Simulations of the effects of scheduled abdominal aortic aneurysm repair on survival.

I simulated survival with and without scheduled repair of abdominal aortic aneurysms with different diameters in different populations. The results imply that scheduled repair should be determined by the combination of a patient's monthly mortality hazard and aneurysm diameter. The median survival of some patients will be extended by the scheduled repair of aneurysms smaller than 55 mm, whereas the median survival of other patients will be curtailed by repair of any aneurysm. The results also suggest that, on average, surveillance is futile: the effect of scheduled aneurysm repair on an individual's median survival did not change but the cohort effect diminished as patients died during surveillance. The results of the U.K. Small Aneurysm Study were reproduced in simulation and are compatible with the repair of aneurysms smaller than 55 mm diameter. Epidemiological simulations suggest that past randomised controlled trials underestimate the effect of aneurysm repair today.