Double sequential external defibrillation (DSED) and vector change defibrillation have been proposed as viable options for patients in refractory ventricular fibrillation (VF) during out-of-hospital cardiac arrest. However, currently there is insufficient evidence to support a widespread implementation of this therapy. As such, a well-designed randomized controlled trial (RCT) employing a standardized approach to alternative defibrillation strategies early in the treatment of refractory VF is required to determine whether these treatments may impact clinical outcomes. This pilot cluster randomized trial will be conducted in the regions of Peel, Halton and the city of Toronto, Ontario, Canada over a one year period of time. All adult (≥ 18 years) patients presenting in refractory VF (defined as patients presenting in VF and remaining in VF after three consecutive standard defibrillation attempts each separated by 2 minutes of CPR) during out-of-hospital cardiac arrest of presumed cardiac etiology will be assigned to be treated by one of three strategies: (1) continued resuscitation using standard defibrillation; (2) resuscitation involving DSED (two defibrillators, one using anterior-posterior pad placement and the second using anterior- anterior pad placement delivering two rapid sequential shocks for all subsequent defibrillation attempts, ± antiarrythmic use and epinephrine as per current provincial standard); or (3) resuscitation involving vector change (change of defibrillation pads from anterior-anterior to an anterior-posterior pad position) defibrillation. The cluster units will be defined by emergency medical service (EMS) agency and each cluster will crossover at three times during the trial so that each agency will spend 4 months in each arm of the study. Outcomes of interest will include return of spontaneous circulation (ROSC), termination of VF after the first interventional shock, termination of VF inclusive of all interventional shocks, and number of defibrillation attempts to obtain ROSC. The primary objectives of the pilot study are to determine the feasibility and required sample size of a full-scale RCT in this population.