Feasibility of early double sequential defibrillation in out-of-hospital cardiac arrest: the double-D randomised pilot trial

BACKGROUND: Double sequential defibrillation (DSD) is a promising treatment for patients with out-of-hospital cardiac arrest (OHCA) with refractory ventricular fibrillation. The reproducibility and generalisability of previous studies are unknown. Additionally, whether DSD could improve survival if applied earlier has never been studied. The DoubleD trial aims to establish whether early DSD (as soon as possible after the first shock) is superior to standard defibrillation. This pilot study evaluated the safety and feasibility of this strategy in preparation for the main trial. METHODS: This Swedish, prehospital, open-label, randomised controlled external pilot trial enrolled patients with OHCA who were still in cardiac arrest after at least one defibrillation in the standard (anterior-lateral) position. Enrolment required two ambulances with manual defibrillators to be present. The inclusion goal was 40 patients, randomised 3:1 to early DSD (with a second defibrillator in the anterior-posterior position) or continued standard defibrillation. Data were collected from study questionnaires, medical charts and defibrillators. The main feasibility and safety outcomes were randomisation prior to three shocks, adherence to protocol and defibrillator malfunction. RESULTS: Between June 2024 and April 2025, 40 patients were randomised: 29 to early DSD and 11 to standard defibrillation. Overall, 32/40 (80%) were randomised before the third defibrillation. In the DSD group, 20/21 (95%) of patients who still had a shockable rhythm after randomisation received DSD. One case of treatment crossover occurred in both DSD and control groups. No defibrillator malfunctions or adverse events were observed. 30-day survival was 12/29 (41%) and 1/11 (9%) for the DSD and control group respectively. CONCLUSION: This is the first time that early DSD has been investigated in clinical practice. The strategy is feasible and appears to be safe. The findings have informed the design of the DoubleD main trial, powered to assess 30-day survival (NCT07174986). TRIAL REGISTRATION NUMBER: NCT06447805.