Hypertrophic cardiomyopathy (HCM) in cats

Which cats get hypertrophic cardiomyopathy (HCM)?

HCM is most common in male cats, and the risk increases with age. The disease occurs in all cat breeds but is more common in certain breeds.

What is HCM?

HCM leads to thickening of the musculature of the heart's left ventricle and an enlarged left atrium, which leads to the heart becoming less elastic. It becomes more difficult for the muscles of the heart to relax between heartbeats and it is not filled with the same amount of oxygenated blood from the lungs. This results in less blood being pumped out of the heart into the body with each heartbeat.

Diseases such as high blood pressure and excessive metabolism can also lead to thickening of the heart's musculature.

Symptoms of HCM in cats

HCM can be difficult to detect. The disease is often suspected when the vet listens to a cat's heart during a routine check-up and hears a murmur or irregular heartbeat (arrhythmia or galloping rhythm). A cat can suffer from heart failure and show severe breathing difficulties due to fluid in the lungs and chest.

Sometimes the disease can manifest itself in the form of small blood clots (thrombi) formed in the heart and carried out into the body. They then get stuck, usually in the carotid artery where it divides to the hind legs, causing paralysis and pain in one or both hind legs. Sudden death also occurs due to heart rhythm disturbances.

How long can a cat live with HCM?

HCM can cause severe heart failure, blood clots and sudden death, but many cats can live for years without symptoms of the disease and even reach an advanced age.

How a cat is diagnosed with HCM

The diagnosis is established with the help of an ultrasound examination of the heart, during which, among other things, measurements are taken of the heart's chambers and atria. If changes are found, regular examinations are recommended to follow the development. There are rapid tests that can be used to primarily rule out the suspicion of heart disease. Blood samples are then taken to measure the concentration of the biomarker NT-proBNP. In order to get a safe diagnosis, however, an ultrasound examination is always required.

How is HCM treated in cats?

In case of early detection of disease without symptoms, medication is rarely used. Many cats can live for several years without clinical symptoms of disease and even reach a normal lifespan. The disease is not curable, but blood clots can be prevented by giving blood-thinning medications. 

A cat suffering from heart failure needs care with oxygen therapy and fluid-reducing medication. For cats affected by heart failure, the prognosis is wait-and-see in the long term and it is bad for cats that have developed blood clots.

Breeding recommendations

There are genetic risk factors for developing HCM. However, the inheritance pattern is not yet fully understood. Affected cats are not born with the disease, but it develops slowly over time. Breeding of cats with HCM is discouraged and many breeders check their breeding stock before mating using ultrasound. There are health programs that include both repeated ultrasound examinations and DNA tests.