What is cardiomyopathy?
Cardiomyopathy is a term used to describe
diseases of the heart muscle. In cats, at least 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.
Blood banks back into the blood vessels of the lungs, resulting in fluid
accumulation in or around them.
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 organised 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 paralysed and cold
to the touch. Although a minority of 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.
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)
rarely provides useful information on heart conduction and size. Cardiac
ultrasound scans, where available, are indispensable in distinguishing between
the different types of cardiomyopathy.
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) may cause a type of
cardiomyopathy. Other causes include dietary deficiency of taurine, an
essential nutrient. This is not seen in cats fed a commercial cat food or fresh
meat. 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. These drugs are generally the most effective
form of treatment and often are the only drug required (in the long term).
4. Aspirin may be used for its effects at
reducing the risk of thrombus formation and hence thrombo-embolic disease
although it is being used less frequently these days for this purpose. Dosing of asprin 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 vet.
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 and
lead near-normal lives.
Does a cat with cardiomyopathy need a special diet?
Except
in cases where taurine deficiency is suspected, no specific diet is recommended
although excessively salty foods are best avoided e.g. dry cat food and some
cat treats, since these will predispose to fluid retention. This is because
they can promote sodium retention, which increases the volume of fluid and
therefore the volume of blood that the heart needs to pump. In some
circumstances low salt diets may be recommended. This may
increase the risk of congestive heart failure. 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. Obese cats usually benefit from a
controlled weight loss programme.
Testing for HCM?
Genetic tests are available for particular
mutations which are recognised in the Maine Coon and Ragdoll breeds. However,
not all cats with HCM will demonstrate these mutations. Therefore, a negative
gene test does not rule out HCM (even in one of the aforementioned breeds). At
present, the most accurate method for diagnosing HCM is the use of cardiac
ultrasound (echocardiography). Go to Hypertrophic cardiomyopathy (HCM) in
cats for more
information on the gene test.
