Oral amiodarone and atrial fibrillation

Abstract

Satyendra Giri and colleagues' results1Giri S White CM Dunn AB et al.Oral amiodarone for prevention of atrial fibrillation after open heart surgery, the Atrial Fibrillation Suppression Trial (AFIST): a randomised placebo-controlled trial.Lancet. 2001; 357: 830-836Summary Full Text Full Text PDF PubMed Scopus (186) Google Scholar are encouraging for the management of this challenging group of patients, yet we have some concerns about the increasing use of amiodarone. Although not seen in the current study, the outpatient administration of amiodarone carries a small risk of proarrhythmia, bradycardia, and, although less likely, tachycardia, especially in patients with structural heart disease.2Pinski SL Helguera ME Antiarrhythmic drug initiation in patients with atrial fibrillation.Prog Cardiovasc Dis. 1999; 42: 75-90Summary Full Text Full Text PDF PubMed Scopus (11) Google Scholar This risk can be kept to a minimum by careful selection of patients, as Giri and colleagues did (normal baseline corrected QT interval, absence of advanced heart block, haemodynamic stability). Their study was not powered to detect an increase in proarrhythmia or proarrhythmia-related mortality in the amiodarone treated group. Amiodarone interacts with digoxin, which was received by 17% of the placebo group and 10% of the amiodarone group. Whether the dose of digoxin was reduced in study participants is unclear. If not reduced, toxic effects from digoxin could have occurred, possibly explaining the increased frequency of nausea in the amiodarone group. Oral administration of amiodarone in the immediate postoperative period can be difficult because patients are intubated. Whether amiodarone was administered through a nasogastric tube or intravenously during that period of time is unclear. Intravenous amiodarone greatly increases cost compared with tablets. Intravenous amiodarone is also more likely to cause hypotension.3Scheinman MM Levine JH Cannom DS et al.Dose-ranging study of intravenous amiodarone in patients with life-threatening ventricular tachyarrhythmias.Circulation. 1995; 92: 3264-3272Crossref PubMed Scopus (243) Google Scholar The lower rate of cerebrovascular accidents in the amiodarone group could potentially be explained by inadequate anticoagulation of the placebo group. This could be clarified if data on the administration and adequacy of anticoagulation (arterial partial thromboplastin time, international normalised ratio, interval from onset of atrial fibrillation to initiation of anticoagulation) were available. Given the limitations of amiodarone use in this population (preoperative dosing required, difficult administration immediately postoperatively, drug interactions, need for screening for toxic effects), alternate approaches for arrhythmia prevention could prove more fruitful. Indeed, four of five studies (table 1) showed a 61–70% relative-risk reduction in postoperative atrial fibrillation using multisite or algorithm-based atrial pacing via temporary pacing wires.4Daubert JC Mabo P Atrial pacing for the prevention of postoperative atrial fibrillation: how and where to pace?.J Am Coll Cardiol. 2000; 35: 1423-1427Summary Full Text Full Text PDF PubMed Scopus (27) Google Scholar By contrast with the findings of Giri and colleagues, pacing is synergistic with β-blocker administration, and can result in reduced hospital stay and cost.4Daubert JC Mabo P Atrial pacing for the prevention of postoperative atrial fibrillation: how and where to pace?.J Am Coll Cardiol. 2000; 35: 1423-1427Summary Full Text Full Text PDF PubMed Scopus (27) Google ScholarTableRandomised studies of pacing for prevention of postoperative atrial fibrillationStudyControlLA pacingRA pacingBiatrial pacingRRR*Biatrial pacing vs control (RA pacing vs control in study by Blommaert et al).ARRFan et al13/31 (41·9%)12/33 (36·4%)12/36 (33·3%)4/32 (12·5%)70%20·8%Daoud et al11/39 (28·2%)··12/38 (31·6%)4/41 (9·8%)65%18·4%Gerstenfeld et al7/21 (33·3%)··6/21 (28·6%)7/19 (36·8%)····Blommaert et al13/48 (27·1%)··5/48 (10·4%)··61%16·6%Levy et al25/65 (38·5%)····9/65 (13·8%)64%24·7%LA=left atrial; RA=right atrial; RRR=relative-risk reduction; ARR=absolute risk reduction.* Biatrial pacing vs control (RA pacing vs control in study by Blommaert et al). Open table in a new tab LA=left atrial; RA=right atrial; RRR=relative-risk reduction; ARR=absolute risk reduction. Atrial fibrillation after open-heart surgery is common and carries a high risk of morbidity. Giri and colleagues are to be congratulated for improving our understanding of this disease. Oral amiodarone and atrial fibrillationAuthors' reply Full-Text PDF