Hypertrophic cardiomyopathy, also called HCM, is the most common heart disease diagnosed in cats. It is most commonly seen in middle-aged to older cats but can affect cats of any age.
Primary Causes of Hypertrophic Cardiomyopathy in Cats
Cardiomyopathy literally means disease of the heart muscle. The term hypertrophic refers to an enlargement. Hypertrophic cardiomyopathy refers to a disease which causes an enlargement of the muscle in the heart.
In cats which develop hypertrophic cardiomyopathy, the muscle of the ventricle of the heart becomes thickened. In most cases, the left ventricle is affected to a greater extent than the right ventricle.
In hypertrophic cardiomyopathy, even though the muscle of the heart is thickened, the chamber inside of the ventricle remains the normal size or sometimes even smaller than normal. This differs from dilated cardiomyopathy where the size of the ventricular chambers is actually larger than normal and referred to as dilated.
The exact cause of hypertrophic cardiomyopathy is unknown in many cases.
There are some breeds in which the disease is inherited and can be passed from the parents to the kittens. These breeds include the Maine Coon, the American Shorthair, the Brishish Shorthair, the Ragdoll and the Persian. There are DNA tests that help identify at least some of the gene mutations which have been found to contribute to the development of HCM in cats. However, the individual tests vary from breed to breed.
Purebred cats are not alone in developing hypertrophic cardiomyopathy though. HCM can affect mixed breed cats also. There are likely other factors that cause the development of hypertrophic cardiomyopathy that remain unknown at the current time.
Secondary Causes of "Hypertrophic" Cardiomyopathy in Cats
A thickening of the heart muscle very similar to that which occurs in hypertrophic cardiomyopathy may occur secondary to other diseases as well.
- Hyperthyroidism is a disorder which causes elevated levels of thyroid hormones in the blood stream. These high levels of thyroid hormone can act on the heart to cause cardiomyopathy.
- Hypertension, or high blood pressure, causes the heart muscle to thicken over time because of the heart must work harder to move the blood through the blood stream.
- Aortic stenosis is a structural abnormality of the cardiovascular system. The aorta is the large vessel that is responsible for moving the blood from the heart to the rest of the body. In cases of aortic stenosis, the aorta becomes narrowed and/or partially blocked near where the vessel leaves the heart. The blockage makes it harder for the heart to move blood through the aorta, causing the heart muscle to thicken as a result.
- Acromegaly is a condition in which abnormally high levels of growth hormone circulate through the blood stream. These hormones act on the heart to cause the heart muscle to thicken.
Some veterinary cardiologists prefer not to refer to these secondary cases of cardiomyopathy as hypertrophic cardiomyopathy. However, regardless of the terminology, the symptoms are similar.