Cardiomyopathy in cats is a common cause of cardiac mortality, but occult cardiomyopathy (OCM) can be difficult to diagnose because clinical examination, electrocardiography, and thoracic radiography have limited specificity and sensitivity. Traditional and Doppler echocardiography are helpful but require technical expertise. Plasma concentrations of B-type natriuretic peptide (BNP) have been shown to reflect cardiac dysfunction. BNP is secreted from atrial and ventricular myocytes during myocardial stretch, pressure overload, and neurohormonal stimuli; blood concentrations increase during acute congestive heart failure and asymptomatic or minimally symptomatic diastolic and systolic dysfunction. N-terminal (NT)-proBNP measured significantly higher in 113 cats with OCM as compared with 114 normal cats. Cats with hypertrophic obstructive cardiomyopathy had significantly higher NT-proBNP concentrations than did cats with nonobstructive forms. The findings suggested that NT-proBNP may be useful in screening for heart disease.
Murmurs are common in cats seen in general practice but discerning a physiologic murmur from a pathologic murmur can be difficult. Echocardiography, the gold standard for diagnosis and differentiation, can be cost prohibitive. Thus, a low-cost blood test that helps identify which patients are likely candidates for OCM would be of value. When using a cutoff value of >46 pmol/L, NT-proBNP concentrations provided ~91% specificity and 86% sensitivity (as compared with echocardiographic diagnosis) in discriminating normal cats from cats with OCM. When the cutoff value was increased to 99 pmol/L, specificity increased to 100% but sensitivity decreased to 71%, which means that all cats were correctly identified when a higher normal value was used but some cats with OCM were not identified. However, using NT-proBNP as a screening tool for cats is an appropriate first step in determining the need for more costly diagnostics, such as echocardiography.
—Amara Estrada, DVM, DACVIM (Cardiology)