OCT for the Identification of Vulnerable Plaque in Acute Coronary Syndrome

Lipid nanoparticles encapsulating curcumin for imaging and stabilization of vulnerable atherosclerotic plaques via phagocytic "eat-me" signals

Curcumin potentiates the stabilization of atherosclerotic plaques by polarizing macrophages, but its non-specific targeting hinders its clinical application. We aim to harness multifunctional lipid nanoparticles (MLNPs) to facilitate the imaging and targeted delivery of curcumin specifically to inflammatory macrophages, counteracting vulnerable plaques and mitigating the risk of ischemic events. Cholesteryl-9-carboxynonanoate-(125I‑iron oxide nanoparticle/Curcumin)-lipid-coated nanoparticles [9-CCN-(125I-ION/Cur)-LNPs], namely MLNPs, are designed to carry hybrid imaging agents. These agents combine 125I-ION with lipids containing phagocytic 'eat-me' signals, inducing macrophages to engulf the MLNPs. Our research demonstrates that the designed MLNPs accurately accumulate at unstable plaques and are precisely visualized and highlighted by both SPECT and MRI. Furthermore, MLNPs achieve high efficiency in delivering 125I-ION and curcumin to macrophages, ultimately leading to significant M1-to-M2 macrophage polarization. These real-time imaging and polarization capabilities of plaques have immediate clinical applicability and may pave the way for novel therapies to stabilize unstable atherosclerotic plaques.

Intracoronary Imaging for Changing Therapeutic Decisions in Patients with Multivascular Coronary Artery Disease

Background and Objectives: Atherosclerotic disease is a major contributor to heart failure, stroke, and myocardial infarction, significantly lowering the quality of life and life expectancy and placing a significant burden on healthcare. Not all lesions deemed non-significant are benign, and conversely, not all significant lesions are causative of ischemia. Fractional flow reserve (FFR) provides a functional assessment of coronary lesions, while optical coherence tomography (OCT) offers detailed imaging of plaque morphology, aiding in therapeutic decision-making. The objective of this study was to evaluate the utility of OCT and FFR as adjunctive tools in the catheterization laboratory for guiding therapeutic decisions in patients with multivessel disease for non-culprit vessels. Specifically, we aimed to assess how OCT and FFR influence therapeutic decision-making in patients with multivessel coronary artery disease. Materials and Methods: A total of 36 patients with acute coronary syndrome (ACS) and multivessel disease were randomized 1:1 into two groups: one guided by FFR alone and the other by a combination of FFR and OCT. For the FFR group, revascularization decisions for non-culprit lesions were based solely on FFR measurements. If the FFR was >0.8, the procedure was concluded, and the patient received maximal medical treatment. If the FFR was ≤0.8, a stent was placed. For the FFR + OCT group, if the FFR was >0.8, the revascularization decision was based on OCT findings. If there were no vulnerable plaques (VP), the procedure was concluded, and the patient received maximal medical treatment. If OCT imaging indicated VP, then the patient underwent revascularization. If the FFR was ≤0.8, the patient underwent revascularization regardless of OCT findings. Results: OCT imaging altered the therapeutic decision in 11 cases where FFR measurements were above 0.8, but the lesions were characterized as VP. Analyzing the total change in the decision to stent, 4 cases in the FFR group and 15 cases in the FFR and OCT groups (4 based on FFR and 11 on OCT) revealed a statistically significant difference (p = 0.0006; Relative Risk = 0.2556; 95% CI: 0.1013 to 0.5603). When analyzing the change in the total decision both to stent and not to stent, we observed a statistically significant difference, with Group 1 having 7 cases and Group 2 having 15 cases (p = 0.0153; Relative Risk = 0.4050; 95% CI: 0.2004 to 0.7698. Conclusions: Based on the findings of this study, OCT significantly increases the percentage of stenting procedures by identifying vulnerable lesions. The use of intracoronary imaging facilitates the timely identification and treatment of these vulnerable lesions. This underscores the crucial role of OCT in enhancing the precision of coronary interventions by ensuring timely intervention for vulnerable lesions, thereby potentially improving patient outcomes.

Predictive value of plaque characteristics for identification of lesions causing ischemia

BACKGROUND

Functional assessment using fractional flow reserve (FFR) and anatomical assessment using optical coherence tomography (OCT) are used in clinical practice for patients with intermediate coronary stenosis. Moreover, coronary computed tomography angiography (CTA) is a common noninvasive imaging technique for evaluating suspected coronary artery disease before being referred for angiography. This study aimed to investigate the association between FFR and plaque characteristics assessed using coronary CTA and OCT for intermediate coronary stenosis.

METHODS

Based on a prospective multicenter registry, 159 patients having 339 coronary lesions with intermediate stenosis were included. All patients underwent coronary CTA before being referred for coronary angiography, and both FFR measurements and OCT examinations were performed during angiography. A stenotic lesion identified with FFR ≤0.80 was deemed diagnostic of an ischemia-causing lesion. The predictive value of plaque characteristics assessed using coronary CTA and OCT for identifying lesions causing ischemia was analyzed.

RESULTS

Stenosis severity and plaque characteristics on coronary CTA and OCT differed between lesions that caused ischemia and those that did not. In multivariate analysis, low attenuation plaque on coronary CTA (odds ratio [OR]=2.78; P=0.038), thrombus (OR=5.13; P=0.042), plaque rupture (OR=3.25; P=0.017), and intimal vasculature on OCT (OR=2.57; P=0.012) were independent predictors of ischemic lesions. Increasing the number of these plaque characteristics offered incremental improvement in predicting the lesions causing ischemia.

CONCLUSIONS

Comprehensive anatomical evaluation of coronary stenosis may provide additional supportive information for predicting the lesions causing ischemia.

Increasing the rate of datasets amenable to CTFFR and quantitative plaque analysis: Value of software for reducing stair-step artifacts demonstrated in photon-counting detector CT

Purpose

To determine the value of an algorithm for reducing stair-step artifacts for advanced coronary analyses in sequential mode coronary CT angiography (CCTA).

Methods

Forty patients undergoing sequential mode photon-counting detector CCTA with at least one stair-step artifact were included. Twenty patients (14 males; mean age 57±17years) with 45 segments showing stair-step artifacts and without atherosclerosis were included for CTFFR analysis. Twenty patients (20 males; mean age 74±13years) with 22 segments showing stair-step artifacts crossing an atherosclerotic plaque were included for quantitative plaque analysis. Artifacts were graded, and CTFFR and quantitative coronary plaque analyses were performed in standard reconstructions and in those reconstructed with a software (entitled ZeeFree) for artifact reduction.

Results

Stair-step artifacts were significantly reduced in ZeeFree compared to standard reconstructions (p<0.05). In standard reconstructions, CTFFR was not feasible in 3/45 (7 %) segments but was feasible in all ZeeFree reconstructions. In 9/45 (20 %) segments without atherosclerosis, the ZeeFree algorithm led to a change of CTFFR values from pathologic in standard to physiologic values in ZeeFree reconstructions. In one segment (1/22, 5 %), quantitative plaque analysis was not feasible in standard but only in ZeeFree reconstruction. The mean overall plaque volume (111±60 mm3), the calcific (77±47 mm3), fibrotic (31±28 mm3), and lipidic (4±3 mm3) plaque components were higher in standard than in ZeeFree reconstructions (overall 75±50 mm3, p<0.001; calcific 51±42 mm3, p<0.001; fibrotic 22±19 mm3, p<0.05; lipidic 3±3 mm3, p=0.055).

Conclusion

Despite the lack of reference standard modalities for CTFFR and coronary plaque analysis, initial evidence indicates that an algorithm for reducing stair-step artifacts in sequential mode CCTA increases the rate and quality of datasets amenable to advanced coronary artery analysis, hereby potentially improving patient management.

Impact of Intravascular Imaging-Guided Stent Optimization According to Clinical Presentation in Patients Undergoing Complex PCI

BACKGROUND

It is unclear whether the beneficial effects of intravascular imaging-guided stent optimization vary by clinical presentation during complex percutaneous coronary intervention (PCI).

OBJECTIVES

In this prespecified, stratified subgroup analysis from RENOVATE-COMPLEX-PCI (Randomized Controlled Trial of Intravascular Imaging Guidance versus Angiography-Guidance on Clinical Outcomes After Complex PCI), we sought to compare the outcomes between intravascular imaging vs angiography guidance according to clinical presentation.

METHODS

Patients with complex coronary artery lesions were randomly assigned to undergo either intravascular imaging-guided PCI or angiography-guided PCI in a 2:1 ratio. The primary endpoint was target vessel failure (TVF), which is a composite of cardiac death, target vessel-related myocardial infarction, or clinically driven target vessel revascularization.

RESULTS

Of 1,639 patients, 832 (50.8%) presented with acute coronary syndrome (ACS) and 807 (49.2%) with chronic coronary syndrome. During a median follow-up of 2.1 years (Q1-Q3: 1.4-3.0 years), there was no significant interaction between the treatment effect of intravascular imaging and clinical presentation (P for interaction = 0.19). Among patients with ACS, the incidences of TVF were 10.4% in the intravascular imaging group and 14.6% in the angiography group (HR: 0.74; 95% CI: 0.48-1.15; P = 0.18). Among patients with CCS, the incidences of TVF were 5.0% in the intravascular imaging group and 10.4% in the angiography group (HR: 0.46; 95% CI: 0.27-0.80; P = 0.006). Achieving stent optimization by intravascular imaging resulted in a reduced risk of TVF among patients with ACS who were randomly assigned to intravascular imaging-guided PCI for complex coronary lesions (optimized vs unoptimized, 6.5% vs 14.1%; HR: 0.49; 95% CI: 0.27-0.87; P = 0.02) but not those with CCS (5.4% vs 4.7%, HR: 1.18; 95% CI: 0.53-2.59; P = 0.69).

CONCLUSIONS

No significant interaction was observed between the benefits of intravascular imaging and clinical presentation in the risk of TVF. Stent optimization by intravascular imaging was particularly important for ACS patients. (Intravascular Imaging- Versus Angiography-Guided Percutaneous Coronary Intervention For Complex Coronary Artery Disease [RENOVATE]; NCT03381872).

Role of Lipid-Lowering and Anti-Inflammatory Therapies on Plaque Stabilization

Atherosclerosis is the predominant underlying etiopathology of coronary artery disease. Changes in plaque phenotype from stable to high risk may spur future major adverse cardiac events (MACE). Different pharmacological therapies have been implemented to mitigate this risk. Over the last two decades, intravascular imaging modalities have emerged in clinical studies to clarify how these therapies may affect the composition and burden of coronary plaques. Lipid-lowering agents, such as statins, ezetimibe, and proprotein convertase subtilisin/kexin type 9 inhibitors, were shown not only to reduce low-density lipoprotein levels and MACE but also to directly affect features of coronary plaque vulnerability. Studies have demonstrated that lipid-lowering therapy reduces the percentage of atheroma volume and number of macrophages and increases fibrous cap thickness. Future studies should answer the question of whether pharmacological plaque stabilization may be sufficient to mitigate the risk of MACE for selected groups of patients with atherosclerotic coronary disease.

Sodium-Glucose Cotransporter-2 Inhibitors Stabilize Coronary Plaques in Acute Coronary Syndrome With Diabetes Mellitus

Sodium-glucose cotransporter-2 inhibitors (SGLT2is) are widely used in cardiology and are effective in treating acute coronary syndrome (ACS). Their effects on unstable plaque in patients with ACS remains unclear. This study aimed to examine the effectiveness of SGLT2is in coronary plaque based on optical coherence tomography (OCT) images and the prognosis of ACS with type 2 diabetes mellitus. This retrospective study included 109 patients in the total cohort and 29 patients in the OCT cohort. Based on SGLT2i administration after ACS, the total cohort was categorized into non-SGLT2i (n = 69) and SGLT2i (n = 40) groups. The OCT cohort had 15 and 14 patients in the non-SGLT2i and SGLT2i groups, respectively. The OCT images of unstable plaque were analyzed in nonstented lesions during ACS catheterization and at the 6-month follow-up. The total cohort was assessed after 1 year for major adverse cardiovascular events, including all-cause mortality, revascularization, cerebrovascular disease, and heart failure hospitalization. SGLT2is improved unstable lesions with a significantly thicker fibrous cap (48 ± 15 μm vs 26 ± 24 μm, p = 0.005), reduced lipid arc (-29 ± 12° vs -18 ± 14°, p = 0.028), higher % decrease in total lipid arc (-35 ± 13% vs -19 ± 18%, p = 0.01), and lower major adverse cardiovascular event incidence (log-rank p = 0.023, hazard ratio 4.72 [1.08 to 20.63]) and revascularization rate (adjusted hazard ratio 6.77 [1.08 to 42.52]) than the non-SGLT2i group. In conclusion, SGLT2is can improve the markers of plaque stability and may improve the prognosis in patients with type 2 diabetes mellitus.

Automatic lumen and anatomical layers segmentation in IVOCT images using meta learning

Automated analysis of the vessel structure in intravascular optical coherence tomography (IVOCT) images is critical to assess the health status of vessels and monitor coronary artery disease progression. However, deep learning-based methods usually require well-annotated large datasets, which are difficult to obtain in the field of medical image analysis. Hence, an automatic layers segmentation method based on meta-learning was proposed, which can simultaneously extract the surfaces of the lumen, intima, media, and adventitia using a handful of annotated samples. Specifically, we leverage a bi-level gradient strategy to train a meta-learner for capturing the shared meta-knowledge among different anatomical layers and quickly adapting to unknown anatomical layers. Then, a Claw-type network and a contrast consistency loss were designed to better learn the meta-knowledge according to the characteristic of annotation of the lumen and anatomical layers. Experimental results on the two cardiovascular IVOCT datasets show that the proposed method achieved state-of-art performance.

Accuracy and limitation of plaque detection by coronary CTA: a section-to-section comparison with optical coherence tomography

Plaques identified by Coronary CT angiography (CCTA) are important in clinical diagnosis and primary prevention. High-risk plaque features by CCTA have been extensively validated using optical coherence tomography (OCT). However, since their general diagnostic performance and limitations have not been fully investigated, we sought to compare CCTA with OCT among consecutive vessel sections. We retrospectively compared 188 consecutive plaques and 84 normal sections in 41 vessels from 40 consecutive patients referred for chest pain evaluation who had both CCTA and OCT with a median time lapse of 1 day. The distance to reference points were used to co-register between the modalities and the diagnostic performance of CCTA was evaluated against OCT. Plaque categories evaluated by CT were calcified, non-calcified and mixed. The diagnostic performance of CCTA was excellent for detecting any plaque identified by OCT with the sensitivity, specificity, negative and positive predictive values and accuracy of 92%, 98%, 99%, 84% and 93%, respectively. The lower than expected negative predictive value was due to failure of detecting sub-millimeter calcified (≤ 0.25 mm²) (N = 12) and non-calcified plaques (N = 4). Misclassification of plaque type accounted for majority of false negative findings (25/41, 61%) which was most prevalent among the mixed plaque (19/41, 46%). There was calcification within mixed plaques (N = 5) seen by CCTA but missed by OCT. Our findings suggest that CCTA is excellent at identifying coronary plaques except those sub-millimeter in size which likely represent very early atherosclerosis, although the clinical implication of very mild atherosclerosis is yet to be determined.

Moving toward Precision Medicine in Acute Coronary Syndromes: A Multimodal Assessment of Non-Culprit Lesions

Patients with acute coronary syndrome and multivessel disease experience several recurrent adverse events that lead to poor outcomes. Given the complexity of treating these patients, and the extremely high risk of long-term adverse events, the assessment of non-culprit lesions becomes crucial. Recently, two trials have shown a possible clinical benefit into treat non-culprit lesions using a fraction flow reserve (FFR)-guided approach, compared to culprit-lesion-only PCI. However, the most recent FLOW Evaluation to Guide Revascularization in Multivessel ST-elevation Myocardial Infarction (FLOWER-MI) trial did not show a benefit of the use of FFR-guided PCI compared to an angiography-guided approach. Otherwise, intracoronary imaging using optical coherence tomography (OCT), intravascular ultrasound (IVUS), or near-infrared spectroscopy (NIRS) could provide both quantitative and qualitative assessments of non-culprit lesions. Different studies have shown how the characterization of coronary lesions with intracoronary imaging could lead to clinical benefits in these peculiar group of patients. Moreover, non-invasive evaluations of NCLs have begun to take ground in this context, but more insights through adequately powered and designed studies are needed. The aim of this review is to outline the available techniques, both invasive and non-invasive, for the assessment of multivessel disease in patients with STEMI, and to provide a systematic guidance on the assessment and approach to these patients.

Detection of thin-cap fibroatheroma in IVOCT images based on weakly supervised learning and domain knowledge

Automatic detection of thin-cap fibroatheroma (TCFA) on intravascular optical coherence tomography images is essential for the prevention of acute coronary syndrome. However, existing methods need to mark the exact location of TCFAs on each frame as supervision, which is extremely time-consuming and expensive. Hence, a new weakly supervised framework is proposed to detect TCFAs using only image-level tags as supervision. The framework comprises cut, feature extraction, relation, and detection modules. First, based on prior knowledge, a cut module was designed to generate a small number of specific region proposals. Then, to learn global information, a relation module was designed to learn the spatial adjacency and order relationships at the feature level, and an attention-based strategy was introduced in the detection module to effectively aggregate the classification results of region proposals as the image-level predicted score. The results demonstrate that the proposed method surpassed the state-of-the-art weakly supervised detection methods.

The Height and Mobility of Protruding Plaque After Carotid Artery Stenting Are Associated with Postoperative Ischemic Lesions

BACKGROUND

Tissue protrusion (TP) is a possible cause of cerebral infarction after carotid artery stenting (CAS). Using optical frequency domain imaging (OFDI) and angioscopy, we investigated the relationship between the morphological features of TP and postoperative new ischemic lesions on magnetic resonance imaging (MRI)-diffusion weighted imaging (DWI) after CAS.

METHODS

Fifty patients who underwent CAS and subsequent poststenting intravascular evaluation using both OFDI and angioscopy were included. CAS was performed for proximal protection via the femoral artery approach, and intravascular evaluation with OFDI and angioscopy were performed after stent placement. We compared the background and poststenting intravascular findings between patients with and without postoperative new ischemic lesions on MRI-DWI.

RESULTS

TP was observed in 42 patients (84%), and postoperative new ischemic lesions on MRI-DWI were observed in 32 patients (64%). The frequency of TP did not differ between the 2 groups, but the height of TP was higher in the DWI-positive group (0.62 mm vs. 0.29 mm, P = 0.0028), and mobile TP was observed only in the DWI-positive group. The height of TP (P = 0.023) was an independent predictor of new periprocedural ischemic brain lesions after CAS, and its cut-off value for mobility was 0.55 mm on the receiver operating characteristic curve (area under the curve, 0.93).

CONCLUSIONS

The height of TP on OFDI and mobile-TP on angioscopy after CAS were associated with postoperative new ischemic lesions on MRI-DWI. The intravascular evaluation using OFDI and angioscopy could be helpful for a detailed evaluation of TP.

Immature neutrophil is associated with coronary plaque vulnerability based on optical coherence tomography analysis

INTRODUCTION

High neutrophil to lymphocyte ratio is considered to predict poor prognosis of acute coronary syndrome (ACS). However, the association of neutrophil subpopulation with plaque vulnerability and the incidence of ACS remains unknown.

METHODS AND RESULTS

Blood samples from 48 patients with unstable angina (UA), 31 with ST-segment elevation myocardial infarction (STEMI) and 33 healthy controls were collected at admission. The morphology of coronary plaques in 48 UA patients were further evaluated by optical coherence tomography (OCT). According to maturation stages of neutrophils and the expression of CD10 and CD101, circulating neutrophils could be divided into pre-neutrophils (CD101-CD10-), immature neutrophils (CD101+CD10-) and mature neutrophils (CD101+CD10+). While the number of pre-neutrophil was quite low in blood and comparable among three groups, the absolute counts and percentage of CD10- immature neutrophils were higher in peripheral bloods of UA and STEMI patients compared with those in healthy controls. The concentration of plasma myeloperoxidase was positively associated with the percentage of CD10- immature neutrophils. Furthermore, UA patients with thin-cap fibroatheroma (TCFA) observed by OCT had a higher proportion and larger number of immature neutrophils as compared to those without TCFA. The percentage of immature neutrophils also closely correlated with plaque rupture and the feature of vulnerable plaque, including thinner fibrous cap and larger lipid core, but did not associate with percent lumen stenosis.

CONCLUSION

Our findings emphasize that the abnormally increased level of CD10- immature neutrophils may sever as a promising marker of the incidence of ACS and plaque vulnerability.

OCTOPUS - Optical coherence tomography plaque and stent analysis software

Background and objective

Compared with other imaging modalities, intravascular optical coherence tomography (IVOCT) has significant advantages for guiding percutaneous coronary interventions, assessing their outcomes, and characterizing plaque components. To aid IVOCT research studies, we developed the Optical Coherence TOmography PlaqUe and Stent (OCTOPUS) analysis software, which provides highly automated, comprehensive analysis of coronary plaques and stents in IVOCT images.

Methods

User specifications for OCTOPUS were obtained from detailed, iterative discussions with IVOCT analysts in the Cardiovascular Imaging Core Laboratory at University Hospitals Cleveland Medical Center, a leading laboratory for IVOCT image analysis. To automate image analysis results, the software includes several important algorithmic steps: pre-processing, deep learning plaque segmentation, machine learning identification of stent struts, and registration of pullbacks for sequential comparisons. Intuitive, interactive visualization and manual editing of segmentations were included in the software. Quantifications include stent deployment characteristics (e.g., stent area and stent strut malapposition), strut level analysis, calcium angle, and calcium thickness measurements. Interactive visualizations include (x,y) anatomical, en face, and longitudinal views with optional overlays (e.g., segmented calcifications). To compare images over time, linked visualizations were enabled to display up to four registered vessel segments at a time.

Results

OCTOPUS has been deployed for nearly 1 year and is currently being used in multiple IVOCT studies. Underlying plaque segmentation algorithm yielded excellent pixel-wise results (86.2% sensitivity and 0.781 F1 score). Using OCTOPUS on 34 new pullbacks, we determined that following automated segmentation, only 13% and 23% of frames needed any manual touch up for detailed lumen and calcification labeling, respectively. Only up to 3.8% of plaque pixels were modified, leading to an average editing time of only 7.5 s/frame, an approximately 80% reduction compared to manual analysis. Regarding stent analysis, sensitivity and precision were both greater than 90%, and each strut was successfully classified as either covered or uncovered with high sensitivity (94%) and specificity (90%). We demonstrated use cases for sequential analysis. To analyze plaque progression, we loaded multiple pullbacks acquired at different points (e.g., pre-stent, 3-month follow-up, and 18-month follow-up) and evaluated frame-level development of in-stent neo-atherosclerosis. In ex vivo cadaver experiments, the OCTOPUS software enabled visualization and quantitative evaluation of irregular stent deployment in the presence of calcifications identified in pre-stent images.

Conclusions

We introduced and evaluated the clinical application of a highly automated software package, OCTOPUS, for quantitative plaque and stent analysis in IVOCT images. The software is currently used as an offline tool for research purposes; however, the software's embedded algorithms may also be useful for real-time treatment planning.

Assessment of fractional flow reserve in intermediate coronary stenosis using optical coherence tomography-based machine learning

Objectives

This study aimed to evaluate and compare the diagnostic accuracy of machine learning (ML)- fractional flow reserve (FFR) based on optical coherence tomography (OCT) with wire-based FFR irrespective of the coronary territory.

Background

ML techniques for assessing hemodynamics features including FFR in coronary artery disease have been developed based on various imaging modalities. However, there is no study using OCT-based ML models for all coronary artery territories.

Methods

OCT and FFR data were obtained for 356 individual coronary lesions in 130 patients. The training and testing groups were divided in a ratio of 4:1. The ML-FFR was derived for the testing group and compared with the wire-based FFR in terms of the diagnosis of ischemia (FFR ≤ 0.80).

Results

The mean age of the subjects was 62.6 years. The numbers of the left anterior descending, left circumflex, and right coronary arteries were 130 (36.5%), 110 (30.9%), and 116 (32.6%), respectively. Using seven major features, the ML-FFR showed strong correlation (r = 0.8782, P < 0.001) with the wire-based FFR. The ML-FFR predicted wire-based FFR ≤ 0.80 in the test set with sensitivity of 98.3%, specificity of 61.5%, and overall accuracy of 91.7% (area under the curve: 0.948). External validation showed good correlation (r = 0.7884, P < 0.001) and accuracy of 83.2% (area under the curve: 0.912).

Conclusion

OCT-based ML-FFR showed good diagnostic performance in predicting FFR irrespective of the coronary territory. Because the study was a small-size study, the results should be warranted the performance in further large-scale research.

Pericoronary adipose tissue radiomics from coronary CT angiography identifies vulnerable plaques characteristics in intravascular OCT

Pericoronary adipose tissue (PCAT) features on CT have been shown to reflect local inflammation, and signals increased cardiovascular risk. Our goal was to determine if PCAT radiomics extracted from coronary CT angiography (CCTA) images are associated with intravascular optical coherence tomography (IVOCT)-identified vulnerable plaque characteristics (e.g., microchannels [MC] and thin-cap fibroatheroma [TCFA]). CCTA and IVOCT images of 30 lesions from 25 patients were registered. Vessels with vulnerable plaques were identified from the registered IVOCT images. PCAT radiomics features were extracted from CCTA images for the lesion region of interest (PCAT-LOI) and the entire vessel (PCAT-Vessel). We extracted 1356 radiomics features, including intensity (first-order), shape, and texture features. Features were reduced using standard approaches (e.g., high feature correlation). Using stratified three-fold cross-validation with 1000 repeats, we determined the ability of PCAT radiomics features from CCTA to predict IVOCT vulnerable plaque characteristics. In identification of TCFA lesions, PCAT-LOI and PCAT-Vessel radiomics models performed comparably (AUC±standard deviation 0.78±0.13, 0.77±0.14). For identification of MC lesions, PCAT-Vessel radiomics model (0.89±0.09) was moderately better associated than that of PCAT-LOI model (0.83±0.12). Both PCAT-LOI and PCAT-Vessel radiomics models also similarly identified coronary vessels thought to be highly vulnerable (i.e., both TCFA and MC) (0.88±0.10, 0.91±0.09). Favorable radiomics features tended to be those describing texture and size of PCAT. PCAT radiomics can identify coronary vessels with TCFA or MC, consistent with IVOCT. CCTA radiomics may improve risk stratification by noninvasively detecting vulnerable plaque characteristics that are only visible with IVOCT.

Automated analysis of fibrous cap in intravascular optical coherence tomography images of coronary arteries

Thin-cap fibroatheroma (TCFA) and plaque rupture have been recognized as the most frequent risk factor for thrombosis and acute coronary syndrome. Intravascular optical coherence tomography (IVOCT) can identify TCFA and assess cap thickness, which provides an opportunity to assess plaque vulnerability. We developed an automated method that can detect lipidous plaque and assess fibrous cap thickness in IVOCT images. This study analyzed a total of 4360 IVOCT image frames of 77 lesions among 41 patients. Expert cardiologists manually labeled lipidous plaque based on established criteria. To improve segmentation performance, preprocessing included lumen segmentation, pixel-shifting, and noise filtering on the raw polar (r, θ) IVOCT images. We used the DeepLab-v3 plus deep learning model to classify lipidous plaque pixels. After lipid detection, we automatically detected the outer border of the fibrous cap using a special dynamic programming algorithm and assessed the cap thickness. Our method provided excellent discriminability of lipid plaque with a sensitivity of 85.8% and A-line Dice coefficient of 0.837. By comparing lipid angle measurements between two analysts following editing of our automated software, we found good agreement by Bland-Altman analysis (difference 6.7° ± 17°; mean ~ 196°). Our method accurately detected the fibrous cap from the detected lipid plaque. Automated analysis required a significant modification for only 5.5% frames. Furthermore, our method showed a good agreement of fibrous cap thickness between two analysts with Bland-Altman analysis (4.2 ± 14.6 µm; mean ~ 175 µm), indicating little bias between users and good reproducibility of the measurement. We developed a fully automated method for fibrous cap quantification in IVOCT images, resulting in good agreement with determinations by analysts. The method has great potential to enable highly automated, repeatable, and comprehensive evaluations of TCFAs.

A-line-based thin-cap fibroatheroma detection with multi-view IVOCT images using multi-task learning and contrastive learning

Automatic detection of thin-cap fibroatheroma (TCFA) is essential to prevent acute coronary syndrome. Hence, in this paper, a method is proposed to detect TCFAs by directly classifying each A-line using multi-view intravascular optical coherence tomography (IVOCT) images. To solve the problem of false positives, a multi-input-output network was developed to implement image-level classification and A-line-based classification at the same time, and a contrastive consistency term was designed to ensure consistency between two tasks. In addition, to learn spatial and global information and obtain the complete extent of TCFAs, an architecture and a regional connectivity constraint term are proposed to classify each A-line of IVOCT images. Experimental results obtained on the 2017 China Computer Vision Conference IVOCT dataset show that the proposed method achieved state-of-art performance with a total score of 88.7±0.88%, overlap rate of 88.64±0.26%, precision rate of 84.34±0.86%, and recall rate of 93.67±2.29%.

Epicardial Adipose Tissue Thickness Is Related to Plaque Composition in Coronary Artery Disease

(1) Background: Currently, limited data are available regarding the relationship between epicardial fat and plaque composition. The aim of this study was to assess the relationship between visceral fat surrounding the heart and the lipid core burden in patients with coronary artery diseases; (2) Methods: Overall, 331 patients undergoing coronary angiography with combined near-infrared spectroscopy and intravascular ultrasound imaging were evaluated for epicardial adipose tissue (EAT) thickness using transthoracic echocardiography. Patients were divided into thick EAT and thin EAT groups according to the median value; (3) Results: There was a positive correlation between EAT thickness and maxLCBI4mm, and maxLCBI4mm was significantly higher in the thick EAT group compared to the thin EAT group (437 vs. 293, p < 0.001). EAT thickness was an independent predictor of maxLCBI4mm ≥ 400 along with age, low-density lipoprotein-cholesterol level, acute coronary syndrome presentation, and plaque burden in a multiple linear regression model. Receiver operating characteristic curve analysis showed that EAT thickness was a predictor for maxLCBI4mm ≥ 400; (4) Conclusions: In the present study, EAT thickness is related to the lipid core burden assessed by NIRS-IVUS in patients with CAD which suggests that EAT may affect the stability of the plaques in coronary arteries.

Intracoronary Imaging of Vulnerable Plaque-From Clinical Research to Everyday Practice

The introduction into clinical practice of intravascular imaging, including intravascular ultrasound (IVUS), optical coherence tomography (OCT) and their derivatives, allowed for the in vivo assessment of coronary atherosclerosis in humans, including insights into plaque evolution and progression process. Intravascular ultrasound, the most commonly used intravascular modality in many countries, due to its low resolution cannot assess many features of vulnerable plaque such as lipid plaque or thin-cap fibroatheroma. Thus, novel methods were introduced to facilitate this problem including virtual histology intravascular ultrasound and later on near-infrared spectroscopy and OCT. Howbeit, none of the currently used modalities can assess all known characteristics of plaque vulnerability; hence, the idea of combining different intravascular imaging methods has emerged including NIRS-IVUS or OCT-IVUS imaging. All of those described methods may allow us to identify the most vulnerable plaques, which are prone to cause acute coronary syndrome, and thus they may allow us to introduce proper treatment before plaque destabilization.

Global research trends in in-stent neoatherosclerosis: A CiteSpace-based visual analysis

BACKGROUND

Recent studies have shown that in-stent neoatherosclerosis (ISNA/NA) is an important cause of late stent failure. A comprehensive understanding of the current state of research in this field will facilitate the analysis of its development trends and hot frontiers. However, no bibliometric correlation has been reported yet. Here, we analyze the relevant literature since the emergence of the concept and provide valuable insights.

METHODS

Publications were collected from the Web of Science Core Collection (WoSCC) and PubMed. Microsoft Excel, SPSS and CiteSpace were used to analyze and present the data.

RESULTS

A total of 498 articles were collected, with Japan and Cardiovasc Res Fdn being the main publishing forces in all country/region and institutions. J AM COLL CARDIOL is the journal with the most published and co-cited articles. According to co-citation analysis, optical coherence tomography, thrombosis, implantation, restenosis, drug-eluting stent, and bare metal stent have become more and more popular recently.

CONCLUSION

ISNA is a niche and emerging field. How to reduce the incidence of ISNA and improve the late patency rate of coronary stents may remain a hot spot for future research. The pathogenesis of ISNA also needs to be explored in more depth.

Automated Segmentation of Microvessels in Intravascular OCT Images Using Deep Learning

Microvessels in vascular plaque are associated with plaque progression and are found in plaque rupture and intra-plaque hemorrhage. To analyze this characteristic of vulnerability, we developed an automated deep learning method for detecting microvessels in intravascular optical coherence tomography (IVOCT) images. A total of 8403 IVOCT image frames from 85 lesions and 37 normal segments were analyzed. Manual annotation was performed using a dedicated software (OCTOPUS) previously developed by our group. Data augmentation in the polar (r,θ) domain was applied to raw IVOCT images to ensure that microvessels appear at all possible angles. Pre-processing methods included guidewire/shadow detection, lumen segmentation, pixel shifting, and noise reduction. DeepLab v3+ was used to segment microvessel candidates. A bounding box on each candidate was classified as either microvessel or non-microvessel using a shallow convolutional neural network. For better classification, we used data augmentation (i.e., angle rotation) on bounding boxes with a microvessel during network training. Data augmentation and pre-processing steps improved microvessel segmentation performance significantly, yielding a method with Dice of 0.71 ± 0.10 and pixel-wise sensitivity/specificity of 87.7 ± 6.6%/99.8 ± 0.1%. The network for classifying microvessels from candidates performed exceptionally well, with sensitivity of 99.5 ± 0.3%, specificity of 98.8 ± 1.0%, and accuracy of 99.1 ± 0.5%. The classification step eliminated the majority of residual false positives and the Dice coefficient increased from 0.71 to 0.73. In addition, our method produced 698 image frames with microvessels present, compared with 730 from manual analysis, representing a 4.4% difference. When compared with the manual method, the automated method improved microvessel continuity, implying improved segmentation performance. The method will be useful for research purposes as well as potential future treatment planning.

Immersive educational curriculum on intracoronary optical coherence tomography image analysis among naïve readers

BACKGROUND

Optical coherence tomography (OCT) is an intravascular imaging modality for analysing coronary vessels. Image interpretation remains an obstacle for novice readers due to technical artefacts and uncertainty in tissue characterization. Despite an expanding clinical and research role for OCT, few training efforts exist, and there is an absence of a national standardized educational curriculum. We sought to determine whether an interactive, feedback-based OCT curriculum improved image interpretation among naive readers.

METHODS

Naive OCT readers completed both a Standard curriculum, comprised of self-directed didactics and consensus statements, and an Augmented curriculum, which provided real-time digital feedback of feature identification and measurements. Modules were separated by a minimum one-week washout period. After each module, and blinded to the exam answers, subjects completed an identical expert-designed 413-item exam to assess technical knowledge and ability to identify and measure vessel features. Performances were compared using Exact Wilcoxon signed-rank tests.

RESULTS

Among the 7 included subjects were 3 medical students, 3 internal medicine residents, and 1 cardiovascular medicine fellow with no prior OCT experience. The technical knowledge score (maximum 13) was significantly higher with the Augmented compared with the Standard curriculum (median 11 vs. 7, p = 0.03). After undergoing the Augmented curriculum, all 7 subjects were able to identify features of plaque rupture (Standard curriculum: 5/7 subjects, p = 0.5) and macrophages (Standard curriculum: 6/7 subjects, p = 0.99), differentiate the components between red and white thrombus (Standard curriculum: 6/7 subjects, p = 0.99), and characterize lipid plaque by attenuation, signal, homogeneity, and borders (Standard curriculum: 5/7 subjects, p = 0.5). Performances on the remaining exam portions did not differ between curricula.

CONCLUSIONS

The need for standardized, effective training in OCT image interpretation is increasingly essential as the intravascular imaging modality becomes widely utilized among interventional cardiologists and trainees. A novel interactive OCT curriculum enhanced naive readers' technical knowledge and may supplement traditional self-learning in refining analytic skills.

Plaque Structural Stress: Detection, Determinants and Role in Atherosclerotic Plaque Rupture and Progression

Atherosclerosis remains a major cause of death worldwide, with most myocardial infarctions being due to rupture or erosion of coronary plaques. Although several imaging modalities can identify features that confer risk, major adverse cardiovascular event (MACE) rates attributable to each plaque are low, such that additional biomarkers are required to improve risk stratification at plaque and patient level. Coronary arteries are exposed to continual mechanical forces, and plaque rupture occurs when plaque structural stress (PSS) exceeds its mechanical strength. Prospective studies have shown that peak PSS is correlated with acute coronary syndrome (ACS) presentation, plaque rupture, and MACE, and provides additional prognostic information to imaging. In addition, PSS incorporates multiple variables, including plaque architecture, plaque material properties, and haemodynamic data into a defined solution, providing a more detailed overview of higher-risk lesions. We review the methods for calculation and determinants of PSS, imaging modalities used for modeling PSS, and idealized models that explore structural and geometric components that affect PSS. We also discuss current experimental and clinical data linking PSS to the natural history of coronary artery disease, and explore potential for refining treatment options and predicting future events.

Computational Fractional Flow Reserve From Coronary Computed Tomography Angiography—Optical Coherence Tomography Fusion Images in Assessing Functionally Significant Coronary Stenosis

Background

Coronary computed tomography angiography (CTA) and optical coherence tomography (OCT) provide additional functional information beyond the anatomy by applying computational fluid dynamics (CFD). This study sought to evaluate a novel approach for estimating computational fractional flow reserve (FFR) from coronary CTA-OCT fusion images.

Methods

Among patients who underwent coronary CTA, 148 patients who underwent both pressure wire-based FFR measurement and OCT during angiography to evaluate intermediate stenosis in the left anterior descending artery were included from the prospective registry. Coronary CTA-OCT fusion images were created, and CFD was applied to estimate computational FFR. Based on pressure wire-based FFR as a reference, the diagnostic performance of Fusion-FFR was compared with that of CT-FFR and OCT-FFR.

Results

Fusion-FFR was strongly correlated with FFR (r = 0.836, P < 0.001). Correlation between FFR and Fusion-FFR was stronger than that between FFR and CT-FFR (r = 0.682, P < 0.001; z statistic, 5.42, P < 0.001) and between FFR and OCT-FFR (r = 0.705, P < 0.001; z statistic, 4.38, P < 0.001). Area under the receiver operating characteristics curve to assess functionally significant stenosis was higher for Fusion-FFR than for CT-FFR (0.90 vs. 0.83, P = 0.024) and OCT-FFR (0.90 vs. 0.83, P = 0.043). Fusion-FFR exhibited 84.5% accuracy, 84.6% sensitivity, 84.3% specificity, 80.9% positive predictive value, and 87.5% negative predictive value. Especially accuracy, specificity, and positive predictive value were superior for Fusion-FFR than for CT-FFR (73.0%, P = 0.007; 61.4%, P < 0.001; 64.0%, P < 0.001) and OCT-FFR (75.7%, P = 0.021; 73.5%, P = 0.020; 69.9%, P = 0.012).

Conclusion

CFD-based computational FFR from coronary CTA-OCT fusion images provided more accurate functional information than coronary CTA or OCT alone.

Clinical Trial Registration

[www.ClinicalTrials.gov], identifier [NCT03298282].

Coronary Computed Tomography Angiography Analysis of Calcium Content to Identify Non-culprit Vulnerable Plaques in Patients With Acute Coronary Syndrome

Background

Aside from the culprit plaque, the presence of vulnerable plaques in patients with acute coronary syndrome (ACS) may be associated with future cardiac events. A link between calcification and plaque rupture has been previously described.

Aim

To assess whether analysis of the calcium component of coronary plaques using CT angiography, coronary computed tomographic angiography (CCTA) can help to detect additional vulnerable plaques in patients with non-ST elevation myocardial infarction (NSTEMI).

Materials And Methods

Cross sectional study of consecutive patients referred for NSTEMI from 30 July to 30 August 2018 with CCTA performed before coronary angiography with systematic optical coherence tomography (OCT) analysis of all coronary arteries within 24 h of clinical onset of NSTEMI. Three types of plaques were defined: culprit plaques defined by angiography (vulnerable culprit plaques–VCP) – plaques with a fibrous cap thickness < 65 microns or thrombus in OCT (vulnerable non-culprit plaque–VNCP) – plaques with a fibrous cap thickness ≥ 65 microns in OCT (stable plaque–SP).

Results

A total of 134 calcified plaques were identified in 29 patients (73% male, 59 ± 14 years) with 29(22%) VCP, 28(21%) VNCP and 77(57%) SP. Using CCTA analysis of the calcium component, factors associated with vulnerable plaques were longer calcification length, larger calcification volume, lower calcium mass, higher Agatston score plaque-specific (ASp), presence of spotty calcifications and an intimal position in the wall. In multivariate analysis, ASp, calcification length and spotty calcifications were independently associated to vulnerable plaques. There was no difference between VCP and VNCP.

Conclusions

CCTA analysis of calcium component of the plaque could help to identify additional vulnerable plaques in NSTEMI patients.

Dual-Resonance (16/32 MHz) Piezoelectric Transducer With a Single Electrical Connection for Forward-Viewing Robotic Guidewire

Peripheral artery disease (PAD) affects more than 200 million people globally. Minimally invasive endovascular procedures can provide relief and salvage limbs while reducing injury rates and recovery times. Unfortunately, when a calcified chronic total occlusion is encountered, ~25% of endovascular procedures fail due to the inability to advance a guidewire using the view provided by fluoroscopy. To enable a sub-millimeter, robotically steerable guidewire to cross these occlusions, a novel single-element, dual-band transducer is developed that provides simultaneous multifrequency, forward-viewing imaging with high penetration depth and high spatial resolution while requiring only a single electrical connection. The design, fabrication, and acoustic characterization of this device are described, and proof-of-concept imaging is demonstrated in an ex vivo porcine artery after integration with a robotically steered guidewire. Measured center frequencies of the developed transducer were 16 and 32 MHz, with -6 dB fractional bandwidths of 73% and 23%, respectively. When imaging a 0.2-mm wire target at a depth of 5 mm, measured -6 dB target widths were 0.498 ± 0.02 and 0.268 ± 0.01 mm for images formed at 16 and 32 MHz, respectively. Measured SNR values were 33.3 and 21.3 dB, respectively. The 3-D images of the ex vivo artery demonstrate high penetration for visualizing vessel morphology at 16 MHz and ability to resolve small features close to the transducer at 32 MHz. Using images acquired simultaneously at both frequencies as part of an integrated forward-viewing, guidewire-based imaging system, an interventionalist could visualize the best path for advancing the guidewire to improve outcomes for patients with PAD.

Vulnerable Plaque in Patients with Acute Coronary Syndrome: Identification, Importance, and Management

MI is a leading cause of morbidity and mortality worldwide. Coronary artery thrombosis is the final pathologic feature of the most cases of acute MI primarily caused by atherosclerotic coronary artery disease. The concept of vulnerable plaque has evolved over the years but originated from early pioneering work unveiling the crucial role of plaque rupture and subsequent coronary thrombosis as the dominant cause of MI. Along with systemic cardiovascular risk factors, developments of intravascular and non-invasive imaging modalities have allowed us to identify coronary plaques thought to be at high risk for rupture. However, morphological features alone may only be one of many factors which promote plaque progression. The current vulnerable-plaque-oriented approaches to accomplish personalized risk assessment and treatment have significant room for improvement. In this review, the authors discuss recent advances in the understanding of vulnerable plaque and its management strategy from pathology and clinical perspectives.

Current and Future Applications of Artificial Intelligence in Coronary Artery Disease

Cardiovascular diseases (CVDs) carry significant morbidity and mortality and are associated with substantial economic burden on healthcare systems around the world. Coronary artery disease, as one disease entity under the CVDs umbrella, had a prevalence of 7.2% among adults in the United States and incurred a financial burden of 360 billion US dollars in the years 2016–2017. The introduction of artificial intelligence (AI) and machine learning over the last two decades has unlocked new dimensions in the field of cardiovascular medicine. From automatic interpretations of heart rhythm disorders via smartwatches, to assisting in complex decision-making, AI has quickly expanded its realms in medicine and has demonstrated itself as a promising tool in helping clinicians guide treatment decisions. Understanding complex genetic interactions and developing clinical risk prediction models, advanced cardiac imaging, and improving mortality outcomes are just a few areas where AI has been applied in the domain of coronary artery disease. Through this review, we sought to summarize the advances in AI relating to coronary artery disease, current limitations, and future perspectives.

Leukocyte Telomere Length Shortening Implies Plaque Instability and Major Adverse Cardiovascular Events in Patients With Angiographically Intermediate Lesions

Background

Telomere shortening, an indicator of aging, is associated with age-related diseases. This study aims to investigate the association between leukocyte telomere length (LTL) and thin-capped fibroatheromata (TCFA) and the impact of using LTL cutoff to determine the incidence of major adverse cardiovascular events (MACEs) in patients with angiographically intermediate coronary lesions.

Methods

This was a signal-center retrospective study focusing on patients who underwent coronary angiography and optical coherence tomography (OCT). The degree of coronary stenosis was assessed by angiography. The presence of TCFA was determined by OCT imaging. A total of 156 patients with angiographically intermediate coronary lesions were enrolled.

Results

Leukocyte telomere lengths were significantly shorter in the TCFA group compared with non-TCFA group [11.95 (10.56, 15.21) kb vs. 13.81 (12.06, 16.11) kb, p = 0.003]. The short-LTL group and long-LTL group were divided according to the optimal cut-off value which was determined by the receiver operating characteristic (ROC) curve analysis. Logistic regression model revealed that short-LTL was independently associated with TCFA incidence (odds ratio [OR] 4.387, 95% CI: 1.902–10.120, p = 0.001) after adjusting for confounding factors. Over a 24-months follow-up, the MACE incidence among patients with short-LTL was significantly higher than those in the long-LTL group (12.5 vs. 2.0%, p = 0.006 by log-rank test). Multivariable cox regression analysis indicated that short-LTL (hazard ratio [HR] 9.716, 95% CI: 1.995–47.319, p = 0.005) was an independent prognostic factor of MACE incidence in angiographically intermediate coronary lesions patients.

Conclusions

Short-LTL was independently associated with the incidence of TCFA and may serve as a prognostic factor for MACE risk on top of conventional risk factors.

The evolving role of cardiac imaging in patients with myocardial infarction and non-obstructive coronary arteries

Myocardial infarction (MI) with non-obstructive coronary arteries (MINOCA) represents a heterogeneous clinical conundrum accounting for about 6%-8% of all acute MI who are referred for coronary angiography. Current guidelines and consensus documents recommend that these patients are appropriately diagnosed, uncovering the causes of MINOCA, so that specific therapies can be prescribed. Indeed, there are a variety of causes that can result in this clinical condition, and for this reason diagnostic cardiac imaging has an emerging critical role in the assessment of patients with suspected or confirmed MINOCA. In last years, different cardiac imaging techniques have been evaluated in this context, and the comprehension of their strengths and limitations is of the utmost importance for their effective use in clinical practice. Moreover, recent evidence is clearly suggesting that a multimodality cardiac imaging approach, combining different techniques, seems to be crucial for a proper management of MINOCA. However, great variability still exists in clinical practice in the management of patients with suspected MINOCA, also depending on the availability of diagnostic tools and local expertise. Herein, we review the current knowledge supporting the use of different cardiac imaging techniques in patients with MINOCA, underscoring the importance of a comprehensive multimodality cardiac imaging approach and proposing a practical diagnostic algorithm to properly identify and treat the specific causes of MINOCA, in order to improve prognosis and the quality of life in these patients.

Nanomaterial-Based Drug Targeted Therapy for Cardiovascular Diseases: Ischemic Heart Failure and Atherosclerosis

Cardiovascular diseases (CVDs) represent the most important epidemic of our century, with more than 37 million patients globally. Furthermore, CVDs are associated with high morbidity and mortality, and also increased hospitalization rates and poor quality of life. Out of the plethora of conditions that can lead to CVDs, atherosclerosis and ischemic heart disease are responsible for more than 2/3 of the cases that end in severe heart failure and finally death. Current therapy strategies for CVDs focus mostly on symptomatic benefits and have a moderate impact on the underlying physiopathological mechanisms. Modern therapies try to approach different physiopathological pathways such as reduction of inflammation, macrophage regulation, inhibition of apoptosis, stem-cell differentiation and cellular regeneration. Recent technological advances make possible the development of several nanoparticles used not only for the diagnosis of cardiovascular diseases, but also for targeted drug delivery. Due to their high specificity, nanocarriers can deliver molecules with poor pharmacokinetics and dynamics such as: peptides, proteins, polynucleotides, genes and even stem cells. In this review we focused on the applications of nanoparticles in the diagnosis and treatment of ischemic heart failure and atherosclerosis.

Circulating Biomarkers Reflecting Destabilization Mechanisms of Coronary Artery Plaques: Are We Looking for the Impossible?

Despite significant strides to mitigate the complications of acute coronary syndrome (ACS), this clinical entity still represents a major global health burden. It has so far been well-established that most of the plaques leading to ACS are not a result of gradual narrowing of the vessel lumen, but rather a result of sudden disruption of vulnerable atherosclerotic plaques. As most of the developed imaging modalities for vulnerable plaque detection are invasive, multiple biomarkers were proposed to identify their presence. Owing to the pivotal role of lipids and inflammation in the pathophysiology of atherosclerosis, most of the biomarkers originated from one of those processes, whereas recent advancements in molecular sciences shed light on the use of microRNAs. Yet, at present there are no clinically implemented biomarkers or any other method for that matter that could non-invasively, yet reliably, diagnose the vulnerable plaque. Hence, in this review we summarized the available knowledge regarding the pathophysiology of plaque instability, the current evidence on potential biomarkers associated with plaque destabilization and finally, we discussed if search for biomarkers could one day bring us to non-invasive, cost-effective, yet valid way of diagnosing the vulnerable, rupture-prone coronary artery plaques.

Intracoronary optical coherence tomography: state of the art and future directions

Optical coherence tomography (OCT) has been increasingly utilised to guide percutaneous coronary intervention (PCI). Despite the diagnostic utility of OCT, facilitated by its high resolution, the impact of intracoronary OCT on clinical practice has thus far been limited. Difficulty in transitioning from intravascular ultrasound (IVUS), complex image interpretation, lack of a standardised algorithm for PCI guidance, and paucity of data from prospective clinical trials have contributed to the modest adoption. Herein, we provide a comprehensive up-do-date overview on the utility of OCT in coronary artery disease, including technical details, device set-up, simplified OCT image interpretation, recognition of the imaging artefacts, and an algorithmic approach for using OCT in PCI guidance. We discuss the utility of OCT in acute coronary syndromes, provide a summary of the clinical trial data, list the work in progress, and discuss the future directions.

Morphology and phenotype characteristics of atherosclerotic plaque in patients with acute coronary syndrome: contemporary optical coherence tomography findings

BACKGROUND

Contemporary optical coherence tomography (OCT) findings in patients with acute coronary syndromes (ACS) are still subject of controversy. We sought to use OCT to evaluate plaque morphology and phenotype classification in patients with ACS.

METHODS

Using optical coherence tomography, culprit lesions were morphologically classified as plaque rupture, plaque erosion, calcified nodule, thin-cap fibroatheroma, thick-cap fibroatheroma (TCFA) or fibrotic, fibrocalcific or fibrolipidic plaque. Quantitative and qualitative analyses also included cholesterol crystals, neovascularization, spotty calcification and thrombus.

RESULTS

Of the 110 lesions imaged from June 2012 to April 2016, 54 (49%) were in patients with unstable angina (UA), 31 (28%) were in non-ST-elevation myocardial infarction (STEMI) patients and 25 (23%) were in STEMI patients. Compared with STEMI patients, patients with UA/non-STEMI were older and had more hypertension, hypercholesterolemia, known coronary artery disease, prior myocardial infarction and higher use of antiplatelet therapy. More patients with STEMI had lipidic arc >90% (36.6 versus 70.8%, P = 0.003), red and mixed thrombus (12.9 versus 28.0% and 7.1 versus 44.0%, respectively, all P < 0.001), plaque rupture (29.4 versus 76.0%, P < 0.001) and TCFA (57.1 versus 84.0%; P = 0.01). Predictors of plaque rupture were STEMI at presentation (odds ratio: 9.35, 95% confidence interval: 1.66-52.61, P = 0.01) and diabetes mellitus (odds ratio: 6.16, 95% confidence interval: 1.33-28.58, P = 0.02).

CONCLUSIONS

In this single-center study, the culprit lesion of patients with STEMI had more lipid, red and mixed thrombus, plaque rupture and TCFA versus patients with UA/non-STEMI. Clinical presentation may be driven by distinct pathophysiologic mechanisms in patients with ACS.

CT texture analysis of vulnerable plaques on optical coherence tomography

PURPOSE

To explore whether CT texture analysis can identify thin-cap fibroatheroma (TCFA) determined by optical coherence tomography (OCT).

METHODS

Thirty-three patients with 43 lesions who underwent both CCTA and OCT within 3 months were retrospectively included. 12 conventional CT-derived plaque features, fat attenuation index (FAI) and 1691 plaque radiomics features were extracted to discriminate TCFA lesions and non-TCFA lesions determined by OCT. Minimum redundancy and maximum relevance (mRMR) method was employed to select radiomics features. The top ranked features were used to construct a forward stepwise logistic radiomics model. The performance of radiomics model was compared with the conventional high-risk plaque (HRP) features model and FAI model for the detection of TCFA.

RESULTS

Out of 1691 features, 35 features were significantly different between TCFA and non-TCFA lesions (all p＜0.05) while only low attenuation plaque (LAP) was more frequent in TCFA group (p = 0.004). There was no significant difference in FAI between TCFA and non-TCFA lesions. Five features were ultimately integrated into the radiomics model after mRMR analysis, which demonstrated significantly higher AUC for the detection of TCFA (0.952; 95 % CI: 0.897-1.000) compared with the conventional HRP features model (0.621; 95 % CI: 0.469-0.773, p < 0.001) and FAI model (0.52; 95 % CI: 0.33-0.70, p < 0.001).

CONCLUSION

CT texture analysis performs better at identifying TCFA determined by OCT compared with conventional CT-derived plaque parameters and FAI. Texture analysis may serve as a potential non-invasive method of evaluating vulnerable plaque.

Vascular imaging of atherosclerosis: Strengths and weaknesses

Atherosclerosis is an inflammatory disease that can lead to several complications such as ischemic heart disease, stroke, and peripheral vascular disease. Therefore, researchers and clinicians rely heavily on the use of imaging modalities to identify, and more recently, quantify the burden of atherosclerosis in the aorta, carotid arteries, coronary arteries, and peripheral vasculature. These imaging techniques vary in invasiveness, cost, resolution, radiation exposure, and presence of artifacts. Consequently, a detailed understanding of the risks and benefits of each technique is crucial prior to their introduction into routine cardiovascular screening. Additionally, recent research in the field of microvascular imaging has proven to be important in the field of atherosclerosis. Using techniques such as contrast-enhanced ultrasound and superb microvascular imaging, researchers have been able to detect blood vessels within a plaque lesion that may contribute to vulnerability and rupture. This paper will review the strengths and weaknesses of the various imaging techniques used to measure atherosclerotic burden. Furthermore, it will discuss the future of advanced imaging modalities as potential biomarkers for atherosclerosis.

High contrast power Doppler imaging in side-viewing intravascular ultrasound imaging via angular compounding

The ability to assess likelihood of plaque rupture can determine the course of treatment in coronary artery disease. One indicator of plaque vulnerability is the development of blood vessels within the plaque, or intraplaque neovascularization. In order to visualize these vessels with increased sensitivity in the cardiac catheterization lab, a new approach for imaging blood flow in small vessels using side-viewing intravascular ultrasound (IVUS) is proposed. This approach based on compounding adjacent angular acquisitions was evaluated in tissue mimicking phantoms and ex vivo vessels. In phantom studies, the Doppler CNR increased from 3.3 ± 1.0 to 13 ± 2.6 (conventional clutter filtering) and from 1.9 ± 0.15 to 7.5 ± 1.1 (SVD filtering) as a result of applying angular compounding. When imaging flow at a rate of 5.6 mm/s in 200 µm tubes adjacent to the lumen of ex vivo porcine arteries, the Doppler CNR increased from 5.3 ± 0.95 to 7.2 ± 1.3 (conventional filtering) and from 23 ± 3.3 to 32 ± 6.7 (SVD filtering). Applying these strategies could allow increased sensitivity to slow flow in side-viewing intravascular ultrasound imaging.

Optical coherence tomography-based machine learning for predicting fractional flow reserve in intermediate coronary stenosis: a feasibility study

Machine learning approaches using intravascular optical coherence tomography (OCT) to predict fractional flow reserve (FFR) have not been investigated. Both OCT and FFR data were obtained for left anterior descending artery lesions in 125 patients. Training and testing groups were partitioned in the ratio of 5:1. The OCT-based machine learning-FFR was derived for the testing group and compared with wire-based FFR in terms of ischemia diagnosis (FFR ≤ 0.8). The OCT-based machine learning-FFR showed good correlation (r = 0.853, P < 0.001) with the wire-based FFR. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the OCT-based machine learning-FFR for the testing group were 100%, 92.9%, 87.5%, 100%, and 95.2%, respectively. The OCT-based machine learning-FFR can be used to simultaneously acquire information on both image and functional modalities using one procedure, suggesting that it may provide optimized treatments for intermediate coronary artery stenosis.

Prognostic irrelevance of plaque vulnerability following plaque sealing in high-risk patients with type 2 diabetes: an optical coherence tomography study

Background

Type 2 diabetes mellitus (T2DM) is associated with an increased cardiovascular risk related at least in part to a more vulnerable plaque phenotype. However, patients with T2DM exhibit also an increased risk following percutaneous coronary intervention (PCI). It is unknown if plaque vulnerability of a treated lesion influences cardiovascular outcomes in patients with T2DM. In this study, we aimed to assess the association of plaque morphology as determined by optical coherence tomography (OCT) with cardiovascular outcome following PCI in high-risk patients with T2DM.

Methods

81 patients with T2DM and OCT-guided PCI were recruited. Pre-interventional OCT and systematic follow-up of median 66.0 (IQR = 8.0) months were performed.

Results

During follow-up, 24 patients (29.6%) died. The clinical parameters age (HR 1.16 per year, 95% CI 1.07–1.26, p < 0.001), diabetic polyneuropathy (HR 3.58, 95% CI 1.44–8.93, p = 0.006) and insulin therapy (HR 3.25, 95% CI 1.21–8.70, p = 0.019) predicted mortality in T2DM patients independently. Among OCT parameters only calcium-volume-index (HR 1.71 per 1000°*mm, 95% CI 1.21–2.41, p = 0.002) and lesion length (HR 1.93 per 10 mm, 95% CI 1.02–3.67, p = 0.044) as parameters describing atherosclerosis extent were significant independent predictors of mortality. However, classical features of plaque vulnerability, such as thickness of the fibrous cap, the extent of the necrotic lipid core and the presence of macrophages had no significant predictive value (all p = ns).

Conclusion

Clinical parameters including those describing diabetes severity as well as OCT-parameters characterizing atherosclerotic extent but not classical features of plaque vulnerability predict mortality in T2DM patients following PCI. These data suggest that PCI may provide effective plaque sealing resulting in limited importance of local target lesion vulnerability for future cardiovascular events in high-risk patients with T2DM.

Reviewing imaging modalities for the assessment of plaque erosion

Plaque rupture followed by intracoronary thrombus formation is recognized as the most common pathophysiological mechanism in acute coronary syndromes (ACS). The second most common underlying substrate for ACS is plaque erosion whose hallmark is thrombus formation without cap disruption. Invasive and non-invasive methods have emerged as a promising tool for evaluation of plaque features that either predict or detect plaque erosion. Optical coherence tomography (OCT), high-definition intravascular ultrasound (IVUS), near-infrared spectroscopy (NIRS), and near-infrared autofluorescence (NIRF) have been used to study plaque erosion. The detection of plaque erosion in the clinical setting, mainly facilitated by OCT, has shed light upon the complex pathophysiology underlying ACS not related to plaque rupture. Coronary computed tomography angiography (CCTA), which is to date the most commonly used non-invasive technique for coronary plaque evaluation, may also have a role in the evaluation of patients predisposed to erosion. Also, computational models enabling quantification of endothelial shear stress may pave the way to new research in coronary plaque pathophysiology. This review focuses on the recent imaging techniques for the evaluation of plaque erosion including invasive and non-invasive assessment.

Relationship between monocyte/lymphocyte ratio and non-culprit plaque vulnerability in patients with acute coronary syndrome: An optical coherence tomography study

The importance of monocyte/lymphocyte ratio (MLR) has been indicated in the initiation and progression of coronary artery disease. However, few previous researches demonstrated the relationship between MLR and plaque vulnerability. We aimed to investigate coronary non-culprit plaque vulnerability in patients with acute coronary syndrome (ACS) by optical coherence tomography (OCT).A total of 72 ACS patients who underwent coronary angiography and OCT test in Beijing Anzhen Hospital were included in this retrospective study. The plaque vulnerability and plaque morphology were assessed by OCT.The non-culprit plaque in high MLR group exhibited more vulnerable features, characterizing as thinner thickness of fibrous cap (P = .013), greater maximum lipid core angle (P = .010) and longer lipid plaque length (P = .041). A prominently negative liner relation was found between MLR and thickness of fibrous cap (R = -0.225, P = .005). Meanwhile, the proportion of OCT-detected thin cap fibro-atheroma (TCFA) (P = .014) and plaque rupture (P = .017) were higher in high MLR group. Most importantly, multivariable logistic regression analysis showed MLR level was identified as an independent contributor to the presence of TCFA (OR:3.316, 95%: 1.448-7.593, P = .005). MLR could differentiate TCFA with a sensitivity of 60.0% and a specificity of 85.1%.Circulating MLR level has potential value in identifying the presence of vulnerable plaque in patients with ACS. MLR, as a non- invasive biomarker of inflammation, may be valuable in revealing plaque vulnerability.

Optical coherence tomography: fundamentals and clinical utility

Although coronary angiography is the standard method employed to assess the severity of coronary artery disease and to guide treatment strategies, it provides only 2D image of the intravascular lesions. In contrast, intravascular imaging modalities such as optical coherence tomography (OCT) produce cross-sectional images of the coronary arteries at a far greater spatial resolution, capable of accurately determining vessel size as well as plaque morphology, eliminating many of the disadvantages inherent to angiography. This review will discuss the role of OCT in the catherization laboratory for the assessment and management of coronary disease.

The relationship between coronary artery calcium density and optical coherence tomography-derived plaque characteristics

BACKGROUND AND AIMS

Although coronary artery calcium (CAC) density has been associated with plaque stability, pathological evidence is lacking. We investigated the relationship between coronary computed tomography (CCT)-derived CAC density and multiple calcified and high-risk plaque (HRP) characteristics using optical coherence tomography (OCT).

METHODS

We analyzed 83 plaques from 33 stable angina patients who underwent both CCT and OCT. CAC density was measured at calcium plaques with ≥90 Hounsfield units (HU) and ≥130 HU using custom CT software. The correlation between median CAC density and OCT-derived calcium size (thickness and area) was assessed. To investigate whether median CAC densities measured at the 90 HU threshold were associated with plaque vulnerability, OCT-derived plaque characteristics and HRP characteristics were compared between the low (90-129 HU), intermediate (130-199 HU) and high (≥200 HU) CAC HU groups.

RESULTS

Median CAC densities at 130 HU were moderately associated with calcium thickness (R = 0.573, p < 0.001) and area (R = 0.560, p < 0.001). Similar results were observed at 90 HU (thickness, R = 0.615, p < 0.001; area, R = 0.612, p < 0.001). Among groups with low, intermediate and high HU levels, calcium thickness (0.42 ± 0.14 mm, 0.60 ± 0.17 mm and 0.77 ± 0.19 mm, respectively; p < 0.001) and area (0.55 ± 0.29 mm², 1.20 ± 0.58 mm² and 1.78 ± 0.87 mm², respectively; p < 0.001) were significantly greater in the high HU group. HRP characteristics, however, did not differ among the three groups.

CONCLUSIONS

OCT-derived calcium size, but not HRP characteristics, were associated with CAC density, suggesting that CAC density is driven mainly by calcified plaque size but not local plaque vulnerability.

Culprit lesion morphology in patients with ST-segment elevation myocardial infarction assessed by optical coherence tomography

AIMS

This study sought to evaluate the incidence of ruptured plaques and nonruptured plaques (NRP) and to compare patient characteristics and detailed plaque morphology features between the two culprit types in ST-segment elevation myocardial infarction (STEMI) patients, using optical coherence tomography (OCT).

METHODS AND RESULTS

Using OCT, the culprit lesions in patients with STEMI were assessed prior to stent implantation. The culprit lesion was categorized as ruptured plaques or NRP, and the plaque components were evaluated. Fifty-two patients (69.3%) presented with ruptured plaques and 23 (30.7%) with NRP. Patients with NRP were younger (58.0 ± 10.4 vs 64.7 ± 9.9 years, P = 0.01) and more often smokers (72.7% vs 37.1%, P = 0.001), compared to ruptured plaques. NRP contained significantly more fibrotic plaque (20.0% [interquartile range (IQR) 13.7-29.8] vs 11.3% [IQR 6.9-18.1], P = 0.005), but less lipidic plaque (44.0% ± 13.7 vs 59.3% ± 13.6, P < 0.001), less superficial [5.0% (IQR 2.8-7.5) vs 8.1% (IQR 5.7-11.0), P = 0.005] and profound macrophages [0.9% (IQR 0.0-1.7) vs 2.2% (IQR 0.9-4.7), P = 0.003]. The prevalence, numbers and lengths of thin-cap fibroatheroma (TCFA) were significantly lower in NRP, compared to ruptured plaques [47.8% vs 88.5%, 0 (IQR 0-1) vs 1 (IQR 1-2) and 0 mm (IQR 0-2.7) vs 4.5 mm (IQR 2.3-7.7), P < 0.001].

CONCLUSIONS

One-third of STEMI patients had culprit lesions without an OCT-detectable ruptured plaque. Culprit lesions with NRP contained less vulnerable plaque components, such as lipid plaque, TCFAs and macrophages compared to ruptured plaques.