Cardiomyopathy in Cats

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 reduced bloodflow 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 blood that can’t flow normally into the stiffened, thickened ventricle. This is the most common form of cardiomyopathy.

Restrictive cardiomyopathy (RCM): Scar tissue causes the heart muscles to stiffen, but there is little or no muscle thickening (hypertrophy), unlike HCM. When the heart can’t relax enough to fill with a large enough amount of blood, then its ability to move blood around the body decreases and signs of heart failure develop.

Dilated cardiomyopathy (DCM): The heart muscle weakens and thins, losing the ability to pump blood to the body. The weakness causes the heart muscle to stretch and the heart to dilate (expand like a balloon).

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. These changes reduce the amount of blood moving from the right ventricle into the lungs, which causes blood to back up in the abdominal blood vessels.

Non-specific 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.

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 to a level 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 traveling blood clots are called emboli. Emboli most commonly lodge 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 diagnosis of the specific type of cardiomyopathy, a cardiac ultrasound (also called an echocardiogram) is required.

Other tests, including blood tests and blood pressure assessment, may be done to see if the cardiomyopathy is 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?

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

• Dilated cardiomyopathy is usually caused by a dietary deficiency of an amino acid called taurine. Commercial cat food is now supplemented with taurine, so DCM in cats is rare and most cases are diagnosed in cats fed imbalanced, home-prepared diets or dog food.
• Hypertrophic cardiomyopathy can be caused by a heritable gene mutation in certain cat breeds such as Maine coon, ragdoll, and sphinx. 
• Restrictive cardiomyopathy is often idiopathic (unknown cause) but can also be genetic or occur secondary to another disease such as hypertrophic cardiomyopathy or degenerative valve disease. 
• 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?

If an underlying cause of heart disease is found, treatment may result in improvement or reversal of 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 where heart disease persists following treatment of the underlying cause, then medication may be needed. Treatment varies in 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. Your veterinarian will use a catheter or needle to remove fluid that may have collected around the abdominal organs or around the lungs (thoracocentesis/chest tap), causing difficulty breathing.
• Beta-blockers (e.g., atenolol) to reduce the heart rate if it is excessive.
• Calcium channel-blockers (e.g., amlodipine, diltiazem) may be used to help the heart muscle relax, allowing the heart to fill more effectively, reducing blood pressure, or controlling heart rate in patients with arrhythmias.
• Pimobendan (Vetmedin®) may be used to increase the strength of heart contraction and make it easier for blood to flow through blood vessels. This treatment is being investigated for use in cats with cardiomyopathy.
• Clopidogrel may 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; too much or too frequent aspirin may cause vomiting and internal bleeding. If your cat shows these signs, stops eating, or appears sick, stop giving aspirin and consult your veterinarian immediately.
• Angiotensin-converting enzyme (ACE) inhibitors (e.g., benazepril) may help to control congestive heart failure.
• Sirolimus (Felycin-CA1®) is a new, conditionally approved medication shown to reduce ventricular hypertrophy that occurs in HCM. This medication may be used before they have any signs of heart disease, based on your cat's echocardiogram results.

What is the prognosis?

The long-term prognosis for a cat with cardiomyopathy varies depending on the cause of this disease. Cats with idiopathic hypertrophic cardiomyopathy may remain stable for several years. The prognosis worsens if congestive heart failure or thromboembolic disease develops, or with a diagnosis of restrictive cardiomyopathy, dilated cardiomyopathy, or arrhythmogenic right ventricular cardiomyopathy.

Does a cat with cardiomyopathy need a special diet?

Your cat’s diet can help support their heart health. 

• Their diet must have sufficient taurine, and some non-traditional feline diets, such as vegetarian diets, may not have enough. Your veterinarian can help you choose an appropriate diet or refer you to a veterinary nutritionist for more detailed recommendations.
• Cats with underlying kidney disease should be fed a special kidney diet to manage this disease. Depending on 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, and 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.