What can changes in serial measurements tell us about prognosis in myxomatous mitral valve disease?

Myxomatous mitral valve disease (MMVD) is the most common acquired heart disease in dogs, representing approximately 75 per cent of cases. MMVD is relatively straightforward to identify on the basis of a typical left apical, systolic heart murmur. However, the disease course varies markedly between affected individuals, with some dogs having static, non-progressive disease, while others may rapidly develop compensatory cardiomegaly and, eventually, congestive heart failure (CHF). Although a diagnosis of heart disease is a source of great concern for many owners, less than half of affected dogs will die as a direct result of MMVD. There would be a clear benefit to owners and clinicians if those dogs likely to experience significant disease progression – the development of cardiomegaly (which might benefit from treatment with pimobendan) and CHF – and, therefore, a shortened life expectancy could be accurately identified. The investigation of potential prognostic factors in MMVD has been an active area of research for many years. Echocardiographic measurements provide the most sensitive method of identifying cardiomegaly and, therefore, progressive disease. However, given how commonly MMVD is diagnosed in practice, it is highly unlikely that it will ever be possible for all affected animals to undergo echocardiography, due to financial and practical constraints. Researchers have, therefore, attempted to identify prognostic markers that do not rely on echocardiography, including circulating biomarkers such as N-terminal pro-B-type natriuretic peptide (NT-proBNP) and the cardiac troponins.