Accuracy, calibration and clinical performance of the new EuroSCORE II risk stratification system

The European System for Cardiac Operative Risk Evaluation (EuroSCORE) has been used for many years since its introduction in 1999. Recently, a new EuroSCORE (EuroSCORE II) has been developed to update the previous version. The EuroSCORE II includes some different predictors and/or introduces a new classification of the already existing predictors. This study presents a validation series for the EuroSCORE II compared with the previous additive and the logistic EuroSCORE and with the Age, Creatinine and Ejection Fraction (ACEF) score. A total of 1090 consecutive adult patients operated on at our institution from September 2010 to October 2011 were admitted to this retrospective study. All the patients received a risk stratification based on the EuroSCORE II and the other scores considered. Accuracy, calibration and clinical performance of the various risk models were assessed. The accuracy of the EuroSCORE II was good (c-statistic 0.81) but not significantly higher than the other scores (range 0.78-0.8). Calibration at the Hosmer-Lemeshow statistic was good for all the scores; the difference between observed (3.75%) and predicted mortality in the overall population was not significant for the EuroSCORE II (3.1%) and the ACEF score (3.4%), whereas the additive EuroSCORE (5.8%) and the logistic EuroSCORE (7.3%) significantly overestimated the risk. In patients at low, mild moderate and high mortality risk, the EuroSCORE II provided a risk prediction not significantly different from the observed mortality rate, whereas in very high-risk patients (observed mortality rate 11%), it significantly underestimated (6.5%) the mortality risk. The accuracy of the EuroSCORE II was acceptable in isolated coronary surgery, and good or excellent in the other operations. The EuroSCORE II represents a useful update of the previous EuroSCORE version, with a much better clinical performance and the same good level of accuracy. It is possible that for the risk stratification of very high-risk patients, other factors (rare but associated with a mortality rate > 50%) should be included in the future models.