Cat - Cardiomyopathy

What is cardiomyopathy?

Cardiomyopathy is a term used to describe diseases of the heart muscle (cardio = heart, myo = muscle, pathy = disease). In cats, various different types of cardiomyopathy have been described. The 3 mostly widely recognised forms are:

1. Hypertrophic cardiomyopathy (HCM, the most common type)
2. Restrictive cardiomyopathy (RCM, the second most common)
3. Dilated cardiomyopathy (DCM, rarely diagnosed).

In all cases, the heart disease may cause heart failure. Cardiomyopathy may be seen as a disease on its own or secondary to another disease. For example, hyperthyroidism (an overactive thyroid gland) can cause hypertrophic changes to the heart and feeding a diet lacking in taurine can cause dilated cardiomyopathy. All commercial cat foods contain correct amounts of taurine for cats.

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. Affected cats may be noticed to be less active, spending more time asleep although this is often considered to be normal behaviour for a cat!

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. These signs are caused by a failure of the heart to efficiently pump blood causing fluid to accumulate in the lungs (pulmonary oedema) or around the lungs (pleural effusion). In some cases, fluid accumulates in the abdomen (ascites).  It is possible to stabilise some, but not all cats with congestive heart failure with medication (see below).
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 (and are called emboli) they can travel in the bloodstream and become lodged in blood vessels. The most common place for the emboli to lodge is at the bottom of the aorta which is the biggest artery in the body. This blocks the blood supply to the back legs which is very painful and the back legs may become paralysed and cold to the touch. In some cats, a partial recovery which may take a long time, is seen. Unfortunately even if cats do recover, the risk of another thromboembolism is extremely high. There are very few treatment options for cats with thromboembolic disease.

How is cardiomyopathy diagnosed?

Heart disease may be suspected in cats showing clinical signs of heart failure such as breathlessness. In other cases, a routine check-up may identify a heart murmur (abnormal heart sound) or abnormal heart rhythm as cause for concern. Further tests are needed to assess the cause and severity of the heart disease. Chest radiographs (x-rays) are helpful particularly in looking for signs of congestive heart failure such as the build up of fluid within or around the lungs, and may also be useful in assessing the size and shape of the heart. Electrocardiography (ECG) may identify an abnormal heart rhythm that may arise as a consequence of cardiomyopathy. Cardiac ultrasound scans (echocardiography) are required to distinguish between the different types of cardiomyopathy.

Blood pressure can be measured if suitable equipment is available, to exclude high blood pressure as a cause of the cardiomyopathy, and to ensure that blood pressure is not too low as a consequence of the reduced cardiac function. Examination of the eyes may provide evidence of high blood pressure in those practices where facilities to measure blood pressure are not available.

Specific tests may be done in order to check that the cardiomyopathy is not secondary to some other disease e.g. hyperthyroidism.

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 heart disease since complete resolution of the heart disease (normally hypertrophic cardiomyopathy) is possible if treated early. In cases of primary cardiomyopathy, where no cause is identified, and in cases where disease remains following treatment for an underlying cause then specific medication for the heart may be needed. In most cases, the cat is likely to need medication for the rest of its life. Cats that do not have any signs of heart failure and just have a heart murmur may not need treeatment.

Treatment varies according to each case but may include:-

1. Diuretics if congestive heart failure is present. Cats with congestive heart failure have too much fluid in their circulation; diuretics are drugs which cause fluid loss from the body into the urine.
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. ACE inhibitors - these drugs help to correct some of the signs of congestive heart failure and are often used with diuretics.
5. 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.

The long term outlook for a cat with cardiomyopathy is extremely variable depending on the cause and severity of this disease. Some cats with 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 high blood pressure 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.