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Biphasic or monophasic defibrillation for adult ventricular fibrillation
  1. Rob Torok, Specialist Registrar,
  2. Jeremy Till, Staff Grade
  1. Emergency Department, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK; kevin.mackway-jones{at}man.ac.uk

    Abstract

    A short cut review was carried out to establish whether biphasic defibrillatory shocks were superior to monophasic shocks in patients in ventricular fibrillation. Altogether 337 papers were found using the reported search, of which seven presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated.

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    Report by Rob Torok,Specialist RegistrarChecked by Jeremy Till, Staff Grade

    Clinical scenario

    An adult is brought into the emergency department following an out of hospital ventricular fibrillatory arrest. Ventricular fibrillation persists despite repeated shocks. You remember reading about biphasic defibrillation and wonder if it offers any advantages.

    Three part question

    In [an adult in ventricular fibrillation] is [external biphasic shock better than monophasic shock] at [achieving defibrillation]?

    Search strategy

    Medline 1966–06/03 using the OVID interface. Biphasic.mp AND (defib$.mp OR shock$.mp OR exp electric countershock) LIMIT to human AND English.

    Search outcome

    Altogether 337 papers were found of which seven related to out of hospital studies relevant to the original question.

    Comment(s)

    The studies shown in table 1 represent two independent groups of patients. The first two studies are a prospective randomised controlled trial (PRCT) and subsequent subgroup analysis of data from it. The last five studies represent ongoing investigation by a group of researchers with some overlap of patient groups between each study because of differing selection criteria and differing dates of study.

    Table 1

    The PRCT provides good evidence for the superiority of biphasic defibrillation over monophasic. Analysis of the data from this study gives an NNT of three for successful defibrillation with first shock, and an NNT of four for successful defibrillation within the first three shocks by biphasic compared with monophasic waveforms. These out of hospital studies follow on from extensive in hospital and animal studies showing the superiority of biphasic defibrillation.

    All the studies reported used the Heartstream Forerunner defibrillator with non-escalating 150 J shocks. This device uses an impedance compensating biphasic truncated exponential waveform. Laboratory and hospital based studies show the superiority of biphasic waveforms to be broadly applicable and not confined to this specific example of a biphasic waveform. Work is ongoing to refine which parameters of the waveform influence effectiveness. Evidence should be appraised for the effectiveness of the specific waveform used when selecting a defibrillator. Local considerations will determine when biphasic devices replace monophasic defibrillators.

    CLINICAL BOTTOM LINE

    Biphasic defibrillation is currently the best treatment for adult VF and should be used when available.

    Report by Rob Torok,Specialist RegistrarChecked by Jeremy Till, Staff Grade

    References

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