Background: Cardiovascular disease (CV) is by over twofold the single greatest cause of morbidity and mortality among active duty Army personnel over the age of 35. It is a problem that strikes at the core of Army Leadership -- the majority of these events occur in senior enlisted and officer personnel. On this basis, the US Army has had a commitment since the origination of the CV Screening Program in the late 1980s, endorsed by the Armed Forces Epidemiologic Board, to identify latent CV disease in the active duty force, including a focus on prevention. A major goal cited for military medicine (Military Health System 2020 Report) is the integration of technology into preventive care.

Electron beam computed tomography (EBCT) for the detection of coronary artery calcium (CAC) is now an established technique that quantifies the extent of calcified atherosclerotic plaques of the coronary arteries and is predictive for subsequent CV events. This technology has been under investigation in the Army since 1998 under a program known as "The Prospective Army Coronary Calcium Project" (PACC Project). This highly successful program, including 2,000 active duty Army men and women, has been a leader among all programs in the development of knowledge on this technology. Participants in the study received a complete CV risk factor screening evaluation and a single EBCT scan. Over the past several years, the PACC Project has been the first to report on two important issues within EBCT scanning for CV risk. The first is ethnic disparity in subclinical atherosclerosis. We found that African Americans are less than half as likely to have coronary artery calcium as a marker of artery disease, despite having more severe heart disease risk factor problems. The second issue is the problem of obesity and metabolic syndrome and its relationship to CAC. This proposal seeks to extend our findings by investigating associations with progression of subclinical atherosclerosis, an established marker of unstable heart disease risk.

Objectives: (1) How common is CAC progression? (2) What CV risk factors are related to CAC progression? Does CAC progress differently in individuals with clustering of coronary risk factors, specifically the metabolic syndrome? (3) Does race influence CAC progression? (4) Continue observations on actuarial relationship between CAC and cardiovascular outcomes in the PACC cohort (enrolled 1998-2003; n = 2,000).

Technical Approach: This will be a prospective cohort study using repeated EBCT scans in PACC participants enrolled between October 1998 and February 2003. Eligible subjects will be up to 200 Caucasian or African American male PACC project participants between the ages of 40 and 55 who had coronary calcium on their first EBCT scan. Volunteers will repeat baseline health surveys and blood work measuring their heart disease risk factors and undergo a second EBCT scan of their heart. The dependent variable will be the change in CAC score, and the main effect variables will be African American race and metabolic syndrome factors. The availability of a complete risk factor assessment (identical to the original PACC data set) will allow for a rich investigation of the dynamic relationships between CAC progression and coronary risk factors in multivariate analysis. Concurrent with this, we will continue to track long-term cardiovascular events in the PACC cohort (originally enrolled between 1998 and 2003, n = 2,000 under a previous grant from the Peer Reviewed Medical Research Program (PRMRP)).

Current Status: The PACC project began in October 1998 and is funded under a previous PRMRP grant. The major objectives of this program (to define the prevalence of CAC among active duty Army personnel, to assess the impact of EBCT results on patient behavior and to establish the relationship between CAC and CV events) have either been completed or are substantially under way. A total of 2,000 participants have been enrolled. Funding for the original Statement of Work continues until 2005. Of the 1,620 male participants, 361 have CAC and form the basis for the current proposal. The project office is currently staffed by two nurses who conduct long-term follow up contacts with participants. Additional funding is needed to support additional personnel for this re-scanning effort.

Preliminary Results: (1) Ethnic disparities in CAC: Valid CV risk assessments in African American personnel using coronary artery computed tomography (coronary CT) require the generalizability of population-based CAC score distributions derived from primarily Caucasian patient populations. We found that CAC was nearly twice as prevalent in Caucasian (19.2%) than in African American participants (10.3%; p = .004). Despite worse risk factor profiles, African Americans were 39% as likely to have any CAC present (multivariate odds ratio 0.39; P = .007). (2) Metabolic Syndrome: Obesity is an emerging substantial problem in the military. Data from PACC show that nearly one in three active duty Army personnel have a body mass index of 30 kg/m2. The early CV toll of obesity is found in insulin resistance (metabolic syndrome). In an analysis of PACC participants, those with metabolic syndrome (8.9%) were more likely to have a positive CAC score, 24.7% (24 of 89), compared to those without, 16.5% (p<0.05).

Anticipated Results and Military Implications: Racial and obesity/metabolic syndrome factors may be strong predictors of atherosclerosis progression. These data will lead to better understanding of the relationship of these variables and future CV risk in military healthcare beneficiaries and potentially optimization of methods of CV risk screening in active duty personnel.