Platelet-Rich Emboli in Cerebral Large Vessel Occlusion Are Associated With a Large Artery Atherosclerosis Source

Impact of obesity-related indicators on first-pass effect in patients with ischemic stroke receiving mechanical thrombectomy

PURPOSE

The first-pass effect (FPE), defined as complete revascularization after a single thrombectomy pass in large vessel occlusion, is a predictor of good prognosis in patients with acute ischemic stroke (AIS) receiving mechanical thrombectomy (MT). We aimed to evaluate obesity-related indicators if possible be predictors of FPE.

METHODS

We consecutively enrolled patients with AIS who were treated with MT between January 2019 and December 2021 at our institution. Baseline characteristics, procedure-related data, and laboratory test results were retrospectively analyzed. A multivariable logistic regression analysis was performed to evaluate the independent predictors of FPE.

RESULTS

A total of 151 patients were included in this study, of whom 47 (31.1%) had FPE. After adjusting for confounding factors, the independent predictors of achieving FPE were low levels of body mass index (BMI) (OR 0.85, 95% CI 0.748 to 0.971), non-intracranial atherosclerotic stenosis (OR 4.038, 95% CI 1.46 to 11.14), and non-internal carotid artery occlusion (OR 13.14, 95% CI 2.394 to 72.11). Patients with lower total cholesterol (TC) (< 3.11 mmol/L) were more likely to develop FPE than those with higher TC (≥ 4.63 mmol/L) (OR 4.280; 95% CI 1.24 to 14.74) CONCLUSION: Lower BMI, non-intracranial atherosclerotic stenosis, non-internal carotid artery occlusion, and lower TC levels were independently associated with increased rates of FPE in patients with AIS who received MT therapy. FPE was correlated with better clinical outcomes after MT.

First pass effect in patients undergoing endovascular treatment for posterior circulation acute ischemic stroke

OBJECTIVE

This study aims to investigate the impact of first pass effect (FPE) on outcomes in the posterior circulation acute ischemic stroke (PC-AIS) and the independent predictors of FPE.

METHODS

This was a multicenter, retrospective study. PC-AIS patients who underwent endovascular treatment were reviewed. The cohort achieving complete or nearly complete reperfusion (defined as expanded treatment in cerebralischemia [eTICI] ≥ 2c) was categorized into the FPE and multiple pass effect (MPE) groups. FPE was defined as achieving eTICI ≥ 2c with a single pass and without the use of rescue therapy. Modified FPE (mFPE) was defined as meeting the criteria for FPE but with eTICI ≥ 2b. The association of FPE with 90-day clinical outcomes and predictors for FPE were both investigated.

RESULTS

The study included a total of 328 patients, with 69 patients (21 %) in the FPE group. For primary outcome, FPE had a significant higher favorable outcome (mRS ≤ 3) rate than MPE (65.2 % vs. 44.8 %, p = 0.003). Similar outcomes were observed in the mFPE. Furthermore, FPE was significantly associated with favorable outcome (adjusted OR 2.23, 95 % CI 1.06-4.73, p = 0.036). Positive predictors for FPE included occlusion in the distal basilar artery, the first-line aspiration or combination, and cardioembolic etiology. Negative predictors for FPE included hypertension and general anesthesia.

CONCLUSION

For PC-AIS patients due to large or medium vessel occlusion, FPE is associated with favorable clinical outcomes. The first-line techniques of aspiration or combination, as well as avoiding general anesthesia, contribute to a better realization of FPE.

Utilizing RNA sequencing to identify gene expression markers of stroke-causing thrombi origin: A pilot study

INTRODUCTION

Stroke embolic source have an unknown origin in 30-40% of cases. Mechanical thrombectomy for acute large vessel occlusion stroke has provided us with a method to directly retrieve the thrombi from patients for analysis. By collecting stroke-causing thrombi from known sources, we can then use high-throughput RNA sequencing (RNAseq) technology to directly measure the gene expression signatures of these clots. This may allow us to identify genetic markers to predict the cause of cryptogenic embolism.

METHODS

This is a prospective study in which RNAseq was used to analyze cerebral thrombi retrieved by mechanical thrombectomy devices in acute ischemic stroke patients. Samples were separated into two groups based on known stroke thrombus etiology, including Carotid group (patients with ipsilateral >70% carotid stenosis) and Atrial fibrillation (AF) group (patients with atrial fibrillation). Gene expression was compared by RNAseq analysis between the groups.

RESULTS

From October 2016 to September 2017, 8 thrombi (4 in Carotid group, 4 in Afib group) were included in this study. There were 131 genes that were significantly up- or down-regulated between the two groups defined as a false discovery rate ≤ 0.05 and a fold change ≥ 2. Twenty-six genes were selected as candidate gene biomarkers based on the criteria in the methods section. Candidate genes HSPA1B, which encodes a heatshock protein, and GPRC5B, which encodes a G-protein, showed the greatest fold differences in expression between the two groups.

CONCLUSION

This study has shown that RNA sequencing of acute ischemic stroke thrombi is feasible and indentified potential novel biomarkers for identifying stroke-causing thrombi origin, especially in cryptogenic stroke.

Multimaterial decomposition in dual-energy CT for characterization of clots from acute ischemic stroke patients

BACKGROUND

Nowadays, there is no method to quantitatively characterize the material composition of acute ischemic stroke thrombi prior to intervention, but dual-energy CT (DE-CT) offers imaging-based multimaterial decomposition. We retrospectively investigated the material composition of thrombi ex vivo using DE-CT with histological analysis as a reference.

METHODS

Clots of 70 patients with acute ischemic stroke were extracted by mechanical thrombectomy and scanned ex vivo in formalin-filled tubes with DE-CT. Multimaterial decomposition in the three components, i.e., red blood cells (RBC), white blood cells (WBC), and fibrin/platelets (F/P), was performed and compared to histology (hematoxylin/eosin staining) as reference. Attenuation and effective Z values were assessed, and histological composition was compared to stroke etiology according to the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) criteria.

RESULTS

Histological and imaging analysis showed the following correlation coefficients for RBC (r = 0.527, p < 0.001), WBC (r = 0.305, p = 0.020), and F/P (r = 0.525, p < 0.001). RBC-rich thrombi presented higher clot attenuation in Hounsfield units than F/P-rich thrombi (51 HU versus 42 HU, p < 0.01). In histological analysis, cardioembolic clots showed less RBC (40% versus 56%, p = 0.053) and more F/P (53% versus 36%, p = 0.024), similar to cryptogenic clots containing less RBC (34% versus 56%, p = 0.006) and more F/P (58% versus 36%, p = 0.003) than non-cardioembolic strokes. No difference was assessed for the mean WBC portions in all TOAST groups.

CONCLUSIONS

DE-CT has the potential to quantitatively characterize the material composition of ischemic stroke thrombi.

RELEVANCE STATEMENT

Using DE-CT, the composition of ischemic stroke thrombi can be determined. Knowledge of histological composition prior to intervention offers the opportunity to define personalized treatment strategies for each patient to accomplish faster recanalization and better clinical outcomes.

KEY POINTS

• Acute ischemic stroke clots present different recanalization success according to histological composition. • Currently, no method can determine clot composition prior to intervention. • DE-CT allows quantitative material decomposition of thrombi ex vivo in red blood cells, white blood cells, and fibrin/platelets. • Histological clot composition differs between stroke etiology. • Insights into the histological composition in situ offer personalized treatment strategies.

The immunologic phenotype of thrombi is associated with future vascular events after cerebral infarction

BACKGROUND

Thrombi retrieved from patients with acute ischemic stroke may contain prognostic information.

OBJECTIVE

To investigate the relationship between the immunologic phenotype of thrombi and future vascular events in patients with a stroke.

METHODS

This study included patients with acute ischemic stroke who underwent endovascular thrombectomy at Chung-Ang University Hospital in Seoul, Korea, between February 2017 and January 2020. Laboratory and histological variables were compared between patients with and without recurrent vascular events (RVEs). Kaplan-Meier analysis followed by the Cox proportional hazards model was used to identify factors related to RVE. Receiver operating characteristic (ROC) analysis was conducted to evaluate the performance of the immunologic score by combining immunohistochemical phenotypes to predict RVE.

RESULTS

A total of 46 patients were included in the study with 13 RVEs (mean±SD age, 72.8±11.3 years; 26 (56.5%) men). Thrombi with a lower percentage of programmed death ligand-1 expression (HR=11.64; 95% CI 1.60 to 84.82) and a higher number of citrullinated histone H3 positive cells (HR=4.19; 95% CI 0.81 to 21.75) were associated with RVE. The presence of high-mobility group box 1 positive cell was associated with reduced risk of RVE, but the association was lost after adjustment for stroke severity. The immunologic score, which consists of the three immunohistochemical phenotypes, showed good performance in predicting RVE (area under the ROC curve, 0.858; 95% CI 0.758 to 0.958).

CONCLUSIONS

The immunological phenotype of thrombi could provide prognostic information after stroke.

Prevalence and clinical features of carotid artery web in patients undergoing endovascular thrombectomy for acute ischemic stroke

PURPOSE

Carotid artery web (CaW) is a rare focal fibromuscular dysplasia that can lead to embolic strokes with large vessel occlusion. This condition can be effectively treated with endovascular thrombectomy (EVT). Our study aims to assess the prevalence of CaW among patients with acute ischemic stroke (AIS) who underwent EVT and to compare the clinical characteristics of CaW with other carotid artery pathologies.

METHODS

We enrolled consecutive patients with AIS who underwent EVT at a single medical center and two regional teaching hospitals in Taiwan from September 2014 to December 2021. We compared CaW with carotid dissection (CaD) and carotid large artery atherosclerosis (CaLAA) in terms of patient demographics and thrombus histological findings.

RESULTS

Of the 576 AIS patients who underwent EVT, four (mean age: 50 years) were diagnosed with CaW, resulting in a prevalence of 0.69%. Among these four patients, three experienced successful reperfusion after EVT and achieved functional independence (defined as a modified Rankin Scale score ≤2) three months post-stroke. Importantly, none of the CaW patients suffered a recurrent stroke within one year. Patients with CaW were younger than those with CaD or CaLAA, and exhibited fewer vascular risk factors. Additionally, CaW was associated with distal occlusion sites. The thrombus composition in CaW patients was similar to that in CaD patients.

CONCLUSIONS

In conclusion, CaW is a rare finding among Asian patients with carotid artery disease who undergo for AIS. It is more prevalent in younger patients with a limited number of vascular risk factors.

Differential expression of Semaphorin-7A /CD163-positive macrophages in large artery and cardiogenic stroke

BACKGROUND

Identification of the causes of stroke of undetermined etiology, specifically cardioembolism (CE) and non-CE causes, can inform treatment planning and prognosis prediction. The objective of this study was to analyze the disparities in thrombus composition, particularly Semaphorin-7A (Sema7A) and CD163, between patients diagnosed with large-artery atherosclerosis (LAA) and those with CE, and to investigate their potential association with prognosis.

METHODS

Thrombi were collected from patients who underwent mechanical thrombectomy at two hospitals. The patients were categorized into two groups: LAA and CE. We compared the levels of Sema7A and CD163 between these groups and analyzed their relationships with stroke severity, hemorrhagic transformation and prognosis.

RESULTS

The study involved a total of 67 patients. Sema7A expression was found to be significantly higher in the CE group compared to LAA (p < 0.001). Conversely, no statistically significant differences were observed for CD163 between the groups. The presence of Sema7A/CD163 did not show any associations with stroke severity or hemorrhagic transformation (all p > 0.05). However, both Sema7A (OR, 2.017; 95% CI, 1.301-3.518; p = 0.005) and CD163 (OR, 2.283; 95% CI, 1.252-5.724; p = 0.03) were associated with the poor prognosis for stroke, after adjusting for stroke severity.

CONCLUSION

This study highlights that CE thrombi exhibited higher levels of Sema7A expression compared to LAA thrombi. Moreover, we found a positive correlation between Sema7A/CD163 levels and the poor prognosis of patients with acute ischemic stroke.

Atrial fibrillation is associated with higher first pass effect following thrombectomy for large vessel occlusion

BACKGROUND

First pass effect (FPE), defined as single-pass complete or near complete reperfusion during endovascular thrombectomy (EVT) for large vessel occlusion (LVO) strokes, is a critical performance metric. Atrial fibrillation (AF)-related strokes have different clot composition compared with non-AF strokes, which may impact thrombectomy reperfusion results. We compared FPE rates in AF and non-AF stroke patients to evaluate if AF-related strokes had higher FPE rates.

METHODS

We conducted a post-hoc analysis of the DIRECT-SAFE trial data, including patients with retrievable clots on the initial angiographic run. Patients were categorized into AF and non-AF groups. The primary outcome was the presence or absence of FPE (single-pass, single-device resulting in complete/near complete reperfusion) in AF and non-AF groups. We used multivariable logistic regression to examine the association between FPE and AF, adjusting for thrombolysis pre-thrombectomy and clot location.

RESULTS

We included 253 patients (67 with AF, 186 without AF). AF patients were older (mean age: 74 years vs 67.5 years, p=0.001), had a higher proportion of females (55% vs 40%, p=0.044), and experienced more severe strokes (median National Institutes of Health Stroke Scale (NIHSS) score: 17 vs 14, p=0.009) than non-AF patients. No differences were observed in thrombolytic agent usage, time metrics, or clot location. AF patients achieved a higher proportion of FPE compared with non-AF patients (55.22% vs 37.3%, adjusted odds ratio 2.00 (95% CI 1.13 to 3.55), p=0.017).

CONCLUSIONS

AF-related strokes in LVO patients treated with EVT were associated with FPE. This highlights the need for preparedness for multiple passes and potential adjuvant/rescue therapy in non-AF-related strokes.

White blood cell subtypes and neutrophil extracellular traps content as biomarkers for stroke etiology in acute ischemic stroke clots retrieved by mechanical thrombectomy

BACKGROUND

Lymphocytes, macrophages, neutrophils, and neutrophil extracellular traps (NETs) associate with stroke risk factors and form a thrombus through different mechanisms. We investigated the total WBCs, WBC subtypes and NETs composition in acute ischemic stroke (AIS) clots to identify possible etiological differences that could help us further understand the process of thrombosis that leads to AIS.

METHODS

AIS clots from 100 cases each of atherothrombotic (AT), cardioembolic (CE) and cryptogenic stroke etiology were collected per-pass as part of the CÚRAM RESTORE registry of AIS clots. Martius Scarlet Blue stain was used to identify the main histological components of the clots. Immunohistochemical staining was used to identify neutrophils, lymphocytes, macrophages, and NETs patterns. The cellular and histological components were quantified using Orbit Image Analysis software.

RESULTS

AT clots were larger, with more red blood cells and fewer WBCs than CE clots. AT clots had more lymphocytes and cryptogenic clots had fewer macrophages than other etiologies. Most significantly, CE clots showed higher expression of neutrophils and extracellular web-like NETs compared to AT and cryptogenic clots. There was also a significantly higher distribution of web-like NETs around the periphery of the CE clots while a mixed distribution was observed in AT clots.

CONCLUSION

The difference in neutrophil and NETs expression in clots from different etiologies may provide insight into the mechanism of clot formation.

Association between thrombus composition and stroke etiology in the MR CLEAN Registry biobank

PURPOSE

The composition of thrombi retrieved during endovascular thrombectomy (EVT) in acute ischemic stroke (AIS) due to large vessel occlusion (LVO) may differ depending on their origin. In this study, we investigated the association between thrombus composition and stroke etiology in a large population of patients from the Dutch MR CLEAN Registry treated with EVT in daily clinical practice.

METHODS

The thrombi of 332 patients with AIS were histologically analyzed for red blood cells (RBC), fibrin/platelets (F/P), and white blood cells (leukocytes) using a machine learning algorithm. Stroke etiology was assessed using the Trial of Org 10,172 in acute stroke treatment (TOAST) classification.

RESULTS

The thrombi of cardioembolic origin contained less RBC and more F/P than those of non-cardioembolic origin (25.8% vs 41.2% RBC [p = 0.003] and 67.1% vs 54.5% F/P [p = 0.004]). The likelihood of a non-cardioembolic source of stroke increased with increasing thrombus RBC content (OR 1.02; [95% CI 1.00-1.06] for each percent increase) and decreased with a higher F/P content (OR 1.02; [95% CI 1.00-1.06]). Thrombus composition in patients with a cardioembolic origin and undetermined origin was similar.

CONCLUSION

Thrombus composition is significantly associated with stroke etiology, with an increase in RBC and a decrease in F/P raising the odds for a non-cardioembolic cause. No difference between composition of cardioembolic thrombi and of undetermined origin was seen. This emphasizes the need for more extensive monitoring for arrhythmias and/or extended cardiac analysis in case of an undetermined origin.

Incidence of Atrial Fibrillation in Large Vessel Occlusion and Large Embolic Stroke of Undetermined Source

INTRODUCTION

Large vessel occlusion (LVO) stroke is a common presentation of acute ischemic stroke and is often unknown or cryptogenic in etiology. There is a strong association between atrial fibrillation (AF) and cryptogenic LVO stroke, making it a unique stroke subgroup. Therefore, we propose that any LVO stroke meeting the criteria for an embolic stroke of an undetermined source (ESUS) be classified as large ESUS (LESUS). The purpose of this retrospective cohort study was to report the etiology of anterior LVO strokes that underwent endovascular thrombectomy.

METHODS

This was a single-center retrospective cohort study characterizing the etiology of acute anterior circulation LVO strokes that received emergent endovascular thrombectomy from 2011 to 2018. Patients with LESUS designation at hospital discharge were changed to cardioembolic etiology if AF was discovered during the two-year follow-up period.  Results: Overall, 155 (45%) of 307 patients in the study were found to have AF. New onset AF was discovered in 12 (23%) of 53 LESUS patients after hospitalization. Furthermore, eight (35%) of 23 LESUS patients who received extended cardiac monitoring were found to have AF.

CONCLUSION

Nearly half the patients with LVO stroke who received endovascular thrombectomy were found to have AF. With the use of extended cardiac monitoring devices after hospitalization, AF is frequently discovered in patients with LESUS and may change the secondary stroke prevention strategy.

Clot Morphology in Acute Ischemic Stroke Decision Making

Stroke is a leading cause of death and disability in the world, and the provision of reperfusion therapy and endovascular therapy, in particular, have revolutionized the treatment of patients with stroke and opened opportunities to look at brain clots retrieved after the procedure. The use of histopathology and molecular profiling of clots is of growing research and clinical interest. However, its clinical implications and incorporation within stroke workflows remain suboptimal. Recent studies have indicated that the study of brain clots may inform the mechanism of stroke and hence guide treatment decision-making in select groups of patients, especially patients without a defined cause or known mechanism. This article provides a comprehensive overview of various clot histopathological examinations in acute stroke-care settings, their clinical utility, and existing gaps and opportunities for further research. We also provide targeted recommendations to improve clot analysis workflow, hence standardizing its incorporation into clinical practice.

Is Composition of Brain Clot Retrieved by Mechanical Thrombectomy Associated with Stroke Aetiology and Clinical Outcomes in Acute Ischemic Stroke?—A Systematic Review and Meta-Analysis

Background: Brain clots retrieved following endovascular thrombectomy in acute ischemic stroke patients may offer unique opportunities to characterise stroke aetiology and aid stroke decision-making in select groups of patients. However, the evidence around the putative association of clot morphology with stroke aetiology is limited and remains inconclusive. This study aims to perform a systematic review and meta-analysis to delineate the association of brain clot composition with stroke aetiology and post-reperfusion outcomes in patients receiving endovascular thrombectomy. Methods: The authors conducted a systematic literature review and meta-analysis by extracting data from several research databases (MEDLINE/PubMed, Cochrane, and Google Scholar) published since 2010. We used appropriate key search terms to identify clinical studies concerning stroke thrombus composition, aetiology, and clinical outcomes, in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: The authors identified 30 articles reporting on the relationship between stroke thrombus composition or morphology and aetiology, imaging, or clinical outcomes, of which 21 were included in the meta-analysis. The study found that strokes of cardioembolic origin (SMD = 0.388; 95% CI, 0.032–0.745) and cryptogenic origin (SMD = 0.468; 95% CI, 0.172–0.765) had significantly higher fibrin content than strokes of non-cardioembolic origin. Large artery atherosclerosis strokes had significantly lower fibrin content than cardioembolic (SMD = 0.552; 95% CI, 0.099–1.004) or cryptogenic (SMD = 0.455; 95% CI, 0.137–0.774) strokes. Greater red blood cell content was also significantly associated with a thrombolysis in cerebral infarction score of 2b–3 (SMD = 0.450; 95% CI, 0.177–0.722), and a positive hyperdense middle cerebral artery sign (SMD = 0.827; 95% CI, 0.472–1.183). No significant associations were found between red blood cell, platelet, or white blood cell content and aetiology, or between clot composition and bridging thrombolysis. Conclusions: This meta-analysis found that fibrin composition is significantly higher in strokes of cardioembolic and cryptogenic origin, and that red blood cell content is positively associated with the hyperdense middle cerebral artery sign and better reperfusion outcomes. Important advances to stroke clinical workup can be derived from these findings, in which many aspects of stroke workflow remain to be optimised. As data are still limited in terms of the association of various thrombus components with stroke aetiology as well as a standardised method of analysis, further studies are required to validate these findings to guide their use in clinical decision-making.

Histology of Cerebral Clots in Cryptogenic Stroke Varies According to the Presence of a Patent Foramen Ovale

Although a pathophysiological impact remains difficult to prove in individual patient care, a patent foramen ovale (PFO) is currently considered of high relevance for secondary prophylaxis in selected patients with cryptogenic ischemic stroke. By quantification of histological clot composition, we aimed to enhance pathophysiological understanding of PFO attributable ischemic strokes. Retrospectively, we evaluated all cerebral clots retrieved by mechanical thrombectomy for acute ischemic stroke treatment between 2011 and 2021 at our comprehensive stroke care center. Inclusion criteria applied were cryptogenic stroke, age (≤60 years), and PFO status according to transesophageal echocardiography, resulting in a study population of 58 patients. Relative clot composition was calculated using orbit image analysis to define the ratio of main histologic components (fibrin/platelets (F/P), red blood cell count (RBC), leukocytes). Cryptogenic stroke patients with PFO (PFO+, n = 20) displayed a significantly higher percentage of RBC (0.57 ± 0.17; p = 0.002) and lower percentage of F/P (0.38 ± 0.15; p = 0.003) compared to patients without PFO (PFO–, n = 38) (RBC: 0.41 ± 0.21; F/P: 0.52 ± 0.20). In conclusion, histologic clot composition in cryptogenic stroke varies depending on the presence of a PFO. Our findings histologically support the concept that a PFO may be of pathophysiological relevance in cryptogenic ischemic stroke.

High Actin Expression in Thrombus of Acute Ischemic Stroke Can Be a Biomarker of Atherothrombotic Origin Stroke

Background

As the treatment target, the imaging information and histologic characteristics of the thrombus may differ according to the stroke subtype. This study aimed to provide the correlative study of stroke etiology with the non-contrast CT, and histological composition of retrieved clots in acute ischemic stroke (AIS).

Materials and Methods

A total of 94 patients with AIS who underwent the endovascular treatment with successfully retrieved clots from January 2017 to October 2020 were enrolled in the present study. Histological analysis was performed using hematoxylin and eosin (H&E) staining and immunostaining with CD3, CD20, CD105, and actin antibodies. CT obtained at the patients' admission was to measure the attenuation and volume of all thrombus.

Results

A total of 94 subjects were included in this study. Fifty-six patients were classified as cardioembolic (CE), and 38 were classified with large-artery atherosclerosis (LAA). The subjects with LAA tend to exhibit higher actin and CD105 levels, and lower Hounsfield Unit (HU) values than subjects with CE. After adjusting for confounders, the actin was positively correlated with CD105 but not with HU values. Logistics regression shows actin was valuable for the prediction of LAA (OR, 1.148; 95% CI, 1.075–1.227; p < 0.001), even adjusted for age, sex, and intervention type (OR, 1.129; 95% CI, 1.048–1.216; p = 0.001), CT density and CD105 (OR, 1.161; 95% CI, 1.056–1.277; p = 0.002). Actin levels have a strong accuracy in differentiating LAA from CE, especially combined with CT density and CD105, which yielded a sensitivity of 63.2%, a specificity of 89.3%, with the area under the curve (AUC) at 0.821 (95% CI, 0.731–0.912).

Conclusion

Our findings suggest that actin's level was a major factor differentiating atherothrombotic origin strokes from the cardioembolic stroke.

Clinical Trial Registration

ChiCTR2100051173.

Absence of Susceptibility Vessel Sign in Patients With Malignancy-Related Acute Ischemic Stroke Treated With Mechanical Thrombectomy

Background and Purpose

Clots rich in platelets and fibrin retrieved from patients with acute ischemic stroke (AIS) have been shown to be independently associated with the absence of the susceptibility vessel sign (SVS) on MRI and active malignancy. This study analyzed the association of SVS and the presence of active malignancy in patients with AIS who underwent mechanical thrombectomy (MT).

Methods

This single-center, retrospective, and cross-sectional study included consecutive patients with AIS with admission MRI treated with MT between January 2010 and December 2018. SVS status was evaluated on susceptibility-weighted imaging. Adjusted odds ratios (aORs) were calculated to determine the association between absent SVS and the presence of active or occult malignancy. The performance of predictive models incorporating and excluding SVS status was compared using areas under the receiver operating characteristics curve (auROC).

Results

Of 577 patients with AIS with assessable SVS status, 40 (6.9%) had a documented active malignancy and 72 (12.5%) showed no SVS. The absence of SVS was associated with active malignancy (aOR 4.85, 95% CI 1.94–12.11) or occult malignancy (aOR 11.42, 95% CI 2.36–55.20). The auROC of predictive models, including demographics and common malignancy biomarkers, was higher but not significant (0.85 vs. 0.81, p = 0.07) when SVS status was included.

Conclusion

Absence of SVS on admission MRI of patients with AIS undergoing MT is associated with malignancy, regardless of whether known or occult. Therefore, the SVS might be helpful in detecting paraneoplastic coagulation disorders and occult malignancy in patients with AIS.

Cancer and stroke: commonly encountered by clinicians, but little evidence to guide clinical approach

The association between stroke and cancer is well-established. Because of an aging population and longer survival rates, the frequency of synchronous stroke and cancer will become even more common. Different pathophysiologic mechanisms have been proposed how cancer or cancer treatment directly or via coagulation disturbances can mediate stroke. Increased serum levels of D-dimer, fibrin degradation products, and CRP are more often seen in stroke with concomitant cancer, and the clot retrieved during thrombectomy has a more fibrin- and platelet-rich constitution compared with that of atherosclerotic etiology. Multiple infarctions are more common in patients with active cancer compared with those without a cancer diagnosis. New MRI techniques may help in detecting typical patterns seen in the presence of a concomitant cancer. In ischemic stroke patients, a newly published cancer probability score can help clinicians in their decision-making when to suspect an underlying malignancy in a stroke patient and to start cancer-screening studies. Treating stroke patients with synchronous cancer can be a delicate matter. Limited evidence suggests that administration of intravenous thrombolysis appears safe in non-axial intracranial and non-metastatic cancer patients. Endovascular thrombectomy is probably rather safe in these patients, but probably futile in most patients placed on palliative care due to their advanced disease. In this topical review, we discuss the epidemiology, pathophysiology, and prognosis of ischemic and hemorrhagic strokes as well as cerebral venous thrombosis and concomitant cancer. We further summarize the current evidence on acute management and secondary preventive therapy.

Thrombosis origin identification of cardioembolism and large artery atherosclerosis by distinct metabolites

BACKGROUND

The diagnosis of cerebral thrombosis origin is challenging and remains unclear. This study aims to identify thrombosis due to cardioembolism (CE) and large artery atherosclerosis (LAA) from a new perspective of distinct metabolites.

METHODS

Distinct metabolites between 26 CE and 22 LAA origin thrombi, which were extracted after successful mechanical thrombectomy in patients with acute ischemic stroke in the anterior circulation, were analyzed with a ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) system. Enriched metabolic pathways related to the metabolites were identified. Least absolute shrinkage selection operator regression analyses and a filtering method were used to select potential predictors. Furthermore, four machine learning classifiers, including decision tree, logistic regression, random forest (RF), and k means unsupervised classification model, were used to evaluate the predictive ability of the selected metabolites.

RESULTS

UPLC-QTOF-MS analysis revealed that levels of 88 and 55 metabolites were elevated in LAA and CE thrombi, respectively. Kyoto Encyclopedia of Genes and Genomes analysis revealed a significant difference between the pathways enriched in the two types of thrombi. Six metabolites (diglyceride (DG, 18:3/24:0), DG (22:0/24:0), phytosphingosine, galabiosylceramide (18:1/24:1), triglyceride (15:0/16:1/o-18:0), and glucosylceramide (18:1/24:0)) were finally selected to build a predictive model. The predictive RF model was confirmed to be the best, with a satisfactory stability and prediction capacity (area under the curve=0.889).

CONCLUSIONS

Six metabolites as potential predictors for distinguishing between cerebral thrombi of CE and LAA origin were identified. The results are useful for understanding the pathogenesis and for secondary stroke prevention.

Factors That Influence Susceptibility Vessel Sign in Patients With Acute Stroke Referred for Mechanical Thrombectomy

Background and Purpose

The presence of a Susceptibility Vessel Sign (SVS) in the acute phase of proximal occlusion ischemic stroke indicates the presence of deoxyhemoglobin in the thrombus. Thrombi composition changes over time. The aim of this study was to investigate whether the absence of SVS is associated with a shorter symptom onset to imaging time.

Methods

We retrospectively analyzed all patients referred for mechanical thrombectomy at Besançon University Hospital between 1 January 2015 and 31 December 2020 for whom readable T2^*-weighted imaging was available. We compared patient characteristics according to the presence or absence of an SVS. We also studied the subgroup for whom the exact symptom onset time was known. We performed a univariate statistical analysis, then a multivariate analysis on the variables that were statistically significant in the univariate analysis.

Results

Of the 389 patients included, 309 (79.4%) were SVS+. We found no significant relationship between SVS– and the time between symptom onset and imaging in the whole cohort. In the multivariate analysis, SVS– was associated with anticoagulant treatment (p < 0.01), and SVS+ with age (p = 0.023) and carotid terminus occlusion (p = 0.042). In the known symptom onset subgroup, SVS– was significantly associated with a shorter symptom onset -imaging time (p < 0.001), and this was confirmed in the multivariate analysis (p = 0.011; OR 0.911; 95% CI [0.844; 0.972]).

Conclusion

In the acute phase of proximal occlusion ischemic stroke, absence of SVS was associated with a shorter symptom onset–imaging time for patients with a known symptom onset time.

Review and update of the concept of embolic stroke of undetermined source

Ischaemic strokes have traditionally been classified according to the TOAST criteria, in which strokes with unclear aetiology are classified as cryptogenic strokes. However, the definition of cryptogenic stroke did not meet the operational criteria necessary to define patient populations for randomized treatment trials. To address this problem, the concept of embolic stroke of undetermined source (ESUS) was developed and published in 2014. A hypothesis that underpinned this concept was that most strokes in patients with ESUS are caused by embolic events, perhaps many cardioembolic, and that anticoagulation would prevent secondary ischaemic events. On this basis, two large randomized trials were conducted to compare the non-vitamin K antagonist oral anticoagulants (NOACs) dabigatran and rivaroxaban with aspirin. Neither NOAC was superior to aspirin in these trials, although subgroups of patients with ESUS seemed to benefit specifically from anticoagulation or antiplatelet therapy. The neutral results of the trials of anticoagulation and insights into ESUS from research conducted since the concept was introduced warrant reassessment of the ESUS construct as a research concept and a treatment target. In this Review, we discuss the evidence produced since the concept of ESUS was introduced, and propose updates to the criteria and diagnostic algorithm in light of the latest knowledge.

Impact of histological clot composition on preprocedure imaging and mechanical thrombectomy

INTRODUCTION:

We studied the relationship of acute ischemic stroke (AIS) large-vessel occlusion clot composition with vessel recanalization and preprocedure imaging.

SUBJECTS AND METHODS:

Individual clots from AIS patients who underwent mechanical thrombectomy (MT) between September 2016 and September 2018 were examined. Clot composition was analyzed histologically through a trichrome staining and image segmentation, and the area occupied by red blood cells (RBCs), fibrin, or mixed composition was quantified.

RESULTS:

Forty-three patients (65.4 ± 12.7 years, 39% of females) who underwent 92 retrieval passes (mean 2.14, range 1–6) were included in this study. Fibrin (44%) occupied the greatest area, followed by mixed composition (34%) and RBCs (22%). A stent retriever was deployed in 81% of cases, 20 patients (47%) achieved first-pass efficacy (FPE) (thrombolysis in cerebral infarction [TICI] 2b-3 after first pass), 41 (95%) achieved successful revascularization (TICI 2b-3), and 21 (49%) had good outcome (modified Rankin Scale [mRS] ≤2) at 90 days. Hyperdense artery sign (HAS) on initial computed tomography was correlated with mixed clot composition (P = 0.01) and lack of fibrin content (P = 0.03). In the univariate analysis, FPE was associated with RBC clot area, atrial fibrillation, and occlusion location but not with fibrin clot area, mixed clot area, stroke etiology, thrombectomy technique, distal emboli, or 90-day mRS. In the multivariate analysis, FPE was significantly correlated with low RBC clot area (odd ratio = 0.96, confidence interval [0.92.99], P = 0.034) but not with atrial fibrillation or location.

CONCLUSION:

Our results suggest that HAS is correlated with mixed clot composition and lower fibrin content and that lower RBC clot composition is associated with FPE in patients undergoing MT.

Histological composition of retrieved emboli in acute ischemic stroke is independent of pre-thrombectomy alteplase use

BACKGROUND AND PURPOSE

Given recent evidence suggesting the clot composition may be associated with revascularization outcomes and stroke etiology, clot composition research has been a topic of growing interest. It is currently unclear what effect, if any, pre-thrombectomy thrombolysis has on clot composition. Understanding this association is important as it is a potential confounding variable in clot composition research. We retrospectively evaluated the composition of retrieved clots from ischemic stroke patients who did and did not receive pre-treatment tPA to study the effect of tPA on clot composition.

MATERIALS AND METHODS

Consecutive patients enrolled in the Stroke Thromboembolism Registry of Imaging and Pathology (STRIP) were included in this study. All patients underwent mechanical thrombectomy and retrieved clots were sent to a central core lab for processing. Histological analysis was performed using Martius Scarlett Blue (MSB) staining and area of the clot was also measured on the gross photos. Student's t test was used for continuous variables and chi-squared test for categorical variables.

RESULTS

A total of 1430 patients were included in this study. Mean age was 68.4±13.5 years. Overall rate of TICI 2c/3 was 67%. A total of 517 patients received tPA (36%) and 913 patients did not (64%). Mean RBC density for the tPA group was 42.97±22.62% compared to 42.80±23.18% for the non-tPA group (P=0.89). Mean WBC density for the tPA group was 3.74±2.60% compared to 3.42±2.21% for the non-tPA group (P=0.012). Mean fibrin density for the tPA group was 26.52±15.81% compared to 26.53±15.34% for the non-tPA group (P=0.98). Mean platelet density for the tPA group was 26.22±18.60% compared to 26.55±19.47% for the non-tPA group (P=0.75). tPA group also had significantly smaller clot area compared to non-tPA group.

CONCLUSIONS

Our study 1430 retrieved emboli and ischemic stroke patients shows no interaction between tPA administration and clot composition. These findings suggest that tPA does not result in any histological changes in clot composition.

Sex differences in thrombosis as it affects acute ischemic stroke

Ischemic stroke is a devastating health problem, affecting approximately 800,000 patients in the US every year, making it the leading cause of combined death and disability in the country. Stroke has historically been thought of as predominantly impacting men, however it is becoming increasingly clear that stroke affects women to a greater degree than men. Indeed, women have worse outcomes compared to men following ischemic stroke. Recent clinical advances have shown great promise in acute stroke therapy, with the use of mechanical endovascular thrombectomy (with and without recombinant tissue plasminogen activator; rtPA) greatly improving outcomes. This observation makes it clear that removal of clots and reperfusion, either mechanically or pharmacologically, is critical for improving outcomes of patients following acute ischemic stroke. Despite these promising advances, long-term neurological sequelae persist in the post-stroke population. This review focuses on mechanisms of thrombosis (clot formation) as it pertains to stroke and important sex differences in thrombosis and responses to treatment. Finally, we describe recent data related to new therapeutic approaches to thrombolysis, with a particular focus on von Willebrand Factor (vWF).

Characterising acute ischaemic stroke thrombi: insights from histology, imaging and emerging impedance-based technologies

Treatment of acute ischaemic stroke (AIS) focuses on rapid recanalisation of the occluded artery. In recent years, advent of mechanical thrombectomy devices and new procedures have accelerated the analysis of thrombi retrieved during the endovascular thrombectomy procedure. Despite ongoing developments and progress in AIS imaging techniques, it is not yet possible to conclude definitively regarding thrombus characteristics that could advise on the probable efficacy of thrombolysis or thrombectomy in advance of treatment. Intraprocedural devices with dignostic capabilities or new clinical imaging approaches are needed for better treatment of AIS patients. In this review, what is known about the composition of the thrombi that cause strokes and the evidence that thrombus composition has an impact on success of acute stroke treatment has been examined. This review also discusses the evidence that AIS thrombus composition varies with aetiology, questioning if suspected aetiology could be a useful indicator to stroke physicians to help decide the best acute course of treatment. Furthermore, this review discusses the evidence that current widely used radiological imaging tools can predict thrombus composition. Further use of new emerging technologies based on bioimpedance, as imaging modalities for diagnosing AIS and new medical device tools for detecting thrombus composition in situ has been introduced. Whether bioimpedance would be beneficial for gaining new insights into in situ thrombus composition that could guide choice of optimum treatment approach is also reviewed.

[Susceptibility vessel sign in subacute stroke patients with large vessel occlusion]

OBJECTIVE

To investigate the presentation of susceptibility vessel sign (SVS) in subacute stroke patients with large vessel occlusion.

METHODS

We collected consecutive stroke patients who were admitted to Peking University First Hospital from December 2017 to August 2019 retrospectively. Those who had intracranial large vessel occlusion and received sensitivity weighted imaging (SWI) within 3 to 14 days after stroke onset were included in our analysis. The diagnosis of large vessel occlusion was based on magnetic resonance angiography (MRA), CT angiography (CTA) or digital subtraction angiography (DSA). The demographic information, clinical characteristics and imaging results were obtained from medical record. The occurrence rates of SVS sign were compared between stroke patients with cardioembolism (CE) and large artery atherosclerosis (LAA). In the sensitivity analysis, we performed a subgroup analysis in those patients who received SWI within 7 to 14 days after stroke onset. We also compared the occurrence rate of SVS sign between the patients with and without atrial fibrillation.

RESULTS

A total of 51 patients, 19 females and 32 males, with an average age of (63.04±11.23) years were analyzed in this study. Compared with LAA group, the patients in CE group were older and more likely to have an atrial fibrillation (P < 0.05). There were no significant differences between the CE group and LAA group in gender, hypertension, diabetes, coronary heart disease, hyperlipidemia, smoking, or National Institute of Health stroke scale(NIHSS) score at admission. SVS sign was found in 30 patients. Of whom, 3 were in CE group and 27 in LAA group. The occurrence rate of SVS sign was higher in the LAA group than in the CE group significantly (65.9% vs. 30.0%, P=0.039). The subgroup analysis showed that, in the patients who received SWI examination within 7 to 14 days after stroke onset, the differences between the two groups were still statistically significant (0 vs. 72.7%, P=0.006). Another sensitivity analysis showed that, the rate of SVS in the patients with atrial fibrillation was significantly lower than those patients without atrial fibrillation (25% vs. 65.1%, P=0.043).

CONCLUSION

In subacute stroke patients, the occurrence rate of SVS sign in CE group was lower than that of LAA group. The significance of SVS sign in the differentiation of stroke subtype needs further validation.

Thrombus Composition, Imaging, and Outcome Prediction in Acute Ischemic Stroke

BACKGROUND AND OBJECTIVES

New imaging techniques have advanced our ability to capture thrombus characteristics and burden in real time. An improved understanding of recanalization rates with thrombolysis and endovascular thrombectomy based on thrombus characteristics has spurred interest in new therapies for acute stroke.

METHODS AND RESULTS

This article reviews the biochemical, structural, and imaging characteristics of intracranial thrombi in acute ischemic stroke; the relationship between thrombus composition and response to lytic and endovascular therapies; and current and future directions for improving outcomes in patients with acute stroke based on thrombus characteristics.

DISCUSSION

Thrombus composition, size, location, and timing from stroke onset correlate with imaging findings in acute ischemic stroke and are associated with clinical outcome. Further research across multiple domains could assist in better applying our knowledge of thrombi to patient selection and individualization of acute therapies.

Studying Stroke Thrombus Composition After Thrombectomy: What Can We Learn?

The composition of ischemic stroke thrombi has gained an increasing amount of interest in recent years. The implementation of endovascular procedures in standard stroke care has granted researchers the unique opportunity to examine patient thrombus material. Increasing evidence indicates that stroke thrombi are complex and heterogenous, consisting of various biochemical (eg, fibrin, von Willebrand Factor, and neutrophil extracellular traps) and cellular (eg, red blood cells, platelets, leukocytes, and bacteria) components. This complex composition may explain therapeutic limitations and also offer novel insights in several aspects of stroke management. Better understanding of thrombus characteristics could, therefore, potentially lead to improvements in the management of patients with stroke. In this review, we provide a comprehensive overview of the lessons learned by examining stroke thrombus composition after endovascular thrombectomy and its potential relevance for thrombectomy success rates, thrombolysis, clinical outcomes, stroke etiology, and radiological imaging.

Histologic differences between in situ and embolized carotid web thrombi: a case report

Background

The significance of carotid webs (CaWs) in ischemic stroke is becoming acknowledged. Histological features of clot composition in situ and secondary cerebrovascular embolized thrombi caused by CaW have not been described concurrently. Understanding clots’ histological composition is essential for understanding the pathophysiology of clot formation in CaW.

Case presentation

A 50-year-old male patient with acute ischemic stroke, which was believed to be caused by ipsilateral CaW, was admitted to the hospital. Mechanical thrombectomy was used to retrieve thromboemboli from the middle cerebral artery. One month thereafter, the patient underwent carotid endarterectomy, and in situ CaW thrombi were retrieved. Histological analysis by hematoxylin and eosin staining revealed that histopathologic embolized thrombi appeared as typical mixed thrombi, 46.03% fibrin/platelet ratio, 48.12% RBCs, and 5.85% white blood cells. In situ thrombi had a higher fibrin/platelet ratio (68.0%), fewer RBCs (17.2%), and 14.8% white blood cells.

Conclusion

The histopathology of large vessel occlusion stroke embolized thrombi by CaW is similar to that of other stroke etiologies. However, the clot composition of embolized thrombi significantly differs from that of in situ thrombi. CaW’s in situ thrombi showed predominantly fibrin, and embolized thrombi had equivalent contents of red blood cells and fibrin/platelets. Histopathological differences between in situ and embolized thrombi suggest new research directions for the etiology of embolization. Further studies are required to confirm these results.

Monocyte-to-Lymphocyte Ratio in Clot Analysis as a Marker of Cardioembolic Stroke Etiology

The aim of the study was to find markers of high-risk cardioembolic etiology (HRCE) in patients with cryptogenic strokes (CS) through the analysis of intracranial clot by flow cytometry (FC). A prospective single-center study was designed including patients with large vessel occlusion strokes. The percentage of granulocytes, monocytes, lymphocytes, and monocyte-to-lymphocyte ratio (MLr) were analyzed in clots extracted after endovascular treatment (EVT) and in peripheral blood. Large arterial atherosclerosis (LAA) strokes and high-risk cardioembolic (HRCE) strokes were matched by demographics and acute reperfusion treatment data to obtain FC predictors for HRCE. Multilevel decision tree with boosting random forest classifiers was performed with each feature importance for HRCE diagnosis among CS. We tested the validity of the best FC predictor in a cohort of CS that underwent extensive diagnostic workup. Among 211 patients, 178 cases underwent per-protocol workup. The percentage of monocytes (OR 1.06, 95% CI 1.01-1.11) and MLr (OR 1.83, 95% CI 1.12-2.98) independently predicted HRCE diagnosis when LAA clots (n = 28) were matched with HRCE clots (n = 28). Among CS (n = 82), MLr was the feature with the highest weighted importance in the multilevel decision tree as a predictor for HRCE. MLr cutoff point of 1.59 yield sensitivity of 91.23%, specificity of 44%, positive predictive value of 78.79%, and negative predictive value of 68.75 for HRCE diagnosis among CS. MLr ≥ 1.6 in clot analysis predicted HRCE diagnosis (OR, 6.63, 95% CI 1.85-23.71) in a multivariate model adjusted for age. Clot analysis by FC revealed high levels of monocyte-to-lymphocyte ratio as an independent marker of cardioembolic etiology in cryptogenic strokes.

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.

Preclinical testing platforms for mechanical thrombectomy in stroke: a review on phantoms, in-vivo animal, and cadaveric models

Preclinical testing platforms have been instrumental in the research and development of thrombectomy devices. However, there is no single model which fully captures the complexity of cerebrovascular anatomy, physiology, and the dynamic artery-clot-device interaction. This article provides a critical review of phantoms, in-vivo animal, and human cadaveric models used for thrombectomy testing and provides insights into the strengths and limitations of each platform. Articles published in the past 10 years that reported thrombectomy testing platforms were identified. Characteristics of each test platform, such as intracranial anatomy, artery tortuosity, vessel friction, flow conditions, device-vessel interaction, and visualization, were captured and benchmarked against human cerebral vessels involved in large-vessel occlusion stroke. Thrombectomy phantoms have been constructed from silicone, direct 3D-printed polymers, and glass. These phantoms represent oversimplified patient-specific cerebrovascular geometry but enable adequate visualization of devices and clots under appropriate flow conditions. They do not realistically mimic the artery-clot interaction. For the animal models, arteries from swine, canines, and rabbits have been reported. These models can reasonably replicate the artery-clot-device interaction and have the unique value of evaluating the safety of thrombectomy devices. However, the vasculature geometries are substantially less complex and flow conditions are different from human cerebral arteries. Cadaveric models are the most accurate vascular representations but with limited access and challenges in reproducibility of testing conditions. Multiple test platforms should be likely used for comprehensive evaluation of thrombectomy devices. Interpretation of the testing results should take into consideration platform-specific limitations.

The role of P2Y12 receptor inhibition in ischemic stroke on microglia, platelets and vascular smooth muscle cells

P2Y12 receptors on platelets have long been the main target of antiplatelet drugs. However, a growing number of studies have revealed that P2Y12 receptor activation on microglia and vascular smooth muscle cells (VSMCs) also aggravates ischemic stroke injury. The proliferation and migration of VSMCs in the vascular wall have important influence on the early lesion of atherosclerosis, which may lead to the origin of cerebral ischemic attack of atherosclerosis. Blockage of cellular P2Y12 receptors could inhibit microglial activation, block formation of platelet-leukocyte aggregates, reduce proinflammatory cytokine levels and suppress migration and proliferation of VSMCs, implying that apart from anti-thrombotic effect, P2Y12 inhibitors have additional neuroprotective, anti-inflammatory and anti-atherosclerotic therapeutic benefits against ischemic stroke. In this review, we will summarize recent advances in studies on P2Y12 receptors and emphatically introduce their significance in microglia, platelets and VSMCs after ischemic stroke, discussing how to exert the beneficial effects of P2Y12 inhibition.

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.

Analysis of microRNA signatures in ischemic stroke thrombus

BACKGROUND

We investigated the microRNA expression pattern from thrombus retrieved by mechanical thrombectomy in acute stroke patients to understand the stroke mechanism.

METHODS

This study included acute ischemic stroke patients who had undergone intra-arterial thrombectomy at Chung-Ang University Hospital in Seoul, Korea between February 2016 and March 2019. The thrombus was retrieved and stored at -70℃ after obtaining informed consent. MicroRNA microarray analysis was performed for the patients with identified stroke mechanisms including (1) large artery atherosclerosis, (2) cardioembolism with atrial fibrillation, and (3) cardioembolism with valvular heart disease. The microRNAs derived from microarray analysis were validated by quantitative real-time polymerase chain reaction (qRT-PCR) from different patient populations. The correlation analysis was performed between microRNA levels and laboratory data to understand the functional relevance of the altered microRNA.

RESULTS

In total, 55 thrombi were obtained from 74 patients, and the microRNAs were analyzed in 45 samples. Microarray analysis of 2578 microRNAs revealed that 50 microRNAs were significantly altered among the three groups. Validation using qRT-PCR showed that miR-378f and miR-450b-5p were significantly elevated among the cardioembolic thrombi; both microRNAs were inversely correlated with the ejection fraction from echocardiography. Thrombi from patients with early neurological deterioration exhibited higher levels of miR-93-5p and lower levels of miR-629-5p than those from neurologically stable patients.

CONCLUSIONS

The microRNA expression pattern can provide information regarding the mechanism of stroke by reflecting the underlying pathological status of the organ from which the thrombus was derived.

Microstructural features of subchondral radiolucent lesions in the medial femoral condyle of juvenile Thoroughbreds: A microcomputed tomography and histological analysis

BACKGROUND

The aetiology of equine medial femoral condyle (MFC) subchondral bone radiolucencies (SR) is unknown.

OBJECTIVES

Characterise the microstructural structural features of MFC SR in juvenile Thoroughbreds with microcomputed tomography (μCT) and histology.

STUDY DESIGN

Cross-sectional post-mortem study.

METHODS

Distal femurs were collected at post-mortem. Conventional tomodensitometry was employed to scout for MFCs with and without SR lesions (SR+ and SR-, respectively). Group 1 were CT MFC SR+ and Group 2 age-matched SR- controls. Both underwent μCT and histological analysis. Group 3 CT MFC SR- foals, <6 months, were selected to search for chondronecrosis. Histological sections, processed from the lesion (Group 1) and a corresponding site in Groups 2 and 3, were assessed for chondronecrosis, fibrin, fibroplasia and osteochondral separation. Group 3 sections were surveyed for chondronecrosis alone.

RESULTS

A total of 178 femurs from 89 Thoroughbreds were harvested. Of these horses 19.1% (95% CI: 10.9%-27.3%) were CT MFC SR+ (17/23; 7.46 ± 4.36 months) and met the inclusion criteria for Group 1. Group 2 included 30 CT MFC SR- specimens (5.00 ± 2.73 months) and Group 3 had 44 CT MFC SR- s (2.68 ± 1.74 months). SR were located axially in foals <7 months of age, and centrally thereafter. All SRs had areas of thickened cartilage on histology and separation at the osteochondral junction containing fibrin (acute event) and fibroplasia (chronicity) in 73.9% (17/23; 95% CI: 56%-91.9%). In Group 1 specimens, chondronecrosis was present in 82.6% (19/23; 95% CI: 67.1%-98.1%) but four MFC SR+ had no evidence of chondronecrosis. Chondronecrosis was not detected in the Group 3 foal MFCs.

MAIN LIMITATIONS

No longitudinal follow-up.

CONCLUSIONS

The absence of chondronecrosis, pathognomic of osteochondrosis, in four MFC SR+s and in all of the CT MFC SR- foals suggests that osteochondrosis is not the cause, or the only cause, of these lesions and favours trauma as an alternate aetiological hypothesis.

Recovery of Hypoxic Regions in a Rat Model of Microembolism

OBJECTIVES

Endovascular treatment (EVT) has become the standard of care for acute ischemic stroke. Despite successful recanalization, a limited subset of patients benefits from the new treatment. Human MRI studies have shown that during removal of the thrombus, a shower of microclots is released from the initial thrombus, possibly causing new ischemic lesions. The aim of the current study is to quantify tissue damage following microembolism.

MATERIALS AND METHODS

In a rat model, microembolism was generated by injection of a mixture of polystyrene fluorescent microspheres (15, 25 and 50 µm in diameter). The animals were killed at three time-points: day 1, 3 or 7. AMIRA and IMARIS software was used for 3D reconstruction of brain structure and damage, respectively.

CONCLUSIONS

Microembolism induces ischemia, hypoxia and infarction. Infarcted areas persist, but hypoxic regions recover over time suggesting that repair processes in the brain rescue the regions at risk.

Supracardiac atherosclerosis in embolic stroke of undetermined source: the underestimated source

The term 'embolic stroke of undetermined source' (ESUS) is used to describe patients with a non-lacunar ischaemic stroke without any identified embolic source from the heart or the arteries supplying the ischaemic territory, or any other apparent cause. When the ESUS concept was introduced, covert atrial fibrillation was conceived to be the main underlying cause in the majority of ESUS patients. Another important embolic source in ESUS is the atherosclerotic plaque in the carotid, vertebrobasilar, and intracranial arteries, or the aortic arch-collectively described as supracardiac atherosclerosis. There is emerging evidence showing that the role of supracardiac atherosclerosis is larger than it was initially perceived. Advanced imaging methods are available to identify plaques which high embolic risk. The role of novel antithrombotic strategies in these patients needs to be assessed in randomized controlled trials. This review presents the evidence which points towards a major aetiological association between atherosclerotic plaques and ESUS, summarizes the imaging features which may aid to identify plaques more likely to be associated with ESUS, discusses strategies to reduce the associated stroke risk, and highlights the rationale for future research in this field.

First approach to distinguish between cardiac and arteriosclerotic emboli of individual stroke patients applying the histological THROMBEX-classification rule

Endovascular treatment of strokes caused by large vessel occlusion enables the histopathological investigation of the retrieved embolus, possibly providing a novel opportunity to contribute to the diagnostic workup of etiology and to define secondary prevention measures in strokes with uncertain genesis. We aimed to develop a classification rule based on pathophysiological considerations and adjustment to reference thrombi for distinction between cardiac and arteriosclerotic emboli and to validate this classification rule on a patient cohort. From 125 patients with stroke due to large vessel occlusion and thrombectomy, 82 patients with known etiology (55 cardioembolic and 27 arterioembolic strokes) were included. The corresponding emboli were histologically evaluated by two raters blinded to the etiology of stroke by means of a novel classification rule. Presumed etiology and classification results were compared. Agreement concerning cardiac emboli was 72.2% (95% CI: 58.4–83.5) for rater I and 78.2% (95% CI: 65.0–88.2) for rater II. Agreement concerning arteriosclerotic emboli was 70.4% (95% CI: 49.8–86.3) for rater I and 74.1% (95% CI: 53.7–88.9) for rater II. Overall agreement reached 71.6% (95% CI: 60.5–81.1) for rater I and 76.8% (95% CI: 66.2–85.4) for rater II. Within the limits of generally restricted accuracy of histological evaluations, the classification rule differentiates between cardiac and arteriosclerotic emboli of acute ischemic stroke patients. Further improvement is needed to provide valuable complementary data for stroke etiology workup.

Association between clot composition and stroke origin in mechanical thrombectomy patients: analysis of the Stroke Thromboembolism Registry of Imaging and Pathology

BACKGROUND

We retrospectively evaluated the composition of retrieved clots from ischemic stroke patients to study the association between histological composition and stroke etiology METHODS: Consecutive patients enrolled in the Stroke Thromboembolism Registry of Imaging and Pathology (STRIP) were included in this study. All patients underwent mechanical thrombectomy and retrieved clots were sent to a central core lab for processing. Histological analysis was performed using martius scarlet blue (MSB) staining, and quantification for red blood cells (RBCs), white blood cells (WBCs), fibrin and platelets was performed using Orbit Image Software. A Wilcoxon test was used for continuous variables and χ² test for categorical variables.

RESULTS

1350 patients were included in this study. The overall rate of Thrombolysis In Cerebral Infarction (TICI) 2c/3 was 68%. 501 patients received tissue plasminogen activator (tPA) (37%). 267 patients (20%) had a large artery atherosclerosis (LAA) source, 662 (49%) a cardioembolic (CE) source, 301 (22%) were cryptogenic, and the remainder had other identifiable sources including hypercoagulable state or dissection. LAA thrombi had a higher mean RBC density (46±23% vs 42±22%, p=0.01) and a lower platelet density (24±18% vs 27±18%, p=0.03) than CE thrombi. Clots from dissection patients had the highest mean RBC density (50±24%) while clots from patients with a hypercoagulable state had the lowest mean RBC density (26±21%).

CONCLUSIONS

Our study found statistically significant but clinically insignificant differences between clots of CE and LAA etiologies. Future studies should emphasize molecular, proteomic and immunohistochemical characteristics to determine links between clot composition and etiology.

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.

Clot composition in retrieved thrombi after mechanical thrombectomy in strokes due to carotid web

BACKGROUND

The association of carotid webs (CaW) and ischemic stroke is being increasingly recognized. Data on the histologic clot architecture in strokes caused by CaW has not been previously described. Understanding thrombi histopathology may provide insight into the pathophysiology of CaW-related strokes.

METHODS

This case series presents three patients with acute ischemic stroke thought to be caused by ipsilateral CaW. Thromboemboli were retrieved from the middle cerebral artery (MCA) by mechanical thrombectomy and histologic analysis was performed.

RESULTS

Three patients aged between 41 and 55 years with few to no vascular risk factors presented with symptoms concerning for an acute MCA territory infarction (National Institutes of Health Stroke Scale (NIHSS) range 10-17). Non-contrast computed tomography (CT) Alberta Stroke Program Early CT Score (ASPECTS) range was 7-8 and all patients had hyperdense vessel sign. Initial CT angiogram was concerning for CaW with no superimposed thrombus, later confirmed with conventional angiography. All patients underwent thrombectomy with full reperfusion. Comprehensive stroke workup failed to reveal other etiologies besides ipsilateral CaW. The histopathologic appearance was of typical fresh mixed thrombi. Qualitative thrombus composition analysis of clot from Case #1 yielded 42.5% fibrin, 50.0% red blood cells (RBC), and 7.5% white blood cells (WBC); Case #2 yielded 46.9% fibrin, 43.4% RBC, and 9.7% WBC; and Case #3 yielded 61.5% fibrin, 31.8% RBC, and 6.7% WBC.

CONCLUSIONS

The clot composition of large vessel occlusion strokes from CaW is comparable to the histopathology of previously reported clots from other stroke etiologies. Advanced staining techniques may aid in further characterizing the thrombi of this poorly understood condition.

4-Hydroxyl-2-Nonenal Localized Expression Pattern in Retrieved Clots is Associated with Large Artery Atherosclerosis in Stroke Patients

OBJECTIVES

The relationship between stroke etiology and clot pathology remains controversial.

MATERIALS AND METHODS

We performed histological analysis of clots retrieved from 52 acute ischemic stroke patients using hematoxylin and eosin staining and immunohistochemistry (CD42b and oxidative/hypoxic stress markers). The correlations between clot composition and the stroke etiological group (i.e., cardioembolic, cryptogenic, or large artery atherosclerosis) were assessed.

RESULTS

Of the 52 clots analyzed, there were no significant differences in histopathologic composition (e.g., white blood cells, red blood cells, fibrin, and platelets) between the 3 etiological groups (P = .92). By contrast, all large artery atherosclerosis clots showed a localized pattern with the oxidative stress marker 4-hydroxyl-2-nonenal (P < .01). From all 52 clots, 4-hydroxyl-2-nonenal expression patterns were localized in 28.8% of clots, diffuse in 57.7% of clots, and no signal in 13.5% of clots.

CONCLUSIONS

A localized pattern of 4-hydroxyl-2-nonenal staining may be a novel and effective marker for large artery atherosclerosis (sensitivity 100%, specificity 82%).

Association Between Thrombus Perviousness Assessed on Computed Tomography and Stroke Cause

Background and Purpose:

A recent study proposed that thrombus perviousness (TP)—the degree to which contrast agents penetrate the thrombus in an occluded vessel measured on noncontrast computed tomography (NCCT) and CT angiography—may be associated with cardioembolic stroke cause with high specificity. Our aim was to investigate which clinical and laboratory parameters affect measures of TP and to validate its diagnostic accuracy in an independent cohort of patients with acute ischemic stroke.

Methods:

Seventy-five patients from a prospectively maintained database with proximal occlusions of the middle cerebral artery (M1) were retrospectively analyzed. Thrombi were segmented on coregistered noncontrast computed tomography and CT angiography to determine the thrombus attenuation increase and void fraction (attenuation increase relative to contralateral side).

Results:

TP measures were significantly higher in patients with cardioembolic stroke compared to patients with stroke attributed to large artery atherosclerosis (median thrombus attenuation increase [interquartile range], 2.79 [–3.54 to 8.85] versus –5.11 [–11.23 to –1.47]; P =0.001). In linear regression analysis for TP including age, time to scan, prior medication with antiplatelets or anticoagulants, and selected laboratory parameters, only stroke cause was significantly associated with TP. In multivariable binary logistic regression analysis for dichotomized stroke cause (ie, cardioembolic versus noncardioembolic stroke), only thrombus attenuation increase was independently associated with cardioembolic stroke (odds ratio of 1.12 [95% CI, 1.04–1.22]; P =0.004). Receiver operating characteristic analysis indicated that TP can identify cardioembolic stroke with an area under the curve of 0.75 (95% CI, 0.63–0.87) for thrombus attenuation increase. With a cutoff value of 6.23 Hounsfield units, cardioembolic strokes were identified with 100% specificity. Results for void fraction were similar.

Conclusions:

The assessment of TP on baseline noncontrast computed tomography/CT angiography in patients with M1 occlusion may aid in determining cardioembolic stroke cause and guide secondary prevention. Selected clinical and laboratory parameters other than stroke cause did not affect TP measures.

Machine Learning Analysis of the Cerebrovascular Thrombi Proteome in Human Ischemic Stroke: An Exploratory Study

Objective: Mechanical retrieval of thrombotic material from acute ischemic stroke patients provides a unique entry point for translational research investigations. Here, we resolved the proteomes of cardioembolic and atherothrombotic cerebrovascular human thrombi and applied an artificial intelligence routine to examine protein signatures between the two selected groups.

Methods: We specifically used n = 32 cardioembolic and n = 28 atherothrombotic diagnosed thrombi from patients suffering from acute stroke and treated by mechanical thrombectomy. Thrombi proteins were successfully separated by gel-electrophoresis. For each thrombi, peptide samples were analyzed by nano-flow liquid chromatography coupled to tandem mass spectrometry (nano-LC-MS/MS) to obtain specific proteomes. Relative protein quantification was performed using a label-free LFQ algorithm and all dataset were analyzed using a support-vector-machine (SVM) learning method. Data are available via ProteomeXchange with identifier PXD020398. Clinical data were also analyzed using SVM, alone or in combination with the proteomes.

Results: A total of 2,455 proteins were identified by nano-LC-MS/MS in the samples analyzed, with 438 proteins constantly detected in all samples. SVM analysis of LFQ proteomic data delivered combinations of three proteins achieving a maximum of 88.3% for correct classification of the cardioembolic and atherothrombotic samples in our cohort. The coagulation factor XIII appeared in all of the SVM protein trios, associating with cardioembolic thrombi. A combined SVM analysis of the LFQ proteome and clinical data did not deliver a better discriminatory score as compared to the proteome only.

Conclusion: Our results advance the portrayal of the human cerebrovascular thrombi proteome. The exploratory SVM analysis outlined sets of proteins for a proof-of-principle characterization of our cohort cardioembolic and atherothrombotic samples. The integrated analysis proposed herein could be further developed and retested on a larger patients population to better understand stroke origin and the associated cerebrovascular pathophysiology.

Fibrin and Platelet-Rich Composition in Retrieved Thrombi Hallmarks Stroke With Active Cancer

BACKGROUND AND PURPOSE

We aim to investigate whether histopathologic examination of thrombi retrieved from acute ischemic stroke patients undergoing endovascular treatment could distinguish cancer-related stroke from other etiologies.

METHODS

Thrombi from patients undergoing endovascular treatment were analyzed. The etiology of stroke was divided into cardioembolism, large artery atherosclerosis, and active cancer groups. All selected thrombi were subjected to hematoxylin and eosin staining. The percentages of fibrin/platelets, red blood cells, and white blood cells within a thrombus were quantified.

RESULTS

One-hundred fifty-two patients (active cancer, 19; cardioembolism, 107; large artery atherosclerosis, 26) were included. Thrombi from the active cancer group exhibited a higher fibrin/platelet composition than did those from the cardioembolism and large artery atherosclerosis groups (median, 85.7% versus 43.9% and 42.5%; P<0.001). Fibrin/platelet composition was the only independent factor (odds ratio, 1.05 [95% CI, 1.02-1.08]) in differentiating cancer-related stroke from stroke caused by cardioembolism and large artery atherosclerosis. A fibrin/platelet proportion of ≥65% accurately predicted cancer-related stroke (area under the curve, 0.84; P<0.001).

CONCLUSIONS

In thrombi retrieved from patients undergoing endovascular treatment, a high fibrin/platelet composition was a probable indicator of cancer-related stroke.

Carotid Atherosclerosis and Patent Foramen Ovale in Embolic Stroke of Undetermined Source

BACKGROUND

Carotid atherosclerosis and likely pathogenic patent foramen ovale (PFO) are two potential embolic sources in patients with embolic stroke of undetermined source (ESUS). The relationship between these two mechanisms among ESUS patients remains unclear.

AIM

To investigate the relation between carotid atherosclerosis and likely pathogenic PFO in patients with ESUS. We hypothesized that ipsilateral carotid atherosclerotic plaques are less prevalent in ESUS with likely pathogenic PFO compared to patients with likely incidental PFO or without PFO.

METHODS

The presence of PFO was assessed with transthoracic echocardiography with microbubble test and, when deemed necessary, through trans-oesophageal echocardiography. The presence of PFO was considered as likely incidental if the RoPE (Risk of Paradoxical Embolism) score was 0-6 and likely pathogenic if 7-10.

RESULTS

Among 374 ESUS patients (median age: 61years, 40.4% women), there were 63 (49.6%) with likely incidental PFO, 64 (50.4%) with likely pathogenic PFO and 165 (44.1%) with ipsilateral carotid atherosclerosis. The prevalence of ipsilateral carotid atherosclerosis was lower in patients with likely pathogenic PFO (7.8%) compared to patients with likely incidental PFO (46.0%) or patients without PFO (53.0%) (p<0.001). After adjustment for multiple confounders, the prevalence of ipsilateral carotid atherosclerosis remained lower in patients with likely pathogenic PFO compared to patients with likely incidental PFO or without PFO (adjusted OR=0.32, 95%CI:0.104-0.994, p=0.049).

CONCLUSIONS

The presence of carotid atherosclerosis is inversely related to the presence of likely pathogenic PFO in patients with ESUS.

Data-driven machine-learning analysis of potential embolic sources in embolic stroke of undetermined source

BACKGROUND AND PURPOSE

Hierarchical clustering, a common 'unsupervised' machine-learning algorithm, is advantageous for exploring potential underlying aetiology in particularly heterogeneous diseases. We investigated potential embolic sources in embolic stroke of undetermined source (ESUS) using a data-driven machine-learning method, and explored variation in stroke recurrence between clusters.

METHODS

We used a hierarchical k-means clustering algorithm on patients' baseline data, which assigned each individual into a unique clustering group, using a minimum-variance method to calculate the similarity between ESUS patients based on all baseline features. Potential embolic sources were categorised into atrial cardiopathy, atrial fibrillation, arterial disease, left ventricular disease, cardiac valvulopathy, patent foramen ovale (PFO) and cancer.

RESULTS

Among 800 consecutive ESUS patients (43.3% women, median age 67 years), the optimal number of clusters was four. Left ventricular disease was most prevalent in cluster 1 (present in all patients) and perfectly associated with cluster 1. PFO was most prevalent in cluster 2 (38.9% of patients) and associated significantly with increased likelihood of cluster 2 [adjusted odds ratio: 2.69, 95% confidence interval (CI): 1.64-4.41]. Arterial disease was most prevalent in cluster 3 (57.7%) and associated with increased likelihood of cluster 3 (adjusted odds ratio: 2.21, 95% CI: 1.43-3.13). Atrial cardiopathy was most prevalent in cluster 4 (100%) and perfectly associated with cluster 4. Cluster 3 was the largest cluster involving 53.7% of patients. Atrial fibrillation was not significantly associated with any cluster.

CONCLUSIONS

This data-driven machine-learning analysis identified four clusters of ESUS that were strongly associated with arterial disease, atrial cardiopathy, PFO and left ventricular disease, respectively. More than half of the patients were assigned to the cluster associated with arterial disease.

Dielectric profile of blood clots to inform ischemic stroke treatments

Platelet and fibrin-rich blood clots can respond differently to red blood cell rich clots during ischemic stroke treatment, which includes thrombolysis and mechanical thrombectomy. Currently, there is no accurate way to identify the type of clot in advance of treatment. If the type of blood clot can be identified, the optimum clot removal process can be chosen and patient outcomes can be improved. In this paper we fabricate physiologically relevant blood clot analogues from human blood, that cover a range of red blood cell, fibrin, and platelet concentrations. We characterize the dielectric profile of these formed clots using an open-ended coaxial probe method across a wide frequency range. After the dielectric measurements are completed, histology on each blood clot is performed to determine the concentration of red blood cells present. In total, 32 unique blood clots were measured.With this completed analysis, we investigate the correlation between the dielectric properties across this frequency range and the red blood cell count of the formed blood clots. Furthermore, we develop a model to predict whether an unknown blood clot can be categorized as red blood cell rich or platelet and fibrin-rich based solely on the measured dielectric properties.Clinical Relevance-Using the dielectric profile of a clot we can predict whether a clot is platelet and fibrin-rich or red blood cell rich allowing clinicians to more easily determine treatment methods during an intervention for ischemic stroke.