I’ve discussed in a previous post the importance of detecting subclinical atherosclerosis.
The process of atherosclerosis (the build up of fatty plaques in all arteries) occurs silently and often the first symptom is sudden death due to a heart attack.
Examining the large arteries in the neck (the carotids) with ultrasound for early fatty plaques helps establish whether atherosclerosis is present or not.
If there is plaque in the carotids this is a strong indicator that atherosclerosis is present throughout the large arteries of the body including the coronary arteries supplying blood to the heart.
Ruptured plaques in the coronary arteries are what cause heart attacks and most cases of sudden cardiac death are due to heart attacks.
If we can identify those who have subclinical (i.e. before significant blockages and symptoms develop) atherosclerosis, we can better target aggressive therapy to those at the highest risk.
Carotid IMT: The window to your vascular age
There is a second technique which uses carotid ultrasound available to evaluate an individual’s longer term risk of heart disease even before plaque develops.
This technique is termed carotid IMT. IMT (intimal-medial thickness ) refers to the thickness of the wall of the artery which includes the thin layer of cells lining the inside of arteries or intima and the smooth muscle in the wall of the artery (media).
The Carotid IMT has been shown to be related to all of the risk factors that medical science knows for atherosclerosis. It progressively increases with normal aging and we have data on what the normal value is for white and black men and women between the ages of 40 and 70.
By making multiple precise and careful measurements of an individual’s CIMT we can determine where that individual stands in comparison to normal individuals of the same age, gender and race.
Individuals whose CIMT is great than that of 75% of individuals of the same age and gender are at significantly higher risk of heart attack and stroke even if no carotid plaque is discovered.
Thus, the CIMT serves somewhat as an early warning signal for unhealthy arteries.
We can also determine a so-called vascular age from this technique.
An example of this is shown to the left. . The individual was an asymptomatic young man. He had no plaque but his CIMT measured 0.770, which is significantly higher than the normal CIMT for a similarly aged white male of 0.598. This is thicker than 80% of normal individuals of the same age and gender. It is normal for an individual who is 65 years old. Thus, this individual’s vascular age is 65 years, 20 years greater than his chronological age.
In my office I usually recommend a combination of CIMT and carotid plaque be performed in individuals in whom I am trying to assess risk of cardiovascular disease between the ages of 40 and 70.
There is no reason to do CIMT in patients who have documented coronary heart disease (heart attack/stroke/stent/bypass surgery), carotid disease (stroke/carotid surgery), or peripheral arterial disease. These patients have already passed the early warning phase of atherosclerosis.
This technique should only be done by physicians/technicians who have been adequately trained and have dedicated themselves to performing the meticulous tiny measurements required in an accurate manner.
Major cardiovascular organizations differ on recommending CIMT for screening purposes. Well-respected scientific papers have clearly established CIMT as reproducible and highly predictive of vascular events but there is no randomized , controlled trial which establishes that utilizing it in conjunction with treatment decisions based on the results will improve cardiovascular outcomes.
For this reason, even though it is cheap, painless, harmless and quick insurance companies do not reimburse for the costs.
*We don’t have good data sets on individuals under the age of 40 years. I offer CIMT to this group and extrapolate the good data but more studies are needed in this age range.
*We don’t have good data sets on ethnicities other than the African-americans and European and American whites.
*Multiple methods of CIMT recording and measurement have been published.
*I don’t find CIMT useful in individuals over the age of 70. Carotid plaque is much more helpful. Most men have carotid plaque by this age. If you don’t have any carotid plaque over the age of 70 years then you are in a very low risk category and are unlikely to benefit from statin or aspirin therapy.
Next post we’ll discuss the third noninvasive tool at cardiologists disposal to assess individuals for subclinical atherosclerosis: a direct look at calcium in the coronary arteries
N.B. As noted here.
The full process underlying intimal thickening is not fully understood but is thought to be similar, though not identical, to that underlying atherosclerosis. The hypothesis that IMT represents subclinical vascular disease may be supported by the finding of graded associations between IMT and concurrent atherosclerotic change visualized in the coronary arteries during angiography. It is important to note, however, that whilst in many cases thickening of the intima–media does represent atherosclerotic change, in other cases it may represent non-atherosclerotic lesions such as hypertrophy in response to shear stress on the artery wall.