Dr. Jonathan CORTESE
Interventional and Diagnostic Neuroradiologist
AP HP Bicêtre Hospital
A new era
Over the past decade, a lot has changed in thrombectomy techniques since the early results of using the Merci device. Strategies and devices have both multiplied so that physicians can be confused before approaching a case. Dr. Jonathan Cortese searched the literature for evidence regarding the potential superiority of any strategy in different clinical situations.
A successful recanalization with TICI 2b, 2c or 3 at the end of a procedure is paramount to achieving a good outcome (mRS≤2). Moreover, it has been demonstrated that the first pass effect (successful recanalization after the first passage) is a strong independent predictor of a good outcome.1 Thus, the last decade has seen many innovations in devices used for thrombectomies in order to improve the rate of successful recanalization.
The stent-retriever: a faithful companion
The two main possible types of devices for thrombectomies are the stent retriever or the aspiration catheter. In the first positive randomized controlled trials for mechanical thrombectomy in acute ischemic occlusions with large vessel occlusions, a majority used the stent retriever as the first-line device: primarily the Solitaire stent (Medtronic, Irvine, California, USA) or the Trevo stent (Stryker, Fremont, California, USA).
Today, there are multiple new generation stent retrievers available on the market, such as the ERIC stent (MicroVention, Aliso Viejo, CA, USA), the EmboTrap II stent (Cerenovus - Johnson & Johnson, New Brunswick, NJ, USA), the Tigertriever stent (Rapid Medical, Yoqneam, Israel), and so on. They bring with them new designs which offer more landing zone to trap the clot as well as different lengths, diameters and geometries. Very promising results have been reported in a recently published post-market series for the Embotrap II (95.7% TICI ≥ 2b recanalization [82.3% with EmboTrap II alone]; 35.7% first pass efficacy),2 and the Tigertriever (94% TICI ≥ 2b recanalization [74% with Tigertriever alone]; 24% first pass efficacy).3
Aspiration for those in a hurry
The competitive strategy of a direct aspiration first pass technique (ADAPT) was described in 2014 by Turk et al.4 The latest results showed that the ADAPT technique has a successful revascularization rate of 78%.5 However, the ASTER study with the Ace 64 catheter (Penumbra Inc, Alameda, CA, USA) did not find any difference between direct aspiration versus stent retriever in terms of recanalization and outcome.6 The COMPASS trial confirmed the non-inferiority of the ADAPT technique compared to using a stent retriever.7
The advantages of the ADAPT strategy are to be found elsewhere: mostly a faster procedure (faster recanalization). Large-bore catheters allow mechanical thrombectomy by engaging and retrieving clots with or without additional devices. Therefore, to improve the recanalization rates, catheters with larger inner diameter have appeared on the market: Sofia 6 Fr (MicroVention, Aliso Viejo, CA, USA), Catalyst 6 and 7 (Stryker Neurovascular, Fremont, California, USA), JET 7 (Penumbra, Alameda, CA, USA), Millipede 088 (Perfuze, Galway, Ireland) and so on.
Interesting results were published using these aspiration catheters such as the Sofia plus (96.5% TICI ≥ 2b recanalization [64.7% with Sofia alone] or the AXS Catalyst 6 (84.1% TICI ≥ 2b recanalization [76.6% with Catalyst alone]).8,9
Keep calm and combine
It goes without saying that combining both strategies to try to improve the revascularization rates, such as in the “Solumbra” or “ARTS” techniques, is obvious. Two randomized controlled studies were conducted to test this hypothesis. First, the 3D stent retriever combined with aspiration study proved the non-inferiority in terms of revascularization rate of the combined strategy (with a 3D stent retriever) compared to aspiration alone.
Second, the ASTER2 trial compared the combination strategy to using a stent retriever alone. The study failed to prove the superiority of the combination strategy in terms of revascularization (p=0.17). However, a higher rate of successful reperfusion was achieved in the contact aspiration combined with stent retriever group vs the stent retriever alone group (TICI ≥2b, 86.2% vs 72.3%, p<0.001) with the initial assigned strategy. Also, a higher rate of first pass effect was found in the combined strategy, but without reaching statistical significance (53.7% vs 44.6%, p=0.056).
Soon we will have the results of the AdaptatiVe Endovascular strategy to the CloT MRI in large intracranial vessel Occlusion (VECTOR) trial.10 This trial also compared a first-line strategy combining the Embotrap device added to contact aspiration versus contact aspiration alone, but here it was employed in patients selected with susceptibility vessel sign occlusions identified in MRI (which is correlated with red thrombi).
Master the flow
Finally, the last “weapon” we should consider is combining a balloon guide catheter (BGC) with a stent retriever or/and distal aspiration. The latest balloon guiding catheters are the FlowGate 2 (Stryker Neurovascular, Fremont, CA, USA), the Walrus (Q’Apel Medical, Fremont, CA, USA), the Cello (Medtronic Neurovascular, Irvine, CA, USA) and the Emboguard (Cerenovus - Johnson & Johnson, New Brunswick, NJ, USA). Here, the main objective is to avoid distal clot migration by temporarily stopping (or reversing if aspiration is used) the proximal arterial flow. It is also very likely to improve the retrieval effect.
In a non-controlled study by the ETIS registry, it was found that the BGC did not improve the revascularization rate or patient outcomes in a matched controlled with propensity score study.11 However, a systematic literature review and meta-analysis of five non-randomized studies and 2 recent studies from a prospective registry demonstrated that using BGC could improve the first pass effect, revascularization rate and/or patient outcomes.12–14
Choose wisely and adjust
When faced with an acute ischemic stroke with a large vessel occlusion, there are many techniques and devices available to achieve our goal of revascularization – and with new and larger aspiration catheters and more efficient retrievable stents being developed every day, this is unlikely to change… Which is a good thing!
We can tailor our treatment to the disease, the clot type and the patient in front of us. However, it is essential that we maintain a high standard of care with a standardized evaluation based on randomized controlled trials and prospective registries. Only then will we truly know what the best strategies are for treating our patients.