Erythrocyte Fraction Within Retrieved Thrombi Contributes to Thrombolytic Response in Acute Ischemic Stroke

Characterization of the 'White' Appearing Clots that Cause Acute Ischemic Stroke

OBJECTIVES

Most clots retrieved from patients with acute ischemic stroke are 'red' in color. 'White' clots represent a less common entity and their histological composition is less known. Our aim was to investigate the composition, imaging and procedural characteristics of 'white' clots retrieved by mechanical thrombectomy.

MATERIALS AND METHODS

Seventy five 'white' thrombi were selected by visual inspection from a cohort of 760 clots collected as part of the RESTORE registry. Clots were evaluated histopathologically.

RESULTS

Quantification of Martius Scarlett Blue stain identified platelets/other as the major component in 'white' clots' (mean of 55% of clot overall composition) followed by fibrin (31%), red blood cells (6%) and white blood cells (3%). 'White' clots contained significantly more platelets/other (p<0.001*) and collagen/calcification (p<0.001*) and less red blood cells (p<0.001*) and white blood cells (p=0.018*) than 'red' clots. The mean platelet and von Willebrand Factor expression was 43% and 24%, respectively. Adipocytes were found in four cases. 'White' clots were significantly smaller (p=0.016*), less hyperdense (p=0.005*) on computed tomography angiography/non-contrast CT and were associated with a smaller extracted clot area (p<0.001*) than 'red' clots. They primarily caused the occlusion of middle cerebral artery, were less likely to be removed by aspiration and more likely to require rescue-therapy for retrieval.

CONCLUSIONS

'White' clots represented 14% of our cohort and were platelet, von Willebrand Factor and collagen/calcification-rich. 'White' clots were smaller, less hyperdense, were associated with significantly more distal occlusions and were less successfully removed by aspiration alone than 'red' clots.

Clot Composition Analysis as a Diagnostic Tool to Gain Insight into Ischemic Stroke Etiology: A Systematic Review

Mechanical thrombectomy renders the occluding clot available for analysis. Insights into thrombus composition could help establish the stroke cause. We aimed to investigate the value of clot composition analysis as a complementary diagnostic tool in determining the etiology of large vessel occlusion (LVO) ischemic strokes (International Prospective Register of Systematic Reviews [PROSPERO] registration # CRD42020199436). Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we ran searches on Medline (using the PubMed interface) and Web of Science for studies reporting analyses of thrombi retrieved from LVO stroke patients subjected to mechanical thrombectomy (January 1, 2006 to September 21, 2020). The PubMed search was updated weekly up to February 22, 2021. Reference lists of included studies and relevant reviews were hand-searched. From 1,714 identified studies, 134 eligible studies (97 cohort studies, 31 case reports, and six case series) were included in the qualitative synthesis. Physical, histopathological, biological, and microbiological analyses provided information about the gross appearance, mechanical properties, structure, and composition of the thrombi. There were non-unanimous associations of thrombus size, structure, and composition (mainly proportions of fibrin and blood formed elements) with the Trial of Org 10172 in Acute Stroke Treatment (TOAST) etiology and underlying pathologies, and similarities between cryptogenic thrombi and those of known TOAST etiology. Individual thrombus analysis contributed to the diagnosis, mainly in atypical cases. Although cohort studies report an abundance of quantitative rates of main thrombus components, a definite clot signature for accurate diagnosis of stroke etiology is still lacking. Nevertheless, the qualitative examination of the embolus remains an invaluable tool for diagnosing individual cases, particularly regarding atypical stroke causes.

The role of leukocytes in acute ischemic stroke-related thrombosis: a notable but neglected topic

Ischemic stroke is one of the most serious diseases today, and only a minority of patients are provided with effective clinical treatment. Importantly, leukocytes have gradually been discovered to play vital roles in stroke thrombosis, including promoting the activation of thrombin and the adhesion and aggregation of platelets. However, they have not received enough attention in the field of acute ischemic stroke. It is possible that we could not only prevent stroke-related thrombosis by inhibiting leukocyte activation, but also target leukocyte components to dissolve thrombi in the cerebral artery. In this review, we expound the mechanisms by which leukocytes are activated and participate in the formation of stroke thrombus, then describe the histopathology of leukocytes in thrombi of stroke patients and the influence of leukocyte composition on vascular recanalization effects and patient prognosis. Finally, we discuss the relevant antithrombotic strategies targeting leukocytes.

Mechanisms of fibrinolysis resistance and potential targets for thrombolysis in acute ischaemic stroke: lessons from retrieved stroke emboli

There has been growing interest and insight into the histological composition of retrieved stroke emboli. One of the main focuses of the stroke clot analysis literature has been the implications of clot composition on mechanical thrombectomy procedures. However, the holy grail of clot analysis may not be in the field of clot–device interaction, but rather, in understanding mechanisms of fibrinolysis resistance. The mechanisms underlying the low response to fibrinolytic therapy, even with the newer, more powerful agents, remain poorly understood. While factors such as embolus size, location and collateral status influence alteplase delivery and recanalisation rates; compositional analyses focused on histological and ultrastructural characteristics offer unique insights into mechanisms of alteplase resistance. In this review, we strive to provide comprehensive review of current knowledge on clot composition and ultrastructural analyses that help explain resistance to fibrinolysis.

Radiology-Pathology Correlations of Intracranial Clots: Current Theories, Clinical Applications, and Future Directions

In recent years, there has been substantial progression in the field of stroke clot/thrombus imaging. Thrombus imaging aims to deduce the histologic composition of the clot through evaluation of various imaging characteristics. If the histology of a thrombus can be reliably determined by noninvasive imaging methods, critical information may be extrapolated about its expected response to treatment and about the patient's clinical outcome. Crucially, as we move into an era of stroke therapy individualization, determination of the histologic composition of a clot may be able to guide precise and targeted therapeutic effort. Most radiologists, however, remain largely unfamiliar with the topic of clot imaging. This article will review the current literature regarding clot imaging, including its histologic backdrop, the correlation of images with cellular components and treatment responsiveness, and future expectations.

Histological composition behind CT-based thrombus density and perviousness in acute ischemic stroke

BACKGROUND

Clot composition could impact recanalization outcomes of thrombectomy, and preoperative imaging markers may help know about the histological components of thrombus.

METHODS

Consecutive patients who underwent thrombectomy from June 2017 to December 2019 were reviewed. The mean Hounsfield unit (HU) of thrombus (aHU) and contralateral artery (cHU) were recorded based on non-enhanced CT. The relative thrombus density was calculated (dHU=aHU-cHU). Hyperdense artery sign (HAS) was identified if dHU≥ 4HU. The clot perviousness was evaluated via thrombus attenuation increase (δHU) on contrast-enhanced CT compared to non-enhanced CT. Pervious clots were identified when δHU≥ 11HU. Tissue quantification for thrombus was based on Martius Scarlet Blue staining, using the Orbit Imaging Analysis Software. Spearman rank correlations was used to detect the association between imaging markers and clot composition. The differences in clinical characteristics were compared according to the presence of HAS or pervious clots.

RESULTS

Fifty-three patients were included. The dHU was positively correlated with erythrocyte fractions (r = 0.337, p = 0.014), while there was no significant association between aHU and erythrocyte components (r = 0.146, p = 0.296). HAS (+) patients showed a comparable proportion of modified Thrombolysis In Cerebral Infarction (mTICI) 2b-3 (94.6% vs. 87.5%, p = 0.740) and modified Rankin Scale score (mRS) 0-2 (35.1% vs. 56.3%, p = 0.152) compared with those HAS (-). Forty-seven cases were available for the analysis of clot perviousness. Clot perviousness was negatively associated with platelet fractions (r = -0.577, p < 0.001). Patients with pervious clots also showed a comparable proportion of mTICI 2b-3 (86.2% vs. 100%, p = 0.283) and mRS 0-2 (37.9% vs. 50.0%, p = 0.416) compared with impervious clots.

CONCLUSIONS

This study suggests that relative thrombus density was positively correlated with erythrocyte fractions, while clot perviousness showed a negative relationship with platelet components. Yet, the presence of HAS or pervious clots did not show significant associations with recanalization and clinical outcomes. The conclusions should be drawn with caution.

Thrombotic Pathology is not Correlated with the Prognosis of Endovascular Treatment for Acute Ischemic Stroke

OBJECTIVE

The aim of the present study was to determine whether there is a correlation between thrombotic pathology and prognosis of endovascular treatment (EVT) for acute ischemic stroke (AIS).

METHODS

Thrombi were taken from 58 patients with cerebral ischemic thrombosis who were consecutively selected for EVT for AIS. The collected thrombi then underwent hematoxylin-eosin staining for pathological examinations to determine the red blood cell (RBC) ratio and fibrin/platelet components. The patients were divided into the following three groups according to their proportions of RBCs in thrombi: RBC-rich group (RBC ratio ≥ 70%), mixed group (RBC ratio at 31-69%), and fibrin/platelet-rich group (RBC ratio ≤ 30%). Prognosis was classified into good (0-2 points on modified Rankin scale [mRS] at postoperative 90 days) and poor (3-6 points on mRS at postoperative 90 days). Correlational analysis was performed between thrombotic pathology and prognosis of EVT for AIS.

RESULTS

Among all patients, the distributions were as follows: 18.96% (11/58) patients in the RBC-rich group, 63.79% (37/58) patients in the mixed group, and 17.24% (10/58) patients in the fibrin/platelet-rich group. In addition, 43.10% (25/58) of the patients had good prognosis and 56.90% (33/58) had poor prognosis.There was no statistically significant difference between the good prognosis and the poor prognosis in the RBC-rich group, the mixed group, and the fibrin/platelet-rich group (P=0.713, 0.829, 0.748).Multivariate logistic regression analysis to explored the association between RBC-rich group and good prognosis while adjusting for other baseline prognostic factors (age, ASPECTS, NIHSS score, and PRT and intravenous alteplase-bridging therapy). Compared to the fibrin/platelet-rich group, the odds ratio(OR) of achieving good prognosis was 0.60 (P = 0.592) for the mixed group and OR = 0.74 (P = 0.793) for the RBC-rich group.Notably, age was found to be negatively associated with good prognosis (OR = 0.91, P = 0.013). The ASPECTS score was found to be positively associated with good prognosis (OR = 2.01, P = 0.002). Alteplase bridging was associated with a marginally significant positive association with good prognosis (OR = 4.23, P = 0.083).

CONCLUSIONS

No correlation was found between thrombotic pathology and prognosis of EVT for AIS. Good prognosis after endovascular treatment was associated with low age, high ASPECTS at admission, and alteplase bridging.

Clinical imaging factors of excellent outcome after thrombolysis in large-vessel stroke: a THRACE subgroup analysis

Background

For patients with stroke with large-vessel occlusion (LVO), study of factors predicting response to intravenous thrombolysis (IVT) would allow identifying subgroups with high expected gain, and those for whom it could be considered as futile, and even detrimental. From patients included in the Mechanical Thrombectomy After Intravenous Alteplase vs Alteplase Alone After Stroke trial, we investigated clinical-imaging factors associated with optimal response to IVT.

Methods

We included patients receiving IVT alone. Excellent outcome was defined by a 3-month modified Rankin Scale (mRS) score ≤1. Clinical-imaging predictors were assessed on multivariate analysis after multiple imputations. The predictive performance of the model was assessed with the C-statistic.

Results

Among 247 patients with LVO treated with IVT alone, 77 (31%) showed 3-month mRS ≤1. Predictors of 3-month mRS ≤1 were no medical history of hypertension (OR 2.43; 95% CI 1.74 to 3.38; p=0.007); no current smoking (OR 2.76; 95% CI 1.79 to 4.26; p=0.02); onset-to-IVT time (OR 0.47 per hour increase; 95% CI 0.23 to 0.78; p=0.003); diffusion-weighted imaging (DWI) volume (OR 0.78 per 10 mL increase; 95% CI 0.68 to 0.89; p=0.0004); presence of susceptibility vessel sign (SVS) (OR 7.89; 95% CI 1.65 to 37.78; p=0.01) and SVS length (OR 0.87 per mm increase; 95% CI 0.80 to 0.94; p=0.001). The prediction models showed a C-statistic=0.79 (95% CI 0.79 to 0.80).

Conclusions

In patients with stroke with anterior-circulation LVO treated with IVT alone, predictors of excellent outcome at 3 months were no medical history of hypertension or current smoking, reduced onset-to-IVT time, small DWI volume, presence of SVS and short SVS length. These predictive factors could help practitioners in decision-making for IVT implementation in reperfusion strategies, all the more for the drip and ship paradigm.

Trial registration number

NCT01062698.

Thrombus Composition and Efficacy of Thrombolysis and Thrombectomy in Acute Ischemic Stroke

Thrombi retrieved from patients with acute ischemic stroke are highly heterogeneous. Recent data suggest that thrombus composition may impact on mechanical thrombectomy, the number of recanalization manoeuvres, resistance to retrieval, and on thrombolytic potential. Our aim was to summarize evidence describing the impact of thrombus composition on efficacy of mechanical thrombectomy and thrombolysis in patients with acute ischemic stroke. The scoping review methodology guided by the Joanna Briggs Institute, an adaption of the Arksey and O'Malley, was followed. Comprehensive searches were conducted in MEDLINE, EMBASE, SCOPUS, and Web of Science. Articles were classified into 4 key themes: (1) composition of stroke thrombi, (2) thrombus composition and mechanical thrombectomy, (3) thrombus composition and thrombolytic therapy, and (4) novel imaging and endovascular approaches. Our search identified 698 articles published from 1987 to June 2020. Additional articles were extracted from reference lists of the selected articles. Overall, 95 topic-specific articles identified for inclusion published in 40 different journals were included. Reports showed that thrombus composition in stroke was highly heterogeneous, containing fibrin, platelets, red blood cells, VWF (von Willebrand Factor), and neutrophil extracellular traps. Thrombi could roughly be divided into fibrin- and red blood cell-rich clots. Fibrin-rich clots were associated with increased recanalization manoeuvres, longer procedure time, and less favorable clinical outcomes compared with red blood cell-rich clots. Advances in detection or treatment of thrombi that take into account clot heterogeneity may be able to improve future endovascular and thrombolytic treatment of stroke.

Imaging-based prediction of histological clot composition from admission CT imaging

BACKGROUND

Thrombus composition has been shown to be a major determinant of recanalization success and occurrence of complications in mechanical thrombectomy. The most important parameters of thrombus behavior during interventional procedures are relative fractions of fibrin and red blood cells (RBCs). We hypothesized that quantitative information from admission non-contrast CT (NCCT) and CT angiography (CTA) can be used for machine learning based prediction of thrombus composition.

METHODS

The analysis included 112 patients with occlusion of the carotid-T or middle cerebral artery who underwent thrombectomy. Thrombi samples were histologically analyzed and fractions of fibrin and RBCs were determined. Thrombi were semi-automatically delineated in CTA scans and NCCT scans were registered to the same space. Two regions of interest (ROIs) were defined for each thrombus: small-diameter ROIs capture vessel walls and thrombi, large-diameter ROIs reflect peri-vascular tissue responses. 4844 quantitative image markers were extracted and evaluated for their ability to predict thrombus composition using random forest algorithms in a nested fivefold cross validation.

RESULTS

Test set receiver operating characteristic area under the curve was 0.83 (95% CI 0.80 to 0.87) for differentiating RBC-rich thrombi and 0.84 (95% CI 0.80 to 0.87) for differentiating fibrin-rich thrombi. At maximum Youden-Index, RBC-rich thrombi were identified at 77% sensitivity and 74% specificity; for fibrin-rich thrombi the classifier reached 81% sensitivity at 73% specificity.

CONCLUSIONS

Machine learning based analysis of admission imaging allows for prediction of clot composition. Perspectively, such an approach could allow selection of clot-specific devices and retrieval procedures for personalized thrombectomy strategies.

Clot composition of embolic strokes of undetermined source: a feasibility study

BACKGROUND

A number of emerging studies have evaluated clot composition in acute ischemic stroke. Studies of clot composition of embolic strokes of undetermined strokes are lacking.

OBJECTIVES

We sought to analyze the RBC to platelet ratios in clots and correlated our findings with stroke etiology.

METHODS

This was a prospective study analyzing clots retrieved by mechanical thrombectomy in acute ischemic stroke patients at our institution. All clots were stained and scanned at 200x magnification by using a Scanscope XT digital scanner (Apergio, Vista, California). Image-J software (National Institutes of Health, Bethesda, Maryland) was used for semi quantitative analysis of percentage RBC's and platelets. Unpaired t-test was used to compare means of RBC to Platelet ratios. Correlation of RBC to Platelet ratios with stroke etiology was performed.

RESULTS

A total of 33 clots from 33 patients were analyzed. Stroke etiology was undetermined in 6 patients, cardioembolic in 14, large vessel atherosclerosis (LVA) in 9, and carotid dissection in 4. The mean RBC to platelet ratio was 0.78:1 (+/- 0.65) in cardioembolic clots, 1.73:1 (+/- 2.38) in LVA and 1.4:1(+/- 0.70) in carotid dissections. Although patients with undetermined etiology had a similar clot composition to cardioembolic stroke (0.36:1+/- 0.33), (p = 0.19), it differed significantly from LVA and dissections respectively (p = 0.037, p = 0.01).

CONCLUSION

In our study, a low RBC to Platelet ratio was found among patients with embolic strokes of undetermined source, however shared similar characteristics with cardioembolic thrombi. Ongoing collection and analysis is needed to confirm these findings and its significance in evaluating stroke etiology.

Immunohistological Analysis of Neutrophils and Neutrophil Extracellular Traps in Human Thrombemboli Causing Acute Ischemic Stroke

Ischemic stroke caused by thromboembolic occlusion of large cerebral arteries, such as the internal carotid (ICA) and/or the middle cerebral artery (MCA), is treated by mechanical thrombectomy (MT). MT allows salvage of the vessel-occluding thrombemboli, which most frequently originate from the left atrium or the left ventricle of the heart or from sites of plaque rupture within large arteries above the heart. Clot composition may influence the efficacy of (intravenous) thrombolysis and MT, respectively. We analyzed 37 human thrombemboli obtained from acute ischemic stroke patients during MT with special emphasis on histological staining of neutrophils and neutrophil extracellular traps (NETs). We found neutrophils as the main cellular component of cerebral thrombemboli but encountered considerable morphological heterogeneity. Neutrophils accumulated in the border region of fibrin-rich structures indicating possible interaction of neutrophils with distinct structural thrombembolus components. Web-like NETs were found in 35 of 37 thrombemboli in varying amounts. NETs were almost exclusively found within fibrin-rich areas. Importantly, stroke etiology, age and present oral anticoagulation was associated with morphological patterns and the amount of neutrophils. Correlation of histological data and imaging data revealed that relative Hounsfield units of cerebral thrombemboli positively correlated with the amount of red blood cells. In summary, our results demonstrate that neutrophils and NETs are substantial constituents of cerebral thrombemboli and contribute to their structural complexity.

Erythrocyte-rich thrombi related to serum iron contribute to single stent retrieval and favorable clinical outcomes in acute ischemic stroke by endovascular treatment

BACKGROUND

Erythrocyte-rich thrombi seem to be associated with favorable clinical outcomes of patients with AIS by endovascular treatment (EVT), as observed from previous studies. However, only few studies show whether erythrocyte-rich thrombi can be associated with favorable clinical outcomes by EVT and which factor can be related to erythrocyte-rich thrombi. This retrospective study aimed to evaluate the relationship between erythrocyte-rich thrombi and favorable clinical outcomes and further explored factors associated with erythrocyte-rich thrombi.

METHODS

This study was carried out retrospectively from March 2016 to April 2019 on patients who suffered acute ischemic stroke and were treated by EVT at this stroke center. The laboratory test and clinical data were assessed for the relationship between erythrocyte-rich thrombi and favorable clinical outcomes and factors associated with erythrocyte-rich thrombi. All thrombi were divided into erythrocyte-rich thrombi group and fibrin-rich thrombi group based on the proportion of area of the predominant composition which was more than 50% in retrieved thrombi.

RESULTS

This retrospective study enrolled 84 patients, including 32 patients in the erythrocyte-rich thrombi group and 52 patients in the fibrin-rich thrombi group. It showed single stent retrieval (p = 0.017, adjusted OR: 4.061, 95% CI: 1.281-12.872) and favorable clinical outcomes (p < 0.001, adjusted OR: 14.648, 95% CI: 4.637-46.270) were both significantly associated with erythrocyte-rich thrombi. A significant difference in the factor associated with erythrocyte-rich thrombi was serum iron, which correlated positively with erythrocyte fraction in thrombi (p < 0.001, r: 0.452).

CONCLUSIONS

Erythrocyte-rich thrombi could contribute to single stent retrieval and favorable clinical outcomes by EVT, and serum iron might be the factor associated with erythrocyte-rich thrombi.

Thrombus heterogeneity in ischemic stroke

The structure of stroke thrombi has gained an increasing amount of interest in recent years. The advent of endovascular thrombectomy has offered the unique opportunity to provide and analyze thrombi removed from ischemic stroke patients. It has become clear that the composition of ischemic stroke thrombi is relatively heterogenous and various molecular and cellular patterns become apparent. Good understanding of the histopathologic characteristics of thrombi is important to lead future advancements in acute ischemic stroke treatment. In this review, we give a brief overview of the main stroke thrombus components that have been recently characterized in this rapidly evolving field. We also summarize how thrombus heterogeneity can affect stroke treatment.

A case report of thrombolysis resistance: thrombus ultrastructure in an ischemic stroke patient

BACKGROUND

Following acute ischemic stroke (AIS), approximately half of patients do not achieve recanalization after intravenous administration of tissue plasminogen activator (rt-PA). Thrombolysis resistance is a possible reason for recanalization failure. Thrombolysis resistance is likely related to the ultrastructure and composition of the thrombus. However, there is a paucity of published information on the relationship between thrombus ultrastructure and thrombolysis resistance.

CASE PRESENTATION

Two patients who underwent mechanical thrombectomy were observed within 4.5 h after stroke onset. One patient failed to respond to rt-PA (defined as thrombolysis resistant), and the other patient did not receive rt-PA treatment (non-rtPA). In each patient, the occluded artery was the internal carotid artery or middle cerebral artery. According to the Trial of ORG 10172 in Acute Stroke Treatment classification, both patients had large atherosclerotic cerebral infarction. By scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we found that the thrombus structure was significantly different between the two patients.

CONCLUSION

Grid-like dense fibrin, compressed polyhedral erythrocytes, and large accumulation of neutrophils may be characteristics of thrombolysis resistant thrombi.

Two-layered susceptibility vessel sign is associated with biochemically quantified thrombus red blood cell content

BACKGROUND AND PURPOSE

Better characterization of the thrombus could be useful to determine acute ischaemic stroke (AIS) aetiology and predict response to thrombolysis and endovascular therapy (EVT). To test the hypothesis that susceptibility vessel sign (SVS) on baseline magnetic resonance imaging (MRI) is related to red blood cell (RBC) content of AIS thrombi, the total haemoglobin contents (HbCs) of AIS thrombi retrieved by EVT from patients with or without SVS or two-layered SVS (TLSVS) were compared.

METHODS

Baseline MRI of 84 anterior AIS patients was reviewed by neuro-radiologists blinded to clinical and biochemical data. Thrombi from these patients were retrieved by EVT and analysed for HbC by quantitative enzyme-linked immunosorbent assay and measurement of haem concentration.

RESULTS

Susceptibility vessel sign and TLSVS were respectively observed in 85.7% and 50.0% of cases. The median HbC content was 253 µg/mg thrombus (interquartile range 177-333) and the median haem content was 219 µg/mg thrombus (131-264). Thrombus HbC and haem content were highly correlated with thrombus RBC content determined by flow cytometry (r = 0.94). Thrombi from patients with TLSVS weighed more [31.1 (16.5-68.3) mg vs. 17.7 (11.7-33.3) mg; P = 0.005] and had a higher HbC content [278 (221-331) µg/mg vs. 196 (139-301) µg/mg; P = 0.010] compared to thrombi from patients without TLSVS. There was no difference in thrombus weight or HbC content according to SVS status.

CONCLUSIONS

Our study shows that TLSVS is significantly associated with a higher thrombus weight and RBC content, as determined by quantitative assays.

Predicting the One-Year Prognosis and Mortality of Patients with Acute Ischemic Stroke Using Red Blood Cell Distribution Width Before Intravenous Thrombolysis

Purpose

Red blood cell (RBC) distribution width (RDW) is known to reflect the heterogeneity of RBC volume, which may be associated with cardiovascular events or mortality after myocardial infarction. However, the association between RDW and stroke, especially regarding endpoints such as death, remains ambiguous. This study aimed to explore the prognostic value of RDW and its effect on mortality among patients with acute ischemic stroke (AIS) undergoing intravenous thrombolysis (IVT) after one year.

Patients and Methods

We retrospectively reviewed patients with AIS treated with IVT between January 2016 and March 2018. We grouped the patients according to modified ranking scale (MRS) scores as follows:0–2, favorable functional outcome group; and 3–6, unfavorable functional outcome. Predictors were determined using multivariate logistic regression (MVLR). The area under receiver-operating characteristic curve (AUC) was used to evaluate the predictive capability of variables. Furthermore, the Cox proportional hazard model was used to assess the contribution of risk factors to the outcome of death at one year later.

Results

MVLR analysis showed that RDW (odds ratio [OR], 1.179; 95% confidence interval [CI], 0.900–1.545; p = 0.232) was not an independent predictor of unfavorable functional outcome, but it (OR 1.371; 95% CI 1.109–1.696; p = 0.004) was an independent biomarker for all-cause mortality. The optimal RDW cut-off value to predict mortality was 14.65% (sensitivity: 42%, specificity: 88.3%, AUC: 0.649, p < 0.001). Furthermore, higher RDW (hazard ratio, 2.860; 95% CI, 1.724–4.745; p < 0.001) indicated a greater risk of death.

Conclusion

The baseline RDW is a potential predictor of mortality in patients with AIS undergoing IVT, but RDW might not be associated with worse survival function among stroke survivors, which will help us to improve treatments and the management of patients with AIS.

Pathophysiologic and Therapeutic Perspectives Based on Thrombus Histology in Stroke

Recent advances in endovascular thrombectomy have enabled the histopathologic analysis of fresh thrombi in patients with acute stroke. Histologic analysis has shown that the thrombus composition is very heterogeneous between patients. However, the distribution pattern of each thrombus component often differs between patients with cardiac thrombi and those with arterial thrombi, and the efficacy of endovascular thrombectomy is different according to the thrombus composition. Furthermore, the thrombus age is related to the efficacy of reperfusion therapy. Recent studies have shown that neutrophils and neutrophil extracellular traps contribute to thrombus formation and resistance to reperfusion therapy. Histologic features of thrombi in patients with stroke may provide some clues to stroke etiology, which is helpful for determining the strategy of stroke prevention. Research on thrombus may also be helpful for improving reperfusion therapy, including the development of new thrombolytic agents.

Structural analysis of ischemic stroke thrombi: histological indications for therapy resistance

Ischemic stroke is caused by a thromboembolic occlusion of cerebral arteries. Treatment is focused on fast and efficient removal of the occluding thrombus, either via intravenous thrombolysis or via endovascular thrombectomy. Recanalization, however, is not always successful and factors contributing to failure are not completely understood. Although the occluding thrombus is the primary target of acute treatment, little is known about its internal organization and composition. The aim of this study, therefore, was to better understand the internal organization of ischemic stroke thrombi on a molecular and cellular level. A total of 188 thrombi were collected from endovascularly treated ischemic stroke patients and analyzed histologically for fibrin, red blood cells (RBC), von Willebrand factor (vWF), platelets, leukocytes and DNA, using bright field and fluorescence microscopy. Our results show that stroke thrombi are composed of two main types of areas: RBC-rich areas and platelet-rich areas. RBC-rich areas have limited complexity as they consist of RBC that are entangled in a meshwork of thin fibrin. In contrast, platelet-rich areas are characterized by dense fibrin structures aligned with vWF and abundant amounts of leukocytes and DNA that accumulate around and in these platelet-rich areas. These findings are important to better understand why platelet-rich thrombi are resistant to thrombolysis and difficult to retrieve via thrombectomy, and can guide further improvements of acute ischemic stroke therapy.

The role of diabetes mellitus on the thrombus composition in patients with acute ischemic stroke

PURPOSE

Diabetes mellitus indicated poor clinical prognosis for patients with acute ischemic stroke. Furthermore, diabetes mellitus could also impact the hemostatic system, while its influence on the histological composition of thrombus is unclear.

METHODS

Consecutive patients with retrieved clots were included. Histologic staining for thrombus included hematoxylin and eosin, Martius Scarlet Blue, immunohistochemistry for von Willebrand factor. The differences in clot composition were compared according to diabetes mellitus history or hyperglycemia (≥7.8 mmol/L) on admission.

RESULTS

A total of 52 patients were included; half of them were diagnosed as diabetes mellitus previously. Diabetic patients showed higher serum glucose on admission (8.90 vs. 7.40, p = 0.012). The baseline characteristics (expect smoking history and thrombus location), procedural, and clinical outcomes were similar between diabetic patients and nondiabetic patients. As for histologic composition, thrombus in patients with diagnosed diabetes mellitus had more fibrin (44.2% vs. 28.3%, p = 0.004) and fewer red blood cells (26.0% vs. 42.9%, p = 0.013) and equivalent content of platelets (24.0% vs. 21.5%, p = 0.694) and von Willebrand factor (0.041 vs. 0.031, p = 0.234) than patients without diabetes mellitus. However, there was no statistical difference in the content of red blood cells (41.6% vs. 27.3%, p = 0.105), fibrin (37.6% vs. 34.3%, p = 0.627), platelets (21.2% vs. 24.2%, p = 0.498), and von Willebrand factor (0.038 vs. 0.034, p = 0.284) between patients with or without hyperglycemia on admission.

CONCLUSION

Clots in diabetic patients had more fibrin and fewer erythrocyte components compared with patients without diabetes mellitus, while hyperglycemia on admission did not show association with clot composition. Further studies are needed to confirm these results.

Insights from thrombi retrieved in stroke due to large vessel occlusion

The recent advances of endovascular procedures to treat stroke due to large cerebral vessel occlusion have made it possible to analyze the retrieved thrombus material. Analysis of cerebral thrombi is emerging as a relevant opportunity to complement the diagnostic workup of etiology, to develop new lytic approaches and to optimize the acute treatment of stroke due to large vessel occlusion. Nonetheless, retrieved thrombi are frequently discarded since their informative potential is often neglected and standards are missing. This review provides an overview of the current knowledge and expanding research relating to thrombus composition analysis in large vessel occlusions. We first discuss the heterogeneity of thrombogenic factors that underlie the thrombotic formation in stroke and its implications to identify stroke etiology and thrombus age. Further, we show that understanding structural characteristics of thrombus is pivotal for the development of new-targeted lytic therapies as well as to improve, through thrombus modeling, the development of thrombectomy devices. Finally, we discuss the on-going attempts to identify a signature of thrombus composition indirectly through imaging and peripheral blood biomarkers, which might in future assist treatment decision-making as well as secondary prevention. Thrombus analysis might contribute to the advancement and optimization of personalized stroke treatments.

Quantitative estimation of thrombus-erythrocytes using MRI. A phantom study with clot analogs and analysis by statistic regression models

BACKGROUND

Thrombus composition has the potential to affect acute ischemic stroke (AIS) treatment.

OBJECTIVE

To evaluate in an in vitro test the correlation of clot composition, especially erythrocytes (red blood cells (RBCs)), with the variation of signal intensity ratio (SIR) obtained with MRI sequences used for AIS, and qualification of the susceptibility vessel sign effect using clot analogs.

MATERIALS AND METHODS

Nine ovine clots were fixed in a gelatin-manganese solution and studied by MRI (T2GE, T2-weighted gradient echo; SWI, susceptibility-weighted imaging; FLAIR, fluid attenuated inversion recovery). RBC concentration was estimated using regression models (SLR, single linear regression; MLR, multiple linear regression; RF, random Forest; and ANN, artificial neural networking), which combined the SIR-histology relationship of three MRI sequences.

RESULTS

Negative correlation was found between SIR and RBC concentration. T2GE SWI could not statistically distinguish clots with RBC content >54% and <23%. SLR was applied only to FLAIR images since T2GE and SWI demonstrated signal saturation. All four regression models showed a correlation between MRI and histology: SLR=0.981; MLR=0.986; RF=0.994, and ANN=0.971. One unknown clot was studied and agreement between SIR and histological analyses was found in all models.

CONCLUSIONS

We presented a method to quantify RBC concentration in clot analogs, combining SWI, T2GE, and FLAIR. This in vitro study has some limitations, so clot collection after thrombectomy with simultaneous imaging analysis is necessary to validate this model.

Clot permeability and histopathology: is a clot's perviousness on CT imaging correlated with its histologic composition?

BACKGROUND

Clot perviousness in large vessel occlusion has been shown to be associated with improved recanalization outcomes with mechanical thrombectomy and intravenous thrombolysis.

OBJECTIVE

To evaluate the association between clot perviousness based on thrombus attenuation increase (TAI) on CT, and histologic composition of clots in acute ischemic stroke (AIS).

METHODS

A retrospective review was completed of patients with AIS secondary to large vessel occlusion, non-contrast CT (NCCT) and CT angiography (CTA) images, and histologic analysis of the retrieved clot. TAI was measured by subtracting clot attenuation on NCCT from the attenuation on CTA. Up to 3 regions of interest (ROIs) were evaluated on each clot; the average attenuation was used for analysis if multiple ROIs were assessed. Pervious clots were defined as TAI ≥10 Hounsfield units (HUs); impervious clots had TAI <10 HU. Histopathologic analyses of clots were assessed for relative compositions of red blood cells (RBCs), white blood cells (WBCs), fibrin, and platelets/other.

RESULTS

57 patients were included. Pervious clots were more likely to be RBC rich (p=0.04); impervious clots were more likely to be fibrin and WBC rich (p=0.01 for both). Pervious clots also had greater RBC density than impervious clots (49.8% and 33.0%, respectively; p=0.006); fibrin density of pervious clots was lower than that of impervious clots (17.8% and 23.2%, respectively; p=0.02).

CONCLUSION

Clot perviousness, assessed on NCCT and CTA imaging, is associated with higher RBC density and lower fibrin density, offering a possible explanation for the higher rates of successful thrombectomy and favorable clinical outcome seen in such patients.

Correlation of imaging and histopathology of thrombi in acute ischemic stroke with etiology and outcome

Mechanical thrombectomy has become the stand of care for patients with large vessel occlusions, yet major improvements in thrombectomy speed, efficacy, and completeness can still be achieved. High rates of clot fragmentation and failure to remove the clot resulting in poor neurological outcomes suggest that in order to further advance the field of stroke intervention we must turn our attention towards understanding the science of clot. Accurately identifying the composition of the occlusive clot prior to intervention could significantly influence the success of the revascularization strategy used to treat them. Numerous features of thromboemboli could be studied and characterized, including quantitative histomorphometry and diagnostic imaging characteristics. Each of these features might logically predict superior thrombectomy outcomes with one device or another. This article aims to review the current literature on histopathological composition of acute ischemic stroke clots, with a particular focus on the correlation between clot composition and diagnostic imaging, stroke etiology and revascularization outcomes.

Endovascular Therapy for Acute Ischemic Stroke of Intracranial Atherosclerotic Origin-Neuroimaging Perspectives

Large vessel occlusion (LVO) due to intracranial atherosclerosis (ICAS) is a common cause of acute ischemic stroke (AIS) in Asians. Endovascular therapy (EVT) has been established as the mainstay of treatment in patients with AIS and LVO. However, only a few patients of Asian descent with ICAS-related LVO (ICAS-LVO) were included in recent randomized controlled trials of EVT for AIS. Therefore, the findings of these trials cannot be directly applied to Asian patients with ICAS-LVO. In embolic LVO due to thrombus from the heart or a more proximal vessel, rapid, and complete recanalization can be achieved in more than 70-80% of patients, and it is important to exclude patients with large cores. In contrast, patients with ICAS-LVO usually have favorable hemodynamic profiles (good collateral status, small core, and less severe perfusion deficit), but poor response to EVT (more rescue treatments and longer procedure times are required for successful recanalization due to higher rates of reocclusion). Patients with ICAS-LVO may have different anatomic (plaque, angioarchitecture), hemodynamic (collateral status), and pathophysiologic (thrombus composition) features on neuroimaging compared to patients with embolic LVO. In this review, we discuss these neuroimaging features, their clinical implications with respect to determination of EVT responses, and the need for development of specific EVT devices and procedures for patients with ICAS-LVO.

Platelet-rich clots as identified by Martius Scarlet Blue staining are isodense on NCCT

BACKGROUND

Current studies on clot characterization in acute ischemic stroke focus on fibrin and red blood cell composition. Few studies have examined platelet composition in acute ischemic stroke clots. We characterize clot composition using the Martius Scarlet Blue stain and assess associations between platelet density and CT density.

MATERIALS AND METHOD

Histopathological analysis of the clots collected as part of the multi-institutional STRIP registry was performed using Martius Scarlet Blue stain and the composition of the clots was quantified using Orbit Image Analysis (www.orbit.bio) machine learning software. Prior to endovascular treatment, each patient underwent non-contrast CT (NCCT) and the CT density of each clot was measured. Correlations between clot components and clinical information were assessed using the χ² test.

RESULTS

Eighty-five patients were included in the study. The mean platelet density of the clots was 15.7% (2.5-72.5%). There was a significant correlation between platelet-rich clots and the absence of hyperdensity on NCCT, (ρ=0.321, p=0.003*, n=85). Similarly, there was a significant inverse correlation between the percentage of platelets and the mean Hounsfield Units on NCCT (ρ=-0.243, p=0.025*, n=85).

CONCLUSION

Martius Scarlet Blue stain can identify patients who have platelet-rich clots. Platelet-rich clots are isodense on NCCT.

Characterization of clot composition in acute cerebral infarct using machine learning techniques

Objective

Clot characteristics can provide information on the cause of cerebral artery occlusion and may guide acute revascularization and secondary prevention strategies. We developed a rapid automated clot analysis system using machine learning (ML) and validated its accuracy in patients undergoing endovascular treatment.

Methods

Pre‐endovascular treatment gradient echo (GRE) images from consecutive patients with middle cerebral artery occlusion were utilized to develop and validate an ML system to predict whether atrial fibrillation (AF) was the underlying cause of ischemic stroke. The accuracy of the ML algorithm was compared with that of visual inspection by neuroimaging specialists for the presence of blooming artifact. Endovascular procedures and outcomes were compared in patients with and without AF.

Results

Of 67 patients, 29 (43.3%) had AF. Of these, 13 had known AF and 16 were newly diagnosed with cardiac monitoring. By visual inspection, interrater correlation for blooming artifact was 0.73 and sensitivity and specificity for AF were 0.79 and 0.63, respectively. For AF classification, the ML algorithms yielded an average accuracy of > 75.4% in fivefold cross‐validation with clot signal profiles obtained from 52 patients and an area under the curve >0.87 for the average AF probability from five signal profiles in external validation (n = 15). Analysis with an in‐house interface took approximately 3 min per patient. Absence of AF was associated with increased number of passes by stentriever, high reocclusion frequency, and additional use of rescue stenting and/or glycogen IIb/IIIa blocker for recanalization.

Interpretation

ML‐based rapid clot analysis is feasible and can identify AF with high accuracy, enabling selection of endovascular treatment strategy.

Red blood cells: the forgotten player in hemostasis and thrombosis

New evidence has stirred up a long-standing but undeservedly forgotten interest in the role of erythrocytes, or red blood cells (RBCs), in blood clotting and its disorders. This review summarizes the most recent research that describes the involvement of RBCs in hemostasis and thrombosis. There are both quantitative and qualitative changes in RBCs that affect bleeding and thrombosis, as well as interactions of RBCs with cellular and molecular components of the hemostatic system. The changes in RBCs that affect hemostasis and thrombosis include RBC counts or hematocrit (modulating blood rheology through viscosity) and qualitative changes, such as deformability, aggregation, expression of adhesive proteins and phosphatidylserine, release of extracellular microvesicles, and hemolysis. The pathogenic mechanisms implicated in thrombotic and hemorrhagic risk include variable adherence of RBCs to the vessel wall, which depends on the functional state of RBCs and/or endothelium, modulation of platelet reactivity and platelet margination, alterations of fibrin structure and reduced susceptibility to fibrinolysis, modulation of nitric oxide availability, and the levels of von Willebrand factor and factor VIII in blood related to the ABO blood group system. RBCs are involved in platelet-driven contraction of clots and thrombi that results in formation of a tightly packed array of polyhedral erythrocytes, or polyhedrocytes, which comprises a nearly impermeable barrier that is important for hemostasis and wound healing. The revisited notion of the importance of RBCs is largely based on clinical and experimental associations between RBCs and thrombosis or bleeding, implying that RBCs are a prospective therapeutic target in hemostatic and thrombotic disorders.

The role of plasminogen activators in stroke treatment: fibrinolysis and beyond

Although recent technical advances in thrombectomy have revolutionised acute stroke treatment, prevalence of disability and death related to stroke remain high. Therefore, plasminogen activators-eukaryotic, bacterial, or engineered forms that can promote fibrinolysis by converting plasminogen into active plasmin and facilitate clot breakdown-are still commonly used in the acute treatment of ischaemic stroke. Hence, plasminogen activators have become a crucial area for clinical investigation for their ability to recanalise occluded arteries in ischaemic stroke and to accelerate haematoma clearance in haemorrhagic stroke. However, inconsistent results, insufficient evidence of efficacy, or reports of side-effects in trial settings might reduce the use of plasminogen activators in clinical practice. Additionally, the mechanism of action for plasminogen activators could extend beyond the vessel lumen and involve plasminogen-independent processes, which would suggest that plasminogen activators have also non-fibrinolytic roles. Understanding the complex mechanisms of action of plasminogen activators can guide future directions for therapeutic interventions in patients with stroke.

Clot Pathophysiology: Why Is It Clinically Important?

Cerebral ischemic stroke treatment may change significantly now that clots are actually physically removed from the patient using thrombectomy. This allows for an analysis of the content of the clots as well as the correlation of the imaging findings and the clot behavior and morphology. This article illustrates how the interaction of different clots varies in the clinical setting and how analysis of clot composition, as well as the search for new pharmacologic targets, can lead to a better understanding of the pathophysiology and therapy resistance, in turn providing possibilities for a better approach in the treatment.

Correlation of imaging and histopathology of thrombi in acute ischemic stroke with etiology and outcome: a systematic review

BACKGROUND AND PURPOSE

Studying the imaging and histopathologic characteristics of thrombi in ischemic stroke could provide insights into stroke etiology and ideal treatment strategies. We conducted a systematic review of imaging and histologic characteristics of thrombi in acute ischemic stroke.

MATERIALS AND METHODS

We identified all studies published between January 2005 and December 2015 that reported findings related to histologic and/or imaging characteristics of thrombi in acute ischemic stroke secondary to large vessel occlusion. The five outcomes examined in this study were (1) association between histologic composition of thrombi and stroke etiology; (2) association between histologic composition of thrombi and angiographic outcomes; (3) association between thrombi imaging and histologic characteristics; (4) association between thrombi imaging characteristics and angiographic outcomes; and (5) association between imaging characteristics of thrombi and stroke etiology. A meta-analysis was performed using a random effects model.

RESULTS

There was no significant difference in the proportion of red blood cell (RBC)-rich thrombi between cardioembolic and large artery atherosclerosis etiologies (OR 1.62, 95% CI 0.1 to 28.0, p=0.63). Patients with a hyperdense artery sign had a higher odds of having RBC-rich thrombi than those without a hyperdense artery sign (OR 9.0, 95% CI 2.6 to 31.2, p<0.01). Patients with a good angiographic outcome had a mean thrombus Hounsfield unit (HU) of 55.1±3.1 compared with a mean HU of 48.4±1.9 for patients with a poor angiographic outcome (mean standard difference 6.5, 95% CI 2.7 to 10.2, p<0.001). There was no association between imaging characteristics and stroke etiology (OR 1.13, 95% CI 0.32 to 4.00, p=0.85).

CONCLUSIONS

The hyperdense artery sign is associated with RBC-rich thrombi and improved recanalization rates. However, there was no association between the histopathological characteristics of thrombi and stroke etiology and angiographic outcomes.