Fibrous Cap Thickness Predicts Stable Coronary Plaque Progression: Early Clinical Validation of a Semiautomated OCT Technology

Abstract

Background: Imaging-based characteristics associated with the progression of stable coronary atherosclerotic lesions are poorly defined. Utilizing a combination of optical coherence tomography (OCT) and intravascular ultrasound (IVUS) imaging, we aimed to characterize the lesions prone to progression through clinical validation of a semiautomated OCT computational program.

Methods: Patients with stable coronary artery disease underwent nonculprit vessel imaging with IVUS and OCT at baseline and IVUS at the 12-month follow-up. After coregistration of baseline and follow-up IVUS images, paired 5-mm segments from each patient were identified, demonstrating the greatest plaque progression and regression as measured by the change in plaque burden. Experienced readers identified plaque features on corresponding baseline OCT segments, and predictors of plaque progression were assessed by multivariable analysis. Each segment then underwent volumetric assessment of the fibrous cap (FC) using proprietary software.

Results: Among 23 patients (70% men; median age, 67 years), experienced-reader analysis demonstrated that for every 100 μm increase in mean FC thickness, plaques were 87% less likely to progress (P = .01), which persisted on multivariable analysis controlling for baseline plaque burden (P = .05). Automated FC analysis (n = 17 paired segments) confirmed this finding (P = .01) and found thinner minimal FC thickness (P = .01) and larger FC surface area of <65 μm (P = .02) and <100 μm (P = .04) in progressing segments than in regressing segments. No additional imaging features predicted plaque progression.

Conclusions: A semiautomated FC analysis tool confirmed the significant association between thinner FC and stable coronary plaque progression along entire vessel segments, illustrating the diffuse nature of FC thinning and suggesting a future clinical role in predicting the progression of stable coronary artery disease.

Keywords: coronary artery disease; intravascular ultrasound; optical coherence tomography.

Graphical abstract

Figure. 1

Flowchart of study patient selection. A total of 23 subjects with stable coronary artery disease who underwent nonculprit vessel imaging with optical coherence tomography and intravascular ultrasound at baseline and intrvascular ultrasound at follow-up were included in the study. Of these, 6 patients did not undergo fibrous cap analysis due to insufficient lipid plaque to assess these parameters. CAD, coronary artery disease; FC, fibrous cap; IVUS, intravascular ultrasound; OCT, optical coherence tomography; PCI, percutaneous coronary intervention.

Figure. 2

Reader measurement of fibrous cap thickness. Cross-sectional OCT images of signal-rich fibrous cap overlying a signal-poor lipid pool. The inset demonstrates the measurement of fibrous cap thickness (white arrow) within a frame, achieved using a length measurement tool on an offline OCT workstation. OCT, optical coherence tomography.

Figure. 3

JEI tool enabling manual correction of automatic wall layer analysis. (A) Original cross-sectional optical coherence tomography image of the lipid-rich plaque. (B) Angular range of FC overlying the lipid-rich plaque, denoted by shaded arcs. (C) Automated segmentation of FC (green line) and lumen (red line) using multilayer approach, demonstrating an inaccuracy (red arrow) in border delineation. (D) FC border correction by experienced reader using the JEI adjustment method. (E) Optimized, recomputed 3-dimensional–connected surfaces after JEI. FC, fibrous cap; JEI, Just-Enough-Interaction.

Central Illustration

Carpet map characterization of FC thickness in progressing vs regressing segment of a single representative patient. The top panel illustrates the extraction of cap thicknesses from our automated FC assessment tool. The middle panel demonstrates color-coded gradations of FCT displayed longitudinally (y-axis) and circumferentially (x-axis) on an unwrapped vessel wall. The shadowed areas represent nonmeasurable regions caused by guidewire shadow, residual blood, and exclusion regions without lipid pool. The bottom panel highlights the clustering of these cap thicknesses between groups, with the vertical dot line indicating the average FCT for each group. FC, fibrous cap; FCT, fibrous cap thickness.