Stroke and heart attack prevention has progressed far beyond merely following cholesterol levels. Here is a summary:
The carotid intima-media thickness test takes advantage of the systemic nature of atherosclerosis. The common carotid artery (see diagram) is easily accessible in the neck by an ultrasound probe. High frequency sound waves allow us to measure the thickness of the inner two layers the carotid called the intima and media--without radiation exposure.
After you undergo the 20-minute scan, your physician will analyze the data within 24 hours and discuss the result with you. The images of your carotid arteries are analyzed by an FDA-approved software program, SonoCalc, that measures the CIMT at many different points on the images of each carotid artery and then averages the thickness.
The test result is basically two numbers that show the average thickness of your carotid arteries and a comment about your level of atherosclerotic plaque accumulation.
The inner two layers of the carotid arteries (the intima and media) gradually thicken with age. The following graph illustrates the correlation of CIMT with age in a particular group of patients. Note how tightly the CIMT correlates with age until the 90s when it starts to vary.
The CIMT can range on average between as low as 0.3 mm (if you are lucky enough to have the arteries of a 20 year old) or as high as 1.4 mm (if you have made it to 100 years old). The average CIMT for your age can be compared to yours. For example, if you are 50 years old and have a left carotid artery thickness of 0.68 mm, then you actually have a left carotid artery that is more like a 46 year old. In this case, you should get another screening test in about 24 months. If your CIMT is 0.78 mm, then you have thicker arteries than average for your age and should get a follow up exam in 18 months to see what the rate of accumulation is. This is done for both the right and left arteries.
The next two numbers are the maximum thickness of the left and right common carotid arteries. If either of these is greater than 1 mm, then you are thought to have some carotid plaque which puts you at increased risk and you should have a exercise stress test to see if you have any significant coronary artery narrowing. If this is negative, then a follow up test should be done in 12 months.
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