Collateral blood vessels in acute ischaemic stroke: a potential therapeutic target

A trial of imaging selection and endovascular treatment for ischemic stroke

BACKGROUND

Whether brain imaging can identify patients who are most likely to benefit from therapies for acute ischemic stroke and whether endovascular thrombectomy improves clinical outcomes in such patients remains unclear.

METHODS

In this study, we randomly assigned patients within 8 hours after the onset of large-vessel, anterior-circulation strokes to undergo mechanical embolectomy (Merci Retriever or Penumbra System) or receive standard care. All patients underwent pretreatment computed tomography or magnetic resonance imaging of the brain. Randomization was stratified according to whether the patient had a favorable penumbral pattern (substantial salvageable tissue and small infarct core) or a nonpenumbral pattern (large core or small or absent penumbra). We assessed outcomes using the 90-day modified Rankin scale, ranging from 0 (no symptoms) to 6 (dead).

RESULTS

Among 118 eligible patients, the mean age was 65.5 years, the mean time to enrollment was 5.5 hours, and 58% had a favorable penumbral pattern. Revascularization in the embolectomy group was achieved in 67% of the patients. Ninety-day mortality was 21%, and the rate of symptomatic intracranial hemorrhage was 4%; neither rate differed across groups. Among all patients, mean scores on the modified Rankin scale did not differ between embolectomy and standard care (3.9 vs. 3.9, P=0.99). Embolectomy was not superior to standard care in patients with either a favorable penumbral pattern (mean score, 3.9 vs. 3.4; P=0.23) or a nonpenumbral pattern (mean score, 4.0 vs. 4.4; P=0.32). In the primary analysis of scores on the 90-day modified Rankin scale, there was no interaction between the pretreatment imaging pattern and treatment assignment (P=0.14).

CONCLUSIONS

A favorable penumbral pattern on neuroimaging did not identify patients who would differentially benefit from endovascular therapy for acute ischemic stroke, nor was embolectomy shown to be superior to standard care. (Funded by the National Institute of Neurological Disorders and Stroke; MR RESCUE ClinicalTrials.gov number, NCT00389467.).

Optimized system for cerebral perfusion monitoring in the rat stroke model of intraluminal middle cerebral artery occlusion

The translational potential of pre-clinical stroke research depends on the accuracy of experimental modeling. Cerebral perfusion monitoring in animal models of acute ischemic stroke allows to confirm successful arterial occlusion and exclude subarachnoid hemorrhage. Cerebral perfusion monitoring can also be used to study intracranial collateral circulation, which is emerging as a powerful determinant of stroke outcome and a possible therapeutic target. Despite a recognized role of Laser Doppler perfusion monitoring as part of the current guidelines for experimental cerebral ischemia, a number of technical difficulties exist that limit its widespread use. One of the major issues is obtaining a secure and prolonged attachment of a deep-penetration Laser Doppler probe to the animal skull. In this video, we show our optimized system for cerebral perfusion monitoring during transient middle cerebral artery occlusion by intraluminal filament in the rat. We developed in-house a simple method to obtain a custom made holder for twin-fibre (deep-penetration) Laser Doppler probes, which allow multi-site monitoring if needed. A continuous and prolonged monitoring of cerebral perfusion could easily be obtained over the intact skull.

Protocol for the perfusion and angiography imaging sub-study of the Third International Stroke Trial (IST-3) of alteplase treatment within six-hours of acute ischemic stroke

RATIONALE

Intravenous thrombolysis with recombinant tissue Plasminogen Activator improves outcomes in patients treated early after stroke but at the risk of causing intracranial hemorrhage. Restricting recombinant tissue Plasminogen Activator use to patients with evidence of still salvageable tissue, or with definite arterial occlusion, might help reduce risk, increase benefit and identify patients for treatment at late time windows.

AIMS

To determine if perfusion or angiographic imaging with computed tomography or magnetic resonance help identify patients who are more likely to benefit from recombinant tissue Plasminogen Activator in the context of a large multicenter randomized trial of recombinant tissue Plasminogen Activator given within six-hours of onset of acute ischemic stroke, the Third International Stroke Trial.

DESIGN

Third International Stroke Trial is a prospective multicenter randomized controlled trial testing recombinant tissue Plasminogen Activator (0·9 mg/kg, maximum dose 90 mg) started up to six-hours after onset of acute ischemic stroke, in patients with no clear indication for or contraindication to recombinant tissue Plasminogen Activator. Brain imaging (computed tomography or magnetic resonance) was mandatory pre-randomization to exclude hemorrhage. Scans were read centrally, blinded to treatment and clinical information. In centers where perfusion and/or angiography imaging were used routinely in stroke, these images were also collected centrally, processed and assessed using validated visual scores and computational measures.

STUDY OUTCOMES

The primary outcome in Third International Stroke Trial is alive and independent (Oxford Handicap Score 0-2) at 6 months; secondary outcomes are symptomatic and fatal intracranial hemorrhage, early and late death. The perfusion and angiography study additionally will examine interactions between recombinant tissue Plasminogen Activator and clinical outcomes, infarct growth and recanalization in the presence or absence of perfusion lesions and/or arterial occlusion at presentation. The study is registered ISRCTN25765518.

FLAIR distal hyperintense vessels as a marker of perfusion-diffusion mismatch in acute stroke

BACKGROUND AND PURPOSE

Distal hyperintense vessels (DHV) on MRI FLAIR sequences in acute brain ischemia are thought to represent leptomeningeal collateral flow. We hypothesized that DHV are more common in acute stroke patients with perfusion-diffusion weighted mismatch (PDM) than in those without.

METHODS

We performed a retrospective study of consecutive anterior circulation stroke patients who underwent multimodal MRI within 8 hours of onset. We correlated DHV occurrence with the presence or absence of PDM, and analyzed DHV correlates when angiography was available.

RESULTS

Twenty-one patients with PDM and 28 without were included. On univariate analysis, there was no significant difference regarding demographic variables between the two groups, with the exception of a higher frequency of atrial fibrillation (33% vs. 7%; P = .02) and intravenous tissue plasminogen activator use (57% vs 25%; P = .03) in the PDM patients. The PDM group more commonly had DHV (85% vs 25%; P < .001). On multivariate analysis, DHV presence (odds ratio, 6.01; 95% confidence-interval, 1.08-33.29; P = .04) and vessel occlusion site (odds ratio, 3.17; 95% confidence-interval, 1.21-8.31; P = .01) were the only variables independently associated with PDM. Conventional angiography was useful correlating DHV presence and collateral flow in a subset of patients.

CONCLUSIONS

DHV may be a surrogate marker for PDM in patients with hyperacute ischemic stroke.

Perfusion-weighted imaging-derived collateral flow index is a predictor of MCA M1 recanalization after i.v. thrombolysis

BACKGROUND AND PURPOSE

Recent studies highlight the role of CC in preserving ischemic penumbra. Some authors suggested the quality of CC could also impact recanalization. The purpose of this study is to test this hypothesis in patients who were treated with i.v. thrombolysis for MCA-M1 occlusion.

MATERIALS AND METHODS

A normalized index derived from Tmax maps (MR-PWI) was defined to quantify the CC deficit (nCCD) in 64 patients with stroke who underwent i.v. thrombolysis. Correlations between nCCD and parameters that may be altered by CC quality were tested (baseline NIHSS, volume of diffusion abnormalities, modified Rankin Scale at 3 months). The correlation between baseline nCCD and MCA-M1 recanalization rate at 24 hours was tested.

RESULTS

The nCCD is significantly correlated with NIHSS and with lesional volume (Pearson correlation test, positive correlations, respectively, 0.40, 0.57; P = .00089, P = 8.7e-07). The nCCD also has a significant predictive value on the full recanalization at 24 hours that decreases as TTT increases (logistic regression, P = .021). Furthermore, among patients who were treated within 3 hours, nCCD and recanalization are significantly correlated (correlation ratio test, eta2 = 0.23, P = .0023): Patients who did not achieve full recanalization have significantly higher nCCD than fully recanalized patients (Mann-Whitney U test, P = .007). In addition, the probability of full recanalization decreases as the nCCD increases (P = .021). nCCD (OR 0.988, 95% CI 0.977-0.999, P = .042) and full recanalization at 24 hours (OR 4.539, 95% CI 1.252-16.456, P = .021) are independent predictors of functional independence at 3 months.

CONCLUSIONS

The nCCD index is a predictor of full MCA-M1 recanalization in patients treated with i.v. thrombolysis.

How baseline severity affects efficacy and safety outcomes in acute ischemic stroke intervention trials

Baseline severity of stroke may be an important predictor of efficacy and safety outcomes in acute stroke intervention trials. This summary explores definitions of baseline variables and outcomes used to measure stroke severity, efficacy, and safety. In addition, the discussion here reviews select acute ischemic stroke intravenous thrombolytic studies, such as the National Institute of Neurological Disorders and Stroke rt-PA Stroke Study and European Cooperative Acute Stroke Studies, select neuroprotectant and endovascular clot retrieval device studies, and large cooperative databases, such as the Virtual International Stroke Trials Archive and Safe Implementation of Treatment in Stroke-International Stroke Thrombolysis Registry, to explore relationships between baseline stroke severity and other possible factors associated with efficacy and safety outcomes. The NIH Stroke Scale and modified Rankin scale will be featured as major stroke outcome measures, based on frequency of use and reliability, familiarity, adaptability, and comparability.

Imaging-based selection in acute ischemic stroke trials - a quest for imaging sweet spots

Ischemic stroke is a very heterogeneous disease that limits the efficacy of acute stroke treatments. Future trials will require advanced imaging to select patients for specific treatments. The most well-established imaging tools are the use of CT to exclude hemorrhage and diffusion-weighted MRI to demonstrate ischemia. While perfusion imaging is one option for patient selection, it has unresolved issues, including standardization and validation, that limit its value. As an alternative to mismatch when addressing stroke, one needs to know the size of the initial irreversible lesion (core), the presence and site/extent of occlusion (clot), and presence of leptomeningeal back filling and Willisian filling (collaterals). These can be summarized as the "3C" approach of core, clot, and collateral interpretation, which together can represent an imaging sweet spot, particularly for time-efficient endovascular treatment trial design.

Posterior cerebral artery laterality on magnetic resonance angiography predicts long-term functional outcome in middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Prominent posterior cerebral artery (PCA) laterality upon 3-dimensional time-of-flight magnetic resonance angiography is often encountered in patients with middle cerebral artery occlusion. We hypothesized that this sign is correlated with improved functional outcome in patients with middle cerebral artery occlusion treated with intravenous recombinant tissue plasminogen activator.

METHODS

Fifty acute ischemic stroke patients with middle cerebral artery occlusion were treated with intravenous recombinant tissue plasminogen activator from April 2007 to October 2009. All patients routinely underwent initial (first 3 hours) magnetic resonance scans on admission, and additional follow-up (14-21 days after stroke onset) computed tomography scans. Two film readers blinded to all clinical information assessed the presence or absence of PCA laterality on magnetic resonance angiography. We retrospectively analyzed the clinical and radiologic data on all patients.

RESULTS

Out of 50 patients, 20 showed PCA laterality on magnetic resonance angiography. National Institute of Health Stroke Scale score 7 days after stroke onset was significantly lower (P=0.007), and infarct volume on follow-up computed tomography was significantly smaller (P=0.009) in patients with PCA laterality than in patients without this sign. Multivariate logistic regression analyses showed an adjusted odds ratio of 8.49 for a favorable outcome (modified Rankin Scale score 0-1 at 6 months) in patients with PCA laterality (95% CI: 1.82 to 55.8, P=0.005).

CONCLUSIONS

The presence of PCA laterality on magnetic resonance angiography before intravenous recombinant tissue plasminogen activator can be used as a predictor of favorable functional outcome in patients with middle cerebral artery occlusion, probably due to improvement of recanalization rate.

Albumin therapy enhances collateral perfusion after laser-induced middle cerebral artery branch occlusion: a laser speckle contrast flow study

Laser speckle contrast (LSC) was used to compare the extent of cortical ischemia in two inbred mouse strains that differed in their degree of collateral circulation, after laser occlusion of the distal middle cerebral artery, and after treatment with 25% albumin (ALB) or saline (control). Sequential LSC images acquired over ∼90 minutes were coaligned, converted to relative flow, and normalized to baseline. After 3-day survival, infarction was quantified by triphenyl tetrazolium chloride or magnetic resonance imaging. In the sparsely collateralized BALB/c strain, mean flow fell to 13% to 14% and 33% to 34% of baseline in central (core) and peripheral (penumbral) regions of interest, and ALB treatment at 30 minutes enhanced perfusion in both regions by ∼2-fold relative to saline, restoring flow to the benign-oligemic range centrally, and to the hyperemic range peripherally. The ALB-induced increment in parenchymal perfusion was disproportionate to the subtle flow increase in the occluded artery itself, suggesting that ALB improved collateral circulation. Cortical infarction in BALB/c mice was reduced 45% by ALB treatment. In contrast to BALB/c mice, the better-collateralized CD-1 strain developed milder ischemia, had smaller infarcts, and showed no differential benefit of ALB. We conclude that where native collateralization is insufficient (BALB/c strain), ALB treatment exerts a significant therapeutic effect after ischemia by augmenting collateral perfusion.

Impact of Collateral Circulation on Early Outcome and Risk of Hemorrhagic Complications after Systemic Thrombolysis

Background

In stroke patients, collateral flow can rapidly be assessed on computed tomography angiography (CTA).

Aims

In this study, the impact of baseline collaterals on early outcome and risk of symptomatic intracerebral hemorrhages after systemic thrombolysis in patients with proximal arterial occlusions within the anterior circulation were analyzed.

Methods

Collateralization scores were determined on the CT angiography source images (0 = absent; 1 ≤ 50%, 2 > 50% but <100%, and 3 = 100% collateral filling) of patients with distal intracranial carotid artery and/or M1 segment occlusions treated from 2008 to December 2011. A collateral score of 0 to 1 was designated as poor and 2 to 3 as good collateral vessel status. Outcome variables included in hospital mortality, favorable outcome at discharge (modified Rankin score ≤ 2), and rates of symptomatic intracerebral hemorrhage based on the European–Australasian Acute Stroke Study II definition.

Results

Among 246 subjects (mean age of 74 years; median National Institutes of Health Stroke Scale N at admission 14), 205 patients (83%) had good collaterals, whereas 41 patients (17%) had poor collaterals, respectively. Patients with poor collaterals had significantly higher rates of in-hospital mortality (41% vs. 12%, P < 0·001), of symptomatic intracerebral hemorrhage (15% vs. 4·9%, P < 0·05) and had significantly lower rates of favorable early clinical outcome (0% vs. 28%, P < 0·001) compared with those with good collaterals. The grade of collateralization was independently associated with in-hospital mortality ( P < 0·001), early clinical outcome ( P < 0·01), and rates of symptomatic intracerebral hemorrhage ( P < 0·01).

Conclusion

Patients with proximal arterial occlusions within the anterior circulation and poor baseline collaterals have a poor early functional outcome and high rates of symptomatic intracerebral hemorrhage after systemic thrombolysis. Since similar findings have also been reported after endovascular therapy, strategies to improve collateral blood flow should be assessed in this patient population.

The vascular neural network--a new paradigm in stroke pathophysiology

The concept of the neurovascular unit as the key brain component affected by stroke is controversial, because current definitions of this entity neglect mechanisms that control perfusion and reperfusion of arteries and arterioles upstream of the cerebral microcirculation. Indeed, although definitions vary, many researchers consider the neurovascular unit to be restricted to endothelial cells, neurons and glia within millimetres of the cerebral capillary microcirculation. This Perspectives article highlights the roles of vascular smooth muscle, endothelial cells and perivascular innervation of cerebral arteries in the initiation and progression of, and recovery from, ischaemic stroke. The concept of the vascular neural network-which includes cerebral arteries, arterioles, and downstream neuronal and glial cell types and structures-is introduced as the fundamental component affected by stroke pathophysiology. The authors also propose that the vascular neural network should be considered the main target for future therapeutic intervention after cerebrovascular insult.

Remote ischemic perconditioning is effective alone and in combination with intravenous tissue-type plasminogen activator in murine model of embolic stroke

BACKGROUND AND PURPOSE

Remote ischemic conditioning is cardioprotective in myocardial infarction and neuroprotective in mechanical occlusion models of stroke. However, there is no report on its therapeutic potential in a physiologically relevant embolic stroke model (embolic middle cerebral artery occlusion) in combination with intravenous tissue-type plasminogen activator (tPA).

METHODS

We tested remote ischemic perconditioning therapy (RIPerC) at 2 hours after embolic middle cerebral artery occlusion in the mouse with and without intravenous tPA at 4 hours. We assessed cerebral blood flow up to 6 hours, neurological deficits, injury size, and phosphorylation of Akt (Serine(473)) as a prosurvival signal in the ischemic hemisphere at 48 hours poststroke.

RESULTS

RIPerC therapy alone improved the cerebral blood flow and neurological outcomes. tPA alone at 4 hours did not significantly improve the neurological outcome even after successful thrombolysis. Individual treatments with RIPerC and intravenous tPA reduced the infarct size (25.7% and 23.8%, respectively). Combination therapy of RIPerC and tPA resulted in additive effects in further improving the neurological outcome and reducing the infarct size (50%). All the therapeutic treatments upregulated phosphorylation of Akt in the ischemic hemisphere.

CONCLUSIONS

RIPerC is effective alone after embolic middle cerebral artery occlusion and has additive effects in combination with intravenous tPA. RIPerC may be a simple, safe, and inexpensive combination therapy with intravenous tPA.

Significance of good collateral compensation in symptomatic intracranial atherosclerosis

BACKGROUND

Collateral circulation stabilizes cerebral blood flow in patients with acute occlusion, but its prognostic role is less studied in intracranial atherosclerosis and appears different in moderate to severe stenosis. We aimed to study the associations between antegrade flow across stenosis, collateral flow via leptomeningeal anastomosis, and the neurological outcome and recurrence risk in patients with symptomatic intracranial stenosis.

METHODS

We examined a cohort of consecutive patients admitted for stroke or transient ischemic attack (TIA) with symptomatic intracranial stenosis confirmed by digital subtraction angiography in a single-center retrospective study. Angiograms were graded systematically in a blinded fashion for antegrade and collateral flow, using Thrombolysis in Cerebral Infarction (TICI) and American Society of Intervention and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) grading, respectively, and integrated to a simple composite circulation score. Demographic and clinical variables, modified Rankin Scale (mRS) scores at 3 months, recurrent stroke or TIA in 12 months were collected. Uni- and multivariate analyses were performed to identify independent predictors of good outcome (mRS 0-2) and recurrence in a logistic regression model.

RESULTS

Among 69 patients with pure intracranial atherosclerosis ≥ 50%, compromised antegrade flow (TICI 0-2a) was observed in 26 (36%) patients and was associated with more severe arterial stenosis (mean 86 vs. 74%, p = 0.001). Poor collateral compensation resulting in a poor composite circulation score was observed in 8 (12%) patients. Patients with a good circulation score (n = 61, 88%) had preserved flow, which was associated with more favorable outcome (OR 7.50, 95% CI 1.11-50.7, p = 0.04) and less recurrent TIA or stroke (OR 0.18, 95% CI 0.04-0.96, p = 0.04). Prognosis was not significantly associated with antegrade or collateral grade per se.

CONCLUSION

Good collateral compensations are more important in patients with symptomatic intracranial stenosis and compromised antegrade flow, and are associated with favorable outcome and less recurrence risk. The feasibility of composite flow assessment should be explored in future studies to identify high-risk intracranial stenosis with compromised hemodynamics.

Pharmacological revascularization of acute ischaemic stroke: focus on challenges and novel strategies

The only currently approved treatment for acute ischaemic stroke (AIS) is alteplase, a thrombolytic agent given intravenously (IV) within 4.5 hours of symptom onset, in an attempt to reopen occluded intracerebral arteries. However, no more than 5% of all AIS patients receive IV alteplase, mainly because of too long symptom-onset-to-hospital intervals. Moreover, this strategy is effective for less than half of the patients treated within the therapeutic window. Early recanalization is the most powerful prognostic factor, and novel drugs or therapeutic strategies are primarily aimed at improving alteplase efficacy to rapidly and safely reopen the occluded arteries. Because IV alteplase-resistant thrombi are those with the largest clot burden, responsible for the most devastating brain-tissue infarctions, development of novel approved AIS therapies is an urgent priority. At present, in the absence of controlled trials, no valid recommendations can be made. However, the most promising emerging strategy is a combination of standard or low-dose IV alteplase with an intra-arterial (IA) procedure, including additional endovascular thrombolytic and/or mechanical clot retrieval. Notably, results of open trials using the IA route had relatively disappointing clinical outcomes, despite remarkable arterial recanalization rates. Controlled trials are urgently needed to evaluate strategies including an IA route. In addition, logistic and cost constraints will likely limit their routine use, even in industrialized countries. Combining of another IV drug and IV alteplase is a far less studied option, although much easier to implement. Add-on IV drugs could be an antiplatelet glycoprotein (GP) IIb/IIIa receptor antagonist, a direct thrombin inhibitor or a second thrombolytic agent, e.g. tenecteplase. However, neuroimaging to measure the clot burden and infarction size will probably be necessary to predict IV alteplase failure and the subsequent use of these eventual additional therapies.

Genetic dissection of the Canq1 locus governing variation in extent of the collateral circulation

Background

Native (pre-existing) collaterals are arteriole-to-arteriole anastomoses that interconnect adjacent arterial trees and serve as endogenous bypass vessels that limit tissue injury in ischemic stroke, myocardial infarction, coronary and peripheral artery disease. Their extent (number and diameter) varies widely among mouse strains and healthy humans. We previously identified a major quantitative trait locus on chromosome 7 (Canq1, LOD = 29) responsible for 37% of the heritable variation in collateral extent between C57BL/6 and BALB/c mice. We sought to identify candidate genes in Canq1 responsible for collateral variation in the cerebral pial circulation, a tissue whose strain-dependent variation is shared by similar variation in other tissues.

Methods and Findings

Collateral extent was intermediate in a recombinant inbred line that splits Canq1 between the C57BL/6 and BALB/c strains. Phenotyping and SNP-mapping of an expanded panel of twenty-one informative inbred strains narrowed the Canq1 locus, and genome-wide linkage analysis of a SWRxSJL-F2 cross confirmed its haplotype structure. Collateral extent, infarct volume after cerebral artery occlusion, bleeding time, and re-bleeding time did not differ in knockout mice for two vascular-related genes located in Canq1, IL4ra and Itgal. Transcript abundance of 6 out of 116 genes within the 95% confidence interval of Canq1 were differentially expressed >2-fold (p-value<0.05÷150) in the cortical pia mater from C57BL/6 and BALB/c embryos at E14.5, E16.5 and E18.5 time-points that span the period of collateral formation.

Conclusions

These findings refine the Canq1 locus and identify several genes as high-priority candidates important in specifying native collateral formation and its wide variation.

IV Thrombolysis-Bridging and Endovascular Treatment for Occlusive Internal Carotid Artery Dissection with Tandem Occlusion

Compared to other etiologies of ischemic stroke, occlusive internal carotid artery dissection responds worse to intravenous (IV) thrombolysis. Intracranial tandem occlusion is a predictor of poor outcome. A direct endovascular approach has been proposed as a safe and probably superior alternative to IV thrombolysis. However, it may lead to considerable treatment delays. We used rapidly initiated IV thrombolysis-bridging and subsequent endovascular treatment in two patients with severe hemispheric ischemia due to occlusive internal carotid artery dissection with tandem occlusion and achieved good outcomes. Minimizing recanalization times likely improves patient outcome and IV thrombolysis-bridging may be a reasonable strategy to achieve this. The positive initial results obtained with endovascular approaches and IV thrombolysis-bridging in this patient group deserve further scientific exploration.