Original ArticleComparison of Four Risk Scores for Contemporary Isolated Coronary Artery Bypass Grafting
Introduction
Several operative risk scores for cardiac surgery have been developed in the last few decades including the Parsonnet Score, [1] EuroSCOREs [2], [3] and Society of Thoracic Surgeon's (STS) score. [4] EuroSCORE I was developed from a European cohort of 14,781 patients having cardiac surgery during 1995 for 30-day mortality, and published as an additive model in 1999 [2] and logistic model in 2003. [3] The STS score was developed to predict operative morbidity and was derived from an American cohort of 774,881 isolated coronary artery bypass grafting (CABG) patients during 2002-2006 and published in 2008. [4]
Despite the early validation of EuroSCORE I in large international populations, [5], [6] more recent studies found the score over-estimated operative mortality, probably because of improving operative and peri-operative management. [7], [8] In Australasian populations characterised by significant ethnic diversity, the EuroSCORE I also over-estimated operative mortality. [9] The AusSCORE was published in 2009 from 11,823 patients undergoing isolated CABG during 2001-2005 from the Australasian Society of Cardiac and Thoracic Surgeon's (ASCTS) database to predict 30-day mortality. [10] To date, there are no studies assessing its external validity.
More recently as a project to revise the original EuroSCORE to fit contemporary cohorts, the EuroSCORE II was developed from an international cohort of 22,381 patients undergoing cardiac surgery during 2010 and published in 2012. [11] Studies which have assessed the external validity of this new score have reported mixed results with EuroSCORE II performing better [12], [13], [14], [15] or similar [16], [17] to EuroSCORE I.
EuroSCORE II, STS Score and AusSCORE have not been directly compared for CABG, or assessed in Australasian cohorts. In addition the comparative value of the different scores for predicting mortality beyond 30 days is uncertain. Our objective was to compare the predictive efficacy of logistic EuroSCORE I, EuroSCORE II, STS Score and AusSCORE for morbidity and mortality at 30 days and longer follow-up after isolated CABG.
Section snippets
Patient selection and data collection
Ethics approval of this study was obtained from our institution's ethics review committee. Consecutive patients undergoing isolated CABG without concomitant valve surgery at Auckland City Hospital were included from July 2010 to June 2012. Relevant clinical characteristics were collected from computerised records. Logistic EuroSCORE I, [3] EuroSCORE II, [11] STS Score [4] and AusSCORE, [10] were retrospectively calculated from all patients using available data.
The EuroSCORE II definitions were
Results
Table 1 presents the baseline characteristics of the study population. Mean age was 64.5+/-10.0 years and 20.2% (168) were female. Mean follow-up was 1.6+/-0.6 years. The median predicted 30-day mortality (interquartile range IQR) for EuroSCORE I was 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%). Table 2 lists the operative variables and post-operative outcomes.
Discussion
Our study shows that EuroSCORE I, EuroSCORE II, STS Score and AusSCORE were all able to discriminate outcomes after CABG with modest accuracy and varying strengths. EuroSCORE II, STS Score and AusSCORE had slightly better calibration than EuroSCORE I for 30-day mortality, but discrimination for outcomes were not superior to EuroSCORE I.
EuroSCORE I had been a success for over a decade since its introduction as the primary international risk score for operative mortality prediction, but recent
Conclusion
In a contemporary cohort of patients undergoing isolated CABG the EuroSCORE II, STS Score and AusSCORE had modest improvements in calibration for 30-day mortality, as compared with EuroSCORE I. All four scores predicted some but not all post-operative complications. Revision of risk models to fit contemporary surgical outcomes is important for calibration, but the room for improvement for discriminating adverse outcomes may be limited. Given the modest C-statistics found in our analysis, there
Disclosures
None of the authors have any disclosures.
Acknowledgements
No funding was utilised in this research. We would like to thank all our colleagues affiliated with the Green Lane Cardiovascular Service for their contributions and support and Charlene Nell, Desktop Support Administrator, for excellent secretarial assistance.
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