Correspondence

Heart Disease Deaths among Firefighters

N Engl J Med 2007; 356:2535-2537June 14, 2007

Article

To the Editor:

It is somewhat surprising that the report by Kales and colleagues (March 22 issue)1 on emergency duties and deaths from heart disease among firefighters in the United States does not cite the possible influence of carbon monoxide as a causative factor in deaths due to coronary heart disease among firefighters suppressing a fire. There is no doubt about the role of moderate and severe carbon monoxide intoxication in myocardial injury or long-term mortality of cardiac origin.2 We performed a study that showed that even in the case of mild carbon monoxide intoxication (carboxyhemoglobin level, <25%), 4% of patients have ischemic changes.3 It has been reported that firefighters who are nonsmokers and who do not use self-contained breathing apparatus correctly may have carboxyhemoglobin levels of up to 14%.4 Even when such apparatus are used correctly, the carboxyhemoglobin level can reach 9.1%.5 We suggest that the increase in cardiovascular demand during fire suppression reported by Kales and colleagues may be partially due, on the one hand, to elevated carboxyhemoglobin levels and, on the other hand, to the union of carbon monoxide with mitochondrial cytochrome oxidase, which directly interferes with cellular respiration.2

Antonio Dueñas-Laita, M.D., Ph.D.
José L. Peréz-Castrillón, M.D., Ph.D.
Hospital Universitario Río Hortera, 47010 Valladolid, Spain

Marta Ruiz-Mambrilla, M.D., Ph.D.
Universidad de Valladolid, 47005 Valladolid, Spain

5 References

1. 1

   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;356:1207-1215
   Full Text | Web of Science | Medline

2. 2

   Henry CR, Satran D, Lindgren B, Adkinson C, Nicholson CI, Henry TD. Myocardial injury and long-term mortality following moderate to severe carbon monoxide poisoning. JAMA 2006;295:398-402
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3. 3

   Duenas-Laita A, Burillo Puzte G, Nogue Xarau S, Ruiz Mambrilla M. Cardiovascular manifestations of carbon monoxide poisoning. J Am Coll Cardiol 2006;47:690-691
   CrossRef | Web of Science | Medline

4. 4

   Cone DC, MacMillan DS, Van Gelder C, Brown DJ, Weir SD, Bogucki S. Noninvasive fireground assessment of carboxyhemoglobin levels in firefighters. Prehosp Emerg Care 2005;9:8-13
   CrossRef | Medline

5. 5

   Stewart RD, Stewart RS, Stamm W, Seelen RP. Rapid estimation of carboxyhemoglobin level in fire fighters. JAMA 1976;235:390-392
   CrossRef | Web of Science | Medline

To the Editor:

In the absence of evidence, one wonders whether the task-related deaths from coronary heart disease reported by Kales et al. could be reduced by identifying firefighters at high risk with the use of exercise stress testing for those over 40 years of age, as recommended by the National Fire Protection Association.1 Although ST-segment depression has poor sensitivity for identifying those at high risk, the Duke treadmill score, heart-rate recovery, functional capacity, chronotropic index, and presence or absence of ectopy after exercise stress testing can greatly enhance diagnostic accuracy.2,3 However, typical exercise stress testing does not induce heat stress, which often occurs during fire suppression, including that imposed by thermally restrictive protective gear. In an observational study of 61 healthy candidates for hazardous materials duty (mean [±SD] age, 34±8 years; mean body-mass index [the weight in kilograms divided by the square of the height in meters], 28.5±4.3), we found little sweating, subjective thermal stress, or change in body temperature (Table 1Table 1Tympanic and Sublingual Temperatures before and after Maximal, Symptom-Limited Treadmill Testing with Electrocardiography (Bruce Protocol).), which rose by only 0.06±0.07°F (0.03±0.04°C) per minute of treadmill exertion. If treadmill testing is performed as part of the medical evaluation of firefighters, it should incorporate heat stress as well as exertion.

Lawrence W. Raymond, M.D.
Thomas A. Barringer, M.D.
Joseph C. Konen, M.D., M.P.H.
Carolinas Medical Center, Charlotte, NC 28232
larryr@med.unc.edu

3 References

1. 1

   NFPA 1582: standard on medical requirements for firefighters, 2000 edition. Quincy, MA: National Fire Protection Association, 2000.
   

2. 2

   Kligfield P, Lauer MS. Exercise electrocardiogram testing: beyond the ST segment. Circulation 2006;114:2070-2082
   CrossRef | Web of Science | Medline

3. 3

   Raymond LW, Barringer TA, Konen JC. Stress testing in the medical evaluation for hazardous materials duty: results and consequences in three groups of candidates. J Occup Environ Med 2005;47:493-502
   CrossRef | Web of Science | Medline

Author/Editor Response

We agree with Dueñas-Laita and colleagues that carbon monoxide is a likely contributing factor in some deaths from coronary heart disease that occur during fire suppression. Smoke exposure may occur at structure fires, despite the use of self-contained breathing apparatus, and during brush and forest fires, when little or no respiratory protection may be worn. Of 17 firefighters who died from coronary heart disease and for whom data on postincident carboxyhemoglobin levels could be determined, 4 (24%) had carboxyhemoglobin levels of 3 to 10%.1 Postincident determinations of carboxyhemoglobin levels usually underestimate peak exposures because of oxygen therapy and the time that has elapsed between the incident and blood sampling. In addition, we found that more than 40% of on-duty firefighters who died from coronary heart disease were smokers.1 Exposure to carbon monoxide from tobacco use is additive to that from exogenous smoke. Increased blood carboxyhemoglobin levels are expected to have an adverse effect on aerobic capacity, anaerobic threshold, and exercise tolerance. Finally, smoke from a fire may contain other cardiotoxins, such as cyanide and particulate matter.2,3 However, the important message — and the common denominator — of the deaths in our study is that various stressors (physical, psychological, and chemical) in different combinations can trigger cardiac events in on-duty firefighters who have underlying coronary heart disease.

We strongly agree with Raymond and colleagues that exercise stress testing should be useful in identifying firefighters at high risk for on-duty cardiovascular events. Likewise, we concur that including abnormal heart-rate recovery, chronotropic incompetence, certain abnormal blood-pressure responses, and dysrhythmias as criteria for an abnormal result on exercise stress testing would probably increase the sensitivity of the procedure. However, the results of such tests must be interpreted along with a comprehensive risk-factor profile for coronary heart disease4 to enhance their predictive value. Moreover, given the lack of direct evidence to support exercise stress testing in screening public safety personnel,5 it is premature to conclude that exercise stress testing in firefighters should include induction of exogenous heat stress. Further research conducted in public-safety cohorts is necessary to determine the best risk-stratification strategies to use in the selection of firefighters for such testing and to develop effective screening and diagnostic protocols.

Stefanos N. Kales, M.D., M.P.H.
Elpidoforos S. Soteriades, M.D., Sc.D.
David C. Christiani, M.D., M.P.H.
Harvard School of Public Health, Boston, MA 02115
skales@challiance.org

5 References

1. 1

   Kales SN, Soteriades ES, Christoudias SG, Christiani DC. Firefighters and on-duty deaths from coronary heart disease: a case control study. Environ Health 2003;2:14-14
   CrossRef | Medline

2. 2

   Booze TF, Reinhardt TE, Quiring SJ, Ottmar RD. A screening-level assessment of the health risks of chronic smoke exposure for wildland firefighters. J Occup Environ Hyg 2004;1:296-305
   CrossRef | Web of Science | Medline

3. 3

   Alarie Y. Toxicity of fire smoke. Crit Rev Toxicol 2002;32:259-289
   CrossRef | Web of Science | Medline

4. 4

   Soteriades ES, Hauser R, Kawachi I, Liarokapis D, Christiani DC, Kales SN. Obesity and cardiovascular disease risk factors in firefighters: a prospective cohort study. Obes Res 2005;13:1756-1763
   CrossRef | Medline

5. 5

   Gibbons RJ, Balady GJ, Bricker JT, et al. ACC/AHA 2002 guideline update for exercise testing: summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). J Am Coll Cardiol 2002;40:1531-1540[Erratum, J Am Coll Cardiol 2006;48:1731.]
   CrossRef | Web of Science | Medline