Electron Beam Tomography for Early Detection of Coronary Artery Disease
by Allister Fyfe, M.D.

Coronary disease remains the single most common cause of death in the United States and by 2030 will be the single largest killer worldwide. In Texas 37% of the population will die of a cardiovascular event. Half of those who die have no prior warning such as chest pain or positive stress test.

Recent insights into the biology of plaque rupture resulting in heart attack or stroke help to explain these apparent inconsistencies. The majority of heart attacks (86%) occur at the site of an atherosclerotic narrowing of less than 70%; such plaques will not show up on stress testing. Accurate prediction of events requires differentiation of coronary artery disease from coronary artery obstruction and independent tests are often required.

A number of risk factors for the development of cardiovascular disease or death have been derived from long-term studies but these only provide a probability estimate. Half of those who suffer a cardiovascular event have no documented risk factors such as high cholesterol, smoking, high blood pressure, diabetes or family history. Given these limitations, new non-invasive screening tests to diagnose coronary artery disease are required. If coronary artery disease is present, the likelihood of a cardiovascular event is 90% and these individuals should be targeted with aggressive therapy.

Ultrafast or Electron beam tomographic (EBT) scanning evolved from StarWars technology in 1985. The absence of moving parts differentiates this scanner from conventional and spiral CT scanners, making EBT 10 times faster and providing resolution as fine as 0.7mm with a similar radiation dose as 2 chest X-rays. EBT scanners can freeze-frame the heart between beats and allow the detection of miniscule calcium deposits in the coronary arteries as small as 1.0 mm3 in a 40-second scan time. Reproducibility is greater than 99%.

Calcium deposition is not an inevitable consequence of aging as long term and large cross-sectional studies in more than 50,000 patients have shown that many elderly have no calcification. Other studies show that calcification is a regulated consequence of cholesterol build-up in arteries. While the absolute amount of calcium present in the coronary arteries has been linked in some studies to the probability of an obstruction or coronary blockage, this is unreliable and not the most appropriate use of EBT.

The important use of the test is to find coronary artery disease with a high degree of accuracy. If a patient has no coronary calcification (i.e. a coronary artery score of 0), the probability that heart catheterization will find any significant atherosclerosis is less than 1 in 1000 for both men and women. A negative test is very reassuring in patients with borderline risk factors including bad family history.

Appropriate candidates for use of EBT as a screening test are males over age 35 and females over age 40 with borderline or no risk factors and a negative stress test. In rare cases where risk factors such as family history are especially worrying, earlier screening is indicated. If the scan is negative, a repeat scan in 5 years can be used for follow-up. EBT is effective and accurate in monitoring atherosclerotic plaque build-up and response to therapy.

The public and employers, interested in cardiovascular prevention, have embraced EBT. Researchers are excited at the possibility of playing a major role in integrating this new technology into traditional cardiovascular practice.