Rhythm conversion in out-of-hospital cardiac arrest and influence on the return of spontaneous circulation at the hospital arrival: a 10-year retrospective study in Croatia

Background While initial non-shockable (NS) rhythms are often associated with poor prognosis, the conversion to shockable rhythms during cardiopulmonary resuscitation (CPR) can significantly influence survival rates. This retrospective cohort study investigated the impact of rhythm conversion on the return of spontaneous circulation (ROSC) in out-of-hospital cardiac arrest (OHCA) patients. Methods The study analyzed data recorded from January 2012 to August 2022 obtained from the Utstein Templates from The Institute of Emergency Medicine of the City of Zagreb. Statistical analysis, including logistic regression, was performed to assess the likelihood of achieving maintained ROSC. Results Study included 2791 cases of OHCA with emergency medical service attempts at resuscitation. A total of 74.92% of patients had an initial NS rhythm with a total conversion rate of 18.27%. Factors significantly associated with rhythm conversion were younger age, male sex (74.13%), public place (32.35%) of and witnessed collapse (75.98%), higher adrenaline dose, use of a mechanical compression machine (41.68%), and shorter response interval. There was no significant difference in the occurrence of conversion between the cases with initial asystole and pulseless electrical activity (PEA). However, cases with converted asystole (33.48%) compared to the ones with converted PEA (20.65%) had significantly greater ROSC maintenance (p = 0.006), as well as when compared to cases with sustained PEA (20.93%, p < 0.001). Logistic regression revealed that women with rhythm conversion, lower adrenaline doses, and provided bystander CPR were significantly more likely to achieve ROSC at hospital admission (P < 0.001). Conclusions This comprehensive study sheds light on the importance of rhythm conversion in patients with OHCA, with greater ROSC achievement, especially in patients with initial asystole, than in patients with initial PEA.