Year : 2013  |  Volume : 16  |  Issue : 3  |  Page : 163--166

The application of European system for cardiac operative risk evaluation II (EuroSCORE II) and Society of Thoracic Surgeons (STS) risk-score for risk stratification in Indian patients undergoing cardiac surgery


Deepak Borde1, Uday Gandhe1, Neha Hargave1, Kaushal Pandey2, Vishal Khullar2,  
1 Department of Cardiac Anesthesia, P.D. Hinduja National Hospital, Lilavati Hospital, Fortis Hospital, Mumbai, Maharashtra, India
2 Department of Cardiac Surgery, P.D. Hinduja National Hospital, Lilavati Hospital, Fortis Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Deepak Borde
Department of Cardiac Anesthesia, P.D. Hinduja National Hospital, Veer Savarkar Marg, Mahim, Mumbai, Maharashtra
India

Abstract

Aims and Objectives: To validate European system for cardiac operative risk evaluation II (EuroSCORE II) and Society of Thoracic Surgeons (STS) risk-score for predicting mortality and STS risk-score for predicting morbidity in Indian patients after cardiac surgery. Materials and Methods: EuroSCORE II and STS risk-scores were obtained pre-operatively for 498 consecutive patients. The patients were followed for mortality and various morbidities. The calibration of the scoring systems was assessed using Hosmer-Lemeshow test. The discriminative capacity was estimated by area under receiver operating characteristic (ROC) curves. Results: The mortality was 1.6%. For EuroSCORE II and STS risk-score C-statics of 5.43 and 6.11 were obtained indicating satisfactory model fit for both the scores. Area under ROC was 0.69 and 0.65 for EuroSCORE II and STS risk-score with P values of 0.068 and 0.15, respectively, indicating poor discriminatory power. Good fit and discrimination was obtained for renal failure, long-stay in hospital, prolonged ventilator support and deep sternal wound infection but the scores failed in predicting risk of reoperation and stroke. Mortality risk was correctly estimated in low (< 2%) and moderate (2-5%) risk patients, but over-estimated in high-risk (> 5%) patients by both scoring systems. Conclusions: EuroSCORE II and STS risk-scores have satisfactory calibration power in Indian patients but their discriminatory power is poor. Mortality risk was over-estimated by both the scoring systems in high-risk patients. The present study highlights the need for forming a national database and formulating risk stratification tools to provide better quality care to cardiac surgical patients in India.



How to cite this article:
Borde D, Gandhe U, Hargave N, Pandey K, Khullar V. The application of European system for cardiac operative risk evaluation II (EuroSCORE II) and Society of Thoracic Surgeons (STS) risk-score for risk stratification in Indian patients undergoing cardiac surgery.Ann Card Anaesth 2013;16:163-166


How to cite this URL:
Borde D, Gandhe U, Hargave N, Pandey K, Khullar V. The application of European system for cardiac operative risk evaluation II (EuroSCORE II) and Society of Thoracic Surgeons (STS) risk-score for risk stratification in Indian patients undergoing cardiac surgery. Ann Card Anaesth [serial online] 2013 [cited 2020 Sep 29 ];16:163-166
Available from: http://www.annals.in/text.asp?2013/16/3/163/114234


Full Text

 Introduction



The European system for cardiac operative risk evaluation (EuroSCORE) has been used for many years since its introduction in 1999. [1] It is widely used for predicting risk of mortality and has served as benchmark for assessment of cardiac surgical practices with more than 1300 formal citations in medical literature. However, in recent years, different publications have highlighted that this scale could be overestimating post-operative risk in certain subgroup of patients. [2] EuroSCORE II is available since October 2011 and has been developed to overcome short comings of original EuroSCORE. [3] Society of Thoracic Surgeons (STS) risk-score in addition to providing risk of mortality, provides risk of post-operative major morbidities. A prospective observational study to compare these two scoring systems for risk prediction in cardiac surgery was designed.

 Materials and Methods



This study includes 537 consecutive patients who underwent cardiac surgery between December 2011 and October 2012. All patients were operated by the same surgical team. Thirty nine patients were excluded from analysis because STS risk-scores could not be calculated for them; the reasons included multiple valve surgeries, tricuspid valve surgery, concomitant MAZE procedure, surgery on aorta, and surgery for congenital heart diseases. The final analysis included 498 patients who underwent isolated coronary artery bypass grafting (CABG), mitral valve replacement (MVR)/mitral valve repair and aortic valve replacement (AVR) or combined CABG with MVR or AVR. The patient characteristics and the operative data are summarized in [Table 1]. Based on history, physical examination and investigations, the operative risk was estimated by EuroSCORE II available at http://www.euroscore.org and STS risk-score available at http://riskcalc.sts.org/STSWebRiskCalc273/de.aspx. The EuroSCORE II assign risks of mortality while STS risk-score assign risk of mortality, length of stay, prolonged ventilation, renal failure, stroke, deep sternal wound (DSW) infection and probability of reoperation to every patient. Patients were prospectively followed up in the post-operative period. The primary end points for the study were in-hospital mortality; and morbidity in the form of length of stay, ventilation duration, stroke, renal failure and DSW infection. The definitions for morbidity were followed as directed by STS available on http://riskcalc.sts.org/STSWebRiskCalc273/support_definitions. Based on their assigned scores patients were categorized into low (< 2), moderate (2-5) and high (> 5) risk of mortality. The statistical analysis was done with the statistical package for windows (SPSS Version 17). The calibration of both scoring systems was assessed using the Hosmer-Lemeshow (HL) test, which compares the observed versus expected mortality by risk decile. Calibration is considered to be poor if the test is significant. The discrimination measures the capacity of a model, in this case EuroSCORE II and STS, to differentiate between the individuals of a sample that suffer an event, death or morbidity and those who do not. The discriminative capacity of the analyzed events of the two scales was estimated by means of receiver operating characteristic (ROC) curves. Their areas under the curve (AUC) were calculated.{Table 1}

 Results



The study population included 498 patients eligible for calculation of EuroSCORE II and STS risk-score. The patients were operated at three tertiary centers by the same surgical team. The age was 60.48 ± 7.51 years, 19.89% patients were female. The prevalence of various risk factors in study population is shown in [Table 1]. The overall mortality was 1.6%. Predicted mortality with EuroSCORE II and STS was 2.01 ± 1.41 and 1.60 ± 1.23, respectively. To validate the scores, their calibration power and discriminatory power were assessed. Using HL test, C-static of 5.43 and 6.11 were obtained for EuroSCORE II and STS risk-score, respectively, indicating satisfactory model fit for both the scores. The calculated area under ROC was 0.69 and 0.65 for EuroSCORE II and STS risk-score, respectively. This could not achieve statistical significance with P values of 0.068 and 0.15, respectively, indicating poor discriminatory power [Figure 1]. The specific observed and predicted morbidity rates with their level of significance are summarized in [Table 2]. Both the scores accurately predicted mortality in low and moderate risk patients, but over-estimated the risk in high risk category as shown in [Table 3] and [Table 4].{Table 2}{Table 3}{Table 4}{Figure 1}

 Discussion



Ideally modern stratification system should use large datasets representing current clinical practice and apply a systematic approach with the contemporary modeling techniques that employ advanced estimation and validation techniques. [4] In a step towards this aim, EuroSCORE II has been published. EuroSCORE II, an update of logistic EuroSCORE model, uses similar methodology but is derived from a more current data set and refined to incorporate evidence-based improvements and aims to reflect better current cardiac surgical practice. The EuroSCORE II was calculated on a consecutive sub cohort of 16,828 patients across 154 centers (four from India) in 43 countries over a 12-week period and its validity estimated in another sub cohort of 5553 subjects. EuroSCORE II was capable of predicting hospital mortality after major cardiac surgery, was well calibrated with an excellent discriminative capacity (AUC: 0.81, 95% confidence interval: 0.78-0.83). Analysis of high quality national and international database is utilized to update risk stratification and should be available to update it continuously. It requires professional organization to support such an initiative, as has been set up for STS database (maintained by STS). This not only improves our knowledge but also provides guidance for quality improvement and shared decision making. External validation study is must before incorporating such database to local clinical practice. Such studies for EuroSCORE II have been recently published from UK, [5],[6] Spain, [7] Italy [8],[9] and Finland. [10] These validation studies demonstrated that EuroSCORE II is a good predictor of perioperative mortality and performs better over previous versions. However, it is important to remember that some of these studies are retrospective and hence may not necessarily represent contemporary cardiac surgical care.

The present study being prospective, demonstrates that using HL test, EuroSCORE II and STS risk-score have good calibration power (P = 0.71 and P = 0.63, respectively) indicating satisfactory model fit. However, the area under the ROC curve 0.69 and 0.65 for EuroSCORE II and STS risk-score, respectively, could not achieve statistical significance (P = 0.068 and P = 0.15 for EuroSCORE II and STS risk-score respectively) indicating poor discriminatory power in the present cohort.

There is only one study for Indian population validating original EuroSCORE. This study (n = 1000) revealed good calibration and discrimination power of the score. [11] The EuroSCORE accurately predicted mortality in low and moderate risk Indian patients but under-estimated in high-risk Indian patients. In contrast, in the present study, the risk was over estimated in high-risk patients by both the scoring systems. Apparently, the application of these scoring systems remains uncertain in high-risk patients where risk assessment is very crucial.

In addition to mortality, various important morbidities indicate quality of care and have economic implications in cardiac surgical patients. The STS risk-score assigns probability of length of stay, prolonged ventilation, renal failure, stroke, DSW infection and reoperation to every patient. In our study, for parameters of STS risk-scores, good fit and discriminatory power was obtained only for renal failure, long-stay in hospital, prolonged ventilator support and DSW infection but the score failed in predicting reoperation and stroke. Apparently, this highlights the difference of risk factors prevalent in Indian population.

STS risk values can be calculated only for selected procedures. Large population of patients undergoing cardiac surgery in India are excluded where double valve replacement, concomitant tricuspid valve surgery, or MAZE procedure is commonplace. In our study, we had to exclude 8% patients (n = 38) from analysis who underwent surgeries for which STS risk-score was not available. In addition, the STS risk-score is time consuming and less user friendly.

Limitations of the study

The small sample size and performance of all surgical procedures by the same surgical team is a major limitation and may limit applicability of our findings to other surgical centers. Based on EuroSCORE II and STS risk-scores, high-risk patients constituted substantial number of patients in the study population 6.2% and 3.2%, respectively; hence making generalizations of the results, particularly for high-risk patients, and for other units is difficult. Our study included only 10% patients with rheumatic heart disease, one of the most common indications of cardiac surgery in India; in addition our study did not include patients undergoing off-pump CABG. The applicability of these scoring systems hence cannot be applied to these patient populations. A large multicenter study is recommended to further validate these scoring systems is thus warranted.

 Conclusions



To conclude, EuroSCORE II and STS risk-scores have satisfactory calibration power in Indian patients indicating good model fit but their discriminatory power is poor. Both the EuroSCORE II and STS risk-scores over estimated mortality in high-risk category (risk-score > 5) of patients. There is definite scope for improvement in applying EuroSCORE II and STS risk-scores to Indian population undergoing cardiac surgery. The present study highlights need for forming a national database and utilizing it for formulating risk stratification tools to provide better quality care to cardiac surgical patients in India.

 Acknowledgments



The authors would like to thank Dr. Shreedhar Joshi MD, FCA, DM for his contribution in preparing this manuscript and Dr. Dnyeshwar Gajbhare, MD for the statistical analysis.

References

1Roques F, Nashef SA, Michel P, Gauducheau E, de Vincentiis C, Baudet E, et al. Risk factors and outcome in European cardiac surgery: Analysis of the EuroSCORE multinational database of 19030 patients. Eur J Cardiothorac Surg 1999;15:816-22.
2Siregar S, Groenwold RH, de Heer F, Bots ML, van der Graaf Y, van Herwerden LA. Performance of the original EuroSCORE. Eur J Cardiothorac Surg 2012;41:746-54.
3Nashef SA, Roques F, Sharples LD, Nilsson J, Smith C, Goldstone AR, et al. EuroSCORE II. Eur J Cardiothorac Surg 2012;41:734-44.
4Takkenberg JJ, Kappetein AP, Steyerberg EW. The role of EuroSCORE II in 21 st century cardiac surgery practice. Eur J Cardiothorac Surg 2013;43:32-3.
5Grant SW, Hickey GL, Dimarakis I, Trivedi U, Bryan A, Treasure T, et al. How does EuroSCORE II perform in UK cardiac surgery; an analysis of 23 740 patients from the Society for Cardiothoracic Surgery in Great Britain and Ireland National Database. Heart 2012;98:1568-72.
6Chalmers J, Pullan M, Fabri B, McShane J, Shaw M, Mediratta N, et al. Validation of EuroSCORE II in a modern cohort of patients undergoing cardiac surgery. Eur J Cardiothorac Surg 2013;43:688-94.
7Carnero-Alcázara M, Guisasolaa JA, Lacruza FJ, Castellanosa LC, Carnicera JC, Medinillaa EV, et al. Validation of EuroSCORE II on a single-centre 3800 patient cohort. Interact CardioVasc Thorac Surg 2013;16:293-300.
8Barili F, Pacini D, Capo A, Rasovic O, Grossi C, Alamanni F, et al. Does EuroSCORE II perform better than its original versions? A multicentre validation study. Eur Heart J 2013;34:22-9.
9Di Dedda U, Pelissero G, Agnelli B, De Vincentiis C, Castelvecchio S, Ranucci M. Accuracy, calibration and clinical performance of the new EuroSCORE II risk stratification system. Eur J Cardiothorac Surg 2013;43:27-32.
10Biancari F, Vasques F, Mikkola R, Martin M, Lahtinen J, Heikkinen J. Validation of EuroSCORE II in patients undergoing coronary artery bypass surgery. Ann Thorac Surg 2012;93:1930-5.
11Malik M, Chauhan S, Malik V, Gharde P, Kiran U, Pandey RM. Is EuroSCORE applicable to Indian patients undergoing cardiac surgery? Ann Card Anaesth 2010;13:241-5.