Cardiac Output by Transesophageal Echocardiography Using Continuous-wave Doppler across the Aortic Valve


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Abstract

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 × aortic valve area. DCO was calculated off-line, by multiplying stroke volume with heart rate: DCO = stroke volume × 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 1·min-1 (range 2.02-7.42 1·min-1), and mean TCO was 4.41 ± 1.17 1·min-1 (range 2.24-8.94 1·min-1). Very high correlation and agreement were found between the two methods: DCO = 0.94 × TCO + 0.19, r=0.94, SEE (standard error of the estimate) = 0.41 1·min-1; 95% confidence interval=0.06 ± 0.83 1·min-1. Relative changes from pre- to postbypass CO (Δ) also showed a strong correlation (ΔDCO=0.93 × ΔTCO + 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 1·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.

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