CT, electron beam

CT, electron beam: Also known as Ultrafast CT (computerized tomography), this is a new (and controversial) noninvasive test for the detection of coronary artery disease (CAD). It is designed to measure calcium deposits in the coronary arteries.

In patients with CAD, the plaques which make up the blockages contain significant amounts of calcium, which can be detected with Ultrafast CT. This test will identify calcium in blockages as mild as 10-20%, which would not be detected by standard physiologic stress testing.

The importance of detecting such mild blockages is controversial, however, because the only “treatment” that is used for such blockages typically involves risk factor modification (especially cholesterol reduction and smoking cessation as well as aspirin and certain vitamins).

A potential limitation of Ultrafast CT is that only a total calcium score is reported. This means that two or three separate blockages of about 30% each will result in the same score as a single 70-80% blockage. The Ultrafast CT does not give an image of specific separate areas of calcification.

The major value of Ultrafast CT appears to be in screening young patients with one or more risk factors for the development of CAD. Ultrafast CT scanning is of limited value for older patients in whom some degree of calcification is commonly found. Additionally, for the reasons described above, the detection of some calcification may not be reflective of significant CAD.

Ultrafast CT was reported to be a better test than treadmill-ECG or technetium-stress test for detecting CAD (J Am Coll Cardiol 2000;36:32-38,326-340). The authors favored it as “a reasonable alternative to traditional stress testing” (pointing also to its cost, brief test time and the fact that a physician does not usually need to be present during the scan). In the same journal, the American College of Cardiology and the American Heart Association issued a consensus statement opposing the widespread use of Ultrafast CT. The controversy continues.