Stent strut streamlining and thickness reduction promote endothelialization

Stent thrombosis (ST) carries a high risk of myocardial infarction and death. Lack of endothelial coverage is an important prognostic indicator of ST after stenting. While stent strut thickness is a critical factor in ST, a mechanistic understanding of its effect is limited and the role of haemodynamics is unclear. Endothelialization was tested using a wound-healing assay and five different stent strut models ranging in height between 50 and 150 µm for circular arc (CA) and rectangular (RT) geometries and a control without struts. Under static conditions, all stent strut surfaces were completely endothelialized. Reversing pulsatile disturbed flow caused full endothelialization, except for the stent strut surfaces of the 100 and 150 µm RT geometries, while fully antegrade pulsatile undisturbed flow with a higher mean wall shear stress caused only the control and the 50 µm CA geometries to be fully endothelialized. Modest streamlining and decrease in height of the stent struts improved endothelial coverage of the peri-strut and stent strut surfaces in a haemodynamics dependent manner. This study highlights the impact of the stent strut height (thickness) and geometry (shape) on the local haemodynamics, modulating reendothelialization after stenting, an important factor in reducing the risk of stent thrombosis.

A case report of successful stent implantation through a fractured stent-strut in a superficial femoral artery based on bench testing simulation

Background Stent implantation through the stent-strut of a previously implanted self-expandable stent in the superficial femoral artery (SFA) is not usually performed because the additional stent cannot dilate sufficiently. The key point to achieve sufficient expansion of an additional stent is to break the stent-strut of the previously implanted stent. However, there is no report of how to break the stent-strut. Case summary A 72-year-old man was admitted to our hospital with acute rest pain and coldness of his left leg; he was diagnosed with acute limb ischaemia. The angiogram demonstrated a fractured stent as well as stent occlusion in the left distal SFA. The guidewire could pass only through the stent-strut because of stent fracture. Fortunately, balloon angioplasty through the stent-strut and thrombolysis achieved successful revascularization. Thereafter, an additional stent was implanted in an attempt to manage the fractured and deformed stent. To obtain sufficient expansion of the additional stent, an experimental study to examine the balloon diameter and pressure to break the stent-strut was performed. Based on the results of the experiment, the stent-strut was successfully broken, and the additional stent was expanded through the stent-strut on the second intervention. Discussion If an additional self-expandable stent is deployed through the stent-strut directly, it would not be sufficiently dilated. The key point in such a case is to break the stent-strut of the previously implanted stent by balloon inflation before deployment of the additional stent. The experimental study examined the balloon diameter and pressure that can break the stent-strut. This information would be useful when we implant an additional stent through a stent-strut.

Coronary Stent Strut Fractures: Classification, Prevalence and Clinical Associations

Introduction. The frequency, characteristics and clinical implications of Strut fractures (SFs) remain incompletely understood. Methods and results. A total of 185 (160 patients) newer-generation drug-eluting stents (DES) were imaged. SFs were found in 21 DES (11.4%) and were classified in four patterns: one single stacked strut (41%); two or more stacked struts (23%); deformation without gap (27%); transection (9%). In multivariable analysis, calcific and bifurcation lesions were associated with SF in DES (OR: 3.5 [1.1–11] and 4.0 [2.2–7.2], p < 0.05). Device eccentricity and asymmetry as well as optical coherence tomography (OCT) features of impaired strut healing were also associated with SF. The prevalence of fractures was similar in a set of 289 bioresorbable scaffolds (BRS). In a separate series of 20 device thromboses and 36 device restenoses, the prevalence of SF was higher (61.2% of DES and 66.7% of BRS, p < 0.001 for both), with a higher frequency of complex SF patterns (p < 0.0001). In logistic regression analysis, fractures were a correlate of device complications (p < 0.0001, OR = 24.9 [5.6–111] for DES and OR = 6.0 [1.8–20] for BRS). Discussion. The prevalence of OCT-diagnosed SF was unexpectedly high in the setting of elective controls and it increased by about three-fold in the setting of device failure. Fractures were associated with increased lesion complexity and device asymmetry/eccentricity and were more frequent in the setting of device failure such as restenosis and thrombosis.

Influence of dual antiplatelet therapy duration on neointimal condition after second-generation drug-eluting stent implantation

Guidelines recommend shorter duration (1–12 months) for dual antiplatelet therapy (DAPT) in the second-generation drug-eluting stent (DES) era. However, whether shorter DAPT duration affects stent strut conditions and neointimal characteristics at mid-term follow-up remains uncertain. Therefore, we studied the relation between DAPT duration and vascular healing response as assessed by optical coherence tomography (OCT). This study was retrospective observational study. Participants comprised 64 patients who underwent serial OCT at both 9 and 18 months after DES implantation. All patients received DAPT until the 9-month follow-up then were divided into two groups: 49 patients who continued DAPT (longer DAPT group); and 15 patients who stopped taking the P2Y12 inhibitor and were treated with aspirin alone (shorter DAPT group) at the 18-month follow-up. Using OCT, we evaluated and compared stent strut conditions and neointimal characteristics between groups at both 9 and 18 months after stent implantation. Baseline clinical and procedural parameters were mostly similar between groups. At the 18-month follow-up, no in-stent thrombus assessed by OCT was observed in either group. No significant differences in OCT characteristics or measurements of neointima were seen between groups at 9- or 18-month follow-ups. Neointimal volume increased from 9 to 18 months in both groups, with a similar degree of neointimal proliferation in both groups (shorter DAPT group, 0.23 ± 0.29 mm3/mm; longer DAPT group, 0.19 ± 0.27 mm3/mm; P = 0.56). In conclusion, interrupting DAPT 9 months after second-generation DES implantation did not affect the development of in-stent thrombus, neointimal proliferation or stent strut coverage at 18-month follow-up compared with continuing DAPT.

Computer Simulation of Platelet Adhesion around Stent Struts in the Presence and Absence of Tissue Defects around Them

Aim. To predict platelet accumulation around stent struts in the presence or absence of tissue defects around them. Methods. Computer simulations were performed using virtual platelets implementing the function of the three membrane proteins: glycoprotein (GP) Ibα, GPIIb/IIIa, and GPVI. These platelets were perfused around the stent struts implanted into the vessel wall in the presence or absence of tissue defects around them using within the simulation platform. The number of platelets that adhered around stent struts was calculated by solving the blood flow using Navier–Stokes equation along with the adhesion of membrane protein modeled within the platform. Results. Platelet accumulation around stent struts occurred mostly at the downstream region of the stent strut array. The majority of platelets adhered at the downstream of the first bend regardless of the tissue defect status. Platelet adhesion around stent struts occurred more rapidly in the presence of tissue defects. Conclusion. Computer simulation using virtual platelets suggested a higher rate of platelet adhesion in the presence of tissue defects around stent struts.

3D Reconstruction of Coronary Artery Stents From Optical Coherence Tomography: Experimental Validation and Clinical Feasibility

The structural morphology of stents (e.g. expansion, lumen scaffolding, strut apposition, tissue protrusion, side branch jailing, strut fracture), and the local hemodynamic environment after stent deployment in coronary arteries are key determinants of procedural success and subsequent clinical outcomes. High-resolution intracoronary imaging has the potential to enable the geometrically correct 3D reconstruction of coronary stents. The aim of this work was to present a novel algorithm for 3D stent reconstruction of coronary artery stents by OCT and angiography, and test experimentally its accuracy, reproducibility, clinical feasibility and ability to perform CFD studies. Our method has the following steps: 3D lumen reconstruction by OCT and angiography, stent strut segmentation on OCT images, packaging, rotation and straightening of the segmented struts, and planar unrolling of the segmented struts, planar stent wireframe reconstruction, rolling back of the planar stent wireframe to the 3D reconstructed lumen, and stent volume reconstruction. We tested the accuracy and reproducibility of our method in stented patient-specific silicone models using micro computed tomography and stereoscopy as reference. The clinical feasibility and CFD studies were performed in clinically stented coronary bifurcations. Our experimental and clinical studies showed that our proposed algorithm can reproduce the complex stent configuration in space with high precision and reproducibility. Furthermore, our studies showed that the algorithm is feasible in clinical cases with stents deployed in diseased, bifurcated coronary arteries, enabling CFD studies to assess the hemodynamic environment. Notably, the high accuracy of our algorithm was consistent across different stent designs and diameters. Our method coupled with patient-specific CFD studies can facilitate stenting optimization, training in stenting techniques, and stent research and development.

Safety study of malapposition of the bio-corrodible nitrided iron stent in vivo

To evaluate the safety of stent malapposition of corrodible nitride iron stent as biodegradable cardiovascular implants, a total of 108 stents were implanted into the abdominal aortas, iliac arteries, and iliac artery bifurcations of 36 New Zealand white rabbits separately. Each rabbit was implanted with three stents. After a follow-up period of 3 months, no thrombus and embolism were found in local and downstream vessels. And no other adverse events occurred either. Stent strut covered by endothelial layer started to show signs of degradation, while struts exposed to bifurcated blood flow covered by a layer of tissue and no rust particle was found on the surface. Also, there were no traces of thrombosis and traces of excess inflammation. The authors conclude that the risk brought by stent malapposition in less than 9 months is acceptable.