The feline heart, like the human heart, is a hollow, muscular organ located in the center of the chest. Both the right and left sides of the organ have an upper chamber (atrium), which collects circulating blood, and a lower chamber (ventricle), which pumps blood from the heart.
Cardiomyopathy, which literally means “disease of the heart muscle,” is brought about by a structural abnormality in the tissue enclosing one or more of these chambers. In general, says Marc Kraus, DVM, a senior lecturer in cardiology at Cornell University’s College of Veterinary Medicine, the heart muscle either grows too thick to function properly or it stretches and becomes too thin. In either case, the abnormality sets the organ’s blood-collecting and blood-pumping mechanics awry, a dysfunction that often leads to congestive heart failure with respiratory distress, paralysis-causing blood clots, and, in some cases, sudden death.
Most feline cardiomyopathies are primary diseases—those whose origins are either genetic or unknown. Some, however, are secondary diseases—those whose causes are specifically identifiable, such as hyperthyroidism or high blood pressure.
Three types of the disorder account for nearly all cardiomyopathies. The most common type by far is hypertrophic cardiomyopathy. Developing with no feasible explanation other than the strong likelihood of hereditary influence, this condition—which occurs most often in male cats—is characterized by a thickening of the muscle tissue associated with the left ventricle. This thickening results in poor heart function and, sometimes, obstruction of blood flow from the heart. It also causes the upper heart chambers to become enlarged. The consequence of these combined factors is a condition in which the heart fails to relax fully and fills with circulating blood. This can result in increased fluid pressure in the lungs and shortness of breath. In addition, blood clots may develop in the left atrium. If a clot breaks up, small pieces of it may circulate and eventually lodge in an artery leading to the legs. This may cause the sudden onset of lameness or paralysis, often accompanied by severe pain.
The second most common type, Dr. Kraus points out, is restrictive cardiomyopathy. This condition is caused by the excessive buildup of scar tissue on the inner lining and muscle of the ventricle, which prevents the organ from relaxing completely, filling adequately, and emptying with each heartbeat.
The third type—dilated cardiomyopathy—is relatively rare, says Dr. Kraus. The condition is chiefly characterized by a poorly contracting dilated left ventricle. The heart walls are thin and flaccid, which results in a decreased forward flow of blood from the heart and, consequently, heart failure. The condition is rare these days, notes Dr. Kraus, due to the fact that cat food manufacturers have, for the past three decades or so, been routinely adding an important amino acid called taurine to their products. Prior to that, a lack of taurine in cat food had been closely linked to the incidence of dilated cardiomyopathy.
Male and female cats of any age—even kittens—are susceptible to one form or another of cardiomyopathy, says Dr. Kraus, although most patients are middle-aged males. And among all feline breeds, he adds, Maine Coons and Ragdolls seem to be at elevated risk. The most common clinical signs include rapid breathing, lethargy, and diminished appetite. If the condition progresses and the heart’s blood-collecting and blood-pumping mechanisms continue to fail, congestive heart failure ensues, which can lead to severe respiratory distress, paralysis-causing blood clots, and eventual death. Owners should know that a cat that is struggling to take in air or has trouble moving its rear legs may be experiencing advanced cardiomyopathy and must receive veterinary help immediately.
The initial objective in diagnosing cardiomyopathy is to exclude other heart conditions that could have similar signs. In most cases, radiographs will be taken. Sometimes an electrocardiogram will be required. The definitive diagnosis, however, will be obtained via an echocardiogram (an ultrasound of the heart), which Dr. Kraus refers to as “the gold standard” for diagnosing this condition. Treatment with certain medications may be initiated. For example, beta-blockers may help the heart muscle relax by slowing the patient’s heart rate, thereby decreasing its need for oxygen. With appropriate care, a cat diagnosed with cardiomyopathy may survive for several years. “But once heart failure occurs,” says Dr. Kraus, “a cat may be able to stay alive for up to a year or so. But some will succumb before that.”