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Eur J Cardiothorac Surg 2006;29:856-857
© 2006 Elsevier Science NL

Letter to the Editor

Do we need the new Italian risk stratification model for CABG patients?

Department of Cardiothoracic Surgery, University of Cologne, Kerpener Str. 62, 50924 Cologne, Germany

Received 24 January 2006; accepted 8 February 2006.

^_* Corresponding author. Tel.: +49 221 4785359; fax: +49 221 4787927. (Email: khosro.hekmat{at}uk-koeln.de).

Key Words: Risk model • Stratification • CABG

We have read with interest the article entitled ‘The Italian CABG Outcome Study: short-term outcomes in patients with coronary artery bypass graft surgery" by Seccareccia et al. [1]. This study was conducted by the Italian National Centre of Epidemiology, Surveillance and Health Promotion to compare 30-day mortality rate in different centers all over Italy. They suggest a new model for preoperative risk stratification. This is a study with a large number of patients (n = 34,310). However, the new risk model reveals not a single variable, which is not already described in previous risk stratification scoring systems.

In addition to the editorial comments published in the same issue [2,3] we believe that the paper has several major drawbacks, which disqualifies the new scoring model. The authors have divided the patients into two groups, which is appreciated from a statistical point of view. Unfortunately, the Hosmer–Lemeshow values of the sample I are missing. Calibration compares the observed mortality with that predicted by the model within severity strata. The most accepted method for measuring calibration is the Hosmer–Lemeshow goodness-of-fit statistic. Small ² values and high corresponding p-values indicate a good calibration. The Hosmer–Lemeshow values of the entire study population is stated in the legend of Table 2. The ² value is 18.08 with a p-value of 0.02, indicating a significant difference between observed and expected number of deaths. Since the whole study population shows an insufficient calibration the new model should be recalibrated before its widespread use in other cohorts.

New scoring models should always be compared with currently used stratification systems like the EuroSCORE [4]. It might be the time for an update of preoperative risk stratification scores, since the EuroSCORE is based on data of patients operated in 1995. Therefore, a comparison with the EuroSCORE in terms of calibration and discrimination would be beneficial.

The mortality rate is below 1% in five centers, with the lowest rate of 0.33% in one center. The Bristol affair in the UK [5] has made clear that mortality rates may be inaccurate. Large national studies should consult national authorities, where all deaths are registered before publication. Mortality is the dependent variable in most risk stratification studies. Its accuracy is much more important than the accuracy of the candidate variables. Menicanti [3] describes the wrong statistics for Center No. 15, where six patients are dead but for the study they were alive. The calculation of calibration and discrimination is therefore unreliable and should be corrected.

References

1. Seccareccia F, Perucci CA, D’Errigo P, Arca M, Fusco D, Rosato S, Greco D, On behalf of the Research Group of the Italian CABG Outcome Study The Italian CABG Outcome Study: short-term outcomes in patients with coronary artery bypass graft surgery. Eur J Cardiothorac Surg 2006;29(1):56-62.[Abstract/Free Full Text]
2. Nashef SA. Editorial comment. The Italian job on CABG outcomes. Eur J Cardiothorac Surg 2006;29(1):62-63.[Free Full Text]
3. Menicanti LA. Editorial comment. Eur J Cardiothorac Surg 2006;29(1):63-64.[Free Full Text]
4. Roques F, Nashef SA, Michel P, Gauducheau E, de Vincentiis C, Baudet E, Cortina J, David M, Faichney A, Gabrielle F, Gams E, Harjula A, Jones MT, Pintor PP, Salamon R, Thulin L. Risk factors and outcome in European cardiac surgery: analysis of the EuroSCORE multinational database of 19030 patients. Eur J Cardiothorac Surg 1999;15(6):816-822[discussion 822–3].[Abstract/Free Full Text]
5. Gibbs JL, Cunningham D, de Leval M, Monro J, Keogh B. Paediatric cardiac surgical mortality after Bristol: paediatric cardiac hospital episode statistics are unreliable. Br Med J 2005;330(7481):43-44[author reply 44].[Free Full Text]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Khosro Hekmat Uwe Mehlhorn Thorsten Wahlers Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hekmat, K. Articles by Wahlers, T. Search for Related Content PubMed PubMed Citation Articles by Hekmat, K. Articles by Wahlers, T. Related Collections Coronary disease