Comparison of 2D and 3D echocardiographic measurement of mitral-aortic angle

The angle between the mitral and aortic valves (MAA) facilitates blood flow ejection in physiological condition. Also the narrowing of MAA increases the risk of systolic anterior movement. By convention, MAA is measured in the 2D echo image (2DE) representing the 3-chambers view (3-ch). However, changes in 3-ch view selection may lead to significant changes in the measured 2D angle, due to the 3D shape of the two annuli. Real-time 3D echo (3DE) represents an alternative way to study MAA. Accordingly, our aim was to measure the impact of minimal variation in 3-ch selection on MAA computation, compared to MAA measured with 3DE (MAA3D). On 3DE data of 21 randomly chosen subjects, aortic and mitral annuli (AoA, MA) were traced using custom software. MAA3D was measured as the angle between the best fitting planes of the two traced annuli. To simulate 2D MAA measurements, the 3D data was sliced: 1) at the position corresponding to 3-ch; 2) using 20 translated planes (1mm step) on both sides of the 3-ch; 3) using 40 rotated planes (1 degree step) around MA saddle point. The intersection of the traced annuli with these planes was used to automatically measure MAA in 2D. Results showed that even slight misalignment (>1mm and >10°) of 2D cut-plane from the ideal 3-ch leads to MAA measures that differ from MAA3D.