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Background: For out-of-hospital cardiac arrest (OHCA) in residential areas, a dispatcher driven alert-system using text messages (TM-system) directing local rescuers (TM-responders) to OHCA patients was implemented and the desired density of automated external defibrillators (AEDs) or TM-responders investigated.Methods: We included OHCA cases with the TM-system activated in residential areas between 2010À2017. For each case, densities/km 2 of activated AEDs and TM-responders within a 1000 m circle were calculated. Time intervals between 112-call and first defibrillation were calculated.Results: In total, 813 patients (45%) had a shockable initial rhythm. In 17% a TM-system AED delivered the first shock. With increasing AED density, the median time to shock decreased from 10:59 to 08:17 min. (p < 0.001) and shocks <6 min increased from 6% to 12% (p = 0.024). Increasing density of TM-responders was associated with a decrease in median time to shock from 10:59 to 08:20 min. (p < 0.001) and increase of shocks <6 min from 6% to 13% (p = 0.005). Increasing density of AEDs and TM-responders resulted in a decline of ambulance first defibrillation by 19% (p = 0.016) and 22% (p = 0.001), respectively. First responder AED defibrillation did not change significantly. Densities of >2 AEDs/km 2 did not result in further decrease of time to first shock but >10 TM-responders/km 2 resulted in more defibrillations <6 min. Conclusion:With increasing AED and TM-responder density within a TM-system, time to defibrillation in residential areas decreased. AED and TM-responders only competed with ambulances, not with first responders. The recommended density of AEDs and TM-responders for earliest defibrillation is 2 AEDs/km 2 and >10 TM-responders/km 2 .

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Background Automated external defibrillators (AEDs) are placed in public, but the majority of out-of-hospital cardiac arrests (OHCA) occur at home. Methods In residential areas 785 AEDs were placed and 5735 volunteer responders recruited. For suspected OHCA, dispatchers activated nearby volunteer responders with text messages, directing two-thirds to an AED first and one-third directly to the patient. We analyzed survival (primary outcome) and neurologically favorable survival to discharge, time to first defibrillation shock and cardiopulmonary resuscitation (CPR) before Emergency Medical Service (EMS) arrival of patients in residences found with ventricular fibrillation (VF), before and after introduction of this text-message alert system. Results Survival from OHCAs in residences increased from 26% to 39% [adjusted relative risk (RR) 1.5 (95% CI 1.03–2.0)]. RR for neurologically favorable survival was 1.4 (95% CI 0.99 - 2.0). No CPR before ambulance arrival decreased from 22% to 9% (RR 0.5, 95% CI 0.3 - 0.7). Text-message-responders with AED administered shocks to 16% of all patients in VF in residences, while defibrillation by EMS decreased from 73% to 39% in residences (p &lt; 0.001). Defibrillation by first responders in residences increased from 22% to 40% (p &lt; 0.001). Use of public AEDs in residences remained unchanged (6% and 5%) (p = 0.81). Time from emergency call to defibrillation decreased from median 11.7 min to 9.3 min; mean difference -2.6 (95% CI -3.5 - -1.6). Conclusion Introducing volunteer responders directed to AEDs, dispatched by text-message was associated with significantly reduced time to first defibrillation, increased bystander CPR and increased overall survival for OHCA patients in residences found with VF.