Literally, the term "cardiomyopathy" means disease of the heart muscle. More specifically, cardiomyopathy (CM) is a disease of the heart muscle in which either the heart walls thicken greatly (hypertrophic and restrictive forms) or stretch greatly (dilated form).
There have been several causes of CM identified. A deficiency of taurine, an essential amino acid, will cause dilated CM. Taurine was deficient in many commercial cat foods until its deficiency was identified; however, cat foods are now properly supplemented. Hyperthyroidism, a non-cancerous growth of the thyroid gland, can cause a variation of the hypertrophic form. The restrictive form is associated with an unidentified inflammatory process within the heart muscle. However, many cases of CM are not caused by any of these processes, and we do not understand their origin.
Cardiomyopathy is a disease that usually takes several weeks to months to progress to a serious stage. During the early weeks of the disease, the cat will probably look normal. Cats have the ability to hide serious illness until it reaches a crisis stage. Therefore, most cats that develop clinical signs of cardiomyopathy will appear to have been ill for only a few days. A few days of inactivity and poor appetite occur first. Just prior to the state of heart failure and death, the cat may become very inactive and exhibit labored breathing. Both may be due to insufficient oxygen transport to the body's tissues; the latter may also be due to a collection of fluid in or around the lungs.
Diagnosis is generally made with a chest radiograph (x-ray). The heart will have an abnormal shape and fluid may be detected in or around the lungs. If a large amount of fluid is present around the lungs, it may be necessary to remove it and take more radiographs because the presence of this fluid interferes with evaluation of the heart. Many cases also require better visualization of the heart with an echocardiogram, or sonogram. This is a non-invasive method of looking at the heart while it is pumping. Sound waves are used to make this dynamic study of the heart. Radiographs can tell us about the size and shape of the heart but nothing about heart function. Ultrasound can provide this information. Ultrasound will also allow measurement of the heart muscle to determine if it is too thick (hypertrophic or restrictive CM) or too thin (dilated CM). Finally, an electrocardiogram (EKG) is useful to evaluate the rhythm of the heart.
Determination of the level of thyroid hormone (T4) in the blood is often indicated in evaluating cats with hypertrophic CM. This simple blood test can help identify an overactive thyroid gland as the underlying cause of the heart disease.
Treatment is based on the type of CM present. Different drugs are used for the different forms. Therefore, if at all possible, tests necessary to define the specific forms are performed before treatment begins. Fortunately, most of these cats can be stabilized with the correct drug; however, continual medication may be necessary since the disease cannot be cured. The exception to this is the cat with hyperthyroidism that is causing CM. This form of CM is potentially reversible if the cat receives appropriate and timely treatment for the thyroid disease.
Most of the cats with cardiomyopathy develop signs of heart failure as previously described. However, cats with CM are prone to producing blood clots within their hearts. When these clots escape the heart, they travel through various arteries leading from the heart. They eventually lodge in a narrow part of the artery. The most common site for clots to lodge is the point at which the aorta splits before going into the rear legs. Thus, these cats often become paralyzed very suddenly and are in significant pain. In many cases, it is paralysis and pain that first becomes noticeable and is the reason that medical treatment is sought. This may be mistaken for an uncomplicated lameness or even a broken leg. Within a few minutes to hours, there are no pulses in one or both rear legs, the legs are cold, and the footpads appear blue due to the lack of oxygen.
Treatment of the paralyzed cat concentrates on drugs to relieve pain and to hasten the return of circulation to the legs. Since these cats also have severe heart disease, they make poor surgical candidates. Therefore, surgery to remove the clot is not advisable due to the high incidence of death during surgery.
The prognosis for CM is variable depending on the form of the disease and the severity at the time of diagnosis.
Many cats will live up to three years if properly medicated. If clinical heart disease is already present when cardiomyopathy is detected the survival rate averages three months to three years. If the disease is detected in its asymptomatic state however, your cat may live a long life with close monitoring of the condition by your veterinarian or a veterinary cardiologist. The survival rate averages about 6 months. The exception is when CM is caused by hyperthyroidism. If hyperthyroidism is successfully treated, the heart function will generally return to normal and the cat will no longer require treatment.
NB: I treat many cats and dogs with cardiomyopathy. Both before and after symptom develop. In my experience, pets with this disease often respond well to an integrative treatment program.--Dr. Jeff
Please note: The information provided here is intended to supplement the recommendations of your veterinarian. Do not disregard veterinary advice or delay treatment based on information on this site. Nothing can replace a complete history and physical examination performed by your veterinarian. -Dr. Jeff
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