By Aquilla Turk
In the last year, five prospective randomised clinical trials have demonstrated the superiority of endovascular thrombectomy over medical management for the treatment of acute ischaemic stroke.1-5 These trials were positive largely because they addressed limitations learned from prior trials.6 Most importantly, these trials were successful because they each used angiographic imaging to rapidly identify large vessel occlusions and then proceeded to thrombectomy as quickly as possible. The technical maturation of stroke devices during this time period also played a significant role as safer and more effective treatments could be performed. While the majority of stroke thrombectomy data is centred on stent retrievers as the primary revascularisation device (as reflected by the new American Heart Association/American Stroke Association guidelines7), there is data demonstrating that an aspiration-first strategy is at least as effective as retrievable stents while being safer, faster and cheaper.
Aspiration is a long standing technique for revascularising occluded vessels.8,9 The challenge of this technique for acute ischaemic stroke has historically been limited by the lack of catheters large enough to provide adequate aspiration force to remove the thrombus yet flexible and soft enough to atraumatically navigate the cerebral vasculature. This shortcoming has been overcome and there are many companies with high-performance aspiration catheters available or in the process of development. Aspiration for treatment of acute ischaemic stroke is best exemplified with the ADAPT (A Direct Aspiration first Pass Technique) technique. This technique utilises aspiration as the first approach to revascularise the occluded vessel, and if this strategy fails, then the aspiration catheter is used in conjunction with a stent retriever to obtain revascularisation. Importantly, this technique is not a competitive strategy against stent-retrievers, instead is a simple strategy with aspiration that adds complexity with stent retrievers if necessary.
The simplicity of ADAPT belies the inherent safety of this approach. Navigating the catheter to a lesion is typically the easiest part of a neurovascular procedure. Attaching the aspiration catheter to a syringe or aspiration pump is all that is required to then perform the thrombectomy. With the catheter attached to the suction system, the catheter is advanced to the proximal end of the thrombus and then suction is initiated. Forward pressure is provided to ensure adequate apposition. The catheter is noted to be engaged with the thrombus when there is no backflow through the suction tubing. The thrombus is then either aspirated through the catheter, or becomes stuck at the catheter tip and the catheter is withdrawn back into the guide catheter. This technique does not require manipulation of the clot or to pass a catheter blindly through thrombus into non-visualised distal vasculature. As such, this technique minimises the importance of the downstream cerebral vasculature and mitigates potential risk from blindly accessing distal vasculature that could potentially harbour a dangerous lesion such as an aneurysm.10
The success of the aspiration procedure is therefore based on the performance of the aspiration catheter. Fortunately, there are now aspiration catheters available with inner lumen diameters up to 0.070 inches that can track over a microwire with the ease of navigating a microcatheter. This allows safe and rapid access to the occluded vessel segment. Improvements in catheter technology have resulted in decreasing procedure times to about 30–40 minutes on average,11 nearly half of that required with stent retrievers.12 The ability to complete the case with a single aspiration catheter also markedly reduces the cost of the case, as expensive devices such as a stent retriever to remove the thrombus are not usually required.12,13 This can often result in a procedure and hospitalisation being profitable for the hospital.
The ADAPT technique has been shown to be effective in opening cerebral vessel occlusions with aspiration alone in approximately 75% of cases. In those cases where aspiration was unable to open the vessel, the adjunctive use of a stent retriever improved the success to at least 95% successful revacularisation to TICI 2b or 3 level.11,12,14 The success of aspiration alone is dependent on using the largest calibre aspiration catheter that the vessel can accommodate. This allows the greatest amount of aspiration with a catheter approximating the diameter of the thrombus. Importantly, from safety and speed aspects, if aspiration does not work, then the large aspiration catheter can be used in conjunction with a stent retriever to open the vessel. This creates a safer procedure since the stent retriever is pulled into the aspiration catheter in the occluded vessel, reducing the risk of distal emboli to new territories and minimising traction on the cerebral vessels. Further, this strategy eliminates the need to track back through the carotid siphon if the retrievable stent fails to achieve revascularisation on the first pass and additional passes are needed.
The ADAPT technique based on aspiration as the primary treatment for mechanical thrombectomy for acute ischaemic stroke is at least as effective and safe as using a stent retriever while being faster and cheaper. The success and maturation of this technique relies on continued development of large and trackable aspiration catheters that can safely and easily track into the tortuous cerebral vasculature. The ability to start simply with aspiration and then add complexity with adjunctive devices such as stent retrievers in the few cases where aspiration does not work is the crux of the success of the ADAPT technique.
Aquilla S Turk is professor of Radiology and director of the Neurointerventional Division at the Medical University of South Carolina, USA
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