Abstract 418: Characteristics of Post-Shock Refibrillation in Out-of-Hospital Cardiac Arrest

Abstract

Introduction: Early defibrillation is critical for out-of-hospital cardiac arrest (OHCA) patients with shockable rhythms. Following successful shocks, refibrillation is common. The present study investigated three outcomes including shock efficacy, refibrillation rate, and refibrillation time (defined as the interval between shock delivery and refibrillation) in OHCA patients. Methods: Adult cases treated with Philips SMART Biphasic 150 J shocks from four US EMS agencies were included. The shocks were delivered by professional level HeartStart FR3 AEDs which are more likely to encounter longer patient down time compared to public access AEDs. Two rhythm experts independently annotated shock success, defined as the presence of a non-shockable rhythm for at least 5 seconds (s) after the shock. Successful shocks followed by a CPR period of ≥ 60 s were further annotated with refibrillation time if it occurred. If post-shock outcome could not be determined due to excessive artifact or post-shock data < 5 s, the shock success and/or the refibrillation were annotated as undeterminable. Annotator disagreements were resolved by review with a third rhythm expert to reach consensus. Results: A total of 464 shocks from 254 cases were analyzed. Shock efficacy was 87.7% for the first shock and 85.5% for all shocks. Shockable rhythms were successfully terminated at least once in 94.2% of the patients. Following successful shocks, the refibrillation rate was 55.9% for the first shock and 61.0% for all shocks. The median refibrillation time was 32.7 s (range: 5.1-582.4 s). The distribution of the refibrillation time is shown in Figure 1. Conclusions: Most patients needed more than one shock mainly due to refibrillation. About 50% of the refibrillations occurred within 30 s, which suggests that identification of early refibrillation for prompt defibrillation may be beneficial.