What are the optical coherence tomography (OCT) characteristics of unstable coronary plaque?

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Last updated: September 18, 2026 • View editorial policy

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OCT Characteristics of Unstable Coronary Plaque

Unstable coronary plaques on OCT are characterized by thin-capped fibroatheromas (fibrous cap <65 μm), large lipid-rich necrotic cores (signal-poor regions with poorly delineated borders), plaque rupture with intimal disruption, thrombus formation, macrophage accumulation, and cholesterol crystals. 1

Key Morphological Features of Vulnerable/Unstable Plaques

Thin-Capped Fibroatheroma (TCFA)

  • Fibrous cap thickness <65 μm overlying a necrotic core is the hallmark finding 1
  • The cap appears as a signal-rich tissue layer, though intensity can vary
  • TCFAs are found with significantly greater frequency in acute coronary syndrome and myocardial infarction patients compared to stable angina 1
  • Some studies use additional criteria: necrotic core subtending >90° arc or comprising >1 quadrant 1

Necrotic/Lipid Core

  • Appears as signal-poor regions with poorly delineated or diffuse borders 1
  • Shows fast OCT signal drop-off with little to no backscattering
  • May contain cholesterol crystals (thin, linear, highly backscattering structures) 1
  • Critical distinction: Calcium has sharply delineated borders, while necrotic core has poorly defined borders 1
  • OCT is most accurate for identifying superficial necrotic cores; deep cores may be obscured by signal attenuation 1

Plaque Rupture

  • Intimal tearing, disruption, or dissection of the fibrous cap (Evidence Level: High) 1
  • Frequently occurs in the context of TCFAs
  • May appear as a cavity when flushed with contrast media
  • Found in 50-70% of culprit lesions in acute coronary syndrome 2

Thrombus

Two distinct types identifiable by OCT (Evidence Level: High) 1:

  • Red thrombus (RBC-rich): Highly backscattering with high attenuation, resembles blood, frequently seen in acute MI 1, 2
  • White thrombus (platelet-rich): Less backscattering, homogeneous appearance with low attenuation, often in unstable angina 1, 2
  • Appears as mass attached to luminal surface or floating within lumen

Plaque Erosion

  • Thrombus present with irregular luminal surface
  • No evidence of cap rupture in multiple adjacent frames (Evidence Level: Low) 1
  • Develops over areas of intimal thickening or thick-cap fibroatheroma 2

Macrophage Accumulation

  • Appear as confluent or punctate highly backscattering focal regions within the artery wall 1
  • May cause shadowing of underlying tissue
  • Correlated with symptom severity 1
  • Associated with thin fibrous caps and large necrotic cores 2

Additional Vulnerability Features

  • Intraplaque vasculature (vasa vasorum): Well-delineated low-backscattering regions or voids 1
  • Cholesterol crystals: Thin, linear, highly backscattering structures within plaque 1
  • Microcalcifications: Associated with vulnerable phenotype 3, 4
  • Calcified nodule: Single or multiple calcium regions protruding into lumen, common in older patients with hypertension and chronic kidney disease 1, 2

Clinical Context and Prognostic Significance

Recent evidence from the OPTICO-ACS study demonstrates that vulnerable plaque morphology (defined by >2 features among TCFA, large lipid arc >180°, microcalcifications, and macrophage infiltration) is independently associated with high thrombus burden (adjusted OR 2.5,95% CI 1.31-4.89) 3. However, high thrombus burden itself—not the underlying plaque vulnerability features—was the independent predictor of long-term major adverse cardiac events (adjusted HR 2.2,95% CI 1.23-3.98) 3.

Important Caveats

Artifacts can mimic unstable features:

  • Tangential signal dropout, blood, or red thrombus may falsely suggest necrotic core 1
  • Superficial macrophages with high attenuation can create appearance of signal-poor regions below 1
  • Small thrombus may be confused with dissection or intimal disruption 1

Measurement limitations:

  • OCT cannot reliably measure necrotic core thickness/volume when the external elastic membrane is not visible due to signal attenuation 1
  • The appearance of small calcifications and microcalcifications is not well established 1

Evidence level considerations: While plaque rupture and thrombus detection have high evidence levels, the OCT definition of necrotic core and TCFA carries only low evidence levels due to limited direct histopathologic correlation studies 1. Nevertheless, these lesions consistently demonstrate higher prevalence in acute coronary syndromes versus stable disease 1.

References

2
Research

Assessment of coronary atherosclerosis using optical coherence tomography.

Journal of atherosclerosis and thrombosis, 2014

4
Research

From biology to imaging: Rethinking vulnerable plaques in coronary artery disease.

European journal of clinical investigation, 2026

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