Use of Echocardiography in Large Animals
Echocardiography is a noninvasive diagnostic tool that uses sound waves in the range of 1.0 to 18.0 MHz to visualize the heart in motion, using either a single icepick (M-mode) or a two-dimensional (2D; B-mode) image.
Noninvasive evaluation of blood flow in the heart and great vessels is performed with pulsed-wave, color-flow, and continuous-wave Doppler echocardiography. Precise localization of abnormal flow within the heart and great vessels is performed with pulsed-wave and color-flow Doppler echocardiography, whereas continuous-wave Doppler echocardiography is used to determine the peak velocity of blood flow and to noninvasively estimate pressure gradients. In contrast to M-mode and 2D echocardiography, for which the best image is obtained with the ultrasound beam perpendicular to the structures being imaged, optimal Doppler signals are obtained with the ultrasound beam parallel to the blood flow being evaluated. For accurate peak blood flow velocities to be recorded with continuous-wave Doppler echocardiography, the ultrasound beam should be as close to parallel as possible (parallel to the mitral valve (Fig. 30.3), and the left atrial area can also be measured from this view.24 The diameters of the aorta and pulmonary artery should be measured from similar locations in the vessel on the 2D echocardiogram and compared. Echocardiography should be considered a useful diagnostic test to evaluate patients with the following complaints, physical examination findings, or tentative diagnoses:1. Cardiac murmur, to determine the etiology of the murmur
a. Any grade 3/6 or louder holosystolic or pansystolic murmur on the left side of the thorax
b. Any grade 4/6 (3/6 in prepurchase setting) or louder holosystolic or pansystolic murmur on the right side of the thorax
c. Any holodiastolic decrescendo murmur
d. Any continuous machinery murmur
2.
Congenital heart defects, especially VSDs and atrial septal defects (ASDs)3. Acquired valvular heart disease
4. Cardiac enlargement
5. Cardiac arrhythmias not associated with high resting vagal tone
6. Unexplained exercise intolerance or collapse or exercise intolerance attributed to cardiac causes
7. Muffled heart sounds, pericardial friction rubs, or pericardial effusion
8. Myocarditis or myocardial dysfunction
9. Congestive heart failure (CHF)
10. Pulmonary hypertension
11. Cardiovascular neoplasia
12. Aortic rupture or other abnormalities of the great vessels
13. Ionophore toxicity or exposure to other myocardial toxins
14. Any unexplained fever of unknown origin, with or without a cardiac murmur
Color-flow Doppler echocardiography should be used to map the size and location of a turbulent jet associated with an intracardiac or extracardiac shunt, valvular regurgitation, or stenosis (rare) and to semiquantitate its severity.25,26 Continuous- wave Doppler echocardiography can then be used to measure the peak velocity of blood flow in the jet, estimating (nonin- vasively) the pressure difference between cardiac chambers using the Bernoulli equation. This can be accurately performed in most patients with a VSD, yielding information about the hemodynamic significance of the defect, but is difficult to impossible to accurately perform in many patients with valvular insufficiencies because of the limited windows available for interrogating blood flow in large animals and the inability to align the ultrasound beam to within 20 degrees of the turbulent blood flow. This poor alignment of the ultrasound beam with the regurgitant jet results in an underestimation of the peak regurgitant jet velocity. Contrast echocardiography, a technique involving microbubble-laden injections of saline, carbon dioxide, or indocyanine green, can also be used to demonstrate valve dysfunction and the direction of intracardiac and extracardiac shunts (VSDs, ASDs) but has largely been replaced by color Doppler echocardiography. TDI should be performed to look for left atrial systolic dysfunction (left atrial stunning) post conversion of AF.27 TDI and speckle tracking are also useful in identifying ventricular myocardial dysfunction.28-32
More on the topic Use of Echocardiography in Large Animals:
- Use of Echocardiography in Large Animals
- Smith Bradford P., Van Metre David C., Pusterla Nicola (eds.). Large Animal Internal Medicine. Part 1. 6th edition. — Elsevier,2020. — 2279 p., 2020
- Cardiac Catheterization in Large Animals
- Congenital Cardiovascular Disease
- Vascular Disease: Aneurysms, Thrombosis, and Embolism
- Valvular Heart Disease
- References
- Peripheral Edema, Pleural Effusion, and Ascites
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- Critical Care and Fluid Therapy Monitoring Techniques