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Biphasic v. Monophasic

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Many hospitals are equipped with monophasic defibrillators. These conventional defibrillators use the monophasic sine wave pattern. As research progressed on implantable cardiac defibrillators, it was evident that the biphasic waveform was much more efficient than the conventional monophasic waveform.

Research then centered on finding a way to apply the biphasic waveform in an external defibrillator. In 1999 Zoll Medical Inc produced an external biphasic defibrillator. To do so, the waveform was slightly modified, to a rectilinear biphasic form - in order to decrease the resistance of current through the skin. Early results showed it to be more effective than the monophasic defibrillator for ventricular fibrillation in patients undergoing ACID implantation procedures.

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At the turn of the century, the ACC/AHA Scientific statement in Circulation reviewed the evidence and made a Class IIb recommendation that low-energy, nonprogressive biphasic waveform defibrillators could be used for out-of-hospital and in-hospital ventricular fibrillation arrest, including persistent or recurrent ventricular fibrillation unresponsive to the initial low-energy shock.

In 2000, Circulation published a study, which stated that in atrial fibrillation and synchronized cardioversion, biphasic energy was superior to the monophasic standard. The energy used was 70, 120, 150, and 170J. With cumulative doses, the efficiency using biphasic energy was significantly improved compared with the monophasic waveform.

Biphasic energy requires less energy to provide the same effects. In 2010, the writing group reviewed all data on biphasic studies conducted since the 2005 guidelines were published, and a number of minor changes were made to update cardioversion dose recommendations. Among these were the recommended initial biphasic energy doses for cardioversion of atrial fibrillation to 120 to 200 J. The initial monophasic dose is 200 J. Atrial flutter and other supraventricular rhythms require less energy, so the AHA/ACC recommends an initial dose of either monophasic or biphasic energy of 50 to 100J. This should be increased in a stepwise fashion if the initial attempt at cardioversion fails.

With respect to stable monomorphic ventricular tachycardia, the committee found that it responds to monophasic or biphasic waveform cardioversion – synchronized shock – at initial energy of 100 J. If the patient doesn’t respond, the group expert consensus recommendations are to increase dose in a stepwise fashion. There were no interim studies between 2005 and 2010 that addressed ventricular tachycardia, and in 2005, there was insufficient evidence to recommend a biphasic dose for cardioversion of monomorphic ventricular tachycardia. The Guidelines recommended unsynchronized shock for the patient with polymorphic ventricular tachycardia. The committee added biphasic dose recommendation for cardioversion of monomorphic ventricular tachycardia, but have emphasized the treatment of polymorphic ventricular tachycardia as an unstable and arrest rhythm by recommending unsynchronized shock.