Discussion

Cardiac murmurs and arrhythmias are detected fairly frequently in horses at suitability for purchase examinations when they often create problems as the veterinary surgeon struggles to determine their significance and advise their clients appropriately.
In many cases though, a thorough examination of the cardiovascular system and a sensible dialogue with the prospective purchaser is all that is required to allow a sale to proceed, or otherwise. Occasionally, making a recommendation that the horse be referred for specialist cardiac examination will be the best course of action to reassure the purchaser and transfer responsibility of advice to a third party. Additionally such secondary examinations are often beneficial to clients in subsequently getting the horse accepted for insurance.
Equine cardiologists are often asked by practitioners about how loud a given murmur should be, or which arrhythmias mean that a horse should definitely fail a 'suitability for purchase' examination. Unfortunately there are no absolute rules. Clearly when any abnormality is detected in a horse showing signs of congestive heart failure, such as a persistently increased resting heart and respiratory rate, dependent ventral oedema, weak pulses, or when the murmur is associated with a precordial thrill, the horse is not a suitable candidate for purchase for any purpose and the decisions and advice are easy. Unfortunately, that scenario is rarely the one encountered in the real world. Much more often, low-medium grade murmurs are detected in clinically normal horses with no other signs of cardiac disease. If the client requesting the prepurchase examination is seeking perfection, then provided you are confident that the murmur you have heard is not caused by normal blood flow, the horse should fail. However recent work shows that between 20 and 50% of mature racing Thoroughbreds have audible cardiac murmurs, yet these murmurs have no discernible effect on their race performance. Clinical experience also suggests that the prevalence of these murmurs is similar in the sports horse population and logic must dictate that if they don't limit the athletic performance of a Thoroughbred racehorse, the chance that similar abnormalities might affect the athletic performance of an event horse, much less a dressage horse is nil.

Questions to answer in every case before useful advice can be given:

Cardiac factors:
- Can you make an accurate diagnosis and can you determine/guestimate the likelihood of progression of the abnormality you have found?

Owner factors:
- Is the horse destined to be a pet, a performer or is it being bought for profit?
- Will mortality, loss of use or veterinary insurance be required?
- Is the horse likely to be resold in future and is resale value important to the purchaser?
- Is the purchaser capable of understanding the risks of horse ownership and the concepts of balance of probabilities?
- Is the owner open to getting/making a deal?
- Are there personal factors which prevent them accepting a less than perfect horse?

Cardiac factors and optimising auscultation to make an accurate diagnosis
Despite advances in technology, cardiac auscultation is still the most important technique for the diagnosis of cardiac disease in horses and is the only tool available in the context of a standard prepurchase examination. With this in mind, it is crucial to develop a systematic and logical approach to this technique and be confident in its interpretation. Hearing a murmur, or an irregular cardiac rhythm, in the context of suitability for purchase examination may not mean a horse is unsuitable for your client, nor for the matter that it is even abnormal!
Cardiac murmurs are usually loudest nearest to the abnormal valve, or to the area of abnormal blood flow. Knowing this is of little diagnostic value though, if the valves can't be confidently located with a stethoscope to assess the point of maximal intensity of a murmur! Similarly timing a murmur to either systole or diastole and assessing its duration by referencing it to the normal heart sounds is also absolutely crucial in making a diagnosis. Without a diagnosis, it is impossible to formulate a prognosis and without either, you will not be able to advise your client appropriately.

There are however certain rules that you must always adhere to to avoid missing important abnormalities
- Always auscultate both sides of the horse's chest
- Always maintain a standard systematic approach so that you listen to all valve areas
- At the start of auscultation, specifically concentrate on heart rate and rhythm before being distracted by attempting to find murmurs. Failure to spot the abnormal rhythm of atrial fibrillation in a performance horse at a prepurchase examination is the one mistake to avoid at all costs; much more important to identify that than to miss a low grade murmur!
- Remember to listen carefully to both systole and diastole individually in each valve area. Humans are not good at multi- tasking and we vets are all tuned in to systole; it is all too easy to miss a low-grade murmur of aortic insufficiency, simply because no effort was made to concentrate specifically on diastole during the examination.
- If the auscultation environment is noisy or difficult make an effort to improve it: turn off radios and politely tell chatterers to be quiet. Move the horse into a quiet location and wait until it is calm. If conditions for your examination cannot be improved, make a note of it and tell the client you were unable to complete an adequate assessment of their horse's heart.
- Always explain to the client what you have heard, even if you think the abnormality you heard was physiological, or of no consequence. Add this information to your report to avoid potential trouble for yourself in future.
- Do not be afraid of offering the client a more specialist cardiac examination, if you are unsure about your diagnosis, or the client requires additional reassurance. If they decline, the risk becomes theirs, not yours. Based on this experience, the majority of horses examined in this way do then proceed to sale.