Performance of the EuroSCORE II and the Society of Thoracic Surgeons Score in Patients Undergoing Aortic Valve Replacement for Aortic Stenosis

Aim:  The aim of this study was to evaluate the performance of the new European System for Cardiac Operative Risk Evaluation (EuroSCORE) II and the Society of Thoracic Surgeons (STS) score in patients undergoing aortic valve replacement (AVR) for aortic stenosis (AS). This study also evaluated the performance of the EuroSCORE II in high-risk patients.

Methods:  Three hundred and six consecutive adult patients underwent AVR with or without coronary artery bypass grafting at our institution from August 2002 to June 2012. The cut-off value of 6% for the EuroSCORE II and 10% for the STS score was used to identify high-risk in this study.

Results:  Operative mortality was 3.5% (N.=11). The mean expected mortality for all patients was 3.1% (O/E ratio=1.12) for the EuroSCORE II and 5.1% (O/E ratio=0.68) for the STS score. Observed versus expected mortality for the high-risk patients was 17.2% versus 11.9% (O/E ratio=1.44) for the EuroSCORE II (N.=29) and 19.3% versus 18.5% (O/E ratio=1.04) for the STS score (N.=31), and that for the low-risk was 2.1% versus 2.2% (O/E ratio=0.95) for the EuroSCORE II and 1.8% versus 3.5% (O/E ratio=0.51) for the STS score. Discrimination power of the STS score was good (area under the receiver operating characteristics curve [AUC] 0.74), but that of the EuroSCORE II was suboptimal (AUC 0.66).

Conclusion:  Good calibration ability of the EuroSCORE II for low-risk patients and that of the STS score for high-risk are observed. However, the EuroSCORE II underestimates the operative mortality in high-risk patients and the STS score overestimates the risk in low-risk patients.