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Cardiology: Hypertrophic Cardiomyopathy in Cats

What is Hypertrophic Cardiomyopathy (HCM)?

The left ventricle, the heart’s main pumping chamber responsible for pumping oxygenated blood to the body, becomes thickened and non-compliant and is unable to fill properly with blood. A backup of blood and thus, increased pressure in the left atrium occurs, causing it to enlarge. This can lead to increased pressure in the vein leading from the lungs to the left atrium, causing pulmonary edema (wet lungs/congestive heart failure). Thrombi (blood clots) can also occur due to the blood “pooling” in the enlarged atrium. These blood clots typically lodge in the large vessels of the rear legs.

What signs can occur with this disease?

Oftentimes cats are asymptomatic. Owners should watch for signs like exercise intolerance, labored/open-mouth breathing, collapse and acute hind limb paralysis. However, signs could be as simple as inappetance or hiding behavior. The cat’s primary veterinarian may hear abnormal heart sounds (murmur or gallop) even before clinical signs are evident.

What causes HCM?

At this time it is still unknown what causes HCM, but heredity may play a role.

Diagnosis

Other diseases that can mimick HCM should be ruled out. These include hyperthyroidism, chronic high blood pressure and other diseases causing the same signs associated with HCM.

  • Laboratory testing: A complete blood count, blood chemistry and a urinalysis may be indicated to evaluate kidney and liver function, especially in older animals, as some of the cardiac drugs may affect these organs. Thyroid levels may also be checked to rule out hyperthyroidism.
  • Radiography (X-rays):Chest radiographs will reveal the general size and shape of the heart and possible heart chamber enlargement. In HCM, a valentine appearing heart is commonly observed. With chest X-rays, the clinician will also be able to detect fluid build up in lungs (pulmonary edema), and/or the space between lungs and the body wall (pleural effusion).
  • Echocardiography: The most valuable and noninvasive tool in diagnosing HCM is an echocardiogram, which is an ultrasound of the heart. The ventricular wall thickness, atrial diameter, the heart’s pumping capabilities and pressures between the various chambers of the heart can be measured. The most common findings are increased left ventricular wall thickness (hypertrophy), increased contractility and an enlarged left atrium. Sometimes aortic outflow obstruction and/or blood clots (thrombi) in the left atrium can be seen.
  • Electrocardiography: (ECG)An ECG can detect arrhythmias and conduction disturbances which can occur with HCM. Not all cats with HCM have abnormal ECGs.
  • Systemic Blood Pressure Measurement: Patients often have normal or low blood pressure, but blood pressure measurement should be part of the evaluation to rule out systemic hypertension.

Can my cat live a normal life?

Yes; however, all cats with HCM should be kept indoors and avoid stressful situations.

Can HCM be cured, and what is the treatment and prognosis?

Unfortunately, HCM cannot be cured. Drug therapy may help the heart muscle to relax more. Many HCM patients will need lifelong drug therapy.
Medications (indicated in most cases) enhance relaxation, are antiarrhythmic, slow the heart rate, and lessen the force of contraction of the heart muscle. Anticlotting agents are used in cats that are at risk for thrombi. Diuretics are commonly used in patients that have pulmonary edema and/or pleural effusion (congestive heart failure) to decrease fluid and salt retention in the body. Oxygen therapy is often required as an emergency therapy in patients with congestive heart failure.
Cats that are in congestive heart failure should eat a sodium restricted diet.
The prognosis of HCM is variable. Some cats that show signs of heart disease may live for many months after good response to drug therapy. Other cats may die very suddenly due to thromboemboli or poor response to drug therapy.

Are all cats affected equally?

Maine Coon cats, Bengals, British Shorthair and Persians have a familial predisposition to the disease; however, HCM can occur in any breed of cat. Males are affected more frequently than females. HCM affects cats of all ages but is most commonly reported at an average age of 5-7 years.