Abstract Body: Introduction
Patients with acute ischemic stroke due to large vessel occlusion (AIS-LVO) and small ischemic cores have the most favorable outcomes after thrombectomy. Core growth and growth rate during transfer from a primary stroke center (PSC) to a comprehensive stroke center (CSC) may hinder outcomes. The effect of the CCC's combined arterial, tissue, and venous outflow on core growth remains unclear. We determined if poor CCC profiles before transfer to a CSC predict ischemic core growth in AIS-LVO.

Methods
AIS-LVO patients in the prospective CRISP2 study with a CT angiogram (CTA) and CT perfusion (CTP) at a PSC and a follow-up CTP or Diffusion-weighted imaging(DWI) after transfer to the CSC were screened for enrollment. CCC was determined on CTA collaterals using the TAN scale(favorable: Tan 2-3), tissue level collaterals on CTP using the hypoperfusion intensity ratio (HIR [Tmax >10s/Tmax>6s volume]; favorable HIR≤0.5), and venous outflow on CTA (favorable cortical venous opacification score 3-6). Patients were grouped into favorable CCC (CCC+; favorable scores at all three levels), unfavorable CCC (CCC-; unfavorable scores at all three levels), or CCCmixed(mixed scores at the levels). Ischemic core was determined on CTP at the PSC and pre-thrombectomy DWI-MRI or CTP at the CSC. Ischemic core growth was assessed using a voxel-based method following co-registration between the PSC and CSC images. The primary outcomes were ischemic core growth volume and rate.

Results
The study included 175 patients; 24.6% were CCC+, 8% were CCC-, and 67.4% were CCCmixed. No differences in baseline demographic or clinical characteristics were found between the groups. CCC- patients had larger baseline ischemic core volumes (median 17.1 ml [IQR: 10.5-56.3]; P<0.001) and penumbra volume (median 115.5 ml [IQR: 62-158;P<0.001). CCC- experienced a higher core growth rate (median 17.9 ml/h [IQR: 10-27.1] vs 2.4 ml/h [IQR: 0.3-7.1] in CCC+, and 3.3 ml/hr [IQR: 0.6-7]; P<0.001) and core growth (median 41.9 ml [IQR: 25.6-64.6] vs 6 ml [IQR:1.2-15.8] in CCC+ and 11.1 mL [IQR:2-25.8]; P<0.001). On regression analysis, CCC- and baseline ischemic core were independently associated with core growth, 95% CI,0.79-3.61, and growth rate, 95% CI,0.48-3.65.

Conclusions
In AIS-LVO patients, CCC- before transfer to a CSC is associated with more core growth and faster growth rates. These results have implications for neuroprotection trial design and informing triage decisions at PSC.