Hypertension (high blood pressure) is a common medical problem in people. These days, we are beginning to recognise it as a very important and common condition in cats.
In people, it is commonly termed primary or essential hypertension, which occurs due to our lifestyle, stress and diets.
In feline hypertension, it is almost always seen as a secondary complication of other medical conditions. In cats, the most common causes of secondary hypertension are chronic kidney failure, hyperthyroidism (an overactive thyroid gland) or cardiac disease. Other very rare causes of hypertension would include acromegaly (a tumour producing excessive amounts of growth hormone) and Cushing's disease (a tumour of the pituitary or adrenal gland resulting in excessive production of corticosteroids by the body).
The hypertension that develops as a consequence of another medical condition, is damaging to organs throughout the body:
The eyes: Blindness and/or bleeding into the eyes as a result of high blood pressures. This may be one of the first signs of hypertension noticed by owners.
The brain: High pressures can cause neurological signs such as abnormal behaviour, seizures or dementia. Owners often notice that their cat's behaviour or temperament changes, starting to forget things or yowling a lot.
The heart: In hypertensive states, the blood vessels around the body constrict, therefore the heart has to work harder to pump blood around the body. As the heart is a muscle, it can become thicker and larger. This can result in heart failure on rare occasions.
The kidneys: Over time, high blood pressure damages the kidneys and may hasten the development of kidney failure.
Since feline hypertension is often seen as a side-effect of other diseases, cats suffering it may first show signs attributable to their underlying problem. For example, in the case of hyperthyroid cats with high blood pressure, weight loss despite a healthy appetite or kidney failure they may be drinking excessively.
In many patients, no specific clinical signs of hypertension will be seen until it is quite advanced. These cats are often taken to a veterinary surgeon when they have suddenly become blind, had a stroke or are in heart failure. Early detection of hypertension is essential in order to minimise the severe and often permanently damaging effects of persistently high blood pressure throughout the body. In some studies, up to 70% of cats with renal disease have high blood pressure and when you consider that most old cats will suffer from renal failure as they age, it is a very important and common problem facing senior cats.
Diagnosis of hypertension is achieved by simply measuring the cat's blood pressure. Most Veterinary practices now have the means to perform this, with equipment similar to that used routinely in people. A small inflatable cuff is placed around one of the cat's front legs or on the tail. Measuring blood pressure only takes a few minutes, is completely pain-free and is extremely well tolerated by most cats. Most Veterinary practices now perform blood pressure measurements as a routine screening procedure in most senior patients, or any of those cats that present with signs attributable to hypertension.
Like us, a cat's blood pressure is supposed to be around 120mmHg (systolic pressure). Accounting for the stress of the visit to the Vet, anything up to 160 is considered ok. Some patients that present with advanced disease can often have pressures in excess of 240mmHg, double normal!
A detailed eye examination is also essential since ocular disease can be one of the subtle indicators in early or pre-hypertensive cats. In mildly affected cats, subtle changes to the appearance of the blood vessels or the retina at the back of the eye may be seen. In more severely affected cats, the changes can be dramatic and include retinal detachment and bleeding into the eye. This is a medical emergency and vision may be restored if pressures are normalised within 1-2 days.
Any cat diagnosed with hypertension, requires a full blood and urine test, as it is essential to diagnose the primary cause of the hypertension. Sometimes more than one condition may exist to cause the blood pressure changes. If any significant signs have developed, treatment must be started immediately, especially if the eyes have sustained any damage.
Medications help dilate the blood vessels throughout the body, which will reduce the blood pressures. There is a great degree of individual variation in response to anti-hypertensive therapy and in some cats it can take some time and effort to stabilise the blood pressure. This may involve trying several drugs and /or combinations.
Response to therapy should ideally be monitored closely by measuring blood pressure and monitoring blood tests. Most hypertensive cats can be fed a normal commercial cat food. Special prescription diets may be recommended in some cases, such as cats with chronic renal failure, where a protein and phosphate restricted diet is extremely important.
In cats with kidney failure, it is important to monitor renal function when using anti-hypertensive drugs. Hypertension in chronic renal failure can occur as the kidneys ability to excrete the waste products declines. This occurs to try to increase the efficiency of the remaining kidney function. There is a short-term gain, but the high pressures can hasten failure of the kidneys as well as damage most other organs throughout the body.
In hypertension, the prognosis is very dependent on the nature and severity of the disease that has caused the high blood pressure. Therefore cats with chronic renal failure that have hypertension, have a worse prognosis than those where the cause of the high blood pressure is reversible, such as hyperthyroidism. 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, control of the blood pressure is still beneficial and affected cats may live for several years with a good quality of life. It is also recommended that blood pressure measurements be performed routinely in older cats, from 10-12 years of age as a screening tool for underlying health concerns.