KCH, the German preoperative score for isolated coronary artery bypass surgery: is it superior to the logistic EuroSCORE?

Background: The accuracy of the logistic EuroSCORE in different patient populations has been questioned. Using the German registry database, the KoronarCHirurgie (KCH) score was introduced as a preoperative risk stratification tool specifically for patients who undergo isolated coronary artery bypass surgery in Germany. However, no direct statistical comparison of this score with the well-established logistic EuroSCORE has been previously performed. The aim of this study was to validate the preoperative German KCH score and to compare it to the logistic EuroSCORE for all coronary artery bypass surgery patients as well as for on-pump and off-pump subgroups.

Methods: We prospectively included all consecutive adult patients admitted to our department between January 1, 2007 and December 31, 2008, who underwent isolated coronary artery bypass surgery. The logistic EuroSCORE and the KCH-3.0 were calculated on admission to hospital. The outcome was defined as 30-day mortality. We performed calibration (Hosmer-Lemeshow test and Anderson-Grunkemeier Observed/Expected "O/E" mortality ratio) and discrimination (receiver operating characteristic "ROC" test) analyses of both scores. The accuracy of the scores was compared using DeLong's test.

Results: A total of 1461 patients (23.96 % females, mean age 66.94 ± 9.43 years) were included. The 30-day mortality rate was 2.87 %. The two models were comparable with regard to the prediction of an individual patient's risk of mortality in the whole study population and in the on-pump and off-pump subgroups (according to the ROC test and DeLong's test). Overall, there was no significant difference between observed and expected mortality according to the Hosmer-Lemeshow test ( P > 0.05). However, the KCH-3.0 was far less likely to overpredict mortality than the logistic EuroSCORE, as demonstrated by the observed mortality/expected mortality (O/E) ratios. The O/E ratio was 0.32 for the logistic EuroSCORE and 0.74 for the KCH-3.0. For the on-pump subgroup the O/E ratios were 0.37 and 0.80, respectively, and 0.24 and 0.63, respectively, for the off-pump subgroup.

Conclusions: The KCH-3.0 is more reliable than the logistic EuroSCORE as a preoperative mortality prediction score for patients undergoing isolated coronary artery bypass surgery, providing predicted mortality rates that are closer to the actual mortality rates with a lower overprediction of mortality.