Abstract WP100: Elevated Hypoperfusion Intensity Ratio (HIR) Observed In Patients With A Large Vessel Occlusion (LVO) Presenting In The Evening

Abstract

Introduction: Circadian variability has been implicated in timing of stroke onset, yet the impact of circadian rhythm on stroke evolution is not known. We aimed to describe this relationship in patients with large vessel occlusion (LVO) with perfusion imaging. Methods: A retrospective observational study was conducted from (1) prospective registries of two stroke centers with systematic use of perfusion imaging and (2) two thrombectomy trials where enrollment was not based on perfusion imaging results. Included patients had stroke due to ICA, M1 or M2 occlusion and baseline perfusion imaging performed within 24h from last-seen-well (LSW). Stroke onset was examined in 8hrs intervals: (1) Night: 23:00-6:59, (2) Day: 7:00-14:59, (3) Evening: 15:00-22:59. Core volume was estimated on CT perfusion (rCBF <30%) or DWI (ADC <620) and the collateral circulation was estimated with the hypoperfusion intensity ratio (HIR = [Tmax>10s]/[Tmax>6s]). Non-parametric testing was conducted using SPSS to account for the non-normalized dependent variables. Results: A total of 1098 cases were included (mean age 69 years, SD 15.5). Median NIHSS, core volumes, and HIR were 16 (IQR 9-21), 18mL (IQR 5-50), and 0.4 (IQR 0.3-0.6) respectively. Most strokes occurred during the Day (n=490, 44.6%), compared to Night (n=242, 22.0%), and evening (n=366, 33.3%). HIR was highest, indicating worse collaterals, in the Evening (p=0.005). Controlling for age and time to scanner, Evening strokes (Figure 1) had significantly elevated HIR compared to Night (p = 0.016) and Day (p = 0.038). Similarly, the largest core volumes were observed in the Evening (p = 0.023) compared to Day. Conclusion: Our retrospective analysis suggests that HIR is significantly higher in the evening, indicating poorer collateral activation which may account for the larger core volumes observed at this time-point.