Cats may develop any of several types of heart disease. The most common feline heart disease is Hypertrophic Cardiomyopathy (HCM). The term "hypertrophic cardiomyopathy" means "a thickening disease of the heart muscle." When HCM develops, the heart muscle becomes hypertrophied (i.e., enlarged, thickened, and stiff). The end result of this change in the heart muscle is a decrease in size of the interior of the main pumping chambers of the heart and a stiffening of the heart muscle, which decreases the heart's ability to stretch when filling with blood. These two main consequences of heart muscle thickening mean that the heart is unable to adequately fill with blood between heartbeats and, therefore, pumps less than normal amounts of blood with each beat. This impairment of the heart's blood pumping ability (along with some other adverse effects of HCM) often leads to heart failure.
The cause of HCM in cats is not known, although in some cases it might be inherited. All breeds of cats can be affected and males are more commonly affected than females. Although HCM has been reported in cats from ages 6 months to 16 years, the average age of feline HCM patients is 5 to 7 years. Symptoms of HCM may be absent or may consist of loss of appetite, labored breathing, weakness with exercise, fainting episodes, coughing, or sudden death with or without any preceding symptoms. In addition to heart failure, cats with HCM are also at risk of forming abnormal blood clots (called thromboembolisms). Most commonly, such cats develop these thromboembolisms in the hind limbs, which will be evident as varying degrees of pain, stiffness, paralysis, or coldness in one or both hind limbs.
In a cat with no symptoms, the veterinarian may become suspicious of HCM if listening to the heart with a stethoscope reveals a heart murmur (which is an abnormal heart sound) or an abnormal heart rhythm. Because these findings, as well as the above-mentioned symptoms of HCM, can also be caused by other diseases, and because many cats with HCM have normal heart sounds and rhythms, the diagnosis of HCM is based on the results of a diagnostic heart work-up. A diagnostic heart work-up can include blood and urine tests, a blood pressure measurement, X-rays, an electrocardiogram (EKG), and an ultrasound examination of the heart.
Treatment of HCM is aimed at decreasing the work demands of the heart, decreasing the heart rate (which gives the heart more time to fill with blood between beats), decreasing the build-up of fluid in the lungs from heart failure, keeping blood pressure normal, controlling any abnormal heart rhythms that may develop, and preventing the formation of thromboembolisms. Medications are presently the mainstay of HCM treatment and are usually given for life.
In many cases of feline HCM, the disease eventually progresses to the end-stage of heart failure. Cats affected with HCM usually have a shorter lifespan than healthy cats. Cats with symptoms of HCM will often have their symptoms alleviated by treatment and may feel much better. HCM-affected cats without symptoms may have a delay in the onset of symptoms if treated early. Some evidence exists to show that early treatment in some cats may even reverse the heart muscle thickening (as seen with ultrasound) to a certain degree. Cats undergoing treatment for HCM should be monitored periodically with follow-up testing in order to identify and treat any complications of HCM that may develop. With treatment, an HCM-affected cat may have an improved quality of life, a longer lifespan than otherwise expected, and may do well for months or even years.