Echocardiography
Basic Information 
Equipment, Anesthesia
• Two-dimensional (2D), motion-mode (M-mode), and Doppler (color-coded, pulsed-wave, continuous-wave) capabilities.
• Simultaneous electrocardiogram (ECG) to allow accurate timing of cardiac measurements and proper interpretation of Doppler signals.
• Cine loop capabilities, allowing review of a number of previous cardiac cycles after freezing the image.
• Displayed image depth of at least 30 cm for adult horses; less depth is needed for ponies and foals. If the depth is less than 30 cm, the entire heart of an adult horse will not fit on the screen and the exam must be performed from both the right and left sides.
• Phased array or sector scanning transducer.
• For adult horses, a low-frequency (2.5 MHz or lower) transducer.
• For yearlings, foals, and ponies, a higher frequency transducer (3.5–5.0 MHz) can be used.
• Anesthesia is not used in horses for transthoracic cardiac ultrasound.
Anticipated Time
Variable, depending on complexity of problem, patient cooperation, and examiner experience
Preparation: Imporant Checkpoints
• Image quality is aided by clipping the hair over the right third and fourth intercostal spaces (ICS) between the olecranon and the point of the shoulder (ie, over the caudal aspect of, and just caudal to, the triceps muscle) and in a comparable location over the left third, fourth, and fifth ICS. Clipping may not be necessary in horses with a fine summer haircoat, particularly in smaller, thinner horses. In this case, more liberal use of alcohol and ultrasound gel will be helpful.
• Isopropyl alcohol to clean the area and ultrasound coupling gel are applied after clipping.
Possible Complications and Common Errors To Be Avoided
Common errors or pitfalls to be avoided:
• Inability to find the heart: Transducer is located too far caudal; relocate one ICS cranial.
• Beware of excessive gain, particularly in the near field.
• Reverberation artifacts are common and cardiac masses are rare; do not overinterpret.
• It is advisable to try to reproduce any visible abnormalities in another image plane to avoid misinterpretation or overinterpretation.
• The muscle of the outermost portion of the posterior free wall of the left ventricle appears hypoechoic compared with the inner portion. Do not confuse with pericardial effusion.
• Hyperechoic areas within the myocardium are common and may not be associated with dysrhythmias or other clinical signs.
• Measurements made from left parasternal images cannot be directly compared with measurements made from a right parasternal approach because they are made across a different axis. Normal values or serial comparisons must be obtained from the same side.
Procedure
• The horse should be standing quietly; stocks are often used but are not necessary if unavailable or the horse is unable or unwilling to stand in stocks.
• The electrocardiogram (ECG) electrodes should be placed according to the ultrasound manufacturer’s instructions. These are usually placed in a base-to-apex configuration. Clipping is not necessary, but sufficient alcohol or water to saturate the area is needed to have a trace with adequate electrode contact and without artifact.
• A systematic approach using standard views is critical to avoid overlooking important information, reduce variability, and be able to convey important findings to others.
The examination is initially performed from the right side and is facilitated by placing the horse’s right leg forward (Figure 1).
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