Background and purpose: Several studies have found a morning peak in onset of stroke. A similar peak has been suggested for subarachnoid hemorrhage (SAH), which seems in contradiction with the physical activities associated with aneurysmal rupture. Most studies included only a few patients with SAH. We analyzed time of onset of aneurysmal SAH in our patients and in data pooled from previous studies. We also studied time of onset in patients with perimesencephalic hemorrhage, which is believed to have a nonaneurysmal venous origin.
Methods: Of all 468 patients registered from 1989 through 1995, 385 fulfilled the criteria for aneurysmal SAH and 37 the criteria for perimesencephalic hemorrhage. Time of onset was categorized in 2-hour and 6-hour intervals. We did a Medline search to find previous studies on time of onset of SAH and pooled the data in 2-hour, 3-hour, and 6-hour intervals. Analysis of all intervals was performed by calculating rate ratios with 95% confidence intervals by means of Poisson methods.
Results: The risk of aneurysmal rupture was lower at night (from 12 PM to 6 AM) in our series and in the pooled-data series. Risk remained high throughout the day and evening, we found the same fluctuation in onset but without a nadir around noon.
Conclusions: The risk of aneurysmal SAH is low during the night and at noon and high during working hours. This circadian fluctuation parallels that of blood pressure and suggests that an increase in blood pressure is a risk factor for aneurysmal rupture.