J Emerg Med. 2025 Sep 30;80:119-133. doi: 10.1016/j.jemermed.2025.09.030. Online ahead of print.

BACKGROUND: Survival rates after out-of-hospital cardiac arrest (OHCA) are lower at night than during the day. Cold exposure may stimulate the sympathetic nervous system and provoke and sustain ventricular tachycardia (VT)/ventricular fibrillation (VF). Diurnal temperature changes and sympathetic stimulation may explain these.

OBJECTIVE: The aim of this study was to investigate our hypothesis that the colder the ambient temperature, the worse the neurologic outcome in VT/VF OHCA patients.

METHODS: We used the All-Japan Registry (2005-2010) combined with atmospheric temperature data and enrolled adult OHCA patients who had been witnessed and resuscitated. The primary outcome was a favorable neurological outcome 1 month after OHCA, and the secondary outcome was the return of spontaneous circulation (ROSC) before hospital admission. Ambient temperature on the primary and secondary outcomes was assessed with adjustment for factors known to potentially affect OHCA outcomes by classifying the initial cardiac rhythm.

RESULTS: Among 263,750 witnessed OHCA patients, neurological survival rates significantly increased with adjusted ORs of 1.09 (95% CI, 1.05-1.13) and 1.07 (95% CI, 1.05-1.10) for 9°C (1 SD) temperature increase in VT/VF patients and overall population, respectively. ROSC rates significantly increased with adjusted HRs of 1.11 (95% CI, 1.08-1.13), 1.06 (95% CI, 1.03-1.08), 1.06 (95% CI, 1.02-1.09), and 1.09 (95% CI, 1.07-1.10) for 9°C (1 SD) temperature increase in VT/VF, pulseless electrical activity (PEA), asystole, and overall population, respectively.

CONCLUSIONS: Cold exposure during OHCA in patients with initial VT/VF rhythm resulted in lower 1-month neurological survival rates, likely due to prolonged time to ROSC. Avoiding cold exposure may improve survival by reducing the time to ROSC.

PubMed:41275845 | DOI:10.1016/j.jemermed.2025.09.030