High-hazard occupations can be both physically demanding and psychologically taxing. Several retrospective studies have shown that cardiovascular events, in particular, those related to coronary artery disease (CAD), account for 45% of the on-duty deaths of firefighters and 22% of the on-duty deaths of police officers.1–3 Nevertheless, it is not clear which work-related factors may contribute to this high incidence of CAD-associated mortality among individuals employed in high-risk occupations or if work-related factors play a role in this heightened risk at all.
Among firefighters, at least, the question of whether CAD-related deaths are precipitated by their work or by specific duties has, to some degree, been answered. A recent study showed that firefighters engaged in certain emergency duties had a risk of cardiovascular death that was markedly higher than the risk associated with performing nonemergency duties.4 Proposed work-related factors that may contribute to the increased CAD-associated mortality in firefighters include extreme physical exertion, exposure to chemical and fine particulate matter, thermal and emotional stress, and unhealthy lifestyles, including inadequate regular exercise and a high prevalence of tobacco use.5–8
Data regarding the prevalence of CAD-related death in police officers are more limited. The aim of this study was to investigate the prevalence of CAD among active New York City police officers, as assessed by coronary artery calcium (CAC) scoring. The CAC score has been shown to correlate with the extent and severity of coronary artery atherosclerosis.9–12 In addition, CAC has been shown to be predictive of future cardiac events.13–17 The prevalence of traditional cardiovascular risk factors among members of this high-risk occupation population was also evaluated. A secondary aim was to evaluate a subset of officers who had exposure to World Trade Center (WTC) dust early after the September 11 attack and to ascertain if there is evidence of an increased incidence of CAD in this cohort.
The study population included 2064 police officers who underwent CAC scoring using electron beam computed tomography (EBCT) at a single diagnostic center as part of a voluntary health screening program for the New York City Police Department (NYPD). The health screening program was arranged by agreement between the union representing the officers and the diagnostic center, which is affiliated with Beth Israel Medical Center. A subset of officers were early responders to the WTC terrorist attack on September 11; data for these officers were included in the evaluation of the group as a whole and were evaluated separately, as well. The EBCT testing was conducted on our population over 2-year period. Clinical data were obtained using a questionnaire to ascertain the presence or absence of traditional cardiac risk factors and symptoms referable to ischemic heart disease. The questionnaire was formulated to ascertain subjects' basic demographic data, existing medical conditions, symptoms, and risk factors including smoking status. This project was approved by the Institutional Review Board of the Medical Center and informed consent was obtained from each subject.
Scanning and Analysis
All subjects underwent heart scans with an Imatron C-100 EBCT scanner (Imatron Corp., South San Francisco, CA). Electrocardiographically triggered imaging, synchronized to 80% of the R-R interval, was performed with a 100-millisecond scanning time. Forty contiguous 3-mm thick slices were obtained, beginning at the carina and proceeding caudally to below the cardiac apex, during a single breath-hold. Data were reconstructed using a 26-cm field of view. By using the method of Agatston et al18 CAC scores were determined based on plaque area and x-ray attenuation; a calcified plaque was deemed to be present if two or more adjacent pixels with a signal density >130 Hounsfield units were evident. A total CAC score was calculated by summing the scores for all calcified plaques found along the length of the individual coronary arteries. In accordance with current general practice guidelines, subjects with a CAC score >100 were considered to be at moderate risk for adverse cardiovascular events, whereas subjects with a CAC score >400 and those with a score placing them at or above the 75th percentile for their age and sex were considered to be at high risk.19–23
Data were analyzed using the SAS system for data analysis. Univariate analysis was conducted to determine factors associated with calcium scores. Because calcium scores have a skewed distribution, the nonparametric Wilcoxon scores rank sum test was used. Logistic regression analysis was conducted to determine multivariate predictors of calcium scores greater than 100. P-values <0.05 were considered statistically significant. The distribution of CAC scores for study participants was compared with an age- and gender-matched general population database developed by Hoff et al24 (the Kondos database).
A total of 2064 police officers underwent EBCT screening for quantification of CAC as a marker of CAD. The mean age of the subjects was 42 ± 6 years. The vast majority of officers in our cohort were younger than 60 years; only 25 subjects (1.2%) were older than 60 years at the time of the study. Male officers comprised 86% of the study population. Tables 1 and 2 show the distribution of CAC scores for male and female officers when compared with the age-based cohort in the general population as represented by the Kondos database.24 Only 15% of men and 15% of women in this cohort had total CAC scores at or above the 75th percentile. In our NYPD population, 77% of men younger than 65 years and 80% of women younger than 60 years had scores below the 50th percentile for their respective age groups and sex. Full 74% of men and 80% of women in this study had an absolute CAC score of 0. The comparison between the distribution of CAC scores in our NYPD population when compared with the general population (the Kondos database) is illustrated further in Fig. 1.
Table 3 shows the prevalence of some of the self-reported traditional risk factors for CAD in this population. As can be seen, 6% of these police officers had a self-reported total cholesterol level of >200 mg/dL, 9% were active smokers, 11% suffered from hypertension, and 3% suffered from diabetes mellitus. In this NYPD population, smoking, both active and as a former habit, is more common in female officers (P < 0.05). Nevertheless, the use of cholesterol-lowering medication is more common in male officers (P < 0.05). As predicted, increasing age is strongly associated with increasing prevalence of hypertension, diabetes, and the use of cholesterol-lowering medications. Our multivariate analysis revealed that increasing age, diabetes, and dyslipidemia (extrapolated from the use of cholesterol-lowering medications) are independent predictors of having higher total CAC scores.
Figure 2 shows data for a subset of 75 officers in our study population who had exposure to WTC dust early after the September 11 terrorist attack. The mean age of this cohort was 41 ± 6 years and 88% were men. As in the general and our NYPD population, the CAC scores of this subgroup of NYPD officers are higher in older subjects when compared with their younger cohort. There was no evidence of increased CAC in this WTC subgroup compared with their age-matched peers.
The results of this study failed to show any evidence of increased prevalence of CAD as evidenced by CAC scores among New York City police officers when compared with the general population. This finding is in contrast to findings from studies that were done with firefighters.1–4 To our knowledge, this is the first study that investigates the prevalence of coronary atherosclerosis disease by using CAC scores as quantified by EBCT as surrogate marker in police officers.
As suggested by previous observation, high risk occupations such as firefighting or military force may carry an increased risk of death from coronary heart disease.1–8 The characteristics of the work performed by firefighters are shared by police officers: heavy physical exertion, emergency responses, psychologically stressful and dangerous duties among others.3–8 Our hypothesis was that the increased risks of mortality and morbidity related to CAD observed in firefighters would also be seen in police officers as well. However, as evidenced by our findings, we were unable to prove this.
This study confirmed the findings of a smaller longitudinal study at the Boston Veteran Administration outpatient clinic.25 In the study by Sparrow et al,25 220 male police officers when compared with their nonpolice officer cohort showed no statistically significant differences in the crude incidence rates of coronary heart disease at 10-year follow-up. The only other available data akin to our population was a study of 232 male retirees from the Iowa Department of Public Safety.26 Franke et al26 found a statistically significant increase in the incidence of self-reported cardiovascular disease when compared with male Iowans of similar age. However, both of the above studies were significantly smaller in sample size compared to this study. Furthermore, this study is novel in the utilization of EBCT to demonstrate the incidence of coronary atherosclerosis disease.
There are several potential explanations for our negative result. The majority of subjects in our study were relatively young. Nearly 75% of our subjects were younger than 40 years. Therefore, considering the number of police officers older than 60 years was relatively few, the result of our study may underestimate the risk of CAD in older officers. Second, confounding factors such as the length of time served as police officer, perceived stress, the presence of traditional CAD risk factors, and the presence of cardiovascular symptoms were not shown to correlate with CAC scores in our study. Finally, by using CAC scores as surrogate markers for subclinical CAD, we may underestimate the true risks of mortality from CAD in this cohort. It has been postulated that some triggering phenomena may exert a single, transient effect of pathophysiologic process of myocardial infarction, such as a surge of adrenergic activity, whereas others exert a more varied and pervasive effect, amplifying risk at multiple points and over a longer period.27,28 These “triggers” that qualitatively alter the otherwise stable phase of coronary atherosclerosis and initiate a cascade of events that culminates in acute myocardial infarction may not be possible to be measured with surrogate markers such as CAC scores. However, CAC has been shown to have a strong correlation with future cardiac events.13–17 Taylor et al17 in Prospective Army Coronary Calcium project showed that in young, asymptomatic men, the presence of coronary artery calcification provides substantial, cost-effective, independent prognostic value in predicting cardiovascular events that is incremental to traditional coronary risk factors.
Multiple observations have been made that exposure to inorganic dust and fumes may increase the risk for ischemic heart disease via mechanisms that likely include systemic inflammation, accelerated atherosclerosis, and altered cardiac autonomic function.29–31 The subset of police officers in our study population who had early exposure to WTC during recovery process from September 11 terrorist attack did not manifest increased CAC scores. Even though this subgroup of our population is small, our study is the only one who looked into prevalence of premature subclinical CAD in this group of police officers. The reason for the negative finding may be the timing of the screening. The progression of developing subclinical CAD in this group may take more than 5 years to become evident. As it is, this finding should be seen as a call to follow these WTC early responders more closely and perform surveillance for the development of premature subclinical CAD in addition to the pulmonary screening that has been done in this population.32,33
Limitations to our study includes the nature of the assessment of the traditional cardiovascular risk factors in our population, which was based purely on self-report. Hence, these risk factors may be underestimated as not all subjects would know their cholesterol levels or their blood pressure measurements unless they have been clinically diagnosed and treated in the past. Another limitation of this study is the potential for referral bias as our subjects were self-referred to our designated diagnostic center to undergo EBCT for CAC scoring. As mentioned previously, these police officers underwent CAC scoring using EBCT as part of a voluntary health screening program for the NYPD. Finally, our population consists mostly of younger male cohort. As it is, only limited information can be inferred toward females and older cohort.
Despite the limitations above, this study is the first study that investigates the prevalence of coronary atherosclerosis disease by using CAC scores as quantified by EBCT in police officers and also in the subset of police officers who had early exposure to WTC dust.
New York City police officers do not have an increased prevalence of CAD compared with the general population based on coronary calcium score. Early exposure to WTC dust does not appear to increase this risk at 5 years. These findings need to be confirmed with a routine follow-up.
Drs Wanahita, See, and Bergmann had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Wanahita, See, Giedd, and Bergmann were involved in study concept and design. Drs Wanahita, See, Somekh, Giedd, and Bergmann were involved in acquisition of data. Drs Wanahita, Friedmann, See, Somekh, Giedd, and Bergmann were involved in analysis and interpretation of data. Drs Wanahita, See, Giedd, and Bergmann were involved in drafting of the manuscript. Drs Wanahita, See, Friedmann, Somekh, Giedd, and Bergmann were involved in critical revision of the manuscript for important intellectual content. Drs Wanahita, Friedmann, and See were involved in statistical analysis. Drs Giedd and Bergmann were involved in study supervision. Albert Barrette and Steven Nelson were responsible for coordination and oversight of the scanning. The authors also wish to acknowledge the dedication and assistance of the EBCT technologists.
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