Abstract

Objective: To investigate whether chronic clinical comorbidity, as collected from emergency medical services (EMS) reports, influences survival after out-of-hospital ventricular fibrillation (VF) cardiac arrest.

Methods: In this observational retrospective cohort study in King County, Washington, USA 1043 people who suffered out-of-hospital VF arrest due to heart disease between 1 January 1999 and 31 December 2003 were studied. Chronic conditions were ascertained and tallied from EMS reports using a uniform abstraction form by people blinded to outcome status. The outcome was survival to hospital discharge.

Results: 75% (776/1043) of patients had at least one chronic health condition and 51% (529/1043) had prior clinically recognised heart disease. Overall, the increasing count of chronic conditions was inversely associated with the odds of survival to hospital discharge after adjustment for potential confounders (OR 0.84 (95% CI 0.74 to 0.95) for each additional chronic condition). The chronic condition–outcome association tended to be more prominent among those with longer EMS response intervals (p = 0.07 for interaction term between condition count and response interval). For example, the OR of survival was 0.72 (95% CI 0.59 to 0.88) for each additional chronic condition when the EMS response interval was 8 min compared with an OR of 0.95 (95% CI 0.79 to 1.14) when the EMS response interval was 3 min.

Conclusion: In this cohort, an increasing burden of clinical comorbidity based on a review of EMS reports was associated with a lower odds of survival after VF arrest. This finding suggests that chronic conditions influence arrest pathophysiology and in turn could help guide resuscitation care.