Abstract 240: High First Shock Success With Reduction In Refractory Ventricular Fibrillation In A Real-world Public Access Defibrillator Registry Of Out-of-hospital Cardiac Arrests

Abstract

Introduction: Refractory VF, which is defined as fibrillation that persists after three or more shocks, has been reported to occur in 20% of VF presenting cardiac arrest patients. This analysis was conducted to assess the frequency of shock resistant VF, during OHCA treated with a public access defibrillator (PAD). Methods: Heartsine Samaritan PAD post-market data collected between October 2012 to January 2021 were analyzed; electrocardiography (ECG) is recorded by the PAD and is assessed for shockability immediately after detecting patient impedance and then following each 2-minute period of CPR. Shock success (SS) was determined for each shock. SS was defined as one in which the initial shockable arrhythmia was terminated for at least five seconds. A consecutive shock was defined as a shock delivered after the first analysis mode following a previous shock. Results: Data was analyzed for 1082 patients who received at least one shock during OHCA. First shock success (FSS) was 88.2% (862/977 assessable shocks). At least three consecutive shocks were delivered in 207/1082 (19.1%) patients. Three patients (3/207, 1.4%) had two unsuccessful shocks followed by termination of VF on the third shock. A further thirteen (13/204, 6.4%) patients had VF which was resistant to defibrillation (i.e., three or more consecutive failed shocks with no observed successful shock). In the remaining 191 patients at least one of the three consecutive shocks was successful, or shock success could not be determined. Conclusion: The prevalence of shock resistant VF for OHCA treated with a PAD is much lower (6.4%) than published data. This low prevalence is in part due to the high FSS observed resulting in reduction in the number of possible shock resistant cases.