Sudden cardiac death (SCD) is the leading cause of death in firefighters. Although on-duty SCD usually occurs in older victims almost exclusively because of coronary heart disease, no studies have examined causation across the career span. In the present retrospective case-control study, cases of SCD in young (aged ≤45 years) firefighters from the National Institute for Occupational Safety and Health fatality investigations (n = 87) were compared with 2 age- and gender-matched control groups: occupationally active firefighters (n = 915) and noncardiac traumatic firefighter fatalities (n = 56). Of the SCD cases, 63% were obese and 67% had a coronary heart disease–related cause of death. The SCD victims had much heavier hearts (522 ± 102 g) than noncardiac fatality controls (400 ± 91 g, p <0.001). Cardiomegaly (heart weight >450 g) was found in 66% of the SCD victims and conveyed a fivefold increase (95% confidence interval [CI] 1.93 to 12.4) in SCD risk. Furthermore, hypertension, including cases with left ventricular hypertrophy, increased SCD risk by 12-fold (95% CI 6.23 to 22.3) after multivariate adjustment. A history of cardiovascular disease and smoking were also independently associated with elevated SCD risk (odds ratio 6.89, 95% CI 2.87 to 16.5; and odds ratio 3.53, 95% CI 1.87 to 6.65, respectively). In conclusion, SCD in young firefighters is primarily related to preventable lifestyle factors. Obesity entry standards, smoking bans, and improved screening and/or wellness program are potential strategies to reduce SCD in younger firefighters.
The leading mode of duty-related death among US firefighters is sudden cardiac death (SCD), which accounts for about 50% of on-duty firefighting fatalities. About 90% of these SCD cases will be attributable to coronary heart disease (CHD) and usually occur in firefighters aged >45 years. In addition, emerging evidence has suggested that obesity and left ventricular (LV) hypertrophy and/or cardiomegaly are present in a large proportion of all those with SCD (with and without CHD) in firefighters and the general population. Although SCD causation in younger subjects, such as athletes, is usually due to non-CHD structural pathologic features, little is known about SCD in young firefighters. We conducted a case-control study of SCD among firefighters aged ≤45 years to examine the associated cardiovascular disease (CVD) risk factors and underlying pathologic features. Our aims were to (1) describe the specific pathologic-anatomic causes of on-duty SCD in these cases, (2) compare the prevalence and severity of CVD risk factors in SCD fatalities with those in healthy, occupationally active firefighter controls, and (3) compare the cardiac findings from the SCD cases at autopsy with those of firefighters who died of on-duty noncardiac causes.
Methods
We conducted a retrospective case-control study that serially reviewed and selected as cases all SCD fatalities (aged ≤45 years) from 1996 to 2012 investigated by the National Institute for Occupational Safety and Health (NIOSH). Two other firefighter groups were chosen as controls: (1) age-matched, career firefighters examined from 2007 to 2009 and (2) age-matched, noncardiac, traumatic fatalities (2004 to 2010) with autopsy reports available.
NIOSH conducts independent investigations of firefighter line-of-duty deaths, and the completed fatality reports are publicly available for download from NIOSH’s Firefighter Fatality Investigation and Prevention Program website. Two physician investigators (J.Y. and D.T.) examined in detail all fatality reports published online from January 1996 to December 2012 to determine whether each case met our inclusion criteria as listed in the following paragraph. A third physician investigator (A.F.) then reviewed the NIOSH database and previously selected cases again, with final decisions on inclusion resolved by the senior investigator (S.N.K.). SCD case data were extracted using a standardized electronic template by 2 of us (D.T. and J.Y.) independently and then were verified for completeness and accuracy (by J.Y.). Any disagreements among the investigators on data extraction were resolved by the senior physician investigator (S.N.K.).
The inclusion criteria for the NIOSH SCD fatality cases were (1) NIOSH investigated cases published on the website from January 1996 to December 2012, (2) firefighters who experienced SCD and died within 24 hours of their last fire service duty or experienced a sudden cardiac event within 24 hours of their last duty and the event was associated with loss of consciousness within 1 hour of onset, and, subsequently, the firefighter never regained consciousness before biologic death, (3) age ≤45 years, and (4) autopsy report or sufficient medical findings available to determine the underlying cause of death.
An existing database previously assembled from career fire departments was reviewed for occupationally active control firefighters. The cohort’s cardiovascular and health status were comprehensively characterized by baseline fire department medical examinations. The inclusion criteria for the occupationally active firefighter controls were (1) age ≤45 years, and (2) no medical restrictions or physical limitations on duty.
Potential age-matched, noncardiac traumatic fatalities (deaths due to blunt trauma, burns, or asphyxiation) were identified for 2004 to 2010 from a firefighter autopsy research data bank maintained by 1 of us (D.S.) and the National Fallen Firefighters Foundation. The inclusion criteria for the National Fallen Firefighters Foundation noncardiac traumatic controls were (1) age ≤45 years, (2) death while on duty, and (3) cause of death determined by autopsy to be due to blunt trauma, burns, or asphyxiation and not related to any cardiovascular pathologic entity.
Among the occupationally active controls, firefighters were considered active smokers if they self-reported smoking within the previous 12 months. Diabetes mellitus was defined using the Framingham criteria (random blood glucose ≥150 mg/dl, previous diagnosis of diabetes, and/or requiring diabetes mellitus medications). Hypertension was considered present if firefighters had a systolic blood pressure of ≥140 mm Hg and/or diastolic blood pressure of ≥90 mm Hg at rest, a previous hypertension diagnosis, and/or required hypertension medication. Firefighters with a total cholesterol level of ≥200 mg/dl, low-density lipoprotein of ≥160 mg/dl, a previous diagnosis of hyperlipidemia, and/or requiring lipid-lowering medications were considered to have dyslipidemia.
In the NIOSH SCD cases, the determinations were according to the same criteria or a description of the risk factors as presented by the NIOSH investigators anywhere in the case report. We also considered a second definition of hypertension that included those with hypertension as defined plus those with LV hypertrophy found on autopsy. Any firefighter was considered to have a history of CHD or CHD equivalent if the NIOSH report or medical record reported previous myocardial infarction, angioplasty, stent placement, or a clinical diagnosis of CHD on the basis of an abnormal calcium score or exercise tolerance test findings. A history of valvular disease was considered present if a previous diagnosis of valvular abnormalities and/or disease or appropriate autopsy findings of valvular disease were present. A “history of chest pain or shortness of breath” was considered present if the firefighter had had episodes of chest pain and/or shortness of breath documented without a CHD diagnosis. We conservatively coded the CVD risk factors in the SCD cases as negative when these were undeterminable or ambiguous from the investigation report.
The use of de-identified data from the occupationally active firefighter controls was previously approved by the institutional review board of Harvard School of Public Health and local institutional review boards, as appropriate. The investigations and autopsy reports from NIOSH and the National Fallen Firefighters Foundation were exempt from institutional review board review (deceased, nonliving subjects).
Statistical analyses were performed using SPSS, version 21.0 (IBM, Armonk, New York) and Stata, version 12.1 SE (StataCorp, College Station, Texas). Categorical variables were compared using Fisher’s exact test and normally distributed continuous variables using Student’s t test. Associations of risk factors with SCD were characterized by odds ratios and associated 95% confidence intervals. Variables to be introduced in the multivariate logistic regression models were selected a priori. p Values <0.05 were considered statistically significant, and all statistical tests were 2-sided.
Results
A total of 87 SCD fatality cases, 915 occupationally active controls, and 56 trauma deaths met the inclusion criteria. The SCD cases dichotomized by age are listed in Table 1 . Cases with cardiomyopathy and/or cardiomegaly in the absence of CHD were most often associated with hypertrophic cardiomyopathy or nonspecific cardiomyopathies. Overall, 67% of SCD cases had CHD as a contributing factor (categories 1 and 4).
| Variable | Age <35 yrs (n = 22) | Age 35–45 yrs (n = 65) | Total (n = 87) |
|---|---|---|---|
| Age (yrs) | 28.0 ± 4.1 | 41.0 ± 3.1 | 37.7 ± 6.6 |
| Men (%) | 21 (96) | 64 (99) | 85 (98) |
| BMI (kg/m 2 ) | 31.6 ± 6.5 (n = 18) | 32.1 ± 6.1 (n = 50) | 32.0 ± 6.2 (n = 68) |
| Obesity category | |||
| BMI ≥30 kg/m 2 (obese) | 12 (67) | 31 (62) | 43 (63) |
| BMI ≥30 but <35 kg/m 2 | 7 (39) | 17 (34) | 24 (35) |
| BMI ≥35 but <40 kg/m 2 | 3 (17) | 7 (14) | 10 (15) |
| BMI ≥40 kg/m 2 | 2 (11) | 7 (14) | 9 (13) |
| Smoker | 4 (18) | 20 (31) | 24 (28) |
| Career status | |||
| Career | 11 (50) | 41 (63) | 52 (60) |
| Volunteer | 11 (50) | 24 (37) | 35 (40) |
| Autopsy findings | |||
| CHD only | 1 (5) | 11 (17) | 12 (14) |
| Hypertrophic cardiomyopathy | 3 (14) | 2 (3) | 5 (6) |
| LV hypertrophy or hypertension heart disease | 1 (5) | 3 (5) | 4 (5) |
| CHD + cardiomegaly | 7 (32) | 39 (60) | 46 (53) |
| Arrhythmia because of idiopathic dilated cardiomyopathy | 3 (14) | 1 (2) | 4 (5) |
| Coronary anomaly | 1 (5) | 1 (2) | 2 (2) |
| Valvular disease (acquired) | 3 (14) | 3 (5) | 6 (7) |
| Congenital heart disease other than coronary anomaly | 0 | 1 (2) | 1 (1) |
| WPW, long QT, and other primary arrhythmia without structural disease | 1 (5) | 0 | 1 (1) |
| Cardiac sarcoidosis | 0 | 2 (3) | 2 (2) |
| Commotio cordis | 0 | 0 | 0 |
| Myocarditis | 0 | 0 | 0 |
| Other cardiovascular causes | 1 (5) | 1 (2) | 2 (2) |
| Cause of SCD not confirmed ∗ | 1 (5) | 1 (2) | 2 (2) |
| Heart weight (g) | 490 ± 84 (n = 18) | 534 ± 107 (n = 47) | 522 ± 102 (n = 65) |
| Heart weight group | |||
| >450 g | 11 (61) | 32 (68) | 43 (66) |
| >550 g | 5 (28) | 22 (47) | 27 (42) |
∗ Cause of SCD could not be confirmed because of lack of autopsy and previous medical records.
The CVD risk factor prevalence between the NIOSH SCD cases and occupationally active firefighter controls is presented in Table 2 . The odds ratios for obesity, smoking, and hypertension were all statistically significant for an association with SCD after multivariate adjustment. A history of CHD, CHD equivalent, or valvular disease diagnosed before death was associated with a sevenfold increase in the risk of SCD, even after multivariate adjustment (95% confidence interval 2.87 to 16.5).
| Variable | NIOSH Cases (n = 87) | Active Controls (n = 915) | Univariate Analysis | Multivariate Analysis | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Model I ∗ , † | Model II † , ‡ | ||||||||||
| OR | 95% CI | p | OR | 95% CI | p | OR | 95% CI | p | |||
| Risk factor | |||||||||||
| Age (yrs) | 37.7 ± 6.6 | 35.4 ± 6.1 | 1.06 | 1.03–1.11 | 0.001 | 1.03 | 0.98–1.08 | 0.268 | 1.02 | 0.97–1.07 | 0.451 |
| Men | 85/87 (98) | 886/915 (97) | 0.72 | 0.17–3.06 | 0.655 | — | — | — | — | — | — |
| BMI (kg/m 2 ) | |||||||||||
| <30 | 25/68 (37) | 582/908 (64) | 1.00 | Ref | 1.00 | Ref | 1.00 | Ref | |||
| ≥30 | 43/68 (63) | 326/908 (36) | 3.07 | 1.84–5.12 | <0.001 | 2.20 | 1.27–3.81 | 0.005 | 1.76 | 0.99–3.11 | 0.053 |
| Smoker § | 24/87 (28) | 70/779 (9) | 3.86 | 2.27–6.56 | <0.001 | 3.53 | 1.87–6.65 | <0.001 | 3.50 | 1.76–6.95 | <0.001 |
| Diabetes mellitus || | 4/87 (5) | 18/908 (2) | 2.38 | 0.79–7.21 | 0.124 | 3.26 | 0.93–11.5 | 0.066 | 2.17 | 0.59–7.95 | 0.243 |
| Hypertension ¶ | 41/87 (48) | 179/904 (20) | 3.69 | 2.34–5.81 | <0.001 | 3.43 | 2.01–5.87 | <0.001 | — | — | — |
| Hypertension 2 # | 62/87 (72) | 179/904 (20) | 10.5 | 6.35–17.2 | <0.001 | — | — | — | 11.8 | 6.23–22.3 | <0.001 |
| Dyslipidemia ∗∗ | 46/87 (53) | 366/908 (40) | 1.66 | 1.07–2.58 | 0.024 | 1.47 | 0.86–2.51 | 0.157 | 1.53 | 0.88–2.68 | 0.134 |
| History of CVD | |||||||||||
| CHD, CHD equivalent, or valvular disease †† | 18/87 (21) | 29/786 (4) | 6.81 | 3.60–12.9 | <0.001 | 6.89 | 2.87–16.5 | <0.001 | 5.72 | 2.40–13.6 | <0.001 |
| Irregular rhythm | 2/87 (2) | 45/786 (6) | 0.39 | 0.09–1.63 | 0.195 | 0.13 | 0.02–1.06 | 0.057 | 0.13 | 0.02–1.04 | 0.054 |
| Abnormal findings on ECG or echocardiogram | 6/87 (7) | 62/786 (8) | 0.86 | 0.36–2.06 | 0.744 | 0.50 | 0.16–1.59 | 0.242 | 0.41 | 0.13–1.31 | 0.132 |
| Chest pain or shortness of breath ‡‡ | 7/87 (8) | 9/786 (1) | 7.55 | 2.74–20.8 | <0.001 | 1.92 | 0.46–8.01 | 0.372 | 2.15 | 0.50–9.29 | 0.307 |
∗ Adjusted by age, BMI (dichotomous), smoking, diabetes mellitus, hypertension, and dyslipidemia.
† Analysis restricted to 68 cases and 765 controls with complete information.
‡ Adjusted by age, BMI (dichotomous), smoking, diabetes mellitus, hypertension 2, and dyslipidemia.
§ Subject was smoking within previous 12 months.
|| Cases: evidence of diabetes mellitus in report; controls: blood glucose ≥150 mg/dl, previous diabetes mellitus diagnosis, and/or taking medication.
¶ Systolic blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm Hg, previous hypertension diagnosis, and/or taking medication.
# Included all cases of hypertension defined in previous footnote plus those with findings of LV hypertrophy on autopsy.
∗∗ Evidence of dyslipidemia mentioned (total cholesterol ≥200 mg/dl or low-density lipoprotein ≥160 mg/dl), previous diagnosis of hyperlipidemia, and/or taking medication.
†† CHD, CHD equivalent: previous myocardial infarction, angioplasty, stent placement, or clinical diagnosis of CHD because of abnormal calcium score or exercise tolerance test findings; valvular disease: previous diagnosis of valvular abnormalities or disease or presence of appropriate autopsy findings.
‡‡ Episodes of chest pain or shortness of breath documented but without a CHD diagnosis.
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