8.1.4 Conditions resulting in a cardiac murmur
Murmurs thought to indicate the presence of mitral regurgitation (MR) are potentially the greatest cause for concern because they are often associated with poor athletic performance and even congestive heart failure. The significance of mitral regurgitation was described in detail in section 6.2.5. As a general rule, if a murmur of MR is quiet (grade 1 or 2) and localised, it is seldom a significant problem at the time of examination (even in high performance horses). Howthe progression of the condition is difficult to predict and therefore there is some degree of risk involved in purchasing the animal, although it may be relatively small in some circumstances. The best way to predict the likely course of the disease is to examine the animal again in a few months time, and if possible to perform serial echocardiographic examinations. However, this is not always possible. The owner's intended use of the horse is also relevant because the longer the period over which they expect good performance, the greater the possibility of deterioration.
If a murmur of MR is grade 3/6 or greater, is widespread, or if there is any suggestion of poor exercise tolerance, echocardiography offers the best proof evaluating the severity of the condition. Whether this is performed will depend on the particular owner and prospective purchaser, but unless the animal is of little financial value it is well worthwhile even if this requires referral. Any signs of volume overload indicate that the condition is haemodynamically sigSome purchasers may be able to take a risk with horses in the early stages of volume overload, because they may perform satisfactorily, particularly for activities such as dressage, show-jumping and hacking, while having moddegrees of MR. If MR is associated with significant volume overload, pathological arrhythmias, or a resting tachycardia, purchase should not usually be recommended.
Mitral valve prolapse may have a better prognosis than degenerative mitral valve disease. If a murmur is thought to be due to prolapse, and preferably this assumption is backed up by echocardiographic evidence, a better prognosis for future athletic use is usually warranted.
Tricuspid regurgitation (TR) is a common finding in fit National Hunt racehorses, when it is seldom the cause of poor athletic performance. It may also be relatively common in other large fit horses. However, in some horses TR may affect performance and, in extreme cases, may even result in congestive heart failure.
When TR is detected at a pre-purchase examination it should be recorded on the examination form. In large, fit horses, if there is no suggestion of limited peror other problems, it is probably acceptable to state that localised murmurs of TR are unlikely to be associated with sufficient regurgitation to prevent the animal's use for athletic activity. Judgement should be circumspect in other types of animal. The best method of estimating the significance of the finding is to perform an echocardiographic examination. Echocardiography is recommended if TR is detected in animals which are seldom affected such as horses under the age of 4, pleasure horses and ponies and, ideally, for accurate evaluation in racehorses.
Aortic regurgitation (AR) is a common finding in the older horse, although it may be found in animals as young as 4 years of age, or even in association with congenital heart disease. The intensity of a murmur of AR is a very poor guide to its significance. However, the resting heart rate and arterial pulse quality are useful guides in advanced disease. The best method of estimating the sigof AR is to perform an echocardiographic examination. Unless there are signs of volume overload, the animal may be suitable for athletic use (see section 6.5.3). Since loud heart murmurs are an obvious cause for concern, an echocardiographic evaluation is often of benefit for the vendor and prospective purchaser. Without this examination, perfectly useful horses will be turned down at pre-purchase examinations. The guidelines for monitoring the proof AR are the same as for MR. If AR is associated with MR, or significant pathological arrhythmias are present, purchase should not usually be recommended.
Animals with complex congenital heart disease are unsuitable for riding or breeding. However, animals with small ventricular septal defects (VSDs) may perform normally and may be suitable for sale for all but the most arduous activities. Unless signs of heart failure are present, the severity of a VSD is difto judge from clinical examination alone; they are nearly always associated with a murmur of grade 5 or 6/6 irrespective of the size of the defect (see section 5.5.3). The best method of estimating the significance of a VSD is to perform an echocardiographic examination. Two-dimensional echocardiography and Doppler echocardiography are very useful for assessing severity and guiding prognostication. Prospective purchasers of animals with a VSD should be informed that these animals are not suitable for breeding and that congenital lesions are often excluded from the conditions of insurance policies.
A guiding rule is that on the few occasions when a murmur is detected but a specific diagnosis cannot be made from accurate auscultation, a specialist opishould be sought if the prospective purchasers wish to proceed. If the regurgitant murmur is relatively quiet it may not be relevant at the time of examination, but it may be important at some point in the future. If a murmur is relatively loud and the client is still interested in purchase, then an echocardioexamination is worthwhile in order to quantify the degree of volume overload if any, and to give as accurate a prognosis as possible.