Comparison of logistic EuroSCORE and EuroSCORE II in predicting operative mortality of 1125 total arterial operations

OBJECTIVES: The purpose of this study was to compare effectiveness of the 1999 logistic EuroSCORE (LES) and of the 2012 EuroSCORE II (ESII) in a real-world patient population of 1125 patients undergoing total arterial grafting (TAG) coronary artery bypass graft (CABG) surgery.
METHODS: The performance of the two risk scores was compared using (i) discrimination (accuracy of discriminating non-survivors from survivors), (ii) calibration (assessment of agreement between the predicted/observed outcomes) and (iii) agreement between the two scores. By averaging medians of LES and ESII and then sub-division into 10 equal groups, actual operative mortality rate was compared with the median LES and ESII within each risk group, the difference plotted against the average risk score (as in a Bland and Altman plot), and using the traditional risk groupings for EuroSCORE of low (0-2.99), medium (3-5.99) and high risk (6.0 and above), the reclassification rate of ESII was compared with that of LES.
RESULTS: In 1125 consecutive total arterial CABG patients, demographics included: mean age 64.6 years, 79% males, 35% diabetic patients, 57% urgent/emergent patients, 37% off-pump and 77% bilateral mammary grafting. Overall operative mortality was 3.2% (36 patients). Comparison of the LES and ESII showed (i) good discrimination for both LES and ESII (area under the curve for LES was 0.85 and for ESII was 0.87); (ii) neither score was well calibrated: LES tended to overestimate and ESII underestimated risk. In general, the ESII provided a better estimate of risk in lower risk patients and LES was better for the highest risk group. (iii) In terms of agreement, in the lower four risk groups the risk was overestimated by both scores, in five of the higher six risk groups ESII underestimated risk and LES overestimated risk, and in the highest risk group LES was very close (17.2 cf. 17.7) compared with ESII (5.6 cf. 17.7). In addition, ESII downgraded risk in 96.8% of survivors and in 97.2% of non-survivors.
CONCLUSIONS: In 1125 consecutive TAG CABG patients, neither LES nor ESII performed well enough to be used as a consistent risk stratification tool; LES overestimated risk but was highly accurate for the highest of 10 risk groups and ESII consistently underestimated risk in all patients.