In vivo evaluation of the first dedicated combined flow-restoration and mechanical thrombectomy device in a swine model of acute vessel occlusion

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.

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.

Endovascular thrombectomy for acute ischemic stroke

This review describes the evolution of endovascular treatment for acute ischemic stroke, current state of the art, and the challenges for the next decade. The rapid development of endovascular thrombectomy (EVT), from the first attempts into standard of care on a global scale, is one of the major achievements in modern medicine. It was possible thanks to the establishment of a scientific framework for patient selection, assessment of stroke severity and outcome, technical development by dedicated physicians and the MedTech industry, including noninvasive imaging for patient selection, and radiological outcome evaluation. A series of randomized controlled trials on EVT in addition to intravenous thrombolytics, with overwhelmingly positive results for anterior circulation stroke within 6 h of onset regardless of patient characteristics with a number needed to treat of less than 3 for any positive shift in outcome, paved the way for a rapid introduction of EVT into clinical practice. Within the "extended" time window of 6-24 h, the effect has been even greater for patients with salvageable brain tissue according to perfusion imaging with a number needed to treat below 2. Even so, EVT is only available for a small portion of stroke patients, and successfully recanalized EVT patients do not always achieve excellent functional outcome. The major challenges in the years to come include rapid prehospital detection of stroke symptoms, adequate clinical and radiological diagnosis of severe ischemic stroke cases, enabling effective recanalization by EVT in dedicated angiosuites, followed by personalized post-EVT stroke care.

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.

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.

The Protective Effects of Statins Towards Vessel Wall Injury Caused by a Stent Retrieving Mechanical Thrombectomy Device : A Histological Analysis of the Rabbit Carotid Artery Model

Objective

Endovascular mechanical thrombectomy (MT) has been regarded as one of the standard treatments for acute ischemic stroke caused by large vessel occlusion. Despite the wide use of stent retrievers for MT, arterial intimal damage caused when deployed stent is pulled has been a certain disadvantage. We hypothesized that statin could protect and stabilize vessel damage after endovascular MT using a stent retriever. In this animal study, we observed the protective effects of the statins towards MT-induced vessel wall injury.

Methods

Twenty-eight carotid arteries of fourteen rabbits were used in the experiments with MT using stent retriever. We divided the rabbits into four groups as follows : group 1, negative control; group 2, positive control; group 3, statin before MT; and group 4, statin after MT. After MT procedures, we harvested the carotid arteries and performed histomorphological and immunohistochemical analyses.

Results

In histomorphological analysis with hematoxylin and eosin and Masson's trichrome stain, significant intimal thickening (p<0.05) was observed in the positive control (group 2), compared to in the negative control (group 1). Intimal thickening was improved in the statin-administered groups (groups 3 and 4 vs. group 2, p<0.05). We also observed that statin administration after MT (group 4) resulted in a more effective decrease in intimal thickness than statin administration before MT (group 3) (p<0.05). We performed immunohistochemical analysis with the antibodies for tumor necrosis factor-alpha (TNF-α), cluster of differentiation (CD)11b, and CD163. In contrast to the negative control (group 1), the stained percentage areas of all immunological markers were markedly increased in the positive control (group 2) (p<0.05). Based on statin administration, the percentage area of TNF-α staining was significantly reduced (p<0.05) in group 3, compared to the positive control group (group 2). However, significant differences were not observed for CD11b and CD163 staining. In group 4, no significant differences were observed for TNF-α, CD11b, and CD163 staining (p≥0.05). The differences in the percentage areas of the different markers between the statin-administered groups (groups 3 and 4) were also not revealed.

Conclusion

We presented that statin administration before and after MT exerted protective effects towards vessel wall injury. The efficacy of statins was greater post-administration than pre-administration. Thus, statin administration in routine prescriptions in the peri-procedural period is strongly advised.

Favorable first-pass recanalization rates with NeVa™ thrombectomy device in acute stroke patients: Initial clinical experience

BACKGROUND

The NeVa™ thrombectomy device (Vesalio LLC, Nashville, USA) has been reported to succeed in large vessel occlusion thrombectomy in animal, in-vitro, and clinical studies. Designed with Drop Zone technology, a closed distal tip, and strong expansive radial force, the device demonstrated particular efficiency in resistant "white" thrombi in preclinical research. Our goal is to determine the safety and performance of this novel stent retriever on first-pass rates and overall recanalization.

METHODS

The Interventional Neurology Database is a prospectively maintained database of anterior and posterior circulation stroke thrombectomy cases. We retrospectively analyzed cases where the NeVa™ thrombectomy device was used as the first-line treatment strategy. Data collection occurred between January 2019 and January 2020. First-pass recanalization, final recanalization, 90-day functional outcome, complication, and bleeding rates are reported.

RESULTS

One hundred eighteen patients were treated with the NeVa™ thrombectomy device. The mean patient age was 69 ± 14 years, the median baseline National Institutes of Health Stroke Scale was 14, and the median initial Alberta Stroke Program Early Computed Tomography score was 8. The median time from groin puncture to successful recanalization was 29 min (interquartile range (IQR): 20-40). First-pass recanalization rates were 56.8% (modified treatment in cerebral infarction (mTICI) 2b/3) and 44.9% (mTICI 2c/3). Final successful recanalization rate was 95.8% (thrombolysis in cerebral infarction 2b/3). Favorable functional outcome (modified Rankin Scale 0-2) was 53% in the "first-pass" subgroup and 42.4% in the total patient population. The median number of passes to achieve the final recanalization score was 1 (IQR 1-2). The rate of embolization into new territory was 1.7%. Four patients (3.3%) had symptomatic hemorrhage.

CONCLUSIONS

In our experience, the NeVa™ device demonstrated high first-pass and overall recanalization rates along with a good safety profile.

Quantitative Characterization of Recanalization and Distal Emboli with a Novel Thrombectomy Device

PURPOSE

The first-pass effect during mechanical thrombectomy improves clinical outcomes regardless of first-line treatment approach, but current success rates for complete clot capture with one attempt are still less than 40%. We hypothesize that the ThrombX retriever (ThrombX Medical Inc.) can better engage challenging clot models during retrieval throughout tortuous vasculature in comparison with a standard stent retriever without increasing distal emboli.

MATERIALS AND METHODS

Thrombectomy testing with the new retriever as compared to the Solitaire stent retriever was simulated in a vascular replica with hard and soft clot analogs to create a challenging occlusive burden. Parameters included analysis of distal emboli generated per clot type, along with the degree of recanalization (complete, partial or none) by retrieval device verified by angiography.

RESULTS

The ThrombX device exhibited significantly higher rates of first-pass efficacy (90%) during hard clot retrieval in comparison with the control device (20%) (p < 0.009), while use of both techniques during soft clot retrieval resulted in equivalent recanalization. The soft clot model generated higher numbers of large emboli (>200 μm) across both device groups (p = 0.0147), and no significant differences in numbers of distal emboli were noted between the ThrombX and Solitaire techniques.

CONCLUSIONS

Irrespective of clot composition, use of the ThrombX retriever demonstrated high rates of complete recanalization at first pass in comparison with a state-of-the-art stent retriever and proved to be superior in the hard clot model. Preliminary data suggest that risk of distal embolization associated with the ThrombX system is comparable to that of the control device.

Relevance of Porcine Stroke Models to Bridge the Gap from Pre-Clinical Findings to Clinical Implementation

In the search of animal stroke models providing translational advantages for biomedical research, pigs are large mammals with interesting brain characteristics and wide social acceptance. Compared to rodents, pigs have human-like highly gyrencephalic brains. In addition, increasingly through phylogeny, animals have more sophisticated white matter connectivity; thus, ratios of white-to-gray matter in humans and pigs are higher than in rodents. Swine models provide the opportunity to study the effect of stroke with emphasis on white matter damage and neuroanatomical changes in connectivity, and their pathophysiological correlate. In addition, the subarachnoid space surrounding the swine brain resembles that of humans. This allows the accumulation of blood and clots in subarachnoid hemorrhage models mimicking the clinical condition. The clot accumulation has been reported to mediate pathological mechanisms known to contribute to infarct progression and final damage in stroke patients. Importantly, swine allows trustworthy tracking of brain damage evolution using the same non-invasive multimodal imaging sequences used in the clinical practice. Moreover, several models of comorbidities and pathologies usually found in stroke patients have recently been established in swine. We review here ischemic and hemorrhagic stroke models reported so far in pigs. The advantages and limitations of each model are also discussed.

Evaluation of the Partial Re-Sheathing Technique with the Solitaire Stent Retrieval System In Vitro Model and a Representative Case

Objective

Vascular injuries are severe complications associated with endovascular thrombectomy. In the present study, we evaluated the re-sheathing technique with the Solitaire stent retrieval system to overcome these complications.

Methods

We examined the diameter and resistance to retrieval of the Solitaire FR device (6 × 20 mm) during full and partial deployment in vitro model. We also examined a representative case in which the re-sheathing technique was used.

Results

We found that the Solitaire device spread elliptically during partial deployment. As the length of the partially deployed device decreased, the maximum diameter also decreased. The distal half of the stent retained 80% of the maximum diameter of the partially deployed Solitaire. The resistance to retrieval was significantly higher during full deployment (mean ± standard deviation; 0.32 ± 0.04 kg) than during half deployment (0.22 ± 0.04 kg) (Mann-Whitney U test; p = 0.006). The re-sheathing technique was used in the representative case due to the high resistance to retrieval, which enabled recanalization without extravasation.

Conclusion

In cases of high resistance to retrieval, minimal re-sheathing may be useful for capturing the thrombus without increasing the risk of vascular injury.

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.

Characterization of strut indentation during mechanical thrombectomy in acute ischemic stroke clot analogs

Background

Although it is common practice to wait for an ‘embedding time’ during mechanical thrombectomy (MT) to allow strut integration of a stentriever device into an occluding thromboembolic clot, there is a scarcity of evidence demonstrating the value or optimal timing for the wide range of thrombus compositions. This work characterizes the behavior of clot analogs of varying fibrin and cellular compositions subject to indentation forces and embedding times representative of those imparted by a stentriever during MT. The purpose of this study is to quantify the effect of thrombus composition on device strut embedding, and to examine the precise nature of clot integration into a stentriever device at a microstructural level.

Method

Clot analogs with 0% (varying densities), 5%, 40%, and 80% red blood cell (RBC) content were created using ovine blood. Clot indentation behavior during an initial load application (loading phase) followed by a 5-min embedding time (creep phase) was analyzed using a mechanical tester under physiologically relevant conditions. The mechanism of strut integration was examined using micro-computed tomography (µCT) with an EmboTrap MT device (Cerenovus, Galway, Ireland) deployed in each clot type. Microstructural clot characteristics were identified using scanning electron microscopy (SEM).

Results

Compressive clot stiffness measured during the initial loading phase was shown to be lowest in RBC-rich clots, with a corresponding greatest maximum indentation depth. Meanwhile, additional depth achieved during the simulated embedding time was most pronounced in fibrin-rich clots. SEM imaging identified variations in microstructural mechanisms (fibrin stretching vs rupturing) which was dependent on fibrin:cellular content, while µCT analysis demonstrated the mechanism of strut integration was predominantly the formation of surface undulations rather than clot penetration.

Conclusions

Disparities in indentation behavior between clot analogs were attributed to varying microstructural features induced by the cellular:fibrin content. Greater indentation was identified in clots with higher RBC content, but with an increased level of fibrin rupture, suggesting an increased propensity for fragmentation. Additional embedding time improves strut integration, especially in fibrin-rich clots, through the mechanism of fibrin stretching with the majority of additional integration occurring after 3 mins. The level of thrombus incorporation into the EmboTrap MT device (Cerenovus, Galway, Ireland) was primarily influenced by the stentriever design, with increased integration in regions of open architecture.

Review of the UBC Porcine Model of Traumatic Spinal Cord Injury

Traumatic spinal cord injury (SCI) research has recently focused on the use of rat and mouse models for in vivo SCI experiments. Such small rodent SCI models are invaluable for the field, and much has been discovered about the biologic and physiologic aspects of SCI from these models. It has been difficult, however, to reproduce the efficacy of treatments found to produce neurologic benefits in rodent SCI models when these treatments are tested in human clinical trials. A large animal model may have advantages for translational research where anatomical, physiological, or genetic similarities to humans may be more relevant for pre-clinically evaluating novel therapies. Here, we review the work carried out at the University of British Columbia (UBC) on a large animal model of SCI that utilizes Yucatan miniature pigs. The UBC porcine model of SCI may be a useful intermediary in the pre-clinical testing of novel pharmacological treatments, cell-based therapies, and the “bedside back to bench” translation of human clinical observations, which require preclinical testing in an applicable animal model.

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.

Posterior Circulation Occlusions May Be Associated with Distal Emboli During Thrombectomy : Factors for Distal Embolization and a Review of the Literature

Background

Distal embolization or movement of the thrombus to previously uninvolved vasculature are feared complications during stroke thrombectomy. We looked at associated factors in a consecutive series of patients who underwent thrombectomy with the same endovascular device.

Methods

We included all patients with acute ischemic stroke in the anterior or posterior circulation, who underwent thrombectomy with the same thrombectomy device for acute stroke from 2013 to 2016. Distal embolization was defined as any movement of the thrombus into a previously uninvolved portion of the cerebral vasculature or the presence of thrombotic material further downstream in the affected vessel, which occurred after the initial angiogram. We studied patient-related as well as technical factors to determine their association with distal emboli.

Results

In this study 167 consecutive acute stroke patients treated with the emboTrap® device (Cerenovus, Irvine, CA, USA) were included with a median National Institutes of Health Stroke Scale (NIHSS) of 15 (range 2–30) and mean age of 67 years (SD 13.1 years). Of the patients in our cohort 20 (11.9%) experienced distal emboli, with 2.3% into a new territory and 9.6% into a territory distal to the primary occlusion. On univariate analysis, age, intravenous tissue plasminogen activator (tPA), posterior circulation occlusions, and general anesthesia were associated with distal emboli. On multivariate analysis, only posterior circulation occlusions (odds ratio OR 4.506 95% confidence interval CI 1.483–13.692, p = 0.008) were significantly associated with distal emboli. Distal embolization was not significantly associated with worse functional outcomes at 3 months, increased mortality or increased bleeding risk.

Conclusion

Posterior circulation occlusions were significantly associated with distal emboli during thrombectomy, possibly due to the lack of flow arrest during such procedures. New techniques and devices should be developed to protect against embolic complications during posterior circulation stroke thrombectomy.

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.

Effective use of balloon guide catheters in reducing incidence of mechanical thrombectomy related distal embolization

BACKGROUND AND PURPOSE

The clinical benefit of endovascular stroke therapy has been demonstrated in several prospective randomized trials. However, in a relevant percentage of patients, mechanical thrombectomy bears the risk of causing new infarction in initially unaffected vascular territories through thrombus fragmentation and migration of clot debris. The goal of this study was to evaluate the use of the balloon guide catheter (BGC) to effectively achieve flow arrest and thrombus aspiration during the intervention to avoid distal embolization.

METHODS

A retrospective study was performed in 139 patients between October 2010 and May 2016 to analyze occlusions in the middle cerebral artery (MCA) or internal carotid artery (ICA) by using a stent retriever with a BGC (n = 73) or a non-BGC (n = 66). The following data were collected: patient age and gender, along with history of diabetes mellitus, hypertension, atrial fibrillation, smoking, obesity, dyslipidemia, and previous ischemic stroke. Data on procedure time, number of passes, and angiographic findings were also collected. The final reperfusion score was rated based on the Thrombolysis in Cerebral Infarction (TICI) grading scale. Successful recanalization was defined as TICI 3 or 2b.

RESULTS

A total of 139 patients underwent mechanical thrombectomy with the stent retriever. Of the 139 patients, 73 (52.5%) underwent placement of a BGC. The mean age was 65.8 ± 13.5 years, and the median National Institutes of Health Stroke Scale (NIHSS) score was 11. The average initial NIHSS score was lower in the BGC group compared with the non-BGC group (mean, 11.2 ± 5.6 vs. 13.2 ± 5.6; P = 0.03). Patients with BGC had fewer incidences of previous ischemic stroke (12.3% vs. 28.8%; P = 0.01). The numbers of passes were similar between the two groups. The procedure time (99 ± 49.4 min vs. 124 ± 72.2 min; P = 0.02) and the time from onset of symptoms to procedure end (302 ± 102 min vs. 357.2 ± 136.1 min; P = 0.009) were shorter in the BGC group. TICI 3 or 2b recanalization scores were higher in the BGC group compared to the non-BGC group [63/73, 86.3% vs. 48/66, 72.7%; odds ratio (OR), 0.6; 95% confidence interval (CI), 0.2-1.4; P = 0.04]. Importantly, distal embolization was less frequent in the BGC group (5/73, 6.8% vs. 21/66, 31.8%; OR, 6.3; 95% CI, 2.2-18.0; P < 0.001).

CONCLUSIONS

The risk of distal embolization was significantly decreased with the use of a BGC.

Single-Center Experience of Mechanical Thrombectomy with the Trevo XP ProVue 6 × 25 mm Stent Retriever in Middle Cerebral Artery Occlusion: Comparison with Trevo XP ProVue 4 × 20 mm

BACKGROUND

There are few studies assessing the suitable stent size for mechanical thrombectomy in middle cerebral artery (MCA) occlusion. We attempted to determine what size of stent is suitable for thrombectomy in MCA occlusion through a comparison of Trevo XP 6 × 25 mm and 4 × 20 mm stents.

METHODS

We changed Trevo XP 4 × 20 mm stents to Trevo XP 6 × 25 mm stents for thrombectomy in MCA occlusion with the hypothesis that a larger stent would have better outcomes. Retrospectively, 87 patients were divided into 2 groups: the Trevo XP 6 × 25 mm stent group and Trevo XP 4 × 20 mm stent group, and a comparative study was performed in terms of clinical and radiologic outcomes and complications.

RESULTS

The proportion of patients with a good clinical outcome and successful recanalization was higher in the Trevo XP 6 × 25 mm stent group than in the Trevo XP 4 × 20 mm stent group, with statistical significance (P = 0.041, P = 0.036). In multivariate analysis, the use of the Trevo 6 × 25 mm stent was a predictive factor for a good clinical outcome (odds ratio, 1.22; 95% confidence interval, 1.06-1.38; P = 0.03) and successful recanalization (odds ratio, 1.89; 95% confidence interval, 1.25-2.87; P = 0.018). However, there was no statistically significant difference in complications between the 2 groups.

CONCLUSIONS

Our study showed that the Trevo XP 6 × 25 mm stent provides better clinical and radiologic outcomes than the Trevo XP 4 × 20 mm stent for MCA occlusion without an increase in the rate of complications.

Retrograde semi-retrieval technique for combined stentriever plus aspiration thrombectomy in acute ischemic stroke

The endovascular treatment of acute ischemic stroke has become a standard procedure. The combination of multiple neuroendovascular devices provides more possibilities for the improvement of the thrombectomy technique. We describe a modified retrieval technique using a distal intracranial catheter (DIC) for the semi-retrieval of stentriever during the thrombectomy procedure. The retrograde semi-retrieval technique involves completely unfolding the stent retriever by pulling a Navien catheter and the partial re-sheath of a retrievable stent forming a tapered configuration by pushing the Navien catheter, which results in the thrombi being embedded into the strut, securing the clot within the stent and there being a shorter distance for the clot to travel. This technique may lessen the occurrence of thrombus fragmentation and injury to the vessel wall. The retrograde semi-retrieval technique is an optional thrombectomy technique that may improve the efficiency of this procedure in the treatment of acute ischemic stroke.

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.

An in vitro evaluation of distal emboli following Lazarus Cover-assisted stent retriever thrombectomy

Background

Formation of clot fragments during mechanical thrombectomy for acute ischemic stroke can occlude the distal vasculature, which may reduce the rate of good clinical outcome.

Objective

To examine the hypothesis that distal embolization can be reduced using stent retriever thrombectomy in combination with Lazarus Cover technology.

Methods

Hard, fragment-prone clots were used to create middle cerebral artery occlusions in a vascular phantom. Three different treatment strategies using Solitaire FR included: group 1—proximal flow control with an 8F balloon guide catheter (BGC), group 2—thrombectomy through a 6F conventional guide catheter (CGC), and group 3—a similar thrombectomy procedure to group 2 but including the Lazarus Cover device. The primary endpoint was distal emboli quantified by the number and size of the clot debris.

Results

The Cover-assisted stent retriever thrombectomy significantly reduced the generation of clot fragments >200 μm as compared with thrombectomy with a CGC, and was similar to the BGC group. Particle size distribution <200 μm was similar across the groups. All groups were associated with high rates of recanalization, with only one failed recanalization with partial clot retention after three passes in one experiment of stent retriever thrombectomy through a CGC. Use of the adjunctive Cover device did not prolong the procedure as compared with control groups.

Conclusions

For a fragment-prone clot, Solitaire thrombectomy in conjunction with the Cover device may lower the risk of distal embolization and is comparable to BGC-protected embolectomy.

The transient intraluminal filament middle cerebral artery occlusion model as a model of endovascular thrombectomy in stroke

The clinical relevance of the transient intraluminal filament model of middle cerebral artery occlusion (tMCAO) has been questioned due to distinct cerebral blood flow profiles upon reperfusion between tMCAO (abrupt reperfusion) and alteplase treatment (gradual reperfusion), resulting in differing pathophysiologies. Positive results from recent endovascular thrombectomy trials, where the occluding clot is mechanically removed, could revolutionize stroke treatment. The rapid cerebral blood flow restoration in both tMCAO and endovascular thrombectomy provides clinical relevance for this pre-clinical model. Any future clinical trials of neuroprotective agents as adjuncts to endovascular thrombectomy should consider tMCAO as the model of choice to determine pre-clinical efficacy.

The Effectiveness of Additional Treatment Modalities after the Failure of Recanalization by Thrombectomy Alone in Acute Vertebrobasilar Arterial Occlusion

Objective

Acute vertebrobasilar artery occlusion (AVBAO) is a devastating disease with a high mortality rate. One of the most important factors affecting favorable clinical outcome is early recanalization. Mechanical thrombectomy is an emerging treatment strategy for achieving a high recanalization rates. However, thrombectomy alone can be insufficient to complete recanalization, especially for acute stroke involving large artery atheromatous disease. The purpose of this study is to investigate the safety and efficacy of mechanical thrombectomy in AVBAO.

Methods

Fourteen consecutive patients with AVBAO were treated with mechanical thrombectomy. Additional multimodal treatments were intra-arterial (IA) thrombolysis, balloon angioplasty, or permanent stent placement. Recanalization by thrombectomy alone and multimodal treatments were assessed by the Thrombolysis in Cerebral Infarction (TICI) score. Clinical outcome was determined using the National Institutes of Health Stroke Scale (NIHSS) at 7 days and the modified Rankin Scale (mRS) at 3 months.

Results

Thrombectomy alone and multimodal treatments were performed in 10 patients (71.4%) and 4 patients (28.6%), respectively. Successful recanalization (TICI 2b-3) was achieved in 11 (78.6%). Among these 11 patients, 3 (27.3%) underwent multimodal treatment due to underlying atherosclerotic stenosis. Ten (71.4%) of the 14 showed NIHSS score improvement of >10. Overall mortality was 3 (21.4%) of 14.

Conclusion

We suggest that mechanical thrombectomy is safe and effective for improving recanalization rates in AVBAO, with low complication rates. Also, in carefully selected patients after the failure of recanalization by thrombectomy alone, additional multimodal treatment such as IA thrombolysis, balloons, or stents can be needed to achieve successful recanalization.

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.

Protected stent retriever thrombectomy prevents iatrogenic emboli in new vascular territories

Introduction

Diagnostic tools to show emboli reliably and protection techniques against embolization when employing stent retrievers are necessary to improve endovascular stroke therapy. The aim of the present study was to investigate iatrogenic emboli using susceptibility-weighted imaging (SWI) in an open series of patients who had been treated with stent retriever thrombectomy using emboli protection techniques.

Methods

Patients with anterior circulation stroke examined with MRI before and after stent retriever thrombectomy were assessed for iatrogenic embolic events. Thrombectomy was performed in flow arrest and under aspiration using a balloon-mounted guiding catheter, a distal access catheter, or both.

Results

In 13 of 57 patients (22.8 %) post-interventional SWI sequences detected 16 microemboli. Three of them were associated with small ischemic lesions on diffusion-weighted imaging (DWI). None of the microemboli were located in a new vascular territory, none showed clinical signs, and all 13 patients have been rated as Thrombolysis in Cerebral Infarction (TICI) 2b (n = 3) or 3 (n = 10). Retrospective reevaluation of the digital subtraction angiography (DSA) detected discrete flow stagnation nearby the iatrogenic microemboli in four patients with a positive persistent collateral sign in one.

Conclusion

Our study demonstrates two things: First, SWI seems to be more sensitive to detect emboli than DWI and DSA and, second, proximal or distal protected stent retriever thrombectomy seems to prevent iatrogenic embolization into new vascular territories during retraction of the thrombus, but not downstream during mobilization of the thrombus. Both techniques should be investigated and refined further.

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.

New method of thrombus preparation using a fluid model for evaluation of thrombectomy devices in a swine model

BACKGROUND

Mechanical thrombectomy is a promising new modality of interventional stroke treatment. Preparation of thrombus is a very important step for the evaluation of the mechanical thrombectomy devices. The objective of this study was to explore a new method of thrombus preparation with fluid model (FM) for assessment of thrombectomy devices used in the recanalization of acute ischemic stroke.

METHODS

Elongation test and catheter injection test were used to evaluate the mechanical properties of thrombi prepared by FM and static model (SM). Histological structures of two artificial clots and specimens of stroke patients were compared. Radiopacity of thrombus made by FM was evaluated in a swine embolization model.

RESULTS

The maximum tensile length of thrombi prepared by FM and SM were significantly higher (4.28 ± 0.23 cm vs 3.16 ± 0.13 cm, P < 0.01) and showed less breakage on catheter injection test (13% vs 60%, P < 0.05). Histological features of thrombi prepared by FM showed mixed thrombus structure, similar to thromboemboli retrieved from acute stroke patients, while clots generated by SM were replete with erythrocytes. A total of twelve vessels in two swine were successfully occluded (TIMI 0 or 1), with sufficient radiopacity of each injected thrombus.

CONCLUSION

The thrombus prepared by FM had good mechanical stability, sufficient radiopacity, and similar histological structure of thromboemboli retrieved from stroke patients, which make it possible to be used in the evaluation of thrombectomy devices.

Endovascular treatment of acute ischemic stroke

Early recanalization of the occluded artery leads to better clinical outcomes in patients with acute ischemic stroke (AIS) through protection of the time-sensitive penumbra. Intravenous administration of pharmacologic thrombolytic agents has been a standard treatment for AIS. To get better rates of recanalization, enhance the time window, and diminish the possibility of intracranial hemorrhage, endovascular thrombectomy was launched, with first authorization of the Merci clot retriever, a corkscrew-like apparatus, followed by approval of the Penumbra thromboaspiration system. Both devices lead to a high rate of recanalization. On the other hand, time to recanalization was on an average of 45 minutes, with most of the patients attaining only partial recanalization. More lately, retrievable stents have shown promise in decreasing the time to recanalization, and attaining a superior rate of complete clot resolution. The retrievable stent can be released within the clot to engage it within the struts of the stent, and afterwards it is taken back by pulling it under flow arrest. Neurointerventional techniques have a persistently ever-increasing and stimulating role in the management of AIS, as indicated by the advent of several important techniques. Stent retrievers have the capability to be ascertained as the most important approach to endovascular stroke treatment.

Evaluation of the Solitaire system in a canine arterial thromboembolic occlusion model: is it safe for the endothelium?

The Solitaire system has recently been increasingly used for acute stroke treatment in which the endothelial safety immediately after its use has not been evaluated. This study was performed to evaluate the endothelial status when using a Solitaire system in a canine arterial occlusion model. Thromboembolic occlusion of both internal maxillary arteries was achieved in five mongrel dogs. In each animal, the Solitaire system (ev3, Irvine, CA, USA) was used for primary thrombectomy on the right side and for temporary stenting on the left side. Efficacy was assessed by comparing the recanalization rates, and safety was assessed using angiographic and microscopic assessments. Endothelial injuries were evaluated with light microscopy (LM) and scanning electron microscopy (SEM). Successful revascularizations were observed following primary thrombectomy in all five animals (100%) and after temporary stenting in two (40%). There was no incidence of vasospasm or vessel perforation in either group. Distal migration of the clot occurred in two animals that underwent primary thrombectomy. Endothelial injury was seen after primary thrombectomy in two animals (40%) and after temporary stenting in one (20%). The lesions presented as defects of the internal elastic lamina on LM and denudation of the wavy endothelial surface on SEM. During mechanical thrombectomy, the Solitaire system can cause endothelial injury both in primary thrombectomy and temporary stenting. Primary thrombectomy is likely to have a higher recanalization rate with increased endothelial injury.

Flat panel detector computed tomography for the interaction between contrast-enhanced thrombi and stent retrievers in stroke therapy: a pilot study

OBJECTIVES

The purpose of this study was to create virtual 3D views of the interaction between contrast-enhanced thrombi and three different types of stent retrievers.

MATERIALS AND METHODS

Artificial thrombi with and without contrast agent were created and introduced into a silicone tube with saline solution. The stent retrievers (Aperio (A), Solitaire FR (B), Revive (C)) were released around the thrombi. For each retriever, two sets (0 min, 5 min) of flat panel computed tomography (CT) data were acquired on a Siemens Axiom Artis Zee biplane angiography system and reconstructed using syngo InSpace 3D software.

RESULTS

The filaments of all three stent retrievers were displaced by the thrombus immediately after deployment. Another study series after 5 min showed further expansion of the stents into the thrombus. A tends to appose best around obstacles. A and B allow cushion-like bulging of clot material into the stent lumen. C showed only moderate curvilinear bulging and a minor degree of interaction in between stent filaments and thrombus.

CONCLUSIONS

Flexible design allows better apposition of the device to the surface of the thrombus. A relatively strong longitudinal structure combined with large gaps in between the stent filaments seems to favor migration into the clot. The main capture mechanism seems to be engagement of the clot between the crossings of stent struts.

What is meant by "TICI"?

BACKGROUND

In 2003, Higashida et al proposed the Thrombolysis In Cerebral Infarction scale to evaluate angiographic intracranial flow. Our aim is to review how subsequently published studies define TICI.

MATERIALS AND METHODS

We used the ISI Web of Knowledge and SciVerse Scopus databases to search for "TICI" and "thrombolysis in cerebral infarction" and for articles that cited the original TICI paper from January 2004 through May 2012. Articles were categorized according to their definition of the TICI categories, typically grades 0-4, with grade 2 (partial reperfusion) subdivided into 2a and 2b, and rate of contrast entry to the perfused area. In addition, we catalogued the type of redefinitions of TICI subcategory 2 and additions of new categories.

RESULTS

Of 236 articles screened, 74 were included. Eight (11%) explicitly followed the TICI scale as originally defined. Thirty-seven (50%) cited Higashida but did not define their scale. Fifteen (21%) used and explained modified scales. Thirteen (18%) used the term TICI, but did not define the scale and did not cite Higashida. Eighteen (24%) specified a 2a subcategory. Nine defined grade 2a as <67% filling, 6 defined it as <50%, and 3 did not offer a percentage. Two studies added a 2c subcategory. Fifty-two (70%) used a cutoff level to define "successful reperfusion." Of these, 65% used TICI ≥2, 33% used TICI ≥2b, and 2% used TICI = 3.

CONCLUSIONS

There is substantial variability in the definition and/or application of the TICI scale in the literature. This variability could considerably impact our understanding of results of revascularization studies.

Histopathologic evaluation of arterial wall response to 5 neurovascular mechanical thrombectomy devices in a swine model

BACKGROUND AND PURPOSE

Five commercial devices are available for mechanical thrombectomy in acute ischemic stroke. This study evaluated and compared the resultant arterial damage from these devices.

MATERIALS AND METHODS

Wall damage after 4 wall-contact devices (the Merci retriever, Catch thromboembolectomy system, and Solitaire FR revascularization devices of 4 and 6 mm) and 1 aspiration device (the Penumbra System) was evaluated in the superficial femoral arteries of 20 male swine. Each device was tested with and without intraluminal clot. Twenty control vessels were not subjected to any intervention. Acute histopathologic changes were evaluated.

RESULTS

In the device samples, endothelial denudation (72.8 ± 29.4% versus 0.9 ± 1.9%, P < .0001), medial layer edema (52 ± 35.9% versus 18.1 ± 27.8%, P = .004), and mural thrombus (5.3 ± 14.2% versus 0%, P = .05) were found to a greater extent compared with the control samples. The aspiration device provoked more intimal layer (100 ± 79.1% versus 58.8 ± 48.9%, P = .27) and medial layer (75 ± 35.4% versus 46.3 ± 34.8%, P = .13) edema than the wall-contact devices.

CONCLUSIONS

All devices caused vascular injuries extending into the medial layer. The aspiration device was associated with more intimal and medial layer edema, compared with the wall-contact devices except for the Catch thromboembolectomy system.

Frequency and relevance of anterior cerebral artery embolism caused by mechanical thrombectomy of middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Spread of thrombus material in previously unaffected vessels is a potential hazard of mechanical thrombectomy, but it has not yet been investigated in detail, to our knowledge. Our purpose was to evaluate the frequency and relevance of these events in mTE of M1 occlusions.

MATERIALS AND METHODS

We retrospectively reviewed all patients treated for isolated M1 occlusion between January 2008 and July 2012. Angiographic images were analyzed to assess emboli in anterior cerebral artery branches induced by mTE and associated devices. Recanalization attempts in the ACA were reported as well as technical success and adverse events of rescue therapies. ACA infarcts on follow-up imaging served as a surrogate for clinical relevance. ACA infarcts were quantified volumetrically and assessed visually for involvement of motor or supplementary motor areas.

RESULTS

New ACA emboli occurred in 12 of 105 (11.4%) M1 recanalization procedures and were caused by a stent-retriever in 11 intances. Attempts to recanalize the ACA were made in 6 patients and were deemed technically successful in 5 with no adverse events. We detected 6 (5.7%) new infarcts on follow-up imaging with an average volume of 26.9 cm(3). Involvement of motor or supplementary motor areas was seen in 4 (3.8%) cases. Three patients developed ACA infarcts despite successful endovascular ACA recanalization.

CONCLUSIONS

The frequency of ACA emboli in mTE of M1 occlusions is relevant, causing ACA infarcts in 5.7% of patients; 3.8% of emboli were likely to hamper motor-function recovery. Endovascular recanalization of major ACA branches reduced the incidence of infarcts with no adverse events.

A novel porcine model of traumatic thoracic spinal cord injury

Spinal cord injury (SCI) researchers have predominately utilized rodents and mice for in vivo SCI modeling and experimentation. From these small animal models have come many insights into the biology of SCI, and a growing number of novel treatments that promote behavioral recovery. It has, however, been difficult to demonstrate the efficacy of such treatments in human clinical trials. A large animal SCI model that is an intermediary between rodent and human SCI may be a valuable translational research resource for pre-clinically evaluating novel therapies, prior to embarking upon lengthy and expensive clinical trials. Here, we describe the development of such a large animal model. A thoracic spinal cord injury at T10/11 was induced in Yucatan miniature pigs (20-25 kg) using a weight drop device. Varying degrees of injury severity were induced by altering the height of the weight drop (5, 10, 20, 30, 40, and 50 cm). Behavioral recovery over 12 weeks was measured using a newly developed Porcine Thoracic Injury Behavior Scale (PTIBS). This scale distinguished locomotor recovery among animals of different injury severities, with strong intra-observer and inter-observer reliability. Histological analysis of the spinal cords 12 weeks post-injury revealed that animals with the more biomechanically severe injuries had less spared white matter and gray matter and less neurofilament immunoreactivity. Additionally, the PTIBS scores correlated strongly with the extent of tissue sparing through the epicenter of injury. This large animal model of SCI may represent a useful intermediary in the testing of novel pharmacological treatments and cell transplantation strategies.

Does mechanical thrombectomy in acute embolic stroke have long-term side effects on intracranial vessels? An angiographic follow-up study

PURPOSE

Mechanical thrombectomy (mTE) proved to be effective treating acute vessel occlusions with an acceptable rate of procedural complications. Potential long-term side effects of the vessel wall trauma caused by mechanical irritation of the endothelium are unknown up to now.

METHODS

From a retrospectively established database of 640 acute stroke treatments, we selected 261 patients with 265 embolic vessel occlusions treated successfully by mTE without permanent implantation of a stent. Analysis comprised the type of devices used and the number of passes performed. Digital subtraction angiography immediately after treatment was evaluated for vasospasm, dissection, and extravasation. Control angiographic images were evaluated for any morphological change compared to the immediate posttreatment angiographic run.

RESULTS

Recanalization was achieved with a median of one (range 1-10) mTE maneuvers. Vasospasm occurred in 69 territories (26.0 %) and was treated with glyceroltrinitrate in three. Dissection was observed in one vessel (0.4 %). Intraprocedural hemorrhage in two patients (0.8 %) was either wire or device induced. Follow-up digital subtraction angiography was available for 117 territories after a median of 107 days, revealing target vessel occlusion in one segment (0.9 %) and a de novo stenosis of four segments (3.4 %). All findings were clinically asymptomatic. Posttreatment vasospasm was more frequent in patients with de novo stenosis and occlusion (p = 0.038).

CONCLUSION

De novo stenoses and occlusions occur in a small proportion of patients after mTE. Because all lesions were clinically asymptomatic, this finding does not affect the overall benefit of the treatment. Vasospasm may predict late vessel wall changes.

Experimental evaluation of immediate recanalization effect and recanalization efficacy of a new thrombus retriever for acute stroke treatment in vivo

BACKGROUND AND PURPOSE

Currently, several new stent retriever devices for acute stroke treatment are under development and early clinical evaluation. Preclinical testing under standardized conditions is an important first step to evaluate the technical performance and potential of these devices. The aim of this study was to evaluate the immediate recanalization effect, recanalization efficacy, thrombus-device interaction, and safety of a new stent retriever intended for thrombectomy in patients with acute stroke.

MATERIAL AND METHODS

The pREset thrombectomy device (4 × 20 mm) was evaluated in 16 vessel occlusions in an established swine model. Radiopaque thrombi (10-mm length) were used for visualization of thrombus-device interaction during application and retrieval. Flow-restoration effect immediately after deployment and after 5-minute embedding time before retrieval, recanalization rate after retrieval, thromboembolic events, and complications were assessed. High-resolution FPCT was performed to illustrate thrombus-device interaction during the embedding time.

RESULTS

Immediate flow restoration was achieved in 75% of occlusions. An increase or stable percentage of recanalizations during embedding time before retrieval was seen in 56.3%; a decrease, in 12.5%; reocclusion of a previously recanalized vessel, in 18.8%; and no recanalization effect at all, in 12.5%. Complete recanalization (TICI 3) after retrieval was achieved in 93.8%; partial recanalization (TICI 2b), in 6.2%. No distal thromboembolic events were observed. High-resolution FPCT illustrated entrapment of the thrombus between the stent struts and compression against the contralateral vessel wall, leading to partial flow restoration. During retrieval, the thrombus was retained in a straight position within the stent struts.

CONCLUSIONS

In this experimental study, the pREset thrombus retriever showed a high recanalization rate in vivo. High-resolution FPCT allows detailed illustration of the thrombus-device interaction during embedding time and is advocated as an add-on tool to the animal model used in this study.

Creation of fibrinogen-enhanced experimental blood clots to evaluate mechanical thrombectomy devices for treatment of acute stroke: an in vitro study

PURPOSE

To explore if addition of fibrinogen to the most commonly used experimental blood clot (EBC) model would improve its mechanical properties and histologic structure.

MATERIALS AND METHODS

Fresh blood from three swine was used to create four EBC types. The Gralla model of thrombin-induced barium-opaque EBC served as the control. In three other EBC types, 50 mg, 100 mg, and 200 mg of bovine fibrinogen were added. Evaluation of EBCs was done with three tests: manual elongation, injection through an 8-F catheter, and an opacity test. Thirty EBCs of each type were evaluated with each test. Histologic evaluation followed.

RESULTS

The control EBCs had low tensile strength and broke at 165% elongation. However, they were elastic and returned to their original length after catheter injection. The EBCs with fibrinogen exhibited increased tensile strength with increasing fibrinogen doses and withstood elongation to 213% (P < .01). Their elasticity decreased with increased tensile strength, and they remained elongated after catheter injection (P < .01 for EBC with 100 mg and 200 mg fibrinogen). Histologic examination showed more thorough mixing of blood with barium and a significantly increased amount of fibrin after addition of fibrinogen.

CONCLUSIONS

Addition of fibrinogen to a Gralla EBC model changes its mechanical properties proportionately to the fibrinogen dose. Fibrinogen increases EBC tensile strength but decreases its elasticity. Fibrinogen also significantly increases the binding of blood cells with fibrin on histologic slides.

Technical feasibility and application of mechanical thrombectomy with the Solitaire FR Revascularization Device in acute basilar artery occlusion

BACKGROUND AND PURPOSE

Acute BAO is a devastating neurological condition associated with a poor clinical outcome and a high mortality rate. Recanalization has been identified as a major prognostic factor for good outcome in BAO. Mechanical thrombectomy using retrievable stents is an emerging treatment option for acute stroke. First clinical trials using stent retrievers have shown promising high recanalization rates. However, these studies mainly included large artery occlusions in the anterior circulation with only a few or single cases of BAO. Therefore, the purpose of this study was to evaluate technical feasibility, safety, and efficacy of mechanical thrombectomy using retrievable stent in the treatment of acute BAO.

MATERIALS AND METHODS

Fourteen consecutive patients with BAO undergoing endovascular therapy using retrievable stents (Solitaire FR Revascularization Device) were included. Additional multimodal treatment approaches included thromboaspiration, intravenous and/or intra-arterial thrombolysis, and PTA/ permanent stent placement. Recanalization rates after multimodal therapy and stent retrieval were determined. Clinical outcome and mortality were assessed 3 months after treatment.

RESULTS

Median patient age was 64.5 years (range 55-85). Median NIHSS score at presentation was 21 (range 5-36). Overall, successful recanalization (TICI 3 or 2b) was achieved in all patients (TICI 3 in 78.6%, 11/14). In 4 patients (28.6%), insufficient recanalization after stent retrieval was due to an underlying atherosclerotic stenosis. Additional deployment of a permanent intracranial stent was performed in 3 patients (21.4%) and PTA alone in 1 patient (7.1%), resulting in final TICI 3 in 1 patient and TICI 2b in 3 patients. Stent retrieval alone was performed in 4 patients (28.6%). Average number of device passes was 1.3 (range 1-3). Median procedure time to maximal recanalization was 47 minutes (range 10-252). No device-related complications or thromboembolic occlusion of a previously unaffected artery occurred. There was no symptomatic intracranial hemorrhage. At 3 months, good functional outcome (mRS 0-2) was observed in 28.6% (4/14); overall mortality was 35.7% (5/14).

CONCLUSIONS

A multimodal endovascular approach using retrievable stents in BAO has high recanalization rates, with very low complication rates. Underlying atherothrombotic stenotic lesions of the basilar artery may still necessitate additional permanent stent placement to achieve complete recanalization.

Improvement of stent retriever design and efficacy of mechanical thrombectomy in a flow model

PURPOSE

In vitro experiments were performed to evaluate the efficacy of mechanical intracranial thrombectomy comparing the newly developed Aperio stent retriever and standard devices for stroke treatment.

METHODS

The Aperio (A), with an increased working length of 4 cm and a special cell design for capturing and withholding clots, was compared to three benchmark devices: the Solitaire retrievable stent (B), the Merci X6 (C), and the Merci L5 retriever (D). In a vascular glass model with pulsatile flow, reminiscent of the M1 segment of the middle cerebral artery, we repeatedly induced occlusion by generating thrombi via a modified Chandler loop system. The numbers of recanalization attempts, peripheral embolizations, and recanalizations at the site of occlusion were recorded during 10 retrieval experiments with each device.

RESULTS

Eleven devices were able to remove the blood clots from the occluded branch. In 34 of 40 experiments, restoration of flow was obtained in 1-3 attempts. The main differences between the study devices were observed in terms of clot withholding and fragmentation during retrieval. Although there was only one fragmentation recorded for device A, disengagement of the whole clot or peripheral embolization of fragments occurred more frequently (5-7 times) with devices B, C, and D.

CONCLUSION

In a vascular model, the design of device A was best at capturing and withholding thrombi during retrieval. Further study will be necessary to see whether this holds true in clinical applications.

Passing the thrombus in endovascular treatment of acute ischemic stroke: do we penetrate the thrombus?

Mechanical thrombectomy is increasingly applied during the treatment of acute stroke. Various devices have been advocated with different sites of force effect at the thrombus. The purpose of this study was to evaluate the angiographic route of passing systematically and therefore to assess the site of deployment of mechanical devices in correlation to the thrombus in interventional stroke treatment. Twenty-one consecutive patients with endovascular treatment for acute ischemic stroke with 26 passing procedures were evaluated prospectively. Occlusion site was the M1-segment in 17 cases (65.4%), ICA termination in five cases (19.2%), M2-segment in two cases (7.7%), the A2-segment in one case (3.8%) and basilar artery in one case (3.8%). On angiographic images the microwire and microcatheter passage was evaluated by illustrating the entry point and course across the occlusion site in relation to the thrombus in different projections and in correlation to the recanalisation result. Results were correlated to the origin of the thrombi according to the TOAST criteria. In all cases the point of entry to the occlusion site was delineated laterally to the thrombus in at least one projection. The course of the wire across the occluded segment in relation to the thrombus was found to be laterally in 22 procedures (84.6%). In the majority of M1-occlusions (12/17, 70.6%) the passage was found in the cranial aspect of the thrombus. In four procedures (15.4%) angiograms in different projections did not unequivocally confirm a passage laterally to the thrombus. The route of passing the thrombus was independent of thrombus origin according to the TOAST criteria. In the majority of cases the complete route of passing the occlusion site was visualized angiographically. Entrance of the microwire and microcatheter at proximal surface of the thrombus takes place laterally to the thrombus and accordingly the passage takes place between the thrombus and the vessel wall independent of thrombus origin. A penetration of the thrombus was not observed. This route of passing has implications on deployment and transmission of force in relation to the thrombus in mechanical approaches and consequently on the development of retrieval devices.

Safety and efficacy of mechanical thrombectomy with solitaire stent retrieval for acute ischemic stroke: a systematic review

Purpose

In recent years, mechanical thrombectomy using Solitaire stent retrieval has been tried for treating acute ischemic stroke with a large artery occlusion. We systematically reviewed published articles to appraise the evidence that supports the safety and efficacy of the mechanical thrombectomy in acute strokes with Solitaire stent.

Materials and Methods

Systematic searches using Medline and Scopus were performed for studies evaluating mechanical thrombectomy using a Solitaire stent in acute ischemic stroke. Articles were included if they were published since 2008, contained at least 5 subjects, and provided clinical results.

Results

Thirteen articles (262 cases) were included in this review. The mean time of the procedures ranged from 37 to 95.6 minutes in 10 studies. The success of recanalization was achieved in 89.7% and the recanalization rate varied from 66.7% to 100% in all 13 studies. The overall rates of the symptomatic hemorrhagic complications and mortality were 6.8% and 11.1%, respectively. A favorable outcome of mRS 2 or under was 47.3%. Procedure-induced complications developed in 3.4%.

Conclusion

The present review suggested that mechanical thrombectomy using a Solitaire stent in acute ischemic stroke was effective in recanalizing the occluded artery. The rate of procedural complications was small.

A comparison of 2 stroke devices: the new Aperio clot-removal device and the solitaire AB/FR

BACKGROUND AND PURPOSE

Several studies have shown promising results for the use of self-expandable intracranial stents for the treatment of acute ischemic stroke. This new technique combines immediate flow restoration after stent deployment with high recanalization rates. In the present study, the safety and efficacy of the new Aperio clot-removal device was tested in comparison with the Solitaire AB device.

MATERIALS AND METHODS

The experiments were performed in swine with a weight of 35-50 kg following established models. The experimental thrombi were prepared by using a new flow model (Thrombus Loop) to produce radiopaque thrombi. Thrombi were cut into lengths of 10 mm and injected into the target vessel. The occlusion was verified by DSA and rated with the help of the TICI score. A microcatheter was placed distal to the thrombus. The devices were placed with the proximal third within the thrombus and were retrieved under continuous aspiration in their released state into the guiding sheath. We performed 23 procedures with the Aperio device and 18 procedures with the Solitaire AB and FR devices. Control angiograms were obtained 3 and 5 minutes after device deployment to evaluate the flow restoration. The number of attempts to reach a TICI 2/3 score was recorded as well as the time to recanalization and the device-related complications. Vasospasm, vascular perforation, intramural arterial dissection, or embolization of a previously uninvolved territory was defined as a device-related complication.

RESULTS

Defined radiopaque thrombi from whole blood could reliably be created by using the Thrombus Loop. Both devices demonstrated a high recanalization rate of 100% (TICI 3) in the target vessel with no device-related complications. No significant differences were found between the 2 devices.

CONCLUSIONS

In this small study, we could show that radiopaque thrombi of whole blood with a defined diameter could be reliably created by using the Thrombus Loop. The new "stent-retriever" (Aperio System) seems to be a very efficient and safe addition to the existing repertoire of clot-removal devices.

Endovascular mechanical recanalisation after intravenous thrombolysis in acute anterior circulation stroke: the impact of a new temporary stent

PURPOSE

Treatment of acute stroke by endovascular mechanical recanalisation (EMR) has shown promising results and continues to be further refined. We evaluated the impact of a temporary stent compared with our results using other mechanical devices.

MATERIALS AND METHODS

We analysed clinical and radiological data of all patients who were treated by EMR after intravenous thrombolysis for acute carotid T- and middle-cerebral artery (M1) occlusions at our centre between 2007 and 2011. A comparison was performed between those patients in whom solely the stent-retriever was applied (group S) and those treated with other devices (group C).

RESULTS

We identified 14 patients for group S and 16 patients for group C. Mean age, National Institute of Health Stroke Scale score, and time to treatment were 67.1 years and 16.5 and 4.0 h for group S and 61.1 years and 17.6 and 4.5 h for group C, respectively. Successful recanalisation (thrombolysis in cerebral infarction scores ≥IIb) was achieved in 93% of patients in group S and 56% of patients in group C (P < 0.05). Mean recanalisation times for M1 occlusions were 23 min (group S) and 29 min (group C) and for carotid-T occlusions were 39 min (group S) and 50 min (group C), and 45% of the patients in group S and 33% in group C had a favourable outcome (Modified Rankin Scale score ≤2).

CONCLUSION

The findings suggest an improvement in recanalisation success by the application of a temporary stent compared with previously used devices. These results are to be confirmed by larger studies.