Mohammad Anadani, MD

Zhu F, Lapergue B, Kyheng M, Blanc R, Labreuche J, Machaa MB, et al. Similar Outcomes for Contact Aspiration and Stent Retriever Use According to the Admission Clot Burden Score in ASTER. Stroke. 2018
Despite the overwhelming evidence supporting the benefit of mechanical thrombectomy in acute stroke treatment, the best thrombectomy technique is still unknown. The ASTER trial (Contact Aspiration Versus Stent Retriever for Successful Recanalization) was a prospective, multicenter, randomized trial that compared contact aspiration technique with stent retriever and showed no difference in the rate of successful recanalization and clinical outcome between two techniques. However, a question remained on what is the optimal approach for patients with large intracranial clot burden.
To address this question, Zhu and his colleagues underwent a post-hoc analysis of the ASTER trial comparing contact aspiration with stent retriever according to the intracranial clot burden. Clot burden was measured using the clot burden score (CBS). The CBS is a scoring system to measure the extent of anterior circulation thrombus and is scored on a scale from 0-10. A score of 10 indicates clot absence, and a score of 0 indicates complete multisegment vessel occlusion.

Of the 381 patients included in the ASTER trial, 231 had CBS assessed in core laboratory and included in the post-hoc analysis. A total of 114 patients had a CBS of 0-6, and 117 patients had a CBS of ³7. The former group were older, had a higher admission NIHSS, and a longer time from symptoms onset to groin puncture, higher incidence of diabetes mellitus and prior antithrombotic medications. Interestingly, the lower CBS group had a higher rate of favorable collaterals.
With respect to angiographic outcome, successful reperfusion (TICI³2B) achieved more in patients with CBS ³7 than patients with CBS<7 (88.9% vs. 81.6%). The difference remained significant after adjusting for potential confounders, with a fully adjusted risk ratio (RR) of 1.09 (95% confidence interval [CI] 1.01-1.28). Similarly, TICI 2C-3 was achieved more in patients with CBS³7 with an adjusted RR of 1.24 (95% CI, 1.01-1.54). There was no difference in first pass mTICI 2b/3, use of rescue therapy, groin to revascularization time, or procedural complications between two groups.
Concerning clinical outcome, 90-day favorable outcome (mRS 0-2) was achieved more often in the CBS³7 group with a fully adjusted RR, 1.19 (95% CI, 1.02-1.4). Similarly, excellent outcome was achieved more in the former group with fully adjusted RR, 1.92 (95% CI 1.52-2.43). There was no difference in mortality and rate hemorrhagic transformation.
The key finding of this study is that there was no difference in angiographic, clinical and safety outcomes between two first-line strategies (contact aspiration vs. stent retriever) when compared according to the CBS subgroups (0-6 and ³7).  In other words, both CA and SR were similarly effective first line strategies regardless of the clot burden.
The study has multiple limitations. The authors used MRA, in addition to CTA, to calculate the score, which questions the practicality of their findings since MRA is not widely available as emergent vessel imaging. Second, imaging of 105 patients were not assessed at a core laboratory, and patients were subsequently excluded, which raises concern of selection bias.
Two randomized trials (ASTER and COMPASS) have proven non-inferiority of contact aspiration when compared to stent retriever. Therefore, the choice of thrombectomy technique should be left up to the physician preference and experience. (Flipping your coin! Do you feel lucky?)
Future studies are needed to investigate the optimal approach for patients with posterior circulation large vessel occlusion, and anterior circulation distal vessel occlusion (M3 branch of middle cerebral artery, and anterior cerebral artery) since both groups were excluded from the above-mentioned randomized trials.