High blood pressure in cats

Hypertension in humans is often called ‘the silent killer’ because people rarely show symptoms until it’s too late (sadly, heart attacks and strokes are often the first sign). Cats can also have hypertension but we usually get a little more warning as they most commonly develop it alongside another health problem.

Hypertension means high blood pressure in cats and is when blood moves through blood vessels with an increased force. This high-velocity, high pressure movement of blood damages blood vessel walls and the body’s major organs.

What causes high blood pressure in cats?

There are two main culprits causing hypertension in cats: hyperthyroidism (an over-active thyroid gland) and kidney disease. A certain kind of heart disease (hypertrophic cardiomyopathy) can also lead to high blood pressure.

Officially, when hypertension in cats is caused by an underlying disease, we refer to it as ‘secondary hypertension.’

Hyperthyroidism

Hyperthyroidism is when the thyroid glands (found either side of your cat’s windpipe) produce too much thyroid hormone. High levels of thyroid hormone influence pretty much every organ in the body leading to hypertension. Your cat will need blood tests to diagnose hyperthyroidism.

Treatment of hypertension and hyperthyroidism is two-fold as the aim of therapy is to control both conditions. It’s possible to cure hyperthyroidism with a radioactive injection to destroy all of the overactive thyroid tissue. Medications are also available to control thyroid levels (oral liquid or tablets) and surgery to remove the glands is sometimes an option. Your vet will discuss these in more detail with you and chat about the pros and cons of each option.

Kidney disease

During their lifetime, cats’ kidneys work very hard filtering toxins from the blood and producing urine. With age, scar tissue within the kidneys causes them to shrink resulting in narrowing of the blood vessels. Cats still need to move the same volume of blood through their shrunken kidneys but in order to do this the blood moves under higher pressure leading to hypertension.

Blood and urine tests will show how well your cat’s kidneys are functioning. Sometimes imaging (such as an ultrasound scan) is also a useful way to look for kidney damage.

Vets use a staging tool (called the IRIS staging system) to determine the most appropriate treatment for cats with kidney disease. Treatments include diets and phosphate-binding supplements (to reduce the kidneys’ work load and slow disease progression) along with various medications.

Hypertrophic cardiomyopathy (HCM)

This is the most common form of heart disease we see in cats. Hypertrophic cardiomyopathy is when the heart muscle thickens and reduces the size of the heart chambers. The same volume of blood still needs to pass through the heart, putting more demand on the heart muscle and causing blood pressure to rise.

Your vet will carry out blood tests and an echocardiography (an ultrasound scan of the heart) if they suspect your cat has HCM. Medication is available to help the heart beat more effectively and reduce its workload.

Other causes of hypertension

Idiopathic hypertension is when your cat has high blood pressure with no obvious underlying cause. Only a fifth of cats with high blood pressure have idiopathic hypertension, and many of these are actually in the very early stages of kidney disease.

Some hormonal conditions and cancers could increase a cat’s chances of developing hypertension although we don’t commonly see this.

How do vets spot hypertension in cats?

If your cat has been diagnosed with one of the above conditions, your vet will already be on their guard and checking for signs of hypertension in your cat. Along with regular blood pressure checks, your vet will also closely examine their eyes (the windows to the soul and a good indicator of high blood pressure!).

Cats with hypertension usually have visible changes on their retina (the membrane at the back of the eye, rich in nerve endings and blood vessels). In some cases, the retina may partially or fully detach from the back of the eye. If hypertension isn’t quickly controlled, the retina may not re-attach and the cat could have long-term vision problems or be completely blind.

There are also some tell-tale signs of hypertension to look out for at home including:

• Sudden blindness — is your cat bumping into things?
• Dilated pupils (larger than normal and often fixed).
• Abnormal behaviour (including confusion and seeming withdrawn and disorientated).
• Seizures.
• Reduced appetite and depression.

How is blood pressure measured in cats?

Even if we suspect your cat has hypertension, we still need to measure their blood pressure to be sure. Just like in people, we use a small cuff to occlude the blood vessels in your cat’s leg (or tail) then slowly release this pressure while listening for blood flow with a Doppler (a small, handheld ultrasound machine). The pressure at which we hear blood flow back into the blood vessels is an accurate estimate of your cat’s systolic blood pressure.

Systolic blood pressure is the pressure of blood when the heart is contracting.

Diastolic blood pressure is the pressure of blood when the heart rests between beats.

We measure blood pressure in mmHG (mm of mercury). A normal systolic blood pressure in cats is between 80 — 140 mmHG and diastolic is 55 — 75mmHG.

There are more invasive ways to measure blood pressure that we don’t commonly do in first-opinion practice as they require a general anaesthetic and surgery to place a catheter directly into an artery.

Treating high blood pressure in cats

High blood pressure can damage major organs and make cats feel very unwell. As previously mentioned, damage to the eyes could lead to irreversible blindness. The brain is also at risk from damage that could result in dementia-type signs or even a coma.

High blood pressure can put extra strain on the heart leading to signs of heart failure. Cats may seem very lethargic and breathless.

The kidneys are also at risk of damage — hypertension makes existing kidney disease worse or can increase the chance of a cat developing it in the first place.

Treatment for high blood pressure in cats

Your vet will treat any underlying disease along with prescribing medication to control your cat’s blood pressure. The most common medication we use is amlodipine, although other drugs are available.

Your cat will need regular checks while on treatment to make sure their blood pressure remains within a safe limit (a low blood pressure can also be dangerous).

We often admit cats for the day when taking their blood pressure as we need to consider ‘the white coat effect’ (scared cats may have falsely high blood pressure readings). Cats can acclimatise to their environment and relax on their comfy bed while we measure their blood pressure throughout the day. We then average out these results to get the most accurate estimate of your cat’s blood pressure.

Can you prevent high blood pressure in cats?

We most commonly see hypertension in older cats so age is one factor we can’t control! Being overweight or obese also makes it more likely a cat will develop hypertension. Keeping your cat at a healthy bodyweight could possibly prevent hypertension (and is good for your cat’s general health anyway).

Many vet practices run clinics especially for their senior cat clients (over 7 years of age). Cats receive regular check-ups including measuring their blood pressure and checking for the early signs of disease (including kidney disease and hyperthyroidism).

The International Society of Feline Medicine (ISFM) recommend the following blood pressure checks:

• Yearly for healthy cats between 7 — 10 years of age
• Every 6 — 12 months for healthy cats over 11 years of age.
• At least every 3 — 6 months for cats with kidney disease, hypertension, or other issues that could increase their blood pressure.

Your veterinary team can tell you more about what they offer and how they can best help your cat during their twilight years.

What’s the outlook for cats with hypertension?

This is tricky to answer as it very much depends on whether your cat has any underlying diseases and if so, how well their symptoms are controlled. It also depends whether your cat already has any irreversible damage as a result of hypertension.

For most cats, medication and regular checks can effectively keep their hypertension in check while allowing them to enjoy their well-deserved retirement.