Bystander placement of automated external defibrillators and out-of-hospital cardiac arrest outcomes: a propensity score-matched cohort study between 2021 and 2022.

Bystander automated external defibrillator (AED) placement is expected to benefit all out-of-hospital cardiac arrest (OHCA) cases, even in the absence of prehospital defibrillation. This study investigated the factors influencing bystander-AED placement and evaluated its impact on neurologically favourable outcomes in bystander-witnessed, out-of-home OHCA cases receiving bystander cardiopulmonary resuscitation (CPR). This retrospective cohort study analysed nationwide EMS-transported emergency and OHCA databases (2021-2022), including 22,443 bystander-witnessed, out-of-home OHCAs with bystander CPR, of which 10,324 involved bystander-AED placement. AEDs were placed by bystanders in 25,333 (10.6%) of 238,871 non-EMS-witnessed OHCA cases. Logistic regression showed the associations of prehospital defibrillation, no bystander CPR, male sex, outdoor location, at-home setting, and family- or friend/colleague-witnessed OHCA with lower bystander-AED placement rates. In contrast, rural municipality EMS, daytime, DA-CPR attempt, presumed cardiac aetiology, shockable initial rhythm, conventional bystander CPR, and care/medical facilities were associated with higher rates. Neurologically favourable survival was 2.2% for bystander-AED and 2.3% for EMS-AED placement cases within care/medical facilities, compared to 19.5% and 11.6%, respectively, outside these facilities. In both logistic regression analyses after propensity score matching, bystander-AED placement improved outcomes of OHCA outside care/medical facilities only in the presence of prehospital defibrillation (adjusted odds ratio 1.24 [1.04-1.48]) but worsened outcomes of OHCA within the facilities in the absence of prehospital defibrillation (0.73 [0.54-0.99]). Bystander-AED placement was common in care/medical facilities but had limited benefits. The effectiveness of bystander-AED placement depends on location, early prehospital defibrillation, and responder training.