Advances in Intravascular Imaging

Image-guided intravascular brachytherapy dose escalation

PURPOSE

Coronary stents reduce IVBT radiation dose with a single layer by 10-30%. However, the impact of multiple stent layers and stent expansion remains unexplored. Individualized dose adjustments considering variations in stent layers and expansion could improve radiation delivery effectiveness.

METHODS

EGSnrc was used to compute the delivered vessel wall dose in various IVBT scenarios. Stent effects were modeled for the stent density of 25%, 50%, and 75% with 1, 2, and 3 layers respectively. Doses were calculated at 1.75 to 5.00 mm away from the source center, normalized to 100% at 2 mm.

RESULTS

Dose fall-off increased with increasing stent density. With a single layer, the dose at 2 mm from source fell from 100% of prescription to 92%, 83% and 73% at 25%, 50% and 75% density, respectively. The computed dose to points with increasing radial distance from the source decreased progressively with increasing stent layers. With three layers, at 75% stent density, the dose at 2 mm from source center fell to 38%.

CONCLUSIONS

A schema for image-guided IVBT dose adjustment is described. While it would be an improvement over current standard of care, myriad factors remain to be addressed in a comprehensive effort to optimize IVBT.

Evolving Diagnostic and Management Advances in Coronary Heart Disease

Despite considerable improvement in diagnostic modalities and therapeutic options over the last few decades, the global burden of ischemic heart disease is steadily rising, remaining a major cause of death worldwide. Thus, new strategies are needed to lessen cardiovascular events. Researchers in different areas such as biotechnology and tissue engineering have developed novel therapeutic strategies such as stem cells, nanotechnology, and robotic surgery, among others (3D printing and drugs). In addition, advances in bioengineering have led to the emergence of new diagnostic and prognostic techniques, such as quantitative flow ratio (QFR), and biomarkers for atherosclerosis. In this review, we explore novel diagnostic invasive and noninvasive modalities that allow a more detailed characterization of coronary disease. We delve into new technological revascularization procedures and pharmacological agents that target several residual cardiovascular risks, including inflammatory, thrombotic, and metabolic pathways.

Trends and impact of intravascular ultrasound and optical coherence tomography on percutaneous coronary intervention for myocardial infarction

Background

Intravascular imaging with either intravascular ultrasound (IVUS) or optical coherence tomography (OCT) during percutaneous coronary intervention (PCI) is associated with improved outcomes, but these techniques have previously been underutilized in the real world. We aimed to examine the change in utilization of intravascular imaging-guided PCI over the past decade in the United States and assess the association between intravascular imaging and clinical outcomes following PCI for myocardial infarction (MI).

Methods

We surveyed the National Inpatient Sample from 2008 to 2019 to calculate the number of PCIs for MI guided by IVUS or OCT. Temporal trends were analyzed using Cochran-Armitage trend test or simple linear regression for categorical or continuous outcomes, respectively. Multivariable logistic regression was used to compare outcomes following PCI with and without intravascular imaging.

Results

A total of 2,881,746 PCIs were performed for MI. The number of IVUS-guided PCIs increased by 309.9 % from 6,180 in 2008 to 25,330 in 2019 (P-trend < 0.001). The percentage of IVUS use in PCIs increased from 3.4 % in 2008 to 8.7 % in 2019 (P-trend < 0.001). The number of OCT-guided PCIs increased 548.4 % from 246 in 2011 to 1,595 in 2019 (P-trend < 0.001). The percentage of OCT guidance in all PCIs increased from 0.0 % in 2008 to 0.6 % in 2019 (P-trend < 0.001). Intravascular imaging-guided PCI was associated with lower odds of in-hospital mortality (adjusted odds ratio 0.66, 95 % confidence interval 0.60-0.72, p < 0.001).

Conclusions

Although the number of intravascular imaging-guided PCIs have been increasing, adoption of intravascular imaging remains poor despite an association with lower mortality.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

Gas bubbles present in liquids underpin many natural phenomena and human-developed technologies that improve the quality of life. Since all living organisms are predominantly made of water, they may also contain bubbles-introduced both naturally and artificially-that can serve as biomechanical sensors operating in hard-to-reach places inside a living body and emitting signals that can be detected by common equipment used in ultrasound and photoacoustic imaging procedures. This kind of biosensor is the focus of the present article, where we critically review the emergent sensing technologies based on acoustically driven oscillations of bubbles in liquids and bodily fluids. This review is intended for a broad biosensing community and transdisciplinary researchers translating novel ideas from theory to experiment and then to practice. To this end, all discussions in this review are written in a language that is accessible to non-experts in specific fields of acoustics, fluid dynamics and acousto-optics.

Effectiveness of synthetic aperture focusing and coherence factor weighting for intravascular ultrasound imaging

Synthetic aperture focusing (SAF) and coherence factor weighting (CFW) have been used to improve the lateral resolution of ultrasound images. Although the two methods are effective for array-based ultrasound imaging, many researchers have also employed the methods for single-element-based imaging including intravascular ultrasound (IVUS) imaging. For single-element-based imaging, CFW is generally calculated from the scanlines obtained by SAF and applied to the scanline obtained after coherent summation of the SAF delayed scanlines, which is called a SAF-CFW method. In the paper, a theoretical model was derived to explore the effectiveness of SAF and CFW for single-element-based imaging, and the model was used to explain that SAF is not effective for IVUS imaging in terms of enhancing the spatial resolution, although it has the advantage of improving a contrast-to-noise ratio (CNR). This means that the SAF-CFW method is not optimal for improving the spatial resolution of IVUS imaging. In contrast, it was found in simulations and experiments that applying CFW to the target scanline itself is beneficial for the spatial resolution rather than a coherent summed scanline for IVUS SAF imaging, but CNR was not as good as SAF and SAF-CFW. As a result of both simulation and experimentation, it could be concluded that focused IVUS transducers without the application of those methods may be more advantageous to improve the spatial and contrast resolution simultaneously, considering the system complexity in the implementation of such imaging methods.

OCT-NIRS Imaging for Detection of Coronary Plaque Structure and Vulnerability

A combination optical coherence tomography and near-infrared spectroscopy (OCT-NIRS) coronary imaging system is being developed to improve the care of coronary patients. While stenting has improved, complications continue to occur at the stented site and new events are caused by unrecognized vulnerable plaques. An OCT-NIRS device has potential to improve secondary prevention by optimizing stenting and by identifying vulnerable patients and vulnerable plaques. OCT is already in widespread use world-wide to optimize coronary artery stenting. It provides automated lumen detection and can identify features of coronary plaques not accurately identified by angiography or intravascular ultrasound. The ILUMIEN IV study, to be completed in 2022, will determine if OCT-guided stenting will yield better clinical outcomes than angiographic guidance alone. While the superb spatial resolution of OCT enables the identification of many plaque structural features, the detection by OCT of lipids, an important component of vulnerable plaques, is limited by suboptimal specificity and interobserver agreement. In contrast, NIRS has been extensively validated for lipid-rich plaque detection against the gold-standard of histology and is the only FDA-approved method to identify coronary lipids. Studies in patients have demonstrated that NIRS detects lipid in culprit lesions causing coronary events. In 2019, the positive results of the prospective Lipid-Rich Plaque Study led to FDA approval of NIRS for detection of high-risk plaques and patients. The complementarity of OCT for plaque structure and NIRS for plaque composition led to the sequential performance of NIRS and OCT imaging in patients. NIRS identified lipid while OCT determined the thickness of the cap over the lipid pool. The positive results obtained with OCT and NIRS imaging led to development of a prototype combined OCT-NIRS catheter that can provide co-registered OCT and NIRS data in a single pullback. The data will provide structural and chemical information likely to improve stenting and deliver more accurate identification of vulnerable plaques and vulnerable patients. More precise diagnosis will then lead to OCT-NIRS guided treatment trials to improve secondary prevention. Success in secondary prevention will then facilitate development of improved primary prevention with invasive imaging and effective treatment of patients identified by non-invasive methods.

A post-market, multi-vessel evaluation of the imaging of peripheral arteries for diagnostic purposeS comparing optical Coherence tomogrApy and iNtravascular ultrasound imaging (SCAN)

Background

Intravascular imaging plays an important part in diagnosis of vascular conditions and providing insight for treatment strategy. Two main imaging modalities are intravascular ultrasound (IVUS) and optical coherence tomography (OCT). The objective of this study was to prove non-inferiority of OCT imaging to IVUS images in matched segments of peripheral vessels in patients with suspected peripheral vascular disease.

Methods

The SCAN study was a prospective, non-inferiority clinical study of matched IVUS and OCT images collected along defined segments of peripheral vessels from twelve subjects (mean age 68 ± 10.3 years; 10 men) displaying symptoms of vascular disease. Luminal diameters were measured by both imaging systems at the distal, middle, and proximal points of the defined segments. Three blinded interventional radiologists evaluated the quality of both imaging modalities in identifying layered structures (3-point grading), plaque (5-point grading), calcification (5-point grading), stent structure (3-point grading), and artifacts (3-point grading) from 240 randomly ordered images. Mean grading scores and luminal diameters were calculated and analyzed with Student’s t-Test and Mann-Whitney-Wilcoxon testing. Intrareader reproducibility was calculated by intraclass correlation (ICC) analysis.

Results

The mean scoring of plaque, calcification, and vascular stent struts by the three readers was significant better in terms of image quality for OCT than IVUS (p < 0.001, p = 0.001, p = 0.004, respectively). The mean scores of vessel wall component visibility and artifacts generated by the two imaging systems were not significantly different (p = 0.19, p = 0.07, respectively). Mean vessel luminal diameter and area at three specific locations within the vessels were not significantly different between the two imaging modalities. No patient injury, adverse effect or device malfunction were noted during the study.

Conclusions

Imaging by OCT provides the physician with better visualization of some vessel and plaque chacteristics, but both IVUS and OCT imaging are safe and effective methods of examining peripheral vessels in order to perform diagnostic assessment of peripheral vessels and provide information necessary for the treatment strategy of peripheral artery disease.

Trial registration

NCT03480685 registered on 29 March 2018.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Development of Dual-Frequency Oblong-Shaped-Focused Transducers for Intravascular Ultrasound Tissue Harmonic Imaging

Tissue harmonic imaging (THI), an essential mode of commercial ultrasound imaging scanners, can provide images with high spatial and contrast resolutions. For THI, the frequency spectrum of a transducer is generally divided for the transmission of fundamental signal and the reception of its second harmonic. Therefore, it is difficult to use the THI mode for intravascular ultrasound (IVUS) imaging because typical IVUS transducers have a narrow -6-dB fractional bandwidth of about 50%. Due to its small aperture (about 0.5 mm) and the strength of IVUS being too weak, it is difficult to construct a high-quality tissue harmonic image. In this paper, we report a recently developed dual-frequency oblong-shaped-focused IVUS transducer for high-quality intravascular THI; the transducer consists of three elements arranged side by side in the horizontal (i.e., elevation) direction. The two outer elements with a center frequency of 35 MHz are responsible for ultrasound transmission and the center element has a center frequency of 70 MHz for the reception of the second-harmonic signals. All three elements have a spherical shape with a radius of 3 mm to efficiently generate harmonics in the region of interest. This configuration of the developed IVUS transducer was determined to facilitate high-quality THI, which was based on the results of Field II simulation and finite-element analysis. The images of wires and a tissue-mimicking phantom indicated that the tissue harmonic images produced by the developed transducer have not only a high spatial resolution but also a deep imaging depth, compared to the 35- and 70-MHz fundamental images.

Combining cholesterol-lowering strategies with imaging data: a visible benefit?

Coronary artery disease is characterised by the development of atherosclerotic plaques and is associated with significant morbidity and mortality on a global level. However, many patients with atherosclerosis are asymptomatic and the prediction of acute coronary events is challenging. The role of imaging studies in characterising plaque morphology and stability is emerging as a valuable prognostic tool, while providing evidence for the beneficial effects of cholesterol-lowering therapy on plaque burden. This review provides an overview of contemporary studies describing the value of imaging strategies for atherosclerotic plaques. Coronary angiography is commonly used in the clinical setting, but requires a significant radiation dose (similar to computed tomography). Magnetic resonance imaging evaluation of coronary vessels would avoid exposure to ionising radiation, but is not yet feasible due to motion artefacts. The roles of alternative imaging techniques, including grey-scale intravascular ultrasound, optical coherence tomography and near-infrared spectroscopy have emerged in recent years. In particular, grey-scale intravascular ultrasound has been effectively applied to detect changes in plaque burden and features of plaques predictive of rupture, as well as plaque characteristics during cholesterol-lowering therapy, providing novel insights into factors that may contribute to treatment effectiveness. Challenges and limitations to the use of imaging techniques are considered in this context, along with future imaging strategies.

Plaque Structural Stress Estimations Improve Prediction of Future Major Adverse Cardiovascular Events After Intracoronary Imaging

BACKGROUND

Although plaque rupture is responsible for most myocardial infarctions, few high-risk plaques identified by intracoronary imaging actually result in future major adverse cardiovascular events (MACE). Nonimaging markers of individual plaque behavior are therefore required. Rupture occurs when plaque structural stress (PSS) exceeds material strength. We therefore assessed whether PSS could predict future MACE in high-risk nonculprit lesions identified on virtual-histology intravascular ultrasound.

METHODS AND RESULTS

Baseline nonculprit lesion features associated with MACE during long-term follow-up (median: 1115 days) were determined in 170 patients undergoing 3-vessel virtual-histology intravascular ultrasound. MACE was associated with plaque burden ≥70% (hazard ratio: 8.6; 95% confidence interval, 2.5-30.6; P<0.001) and minimal luminal area ≤4 mm(2) (hazard ratio: 6.6; 95% confidence interval, 2.1-20.1; P=0.036), although absolute event rates for high-risk lesions remained <10%. PSS derived from virtual-histology intravascular ultrasound was subsequently estimated in nonculprit lesions responsible for MACE (n=22) versus matched control lesions (n=22). PSS showed marked heterogeneity across and between similar lesions but was significantly increased in MACE lesions at high-risk regions, including plaque burden ≥70% (13.9±11.5 versus 10.2±4.7; P<0.001) and thin-cap fibroatheroma (14.0±8.9 versus 11.6±4.5; P=0.02). Furthermore, PSS improved the ability of virtual-histology intravascular ultrasound to predict MACE in plaques with plaque burden ≥70% (adjusted log-rank, P=0.003) and minimal luminal area ≤4 mm(2) (P=0.002). Plaques responsible for MACE had larger superficial calcium inclusions, which acted to increase PSS (P<0.05).

CONCLUSIONS

Baseline PSS is increased in plaques responsible for MACE and improves the ability of intracoronary imaging to predict events. Biomechanical modeling may complement plaque imaging for risk stratification of coronary nonculprit lesions.

Presence of multiple coronary angiographic characteristics for the diagnosis of acute coronary thrombus

BACKGROUND

Coronary angiography is frequently employed to aid in the diagnosis of acute coronary thrombosis, but there is limited data to support its efficacy. The aim of the study was to evaluate sensitivity and specificity of five commonly used angiographic characteristics for diagnosis of acute coronary thrombosis: Ambrose complex lesion morphology; spherical, ovoid, or irregular filling defect; abrupt vessel cutoff; intraluminal staining; and any coronary filling defect.

METHODS

Coronary angiography of 80 acute myocardial infarction or stable coronary artery disease subjects were assessed in blinded fashion, for the presence or absence of five angiographic characteristics. Only lesions of ≥ 10% stenosis were included in the analysis. Presence or absence of each angiographic characteristic was compared between lesions with or without the following study defined outcomes: 1) histologically confirmed thrombus, 2) highly probable thrombus, and 3) highly unlikely thrombus.

RESULTS

A total of 323 lesions were evaluated. All studied angiographic characteristics were associated with histologically confirmed and highly probable thrombotic lesions vs. lesions not meeting criteria for these outcomes (p < 0.03), except for complex Ambrose morphology which was not associated with any of the study outcomes (p > 0.05). Specificity for identifying histologically confirmed or highly probable thrombotic lesion was high (92-100%), especially for spherical, ovoid, or irregular filling defect (99-100%) and intraluminal staining (99%). Sensitivity for identification of histologically confirmed or highly probable thrombotic lesions was low for all tested angiographic characteristics (17-60%).

CONCLUSIONS

The presence of spherical, ovoid, or irregular filling defect or intraluminal staining was highly suggestive of coronary thrombus. However, none of the evaluated angiographic characteristics were useful for ruling out the presence of coronary thrombus. If confirmed in an independent cohort, these angiographic characteristic will be of significant value in confirming the diagnosis of acute coronary thrombosis.

Intravascular Ultrasound and Near-Infrared Spectroscopic Characterization of Thin-Cap Fibroatheroma

Thin-cap fibroatheromas (TCFAs) are considered precursors for plaque rupture and subsequent acute coronary events. We investigated intravascular ultrasound (IVUS) and near-infrared spectroscopy (NIRS) characteristics of lesions that were histopathologic TCFAs. IVUS, NIRS, and histopathology were performed in 271 atherosclerotic lesions from 107 fresh coronary arteries from 54 patients at necropsy. The plaque burden and remodeling index calculated by IVUS and maximum lipid core burden index within any 4-mm segment (maxLCBI_4mm) calculated by NIRS were compared among each plaque type based on histopathologic classifications but focusing on TCFA. Lesions classified as TCFAs had the largest plaque burden, the highest remodeling index, and the greatest maxLCBI_4mm. Plaque burden ≥69% (90% sensitivity, 75% specificity, and area under the curve 0.87); remodeling index ≥1.07 (80% sensitivity, 79% specificity, and area under the curve 0.84); and maxLCBI_4mm ≥323 (80% sensitivity, 85% specificity, and area under the curve 0.84) predicted a histopathologic TCFA. In conclusion, a large plaque burden and a high remodeling index assessed by IVUS and lipid-rich plaque determined by the NIRS maxLCBI_4mm are useful predictive markers of TCFA.

Combined frequency domain photoacoustic and ultrasound imaging for intravascular applications

Intravascular photoacoustic (IVPA) imaging has the potential to characterize lipid-rich structures based on the optical absorption contrast of tissues. In this study, we explore frequency domain photoacoustics (FDPA) for intravascular applications. The system employed an intensity-modulated continuous wave (CW) laser diode, delivering 1W over an intensity modulated chirp frequency of 4-12MHz. We demonstrated the feasibility of this approach on an agar vessel phantom with graphite and lipid targets, imaged using a planar acoustic transducer co-aligned with an optical fibre, allowing for the co-registration of IVUS and FDPA images. A frequency domain correlation method was used for signal processing and image reconstruction. The graphite and lipid targets show an increase in FDPA signal as compared to the background of 21dB and 16dB, respectively. Use of compact CW laser diodes may provide a valuable alternative for the development of photoacoustic intravascular devices instead of pulsed laser systems.

Intracoronary Imaging in the Detection of Vulnerable Plaques

Coronary artery disease is the result of atherosclerotic changes to the coronary arterial wall, comprising endothelial dysfunction, vascular inflammation and deposition of lipid-rich macrophage foam cells. Certain high-risk atherosclerotic plaques are vulnerable to disruption, leading to rupture, thrombosis and the clinical sequelae of acute coronary syndrome. Though recognised as the gold standard for evaluating the presence, distribution and severity of atherosclerotic lesions, invasive coronary angiography is incapable of identifying non-stenotic, vulnerable plaques that are responsible for adverse cardiovascular events. The recognition of such limitations has impelled the development of intracoronary imaging technologies, including intravascular ultrasound, optical coherence tomography and near-infrared spectroscopy, which enable the detailed evaluation of the coronary wall and atherosclerotic plaques in clinical practice. This review discusses the present status of invasive imaging technologies; summarises up-to-date, evidence-based clinical guidelines; and addresses questions that remain unanswered with regard to the future of intracoronary plaque imaging.

A Review of Intravascular Ultrasound-based Multimodal Intravascular Imaging: The Synergistic Approach to Characterizing Vulnerable Plaques

Catheter-based intravascular imaging modalities are being developed to visualize pathologies in coronary arteries, such as high-risk vulnerable atherosclerotic plaques known as thin-cap fibroatheroma, to guide therapeutic strategy at preventing heart attacks. Mounting evidences have shown three distinctive histopathological features-the presence of a thin fibrous cap, a lipid-rich necrotic core, and numerous infiltrating macrophages-are key markers of increased vulnerability in atherosclerotic plaques. To visualize these changes, the majority of catheter-based imaging modalities used intravascular ultrasound (IVUS) as the technical foundation and integrated emerging intravascular imaging techniques to enhance the characterization of vulnerable plaques. However, no current imaging technology is the unequivocal "gold standard" for the diagnosis of vulnerable atherosclerotic plaques. Each intravascular imaging technology possesses its own unique features that yield valuable information although encumbered by inherent limitations not seen in other modalities. In this context, the aim of this review is to discuss current scientific innovations, technical challenges, and prospective strategies in the development of IVUS-based multi-modality intravascular imaging systems aimed at assessing atherosclerotic plaque vulnerability.

Adaptive windowing in contrast-enhanced intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is one of the most commonly-used interventional imaging techniques and has seen recent innovations which attempt to characterize the risk posed by atherosclerotic plaques. One such development is the use of microbubble contrast agents to image vasa vasorum, fine vessels which supply oxygen and nutrients to the walls of coronary arteries and typically have diameters less than 200μm. The degree of vasa vasorum neovascularization within plaques is positively correlated with plaque vulnerability. Having recently presented a prototype dual-frequency transducer for contrast agent-specific intravascular imaging, here we describe signal processing approaches based on minimum variance (MV) beamforming and the phase coherence factor (PCF) for improving the spatial resolution and contrast-to-tissue ratio (CTR) in IVUS imaging. These approaches are examined through simulations, phantom studies, ex vivo studies in porcine arteries, and in vivo studies in chicken embryos. In phantom studies, PCF processing improved CTR by a mean of 4.2dB, while combined MV and PCF processing improved spatial resolution by 41.7%. Improvements of 2.2dB in CTR and 37.2% in resolution were observed in vivo. Applying these processing strategies can enhance image quality in conventional B-mode IVUS or in contrast-enhanced IVUS, where signal-to-noise ratio is relatively low and resolution is at a premium.

Genetics paired with CT angiography in the setting of atherosclerosis

Coronary artery disease (CAD) continues to be the leading cause of morbidity and mortality globally. Although the etiological mechanisms for CAD have not been fully elucidated, however, most would agree that atherosclerotic plaques progressively narrow the coronary arteries are the earliest manifestations and the principal cause of CAD. The emergence of revolutionary imaging technologies such as cardiac CT angiography, noninvasive computed fractional flow reserve and intravascular ultrasound provided the possibility of detecting and monitoring phenotypes associated with subclinical atherosclerosis. Meanwhile, with the widespread use of high-throughput genotyping pipeline such as next-generation sequencing, combined with big data-driven solutions in bioinformatics, translating the emerging genetic technologies into clinical practice and, therefore, provide valuable insight into the CAD study. In this review, we briefly describe the latest noninvasive cardiac imaging techniques for atherosclerosis-related phenotypes' detection, mainly focusing on the coronary artery calcification, plaque burden and stenosis. Furthermore, we highlight the state-of-the-art genotyping techniques and its application in the field of CAD translational study. Finally, we discuss the clinical relevance of genetics paired with noninvasive imaging in the setting of coronary artery atherosclerosis.

Acute coronary syndromes without coronary plaque rupture

The latest advances in plaque imaging have provided clinicians with opportunities to treat acute coronary syndrome (ACS) and provide individualized treatment recommendations based not only on clinical manifestations, angiographic characteristics, and biomarker data, but also on the findings of plaque morphology. Although a substantial proportion of ACS events originate from plaques with an intact fibrous cap (IFC), clinicians predominantly equate ACS with plaque rupture arising from thin-cap fibroatheromas. In this Review, we discuss the recent advances in our understanding of plaque morphology in ACS with IFC, reviewing contemporary data from intravascular imaging. We also explore whether use of such imaging might provide a roadmap for more effective management of patients with ACS.

Acute Myocardial Infarction in Women: A Scientific Statement From the American Heart Association

Cardiovascular disease is the leading cause of mortality in American women. Since 1984, the annual cardiovascular disease mortality rate has remained greater for women than men; however, over the last decade, there have been marked reductions in cardiovascular disease mortality in women. The dramatic decline in mortality rates for women is attributed partly to an increase in awareness, a greater focus on women and cardiovascular disease risk, and the increased application of evidence-based treatments for established coronary heart disease. This is the first scientific statement from the American Heart Association on acute myocardial infarction in women. Sex-specific differences exist in the presentation, pathophysiological mechanisms, and outcomes in patients with acute myocardial infarction. This statement provides a comprehensive review of the current evidence of the clinical presentation, pathophysiology, treatment, and outcomes of women with acute myocardial infarction.

Microbubble-mediated intravascular ultrasound imaging and drug delivery

Intravascular ultrasound (IVUS) provides radiation-free, real-time imaging and assessment of atherosclerotic disease in terms of anatomical, functional, and molecular composition. The primary clinical applications of IVUS imaging include assessment of luminal plaque volume and real-time image guidance for stent placement. When paired with microbubble contrast agents, IVUS technology may be extended to provide nonlinear imaging, molecular imaging, and therapeutic delivery modes. In this review, we discuss the development of emerging imaging and therapeutic applications that are enabled by the combination of IVUS imaging technology and microbubble contrast agents.

Association between tissue characteristics of coronary plaque and distal embolization after coronary intervention in acute coronary syndrome patients: insights from a meta-analysis of virtual histology-intravascular ultrasound studies

Background and Objectives

The predictive value of plaque characteristics assessed by virtual histology-intravascular ultrasound (VH-IVUS) including fibrous tissue (FT), fibrofatty (FF), necrotic core (NC) and dense calcium (DC) in identifying distal embolization after percutaneous coronary intervention (PCI) is still controversial. We performed a systematic review and meta-analysis to summarize the association of pre-PCI plaque composition and post-PCI distal embolization in acute coronary syndrome patients.

Methods

Studies were identified in PubMed, OVID, EMBASE, the Cochrane Library, the Current Controlled Trials Register, reviews, and reference lists of relevant articles. A meta-analysis using both fixed and random effects models with assessment of study heterogeneity and publication bias was performed.

Results

Of the 388 articles screened, 10 studies with a total of 872 subjects (199 with distal embolization and 673 with normal flow) met the eligibility of our study. Compared with normal flow groups, significant higher absolute volume of NC [weighted mean differences (WMD): 5.79 mm³, 95% CI: 3.02 to 8.55 mm³; p<0.001] and DC (WMD: 2.55 mm³, 95% CI: 0.22 to 4.88 mm³; p = 0.03) were found in acute coronary syndrome patients with distal embolization. Further subgroup analysis demonstrated that the predictive value of tissue characteristics in determining distal embolization was correlated to clinical scenario of the patients, definition of distal embolization, and whether the percutaneous aspiration thrombectomy was applied.

Conclusion

Our study that pooled current evidence showed that plaque components were closely related to the distal embolization after PCI, especially the absolute volume of NC and DC, supporting further studies with larger sample size and high-methodological quality.

The utility of stent enhancement to guide percutaneous coronary intervention for bifurcation lesions

AIMS

Percutaneous coronary intervention (PCI) of bifurcation lesions is complex and is technically very demanding. Coronary angiography is considered the gold standard method to guide PCI but has several limitations. The purpose of this study was to determine the utility of stent enhancement with StentBoost® (StB), a novel fluoroscopic imaging technique, and its potential role during bifurcation PCI.

METHODS AND RESULTS

This prospective study included 97 patients who underwent bifurcation PCI (98 bifurcations), using StB. Bifurcation lesions were classified according to the modified Medina classification. StB was performed in all patients to obtain improved stent visualisation and to detect optimal release and deployment. Therefore, three groups were formed, according to the quality of image: optimal visualisation, suboptimal visualisation and poor visualisation. Most of the bifurcation disease involved the main vessel (99%) and in 80 patients (81.6%) there was side branch involvement. Most bifurcations had both main vessel and side branch lesions (Medina 1,1,1) (70 patients, 71.4%). StB image quality was good in 79.6% of the cases (optimal visualisation of the stent and guidewire), was suboptimal in 19.4%, and poor in 1% (overlapping of structures or devices). In three cases, StB enabled the identification of the guidewire and angioplasty balloon passing outside stent borders during rewiring of the side branch.

CONCLUSIONS

Imaging techniques have a primary role during bifurcation PCI. StentBoost is a simple and quick method that offers several advantages, enabling improved stent visualisation, appropriate rewiring of the side branch, adequate stent expansion and optimal apposition of the struts to the wall.

Intravascular photoacoustic imaging: a new tool for vulnerable plaque identification

The vulnerable atherosclerotic plaque is believed to be at the root of the majority of acute coronary events. Even though the exact origins of plaque vulnerability remain elusive, the thin-cap fibroatheroma, characterized by a lipid-rich necrotic core covered by a thin fibrous cap, is considered to be the most prominent type of vulnerable plaque. No clinically available imaging technique can characterize atherosclerotic lesions to the extent needed to determine plaque vulnerability prognostically. Intravascular photoacoustic imaging (IVPA) has the potential to take a significant step in that direction by imaging both plaque structure and composition. IVPA is a natural extension of intravascular ultrasound that adds tissue type specificity to the images. IVPA utilizes the optical contrast provided by the differences in the absorption spectra of plaque components to image composition. Its capability to image lipids in human coronary atherosclerosis has been shown extensively ex vivo and has recently been translated to an in vivo animal model. Other disease markers that have been successfully targeted are calcium and inflammatory markers, such as macrophages and matrix metalloproteinase; the latter two through application of exogenous contrast agents. By simultaneously displaying plaque morphology and composition, IVPA can provide a powerful prognostic marker for disease progression, and as such has the potential to transform the current practice in percutaneous coronary intervention.

Mechanisms, pathophysiology, and clinical aspects of incomplete stent apposition

Incomplete stent apposition (ISA) is characterized by the lack of contact of at least 1 stent strut with the vessel wall in a segment not overlying a side branch; it is more commonly found in drug-eluting stents than bare-metal stents. The accurate diagnosis of ISA, initially only possible with intravascular ultrasound, can currently be performed with higher accuracy by optical coherence tomography, which also enables strut-level assessment due to its higher axial resolution. Different circumstances related both to the index procedure and to vascular healing might influence ISA occurrence. Although several histopathology and clinical studies linked ISA to stent thrombosis, potential selection bias precluded definitive conclusions. Initial studies usually performed single time point assessments comparing overall ISA percentage and magnitude in different groups (i.e., stent type), thus hampering a comprehensive understanding of its relationship with vascular healing. Serial intravascular imaging studies that evaluated vascular response heterogeneity recently helped fill this gap. Some particular clinical scenarios such as acute coronary syndromes, bifurcations, tapered vessels, overlapping stents, and chronic total occlusions might predispose to ISA. Interventional cardiologists should be committed to optimal stent choices and techniques of implantation and use intravascular imaging guidance when appropriate to aim at minimizing acute ISA. In addition, the active search for new stent platforms that could accommodate vessel remodeling over time (i.e., self-expandable stents) and for new polymers and/or eluting drugs that could induce less inflammation (hence, less positive remodeling) could ultimately reduce the occurrence of ISA and its potentially harmful consequences.

Molecular imaging of inflammation in atherosclerosis

Acute rupture of vulnerable plaques frequently leads to myocardial infarction and stroke. Within the last decades, several cellular and molecular players have been identified that promote atherosclerotic lesion formation, maturation and plaque rupture. It is now widely recognized that inflammation of the vessel wall and distinct leukocyte subsets are involved throughout all phases of atherosclerotic lesion development. The mechanisms that render a stable plaque unstable and prone to rupture, however, remain unknown and the identification of the vulnerable plaque remains a major challenge in cardiovascular medicine. Imaging technologies used in the clinic offer minimal information about the underlying biology and potential risk for rupture. New imaging technologies are therefore being developed, and in the preclinical setting have enabled new and dynamic insights into the vessel wall for a better understanding of this complex disease. Molecular imaging has the potential to track biological processes, such as the activity of cellular and molecular biomarkers in vivo and over time. Similarly, novel imaging technologies specifically detect effects of therapies that aim to stabilize vulnerable plaques and silence vascular inflammation. Here we will review the potential of established and new molecular imaging technologies in the setting of atherosclerosis, and discuss the cumbersome steps required for translating molecular imaging approaches into the clinic.

Almanac 2013: acute coronary syndromes

Unstable coronary artery plaque is the most common underlying cause of acute coronary syndromes (ACS) and can manifest as unstable angina, non-ST segment elevation infarction (NSTE-ACS), and ST elevation myocardial infarction (STEMI), but can also manifest as sudden cardiac arrest due to ischaemia induced tachyarrhythmias. ACS mortality has decreased significantly over the last few years, especially from the more extreme manifestations of ACS, STEMI, and cardiac arrest. This trend is likely to continue based on recent therapeutic progress which includes novel antiplatelet agents such as prasugrel, ticagrelor, and cangrelor.

Correlation between plaque composition as assessed by virtual histology and C-reactive protein

Background

Previous studies have shown that coronary plaque composition plays a pivotal role in plaque instability, and imaging modalities and serum biomarkers have been investigated to identify vulnerable plaque. Virtual histology IVUS (VH-IVUS) characterizes plaque components as calcified, fibrotic, fibrofatty, or necrotic core. C-reactive protein (hsCRP) is an independent risk factor and a powerful predictor of future coronary events. However, a relationship between inflammatory response indicated by CRP and plaque characteristics in ACS patients remains not well established.

Objective

To determine, by using VH-IVUS, the relation between coronary plaque components and plasma high-sensitivity CRP levels in patients with acute coronary syndromes (ACS).

Methods

52 patients with ACS were enrolled in this prospective study. Electrocardiographically-gated VH-IVUS were performed in the culprit lesion before PCI. Blood sample was drawn from all patients before the procedure and after 24 hours, and hs-CRP levels were determined.

Results

Mean age was 55.3±4.9 years, 76.9% were men and 30.9% had diabetes. Mean MLA was 3.9±1.3 mm², and plaque burden was 69±11.3%, as assessed by IVUS. VH-IVUS analysis at the minimum luminal site identified plaque components: fibrotic (59.6±15.8%), fibrofatty (7.6±8.2%), dense calcium (12.1±9.2%) and necrotic core (20.7±12.7%). Plasma hs-CRP (mean 16.02±18.07 mg/L) did not correlate with necrotic core (r=-0.089, p = 0.53) and other plaque components.

Conclusions

In this prospective study with patients with ACS, the predominant components of the culprit plaque were fibrotic and necrotic core. Serum hs C-reactive protein levels did not correlate with plaque composition.

Spectroscopic photoacoustic imaging of lipid-rich plaques in the human aorta in the 740 to 1400 nm wavelength range

Spectroscopic photoacoustic imaging has the potential to discriminate between normal and lipid-rich atheromatous areas of arterial tissue by exploiting the differences in the absorption spectra of lipids and normal arterial tissue in the 740 to 1400 nm wavelength range. Identification of regions of high lipid concentration would be useful to identify plaques that are likely to rupture (vulnerable plaques). To demonstrate the feasibility of visualizing lipid-rich plaques, samples of human aortas were imaged in forward mode, at wavelengths of 970 and 1210 nm. It was shown that the structure of the arterial wall and the boundaries of lipid-rich plaques obtained from the photoacoustic images were in good agreement with histology. The presence of lipids was also confirmed by comparing the photoacoustic spectra (740 to 1400 nm) obtained in a region within the plaque to the spectral signature of lipids. Furthermore, a lipid-rich plaque was successfully imaged while illuminating the sample through 2.8 mm of blood demonstrating the possibility of implementing the photoacoustic technique in vivo.

Intravascular optical imaging technology for investigating the coronary artery

There is an ever-increasing demand for new imaging methods that can provide additional information about the coronary wall to better characterize and stratify high-risk plaques, and to guide interventional and pharmacologic management of patients with coronary artery disease. While there are a number of imaging modalities that facilitate the assessment of coronary artery pathology, this review paper focuses on intravascular optical imaging modalities that provide information on the microstructural, compositional, biochemical, biomechanical, and molecular features of coronary lesions and stents. The optical imaging modalities discussed include angioscopy, optical coherence tomography, polarization sensitive-optical coherence tomography, laser speckle imaging, near-infrared spectroscopy, time-resolved laser induced fluorescence spectroscopy, Raman spectroscopy, and near-infrared fluorescence molecular imaging. Given the wealth of information that these techniques can provide, optical imaging modalities are poised to play an increasingly significant role in the evaluation of the coronary artery in the future.

Intravascular imaging tools in the cardiac catheterization laboratory: comprehensive assessment of anatomy and physiology

Intravascular imaging modalities have an imperative role in contemporary cardiovascular research. Currently, there are several invasive imaging modalities available in the cardiac catheterization laboratory and new technologies are under development. In the current review, we aimed to provide an update on the research applications of contemporary intravascular imaging tools in the cardiac catheterization laboratory. For the purpose of this review, we separately discuss imaging tools for assessment of epicardial disease (fractional flow reserve and hyperemic stenosis resistance), microvascular function (coronary flow reserve, hyperemic microvascular resistance, and index of microcirculatory resistance), endothelial function, atherosclerotic plaque and vascular remodeling (intravascular ultrasound, optical coherence tomography, angioscopy, and near-infrared spectroscopy), and finally the emerging modalities (palpography and wall shear stress profiling).