Why do Fire Ground Duties Trigger Sudden Cardiac Events in Firefighters?

Thomas Hales

Disclosures

Exerc Sport Sci Rev. 2016;44(3):89 

Fire suppression involves physically demanding work in hot, dangerous environments with heavy encapsulating protective gear while being exposed to toxic chemicals and particulate matter in fire smoke. Thus, it is not surprising that firefighters have high rates of injuries and illness. Approximately 85–100 firefighters die each year on duty with approximately 35–45 being caused by sudden cardiac events. But these on-duty sudden cardiac events do not occur randomly. Rather, they occur in a much higher proportion on the fire ground when firefighters are performing fire suppression operations.[2] For more than two decades, Smith et al.[4] has meticulously documented the physiologic effects of fire suppression on the cardiovascular system. In the current issue of the Journal, Smith et al.[4] summarizes this research and proposes flow diagrams about how these physiologic changes, in combination with other risk factors, could trigger a sudden cardiac event in susceptible firefighters. This commentary reviews the association between firefighting and cardiovascular disease and suggests additional research to direct prevention efforts.

A number of mortality studies have examined the relation between cardiovascular disease and firefighting, yet few have found elevated standardized mortality ratios. This lack of an association probably is caused by the healthy worker effect, an inherent bias of occupational cohort mortality studies.[1] Mortality studies that examined the cardiovascular disease risk by duration of employment found markedly lower standardized mortality ratios at the beginning of a firefighter's career that catch up or even surpass the risk of the general population at the end of their careers. This rising standardized mortality ratio with increasing duration of employment suggests occupational involvement.

Heavy physical exertion can trigger myocardial infarctions and sudden cardiac events in susceptible members of the general population. Given that fire suppression requires heavy physical exertion, the increased risk of a sudden cardiac event on the fire ground could be caused solely by physical exertion. But firefighter physical training also requires heavy exertion, and the risk of a sudden cardiac event during physical training is much lower than work on the fire ground,[2] suggesting that the fire ground has other triggers. Carbon monoxide would be an obvious candidate because it is frequently found in fire smoke and is known to cause cardiac arrhythmias and coronary ischemia. However, the National Institute for Occupational Safety and Health has investigated the deaths of more than 300 on-duty firefighters caused by sudden cardiac events. Only five cases had carboxyhemoglobin levels (>5%), suggesting that carbon monoxide plays a minor, if any, role. Fire suppression also exposes firefighters to particulate matter. Particulate matter in air pollution has been linked to cardiovascular mortality, the initiation/progression of atherosclerosis, and the triggering of heart attacks.[3]

The present review showcases research Smith et al.[4] conducted regarding the cardiac, vascular, and hemostatic changes during live fire training. However, the clinical significance of these changes, particularly regarding triggering a sudden cardiac event, is less clear. To direct intervention efforts, additional research is needed to determine the relative contributions of physical exertion and fire smoke exposure to these physiologic changes. For example, if physical exertion solely was responsible for the physiologic changes, prevention efforts would involve increased staffing to reduce an individual firefighter's workload. If, on the other hand, fire smoke was found to be the sole offending agent, then proper and continual use of personal protective gear during all phases of fire suppression including overhaul should be emphasized. Finally, as Smith et al.[4] mention, in addition to these occupational interventions, efforts to reduce on-duty sudden cardiac events should include eating a heart-healthy diet, maintaining a healthy weight, getting regular exercise, getting adequate sleep, no tobacco, and avoiding excessive alcohol consumption.

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