title: Biphasic versus monophasic waveforms for transthoracic defibrillation in out-of-hospital cardiac arrest.
abstract: BACKGROUND
  Transthoracic defibrillation is a potentially life-saving treatment for people with ventricular fibrillation (VF) and haemodynamically unstable ventricular tachycardia (VT). In recent years, biphasic waveforms have become more commonly used for defibrillation than monophasic waveforms. Clinical trials of internal defibrillation and transthoracic defibrillation of short-duration arrhythmias of up to 30 seconds have demonstrated the superiority of biphasic waveforms over monophasic waveforms. However, out-of-hospital cardiac arrest (OHCA) involves a duration of VF/VT of several minutes before defibrillation is attempted.
  
  
  OBJECTIVE
  To determine the efficacy and safety of biphasic defibrillation waveforms, compared to monophasic, for resuscitation of people experiencing out-of-hospital cardiac arrest.
  
  
  METHODS
  We searched the following electronic databases for potentially relevant studies up to 10 September 2014: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE. Also we checked the bibliographies of relevant studies and review articles, contacted authors of published reviews and reviewed webpages (including those of device manufacturers) relevant to the review topic. We handsearched the abstracts of conference proceedings for the American Heart Association, American College of Cardiology, European Society of Cardiology, European Resuscitation Council, Society of Critical Care Medicine and European Society of Intensive Care Medicine. Regarding language restrictions, we did not apply any.
  
  
  METHODS
  We included randomised controlled trials (RCTs) that compared biphasic and monophasic waveform defibrillation in adults with OHCA. Two review authors independently screened the literature search results.
  
  
  METHODS
  Two review authors independently extracted data from the included trials and performed 'Risk of bias' assessments. We resolved any disagreements by discussion and consensus. The primary outcome was the risk of failure to achieve return of spontaneous circulation (ROSC). Secondary outcomes included risk of failure to revert VF to an organised rhythm following the first shock or up to three shocks, survival to hospital admission and survival to discharge.
  
  
  RESULTS
  We included four trials (552 participants) that compared biphasic and monophasic waveform defibrillation in people with OHCA. Based on the assessment of five quality domains, we identified two trials that were at high risk of bias, one trial at unclear risk of bias and one trial at low risk of bias. The risk ratio (RR) for failure to achieve ROSC after biphasic compared to monophasic waveform defibrillation was 0.86 (95% CI 0.62 to 1.20; four trials, 552 participants). The RR for failure to defibrillate on the first shock following biphasic defibrillation compared to monophasic was 0.84 (95% CI 0.70 to 1.01; three trials, 450 participants); and 0.81 (95% CI 0.61 to 1.09; two trials, 317 participants) for one to three stacked shocks. The RR for failure to achieve ROSC after the first shock was 0.92 (95% CI 0.81 to 1.04; two trials, 285 participants). Biphasic waveforms did not reduce the risk of death before hospital admission (RR 1.05, 95% CI 0.90 to 1.23; three trials, 383 participants) or before hospital discharge (RR 1.05, 95% CI 0.78 to 1.42; four trials, 550 participants). There was no statistically significant heterogeneity in any of the pooled analyses. None of the included trials reported adverse events.
  
  
  CONCLUSIONS
  It is uncertain whether biphasic defibrillators have an important effect on defibrillation success in people with OHCA. Further large studies are needed to provide adequate statistical power.
authors.affiliation: Service Development and Planning, Ambulance Service of NSW, Locked Bag 105, Rozelle, NSW, Australia, 2039.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Faddy
authors.forename: Paul A
authors.initials: PA
authors.lastname: Jennings
mesh_terms: D001775:Blood Circulation; D047548:Defibrillators; D004554:Electric Countershock / Q000379:methods* / Q000401:mortality; D006801:Humans; D058687:Out-of-Hospital Cardiac Arrest / Q000401:mortality / Q000628:therapy*; D016032:Randomized Controlled Trials as Topic; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000628:therapy*