Automated Cardiac Output Measurement by Spatiotemporal Integration of Color Doppler Data

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Abstract
Background A new Doppler echocardiographic technique has been developed for automated cardiac output measurement (ACOM) that assumes neither a flat flow profile nor collinearity with the scan line, but clinical validation of this method is lacking. Methods and Results In 165 subjects (50 intensive care patients, 10 dobutamine echocardiography patients, and 105 normal volunteers; age, 49.4±19.3 years; 92 men), ACOM was performed in the left ventricular outflow tract (LVOT), with the color baseline shifted to avoid aliasing. ACOM was also tested in a pulsatile in vitro model. Stroke volume was calculated by double integration of Doppler signals in space (across the LVOT) and in time (through the systolic period), assuming hemiaxial symmetry: ∫∫π r v(r,t) dr dt, where v(r,t) is the velocity at a distance r from the center of the LVOT at time t during systole. Stroke volume from ACOM was compared with thermodilution (TD), aortic valve pulsed-wave Doppler (PWAO), and left ventricular echocardiographic (two-dimensional [2D]) methods. There was good correlation between ACOM and PWAO ( r =.93), TD ( r =.86), and 2D ( r =.74), with close agreement seen. ACOM had higher correlation and agreement with TD than did either PWAO ( P <.02) or 2D ( P <.01). ACOM was also able to track accurately the changes in cardiac output with dobutamine infusion in comparison with PWAO ( r =.94). In vitro assessment demonstrated excellent correlation ( r =.98, y =1.0 x +1.94) with little impact of pulse repetition frequency or misalignment up to 30°. Gain dependency was noted but could be optimized by visual inspection of the color image. Conclusions Automatic integration of numerical data within color Doppler flow fields is a feasible new method for quantifying flow. It is simpler and faster, requires fewer assumptions, and uses only one apical view. ACOM is a promising new approach to echocardiographic quantification that deserves further study and refinement.