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CARDIOMYOPATHY

What is cardiomyopathy?

Cardiomyopathy is a term used to describe diseases of the heart muscle. In cats, three classes of cardiomyopathy have been described. In all cases, the heart disease may result in clinical signs of heart failure. Cardiomyopathy may be seen as a primary condition or secondary to other diseases.

What are the clinical signs seen with cardiomyopathy?

In the early stages of disease, the cat may be able to cope and hence show no signs of disease. This situation is referred to as compensated heart disease. Often the cats will alter their activity levels to those that they can cope with which makes it difficult to diagnose cardiomyopathy until it is quite advanced.

The major longterm concerns with all types of cardiomyopathy are:-

1. Development of congestive heart failure: Breathlessness and lethargy are the most frequently  noticed signs of congestive heart failure and these result from a failure of the heart to efficiently pump blood.

2. Thromboembolic disease: Altered flow of blood in enlarged heart chambers predisposes to the formation of a blood clot within the chambers of the heart. This becomes organised and is known as a thrombus. If parts of the thrombus become dislodged they can travel in the bloodstream and become lodged in smaller blood vessels. These particles are called emboli and the most common place for them to lodge is at the bottom of the aorta which is the biggest artery in the body. This results in obstruction of the blood supply to the back legs which is usually very painful and the back legs become paralysed and cold to the touch. Although some cats may recover completely with appropriate treatment, this is a potentially fatal complication of any cardiomyopathy. In some cats, a partial recovery which may take a long time, is seen.

3. Hypertension: High blood pressure, or hypertension, is a possible complication associated with hypertrophic cardiomyopathy in particular. This may result in spontaneous bleeding, such as nose-bleeds or haemorrhage within the eye and may also cause retinal detachment and blindness. This may be noticed as a sudden loss of vision and development of widely dilated pupils. This is an emergency situation since the blindness will be permanent unless the retina re-attaches within a couple of days. Hypotensive drugs are those which lower the blood pressure and these may be used to control cats with this problem. Measuring blood pressure in cats is extremely difficult due to their small size and  the rise in blood pressure with stress which makes interpretation of results problematic. For these reasons, hypertension may

only be detected once a problem has occurred. Examination of the eyes may give early indications of hypertension since the blood vessels of the retina may show changes and small haemorrhages may be noticed.

How is cardiomyopathy diagnosed?

Diagnosis of heart disease can be suspected on the basis of clinical signs, such as those of congestive heart failure, in addition to more specific tests such as chest x-rays. Electrocardiography (ECG) may also provide useful information on heart conduction and size. Cardiac ultrasound scans, where available, help to distinguish between the different types of cardiomyopathy.

In cases where hypertension is a possibility, blood pressure can be evaluated if suitable equipment is available. Retinal examination may provide evidence of hypertension where blood pressure measurements cannot be made.

Specific tests may be done in order to check that the cardiomyopathy is not secondary to some other disease. (see below).

What causes cardiomyopathy?

There are many causes of cardiomyopathy, however, in older cats thyroid disease (hyperthyroidism) commonly causes cardiomyopathy. Other causes include kidney failure and a rare cause is dietary deficiency of taurine, an essential nutrient. This is not seen in cats fed a commercial cat food. Often, no cause of the cardiomyopathy is found.

How is cardiomyopathy treated?

In cases where an underlying cause of the heart disease is found, then treatment of this may result in improvement or reversal of the heart disease. Hyperthyroidism is the most treatable cause of cardiomyopathy since complete resolution of the heart disease is possible if treated early. In cases where no cause is identified, (referred to as idiopathic cardiomyopathy), and in cases where disease remains following treatment for an underlying cause then medication may be needed.

Treatment varies according to each case but may include:-

1. Diuretics if congestive heart failure is present.

2. Beta blockers to reduce the heart rate where this is excessive.

3. Calcium channel blockers to help the heart muscle relax and hence help more effective filling of the heart.

4. Aspirin may be used for its effects at reducing the risk of thrombus formation and hence thrombo-embolic disease. Dosing of aspirin should always be as advised by a veterinary surgeon since aspirin may be toxic to cats. Aspirin poisoning, which occurs if the dose or frequency of aspirin administration is too high, may cause vomiting and internal bleeding. If your cat shows these signs, goes off their food or is sick then aspirin therapy should be stopped and you should consult your vet.

5. ACE inhibitors - these drugs also help to control congestive heart failure.

The longterm outlook for a cat with cardiomyopathy is extremely variable depending on the cause of this disease. Cats with idiopathic cardiomyopathy may remain stable for several years.

Does a cat with cardiomyopathy need a special diet?

Other than in cases of taurine deficiency, no specific diet is recommended although excessively salty foods should be avoided since these will predispose to fluid retention. This may increase the risk of congestive heart failure and hypertension developing. Proprietary cat foods are usually adequate although special low salt diets are available and may be recommended by your veterinary surgeon in specific cases. Cat treats are often quite salty and probably should be avoided.