Changes in temperature affect the risk of abdominal aortic aneurysm rupture

Background: There is a well-established link between exposure to hot and cold temperatures and an increased risk of cardiovascular hospitalization or death. There is also contrasting evidence of a seasonal increase in aortic ruptures related to atmospheric pressure, but an association with environmental temperature has never been formally modelled. Methods: Using a prospective database, we identified 295 patients who were operated in a single centre for ruptured abdominal aortic aneurysm in south-east Queensland between 1990 and 2010. We matched patients to their nearest weather station to estimate their exposure to temperature and air pressure in the days leading up to their rupture. We used the case-crossover method to estimate the risks of temperature, which we allowed to be non-linear (increased risks at high and low temperatures) and delayed by up to 25 days. Results: There was an immediate increase in risk after exposure to cold, and a delayed risk after exposure to heat. An increased risk after exposure to high pressures disappeared after adjusting for temperature. At a mean temperature of 19°C (66°F), the odds ratio for rupture was 1.73 (95% confidence interval: 1.09, 2.76) compared with the reference temperature of 24°C. Conclusion: This is the first study to demonstrate an association between temperature and risk of aortic aneurysm rupture in the Southern Hemisphere. The physiological changes caused by thermoregulation may be a trigger for those people with a fragile aneurysm.