Circadian Variation in the Rupture of Abdominal Aortic Aneurysms

Abstract

Circadian variations in the incidence of myocardial infarction, sudden death, and stroke have been attributed to diurnal fluctuations in catecholamine release, blood pressure, heart rate, fibrinolytic activity, and platelet aggregation. As similar factors could precipitate the rupture of an abdominal aortic aneurysm, a retrospective chart review was undertaken in an effort to define the timing of aneurysm rupture and any associated circadian variation. One hundred forty-three patients with a ruptured abdominal aortic aneurysm (rAAA) and a documented time of presentation were evaluated. Eighty-one patients (56.7%) presented within 2 hours of the onset of symptoms and were examined for diurnal variability in their presentation. The hourly rate of rAAA presentation between 8 AM and 10 PM (4.3 per hour) was more than twice that observed during the night (2.1 per hour, p<0.001). The distribution of presentation times among this group was significantly different from uniform (p=0.05), implying circadian variability to aneurysm rupture. The time-dependent rate of rAAA presentation could be predicted (R2=0.77) with cosinor regression methods, although this model was not statistically significant (F= 4.9, p >0.10). Abdominal aortic aneurysm rupture occurs with a diurnal variation having a peak during waking hours. The relationship of aneurysm rupture to known physiological circadian rhythms may give further insight into the underlying pathophysiology and has implications for patient management.