Objective To describe the First Responder Shock Trial (FIRST), which aims to determine whether equipping frequently responding, smartphone-activated (GoodSAM) first responders with an ultraportable AED can increase 30-day survival rates in OHCA.

Methods The FIRST trial is an investigator-initiated, bi-national (Victoria, Australia and New Zealand), registry-nested cluster-randomised controlled trial where the unit of randomisation is the smartphone-activated (GoodSAM) first responder. High-frequency GoodSAM responders are randomised 1:1 to receive an ultraportable, single-use AED or standard alert procedures using the GoodSAM app.

The primary outcome is survival to 30 days. The secondary outcome measures (shockable rhythm, return of spontaneous circulation, event survival, and time to first shock delivery) are routinely collected by OHCA registries in both regions. The trial was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR) (Registration: ACTRN12622000448741) on 22 March 2022.

Results The trial started in November 2022 and the last patient is expected to be enrolled in November 2024. We aim to detect a 7% increase in the proportion of 30-day survivors, from 9% in patients attended by control responders to 16% in patients attended by responders randomised to the ultraportable AED intervention arm. With 80% power, an alpha of 0.05, a cluster size of 1.5 and a coefficient of variation for cluster sizes of 1, the sample size required to detect this difference is 714 (357 per arm).

Conclusion The FIRST study will increase our understanding of the potential role of portable AED use by smartphone-activated community responders and their impact on survival outcomes.