Abstract
Introduction: Circadian rhythms have recently been shown to influence stroke incidence and progression of infarct. We aimed to describe the diurnal variations in the incidence and perfusion profiles of patients with ischemic stroke using a large, multi-center, automated imaging database. Methods: The RAPID Insights database was queried from 02/01/2016 to 01/31/2022 for patients with perfusion imaging and automated detection of an ischemic stroke due to a presumed large vessel occlusion. Exclusion criteria included: patient age ≤25, mismatch volume of <0 cc, and failure to register a positive value on either cerebral blood flow (CBF) reduction of 38% less than normal or total mismatch volume. Imaging time was subdivided into three epochs: Night: 23:00h-06:59h and Day: 07:00h-14:59h, and Evening: 15:00h-22:59h. Perfusion parameters were defined as the following: core volume was defined as CBF of <30% of normal, penumbra was defined as a Tmax delay of >6 seconds minus core volume, and collateral circulation was estimated with the Hypoperfusion Intensity Ratio (HIR = [Tmax>10s]/[Tmax>6s]), where a higher HIR suggests poorer collateral status. All perfusion parameters were analyzed on a 24-hour continuous cycle. Statistical significance was tested using a sinusoidal regression analysis. Results: A total of 18,137 cases were analyzed. The peak incidence of ischemic stroke occurred around noon. A sinusoidal pattern was present, with larger ischemic core volumes and higher HIR during the night compared to the day: peak ischemic core volume of 23.40 cc occurred with imaging performed at 3:56 AM (p<0.001) and peak HIR of 0.35 at 3:40 AM (p<0.001). Conclusion: We found that ischemic core volumes were larger and collateral status worse at nighttime compared to daytime in this large national database. These findings support the notion that poor collateral recruitment with subsequent larger ischemic stroke volumes may occur at night. Fig 1. Logarithmic values of ischemic core volumes and hypoperfusion intensity ratios (HIR) are plotted against a 24-hour cycle, demonstrating a sinusoidal pattern for both.
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