MERCI 1: a phase 1 study of Mechanical Embolus Removal in Cerebral Ischemia

Fabrication of Shape Memory Polymer Endovascular Thrombectomy Device for Treating Ischemic Stroke

Stroke is the second result for death and ischemic stroke constitutes most of all stroke cases. Ischemic stroke takes place when blood clot or embolus blocks cerebral vessel and interrupts blood flow, which often leads to brain damage, permanent disability, or death. There is a 4.5-h (golden hour) treatment window to restore blood flow prior to permanent neurological impairment results. Current stroke treatments consist mechanical system or thrombolytic drug therapy to disrupt or dissolve thrombus. Promising method for stroke treatment is mechanical retrieving of thrombi employing device deployed endovascularly. Advent of smart materials has led to research fabrication of several minimally invasive endovascular devices that take advantage of new materials capabilities. One of these capabilities is shape memory, is capability of material to store temporary form, then activate to primary shape as subjected to stimuli. Shape memory polymers (SMPs) are employed as good materials for thrombectomy device fabrication. Therefore, current review presents thrombectomy device development and fabrication with SMPs. Design, performance, limitations, and in vitro or in vivo clinical results of SMP-based thrombectomy devices are identified. Review also sheds light on SMP's future outlook and recommendations for thrombectomy device application, opening a new era for advanced materials in materials science.

Progressive microvascular failure in acute ischemic stroke: A systematic review, meta-analysis, and time-course analysis

This systematic review, meta-analysis, and novel time course analysis examines microvascular failure in the treatment of acute ischemic stroke (AIS) patients undergoing endovascular therapy (EVT) and/or thrombolytic administration for stroke management. A systematic review and meta-analysis following PRIMSA-2020 guidelines was conducted along with a novel curve-of-best fit analysis to elucidate the time-course of microvascular failure. Scopus and PubMed were searched using relevant keywords to identify studies that examine recanalization and reperfusion assessment of AIS patients following large vessel occlusion. Meta-analysis was conducted using a random-effects model. Curve-of-best-fit analysis of microvascular failure rate was performed with a negative exponential model. Twenty-seven studies with 1151 patients were included. Fourteen studies evaluated patients within a standard stroke onset-to-treatment time window (≤6 hours after last known normal) and thirteen studies had an extended time window (>6 hours). Our analysis yields a 22% event rate of microvascular failure following successful recanalization (95% CI: 16-30%). A negative exponential curve modeled a microvascular failure rate asymptote of 28.5% for standard time window studies, with no convergence of the model for extended time window studies. Progressive microvascular failure is a phenomenon that is increasingly identified in clinical studies of AIS patients undergoing revascularization treatment.

Key design elements of successful acute ischemic stroke treatment trials

PURPOSE

We review key design elements of positive randomized controlled trials (RCTs) in acute ischemic stroke (AIS) treatment and summarize their main characteristics.

METHOD

We searched Medline, Pubmed and Cochrane databases for positive RCTs in AIS treatment. Trials were included if (1) they had a randomized controlled design, with (at least partial) blinding for endpoints, (2) they tested against placebo (or on top of standard therapy in a superiority design) or against approved therapy; (3) the protocol was registered and/or published before trial termination and unblinding (if required at study commencement); (4) the primary endpoint was positive in the intention to treat analysis; and (5) the study findings led to approval of the investigational product and/or high ranked recommendations. A topical approach was used, therefore the findings were summarized as a narrative review.

FINDINGS

Seventeen positive RCTs met the inclusion criteria. The majority of trials included less than 1000 patients (n = 15), had highly selective inclusion criteria (n = 16), used the modified Rankin score as a primary endpoint (n = 15) and had a frequentist design (n = 16). Trials tended to be national (n = 12), investigator-initiated and performed with public funding (n = 11).

DISCUSSION

Smaller but selective trials are useful to identify efficacy in a particular subgroup of stroke patients. It may also be of advantage to limit the number of participating countries and centers to avoid heterogeneity in stroke management and bureaucratic burden.

CONCLUSION

The key characteristics of positive RCTs in AIS treatment described here may assist in the design of further trials investigating a single intervention with a potentially high effect size.

Downregulation of TNFAIP1 alleviates OGD/R‑induced neuronal damage by suppressing Nrf2/GPX4‑mediated ferroptosis

TNFα-induced protein 1 (TNFAIP1) serve a role in neurovascular disease. However, the potential role and molecular mechanism of TNFAIP1 in cerebral ischemia-reperfusion (I/R) remains elusive. In the present study, reverse transcription-quantitative PCR and western blotting were used to assess TNFAIP1 mRNA and protein expression levels in PC12 cells. Furthermore, using Cell Counting Kit-8, flow cytometry and western blotting, cell viability and apoptosis were evaluated. Oxidative stress was evaluated using DCFH-DA staining and ELISA was used for assessment of inflammatory factors. Expression of components in the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and ferroptosis were assessed using western blotting analysis and an iron assay kit. TNFAIP1 expression was significantly upregulated in oxygen glucose deprivation and reperfusion (OGD/R)-injured PC12 cells. However, knocking down TNFAIP1 expression restored PC12 cell viability and decreased apoptosis following OGD/R-challenge. Furthermore, TNFAIP1 silencing significantly suppressed OGD/R-induced oxidative stress and inflammatory damage in PC12 cells. TNFAIP1 knockdown inhibited ferroptosis via activation of the Nrf2 signaling pathway in OGD/R-injured PC12 cells. Erastin treatment reversed the beneficial effects of TNFAIP1 knockdown on PC12 cell viability, apoptosis alleviation, oxidative stress and inflammation following OGD/R treatment. These results suggested that TNFAIP1 knockdown could alleviate OGD/R-induced neuronal cell damage by suppressing Nrf2-mediated ferroptosis, which might lay the foundation for the investigation of targeted-therapy for cerebral I/R injury in clinic.

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.

Food and Drug Association Approval Process for Devices Used in Endovascular Treatment of Stroke

PURPOSE OF THE REVIEW

This article reviews the Food and Drug Administration's (FDA's) process for approval of new medical devices and describes the evolution of endovascular devices used for the treatment of acute ischemic stroke.

RECENT FINDINGS

Several recent studies have established the benefit of endovascular treatment of acute ischemic stroke from emergent large vessel occlusion. This has led to endovascular treatment becoming the usual care in acute stroke management and has generated greater-than-ever interest in the development of newer and more effective devices.

SUMMARY

In the United States, the FDA is the regulatory authority that is empowered with the approval and monitoring of new medical devices for widespread use in the population. The FDA categorizes medical devices into 3 classes based mainly on their potential risks to patients and/or users; class I devices pose the least risk and have the least stringent approval process, while class III devices pose the highest risk and undergo the most stringent and time-consuming approval process. There are 4 main pathways to approval: premarket notification, also known as the 510(k) pathway; premarket approval (PMA), de novo, and Humanitarian Device Exemption pathway. These pathways are described in detail in the article. The FDA also mandates postmarketing surveillance to identify any untoward and unexpected long-term complications.

Modelling the effects of cerebral microthrombi on tissue oxygenation and cell death

Thrombectomy, the mechanical removal of a clot, is the most common way to treat ischaemic stroke with large vessel occlusions. However, perfusion cannot always be restored after such an intervention. It has been hypothesised that the absence of reperfusion is at least partially due to the clot fragments that block the downstream vessels. In this paper, we present a new way of quantifying the effects of cerebral microthrombi on oxygen transport to tissue in terms of hypoxia and ischaemia. The oxygen transport was simulated with the Green's function method on physiologically representative microvascular cubes, which was found independent of both microvascular geometry and length scale. The microthrombi occlusions were then simulated in the microvasculature, which were extravasated over time with a new thrombus extravasation model. The tissue hypoxic fraction was fitted as a sigmoidal function of vessel blockage fraction, which was then taken to be a function of time after the formation of microthrombi occlusions. A novel hypoxia-based 3-state cell death model was finally proposed to simulate the hypoxic tissue damage over time. Using the cell death model, the impact of a certain degree of microthrombi occlusions on tissue viability and microinfarct volume can be predicted over time. Quantifying the impact of microthrombi on oxygen transport and tissue death will play an important role in full brain models of ischaemic stroke and thrombectomy.

Guide-Wired Helical Microrobot for Percutaneous Revascularization in Chronic Total Occlusion in-Vivo Validation

OBJECTIVE

For the revascularization in small vessels such as coronary arteries, we present a guide-wired helical microrobot mimicking the corkscrew motion for mechanical atherectomy that enables autonomous therapeutics and minimizing the radiation exposure to clinicians.

METHODS

The microrobot is fabricated with a spherical joint and a guidewire. A previously developed external electromagnetic manipulation system capable of high power and frequency is incorporated and an autonomous guidance motion control including driving and steering is implemented in the prototype. We tested the validity of our approach in animal experiments under clinical settings. For the in vivo test, artificial thrombus was fabricated and placed in a small vessel and atherectomy procedures were conducted.

RESULTS

The devised approach enables us to navigate the helical robot to the target area and successfully unclog the thrombosis in rat models in vivo.

CONCLUSION

This technology overcomes several limitations associated with a small vessel environment and promises to advance medical microrobotics for real clinical applications while achieving intact operation and minimizing radiation exposures to clinicians.

SIGNIFICANCE

Advanced microrobot based on multi-discipline technology could be validated in vivo for the first time and that may foster the microrobot application at clinical sites.

Impact of eloquent motor cortex-tissue reperfusion beyond the traditional thrombolysis in cerebral infarction (TICI) scoring after thrombectomy

Background

Targeted eloquence-based tissue reperfusion within the primary motor cortex may have a differential effect on disability as compared with traditional volume-based (thrombolysis in cerebral infarction, TICI) reperfusion after endovascular thrombectomy (EVT) in the setting of acute ischemic stroke (AIS).

Methods

We explored the impact of eloquent reperfusion (ER) within primary motor cortex (PMC) on clinical outcome (modified Rankin Scale, mRS) in AIS patients undergoing EVT. ER-PMC was defined as presence of flow on final digital subtraction angiography (DSA) within four main cortical branches, supplying the PMC (middle cerebral artery (MCA) – precentral, central, postcentral; anterior cerebral artery (ACA) – medial frontal branch arising from callosomarginal or pericallosal arteries) and graded as absent (0), partial (1), and complete (2). Prospectively collected data from two centers were analyzed. Multivariate analysis was conducted to assess the impact of ER-PMC on 90-day disability (mRS) among patients with anterior circulation occlusion who achieved partial reperfusion (TICI 2a and 2b).

Results

Among the 125 patients who met the study criteria, ER-PMC distribution was: absent (0) in 19/125 (15.2%); partial (1) in 52/125 (41.6%), and complete (2) in 54/125 (43.2%). TICI 2b was achieved in 102/125 (81.6%) and ER-PMC was substantially higher in those patients (P<0.001). In multivariate analysis, in addition to age and symptomatic intracranial hemorrhage, ER-PMC had a profound independent impact on 90-day disability (OR 6.10, P=0.001 for ER-PMC 1 vs 0 and OR 9.87, P<0.001 for ER-PMC 2 vs 0), while the extent of total partial reperfusion (TICI 2b vs 2a) was not related to 90-day mRS.

Conclusions

Eloquent PMC-tissue reperfusion is a key determinant of functional outcome, with a greater impact than volume-based (TICI) degree of partial reperfusion alone. PMC-targeted revascularization among patients with partial reperfusion may further diminish post-stroke disability after EVT.

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.

A short history of thrombectomy - Procedure and success analysis of different endovascular stroke treatment techniques

Background

The historical development of interventional stroke treatment shows a wide variation of different techniques and materials used. Thus, the question of the present work is whether the technical and procedural differences of thrombectomy techniques lead to different technical and clinical results.

Methods and results

Analysis of a mixed retrospective/prospective database of all endovascular treated patients with an occlusion of the Carotid-T or M1 segment of the MCA at a single comprehensive stroke center since 2008. Patients were classified regarding the technical approach used. Six hundred sixty-eight patients were available for the final analysis. Reperfusion rates ranged between 56% and 100% depending on the technical approach. The use of balloon guide catheters and most recently the establishment of combination techniques using balloon guide catheters, aspiration catheters and stent retrievers have shown a further significant increase in the rates of successful recanalization, full recanalization and first-pass recanalization. Additionally, the technical development of interventional techniques has led to a subsequent drop in complications, embolization into previously unaffected territories in particular.

Conclusion

Technical success of MT has improved substantially over the past decade owing to improved materials and procedural innovations. Combination techniques including flow modulation have emerged to be the most effective approach and should be considered as a standard of care.

Level of evidence: Level 3, retrospective study.

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.

Validation of the extended thrombolysis in cerebral infarction score in a real world cohort

Background

A thrombolysis in cerebral infarction (TICI) score of 2b is defined as a good recanalization result although the reperfusion may only cover 50% of the affected territory. An additional mTICI2c category was introduced to further differentiate between mTICI scores. Despite the new mTICI2c category, mTICI2b still covers a range of 50–90% reperfusion which might be too imprecise to predict neurological improvement after therapy.

Aim

To compare the 7-point “expanded TICI” (eTICI) scale with the traditional mTICI in regard to predict functional independence at 90 days.

Methods

Retrospective review of 225 patients with large artery occlusion. Angiograms were graded by 2 readers according the 7-point eTICI score (0% = eTICI0; reduced clot = eTICI1; 1–49% = eTICI2a, 50–66% = eTICI2b50; 67–89% = eTICI2b67, 90–99% = eTICI2c and complete reperfusion = eTICI3) and the conventional mTICI score. The ability of e- and mTICI to predict favorable outcome at 90days was compared.

Results

Given the ROC analysis eTICI was the better predictor of favorable outcome (p-value 0.047). Additionally, eTICI scores 2b50, 2b67 and 2c (former mTICI2b) were significantly superior at predicting the probability of a favorable outcome at 90 days after endovascular therapy with a p-value of 0.033 (probabilities of 17% for mTICI2b50, 24% for mTICI2b67 and 54% for mTICI2c vs. 36% for mTICI2b).

Conclusions

The 7-point eTICI allows for a more accurate outcome prediction compared to the mTICI score because it refines the broad range of former mTICI2b results.

Comparison of Mechanical Thrombectomy with Contact Aspiration, Stent Retriever, and Combined Procedures in Patients with Large-Vessel Occlusion in Acute Ischemic Stroke

Background

We investigated the properties and effects of 5 mechanical thrombectomy procedures in patients with acute ischemic stroke. The relationships between the type of procedure, the time required, the success of recanalization, and the clinical outcome were analyzed.

Material/Methods

This prospective comparative analysis included 500 patients with acute ischemic stroke and large-vessel occlusion. We compared contact aspiration thrombectomy (ADAPT, n=100), stent retriever first line (SRFL, n=196), the Solumbra technique (n=64), mechanical thrombectomy plus stent implantation (n=81), and a combined procedure (n=59).

Results

ADAPT provided shorter procedure (P<0.001) and recanalization times (P<0.001) than the other techniques. Better clinical outcome was achieved for ischemia in the anterior circulation than ischemia in the posterior fossa (P<0.001). Compared to the other techniques, patients treated with ADAPT procedure had increased odds of achieving better mTICI scores (P=0.002) and clinical outcome (NIHSS) after 7 days (P=0.003); patients treated with SRFL had increased odds of achieving better long-term clinical status (3M-mRS=0–2; P=0.040). Patients with SRFL and intravenous thrombolysis (IVT) had increased odds of better clinical status (3M-mRS=0–2; P=0.031) and decreased odds of death (P=0.005) compared to patients with SRFL without IVT. The other treatment approaches had no additional effect of IVT. Patients with SRFL with a mothership transfer had increased odds of achieving favorable clinical outcome (3M-mRS) compared to SRFL with the drip-and-ship transfer paradigm (P=0.015).

Conclusions

Our results showed that ADAPT and SRFL provided significantly better outcomes compared to the other examined techniques. A mothership transfer and IVT administration contributed to the success of the SRFL approach.

Neuro-Interventional Management of Acute Ischemic Stroke

Restoration of cerebral blood flow is the most important step in preventing irreversible damage to hypoperfused brain cells after ischemic stroke from large-vessel occlusion. For those patients who do not respond to (or are not eligible for) intravenous thrombolysis, endovascular therapy has become standard of care. A shift is currently taking place from rigid time windows for intervention (time is brain) to physiology-driven paradigms that rely heavily on neuroimaging. At this time, one can reasonably anticipate that more patients will be treated, and that outcomes will keep improving. This article discusses in detail recent advances in endovascular stroke therapy.

Permanent implantation of the Solitaire device as a bailout technique for large vessel intracranial occlusions

The Solitaire (Medtronic Inc, Mansfield, Massachusetts, USA) is a stentriever device for endovascular treatment of acute ischemic stroke. Temporary endovascular bypass and mechanical thrombectomy are well-described applications of this device. However, few reports of permanent stent placement have been published. We present a series of five cases in which the Solitaire stent was implanted to restore distal flow after failure of conventional mechanical thrombectomy. All patients presented with large vessel occlusions with thrombi that were resistant to retrieval or suction-aspiration. Immediately after implantation the patients were given a loading dose of abciximab and then transitioned to dual antiplatelet therapy within 24 hours. Our series suggests that permanent deployment of the Solitaire may be considered as a bailout technique in the treatment of cerebral large vessel occlusion. Long-term antiplatelet therapy is required after deployment.

A Guide-Wired Helical Microrobot for Mechanical Thrombectomy: A Feasibility Study

In this paper, we present a novel guide-wired helical microrobot for mechanical thrombectomy in cardiovascular system, especially for calcified thrombus therapeutics. We designed and fabricated a prototype of the helical shape microrobot equipped with a freely rotatable spherical joint connected to a catheter guidewire, that enables drilling capability to remove calcified objects in vascular. The guidewire helps supporting and maneuvering the microrobot against blood flow during thrombus removal procedure. In addition to the microrobot, an enhanced electromagnetic navigation system (ENS) is implemented to utilize high frequency operation based on resonant effect, which enables powerful drilling force of the microrobot. The in-vitro experimental results illustrate that the suggested method could successfully enhance the locomotion and the drilling force of the helical microrobot that would be sufficient for future mechanical thrombectomy application in cardiovascular therapeutics.

Mechanical Thrombectomy: Emerging Technologies and Techniques

BACKGROUND

The treatment of acute ischemic stroke due to large vessel occlusion (LVO) has revolutionized in the last decade. We sought to compile the most relevant literature published about the evolution in treating this disabling and fatal disease.

METHODS

A literature review of recent studies describing early treatment options like intravenous tissue plasminogen activator to the latest mechanical thrombectomy (MT) techniques was performed. We described in a chronological order the evolution of LVO treatment.

RESULTS

Recanalization rates with newer techniques and MT devices approach a 90% of effectiveness. Timely interventions have also resulted in better clinical outcomes with approximately 50% of patient achieving functional independence at 90 days. At least 14 new third generation thrombectomy devices are currently being evaluated in in vitro and clinical studies.

CONCLUSIONS

The treatment of LVO with MT is feasible and safe. MT is standard of care in treating acute ischemic stroke due to LVO.

Reperfusion therapy in acute ischemic stroke: dawn of a new era?

Following the success of recent endovascular trials, endovascular therapy has emerged as an exciting addition to the arsenal of clinical management of patients with acute ischemic stroke (AIS). In this paper, we present an extensive overview of intravenous and endovascular reperfusion strategies, recent advances in AIS neurointervention, limitations of various treatment paradigms, and provide insights on imaging-guided reperfusion therapies. A roadmap for imaging guided reperfusion treatment workflow in AIS is also proposed. Both systemic thrombolysis and endovascular treatment have been incorporated into the standard of care in stroke therapy. Further research on advanced imaging-based approaches to select appropriate patients, may widen the time-window for patient selection and would contribute immensely to early thrombolytic strategies, better recanalization rates, and improved clinical outcomes.

The Role of Circular RNAs in Cerebral Ischemic Diseases: Ischemic Stroke and Cerebral Ischemia/Reperfusion Injury

Cerebral ischemic diseases including ischemic stroke and cerebral ischemia reperfusion injury can result in serious dysfunction of the brain, which leads to extremely high mortality and disability. There are no effective therapeutics for cerebral ischemic diseases to date. Circular RNAs are a kind of newly investigated noncoding RNAs. It is reported that circular RNAs are enriched in multiple organs, especially abundant in the brain, which indicates that circular RNAs may be involved in cerebral physiological and pathological processes. In this chapter, we will firstly review the pathophysiology, underlying mechanisms, and current treatments of cerebral ischemic diseases including ischemic stroke and cerebral ischemia/reperfusion injury. Secondly, the characteristics and function of circular RNAs will be outlined, and then we are going to introduce the roles circular RNAs play in human diseases. Finally, we will summarize the function of circular RNAs in cerebral ischemic diseases.

8-F balloon guide catheter for embolization of anterior circulation aneurysms: an institutional experience in 152 patients

The use of 8-F balloon guide catheter (BGC) for proximal flow control was previously shown to prevent distal embolic complications during mechanical clot retrieval in patients with acute ischemic stroke. In this retrospective study, the utility of 8-F BGCs for proximal flow control during endovascular coiling of anterior circulation aneurysms was investigated. Patients who underwent endovascular coiling for anterior circulation aneurysms between August 2013 and December 2016 were retrospectively analyzed. Among a total of 152 patients included in this series, 64 patients presented with aneurysmal rupture, whereas the aneurysms were detected incidentally or due to mass effects in the remaining patients. 8-F BGCs were successfully navigated in all patients. The balloon was inflated during navigation in 19 patients. Inflation of the catheter balloon during coil embolization was required in 34 patients; this was performed as an emergency maneuver in six of these patients. Thromboembolic complications occurred in one patient. 8-F BGC can be effectively used for proximal flow control during endovascular treatment of anterior circulation aneurysms. The other advantages included improved navigation of tortuous arterial anatomy, coil stabilization during aneurysmal coiling, and freedom to utilize aneurysmal neck-remodeling balloons for additional adjunctive techniques or to deploy rescue stents. This novel approach might be safely and effectively used in patients undergoing endovascular treatment for anterior circulation aneurysms.

Improving Cerebral Blood Flow after Arterial Recanalization: A Novel Therapeutic Strategy in Stroke

Ischemic stroke is caused by a disruption in blood supply to a region of the brain. It induces dysfunction of brain cells and networks, resulting in sudden neurological deficits. The cause of stroke is vascular, but the consequences are neurological. Decades of research have focused on finding new strategies to reduce the neural damage after cerebral ischemia. However, despite the incredibly huge investment, all strategies targeting neuroprotection have failed to demonstrate clinical efficacy. Today, treatment for stroke consists of dealing with the cause, attempting to remove the occluding blood clot and recanalize the vessel. However, clinical evidence suggests that the beneficial effect of post-stroke recanalization may be hampered by the occurrence of microvascular reperfusion failure. In short: recanalization is not synonymous with reperfusion. Today, clinicians are confronted with several challenges in acute stroke therapy, even after successful recanalization: (1) induce reperfusion, (2) avoid hemorrhagic transformation (HT), and (3) avoid early or late vascular reocclusion. All these parameters impact the restoration of cerebral blood flow after stroke. Recent advances in understanding the molecular consequences of recanalization and reperfusion may lead to innovative therapeutic strategies for improving reperfusion after stroke. In this review, we will highlight the importance of restoring normal cerebral blood flow after stroke and outline molecular mechanisms involved in blood flow regulation.

Clinical and Angiographic Outcomes with the Combined Local Aspiration and Retriever in the North American Solitaire Stent-Retriever Acute Stroke (NASA) Registry

Background

Various techniques are used to enhance the results of mechanical thrombectomy with stent-retrievers, including proximal arrest with balloon guide catheter (BGC), conventional large bore proximal catheter (CGC), or in combination with local aspiration through a large-bore catheter positioned at the clot interface (Aspiration-Retriever Technique for Stroke [ARTS]). We evaluated the impact of ARTS in the North American Solitaire Acute Stroke (NASA) registry.

Summary

Data on the use of the aspiration technique were available for 285 anterior circulation patients, of which 29 underwent ARTS technique, 131 CGC, and 125 BGC. Baseline demographics were comparable, except that ARTS patients are less likely to have hypertension or atrial fibrillation. The ARTS group had more ICA occlusions (41.4 vs. 22% in the BGC, p = 0.04 and 26% in CGC, p = 0.1) and less MCA/M1 occlusions (44.8 vs. 68% in BGC and 62% in CGC). Time from arterial puncture to reperfusion or end of procedure with ARTS was shorter than with CGC (54 vs. 91 min, p = 0.001) and was comparable to the BGC time (54 vs. 67, p = 0.11). Final degree of reperfusion was comparable among the groups (TICI [modified Thrombolysis in Cerebral Infarction] score 2b or higher was 72 vs. 70% for CGC vs. 78% for BGC). Procedural complications, mortality, and good clinical outcome at 90 days were similar between the groups.

Key Messages

The ARTS mechanical thrombectomy in acute ischemic stroke patients appears to yield better results as compared to the use of CGCs with no significant difference when compared to BGC. This early ARTS technique NASA registry data are limited by the earlier generation distal large bore catheters and small sample size. Future studies should focus on the comparison of ARTS and BGC techniques.

Enhanced Fibrinolysis with Magnetically Powered Colloidal Microwheels

Thrombi that occlude blood vessels can be resolved with fibrinolytic agents that degrade fibrin, the polymer that forms between and around platelets to provide mechanical stability. Fibrinolysis rates however are often constrained by transport-limited delivery to and penetration of fibrinolytics into the thrombus. Here, these limitations are overcome with colloidal microwheel (µwheel) assemblies functionalized with the fibrinolytic tissue-type plasminogen activator (tPA) that assemble, rotate, translate, and eventually disassemble via applied magnetic fields. These microwheels lead to rapid fibrinolysis by delivering a high local concentration of tPA to induce surface lysis and, by taking advantage of corkscrew motion, mechanically penetrating into fibrin gels and platelet-rich thrombi to initiate bulk degradation. Fibrinolysis of plasma-derived fibrin gels by tPA-microwheels is fivefold faster than with 1 µg mL^-1 tPA. µWheels following corkscrew trajectories can also penetrate through 100 µm sized platelet-rich thrombi formed in a microfluidic model of hemostasis in ≈5 min. This unique combination of surface and bulk dissolution mechanisms with mechanical action yields a targeted fibrinolysis strategy that could be significantly faster than approaches relying on diffusion alone, making it well-suited for occlusions in small or penetrating vessels not accessible to catheter-based removal.

Application of emerging technologies to improve access to ischemic stroke care

During the past 20 years, the traditional supportive treatment for stroke has been radically transformed by advances in catheter technologies and a cohort of prominent randomized controlled trials that unequivocally demonstrated significant improvement in stroke outcomes with timely endovascular intervention. However, substantial limitations to treatment remain, among the most important being timely access to care. Nonetheless, stroke care has continued its evolution by incorporating technological advances from various fields that can further reduce patients' morbidity and mortality. In this paper the authors discuss the importance of emerging technologies—mobile stroke treatment units, telemedicine, and robotically assisted angiography—as future tools for expanding access to the diagnosis and treatment of acute ischemic stroke.

Quantitative Imaging of Cerebral Thromboemboli In Vivo

Background and Purpose—

Quantitative imaging for the noninvasive assessment of thrombolysis is needed to advance basic and clinical thrombosis-related research and tailor tissue-type plasminogen activator (tPA) treatment for stroke patients. We quantified the evolution of cerebral thromboemboli using fibrin-targeted glycol chitosan–coated gold nanoparticles and microcomputed tomography, with/without tPA therapy.

Methods—

We injected thrombi into the distal internal carotid artery in mice (n=50). Fifty-five minutes later, we injected fibrin-targeted glycol chitosan–coated gold nanoparticles, and 5 minutes after that, we treated animals with tPA or not (25 mg/kg). We acquired serial microcomputed tomography images for 24 hours posttreatment.

Results—

Thrombus burden at baseline was 784×10 3 ±59×10 3 μm 2 for the tPA group (n=42) and 655×10 3 ±103×10 3 μm 2 for the saline group (n=8; P =0.37). Thrombus shrinkage began at 0.5 to 1 hour after tPA therapy, with a maximum initial rate of change at 4603±957 μm 2 /min. The rate of change lowered to ≈61% level of the initial in hours 1 to 2, followed by ≈29% and ≈1% in hours 2 to 3 and 3 to 24, respectively. Thus, 85% of total thrombolysis over 24 hours (≈500 μm 2 , equivalent to 64% of the baseline thrombus burden) occurred within the first 3 hours of treatment. Thrombus burden at 24 hours could be predicted at around 1.5 to 2 hours. Saline treatment was not associated with significant changes in the thrombus burden. Infarct size was smaller in the tPA group versus saline group (18.1±2.3 versus 45.8±3.3 mm 2 ; P <0.01). Infarct size correlated to final thrombus burden ( r =0.71; P <0.01). Time to thrombolysis, completeness of thrombolysis, and tPA therapy were independent predictors of infarct size.

Conclusions—

Thromboembolic burden and the efficacy of tPA therapy can be assessed serially, noninvasively, and quantitatively using high-resolution microcomputed tomography and a fibrin-binding nanoparticle imaging agent.

Risk of Thrombus Fragmentation during Endovascular Stroke Treatment

BACKGROUND AND PURPOSE

Periprocedural thrombus fragmentation is a relevant risk in endovascular stroke treatment. Because factors influencing its occurrence are largely unknown, this study addresses a potential relationship between thrombus histology and clot stability.

MATERIALS AND METHODS

Eighty-five patients with anterior circulation stroke treated with thrombectomy were included in this retrospective study. The number and location of emboli after retrieving the primary thrombus, the number of maneuvers, and TICI scores were evaluated. H&E and neutrophil elastase staining of retrieved clots was performed, and semiquantitative measurements of thrombus components were correlated with procedural parameters.

RESULTS

An inverse correlation between maneuvers required for thrombus retrieval and the number of distal and intermediate emboli was observed (Spearman r, -0.23; P = .032). Younger patients were at higher risk for periprocedural thrombus fragmentation (Spearman r, -0.23; P = .032). Bridging thrombolysis tended to be associated with fewer maneuvers (2 vs 3, P = .054) but more emboli (1 vs 0, P = .067). While no consistent correlation between procedural parameters and red/white blood cells and fibrin-/platelet fractions could be found, higher amounts of neutrophil elastase-positive cells within the thrombus were independently associated with the occurrence of multiple emboli (adjusted OR, 4.6; 95% CI, 1.1-19.7; P = .041) and lower rates of complete recanalization (adjusted OR, 0.3; 95% CI, 0.1-0.9; P = .050).

CONCLUSIONS

Younger age, easy-to-retrieve thrombi, and bridging thrombolysis may be risk factors for periprocedural thrombus fragmentation. Findings from standard histologic stains did not provide insight into thrombectomy-relevant thrombus stability. However, higher neutrophil levels in the thrombus tissue were related to an increased risk of periprocedural thrombus fragmentation. This observation aligns with the proposed thrombolytic capacity of neutrophil elastase and points to its potential clinical relevance in the context of stroke thrombectomy.

Endovascular stroke treatment now and then-procedural and clinical effectiveness and safety of different mechanical thrombectomy techniques over time

BACKGROUND

The most essential development in endovascular stroke treatment (EST) was the shift from intra-arterial thrombolysis to endovascular thrombectomy with dedicated thrombectomy devices, most notably the introduction of stent-retrievers. We evaluated procedural and clinical effectiveness and safety of different EST techniques over time.

METHODS

We retrospectively analyzed EST cases that were treated by the same interventionalist before (n=36) and after (n=50) stent-retrievers were established as the treatment device of first choice. EST techniques in the first cohort comprised intra-arterial thrombolysis (n=24), manual thrombus aspiration (n=15), the use of the Penumbra thrombectomy system (n=13) and the Phenox clot retriever (n=3), intracranial stenting (n=10), and EST with stent-retrievers as a salvage procedure (n=11). In the second cohort, EST with stent-retrievers was the treatment option of first choice (n=47). Intra-arterial thrombolysis (n=15) and stenting of the occluded vessel (n=1) were performed, whenever EST with stent-retrievers failed.

RESULTS

In both cohorts, revascularization rates (TICI ≥2b) were high (91.7% and 86.0%, respectively). A significantly lower number of interventional techniques per case were required in the second cohort (mean ± SD, 1.4±0.5 vs. 2.1±0.9, P<0.001). Recanalization was achieved almost twice as fast in the second cohort (85 vs. 163 minutes on average, P<0.001). The rate of patients achieving good functional outcome (mRS ≤2) was higher in the second cohort (40.0% vs. 22.2%, P=0.083).

CONCLUSIONS

Our findings imply that when stent-retrievers were established as first-line the treatment device a significantly lower number of interventional techniques per case were required and recanalization was achieved almost twice as fast.

Treatment of Acute Ischemic Stroke

Although stroke declined from the third to fifth most common cause of death in the United States, the annual incidence and overall prevalence continue to increase. Since the available US Food and Drug Administration-approved treatment options are time dependent, improving early stroke care may have more of a public health impact than any other phase of care. Timely and efficient stroke treatment should be a priority for emergency department and prehospital providers. This article discusses currently available and emerging treatment options in acute ischemic stroke focusing on the preservation of salvageable brain tissue, minimizing complications, and secondary prevention.

Direct Thrombus Imaging in Stroke

There is an emergent need for imaging methods to better triage patients with acute stroke for tissue-plasminogen activator (tPA)-mediated thrombolysis or endovascular clot retrieval by directly visualizing the size and distribution of cerebral thromboemboli. Currently, magnetic resonance (MR) or computed tomography (CT) angiography visualizes the obstruction of blood flow within the vessel lumen rather than the thrombus itself. The present visualization method, which relies on observation of the dense artery sign (the appearance of cerebral thrombi on a non-enhanced CT), suffers from low sensitivity. When translated into the clinical setting, direct thrombus imaging is likely to enable individualized acute stroke therapy by allowing clinicians to detect the thrombus with high sensitivity, assess the size and nature of the thrombus more precisely, serially monitor the therapeutic effects of thrombolysis, and detect post-treatment recurrence. This review is intended to provide recent updates on stroke-related direct thrombus imaging using MR imaging, positron emission tomography, or CT.

History, Evolution, and Importance of Emergency Endovascular Treatment of Acute Ischemic Stroke

More than 800,000 people in North America suffer a stroke each year, with ischemic stroke making up the majority of these cases. The outcomes of ischemic stroke range from complete functional and cognitive recovery to severe disability and death; outcome is strongly associated with timely reperfusion treatment. Historically, ischemic stroke has been treated with intravenous thrombolytic agents with moderate success. However, five recently published positive trials have established the efficacy of endovascular treatment in acute ischemic stroke. In this review, we will discuss the history of stroke treatments moving from various intravenous thrombolytic drugs to intra-arterial thrombolysis, early mechanical thrombectomy devices, and finally modern endovascular devices. Early endovascular therapy failures, recent successes, and implications for current ischemic stroke management and future research directions are discussed.

The use of stent retrievers in acute ischemic stroke

INTRODUCTION

Acute ischemic stroke (AIS) is one of the leading causes of mortality and adult disability worldwide. For two decades, the preferred approach for AIS was intravenous recombinant tissue plasminogen activator (IV tPA). However, IV tPA cannot be given to many AIS patients who do not meet strict criteria for its use. IV tPA has also had lesser benefit in patients with large clot burden in the context of large vessel occlusion (LVO).

AREAS COVERED

Endovascular stroke therapy had been an 'unproven' therapy despite numerous trials of intra-arterial pharmacologic thrombolysis and mechanical thrombectomy. With the advent of stent-retriever devices, there has been a paradigm shift in the utilization of endovascular therapies for AIS. Our review discusses cerebrovascular hemodynamics, the basis of the recanalization models in AIS, aspects of intravenous thrombolysis, prior generations of endovascular therapy, and the recent successful AIS stent retriever trials. Expert commentary: Recently 'stent-retrievers', a new generation of mechanical thrombectomy devices, were shown to be associated with improved functional outcomes in AIS secondary to proximal intracranial anterior circulation LVO. Stent retrievers are a major advance in AIS care and will have significant impact on the evolution of stroke systems of care.

Increasing Efficacy of Thrombectomy by Using Digital Subtraction Angiography to Confirm Stent Retriever Clot Integration

Physicians performing thrombectomy for acute stroke have had increasing success as thrombectomy-specific devices have continued to evolve. As the devices evolve, so too must the techniques. The current generation of stent retriever thrombectomy devices requires five minutes of dwell time, regardless of the particularities of the case. We have noticed the presence of flow through the stent immediately prior to removal portends a lower chance of successful thrombus retrieval than when no flow is seen, regardless of dwell time. We hypothesize that interventionalists can use the presence or absence of flow to predict adequacy of seating time and decrease the number of deployments per case. This could significantly decrease time to recanalization by avoiding time-consuming, unsuccessful pulls. This is a technical report of a few cases of stent retriever thrombectomy. We propose using post-deployment digital subtraction angiography to confirm thrombus-device integration and increase the chance of thrombus removal.

Evolution of endovascular stroke therapies and devices

Acute ischemic stroke is caused by occlusion of a cerebral artery, resulting in loss of brain tissue and neurologic deficits. However, a portion of the ischemic brain can be salvaged if blood flow is restored within an appropriate time frame. The past year has seen the publication of five positive randomized controlled trials demonstrating substantial benefit of mechanical thrombectomy in select patients with large vessel cerebrovascular occlusion. This progress is related to several factors, but most importantly, dramatic improvements in speed and rates of recanalization with the latest generation devices. In this article, we review the evolution of endovascular acute ischemic stroke therapies and key design features of the most widely used devices.

Direct Microsurgical Embolectomy for Acute Occlusion of the Internal Carotid Artery and Middle Cerebral Artery

BACKGROUND

Surgical embolectomy is the most promising therapy for physically removing emboli from major cerebral arteries. However, it requires an experienced surgical team, time-consuming steps, and is not incorporated into acute stroke therapy.

METHODS

We established seamless collaboration between services, refined surgical techniques, and conducted a prospective trial of emergency surgical embolectomy. Surgical indications included the presence of acute hemispheric symptoms, absence of low-density area on computed tomography, evidence of internal carotid artery terminus or proximal middle cerebral artery occlusion, and availability of resources to start surgery within 3 hours of symptom onset. The indications were confirmed by an interdisciplinary team. We assessed revascularization rates, time from admission to surgery and from surgery to recanalization, procedural complications, and clinical outcomes.

RESULTS

Between 2005 and 2014, 14 consecutive patients with acute proximal middle cerebral artery or internal carotid artery terminus occlusion underwent emergency surgical embolectomy. All patients showed complete recanalization. Twelve patients survived and 7 had fair functional outcome (Rankin Scale score, ≤3). No significant procedural adverse events occurred. The mean times from admission to start of surgery, from surgery to recanalization, and from onset to recanalization were 14 minutes, 79 minutes, and 223 minutes, respectively.

CONCLUSIONS

Our results suggest that microsurgical embolectomy can rapidly, safely, and effectively retrieve clots and deserves reappraisal, although the choice largely depends on local institutional expertise.