Our results indicate superior efficacy with the higher dose of intravenous amiodarone for the routine treatment of acute atrial fibrillation or flutter in a coronary care unit setting. The divergence between the two groups after 10 hours suggests a sustained beneficial effect of prolonged high dose infusion as compared to low dose. The presence of severe co-morbidity in the majority of patients is considered pro-arrhythmic and would be expected to reduce the rate of conversion, and also increase the probability of recurrence of arrhythmia, as compared to that in more selected populations. Infections, heart failure, recent surgery, and myocardial ischaemia were the most common co-morbid conditions. Few patients needed cardioversion. No adverse event requiring specific treatment was seen. Both doses were effective for rate control. Only two patients received additional medication for rate control. As we wished to study the effect of amiodarone monotherapy to establish a simple routine treatment algorithm in a typical clinical setting, we did not include pre-specified combined treatment strategies. An open label, single blind, alternate dose design was considered adequate to address our hypothesis, as the prescribed end points were objective. Selection bias was minimised as allocation was not known to the investigators before informed consent had been obtained. The equal distribution of flutter and fibrillation in the two groups indicates that preferential selection has not occurred. Having no placebo control group follows from our inclusion criteria in that rapid treatment was indicated on clinical grounds. In patients admitted to a coronary care unit, atrial fibrillation or flutter with tachycardia is a major cause of haemodynamic instability. Amiodarone has been established to have a rapid frequency modulating effect in addition to its efficacy with regard to conversion to sinus rhythm. It is most likely that the rate of conversion for both groups reflects an effect of the two treatment regimens evaluated. Our patients cannot be directly compared to populations in previous studies where patients with heart failure, recent myocardial infarction, pulmonary disease, and hypotension were generally not included. Such patients constituted a significant part of our material. A high spontaneous conversion rate has been reported in patients without such specified clinical predictors whereas conversion was notably diminished when these were present.
In our study, standard high dose intravenous amiodarone maintenance treatment following a loading dose of 300 mg/30 mins represents effective treatment for acute onset atrial fibrillation or flutter in the routine coronary care unit setting. The tendency towards increased late conversions in the high dose group suggests that amiodarone treatment should be continued for 24 hours before cardioversion in stabilised patients. A high dose, intravenous amiodarone regimen may represent an effective and safe strategy in the routine coronary care unit setting for treatment of atrial fibrillation or flutter.
The establishment of an effective routine treatment algorithm for the large and heterogeneous population seen in the coronary care unit would simplify clinical practice, however, further large scale studies are required to confirm our findings.