Cardiomyopathy in Cats

By Malcolm Weir, DVM, MSc, MPH; Ernest Ward, DVM

What is cardiomyopathy?

Cardiomyopathy is a term used to describe diseases of the heart muscle. In cats, the following classes of cardiomyopathy have been described:

Hypertrophic cardiomyopathy (HCM): The heart muscle in the left ventricle (the part of the heart that pumps blood out to the body) becomes thick (hypertrophied), reducing the amount of blood that can enter the ventricle. This decreases the heart’s ability to supply blood and oxygen to the body and causes another part of the heart (left atrium) to dilate with the blood that can’t flow normally into the stiffened, thickened ventricle.

Restrictive cardiomyopathy (RCM): Scar tissue causes the heart muscles to stiffen, but unlike HCM, there is little or no muscle thickening (hypertrophy). The heart’s ability to pump blood and oxygen to the body is impaired similarly to HCM.

Nonspecific or unclassified cardiomyopathy (NCM): The heart muscle has changes that cause a decrease in heart function but don’t fit into the above categories. This condition could represent a combination of cardiomyopathies or a transition from one type to another.

Arrhythmogenic right ventricular cardiomyopathy (ARVC): The right ventricle (all or part of it) becomes very thin and is often replaced by scar tissue or fatty scar tissue. This results in a reduction of blood moving from the right ventricle into the lungs, backing up blood into the vessels of the abdomen.

Dilated cardiomyopathy (DCM): The heart muscle weakens and thins, losing the ability to pump blood to the body.

What are the clinical signs of cardiomyopathy?

In the early stages, the cat may not show any signs of disease. This is referred to as compensated heart disease. Often, cats reduce their activity levels to those that they can cope with, which means it may be difficult to diagnose cardiomyopathy until it is quite advanced. In the long term, cats with any type of cardiomyopathy are at an increased risk of developing congestive heart failure and thromboembolic disease (blood clots).

In later stages, the following signs may appear:

Development of congestive heart failure: Breathlessness and tiredness are the most frequently noticed signs of congestive heart failure. These signs result from failure of the heart to pump blood efficiently. Your cat may also develop ascites (fluid buildup in the abdomen), causing a pendulous belly.

Thromboembolic disease: Altered blood flow in the enlarged heart chambers increases the risk of a blood clot forming within the heart (called a thrombus). If parts of the thrombus become dislodged, they can travel in the bloodstream and block smaller blood vessels. These travelling blood clots are called emboli. The most common place for them to lodge is at the bottom of the aorta, which is the largest artery in the body. A blood clot in this area results in obstruction of the blood supply to the back legs, which is very painful and leads to paralysis. This blockage is commonly described as a saddle thrombus or saddle thrombosis. Although some cats may recover with appropriate treatment, this is a potentially fatal complication of any cardiomyopathy.

Sudden death: Unfortunately, unexpected death is a consequence of cardiomyopathy. It is believed to be caused by a fatal arrhythmia or a blood clot that blocks blood flow out of the heart or into the brain.

How is cardiomyopathy diagnosed?

Heart disease may be suspected based on clinical signs, physical examination, chest X-rays, and electrocardiography (ECG). To make a specific diagnosis of the type of cardiomyopathy, a cardiac ultrasound (also called an echocardiogram) is required.

"Heart disease may be suspected based on clinical signs, physical examination, chest X-rays, and electrocardiography (ECG)."

Other tests, including blood tests and blood pressure assessment, may be done to check that the cardiomyopathy is not secondary to another condition such as hyperthyroidism or hypertension. Your vet may examine the retinas in your cat’s eyes as they may show evidence of hypertension. (See handouts “Hypertension or High Blood Pressure in Cats" and “Hyperthyroidism in Cats” for more information.)

What causes cardiomyopathy?

Top image shows a heart with dilated cardiomyopathy. In indicates how larger valve openings cause an inefficient flow of blood from the ventricle to the atrium. The thinning ventricle wall prevents the heart from pumping sufficient oxygen to the body. The bottom image shows a heart with hypertrophic cardiomyopathy. It indicates how the abnormally thick, muscular wall of the ventricle makes it difficult for the heart to pump sufficient blood and oxygen to the body.In most cases of cardiomyopathy in cats, the cause is unknown. Dilated cardiomyopathy is most commonly caused by a dietary deficiency of taurine, an amino acid. Commercial cat food is now supplemented with taurine, so DCM in cats is rare, and most cases are diagnosed in cats that are fed imbalanced home-prepared diets or dog food.

There is a heritable gene mutation that causes hypertrophic cardiomyopathy in certain cat breeds such as Maine coon, ragdoll, and sphinx. Restrictive cardiomyopathy is often idiopathic in origin (unknown cause) but can also be genetic or occur secondary to another disease such as hypertrophic cardiomyopathy or degenerative valve disease.

"In most cases of cardiomyopathy in cats, the cause is unknown."

Some cases of cardiomyopathy may be congenital (present from birth). In older cats, secondary hypertrophic cardiomyopathy can result from hyperthyroidism (an overactive thyroid gland) or systemic hypertension (high blood pressure).

How is cardiomyopathy treated?

In cases where an underlying cause of heart disease is found, treatment may result in improvement or reversal of the heart disease.

Hyperthyroidism is the most treatable cause of cardiomyopathy: complete resolution of heart disease is possible if diagnosed and treated early.

In cases where no underlying cause is identified, and in cases where the heart disease persists following treatment of the underlying cause, then medication may be needed.

Treatment varies according to each case, but may include:

  • Diuretics (e.g., furosemide or spironolactone), if congestive heart failure is present, to reduce fluid that may be accumulating in the lung tissue.
  • Draining excess fluid from either the chest or the abdomen. Using a catheter or needle to remove fluid that may have built up around the lungs (thoracocentesis/chest tap), causing difficulty breathing, or to remove fluid that has collected around the abdominal organs. 
  • Beta-blockers (e.g., atenolol) to reduce the heart rate if it is excessive.
  • Calcium channel-blockers (e.g., amlodipine) to help the heart muscle relax, allowing the heart to fill more effectively.
  • Pimobendan (Vetmedin®) to increase the strength of heart contraction and to make it easier for blood to flow through blood vessels. This treatment is being investigated for use in cats with cardiomyopathy.
  • Clopidogrel may be used to reduce the risk of thrombus formation and thromboembolic disease. Previously, aspirin was used for this purpose, but studies have found aspirin alone to be inadequate. Clopidogrel may be combined with aspirin or another anti-clotting medication called rivaroxaban to increase efficacy. Aspirin dose should always be advised by a veterinarian. Administering too much aspirin or too frequently may cause vomiting and internal bleeding. If your cat shows these signs, stops eating, or appears sick, stop the aspirin therapy and consult your veterinarian immediately.
  • Angiotensin converting enzyme (ACE) inhibitors (e.g., benazepril) also help to control congestive heart failure.

What is the prognosis?

The long-term prognosis 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?

Cats with underlying kidney disease should be fed a special kidney diet to manage this disease. Depending on the clinical signs, your veterinarian may recommend a special heart diet instead of the kidney diet. Low sodium diets are often recommended for cats with idiopathic cardiomyopathy. This may decrease the risk of developing congestive heart failure and hypertension. Cat treats are often quite salty and should be avoided. Your veterinarian will make specific dietary recommendations based on your pet's condition.

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