Background The effectiveness and safety of endovascular thrombectomy (EVT) in the late window (6–24 hours) for acute ischemic stroke (AIS) patients selected without advanced imaging is undetermined. We aimed to assess clinical outcomes and the relationship with time-to-EVT treatment beyond 6 hours of stroke onset without advanced neuroimaging.

Methods Patients who underwent EVT selected with non-contrast CT/CT angiography (without CT perfusion or MR imaging), between October 2015 and March 2020, were included from a national stroke registry. Functional and safety outcomes were assessed in both early (<6 hours) and late windows with time analyzed as a continuous variable.

Results Among 3278 patients, 2610 (79.6%) and 668 (20.4%) patients were included in the early and late windows, respectively. In the late window, for every hour delay, there was no significant association with shift towards poorer functional outcome (modified Rankin Scale (mRS)) at discharge (adjusted common OR 0.98, 95% CI 0.94 to 1.01, p=0.27) or change in predicted functional independence (mRS ≤2) (24.5% to 23.3% from 6 to 24 hours; aOR 0.99, 95% CI0.94 to 1.04, p=0.85). In contrast, predicted functional independence was time sensitive in the early window: 5.2% reduction per-hour delay (49.4% to 23.5% from 1 to 6 hours, p=0.0001). There were similar rates of symptomatic intracranial hemorrhage (sICH) (3.4% vs 4.6%, p=0.54) and in-hospital mortality (12.9% vs 14.6%, p=0.33) in the early and late windows, respectively, without a significant association with time.

Conclusion In this real-world study, there was minimal change in functional disability, sICH and in-hospital mortality within and across the late window. While confirmatory randomized trials are needed, these findings suggest that EVT remains feasible and safe when performed in AIS patients selected without advanced neuroimaging between 6–24 hours from stroke onset.