Cardiovascular disease (CVD) accounts for 45% of deaths in on-duty firefighters, in contrast to 15% of all deaths occurring on conventional jobs. Therefore, with the goal of developing a tailored prevention program, we assessed CVD risk in a cohort of 50 firefighters using imaging and traditional risk factors. Participants were aged ≥40 years without a history of CVD or diabetes. CVD risk was assessed by way of history, physical examination, blood tests, risk scores, coronary artery calcium (CAC), and carotid intima-media thickness (cIMT). Median age was 46 years; 90% of subjects were men, 92% were white, and 30% were former smokers. Only 4% of subjects were hypertensive but 48% were prehypertensive. Only 14% of subjects had a normal body mass index; 38% were overweight, 48% were obese, and 46% had a high waist circumference. Based on fasting glucose ≥100 mg/dl or hemoglobin A 1c ≥5.6%, 50% of subjects had prediabetes and 2% had diabetes. Median total cholesterol was 196 mg/dl; median high-sensitivity C-reactive protein was 1.0 mg/L. CAC was detected in 22% of subjects and carotid plaque was detected in 36%. Using standard reference databases, 54% of subjects had cIMT greater than the seventy-fifth percentile; 66% had carotid plaque and/or cIMT greater than the seventy-fifth percentile. Atherogenic lipoprotein markers and risk scores did not differ between firefighters who had subclinical atherosclerosis and those who did not. Traditional CVD risk assessment does not adequately identify at-risk firefighters. In contrast, CAC and cIMT were useful for identifying increased risk and implementing primary prevention. In conclusion, early detection and integration of imaging with traditional risk assessment will be important in preventing premature death and disability among firefighters.
Cardiovascular events account for 45% of deaths in on-duty firefighters, in contrast to 15% of all deaths occurring on conventional jobs. Myocardial infarction is the number one killer of firefighters, and these events occur almost exclusively in susceptible firefighters with underlying cardiovascular disease (CVD). For every fatal on-duty CVD event, there are an estimated 17 nonfatal on-duty CVD events. The aim of our study is to improve the primary prevention of CVD in firefighters. We hypothesized that “risk assessment” and “risk reduction” will ultimately prevent premature death and disability due to CVD and enhance cardiovascular health among operational firefighters without known CVD and/or diabetes. Here we present the baseline study findings, which focused on CVD risk assessment in asymptomatic firefighters through traditional means (including medical history, physical examination, CVD risk factors, blood tests, and calculation of risk scores) and through imaging of coronary artery calcium (CAC) and carotid intima-media thickness (cIMT).
Methods
All participants met the following eligibility criteria: (1) aged ≥40 years, (2) currently serving as an operational firefighter, and (3) having a primary care provider. Exclusion criteria included (1) known CVD, including coronary artery disease, cerebrovascular disease, peripheral artery disease, abdominal aortic aneurysm, or any previous CVD event or (2) diabetes. Recruitment flyers were displayed at local firehouses. The first 50 consecutive eligible firefighters were enrolled from January 2012 to April 2012. Informed consent was obtained from all participants. The Johns Hopkins Medicine Institutional Review Board approved the study.
The initial visit included consent, fasting blood tests, CAC, and cIMT. Within 2 to 3 weeks, there was another 1-hour visit that consisted of a detailed medical history, physical examination, review of blood and imaging test results, evaluation of risk factors, and calculation of risk scores.
Risk factors assessed included blood pressure, weight, body mass index (BMI), waist circumference, family history, and smoking history. Manual systolic and diastolic blood pressures were measured in a seated position in the left arm after a 5-minute rest period. Height, weight, and BMI were measured using a Seca 703 (Seca North America, Hanover, Maryland) electronic column scale. Waist circumference was measured at the bilateral upper iliac crests at end-expiration.
Firefighters were educated about CVD risk factors and a healthy diet, aerobic exercise, maintenance of a normal weight, and smoking cessation based on the ABC approach. CVD risk was summarized, and an individualized, lifestyle-focused, risk reduction plan was developed for each participant, including written recommendations for both lifestyle and medication. A letter with recommendations and test results was sent to the participant and the primary care provider.
All participants underwent a CAC scan. Electrocardiogram-gated noncontrast images of the heart were obtained for calcium scoring. Quantification of CAC was by the Agatston method. CAC was expressed as the absolute score as well as relative population percentile by age, gender, and ethnicity based on reference data from the Multi-Ethnic Study of Atherosclerosis.
All participants underwent a carotid artery ultrasound to measure cIMT. The scan was performed by a single registered vascular technologist using a GE LOGIQ e ultrasound system (GE Healthcare, Milwaukee, Wisconsin). cIMT was measured at end-diastole in the far wall of the bilateral distal common carotid arteries according to a standard protocol. Carotid plaque was defined as focal intima-media thickening 50% greater than the surrounding wall or a focal region of cIMT >1.5 mm. cIMT was measured using M’Ath (Intelligence in Medical Technologies, France) edge-detection software. Atherosclerosis Risk in Communities (ARIC) was used as the main reference database to determine the cIMT percentile based on age, gender, and ethnicity. The percentile was extrapolated from ARIC if the subject was aged <45 years. ARIC was used for the Hispanic participant. For the Asian participant, the Atherosclerosis RIsk of Rural Areas iN Korea General Population study was used. Carotid ultrasound interpretation and cIMT measurements were performed by a single experienced reading physician. The mean and maximum cIMT were reported for each side, along with the presence or absence of plaque. Each side was categorized as less than the twenty-fifth, twenty-fifth to seventy-fifth, or greater than the seventy-fifth percentile.
Venous blood was drawn after fasting for ≥8 hours. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and subclasses, lipoprotein(a) cholesterol, low-density lipoprotein cholesterol (LDL-C), intermediate-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol and subclasses, non-HDL-C, and remnant lipoprotein cholesterol were measured using the Vertical Autoprofile method (Atherotech Diagnostics Lab, Birmingham, Alabama). Triglycerides, apolipoprotein B (apo B), apolipoprotein A-I, insulin, hemoglobin A 1c , and high-sensitivity C-reactive protein were measured on the Abbott Architect c8000. Whole particle molar lipoprotein(a) concentration was measured using the Denka-Seiken assay. homeostatic model assessment-insulin resistance (HOMA-IR) and homeostatic model assessment-beta cell activity (HOMA-B) were calculated from fasting glucose and insulin levels.
Three risk scores were initially calculated to stratify participants into low (<10%), intermediate (10% to 20%), and high (>20%) 10-year risk: the Adult Treatment Panel III Framingham Risk Score (FRS), the Reynolds Risk Score, and the CVD-modified FRS. Post hoc analysis included the new Pooled Cohort Equations for atherosclerotic cardiovascular disease (ASCVD) risk prediction from the American College of Cardiology/American Heart Association. This tool can be used to identify subjects without clinical ASCVD or diabetes, who are aged 40 to 75 years with LDL-C 70 to 189 mg/dl and have an estimated 10-year ASCVD risk of ≥7.5%, who would benefit from statin therapy.
Baseline demographic and clinical characteristics are summarized using frequencies and percentages for categorical data and medians and interquartile ranges for continuous data. For some analyses, participants were classified as having CVD if they had any of the following: (1) any coronary artery calcification, (2) any carotid plaque, or (3) cIMT greater than the seventy-fifth percentile. Group comparisons were made using Fisher’s exact tests or Wilcoxon rank sum tests. The distributions of continuous outcome measures were assessed for normality and, if necessary, transformations were performed. The presence or absence of plaque was evaluated as a dichotomous outcome. The mean of the mean cIMT and the mean of the maximum cIMT were analyzed. For comparison of metabolic conditions across outcomes, the Cochran-Armitage test for trend was used because of the ordinal data. Statistical analyses were performed using SAS, version 9.3 (SAS Institute Inc., Cary, North Carolina). All p values are 2-sided and p <0.05 was considered statistically significant in all analyses.
Results
Demographic and clinical characteristics of the 50 participants overall and stratified by CVD status are listed in Table 1 . Sixty-four percent were from Baltimore County and 36% were from Howard County, Maryland. Age ranged from 40 to 58 years. At baseline, 24% of subjects were taking daily aspirin, 22% were taking a statin, 16% were taking an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker, and 4% were taking a β blocker. No statistically significant differences were observed between the 2 groups for age, gender, race, smoking status, blood pressure, family history, heart age, or any of the risk scores.
| Characteristic | All (n = 50) | CVD | p Value | |
|---|---|---|---|---|
| Yes (n = 36) | No (n = 14) | |||
| Age (yrs) | 47 (43–50) | 46 (43–50) | 48 (45–51) | 0.31 |
| Men | 45 (90) | 33 (92) | 12 (86) | 0.61 |
| Women | 5 (10) | 3 (8) | 2 (14) | |
| White | 46 (92) | 32 (89) | 14 (100) | |
| Black | 2 (4) | 2 (6) | 0 | 0.99 |
| Hispanic | 1 (2) | 1 (3) | 0 | |
| Asian | 1 (2) | 1 (3) | 0 | |
| Never smoker | 35 (70) | 24 (67) | 11 (79) | |
| Former smoker † | 15 (30) | 12 (33) | 3 (21) | 0.51 |
| Current smoker | 0 | 0 | ||
| Systolic BP (mm Hg) | 117 (110–124) | 118 (111–123) | 115 (106–126) | 0.43 |
| Diastolic BP (mm Hg) | 75 (68–82) | 76 (68–83) | 74 (70–78) | 0.76 |
| Family history of premature CHD ‡ | 16 (32) | 9 (25) | 7 (50) | 0.11 |
| FRS (% 10-year risk) § | 3 (2–4) | 3 (2–4) | 3 (2–4) | 0.72 |
| Reynolds Risk Score (% 10-year risk) ‖ | 2 (2–4) | 2 (2–4) | 2.5 (2–4) | 0.87 |
| CVD-modified FRS (% 10-year risk) ¶ | 6 (5–8) | 6 (4–8) | 8 (5–8) | 0.61 |
| Heart age (yrs) | 46 (42–51) | 44 (42–51) | 50 (42–51) | 0.65 |
| ASCVD risk score | 2.5 (1.7–3.7) | 2.4 (1.6–3.6) | 2.6 (2.3–3.9) | 0.63 |
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