Assessment and relevance of carotid intima-media thickness (C-IMT) in primary and secondary cardiovascular prevention

Abstract

Interventions aimed to prevent cardiovascular diseases (CVD) are more effective if administered to subjects carefully selected according to their CVD risk. Usually, this risk is evaluated on the basis of the presence and severity of conventional vascular risk factors (VRFs); however, atherosclerosis, the main pathologic substrate of CVD, is not directly revealed by VRFs. The measurement of the arterial wall, using imaging techniques, has increased the early identification of individuals prone to develop atherosclerosis and to quantify its changes over time. B-mode ultrasound is a technique which allows a non-invasive assessment of the arterial wall of peripheral arteries (e.g. extracranial carotid arteries), and provides measures of the intima-media thickness complex (C-IMT) and additional data on the occurrence, localization and morphology of plaques. Being an independent predictor of vascular events, C-IMT has been considered as a tool to optimize the estimation of CVD risk but this application is still a matter of debate. Though the technique is innocuous, relatively inexpensive and repeatable, its use in the clinical practice is limited by the lack of standardized protocols and clear guidelines. This review outlines the rationale for the potential use of C-IMT in the stratification of cardio- and cerebro-vascular risk and discusses several topics related to the measurement of this variable, which are still controversial among experts of the field.

Fig. (1)

Typical ultrasound image of an extracranial carotid artery where the common carotid artery (CC), the bifurcation (Bif), the internal carotid artery (ICA) and the external carotid artery (ECA) are easily recognizable. The intima-media thickness (C-IMT) is delimited by black and white arrows.

Fig. (2)

Ultrasonographic image of a common carotid which shows the importance of evaluating the artery in its entire length. Note the chance of underestimation of atherosclerosis burden if only the first distal centimeter of the common carotid artery is considered (as actually is in several clinical and epidemiological studies).

Fig. (3)

Ultrasound image of an extracranial carotid with an atherosclerotic lesion in the near wall of bifurcation. If only C-IMT of the far wall of the common carotid artery is considered, this patient would be classified as normal.

Fig. (4)

Threshold values ​​above which C-IMT_max has to be considered as abnormally high. These values ​​correspond to the 60^th percentile for men and to the 80^th percentile for women of the C-IMT_max distributions obtained in different age decades in a group of about 2000 Italian dyslipidemic patients [35].