Ischaemic stroke

An ischaemic stroke happens when a blockage cuts off the blood supply to the brain. You may also hear it referred to as a clot.

What is an ischaemic stroke?

Around 85% of strokes are ischaemic. About 15% of strokes are due to bleeding in or around the brain, known as haemorrhagic stroke.

In ischaemic stroke, the blockage can be caused by a blood clot forming in an artery leading to the brain, or within one of the small vessels deep inside the brain. 

What is a stroke?

A stroke is a brain attack. It happens when the blood supply to part of your brain is cut off, killing brain cells. Damage to brain cells can affect how the body works. It can also change how someone thinks and feels. Read more about the different types of stroke. And find out how to spot the signs of a stroke or transient ischaemic attack (TIA or mini-stroke). 

What causes an ischaemic stroke?

There are a number of reasons why blockages can form and cause an ischaemic stroke.


Atherosclerosis occurs when fatty deposits build up on the inside walls of your arteries. These deposits are called plaques or atheromas.

They cause your arteries to become harder and narrower, making them more likely to become blocked. The narrowing of your arteries is called stenosis.

Our arteries naturally become thicker
and less flexible as we get older, but atherosclerosis can speed this process up.

Lifestyle factors like smoking, lack of exercise and eating unhealthy food, as well as certain medical conditions, such as high blood pressure, high cholesterol or diabetes, can lead to atherosclerosis.

Atheromas can build up in any artery, especially the ones in your neck leading to your brain. As well as narrowing the artery, making it harder for blood to pass through it, the fatty deposits can break down or become inflamed. When this happens a blood clot forms around the atheroma, which can block the artery. It may break off and move through the bloodstream, causing a blockage to an artery in the brain.

Small vessel disease

Small vessel disease damages the tiny blood vessels deep inside the brain. This reduces blood flow, which means brain cells are
not getting the oxygen and nutrients they need. A brain scan might show small scars in the white matter, which can be linked with thinking and mobility problems.

Small vessel disease can cause a stroke, or several very small strokes. Over time, small vessel disease can lead to a type of dementia called vascular dementia. High blood pressure is a major risk factor for small vessel disease.

Heart conditions

Atrial fibrillation

Some conditions can cause blood clots to form in your heart, which can then move through your bloodstream up into your brain. This is called an embolism.

The most common condition to cause this is atrial fibrillation or AF (a type of irregular heartbeat). Some people with atrial fibrillation can feel their heart beating irregularly, but many cannot. AF can come and go at intervals. A GP can check for AF, and refer you for tests if AF is suspected.

Other heart conditions, such as a recent heart attack or a mechanical heart valve, can cause embolisms too.

Patent foramen ovale (PFO)

‘Foramen ovale’ is the name of the hole between the right and left side of the heart of a baby in the womb. This hole normally closes after birth, but in as many as one in four people it remains open or ‘patent’.

A PFO is sometimes referred to as a ‘hole in the heart’.

Having a PFO can be a risk for stroke, if a blood clot forms in the heart and passes from one side of the heart to the other and up to the brain.

In children, surgery can be used to close the PFO. If an adult has a stroke and a PFO is thought to be the most likely cause, treatment options include blood thinning medication to reduce the risk of clots, or surgery to close the PFO. Your doctor will talk to you about the best treatment for you.

Arterial dissection

Sometimes tears in the lining of an artery can develop and allow blood to get between the layers in your artery walls. This is called arterial dissection. It can happen for no clear reason or it can be the result of an injury.

As blood builds up a clot can form. If this clot restricts the flow of blood to your brain, or moves up into your brain, it can cause a stroke.

How is an ischaemic stroke diagnosed and treated?


If someone has any signs of a stroke, it’s time to call 999. Click here for information about the signs of stroke.

Ambulance paramedics are trained in stroke, and will assess the person and take them to the right type of hospital for the treatment they need.

This could be a hospital with a specialist stroke unit or a hyper-acute stroke unit (HASU).
A stroke unit has an inter-disciplinary team of trained professionals who are experienced in stroke care.

The quicker your stroke is diagnosed and treated, the better your chances of recovery. Once you’re admitted to hospital, you will have tests and checks to confirm if you have had a stroke, and what type of stroke it is.

Brain scan

If you have a suspected stroke, you should receive a brain scan, within one hour if possible. A brain scan can help doctors decide on the right treatment for you if are:

  • Eligible for an urgent clot-busting alteplase injection (thrombolysis).
  • Eligible for mechanical clot removal (thrombectomy).
  • Taking blood-thinning medication.
  • Thought to have bleeding in or around
  • your brain.

You will either have a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan. Both of these produce pictures of your brain and will help doctors to rule out other causes of your symptoms and see how much of your brain has been affected. It will also help them decide how best to treat you, as treatments are different depending on the cause of your stroke.

Sometimes these scans will involve an injection to highlight the arteries of the neck and brain more clearly, known as computed tomography angiography (CTA) or magnetic resonance angiography (MRA).

Other checks and tests

Your blood pressure is checked, and you will have blood tests for health conditions linked to stroke, such as diabetes and high cholesterol.

You may have other tests to check for conditions that could have contributed to your stroke. These include an electrocardiogram (ECG), which checks for an irregular heartbeat, or a Doppler ultrasound scan to check for narrowing of the arteries in your neck.

Ischaemic stroke treatment


Around 12% of people with an ischaemic stroke are eligible for clot-busting treatment, known as thrombolysis.

Thrombolysis uses medication to break up a clot that is blocking the blood supply to your brain. It needs to be given within four and
a half hours of stroke symptoms starting. In some circumstances your doctor may decide that it could still be of benefit beyond four and a half hours.

Who can have thrombolysis?

Not everyone who has an ischaemic stroke is suitable for thrombolysis. A scan can tell doctors if you had an ischaemic stroke, and they then assess whether thrombolysis is possible for you.

If you are not suitable, it may be because:

  • Your stroke was not caused by a clot.

  • You do not know or cannot tell doctors when your symptoms began.

  • You do not reach the hospital within the time limits for receiving thrombolysis (within three hours but can be up to four and a half hours for some individuals).

  • You have a bleeding disorder.

  • You have recently had brain surgery.

  • You have had another stroke or head injury within the past three months.

  • Your current medication is not compatible with alteplase.

  • If you are suitable for thrombolysis, your medical team will explain the treatment to you. You do not have to sign any paperwork – a verbal agreement is enough. If you are unable to give your consent, either because of the effects of your stroke or another reason, the medical team will seek permission from your next of kin or another family member.

Time is critical so if it isn’t immediately possible to talk to your family, the medical staff will make the decision based on what they feel is in your best interests.

Thrombolysis uses a drug called alteplase, or recombinant tissue plasminogen activator (rt-PA). You are given alteplase through a small tube into a vein in your arm. During this procedure, which takes around one hour, the medical team will closely monitor your blood pressure, body temperature, breathing and blood sugar levels to ensure that they remain stable.

Risks and benefits

After thrombolysis, 10% more patients recover with no significant disability. Despite its benefits, there is a risk that thrombolysis can cause bleeding in the brain. Within seven days of having thrombolysis, about one in 25 people treated will have bleeding in the brain, and this can be fatal in about one in 40 cases.

Doctors carefully balance the risk to the patient against the potential benefit of the treatment. So someone may not be eligible for thrombolysis if they have conditions like internal bleeding or head injury, an aneurysm or uncontrolled high blood pressure.


Thrombectomy involves extracting the blood clot using a clot retrieval device. This is done by inserting a mesh device into an artery in your groin, moving it up to your brain, and pulling the blood clot out.

This process can be used for strokes where the blood clot is in a large artery, in roughly 10% of people with ischaemic stroke. It is usually carried out as soon as possible after the stroke and within six hours at the latest. However it can be done up to 24 hours after the stroke, if doctors think it will benefit the person.

Thrombectomy is a relatively new procedure, and is gradually becoming more available in stroke units across the UK.

What happens if the clot is not treated?

If left untreated, the blood clot will usually break up naturally within a few days or weeks. You will have treatment to reduce your risk of another stroke, such as medications to prevent clots forming and reduce blood pressure. If you are being looked after on a specialist stroke unit, the expert care you will receive can support your recovery.


In a very small number of cases an operation may be needed to relieve pressure on your brain. When the brain is injured the tissues can swell, just like a bruise. If there is a lot of swelling, there is a danger that it will put increased pressure onto other areas of your brain, causing further damage. If this is the case you will need a procedure called a decompressive hemicraniectomy. This involves opening up a section of your skull to allow the brain to swell outwards and relieve some of the pressure. This can only be carried out in neurosurgery centres so people often have to move hospital for this treatment.

Preventing another clot

Most people who have an ischaemic stroke will be given anti-platelet medication, which helps to prevent clots from forming. For most people this will be a daily dose of aspirin, and doctors will advise you how long you will need to take this.

If you receive thrombolysis, you have to wait at least 24 hours before you can begin taking aspirin. If aspirin is not suitable for you, you may be given an alternative drug, such as clopidogrel.

In the longer term, you will be prescribed blood-thinning medication to take indefinitely. For most people, this will be an anti-platelet medication, but for others such as those with atrial fibrillation, it will be an anticoagulant such as warfarin, apixaban, dabigatran, edoxaban or rivaroxaban.