Abstract 18366: Cutoff of 1.0 cm 2 For Severe Aortic Stenosis? A Case for Redefining this Cutoff Based on Eccentricity of LVOT Geometry

Abstract

Background: Current guidelines define severe aortic stenosis (AS) as aortic valve area (AVA) of <1.0 cm 2 . This cutoff is based on the assumption of a circular left ventricular outflow tract (LVOT) cross sectional area (CSA) for the continuity equation (CE). However, patients with AS have chronic pressure load and may have remodeling of the LVOT geometry from circular to elliptical. An elliptical LVOT with a smaller dimension in the anterior-posterior plane would result in a lower calculated AVA. Many patients have discrepant indices of severe AS where AVA by CE is severe (<1.0 cm 2 ) yet peak velocity (V2) and mean gradient (MG) are in the moderate or mild range. We hypothesized that discordance of AS severity by AVA versus V2 or MG may be due to inaccurate circular LVOT CSA assumption in patients with AS where chronic pressure load results in an elliptical LVOT geometry. Methods: We assessed LVOT geometry by direct planimetry using 3D transesophageal echo (TEE) and calculated an eccentricity index (ratio of two orthogonal linear measurements and also ratio of CSA direct planimetry/CSA by circular LVOT assumption) in 54 patients with severe AS undergoing TTE and TEE within one month of each other. We compared AVA by elliptical LVOT (AVA LVOT ) to conventional circular LVOT CE. We then applied a correction factor for AVA underestimation based on the measured LVOT eccentricity index in a separate cohort of 49 patients with discrepant AS indices (AVA <1.0 cm 2 but MG <30 mmHg). Results: LVOT shape was elliptical in 53 of 54 (98%) patients with a mean eccentricity index of 0.88 ± 0.06 by 3D TEE. The mean LVOT CSA assuming circular geometry underestimated the true CSA determined by direct planimetry by approximately 14% (3.25 vs. 3.71 cm 2 , p<0.001). AVA LVOT was higher than AVA by conventional CE (0.71 vs. 0.61 cm 2 , p=0.003). After multiplying the LVOT CSA by correction factor of 1.14 (to account for 14% underestimation of LVOT area) in 49 patients with discrepant severe AS (mean AVA, V2 and MG of 0.88 cm 2 , 3.2 m/s and 23 mmHg, respectively), the mean AVA increased to 1.0 cm 2 . Conclusions: The LVOT geometry in patients with AS is predominantly elliptical with an eccentricity index of 0.88. The cutoff for severe AS valve area by conventional CE should be 0.8 cm 2 to adjust for elliptical LVOT geometry.