Abstracts & Commentary
Synopsis: EBCT cannot be recommended for widespread use at this time based on the available evidence.
Sources: Arad Y. Prev Cardiol. 2002;5:62-67; Redberg RF, Shaw LJ. Prev Cardiol. 2002;5:71-78.
Since more than 70% of myocardial infarctions (MIs) occur in coronary arteries in which the degree of stenosis is 50% or less,1,2 alternative screening techniques for hemodynamically insignificant coronary artery disease (CAD) is of increasing importance. Also, it should be noted that asymptomatic individuals usually have hemodynamically insignificant coronary artery stenosis, which usually does not provoke signs of ischemia on routine exercise stress testing. A screening technique that can effectively screen for latent CAD by indirectly determining the atherosclerotic burden even in those individuals who do not have hemodynamically significant stenotic lesions could be enormously helpful in identifying individuals who need aggressive lifestyle changes and CAD risk reduction.
Redberg and Shaw from the Division of Cardiology at the University of California in San Francisco reviewed the results of Electron Beam Computed Tomography (EBCT) studies. They also reviewed the comprehensive ACC/AHA Expert Consensus Document on EBCT which did not recommend widespread use of EBCT for screening of CAD at this time. After analyzing all of this data, they concluded that while the potential of EBCT and other tests under study for CAD is exciting, EBCT cannot be recommended for widespread use at this time based on the available evidence.
Comment by Harold L. Karpman, MD, FACC, FACP
Because clinically significant atherosclerotic CAD is frequently present in completely asymptomatic persons, up to 50% of patients with newly diagnosed CAD will initially present with either an acute MI or sudden death. It has been clearly demonstrated that relying on coronary artery lumen size alone to estimate the degree of CAD may be deceptive since the lumen size may remain normal or be only minimally effected even though a significant atherosclerotic burden has been present in the walls of the coronary arteries for many years. More recently, it has become clear that the extent of the atherosclerotic burden rather than simply the presence of risk factors per se may be the strongest determinate of the likelihood of a patient developing symptomatic CAD.4
The measurement of coronary artery calcification is slowly earning respect as a powerful early marker of the atherosclerotic burden in the coronary arteries.5 Proponents for the use of EBCT in risk screening for CAD point out that it is an ideal screening device since high quality coronary artery image acquisition is extremely rapid with only minimal motion artifacts encountered during the performance of this study. In addition, they argue that coronary calcium scores should be evaluated according to the patient’s age and gender and that calcification identifies the vulnerable person with significant CAD but not necessarily the vulnerable lesion. Opponents of this procedure note that it is extremely costly and that the information provided may be of little more value than the clearly validated, office-based, noninvasive and inexpensive Framingham risk model.
The lack of data in the current literature that would define which asymptomatic populations would benefit from EBCT forced the ACC/AHA Expert Consensus Document on EBCT to not recommend widespread use of this technique for screening for CAD at this time.3 Emerging data from studies using techniques such as intravascular coronary ultrasonography and the results of ongoing large clinical trials may contribute to changing this conclusion but, for the time being, it would appear that EBCT should not be recommended for pure screening use at this time. However, I feel convinced that EBCT will end up being a superb screening technique to identify patients at increased risk of MI or other serious coronary events and, in many instances, may prove to be incredibly useful in motivating affected individuals to alter their lifestyle in a positive way and to accept therapy with lipid-lowering drugs and/or other agents that will improve endothelial function and diminish the atherosclerotic burden over time.
Dr. Karpman, Clinical Professor of Medicine, UCLA School of Medicine, is Associate Editor of Internal Medicine Alert.
References
1. Fuster V, et al. N Engl J Med. 1992;326:310-318.
2. Fuster V, Lewis A. Circulation. 1994;90(4):2126-2146.
3. O’Rourke RA, et al. Circulation. 2000;102(1):126-140.
4. Hasdai D, et al. Am J Cardiol. 1997;79:1005-1011.
5. Stary HC. Eur Heart J. 1990;11(suppl E):3-19.
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