Out-of-Hospital Cardiac Arrest and Airborne Fine Particulate Matter: A Case–Crossover Analysis of Emergency Medical Services Data in Indianapolis, Indiana

BACKGROUND: Previous studies have found particulate matter (PM) < 2.5 μm in aerodynamic diameter (PM(2.5)) associated with heart disease mortality. Although rapid effects of PM(2.5) exposure on the cardiovascular system have been proposed, few studies have investigated the effect of short-term exposures on out-of-hospital cardiac arrest (OHCA). OBJECTIVES: We aimed to determine whether short-term PM(2.5) exposures increased the risk of OHCA and whether risk depended on subject characteristics or presenting heart rhythm. METHODS: A case–crossover analysis determined hazard ratios (HRs) for OHCAs logged by emergency medical systems (EMS) versus hourly and daily PM(2.5) exposures at the time of the OHCA and for daily and hourly periods before it. RESULTS: For all OHCAs (n = 1,374), exposures on the day of the arrest or 1–3 days before arrest had no significant effect on the incidence of OHCA. For cardiac arrests witnessed by bystanders (n = 511), OHCA risk significantly increased with PM(2.5) exposure during the hour of the arrest (HR for a 10-μg/m(3) increase in PM(2.5) exposure = 1.12; 95% confidence interval, 1.01–1.25). For the subsets of subjects who were white, 60–75 years of age, or presented with asystole, OHCA risk significantly increased with PM(2.5) during the hour of the arrest (HRs for a 10-μg/m(3) increase in PM(2.5) = 1.18, 1.25, or 1.22, respectively; p < 0.05). HR generally decreased as the time lag between PM(2.5) exposure and OHCA increased. CONCLUSION: The results suggest an acute effect of short-term PM(2.5) exposure in precipitating OHCAs, and a need to investigate further the role of subject factors in the effects of PM on the risk of OHCA.