Comparative Efficacy of Monophasic and Biphasic Waveforms for Transthoracic Cardioversion of Atrial Fibrillation and Atrial Flutter

Osnat T. Gurevitz, MD; Naser M. Ammash, MD; Joseph F. Malouf, MD; Krishnaswamy Chandrasekaran, MD; Ana Gabriela Rosales, MS; Karla V. Ballman, PhD; Stephen C. Hammill, MD; Roger D. White, MD; Bernard J. Gersh, MB, ChB; Paul A. Friedman, MD


Am Heart J. 2005;149(2):316-321. 

In This Article

Abstract and Introduction


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.


Atrial fibrillation is the most common sustained arrhythmia encountered in clinical practice and frequently necessitates direct-current cardioversion.[1] The failure rate of restoring sinus rhythm with standard (monophasic waveform) transthoracic cardioversion is 6% to 33%.[2] To increase cardioversion success rates, new techniques have been introduced, including internal cardioversion,[3] dual simultaneous external defibrillation,[4] pretreatment with class III antiarrhythmic drugs such as ibutilide,[2] and use of biphasic waveforms. Biphasic waveforms decrease the internal[5,6,7,8,9,10] and external[11,12,13] ventricular defibrillation thresholds and the internal[14] and epicardial[15] atrial defibrillation thresholds. Small randomized studies have also demonstrated the clinical efficacy of biphasic waveforms for transthoracic cardioversion of atrial fibrillation.[16,17]

This study compared results with biphasic versus monophasic waveforms in a large series of consecutive patients with atrial fibrillation or atrial flutter. Our prospective cardioversion protocol used ibutilide in the event of cardioversion failure; in addition, we sought to determine the drug's utility after biphasic waveforms were adopted.