Correlating the progression or severity of disease with a specific biologic substance can greatly influence the ability to
predict outcome. This concept is a rapidly expanding area of study in both human and veterinary medicine. Troponin I, or cTn1,
is a cardiac biomarker released when myocardial injury has occurred. Since it has a half-life of less than 70 minutes, elevated
circulating concentrations represent ongoing myocardial remodeling associated with chronic cardiac disease.
A study published in the Journal of Veterinary Internal Medicine this year shows promising results for this biomarker, which has been well-studied in human cases. The availability of more
sensitive assays has made detection of small concentrations of troponin I possible, increasing its utility as a prognostic
indicator in people. An acute phase protein called C-reactive protein (CRP), released rapidly with tissue destruction or inflammation, has also proved to be a good prognostic indicator in people
with heart failure. The goal of this study was to look at whether plasma concentrations of troponin 1 and CRP correlated with
the severity of cardiac disease in dogs and whether other cardiac assessments such as heart rate, systolic arterial pressure,
and various echocardiographic findings were associated with troponin 1 and CRP concentrations.
Both healthy dogs and a group of dogs with myxomatous mitral valve disease (MMVD), the most common acquired heart disease
in dogs, were included in the study. The dogs had to weigh less than 33 lb (15 kg) and be either free of cardiac disease or
have physical or echocardiographic evidence of MMVD. For each participant, an owner interview was conducted and a physical
examination was performed. An indirect blood pressure measurement, blood sample collection, and an echocardiographic evaluation
were done during the same visit. Troponin I concentrations were measured via an enzyme-linked immunosorbent assay (ELISA),
and a commercially available canine CRP ELISA was used to measure CRP concentrations. For each dog, disease severity was assessed
based on echocardiographic findings, including mitral regurgitation scores, jet size, and left-atrial-to-aortic-root ratio.
A comparison of results revealed that troponin I concentrations were significantly higher in the dogs with moderate to severe
cardiac disease and very low or undetectable in the healthy dogs. However, age and troponin 1 concentration were also strongly
associated in the dogs with heart disease. With advancing age, ongoing myocardial damage results in troponin 1 leakage. Previous
studies have shown an association between the development of arteriosclerosis and age in dogs, which may help explain the
age-related increases. While CRP was detected in all the dogs, the concentrations did not appear to be linked to the severity
of cardiac disease as they are in people. Since CRP can increase in response to inflammation of other organ systems, it is
not specific for cardiac disease. There was, however, a significant association among heart rate, troponin I concentration,
and severity of MMVD, suggesting that there may be a strong connection between increasing severity of the cardiac disease
and the activation of the sympathetic nervous system.
As a biomarker for canine chronic heart diseases, troponin I shows promise. Still, further studies are needed to identify
the reliability of troponin 1 plasma concentrations in combination with other diagnostic tests as a predictor of outcome.
Ljungvall I, Höglund K, Tidholm A, et al. Cardiac troponin I is associated with severity of myxomatous mitral valve disease,
age, and C-reactive protein in dogs. J Vet Intern Med 2010;24(1):153-159.