Hypertrophic Cardiomyopathy is an autosomal dominant genetically inherited disease of the myocardium (heart muscle). It remains the most prevalent heart disease in ALL domestic cats and is not subject to a single breed, although several breeds are presenting with a higher prevalence, including Sphynx. It is recognizable as a thickening of the left ventricle (the left chamber) of the heart.

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HCM can develop at any time between the ages of 1 and 8 years old. Scanning breeding cats regularly by board certified cardiologists is the best tool we have right now, although it is not a guarantee against a Sphynx ever developing HCM. It is crucial to the continuation and improvement of the Sphynx breed to have ethical breeders being proactive in detecting the disease in their breeding animals and removing affected or suspect Sphynx from their respective programs.

 

What is hypertrophic cardiomyopathy?

Hypertrophic cardiomyopathy (HCM) is the most common heart disease of cats, whether they are random bred or pedigreed. It is a heart muscle disease in which the papillary muscles (the muscles in the left ventricle that anchor the mitral valve) and the walls of the left ventricle become abnormally thickened. HCM is often a progressive disease, and a proportion of affected cats develop heart failure if the muscle hypertrophy and subsequent scarring of the heart muscle significantly affects heart function.

 

What causes HCM in cats?

This is currently unknown in most cats although familial (hereditary) HCM has been observed in several breeds, such as the Maine Coon and American shorthair. Anecdotal information suggests there is familial HCM in many other breeds. Heart muscle hypertrophy in cats can be caused by other diseases, such as systemic hypertension (high blood pressure) and hyperthyroidism. HCM is a primary disease of the heart muscle. Hypertension and hyperthyroidism cause secondary thickening of the left ventricle and so are not causes of HCM (although it is possible that they may exacerbate the disease if they become present in a cat with mild to moderate HCM). HCM is diagnosed when these other causes are ruled out.

 

Is HCM genetic?

In Maine Coons and American Shorthairs, HCM has been confirmed as an autosomal dominant inherited trait, as it is in humans where over 130 gene mutations in 10 genes have been found to cause the disease. The disease has variable expression; meaning some cats are severely affected, others are only mildly to moderately affected, and some cats may not have evidence of the disease yet produce affected offspring. While a specific feline gene mutation has not yet been identified, research is underway in the Maine Coon cat. However, since few veterinary cardiologists and geneticists have the expertise to study genes, it is unlikely that the responsible gene or genes for each affected breed will be found at any time in the near future. If a gene is identified as a cause of HCM in Maine Coon cats, it may not be the same gene responsible for HCM in other breeds. HCM will require investigation in each breed individually. Can HCM have a nutritional cause? There is no evidence in cats, humans or other species of animals that HCM can have a nutritional cause.

 

How is HCM diagnosed?

HCM is diagnosed using ultrasound of the heart – an echocardiogram. Echocardiography is a good way to detect moderate to severely affected cats. However, it may not always detect the mildly affected cats where changes in the heart can be minimal. In addition to an echocardiogram, other tests may also be useful in assessing cats with HCM. For example, a chest x-ray is necessary to detect heart failure in cats with severe HCM. An electrocardiogram is useful in cats that have an abnormal heart rhythm. Blood pressure measurement and blood testing for hyperthyroidism is indicated to rule out other diseases that mimic HCM, especially mild to moderate HCM. Ideally, an echocardiogram to test cats for HCM should be performed by a board-certified radiologist or cardiologist.

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Should my cats be tested for HCM and how often should they be tested?

In clinical practice, the most common patients tested for HCM with echocardiography are cats with suggestive clinical signs of heart disease, such as a heart murmur. Testing cats used in a pedigreed breeding program is a more difficult endeavor. Echocardiography is not a perfect tool for diagnosis of HCM – some affected individuals will escape detection and access to good quality ultrasound services may be difficult and expensive for some breeders. At the very least, breeding cats should be auscultated (examined by a vet with a stethoscope) for heart murmurs or arrhythmias once yearly. Any cat with an abnormality should have an echocardiogram. A significant percentage of cats with HCM will not have a heart murmur, however. Since HCM can occur at any age, a single normal echocardiogram does not guarantee a cat is free of disease. Breeding cats should probably have an echocardiogram yearly during their breeding years. Examining retired cats periodically is also advantageous as this may allow the identification of affected cats that have offspring in a breeding program.

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At what age should a cat be tested for HCM?

HCM can affect cats at any age. It has been seen in kittens only a few months of age and in cats over the age of 10. In Maine Coons, most affected male cats have evidence of disease by 2 years of age, and most affected females have evidence of disease by 3 years of age although instances have been documented where the disease has not shown up until 7 years of age. Ragdolls with severe disease seem to develop it earlier in life, often at under 1 year of age. Guidelines for other breeds have not yet been developed. It is therefore hard to recommend a specific age to start testing. It may make sense to test most breeding cats for the first time by the age of 2 years.

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What do I do if my cat is diagnosed with HCM?

The cat should be removed from the breeding program and all offspring should be watched closely for the development of HCM. Statistically, 50% of the cat’s offspring would be expected to have the gene that causes HCM if one parent was a heterozygote. However, the most prudent approach may be not to use any of the offspring in a breeding program. The parents of an affected cat should also be examined