The relation of left ventricular geometry to left ventricular outflow tract shape and stroke volume index calculations

BACKGROUND: Stroke volume (SV) and aortic valve area calculations require the left ventricular (LV) outflow tract (LVOT) or aortic annular area calculations that involve squaring the respective diameters. Area calculation errors became evident with transcatheter aortic valve replacement where areas were underestimated due to an elliptical annulus. We hypothesized that LVOT and annular shape are more elliptical in patients with greater relative LV wall thickness (RWT) leading to underestimation of SV index using 2D Doppler echocardiography. METHODS: We studied 203 consecutive patients referred to an outpatient noninvasive laboratory for Doppler echocardiograms which included acceptable 3-dimensional images. 3-dimensional assessment of the LVOT at 3-5 mm from the valve insertion, at the site of valve insertion, and at the sinus of Valsalva (SOV) was performed with assessment of the minor axis (MN), major axis (MJ), and areas at mid-systole. SV index was calculated from LVOT and annular diameters obtained from 2-dimensional echo and from 3-dimensional LVOT areas. RESULTS: An inverse relation of RWT with MN/MJ at mid-systole for the LVOT (r = 0.5812, P < 0.0001) and annulus (r = 0.6865, P < 0.0001) was noted. LVOT and annulus areas were similar among groups at mid-systole. SV index calculated from 2D LVOT dimensions was significantly smaller than using 3D LVOT areas (35.6 ± 8.9 vs 53.6 ± 16.1 mL, P < 0.0001). CONCLUSION: There is an inverse relation between MN/MJ and RWT at the LVOT and aortic annulus despite the LVOT and annular areas being similar across most geometries resulting in SV index underestimation calculated using LVOT diameters vs 3D LVOT areas.