Hypertrophic Cardiomyopathy in Cats

This is the most common cause of heart disease in cats and the most frequent cause of spontaneous death in indoor adult cats. In cats with this condition, the walls of the ventricles become thick. However, because the muscle fibers are replaced by fibrous connective tissue (scar tissue), the thicker heart walls do not translate into increased pumping power. In fact, the heart is actually weakened as the affected wall of the heart becomes less elastic and the heart chambers get smaller.

Early signs of hypertrophic cardiomyopathy are vague and indefinite. Increased heart rate and a murmur are common signs. Decreased appetite, weight loss, and an increase in respiratory rate may all be noted. Loss of pep and appetite and reduced exercise tolerance may go unnoticed, because cats are able to recognize their own physical limitations and restrict their activities accordingly. Other than possibly hearing a heart murmur, it is unusual to detect heart disease before signs of congestive heart failure. The first and only sign may be sudden death.

Coughing is rarely a sign of cardiovascular disease in cats. A chronic cough is more likely to indicate bronchitis or feline asthma. As the left ventricle loses its function, cats may show signs of pulmonary edema and pleural effusion, though, and these cats may cough.

The appearance of a blood clot in an artery may be the first indication of cardiomyopathy of any type.

Diagnosis is by chest X-ray, electrocardiogram, ultrasound of the heart, and thyroid function tests. Echocardiograms, especially with Doppler technology, are excellent diagnostic tools.

Hypertrophic cardiomyopathy tends to affect cats 1 to 5 years of age. It has been detected in kittens as young as 3 months, however, and in cats as old as 10 years. Maine Coon Cats, Ragdolls, British Shorthairs, American Shorthairs, and Devon Rexes show a familial inheritance.

Treatment: Cats with hypertrophic cardiomyopathy require drugs that relax the heart and increase its efficiency. Most of the drugs used to treat heart disease in people are used for similar purposes in small animals. The specific drug chosen depends on the stage of illness and presence or absence of complicating factors, such as arrhythmia. Drug choices include diuretics, calcium channel blockers, beta blockers, and ACE inhibitors. Most of these medications are not approved for cats and should only be used directly under your veterinarian's guidance.

Aspirin may be used to try to prevent clot formation, and low-salt diets such as Hill's Prescription Diet Feline h/d or Purina's CV Cardiovascular for cats, are recommended. Cats metabolize aspirin very slowly and the dose and frequency must be prescribed by your veterinarian.

Restricting the cat's activity reduces the strain on the heart. Your veterinarian may prescribe a period of cage rest.

Dilated Cardiomyopathy

Dilated cardiomyopathy occurs when the heart muscle loses its tone and becomes flaccid. The heart chambers overfill, the walls of the ventricles become thinner, and the chambers enlarge. One cause of dilated cardiomyopathy is taurine deficiency. Taurine is an essential amino acid present in high concentrations in animal tissue. Feeding dog food or a grain-based cat food could lead to taurine deficiency. Most commercial cat foods are currently supplemented with taurine. Dog foods are not, so a cat eating dog food has a high risk of developing dilated cardiomyopathy.

Another cause of dilated cardiomyopathy is myocarditis, which is inflammation of the heart muscle. Viruses and autoimmune diseases have been implicated as the cause of myocarditis in humans, although its cause is unknown in cats.

Dilated cardiomyopathy is often a rapid-onset disease that progresses over two or three days as the heart begins to fail. The most frequent sign is labored breathing at rest. The cat often sits with his head and neck extended and elbows out, straining to take in air. Cool feet and ears and a body temperature below normal are signs of poor circulation. Heart murmurs are common. The pulse is often rapid and thready and may be irregular or even slow. Loss of appetite, rapid weight loss, weakness, fainting attacks, and crying out spells often accompany the signs. A clot blocking the vascular pathway to the rear legs may be the first sign. Echocardiography is the best method for diagnosing dilated cardiomyopathy.

Treatment: Treatment of dilated cardiomyopathy is directed at correcting any taurine deficiency and controlling fluid retention. Fluid retention is best managed using diuretics such as furosemide (Lasix). Cats with taurine deficiency cardiomyopathy who survive the first week of supplementation have an increased chance for survival, but it can take four to six months for the heart muscle to heal.

This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.