What are the causes of stroke?

Ischaemic strokes occur when the blood supply to the brain is heavily reduced or blocked. This is often caused by a blood clot. Any clot that forms in the body can get carried by the bloodstream until it lodges in the brain.

Blood clots can arise in different ways:

  • in blood vessels anywhere in the body (caused by atherosclerosis)
  • in the chambers of the heart (e.g. as a result of atrial fibrillation).

Your medical history and your medical condition will determine the type of blood clot that is more likely to form. The type of clot will determine the type of anti-clotting medicine (antiplatelet or anticoagulant) you receive.

Blood clots due to atherosclerosis

Ischaemic strokes are often caused by blockages in major blood vessels near the heart and neck (e.g. in the carotid arteries) due to atherosclerosis.

Atherosclerosis is a disease of the blood vessels caused by cholesterol deposits (called plaques) that build up and line the artery walls. The fatty plaques themselves can cause an ischaemic stroke by narrowing the inside of the arteries and reducing blood flow to the brain. Atherosclerosis also increases the risk of a heart attack by restricting blood flow to the heart.

Certain types of blood cells (platelets) can stick to the plaques to form a blood clot. If the clots are big enough they can block the supply of blood and oxygen to the brain. The plaques can also break off and travel in the blood stream to lodge in the brain.

Blood clots that form in blood vessels are usually treated with antiplatelet medicines.

Find out more about the symptoms of a stroke, the medicines that are used to prevent and treat a stroke and what you can do to prevent a stroke.

Blood clots that form in the heart

A stroke can also be caused by a blood clot that forms in the heart. This happens when blood flow through the heart chambers is slowed down, causing the blood to pool and form a clot. These blood clots can lead to stroke if they travel to the brain in the blood stream. This can happen in people with an irregular heartbeat (atrial fibrillation), or who have artificial heart valves.

This type of blood clot (fibrin-based) is usually treated with anticoagulant medicines such as warfarin.

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