Implementation of Double Sequential Defibrillation (DSD): An Aotearoa New Zealand Observational Study

Abstract

BACKGROUND AND OBJECTIVES: Double sequential defibrillation (DSD) was introduced in Aotearoa New Zealand Emergency Medical Services (EMS) in October 2023 for refractory ventricular fibrillation (VF) and ventricular tachycardia (VT). Its usage, paramedic's adherence to guidelines, and clinical impact remain uncertain. This study aimed to (1) compare demographic and clinical characteristics between pre- and post-DSD implementation periods, including subgroup analysis of DSD versus no-DSD (NDSD) patients post- implementation, and (2) evaluate survival outcomes across all subgroups, including early- and late-DSD. METHODS: This retrospective cohort study used data across two 18-month periods: pre-period (April 2022-September 2023) and post-period (January 2024-June 2025). All cardiac arrests receiving more than three prehospital defibrillations were included. Post-period analyses compared NDSD and DSD patients, with DSD classified as early-DSD (≤3 shocks before DSD) or late-DSD (>3 shocks before DSD). Chi-Square and Mann- Whitney U tests assessed group differences, and logistic regression examined associations with survival outcomes. RESULTS: Among 1,401 patients (pre-period n=663; post-period n=738), no significant difference in ROSC or 30-day survival was observed (p>0.05). Forty-three percent of patients received DSD. Compared with NDSD, adjusted models showed lower odds of ROSC with any-DSD (aOR 0.59, 95%CI 0.41-0.85) and late-DSD (aOR 0.46, 95%CI 0.30-0.71). Similar results were seen for 30-day survival. Early-DSD showed no significant associations. CONCLUSIONS: No survival benefit was observed after DSD implementation. Lower survival among DSD patients may reflect confounding due to its use in patients with the poorest prognosis. Further research is needed to clarify optimal timing and drivers of DSD use.