Cardiac output by transesophageal echocardiography using continuous-wave Doppler across the aortic valve.

BACKGROUND: The use of transesophageal echocardiography for the determination of cardiac output (CO) has been limited to date. We assessed the capability of aortic continuous-wave Doppler transesophageal echocardiography to determine CO (DCO) in a transgastric long-axis imaging plane of the heart by comparing DCO to thermodilution CO (TCO).
METHODS: DCO was determined in 63 consecutive patients undergoing cardiac surgery. Aortic valve area was obtained from the transverse short-axis view of the valve assuming a triangular shape for the valve orifice. Stroke volume was calculated as the product of velocity-time integral and aortic valve area: stroke volume = velocity-time integral x aortic valve area. DCO was calculated off-line, by multiplying stroke volume with heart rate: DCO = stroke volume x heart rate.
RESULTS: The aortic valve orifice was easily imaged in all patients. Excellent-quality continuous-wave Doppler flow profiles were obtained in nearly all (62 of 63). A total of 109 DCO determinations were performed. Mean DCO was 4.35 +/- 1.18 l.min-1 (range 2.02-7.42 l.min-1), and mean TCO was 4.41 +/- 1.17 l.min-1 (range 2.24-8.94 l.min-1). Very high correlation and agreement were found between the two methods: DCO = 0.94 x TCO + 0.19, r = 0.94, SEE (standard error of the estimate) = 0.41 l.min-1; 95% confidence interval = 0.06 +/- 0.83 l.min-1. Relative changes from pre- to postbypass CO (delta) also showed a strong correlation (delta DCO = 0.93 x delta TCO + 5.4%, r = 0.82, SEE = 17.8%). For CO changes greater than 10%, Doppler was in accordance with thermodilution in 43 of 45 measurements. DCO repeatability coefficient was 0.51 l.min-1.
CONCLUSIONS: Compared to thermodilution, continuous-wave Doppler measurements of blood flow velocity across the aortic valve in the transesophageal echocardiographic transgastric view allow accurate CO determination.