Preoperative amiodarone as prophylaxis against atrial fibrillation after heart surgery
CommentIn this study, administering low dose oral amiodarone for two weeks prior to heart surgery significantly reduced the incidence of post-operative atrial fibrillation (from 42% to 23%). As a result, hospital length of stay and cost were reduced as well.
It is unfortunate that no primary endpoints were specified in the methods section. This leaves the authors open to the criticism that, had the results been less impressive, the data might have been analyzed differently in an attempt to come up with something significant.
It is worth noting that, although the authors compare beta-blocker vs. no beta-blocker in the two study groups and found no statistically significant difference, they did not give the numbers for the other "grouping": amiodarone vs. placebo in the subgroups of patients taking and not taking beta-blockers. According to the two by two table I constructed above, the difference between amiodarone and placebo is much more impressive in the subgroup of patients taking beta-blockers preoperatively (27% vs. 61%), than in the subgroup not on beta-blockers (21% vs. 33%). It is not clear to me why this should be the case. Beta-blocker withdrawal might be a contributing factor, although over 90% of patients who took beta-blockers before surgery continued to take them post-operatively. Perhaps the post-op doses or absorption were lower. Or perhaps this is just a fluke of post-hoc analysis.
The role of amiodarone vs. beta-blockade remains to be clarified. In patients not on beta-blockers who can tolerate beta-blocker therapy, it is not clear that amiodarone is much better for preventing atrial fibrillation. In patients already on beta-blockers and at risk for beta-blocker withdrawal, on the other hand, it would seem to be more useful. In patients who cannot tolerate beta-blockers, amiodarone certainly seems like a reasonable alternative, although, as noted above, the benefits in this subgroup might be less than the 50% found by the authors in the entire study group.
January 12, 1998
ReferencesReferences related to this article from the NLM's PubMed database.
Reader CommentsDate: Wed, 21 Jan 1998
From: "C. Sitges Serra" <firstname.lastname@example.org>
Surprisingly, authors make no comment about thyroid function before and/or after receiving Amiodarone. It´s well known that Amiodarone has a high content of Iodine in its molecule and, in a high percentage of patients it may provoke clinical and/or subclinical changes on respect to thyroid gland function such as hyperthyroidism or mild changes in TSH or Thyroxine.
Amiodarone has been very questioned among cardiologists because of its benefit/risk ratio and also because there are the other therapies such as Propafenone Clorhidrate that might have similar benefits at lower risk. Lung and liver fibrosis are among other side effects that Amiodarone might cause, though probably that would need long periods of treatment.
C. Sitges-Serra(General Practitioner).
A study looking at amiodarone vs. beta-blockers or drugs such as propafenone (presumably initiated in the hospital) would be very useful.
Date: Fri, 06 Feb 1998
It is an interesting study. Have there been any studies in the past regarding alterations in the thyroid functions after cardio pulmonary bypass? If there are any, giving Amiodarone intra / perioperatively may have effects, and might make things look differently?
Date: Wed, 25 Feb 1998
I just got around to analyzing this article carefully for our internal medicine residents' journal club today, and noticed a few more problems.
One is that results are liberally mixed in with methods (eg., fourth sentence under Methods: Study Protocol, pp. 1786): "Patients were enrolled a mean (+/- SD) of 13 +/- 7 day before surgery." And "Outpt compliance by pill count was 96%." And "A home-nurse evaluation was performed 7 +/- 2 days after the pts were discharged..." etc.
There is no power analysis (more important with a negative trial, but nevertheless should be performed a priori).
In Table 1, standard deviations are given for data one would not expect to be normally distributed (eg., NYHA functional class and others).
On page 1788 in the second full sentence, 7/64 is not 14%, as reported, but 11%. Likewise, 11/60 is not 31%, but 18%.
No "fatal" errors, but concerning nonetheless.
John Foxworth, PharmD
The discrepancies in the percentages you point out are probably due to the fact that patients who developed atrial fibrillation were excluded from further analysis. Thus, the denominators are smaller than the original 64 and 60, and the percentages are correspondingly higher.
I agree with all of your other comments. -- mj
June 19, 1997
to the editor about this article, from the May 7, 1998 New England
Journal of Medicine.
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