Hypertrophic cardiomyopathy (HCM) in cats

What is HCM?

HCM is a disease of the muscular wall of the heart. In cats with HCM, the walls of the heart become abnormally thickened. This reduces the volume of the chambers of the heart and affects the ability of the heart muscle to fully relax. HCM, therefore, reduces the volume of blood that the heart is able to pump around the body with each contraction.

HCM can develop in cats from 4 months onwards. It can affect both male and female cats, and any breed. However, some breeds are more susceptible to HCM, such as Maine Coons, Ragdolls and Norwegian Forest cats.

Clinical signs of HCM

It is useful to know what is normal for your cat throughout its life. This will enable you to identify problems more quickly. Our guide to doing a simple examination of your pet can be found here. Take a resting respiratory rate from your cat whilst they are sleeping. This can be done by counting how many times the chest moves either in or out over 30 seconds, and multiplying the number by two. This will give you the number of breaths the cat takes over one minute (breaths per minute) and can be very useful when speaking to a vet. A normal respiration rate for a healthy adult cat is around 20-30 breaths per minute.

If your cat has been diagnosed with HCM, there is some simple monitoring you can do at home to identify the signs, and establish whether your cat is getting better, or deteriorating. These include:

• Difficulty breathing (dyspnoea)
• Rapid breathing (tachypnoea)
• Cold ears and paws, and pale mucous membranes (gums and eyes) - suggestive of poor circulation

Stress can cause signs of HCM to worsen, so try to minimise this as much as possible. If you are monitoring your cat’s respiratory rate at home, ask your vet at what point you should contact them if the respiratory rate is abnormally high. For example, a respiratory rate of over 40 breaths per minute may indicate that your cat needs to see a vet urgently. However, it does depend on the cat, its treatment and the severity of the disease. If in doubt, it is always best to call your vet if you have any concerns.

What complications can arise with HCM?

HCM can cause several serious and sadly, sometimes fatal, health problems. Common sequelae include heart failure, thromboembolism (obstruction of a blood vessel with a blood clot) and even sudden death.

When should you contact your vet?

• If you notice any of the clinical signs above
• Your cat appears very lethargic or stops eating

Still worried?

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This article was written by Tanith Lee RVN. Tan qualified as a Registered Veterinary Nurse (RVN) in 2014. Since then she has worked in a variety of first opinion and referral clinics throughout the UK. She completed the ISFM Diploma in Feline Nursing with Distinction in 2016, and is currently completing the ISFM Advanced Certificate in Feline Behaviour. Tan is our Veterinary Practice Manager for FirstVet in the UK.