Postoperative Atrial Fibrillation
Abstract & Commentary
Synopsis: There was little difference in a cardioversion vs. a rate control strategy for restoring sinus rhythm in post heart surgery patients who go into atrial fibrillation.
Source: Lee JK, et al. Am Heart J 2000;140:871-877.
Atrial fibrillation (AF) after heart surgery is a common problem, despite recent attempts to prevent it with prophylactic drug therapy. Thus, Lee and colleagues evaluated two strategies for managing AF in 50 postoperative heart surgery patients: conversion to sinus rhythm vs. heart rate control. The conversion strategy initially used pharmacologic therapy with sotalol or propafenone, or occasionally amiodarone or procainamide. If cardioversion did not occur within 48 hours, electrical cardioversion was used. In the rate control arm, initial therapy was usually intravenous diltiazem or beta-blockers and digoxin. Adequate rate control was defined as average heart rates less than 110 beats per minute. Intravenous heparin and warfarin were given to both groups. Continuous ECG monitoring was used until hospital discharge to detect recurrences of AF. The hypothesis tested was that a cardioversion strategy would restore normal sinus rhythm sooner and result in reduced hospital stay vs. a rate control strategy. The patients randomized to both groups were very similar. Of interest, about two-thirds were on beta-blockers at the time of randomization. AF occurred most frequently on the third postoperative day. Five patients crossed over from rate control to cardioversion: three by physician request after their AF recurred; one because of a contraindication to anticoagulation; and one because of failure of rate control. Five patients spontaneously converted before drug administration; three in the rate control arm and two in the cardioversion arm. Rate control required the administration of two drugs in the majority of patients. Time to conversion to sinus rhythm averaged 11 hours and was not different between the two arms. Hospital stay was less in the cardioversion arm (9 days vs 13 days; P = 0.05). There was no difference in relapse rates between the two groups (37% cardioversion vs 57% rate control; P = NS), but by eight weeks, more than 90% in both groups were in sinus rhythm. Complications were more frequent in the cardioversion arm mainly due to the adverse effects of the antiarrhythmic drugs. Lee et al concluded that there was little difference in a cardioversion vs. a rate control strategy for restoring sinus rhythm in post heart surgery patients who go into AF.
Comment by Michael H. Crawford, MD
Several recent studies have described the benefits of preoperative prophylactic therapy to prevent AF after heart surgery with beta-blockers, sotolol, or aminodarone. This approach has not achieved widespread acceptance possibly due to higher costs, increased complications, or the less than 100% success of using these agents preoperatively. Thus, Lee et al focused on the issue of which postoperative strategy is best if AF develops in the postoperative heart surgery patient. In this study, despite the fact that two-thirds of the patients were on beta-blockers perioperatively, 18% of their heart surgery patients surveyed developed AF. Perhaps this incidence would have been less if amiodarone had been used instead, but at what extra cost? Regardless, a strategy for the patient who develops AF is needed. An aggressive cardioversion approach with antiarrhythmic drugs is preferred by many, because it is believed to eliminate the problem and immediately reduce the risk of stroke, possibly without having to anticoagulate the patient. In this study, a conservative approach was used in which all patients were anticoagulated, which is probably wise if no contraindications exist.
The results of this comparative strategy study showed that rate control was as effective as cardioversion for the main study end point of conversion to sinus rhythm. This is probably due to the high incidence of spontaneous conversion in both groups. In fact, 10% of the subjects in both groups converted before any drugs could be administered. Hospital stay was less in the cardioversion group, possibly because recurrent AF during the hospital stay was more common in the rate control group. However, by eight weeks, more than 90% of the patients in both groups were in sinus rhythm. Thus, AF postoperatively seems to be a transient problem in most patients.
There are several limitations to this study. It was not blinded, because that would have been very hard to do. Thus, hospital stay could have been prolonged in the rate control group because the physicians were less likely to discharge these patients off antiarrhythmic drugs. Also, there was no standard therapy. Physicians were allowed any reasonable treatment within the confines of the two strategies. This makes conclusions about specific treatments difficult to determine. The number of patients was small and Lee et al referred to this as a pilot study for a possible larger trial. Finally, 70% of the patients had coronary surgery only. Thus, similar results may not be obtainable in valve surgery patients.
At this point, one must conclude that considerable physician latitude is permissible. Some may choose an aggressive prophylactic therapy approach. Others may be selective about prophylaxis and aggressively treat AF if it develops. Others may reasonably control rate unless this is not possible or it fails. Whatever strategy is chosen, immediate anticoagulation with heparin is recommended and coumadin for 4-12 weeks should be seriously considered for all who develop even transient AF postoperatively. Finally, specific treatable causes of AF should be sought such as fever, thyrotoxicosis, or mechanical stimulation of the atria from catheters.
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