The Challenges of Subclinical Myocardial Disease in Cats

Myocardial disease is common in cats with a prevalence of around 15% of the general population, that increases up to approximately 30% in older cats.

Hypertrophic cardiomyopathy is the most common form of myocardial disease but other, less common forms of myocardial disease, including restrictive cardiomyopathy (RCM), dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ARVC) are important to recognise.

How do cats with subclinical myocardial disease present?

Identifying cats with subclinical myocardial disease can be challenging. Unlike dogs with mitral valve disease for example, the detection of a heart murmur is not a reliable screening tool in cats. Although most cats with HCM have an audible heart murmur, up to 30% of cats with non-obstructive forms of disease do not have a murmur. Murmurs can also be variable (dynamic) making their detection and characterisation inconsistent. On the other hand, murmurs are common in healthy cats. The detection of other abnormalities on auscultation such as gallop sounds or arrhythmia is very important as these are rare in healthy cats and should prompt further investigations. A normal physical examination does not therefore rule out subclinical disease and sudden onset of CHF, ATE or sudden death may occur without warning signs.

Although in the majority of cats, myocardial disease remains subclinical throughout their lives, about a third of affected cats will develop clinical signs of congestive heart failure (CHF), arterial thromboembolism (ATE) or both. Sudden death is uncommon but can occur without previous signs. It is therefore of high importance to identify risk factors that can help distinguish cats that have a favourable outcome from cats at risk of developing clinical signs or cardiac death.

Younger, asymptomatic cats are more likely to have a favourable prognosis whereas the presence of a gallop sound or arrhythmia on physical examination is associated with increased risk of complications.

What treatment should be considered for cats with subclinical myocardial disease?

Treatment of cats with subclinical myocardial disease is limited as randomised clinical trials showing effective treatment to delay or prevent life-threatening complications are lacking. However, owner education to recognise early signs (e.g. resting respiratory rate) and prophylactic treatment for ATE are two examples of interventions that can reduce the risk of life-threatening complications.

Recently published guidelines for the classification, diagnosis, and management of cardiomyopathies in cats, provide a staging system for cardiomyopathy that helps identifying cats at low and high risk of developing life-threatening complications.

References and suggested reading:

Luis Fuentes V, Abbott J, Chetboul V, et al. ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. J Vet Intern Med. 2020;34(3):1062-1077. doi:10.1111/jvim.15745

Fox PR, Keene BW, Lamb K, et al. International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study [published correction appears in J Vet Intern Med. 2018 Nov;32(6):2310]. J Vet Intern Med. 2018;32(3):930-943. doi:10.1111/jvim.15122.