The asymptomatic patient

Abstract

Asymptomatic patients: I am hearing a heart murmur for the first time in an adult dog. What should I do? Incidentally discovered heart murmurs in adult dogs are common. Degenerative (myxomatous) mitral valve disease (DMVD) is by far the most common cause of acquired murmurs in dogs. Other possible causes would include dilated cardiomyopathy, bacterial endocarditis, previously undiscovered congenital heart disease and non-cardiac causes such as haemic murmurs and flow murmurs. In dogs with an appropriate signalment, a murmur with timing and location consistent with mitral regurgitation makes DMVD very likely. Factors that might make this less likely (or rule it out altogether) would include; the finding of a murmur that is audible continuously or in diastole, finding a murmur in a large breed dog or the presence of clinical signs indicative of significant systemic disease e.g. pallor or pyrexia. The single best diagnostic test to determine whether or not a murmur is caused by cardiac disease and to characterise the specific cause of a murmur is echocardiography. In some circumstances, echocardiography may not be possible due to cost or lack of access to appropriate equipment or expertise. In a patient suspected of having DMVD it is important to stage their disease as accurately as possible to ensure appropriate treatment can be instituted if appropriate. Asymptomatic patients: I am hearing a heart murmur for the first time in an adult cat. What should I do? Cardiomyopathies are the most common heart diseases in cats with hypertrophic cardiomyopathy (HCM) being the most prevalent form. HCM affects 15% of apparently healthy cats. Cardiac auscultation in cats is challenging as it lacks both sensitivity and specificity. Cardiomyopathies may not cause a heart murmur, thus some cats with clinically significant heart disease have a normal cardiac auscultation. Conversely, a murmur may be present in some cats with structurally normal hearts. Thus, absence/presence of murmurs may not always help in determining which cats have heart disease. However, the majority of cats with a murmur do have structural heart disease, especially older cats with loud (≥3/6) murmurs. In HCM, murmurs are commonly caused by dynamic LV outflow tract obstruction. Normal cats can have murmurs due to dynamic RV outflow tract obstruction (clinically benign). NT-proBNP is increased in cats with moderate-severe asymptomatic cardiomyopathy, thus it may be used as a first-line test to assess the likelihood of heart disease in a cat with a murmur. But echocardiography is required to confirm the presence of heart disease, and most importantly to assess for risk factors associated with increased risk of CHF and ATE (e.g. left atrial size). Systemic diseases that may cause a murmur should also be excluded, i.e. check blood pressure, haematocrit and T4 (cats >6 years). Normal and HCM cats may have heart murmurs, but a loud murmur in a cat >6 years is more likely to be associated with HCM and further investigations are recommended. Early interventions in cardiomyopathic cats may reduce the risk of serious complications, thus early detection of occult cardiomyopathies is paramount.