A mammal’s heart is composed of four chambers. There
are left and right atria and ventricles. These chambers act as 2
different pumps. The left side pumps oxygenated blood to the body and
the right side pumps blood through the lungs so it can become
oxygenated. The path blood travels through the body is from the lungs to
the left atrium through the mitral valve and into the left ventricle. It
is then pumped out through the aorta to the body. Blood depleted of
oxygen returns to the right atrium via the vena cava. It goes through
the tricuspid valve into the right ventricle where it is pumped out to
the lungs to begin the cycle again.
Hypertrophic cardiomyopathy (HCM) is a heart condition
characterized by a thickening of the muscle comprising the left
ventricle of the heart. This decreases the size of the left ventricular
chamber and means the heart has to pump more times per minute to pump a
normal volume of blood through the body. This problem develops most
commonly in cats. Most cats are diagnosed on physical examination when a
heart murmur or abnormal heart rhythm is noted. Some cats go into heart
failure when the lungs start to accumulate fluid (edema) and they can
develop severe and life threatening breathing problems. The edema
develops from blood backing up into the lungs causing fluid leakage out
of the blood vessels.
Occasionally, cats may see their veterinarian after
developing sudden paralysis. This occurs due to abnormal blood flow
through the heart which predisposes them to abnormal clot formation.
These clots will start in the heart, travel down the aorta and become
lodged at the point where the aorta splits to supply blood to the hind
legs (aortic thromboembolism). This obstructs blood supply to the hind
legs and results in paralysis.
Evidence is mounting that the cause of HCM may be
genetic in origin however, the exact mechanism is unknown at this time.
One disease that may be associated with the development of HCM in cats
is hyperthyroidism. In some cases, treatment of the hyperthyroidism may
correct the heart problem but some cats may require heart medication for
a period of time before and after treatment of the thyroid disease.
In addition to a physical exam and lab tests,
radiographs of the chest are also used in the diagnosis of HCM. The
radiographs may be normal or show enlargement of the left atrium. Some
cats have a valentine shaped heart. The diagnostic test of choice is an
echocardiogram (heart ultrasound) which determines the size and shape of
the heart chamber. Since high blood pressure (hypertension) can also be
seen with HCM, the blood pressure is often checked as well. All of these
diagnostic tests help your doctor decide which means of therapy would be
most beneficial to your cat.
Cats that have heart failure or paralysis are treated
much differently than patients with no symptoms. HCM is life threatening
and aggressive therapy is often required in cases of heart failure or
paralysis. Treatment of cats with aortic thromboembolism is often
supportive and aimed at helping the heart pump more effectively as well
as managing the pain caused by the clot. With time, some cats will
recover the ability to use their legs. This may take days to weeks
however and prognosis is also dependent on the ability to manage their
HCM. Some medications made specifically to destroy the clots have been
used clinically and experimentally with mixed results. Unfortunately,
despite treatment, clots often recur.
Cats with congestive heart failure are treated with a
combination of medications and oxygen to decrease the congestion and to
help the heart pump more effectively. The long-term prognosis is
variable but with rapid and early intervention, cats with HCM are
leading longer lives.
