Predictors of occurrence of shockable rhythm and return of spontaneous circulation in patients with witnessed cardiac arrest

Introduction: Out-of-hospital cardiac arrest (OHCA) is a global health challenge with an average survival rate of 8%. Outcomes depend on factors such as arrest location, time to return of spontaneous circulation (ROSC), patient demographics, and initial rhythm type. Material and methods: EuReCa_Serbia is part of the EuReCa ONE study on OHCA survival in Europe. It included OHCAs managed by EMS, including pediatric and non-cardiogenic cases. Data were collected per the EuReCa ONE protocol from October 1, 2014, to December 31, 2021. Results: We examined predictors of shockable initial rhythms, ROSC, and hospital admission using univariable and multivariable binary logistic regression analysis. OHCAs in areas with over 100,000 inhabitants and at patient residences were significantly less likely to have shockable rhythms (57.4% and 65.4% less likely), while younger age and cardiogenic cause increased the likelihood (1.7 and 8.5 times more likely). Shockable rhythms strongly predicted any ROSC, increasing the likelihood by 3.9 times, and ROSC at hospital admission by 3.3 times. Urban and residential locations reduced the chances of ROSC by 55.8% and 51.1%, respectively. EMS dispatcher assistance improved the likelihood of ROSC at admission by 1.7 times, while a delay of 10 or more minutes from EMS call to defibrillation reduced the likelihood by 86.1%.