The Multi-Ethnic Study of Atherosclerosis (MESA) was initiated in July 2000 to investigate the prevalence, correlates, and progression of subclinical cardiovascular disease in individuals without known cardiovascular disease.6
This prospective cohort study includes 6,814 women and men ages 45–84 years old recruited from six U.S. communities (Baltimore, MD; Chicago, IL; Forsyth County, NC; Los Angeles County, CA; Northern Manhattan, NY; and St. Paul, MN). The cohort is comprised of 38% Caucasian (N
=2,624), 28% African-American (N
=1,895), 22% Hispanic (N
=1,492) and 12% Chinese (N
Medical history, anthropometric measurements, and laboratory data for the present study were taken from the first examination of the MESA cohort (July 2000 to August 2002). Information about age, gender, race/ethnicity, and medical history were obtained by questionnaires. Current smoking was defined as having smoked a cigarette in the last 30 days. Former smoking was defined as previous smoking who was not met the criteria of current smoking. Diabetes mellitus was defined as a fasting glucose > 126 mg/dL or use of hypoglycemic medications.
Resting blood pressure was measured three times in the seated position using a Dinamap model Pro 100 automated oscillometric sphygmomanometer (Critikon, Tampa, FL) and the average of the second and third readings was recorded. Hypertension was defined as a systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, or use of prescribed medications for hypertension. Body mass index (BMI) was calculated from the equation weight (kg)/height (m2).
Total and high-density lipoprotein (HDL) cholesterol were measured from blood samples obtained after a 12 hour fast. Low-density lipoprotein (LDL) cholesterol was calculated with the Friedewald equation. C-reactive protein (CRP) was measured usuing the BNII nephelometer (N High Sensitity CRP; Dade Behring Inc., Deerfield, IL) at the Laboratory for Clinical Biochemistry Research (University of Vermont, Burlington, VT). Analytical intra-assay CVs ranged from 2.3 to 4.4% and inter-assay CVs ranged from 2.1 to 5.7%.
After signing informed consent, all participants underwent two CT scans at the same time for evaluation of coronary artery calcium and MAC. This study was approved by the Institutional Review Board at all participating centers. Three sites used an Imatron C-150XL CT scanner (GE-Imatron, San Francisco, CA) and three sites used a multidetector CT scanner (four slice). This method has been reported previously8
. Image slices were obtained in the supine position with no couch angulation. A minimum of 35 contiguous images with a 2.5 or 3mm slice thickness were obtained starting above the left main coronary artery to the bottom of both ventricles. Each scan was obtained in a single breath hold. Section thickness of 3 mm, field of view of 35 cm, and matrix of 512 × 512 were used to reconstruct raw image data. The nominal section thickness was 3.0 mm for electron beam CT and 2.5 mm for four-detector row CT. Spatial resolution can be described by the smallest volume element, or voxel, for the protocol for each system: 1.15 mm3
for four-detector row CT (0.68 mm × 0.68 mm × 3.00 mm). MAC was defined by presence of calcium on mitral valve by CT scan at the enrollment.
Demographics and CVD risk factors were compared between those with and without MAC. Differences in characteristics were compared using ANOVA for continuous variables and χ2 tests for categorical variables. We used logistic regression models to assess the relationship between each risk factor and the presence of calcium and adjusted for all other risk factors in the model. The odds ratios we estimate approximate relative risks because our endpoint is quite rare (prevalence of 9%). The following covariates were used in the multivariable adjustment: age, gender, body mass index, HDL, LDL, lipid lowering medications, smoking status, family history of heart attack, hypertension, and diabetes mellitus.
Among those with detectable MAC, the relationship between risk factors and the quantity of calcification [(ln)Agatston score] was assessed with multi-variable linear regression. The relationship was expressed as a percent difference in calcification for a given increment in the risk factor. The ‘Relative Difference’ is the anti-log of the regression coefficient using log-transformed calcium score as the dependent variable in each multiple linear regression analysis. Statistical analyses were performed with SPSS 13.0.1 software for Windows (SPSS Inc, Chicago, Ill) and STATA 10.0 for Windows (Stata Corp, College Station, Tx).