Time to Endovascular Treatment and Clinical Outcome in Acute Ischemic Stroke With M2-Segment Occlusion

Background: In large vessel occlusion (LVO) stroke, shorter time from stroke onset to endovascular thrombectomy (EVT), and faster recanalization in the early window (<6 hours from last seen well) are associated with better outcomes. This association is less well known for patients with M2 occlusions. Methods: We conducted a pooled analysis of the MR CLEAN (Multicenter Randomized Clinical Trial of Endovascular Treatment of Acute Ischemic Stroke in the Netherlands) MED and NO-IV trials and analyzed the effect of time delay in EVT-treated LVO (grouped as intracranial internal carotid artery (ICA), ICA-Terminus, or M1-segment) and M2 occlusion patients with known stroke onset times. The primary outcome was the ordinal 90-day modified Rankin Scale score. Secondary outcomes included 90-day functional independence (modified Rankin Scale score 0-2) and mortality. Results: We included 94 patients with M2 occlusions and 423 with LVOs. In LVOs, longer times between stroke onset to start of EVT or to successful recanalization were associated with worse functional outcomes (adjusted common odds ratio [acOR], 0.92 [ 95% CI, 0.87-0.98] and acOR, 0.91 [95% CI, 0.86-0.95] per 15 minutes, respectively). Every 15-minute delay to start of EVT reduced the probability of functional independence by 2.3%. For M2 occlusions, no significant association was found between time to EVT or successful recanalization and functional outcome (acOR, 1.09 [95% CI, 0.97-1.22] and acOR, 1.04 [95% CI, 0.92-1.19] per 15 minutes). Patients with LVOs showed a significant 0.7% increased probability of 90-day mortality per 15-minute delay in the start of EVT, whereas patients with M2 occlusions showed no significant association. Conclusions: Treatment delays worsen functional outcomes in patients with LVOs. However, this was not shown in patients with M2 occlusions, suggesting that outcomes after EVT for patients with M2 occlusions in the early window depend less on time to treatment.