Comparison of the EuroSCORE II and Society of Thoracic Surgeons 2008 risk tools

Risk stratification in cardiac surgery is uniquely detailed, led latterly by the EuroSCORE and the Society of Thoracic Surgeons (STS) risk calculators. The recently published EuroSCORE II (ES2) algorithms update estimated mortality in a broad spectrum of cardiac procedures. The 2008 STS tool, in comparison, predicts multiple outcomes for specific procedures. We sought to identify and compare the external validity of both contemporaneous tools in our population.

Data from our hospital database were collated for the period February 2001 to March 2010. Logistic regression coefficients from the risk calculations were applied to the data and the results presented as receiver-operating characteristic (ROC) curves. Statistical analyses were performed using the area under the ROC curve (AUROC) and the Hosmer-Lemeshow (H-L) goodness-of-fit test, with comparisons using the DeLong method.

A total of 15 497 procedures were identified, of which 14 432 were appropriate for STS risk scoring (i.e. valve and/or graft procedures with no tricuspid valve operations etc.). For all procedures, ES2 and STS were equivalent (AUROC 0.818 vs 0.805, respectively, P = 0.343). For procedures appropriate for STS risk scoring, results were similar (AUROC ES2 vs STS, 0.816 vs 0.810, P = 0.714), whereas for procedures excluded by STS, the result was marginally worse (AUROC ES2 vs STS, 0.773 vs 0.784, P = 0.751). Goodness of fit in all cases was poor, primarily where risk was higher than 15% (H-L P < 0.0001).

EuroSCORE II and STS both provide equivalent discrimination in predicting mortality in a British population, including those undergoing procedures for which the STS does not normally predict. Accounting for decile-grouped Hosmer-Lemeshow tests not being ideal for the assessment of calibration, both tools show good calibration for patients with low to moderate risk, with divergence from ~15% predicted risk.