Early mortality in coronary bypass surgery: the EuroSCORE versus The Society of Thoracic Surgeons risk algorithm

Background We compare two widely used risk algorithms for coronary bypass surgery: The European System for Cardiac Operative Risk Evaluation (EuroSCORE) and The Society of Thoracic Surgeons (STS) risk stratification algorithm. Methods Risk factors for all adult patients undergoing heart surgery at the University Hospital of Lund between 1996 and 2001 were collected prospectively at preoperative admission. Predictive accuracy for 30-day mortality was assessed by comparing the observed and the expected mortality for equal-sized quintiles of risk by using the Hosmer-Lemeshow goodness-of-fit test. The discriminatory power was evaluated by calculating the areas under receiver operating characteristics (ROC) curves. Results The study included 4497 coronary artery bypass-only operations. The average age was 66.4 ± 9.3 years (range 31 to 90 years). Most patients were men (77.0% versus 23.0%). The actual 30-day mortality was 1.89%. The Hosmer-Lemeshow goodness-of-fit test gave a p value of 0.81 (EuroSCORE) and 0.83 (STS), which indicates a good accuracy of both models. The area under the ROC curve was 0.84 (95% confidence interval [CI] 0.80 to 0.88) for EuroSCORE and 0.71 (95% CI 0.66 to 0.77) for STS. The discriminatory power (area under the ROC curve) was significantly larger for EuroSCORE compared with STS (p< 0.00005). Conclusions In this large, single institution study the additive EuroSCORE algorithm had a significantly better discriminatory power to predict 30-day mortality than the STS risk algorithm for patients undergoing coronary artery bypass.