Key result
Single-sample pulsed Doppler overestimates mitral velocity profiles, skewing cardiac output calculations by ~13%.
Why the study?
Information on blood velocity distribution across the natural mitral valve is needed for basic fluid dynamic studies and for precise cardiac output estimates by Doppler echocardiography.
Effect estimate: r = 0.65
p-value: p=<0.01
Assuming a flat mean velocity profile across the mitral valve when using a single center sample volume with pulsed Doppler ultrasound can introduce errors of +13 +/- 15% in cardiac output measurements due to skewed diastolic velocity profiles from an anterior vortex.
OBJECTIVES: This study investigated the velocity distribution across the natural mitral valve. BACKGROUND: Information about the blood velocity distribution across the mitral valve is of interest in basic fluid dynamic studies of the natural mitral valve and is needed for precise cardiac output estimates by Doppler echocardiography. METHODS: The velocity distribution across the mitral valve was measured by epicardial Doppler echocardiography in ten 90-kg anesthetized pigs. By rotating the ultrasound transducer in 30 degrees intervals from the apical position, we constructed two-dimensional velocity profiles across the left ventricular inflow tract from diameters from each rotation arranged around a reference point. The time-averaged mitral velocity profile was calculated to estimate the error in cardiac output calculations that may occur with pulsed Doppler ultrasound when a single sample volume is used to record the mean velocity across the mitral orifice. RESULTS: The time-averaged diastolic cross-sectional mitral velocity profiles at the level of the mitral annulus and leaflet tips were variably skewed because of the development of a large anterior vortex in the left ventricle during the deceleration of early diastolic inflow and atrial systole. The ratio of the time-velocity integral of the center sample volume to the spatially averaged time-velocity integral was 1.13 +/- 0.15 (mean +/- SD) (range 0.80 to 1.32). Using regression analysis, we found a correlation between the degree of nonuniformity of the cross-sectional velocity distribution and the peak velocity of the anterior vortex (r = 0.65, p < 0.01). CONCLUSIONS: The assumption of a flat mean velocity profile across the mitral valve can introduce errors of +13 +/- 15% (mean +/- SD) in cardiac output measured with pulsed Doppler ultrasound when one is interrogating a single center sample volume.
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Kim et al. (1994) studied Natural mitral valve flow velocity distribution (porcine model) (n=10). Epicardial Doppler echocardiography using a single center sample volume vs. Spatially averaged two-dimensional mitral velocity profile was evaluated on Ratio of center sample volume time-velocity integral to spatially averaged time-velocity integral (and degree of cross-sectional velocity nonuniformity) (r = 0.65, p=<0.01). Pulsed Doppler ultrasound using a single center sample volume overestimated spatially averaged mitral velocity profiles, introducing cardiac output errors of +13 ± 15%.
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