Initial energy setting, outcome and efficiency in direct current cardioversion of atrial fibrillation and flutter

OBJECTIVES The purpose of this study was to design a more efficient protocol for the electrical cardioversion of atrial arrhythmias. BACKGROUND Guidelines for electrical cardioversion of atrial arrhythmias recommend starting with low energy shocks, which are often ineffective. METHODS We recorded the sequence of shocks in 1,838 attempts at cardioversion for atrial fibrillation (AF) and 678 attempts at cardioversion for atrial flutter. These data were used to calculate the probability of success for each shock of a standard series and the probability of success with a single shock at each intensity. In 150 cases, a rhythm strip with the time of each shock allowed us to calculate the time expended on unsuccessful shocks. RESULTS We analyzed the effects of 5,152 shocks delivered to patients for AF and 1,238 shocks delivered to patients for atrial flutter. The probability of success on the first shock in AF of >30 days duration was 5.5% at <200 J, 35% at 200 J and 56% at 360 J. In atrial flutter, an initial 100 J shock worked in 68%. In AF of >30 days duration, shocks of <200 J had a 6.1% probability of success; this fell to 2.2% with a duration >180 days. In those with AF for >180 days, the initial use of a 360 J shock was associated with the eventual use of less electrical energy than with an initial shock of ≤100 J (581 ± 316 J vs. 758 ± 433 J, p < 0.01, Mann-Whitney U test). CONCLUSIONS An initial energy setting of ≥360 J can achieve cardioversion of AF more efficiently in patients than traditional protocols, particularly with AF of longer duration.