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Simplified schematic of the therapeutic mechanism of flow diversion treatment for aneurysms. (a) An aneurysm is (b) treated by implantation of a flow diverter, which reduces flow activity within the aneurysm and (c) promotes clot formation within the aneurysm over hours to days; concurrently, a new arterial lining, called neointima, starts growing over the device. (d) Over weeks to months, the vessel remodels itself by resorbing the aneurysm along with completion of neointimal coverage of the device. While the aneurysm which is essentially a " dead-end " clots off, the natural pressure gradient maintains blood flow through side branches covered by the mesh.
Source publication
Cerebral aneurysms are pathological focal evaginations of the arterial wall at and around the junctions of the circle of Willis. Their tenuous walls predispose aneurysms to leak or rupture leading to hemorrhagic strokes with high morbidity and mortality rates. The endovascular treatment of cerebral aneurysms currently includes the implantation of f...
Contexts in source publication
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... go through the fine mesh and are trapped inside the aneurysm, (c) the fine-mesh screen is paved over by a new arterial wall lining, and (d) the thrombosed aneurysm is resorbed by the body's wound healing mechanisms-the end result of which is a remodeled vessel returned to its normal physiological state. These events are schematically described in Fig. 1. While it is a relatively straightforward list, needless to mention, the actual interplay of the various processes involved is quite ...
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... porosity and/or maximizing pore density need to be balanced against practical considerations such as additional metal-to-artery burden resulting in in-stent thrombosis, increased device stiffness resulting in difficulties with navigating tortuous vessels, as well as coverage of side-branch ostia resulting in perforator occlusions. As shown in Fig. 1, the physiological pressure gradient across perforators jailed by flow diverters maintains the flow through these side branches, and the rate of perforator infarction is thus only about 3% [43]. This is also supported by the results from the flow studies that have eval- uated the flow through side branches [7,18,[44][45][46]; at ...
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... in many other in silico studies, a literature-derived inflow waveform was used as the inlet boundary condition for the model used here. The CFD simulations of devices placed in patient- derived geometries (as shown in Fig. 10) will preferably incorpo- rate the pressure and flow waveforms obtained in the same subject. Other conditions that can help improve the accuracy of the calculated results include fluid-structure interactions, which incorporate the compliance of the blood vessels in addition to the resistance of the distal capillary ...
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... flow-related parameters that can predict the long-term aneurysm occlusion after flow diversion. If successful, such studies could facilitate optimal device selection prior to treatment, and companion clinical angiographic studies could help guide the treatment by assessing the device efficacy in near-real time during the procedure. For example, Fig. 10 shows the device-induced flow alterations in two right carotid aneur- ysms; the aneurysm with the 99% kinetic energy (KE) reduction was completely occluded at 6 months follow-up, while the one with 52% KE reduction still had residual filling at 6 months follow-up. The sample sizes are, again, sparse but both in vivo [22,23,32,63] and ...
Citations
... 5 Aneurysm occlusion also depends highly on the device surface area and porosity, and thus, it is not possible to reduce device surface area without adversely affecting flow diversion properties. 6 To suppress the propensity of intrastent thrombus formation, patients must undergo dual antiplatelet treatment before and after flow diverter procedures to reduce the risk for thromboembolic events, which can in turn create a separate risk for hemorrhagic complications. 5 To address this problem, surface treatments and coating technologies have been developed to improve device thromboresistance with the aim of limiting intrastent thrombus formation and potentially reducing dependence on antiplatelet drugs. ...
Background
Surface modification of flow-diverting stents has been explored to reduce thrombus-related complications that may arise under clinical use. This study investigated the thromboresistant properties of the flow redirection endoluminal device (FRED) X, a flow diverter treated with a copolymer of poly(2-methoxyethyl acrylate) (PMEA; X Technology).
Methods
The performance of FRED, FRED X, and Pipeline Flex with Shield Technology (sPED) was evaluated in an in vitro blood loop model. Blood activation level was assessed by the concentration of thrombin-antithrombin complex (TAT), β-thromboglobulin (β-TG), and platelet count, and qualitatively by scanning electron microscopy (SEM). Cellular adhesion characteristics were measured using human aortic endothelial cells that were seeded on flat sheets mimicking the surface of FRED, FRED X, and sPED, and evaluated with fluorescence microscopy. Statistical comparisons were conducted using one-way analysis of variance (ANOVA) with Tukey post hoc tests.
Results
FRED X, sPED, and control blood loops showed significantly reduced blood activation levels (TAT and β-TG) compared with FRED (p<0.01). Consequently, FRED showed a significant decrease in platelet count compared with FRED X, sPED, and control loops (p<0.01). SEM imaging showed the lowest accumulation of blood cell-like deposits on FRED X compared with sPED and FRED, while FRED had the highest accumulation. Endothelial cells adhered and were widely spread on X Technology-treated sheets, while minimal cell adhesion was observed on phosphorylcholine-treated sheets.
Conclusion
The X Technology surface modification of FRED X demonstrated superior thromboresistant properties over untreated FRED while maintaining comparable cellular adhesion. Taken together, these properties may help mitigate material-related thromboembolic complications.
... A smoother surface reduces the chance of vessel injuries during the deployment or repositioning of the FDS after deployment. The porosity and pore density of the developed FDS are comparable to the current laser-cut and braided neurovascular flow diverters [48]. The bending deflection rate increased with the applied load increase. ...
The flow diverting stent (FDS) has become a promising endovascular device for the treatment of aneurysms. This research presents a novel biodegradable and non-braided Polycaprolactone (PCL) FDS. The PCL FDS was designed and developed using an in-house fabrication unit and coated on two ends with BaSO4 for angiographic visibility. The mechanical flexibility and quality of FDS surfaces were examined with the UniVert testing machine, scanning electron microscope (SEM), and 3D profilometer. Human umbilical vein endothelial cell (HUVEC) adhesion, proliferation, and cell morphology studies on PCL FDS were performed. The cytotoxicity and NO production by HUVECs with PCL FDS were also conducted. The longitudinal tensile, radial, and bending flexibility were found to be 1.20 ± 0.19 N/mm, 0.56 ± 0.11 N/mm, and 0.34 ± 0.03 N/mm, respectively. The FDS was returned to the original shape and diameter after repeated compression and bending without compromising mechanical integrity. Results also showed that the proliferation and adhesion of HUVECs on the FDS surface increased over time compared to control without FDS. Lactate dehydrogenase (LDH) release and NO production showed that PCL FDS were non-toxic and satisfactory. Cell morphology studies showed that HUVECs were elongated to cover the FD surface and developed an endothelial monolayer. This study is a step forward toward the development and clinical use of biodegradable flow diverting stents for endovascular treatment of the aneurysm.
... 5,6 Although the braided design of flow-diverting stents promotes excellent vessel wall apposition, this same design feature allows for localized geometric distortion of the stent that is influenced by the recipient artery geometry and may compromise aneurysm occlusion. 7,8 Multiple treatment strategies have been devised to overcome the effects of localized geometric stent distortion and increase aneurysm occlusion rates following endoluminal flow diversion. 9,10 One such strategy includes the deployment of multiple overlapping flowdiverting stents at the time of initial aneurysm treatment to effectively decrease stent wall porosity and increase metal coverage across an aneurysm neck. ...
BACKGROUND
The purpose of this study is to evaluate the impact multiple overlapping flow‐diverting stents have on aneurysm occlusion rates and iatrogenic complications relative to single flow‐diverting stents.
METHODS
A retrospective review of a multicenter aneurysm database from 2012 to 2020 was performed to identify saccular aneurysms treated initially with single and multiple flow‐diverting stents with ≥12‐month angiographic and clinical follow‐up. Aneurysm occlusion rates as a function of stent number served as a primary outcome measure with iatrogenic complications serving as a secondary outcome measure.
RESULTS
A total of 250 patients were initially treated with a single Pipeline embolization device (PED), and 48 patients were initially treated with multiple PEDs. There was no significant difference in aneurysm size, morphology, or dual‐antiplatelet therapy regimen used between groups. There was no significant difference in the aneurysm occlusion (single, 83.6%, versus multiple, 83.4%; P =0.65) or retreatment rates (single, 8.0%, versus multiple, 10.4%; P =0.58) between groups. There was no significant difference in the number of procedure‐related complications between groups (single, 8.0%, versus multiple, 4.2%; P =0.42), with 0.8% of patients treated with a single PED and 2.1% of patients treated with multiple PEDs experiencing a procedure‐related ischemic stroke.
CONCLUSIONS
There is no significant difference in overall aneurysm occlusion rates between aneurysms treated initially with single versus multiple overlapping PEDs nor are there significant differences in procedure‐related complications. Single PED flow diversion may be preferred whenever possible, with multiple PED constructs reserved for extenuating clinical circumstances as may be encountered with giant aneurysms.
... The post-treatment hemodynamic parameters, including time-averaged inflow rate, aneurysm-averaged velocity, wall shear stress, total absolute circulation, and turnover time (the aneurysm sac volume divided by the inflow rate at the neck plane), are provided using computational fluid dynamics analysis [9]. The flow-related parameters are used to anticipate the flow diverter performance in aneurysm occlusion, and this information helps clinicians to select the optimal devices before treatment [10]. ...
... In addition to the appropriate selection of pore size and density, the device positioning against the parent artery wall remains vital. The dependency of aneurysm occlusion on the space or gap between the flow diverter and the parent artery has been considered using CFD investigations, and the results demonstrate that even a small gap causes the aneurysm to be blocked incomplete and remain permeable longer because of the jet-like blood flow through the gap into the aneurysm sac [10,16,17]. ...
Virtual reality (VR) has the potential to be a powerful tool for the visualization of simulated blood flow in cerebral aneurysms. This paper presents our study aimed at developing the VR visualization of computational fluid dynamics (CFD) simulations of cerebral aneurysms treated with flow-diverting (FD) stents. First, a spherical sidewall aneurysm located at a simplified internal carotid artery was considered for investigating the impact of stent deployment and positioning on the corresponding spatially time-varying blood flow behavior. The three-dimensional unsteady blood flow over a cardiac cycle was simulated numerically using the finite volume method, and the distributions of hemodynamic parameters inside the aneurysm sac, and on its wall, were presented with and without stent cases. Two stent positions, with and without a gap between the artery wall and stent, were considered to show the influence of correct stent position on aneurysm treatment. Second, a straightforward workflow was developed to import, process, and visualize the CFD analysis data in a VR environment by using open-source software with a high resolution. The Unity3D engine was used for displaying the processed animations in a VR environment operated on a head-mounted display (HMD). The refining process of each frame of time-varying CFD data was automated. The animated flow elements rendered in the VR environment were velocity vectors, velocity contours, streamlines, particle traces, and point clouds. CFD results showed that proper stenting facilitates thrombosis and occlusion of the aneurysm by modification of the flow patterns, which leads to lower inflow jet velocities into the aneurysm, longer turnover time, lower aneurysm-averaged kinetic energy, and lower wall shear stress. Additionally, the results indicated that a gap between the stent and the parent artery may lead to undesirable hemodynamic alterations. The VR visualization illustrated that the recognition of the potential in danger regions of aneurysms and the evaluation of the performance of FD stents in aneurysm treatment can be conducted without the need for several slices through the parent artery and aneurysm, as is required for traditional postprocessing methods. Through VR visualization, the details of the simulation results become readily available by navigating in the 3D animated flow elements using a high-degree-of-freedom headset.
... Three-dimensional models of the aneurysm and stents were constructed using CATIA computer-aided design software (V5-6R2012; Dassault Systèmes, Paris, France). A stent was constructed only at the aneurysm neck to improve the efficiency of the CFD analysis (23). An element of size 0.2 mm was used for the aneurysm, and an element of size 0.005 mm was generated near the location where the stent was deployed. ...
Purpose: The flow diversion effect of an intracranial stent is closely related to its metal coverage rate (MCR). In this study, the flow diversion effects of Enterprise and low-profile visualized intraluminal support (LVIS) stents are compared with those of a Pipeline flow diverter, focusing on the MCR change. Moreover, the changes in the flow diversion effect caused by the additional manipulations of overlapping and compaction are verified using computational fluid dynamics (CFD) analysis.
Methods: CFD analysis was performed using virtually generated stents mounted in an idealized aneurysm model. First, the flow diversion effects of single Enterprise, LVIS, and Pipeline devices were analyzed. The Enterprise and LVIS were sequentially overlapped and compared with a Pipeline, to evaluate the effect of stent overlapping. The effect of compacting a stent was evaluated by comparing the flow diversion effects of a single and two compacted LVIS with those of two overlapped, uncompacted LVIS and uncompacted and compacted Pipeline. Quantitative analysis was performed to evaluate the hemodynamic parameters of energy loss, average velocity, and inflow rate.
Results: Statistically significant correlations were observed between the reduction rates of the hemodynamic parameters and MCR. The single LVIS without compaction induced a reduction in all the hemodynamic parameters comparable to those of the three overlapped Enterprise. Moreover, the two overlapped, uncompacted LVIS showed a flow diversion effect as large as that induced by the single uncompacted Pipeline. Compacted stents induced a better flow diversion effect than uncompacted stents. The single compacted LVIS induced a flow diversion effect similar to that induced by the two uncompacted LVIS or single uncompacted Pipeline.
Conclusions: The MCR of a stent correlates with its flow diversion effect. Overlapping and compaction can increase the MCR of an intracranial stent and achieve a flow diversion effect as large as that observed with a flow diverter.
... The mechanism by which a flow diverter redirects blood flow from the aneurysm to the main blood vessel is as follows: (1) the installation of fine webs at the neck of the aneurysm can reduce the velocity of blood flow to the defect site; (2) slow blood flow can encourage clot formation in the aneurysm because platelets are activated as they pass through the fine webs of the diverter and then become trapped in the aneurysm; (3) the fine webs of the diverter are eventually covered with a new artery wall layer; (4) the thrombotic aneurysm is reabsorbed over the course of wound healing, then the repaired vessel returns to its normal physiological state. 13 Recent evidence shows that flow diverters could achieve better occlusion means compared with coiling and have fewer neurological complications and lower risk of death. 3 Previous studies revealed that flow diverters have higher occlusion rates of up to 64% within 6 months and 94% within 3 years post-implantation compared with coiling. ...
An unruptured aneurysm is often asymptomatic or present without neurological deficits, causing severe morbidity. However, the potential of this defect to rupture requires proper management. Herein, we report a case of an unruptured saccular aneurysm of the ophthalmic artery with initial clinical seizures. The patient was treated by flow diversion which redirects the blood flow that normally leads to the protrusion of the aneurysm back to the main vessel. Flow diversion is chosen because it is less risky and has a faster recovery time than other treatment options, but it is more expensive than others. Although this technology is not new, there is no report on its implementation in Indonesia. The patient was prescribed antiplatelet treatment for at least 6 months post-treatment, then she showed no sign of seizure or new focal neurological deficits 4 months post-treatment. The patients were expected to undergo digital subtraction angiography evaluation 6 months after flow diversion treatment, but it has not been performed due to the coronavirus disease 2019 pandemic.
... Generally, endovascular stents approved by the FDA for intracranial applications with porosities ranging from 60 to 92% [7,9]. The stent design influences efficiency of the stent in decreasing the aneurysmal inflow [10]. Specific measurements of hemodynamic variations in an aneurysm because of the existence of FD stents have been performed mainly in vitro and/or through empirical studies over the past decades. ...
This study investigates the effect of stent thickness and stent porosity which are important factors determining the post-treatment intra-aneurysmal hemodynamics. The study uses computational fluid dynamics (CFD) to estimate the hemodynamic behaviour: flow velocity, pressure distributions, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), besides relative residence time (RRT) blood flow distribution in a proposed stent and three other commercially available stents. The hemodynamic behaviour is compared between four different cases. In each case, each stent has the specific thickness and porosity values. The results show that the velocity magnitude inside the sac declined in thinner stents and lower porosity stents, TAWSS on the aneurysmal wall declined linearly in lower porosity stents, OSI and RRT increased obviously in thicker stents and higher porosity stents. Finally, the results conclude that the stent with the lowest thickness and porosity has the best performance that leads to post-stent thrombus formation and healing. However, the proposed stent design, a more porous construct, has a higher RRT compared to the used commercially available stents, which helps promote the thrombus growth inside the aneurysm sac.
... and progressive thrombosis. 1 Neoendothelialization along the surface of the FDS occurs, which reconstructs the parent vessel. 2 The following FDS are currently approved for clinical use in Europe: Silk and Silk Vista Baby (Balt Extrusion), Pipeline Embolization Device (PED) (Medtronic), Surpass Streamline and Surpass Evolve (Stryker Neurovascular), Flow-Redirection Endoluminal Device (FRED) and FRED jr (MicroVention), Derivo (Acandis), and p64/p48MW (phenox). ...
BACKGROUND
Flow diverters have become an important tool in the treatment of intracranial aneurysms, especially when dealing with difficult-to-treat or complex aneurysms. The p64 is the only fully resheathable and mechanically detachable flow diverter available for clinical use.
OBJECTIVE
To evaluate the safety and effectiveness of p64 for the treatment of intracranial saccular unruptured aneurysms arising from the anterior circulation over a long-term follow-up period.
METHODS
We retrospectively reviewed our prospectively maintained database to identify all patients who underwent treatment for an intracranial saccular (unruptured or beyond the acute hemorrhage phase) aneurysm arising from the anterior circulation with ≥1 p64 between December 2011 and December 2019. Fusiform aneurysms and dissections were excluded. Aneurysms with prior or concomitant saccular treatment (eg, coiling and clipping) were included. Aneurysms with parent vessel implants other than p64 were excluded. Anatomic features, intraprocedural complications, clinical outcome, as well as clinical and angiographic follow-ups were all recorded.
RESULTS
In total, 530 patients (388 females; median age 55.9 yr) with 617 intracranial aneurysms met the inclusion criteria. The average number of devices used per aneurysm was 1.1 (range 1-3). Mean aneurysm dome size was 4.8 mm (range 1-27 mm). Treatment-related morbimortality was 2.4%. Early, mid-term, and long-term angiographic follow-up showed complete or near-complete aneurysm occlusion in 76.8%, 89.7%, and 94.5%, respectively.
CONCLUSION
Treatment of intracranial saccular unruptured aneurysms of the anterior circulation using p64 is a safe and effective treatment option with high rate of occlusion at long-term follow-up and low morbimortality.
... and progressive thrombosis. 1 Neoendothelialization along the surface of the FDS occurs, which reconstructs the parent vessel. 2 The following FDS are currently approved for clinical use in Europe: Silk and Silk Vista Baby (Balt Extrusion), Pipeline Embolization Device (PED) (Medtronic), Surpass Streamline and Surpass Evolve (Stryker Neurovascular), Flow-Redirection Endoluminal Device (FRED) and FRED jr (MicroVention), Derivo (Acandis), and p64/p48MW (phenox). ...
Abstract
Background: Flow diverters have become an important tool in the treatment of intracranial aneurysms, especially when dealing with difficult-to-treat or complex aneurysms. The p64 is the only fully resheathable and mechanically detachable flow diverter available for clinical use.
Objective: To evaluate the safety and effectiveness of p64 for the treatment of intracranial saccular unruptured aneurysms arising from the anterior circulation over a long-term follow-up period.
Methods: We retrospectively reviewed our prospectively maintained database to identify all patients who underwent treatment for an intracranial saccular (unruptured or beyond the acute hemorrhage phase) aneurysm arising from the anterior circulation with ≥1 p64 between December 2011 and December 2019. Fusiform aneurysms and dissections were excluded. Aneurysms with prior or concomitant saccular treatment (eg, coiling and clipping) were included. Aneurysms with parent vessel implants other than p64 were excluded. Anatomic features, intraprocedural complications, clinical outcome, as well as clinical and angiographic follow-ups were all recorded.
Results: In total, 530 patients (388 females; median age 55.9 yr) with 617 intracranial aneurysms met the inclusion criteria. The average number of devices used per aneurysm was 1.1 (range 1-3). Mean aneurysm dome size was 4.8 mm (range 1-27 mm). Treatment-related morbimortality was 2.4%. Early, mid-term, and long-term angiographic follow-up showed complete or near-complete aneurysm occlusion in 76.8%, 89.7%, and 94.5%, respectively.
Conclusion: Treatment of intracranial saccular unruptured aneurysms of the anterior circulation using p64 is a safe and effective treatment option with high rate of occlusion at long-term follow-up and low morbimortality.
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... Furthermore, the compression technique increases metal coverage by the LVIS at the aneurysm neck, which not only changes the hemodynamic characteristics of the aneurysm, but also provides a good platform for intimal growth and vascular wall repair, thereby reducing aneurysm recurrence. Finally, the higher degree of metal surface area coverage at the aneurysm neck provides a more robust flow diversion effect compared with the other available stents (25). These factors likely account for the very high levels of complete and adequate aneurysm occlusion observed in the present study. ...
Objective: To investigate the safety and efficacy of low-profile visualized intraluminal support (LVIS) stent-assisted coiling of intracranial tiny aneurysms using a “compressed” stent technique.
Methods: We retrospectively analyzed patients with tiny aneurysms treated in our hospital with LVIS devices using a compressed stent technique. We analyzed patients' imaging outcomes, clinical outcomes, and complications.
Results: Forty-two tiny aneurysms in 42 patients were included in this study cohort; 8 patients presented with subarachnoid hemorrhage at admission. The immediate postoperative complete embolization rate was 76.2% (32/42). After an average of 8.5 months of imaging follow-up, the complete embolization rate was 90.5% (38/42), and no aneurysm recanalization occurred. After an average of 24.4 months of clinical follow-up, 95.2% (40/42) of the patients achieved favorable clinical outcomes (modified Rankin scale = 0/1). Operation-related complications occurred in two patients (4.8%); one intraoperative acute thrombosis, and one significant unilateral decreased vision during the postoperative follow-up.
Conclusion: LVIS stent-assisted coiling of intracranial tiny aneurysms using a compressed stent technique is safe and effective. Combined stent compression technology is beneficial to maximize the complete embolization of aneurysms and reduce aneurysm recanalization. This study expands the clinical applicability of LVIS stents.
