Bystander defibrillation increases 30-day survival even with short emergency medical service response time

Abstract

Abstract Background Rates of bystander initiated defibrillation are increasing in many areas of the world (1-4), but the effect of defibrillation at different time points after recognition of out-of-hospital cardiac arrest (OHCA) remains largely unknown. Purpose To assess the effect on 30-day survival of bystander defibrillation at different intervals of emergency medical service (EMS) response time. Methods We included OHCAs from 2016 through 2020 from the Danish Cardiac Arrest Registry. Cases were included if they were ≥18 years of age, bystander witnessed, received bystander cardiopulmonary resuscitation (CPR), had EMS response time of 25 minutes or less and only the first OHCA for each subject was considered. We excluded cases witnessed by EMS or if they had missing values of OHCA-related variables. Crude survival proportions were calculated for each minute of EMS response time. Relative risks (RR) and corresponding 95 % confidence intervals (95 % CI) of the outcome (30-day survival) for eight different intervals of EMS response time were estimated using a causal inference framework utilizing Targeted Maximum Likelihood Estimation (TMLE) with ensemble Super Learning, adjusting for age, sex, place of arrest (public/private), initial cardiac rhythm (shockable/not shockable), and comorbidities (prior acute myocardial infarction, ischemic heart disease, heart failure, chronic obstructive pulmonary disease, stroke, cancer). Results We included 7,471 cases of bystander witnessed OHCA receiving CPR before EMS arrival. Of these, 14.7 % (1,098/7,471) received bystander defibrillation before arrival of EMS. Overall, 44.5 % (489/1,098) survived to 30 days when bystander defibrillation was performed versus 18.8 % (1,200/6,373) when no bystander defibrillation was performed. When examining the crude survival proportion for each minute of EMS response time, we found that 30-day survival was consistently higher in the group receiving bystander defibrillation for the first 20 minutes after which the survival was approximately the same for the two groups (Figure 1). When adjusting for confounders, we found statistically significantly increased relative risks of 30-day survival for patients receiving bystander defibrillation, compared to patients not bystander defibrillated, for all intervals of EMS response time, except for response times of 0-2 min., where the increase did not reach statistical significance (0-2 min: RR; 1.34 [95 % CI: 0.88-2.05], 2-4 min: RR; 1.37 [95 % CI: 1.10-1.70], 4-6 min: RR; 1.55 [95 % CI: 1.33-1.80], 6-8 min: RR; 2.23 [95 % CI: 1.86-2.67], 8-10 min: RR; 1.99 [95 % CI: 1.55-2.55], 10-12 min: RR; 1.89 [95 % CI: 1.34-2.68], 12-15 min: RR; 1.86 [95 CI: 1.22-2.84], >15 min: RR; 1.98 [95 % CI: 1.16-3.38]) (Figure 2). Conclusion For all intervals of EMS response time, bystander defibrillation increased 30-day survival of OHCA. The effect was significant for EMS response times as short as 2-4 minutes.