Radial wall strain: a novel angiographic measure of plaque composition and vulnerability

Advancements in imaging of intracranial atherosclerotic disease: beyond the arterial lumen to the vessel wall

Intracranial atherosclerotic disease (ICAD) significantly increases the risk of ischemic stroke. It involves the accumulation of plaque within arterial walls and narrowing or blockage of blood vessel lumens. Accurate imaging is crucial for the diagnosis and management of ICAD at both acute and chronic stages. However, imaging the small, tortuous intracranial arterial walls amidst complex structures is challenging. Clinicians have employed diverse approaches to improve imaging quality, with a particular emphasis on optimizing the acquisition of images using new techniques, enhancing spatial and temporal resolution of images, and refining post-processing techniques. ICAD imaging has evolved from depicting lumen stenosis to assessing blood flow reserve and identifying plaque components. Advanced techniques such as fractional flow reserve (FFR), high-resolution vessel wall magnetic resonance (VW-MR), optical coherence tomography (OCT), and radial wall strain (RWS) now allow direct visualization of flow impairment, vulnerable plaques, and blood flow strain to plaque, aiding in the selection of high-risk stroke patients for intervention. This article reviews the progression of imaging modalities from lumen stenosis to vessel wall pathology and compares their diagnostic value for risk stratification in ICAD patients.

Artificial Intelligence in Imaging for Personalized Management of Coronary Artery Disease

The precision of imaging and the number of other risk-assessing and diagnostic methods are constantly growing, allowing for the uptake of additional strategies for individualized therapies. Personalized medicine has the potential to deliver more adequate treatment, resulting in better clinical outcomes, based on each patient's vulnerability or genetic makeup. In addition to increased efficiency, costs related to this type of procedure can be significantly lower. Useful assistance in designing individual therapies may be assured by the adoption of artificial intelligence (AI). Recent years have brought essential developments in deep and machine learning techniques. Advances in technologies such as convolutional neural networks (CNNs) have enabled automatic analyses of images, numerical data, and video data, providing high efficiency in the creation of prediction models. The number of AI applications in medicine is constantly growing, and the effectiveness of these techniques has been demonstrated in coronary computed tomography angiography (CCTA), optical coherence tomography (OCT), and many others. Moreover, AI models may be useful in direct therapy optimization for patients with coronary artery disease (CAD), who are burdened with high risk. The combination of well-trained AI with the design of individual treatment pathways can lead to improvements in health care. However, existing limitations, such as non-adapted guidelines or the lack of randomized clinical trials to evaluate AI's true accuracy, may contribute to delays in introducing automatic methods into practical use. This review critically appraises the developed tools that are potentially useful for clinicians in guiding personalized patient management, as well as current trials in this field.

Illusion of revascularization: does anyone achieve optimal revascularization during percutaneous coronary intervention?

This Perspective article is a form of 'pastiche', inspired by the 1993 review by Lincoff and Topol entitled 'Illusion of reperfusion', and explores how their concept continues to apply to percutaneous revascularization in patients with coronary artery disease and ischaemia. Just as Lincoff and Topol argued that reperfusion of acute myocardial infarction was facing unresolved obstacles that hampered clinical success in 1993, we propose that challenging issues are similarly jeopardizing the potential benefits of stent-based angioplasty today. By analysing the appropriateness and efficacy of percutaneous coronary intervention (PCI), we emphasize the limitations of relying solely on visual angiographic guidance, which frequently leads to inappropriate stenting and overtreatment in up to one-third of patients and the associated increased risk of periprocedural myocardial infarction. The lack of optimal revascularization observed in half of patients undergoing PCI confers risks such as suboptimal physiology after PCI, residual angina and long-term stent-related events, leaving an estimated 76% of patients with an 'illusion of revascularization'. These outcomes highlight the need to refine our diagnostic tools by integrating physiological assessments with targeted intracoronary imaging and emerging strategies, such as co-registration systems and angiography-based computational methods enhanced by artificial intelligence, to achieve optimal revascularization outcomes.

Biomechanical factors and atherosclerosis localization: insights and clinical applications

Although the entire vascular bed is constantly exposed to the same risk factors, atherosclerosis manifests a distinct intra-individual pattern in localization and progression within the arterial vascular bed. Despite shared risk factors, the development of atherosclerotic plaques is influenced by physical principles, anatomic variations, metabolic functions, and genetic pathways. Biomechanical factors, particularly wall shear stress (WSS), play a crucial role in atherosclerosis and both low and high WSS are associated with plaque progression and heightened vulnerability. Low and oscillatory WSS contribute to plaque growth and arterial remodeling, while high WSS promotes vulnerable changes in obstructive coronary plaques. Axial plaque stress and plaque structural stress are proposed as biomechanical indicators of plaque vulnerability, representing hemodynamic stress on stenotic lesions and localized stress within growing plaques, respectively. Advancements in imaging and computational fluid dynamics techniques enable a comprehensive analysis of morphological and hemodynamic properties of atherosclerotic lesions and their role in plaque localization, evolution, and vulnerability. Understanding the impact of mechanical forces on blood vessels holds the potential for developing shear-regulated drugs, improving diagnostics, and informing clinical decision-making in coronary atherosclerosis management. Additionally, Computation Fluid Dynamic (CFD) finds clinical applications in comprehending stent-vessel dynamics, complexities of coronary bifurcations, and guiding assessments of coronary lesion severity. This review underscores the clinical significance of an integrated approach, concentrating on systemic, hemodynamic, and biomechanical factors in atherosclerosis and plaque vulnerability among patients with coronary artery disease.

Consensus document on the clinical application of invasive functional coronary angiography from the Japanese Association of Cardiovascular Intervention and Therapeutics

Invasive functional coronary angiography (FCA), an angiography-derived physiological index of the functional significance of coronary obstruction, is a novel physiological assessment tool for coronary obstruction that does not require the utilization of a pressure wire. This technology enables operators to rapidly evaluate the functional relevance of coronary stenoses during and even after angiography while reducing the burden of cost and complication risks related to the pressure wire. FCA can be used for treatment decision-making for revascularization, strategy planning for percutaneous coronary intervention, and procedure optimization. Currently, various software-computing FCAs are available worldwide, with unique features in their computation algorithms and functions. With the emerging application of this novel technology in various clinical scenarios, the Japanese Association of Cardiovascular Intervention and Therapeutics task force was created to outline expert consensus on the clinical use of FCA. This consensus document advocates optimal clinical applications of FCA according to currently available evidence while summarizing the concept, history, limitations, and future perspectives of FCA along with globally available software.

Relationship of Coronary Angiography-Derived Radial Wall Strain With Functional Significance, Plaque Morphology, and Clinical Outcomes

BACKGROUND

Coronary angiography-derived radial wall strain (RWS) is a newly developed index that can be readily accessed and describes the biomechanical features of a lesion.

OBJECTIVES

The authors sought to investigate the association of RWS with fractional flow reserve (FFR) and high-risk plaque (HRP), and their relative prognostic implications.

METHODS

We included 484 vessels (351 patients) deferred after FFR measurement with available RWS data and coronary computed tomography angiography. On coronary computed tomography angiography, HRP was defined as a lesion with both minimum lumen area <4 mm2 and plaque burden ≥70%. The primary outcome was target vessel failure (TVF), a composite of target vessel revascularization, target vessel myocardial infarction, or cardiac death.

RESULTS

The mean FFR and RWSmax were 0.89 ± 0.07 and 11.2% ± 2.5%, respectively, whereas 27.7% of lesions had HRP, 15.1% had FFR ≤0.80. An increase in RWSmax was associated with a higher risk of FFR ≤0.80 and HRP, which was consistent after adjustment for clinical or angiographic characteristics (all P < 0.05). An increment of RWSmax was related to a higher risk of TVF (HR: 1.23 [95% CI: 1.03-1.47]; P = 0.022) with an optimal cutoff of 14.25%. RWSmax >14% was a predictor of TVF after adjustment for FFR or HRP components (all P < 0.05) and showed a direct prognostic effect on TVF, not mediated by FFR ≤0.80 or HRP in the mediation analysis. When high RWSmax was added to FFR ≤0.80 or HRP, there were increasing outcome trends (all P for trend <0.001).

CONCLUSIONS

RWS was associated with coronary physiology and plaque morphology but showed independent prognostic significance.

Clinical quantitative coronary artery stenosis and coronary atherosclerosis imaging: a Consensus Statement from the Quantitative Cardiovascular Imaging Study Group

The detection and characterization of coronary artery stenosis and atherosclerosis using imaging tools are key for clinical decision-making in patients with known or suspected coronary artery disease. In this regard, imaging-based quantification can be improved by choosing the most appropriate imaging modality for diagnosis, treatment and procedural planning. In this Consensus Statement, we provide clinical consensus recommendations on the optimal use of different imaging techniques in various patient populations and describe the advances in imaging technology. Clinical consensus recommendations on the appropriateness of each imaging technique for direct coronary artery visualization were derived through a three-step, real-time Delphi process that took place before, during and after the Second International Quantitative Cardiovascular Imaging Meeting in September 2022. According to the Delphi survey answers, CT is the method of choice to rule out obstructive stenosis in patients with an intermediate pre-test probability of coronary artery disease and enables quantitative assessment of coronary plaque with respect to dimensions, composition, location and related risk of future cardiovascular events, whereas MRI facilitates the visualization of coronary plaque and can be used in experienced centres as a radiation-free, second-line option for non-invasive coronary angiography. PET has the greatest potential for quantifying inflammation in coronary plaque but SPECT currently has a limited role in clinical coronary artery stenosis and atherosclerosis imaging. Invasive coronary angiography is the reference standard for stenosis assessment but cannot characterize coronary plaques. Finally, intravascular ultrasonography and optical coherence tomography are the most important invasive imaging modalities for the identification of plaques at high risk of rupture. The recommendations made in this Consensus Statement will help clinicians to choose the most appropriate imaging modality on the basis of the specific clinical scenario, individual patient characteristics and the availability of each imaging modality.

Coronary Physiology-Based Approaches for Plaque Vulnerability: Implications for Risk Prediction and Treatment Strategies

In the catheterization laboratory, the measurement of physiological indexes can help identify functionally significant lesions and has become one of the standard methods to guide treatment decision-making. Plaque vulnerability refers to a coronary plaque susceptible to rupture, enabling risk prediction before coronary events, and it can be detected by defining a certain type of plaque morphology on coronary imaging modalities. Although coronary physiology and plaque vulnerability have been considered different attributes of coronary artery disease, the underlying pathophysiological basis and clinical data indicate a strong correlation between coronary hemodynamic properties and vulnerable plaque. In prediction of coronary events, emerging data have suggested independent and additional implications of a physiology-based approach to a plaque-based approach. This review covers the fundamental interplay between coronary physiology and plaque morphology during disease progression with clinical data supporting this relationship and examines the clinical relevance of physiological indexes in prediction of clinical outcomes and therapeutic decision-making along with plaque vulnerability.

Two birds with one stone: integrated assessment of coronary physiology and plaque vulnerability from a single angiographic view-a case report

Background

Physiology-guided coronary revascularization was shown to improve clinical outcomes in multiple patient subsets, whilst in those presenting with acute coronary syndromes, it seems to be associated with an excess of cardiovascular events. One of the major drawbacks in this setting is the potential deferral of non-flow-limiting but 'vulnerable' coronary plaques.

Case summary

A 40-year-old patient presented with a myocardial infarction without ST-segment elevation (NSTEMI). At the invasive coronary angiography (ICA) a sub-occlusive stenosis on his left circumflex artery was detected and treated with percutaneous coronary intervention (PCI). The treatment of a concomitant intermediate eccentric focal stenosis on the right coronary artery (RCA) was deferred after a negative pressure wire-based physiological assessment. The patient was re-admitted 9 months later due to a recurrent NSTEMI, and a severe progression of the deferred RCA lesion was found at the ICA. In retrospect, an angiography-based assessment of physiological severity and plaque vulnerability of the non-culprit RCA stenosis by means of Murray's law-based QFR (μQFR) and radial wall strain (RWS) was performed. At baseline, μQFR value (0.90) corroborated the non-ischaemic findings of wire-based assessment. However, RWS analysis showed a marked hotspot (maximum RWS value 27.7%), indicating the presence of a vulnerable plaque.

Discussion

Radial wall strain is a novel biomechanical deformation index derived from coronary angiography. Segments with high RWS are associated with lipid-rich plaques that are prone to progression and plaque rupture. Therefore, the identification of RWS hotspots might potentially improve the risk stratification of non-culprit lesions and empower secondary prevention strategies.

Radial Wall Strain Assessment From AI-Assisted Angiography: Feasibility and Agreement With OCT as Reference Standard

Background

High-strain spots in coronary arteries are associated with plaque vulnerability and predict future events. Artificial intelligence currently enables the calculation of radial wall strain (RWS) from coronary angiography (RWSAngio). This study aimed to determine the agreement between novel RWSAngio and RWS derived from optical coherence tomography (OCT) followed by finite element analysis, as the established reference standard (RWSOCT).

Methods

All lesions from a previous OCT study were enrolled. OCT was automatically coregistered with angiography. RWSAngio was computed as the relative luminal deformation throughout the cardiac cycle, whereas RWSOCT was analyzed using finite element analysis on OCT cross-sections at 1-mm intervals. The luminal deformation in the direction of minimal lumen diameter was used to derive RWSOCT, using the same definition as RWSAngio. The maximal RWSOCT and RWSAngio at healthy segments adjacent to the interrogated lesion were also analyzed.

Results

Finite element analysis was performed in 578 OCT cross-sections from 45 lesions stemming from 36 patients. RWSAngio showed good correlation and agreement with RWSOCT (r = 0.91; P < .001; Lin coefficient = 0.85). RWSAngio in atherosclerotic segments was significantly higher than that in healthy segments (12.6% [11.0, 16.0] vs 4.5% [2.9, 5.5], P < .001). The intraclass correlation coefficients for intra- and interobserver variability in repeated RWSAngio analysis were 0.92 (95% CI, 0.87-0.95) and 0.88 (95% CI, 0.81-0.92), respectively. The mean analysis time of RWSOCT and RWSAngio for each lesion was 95.0 ± 41.1 and 0.9 ± 0.1 minutes, respectively.

Conclusions

Radial wall strain from coronary angiography can be rapidly and easily computed solely from angiography, showing excellent agreement with strain derived from coregistered OCT. This novel and simple method might provide a cost-effective biomechanical assessment in large populations.

Short-Term Risk Stratification of Non-Flow-Limiting Coronary Stenosis by Angiographically Derived Radial Wall Strain

BACKGROUND

Deferred revascularization of mildly stenotic coronary vessels based exclusively on physiological evaluation is associated with up to 5% residual incidence of future adverse events at 1 year.

OBJECTIVES

We aimed to evaluate the incremental value of angiography-derived radial wall strain (RWS) in risk stratification of non-flow-limiting mild coronary narrowings.

METHODS

This is a post hoc analysis of 824 non-flow-limiting vessels in 751 patients from the FAVOR III China (Comparison of Quantitative Flow Ratio Guided and Angiography Guided Percutaneous Intervention in Patients With Coronary Artery Disease) trial. Each individual vessel had ≥1 mildly stenotic lesion. The primary outcome was vessel-oriented composite endpoint (VOCE), defined as the composite of vessel-related cardiac death, vessel-related myocardial infarction (nonprocedural), and ischemia-driven target vessel revascularization at 1-year follow-up.

RESULTS

During 1-year follow-up, VOCE occurred in 46 of 824 vessels, with a cumulative incidence of 5.6%. Maximum RWS (RWSmax) was predictive of 1-year VOCE with an area under the curve of 0.68 (95% CI: 0.58-0.77; P < 0.001). The incidence of VOCE was 14.3% in vessels with RWSmax >12% vs 2.9% in those with RWSmax ≤12%. In the multivariable Cox regression model, RWSmax >12% was a strong independent predictor of 1-year VOCE in deferred non-flow-limiting vessels (adjusted HR: 4.44; 95% CI: 2.43-8.14; P < 0.001). The risk of deferred revascularization based on combined normal RWSmax and Murray-law-based quantitative flow ratio (μQFR) was significantly reduced compared with μQFR alone (adjusted HR: 0.52; 95% CI: 0.30-0.90; P = 0.019).

CONCLUSIONS

Among vessels with preserved coronary flow, angiography-derived RWS analysis has the potential to further discriminate vessels at risk of 1-year VOCE. (Comparison of Quantitative Flow Ratio Guided and Angiography Guided Percutaneous Intervention in Patients With Coronary Artery Disease [FAVOR III China Study]; NCT03656848).