Optimal Elective Treatment Threshold for Men with Asymptomatic Infrarenal Abdominal Aortic Aneurysms: A Monte Carlo Simulation Study.

OBJECTIVE: The optimal timing for elective infrarenal abdominal aortic aneurysm (AAA) repair in men remains uncertain, particularly among patients with varying comorbidities. A microsimulation model was used to evaluate how patient risk and aneurysm behaviour influence survival outcomes when repair is delayed or expedited. METHODS: This was a Monte Carlo simulation study. A ten year microsimulation compared elective endovascular aortic repair (EVAR) and open surgical repair (OSR) in men with an initial infrarenal AAA diameter of 55 mm. Eight scenarios were simulated: four risk groups by age, renal function, and chronic obstructive pulmonary disease, each for EVAR and OSR, with 10 000 patients per scenario. The model incorporated aneurysm growth, rupture risk, and baseline and peri-operative mortality, and evaluated treatment thresholds from 55 - 75 mm. The primary outcome was the diameter threshold minimising all cause mortality; the secondary outcome was maximising cumulative life years (CLYs). RESULTS: Optimal thresholds for minimising mortality were consistent across risk groups, ranging from 56 - 57 mm for EVAR and 55 - 57 mm for OSR. Thresholds maximising CLYs for EVAR remained stable between 55 mm and 57 mm. For OSR, thresholds increased with patient risk, ranging from 57 mm in low risk patients to 64 mm in high risk patients. In high risk patients undergoing OSR, treatment at 55 mm instead of at the CLY optimal threshold of 64 mm resulted in a loss of 2.1% of CLYs (95% confidence interval 1.7% gain to 5.8% loss). Sensitivity analyses demonstrated minimal impact of variation in out of hospital death, peri-operative death, rupture rates, and growth rates on mortality optimal thresholds, while CLY optimal thresholds, particularly for OSR, showed greater variability. CONCLUSION: Optimal elective AAA repair thresholds differ depending on the outcome prioritised. Mortality minimising thresholds were stable across risk groups, whereas CLY optimal thresholds varied substantially, particularly for OSR in high risk patients. Patient life expectancy emerged as the dominant determinant of optimal timing, supporting a more individualised, risk based approach to AAA management.