Interventionalist Perspective on the New Endovascular Trials

Acute Ischemic Stroke Comorbid with Type 2 Diabetes: Long-Term Prognosis Determinants in a 36-Month Prospective Study for Personalized Medicine

Ischemic stroke (IS) is often comorbid with type 2 diabetes mellitus (T2DM) wherein the determinants of long-term outcomes, beyond the acute stroke phase, are not adequately known. This study identified the determinants of long-term outcomes for diabetic IS patients through a prospective nested case-control study in 624 patients treated with conservative measures (38.60% females, mean age: 63.85 years). After 36-month follow-up, 117 (18.8%) patients with poor outcome were enrolled in the case group. The poor outcome was defined with a modified Rankin Scale (mRS) score ≥3. Meanwhile, 374 (59.9%) patients with good outcome, defined as (mRS score <3), were included in the control group. Patients who died (n = 32) or lost to follow-up (n = 101) were excluded in analysis. Poor prognostic outcome was positively associated with (1) the pulse rate at admission, (2) diastolic blood pressure (DBP), and (3) fasting blood glucose (FBG) during follow-up, whereas physical activity and lipid-lowering treatment during follow-up were negatively associated. Importantly, a forecasting model with these indicators distinguished the patients with good versus poor outcomes with 70.1% sensitivity and 73.5% specificity. Health care professionals and laboratory medicine scholars may want to monitor an increase in DBP and FBG during follow-up, as well as physical activity and lipid-lowering treatment, in relationship to the prognosis of IS with comorbid T2DM after conservative therapies. The proposed predictive model for personalized/precision medicine requires field testing in independent studies, and might help risk stratification with theranostic tests for patients with acute IS who also have a diagnosis of T2DM.

Mechanical thrombectomy and intravascular imaging for cerebral venous sinus thrombosis: a preclinical model

OBJECTIVE

Although the majority of patients with cerebral venous sinus thrombosis (CVST) will improve with anticoagulation therapy, a portion of patients will either present in a comatose state or continue to deteriorate clinically despite early anticoagulation. In these cases, along with treating the underlying thrombophilia, timely thrombolysis may be beneficial. Repurposed arterial thrombectomy devices may not perform as expected in the cerebral venous sinus, and there are currently no preclinical endovascular thrombectomy (EVT) models for CVST. Contrary to arterial stroke research, preclinical models utilized to test various endovascular techniques and devices are lacking. The purpose of this research was to develop a reliable preclinical animal model for the testing of endovascular strategies to treat CVST.

METHODS

Five consecutive male Yorkshire swine weighing 45 kg were utilized. Thrombosis of the superior sagittal sinus was induced with a bovine thrombin injection via a microcatheter under distal balloon occlusion for 15 minutes. Combined arterial injections and superselective sinus injections confirmed the extent of thrombosis. EVT was subsequently performed using a second-generation stent retriever, followed by intravascular optical coherence tomography (OCT) imaging to assess the luminal environment after thrombectomy.

RESULTS

Thrombosis of the superior sagittal sinus, EVT, and subsequent OCT imaging were technically successful in 4 of the 5 swine. Recanalization of the sinus with a second-generation stent retriever was successful after one attempt in 3 of 4 swine (75%), and 1 swine required two attempts. OCT imaging after thrombectomy revealed regions of residual sinus luminal thrombus despite complete angiographic recanalization. Thrombosed bridging cortical veins were also observed before draining into the sinus, along with patent cortical veins.

CONCLUSIONS

The authors describe a preclinical model to assess endovascular techniques and devices for the treatment of CVST. Repurposed devices from arterial stroke may not perform as expected, given the unique features of venous sinus thrombosis. Residual bridging cortical vein thrombus and residual sinus thrombus, visualized on intravascular OCT, may be present despite complete sinus recanalization on angiography, and this may be the etiology of the poor clinical outcome despite technical success. In the setting of bridging cortical vein thrombus after successful sinus thrombectomy, direct chemical thrombolysis may be warranted to dissolve the remaining clot. This model may be helpful in developing and testing a new generation of devices designed specifically for CVST treatment.

Simultaneous patient presentation for endovascular thrombectomy in acute ischemic stroke

BACKGROUND

Increased demand for endovascular thrombectomy has increased the likelihood of simultaneous patient presentation leading to competing demand for time-critical treatment that could adversely impact patient outcomes. We aimed to quantify the occurrence of simultaneous patient presentation at different patient volumes.

METHODS

Empirical distributions for time of patient presentation and case duration were used to probabilistically generate arrival time and case duration for a set annual patient volume, ranging from 1 to 500 cases per year, for 16 000 independent trials at each volume. Time series were generated for each trial to represent the number of cases being performed at each minute of the year. Time series were used to calculate daily thrombectomy demand, annual concurrent demand, and hourly excess demand.

RESULTS

The patient volumes at which at least one annual occurrence of concurrent demand by two patients was 50% and 97.5% likely were 45 and 101, respectively. The volumes at which at least one annual occurrence of concurrent demand by three patients was 50% and 97.5% likely were 216 and 387, respectively. There was dramatic variation in the occurrence of excess demand by two or more patients throughout the day.

CONCLUSIONS

The occurrence of simultaneous presentation by multiple patients for endovascular thrombectomy varies with annual patient volume and time of day. Understanding these trends and the associated patient impact can inform intelligent strategies at regional and national levels for optimizing patient care within real-world financial and operational constraints.

Mechanical recanalization in ischemic anterior circulation stroke within an 8-hour time window: a real-world experience

PURPOSE

We aimed to assess the safety and effectiveness of mechanical recanalization in patients with ischemic stroke in the anterior circulation within 8 h since symptoms onset and with unknown onset time. We compared time intervals <6 h vs. 6-8 h/unknown onset time, as only limited data are available for a time window beyond 6 h.

METHODS

Our cohort included 110 consecutive patients (44 males; mean age, 73.0±11.5 years) with ischemic stroke in the anterior circulation due to the acute occlusion of a large intracranial artery who underwent mechanical recanalization within an 8-hour time window or with unknown onset time. All patients underwent unenhanced computed tomography (CT) of the brain, CT angiography of the cervical and intracranial arteries and digital subtraction angiography. Perfusion CT was performed in patients beyond a 6-hour time window/with unknown onset time. We collected the following data: baseline characteristics, presence of risk factors, neurologic deficit at the time of treatment, time to therapy, recanalization rate, and 3-month clinical outcome. Successful recanalization was defined as Thrombolysis in Cerebral Infarction score of 2b/3 and good clinical outcome as modified Rankin scale value of 0-2 points.

RESULTS

Successful recanalization was achieved in 82 patients (74.5%): in 61 patients treated within 6 h (73.5%), 7 patients treated within 6-8 h (63.6%), and 13 patients with unknown onset time (81.3%). Good 3-month clinical outcome was achieved in 61 patients (55.5%): in 46 patients treated within 6 h (55.4%), 5 patients treated within 6-8 h (45.5%), and 10 patients with unknown onset time (62.5%). Recanalization success or clinical outcome were not significantly different between patients treated at different time windows.

CONCLUSION

Our data confirms the safety and effectiveness of mechanical recanalization performed in carefully selected patients with ischemic stroke in the anterior circulation within 8 h of stroke onset or with unknown onset time in everyday practice.

Techniques for endovascular treatment of acute ischemic stroke

Early recanalization of occluded vessels in patients with acute ischemic stroke (AIS) by either intravenous thrombolysis (IVT) or endovascular revascularization has been shown to be associated with improved clinical outcomes and reduced mortality. Since the initial report regarding endovascular treatment (EVT) of AIS in 1983, endovascular techniques have been tremendously improved, advancing from intra-arterial administration of thrombolytic drugs to stent retrievers. IVT has been evaluated in several large randomized trials and has been shown to improve clinical outcomes at 90 days if treatment was initiated within 3h of stroke onset, while its benefit at 3-4.5h was subsequently demonstrated in the European Cooperative Acute Stroke Study (ECASS) III. Thus, EVT had to be evaluated against IVT. The first randomized controlled trials (RCTs) were published in 2013, and demonstrated no major differences between IVT and EVT for AIS, although these trials had important limitations. The positive results of the Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke (MR CLEAN) in the Netherlands, followed by five other positive RCTs, finally established the efficacy of mechanical thrombectomy (MT) with stent retrievers (also called 'stentrievers') in AIS due to large vessel occlusion within 6h of stroke onset. Currently, the European and US guidelines recommend MT with stent retrievers as a first-line treatment in the management of AIS. The recent publication of the DWI or CTP Assessment with Clinical Mismatch in the Triage of Wake-Up and Late-Presenting Strokes Undergoing Neurointervention (DAWN) trial is expected to lead to extension of the time window for patients carefully selected by imaging. Thus, optimizing the selection of patients as well as the EVT procedures and techniques used is still an important goal to be evaluated in further trials.

Can clot density predict recanalization in acute ischemic stroke treated with intravenous tPA?

Stroke has become an absolute emergency that is treated by additional endovascular means or by replacing pharmacological options. Modern neuroradiological techniques such as computed tomography (CT) allow us to examine multiple parameters of the diseased brain. These focused on the parenchyma and hemodynamics for pretherapeutic decisions. However, it has become evident that the clot is the current target for interventional measures. Clot length is established as a marker for recanalization. The dense artery sign is known as an acute CT sign of stroke that is readily visible on acute nonenhanced CT. The rationale behind our study was to study if clot density might represent clot vulnerability or resistance to treatment. We conducted a prospective study of all consecutive stroke patients admitted to our hospital over 1 year, who presented with signs of acute middle cerebral artery stroke within the therapeutic window, and who underwent either intravenous or combined intravenous and intra-arterial thrombolysis. All patients were evaluated with a complete stroke CT protocol, transcranial color-coded duplex sonography monitoring, and clinical evaluation with the National Institutes of Health Stroke Scale (NIHSS) score. We measured clot length using planimetry on unenhanced CT and measured Hounsfield units in the clots on the same images. A total of 31 patients were included in the study (19 men, 12 women, aged 35–90 years). We found that patients with a longer clot on the unenhanced CT had a higher NIHSS score, confirming previous literature. However, we found that patients with a lower clot density recanalized to a more marked degree and had a better clinical outcome. Patients who did not recanalize had a higher clot density (49 Hounsfield units) than those who did recanalize (23 Hounsfield units). Overall, measuring the clot seems to be an important additional parameter to be taken into account. In our study, CT clot density seems to correlate with clinical outcome and recanalization. The higher density seems to represent a higher red blood cell content. This is evidence that clot composition could play a much more important role in acute stroke than thought until now and characterizing it with imaging may help in choosing the adequate treatment modality. Higher density seems to reflect erythrocyte content. Therefore, patients with a longer and denser clot may necessitate direct thrombectomy.

Subacute endovascular recanalization of symptomatic cerebral artery occlusion: a propensity score-matched analysis

BACKGROUND

The interval between the onset of cerebral vessel occlusion and recanalization has been shown to be an independent predictor of poor outcomes. However, endovascular recanalization of symptomatic cerebral vessel occlusion in the subacute period has not been well documented. We investigated the safety and efficacy of subacute recanalization of occluded cerebral vessels in patients with ischemic stroke or transient ischemic attacks (TIAs).

METHODS

Between 2014 and 2015, 98 patients were admitted to the emergency room for ischemic stroke or TIA with a small infarct core, which was defined as modest early ischemic change on non-contrast CT or overt diffusion-perfusion mismatch. All patients underwent pre-transfemoral cerebral angiography and post-endovascular treatment. The patients were classified according to acute (onset-to-groin puncture time ≤6 hours) or subacute (onset-to-groin puncture time >6 hours) recanalization. Using propensity score analysis, recipients of acute and subacute recanalization underwent 1:1 matching.

RESULTS

Following 1:1 propensity score matching, 32 patients who underwent acute and 32 who underwent subacute intra-arterial thrombolysis were matched. There were no significant differences in National Institutes of Health Stroke Scale at discharge, modified Rankin scale (mRS), the proportion of patients with an mRS value of 0-2, mortality at discharge, intracerebral bleeding, postprocedural infarct extension, newly detected infarction, and hyperintense acute reperfusion marker on follow-up images between the acute and subacute recanalization groups.

CONCLUSIONS

In selected patients with clinically unstable cerebral artery occlusions, a diffusion-perfusion mismatch and small CT lesions, subacute and acute recanalization has comparable safety and efficacy rates.

Time Course of Evolution of Disability and Cause-Specific Mortality After Ischemic Stroke: Implications for Trial Design

Background

Outcome in stroke trials is often based on a 3‐month modified Rankin scale (mRS). How 3‐month mRS relates to longer‐term outcomes will depend on late recovery, delayed stroke‐related deaths, recurrent strokes, and nonstroke deaths. We evaluated 3‐month mRS and death/disability at 1 and 5 years in a population‐based cohort study.

Methods and Results

In 3‐month survivors of ischemic stroke (Oxford Vascular Study; 2002‐2014), we related 3‐month mRS to disability (defined as mRS >2) at 1 and 5 years and/or death rates (age/sex adjusted). Accrual of disability and index‐stroke‐related and nonstroke deaths in each poststroke year was categorized according to 3‐month mRS. Among 1606 patients with acute ischemic stroke, 181 died within 3 months, but 126 index‐stroke‐related deaths and 320 other deaths occurred during the subsequent 4866 patient‐years of follow‐up up to 5 years. Although 69/126 (54.8%) post‐3‐month index‐stroke‐related deaths occurred after 1 year, mRS>2 at 1 year strongly predicted these deaths (adjusted hazard ratio=21.94, 95%CI 7.88‐61.09, P<0.0001). Consequently, a 3‐month mRS >2 was a strong independent predictor of death at both 1 year (adjusted hazard ratio=6.67, 95%CI 4.16‐10.69, P<0.0001) and 5 years (adjusted hazard ratio=2.93, 95%CI 2.38‐3.60, P<0.0001). Although mRS improved by ≥1 point from 3 months to 1 year in 317/1266 (25.0%) patients with 3‐month mRS ≥1, improvement in mRS after 1 year was limited (improvement by ≥1 point: 91/858 [10.6%]; improvement to mRS ≤2: 13/353 [3.7%]).

Conclusions

Our results reaffirm use of the 3‐month mRS outcome in stroke trials. Although later recovery does occur, extending follow‐up to 1 year would capture most long‐term stroke‐related disability. However, administrative mortality follow‐up beyond 1 year has the potential to demonstrate translation of early disability gains into additional reductions in long‐term mortality without much erosion by non‐stroke‐related deaths.

Relay-balloon technique for recanalization of acute symptomatic proximal internal carotid artery occlusion with short balloon-tipped guiding catheter landing zone

Background

Endovascular recanalization of a completely occluded proximal internal carotid artery (ICA) with underlying stenosis may be challenging owing to a possible thrombotic component. This is especially true when the landing zone for a balloon-tipped guiding catheter (BGC) at the bulb portion is insufficient. Sequential application of the balloons of a BGC and an angioplasty catheter may prevent thromboembolism during revascularization. This study analyzed the safety and effectiveness of this relay-balloon technique.

Methods

Ten consecutive patients with acute symptomatic proximal ICA occlusion were treated by the relay-balloon technique. Outcomes analyzed included technical success rate, procedure-related complications, and short-term clinical outcomes.

Results

Successful revascularization was achieved in all 10 patients. One patient experienced a post-procedural infarct extension, but there was no change in National Institutes of Health Stroke Scale (NIHSS) score. Mean NIHSS score decreased from 12.0±5.6 (range 0–18) initially to 6.8±5.4 (range 0–18) at discharge.

Conclusions

The relay-balloon technique is safe and effective in the endovascular revascularization of acute symptomatic proximal ICA occlusions, which are at high risk of distal thromboembolism due to insufficient landing zone for the BGC.

The neuroprotective compound P7C3-A20 promotes neurogenesis and improves cognitive function after ischemic stroke

Ischemic stroke is a devastating condition with few therapeutic interventions available. The neuroprotective compound P7C3-A20 inhibits mature neuronal cell death while also increasing the net magnitude of postnatal neurogenesis in models of neurodegeneration and acute injury. P7C3 compounds enhance flux of nicotinamide adenine dinucleotide (NAD) in mammalian cells, a proposed therapeutic approach to treating cerebral ischemia. The effectiveness of P7C3-A20 treatment on chronic histopathological and behavioral outcomes and neurogenesis after ischemic stroke has not previously been established. Here, a transient middle cerebral artery occlusion in rats was followed by twice daily injection of P7C3-A20 or vehicle for 7days. P7C3-A20-treated rats performed significantly better than vehicle-treated controls in sensorimotor cylinder and grid-walk tasks, and in a chronic test of spatial learning and memory. These behavioral improvements with P7C3-A20 treatment were correlated with significantly decreased cortical and hippocampal atrophy, and associated with increased neurogenesis in the subventricular zone and hippocampal dentate gyrus subgranular zone. Furthermore, cerebral ischemia significantly reduced NAD in the cortex but P7C3-A20 treatment restored NAD to sham levels. Thus, P7C3-A20 treatment mitigates neurodegeneration and augments repair in the brain after focal ischemia, which translates into chronic behavioral improvement. This suggests a new therapeutic approach of using P7C3 compounds to safely augment NAD and thereby promote two independent processes critical to protecting the brain from ischemic stroke: mature neuron survival and postnatal neurogenesis throughout the post-ischemic brain.

Aspiration Thrombectomy After Intravenous Alteplase Versus Intravenous Alteplase Alone

Background and Purpose—

Thrombectomy, primarily with stent retrievers with or without adjunctive aspiration, provided clinical benefit across multiple prospective randomized trials. Whether this benefit is exclusive to stent retrievers is unclear.

Methods—

THERAPY (The Randomized, Concurrent Controlled Trial to Assess the Penumbra System’s Safety and Effectiveness in the Treatment of Acute Stroke; NCT01429350) was an international, multicenter, prospective, randomized (1:1), open label, blinded end point evaluation, concurrent controlled clinical trial of aspiration thrombectomy after intravenous alteplase (IAT) administration compared with intravenous-alteplase alone in patients with large vessel ischemic stroke because of a thrombus length of ≥8 mm. The primary efficacy end point was the percent of patients achieving independence at 90 days (modified Rankin Scale score, 0–2; intention-to-treat analysis). The primary safety end point was the rate of severe adverse events (SAEs) by 90 days (as treated analysis). Patients were randomized 1:1 across 36 centers in 2 countries (United States and Germany).

Results—

Enrollment was halted after 108 (55 IAT and 53 intravenous) patients (of 692 planned) because of external evidence of the added benefit of endovascular therapy to intravenous-alteplase alone. Functional independence was achieved in 38% IAT and 30% intravenous intention-to-treat groups ( P =0.52). Intention-to-treat ordinal modified Rankin Scale odds ratio was 1.76 (95% confidence interval, 0.86–3.59; P =0.12) in favor of IAT. Secondary efficacy analyses all demonstrated a consistent direction of effect toward benefit of IAT. No differences in symptomatic intracranial hemorrhage rates (9.3% IAT versus 9.7% intravenous, P =1.0) or 90-day mortality (IAT: 12% versus intravenous: 23.9%, P =0.18) were observed.

Conclusions—

THERAPY did not achieve its primary end point in this underpowered sample. Directions of effect for all prespecified outcomes were both internally and externally consistent toward benefit. It is possible that an alternate method of thrombectomy, primary aspiration, will benefit selected patients harboring large vessel occlusions. Further study on this topic is indicated.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01429350.

How many stroke patients might be eligible for mechanical thrombectomy?

Introduction

Recent studies showed improved patient outcomes with endovascular treatment of acute stroke compared to medical care, including IV rtPA, alone. Seven trials have reported results, each using different clinical and imaging criteria for patient selection. We compared eligibility for different trial protocols to estimate the number of patients eligible for treatment.

Patients and methods

Patient data were extracted from a single centre database that combined patients recruited to three clinical studies, each of which obtained both CTA and CTP within 6 h of stroke onset. The published inclusion and exclusion criteria of seven intervention trials (MR CLEAN, EXTEND-IA, ESCAPE, SWIFT-PRIME, REVASCAT, THERAPY and THRACE) were applied to determine the proportion that would be eligible for each of these studies.

Results

A total of 263 patients was included. Eligibility for IAT in individual trials ranged from 53% to 3% of patients; 17% were eligible for four trials and under 10% for two trials. Only three patients (1%) were eligible for all studies. The most common cause of exclusion was absence of large artery occlusion (LAO) on CTA. When applying simplified criteria requiring an ASPECT score > 6, 16% were eligible for IAT, but potentially 40% of these patients were excluded by perfusion criteria and more than half by common NIHSS thresholds.

Conclusion

Around 15% of patients presenting within 6 h of stroke onset were potentially eligible for IAT, but clinical trial eligibility criteria have much more limited overlap than is commonly assumed and only 1% of patients fulfilled criteria for all recent trials.

Evolution of endovascular stroke therapies and devices

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

Molecular, cellular and functional events in axonal sprouting after stroke

Stroke is the leading cause of adult disability. Yet there is a limited degree of recovery in this disease. One of the mechanisms of recovery is the formation of new connections in the brain and spinal cord after stroke: post-stroke axonal sprouting. Studies indicate that post-stroke axonal sprouting occurs in mice, rats, primates and humans. Inducing post-stroke axonal sprouting in specific connections enhances recovery; blocking axonal sprouting impairs recovery. Behavioral activity patterns after stroke modify the axonal sprouting response. A unique regenerative molecular program mediates this aspect of tissue repair in the CNS. The types of connections that are formed after stroke indicate three patterns of axonal sprouting after stroke: reactive, reparative and unbounded axonal sprouting. These differ in mechanism, location, relationship to behavioral recovery and, importantly, in their prospect for therapeutic manipulation to enhance tissue repair.

Cyclooxygenase- and cytochrome P450-derived eicosanoids in stroke

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in cardiovascular diseases and stroke. Evidence has demonstrated the important functions of these eicosanoids in regulating cerebral vascular tone, cerebral blood flow, and autoregulation of cerebral circulation. Although COX-2 inhibitors have been suggested as potential treatments for stroke, adverse events, including an increased risk of stroke, occur following long-term use of coxibs. It is important to note that prolonged treatment with rofecoxib increased circulating levels of 20-hydroxyeicosatetraenoic acid (20-HETE), and 20-HETE blockade is a possible strategy to prevent coxib-induced stroke events. It appears that 20-HETE has detrimental effects in the brain, and that its blockade exerts cerebroprotection against ischemic stroke and subarachnoid hemorrhage (SAH). There is clear evidence that activation of EP2 and EP4 receptors exerts cerebroprotection against ischemic stroke. Several elegant studies have contributed to defining the importance of stabilizing the levels of epoxyeicosatrienoic acids (EETs), by inhibiting or deleting soluble epoxide hydrolase (sEH), in stroke research. These reports support the notion that sEH blockade is cerebroprotective against ischemic stroke and SAH. Here, we summarize recent findings implicating these eicosanoid pathways in cerebral vascular function and stroke. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of ischemic stroke and SAH.

Management of the Interventional Stroke Patient

OPINION STATEMENT

The acute treatment of major ischemic stroke has been revolutionized by strong and consistent evidence from multiple randomized trials. Endovascular treatment by mechanical thrombectomy will be increasingly chosen as an adjunctive or alternative to intravenous thrombolysis. To apply this form of stroke treatment is associated with the challenge of optimal periinterventional treatment. The patient has to be identified, counselled, prepared, monitored, cardiovascularly stabilized, possibly sedated and ventilated, and postprocedurally treated in the optimal way. However, most aspects of periinterventional treatment have as yet not been clarified and require prospective research. Among these, the question of general anesthesia vs conscious sedation has received most attention and may be the most crucial one. Based on a great amount of retrospective data, it appears reasonable to start the intervention under conscious sedation of the non-intubated patient with standby measures for emergent intubation, until prospective randomized trials have clarified that issue. Periinterventional management will significantly affect the success of recanalization.