Stroke

What happens when blood supply to the brain fails, how to recognise a stroke fast (BE-FAST), why 'time is brain', clot-busting drugs and clot retrieval, recovery and prevention.

A stroke occurs when the blood supply to part of the brain is interrupted. Stroke is among the leading causes of death and the leading causes of disability worldwide.

Two main kinds

Ischaemic stroke (about 85% of strokes in many countries) is caused by a blockage — a clot forming in a brain artery, or travelling from elsewhere, often the heart (for instance in atrial fibrillation) or the neck arteries. Haemorrhagic stroke is caused by bleeding, either into the brain tissue or into the space around it (subarachnoid haemorrhage, often from an aneurysm). A transient ischaemic attack (TIA), or "mini-stroke", causes temporary symptoms that resolve; it is a serious warning sign.

Recognise it fast

Public campaigns use FAST — Face drooping, Arm weakness, Speech difficulty, Time to call emergency services — sometimes extended to BE-FAST by adding sudden loss of Balance and Eyesight problems. Other symptoms include sudden numbness on one side, confusion, or a sudden, severe headache. Note the time symptoms started — treatment decisions depend on it.

Time is brain

A widely cited 2006 estimate by Jeffrey Saver suggested that during a typical large ischaemic stroke, around 1.9 million neurons die every minute it goes untreated. Around the dying core is a region, the penumbra, that can be saved if blood flow returns quickly.

Treatment

For ischaemic stroke, clot-dissolving drugs (thrombolysis, such as alteplase or tenecteplase) can be given within a window of a few hours after onset. Since a series of landmark trials published in 2015, mechanical thrombectomy — threading a catheter from the groin or wrist to the brain and pulling the clot out — has transformed outcomes for strokes caused by large-vessel blockages, and can sometimes be done many hours after onset if scans show salvageable tissue. Haemorrhagic strokes are treated by controlling blood pressure, reversing blood thinners and sometimes surgery.

Recovery and prevention

Recovery depends on rehabilitation that harnesses neuroplasticity; the greatest gains usually come in the first months. Most strokes are linked to modifiable risk factors: high blood pressure (the biggest), smoking, diabetes, high cholesterol, atrial fibrillation, physical inactivity and diet.