pressure monitoring in cats is easy to do
literally means disease of the heart muscle. The term is reserved
for those cases where the cause of the disease is unknown.
the cause of the hypertrophy (enlargement) of the heart muscle
is known, it is called secondary myocardial hypertrophy. There
are a number of well recognised diseases which cause changes
in the heart muscle, including taurine deficiency, which can
lead to dilation of the heart, and hyperthyroidism, which
is usually associated with hypertrophy of the heart muscle.
Therapy in these cases is directed towards short term support
of heart function while the primary disease is being treated.
to describe primary (without demonstrable underlying cause)
cardiomyopathies in the cat is complex.
cases can be classified under one of three headings.
condition is characterised by enlargement of the heart chambers
and weakening of the heart muscle. When this occurs the heart
is no longer able to pump the blood out of the heart in sufficient
quantities to meet demand.
picture of a heart from a cat suffering from cardiomyopathy
of the scan showing thickening of the heart muscle and
reduction in the size of the heart chambers
of these conditions are characterised by impaired relaxation
of the heart muscle. In HCM inward thickening of the heart
muscle results in a reduction in chamber volume thereby reducing
the volume of blood that the heart can pump with each contraction.
In RCM fibrosis (scarring) of the heart muscle results in
a chamber that can no longer expand in the normal way.
the underlying disease process is important (because it affects
the choice of drugs that can be used to treat the cat) the
presentation of disease is similar. Most commonly
cats will present in heart failure, but thromboembolic (blocking
of a blood vessel by a blood clot) disease can also be responsible
for the cat's clinical signs.
dogs, coughing is not a major sign of heart failure in cats.
Most frequently, breathlessness, lethargy and a loss of appetite
are the first problems noticed. These signs can appear quite
quickly, typically over a few hours/days. However, it is important
to remember that the underlying heart disease has usually
been present for a considerable period of time. Heart failure
becomes obvious when the heart is no longer able to meet the
demands for pumping blood around the body. In cats, the signs
of heart failure arise due to an increase in venous pressures
leading to fluid leaking into the lung tissue (pulmonary oedema)
or around the lungs (pleural effusion). Both of these processes
prevent the lungs from functioning normally, leading to the
breathlessness and lethargy.
the enlarged heart is no longer able to pump efficiently,
stasis of the blood occurs resulting in activation of the
clotting system. This results in the formation of an embolus
(or clot) usually in the left atrium. Small pieces of the
embolus can break off and travel through the circulation,
becoming trapped in smaller arteries. The most common place
for the embolus to be trapped is at the point at which the
blood supply to each of the hind legs and the tail branches
(aortic trifurcation). The resulting obstruction causes sudden
loss of use of both hind legs and the tail,
become cold, hard and painful. This sudden event can sometimes
be mistaken for a cat that has been in a road traffic accident.
Although some cats may recover full function of their limbs
with appropriate treatment, their longer term outlook is often
bleak due to the underlying heart disease and the possibility
of other clots occurring.
affecting the heart
(high blood pressure) is common, particularly in older cats
and can result in damage to blood vessels. The blood vessels
in the retina of the eye are particularly sensitive to hypertensive
damage, which may result in retinal detachment and sudden
onset blindness. Affected cats appear confused and disorientated,
with widely dilated pupils. Retinal detachment is an emergency
situation as blindness will become permanent unless the retina
reattaches within a few days. In addition, the elevated blood
pressure damages the glomerulus (the functional unit within
the kidney), the heart (causing a thickening of the walls
as the muscular wall is having to work harder pumping against
a high resistance within the blood vessels) and the brain,
causing small blood vessels to rupture. Drugs that lower blood
pressure (hypotensive agents) are routinely used in the treatment
of hypertension in cats. Other diseases, for example, chronic
renal failure can also lead to hypertension, meaning that
a number of different tests may be required to establish the
underlying cause of the increase in blood pressure. Primary
hypertension is rare in cats, unlike the situation in man.
recent years, the ability to measure blood pressure in cats
has improved and an increasing number of practices have the
disease can often be suspected on the basis of the presenting
clinical signs as well as the age and breed of the cat. A
precise diagnosis depends on more specific tests. Radiographs
(X-rays) of the chest and electrical recordings of heart activity
(ECG) are commonly used. Ultrasound examination (echocardiography)
is usually required to make a definitive diagnosis as it is
the best way of assessing heart size and function. Ultrasound
will also detect the presence of secondary problems such as
thromboembolism or obstruction of the outflow of blood (which
may occur due to extreme hypertrophy
of the heart muscle). Depending on the presentation of the
case, other tests may also be valuable (such as a general
blood screen, ocular examination
or measurement of thyroid hormone levels), which can be useful
when looking for primary disease problems causing secondary
changes of the heart muscle.
present, the cause of cardiomyopathy in most cases is unknown.
However, a number of factors are suspected to play a role,
such as previous viral disease and/or genetics. Cardiomyopathy
seems to be more common in young and middle aged male cats.
In people, the majority of cases of HCM are secondary to a
genetic mutation; over 120 different mutations have been identified.
Recently, mutations which can lead to HCM have been identified
in the Maine Coon and Ragdoll breeds; however, it is well
recognised that there are many other breed predispositions
and there are thought to be many more, as yet unidentified
mutations, present in the feline population.
is cardiomyopathy treated?
will, to some extent, depend on the presenting signs, severity
and type of cardiomyopathy. Where an underlying cause can
be identified and corrected, the secondary
cardiac dysfunction may resolve. Where no underlying cause
is found, treatment is aimed at management of heart rate and
the cardiomyopathy itself is usually progressive, although
progression may be slow. Treatment is focused on:
of circulating volume to remove fluid from within (pulmonary
oedema) or around (pleural effusion)
the lungs. This is usually achieved by use of a diuretic
commonly frusemide). Pleural fluid can also be drained directly
by placing a needle or catheter through the chest wall and
removing the fluid.
heart function; the drugs used will depend on the cause
of the cardiomyopathy. Most commonly used drugs would include:
•ACE (angiotensin converting enzyme) inhibitor, which causes
vasodilation reducing the heart's work load.
channel blockers, which will help the heart muscle relax
so there is more room for blood to fill the ventricle
which are sometimes used to slow the heart rate down
in cases where the heart rate is excessively fast so
there is no time for chamber filling to occur.
of the risk of thromboembolism; this may be achieved by
the use of one or more of the following: low doses of aspirin
to inhibit platelet function; clopidogrel, another platelet
inhibitor; or a form of heparin, which decreases blood clotting.
It is important that the dose rate and interval is followed
as it is easy to overdose a cat, with fatal consequences.
cats in which hypertension is the major problem, amlodipine
is used to reduce the blood pressure. Whereas cats with
hyperthyroidism should have the overactive thyroid treated.
is the long term outlook for cats with cardiomyopathy?
outlook for cats is very variable and depends on the type
and severity of the disease, whether or not congestive heart
failure develops and whether the heart disease is a primary
problem, or if it is secondary to another disease such as hypertension
or hyperthyroidism. Some cases will remain stable for years.
In general, cats with thromboembolic disease, and those with
heart failure which does not respond well to treatment, have
a poorer outlook.
in cases where taurine deficiency is suspected, no specific
dietary change is usually required, although obese cats usually
benefit from a controlled weight loss programme.
Highly salty foods, which include some cat treats, are best
avoided. 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.
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.
there a screening scheme available to detect cardiomyopathy
there is a Feline Advisory Bureau scheme available which is
aimed at detecting the presence or absence of hypertrophic
cardiomyopathy (HCM). It is run in association with the Veterinary
Cardiovascular Society (VCS).
further information about the Scheme, please click here...
information on HCM in cats can also be gained from: Susan
Little's information on HCM for Cat Breeders: http://www.catvet.homestead.com