Sudden cardiac arrest (SCA) is a life-threatening emergency that can lead to death within minutes. In 2023, emergency medical services in Germany performed out-of-hospital resuscitation on over 55,000 individuals.¹⁾ While one in three of these patients regained spontaneous circulation and were taken to hospital, the overall survival rate remained low - only 10.4 percent of the patients ultimately survived.

The key signs of SCA are unconsciousness, absence of breathing and lack of a pulse. A victim’s chances of survival critically depend on how quickly resuscitation is initiated - every minute matters. While emergency services take an average of nearly 7 minutes (± approx. 4 minutes) to arrive, irreversible brain damage can begin after just 3 to 5 minutes without oxygen. This makes it essential for bystanders to start resuscitation immediately.¹⁾

“Unfortunately, the rate of layperson resuscitation in Germany is only around 55 percent," says Dr. Jan-Steffen Pooth, emergency physician and assistant doctor at the Centre for Emergency and Rescue Medicine at Freiburg University Medical Centre. "That’s relatively low compared to other European countries; Scandinavian countries, for example, exceed 70 percent. If more people performed at least chest compressions, we could save several thousand lives every year."

First responder alerting systems shorten resuscitation-free interval

Many people are hesistant to perform resuscitation due to a lack of confidence. Therefore, since 2021 international resuscitation guidelines have recommended the use of smartphone alerting systems (SAS) that mobilise trained responders in the vicinity. When an emergency call indicates a suspected cardiac arrest, the emergency dispatch centre not only sends out an ambulance but also simultaneously activates the first responder system. Qualified individuals - known as first responders - located within a defined radius of the incident receive an alert on their smartphones, enabling them to provide potentially life-saving assistance before the emergency services arrive.

National and international studies clearly show that first responder alerting systems can significantly reduce the critical time without resuscitation. However, conclusive evidence on improved survival rates is still lacking, as previous research has involved relatively small patient groups of only 300 to 400 individuals. "Nonetheless, we estimate a realistic increase in survival of around 40 to 50 percent," Dr. Pooth explains. "In regions using such alerting systems, this could mean that approximately 15 percent of people survive an out-of-hospital cardiac arrest, compared to 11 percent without the system." The HEROES trial (Out-of-Hospital Cardiac Arrest & SmartphonE RespOndErS) aims to include data from over 2,200 patient cases to scientifically confirm this effect.²⁾

‘Region of Lifesavers’ app provides comprehensive support in an emergency

Because emergency medical services in Germany are organised at the federal level, a variety of regional systems exist for alerting first responders.³⁾ These systems differ in both functionality and in how many - and which - individuals are notified. However, they all rely on app-based platforms. Unlike SMS alerts, apps offer the advantage of detecting whether a smartphone is switched on and able to receive the alert.

For the HEROES trial, researchers are utilising the ‘Region of Lifesavers’ app, developed in Freiburg and in use since 2018. This app not only alerts medically trained first responders to emergencies but also guides them to the nearest publicly accessible automated external defibrillator (AED). Since cardiac arrests are often accompanied by ventricular fibrillation or other life-threatening arrhythmias, these devices can deliver a potentially life-saving electric shock.

Four volunteers are activated based on distance, topography and available means of transport. Two individuals immediately begin resuscitation efforts, one fetches a defibrillator and the fourth either coordinates with the emergency services or provides support to the victim’s family members.

HEROES trial carries out before and after comparison

Launched on 1 January 2024, the HEROES trial primarily aims to determine how many resuscitated individuals are discharged from hospital alive. In addition, researchers are assessing patients’ neurological outcomes and investigating whether specific subgroups - such as those experiencing ventricular fibrillation - particularly benefit from early defibrillator use. To this end, data is being collected from eleven regions across Germany, both before and after the implementation of the ‘Region of Lifesavers’ system. "We deliberately chose not to conduct an intervention study in which the control centre randomly decides whether to activate the app in suspected cardiac arrest cases," explains Pooth. "Instead, we selected regions where no first responder alerting system was previously in place." These include rural areas such as the Upper Palatinate and Rottweil, as well as urban centres such as Stuttgart, Tübingen and the Main-Taunus district - together representing a population of over five million.

During the first eight months of the initial trial phase, the regional teams recorded well over the required 1,109 patient cases - excluding minors, individuals who experienced cardiac arrest as a result of an accident, and those who suffered cardiac arrest during emergency medical treatment. In parallel, they established the formal and technical foundations required for operating the first responder alerting system. Phase II focused on rolling out the app and recruiting qualified first responders. Since the launch of Phase III in January 2025, emergency control centres have been actively using the ‘Region of Lifesavers’ system to request immediate assistance. Early evaluations indicate that trained responders arrive in over 70 percent of alerts and are able to initiate life-saving interventions.

A great deal of community committment

The coordination of the trial, including database management and data analysis, is handled by Freiburg University Medical Centre, supported by funding from the German Heart Foundation and the Centre for Emergency and Rescue Medicine. The Institute for Medical Biometry and Statistics (IMBI) in Freiburg also contributes its expertise in statistical evaluation. In contrast, the regional trial teams operate on a voluntary basis, covering their expenses through the budgets of participating hospitals. Beyond the extensive data collection, the preparatory work has proved especially challenging: each federal state involved required separate ethics approval, and the stringent data protection regulations necessitated individual agreements with every control centre, hospital and emergency service.

Results to promote nationwide dissemination

The trial coordinator in Freiburg is confident that all regions will benefit from the first responder alerting system although the impact may vary in intensity. In rural areas, for instance, volunteers can already be alerted via radio. In such regions, the app supplements existing structures, whereas in areas without prior alerting systems in place, its introduction marks a significant leap forward in emergency response.

"Our data will benefit all first responder systems and should help to establish a nationwide network of first responder alerting systems. If we can prove the benefits, then it will hopefully be possible to obtain funding from health insurance companies in the future, for example," explains Pooth. So far, all systems have operated on a non-profit basis with funding from private initiatives, foundations and/or municipal donors. However, establishing an overall concept across Germany will involve some effort and costs, and the HEROES trial can hopefully make a decisive contribution towards achieving this.

The observational trial will record patient data up until 31 August 2025 and results are expected to be available from late 2025.