Dynamic change of mitral apparatus as potential cause of left ventricular outflow tract obstruction in hypertrophic cardiomyopathy

AIMS: the geometry of the mitral apparatus changes dynamically throughout systole and diastole. We investigated how geometric dynamics of the mitral apparatus could affect the haemodynamics of the outflow tract in patients with hypertrophic cardiomyopathy presenting with systolic anterior motion (HCM(SAM)) using three-dimensional (3D) echocardiography. METHODS AND RESULTS: we obtained transthoracic volumetric images in 21 patients with HCM(SAM) with differing trans-left ventricular (LV) outflow tract pressure gradient (PG(LVOT)) and in 23 controls. Original software was used to crop the 3D data into 18 radial planes; the mitral annulus, leaflets, coaptation point, protruding septum, and papillary muscles (PMs) tips were traced in each plane. The data were then reconstructed for 3D distance measurements and volumetric assessment. Shorter coaptation-septal distance (12 ± 4 vs. 21 ± 3 mm, P < 0.001), shorter inter-PM distance (13 ± 5 vs. 18 ± 4 mm, P = 0.02), and larger mitral tenting volume/body surface area (TVindex) (2.1 ± 1 vs. 0.5 ± 0.3 mL/m(2), P < 0.001) were associated with HCM(SAM) vs. control. PG(LVOT) increased with TVindex (r = 0.51, P = 0.01), and decreased with coaptation-septal distance(r = -0.83, P < 0.001) and the inter-PM distance (r = -0.69, P < 0.001) at mid-systole but not at mid-diastole (all P> 0.05). In addition, the coaptation-septal distance, TVindex, and inter-PM distance correlated each other (all P < 0.05). After adjustment for measures of mitral geometric change, the coaptation-septal distance was closely associated with PG(LVOT) (β = -0.73, P < 0.001). CONCLUSION: these findings suggest that dynamic geometric changes by interaction of PMs, mitral tenting, and the coaptation point at mid-systole may be important contributors to outflow obstruction in HCM(SAM).