Abstract 300: Determinants of Left Ventricular Outflow Tract Obstruction in Patients With Asymmetric Septal Hypertrophy: Insights From Geometric Analysis Using 3D Echocardiography
Background: We hypothesized that geometric differences in mitral valve leaflets and subvalvular apparatus could determine development of systolic anterior motion of mitral valve (SAM) and consequent left ventricular outflow tract obstruction (LVOTO) in patients with asymmetric septal hypertrophy (ASH).
Methods: Real-time 3D echocardiography (RT3DE) was done in 33 patients with ASH and 25 normal controls. Patients included 15 with resting LVOTO (Group I) and 18 without resting or provoked LVOTO (Group II). A customized software (Omni4D) was used to measure mitral leaflet areas (MLA) at end diastole and other geometric indices including annular area, height and circumference, septal thickness, and the distances and angles between papillary muscles (PM), fibrous trigone, and mitral centroid. All leaflet areas and distances were indexed to body surface area.
Results: Septal thickness was not different between ASH groups. Anterior MLA was larger in both ASH patient groups compared with controls, and was significantly larger in LVOTO Group I than in no-LVOTO Group II (9.09±2.90, 7.22±2.90 vs. 5.04±1.23 cm2, p<0.001, respectively). Posterior MLA was also larger in ASH patients than in controls, but without significant differences between patient groups. Mitral annular area, height, and circumference were not different between patients and controls. The distances and angles between medial PM and other anatomical landmarks were not different among three groups. However, the distance between lateral PM and medial trigone was significantly shorter in Group I, resulting in shorter interpapillary muscle distance. Multivariate analysis showed that anterior MLA was the only independent predictor of LVOTO in ASH patients (odds ratio = 2.01, p<0.001).
Conclusion: Larger MLA is a characteristic finding in ASH patients and anterior MLA is associated with development of LVOTO, along with reduced PM tethering distances, predisposing to greater ML mobility and therefore SAM.