Assessment of coronary arterial plaque by optical coherence tomography

The role of optical coherence tomography in guiding percutaneous coronary interventions: is left main the final challenge?

Left main (LM) coronary artery disease is a high-risk lesion subset, with important prognostic implications for the patients. Recent advances in the field of interventional cardiology have narrowed the gap between surgical and percutaneous approach of this complex lesion setting. However, the rate of repeat revascularization remains higher in the case of percutaneous coronary intervention (PCI) on long-term follow-up. As such, the need for better stent optimization strategies has led to the development of intravascular imaging techniques, represented mainly by intravascular ultrasound (IVUS) and optical coherence tomography (OCT). These techniques are both able to provide excellent pre- and post-PCI guidance. While IVUS is an established modality in optimizing LM PCI, and is recommended by international revascularization guidelines, data and experience on the use of OCT are still limited. This review paper deeply analyzes the current role of OCT imaging in the setting of LM disease, particularly focusing on its utility in assessing plaque morphology and distribution, vessel dimensions and proper stent sizing, analyzing mechanisms of stent failure such as malapposition and underexpansion, guiding bifurcation stenting, as well as offering a direct comparison with IVUS in this critical clinical scenario, based on the most recent available data.

Utility of optical coherence tomography in acute coronary syndromes

Studies utilizing intravascular imaging have replicated the findings of histopathological studies, identifying the most common substrates for acute coronary syndromes (ACS) as plaque rupture, erosion, and calcified nodule, with spontaneous coronary artery dissection, coronary artery spasm, and coronary embolism constituting the less common etiologies. The purpose of this review is to summarize the data from clinical studies that have used high-resolution intravascular optical coherence tomography (OCT) to assess culprit plaque morphology in ACS. In addition, we discuss the utility of intravascular OCT for effective treatment of patients presenting with ACS, including the possibility of culprit lesion-based treatment by percutaneous coronary intervention.

Exploring new insights in coronary lesion assessment and treatment in patients with diabetes mellitus: the impact of optical coherence tomography

In this review, we summarise new insights into diagnostic approaches and treatment strategies for coronary artery disease (CAD) in patients with diabetes mellitus (DM). Despite the improvements in therapy, the clinical management of DM patients remains challenging as they develop more extensive CAD at a younger age and consistently have worse clinical outcomes than non-DM patients. Current diagnostic modalities as well as revascularisation treatments mainly focus on ischemic lesions. However, the impact of plaque morphology and composition are emerging as strong predictors of adverse cardiac events even in the absence of identified ischemia. In particular, the presence of vulnerable plaques such as thin-cap fibroatheroma (TCFA) lesions has been identified as a very strong predictor of future adverse events. This emphasises the need for an approach combining both functional and morphological methods in the assessment of lesions. In particular, optical coherence tomography (OCT) has proven to be a valuable asset by truly identifying TCFAs. New treatment strategies should consist of individualised and advanced medical regimens and may evolve towards plaque sealing through percutaneous treatment.

Current Role of Intracoronary Imaging for Implementing Risk Stratification and Tailoring Culprit Lesion Treatment: A Narrative Review

Our understanding of the pathophysiology of acute coronary syndrome and of the vascular biology of coronary atherosclerosis has made enormous progress with the implementation of intravascular imaging. Intravascular imaging contributes to overcoming the known limitations of coronary angiography and allows for the in vivo discrimination of plaque morphology giving insight into the underlying pathology of the disease process. The possibility of using intracoronary imaging to characterize lesion morphologies and correlate them with clinical presentations may influence the treatment of patients and improve risk stratification, offering the opportunity for tailored management. This review examines the current role of intravascular imaging and describes how intracoronary imaging represents a valuable tool for modern interventional cardiology in order to improve diagnostic accuracy and offer a tailored approach to the treatment of patients with coronary artery disease, especially in the acute setting.

Long-term outcomes of patients with normal fractional flow reserve and thin-cap fibroatheroma

BACKGROUND

The long-term prognostic implications of fractional flow reserve (FFR)-negative lesions hosting vulnerable plaques remain unsettled.

AIMS

The aim of this study was to evaluate the association of non-ischaemic lesions hosting optical coherence tomography (OCT)-detected thin-cap fibroatheromas (TCFA) with first and recurrent cardiovascular events during follow-up up to 5 years in a diabetes mellitus (DM) patient population.

METHODS

COMBINE OCT-FFR is a prospective, international, double-blind, natural history study. Patients with DM and with ≥1 FFR-negative lesion were classified into 2 groups based on the presence or absence of ≥1 TCFA lesion. The primary endpoint (PE) is a composite of cardiac mortality, target vessel-related myocardial infarction (TV-MI), clinically driven target lesion revascularisation (TLR), or unstable angina (UA) requiring hospitalisation during follow-up up to 5 years.

RESULTS

Among 390 DM patients (age 67.5±9 years; 37% female) with ≥1 FFR-negative lesion, 292 (74.9%) were TCFA-negative while 98 (25.1%) were TCFA-positive. The PE occurred more frequently in TCFA-positive than in TCFA-negative patients (21.4% vs 8.2%, hazard ratio [HR] 2.89, 95% confidence interval [CI]: 1.61-5.20; p<0.001; 6.42 vs 2.46 events per 100 patient-years, rate ratio [RR] 2.61, 95% CI: 1.38-4.90; p=0.002). Furthermore, when TV-MI, TLR, and UA were treated as recurrent components of the PE, TCFA-positive patients experienced a higher risk of recurrent events (HR 2.89, 95% CI; 1.74-4.80; p<0.001; 13.45 vs 2.87 events per 100 patient-years, RR 4.69, 95% CI: 2.86-7.83; p<0.001). A multivariable analysis identified the presence of TCFA as an independent predictor of the PE (HR 2.76, 95% CI: 1.53-4.97; p<0.001).

CONCLUSIONS

OCT-detected TCFA-positive lesions, although not ischaemia-generating, are associated with an increased risk of adverse events during long-term follow-up.

CLINICALTRIALS

gov: NCT02989740.

The Relation Between Red Blood Cell Distribution Width and Coronary Atherosclerotic Plaque Vulnerability Detected by Intracoronary Optical Coherence Tomography

BACKGROUND

A higher red blood cell distribution width (RDW) predicts major adverse cardiac events in patients with coronary artery disease (CAD). However, there are only a few studies regarding the relationship between RDW and vulnerable plaques. Thus, the purpose of the present study is to retrospectively explore the predictive value of the association between RDW and plaque vulnerability assessed by optical coherence tomography (OCT) in patients with cardiovascular (CV) diseases.

METHODS

This study included 35 patients with stable angina pectoris (SAP) and 70 patients with the acute coronary syndrome (ACS). We documented clinical features as well as peripheral RDW. Plaque vulnerability was determined by OCT. We defined thin-cap fibroatheroma (TCFA) as a lipid-rich plaque (fibrous cap <65 μm thick).

RESULTS

Plaque rupture was detected more frequently in patients with ACS compared with patients with SAP (62.9 vs. 2.9%, p<0.001, and the corresponding TCFA were 50.69±15.68 vs. 80.03±21.60 μm, p<0.001, respectively). A higher RDW was found in patients with ACS than in patients with SAP (p<0.001). A cut-off value of RDW >13.85% could detect ruptured plaque with a sensitivity of 72.3% and a specificity of 62%.

CONCLUSION

TCFA and plaque rupture were detected more frequently in patients with ACS compared with SAP. Elevated RDW was positively the predictive value of the association between plaque vulnerability.

When coronary imaging and physiology are discordant, how best to manage coronary lesions? An appraisal of the clinical evidence

BACKGROUND

Discordant physiology and anatomy may occur when nonsevere angiographic stenosis has positive physiology as well as the opposite situation.

AIM

To underline the reasons behind the discrepancy in physiology and anatomy and to summarize the information that coronary imaging may add to physiology.

METHODS

A review of the published literature on physiology and intravascular imaging assessment of intermediate lesions was carried out.

RESULTS

The limitations of angiography, the possibility of an underlying diffuse disease, the presence of a "grey zone" in both techniques, the amount of myocardial mass that subtends the stenosis, and plaque vulnerability may play a role in such discrepancy. Intracoronary imaging has a poor diagnostic accuracy compared to physiology. However, it may add information about plaque vulnerability that might be useful in deciding whether to treat or not a certain lesion.

CONCLUSIONS

Coronary revascularization is recommended for patients with ischemia based on physiology. Intracoronary imaging adds information on plaque vulnerability and can help on the decision whether to revascularize or not a lesion.

Expert consensus statement for quantitative measurement and morphological assessment of optical coherence tomography: update 2022

In this updated expert consensus document, the methods for the quantitative measurement and morphological assessment of optical coherence tomography (OCT)/optical frequency domain imaging images (OFDI) are briefly summarized. The focus is on the clinical application and the clinical evidence of OCT/OFDI to guide percutaneous coronary interventions.

Comparative study of deep neural networks with unsupervised Noise2Noise strategy for noise reduction of optical coherence tomography images

As a powerful diagnostic tool, optical coherence tomography (OCT) has been widely used in various clinical setting. However, OCT images are susceptible to inherent speckle noise that may contaminate subtle structure information, due to low-coherence interferometric imaging procedure. Many supervised learning-based models have achieved impressive performance in reducing speckle noise of OCT images trained with a large number of noisy-clean paired OCT images, which are not commonly feasible in clinical practice. In this article, we conducted a comparative study to investigate the denoising performance of OCT images over different deep neural networks through an unsupervised Noise2Noise (N2N) strategy, which only trained with noisy OCT samples. Four representative network architectures including U-shaped model, multi-information stream model, straight-information stream model and GAN-based model were investigated on an OCT image dataset acquired from healthy human eyes. The results demonstrated all four unsupervised N2N models offered denoised OCT images with a performance comparable with that of supervised learning models, illustrating the effectiveness of unsupervised N2N models in denoising OCT images. Furthermore, U-shaped models and GAN-based models using UNet network as generator are two preferred and suitable architectures for reducing speckle noise of OCT images and preserving fine structure information of retinal layers under unsupervised N2N circumstances.

Gender-based in vivo comparison of culprit plaque characteristics and plaque microstructures using optical coherence tomography in acute coronary syndrome

Introduction: Women perform worse after acute coronary syndrome (ACS) than men. The reason for these differences is unclear. The aim was to ascertain gender differences in the culprit plaque characteristics in ACS.

Methods: Patients with ACS undergoing percutaneous coronary intervention for the culprit vessel underwent optical coherence tomography (OCT) imaging. Culprit plaque was identified as lipid rich,fibrous, and calcific plaque. Mechanisms underlying ACS are classified as plaque rupture, erosion,or calcified nodule. A lipid rich plaque along with thin-cap fibroatheroma (TCFA) was a vulnerable plaque. Plaque microstructures including cholesterol crystals, macrophages, and microvessels were noted.

Results: A total of 52 patients were enrolled (men=29 and women=23). Baseline demographic features were similar in both the groups except men largely were current smokers (P <0.001). Plaque morphology,men vs. women: lipid rich 88.0% vs. 90.5%; fibrous 4% vs 0%; calcific 8.0% vs. 9.5% (P = 0.64). Of the ACS mechanisms in males versus females; plaque rupture (76.9 % vs. 50 %), plaque erosion (15.4 % vs.40 %) and calcified nodule (7.7 % vs. 10 %) was noted (P = 0.139). Fibrous cap thickness was (50.19 ±11.17 vs. 49.00 ± 10.71 mm, P = 0.71) and thin-cap fibroatheroma (96.2% vs. 95.0%, P = 1.0) in men and women respectively. Likewise no significant difference in presence of macrophages (42.3 % vs. 30%, P = 0.76), microvessels (73.1% vs. 60 %, P = 0.52) and cholesterol crystals (92.3% vs. 80%, P = 0.38).

Conclusion: No significant gender-based in-vivo differences could be discerned in ACS patients’ culprit plaques morphology, characteristics, and underlying mechanisms.

Diagnostic Accuracy of Optical Frequency Domain Imaging for Identifying Necrotic Cores with Intraplaque Hemorrhage in Advanced Human Carotid Plaques

This study investigated whether optical frequency domain imaging (OFDI) can identify carotid artery vulnerable plaque characteristics, focusing on lipid-rich necrotic core (NC) and intraplaque hemorrhage (IPH). Fourteen patients scheduled for carotid endarterectomy underwent OFDI scan during preoperative angiography. Atherosclerotic plaque specimens obtained from carotid endarterectomy were cut every 3-4 mm into 4-μm transverse cross-sections and stained with standard methods. Each cross-section was matched with OFDI, and histologically classified into either fibrous, calcific, pathological intimal thickening (PIT), and NC. Of 75 histologic cross-sections, 6 were categorized as fibrous (8%), 18 as calcific (24%), 9 as PIT (12%), and 42 as NC (56%). Tissues categorized as NC had significantly higher OFDI signal attenuation rates than the other tissues (p <0.001), followed by PIT, calcific, and fibrous tissues. The receiver operating characteristic analysis indicated that attenuation rates of >0.023 and >0.031 predicted the presence of NC and IPH with high areas under the curve of 0.91 and 0.88, respectively. OFDI provides potential capability for the detection of NCs with IPH of carotid artery plaques by quantitatively analyzing the attenuation rate.

Shape prior generation and geodesic active contour interactive iterating algorithm (SPACIAL): fully automatic segmentation for 3D lumen in intravascular optical coherence tomography images

PURPOSE

Fully automatic lumen segmentation in intravascular optical coherence tomography (OCT) images can assist physicians in quickly estimating the health status of vessels. However, OCT images are usually degraded by residual blood, catheter walls, guide wire artifacts, etc., which significantly reduce the quality of segmentation. To achieve accurate lumen segmentation in low-quality images, we propose a novel segmentation algorithm named SPACIAL: Shape Prior generation and geodesic Active Contour Interactive iterAting aLgorithm, which is guided by an adaptively generated shape prior.

METHODS

In this framework, the active contour evolves under the guidance of shape prior, while the shape prior is automatically and adaptively generated based on the active contour. The active contour and the shape prior interactively iterate each other, which can generate the adaptive shape prior and consequently lead to accurate segmentation results. In addition, a fast algorithm is introduced to accelerate the segmentation in 3D images.

RESULTS

The validity of the model is verified in 3240 images from 12 OCT pullbacks. The experimental results show satisfactory segmentation accuracy and time efficiency: the average Dice coefficient of SPACIAL is 93.6(2.4)%, and 5.7 times faster than that of the classical level set method.

CONCLUSION

The proposed SPACIAL can quickly and efficiently perform accurate lumen segmentation on low quality OCT images, which is of great importance to cardiovascular disease diagnosis . The SPACIAL method shows great potential in clinical applications.

Thin-cap fibroatheroma predicts clinical events in diabetic patients with normal fractional flow reserve: the COMBINE OCT-FFR trial

AIMS

The aim of this study was to understand the impact of optical coherence tomography (OCT)-detected thin-cap fibroatheroma (TCFA) on clinical outcomes of diabetes mellitus (DM) patients with fractional flow reserve (FFR)-negative lesions.

METHODS AND RESULTS

COMBINE OCT-FFR study was a prospective, double-blind, international, natural history study. After FFR assessment, and revascularization of FFR-positive lesions, patients with ≥1 FFR-negative lesions (target lesions) were classified in two groups based on the presence or absence of ≥1 TCFA lesion. The primary endpoint compared FFR-negative TCFA-positive patients with FFR-negative TCFA-negative patients for a composite of cardiac mortality, target vessel myocardial infarction, clinically driven target lesion revascularization or unstable angina requiring hospitalization at 18 months. Among 550 patients enrolled, 390 (81%) patients had ≥1 FFR-negative lesions. Among FFR-negative patients, 98 (25%) were TCFA positive and 292 (75%) were TCFA negative. The incidence of the primary endpoint was 13.3% and 3.1% in TCFA-positive vs. TCFA-negative groups, respectively (hazard ratio 4.65; 95% confidence interval, 1.99-10.89; P < 0.001). The Cox regression multivariable analysis identified TCFA as the strongest predictor of major adverse clinical events (MACE) (hazard ratio 5.12; 95% confidence interval 2.12-12.34; P < 0.001).

CONCLUSIONS

Among DM patients with ≥1 FFR-negative lesions, TCFA-positive patients represented 25% of this population and were associated with a five-fold higher rate of MACE despite the absence of ischaemia. This discrepancy between the impact of vulnerable plaque and ischaemia on future adverse events may represent a paradigm shift for coronary artery disease risk stratification in DM patients.

Automated classification of coronary atherosclerotic plaque in optical frequency domain imaging based on deep learning

BACKGROUND AND AIMS

We developed a deep learning (DL) model for automated atherosclerotic plaque categorization using optical frequency domain imaging (OFDI) and performed quantitative and visual evaluations.

METHODS

A total of 1103 histological cross-sections from 45 autopsy hearts were examined to compare the ex vivo OFDI scans. The images were segmented and annotated considering four histological categories: pathological intimal thickening (PIT), fibrous cap atheroma (FA), fibrocalcific plaque (FC), and healed erosion/rupture (HER). The DL model was developed based on pyramid scene parsing network (PSPNet). Given an input image, a convolutional neural network (ResNet50) was used as an encoder to generate feature maps of the last convolutional layer.

RESULTS

For the quantitative evaluation, the mean F-score and IoU values, which are used to evaluate how close the predicted results are to the ground truth, were used. The validation and test dataset had F-score and IoU values of 0.63, 0.49, and 0.66, 0.52, respectively. For the section-level diagnostic accuracy, the areas under the receiver-operating characteristic curve produced by the DL model for FC, PIT, FA, and HER were 0.91, 0.85, 0.86, and 0.86, respectively, and were comparable to those of an expert observer.

CONCLUSIONS

DL semantic segmentation of coronary plaques in OFDI images was used as a tool to automatically categorize atherosclerotic plaques using histological findings as the gold standard. The proposed method can support interventional cardiologists in understanding histological properties of plaques.

Evaluation of coronary plaques and atherosclerosis using optical coherence tomography

Introduction: Coronary angiography (CAG) is the standard modality for assessing coronary stenosis; however, it has limitations in assessing coronary plaque morphology. Optical coherence tomography (OCT) is a high-resolution (10-20 μm) light-based intravascular imaging technique that can identify more detailed coronary plaque morphology compared to other intravascular imaging modalities. OCT is remarkable for characterizing fibrous, fibrocalcific, and lipid-rich plaques. The capabilities of OCT are well suited for discriminating three types of unstable plaque morphologies underlying coronary thrombosis, such as plaque rupture, erosion, and calcified nodules. The high resolution of OCT makes it possible to identify important features of vulnerable plaques, such as thin-cap (<65 μm thick) fibroatheroma, macrophages, vasa vasorum, and cholesterol crystals.Areas covered: This review summarizes the clinical impact of OCT and its efficacy in identifying plaque components and morphological features associated with plaque vulnerability.Expertopinion: The unique properties of OCT as a tool for investigating high-risk lesions have greatly contributed to a better understanding of plaque vulnerability. Consequently, OCT has led to significant changes in medical treatment and percutaneous coronary intervention strategies for acute coronary syndrome. Further development and investigation of OCT are necessary to better predict and manage acute coronary events in the future.

Atherothrombosis in Acute Coronary Syndromes-From Mechanistic Insights to Targeted Therapies

The atherothrombotic substrates for acute coronary syndromes (ACS) consist of plaque ruptures, erosions and calcified nodules, while the non-atherothrombotic etiologies, such as spontaneous coronary artery dissection, coronary artery spasm and coronary embolism are the rarer causes of ACS. The purpose of this comprehensive review is to (1) summarize the histopathologic insights into the atherothrombotic plaque subtypes in acute ACS from postmortem studies; (2) provide a brief overview of atherogenesis, while mainly focusing on the events that lead to plaque destabilization and disruption; (3) summarize mechanistic data from clinical studies that have used intravascular imaging, including high-resolution optical coherence tomography, to assess culprit plaque morphology and its underlying pathobiology, especially the newly described role of innate and adaptive immunity in ACS secondary to plaque erosion; (4) discuss the utility of intravascular imaging for effective treatment of patients presenting with ACS by percutaneous coronary intervention; and (5) discuss the opportunities that these mechanistic and imaging insights may provide for more individualized treatment of patients with ACS.

Sweat the small stuff: The human microvasculature and heart disease

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

Multi-modality intravascular imaging for guiding coronary intervention and assessing coronary atheroma: the Novasight Hybrid IVUS-OCT system

Intravascular imaging has evolved alongside interventional cardiology as an adjunctive tool for assessing plaque pathology and for guiding and optimising percutaneous coronary intervention (PCI) in challenging lesions. The two modalities which have dominated the field are intravascular ultrasound (IVUS), which relies on sound waves and optical coherence tomography (OCT), relying on light waves. These approaches however have limited efficacy in assessing plaque morphology and vulnerability that are essential for guiding PCI in complex lesions and identifying patient at risk that will benefit from emerging therapies targeting plaque evolution. These limitations are complementary and, in this context, it has been recognised and demonstrated in multi-modality studies that the concurrent use of IVUS and OCT can help overcome these deficits enabling a more complete and accurate plaque assessment. The Conavi Novasight Hybrid IVUS-OCT catheter is the first commercially available device that is capable of invasive clinical coronary assessment with simultaneously acquired and co-registered IVUS and OCT imaging. It represents a significant evolution in the field and is expected to have broad application in clinical practice and research. In this review article we present the limitations of standalone intravascular imaging techniques, summarise the data supporting the value of multimodality imaging in clinical practice and research, describe the Novasight Hybrid IVUS-OCT system and highlight the potential utility of this technology in coronary intervention and in the study of atherosclerosis.

A Pathophysiologic Primary Prevention Review of Aspirin Administration to Prevent Cardiovascular Thrombosis

OBJECTIVE

Cardiovascular disease is the leading metabolic cause of mortality in the United States. Among current therapies, low-dose aspirin has been shown to reduce cardiovascular thrombosis. However, aspirin also causes major complications (hemorrhagic stroke and gastrointestinal bleeding). The American Heart Association recommends that aspirin only be prescribed for "high-risk" individuals. No guidelines are available as to the duration of aspirin therapy.

METHODS

A reasonable approach to aspirin administration is to determine the appropriateness of aspirin therapy based on the pathophysiology of coronary artery thrombosis. It suggests that the coronary artery calcium (CAC) score be used as the basis for determining "high risk." This score was shown to accurately predict future cardiovascular events. The greater the CAC score, the greater the extent of coronary artery atherosclerotic plaque and future cardiovascular risk.

RESULTS

A CAC score >400 places an individual at very-high 10-year risk for an atherosclerotic event. Since aggressive medical therapy initiates stabilization of unstable atherosclerotic plaques within 1 month and reversal within 2 years, this treatment significantly reduces the risk of the individual for a cardiovascular event. Thus, most individuals aged <75 years with a CAC score of >400 should receive aspirin therapy for a maximum of 2 years.

CONCLUSION

Utilization of a CAC score greatly simplifies the decision of whom to treat with aspirin and for what duration. Importantly, focusing on two factors (hemorrhage and plaque stabilization) is easily understood by both the physician and the patient.

ABBREVIATIONS

CAC = coronary artery calcium; CVD = cardiovascular disease; LDL = low-density lipoprotein; OCT = optical coherence tomography.

Optical coherence tomography-guided percutaneous coronary intervention: a review of current clinical applications

Optical coherence tomography (OCT) is an emerging high-resolution intravascular imaging modality that can provide physicians with critical information, thereby enabling precise characterization of plaque morphology and luminal geometry and facilitating pre-intervention lesion assessment. As OCT has a higher sensitivity for lipid-rich plaque characterization than intravascular ultrasound, vulnerable plaque detection by OCT has thus been investigated. By evaluating both the calcium thickness and arc, OCT can be the ideal method for determining both the indication and endpoint of rotational atherectomy for calcified lesions prior to stent implantation. OCT has become applicable for the optimization of stent implantation with immediate and semi-automatic quantification of stent apposition and expansion to achieve potentially better clinical outcomes. In bifurcation lesions, OCT allows the visualization of the stent-link location overhanging the side-branch ostium and the guidewire recrossing point prior to the final kissing balloon inflation through three-dimensional reconstructed OCT images, providing us with deep insights into the mechanical optimization of stent struts. Furthermore, recent studies have reported several OCT-derived predictors of adverse clinical events. Important limitations of OCT, including the excessive contrast volume needed and observation of aorto-ostial lesions, may partially be overcome through the use of low-molecular-weight dextran and a guide extension catheter. The clinical applications of OCT have been expanding, and evidence on its clinical utility has been accumulating.

Optical Coherence Tomography based treatment approach for patients with Acute Coronary Syndrome

INTRODUCTION

Areas covered:In this review, we outline the underlying causes of acute coronary syndrome (ACS) as evaluated by optical coherence tomography (OCT). We report both the definitions of each mechanism and its frequency as reported in the literature to date. Finally, we present an algorithm based on the findings in the review that gives an outlined approach to perform intervention on ACS patients.Expert opinion:Although the most common and most accepted intervention in ACS cases is stent implantation, data suggest a stentless approach in cases of plaque erosion, which generally occurs in younger patients presenting with an acute coronary syndrome that have TIMI flow of 2/3 and either a small or large burden of thrombus and underlying stenosis of less than 50%.

N2NSR-OCT: Simultaneous denoising and super-resolution in optical coherence tomography images using semisupervised deep learning

Optical coherence tomography (OCT) imaging shows a significant potential in clinical routines due to its noninvasive property. However, the quality of OCT images is generally limited by inherent speckle noise of OCT imaging and low sampling rate. To obtain high signal-to-noise ratio (SNR) and high-resolution (HR) OCT images within a short scanning time, we presented a learning-based method to recover high-quality OCT images from noisy and low-resolution OCT images. We proposed a semisupervised learning approach named N2NSR-OCT, to generate denoised and super-resolved OCT images simultaneously using up- and down-sampling networks (U-Net (Semi) and DBPN (Semi)). Additionally, two different super-resolution and denoising models with different upscale factors (2× and 4×) were trained to recover the high-quality OCT image of the corresponding down-sampling rates. The new semisupervised learning approach is able to achieve results comparable with those of supervised learning using up- and down-sampling networks, and can produce better performance than other related state-of-the-art methods in the aspects of maintaining subtle fine retinal structures.

Interobserver variability in assessments of atherosclerotic lesion type via optical frequency domain imaging

BACKGROUND

To date, there have been no data available regarding the diagnostic performance of optical frequency domain imaging (OFDI) for in vivo histological classification of atherosclerotic lesions. This study investigated whether OFDI can be used to diagnose and classify histological atherosclerotic lesions in the coronary artery by ex vivo histological examinations.

METHODS

Three-hundred-fifteen histological cross-sections from 21 autopsy hearts were matched with the OFDI images. Histological cross-sections were classified into six categories: adaptive intimal thickening (AIT), pathological intimal thickening (PIT), fibrous cap atheroma (FA), fibrocalcific plaque (FC), calcified nodule, and healed erosion/rupture. The five observers with different years of experience in the interpretation of OFDI provided a single diagnosis for the OFDI scans of each cross-section according to the aforementioned six histological categories. The diagnostic accuracy and interobserver variability of lesion types for each OFDI observer were determined using histology as the gold standard.

RESULTS

The overall agreement rates between OFDI and histopathologic diagnosis for OFDI observers 1-5 were 81%, 70%, 68%, 61%, and 50% (κ values of 0.75, 0.61, 0.58, 0.49, and 0.36), respectively. Although the diagnostic accuracy of OFDI for detecting AIT and FC was excellent for all five observers, the sensitivity, and positive predictive values of OFDI for detecting PIT and FA were low in proportion to years of experience.

CONCLUSION

The diagnostic accuracy of atherosclerotic tissue properties from OFDI scans correlated with the observers' years of experience, especially when lesions contained lipid components.

Advances in IVUS/OCT and Future Clinical Perspective of Novel Hybrid Catheter System in Coronary Imaging

Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have been developed and improved as both diagnostic and guidance tools for interventional procedures over the past three decades. IVUS has a resolution of 100 μm with a high tissue penetration and capability of assessing the entire structure of a coronary artery including the external elastic membrane, whereas OCT has a higher resolution of 10–20 μm to assess endoluminal structures with a limited tissue penetration compared to IVUS. Recently, two companies, CONAVI and TERUMO, integrated IVUS and OCT into a single catheter system. With their inherent strength and limitations, the combined IVUS and OCT probes are complementary and work synergistically to enable a comprehensive depiction of coronary artery. In this review, we summarize the performance of the two intracoronary imaging modalities—IVUS and OCT—and discuss the expected potential of the novel hybrid IVUS–OCT catheter system in the clinical field.

Noise reduction in optical coherence tomography images using a deep neural network with perceptually-sensitive loss function

Optical coherence tomography (OCT) is susceptible to the coherent noise, which is the speckle noise that deteriorates contrast and the detail structural information of OCT images, thus imposing significant limitations on the diagnostic capability of OCT. In this paper, we propose a novel OCT image denoising method by using an end-to-end deep learning network with a perceptually-sensitive loss function. The method has been validated on OCT images acquired from healthy volunteers' eyes. The label images for training and evaluating OCT denoising deep learning models are images generated by averaging 50 frames of respective registered B-scans acquired from a region with scans occurring in one direction. The results showed that the new approach can outperform other related denoising methods on the aspects of preserving detail structure information of retinal layers and improving the perceptual metrics in the human visual perception.

Efficacy and Reproducibility of Attenuation-Compensated Optical Coherence Tomography for Assessing External Elastic Membrane Border and Plaque Composition in Native and Stented Segments - An In Vivo and Histology-Based Study

BACKGROUND

Attenuation-compensated (AC) technique was recently introduced to improve the plaque characterization of optical coherence tomography (OCT). Histological validation demonstrated promising results but the efficacy and reproducibility of this technique for assessing in-vivo tissue composition remains unclear.Methods and Results:OCT images portraying native (n=200) and stented (n=200) segments and 31 histological cross-sections were analyzed. AC-OCT appeared superior to conventional (C)-OCT in detecting the external elastic lamina (EEM) borders (76% vs. 65.5%); AC-OCT enabled larger EEM arc detection compared with C-OCT (174.2±58.7° vs. 137.5±57.9°; P<0.001). There was poor agreement between the 2 techniques for detection of lipid in native and lipid and calcific tissue in stented segments (κ range: 0.164-0.466) but the agreement of C-OCT and AC-OCT was high for calcific tissue in native segments (κ=0.825). Intra and interobserver agreement of the 2 analysts was moderate to excellent with C-OCT (κ range: 0.681-0.979) and AC-OCT (κ range: 0.733-0.892) for all tissue types in both native and stented segments. Ex-vivoanalysis demonstrated that C-OCT was superior to AC-OCT (κ=0.545 vs. κ=0.296) for the detection of the lipid component in native segments.

CONCLUSIONS

The AC technique allows better delineation of the EEM but it remains inferior for lipid pool detection and neointima characterization. Combined AC- and C-OCT imaging may provide additional value for complete assessment of plaque and neointima characteristics.

Associations of coronary plaque characteristics by integrated backscatter intravascular ultrasound with detectability of vessel external elastic lamina using optical frequency domain imaging in human coronary arteries: A sub-analysis of the MISTIC-1 trial

OBJECTIVES

We sought to examine associations between plaque characteristics by intravascular ultrasound (IVUS) and detectability of external elastic lamina (EEL) by optical frequency domain imaging (OFDI) in human coronary arteries.

BACKGROUND

It is often challenging to detect EEL which represents vessel size by light-based imaging modalities due to light intensity attenuation through atherosclerotic plaque.

METHODS

IVUS and OFDI prior to stent implantation were sequentially investigated per protocol. We identified corresponding cross-sections by minimum lumen area (MLA) or just distally to side branches as anatomical landmarks. Plaque characterization was determined by integrated backscatter IVUS analysis. We categorized detectable EEL arc by OFDI into four groups: 0≤ and <1 quadrant (group 1), 1≤ and <2 quadrants (group 2), 2≤ and <3 quadrants (group 3), or 3≤ and <4 quadrants (group 4).

RESULTS

We prospectively studied 103 vessels in 93 patients with stable coronary artery disease. Corresponding 711 cross-sections were analyzed. Cross-sections with detectable EEL arc <2 quadrants (group 1 or 2) were observed in 86.1% of MLA sites but only in 29.3% of non-MLA sites (p < .05). Percentage plaque area (%PA) appeared to be the strongest predictor to detect EEL arc <2 quadrants with the cut-off of 60.3% (AUC 0.90; sensitivity 79.8%, specificity 85.5%). Lipid pool and calcification remained statistically significant in predicting detectable EEL arc <2 quadrants after adjustment with %PA.

CONCLUSIONS

Presence of large plaque burden, lipid pool, and calcification significantly predicts the detectability of EEL by OFDI assessment. Locations with detectable EEL arc <2 quadrants should thus be avoided for optimal stent landing zone.

Reliable in vivo intravascular imaging plaque characterization: A challenge unmet

Intravascular imaging has enabled in vivo assessment of coronary artery pathology and detection of plaque characteristics that are associated with increased vulnerability. Prospective invasive imaging studies of coronary atherosclerosis have demonstrated that invasive imaging modalities can detect lesions that are likely to progress and cause cardiovascular events and provided unique insights about atherosclerotic evolution. However, despite the undoubted value of the existing imaging techniques in clinical and research arenas, all the available modalities have significant limitations in assessing plaque characteristics when compared with histology. Hybrid/multimodality intravascular imaging appears able to overcome some of the limitations of standalone imaging; however, there are only few histology studies that examined their performance in evaluating plaque pathobiology. In this article, we review the evidence about the efficacy of standalone and multi-modality/hybrid intravascular imaging in assessing plaque morphology against histology, highlight the advantages and limitations of the existing imaging techniques and discuss the future potential of emerging imaging modalities in the study of atherosclerosis.

Comparison of angioscopy and histopathology for the evaluation of carotid plaque characteristics: an ex vivo validation study

Intravascular angioscopy is widely used for evaluating plaque characteristics through the plaque color in the coronary artery. This study evaluated whether angioscopy is capable of identifying various plaque morphologies, including necrotic core and intraplaque hemorrhage (IPH) in the carotid artery. Nine patients underwent carotid endarterectomy for carotid artery stenosis, and these specimens were imaged ex vivo by angioscopy within 6 h. An angioscopic examination of carotid plaque evaluated its color intensity as follows: white, yellow, or red. The IPH area, necrotic core area, and fibrous cap thickness was measured on histological sections at each site. A total of 7 plaques were graded as white plaques, 10 as yellow, and 8 as red by angioscopy. The IPH area and the percent area occupied by IPH were larger in red and yellow plaques than in white plaques (10.7 ± 9.3 mm², 9.4 ± 7.8 mm², and 2.2 ± 1.7 mm², respectively, P = 0.074; and 25 ± 10%, 19 ± 13%, and 7 ± 5%, respectively, P = 0.008). Furthermore, the thickness of the fibrous cap was significantly thinner in red plaques than in yellow and white plaques (128 ± 34 µm, 328 ± 136 µm, and 285 ± 102 µm, respectively, P = 0.002). The ROC analysis for predicting a presence of red plaques identified that the optimal cutoff value of fibrous cap thickness was 181 µm (area under the curve = 0.987, 100% sensitivity, 90% specificity). The prevalence of red plaques on intravascular angioscopy may represent the existence of plaques containing relatively larger necrotic core and IPH with a thin fibrous cap.

Imaging assessment and accuracy in coronary artery autopsy: comparison of frequency-domain optical coherence tomography with intravascular ultrasound and histology

Optical coherence tomography (OCT) is a coronary artery imaging technique with high resolution. Second-generation frequency-domain OCT (FD-OCT) technology allows safer and faster clinical application compared with first-generation time-domain OCT (TD-OCT). Only limited validation studies compare FD-OCT with other modes of analysis: histology, which is the current gold standard, and intravascular ultrasound (IVUS). This study therefore aims to demonstrate the accuracy of FD-OCT images compared with IVUS and histology. FD-OCT and IVUS images were acquired from 203 segments from 31 coronary arteries obtained at autopsy from 20 cadavers. Of these, 30 randomly-selected pairs were used to create three classifications of plaque type based on morphological features in FD-OCT and IVUS compared with corresponding histopathology. The remaining 173 pairs were used to demonstrate the diagnostic accuracy for classification of coronary plaques by FD-OCT. Plaque type distributions were 27% fibroatheroma, 22% fibrocalcific plaque and 51% fibrous plaque. The diagnostic accuracies of FD-OCT for fibroatheroma, fibrocalcific plaque and fibrous plaque were 90, 95 and 93%, respectively. Those of IVUS were 81, 89 and 84%, respectively. FD-OCT achieved high diagnostic accuracy for the classification of coronary plaques comparable to TD-OCT. Physicians should consider the differences in the ability to classify plaque morphology of OCT of imaging devices when applying their use.

Optical coherence tomography-verified morphological correlates of high-intensity coronary plaques on non-contrast T1-weighted magnetic resonance imaging in patients with stable coronary artery disease

Aims

Coronary high-intensity plaques (HIPs) with a high plaque-to-myocardial signal intensity ratio (PMR) on non-contrast T1-weighted imaging in patients with stable coronary artery disease (CAD) are associated with future coronary events. To characterize the morphological substrate of HIP, we performed a correlative optical coherence tomography (OCT) study.

Methods and results

We examined 137 lesions in 105 patients with stable angina pectoris or silent myocardial ischaemia scheduled for percutaneous coronary intervention (PCI) using a 3 T magnetic resonance scanner. Pre-interventional OCT was performed for PCI target lesions. HIP was defined as PMR ≥ 1.4. Of the 137 lesions, 34% were HIP and 66% were non-HIP. The prevalence of lipid-rich plaque (96% vs. 70%, P < 0.001), macrophage accumulation (65% vs. 46%, P = 0.046), cholesterol crystals (46% vs. 22%, P = 0.006), and healed plaque rupture (multiple layers of different optical densities overlaying a large lipid accumulation, 72% vs. 18%, P < 0.001) was significantly higher in the HIP group than the non-HIP group; no significant differences were observed for the presence of thin cap fibroatheroma, intracoronary thrombus, and plaque rupture between the two groups. Multivariable stepwise logistic regression analysis showed that HIP was significantly associated with the presence of healed plaque rupture [odds ratio (OR) 9.32; 95% confidence interval (95% CI) 4.05–22.71; P < 0.001] and lipid-rich plaque (OR 4.38; 95% CI 1.08–29.77; P = 0.038).

Conclusions

The significant association between HIP- and OCT-derived healed plaque rupture and large lipid core provides new insights into the characteristics of high-risk plaques, even in clinically stable CAD.

Neointimal coverage of jailed side branches in coronary bifurcation lesions: an optical coherence tomography analysis

OBJECTIVES

The jailed strut at the side-branch (SB) orifice may be a cause of delayed neointimal coverage and SB flow disturbance after single stenting to bifurcation. The aim of this study was to characterize the exact relationship between the jailed strut pattern at the SB orifice immediately after stent implantation and neointimal coverage of the jailed SB orifice in the chronic phase.

PATIENTS AND METHODS

A total of 29 bifurcation (left anterior descending coronary artery and diagonal branch) lesions treated by optical coherence tomography-guide single-stent implantation and followed at 18 months after a percutaneous coronary intervention were included in this study.

RESULTS

Using three-dimensional optical coherence tomography images, the jailed stent strut pattern was classified into two groups on the basis of the presence of a stent strut link at the SB orifice (link group: n=11, and no-link group: n=18). SB orifice obstruction by neointima was significantly greater in the link group than in the no-link group during the 18-month follow-up period (26.8±21.9 vs. 9.5±22.1%, P=0.049).

CONCLUSION

This single-center observational study with a small sample size showed that a jailed strut pattern at the SB orifice might be related to neointimal coverage of the SB orifice in bifurcation lesions treated with single-stent implantation. Further large-scale studies with long-term follow-up will be necessary to determine the exact relationship between the jailed strut pattern at the SB orifice and SB flow disturbance because of delayed neointimal coverage as well as clinical outcome.

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.

Automated lipid-rich plaque detection with short wavelength infra-red OCT system

Aims

Vulnerable coronary plaque is characterized by a large lipid core. Although commercially-available optical coherence tomography (OCT) systems use near-infrared light at 1300 nm wavelength, lipid shows characteristic absorption at 1700 nm. Therefore, we developed a novel, short wavelength infra-red, spectroscopic, spectral-domain OCT. The aim of the present study is to evaluate the accuracy of short wavelength (1700 nm) infra-red optical coherence tomography (SWIR-OCT) for identification of lipid tissue within coronary plaques.

Methods and results

Twenty-three coronary arteries from 10 cadavers were imaged at physiological pressure with 2.7 Fr SWIR-OCT catheter. When a blood-free image was observed, the SWIR-OCT imaging core was withdrawn at a rate of 20 mm/s using an automatic pullback device. SWIR-OCT images were acquired at 94 frames/s and digitally archived. SWIR-OCT generated grey-scale cross sectional images and colour tissue maps of all of the plaque by using a lipid analysis algorithm. After SWIR-OCT imaging, the arteries were pressure-fixed, sliced by cryostat and stained with Oil Red O, and then corresponding histology was collected in matched images. Regions of interest, selected from histology, were 117 lipidic and 34 fibrotic/calcified regions. SWIR-OCT showed high sensitivity (89%) and specificity (92%) for identifying lipid tissue within coronary plaques. The positive predictive value and negative predictive value were 97% and 74%, respectively.

Conclusion

SWIR-OCT accurately identified lipid tissue in coronary autopsy specimens. This new technique may hold promise for identifying histopathological features of coronary plaque at risk for rupture.

Difference in plaque characteristics of coronary culprit lesions in a cohort of Egyptian patients presented with acute coronary syndrome and stable coronary artery disease: An optical coherence tomography study

Aims

This study was designed to utilize frequency-domain optical coherence tomography (FD-OCT) for assessment of plaque characteristics and vulnerability in patients with acute coronary syndrome (ACS) compared to stable coronary artery disease (SCAD).

Methods and results

We enrolled 48 patients; divided into an ACS-group (27 patients) and SCAD-group (21 patients) according to their clinical presentation. Hypertension and diabetes mellitus were more prevalent in SCAD group. Patients with ACS showed higher frequency of lipid-rich plaques (96.3% vs. 66.7%, P = .015), lower frequency of calcium plaques (7.4% vs. 57.1%, P < .001), and fibrous plaques (14.8% vs. 81%, P < .001) when compared with SCAD patients. The TCFA (defined as lipid-rich plaque with cap thickness <65 μm) identified more frequently (33.3% vs. 14.3%, P = .185), with a trend towards thinner median fibrous cap thickness (70 (50–180) µm vs. 100 (50–220) µm, P = .064) in ACS group. Rupture plaque (52% vs. 14.3%, P = .014), plaque erosion (18.5% vs. 0%, P = .059) and intracoronary thrombus (92.6% vs. 14.3%, P < .001) were observed more frequently in ACS group, while cholesterol crystals were identified frequently in patients with SCAD (0.0% vs. 33.3%, P = .002).

Conclusion

The current FD-OCT study demonstrated the differences of plaque morphology and identified distinct lesion characteristics between patients with ACS and those with SCAD. These findings could explain the clinical presentation of patients in both groups.

Optimization of coronary optical coherence tomography imaging using the attenuation-compensated technique: a validation study

Aim

To optimize conventional coronary optical coherence tomography (OCT) images using the attenuation-compensated technique to improve identification of plaques and the external elastic lamina (EEL) contour.

Methods and Results

The attenuation-compensated technique was optimized via manipulating contrast exponent C, and compression exponent N, to achieve an optimal contrast and signal-to-noise ratio (SNR). This was applied to 60 human coronary lesions (38 native and 22 stented) ex vivo conventional coronary OCT images acquired from heart autopsies of 10 patients and matching histology was available as reference. Three independent reviewers assessed the conventional and attenuation-compensated OCT images blindly for plaque characteristics and EEL detection. Conventional OCT and compensated OCT assessment were compared against histology. Using an optimized algorithm, the attenuation-compensated OCT images had a 2-fold improvement in contrast between different tissues in both stented and non-stented epicardial coronaries (P < 0.05). Overall sensitivity and specificity for plaque classification increased from 84 to 89% and from 92 to 94%, respectively, with substantial agreement among the three reviewers (Fleiss' Kappa k, 0.72 and 0.71, respectively). Furthermore, operators were 2.5 times more likely to identify the EEL contour in the attenuation-compensated OCT images (k = 0.72) than in the conventional OCT images (k = 0.36).

Conclusion

The attenuation-compensated technique can be retrospectively applied to conventional OCT images and improves the detection of plaque characteristics and the EEL contour. This approach could complement conventional OCT imaging in the evaluation of plaque characteristics and quantify plaque burden in the clinical setting.

A Survey on Coronary Atherosclerotic Plaque Tissue Characterization in Intravascular Optical Coherence Tomography

PURPOSE OF REVIEW

Atherosclerotic plaque deposition within the coronary vessel wall leads to arterial stenosis and severe catastrophic events over time. Identification of these atherosclerotic plaque components is essential to pre-estimate the risk of cardiovascular disease (CVD) and stratify them as a high or low risk. The characterization and quantification of coronary plaque components are not only vital but also a challenging task which can be possible using high-resolution imaging techniques.

RECENT FINDING

Atherosclerotic plaque components such as thin cap fibroatheroma (TCFA), fibrous cap, macrophage infiltration, large necrotic core, and thrombus are the microstructural plaque components that can be detected with only high-resolution imaging modalities such as intravascular ultrasound (IVUS) and optical coherence tomography (OCT). Light-based OCT provides better visualization of plaque tissue layers of coronary vessel walls as compared to IVUS. Three dominant paradigms have been identified to characterize atherosclerotic plaque components based on optical attenuation coefficients, machine learning algorithms, and deep learning techniques. This review (condensation of 126 papers after downloading 150 articles) presents a detailed comparison among various methodologies utilized for plaque tissue characterization, classification, and arterial measurements in OCT. Furthermore, this review presents the different ways to predict and stratify the risk associated with the CVD based on plaque characterization and measurements in OCT. Moreover, this review discovers three different paradigms for plaque characterization and their pros and cons. Among all of the techniques, a combination of machine learning and deep learning techniques is a best possible solution that provides improved OCT-based risk stratification.

Histopathological validation of optical coherence tomography findings of the coronary arteries

Optical coherence tomography (OCT), a catheter-based imaging modality for the visualization of coronary arteries, is widely used during percutaneous coronary intervention to improve the understanding of the anatomy of coronary artery stenosis and to elucidate the mechanisms of atherosclerosis. In this review, we provide a short description of the histopathological validations of OCT for visualizing atherosclerotic plaques and vascular healing response after drug-eluting stent (DES) implantation. Because OCT measures the intensity of light returning from within a tissue, tissue having a higher heterogeneity of optical index of refraction, such as microcalcification deposition and foam cell accumulation on the luminal surface, may exhibit stronger optical scattering that appears as a thin-cap fibroatheroma image. Furthermore, even if OCT shows exposed uncovered stent struts, some of the struts could be re-endothelialized. In our ex vivo histopathological experience, re-endothelialization at the surface of stent struts was confirmed by histopathological analysis, although OCT images showed exposed uncovered struts after DES implantation. Therefore, careful interpretation is required to assess tissue morphology and stent strut coverage by OCT.

Optical Coherence Tomography Guidance in Management of Acute Coronary Syndrome Caused by Plaque Erosion

For several decades, most physicians have believed that acute coronary syndrome (ACS) is caused by coronary thrombosis resulting from rupture of vulnerable plaque characterized by a thin fibrous cap overlying a large necrotic core and massive inflammatory cell infiltration. However, nearly one-third of ACS cases are caused by plaque erosion characterized by intact fibrous cap, less or absent necrotic core, less inflammation, and large lumen. Because of the limitations of current imaging modalities, including angiography and intravascular ultrasound, the importance of plaque erosion as a cause of acute coronary events is less well known. Optical coherence tomography (OCT) as an emerging modality with extremely high resolution is the only intravascular imaging modality available for identification of plaque erosion in vivo, which provides new insight into the mechanism of ACS. More importantly, the introduction of OCT to clinical practice enables us to differentiate the patients with ACS caused by plaque erosion from those caused by plaque rupture, thereby providing precise and personalized therapy based on the different underlying mechanisms. We systematically review the morphological characteristics of plaque erosion identified by OCT and its implications for the management of ACS.

Impact of coronary plaque morphology assessed by optical coherence tomography on cardiac troponin elevation in patients with non-ST segment elevation acute coronary syndrome

OBJECTIVES

This study aimed to use optical coherence tomography (OCT) to study the relationship between plaque morphology prior to percutaneous coronary intervention (PCI) and post-PCI cardiac troponin (cTn) elevations in patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS). Furthermore, the relationship between these findings and the adverse cardiac events during follow-up was assessed.

BACKGROUND

Association between post-PCI cTn elevations and OCT findings in NSTE-ACS patients is unclear.

METHODS

We evaluated 167 patients with stable or falling cTn values after admission who underwent PCI. Periprocedural myocardial injury (PMI) was defined as an cTn increase of more than 70× upper limit of normal (ULN) in troponin-negative patients before PCI, or more than new 70× ULN elevation from the previous nadir level in pre-PCI troponin-positive patients. Clinical and OCT findings were compared between patients with (n = 48, 29%) and without (n = 119, 71%) PMI.

RESULTS

PMI was associated with age, prior PCI, low estimated glomerular filtration rate (eGFR), OCT-derived thin-cap fibroatheroma (TCFA), plaque rupture, and lipid length. In multivariable analysis, TCFA (odds ratio [OR], 2.88; P = 0.011), eGFR (OR, 0.97, P = 0.003), and lipid length (OR, 1.12, P = 0.020) were independent predictors of PMI. At a median follow-up of 38 months, event-free survival was significantly worse in patients with PMI (log-rank test χ²  = 6.47, P = 0.011).

CONCLUSIONS

OCT analysis showed that PMI occurs more frequently in lesions with TCFA in NSTE-ACS patients, and may identify patients having a higher risk of adverse cardiac events during follow-up. © 2017 Wiley Periodicals, Inc.

Advances in Intravascular Imaging: New Insights into the Vulnerable Plaque from Imaging Studies

The term “vulnerable plaque” denotes the plaque characteristics that are susceptible to coronary thrombosis. Previous post-mortem studies proposed 3 major mechanisms of coronary thrombosis: plaque rupture, plaque erosion, and calcified nodules. Of those, characteristics of rupture-prone plaque have been extensively studied. Pathology studies have identified the features of rupture-prone plaque including thin fibrous cap, large necrotic core, expansive vessel remodeling, inflammation, and neovascularization. Intravascular imaging modalities have emerged as adjunctive tools of angiography to identify vulnerable plaques. Multiple devices have been introduced to catheterization laboratories to date, including intravascular ultrasound (IVUS), virtual-histology IVUS, optical coherence tomography (OCT), coronary angioscopy, and near-infrared spectroscopy. With the use of these modalities, our understanding of vulnerable plaque has rapidly grown over the past several decades. One of the goals of intravascular imaging is to better predict and prevent future coronary events, for which prospective observational data is still lacking. OCT delineates microstructures of plaques, whereas IVUS visualizes macroscopic vascular structures. Specifically, plaque erosion, which has been underestimated in clinical practice, is gaining an interest due to the potential of OCT to make an in vivo diagnosis. Another potential future avenue for intravascular imaging is its use to guide treatment. Feasibility of tailored therapy for acute coronary syndromes (ACS) guided by OCT is under investigation. If it is proven to be effective, it may potentially lead to major shift in the management of millions of patients with ACS every year.

Optical coherence tomography guidance during bioresorbable vascular scaffold implantation

Bioresorbable vascular scaffold (BRS) represent a revolutionary concept in interventional cardiology. After initial enthusiasm, recent real world registries, including patients with increasing lesion complexity, reported not trivial rates of scaffold thrombosis (ScT). The importance of correct patients selection as well as technical aspects during BRS implantation procedures has been highlighted in several studies suggesting that the high rate of ScT might be related to uncorrected patients/lesions selection together with underutilization of intracoronary imaging guidance leading to suboptimal BRS implantation. The high-resolution power together with the lack of shadowing observed beyond polymer struts makes optical coherence tomography (OCT) the optimal imaging technique to guide BRS implantation and identifies eventually scaffolds failures.

Current clinical applications of coronary optical coherence tomography

Optical coherence tomography (OCT) is an intra-coronary diagnostic technique that provides detailed imagings of blood vessels in the current cardiac catheterization laboratory. The higher resolution of OCT often provides superior delineation of each structure compared with intravascular ultrasound (IVUS), and it can reliably visualize the microstructure of normal and diseased arteries. The capabilities of OCT are well suited for the identification of calcified plaque and neointima formation after stent implantation. It has been reported that OCT-guided percutaneous coronary intervention (PCI) resulted in equivalent clinical and angiographic outcomes in comparison with IVUS-guided PCI. Recently, the three-dimensional reconstruction of OCT and a real-time point-to-point correspondence between coronary angiographic and OCT/OFDI images have been developed and provide useful information to PCI operators. The unique capabilities of OCT as an investigational tool for high-risk lesions will serve the cardiology community well, as it moves us toward a better understanding of atherosclerotic plaque. In addition, because of the development of new OCT technology, OCT has become a notable catheter-based imaging technology that can provide practical guidance for PCI in clinical settings.