Background: The purpose of this study was to evaluate the agreement of cardiac output measurements obtained by electrical velocimetry (CO(EV)) and those that derived from the direct Fick-oxygen principle (CO(F)) in infants and children with congenital heart defects.
Methods: Simultaneous measurements of CO(EV) and CO(F) were compared in 32 paediatric patients, aged 11 days to 17.8 yr, undergoing diagnostic right and left heart catheterization. For non-invasive measurements of cardiac output by electrical velocimetry, which is a variation of impedance cardiography, standard surface electrodes were applied to the left side of the neck and the left side of the thorax at the level of the xiphoid process. Cardiac output determined using direct Fick-oxygen principle was calculated by direct measurement of oxygen consumption (VO2) and invasive determination of the arterio-venous oxygen content difference.
Results: An excellent correlation (r=0.97) was found between CO(EV) and CO(F) (P<0.001). The slope of the regression equation [0.96 (SD 0.04)] was not significantly different from the line of identity. The bias between the two methods (CO(EV)-CO(F)) was 0.01 litre min(-1) and the limits of agreement, defined as the bias (2 SD), were -0.47 and +0.45 litre min(-1).
Conclusions: CO(EV) demonstrates acceptable agreement with data derived from CO(F) in infants and children with congenital heart disease. The new technique is simple, completely non-invasive, and provides beat-to-beat estimation of CO.