Hemodynamic-Induced Changes in Aortic Valve Area: Implications for Doppler Cardiac Output Determinations

Monitoring cardiac output (CO) by transesophageal echocardiography involves measurements of ascending aortic flow and an initial measurement of aortic valve area (AVA). Hemodynamic-induced changes in AVA are a potential source of error for this simplified method. Our goal was to quantify these changes in AVA and their effects on CO calculations. In 17 anesthetized patients, a dobutamine infusion was titrated to achieve a 50% increase in ascending aortic flow velocity (Vmax). Hemodynamic and echocardiographic variables, including Vmax and planimetry of AVA, were determined at baseline and at maximal dobutamine dose. Dobutamine produced a 3.0 ± 1.4 L/min increase in CO, a 54.5% ± 19.6% increase in Vmax, and a 50.6% ± 34.2% increase in systolic blood pressure. AVA increased by 4.3% ± 2.6% during dobutamine infusion (P < 0.001). The simplified CO method, which does not account for increases in AVA, produced a 0.32 ± 0.24 L/min underestimation of CO. This investigation demonstrates hemodynamic-induced changes in AVA. The use of a single AVA measurement for all subsequent CO calculations introduces a clinically acceptable degree of error, supporting a simplified CO protocol requiring less probe manipulation and reduced procedural time.