Page 994 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 969

VetBooks.ir identify structural anomalies and to assess the car- tematic way using routine images (Figs. 8.5–8.8).
Echocardiography should be performed in a sys-
diovascular effects of these findings. Low-frequency
probes (2–4 MHz) are required. While a decrease
vided the machine used has sufficient capabilities
in image resolution is associated with such low- Most evaluation is performed on the right side, pro-
frequency probes, these frequencies are necessary to achieve a depth of penetration of 27–30 cm.
to attain sufficient depth of penetration (24–30 cm). Additional imaging on the left side is indicated when
In all instances, simultaneous ECG recording (dis- the depth of penetration is not sufficient to image
played on the ultrasound screen) during echocar- the left heart from the right side and when any mur-
diography is indicated to allow assessment of the murs attributable to left-heart disease are detected.
timing of cardiac events. With M-mode imaging (Fig. 8.9) chamber size
Echocardiographic examination is indicated in and functional indices can be assessed. The timing of
any situation where cardiac disease is suspected, valve or wall motion relative to the ECG recording
including in congenital cases, which may present with can be assessed. M-mode is most frequently used to
a cardiac murmur or cyanosis. Echocardiography assess left ventricular functional indices. Reference
provides additional information whenever a cardiac intervals have been published for Standardbred and
murmur, not considered to be a functional murmur, Thoroughbred racehorses. Heart size is poorly corre-
is detected. It is also indicated to assess underlying lated with body weight in the horse and a comparison
cardiac function when a potentially pathological with reference intervals should be carried out with
arrhythmia is detected or when myocardial disease or due consideration to the breed of the horse and to the
pericardial disease is suspected. Echocardiography individual animal’s performance history. Larger car-
may also be indicated when pyrexia of unknown diac dimensions would be likely in an animal with a
origin is present (e.g. endocarditis), when exposure prolonged history of a high level of exercise.
to a known cardiotoxin such as monensin has been Doppler imaging can be used to assess blood flow.
detected (in the assessment of ventricular function) Accurate assessment of flow velocities with pulsed-
and in any case of unexplained poor performance. wave or continuous-wave (Fig. 8.10) Doppler
Once an abnormality has been demonstrated, echocardiography necessitates that the ultrasound
repeated echocardiography can be used to assess beam be as close to parallel to the measured flow
the progression of the lesion and its cardiovascular as possible. This is difficult or impossible to obtain
effects over time. in most instances where valvular regurgitation has

8.5 8.6

Fig. 8.5 Right-sided, long-axis, four-chamber view. Fig. 8.6 Right-sided, long-axis, outflow tract view
Image taken from the right 4th ICS. The probe is highlighting the pulmonic valve. Image taken from the
angled slightly caudally until all four cardiac chambers right 4th ICS. The probe is angled cranially until the
are visible. RV = right ventricle; RA = right atrium; pulmonary artery is visualised. RV = right ventricle;
LV = left ventricle; LA = left atrium; Ao = aorta. RA = right atrium; Ao = aorta; PA = pulmonary artery.