IDENTIFYING FUTURE CULPRIT LESIONS Victor J. Dzau, MD (Boston, Massachusetts): Dr. Gersh mentioned that it is difficult to predict culprit lesions. Is it possible to identify areas of vasomotor abnormality or specific characteristics of a lesion using intravascular ultrasound (IVUS) as markers of a potential culprit lesion? Bernard J. Gersh, MB, ChB, DPhil, (Washington, DC): I expect that this is likely, and this is a very exciting frontier. We still do not know if IVUS and other technologies can successfully classify and estimate the density of the lipid core prospectively, but I expect that this may be possible in the future. Peter Ganz, MD (Boston, Massachusetts): I think this is a very important area to pursue, but I am somewhat more pessimistic about the ability of these approaches to identify culprit lesions. In a recently published study, the average thickness of the fibrous cap that ruptured was 25 microns, and all caps that ruptured were thinner than 65 microns. So if one wants to identify the thickness of the fibrous cap, a technique with outstanding resolution is necessary. Currently, the resolution of IVUS is about 150 microns, and the resolution of magnetic resonance imaging is about 300–400 microns. It is an important area for future research, but currently available techniques may not be capable of identifying the thickness of the fibrous cap. Dr. Dzau: What about the lipid core and the vasomotor activity of those lesions? Dr. Ganz: They do appear to have characteristic vasomotor abnormalities. There have been 2 studies published that assessed the vasomotor activity of infarcted unstable angina sites compared with stable angina sites. Clearly, the unstable angina sites have much greater disturbances in reactivity than the more stable sites. Thus, this may be one possible way to predict future events. IVUS is a possible procedure, although it is not as good for tissue characterization as would be hoped. Magnetic resonance imaging would be a tremendous method of tissue characterization and research is currently ongoing.