What is feline hypertrophic cardiomyopathy & what does it do?

Feline hypertrophic cardiomyopathy (HCM) is the most common heart disease seen in felines. Hypertrophic cardiomyopathy is a term used when there is no known cause, however secondary, is brought about by other conditions such as high blood pressure, hyperthyroidism etc. Cats with secondary hypertrophic cardiomyopathy tend to be older.

The main feature of hypertrophic cardiomyopathy is excessive thickening of the left ventricular wall, papillary muscles & septum.  This enlargement causes stiffening & prevents the heart from expanding (to receive blood) properly.  It may also reduce the ability of the valves to work properly, and in some circumstances obstruct the flow of blood out of the heart. Arrhythmias, irregularities of the heart beat & conduction disturbances are also common complications of hypertrophic cardiomyopathy.

The thickened wall sometimes distorts one leaflet of the mitral valve, causing it to leak.

Fluid can leak into the lungs causing heart failure.

Blood clots can form in the left atrium & be carried into the systemic arterial system, most often lodging in the terminal artery, causing paralysis of the hind legs.

Cardio=heart, myopathy=muscle disease & hypertrophic=thickened. Hypertrophic cardiomyopathy tends to affect cats one to five years of age, and male cats are more commonly affected.

What are the symptoms of hypertrophic cardiomyopathy?

A cat with hypertrophic cardiomyopathy may display no symptoms at all, but die suddenly & unexpectedly.  Symptoms may include.

• Lethargy
• Anorexia
• Weight loss
• Rapid,  laboured & noisy breathing
• Decreased activity
• Congestive heart failure
• Irregular heart rhythm
• Heart murmur
• Gagging
• Lameness or paralysis of the hind legs

Are some cats more prone than others?

In humans HCM can be inherited as an autosomal manner. It appears Maine Coons & American Shorthairs also have a predisposition towards HCM.

How is hypertrophic cardiomyopathy diagnosed?

A physical examination may reveal abnormal heart or lung sounds, irregular or gallop heart rhythm or heart murmur, this may well be the first indication that your cat has HCM.

Echocardiogram (heart ultrasound) is the best diagnostic tool for HCM. Your veterinarian will evaluate the size, shape & functioning of the heart.

X-Ray can show if there is fluid in the chest & heart enlargement.

Electrocardiogram

Blood tests including a complete blood count & chemistry panel. These can help provide information on the function of other organs. This information is important when determining methods of treatment.

Thyroid function test to determine if the cause is due to hyperthyroidism.

Arterial blood pressure to check for hypertension.

How is hypertrophic cardiomyopathy treated?

Asymptomatic cats may require no treatment, but your veterinarian will want to monitor him/her closely.

It is not possible to cure HCM, treatment is aimed at controlling symptoms & preventing complications.

The thick ventricles of HCM contract and relax abnormally, and to assist the relaxation phase some drugs may be necessary. Beta blocking drugs & calcium blocking channels may be prescribed to assist.

If the cat has congestive heart failure, diuretics may be prescribed.

Controlled doses of blood thinning drugs such as aspirin for cats who have a high risk of clot formation.

Restricting activity also reduces the strain on the heart & your veterinarian may prescribe a period of cage rest.