To assess left ventricular outflow tract (LVOT) geometry using three-dimensional transesophageal echocardiography (3D TEE), in order to provide a theoretical basis for underestimation of aortic valve area by continuity equation.

Fifty patients who underwent two-dimensional transthoracic echocardiography (2D TTE) and 3D TEE of 50 patients from May 2010 to February 2011 were assessed retrospectively. LVOT diameters were measured at distal (aortic annulus, A1), middle (5 mm from the annulus) and proximal (10 mm from the annulus) level, and cross-sectional areas (CSA) were calculated respectively. CSA and stroke volume (SV) calculated from 2D TTE circular area formula (2D TTE_circular), 3D TEE elliptical area formula (3D TEE_elliptical) and 3D TEE planimetry (3D TEE_planimetry) were compared.

3D TEE revealed that LVOT was funnel-shaped in most of the patients (76%). CSA was circular at A1 with the smallest area, and was elliptic at A2 and A3 with larger areas. There was no significant difference among CSA_circular [(3.7±0.9) cm²] , CSA_elliptical [(3.9±0.8) cm²] and CSA_planimetry [(3.9±1.0) cm²] at A1 level (F=1.025, P=0.45). CSA_circular was (3.4±0.8) cm² at A2 and (3.5±0.9) cm² at A3, and CSA_planimetry was (4.0±1.0) cm² at A2 and (5.0±1.4) cm² at A3. CSA_circular was significantly smaller than CSA_planimetry at both A2 and A3 leves (F=8.055, 22.098; P=0.001,<0.001). There was no significant difference among SV_circular, SV_elliptical, and SV_planimetry at A1 level (F=0.579, P=0.56). SV_circular was (64±18) ml at A2 and (67±19) ml at A3, and SV_planimetry was (76±23) ml at A2 and (95±33) ml at A3. SV_circular was significantly smaller than SV_planimetry at both A2 and A3 level (F=5.168, 15.638; P=0.004,<0.001).

LVOT is uniformly funnel-shaped with the smallest CSA at the annulus. Using of 3D measurement of LVOT diameters or area may improve the accuracy of calculating SV, reduce the risk for underestimation of aortic valve area and improve accuracy of diagnosing aortic stenosis.