Most strokes are caused by a blood clot travelling to the circulation in the brain and blocking an artery, thereby starving brain tissue of its normal blood supply and causing tissue to die. This is called an ischaemic stroke. The clot-busting drug rtPA can restore blood flow by dissolving the clot causing the blockage, in a procedure known as thrombolysis. If given within a few hours of stroke onset, rtPA improves the chances of recovery to being able to live independently, but in many people treatment does not succeed in opening the blocked blood vessel. In particular, as few as 10% of blockages in some large arteries in the brain are opened successfully by thrombolysis with rtPA. These large artery blockages cause the most severe strokes, which are very likely to result in death or dependence.
An alternative approach to their treatment is to use a clot removal device (mechanical thrombectomy): this involves feeding a long tube through the circulation to reach the blockage and trying to break up or pull out the clot, for which various different designs of device are available. This is a specialist procedure that requires considerable resources – a trained specialist (interventional neuroradiologist), special hospital facilities that are not widely available, and a support team. While these devices have a very good success rate at opening arteries, the additional time that it takes to organise and complete the procedure means that much of the damage to the brain may already have occurred by the time the blood flow is restored and there may therefore not be much benefit to patients. PISTE will be the pilot phase of a trial that will compare the outcomes in people with stroke caused by a blockage in a large artery who are treated with standard thrombolysis with rtPA against those who are randomly allocated to also proceed to a mechanical thrombectomy with a clot removal device.
Large artery strokes leave a high proportion of people dead or severely disabled. If mechanical clot-removal devices are able to significantly improve on the rates of opening the arteries that the current drug treatments can achieve, it may be possible to avoid these very bad outcomes in the group of patients with the most severe strokes.