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HCM is an evilly unpredictable disease. The many faces of HCM, plus the fact that cats are notorious for hiding any evidence they have disease, can end up being lethal. It is not unusual for there to be no clues to the presence of HCM until it's too late for even heroic treatment to be of much help. However, sometimes there are signs that all is not well before the disease has progressed too far, but even then it is impossible to predict its course with any certainty.

Some cats may develop only mild hypertrophy and suffer little compromise of heart function, while others progress to more severe disease. HCM may worsen quickly over a period of months; it may progress slowly over several years; its severity may not change for some years and then suddenly worsen or it may not. Some cats with HCM may die suddenly (presumably from an abnormal heart rhythm) even though they seemed healthy only moments before.

Prognosis generally depends on the severity of the disease. A cat with mild to moderate disease may enjoy an essentially normal life for a number of years (although a few will die suddenly). Cats with severe disease can sometimes go without problems for a surprisingly long time but most get into trouble within months to a year or two. The long-term outlook is more guarded if the cat has more than a mildly enlarged left atrium (a sign of severe disease) since they can develop a blood clot and may be headed toward heart failure.

Heart failure (fluid accumulation in and/or around the lungs) is a poor prognostic sign. Mild to moderate heart failure can be readily managed for a short while but often it becomes refractory to drug therapy in a short time, usually months. Severe heart failure is often difficult to manage and often becomes even more difficult to manage over time as the disease progresses. The prognosis for a cat with moderate to severe heart failure, unfortunately, is guarded to poor. Survival, on average, is only a few months.

A veterinarian may prescribe one or more medications to manage a cat's condition. Treatment will vary depending on the cat's clinical signs and how HCM has affected the heart. One should be aware that HCM cannot be cured and no medication has been proven to alter the natural history of the disease prior to the onset of heart failure. However, once a cat is in heart failure medication will help a cat with HCM live longer and more comfortably. The veterinarian will want to reexamine the cat periodically to see if there is any change in its condition and to evaluate whether or not any changes in treatment are needed.

Thromboembolism (a blood clot) often has a very poor prognosis. It initially causes acute and severe pain and severe clinical signs. Pain management is mandatory during the first hours after the onset of clinical signs. Thankfully the sensory nerves stop functioning over time and so the pain subsides. Many cats are put to sleep during this phase of the disease. Although definitive therapy (i.e., treatment to break down or remove the clot) is potentially available, the high recurrence rate of thromboembolism dissuades most veterinarians from attempting this type of therapy. A significant percentage of cats will break the clot down by themselves and regain limb function over time. Consequently, it is never wrong to watch and support a cat with thromboembolism for two to three days to see if this will happen. However, a cat that has survived a thromboembolism has a significant risk of developing another over the following weeks to months; efforts to prevent their recurrence may not succeed. In addition, many of these cats have severe underlying heart disease that limits therapeutic options and shortens survival time.

Your veterinarian can explain the specifics of your cat's condition, the possible treatment options, and their potential outcomes. Don't feel hesitant to ask your veterinarian any questions you might have about your cat's illness. He or she wants to help your cat as much as you do.


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The purpose of this web site is to describe feline HCM.
It is not intended to be a diagnostic or prognostic tool or to provide medical or treatment advice.
If your pet is ill, please have it examined by your veterinarian.

Copyright © 1997-2009 Mark D. Kittleson, DVM, PhD, Diplomate ACVIM (Cardiology);
Jody A. Chinitz; and Marcia J. Munro.
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