Optical Coherence Tomography and Virtual-Histology Intravascular Ultrasound

The ultimate goal of studies such as the one by Brown et al1 in this issue of Circulation: Cardiovascular Imaging is to provide the clinician with a diagnostic tool that identifies high-risk plaques prospectively to treat and prevent acute events. This tool must have a high positive predictive value and negative predictive value in the clinical setting and not require specific expertise or core-laboratory analysis to determine whether a plaque is vulnerable and should be treated pre-emptively—a yes/no, treat/don’t treat tool. Optical coherence tomography (OCT) has been proposed as that tool. OCT criteria for a thin-cap fibroatheroma (TCFA) include the presence and amount of lipid plaque and a thin fibrous cap with macrophage infiltration. However, in a core-laboratory study by Kim et al in which the intraobserver reproducibility was high, the interobserver intraclass correlation coefficient among 4 highly trained individuals (a better, but still idealized representation of what would happen clinically) was only 0.49 (95% confidence interval: 0.26–0.69) for fibrous cap thickness and 0.77 (95% confidence interval: 0.53–0.97) and 0.71 (95% confidence interval: 0.55–0.86) for maximum and average lipid arc, respectively.2 Quantification of lipid by OCT is problematic and is restricted to the arc of lipidic plaque because penetration through lipid or necrotic core (as well as assessment of plaque burden in high-risk plaques3) is one of the limitations of OCT. Furthermore, limitations to the accurate OCT assessment of lipidic plaque include artifacts caused by shallow or …