The heart has four chambers: two chambers at the top, the
right and left aorta; and two chambers on the bottom, the right and left
ventricles. The left ventricle is responsible for receiving oxygenated blood
from the lungs and pumping the blood out into the aortic valve, the main artery
of the body, which feeds the oxygenated blood to all parts of the body.
Hypertrophic cardiomyopathy (HCM) affects the left ventricle, and its
functional ability to pump blood into the aorta. The normal, healthy left
ventricle is already thicker than the right ventricle, owing to its greater
workload in pumping blood out into the body. In hypertrophic cardiomyopathy,
the muscle of the left ventricle is abnormally enlarged or thickened. A cat may
have other diseases of the heart, but they will be independent of HCM.
There is an apparent genetic predisposition for this
condition. Some families have had a high number of cases, particularly Maine
coon cats, where a mutation that is associated with the disease was identified
in one large family. The role of genetics has not been definitively determined
in other families or breeds, although some association has been documented in
American Shorthairs and Persians.
It occurs more often in cats five to seven years of age,
although the age range of reported cases ranges from three months to 17 years,
with most cases affecting males. Heart murmurs in older cats are generally
caused by hyperthyroidism or hypertension rather than HCM.
Symptoms and Types
Loss of appetite (anorexia)
Lethargy
Weak pulse
Difficulty breathing
Short, rough, snapping breathing sounds (crackles)
Abnormal heart sounds (i.e., muffled, galloping rhythm,
murmurs)
Inability to tolerate exercise or exertion
Sudden hind-limb paralysis with cold limbs due to clot in
the terminal aorta
Bluish discoloration of foot pads and nailbeds (indicates a
lack of oxygen flow to the legs)
Collapse
Sudden heart failure
Causes
The cause for hypertrophic cardiomyopathy may remain unknown
in many cases. However, genetic mutations and predispositions are known to lead
to HCM in cats. And though not a direct cause of the condition, hypertension
and/or hyperthyroidism can further complicate HCM in cats.
Diagnosis
You will need to provide a thorough history of your pet's
health leading up to the onset of symptoms, including any information you have
about your cat's genetic background.
An electrocardiogram (or EKG) recording can be used to
examine the electrical currents in the heart muscles, and may reveal any
abnormalities in cardiac electrical conduction (which underlies the heart’s
ability to contract/beat), and can also help your veterinarian to determine the
origin of the abnormal heart rhythms, if they are present. However, an ECG may
not be adequate for a definitive diagnosis. Radiograph and echocardiograph
(ultrasound) imaging will be more useful for visually examining the heart for
enlargement or thickening of the walls, or for thickening of the mitral valve
(which controls the flow of blood between the left ventricle and the left
atrium). Other conditions will need to be either ruled out of confirmed before
your doctor settles on HCM. There are two conditions, which are especially
likely to mimic HCM, that your cat will be checked for. Your cat will need to
have its blood pressure checked in order to rule out hypertension, and the
blood will be tested for high levels of thyroid hormones. Hyperthyroidism will
exhibit may of the same symptoms as HCM, such as lethargy, short breath, and
irregular heart rhythm.
Treatment
If there is a diagnosis of HCM, your cat will be
hospitalized for appropriate care, especially if it is suffering from
congestive heart failure, a common outcome of this disease. Your cat will be
placed in a quiet environment to minimize stress, and if it is having trouble
breathing it will be given oxygen therapy. If your cat’s body temperature is
low, your veterinarian will warm the cat in blankets to gently raise the body
temperature.
There are several possible medications that can be used to
treat hypertrophic cardiomyopathy:
Diltiazim to slow the heart rate, treat irregular heart
beats, and possibly reduce the enlargement in the left ventricle
Beta blockers to slow the heart rate, correct irregular
heart beats, and control blockage of the blood flow. These are not used if the
cat has congestive heart failure
Ace inhibitors, in cases with congestive heart failure, to
improve the flow through the ventricle
Aspirin to decrease risk of blood clots
Warfarin to prevent blood clotting
Furosemide (diuretic) to remove excess fluid from the body
Spironolactone (a diuretic used sometimes in conjunction
with furosemide) for cats with congestive heart failure
Nitroglycerin ointment, to improve flow by dilating
(opening) the ventricle and arteries
Living and Management
The cat should be put on a sodium-restricted diet,
especially if there is congestive heart failure, to keep the pressure in the
blood stable. Providing a quiet and safe space for your cat, away from other
pets and active children, is important to its recovery. Environmental stress
may activate the nervous system, placing excess stress on the already
overstressed left ventricle, and possibly leading to heart failure.
You will need to monitor your cat closely during the
recovery period, watching for difficulty breathing, lethargy, weakness, lack of
appetite, and painful hind-limb weakness or paralysis. If your cat is being
treated with warfarin, its blood will need to be tested to determine whether
the drug is effectively decreasing the likelihood of a blood clot. Use of
warfarin can also lead to uncontrolled bleeding and bruising. You will need to
take care that your cat is kept from activities that may lead to injury while
it is on this drug. If your cat is taking an ACE inhibitor, or spironolactone,
kidney function and electrolytes will need to be monitored. After six months, a
repeat ultrasound examination of the heart will be required to determine
progress, and whether further treatment will be required.
Jeffry wahyudi, DVM
Reference
http://www.petmd.com/cat/conditions/cardiovascular/c_ct_cardiomyopathy_hypertrophic?page=2
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