LETTER TO THE EDITOR
Coronary artery revascularization in patients with sustained ventricular arrhythmias in the chronic phase of a myocardial infarction
Paul Khairy, MD, CM, FRCPCa
a Montreal Heart Institute, 5000 Belanger E., Montreal, Quebec, Canada H1T 1C8
pkhairy{at}videotron.ca
Although Brugada et al. (1) are to be commended for their efforts to clarify the complex relationship between postinfarction sustained ventricular arrhythmias and coronary revascularization, their study is limited by important methodologic flaws and questionable inferences. First, only crude unadjusted estimates of effects were reported. Therefore, the analysis failed to control for numerous potential confounding variables such as age, gender, ejection fraction, type of revascularization, number of diseased vessels and medical therapy. Second, analysis of cohort data must fundamentally account for unequal lengths of time that participants are observed for the outcome of interest (e.g., number of recurrent ventricular arrhythmias per unit time per person) (2). Whereas the Kaplan-Meier product-limit estimate may be a useful statistical tool to assess event-free survival in a given population, comparing uncontrolled subgroups is highly disputable. Moreover, unstable estimates result when the number of events (Ak) at each time (Tk) is a large portion of the number at risk at that time (Nk) (i.e., Ak/Nk must be small) (3). This condition is violated in both analyses reported in Figures 1 and 2 (1). A multivariate predictive model that accounts for length of follow-up and adjusts for covariates (e.g., Cox proportional hazards survival model or Poisson regression) would have been a more appropriate and meaningful method of analysis. Furthermore, most reported p values are derived from markedly underpowered comparisons and may therefore be deceiving. For example, to detect a 15% difference at 80 months (see Fig. 2) in recurrent events in noninducible (n = 10) compared to inducible patients (n = 52), only a power of 13.6% is obtained (given a standard two-tailed  = 0.05).
Perhaps most questionable is the unsubstantiated inference that their results suggest "that the combination of coronary artery revascularization and antiarrhythmic therapy (drug therapy or defibrillator implantation) is an excellent combination and should be used systematically." Conclusions regarding the value of revascularization can clearly not be deduced from a study of only revascularized patients, especially if one considers the high reported rate of recurrent ventricular arrhythmias despite routine revascularization (i.e., 32/62 = 58%). Great caution must be exerted in interpreting the reported data to avoid unfounded conclusions and their important implications.
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References
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1. Brugada J, Aguinaga L, Mont L, Betriu A, Mulet J, Sanz G. Coronary artery revascularization in patients with sustained ventricular arrhythmias in the chronic phase of a myocardial infarction: effects on the electrophysiologic substrate and outcome. J Am Coll Cardiol. 2001;37:529–533[Abstract/Free Full Text]
2. Kelsey JL, Whittemore AS, Evans AS, Thompson WG. Methods in Observational Epidemiology. 2nd ed. New York, NY: Oxford University Press; 1996. p. 130–166
3. Rothman KJ, Greenland S. Measures of disease frequency. Rothman KJ, Greenland S. Modern Epidemiology. 2nd ed. Philadelphia, PA: Lippincott, Williams & Williams; 1998. p. 29–46
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