Elsewhere on this website are descriptions of the most common tests and procedures that we do at Pima Heart & Vascular. One test not on this website that I often order is called a coronary calcium scan and it is very helpful in detecting the presence of coronary artery disease in people who have no symptoms. The test is done by performing a special CT scan of the chest. The x-ray intensity is lower than usual, as the CT scan only needs to “see” the calcium in the coronary arteries and not the finer detail necessary to image the lungs or other tissues. Calcium is very radiopaque, meaning that it absorbs x-rays easily, allowing for lower dosing of the x-rays.
To understand why it is helpful to look for calcium in the coronary arteries, we have to go back to an earlier discussion about the nature of atherosclerosis (the process of plaque accumulation in arteries) that was the subject of a blog in March. Plaque forms due to accumulation of cholesterol, other lipids, inflammatory cells and molecules, and other extracellular “debris.” The plaque that grows can lead to narrowing of the lumen of the artery, compromising blood flow, which can then cause angina.
Another process occurs simultaneously—calcification (the process of calcium depositing in tissue, organs, and blood vessels). Calcium, which is present in the blood, is attracted to areas of inflammation. Plaque formation in the coronary arteries is associated with (and partly caused by) inflammation, so calcium will deposit in these plaques. Thus, the presence of calcium in the coronary arteries is a sign that there is plaque there. This chain of events helps us to realize that calcification is not the cause of the plaque, but the result of its creation.
A coronary calcium scan—sometimes called a “heart scan” or “coronary calcium CT”—images the calcium in the coronary arteries and comes up with a calcium score, a number that represents how much calcium is present. Most reports will also provide a percentile rank, a number that tells you where your score is relative to other men or women your age, allowing you to know if your score is average (around the 50th percentile), unusually high (above the 75th percentile) or unusually low (below the 25th percentile).
These scans will also give a score for each of the coronary arteries. It it important to understand, however, that it is the total score that is relevant, not the score of each individual artery. A higher score in one particular vessel doesn’t necessarily mean that that vessel has the tightest blockage. The vessel that we think of as being the most important—the “LAD” (left anterior descending)—has a greater tendency to calcify, so the score in that vessel is frequently highest, even if it doesn’t have the most plaque. Furthermore, the calcium score doesn’t tell us how narrow any of the vessels are, only that the general plaque burden (amount of total plaque in the arteries) is low, average or high. To see if a person has a significant blockage (tight enough to compromise blood flow), a stress test is helpful. A calcium score and a stress test, therefore, are complementary tests.
We use the calcium score to adjust our estimate of a person’s overall risk of having a cardiovascular event (a heart attack, a stroke or dying of cardiovascular disease) upward or downward. Often, we consider doing a coronary calcium scan in patients who are at intermediate risk, based on their Framingham data, intermediate being between 5%-20% over 10 years. Some physicians use a calcium score above 0 as a reason to treat intermediate risk patients with a statin medication (the subject of next week’s blog). Others choose to only do so if the calcium score is over 100 or a person is in greater than the 75th percentile. But these are approaches to discuss with your personal physician.
As I indicated earlier, it is important to understand that the calcium itself isn’t what is dangerous—and it is unrelated to how much calcium you eat in your diet. But calcification is a marker of what IS dangerous—atherosclerosis, the process of plaque buildup in the coronary arteries. Seeing calcium in the arteries is like seeing smoke in the distance. . . and where there’s smoke, there’s fire!
Greg Koshkarian, MD, FACC