Associations of common carotid intima-media thickness with coronary heart disease risk factors and events vary with distance from the carotid bulb.

BACKGROUND: Common carotid artery (CCA) intima-media thickness (IMT) can be measured using ultrasound near to or below the carotid bulb. This might affect associations of IMT with coronary heart disease (CHD) risk factors and events.

METHODS: IMT measurements were performed near and below the divergence of the CCA bulb in 279 white individuals aged 45 to 54 years free of CHD at baseline and a subset of the Multi-Ethnic Study of Atherosclerosis, a cohort composed of whites, blacks, Chinese, and Hispanic subjects. Participants were followed for an average of 8.2 years. Far wall mean of the maximum IMT (MMaxIMT) and mean of the mean IMT of the right and left CCAs were averaged. Framingham risk factors were used in multivariate linear regression models. Parsimonious Cox proportional regression models included first-time CHD as outcome.

RESULTS: Mean of the mean IMT below the bulb was smaller than near the bulb (0.51 ± 0.078 vs 0.56 ± 0.088 mm, P < .001) and had similar associations with risk factors (model R(2) = 0.215 vs 0.186). MMaxIMT below the bulb was associated with risk factors (model R(2) = 0.211), but MMaxIMT near to the bulb was not (R(2) = 0.025). Mean of the mean IMT and MMaxIMT below the bulb were associated with CHD events (hazard ratios, 1.67 [P = .047] and 1.72 [P = .037], respectively) but not when measured near the bulb.

CONCLUSIONS: CCA IMT measurements made below the bulb are smaller but have more consistent associations with CHD risk factors and outcomes compared with IMT measured near the bulb.