So far, there is one randomized trial, which compared the safety and efficacy of MT plus standard medical therapy vs. standard medical therapy in patients suffering from posterior circulation strokes [16]. The BEST trial was terminated early due to a high cross-over rate. But despite the overall negative results, patients treated with MT achieved better outcomes. However, this stroke cohort is associated with the poorest outcome of all stroke subtypes, resulting in a morbidity and mortality rate up to 70% [17]. The multi-center ENDOSTROKE registry showed at least that the use of stent retriever is an independent predictor of recanalization in the posterior circulation, however, recanalization itself did not predict clinical outcome in this study [7]. In our study, we analyzed the performance of the SAVE technique based on our experience with this method for the anterior circulation [11]. Similar to our previous results, we observed SAVE to be an effective and safe thrombectomy method in patients suffering from LVO in the posterior circulation.
As the central requirement of MT is a fast recanalization of the occlusion with complete reperfusion of the affected territory, new devices and different strategies were developed during the last years. Promising techniques using large-bore aspiration catheters and/or new generation stent retrievers had shown promising results with high reperfusion rates, however, those techniques were mainly applied in the anterior circulation [18,19]. For the subgroup of posterior circulation strokes comparative analysis of different stroke techniques remain scarce. In our study, the final successful reperfusion rate (mTICI ≥2b) of 89% with SAVE is comparable to those of previous stent retriever series of 81% and 83% published in two meta-analysis of Gory et al. and Ye et al., respectively, [22,23] and the ENDOSTROKE registry, which reported a TICI 2b/3 rate of 79% [7]. Previous studies, which were not included in the meta-analyses showed successful reperfusion in 70% and 73% of cases, respectively [24,25]. A recent study in fact demonstrated aspiration only as the better first-line strategy for BAO patients compared to stent retriever for complete reperfusion with rates of 54% and 32%, respectively [6], and were comparable to 67% mTICI 3 results with SAVE in our study. However, another study did not show differences between aspiration only and stent retrieving with regard to complete reperfusion [23]. Unfortunately, a comparison of the first-pass results is not possible due to lack of such information in the aforementioned studies; however, first-pass reperfusion results with SAVE were promising with 56—67% (mTICI ≥2b/≥2c/3) and significantly higher compared to aspiration only, which led to a significant lower number of thrombectomy attempts with SAVE. However, it is to mention that the use of the mTICI score in the posterior circulation is not fully validated as demonstrated recently, which makes it more difficult to compare reperfusion results to those of anterior circulation strokes [26].
New aspiration catheters and aspiration pumps have been implemented with different results in achieving high and constant flows [20,21]. In our study, there might have been bias due to the use of aspiration pumps and vacuum pressure syringes (which were used at the beginning). As shown by Nikoubashman et al. the Penumbra aspiration pump might achieve significantly lower flow compared to sixty-milliliter VacLok vacuum pressure syringes, mostly due to the high resistance of the connecting tubing with diminished blood flow reversal (in the anterior circulation without balloon protection) [20].
Although the procedure times by using SAVE tended to be longer compared to aspiration only, no differences in clinical outcome at discharge were observed, which might possibly be explained by the better reperfusion results. However, as stated in the literature up to now [6], this study also did not show a technique’s clinical benefit towards a specific technique.
Effectiveness of proximal flow arrest/aspiration in the posterior circulation is matter of debateand limited to few cases27,28]. While in the anterior circulation the use of a balloon guide catheter with subsequent flow arrest is a predictor of first-pass success [29], in most of the patients with posterior stroke an antegrade flow in the basilar artery cannot be prevented due to maintained blood flow from the contralateral vertebral artery. Interestingly, in our cohort the rate of complete reperfusion was high, suggesting that loss of fragments during the retrieval maneuver is a rare phenomenon even when proximal aspiration is only applied in one of the feeding vertebral arteries. This emphasizes the meaning of distal protection by wedging the clot between stent retriever and aspiration catheter tip during the withdrawal as one major key element of SAVE. However, other factors such as contralateral low flow conditions due to vertebral artery aplasia or hypoplasia might also influence reperfusion success and were not considered in the analysis [30].
A limitation of our study is the retrospective design with the attendant selection bias. The small sample size limits the validity of the data. The observed differences between the techniques should be interpreted with caution as in our institute experience with SAVE is high compared to the aspiration only technique. The small sample size and missing evaluation of the aforementioned anatomic factors might prevent the conclusion that SAVE is more effective than aspiration. Clinical outcome after 90 days is missing; however, our intention was to focus on the angiographic results as complete reperfusion is a basic requirement for recovery of stroke patients. A prospective trial is warranted to demonstrate efficacy of SAVE for posterior circulation strokes.