Diagnosing feline myocardial disease

Feline myocardial disease can be a frustrating disease for veterinarians and pet owners. The prevalence of hypertrophic cardiomyopathy (HCM) is 15%, and up to 3% of adult cats have silent disease.^1,2 According to Neal Peckens, DVM, DACVIM (cardiology), cardiologist and junior partner at CVCA Cardiac Care for Pets in Virginia, data from multiple studies of cats presenting with aortic thromboembolism show that less than 35% of the affected cats were determined to be at risk for disease and only 8% to 12% had a diagnosis of myocardial disease prior to presentation. “We are missing [feline myocardial disease]. We have to do something better,” Peckens said during a session on the diagnosis of feline myocardial disease at the 2022 American Veterinary Medical Association Convention in Philadelphia, Pennsylvania.

Limitations of physical examination and radiography

Auscultation, a powerful tool in the detection of canine cardiac disease, is not as helpful in feline disease, Peckens noted. “There are more benign murmurs than cats with murmurs from heart disease,” he said. The positive predictive value (PPV), or probability that a cat with a murmur has cardiac disease, is only 31%.^1,2

Auscultation of abnormal heart sounds, including gallop rhythms and arrhythmias are more likely to be indicative of underlying myocardial disease. In a study of 227 cats, 17% of cats with cardiac disease had a gallop rhythm while no normal cats had this abnormality.³

The auscultation of any of these abnormalities should prompt further investigation, but in-clinic diagnostics have been historically limited. Thoracic radiographs are of limited utility in asymptomatic cats. Hypertrophic cardiomyopathy, the most common cardiac disease in cats, involves changes to the myocardium within the cardiac silhouette on radiographs, making cardiomegaly difficult to observe. Even in the presence of left atrial enlargement, the sensitivity of thoracic radiographs in detecting myocardial disease in only 70%.⁴ Peckens noted that a vertebral heart score (VHS) can be used to objectively measure the size of the heart. A VHS greater than 8 is considered enlarged in cats.

Biomarkers offer an in-clinic solution

A newer test to evaluate the heart uses a cardiac biomarker called NT-proBNP, which is “essentially a blood chemistry for the heart,” said Peckens. This biomarker is released by ventricles under increased stretch or stress. A quantitative test is available at reference laboratories and can be used for serial monitoring. The normal cutoff is 100 to discern disease.^3,5 A higher magnitude increase correlates with disease severity.

A cage-side qualitative SNAP test is available as well. The qualitative test has a lower sensitivity than the quantitative test. A visual positive occurs around an NT-proBNP level of 150. Despite the difference in sensitivity, Peckens still feels it is useful, saying “it is a rare day when a cat with a BNP between 100 and 150 has actionable disease.” The SNAP test can be used in clinic during respiratory emergencies to help differentiate cardiac from noncardiac causes and as a preanesthetic screening tool. Peckens suggested that “if you have an abnormal SNAP, I’d press pause on anesthesia.”

The optimal use of NT-proBNP is debated among cardiologists. Peckens recommended screening all cats, especially as they age or on auscultation of a murmur. However, as with any test, there are downsides. “NT-proBNP is not specific to heart disease,” said Peckens. “It is specific to heart muscle stress.” Because hyperthyroidism and systemic hypertension place stress on the heart muscle, both these diseases can elevate BNP levels. Additionally, BNP is renally excreted, leading to potential elevations in renal disease. In the presence of these concurrent diseases, BNP levels should be interpreted with caution.

Echocardiogram remains the gold standard

Peckens noted that although the NT-proBNP offers a powerful in-clinic tool for screening cats for cardiac disease, echocardiogram remains the gold standard for diagnosis of feline myocardial disease. It provides valuable information including the type of cardiac disease, severity, and assessment for risk of thromboembolic disease.

“When we talk about heart muscle disease in the cat, I feel like it frequently gets put into this monolith of HCM,” Peckens said. “[Cats] don’t all have HCM.” Other cardiac diseases include hypertrophic obstructive cardiomyopathy, restrictive cardiomyopathy, unclassified cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy. The type of disease, as well as the risk of thromboembolic disease dictate the treatment plan.

Take Home Points

Feline myocardial disease poses a diagnostic challenge for veterinarians as numerous cats can have occult disease. Additionally, many cats have functional heart murmurs that are not due to underlying cardiac disease. Use of NT-proBNP can help to screen feline populations for cardiac disease and improve patient selection for echocardiogram, which remains the gold standard to diagnose and direct treatment of feline cardiac disease.

Kate Boatright, VMD, is a practicing veterinarian and freelance speaker and author in western Pennsylvania. She is passionate about mentorship, education, and addressing common sources of stress for veterinary teams and recent graduates. Outside of clinical practice, Boatright is actively involved in organized veterinary medicine at the local, state, and national levels.

References

1. Paige CF, Abbott JA, Pyle RL, Elvinger R. Prevalence of cardiomyopathy in apparently healthy cats. JAVMA. 2009;234:1398-403.
2. Payne JR, Brodbelt DC, Fuentes VL. Cardiomyopathy prevalence in 780 apparently healthy cats in rehoming centres (the CatScan study). J Vet Cardiol. 2015; 17(S1):244-57.
3. Fox PR, Rush JE, Reynolds CA, et al. Multicenter evaluation of plasma N-terminal probrain natriuretic peptide as a biochemical screening test for asymptomatic (occult) cardiomyopathy in cats. JVIM. 2011;25:1010-1016.
4. Schober KE, Maerz I, Ludewig E, Stern JA. Diagnostic accuracy of electrocardiography and thoracic radiography in the assessment of left atrial size in cats: comparison with transthoracic 2-dimensional echocardiography. JVIM. 2007;21:709-718.
5. Wess G, Daisenberger P, Mahling M, et al. Utility of measuring plasma N-terminal pro-brain natriuretic peptide in detecting hypertrophic cardiomyopathy and differentiating grades of severity in cats. Vet Clin Pathol. 2011;40(2):237-44.