Comparative efficacy of monophasic and biphasic waveforms for transthoracic cardioversion of atrial fibrillation and atrial flutter

Background Transthoracic cardioversion fails to restore sinus rhythm in 6% to 33% of patients with atrial fibrillation. This study sought to determine the relative efficacy of biphasic waveforms compared with monophasic waveforms in the treatment of atrial arrhythmias. Methods A total of 912 patients underwent 1022 transthoracic cardioversions between May 2000 and December 2001. A monophasic damped sine waveform was used in the first 304 cases, and a rectilinear biphasic defibrillator was used in the next 718 cases. Results Use of a biphasic waveform was associated with 94% success in conversion to sinus rhythm compared with 84% with a monophasic waveform (P < .001). The cumulative energy required to restore sinus rhythm was lower with biphasic shocks in both atrial fibrillation and atrial flutter groups (554 ± 413 J for monophasic vs 199 ± 216 J for biphasic shocks in the atrial fibrillation group, P < .001; 251 ± 302 J vs 108 ± 184 J, respectively, in the atrial flutter group, P < .001). In a multivariate analysis, use of a biphasic shock was associated with a 3.9-fold increase in success of cardioversion. Conclusion When used to cardiovert atrial arrhythmias, the rectilinear biphasic waveform was associated with higher success rates and lower cumulative energies than the monophasic damped sine waveform.