What to do about fibrin rich ‘tough clots’? Comparing the Solitaire stent retriever with a novel geometric clot extractor in an in vitro stroke model

Association between thrombus composition and first-pass recanalization after thrombectomy in acute ischemic stroke

BACKGROUND

Achieving first-pass recanalization (FPR) has become the primary procedural objective during thrombectomy in acute ischemic stroke patients as it correlates with the best clinical outcome. Understanding factors contributing to FPR failures is essential to enhance FPR success rates. As the central target of thrombectomy, the thrombus itself may be a significant factor influencing FPR.

OBJECTIVES

This study aimed to investigate the association between thrombus composition and FPR success rates.

METHODS

In total, thrombi from 267 ischemic stroke patients were collected in the AZ Groeninge Hospital (Kortrijk, Belgium). Thrombus composition was determined via detailed histologic analysis of red blood cells (RBCs), fibrin, von Willebrand factor, platelets, leukocytes, citrullinated histone 3 (marker for neutrophil extracellular traps), and intracellular and extracellular DNA. FPR was defined as obtaining a modified thrombolysis in cerebral infarction (mTICI) score of 2c/3 after the first pass.

RESULTS

An mTICI score of 2c/3 was obtained in 180 patients, which was achieved via a successful FPR procedure in 126 cases or after multiple passes in 54 cases. Interestingly, thrombi from FPR cases had a different composition from thrombi that needed multiple passes to obtain an mTICI score of 2c/3. FPR thrombi contained significantly more RBCs (P = .0264), less fibrin (P = .0196), and less extracellular DNA (P = .0457).

CONCLUSION

Our results indicate that thrombi characterized by lower RBC content, higher fibrin levels, and increased extracellular DNA are less likely to result in an FPR. These results are important to guide future research aiming at improving procedures or technologies to obtain FPR rates in RBC-poor thrombi.

Evaluation of partial resheathing of EmboTrap III using the microcatheter (PREMIER) technique for fibrin-rich hard clots in an in vitro vessel model

Background and purpose

Despite the ongoing advancements in mechanical thrombectomy for large vessel occlusions causing acute ischemic stroke, successful recanalization is not achieved in all patients. One contributing factor is the presence of fibrin-rich hard clots. We proposed a new technique called the PREMIER technique, which aims to retrieve fibrin-rich clots. This study evaluated the efficacy of the PREMIER technique on fibrin-rich and erythrocyte-rich clots by comparing it with the simple use of EmboTrap III in an in vitro vessel model.

Methods

The PREMIER technique involves partially resheathing a fully deployed EmboTrap III (CERENOVUS, Johnson & Johnson Medical Devices, Irvine, California, USA) using a microcatheter to capture and retrieve a hard clot between the inner channel and outer cages of EmboTrap III. We compared recanalization rate of the PREMIER technique with the simple use of EmboTrap III in an in vitro vessel model, occluding the M1 segment with fibrin-rich hard clots (0% erythrocyte composition) and erythrocyte-rich clots (50% erythrocyte composition).

Results

Among the 40 procedures (10 each for the PREMIER technique and the simple use of EmboTrap III for two different clots) for fibrin-rich clots, the PREMIER technique achieved successful recanalization in all 10 cases, with a significantly higher recanalization rate than the EmboTrap III (100% vs. 50%, p = 0.03). For erythrocyte-rich clots, the recanalization rate was not significantly different in the PREMIER technique compared with the simple use of EmboTrap III (80% vs. 70%, p = 1.00).

Conclusion

The PREMIER technique is a novel technique for acute large-vessel occlusions caused by fibrin-rich hard clots that hinders successful recanalization during mechanical thrombectomy.

Endovascular thrombectomy beyond 24 hours from last known well: a systematic review with meta-analysis

BACKGROUND

Different studies have demonstrated the benefit of endovascular treatment (EVT) up to 24 hours after acute ischemic stroke (AIS) onset. Recent cohort observational studies suggest that patients with large vessel occlusion AIS may benefit from EVT beyond 24 hours from the last known well (LKW) when adequately selected. We aimed to examine the safety and efficacy of EVT beyond 24 hours from LKW using a meta-analysis of all the literature available.

METHODS

A systematic search from inception to April 2023 was conducted for studies including AIS patients with EVT beyond 24 hours from LKW in Medline, Embase, Scopus, and Web of Science. Outcomes of interest included favorable functional outcome (90-day modified Rankin scale (mRS) 0-2), successful reperfusion (modified Thrombolysis in Cerebral Infarction (mTICI) 2b-3), symptomatic intracerebral hemorrhage (sICH), and 90-day mortality. Data were pooled using a random-effects model.

RESULTS

Twelve studies with 894 patients were included. The rate of favorable functional outcome was 40% (95% CI 31% to 49%; I2=76%). The rate of successful reperfusion was 83% (95% CI 80% to 85%; I2=0%). The sICH rate was 7% (95% CI 5% to 9%; I2=0%) and the 90-day mortality rate was 28% (95% CI 24% to 33%; I2=0%). There was no significant difference in favorable outcomes (OR=0.69; 95% CI 0.41 to 1.14) and 90-day mortality (OR=1.35; 95% CI 0.90 to 2.00) among patients who underwent EVT <24 hours versus >24 hours.

CONCLUSIONS

EVT beyond 24 hours from LKW may achieve favorable clinical outcomes and high reperfusion rates, with acceptable intracranial hemorrhage rates in selected patients. Considering the current certainty of the evidence and heterogenous individual study results, larger prospective trials are warranted.

Mechanical thrombectomy using the Nimbus stent-retriever - initial experiences in a single-center observational study

BACKGROUND

The Nimbus stent-retriever (NSR) was developed for mechanical thrombectomy of wall-adherent thrombi in cerebral arteries. It features a novel geometry with a proximal spiral section and a distal barrel section. The new device is designed to retrieve tough clots with a micro-clamping technique. In the first case series reporting on the NSR, we share our initial experience about the first 12 treated cases.

METHODS

In total, 12 patients (5 men, 7 women; mean age 78 years) with occlusion of the internal carotid artery or the middle cerebral artery (M1 or M2 segment) were treated with the NSR, 11 after unsuccessful recanalization attempts with conventional stent-retrievers or aspiration thrombectomy.

RESULTS

Retrieving maneuvers with the NSR recovered a thrombus in 7 patients (58%), of which 6 resulted in vessel recanalization mTICI ≥ 2b. Successful recanalization improved the mTICI score by a median of 3 points. In 5 of 7 cases, this required only one thrombectomy maneuver. In 5 cases, no improvement of recanalization could be achieved with the NSR (1-3 attempts). No NSR-related complications occurred in this case series.

CONCLUSIONS

In our initial experience, the NSR appeared to be a safe and effective second-line stent-retriever after unsuccessful MT with conventional stent-retrievers or aspiration thrombectomy allowing for mTICI ≥ 2b rescue thrombectomy in ab 50% of cases. No NSR associated complications occurred in our case series.

Making acute ischemic stroke thrombi visible in MRI imaging

Knowledge of thrombus behavior and visualization on MRI in acute ischemic stroke is less than optimal. However, MRI sequences could be enhanced based on the typical T1 and T2 relaxation times of the target tissues, which mainly determine their signal intensities on imaging. We studied the relaxation times of a broad spectrum of clot analogs along with their image characteristics of three sequences analyzed: a T1-weighted turbo inversion-recovery sequence (T1w Turbo IR), a T1-weighted turbo spin echo with fat suppression (T1w TSE SPIR), and a T2-weighted 3D TSE with magnetization refocusing to remove T1 dependence (T2w TSE DRIVE). We compared their imaging behavior with the intensity values of normal brain tissue using the same imaging protocols as for clots. Each histological and biochemical clot component contributed to each of the relaxation times. Overall, histological composition correlated strongly with T1 times, and iron content, specifically, with T2 relaxation time. Using decision trees, fibrin content was selected as the primary biomarker for T1 relaxation times, inducing an increase. Up to four clot subgroups could be defined based on its distinctive T1 relaxation time. Clot signal intensity in the T1 and T2-weighted images varied significantly according to T1 and T2 relaxation times. Moreover, in comparison with normal brain tissue intensity values, T2w DRIVE images depict thrombi according to the principle of the more fibrin, the higher the intensity, and in T1w TSE, the more erythrocytes, the higher the intensity. These findings could facilitate improvements in MRI sequences for clot visualization and indicate that T2w DRIVE and T1w TSE sequences should depict the vast majority of acute ischemic stroke thrombi as more hyperintense than surrounding tissues.

Efficacy of endovascular therapy for stroke in developing country: A single-centre retrospective observational study in Indonesia from 2017 to 2021

Background

Indonesia as a developing nation faces a plethora of challenges in applying endovascular therapy (EVT), mostly due to the lack of physicians specialized in neuro-intervention, high operational cost, and time limitation. The efficacy of EVT in improving functional outcomes of stroke in developing countries has not been previously studied.

Methods

This retrospective cohort study was conducted at Dr. Cipto Mangunkusumo Hospital (Jakarta, Indonesia) from January 2017 to December 2021. Large vessel occlusion (LVO) diagnosis was established based on a combination of clinical and imaging characteristics. We assessed patients' functional independence on day-90 based on modified Rankin Scale (mRS) between the endovascular treatment group and the conservative group (those receiving intravascular thrombolysis or medical treatment only). Functional independence was defined as mRS ≤2.

Results

Among 111 stroke patients with LVO, we included 32 patients in the EVT group and 50 patients in the conservative group for this study. Patients with younger age (p = 0.004), lower hypertension rate (p < 0.001), higher intubation rate (p = 0.014), and earlier onset of stroke were observed in the EVT group. The proportion of mRS ≤2 at day-90 in the EVT group was higher than the conservative group (28.1 % vs. 18.0 %; p = 0.280). Patients within mRS ≤2 group had earlier onset-to-puncture time (p = 0.198), onset-to-recanalization time (p = 0.341), lower NIHSS (p = 0.026) and higher ASPECTS (p = 0.001) on admission. In multivariate analysis, ASPECTS (aOR 2.43; 95%CI 1.26-4.70; p = 0.008) defined functional independence in the EVT group.

Conclusion

The endovascular therapy group had a higher proportion of mRS ≤2 at day-90 than the conservative group despite its statistical insignificance.

In vitro models for the experimental evaluation of mechanical thrombectomy devices in acute ischemic stroke

Mechanical thrombectomy has become an important method for the treatment of acute ischemic stroke for large vessel occlusions. The current hotspots of mechanical thrombectomy are optimizing the treatment methods, improving the recanalization rate and reducing complications. The in vitro model has become a common and convenient method for mechanical thrombectomy research. This review summarizes the in vitro model in the following aspects: the preparation of clot analogues; the experimental platform; the application of the in vitro model in the testing of thrombectomy devices; and the advantages, limitations and future trends of the in vitro experimental model. This review describes the characteristics and applications of the in vitro experimental model with the hope that the in vitro experimental model will be further improved and play a more effective role in the study of mechanical thrombectomy.

Temporal trends in results of endovascular treatment of anterior intracranial large cerebral vessel occlusion: A 7-year study

BACKGROUND

Technical improvements in devices, changes in angiographic grading scales and various confounding factors have made difficult the detection of the temporal evolution of angiographic and clinical results after endovascular treatment (EVT) for acute ischemic Stroke (AIS). We analyzed this evolution in time using the Endovascular Treatment in Ischemic Stroke (ETIS) registry.

MATERIALS AND METHODS

We analyzed the efficacy outcomes of EVT performed from January 2015 to January 2022, and modelized the temporal trends using mixed logistic regression models, further adjusted for age, intravenous thrombolysis prior to EVT, general anesthesia, occlusion site, balloon catheter use and the type of first-line EVT strategy. We assessed heterogeneity in temporal trends according to occlusion site, balloon catheter use, cardio embolic etiology, age (<80 years vs ⩾80 years) and first-line EVT strategy.

RESULTS

Among 6104 patients treated from 2015 to 2021, the rates of successful reperfusion (71.1%-89.6%) and of complete first pass effect (FPE) (4.6%-28.9%) increase, whereas the rates of patients with >3 EVT device passes (43.1%-17.5%) and favorable outcome (35.8%-28.9%) decrease significantly over time. A significant heterogeneity in temporal trends in successful reperfusion according to the first-line EVT strategy was found (p-het = 0.018). The temporal trend of increasing successful reperfusion rate was only significant in patients treated with contact aspiration in first-line (adjusted overall effect p = 0.010).

CONCLUSION

In this 7-year-old large registry of ischemic stroke cases treated with EVT, we observed a significant increase with time in the rate of recanalization whereas there was a tendency toward a decrease in the rate of favorable outcome over the same period.

A review of mechanical thrombectomy techniques for acute ischemic stroke

Mechanical thrombectomy is established as standard of care in the management of acute ischemic stroke due to large vessel occlusion and evidence-based guidelines for mechanical thrombectomy have been defined. As research continues to further expand the eligibility criteria for thrombectomy and the number of thrombectomy procedures increase worldwide, there is also growing focus on innovation of thrombectomy devices, procedural techniques, and related outcomes. Thrombectomy primarily involves use of stent retrievers and distal aspiration techniques, but variations and different combinations of techniques have been reported. As this is a rapidly evolving area in stroke management, there is debate as to which, if any, of these techniques leads to improved clinical outcomes over another and there is a lack of data comparing them. In this review, currently published and distinct techniques of mechanical thrombectomy are described methodically along with illustrations to aid in understanding the subtle differences between the techniques. The perceived benefits of each variation are discussed.

NIMBUS geometric clot extractor for challenging clots: Real-world clinical experience and clot composition

PURPOSE

Revascularization rates following mechanical thrombectomy (MT) for acute ischemic stroke (AIS) remain suboptimal for patients with fibrin-rich, recalcitrant clots. The NIMBUS Geometric Clot Extractor has demonstrated promising in vitro revascularization rates using fibrin-rich clot analogs. This study assessed the retrieval rate and composition of clot using NIMBUS in a clinical setting.

METHODS

This retrospective study included patients who underwent MT with NIMBUS at two high-volume stroke centers between December 2019 and May 2021. NIMBUS was used for clots deemed challenging to remove at the interventionalist's discretion. At one of the centers, per pass clot was collected for histological analysis by an independent lab.

RESULTS

A total of 37 patients (mean age 76.87 ± 11.73 years; 18 female; mean time from stroke onset 11.70 ± 6.41 h) were included. NIMBUS was used as first and second-line device in 5 and 32 patients, respectively. The main reason for using NIMBUS (32/37) was the failure of standard MT techniques after a mean 2.86 ± 1.48 number of passes. Substantial reperfusion (mTICI ≥2b) was achieved in 29/37 patients (78.4%) with a mean of 1.81 ± 1.00 NIMBUS passes (mean 4.68 ± 1.68 passes with all devices), and NIMBUS was the final device used in 79.3% (23/29) of those cases. Clot specimens from 18 cases underwent composition analysis. Fibrin and platelets represented 31.4 ± 13.7% and 28.8 ± 18.8% of clot components; 34.4 ± 19.5% were red blood cells.

CONCLUSIONS

In this series, NIMBUS was effective in removing tough clots rich in fibrin and platelets in challenging real-world situations.

Direct Aspiration versus Combined Technique for Distal Medium-Vessel Occlusions: Comparison on a Human Placenta Model

BACKGROUND AND PURPOSE

Mechanical thrombectomy appears to be a promising option for distal medium-vessel occlusions, for which intravenous thrombolysis is effective but may be insufficient when used alone. This study aimed to determine the optimal technique for these distal mechanical thrombectomies using the human placenta model.

MATERIALS AND METHODS

Twenty-four procedures were performed, allowing comparison of direct aspiration (n = 12) versus the combined technique (n = 12). Two positions of the aspiration catheter were tested for each of these techniques: in direct contact with the clot and at a distance from it (5-10 mm). Two types of clots were tested: red blood cell-rich clots and fibrin-rich clots. First-pass recanalization and induced arterial collapse and traction were assessed.

RESULTS

The first-pass recanalization was less frequent for direct aspiration than for the combined technique, without reaching statistical significance (41.7% versus 75.0%, P = .098). Full collapse (P < .001) and extended arterial traction (P = .001) were significantly less frequent for direct aspiration. For direct aspiration with the aspiration catheter not in direct contact with the clot, there was not a single first-pass recanalization and there was systematic arterial collapse, resulting in a no-flow in the aspiration syringe.

CONCLUSIONS

The combined technique appears to be more harmful, and although direct aspiration has a lower rate of first-pass recanalization, it seems appropriate to try direct aspiration as a first-line procedure. However, if the aspiration catheter cannot reach the clot, it is not useful or even risky to try aspiration alone. These results need to be confirmed by clinical studies.

First Experience with the Nimbus Stentretriever

Purpose

To share our first experience with the Nimbus stentretriever, a multizone device designed to assist neurointerventionalists in handling fibrin-rich clots in endovascular stroke treatment.

Methods

We retrospectively analyzed the data of patients who were treated with the Nimbus stentretriever at our high-volume stroke center between May 2021 and May 2022. We evaluated the number of passes before Nimbus was used, the number of passes with nimbus, as well as the recanalization success before and after Nimbus according to the modified treatment in cerebral ischemia (mTICI) scale. Also, patient characteristics, procedural times and clinical outcomes were documented.

Results

A total of 21 consecutive patients were included in the study. An mTICI 2b/3 could be achieved in 76.2% and mTICI 2c/3 could be achieved in 57.1%. The mean number of passes was 3.4 before the use of Nimbus, 2.2 with Nimbus, and 5.4 for all passes with and without Nimbus and 4 occlusions (19.0%) were successfully recanalized with direct aspiration after the use of Nimbus. We observed seven subarachnoid hemorrhages (33.3%) and two cases of vasospasm.

Conclusion

In our series, the use of Nimbus resulted in successful recanalization in half of the patients after otherwise unsuccessful thrombectomy maneuvers; therefore, it should be considered as a rescue option if the maneuver with conventional stent retrievers was unsuccessful.

A Review of the Advancements in the in-vitro Modelling of Acute Ischemic Stroke and Its Treatment

In-vitro neurovascular models of large vessel occlusions (LVOs) causing acute ischemic stroke (AIS) are used extensively for pre-clinical testing of new treatment devices. They enable physicians and engineers to examine device performance and the response of the occlusion to further advance design solutions for current unmet clinical needs. These models also enable physicians to train on basic skills, to try out new devices and new procedural approaches, and for the stroke team to practice workflows together in the comfort of a controlled environment in a non-clinical setting. Removal of the occlusive clot in its entirety is the primary goal of the endovascular treatment of LVOs via mechanical thrombectomy (MT) and the medical treatment via thrombolysis. In MT, recanalization after just one pass is associated with better clinical outcomes than procedures that take multiple passes to achieve the same level of recanalization, commonly known as first pass effect (FPE). To achieve this, physicians and engineers are continually investigating new devices and treatment approaches. To distinguish between treatment devices in the pre-clinical setting, test models must also be optimized and expanded become more nuanced and to represent challenging patient cohorts that could be improved through new technology or better techniques. The aim of this paper is to provide a perspective review of the recent advancements in the in-vitro modeling of stroke and to outline how these models need to advance further in future. This review provides an overview of the various in-vitro models used for the modeling of AIS and compares the advantages and limitations of each. In-vitro models remain an extremely useful tool in the evaluation and design of treatment devices, and great strides have been made to improve replication of physiological conditions. However, further advancement is still required to represent the expanding indications for thrombectomy and thrombolysis, and the generation of new thrombectomy devices, to ensure that smaller treatment effects are captured.

Clot composition characterization using diffuse reflectance spectroscopy in acute ischemic stroke

Acute ischemic stroke caused by large vessel occlusion is treated with endovascular thrombectomy, but treatment failure may occur when clot composition and thrombectomy technique mismatch. In this proof-of-concept study, diffuse reflectance spectroscopy (DRS) is evaluated for identification of clot composition ex vivo. DRS spectra and histology were acquired from 45 clot units retrieved from 29 stroke patients. DRS spectra correlated to clot RBC content, R= 81, p < .001, and could discriminate between RBC-rich and fibrin-rich clots, p < 0.001. Sensitivity and specificity for detection of RBC-rich clots were 0.722 and 0.846 respectively. Applied in an intravascular device, DRS could potentially provide intraprocedural information on clot composition that could increase endovascular thrombectomy efficiency.

Comparison of stent retriever thrombectomy using 3-dimensional patient-specific models of intracranial circulation with actual middle cerebral artery occlusion thrombectomy cases

BACKGROUND AND PURPOSE

Stent retriever (SR) thrombectomy is commonly used for the treatment of emergent large vessel occlusion (ELVO) in acute ischemic stroke. Clot imaging parameters such as clot length, diameter, distance to the internal carotid artery terminus, and vessel angle where the SR is deployed may predict the likelihood of achieving first pass effect (FPE). Most of the proposed factors that seem to affect recanalization success have been studied individually, and conflicting data derived from clinical versus in vitro studies using 3-dimensional printed models of intracranial circulation currently exist.

METHODS

Using patient-specific 3-dimensional phantoms of the cervical and intracranial circulation, we simulated middle cerebral arteries (MCA) M1 and M2 occlusions treated with SR thrombectomy using Solitaire (Medtronic) or Trevo (Styker). Our primary outcome was FPE, defined as Thrombolysis in Cerebral Infarction score of 2c-3 achieved after a single thrombectomy attempt. We also performed retrospective analysis of same clot imaging characteristics of consecutive cases of MCA occlusion and its association with FPE matching the 3-dimensional in vitro experiments. Analysis was conducted using IBM SPSS Statistics Version 25 (IBM Corp., Armonk, NY). Chi-square tests and bivariate logistic regressions were the main statistical tests used in analysis. A p-value of less than .05 was considered to indicate statistical significance. Ninety-five confidence intervals (95% CI) were generated.

RESULTS

We compared 41 thrombectomy experiments performed using patient-specific 3-dimensional in vitro models with a retrospective cohort of 41 patients treated with SR thrombectomy. We found that in the in vitro cohort, higher MCA angulation was associated with a lower likelihood of FPE (odds ratio [OR] = 0.967, 95% CI = 0.944-0.991, p = .008). Meanwhile in the in vivo cohort, higher MCA angulation was associated with a higher likelihood of FPE (OR = 1.039, 95% CI = 1.003-1.077, p = .033). Neither clot length nor location of clot (M1 vs. M2) was associated with a difference in FPE rates in either cohort.

DISCUSSION

Comparison of SR thrombectomy performed during actual MCA occlusion cases versus patient-specific 3-dimensional replicas revealed MCA angulation as an independent predictor of procedure success or failure. However, the opposite direction of effect was observed between the two studied environments, indicating potential limitations of studying SR thrombectomy using 3-dimensional models of LVO.

The prognostic value of extracranial vascular characteristics on procedural duration and revascularization success in endovascularly treated acute ischemic stroke patients

Introduction

Vascular anatomy might affect endovascular treatment success in acute ischemic stroke patients with large vessel occlusion. We investigated the prognostic value of extracranial vascular characteristics on procedural time and revascularization success in patients with large vessel occlusion in the anterior cerebral circulation.

Patients and methods

We included 828 patients endovascularly treated within 6.5 hours of symptom onset from the Dutch MR CLEAN-Registry. We evaluated aortic arch configuration, stenosis and tortuosity of supra-aortic arteries, and internal carotid arteries (ICAs) on pre-intervention CTA. We constructed logistic prediction models for outcome variables procedural duration (≥60 minutes) and non-successful revascularization (extended thrombolysis in cerebral infarction (eTICI) of 0–2A) using baseline characteristics and assessed the effect of extracranial vascular characteristics on model performance.

Results

Cervical ICA tortuosity and stenosis ≥99% improved prediction of long procedural duration compared with baseline characteristics from area under the curve of 0.61 (95% CI: 0.57–0.65) to 0.66 (95% CI: 0.62–0.70) (P < 0.001). Cervical ICA tortuosity was significantly associated with non-successful recanalization. Prediction of non-successful revascularization did not improve after including aortic arch elongation, acute take-off angle, aortic variant, origin stenosis of supra-aortic arteries, and cervical ICA tortuosity, with an area under the curve of 0.63 (95% CI: 0.59–0.67) compared with 0.59 (95% CI: 0.55–0.63) (P = 0.11).

Conclusion

Extracranial vascular characteristics have additional prognostic value for procedural duration, but not for revascularization success, compared with baseline characteristics. Performance of both prediction models is limited in patients treated for large vessel occlusion.

Endovascular administration of magnetized nanocarriers targeting brain delivery after stroke

The increasing use of mechanical thrombectomy in stroke management has opened the window to local intraarterial brain delivery of therapeutic agents. In this context, the use of nanomedicine could further improve the delivery of new treatments for specific brain targeting, tracking and guidance. In this study we take advantage of this new endovascular approach to deliver biocompatible poly(D-L-lactic-co-glycolic acid) (PLGA) nanocapsules functionalized with superparamagnetic iron oxide nanoparticles and Cy7.5 for magnetic targeting, magnetic resonance and fluorescent molecular imaging. A complete biodistribution study in naïve (n = 59) and ischemic (n = 51) mice receiving intravenous or intraarterial nanocapsules, with two different magnet devices and imaged from 30 min to 48 h, showed an extraordinary advantage of the intraarterial route for brain delivery with a specific improvement in cortical targeting when using a magnetic device in both control and ischemic conditions. Safety was evaluated in ischemic mice (n = 69) showing no signs of systemic toxicity nor increasing mortality, infarct lesions or hemorrhages. In conclusion, the challenging brain delivery of therapeutic nanomaterials could be efficiently and safely overcome with a controlled endovascular administration and magnetic targeting, which could be considered in the context of endovascular interventions for the delivery of multiple treatments for stroke.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Diverse thrombus composition in thrombectomy stroke patients with longer time to recanalization

BACKGROUND AND PURPOSE

Delayed time to recanalization is associated with reduced recanalization success of mechanical thrombectomy (MT) and thrombolysis in acute ischemic stroke (AIS). The reasons for this are unclear. We hypothesized that alterations in thrombus structure and composition could be responsible for this.

METHODS

Retrieved thrombi from AIS patients who underwent MT less than 8 h from symptom onset to groin puncture (SOGP) were evaluated. Patients were divided into early (≤4 h.) vs delayed (> 4 h) groups based SOGP timing. Thrombi were histologically analysed using Martius Scarlett Blue and immunohistochemistry staining for von Willebrand Factor (vWF), anti-citrullinated H3 (H3Cit; NETs [neutrophil extracellular traps] marker). We used inferential statistics including, t-test, artificial neural network (ANN) to interpret the data.

RESULTS

A total of 137 thrombi were collected. The overall average percentage of red blood cells (RBC), white blood cells (WBC), platelet, fibrin, H3Cit, and vWF components in thrombi was 45.83%, 3.58%, 22.23%, 28.27%, 19.97% and 16.23% respectively. Delayed group had higher WBCs, (p = 0.02), fibrin (p = 0.02), H3Cit (p = 0.04) and vWF (p = 0.03) thrombus fractions compared to early group. Based on ANN model, the most important factors for predicting the number of passes required for successful recanalization are fibrin and RBC contents of the thrombus followed by vWF and H3Cit contents.

CONCLUSIONS

Longer time to recanalization was associated with increased WBCs, fibrin, H3Cit and vWF fractions of thrombi reflecting possible in situ maturation of thrombus components. Increased fibrin, NETs and vWF composition may reduce likelihood of revascularization by altering thrombus mechanical properties.

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.

Aspects of ischemic stroke biomechanics derived using ex-vivo and in-vitro methods relating to mechanical thrombectomy

Establishing the underlying biomechanics of acute ischemic stroke (AIS) and its treatment is fundamental to developing more effective clinical treatments for one of society's most impactful diseases. Recent changes in AIS management, driven by clinical evidence of improved treatments, has already led to a rapid rate of innovation, which is likely to be sustained for many years to come. These unprecedented AIS triage and treatment innovations provide a great opportunity to better understand the disease. In this article we provide a perspective on the recreation of AIS in the laboratory to inform contemporary device design and procedural techniques in mechanical thrombectomy. Presentation of these findings, which have been used to solve the applied problem of designing mechanical thrombectomy devices, is intended to help inform the development of basic biomechanics solutions for AIS.

A review on the association of thrombus composition with mechanical and radiological imaging characteristics in acute ischemic stroke

Thrombus composition and mechanical properties significantly impact the ease and outcomes of thrombectomy procedures in patients with acute ischemic stroke. A wide variation exists in the composition of thrombi between patients. If a relationship can be determined between the composition of a thrombus and its mechanical behaviour, as well as between the composition of a thrombus and its radiological imaging characteristics, then there is the potential to personalise thrombectomy treatment based on each individual thrombus. This review aims to give an overview of the current literature addressing this issue. Here, we present a scoping review detailing associations between thrombus composition, mechanical behaviour and radiological imaging characteristics. We conducted two searches 1) on the association between thrombus composition and the mechanical behaviour of the tissue and 2) on the association between radiological imaging characteristics and thrombus composition in the acute stroke setting. The review suggests that higher fibrin and lower red blood cell (RBC) content contribute to stiffer thrombi independent of the loading mode. Further, platelet-contracted thrombi are stiffer than non-contracted compositional counterparts. Fibrin content contributes to the elastic portion of viscoelastic behaviour while RBC content contributes to the viscous portion. It is possible to identify fibrin-rich or RBC-rich thrombi with computed tomography and magnetic resonance imaging vessel signs. Standardisation is required to quantify the association between thrombus density on non-contrast computed tomography and the RBC content. The characterisation of the thrombus fibrin network has not been addressed so far in radiological imaging but may be essential for the prediction of device-tissue interactions and distal thrombus embolization. The association between platelet-driven clot contraction and radiological imaging characteristics has not been explicitly investigated. However, evidence suggests that perviousness may be a marker of clot contraction.

Studying Stroke Thrombus Composition After Thrombectomy: What Can We Learn?

The composition of ischemic stroke thrombi has gained an increasing amount of interest in recent years. The implementation of endovascular procedures in standard stroke care has granted researchers the unique opportunity to examine patient thrombus material. Increasing evidence indicates that stroke thrombi are complex and heterogenous, consisting of various biochemical (eg, fibrin, von Willebrand Factor, and neutrophil extracellular traps) and cellular (eg, red blood cells, platelets, leukocytes, and bacteria) components. This complex composition may explain therapeutic limitations and also offer novel insights in several aspects of stroke management. Better understanding of thrombus characteristics could, therefore, potentially lead to improvements in the management of patients with stroke. In this review, we provide a comprehensive overview of the lessons learned by examining stroke thrombus composition after endovascular thrombectomy and its potential relevance for thrombectomy success rates, thrombolysis, clinical outcomes, stroke etiology, and radiological imaging.

The effectiveness of systemic and endovascular intra-arterial thrombectomy protocol for decreasing door-to-recanalization time duration

Objective

Variable treatment strategies and protocols have been applied to reduce time durations in the process of acute stroke management. The aim of this study is to investigate the effectiveness of our intra-arterial thrombectomy (IAT) protocol for decreasing door-to-recanalization time duration and improve successful recanalization.

Methods

A systemic and endovascular protocol included door-to-image, image-to-puncture and puncture-to-recanalization. We retrospectively analyzed the patients of pre- (Sep 2012–Apr 2014) and post-IAT protocol (May 2014–Jul 2018). Univariate analysis was used for the statistical significance according to variable factors (age, gender, the location of occluded vessel, successful recanalization TICI 2b-3). Independent t-test was used to compare the time duration.

Results

Among all 267 patients with acute stroke of anterior circulation, there were 50 and 217 patients with pre- and post-IAT protocol. Age, gender, and the location of occluded vessel have no statistical significance (p＞0.05). In pre- and post-IAT group, successful recanalization was 39 of 50 (78.0%) and 185/217 (85.3%), respectively (p＜0.05). Post-IAT (48.8%, 106/217) group had a higher tendency of good outcome than pre-IAT group (36.0%, 18/50) (p＞0.05). Pre- and post-IAT group showed 61.7±21.4 vs. 25±16.0 (p＜0.05), 102.0±29.8 vs. 82.7±30.4 (min) (p＜0.05), and 79.1±47.5 vs. 58.4±75.3 (p＜0.05) in three steps, respectively.

Conclusions

We suggest that the application of systemic and endovascular IAT protocols showed a significant time reduction for faster recanalization in patients with LVO. To build-up the well-designed IAT protocol through puncture-to-recanalization can be needed to decrease time duration and improve clinical outcome in recanalization therapy in acute stroke patients.

Embotrap Extraction & Clot Evaluation & Lesion Evaluation for NeuroThrombectomy (EXCELLENT) Registry design and methods

Background

Relationships between occlusive clot histopathology, baseline characteristics, imaging findings, revascularization rates, and clinical outcomes of stroke patients with large vessel occlusion (LVO) are not well understood. This study will assess the real-world experience on the efficacy and safety of using the EmboTrap device as the first approach in LVO patients and explore the associations between clot histological characteristics, imaging and clinical findings, revascularization rates, and clinical outcomes.

Methods

Prospective, global, multicenter, single-arm, imaging core laboratory, and clot analysis central laboratory observational registry. Adult patients (>18 years) with LVO, treated with EmboTrap as the first attempted device, will be eligible for study participation.

Results

Up to 1000 subjects at 50 international sites may be enrolled. Occlusive clots will be collected from at least 500 subjects. Independent central and imaging core laboratories will perform clot analysis and image adjudication. Statistical analysis will assess the association between imaging and clinical findings, clot characteristics, subject comorbidities, revascularization, and clinical outcomes. Study endpoints are functional independence (modified Rankin Scale score ≤2 at 90 days), expanded Thrombolysis In Cerebral Infarction (eTICI) score ≥2b50 rate, first-pass effect, number of passes, embolization into new territory, symptomatic intracranial hemorrhage, and 90-day mortality.

Conclusions

The EXCELLENT registry will provide reproducible effectiveness and safety data of EmboTrap for its use for mechanical thrombectomy. Additionally, the study will characterize the blood clots retrieved during mechanical thrombectomy with respect to their composition and histopathological analysis and potential correlations with clinical and imaging findings.

Trial registration number

NCT03685578.

In vitro and in silico modeling of endovascular stroke treatments for acute ischemic stroke

Acute ischemic stroke occurs when a thrombus obstructs a cerebral artery, leading to sub-optimal blood perfusion to brain tissue. A recently developed, preventive treatment is the endovascular stroke treatment (EVT), which is a minimally invasive procedure, involving the use of stent-retrievers and/or aspiration catheters. Despite its increasing use, many critical factors of EVT are not well understood. In this respect, in vitro, and in silico studies have the great potential to help us deepen our understanding of the procedure, perform further device and procedural optimization, and help in clinical training. This review paper provides an overview of the previous in vitro and in silico evaluations of EVT treatments, with a special emphasis on the four main aspects of the adopted experimental and numerical set-ups: vessel, thrombus, device, and procedural settings.

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.

Mechanisms of fibrinolysis resistance and potential targets for thrombolysis in acute ischaemic stroke: lessons from retrieved stroke emboli

There has been growing interest and insight into the histological composition of retrieved stroke emboli. One of the main focuses of the stroke clot analysis literature has been the implications of clot composition on mechanical thrombectomy procedures. However, the holy grail of clot analysis may not be in the field of clot–device interaction, but rather, in understanding mechanisms of fibrinolysis resistance. The mechanisms underlying the low response to fibrinolytic therapy, even with the newer, more powerful agents, remain poorly understood. While factors such as embolus size, location and collateral status influence alteplase delivery and recanalisation rates; compositional analyses focused on histological and ultrastructural characteristics offer unique insights into mechanisms of alteplase resistance. In this review, we strive to provide comprehensive review of current knowledge on clot composition and ultrastructural analyses that help explain resistance to fibrinolysis.

How to Improve the Management of Acute Ischemic Stroke by Modern Technologies, Artificial Intelligence, and New Treatment Methods

Stroke remains one of the leading causes of death and disability in Europe. The European Stroke Action Plan (ESAP) defines four main targets for the years 2018 to 2030. The COVID-19 pandemic forced the use of innovative technologies and created pressure to improve internet networks. Moreover, 5G internet network will be helpful for the transfer and collecting of extremely big databases. Nowadays, the speed of internet connection is a limiting factor for robotic systems, which can be controlled and commanded potentially from various places in the world. Innovative technologies can be implemented for acute stroke patient management soon. Artificial intelligence (AI) and robotics are used increasingly often without the exception of medicine. Their implementation can be achieved in every level of stroke care. In this article, all steps of stroke health care processes are discussed in terms of how to improve them (including prehospital diagnosis, consultation, transfer of the patient, diagnosis, techniques of the treatment as well as rehabilitation and usage of AI). New ethical problems have also been discovered. Everything must be aligned to the concept of “time is brain”.

Fibrin-Platelet Clots in Acute Ischemic Stroke. Predictors and Clinical Significance in a Mechanical Thrombectomy Series

Introduction: The histological composition of the clot influences its mechanical properties, affects the efficacy of endovascular treatment (EVT), and could determine the clinical outcome of patients with acute ischemic stroke (AIS). Insights into clot composition may guide therapeutic decision-making prior to EVT and facilitate revascularization therapies. Material and Methods: Consecutive patients with AIS recorded in a prospective single-center reperfusion registry from December 2015 to December 2019 and treated with EVT were included. Baseline, laboratory [including post-procedural C-reactive protein (CRP)], radiological, and angiographic variables were analyzed. We aimed to study the relationship between histological composition of the clot with basal neuroimaging, laboratory markers, and recanalization technique. The secondary outcome was to analyze the correlation between clot composition and functional outcome at 3 months assessed by the modified Rankin scale (mRS). Results: From the study period, 360 AIS patients treated with EVT were included, of whom 189 (53%) fulfilled the inclusion criteria. One hundred (53%) cases of fibrin-predominant clot (FPC) were recorded. Full recanalization in FPC cases was achieved with higher probability when stent retrievers (SR) were selected as the first-line device (68.2%, p = 0.039). Patients with FPC had higher levels of CRP (p = 0.02), lower frequency of the hyperdense middle cerebral artery (HMCA) in baseline imaging (p = 0.039), and higher rates of mortality (p = 0.012). The multivariate analysis showed that the absence of HMCA (OR = 0.420; 95% CI 0.197-0.898; p = 0.025) and higher levels of CRP (OR = 1.01; 95% CI 1.003-1.019; p = 0.008) were predictors of FPC. Leukocytes and platelet counts were not associated with clot histology. Conclusions: The absence of HMCA and higher levels of CRP were markers of FPC. In patients with FPC, complete recanalization was most likely to be achieved when a SR was selected as first line of treatment. Mortality was higher in patients within this histologic group.

Assessment of Blood Clot Composition by Spectral Optical Coherence Tomography: An In Vitro Study

PURPOSE

Optical coherence tomography (OCT) has the potential for in vivo clot composition characterization in difficult mechanical embolectomy cases. We performed an in vitro study to determine the OCT characteristics of red blood cells (RBCs) and fibrin rich clots.

MATERIALS AND METHODS

Analogues of 5 compositions of clots (5% to 95% RBCs from Group A to E) were created from human blood. The blood mixture was injected into the bifurcation of a 3D printed bifurcated silicone tube. The OPTISTM Integrated System (St. Jude Medical Inc.) was used to identify the magnitude of OCT signals from different compositions of clots. Martius Scarlett Blue trichrome (MSB) staining was performed to confirm the composition of RBCs and fibrin in each clot.

RESULTS

Group A and B showed less signal attenuation (less than 30%) from its surface to the inside, which indicated high penetration (low-back scattering). Group C indicated intermediate signal attenuation (60%) from its surface to inside the clots, in which signals were found even at the periphery of the clot. Group D and E were superficially signal rich with more signal attenuation (more than 80%) from its surface to the inside indicating low penetration (high-back scattering). Signal-free shadowing was shown in 3 clots in Group E. MSB staining indicated color change (from red in fibrin-rich clots to yellow in RBC-rich clots).

CONCLUSION

Different compositions of clots can be assessed using OCT. Fibrin-rich clots have homogeneous signals with high penetration, while RBC-rich clots can be recognized as superficially signal rich with low penetration.

Thrombus Composition and Efficacy of Thrombolysis and Thrombectomy in Acute Ischemic Stroke

Thrombi retrieved from patients with acute ischemic stroke are highly heterogeneous. Recent data suggest that thrombus composition may impact on mechanical thrombectomy, the number of recanalization manoeuvres, resistance to retrieval, and on thrombolytic potential. Our aim was to summarize evidence describing the impact of thrombus composition on efficacy of mechanical thrombectomy and thrombolysis in patients with acute ischemic stroke. The scoping review methodology guided by the Joanna Briggs Institute, an adaption of the Arksey and O'Malley, was followed. Comprehensive searches were conducted in MEDLINE, EMBASE, SCOPUS, and Web of Science. Articles were classified into 4 key themes: (1) composition of stroke thrombi, (2) thrombus composition and mechanical thrombectomy, (3) thrombus composition and thrombolytic therapy, and (4) novel imaging and endovascular approaches. Our search identified 698 articles published from 1987 to June 2020. Additional articles were extracted from reference lists of the selected articles. Overall, 95 topic-specific articles identified for inclusion published in 40 different journals were included. Reports showed that thrombus composition in stroke was highly heterogeneous, containing fibrin, platelets, red blood cells, VWF (von Willebrand Factor), and neutrophil extracellular traps. Thrombi could roughly be divided into fibrin- and red blood cell-rich clots. Fibrin-rich clots were associated with increased recanalization manoeuvres, longer procedure time, and less favorable clinical outcomes compared with red blood cell-rich clots. Advances in detection or treatment of thrombi that take into account clot heterogeneity may be able to improve future endovascular and thrombolytic treatment of stroke.

Characterizing blood clots using acoustic radiation force optical coherence elastography and ultrasound shear wave elastography

Thromboembolism in a cerebral blood vessel is associated with high morbidity and mortality. Mechanical thrombectomy (MT) is one of the emergenc proceduresperformed to remove emboli. However, the interventional approaches such as aspiration catheters or stent retriever are empirically selected. An inappropriate selection of surgical devices can influence the success rate during embolectomy, which can lead to an increase in brain damage. There has been growing interest in the study of clot composition and using a priori knowledge of clot composition to provide guidance for an appropriate treatment strategy for interventional physicians. Developing imaging tools which can allow interventionalists to understand clot composition could affect management and device strategy. In this study, we investigated how clots of different compositions can be characterized by using acoustic radiation force optical coherence elastography (ARF-OCE) and compared with ultrasound shear wave elastography (SWE). Five different clots compositions using human blood were fabricated into cylindrical forms from fibrin-rich (21% red blood cells, RBCs) to RBC-rich (95% RBCs). Using the ARF-OCE and SWE, we characterized the wave velocities measured in the time-domain. In addition, the semi-analytical finite element model was used to explore the relationship between the phase velocities with various frequency ranges and diameters of the clots. The study demonstrated that the wave group velocities generally decrease as RBC content increases in ARF-OCE and SWE. The correlation of the group velocities from the OCE and SWE methods represented a good agreement as RBC composition is larger than 39%. Using the phase velocity dispersion analysis applied to ARF-OCE data, we estimated the shear wave velocities decoupling the effects of the geometry and material properties of the clots. The study demonstrated that the composition of the clots can be characterized by elastographic methods using ARF-OCE and SWE, and OCE demonstrated better ability to discriminate between clots of different RBC compositions, compared to the ultrasound-based approach, especially in clots with low RBC compositions.

Acute ischemic stroke endovascular therapy

Endovascular therapy (EVT) has become the standard treatment for large-vessel occlusion (LVO) acute ischemic stroke (AIS). EVT is now indicated in patients up to 24h from their last known well, provided that the patient meets specific clinical and imaging criteria. Improvements in thrombectomy devices, techniques, and operator experience have allowed successful EVT of ICA terminus, M1-MCA occlusions as well as proximal M2-MCA, basilar artery occlusions, and revascularization of tandem lesions. Mechanical thrombectomy failures still occur due to several factors, however, highlighting the need for further device and technical improvements. An ongoing debate exists regarding the need for pre-EVT thrombolytic agents, thrombectomy techniques, distal occlusions, anesthesia methods, the role of advanced neuroimaging, the treatment of patients with larger infarct core, and those presenting with milder stroke symptoms. Many of these questions are the subject of current or upcoming clinical trials. This review aims to provide an outline and discussion about the established recommendations and emerging topics regarding EVT for LVO AIS.

Nomogram to Predict Poor Outcome after Mechanical Thrombectomy at Older Age and Histological Analysis of Thrombus Composition

An easy scoring system to predict the risk of poor outcome after mechanical thrombectomy among the elderly is currently not available. Therefore, we aimed to develop a nomogram for predicting the probability of negative prognosis in aged patients with acute ischemic stroke undergoing thrombectomy. In addition, we sought to investigate the association between histological thrombus composition and stroke characteristics. To this end, we prospectively studied a developed cohort using data collected from a stroke center from November 2015 to December 2019. The main outcome was functional independence, defined as a modified Rankin Scale score ≤ 2 at 90 days following a mechanical thrombectomy. A nomogram model based on multivariate logistic models was generated. The retrieved thrombi were stained with hematoxylin and eosin and assessed according to histological composition. Our results demonstrated that age ≥ 72 years was independently associated with poor outcome. A total of 304 participants completed the follow-up data to generate the nomogram model. After multivariate logistic regression, five variables remained independent predictors of outcome, including older age, hemorrhagic transformation, thrombolysis in cerebral infarction score, National Institute of Health Stroke score, and neutrophil-to-lymphocyte ratio, and were used to generate the nomogram. The area under the receiver-operating characteristic curve of the model was 0.803. The clots from elderly subjects with large-artery atherosclerosis, anterior circulation, and successful recanalization groups had a higher percentage of fibrin compared to those of younger patients. This is the first nomogram to be developed and validated in a stroke center cohort for individualized prediction of poor outcome in elderly patients after mechanical thrombectomy. Clot composition provides valuable information on the underlying pathogenesis of oxidation in older patients.

Per-pass analysis of acute ischemic stroke clots: impact of stroke etiology on extracted clot area and histological composition

Background

Initial studies investigating correlations between stroke etiology and clot composition are conflicting and do not account for clot size as determined by area. Radiological studies have shown that cardioembolic strokes are associated with shorter clot lengths and lower clot burden than non-cardioembolic clots.

Objective

To report the relationship between stroke etiology, extracted clot area, and histological composition at each procedural pass.

Methods

As part of the multi-institutional RESTORE Registry, the Martius Scarlett Blue stained histological composition and extracted clot area of 612 per-pass clots retrieved from 441 patients during mechanical thrombectomy procedures were quantified. Correlations with clinical and procedural details were investigated.

Results

Clot composition varied significantly with procedural passes; clots retrieved in earlier passes had higher red blood cell content (H4=11.644, p=0.020) and larger extracted clot area (H4=10.730, p=0.030). Later passes were associated with significantly higher fibrin (H4=12.935, p=0.012) and platelets/other (H4=15.977, p=0.003) content and smaller extracted clot area. Large artery atherosclerotic (LAA) clots were significantly larger in the extracted clot area and more red blood cell-rich than other etiologies in passes 1–3. Cardioembolic and cryptogenic clots had similar histological composition and extracted clot area across all procedural passes.

Conclusion

LAA clots are larger and associated with a large red blood cell-rich extracted clot area, suggesting soft thrombus material. Cardioembolic clots are smaller in the extracted clot area, consistent in composition and area across passes, and have higher fibrin and platelets/other content than LAA clots, making them stiffer clots. The per-pass histological composition and extracted clot area of cryptogenic clots are similar to those of cardioembolic clots, suggesting similar formation mechanisms.

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.

Thrombus heterogeneity in ischemic stroke

The structure of stroke thrombi has gained an increasing amount of interest in recent years. The advent of endovascular thrombectomy has offered the unique opportunity to provide and analyze thrombi removed from ischemic stroke patients. It has become clear that the composition of ischemic stroke thrombi is relatively heterogenous and various molecular and cellular patterns become apparent. Good understanding of the histopathologic characteristics of thrombi is important to lead future advancements in acute ischemic stroke treatment. In this review, we give a brief overview of the main stroke thrombus components that have been recently characterized in this rapidly evolving field. We also summarize how thrombus heterogeneity can affect stroke treatment.

Association of Time From Stroke Onset to Groin Puncture With Quality of Reperfusion After Mechanical Thrombectomy: A Meta-analysis of Individual Patient Data From 7 Randomized Clinical Trials

Importance

Reperfusion is a key factor for clinical outcome in patients with acute ischemic stroke (AIS) treated with endovascular thrombectomy (EVT) for large-vessel intracranial occlusion. However, data are scarce on the association between the time from onset and reperfusion results.

Objective

To analyze the rate of reperfusion after EVT started at different intervals after symptom onset in patients with AIS.

Design, Setting, and Participants

We conducted a meta-analysis of individual patient data from 7 randomized trials of the Highly Effective Reperfusion Using Multiple Endovascular Devices (HERMES) group. This is a multicenter cohort study of the intervention arm of randomized clinical trials included in the HERMES group. Patients with anterior circulation AIS who underwent EVT for M1/M2 or intracranial carotid artery occlusion were included. Each trial enrolled patients according to its specific inclusion and exclusion criteria. Data on patients eligible but not enrolled (eg, refusals or exclusions) were not available. All analyses were performed by the HERMES biostatistical core laboratory using the pooled database. Data were analyzed between December 2010 and April 2015.

Main Outcomes and Measures

Successful reperfusion was defined as a modified thrombolysis in cerebral infarction score of 2b/3 at the end of the EVT procedure adjusted for age, occlusion location, pretreatment intravenous thrombolysis, and clot burden score and was analyzed in relation to different intervals (onset, emergency department arrival, imaging, and puncture) using mixed-methods logistic regression.

Results

Among the 728 included patients, with a mean (SD) age of 65.4 (13.5) years and of whom 345 were female (47.4%), decreases in rates of successful reperfusion defined as a thrombolysis in cerebral infarction score of 2b/3 were observed with increasing time from admission or first imaging to groin puncture. The magnitude of effect was a 22% relative reduction (odds ratio, 0.78; 95% CI, 0.64-0.95) per additional hour between admission and puncture and a 26% relative reduction (odds ratio, 0.74; 95% CI, 0.59-0.93) per additional hour between imaging and puncture.

Conclusions and Relevance

Because the probability of reperfusion declined significantly with time between hospital arrival and groin puncture, we provide additional arguments for minimizing the intervals after symptom onset in anterior circulation acute ischemic stroke.

Clot Analog Attenuation in Non-contrast CT Predicts Histology: an Experimental Study Using Machine Learning

Exact histological clot composition remains unknown. The purpose of this study was to identify the best imaging variables to be extrapolated on clot composition and clarify variability in the imaging of thrombi by non-contrast CT. Using a CT-phantom and covering a wide range of histologies, we analyzed 80 clot analogs with respect to X-ray attenuation at 24 and 48 h after production. The mean, maximum, and minimum HU values for the axial and coronal reconstructions were recorded. Each thrombus underwent a corresponding histological analysis, together with a laboratory analysis of water and iron contents. Decision trees, a type of supervised machine learning, were used to select the primary variable altering attenuation and the best parameter for predicting histology. The decision trees selected red blood cells (RBCs) for correlation with all attenuation parameters (p < 0.001). Conversely, maximum attenuation on axial CT offered the greatest accuracy for discriminating up to four groups of clot histology (p < 0.001). Similar RBC-rich thrombi displayed variable imaging associated with different iron (p = 0.023) and white blood cell contents (p = 0.019). Water content varied among the different histologies but did not in itself account for the differences in attenuation. Independent factors determining clot attenuation were the RBCs (β = 0.33, CI = 0.219-0.441, p < 0.001) followed by the iron content (β = 0.005, CI = 0.0002-0.009, p = 0.042). Our findings suggest that it is possible to extract more and valuable information from NCCT that can be extrapolated to provide insights into clot histological and chemical composition.

Endovascular Treatment of Acute Ischemic Stroke

PURPOSE OF REVIEW

Endovascular thrombectomy (ET), the standard of treatment for emergent large vessel occlusion (ELVO) strokes, has been subject to rigorous efforts to further improve its usage and delivery for optimised patient outcomes. This review aims to provide an outline and discussion about the recently established and emerging recommendations regarding endovascular treatment of stroke.

RECENT FINDINGS

The indications for ET have expanded continually, with perfusion imaging now enabling selection of patients presenting 6-24 h after last-known-well, and improved device and operator proficiency allowing treatment of M2-MCA occlusions and tandem occlusions. Further inclusion of paediatric patients and patients with larger infarct core or milder stroke symptoms for ET has been proposed; however, this remains unproven. This growing applicability is supported by more efficient systems of care, employing modern techniques such as telemedicine, mobile stroke units and helicopter medical services. Ongoing debate exists regarding thrombolytic agent, thrombectomy technique, anaesthesia method and the role of advanced neuroimaging, with upcoming RCTs expected to provide clarification. The journey to further improving the efficacy of ET has advanced and diversified rapidly over recent years, involving improved patient selection, increased utility of advanced neuroimaging and ongoing device redevelopment, within the setting of more efficient, streamlined systems of care. This dynamic and ongoing influx of evidence-based refinements is key to further optimising outcomes for ELVO patients.

Mechanical behavior of in vitro blood clots and the implications for acute ischemic stroke treatment

BACKGROUND

Clot mechanical properties are influenced by composition and the arrangement of components within the clot. This work investigates the effects of platelet-driven contraction on blood clot microstructure and mechanical behavior, and provides insight into some implications for mechanical thrombectomy.

METHODS

Platelet-contracted clot analogues (PCCs) and non-contracted clot analogues (NCCs) were prepared from blood mixtures of various hematocrits (%H), that is, the volume percentage of red blood cells (RBCs) in the mixture. Mechanical testing was performed to compare the behavior of the analogues with previously tested human thromboemboli. Scanning electron microscopy and histology investigated the clot microstructure and composition. The association between clot properties and their behavior during mechanical behavior was also investigated.

RESULTS

Overall, PCCs were found to be stiffer than NCCs, across all hematocrits. PCCs with a low %H resisted complete ingestion via contact aspiration alone or complete retrieval with stent-retrievers. PCCs with a higher %H and all NCCs were fully retrievable, although the likelihood of fragmentation was increased in clots with a greater %H. Histologically, there was little difference in the RBC and fibrin content between PCCs and NCCs with the same %H. However, the microstructure of the two groups differed significantly.

CONCLUSION

A selection of repeatable clot analogues with a range of mechanical properties have been developed for in vitro modeling of acute ischemic stroke. Platelet contraction significantly affects clot volume and microstructure, and in turn clot stiffness. The significant difference in mechanical properties and microstructure, but without an appreciable difference in histology, implies that histological studies of explanted human clots alone may not prove to be predictive of the mechanical behavior of the clots in thrombectomy.

Texture parameters of R2* maps are correlated with iron concentration and red blood cells count in clot analogs: A 7-T micro-MRI study

BACKGROUND AND PURPOSE

Previous studies have suggested that mechanical revascularization in acute ischemic stroke (AIS) patients could be affected by clot histology. In this 7-T micro-MRI study, we used R2* relaxometry of clot analogs to evaluate the relationship between texture parameters of R2* maps and clot constituents.

MATERIALS AND METHODS

Twelve AIS clot analogs were experimentally generated to obtain a wide range of red blood cell concentrations. All clots underwent a MR acquisition using a 7-T micro-MR system. A 3D multi-echo gradient-echo sequence was performed and R2* maps were generated. First order and second order statistics of R2* histograms within the clots were calculated. Iron concentration in clots was measured using absorption spectrometry and red blood cell count (RBC) was obtained by histopathological analysis.

RESULTS

RBC count was strongly correlated with iron concentration within clots (r=0.87, P<.001). Higher RBC count and iron concentration were significantly correlated with first order parameters including: (a) global positive shift of the R2* histogram with higher '10th percentile', 'median', 'mean' and '90th percentile'; (b) increase of the global magnitude of voxel values with higher 'total energy' and 'root mean squared'; (c) greater uniformity of the voxel values with higher 'uniformity' and lower 'entropy'. Second order statistical parameters confirmed that higher RBC count and iron concentration correlated with (a) greater concentration of high gray-level values in the image; (b) more "coarse" texture of R2* maps.

CONCLUSIONS

Texture analysis of MRI-R2* maps can accurately estimate the red blood cell count and iron content of AIS clot analogs.

Longer 6-mm Diameter Stent Retrievers Are Effective for Achieving Higher First Pass Success with Fibrin-Rich Clots

First pass success (FPS) can be defined as in vitro retrieval of clot in a single pass during mechanical thrombectomy (MT) for acute large vessel occlusion (LVO). Despite advancements in MT technology, retrieval of fibrin-rich clots remains a challenge. Therefore, the effect of stent retriever length on FPS for fibrin-rich clots was investigated by using Solitaire^TM 6 × 40 versus 6 × 30 mm devices with a balloon guide catheter (BGC) or distal access catheter (DAC) and sheath, in an in vitro model of anterior circulation neurovascular anatomy. Additionally, vascular safety of the Solitaire^TM 6 × 40 versus 6 × 30 mm devices was evaluated in a porcine model for differences in: luminal thrombus, inflammation, endothelial coverage, fibrin deposits, smooth muscle cell loss, elastic lamina and adventitia disruption, intimal hyperplasia, and lumen reduction, at 0, 30, and 90 days post-treatment. In vitro overall FPS was measured as: Solitaire^TM 6 × 40 (95%) and Solitaire^TM 6 × 30 (67%). FPS for clot location in middle cerebral artery was: (a) BGC (6 × 40 mm: 100%; 6 × 30 mm: 100%; n = 8); (b) DAC with 088 sheath (6 × 40 mm: 83%; 6 × 30 mm: 33%; n = 12). FPS for clot location in internal carotid artery was: (a) BGC (6 × 40 mm: 100%; 6 × 30 mm: 80%; n = 11); (b) DAC with 088 sheath (6 × 40 mm: 100%; 6 × 30 mm: 67%; n = 10). Stent length had a significant effect (Fisher's exact test; p < 0.05) on FPS. In vivo evaluation in the porcine model showed no difference in vascular safety parameters between the Solitaire^TM 6 × 40 and 6 × 30 mm devices (p > 0.05) at all time points in the study. Longer stent retrievers may be safe and effective in improving FPS for fibrin-rich clots in in vitro and in vivo models of LVO.

ANCD thrombectomy device: in vitro evaluation

Introduction

Endovascular treatment of stroke, although highly effective, may fail to reach complete recanalization in around 20% of cases. The Advanced Thrombectomy System (ANCD) is a novel stroke thrombectomy device designed to reduce clot fragmentation and facilitate retrieval by inducing local flow arrest and allowing distal aspiration in combination with a stent retriever. We aimed to assess the preclinical efficacy of ANCD.

Methods

Soft red blood cell (RBC)-rich (n=20/group) and sticky fibrin-rich (n=30/group) clots were used to create middle cerebral artery (MCA) occlusions in two vascular phantoms. Three different treatment strategies were tested: (1) balloon guide catheter + Solitaire (BGC+SR); (2) distal access catheter + SR (DAC+SR); and (3) ANCD+SR, until complete recanalization was achieved or to a maximum of three passes. The recanalization rate was determined after each pass.

Results

After one pass, ANCD+SR resulted in an increased recanalization rate (94%) for all clots together compared with BGC+SR (66%; p<0.01) or DAC+SR (80%; p=0.04). After the final pass the recanalization rate increased in all three groups but remained higher with ANCD+SR (100%) than with BGC+SR (74%; p<0.01) or DAC+SR (90%; p=0.02). The mean number of passes was lower with ANCD+SR (1.06) than with BGC+SR (1.46) or DAC+SR (1.25) (p=0.01). A logistic regression model adjusted for treatment arm, clot type, and model used showed that both RBC-rich clots (OR 8.1, 95% CI 1.6 to 13.5) and ANCD+SR (OR 3.9, 95% CI 1.01 to 15.8) were independent predictors of first-pass recanalization.

Conclusion

In in vitro three-dimensional models replicating MCA-M1 occlusion, ANCD+SR showed significantly better recanalization rates in fewer passes than other commonly used combinations of devices.

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

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

Thrombus perviousness is not associated with first-pass revascularization using stent retrievers

BACKGROUND AND PURPOSE

Recent studies suggest that thrombus imaging characteristics such as Hounsfield unit (HU) and perviousness assessed on noncontrast computed tomography (NCCT) and CT angiography (CTA) can predict successful recanalization. We assessed whether these thrombus imaging characteristics could predict successful first-pass recanalization.

METHODS

We retrospectively reviewed cases of mechanical thrombectomy over a three-year period in which patients received a multiphase CTA and were treated with a stent retriever on first pass. Thrombus attenuation, thrombus enhancement on arterial- and delayed-phase CTA and percentage washout were calculated and their association with first-pass recanalization, successful recanalization and distal embolic complications was studied.

RESULTS

Fifty-two mechanical thrombectomy patients were included. First-pass recanalization was achieved in 59.6% and complete revascularization (Thrombolysis in Cerebral Infarction scale 2b/3) was achieved in 84.6%. There was no correlation between first-pass recanalization with thrombus density on NCCT ( p = 0.94), percentage enhancement on arterial ( p = 0.61) and delayed-phase CTA ( p = 0.23) or thrombus length ( p = 0.16). There was no correlation between number of passes and either thrombus density on NCCT ( p = 0.91) or percentage enhancement on arterial- ( p = 0.79) and delayed-phase ( p = 0.14) CTA or thrombus length ( p = 0.34). Clot length was significantly higher in patients with distal embolic complications than in those without (18.5 ± 7.9 vs 11.4 ± 6.6 mm, p = 0.005).

CONCLUSIONS

Our data suggest that thrombus imaging characteristics on multiphase CTA cannot predict first-pass recanalization or successful revascularization in acute ischemic stroke patients treated with stent retrievers. Longer clot length was associated with higher risk of distal embolic complications.

MRI Quantitative T2* Mapping to Predict Dominant Composition of In Vitro Thrombus

BACKGROUND AND PURPOSE

MR imaging quantitative T2* mapping, which provides information about thrombus composition and specifically the red blood cell content, may be obtained in the setting of acute ischemic stroke before treatment. This could be useful to adapt the endovascular strategy. We aimed to analyze the red blood cell content of in vitro thrombi in relation to the thrombus-T2* relaxation time.

MATERIALS AND METHODS

Thirty-five thrombus analogs of different compositions were scanned with an MR imaging quantitative T2* mapping sequence. Two radiologists, blinded to thrombus composition, measured the thrombus-T2* relaxation time twice at an interval of 2 weeks. Quantitative histologic evaluations of red blood cell content were performed. Inter- and intraobserver reproducibility of the thrombus-T2* relaxation time was assessed by calculating intraclass correlation coefficients. Finally, a Spearman product moment correlation between the thrombus-T2* relaxation time and red blood cell content was performed.

RESULTS

The median thrombus-T2* relaxation time was 78.5 ms (range, 16-268 ms; interquartile range, 60.5 ms). The median red blood cell content was 55% (range, 0%-100%; interquartile range, 75%). Inter- and intraobserver reproducibility of the thrombus-T2* relaxation time was excellent (>0.9). The Spearman rank correlation test found a significant inverse correlation between thrombus-T2* relaxation time and red blood cell content (ρ = -0.834, P < .001).

CONCLUSIONS

MR imaging quantitative T2* mapping can reliably identify the thrombus red blood cell content in vitro. This fast, easy-to-use sequence could be implemented in routine practice to predict stroke etiology and adapt devices or techniques for endovascular treatment of acute ischemic stroke.