This document summarizes a clinical trial that compared two novel defibrillation strategies (double sequential external defibrillation (DSED) and vector change defibrillation) to standard practice for patients in refractory ventricular fibrillation during out-of-hospital cardiac arrest. The primary outcome was survival to hospital discharge. Paramedic services were randomly assigned to provide standard defibrillation, DSED, or vector change defibrillation over 6-month periods. The trial aimed to determine if DSED or vector change defibrillation results in greater survival rates compared to standard defibrillation.

1. Defibrillation Strategies for Refractory
Ventricular Fibrillation
TRIAL NAME-DOSE VF TRAIL
PUBLISHED IN NEJM NOV 24-2022
FUNDING: Supported by the Heart and Stroke
Foundation of Canada Grant-in-Aid program.

2. BACKGOUND
• Despite advances in defibrillation technology, shock-refractory
ventricular fibrillation remains common during out-of-hospital
cardiac arrest
• More than 350,000 unexpected deaths each year in North America
• Antiarrhythmic medications such as amiodarone and lidocaine have
been used to prevent refibrillation, neither drug has been definitively
shown to improve survival to hospital discharge or neurologically
intact survival

3. Objective
Compare two novel therapeutic defibrillation strategies (DSED and
vector change defibrillation) against standard practice for patients
remaining in refractory VF during out-of-hospital cardiac arrest.
• Double sequential external defibrillation (DSED), the technique of
providing rapid sequential shocks from two defibrillators with
defibrillation pads placed in two different planes (anterior– lateral
and anterior–posterior)
• Vector-change (VC) defibrillation, the technique of switching
defibrillation pads from the anterior–lateral to the anterior–posterior
position

4. • Research Question: Among adult (≥ 18 years) patients
presenting in refractory VF or pulseless ventricular tachycardia (pVT)
during out-of-hospital cardiac arrest, does DSED or vector change
defibrillation (anterior-posterior compared to anterior-anterior pad
position) result in greater rates of survival to hospital discharge
compared to standard defibrillation.
• Inclusion Criteria:
 ≥18 years of age
 non-traumatic cardiac arrest of presumed cardiac etiology,
 presenting rhythm of ventricular fibrillation/pVT; with no ROSC or
non VF rhythm after three consecutive shocks separated by 2-minute
intervals of cardiopulmonary resuscitation(CPR)

5. • Intervention:
(1) Resuscitation involving DSED, or
(2) Resuscitation involving vector change defibrillation (anterior-anterior
compared to anterior-posterior pad position).
Exclusion Criteria:
 Traumatic cardiac arrest,
 patients with pre-existing do not resuscitate orders,
 presumed pregnancy,
 patients in recurrent ventricular fibrillation (defined as those with a
secondary presentation of VF (not the presenting rhythm) or those
presenting in VF but did not receive three consecutive defibrillation
attempts).
 Patient’s whose initial care was provided by non-participating EMS
agencies or fire services.

6. Outcomes
PRIMARY OUTCOME :
 survival to hospital discharge.
SECONDARY OUTCOMES
 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.

7. Methods
Study Design and Population:
1. three-arm, cluster randomized trial with crossover conducted in six regions of Ontario,
Canada (Peel, Halton, Toronto, Simcoe, London and Ottawa) from March 2018 through May
2022.
2. Two treatment strategies (DSED and vector change) simultaneously assessed against a
common control group (standard defibrillation).
Patient Recruitment and Randomization
• Randomization was performed at the level of the paramedic service. Random treatment
sequences were computer-generated by the coordinating center before the start of the
trial.
• Each cluster (paramedic service) crossed over every 6 months to one of the three treatment
groups (standard defibrillation, VC defibrillation, or DSED).
• During the trial, each service had to cross over to each of the treatment groups at least once

8. • Trial Protocol and Intervention
 provincial protocol consistent with American Heart Association
guidelines
 Continuous chest compressions were performed before application
of the defibrillator pads.
 rhythm analysis occurred at standard 2-minute intervals
 the first three defibrillation attempts occurred with defibrillation
pads placed in the anterior–lateral position (standard defibrillation)
 after three consecutive shocks, three types of defibrillation