Carotid Artery Disease As A Risk Factor In Stroke

Main Category: Cardiovascular / Cardiology
Also Included In: Stroke
Article Date: 27 Sep 2008 - 0:00 PDT

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A decision on whether a patient should undergo surgery for a constricted carotid artery as a means to prevent stroke will be made on a much more exact basis thanks to modern imaging techniques. A study on the innovative CT-angiography method is being presented at the World Stroke Congress in Vienna. It allows greater precision in assessing the actual risk of stroke, and identification of those who are the correct candidates for carotid artery surgery.

Computer assisted analysis of images provided by CT angiography offer neurologists more precise information on which patients can profit from carotid artery surgery than do conventional investigative methods. That is the outcome of the most recent research project carried out by a team of scientists under Dr. Max Wintermark (Department of Neuroradiology at the University of California, San Francisco), and presented at the 6th World Stroke Congress in Vienna (A).

Deposits (atherosclerotic plaque) in arteries to the brain, particularly the main carotid brain artery, are among the most common causes of strokes. Major studies, such as the NASCET study, have shown that when the degree of narrowing of the carotid artery is above 70%, the risk of stroke doubles from 8% to 15%. The criterion of narrowing of the carotid artery of more than 70% is usually used to select patients for stenting or carotid surgery (endarteriectomy). This approach, however, does not take into account the composition of the arterial deposits, which might be a crucial factor in whether there is an actual increased risk for the individual patient.

This is a problematic issue. Dr. Max Wintermark: "Performing surgery in all patients with a more than 70% narrowing of the carotid artery and with an inherent risk of stroke of 15%, means that only 15 out of 100 patients you are exposing to surgery would have developed a stroke, and 85 out of 100 would not need the surgery. Conversely, not operating patients with less than 70% narrowing, 8% of this group will suffer stroke which is a significant number, considering the fact that two third of the population over 65 has this problem."

To better assess the actual risk, researchers are looking for a marker that will better identify patients at risk of stroke compared to the degree of luminal narrowing. This has led to the concept that the composition of deposits plays an important role in assessing stroke risk: So it is vital to find a diagnostic tool to distinguish between dangerous deposits ("vulnerable" plaques) and those which present no danger. "Our study demonstrates that multidetector-row CT-angiography (CTA) can give extremely precise information on the exact composition of plaque using this non-invasive method." This has been shown through comparisons of CT investigative results with analysis of tissue in the laboratory (histological analysis.)

For the study, multidetector-row computer tomography angiographies (CTAs) of the carotid arteries of eight patients with transient ischemic strokes were obtained. Then the plaque constricting the carotid artery of each patient was removed (endarterectomy). The tissue removed was then investigated by histological methods, and this histological assessment served as a gold standard. Comparing the data arrived at, researchers identified a so-called algorithm, a mathematical formula by which the computer can convert the grey tones of a point on the image (pixel) delivered by CT into tissue composition.

In a control test, computer analyses arrived at with this formula were compared with histological results with very promising results. Overall, the CTA analyses concurred 72.6% with histological analyses. In cases of calcification, CTA analyses were 100% correct. As regards other components of atherosclerotic plaque, such as hemorrhage, connective tissue or so called lipid-rich necrotic cores, the problem is that these components exhibit similar gray tones, and thus can only be differentiated from one another to a limited degree. However the algorithm method of analysis used by the Californian research team was able to correctly identify 79.6% of lipid cores and 71.2% of major hemorrhage. Fibrous cap thickness was 77% correctly identified, and ulceration even to 85.5%.

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