Feline Cardiomyopathy
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©1996, 1997 HomeVet
What
Is Cardiomyopathy?
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). In either
form, the heart's function is greatly compromised leading
to an eventual state of heart failure.
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What
Causes Cardiomyopathy?
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.
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What
Does a Cat With Cardiomyopathy Look Like?
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.
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How
Is This Disease Diagnosed?
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.
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What
Is Involved With Treatment?
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.
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Are
There Complications That May Occur?
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.
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What
is the Prognosis for Cats With Cardiomyopathy?
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.
Please note:
The information provided here is meant to supplement
that provided by your veterinarian. Nothing can replace
a complete history and physical examination performed
by your veterinarian. - Dr. Jeff
I greatly value your feedback. Please let me know what
you think of this site and what you would like to see
on it. drjeff@homevet.com
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Last modified
at 4:41 PM on 12/31/98.
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