Unveiling gender differences in shockable initial rhythm: the impact of comorbidities and resuscitation in out-of-hospital cardiac arrest

Recent studies have revealed sex as a modifier of outcomes in cardiovascular disease [1-5]. Women have lower survival rates following out-of-hospital cardiac arrest (OHCA), partly due to the lower occurrence of shockable initial rhythm(SIR), a key survival predictor [6]. Previous studies on gender differences post-OHCA have focused on survival outcomes but not modifiable factors affecting SIR in a nationwide sample [7-11].

To explore elements contributing to sex differences in shockable initial rhythm in OHCA.

This study is based on data from the Danish OHCA registry (2016 to 2021). It includes individuals aged ≥18 years, excluding non-cardiac medical causes. Data on age, sex, initial rhythm, localization, cardiopulmonary resuscitation(CPR), and comorbidities were linked to each patient. Logistic regression assessed SIR predictors and odds ratio (OR) quantified associations, stratified by sex. A significant association was defined by p-value <0.005.

30,356 patients were included. Men had a higher likelihood of SIR than women, were younger, more likely to experience OHCA in public, and to receive bystander CPR. Logistic regression revealed that increasing age was associated with reduced SIR odds (OR = 0.98 for both sexes). Unwitnessed events were associated with reduced SIR odds (OR = 0.38 for females and 0.32 for males), while public OHCA settings and bystander CPR with increased SIR odds (respectively OR = 1.46 for females and 1.55 for males; OR = 1.29 for females and OR=1.51 for males). Conduction disorders were associated with reduced SIR odds in males (OR = 0.8). Paroxysmal tachycardia was positively associated with SIR(OR = 1.39 for females, 1.42 for males), as did other cardiac arrhythmias (OR = 4.43 for females, 3.48 for males). Ischemic artery disease and myocardial infarction were associated with increased SIR odds (respectively OR= 1.44 for females, OR=1.73 for males, and OR=2.51 for females, OR= 1.77 for males), as did cardiomyopathy (OR = 2.72 for females, OR= 1.49 for males). Chronic obstructive pulmonary disease was negatively associated with SIR (OR = 0.52 for females, 0.50 for males), as did cerebrovascular disease (OR = 0.86), renal disease (OR = 0.74) and cancer (OR = 0.84) in men but not significantly in women. Psychiatric disorders were associated with reduced SIR odds in both women (OR = 0.66) and men (OR = 0.78).

Our study reveals that men have SIR in OHCA nearly twice as often as women. More favorable resuscitation conditions, contributed to higher likelihood of SIR in men. Particularly the impact of bystander CPR, highlights the importance of improving CPR response for women. Cardiac and non-cardiac conditions influenced SIR differently, suggesting sex differences in the pathophysiology of cardiac arrest. This emphasizes the need for a shift from a "one-size-fits-all" to tailored prevention, early gender-sensitive risk stratification, and customized resuscitation protocols.