Exclusives, Training

Firefighting and On-Duty Cardiac Deaths

Research Review: Smith DL, Haller JM, Korre M, et al. Pathoanatomic findings associated with duty-related cardiac death in US firefighters: A case-control study. J Am Heart Assoc. 2018;7(18):e009446. doi: 10.1161/JAHA.118.009446.

Background

EMS is a part of the broader family of first responders; they’re integral to public welfare and safety. During firefighting operations, EMS is often dispatched because of the multiple risks that firefighters face. Research has documented significant cardiovascular strain among firefighters due to the stressors that they encounter.

These stressors might trigger a cardiac event in firefighters with underlying cardiovascular disease.1–3 (See Figure 1.) Indeed, the most common life-threatening condition for which EMS will treat firefighters is a sudden cardiac event.

Figure 1: Duty-related physiological stressors and mediating factors that affect cardiovascular responses associated with responses from firefighting

Given the unique challenges that cardiac events present when they occur on a fire scene, it’s important to understand underlying pathological causes of duty-related cardiac events among firefighters before you encounter them in the field.

Sudden cardiac deaths (SCD) account for roughly 40–50% of annual duty-related fatalities in the fire service.4 Overt coronary heart disease (CHD) has long been the reported underlying condition associated with SCD, with a 3- to 5-fold increased risk of SCD of in individuals with CHD.5,6

Left ventricular hypertrophy (LVH) (i.e., thicker left ventricle wall) and cardiomegaly (i.e., abnormal increase in heart mass) have also been associated with SCD.7–9 However, the combined and independent roles of LVH, cardiomegaly and CHD in the fire service hasn’t been extensively studied.

Methods

With the help of the United States Fire Administration (USFA) and the National Fallen Firefighters Foundation (NFFF) autopsy reports for duty-related firefighter fatalities between 1999 and 2014 were obtained. On-duty fatality was defined based on the USFA’s guidelines; injury or illness sustained while on duty that proved fatal, including illness resulting from a sudden cardiac event or stroke within 24 hours of training or emergency response.

Only data for male firefighters between the ages of 18 to 65 were used in the current study given the low number of female fatalities and increasing prevalence of cardiovascular disease with age.

Figure 2 presents the process of classifying autopsy reports for this study. Two study investigators independently and carefully examined each autopsy and disagreements were resolved by a senior investigator.

Figure 2: Process for categorizing fatalities included in the research study

Data were then extracted from reports that met the inclusion criteria. Fatalities were grouped into: 1) non-cardiac (trauma controls); 2) cardiac cases; and 3) other (indeterminate). Cardiac cases were further classified as having CHD, cardiomegaly/LVH, CHD and cardiomegaly/LVH, or other cardiovascular disease, such as cardiomyopathies, primary arrhythmia and valvular disease.

Fatalities that weren’t cardiac in nature were classified as non-cardiac trauma (e.g., trauma, brain injury, smoke inhalation). Fatalities classified as ambiguous (i.e., not cardiac or traumatic) were classified into the “other” group. All autopsies were subsequently reviewed and relevant data were extracted independently by two investigators.

Data collected included anthropometric measurements (i.e., height and weight), measurements of heart mass and size, extent of coronary artery stenosis due to CHD, and the presence or absence of a thrombosis (i.e., blood clot) in the coronary arteries.

Results

A total of 627 autopsy reports met the criteria for the study. As seen as in Figure 2, 276 (44%) of the fatalities were cardiac in nature and 351 (55%) were due to non-cardiac causes.

Blunt force trauma was the most common cause of death on the non-cardiac fatalities.

As seen in Table 1, the groups differed on several key characteristics; firefighters in the cardiac group were, on average, older and had six more years of service.

Table 1: Descriptive characteristics of cardiac cases and non-cardiac controls
Values are average ± standard deviation or percentage
*Significant difference between groups

Figure 3 shows the heart weights for cardiac cases vs. non-cardiac controls. Cardiac fatality victims had hearts that were on average 120 grams heavier than the traumatic victims.

Figure 3: Difference in heart weight between cardiac causes and non-cardiac controls
*Significant difference between groups

Additional data is reported in Table 2. Approximately 75% of cardiac fatalities had hearts that were heavier than the common definition of cardiomegaly ( > 450 g). Importantly, nearly one-third of traumatic controls also had enlarged hearts.

Table 2: Autopsy findings of cardiac cases and non-cardiac controls
Values are presented as percentages
*Significant difference between groups

Approximately 60% of cardiac cases had at least one coronary artery with > 75% stenosis, while only 8% of traumatic controls had this level of atherosclerosis. A coronary thrombus (i.e., clot) was found in 16% of cardiac cases, but none in the traumatic victims.

There were several key findings from this study:

  • Only 16% of cardiac cases had evidence of an intracoronary thrombus, which provides definitive evidence that the firefighter died of a heart attack;
  • 82% of the cardiac cases had both CHD and cardiomegaly/LVH, 5.4% had CHD alone and 5.8% had cardiomegaly/LVH alone;
  • A heart weight greater than 450 grams was associated with a six-fold increased risk of cardiac death; and
  • A coronary artery with 75% or greater stenosis was associated with a nine-fold increased risk of cardiac death.

Discussion

Utilizing a careful design, the underlying pathological conditions associated with SCD were documented. One of the most surprising findings of the study is that only 16% of cardiac cases had definitive proof of a myocardial infarction (i.e., heart attack), as evidenced by a thrombus in a coronary artery.

This is important, since it’s long been assumed that heart attacks are responsible for most firefighter sudden cardiac events. In fact, many fire service agencies use the terms sudden cardiac event and heart attack interchangeably.

For EMS providers, it’s important to note that cardiac cases may present with symptoms of an evolving myocardial infarction or as sudden cardiac arrest.

CHD has long been thought to be the predominant form of cardiovascular disease in the general population and in the fire service.

Our data indicate that most cardiac deaths occurred in firefighters with both CHD and cardiac enlargement (cardiomegaly or left ventricular hypertrophy).

These data underscore the complexity of cardiovascular disease as CHD can lead to cardiac enlargement and ischemia, and ischemia can lead to greater risk of arrhythmia in individuals with a structurally enlarged heart.

CHD is a strong predictor of sudden cardiac death in the fire service and medical screening and prevention should continue to focus on this. However, this study found that cardiomegaly (i.e., a heart weight of > 450 g) was also a strong independent predictor of SCD risk, and we believe that new screening protocols should focus on this emerging risk.

Although not directly assessed in this study, it appears that atherosclerosis and cardiac structural changes predispose to ventricular arrhythmias, predisposing individuals with both conditions to a greater risk of experiencing a cardiac event. These findings support the need for screening for the presence of CHD as well as structurally enlarged heart among firefighters.

Conclusion

Using autopsy data from on-duty fatalities that occurred over a 15-year period, the underlying cardiac pathological conditions associated with sudden cardiac death were investigated among firefighters. Our data suggest a need for updated and improved medical screening for firefighters. Particularly, screening for CHD and cardiac enlargement should be incorporated into a firefighter’s routine screening.

Given the important role of EMS in ensuring both civilian and firefighter safety, EMS personnel should be alert to the potential to encounter either sudden cardiac arrest or a myocardial infarction in firefighters when responding to stressful emergency operations.

References

1. Soteriades ES, Smith DL, Tsismenakis AJ, et al. Cardiovascular disease in US firefighters: A systematic review. Cardiol Rev. 2011;19(4):202–215.

2. Smith DL, Barr DA, Kales SN. Extreme sacrifice: Sudden cardiac death in the US fire service. Extreme Physiol & Med. 2013;2(1):1–9.

3. Smith DL, DeBlois JP, Kales SN, et al. Cardiovascular strain of firefighting and the risk of sudden cardiac events. Exerc Sport Sci Rev. 2016;44(3):90–97.

4. Fahy RF, LeBlanc PR, Molis JL. Firefighter fatalities in the United States—2016. National Fire Protection Association: Quincy, Mass., 2017.

5. Deo R, Albert CM. Epidemiology and genetics of sudden cardiac death. Circulation. 2012;125(4):620–637.

6. Cupples LA, Gagnon DR, Kannel WB. Long- and short-term risk of sudden coronary death. Circulation. 1992;85(1):11–18.

7. Dean JH, Gallagher PJ. Cardiac ischemia and cardiac hypertrophy. An autopsy study. Arch Pathol Lab Med. 1980;104(4):175–178.

8. Jimenez RA, Myerburg RJ. Sudden cardiac death. Magnitude of the problem, substrate/trigger interaction, and populations at high risk. Cardiol Clin. 1993;11(1):1–9.

9. Burke AP, Farb A, Liang YH, et al. Effect of hypertension and cardiac hypertrophy on coronary artery morphology in sudden cardiac death. Circulation. 1996;94(12):3138–3145.