Trends in outcomes after out-of-hospital cardiac arrest following two decades of guideline updates: insights from All-Japan Utstein registry

Background Out-of-hospital cardiac arrest (OHCA) remains a major public health challenge, with survival dependent on early recognition, prehospital care, and evolving resuscitation strategies. Although international resuscitation guidelines have been repeatedly updated over the past two decades, it remains unclear whether outcome improvements have been uniformly achieved across clinical phenotypes defined by witness status and initial rhythm. Purpose To evaluate long-term trends in outcomes after adult OHCA using a nationwide registry and to investigate whether the impact of guideline-era changes differs according to witness status and initial cardiac rhythm. Methods We analyzed adult OHCA patients recorded in the nationwide All-Japan Utstein Registry between 2005 and 2023. This registry prospectively collects standardized Utstein-style data from emergency medical services across Japan. Patients were stratified by witness status and initial cardiac rhythm, and temporal trends were assessed across consecutive guideline eras. Multivariable logistic regression models were used to evaluate associations between guideline era and outcomes after adjustment for demographic and prehospital characteristics. The primary outcomes were 1-month survival and favorable neurological outcome, defined as cerebral performance category (CPC) 1–2. Results Overall, both survival and favorable neurological outcomes improved over the study period. However, substantial heterogeneity was observed among clinical phenotypes. Patients with witnessed shockable rhythms experienced marked improvements, particularly during earlier eras, whereas both witnessed and unwitnessed non-shockable phenotypes showed persistently poor outcomes with minimal change over time. Consequently, disparities in outcomes across phenotypes defined by initial rhythm and witness status widened across eras. Around 2020, a transient decline in outcomes was observed across several subgroups, temporarily interrupting the previously improving trend. This deviation coincided with the global COVID-19 pandemic period, suggesting that system-level disruptions may have influenced OHCA care delivery, although causality cannot be determined from registry-based data. Conclusions Over two decades, outcomes after OHCA have improved overall, yet these gains have been unevenly distributed across patient phenotypes. The widening disparity across phenotypes defined by initial rhythm and witness status highlights persistent unmet needs despite ongoing guideline evolution.