Abstract 106: Collateral Circulation in Thrombectomy for Stroke Beyond 6 Hours: Dawn Collaterals

Background: Collaterals govern the pace and severity of cerebral ischemia, distinguishing fast or slow progressors and corresponding therapeutic opportunities. The fate of sustained collateral perfusion or collateral failure is poorly characterized without arterial revascularization. We characterized the nature and impact of collaterals in the late time window for thrombectomy established in DAWN. Methods: The DAWN Imaging Core Lab prospectively scored collateral grade on baseline CTA and DSA (endovascular arm only), blinded to all other data. CTA collaterals were graded with the Tan scale and DSA collaterals were scored by ASITN grade. Descriptive statistics characterized CTA collateral grade in all DAWN subjects and DSA collaterals in the endovascular arm. The relationship between collateral grade and day 90 outcomes was separately analyzed for each treatment arm. Results: Collateral circulation to the ischemic territory was evaluated on CTA (n=144; median 2, 0-3) and DSA (n=57; median 2, 1-4) before thrombectomy in 161 DAWN subjects (mean age 69.8 ± 13.6 years; 55.3% women; 91 endovascular therapy, 70 control). CTA revealed a broad range of collaterals (grade 3=100%, n=64; 2=50-99%, n=45; 1=0-49%, n=31; 0=0%, n=4). DSA also showed a diverse range of collateral grades (grade 4, n=4; 3, n=22; 2, n=27; 1, n=4). Across treatment arms, baseline demographics, clinical variables except AF (41.6% endovascular vs. 25.0%, p=0.04) and CTA collateral grades were balanced. More robust CTA collateral grade was linked with lower baseline NIHSS (r=-0.25; p=0.003), smaller core infarct volumes (r=-0.36, p Conclusions: DAWN subjects enrolled at 6-24 hours after onset with small infarct cores had a wide range of collateral grades on both CTA and DSA. In this late time window, better collaterals manifest milder stroke severity at baseline, smaller infarct cores and better clinical outcomes.