What is cardiomyopathy?

Cardiomyopathy is a term used to describe diseases of the heart muscle. In cats, at least 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. 

On examination a murmur may or may not be heard. Unlike in dogs, murmurs (and their grade) do not always indicate significant heart disease. Equally, the absence of a murmur does not rule out cardiac disease. 

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. Blood banks back into the blood vessels of the lungs, resulting in fluid accumulation in or around them. 
  2. Thromboembolic disease:     Altered flow of blood in abnormal 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 very painful and the back legs become paralysed and cold to the touch. Although a minority of 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. 

How is cardiomyopathy diagnosed ? 

Tentative diagnosis of heart disease can be made on the basis of clinical signs, such as breathlessness and lethargy, in addition to more specific tests such as chest x-rays and the blood test Cardiopet proBNP (this measures the degree of heart muscle damage). Electrocardiography (ECG) rarely provides useful information on heart conduction and size. Cardiac ultrasound scans give a definitive diagnosis and are indispensable in distinguishing between the different types of cardiomyopathy.

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) may cause a type of cardiomyopathy. Other causes include dietary deficiency of taurine, an essential nutrient. This is not seen in cats fed a commercial cat food or fresh meat. 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 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.    These drugs are generally the most effective form of treatment and often are the only drug required (in the long term);

          4. Clopidogrel may be used for its effects at reducing the risk of thrombus (clot) formation and hence thrombo-embolic disease; 

           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 and lead near-normal lives.

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, e.g. dry cat food should be avoided since these will predispose to fluid retention. This may increase the risk of congestive heart failure. 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.