Risk models for contemporary isolated coronary artery bypass grafting: comparison of EuroSCORE I, EuroSCORE II and AusSCORE

Purpose: EuroSCORE had been the most widely used risk model for predicting outcomes after cardiac surgery for over a decade, but recent studies have found the score to over-estimate operative mortality. The revised EuroSCORE II and AusSCORE, based on an Australasian population, were recently developed. We compared the prognostic utility of EuroSCORE I, EuroSCORE II and AusSCORE for coronary artery bypass grafting (CABG). Methods: EuroSCORE I, EuroSCORE II and AusSCORE were retrospective calculated for patients undergoing isolated CABG during July 2010-June 2012. Their discriminative ability and calibration for outcomes were assessed. Results: 818 patients were followed-up for 1.4±0.6 years. Mortality at 30 days, follow-up and composite surgical morbidity were 1.6% (13), 2.9% (24) and 17.8% (146). Mean EuroSCORE I, EuroSCORE II and AusSCORE were 4.5±5.0%, 2.6±3.1% and 0.9±1.3%. C-statistic of these scores for 30-day mortality were 0.675 (0.531-0.819), 0.642 (0.503-0.780) and 0.661 (0.516-0.807) respectively. Hosmer-Lemeshow test p-values were 0.061, 0.150 and 0.420 respectively. C-statistics of mortality at follow-up were 0.639 (0.525-0.752), 0.604 (0.483-0.752) and 0.593 (0.480-0.705); and composite surgical morbidity 0.678 (0.631-0.726), 0.634 (0.582-0.686) and 0.645 (0.593-0.698). EuroSCORE I was best model at detecting stroke (c=0.736) and ventilation>24 hours (c=0.712), and EuroSCORE II at detecting deep sternal wound infection (c=0.720) and return to theatre (c=0.626). Conclusion: Apart from slightly improved calibrations, the newer EuroSCORE II and AusSCORE were not superior to EuroSCORE I at discriminating outcomes after CABG. Revision of risk models to fit contemporary surgical outcomes is important, but there may only be modest room for improvement in discrimination.