Assessing the Outcomes of Coronary Artery Bypass Graft Surgery: How Many Risk Factors Are Enough?

Objectives. We sought to determine whether more comprehensive risk-adjustment models have significant impact on hospital risk-adjusted mortality rates after coronary artery bypass graft surgery (CABG) in Ontario, Canada. Background. The Working Group Panel on the Collaborative CABG Database Project has categorized 44 clinical variables into 7 core, 13 level 1 and 24 level 2 variables, to reflect their relative importance in determining short-term mortality after CABG. Methods. Using clinical dat for all 5,517 patients undergoing isolated CABG in Ontario in 1993, we developed 12 increasingly comprehensive risk-adjustment models using logistic regression analysis of 6 of the Panel’s core variables and 6 of the Panel’s level 1 variables. We studied how the risk-adjusted mortality rates of the nine cardiac surgery hospitals in Ontario changed as more variables were included in these models. Results. Incorporating six of the core variables in risk-adjustment model led to model with an are under the receiver operating characteristic (ROC) curve of 0.77. The ROC curve are slightly improved to 0.79 with the inclusion of six additional level 1 variables (p = 0.063). Hospital risk-adjusted mortality rates and relative rankings stabilized after adjusting for six core variables. Adding an additional six level 1 variables to risk-adjustment model had minimal impact on overall results. Conclusions. small number of core variables appear to be sufficient for fairly comparing risk-adjusted mortality rates after CABG across hospitals in Ontario. For efficient interprovider comparisons, risk-adjustment models for CABG could be simplified so that only essential variables are included in these models.