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Determining the cause of respiratory distress in cats

Wells SM, Shofer 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

When a cat in respiratory distress (dyspnea) is brought to a veterinary hospital, it creates a challenging emergency situation that requires quick assessment and appropriate intervention. The patient must be handled carefully to avoid decompensation or death. The two most common causes of dyspnea in cats are congestive heart failure and respiratory tract disease. A minimally invasive or patient-side test to help identify cats with heart failure would be clinically useful. From the results of previous studies, the circulating concentrations of cardiac troponin I (cTnI) are supportive in distinguishing cats with dyspnea due to respiratory disease from those with underlying heart disease. It has been noted that cTnI concentrations may be elevated in cats with hypertrophic cardiomyopathy, myocardial contusions (trauma), hyperthyroidism, and renal insufficiency. 

The authors here performed a multicenter, prospective study to determine whether the measurement of cnTI concentration with a cage-side analyzer could be used to differentiate cardiac from non-cardiac causes of dyspnea in cats. The study included 37 healthy cats ranging in age from 1 to 12 years of age. Also included in the study were 39 dyspneic cats, 25 of which had congestive heart failure due to various cardiac diseases. The median cTnI in the cats with cardiac disease was 1.68 ng/mL (range, 0.24 to 50 ng/mL). Fourteen cats were found to have a non-cardiac cause of dyspnea. The median cTnI in these cats was 0.16 ng/mL (range, 0.02 to 0.66 ng/mL). In comparison, the median concentration of cTnI in the healthy cats was 0.02 ng/mL (range, 0 to 0.17 ng/mL). The normal reference range for cTnI is 0 to 0.09 ng/mL. 

The results showed that the 25 cats with a cardiac disease had a significantly higher blood cTnI concentration than the 37 healthy cats or the 14 cats with non-cardiac disease. On this basis, the authors believe cTnI concentrations less than 0.24 ng/mL can be used to rule out congestive heart failure as the cause of dyspnea, whereas concentrations greater than 0.66 ng/mL suggest a cardiac cause. Due to overlap in concentration values between the three groups, cTnI concentrations between 0.24 and 0.66 ng/mL were not useful for determining the cause of dyspnea; consequently, other diagnostic tests would be needed to determine the underlying disease. The study’s conclusion is measurement of cTnI concentrations with a cage-side assay in an emergency situation may be useful to clinicians for differentiating cardiac from non-cardiac causes of dyspnea in cats. [VT]

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