The Interaction Effect of Age, Initial Rhythm, and Location on Outcomes After Out-of-Hospital Cardiac Arrest: A Retrospective Cohort Study

<b>Background</b>: Out-of-hospital cardiac arrest (OHCA) is a critical global health challenge and a leading cause of mortality. This study investigates the combined effect of initial cardiac arrest rhythm, patient age, and location on the return of spontaneous circulation (ROSC) in OHCA patients. <b>Methods</b>: This retrospective study analyzed medical records from the National Emergency Medical Service (EMS) in Poland between January 2021 and June 2022. Data from 33,636 patients with OHCA who received cardiopulmonary resuscitation (CPR) at the scene were included. <b>Results</b>: Public incidents were associated with higher ROSC rates (54.10% vs. 31.53%, <i>p</i> < 0.001). Initial shockable rhythms (VF/pVT) significantly increased the odds of ROSC (OR = 3.74, 95% CI 3.39-4.13, <i>p</i> < 0.001). Obesity decreased the odds of ROSC in at-home cases (OR = 0.85, 95% CI 0.73-0.99, <i>p</i> = 0.036) but had no significant effect in public cases. The effect of age on ROSC outcomes varied significantly depending on the location. In patients younger than 60 years, better ROSC outcomes were observed in at-home cases, while for those older than 60 years, the odds of ROSC were higher in public locations. Each additional year of age decreased the odds of ROSC by 1.62% in at-home incidents (<i>p</i> < 0.001) and by 0.40% in public incidents (<i>p</i> = 0.009). Sex differences were significant in public locations, with women having higher odds of ROSC compared to men (OR = 0.57, 95% CI 0.37-0.87, <i>p</i> = 0.009 for VF/pVT). <b>Conclusions</b>: The interaction between the location of OHCA, initial cardiac rhythm, and patient age significantly impacts ROSC outcomes. Public locations show higher ROSC rates, especially in cases with shockable rhythms (VF/pVT). Age modifies ROSC outcomes, with younger patients benefiting more at home, and older patients showing better outcomes in public places.