Collateral perfusion: time for novel paradigms in cerebral ischemia

Relative Cerebral Blood Flow as an Indirect Imaging Surrogate in Patients With Anterior Circulation Large Vessel Occlusion and Association of Baseline Characteristics With Poor Collateral Status

BACKGROUND

In acute ischemic stroke (AIS), collateral status (CS) is an important predictor of favorable outcomes in patients with AIS. Among quantitative cerebral perfusion parameters, relative cerebral blood flow (rCBF) is considered an accurate perfusion-based indicator of CS. This study investigated the relationship between admission laboratory values, baseline characteristics, and CS as assessed by rCBF in patients with AIS-large vessel occlusion.

METHODS AND RESULTS

In this retrospective multicenter study, consecutive patients presenting with AIS secondary to anterior circulation large vessel occlusion who underwent pretreatment computed tomography perfusion were included. The computed tomography perfusion data processed by RAPID (IschemaView, Menlo Park, CA) generated the rCBF. Binary logistic regression models assessed the relationship between patients' baseline characteristics, admission laboratory values, and poor CS. The primary outcome measure was the presence of poor CS, which was defined as rCBF <38% at a lesion size ≥27 mL. Between January 2017 and September 2022, there were 221 consecutive patients with AIS-large vessel occlusion included in our study (mean age 67.0±15.8 years, 119 men [53.8%]). Logistic regression showed that male sex (odds ratio [OR], 2.98 [1.59-5.59]; P=0.001), chronic kidney disease (OR, 5.18 [2.44-11.0]; P<0.001), admission National Institutes of Health Stroke Scale score ≥12 (OR, 5.17 [2.36-11.36]; P<0.001), and systolic blood pressure <140 (OR, 2.00 [1.07-3.76]; P=0.030) were associated with poor CS.

CONCLUSIONS

Higher stroke severity on admission with National Institutes of Health Stroke Scale score ≥12, systolic blood pressure <140, chronic kidney disease, and male sex are statistically significantly associated with poor CS in patients with AIS due to anterior circulation large vessel occlusion as defined by rCBF <38%.

Head Down Tilt 15° in Acute Ischemic Stroke with Poor Collaterals: A Randomized Preclinical Trial

Cerebral collaterals are recruited after arterial occlusion with a protective effect on tissue outcome in acute ischemic stroke. Head down tilt 15° (HDT15) is a simple, low cost and accessible procedure that could be applied as an emergency treatment, before recanalization therapies, with the aim to increase cerebral collateral flow. Spontaneously hypertensive rats have been shown to display anatomical differences in morphology and function of cerebral collaterals, compared to other rat strains, resulting in an overall poor collateral circulation. We investigate the efficacy and safety of HDT15 in spontaneously hypertensive (SHR) rats, which were considered as an animal stroke model with poor collaterals. Cerebral ischemia was induced by 90 minute endovascular occlusion of the middle cerebral artery (MCA). SHR rats were randomized to HDT15 or flat position (n = 19). HDT15 was applied 30 minutes after occlusion and lasted 60 minutes, until reperfusion. HDT15 application increased cerebral perfusion (+16.6% versus +6.1%; p = 0.0040) and resulted in a small reduction of infarct size (83.6 versus 107.1 mm3; - 21.89%; p = 0.0272), but it was not associated with early neurological improvement, compared to flat position. Our study suggests that the response to HDT15 during MCA occlusion is dependent on baseline collaterals. Nonetheless, HDT15 promoted a mild improvement of cerebral hemodynamics even in subjects with poor collaterals, without safety concerns.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

Remodeling of the Neurovascular Unit Following Cerebral Ischemia and Hemorrhage

Formulated as a group effort of the stroke community, the transforming concept of the neurovascular unit (NVU) depicts the structural and functional relationship between brain cells and the vascular structure. Composed of both neural and vascular elements, the NVU forms the blood-brain barrier that regulates cerebral blood flow to meet the oxygen demand of the brain in normal physiology and maintain brain homeostasis. Conversely, the dysregulation and dysfunction of the NVU is an essential pathological feature that underlies neurological disorders spanning from chronic neurodegeneration to acute cerebrovascular events such as ischemic stroke and cerebral hemorrhage, which were the focus of this review. We also discussed how common vascular risk factors of stroke predispose the NVU to pathological changes. We synthesized existing literature and first provided an overview of the basic structure and function of NVU, followed by knowledge of how these components remodel in response to ischemic stroke and brain hemorrhage. A greater understanding of the NVU dysfunction and remodeling will enable the design of targeted therapies and provide a valuable foundation for relevant research in this area.

Effect of baseline infarct size on endovascular thrombectomy with or without intravenous alteplase in stroke patients: a subgroup analysis of a randomized trial (DIRECT-MT)

BACKGROUND

DIRECT-MT showed that endovascular thrombectomy was non-inferior to thrombectomy preceded by intravenous alteplase with regard to functional outcome in patients with acute ischemic stroke. In this post-hoc analysis, we examined whether infarct size modified the effect of alteplase.

METHODS

All patients with baseline Alberta Stroke Program Early Computed Tomography Score (ASPECTS) grade were included. The primary outcome was the 90-day modified Rankin Scale (mRS) score. Multivariable ordinal logistic regression analysis was used to calculate the adjusted common odds ratio (OR) for better functional outcome based on the mRS for thrombectomy alone versus combination therapy. An interaction term was entered to test for an interaction with baseline ASPECTS subgroups: 0-4 versus 5-7 versus 8-10.

RESULTS

Of 649 patients, 323 (49.8%) were in the thrombectomy-alone group and 326 (50.2%) in the combination-therapy group. There was no significant treatment-by-trichotomized ASPECTS interaction with alteplase prior to endovascular treatment for the primary endpoint of ordinal mRS (p-value interaction term relative to ASPECTS 8-10: ASPECTS 0-4, p=0.386; ASPECTS 5-7, p=0.936). Adjusted common OR for improvement in the 90-day mRS with thrombectomy alone compared with combination therapy were 1.99 (95% confidence intervals, 0.72-5.46) for ASPECTS 0-4, 1.07 (0.62-1.86) for ASPECTS 5-7, and 1.03 (0.74-1.45) for ASPECTS 8-10. There was no significant difference in the safety outcomes between the two groups.

CONCLUSIONS

Baseline infarct size may not modify the effect of alteplase prior to endovascular thrombectomy with regard to favorable functional outcomes and adverse events.

Physiologic predictors of collateral circulation and infarct growth during anesthesia - Detailed analyses of the GOLIATH trial

Collateral circulation plays a pivotal role in acute ischemic stroke due to large vessel occlusion (LVO) and may be affected by multiple variables during sedation for endovascular therapy (EVT). We conducted detailed analyses of the GOLIATH trial to identify predictors of collateral circulation grade and infarct growth. We also modified the ASITN collateral grading scale and sought to determine its impact on clinical outcome and infarct growth. Multivariable analysis was used to identify predictors of collaterals and infarct growth. Ordinal analysis demonstrated nominal, but non-significant association between modified ASITN scale and infarct growth. Among all analyzed baseline clinical and procedural variables, the most significant predictors of infarct growth at 24 h were phenylephrine dose (estimate 6.78; p = 0.014) and baseline infarct volume (estimate 0.93; p = 0.03). The most significant predictors of worse collateral grade were mean arterial pressure (MAP) <70 mmHg (OR 0.35; p = 0.048) and baseline infarct volume (OR 0.96; p = 0.003). Hypotension during sedation for EVT for LVO negatively impacts collateral circulation, while higher pressor dose is a strong predictor of infarct growth. Avoidance of anesthesia-induced hypotension and consequent need for pressor therapy may prevent collateral failure and minimize infarct growth.

Impact of stroke co-morbidities on cortical collateral flow following ischaemic stroke

Acute hyperglycaemia and chronic hypertension worsen stroke outcome but their impact on collateral perfusion, a determinant of penumbral life span, is poorly understood. Laser-speckle contrast imaging (LSCI) was used to determine the influence of these stroke comorbidities on cortical perfusion after permanent middle cerebral artery occlusion (pMCAO) in spontaneously hypertensive stroke prone rats (SHRSP) and normotensive Wistar rats. Four independent studies were conducted. In animals without pMCAO, cortical perfusion remained stable over 180 min. Following pMCAO, cortical perfusion was markedly reduced at 30 min then gradually increased, via cortical collaterals, over the subsequent 3.5 h. In the contralateral non-ischaemic hemisphere, perfusion did not change over time. Acute hyperglycaemia (in normotensive Wistar) and chronic hypertension (SHRSP) attenuated the restoration of cortical perfusion after pMCAO. Inhaled nitric oxide did not influence cortical perfusion in SHRSP following pMCAO. Thus, hyperglycaemia at the time of arterial occlusion or pre-existing hypertension impaired the dynamic recruitment of cortical collaterals after pMCAO. The impairment of collateral recruitment may contribute to the detrimental effects these comorbidities have on stroke outcome.

The impact of general anesthesia, baseline ASPECTS, time to treatment, and IV tPA on intracranial hemorrhage after neurothrombectomy: pooled analysis of the SWIFT PRIME, SWIFT, and STAR trials

BACKGROUND

Despite the proven benefit of neurothrombectomy, intracranial hemorrhage (ICH) remains the most serious procedural complication. The aim of this analysis was to identify predictors of different hemorrhage subtypes and evaluate their individual impact on clinical outcome.

METHODS

Pooled individual patient-level data from three large prospective multicenter studies were analyzed for the incidence of different ICH subtypes, including any ICH, hemorrhagic transformation (HT), parenchymal hematoma (PH), subarachnoid hemorrhage (SAH), and symptomatic intracranial hemorrhage (sICH). All patients (n=389) treated with the Solitaire device were included in the analysis. A multivariate stepwise logistic regression model was used to identify predictors of each hemorrhage subtype.

RESULTS

General anesthesia and higher baseline Alberta Stroke Program Early CT score (ASPECTS) were associated with a lower probability of any ICH (OR 0.36, p=0.003), (OR 0.80, p=0.032) and HT (OR 0.54, p=0.023), (OR 0.78, p=0.001), respectively. Longer time from onset to treatment was associated with a higher likelihood of HT (OR 1.08, p=0.001) and PH (OR 1.11, p=0.015). Intravenous tissue plasminogen activator (IV-tPA) was also a strong predictor of PH (OR 7.63, p=0.013). Functional independence at 90 days (modified Rankin Scale (mRS) 0-2) was observed significantly less frequently in all hemorrhage subtypes except SAH. None of the patients who achieved functional independence at 90 days had sICH.

CONCLUSIONS

General anesthesia and smaller baseline ischemic core are associated with a lower probability of HT whereas IV-tPA and prolonged time to treatment increase the risk of PH after neurothrombectomy.

TRIAL REGISTRATION NUMBERS

SWIFT-NCT01054560; post results, SWIFT PRIME-NCT01657461; post results, STAR-NCT01327989; post results.

Noninterventional Treatment Options for Stroke

Given the need for early restoration of blood flow and preservation of partially damaged brain cells after ischemic stroke, the noninterventional treatment of stroke relies heavily on the speedy recognition and classification of the clinical syndrome. Initiation of systemic thrombolysis with careful observation of contraindications within the 3.0 (4.5)-hour time window is the approved therapy of choice. Management of hemorrhagic complications and resumption of oral anticoagulation if indicated are also discussed in this article.

Advanced Neuroimaging of Acute Ischemic Stroke: Penumbra and Collateral Assessment

Acute ischemic stroke (AIS) occurs when there is a sudden loss in cerebral blood flow due to embolic or thromboembolic occlusion of a cerebral or cervical artery. Patients with AIS require emergent neuroimaging to guide treatment, which includes intravenous thrombolysis and endovascular mechanical thrombectomy (EMT). Recent advances in AIS treatment by EMT has been driven in part by advances in computed tomography (CT) and MR imaging neuroimaging evaluation of ischemic penumbra and pial collateral vessels. The authors review advanced noninvasive brain imaging by CT and MR imaging for the evaluation of AIS focusing on penumbral and collateral imaging.

Cerebral venous collaterals: A new fort for fighting ischemic stroke?

Stroke therapy has entered a new era highlighted by the use of endovascular therapy in addition to intravenous thrombolysis. However, the efficacy of current therapeutic regimens might be reduced by their associated adverse events. For example, over-reperfusion and futile recanalization may lead to large infarct, brain swelling, hemorrhagic complication and neurological deterioration. The traditional pathophysiological understanding on ischemic stroke can hardly address these occurrences. Accumulating evidence suggests that a functional cerebral venous drainage, the major blood reservoir and drainage system in brain, may be as critical as arterial infusion for stroke evolution and clinical sequelae. Further exploration of the multi-faceted function of cerebral venous system may add new implications for stroke outcome prediction and future therapeutic decision-making. In this review, we emphasize the anatomical and functional characteristics of the cerebral venous system and illustrate its necessity in facilitating the arterial infusion and maintaining the cerebral perfusion in the pathological stroke content. We then summarize the recent critical clinical studies that underscore the associations between cerebral venous collateral and outcome of ischemic stroke with advanced imaging techniques. A novel three-level venous system classification is proposed to demonstrate the distinct characteristics of venous collaterals in the setting of ischemic stroke. Finally, we discuss the current directions for assessment of cerebral venous collaterals and provide future challenges and opportunities for therapeutic strategies in the light of these new concepts.

Cerebral collateral therapeutics in acute ischemic stroke: A randomized preclinical trial of four modulation strategies

Cerebral collaterals are dynamically recruited after arterial occlusion and highly affect tissue outcome in acute ischemic stroke. We investigated the efficacy and safety of four pathophysiologically distinct strategies for acute modulation of collateral flow (collateral therapeutics) in the rat stroke model of transient middle cerebral artery (MCA) occlusion. A composed randomization design was used to assign rats (n = 118) to receive phenylephrine (induced hypertension), polygeline (intravascular volume load), acetazolamide (cerebral arteriolar vasodilation), head down tilt (HDT) 15° (cerebral blood flow diversion), or no treatment, starting 30 min after MCA occlusion. Compared to untreated animals, treatment with collateral therapeutics was associated with lower infarct volumes (62% relative mean difference; 51.57 mm³ absolute mean difference; p < 0.001) and higher chance of good functional outcome (OR 4.58, p < 0.001). Collateral therapeutics acutely increased cerebral perfusion in the medial (+40.8%; p < 0.001) and lateral (+19.2%; p = 0.016) MCA territory compared to pretreatment during MCA occlusion. Safety indicators were treatment-related mortality and cardiorespiratory effects. The highest efficacy and safety profile was observed for HDT. Our findings suggest that acute modulation of cerebral collaterals is feasible and provides a tissue-saving effect in the hyperacute phase of ischemic stroke prior to recanalization therapy.

The circle of Willis predicts the antihypertensive effects of carotid artery stenting

OBJECTIVE Carotid artery stenting (CAS) has antihypertensive effects, but the durability and degree of this response remain variable. The authors propose that this clinical variability is a function of the presence or absence of a complete circle of Willis (COW). Incomplete COWs perfuse through a higher-resistance pial collateral pathway, and therefore patients may require a higher mean arterial pressure (MAP). Carotid artery revascularization in these patients would reduce the end-organ collateral demand that has been hypothesized to drive the MAP response. METHODS Using a retrospective, nonrandomized within-subject case-control design, the authors compared the postoperative effects of CAS in patients with and without a complete COW by using changes in MAP and antihypertensive medication as end points. They recorded MAP and antihypertensive medications 3 months prior to surgery, preoperatively, immediately postoperatively, and at the 3-month follow-up. RESULTS Data were collected from 64 consecutive patients undergoing CAS. Patients without a complete COW (25%) were more likely to demonstrate a decrease in BP response to stenting (i.e., a drop in MAP of 10 mm Hg and/or a reduction or cessation of BP medications at 3 months postoperatively). Of the patients in the incomplete COW cohort, 75% had this outcome, whereas of those in the complete COW cohort, only 41% had it (p < 0.041). These findings remained statistically significant in a logistic regression analysis for possible confounders (p < 0.024). A receiver operating curve analysis of preoperative data indicated that a MAP > 96.3 mm Hg was 55.5% sensitive and 57.4% specific for predicting a complete COW and that patients with a MAP > 96.3 mm Hg were more likely to demonstrate a good MAP decrease following CAS (p < 0.0092). CONCLUSIONS CAS is associated with a significant decrease in MAP and/or a reduction/cessation in BP medications in patients in whom a complete COW is absent.

Collateral flow predicts outcome after basilar artery occlusion: The posterior circulation collateral score

Background and Aim

Our aim was to assess the prognostic value of a semiquantitative computed tomography angiography-based grading system, for the prediction of outcome in patients with acute basilar artery occlusion, based on the presence of potential collateral pathways on computed tomography angiography: the posterior circulation collateral score (PC-CS).

Methods

One hundred forty-nine patients with acute basilar artery occlusion from the Basilar Artery International Cooperation Study were included. We related poor outcome at one month, defined as a modified Rankin scale score of 4 or 5, or death to collateral flow with Poisson regression. We used a 10 points grading system to quantify the potential for collateral flow in the posterior communicating arteries and the cerebellar arteries. Additionally, the relation between the presence and size of posterior communicating arteries and outcome was analyzed.

Results

Thirty-six patients had poor (PC-CS: 0–3), 59 patients intermediate (PC-CS: 4–5), and 54 patients good (PC-CS: 6–10) collaterals. Multivariable analyses showed a statistically significant lower risk of poor outcome in patients with a good PC-CS than in patients with a poor PC-CS (risk ratio (RR): 0.74, 95% confidence interval (CI): 0.58–0.96), but not for patients with an intermediate PC-CS compared with patients with a poor PC-CS (RR: 0.95, 95% CI: 0.78–1.15). Multivariable analyses showed a statistically significant lower risk of poor outcome for the presence of at least one posterior communicating artery and for larger caliber of posterior communicating arteries (RR: 0.79, 95% CI: 0.66–0.95 and 0.76, 95% CI: 0.61–0.96, respectively).

Conclusions

The PC-CS predicted poor outcome at one month. In a separate analysis, both the absence and smaller caliber of posterior communicating arteries predicted poor outcome.

Contribution and additional impact of imaging to the SPAN-100 score

BACKGROUND AND PURPOSE

Stroke Prognostication by Using Age and NIHSS score (SPAN-100 index) facilitates stroke outcomes. We assessed imaging markers associated with the SPAN-100 index and their additional impact on outcome determination.

MATERIALS AND METHODS

Of 273 consecutive patients with acute ischemic stroke (<4.5 hours), 55 were characterized as SPAN-100-positive (age +NIHSS score ≥ 100). A comprehensive imaging review evaluated differences, using the presence of the hyperattenuated vessel sign, ASPECTS, clot burden score, collateral score, CBV, CBF, and MTT. The primary outcome assessed was favorable outcome (mRS ≤ 2). Secondary outcomes included recanalization, lack of neurologic improvement, and hemorrhagic transformation. Uni- and multivariate analyses assessed factors associated with favorable outcome. Area under the curve evaluated predictors of favorable clinical outcome.

RESULTS

Compared with the SPAN-100-negative group, the SPAN-100-positive group (55/273; 20%) demonstrated larger CBVs (<0.001), poorer collaterals (P < .001), and increased hemorrhagic transformation rates (56.0% versus 36%, P = .02) despite earlier time to rtPA (P = .03). Favorable outcome was less common among patients with SPAN-100-positive compared with SPAN-100-negative (10.9% versus 42.2%; P < .001). Multivariate regression revealed poorer outcome for SPAN-100-positive (OR = 0.17; 95% CI, 0.06-0.38; P = .001), clot burden score (OR = 1.14; 95% CI, 1.05-1.25; P < .001), and CBV (OR = 0.58; 95% CI, 0.46-0.72; P = .001). The addition of the clot burden score and CBV improved the predictive value of SPAN-100 alone for favorable outcome from 60% to 68% and 74%, respectively.

CONCLUSIONS

SPAN-100-positivity predicts a lower likelihood of favorable outcome and increased hemorrhagic transformation. CBV and clot burden score contribute to poorer outcomes among high-risk patients and improve stroke-outcome prediction.

Reduced cerebral monocarboxylate transporters and lactate levels by ethanol and normobaric oxygen therapy in severe transient and permanent ischemic stroke

OBJECTIVES

Neuroprotective benefits of ethanol (EtOH) and normobaric oxygenation (NBO) were previously demonstrated in transient and permanent ischemic stroke. Here we sought to identify whether the enhanced lactic acidosis and increased expression of monocarboxylate transporters (MCTs) observed after stroke might be attenuated by single and/or combined EtOH and NBO therapies.

METHODS

Sprague-Dawley rats (n=96) were subjected to right middle cerebral artery occlusion (MCAO) for 2 or 4h (transient ischemia), or 28 h (permanent ischemia) followed by 3, 24h, or no reperfusion. Rats received: (1) either an intraperitoneal injection of saline (sham treatment), one dose of EtOH (1.5 g/kg), two doses of EtOH (1.5 g/kg at 2h of MCAO, followed by 1.0 g/kg 2h after 1st dose), or (2) EtOH+95% NBO (at 2h of MCAO for 6h in permanent ischemia). Lactate levels were detected at 3 and 24h of reperfusion. Gene and protein expressions of MCT-1, -2, -4 were assessed by real-time PCR and western blotting.

RESULTS

A dose-dependent EtOH neuroprotection was found in transient ischemia. Following transient ischemia, a single dose of EtOH (in 2h-MCAO) or a double dose (in 4h-MCAO), significantly attenuated lactate levels, as well as the mRNAs and protein expressions of MCT-1, MCT-2, and MCT-4. However, while two doses of EtOH alone was ineffective in permanent stroke, the combined therapy (EtOH+95% NBO) resulted in a more significant attenuation in all the above levels and expressions.

CONCLUSIONS

Our study demonstrates that acute EtOH administration attenuated lactic acidosis in transient or permanent ischemic stroke. This EtOH-induced beneficial effect was potentiated by NBO therapy in permanent ischemia. Because both EtOH and NBO are readily available, inexpensive and easy to administer, their combination could be implemented in the clinics shortly after stroke.

Cerebral collateral flow defines topography and evolution of molecular penumbra in experimental ischemic stroke

Intracranial collaterals are dynamically recruited after arterial occlusion and are emerging as a strong determinant of tissue outcome in both human and experimental ischemic stroke. The relationship between collateral flow and ischemic penumbra remains largely unexplored in pre-clinical studies. The aim of the present study was to investigate the pattern of collateral flow with regard to penumbral tissue after transient middle cerebral artery (MCA) occlusion in rats. MCA was transiently occluded (90min) by intraluminal filament in adult male Wistar rats (n=25). Intracranial collateral flow was studied in terms of perfusion deficit and biosignal fluctuation analyses using multi-site laser Doppler monitoring. Molecular penumbra was defined by topographical mapping and quantitative signal analysis of Heat Shock Protein 70kDa (HSP70) immunohistochemistry. Functional deficit and infarct volume were assessed 24h after ischemia induction. The results show that functional performance of intracranial collaterals during MCA occlusion inversely correlated with HSP70 immunoreactive areas in both the cortex and the striatum, as well as with infarct size and functional deficit. Intracranial collateral flow was associated with reduced areas of both molecular penumbra and ischemic core and increased areas of intact tissue in rats subjected to MCA occlusion followed by reperfusion. Our findings prompt the development of collateral therapeutics to provide tissue-saving strategies in the hyper-acute phase of ischemic stroke prior to recanalization therapy.

Collateralization and ischemia in hemodynamic cerebrovascular insufficiency

BACKGROUND

Moyamoya disease and atherosclerotic cerebrovascular occlusive disease lead to hemodynamic impairment of cerebral blood flow. One major differentiation between both disease entities lies in the collateralization pathways. The clinical implications of the collateralization pathways for the development of hemodynamic ischemia remain unknown. The aim was to characterize collateralization and ischemia patterns in patients with chronic hemodynamic compromise.

METHODS

Hemodynamic compromise was verified using acetazolamide-stimulated xenon-CT or SPECT in 54 patients [30 moyamoya and 24 atherosclerotic cerebrovascular disease (ACVD)]. All patients received MRI to differentiate hemodynamic ischemia into anterior/posterior cortical border zone infarction (CBI), inferior border zone infarction (IBI) or territorial infarction (TI). Digital subtraction angiography was applied to evaluate collateralization. Collateralization was compared and correlated with the localization of ischemia and number of vascular territories with impaired cerebrovascular reserve capacity (CVRC).

RESULTS

MM patients showed collateralization significantly more often via pericallosal anastomosis and the posterior communicating artery (flow in the anterior-posterior direction; MM: 95%/95% vs. ACVD: 23%/12%, p < 0.05). ACVD patients demonstrated collateralization via the anterior and posterior communicating arteries (flow in the posterior-anterior direction, MM: 6%/5% vs. ACVD: 62%/88%, p < 0.05). Patterns of infarction were comparable (aCBI: MM: 36% vs. ACVD: 35%; pCBI: MM: 10% vs. ACVD: 20%; IBI: MM: 35% vs. ACVD: 41%; TI: MM: 13% vs. ACVD: 18%). The number and localization of vascular territories with impaired CVRC were comparable.

CONCLUSIONS

Despite significant differences in collateralization, the infarct patterns and severity of CVRC impairment do not differ between MMV and ACVD patients. Cerebral collateralization does not allow reaching conclusions about the localization of cerebral ischemia or severity of impaired CVRC in chronic hemodynamic impairment.

Impact of collaterals on successful revascularization in Solitaire FR with the intention for thrombectomy

BACKGROUND AND PURPOSE

Collaterals at angiography before endovascular therapy were analyzed to ascertain the effect on a novel end point of successful revascularization without symptomatic hemorrhage in the Solitaire FR With the Intention for Thrombectomy (SWIFT) study.

METHODS

Collateral grade (American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology) on baseline angiography was independently assessed, blind to other data, with statistical analyses delineating the relationship with clinical, laboratory, and imaging parameters.

RESULTS

Angiographic data on collaterals were available in 119 of 144 subjects (mean age, 67±12 years; 52% woman; median National Institutes of Health Stroke Scale, 18 [range, 8-28]). Worse collaterals were noted in subjects with elevated baseline blood glucose (P=0.013) and those with elevated baseline systolic blood pressure (P=0.039). Multivariate predictors of partial or worse collaterals included absence of prior hypertension (odds ratio, 4.049, P=0.012), smoking history (odds ratio, 3.822; P=0.013), and higher blood glucose (odds ratio, 1.017; P=0.022). Collaterals were strongly related to Alberta Stroke Program Early CT Score (ASPECTS) at baseline (0-1: median 8 [3-10]; 2-9 [5-10]; 3-9 [7-10]; 4-9 [8-10]; P<0.001) and 24 hours (0-1: median 1 [0-5]; 2-6 [0-10]; 3-8 [0-10]; 4-8 [4-8]; P<0.001). Better collaterals were linked with Thrombolysis in Cerebral Infarction 2b/3 reperfusion (P=0.019), better median National Institutes of Health Stroke Scale at day 7/discharge (P<0.001), and better day 90 modified Rankin Scale (P<0.001). Better collateral grade was associated with successful revascularization without symptomatic hemorrhage, mean 2.3 (95% confidence interval, 2.1-2.5) versus 1.9 (95% confidence interval, 1.7-2.2), P=0.021.

CONCLUSIONS

Better collaterals were associated with lower glucose, lower blood pressure, smaller baseline infarcts in SWIFT, and greater likelihood of successful revascularization without hemorrhage and good clinical outcomes.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01054560.

The future of ischemic stroke: flow from prehospital neuroprotection to definitive reperfusion

Recent advances in ischemic stroke enable a seamless transition of the patient flow from the prehospital setting to definitive reperfusion, without the arbitrary separation of therapeutic phases of ischemia based on time alone. In 2013, the framework to understand and directly address the pathophysiology of cerebral blood flow that determines the timeline or evolution of ischemia in an individual case is given. This continuum of flow and the homeostasis of brain perfusion balanced by collaterals may be captured with serial imaging. Ongoing imaging core laboratory activities permit large-scale measurement of angiographic and tissue biomarkers of ischemia. Prehospital neuroprotection has become a reality and may be combined with revascularization therapies. Recent studies confirm that image-guided thrombolysis may be achieved without restrictive time windows. Baseline imaging patterns may be used to predict response to therapy and serial imaging may discern recanalization and reperfusion. Advanced techniques, such as arterial spin-labeled MRI, may also report hyperperfusion associated with hemorrhagic transformation. Endovascular therapies, including novel stent retriever devices, may augment revascularization and angiographic core laboratories may define optimal reperfusion. Serial evaluation of collaterals and reperfusion may identify definitive reperfusion linked with good clinical outcome rather than imposing arbitrary definitions of effective recanalization. Reperfusion injury and hemorrhagic transformation of various types may be detailed to explain clinical outcomes. Similar approaches may be used in intracranial atherosclerosis where flow, and not the degree of luminal stenosis, is paramount. Fractional flow may now be measured with computational fluid dynamics to identify high-risk lesions that require revascularization to restore the equilibrium of antegrade and collateral perfusion. Serial perfusion imaging of such cases may also illustrate inadequate cerebral blood volume gradients that may be more informative than blood flow delay alone. In sum, the growing understanding of collateral perfusion throughout all stages of ischemic stroke provides a framework for the future of ischemic stroke.

Developing precision stroke imaging

Stroke experts stand at the cusp of a unique opportunity to advance the care of patients with cerebrovascular disorders across the globe through improved imaging approaches. NIH initiatives including the Stroke Progress Review Group promotion of imaging in stroke research and the newly established NINDS Stroke Trials network converge with the rapidly evolving concept of precision medicine. Precision stroke imaging portends the coming shift to individualized approaches to cerebrovascular disorders where big data may be leveraged to identify and manage stroke risk with specific treatments utilizing an improved neuroimaging infrastructure, data collection, and analysis. We outline key aspects of the stroke imaging field where precision medicine may rapidly transform the care of stroke patients in the next few years.

Collateral lessons from recent acute ischemic stroke trials

Numerous acute ischemic stroke trials have recently published detailed results, providing an opportunity to consider the role of collaterals in stroke pathophysiology and their influential effect on patient outcomes. Safety and Efficacy of NeuroFlo Technology in Ischemic Stroke (SENTIS), the largest randomized controlled trial of device therapy to date, tested the potential augmentation of collateral perfusion. SYNTHESIS Expansion, Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy (MR RESCUE), and Interventional Management of Stroke (IMS) III chronicled the saga of endovascular therapy trialed against medical treatment for acute ischemic stroke. These recent randomized studies, however, largely neglect current device technology available for endovascular therapy as advanced by the TREVO2 and SOLITAIRE™(TM) FR With the Intention For Thrombectomy (SWIFT) studies. Such exhaustive efforts in recent trials have failed to introduce a new treatment for stroke that unequivocally improves patient outcomes. Collateral perfusion is widely recognized to vary across individuals in any population and exerts a dramatic effect on baseline variables including the time course of ischemic injury, stroke severity, imaging findings, and therapeutic opportunities. Similarly, collaterals have been recognized to influence recanalization, reperfusion, hemorrhagic transformation, and subsequent neurological outcomes after stroke. Collateral lessons may be gleaned from these trials, to expand consideration of overall study results and perhaps most importantly, alter ongoing and new trials in development. Detailed analyses of available information on collaterals from these trials demonstrate that collaterals may be more influential than the choice of treatment modality or intervention.

Vascular remodeling after ischemic stroke: mechanisms and therapeutic potentials

The brain vasculature has been increasingly recognized as a key player that directs brain development, regulates homeostasis, and contributes to pathological processes. Following ischemic stroke, the reduction of blood flow elicits a cascade of changes and leads to vascular remodeling. However, the temporal profile of vascular changes after stroke is not well understood. Growing evidence suggests that the early phase of cerebral blood volume (CBV) increase is likely due to the improvement in collateral flow, also known as arteriogenesis, whereas the late phase of CBV increase is attributed to the surge of angiogenesis. Arteriogenesis is triggered by shear fluid stress followed by activation of endothelium and inflammatory processes, while angiogenesis induces a number of pro-angiogenic factors and circulating endothelial progenitor cells (EPCs). The status of collaterals in acute stroke has been shown to have several prognostic implications, while the causal relationship between angiogenesis and improved functional recovery has yet to be established in patients. A number of interventions aimed at enhancing cerebral blood flow including increasing collateral recruitment are under clinical investigation. Transplantation of EPCs to improve angiogenesis is also underway. Knowledge in the underlying physiological mechanisms for improved arteriogenesis and angiogenesis shall lead to more effective therapies for ischemic stroke.

Bone marrow mononuclear cells exert long-term neuroprotection in a rat model of ischemic stroke by promoting arteriogenesis and angiogenesis

Transplanted bone marrow-derived mononuclear cells (BMMNCs) can promote arteriogenesis and angiogenesis by incorporating into vascular walls and differentiating into smooth muscle cells (SMCs) and endothelial cells (ECs). Here, we explored whether BMMNCs can enhance arteriogenesis and angiogenesis and promote long-term functional recovery in a rat model of permanent middle cerebral artery occlusion (pMCAO). Sprague-Dawley rats were injected with vehicle or 1×10(7) BMMNCs labeled with BrdU via femoral vein 24 h after induction of pMCAO. Functional deficits were assessed weekly through day 42 after pMCAO, and infarct volume was assessed on day 7. We visualized the angioarchitecture by latex perfusion on days 14 and 42. BMMNC transplantation significantly reduced infarct volume and neurologic functional deficits compared with untreated or vehicle-treated ischemic groups. In BMMNC-treated rats, BrdU-positive cells were widely distributed in the infarct boundary zone, were incorporated into vessel walls, and enhanced the growth of leptomeningeal anastomoses, the circle of Willis, and basilar arteries. BMMNCs were shown to differentiate into SMCs and ECs from day 14 after stroke and preserved vascular repair function for at least 6 weeks. Our data indicate that BMMNCs can significantly enhance arteriogenesis and angiogenesis, reduce infarct volume, and promote long-term functional recovery after pMCAO in rats.

Imaging of cerebral ischemia: from acute stroke to chronic disorders

Cerebral ischemia manifests widely in patient symptoms. Along with the clinical examination, imaging serves as a powerful tool throughout the course of ischemia-from acute onset to evolution. A thorough understanding of imaging modalities, their strengths and their limitations, is essential for capitalizing on the benefit of this complementary source of information for understanding the mechanism of disease, making therapeutic decisions, and monitoring patient response over time.

Fractional Flow in Cerebrovascular Disorders

There is an urgent need for stroke experts to advance the care of their patients, yet current approaches are outmoded and have not been successful. The traditional emphasis on anatomical identification of disease, using percent luminal stenosis, results in suboptimal identification of lesions likely to produce recurrent ischemia and, consequently, results in poor patient selection and hampers the development of new aggressive treatments. The traditional emphasis on time since symptom onset and alleged need to achieve complete revascularization in patients with acute ischemic stroke ignores the very nature and degree of the underlying culprit lesion and hampers our understanding of the relationships between the patient's original ischemic state, revascularization, reperfusion, reperfusion injury and hemorrhagic transformation. The trajectory for the study and care of cerebrovascular patients needs to adapt, as it has in cardiology, employing hemodynamics and pathophysiology as the new guideposts for advancement. We introduce fractional flow as one hemodynamic parameter to be utilized to set a course on this new path for the care of stroke patients.