Risk Factors for the Progression of Coronary Artery Calcification in Asymptomatic Subjects Results From the Multi-Ethnic Study of Atherosclerosis (MESA) Epidemiology

Background —The Multi-Ethnic Study of Atherosclerosis (MESA) provides an opportunity to study the association of traditional cardiovascular risk factors with the incidence and progression of coronary artery calcium (CAC) in a large community-based cohort with no evidence of clinical cardiovascular disease. Methods and Results —Follow-up CAC measurements were available for 5756 participants with an average of 2.4 years between scans. The incidence of newly detectable CAC averaged 6.6% per year. Incidence increased steadily across age, ranging from (cid:1) 5% annually in those (cid:1) 50 years of age to (cid:2) 12% in those (cid:2) 80 years of age. Median annual change in CAC for those with existing calcification at baseline was 14 Agatston units for women and 21 Agatston units for men. Most traditional cardiovascular risk factors were associated with both the risk of developing new incident coronary calcium and increases in existing calcification. These included age, male gender, white race/ethnicity, hypertension, body mass index, diabetes mellitus, glucose, and family history of heart attack. Factors also existed that were related only to incident CAC risk, such as low- and high-density lipoprotein cholesterol and creatinine. Diabetes mellitus had the strongest association with CAC progression for blacks and the weakest for Hispanics, with intermediate associations for whites and Chinese. thickness for MDCT scanners. The methodology for acquisition and interpretation of the scans has been reported previously. 21 The results of the 2 scans were averaged to provide a more accurate point estimate of the amount of calcium present. The amount of calcium was quantified with the Agatston scoring method. 22 Calcium scores were adjusted with a standard calcium phantom that was scanned along with the participant. 23 The phantom contained 4 bars of known calcium density and provided a way to calibrate the x-ray attenuation level between measurements conducted on different machines. This was important because scanners were changed between baseline and follow-up at 3 of the 6 sites. Any detectable calcium was defined as a CAC score (cid:2) 0; a minimum focus of calcification was based on at least 4 contiguous voxels, which resulted in identification of calcium of 1.15 mm 3 for the MDCT scanners and 1.38 mm 3 for the EBCT scanners. 21 The nominal section thickness was 3.0 mm for EBCT scanners and 2.5 mm for MDCT scanners. Interobserver agreement and intraob- server agreement were found to be very high ( (cid:1) (cid:3) 0.93 and 0.90, respectively). Follow-up CAC measurements were performed on half the cohort (randomly selected) at a second examination (Sep-tember 2002 through January 2004) and the other half of the cohort at a third examination (March 2004 through July 2005) at an average of 1.6 and 3.2 years after the participant’s first examination, respectively. As for the baseline examination, the results from 2 consecutive scans were averaged. A full characterization of the distribution of CAC at baseline by age, gender, and race has been published previously. 24