Cardiomyopathy in Cats

Category: Uncategorised Written by Super User

Cardiomyopathy is the name given to any disease affecting the heart muscle itself.

This is the most common form of heart disease seen in cats, and the most common cause of heart failure.

Disease of the heart valves (causing 'leaky' valves which prevent the heart functioning normally) are an important and common cause of heart disease in humans and in dogs, but this is rarely seen in cats.

Cardiomyopathies (disease of the heart muscle) are described according to the effect they have on the structure and function of the cardiac (heart) muscle. The main classification is to divide the disease into:

  1. Hypertrophic cardiomyopathy (HCM) - this is the most common form of heart disease in cats and occurs where there is an increase in the thickness of the muscular wall of the heart. This reduces the volume of blood within the heart and also prevents the heart muscle relaxing properly between contractions.
  2. Dilated cardiomyopathy (DCM) - this is where the muscular wall of the heart generally becomes thinner than usual, the heart enlarges, and the heart muscle cannot contract effectively.
  3. Restrictive cardiomyopathy (RCM) - here primarily there is fibrosis of the wall of the heart, making it stiff and inelastic, so preventing the heart chambers filling normally.
  4. Intermediate cardiomyopathy (ICM) - these cases have changes consistent with more than one type of disease - for example a mixture of both hypertrophy and dilatation present.

Underlying causes
Although in the majority of cases of heart disease in cats, the underlying cause is unknown, there are various potential recognised causes, and your vet may need to investigate some of these. Known potential underlying causes include:

Cardiomyopathy secondary to other diseases

Nutritional causes

Infiltrative of the heart muscle

Exposure to toxins

Hereditary causes

What happens in cardiomyopathy?
In cardiomyopathy, the underlying abnormality of the cardiac muscle leads to a compromise in cardiac function. The alteration in heart function depends on the type of cardiomyopathy though:

Early signs of heart disease
In the initial phase of disease, cats may show no signs at all and appear completely normal. In fact a number of cats with cardiomyopathy may never actually develop clinical disease. However, while in some cats, progression of the underlying disease is slow, in others it can be quite rapid.

Some early signs of heart disease may be detectable during a clinical examination by your vet, prior to the onset of any overt signs. This is one of the reasons why every cat should be checked at least one a year by a vet (and ideally more often in older cats). Early warning signs that your vet might detect include:

Many cats, especially with early disease, may only have changes in the cardiac muscle that are detected on an ultrasound examination of the heart. These cats are clinically silent (or symptomatic), although many will go n to develop signs later on.

Heart failure
If heart function is significantly impaired by cardiomyopathy, this will lead to heart failure (often called congestive heart failure), where there is compromise to blood flow through the heart and blood output from the heart.

When cats develop clinical signs sometimes occur without prior warning, and some cats can deteriorate very rapidly. Some cats with heart disease show signs of collapse, or 'fainting'. However, this is relatively uncommon and usually associated with marked disturbances to the normal rhythm of the heart (which can lead to episodes where the brain is staved of oxygen through poor blood flow).

Unlike dogs, cats are not exercised in the same way (e.g., taken for walks on a lead) so it is often much more difficult to detect that they have reduced exercise ability - often an early sign of heart disease. Cats are likely just to spend a little more time resting or sleeping and this may not be very obvious. Because detecting early disease (especially without an examination by your vet) is often difficult, and cats are good at hiding signs of disease, there may be no obvious signs until a 'critical point' is reached due to advance of the disease or perhaps when the cat becomes stressed, that may result in sudden or rapid development of quite marked signs.

In cats, the most common sign of heart failure is the development of difficult breathing (called dyspnoea) and/or more rapid breathing (called tachypnoea). This is generally caused by either a build up of fluid in the chest cavity around the lungs (called a pleural effusion), or due to a build up of fluid within the lungs themselves (called pulmonary oedema).

Along with breathing difficulties, cats may have cold extremities (e.g., ears and paws), and may have pale mucous membranes (gums and eyes) suggesting poor circulation. Occasionally the mucous membranes of the mouth and eyes, and even the skin, may show signs of cyanosis (a bluish colour). Coughing is rarely seen in cats with heart disease, although it is quite common in dogs. In cats, when coughing is seen, this is much more likely to be caused by a disease of the airways (such as bronchitis).

Feline aortic thromboembolism (FATE)
Another sign which can occur in cats, and may sometimes be the first indicator of underlying heart disease, is the development of what is known as 'feline aortic thromboembolism' or FATE. A thrombus (blood clot) may develop within one of the heart chambers (usually left atrium) in a cat with cardiomyopathy. This occurs mainly because the blood is not flowing normally through the heart. The thrombus, or clot, is initially attached to the wall of the heart, but may become dislodged and be carried into the blood leaving the heart. A thrombus that moves into the blood circulation is called an embolus, hence the term 'thromboembolism'. Once in the circulation, these emboli can lodge in a small artery and obstruct the flow of blood to a region of the body. Although this can happen at a number of different sites, most commonly this happens towards the end of the major artery that leaves the heart (the aorta) as it divides to supply blood to the back legs. This complication is seen most commonly with HCM, and will cause a sudden onset of paralysis to one or both back legs, with severe pain and considerable distress.

Differentiation of forms of cardiomyopathy
Various diagnostic tests can be done to assist the diagnosis of heart disease in cats.

The underlying cause of the cardiomyopathy can only rarely be treated, but if it develops secondary to taurine deficiency in the diet (which can be a cause of DCM), or secondary to things like hypertension (high blood pressure) or hyperthyroidism (overactive thyroid gland), then treating the underlying disease may improve cardiac function.

Where heart failure develops, various drug treatments may be available to help improve and manage the condition. These may include drugs such as:

Unfortunately the true effectiveness of many drugs in treating heart disease in cats is unknown, and more clinical trials are needed. Different drugs also act in different ways, and so may be helpful in different situations. In general, diuretics are the most useful drugs to manage the signs of congestive heart failure, but with early diagnosis of heart disease treatment may help to slow or delay its progression and maintain a good quality of life.

 Article published from International Cat Care