Three-layered structure: INTIMA, MEDIA, ADVENTITIA.
Signal-poor muscular MEDIA layer positioned between the thin high backscattering INTIMA layer and a heterogeneous high backscattering ADVENTITIA layer.
The dark band of media is surrounded by the internal elastic membrane and external elastic membrane, two thin layers of elastic fibers at the border between the intima and media, the media and adventitia.
A fibroatheroma is a combination of a fibrous cap (arrows) and a necrotic core (asterisks). A fibrous cap is a signal-rich tissue layer overlaying a signal-poor region. The necrotic core is a signal-poor region within an atherosclerotic plaque with poorly delineated borders, a rapid signal drop-off and little or no signal backscattering within a lesion that is covered by a fibrous cap. It is imperative to note the distinction between signal-poor regions of calcium which have sharply delineated borders and signal-poor regions of necrotic core which have poorly defined borders.
A thin cap fibroatheroma is defined as a delineated necrotic core with an overlying fibrous cap where the minimal cap thickness (arrows) is less than a predetermined threshold (usually <65 µm). Other data suggests a cap thickness threshold of <55 µm associated with plaque rupture and >85 µm associated with plaque stability.
Macrophages appear as signal-rich, distinct or confluent punctate focal regions (arrows) that exceed the background intensity speckle noise. Macrophages attenuate the OCT light significantly and as a result superficial macrophages can shadow underlying tissue giving the appearance of a necrotic core.
Malapposition (arrows) occurs when the axial distance between the stent strut’s surface to the luminal surface is greater than the strut thickness (including the polymer if present). If this distance is less than the strut thickness, then the strut is considered apposed. Two forms of apposition have been described: protruding, where the endoluminal strut boundary is located above the level of the luminal surface, and embedded, where the endoluminal strut boundary is below the level of the luminal surface.
Thrombus protruding into the lumen (asterisks) in-between or over the stent struts. Within the stent there may be red thrombus (as depicted above) which appears as a highly backscattering and highly attenuating mass or white thrombus which appears as relatively less backscattering with very little signal attenuation.
Appear as a drop in the signal on the abluminal side of the vessel by opaque object. Shadows can completely occlude or may diminish the image intensity of deeper structures. Common objects that create shadows are opaque and include the guidewire and metallic stent struts. Blood in the catheter (arrow) can also cause shadowing.
Prior to stent implantation OCT can provide quick and accurate measurements of the minimal luminal area (MLA), distal and proximal reference areas, diameters and lesion length. OCT can be used to determine landing zones to estimate the optimal stent length.
There are two types of pullback modes: the 75 mm Survey Mode and the 54 mm High Resolution Mode:
There are two measurement methods used to determine stent diameter sizing:
External Elastic Lamina
Benefits of using External Elastic Lamina to determine stent diameter:
1Lancet 2016; 388: 2618–28.
Figure I. External Elastic Lamina. The white arrow below indicates the external elastic lamina (EEL) which is situated directly between the media and adventitia layers.
How to use Luminal measurement to determine stent diameter:
1European Heart Journal, Volume 38, Issue 42, 7 November 2017, Pages 3139–3147.
2Lancet 2016; 388: 2618–28.
B 3D Navigation with Rendered Stent on
C 3D Navigation with Rendered Stent and Flythrough on
3D Rendering of OCT is a new software feature which can be performed real time.3D Rendering can be performed via 3D Navigation or via the Segmental Lumen function.The 3D Navigation 3D Rendering is an excellent function to use to visualize vessel geometry and the ostium of the side branch as seen above.The Segmental Lumen function is a helpful tool to use if visualization within the lumen is desired.
The stent display function is a recently developed tool which color codes malapposed stent struts based on the severity of the malapposed stent strut as seen in Figure A and Figure B. As indicated by the white box noted in Figure A, white, yellow and red colors are provided to each stent strut based on the degree of the malapposition. As depicted in the above in figures via the white arrows, these color coded regions appear on the angiogram and on the longitudinal and cross sectional OCT images. Simultaneous measurements can be made as well.
The following OCT detected tissue modifications may be seen post atherectomy:1
Type I. Superficial intimal flap with smooth luminal border:
Nodule: flaps length <0.5 mm. (Figure A)
Type II. Deep intimal cut with irregular luminal border:
Fissure: 0–0.5 mm depth and 1 mm length. (Figure B)
Gutter: 0.5–1 mm depth and >1 mm length.
Type III. Deeper intimal-medial dissection with non-cylindrical lumen:
Crater: <1 mm depth and <3 mm length. (Figure C)
Lacuna: >1 mm depth and >3 mm length.
-There is no significance difference between the rate of each tissue modification seen with OA and RA. Craters and Lacunae occur in a third of lesions of OA and RA.1
-There is a difference between OA and RA regarding the severity of each tissue modification. Post OA lacunae were significantly deeper and have a bulging appearance.1
-Post OA modification of calcified plaque resulted in better stent apposition and expansion.1
-Overall, OA results in more severe tissue modification as compared to RA which may explain better stent placement but at the same time has higher risk of deep dissections, which may lead to perforation.1
1Catheter Cardiovasc Interv, 2015 Nov 15;86(6):1024-32.
A major edge dissection is defined as a dissection ≥60 degrees of the circumference and/or ≥3 mm in length. An additional stent implantation may be considered for a major edge dissection, especially if it is associated with an intra-dissection lumen <90% of the respective proximal or distal reference area.1Stent edge dissections may be covered with an additional stent as illustrated in Figure I or observed without further intervention as seen in Figure II.
1Lancet 2016; 388:2618-28.
Figure I. An example of a stent edge dissection (white arrow) measuring to be 127 degrees of the lumen circumference in the cross sectional OCT image and 6.2 mm in length (yellow arrow) as measured in the longitudinal OCT L-mode. The following image demonstrates the same patient post stenting over the stent edge dissection. There is no longer a dissection flap present in the cross sectional OCT image.
Figure II. An example of a small distal stent edge dissection which was less than 60 degrees of the lumen circumference and less than 3 mm. A decision was made that no further intervention was required for this case.
It is recommended that if stent malapposition is detected, further stent expansion should be considered during the intervention if there is stent under-expansion. Stent under-expansion is defined as an MSA of the proximal segment <90% of the proximal reference lumen area or an MSA of the distal segment <90% of the distal reference lumen area.1
1Lancet 2016; 388:2618-28.
Figure I. An example of a malapposed stent which met criteria for stent under-expansion. A decision was made to further expand the stent with multiple balloon inflations. The following image demonstrates the same vessel with significantly improved apposition of the stent struts.
The management of tissue prolapse seen between stent struts is controversial. While there is an association between in-stent tissue prolapse and myocardial infarction size likely due to the higher incidence of tissue prolapse seen with a larger thrombus burden resulting in larger myocardial infarctions, better characterization of prolapse type and extent are needed with OCT to determine whether some types of tissue prolapse carry a true clinical significance.1
1JACC Cardiovascular Interventions. Instrastent tissue prolapse and late cardiac events: innocent bystander or culprit? 2016 July; Vol 9, issue 14.
The OCT pullback of the RCA proximal lesion showed a significant stenosis with fibrous plaque and fibroatheroma. Distal reference vessel had a mean lumen diameter of 3.14 mm and a mean of external elastic lamina (EEL) of 4.02 mm. Proximal reference showed a mean lumen diameter of 3.44 mm and a mean EEL of 4.28 mm. The lesion length was 12.0 mm. An appropriate stent size should be 3.25 mm on the basis of luminal measurement, while it should be 3.75 mm according to EEL. 3.5/12-mm drug eluting stent was implanted on operator’s discretion.
Post stent OCT showed a good stent expansion and apposition. In-stent dissections around the 35 mm mark of the video were observed but stent edge dissection was not detected by the OCT pullback. These OCT findings confirm the successful stent deployment and did not warrant additional post dilation