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ORIGINAL ARTICLE
Year : 2022 | Volume
: 9
| Issue : 5 | Page : 353-358
Our initial experience in optical coherence tomography in peripheral vasculature: A pictorial essay
Vikram Patra1, Rishi Dhillan2, Rohit Mehra3, Ajay Kumar Dabas4, Rahul Merkhed5, VNM Dattatreya Chamiraju2
1 Department of Vascular and Endovascular Surgery, 92 Base Hospital, Jammu and Kashmir, India
2 Department of Vascular and Endovascular Surgery, Army Hospital (R&R), Delhi, India
3 Department of Vascular and Endovascular Surgery, Command Hospital (Southern Command), Pune, Maharashtra, India
4 Department of Vascular and Endovascular Surgery, Command Hospital (Northern Command), Udhampur, Jammu and Kashmir, India
5 Department of Vascular and Endovascular Surgery, Command Hospital (Air Force), Bengaluru, Karnataka, India
Correspondence Address:
Dr. Rohit Mehra
Department of Vascular and Endovascular Surgery, Command Hospital (Southern Command), Pune, Maharashtra
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/ijves.ijves_90_22
Background: Optical coherence tomography (OCT) has been a cornerstone for intracoronary interventions for substantial years. The extrapolation of the benefits of this cutting-edge technology to the peripheral vasculature is still in its nascent stage. This pictorial essay was an endeavor to exhibit the role of OCT as a tool for visualization of peripheral vasculature. Aim: To ascertain adjunctive use of intravascular imaging through OCT of in vivo peripheral human arterial vasculature and to distinguish between lipid-rich, fibrous, and calcified atherosclerotic plaques and other lesions of peripheral vasculature. Subjects and Methods: OCT imaging was performed with commercially available OCT system which is a short mono-rail design with a fiberoptic imaging core integrated into a catheter. The optic imaging core rotates at a rate of 100–180 revolutions/s. OCT pull backs were performed in an automated fashion with simultaneous flushing of iso-osmolar contrast (Visipaque) and normal saline. The visualization of different lesions of peripheral human vasculature through the eye of OCT is presented here as a pictorial essay. Results: OCT has an evolving potential as a tool for monitoring, lesion characterization, assessment of retrogression, progression, and disease stabilization in peripheral vasculature. The technique provides optimal high-resolution lesion characterization akin to an optical biopsy. Conclusions: OCT as a tool for in vivo analysis of human peripheral vasculature provides superlative results. Larger studies will be required to validate a protocol for optimal usage in the peripheral human arteries.
Keywords: Frequency domain optical coherence tomography, optical coherence tomography, peripheral arterial disease, peripheral vasculature
Intracoronary optical coherence tomography (OCT) has been an integral part of cardiac catheterization procedures for times immemorial. Its vivid clinical applications, including plaque morphology assessment, stent placement guidance, and follow-up stent assessment among others, have been proposed and to a certain extent validated too. Initial studies on OCT imaging in peripheral vasculature including femoropopliteal segment and tibial and carotid vessels have demonstrated favorable usage and close correlation with histopathological findings.[1],[2],[3]
Reported literature on in-stent binary restenosis, peristrut low-intensity areas, and in-stent calcified deposits have potentiated the role of OCT in peripheral vasculature, neointimal hyperplasia, and neoatherosclerosis.[3]
The aim of the study was to ascertain adjunctive use of intravascular imaging through OCT of in vivo peripheral human arterial vasculature and to distinguish between lipid-rich, fibrous, and calcified atherosclerotic plaques and other lesions of peripheral vasculature, as the existing data on the subject are scarce despite increasing potential for replication of results shown by intracoronary OCT, in peripheral vasculature. The authors could not recruit any such study from the Indian subcontinent.
Subjects and MethodsWe present a series of representative pre- and postconventional angiographic and OCT images of the corresponding arterial segment being addressed. The images have been chosen to represent different patterns of lesion and segments encountered in peripheral arterial disease. The images belong to patients who had presented to a tertiary care vascular surgery unit with established peripheral arterial disease and had willingly consented to be a part of the study. A total of 16 patients were enrolled in the study, till the writing of these preliminary results.
Inclusion criteria
Age >18 yearsPatients with presence of Rutherford Grade IV-VI lesionsPresence of ≥1 tibial artery involvement requiring endovascular management.Exclusion criteria
Patients who do not have peripheral vasculature appropriate for endovascular interventionEstimated glomerular filtration rate <30 mL/min/1.73 m2 and not on hemodialysisPatient unwilling for recruitment into the study.The near infrared light used in OCT can generate images of as low as 10 microns, vis-à-vis resolution generated by other modalities like intravascular ultrasound which is of the order of 100 μ. One of the critical requirements of intravascular imaging is a fast acquisition and OCT proves second to none with its short acquisition time with imaging speeds of 100 frames/s.
A blood-free field for acquisition is essential in intravascular OCT as blood has strong light-scattering properties. The standard coronary vessel can be freed of blood by a bolus of 12–15 cc contrast; however, extrapolating the same principle to the peripheral vasculature would require a sizable quantity of contrast bolus. This might not be a conducive condition in several patients of peripheral arterial disease who usually have other vascular bed involvement. To answer this stalemate situation, we improvised the agent needed to render the blood vessel free of blood from contrast to normal saline, which is readily available, cost-efficient, and renal safe. In addition to this, we deployed the access sheath (usually a 6F) as close to the area of interest as possible. The endovascular approach to the diseased segment was ipsilateral antegrade access as the currently available OCT hardware fails to engage distal lower limb vasculature through the contralateral retrograde access, due to the OCT catheter length insufficiency.
OCT imaging was performed with commercially available OCT system which is a short monorail design with a fiberoptic imaging core integrated into a catheter. The optic imaging core rotates at a rate of 100–180 revolutions/s. OCT pull backs were performed in an automated fashion with simultaneous flushing of iso-osmolar contrast (Visipaque) and normal saline.[4]
The study was done in accordance with the Declaration of Helsinki.
ResultsPeripheral arterial disease lesions have a myriad of spectrum few of which have been depicted in [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], using OCT imaging and representative pre- and postangiographic digital subtraction images.
Figure 1: Lesion characterization: (a) Calcium is seen as a signal poor, heterogeneous lesion with sharp edges and low absorption (white arrow). (b) Fibrous lesion exhibits as a signal rich (bright-full of light - marked with white line), homogenous lesion with low absorption and diffuse edges. (c) A lipidic lesion also exhibits as signal rich (bright) but has high absorption with shadowy edges
Figure 2: Calcium differentiation in arterial walls: “Superficial” calcium is seen closer to lumen (single white arrow), “deeper” far from the lumen (double white arrow) and 'nodular' abutting the lumen (yellow arrow)
Figure 3: Thrombus type differentiation: (a and d) “Red” thrombus has high absorption and high backscattering, (b and c) “White” thrombus exhibits low absorption and low backscattering
Figure 4: (a) MLA of 1.18 mm2 (yellow circle) with a stenosis of 80.7%. The MLA was preferentially balloon dilated, (b and c) The pre- and postangioplasty digital subtraction angiograms reveal achievement of desired luminal opacification
Figure 5: (a) Organized thrombus in the intimomedial layer, (b) superficial and deep calcium, (c) MLA (1.68 mm2), (d) superficial calcium, (e) macrophages: bright spots in the media (f) fibrous plaque. All the above characters were evident in the same pull back involving single arterial segment
Figure 6: The figure shows a cross-sectional image showing atheromatic plaque with varied fibrotic cap thickness
Figure 7: The cross-sectional image depicts (a and e) plaque erosion, (b) plaque rupture (9 o'clock), (c and d) white thrombus
Figure 8: (a) Cross-sectional OCT image depicting ISR (white arrow) of a stent placed in left superficial femoral artery (double black arrow) and the anterior tibial artery (single black arrow), (b) Digital subtraction images of the segment pre-angioplasty and (c) Post-angioplasty. ISR: In-stent restenosis, OCT: Optical coherence tomography
Figure 9: Cross-sectional OCT image depicting old, organized thrombus with few areas of recanalization (white dotted arrow). OCT: Optical coherence tomography
Figure 10: OCT image depicting ISR, the stent struts have been marked with white arrows. The green line depicts the constricted vessel lumen. ISR: In-stent restenosis, OCT: Optical coherence tomography
Figure 11: OCT image depicting distal anastomotic site of a femoropopliteal bypass graft (ringed extended polytetrafluoroethylene) (marked by yellow circle), with intraluminal thrombus and neointimal hyperplasia. OCT: Optical coherence tomography Discussion This pictorial essay describes the potential dynamic use of intravascular OCT with the high-resolution intravascular imagery providing cardinal insight on the lesions, guiding its optimal management, and enriching the reasoning for endovascular management failure.
In-stent restenosis (ISR) is defined by gradual renarrowing of the stented arterial segment. The natural history of this luminal compromise is still not well understood. The disease has been estimated to have a slow progression and abysmal durability of reintervention due to which few authors have suggested a surveillance program for ISR rather than upfront intervention.[5]
OCT images provide an impressive insight into ISR and might open a new frontier in the surveillance and reintervention strategies in times to come. Precise calculation of luminal compromise and real-time evaluation of technical success for treatment modalities such as atherectomy or balloon angioplasty will be a value addition to the existing modalities.
Calcified plaques have been a source of vexation for the management strategies of peripheral arterial disease, stent under expansion being one such colossal stumbling block. Fujino et al. have validated an OCT-based calcium scoring system to predict stent under expansion. The lesions with calcium having maximum angle >180°, maximum thickness and length >0.5 mm, and >5 mm respectively, may be at risk of stent under expansion, as per the authors.[6]
OCT has an inherent technological edge in detecting thinner and shorter calcium deposits than conventional angiography.[7] OCT also provides details of calcium thickness unlike intravascular ultrasound where the luminal surface of the calcium reflects the sound waves.
Based on OCT, calcified plaques can be further classified into superficial (closer to the lumen), deep (farther away from the lumen), and nodular calcium (extending into the lumen). Combining OCT with ablative techniques like intravascular lithotripsy in peripheral vasculature helps in visualizing the calcium fractures paving way for further intervention like stenting.[8]
Macrophages play a central role in natural history of a plaque by sustaining inflammation and facilitating progression to a complicated plaque morphology.[9] Identification of macrophages in the plaque on OCT imaging, unlike any other current intravascular imaging modalities, adds another dimension to the already nascent concept of macrophage targeting for future antiatherosclerotic therapies.[10]
Additional real-time plaque characteristics assessment like active or impending plaque rupture further facilitates the treatment methodology with better ergonomics.
Anatomical measurements obtained from OCT like minimal luminal area, minimal luminal diameter, and percent luminal area stenosis help in deciding on the functionally significant lesions. It also helps in deciding the ideal location for balloon angioplasty to obtain maximal benefit.
The imaging obtained while using normal saline instead of contrast to render the target artery blood free during pull back of OCT catheter has probably opened another Pandora's box. Intracoronary use of saline as an alternative media has been reported and the same was used as a precedence in this study.[11] We did not encounter any major acquisition flaws and the images revealed no loss of resolution. Kendrick et al. have worked on the hypothesis of alternative flush medias in a small cohort and expressed confidence in the use of alternative flush medias.[12] Larger series would, however, be required to confirm this striking finding and will go a long way in preventing the contrast induced toxicities and side effects.
The current world literature has expressed ample credence and optimism on the use of OCT in peripheral vasculature, though larger studies are required for validation.[13]
ConclusionsThe world of peripheral vascular interventions is revolutionizing and adapting at a rapid pace. As the wheel rolls, newer intravascular imagery will need to keep pace to provide value addition to the diagnostics and assessment of stent dynamics. This pictorial essay potentiates the superior resolution of OCT in providing a finer outline to neointimal hyperplasia, dissection flaps, ISR, and the distinctive, unparalleled in vivo plaque characterization. Stent strut apposition is another such field, which with increasing technological advancement in OCT will benefit the world of vascular sciences.
This real-time arterial wall architecture imaging had redefined the intracoronary imaging and is now knocking the corridors of peripheral vascular architecture. We seem to be standing at redefining endovascular reach of OCT.
Acknowledgment
The authors acknowledge Mr. Sunil Kumar Bhatti and Ms. Jaspreet Kaur for extending the technical guidance.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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