6.7 Myocardial disease
Myocardial disease can affect cardiac function because the normal electrical activation processes are disturbed, or because of abnormal contraction or relaxation of cardiac muscle. The incidence of myocardial disease in the horse is a matter of some debate. Certainly, few animals develop myocardial failure without severe underlying valvular heart disease. However, lower grade disease leading to the development of arrhythmias or to sufficiently poor myocardial function to result in poor athletic performance may be more common than has been recognised previously. The use of echocardiography, in conjunction with exercise and 24-hour ECGs and clinical pathology where appropriate, may lead to an improvement in the understanding of myocardial disease in the horse.
The aetiology of myocardial disease in horses is poorly understood, although there are a number of situations in which myocardial disease may be identified. The most common is myocarditis which may occur in animals which have suffered from viral or bacterial respiratory infection. Myocardial fibrosis and/or necrosis have also been recorded. In addition, myocardial function may be affected by systemic disease such as septicaemia. Drugs, toxins and electrolyte disturbances may also result in arrhythmias and/or poor myocardial function. Idiopathic cardiomyopathy, which is common in other domestic species such as the dog and cat, is seldom recognised in the horse. This may be partly because of a failure to recognise the disease. However, the difficulty in making a specific, definitive diagnosis of myocardial disease may also lead to overdiagnosis of these conditions.
6.7.1 Diagnosis of myocardial disease
6.7.2 Specific myocardial condiation
6.7.3 Treatment of myocardial disease