To the Editor: It is somewhat surprising that the report byKales and colleagues (March 22 issue)1 on emergency duties anddeaths from heart disease among firefighters in the United Statesdoes not cite the possible influence of carbon monoxide as acausative factor in deaths due to coronary heart disease amongfirefighters suppressing a fire. There is no doubt about therole of moderate and severe carbon monoxide intoxication inmyocardial injury or long-term mortality of cardiac origin.2We performed a study that showed that even in the case of mildcarbon monoxide intoxication (carboxyhemoglobin level, <25%),4% of patients have ischemic changes.3 It has been reportedthat firefighters who are nonsmokers and who do not use self-containedbreathing apparatus correctly may have carboxyhemoglobin levelsof up to 14%.4 Even when such apparatus are used correctly,the carboxyhemoglobin level can reach 9.1%.5 We suggest thatthe increase in cardiovascular demand during fire suppressionreported by Kales and colleagues may be partially due, on theone hand, to elevated carboxyhemoglobin levels and, on the otherhand, to the union of carbon monoxide with mitochondrial cytochromeoxidase, 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
References
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. [Free Full Text]
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. [Free Full Text]
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. [Free Full Text]
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. [Medline]
Stewart RD, Stewart RS, Stamm W, Seelen RP. Rapid estimation of carboxyhemoglobin level in fire fighters. JAMA 1976;235:390-392. [Free Full Text]
To the Editor: In the absence of evidence, one wonders whetherthe task-related deaths from coronary heart disease reportedby Kales et al. could be reduced by identifying firefightersat high risk with the use of exercise stress testing for thoseover 40 years of age, as recommended by the National Fire ProtectionAssociation.1 Although ST-segment depression has poor sensitivityfor 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 testingcan greatly enhance diagnostic accuracy.2,3 However, typicalexercise stress testing does not induce heat stress, which oftenoccurs during fire suppression, including that imposed by thermallyrestrictive protective gear. In an observational study of 61healthy candidates for hazardous materials duty (mean [±SD]age, 34±8 years; mean body-mass index [the weight inkilograms divided by the square of the height in meters], 28.5±4.3),we found little sweating, subjective thermal stress, or changein body temperature (Table 1), which rose by only 0.06±0.07°F(0.03±0.04°C) per minute of treadmill exertion. Iftreadmill testing is performed as part of the medical evaluationof firefighters, it should incorporate heat stress as well asexertion.
Table 1. Tympanic and Sublingual Temperatures before and after Maximal, Symptom-Limited Treadmill Testing with Electrocardiography (Bruce Protocol).
Lawrence W. Raymond, M.D. Thomas A. Barringer, M.D. JosephC. Konen, M.D., M.P.H. Carolinas Medical Center Charlotte, NC 28232 larryr{at}med.unc.edu
References
NFPA 1582: standard on medical requirements for firefighters, 2000 edition. Quincy, MA: National Fire Protection Association, 2000.
Kligfield P, Lauer MS. Exercise electrocardiogram testing: beyond the ST segment. Circulation 2006;114:2070-2082. [Free Full Text]
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]
The authors reply: We agree with Dueñas-Laita and colleaguesthat carbon monoxide is a likely contributing factor in somedeaths from coronary heart disease that occur during fire suppression.Smoke exposure may occur at structure fires, despite the useof self-contained breathing apparatus, and during brush andforest fires, when little or no respiratory protection may beworn. Of 17 firefighters who died from coronary heart diseaseand for whom data on postincident carboxyhemoglobin levels couldbe determined, 4 (24%) had carboxyhemoglobin levels of 3 to10%.1 Postincident determinations of carboxyhemoglobin levelsusually underestimate peak exposures because of oxygen therapyand the time that has elapsed between the incident and bloodsampling. In addition, we found that more than 40% of on-dutyfirefighters who died from coronary heart disease were smokers.1Exposure to carbon monoxide from tobacco use is additive tothat from exogenous smoke. Increased blood carboxyhemoglobinlevels are expected to have an adverse effect on aerobic capacity,anaerobic threshold, and exercise tolerance. Finally, smokefrom a fire may contain other cardiotoxins, such as cyanideand particulate matter.2,3 However, the important message —and the common denominator — of the deaths in our studyis that various stressors (physical, psychological, and chemical)in different combinations can trigger cardiac events in on-dutyfirefighters who have underlying coronary heart disease.
We strongly agree with Raymond and colleagues that exercisestress testing should be useful in identifying firefightersat high risk for on-duty cardiovascular events. Likewise, weconcur that including abnormal heart-rate recovery, chronotropicincompetence, certain abnormal blood-pressure responses, anddysrhythmias as criteria for an abnormal result on exercisestress testing would probably increase the sensitivity of theprocedure. However, the results of such tests must be interpretedalong with a comprehensive risk-factor profile for coronaryheart disease4 to enhance their predictive value. Moreover,given the lack of direct evidence to support exercise stresstesting in screening public safety personnel,5 it is prematureto conclude that exercise stress testing in firefighters shouldinclude induction of exogenous heat stress. Further researchconducted in public-safety cohorts is necessary to determinethe best risk-stratification strategies to use in the selectionof firefighters for such testing and to develop effective screeningand 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{at}challiance.org
References
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]
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]
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. [Web of Science][Medline]
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.] [Free Full Text]
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