Sex differences in the association of comorbidity with shockable initial rhythm in out-of-hospital cardiac arrest

Background: Lower survival chances after out-of-hospital cardiac arrest (OHCA) in women is associated with lower odds of a shockable initial rhythm (SIR). We hypothesized that sex differences in the prevalence of SIR are due to sex differences in comorbidities. We aimed to establish to what extent sex differences in the cumulative comorbidity burden, measured using the Charlson Comorbidity Index (CCI), or in individual comorbidities, account for the lower proportion of SIR in women. Methods: The association between CCI or its constituent comorbidities, and presence of SIR was studied using data (2010–2014) from a Dutch community-based OHCA registry, and included 2510 OHCA patients aged ≥18y with presumed cardiac cause. Results: The mean age was 67.8 ± 13.8y, 71% were men. Women were more often in high CCI categories than men. However, moderate or high disease burden was associated with lower odds of SIR compared to no disease burden only in men (OR 99 %CI 0.73 [0.53–1.00] and OR 0.54 [0.37–0.80] P-trend < 0.001), but not in women (1.00 [0.58–1.72] and 1.02 [0.57–1.84 P-trend 0.93). Adding CCI to a multivariable model did not alter the OR of sex with SIR. Of the individual comorbidities, only previous myocardial infarction was both differently distributed between sexes (men 22.7% vs. women 13.1%, p < 0.001) and associated with odds of SIR (higher in both sexes). Adding this variable to the model changed the association of sex with initial rhythm from 0.49 (0.38–0.64) to 0.53 (0.41–0.69). Conclusion: Sex differences in comorbidities explained lower odds of SIR in women only modestly: differences in previous myocardial infarction contributed little, and cumulative comorbidity not at all.