Impact of left ventricular outflow tract area on systolic outflow velocity in hypertrophic cardiomyopathy: A real-time three-dimensional echocardiographic study

Objectives The aim of this study was to use real-time three-dimensional echocardiography (3DE) to investigate the quantitative relation between minimal left ventricular (LV) outflow tract area (ALVOT) and maximal LV outflow tract (LVOT) velocity in patients with hypertrophic obstructive cardiomyopathy (HCM). Background In patients with HCM, LVOT velocity should change inversely with minimal ALVOT unless LVOT obstruction reduces the pumping capacity of the ventricle. Methods A total of 25 patients with HCM with systolic anterior motion (SAM) of the mitral valve leaflets underwent real-time 3DE. The smallest ALVOT during systole was measured using anatomically oriented two-dimensional “C-planes” within the pyramidal 3DE volume. Maximal velocity across LVOT was evaluated by two-dimensional Doppler echocardiography (2DE). For comparison with 3DE ALVOT, the SAM-septal distance was determined by 2DE. Results Real-time 3DE provided unique information about the dynamic SAM-septal relation during systole, with ALVOT ranging from 0.6 to 5.2 cm2 (mean: 2.2 ± 1.4 cm2). Maximal velocity (v) correlated inversely with ALVOT (v = 496 ALVOT−0.80, R = −0.95, p < 0.001), but the exponent (−0.80) was significantly different from −1.0 (95% confidence interval: −0.67 to −0.92), indicating a significant impact of small ALVOT on the peak LVOT flow rate. By comparison, the best correlation between velocity and 2DE SAM-septal distance was significantly (p < 0.01) poorer at −0.83, indicating the superiority of 3DE for assessing ALVOT. Conclusions Three-dimensional echocardiography-measured ALVOT provides an assessment of HCM geometry that is superior to 2DE methods. These data indicate that the peak LVOT flow rate appears to be significantly decreased by reduced ALVOT. Real-time 3DE is a potentially valuable clinical tool for assessing patients with HCM.