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Cardiac output measured by Doppler echocardiography in patients with aortic prosthetic valves.

Quantification of blood flow is important for the correct interpretation of pressure gradients across prosthetic valves. Cardiac output was assessed simultaneously by Doppler echocardiography and the Fick oxygen method in 20 patients with aortic prosthetic valves. Velocity integral and diameter were measured in the outflow tract close to the valve at a site where the colour flow map showed no interference by valvular velocity. Doppler cardiac output was calculated by multiplying systolic velocity integral with area and heart rate. The variability of the haemodynamic parameters was tested in 10 additional patients. The non-invasive results correlated closely with the invasive results (r = 0.91, SEE 0.6 l min-1). Analysis of variance showed that no bias was introduced when cardiac output was determined by two different observers and on different days. Coefficient of variation for velocity integral, outflow area, heart rate and cardiac output were 9.6%, 7.2%, 6% and 10.8%, respectively. In conclusion, Doppler echocardiography is useful for estimating cardiac output in patients with aortic prosthetic valves.