Page 723 - The Veterinary Care of the Horse

ELECTROCARDIOGRAPHY

An electrocardiogram (ECG) is a recording of the electrical activity of the heart. It is a useful
VetBooks.ir tool for measuring the heart rate and recording any arrhythmias. Deviations from the normal

pattern of electrical activity can also be seen if there is damage to the cardiac muscle.

ECHOCARDIOGRAPHY
Echocardiography is a specialized ultrasound examination of the heart. It is used to assess the

size, structure and motion of the heart. It may be helpful in identifying any changes such as
enlargement of a heart chamber or congenital defects. A special (Doppler) technique may be

used to investigate the flow of blood through the heart. It can help to identify the source of a
murmur. The function of individual valves and the degree of regurgitation (back flow from

leaky valves) can be determined.

EXERCISE TOLERANCE TEST

The horse’s heart is examined at rest and immediately after moderate exercise. The time

taken for the heart to return to the resting rate is recorded. The amount and type of exercise
will depend on the age and type of horse, its level of fitness, co-existing health problems, the

state of the going etc. Moderate exercise for a fit racehorse would be completely unrealistic
for a Shetland pony! In general, ten minutes of brisk exercise at trot and canter is sufficient
for most fit, working horses.

Immediately following the exercise, the heart rate is likely to be between 60 and 110

beats per minute. (The maximum heart rate following a fast gallop is around 225 beats per
minute.) Rates of greater than 125 may indicate that the heart is not functioning as it should.
As a general rule, it should return to close to the resting rate within 20 minutes if the horse is

left undisturbed and not excited in any way. This test is obviously not performed if the horse
is considered to be unfit for any kind of exercise.

The results of these tests are interpreted together with the findings of the full clinical
examination. Some of the most common conditions will now be considered.

Heart murmurs

Abnormal ‘whooshing’ sounds are sometimes heard between the normal heart sounds. These

sounds are known as murmurs and they vary in their significance. They may be the result of
turbulence in the blood flow due to a leaky heart valve. They are classified according to the
following.

• Whether they occur in systole or diastole and also their timing within this period, e.g. can