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Eur J Cardiothorac Surg 2004;25:691-694
© 2004 Elsevier Science NL

Risk-stratification in thoracic aortic surgery: should the EuroSCORE be modified?

Department of Cardiovascular Surgery, University Hospital,CH-3010 Berne, Switzerland

Received 26 October 2003; received in revised form 2 January 2004; accepted 7 January 2004.

^* Corresponding author. Tel.: +41-31-632-23-76
e-mail: franzimmer{at}yahoo.de

	Abstract

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Objectives: Risk-stratification in cardiac surgical procedures is of major interest. Recent studies have shown, that the EuroSCORE is a very good and reliable risk-stratification score in CABG and in valve surgery. The aim of the study was to evaluate the EuroSCORE in patients undergoing surgery on the thoracic aorta. Methods: Three hundred and sixty-seven consecutive patients underwent surgery of the thoracic aorta and were scored, according to the additive and logistic EuroSCORE algorithm. We compared correlation of predicted and observed mortality and evaluated a modification of the EuroSCORE in order to improve the scoring system. Score validity was assessed by calculating the area under the receiver operating characteristic curve (ROC). Results: Overall hospital mortality was 10.1%. Additive EuroSCORE predicted mortality was 2.3% for 3–6% risk, 12.9% for 7–8% risk, 18.4% for 9–12% risk and 27.3% for a risk >12%. The modified score predicted mortality was 1% for 3–6% risk, 8.2% for 7–8% risk, 12.1% for 9–14% risk, 18.6% for 15–24% risk and 28.6% for a risk >24%. Area under the ROC-curve was 0.68 for the EuroScore and 0.91 in the modified score, 0.72 and 0.86 in the logistic model. Conclusions: The modified score, taking into account aortic dissection (6 points) and preoperative malperfusion (12 points) significantly improves the predictive value of the EuroSCORE in patients undergoing thoracic aortic surgery.

Key Words: Aortic surgery • Risk-stratification • EuroSCORE

	1. Introduction

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Risk-stratification in major surgical procedures is of increasing interest. In the last few decades several risk-stratification scores in patients undergoing cardiac surgical procedures have been established [1–4]. Beside the predictive value of early outcome in a collective of patients, risk-stratification allows furthermore to perform a quality control. Comparison of predicted and observed mortality leads to an evaluation of surgical teams and/or new therapeutic strategies [4]. The EuroSCORE has been described by Roques an his colleagues and represents a validated tool for risk-stratification in cardiac surgical procedures as well as in surgery of the thoracic aorta [1]. The EuroSCORE has been validated in several studies and in different institutions [2,3]. The results were very promising and most of the authors concluded, that the EuroSCORE has a good predictive value to assess in-hospital mortality. It was Kawachi and his colleagues who evaluated the EuroSCORE in a collective of Japanese patients. They concluded that EuroSCORE was not only reliable for Japanese patients undergoing cardiac but also thoracic aortic surgery [3,5]. The purpose of this study was to validate the EuroSCORE in our patients undergoing surgery on the thoracic aorta, including patients with acute type A aortic dissection.

	2. Patients and methods

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
2.1. Patients
Between January 1994 and December 2000, 367 patients underwent surgery for thoracic aortic diseases in our institution. Mean age of the patients was 60.0±13.9 years. Two hundred and seventy-one patients (73.8%) were male. The in-hospital mortality was 10.1%. Hundred and thirty-three patients (36.2%) suffered from acute type A aortic dissection. The remaining patients presented with aortic aneurysms of the ascending aorta and/or the aortic arch. According to the EuroSCORE, patients were divided into four groups: Group 1 (ES 3–6): 136 patients (37.1%) with an in-hospital mortality of 2.3%; Group 2 (ES 7–8): 116 patients (31.6%) with an in-hospital mortality of 12.9%; Group 3 (ES 9–12): 104 patients (28.3%) with an in-hospital mortality of 18.4%; Group 4 (ES>12): 11 patients with an in-hospital mortality of 27.3% (Table 1).

2.3. Statistical methods
Based on the description of the original EuroSCORE [1] additional variables (Table 1) entered in the model were selcted using bivariate tests, ² tests for categorical covariate and t-test or Wilcoxon rank sum tests for continuous covariates. Non-significant variables were eliminated from the model one at a time. ROC-curve was used to asses how well the model could discriminate between patients who lived and patients who died. A P-value <0.05 was considered statisticall significant.

	3. Results

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
One hundred and eight patients (29.4%) received a composite graft (button technique), 196 patients (53.4%) a replacement of the ascending aorta, the hemiarch or the aortic arch, 146 patients (39.8%) had additional cardiac interventions, 72 (49.3%) of them had isolated valve surgery and 20 (13.7%) valve surgery in combination with CABG. Hundred and eighty-nine patients were operated with the use of deep hypothermic circulatory arrest (DHCA). Hundred and fourty seven patients were operated on emergency base (within 24 h after onset of symptoms).

The presence of acute type A dissection and preoperative malperfusion was significantly less frequent in patients who survived early postoperative period (<30 days), with an odds-ratio of 1.87 for type A aortic dissection and 2.72 for the presence of preoperative malperfusion. The use of DHCA does not increase mortality with an odds-ratio of 0.82 (Table 1). The percentage of acute type A aortic dissection, as well as the incidence of preoperative malperfusion is increasing from groups 1 to 4 (Table 2). The area under the ROC-curve for the additive EuroSCORE was 0.68 and for the logistic model 0.72.

	4. Discussion

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
The EuroSCORE is an established and validated score to perform risk-stratification in patients undergoing cardiac surgical procedures [2]. Risk-stratification in patients undergoing thoracic aortic surgery is very difficult, due to the heterogeneity of the type of diseases. Based on the underlying pathology, mortality is different between patients undergoing surgery for acute type A aortic dissection and for patients undergoing surgery for aortic aneurysms [8]. It is furthermore well known, that the presence of malperfusion syndrome significantly increases the risk of mortality and morbidity. The EuroSCORE was established in a typical collective of patients undergoing cardiac surgical procedures. In the original score the majority of patients underwent surgery for coronary artery disease and only a few patients have been operated on the ascending aorta [1]. The area under the ROC-curve for the additive score was very low with 0.68, reflecting a low sensitivity and specificity of the EuroSCORE in our collective of patients who underwent surgery of the thoracic aorta. As recently published by Roques and his colleagues, we can confirm that the logistic EuroSCORE in high risk-patients is a better risk predictor, with an increase of the area under the ROC-curve up to 0.72 [6,7]. Based on statistical calculations we modified the EuroSCORE by adding six points for acute type A aortic dissection and 12 points for the presence of malperfusion syndrome. By implicating these changes we could increase the area under the ROC-curve in the additive model from 0.68 to 0.91 and in the logistic model the area under the ROC-curve was 0.86, which is excellent. Validation of the modification of the EuroSCORE in a collective of 590 patients undergoing thoracic aortic surgery by extending the data base up to December 2002, we could confirm our findings, with an EuroSCORE in the additive model of 0.88. Similar results were found in the sub-group of patients who were not taken into account for modification of EuroSCORE, including 223 patients being operated between January 2001 and December 2002 at our institution, leads to a ROC-curve of 0.86 in the additive model.

Aim of the study was to improve the predictive value of the EuroSCORE in patients undergoing surgery of the thoracic aorta. We therefore decided not to modify the original EuroSCORE but to analyse aspects which may influence early outcome in this type of surgery. Statistical analysis clearly underlined the importance of the presence of acute type A aortic dissection (odds-ratio 1.87) and malperfusion syndrome (odds-ratio 2.72) with regard to outcome. In patients presented with pericardial tamponade and haemodynamical instability (odds-ratio 2.59) three points were added, based on the original EuroSCORE for a critical preoperative state. Emergency procedures (odds-ratio 2.08), including mainly patients suffering from acute type A aortic dissection, received two additional points based on the data of the original EuroSCORE.

We are aware that especially the definition of malperfusion syndrome has some major limitations, as intestinal malperfusion syndromes are frequently detected in the early postoperative period only. In our study, malperfusion syndrome was included in the analyses of the EuroSCORE, if it occurred during hospitalisation, requiring surgery, which was mainly the case for intestinal malperfusion syndrome or malperfusion of the extremities or in the presence of preoperative neurological deficits, due to a cerebral or spinal malperfusion. As the EuroSCORE is a model of preoperative risk-stratification, this aspect may be an important limitation of the suggested modification of the EuroSCORE. On the other hand, quality control, which is an important aspect of risk-stratification scores, is not influenced by this limitation. However, larger studies and more data are required to establish a reliable risk-stratification score for patients undergoing surgery of the thoracic aorta. We would like to encourage other centres to participate in a multi-centre study in order to perform these statistical analyses in a larger collective of patients.

We therefore conclude that the modified score, by adding six points for acute type A aortic dissection and 12 points for the presence of malperfusion syndrome, significantly improves the predictive value of the EuroSCORE in patients undergoing thoracic aortic surgery.

	Footnotes

 
Presented at the joint 17th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 11th Annual Meeting of the European Society of Thoracic Surgeons, Vienna, Austria, October 12–15, 2003.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 
Mr S Nashef (Cambridge, UK): I have to commend you on the accurate and correct statistical methodology used in assessment. As you know, there is no such thing as a perfect score for everything, and it will always be possible to find ways of improving and adding to the score, particularly in certain patient sub-groups such as specialized groups with aortic dissection. I think you probably know what I am going to say next. When you have a group of patients in whom the majority score is more than six, you really have a high risk group, and you perhaps should not be using the additive model for assessing mortality in these patients, because we know that all additive models tend to slightly overestimate risk in low risk groups and substantially underestimate risks in high risk groups. So they are useful for a general patient population, but you perhaps would have been better using the logistic model before proposing modification. And finally, we are planning to relaunch data collection in order to see what has changed over the last decade in terms of risk profile in cardiac surgery in 2005, and we sincerely hope that your center will participate in this effort.

Dr M. Schepens (Nieuwegein, The Netherlands): Malperfusion is a syndrome that you often detect only after surgery. So how can you predict because you are going on with your repair for type A dissection, and postoperatively diuresis is decreasing after, e.g. 4 h postop. So your preoperative risk-stratification is of no value anymore?

Dr Immer: That is an excellent comment, and we were discussing for hours about that, but in fact, preoperative you can recognize cerebral malperfusion or myocardial malperfusion, but you are not able to detect in most of the patients intestinal malperfusion, and what we did to analyze the data, we took all the patients in accordance to the postoperative course. So I agree with you that this is a difficult point, but as we have shown previously, we think that the presence of malperfusion is one of the most important things, but in fact that is the problem of predicting score but it allows to perform a quality control.

Dr B. Osswald (Heidelberg, Germany): You did tell us that an additional scoring point of three for aortic surgery would increase the risk by 3%, which is not necessarily the case.

Dr Immer: Our aim was not to modify an excellent score, and that is the reason why we left the three points for thoracic aortic surgery. We wanted just to suggest to add two more criteria. But that is the problem: if you have elective aortic surgery, mortality would be below 3%, and we wanted to leave the EuroSCORE like it was described by the authors.

	References

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion Appendix A. Conference... References

 

1. Nashef S.A., Roques F., Michel P., Gauducheau E., Lemeshow S., Salamon R. European system for cardiac operative risk evaluation (EuroSCORE). Eur J Cardiothorac Surg 1999;16(1):9-13.[Abstract/Free Full Text]
2. Stoica S.C., Sharples L.D., Ahmed I., Roques F., Large S.R., Nashef S.A. Preoperative risk prediction and intraoperative events in cardiac surgery. Eur J Cardiothorac Surg 2002;21(1):41-46.[Abstract/Free Full Text]
3. Kawachi Y., Nakashima Y., Toshima Y., Arinaga K., Kawano H. Risk stratification analysis of operative mortality in heart and thoracic aorta surgery: comparison between Parsonnet and EuroSCORE additive model. Eur J Cardiothorac Surg 2001;20(5):961-966.[Abstract/Free Full Text]
4. Bridgewater B., Grayson A.D., Jackson M., Brooks N., Grotte G.J., Keenan D.J., Millner R., Fabri B.M., Jones M. North west quality improvement programme in cardiac interventions. Surgeon specific mortality in adult cardiac surgery: comparison between crude and risk stratified data. Br Med J 2003;327(7405):13-17.[Abstract/Free Full Text]
5. Kawachi Y., Nakashima A., Kosuga T., Tomoeda H., Nishimura Y., Toshima Y. Early and late results of cardiac and thoracic aortic surgery in octogenarians. Circ J 2003;67(6):539-544.[CrossRef][Medline]
6. Michel P., Roques F., Nashef S.A. Logistic or additive EuroSCORE for high-risk patients ?. Eur J Cardiothorac Surg 2003;23(5):684-687.[Abstract/Free Full Text]
7. Roques F., Michel P., Goldstone A.R., Nashef S.A. The logistic EuroSCORE. Eur Heart J 2003;24(9):881-882.[Free Full Text]
8. Immer F.F., Krähenbühl E.S., Immer-Bansi A.S., Berdat P.A., Kipfer B., Eckstein F.S., Saner H., Carrel T.P. Quality of life after interventions on the thoracic aorta with deep hypothermic circulatory arrest. Eur J Cardiothorac Surg 2002;21(1):10-14.[Abstract/Free Full Text]

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