Increased intimal–medial thickness (CIMT, IMT) of the common carotid artery as assessed by ultrasound is an index of atherosclerosis, and is associated with symptomatic coronary artery disease. In addition, IMT is also predictive of cerebrovascular disease, stroke, left ventricular hypertrophy, and coronary artery calcium, ankle brachial index kidney disease. It is widely accepted that IMT is the only surrogate end point for CAD that is endorsed by clinical studies. This is evidenced by the fact that the US Food and Drug Administration recognize IMT as a valid end point in the evaluation of new drugs. It can also identify the most dangerous type of plaque: vulnerable plaque.
Both ultrasound and autopsy studies have found that carotid atherosclerosis correlates well with atherosclerosis elsewhere in the circulation and can be used as a marker of general atherosclerosis. Recent guidelines have given CIMT and plaque-based risk prediction a class II A recommendation.
The CIMT determines early atherosclerosis in the carotid artery by measuring the diameter of the media and intima, which is where foam cells accumulate in the early stages of atherosclerosis. In healthy adults CIMT ranges from 0.25-1.5 mm. Normal values based on age and gender for black-and-white races have been established. This test is especially useful for asymptomatic patients between ages between 40 and 70 years old.
CIMT is different from the standard Carotid Doppler Ultrasound which measures blood flow velocity. Faster velocity indicates stenosis by virtue of a narrowing of the artery. Unfortunately, in the early stages of plaque formation, there is little narrowing. Thus, a standard carotid Doppler will not identify subtle thickening of the arterial wall and may miss subclinical atherosclerosis and the opportunity to begin treatment early, potentially mitigating the need for a surgical procedure down the road.
Since the 1990s, many statin drug trials have used CIMT for evaluating the regression and progression of atherosclerosis . CIMT has been shown in large-scale, prospective studies (Atherosclerosis Risk in Communities Study, Multiethnic Study of Atherosclerosis ) to be an independent predictor of heart attack and stroke. CIMT is more accurate in predicting heart attack and stroke than any other risk factor alone and increased CIMT is an independent risk factor even in the absence of any other risk factors. Call to schedule!