Blood flow to the brain can be slowed or completely stopped when a brain artery is blocked by a blood clot (embolus) that has travelled from the neck or the heart and lodged inside the brain. This in turn causes a lack of oxygen and nutrients (glucose deprivation) in the brain, which can lead to permanent damage to the brain within just a few minutes to hours, depending on the severity of the blockage. This is known as an ‘acute ischaemic stroke’ (AIS) and requires emergency medical attention.
When admitted to hospital with symptoms of AIS, a patient is assessed by a medical team to determine the severity of symptoms and how long the blockage has been present, usually taken as the ‘time since last seen normal’. If this is less than 4.5 hours, the standard treatment is a drug called rt-PA, a 'clot-buster' that breaks down the clot ('thrombolysis'). However, this is effective only in about 40% of the time, and if the blockage involves a large artery in the brain, endovascular clot retrieval (also known as 'ECR', or Mechanical Thrombectomy - 'MT') is the superior treatment and now standard of care. Studies have shown that this technique is effective in treating the condition in all stroke patients up to 6 hours after onset, and in a certain smaller proportion of stroke patients based on neuro-imaging up to 24 hours after onset.
ECR is a recently developed technique using an endovascular procedure performed through a small incision in the groin, where access into the femoral artery is gained with a plastic sheath. This procedure can be carried out under general anaesthesia, or with sedation and local anaesthesia. Through the femoral artery sheath, thin tubes ('catheters') are introduced and then manoeuvered through the arteries in the neck to the site of the clot in the brain under real time x-ray guidance. A smaller catheter (‘microcatheter’) is used to cross the clot, and then a 'stent retriever' - a small wire mesh cage - is passed through the microcatheter to capture the clot. The stent retriever is then removed while suction is applied through a larger catheter on the blood clot. The entire unit containing the clot, stent retriever and suction catheter is brought out of the insertion site in the groin. Once normal blood flow is restored in the previously blocked artery, the incision in the groin is closed.
After this procedure, a patient is generally kept in hospital for observation for at least 24 hours. ECR is effective in restoring blood flow in 80-95% of cases, particularly if the procedure is completed within 6 hours of the onset of the stroke. In 2015, ECR was shown in several large international randomized controlled trials to reduce severe disability or death by 50%, when performed within 6 hours. More recently in 2018, two new international trials (DAWN and DEFUSE-3) have demonstrated effectiveness of ECR up to 24 hours, depending on the patient’s blood flow circulation in the brain as seen on CT or MRI scans.