Academic journal article Environmental Health Perspectives

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

Academic journal article Environmental Health Perspectives

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

Article excerpt

In the last decade, several studies have associated exposure to airborne particulate matter (PM) with cardiac morbidity and mortality as well as effects on cardiac rhythms and electrocardiography. Although the exact nature of the mechanisms is still uncertain, some studies indicate that at least part of the increased mortality is attributable to acute cardiac events triggered by high PM levels. Attention has focused especially on the fraction of PM consisting of particles with aerodynamic diameter < 2.5 [micro]m ([PM.sub.2.5]), which is considered a leading factor in inducing cardiovascular risks. For example, a hospital-based study by Peters et al. (2001) found that increased risk of myocardial infarction (MI) was associated with higher levels of [PM.sub.2.5] in the 1- to 3-hr period immediately preceding the MI. Previous studies investigating a link between heart disease deaths and short-term increases in particulate air pollution have found mixed results. Levy et al. (2001) found no association between daily [PM.sub.2.5] levels and out-of-hospital cardiac arrest (OHCA). Sullivan et al. (2003) found an association of OHCA with daily [PM.sub.2.5] only for the subset of smokers with previously existing heart disease and only for exposure measured 2 days before the OHCA. Murakami and Ono (2006) found a significant increased risk of MI associated with 1-hr peaks of suspended PM.

Our goal was to investigate the effect of short-term exposure to [PM.sub.2.5] on the incidence of OHCA, as reported in an emergency medical services (EMS) database. Additional objectives were to investigate the role of subject characteristics, that is, age, sex, race, and presenting heart rhythm on PM-induced risks; and to compare the effect of exposure averaging time and measurement method on the ability to detect an association between PM exposure and risk of OHCA. The study was conducted in Indianapolis, Indiana, a major metropolitan area with average annual [PM.sub.2.5] levels close to the current U.S. Environmental Protection Agency (2007) standard of 15 [micro]g/[m.sup.3].

Methods

Study site and population. The Indiana University and the Purdue University Human Subjects Research Committees approved all data-collecting procedures. The Wishard Ambulance Service, which provides EMS to the population within the historic city limits of Indianapolis, provided data on OHCAs, collected according to Utstein guidelines (Cummins et al. 1991). The service makes approximately 65,000 emergency runs per year, of which approximately 1,000 per year are classified as cardiac arrest. Approximately 600 per year of the cardiac arrests result from trauma or are classified as dead on arrival (DOA; signs of rigor mortis, algor mortis, or livor mortis). Of the remaining 400 per year, approximately 150 per year are witnessed by bystanders. Data from 2 July 2002 to 7 July 2006 were used. We analyzed either all non-DOA incidents during the study period (n = 1,374) or all non-DOA incidents witnessed by bystanders (n = 511). We analyzed the witnessed cases in relation to hourly exposures because we assumed that the time of the cardiac arrest was known with greater accuracy compared with the other cases. The non-DOA cases, for which the time of incidence was considered less accurate, we analyzed in relation to daily average exposures. For each case, the following data were available: a) time of the initial call to EMS, b) time of arrival at site of the cardiac arrest, c) age, sex, and race of the subject, d) presenting heart rhythm (when available), e) ZIP code of the site location. We stratified some of the analyses by age, sex, and race in attempt to see whether particular subgroups were more susceptible to the effect of PM on OHCA. Analyses were also stratified by presenting heart rhythm in an attempt to investigate the characteristics of OHCAs associated with PM exposure.

[PM.sub.2.5] data. We obtained average daily [PM.sub.2.5] values from data collected by the City of Indianapolis site 44 (Michigan Street) for 2002 and site 41 (Washington Park) for 2003-2006. …

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