Short description

HCM = Hypertrophic Cardiomyopathy

Cardiomyopathy

Is the illness of the heart muscle. This subject is quite complex. There exist various illnesses of the heart muscle:

DCM Dilated cardiomyopathy

Characteristic is the dilatation of the ventricles and the weakening of the heart muscle that the heart is not able any longer to pump the necessary volume of blood out from the heart.

HCM Hypertrophic cardiomyopathy

In HCM the heart muscle thickens inwards, affected are mostly the left ventricle and the mitral valves that the volume of the left ventricle is reduced and less blood can be pumped at each contraction.

RCM Restrictive cardiomyopathy

In RCM the fibrin of the endocard (inner heart wall) in the ventricle thickens that the ventricle cannot extend normally.

Symptoms

Compared with dogs, coughing is not always a characteristic sign in cats for heart problems. Very frequently breathlessness, lethargy and loss of appetite may be noticed. These signs may appear very fast within a few hours. But they may appear after months and years, whilst the heart disease is already present for a long time.
The disease can become apparent at any stage of age, in very young cats, in adults, in old cats. Or the disease is noticed by the sudden death of the cat.
In cats the venous pressure increases, which leads to a leaking of fluid into the lungs (pulmonary edema) or into the tissues around the lungs (pleural effusion) that the lungs cannot work properly, which leads to breathlessness or lethargy.
The disease can also result in the formation of clots (thrombosis, embolism). As the thickened ventricle cannot pump off the blood properly and efficiently, it can come to a stasis of the blood resulting in clots, which may become trapped in thinner arteries and thus blocking them. The most frequent location, where a thrombosis is built, is where the aorta branches to the arteries for the hind legs and the tail (aortic trifurcation), consequently the hind legs may be lame and the tail may become cold, because they are not supported with enough blood. Though it is possible to treat the lameness with drugs (for thinning of the blood) the heart disease remains uncured and the risks for future clotting remain.
High blood pressure (hypertension) occurs also, mainly in older cats, which may lead to damaging of the vessels. Especially the thin vessels in the retina can become damaged and disrupted, which can result in retinal detachment and sudden blindness. The cats appear to be confused and disorientated and have widely opened pupils. Also hypertension can damage the glomerulus (a small bundle of vessels and nerves in the cortex) of the kidneys. Also small vessels in the brain can be disrupted.
High blood pressure in cats is almost always the result of a disease, whilst in humans primary hypertension can occur, which is very rare in cats.

Treatment

Not every cat carrying HCM must become ill. But when the damage appears, it cannot not be cured. Unfortunately HCM is a progressive disease, but progression can be also very slow.
Mostly the symptoms are treated, i.e. reduction of the high blood pressure, support for the heart rate:

• Reduction of the fluid in the lungs and around the lungs through diuretic drugs (water diuresis) or through puncture.
• Drugs supporting the heart function, depending on the cause of the cardiomyopathy:

• ACE-blocker (angiotensin converting enzyme), which cause a dilation of the vessels (vasodilation) to reduce the blood pressure and reducing the heart's load.
• Calcium-channel-blocker (CB) - drugs, which prohibit the intrusion of the calcium-ions through the slower calcium-channel and thus to relax the heart muscle that more blood can fill the ventricle. CB also lowers the blood pressure.
• Beta-blocker (β-Adrenoceptor-blocker), which are sometimes used to lower the heart rate, when it is excessively fast that there is not enough time to fill the ventricle with enough blood.

ATTENTION:
Do not treat the cat by your own. Only the veterinary can prescribe the needed drugs!

Inheritance in cats

Genetics of HCM is very complex, in humans about 200 mutations have been detected.
One can assume that also in cats many different gene mutations do exist, which are responsible for HCM.

One gene mutation - a significant reduction of the cardiac protein, myosin-binding protein C = cMyBP-C  - was found in 2004 by Kate Meurs, D.V.M., Ph.D., DACVIM, the Richard L. Ott Professor of Small Animal Medicine and Research at Washington State University, and Mark Kittleson, D.V.M., Ph.D., DACVIM, professor of cardiovascular medicine at the University of California-Davis School of Veterinary Medicine, in the Maine Coon.
This mutation is autosomal dominant inherited, i.e. independent of the sex linked chromosome Y or X.

In 2007 the mutation in the same gene (cMyBP-C) was found by Kate Meurs for the Ragdoll, but at a different location (locus). That means it is a different mutation in the Ragdoll than in the Maine Coon. This is like in humans, where 90 different mutation causing HCM  in the same gene are known.
This mutation is autosomal dominant inherited, i.e. independent of the sex linked chromosome Y or X.

Cat breeds, which are known by today possibly to inherit HCM

• Maine Coon
• Ragdoll
• Sphynx
• Devon Rex
• Persian - Exotic
• American Shorthair
• British Shorthair
• Scottish Fold
• Siberian
• Norwegian Forest
• Turkish Van

Test methods in cats

The traditional method is the echocardiogram. But it can detect the disease, when HCM has affected the cat already, but it cannot detect the gene causing HCM. And the echocardiogram has to be repeated every year.
Echocardiography is efficient for cats which are already moderately or severely affected, but it cannot detect every change in mildly affected cats.

Since 2006 there is a DNA-test for Maine Coon available for one type of HCM (reduction of the protein cMyBP-C).
Since 2008 there is a DNA-test for Ragdoll available for one type of HCM (reduction of the protein cMyBP-C, the same gene, but a different locus).

Please note that this DNA-test tests for only one mutation.

Consequences for breeding cats

Positively tested cats should not be used for breeding, as in every inherited defect, i.e. affected cats should be neutered. Please think about that every hormone stress is a stress for the cat, which - for sure - will have the negative effect to speed up the progression of the disease.