Circadian variation in ictus of aneurysmal subarachnoid hemorrhage

Background Temporal patterns in aneurysmal subarachnoid hemorrhage (aSAH) may provide insight into modulation, and therefore, prevention of hemorrhage. We investigated the time of hemorrhage and its relationship to traditional risk factors among patients admitted with aSAH. Methods Admitted patients with aSAH were prospectively followed through outcomes and baseline demographics were abstracted through chart review. The group temporal distribution by hour of onset was summarized with cosinor nonlinear least squares. aSAH onset was gathered into night (2300-0500), morning (0500-1100), afternoon (1100-1700), and evening (0500-2300) daily phases. The odds ratio (OR) with 95% CI was calculated for having an aSAH during the morning, afternoon, and evening hours using night as a reference. Multinomial logit models were fitted using aSAH cases across time blocks to determine their associations with different risk factors. Results 202 patients had the hour of hemorrhage available, and 49 had phase identifiable [total 251: 38 (15%) night, 98 (39%) morning, 58 (23%) afternoon, 57 (23%) evening]. The peak hours of aSAH were between 0700 and 0800 representing 13% of the sample, with a significant cosinor-fitted phase of 7.33(95% CI 5.30, 9.36). For all aSAH cases, morning onset was significantly more common than night onset (OR = 2.58, 95% CI = 1.77-3.75). Nonsmokers were more likely to have aSAH in the morning than smokers (P = 0.043, OR = 3.10, 95% CI = 1.33-7.23). Conclusions aSAH occur in a diurnal, morning prevalent pattern regardless of traditional aSAH risk factors. The association of these risk factors with existing onset patterns should be investigated in future studies.