The impact of comorbidity burden on cardiac arrest mortality: A population-based cohort study.

Aim: Patients experiencing cardiac arrest are often burdened with comorbidities that increase mortality. This study examined the impact of comorbidity burden on cardiac arrest mortality by quantifying biological interaction.

Methods: Nationwide population-based Danish cohort study of adult patients hospitalized for cardiac arrest during 1996-2021 and 5:1 matched comparisons from the general population (matched on age, sex, calendar year, and all Charlson Comorbidity Index comorbidities). Mortality rates and hazard ratios for the association between cardiac arrest and mortality was calculated according to comorbidity burden (none, low, moderate, severe). Biological interaction was examined by calculating interaction contrasts (difference in rate differences).

Results: For no comorbidity burden, the 30-day mortality rate per 1,000 person-years was 18,110 in the cardiac arrest cohort and 24 in the comparison cohort (hazard ratio = 1,435). For low comorbidity burden, the 30-day mortality rate increased to 20,272 in the cardiac arrest cohort and 41 in the comparison cohort (hazard ratio = 504). The corresponding interaction contrast of 2,145 indicated that 11% of the mortality rate in patients with cardiac arrest and low comorbidity burden was explained by interaction between the two. This percentage increased to 20% for moderate and to 28% for severe comorbidity burden. Within 31-365-day follow-up, the percentage of the mortality rate explained by interaction was 28% for low, 38% for moderate, and 41% for severe comorbidity burden. The interaction effect was present for both out-of-hospital and in-hospital cardiac arrest.

Conclusions: Comorbidity burden interacted with cardiac arrest to increase mortality beyond that explained by their separate effects.