What a Coronary Artery Calcium Scan Reveals
Deposits of calcium can build up on your artery walls as part of plaques. This buildup, called calcification, is an early sign of CHD before symptoms develop. Calcification indicates the presence of atherosclerosiswhich narrows and hardens coronary arteriesand possible blockages in the arteries that could trigger a heart attack. Calcification becomes more likely as we age.
A CAC scan, sometimes called an electron-beam CT or a multi-detector CT, looks for calcium in artery walls. The calcium appears as white specks or streaks on the x-rays generated by the chest scan. The screening itself is quick, painless and noninvasive. A technician uses a computer program to derive your calcium, or Agatston, scorethe measurement of the amount of calcium found in your arteries.
Your Agatston score indicates the likelihood of narrowing in your arteries. The higher the score, the more likely you are to have atherosclerosis. Your doctor will make any lifestyle and drug therapy recommendations based on your score and other risk factors.
Getting a test to find out whether you might be at high risk for heart disease may sound like a no-brainer. But, despite its reliability in predicting CHD, a CAC scan has some downsidesincluding radiation exposure and cost. Radiation levels from CAC scans tend to be relatively lowabout the same as the amount of naturally occurring radiation you're exposed to over one year. Yet, the long-term risk of cancer as a result of a one-time CAC scan remains uncertain.
Adults who already have had a number of other radiation tests may need to take extra precautions: Radiation exposure is cumulative, meaning that every time you're exposed to radiation, it builds up in your body, increasing your cancer risk.
The study authors caution that although "recent efforts have been made to standardize equipment and imaging protocols to reduce radiation exposure during CAC imaging...the extent to which these recommendations have been implemented in general medical practice is not known."
A 2009 study of radiation doses generated from CT scans found that they can vary widely from facility to facility. Patient size, the body part scanned, equipment and imaging protocols can also affect radiation dose. You and your doctor must carefully weigh the radiation risk from CAC scans against the test's benefits. This can be difficult; findings from past studies have been limited in determining the amount of risk from cardiovascular diagnostic imaging.
Steer clear of walk-in centers that offer the test without a doctor's prescription. Your decision to have the test should be made only after talking with your doctor. If you decide to undergo a scan, stick with an imaging facility that's accredited by the American College of Radiology.
Many insurance companies and Medicare don't cover screening tests like CAC scans, so you may have to pay for the test out of pocket. Depending on where you live, its cost can range from approximately $100 to $500.
Finally, as with many screenings, there's also a chance of a false-positive result. In the case of CAC, the test can give a high score even if your arteries aren't blocked, which may lead to further unnecessaryand costlytesting as well as needless worry. Moreover, under rare circumstances, the test can produce a false-negative result, when atherosclerosis exists but doesn't show on the scans, lulling you into believing your risk is low.
But, despite these drawbacks, the American Heart Association and the American College of Radiology recommend that CAC scans be considered for individuals at intermediate risk or low-to-intermediate risk for cardiovascular disease if the decision to start lifelong statin and aspirin therapy is unclear. They recommend against the scan for low-risk individuals.
Prediction, not prevention
If your scan doesn't detect calcification, it doesn't necessarily mean that you're safe from a heart attack; other factors can contribute to your risk as well, such as "soft" plaque that doesn't contain calcium. And if your scan reveals calcium deposits, keep in mind that, although calcification is a good predictor of heart attack, there's no existing evidence to suggest that initiating preventive therapy improves calcium scores (unlike measures to lower cholesterol or blood pressure, in which decades of research show that lowering them helps prevent heart attacks).
There's also no value in repeating a CAC scan to see whether preventive measures have improved the score. That said, discovering you have significant calcium buildup may encourage you and your doctor to consider more aggressive measures to prevent a heart attack, such as taking a daily statin or a low-dose aspirin, along with making significant lifestyle changes.
Source: Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50