The study will assess 30-day survival for cases where volunteer citizen responders ('heart runners') were activated through a smartphone app to retrieve an AED in case of suspected out-of-hospital cardiac arrest (OHCA) versus standard emergency medical services care. The study will randomize emergency medical dispatch center incoming calls which are suspected out-of-hospital cardiac arrest, such that half will be randomized to activation of heart runners and half to no activation of heart runners (standard care). The study will also assess physical or psychological risks involved for the activated heart runners.

Chances of survival after out-of-hospital cardiac arrest decrease 10% per minute from collapse until defibrillation. Activating volunteer citizens through the emergency medical dispatch center can potentially increase rates of bystander defibrillation and survival. The HeartRunner trial will investigage the effect of activating registered volunteer citizens through a mobile app integrated with the emergency medical services on 30-day survival following out-of-hospital cardiac arrest. Both arms will receive standard care by the Emergency Medical Services. The intervention arm will additionally receive the activation of volunteer citizen responders. The randomization will take place independently in 3 different strata according to heart runner distance to OHCA (< 3 min, 3-9 min, > 9 min). The trial will also assess whether it is safe, both physically and psychologically, to activate volunteer citizen responders to respond to out-of-hospital cardiac arrests.

Inclusion Criteria:

• All out-of-hospital cardiac arrests recognized by Emergency Medical Dispatcher and where the HeartRunner system is activated.
• Non-traumatic etiology, this excludes intoxication, drowning or suicide.
• Age > 7 years

Exclusion Criteria:

• Caller is not in direct contact with the patient
• If Emergency Medical Dispatcher deems AED is not indicated, e.g., in nursing homes where trained personal is present.
• OHCAs not treated by the EMS due to ethical reasons or obvious signs of death
• OHCAs with no heart runners within 1800 meters
• Not true cardiac arrest (suspected, but not verified)
• EMS-witnessed OHCAs

Emergency medical dispatchers are instructed not to activate heart runners in case any of the exclusion criteria above. However, since it can be challenging for emergency medical dispatchers to gather sufficient information about the patient within the first few minutes, heart runners will admittedly be activated even though they should not have been. Since randomization will occur for all cases in which a heart runner is activated, cases with any of the exclusion criteria will be secondarily excluded.

These cases will be accounted for but not included in analyses of outcome. Our pilot study showed approximately 60% of suspected cardiac arrests were true cardiac arrests. Therefore, we expect 40% of cases for which heart runners were dispatched not to be true cardiac arrests.