Circadian Rhythm and Risk of Hemorrhagic Transformation after Acute Ischemic Stroke Treated with Intravenous Thrombolysis - A Systematic Review.

Background: A circadian pattern for the onset of acute ischemic stroke (AIS) has been described, with a higher risk in the early morning and a lower risk during nighttime. However, data assessing the circadian distribution of hemorrhagic transformation after intravenous thrombolysis (ivT) are still incongruent.

Objectives: This review aimed to evaluate whether the time interval based on AIS onset or ivT time could influence the occurrence of intracranial hemorrhage (ICH) related to ivT and if the circadian rhythm of endogenous production of tissue plasminogen activator (t-PA) favors ICH occurrence.

Methods: We conducted a systematic review following the PRISMA guidelines, searching PubMed and Embase for articles in English using the keywords: 'stroke', 'thrombolysis', and 'circadian'. Articles investigating the AIS onset or ivT time effects on circadian variations of ICH in AIS adult patients treated with ivT were included. Based on ICH's incidence and odds ratio, time intervals associated with higher risk and time intervals associated with lower risk were defined. The Newcastle-Ottawa Scale was used to assess the risk of bias. The resulting data were reported in a qualitative narrative synthesis.

Results: From the 70 abstracts returned by electronic literature search, six studies with 33,365 patients fulfilled the inclusion criteria, out of which three were retrospective analysis studies, one case-control study, one prospective study, and one post hoc analysis of a multicentre trial. Some studies assessed the relationship between ICH occurrence and circadian rhythm depending on AIS onset time (n = 2), treatment time (n = 2), or both (n = 4). All studies investigated the patients' comorbidities as confounding variables for the circadian pattern of symptomatic ICH (sICH). Two studies found no association between AIS onset or ivT time and patient risk factors, but the other four found several differences and used multivariate logistic regression models to balance these covariates. The overall score of the Newcastle- Ottawa scale was 83.3%, which might be interpreted as overall high quality.

Conclusion: ICH occurred after ivT seems to follow a circadian pattern; the 18:00-00:00 time frame was the safest one, and patients with AIS onset or ivT time between these hours had the lowest incidence of any ICH, including sICH. The 06:00-12:00 block was associated with the highest incidence of ICH and sICH. However, the analysis is limited by the small number of included studies and the heterogeneous findings reported. Further homogenized studies using comparable time frames and sICH definitions are needed to demonstrate this circadian pattern. The review protocol was registered in the OSF database under reference UHNF, doi:10.17605/OSF.IO/UHNF6.