Collaterals in ischemic stroke

Association of blood pressure parameters post mechanical thrombectomy in anemic versus non-anemic patients and clinical outcomes

INTRODUCTION

Higher blood pressure (BP) is considered to be detrimental in patients who undergo mechanical thrombectomy (MT), however, the impact of BP post-MT based on comorbidities like anemia has not been well studied. We aim to determine the association of 24-h post-MT BP parameters with clinical outcomes depending on their anemia status.

METHODS

We conducted a retrospective chart review of patients who underwent MT at a comprehensive stroke center from 1/2015 to 12/2020. Patients were dichotomized into anemic and non-anemic groups based on the World Health Organization's definition of anemia [hemoglobin < 12.0 g/dL in women and < 13.0 g/dL in men]. We performed a multivariable analysis with binary logistic regression with the 24-h post-MT BP parameters as predictors. The outcomes were functional dependence (3-month mRS 3-6), mortality, and an early neurological improvement.

RESULTS

220 patients met the inclusion criteria. 158 (71.82 %) patients had functional dependence at 3-months. In the multivariable analysis, the parameters of a higher mean SBP (132.9 ± 11.94 vs.126.52 ± 13.3; OR, 1.05; 95 % CI, 1.02-1.09; P 0.011), a higher mean MAP (93.35 ± 8.44 vs.89.69 ± 10.03; OR,1.06; 95 % CI, 1.01-1.11; P 0.029) and a higher maximum MAP (115.26 ± 11.73 vs.109.37 ± 12.51; OR,1.05; 95 % CI, 1.01-1.08; P 0.023)were significantly associated with functional dependence in non-anemic patients, while a lower mean DBP (65.53 ± 9.73 vs. 71.94 ± 10.16; OR, 0.92; 95 % CI, 0.86-0.98; P 0.007), lower mean MAP (85.7 ± 8.65 vs. 91.38 ± 10; OR, 0.93; 95 % CI, 0.86-0.99; P 0.02), a lower minimum DBP (49.27 ± 10.51 vs. 55.1 ± 11.23; OR, 0.93; 95 % CI, 0.88-0.99; P 0.019), a lower minimum MAP (68.96 ± 9.54 vs. 74.73 ± 10.47; OR, 0.93; 95 % CI, 0.87-0.99; P 0.023) were significantly associated with mortality in patients with anemia, and a lower minimum DBP (54.75 ± 10.42 vs. 59.69 ± 8.87; OR, 0.95; 95 % CI, 0.91-0.99; P 0.012) and a lower minimum MAP (71.92 ± 14.7 vs.75.67 ± 14.17; OR, 0.97; 95 % CI, 0.94-0.99; P 0.047) were significantly associated with an early neurological improvement in non-anemic patients. For patients with anemia, there was no association between 24-hour BP Parameters post-MT and functional dependence and early neurological improvement, and between 24-hour BP Parameters post-MT and mortality in non-anemic patients.

CONCLUSION

In our study, higher BP parameters were associated with worse outcomes in patients without anemia, however, this effect was not found in patients with anemia. Certain lower BP parameters were associated with higher 3-month mortality in anemic patients; however, this effect was not found in non-anemic patients. Higher BP post-MT can potentially promote perfusion and thus is not associated with worse outcomes in anemic patients post-MT, whereas in non-anemic patients it may potentially lead to reperfusion injury While our study is limited because of size and its retrospective nature, the findings suggest that an individualized approach to tailor the target BP post-MT to a patient's risk factor profile and associated co-morbid conditions to achieve optimization of medical care post-MT and associated co-morbid conditions to achieve optimization of medical care post-MT.

Computational modeling of multiscale collateral blood supply in a whole-brain-scale arterial network

The cerebral arterial network covering the brain cortex has multiscale anastomosis structures with sparse intermediate anastomoses (O[102] μm in diameter) and dense pial networks (O[101] μm in diameter). Recent studies indicate that collateral blood supply by cerebral arterial anastomoses has an essential role in the prognosis of acute ischemic stroke caused by large vessel occlusion. However, the physiological importance of these multiscale morphological properties-and especially of intermediate anastomoses-is poorly understood because of innate structural complexities. In this study, a computational model of multiscale anastomoses in whole-brain-scale cerebral arterial networks was developed and used to evaluate collateral blood supply by anastomoses during middle cerebral artery occlusion. Morphologically validated cerebral arterial networks were constructed by combining medical imaging data and mathematical modeling. Sparse intermediate anastomoses were assigned between adjacent main arterial branches; the pial arterial network was modeled as a dense network structure. Blood flow distributions in the arterial network during middle cerebral artery occlusion simulations were computed. Collateral blood supply by intermediate anastomoses increased sharply with increasing numbers of anastomoses and provided one-order-higher flow recoveries to the occluded region (15%-30%) compared with simulations using a pial network only, even with a small number of intermediate anastomoses (≤10). These findings demonstrate the importance of sparse intermediate anastomoses, which are generally considered redundant structures in cerebral infarction, and provide insights into the physiological significance of the multiscale properties of arterial anastomoses.

Inter-Rater Reliability of Collateral Status Assessment Based on CT Angiography: A Retrospective Study of Middle Cerebral Artery Ischaemic Stroke

The importance of assessing the collateral status (CS) in patients with ischaemic stroke (IS) has repeatedly been emphasised in clinical guidelines. Various publications offer qualitative or semiquantitative scales with gradations corresponding to the different extents of the collaterals, visualised mostly on the basis of CTA images. However, information on their inter-rater reliability is limited. Therefore, the aim of this study is to investigate the inter-rater reliability of the scales for collateral assessment. CTA images of 158 patients in the acute period of IS were used in the study. The assessment of CS was performed by two experts using three methodologies: the modified Tan scale, the Miteff scale, and the Rosenthal scale. Cohen's kappa, weighted kappa and Krippendorff's alpha were used as reliability measures. For the modified Tan scale and the Miteff and Rosenthal scales, the weighted kappa values were 0.72, 0.49 and 0.59, respectively. Although the best measure of consistency was found for the modified Tan scale, no statistically significant differences were revealed among the scales. The impact of the CS on the degree of neurological deficit at discharge was shown for the modified Tan and Rosenthal scales. In conclusion, the analysis showed a moderate inter-rater reliability of the three scales, but was not able to distinguish the best one among them.

Collateral Flow in Intracranial Atherosclerotic Disease

Intracranial atherosclerotic disease (ICAD) is a major cause of ischemic stroke and transient ischemic attack (TIA) worldwide. The culprit of ICAD is frequently a high-grade intracranial atherosclerotic stenosis (ICAS) pertaining to the infarct territory, and by then, the ICAS is described as symptomatic. A high-grade ICAS may progressively limit cerebral perfusion downstream, demanding collateral compensation. Collateral circulation refers to the pre-existing and dynamic emergence of vascular channels that maintain and compensate for a failing principal vascular route. Collaterals through the Circle of Willis and leptomeningeal circulation are of utmost importance in this regard. In this article, we first discussed the epidemiology, stroke mechanisms, contemporary therapeutics, and prognosis of symptomatic ICAD. Then, we reviewed the collateral routes in ICAS, factors associated with recruitment and development of the collaterals and diagnostic imaging modalities in assessing the origin and function of collateral circulation. We discussed the associations between collateral circulation and clinical outcomes after acute reperfusion treatment in ICAD-related ischemic strokes with or without large vessel occlusion (LVO). We also conducted a systematic review and meta-analysis on the associations of collateral circulation with the risk of recurrent stroke and the functional outcome in symptomatic ICAS patients on medical treatment as secondary stroke prevention. Finally, we summarized current evidence in these aspects and proposed the future directions.

Collaterals and Elusive Ischemic Penumbra

As alternative blood supply routes, collateral blood vessels can play a crucial role in determining patient outcomes in acute and chronic intracranial occlusive diseases. Studies have shown that increased collateral circulation can improve functional outcomes and reduce mortality, particularly in those who are not eligible for reperfusion therapy. This article aims to discuss the anatomy and physiology of collateral circulation, describe current imaging tools used to measure collateral circulation, and identify the factors that influence collateral status.

The role of neurophysiological tools in the evaluation of ischemic stroke evolution: a narrative review

Ischemic stroke is characterized by a complex cascade of events starting from vessel occlusion. The term "penumbra" denotes the area of severely hypo-perfused brain tissue surrounding the ischemic core that can be potentially recovered if blood flow is reestablished. From the neurophysiological perspective, there are local alterations-reflecting the loss of function of the core and the penumbra-and widespread changes in neural networks functioning, since structural and functional connectivity is disrupted. These dynamic changes are closely related to blood flow in the affected area. However, the pathological process of stroke does not end after the acute phase, but it determines a long-term cascade of events, including changes of cortical excitability, that are quite precocious and might precede clinical evolution. Neurophysiological tools-such as Transcranial Magnetic Stimulation (TMS) or Electroencephalography (EEG)-have enough time resolution to efficiently reflect the pathological changes occurring after stroke. Even if they do not have a role in acute stroke management, EEG and TMS might be helpful for monitoring ischemia evolution-also in the sub-acute and chronic stages. The present review aims to describe the changes occurring in the infarcted area after stroke from the neurophysiological perspective, starting from the acute to the chronic phase.

Blood Pressure Variability After Cerebrovascular Events—A Possible New Therapeutic Target: A Narrative Review

Blood pressure variability, the variation of blood pressure during a certain period, results from the interaction of hemodynamic, neuronal, humoral, behavioral, and environmental factors. Cerebral autoregulation is impaired in acute cerebrovascular disease. In these patients, increased blood pressure variability may provoke or exacerbate secondary brain injury. In fact, available data showed that increased Blood pressure variability is associated with worse outcomes after acute ischemic stroke, intracerebral hemorrhage, and aneurysmal subarachnoid hemorrhage. Consequently, blood pressure variability may represent a usual modifiable therapeutic target. This concept this particularly attractive because reduction of blood pressure variability can be feasible in regions with lower resources and can be applicable to patients with various forms of acute stroke. Prospective studies are needed to further clarify the relationship between blood pressure variability and secondary brain damage, and the determinants of blood pressure variability in different clinical populations. Ultimately, cerebrovascular disease-specific randomized controlled trials aimed at reducing blood pressure variability, irrespective of the absolute blood pressure values, are needed to determine if reduction of blood pressure variability can improve outcomes in patients with acute cerebrovascular disease.

Digital subtraction angiography in cerebrovascular disease: current practice and perspectives on diagnosis, acute treatment and prognosis

Digital Subtraction Angiography (DSA) is the gold-standard imaging modality in acute cerebrovascular diagnosis. The role of DSA has become increasingly prominent since the incorporation of endovascular therapy in standards of care for acute ischemic stroke. It is used in the assessment of cerebral vessel patency; however, the therapeutic role of DSA from a prognostic standpoint merits further investigation. The current paper provides an update on current practice on diagnostic, therapeutic and prognostic use of DSA in acute cerebrovascular diseases and various indications and perspectives that may apply, or limit its use, in ongoing surveillance or prognosis. Pre-clinical and clinical studies on the aspects, including but not limited to the morphology of cerebrovasculature in acute ischaemic stroke, are required to delineate and inform its prognostic role.

Pre-stroke Physical Activity and Cerebral Collateral Circulation in Ischemic Stroke: A Potential Therapeutic Relationship?

Favorable cerebral collateral circulation contributes to hindering penumbral tissue from progressing to infarction and is associated with positive clinical outcomes after stroke. Given its clinical importance, improving cerebral collateral circulation is considered a therapeutic target to reduce burden after stroke. We provide a hypothesis-generating discussion on the potential association between pre-stroke physical activity and cerebral collateral circulation in ischemic stroke. The recruitment of cerebral collaterals in acute ischemic stroke may depend on anatomical variations, capacity of collateral vessels to vasodilate, and individual risk factors. Physical activity is associated with improved cerebral endothelial and vascular function related to vasodilation and angiogenic adaptations, and risk reduction in individual risk factors. More research is needed to understand association between cerebral collateral circulation and physical activity. A presentation of different methodological considerations for measuring cerebral collateral circulation and pre-stroke physical activity in the context of acute ischemic stroke is included. Opportunities for future research into cerebral collateral circulation, physical activity, and stroke recovery is presented.

Bridging Thrombolysis versus Direct Mechanical Thrombectomy in Stroke Due to Basilar Artery Occlusion

Background and Purpose

Mechanical thrombectomy (MT) is an effective treatment for patients with basilar artery occlusion (BAO) acute ischemic stroke. It remains unclear whether bridging intravenous thrombolysis (IVT) prior to MT confers any benefit. This study compared the outcomes of acute BAO patients who were treated with direct MT versus combined IVT plus MT.

Methods

This multicenter retrospective cohort study included patients who were treated for acute BAO from eight comprehensive stroke centers between January 2015 and December 2019. Patients received direct MT or combined bridging IVT plus MT. Primary outcome was favorable functional outcome defined as modified Rankin Scale 0–3 measured at 90 days. Secondary outcome measures included mortality and symptomatic intracranial hemorrhage (sICH).

Results

Among 322 patients, 127 (39.4%) patients underwent bridging IVT followed by MT and 195 (60.6%) underwent direct MT. The mean±standard deviation age was 67.5±14.1 years, 64.0% were male and median National Institutes of Health Stroke Scale was 16 (interquartile range, 8 to 25). At 90-day, the rate of favorable functional outcome was similar between the bridging IVT and direct MT groups (39.4% vs. 34.4%, P=0.361). On multivariable analyses, bridging IVT was not as Comorbidisociated with favorable functional outcome, mortality or sICH. In subgroup analyses, patients with underlying atherosclerosis treated with bridging IVT compared to direct MT had a higher rate of favorable functional outcome at 90 days (37.2% vs. 15.5%, P=0.013).

Conclusions

Functional outcomes were similar in BAO patients treated with bridging IVT versus direct MT. In the subgroup of patients with underlying large-artery atherosclerosis stroke mechanism, bridging IVT may potentially confer benefit and this warrants further investigation.

Immune Modulation as a Key Mechanism for the Protective Effects of Remote Ischemic Conditioning After Stroke

Remote ischemic conditioning (RIC), which involves a series of short cycles of ischemia in an organ remote to the brain (typically the limbs), has been shown to protect the ischemic penumbra after stroke and reduce ischemia/reperfusion (IR) injury. Although the exact mechanism by which this protective signal is transferred from the remote site to the brain remains unclear, preclinical studies suggest that the mechanisms of RIC involve a combination of circulating humoral factors and neuronal signals. An improved understanding of these mechanisms will facilitate translation to more effective treatment strategies in clinical settings. In this review, we will discuss potential protective mechanisms in the brain and cerebral vasculature associated with RIC. We will discuss a putative role of the immune system and circulating mediators of inflammation in these protective processes, including the expression of pro-and anti-inflammatory genes in peripheral immune cells that may influence the outcome. We will also review the potential role of extracellular vesicles (EVs), biological vectors capable of delivering cell-specific cargo such as proteins and miRNAs to cells, in modulating the protective effects of RIC in the brain and vasculature.

Cerebral white matter vasculature: still uncharted?

White matter vasculature plays a major role in the pathophysiology of permanent neurological deficits following a stroke or progressive cognitive alteration related to small vessel disease. Thus, knowledge of the complex vascularization and functional aspects of the deep white matter territories is paramount to comprehend clinical manifestations of brain ischemia. This review provides a structured presentation of the existing knowledge of the vascularization of the human cerebral white matter from seminal historical studies to the current literature. First, we revisit the highlights of prenatal development of the endoparenchymal telencephalic vascular system that are crucial for the understanding of vessel organization in the adult. Second, we reveal the tangled history of debates on the existence, clinical significance, and physiological role of leptomeningeal anastomoses. Then, we present how conceptions on white matter vascularization transitioned from the mixed ventriculopetal/ventriculofugal theory, in which a low-flow area was interposed in between concurrent arterial flows, to the purely ventriculopetal theory. The latter model explains variable white matter sensitivity to ischemia by various organizations of ventriculopetal vessel terminals having different origin/length properties and interconnection patterns. Next, arteries supplying primarily the white matter are described according to their length and overall structure. Furthermore, the known distribution territories, to date, are studied in relation to primary anatomical structures of the human cerebral white matter, emphasizing the sparsity of the "ground-truth" data available in the literature. Finally, the implications for both large vessel occlusion and chronic small vessel disease are discussed, as well as the insights from neuroimaging. All things considered, we identify the need for further research on deep white matter vascularization, especially regarding the arterial supply of white matter fiber tracts.

Corneal nerve loss as a surrogate marker for poor pial collaterals in patients with acute ischemic stroke

In patients with acute ischemic stroke, pial collaterals play a key role in limiting neurological disability by maintaining blood flow to ischemic penumbra. We hypothesized that patient with poor pial collaterals will have greater corneal nerve and endothelial cell abnormalities. In a cross-sectional study, 35 patients with acute ischemic stroke secondary to middle cerebral artery (MCA) occlusion with poor (n = 12) and moderate-good (n = 23) pial collaterals and 35 healthy controls underwent corneal confocal microscopy and quantification of corneal nerve and endothelial cell morphology. In patients with MCA stroke, corneal nerve fibre length (CNFL) (P < 0.001), corneal nerve fibre density (CNFD) (P = 0.025) and corneal nerve branch density (CNBD) (P = 0.002) were lower compared to controls. Age, BMI, cholesterol, triglycerides, HDL, LDL, systolic blood pressure, NIHSS and endothelial cell parameters did not differ but mRS was higher (p = 0.023) and CNFL (p = 0.026) and CNBD (p = 0.044) were lower in patients with poor compared to moderate-good collaterals. CNFL and CNBD distinguished subjects with poor from moderate-good pial collaterals with an AUC of 72% (95% CI 53–92%) and 71% (95% CI 53–90%), respectively. Corneal nerve loss is greater in patients with poor compared to moderate-good pial collaterals and may act as a surrogate marker for pial collateral status in patients with ischemic stroke.

Increased incidence and treatment of intracranial atherosclerotic disease during mechanical thrombectomy is safe, even with an increased number of passes

BACKGROUND

The incidence of intracranial atherosclerotic disease (ICAD) in acute ischemic stroke treated with mechanical thrombectomy (MT) is not well defined, and its description may lead to improved stroke devices and rates of first pass success.

METHODS

A retrospective study was performed on MT patients from 2012 to 2019 at a comprehensive stroke center using chart review and angiogram analysis. Angiograms at the time of MT were reviewed for ICAD, and location and severity were recorded. Patients with ICAD were divided according to ICAD location relative to the large vessel occlusion (LVO) site. Statistical analyses were performed on baseline demographics, comorbidities, MT procedure variables, outcome variables, and their association with ICAD.

RESULTS

Of the 533 patients (mean age 70.4 (SD 13.20) years, 43.5% women), 131 (24.6%) had ICAD. There was no significant difference in favorable discharge outcomes (modified Rankin Scale score of 0-2; 23.8% ICAD vs 27.0% non-ICAD; p=0.82) or groin puncture to recanalization times (average 43.5 (range 8-181) min for ICAD vs 40.2 (4-204) min for non-ICAD; p=0.42). Patients with ICAD experienced a significantly higher number of passes (average 1.8 (range 1-7) passes for ICAD vs 1.6 (1-5) passes for non-ICAD; p=0.0059). Adjusting for age, ≥3 device passes, baseline National Institutes of Health Stroke Scale, rates of angioplasty only, rates of concurrent angioplasty and stenting, coronary artery disease and atrial fibrillation incidences, and time from emergency department arrival to recanalization, yielded no significant difference in rates of favorable outcomes between the two groups.

CONCLUSION

Patients who underwent MT with underlying ICAD had similar rates of favorable outcomes as those without, but required a higher number of device passes.

Modelling the leptomeningeal collateral circulation during acute ischaemic stroke

A novel model of the leptomeningeal collateral circulation is created by combining data from multiple sources with statistical scaling laws. The extent of the collateral circulation is varied by defining a collateral vessel probability. Blood flow and pressure are simulated using a one-dimensional steady state blood flow model. The leptomeningeal collateral vessels provide significant flow during a stroke. The pressure drop over an occlusion predicted by the model ranges between 60 and 85 mmHg depending on the extent of the collateral circulation. The linear transport of contrast material was simulated in the circulatory network. The time delay of peak contrast over an occlusion is 3.3 s in the model, and 2.1 s (IQR 0.8-4.0 s) when measured in dynamic CTA data of acute ischaemic stroke patients. Modelling the leptomeningeal collateral circulation could lead to better estimates of infarct volume and patient outcome.

Cerebral collaterals in acute ischaemia: Implications for acute ischaemic stroke patients receiving reperfusion therapy

The cerebral collaterals play an important role in penumbral tissue sustenance after an acute ischaemic stroke. Recent studies have demonstrated the potential role of collaterals in the selection of acute ischaemic stroke patients eligible for reperfusion therapy. However, the understanding of the significance and evidence around the role of collateral status in predicting outcomes in acute ischaemic stroke patients treated with reperfusion therapy is still unclear. Moreover, the use of pre-treatment collaterals in patient selection and prognosis is relatively underappreciated in clinical settings. A focused review of the literature was performed on the various methods of collateral evaluation and the role of collateral status in acute ischaemic stroke patients receiving reperfusion therapy. We discuss the methods of evaluating pre-treatment collaterals in clinical settings. The patient selection based on collateral status as well as the prognostic and therapeutic value of collaterals in acute ischaemic stroke, in settings of intravenous thrombolysis or endovascular therapy alone, and bridge therapy, are summarized. Recommendations for future research and possible pharmacological intervention strategies aimed at collateral enhancement are also discussed. Collaterals may play an important role in identifying acute ischaemic stroke patients who are likely to benefit from endovascular treatment in an extended time window. Future neuroscientific efforts to better improve our understanding of the role of collaterals in acute ischaemia as well as clinical studies to delineate its role in patient selection and acute stroke prognosis are warranted.