The etiology of target large vessel occlusion (i.e., embolic or ICAS-related occlusion) was determined by core laboratory imaging analyses based on angiographic diagnosis according to previous reports (Y.H.H. & J.S.L.) [12 (link),14 (link),16 (link)]. In brief, after confirmation of arterial occlusion, uncommon cerebral arterial diseases such as dissection, moyamoya disease, and vasculitis were evaluated. If the occluded vessel was completely recanalized after primary thrombectomy, the etiology was classified as embolic occlusion (Embolic group). A remnant stenosis of >70%, or a lesser degree of stenosis with a tendency toward reocclusion and/or flow impairment during the procedure, was classified as ICAS-related occlusion (ICAS group). If grading was difficult to determine or discordant, consensus was reached by the two graders (Y.H.H and J.S.L). In addition, this mechanism was further evaluated and could be amended by repeat angiography following EVT during admission (J.S.Y.). Consequently, Embolic and ICAS groups were included in the analyses.