Incidence and outcomes of out-of-hospital cardiac arrest from initial asystole: a systematic review and meta-analysis

Abstract

Aim: To examine global variation in the incidence and outcomes of Emergency Medical Services (EMS) attended and treated out-of-hospital cardiac arrest (OHCA) from initial asystole.

Data sources: We systematically reviewed electronic databases for studies between 1990 and August 2024 reporting EMS-attended or treated asystolic OHCA populations. The primary outcome was survival to hospital discharge or 30-days. Random-effects models were used to pool primary and secondary outcomes and meta-regression was used to examine sources of heterogeneity. Study quality was assessed using the Joanna Briggs Institute critical appraisal tool for prevalence studies.

Results: The search returned 4464 articles, of which 82 studies were eligible for inclusion encompassing 540,054 EMS-treated patients across 35 countries. Five studies reported on EMS attended populations (n = 35,561). The studies included in the review had high clinical and statistical heterogeneity. The pooled proportion of EMS-treated initial asystolic OHCA was 53.0% (95% CI: 49.0%, 58.0%; I² = 100%). The overall pooled proportion of survivors to hospital discharge or 30-days was 1.5% (95% CI: 1.2%, 1.8%, I² = 97%). The pooled proportion of event survivors was 11.6% (95% CI 6.5%, 17.8%, I² = 99%), the pooled proportion of prehospital ROSC was 16.0% (95% CI 14.0%, 17.0%, I² = 100%) and the pooled proportion of neurologically favourable survival at longest follow-up was 0.6% (95% CI 0.5%, 0.8%, I² = 100%). The overall pooled incidence of EMS-treated asystolic OHCA was 11.0 cases per 100,000 person-years (95% CI: 10.5, 11.5, I² = 100%). In stratified analysis of survival to hospital discharge or 30-days, population type, study duration, study design and aetiology were the only variables that were significantly associated with survival to hospital discharge or 30-days. In adjusted analysis, population type, study duration, highest EMS skill level and region were significantly associated with the primary outcome. In the multivariable analysis of incidence, study region, arrest aetiology, sample size, year of publication, study population, study duration and study quality significantly explained variation in incidence across studies.

Conclusion: Initial asystolic OHCA made up 53% of all EMS-treated patients and pooled survival rates were extremely poor. Research efforts in this population should focus on developing prevention strategies as well as adherence to termination or withholding of resuscitation guidelines for asystolic OHCA.

Keywords: Asystole; Cardiac arrest; Cardiopulmonary resuscitation; Emergency medical services; Outcomes; Systematic review.