A COMPARISON OF 4 SEVERITY-ADJUSTED MODELS TO PREDICT MORTALITY AFTERCORONARY-ARTERY BYPASS GRAFT-SURGERY

Objective: To assess the validity of four severity-adjusted models to predict mortality following coronary artery bypass graft surgery by us ing an independent surgical database. Design: A prospective observatio nal study wherein predicted mortality for each patient was obtained by using four different published severity-adjusted models. Setting: A u niversity-affiliated teaching community hospital. Patients: Eight hund red sixty-eight consecutive patients who underwent coronary artery byp ass graft surgery without accompanying valve or aneurysm repair during the period from 1991 to 1993. Interventions: None. Main Outcome Measu res: Predicted mortality rates for each model were obtained by averagi ng individual patient predictions and were compared with actual mortal ity rates. We assessed the accuracy of overall prediction for the tota l series, as well as compared individual patient predictions created b y each model. The discrimination of models was assessed with receiver operating characteristic curves and the Hosmer-Lemeshow goodness-of-fi t statistic. Results: The observed crude mortality rate was 3.7%. The predicted mortality rate ranged from 2.8% to 9.2%, despite relatively good discrimination by the models (area under the receiver operating c haracteristic curve, 0.70 to 0.74). The individual patient mortality p redicted by different models varied by as much as a ninefold differenc e. Conclusions: The currently used coronary artery bypass graft predic tive models, although generally accurate, have significant shortcoming s and should be used with caution. The predicted mortality rate follow ing coronary artery bypass graft surgery varied by a factor of 3.3 fro m lowest to highest, making the choice of model a critical factor when assessing outcome. The use of these models for individual patient ris k estimations is risky because of the marked discrepancies in individu al predictions created by each model.