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Three Part Question

In [a patient presenting with acute atrial fibrillation] do [biphasic rather than monophasic waveform shocks] result in [better cardioversion rates]?

Clinical Scenario

A 44 year old man presents to the Emergency Department with a six hour history of palpitations. His ECG confirms that he is in atrial fibrillation and a detailed history suggests that this is acute atrial fibrillation of less than 48 hours duration. It is decided that cardioversion is the treatment of choice, but which waveform is likely to be more effective? Monophasic or biphasic?

Search Strategy

Medline1966 –08/04 using the OVID interface. Cochrane database.
[exp Atrial Fibrillation/ or atrial fibrillation.mp] AND [Electric Countershock/ or cardioversion.mp OR electroversion.mp] AND biphasic.mp LIMIT to human

Search Outcome

The search identified 107 papers, of which four are relevant.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Mittal et al, 2000, USA	165 adults in AF (30 < 48hours)	Prospective randomised trial	Conversion of AF to sinus rhythm	Efficacy of first shock significantly greater for biphasic than monophasic (p<0.0001)	Small sub group of patients with acute AF
Page et al, 2002, USA	203 haemodynamicaly stable adults in AF. (21 with AF < 48hours duration)	Randomised triple blind trial	Successful cardioversion	Significantly greater number of shocks and total energy delivered to patients randomised to monophasic shocks (p<0.0001)	Small sub group of patients with acute AF
Niebauer et al, 2004, USA	3703 cardioversion procedures for AF. 1503 biphasic (195 acute) 2200 monophasic (363 acute)	Retrospective Review	Cardioversion success	Overall success rate for biphasic 99.1%, for monophasic 92.4%. Difference significant in all subgroup comparisons including duration of AF	Retrospective
Koster et al, 2004, Canada	73 adults in AF (6 < 48hrs duration)	Single blind randomised trial	Shock success	Cumulative success rates significantly higher in patients randomised to biphasic shock (97% vs. 38% p<0.0001)	Very small sub-group of patients with acute AF

Comment(s)

There is a wealth of evidence in the published literature that biphasic waveforms are more effective than monophasic waveforms at cardioversion of atrial fibrillation. The vast majority of this work however pertains to patients with chronic atrial fibrillation i.e. present for more than 48 hours. The four studies in the table above include subgroups of patients with AF of < 48 hours duration. Only Niebauers large retrospective study performs a subgroup analysis, which concludes that the superior effectiveness of the biphasic waveform can be extrapolated to the acute group.

Clinical Bottom Line

It is likely that biphasic cardioversion is more effective than monophasic cardioversion in patients with acute atrial fibrillation.

References

1. Mittal S, Ayati S, Stein KM et al. Transthoracic cardioversion of atrial fibrillation: comparison of rectilinear biphasic versus damped sine wave monophasic shocks. Circulation. 101(11):1282-7, 2000 Mar 21.
2. Page RL, Kerber RE, Russell JK et al. Biphasic versus monophasic shock waveform for conversion of atrial fibrillation: the results of an international randomized, double-blind multicenter trial. Journal of the American College of Cardiology. 39(12):1956-63, 2002 Jun 19.
3. Niebauer MJ, Brewer JE, Chung MK, Tchou PJ. Comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform for external cardioversion of atrial fibrillation and flutter. American Journal of Cardiology. 93(12):1495-9, 2004 Jun 15.
4. Koster RW, Dorian P, Chapman FW. A randomized trial comparing monophasic and biphasic waveform shocks for external cardioversion of atrial fibrillation. American Heart Journal. 147(5):e20, 2004 May.