13.1
When to do coronary intravascular imaging?
Coronary intravascular imaging can be performed before, during, and after PCI to determine the need for coronary revascularization, and help plan and optimize the result of PCI, as described below. Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) are the currently available modalities for coronary intravascular imaging.
Although some operators have advocated imaging of all coronary lesions undergoing PCI , the benefit of intravascular imaging appears greater in more complex lesions, such as :
- 1.
Left main lesions.
- 2.
Long lesions .
- 3.
Chronic total occlusions .
- 4.
Stent failure (in-stent restenosis or stent thrombosis).
- 5.
Severely calcified lesions.
- 6.
Complex bifurcations.
- 7.
Acute coronary syndrome lesions.
- 8.
To minimize contrast administration (with IVUS) .
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 ) .
Figure 13.1
Use of OCT to determine the presence and location of the culprit lesion in a patient with STEMI without an angiographically obvious culprit lesion. Coronary angiography demonstrated a mild-to-moderate lesion in the proximal left anterior descending artery ( arrow , panel A) in a 44-year-old woman with ST-segment elevation myocardial infarction. OCT showed a ruptured fibrous cap with red thrombus in the proximal LAD (panel B). Cardiac magnetic resonance revealed T2 signal hyperintensity (panel C) along with subendocardial late gadolinium enhancement ( arrows , panel D) in the anteroseptal wall.
Reproduced with permission from Opolski MP, Spiewak M, Marczak M, et al. Mechanisms of myocardial infarction in patients with nonobstructive coronary artery disease: results from the optical coherence tomography study. JACC Cardiovasc Imaging 2019;12:2210–21.
- 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
Imaging modality selection
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.
| IVUS | OCT | |
|---|---|---|
| Requires contrast administration | No | Yes |
| Image resolution | +/++ | +++ |
| Tissue penetration | +++ | + |
| Speed of pullback | + | +++ |
| Ease of image interpretation | ++ | +++ |
| Need for predilation of severe lesions | + | ++ |
| Imaging thrombus | + | +++ |
| Imaging calcium | ++ | +++ |
| Imaging aorto-ostial lesions | +++ | + |
| Plaque morphology | ++ | +++ |
| Imaging stents | ++ | +++ |
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
OCT step-by-step
Starting point : The guide catheter is well engaged in the target coronary vessel and a guidewire has been advanced across the coronary area of interest. Moreover, unless contraindicated, intracoronary nitroglycerin has been administered.
Usually a ≥6 French guide catheter is needed for adequate contrast injection to create a blood-free field with manual injection. Injection of contrast through a 5 French guide catheter would require a power injector to adequately fill the lumen and allow high-quality OCT acquisition.
13.3.1
Step 1: Prepare OCT catheter for use
13.3.1.1
Goal
Prepare the OCT catheter for use.
13.3.1.2
How?
- 1.
The OCT catheter is removed from the sterile packaging.
- 2.
The OCT catheter is flushed with 100% contrast.
- 3.
The OCT pullback device is inserted in a dedicated sterile bag.
- 4.
The OCT catheter is connected to the OCT pullback device.
13.3.1.3
What can go wrong?
13.3.1.3.1
Failure of OCT catheter to image
Causes:
- •
Defective catheter.
- •
Kinking of the catheter shaft.
- •
Damage of the pullback device (for example by improper disconnection of an OCT catheter from the pullback device).
- •
Damage of the imaging lens during wire insertion on the short monorail segment.
Prevention:
- •
Gentle and careful equipment handling.
Treatment:
- •
Catheter malfunction: replace with new catheter.
- •
Pullback device malfunction: call for repair.
13.3.2
Step 2: Advance OCT catheter past target coronary segment
13.3.2.1
Goal
Advance the OCT catheter distal to the target coronary vessel segment.
13.3.2.2
How?
After distal wiring of the target vessel using a 0.014 in. coronary guidewire, the OCT catheter is advanced distal to the coronary area of interest. The OCT catheter has 3 markers: the most distal is at the catheter tip, the middle is at the wire exit port, and the most proximal is 50 mm from the imaging lens. To ensure that the lesion of interest is imaged, the middle marker should be positioned at least 5–7 mm distal to the target site for imaging.
The two proximal imaging markers can help determine the optimal mode for image acquisition (high-resolution vs survey mode, see step 5 below), as they demarcate the approximate length of the high-resolution imaging run. The two proximal markers are integrated within the imaging core, hence they track with the movement of the imaging lens during pullback.
13.3.2.3
Challenges
13.3.2.3.1
Failure to advance OCT catheter through the lesion
Causes:
- •
Severely stenotic lesion.
- •
Severe calcification.
- •
Severe tortuosity.
- •
Poor guide catheter support.
Prevention:
- •
Severely stenosed or calcified lesions may need balloon predilation, to allow: (1) advancement of the OCT catheter and (2) contrast penetration through the lesion for visualization.
- •
Obtaining good guide catheter support, as outlined in Section 9.5.8.
- •
Consider using a supportive coronary guidewire in severely tortuous anatomy.
Treatment:
- •
Remove OCT catheter and predilate the lesion with a small balloon.
- •
Increase guide catheter support.
13.3.2.4
What can go wrong?
13.3.2.4.1
Kinking of the OCT catheter
Causes:
- •
Forceful OCT catheter advancement.
Prevention:
- •
Lesion preparation for highly stenotic lesions.
- •
Avoid forceful OCT catheter advancement.
Treatment:
- •
Replace catheter with a new one if malfunction persists after straightening the OCT catheter.
13.3.3
Step 3: Flush OCT catheter
13.3.3.1
Goal
Remove any blood from within the OCT catheter to enable accurate vessel visualization.
13.3.3.2
How?
The OCT catheter is flushed with 100% contrast followed by confirmation of clearance of blood ( Fig. 13.2 ) and air from within the catheter. This step is important to prevent shadow (from air) or attenuation (from blood) artifacts during OCT image acquisition.
13.3.4
Step 4: Calibration
13.3.4.1
Goal
Calibrate the OCT catheter to allow automated measurements.
13.3.4.2
How?
Push the calibration button. To ensure accurate calibration, do not calibrate while purging the catheter.
13.3.5
Step 5: Perform OCT imaging run
13.3.5.1
Goal
Obtain high-quality OCT images of the target coronary segment.
13.3.5.2
How?
- 1.
The desired pullback length is selected (54 mm for the high-resolution mode vs 75 mm for the survey mode) for the Illumien OPTIS system (Abbott Vascular) ( Table 13.3 ). The OCT survey mode provides a rapid pullback of 75 mm over 2.1 seconds (pullback speed 36 mm/sec) (i.e. 5 frames/mm) and is the standard mode for pre-PCI imaging. The high-resolution mode images a 54 mm segment at 10 frames per mm over 3 seconds, providing twice the frame density as the survey mode and is the optimal acquisition method when high detail is desired.
