New devices called stent retrievers, which effectively reverse strokes, have revolutionised the treatment of certain stroke patients, according to new US research.
“Stent retrievers are a major advance in acute ischaemic stroke care and will have significant impact on the evolution of stroke systems of care,” according to the article by Loyola Medicine neurologists Dr Rick Gill and Dr Michael J Schneck. Gill is the outgoing chief resident and Schneck is a professor in the department of neurology of Loyola University Chicago Stritch School of Medicine.
87% of strokes are ischaemic, meaning they are caused by clots that block blood flow to a portion of the brain. In selected patients, stent retrievers can be used to remove such clots. Loyola used stent retrievers on 34 patients in 2015, and 21 patients during the first six months of 2016.
A stent retriever is a self-expanding mesh tube attached to a wire, which is guided through a catheter (thin tube). The endovascular specialist inserts the catheter in an artery in the groin and guides the catheter through various blood vessels all the way up to the brain.
Once the stent retriever reaches the blockage, the endovascular specialist deploys it. The device pushes the gelatinous blood clot against the wall of the blood vessel, immediately restoring blood flow. The stent retriever then is used to grab the clot, which is pulled out when the surgeon removes the catheter.
“With the advent of stent retriever devices, there has been a paradigm shift in the utilisation of endovascular therapies for acute ischemic stroke,” Gill and Schneck write. (Endovascular refers to catheter-based surgery.)
Gill and Schneck describe how the current generation of stent retrievers, including the TREVO and Solitaire devices, are a remarkable improvement over earlier devices such as MERCI and Penumbra that employed different technology. Studies of these earlier devices showed results that were equivocal at best. But more recent trials of stent retrievers consistently show the newer devices are clearly superior to the intravenous drug tissue plasminogen activator (tPA) alone in reducing disability from strokes.
The clot-busting drug tPA can restore blood flow and limit stroke damage, if it is given within 4.5 hours of the onset of the stroke and the clot is small enough. (If the patient is older than 80, the cutoff time is three hours.) But in many patients, tPA either would not be safe to take, or would not be sufficient by itself to restore blood flow. In such patients, stent retrievers often can be used to remove the clot.
Gill and Schneck foresee future device improvements that will do an even better job of restoring blood flow and increasing the number of patients who could benefit.
Stent retrievers also will affect where stroke patients are treated. Paramedics will play an important role in routing higher severity stroke patients, who could benefit from stent retrievers, to centres that have the capability to perform neuro-endovascular procedures, Gill and Schneck write.
Introduction: Acute ischemic stroke (AIS) is one of the leading causes of mortality and adult disability worldwide. For two decades, the preferred approach for AIS was intravenous recombinant tissue plasminogen activator (IV tPA). However, IV tPA cannot be given to many AIS patients who do not meet strict criteria for its use. IV tPA has also had lesser benefit in patients with large clot burden in the context of large vessel occlusion (LVO).
Areas covered: Endovascular stroke therapy had been an ‘unproven’ therapy despite numerous trials of intra-arterial pharmacologic thrombolysis and mechanical thrombectomy. With the advent of stent-retriever devices, there has been a paradigm shift in the utilization of endovascular therapies for AIS. Our review discusses cerebrovascular hemodynamics, the basis of the recanalization models in AIS, aspects of intravenous thrombolysis, prior generations of endovascular therapy, and the recent successful AIS stent retriever trials.
Expert commentary: Recently ‘stent-retrievers’, a new generation of mechanical thrombectomy devices, were shown to be associated with improved functional outcomes in AIS secondary to proximal intracranial anterior circulation LVO. Stent retrievers are a major advance in AIS care and will have significant impact on the evolution of stroke systems of care.
Rick Gill, Michael J Schneck