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Feline Hypertrophic Cardiomyopathy

Randy Walker DVM

About Feline Hypertrophic Cardiomyopathy...

Feline Hypertrophic Cardiomyopathy is a severe heart disease of cats which is being seen more and more frequently. Broken down into their root meanings these words describe the disease. "Feline" means "pertaining to cats". "Hyper" means "exaggerated" or "greater than normal". "Trophic" means "form" or "body''. "Cardio" means "pertaining to the heart." "Myo" means ''muscle" and "Pathy" means "disease of". So, when broken down into their root meanings, the words "Feline Hypertrophic Cardiomyopathy" describe "a condition of cats in which the heart becomes diseased due to an abnormal enlargement of the heart muscle".

Briefly, Describe The Normal Cat's Heart And The Differences In The Heart Of The Cat With Hypertrophic Cardiomyopathy.

The normal cat's heart is a four chambered muscular pump designed to propel blood to the lungs to gain oxygen and to send that oxygenated blood out to the various body tissues. Under normal circumstances the heart wall has a certain thickness which in turn causes the chambers within these wall to have a certain volume. In the hypertrophic heart the heart muscle itself increases in thickness (size) which in turn causes the chambers within the heart to become smaller. Since the chambers are now smaller, they will fill with less blood than normal and consequently the heart will become a much bless efficient pump. Less blood is pumped with each beat and this leads to serious health problems.

What Are The Typical Clinical Symptoms Of Feline Hypertrophic Cardiomyopathy?

The symptoms of hypertrophic cardiomyopathy will vary from cat to cat with no two cases being the same. Often the symptoms can be very subtle in the early stages. Common symptoms of Feline Hypertrophic Cardiomyopathy are lethargy (just lays around), tiring easily, thinness, rapid heart rate, "gallop" heart rhythm, often lack of appetite, sometimes a persistent cough, and sometimes trouble breathing. In those cases where the hypertrophic cardiomyopathy is secondary to hyperthyroidism (discussed below) the patient will often have enlarged thyroid glands and, rather than the signs listed

above, may actually have abnormally increased energy and appetite due to the stimulation by the thyroid hormone. Due to the variable clinical signs, hypertrophic cardiomyopathy cannot be accurately diagnosed on the basis of the history and physical exam alone and must always be ruled-in or ruled-out with diagnostic tests.

How Is Hypertrophic Cardiomyopathy Diagnosed?

Hypertrophic cardiomyopathy is diagnosed on the basis of history, physical exam, and appropriate diagnostic tests. Common diagnostic tests used to detect cardiomyopathy are (1) echocardiogram (ultrasound of the heart), (2) radiographs and (3) thyroid hormone assay among others.

Exactly What Is An Echocardiogram And How Important Is It In Diagnosing Cardiomyopathy?

Echocardiogram is the term for an ultrasound examination of the heart. Only through an echocardiogram are we able to accurately measure the width of the heart walls, the size of the heart chambers, the contractility and efficiency of the heart, the function of the heart valves and other important information. Only by accurately determining which areas of the heart are affected and how severely can we formulate a rational approach to the treatment of this disease.

What Is The Connection Between Feline Hypertrophic Cardiomyopathy And Hyperthyroidism?

About half (50%) of the cases of Hypertrophic cardiomyopathy are secondary to hyperthyroidism (excess of thyroid hormone in the bloodstream). The other half of the cases are of unknown origin. Hyperthyroidism leads to hypertrophic cardiomyopathy due to the prolonged, continuous stimulation of the heart muscle by the thyroid hormone.

Which Individuals Are Most At Risk From Hypertrophic Cardiomyopathy?

Cardiomyopathy can potentially affect any cat at any age but the most commonly affected cats are middle-aged. Cardiomyopathy is slightly more common in males than females.

What Causes Feline Hypertrophic Cardiomyopathy?

As stated above, about half (50%) of cases of cardiomyopathy are secondary to hyperthyroidism. The cause for the remaining cases is usually unknown although the tendency for this disease to develop is thought to be inherited in many cases. Unlike Feline Dilated cardiomyopathy (an entirely different disease), feline hypertrophic cardiomyopathy has not been shown to have a nutritional basis.

How Is Feline Hypertrophic Cardiomyopathy Treated?

This depends to a large extent on whether or not the patient also has hyperthyroidism. If the patient has hyperthyroidism as the underlying cause of the cardiomyopathy then the hyperthyroidism is treated as the primary problem and many of these hearts will improve and even return to normal secondary to controlling the hyperthyroidism. These cases may require heart medications for only a brief period of time or sometimes not at all. For those cases of hypertrophic cardiomyopathy that are not secondary to hyperthyroidism the patient is given various cardiac and blood pressure medications to help the heart work more efficiently.

What Is The Prognosis For Feline Hypertrophic Cardiomyopathy?

Here again, the prognosis will vary depending on many factors, the main ones being whether or not the heart condition is caused by hyperthyroidism and also the patient's age, general physical condition, and the length of time the condition has been allowed to continue before being diagnosed and treated. In cases where the cardiomyopathy is secondary to hyperthyroidism the prognosis is often quite good as long as the hyperthyroidism is kept under control. In cases where hyperthyroidism is not a factor many patients will respond to various cardiac and blood pressure medications and often can be maintained on these long term. It should be noted, however, that there is no cure for primary hypertrophic cardiomyopathy.

- Randy Walker DVM
Sun Lakes Animal Clinic
May 15,2004

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