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Background Aspiration thrombectomy (AT) is a widely adopted treatment for acute ischemic stroke with low complication rates. Traditional delivery of aspiration catheters relies on microcatheters and microwires. Their removal prior to active aspiration has been observed to incidentally promote clot engagement; however, the mechanical basis and clinical relevance of this interaction remain poorly understood. Recently developed internal delivery catheters (DCs), such as Tenzing (Route 92 Medical, San Mateo, CA), closely match the aspiration catheter lumen and appear to accentuate this effect, enabling quantification of the underlying mechanism.Methods A physiologic benchtop cerebrovascular model was used to measure vacuum pressures generated during DC withdrawal and assess their effect on clot interaction. Test configurations included three aspiration catheter sizes (0.054″, 0.070″, 0.088″) tested with and without a Tenzing DC using synthetic thrombi. Vacuum pressure data were synchronized with fluoroscopic imaging and correlated with clot engagement and ingestion outcomes.Results Tenzing DC withdrawal produced a brief but substantial negative pressure spike (0.45-1.81 s), reaching 52-97% of maximum syringe vacuum (−560 mmHg). This transient vacuum coincided with initial clot motion prior to active aspiration. Overall rates of successful clot capture were similar with and without DC use; however, DC-assisted trials showed a higher incidence of corked and fully ingested clots (p < 0.05).Conclusion Withdrawal of a closely size-matched DC generates a previously unquantified transient vacuum that initiates pre-aspiration clot engagement. This study identifies synthetic aperture aspiration as a mechanism creating a localized low-pressure field that may promote early clot mobilization and wall detachment prior to active suction. While DC withdrawal likely contributes to clot engagement, the primary value of a delivery catheter remains safe navigation and device delivery.Disclosures K. Han: None. J. Wells: None. K. Hakes: None. C. Rapoport: None. T. Stearns: None. C. Barton: None. A. Wintermantel: None. C. Ogilvy: None. M. Young: 2; C; Route 92.Abstract O-009 Table 1Comparative vacuum pressures from Tenzing removal vs. syringe vacuum at the catheter hubClot type/Cath SizeTenzing Vacuum Pressure (mmHg)Std. Dev.Catheter Vacuum Pressure (mmHg)Std. Dev.Percent DifferenceSoft 88-531.12.5-542.09.92.0%Soft 70-468.7115.6-546.83.815.4%Soft 54-529.1104.5-551.54.64.2%Hard 88-540.129.5-547.34.131.3%Hard 70-289.664.8-547.84.361.7%Hard 54-463.512.1-555.34.118.0%Abstract O-009 Figure 1