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?

An ischaemic stroke happens when a blockage cuts off the blood supply to part of your brain, killing brain cells. Damage to brain cells can affect how the body works. It can also change how you think and feel.

It’s the most common type of stroke, and around 85% of strokes in the UK are ischaemic strokes. The other 15% of strokes are due to bleeding in or around the brain, known as haemorrhagic stroke.

What causes an ischaemic stroke?

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

Atherosclerosis (narrowed arteries)

Atherosclerosis is where fatty deposits build up on the inside walls of the blood vessels carrying blood away from the heart (arteries). These deposits are called plaques or atheromas. Atheromas can build up in the large arteries in your neck leading to the brain, making them narrower and stiffer.

Atheromas can break down or become inflamed. When this happens a clot forms around the atheroma, which can block the blood vessel. It may break off and move through the bloodstream into the brain, causing a stroke.

Some things can make you more likely to have a build-up of fatty materials in your blood vessels. These include:

  • Medical conditions including high blood pressure, high cholesterol and diabetes.
  • Lifestyle factors such as smoking and being overweight.

After a stroke, you should get advice about treating your medical conditions, and making healthy lifestyle changes.

Small vessel disease

Small vessel disease means having damage to the tiny blood vessels deep inside the brain. The blood vessels become narrowed which reduces blood flow, and makes a stroke more likely. It can also lead to many small strokes, as well as increasing the risk of bleeding in the brain.

Small vessel disease can be diagnosed on a brain scan, where it looks like scars in the brain structure. It can affect your thinking ability and your mood, and it’s linked to cognitive decline and dementia.

High blood pressure is a common cause of small vessel disease. If you have high blood pressure, you will be offered treatment and advice for healthy lifestyle changes you can make to reduce your blood pressure.

Heart conditions

Atrial fibrillation

Atrial fibrillation (AF) means your heartbeat is irregular and may be abnormally fast. Because the heart doesn’t empty itself of blood at each heartbeat, a clot can form in the blood left behind. If this clot travels through the bloodstream to the brain, it causes a stroke.

AF often has no symptoms, but it can cause palpitations (feeling as if your heart is racing or skipping a beat).

Patent foramen ovale (PFO)

All babies in the womb have an opening between the right and left side of their heart, known as the ‘foramen ovale’. This gap is needed while the baby is connected to the mother’s blood supply. After birth, the baby’s blood circulation changes, and this gap usually closes up.

However, in as many as one in four people, the gap stays open. This is known as a ‘patent’ (open) foramen ovale, or PFO. It’s sometimes referred to as a ‘hole in the heart’.

A PFO may be a risk for stroke if a blood clot forms in the heart and travels up to the brain. PFO does not always cause problems, and may not need to be treated.

In children, surgery is sometimes be used to close the PFO. If you have a stroke, you will be assessed to decide if a PFO could have been a reason for your stroke, and what treatment you need. 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

Arterial dissection is when the lining of an artery (a blood vessel leading away from the heart) gets torn. It can happen after an injury, but it can also happen with no obvious cause. Blood builds up in the damaged area, and 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 immediately.

Ambulance paramedics are trained in stroke. They 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. A stroke unit has an inter-disciplinary team of trained professionals who are experienced in stroke care.

The important thing when a stroke happens is time. The faster someone can get to a specialist stroke unit, the better their chances of reducing damage to the brain.

Once you’re admitted to hospital, you 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, a brain scan should be carried out urgently, and if possible within one hour. A brain scan can help doctors decide if you are suitable for an emergency treatment such as clot-busting treatment (thrombolysis) and mechanical clot removal (thrombectomy).

A computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan is used to produce pictures of your brain. Doctors use scans to rule out other causes of your symptoms, and see how much of your brain has been affected. It also helps them decide how best to treat you, as treatments are different depending on the cause and timing of your stroke.

Some types of scan involve an injection to highlight the blood vessels 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 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 blood vessels in your neck.

How is an ischaemic stroke treated?

The main treatments aiming to break up or remove clots from the brain are usually only available within a few hours of a stroke. But there is also a range of other types of care, including medication to reduce your blood pressure and reduce your risk of another stroke. You will be monitored for signs of complications and given any treatment you need. You will be assessed to find out how the stroke has affected you, and what help you need with your recovery.

The two ways of treating clots in the brain are:

  1. Thrombolysis (clot-busting medication)
  2. Thrombectomy (mechanical clot removal)

Thrombolysis (clot-busting treatment)

Thrombolysis uses a clot-busting medicine to break up clots in the brain. This helps to save more of the brain by allowing blood to return to the brain cells more quickly. Fewer brain cells die, and the impact of the stroke can be reduced.

Thrombolysis needs to be given within four and a half hours of stroke symptoms starting. In some circumstances doctors may decide that it could still be of benefit beyond four and a half hours.

Who can have thrombolysis?

This treatment is only suitable in around 12% of strokes, as there are guidelines for who can and can’t have it, to make sure it’s safe and effective.

To have thrombolysis, the person needs to reach hospital within the time limits for treatment (usually four and a half hours after symptoms begin). If they don’t know when symptoms began, perhaps because the stroke happened while they were asleep, this may rule out thrombolysis.

Other reasons why thrombolysis can’t be given include:

  • Your stroke was due to bleeding in the brain, not a clot.
  • Your stroke is very mild.
  • 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 the clot-busting medication (alteplase).

If you are able to have 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.

Risks and benefits

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 (clot removal)

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

Like thrombolysis, thrombectomy can help reduce brain damage by restoring blood flow in the brain. This means that fewer brain cells die, lowering the chance of serious disability.

This procedure can be given to around 10% of people with ischaemic stroke. It is only used when the clot is in a large blood vessel in the brain. It should be 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. It’s often used in combination with thrombolysis (clot-busting medication).

What happens if the clot is not treated?

Clot removal and clot-busting treatment are effective at reducing disability after stroke, but only around 10-15% of people are able to have them. These treatments are given on top of the standard stroke care, which includes tests, medication and therapy.

Without removal or clot-busting treatment, the blood clot usually breaks up naturally within a few days or weeks. You are assessed to find out how the stroke is affecting you. You will be supported to recover by specialist doctors, nurses and therapists working in a team to give you expert care. You will also be given treatments to reduce your risk of another stroke, such as blood thinning medications and pills for high blood pressure.

Surgery: decompressive hemicraniectomy

When the brain is injured the tissues can swell, just like a bruise. If there is a lot of swelling, it can put pressure on other areas of your brain, causing further damage.

In a very small number of cases an operation may be needed to relieve pressure on your brain. A decompressive hemicraniectomy involves opening up a section of your skull to allow the brain to swell outwards and relieve some of the pressure.

Treatments to reduce the risk of another stroke

Most people who have an ischaemic stroke will be given blood–thinning medication to help prevent clots from forming. For most people this will be a daily dose of aspirin followed by clopidogrel. If you receive thrombolysis, you normally have to wait at least 24 hours before you can begin taking aspirin.

Most people will need to take blood-thinning medication for life. There are two main types of blood-thinning medication, known as antiplatelets and anticoagulants. Many people need antiplatelets such as aspirin and clopidogrel.

People with heart conditions like atrial fibrillation are more likely to have an anticoagulant such apixaban, dabigatran, edoxaban, rivaroxaban or warfarin. Find out more about blood-thinning medications at

Surgery for narrowed arteries in the neck (carotid artery disease)

Around 15% of ischaemic strokes are due to narrowed arteries in the neck, known as carotid artery disease. This is diagnosed using specialist ultrasound scans of your neck. Carotid artery disease is due to atherosclerosis, the build-up of fatty materials in your arteries.

Carotid artery disease is sometimes treated using a surgical procedure. This means either removing the artery lining, or inserting a mesh cylinder (stent) to keep the artery open. You’ll be assessed to decide on the best treatment to help reduce your risk of a stroke, which might include medication instead of surgery

Information guides

Where to get help and information from the Stroke Association

Call us on 0303 3033 100,from a textphone 1800 0303 3033 100
Our Helpline offers information and support for anyone affected by stroke, including family, friends and carers.

Read our information
Call the Helpline to ask for printed copies of our guides.

Other sources of help and information

Atrial Fibrillation Association (AFA)
Phone: 01789 867 502
Provides information and support for people with atrial fibrillation.

Brain and Spine Foundation
Phone: 0808 808 1000
Provides information and support to people affected by neurological conditions including stroke. The helpline is run by neuroscience nurses.

Chest, Heart and Stroke Scotland
Phone: 0808 801 0899
Provides information on local stroke groups in Scotland. It also runs an advice line staffed by nurses.

Different Strokes
Phone: 0345 130 7172
Provides information and support for younger stroke survivors, including guides for survivors, their family and employers.

Phone: 0808 800 2244
A national charity supporting people with a brain injury. They have local groups and branches, which include rehabilitation programmes, carer support, social activities, community outreach and respite care.

Information on health.

Disclaimer: The Stroke Association provides the details of other organisations for information only. Inclusion on My Stroke Guide does not constitute a recommendation or endorsement.