External Validation of the Society of Thoracic Surgeons Ascending Aorta and Aortic Root Surgery Risk Calculator in a French Cohort

Objective To externally validate the Society of Thoracic Surgeons Ascending Aorta and Aortic Root Surgery Risk Model (STS AAARS) in a French cohort and compare operative-mortality performance with the European System for Cardiac Operative Risk Evaluation II (EuroSCORE II). Methods We conducted an external validation in consecutive adults undergoing nonemergent proximal aortic surgery from 2008 through 2026. Patient-level predictions were obtained from the official online STS calculator. The primary outcome was operative mortality. Calibration was assessed using observed-to-expected ratios, calibration-in-the-large, calibration slope, and flexible calibration curves; discrimination was assessed using the area under the receiver-operating characteristic curve. Results Among 781 patients, 10 operative deaths occurred (1.3%) versus 0.89% predicted by STS AAARS (observed-to-expected ratio, 1.44; 95% confidence interval, 0.69-2.64), whereas EuroSCORE II predicted 3.55% (observed-to-expected ratio, 0.36). Among 779 patients with both scores, areas under the curve were 0.786 (0.662-0.893) and 0.710 (0.518-0.890), respectively (P=.364). For the morbidity/mortality composite, the observed-to-expected ratio was 1.50 and the area under the curve was 0.603. Ratios were 0.75 for stroke, 3.00 for renal failure, 1.57 for reoperation, 0.69 for prolonged ventilation, 1.12 for long stay, and 0.10 for short stay. Conclusions The STS AAARS showed close operative-mortality calibration and substantially closer agreement with observed mortality than EuroSCORE II. Performance varied across secondary endpoints, supporting endpoint-specific interpretation and further European validation before benchmarking.