Hypertrophic cardiomyopathy is a life-threatening disease of cats. The disease most often occurs in cats between the age of 6-9 years. The cause of the disease is unknown; however a genetic basis for the disease is possible. Hypertrophic cardiomyopathy is diagnosed more frequently in male than in female cats. Persian cats appear to be particularly predisposed.

Feline Hypertrophic Cardiomyopathy

Cats with HCM have an enlarged left ventricular wall as well as an enlarged interventricular septa. Due to these enlarged structures, the cavity of the left ventricle is reduced in size. During the filling phase of the heartbeat, the left ventricle does not fill sufficiently. There is a reduced amount of blood in the left ventricle of a cat with hypertrophic cardiomyopathy than in a normal cat's left ventricle.

Normal Cat's Heart

Cat with HCM

Blood from the left ventricle is pumped out the aorta, into the general circulation. Since there is less blood volume in the left ventricle (due to HCM), the heart compensates by pumping harder and faster. This change in heart rate and ejection pressure accounts for many of the symptoms associated with HCM.

Clinical signs

Early signs of HCM may go unnoticed. Sometimes the only noticeable change is a reduction in the cat's normal activity level. Owners often attribute this to laziness, boredom, or age.

As symptoms progress, the cat becomes more depressed and inactive. He (she) is reluctant to move about and does not eat or drink. The slightest activity is often followed by open-mouth and rapid breathing. This abnormal breathing is due to pulmonary edema. Very often, many cats appear normal until they undergo a stressful event.

Thromboemboli of the aorta is a common problem associated with HCM in cats. The blood clot that forms (thrombus) in the posterior aorta blocks the blood supply to the rear legs. Most of these cats are paralyzed and in extreme pain.

Cats showing symptoms of HCM should be examined by a veterinarian. Immediate hospitalization with x-rays, blood tests, and an ECG is usually required. Cardiac ultrasound is often necessary to differentiate feline hypertrophic cardiomyopathy from other forms of feline cardiomyopathy.