External Validation of SYNTAX Score II in a Real-World Cohort Undergoing Coronary Artery Bypass Grafting

In this multicenter retrospective study of 1,454 consecutive patients undergoing isolated coronary artery bypass grafting (CABG), the SYNTAX Score II was externally validated for predicting four-year mortality. Mortality was 8.4 percent, with tertiles of SYNTAX Score II significantly stratifying survival, although the anatomical SYNTAX Score alone was not predictive. Independent predictors of mortality included age, creatinine clearance, left ventricular ejection fraction (LVEF), and chronic obstructive pulmonary disease (COPD). Calibration analysis showed systematic overestimation of mortality, particularly at higher scores (observed/expected ratio 0.61), while discrimination was acceptable (c-statistic 0.73), comparable to European System for Cardiac Operative Risk Evaluation (EuroSCORE) II, logistic EuroSCORE, and Age, Creatinine, and Ejection Fraction (ACEF). These findings suggest that although the SYNTAX Score II provides reasonable prognostic accuracy in real-world CABG patients, its predictions should be interpreted with caution, especially at higher values, due to its improved surgical outcomes since its development. Simpler scores, such as ACEF, may offer equivalent predictive value while being easier to use. Additionally, newer recalibrated models like SYNTAX Score II 2020 may better reflect contemporary practices.