Optical Coherence Tomography and Virtual-Histology Intravascular Ultrasound

Abstract

T he ultimate goal of studies such as the one by Brown et al 1 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 plaques 3 ) is one of the limitations of OCT. Furthermore, limitations to the accurate OCT assessment of lipidic plaque include artifacts caused by shallow or tangential beam angulation and drop-put and confounders, such as the presence of macrophages, foam cells, microcalcifications, or hemosiderin, in the fibrous cap-all of which can produce the appearance of lipid, whether or not lipid is actually present. See Article by Brown et alAlthough the study by Brown et al 1 is titled "Direct comparison of virtual-histology intravascular ultrasound and optical coherence tomography imaging for identification of thin-cap fibroatheroma," in reality it is less of a direct comparison of 2 techniques than one of an increasing number of, albeit, small studies questioning the accuracy of OCT, 2,4-6 as well as a rehabilitation of virtual histology (VH)-intravascular ultrasound (IVUS), suggesting that a combination of the 2 techniques is better than either alone.VH-IVUS was developed to improve on the limited tissue characterization of grayscale IVUS. Proposed criteria for a VH-fibroatheroma included >10% confluent necrotic core for 3 consecutive frames and confluent necrotic core >10% in contact with the lumen for 3 consecutive frames for VH-TCFA. Although used to good advantage in 3 important prospective studies-Providing Regional Observations to Study Predictors of Events in the Coronary Tree (PROSPECT), 7 VH-IVUS in Vulnerable Athersclerosis (VIVA), 8 and European Collaborative Project on Inflammation and Vascular WallRemodeling in Atherosclerosis -Intravascular Ultrasound (ATHEROREMO-IVUS) 9 -VH-IVUS has fallen i...

Relationship between plaque composition by virtual histology intravascular ultrasound and clinical outcomes after percutaneous coronary intervention in saphenous vein graft disease patients: study protocol of a prospective cohort study

“…The direct comparison between VH-IVUS and OCT by Brown et al found that both VH-IVUS and OCT could identify advanced coronary plaques and that combined VH-IVUS/OCT was better than either alone [33]. However, OCT has a low signal penetration through lipid or necrotic core, and cannot adequately acquire images of the whole vessels with large lumen diameter or large necrotic core [29, 34]. This presents a problem for imaging of large vessels including vein grafts.…”

“…This presents a problem for imaging of large vessels including vein grafts. The presence of macrophages, foam cells, microcalcifications, or hemosiderin, often co-existent with the necrotic core, could be adverse to accurate OCT assessment of lipidic plaque [29, 34]. VH-IVUS, which has become clinically available, can assess both plaque morphology and tissue characteristics using spectral and amplitude analysis of backscattered radiofrequency ultrasound signal.…”

Incidence of late‐acquired stent malapposition of drug eluting stents with second generation permanent and biodegradable polymer coatings—A prospective, randomized comparison using optical coherence tomography

“…A lipid plaque was defined as a low signal region with diffuse border and a maximum arc of lipid ≥90°. This maximum arc is an excellent discriminator of fibroatheroma and together a fibrous cap thickness ≤85 µm identifies thin‐cap fibroatheroma when combined with a fibrous cap thickness ≤85 µm . Measurements of fibrous cap thickness were not possible, as OCT recordings were performed after stenting.…”

Outcome after Elective Percutaneous Coronary Intervention Depends on Age in Patients with Stable Coronary Artery Disease – An Analysis of Relative Survival in a Multicenter Cohort and an OCT Substudy

“…A lipid plaque was defined as a low signal region with diffuse border and a maximum arc of lipid ≥ 90°. This maximum arc is an excellent discriminator of fibroatheroma [ 19 ] and together a fibrous cap thickness ≤85 μm identifies thin-cap fibroatheroma when combined with a fibrous cap thickness ≤85 μm [ 20 ]. Meassurements of fibrous cap thickness were not possible, as OCT recordings were performed after stenting.…”