General Information
Hypertrophic cardiomyopathy (HCM) is an inherited disorder of cats that manifests as thickening of the ventricles (lower chambers of heart), primarily on the left side, such that the heart muscle has a decreased ability to relax and fill normally with blood. Breeds such as the Maine Coone and Ragdoll have been found to be predisposed.
Diagnosis
Cats with heart disease may be identified based on physical exam findings, such as a heart murmur or arrhythmia (abnormal heart rhythm). However, in some cases, there are no abnormalities on physical exam. The best way to diagnose heart disease is by referral to a cardiologist for an echocardiogram (ultrasound of the heart), which evaluates for specific heart chamber enlargement, to evaluate heart function, and to evaluate for other complications or sequelae of heart disease. Other diagnostics, such as a blood pressure or blood work may be recommended to further evaluate for other concurrent diseases or factors which may complicate management of heart disease.
Complications and Sequelae
The progression of HCM is variable in each cat and should be monitored on a regular basis. Over time, signs of heart failure may develop, which include an increased respiratory rate and effort (heart failure), loss of appetite, lethargy, weakness, exercise intolerance, and collapse. In addition, cats with heart disease and severe enlargement of the atria (top chambers of the heart) may be more prone to forming clots in the heart, and throwing clots to various parts of the body, which results in paralysis or lameness of the hindlimbs or right front limb, acute kidney failure, sudden difficulty breathing, or sudden death. Arrhythmias (abnormal heart rhythms) may also be present, and increase the risk for sudden death.
Systolic anterior motion of the mitral valve (SAM) is an abnormal movement of the mitral valve, which separates the left atrium from the left ventricle. Normally when the heart contracts, this valve is closed, preventing backflow of blood from the ventricle to the atrium. With SAM, one of the mitral valve leaflets actually swings in the opposite direction, and obstructs the outflow of blood from the left ventricle to the body.
Diseases which cause high blood pressure, such as hyperthyroidism and kidney disease, can be complicating factors in the management of heart disease, and should be monitored and treated as needed.
Treatment
In the asymptomatic stages of HCM, treatment may or may not be indicated, depending on the echocardiographic findings. Medications, such as beta blockers or calcium channel blockers may be used to help improve relaxation of the heart muscle, or to slow the heart rate in an attempt to reduce SAM. In addition, if significant enlargement of one or both atria is present, anti-platelet medications are recommended to reduce the risk of blood clot formation. Diet changes and exercise restrictions are often not indicated, other than high sodium diets and treats are discouraged.
Prognosis
HCM is often a progressive disease. With careful monitoring, appropriate medical therapy can be implemented earlier in hopes of prevent rapid decline into severe heart failure. This way, we can hopefully limit visit to the hospital or emergency room, and keep your pet feeling as good as possible for as long as possible.
If your pet begins to show any signs of breathing difficulty, loss of appetite, sudden lameness or paralysis, exercise intolerance, or collapse, he or she should be evaluated sooner. Please call us if any of the above clinical signs become apparent.
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