European Heart Journal Advance Access published online on August 1, 2008
European Heart Journal, doi:10.1093/eurheartj/ehn353
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Still without impact on adverse post-operative outcomes: pre-operative statin therapy in patients undergoing cardiac surgery
Department of Sports Medicine
Medical Clinic
University of Tuebingen
Tuebingen
Germany
Department of Sports Medicine
Medical Clinic
University of Tuebingen
Tuebingen
Germany
Email: Perikles.simon{at}med.uni-tuebingen.de
With interest we read the systematic review by Liakopoulos et al.1 In their meta-analysis of mainly observational studies, the authors conclude that the early clinical outcome is substantially improved in statin pre-treated patients.
The authors correctly address an unequal distribution of potentially confounding factors among patient groups as a limitation for the correct interpretation of their results. More explicitly, factors such as pre-operative treatment with β-blocker may indeed contribute in a substantial way to the outcome of their meta-analysis. The authors report treatment with β-blocker to be significantly 1.3-fold more frequent in the group of statin-treated patients with P < 0.01. Just to elucidate the strength of this potential confound: the precise significance level is P = 3 x 10–127 based on a two-sided Fisher's exact t-test.
Observational studies underlying this meta-analysis already report and discuss group differences in the underlying risk factors and their management2–4 as well as group differences in the emergency status of the cardiac surgery2 as significant contributors to an effect on post-operative outcomes.
The studies of Ali and Buth2 (weighted with 26.62% in the meta-analysis), Clark et al.3 (18.04%) and Powell et al.4 (11.27%) statistically adjusted their odds ratios (ORs) for the respective confounds. Ali and Buth reported an unadjusted reduction in an early, all-cause mortality of OR of 0.50 [95% confidence interval (CI) = 0.38–0.67, P = 0.0001], but an adjusted non-significant OR of 0.9 (95% CI = 0.6–1.2, P = 0.36), Clark et al. calculate an adjusted OR of 0.55 (95% CI: 0.32–0.93) compared with an unadjusted OR of 0.43 (95% CI: 0.28–0.66) and Powell et al. reported an unadjusted OR of 0.62 (95% CI: 0.40–0.96) but a non-significant adjusted OR of 0.83 (95% CI: 0.50–1.37, P = 0.46). Especially the studies of Ali and Buth and Powell et al. demonstrate the uncertainty of the statistical significance of pre-operative statin treatment on clinical outcomes using unadjusted data.
According to the MOOSE Guidelines for Meta-Analyses and Systematic Reviews of Observational Studies,5 indication of statistical uncertainty of findings has to be presented within the result section of a meta-analysis. In the meta-analysis by Liakopoulos et al., it would therefore have been necessary to report the discrepancy between the unadjusted data that have been used in their analysis and the adjusted data of the original contributions.
Most importantly, in this particular case, a proper meta-analysis would have required complete raw data sets including information about all relevant confounding variables. This will not be possible for the topic of pre-operative statin treatment, because the original contributions largely differ in the number and type of confounding variables adjusted for.
Clinically relevant conclusions may, therefore, rely on the convincing negative outcomes of the study of Ali and Buth until randomized controlled trials may show a beneficial effect of pre-operative statin therapy on early post-operative adverse outcomes in cardiac surgery patients.
References
- Liakopoulos OJ, Choi YH, Haldenwang PL, Strauch J, Wittwer T, Dörge H, Stamm C, Wassmer G, Wahlers T. Impact of preoperative statin therapy on adverse postoperative outcomes in patients undergoing cardiac surgery: a meta-analysis of over 30000 patients. Eur Heart J (2008) 29:1548–1559.
[Abstract/Free Full Text] - Ali IS, Buth KJ. Preoperative statin use and outcomes following cardiac surgery. Int J Cardiol (2005) 103:12–18.[CrossRef][Web of Science][Medline]
- Clark LL, Ikonomidis JS, Crawford FA Jr, Crumbley A III, Kratz JM, Stroud MR, Woolson RF, Bruce JJ, Nicholas JS, Lackland DT, Zile MR, Spinale FG. Preoperative statin treatment is associated with reduced postoperative mortality and morbidity in patients undergoing cardiac surgery: an 8-year retrospective cohort study. J Thorac Cardiovasc Surg (2006) 131:679–685.
[Abstract/Free Full Text] - Powell BD, Bybee KA, Valeti U, Thomas RJ, Kopecky SL, Mullany CJ, Wright RS. Influence of preoperative lipid-lowering therapy on postoperative outcome in patients undergoing coronary artery bypass grafting. Am J Cardiol (2007) 99:785–789.[CrossRef][Web of Science][Medline]
- Stroup DF, Berlin JA, Morton SC, Olkin I, Williamson GD, Rennie D, Moher D, Becker BJ, Sipe TA, Thacker SB. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. J Am Med Assoc (2000) 283:2008–2012.
[Abstract/Free Full Text]
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