The Impact of Inter-Hospital Transfer before Endovascular Thrombectomy on Long-Term Outcomes after Acute Ischemic Stroke

BACKGROUND: The impact of inter-hospital transfer before endovascular thrombectomy (EVT) on short-term outcomes has been reported, but its effect on long-term outcomes remains unclear. We examined long-term clinical outcomes after EVT, stratified by whether patients underwent inter-hospital transfer. METHODS: We conducted a population-based cohort study using linked administrative data from Ontario, Canada (2017-2023). We included all community-dwelling residents hospitalized with acute ischemic stroke who received EVT. Inter-hospital transfer was defined as any transfer from a non-comprehensive stroke center (CSC) to a CSC before EVT. The primary outcome was all-cause mortality at maximum follow-up, assessed using propensity score-weighted hazard ratios. RESULTS: Of 68523 ischemic stroke patients, 5394 (7.9%) underwent EVT, with 42.9% transferred before EVT. Direct-to-CSC patients were older, had higher rates of atrial fibrillation and dyslipidemia and were more likely to reside in urban areas. Propensity score-weighted analysis comparing transferred versus direct-to-CSC patients showed no difference in all-cause mortality, but the hazard ratio varied over time, violating the proportional hazards assumption. Transfer was associated with higher early mortality than direct-to-CSC, which declined over time, with mortality lower after 6.3 months, remaining below 1 over prolonged follow-up out to 34.6 months. Transferred patients were more likely to be admitted to long-term care (aHR 1.17, 95% CI: 1.03-1.33), but there was no significant difference in recurrent stroke. CONCLUSIONS: Nearly half of EVT patients underwent inter-hospital transfer, which showed a time-varying association with all-cause mortality, with early risk that attenuated after 6.3 months and reversed over time.