Coronary intravascular imaging

13.1.1

Before PCI

Is revascularization needed ?

• 1.

  Determine significance of left main coronary lesions

  Left main lesions with minimum lumen area (MLA)>6.0 mm ² by IVUS or >5.4 mm ² by OCT do not require revascularization . However, assessment of ostial left main lesions can be challenging with OCT and there are no outcomes data with OCT of the left main. Moreover, the left main minimal lumen area cut off for determining that a lesion is functionally significant differs between various populations, hence caution is needed when interpreting those measurements.

  In non-left main lesions, intravascular imaging should not be used for determining their hemodynamic severity and need for revascularization.

• 2.

  Determine the culprit lesion in patients with acute coronary syndromes (ACS)

  The presence of plaque ulceration, erosion, thrombus, or a calcified nodule can help determine the presence and location of culprit lesion(s) in ACS patients. OCT is preferred over IVUS due to higher resolution ( Fig. 13.1 ) .

  

• 3.

  Evaluate angiographically ambiguous lesions, such as suspected dissection, thrombus, and calcified nodule .

• 4.

  Determine cause of stent failure ( in-stent restenosis and stent thrombosis ).

• 5.

  Predict risk of distal embolization: lesions with large lipid core plaque ( Section 25.2.3.2 ) or large thrombus ( Section 20.9.6 ) are at increased risk.

13.1.2

During PCI

• 1.

  Determine the need for lesion preparation before stenting.

  Atherectomy or intracoronary lithotripsy may be required in heavily calcified lesions ( Sections 13.3.6.2.3 and 19.13 ).

• 2.

  Assist with chronic total occlusion crossing (IVUS).

• 3.

  Select stent landing zone free of atherosclerosis to avoid geographic miss.

• 4.

  Choose balloon and stent diameter and length by measuring the lesion length and reference vessel diameter.

• 5.

  Evaluate result after stenting, as follows:

  • Stent expansion.

  • Stent strut apposition.

  • Tissue protrusion.

  • Edge dissection.

  • Geographic miss (residual disease).

• 6.

  Use of IVUS for evaluating the result of PCI can reduce the volume of contrast required and therefore the risk for contrast-induced acute kidney injury ( Section 28.3 ), especially in high-risk patients .

13.1.3

After PCI

• 1.

  Determine the mechanism of stent failure (stent thrombosis and in-stent restenosis).

13.2.1

Goals

Choose the optimal imaging modality to achieve the desired goal.

13.2.2

How?

There are two major intravascular imaging modalities, IVUS and optical coherence tomography (OCT), with important differences as outlined in Table 13.1 . OCT has 10-fold higher resolution (10–15 µm compared with 100 µm for IVUS), but requires blood clearing which is usually achieved by contrast injection, and has low penetration. OCT is superior to IVUS in detecting thrombus, dissection, and assessing plaque morphology and stent strut coverage and apposition.

Imaging modality selection depends on:

• 1.

  The goal of imaging ( Table 13.2 ).

  Table 13.2

  Intravascular imaging modality selection depending on the goal of imaging.

  GOAL	Preferred coronary imaging modality	Comment
  Baseline assessment
  Determine significance of left main lesions	IVUS	OCT can be used for non aorto-ostial lesions
  Determine culprit lesion for ACS	OCT
  Evaluate suspected dissection or thrombus	OCT	OCT has higher resolution than IVUS but may cause extension of the dissection due to contrast injection
  Determine cause of stent failure	IVUS or OCT
  Assess presence, extent, and composition of coronary plaque	IVUS or OCT—IVUS is preferred for assessing plaque volume
  During PCI
  Determine need for lesion preparation before stenting	IVUS or OCT
  Facilitate CTO crossing	IVUS
  Select stent landing zone	IVUS or OCT
  Choose balloon and stent diameter and length	IVUS or OCT
  Evaluate stent expansion	IVUS or OCT
  Evaluate stent apposition	OCT
  Evaluate stent edge dissections	OCT
  Minimize contrast utilization	IVUS

• 2.

  Patient and lesion characteristics (such as lesion location and chronic or acute kidney disease).

• 3.

  Local availability and expertise in acquiring and interpreting intravascular images.

• 4.

  Chronic kidney disease: IVUS is preferred in patients with chronic kidney disease (as it does not require contrast administration) to minimize the risk of acute kidney injury ( Section 28.3 ). Dextran can be used instead of contrast for OCT imaging but has received limited study.

13.3.1

Step 1: Prepare OCT catheter for use

13.3.2

Step 2: Advance OCT catheter past target coronary segment

13.3.3