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Hypertrophic Cardiomyopathy (HCM)  

(This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian.)


Anatomy of the heart of a cat:
HCM is a disease that causes thickening of the heart muscle resulting in poor relaxing and filling ability. As the heartís pumping chamber (ventricle) becomes progressively thicker, less blood can enter the chamber; thus, less blood is ejected out to the body. The cause of HCM is unknown, although certain breeds of cats (Maine Coon and Ragdoll) appear to be predisposed. Middle-aged male cats may be more commonly affected. Sometimes heart muscle thickening similar to HCM can develop secondary to other disorders such as hyperthyroidism (elevated thyroid hormone) and systemic hypertension (elevated blood pressure). Blood pressure measurement and, in cats over five years of age, a blood thyroid hormone test should be done to exclude these secondary causes when cardiac hypertrophy (thickening) is diagnosed.

Some pets show no sign of illness, especially early in the disease. In other cases, signs of left-sided congestive heart failure (fluid accumulation in the lung) may occur. These signs include lethargy, decreased activity level, rapid and/or labored breathing and possibly open mouth breathing with excitement or exercise. Sometimes left and right-sided congestive heart failure develop with fluid accumulation inside the chest or abdominal cavity causing greater respiratory (breathing) effort and abdominal distention. Once fluid accumulations have occurred, clinical heart failure is present and aggressive medical therapy should be sought. Other signs of this disease can include sudden weakness, collapsing episodes, and unfortunately even sudden death due to disturbances in heart rhythm. In some cats with a very large heart chamber (i.e. left atrium) a blood clot may form and if it enters the circulation may cause weakness or paralysis (usually of the rear legs). If this occurs, contact your veterinarian right away to determine if complications related to heart disease (or another disease) are present.

A physical examination performed by your veterinarian may reveal a heart murmur, abnormal heart sounds, abnormal lung sounds, or irregularities in heart rhythm. Chest radiographs (x-rays), an electrocardiogram (ECG..sometimes called an EKG), and an echocardiogram (heart ultrasound) are tests often utilized to confirm a suspected diagnosis and to determine severity. A routine physical exam and one or more of these tests may be recommended every six months to one year to look for any progression of disease in cats without clinical signs.

Asymptomatic pets may not need medical therapy depending on the findings of the tests listed above, but routine reevaluations will often be recommended. Other cats will need medications to slow the heart rate, and promote relaxation of the pumping chambers (ventricles). If arrhythmias or congestive heart failure signs are present, additional medications used may be required. Since this disease can be progressive, the number and the amount of medications used may change with time. Therapy is always tailored to the needs of the individual patient. If congestive heart failure is present, dietary salt reduction is also recommended.

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