Though there are many different conditions that can cause heart disease in cats, cardiomyopathies are among commonly diagnosed heart disease. There are several different types of feline cardiomyopathy. Each has different causes and different treatment methods may be required for each as well.
Hypertrophic Cardiomyopathy (HCM) in Cats
Hypertrophic cardiomyopathy, also known as simply HCM, is by far the most commonly seen form of cardiomyopathy. The exact cause of hypertrophic cardiomyopathy is often unknown but it does appear to be an inherited disorder in some feline breeds, including Maine Coons, American short hairs, British short hairs and Persians.
In feline hypertrophic cardiomyopathy, the muscle of the ventricle of heart is thickened and usually the left ventricle is involved. The thickening of the heart muscle results in abnormalities in the ability of the heart to pump the blood properly. These abnormalities lead to heart failure when they become severe enough that the heart is unable to compensate for the abnormalities.
Hypertrophy (thickening) of the heart muscle may also occur as a result of other influences on the heart. The most common causes of this form of thickening are high blood pressure, hyperthyroidism (a metabolic disease that results in increased thyroid hormones circulating in the blood), aortic stenosis (an occlusion in the large vessel that leaves the heart) and acromegaly (a metabolic disorder that results in increased levels of growth hormones in the blood.)
Many veterinary cardiologists feel that thickening of the ventricles of the heart resulting from these secondary influences should not be termed hypertrophic cardiomyopathy. However, the resulting symptoms are often very similar to those seen with HCM.
Treatment of hypertrophic cardiomyopathy in cats involves a variety of different types of medications designed to make it easier for the heart to achieve its pumping function and also to remove excess fluid from the lungs and other body tissues. In addition, medications that reduce the likelihood of clot formation are indicated as part of the treatment regimen.
Feline Dilated Cardiomyopathy
Dilated cardiomyopathy was once a relatively common heart disease in cats. It was related to commercial cat food diets that were deficient in taurine. Once this discovery was made, most cat food manufacturers added adequate amounts of taurine to their feline diets. As a result, dilated cardiomyopathy is currently not seen all that often. However, it is still occasionally diagnosed in cats that are being fed homemade diets which are improperly balanced and do not contain enough taurine.
Unlike hypertrophic cardiomyopathies where the muscle ventricle of the heart is thickened but the chamber size is normal or decreased in size, dilated cardiomyopathy results in heart chambers that are dilated in size.
Cats with dilated cardiomyopathy that is due to taurine deficiency generally respond well to supplementation with taurine. Other drugs which may used to treat dilated cardiomyopathy are similar to those used in hypertrophic cardiomyopathy.
Restrictive Feline Cardiomyopathy
In restrictive cardiomyopathy, the heart muscle in the ventricle of the cat contains a large amount of fibrosis (an extreme amount of fibrous tissue). This results in the ventricles being stiffer than normal, making it more difficult for them to contract normally. This leads to a failure of the heart's ability to pump blood effectively.
Symptoms of restrictive cardiomyopathy in cats are similar to those seen with other cardiomyopathies. Treatment options are also similar.
Arrhythmogenic Right Ventricular Cardiomyopathy in Cats
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of cardiomyopathy that affects the right side of the heart. Symptoms are those of right-sided heart failure, including ascites (fluid in the abdominal cavity) and swelling in the legs. An arrhythmia (abnormal heart rate or rhythm) may also be present. As with all forms of cardiomyopathy, thromboembolism (a blood clot that breaks loose and lodges in a blood vessel) is also possible.
There are also a number of unclassified feline cardiomyopathies that do not seem to fit well into any category. These cardiomyopathies are still not understood very well.