Location of Left Ventricular Outflow Tract Measurements for Stroke Volume Estimation With Echocardiography

The location of the left ventricular outflow tract (LVOT) for measurement of Doppler LVOT stroke volume (SV) remains contentious. Current guidelines recommend LVOT measures at or within 5 mm to 10 mm of the aortic annulus. We aimed to determine the Doppler LVOT SV location that most closely agreed with gold standard cardiac magnetic resonance imaging (CMR).

This was a retrospective, single-centre, observational study of volunteer participants free of known cardiac disease, using both athlete and nonathlete controls. Participants had their Doppler LVOT SV measured using the area at the annulus, 3 mm, 6 mm, and 9 mm away from the annulus. This was compared to the gold standard CMR SV.

Overall, 181 participants had their Doppler LVOT SV measured by echocardiography and CMR, under baseline resting condition. In this population free of cardiac disease, the LVOT area increased progressively from 0 mm to 9 mm from the annulus (4.4, 4.9, 5.7, and 6.95 cm²). The SV obtained at 3 mm from the annulus most closely agreed with CMR. The mean bias and upper and lower limits of agreement of CMR SV vs Doppler LVOT SV were: at 0 mm (11%, -17.78 to 39.76); 3 mm (0.40% -36.78 to 37.58); 6 mm (-16.48%, -72.16 to 39.19); and 9 mm (-43.16%, -114.93 to 28.61).

In patients free of known cardiac disease, measures of LVOT SV within 10 mm of the annulus are not equivalent. LVOT area and SV at 3 mm most closely approximates gold standard CMR SV. LVOT area at the annulus and 6 mm away are within 17% of the CMR SV. The LVOT is larger at 9 mm in this cohort, resulting in a significant overestimation of LV SV.