Cats of all ages can develop hypertension,
although middle-aged and older cats are affected most
frequently. As a rule, the most common diseases associated
with hypertension in cats are kidney failure and hyperthyroidism,
which also tend to occur more often in middle-aged and
older cats
Most cats with hypertension have an
underlying illness responsible for its development; kidney
disease and hyperthyroidism are the two most common diseases
associated with high blood pressure in cats. In rare
circumstances, primary hypertension -- high blood pressure
without an associated or underlying cause -- can occur.
The diagnosis is made by measuring the blood pressure,
and treatment is usually initiated if the elevation is
severe or if symptoms due to the high blood pressure
are present. The long-term outlook with treatment for
high blood pressure has not yet been determined. However,
with increased awareness of the condition and early identification
of elevated blood pressure readings, serious consequences
of hypertension may be prevented from developing
Because hypertension is commonly associated
with an underlying cause, the clinical signs seen in
an individual cat are often due to the disease that causes
the elevated blood pressure. Examples of possible symptoms
associated with the underlying disease of renal failure
include lethargy, anorexia, weight loss, polydipsia,
polyuria, and vomiting. Clinical signs of hyperthyroidism,
another disease associated with high blood pressure,
include weight loss, vomiting, polydipsia, polyuria,
and polyphagia. Signs due to hypertension itself vary,
and may range from no clinical signs to ocular abnormalities
such as hyphema, retinal detachment, and increased tortuosity
of retinal vessels. Neurological abnormalities such as
seizures, collapse, and abnormal behavior secondary to
complications from hemorrhage or arterial spasm may also
occur
Many cats with high blood pressure
have no signs at all, although some cats develop signs
secondary to the disease that has caused the elevation
in blood pressure. For example, cats experiencing hypertension
due to kidney failure may have a poor appetite, and experience
weight loss, increased thirst or urination, and vomiting.
With hyperthyroidism, another disease causing high blood
pressure, symptoms include weight loss, vomiting, increased
thirst, increased activity, and increased appetite. Cats
with primary hypertension usually will have symptoms
that result from damage to the eyes, kidneys, heart or
blood vessels, or central nervous systems, since these
are the systems primarily affected by hypertension. Signs
may include blindness due to bleeding or retinal detachment.
Neurological signs such as seizures, fainting, weakness,
or collapse can occur when hypertension leads to blood
vessel injury in the central nervous system
Blood pressure is determined by cardiac
output and the total resistance to blood flow in blood
vessels throughout the body. Cardiac output itself is
related to the heart rate and to the amount of blood
pumped by the heart with each beat. Regulation of blood
pressure encompasses a very complex interplay between
receptors in the brain, the peripheral blood vessels,
and the kidneys, endocrine, and cardiovascular systems.
When blood pressure is high, complications can occur
due to release of fluid, plasma, or bleeding into the
tissues. Spasm of blood vessels may result in lack of
oxygen in cells in target organs such as the eyes, kidneys,
heart, and brain. Changes, including heart muscle thickening,
may occur secondary to hypertension.
Hypertensive cats usually are taken to the veterinarian
because of signs secondary to the underlying cause of their
high blood pressure, or because of damage to the eyes,
kidneys, cardiovascular system, or central nervous system.
On physical examination, findings such as retinal hemorrhage
or detachment may be seen. Other changes like blood in
the eye or blood vessel abnormalities in the retina may
be detected. Reduced kidney size may occur in cats with
long-standing kidney disease. Heart murmurs are often heard,
but lung changes secondary to heart disease are not usually
due to hypertension alone. Additional heart changes, such
as an abnormally rapid heart rate or the presence of an
extra heart sound called a gallop rhythm, are also common.
Cats with hyperthyroidism may be agitated or pant during
their exams, and usually have an enlarged thyroid gland
that can be palpated in the neck.
Hypertension is diagnosed most commonly through indirect
blood pressure measurement. Bloodwork, x-rays, and ultrasound
examination are performed to look for underlying causes
of hypertension as well as changes secondary to it. Treatment
focuses on the use of oral medications to control blood
pressure, although in crisis situations there are drugs
that can be used intravenously if deemed appropriate. There
are many different classes on anti-hypertensive drugs.
The calcium channel blocker amlodipine, marketed as Norvasc,
is one of the most commonly prescribed anti-hypertensive
drugs for cats
The diagnosis is made by documenting
elevated readings during blood pressure measurement.
The normal range for blood pressure in cats is up to
180 to 200 mm Hg for systolic readings; systolic refers
to the phase of the heart's cycle characterized by contraction
of the ventricles. For diastolic readings, which measure
ventricular filling, the normal range is 100 to 110 mm
Hg. Since stress associated with blood pressure measurement
can elevate readings above this range even in normal
cats, the results must be interpreted in light of the
individual cat's situation. Measuring blood pressure
in a quiet, calm environment is important, because allowing
cats to become acclimated to their surroundings will
help eliminate some of the "white coat syndrome." A diagnosis
of hypertension is more plausible if the cat has symptoms
that are common with disorders known to be associated
with hypertension, if such disorders have already been
diagnosed, or if signs such as bleeding in the eyes,
retinal detachment, blindness, or severe neurological
abnormalities are present.
Once the diagnosis is established, other pieces of information
are important in assessing feline hypertension. A complete
blood count, chemistry profile, urinalysis, and thyroid
hormone level will detect evidence of kidney failure, hyperthyroidism,
and other complicating disorders. X-rays of the chest and
abdomen should be obtained to screen for obvious structural
disorders such as tumors, abnormalities of kidney shape
or size, and heart enlargement. Ultrasound examination
of the abdomen may be used if abnormalities are suspected,
and an ultrasound of the heart, or echocardiogram, may
be necessary if the cat has a heart murmur or if changes
appear in the chest x-rays. Since many cats with hypertension
have heart murmurs, echocardiography is used frequently
to assess for changes in the heart secondary to hypertension
and for other structural heart muscle or valve disorders
that are common in older cats.
The long-term prognosis for most cats
with hypertension is unknown, and depends to some degree
on the underlying cause. Blindness of short duration
due to retinal detachment or hemorrhage may resolve,
but most cats that have been blind for longer than one
or two days will remain blind, even after their blood
pressure has been controlled and the hemorrhage or detachment
resolves. Very old cats with severe central nervous system
abnormalities or severe heart disease do not have a good
prognosis. If hypertension is diagnosed and treated before
signs occur, serious complications may be prevented,
but the effects of such treatment over many years have
not yet been investigated
Although primary hypertension can
occur, its cause is unknown. High blood pressure in cats
is usually associated with underlying kidney or thyroid
disease.
Mild hypertension may not need to be treated.
However, treatment may be indicated for cats with moderate
to severe blood pressure elevations, and for cats that already
have signs due to high blood pressure. In addition, any concurrent
disorder
Many different types of drugs can be used to treat
hypertension. Diuretics decrease blood volume, which
in turn can decrease cardiac output. Diuretics may
also decrease blood vessel resistance by decreasing
total body salts and water. Examples of diuretics that
can be used include furosemide, marketed as Lasix;
spironolactone, marketed as Aldactone; and hydrochlorothiazide,
marketed as HydroDIURIL.
A class of drugs called beta-blockers can be used
to decrease blood pressure. These drugs help lower
heart rate, and in turn lower cardiac output. Members
of this group include propranolol, marketed as Inderal,
and atenolol, marketed as Tenormin. Alpha-blocker drugs,
such as prazosin, marketed as Minipress, can be used
to decrease blood vessel resistance. Angiotensin converting
enzyme, or ACE, inhibitors are another class of drugs
used to manage hypertension. These medications have
multiple effects that might help to lower blood pressure.
Enalapril and lisinopril are the most common ACE-inhibitors
used today. Finally, calcium channel blocking drugs
may be used to decrease cardiac output and blood vessel
resistance, thereby lowering blood pressure. Diltiazem,
marketed as Cardizem, and amlodipine, marketed as Norvasc,
are the calcium channel blockers used most commonly
in cats. Amlodipine is probably the most frequently
prescribed drug used in the treatment of hypertension
in cats.
Once treatment is started, blood pressure should be
reevaluated to see if it is improving. In addition,
it is important to ensure that the blood pressure has
not dropped too low. Other follow-up procedures depend
on the presence of additional diseases.
Since there is no known way to prevent
hyperthyroidism or kidney disease, there is no way to
prevent high blood pressure secondary to these disorders.
As awareness of hypertension increases, and more veterinarians
learn to assess it, hopefully more cats will be diagnosed
before complications arise. This should enable earlier
treatment and lessen the incidence of complications due
to high blood pressure.
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