title: Biphasic and monophasic shocks for transthoracic defibrillation: a meta analysis of randomised controlled trials.
abstract: BACKGROUND
  Biphasic waveforms are routinely used for implantable defibrillators. These waveforms have been less readily adopted for external defibrillation. This study was performed in order to evaluate the efficacy and harms of biphasic waveforms over monophasic waveforms for the transthoracic defibrillation of patients in ventricular fibrillation (VF) or haemodynamically unstable ventricular tachycardia.
  
  
  METHODS
  Studies included randomised controlled trials comparing monophasic and biphasic external defibrillation for participants with VF or hemodynamically unstable ventricular tachycardia. Seven trials (1129 patients) were included in the analysis. All trials were conducted during electrophysiology procedures or implantable cardioverter/defibrillator testing.
  
  
  RESULTS
  Compared with 200 J monophasic shocks, 200 J biphasic shocks reduced the risk of post-first shock asystole or persistent VF by 81% (relative risk (RR) 0.19; 95% confidence intervals (CI) 0.06-0.60) for the first shock. Reducing the energy of the biphasic waveform to 115-130 J resulted in similar effectiveness compared with the monophasic waveform at 200 J (RR 1.07, CI 0.66-1.74). Low energy biphasic shocks produce less myocardial injury than higher energy monophasic shocks as determined by ST segment deflection after shock.
  
  
  CONCLUSIONS
  Biphasic waveforms defibrillate with similar efficacy at lower energies than standard 200 J monophasic waveforms, and greater efficacy than monophasic shocks of the same energy. Available data suggests that lower delivered energy and voltage result in less post-shock myocardial injury.
authors.affiliation: Cardiology Department, St Vincent's Hospital Sydney, Victoria St, Darlinghurst, NSW 2010, Australia. sfaddy@health.usyd.edu.au
authors.forename: Steven C
authors.initials: SC
authors.lastname: Faddy
authors.forename: Jane
authors.initials: J
authors.lastname: Powell
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Craig
mesh_terms: D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000379:methods*; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D017180:Tachycardia, Ventricular / Q000628:therapy