The role of modern endovascular treatment has been extensively studied for anterior circulation strokes, leading to clear guidelines outlining the management in this patient group. This is not the case for posterior circulation strokes, which have been excluded from the pivotal endovascular stroke trials. Therefore, the authors aimed to characterize the predictors of successful recanalization and outcomes of endovascular therapy for posterior circulation stroke patients.
Consecutive large vessel posterior circulation stroke patients who underwent endovascular treatment (thrombectomy, aspiration or both) within 24 hours at 8 centers within the USA between March 2012 and July 2015 were included. Patients with large brainstem strokes were excluded although no parameters to estimate the extent of infarct were provided. Imaging modality choice depended on each center’s acute stroke imaging protocol and local investigators were in charge of its analysis. Successful recanalization and functional outcomes were defined as a Thrombolysis in Cerebral Infarction (TICI) score of 2b-3 and a Modified Rankin Score (mRS) of 0-2, respectively.
A total of 100 patients were included in the analysis after 2 individuals who achieved successful recanalization with local intra-arterial thrombolysis alone, were excluded. The population baseline characteristics were similar to those seen in anterior circulation stroke trials, except for a male predominance (67%), higher mean admission NIHSS score (19.2), higher rate of general anesthesia (60%), and low rate of t-PA administration (32%). The occlusion sites in order of frequency were the Basilar artery (including top of the Basilar), Posterior Cerebral artery and Vertebral artery. Interestingly, the symptom onset to groin puncture time was 562 +/- 466 minutes but successful recanalization was still achieved in 80% of cases (58% with stent retrievers and 42% with aspiration devices). Adverse events including symptomatic ICH and mortality were seen in 5% and 30% of cases, respectively. Indeed, only 35% of patients had a favorable outcome at 3 months, a number that is similar to that achieved in the control group of some of the landmark endovascular trials (E.g. SWIFT PRIME). When looking into the univariate analysis of predictors of favorable versus poor clinical outcomes, the authors found that lower baseline NIHSS scores, shorter symptom-onset-to-groin-puncture, higher percentage of t-PA administration and successful recanalization rate, were overrepresented in those with favorable outcomes at 3 months. Lesser general anesthesia administration showed a trend towards better outcomes. However, the multivariate analysis revealed that only successful recanalization and shorter treatment times (symptom-onset-to-groin-puncture and symptom-onset-to-recanalization) were the only independent predictors of good functional outcomes at 3 months. The rate of favorable clinical outcomes was inversely correlated to the symptom-onset-to-groin-puncture time in a multivariate analysis that included only patients who achieved successful recanalization alone (not significant when looking at the entire population). Additionally, the initiation of endovascular therapy within 6 hours from symptom onset increased the likelihood of favorable clinical outcomes by two-fold in this population. The type of recanalization strategy (stent retriever versus aspiration) did not impact the clinical outcomes or the recanalization rates.
Overall, this paper illustrates the early stages of endovascular acute stroke therapy for posterior circulation stroke patients. Time to treatment, particularly within the first 6 hours, appears to be a strong predictor of favorable clinical outcomes, a concept that has been well described in anterior circulation strokes. In addition to this, both endovascular techniques (stent retrievers or aspiration devices) appear to be effective in achieving successful recanalization in this population. However, readers should be cautions when interpreting the results derived from this paper considering its retrospective design, the non-randomized nature of patient selection, the heterogeneity of acute stroke care protocols and imaging interpretation and modalities in different centers, the small sample size and the lack of Bonferroni correction for the subgroup analyses. The time for prospective randomized trials investigating endovascular therapy for posterior circulation stroke patients has come!