Abstract 336: Bystander CPR Maintains Shockable Rhythm in Sudden Cardiac Arrest Across EMS Response Times

Abstract

Introduction: Presentation with shockable rhythm markedly improves survival from out-of-hospital sudden cardiac arrest (SCA). Shockable rhythms (ventricular fibrillation/tachycardia; VF/VT) are known to deteriorate to asystole or pulseless electrical activity (PEA) over time, but little population-based data is available regarding this phenomenon. Also, bystander CPR (BCPR) improves survival from SCA but its association with maintenance of shockable rhythms is unclear. Hypothesis: With longer EMS response time, the proportion of EMS-assessed shockable initial rhythms will decrease. BCPR may influence this association. Methods: We analyzed EMS-assessed initial rhythm of SCA cases from the Oregon SUDS study in the Portland, OR metro area (pop ~1 million). For this analysis, we included bystander-witnessed SCA cases (2002-2018) aged ≥18 with resuscitation attempted by EMS. SCA was defined as a sudden, unexpected pulseless condition of likely cardiac origin. We assessed initial rhythm proportions across EMS response times using Cochran-Armitage trend tests. Results: Among 3,309 SCA cases, 1,748 (53%) were bystander-witnessed, and of these, 706 (40%) received BCPR. Response time was 7.3 ± 3.4 minutes for cases with BCPR and 6.8 ± 3.1 minutes without BCPR (p=0.01). In the group receiving BCPR, the proportion with shockable rhythm remained near 60% across response times from <3 to ≥12 minutes (Figure, solid line; p=0.88), and proportions of PEA and asystole remained stable. In the group without BCPR, shockable rhythm declined from 70% at <3 minutes to 44% at ≥12 minutes response time (Figure, dashed line; p<0.001), while non-shockable rhythms increased. Conclusions: Among community-based SCA cases who received bystander CPR, there was no significant decrease in shockable rhythm as response time increased. In contrast, among SCA cases without bystander CPR, longer response times were associated with a lower proportion of shockable rhythms.