The Trevo device: preclinical data of a novel stroke thrombectomy device in two different animal models of arterial thrombo-occlusive disease

New device multisegment Mechanical Thrombectomy System for endovascular treatment in acute ischaemic stroke: study protocol for a prospective, multicentre, randomised controlled trial

INTRODUCTION

Endovascular treatment is the standard of care for acute large vessel occlusion (LVO) in the anterior circulation. However, successful complete recanalisation is considerably difficult when the vessels are severely tortuous. At the bend, the stent retriever can distort, collapse and lose its ability to capture the clot due to structural change. The aim of the present study is to evaluate the safety and efficacy of the new thrombectomy device multisegment Mechanical Thrombectomy (MT) System for endovascular treatment of acute ischaemic stroke (AIS).

METHODS AND ANALYSIS

The present study is a prospective, multicentre, randomised controlled trial conducted in 11 stroke centres in China. The safety and efficacy of vascular recanalisation in patients with AIS who will be treated with a new thrombectomy device-multi-segment MT System or with Solitare FR within 8 hours of symptom onset will be compared. A total of 238 subjects who met the inclusion and exclusion criteria will be randomised into either a treatment group or a control group by an internet-based Central Random System in a 1:1 manner, and 30 subjects will be recruited into the small sample study. SAS V.9.4 statistical software will be used for statistical analysis of the primary endpoint indicators and other indicators.

ETHICS AND DISSEMINATION

The study involving human participants was reviewed and approved by the Ethics Committee of Drugs (devices) Clinical Experiment in Henan Provincial People's Hospital (reference number: AF/SC-07/04.0) and other research centres participating in the clinical trial. The results yielded from this study will be presented at international conferences and sent to a peer-review journal to be considered for publication. The Standard Protocol Items: Recommendations for Interventional Trials checklist was utilised when drafting the study protocol.

TRIAL REGISTRATION NUMBER

Registry on 10 September 2021 with Chinese clinical trial registry: ChiCTR2100051048.

In vivo evaluation of histopathologic findings of vascular damage after mechanical thrombectomy with the Tromba device in a canine model of cerebral infarction

A novel stent retriever device for in vivo mechanical thrombectomy for acute cerebral infarction has been developed. In this study, we compared the thrombus removal capacity, potential complications, and extent of vessel wall damage of this novel device with those of the Solitaire FR device by performing a histopathologic analysis using an autopsied canine model. Through this experimental evaluation, we aimed to assess the safety and efficacy of the newly developed thrombus removal device for cerebral infarction. Blood clots (autologous thrombus) were injected into 12 canines. Mechanical thrombectomy was performed in six canines using the newly developed Tromba thrombectomy device (experimental group) and in the other six canines using the Solitaire FR thrombectomy device (control group). Angiographic and histopathologic evaluations were performed 1 month after the blood vessels underwent mechanical thrombectomy. In the experimental group, the reperfusion patency was classified as "no narrowing" in five cases and "moderate narrowing (25%-50% stenosis)" in one case. In the control group, the reperfusion patency was classified as "no narrowing" in four cases, "moderate narrowing (25%-50% stenosis)" in one case, and "slight narrowing (less than 25% stenosis)" in one case. In the experimental group, intimal proliferation was observed in only two cases, endothelial loss was observed in two cases, and device-induced medial injury was observed in one case. In the control group, intimal proliferation was observed in two cases, endothelial loss was observed in one case, and thrombosis (fibrin/platelet) was observed in one case. The Tromba thrombectomy device showed no significant difference to the conventional Solitaire device in angiographic and histopathologic evaluations after thrombus removal. The stability and efficiency of the newly developed Tromba device are considered to be high and comparable to those of Solitaire.

Nonhuman Primate Models of Ischemic Stroke and Neurological Evaluation After Stroke

Nonhuman primates are closer to human beings than rodents in genetics, neuroanatomy, physiology and immunology. Nonhuman primates are therefore considered an ideal preclinical model to replicate various aspects of human stroke. Ischemia stroke models in nonhuman primates can better fit the physiological symptoms and changes in humans after cerebral ischemia. Currently, various construction methods and neurological evaluation methods have been developed and applied to stroke models of nonhuman primates, including craniectomy models, endovascular stroke models, autologous thrombus models and intraluminal filament models. Meanwhile, new innovative methods have emerged, such as the endothelin-1 model and photothrombosis model. In the past thirty years, these model studies have explored various mechanisms that are initiated in the first minutes, hours, and days after a stroke. Permanent and temporary middle cerebral artery occlusion models have been trying to simulate the complex situation of human stroke. However, a comprehensive comparison of the above methods, including their advantages and disadvantages, difficulty and application fields, is limited. Here, we introduce various modeling methods that are currently available for nonhuman primate stroke models, compare the differences between these different preparation methods, and analyze the advantages and disadvantages of the various methods and the fields of application. The imaging detection methods of nonhuman primates after cerebral ischemia and the neurological evaluation methods after stroke are also discussed briefly. Methods are sorted and compared so that scholars can choose appropriate modeling methods and evaluation methods to establish nonhuman primate stroke models.

The Jrecan Device: Preclinical Data of a Novel Thrombectomy Device in Acute Thromboembolism Model of Beagle Dogs

Objective

The aim of this study is to investigate the safety and efficiency of a Jrecan^® flow restoration system, a novel thrombectomy device, in an arterial thromboembolic occlusion model of Beagle dogs.

Methods

A total of 12 Beagle dogs with acute thromboembolism were randomized to receive mechanical thrombectomy with either Jrecan^® flow restoration device or Trevo^TM PROVUE Device (2:1). The efficacy and safety of the two devices, including recanalization rate, the presence of distal embolism, vasospasm, vessel perforation, and vessel injuries were evaluated through DSA and microscopic examination.

Result

A 100% recanalization rate (mTICI 2b/3) was achieved in both groups. Endothelial and subendothelial injuries occurred in all target vessels. Focal disruption of internal elastic lamina was observed in 4 cases. The mean vessel injury score of the Jrecan^® group was 1.16 ± 0.48, significantly lower than that of the Trevo^TM group (1.54 ± 0.8) (P < 0.001).

Conclusion

The Jrecan^® and Trevo^TM devices demonstrated an equally high recanalization rate in Beagle dogs with acute thromboembolism. However, histological findings revealed that the Jrecan^® stent seemed to be safer than the Trevo^TM device during clot retrieval, which might be related to a more appropriate radial force provided by the Jrecan^® stent that resulted from its wider cell design.

Stentrievers : An engineering review

The advent of endovascular therapy for acute large vessel occlusion has revolutionized stroke treatment. Timely access to endovascular therapy, and the ability to restore intracranial flow in a safe, efficient, and efficacious manner has been critical to the success of the thrombectomy procedure. The stentriever has been a mainstay of endovascular stroke therapy, and current guidelines recommend the usage of stentrievers in the treatment of large vessel occlusion stroke. Despite the success of existing stentrievers, there continues to be significant development in the field, with newer stentrievers attempting to improve on each of the three key aspects of the thrombectomy procedure. Here, we elucidate the technical requirements that a stentriever must fulfill. We then review the basic variables of stent design, including the raw material and its form, fabrication method, geometric configuration, and further additions. Lastly, a selection of stentrievers from successive generations are reviewed using these engineering parameters, and clinical data is presented. Further avenues of stentriever development and testing are also presented.

A new aspiration device equipped with a hydro-separator for acute ischemic stroke due to challenging soft and stiff clots

OBJECTIVE

Fragile soft clots and stiff clots remain challenging in the treatment of acute ischemic stroke. This study aims to investigate the impact of clot stiffness on the efficacy of thrombectomy devices and a new aspiration catheter with a hydro-separator.

METHODS

The Neurostar aspiration catheter has a novel hydro-separator technology that macerates clots by a stream of saline inside the catheter. The Neurostar catheter and two commercially available devices, the SOFIA aspiration catheter and Solitaire stent retriever, were tested in this study. We evaluated the efficacy of each device on clots with various stiffness in a simple in vitro model. We also assessed single-pass recanalization performance in challenging situations with large erythrocyte-rich clots and fibrin-rich clots in a realistic vascular model.

RESULTS

We observed an inverse association between the clot stiffness and recanalization rates. The aspiration catheter, SOFIA ingested soft clots but not moderately stiff clots. When removing soft clots with the stent retriever, fragmentation was observed, although relatively stiff clots were well-integrated and removed. The Neurostar ingested soft clots similar to the aspiration catheter, and also aspirated stiff clots by continuous suction with hydro-separator. In the experiments with challenging clots, the Neurostar led to significantly higher recanalization rates than the stent retriever and aspiration catheter.

CONCLUSIONS

The stiffness of the clots affected the efficacy of endovascular thrombectomy based on the type of device. The Neurostar catheter with hydro-separator resulted in better success rates than a commercially available aspiration catheter and stent retriever in this experimental model.

Preclinical modeling of mechanical thrombectomy

Mechanical thrombectomy to treat large vessel occlusions (LVO) causing a stroke is one of the most effective treatments in medicine, with a number needed to treat to improve clinical outcomes as low as 2.6. As the name implies, it is a mechanical solution to a blocked artery and modeling these mechanics preclinically for device design, regulatory clearance and high-fidelity physician training made clinical applications possible. In vitro simulation of LVO is extensively used to characterize device performance in representative vascular anatomies with physiologically accurate hemodynamics. Embolus analogues, validated against clots extracted from patients, provide a realistic simulated use experience. In vitro experimentation produces quantitative results such as particle analysis of distal emboli generated during the procedure, as well as pressure and flow throughout the experiment. Animal modeling, used mostly for regulatory review, allows estimation of device safety. Other than one recent development, nearly all animal modeling does not incorporate the desired target organ, the brain, but rather is performed in the extracranial circulation. Computational modeling of the procedure remains at the earliest stages but represents an enormous opportunity to rapidly characterize and iterate new thrombectomy concepts as well as optimize procedure workflow. No preclinical model is a perfect surrogate; however, models available can answer important questions during device development and have to date been successful in delivering efficacious and safe devices producing excellent clinical outcomes. This review reflects on the developments of preclinical modeling of mechanical thrombectomy with particular focus on clinical translation, as well as articulate existing gaps requiring additional research.

Comparing the efficacy and safety of the Skyflow device with those of the Solitaire FR stent in patients with acute ischemic stroke: a prospective, multicenter, randomized, non-inferiority clinical trial

BACKGROUND

Mechanical thrombectomy is the standard treatment for acute ischemic stroke (AIS) with large vessel occlusion (LVO) in the anterior circulation. This trial aimed to indicate whether Skyflow, a new thrombectomy device, could achieve the same safety and efficacy as Solitaire FR in the treatment of AIS.

METHODS

This study was a prospective, multicenter, randomized, single blind, parallel, positive controlled, non-inferiority clinical trial. Patients with intracranial anterior circulation LVO within 8 hours from onset were included to receive thrombectomy treatment with either the Skyflow or Solitaire FR stent retriever. The primary endpoint was the rate of successful reperfusion (modified Treatment In Cerebral Infarction (mTICI) ≥2b) after the operation. The safety endpoints were the rate of symptomatic intracranial hemorrhage (sICH) and subarachnoid hemorrhage (SAH) at 24 hours after operation.

RESULTS

A total of 95 and 97 patients were involved in the Skyflow group and Solitaire FR group, respectively. A successful reperfusion (mTICI ≥2b) was finally achieved in 84 (88.4%) patients in the Skyflow group and 80 (82.5%) patients in the Solitaire FR group. Skyflow was non-inferior to Solitaire FR in regard to the primary outcome, with the criterion of a non-inferiority margin of 12.5% (p=0.0002) after being adjusted for the combined center effect and the National Institutes of Health Stroke Scale (NIHSS) score. The rate of periprocedural sICH and SAH did not differ significantly between the two groups.

CONCLUSION

Endovascular thrombectomy with the Skyflow stent retriever was non-inferior to Solitaire FR with regard to successful reperfusion in AIS due to LVO (with a pre-specified non-inferiority margin of 12.5%).

Simulation of stent retriever thrombectomy in acute ischemic stroke by finite element analysis

Stent retriever thrombectomy has become an effective method for treating acute ischemic stroke. Successful recanalization cannot be achieved for all patients. The outcome of mechanical thrombectomy may be associated with some mechanical factors, requiring efficient tools that are able to assess the interaction between stent retrievers and clots. In this study, a simulation by finite element analysis was developed to evaluate the outcome of stent retriever thrombectomy for clots of different sizes and frictional properties. The deployment and retrieval of the stent retriever were conducted in a middle cerebral artery model. The recanalization, deformation of the clot and stent retriever and the stress induced in the clot were assessed. The results showed that higher friction could lead to failed recanalization and increased stress in the clot. The simulation method can be used to characterize the mechanical behaviour of stent retrievers and clots, offering a potential tool for the optimization of device design and the selection of surgical strategies.

Preclinical testing platforms for mechanical thrombectomy in stroke: a review on phantoms, in-vivo animal, and cadaveric models

Preclinical testing platforms have been instrumental in the research and development of thrombectomy devices. However, there is no single model which fully captures the complexity of cerebrovascular anatomy, physiology, and the dynamic artery-clot-device interaction. This article provides a critical review of phantoms, in-vivo animal, and human cadaveric models used for thrombectomy testing and provides insights into the strengths and limitations of each platform. Articles published in the past 10 years that reported thrombectomy testing platforms were identified. Characteristics of each test platform, such as intracranial anatomy, artery tortuosity, vessel friction, flow conditions, device-vessel interaction, and visualization, were captured and benchmarked against human cerebral vessels involved in large-vessel occlusion stroke. Thrombectomy phantoms have been constructed from silicone, direct 3D-printed polymers, and glass. These phantoms represent oversimplified patient-specific cerebrovascular geometry but enable adequate visualization of devices and clots under appropriate flow conditions. They do not realistically mimic the artery-clot interaction. For the animal models, arteries from swine, canines, and rabbits have been reported. These models can reasonably replicate the artery-clot-device interaction and have the unique value of evaluating the safety of thrombectomy devices. However, the vasculature geometries are substantially less complex and flow conditions are different from human cerebral arteries. Cadaveric models are the most accurate vascular representations but with limited access and challenges in reproducibility of testing conditions. Multiple test platforms should be likely used for comprehensive evaluation of thrombectomy devices. Interpretation of the testing results should take into consideration platform-specific limitations.

Stroke thrombectomy complication management

Endovascular mechanical thrombectomy (EVT) is widely accepted as the first-line treatment for acute ischemic stroke in patients with large vessel occlusion. Being an invasive treatment, this method is associated with various preoperative, perioperative, and postoperative complications. These complications may influence peri-interventional morbidity and mortality and therefore treatment efficacy and clinical outcome. The aim of this review is to discuss the most common types of complications associated with EVT, the probable mechanisms of injury, and effective methods to manage and prevent complications.

Histological evaluation of acute ischemic stroke thrombi may indicate the occurrence of vessel wall injury during mechanical thrombectomy

Background

Several animal studies have demonstrated that mechanical thrombectomy (MT) for acute ischemic stroke (AIS) may cause vessel wall injury (VWI). However, the histological changes in human cerebral arteries following MT are difficult to determine.

Objective

To investigate the occurrence of VWI during MT by histological and immunohistochemical evaluation of AIS clots.

Methods

As part of the multicenter STRIP registry, 277 clots from 237 patients were analyzed using Martius Scarlett Blue stain and immunohistochemistry for CD34 (endothelial cells) and smooth muscle actin (smooth muscle cells).

Results

MT devices used were aspiration catheters (100 cases), stentriever (101 cases), and both (36 cases). VWI was found in 33/277 clots (12%). There was no significant correlation between VWI and MT device. The degree of damage varied from grade I (mild intimal damage, 24 clots), to grade II (relevant intimal and subintimal damage, 3 clots), and III (severe injury, 6 clots). VWI clots contained significantly more erythrocytes (p=0.006*) and less platelets/other (p=0.005*) than non-VWI clots suggesting soft thrombus material.

Thrombolysis correlated with a lower rate of VWI (p=0.04*). VWI cases showed a significantly higher number of passes (2 [1–4] vs 1 [1–3], p=0.028*) and poorer recanalization outcome (p=0.01*) than cases without VWI.

Conclusions

Histological markers of VWI were present in 12% of AIS thrombi, suggesting that VWI might be related to MT. VWI was associated with soft thrombus consistency, higher number of passes and poorer revascularization outcome. There was no significant correlation between VWI and MT device.

Thrombectomy for Acute Ischemic Stroke With a New Device-Skyflow: Study Protocol for a Prospective, Multicenter, Stratified Randomized, Single-Blinded, Parallel, Positive Controlled, Non-inferiority Clinical Trial

Background: Stent retriever thrombectomy is the standard treatment for acute ischemic stroke (AIS) with large vessel occlusion (LVO) in anterior circulation. The aim of the trial is to evaluate whether the new thrombectomy device-Skyflow can achieve the same safety and efficacy as Solitaire FR in the treatment. Method: This study is a prospective, multicenter, stratified randomized, single blind, paralleled, positive controlled, non-inferiority clinical trial. The safety and efficacy of vascular recanalization in AIS patients who are treated with either a new thrombectomy device-Skyflow or with Solitaire FR and within 8 h of symptom onset will be compared. A total of 192 patients will be enrolled, each group with 96 patients. The primary endpoint is successful recanalization rate after the operation. The secondary efficacy endpoints are the time from artery puncture to successful recanalization (mTICI 2b-3), NIHSS scores of 24 h (18-36 h), and 7 ± 2 days after the operation, mRS scores, and the rate of patients with mRS 0-2 scores 90 ± 14 days after the operation, and the success rate of instrument operation. The safety endpoints are the rate of symptomatic intracranial hemorrhage (sICH) and subarachnoid hemorrhage at 24 h (18-36 h) post-operation, incidence of adverse events (AE) and serious adverse events (SAE), all-cause mortality, and incidence of device defects. Discussion: This trial will provide information on the safety and efficacy of Sky-flow stent retriever in the treatment of AIS patients with anterior circulation LVO. The success of this trial will be the basis for the product to be finally officially listed and applied in China. Trial registration: Registered on 11 March 2018 with Chinese clinical trial registry. Registration number is ChiCTR1800015166.

Clinical effectiveness of endovascular stroke treatment in the early and extended time windows

BACKGROUND

The clinical efficacy of mechanical thrombectomy has been unequivocally demonstrated in multiple randomized clinical trials. However, these studies were performed in carefully selected centers and utilized strict inclusion criteria.

AIM

We aimed to assess the clinical effectiveness of mechanical thrombectomy in a prospective registry.

METHODS

A total of 2008 patients from 76 sites across 12 countries were enrolled in a prospective open-label mechanical thrombectomy registry. Patients were categorized into the corresponding cohorts of the SWIFT-Prime, DAWN, and DEFUSE 3 trials according to the basic demographic and clinical criteria without considering specific parenchymal imaging findings. Baseline and outcome variables were compared across the corresponding groups.

RESULTS

As compared to the treated patients in the actual trials, registry-derived patients tended to be younger and had lower baseline ASPECTS. In addition, time to treatment was earlier and the use of intravenous tissue plasminogen activator (IV-tPA) and general anesthesia were higher in DAWN- and DEFUSE-3 registry derived patients versus their corresponding trials. Reperfusion rates were higher in the registry patients. The rates of 90-day good outcome (mRS0-2) in registry-derived patients were comparable to those of the patients treated in the corresponding randomized clinical trials (SWIFT-Prime, 64.5% vs. 60.2%; DAWN, 50.4% vs. 48.6%; Beyond-DAWN: 52.4% vs. 48.6%; DEFUSE 3, 52% vs. 44.6%, respectively; all P > 0.05). Registry-derived patients had significant less disability than the corresponding randomized clinical trial controls (ordinal modified Rankin Scale (mRS) shift odds ratio (OR), P < 0.05 for all).

CONCLUSION

Our study provides favorable generalizability data for the safety and efficacy of thrombectomy in the "real-world" setting and supports that patients may be safely treated outside the constraints of randomized clinical trials.

Mechanical thrombectomy injury to the arterial wall: A comparison between catheter aspiration and stent retriever

PURPOSE

To compare the extent of arterial wall damage when SR and CA were used for treatment of AIS models to evaluate their efficacy and safety.

METHODS

A thrombin-induced thrombus was pre-injected into the right distal external carotid-maxillary artery (ECMA) in 12 dogs to create an acute thrombus occlusion model and were randomly divided into the SR group (n = 6; received SR treatment) and CA group (n = 6; received CA treatment). Device safety was also assessed by five passages through the normal left ECMA using each device. Device manipulation-related damage to arterial walls, final flow restoration, recanalization time and complications were recorded.

RESULTS

Sixteen retriever and 10 aspiration attempts were performed in the SR and CA groups. Reperfusion time was significantly reduced in the CA group (17.83 ± 1.96 vs. 28.33 ± 3.26 in the SR group; P = 0.02). Stent retriever thrombectomy resulted in an increased risk of endothelium denudation (1.17 ± 0.24 in SR group vs. 0.42 ± 0.15 in CA group; P = 0.01) and reduced frequency of vessel vasospasm (0.67 ± 0.14 in SR group vs. 0.25 ± 0.13 in CA group; P = 0.04). Injury score and thrombus deposition were similar between the two groups (P > 0.05). TICI 2b/3 flow restoration values of the right ECMA were 100 % in both groups. Device-related complications, including dissection (P = 0.21), side branch influence (P = 0.24), and distal thromboembolism (P = 1.00), did not differ between the two groups.

CONCLUSION

Both devices had similar efficacy and caused minimal arterial wall damage in our dog models. SR was more likely to cause endothelium denudation, while CA had a greater risk of vasospasm.

A novel rabbit thromboembolic occlusion model

BACKGROUND

To develop a preclinical thromboembolic occlusion model for studying revascularization strategies.

METHODS

Clot analog with barium sulfate was injected into the distal aorta in 9 New Zealand white rabbits. The situation of aorta occlusion was compared among fibrin-rich (n=4), red blood cell (RBC)-rich (n=3), and whole blood clot analogs (n=2) using digital subtraction angiography. Arterial geometries, histologic features and circumferential stretch of the distal aorta in rabbits were compared with the common carotid artery in swine and the distal internal carotid artery (ICA) in humans. Aspiration thrombectomy and mechanical thrombectomy using a stent retriever were performed in two rabbits.

RESULTS

The aortic bifurcation was occluded after a single delivery of clot in 4 cases. It was occluded after the second clot injection in the 5 remaining rabbits. Fragmentation of RBC-rich clots occurred during clot injection in 2 cases. The mean diameters of the distal aorta and right common iliac artery in rabbits were 3.7±0.4 and 2.8±0.3 mm, respectively; the mean diameters of human ICA, and first and second segments of the middle cerebral artery (M1, M2) were 3.6±0.4, 3.1±0.4, and 2.4±0.4 mm, respectively. Arterial revascularization was achieved in both rabbits. Geometric, mechanical and histological factors of the distal aorta in rabbit were more close to human distal ICA than swine carotid artery.

CONCLUSION

Arterial occlusion can be achieved at the aortic bifurcation in rabbits, which is comparable to human ICA bifurcation. This thrombectomy model has the potential to be used for testing of thrombectomy devices.

Histopathologic findings of vascular damage after mechanical thrombectomy using stent retriever in canine models

Although mechanical thrombectomy is a powerful predictor of stroke outcome, it induces vessel wall injury in the acute phase. This study aimed to analyze the degree and the condition of recovery of wall injury after the acute phase via angiography and histopathological analysis of autopsied canine models. Digital subtraction angiography (DSA) and embolization with autologous thrombus were performed in six canines. The model of arterial occlusion was effective in all target vessels. Mechanical thrombectomy was performed in completely occluded vessels using stent retriever. Follow-up angiographic and histopathologic evaluations were performed 1 month later. Complete recanalization using stent retriever was achieved in four cases. Slight residual vessel narrowing after recanalization and moderate narrowing was observed in one case each. Histopathological analysis showed that inflammation, hemorrhage, and device-induced medial injury were not observed in any of the cases. Severe intimal proliferation (grade 4), marked diffuse thrombosis (grade 4), and weak vascular endothelial cell loss (grade 1) were observed in one case and weak endovascular proliferation was observed in one case. Although successful complete recanalization was achieved with a single mechanical thrombectomy attempt and no change was observed in the follow-up DSA, special attention should be paid to postoperative follow-up, as device-induced intimal proliferation, diffuse thrombosis, and endothelial cell loss may remain after 1 month.

Biomechanics and hemodynamics of stent-retrievers

In 2015, multiple randomized clinical trials showed an unparalleled treatment benefit of stent-retriever thrombectomy as compared to standard medical therapy for the treatment of a large artery occlusion causing acute ischemic stroke. A short time later, the HERMES collaborators presented the patient-level pooled analysis of five randomized clinical trials, establishing class 1, level of evidence A for stent-retriever thrombectomy, in combination with intravenous thrombolysis when indicated to treat ischemic stroke. In the years following, evidence continues to mount for expanded use of this therapy for a broader category of patients. The enabling technology that changed the tide to support endovascular treatment of acute ischemic stroke is the stent-retriever. This review summarizes the history of intra-arterial treatment of stroke, introduces the biomechanics of embolus extraction with stent-retrievers, describes technical aspects of the intervention, provides a description of hemodynamic implications of stent-retriever embolectomy, and proposes future directions for a more comprehensive, multi-modal endovascular approach for the treatment of acute ischemic stroke.

Characterization of thrombus composition with multimodality CT-based imaging: an in-vitro study

BACKGROUND

CT is the most commonly used imaging modality for acute ischemic stroke evaluation. There is growing interest to use pre-operative imaging to characterize clot composition in stroke. We performed an in-vitro study examining the ability of various CT techniques in differentiation between different clot types.

METHODS

Five clot types with varying fibrin and red blood cells (RBCs) densities (5% RBC and 95% fibrin; 25% RBC and 75% fibrin; 50% RBC and 50% fibrin; 75% RBC and 25% fibrin; 95% RBC and 5% fibrin) were prepared and scanned using various CT scanning protocols (single-energy, dual-energy, photon-counting detector CT, mixed images, and virtual monoenergetic images). Martius Scarlett Blue trichrome staining was performed to confirm the composition of each clot. Mean CT values of each type of clot under different scanning protocol were calculated and compared.

RESULTS

Mean CT values of the CT numbers in the five clot specimens for 5%, 25%, and 50% RBC clot were similar across modalities, and increased significantly for 75% and 95% RBC clots (P<0.0001). Mean CT values are highest in the Mono +50 keV images in each type of clot, and they were also significantly higher than all other imaging protocols (P<0.001). Dual-energy CT with Mono +50 keV images showed the greatest difference between attenuation in each type of clot.

CONCLUSION

Mono +50 keV dual-energy CT scan may be helpful for differentiating between RBC-rich and fibrin-rich thrombi seen in large-vessel occlusion patients.

Dielectric profile of blood clots to inform ischemic stroke treatments

Platelet and fibrin-rich blood clots can respond differently to red blood cell rich clots during ischemic stroke treatment, which includes thrombolysis and mechanical thrombectomy. Currently, there is no accurate way to identify the type of clot in advance of treatment. If the type of blood clot can be identified, the optimum clot removal process can be chosen and patient outcomes can be improved. In this paper we fabricate physiologically relevant blood clot analogues from human blood, that cover a range of red blood cell, fibrin, and platelet concentrations. We characterize the dielectric profile of these formed clots using an open-ended coaxial probe method across a wide frequency range. After the dielectric measurements are completed, histology on each blood clot is performed to determine the concentration of red blood cells present. In total, 32 unique blood clots were measured.With this completed analysis, we investigate the correlation between the dielectric properties across this frequency range and the red blood cell count of the formed blood clots. Furthermore, we develop a model to predict whether an unknown blood clot can be categorized as red blood cell rich or platelet and fibrin-rich based solely on the measured dielectric properties.Clinical Relevance-Using the dielectric profile of a clot we can predict whether a clot is platelet and fibrin-rich or red blood cell rich allowing clinicians to more easily determine treatment methods during an intervention for ischemic stroke.

Effect of Stiffness of Large Extravascular Hematomas on Their Susceptibility to Boiling Histotripsy Liquefaction in Vitro

Large intra-abdominal, retroperitoneal and intramuscular hematomas are common consequences of sharp and blunt trauma and post-surgical bleeds, and often threaten organ failure, compartment syndrome or spontaneous infection. Current therapy options include surgical evacuation and placement of indwelling drains that are not effective because of the viscosity of the organized hematoma. We have previously reported the feasibility of using boiling histotripsy (BH)-a pulsed high-intensity focused ultrasound method-for liquefaction of large volumes of freshly coagulated blood and subsequent fine-needle aspiration. The goal of this work was to evaluate the changes in stiffness of large coagulated blood volumes with aging and retraction in vitro, and to correlate these changes with the size of the BH void and, therefore, the susceptibility of the material to BH liquefaction. Large-volume (55-200 mL) whole-blood clots were fabricated in plastic molds from human and bovine blood, either by natural clotting or by recalcification of anticoagulated blood, with or without addition of thrombin. Retraction of the clots was achieved by incubation for 3 h, 3 d or 8 d. The shear modulus of the samples was measured with a custom-built indentometer and shear wave elasticity (SWE) imaging. Sizes of single liquefied lesions produced with a 1.5-MHz high-intensity focused ultrasound transducer within a 30-s standard BH exposure served as the metric for susceptibility of clot material to this treatment. Neither the shear moduli of naturally clotted human samples (0.52 ± 0.08 kPa), nor their degree of retraction (ratio of expelled fluid to original volume 50%-58%) depended on the length of incubation within 0-8 d, and were significantly lower than those of bovine samples (2.85 ± 0.17 kPa, retraction 5%-38%). In clots made from anticoagulated bovine blood, the variation of calcium chloride concentration within 5-40 mmol/L did not change the stiffness, whereas lower concentrations and the addition of thrombin resulted in significantly softer clots, similar to naturally clotted human samples. Within the achievable shear modulus range (0.4-1.6 kPa), the width of the BH-liquefied lesion was more affected by the changes in stiffness than the length of the lesion. In all cases, however, the lesions were larger compared with any soft tissue liquefied with the same BH parameters, indicating higher susceptibility of hematomas to BH damage. These results suggest that clotted bovine blood with added thrombin is an acceptable in vitro model of both acute and chronic human hematomas for assessing the efficiency of BH liquefaction strategies.

Immediate effects of first-line thrombectomy devices for intracranial atherosclerosis-related occlusion: stent retriever versus contact aspiration

BACKGROUND

Although stent retriever (SR) is recommended as a frontline device of endovascular treatment (EVT) for embolic large artery occlusion causing acute ischemic stroke, contact aspiration (CA) device showed similar efficacy in the recent trials. However, the efficacy of the both devices as first-line therapy for intracranial atherosclerotic stenosis (ICAS)-related large vessel occlusion has not yet been established. Therefore, we compared the immediate effects and final outcomes of SR and CA as first-line devices for treating ICAS-related occlusions.

METHODS

We retrospectively analyzed the data of patients who underwent EVT for acute ischemic stroke from the registry of three Korean hospitals. Patients with ICAS-related occlusion who were treated within 24 h of onset of the symptoms were included. We investigated immediate reperfusion performance, immediate safety outcomes, and 3-month clinical outcomes for the two first-line devices.

RESULTS

Of the 720 registered patients, 111 were eligible for this study. Forty-nine patients (44.1%) used SR and 62 (55.9%) used CA as the first-line device. Achieving successful reperfusion immediately after first-line thrombectomy was more frequent in the SR group than that in the CA group (77.6% vs. 43.5%, p = 0.001), with fewer additional rescue treatments (12.2% vs. 59.7%, p < 0.001). The incidence of iatrogenic dissection or rupture was lower in the SR group than that in the CA group (8.2% vs. 29.0%, p = 0.012). After additional rescue treatments, however, the final successful reperfusion rate did not differ between the two groups (SR 87.8% vs. CA 77.4%, p = 0.247), and there was no significant difference in the 3-month good outcomes (modified Rankin Scale, p = 0.524).

CONCLUSIONS

First-line SR thrombectomy showed higher immediate reperfusion and less vessel injury for ICAS-related occlusions than CA. However, there was no significant difference in the final reperfusion status or 3-month outcomes from additional rescue treatments.

Safety and Efficacy Evaluation of Aspiration Thrombectomy With Large Bore Catheters in a Porcine Model

OBJECTIVE

Thrombectomy with aspiration catheters has shown to be effective for treatment of intracranial large vessel occlusion (LVO). We present preclinical evaluation of the safety and efficacy of React68 and React71 (Medtronic PLC, Irvine, CA) catheters in animal models of LVO.

METHODS

In vivo evaluation of catheter safety was performed in superficial cervical, internal maxillary, and renal arteries in a porcine model with or without clot (LVO). Animals were survived for 3 days and 30 days. Angiographic outcomes, usability, and histological parameters were compared for treatment with React68, React71, and ACE68 (Penumbra, Alameda, CA) catheters.

RESULTS

The in vivo angiographic analysis in a porcine thrombectomy LVO model demonstrated that there was no statistically significant difference in the rate of Thrombolysis in Cerebral Infarction scale 2b/3 recanalization between React68, React71, and ACE68 catheters. There were no physical or neurologic deficits in any of the treated animals throughout the survival period. Histologic analysis showed statistically non-inferior safety profile of React68 and React71 catheters relative to ACE68 catheters, with minimal but similar mild internal elastic lamina disruption and smooth muscle loss, but a lack of inflammation, fibrin deposits, and changes in the adventitia at both time points examined.

CONCLUSIONS

React68 and React71 aspiration catheters have an excellent safety, efficacy, and usability profile in animal models of LVO.

Delayed mid-basilar artery stenosis following paediatric acute mechanical thrombectomy: a rare complication from a rare case

There is limited literature on the use of mechanical thrombectomy with stent-retrievers in paediatric stroke, especially in the posterior circulation. We report a paediatric case of acute basilar artery occlusion successfully treated by mechanical thrombectomy using stent-retriever but complicated by delayed basilar artery stenosis. This case emphasises prudent selection of thrombectomy device and meticulous long-term follow-up when employed in paediatric stroke.

Pathological Safety Assessment in Preclinical Neurothrombectomy Studies

The design, production, and preclinical testing of neurothrombectomy devices is in a burgeoning phase as the demand escalates for safe and reliable treatment options following neurovascular stroke. Currently, there is a paucity of published data describing the development of iatrogenic vascular lesions occurring secondary to neurothrombectomy procedures. In an effort to test new devices, demonstrate device safety, satisfy regulatory requirements, and develop an understanding of the potential for associated vascular pathology, investigators are establishing appropriate methodology in suitable animal models. Significant challenges exist in identifying a single animal species that can be consistently utilized in all phases of device development. These aforementioned challenges are underscored by the intricacies of neurovascular pathology, thrombovascular interactions, and vascular responses to injury.

Large animals in neurointerventional research: A systematic review on models, techniques and their application in endovascular procedures for stroke, aneurysms and vascular malformations

Neuroendovascular procedures have led to breakthroughs in the treatment of ischemic stroke, intracranial aneurysms, and intracranial arteriovenous malformations. Due to these substantial successes, there is continuous development of novel and refined therapeutic approaches. Large animal models feature various conceptual advantages in translational research, which makes them appealing for the development of novel endovascular treatments. However, the availability and role of large animal models have not been systematically described so far. Based on comprehensive research in two databases, this systematic review describes current large animal models in neuroendovascular research including their primary use. It may therefore serve as a compact compendium for researchers entering the field or looking for opportunities to refine study concepts. It also describes particular applications for ischemic stroke and aneurysm therapy, as well as for the treatment of arteriovenous malformations. It focuses on most promising study designs and readout parameters, as well as on important pitfalls in endovascular translational research including ways to circumvent them.

Endovascular Metal Devices for the Treatment of Cerebrovascular Diseases

Cerebrovascular disease involves various medical disorders that obstruct brain blood vessels or deteriorate cerebral circulation, resulting in ischemic or hemorrhagic stroke. Nowadays, platinum coils with or without biological modification have become routine embolization devices to reduce the risk of cerebral aneurysm bleeding. Additionally, many intracranial stents, flow diverters, and stent retrievers have been invented with uniquely designed structures. To accelerate the translation of these devices into clinical usage, an in-depth understanding of the mechanical and material performance of these metal-based devices is critical. However, considering the more distal location and tortuous anatomic characteristics of cerebral arteries, present devices still risk failing to arrive at target lesions. Consequently, more flexible endovascular devices and novel designs are under urgent demand to overcome the deficiencies of existing devices. Herein, the pros and cons of the current structural designs are discussed when these devices are applied to the treatment of diseases ranging broadly from hemorrhages to ischemic strokes, in order to encourage further development of such kind of devices and investigation of their use in the clinic. Moreover, novel biodegradable materials and drug elution techniques, and the design, safety, and efficacy of personalized devices for further clinical applications in cerebral vasculature are discussed.

Retained Solitaire FR device after mechanical thrombectomy: Case review and management strategies

Solitaire FR device is a Food and Drug Administration-approved device for mechanical thrombectomy. It has been tested in various clinical trials for its safety and efficacy. We report a case of inadvertent detachment of the Solitaire FR device at stent-stent wire interface while performing mechanical thrombectomy. We review a rare phenomenon of retained Solitaire FR stent retriever in situ and discuss technique of avoidance and its management.

Clot Pathophysiology: Why Is It Clinically Important?

Cerebral ischemic stroke treatment may change significantly now that clots are actually physically removed from the patient using thrombectomy. This allows for an analysis of the content of the clots as well as the correlation of the imaging findings and the clot behavior and morphology. This article illustrates how the interaction of different clots varies in the clinical setting and how analysis of clot composition, as well as the search for new pharmacologic targets, can lead to a better understanding of the pathophysiology and therapy resistance, in turn providing possibilities for a better approach in the treatment.

Experimental evaluation of the NeVa™ thrombectomy device a novel stent retriever conceived to improve efficacy of organized clot removal

BACKGROUND AND PURPOSE

Stent retrievers are recognized as the most effective devices for intracranial thrombectomy. Although highly effective, such devices fail in clot removal when the brain vessel occlusion is due to organized, firm clots. The mechanism of failure is that during the retrieval, devices remain compressed by the organized clot and slide between it and the vessel wall without any removal effect. The aim of the current study is to present the preclinical evaluation of the Neva™ device, a novel stent retriever designed to improve the incorporation and removal of organized thrombi.

MATERIALS AND METHODS

Preclinical evaluation of the Neva™ device was divided in three main chapters: efficacy analysis, mechanical analysis and safety analysis. Efficacy and mechanical analysis aimed to investigate the behavior during the retrieval of the Neva™ device and its interaction with experimental organized clots. Safety analysis was conducted on animals in order to investigate the effect of the Neva™ device on real arteries after simulated thrombectomy maneuvers.

RESULTS

Neva™ device showed a high rate of "optimal clot integration" and "effective clot removal" which was related to constant cohesion to the vessel wall during retrievals. Safety analysis showed as the most frequent finding the disruption of the intima of the tested vessels with, in some cases, minimal disruption of the internal elastic lamina.

CONCLUSIONS

The Neva™ device has demonstrated safety and efficacy in a pre-clinical study. Such encouraging, preliminary results have to be compared with those of clinical trials.

Large animal models of stroke and traumatic brain injury as translational tools

Acute central nervous system injury, encompassing traumatic brain injury (TBI) and stroke, accounts for a significant burden of morbidity and mortality worldwide. Studies in animal models have greatly enhanced our understanding of the complex pathophysiology that underlies TBI and stroke and enabled the preclinical screening of over 1,000 novel therapeutic agents. Despite this, the translation of novel therapeutics from experimental models to clinical therapies has been extremely poor. One potential explanation for this poor clinical translation is the choice of experimental model, given that the majority of preclinical TBI and ischemic stroke studies have been conducted in small animals, such as rodents, which have small lissencephalic brains. However, the use of large animal species such as nonhuman primates, sheep, and pigs, which have large gyrencephalic human-like brains, may provide an avenue to improve clinical translation due to similarities in neuroanatomical structure when compared with widely adopted rodent models. This purpose of this review is to provide an overview of large animal models of TBI and ischemic stroke, including the surgical considerations, key benefits, and limitations of each approach.

Preclinical Evaluation of the NeVaTM Stent Retriever: Safety and Efficacy in the Swine Thrombectomy Model

Background

A novel stent retriever device with an enhanced radial force profile, enlarged offset openings, and a closed distal end has been developed.

Objective

Evaluate the safety and effectiveness of the NeVa^TM thrombectomy device in animal model of thrombo-occlusive disease.

Materials and Methods

Seven swine were used in safety and efficacy studies. Thrombo-occlusive disease was modeled using 4 emboli morphologies; 2 distinct models of autologous whole blood thrombi, plasma-enriched thrombi, and Onyx® emboli. A total of 35 vascular occlusions and retrievals were performed using emboli of variable sizes. Pre- and post-modified thrombolysis in cerebral ischemia (mTICI) scores, number of retrievals, and the presence of angiographic complications were recorded. In the safety study, a total of 6 clot retrievals were completed and the vascular territory examined grossly and harvested for histopathological evaluation. A semiquantitative vasospasm study was performed. Radial force testing was performed on NeVa^TM and control devices for comparison.

Results

Near-full or full reperfusion (mTICI 2b/3) was achieved in 34/35 occlusions after a mean of 1.2 passes. Full reperfusion (TICI 3) was achieved in 17/17 of whole blood clot occlusions (ranging between 10 and 20 mm) after a mean of 1.06 passes. The rate of mTICI 2b/3 reperfusion was 10/11 (mean, 1.6 passes) and 5/5 (mean, 1.0 passes) for Onyx® and plasma-enriched clot emboli, respectively. Histopathological vessel injury and vasospasm scores were comparable to predicate studies. Radial force curves demonstrated increased expansive radial force and similar compressive radial force compared to predicate devices.

Conclusions

Our preclinical results support the use of the NeVa^TM device in a clinical trial to determine if this novel design improves upon current stent retriever outcomes.

Recent progress in translational research on neurovascular and neurodegenerative disorders

The already established and widely used intravenous application of recombinant tissue plasminogen activator as a re-opening strategy for acute vessel occlusion in ischemic stroke was recently added by mechanical thrombectomy, representing a fundamental progress in evidence-based medicine to improve the patient’s outcome. This has been paralleled by a swift increase in our understanding of pathomechanisms underlying many neurovascular diseases and most prevalent forms of dementia. Taken together, these current advances offer the potential to overcome almost two decades of marginally successful translational research on stroke and dementia, thereby spurring the entire field of translational neuroscience. Moreover, they may also pave the way for the renaissance of classical neuroprotective paradigms.

This review reports and summarizes some of the most interesting and promising recent achievements in neurovascular and dementia research. It highlights sessions from the 9th International Symposium on Neuroprotection and Neurorepair that have been discussed from April 19th to 22nd in Leipzig, Germany. To acknowledge the emerging culture of interdisciplinary collaboration and research, special emphasis is given on translational stories ranging from fundamental research on neurode- and -regeneration to late stage translational or early stage clinical investigations.

Correlation of imaging and histopathology of thrombi in acute ischemic stroke with etiology and outcome: a systematic review

BACKGROUND AND PURPOSE

Studying the imaging and histopathologic characteristics of thrombi in ischemic stroke could provide insights into stroke etiology and ideal treatment strategies. We conducted a systematic review of imaging and histologic characteristics of thrombi in acute ischemic stroke.

MATERIALS AND METHODS

We identified all studies published between January 2005 and December 2015 that reported findings related to histologic and/or imaging characteristics of thrombi in acute ischemic stroke secondary to large vessel occlusion. The five outcomes examined in this study were (1) association between histologic composition of thrombi and stroke etiology; (2) association between histologic composition of thrombi and angiographic outcomes; (3) association between thrombi imaging and histologic characteristics; (4) association between thrombi imaging characteristics and angiographic outcomes; and (5) association between imaging characteristics of thrombi and stroke etiology. A meta-analysis was performed using a random effects model.

RESULTS

There was no significant difference in the proportion of red blood cell (RBC)-rich thrombi between cardioembolic and large artery atherosclerosis etiologies (OR 1.62, 95% CI 0.1 to 28.0, p=0.63). Patients with a hyperdense artery sign had a higher odds of having RBC-rich thrombi than those without a hyperdense artery sign (OR 9.0, 95% CI 2.6 to 31.2, p<0.01). Patients with a good angiographic outcome had a mean thrombus Hounsfield unit (HU) of 55.1±3.1 compared with a mean HU of 48.4±1.9 for patients with a poor angiographic outcome (mean standard difference 6.5, 95% CI 2.7 to 10.2, p<0.001). There was no association between imaging characteristics and stroke etiology (OR 1.13, 95% CI 0.32 to 4.00, p=0.85).

CONCLUSIONS

The hyperdense artery sign is associated with RBC-rich thrombi and improved recanalization rates. However, there was no association between the histopathological characteristics of thrombi and stroke etiology and angiographic outcomes.

Association between proximal internal carotid artery steno-occlusive disease and diffuse wall thickening in its petrous segment: a magnetic resonance vessel wall imaging study

PURPOSE

Significant stenosis or occlusion in carotid arteries may lead to diffuse wall thickening (DWT) in the arterial wall of downstream. This study aimed to investigate the correlation between proximal internal carotid artery (ICA) steno-occlusive disease and DWT in ipsilateral petrous ICA.

METHODS

Symptomatic patients with atherosclerotic stenosis (>0%) in proximal ICA were recruited and underwent carotid MR vessel wall imaging. The 3D motion sensitized-driven equilibrium prepared rapid gradient-echo (3D-MERGE) was acquired for characterizing the wall thickness and longitudinal extent of the lesions in petrous ICA and the distance from proximal lesion to the petrous ICA. The stenosis degree in proximal ICA was measured on the time-of-flight (TOF) images.

RESULTS

In total, 166 carotid arteries from 125 patients (mean age 61.0 ± 10.5 years, 99 males) were eligible for final analysis and 64 showed DWT in petrous ICAs. The prevalence of severe DWT in petrous ICA was 1.4%, 5.3%, 5.9%, and 80.4% in ipsilateral proximal ICAs with stenosis category of 1%-49%, 50%-69%, 70%-99%, and total occlusion, respectively. Proximal ICA stenosis was significantly correlated with the wall thickness in petrous ICA (r = 0.767, P < 0.001). Logistic regression analysis showed that proximal ICA stenosis was independently associated with DWT in ipsilateral petrous ICA (odds ratio (OR) = 2.459, 95% confidence interval (CI) 1.896-3.189, P < 0.001].

CONCLUSION

Proximal ICA steno-occlusive disease is independently associated with DWT in ipsilateral petrous ICA.

Utility of single-energy and dual-energy computed tomography in clot characterization: An in-vitro study

Background and purpose Because computed tomography (CT) is the most commonly used imaging modality for the evaluation of acute ischemic stroke patients, developing CT-based techniques for improving clot characterization could prove useful. The purpose of this in-vitro study was to determine which single-energy or dual-energy CT techniques provided optimum discrimination between red blood cell (RBC) and fibrin-rich clots. Materials and methods Seven clot types with varying fibrin and RBC densities were made (90% RBC, 99% RBC, 63% RBC, 36% RBC, 18% RBC and 0% RBC with high and low fibrin density) and their composition was verified histologically. Ten of each clot type were created and scanned with a second generation dual source scanner using three single (80 kV, 100 kV, 120 kV) and two dual-energy protocols (80/Sn 140 kV and 100/Sn 140 kV). A region of interest (ROI) was placed over each clot and mean attenuation was measured. Receiver operating characteristic curves were calculated at each energy level to determine the accuracy at differentiating RBC-rich clots from fibrin-rich clots. Results Clot attenuation increased with RBC content at all energy levels. Single-energy at 80 kV and 120 kV and dual-energy 80/Sn 140 kV protocols allowed for distinguishing between all clot types, with the exception of 36% RBC and 18% RBC. On receiver operating characteristic curve analysis, the 80/Sn 140 kV dual-energy protocol had the highest area under the curve for distinguishing between fibrin-rich and RBC-rich clots (area under the curve 0.99). Conclusions Dual-energy CT with 80/Sn 140 kV had the highest accuracy for differentiating RBC-rich and fibrin-rich in-vitro thrombi. Further studies are needed to study the utility of non-contrast dual-energy CT in thrombus characterization in acute ischemic stroke.

[Mechanical thrombectomy: Acute complications and delayed sequelae]

BACKGROUND

Due to the positive evidence for mechanical thrombectomy (mTE), it will be increasingly used in future. Profound knowledge of potential complications, prevention and management of complications is necessary to safely implement mTE into clinical practice.

AIM

Description of specific complications of mTE and their clinical relevance, measures for prevention and management. Summary of the current knowledge on long-term side effects of mTE.

MATERIAL AND METHODS

Analysis of current trial results and selected case series to address specific topics. Summary of own practical clinical experience.

RESULTS

Vascular injury (1-5%) and emboli (5-9%) are the most relevant intraprocedural complications but the clinical outcome is variable. Measures for prevention and management are described in detail. Vasospasms frequently occur (20-26%) but rarely need specific treatment and do not affect the clinical course. In the case of restrictive indications the frequency of symptomatic hemorrhage is similar to that for medicinal treatment (up to 8%). Contrast medium enhancement in the area of the infarction on post-treatment imaging should not be mistaken for hemorrhages. Focal subarachnoid contrast medium enhancement or hemorrhage occurs in up to 24% of cases and is predominantly benign. In follow-up imaging stenoses or occlusions can be detected in 4-10% of the treated vessels, most of which are asymptomatic. They are considered to be caused by microtrauma to the vascular wall.

CONCLUSION

Clinically relevant complications of mTE are rare. Preventive measures and effective management of complications may even increase safety. Stenoses occasionally occur as a long-term side effect but are asymptomatic in the majority of cases.

Main Trunk and Division Middle Cerebral Artery Occlusions: Differences in Recanalization Times, Number of Stent Retriever Passes and Clinical Outcomes: A Single-Center Experience

BACKGROUND AND PURPOSE

In this article, we present our experience with the recanalization of the middle cerebral artery (MCA), we hypothesize that there are higher rates of recanalization with fewer stent retriever passes and better clinical outcomes in patients with division MCA occlusions. A more complex anatomy at the bifurcation may prevent a faster recanalization in main trunk MCA occlusions.

METHODS

We retrospectively identified consecutive patients admitted with MCA occlusions who underwent mechanical thrombectomy using stent retrievers. We categorized patients into division MCA and main trunk MCA occlusions based on angiography. Variables were compared between the groups. We further analyzed patients with trunk MCA occlusions to identify reasons for delays in recanalization.

RESULTS

There were 32 MCA occlusions that underwent mechanical thrombectomy and eligible for the analysis during the study period. Of those, 11 were main trunk MCA occlusions. Univariate analysis disclosed a trend toward a lower GP-to-recanalization time (p = 0.05) and a lower number of passes required for recanalization in division MCA occlusions. However, there was a significantly better outcome in patients with division MCA occlusion after multivariate analysis. Analyzing main trunk MCA occlusion data, we found that the need for more than one pass to achieve recanalization led to a trend toward a longer GP-to-recanalization time and a worse outcome. When the stent was placed in the dominant division, the chances of recanalization were significantly higher.

CONCLUSIONS

Division MCA occlusions have higher recanalization rates with fewer stent retriever passes and better clinical outcomes than main trunk MCA occlusions, likely due to a more favorable anatomy. Measures like placing the stent retriever in the dominant division may decrease recanalization times and improve clinical outcomes in main trunk MCA occlusions.

The pREset Stent Retriever for Endovascular Treatment of Stroke Caused by MCA Occlusion: Safety and Clinical Outcome

PURPOSE

The purpose of this study was to analyze the safety and efficacy of the pREset device, a stent retriever system, for endovascular mechanical thrombectomy (MT) in acute ischemic stroke (AIS) after middle cerebral artery (MCA) occlusion.

METHODS

Retrospectively, 48 consecutive patients (mean age ± standard deviation, 71.0 ± 11.9 years; 24 women) treated for acute MCA occlusion using pREset solely or in combination with other MT devices were identified. Recanalization success was evaluated using the modified thrombolysis in cerebral infarction score (TICI), and complications were detected by 24-h follow-up computed tomography or magnetic resonance imaging. MCA anatomy was assessed in angiograms. Clinical outcome was evaluated with National Institutes of Health Stroke Scale (NIHSS) score at admission and discharge, and modified Rankin scale (mRS) score at discharge and follow-up.

RESULTS

Successful recanalization (TICI 2b/3) was achieved in 39 patients (81.3 %). Rate of procedure-related complications was 8.3 %. In four patients, a subarachnoid hemorrhage occurred (8.3 %), and parenchymal hematoma was detected in four patients (8.3 %). None of those events was associated with clinical deterioration. MCA curvature significantly influenced recanalization success (P < 0.005). Successful recanalization correlated significantly with lower NIHSS scores and favorable clinical outcome (mRS score 0-2) at discharge (P < 0.05). Mortality within 90 days was significantly lower in patients with TICI 2b/3 (P < 0.005).

CONCLUSIONS

High recanalization rates, low complication rates, and a significantly improved outcome after successful recanalization strongly suggest that MT with pREset is an adequate therapy for AIS after MCA occlusion. Vessel curvature is a significant determining factor for recanalization success.

Shear-Activated Nanoparticle Aggregates Combined With Temporary Endovascular Bypass to Treat Large Vessel Occlusion

Background and Purpose—

The goal of this study is to combine temporary endovascular bypass (TEB) with a novel shear-activated nanotherapeutic (SA-NT) that releases recombinant tissue-type plasminogen activator (r-tPA) when exposed to high levels of hemodynamic stress and to determine if this approach can be used to concentrate r-tPA at occlusion sites based on high shear stresses created by stent placement.

Methods—

A rabbit model of carotid vessel occlusion was used to test the hypothesis that SA-NT treatment coupled with TEB provides high recanalization rates while reducing vascular injury. We evaluated angiographic recanalization with TEB alone, intra-arterial delivery of soluble r-tPA alone, or TEB combined with 2 doses of intra-arterial infusion of either the SA-NT or soluble r-tPA. Vascular injury was compared against stent-retriever thrombectomy.

Results—

Shear-targeted delivery of r-tPA using the SA-NT resulted in the highest rate of complete recanalization when compared with controls ( P =0.0011). SA-NT (20 mg) had a higher likelihood of obtaining complete recanalization as compared with TEB alone (odds ratio 65.019, 95% confidence interval 1.77, >1000; P =0.0231), intra-arterial r-tPA alone (odds ratio 65.019, 95% confidence interval 1.77, >1000; P =0.0231), or TEB with soluble r-tPA (2 mg; odds ratio 18.78, 95% confidence interval 1.28, 275.05; P =0.0322). Histological analysis showed circumferential loss of endothelium restricted to the area where the TEB was deployed; however, there was significantly less vascular injury using a TEB as compared with stent-retriever procedure (odds ratio 12.97, 95% confidence interval 8.01, 21.02; P <0.0001).

Conclusions—

A novel intra-arterial, nanoparticle-based thrombolytic therapy combined with TEB achieves high rates of complete recanalization. Moreover, this approach reduces vascular trauma as compared with stent-retriever thrombectomy.

Inadvertent Stent Retriever Detachment: A Multicenter Case Series and Review of Device Experience FDA Reports

Mechanical thrombectomy using retrievable stents or stent retriever devices has become the mainstay of intra-arterial therapy for acute ischemic stroke. The recent publication of a series of positive trials supporting intra-arterial therapy as standard of care for the treatment of large vessel occlusion will likely further increase stent retriever use. Rarely, premature stent detachment during thrombectomy may be encountered. In our multicenter case series, we found a rate of detachment of less than 1% (n = 7/1,067), and all were first-generation Solitaire FR devices. A review of the US Food and Drug Administration database of device experience yielded 90 individual adverse reports of detachment. There were 82, 1 and 7 detachments of Solitaire FR (first generation), Solitaire FR2 (second generation) and Trevo devices, respectively. We conclude with a brief overview of the technical and procedural considerations which may be helpful in avoiding this rare complication.

A Novel Canine Model of Acute Vertebral Artery Occlusion

Background

The extended time window and theoretic reduction in hemorrhage make mechanical strategies an attractive approach for the treatment of patients with ischemic stroke. However, a limited availability of suitable animal models of cerebrovascular thrombosis has hampered the study of novel endovascular interventions. The aim of the present study was to develop a new technique for site-specific placement of a thrombus in a canine model that would allow for the evaluation of mechanical thrombectomy and clot retrieval methods and the visualization of thrombus dislocation or fragmentation during angiographic manipulation.

Methods

Angiography and embolization with a preformed thrombus were performed in 12 canines. Under fluoroscopic guidance, an embolism protection device (EPD) was anchored to the middle segment of the left vertebral artery (VA) via the left femoral arterial sheath. A preformed radiopaque clot was injected through the guide catheter into the left VA, via the contralateral femoral artery, proximal to the EPD. After 15 min of occlusion, the EPD was removed and persistent occlusion of the VA was documented angiographically.

Results

Angiography performed during the observation period confirmed the persistence of VA occlusion in each case, and displacement of the radiopaque clots did not occur during the 3-hour observation period. The technique allowed selective embolization of targeted vessels without thrombus fragmentation.

Conclusion

This study demonstrates, for the first time, a canine model of post-circulation embolism induced by autologous blood clot placement. This model can be rapidly formed and easily operated, and the site of thrombosis can be readily controlled.

Histological examination of vascular damage caused by stent retriever thrombectomy devices

Background and objectives

Although the recently marketed stent retriever thrombectomy devices have demonstrated a high recanalization rate and favorable clinical outcomes, there is a concern about the risks of intimal injuries when pulling out the stent in the unfolded position. In this study, the Solitaire Flow Restoration System and the Trevo retriever were used in a histopathological comparison of vascular injuries caused by stent retriever thrombectomy devices.

Methods

Rabbit carotid arteries were used in the experiments with stent retriever thrombectomy devices. Carotid artery samples were harvested either 1 or 2 weeks postoperatively for histological examination.

Results

Histological changes caused by the use of stent retriever thrombectomy devices were observed from the intimal to medial layers. With the Solitaire FR 4 mm, intimal and medial thickening was observed 1 week postoperatively, and progression of intimal thickening was observed 2 weeks postoperatively. The extent of intimal thickening tended to be greater with the Solitaire FR 6 mm than with the Solitaire FR 4 mm, but this difference was not significant. Compared with the Solitaire FR 4 mm, the Trevo had a significantly smaller area of intimal thickening.

Conclusions

Although there are some differences among devices, results from this study indicate that stent retriever thrombectomy devices induce vascular damage that extends to the medial layer.

Optimizating Clot Retrieval in Acute Stroke: The Push and Fluff Technique for Closed-Cell Stentrievers

BACKGROUND AND PURPOSE

We aimed to investigate the safety and efficacy of the Push and Fluff technique (PFT) as compared with the standard unsheathing technique for closed-cell stent retrievers in acute ischemic stroke.

METHODS

Acute ischemic stroke thrombectomy database was analyzed (September 2010 to January 2015) with the Trevo Retriever as a primary strategy. The PFT was compared with our internal standard unsheathing technique and with the Trevo Versus Merci Retrievers for Thrombectomy Revascularization of Large Vessel Occlusions in Acute Ischemic Stroke 2 (TREVO2) trial. Additionally, a silicon flow model was used to compare cell size/configuration, wall apposition/device diameter, and degree of foreshortening/device length across the 2 techniques.

RESULTS

One hundred fifty-one out of 662 patients qualified for the study. The PFT (n=71) was associated with higher rates of first-pass reperfusion (54% versus 35%, P=0.03; 54% versus 32.6%, P<0.01), lower number of passes (1.3±0.8 versus 1.8±1.0, P<0.01; 1.7±1.0 versus 2.4±1.6, P<0.01), and higher rates of modified treatment in cerebral ischemia-3 reperfusion (58% versus 40%, P=0.03; 58% versus 14%, P<0.01) as compared with the standard unsheathing technique (n=81) and the TREVO2 Trevo arm (n=88), respectively. No differences in hemorrhagic complications were observed across the groups. The in vitro model indicated that, compared with standard unsheathing technique, PFT resulted in improved wall apposition (device diameter, 75% larger) and cell size (mean area, 51% larger) at the cost of a mild degree of foreshortening (25% length reduction).

CONCLUSIONS

The PFT is safe and leads to optimization of wall apposition and cell size/configuration, resulting in higher chances of first-pass reperfusion, lower number of passes, and better rates of complete reperfusion.

Early middle cerebral artery stenosis following stent-assisted thrombectomy

Stent-assisted thrombectomy (SAT) is an extensively used endovascular treatment method for stroke in which the thrombectomy stents come into direct contact with the vascular intimal surface and entrap the thrombus causing the arterial occlusion. Although there are a few studies that demonstrate that the vessel wall changes in the arteries where stroke intervention is performed, we observed progressive stenosis in early follow-up imaging studies in a case. We present a middle cerebral artery (MCA) stroke patient who had four repetitive stent passes during SAT and developed distal MCA stenosis 2 months after SAT at the control magnetic resonance angiography (MRA). Inclusion of early follow-up MRA studies would be helpful in defining the silent vascular changes in patients who have undergone repetitive SAT.

Evaluation of the JRecan device for thrombus retrieval: efficacy and safety in a swine model of acute arterial occlusion

OBJECTIVE

To evaluate the recanalization efficacy and safety of a novel stent retriever in a swine model of acute arterial occlusion.

METHODS

The JRecan thrombectomy device, a stent retriever with a weaving stent design, was evaluated in 18 occluded cervicocerebral vessels of swine. The flow restoration effect immediately upon deployment, the reperfusion rate after retrieval, thromboembolic events, and complications were assessed. The histologic structure of the renal arteries after retriever passage was measured to further assess the safety of JRecan.

RESULTS

Immediate flow restoration was achieved in 66.7% of occlusions (12/18). The reperfusion rate was 94.4% (two Thrombolysis in Cerebral Infarction (TICI) 2b and 15 TICI 3). Distal thromboembolic events did not occur. Microscopic examination of the arteries after retrieval showed mild degrees of endothelial loss in 96.6% (29/30), fibrin or platelet deposition in 53.3% (16/30), and disruption of the internal elastic lamina in 10% (3/30), without severe pathologic lesions.

CONCLUSIONS

The JRecan is highly effective at clot removal with a favorable safety profile and merits further development as a stent retriever for the treatment of acute ischemic stroke.