Automated external defibrillator electrode size and termination of ventricular fibrillation in out-of-hospital cardiac arrest.

Smaller electrodes allow more options for design of automated external defibrillator (AED) user interfaces. However, previous studies employing monophasic-waveform defibrillators found that smaller electrode sizes have lower defibrillation shock success rates. We hypothesize that, for impedance-compensated, biphasic truncated exponential (BTE) shocks, smaller electrodes increase transthoracic impedance (TTI) but do not adversely affect defibrillation success rates. METHODS AND RESULTS: In this prospective before-and-after clinical study, Amsterdam police and firefighters used AEDs with BTE waveforms: an AED with larger electrodes in 2016-2017 (113 cm), and an AED with smaller electrodes in 2017-2020 (65 cm). We analyzed 157 and 178 patient cases with an initial shockable rhythm where the larger and smaller electrodes were used, respectively. A single 200-J shock terminated ventricular fibrillation (VF) in 86% of patients treated with large electrodes and 89% of patients treated with smaller electrodes. Small electrodes had a non-inferior first shock defibrillation success rate compared to large electrodes, with a difference of 3% (95% CI: -3% -9%) with the lower confidence limit remaining above the defined non-inferiority threshold. TTI was significantly higher for the smaller electrodes (median: 100 Ω) compared to the larger electrodes (median: 88 Ω) (p < 0.001). CONCLUSIONS: For AEDs with impedance-compensating BTE waveforms, TTI was higher for smaller electrodes than the large electrode electrodes. Overall defibrillation shock success for AEDs with smaller electrodes was non-inferior to the AEDs with larger electrodes.