What is optical coherence tomography (OCT) in patients with suspected or known coronary artery disease?

What is Optical Coherence Tomography (OCT) in Coronary Arteries?

Optical coherence tomography (OCT) is a catheter-based intravascular imaging technology that uses near-infrared light to generate high-resolution (10-20 μm) cross-sectional and three-dimensional images of coronary artery microstructure, providing approximately 10 times greater resolution than intravascular ultrasound (IVUS). 1

Technical Principles

OCT operates on the principle of low-coherence interferometry, similar to ultrasound but using light waves instead of sound waves 2:

• Light source: Emits near-infrared light (wavelength ~1.3 μm) through a rotating single optical fiber coupled with an imaging lens 1, 2
• Resolution capabilities: Achieves axial resolution of 10-20 μm and lateral resolution of 20-90 μm, enabling visualization at nearly microscopic detail 1
• Penetration depth: Limited to 1-2 mm (compared to 5-6 mm for IVUS), which restricts assessment of deeper vessel wall structures 1

Image Acquisition Requirements

OCT requires "bloodless" imaging because light waves are attenuated by blood 1:

• Blood must be cleared from the target vessel using contrast medium via hand or power injection 1
• Modern frequency-domain OCT (FD-OCT) systems use non-occlusive flushing techniques with contrast or crystalloid solutions 3, 2
• Automated pullback speeds range from 0.5 to 10 mm/s, allowing accurate lesion length assessment 1
• Fast scanning speed enables image acquisition in seconds 3

Clinical Applications in Coronary Artery Disease

Primary Role: PCI Optimization (Not Primary Diagnosis)

The American College of Cardiology recommends OCT primarily for optimizing percutaneous coronary intervention outcomes, especially in complex lesions and high-risk patients, rather than for primary diagnosis of coronary artery disease 3:

• OCT navigation during PCI reduces adverse outcomes: the RENOVATE-COMPLEX PCI study showed reduction in combined endpoint (cardiac death, target vessel MI, revascularization) from 12.3% to 7.7% over 2 years (HR 0.64; P=0.008) 3
• The OCTOBER study demonstrated decreased major events from 14.1% to 10.1% over 2 years (HR 0.70; P=0.035) 3
• The ILUMIEN IV study showed significant reduction in stent thrombosis (0.5% vs 1.4%; HR 0.36; P=0.02) 3

Stent Assessment and Optimization

OCT provides detailed evaluation of stent deployment 3, 4:

• Stent expansion: Minimum stent area <4.5-5.0 mm² by OCT is an independent predictor of adverse events 3
• Stent malapposition: Detects non-apposition to vessel wall with high sensitivity 3
• Edge dissections: Identifies coronary artery dissections at stent edges 3
• Tissue prolapse: Visualizes plaque or thrombus protruding through stent struts 1
• Neointimal coverage: Assesses stent strut coverage by neointima at follow-up 3

Plaque Characterization

OCT differentiates atherosclerotic plaque types with high accuracy 4, 5:

• Fibrous plaques: Appear as homogeneous, signal-rich regions 5
• Lipid-rich plaques: Characterized by signal-poor regions with diffuse borders 5, 3
• Calcified plaques: OCT measures calcium thickness as light is not attenuated by calcium 3
• Thin-cap fibroatheroma: Identifies vulnerable plaques with fibrous cap <65 μm thickness 6, 7

Acute Coronary Syndrome Evaluation

In acute coronary syndrome, OCT detects plaque rupture in 50-70% of culprit lesions 3, 5:

• Thrombus differentiation: Red (erythrocyte-rich) thrombi show high scattering; white (platelet-rich) thrombi show low scattering 3, 5
• Plaque erosion: Develops over areas of intimal thickening and/or thick-cap fibroatheroma 5
• MINOCA evaluation: OCT or IVUS is recommended to identify unrecognized causes such as thrombus, plaque rupture/erosion, or spontaneous coronary artery dissection 3

Limitations and Technical Considerations

Imaging Constraints

OCT has specific limitations that affect its clinical utility 1:

• Ostial lesions: Difficult to evaluate due to blood admixture 1
• Vessel size: Challenges in excessively large or small vessels 1
• Severe stenoses: May not adequately opacify with contrast unless specialized techniques are used 1
• Limited depth penetration: 1-2.5 mm depth does not allow accurate assessment of overall plaque burden 3

Contrast Requirements

Unlike IVUS, OCT requires contrast injection for blood clearance 1:

• This requirement limits evaluation of certain lesion subsets 1
• Angiographic coregistration is possible with specific systems for precise mapping 1

Comparison with IVUS

OCT provides 10-fold higher resolution than IVUS but with reduced penetration depth 1:

• OCT resolution: 10-20 μm axial, 20-90 μm lateral 1
• IVUS resolution: ~70 μm (newer high-definition systems offer better resolution) 1
• OCT penetration: 1-2 mm 1
• IVUS penetration: 5-6 mm 1

Guideline Recommendations

The 2011 ACCF/AHA/SCAI guidelines state that the appropriate role for OCT in routine clinical decision making has not been established, though it permits detailed imaging of plaque morphology and arterial response to stent implantation 1. However, more recent evidence supports its use for PCI optimization in complex cases 3.

OCT is most beneficial in left main artery disease, complex lesions, and high-risk patients where intravascular visualization provides the greatest clinical benefit 3.