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cTnI as a predictor of cardiac death in cats with HCM | VETgirl Veterinary CE Podcasts

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Hypertrophic cardiomyopathy (HCM) is the most common form of heart disease in cats and carries a particularly poor prognosis for those cats with HCM that experience aortic thromboembolism (ATE), congestive heart failure (CHF), and distortion of cardiac chamber dimensions and function. Assessment of cardiac biomarkers such as cardiac troponin I (cTnI) and N-terminal pro-B-type natriuretic peptide (NTproBNP) in various disease states has increased in human and veterinary medicine but little prognostic data is available for these biomarkers with HCM in cats. Both cardiac biomarkers appear to carry prognostic value in humans with HCM. So, Borgeat et al out of Royal Veterinary College wanted to investigated whether a single measurement of NTproBNP or cTnI would provide such value in cats with HCM in a study called Plasma Cardiac Troponin I Concentration and Cardiac Death in Cats with Hypertrophic Cardiomyopathy.

They performed a prospective study to evaluate this from February 2010 to May 2011. Cats that were diagnosed with HCM based on echocardiography were included. Exclusion criteria included those cats with underlying disease such as hyperthyroidism, hypertension, non-HCM cardiomyopathy, or chronic kidney disease. A total of 41 cats met the inclusion criteria. Overall, 24/41 (59%) died by the end of the study period; 21/24 died due to heart disease. In this study, 16 cats were euthanized, while 5 died suddenly.

What they found in this study? cTnI concentrations were higher in cats with left ventricular wall hypokinesis (e.g., reduced systolic function), but there was no association of left ventricular hypokinesis with NT-proBNP. NTproBNP concentrations were higher in cats with CHF (as previously demonstrated in other studies).

In cats that had cTnI levels >0.7 ng/mL, there was a significantly shorter survival time (median: 40 days). In this study, they controlled for whether or not the cat had CHF and what the echocardiographic measurements were; regardless of these factors, a cTnI level > 0.7 ng/mL was “independently associated with time to cardiac death.”

In cats that had NTproBNP levels > 250 pmol/L, there was also a significantly shorter survival time (median: 764 days). Based on statistical analysis, NTproBNP levels > 250 pmol/L were associated with cardiac death (P = .023); however, this did not remain significant (P = .951) when controlling for echocardiographic findings (e.g., specifically left atrial size and function) or clinical signs. Overall, when echocardiographic data was included in the analysis, cTnI lost its independent predictive value for time to cardiac death.

The authors assert that the study demonstrates the predictive value for survival of a single cTnI measurement in cats with HCM. A cutoff value of >0.7 ng/mL was reported as the most predictive cTnI value for cardiac death.  NTproBNP did not provide the same predictive value as cTnI independent of CHF status. The study is unique in that it provided two models for predictive value of cTnI for cardiac death. In the first model, echocardiographic data was not included, to simulate a general practice or emergency setting whereby echocardiography may not available in the first 24 hours when initial treatment decisions would be made. In the second model, echocardiographic data was included, and cTnI lost its independent predictive value (supplanted by echocardiographic evidence of LV hypokinesis), suggesting a significant relationship or association between these two parameters, as seen in humans.

So what we can take from this VETgirl podcast?

This small prospective study provided some very useful information that seems to fit well with what we know about the biomarkers NTproBNP and cTnI. NTproBNP is a marker for myocardial stretch, which correlates well to chamber enlargement and congestive heart failure. However, it did not independently correlate with cardiac death if CHF status was included. cTnI is a marker for myocardial injury or inflammation and did independently correlate with cardiac death in the model in which echocardiographic data was excluded. Elevated cTnI levels lost independent predictive value when echocardiographic data was included, and cTnI appeared to be related to left ventricular systolic dysfunction (hypokinesis).  This would make sense physiologically, as cats with HCM (typically a disease of diastolic dysfunction) who progress to systolic dysfunction would be expected to have higher degree of myocardial injury.

The plasma concentration of cTnI (cutoff >0.7 ng/mL) is a predictor of cardiac death in cats with HCM that is independent of the presence of heart failure or left atrial dilatation. Elevated cTnI levels appear to be predictive of cardiac death/survival time in cats with HCM when echocardiographic data is not included in a survival model. This could allow for practical application of a single cTnI level to provide survival estimates (and guide potential treatment decisions, in some cases) in a general practice or emergency setting for owners of cats with HCM. 

Thus, practically, a single cTnI blood level in a general or emergency practice setting might provide a pet owner with a reasonable idea of how advanced their cat’s myocardial dysfunction is, which appears to correlate with expected survival. This could impact a pet owner’s ability to make immediate informed decisions (e.g., euthanasia, etc.) regarding treatment rather waiting 24 hours or more for echocardiography.

Cool study! Now, if we could just readily get these two cardiac biomarkers available…

References:

1. Borgeat K, Sherwood K, Payne JR, et al. Plasma Cardiac Troponin I Concentration and Cardiac Death in Cats with Hypertrophic Cardiomyopathy. J Vet Intern Med 2014;28:1731-1737.

2. Herndon WE, Kittleson MD, Sanderson K, et al. Cardiac troponin I in feline hypertrophic cardiomyopathy. J Vet Intern Med 2002;16(5):558-564.

3. Sleeper MM, Clifford CA, Laster LL. Cardiac troponin I in the normal dog and cat. J Vet Intern Med 2001;15(5):501-503.

Abbreviations:

CHF: Congestive heart failure

CKD: Chronic kidney disease

cTnI: cardiac troponin I

HCM: Hypertrophic cardiomyopathy

LV: Left ventricular

NTproBNP: N-terminal pro-B-type natriuretic peptide

 

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