Passive Advancement of the Aspiration Catheter During Mechanical Thrombectomy is Independently Associated with Superior Recanalization Outcomes

Background Passive advancement--antegrade movement of the aspiration catheter upon inner delivery device withdrawal without active operator force--is a physical phenomenon observed during mechanical thrombectomy, with anecdotal reports of favorable recanalization outcomes. This study characterizes its prevalence and associations with recanalization. Methods Consecutive thrombectomy cases at two high-volume stroke centers (January 2019-December 2025) were retrospectively reviewed. Stored fluoroscopy and angiograms were assessed for passive advancement and final catheter tip position at arterial branch points. Per-pass and per-vessel mixed-effects multivariable regression identified independent associations with eTICI score, first-pass effect (FPE, eTICI [&ge;]2c-3), modified FPE (mFPE, eTICI [&ge;]2b-3), secondary occlusion, and complications. Results Of 1,824 passes in 995 consecutive patients (1,027 occlusions), 733 had imaging adequate for passive advancement assessment. Passive advancement occurred in 525/733 passes (71.6%), including to an arterial branch in 306/733 (41.7%). On per-pass analysis, passive advancement was associated with higher eTICI [&ge;]2b-3 (71.0% vs 19.7%) and eTICI [&ge;]2c-3 (57.5% vs 10.1%); advancement to a branch amplified these associations (90.5% vs 32.1% and 79.4% vs 18.7%; all p<0.001). Among 429 first passes, mFPE was 74.1% vs 10.8% and FPE 63.4% vs 7.5% with vs without passive advancement; rates reached 95.0% and 87.2%, respectively, at a branch point (all p<0.001). Passive advancement to a branch was inversely associated with secondary occlusion (13.3% vs 31.3%; p<0.001). On multivariable analysis, passive advancement independently predicted eTICI score, eTICI [&ge;]2b-3, and eTICI [&ge;]2c-3 (all p<0.001); final catheter position at a branch was the dominant independent predictor of FPE, mFPE, secondary occlusion, any complication, and intracranial complication on per-vessel analysis (all p[&le;]0.046). Conclusions Passive advancement is a prevalent physical phenomenon and an independent predictor of successful recanalization. When advancing to an arterial branch point, it is associated with mFPE >87%. Passive advancement should be a technical objective of aspiration thrombectomy.