Sex differences in out-of-hospital cardiac arrest: The impact of comorbidities on first monitored rhythm

BACKGROUND AND AIM: Women have lower survival rates after out-of-hospital cardiac arrest (OHCA). This study aimed to investigate sex differences in shockable initial rhythm, an important predictor of survival, under comparable resuscitation circumstances, and explore how specific comorbidities are associated with initial rhythm in men and women.

METHODS: This was a nationwide, registry-based cohort study of adult patients with OHCA of presumed medical cause in Denmark from 2016 to 2021. We examined shockable initial rhythm rates across sex, age, year of arrest, and resuscitation conditions. Multivariable logistic regression using interaction analyses were used to assess the sex-specific associations between comorbidities and shockable initial rhythm, adjusting for resuscitation conditions.

RESULTS: A total of 22,943 patients were included. Women were older at the time of OHCA and had less favorable resuscitation conditions. Men were twice as likely as women to present with shockable initial rhythm - which persisted also in the matched cohort and in the subset of patients with identical resuscitation conditions. Women showed an earlier and steeper decline in shockable initial rhythm rates around age 45. Substance use disorders (OR = 0.42 in men and OR = 0.71 in women, p<0.005) and atrial fibrillation (OR=1.95 in women and OR=1.54 in men, p<0.05) showed sex-specific associations with shockable initial rhythm.

CONCLUSION: Women showed lower shockable initial rhythm rates than men after OHCA, a disparity not solely explained by age and resuscitation conditions. These findings highlight the need for further research into sex-specific mechanisms to optimize prevention and resuscitation strategies.