Health

Hypertrophic Cardiomyopathy (Feline)

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Feline hypertrophic cardiomyopathy is a disease characterized by enlargement of the heart cells (cardiomyocytes), resulting in progressive thickening of the wall of the lower, predominantly left, heart chamber (ventricle). This thickening of the heart wall reduces the ability of the heart to pump blood efficiently, thereby reducing blood flow and oxygen to tissues and organs throughout the body. Fluid may accumulate in the lungs, and difficulty breathing may be one of the first signs noted in cats with heart disease. This disease may also result in the formation of blood clots within the heart that break off and travel through the blood to distant sites such as the arteries that supply blood to the rear legs and kidneys.

In most cases, the underlying cause of feline primary hypertrophic cardiomyopathy remains unknown. It is suspected that there may be a genetic basis for this disease, and a hereditary cause has recently been identified in some cat breeds (Persian, ragdoll, American shorthair and Maine coon).

Common name: Hypertrophic cardiomyopathy (HCM), Feline hypertrophic cardiomyopathy, Feline heart disease.
Scientific name: Feline primary hypertrophic cardiomyopathy, Feline hypertrophic cardiomyopathy.

Diagnosis

Signalment
Cats of any age (3 months to geriatric), breed or sex are susceptible to developing this disease, though some cats appear to be at higher risk. This disease is diagnosed most often in young male cats (1 to 4 years of age). There is also a higher incidence within some cat breeds (Persian, ragdoll, American shorthair, Maine coon) where a hereditary basis for the disease has been found.

Incidence/prevalence
The incidence of this disease is currently unknown. Heart disease is thought to occur much less frequently in cats than in humans or dogs.

Geographic distribution
There is no geographic distribution for this disease. Cats in any part of the world may develop this disease and are considered equally at risk. The disease may appear more frequently in regions where cats are often inbred and more likely to be genetically related.

Clinical signs (primary, most to least frequent, scientific term, synonyms)
Asymptomatic (no clinical signs), Cardiac arrhythmia (abnormal heartbeat or heart rate or rhythm).

Clinical signs (secondary, most to least frequent, scientific term, synonyms)
Tachypnea (rapid, shallow breathing), Dyspnea (difficulty breathing), Vomiting or gagging, Panting, Coughing, Anorexia (poor or no appetite), “Dog-sitting” posture (prefers not to lie down, especially on side, wide front-leg stance when sitting), Lethargy (sedate, decreased activity level), Syncope (fainting), Sudden death, Rear leg weakness or paralysis.

Causes (scientific, common term)
Idiopathic (unknown), Familial (hereditary, genetic).

Organ systems affected (most to least affected)
Heart, Lungs, Blood vessels – caudal aorta (bifurcation), renal arteries, Kidneys.

Diagnostic tests
Physical examination with auscultation (heart and lung sounds), Thoracic radiography (chest X-ray), Blood tests (serum chemistry, thyroid hormone test), Echocardiography (heart ultrasound), Electrocardiography (EKG), Blood pressure monitoring or Doppler.

Differential Diagnosis
Dilated cardiomyopathy, Restrictive cardiomyopathy, Feline secondary hypertrophic cardiomyopathy (heart disease secondary to genetic or hereditary defects), Hyperthyroidism (overactive thyroid gland), Renal (kidney) disease, Systemic hypertension (high blood pressure), Diabetes mellitus, Glycogen storage disease (type II glycogenosis), Systemic viral infection (feline panleukopenia), Feline asthma, Bacterial, viral or fungal pneumonia, Renal (kidney) disease (acute or chronic renal failure).

Overview

Feline hypertrophic cardiomyopathy (HCM) is the most common form of heart disease in cats today. Although several types of feline heart disease exist, this is the only known “primary” heart disease (meaning no underlying cause has yet been identified). In most cats, the cause remains unknown. This disease is suspected to be genetic or hereditary in all cats, but a hereditary predisposition has been identified in only a few cat breeds (Persian, ragdoll, American shorthair, Maine coon). The disease affects cats of any age, from several months old to geriatric. Young males (1 to 4 years old) are at greatest risk.

Feline hypertrophic cardiomyopathy (HCM) induces enlargement of heart cells (cardiomyocytes), resulting in progressive thickening of the wall of the lower, predominantly left, heart chamber (left ventricle). Thickening of the wall reduces the heart's ability to efficiently pump blood, thereby reducing blood and oxygen flow to the body's tissues and organs. Stretching and thinning of the wall of the left upper heart chamber (atrium) may also occur and lead to the formation of blood clots within the atrium. Clots may travel through the blood to distant sites such as the arteries supplying the kidneys and rear legs (thromboemboli).

In the early stages of the disease, cats often show either no signs of illness or vague signs that could be attributed to any number of diseases. As the disease progresses, clinical signs may include any of the following: decreased activity (lethargy), difficulty breathing (dyspnea), rapid breathing (tachypnea), decreased or no appetite (anorexia), vomiting, gagging, “dog-sitting” posture (reluctance to lie down, wide front-leg stance), syncope (fainting) and sudden death. Emboli from blood clots may lodge in the main artery supplying the rear legs, resulting in rear limb weakness or paralysis. The rear legs may feel cold, and the leg pulse may be reduced or absent. Blood clots lodged in the arteries supplying the kidneys may result in signs of renal disease or failure.

Treatment

Home Care
Feline hypertrophic cardiomyopathy is difficult if not impossible to diagnose at home. Cats with a family history or that are suspected of having heart disease should be thoroughly evaluated by a veterinary medical professional. Cats with signs suggestive of blood clots affecting the rear legs should be evaluated as soon as possible (this is a medical emergency).

Professional Care
In many cases, a heart murmur can be detected on a routine physical examination. Often a veterinarian can make a diagnosis of heart disease based on physical examination and thoracic radiographs (chest x-rays) and/or ultrasonography. Blood tests will often be recommended to evaluate for any underlying cause for the heart disease. In some cases, additional tests may be necessary to determine the degree of heart disease and to formulate an appropriate treatment plan.

Medications may be necessary to assist the heart in functioning, decrease fluid accumulation (lungs), prevent blood clots and minimize damage caused by lack of oxygen. These medications must be adjusted periodically necessitating continued follow-up veterinary care.

Action
In many cases, a heart murmur can be detected on a routine physical examination. Often a veterinarian can make a diagnosis of heart disease based on physical examination and thoracic radiographs (chest X-rays). Blood tests will often be recommended to evaluate any underlying cause for the heart disease. In some cases, additional tests may be necessary to determine the degree of heart disease and to formulate an appropriate treatment plan.

Medications may be necessary to assist the heart in functioning, decrease fluid accumulation (lungs), prevent blood clots and minimize damage caused by lack of oxygen. These medications must be adjusted periodically, so it is important to follow the guidelines established by the veterinarian.

Outcome
While there is no cure, symptoms can often be controlled successfully with proper treatment. With early diagnosis and treatment, most cats will have a good prognosis.

References/Additional Readings

Ware, W.A. Cardiovascular System Disorders. In: Nelson, R.W., Couto, C.G., 3rd Ed. Small Animal Internal Medicine. St. Louis: Mosby, Inc., 2003; 122-133.

Jones, C.J., Hunt, R.D., King, N.W. Cardiovascular System. In: 6th Ed. Veterinary Pathology. Baltimore: Williams & Wilkins, 1997; 985-986.

Van Vleet, J.F., Ferrans, V.J., Cardiovascular System. In: McGavin, M.D., Zachary, J.F., 4th Ed. Pathologic Basis of Veterinary Disease. St. Louis: Mosby Elsevier, 2007; 588-591.


Author

Colleen M. Almgren, DVM, PhD


Editor

Steven Hansen, DVM, MS, MBA

DABVT, DABT


© 2007. The American Society for the Prevention of Cruelty to Animals (ASPCA)


Please note that PetVet should only be used as a guide and in no way should be substituted for licensed veterinary care.

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