Stroke

The study does suggest, however, that score remains a strong predictor of clinical outcome.

A higher clot burden score (CBS) is associated with poorer outcomes among patients with acute ischemic stroke who undergo mechanical thrombectomy, according to a post-hoc analysis of the ASTER trial published online recently in Stroke. As in the main trial, however, outcomes did not differ based on whether patients were treated with direct aspiration or stent retriever thrombectomy.

“With the advent of new mechanical thrombectomy techniques such as contact aspiration, MT approaches have diversified, which raises the question of the optimal endovascular strategy for a large intracranial clot burden,” lead author François Zhu, MD, (University Hospital of Nancy, France) told Neurovascular Exchange in an email. So far, he pointed out, no study has directly compared direct aspiration with stent retriever thrombectomy as a factor of intracranial thrombus extent.

For the ASTER trial, 381 patients with acute ischemic stroke were randomized to first-line endovascular treatment using contact aspiration or stent retriever thrombectomy. No differences in efficacy or safety were seen between the two groups, as assessed by 24-hour change in NIHSS, 90-day mRS, and rate of adverse events.

“The ASTER trial showed that both stent retriever thrombectomy and primary aspiration (termed "contact aspiration" in ASTER) were equally effective in achieving recanalization,” commented Maxim Mokin, MD, PhD (University of South Florida, Tampa). “The question remained whether, for small or large clots, one type of treatment would be preferable [over] the other.”

This post-hoc analysis involved the 231 patients from ASTER for whom CBS was available. Overall, 114 had a clot burden score of 0-6 and 117 had a score ≥ 7 at admission. The investigators looked at whether treatment modality affected outcomes as a factor of CBS score.

After calculating multiple imputations and adjusting for center, first-line strategy, intravenous thrombolysis, age, direct admission, diabetes, current smoking, previous use of antithrombotic medications, admission NIHSS, favorable collaterals, and time from onset to groin puncture, successful reperfusion at the end of the procedure and a favorable outcome were achieved more frequently among patients with a CBS ≥ 7.

Outcomes by Clot Burden Score

There were no angiographic or clinical outcome differences between the two groups of patients with regard to first-line mechanical thrombectomy strategy (i.e., aspiration vs stent retriever). There also was no significant interaction between first-line mechanical thrombectomy strategy and CBS group regarding safety.

“This study showed that both contact aspiration and primary stent retriever thrombectomy achieve similar recanalization rates regardless of clot size/burden,” said Mokin, adding that it provides additional “evidence confirming that the primary aspiration approach to thrombectomy is at least equally effective as stent retriever thrombectomy. This is important because the landmark randomized trials mainly utilized stent retrievers, so there was a lot of hesitancy from some neurointerventional doctors to accept aspiration as a legitimate treatment strategy.”

Confirms Importance of CBS

“Our study confirmed that the admission CBS is a reliable prognostic indicator, associated with reperfusion efficiency and 90-day favorable clinical outcome after MT,” said Zhu. Given the lack of difference in outcomes by treatment modality, however, it provides no specific guidance with regard to which approach operators should use.

CBS for use as an objective measure of clot burden is increasingly being recognized as an important variable in clinical trials, Zhu added. He noted that while it is not used in routine clinical practice in his center, it is included in their multicenter registry database.

Mokin pointed out that while most operators still rely on clot length to determine clot burden, CBS is superior because it also takes into account the location of the occluded segment(s).

Zhu noted some important limitations of the study, including the dichotomization of the CBS rather than using it as a continuous variable, and the fact that CBS assessment depends on the susceptibility vessel sign, which is not universally present. “In another ancillary study of the ASTER trial, the absence of SVS and thus CBS was noted in 29.2% of cases. This raises the question of the [accurate] estimation of the thrombus burden on MRI for [some types of] clots, probably ‘white’ clots,” he noted.

In addition, “CBS is assessed [on CT angiography] by the lack of opacification of the middle cerebral artery occlusion, by anterograde and retrograde flow,” he continued. “The latter depend on collateral circulation statement and are not homogenous [across] patients.”

These findings, said Zhu, highlight the need for further randomized trials. “We all are impatiently waiting the ASTER 2 results,” he concluded. That trial is evaluating outcomes of combined contact aspiration and stent retriever thrombectomy.

Source:

Zhu F, Lapergue B, Kyheng M, et al. Similar outcomes for contact aspiration and stent retriever use according to the admission clot burden score in ASTER. Stroke. 2018;Epub ahead of print.

Disclosures:

Zhu reports no relevant conflicts of interest.

Mokin reports being a speaker for Penumbra, Inc.