CARDIOMYOPATHY
What is cardiomyopathy?
Cardiomyopathy is a term used to describe diseases of the heart muscle. In
cats, three classes of cardiomyopathy have been described. In all cases, the
heart disease may result in clinical signs of heart failure. Cardiomyopathy
may be seen as a primary condition or secondary to other diseases.
What are the clinical signs seen with cardiomyopathy?
In the early stages of disease, the cat may be able to cope and hence show
no signs of disease. This situation is referred to as compensated heart disease.
Often the cats will alter their activity levels to those that they can cope
with which makes it difficult to diagnose cardiomyopathy until it is quite advanced.
The major long-term concerns with all types of cardiomyopathy are:-
1. Development of congestive heart failure: Breathlessness and lethargy
are the most frequently noticed signs of congestive heart failure and these
result from a failure of the heart to efficiently pump blood.
2. Thromboembolic disease: Altered flow of blood in enlarged heart
chambers predisposes to the formation of a blood clot within the chambers of
the heart. This becomes organized and is known as a thrombus. If parts of the
thrombus become dislodged they can travel in the bloodstream and become lodged
in smaller blood vessels. These particles are called emboli and the most common
place for them to lodge is at the bottom of the aorta which is the biggest artery
in the body. This results in obstruction of the blood supply to the back legs
which is usually very painful and the back legs become paralyzed and cold to
the touch. Although some cats may recover completely with appropriate treatment,
this is a potentially fatal complication of any cardiomyopathy. In some cats,
a partial recovery which may take a long time, is seen.
3. Hypertension: High blood pressure, or hypertension, is a possible
complication associated with hypertrophic cardiomyopathy in particular. This
may result in spontaneous bleeding, such as nosebleeds or hemorrhage within
the eye and may also cause retinal detachment and blindness. This may be noticed
as a sudden loss of vision and development of widely dilated pupils. This is
an emergency situation since the blindness will be permanent unless the retina
reattaches within a couple of days. Hypotensive drugs are those which lower
the blood pressure and these may be used to control cats with this problem.
Measuring blood pressure in cats is extremely difficult due to their small size
and the rise in blood pressure with stress which makes interpretation of results
problematic. For these reasons, hypertension may only be detected once a problem
has occurred. Examination of the eyes may give early indications of hypertension
since the blood vessels of the retina may show changes and small hemorrhages
may be noticed.
How is cardiomyopathy diagnosed?
Diagnosis of heart disease can be suspected on the basis of clinical signs,
such as those of congestive heart failure, in addition to more specific tests
such as chest x-rays. Electrocardiography (ECG/EKG) may also provide useful
information on heart conduction and size. Cardiac ultrasound scans, where available,
help to distinguish between the different types of cardiomyopathy.
In cases where hypertension is a possibility, blood pressure can be evaluated
if suitable equipment is available. Retinal examination may provide evidence
of hypertension where blood pressure measurements cannot be made.
Specific tests may be done in order to check that the cardiomyopathy is not
secondary to some other disease. (See below).
What causes cardiomyopathy?
There are many causes of cardiomyopathy, however, in older cats thyroid disease
(hyperthyroidism) commonly causes cardiomyopathy. Other causes include kidney
failure and a rare cause is dietary deficiency of taurine, an essential nutrient.
This is not seen in cats fed a commercial cat food. Often, no cause of the cardiomyopathy
is found.
How is cardiomyopathy treated?
In cases where an underlying cause of the heart disease is found, then treatment
of this may result in improvement or reversal of the heart disease. Hyperthyroidism
is the most treatable cause of cardiomyopathy since complete resolution of the
heart disease is possible if treated early. In cases where no cause is identified,
(referred to as idiopathic cardiomyopathy), and in cases where disease remains
following treatment for an underlying cause then medication may be needed.
Treatment varies according to each case but may include:-
1. Diuretics if congestive heart failure is present.
2. Beta blockers to reduce the heart rate where this is excessive.
3. Calcium channel blockers to help the heart muscle relax and hence help
more effective filling of the heart.
4. Aspirin may be used for its effects at reducing the risk of thrombus formation
and hence thromboembolic disease. Dosing of aspirin should always be as advised
by a veterinary surgeon since aspirin may be toxic to cats. Aspirin poisoning,
which occurs if the dose or frequency of aspirin administration is too high,
may cause vomiting and internal bleeding. If your cat shows these signs, goes
off their food or is sick then aspirin therapy should be stopped and you should
consult your veterinarian.
5. ACE inhibitors - these drugs also help to control congestive heart failure.
The long-term outlook for a cat with cardiomyopathy is extremely variable
depending on the cause of this disease. Cats with idiopathic cardiomyopathy
may remain stable for several years.
Does a cat with cardiomyopathy need a special diet?
Other than in cases of taurine deficiency, no specific diet is recommended
although excessively salty foods should be avoided since these will predispose
to fluid retention. This may increase the risk of congestive heart failure and
hypertension developing. Proprietary cat foods are usually adequate although
special low salt diets are available and may be recommended by your veterinary
surgeon in specific cases. Cat treats are often quite salty and probably should
be avoided.
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