Coronary arteries aren't what they seem 12. November 2007 William Davis (5) Why do stress tests so often fail to detect coronary atherosclerotic plaque? Why do even heart catheterizations--the "gold standard"--fail to disclose the full extent of plaque within the walls of coronary arteries? We owe much of the explanation of these phenomena to Dr. Seymour Glagov, retired professor of pathology at the University of Chicago. When studying the coronary arteries of people who died, he observed that people commonly had plenty of atherosclerotic plaque lining the artery wall, yet it did not necessarily impinge on the artery "lumen," or the internal path for blood to flow. The only time the lumen became obstructed by plaque was when either 1) plaque grew to overwhelming levels and was severe and extensive, or 2) when a plaque had "ruptured," meaning its thin covering had been penetrated and eroded by the underlying plaque tissue like a volcano emerging from the surface and erupting. This groundbreaking observation, now dubbed "the Glagov phenomenon," explains why someone can have a normal stress test on Tuesday but erupt a plaque on Wednesday. The Glagov phenomenon also explains why heart scans can detect plaque when both stress tests and heart catheterizations fail to do so. Many physicians will then interpret this to mean that the heart scan was wrong. With the Glagov phenomenon in mind, you can see that the heart scan is not wrong, it is simply detecting coronary atherosclerotic plaque at a stage that is not yet detectable by the other methods. In the illustration, you can see that the lumen of the vessel is maintained--despite the artery on the left having minimal plaque, the artery on the right containing moderate plaque. If either artery were examined by a test that relies on blood flow--stress test or heart catheterization--both would appear normal. But a test that examines the artery wall, such as a heart scan, would readily detect the artery on the right and probably even the artery on the left.I am very grateful to Dr. Glagov and his insight into this important process. Otherwise, we might still be floundering around trying to understand the apparent discrepances between these tests that simply provide different perspectives on the same problem.