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

Objectives: 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.

Methods: 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.

Results: 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.

Conclusions: 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.