Hypertrophic Cardiomyopathy in Cats: Causes, Symptoms and Treatment

Hypertrophic cardiomyopathy can be a genetic condition, especially in breeds such as Maine Coon and Ragdoll cats. Gorodenkoff / Shutterstock

Hypertrophic cardiomyopathy (HCM) is the most common heart condition seen in cats. It causes abnormal thickening of the heart wall, making it harder for the heart to pump blood around your cat’s body. Most cats with HCM show no symptoms until it progresses to the point of heart failure. This means detecting or treating HCM in the early phases can be difficult.

Some breeds are more prone to HCM, so we know genetics plays a role. It can also be caused by high blood pressure (hypertension) or hyperthyroidism. But it can happen in cats with none of these risk factors. This means taking your cat for regular check-ups is important – whatever their breed, age or health.

Although HCM is a serious and ultimately life-threatening disease, many cats live comfortably with it for a long time, especially with treatment.

What is Hypertrophic Cardiomyopathy in Cats?

Your cat’s heart is essentially a pump made of muscle. It consists of four chambers (right and left ventricle and right and left atrium) that fill with blood, and muscular walls that contract to pump that blood out of the heart and around the body.

With HCM, the heart muscle becomes abnormally thickened (hypertrophy). This makes the heart walls stiffer, making it harder to contract. The thickening of the walls also means the chambers within the heart become smaller, so they cannot fill with enough blood. Overall, as the disease progresses it becomes harder and harder for your cat’s heart to pump blood effectively.

Your cat’s body will compensate for a long time, meaning they may not show signs of being unwell. But eventually, the heart will struggle to cope, and symptoms will develop. These will usually be signs of the complications of HCM as opposed to HCM itself.

Causes of Hypertrophic Cardiomyopathy in Cats

Hypertrophic cardiomyopathy can be an inherited disease and is especially common in breeds such as Maine Coon cats and Ragdoll cats. Peredniankina / Shutterstock.com

We know HCM is an inherited disease. It is the most common inherited heart disease in both people and cats. The CatScan study looked at the prevalence of cardiomyopathy in 78 apparently-healthy cats, finding HCM in around 15%. Other studies have found similar results, meaning around 1 in 7 cats are thought to have it.

Certain breeds are known to be more commonly affected:

• Maine Coon
• Ragdoll
• Sphynx
• British Shorthair
• British Longhair

Research is underway to identify exactly what genes may play a part – which will be important to improving genetic screening.

The CatScan study showed several other risk factors for developing HCM, including a heart murmur, being male, middle-aged or older, and being overweight. However, HCM has been shown to occur in cats of all ages, sexes, and conditions. Other conditions such as high blood pressure and hyperthyroidism can also cause HCM. So, regular check-ups of your cat’s heart are important even if they aren’t high-risk.

Symptoms of Hypertrophic Cardiomyopathy in Cats

Most cats with HCM have no outward symptoms in the early stages. As the heart struggles to pump enough blood it will compensate by increasing the speed at which it beats. The earliest signs of HCM in cats are increased heart rate and the development of a heart murmur. Regular check-ups with your veterinarian can pick up on these subtle signs. However, not all cats with HCM will have any detectable changes.

As a cat owner, you will most likely not see any signs of illness in your cat until they develop a complication of HCM, such as congestive heart failure or a blood clot. Unfortunately, sudden death is also possible from undiagnosed HCM.

Congestive Heart Failure

As HCM progresses, the heart struggles to pump blood effectively around the body. This can lead to fluid backing up in the lungs (pulmonary edema or pleural effusion) resulting in congestive heart failure. This is the most common outcome of HCM in cats. Symptoms of heart failure in cats can come on suddenly or over time and include breathing difficulties, appetite loss and lethargy.

Treating heart failure is the mainstay of treatment for cats with HCM. Although both HCM and heart failure are serious and life-threatening conditions, medication can successfully stabilize cats for months to years.

Blood Clots

As well as heart failure, cats with HCM are at risk of developing blood clots within the heart. Pieces of these clots can travel through the bloodstream and get lodged causing a rapidly life-threatening condition called Feline Arterial Thromboembolism (FATE). This most often affects the back legs, causing sudden onset of symptoms:

• Pain
• Paralysis/weakness
• Cold
• Pallor/blue tinge
• Stiffness

FATE is a devastating condition that commonly results in euthanasia – although there are recent advancements in treatment.

Sadly, cats with HCM are also at a greater risk of sudden death with no other symptoms of illness beforehand. This may be due to irregular heart rhythms (arrhythmia) or undetected clots.

Diagnosis of Hypertrophic Cardiomyopathy in Cats

Hypertrophic cardiomyopathy is diagnosed with an ultrasound of your cat’s heart, called an echocardiogram, or ‘echo’. Sungthong / Shutterstock

Your veterinarian may suggest screening for HCM if your cat is an at-risk breed or if they have noticed another abnormality such as a heart murmur or fast/irregular heartbeat. It is also recommended for cats suffering from high blood pressure or hyperthyroidism.

HCM is diagnosed using an ultrasound of your cat’s heart – called an echocardiogram, or ‘echo’. Echocardiography is usually performed by a specialist veterinary cardiologist who will measure the thickness of the heart walls. They will also check for signs of chamber enlargement and the development of blood clots inside the heart. As part of a cardiac assessment, your cat should have their blood pressure checked, as well as blood tests and an ECG.

If your veterinarian is worried your cat may be suffering from heart failure they may recommend chest x-rays (radiography) as well.

Genetic Screening for Cats with Hypertrophic Cardiomyopathy

We know that many cases of HCM may have a genetic basis. The specific genes involved have been identified in certain breeds (including the Maine Coon and the Ragdoll), meaning genetic screening is available.

If your cat is found to have this gene mutation, they have an increased chance of developing HCM. However, not all cats with the gene mutation will go on to develop HCM. Therefore, it is recommended that cats with a positive genetic screen also have regular ultrasound scans of their heart to identify changes early. As HCM can occur at any stage of life, a single normal ultrasound does not rule out the risk of developing it at a later stage.

It is recommended that cats with positive genetic screening should not be bred from, as there is a high chance of them passing the mutated gene on to their kittens. If you are considering breeding from a Ragdoll or Maine Coon cat, genetic screening for HCM is recommended.

Treating Cats with Hypertrophic Cardiomyopathy

In cats with an underlying condition, such as high blood pressure or hyperthyroidism, treating this successfully can improve or even reverse HCM.

However, there is currently no specific treatment to prevent HCM in predisposed cats or for HCM itself. So, in cats without an underlying cause, nothing can be done to slow the disease. Instead, treatment is aimed at treating the consequences of the HCM (if present), by:

• Reducing the risk of blood clots
• Treating signs of heart failure

For cats with no symptoms and only mild changes seen on echo, The American College of Veterinary Internal Medicine (ACVIM) guidelines for cardiomyopathies in cats only recommend annual monitoring with heart scans. They consider these cats “low risk of congestive heart failure or arterial thromboembolism, and in general, treatment is not recommended”.

For cats who have more significant changes seen on echo, such as enlarged heart chambers, they recommend beginning clopidogrel. This drug helps to prevent the development of clots. These cats are at risk of both blood clots and congestive heart failure, so they should be monitored closely.

As HCM progresses, it causes congestive heart failure. Diuretics such as furosemide are the main treatment for heart failure in cats. They reduce the fluid build-up in the lungs allowing your cat to breathe more easily. Other drugs your veterinarian may consider include ACE-inhibitors and pimobendan.

Caring For Your Cat with Hypertrophic Cardiomyopathy

Cats who have been diagnosed with, or at risk of, hypertrophic cardiomyopathy should have regular check-ups with their veterinarian, including heart scans. Gorodenkoff / Shutterstock

If you know your cat is at risk of HCM or has early signs of HCM, you should take them for regular check-ups with your veterinarian, including an annual ultrasound of their heart.

Alongside ensuring they receive any medication it may help to feed a diet designed for cats with heart disease. These contain omega-3 fatty acids, optimal levels of taurine, reduced sodium, and high-quality, highly digestible protein. It is sensible to avoid salty treats, as these can cause fluid retention which may worsen heart failure.

Preventing Hypertrophic Cardiomyopathy in Cats

No treatment can prevent the development of HCM in predisposed cats. So, regular monitoring is the best way to help your cat if they are at risk of HCM.

However, it is important to highlight that secondary HCM can be prevented – and even reversed – through quick treatment of high blood pressure and hyperthyroidism.