HCM in the cat. On the left a normal heart, on the right a heart with thickened heart walls.
The difference in the space of the ventricles is clear.

 What causes HCM?

The precise cause of both congenital and older HCM is unknown. It is described in the literature that abnormal anatomy of the left ventricle, and therefore abnormal position of the papillary muscles, causes the heart valves to make wrong movements. This narrows the outflow opening to the body artery (aorta). Therefore, the heart has to do harder to pump the blood around and the heart muscle gets thicker over time. The thicker heart muscle is more difficult to relax and the cavity in the heart becomes smaller, so that less blood is pumped around per heartbeat. As compensation, the heart beats faster, so that the heart muscle wall becomes even more overloaded. Ultimately, the heart can no longer cope, the left atrium can be enlarged, the valves can leak and fluid flows out to the lungs. In the enlarged left atrium, blood clots can develop (thrombosis), which can then get stuck elsewhere in the body.

At which breeds and ages does HCM occur?

It is more common in certain breeds than in others, for example in the Press, Main Coon and Ragdoll. But it also occurs regularly with domestic cats. It is slightly more common with males than with cats. We usually see HCM in middle-aged and senior-aged cats, but unfortunately it also occurs in younger animals.

The better breeders have their animals examined before they start breeding. This can be done by means of a heart echo. If it is known that an animal is genetically burdened with this disease, the animal should be excluded from breeding, even though the animal itself is not (yet) sick.

What are the symptoms of a cat with HCM?

Cats with HCM initially have no complaints. Often it is found by accident. During the vaccination consultation, for example, a heart noise or gallop rhythm may be observed. Only when the heart gets into trouble does the animal get complaints. Your cat then becomes short of breath and slower. Sometimes the cat jumps harder, wants to eat less and lose weight. Later the cat becomes more and more oppressive. Your cat may also be acutely paralyzed with one or both hind legs due to thrombosis. Your cat may even die acutely due to heart failure.

How is HCM diagnosed?

A first indication of a heart problem is when a clinical noise or gallop rhythm is heard by the veterinarian during the clinical examination. But even if no heart noise is heard, there can still be HCM. Your cat may exhibit accelerated or commuting breathing due to pulmonary edema or free fluid in the chest cavity. If the cat is paralyzed by thrombosis, the paws feel cold, the cat has a lot of pain and the wrist (which the vet feels at the artery in the groin!) Is weak or even absent.

If the cat is stuffy, it is important that X-rays of the chest cavity are taken. To properly examine the heart, an ultrasound is the most appropriate diagnosis. Without heart echo, no HCM can be diagnosed. If a thickening of the heart muscle wall is found, it is important to exclude other diseases. Your veterinarian will measure your cat's blood pressure and do blood tests for thyroid function. Sometimes your veterinarian also makes a heart video to detect any arrhythmia.

Does a heart murmur always mean that the cat has HCM?

No! A heart murmur can have many causes, from fever and stress to a thyroid problem or high blood pressure. But your cat can also have a heart problem such as HCM. Even if your cat is not sick, just running and playing, there may be a heart problem. The anesthetic risk of a cat with a heart murmur can also be considerably increased. It is therefore always advisable to have a heart echo made if a heart noise is heard. On the outside you cannot see the seriousness and you should never underestimate it. On the other hand, it is unwise to give a cat with a heart murmur just heart medications. Because maybe the cat has no heart problem at all and the heart noise has no meaning or other cause.

What is the treatment of a cat with HCM?

If your cat is very stuffy, your vet will give the cat oxygen. Avoiding stress and rest is also very important. In addition, your cat will receive medication (furosemide) to dissipate fluid in the lungs. If there is free fluid, it is advisable to puncture the chest cavity (chest puncture). For example, if 200 ml of fluid is removed from the chest cavity in a few minutes, this immediately relieves the cat.

If your cat is more stable, your vet will prescribe medication (usually beta-blockers: atenolol) to help relax the heart muscle and lower the heart rate. When the left