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66 ADVANCES IN FELINE CARDIAC DIAGNOSTICS PEER REVIEWED Case notes: Evaluation of NT-proBNP would be a reasonable first step if Tux's owner were not able to pursue echocardiography. An NT-proBNP level <100 pmol/L would provide assurance that significant heart disease is not associated with Tux's new heart murmur. An NT-proBNP value >100 pmol/L could be consistent with the presence of heart disease and should prompt echocardiography or close monitoring. Assessment of NT-proBNP also provides valuable information for differentiating between cardiac and noncardiac causes of respiratory distress. 13,14 An NT-proBNP level >265 pmol/L suggests CHF in a cat with respiratory distress. 12,14 Values <265 pmol/L but >100 pmol/L could indicate a noncardiac cause of dyspnea and concurrent heart disease. A feline SNAP BNP test ( idexx.com ) is available and can be helpful in an urgent care setting to determine whether a dyspneic cat is likely to have CHF. A negative SNAP result correlates to an NT-proBNP level <100 pmol/L, indicating that CHF is unlikely in a dyspneic cat. A positive SNAP result correlates to an NT-proBNP level >270 pmol/L, supporting CHF in a dyspneic patient; however, concurrent respiratory causes of dyspnea and preclinical heart disease could also be the cause of a positive SNAP result. The final SNAP result should always be interpreted in light of the clinical examination and other diagnostic tests. Analysis of BNP in pleural fluid also correlates well to blood concentrations and may prove useful in some clinical situations. 15 Case notes: Biomarker testing is not indicated for Elvis because other diagnostic testing rapidly yields his diagnosis of CHF. GENETICS Genetic testing using blood or cheek swab samples is available for known mutations associated with HCM in 2 cat breeds. Both mutations are single nucleotide substitutions in the cardiac myosin-binding protein C gene. The A31P substitution is found in the Maine coon breed, and the R820W mutation is found in ragdoll cats. 16,17 Genotype determination may help guide breeding programs and cardiac therapy, but it should not be used as a substitute for echocardiography because other, undiscovered mutations are associated with HCM in both of these breeds. 18–20 In addition, because of the many factors that can influence disease expression, genotype does not always equate to phenotype in individual patients. Case notes: Because Tux and Elvis are mixed- breed cats, genetic testing is not recommended. SYSTEMIC DISEASE WORKUP The hallmark echocardiographic finding of HCM is left ventricular hypertrophy. However, other disease processes can also induce wall thickening. The most common systemic causes of left ventricular hypertrophy include systemic hypertension and hyperthyroidism. Less common causes include acromegaly, infiltrative myocardial diseases (eg, lymphoma), and left ventricular outflow obstructions (eg, aortic stenosis or mitral valve dysplasia causing systolic anterior motion). The echocardiographic finding of left ventricular hypertrophy should therefore prompt an assessment of blood pressure and thyroid concentration in any middle- aged to older cat. Treatment of systemic hypertension or hyperthyroidism is expected to improve or resolve echocardiographic abnormalities, but coexisting primary HCM and systemic disease is possible. Case notes: Blood pressure and thyroid status should be evaluated in Elvis. However, thyroid testing is not necessary in Tux given his young Brent Aona Brent Aona is a cardiology resident at North Carolina State University College of Veterinary Medicine. He completed his undergraduate and graduate studies at The Ohio State University, where he received his DVM. This was followed by a small animal rotating internship at Tufts University, after which he began his residency in cardiology at North Carolina State University. His clinical research is focused on echosonography of congenital cardiac defects, and his main clinical interest is interventional cardiology. Darcy Adin Darcy Adin is a clinical assistant professor of cardiology at North Carolina State University College of Veterinary Medicine. She received her DVM from Cornell University. She completed a rotating internship at VCA South Shore Animal Hospital and a cardiology residency at the University of California, Davis, with ACVIM board certification in cardiology in 2000. Dr. Adin has held positions in both academic and private specialty practice. Her clinical research focuses on the investigation of neurohormonal modulation of and new treatment options for congestive heart failure.