Noninvasive measurement of carotid extra-media thickness: associations with cardiovascular risk factors and intima-media thickness.

OBJECTIVES: We sought to develop a noninvasive technique to quantify the thickness of a segment of the carotid artery wall that incorporates the adventitia and to identify whether differences in this measure are associated with cardiovascular risk factors.

BACKGROUND: There is increasing evidence that the arterial adventitia undergoes extensive structural alteration, including thickening, in response to arterial injury. However, there is currently no widely accepted noninvasive technique for studying the thickness of the arterial adventitia in humans.

METHODS: The carotid artery and jugular vein were imaged simultaneously in longitudinal section with the use of high-resolution ultrasound. The distance from the jugular intima-lumen interface to the carotid media-adventitia margin was denominated as the carotid extra-media thickness (EMT). This measure includes the arterial adventitia but not the arterial intima or media. We measured the carotid EMT and intima-media thickness (IMT) in 175 subjects, including 54 with diabetes, 43 with dyslipidemia, 26 with other cardiovascular risk factors, and 52 healthy control subjects.

RESULTS: When compared with control subjects, the EMT was increased in both the diabetes (p < 0.0001) and dyslipidemia (p = 0.04) groups. Multivariate linear regression analyses revealed that diabetes, high-density lipoprotein cholesterol (inverse association), and systolic blood pressure (J-shaped association) were the factors most strongly associated with EMT. These associations appear to be independent of carotid IMT.

CONCLUSIONS: Carotid EMT can be assessed by ultrasonography. It is physically distinct from IMT and provides additional information concerning the vascular changes associated with cardiovascular risk factors. As such, the measurement of EMT, in addition to IMT, may provide a more complete indication of the structural modification of the vasculature associated with cardiovascular risk factors than that obtained by the measurement of carotid IMT alone.