Cat - Hypertension

What is hypertension?

Hypertension is the medical term for high blood pressure which is a common problem in people and also an important condition in cats.

What causes hypertension?

Most cases of feline hypertension are seen as a secondary complication of other medical conditions although primary hypertension (hypertension without any underlying disease) may also be seen. This is in contrast to people where primary hypertension is most common. In cats, the most common causes of secondary hypertension are hyperthyroidism (an overactive thyroid gland) and chronic kidney disease. Another more rare cause of hypertension include hyperaldosteronism (a tumour of the adrenal glands producing excessive amounts of the hormone, aldosterone).

What effects does hypertension have on my cat?

Hypertension is damaging to the body. The effects are most serious in certain vulnerable organs:

• The eyes: Bleeding into the eyes, retinal swelling and detachment, can occur resulting in (often permanent) damage to the cat's vision. In some cases, bleeding into the front of the eye can be seen without the use of special veterinary equipment, but in most cases a thorough ophthalmologic examination is required to identify the signs of hypertension.
• The brain and nervous system: Bleeding in this area of the body can cause neurological signs such as odd behaviour, a wobbly or drunken gait, seizures, dementia and coma.
• The heart: Over time, the muscle of one of the heart chambers (the left ventricle) becomes thickened and can cause a heart murmur. If this is identified it is important that blood pressure is measured, since otherwise it could be mistaken for primary cardiomyopathy (disease of the heart muscle).
• The kidneys: Over time, high blood pressure damages the kidneys and may increase the risk of kidney failure developing.

What other clinical signs might my cat show?

Since hypertension is often seen as an effect of other diseases, cats with hypertension may be showing signs attributable to their underlying problem. For example, in the case of hyperthyroid cats with high blood pressure, weight loss in spite of a huge appetite and hyperactivity may be the major clinical signs. In many patients, no specific clinical signs of hypertension will be seen until this is quite advanced. These cats are often taken to a veterinary surgeon when they have suddenly become blind. Early recognition of hypertension is therefore important in order to minimise the severe and often permanently damaging effects of persistently high blood pressure.

How can hypertension be diagnosed?

Diagnosis of hypertension is ideally made following measurement of blood pressure. Various techniques and equipment are available and many practices now have these facilities. The equipment used is similar to that used routinely in people, with an inflatable cuff placed around one of the front legs or the tail. Measuring blood pressure only takes a few minutes, is completely pain-free and is extremely well tolerated by most cats.

A detailed eye examination is also essential since ocular disease is common in hypertensive cats. In mildly affected cats, subtle changes to the appearance of the blood vessels at the back of the eye (retina) and to the retina itself may be seen. In more severely affected cats, the changes can be dramatic and include retinal detachment and bleeding into the eye. Abnormalities are usually detected in both eyes although they may be more severe in one. In the absence of blood pressure measurement devices, a thorough ocular examination (examination of the eyes) is often able to diagnose hypertension and can be used to monitor progress once treatment has been started.

Is hypertension a treatable condition?

Yes, in any diagnosed hypertensive, management has two broad aims:

1. To reduce the blood pressure using anti-hypertensive drugs. A number of orally administered agents are available for treatment of hypertension although many of these are not specifically licensed for this use. Examples of drugs commonly used are amlodipine (trade name 'Istin®') and benazepril (trade name 'Fortekor®').
2. To search for an underlying disease, such as kidney disease, which has caused the hypertension. In some cases, for example hyperthyroidism, treatment of this will also resolve the high blood pressure.

What does treatment of hypertension involve?

Your veterinary surgeon will assess your cat for the presence of any complications associated with their hypertension, such as eye and kidney disease, so that these can be appropriately monitored following therapy. There is a great degree of individual variation in response to anti-hypertensive therapy and in some cats it can take some time to stabilise the blood pressure. This may involve trying several drugs and/or using more than one drug simultaneously. Response to therapy may involve measuring blood pressure and monitoring ocular abnormalities. It is usually possible for your cat to be stabilised as an out-patient.

Does my cat need a special diet?

Feeding a low salt diet may be of some value although it is unlikely to be sufficient as a sole treatment of hypertension. Feeding of cat treats should be discouraged since most of these are quite high in salt.

What is the long-term outlook for my cat?

In primary hypertensive cases (where there is no underlying disease that has caused the high blood pressure) it is usually possible to manage the hypertension and prevent future complications such as damage to the eyes. In cases of secondary hypertension, the long-term outlook is very dependent on the nature and severity of the disease which has caused the high blood pressure.

It is important in all cases that the hypertension is monitored as accurately as possible on a regular basis in order to pre-empt any problems such as blindness. In cats where blindness has occurred as an effect of hypertension, return of some vision may be possible if treatment is started immediately. Even if vision does not return control of the blood pressure is still very beneficial and affected cats may live for several years with a good quality of life.