Challenges in comparing risk-adjusted bypass surgery mortality results - Results from the Cooperative Cardiovascular Project

OBJECTIVES We sought to evaluate the predictive accuracy of four bypass sur gery mortality clinical risk models and to examine the extent to which hosp itals' risk-adjusted surgical outcomes vary depending on which risk-adjustm ent method is applied. BACKGROUND Cardiovascular "report cards" often compare risk-adjusted surgic al outcomes; however, it is unclear to what extent the risk-adjustment proc ess itself may affect these metrics. METHODS As part of the Cooperative Cardiovascular Project's Pilot Revascula rization Study, we compared the predictive accuracy of four bypass clinical risk models among 3,654 Medicare patients undergoing surgery at 28 hospita ls in Alabama and Iowa. We also compared the agreement in hospital-level ri sk-adjusted bypass outcome performance ratings depending on which of the fo ur risk models was applied. RESULTS Although the four risk models had similar discriminatory abilities (C-index, 0.71 to 0.74), certain models tended to overpredict mortality in higher-risk patients. There was high correlation between a hospital's risk- adjusted mortality rates regardless of which of the four models was used (c orrelation between risk-adjusted rating, 0.93 to 0.97). In contrast, there was limited agreement in which hospitals were identified as "performance ou tliers" depending on which risk-adjustment model was used and how outlier s tatus was defined. CONCLUSIONS A hospital's risk-adjusted bypass surgery mortality rating, rel ative to its peers, was consistent regardless of the risk-adjustment model applied, supporting their use as a means of provider performance feedback. Designation of performance outliers, however, can vary significantly depend ing on the benchmark and methods used for this determination. (C) 2000 by t he American College of Cardiology.