CAROTID INTIMA-MEDIA THICKNESS TEST
Ultrasonographic measurement of intima media thickness has been reported as a procedure to detect the early stages of atherosclerosis.
Is used to determine the extent of plaque buildup in the walls of the arteries supplying blood to the head: the intima and media, the two inner layers of the carotid artery.
If a CIMT shows increased thickness in the inner layers of the carotid artery, you may be at risk for cardiovascular disease, it is used assess the health of the carotid arteries and the risk of cardiovascular disease-related events like heart attacks and strokes, even in asymptomatic patients.
RISK FACTORS FOR CARDIOVASCULAR DISEASE:
high blood pressure
an inactive lifestyle
WHY IS THE CAROTID INTIMA-MEDIA SEEN:
Increased thickness in the intima and media is associated with an increasingly diseased artery.
Because of this link, CIMT is an important test for detecting disease in its earliest stage, when interventions such as diet, lifestyle, and medications can have the greatest impact.
WHAT IS SEEN:
The carotid (neck) arteries provide a “window” to the coronary (heart) arteries, so hardening of the carotid arteries is directly related to the hardening of the coronary arteries. As the carotid artery is closer to the surface of the skin it is easier to access than the coronary artery and provides us with just as valuable information.
LENGTH OF THE EXAM:
30 to 45 minutes.
CIMT testing is conducted in supine position on scan bed with head of the patient resting comfortably, and neck slightly hyper-extended and rotated in direction opposite to the probe. A wedge pillow at an angle of 45° standardizes lateral rotation. Optimization of images is done by adjusting patient's neck position especially in anterior scanning planes, and rolled towels are given under neck and legs for comfort. With the use of external landmarks such as the Meijer arc or similar device, transducer angle is standardized. Height and location of ultrasound system keyboard and monitor, examination bed, and chair are adjusted accordingly to avoid any musculoskeletal injuries to patients.
The six values of mean CIMT (three on each side) are obtained and averaged to get mean CIMT. Reliance on a single absolute threshold abnormality will result in under-detection of diseases in younger individuals and over-detection in older individuals.
WHAT IS SEEN:
INTERPRETING THE RESULTS:
In healthy middle-aged adults, CIMT values between 0.6 and 0.7 mm have been considered normal, while CIMT of 1 mm or more has been associated with significant increased absolute risk of CHD.
ADVANTAGES OF THE TEST:
CIMT can be used repeatedly and reproducibly with no adverse effects on the patients. It can be performed noninvasively with no risk of vessel dissection, vessel closure, or coronary spasm
CIMT scanning protocol can detect atherosclerotic diseases in early and asymptomatic stages
CIMT directly visualizes vasculature unlike indirect biomarkers such as low-density LDL-C or even the more advanced biomarkers like high-sensitivity C-reactive protein or lipoprotein-associated phospholipase A2 (Lp-PLA2)
CIMT with plaque interrogation can be performed in any basic ultrasound ambulatory setting with favorable speed and cost factors
CIMT can be easily quantified via automated boundary detection software, and the carotid interrogation is radiation free and thus safer than other imaging tests such as coronary calcium scoring or CT-CAG
CIMT allows for observation of the arterial wall, the actual site of the atherosclerotic disease, rather than the lumen
CIMT is not dependent on calcification of the plaque as are some of the other assessment tools such as coronary artery calcification score.
CHALLENGES OF CMT:
In addition to several advantages of CIMT, there are also a few shortcomings of this procedure; however, some of them were resolved.
There is no standardized protocol for measurement of CIMT, which might lead to inaccurate estimation of the progression and regression of the CIMT during the follow-up studies or in the evaluation of any therapeutic intervention on the measured CIMT
Resolution: Implementation of edge detection software programs improved reproducibility and reduced reader variation
Different portions of the carotid artery have been used to measure the CIMT, common carotid, bifurcation, internal carotid, and combined CIMT, which may influence the value of the measured CIMT
Resolution: Iglesias del Sol and colleagues measured CIMT at the common carotid, bifurcation, internal carotid, and combined CIMT, and they found that all the measurement sites had the same ability to predict future cardiovascular events
Measurement of CIMT involves a combined measure of the intimal and medial layers of the arterial wall, whereas the atherosclerotic process is restricted in the intimal layer, particularly in its early phase
CIMT is only an indirect assessment of the possible atherosclerotic burden in the coronary arteries, as in CIMT, carotid arteries and not coronary arteries are visualized since CAD is the commonest cause of cardiovascular-related deaths. The detection of atherosclerosis in the carotids by CIMT may not represent atherosclerosis in the carotid artery
Resolution: Atherosclerosis has been reported to be more or less present equally in the coronary, cerebral, and carotid arteries, and autopsy study showed close histological relationship between coronary, cerebral, and carotid atherosclerotic disease.
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