Intracoronary optical diagnostics current status, limitations, and potential

Management of vulnerable patient phenotypes and acute coronary syndrome mechanisms

Atherosclerosis is a chronic vascular disease. Its prevalence increases with aging. However, atherosclerosis may also affect young subjects without significant exposure to the classical risk factors. Recent evidence indicates clonal hematopoiesis of indeterminate potential (CHIP) as a novel cardiovascular risk factor that should be suspected in young patients. CHIP represents a link between impaired bone marrow and atherosclerosis. Atherosclerosis may present with an acute symptomatic manifestation or subclinical events that favor plaque growth. The outcome of a plaque relies on a balance of innate and environmental factors. These factors can influence the processes that initiate and propagate acute plaque destabilization leading to intraluminal thrombus formation or subclinical vessel healing. Thirty years ago, the first autopsy study revealed that coronary plaques can undergo rupture even in subjects without a known cardiovascular history. Nowadays, cardiac magnetic resonance studies demonstrate that this phenomenon is not rare. Myocardial infarction is mainly due to plaque rupture and plaque erosion that have different pathophysiological mechanisms. Plaque erosion carries a better prognosis as compared to plaque rupture. Thus, a tailored conservative treatment has been proposed and some studies demonstrated it to be safe. On the contrary, plaque rupture is typically associated with inflammation and anti-inflammatory treatments have been proposed in response to persistently elevate biomarkers of systemic inflammation. In conclusion, atherosclerosis may present in different forms or phenotypes. Vulnerable patient phenotypes, identified by using intravascular imaging techniques, biomarkers, or even genetic analyses, are characterized by distinctive pathophysiological mechanisms. These different phenotypes merit tailored management.

Optical frequency domain imaging (OFDI) represents a novel technique for the diagnosis of giant cell arteritis

BACKGROUND/OBJECTIVES

Giant cell arteritis (GCA) is an inflammatory vascular disease in which prompt and accurate diagnosis is critical. The efficacy of temporal artery biopsy (TAB) is limited by 'skip' lesions and a delay in histological analysis. This first-in-man ex-vivo study aims to assess the accuracy of optical frequency domain imaging (OFDI) in diagnosing GCA.

SUBJECTS/METHODS

29 TAB samples of patients with suspected GCA were submerged in 0.9% sodium chloride and an OFDI catheter was passed through the lumen to create cross-sectional images prior to histological analysis. The specimens were then preserved in formalin for histological examination. Mean intimal thickness (MIT) on OFDI was measured, and the presence of both multinucleate giant cells (MNGCs) and fragmentation of the internal elastic lamina (FIEL) was assessed and compared with histology, used as the diagnostic gold standard.

RESULTS

MIT in patients with/without histological evidence of GCA was 0.425 mm (±0.43) and 0.13 mm (±0.06) respectively compared with 0.215 mm (±0.09) and 0.135 mm (±0.07) on OFDI. MIT measured by OFDI was significantly higher in patients with histologically diagnosed arteritis compared to those without (p = 0.0195). For detecting FIEL and MNGCs, OFDI had a sensitivity of 75% and 28.6% and a specificity of 100% and 77.3% respectively. Applying diagnostic criteria of MIT > 0.20 mm, or the presence of MNGCs or FIEL, the sensitivity of detecting histological arteritis using OFDI was 91.4% and the specificity 94.1%.

CONCLUSIONS

OFDI provided rapid imaging of TAB specimens achieving a diagnostic accuracy comparable to histological examination. In-vivo imaging may allow imaging of a longer arterial section.

Role of intravascular ultrasound and optical coherence tomography in intracoronary imaging for coronary artery disease: a systematic review

Coronary angiography has long been the standard for coronary imaging, but it has limitations in assessing vessel wall anatomy and guiding percutaneous coronary intervention (PCI). Intracoronary imaging techniques like intravascular ultrasound (IVUS) and optical coherence tomography (OCT) can overcome these limitations. IVUS uses ultrasound and OCT uses near-infrared light to visualize coronary pathology in unique ways due to differences in temporal and spatial resolution. These techniques have evolved to offer clinical utility in plaque characterization and vessel assessment during PCI. Meta-analyses and adjusted observational studies suggest that both IVUS and OCT-guided PCI correlate with reduced cardiovascular risks compared to angiographic guidance alone. While IVUS demonstrates consistent clinical outcome benefits, OCT evidence is less robust. IVUS has progressed from early motion detection to high-resolution systems, with smaller compatible catheters. OCT utilizes near infrared light to achieve unparalleled resolutions, but requires temporary blood clearance for optimal imaging. Enhanced visualization and guidance make IVUS and OCT well-suited for higher risk PCI in patients with diabetes and chronic kidney disease by allowing detailed visualization of complex lesions and ensuring optimal stent deployment and positioning in PCI for patients with type 2 diabetes and chronic kidney disease, improving outcomes. IVUS and recent advancements in zero- and low-contrast OCT techniques can reduce nephrotoxic contrast exposure, thus helping to minimize PCI complications in these high-risk patient groups. IVUS and OCT provide valuable insights into coronary pathophysiology and guide interventions precisely compared to angiography alone. Both have comparable clinical outcomes, emphasizing the need for tailored imaging choices based on clinical scenarios. Continued refinement and integration of intravascular imaging will likely play a pivotal role in optimizing coronary interventions and outcomes. This systematic review aims to delve into the nuances of IVUS and OCT, highlighting their strengths and limitations as PCI adjuncts.

Plaque burden estimated from optical coherence tomography with deep learning: In vivo validation using co-registered intravascular ultrasound

OBJECTIVES

The objective of the present study was to compare plaque burden (PB) calculated from optical coherence tomography (OCT) using deep learning (DL) with PB derived from co-registered intravascular ultrasound (IVUS).

BACKGROUND

A DL algorithm was developed for automated plaque characterization and PB quantification from OCT images. However, the performance of this algorithm for PB quantification has not been validated.

METHODS

Five-year follow-up OCT and IVUS images from 15 patients implanted with bioresorbable vascular scaffold (BVS) at baseline were analyzed. Precise co-registration for 72 anatomical slices was achieved utilizing unique BVS radiopaque markers. PB derived from OCT DL and IVUS were compared. OCT cross-sections were divided into four subgroups with different media visibility level. The impact of media visibility on the numerical difference between OCT-derived and IVUS-derived PB was investigated. The stent sizes selected by OCT DL and IVUS were compared.

RESULTS

Sixty-four paired OCT and IVUS cross-sections were compared. OCT DL showed good concordance with IVUS for PB assessment (ICC = 0.81, difference = -3.53 ± 6.17%, p < 0.001). The numerical difference between OCT DL-derived PB and IVUS-derived PB was not substantially impacted by missing segments of media visualization (p = 0.21). OCT DL showed a diagnostic accuracy of 92% in identifying PB > 65%. The stent sizes selected by OCT DL were smaller compared to the ones selected by IVUS (difference = 0.30 ± 0.34 mm, p < 0.001).

CONCLUSIONS

The DL algorithm provides a feasible and reliable method for automated PB estimation from OCT, irrespective of media visibility. OCT DL showed good diagnostic accuracy in identifying PB > 65%, revealing its potential to complement conventional OCT imaging.

Automatic Classification of A-Lines in Intravascular OCT Images Using Deep Learning and Estimation of Attenuation Coefficients

Intravascular Optical Coherence Tomography (IVOCT) images provide important insight into every aspect of atherosclerosis. Specifically, the extent of plaque and its type, which are indicative of the patient’s condition, are better assessed by OCT images in comparison to other in vivo modalities. A large amount of imaging data per patient require automatic methods for rapid results. An effective step towards automatic plaque detection and plaque characterization is axial lines (A-lines) based classification into normal and various plaque types. In this work, a novel automatic method for A-line classification is proposed. The method employed convolutional neural networks (CNNs) for classification in its core and comprised the following pre-processing steps: arterial wall segmentation and an OCT-specific (depth-resolved) transformation and a post-processing step based on the majority of classifications. The important step was the OCT-specific transformation, which was based on the estimation of the attenuation coefficient in every pixel of the OCT image. The dataset used for training and testing consisted of 183 images from 33 patients. In these images, four different plaque types were delineated. The method was evaluated by cross-validation. The mean values of accuracy, sensitivity and specificity were 74.73%, 87.78%, and 61.45%, respectively, when classifying into plaque and normal A-lines. When plaque A-lines were classified into fibrolipidic and fibrocalcific, the overall accuracy was 83.47% for A-lines of OCT-specific transformed images and 74.94% for A-lines of original images. This large improvement in accuracy indicates the advantage of using attenuation coefficients when characterizing plaque types. The proposed automatic deep-learning pipeline constitutes a positive contribution to the accurate classification of A-lines in intravascular OCT images.

Method for parametric imaging of attenuation by intravascular optical coherence tomography

Catheter-based intravascular optical coherence tomography (IVOCT) is a powerful imaging modality for visualization of atherosclerosis with high resolution. Quantitative characterization of various tissue types by attenuation coefficient (AC) extraction has been proven to be a potentially significant application of OCT attenuation imaging. However, existing methods for AC extraction from OCT suffer from the challenge of variability in complex tissue types in IVOCT pullback data such as healthy vessel wall, mixed atherosclerotic plaques, plaques with a single component and stent struts, etc. This challenge leads to the ineffectiveness in the tissue differentiation by AC representation based on single scattering model of OCT signal. In this paper, we propose a novel method based on multiple scattering model for parametric imaging of optical attenuation by AC retrieval from IVOCT images conventionally acquired during cardiac catheterization. The OCT signal characterized by the AC is physically modeled by Monte Carlo simulation. Then, the pixel-wise AC retrieval is achieved by iteratively minimizing an error function regarding the modeled and measured backscattered signal. This method provides a general scheme for AC extraction from IVOCT without the premise of complete attenuation of the incident light through the imaging depths. Results of computer-simulated and clinical images demonstrate that the method can avoid overestimation at the end of the depth profile in comparison with the approaches based on the depth-resolved (DR) model. The energy error depth and structural similarity are improved by about 30% and 10% respectively compared with DR. It provides a useful way to differentiate and characterize arterial tissue types in IVOCT images.

Coronary Atherosclerosis Imaging

Identifying patients at increased risk of coronary artery disease, before the atherosclerotic complications become clinically evident, is the aim of cardiovascular prevention. Imaging techniques provide direct assessment of coronary atherosclerotic burden and pathological characteristics of atherosclerotic lesions which may predict the progression of disease. Atherosclerosis imaging has been traditionally based on the evaluation of coronary luminal narrowing and stenosis. However, the degree of arterial obstruction is a poor predictor of subsequent acute events. More recent techniques focus on the high-resolution visualization of the arterial wall and the coronary plaques. Most acute coronary events are triggered by plaque rupture or erosion. Hence, atherosclerotic plaque imaging has generally focused on the detection of vulnerable plaque prone to rupture. However, atherosclerosis is a dynamic process and the plaque morphology and composition may change over time. Most vulnerable plaques undergo progressive transformation from high-risk to more stable and heavily calcified lesions, while others undergo subclinical rupture and healing. Although extensive plaque calcification is often associated with stable atherosclerosis, the extent of coronary artery calcification strongly correlates with the degree of atherosclerosis and with the rate of future cardiac events. Inflammation has a central role in atherogenesis, from plaque formation to rupture, hence in the development of acute coronary events. Morphologic plaque assessment, both invasive and non-invasive, gives limited information as to the current activity of the atherosclerotic disease. The addition of nuclear imaging, based on radioactive tracers targeted to the inflammatory components of the plaques, provides a highly sensitive assessment of coronary disease activity, thus distinguishing those patients who have stable disease from those with active plaque inflammation.

Plaque burden influences accurate classification of fibrous cap atheroma by in vivo optical coherence tomography in a porcine model of advanced coronary atherosclerosis

AIMS

In vivo validation of coronary optical coherence tomography (OCT) against histology and the effects of plaque burden (PB) on plaque classification remain unreported. We aimed to investigate this in a porcine model with human-like coronary atherosclerosis.

METHODS AND RESULTS

Five female Yucatan D374Y-PCSK9 transgenic hypercholesterolaemic minipigs were implanted with a coronary shear-modifying stent to induce advanced atherosclerosis. OCT frames (n=201) were obtained 34 weeks after implantation. Coronary arteries were perfusion-fixed, serially sectioned and co-registered with OCT using a validated algorithm. Lesions were adjudicated using the Virmani classification and PB assessed from histology. OCT had a high sensitivity, but modest specificity (92.9% and 74.6%), for identifying fibrous cap atheroma (FCA). The reduced specificity for OCT was due to misclassification of plaques with histologically defined pathological intimal thickening (PIT) as FCA (46.1% of the frames with histological PIT were misclassified). PIT lesions misclassified as FCA by OCT had a statistically higher PB than in other OCT frames (median 32.0% versus 13.4%; p<0.0001). Misclassification of PIT lesions by OCT occurred when PB exceeded approximately 20%.

CONCLUSIONS

Compared with histology, in vivo OCT classification of FCA had high sensitivity but reduced specificity due to misclassification of PITs with high PB.

Optical and x-ray technology synergies enabling diagnostic and therapeutic applications in medicine

X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radio-optical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine.

Translating Evidence of HDL and Plaque Regression

Considerable evidence from preclinical and population studies suggests that HDLs (high-density lipoproteins) possess atheroprotective properties. Reports from HDL infusion studies in animals and early clinical imaging trials reported evidence of plaque regression. These findings have stimulated further interest in developing new agents targeting HDL. However, the results of more recent imaging studies in the setting of high-intensity statin use have been disappointing. As the concept of plaque changes with HDL therapeutics evolves and imaging technology to evaluate these effects advances, there will become increasing opportunity to determine the effects of HDL agents on atherosclerotic plaque (Graphic Abstract).

In vivo Molecular Imaging of Glutamate Carboxypeptidase II Expression in Re-endothelialisation after Percutaneous Balloon Denudation in a Rat Model

The short- and long-term success of intravascular stents depends on a proper re-endothelialisation after the intervention-induced endothelial denudation. The aim of this study was to evaluate the potential of in vivo molecular imaging of glutamate carboxypeptidase II (GCPII; identical with prostate-specific membrane antigen PSMA) expression as a marker of re-endothelialisation. Fifteen Sprague Dawley rats underwent unilateral balloon angioplasty of the common carotid artery (CCA). Positron emission tomography (PET) using the GCPII-targeting tracer [¹⁸F]DCFPyL was performed after 5-21 days (scan 60-120 min post injection). In two animals, the GCPII inhibitor PMPA (23 mg/kg BW) was added to the tracer solution. After PET, both CCAs were removed, dissected, and immunostained with the GCPII specific antibody YPSMA-1. Difference of GCPII expression between both CCAs was established by PCR analysis. [¹⁸F]DCFPyL uptake was significantly higher in the ipsilateral compared to the contralateral CCA with an ipsi-/contralateral ratio of 1.67 ± 0.39. PMPA blocked tracer binding. The selective expression of GCPII in endothelial cells of the treated CCA was confirmed by immunohistological staining. PCR analysis verified the site-specific GCPII expression. By using a molecular imaging marker of GCPII expression, we provide the first non-invasive in vivo delineation of re-endothelialisation after angioplasty.

Spontaneous Coronary Artery Dissection: Diagnosis and Management

PURPOSE OF REVIEW

Spontaneous coronary artery dissection (SCAD) is a non-iatrogenic and non-traumatic separation of the coronary arterial wall. While SCAD represents an important cause of myocardial infarction, optimal diagnostic and therapeutic options remain challenging. We sought to review recent studies and provide an update on diagnosis and management of SCAD.

RECENT FINDINGS

Coronary angiography is the first-line diagnostic modality for SCAD, with three angiographic features commonly observed in SCAD: type 1 (pathognomonic angiographic appearance with contrast staining of the arterial wall), type 2 (long coronary stenosis), and type 3 (focal tubular stenosis). In addition, adjunctive intracoronary imaging can aid in identifying coronary dissections. Conservative management with beta-blockers and aspirin remains the mainstay of therapy. However, patients with high-risk features and recurrent symptoms may require revascularization. Several techniques have been reported, such as long stents to seal the entire length of the dissection, stepwise stenting starting at the distal edge followed by proximal edge stenting, use of bioabsorbable stents, and cutting balloon angioplasty. Furthermore, cardiac rehabilitation appears to be safe and offers significant benefits for patients with SCAD. Coronary angiographic classification contributed to the increased recognition of SCAD in recent years. Selecting the most suitable and appropriate therapy based on accurate diagnosis is the cornerstone of management in SCAD. Further studies are needed to establish optimal treatment of SCAD depending on anatomical and/or clinical features.

Reversed single string technique for coronary bifurcation stenting-First report of case demonstrations in vitro

OBJECTIVES

This work reports the concept and the practical feasibility of Reversed Single String bifurcation stenting technique by demonstrating three in vitro cases.

BACKGROUND

Provisional T stenting is the most used interventional technique to treat coronary bifurcation lesions. However, after main branch (MB) stenting, treatment of the side branch (SB) may become indicated to provide a good final result. Currently applied methods all have their structural limitations with respect to wall coverage, multiple strut layers, poor apposition rate. We reasoned that reversing the Single String technique principle could be used as a bail out after inadequate provisional T stenting.

METHODS AND RESULTS

We simulated in three silicone bifurcation phantoms a scenario whereby stenting the SB becomes indicated after provisional T stenting. Thereafter, as first step of Reversed Single String, a stent was deployed into the SB ostium with one single protruding stent-cell into the MB. After wiring that stent-cell and positioning MB balloon across it, final kissing balloon dilation was performed. Results of the in vitro Reversed Single String cases were evaluated by X-ray angiography, optical frequency domain imaging, and 3-Dimensional (3D) reconstruction (OFDI). Each case was successfully performed and completed. In the bifurcation area, perfect apposition was documented in over 81% of the struts. Malapposition remained below 4% of struts in each case. 3D OFDI reconstruction did not reveal any strut fracture.

CONCLUSION

This report suggests that Reversed Single String technique might offer a potential bail out solution for provisional T-stenting cases, when treatment of the SB becomes indicated. © 2017 Wiley Periodicals, Inc.

Microcalcifications, Their Genesis, Growth, and Biomechanical Stability in Fibrous Cap Rupture

For many decades, cardiovascular calcification has been considered as a passive process, accompanying atheroma progression, correlated with plaque burden, and apparently without a major role on plaque vulnerability. Clinical and pathological analyses have previously focused on the total amount of calcification (calcified area in a whole atheroma cross section) and whether more calcification means higher risk of plaque rupture or not. However, this paradigm has been changing in the last decade or so. Recent research has focused on the presence of microcalcifications (μCalcs) in the atheroma and more importantly on whether clusters of μCalcs are located in the cap of the atheroma. While the vast majority of μCalcs are found in the lipid pool or necrotic core, they are inconsequential to vulnerable plaque. Nevertheless, it has been shown that μCalcs located within the fibrous cap could be numerous and that they behave as an intensifier of the background circumferential stress in the cap. It is now known that such intensifying effect depends on the size and shape of the μCalc as well as the proximity between two or more μCalcs. If μCalcs are located in caps with very low background stress, the increase in stress concentration may not be sufficient to reach the rupture threshold. However, the presence of μCalc(s) in the cap with a background stress of about one fifth to one half the rupture threshold (a stable plaque) will produce a significant increase in local stress, which may exceed the cap rupture threshold and thus transform a non-vulnerable plaque into a vulnerable one. Also, the classic view that treats cardiovascular calcification as a passive process has been challenged, and emerging data suggest that cardiovascular calcification may encompass both passive and active processes. The passive calcification process comprises biochemical factors, specifically circulating nucleating complexes, which would lead to calcification of the atheroma. The active mechanism of atherosclerotic calcification is a cell-mediated process via cell death of macrophages and smooth muscle cells (SMCs) and/or the release of matrix vesicles by SMCs.

In vivo label-free structural and biochemical imaging of coronary arteries using an integrated ultrasound and multispectral fluorescence lifetime catheter system

Existing clinical intravascular imaging modalities are not capable of accurate detection of critical plaque pathophysiology in the coronary arteries. This study reports the first intravascular catheter combining intravascular ultrasound (IVUS) with multispectral fluorescence lifetime imaging (FLIm) that enables label-free simultaneous assessment of morphological and biochemical features of coronary vessels in vivo. A 3.7 Fr catheter with a fiber-optic channel was constructed based on a 40 MHz clinical IVUS catheter. The ability to safely acquire co-registered FLIm-IVUS data in vivo using Dextran40 solution flushing was demonstrated in swine coronary arteries. FLIm parameters from the arterial wall were consistent with the emission of fluorophores present in healthy arterial wall (collagen, elastin). Additionally, structural and biochemical features from atherosclerotic lesions were acquired in ex vivo human coronary samples and corroborated with histological findings. Current results show that FLIm parameters linked to the amount of structural proteins (e.g. collagen, elastin) and lipids (e.g. foam cells, extracellular lipids) in the first 200 μm of the intima provide important biochemical information that can supplement IVUS data for a comprehensive assessment of plaques pathophysiology. The unique FLIm-IVUS system evaluated here has the potential to provide a comprehensive insight into atherosclerotic lesion formation, diagnostics and response to therapy.

Intravascular imaging in coronary artery disease

Although it is the method used by most interventional cardiologists to assess the severity of coronary artery disease and guide treatment, coronary angiography has many known limitations, particularly the fact that it is a lumenogram depicting foreshortened, shadowgraph, planar projections of the contrast-filled lumen rather than imaging the diseased vessel itself. Intravascular imaging-intravascular ultrasound and more recently optical coherence tomography-provide a tomographical or cross-sectional image of the coronary arteries. These techniques are clinically useful to answer questions such as whether the stenosis is clinically relevant; the identification of the culprit lesion; or whether the plaque (or patient) is at high risk of future adverse events. They can also be used to optimise stent implantation to minimise stent-related adverse events, provide answers to the likelihood of distal embolisation or peri-procedural myocardial infarction during stent implantation, and provide reasons for stent thrombosis or restenosis. This review considers the usefulness of intravascular imaging in day-to-day practice.

Lipid Lowering Therapy to Modify Plaque Microstructures

Due to the pandemics of obesity and diabetes mellitus, especially in the Western countries, atherosclerotic cardiovascular disease (ASCVD) has become a major health burden and is expected to increase in the future. Modifying lipid targets, especially low-density lipoprotein cholesterol (LDL-C) level, has become the first-line therapy for primary and secondary prevention of ASCVD. Intravascular imaging modalities have contributed to elucidating clinical efficacy of lipid lowering therapy on atherosclerotic plaques. Optical coherence tomography (OCT) is a high-resolution imaging tool enables visualization of plaque microstructures associated with its instability. This modality has demonstrated favorable changes in plaque microstructures under lowering LDL-C level. In addition, clinical studies using OCT have suggested potential association of other lipid targets, including triglyceride and high-density lipoprotein cholesterol with plaque microstructures. Given continuing cardiovascular risks despite statin therapy, OCT will be an important imaging modality to evaluate novel therapeutic approaches that potentially modulates plaque instability.

Plaque burden, microstructures and compositions underachieving very low LDL-C levels

PURPOSE OF REVIEW

To summarize the impact of lowering LDL-C on plaque progression, microstructures and compositions.

RECENT FINDINGS

Low-density lipoprotein cholesterol (LDL-C) is a major therapeutic target to prevent atherosclerotic cardiovascular disease. Intravascular imaging has elucidated antiatherosclerotic effects of lowering LDL-C in vivo. Intensive control of LDL-C with a statin has been shown to slow plaque progression and induce its regression if very low LDL-C level is achieved. This therapeutic approach has been also demonstrated to modulate plaque microstructures and compositions. These mechanistic insights on intravascular imaging support the benefit of lowering LDL-C in achieving better cardiovascular outcomes.

SUMMARY

Lowering LDL-C level has become the first-line therapy in the primary and secondary prevention settings. The effects of lowering LDL-C on plaque progression, microstructures and compositions will be reviewed in this article.

Evaluation of the characterization of thrombi in vitro by optical coherence tomography

AIM

The purpose of this study was to provide a new assessable method of the optical coherence tomography (OCT) in characterization of thrombi with different concentrations of red blood cell (RBC).

METHODS AND RESULTS

A series of thrombus models were constructed by using human blood in vitro. The thrombi were made by using human blood with different concentration of RBC (from 1% to 35%). Then tip of an FD-OCT catheter was put on the top of the thrombus to scan. After OCT being performed, all the acquired images were processed by a newly developed software to analyze the RBC levels related thrombus characteristics including attenuation, backscattering and light penetration depth. The attenuation was correlated with RBC concentration up to 9%. However, no apparent change was observed in thrombus with RBC concentration range from 10% to 35%. The same trend was seen in backscattering and penetration depth.

CONCLUSIONS

FD-OCT is able to detect thrombus with different RBC concentrations up to 9%.

Optical Coherence Tomography in the Diagnosis and Management of Spontaneous Coronary Artery Dissection

Spontaneous coronary artery dissection (SCAD) is an infrequent condition that has been underdiagnosed and misdiagnosed. The use of intracoronary imaging with intravascular ultrasound or optical coherence tomography enables the accurate diagnosis of this challenging condition. Diagnostic and management algorithms have been proposed to improve the diagnosis and therapeutic stratification of SCAD. Optical coherence tomography has superior spatial resolution than intravascular ultrasound, and is instrumental in the diagnosis of SCAD cases where angiographic findings are ambiguous for confirming SCAD. Understanding the role and appropriate and careful use of this technology is expected to improve the diagnosis of SCAD, and also improve outcomes with percutaneous coronary intervention, when clinically indicated.

Fundamentals of Optical Coherence Tomography: Image Acquisition and Interpretation

Optical coherence tomography (OCT) is an intravascular imaging modality that enables high-resolution cross-sectional imaging of coronary arteries in vivo. With resolution that is a 10-fold improvement compared with intravascular ultrasonography, OCT can facilitate detailed plaque characterization. This article introduces the basic principles of OCT image acquisition and interpretation. Qualitative analysis entails the evaluation of plaque morphology, including features associated with plaque vulnerability to rupture. Quantitative analysis and recognition of OCT image artifacts are also discussed.

Single String Technique for Coronary Bifurcation Stenting: Detailed Technical Evaluation and Feasibility Analysis

OBJECTIVES

The study aimed to evaluate the adequacy and feasibility of the single string bifurcation stenting technique.

BACKGROUND

Double-stent techniques may be required for complex bifurcations. Currently applied methods all have their morphological or structural limitations with respect to wall coverage, multiple strut layers, and apposition rate.

METHODS

Single string is a novel method in which, first, the side branch (SB) stent is deployed with a single stent cell protruding into the main branch (MB). Second, the MB stent is deployed across this protruding stent cell. The procedure is completed by final kissing balloon dilation. The single string technique was first tested in vitro (n = 20) and next applied in patients (n = 11) with complex bifurcation stenoses.

RESULTS

All procedures were performed successfully, crossing a single stent cell in 100%. Procedure duration was 23.0 ± 7.9 min, and the fluoroscopy time was 9.4 ± 3.5 min. The results were evaluated by optical coherence tomography, showing fully apposed struts in 83.0 ± 9.2% in the bifurcation area. Residual area obstruction in the MB was 6.4 ± 5.6% and 25.0 ± 16.9% in the SB, as evaluated by micro computed tomography. All the human cases were performed successfully with excellent angiographic results: the residual area stenosis was 27 ± 8% and 29 ± 10% in the MB and in the SB, respectively, by 3-dimensional quantitative coronary angiography. No relevant periprocedural enzyme increase was observed. During follow-up (6 ± 4 months), no adverse clinical events (death, myocardial infarction, target vessel revascularization) were noted.

CONCLUSIONS

The single string technique for complex bifurcation dilation was shown to be adequate in vitro and feasible in humans, with favorable results in terms of stent overlap, malapposition rate, and low residual obstruction in both the MB and SB.

Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

Current clinical intravascular optical coherence tomography (IV-OCT) imaging systems have limited in-vivo flow imaging capability because of non-uniform catheter rotation and inadequate A-line scan density. Thus any flow-localisation method that seeks to identify sites of variation within the OCT image data-sets, whether that is in amplitude or phase, produces non-representative correlation (or variance) maps. In this study, both mean and the variation within a set of cross-correlation maps, for static OCT imaging was used to differentiate flow from nonflow regions. Variation was quantified by use of standard deviation. The advantage of this approach is its ability to image flow, even in the presence of motion artifacts. The ability of this technique to suppress noise and capture flow maps was demonstrated by imaging microflow in an ex-vivo porcine coronary artery model, by nailfold capillary imaging and in-vivo microvessel imaging from within the human coronary sinus.

Comparison of two dimensional quantitative coronary angiography (2D-QCA) with optical coherence tomography (OCT) in the assessment of coronary artery lesion dimensions

Objectives

There is limited data on how well 2D-QCA and OCT agree with each other for measurement of coronary artery lumen dimensions. We aimed to assess the agreement between the two modalities.

Methods

Patients undergoing OCT for assessment of coronary artery lesions were reviewed. Minimum luminal diameter (MLD), proximal reference diameter and distal reference diameter were measured for each lesion prior to stenting.

Results

OCT was performed in 64 patients and 40 lesions were suitable for analysis. There was a good correlation for proximal and distal reference diameters (r = 0.86, p < 0.0001 and r = 0.92, p < 0.0001 respectively). There was good agreement on Bland–Altman analysis; the proximal and distal reference diameters measured by QCA were on average 0.09 mm (95% CI, − 0.52 to 0.53 mm) and 0.1 mm (95% CI, − 0.59 to 0.6 mm) smaller than OCT respectively. There was a satisfactory correlation (r = 0.63, p = < 0.0001) between QCA and OCT for MLD. However, the MLD by QCA was 0.49 mm (95% CI, − 1.57 to 0.59 mm) smaller than OCT, suggesting a poor agreement for MLD.

Conclusions

There is a good correlation and agreement between QCA and OCT for measurement of proximal and distal reference diameters. However, the MLD was underestimated by QCA.

Perspectives on Imaging the Left Main Coronary Artery Using Intravascular Ultrasound and Optical Coherence Tomography

Percutaneous coronary intervention (PCI) for significant left main coronary artery (LMCA) stenosis is increasingly being viewed as a viable alternative to coronary artery bypass grafting (CABG) (1). This is leading to an expectation of increasing numbers of such procedures with a consequent focus on both the ability to image lesion severity and assess more accurately the results of PCI. While there have been advances in physiological assessment of left main severity using fractional flow reserve (FFR) and in non-invasive assessment of the left main using coronary computerized tomography CT (2), imaging of the LMCA using intravascular ultrasound (IVUS) and more recently optical coherence tomography (OCT) has the specific advantage of being able to provide very detailed anatomical information both pre- and post-PCI, such that it is timely to review briefly the current status of these two imaging technologies in the context of LMCA intervention. This is presented specifically contrasting the use of these technologies both in pre-PCI lesion severity assessment, and peri-PCI procedural evaluation. Not discussed here is the separate issue of longer-term surveillance of asymptomatic patients having undergone LMCA stenting, which may appropriately be performed non-invasively using coronary CT, reviewed in detail elsewhere (2).

Intravascular optical coherence tomography light scattering artifacts: merry-go-rounding, blooming, and ghost struts

We sought to elucidate the mechanisms underlying two common intravascular optical coherence tomography (IV-OCT) artifacts that occur when imaging metallic stents: “merry-go-rounding” (MGR), which is an increase in strut arc length (SAL), and “blooming,” which is an increase in the strut reflection thickness (blooming thickness). Due to uncontrollable variables that occur in vivo, we performed an in vitro assessment of MGR and blooming in stented vessel phantoms. Using Xience V and Driver stents, we examined the effects of catheter offset, intimal strut coverage, and residual blood on SAL and blooming thickness in IV-OCT images. Catheter offset and strut coverage both caused minor MGR, while the greatest MGR effect resulted from light scattering by residual blood in the vessel lumen, with 1% hematocrit (Hct) causing a more than fourfold increase in SAL compared with saline (p<0.001 ). Residual blood also resulted in blooming, with blooming thickness more than doubling when imaged in 0.5% Hct compared with saline (p<0.001 ). We demonstrate that a previously undescribed mechanism, light scattering by residual blood in the imaging field, is the predominant cause of MGR. Light scattering also results in blooming, and a newly described artifact, three-dimensional-MGR, which results in “ghost struts” in B-scans.

Techniques and best practices for optical coherence tomography: a practical manual for interventional cardiologists

Optical coherence tomography (OCT) is a novel intracoronary imaging modality that utilizes near-infrared light to provide information regarding lesion length and severity, vessel lumen diameter, plaque morphology, as well as the opportunity for stent procedure guidance and follow-up. While analogous to intravascular ultrasound (IVUS), the specific imaging properties, including significantly higher resolution, and technical specifications of OCT offer the ability for intracoronary diagnostic and interventional procedure guidance roles that require a thorough understanding of the technology. We provide coronary interventionalist's a user's guide to OCT, focusing on techniques and approaches to optimize imaging, with a focus on efficiency, safety and strategies for effective imaging.

Nonangiographic assessment of coronary artery disease: a practical approach to optical coherence tomography and fractional flow reserve

In an era of increased scrutiny of the appropriateness and safety of revascularization, interventional cardiologists must evolve by adding key tools to their armamentarium. This review highlights the utility of optical coherence tomography and fractional flow reserve in the catheterization lab and provides a practical guide for using these technologies during coronary intervention in various lesion subsets. We propose that fractional flow reserve informs the decision to intervene and optical coherence tomography guides the optimization of the outcome.

Clinical classification of plaque morphology in coronary disease

In published post-mortem pathological studies, more than two-thirds of acute coronary events are associated with the rupture of lipid-rich, voluminous, and outwardly remodelled plaques covered by attenuated and inflamed fibrous caps in the proximal part of coronary arteries. Superficial erosion of the plaques is responsible for most of the remaining events; the eroded plaques usually do not demonstrate much lipid burden, do not have thin fibrous caps, are not positively remodelled, and are not critically occlusive. Both noninvasive and invasive imaging studies have been performed to clinically define the plaque characteristics in acute coronary syndromes in an attempt to identify the high-risk plaque substrate susceptible to development of an acute coronary event. Optical coherence tomography (OCT)--an intravascular imaging modality with high resolution--can be used to define various stages of plaque morphology, which might allow its use for the identification of high-risk plaques vulnerable to rupture, and their amenability to pre-emptive interventional treatment. OCT might also be employed to characterize plaque pathology at the time of intervention, to provide a priori knowledge of the mechanism of the acute coronary syndrome and, therefore, to enable improved management of the condition.

Atherosclerosis and atheroma plaque rupture: imaging modalities in the visualization of vasa vasorum and atherosclerotic plaques

Invasive angiography has been widely accepted as the gold standard to diagnose cardiovascular pathologies. Despite its superior resolution of demonstrating atherosclerotic plaque in terms of degree of lumen stenosis, the morphological assessment for the plaque is insufficient for the analysis of plaque components, and therefore, unable to predict the risk status or vulnerability of atherosclerotic plaque. There is an increased body of evidence to show that the vasa vasorum play an important role in the initiation, progression, and complications of atherosclerotic plaque leading to major adverse cardiac events. This paper provides an overview of the evidence-based reviews of various imaging modalities with regard to their potential value for comprehensive characterization of the composition, burden, and neovascularization of atherosclerotic plaque.

Plaque vulnerability of coronary artery lesions is related to left ventricular dilatation as determined by optical coherence tomography and cardiac magnetic resonance imaging in patients with type 2 diabetes

Background

Patients with type 2 diabetes are at increased risk for both, left ventricular (LV)-dilatation and myocardial infarction (MI) following the rupture of a vulnerable plaque. This study investigated the to date incompletely understood relationship between plaque vulnerability and LV-dilatation using optical coherence tomography (OCT) and cardiac magnetic resonance imaging (CMR) in patients with type 2 diabetes and stable coronary artery disease.

Methods

CMR was performed in 58 patients with type 2 diabetes, in which 81 coronary lesions were investigated using OCT.

Results

A decreased minimal fibrous cap thickness (FCT) of coronary lesions was associated with an increase of several CMR-derived parameters including LV-end diastolic volume (LVEDV, r = 0.521, p < 0.001), LV-end diastolic diameter (r = 0.502, p < 0.001) and LV-end systolic volume (r = 0.467, p = 0.001). Similar results were obtained for mean FCT.

Furthermore, patients with dilated versus non-dilated LV differed significantly in several cardiovascular risk factors including previous MI (47.1% vs. 14.6%, p = 0.009), HDL-cholesterol (40.35 ± 5.57 mg/dl vs. 45.20 ± 10.79 mg/dl, p = 0.029) and smoking (82.4% vs. 51.2%, p = 0.027). However, minimal FCT is associated to LV-dilatation independent of previous MIs (odds ratio 0.679, p = 0.022).

Receiver-operating curve analysis demonstrated that CMR-derived LVEDV predicts plaque vulnerability with low-moderate diagnostic efficiency (area under the curve 0.699) and considerate specificity (83.3%) at the optimal cut-off value (159.0 ml).

Conclusion

These data suggest that vulnerability of coronary lesions is associated with LV-dilatation in high risk patients with type 2 diabetes. CMR may be a useful adjunct to the risk-stratification in this population. Future studies are warranted to investigate potential mechanisms linking plaque vulnerability and LV-dilatation.