Measurement of the thickness of the fibrous cap by optical coherence tomography

Cardiac Optical Coherence Tomography: History, Current Status, and Perspective

For more than 2 decades since the first imaging procedure was performed in a living patient, intravascular optical coherence tomography (OCT), with its unprecedented image resolution, has made significant contributions to cardiovascular medicine in the realms of vascular biology research and percutaneous coronary intervention. OCT has contributed to a better understanding of vascular biology by providing insights into the pathobiology of atherosclerosis, including plaque phenotypes and the underlying mechanisms of acute coronary syndromes such as plaque erosion, neoatherosclerosis, stent thrombosis, and myocardial infarction with nonobstructive coronary arteries. Moreover, OCT has been used as an adjunctive imaging tool to angiography for the guidance of percutaneous coronary intervention procedures to optimize outcomes. However, broader application of OCT has faced challenges, including subjective interpretation of the images and insufficient clinical outcome data. Future developments including artificial intelligence-assisted interpretation, multimodality catheters, and micro-OCT, as well as large prospective outcome studies could broaden the impact of OCT on cardiovascular medicine.

Optical Coherence Tomography in Vulnerable Plaque and Acute Coronary Syndrome

Optical coherence tomography (OCT) is an intravascular imaging technique that uses near-infrared light. OCT provides high-resolution cross-sectional images of coronary arteries and enables tissue characterization of atherosclerotic plaques. OCT can identify plaque rupture, plaque erosion, and calcified nodule in culprit lesions of acute coronary syndrome. OCT can also detect important morphologic features of vulnerable plaques such as thin fibrous caps, large lipid cores, macrophages accumulation, intraplaque microvasculature, cholesterol crystals, healed plaques, and intraplaque hemorrhage.

Role of plaque imaging for identification of vulnerable patients beyond the stage of myocardial ischemia

Chronic coronary syndrome (CCS) is a progressive disease, which often first manifests as acute coronary syndrome (ACS). Imaging modalities are clinically useful in making decisions about the management of patients with CCS. Accumulating evidence has demonstrated that myocardial ischemia is a surrogate marker for CCS management; however, its ability to predict cardiovascular death or nonfatal myocardial infarction is limited. Herein, we present a review that highlights the latest knowledge available on coronary syndromes and discuss the role and limitations of imaging modalities in the diagnosis and management of patients with coronary artery disease. This review covers the essential aspects of the role of imaging in assessing myocardial ischemia and coronary plaque burden and composition. Furthermore, recent clinical trials on lipid-lowering and anti-inflammatory therapies have been discussed. Additionally, it provides a comprehensive overview of intracoronary and noninvasive cardiovascular imaging modalities and an understanding of ACS and CCS, with a focus on histopathology and pathophysiology.

Combining IVUS + OCT Data, Biomechanical Models and Machine Learning Method for Accurate Coronary Plaque Morphology Quantification and Cap Thickness and Stress/Strain Index Predictions

Assessment and prediction of vulnerable plaque progression and rupture risk are of utmost importance for diagnosis, management and treatment of cardiovascular diseases and possible prevention of acute cardiovascular events such as heart attack and stroke. However, accurate assessment of plaque vulnerability assessment and prediction of its future changes require accurate plaque cap thickness, tissue component and structure quantifications and mechanical stress/strain calculations. Multi-modality intravascular ultrasound (IVUS), optical coherence tomography (OCT) and angiography image data with follow-up were acquired from ten patients to obtain accurate and reliable plaque morphology for model construction. Three-dimensional thin-slice finite element models were constructed for 228 matched IVUS + OCT slices to obtain plaque stress/strain data for analysis. Quantitative plaque cap thickness and stress/strain indices were introduced as substitute quantitative plaque vulnerability indices (PVIs) and a machine learning method (random forest) was employed to predict PVI changes with actual patient IVUS + OCT follow-up data as the gold standard. Our prediction results showed that optimal prediction accuracies for changes in cap-PVI (C-PVI), mean cap stress PVI (meanS-PVI) and mean cap strain PVI (meanSn-PVI) were 90.3% (AUC = 0.877), 85.6% (AUC = 0.867) and 83.3% (AUC = 0.809), respectively. The improvements in prediction accuracy by the best combination predictor over the best single predictor were 6.6% for C-PVI, 10.0% for mean S-PVI and 8.0% for mean Sn-PVI. Our results demonstrated the potential using multi-modality IVUS + OCT image to accurately and efficiently predict plaque cap thickness and stress/strain index changes. Combining mechanical and morphological predictors may lead to better prediction accuracies.

New insights into fibrous cap thickness of vulnerable plaques assessed by optical coherence tomography

Objective

Vulnerable plaques with fibrous cap thickness (FCT) of ≤65 μm are prone to rupture and/or thrombosis. However, plaques with FCT > 65 μm cause acute myocardial infarction and even sudden death. We aimed to investigate the relationship between 65 < FCT ≤ 80 μm and plaque rupture and/or thrombosis using optical coherence tomography (OCT).

Methods

OCT was performed on culprit lesions in 502 consecutively enrolled patients to identify FCT. Patients were classified into three groups according to FCT: Group A (FCT ≤ 65 μm, n = 147), Group B (65 < FCT ≤ 80 μm, n = 84) and Group C (FCT > 80 μm, n = 271). Clinical and laboratory data was collected from the inpatient medical record system.

Results

Plaques with thinner FCT, especially < 65 μm, were more susceptible to rupture and/or thrombosis (P < 0.001). Plaques with FCT between 65 and 80 μm had a higher probability of rupture and/or thrombosis than those with FCT > 80 μm (P < 0.001). In multivariable analysis, FCT ≤ 65 μm and 65 < FCT ≤ 80 μm were independent predictors for plaque rupture ([FCT ≤ 65 μm vs. FCT > 80 μm]: OR = 8.082, 95% CI = 4.861 to 13.435, P < 0.001; [65 < FCT ≤ 80 μm vs. FCT > 80 μm]: OR = 2.463, 95% CI = 1.370 to 4.430, P = 0.003), thrombosis ([FCT ≤ 65 μm vs. FCT > 80 μm]: OR = 25.224, 95% CI = 13.768 to 46.212, P < 0.001; [65 < FCT ≤ 80 μm vs. FCT > 80 μm]: OR = 3.675, 95% CI = 2.065 to 6.542, P < 0.001) and plaque rupture with thrombosis ([FCT ≤ 65 μm vs. FCT > 80 μm]: OR = 22.593, 95% CI = 11.426 to 44.674, P < 0.001; [65 < FCT ≤ 80 μm vs. FCT > 80 μm]: OR = 4.143, 95% CI = 1.869 to 9.184, P < 0.001).

Conclusions

OCT-assessed 65 < FCT ≤ 80 μm was independently associated with increased risk of plaque rupture and/or thrombosis compared with FCT > 80 μm.

Harnessing imaging biomarkers to refine individualized cardiovascular disease risk: a case-based discussion

Traditional models of cardiovascular risk assessment rely on population-level risk factors and may not accurately capture individualized risk. Imaging biomarkers such as plaque characterization and pericoronary fat inflammation may offer refined risk prediction and allow physicians to personalize care-plans for cardiovascular disease prevention. The integration of plaque morphology and pericoronary inflammation into clinical care is highlighted using a case-based discussion. This article reviews the existing body of evidence supporting the use of novel biomarkers in an individualized comprehensive risk assessment algorithm.

Reproducibility between three-dimensional turbo spin-echo and two-dimensional dual inversion recovery turbo spin-echo for coronary vessel wall imaging in Kawasaki disease

Magnetic resonance vessel wall imaging is desirable for evaluating Kawasaki disease (KD)-associated coronary arterial lesions. To evaluate the reproducibility of three-dimensional turbo spin-echo (3D-TSE) and two-dimensional dual inversion-recovery turbo spin-echo (2D-DIR-TSE) for coronary vessel wall imaging in KD. Ten patients were prospectively enrolled. Coronary vessel wall imaging with axial-slice orientation 3D-TSE and 2D-DIR-TSE were acquired for cross-sectional images in aneurysmal and normal regions. Lumen area (LA), wall area (WA), and normalized wall index (NWI) of cross-sectional images were measured in both regions. Reproducibility between 3D-TSE and 2D-DIR-TSE was evaluated via intraclass correlation coefficients (ICCs) and Bland–Altman plots. 48 points (aneurysmal, 27; normal, 21) were evaluated. There were high ICCs between 3D-TSE and 2D-DIR-TSE in LA (0.95) and WA (0.95). In aneurysmal regions, 95% limits of agreement were LA, WA, and NWI of − 29.9 to 30.4 mm², − 18.8 to 15.0 mm², and − 0.22 to 0.20, respectively. In normal regions, the 95% limits of agreement were LA, WA, and NWI of − 4.44 to 4.38 mm², − 3.51 to 4.30 mm², and − 0.14 to 0.16, respectively. No fixed and proportional biases between 3D-TSE and 2D-DIR-TSE images in aneurysmal and normal regions were noted. 3D-TSE was reproducible with conventional 2D-DIR-TSE for coronary vessel wall assessment on KD.

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.

Effect of alirocumab on coronary plaque in patients with coronary artery disease assessed by optical coherence tomography

BACKGROUND

Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors have been demonstrated to produce significantly greater reduction in LDL cholesterol levels and cardiovascular events than standard statin therapy. However, evidence on the impact of PCSK9 inhibitors on coronary plaque composition and morphology is limited.

METHODS

In this open-label randomized study, eligible patients with intermediate coronary lesions and elevated LDL cholesterol values were randomized to either alirocumab 75 mg Q2W plus statin (atorvastatin 20 mg/day or rosuvastatin 10 mg/day) therapy or standard care. Optical coherence tomography (OCT) assessments for target lesions were obtained at baseline and at 36 weeks of follow-up.

RESULTS

LDL cholesterol levels were significantly decreased in both the alirocumab and standard care arms, whereas the absolute reduction in LDL cholesterol was significantly greater in patients treated with alirocumab (1.72 ± 0.51 vs. 0.96 ± 0.59, P < 0.0001). Compared with standard care, the addition of alirocumab to statins was associated with significantly greater increases in minimum fibrous cap thickness (18.0 [10.8-29.2] μm vs 13.2 [7.4-18.6] μm; P = 0.029), greater increases in minimum lumen area (0.20[0.10-0.33] mm2 vs 0.13 [0.12-0.24] mm2; P = 0.006) and a greater diminution in maximum lipid arc (15.1̊ [7.8-24.5] vs. 8.4̊ [2.0-10.5]; P = 0.008).

CONCLUSIONS

The addition of alirocumab to statins can not only provide additional LDL cholesterol lowering effects but also have a potential role in promoting a more stable plaque phenotype.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04851769 . Registered 2 Mar 2019.

Using Optical Coherence Tomography and Intravascular Ultrasound Imaging to Quantify Coronary Plaque Cap Stress/Strain and Progression: A Follow-Up Study Using 3D Thin-Layer Models

Accurate plaque cap thickness quantification and cap stress/strain calculations are of fundamental importance for vulnerable plaque research. To overcome uncertainties due to intravascular ultrasound (IVUS) resolution limitation, IVUS and optical coherence tomography (OCT) coronary plaque image data were combined together to obtain accurate and reliable cap thickness data, stress/strain calculations, and reliable plaque progression predictions. IVUS, OCT, and angiography baseline and follow-up data were collected from nine patients (mean age: 69; m: 5) at Cardiovascular Research Foundation with informed consent obtained. IVUS and OCT slices were coregistered and merged to form IVUS + OCT (IO) slices. A total of 114 matched slices (IVUS and OCT, baseline and follow-up) were obtained, and 3D thin-layer models were constructed to obtain stress and strain values. A generalized linear mixed model (GLMM) and least squares support vector machine (LSSVM) method were used to predict cap thickness change using nine morphological and mechanical risk factors. Prediction accuracies by all combinations (511) of those predictors with both IVUS and IO data were compared to identify optimal predictor(s) with their best accuracies. For the nine patients, the average of minimum cap thickness from IVUS was 0.17 mm, which was 26.08% lower than that from IO data (average = 0.23 mm). Patient variations of the individual errors ranged from ‒58.11 to 20.37%. For maximum cap stress between IO and IVUS, patient variations of the individual errors ranged from ‒30.40 to 46.17%. Patient variations of the individual errors of maximum cap strain values ranged from ‒19.90 to 17.65%. For the GLMM method, the optimal combination predictor using IO data had AUC (area under the ROC curve) = 0.926 and highest accuracy = 90.8%, vs. AUC = 0.783 and accuracy = 74.6% using IVUS data. For the LSSVM method, the best combination predictor using IO data had AUC = 0.838 and accuracy = 75.7%, vs. AUC = 0.780 and accuracy = 69.6% using IVUS data. This preliminary study demonstrated improved plaque cap progression prediction accuracy using accurate cap thickness data from IO slices and the differences in cap thickness, stress/strain values, and prediction results between IVUS and IO data. Large-scale studies are needed to verify our findings.

Is the effect of atorvastatin 60 mg on stabilization of lipid-rich plaque equivalent to that of rosuvastatin 10 mg? A serial optical coherence tomography combined with intravascular ultrasound imaging

OBJECTIVES

This study aimed to compare the effect of atorvastatin 60 (AT60) mg to that of rosuvastatin 10 (RT10) mg on the morphological changes in lipid-rich plaques (LRPs) and plaque volume, using serial optical coherence tomography (OCT) and intravascular ultrasound imaging (IVUS).

BACKGROUND

Intensive lipid lowering therapy by statin provides more clinical benefit compared to that of moderate lipid lowering therapy.

METHODS

Fifty patients who underwent OCT and IVUS at baseline, 6, and 12 months were grouped by statin therapy into the AT60 mg (n = 27) and RT10 mg (n = 23) groups. The relationships between absolute and percentage changes in biomarkers and fibrous cap thickness (FCT) during follow-up were investigated using a simple regression analysis.

RESULTS

At 6 months, the mean low-density lipoprotein cholesterol level reduced from 113.5 to 65.5 mg/dl (AT60 mg group) and 100.2 to 72.2 mg/dl (RT10 mg groups). A continuous increase in FCT from baseline to 12 months was observed in both groups (p < .001, p < .001, respectively). Mean lipid arc significantly decreased in both AT60 mg (189.0 ± 55.9°, 170.9 ± 60.2°, 155.6 ± 50.6°, p < .001) and RT10 mg (160.0 ± 45.6°, 151.2 ± 48.5°, 141.1 ± 52.9°, p = .010) groups. Plaque burden did not change significantly in both groups.

CONCLUSIONS

Lipid-lowering therapy effect with AT60 mg was equivalent to that of RT10 mg in terms of change in plaque morphology. AT60 mg showed more intensive low-density lipid cholesterol level reduction compared to RT10 mg while RT10 mg was effective in increasing the high-density lipid cholesterol level. Both statin therapies could effectively stabilize LRPs.

Micro Optical Coherence Tomography for Coronary Imaging

Intravascular optical coherence tomography (IVOCT) that produces images with 10 μm resolution has emerged as a significant technology for evaluating coronary architectural morphology. Yet, many features that are relevant to coronary plaque pathogenesis can only be seen at the cellular level. This issue has motivated the development of a next-generation form of OCT imaging that offers higher resolution. One such technology that we review here is termed micro-OCT (μOCT) that enables the assessment of the cellular and subcellular morphology of human coronary atherosclerotic plaques. This chapter reviews recent advances and ongoing works regarding μOCT in the field of cardiology. This new technology has the potential to provide researchers and clinicians with a tool to better understand the natural history of coronary atherosclerosis, increase plaque progression prediction capabilities, and better assess the vessel healing process after revascularization therapy.

Cardiovascular Imaging Techniques for Detection of Vulnerable Plaques

Various cardiovascular imaging techniques were developed for the detection of vulnerable atherosclerotic plaques, hoping to be able to predict a cardiovascular event. Plaque vulnerability results from compound pathophysiological mechanisms that lead to structural and morphological changes in lesions. The aim of this review is to present the most recent techniques for the assessment of vulnerable coronary plaques such as cardiac computed tomography angiography (CCTA), optical coherence tomography, or virtual histology intravascular ultra-sound, based on literature data from the last 3 years. CCTA permits direct visualization of the intravascular lumen, together with characterization of the arterial wall. Recent studies maintain that low-attenuation plaques, spotty calcifications, positive vessel remodeling, and the napkin-ring sign are considered main markers of plaque vulnerability and instability. Emerging analytical techniques, such as machine learning or radiomics, will probably demonstrate useful as an auxiliary diagnostic tool for vulnerable plaque detection. The data from the two imaging techniques together provide useful information, especially in patients undergoing a PCI procedure for an acute coronary syndrome. Invasive and noninvasive imaging techniques are able to deliver a large amount of scientific data to assess vulnerable coronary atheromatous plaques. Recent studies demonstrated that information defined by the two techniques is complementary, and using both methods is essential for adequate diagnosis, therapeutic strategy, and prognostic assessment.

The impact of vildagliptin on the daily glucose profile and coronary plaque stability in impaired glucose tolerance patients with coronary artery disease: VOGUE-A multicenter randomized controlled trial

Background

The impact of reduction in glycemic excursion on coronary plaques remains unknown. This study aimed to elucidate whether a dipeptidyl peptidase 4 inhibitor could reduce the glycemic excursion and stabilize the coronary plaques compared with conventional management in coronary artery disease (CAD) patients with impaired glucose tolerance (IGT).

Methods

This was a multicenter, randomized controlled trial including CAD patients with IGT under lipid-lowering therapy receiving either vildagliptin (50 mg once a day) or no medication (control group) regarding glycemic treatment. The primary endpoint was changes in the minimum fibrous cap thickness and lipid arc in non-significant native coronary plaques detected by optical coherence tomography at 6 months after intervention. Glycemic variability expressed as the mean amplitude of glycemic excursion (MAGE) measured with a continuous glucose monitoring system was evaluated before and 6 months after intervention.

Results

A total of 20 participants with 47 lesions were allocated to either the vildagliptin group (10 participants, 22 lesions) or the control group (10 participants, 25 lesions). The adjusted difference of mean changes between the groups was − 18.8 mg/dl (95% confidence interval, − 30.8 to − 6.8) (p = 0.0064) for the MAGE (vildagliptin, − 20.1 ± 18.0 mg/dl vs. control, 2.6 ± 12.7 mg/dl), − 22.8° (− 40.6° to − 5.1°) (p = 0.0012) for the mean lipid arc (vildagliptin, − 9.0° ± 25.5° vs. control, 15.8° ± 16.8°), and 42.7 μm (15.3 to 70.1 μm) (p = 0.0022) for the minimum fibrous cap thickness (vildagliptin, 35.7 ± 50.8 μm vs. control, − 15.1 ± 25.2 μm).

Conclusions

Vildagliptin could reduce the MAGE at 6 months and may be associated with the decreased lipid arc and increased minimum FCT of the coronary plaques in CAD patients with IGT as compared with the control group. These findings may represent its potential stabilization effect on coronary plaques, which are characteristic in this patient subset.

Trial registration Registered in the UMIN clinical trial registry (UMIN000008620), Name of the registry: VOGUE trial, Date of registration: Aug 6, 2012, URL: https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000010058

Using optical coherence tomography and intravascular ultrasound imaging to quantify coronary plaque cap thickness and vulnerability: a pilot study

Background

Detecting coronary vulnerable plaques in vivo and assessing their vulnerability have been great challenges for clinicians and the research community. Intravascular ultrasound (IVUS) is commonly used in clinical practice for diagnosis and treatment decisions. However, due to IVUS limited resolution (about 150–200 µm), it is not sufficient to detect vulnerable plaques with a threshold cap thickness of 65 µm. Optical Coherence Tomography (OCT) has a resolution of 15–20 µm and can measure fibrous cap thickness more accurately. The aim of this study was to use OCT as the benchmark to obtain patient-specific coronary plaque cap thickness and evaluate the differences between OCT and IVUS fibrous cap quantifications. A cap index with integer values 0–4 was also introduced as a quantitative measure of plaque vulnerability to study plaque vulnerability.

Methods

Data from 10 patients (mean age: 70.4; m: 6; f: 4) with coronary heart disease who underwent IVUS, OCT, and angiography were collected at Cardiovascular Research Foundation (CRF) using approved protocol with informed consent obtained. 348 slices with lipid core and fibrous caps were selected for study. Convolutional Neural Network (CNN)-based and expert-based data segmentation were performed using established methods previously published. Cap thickness data were extracted to quantify differences between IVUS and OCT measurements.

Results

For the 348 slices analyzed, the mean value difference between OCT and IVUS cap thickness measurements was 1.83% (p = 0.031). However, mean value of point-to-point differences was 35.76%. Comparing minimum cap thickness for each plaque, the mean value of the 20 plaque IVUS-OCT differences was 44.46%, ranging from 2.36% to 91.15%. For cap index values assigned to the 348 slices, the disagreement between OCT and IVUS assignments was 25%. However, for the OCT cap index = 2 and 3 groups, the disagreement rates were 91% and 80%, respectively. Furthermore, the observation of cap index changes from baseline to follow-up indicated that IVUS results differed from OCT by 80%.

Conclusions

These preliminary results demonstrated that there were significant differences between IVUS and OCT plaque cap thickness measurements. Large-scale patient studies are needed to confirm our findings.

In vivo imaging of vulnerable plaque with intravascular modalities: its advantages and limitations

In vivo imaging of plaque instability has been considered to have a great potential to predict future coronary events and evaluate the stabilization effect of novel anti-atherosclerotic medical therapies. Currently, there are several intravascular imaging modalities which enable to visualize plaque components associated with its vulnerability. These include virtual histology intravascular ultrasound (VH-IVUS), integrated backscatter IVUS (IB-IVUS), optical coherence tomography (OCT), near-infrared spectroscopy and coronary angioscopy. Recent studies have shown that these tools are applicable for risk stratification of cardiovascular events as well as drug efficacy assessment. However, several limitation exists in each modality. The current review paper will outline advantages and limitation of VH-IVUS, IB-IVUS, OCT, NIRS and coronary angioscopy imaging.

OPtical frequency domain imaging vs. INtravascular ultrasound in percutaneous coronary InterventiON in patients with Acute Coronary Syndrome: Study protocol for a randomized controlled trial

BACKGROUND

A recent clinical trial demonstrated that optical frequency domain imaging (OFDI) guidance in percutaneous coronary intervention (PCI) is noninferior to intravascular ultrasound (IVUS) guidance in patients with coronary artery disease with regard to target vessel failure (composed of cardiac death, myocardial infarction attributed to the target vessel, and clinically-driven target vessel revascularization) at 12 months. The impact of OFDI guidance in PCI for patients with acute coronary syndrome (ACS) remains uncertain.

METHODS

OPINION ACS is a multicenter, prospective, randomized, controlled, open-label, parallel group, non-inferiority trial in Japan. Eligible patients will be randomly assigned to receive either OFDI- or IVUS-guided PCI. PCI is performed using the sirolimus-eluting stent in accordance with certain OFDI and IVUS criteria for optimal stent deployment. All patients will undergo follow-up angiography and OFDI imaging at 8 months. The primary endpoint is the minimum lumen area, as measured by OFDI at 8 months.

CONCLUSION

The OPINION ACS trial outcomes will provide insights regarding the impact of OFDI-guided PCI on in-stent restenosis at 8 months in patients with ACS.

The Role of Imaging for MINOCA (Myocardial Infarction with No Obstructive Coronary Artery Disease): a Review of Literature and Current Perspectives

Purpose of Review

The objective of this review is to summarize scientific statements on the diagnosis and management of myocardial infarction with no obstructive coronary artery disease (MINOCA); define the diagnostic role of optical coherence tomography (OCT), intravascular ultrasound (IVUS), and cardiac magnetic resonance imaging (CMR); and provide representative case examples.

Recent Findings

The majority of patients with MINOCA are evaluated by conventional coronary angiography. However, intracoronary imaging using OCT or IVUS permits more accurate understanding of the underlying pathology. These and other imaging modalities provide significant diagnostic and prognostic value.

Summary

Although nonobstructive disease is the hallmark of the disease, MINOCA is associated with significant morbidity and mortality. Every effort to define the underlying pathology is necessary and requires more standardized use of imaging in clinical practice.

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.

Automated A-line coronary plaque classification of intravascular optical coherence tomography images using handcrafted features and large datasets

We developed machine learning methods to identify fibrolipidic and fibrocalcific A-lines in intravascular optical coherence tomography (IVOCT) images using a comprehensive set of handcrafted features. We incorporated features developed in previous studies (e.g., optical attenuation and A-line peaks). In addition, we included vascular lumen morphology and three-dimensional (3-D) digital edge and texture features. Classification methods were developed using expansive datasets (∼7000  images), consisting of both clinical in-vivo images and an ex-vivo dataset, which was validated using 3-D cryo-imaging/histology. Conditional random field was used to perform 3-D classification noise cleaning of classification results. We tested various multiclass approaches, classifiers, and feature selection schemes and found that a three-class support vector machine with minimal-redundancy-maximal-relevance feature selection gave the best performance. We found that inclusion of our morphological and 3-D features improved overall classification accuracy. On a held-out test set consisting of >1700 images, we obtained an overall accuracy of 81.58%, with the following (sensitivity/specificity) for each class: other (81.43/89.59), fibrolipidic (94.48/87.32), and fibrocalcific (74.82/95.28). The en-face views of classification results showed that automated classification easily captured the preponderance of a disease segment (e.g., a calcified segment had large regions of fibrocalcific classifications). Finally, we demonstrated proof-of-concept for streamlining A-line classification output with existing fibrolipidic and fibrocalcific boundary segmentation methods, to enable fully automated plaque quantification. The results suggest that our classification approach is a viable step toward fully automated IVOCT plaque classification and segmentation for live-time treatment planning and for offline assessment of drug and biologic therapeutics.

Percutaneous coronary intervention for a Chinese familial hypercholesterolemia homozygous under the guidance of optical coherence tomography

Homozygous familial hypercholesterolemia developed into severe cardiovascular consequences early. Untreated HoFH usually cannot survive over 30 years old. Acute coronary syndrome(ACS) caused by plaque rupture is one of the main causes of death in HoFH. As the highest resolution intravascular imaging technique, optical coherence tomography(OCT) can clearly show the thickness and structural characteristics of atherosclerotic plaque caps. In this study, a Chinese male HoFH received percutaneous coronary intervention for unstable angina. After analyzed his genetic and follow-up data, OCT was performed during interventional therapy. Multiple lipid rich plaques accompanied with inflammatory cell infiltration and a thin-cap fibroatheroma(TCFA) were noted, which reflected the vulnerability of plaques. The utility of OCT had certain guiding significance for strategy of interventional therapy and the long-term drug management. And this case suggested that it was important to undergo OCT examination for patients with HoFH who required percutaneous coronary intervention.

Evaluation of plaque characteristics in coronary artery patients with impaired glucose tolerance through optical coherence tomography

OBJECTIVE

With the adoption of optical coherence tomography (OCT), this study targets the impacts on plaque characteristics brought about by impaired glucose tolerance (IGT) in patients with coronary artery disease.

METHODS

For this study, 150 patients with coronary artery disease were recruited. Regarding glycosylated hemoglobin (HbAlc), the patients were sectioned into normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and diabetes mellitus (DM) groups. Coronary angiography (CAG) and OCT were conducted for 150 patients.

RESULTS

There were 186 plaques discovered in 150 patients (37, 40, 44, and 65 in the NGT, IFG, IGT, and DM groups, respectively). Compared to the NGT group, the lipid core size, which is presented as the average angle of the lipid arc, was markedly larger in the IFG,IGT and DM groups ( 135.7 ± 32.7 Ê, 161.2 ± 55.7 Ê, 162.5 ± 55.8 Ê, and 170.2 ± 59.7 Ê, respectively, all P values< 0.05). Meanwhile, the fibrous cap over the lipid core in the NGT group was remarkably thicker than that in the IFG, IGT, and DM groups (115.7 ± 47.7 μm vs. 77.7 ± 23.5 μm, 75.1 ± 23.2 µm, 71.2 ± 22.1 µm, all P values<0.05).

CONCLUSION

Coronary plaques in coronary artery patients with NDT are more stable than in those with IGT and DM.

Coronary Plaque Characteristics in Patients With Diabetes Mellitus Who Presented With Acute Coronary Syndromes

BACKGROUND

Diabetes mellitus (DM) is a major risk factor for cardiovascular events. We aimed to investigate the coronary plaque phenotype of diabetic patients who presented with acute coronary syndromes by optical coherence tomography.

METHODS AND RESULTS

A total of 322 patients with acute coronary syndromes who underwent preintervention optical coherence tomography imaging of the culprit lesion were included. Culprit plaque characteristics were compared between patients with DM (n=95) and those without DM (n=227). In the subgroup of 250 patients in whom sufficient length of nonculprit region in the culprit vessel was imaged by optical coherence tomography, the characteristics of nonculprit plaques were also evaluated. Patients with DM had a higher prevalence of lipid-rich plaque (58.9% versus 44.9%, P=0.030) and macrophage accumulation (60.0% versus 44.9%, P=0.019) in the culprit lesion compared with patients without DM. The prevalence of plaque rupture (33.7% versus 30.4%, P=0.896) and plaque erosion (21.1% versus 22.0%, P=0.458) was similar. In the nonculprit lesions, the DM group had greater maximal lipid arc (248.9°±83.9° versus 179.9°±58.3°, P=0.006), thinner fibrous cap thickness (103.3±56.2 μm versus 140.7±70.0 μm, P=0.013), and a higher prevalence of thin-cap fibroatheroma (17.2% versus 6.3%, P=0.031), compared with the non-DM group.

CONCLUSIONS

Compared with patients without DM, those with DM had more vulnerable features in both culprit and nonculprit lesions, thus indicating a higher level of panvascular instability.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01110538.

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.

Voxel-based plaque classification in coronary intravascular optical coherence tomography images using decision trees

Intravascular Optical Coherence Tomography (IVOCT) is a high contrast, 3D microscopic imaging technique that can be used to assess atherosclerosis and guide stent interventions. Despite its advantages, IVOCT image interpretation is challenging and time consuming with over 500 image frames generated in a single pullback volume. We have developed a method to classify voxel plaque types in IVOCT images using machine learning. To train and test the classifier, we have used our unique database of labeled cadaver vessel IVOCT images accurately registered to gold standard cryo-images. This database currently contains 300 images and is growing. Each voxel is labeled as fibrotic, lipid-rich, calcified or other. Optical attenuation, intensity and texture features were extracted for each voxel and were used to build a decision tree classifier for multi-class classification. Five-fold cross-validation across images gave accuracies of 96 % ± 0.01 %, 90 ± 0.02% and 90 % ± 0.01 % for fibrotic, lipid-rich and calcified classes respectively. To rectify performance degradation seen in left out vessel specimens as opposed to left out images, we are adding data and reducing features to limit overfitting. Following spatial noise cleaning, important vascular regions were unambiguous in display. We developed displays that enable physicians to make rapid determination of calcified and lipid regions. This will inform treatment decisions such as the need for devices (e.g., atherectomy or scoring balloon in the case of calcifications) or extended stent lengths to ensure coverage of lipid regions prone to injury at the edge of a stent.

Impact of CD14++CD16+ monocytes on coronary plaque vulnerability assessed by optical coherence tomography in coronary artery disease patients

BACKGROUND AND AIMS

This study examined the impact of CD14⁺⁺CD16⁺ monocytes on coronary plaque vulnerability, as assessed by optical coherence tomography (OCT), and investigated their association with daily glucose fluctuation. Although increased CD14⁺⁺CD16⁺ monocyte levels have been reported to increase cardiovascular events, their impact on coronary plaque vulnerability in coronary artery disease (CAD) patients with or without diabetes mellitus (DM) remains unclear.

METHODS

This prospective observational study included 50 consecutive patients with CAD, receiving lipid-lowering therapy and undergoing coronary angiography and OCT. Patients were divided into 3 tertiles according to the CD14⁺⁺CD16⁺ monocyte percentages assessed by flow cytometry. Standard OCT parameters were assessed for 97 angiographically intermediate lesions (diameter stenosis: 30-70%). Daily glucose fluctuation was analyzed by measuring the mean amplitude of glycemic excursion (MAGE).

RESULTS

CD14⁺⁺CD16⁺ monocytes negatively correlated with fibrous cap thickness (r = -0.508, p < 0.01). The presence of thin-cap fibroatheroma (TCFA) was increased stepwise according to the tertile of CD14⁺⁺CD16⁺ monocytes (0 [tertile 1] vs. 5 [tertile 2] vs. 10 [tertile 3], p < 0.01). CD14⁺⁺CD16⁺ monocytes were a significant determinant of TCFA (OR 1.279, p = 0.001). In non-DM patients, a significant relationship was found between CD14⁺⁺CD16⁺ monocytes and MAGE (r = 0.477, p = 0.018).

CONCLUSIONS

CD14⁺⁺CD16⁺ monocytes were associated with coronary plaque vulnerability in CAD patients with well-regulated lipid levels both in DM and non-DM patients. Cross-talk between glucose fluctuation and CD14⁺⁺CD16⁺ monocytes may enhance plaque vulnerability, particularly in non-DM patients. CD14⁺⁺CD16⁺ monocytes could be a possible therapeutic target for coronary plaque stabilization.

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.

OCT guidance during stent implantation in primary PCI: A randomized multicenter study with nine months of optical coherence tomography follow-up

AIMS

To assess the possible merits of optical coherence tomography (OCT) guidance in primary percutaneous coronary intervention (pPCI).

METHODS AND RESULTS

201 patients with ST-elevation myocardial infarction (STEMI) were enrolled in this study. Patients were randomized either to pPCI alone (angio-guided group, n=96) or to pPCI with OCT guidance (OCT-guided group, n=105) and also either to biolimus A9 or to everolimus-eluting stent implantation. All patients were scheduled for nine months of follow-up angiography and OCT study. OCT guidance led to post-pPCI optimization in 29% of cases (59% malapposition and 41% dissections). No complications were found related to the OCT study. OCT analysis at nine months showed significantly less in-segment area of stenosis (6% [-11, 19] versus 18% [3, 33]; p=0.0002) in favor of the OCT-guided group. The rate major adverse cardiovascular events were comparable at nine months in both groups (3% in the OCT group versus 2% in the angio-guided group; p=0.87).

CONCLUSIONS

This study demonstrates the safety of OCT guidance during pPCI. The use of OCT optimized stent deployment in 1/3 of patients in this clinical scenario and significantly reduced in-segment area of stenosis at nine months of follow-up. Whether such improvements in OCT endpoints will have a positive impact on late clinical outcomes, they demand both a larger and longer-term follow-up study.

Early Detection and Treatment of the Vulnerable Coronary Plaque

Early identification and treatment of the vulnerable plaque, that is, a coronary artery lesion with a high likelihood of rupture leading to an acute coronary syndrome, have gained great interest in the cardiovascular research field. Postmortem studies have identified clear morphological characteristics associated with plaque rupture. Recent advances in invasive and noninvasive coronary imaging techniques have empowered the clinician to identify suspected vulnerable plaques in vivo and paved the way for the evaluation of therapeutic agents targeted at reducing plaque vulnerability. Local treatment of vulnerable plaques by percutaneous coronary intervention and systemic treatment with anti-inflammatory and low-density lipoprotein–lowering drugs are currently being investigated in large randomized clinical trials to assess their therapeutic potential for reducing adverse coronary events. Results from these studies may enable a more patient-tailored strategy for the treatment of coronary artery disease.

Intravascular optical coherence tomography [Invited]

Shortly after the first demonstration of optical coherence tomography for imaging the microstructure of the human eye, work began on developing systems and catheters suitable for intravascular imaging in order to diagnose and investigate atherosclerosis and potentially to monitor therapy. This review covers the driving considerations of the clinical application and its constraints, the major engineering milestones that enabled the current, high-performance commercial imaging systems, the key studies that laid the groundwork for image interpretation, and the clinical research that traces intravascular optical coherence tomography (OCT) from early human pilot studies to current clinical trials.

Radiofrequency Ablation of the Atherosclerotic Plaque: a Proof of Concept Study in an Atherosclerotic Model

Increased plaque vascularization is causatively associated with the progression of unstable atherosclerotic vessel disease. We investigated the safety and efficacy of heat-generating radiofrequency ablation (RFA) in reducing the number of vessels in the plaque and adventitia and its effect on plaque size and composition. To this end, New Zealand White rabbits were fed a cholesterol-enriched diet and subjected to balloon denudation of the infrarenal aorta to induce atherosclerotic plaque formation. After 13 weeks, the proximal or distal half of the infrarenal aorta was exposed to transluminal RFA. The untreated half served as an intra-individual control. Optical coherence tomography (OCT) was performed directly after RFA. We found that RFA on the rabbit atherosclerotic plaque is safe and leads to decreased intraplaque vessel density and smooth muscle cell content but does not affect other components of plaque composition or size.

Three-dimensional morphological response of lipid-rich coronary plaques to statin therapy: a serial optical coherence tomography study

OBJECTIVE

Previous studies have suggested that intensive statin therapy, compared with moderate statin therapy, provided greater reduction of LDL and better protection against major cardiovascular events. However, the exact dose-dependent mechanism of plaque stabilization remains unclear. The aim of this study is to investigate the three-dimensional (3D) response of fibrous caps overlying lipid plaques to statin therapy.

METHODS

We applied a novel computer algorithm to investigate the fibrous cap 3D morphological change over time in patients with coronary artery disease. Patients were treated with either atorvastatin 20 mg/day (moderate intensity) or atorvastatin 60 mg/day (high intensity). Optical coherence tomography was performed at baseline, 6, and 12 months. A total of 31 lipid plaques from 21 patients were analyzed.

RESULTS

Conventional metrics such as the minimum fibrous cap thickness change between the two treatment groups were not significantly different between the baseline and the 12-month follow-up. In contrast, the 3D metric thin cap (<80 μm) surface area change between the baseline and the 12-month follow-up showed dose-dependent, significant differences between the statin treatment groups (P<0.001). 3D reconstructions of fibrous caps further indicated that fibrous caps showed diverse (scattered vs. confluent) patterns and could evolve in a complex manner.

CONCLUSION

High-intensity statin therapy more effectively stabilized fibrous caps at follow-up. The new 3D algorithm provided more comprehensive and detailed information on the changes in plaque phenotype in response to statin therapy.

Invasive or non-invasive imaging for detecting high-risk coronary lesions?

INTRODUCTION

Advances in our understanding about atherosclerotic evolution have enabled us to identify specific plaque characteristics that are associated with coronary plaque vulnerability and cardiovascular events. With constant improvements in signal and image processing an arsenal of invasive and non-invasive imaging modalities have been developed that are capable of identifying these features allowing in vivo assessment of plaque vulnerability. Areas covered: This review article presents the available and emerging imaging modalities introduced to assess plaque morphology and biology, describes the evidence from the first large scale studies that evaluated the efficacy of invasive and non-invasive imaging in detecting lesions that are likely to progress and cause cardiovascular events and discusses the potential implications of the in vivo assessment of coronary artery pathology in the clinical setting. Expert commentary: Invasive imaging, with its high resolution, and in particular hybrid intravascular imaging appears as the ideal approach to study the mechanisms regulating atherosclerotic disease progression; whereas non-invasive imaging is expected to enable complete assessment of coronary tree pathology, detection of high-risk lesions, more accurate risk stratification and thus to allow a personalized treatment of vulnerable patients.

In vivo coronary lesion differentiation with computed tomography angiography and intravascular ultrasound as compared to optical coherence tomography

BACKGROUND

In vitro studies have shown the feasibility of coronary lesion grading with computed tomography angiography (CTA), intravascular ultrasound (IVUS) and optical coherence tomography (OCT) as compared to histology, whereas OCT had the highest discriminatory capacity.

OBJECTIVE

We investigated the ability of CTA and IVUS to differentiate between early and advanced coronary lesions in vivo, OCT serving as standard of reference.

METHODS

Multimodality imaging was prospectively performed in 30 NSTEMI patients. Plaque characteristics were assessed in 1083 cross-sections of 30 culprit lesions, co-registered among modalities. Absence of plaque, fibrous and fibrocalcific plaque on OCT were defined as early plaque, whereas lipid rich-plaque on OCT was defined as advanced plaque. Odds ratios adjusted for clustering were calculated to assess associations between plaque types on CTA and IVUS with early or advanced plaque.

RESULTS

Normal findings on CTA as well as on IVUS were associated with early plaque. Non-calcified, calcified plaques and the napkin ring sign on CTA were associated with advanced plaque. On IVUS, fatty and calcified plaques were associated with advanced plaque.

CONCLUSIONS

In vivo coronary plaque characteristics on CTA and IVUS are associated with plaque characteristics on OCT. Of note, normal findings on CTA and IVUS relate to early lesions on OCT. Nevertheless, multiple plaque features on CTA and IVUS are related to advanced plaques on OCT, which may make it difficult to use qualitative plaque assessment in clinical practice.

Plaque Characteristics in Coronary Artery Disease Patients with Impaired Glucose Tolerance

BACKGROUND

Impaired glucose tolerance (IGT) patients are known to have a high risk of cardiovascular events and their prognosis has been reported to be poor. The present study aimed to compare coronary plaque characteristics among coronary artery disease (CAD) patients with normal glucose tolerance (NGT), those with IGT, and those with diabetes mellitus (DM) by using optical coherence tomography (OCT).

METHODS

The present study included 101 coronary artery disease patients (mean age, 67.9 ± 10.4 years; 82.4% male). OCT was performed for target and non-target vessels during percutaneous coronary intervention. The patients were divided into the following 3 groups: the NGT, IGT, and DM groups.

RESULTS

A total of 136 non-target residual plaques were found in 101 patients (27, 30, and 44 in the NGT, IGT, and DM groups, respectively). The size of the lipid core expressed as the mean angle of the lipid arc was significantly greater in the IGT and DM groups than in the NGT group (163.0 ± 58.7°, 170.1 ± 59.3°, and 130.9 ± 37.7°, respectively, P < 0.05). The fibrous cap covering the lipid core was significantly thinner in the IGT group than in the NGT group (77.0 ± 23.4 μm vs. 105.6 ± 47.0 μm, P = 0.040).

CONCLUSION

The coronary plaques in CAD patients are more vulnerable when having IGT compared to those with NGT, and similar to those with DM. This finding may explain the high risk of cardiovascular events in CAD patients with IGT.

Comparison of coronary arterial lumen dimensions on angiography and plaque characteristics on optical coherence tomography images and their changes induced by statin

Background

Coronary angiography (CAG) is widely used to assess lumen dimensions, and optical coherence tomography (OCT) is used to evaluate the characteristics of atherosclerotic plaque. This study was aimed to compare coronary lumen dimensions using CAG and plaque characteristics using OCT and their changes during statin therapy.

Methods

We identified 97 lipid-rich plaques from 69 statin-naïve patients, who received statin therapy in the following 12 months. CAG and OCT examinations were conducted at baseline and 12-month follow-up period.

Results

Lesion length, as measured by CAG, was closely correlated with lipid length by OCT (baseline: r = 0.754, p < 0.001; follow-up: r = 0.639, p < 0.001). However, no significant correlations were found between the other findings on OCT and data on CAG. With 12-month statin therapy, microstructures of lipid-rich plaques were significantly improved, but CAG-derived lumen dimensions were not improved. Moreover, we found no significant relationship between changes in OCT measurements and changes in CAG data over time.

Conclusion

Lipid length on OCT and lesion length on CAG were closely correlated. However, plaque microstructural characteristics on OCT showed no significantly statistically correlations with lumen dimensions on CAG, neither did their evolutionary changes induced by statin over time.

A retrospectively registered study

Clinical trial registry: ClinicalTrial.gov. Registered number: NCT01023607. Registered 1 December 2009.

Coronary Plaque Characterization Assessed by Optical Coherence Tomography and Plasma Trimethylamine-N-oxide Levels in Patients With Coronary Artery Disease

Optical coherence tomography (OCT) has been considered as the ideal tool for the evaluation of atherosclerotic plaques. Circulating trimethylamine-N-oxide (TMAO), which is a metabolite of the dietary lipid phosphatidylcholine, has recently been linked to elevated coronary artery disease (CAD) risk. The objective of the study was to investigate the relation between circulating TMAO level and coronary plaque vulnerability assessed by OCT in patients with CAD. A total of 26 patients with CAD were recruited to assess coronary plaque using OCT and measure plasma TMAO level. According to plaque rupture status, patients were divided into plaque rupture group (n = 12) and nonplaque rupture group (n = 14). Plasma TMAO level was significantly higher in patients with plaque rupture than in those with nonplaque rupture (8.6 ± 4.8 μmol/L vs 4.2 ± 2.4 μmol/L, p = 0.011). Moreover, positive correlations between plasma TMAO level and lipid arc (r = 0.43, p = 0.031), lipid volume index (r = 0.39, p = 0.048) were also observed. In conclusion, circulating TMAO level may reflect coronary plaque vulnerability and progression.

Fibrous Cap Thickness by Optical Coherence Tomography In Vivo

BACKGROUND

Optical coherence tomography (OCT) imaging is considered to be the only imaging modality with sufficient resolution to measure fibrous cap thickness (FCT) in vivo. However, reproducibility of the measurements in vivo has been unsatisfactory.

OBJECTIVES

The authors aimed to investigate whether satisfactory reproducibility of FCT measurements by OCT in vivo can be achieved between independent observers.

METHODS

One hundred seventy OCT pullbacks were analyzed by 2 independent observers with intravascular imaging expertise in accordance with current guidelines to assess the interobserver variability of FCT measurement by intraclass correlation coefficient (ICC). The main sources of the variability were analyzed and incorporated in lesion assessment criteria. The same 170 OCT pullbacks were reanalyzed by the same observers using the developed criteria, and the interobserver reproducibility of the measurements was reassessed. On the basis of the developed criteria, a third independent observer interpreted all 170 OCT images. Assessment of the maximal lipid arc was also undertaken similarly before and after the development of interpretation criteria.

RESULTS

The original ICC of the FC thickness was 0.56 (95% confidence interval [CI]: 0.38 to 0.69). The poor definition of necrotic core facing border of FC and the neointimal presence of macrophages and calcification contributed to the high interobserver variability of FCT measurement. The ICC of FCT measurements by OCT in vivo was 0.88 (95% CI: 0.80 to 0.93) after we developed lesion assessment criteria. The ICC for the maximal lipid arc assessment before and after was 0.76 and 0.82 respectively. The third independent observer was extensively coached and returned the ICC of 0.82 (95% CI: 0.74 to 0.87) with observer 1 and 0.90 (95% CI: 0.86 to 0.94) with observer 2.

CONCLUSIONS

Careful consideration of OCT features mimicking fibroatheroma lesions and imaging artifacts contributed to significantly higher levels of interobserver agreement. Interobserver variation can be partially resolved by development of standard interpretation algorithms.