Differential left ventricular outflow tract remodeling and dynamics in aortic stenosis

Background Left ventricular outflow tract (LVOT) geometry is variable and often elliptical, which can affect aortic valve area calculation in patients with aortic stenosis (AS). Specific differences in LVOT geometry and dynamics between patients with AS and normal control subjects have not been described. The aim of this study was to test the hypothesis that differences in LVOT geometry in patients with AS might relate to variable LVOT remodeling and stiffness relative to normal control subjects. Methods In 54 patients with severe AS and 33 control subjects without AS, LVOT geometry, dynamics, remodeling, and stiffness were assessed by three-dimensional transesophageal echocardiography. LVOT stiffness was measured by calculating the distensibility coefficient, defined as the percentage change in LVOT area relative to change in left ventricular pressure. LVOT remodeling was assessed by measuring the posterior LVOT wall thickness. Multivariate linear regression analysis was used to determine independent associations with peak systolic LVOT ellipticity. LVOT area by three-dimensional transesophageal echocardiographic planimetry was compared with areas obtained assuming circular or elliptical geometry. Results At end-diastole, LVOT geometry was similar between patients with AS and normal control subjects. In patients with AS, however, the percentage change in cross-sectional area (7.5% vs 14.7%, P <.001) from end-diastole to peak systole was lower compared with normal control subjects, while peak systolic ellipticity index was higher in patients with AS (1.18 vs 1.08, P <.001). Compared with control subjects, patients with AS had lower distensibility coefficients (4.7 ± 1.9 × 10⁴ vs 12.5 ± 5.3 × 10⁴ mm Hg^-1, P <.001) and higher posterior LVOT wall thickness (3.5 ± 0.8 vs 2.3 ± 0.5 mm, P <.001). In multivariate analysis, posterior LVOT wall thickness and distensibility coefficient were independently associated with peak systolic LVOT ellipticity index. LVOT area underestimation by transthoracic echocardiography was higher in patients with AS when assuming circular geometry (20% vs 12%, P =.001). Conclusions The LVOT is less distensible and undergoes remodeling in severe AS. These changes lead to greater peak systolic ellipticity and greater LVOT cross-sectional area underestimation relative to normal control subjects. These findings have important implications for the assessment of AS severity.