Rachel Forman, MD
I was happy to see that although the ESO-WSO 2020 annual meeting was postponed, we still had the opportunity to virtually hear the results of some recent large clinical trials. One of the five trials presented was the Basilar Artery International Collaboration Study (BASICS) presented by Dr. Wouter Schonewille from The Netherlands. Posterior circulation occlusions have been largely excluded from the main endovascular randomized control trials, so these results were highly anticipated.
Many of us are familiar with the devastating effects of a basilar artery occlusion (BAO), and from a personal experience, some of these cases have been very challenging without having the guidance of large trials as we do with anterior circulation occlusions. The clinical presentations, stroke severity, and collateral patterns are inherently different. This trial was an international, multicenter, controlled trial with randomized treatment-group assignments investigating the efficacy and safety of endovascular therapy (EVT) plus best medical management (BMM) versus BMM alone <6 hours of estimated time of BAO. Patients were randomly assigned (1:1 ratio) to EVT+BMM or BMM alone and stratified according to: randomizing center, use of IVT, and NIHSS (<20 vs >20). The enrollment period was from 2011 through 2019. Patients were excluded with intracranial hemorrhage, extensive brainstem ischemia, or cerebellar mass effect/acute hydrocephalus. The calculated sample size was 300 patients assuming favorable outcome in 46% with EVT+BMM and 30% with BMM. Primary outcome was mRS <3 at 90 days. Secondary outcome measures included clinical outcomes (mRS 0-2 at 90 days and mRS distribution) and imaging outcomes (posterior circulation ASPECTS score at 24 hours and basilar artery patency at 24 hours).
300 patients were randomized (154 received EVT+BMM and 146 BMM alone). No patients were lost to follow up. 3 patients in the EVT+BMM group crossed over to BMM alone, and 7 patients in the BMM group crossed over to EVT+BMM. Patient demographics were similar between the two groups: median NIHSS was 21 and 22 and average age 66.8 and 67.1 (BMM+EVT and BMM only). Overall, medical history among patients was similar between the two groups; however, history of atrial fibrillation was significantly higher in the BMM+EVT group (28.6% vs 15.1%). This is an important point to pause on, as the difference in clot morphology and the alternative stroke etiologies (i.e., intracranial atherosclerosis) can have varying effects as far as management and outcomes. The primary outcome (mRS <3) was 44.2% in the EVT+BMM group vs 37.7% in the BMM group, and this did not reach statistical significance [1.18 RR (0.92-1.50)]. Secondary clinical outcomes were also not significantly different. On subgroup analysis, stroke severity (NIHSS >10) was significantly in favor of EVT+BMM (not the case for NIHSS <10 that favored BMM). Additionally, patients who received IVT favored EVT+BMM on subgroup analysis. Safety outcomes (sICH at <3 days and 90 day mortality) did not differ between the two groups. One limitation of the study mentioned in the comments section during the presentation was that older EVT devices were used in some cases.
The concluding remarks were that there was a limited risk difference of 6.5% after EVT in BAO due to better than expected outcomes after BMM only and that the trial was underpowered to show a statistically significant benefit of EVT in patients treated <6 hours of estimated time of BAO. The authors’ takeaway was that EVT appears effective in patients with BAO and a moderate-severe deficit (NIHSS >10); however, BMM may be the best option in patients with milder symptoms.
I was curious to speak with our endovascular group at MGH and had the chance to discuss the trial presentation with Dr. Thabele (Bay) Leslie-Mazwi. He said he found the results interesting and added that “posterior circulation stroke is a diverse entity, much more so than anterior circulation stroke. The combination of highly variable collateral patterns and perforated territories, with the density of brainstem neurologic function, make this much less predictable. It also is important to determine etiology of stroke, as embolic phenomena are much more amenable to thrombectomy than atherothrombosis on intrinsic disease. It may be more challenging to apply blanket rules to the posterior circulation population as a result.” Another important point that he brought up was that the details of best medical management were not specified in this presentation (except that eligible patients received tPA) and that this remains to be clearly defined. Overall, this is really important work that can help guide treatment in an area with many unknowns.