Out-of- H ospital cardiac arrest & Smartphon E R esp O nd E r S trial ( HEROES Trial): Methodology and study protocol of a pre-post-design trial of the effect of implementing a smartphone alerting system on survival in out-of-hospital cardiac arrest.

BACKGROUND: Since 2021, international guidelines for cardiopulmonary resuscitation recommend the implementation of so-called "life-saving systems". These systems include smartphone alerting systems (SAS), which enable dispatch centres to alert first responders via smartphone applications, who are in proximity of a suspected out-of-hospital cardiac arrest (OHCA). However, the effect of SAS on survival remains unknown.

AIM: The aim is to assess the rate of survival to hospital discharge in adult patients with OHCA not witnessed by emergency medical services (EMS): before and after SAS implementation.

DESIGN: Multicentre, prospective, observational, intention-to-treat, pre-post design clinical trial.

POPULATION: Adults (aged ≥ 18 years), OHCA not witnessed by EMS, no traumatic cause for cardiac arrest, cardiopulmonary resuscitation initiated or continued by EMS.

SETTING: Dispatch-centre-based.

OUTCOMES: Primary: survival to hospital discharge. Secondary: time to first compression, rate of basic life support measures before EMS arrival, rate of patients with shockable rhythm at EMS arrival, Cerebral Performance Category at hospital discharge, and duration of hospital stay.

SAMPLE SIZE: Assuming an absolute difference in survival rates to hospital discharge of 4% in the two groups (11% before implementation of the SAS versus 15% after) and 80% power, and a type 1 error rate of 0.05, the required sample size is N  = 1,109 patients per group (at least N  = 2,218 evaluated patients in total).

CONCLUSIONS: The HEROES trial will investigate the effects of a SAS on the survival rate after OHCA.

TRIAL REGISTRATION: German Clinical Trials Register (DRKS, ID: DRKS00032920).