Causes of Cardiomyopathy in Cats

Types of Cardiomyopathy in Cats

Diseases of the heart muscle are classified based on the effect that they have on the heart muscle’s structure and function. In cats, this includes hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), restrictive cardiomyopathy (RM), and unclassified cardiomyopathy.

Hypertrophic Cardiomyopathy (HCM) in Cats

Hypertrophic cardiomyopathy (HCM) is the most commonly diagnosed heart disease in cats. It is characterized by the thickening of the heart’s muscular walls which can lead to a decrease in the heart’s ability to pump blood efficiently.

In cats with HCM, the left ventricle of the heart (also considered the primary pump muscle) is thickened. When the ability to pump is compromised, there will be a consequent decrease in the volume of blood being pumped. This can eventually have an impact on the oxygenation of the body cells as they starve for oxygen. The muscle cells of the heart may also die because of a lack of oxygen. This can further compromise heart function which can eventually lead to arrhythmias (irregular heart rhythm, or there could be too rapid or too slow of a heartbeat).

The inefficiency of the left ventricle to pump may also cause blood to back-flow to the other chambers of the heart and the lungs. This is an important predisposing factor for congestive heart failure and the development of blood clots in the heart.

The cause of HCM in cats has not been fully identified, but many experts believe that there could be a genetic link since there is a higher prevalence in certain breeds of cats. Mutation of cardiac genes has also been identified in some cats with HCM.

Symptoms of Hypertrophic Cardiomyopathy in Cats

Many cats with hypertrophic cardiomyopathy are asymptomatic (don’t show any symptoms), while some exhibit signs associated with congestive heart failure - difficulty breathing (labored, rapid, and open-mouthed) and lethargy. The accumulation of fluid in and around the lungs is responsible for these symptoms.

Cat breeds that appear to be more at risk for developing HCM include:

• Persian cats
• Sphynx
• Maine Coon
• British Shorthair
• Chartreux
• Ragdoll

Treatment and Prognosis for Cats with HCM

There is no known cure for HCM in cats, but early diagnosis and the appropriate treatment regimen can increase the chance of a favorable prognosis and a better quality of life. Treatment is aimed at controlling the heart rate, alleviating symptoms of congestive heart failure, and preventing blood clot formation that can increase the risks of thromboembolism (reduced blood flow caused by a blocked blood vessel).

As for the prognosis, cats that don’t exhibit any symptoms have been observed to survive for years. Being a progressive disease, a worse prognosis is associated when congestive heart failure and thromboembolism are present.

Dilated Cardiomyopathy (DCM) in Cats

Dilated cardiomyopathy is characterized by the thinning of the muscular wall of the heart (particularly of the left ventricle) and accompanied by a distinct enlargement of the heart. When this happens, the heart becomes overloaded as it is unable to contract and pump blood effectively. In severe cases, DCM usually progresses to congestive heart failure.

Cases of dilated cardiomyopathy in cats are rarely seen today. In the past, it was linked to a deficiency of taurine (a type of amino acid), a problem that has been addressed with premium quality cat food. Today, most cases of DCM in cats are of unknown origin. In some feline breeds, a genetic predisposition has been identified.

Some cat breeds that are commonly affected by DCM include Siamese, Burmese, and Abyssinian. More cases have been diagnosed in cats ten years old and older, although the problem can also affect younger cats.

A reduction in cardiac flow associated with DCM can lead to the following symptoms:

• Depression
• Loss of appetite
• Weakness
• Pain and partial paralysis occur when thromboembolism is present

A physical exam will reveal a soft heart murmur, a heart rate that may be low, high, or normal, hypothermia, and abnormal heart rhythm.

The treatment for DCM will depend on the severity of symptoms. Severe cases may require medications to control abnormal heart rhythms, low blood pressure, and any complications caused by blood clots. Medications may be given to prevent kidney failure. Dietary changes may also be recommended by your vet. A low-sodium diet can help reduce fluid stress on the heart.

Unfortunately, even with intensive treatment and care, most cats with DCM have a poor prognosis. A cat’s quality of life is a more important consideration rather than prolonged longevity in these cases.

Restrictive Cardiomyopathy (RM) in Cats

Restrictive cardiomyopathy is associated with the buildup of scar tissue (fibrosis) on the ventricle’s inner lining. Fibrosis can affect ventricular efficiency, preventing the ventricle from normally relaxing, filling, and emptying. The symptoms exhibited by affected cats are similar to HCM.

Unclassified Cardiomyopathy

Cardiomyopathy is said to be unclassified when the heart muscle is affected but no specific cause has been established. The problem is commonly observed in middle-aged to senior cats, although cases have been diagnosed in younger cats.

Diagnosing Cardiomyopathy in Cats

In addition to a thorough physical exam, your vet will perform several medical tests and procedures to diagnose cardiomyopathy and identify the specific type. These measures are necessary to rule out other medical conditions.

• Electrocardiogram - The procedure is useful in examining the electrical currents in the muscles of the heart. Any abnormalities in the conduction of electrical impulses (which is responsible for initiating heart contraction) may also be revealed, as well as the origin of any abnormal heart rhythms.
  
• Chest x-ray (thoracic radiograph) - Results may reveal enlargement of the heart and if there is an accumulation of fluid in the chest.
  
• Ultrasound (echocardiography) - Allows visualization of the heart size and the ability of the ventricles to contract. Other important data that may be obtained from an echocardiogram when cardiomyopathy is present include the thin walls of the ventricle, an enlarged heart (particularly the left ventricle and left atrium), and low contraction ability of the heart.

Caring for a Cat with Cardiomyopathy

Cats that have been diagnosed with any type of cardiomyopathy will require follow-up treatments and monitoring. Prescribed medications must be given even when the cat appears to have recovered unless instructed by your vet to stop giving them. Take note that a precise dosage and consistency are essential for medical management to show positive results.

Read more:

Pulmonary Hypertension in Dogs and Cats

Heartworm Infection in Cats

Common Diseases in Cats

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