Smoke From Wildfires Linked to Cardiac Arrests, Ischemic Events

Amy Reyes

July 15, 2015

MELBOURNE, AUSTRALIA — Exposure to the smoke from wildfires that hit the southeast region of Australia in December 2006 and January 2007, specifically to particulate matter at high PM2.5 concentrations, was associated with an upswing in out-of-hospital cardiac arrests in men and ischemic heart disease (IHD) events in women[1]. The findings are from a study published July 15, 2015 in the Journal of the American Heart Association with first author Dr Anjali Haikerwal (Monash University, Melbourne, Australia).

The study shows the associations between cardiac arrest and IHD as a result of exposure to high levels of PM2.5 smoke for up to 2 days. The researchers also found that cardiac arrests and IHD disproportionately affected men and women who were 65 years old and older.

A PM2.5 concentration refers to particles with an aerodynamic diameter <2.5 μm. High concentrations of PM2.5 particulates have been linked to MIs, heart failure, and cardiovascular disease. The American Heart Association characterizes PM2.5 as a risk factor that contributes to CVD mortality and morbidity.

The researchers examined the associations of arrests and ischemic events with PM2.5 concentrations during the 2-month wildfire season, using a time-stratified case-crossover study design. There were 457 out-of-hospital cardiac arrests, 2106 emergency-department visits, and 3274 hospital admissions for IHD.

Researchers found that increased exposure by an interquartile range of 9.04 μg/m3 in PM2.5 over 2 days was associated with a 6.98% increase in risk of out-of-hospital cardiac arrests, with a stronger association shown by men (9.05%) and by adults aged ≥65 years (7.25%).

IHD-related emergency-department visits increased by 2.07%. And after 2 days, IHD-related hospital admissions rose 1.86%, with more women (3.21%) and older adults (2.41%) being admitted to the hospital.

While there have been some studies that examine PM2.5 in terms of wildfire smoke, these are largely based on data from air monitors, which are usually extracted from within metropolitan or regional areas where air monitors are established, according to the authors. That has made it difficult to get an accurate measurement of PM2.5 exposure from wildfire smoke.

To get around this, Haikerwal and colleagues used a novel modeling technique for more accurate readings. They say they were able to provide extremely fine spatial air-quality data for the entire state of Victoria to assess areas affected by wildfires and smoke. They found that PM2.5 levels rose as high as 100 μg/m3, which far exceeds allowable standards of 25 μg/m3 in Australia and 35 μg/m3 in the US for a 24-hour period.

The researchers say more work needs to be done to explain the differences of cardiovascular disease in men and women. Furthermore, "improvements in the understanding of these priority areas is needed so that effective and timely public-health strategies can be developed and implemented to reduce the burden of disease during wildfire events. This will have further implications for setting appropriate air-quality standards, enhancing healthcare infrastructure, and improving timely risk communication and health advice during wildfires."

The study was funded by Bushfire Cooperative Research Centre, now a part of Bushfire & Natural Hazards Cooperative Research Centre, Melbourne, Victoria, Australia. The authors had no relevant financial relationships.

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