8.1.3 Findings at the pre-purchase examination
If a murmur or an arrhythmia which is classified as functional is detected during the initial examination, no further steps need be taken. However, if a murmur is pan or holosystolic or holodiastolic, it is likely to result from a pathological process and needs further, careful evaluation. The vital part of the examination is therefore to decide whether a murmur is associated with a pathological process or is functional in origin (Table 3.4).
If the resting heart rate is elevated (>45 per minute), cardiac disease should be suspected unless another cause is detected. It is therefore very important that a true resting heart rate is recorded. Animals with a loud heart murmur (grade 4 or greater) and a tachycardia, are unlikely to be suitable for purchase under any circumstances. However, assessment of the severity of pathological murmurs often requires further investigation such as echocardiography.
The period of time that a murmur has been known to be present can be a useful guide to the rate of progression and may be helpful during a pre-purchase examination if such information is reliable. A condition which has been present for some months or years with no deterioration is less likely to deteriorate rapidly after purchase. This is, however, only a guideline.
The exercise phase
The exercise section of the pre-purchase examination is often fraught with difIdeally the animal should be put through arduous work in surroundings which allow this to be performed safely. Often circumstances are far from ideal. In particular, lunging animals as an alternative to ridden exercise is to be avoided if possible because it is seldom possible to raise the heart rate to maximal levels. Some arrhythmias occur during the post-exercise period and may be confused with pathological arrhythmias. These are particularly common following sub-maximal exercise (see below).
The effect of exercise on cardiac murmurs is often taken as a useful guide to significance. This rule of thumb should be avoided if possible, as it is often used as an alternative to making a specific diagnosis of the source of a murmur. Murmurs which are functional in origin are variable at different heart rates and may become less apparent after exercise. However, mild or moderate intensity murmurs of valvular regurgitation, which may have an important bearing on future use, cannot always be heard easily under the conditions of a post-exercise examination. In addition, some functional murmurs become louder after exercise (see section 3.8.2).
During the exercise phase of the examination, it is very difficult to judge whether the level of physical fitness is affected by underlying heart disease or by the amount of training which the horse has been given. Guidelines for the expected heart rates at different gaits and expected rate of recovery to resting heart rates are given in section 3.8.3. However, a standardised exercise test cannot be performed during a pre-purchase examination, so the onus is on interpretation of the level of fitness, taking all factors into consideration, before any inference is drawn regarding the effects of cardiac disease.