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Measurement of cardiac output in standing horses by Doppler echocardiography and thermodilution
K J Blissitt1, L E Young, R S Jones
1Department of Veterinary Clinical Studies, University of Edinburg, Royal (Dick) School of Veterinary Studies, Roslin, Midlothian, UK.
Insights
Doppler echocardiography offers a safe, noninvasive method for measuring cardiac output in horses, closely correlating with thermodilution. Measurements from the aorta showed better agreement than those from the pulmonary artery.
Area of Science:
- Veterinary Medicine
- Cardiovascular Physiology
- Diagnostic Imaging
Background:
- Accurate measurement of cardiac output is crucial for assessing cardiovascular function in horses.
- Thermodilution is a common invasive method, but noninvasive alternatives are sought.
Purpose of the Study:
- To compare cardiac output measurements obtained via Doppler echocardiography with simultaneous thermodilution in conscious horses.
- To evaluate the influence of measurement site and technique on Doppler-derived cardiac output.
- To assess the agreement and correlation between the two methods.
Main Methods:
- Cardiac output was measured in 9 conscious horses using both Doppler echocardiography and thermodilution.
- Doppler measurements involved recording mean blood flow velocities from the aorta and pulmonary artery.
- Flow area was calculated from vessel diameter measured via 2D ultrasound, with variations in technique explored.
Main Results:
- Doppler echocardiography measurements of cardiac output showed close correlation with thermodilution (r=0.89 for aorta, r=0.77 for pulmonary artery).
- Measurements using aortic outflow correlated more closely with thermodilution than pulmonary artery measurements.
- No significant bias was found when using the leading edge method for ascending aorta measurements, with narrow limits of agreement (+/- 12.26 l/min).
Conclusions:
- Doppler echocardiography is a safe and noninvasive method for determining cardiac output in horses.
- The agreement between Doppler echocardiography and thermodilution in horses is comparable to findings in human studies.
- Optimized Doppler techniques, particularly focusing on the aorta, provide reliable cardiac output estimations.
Abstract:
Measurement of cardiac output by Doppler echocardiography were compared to simultaneous measurements by thermodilution in 9 conscious horses. In the Doppler technique, mean blood flow velocities for estimation of cardiac output were recorded from the aorta and pulmonary artery. The flow area of each vessel was calculated from the vessel diameter, measured from a 2-dimensional ultrasound image. Differences in the site and method of measuring the vessel diameter altered the estimation of cardiac output by the Doppler method. Cardiac output was modified by the i.v. infusion of 4 micrograms/kg bwt/min dopamine and 4 micrograms/kg bwt/min dobutamine and by the i.v. administration of 10 micrograms/kg bwt detomidine and 20 micrograms/kg bwt butorphanol. Doppler measurements of cardiac output correlated closely with measurement by thermodilution. Measurements from the aortic outflow correlated more closely with thermodilution, than those from the pulmonary artery (r = 0.89 and r = 0.77, respectively). Doppler measurements when the mean flow velocity was recorded from the aorta and the flow area was measured from the ascending aorta using the leading edge method. There was no significant bias between the 2 techniques when Doppler flow velocities were recorded by this method and the limits of agreement were narrow (+/- 12.26 l/min). The differences between the 2 methods increased with increasing cardiac output. Doppler echocardiography is a safe noninvasive method of measuring cardiac output in horses. The agreement between Doppler echocardiography and thermodilution in this study is similar to that reported in man and is similar to that reported between thermodilution and other techniques in man.