Biphasic Versus Monophasic Shock Waveform for Conversion of Atrial Fibrillation - Biphasic Versus Monophasic Shock Waveform for Conversion of Atrial Fibrillation.


How does the efficacy of biphasic shocks compare with that of monophasic shocks for cardioversion of atrial fibrillation (AF)?

Study Design

Study Design:

Patients Enrolled: 203

Drug/Procedures Used:

Two hundred three patients (mean age 65 years, mean left atrial diameter 4.8 cm) were randomly assigned to undergo transthoracic cardioversion of AF with either a monophasic (107) or biphasic (96) shock using anterior-posterior electrodes. The investigators were blinded to the type of waveform being used. A step-up protocol of 100, 150, 200 J was used in both groups. The fourth shock was 360 J in the monophasic group and 200 J in the biphasic group. If cardioversion was unsuccessful, the patient crossed-over to the alternative waveform, at maximum output.

Principal Findings:

Biphasic shocks restored sinus rhythm significantly more often than monophasic shocks at 100 J (60 vs. 22%), 150 J (77 vs. 44%), and 200 J (90 vs. 53%). After the fourth shock, there was not a significant difference in the cumulative success rate (91% biphasic vs. 85% monophasic). Fewer shocks were needed to restore sinus rhythm with the biphasic than with the monophasic waveform (1.7 vs. 2.8), and less total energy also was needed (217 vs. 548 J). Dermal injury was less common after the biphasic than after the monophasic shocks (17 vs. 41%).


Compared to monophasic shocks, biphasic shocks allow the restoration of sinus rhythm with fewer shocks, less total energy, and with a lower risk of dermal injury. It is interesting to note that even in the biphasic group, cardioversion was ineffective in approximately 10% of patients. In these patients, 1 mg of ibutilide lowers the defibrillation energy requirement, greatly increasing the probability of successful cardioversion with another 200 J biphasic shock.

Clinical Topics: Arrhythmias and Clinical EP, EP Basic Science, Statins

Keywords: Electric Countershock, Probability, Sulfonamides

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