BACKGROUND: It remains unclear whether outcomes of patients treated with endovascular thrombectomy with large-vessel occlusion and unwitnessed onset of stroke differ from those with witnessed onset in the extended time window.

METHODS: We enrolled patients with anterior circulation large-vessel occlusion (internal carotid artery, M1, or M2 segment of the middle cerebral artery) undergoing endovascular thrombectomy within 6 to 24 hours from the time last seen well, from 2014 to 2022, at 66 sites in Europe, North America, and Asia. Patients with a prestroke modified Rankin Scale score of >3 or age <18 were excluded. We categorized patients by onset mode as witnessed or unwitnessed. The primary outcome was the modified Rankin Scale shift at 90 days. Secondary outcomes were functional independence, a composite of functional independence or return of Rankin to prestroke level, symptomatic intracranial hemorrhage, mortality, and a composite of severe disability or mortality at 90 days. We applied inverse probability of treatment weighting to compare outcomes between the groups.

RESULTS: Of 5098 patients assessed for eligibility, we included 2073, of whom 1760 (84.9%) had unwitnessed onset, and 313 (15.1%) were witnessed. In the univariate comparison (before inverse probability of treatment weighting), 38.8% of the unwitnessed and 45.7% of the witnessed patients achieved functional independence (P=0.022). Mortality was 21.6% among unwitnessed and 22.0% among witnessed (P=0.847), and symptomatic intracranial hemorrhage rates were 6.6% and 5.8%, respectively (P=0.623). The primary outcome (modified Rankin Scale shift) showed no difference comparing unwitnessed to witnessed patients (odds ratio, 1.35 [95% CI, 0.82-2.20]; P=0.235) in the inverse probability of treatment weighting. Unwitnessed patients were more likely to achieve functional independence or return of Rankin (1.53 [1.01-2.33]; P=0.045). Other secondary outcomes did not differ between the witnessed and unwitnessed patients.

CONCLUSIONS: In the extended time window, unwitnessed patients with large-vessel occlusion undergoing endovascular thrombectomy have at least the same likelihood of favorable outcomes as witnessed patients.

REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04096248.