTRICULAR OUTFLOWOBSTRUCTION IN HYPERTROPHIC CARDIOMYOPATHY

We determined resting echocardiographic features predictive of latent left ventricular (LV) outflow obstruction in 50 consecutive patients w ith nonobstructive hypertrophic cardiomyopathy (26 provocable, 24 nonp rovocable with amyl nitrite inhalation) to have a better understanding of the pathophysiology of this condition and to identify such patient s without pharmacologic provocation. Measurements included wall thickn ess, type of hypertrophy, LV outflow tract diameter, degree of mitral systolic anterior motion, outflow pressure gradient, and ventricular v olume. The direction of the ejection streamline was measured to assess the magnitude of the drag force acting on the mitral valve. Thirteen of 16 patients (81%) with proximal septal bulge were provocable, where as only 3 of 8 patients (38%) with asymmetric septal hypertrophy and 1 0 of 26 (38%) with concentric hypertrophy were provocable (p <0.05), L V outflow tract was significantly narrower and the angle between the e jection flow and the mitral valve was larger in provocable patients. t he sensitivity for predicting provocable patients by a combination of a narrow outflow tract (less than or equal to 2 cm) and a large angle (greater than or equal to 35 degrees) was 65%, with a specificity of 8 0% and a positive predictive value of 79%. When these criteria were co mbined with the presence of septal bulge, the sensitivity was 35%, but the specificity and the positive predictive value were both 100%. pat ients with nonobstructive hypertrophic cardiomyopathy with proximal Se ptal bulge, a narrow LV outflow tract, and an oblique angle between th e election flow and the mitral valve appeared to be predisposed for la tent outflow obstruction, These features are consistent with the prese nce of the large Venturi and drag forces. Thus, the left ventricle, wh ich is capable of increasing both the Venturi and the drag forces on t he basis Of the morphologic change, contributes to the development of outflow obstruction with amyl nitrite inhalation.