Trevo System: single-center experience with a novel mechanical thrombectomy device

Blood clot fracture properties are dependent on red blood cell and fibrin content

Thrombus fragmentation during endovascular stroke treatment, such as mechanical thrombectomy, leads to downstream emboli, resulting in poor clinical outcomes. Clinical studies suggest that fragmentation risk is dependent on clot composition. This current study presents the first experimental characterization of the composition-dependent fracture properties of blood clots, in addition to the development of a predictive model for blood clot fragmentation. A bespoke experimental test-rig and compact tension specimen fabrication has been developed to measure fracture toughness of thrombus material. Fracture tests are performed on three physiologically relevant clot compositions: a high-fibrin clot made from a 5% haematocrit (H) blood mixture, a medium-fibrin clot made form a 20% H blood mixture, a low-fibrin clot made from a 40% H blood mixture. Fracture toughness is observed to significantly increase with increasing fibrin content, i.e. red blood cell-rich clots are more prone to tear during loading compared to the fibrin-rich clots. Results also reveal that the mechanical behaviour of clot analogues is significantly different in compression and tension. Finite element cohesive zone modelling of clot fracture experiments show that fibrin fibres become highly aligned in the direction perpendicular to crack propagation, providing a significant toughening mechanism. The results presented in this study provide the first characterization of the composition-dependent fracture behaviour of blood clots and are of key importance for development of next-generation thrombectomy devices and clinical strategies. STATEMENT OF SIGNIFICANCE: This study provides a characterisation of the composition-dependent fracture toughness of blood clots. This entails the development of novel experimental techniques for fabrication and testing of blood clot compact tension fracture specimens. The study also develops cohesive zone models of fracture initiation and propagation in blood clots. Results reveal that the fracture resistance of fibrin-rich clots is significantly higher than red blood cell rich clots. Simulations also reveal that stretching and realignment of the fibrin network should be included in blood clot material models in order to accurately replicate compression-tension asymmetry and fibrin enhanced fracture toughness. The results of this study have potentially important clinical implications in terms of clot fracture risk and secondary embolization during mechanical thrombectomy procedures.

Mechanical Thrombectomy Using the New ERIC Retrieval Device Is Feasible, Efficient, and Safe in Acute Ischemic Stroke: A Swiss Stroke Center Experience

BACKGROUND AND PURPOSE

Intravenous thrombolysis and mechanical thrombectomy predominantly using stent retrievers have been shown to effectively restore cerebral blood flow and improve functional outcome in patients with acute ischemic stroke. We sought to determine the safety and feasibility of mechanical thrombectomy using the new ERIC retrieval device.

MATERIALS AND METHODS

We identified 36 consecutive patients from our Stroke Center registry with acute ischemic stroke who were treated with the new ERIC retriever from September 2013 to December 2014. Patients with ischemic stroke meeting the following criteria were eligible: onset-to-treatment time of ≤4.5 hours or wake-up stroke (n = 10) with relevant CT perfusion mismatch, NIHSS score of ≥4, and proof of large-vessel occlusion in the anterior circulation on CT angiography. We assessed the baseline characteristics including age, sex, comorbidities, stroke severity, site of vessel occlusion, presence of tissue at risk, and treatment-related parameters such as onset-to-treatment time, recanalization grade, and outcome.

RESULTS

The mean age was 70 ± 13 years, and the median NIHSS score on admission was 18 (interquartile range, 10-20). Seventeen of 36 patients were on platelet inhibitors or anticoagulants before endovascular treatment (47.2%); 20 patients received intravenous thrombolysis (55.5%). The ERIC was used as the sole retriever in 28 patients (77.8%) and as a rescue device in 8. Excellent recanalization was achieved in 30/36 patients (83.3%) with TICI 3 in 19/36 and 2b in 11/36, respectively. Median procedural time in these patients was 90 minutes (interquartile range, 58-133 minutes). No intraprocedural complications occurred.

CONCLUSIONS

In this observational study, the new ERIC retrieval device was technically feasible, safe, and effective in acute ischemic stroke with large-vessel occlusion.

Mechanical thrombectomy with the Trevo ProVue device in ischemic stroke patients: does improved visibility translate into a clinical benefit?

PURPOSE

To investigate the efficacy and safety of the Trevo ProVue (TPV) stent retriever in stroke patients with large artery occlusions, with particular attention to the full structural radiopacity of the TPV.

MATERIALS AND METHODS

Case files and images of TPV treatments were reviewed for clinical and technical outcome data, including revascularization rates, device and procedure related complications, and outcome at discharge and after 90 days.

RESULTS

76 patients were treated with TPV. Mean National Institutes of Health Stroke Scale (NIHSS) score was 18 and 68% had additional intravenous thrombolysis. 63 occlusions were in the anterior circulation: 44 M1 (58%), 8 M2 (11%), 8 internal carotid artery-terminus (11%), 2 internal carotid artery- left (3%), 1 A2 (1%), and 13 vertebrobasilar (17%). 58 of 76 (76%) were solely treated with TPV; the remainder were treated with additional stent retrievers. Mean number of passes in TPV only cases was 2.2 (SD 1.2). In rescue cases, 3.2 (SD 2.2) passes were attempted with the TPV followed by 2.6 rescue device passes (SD 2). TPV related adverse events occurred in 4/76 cases (5%) and procedural events in 6/76 cases (8%). Mean procedural duration was 64 min (SD 42). Thrombolysis in Cerebral Infarction (TICI) 2b/3 recanalization was achieved in 69/76 patients (91%), including 50% TICI 3. Of 56 survivors (74%), 37 (49%) showed a favorable outcome at 90 days (Solitaire With the Intention for Thrombectomy trial criteria), statistically associated with age, baseline NIHSS, onset to revascularization time, and TICI 2b-3 reperfusion. TPV radiopacity allowed for visual feedback, changing the methodology of stent retriever use in 44/76 cases (58%).

CONCLUSIONS

Neurothrombectomy with TPV is feasible, effective, and safe. The recanalization rate compares favorably with reported data in the literature. Improved structural radiopacity may facilitate neurothrombectomy or influence the course of action during retrieval.

State-of-the-art endovascular treatment of acute ischemic stroke

Stroke is the third leading cause of death in the USA. An estimated 795,000 new or recurrent stroke events occur annually, mostly ischemic in nature. Arterial recanalization and subsequent reperfusion performed shortly after symptom onset can help to restore brain function in acute ischemic stroke (AIS). The only treatment currently approved by the United States Food and Drug Administration is intravenous tissue plasminogen activator, administered within 4.5 h of symptom onset. However, this short window often precludes effective intervention. Mechanical neurothrombectomy devices offer many potential advantages over pharmacologic thrombolysis, including more rapid achievement of recanalization, enhanced efficacy in treating large-vessel occlusions, and a potentially lower risk of hemorrhagic events. The goal of this chapter is to describe the state-of-the-art neurothrombectomy devices and stenting techniques for endovascular treatment of acute ischemic stroke, as well as to highlight recent advances in reperfusion therapies. Ongoing clinical trials, some with randomized, controlled designs, are included.

Recanalization and Reperfusion Therapies of Acute Ischemic Stroke: What have We Learned, What are the Major Research Questions, and Where are We Headed?

Two placebo-controlled trials have shown that early administration of intravenous recombinant tissue plasminogen activator (rt-PA) after ischemic stroke improves outcomes up to 4.5 h after symptoms onset; however, six other trials contradict these results. We also know from analysis of the pooled data that benefits from treatment decrease as time from stroke onset to start of treatment increases. In addition to time, another important factor is patient selection through multimodal imaging, combining data from artery status, and salvageable tissue measures. Nonetheless, at the present time randomized controlled trials (RCTs) cannot demonstrate any beneficial outcomes for neuroimaging mismatch selection after 4.5 h from symptoms onset. By focusing on cases of large arterial occlusion, we know that recanalization is crucial, so endovascular treatment is an approach of interest. The use of intra-arterial thrombolysis was tested in two small RCTs that demonstrated clear benefits in terms of higher recanalization and also in clinical outcomes. But a new paradigm of stroke treatment may have begun with mechanical thrombectomy. In this field, Merci devices have been overtaken by fully deployed closed-cell self-expanding stents (stent-retrievers or “stent-trievers”). However, despite the high rate of recanalization achieved with stent-retrievers compared with other recanalization treatments, the use of these devices cannot clearly demonstrate better outcomes. Thus, futile recanalization occurs when successful recanalization fails to improve functional outcome. Recently, three RCTs, namely synthesis, IMS-III, and MR-rescue, have not been demonstrated any clear benefit for endovascular treatment. Most likely, these trials were not adequately designed to prove the superiority of endovascular treatment because they did not use optimal target populations, vascular status was not evaluated in all patients, relatively high rates of patients did not have enough mismatch, time from baseline neuroimaging to recanalization were too long or the devices used are now obsolete relative to stent-retrievers. Several RCTs currently underway are trying to determine whether bridging therapy is more effective than intravenous treatment and if mechanical thrombectomy is more effective than best medical treatment in patients ineligible for intravenous thrombolysis.

Reperfusion therapies for acute ischemic stroke: an update

Acute ischemic stroke is a major cause of morbidity and mortality in developed countries. Intravenous thrombolysis with tissue plasminogen activator (tPA) within 4.5 hours of symptoms onset significantly improves clinical outcomes in patients with acute ischemic stroke. This narrow window for treatment leads to a small proportion of eligible patients to be treated. Intravenous or intra-arterial trials, combined intravenous/intra-arterial trials, and newer devices to mechanically remove the clot from intracranial arteries have been investigated or are currently being explored to increase patient eligibility and to improve arterial recanalization and clinical outcome. New retrievable stent-based devices offer higher revascularization rates with shorter time to recanalization and are now generally preferred to first generation thrombectomy devices such as Merci Retriever or Penumbra System. These devices have been shown to be effective for opening up occluded vessels in the brain but its efficacy for improving outcomes in patients with acute stroke has not yet been demonstrated in a randomized clinical trial. We summarize the results of the major systemic thrombolytic trials and the latest trials employing different endovascular approaches to ischemic stroke.

Endovascular stroke therapy

BACKGROUND

Following the development of intravenous thrombolysis as a successful treatment for ischaemic stroke, advances in neurointerventional radiology have facilitated endovascular approaches to treatment. This article reviews the available endovascular therapeutic options and their evidence-base.

SUMMARY

Initial studies demonstrated that endovascular treatment of ischaemic stroke with intra-arterial thrombolysis and/or the use of clot-retrieval, thrombus aspiration and stent-retriever devices produced early recanalisation and reperfusion and improved neurological outcome. More recent randomised trials, however, have failed to show translation of recanalisation into successful clinical outcome with 'time to treatment' proving crucial. In this rapidly evolving field, combined therapy incorporating intravenous and intra-arterial thrombolysis in combination with endovascular clot-retrieval has been developed and further studies are expected to yield better evidence to guide the optimal treatment of acute cerebral ischaemia.

Early Postmarket Experience After US Food and Drug Administration Approval With the Trevo Device for Thrombectomy for Acute Ischemic Stroke

BACKGROUND:

TREVO 2 showed the Trevo stent retriever to be more successful for revascularization than Merci for acute stroke intervention in patients treated within 8 hours of symptom onset. These results led to US Food and Drug Administration approval of Trevo.

OBJECTIVE:

To report the first postmarket experience with Trevo since US Food and Drug Administration approval at a single high-volume comprehensive stroke center in the United States.

METHODS:

A retrospective analysis of prospectively collected data was conducted in patients who underwent intervention for ischemic stroke with the Trevo device. Trevo was used alone or in conjunction with other intra-arterial devices. Two groups of patients were identified: those with symptom onset within (group 1) and those with symptom onset beyond (group 2) 8 hours. Recanalization, outcome, symptomatic intracranial hemorrhage, and in-hospital and 90-day mortality were assessed.

RESULTS:

Fifty-two patients were identified, 27 in group 1 and 25 in group 2. Thrombolysis in Cerebral Infarction grade 2 to 3 revascularization was achieved in 93% of group 1 and 84% of group 2 patients. In-hospital mortality and symptomatic intracranial hemorrhage rates were 3.8% and 12% for groups 1 and 2, respectively. Ninety-day mortality was 15% and 24% for groups 1 and 2, respectively. In groups 1 and 2, 48% and 42% of patients, respectively, had good outcomes (modified Rankin Scale score, 0–2), and 50% in both groups of patients achieved Thrombolysis in Cerebral Infarction grade 3 revascularization. Group 2 had longer revascularization times and required adjuvant devices more frequently.

CONCLUSION:

Our postmarket experience shows that in highly selected patients Trevo is safe and effective, even beyond 8 hours, despite longer procedure times and the need for adjuvant devices.

Thrombectomy in patients with large cerebral artery occlusion: a single-center experience with a new stent retriever

INTRODUCTION

The Trevo device, a new stent retriever, may be utilized in patients with large cerebral artery occlusion.

METHODS

Fifty patients with large cerebral artery occlusion and treated with the Trevo device were analyzed. Patients may have received intravenous thrombolysis as a bridging concept in addition to thrombectomy. Outcome and recanalization parameters were documented using the National Institutes of Health Scale, the modified Ranking Scale (mRS) and Thrombolysis in Cerebral Infarction (TICI) score.

RESULTS

In all, 82% (95% confidence interval [CI]: 69%-91%) were documented with TICI 2b and 3. Good clinical outcome after 90 days (mRS ≤ 2) was assessed in 61% (95% CI: 46%-75%). Symptomatic intracerebral hemorrhage occurred in 6 patients (12%, 95% CI: 1%-17%). The overall mortality rate was 14% (95% CI: 6%-27%).

CONCLUSION

Thrombectomy with the new stent retriever device is feasible and effective and has an acceptable risk of intra-cerebral hemorrhage even in combination with pharmacological revascularization techniques.

Neurothrombectomy in the treatment of acute ischaemic stroke

Major ischaemic stroke is a leading cause of morbidity and mortality in industrialized countries. For patients with acute stroke, fast and effective vessel recanalization is important for successful treatment. Neurothrombectomy--that is, angiographically performed mechanical thrombus removal from intracranial arteries--results in higher recanalization rates than with pharmaceutical thrombolysis alone, but the value of this treatment in terms of clinical outcome remains to be established. This article summarizes the history of intra-arterial stroke treatment, outlines the recent developments and the different techniques used, and discusses the results of current studies on neurothrombectomy. Owing to the high morphological and clinical variability of stroke, careful patient selection in future randomized controlled trials will be crucial for assessment of the true potential of neurothrombectomy.

Neurothrombectomy for the treatment of acute ischemic stroke: results from the TREVO study

BACKGROUND

Fast recanalization has been shown to be one of the most important factors for good clinical outcome in stroke patients with acute large vessel occlusion. While intravenous thrombolysis has been shown to be of limited effect in patients with large clot burden, intra-arterial neurothrombectomy offers a new and promising possibility to achieve high recanalization rates within a short time. The Trevo device is a stent-like retriever and was primarily designed to remove thrombus in patients experiencing an acute ischemic stroke. We report on the results of the TREVO Study, which was a prospective, multicenter study in acute stroke patients treated with the Trevo device.

METHODS

Patients were recruited in seven European centers under the control of an external monitor. Centers were selected because of their long experience with interventional stroke therapy especially with neurothrombectomy. We included adults aged 18-85 years with angiographically confirmed large vessel occlusion strokes and NIHSS scores of 8-30 and treatable within 8 h of symptom onset. The primary endpoint was revascularization, defined as at least TICI (thrombolysis in cerebral infarction) 2a. The revascularization scores were assessed by an independent core lab. Secondary endpoints were clinical outcome at 90 days (mRS 90), any device-related serious adverse events and the rate of symptomatic intracerebral hemorrhages.

RESULTS

60 patients were enrolled. The overall recanalization rate (≥TICI 2a) was 91.7% and TICI 2b and 3 was achieved in 78.3%. At 90 days, 55% of the patients had a favorable neurological outcome (mRS 0-2) and 20% had died. Patients with successful recanalization (TICI 2a,b/3) had a good 90-day neurological outcome (mRS 0-2) in 60%, whereas no patient without recanalization had a mRS 90 <3. The overall rate of symptomatic intracerebral hemorrhage according to the SITS-MOST criteria was 5% (3/60).

CONCLUSIONS

The study suggest that the Trevo Stentriever™ is a safe and effective device, which may offer the possibility of a high reperfusion rate and a high rate of patients with good clinical outcome after acute ischemic stroke due to proximal arterial occlusion. Randomized trials comparing intravenous thrombolysis with neurothrombectomy are now urgently needed to evaluate this new approach of interventional stroke therapy.

Safety and efficacy of endovascular sonolysis using the EkoSonic endovascular system in patients with acute stroke

BACKGROUND AND PURPOSE

Sonolysis is a new therapeutic procedure for arterial recanalization. The aim of this study was to confirm the safety and efficacy of endovascular sonolysis by using the EkoSonic Endovascular System in subjects with acute ischemic stroke.

MATERIALS AND METHODS

Patients with acute ischemic stroke with occlusion of the middle cerebral artery or basilar artery were enrolled consecutively in this prospective study. The control group (44 MCA and 12 BA occlusions) was selected from historical controls. EkoSonic Endovascular System was started within 8 hours after stroke onset. The NIHSS score at hospital admission, after 24 hours, and at 7 days; arterial recanalization; early neurologic improvement; symptomatic intracerebral hemorrhage; and favorable 3-month clinical outcome defined as a modified Rankin Scale score of 0-2 were evaluated by statistical means.

RESULTS

Fourteen patients (10 men; mean age, 65.1 ± 11.2 years; median NIHSS score, 16.5) underwent EkoSonic endovascular sonolysis. Arterial recanalization after endovascular treatment was achieved in 6 of 7 (85.7%) patients with MCA occlusion (4 complete recanalizations) and in all 7 (100%) patients with BA occlusion (6 complete recanalizations). No (0%) symptomatic intracerebral hemorrhage or periprocedural complications occurred. Seven (50%) patients were independent at 3 months (median mRS score, 2). Early neurologic improvement and favorable clinical outcome were significantly more frequent in patients with MCA occlusion undergoing EkoSonic endovascular sonolysis than in controls (100% and 71.4% versus 4.6% and 13.6% of patients; P = .0001 and P = .003, respectively). Three-month mortality was significantly lower in patients with BA occlusion undergoing EkoSonic endovascular sonolysis than in controls (0% versus 66.7% patients, P = .013).

CONCLUSIONS

In this small study, EkoSonic endovascular sonolysis allowed safe and potentially effective revascularization in patients experiencing acute ischemic stroke.

Selecting endovascular treatment strategy according to the location of intracranial occlusion in acute stroke

BACKGROUND

Selection of endovascular approaches for acute stroke patients remains unclear. The efficacy of intra-arterial therapy (IAT) has been demonstrated in the past. However, in the last years, the use of mechanical thrombectomy by retrievers (RET) is increasing at the expense of IAT. We aimed to compare several clinical outcomes between patients treated with IAT or RET.

METHODS

In a 6-year period, acute stroke patients (<8 h) with confirmed internal carotid artery (ICA) occlusion or middle cerebral artery (MCA) occlusion undergoing endovascular therapy were prospectively included in our database. Patients who underwent intra-arterial tissue plasminogen activator (tPA) ± microguidewire mechanical clot disruption (IAT group) were compared with those who underwent thrombectomy with the Solitaire® or Trevo® retrievers (RET group). Recanalization (REC) was considered if at the end of the endovascular procedure thrombolysis in cerebral infarction score was 2a-3. Dramatic clinical improvement (DCI) was defined as a decrease of ≥10 NIHSSS points from baseline to discharge or 7 days.

RESULTS

One hundred and eighty patients were included, 100 (55.6%) patients in the IAT group and 80 patients (44.4%) in the RET group. There were no differences in baseline characteristics (age, gender, risk factors profile, previous treatment with i.v. tPA, baseline NIHSS, extracranial ICA angioplasty and time to REC). Rates of REC, DCI and symptomatic intracranial hemorrhage were also similar between groups. Among patients with ICA occlusions (41 IAT, 34 RET), REC was significantly higher with RET (83.9 vs. 61%; p = 0.04).There was a trend towards a higher DCI rate in the RET group (32.3%) compared with the IAT group (14.6%; p = 0.06). According to MCA occlusions, there were no major differences in the main outcome variables. The number needed to treat to achieve one additional DCI with RET compared with IAT was 12 for MCA occlusions, and only 5 for ICA occlusions.

CONCLUSIONS

Among acute stroke patients undergoing endovascular therapies, the benefits of RET over IAT are greater in ICA occlusions. Retrievers may be considered as the first therapeutic option in these patients.

Stentrievers versus other endovascular treatment methods for acute stroke: comparison of procedural results and their relationship to outcomes

BACKGROUND AND PURPOSE

The use of stentrievers (ST) is rapidly growing due to several potential benefits over other available treatments. ST potentially restore flow before clot retrieval and reduce procedural time. We aimed to study the impact of these potential benefits.

METHODS

Patients with acute stroke treated with endovascular procedures in two stroke centers were studied. According to device availability, patients were treated either with intra-arterial tissue plasminogen activator (IAT), Merci or ST. We defined time to initial flow restoration as time from symptom onset to first pass of contrast to previously occluded arteries either through the deployed device or after recanalization. Complete recanalization (Thrombolysis In Cerebral Infarction >2b), day 5 National Institute of Health Stroke Scale (NIHSS) score and favorable outcome at 3 months (modified Rankin Scale score≤2) were recorded.

RESULTS

A total of 315 patients were studied: 127 IAT, 119 Merci, 69 ST (26 Trevo, 43 Solitaire). No major differences were observed in baseline characteristics between the treatment groups. The rate of complete recanalization was higher with ST (67.2%) than with IAT (50.8%) or Merci (57.3%) (p=0.05). Time from groin puncture to final recanalization was lower with ST (88±46 min) than with IAT (103±70 min) or Merci (128±62 min) (p<0.01) and time from groin puncture to initial flow restoration was shorter with ST (36±18 min) than with IAT (92±67 min) or Merci (114±57 min) (p<0.01). Discharge NIHSS was lower in the ST group (7, IQR 1-26) than in the IAT (14, 2-30) or Merci (12, 5-30) groups (p=0.05) and the rate of favorable outcome was higher: ST (52.9%) vs IAT (33.9%) and Merci (40%) (p=0.03). The use of a ST increased the odds of a favorable outcome (OR 1.9, 95% CI 1.04 to 3.39; p=0.037).

CONCLUSIONS

In acute endovascular treatment of stroke, the use of ST may increase recanalization and reduce time to flow restoration leading to improved outcomes.

Trevo versus Merci retrievers for thrombectomy revascularisation of large vessel occlusions in acute ischaemic stroke (TREVO 2): a randomised trial

BACKGROUND

Present mechanical devices are unable to achieve recanalisation in up to 20-40% of large vessel occlusion strokes. We compared efficacy and safety of the Trevo Retriever, a new stent-like device, with its US Food and Drug Administration-cleared predecessor, the Merci Retriever.

METHODS

In this open-label randomised controlled trial, we recruited patients at 26 sites in the USA and one in Spain. We included adults aged 18-85 years with angiographically confirmed large vessel occlusion strokes and US National Institutes of Health Stroke Scale (NIHSS) scores of 8-29 within 8 h of symptom onset. We randomly assigned patients (1:1) with sequentially numbered sealed envelopes to thrombectomy with Trevo or Merci devices. Randomisation was stratified by age (≤68 years vs 69-85 years) and NIHSS scores (≤18 vs 19-29) with alternating blocks of various sizes. The primary efficacy endpoint, assessed by an unmasked core laboratory, was thrombolysis in cerebral infarction (TICI) scores of 2 or greater reperfusion with the assigned device alone. The primary safety endpoint was a composite of procedure-related adverse events. Analyses were done by intention to treat. This study is registered with ClinicalTrials.gov, number NCT01270867.

FINDINGS

Between Feb 3, 2011, and Dec 1, 2011, we randomly assigned 88 patients to the Trevo Retriever group and 90 patients to Merci Retriever group. 76 (86%) patients in the Trevo group and 54 (60%) in the Merci group met the primary endpoint after the assigned device was used (odds ratio 4·22, 95% CI 1·92-9·69; p(superiority)<0·0001). Incidence of the primary safety endpoint did not differ between groups (13 [15%] patients in the Trevo group vs 21 [23%] in the Merci group; p=0·1826).

INTERPRETATION

Patients who have had large vessel occlusion strokes but are ineligible for (or refractory to) intravenous tissue plasminogen activator should be treated with the Trevo Retriever in preference to the Merci Retriever.

FUNDING

Stryker Neurovascular.