Hypertrophic Cardiomyopathy (HCM)

Heart problems are fairly common in cats, with some suggestions that around 15% (about 1 in every 7) of all cats have heart disease. This gets more common as your cat gets older. Thankfully, just because they have heart disease, this doesn't mean that they will need treatment or become ill from it...most are fine!

What is a Cardiomyopathy?

Cardiomyopathy is a term meaning abnormal heart muscle. This is the most common type of heart disease in cats. There are various different types, with the most common being Hypertrophic Cardiomyopathy (HCM), which causes thickening and stiffening of the heart.

What causes HCM?

Usually HCM is a genetic condition, which means that although your cat was born with a normal heart, they were always going to develop the problem at some point in their lifetime. As cats get older, there are also other things that can cause thickening of their heart - such as on overactive thyroid (hyperthyroidism) and high blood pressure (hypertension). We will usually test for these and treat them if present, and this can help the heart improve and work better.

How do we diagnose HCM?

Some cats may have a heart murmur (which is an abnormal sound which we can hear with a stethoscope) but this doesn’t mean there is a heart problem. Some cats can have a heart murmur and a completely normal heart. Other cats can have a heart that sounds perfect with a stethoscope but they have severe heart problems. 

Because of this, we will usually recommend a test of some sort to see if your cat has HCM. The best test is usually an ultrasound scan (“echocardiogram”). This can be done without any sedation in most cats; more nervous cats can have some anti-anxiety medication at home before they come in...just ask! This just involves a small region of hair being shaved and allows us to see exactly what is going on with your cat’s heart. Some cats can have a blood test to see if they would benefit from an ultrasound. After this, some cats may need other tests to help us work out what is going on (eg ECG, blood tests, X-rays etc).

My cat has been diagnosed with HCM...what now?

The good news is, that even though they have thickened heart muscle, most cats will continue to live a completely normal life without any symptoms and without needing medication. About 70% cats with HCM will never have any symptoms or life-threatening issue from their heart problems. This, of course, means 30% will develop complications. We often advise repeating the ultrasound to monitor for things getting worse.

What can happen if things get worse?

There are two complications from worsening heart disease.

Congestive Heart Failure (CHF):

As the heart gets worse, then fluid can build up in or around the lungs. This is called Congestive Heart Failure, or CHF. This leads to difficulty breathing.

By monitoring your cat’s breathing carefully (including counting breathing rates - see below), we can start medications to help get rid of this fluid when it builds up. If there is fluid sitting in the chest and squashing the lungs, we often need to drain this under sedation which will help make your cat feel better. As this fluid gets worse, this makes your cat more tired and they sleep more. If we do not control the fluid adequately, then the breathing will get worse and worse and eventually can be life-threatening. Regular monitoring is important to adjust the treatment to keep your cat happy.

Blood clots:

As the heart disease gets worse, the blood inside can become more “sticky” and more likely to form blood clots (“thrombosis”). They usually form in the heart and then bits of the clot can break off and block the main artery in the body. This often results in paralysis of the back legs and extreme pain. Unfortunately, this is a very serious condition and most cats don’t survive. For this reason, we do everything we can to reduce the risk of this happening. We use medications for this.

Checking breathing

As fluid in or around the lungs makes breathing more difficult, then your cat’s breathing will get faster and often deeper. As such, a great, cheap and accurate way of monitoring your cat is by checking their breathing rates. This is best done when they are sleeping (as breathing rates increase when they are awake, and even more so when they are excited/exercising).

Try and do this at the same time each day, when your cat has been asleep for 20 minutes or so. Count how many times your cat’s chest rises in 30 seconds (note that your cat’s chest will move up once and down once in each breath) - double your number to get a breathing rate per minute. In most cats, a normal rate is less than 20 breaths per minute. We get concerned if the rate is above 30 breaths per minute.

Any cat will occasionally have a rate over 30 breaths per minute (eg if they are dreaming, or really hot) and breathing can look deeper when they are purring. Cats with CHF tend to have a gradual increase in their breathing rates over a number of days, and this is sustained. If your cat’s breathing rate is consistently over 30 breaths per minute, then you should contact your vet ASAP. This may have to be an urgent or emergency appointment if you are concerned. There is also a free app you can download on your phone (search “Cardalis”) to help you measure and record the breathing rates; you can then show these to your vet at recheck appointments.

What medications can we use?

Diuretics (“water tablets”)

The fluid in the lungs (CHF) sits inside the lungs, much like water inside a wet sponge. This means it cannot be physically removed using a needle. So we use medicines called diuretics (also known as “water tablets”). There are various different types, most commonly either furosemide (aka frusemide, Libeo) or torasemide (aka torsemide, Upcard, Isemid). These will help get rid of the excess fluid; the body does this by weeing out the excess fluid. To compensate, your cat will drink more water (this is normal). 

These medications will continue for life, although we will vary the dose depending on how your cat is doing. Higher doses are often required at the beginning to get rid of the fluid and then we may be able to lower the dose longer term. Frequent check ups are required in order to make sure the medications and the doses are correct. 

Anti-thrombotics (“blood thinners”)

We can reduce the risk of blood clots forming by using medications such as clopidogrel (sometimes called Plavix), rivaroxaban (Xarelto) or aspirin. Clopidogrel is the most commonly used anti-thrombotic medicine we use. We use it once a day and it works well with minimal side effects. The medicine inside the tablet is unfortunately bitter in taste, so some cats don’t like it. You can try hiding it in a little bit of something tasty (try warming the food a little first) or simply give the tablet straight into the mouth. Sometimes we crush the tablet and put the powder into an empty capsule - you can ask your vet about this as an option. If your cat won’t take clopidogrel, don’t worry, we can try something different.

What happens then?

If things do get worse, and your cat develops difficulty breathing (CHF), then we use medicines to make sure your cat goes back to feeling great again. Our aim is to make sure your cat is happy and has a good quality of life. Cats will frequently do really well for even a number of years. They will of course need life-long medication and regular check ups. There will be ups and downs, and medicine doses may need adjusting or extra medications added in, so keep in touch with your vet regularly and especially if you don’t think they are doing well.

Are there any operations that can help?

There are no operations which can help HCM in cats. There is lots of research going on at the moment into new medications which may help slow the disease progression. They are still being studied to make sure they are safe and effective, so hopefully won’t be too long before they become available.