IN RESPONSE:
We agree with Dr. Cheng that our data did not show that intravenous heparin had a significant benefit for hospitalized patients with atrial fibrillation that had lasted less than 48 hours. Our study, however, was underpowered to detect such a difference, with an estimated sample size in excess of 2500 patients (
level, 0.05; power, 8%) needed to show statistical significance given the low incidence of clinical thromboembolism in this group. Our recommendation that heparin anticoagulation be administered on admission is based on our concern that delaying anticoagulation may inadvertently allow many patients to go "unprotected" for an excess of 48 hours. Treatment of atrial fibrillation would then necessitate a month of warfarin therapy before cardioversion or transesophageal echocardiography-guided early cardioversion [1, 2].
Dr. Federman raises an important issue of identification of patient subgroups that are more or less likely to spontaneously convert to sinus rhythm. Several small series [3, 4] and preliminary data from a larger series [5] suggest that patients presenting with atrial fibrillation will spontaneous convert to sinus rhythm. According to preliminary data, atrial fibrillation that had begun less than 24 hours before presentation was the best clinical predictor of spontaneous conversion to sinus rhythm [4]. We agree that such information would be valuable for planning expeditious cardioversion for patients in whom spontaneous cardioversion would not be expected; observation might be more reasonable for patients with a high likelihood of spontaneous cardioversion.
1. Manning WJ, Silverman DI, Keighley CS, Oettgen P, Douglas PS. Transesophageal echocardiographically facilitated early cardioversion from atrial fibrillation using short-term anticoagulation: final results of a prospective 4.5 year study. J Am Coll Cardiol. 1995; 25:1354-61.
2. Klein AL, Grimm RA, Black IW, Leung DY, Chung MK, Vaughn SE, et al. Cardioversion guided by transesophageal echocardiography: the ACUTE pilot study. A randomized, controlled trial. Ann Intern Med. 1997; 126:200-9.
3. Falk RH, Knowlton AA, Bernard SA, Gotlieb NE, Battinelli NJ. Digoxin for converting recent-onset atrial fibrillation to sinus rhythm. A randomized, double-blinded trial. Ann Intern Med. 1987; 106:503-6.
4. Galve E, Ruis T, Ballester R, Artaza MA, Arnau JM, Garcia-Dorado D, et al. Intravenous amiodarone in treatment of recent-onset atrial fibrillation: results of a randomized controlled study. J Am Coll Cardiol. 1996; 27:1079-82.
5. Danias PG, Caulfield TA, Weigner MJ, Silverman DI, Manning WJ. Predictors of spontaneous conversion of new onset atrial fibrillation to sinus rhythm [Abstract]. Circulation. 1996; 94:I-572.
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