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Frank. S. Rosenthal,¹ John P. Carney,¹ and Michael L. Olinger²

¹School of Health Sciences, Purdue University, West Lafayette, Indiana, USA; ²Department of Emergency Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA

Abstract
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/m³ 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/m³ 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.

Key words: air pollution, cardiac arrest, cardiovascular system, case-crossover, EMS, environmental health, out-of-hospital, particulate matter. Environ Health Perspect 116:631–636 (2008) . doi:10.1289/ehp.10757 available via http://dx.doi.org/ [Online 22 February 2008]

Address correspondence to F.S. Rosenthal, Purdue University School of Health Sciences, 550 Stadium Mall Dr., West Lafayette, IN 47907 USA. Telephone: (765) 494-0812. Fax: (765) 496-1377. E-mail: frank@purdue.edu

A. Childs provided helpful discussion on the methods of collection and validity of the PM_2.5 data. T. Arkins assisted in the management and transfer of out-of-hospital cardiac arrest data. B. Craig provided helpful discussion on statistical methods.

The authors declare they have no competing financial interests.

Received 10 August 2007 ; accepted 20 February 2008.