Hypertrophic Cardiomyopathy (HCM) in Cats

Written by Small Door's medical experts

The most common heart disease in cats is hypertrophic cardiomyopathy (HCM). This is a progressive disease that may lead to congestive heart failure or blood clots. While there is no cure for HCM, there are treatments available that may help to improve and maintain your cat’s quality of life. Read on to learn more about this disease and how it affects cats.

In this article

What is HCM in cats?

The heart is an organ made of muscle that controls the circulation of blood throughout the body by contracting (or squeezing) and relaxing. With HCM, the heart walls become thicker and larger, specifically the left ventricle of the heart, which is the heart’s main pumping chamber. This thickening makes it hard for your cat’s heart to contract and relax normally. 

Signs and symptoms of hypertrophic cardiomyopathy in cats

Cats will often show no outward signs of HCM if they have mild to moderate disease. Signs and symptoms may emerge in more severe cases of HCM, and may include: 

  • Respiratory distress (shown as open mouth breathing, rapid breathing, labored breathing, or panting)

  • Decreased appetite 

  • Lethargy or extreme tiredness

  • Heart murmur or gallop (an abnormal rhythm of the heart diagnosed by your veterinarian by listening to your cat’s heart with a stethoscope)

  • Sudden paralysis

  • Sudden death

It should be noted that cats are extremely proficient at masking symptoms of being sick and often only show very subtle signs of illness. This is why regular wellness exams with your veterinarian are important, as these visits may help catch signs and symptoms of cardiac disease in its early stages. 

Is hypertrophic cardiomyopathy painful in cats?

Generally, this condition is not painful in cats, but it may cause painful complications, such as a feline aortic thromboembolism (abbreviated as ATE, also called a saddle thrombus). An ATE is a blood clot that forms in the aorta, travels through blood vessels and becomes lodged in a distant location of the body (usually occurring in the hind legs). This blood clot forms a blockage that restricts blood flow and oxygen to the tissues, which causes sudden paralysis, severe pain, and even sudden death. This is a life-threatening condition that requires immediate medical attention. 

Causes of hypertrophic cardiomyopathy in cats

The exact cause for hypertrophic cardiomyopathy is not clearly known at this time. However, given that certain breeds seem to be more commonly affected, a genetic link likely plays a role.

High blood pressure or hyperthyroidism can also cause thickening of the heart, however, your veterinarian will rule these conditions out before making a diagnosis of hypertrophic cardiomyopathy. 

How common is HCM in cats?

HCM is the most common feline cardiac disease. HCM is estimated to occur in about 14% of cats, according to the Merck Veterinary Manual.

Is HCM more common in certain breeds?

HCM is more common in some feline breeds. The breeds most affected are: 

  • Persians

  • Ragdolls

  • Maine Coons

  • Sphynx

  • British Shorthairs

  • Norwegian Forest Cats

  • Bengals

Diagnosing feline hypertrophic cardiomyopathy

HCM may occur from approximately 6 months onwards in cats, but is most often diagnosed at middle age. Male cats also appear to be more commonly affected. 

The most definitive method of diagnosing feline hypertrophic cardiomyopathy is through an echocardiogram (an ultrasound of the heart) that is performed by a veterinary cardiologist. 

Other types of diagnostics your veterinarian may also perform include: 

  • Radiographs (X-rays): X-rays of the heart and lungs may show if there is any enlargement of the heart or fluid accumulation around the heart and/or in the lungs. 

  • Electrocardiogram (ECG): An ECG will show the heart’s rhythm and electrical activity through sensors that are placed on your cat’s skin.

  • NT-pro-BNP blood test: This is a blood test that checks for specific types of protein that becomes elevated in cats with cardiac stress. 

  • Blood pressure measurement: Much like in humans, a tiny blood pressure cuff is placed on your cat’s leg to measure their blood pressure. 

Stages of HCM in cats

The severity, or level of cardiac disease, in cats with HCM is classified by a staging system. There are five stages of HCM that range from Stage A in which a cat has a normal echocardiogram but predisposition due to breed, through Stages B1, B2, C, and all the way to Stage D in which a cat’s heart failure is refractory to any medications and the pet is considered terminal. 

Management of HCM in cats

While there is unfortunately no cure or treatment to stop the progression of HCM in cats, your veterinarian may formulate a treatment plan to help manage your cat’s symptoms and help keep them as comfortable as possible. 

Goals of treatment include regulating your cat’s heart rate, preventing or removing fluid accumulation/lung congestion associated with CHF, and preventing blood clots from forming. 

Is there a cure for feline hypertrophic cardiomyopathy in cats?

Currently, there is no cure for feline hypertrophic cardiomyopathy. 

Is feline hypertrophic cardiomyopathy contagious for humans or other pets?

No, feline hypertrophic cardiomyopathy is not contagious for humans or other pets. 

Should cats that are related to a cat with HCM be tested?

Cats related to another cat diagnosed with HCM or cats that may be at-risk for developing HCM due to their breed may be tested. Currently, the only screening blood test to detect HCM in asymptomatic cats (cats without any signs or symptoms of HCM) is the NT-pro-BNP blood test. The other testing method that may be used is an echocardiogram. 

What is the cost of treating feline hypertrophic cardiomyopathy?

The cost of treatment varies greatly depending on the stage of the disease. Your veterinarian will order specific tests to determine the condition accurately. Different factors such as who will perform the tests (i.e. your veterinarian or a specialist) as well as the area in which you live all can affect cost. Blood work may cost a few hundred dollars, whilst more complex diagnostics and specialist consultations could reach several thousand dollars.  

Prognosis for cats with Hypertrophic cardiomyopathy

The prognosis or life expectancy of cats with HCM may vary depending on their stage of disease at diagnosis. Cats with mild compromised heart function may survive for years. Approximately 20% of cats with HCM developed congestive heart failure within five years of their diagnosis, and had an average survival time of 12 months while also being treated with medications, according to a study noted by experts at the NC State Veterinary Hospital

Are cats with HCM at risk of sudden death?

Yes, while rare, cats with HCM are at risk of sudden death. 

How to prevent hypertrophic cardiomyopathy in cats

Unfortunately, there is currently no prevention available for HCM in cats. 

Is there a vaccine for HCM in cats?

There is no vaccine for HCM in cats at this time. 

Summary of hypertrophic cardiomyopathy in cats

HCM is a common and progressive cardiac disease occurring in cats. It often has no symptoms, but may lead to serious complications. However, medical treatments may help to improve your cat’s heart function and quality of life. If you have concerns about your cat’s cardiac health, talk to your veterinarian about diagnostic and treatment options.

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