LETTER
Amiodarone and Ventricular Arrhythmia Suppression
James R. Cook
15 February 1993 | Volume 118 Issue 4 | Page 316
TO THE EDITOR:
In their interesting report on the "rapid and dramatic" reduction in ventricular arrhythmias in patients treated with oral amiodarone, Kim and colleagues [1] correctly point out the possible confounding effects of other antiarrhythmics administered early in the course of amiodarone loading. Despite this caveat, the graphs and P values presented appear impressive. However, several problems in the analysis may render the conclusion erroneous. First, use of analysis of variance (ANOVA) requires an implicit assumption of normally distributed data. No mention was made of data transformation (that is, logarithms), often used to reduce the influence of extreme values and approximate a normally distributed variance. In subsequent analyses, the authors used the Kruskal-Wallis test, a statistic useful for analysis of non-normally distributed data, but the required comparison with the chi-square distribution to test for significance was not cited [2]. In the absence of this and an F statistic for the ANOVA, the source of the reported P value is unclear. Finally, no attempt appears to have been made to adjust for an acceptable level of significance when multiple comparisons were considered [3].
Previous studies have demonstrated arrhythmia suppression in patients treated with amiodarone [4], but others have shown placebo "therapy" also results in significant arrhythmia suppression when similar efficacy criteria are used [5]. I believe that correct analysis will not support their conclusion.
1. Kim SG, Mannino MM, Chou R, Roth S, Roth JA, Desai B, et al. Rapid suppression of spontaneous ventricular arrhythmias during oral amiodarone loading. Ann Intern Med. 1992; 117:197-201.
2. Fleiss JL. The design and analysis of clinical experiments. New York: John Wiley & Sons; 1986:78.
3. Glantz SA, Slinker BK. Primer of applied regression and analysis of variance. New York: McGraw-Hill, Inc.; 1990:292.
4. Marchlinski FE, Buxton AE, Flores BT, Doherty JU, Waxman HJ, Josephson ME. Value of Holter monitoring in identifying risk for sustained ventricular arrhythmia recurrence on amiodarone. Am J Cardiol. 1985; 55:709-12.
5. Pratt CM, Hallstrom A, Theroux P, Romhilt D, Coromilas J, Myles J. Avoiding interpretive pitfalls when assessing arrhythmia suppression after myocardial infarction: insights from the long-term observations of the placebo-treated patients in the Cardiac Arrhythmia Pilot Study (CAPS). J Am Coll Cardiol. 1991; 17:1-8.
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