Comparison of four risk scores for contemporary isolated coronary artery bypass grafting.

Background: EuroSCORE and the Society of Thoracic Surgeons' (STS) Score have been the most widely used risk scores for cardiac surgery. The revised EuroSCORE II and the AusSCORE, based on an Australasian population, were recently developed. We compared the prognostic utility of these four scores for mortality as well as morbidity in patients undergoing isolated coronary artery bypass grafting (CABG).

Methods: The scores were retrospectively calculated for isolated CABG patients at Auckland City Hospital during July 2010-June 2012. Discrimination and calibration of outcomes were assessed.

Results: 818 patients were followed for 1.6+/-0.6 years. Mortality at 30 days was 1.6% and 2.9% on follow up. Median predicted 30 day mortality (Interquartile range) for EuroSCORE I were 2.8% (1.6%, 5.2%), EuroSCORE II 1.6% (1.0%, 2.8%), STS Score 2.3% (1.3%, 4.5%) and AusSCORE 0.5% (0.2%, 1.1%). C-statistics and Hosmer-Lemeshow test p-values for these scores for 30-day mortality were Euro score I 0.675 (95%CI 0.531-0.819)/0.061, EuroSCORE II 0.642 (0.503-0.780)/0.150, STS Score 0.641 (0.507-0.775)/0.243 and AusSCORE 0.661 (0.516-0.807)/0.420. Only EuroSCORE I and STS scores were significant for predicting mortality at follow-up (c=0.639 and 0.666). All scores predicted composite morbidity. C-statistics were EuroSCORE I 0.678, EuroSCORE II 0.634, STS score 0.584 and AusSCORE 0.645.

Conclusion: EuroSCORE II, STS Score and AusSCORE had slightly improved calibration but similar discrimination for 30-day mortality compared to EuroSCORE I. Revision of risk models to fit contemporary surgical outcomes is important, but there may only be modest room for improvement in discrimination.