Ready-made, recalibrated, or remodeled? Issues in the use of risk indexes for assessing mortality after coronary artery bypass graft surgery

Background-Risk indexes for operative mortality after-cardiac surgery are u sed for comparative profiling of surgeons or centers. We examined-whether c linicians and managers should use an existing index without modification, r ecalibrate it for their populations, or derive a new model altogether. Methods and Results-Drawing on 7491 consecutive patients who underwent isol ated CABG at 2 Toronto teaching hospitals between 1993 and 1996, we compare d 3 strategies: (1) using a ready-made model originally derived and validat ed in our jurisdiction;:, (2) recalibrating the ready-made model to better fit the population; and (3) deriving anew model with additional risk factor s. We assessed statistical accuracy; ie, area under a receiver-operator cha racteristic curve(ROC); precision, ie, statistical goodness-of-fit; and act ual impact on both risk-adjusted operative mortalities,(RAOM) and performan ce rankings for 14 surgeons.:The new model was slightly more accurate than the ready-made model (ROC, 0.78 versus 0.76; P<0.05),: albeit not different from the recalibrated model (ROC,0.77). The ready-made model showed poor f it between the predicted and observed results (P<0.001), leading-to signifi cant underestimation of RAOM (1.6+/-0.2%)compared with-the other strategies (2.5+/-0.2%; P=0.048). Remodeling also changed the performance rankings am ong half the surgeons with higher RAOM, Conclusions-Poorly calibrated risk algorithms can bias the calculation of R AOM and:alter the results of surgeon-specific profiles. Any existing index used for risk assessment in cardiac surgery should be episodically recalibr ated or compared with new models derived from local subjects to ensure that its performance remains optimal.