Baseline local hemodynamics as predictor of lumen remodeling at 1-year follow-up in stented superficial femoral arteries

Nature of aortic annulus: Influence of annulus dynamic on the aortic valve hemodynamics

Accurate imaging reports of the aortic valve indicate that the diameter of the aortic annulus changes regularly during a cardiac cycle. Most of these studies aim to demonstrate the proper method for estimating the aortic annulus diameter before performing TAVR surgery, revealing that the aortic annulus is dynamic and not constant throughout the cardiac cycle. This raises the question of how fixing the aortic annulus might affect valve function, which is a question that still needs to be addressed. Therefore, the present study seeks to address this question and elucidate the dynamic impact of the aortic annulus on aortic valve hemodynamics. Two computational models based on this hypothesis were created and solved, and then their results were compared. Both models are identical, except for the intrinsic dynamic nature of the aortic annulus. One model consists of the dynamic behavior, and the other simulates a fixed annulus, resembling the effect of a TAVR operation, SAVR, or any phenomenon that eliminates the dynamic nature of the annulus. Our research findings indicate that the dynamic nature of the annulus enhances blood flow (+2.7 %), increases mean velocity (+11.9) and kinetic energy density (+34 %), prolongs momentum retention during systole, stabilizes the flow jet at the end of systole, reduces the required pressure to keep the leaflets open (-40.9 % at 0.3s), and sustains ventricular pressure superiority (+9.4 %) over the aorta for a longer duration (+17.7 % of systole), a crucial factor in preventing backflow during aortic valve closure. Based on these results, more attention should be paid to the dynamic nature of the annulus.

Modelling lower-limb peripheral arterial disease using clinically available datasets: impact of inflow boundary conditions on hemodynamic indices for restenosis prediction

BACKGROUND AND OBJECTIVES

The integration of hemodynamic markers as risk factors in restenosis prediction models for lower-limb peripheral arteries is hindered by fragmented clinical datasets. Computed tomography (CT) scans enable vessel geometry reconstruction and can be obtained at different times than the Doppler ultrasound (DUS) images, which provide information on blood flow velocity. Computational fluid dynamics (CFD) simulations allow the computation of near-wall hemodynamic indices, whose accuracy depends on the prescribed inlet boundary condition (BC), derived from the DUS images. This study aims to: (i) investigate the impact of different DUS-derived velocity waveforms on CFD results; (ii) test whether the same vessel areas, subjected to altered hemodynamics, can be detected independently of the applied inlet BC; (iii) suggest suitable DUS images to obtain reliable CFD results.

METHODS

CFD simulations were conducted on three patients treated with bypass surgery, using patient-specific DUS-derived inlet BCs recorded at either the same or different time points than the CT scan. The impact of the chosen inflow condition on bypass hemodynamics was assessed in terms of wall shear stress (WSS)-derived quantities. Patient-specific critical thresholds for the hemodynamic indices were applied to identify critical luminal areas and compare the results with a reference obtained with a DUS image acquired in close temporal proximity to the CT scan.

RESULTS

The main findings indicate that: (i) DUS-derived inlet velocity waveforms acquired at different time points than the CT scan led to statistically significantly different CFD results (p<0.001); (ii) the same luminal surface areas, exposed to low time-averaged WSS, could be identified independently of the applied inlet BCs; (iii) similar outcomes were observed for the other hemodynamic indices if the prescribed inlet velocity waveform had the same shape and comparable systolic acceleration time to the one recorded in close temporal proximity to the CT scan.

CONCLUSIONS

Despite a lack of standardised data collection for diseased lower-limb peripheral arteries, an accurate estimation of luminal areas subjected to altered near-wall hemodynamics is possible independently of the applied inlet BC. This holds if the applied inlet waveform shares some characteristics - derivable from the DUS report - as one matching the acquisition time of the CT scan.

A systematic review of clinical and biomechanical engineering perspectives on the prediction of restenosis in coronary and peripheral arteries

Objective

Restenosis is a significant complication of revascularization treatments in coronary and peripheral arteries, sometimes necessitating repeated intervention. Establishing when restenosis will happen is extremely difficult due to the interplay of multiple variables and factors. Standard clinical and Doppler ultrasound scans surveillance follow-ups are the only tools clinicians can rely on to monitor intervention outcomes. However, implementing efficient surveillance programs is hindered by health care system limitations, patients' comorbidities, and compliance. Predictive models classifying patients according to their risk of developing restenosis over a specific period will allow the development of tailored surveillance, prevention programs, and efficient clinical workflows. This review aims to: (1) summarize the state-of-the-art in predictive models for restenosis in coronary and peripheral arteries; (2) compare their performance in terms of predictive power; and (3) provide an outlook for potentially improved predictive models.

Methods

We carried out a comprehensive literature review by accessing the PubMed/MEDLINE database according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search strategy consisted of a combination of keywords and included studies focusing on predictive models of restenosis published between January 1993 and April 2023. One author independently screened titles and abstracts and checked for eligibility. The rest of the authors independently confirmed and discussed in case of any disagreement. The search of published literature identified 22 studies providing two perspectives-clinical and biomechanical engineering-on restenosis and comprising distinct methodologies, predictors, and study designs. We compared predictive models' performance on discrimination and calibration aspects. We reported the performance of models simulating reocclusion progression, evaluated by comparison with clinical images.

Results

Clinical perspective studies consider only routinely collected patient information as restenosis predictors. Our review reveals that clinical models adopting traditional statistics (n = 14) exhibit only modest predictive power. The latter improves when machine learning algorithms (n = 4) are employed. The logistic regression models of the biomechanical engineering perspective (n = 2) show enhanced predictive power when hemodynamic descriptors linked to restenosis are fused with a limited set of clinical risk factors. Biomechanical engineering studies simulating restenosis progression (n = 2) are able to capture its evolution but are computationally expensive and lack risk scoring for individual patients at specific follow-ups.

Conclusions

Restenosis predictive models, based solely on routine clinical risk factors and using classical statistics, inadequately predict the occurrence of restenosis. Risk stratification models with increased predictive power can be potentially built by adopting machine learning techniques and incorporating critical information regarding vessel hemodynamics arising from biomechanical engineering analyses.

Senescent endothelial cells' response to the degradation of bioresorbable scaffold induces intimal dysfunction accelerating in-stent restenosis

Atherosclerotic cardiovascular disease is a typical age-related disease accompanied by stiffening arteries. We aimed to elucidate the influence of aged arteries on in-stent restenosis (ISR) after the implantation of bioresorbable scaffolds (BRS). Histology and optical coherence tomography showed increased lumen loss and ISR in the aged abdominal aorta of Sprague-Dawley rats, with apparent scaffold degradation and deformation, which induce lower wall shear stress (WSS). This was also the case at the distal end of BRS, where the scaffolds degraded faster, and significant lumen loss was followed by a lower WSS. In addition, early thrombosis, inflammation, and delayed re-endothelialization were presented in the aged arteries. Degradation of BRS causes more senescent cells in the aged vasculature, increasing endothelial cell dysfunction and the risk of ISR. Thus, profoundly understanding the mechanism between BRS and senescent cells may give a meaningful guide for the age-related scaffold design. STATEMENT OF SIGNIFICANCE: The degradation of bioresorbable scaffolds aggravates senescent endothelial cells and a much lower wall shear stress areas in the aged vasculature, lead to intimal dysfunction and increasing in-stent restenosis risk. Early thrombosis and inflammation, as well as delayed re-endothelialization, are presented in the aged vasculature after bioresorbable scaffolds implantation. Age stratification during the clinical evaluation and senolytics in the design of new bioresorbable scaffolds should be considered, especially for old patients.

An Oscillatory Shear Index-Based Model to Describe Progressive Carotid Artery Stenosis

Background and aims: This study describes and demonstrates the applicability of a novel in silico method for modeling progressive carotid artery stenosis using the oscillatory shear index (OSI) as the basis of stenosis. Methods: Three-dimensional reconstructions of 11 carotid arteries were generated using patient-derived magnetic resonance angiography and duplex ultrasound data. Computational fluid dynamic simulations were sequentially generated following computational stenosis assessment, and corresponding changes in OSI were observed and used as measure of morphological stabilization. Results: 6 carotid models showed progressive stenosis with statistically significant increases in regions of high OSI (OSI >.2, P < .05) with eventual carotid occlusion in 1 of the cases. Three models remained free or nearly free of increased OSI, whereas 1 model showed an overall decrease in high OSI regions (P < .05) and another trended in that direction but did not achieve statistical significance (P = .145). Conclusions: To our knowledge, this is the first computational model describing progressive stenosis in any peripheral artery including the carotid. Taken together, this study provides a novel framework for computational hemodynamic investigations on progressive atherosclerosis in the carotid artery.

An intricate interplay between stent drug dose and release rate dictates arterial restenosis

Since the introduction of percutaneous coronary intervention (PCI) for the treatment of obstructive coronary artery disease (CAD), patient outcomes have progressively improved. Drug eluting stents (DES) that employ anti-proliferative drugs to limit excess tissue growth following stent deployment have proved revolutionary. However, restenosis and a need for repeat revascularisation still occurs after DES use. Over the last few years, computational models have emerged that detail restenosis following the deployment of a bare metal stent (BMS), focusing primarily on contributions from mechanics and fluid dynamics. However, none of the existing models adequately account for spatiotemporal delivery of drug and the influence of this on the cellular processes that drive restenosis. In an attempt to fill this void, a novel continuum restenosis model coupled with spatiotemporal drug delivery is presented. Our results indicate that the severity and time-course of restenosis is critically dependent on the drug delivery strategy. Specifically, we uncover an intricate interplay between initial drug loading, drug release rate and restenosis, indicating that it is not sufficient to simply ramp-up the drug dose or prolong the time course of drug release to improve stent efficacy. Our model also shows that the level of stent over-expansion and stent design features, such as inter-strut spacing and strut thickness, influence restenosis development, in agreement with trends observed in experimental and clinical studies. Moreover, other critical aspects of the model which dictate restenosis, including the drug binding site density are investigated, where comparisons are made between approaches which assume this to be either constant or proportional to the number of smooth muscle cells (SMCs). Taken together, our results highlight the necessity of incorporating these aspects of drug delivery in the pursuit of optimal DES design.

Superficial Femoral Artery Recanalization Using Fiber Optic RealShape Technology

Purpose: Report of a successful case of endovascular recanalization of an occluded superficial femoral artery (SFA) using Fiber Optic RealShape (FORS) technology. Case Report: A 79-year-old male was referred for evaluation of multiple ischemic pretibial ulcers of the right lower extremity. Computed tomography–angiography (CTA) imaging confirmed significant stenosis of the right common femoral artery (CFA) and an occlusion of the SFA from its origin to the Hunter’s canal. The patient was treated with a hybrid surgical procedure: an endarterectomy of the CFA and SFA origin was performed combined with an endovascular recanalization of the occluded SFA using FORS technology. During recanalization, the FORS guidewire slowly twisted subintimally around the occluded lumen of the SFA, maintaining the created corkscrew shape after pre-dilation with the percutaneous transluminal angioplasty (PTA) balloon and subsequent stenting. Conclusions: FORS technology can be successfully used during recanalization of an occluded SFA without the use of fluoroscopy. The corkscrew shape formed during recanalization in this case was retained during PTA balloon pre-dilation and stenting; this potentially improves hemodynamics and thereby reduces the risk of in-stent restenosis. However, expanding patient series and longer follow-up data are needed to increase the understanding of the feasibility and effectiveness of using FORS in the treatment of peripheral arterial occlusive disease.

Superficial femoral artery stenting: Impact of stent design and overlapping on the local hemodynamics

BACKGROUND

Superficial femoral arteries (SFAs) treated with self-expanding stents are widely affected by in-stent restenosis (ISR), especially in case of long lesions and multiple overlapping devices. The altered hemodynamics provoked by the stent is considered as a promoting factor of ISR. In this context, this work aims to analyze the impact of stent design and stent overlapping on patient-specific SFA hemodynamics.

METHODS

Through a morphing technique, single or multiple stents were virtually implanted within two patient-specific, post-operative SFA models reconstructed from computed tomography. The stented domains were used to perform computational fluid dynamics simulations, quantifying wall shear stress (WSS) based descriptors including time-averaged WSS (TAWSS), oscillatory shear index (OSI), transverse WSS (transWSS), and WSS ratio (WSSRATIO). Four stent designs (three laser-cut - EverFlex, Zilver and S.M.A.R.T. - and one prototype braided stent), and three typical clinical scenarios accounting for different order of stent implantation and overlapping length were compared.

RESULTS

The main hemodynamic differences were found between the two types of stent designs (i.e. laser-cut vs. braided stents). The braided stent presented lower median transWSS and higher median WSSRATIO than the laser-cut stents (p < 0.0001). The laser-cut stents presented comparable WSS-based descriptor values, except for the Zilver, exhibiting a median TAWSS ∼30% higher than the other stents. Stent overlapping provoked an abrupt alteration of the WSS-based descriptors. The overlapping length, rather than the order of stent implantation, highly and negatively impacted the hemodynamics.

CONCLUSION

The proposed computational workflow compared different SFA stent designs and stent overlapping configurations, highlighting those providing the most favorable hemodynamic conditions.

A predictive multiscale model of in-stent restenosis in femoral arteries: linking haemodynamics and gene expression with an agent-based model of cellular dynamics

In-stent restenosis (ISR) is a maladaptive inflammatory-driven response of femoral arteries to percutaneous transluminal angioplasty and stent deployment, leading to lumen re-narrowing as consequence of excessive cellular proliferative and synthetic activities. A thorough understanding of the underlying mechanobiological factors contributing to ISR is still lacking. Computational multiscale models integrating both continuous- and agent-based approaches have been identified as promising tools to capture key aspects of the complex network of events encompassing molecular, cellular and tissue response to the intervention. In this regard, this work presents a multiscale framework integrating the effects of local haemodynamics and monocyte gene expression data on cellular dynamics to simulate ISR mechanobiological processes in a patient-specific model of stented superficial femoral artery. The framework is based on the coupling of computational fluid dynamics simulations (haemodynamics module) with an agent-based model (ABM) of cellular activities (tissue remodelling module). Sensitivity analysis and surrogate modelling combined with genetic algorithm optimization were adopted to explore the model behaviour and calibrate the ABM parameters. The proposed framework successfully described the patient lumen area reduction from baseline to one-month follow-up, demonstrating the potential capabilities of this approach in predicting the short-term arterial response to the endovascular procedure.

Multiscale Computational Modeling of Vascular Adaptation: A Systems Biology Approach Using Agent-Based Models

The widespread incidence of cardiovascular diseases and associated mortality and morbidity, along with the advent of powerful computational resources, have fostered an extensive research in computational modeling of vascular pathophysiology field and promoted in-silico models as a support for biomedical research. Given the multiscale nature of biological systems, the integration of phenomena at different spatial and temporal scales has emerged to be essential in capturing mechanobiological mechanisms underlying vascular adaptation processes. In this regard, agent-based models have demonstrated to successfully embed the systems biology principles and capture the emergent behavior of cellular systems under different pathophysiological conditions. Furthermore, through their modular structure, agent-based models are suitable to be integrated with continuum-based models within a multiscale framework that can link the molecular pathways to the cell and tissue levels. This can allow improving existing therapies and/or developing new therapeutic strategies. The present review examines the multiscale computational frameworks of vascular adaptation with an emphasis on the integration of agent-based approaches with continuum models to describe vascular pathophysiology in a systems biology perspective. The state-of-the-art highlights the current gaps and limitations in the field, thus shedding light on new areas to be explored that may become the future research focus. The inclusion of molecular intracellular pathways (e.g., genomics or proteomics) within the multiscale agent-based modeling frameworks will certainly provide a great contribution to the promising personalized medicine. Efforts will be also needed to address the challenges encountered for the verification, uncertainty quantification, calibration and validation of these multiscale frameworks.

Towards a better understanding of the posttreatment hemodynamic behaviors in femoropopliteal arteries through personalized computational models based on OCT images

The hemodynamic behavior following endovascular treatment of patients with peripheral arterial disease plays a significant role on the occurrence of restenosis in femoro-popliteal (FP) arteries. The atheroprone flow conditions that are generally accepted to promote restenosis can be calculated by computational fluid dynamics (CFD) analyses, and these results can be used to assess individualized treatment outcomes. However, the impact of endovascular therapy on the flow behaviors of FP arteries are still poorly understood, as the imaging modalities used in existing numerical works (X-ray angiography, computed tomography angiography) are unable to accurately represent the post-treatment arterial geometry due to their low resolutions. Therefore, this study proposes a new algorithm that combines intra-arterial lumen geometry obtained from high-resolution optical coherence tomography (OCT) images with centerlines generated from X-ray images to reconstruct the FP artery with an in-plane resolution of 10 µm. This superior accuracy allows modeling characteristic geometrical structures, such as angioplasty-induced arterial dissections, that are too small to be reconstructed with other imaging modalities. The framework is applied on the clinical data of patients treated either with only-percutaneous transluminal angioplasty (PTA) (n = 4) or PTA followed by stenting (n = 4). Based on the generated models, PTA was found to cause numerous arterial dissections, covering approximately 10% of the total surface area of the lumen, whereas no dissections were identified in the stented arteries. CFD simulations were performed to investigate the hemodynamic conditions before and after treatment. Regardless of the treatment method, the areas affected by low time-averaged wall shear stress (< 0.5 Pa) were significantly higher (p < 0.05) following endovascular therapy (pre-PTA: 0.95 ± 0.59 cm²; post-PTA: 2.10 ± 1.09cm²; post-stent: 3.10 ± 0.98 cm²). There were no statistical differences between the PTA and the stent groups. However, within the PTA group, adverse hemodynamics were mainly concentrated at regions created by arterial dissections, which may negatively impact the outcomes of a leave-nothing-behind strategy. These observations show that OCT-based numerical models have great potential to guide clinicians regarding the optimal treatment approach.

Wall Shear Stress Topological Skeleton Analysis in Cardiovascular Flows: Methods and Applications

A marked interest has recently emerged regarding the analysis of the wall shear stress (WSS) vector field topological skeleton in cardiovascular flows. Based on dynamical system theory, the WSS topological skeleton is composed of fixed points, i.e., focal points where WSS locally vanishes, and unstable/stable manifolds, consisting of contraction/expansion regions linking fixed points. Such an interest arises from its ability to reflect the presence of near-wall hemodynamic features associated with the onset and progression of vascular diseases. Over the years, Lagrangian-based and Eulerian-based post-processing techniques have been proposed aiming at identifying the topological skeleton features of the WSS. Here, the theoretical and methodological bases supporting the Lagrangian- and Eulerian-based methods currently used in the literature are reported and discussed, highlighting their application to cardiovascular flows. The final aim is to promote the use of WSS topological skeleton analysis in hemodynamic applications and to encourage its application in future mechanobiology studies in order to increase the chance of elucidating the mechanistic links between blood flow disturbances, vascular disease, and clinical observations.