KCH, the German Preoperative Score for Isolated Coronary Artery Bypass Surgery: Is it Superior to the Logistic EuroSCORE?

Abstract

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.

Key words

coronary artery bypass grafts surgery - CABG - outcomes (includes mortality - morbidity) - statistics - scoring system - cardiac surgery - mortality prediction

References

• 1 Roques F, Nashef S A M, Michel P et al. Risk factors and outcome in European cardiac surgery: analysis of the EuroSCORE multinational database of 19 030 patients.  Eur J Cardiothorac Surg. 1999;  15 816-823
• 2 Nashef S A M, Roques F, Michel P, Gauducheau E, Lemeshow S, Salamon R. European system for cardiac operative risk evaluation (EuroSCORE).  Eur J Cardiothorac Surg. 1999;  16 9-13
• 3 Roques F, Michel P, Goldstone A R, Nashef S A M. The logistic EuroSCORE.  Eur Heart J. 2003;  24 1-2
• 4 Roques F, Nashef S A, Michel P, Pinna Pintor P, David M, Baudet E. The EuroSCORE study group . Does EuroSCORE work in individual European countries?.  Eur J Cardiothorac Surg. 2000;  18 (1) 27-30
• 5 Kawachi Y, Nakashima A, Toshima Y, Arinaga K, Kawano H. Evaluation of the quality of cardiovascular surgery care using risk stratification analysis according to the EuroSCORE additive model.  Circ J. 2002;  66 (2) 145-148
• 6 Nashef S A, Roques F, Hammill B G et al. Validation of European system for cardiac operative risk evaluation (EuroSCORE) in North American cardiac surgery.  Eur J Cardiothorac Surg. 2002;  22 (1) 101-105
• 7 Bhatti F, Grayson A D, Grotte G et al. North West Quality Improvement Programme in cardiac interventions. The logistic EuroSCORE in cardiac surgery: how well does it predict operative risk?.  Heart. 2006;  92 1817-1820
• 8 Sergeant P, de Worm E, Meyns B. Single centre, single domain validation of the EuroSCORE on a consecutive sample of primary and repeat CABG.  Eur J Cardiothorac Surg. 2001;  20 1176-1182
• 9 Gummert J F, Funkat A, Osswald B et al. EuroSCORE overestimates the risk of cardiac surgery: results from the national registry of the German society of thoracic and cardiovascular surgery.  Clin Res Cardiol. 2009;  98 (6) 363-369
• 10 Bundesgeschäftsstelle Qualitätssicherung gGmbH .Neue Risikoadjustierung in der Koronarchirurgie: der KCH-Score. In: Mohr V D, Bauer J, Döbler K, Eckert O, Fischer B, Woldenga C Qualität sichtbar machen. BQS-Qualitätsreport 2004. Düsseldorf: BQS Bundesgeschäftsstelle Qualitätssicherung gGmbH; 2005. http://www.bqs-outcome.de/2005/ergebnisse/leistungsbereiche/koronarchirurgie/buaw/risikoadj Accessed September 05, 2010
• 11 Bundesgeschäftsstelle Qualitätssicherung gGmbH .Risikoadjustierung in der Koronarchirurgie: der KCH 2.0-Score. In: Veit C, Bauer J, Döbler K, Eckert O, Fischer B, Woldenga C Qualität sichtbar machen. BQS-Qualitätsreport 2007. Düsseldorf: BQS Bundesgeschäftsstelle Qualitätssicherung gGmbH; 2008. http://www.bqs-outcome.de/2007/ergebnisse/leistungsbereiche/koronarchirurgie/buaw/risikoadjustierung Accessed September 05, 2010
• 12 Bundesgeschäftsstelle Qualitätssicherung gGmbH .Risikoadjustierung in der Koronarchirurgie: der KCH 2.0-Score. In: Veit C, Bauer J, Döbler K, Fischer B Qualität sichtbar machen. BQS-Qualitätsreport 2008. Düsseldorf: BQS Bundesgeschäftsstelle Qualitätssicherung gGmbH; 2009. http://www.bqs-outcome.de/2007/ergebnisse/leistungsbereiche/koronarchirurgie/buaw/risikoadjustierung Accessed September 05, 2010
• 13 Anderson R P, Jin R, Grunkemeier G L. Understanding logistic regression analysis in clinical reports: an introduction.  Ann Thorac Surg. 2003;  75 753-757
• 14 DeLong E R, DeLong D M, Clarke-Pearson D L. Comparing the areas under two or more correlated receiver operating characteristic curves: a nonparametric approach.  Biometrics. 1988;  44 837-845
• 15 Sakr Y, Krauss C, Amaral A et al. Comparison of the performance of SAPS II, SAPS3, APACHE II, and their customized prognostic models in a surgical intensive care unit.  Br J Anaesth. 2008;  101 798-803
• 16 Heart surgery in United Kingdom. http://heartsurgery.cqc.org.uk/ Accessed September 05, 2010
• 17 Gummert J F, Funkat A, Beckmann A et al. Cardiac surgery in Germany during 2008. A report on behalf of the German Society for Thoracic and Cardiovascular Surgery.  Thorac Cardiovasc Surg. 2009;  57 315-323
• 18 Hannan E L, Siu A L, Kumar D, Kilburn Jr H, Chassin M R. The decline in coronary artery bypass graft surgery in New York State: the rule of surgeon volume.  J Am Med Assoc. 1995;  273 (3) 209-213
• 19 Ivanov J, Tu J V, Naylor C D. Ready-made, recalibrated, or remodeled? Issues in the use of risk indexes for assessing mortality after coronary artery bypass graft surgery.  Circulation. 1999;  99 2098-2104
• 20 Pitkänen O, Niskanen M, Rehnberg S, Hippeläinen M, Hynynen M. Intra-institutional prediction of outcome after cardiac surgery: comparison between a locally derived model and the EuroSCORE.  Eur J Cardiothoracic Surg. 2000;  18 (6) 703-710
• 21 Reid C, Billah B, Dinh D et al. An Australian risk prediction model for 30-day mortality after isolated coronary artery bypass: the AusSCORE.  J Thorac Cardiovasc Surg. 2009;  138 (4) 904-910
• 22 D'Errigo P, Seccareccia F, Rosato S The Research Group of the Italian CABG Outcome Project et al. Comparison between an empirically derived model and the EuroSCORE system in the evaluation of hospital performance: the example of the Italian CABG Outcome Project.  Eur J Cardiothorac Surg. 2008;  33 325-333
• 23 Carvalho M R, Silva N A, Klein C H, Oliveira G M. Application of the EuroSCORE in coronary artery bypass surgery in public hospitals in Rio de Janeiro, Brazil.  Rev Bras Cir Cardiovasc. 2010;  25 (2) 209-217
• 24 van Straten A H, Tan E M, Hamad M A, Martens E J, van Zundert A A. Evaluation of the EuroSCORE risk scoring model for patients undergoing coronary artery bypass graft surgery: a word of caution.  Neth Heart J. 2010;  18 (7–8) 355-359
• 25 Yap C H, Reid C, Yii M et al. Validation of the EuroSCORE model in Australia.  Eur J Cardiothorac Surg. 2006;  29 (4) 441-446
• 26 Zheng Z, Li Y, Zhang S, Hu S. Chinese CABG Registry Study . The Chinese coronary artery bypass grafting registry study: how well does the EuroSCORE predict operative risk for Chinese population?.  Eur J Cardiothorac Surg. 2009;  35 (1) 54-58
• 27 Gogbashian A, Sedrakyan A, Treasure T. EuroSCORE: a systematic review of international performance.  Eur J Cardiothorac Surg. 2004;  25 (5) 695-700
• 28 Omar R Z, Ambler G, Royston P, Eliahoo J, Taylor K M. Cardiac surgery risk modeling for mortality: a review of current practice and suggestions for improvement.  Ann Thorac Surg. 2004;  77 (6) 2232-2237
• 29 Nissinen J, Biancari F, Wistbacka J O et al. Is it possible to improve the accuracy of EuroSCORE?.  Eur J Cardiothorac Surg. 2009;  36 799-804