FELINE HYPERTENSION

Hypertension is the medical term for high blood pressure.

Which cats are likely to get high blood pressure?

In humans, hypertension is related to several factors, including a stressful lifestyle.
Although not all causes of feline hypertension have been identified, stress does not
appear to play a role in the development of this disorder in cats. However, kidney,
thyroid, and heart disease are known to cause feline hypertension.

What are the clinical signs?

Visual abnormalities are the most common clinical findings with feline hypertension.
These abnormalities can include dilated pupils that do not constrict with light, blood
within the chamber of the eye, and blindness. Blindness develops because high blood
pressure in the eye causes the retina to detach. These cats may bump into things or begin
to appear clumsy.

In some cases, hypertension is suspected because of a heart murmur or kidney-related
signs, such as increased water intake or urination.

What causes hypertension?

Kidney failure and hyperthyroidism have been identified as the two most common
predisposing factors for development of feline hypertension. Certain heart diseases can
also cause hypertension.

Kidney disease. It appears that several different mechanisms may lead to development
of hypertension in cats with kidney disease. One theory suggests that as a cat ages, the
kidneys undergo normal aging changes, including a slow accumulation of scar tissue.
With time, this scar tissue causes the kidneys to shrink in size. When the kidney shrinks,
it is harder for the blood to filter through. Because the kidneys normally receive 20% of
the blood with every heartbeat, blood backs up into the arteries and leads to an increase in
blood pressure. One study found that about 60% of cats in old-age kidney failure have
hypertension. Even elderly cats in the early stages of kidney disease may also have
hypertension.

Hyperthyroidism. The thyroid gland is located in the neck and plays a very important
role in regulating the body's rate of metabolism. Hyperthyroidism is a disorder characterized by the overproduction of thyroid hormone and a subsequent increase in the
metabolic rate. This is a fairly common disease of older cats. Although the thyroid gland
enlarges, it is usually a non-malignant change (benign). Less than 2% of feline
hyperthyroid cases involve a malignant change in the gland.

This disease, including the heart, affects many organs. The heart is stimulated to pump
faster and more forcefully, and eventually, the heart enlarges to meet these increased
demands for blood flow. The increased pumping pressure leads to a greater output of
blood and high blood pressure. About 25% of cats with hyperthyroidism have high blood
pressure, although most of them do not have blood pressures high enough to cause
blindness.

How is it diagnosed?

Hypertension should be suspected in any older cat with kidney disease or
hyperthyroidism. Onset of sudden, unexplained blindness should raise a strong suspicion
for hypertension and the associated diseases should be considered. Also, the presence of
a heart murmur or kidney-related problems may signal the presence of a hypertensive
state.

Blood pressure is determined much as it is in humans with a blood pressure cuff and a
Doppler machine (instead of a stethoscope).

What is involved in treatment?

There are several medications available. The first choice will be based on effectiveness
and ease of administration. Depending on how your cat responds, dose, frequency, or
type may be changed. We will monitor your cat weekly until a safe blood pressure has
been maintained.

What is the prognosis?

The underlying disease that caused hypertension to develop must be cured or controlled.
Long-term success depends on whether or not this is possible. If the cat has kidney,
heart, or thyroid disease, it is important to treat those aggressively. Hyperthyroidism is
curable, but hypertrophic cardiomyopathy and old-age kidney failure are not. However,
even those can be managed successfully in many cats.

If the cat has blindness due to detached retinas, a medical emergency exists. Blood
pressure must be lowered quickly for preservation of vision. If the retinas remain
detached for more than a day or two, the prognosis is poor for a return of normal vision.
Therefore, the key to a successful outcome is rapid diagnosis and early administration of
the proper medication to lower blood pressure.

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