Smartphone-activated volunteer responders and survival to discharge after out-of-hospital cardiac arrests in Victoria, 2018–23: an observational cohort study

Objectives: To compare the likelihood of patient survival to discharge and of bystander cardiopulmonary resuscitation (CPR) and defibrillation for cases of out-of-hospital cardiac arrest in which at least one smartphone-activated volunteer responder (SAVR) arrived before emergency medical services (EMS) with cases in which EMS arrived first. Study design: Population-based observational cohort study; analysis of Victorian Ambulance Cardiac Arrest Registry (VACAR) data. Setting: Victoria, 12 February 2018 – 31 August 2023. Participants: All cases of out-of-hospital cardiac arrest not witnessed by EMS personnel, except events in residential aged care facilities, in which EMS personnel did not attempt resuscitation, or for which the EMS dispatch code was ineligible for SAVR activation; events during coronavirus disease 2019 pandemic lockdowns were also excluded (SAVR program pause: rural areas: 23 March 2020 – 16 October 2020; metropolitan areas: 23 March 2020 – 9 November 2020). Main outcome measures: Primary outcome: survival to hospital discharge. Secondary outcomes: bystander CPR, bystander defibrillation, any return of spontaneous circulation. Results: Of 9196 cases of out-of-hospital cardiac arrest included in our analysis, 1158 (12.6%) had been attended by SAVRs: before EMS arrival in 564 cases (48.7%) and after EMS arrival in 594 cases (51.3%). The risk-adjusted odds of patient survival to hospital discharge were higher for events in which SAVRs arrived before EMS than for those not attended by SAVRs (adjusted odds ratio [aOR], 1.37; 95% confidence interval [CI], 1.02–1.85), as were those of bystander CPR (aOR, 7.59; 95% CI, 4.97–11.6) and bystander defibrillation (aOR, 16.0; 95% CI, 9.23–27.7); the likelihood of return of spontaneous circulation was similar for the two event groups. SAVRs arriving after EMS did not influence any of the assessed outcomes. Conclusion: The arrival of SAVRs before EMS personnel was associated with greater likelihood of patient survival to hospital discharge and of bystander CPR and defibrillation.