Increased common carotid intima-media thickness. Adaptive response or a reflection of atherosclerosis? Findings from the Rotterdam Study.

BACKGROUND AND
PURPOSE: Carotid intima-media thickness (IMT) measurements are used widely to study atherosclerosis. Some have suggested that an increased IMT reflects a nonatherosclerotic adaptive response to changes in shear stress and tensile stress. This stems from the hypothesis that changes in shear stress and subsequently in lumen diameter are followed by changes in IMT to keep tensile stress constant. We studied the relation of common carotid IMT to common carotid end-diastolic lumen diameter and tensile stress, as approximated by mean arterial pressure (lumen diameter/IMT)].
METHODS: A cross-sectional analysis was performed with data obtained from the first 1715 participants in the Rotterdam Study, a population-based cohort study among 7983 subjects aged 55 years and over who underwent ultrasonographic examination of the carotid arteries. End-diastolic lumen diameter and IMT of the common carotid arteries were evaluated and quantified.
RESULTS: With increasing IMT, inner and outer lumen diameters increased gradually, and beyond an IMT of 1.10 mm, the inner lumen diameter decreased. Tensile stress increased with increasing lumen diameter instead of being constant. The lumen-to-IMT ratio was constant across levels of mean arterial pressure.
CONCLUSIONS: Our findings are compatible with the view that at lower degrees of IMT, the thickening appears to reflect an equilibrium state in which the effects of pressure and flow on the arteries are in balance, given a characteristic relation between shear stress and local transmural pressure. Beyond a certain level, IMT more likely may represent atherosclerosis. Regardless of whether common carotid IMT reflects local atherosclerosis, it may still serve as a graded marker for cardiovascular risk.