Accuracy of the Aristotle Basic Complexity Score for Classifying the Mortality and Morbidity Potential of Congenital Heart Surgery Operations

Background: The Aristotle Basic Complexity Score (ABC score) was derived by consensus of an international surgeon panel to facilitate assessment of surgical performance for quality improvement in congenital heart surgery. The utility of the ABC score depends on its ability to correctly classify procedures according to their potential for morbidity, mortality, and technical difficulty. This collaborative study combined two multiinstitution databases to assess how well the ABC score predicts the actual morbidity and mortality potential of 131 congenital heart surgery procedures. Methods: Data from the European Association of Cardiothoracic Surgery (EACTS) congenital database (17,838 operations, 56 centers) and the Society of Thoracic Surgeons (STS) congenital database (18,024 operations, 32 centers) were analyzed. Discrimination of the ABC score for predicting in-hospital mortality and postoperative length of stay (PLOS) of more than 21 days was quantified by the C statistic. Procedure-specific rates of mortality and prolonged PLOS were compared with predictions from a logistic regression model, and an exact binomial test was used to identify procedures that were mortality and morbidity outliers. Results: There was a significant positive correlation between the ABC score of a procedure and its observed procedure-specific risk of mortality (C = 0.70) and prolonged PLOS (C = 0.67). Several individual procedures were identifed as mortality and morbidity outliers. Conclusions: The ABC score generally discriminates between low-risk and high-risk congenital procedures making it a potentially useful covariate for case-mix adjustment in congenital heart surgery outcomes analysis. Planned revisions of the ABC score will incorporate empirical data and will benefit from the large sample sizes of the STS and EACTS databases.