Variations of shock efficacy and refibrillation in different AED user groups.

Background: Automated external defibrillator (AED) outcomes in out-of-hospital cardiac arrest (OHCA) are known to be impacted by diverse usage scenarios including time to shock. This study compared shock efficacy and refibrillation rate across AED user groups and analyzed influencing factors.

Methods: We examined ECG data from 2,358 adult OHCA cases in the US and Europe treated with three AED models (HS1, FRx, and FR3), all delivering low-energy, impedance-compensating biphasic shocks. Cases were grouped by AED used: lay-responder (HS1), trained first-responder (FRx), and EMS (FR3). Shock success and refibrillation were compared, and regression analyses assessed their associations with amplitude spectrum area (AMSA) and shock impedance.

Results: Among 953 shocks in 560 patients, overall shock efficacy differed: 95.0% (lay-responder), 94.0% (first-responder), and 86.6% (EMS) (p<0.001). First shock efficacy was 96.9% (lay-responder), 94.5% (first-responder), and 89.0% (EMS) (p=0.007). Refibrillation rates varied significantly among groups (p=0.016). Among patients who refibrillated within two minutes after a successful first shock, the median time to refibrillation was 38.7 (lay-responder), 31.0 (first-responder), and 27.4 (EMS) seconds. Shock impedance was not associated with shock efficacy or refibrillation. Higher AMSA was significantly associated with reduced refibrillation (hazard ratio, 0.95; 95% CI, 0.92-0.98) but did not fully explain group differences.

Conclusions: Across use scenarios, low-energy biphasic shocks were highly effective, independent of shock impedance. Lay and minimally trained responders achieved better shock efficacy and lower refibrillation rates than first responders or EMS, which typically have longer response times. While AMSA correlated with refibrillation, additional factors may also influence AED outcomes.