A biomarker is typically a substance in the blood that can be objectively measured and indicates a biologic or pathologic process or response to therapy.1
There are scores of cardiac biomarkers, but this article will focus on the 2 most clinically useful ones in the dog and cat: cardiac troponin I (cTnI) and N-terminal pro–B-type natriuretic peptide (NT-proBNP).
Cardiac TnI is an intracellular cardiac myofibrillar protein released into the circulation when cardiac myocyte injury and cell death or necrosis occur. It is a leakage cardiac biomarker; that is, it leaks into the circulation from damaged cardiomyocytes.
NT-proBNP is a neurohormone secreted from the atria and ventricles in response to volume expansion or pressure overload. It is a functional cardiac biomarker that is increased with stress, stretch, or strain on cardiomyocytes due to occult or overt heart disease.
Troponin is a protein that regulates interactions between actin and myosin within the sarcomere. This protein leaks into the bloodstream when the cardiomyocyte is disturbed. On the basis of many experimental and clinical studies in animals, cTnI is an excellent marker for myocardial injury because its increase and duration are proportional to the severity of injury.2–8 Cardiac TnI has maintained protein homology among all mammalian species. As a result, human troponin immunoassays can be used reliably in the dog and cat or any other domestic animal species. Many of the larger veterinary diagnostic laboratories now offer a cTnI assay.