Imaging Atherosclerosis by Carotid Intima-media Thickness in vivo: How to, Where and in Whom ?

Abstract

Carotid intima-media thickness (CIMT) can be reliably determined in vivo by carotidian ultrasound and is an accessible and reliable method to assess subclinical atherosclerosis. Available epidemiological data showed that CIMT is significantly correlated with future cardiovascular events. However it has limited value to help risk stratification on top of standard risk-derived functions such as Framingham risk score. It is particularly useful in individuals classified as being at intermediate or high risk by the presence of multiple conventional risk factors.CIMT HAS A CLASS IIA (LOE: B) reccommendation for cardiovascular risk assessment according to the practice guidelines published in 2010, emphasizing the presence of high risk if the common carotid artery intima-media thickness is above the 75(th) percentile. There is no indication to measure IMT in patients with full-blown atherosclerotic carotid disease, although carotidian ultrasound still remains a very useful tool to assess the severity of disease even in these subjects.Progression of CIMT (also associated with increasing age) can be delayed by some drugs (statins, colestipol and niacin) and by risk factors modification. However, there is no consistent data demonstrating a link between progression of CIMT and coronary and cerebral events. Subsequently, studies using CIMT progression as primary outcome to indicate the influence of a certain therapy on cardiovascular risk are inherently misleading as suggested in the recently published ACC/AHA Guidelines.

Keywords: accelerated atherosclerosis; inflammation; metabolic syndrome; rheumatoid arthritis.

Figure 1. Two-dimensional longitudinal image of common carotid artery (CCA) showing double contour of anterior wall (AW) and posterior wall (PW) ("the double line" sign). The carotid intima- media thickness (CIMT) represents the combined thickness of the hypo-echoic space plus the hyper- echoic line situated towards the interior of the vessel. The measurement could be done at the level of anterior wall (near wall) or at the level of the posterior wall (far wall). See text

Figure 2. 2D aspect of the common carotid artery bifurcation: internal carotid artery (ICA) and external carotid artery (ECA)

Figure 3. Example measurement of far wall common carotid artery (CCA) intima-media thickness (CIMT). The arrows from top to bottom show: the near wall, lumen and the far wall. The white arrowhead marks media – adventitia boundary. Measurement of CIMT involves tracing the blood-intima and media-adventitia interfaces of the far wall using a leading edge–to–leading edge technique along a 1 cm region. Mean CIMT should be reported. Simple point by point measurement are not accepted

Figure 4. Carotid ultrasound imaging pitfalls and potential solutions. 4A. Improper allignement of transducer with the vessel leads to lost of double lines sign at the level of common carotid artery. 4B. Image not horizontal. 4C. Correct alllignement of the transducer along with the common carotid artery segment.