Arterial Ischaemic Stroke (AIS)
A stroke occurs when a clot in a major vessel blocks the flow of blood and oxygen to the brain, causing death of brain tissue if untreated. Stroke is often characterised by a patient’s sudden impairment of consciousness, inability to move one side of the body and limitation in speech. The centre of the brain injury is called the ischaemic core (dead brain tissue), and the larger surrounding brain injury is known as the penumbra (meaning shadow around the core). The ischaemic core is dead brain tissue which is unsalvageable, but the penumbra is ischaemic tissue (deprived of oxygen) which can potentially be recovered if the patient is treated quickly.
Current standard therapy relies on early intervention following stroke onset to restore blood flow to the brain by either chemically dissolving or physically removing the clot. Intravenous thrombolytic therapy (IVT) in the form of recombinant tissue plasminogen activator (alteplase or tenecteplase; rt-PA) can be administered within four and a half hours, aiming to dissolve the clot within the brain artery. This therapy is usually combined with endovascular thrombectomy (EVT) which aims to mechanically remove the clot and is ideally performed within 24 hours of the stroke. Brain imaging, using a computed tomography (CT) scan and/or magnetic resonance imaging (MRI) scan, is performed upon hospital admission for patients displaying symptoms of stroke. Physicians assess the loss of neurological functions using the modified Rankin Scale (mRS), which scores severity of disability. The location of the brain clot determines whether a stroke patient is eligible for IVT and EVT treatment, as well as having an impact on overall patient prognosis.
Globally, 15m patients suffer from a stroke annually, and over five and half million do not survive. Around 40% of AIS patients do not survive the first year, with most patients who do survive experience permanent life-long disability and further impairment of function over time due to brain tissue damage. As many as 50% of stroke survivors suffer disability and strokes are one of the most frequent causes of dementia. A quarter of stroke patients will experience another stroke within five years, with 12% of AIS patients being readmitted to hospital within 30 days of discharge.
Most patients require ongoing care and face limitations in their daily social activity, as well as significant rehabilitation costs and loss of earnings. Families often have to shoulder excessive rehabilitation costs and lost income. In the United States alone, recent estimates place the cost of stroke in excess of $34bn per year.
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