Patient-specific computational simulation of coronary artery bifurcation stenting

Unravelling the progress and potential of drug-eluting stents and drug-coated balloons in cardiological insurgencies

AIM

Coronary artery disease (CAD) is the leading cause of mortality. Though percutaneous transluminal angioplasty followed by stenting is still the default treatment of choice for revascularization of obstructive CAD, the high rate of restenosis compromises the outcomes of endovascular procedures. To overcome restenosis, drug-eluting stents (DES) and drug-coated balloons (DCB) are designed that release antiproliferative drugs like sirolimus, paclitaxel, everolimus, etc., over time to inhibit cell growth and proliferation. Our review aims to summarize the challenges and progress of DES/DCBs in clinical settings.

MATERIAL AND METHODS

The comprehensive review, search and selection encompasses in relevant articles through Google Scholar, Springer online, Cochrane library and PubMed that includes research articles, reviews, letters and communications, various viewpoints, meta-analyses, randomized trials and quasi-randomized trials. Several preclinical and clinical data have been included from National Institutes of Health and clinicaltrials.gov websites.

KEY FINDINGS

Challenges like delayed endothelialization, stent thrombosis (ST), and inflammation was prominent in first-generation DES. Second-generation DES with improved designs and drug coatings enhanced biocompatibility with fewer complications. Gradual absorption of bioresorbable DES over time mitigated long-term issues associated with permanent implants. Polymer-free DES addressed the inflammation concerns but still, they leave behind metallic stents in the vasculature. As an alternative therapeutic strategy, DCB were developed to minimize inflammation in the vessel. Although both DES and DCBs have shown considerable progress, challenges persist.

SIGNIFICANCE

This review illustrates the advancements in the designs, preparation technologies, biodegradable materials, and drugs used as well as challenges associated with DES and DCBs in clinical settings.

Experimental validation and clinical feasibility of 3D reconstruction of coronary artery bifurcation stents using intravascular ultrasound

The structural morphology of coronary stents and the local hemodynamic environment following stent deployment in coronary arteries are crucial determinants of procedural success and subsequent clinical outcomes. High-resolution intracoronary imaging has the potential to facilitate geometrically accurate three-dimensional (3D) reconstruction of coronary stents. This work presents an innovative algorithm for the 3D reconstruction of coronary artery stents, leveraging intravascular ultrasound (IVUS) and angiography. The accuracy and reproducibility of our method were tested in stented patient-specific silicone models, with micro-computed tomography serving as a reference standard. We also evaluated the clinical feasibility and ability to perform computational fluid dynamics (CFD) studies in a clinically stented coronary bifurcation. Our experimental and clinical studies demonstrated that our proposed algorithm could reproduce the complex 3D stent configuration with a high degree of precision and reproducibility. Moreover, the algorithm was proved clinically feasible in cases with stents deployed in a diseased coronary artery bifurcation, enabling CFD studies to assess the hemodynamic environment. In combination with patient-specific CFD studies, our method can be applied to stenting optimization, training in stenting techniques, and advancements in stent research and development.

Definitions and Standardized Endpoints for Treatment of Coronary Bifurcations

The Bifurcation Academic Research Consortium (Bif-ARC) project originated from the need to overcome the paucity of standardization and comparability between studies involving bifurcation coronary lesions. This document is the result of a collaborative effort between academic research organizations and the most renowned interventional cardiology societies focused on bifurcation lesions in Europe, the United States, and Asia. This consensus provides standardized definitions for bifurcation lesions; the criteria to judge the side branch relevance; the procedural, mechanistic, and clinical endpoints for every type of bifurcation study; and the follow-up methods. Considering the complexity of bifurcation lesions and their evaluation, detailed instructions and technical aspects for site and core laboratory analysis of bifurcation lesions are also reported. The recommendations included within this consensus will facilitate pooled analyses and the effective comparison of data in the future, improving the clinical relevance of trials in bifurcation lesions, and the quality of care in this subset of patients.

Computational fluid dynamics as supporting technology for coronary artery disease diagnosis and treatment: an international survey

Background

Computational fluid dynamics (CFD) is emerging as an effective technology able to improve procedural outcomes and enhance clinical decision-making in patients with coronary artery disease (CAD). The present study aims to assess the state of knowledge, use and clinical acceptability of CFD in the diagnosis and treatment of CAD.

Methods

We realized a 20-questions international, anonymous, cross-sectional survey to cardiologists to test their knowledge and confidence on CFD as a technology applied to patients suffering from CAD. Responses were recorded between May 18, 2022, and June 12, 2022.

Results

A total of 466 interventional cardiologists (mean age 48.4 ± 8.3 years, males 362), from 42 different countries completed the survey, for a response rate of 45.9%. Of these, 66.6% declared to be familiar with the term CFD, especially for optimization of existing interventional techniques (16.1%) and assessment of hemodynamic quantities related with CAD (13.7%). About 30% of respondents correctly answered to the questions exploring their knowledge on the pathophysiological role of some CFD-derived quantities such as wall shear stress and helical flow in coronary arteries. Among respondents, 85.9% would consider patient-specific CFD-based analysis in daily interventional practice while 94.2% declared to be interested in receiving a brief foundation course on the basic CFD principles. Finally, 87.7% of respondents declared to be interested in a cath-lab software able to conduct affordable CFD-based analyses at the point-of-care.

Conclusions

Interventional cardiologists reported to be profoundly interested in adopting CFD simulations as a technology supporting decision making in the treatment of CAD in daily practice.

Post-procedure micro-CT analyses of coronary artery stenting in left main vessels of reanimated and perfusion-fixed human hearts

BACKGROUND

Percutaneous coronary interventions (PCIs) within left main coronary arteries are high-risk procedures that require optimization of interactions between stent(s) and diseased vessels. Optical Coherence Tomography (OCT) is a widely accepted tool that enhances physicians' ability to assess proper stent appositions during clinical procedures. The primary aim of this study was to develop complementary post-procedure imaging methodologies to better assess and interpret outcomes of left main PCI procedures, utilizing both reanimated and perfusion-fixed human hearts.

METHODS

PCIs were performed while obtaining OCT scans within the left main anatomies of six human hearts. Subsequently, each heart was scanned with a micro-CT scanner with optimized parameters to achieve resolutions up to 20 µm. Scans were reconstructed and imported into a DICOM segmentation software to generate computational models of implanted stents and associated coronary vessels. 2D images from OCT that were obtained during PCIs were compared to the 3D models generated from micro-CT reconstructions. In addition, the 3D models were utilized to create virtual reality scenes and enlarged 3D prints for development of "mixed reality" tools relative to bifurcation stenting within human left main coronary arteries.

RESULTS

We developed reproducible methodologies for post-implant analyses of coronary artery stenting procedures. In addition, we generated high-resolution 3D computational models, with ~ 20-micron resolutions, of PCIs performed within reanimated and perfusion-fixed heart specimens.

CONCLUSIONS

Generated computational models of left main PCIs performed in isolated human hearts can be used to obtain detailed measurements that provide further clinical insights on procedural outcomes. The 3D models from these procedures are useful for generating virtual reality scenes and 3D prints for physician training and education.

Uncertainty Quantification in the In Vivo Image-Based Estimation of Local Elastic Properties of Vascular Walls

Introduction: Patient-specific computational models are a powerful tool for planning cardiovascular interventions. However, the in vivo patient-specific mechanical properties of vessels represent a major source of uncertainty. In this study, we investigated the effect of uncertainty in the elastic module (E) on a Fluid–Structure Interaction (FSI) model of a patient-specific aorta. Methods: The image-based χ-method was used to compute the initial E value of the vascular wall. The uncertainty quantification was carried out using the generalized Polynomial Chaos (gPC) expansion technique. The stochastic analysis was based on four deterministic simulations considering four quadrature points. A deviation of about ±20% on the estimation of the E value was assumed. Results: The influence of the uncertain E parameter was evaluated along the cardiac cycle on area and flow variations extracted from five cross-sections of the aortic FSI model. Results of stochastic analysis showed the impact of E in the ascending aorta while an insignificant effect was observed in the descending tract. Conclusions: This study demonstrated the importance of the image-based methodology for inferring E, highlighting the feasibility of retrieving useful additional data and enhancing the reliability of in silico models in clinical practice.

Image-Based Finite Element Modeling Approach for Characterizing In Vivo Mechanical Properties of Human Arteries

Mechanical properties of the arterial walls could provide meaningful information for the diagnosis, management and treatment of cardiovascular diseases. Classically, various experimental approaches were conducted on dissected arterial tissues to obtain their stress-stretch relationship, which has limited value clinically. Therefore, there is a pressing need to obtain biomechanical behaviors of these vascular tissues in vivo for personalized treatment. This paper reviews the methods to quantify arterial mechanical properties in vivo. Among these methods, we emphasize a novel approach using image-based finite element models to iteratively determine the material properties of the arterial tissues. This approach has been successfully applied to arterial walls in various vascular beds. The mechanical properties obtained from the in vivo approach were compared to those from ex vivo experimental studies to investigate whether any discrepancy in material properties exists for both approaches. Arterial tissue stiffness values from in vivo studies generally were in the same magnitude as those from ex vivo studies, but with lower average values. Some methodological issues, including solution uniqueness and robustness; method validation; and model assumptions and limitations were discussed. Clinical applications of this approach were also addressed to highlight their potential in translation from research tools to cardiovascular disease management.

Treatment of coronary bifurcation lesions, part II: implanting two stents. The 16th expert consensus document of the European Bifurcation Club

The European Bifurcation Club (EBC) supports a continuous review of the field of coronary artery bifurcation interventions and aims to facilitate a scientific discussion and an exchange of ideas on the management of bifurcation disease. The recent focus of meetings and consensus statements has been on the technical issues in bifurcation stenting, recognising that the final result of a bifurcation procedure and the long-term outcome for our patients are strongly influenced by factors, including preprocedural strategy, stenting technique selection, performance of optimal procedural steps, the ability to identify and correct complications and finally, and most important, the overall performance of the operator. Continuous refinement of bifurcation stenting techniques and the promotion of education and training in bifurcation stenting techniques represent a major clinical need. Accordingly, the consensus from the latest EBC meeting in Brussels, October 2021, was to promote education and training in bifurcation stenting based on the EBC principle. Part II of this 16th EBC consensus document aims to provide a step-by-step overview of the pitfalls and technical troubleshooting during the implantation of the second stent either in the provisional stenting (PS) strategy or in upfront 2-stent techniques (e.g., 2-stent PS pathway and double kissing crush stenting). Finally, a detailed overview and discussion of the numerous modalities available to provide continuous education and technical training in bifurcation stenting techniques are discussed, with consideration of their future application in enhancing training and practice in coronary bifurcation lesion treatment.

Blood flow modeling reveals improved collateral artery performance during the regenerative period in mammalian hearts

Collateral arteries bridge opposing artery branches, forming a natural bypass that can deliver blood flow downstream of an occlusion. Inducing coronary collateral arteries could treat cardiac ischemia, but more knowledge on their developmental mechanisms and functional capabilities is required. Here we used whole-organ imaging and three-dimensional computational fluid dynamics modeling to define spatial architecture and predict blood flow through collaterals in neonate and adult mouse hearts. Neonate collaterals were more numerous, larger in diameter and more effective at restoring blood flow. Decreased blood flow restoration in adults arose because during postnatal growth coronary arteries expanded by adding branches rather than increasing diameters, altering pressure distributions. In humans, adult hearts with total coronary occlusions averaged 2 large collaterals, with predicted moderate function, while normal fetal hearts showed over 40 collaterals, likely too small to be functionally relevant. Thus, we quantify the functional impact of collateral arteries during heart regeneration and repair-a critical step toward realizing their therapeutic potential.

Definitions and Standardized Endpoints for Treatment of Coronary Bifurcations

The Bifurcation Academic Research Consortium (Bif-ARC) project originated from the need to overcome the paucity of standardization and comparability between studies involving bifurcation coronary lesions. This document is the result of a collaborative effort between academic research organizations and the most renowned interventional cardiology societies focused on bifurcation lesions in Europe, the United States, and Asia. This consensus provides standardized definitions for bifurcation lesions; the criteria to judge the side branch relevance; the procedural, mechanistic, and clinical endpoints for every type of bifurcation study; and the follow-up methods. Considering the complexity of bifurcation lesions and their evaluation, detailed instructions and technical aspects for site and core laboratory analysis of bifurcation lesions are also reported. The recommendations included within this consensus will facilitate pooled analyses and the effective comparison of data in the future, improving the clinical relevance of trials in bifurcation lesions, and the quality of care in this subset of patients.

Introduction of a Novel Image-Based and Non-Invasive Method for the Estimation of Local Elastic Properties of Great Vessels

Background: In the context of a growing demand for the use of in silico models to meet clinical requests, image-based methods play a crucial role. In this study, we present a parametric equation able to estimate the elasticity of vessel walls, non-invasively and indirectly, from information uniquely retrievable from imaging. Methods: A custom equation was iteratively refined and tuned from the simulations of a wide range of different vessel models, leading to the definition of an indirect method able to estimate the elastic modulus E of a vessel wall. To test the effectiveness of the predictive capability to infer the E value, two models with increasing complexity were used: a U-shaped vessel and a patient-specific aorta. Results: The original formulation was demonstrated to deviate from the ground truth, with a difference of 89.6%. However, the adoption of our proposed equation was found to significantly increase the reliability of the estimated E value for a vessel wall, with a mean percentage error of 9.3% with respect to the reference values. Conclusion: This study provides a strong basis for the definition of a method able to estimate local mechanical information of vessels from data easily retrievable from imaging, thus potentially increasing the reliability of in silico cardiovascular models.

First-in-Human Computational Preprocedural Planning of Left Main Interventions Using a New Everolimus-Eluting Stent

Left main coronary artery stenting requires rigorous planning and optimal execution. This case series presents a new approach to left main stenting guided by preprocedural patient-specific computational simulations. Three patients with significant left main artery disease underwent simulation-guided intervention using a novel stent scaffold purpose-built for large coronary arteries. (Level of Difficulty: Advanced.).