6.5.2 Clinical signs and prognosis
In mild cases, the athletic performance of the horse is usually unaffected, and the finding of a murmur of AR is not sufficient alone to warrant a reduction in the level of exercise. The condition is likely to deteriorate with time, but usually AR is not the reason for the eventual retirement or death of the animal. If the condition is more severe, the arterial pulse may become bounding, or 'water hammer' in character, due to the volume overload and rapid diastolic run-off in pressure. The pulse quality has been shown to be a very useful clinical guide to the severity of the disease. The resting heart rate can also be a useful guide to significance, as with other conditions. Resting heart rates in excess of 45 per minute are a cause for concern and would indicate the need for further investigation.
The intensity of the murmur of AR is of very little value as a guide to severity. Some animals with very loud murmurs of AR (grades 5 or 6/6) may have relalittle volume overload, while animals with quieter murmurs may have sufficient volume overload to result in clinical signs of poor athletic performance or even CHF. Identification of coexisting disease is another important conFor example, if the condition is found in conjunction with MR, the prognosis is much worse.
Endocarditis, although relatively uncommon, most commonly affects the aortic valve in adult horses. Identification of a murmur of AR in a sick animal should therefore lead to consideration of the possibility of an infectious cause for valvular incompetence. Many more animals will coincidentally have a murmur of AR and an illness other than endocarditis; however, the condition carries a grave prognosis if not diagnosed and treated early. Therefore, unless there are other obvious reasons for an illness in an animal with a murmur of AR, further investigative tests are warranted.