Weekly and yearly rhythms in plasma fibrinogen in hospitalized male military veterans

The variation in plasma fibrinogen level demonstrating prominent circaseptan and circannual cycles is clinically relevant. There is a correlation between increasing level of fibrinogen and other hemostatic factors and risk of myocardial infarction and sudden death.24 The circaseptan and circannual cycles in fibrinogen concentration described in this study may help to explain further the variation in frequency of coronary events. Furthermore, the recent demonstration of a circadian pattern in the efficacy of tissue plasminogen activator,25 with peak efficacy occurring at 2000 hours—10 hours after the peak incidence of myocardial infarction—implies that further patterns to coronary artery syndromes may be predicted and the treatment efficacy may rely on demonstrated circaseptan and circannual cycles of these events.