Some of the patients affected by Out-of-hospital cardiac arrest (OHCA) with ventricular fibrillation (VF)/ventricular tachycardia (VT) do not respond to initial defibrillation. The survival decreases with number of defibrillations required to terminate VF/VT. In 2022, one prospective cluster randomized trial showed increased survival among (OHCA) patients in refractory VF using Double Sequential Defibrillation (DSD). If DSD can increase survival among all patients in VF that dont respond to one defibrillation, i.e. before it has become refractory is not known.

The aim of this trial is to assess survival with a double defibrillation strategy initiated as soon as possible among patients with Out of Hospital Cardiac Arrest with initial shockable rhythm and at least one failed standard defibrillation, compared with continued resuscitation using standard defibrillation.

Background: Out-of-hospital cardiac arrest (OHCA) affects about 270,000 individuals in Europe annually.[1] In OHCA, presenting with ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) amendable to defibrillation are among the strongest predictors of survival.[2] If defibrillation can be done successfully within the first 3-5 minutes survival can be as high as 70 %.[3] However, some patients in VT/VF do not respond to initial defibrillation, and survival decreases with number of defibrillations required to terminate VT/VF.[4]

In 2022, one prospective cluster randomized trial showed increased survival among OHCA patients in refractory VF using an alternative defibrillation strategy with either, switching to Anterior-Posterior defibrillation pad placements (A-P) or Double Sequential Defibrillation "DSD", (Using two defibrillators, one in the standard anterior-lateral position (A-L) and one in A-P position and defibrillation in rapid sequence) compared to standard defibrillation pad placement.[5] Refractory VF was defined as VF that persisted despite three consecutive defibrillations with defibrillation pads in the standard position.

These results prompted the International Liaison Committee on Resuscitation (ILCOR) to release a statement of treatment recommendation on DSD in March 6, 2023. It suggested that "…either vector change or DSD may be considered for adults with cardiac arrest who remain in VF or pulseless VT despite three defibrillations (weak recommendation, low certainty of evidence)." [6] Further, if DSD would be used it should be performed with a methodology similar to that described in the trial by Cheskes et al.

However, several questions remain. Knowledge gaps highlighted in the ILCOR statement included if the results from this one cluster randomized trial could be reproduced in any other setting. Further, since survival is inversely associated with the number of defibrillation shocks, if earlier application of DSD could lead to even higher survival for patients not in refractory VF has never been studied.

Study rationale: In order to evaluate if an early DSD-strategy could benefit all patients with VT/VF after the first shock, including those not in refractory VF, the Double-D trial is designed. If DSD would prove to be superior to standard defibrillation in a broader cardiac arrest population, also among those not in refractory VF, this would have a large impact on how Advanced Cardiac Life Support (ACLS) should be performed.

Design: This is an academic, investigator initiated, open-label pilot study with a randomized controlled trial (RCT) design and 1:1 allocation (1 DSD: 1 standard). Screening for inclusion will be performed in all cardiac arrests by participating EMS units where there are two study-specific defibrillators available on site.

Study population: Adult OHCA patients with pulseless VT/VF at initial rhythm analysis, at least one defibrillation performed in standard A-L position without return of spontaneous circulation (ROSC).

P: Adult patients, 18 years or older, with OHCA, initial shockable rhythm (VT/VF) and, at least, one defibrillation performed in standard position and ongoing CPR (no ROSC).

I: Application of a second defibrillator with pad-placement in the anterior-posterior (A-P) position as early as possible after the first shock and double sequential defibrillation after the following rhythm analysis if the patient is still in VT/VF.

C: Standard defibrillation electrode placement (A-L) and routine defibrillation with one defibrillator after the following rhythm analysis if the patient is still in VT/VF.

O: Primary outcome is 30-day survival.

The trial will be conducted by participating ambulance units attending OHCA´s. These units will perform screening for inclusion, randomization, intervention or control treatment and initial follow up.

Inclusion Criteria:

• OHCA patients with VT/VF at first rhythm analysis and at least one defibrillation performed in standard (A-L) position

Exclusion Criteria:

• Age < 18 years
• Obvious pregnancy
• Known preexisting Do Not Attempt Resuscitation order