Underuse of bystander defibrillation on females during out-of-hospital cardiac arrest: a retrospective observational study in Aotearoa New Zealand

• High overall bystander CPR rates (76.9%) with no sex-based differences. • Only 1.9% of females received defibrillation vs 5.4% of males in cardiac arrest. • Females had 39% lower odds of bystander defibrillation despite equal CPR rates. • In shockable rhythm cases, the disparity was not significant after adjustment, suggesting that patient and event characteristics mediate this relationship. • Ethnicity and deprivation create layered inequities in emergency cardiac care. Early bystander CPR and defibrillation improve cardiac arrest survival. International studies show women receive fewer bystander interventions after out-of-hospital cardiac arrest (OHCA) than men. We investigated associations between sex and bystander interventions in OHCA in Aotearoa New Zealand. Retrospective cohort study of adult OHCA with attempted resuscitation (January 2019-December 2023). Variables included demographics, ethnicity, socioeconomic deprivation, rurality, location type, and witness status. Logistic regression assessed associations between sex and bystander CPR and bystander defibrillation (shock delivered), adjusting for covariates. Of 9,377 OHCA events, 29.6% occurred in females. Bystander CPR rates were similar between females (75.7%) and males (77.3%) (AOR 1.06, 95% CI: 0.94-1.18, p=.36). However, bystander defibrillation occurred in only 1.9% of females versus 5.4% of males. Females had 65% lower odds of receiving bystander defibrillation in unadjusted analysis (UOR 0.35, 95% CI: 0.26-0.47, p