Subclinical Heart Disease Common but Rarely Fatal in New Zealand Cats

Prevalence of Cardiomyopathy and Cardiac Mortality in a Colony of Non-Purebred Cats in New Zealand

J. Seo, R. Owen, H. Hunt, V. Luis Fuentes, D.J. Connolly, J.S. Munday

Background:
Cardiomyopathy, particularly hypertrophic cardiomyopathy (HCM), is a prevalent but often subclinical cardiac disease in cats. Although HCM prevalence has been studied in cats from the UK and USA, no prior data were available for New Zealand. This study aimed to determine the prevalence of cardiomyopathy and cardiac-related mortality in a colony of non-purebred New Zealand cats to better understand the disease's clinical relevance in this population.

Methods:
The study had two parts: a prospective evaluation of echocardiographic prevalence and a retrospective review of cardiac mortality. A total of 132 healthy, non-neonatal, non-pregnant cats from a research colony underwent physical examination and echocardiography between 2021 and 2022. Echocardiographic findings were classified following American College of Veterinary Internal Medicine guidelines. Mortality data from February 2012 to February 2022 were reviewed, and causes of death were determined through post-mortem examinations.

Results:
Echocardiography revealed cardiomyopathy in 18.2% of cats (24/132), with HCM confirmed in 15.2% (20/132) after excluding secondary causes such as hyperthyroidism and hypertension. Only 40% of HCM-affected cats had a detectable murmur on physical exam. From mortality records of 132 cats, 5.3% died due to heart disease, and 3.8% specifically from HCM. Most cats with HCM lived without developing clinical signs or cardiac-related mortality. Furthermore, cardiac lesions were common at necropsy but often unrelated to the cause of death, suggesting subclinical HCM may have limited progression in many cases.

Limitations:
The study was conducted in a single research colony, which may not fully represent the general New Zealand cat population, particularly purebreds. Echocardiographic evaluations were performed by a single cardiologist and were limited to two-dimensional imaging without sedation. The retrospective mortality data relied on multiple pathologists, introducing potential variability in post-mortem diagnoses.

Conclusions:
Subclinical hypertrophic cardiomyopathy is common in non-purebred cats in New Zealand, with an estimated prevalence of 9.5–22.4%. However, it infrequently progresses to fatal disease. These findings emphasize the importance of echocardiographic screening for accurate diagnosis, particularly before procedures involving anesthesia or fluid therapy, but also suggest that many cats with HCM may have a favorable long-term prognosis.

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