Podcasts

Join Now

Cardiac troponin I in cats with dyspnea | VETgirl Veterinary CE Podcasts

Need Help?

Who likes treating dyspneic cats?

Is it cardiac? Or respiratory? Should you reach for a small dose of a diuretic, steroid, or albuterol inhaler?

Well, in today’s VETgirl podcast, we review the clinical utility of measuring cardiac troponin I blood concentrations with a cage side analyzer to differentiate cats with cardiac and noncardiac causes of dyspnea.

Cats presenting with respiratory signs present a variety of challenges for diagnostic workup and treatment including patient compliance, patient degree of distress, and relative difficulty in differentiating cardiac from non-cardiac causes of dyspnea based on thoracic radiography alone as compared with dogs. For that reason, there’s been some thought that measuring a blood test – specifically troponins – can aid in diagnosis. Especially when we can measure this blood test quickly through a bed-side or cage-side analyzer.

Cardiac troponins (C, I and T) are proteins involved in contraction of both cardiac and skeletal muscle in dogs, cats, and humans. In particular, troponins I and T are released into the bloodstream with cardiac myocyte injury (VETgirl always remembers this as the “ALT for the heart”). Circulating cTnI can be readily measured in dogs and cats and has been shown to be elevated in cats with cardiac, renal, and thyroid disease, but many of the assays currently available for its measurement require several days for results. So, Wells et al out of New England Animal Medical Center and co-authors out of University of Pennsylvania wanted to conduct a study to evaluate if a cage-side cTnI analyzer would be useful in differentiating cardiac etiologies from noncardiac etiologies in dyspneic cats.

In this study, they enrolled 37 healthy cats and 39 dyspneic cats. Of the dyspneic cats, 25/39 (64%) had cardiac causes (e.g., congestive heart failure), while 14/39 (35.9%) had non-cardiac causes (e.g., respiratory, neoplasia, etc.). Wells et al found that in healthy cats, the median cTnI was 0.02 ng/mL (with a reference range of 0-0.09 ng/mL for ELISA test used in this study), as compared to dyspneic cats with cardiac disease (median cTnI: 1.68 ng/mL). In non-cardiac dyspnea cats, the median cTnI was 0.16 ng/mL. There was significant overlap that existed between the two groups of dyspneic cats. That said, overall, cats with cardiac causes of dyspnea had significantly greater cTnI concentrations compared with healthy cats and non-cardiac dyspneic cats.

In this study, they found the following:

  • A cTnI cutoff value of > 0.24 ng/mL had 100% sensitivity (which is the ability to detect all cardiac cats) but a low specificity (57.1%), thus also likely to include a significant number of non-cardiac cats.
  • A cTnI cutoff of > 0.66 ng/mL had 100% specificity (which is the ability to exclude all non-cardiac cats) but a low sensitivity (72%), thus likely to “miss” a significant number of cardiac cats.
  • A cTnI cutoff of > 0.5 ng/mL provided the best combination of sensitivity/specificity at 84% and 85.7%, respectively.

So, what did we conclude form this study? Cats with cardiac causes of dyspnea had greater blood cTnI concentrations as measured with a cage-side analyzer than cats with noncardiac causes and healthy cats; however, some overlap existed between the two groups of dyspneic cats.  That said, cage-side analysis of blood cTnI may provide additional diagnostic value in cats presenting to a veterinary hospital with respiratory signs. You know, for when you get draw blood of a dyspneic cat and all.

Note: Results of the study are similar to previous studies in cats (Herndon et al; Connolly et al) and indicate that cTnI can be a useful aid in differentiating cats with cardiac causes of dyspnea from cats with non-cardiac causes of dyspnea.

A few VETgirl observations though. Overall, this study is well-constructed with a simple, easily measured objective. And it’s prospective to boot! That said, the sample size (n=76) is relatively small. Another concern is that, although several of these studies (Wells, Herndon, Connolly) indicate that measurement of blood cTnI can be useful in determining the likelihood of a cardiac cause of dyspnea in cats, the predictive power for cTnI is not quite as high as the predictive power for another cardiac biomarker, NT-proBNP, for differentiating cardiac dyspnea from noncardiac dyspnea in cats based on the prior studies evaluating NT-proBNP (See Suggested Reading below).

The advantage of cTnI over NT-proBNP at this time is that a cage-side “stat” test is currently commercially available, which means a clinician can have a cTnI blood level available within minutes of venipuncture. Such a cage-side test is not yet commercially available for NT-proBNP but currently in development.

Finally, don’t rely on just a blood test, ok? Measurement of circulating biomarkers provides a diagnostic advantage to thoracic radiographs and echocardiography in dyspneic cats in that blood sampling requires shorter and less stressful restraint. They are not to be used as substitutes for diagnostic imaging, but can enable a practitioner to begin emergent treatment for CHF (oxygen, diuretics, vasodilators) vs respiratory disease (oxygen, bronchodilators, corticosteroids, sedatives) with a higher degree of confidence in order to stabilize the dyspneic feline patient for diagnostic imaging modalities.

Suggested reading:

  1. Wells SM, Schofer FS, Walters PC, et al. Evaluation of blood cardiac troponin I concentrations obtained with a cage side analyzer to differentiate cats with cardiac and noncardiac causes of dyspnea.  J Am Vet Med Assoc 2014;244:425-430.
  2. Herndon WE, Rishniw M, Schrope D, et al. Assessment of plasma cardiac troponin I concentrations as a means to differentiate cardiac and noncardiac causes of dyspnea in cats. J Am Vet Med Assoc 2008;233:1261-1264.
  3. Connolly DJ, Brodbelt DC, Copeland H, et al. Assessment of diagnostic accuracy of circulating cardiac troponin I concentration to distinguish between cats with cardiac and non-cardiac causes of respiratory distress. J Vet Cardiol 2009;11:71-78.
  4. Fox PR, Oyama MA, Reynolds C, et al. Utility of plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) to distinguish between congestive heart failure and non-cardiac causes of acute dyspnea in cats. J Vet Cardiol 2009;11:S51-S61.
  5. Connolly DJ, Magalhaes RJ, Fuentes VL, et al. Assessment of the diagnostic accuracy of circulating natriuretic peptide concentrations to distinguish between cats with cardiac and non-cardiac causes of respiratory distress. J Vet Cardiol 2009;11:S41-50.
  6. Swift S, Dukes-McEwan J, Fonfara S, etal. Aetiology and outcome in 90 cats presenting with dyspnoea in a referral population. J Small Anim Pract 2009;50(9):466-73.

Abbreviations:

cTnI: Cardiac troponin I

ALT: Alanine aminotransferase

CHF: Congestive heart failure

NT-proBNP: N-terminal pro-brain natriuretic peptide

 

Only VETgirl members can leave comments. Sign In or Join VETgirl now!