Abstract Number: Esoc2026lb205 Technical Factors Influencing First Pass Effect in Mechanical Thrombectomy for Acute Ischemic Stroke: A Multicenter Prospective Observational Study.

Abstract Background and aims The first pass effect (FPE) is associated with improved clinical outcomes in large vessel occlusion (LVO) stroke treated by mechanical thrombectomy. However, the optimal technique to achieve FPE remains unclear, with no demonstrated superiority of direct aspiration (DA), stent retriever (SR), or combined technique (CT). This prospective study Methods We conducted a prospective multicenter study across 14 French centers between April and October 2024. Patients with acute ischemic stroke due to anterior circulation LVO (terminal internal carotid artery or M1 segment of the middle cerebral artery) were included. Clinical, procedural, and follow-up data were collected to compare thrombectomy strategies. The primary endpoint was successful reperfusion (final mTICI ≥2b). All patients were enrolled in the prospective French ETIS registry. Results A total of 248 patients were included: 138 (56%) treated with DA, 5 (2%) with SR, and 105 (42%) with CT. Mean age was 72 years, 42.5% were men, and median baseline NIHSS was 17 (12–20), with no significant differences between groups. No thrombectomy strategy was superior in achieving FPE (DA 54.5%, CT 42.9%, SR 2.6%; p=0.64). FPE was more frequent when the aspiration catheter was blocked against the clot (p=0.047) and when the microcatheter was withdrawn before aspiration (p=0.022). FPE was associated with lower rates of symptomatic intracranial hemorrhage (p=0.004) and better 3-month functional outcome (p=0.017). Conclusions Technical factors such as microcatheter withdrawal and effective catheter–clot interaction appear to enhance FPE. Larger studies are warranted to further optimize thrombectomy techniques. Conflict of interest