Abstract 14146: Systolic Anterior Motion of the Mitral Valve Alters Three-Dimensional Hemodynamics in the Ascending Aorta in Hypertrophic Cardiomyopathy
Background: Systolic anterior motion (SAM) of the mitral valve is a diagnostic feature of hypertrophic cardiomyopathy (HCM) that can be assessed using echocardiography and cardiovascular MRI. SAM contributes to the left ventricular outflow tract (LVOT) pressure gradients in patients with obstructive HCM. We applied three-dimensional, time resolved phase contrast (4D flow) MRI to visualize and quantify 3D blood flow in the LVOT and ascending aorta (AAo) in patients with HCM to investigate the impact of dynamic outflow obstruction on LVOT and AAo flow dynamics in patients with and without SAM.
Methods: HCM patients (n=20, age: 56.0 ± 11) and volunteers (n=10, age: 54.8 ± 9) underwent 4D flow MRI as part of an IRB-approved protocol. Fifteen patients exhibited SAM (SAM+), while 5 patients and all volunteers did not (SAM-). A 3D blood velocity profile in the LVOT was generated from 4D flow data using flow visualization software (EnSight, CEI, Apex, NC) and then queried throughout the cardiac cycle to determine peak LVOT velocity. Gradients were calculated using the simplified Bernoulli equation (p = 4v2, p = gradient, v = velocity). Helical flow in the AAo was assessed by two observers using the scale: 0 = none, 1 = mild, 2 = severe. Results were compared using a Wilcoxon signed-rank test.
Results: SAM+ subjects had a higher LVOT pressure gradient (55.7 ± 29.9 mmHg) than both SAM- patients (9.9 ± 1.3 mmHg, p = 0.001) and volunteers (10.5 ± 5.6 mmHg, p = 0.001). SAM+ patients also exhibited higher grade helical flow (1.5 ± 0.5) than volunteers (0.4 ± 0.5, p < 0.001), but no difference from SAM- patients (0.9 ± 0.5, p = 0.08). There was no difference in pressure gradient (p=0.86) or helical grade (p=0.07) between SAM- patients and volunteers.
Conclusions: SAM of the mitral valve and the resulting dynamic LVOT obstruction creates downstream 3D flow derangement that can be visualized in the LVOT and AAo. These flow disturbances may be useful in detecting and characterizing patients with obstructive HCM.
- © 2013 by American Heart Association, Inc.