A mammal’s heart is composed of four chambers. There are left and right atria and ventricles. These chambers act as 2 different pumps. The left side pumps oxygenated blood to the body and the right side pumps blood through the lungs so it can become oxygenated. The path blood travels through the body is from the lungs to the left atrium through the mitral valve and into the left ventricle. It is then pumped out through the aorta to the body. Blood depleted of oxygen returns to the right atrium via the vena cava. It goes through the tricuspid valve into the right ventricle where it is pumped out to the lungs to begin the cycle again.
Hypertrophic cardiomyopathy (HCM) is a heart condition characterized by a thickening of the muscle comprising the left ventricle of the heart. This decreases the size of the left ventricular chamber and means the heart has to pump more times per minute to pump a normal volume of blood through the body. This problem develops most commonly in cats. Most cats are diagnosed on physical examination when a heart murmur or abnormal heart rhythm is noted. Some cats go into heart failure when the lungs start to accumulate fluid (edema) and they can develop severe and life threatening breathing problems. The edema develops from blood backing up into the lungs causing fluid leakage out of the blood vessels.
Occasionally, cats may see their veterinarian after developing sudden paralysis. This occurs due to abnormal blood flow through the heart which predisposes them to abnormal clot formation. These clots will start in the heart, travel down the aorta and become lodged at the point where the aorta splits to supply blood to the hind legs (aortic thromboembolism). This obstructs blood supply to the hind legs and results in paralysis.
Evidence is mounting that the cause of HCM may be genetic in origin however, the exact mechanism is unknown at this time. One disease that may be associated with the development of HCM in cats is hyperthyroidism. In some cases, treatment of the hyperthyroidism may correct the heart problem but some cats may require heart medication for a period of time before and after treatment of the thyroid disease.
In addition to a physical exam and lab tests, radiographs of the chest are also used in the diagnosis of HCM. The radiographs may be normal or show enlargement of the left atrium. Some cats have a valentine shaped heart. The diagnostic test of choice is an echocardiogram (heart ultrasound) which determines the size and shape of the heart chamber. Since high blood pressure (hypertension) can also be seen with HCM, the blood pressure is often checked as well. All of these diagnostic tests help your doctor decide which means of therapy would be most beneficial to your cat.
Cats that have heart failure or paralysis are treated much differently than patients with no symptoms. HCM is life threatening and aggressive therapy is often required in cases of heart failure or paralysis. Treatment of cats with aortic thromboembolism is often supportive and aimed at helping the heart pump more effectively as well as managing the pain caused by the clot. With time, some cats will recover the ability to use their legs. This may take days to weeks however and prognosis is also dependent on the ability to manage their HCM. Some medications made specifically to destroy the clots have been used clinically and experimentally with mixed results. Unfortunately, despite treatment, clots often recur.
Cats with congestive heart failure are treated with a combination of medications and oxygen to decrease the congestion and to help the heart pump more effectively. The long-term prognosis is variable but with rapid and early intervention, cats with HCM are leading longer lives.
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