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Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography
H Dittmann1, W Voelker, K R Karsch
1Medical Department III, University of Tuebingen, West Germany.
Insights
Pulsed Doppler echocardiography accurately measures cardiac output when flow area and sampling site are optimized. Measurements at the aortic annulus, using M-mode tracings, provided the highest accuracy compared to thermodilution.
Area of Science:
- Cardiovascular Physiology
- Echocardiography
- Hemodynamics
Background:
- Accurate measurement of cardiac output is crucial for assessing cardiovascular function.
- Thermodilution is a standard method, but non-invasive techniques like Doppler echocardiography are desirable.
- Previous studies show variable accuracy for Doppler-derived cardiac output.
Purpose of the Study:
- To evaluate the accuracy of pulsed Doppler echocardiography for cardiac output determination.
- To compare Doppler measurements with thermodilution across different sampling sites and area calculations.
- To identify optimal parameters for accurate non-invasive cardiac output assessment.
Main Methods:
- Simultaneous cardiac output measurement in 40 patients using pulsed Doppler echocardiography and thermodilution.
- Doppler sampling at mitral annulus, mitral leaflet tips, and aortic annulus.
- Calculation of cross-sectional areas using M-mode and 2D echocardiography; cardiac output derived from time-velocity integrals, areas, and heart rate.
Main Results:
- Doppler flow measurements showed significant correlation with thermodilution (r = 0.79–0.93).
- Aortic annulus measurements using M-mode annular area yielded the highest accuracy (r = 0.93, SEE = 0.589 L/min).
- Incorrect sampling sites (mitral tips, mitral annulus) and area calculations (aortic bulb) led to under- or overestimation of cardiac output.
Conclusions:
- The accuracy of pulsed Doppler cardiac output measurement is highly dependent on the chosen flow area and sampling site.
- Optimal accuracy is achieved when Doppler measurements are taken at the aortic annulus, utilizing M-mode derived annular area.
- Ensuring measurements are taken at the same level within the left ventricular inflow or outflow tract is critical for reliable results.
Abstract:
In 40 patients cardiac output was simultaneously determined by pulsed Doppler echocardiography and thermodilution (range 4.0 to 10.2 liters/min). The sample volume was located in the center of the mitral anulus, at the tips of the mitral leaflets and in the center of the aortic anulus. Circular cross-sectional areas of the mitral anulus, aortic anulus and aortic bulbus were calculated from M-mode and two-dimensional echocardiographic diameters. The varying short axis of the elliptical mitral opening area was obtained from the diastolic leaflet separation in the M-mode, and the long axis was derived from the maximal mitral orifice area or mitral anulus diameter. Cardiac output was calculated by multiplying time-velocity integrals with the different areas and heart rate. Doppler flow measurements correlated significantly with the thermodilution method (r = 0.79 to 0.93). Flow measurements at the aortic anulus were most accurate (r = 0.93, SEE = 0.589 liter/min) if the annular area was derived from the M-mode tracing. Measurement of the anulus in the apical five chamber view yielded a significant underestimation and the area of the aortic bulbus provided an overestimation of cardiac output. Left ventricular inflow was underestimated at the mitral leaflet tips and overestimated at the mitral anulus. The accuracy of pulsed Doppler cardiac output measurements strongly depends on the assumed flow area and sampling site. Both should be determined at the same level in the inflow or outflow tract of the left ventricle. Measurement of cardiac output in the center of the aortic anulus provided the highest accuracy.