Three-Dimensional Morphology of the Left Ventricular Outflow Tract: Impact on Grading Aortic Stenosis Severity

Abstract

Background: Left ventricular outflow tract (LVOT) measurement is a critical step in the quantification of aortic valve area. The assumption of a circular morphology of the LVOT may induce some errors. The aim of this study was to assess the three-dimensional (3D) morphology of the LVOT and its impact on grading aortic stenosis severity.

Methods: Fifty-eight patients with aortic stenosis were studied retrospectively. LVOT dimensions were measured using 3D transesophageal echocardiography at three levels: at the hinge points (HP) of the aortic valve and at 4 and 8 mm proximal to the annular plane. Results were compared with standard two-dimensional echocardiographic measurements.

Results: Three-dimensional transesophageal echocardiography showed a funnel shape that was more circular at the HP and more elliptical at 4 and 8 mm proximal to the annular plane (circularity index = 0.92 vs 0.83 vs 0.76, P < .001). Cross-sectional area was smaller at the HP and larger at 4 and 8 mm from the annular plane (3.6 vs 3.9 vs 4.1 cm², P = .001). The best correlation between two-dimensional and 3D transesophageal echocardiographic dimensions was at the HP (intraclass correlation coefficient = 0.75; 95% CI, 0.59-0.86). When the HP approach was selected, there was a reduction in the percentage of patients with low flow (from 41% to 29%).

Conclusions: A large portion of patients with aortic stenosis have funnel-shaped and elliptical LVOTs, a morphology that is more pronounced in the region farther from the annular plane. Two-dimensional LVOT measurement closer to the annular plane has the best correlation with 3D measurements. Measurement of the LVOT closer to the annular plane should be encouraged to reduce measurement errors.

Keywords: 3D echocardiography; Aortic stenosis; Left ventricular outflow tract.