Local Hemodynamic Forces After Stenting: Implications on Restenosis and Thrombosis

Impact of the stent footprint on endothelial wall shear stress in patient-specific coronary arteries: A computational analysis from the SHEAR-STENT trial

BACKGROUND AND OBJECTIVE

Wall shear stress (WSS) has been known to play a critical role in the development of several complications following coronary artery stenting, including in-stent restenosis and thrombosis. Computational fluid dynamics is often used to quantify the post-stenting WSS, which may potentially be used as a predictive metric. However, large-scale studies for WSS-based risk stratification often neglect the footprint of the stent due to reconstruction challenges. The primary objective of this study is to statistically evaluate the impact of the stent footprints (Xience and Resolute stents) on the computed endothelial WSS and quantitatively identify the relationship between these local hemodynamic alterations and the global properties of the vessel, such as curvature, on WSS. The ultimate goal is to evaluate whether and when it is worth including the footprint of the stent in an in-silico study to compute the WSS reliably.

METHODS

A previously developed semi-automated reconstruction approach for patient-specific coronaries was employed as a part of the SHEAR-STENT trial. A subset of patients was analyzed (N=30), and CFD simulations were performed with and without the stent to evaluate the impact of the stent footprint on WSS. Due to the computationally expensive nature of transient analyses, a sub-cohort of ten patients were used to assess the reliability of WSS obtained from steady computations as a surrogate for the time-averaged results. Global and local vessel curvature data were extracted for all cases and evaluated against stent-induced alterations in the WSS. The differences between the Xience and Resolute stent platforms were also examined to quantify each stent's unique WSS footprint.

RESULTS

Results from the surrogate analysis indicate that steady WSS serves as an excellent approximation of the time-averaged computations. The presence of either stent footprint causes a statistically significant decrease in the space-averaged WSS, and a significant increase in the endothelial regions exposed to very low WSS as well (<0.5 Pa). Negative correlations were observed between vessel curvature and WSS differences, indicating that macroscopic vessel characteristics play a more prominent role in determining endothelial WSS at higher curvature values. In our pool of cases, comparison of Xience and Resolute stents revealed that the Resolute platform seems to lead to lower space-averaged WSS and an increase in areas of very low WSS.

CONCLUSION

These results outline (1) the necessity of including the stent footprint for accurate in-silico WSS analysis; (2) the global features of stented arteries serving as the dominant determinant of WSS past a certain curvature threshold; and (3) the Xience stent resulting in a milder presence of hemodynamically unfavorable WSS regions compared to the Resolute stent.

Routine preoperative transthoracic echocardiography for predicting incomplete endothelialization of the watchman left atrial appendage occluder: A single-center five-year study

BACKGROUND & OBJECTIVES

Incomplete endothelialization of the left atrial appendage(LAA) occluder potentially affects the long-term efficacy of stroke prevention in atrial fibrillation(AF) patients. This study aims to explore the value of routine preoperative transthoracic echocardiography(TTE) in predicting the endothelialization of Watchman LAA occluder.

METHODS

This single-center retrospective study included 437 AF patients who underwent the LAA closure with Watchman 2.5 occluder from January 2017 to December 2022. Cardiac CTA was performed 3-6 months after the procedure. Based on contrast infiltration into the LAA cavity, two groups were defined as follows: completely and incompletely endothelialized. The baseline and pre-procedural TTE parameters were analyzed.

RESULTS

The average age was 70.2 years old, with 208 females(47.6 %). The incompletely endothelialized group had an older age (71.4 ± 7.5 vs 69.8 ± 7.6,p = 0.053), a larger left atrial(LA) diameter (44.0 ± 5.9 vs 42.7 ± 6.1 mm,p = 0.045) and a lower left ventricular ejection fraction(LVEF%)(62.5 ± 7.5 vs 63.0 ± 5.4 %,p = 0.016) than the completely endothelialized group. Univariate analysis revealed that incomplete endothelialization was associated with persistent AF(OR:1.68;95 % CI:1.08-2.10;p = 0.021), a higher LA diameter(OR:1.04;95 % CI:1.00-1.07;p = 0.046), a higher left ventricular diastolic diameter(LVDD)(OR:1.05;95 % CI:1.00-1.10;p = 0.032),and the presence of mild mitral stenosis (mean pressure gradient <5 mmHg and mitral valve area > 1.5 cm2,OR:11.29;95 % CI:1.25-102.10;p = 0.031), while it was negatively correlated with mild left ventricular diastolic dysfunction (OR:0.49;95 % CI:0.26-0.94;p = 0.033). Multivariate analysis demonstrated that mild mitral stenosis(OR: 13.79;95 % CI:1.37-139.13;p = 0.026) was an independent predictor for incomplete endothelialization.

CONCLUSION

Preoperative TTE may predict the outcomes of endothelialization after left atrial appendage occlusion. Mild or severe mitral stenosis is an independent predictive factor for poor endothelial coverage.

Fluid Shear Stress-Regulated Vascular Remodeling: Past, Present, and Future

The vascular system remodels throughout life to ensure adequate perfusion of tissues as they grow, regress, or change metabolic activity. Angiogenesis, the sprouting of new blood vessels to expand the capillary network, versus regression, in which endothelial cells die or migrate away to remove unneeded capillaries, controls capillary density. In addition, upstream arteries adjust their diameters to optimize blood flow to downstream vascular beds, which is controlled primarily by vascular endothelial cells sensing fluid shear stress (FSS) from blood flow. Changes in capillary density and small artery tone lead to changes in the resistance of the vascular bed, which leads to decreased or increased flow through the arteries that feed these small vessels. The resultant changes in FSS through these vessels then stimulate their inward or outward remodeling, respectively. This review summarizes our knowledge of endothelial FSS-dependent vascular remodeling, offering insights into potential therapeutic interventions. We first provide a historical overview, then discuss the concept of set point and mechanisms of low-FSS-mediated and high-FSS-mediated inward and outward remodeling. We then cover in vivo animal models, molecular mechanisms, and clinical implications. Understanding the mechanisms underlying physiological endothelial FSS-mediated vascular remodeling and their failure due to mutations or chronic inflammatory and metabolic stresses may lead to new therapeutic strategies to prevent or treat vascular diseases.

Advancements in Coronary Bifurcation Stenting Techniques: Insights From Computational and Bench Testing Studies

Coronary bifurcation lesions present complex challenges in interventional cardiology, necessitating effective stenting techniques to achieve optimal results. This literature review comprehensively examines the application of computational and bench testing methods in coronary bifurcation stenting, offering insights into procedural aspects, stent design considerations, and patient-specific characteristics. Structural mechanics finite element analysis, computational fluid dynamics, and multi-objective optimization are valuable tools for evaluating stenting strategies, including provisional side branch stenting and two-stenting techniques. We highlight the impact of procedural factors, such as balloon positioning and rewiring techniques, and stent design features on the outcome of percutaneous coronary interventions with stents. We discuss the importance of patient-specific characteristics in deployment strategies, such as bifurcation angle and plaque properties. This understanding informs present and future research and clinical practice on bifurcation stenting. Computational simulations are a continuously maturing advance that has significantly enhanced stenting devices and techniques for coronary bifurcation lesions over the years. However, the accurate account of patient-specific vessel and lesion characteristics, both in terms of anatomical and accurate physiological behavior, and their large variation between patients, remains a significant challenge in the field. In this context, advancements in multi-objective optimization offer significant opportunities for refining stent design and procedural practices.

Hemodynamic microenvironment of coronary stent strut malapposition

OBJECTIVE

This study aims to investigate the micro-hemodynamic effects of strut malapposition in patient-specific stented coronary bifurcations.

METHODS

Using the mapping-back technique, three-dimensional reconstructions of clinical post-stenting artery bifurcations with strut malapposition were accurately generated from optical coherence tomography scans of 9 patients. Computational fluid dynamics (CFD) simulations were then conducted with these models to examine the impact of strut malapposition on various fluid dynamic parameters, including flow patterns, vorticity, strain rates, viscosity, and wall shear stress (WSS). For statistical analysis, virtually apposed models were created to evaluate WSS metrics. Additionally, follow-up data for 5 out of the 9 patients were reviewed to assess evidence of late thrombosis and restenosis.

RESULTS

Malapposed struts induce significant alterations in flow dynamics, including the formation of recirculation regions and the transition from laminar to disturbed flow. The local curvature of the lumen also affects the development of these recirculation regions. Our study demonstrates, for the first time, that the vorticity on the abluminal side of malapposed struts exhibits an opposite sign compared to the surrounding region. The strain rate around these struts shows a distinct transition, with high values at the stent surface that rapidly diminish within the strut-lumen gap. This transition is accompanied by an increase in viscosity within these regions. Furthermore, as the malapposition distance increases, strain rates on the malapposed struts increase while viscosity decreases. Significant differences in WSS metrics were observed between clinically malapposed and virtually apposed scenarios. In clinical follow-up cases, no evidence of thrombosis was found despite the complex micro-hemodynamics in these patients.

CONCLUSION

There is complex interplay between stent malapposition and hemodynamics within a patient-specific bifurcation. The significant impact of local lumen curvature on flow dynamics underscores the limitations of idealized artery models. Moreover, the absence of thrombosis in subsequent clinical follow-up cases suggests that additional factors, such as antiplatelet medication, may play a significant role in mitigating these risks.

Deforming Patient-Specific Models of Vascular Anatomies to Represent Stent Implantation via Extended Position Based Dynamics

PURPOSE

Angioplasty with stent placement is a widely used treatment strategy for patients with stenotic blood vessels. However, it is often challenging to predict the outcomes of this procedure for individual patients. Image-based computational fluid dynamics (CFD) is a powerful technique for making these predictions. To perform CFD analysis of a stented vessel, a virtual model of the vessel must first be created. This model is typically made by manipulating two-dimensional contours of the vessel in its pre-stent state to reflect its post-stent shape. However, improper contour-editing can cause invalid geometric artifacts in the resulting mesh that then distort the subsequent CFD predictions. To address this limitation, we have developed a novel shape-editing method that deforms surface meshes of stenosed vessels to create stented models.

METHODS

Our method uses physics-based simulations via Extended Position Based Dynamics to guide these deformations. We embed an inflating stent inside a vessel and apply collision-generated forces to deform the vessel and expand its cross-section.

RESULTS

We demonstrate that this technique is feasible and applicable for a wide range of vascular anatomies, while yielding clinically compatible results. We also illustrate the ability to parametrically vary the stented shape and create models allowing CFD analyses.

CONCLUSION

Our stenting method will help clinicians predict the hemodynamic results of stenting interventions and adapt treatments to achieve target outcomes for patients. It will also enable generation of synthetic data for data-intensive applications, such as machine learning, to support cardiovascular research endeavors.

Study of the Structure of Hyperbranched Polyglycerol Coatings and Their Antibiofouling and Antithrombotic Applications

While blood-contacting materials are widely deployed in medicine in vascular stents, catheters, and cannulas, devices fail in situ because of thrombosis and restenosis. Furthermore, microbial attachment and biofilm formation is not an uncommon problem for medical devices. Even incremental improvements in hemocompatible materials can provide significant benefits for patients in terms of safety and patency as well as substantial cost savings. Herein, a novel but simple strategy is described for coating a range of medical materials, that can be applied to objects of complex geometry, involving plasma-grafting of an ultrathin hyperbranched polyglycerol coating (HPG). Plasma activation creates highly reactive surface oxygen moieties that readily react with glycidol. Irrespective of the substrate, coatings are uniform and pinhole free, comprising O─C─O repeats, with HPG chains packing in a fashion that holds reversibly binding proteins at the coating surface. In vitro assays with planar test samples show that HPG prevents platelet adhesion and activation, as well as reducing (>3 log) bacterial attachment and preventing biofilm formation. Ex vivo and preclinical studies show that HPG-coated nitinol stents do not elicit thrombosis or restenosis, nor complement or neutrophil activation. Subcutaneous implantation of HPG coated disks under the skin of mice shows no evidence of toxicity nor inflammation.

The Influence of Embolization of Internal Carotid Artery Aneurysms on Arterial Tortuosity: A Prospective Cohort Study

PURPOSE

To measure changes in quantitative tortuosity descriptors of the internal carotid artery (ICA) after intracranial aneurysm embolization, and to determine possible factors associated with changes in tortuosity.

MATERIALS AND METHODS

An analysis of 52 patients with embolized intracranial aneurysms was performed. ICA tortuosity was assessed by digital subtraction angiograms obtained prior to the embolization and after the first follow-up examination. For each patient, tortuosity descriptors were calculated: relative length (RL), sum of angle metrics (SOAM), triangular index, product of angle distance (PAD), and inflection count metric (ICM). To represent changes in tortuosity for each descriptor, delta (Δ) value was defined as value of the descriptor prior to embolization minus value of the descriptor on follow-up examination.

RESULTS

In a median follow-up of 14 months, no statistically significant changes in tortuosity were observed on the nonembolized side. On the embolized side, SOAM (2.89 [SD ± 0.92] vs 2.38 [SD ± 0.94]; P < .001), PAD (5.01 [SD ± 1.83] vs 3.95 [SD ± 1.72]; P < .001), and ICM (12.18 [SD ± 4.55] vs 9.76 [SD ± 4.04]; P = .006) were significantly higher after embolization than before embolization. Median ΔRL (-0.02 [-0.045 to 0.002] vs -0.01 [-0.02 to 0.003]; P = .003), ΔPAD (0.84 [0.30-1.82] vs 0.10 [-0.001 to 1.10]; P < .001), and ΔICM (2.05 [0.42-3.50] vs 0.27 [0.02-2.16]; P = .004) were significantly higher on the embolized side. Tortuosity correlated with elapsed time after embolization.

CONCLUSIONS

Tortuosity of the ipsilateral ICA increased after intracranial aneurysm embolization.

Sutureless vascular anastomotic approaches and their potential impacts

Sutureless anastomotic devices present several advantages over traditional suture anastomosis, including expanded global access to microvascular surgery, shorter operation and ischemic times, and reduced costs. However, their adaptation for arterial use remains a challenge. This review aims to provide a comprehensive overview of sutureless anastomotic approaches that are either FDA-approved or under investigation. These approaches include extraluminal couplers, intraluminal devices, and methods assisted by lasers or vacuums, with a particular emphasis on tissue adhesives. We analyze these devices for artery compatibility, material composition, potential for intimal damage, risks of thrombosis and restenosis, and complications arising from their deployment and maintenance. Additionally, we discuss the challenges faced in the development and clinical application of sutureless anastomotic techniques. Ideally, a sutureless anastomotic device or technique should eliminate the need for vessel eversion, mitigate thrombosis through either biodegradation or the release of antithrombotic drugs, and be easily deployable for broad use. The transformative potential of sutureless anastomotic approaches in microvascular surgery highlights the necessity for ongoing innovation to expand their applications and maximize their benefits.

Treatment of common femoral artery steno-occlusive disease: a comprehensive review of anatomical and hemodynamic considerations

Open surgical repair, often in the form of endarterectomy, is still the gold standard for steno-occlusive disease in the common femoral artery, despite the success of lower-risk endovascular alternatives in other peripheral arterial regions. Stenting in the common femoral artery is not widely adopted due to the proximity of the artery to the mobile hip joint, and the perceived risk this has on the stent structure due to kinking. The purpose of this review was to assess how hip movement contributes to the anatomical and biomechanical challenges proposed in the common femoral artery, and how these challenges impact the hemodynamics with both open surgical and endovascular stent treatments. The findings demonstrated that the common femoral artery is a fixed arterial segment which does not bend or twist as previously perceived. However, high degrees of bending and twisting are evident in the vessels directly proximal and distal to the common femoral artery. Mechanical testing suggests that the latest generation braided Nitinol stents could be well-suited to these challenges. Both endarterectomy and stenting provide good hemodynamic results regarding limb perfusion. However, other hemodynamic parameters, such as wall shear stress, may not be optimized with either modality, increasing the risk of chronic restenosis. As a high proportion of common femoral artery disease extends into the adjacent arterial segments, further research is warranted to ascertain the optimum hemodynamic stent configuration, as a lower-risk alternative to open surgery.

In-stent Restenosis After Stenting for Superior Mesenteric Artery Dissection Is Associated With Stent Landing Zone: From Clinical Prediction to Hemodynamic Mechanisms

OBJECTIVE

To identify risk factors for in-stent restenosis (ISR) in patients undergoing stent placement for superior mesenteric artery dissection (SMAD) and to determine the hemodynamic mechanism underlying ISR.

METHODS

For this retrospective study, patients with SMAD who had ISR after stent placement were included in the ISR group, and age- and sex-matched patients with SMAD who did not experience ISR after stent placement were included in the control group. Clinical, imaging, and hemodynamic data were assessed. Multivariable regression was used to identify independent ISR risk factors. Structural and fluid dynamics simulations were applied to determine the hemodynamic mechanism underlying the occurrence of ISR.

RESULTS

The study population included 26 patients with ISR and 26 control patients. Multivariate analysis demonstrated that stent-to-vascular (S/V) ratio (odds ratio [OR], 1.14; 95% confidence interval [CI]: 1.00-1.29; p=0.045), stent proximal position >10 mm away from the SMA root (OR, 108.67; 95% CI: 3.09-3816.42; p=0.010), and high oscillatory shear index (OSI) area (OR, 1.25; 95% CI: 1.02-1.52; p=0.029) were predictors of ISR. In structural and fluid dynamics simulations, a stent proximal position near the abdominal aorta (AA) or entering into the AA reduced the contact area between the proximal struts of the stent and the vascular wall, and alleviated the distal lumen overdilation.

CONCLUSION

The S/V ratio, stent proximal position away from the SMA root (>10 mm), and high OSI area are independent risk factors for ISR in patients with SMAD undergoing stent placement. Deploying the proximal end of the stent near the AA or entering into the AA appears to improve the hemodynamic environment in the SMA lumen and ultimately reduce the risk of ISR.

CLINICAL IMPACT

In-stent restenosis is an uncommon but potentially catastrophic complication after stent placement for the management of superior mesenteric artery dissection. This study identified risk factors for in-stent restenosis and demonstrated that, as long as the stent can fully cover the dissection range, deploying the proximal end of the stent near the abdominal aorta or less entering into the abdominal aorta may reduce the risk of in-stent restenosis in this patient population.

Comparison of endothelial shear stress between ultrathin strut bioresorbable polymer drug-eluting stent vs durable-polymer drug-eluting stent post-stent implantation: An optical coherence tomography substudy from BIOFLOW II

BACKGROUND

Recent clinical data indicate a different performance of biodegradable polymer (BP)-drug eluting stent (DES) compared to durable polymer (DP)-DES. Whether this can be explained by a beneficial impact of BP-DES stent design on the local hemodynamic forces distribution remains unclear.

OBJECTIVES

To compare endothelial shear stress (ESS) distribution after implantation of ultrathin (us) BP-DES and DP-DES and examine the association between ESS and neointimal thickness (NIT) distribution in the two devices at 9 months follow up.

METHODS AND RESULTS

We retrospectively identified patients from the BIOFLOW II trial that had undergone OCT imaging. OCT data were utilized to reconstruct the surface of the stented segment at baseline and 9 months follow-up, simulate blood flow, and measure ESS and NIT in the stented segment. The patients were divided into 3 groups depending on whether DP-DES (N = 8, n = 56,160 sectors), BP-DES with a stent diameter of >3 mm (strut thickness of 80 μm, N = 6, n = 36,504 sectors), or BP-DES with a stent diameter of ≤3 mm (strut thickness of 60 μm, N = 8, n = 50,040 sectors) were used for treatment. The ESS, and NIT distribution and the association of these two variables were estimated and compared among the 3 groups.

RESULTS

In the DP-DES group mean NIT was 0.18 ± 0.17 mm and ESS 1.68 ± 1.66 Pa; for the BP-DES ≤3 mm group the NIT was 0.17 ± 0.11 mm and ESS 1.49 ± 1.24 Pa and for the BP-DES >3 mm group 0.20 ± 0.23 mm and 1.42 ± 1.24 Pa respectively (p < 0.001 for both NIT and ESS comparisons across groups). A negative correlation between NIT and baseline ESS was found, the correlation coefficient for all the stented segments was -0.33, p < 0.001.

CONCLUSION

In this OCT sub-study of the BIOFLOW II trial, the NIT was statistically different between groups of patients treated with BP-DES and DP-DES. In addition, regions of low ESS were associated with increased NIT in all studied devices.

Morphological characteristics of in-stent restenosis with different degrees of area stenosis: an optical coherence tomography study

The morphological characteristics of in-stent restenosis (ISR) in relation to varying degrees of area stenosis have not been comprehensively examined. This study aimed to explore the tissue characteristics of patients experiencing ISR with different degrees of area stenosis through the utilization of optical coherence tomography (OCT). In total, 230 patients with ISR who underwent OCT were divided into the following three groups: area stenosis (AS) < 70% (n = 26); 70-80% (n = 119) and AS ≥ 80% (n = 85). Among the 230 patients, the clinical presentation as stable angina was 61.5% in AS < 70%, followed by 47.2% in 70% < AS ≤ 80%, and 31.8% in AS ≥ 80% (P = 0.010). The OCT findings showed that heterogeneous neointima, ISNA, LRP, neointima rupture, TCFA-like pattern, macrophage infiltration, red and white thrombus was more common with AS increased. Ordinal logistic regression analysis showed that higher AS was associated with previous dyslipidemia (odds ratio [OR], 4.754; 95% confidence interval [CI], 1.419-15.927, P = 0.011), neointimal rupture (OR: 3.640; 95% CI, 1.169-11.325, P = 0.026), red thrombus (OR: 4.482; 95% CI, 1.269-15.816, P = 0.020) and white thrombus (OR: 5.259; 95% CI, 1.660-16.659, P = 0.005). Patients with higher degrees of area stenosis in the context of ISR exhibited a greater number of discernible morphological characteristics as identified through OCT analysis. Furthermore, previous dyslipidemia, neointimal rupture, white thrombus and red thrombus were highly associated with and the progression of ISR lesions.

Hybrid interpenetrating network of polyester coronary stent with tunable biodegradation and mechanical properties

Poly(l-lactide) (PLLA) is an important candidate raw material of the next-generation biodegradable stent for percutaneous coronary intervention, yet how to make a polyester stent with sufficient mechanical strength and relatively fast biodegradation gets to be a dilemma. Herein, we put forward a hybrid interpenetrating network (H-IPN) strategy to resolve this dilemma. As such, we synthesize a multi-functional biodegradable macromer of star-like poly(d,l-lactide-co-ɛ-caprolactone) with six acrylate end groups, and photoinitiate it, after mixing with linear PLLA homopolymer, to trigger the free radical polymerization. The resultant crosslinked polymer blend is different from the classic semi-interpenetrating network, and partial chemical crosslinking occurs between the linear polymer and the macromer network. Combined with the tube blow molding and the postprocessing laser cutting, we fabricate a semi-crosslinked-polyester biodegradable coronary stent composed of H-IPN, which includes a physical network of polyester spherulites and a chemical crosslinking network of copolyester macromers and a part of homopolymers. Compared with the currently main-stream PLLA stent in research, this H-IPN stent realizes a higher and more appropriate biodegradation rate while maintaining sufficient radial strength. A series of polymer chemistry, polymer physics, polymer processing, and in vitro and in vivo biological assessments of medical devices have been made to examine the H-IPN material. The interventional implanting of the H-IPN stent into aorta abdominalis of rabbits and the follow-ups to 12 months have confirmed the safety and effectiveness.

Restoring endothelial function: shedding light on cardiovascular stent development

Complete endothelialization is highly important for maintaining long-term patency and avoiding subsequent complications in implanting cardiovascular stents. It not only refers to endothelial cells (ECs) fully covering the inserted stents, but also includes the newly formed endothelium, which could exert physiological functions, such as anti-thrombosis and anti-stenosis. Clinical outcomes have indicated that endothelial dysfunction, especially the insufficiency of antithrombotic and barrier functions, is responsible for stent failure. Learning from vascular pathophysiology, endothelial dysfunction on stents is closely linked to the microenvironment of ECs. Evidence points to inflammatory responses, oxidative stress, altered hemodynamic shear stress, and impaired endothelial barrier affecting the normal growth of ECs, which are the four major causes of endothelial dysfunction. The related molecular mechanisms and efforts dedicated to improving the endothelial function are emphasized in this review. From the perspective of endothelial function, the design principles, advantages, and disadvantages behind current stents are introduced to enlighten the development of new-generation stents, aiming to offer new alternatives for restoring endothelial function.

Stent underexpansion is associated with high wall shear stress: a biomechanical analysis of the shear stent study

Coronary stent underexpansion is associated with restenosis and stent thrombosis. In clinical studies of atherosclerosis, high wall shear stress (WSS) has been associated with activation of prothrombotic pathways, upregulation of matrix metalloproteinases, and future myocardial infarction. We hypothesized that stent underexpansion is predictive of high WSS. WSS distribution was investigated in patients enrolled in the prospective randomized controlled study of angulated coronary arteries randomized to undergo percutaneous coronary intervention with R-ZES or X-EES. WSS was calculated from 3D reconstructions of arteries from intravascular ultrasound (IVUS) and angiography using computational fluid dynamics. A logistic regression model investigated the relationship between WSS and underexpansion and the relationship between underexpansion and stent platform. Mean age was 63±11, 78% were male, 35% had diabetes, mean pre-stent angulation was 36.7°±14.7°. Underexpansion was assessed in 83 patients (6,181 IVUS frames). Frames with stent underexpansion were significantly more likely to exhibit high WSS (> 2.5 Pa) compared to those without underexpansion with an OR of 2.197 (95% CI = [1.233-3.913], p = 0.008). There was no significant association between underexpansion and low WSS (< 1.0 Pa) and no significant differences in underexpansion between R-ZES and X-EES. In the Shear Stent randomized controlled study, underexpanded IVUS frames were more than twice as likely to be associated with high WSS than frames without underexpansion.

Ticagrelor versus Clopidogrel in the Dual Antiplatelet Regimen for Unruptured Intracranial Aneurysm Treated with Stent-Assisted Coil Embolization: A Single-Center Cohort Study

BACKGROUND

Dual antiplatelet therapy (DAPT) of aspirin plus clopidogrel is commonly used in patients with unruptured intracranial aneurysms treated with stent-assisted coil (SAC) embolization. However, the unpredictable clopidogrel efficacy of the 5%-55% nonresponders limits its use. Ticagrelor, as a potential alternative of clopidogrel, is an antiplatelet agent with low resistance rates but uncertain efficacy and safety in these patients.

METHODS

A single-center cohort study was performed to compare the efficacy and safety of ticagrelor with clopidogrel in the DAPT regimen in patients with unruptured intracranial aneurysms and treated with SAC. The patients with clopidogrel resistance identified as inadequate adenosine diphosphate inhibition rate determined by thromboelastography were treated with ticagrelor instead, and both drugs achieved adequate suppression of platelet aggregation when stents were implanted. The occurrence of major adverse cardiovascular and cerebrovascular events (MACCE) and bleeding events was recorded through 6 months follow-up.

RESULTS

Data from 86 patients with 99 unruptured intracranial aneurysms and treated by SAC with clopidogrel were compared with those from 108 patients with 111 aneurysms and treated with ticagrelor. Neither the baseline characteristics nor the incidence of the MACCE or bleeding events differed between the groups. Ticagrelor exerted significantly higher adenosine diphosphate inhibition rate than that of the clopidogrel. Multivariable logistic regression analysis showed that the incidence of MACCE was related to hematocrit and fibrinogen levels.

CONCLUSIONS

Ticagrelor seemed to be as effective and safe as clopidogrel for SAC in unruptured intracranial aneurysms. Hematocrit and fibrinogen levels were independent risk factors for the incidence of MACCE.

Strategies to counteract adverse remodeling of vascular graft: A 3D view of current graft innovations

Vascular grafts are widely used for vascular surgeries, to bypass a diseased artery or function as a vascular access for hemodialysis. Bioengineered or tissue-engineered vascular grafts have long been envisioned to take the place of bioinert synthetic grafts and even vein grafts under certain clinical circumstances. However, host responses to a graft device induce adverse remodeling, to varied degrees depending on the graft property and host's developmental and health conditions. This in turn leads to invention or failure. Herein, we have mapped out the relationship between the design constraints and outcomes for vascular grafts, by analyzing impairment factors involved in the adverse graft remodeling. Strategies to tackle these impairment factors and counteract adverse healing are then summarized by outlining the research landscape of graft innovations in three dimensions-cell technology, scaffold technology and graft translation. Such a comprehensive view of cell and scaffold technological innovations in the translational context may benefit the future advancements in vascular grafts. From this perspective, we conclude the review with recommendations for future design endeavors.

Intravascular Imaging for Guiding In-Stent Restenosis and Stent Thrombosis Therapy

Advances in stent technology and the design of endovascular devices with thinner struts, anti-inflammatory and antithrombotic polymers, and better drug kinetics have enhanced the safety and efficacy of the second-generation drug-eluting stents and broadened their use in the therapy of high-risk patients and complex anatomies. However, despite these developments, in-stent restenosis and stent thrombosis remain the Achilles' heel of percutaneous coronary intervention, with their cumulative incidence reaching up to 10% at 5 years following percutaneous coronary intervention. The treatment of stent failure poses challenges and is associated with a worse prognosis than conventional percutaneous coronary intervention. Several studies have recently highlighted the value of intravascular imaging in identifying causes of stent failure, underscored its role in treatment planning, and registries have shown that its use may be associated with better clinical outcomes. The present review aims to summarize the evidence in the field; it discusses the value of intravascular imaging in identifying the mechanisms of in-stent restenosis and stent thrombosis in assessing the morphological characteristics of neointima tissue that appears to determine long-term outcomes in evaluating procedural results, and presents the findings of studies supporting its value in guiding therapy in stent failure.

Vascular Injury After Stenting - Insights of Systemic Mechanisms of Vascular Repair

BACKGROUND

The role of circulating progenitor cells (CPC) in vascular repair following everolimus-eluting stent (EES) implantation is largely unknown. The aim of the study was to investigate the relationship between temporal variation in CPC levels following EES implantation and the degree of peri-procedural vascular damage, and stent healing, as measured by optical coherence tomography (OCT).

METHODS AND RESULTS

CPC populations (CD133+/KDR+/CD45low) included patients with stable coronary artery disease undergoing stent implantation, and were evaluated using a flow cytometry technique both at baseline and at 1 week. OCT evaluation was performed immediately post-implantation to quantify the stent-related injury and at a 9-month follow up to assess the mid-term vascular response. Twenty patients (mean age 66±9 years; 80% male) with EES-treated stenoses (n=24) were included in this study. Vascular injury score was associated with the 1-week increase of CD133+/KDR+/CD45low (β 0.28 [95% CI 0.15; 0.41]; P<0.001) and with maximum neointimal thickness at a 9-month follow up (β 0.008 [95% CI 0.0004; 0.002]; P=0.04). Inverse relationships between numbers of uncoated and apposed struts for the 9-month and the 1-week delta values of CD133+/KDR+/CD45low (β -12.53 [95% CI -22.17; -2.90]; P=0.011), were also found.

CONCLUSIONS

The extent of vessel wall injury influences early changes in the levels of CPC and had an effect on mid-term vascular healing after EES implantation. Early CPC mobilisation was associated with mid-term strut coverage.

Optical Coherence Tomography Evaluation of Carotid Artery Stenosis and Stenting in Patients With Previous Cervical Radiotherapy

Objectives

Cervical radiotherapy can lead to accelerated carotid artery stenosis, increased incidence of stroke, and a higher rate of in-stent restenosis in irradiated patients. Our objective was to reveal the morphological characteristics of radiation-induced carotid stenosis (RICS) and the stent–vessel interactions in patients with previous cervical radiotherapy by optical coherence tomography (OCT).

Materials and Methods

Between November 2017 and March 2019, five patients with a history of cervical radiotherapy were diagnosed with severe carotid artery stenosis and underwent carotid artery stenting (CAS). OCT was conducted before and immediately after the carotid stent implantation. Two patients received OCT evaluation of carotid stenting at 6- or 13-month follow-up.

Results

The tumor types indicating cervical radiotherapy were nasopharyngeal carcinoma (n = 3), cervical esophageal carcinoma (n = 1), and cervical lymphoma (n = 1). The median interval from the radiotherapy to the diagnosis of RICS was 8 years (range 4–36 years). Lesion characteristics of RICS were detected with heterogeneous signal-rich tissue, dissection, and advanced atherosclerosis upon OCT evaluation. Post-interventional OCT revealed 18.2–57.1% tissue protrusion and 3.3–13.8% stent strut malapposition. Follow-up OCT detected homogeneous signal-rich neointima and signal-poor regions around stent struts. In the patient with high rates of tissue protrusion and stent strut malapposition, the 6-month neointima burden reached 48.9% and microvessels were detected.

Conclusion

The morphological features of RICS were heterogeneous, including heterogeneous signal-rich tissue, dissection, and advanced atherosclerosis. Stenting was successful in all 5 patients with severe RICS. One patient, with high rates of tissue protrusion and stent strut malapposition immediately after stenting, received in-stent neointimal hyperplasia at a 6-month follow-up.

Recent advance in treatment of atherosclerosis: Key targets and plaque-positioned delivery strategies

Atherosclerosis, a chronic inflammatory disease of vascular wall, is a progressive pathophysiological process with lipids oxidation/depositing initiation and innate/adaptive immune responses. The coordination of multi systems covering oxidative stress, dysfunctional endothelium, diseased lipid uptake, cell apoptosis, thrombotic and pro-inflammatory responding as well as switched SMCs contributes to plaque growth. In this circumstance, inevitably, targeting these processes is considered to be effective for treating atherosclerosis. Arriving, retention and working of payload candidates mediated by targets in lesion direct ultimate therapeutic outcomes. Accumulating a series of scientific studies and clinical practice in the past decades, lesion homing delivery strategies including stent/balloon/nanoparticle-based transportation worked as the potent promotor to ensure a therapeutic effect. The objective of this review is to achieve a very brief summary about the effective therapeutic methods cooperating specifical targets and positioning-delivery strategies in atherosclerosis for better outcomes.

Modelling of hemodynamics in bifurcation lesions of coronary arteries before and after myocardial revascularization

Modelling of patient-specific hemodynamics for a clinical case of severe coronary artery disease with the bifurcation stenosis was carried out with allowance for standard angiographic data obtained before and after successfully performed myocardial revascularization by stenting of two arteries. Based on a non-Newtonian fluid model and an original algorithm for fluid dynamics computation operated with a limited amount of initial data, key characteristics of blood flow were determined to analyse the features of coronary disease and the consequences of its treatment. The results of hemodynamic modelling near bifurcation sites are presented with an emphasis on physical, physiological and clinical phenomena to demonstrate the feasibility of the proposed approach. The main limitations and ways to minimize them are the subjects of discussion as well. This article is part of the theme issue 'Transport phenomena in complex systems (part 2)'.

Coronary Artery Stenting Affects Wall Shear Stress Topological Skeleton

Despite the important advancements in the stent technology for the treatment of diseased coronary arteries, major complications still affect the post-operative long-term outcome. The stent-induced flow disturbances, and especially the altered wall shear stress (WSS) profile at the strut level, play an important role in the pathophysiological mechanisms leading to stent thrombosis (ST) and in-stent restenosis (ISR). In this context, the analysis of the WSS topological skeleton is gaining more and more interest by extending the current understanding of the association between local hemodynamics and vascular diseases. The present study aims to analyze the impact that a deployed coronary stent has on the WSS topological skeleton. Computational fluid dynamics simulations were performed in three stented human coronary artery geometries reconstructed from clinical images. The selected cases presented stents with different designs (i.e., two contemporary drug eluting stents and one bioresorbable scaffold) and included regions with stent malapposition or overlapping. A recently proposed Eulerian-based approach was applied to analyze the WSS topological skeleton features. The results highlighted that the presence of single or multiple stents within a coronary artery markedly impacts the WSS topological skeleton. In particular, repetitive patterns of WSS divergence were observed at the luminal surface, highlighting a WSS contraction action proximal to the struts and a WSS expansion action distal to the struts. This WSS action pattern was independent from the stent design. In conclusions, these findings could contribute to a deeper understanding of the hemodynamic-driven processes underlying ST and ISR.

Semi-Automatic Reconstruction of Patient-Specific Stented Coronaries based on Data Assimilation and Computer Aided Design

PURPOSE

The interplay between geometry and hemodynamics is a significant factor in the development of cardiovascular diseases. This is particularly true for stented coronary arteries. To elucidate this factor, an accurate patient-specific analysis requires the reconstruction of the geometry following the stent deployment for a computational fluid dynamics (CFD) investigation. The image-based reconstruction is troublesome for the different possible positions of the stent struts in the lumen and the coronary wall. However, the accurate inclusion of the stent footprint in the hemodynamic analysis is critical for detecting abnormal stress conditions and flow disturbances, particularly for thick struts like in bioresorbable scaffolds. Here, we present a novel reconstruction methodology that relies on Data Assimilation and Computer Aided Design.

METHODS

The combination of the geometrical model of the undeployed stent and image-based data assimilated by a variational approach allows the highly automated reconstruction of the skeleton of the stent. A novel approach based on computational mechanics defines the map between the intravascular frame of reference (called L-view) and the 3D geometry retrieved from angiographies. Finally, the volumetric expansion of the stent skeleton needs to be self-intersection free for the successive CFD studies; this is obtained by using implicit representations based on the definition of Nef-polyhedra.

RESULTS

We assessed our approach on a vessel phantom, with less than 10% difference (properly measured) vs. a customized manual (and longer) procedure previously published, yet with a significant higher level of automation and a shorter turnaround time. Computational hemodynamics results were even closer. We tested the approach on two patient-specific cases as well.

CONCLUSIONS

The method presented here has a high level of automation and excellent accuracy performances, so it can be used for larger studies involving patient-specific geometries.

Disturbed flow's impact on cellular changes indicative of vascular aneurysm initiation, expansion, and rupture: A pathological and methodological review

Aneurysms are malformations within the arterial vasculature brought on by the structural breakdown of the microarchitecture of the vessel wall, with aneurysms posing serious health risks in the event of their rupture. Blood flow within vessels is generally laminar with high, unidirectional wall shear stressors that modulate vascular endothelial cell functionality and regulate vascular smooth muscle cells. However, altered vascular geometry induced by bifurcations, significant curvature, stenosis, or clinical interventions can alter the flow, generating low stressor disturbed flow patterns. Disturbed flow is associated with altered cellular morphology, upregulated expression of proteins modulating inflammation, decreased regulation of vascular permeability, degraded extracellular matrix, and heightened cellular apoptosis. The understanding of the effects disturbed flow has on the cellular cascades which initiate aneurysms and promote their subsequent growth can further elucidate the nature of this complex pathology. This review summarizes the current knowledge about the disturbed flow and its relation to aneurysm pathology, the methods used to investigate these relations, as well as how such knowledge has impacted clinical treatment methodologies. This information can contribute to the understanding of the development, growth, and rupture of aneurysms and help develop novel research and aneurysmal treatment techniques.

Current status and outlook of biodegradable metals in neuroscience and their potential applications as cerebral vascular stent materials

Over the past two decades, biodegradable metals (BMs) have emerged as promising materials to fabricate temporary biomedical devices, with the purpose of avoiding potential side effects of permanent implants. In this review, we first surveyed the current status of BMs in neuroscience, and briefly summarized the representative stents for treating vascular stenosis. Then, inspired by the convincing clinical evidence on the in vivo safety of Mg alloys as cardiovascular stents, we analyzed the possibility of producing biodegradable cerebrovascular Mg alloy stents for treating ischemic stroke. For these novel applications, some key factors should also be considered in designing BM brain stents, including the anatomic features of the cerebral vasculature, hemodynamic influences, neuro-cytocompatibility and selection of alloying elements. This work may provide insights into the future design and fabrication of BM neurological devices, especially for brain stents.

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The current status of the application of biodegradable metals (BM) in neuroscience was presented.

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We analyzed the possibility of producing biodegradable cerebrovascular Mg alloy stents for ischemic stroke treatment.

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Key factors in designing BM brain stents were discussed.

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This work may provide insights into the future design and fabrication of BM neurological devices, especially for brain stents.

Nanoparticles-reinforced poly-l-lactic acid composite materials as bioresorbable scaffold candidates for coronary stents: Insights from mechanical and finite element analysis

Current generation of bioresorbable coronary scaffolds (BRS) posed thrombogenicity and deployment issues owing to its thick struts and overall profile. To this end, we hypothesize that the use of nanocomposite materials is able to provide improved material properties and sufficient radial strength for the intended application even at reduced strut thickness. The nanocomposite formulations of tantalum dioxide (Ta₂O₅), L-lactide functionalized (LA)-Ta₂O₅, hydroxyapatite (HA) and LA-HA with poly-l-lactic acid (PLLA) were evaluated in this study. Results showed that tensile modulus and strength were enhanced with non-functionalized nanofillers up until 15 wt% loading, whereas ductility was compromised. On the other hand, functionalized nanofillers/PLLA exhibited improved nanofiller dispersion which resulted higher tensile modulus, strength, and ductility. Selected nanocomposite formulations were evaluated using finite element analysis (FEA) of a stent with varying strut thickness (80, 100 and 150 μm). FEA data has shown that nanocomposite BRS with thinner struts (80-100 μm) made with 15 wt% LA-Ta₂O₅/PLLA and 10 wt% LA-HA/PLLA have increased radial strength, stiffness and reduced recoil compared to PLLA BRS at 150 μm. The reduced strut thickness can potentially mitigate issues such as scaffold thrombosis and promote re-endothelialisation of the vessel.

Investigation of Drug Eluting Stents performance in human atherosclerotic artery through in silico modeling

Atherosclerosis is a chronic inflammatory disease associated with heart attack and stroke. It causes the growth of atherosclerotic plaques inside the arterial vessels, which in turn results to the reduction of the blood flow to the different organs. Drug-Eluting Stents (DES) are mesh-like wires, carrying pharmaceutical coating, designed to dilate and support the arterial vessel, restore blood flow and through the controlled local drug delivery inhibit neo-intimal thickening. In silico modeling is an efficient method of accurately predicting and assessing the performance of the stenting procedure. The present in silico study investigates the performance of two different stents (Bare Metal Stent, Drug-Eluting Stent) in a patient-specific coronary artery and assesses the effect of stent coating, considering that the same procedural approach is followed by the interventional cardiologist. The results demonstrate that even if small differences are obtained in the two models, the incorporation of the stent coatings (in DES) does not significantly affect the outcomes of the stent deployment, the stresses and strains in the scaffold and the arterial tissue. Nevertheless, it is suggested that regarding the DES expansion, higher pressure should be applied at the inner surface of the stent.

Hemodynamic alternations following stent deployment and post-dilation in a heavily calcified coronary artery: In silico and ex-vivo approaches

In this work, hemodynamic alterations in a patient-specific, heavily calcified coronary artery following stent deployment and post-dilations are quantified using in silico and ex-vivo approaches. Three-dimensional artery models were reconstructed from OCT images. Stent deployment and post-dilation with various inflation pressures were performed through both the finite element method (FEM) and ex vivo experiments. Results from FEM agreed very well with the ex-vivo measurements, interms of lumen areas, stent underexpansion, and strut malapposition. In addition, computational fluid dynamics (CFD) simulations were performed to delineate the hemodynamic alterations after stent deployment and post-dilations. A pressure time history at the inlet and a lumped parameter model (LPM) at the outlet were adopted to mimic the aortic pressure and the distal arterial tree, respectively. The pressure drop across the lesion, pertaining to the clinical measure of instantaneous wave-free flow ratio (iFR), was investigated. Results have shown that post-dilations are necessary for the lumen gain as well as the hemodynamic restoration towards hemostasis. Malapposed struts induced much higher shear rate, flow disturbances and lower time-averaged wall shear stress (TAWSS) around struts. Post-dilations mitigated the strut malapposition, and thus the shear rate. Moreover, stenting induced larger area of low TAWSS (<0.4 Pa) and lager volume of high shear rate (>2000 s^-1), indicating higher risks of in-stent restenosis (ISR) and stent thrombosis (ST), respectively. Oscillatory shear index (OSI) and relative residence time (RRT) indicated the wall regions more prone to ISR are located near the malapposed stent struts.

The relationship between coronary stent strut thickness and the incidences of clinical outcomes after drug-eluting stent implantation: A systematic review and meta-regression analysis

BACKGROUND

Drug-eluting stents (DESs) have been developed with thinner stent struts, and more biocompatible polymers and anti-proliferative drugs to improve the clinical performance. However, it remains unclear whether thinner struts are associated with favorable short- and long-term clinical outcomes such as target lesion revascularization (TLR), periprocedural myocardial infarction (PMI), and stent thrombosis (ST).

METHODS

We searched MEDLINE, Embase and other online sources for randomized controlled trials (RCTs) comparing clinical outcomes between a DES and other stent(s), with independent clinical event adjudication. We investigated stent-related events (TLR, PMI, and ST) in 5 years. Each outcome was analyzed with random-effects meta-regression model against strut thickness, then adjusted for DES generation and patient and lesion characteristics.

RESULTS

We identified 49 RCTs enrolling 97,465 patients, of which strut thickness ranged from 60 to 140 μm. Incidences of 1-year TLR, PMI, and early ST were reduced with thinner stent struts, when adjusted for stent generation (adjusted relative risk [RR] per 10 μm increase 1.12 [95% CI 1.04-1.21], 1.15 [95% CI 1.05-1.26], and 1.15 [95% CI 1.06-1.25], respectively). Strut thickness was not independently associated with incidences of 5-year TLR, late and very late ST. In addition, early DESs contributed to a higher incidence of very late ST (adjusted RR 2.97 [95% CI 1.36-6.50]).

CONCLUSIONS

In this meta-regression analysis, a thinner strut thickness was associated with reduced incidences of early stent-related adverse events (1-year TLR, PMI, and early ST), but not with later events (5-year TLR, late ST, and very late ST).

The impact of plaque type on strut embedment/protrusion and shear stress distribution in bioresorbable scaffold

AIMS

Scaffold design and plaque characteristics influence implantation outcomes and local flow dynamics in treated coronary segments. Our aim is to assess the impact of strut embedment/protrusion of bioresorbable scaffold on local shear stress distribution in different atherosclerotic plaque types.

METHODS AND RESULTS

Fifteen Absorb everolimus-eluting Bioresorbable Vascular Scaffolds were implanted in human epicardial coronary arteries. Optical coherence tomography (OCT) was performed post-scaffold implantation and strut embedment/protrusion were analysed using a dedicated software. OCT data were fused with angiography to reconstruct 3D coronary anatomy. Blood flow simulation was performed and wall shear stress (WSS) was estimated in each scaffolded surface and the relationship between strut embedment/protrusion and WSS was evaluated. There were 9083 struts analysed. Ninety-seven percent of the struts (n = 8840) were well-apposed and 243 (3%) were malapposed. At cross-section level (n = 1289), strut embedment was significantly increased in fibroatheromatous plaques (76 ± 48 µm) and decreased in fibrocalcific plaques (35 ± 52 µm). Compatible with strut embedment, WSS was significantly higher in lipid-rich fibroatheromatous plaques (1.50 ± 0.81 Pa), whereas significantly decreased in fibrocalcified plaques (1.05 ± 0.91 Pa). After categorization of WSS as low (<1.0 Pa) and normal/high WSS (≥1.0 Pa), the percent of low WSS in the plaque subgroups were 30.1%, 31.1%, 25.4%, and 36.2% for non-diseased vessel wall, fibrous plaque, fibroatheromatous plaque, and fibrocalcific plaque, respectively (P-overall < 0.001).

CONCLUSION

The composition of the underlying plaque influences strut embedment which seems to have effect on WSS. The struts deeply embedded in lipid-rich fibroatheromas plaques resulted in higher WSS compared with the other plaque types.

Celastrol ameliorates vascular neointimal hyperplasia through Wnt5a-involved autophagy

Neointimal hyperplasia caused by the excessive proliferation of vascular smooth muscle cells (VSMCs) is the pathological basis of restenosis. However, there are few effective strategies to prevent restenosis. Celastrol, a pentacyclic triterpene, has been recently documented to be beneficial to certain cardiovascular diseases. Based on its significant effect on autophagy, we proposed that celastrol could attenuate restenosis through enhancing autophagy of VSMCs. In the present study, we found that celastrol effectively inhibited the intimal hyperplasia and hyperproliferation of VSMCs by inducing autophagy. It was revealed that autophagy promoted by celastrol could induce the lysosomal degradation of c-MYC, which might be a possible mechanism contributing to the reduction of VSMCs proliferation. The Wnt5a/PKC/mTOR signaling pathway was found to be an underlying mechanism for celastrol to induce autophagy and inhibit the VSMCs proliferation. These observations indicate that celastrol may be a novel drug with a great potential to prevent restenosis.

A multi-objective optimization of stent geometries

Stents are scaffolding cardiovascular implants used to restore blood flow in narrowed arteries. However, the presence of the stent alters local blood flow and shear stresses on the surrounding arterial wall, which can cause adverse tissue responses and increase the risk of adverse outcomes. There is a need for optimization of stent designs for hemodynamic performance. We used multi-objective optimization to identify ideal combinations of design variables by assessing potential trade-offs based on common hemodynamic indices associated with clinical risk and mechanical performance of the stents. We studied seven design variables including strut cross-section, strut dimension, strut angle, cell alignment, cell height, connector type and connector arrangement. Optimization objectives were the percentage of vessel area exposed to adversely low time averaged WSS (TAWSS) and adversely high Wall Shear Stress (WSS) assessed using computational fluid dynamics modeling, as well as radial stiffness of the stent using FEA simulation. Two multi-objective optimization algorithms were used and compared to iteratively predict ideal designs. Out of 50 designs, three best designs with respect to each of the three objectives, and two designs in regard to overall performance were identified.

In-Stent Restenosis Progression in Human Superficial Femoral Arteries: Dynamics of Lumen Remodeling and Impact of Local Hemodynamics

In-stent restenosis (ISR) represents a major drawback of stented superficial femoral arteries (SFAs). Motivated by the high incidence and limited knowledge of ISR onset and development in human SFAs, this study aims to (i) analyze the lumen remodeling trajectory over 1-year follow-up period in human stented SFAs and (ii) investigate the impact of altered hemodynamics on ISR initiation and progression. Ten SFA lesions were reconstructed at four follow-ups from computed tomography to quantify the lumen area change occurring within 1-year post-intervention. Patient-specific computational fluid dynamics simulations were performed at each follow-up to relate wall shear stress (WSS) based descriptors with lumen remodeling. The largest lumen remodeling was found in the first post-operative month, with slight regional-specific differences (larger inward remodeling in the fringe segments, p < 0.05). Focal re-narrowing frequently occurred after 6 months. Slight differences in the lumen area change emerged between long and short stents, and between segments upstream and downstream from stent overlapping portions, at specific time intervals. Abnormal patterns of multidirectional WSS were associated with lumen remodeling within 1-year post-intervention. This longitudinal study gave important insights into the dynamics of ISR and the impact of hemodynamics on ISR progression in human SFAs.

Clinical outcomes with unselected use of an ultrathin-strut sirolimus-eluting stent: a report from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR)

AIMS

The aim of this study was to assess the real-world clinical performance of a sirolimus-eluting ultrathin-strut drug-eluting stent (DES) (Orsiro) in a large nationwide cohort of patients undergoing percutaneous coronary intervention (PCI).

METHODS AND RESULTS

From the Swedish Coronary Angiography and Angioplasty Registry, the two-year outcomes of 4,561 patients implanted with Orsiro (Orsiro group) and 69,570 receiving other newer-generation DES (n-DES group) were analysed. The rate of definite stent thrombosis was low in both groups (0.67% and 0.83% for Orsiro and n-DES, respectively; adjusted hazard ratio [HR] 0.90, 95% confidence interval [CI]: 0.55-1.46, p-value 0.66). Restenosis was also infrequent (1.5% vs 2.0% with Orsiro and n-DES, adjusted HR 0.81, 95% CI: 0.63-1.03, p-value=0.09). The risk of target lesion revascularisation by PCI was lower in the Orsiro group (1.6% vs 2.3%, adjusted HR 0.75, 95% CI: 0.60-0.94, p-value=0.013). All-cause mortality and myocardial infarction did not show a statistically significant difference between the two groups (mortality of 7.5% in both groups, adjusted HR 0.99, 95% CI: 0.72-1.35, p-value=0.94; 6.0% vs 5.2% for myocardial infarction, adjusted HR 1.19, 95% CI: 1.00-1.43, p-value=0.06).

CONCLUSIONS

In a nationwide scenario, the use of a sirolimus-eluting ultrathin-strut DES portended favourable clinical outcomes.

Impact of Malapposed and Overlapping Stents on Hemodynamics: A 2D Parametric Computational Fluid Dynamics Study

Despite significant progress, malapposed or overlapped stents are a complication that affects daily percutaneous coronary intervention (PCI) procedures. These malapposed stents affect blood flow and create a micro re-circulatory environment. These disturbances are often associated with a change in Wall Shear Stress (WSS), Time-averaged WSS (TAWSS), relative residence time (RRT) and oscillatory character of WSS and disrupt the delicate balance of vascular biology, providing a possible source of thrombosis and restenosis. In this study, 2D axisymmetric parametric computational fluid dynamics (CFD) simulations were performed to systematically analyze the hemodynamic effects of malapposition and stent overlap for two types of stents (drug-eluting stent and a bioresorbable stent). The results of the modeling are mainly analyzed using streamlines, TAWSS, oscillatory shear index (OSI) and RRT. The risks of restenosis and thrombus are evaluated according to commonly accepted thresholds for TAWSS and OSI. The small malapposition distances (MD) cause both low TAWSS and high OSI, which are potential adverse outcomes. The region of low OSI decrease with MD. Overlap configurations produce areas with low WSS and high OSI. The affected lengths are relatively insensitive to the overlap distance. The effects of strut size are even more sensitive and adverse for overlap configurations compared to a well-applied stent.

The Combined Contribution of Vascular Endothelial Cell Migration and Adhesion to Stent Re-endothelialization

Coronary stent placement inevitably causes mechanical damage to the endothelium, leading to endothelial denudation and in-stent restenosis (ISR). Re-endothelialization depends mainly on the migration of vascular endothelial cells (VECs) adjacent to the damaged intima, as well as the mobilization and adhesion of circulating VECs. To evaluate the combined contribution of VEC migration and adhesion to re-endothelialization under flow and the influence of stent, in vitro models were constructed to simulate various endothelial denudation scales (2 mm/5 mm/10 mm) and stent deployment depths (flat/groove/bulge). Our results showed that (1) in 2 mm flat/groove/bulge models, both VEC migration and adhesion combined completed the percentage of endothelial recovery about 27, 16, and 12%, and migration accounted for about 21, 15, and 7%, respectively. It was suggested that the flat and groove models were in favor of VEC migration. (2) With the augmentation of the injury scales (5 and 10 mm), the contribution of circulating VEC adhesion on endothelial repair increased. Taken together, endothelial restoration mainly depended on the migration of adjacent VECs when the injury scale was 2 mm. The adhered cells contributed to re-endothelialization in an injury scale-dependent way. This study is helpful to provide new enlightenment for surface modification of cardiovascular implants.

Perivascular tissue stem cells are crucial players in vascular disease

Perivascular tissue including adipose layer and adventitia have been considered to play pivotal roles in vascular development and disease progression. Recent studies showed that abundant stem/progenitorcells (SPCs) are present in perivascular tissues. These SPCs exhibit capability to proliferate and differentiate into specific terminal cells. Adult perivascular SPCs are quiescent in normal condition, once activated by specific molecules (e.g., cytokines), they migrate toward the lumen side where they differentiate into both smooth muscle cells (SMCs) and endothelial cells (ECs), thus promoting intima hyperplasia or endothelial regeneration. In addition, perivascular SPCs can also regulate vascular diseases via other ways including but not limited to paracrine effects, matrix protein modulation and microvessel formation. Perivascular SPCs have also been shown to possess therapeutic potentials due to the capability to differentiate into vascular cells and regenerate vascular structures. This review summarizes current knowledge on resident SPCs features and discusses the potential benefits of SPCs therapy in vascular diseases.

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

In-stent restenosis (ISR) is the major drawback of superficial femoral artery (SFA) stenting. Abnormal hemodynamics after stent implantation seems to promote the development of ISR. Accordingly, this study aims to investigate the impact of local hemodynamics on lumen remodeling in human stented SFA lesions. Ten SFA models were reconstructed at 1-week and 1-year follow-up from computed tomography images. Patient-specific computational fluid dynamics simulations were performed to relate the local hemodynamics at 1-week, expressed in terms of time-averaged wall shear stress (TAWSS), oscillatory shear index and relative residence time, with the lumen remodeling at 1-year, quantified as the change of lumen area between 1-week and 1-year. The TAWSS was negatively associated with the lumen area change (ρ = - 0.75, p = 0.013). The surface area exposed to low TAWSS was positively correlated with the lumen area change (ρ = 0.69, p = 0.026). No significant correlations were present between the other hemodynamic descriptors and lumen area change. The low TAWSS was the best predictive marker of lumen remodeling (positive predictive value of 44.8%). Moreover, stent length and overlapping were predictor of ISR at follow-up. Despite the limited number of analyzed lesions, the overall findings suggest an association between abnormal patterns of WSS after stenting and lumen remodeling.

Impact of bioresorbable scaffold design characteristics on local haemodynamic forces: an ex vivo assessment with computational fluid dynamics simulations

AIMS

Bioresorbable scaffold (BRS) regions exposed to flow recirculation, low time-averaged wall shear stress (TAWSS) and high oscillatory shear index (OSI) develop increased neointima tissue. We investigated haemodynamic features in four different BRSs.

METHODS AND RESULTS

Fantom (strut height [SH] = 125 µm), Fantom Encore (SH = 98 µm), Absorb (SH = 157 µm) and Magmaris (SH = 150 µm) BRSs were deployed in phantom tubes and imaged with microCT. Both 2D and 3D geometrical scaffold models were reconstructed. Computational fluid dynamics (CFD) simulation was performed to compute TAWSS and OSI. Thicker struts had larger recirculation zones and lower TAWSS in 2D. Absorb had the largest recirculation zone and the lowest TAWSS (240 µm and -0.18 Pa), followed by Magmaris (170 µm and -0.15 Pa), Fantom (140 µm and -0.14 Pa) and Fantom Encore (100 µm and -0.13 Pa). Besides strut size, stent design played a dominant role in 3D. The highest percentage area adverse TAWSS (<0.5 Pa) and OSI (>0.2) were found for Fantom (56% and 30%) and Absorb (53% and 33%), followed by Fantom Encore (30% and 25%) and Magmaris (25% and 20%). Magmaris had the smallest areas due to a small footprint and rounded struts.

CONCLUSIONS

Due to stent design, both Fantom Encore and Magmaris showed smaller TAWSS and OSI than Fantom and Absorb. This study quantifies which scaffold features are most important to reduce long-term restenosis.

Comparison of overexpansion capabilities and thrombogenicity at the side branch ostia after implantation of four different drug eluting stents

Interventions in bifurcation lesions often requires aggressive overexpansion of stent diameter in the setting of long tapering vessel segment. Overhanging struts in front of the side branch (SB) ostium are thought to act as a focal point for thrombi formation and consequently possible stent thrombosis. This study aimed to evaluate the overexpansion capabilities and thrombogenicity at the SB ostia after implantation of four latest generation drug-eluting stents (DES) in an in-vitro bifurcation model. Four clinically available modern DES were utilized: one bifurcation dedicated DES (Bioss LIM C) and three conventional DES (Ultimaster, Xience Sierra, Biomime). All devices were implanted in bifurcation models with proximal optimization ensuring expansion before perfusing with porcine blood. Optical coherence tomography (OCT), immunofluorescence (IF) and scanning electron microscope analysis were done to determine thrombogenicity and polymer coating integrity at the over-expanded part of the stents. Computational fluid dynamics (CFD) was performed to study the flow disruption. OCT (p = 0.113) and IF analysis (p = 0.007) demonstrated lowest thrombus area at SB ostia in bifurcation dedicated DES with favorable biomechanical properties compared to conventional DES. The bifurcated DES also resulted in reduced area of high shear rate and maximum shear rate in the CFD analysis. This study demonstrated numerical differences in terms of mechanical properties and acute thrombogenicity at SB ostia between tested devices.

Durable Polymer Versus Biodegradable Polymer Drug-Eluting Stents After Percutaneous Coronary Intervention in Patients with Acute Coronary Syndrome: The HOST-REDUCE-POLYTECH-ACS Trial

BACKGROUND

Large-scale randomized comparison of drug-eluting stents (DES) based on durable polymer versus biodegradable polymer technology is currently insufficient in patients with acute coronary syndrome (ACS). The present study aimed to prove the noninferiority of the durable polymer DES (DP-DES) compared with the biodegradable polymer DES (BP-DES) in such patients.

METHODS

The HOST-REDUCE-POLYTECH-ACS (Harmonizing Optimal Strategy for Treatment of Coronary Artery Diseases-Comparison of Reduction of Prasugrel Dose or Polymer Technology in ACS Patients) trial is an investigator-initiated, randomized, open-label, adjudicator-blinded, multicenter, noninferiority trial comparing the efficacy and safety of DP-DES and BP-DES in patients with ACS. The primary end point was a patient-oriented composite outcome (a composite of all-cause death, nonfatal myocardial infarction, and any repeat revascularization) at 12 months. The key secondary end point was device-oriented composite outcome (a composite of cardiac death, target-vessel myocardial infarction, or target lesion revascularization) at 12 months.

RESULTS

A total of 3413 patients were randomized to receive the DP-DES (1713 patients) and BP-DES (1700 patients). At 12 months, patient-oriented composite outcome occurred in 5.2% in the DP-DES group and 6.4% in the BP-DES group (absolute risk difference, -1.2%; P_{noninferiority}<0.001). The key secondary end point, device-oriented composite outcome, occurred less frequently in the DP-DES group (DP-DES vs BP-DES, 2.6% vs 3.9%; hazard ratio, 0.67 [95% CI, 0.46-0.98]; P=0.038), mostly because of a reduction in target lesion revascularization. The rate of spontaneous nonfatal myocardial infarction and stent thrombosis were extremely low, with no significant difference between the 2 groups (0.6% versus 0.8%; P=0.513 and 0.1% versus 0.4%; P=0.174, respectively).

CONCLUSIONS

In ACS patients receiving percutaneous coronary intervention, DP-DES was noninferior to BP-DES with regard to patient-oriented composite outcomes at 12 months after index percutaneous coronary intervention. Registration: URL: https://wwwclinicaltrials.gov; Unique identifier: NCT02193971.

Thin, very thin, or ultrathin-strut biodegradable or durable polymer-coated drug-eluting stents

PURPOSE OF REVIEW

The current article will review recently published clinical studies that evaluate very thin or ultrathin-strut drug-eluting stents (DES), focusing on major randomized clinical trials in broad patient populations.

RECENT FINDINGS

Multiple randomized trials recently assessed the clinical performance of novel very thin to ultrathin-strut DES. Most randomized trials established noninferiority of the novel device. To date, only one major randomized clinical trial (i.e., BIOFLOW V) showed superiority of an ultrathin-strut biodegradable polymer-coated sirolimus-eluting stent over a very thin-strut durable polymer-coated everolimus-eluting stent in a relatively broad patient population. There are signals that the same ultrathin-strut biodegradable polymer-coated sirolimus-eluting stent may improve clinical outcome in specific patient populations. For example, in the randomized BIOSTEMI trial, 1-year superiority of the ultrathin-strut DES was found in patients presenting with an acute ST-segment elevation myocardial infarction. Yet, substudies of large randomized trials that assessed patients with small-vessel treatment showed equivocal results.

SUMMARY

Although two randomized trials showed advantages for ultrathin-strut DES, other clinical trials provided no significant evidence that ultrathin-strut DES improve clinical outcome. The question whether ultrathin-strut DES may reduce the repeat revascularization risk following implantation in small vessels is a matter of further debate and future research.

The Evolution of Data Fusion Methodologies Developed to Reconstruct Coronary Artery Geometry From Intravascular Imaging and Coronary Angiography Data: A Comprehensive Review

Understanding the mechanisms that regulate atherosclerotic plaque formation and evolution is a crucial step for developing treatment strategies that will prevent plaque progression and reduce cardiovascular events. Advances in signal processing and the miniaturization of medical devices have enabled the design of multimodality intravascular imaging catheters that allow complete and detailed assessment of plaque morphology and biology. However, a significant limitation of these novel imaging catheters is that they provide two-dimensional (2D) visualization of the lumen and vessel wall and thus they cannot portray vessel geometry and 3D lesion architecture. To address this limitation computer-based methodologies and user-friendly software have been developed. These are able to off-line process and fuse intravascular imaging data with X-ray or computed tomography coronary angiography (CTCA) to reconstruct coronary artery anatomy. The aim of this review article is to summarize the evolution in the field of coronary artery modeling; we thus present the first methodologies that were developed to model vessel geometry, highlight the modifications introduced in revised methods to overcome the limitations of the first approaches and discuss the challenges that need to be addressed, so these techniques can have broad application in clinical practice and research.