Evaluation of a newly designed flow diverter for the treatment of intracranial aneurysms in an elastase-induced aneurysm model, in New Zealand white rabbits

Silk + flow-diverter stent for the treatment of intracranial aneurysms associated with balloon angioplasty: A retrospective study

Background

The silk + flow-diverter stent is increasingly used to treat complex intracranial aneurysms including wide-neck and fusiform aneurysms. Balloon angioplasty has been used to better appose the flow diverter (FD) to the vessel wall and, thus, improve aneurysm occlusion rates and decrease periprocedural complications. Sparse data are available concerning the results of this technique. We report our experience with silk + FD associated with balloon angioplasty for the treatment of intracranial aneurysms.

Methods

A retrospective study was conducted on all patients treated by the silk + FD. Clinical charts, procedural data, and angiographic results were reviewed and compared between those treated with balloon angioplasty. A multivariate analysis was conducted to identify predictors of complications, occlusion, and outcome.

Results

Between July 2014 and May 2016, we identified 209 patients with 223 intracranial aneurysms. There were 176 (84.2%) women and 33 (15.8%) men. The most common stent size used was 4.5 mm in 101 patients (46.1%), followed by 4 mm in 57 patients (26%). Univariate analysis observed that stent diameter was significantly related to aneurysm occlusion (P < 0.05). Patients with more than 1 aneurysm treated with silk + stent have a 9.07 times greater chance of having complications in the procedure than patients with only 01 aneurysm (OR = 9.07; P = 0.0008). Patients who had angioplasty without the use of a balloon have a 13.69-times-higher risk of complications (OR = 13.69; P = 0.0003). Older age, larger aneurysms, and the use of more than 1 FD device were predictors of recanalization.

Conclusion

Endovascular treatment of intracranial aneurysms with the silk + FD associated with balloon angioplasty is a safe and effective therapeutic option. Balloon angioplasty in combination with FD lowers the risk of complications. Higher complication rates and worse outcomes are associated with older age and large aneurysms.

Imaging of intracranial aneurysms in animals: a systematic review of modalities

Intracranial aneurysm (IA) animal models are paramount to study IA pathophysiology and to test new endovascular treatments. A number of in vivo imaging modalities are available to characterize IAs at different stages of development in these animal models. This review describes existing in vivo imaging techniques used so far to visualize IAs in animal models. We systematically searched for studies containing in vivo imaging of induced IAs in animal models in PubMed and SPIE Digital library databases between 1 January 1945 and 13 July 2022. A total of 170 studies were retrieved and reviewed in detail, and information on the IA animal model, the objective of the study, and the imaging modality used was collected. A variety of methods to surgically construct or endogenously induce IAs in animals were identified, and 88% of the reviewed studies used surgical methods. The large majority of IA imaging in animals was performed for 4 reasons: basic research for IA models, testing of new IA treatment modalities, research on IA in vivo imaging of IAs, and research on IA pathophysiology. Six different imaging techniques were identified: conventional catheter angiography, computed tomography angiography, magnetic resonance angiography, hemodynamic imaging, optical coherence tomography, and fluorescence imaging. This review presents and discusses the advantages and disadvantages of all in vivo IA imaging techniques used in animal models to help future IA studies finding the most appropriate IA imaging modality and animal model to answer their research question.

An Effective and Simple Way to Establish Elastase-Induced Middle Carotid Artery Fusiform Aneurysms in Rabbits

Objective

Elastase-induced aneurysms in rabbits have been proposed as a preclinical tool for device development, but there is still much deficiency in those aneurismal models. So we need to explore the efficient and convenient animal models for the investigation of intracranial aneurysms. Then, we compared and analyzed three methods of elastase-induced carotid artery aneurysms in rabbits and aimed to find a simple, effective, and reproducible method for creating elastase-induced aneurysms.

Methods

42 standard feeding male adult Japanese white rabbits (3.05 ± 0.65 kg) were randomly divided into 3 groups and treated with elastase ablation to create common carotid artery (RCCA) aneurysm models: Group A (root-RCCA medication group, n = 12), Group B (mid-RCCA medication group, n = 18), and Group C (ligated RCCA+medication group, n = 12). For Group A, the origin of the RCCA was blocked by two temporary aneurysm clips, and the resulting 2 cm cavity was infused with elastase for 20 min, then the clip was removed and the RCCA was not ligated. For Group B, the middle part of RCCA was treated the same way as Group A and the RCCA was not ligated. For Group C, the middle part of RCCA was treated as Group B, but the distal RCCA was ligated. After the aneurysm models were created for 3 weeks, prior to sacrificing the animals, color Doppler ultrasound and angiography were performed for blood flow measurements inside the aneurysms. Histological analysis (such as SMA-α, CD31, CD34, CD68, collagen IV, and Ki67) and the other relevant indexes were compared between the ideal model's aneurysmal tissues and the human intracranial aneurysm's tissues to confirm whether we have successfully established elastase-induced aneurysm models.

Results

Compared with human intracranial aneurysm specimens by the color Doppler ultrasound, angiography, and changes in the inner diameter of arteries, all three methods have successfully established the elastase-induced aneurysm models. Histology showed that biological responses were similar to both human cerebral aneurysms and previously published elastase-induced rabbit aneurysm models. Group A and Group B had the same morphology, but Group A had a higher mortality rate than Group B. Group B and Group C had different morphology. The aneurysm of Group C was more similar to human cerebral aneurysms but had a higher mortality rate than Group B. Group B was confirmed not only as an alternative method but also as a more safe and effective method for creating elastase-induced aneurysm models.

Conclusion

Through analysis and comparison, the Group B is proven to be the simplest, reproducible, and most effective modeling method. The aneurysm model established by Group B can be used for basic research related to aneurysm mechanism. We have provided a new and effective method for basic research on aneurysm.

Intravenous versus intra-arterial digital subtraction angiography: Occlusion rate and complication assessment of experimental aneurysms after flow diverter treatment in rabbits

PURPOSE

Conventional intra-arterial digital subtraction angiography, which requires surgical exposure and ligation of the femoral or carotid artery, is a limited method of evaluating elastase-induced aneurysms in New Zealand white rabbits. The purpose of this study was to assess aneurysm morphology, occlusion rates and complications after flow diverter treatment comparing intravenous and intra-arterial digital subtraction angiography.

METHODS

We previously published a preclinical study in which we evaluated the occlusion rates of elastase-induced aneurysms after treatment with a prototype flow diverter, by using intra-arterial digital subtraction angiography at three months ( n = 9) and six months ( n = 9). In addition to that intravenous digital subtraction angiography before treatment, after one month (early follow-up group) and after three months (late follow-up group) was performed. Occlusion rates were compared within the two groups by means of residual contrast filling.

RESULTS

Baseline aneurysm characteristics revealed no significant differences between intra-arterial digital subtraction angiography and intravenous digital subtraction angiography. Aneurysm occlusion rates in both follow-up groups using intravenous digital subtraction angiography were significantly higher compared to intra-arterial digital subtraction angiography (early follow-up group: intravenous digital subtraction angiography (one month) versus intra-arterial digital subtraction angiography (three months); p = 0.03 and late follow-up group: intravenous digital subtraction angiography (three months) versus intra-arterial digital subtraction angiography (six months); p = 0.04). Intravenous digital subtraction angiography is feasible to detect and reproduce device occlusions, in-stent stenosis and post-stent stenosis.

CONCLUSION

Intravenous digital subtraction angiography can not give a sufficient statement on the aneurysm occlusion process compared to intra-arterial digital subtraction angiography and is therefore not recommended for imaging follow-up after flow diverter treatment in rabbits. Regarding untreated aneurysms and complications like device occlusions, in-stent stenosis and post-stent stenosis intravenous digital subtraction angiography proofed to be a good alternative to intra-arterial digital subtraction angiography in our study.

Transient in-stent stenosis: a common finding after flow diverter implantation

Background and purpose

In recent years, implantation of flow diverters has emerged as an option for the endovascular treatment of intracranial aneurysms. One complication of treatment with flow diverters is the occurrence of in-stent stenosis, which has been reported to be partially reversible. The purpose of our study was to assess the incidence and dynamics of in-stent stenosis on angiographic short term and long term follow-up after treatment with flow diverters.

Methods

A retrospective review of our prospectively maintained database identified all patients with intracranial internal carotid artery (ICA) aneurysms treated by flow diverters at our institution between 2014 and 2017. Clinical charts, procedural data, and angiographic results were reviewed.

Results

18 patients were included. The mean short term follow-up was 92±19 days and mean long term follow-up was 449±120 days after treatment. No neurologic complications were observed. There was no procedure related mortality. Long term angiographic results showed complete occlusion in 83.3%, neck remnants in 11.1%, and incomplete occlusion in 5.5% of cases. In-stent stenosis was observed in all cases. Mean stenosis improved significantly from 30% on short term follow-up to 12% on long-term follow-up (P<0.0001).

Conclusion

In-stent stenosis is a common finding on short term follow-up after the treatment with flow diverters but improves over time.

Animal models of cardiovascular disease as test beds of bioengineered vascular grafts

The last two decades have seen many advances in regenerative medicine, including the development of tissue engineered vessels (TEVs) for replacement of damaged or diseased arteries or veins. Biomaterials from natural sources as well as synthetic polymeric materials have been employed in engineering vascular grafts. Recently, cell-free grafts have become available opening new possibilities for the next generation, off-the-shelf products. These TEVs are first tested in small or large animal models, which are usually young and healthy. However, the majority of patients in need of vascular grafts are elderly and suffer from comorbidities that may complicate their response to the implants. Therefore, it is important to evaluate TEVs in animal models of vascular disease in order to increase their predictive value and learn how the disease microenvironment may affect the patency and remodeling of vascular grafts. Small animals with various disease phenotypes are readily available due to the availability of transgenic or gene knockout technologies and can be used to address mechanistic questions related to vascular grafting. On the other hand, large animal models with similar anatomy, hematology and thrombotic responses to humans have been utilized in a preclinical setting. We propose that large animal models with certain pathologies or age range may provide more clinically relevant platforms for testing TEVs and facilitate the clinical translation of tissue engineering technologies by increasing the likelihood of success in clinical trials.

Degradation of elastic fiber and elevated elastase expression in long head of biceps tendinopathy

Tendinopathy of the long head of the biceps (TLHB) involves various types of extracellular matrix degeneration, but previous studies have not evaluated elastic fibers. The purpose of this study was to investigate elastic fiber distribution in long head of the biceps (LHB). The TLHB tendons of 16 consecutive patients (eight men and eight women; average age of 55.75 years; age range of 40-71 years) were transected and harvested. Three cadaveric LHB tendons were used as the control group. The expression of collagen type I was decreased, but type III was increased in TLHB. Disruption of elastic fibers was particularly observed in grade II specimens where the level of elastase-positive staining was significantly higher than in grade I specimens. Elastic fibers were not observed in the grade III area, implying a higher expression of elastase than in the grade I area. Results of Western blotting showed that the expression of elastin was higher in the control group and the levels of elastin significantly decreased in grades II and III of TLHB. Levels of osteopontin and elastase were increased in primary culture of human tenocytes after experiencing elastic derived peptide treatment. These results suggested that elastase may be caused by the disruption of elastic fibers in the development of chronic tendinopathy and that elastic derived peptide may enhance elastase and osteopontin expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1919-1926, 2017.

A Novel Flow Diverter (Tubridge) for the Treatment of Recurrent Aneurysms: A Single-Center Experience

Objective

The Tubridge flow diverter (FD) is a novel device aimed at reconstructing the parent artery and occluding complex aneurysms. Retreatment of recurrent aneurysms using the FD is challenging. We report our initial experience in the repair of aneurysm recurrence with the FD.

Materials and Methods

A database was reviewed prospectively, and 8 patients with 8 recurrent aneurysms (mean size, 16.7 mm) were identified. Four aneurysms had previously ruptured. The previous aneurysm treatment consisted of coiling in 1 aneurysm and single-stent-assisted coiling in 7 aneurysms. The procedural complications and clinical and angiographic outcomes were analyzed.

Results

Six aneurysms were treated by using a single Tubridge FD alone, while the remaining 2 were treated with FD + coiling. The immediate results of the 8 aneurysms were that they all showed incomplete occlusion. Neither major ischemic nor hemorrhagic complications occurred; however, 1 patient experienced a vasospasm. Follow-up angiographies were available for 7 aneurysms; the mean follow-up was 16.9 months (7–36 months). Five aneurysms were completely occluded, whereas 2 had a residual neck. Severe asymptomatic stenosis of 1 parent artery of a vertebral artery dissecting aneurysm was found. All visible branches covered by the FD were patent. All patients were clinically assessed as having attained a favorable outcome (modified Rankin Scale score ≤ 2) at discharge and follow-up.

Conclusion

In selected patients, the Tubridge FD can provide a safe and efficient option for the retreatment of recurrent aneurysms. Nevertheless, attention should be paid to several technical points.

Peritendinous elastase treatment induces tendon degeneration in rats: A potential model of tendinopathy in vivo

The purpose of this study was to investigate the role of elastase on tendinopathy, as well as to evaluate the potential for peritendinous injections of elastase into rats to cause tendinopathy. We first investigated the expression of elastase in the tendons of patients with tendinopathy, and then established the effects of elastase injection on the Achilles tendons of rats. Ultrasonographic and incapacitance testing was used to conduct tests for 8 weeks. Tendon tissues were collected for histological observation and protein levels of collagen type I and type III were detected using Western blotting. The percentage of elastase-positive cells increased in human specimens with grades II and III tendinopathy. The rat model demonstrated that the thickness of the tendon increased after elastase injection during Week 2-8. Hypercellularity and focal lesions were detected after Week 2. The expression of elastase was increased and elastin was decreased in Week 8. Collagen type I expression was decreased, but type III was increased in Week 4. These results suggested that elastase may be involved in the development of chronic tendinopathy, and that peritendinous injection of elastase may result in tendinopathy in rats.

Preclinical Testing of a Novel Thin Film Nitinol Flow-Diversion Stent in a Rabbit Elastase Aneurysm Model

BACKGROUND AND PURPOSE

Thin film nitinol can be processed to produce a thin microporous sheet with a low percentage of metal coverage (<20%) and high pore attenuation (∼70 pores/mm(2)) for flow diversion. We present in vivo results from the treatment of experimental rabbit aneurysms by using a thin film nitinol-based flow-diversion device.

MATERIALS AND METHODS

Nineteen aneurysms in the rabbit elastase aneurysm model were treated with a single thin film nitinol flow diverter. Devices were also placed over 17 lumbar arteries to model perianeurysmal branch arteries of the intracranial circulation. Angiography was performed at 2 weeks (n = 7), 1 month (n = 8), and 3 months (n = 4) immediately before sacrifice. Aneurysm occlusion was graded on a 3-point scale (grade I, complete occlusion; grade II, near-complete occlusion; grade III, incomplete occlusion). Toluidine blue staining was used for histologic evaluation. En face CD31 immunofluorescent staining was performed to quantify neck endothelialization.

RESULTS

Markedly reduced intra-aneurysmal flow was observed on angiography immediately after device placement in all aneurysms. Grade I or II occlusion was noted in 4 (57%) aneurysms at 2-week, in 6 (75%) aneurysms at 4-week, and in 3 (75%) aneurysms at 12-week follow-up. All 17 lumbar arteries were patent. CD31 staining showed that 75% ± 16% of the aneurysm neck region was endothelialized. Histopathology demonstrated incorporation of the thin film nitinol flow diverter into the vessel wall and no evidence of excessive neointimal hyperplasia.

CONCLUSIONS

In this rabbit model, the thin film nitinol flow diverter achieved high rates of aneurysm occlusion and promoted tissue in-growth and aneurysm neck healing, even early after implantation.

In Vitro Evaluation of Intra-Aneurysmal, Flow-Diverter-Induced Thrombus Formation: A Feasibility Study

BACKGROUND AND PURPOSE

Intracranial aneurysm treatment by flow diverters aims at triggering intra-aneurysmal thrombosis. By combining in vitro blood experiments with particle imaging velocimetry measurements, we investigated the time-resolved thrombus formation triggered by flow diverters.

MATERIALS AND METHODS

Two test setups were built, 1 for particle imaging velocimetry and 1 for blood experiments, both generating the same pulsatile flow and including a silicone aneurysm model. Tests without flow diverters and with 2 different flow-diverter sizes (diameter: 4.5 and 4.0 mm) were performed. In the blood experiments, the intra-aneurysmal flow was monitored by using Doppler sonography. The experiments were stopped at 3 different changes of the spatial extent of the signal.

RESULTS

No thrombus was detected in the aneurysm model without the flow diverter. Otherwise, thrombi were observed in all aneurysm models with flow diverters. The thrombi grew from the proximal side of the aneurysm neck with fibrin threads connected to the flow diverter and extending across the aneurysm. The thrombus resulting from the 4.0-mm flow diverter grew along the aneurysm wall as a solid and organized thrombus, which correlates with the slower velocities near the wall detected by particle imaging velocimetry. The thrombus that evolved by using the 4.5-mm flow diverter showed no identifiable growing direction. The entire thrombus presumably resulted from stagnation of blood and correlates with the central vortex detected by particle imaging velocimetry.

CONCLUSIONS

We showed the feasibility of in vitro investigation of time-resolved thrombus formation in the presence of flow diverters.

Increasing the visibility of thin NITINOL vascular implants

New implants for vascular therapy like flow diverters are made of tiny braided wires. The radio opacity of these wires is poor, which makes assessment of implant expansion and exact positioning difficult. Additional markers only allow the estimation of the current device position, but they also induce artefacts that impair the assessment during the intervention and in follow-up examination. A new strategy to increase implant visibility is the braiding of composite wires with a radiopaque core along the whole implant. This paper shows some useful combinations of these new wires on a phantom study with five vascular implants.

Urgent off-label use of the pipeline flow diverter stent in selected ischemic cerebrovascular conditions: thrombotic segments and tortuous arteries

OBJECTIVE

Flow diverter stents were originally designed for the endovascular management of certain types of cerebral aneurysms; however, these devices present characteristics that make them more suitable that regular carotid stents or neurostents for the management of selected ischemic cerebrovascular conditions.

METHODS

Eight patients with steno-occlusive disease of the internal carotid (ICA) or vertebral (VA) arteries underwent endovascular reconstruction by means of flow diverter stent implant at our center. Five patients presented with ICA steno-occlusive lesions that involved tortuous segments not amenable to regular carotid stent placement and three patients presented with severe and complex proximal VA dissections.

RESULTS

In all cases the procedures were considered technically successful. Flow diverter stent implant allowed recanalization of the treated vessels (stenosis of 89±10.5% was improved to 26±13%) without procedure related complications. At the 3 month clinical and radiological follow-up, patients either improved or remained stable, and showed stent patency. One patient presented with asymptomatic occlusion of the revascularized artery at 13 months, emphasizing the need for prolonged antiplatelet therapy.

CONCLUSIONS

This preliminary series of patients with high risk steno-occlusive lesions affecting tortuous arterial segments or presenting with heavy thrombotic load managed by the implant of flow diverter stents shows that this approach is feasible, safe, and effective in achieving arterial recanalization. Further studies will elucidate the role of this technique in ischemic cerebrovascular settings.