Site owned by Pedernales Veterinary
Center all rights ® 2009
Site last updated on:07/09/2011
Design by: Comfort Webs.com
Issues with website please contact
webmaster: linda@comfortwebs.com
Name
Hypertension, Feline
Short Description
Hypertension
Affected Animals: 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
Overview: 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
Clinical Signs: 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
Symptoms: 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
Description:
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
Diagnosis: 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.
Prognosis: 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
Transmission or Cause: Although primary hypertension can occur, its
cause is unknown. High blood pressure in cats is usually associated
with underlying kidney or thyroid disease.
Treatment: 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.
Prevention: 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.
