Early Loss of Immediate Reperfusion While Stent Retriever in Place Predicts Successful Final Reperfusion in Acute Ischemic Stroke Patients

Association of Stent-Retriever Characteristics in Establishing Successful Reperfusion During Mechanical Thrombectomy : Results from the ESCAPE-NA1 Trial

BACKGROUND

Successful reperfusion determines the treatment effect of endovascular thrombectomy. We evaluated stent-retriever characteristics and their relation to reperfusion in the ESCAPE-NA1 trial.

METHODS

Independent re-scoring of reperfusion grade for each attempt was conducted. The following characteristics were evaluated: stent-retriever length and diameter, thrombus position within stent-retriever, bypass effect, deployment in the superior or inferior MCA trunk, use of balloon guide catheter and distal access catheter. Primary outcome was successful reperfusion defined as expanded thrombolysis in cerebral infarction (eTICI) 2b-3 per attempt. The secondary outcome was successful reperfusion eTICI 2b-3 after the first attempt. Separate regression models for each stent-retriever characteristic and an exploratory multivariable modeling to test the impact of all characteristics on successful reperfusion were built.

RESULTS

Of 1105 patients in the trial, 809 with the stent-retriever use (1241 attempts) were included in the primary analysis. The stent-retriever was used as the first-line approach in 751 attempts. A successful attempt was associated with thrombus position within the proximal or middle third of the stent (OR 2.06; 95% CI: 1.24-3.40 and OR 1.92; 95% CI: 1.16-3.15 compared to the distal third respectively) and with bypass effect (OR 1.7; 95% CI: 1.07-2.72). Thrombus position within the proximal or middle third (OR 2.80; 95% CI: 1.47-5.35 and OR 2.05; 95% CI: 1.09-3.84, respectively) was associated with first-pass eTICI 2b-3 reperfusion. In the exploratory analysis accounting for all characteristics, bypass effect was the only independent predictor of eTICI 2b-3 reperfusion (OR 1.95; 95% CI: 1.10-3.46).

CONCLUSION

The presence of bypass effect and thrombus positioning within the proximal and middle third of the stent-retriever were strongly associated with successful reperfusion.

Refractory Stroke Thrombectomy: Prevalence, Etiology, and Adjunctive Treatment in a North American Cohort

BACKGROUND AND PURPOSE

Acute stroke intervention refractory to mechanical thrombectomy may be due to underlying vessel wall pathology including intracranial atherosclerotic disease and intracranial arterial dissection or recalcitrant emboli. We studied the prevalence and etiology of refractory thrombectomy, the safety and efficacy of adjunctive interventions in a North American-based cohort.

MATERIALS AND METHODS

We performed a multicenter, retrospective study of refractory thrombectomy, defined as unsuccessful recanalization, vessel reocclusion in <72 hours, or required adjunctive antiplatelet glycoprotein IIb/IIIa inhibitors, intracranial angioplasty and/or stenting to achieve and maintain reperfusion. Clinical and imaging criteria differentiated etiologies for refractory thrombectomy. Baseline demographics, cerebrovascular risk factors, technical/clinical outcomes, and procedural safety/complications were compared between refractory and standard thrombectomy groups. Multivariable logistic regression analysis was performed to determine independent predictors of refractory thrombectomy.

RESULTS

Refractory thrombectomy was identified in 25/302 cases (8.3%), correlated with diabetes (44% versus 22%, P = .02) as an independent predictor with OR = 2.72 (95% CI, 1.05-7.09; P = .04) and inversely correlated with atrial fibrillation (16% versus 45.7%, P = .005). Refractory etiologies were secondary to recalcitrant emboli (20%), intracranial atherosclerotic disease (60%), and/or intracranial arterial dissection (44%). Four (16%) patients were diagnosed with early vessel reocclusion, and 21 patients underwent adjunctive salvage interventions with glycoprotein IIb/IIIa inhibitor infusion alone (32%) or intracranial angioplasty and/or stenting (52%). There were no significant differences in TICI 2b/3 reperfusion efficacy (85.7% versus 90.9%, P = .48), symptomatic intracranial hemorrhage rates (0% versus 9%, P = .24), favorable clinical outcomes (39.1% versus 48.3%, P = .51), or mortality (13% versus 28.3%, P = .14) versus standard thrombectomy.

CONCLUSIONS

Refractory stroke thrombectomy is encountered in <10% of cases, independently associated with diabetes, and related to underlying vessel wall pathology (intracranial atherosclerotic disease and/or intracranial arterial dissection) or, less commonly, recalcitrant emboli. Emergent salvage interventions with glycoprotein IIb/IIIa inhibitors or intracranial angioplasty and/or stenting are safe and effective adjunctive treatments.

Biomechanics and hemodynamics of stent-retrievers

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

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

Objective

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

Methods

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

Results

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

Conclusion

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

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

Background

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

Method

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

Results

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

Conclusions

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

First-in-man experience of the Versi Retriever in acute ischemic stroke

OBJECTIVE

To describe our initial experience with the Versi Retriever for mechanical thrombectomy in patients with acute ischemic stroke.

METHODS

This study is a single-center, single-arm, first-in-man registry under institutional review board control to evaluate the efficacy and safety of the new stent retriever, the Versi Retriever. Patients with acute ischemic stroke were consecutively enrolled between September and November 2017. The clinical and procedural data were retrospectively analyzed. The angiographic result after the procedure was self-graded based on the Thrombolysis in Cerebral Infarction (TICI) scale by each operator.

RESULTS

Eleven patients with a mean age of 69.4 years were treated with the Versi Retriever. Median National Institutes of Health Stroke Scale score on admission was 16 (IQR 10-34). The occluded vessel was located in the anterior circulation in 81.8%. Revascularization rates of TICI 2b-3 and TICI 3 at final angiogram were achieved in 100% and 63.6%, respectively. A favorable functional outcome (modified Rankin Scale 0-2) at 90 days was obtained in 72.7%. No symptomatic intracranial hemorrhage occurred and no procedure-related complication was observed.

CONCLUSIONS

Our initial experience suggests that the Versi Retriever is a safe and effective stent retriever for mechanical thrombectomy in patients with acute ischemic stroke.

CLINICAL TRIAL REGISTRATION

NCT03366818.

High-Resolution Imaging of Interaction Between Thrombus and Stent-Retriever in Patients With Acute Ischemic Stroke

Background

Currently, acute ischemic stroke is still a leading cause of mortality and morbidity. Approximately 2 years ago, mechanical thrombectomy was proven beneficial as a revolutionary new therapy for stroke in the MR‐CLEAN trial (A Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands). However, the mechanisms by which the thrombectomy device, or stent‐retriever, interacts with the thrombus are largely unknown. A better understanding could lead to improved efficacy of mechanical thrombectomy devices.

Methods and Results

Seven stent‐retrievers with thrombi still entrapped were collected directly after thrombectomy. The stent‐retrievers were studied using micro computed tomography, followed by scanning electron microscopy and light microscopy. Two independent observers rated interaction type and thrombus surface structure (porous filamentous or dense) at the interaction sites.

A total of 79 interaction sites between thrombus and stent‐retriever were categorized. Thrombus‐stent‐retriever interaction was found to be adhesive (n=44; 56%) or mechanical (n=35; 44%). Adhesive interaction was most frequently observed at interaction sites with a dense surface, compared with interaction sites with a porous filamentous fibrin surface (38/58; 66% versus 6/21; 29%, P=0.011).

Conclusions

The interaction between thrombus and stent‐retriever was predominantly adhesive, not mechanical. Adhesive interaction was strongly associated with the presence of a dense thrombus surface without a porous filamentous fibrin network.

Dwell Time of Stentriever Influences Complete Revascularization and First-Pass TICI 3 Revascularization in Acute Large Vessel Occlusive Stroke

OBJECTIVE

In acute ischemic stroke with large vessel occlusion, the interaction between the clot retriever and the stent is critical for achieving successful recanalization. The ideal time of stent deployment (dwell time [DT]) to improve revascularization is currently unknown. We systematically analyzed the effect of different DT on final angiographic and clinical outcomes of patients who underwent mechanical thrombectomy.

METHODS

The DT was progressively increased from 3 minutes to 5 minutes and then 8 minutes during the study period. The effect of DT on recanalization attempts, successful angiographic outcome (thrombolysis in cerebral ischemia [TICI] 2b or TICI 3), total revascularization time, and immediate and 3-month clinical outcomes were evaluated. The DT of 3 minutes and 5 minutes (DT3-5) was compared against DT of 8 minutes (DT8).

RESULTS

Forty patients were included in the analysis. Good angiographic outcome was observed in 94.1% of patients in the DT8 cohort with an average attempt of 1.2 compared with 78.3% with average attempts of 2.0 in other group. Single-pass good recanalization (TICI 2b or 3) and single-pass complete revascularization (TICI3) was significantly higher in the DT group compared with the DT3-5 group (82.4% vs. 43.5% [P = 0.013] and 42.9% vs. 8.7% [P = 0.003], respectively). A favorable trend toward a reduced overall procedural time (34.59 vs. 55.59 minutes) was observed, but was not statistically significant (P = 0.15).

CONCLUSIONS

Mild prolongation of DT to 8 minutes improves revascularization outcome with fewer attempts, possibly because of better clot-stent interaction.

Causes and Solutions of Endovascular Treatment Failure

In a meta-analysis of individual patient data from 5 randomized controlled trials, endovascular treatment (EVT) mainly using a stent retriever achieved successful recanalization in 71.1% of patients suffering from acute stroke due to anterior circulation large artery occlusion (LAO). However, EVT still failed in 28.9% of LAO cases in those 5 successful trials. Stent retriever failure may occur due to anatomical challenges (e.g., a tortuous arterial tree from the aortic arch to a target occlusion site), a large quantity of clots, tandem occlusion, clot characteristics (fresh versus organized clots), different pathomechanisms (embolic versus non-embolic occlusion), etc. Given that recanalization success is the most important factor in the neurological outcome of acute stroke patients, it is important to seek solutions for such difficult cases. In this review, the basic technique of EVT is briefly summarized and then various difficult cases with diverse conditions are discussed along with suggested solutions.

Interaction between the stent strut and thrombus characterized by contrast-enhanced high-resolution cone beam CT during deployment of the Solitaire stent retriever

Background

The mechanism by which a stent retriever removes intraluminal thrombus from an occluded vessel in humans has not previously been studied. This study performed contrast-enhanced high-resolution cone beam CT (CE-HRCBCT) during deployment of the stent retriever to observe the interaction between the strut and intraluminal thrombus intraoperatively. We also discuss the mechanism by which the thrombus is retrieved.

Methods

In 11 patients, mechanical thrombectomy was performed with a Solitaire stent retriever. The presence or absence of flow restoration (FR) was evaluated immediately and at least 5 min after deployment. Stent retriever findings on CE-HRCBCT were divided into two groups: (1) complete expansion; and (2) incomplete expansion.

Results

FR was observed in all 11 cases (100%) immediately after deployment of the Solitaire stent retriever. Complete expansion was observed in only one case and incomplete expansion was observed in 10 cases. The thrombus was observed mainly near to or outside the strut of the stent retriever by CE-HRCBCT. Loss of FR was seen in only one of the 11 cases. Regardless of this, successful recanalization was achieved with only the stent retriever in nine cases.

Conclusions

CE-HRCBCT showed that the Solitaire stent retriever rarely expanded fully and the thrombus was mainly near to or outside the strut. It may not be necessary to wait a long time to allow the stent to expand fully into the thrombus because the main capture mechanism seems to be engagement of the clot between the crossings of the struts of the Solitaire.

Quantitative assessment of device-clot interaction for stent retriever thrombectomy

PURPOSE

Rapid revascularization in emergent large vessel occlusion with endovascular embolectomy has proven clinical benefit. We sought to measure device-clot interaction as a potential mechanism for efficient embolectomy.

METHODS

Two different radiopaque clot models were injected to create a middle cerebral artery occlusion in a patient-specific vascular phantom. A radiopaque stent retriever was deployed within the clot by unsheathing the device or a combination of unsheathing followed by pushing the device (n=8/group). High-resolution cone beam CT was performed immediately after device deployment and repeated after 5 min. An image processing pipeline was created to quantitatively evaluate the volume of clot that integrates with the stent, termed the clot integration factor (CIF).

RESULTS

The CIF was significantly different for the two deployment variations when the device engaged the hard clot (p=0.041), but not the soft clot (p=0.764). In the hard clot, CIF increased significantly between post-deployment and final imaging datasets when using the pushing technique (p=0.019), but not when using the unsheathing technique (p=0.067). When we investigated the effect of time on CIF in the different clot models disregarding the technique, the CIF was significantly increased in the final dataset relative to the post-deployment dataset in both clot models (p=0.004-0.007).

CONCLUSIONS

This study demonstrates in an in vitro system the benefit of pushing the Trevo stent during device delivery in hard clot to enhance integration. Regardless of delivery technique, clot-device integration increased in both clot models by waiting 5 min.