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

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.

Article From Exerc Sport Sci Rev. 2016;44(3):89

References
1. Choi BC. A technique to re-assess epidemiologic evidence in light of the healthy
worker effect: the case of firefighting and heart disease. J. Occup. Environ. Med.
2000; 42:1021–34.
2. Kales SN, Soteriades ES, Christophi CA, Christiani DC. Emergency duties and deaths
from heart disease among firefighters in the United States. N. Engl. J. Med. 2007;
356:1207–15.
3. Pope CA 3rd, Muhlestein JB, May HT, Renlund DG, Anderson JL, Horne BD. Ischemic
heart disease events triggered by short-term exposure to fine particulate air
pollution. Circulation. 2006; 114:2443–8.
4. Smith DL, DeBlois JP, Kales SN, Horn GP. Cardiovascular strain of firefighting and
the risk of sudden cardiac events. Exerc. Sport Sci. Rev. 2016; 44:90–7.