Performance of European system for cardiac operative risk evaluation in Veterans General Hospital Kaohsiung cardiac surgery

BACKGROUND: The European System for Cardiac Operative Risk Evaluation (EuroSCORE) model is a widely-used risk prediction algorithm for in-hospital or 30-day mortality in adult cardiac surgery patients. Recent studies indicated that EuroSCORE tends to overpredict mortality. The aim of our study is to evaluate the validity of EuroSCORE in Veterans General Hospital Kaohsiung (VGHKS) cardiac surgery including a number of different surgical and risk subgroups. METHODS: From January 2006 to December 2009, 1,240 adult patients who underwent cardiac surgery in VGHKS were included in this study. The study was followed the guidelines of the Ethics Committee of Kaohsiung Veterans General Hospital, Taiwan. Both additive and logistic score of all patients were calculated depending on the formula in the official EuroSCORE website. The entire cohort, different surgical type and risk stratification subgroups were analyzed. Model discrimination was tested by determining the area under receiver operating characteristic (ROC) curve. Model calibration was tested by the Hosmer-Lemeshow chi-square test. Clinical performance of model was assessed by comparing the observed and predicted mortality rates. RESULTS: There were significant differences between the VGHKS and European cardiac surgical populations. The additive score and logistic score for the overall group were 7.16% and 12.88%, respectively. Observed mortality was 10.72% overall, 5.68% for isolated coronary artery bypass grafting (CABG), 4.67% for the mitral valve only and 4.25% for the aortic valve only group. The discriminative ability EuroSCORE was very good in all and various surgical subgroups, with area under the ROC curve from 0.75 to 0.87. The addictive and logistic models of EuroSCORE showed excellent accuracy, 0.839 and 0.845, respectively. Good calibration power was recognized by p value higher than 0.05 for the entire cohort and all subgroups of patients except for isolated CABG. The logistic EuroSCORE model overestimated mortality to different degrees in the various subgroups, indicating that the logistic EuroSCORE needs to be recalibrated by a factor about 0.55 for uncomplicated surgery and low-risk groups, and 0.85 for high-risk patients with original additive score more than six. CONCLUSION: EuroSCORE is simple and easy to use. In the present study, the model demonstrated excellent accuracy in all and various surgical subgroups in VGHKS cardiovascular surgery populations. Good calibration ability in all and different risk categories was identified except for isolated CABG group. Recalibration factors of 0.55 and 0.85 were suggested for the various operative subgroups and risk categories.