Flow Effects on Coagulation and Thrombosis

Effect of mechanical forces on cellular response to radiation

While the cellular interactions and biochemical signaling has been investigated for long and showed to play a major role in the cell's fate, it is now also evident that mechanical forces continuously applied to the cells in their microenvironment are as important for tissue homeostasis. Mechanical cues are emerging as key regulators of cellular drug response and we aimed to demonstrate in this review that such effects should also be considered vital for the cellular response to radiation. In order to explore the mechanobiology of the radiation response, we reviewed the main mechanoreceptors and transducers, including integrin-mediated adhesion, YAP/TAZ pathways, Wnt/β-catenin signaling, ion channels and G protein-coupled receptors and showed their implication in the modulation of cellular radiosensitivity. We then discussed the current studies that investigated a direct effect of mechanical stress, including extracellular matrix stiffness, shear stress and mechanical strain, on radiation response of cancer and normal cells and showed through preliminary results that such stress effectively can alter cell response after irradiation. However, we also highlighted the limitations of these studies and emphasized some of the contradictory data, demonstrating that the effect of mechanical cues could involve complex interactions and potential crosstalk with numerous cellular processes also affected by irradiation. Overall, mechanical forces alter radiation response and although additional studies are required to deeply understand the underlying mechanisms, these effects should not be neglected in radiation research as they could reveal new fundamental knowledge for predicting radiosensitivity or understanding resistance to radiotherapy.

Mechano-Redox Control of Integrins in Thromboinflammation

Significance: How mechanical forces and biochemical cues are coupled remains a miracle for many biological processes. Integrins, well-known adhesion receptors, sense changes in mechanical forces and reduction-oxidation reactions (redox) in their environment to mediate their adhesive function. The coupling of mechanical and redox function is a new area of investigation. Disturbance of normal mechanical forces and the redox balance occurs in thromboinflammatory conditions; atherosclerotic plaques create changes to the mechanical forces in the circulation. Diabetes induces redox changes in the circulation by the production of reactive oxygen species and vascular inflammation. Recent Advances: Integrins sense changes in the blood flow shear stress at the level of focal adhesions and respond to flow and traction forces by increased signaling. Talin, the integrin-actin linker, is a traction force sensor and adaptor. Oxidation and reduction of integrin disulfide bonds regulate their adhesion. A conserved disulfide bond in integrin αlpha IIb beta 3 (αIIbβ3) is directly reduced by the thiol oxidoreductase endoplasmic reticulum protein 5 (ERp5) under shear stress. Critical Issues: The coordination of mechano-redox events between the extracellular and intracellular compartments is an active area of investigation. Another fundamental issue is to determine the spatiotemporal arrangement of key regulators of integrins' mechanical and redox interactions. How thromboinflammatory conditions lead to mechanoredox uncoupling is relatively unexplored. Future Directions: Integrated approaches, involving disulfide bond biochemistry, microfluidic assays, and dynamic force spectroscopy, will aid in showing that cell adhesion constitutes a crossroad of mechano- and redox biology, within the same molecule, the integrin. Antioxid. Redox Signal. 37, 1072-1093.

Clinical Application of Thromboelastography in Acute Ischemic Stroke

Acute ischemic stroke (AIS), characterized by high morbidity and mortality, has imposed a considerable burden on society. Despite rapid development in the treatment of AIS, there is still a high risk of recurrence. Furthermore, there is a time delay in waiting for the results of conventional coagulation tests in candidate patients for intravenous thrombolysis therapy. Heterogeneous responses to antiplatelet, intravascular thrombolysis, and endovascular therapies also worsen the situation. Thromboelastography (TEG), as a global and portable detection method for hemostasis, facilitates clinicians in disease monitoring, treatment evaluation, and prognosis prediction in AIS. In this narrative review, we provided a comprehensive summary of the clinical application of TEG in ischemic stroke and gave insights to further studies.

Hemocompatibility of micropatterned biomaterial surfaces is dependent on topographical feature size

Small-diameter synthetic vascular grafts that have improved hemocompatibility and patency remain an unmet clinical need due to thrombosis. A surface modification that has potential to attenuate these failure mechanisms while promoting an endothelial layer is the micropatterning of luminal surfaces. Anisotropic features have been shown to downregulate smooth muscle cell proliferation, direct endothelial migration, and attenuate platelet adhesion and activation. However, the effect of micropatterning feature size and orientation relative to whole blood flow has yet to be investigated within a systematic study. In this work, hemocompatibility of micropattern grating sizes of 2, 5, and 10 µm were investigated. The thrombogenicity of the micropattern surface modifications were characterized by quantifying FXIIa activity, fibrin formation, and static platelet adhesion in vitro. Additionally, dynamic platelet attachment and end-point fibrin formation were quantified using an established, flowing whole blood ex vivo non-human primate shunt model without antiplatelet or anticoagulant therapies. We observed a higher trend in platelet attachment and significantly increased fibrin formation for larger features. We then investigated the orientation of 2 µm gratings relative to whole blood flow and found no significant differences between the various orientations for platelet attachment, rate of linear platelet attachment, or end-point fibrin formation. MicroCT analysis of micropatterned grafts was utilized to quantify luminal patency. This work is a significant step in the development of novel synthetic biomaterials with improved understanding of hemocompatibility for use in cardiovascular applications.

Endothelial microparticles: A mechanosensitive regulator of vascular homeostasis and injury under shear stress

Hemodynamic shear stress (SS), a frictional force generated by blood flow, regulates vascular homeostasis. High and steady SS maintains physiological function of endothelial cells while low and disturbed SS promotes disturbance of vascular homeostasis and the development of atherosclerosis. Endothelial microparticle (EMP), a vesicular structure shed from endothelial cells, has emerged as a surrogate biomarker of endothelial injury and dysfunction. EMP release is triggered by disturbed SS in addition to multiple inflammatory cytokines. This review systematically summarizes the impact of SS on EMPs and the role of EMPs under SS in modulating vascular homeostasis and injury, including endothelial survival, vasodilation, inflammatory response, vascular permeability, and coagulation system.

Peri-device leakage not CHA2DS2-VASc is associated with post-left atrial appendage closure cardiovascular event

OBJECTIVE

In patients with non-valvular atrial fibrillation (NVAF), the left atrial appendage occluder (LAAO) is an alternative treatment for stroke prevention. However, thromboembolic event still occur, and the predictors are unknown.

METHODS

The first Asian long-term follow-up study consisted of 308 patients with mean age 71.9±9.5 years, mean CHA₂DS₂-VASc 4.1 ± 1.8 since 2013. Primary outcome was defined as any type of ischemic stroke/transient ischemic attack (TIA), systemic embolization and cardiovascular death.

RESULTS

There was no procedural-related TIA or stroke. After a mean follow-up of 38±16 months, the ischemic stroke/TIA rate was 1.9 and cardiovascular death rate 0.3 per 100 patient-year. The rate of peri-device leak (PDL) was 11.9% and device-related thrombus (DRT) 2.6%. In the multivariable analyses, PDL was the only independent predictor of stroke/TIA (hazard ratio 5.5, p=0.008). CHA₂DS₂-VASc score, prior history of stroke, DRT and post-procedural anti-thrombotic regimen/duration were not associated with outcomes. Implantation of Watchman was associated with PDL (odds ratio 4.35, p=0.001).

CONCLUSIONS

PDL is the only independent predictor of post-LAAO stroke. The risk of stroke for patients with NVAF may be controllable after LAA is occluded, because PDL is preventable and treatable.

Location matters: Offset in tissue-engineered vascular graft implantation location affects wall shear stress in porcine models

Objective

Although surgical simulation using computational fluid dynamics has advanced, little is known about the accuracy of cardiac surgical procedures after patient-specific design. We evaluated the effects of discrepancies in location for patient-specific simulation and actual implantation on hemodynamic performance of patient-specific tissue-engineered vascular grafts (TEVGs) in porcine models.

Methods

Magnetic resonance angiography and 4-dimensional (4D) flow data were acquired in porcine models (n = 11) to create individualized TEVGs. Graft shapes were optimized and manufactured by electrospinning bioresorbable material onto a metal mandrel. TEVGs were implanted 1 or 3 months postimaging, and postoperative magnetic resonance angiography and 4D flow data were obtained and segmented. Displacement between intended and observed TEVG position was determined through center of mass analysis. Hemodynamic data were obtained from 4D flow analysis. Displacement and hemodynamic data were compared using linear regression.

Results

Patient-specific TEVGs were displaced between 1 and 8 mm during implantation compared with their surgically simulated, intended locations. Greater offset between intended and observed position correlated with greater wall shear stress (WSS) in postoperative vasculature (P < .01). Grafts that were implanted closer to their intended locations showed decreased WSS.

Conclusions

Patient-specific TEVGs are designed for precise locations to help optimize hemodynamic performance. However, if TEVGs were implanted far from their intended location, worse WSS was observed. This underscores the importance of not only patient-specific design but also precision-guided implantation to optimize hemodynamics in cardiac surgery and increase reproducibility of surgical simulation.

Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall

The mechanism underlying the association between elevated red cell distribution width (RDW) and poor prognosis in variety of diseases is unknown although many researchers consider RDW a marker of inflammation. We hypothesized that RDW directly affects intravascular hemodynamics, interactions between circulating cells and vessel wall, inducing local changes predisposing to atherothrombosis. We applied different human and animal models to verify our hypothesis. Carotid plaques harvested from patients with high RDW had increased expression of genes and proteins associated with accelerated atherosclerosis as compared to subjects with low RDW. In microfluidic channels samples of blood from high RDW subjects showed flow pattern facilitating direct interaction with vessel wall. Flow pattern was also dependent on RDW value in mouse carotid arteries analyzed with Magnetic Resonance Imaging. In different mouse models of elevated RDW accelerated development of atherosclerotic lesions in aortas was observed. Therefore, comprehensive biological, fluid physics and optics studies showed that variation of red blood cells size measured by RDW results in increased interactions between vascular wall and circulating morphotic elements which contribute to vascular pathology.

Externalization of Mitochondrial PDCE2 on Irradiated Endothelium as a Target for Radiation-Guided Drug Delivery and Precision Thrombosis of Pathological Vasculature

Endothelial cells are highly sensitive to ionizing radiation, and exposure leads to multiple adaptive changes. Remarkably, part of this response is the translocation of normally intracellular proteins to the cell surface. It is unclear whether this ectopic expression has a protective or deleterious function, but, regardless, these surface-exposed proteins may provide unique discriminatory targets for radiation-guided drug delivery to vascular malformations or tumor vasculature. We investigated the ability of an antibody–thrombin conjugate targeting mitochondrial PDCE2 (E2 subunit of pyruvate dehydrogenase) to induce precision thrombosis on irradiated endothelial cells in a parallel-plate flow system. Click-chemistry was used to create antibody–thrombin conjugates targeting PDCE2 as the vascular targeting agent (VTA). VTAs were injected into the parallel-plate flow system with whole human blood circulating over irradiated cells. The efficacy and specificity of fibrin-thrombus formation was assessed relative to non-irradiated controls. The PDCE2-targeting VTA dose-dependently increased thrombus formation: minimal thrombosis was induced in response to 5 Gy radiation; doses of 15 and 25 Gy induced significant thrombosis with equivalent efficacy. Negligible VTA binding or thrombosis was demonstrated in the absence of radiation or with non-targeted thrombin. PDCE2 represents a unique discriminatory target for radiation-guided drug delivery and precision thrombosis in pathological vasculature.

Reduced risk of arterial thromboembolism in cats with pleural effusion due to congestive heart failure

OBJECTIVES

The aim of the study was to determine whether cardiogenic pleural effusion in cats is associated with a lower risk of arterial thromboembolism (ATE) compared with cats with cardiac disease without evidence of pleural effusion.

METHODS

A cross-sectional study was conducted on owned cats with natural occurring cardiac diseases. Cats included were classified in three groups: those with cardiac disease but no evidence of congestive heart failure (CHF); those with evidence of cardiogenic pulmonary oedema; and those with evidence of cardiogenic pleural effusion. Prevalence of ATE was calculated and the variables analysed for an association with this outcome were the presence and type of CHF, sex and neuter status, age, breed, type of cardiac diseases and left atrial (LA) dimension. A multivariable logistic regression model was used to fit the association between ATE and these variables.

RESULTS

A total of 366 cats with cardiac disease met the inclusion criteria: 179 were included in the group with cardiac disease but no evidence of CHF, 66 in the group with evidence of cardiogenic pulmonary oedema and 121 in the group with evidence of cardiogenic pleural effusion. Prevalence of ATE (58/366 [15.8%]) was significantly different among groups (with no evidence of CHF, 28/179 [15.6%]; with evidence of cardiogenic pulmonary oedema, 22/66 [33.3%]; with evidence of cardiogenic pleural effusion, 8/121 [6.6%]; P <0.001). Cats with ATE had a significantly higher LA to aortic root ratio (2.30 ± 0.46) than those without ATE (2.04 ± 0.46; P <0.001). Multivariable logistic regression analysis indicated that the group with evidence of cardiogenic pleural effusion was associated with a lower risk of developing ATE compared with groups with cardiac disease but no evidence of CHF and with evidence of cardiogenic pulmonary oedema (P = 0.005 and P <0.001, respectively).

CONCLUSIONS AND RELEVANCE

Presence of cardiogenic pleural effusion is associated with a lower risk of developing ATE, while LA enlargement is a risk factor for ATE.

Predictors of ischemic events in patients with unilateral extracranial vertebral artery dissection: A single-center exploratory study

Objective

Extracranial vertebral artery dissection (EVAD) is one of the main causes of stroke in young and middle-aged patients. However, the diagnosis is challenging. This study aimed to identify the characteristics of EVAD on color duplex ultrasonography (CDU) and high-resolution magnetic resonance imaging (hrMRI), hoping to improve the accuracy and determine the relative contribution of vessel findings and clinical factors to acute ischemic events.

Methods

Patients with unilateral EVAD were recruited and divided into ischemia and non-ischemia groups. Clinical features of patients and the lesion location; a variety of signs which indicate dissection, including the presence of an intimal flap, double lumen, intramural hematoma, dissecting aneurysm, intraluminal thrombus, and irregular lumen; and other quantitative parameters of each dissected segment on CDU and hrMRI were reviewed, respectively. Multiple logistic regression was performed to explore the association between clinical, imaging characteristics, and ischemic events in patients with unilateral EVAD.

Results

Ninety-six patients with unilateral EVAD who met the inclusion criteria were enrolled during a six-year period. Overall, 41 cases (42.7%) were confirmed as ischemic stroke (n = 40) or transient ischemic attack (n = 1) during the 48 h after the onset of symptoms. Men, infections during the last week, and smoking were more common in the ischemia group. Intraluminal thrombus and occlusion on CDU were more prevalent in patients with cerebral ischemia than in those without (36.6 vs. 5.5%; p < 0.001, and 39.0 vs. 9.1%; p = 0.001, respectively). On hrMRI, intraluminal thrombus and occlusion were also more frequent in the ischemia group than in the non-ischemia group (34.1 vs. 5.5%; p < 0.001, and 34.1 vs. 9.1%; p = 0.003, respectively). In addition, lesion length on hrMRI was significantly longer for patients with ischemia (81.5 ± 41.7 vs. 64.7 ± 30.8 mm; p = 0.025). In multivariable logistic regression analysis, male gender, infections during the last week, and the presence of intraluminal thrombus on CDU and hrMRI were independently associated with acute ischemic events.

Conclusion

Male sex, infections during the last week, and the presence of intraluminal thrombus due to dissection are associated with an increased risk of ischemic events in patients with unilateral EVAD.

Effects of different bypass surgeries on LSA revascularization in patients with left subclavian occlusion

INTRO

Left subclavian artery bypass surgery is mainly carried out for patients with severe left subclavian occlusion. This paper aimed to evaluate the hemodynamic effects of different surgical bypass modes on left subclavian artery revascularization.

METHODS

Three-dimensional models of the aorta were reconstructed from CTA images of a patient with left subclavian artery occlusion, a patient with type B aortic dissection with left subclavian artery coverage during thoracic endovascular aortic repair, and a healthy 74 year-old man, resulting in six modes for each person: healthy left subclavian artery mode, left subclavian artery occlusion mode and four bypass modes. Hemodynamic parameters, including flow field, flow distribution, pressure gradient, and wall shear stress, were calculated using computational fluid dynamics.

RESULTS

After left subclavian artery bypass surgery, distal left subclavian artery blood flow resulting from left common carotid artery to distal left subclavian artery bypass was 100% of that in the healthy mode, while the other modes yielded flows at least 91%. Moreover, reversed flow only completely disappeared with left common carotid artery to distal left subclavian artery bypass, whereas reverse flow was observed in the other three modes in early systole.

CONCLUSION

Left common carotid artery to distal left subclavian artery bypass can effectively reduce reverse blood flow in the left vertebral artery, and it is a feasible, effective, and safe option for left subclavian artery revascularization in patients with left subclavian occlusion.

Nuclear Progestin Receptor-mediated Linkage of Blood Coagulation and Ovulation

Ovulation is a dramatic remodeling process that includes rupture of blood capillaries and clotting, but coagulation is not thought to directly regulate this process. Herein, we report remarkable increases of coagulation factors V (f5, ~3145-fold) and tissue factor (f3a, ~120-fold) in zebrafish ovarian follicle cells during ovulation. This increase was mediated through the nuclear progestin receptor (Pgr), which is essential for ovulation in zebrafish, and was totally abolished in ovarian follicular cells from pgr-/- mutants. In addition, promoter activities of f5 and f3a were significantly enhanced by progestin (DHP) via Pgr. Similar regulation of human F5 promoter activity was induced via human PGRB, suggesting a conserved mechanism. Site-directed mutagenesis of the zebrafish f5 promoter further demonstrated a direct regulation of coagulation factors via progestin response elements. Moreover, a stark increase of erythrocytes occurred in capillaries meshed in wild-type preovulatory follicles but was absent in pgr-/- mutants. Interestingly, anticoagulants significantly inhibited ovulation both in vitro and in vivo, respectively. Furthermore, reduced fecundity was observed in f5+/- female zebrafish. Taken together, our study provides plausible evidence for steroid regulation of coagulation factors, and a new hypothesis for blood clotting-triggered ovulation in vertebrates.

The Fatal Circle of NETs and NET-Associated DAMPs Contributing to Organ Dysfunction

The innate immune system is the first line of defense against invading pathogens or sterile injuries. Pattern recognition receptors (PRR) sense molecules released from inflamed or damaged cells, or foreign molecules resulting from invading pathogens. PRRs can in turn induce inflammatory responses, comprising the generation of cytokines or chemokines, which further induce immune cell recruitment. Neutrophils represent an essential factor in the early immune response and fulfill numerous tasks to fight infection or heal injuries. The release of neutrophil extracellular traps (NETs) is part of it and was originally attributed to the capture and elimination of pathogens. In the last decade studies revealed a detrimental role of NETs during several diseases, often correlated with an exaggerated immune response. Overwhelming inflammation in single organs can induce remote organ damage, thereby further perpetuating release of inflammatory molecules. Here, we review recent findings regarding damage-associated molecular patterns (DAMPs) which are able to induce NET formation, as well as NET components known to act as DAMPs, generating a putative fatal circle of inflammation contributing to organ damage and sequentially occurring remote organ injury.

Binding properties of flowing fibrin-targeted microbubbles evaluated with a thrombus-embedded microchannel

Fibrin is found in both arterial and venous thrombi, which provides an important target for thrombus-targeted microbubbles (MBs) used in MB-enhanced ultrasound imaging and sonothrombolysis. A fibrin-targeted peptide, Cys-Arg-Glu-Lys-Ala (CREKA), is used to modify the commercially available SonoVue ultrasound contrast agent using a conjugation method, and the binding capacity and binding strength of the fibrin-targeted CREKA-modified SonoVue MBs are evaluated with a thrombus-embedded microchannel at a typical shear rate range of venous and arterial blood flow. The experimental results indicate that the targeted MBs bind firmly to the thrombus surface when they flow along the microchannel at a wall shear rate of up to 1000 s^-1. This work not only provides an effective method for the fabrication of fibrin-targeted MBs based on commercially available SonoVue MBs but also demonstrates an approach for evaluation of the binding properties of flowing targeted MBs under well-controlled flow conditions.

Magnet-Guided Bionic System with LIFU Responsiveness and Natural Thrombus Tropism for Enhanced Thrombus-Targeting Ability

Background

Arterial thrombosis is a serious threat to human health. Recently, many thrombus-targeted nanoparticles (NPs) have been constructed for detecting thrombi or monitoring thrombolysis, but their thrombus-targeting performance is limited. Considering this drawback, we designed a specific bionic system with enhanced thrombus-targeting ability.

Materials and Methods

In the bionic system, gelatin was chosen as a carrier, and Fe₃O₄ served as a magnetic navigation medium and a magnetic resonance (MR) imaging agent. The CREKA peptide, which targets fibrin, was conjugated to the surface of gelatin to prepare targeted NPs (TNPs), which were then engulfed by macrophages to construct the bionic system. At the targeted site, the bionic system released its interior TNPs under low-intensity focused ultrasound (LIFU) irradiation. Moreover, the targeting performance was further improved by the conjugated CREKA peptide.

Results

In this study, we successfully constructed a bionic system and demonstrated its targeting ability in vitro and in vivo. The results indicated that most TNPs were released from macrophages under LIFU irradiation at 2 W/cm² for 10 min in vitro. Additionally, the enhanced thrombus-targeting ability, based on the natural tropism of macrophages toward inflammatory thrombi, magnetic navigation and the CREKA peptide, was verified ex vivo and in vivo. Moreover, compared with the bionic system group, the group treated with TNPs had significantly decreased liver and spleen signals in MR images and significantly enhanced liver and spleen signals in fluorescence images, indicating that the bionic system is less likely to be cleared by the reticuloendothelial system (RES) than TNPs, which may promote the accumulation of the bionic system at the site of the thrombus.

Conclusion

These results suggest that the magnet-guided bionic system with LIFU responsiveness is an excellent candidate for targeting thrombi and holds promise as an innovative drug delivery system for thrombolytic therapy.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Computational Fluid Dynamics for the Prediction of Endograft Thrombosis in the Superficial Femoral Artery

PURPOSE

Contemporary diagnostic modalities, including contrast-enhanced computed tomography (CTA) and duplex ultrasound, have been insufficiently able to predict endograft thrombosis. This study introduces an implementation of image-based computational fluid dynamics (CFD), by exemplification with 4 patients treated with an endograft for occlusive disease of the superficial femoral artery (SFA). The potential of personalized CFD for predicting endograft thrombosis is investigated.

MATERIALS AND METHODS

Four patients treated with endografts for an occluded SFA were retrospectively included. CFD simulations, based on CTA and duplex ultrasound, were compared for patients with and without endograft thrombosis to investigate potential flow-related causes of endograft thrombosis. Time-averaged wall shear stress (TAWSS) was computed, which highlights areas of prolonged residence times of coagulation factors in the graft.

RESULTS

CFD simulations demonstrated normal TAWSS (>0.4 Pa) in the SFA for cases 1 and 2, but low levels of TAWSS (<0.4 Pa) in cases 3 and 4, respectively. Primary patency was achieved in cases 1 and 2 for over 2 year follow-up. Cases 3 and 4 were complicated by recurrent endograft thrombosis.

CONCLUSION

The presence of a low TAWSS was associated with recurrent endograft thrombosis in subjects with otherwise normal anatomic and ultrasound assessment and a good distal run-off.

Thrombus formation in the noncoronary sinus of Valsalva following primary graft dysfunction

We hereby present a case of thrombus formation in the noncoronary sinus of Valsalva following primary graft dysfunction. The case highlights that stagnant and nonpulsatile flow can form thrombi in the noncoronary sinus since this sinus does not have a natural distal runoff.

COVID-19 and thrombosis: The role of hemodynamics

Severe coronavirus disease 2019 (COVID-19) is characterized by an increased risk of thromboembolic events, a leading cause for adverse outcomes in patients afflicted by the more serious manifestation of the disease. These thromboembolic complications expressed as sepsis-induced coagulopathy, disseminated intravascular coagulation, venous and arterial thromboembolism, pulmonary embolism, microthrombosis, and thrombotic microangiopathy have been observed to affect different organs such as the lungs, heart, kidneys, and brain. Endothelial injury and dysfunction have been identified as the critical pathway towards thrombogenesis, and contributions of other mechanisms such as hypercoagulability, cytokine storm, neutrophils have been studied. However, the contribution of hemodynamic pathways towards thrombosis in severe COVID-19 cases has not been investigated. From the classical theory of Virchow's triad to the contemporary studies on the effect of shear enhanced platelet activation, it is well established that hemodynamics plays a role in the initiation and growth of thrombosis. This article reviews recent studies on COVID-19 related thrombotic events and offers hypotheses on how hemodynamics may be responsible for some of the adverse outcomes observed in severe COVID-19 cases. While thrombogenesis through endothelial injury and the effects of hypercoagulability on thrombosis are briefly addressed, the crux of the discussion is focused on hemodynamic factors such as stasis, turbulent flow, and non-physiological shear stress and their effects on thrombosis. In addition, hemodynamics-dependent venous, arterial, and microvascular thrombosis in COVID-19 cases is discussed. We also propose further investigation of diagnostic and therapeutic options that address the hemodynamics aspects of COVID-19 thrombus formation to assess their potential in patient care.

The addition of Tirofiban infusion to heparin for intraoperative heparin resistance associated with Marfan Syndrome

Marfan syndrome classically presents with aortic root aneurysms. Aortic ectasia causes diverse blood flow alterations, influencing the behavior of coagulation factors and platelet activity. Heparin resistance has also been reported associated with Marfan Syndrome in a small number of patients, probably due to antithrombin III (ATIII) deficiency or various mutations. The ascending aorta and the aortic valve are replaced with prosthetic material during Bentall- de Bonno procedures. Resistance to anticoagulation during extracorporeal circulation, represents a significant challenge for both anesthesiologists and the surgical team. Resistance to heparin was observed in a patient with Marfan syndrome undergoing a Bentall procedure. ATIII concentrate was not available, and ACT did not increase despite high doses of heparin. An alternate anticoagulation approach was used successfully.

A New Score for Determining Thrombus Burden in STEMI Patients: The MAPH Score

Aim

to investigate whether the MAPH score, which is a new score that combines blood viscosity biomarkers such as mean platelet volume (MPV), total protein and hematocrit, can be used to predict thrombus burden in ST-segment elevation myocardial infarction (STEMI) patients.

Methods

A total of 473 consecutive patients with STEMI were included in the study. Intracoronary tirofiban/abciximab infusion was applied to patients with thrombus load ≥3 and these patients (n = 71) were defined as the patient group with high thrombus load. MPV, age, hematocrit and total protein values of the patients were recorded. High shear rate (HSR) and low shear rate (LSR) were calculated from total protein and hematocrit values. Cut-off values were determined for high thrombus load by using Youden index, and score was determined as 0 or 1 according to cut-offs. The sum of the scores was calculated as the MAPH score.

Results

The mean age of the patients included in the study was 59.6 ± 12.6 (n = 354 male, 74.8%). There was no difference between the groups in terms of gender, HT and DM (P = .127, P = .402 and P = .576, respectively). In the group with high thrombus load; total protein, MPV and hematocrit values were higher (P < .001, P = .001 and P = .03, respectively). Comparison of receiver operating characteristic (ROC) curve analysis revealed that the MAPH score had better performance in predicting higher thrombus load than both other self-containing parameters and HSR and LSR.

Conclusion

The MAPH score may be a new score that can be used to determine thrombus burden in STEMI patients.

PIEZO1 mediates a mechanothrombotic pathway in diabetes

[Figure: see text].

Semi-Automatic Planning and Three-Dimensional Electrospinning of Patient-Specific Grafts for Fontan Surgery

This paper proposes a semi-automatic Fontan surgery planning method for designing and manufacturing hemodynamically optimized patient-specific grafts. Fontan surgery is a palliative procedure for patients with a single ventricle heart defect by creating a new path using a vascular graft for the deoxygenated blood to be directed to the lungs, bypassing the heart. However, designing patient-specific grafts with optimized hemodynamic performance is a complex task due to the variety of patient-specific anatomies, confined surgical planning space, and the requirement of simultaneously considering multiple design criteria for vascular graft optimization. To address these challenges, we used parameterized Fontan pathways to explore patient-specific vascular graft design spaces and search for optimal solutions by formulating a nonlinear constrained optimization problem, which minimizes indexed power loss (iPL) of the Fontan model by constraining hepatic flow distribution (HFD), percentage of abnormal wall shear stress (%WSS) and geometric interference between Fontan pathways and the heart models (InDep) within clinically acceptable thresholds. Gaussian process regression was employed to build surrogate models of the hemodynamic parameters as well as InDep and [Formula: see text] (conduit model smoothness indicator) for optimization by pattern search. We tested the proposed method on two patient-specific models (n=2). The results showed the automatically optimized (AutoOpt) Fontan models hemodynamically outperformed or at least are comparable to manually optimized Fontan models with significantly reduced surgical planning time (15 hours versus over 2 weeks). We also demonstrated feasibility of manufacturing the AutoOpt Fontan conduits by using electrospun nanofibers.

A Pilot Study Characterizing Flow Patterns in the Thoracic Aorta of Patients With Connective Tissue Disease: Comparison to Age- and Gender-Matched Controls via Fluid Structure Interaction

Prior computational and imaging studies described changes in flow patterns for patients with Marfan syndrome, but studies are lacking for related populations. This pilot study addresses this void by characterizing wall shear stress (WSS) indices for patients with Loeys-Dietz and undifferentiated connective tissue diseases. Using aortic valve-based velocity profiles from magnetic resonance imaging as input to patient-specific fluid structure interaction (FSI) models, we determined local flow patterns throughout the aorta for four patients with various connective tissue diseases (Loeys-Dietz with the native aorta, connective tissue disease of unclear etiology with native aorta in female and male patients, and an untreated patient with Marfan syndrome, as well as twin patients with Marfan syndrome who underwent valve-sparing root replacement). FSI simulations used physiological boundary conditions and material properties to replicate available measurements. Time-averaged WSS (TAWSS) and oscillatory shear index (OSI) results are presented with localized comparison to age- and gender-matched control participants. Ascending aortic dimensions were greater in almost all patients with connective tissue diseases relative to their respective control. Differences in TAWSS and OSI were driven by local morphological differences and cardiac output. For example, the model for one twin had a more pronounced proximal descending aorta in the vicinity of the ductus ligamentum that impacted WSS indices relative to the other. We are optimistic that the results of this study can serve as a foundation for larger future studies on the connective tissue disorders presented in this article.

Prevalence and clinical outcomes of hospitalized patients with upper extremity deep vein thrombosis

OBJECTIVE

Upper extremity (UE) deep vein thrombosis (DVT) is a common and increasing complication in hospitalized patients. The objective of the present study was to determine the prevalence, treatment strategies, complications, and outcomes of UE-DVT.

METHODS

We performed a retrospective single-institution study of patients with a diagnosis of UE-DVT from January 2016 through February 2018 (26 months). Patients aged ≥18 years who had been admitted to the hospital and who had had positive UE duplex ultrasound findings for acute UE-DVT were included in the present study. The outcomes were in-hospital mortality, major bleeding, pulmonary embolism (PE), and recurrent UE-DVT.

RESULTS

Among 63,045 patients admitted to the hospital, 1000 (1.6%) had been diagnosed with UE-DVT. Of 3695 UE venous duplex ultrasound examinations performed during the study period, almost one third (27.0%) were positive for acute UE-DVT. The mean age was 55.0 ± 17.2 years, and most patients were men (58.3%), white (49.2%), and overweight (mean body mass index, 29.4 ± 10.3 kg/m²). The most affected vein was the right internal jugular vein (54.8%). Most of the patients (96.9%) has been receiving venous thromboembolism prophylaxis or anticoagulation therapy at the diagnosis. Most patients (77.8%) had had an intravenous device (IVD) in place at the diagnosis. Most of the patients (84.4%) were treated with anticoagulation therapy in the hospital but only one half (54.5%) were discharged with anticoagulation therapy. In-hospital mortality was 12.1% unrelated to UE-DVT, major bleeding occurred in 47.6% of the patients during hospitalization (fatal bleeding, 1%), PE was diagnosed in 4.8% of the patients, and 0.7% were fatal. Recurrent UE-DVT occurred in 6.1% of the patients. On multivariable analysis, the risk of death was increased by older age, cancer, intensive care unit admission, concomitant lower extremity DVT, and bleeding before the UE-DVT diagnosis. The presence of an IVD increased the risk of PE and the risk of recurrent UE-DVT. The risk of major bleeding was increased by the presence of an IVD, female sex, and concomitant lower extremity DVT.

CONCLUSIONS

UE-DVT is a common complication in hospitalized patients (1.6%). Consequent acute PE and recurrent DVT remain important complications, as does bleeding. It is unclear whether standard thromboprophylaxis effectively protects against UE-DVT. More studies dedicated to UE-DVT are required to provide appropriate guidance on prophylaxis and treatment.

Development of a computational fluid dynamic model to investigate the hemodynamic impact of REBOA

Background: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a lifesaving intervention for major truncal hemorrhage. Balloon-tipped arterial catheters are inserted via the femoral artery to create a temporary occlusion of the aorta, which minimizes the rate of internal bleeding until definitive surgery can be conducted. There is growing concern over the resultant hypoperfusion and potential damage to tissues and organs downstream of REBOA. To better understand the acute hemodynamic changes imposed by REBOA, we developed a three-dimensional computational fluid dynamic (CFD) model under normal, hemorrhage, and aortic occlusion conditions. The goal was to characterize the acute hemodynamic changes and identify regions within the aortic vascular tree susceptible to abnormal flow and shear stress. Methods: Hemodynamic data from established porcine hemorrhage models were used to build a CFD model. Swine underwent 20% controlled hemorrhage and were randomized to receive a full or partial aortic occlusion. Using CT scans, we generated a pig-specific aortic geometry and imposed physiologically relevant inlet flow and outlet pressure boundary conditions to match in vivo data. By assuming non-Newtonian fluid properties, pressure, velocity, and shear stresses were quantified over a cardiac cycle. Results: We observed a significant rise in blood pressure (∼147 mmHg) proximal to REBOA, which resulted in increased flow and shear stress within the ascending aorta. Specifically, we observed high levels of shear stress within the subclavian arteries (22.75 Pa). Alternatively, at the site of full REBOA, wall shear stress was low (0.04 ± 9.07E-4 Pa), but flow oscillations were high (oscillatory shear index of 0.31). Comparatively, partial REBOA elevated shear levels to 84.14 ± 19.50 Pa and reduced flow oscillations. Our numerical simulations were congruent within 5% of averaged porcine experimental data over a cardiac cycle. Conclusion: This CFD model is the first to our knowledge to quantify the acute hemodynamic changes imposed by REBOA. We identified areas of low shear stress near the site of occlusion and high shear stress in the subclavian arteries. Future studies are needed to determine the optimal design parameters of endovascular hemorrhage control devices that can minimize flow perturbations and areas of high shear.

'Heart-like' cross-sectional shape can better improve the hemodynamics in spiral laminar flow graft for small-caliber bypass application: a numerical study

Small-caliber grafts remain disappointed in the long-term bypass surgeries of coronary and peripheral arterial diseases. In order to improve the hemodynamics in small-caliber artery bypass grafts (ABGs), an improved spiral laminar flow (improved-SLF) graft with a 'heart-like' cross-sectional shape was proposed and verified by computational fluid dynamics simulation in this study. The results show that such graft can indeed induce a spiral flow and enhance the WSS distribution on the graft section. Furthermore, the helically distributed ribbon of unfavorable WSS observed in the original SLF graft was eliminated in the improved-SLF graft due to its smoothed and gentle helical ridge. On the other hand, improved-SLF ABG improved the WSS distribution in the distal anastomosis as well, because it maintained the strength of spiral flow when entering the anastomosis region. Finally, the improved-SLF ABG slightly increased the pressure drop along the bypass due to its small change of the general graft structure. As a proof-of-concept study, it can be concluded that improved-SLF graft can not only evenly enhance the WSS distribution in the graft section, but also improve the hemodynamic environment in the distal anastomosis without significantly increasing the pressure drop along the bypass, indicating such new helical-type graft may be more suitable to be used in the small-caliber graft bypass surgeries.

Shear Stress Alterations Activate BMP4/pSMAD5 Signaling and Induce Endothelial Mesenchymal Transition in Varicose Veins

Chronic venous diseases, including varicose veins, are characterized by hemodynamic disturbances due to valve defects, venous insufficiency, and orthostatism. Veins are physiologically low shear stress systems, and how altered hemodynamics drives focal endothelial dysfunction and causes venous remodeling is unknown. Here we demonstrate the occurrence of endothelial to mesenchymal transition (EndMT) in human varicose veins. Moreover, the BMP4-pSMAD5 pathway was robustly upregulated in varicose veins. In vitro flow-based assays using human vein, endothelial cells cultured in microfluidic chambers show that even minimal disturbances in shear stress as may occur in early stages of venous insufficiency induce BMP4-pSMAD5-based phenotype switching. Furthermore, low shear stress at uniform laminar pattern does not induce EndMT in venous endothelial cells. Targeting the BMP4-pSMAD5 pathway with small molecule inhibitor LDN193189 reduced SNAI1/2 expression in venous endothelial cells exposed to disturbed flow. TGFβ inhibitor SB505124 was less efficient in inhibiting EndMT in venous endothelial cells exposed to disturbed flow. We conclude that disturbed shear stress, even in the absence of any oscillatory flow, induces EndMT in varicose veins via activation of BMP4/pSMAD5-SNAI1/2 signaling. The present findings serve as a rationale for the possible use of small molecular mechanotherapeutics in the management of varicose veins.

Retinal and peripapillary vessel density increase in recovered COVID-19 children by optical coherence tomography angiography

PURPOSE

To evaluate retinal vascular changes in children who have recovered from coronavirus disease (COVID-19) using optical coherence tomography angiography (OCTA) and to compare the results with age-matched healthy children.

METHODS

In this cross-sectional case-control study, children 6-18 years of age with laboratory-confirmed SARS-CoV-2 infection were compared with historic healthy controls. All participants underwent ophthalmological examination, including fundus photography and OCTA of the macular region and optic disk. COVID-19 children were examined 4-8 weeks after COVID-19 diagnoses. Demographic data, medical history, and COVID-19 symptoms were noted. OCTA parameters in the superficial capillary plexus (SCP) were analyzed according to ETDRS sectors and peripapillary quadrants.

RESULTS

A total of 72 patients were included: 27 recovered COVID-19 children and 45 controls. Mean age for cases was 11.96 ± 3.8 years (18 females [66%]); for controls, 11.02 ± 2.0 years (29 females [64%]). Macular OCTA of the SCP showed a significant increase in retinal vessel density (VD) in recovered COVID-19 children compared with healthy controls in the inner ring (P = 0.001). Macular perfusion density (mPD) was also increased in the inner ring (P = 0.001). Peripapillary OCTA evidenced a significant higher flux index (FI) in all four quadrants (P < 0.001).

CONCLUSIONS

Recovered COVID-19 children present increased retinal VD, mPD, and peripapillary FI shortly after recovery. Since the retinal vasculature is considered a unique window to assess microvascular changes, these findings may represent a potential in vivo biomarker of vascular abnormalities in COVID-19 children in other organs.

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.

Increased matrix metalloproteinase 9 activity correlates with flow-mediated intraluminal thrombus deposition and wall degeneration in human abdominal aortic aneurysm

Objective

We have previously demonstrated that human abdominal aortic aneurysm (AAA) rupture occurs in zones of low wall shear stress where flow recirculation and intraluminal thrombus (ILT) deposition are increased. Matrix metalloproteinase-9 (MMP-9) is involved in the pathogenesis of AAA via its lytic effect on collagen and elastin. We hypothesize that flow-mediated ILT deposition promotes increased local inflammatory and MMP-9 activity that leads to AAA wall degeneration. The purpose of this study was to examine the correlation between predicted pulsatile flow dynamics and regional differences in MMP-9, elastin, collagen, and ILT deposition in human AAA.

Methods

Full-thickness aortic tissue samples were collected from 24 patients undergoing open AAA repair. Control infrarenal aortic tissue was obtained from 6 patients undergoing aortobifemoral bypass. Full-thickness aortic tissue and ILT were assessed for MMP-9 levels using a cytokine array assay. Histologic and immunohistochemical assessment of inflammation, collagen and elastin content, and MMP-9 levels were also measured. Three-dimensional AAA geometry was generated from computed tomography angiogram (CTA) images using Mimics software and computational fluid dynamics was used to predict pulsatile aortic blood flow.

Results

The majority of AAA showed eccentric ILT deposition which was correlated with predicted recirculation blood flow (R² = –0.17; P < .05). The regions of high ILT were associated with significant increases in inflammation and loss of elastin and collagen compared with regions of low ILT, or with control tissue. MMP-9 was significantly higher in areas of high ILT deposition compared with areas devoid of ILT. Tissue MMP-9 was correlated with the thickness of ILT deposition (R² = 0.46; P < .05), and was also present in high levels in thick compared with thin ILT.

Conclusions

We have shown a correlation between flow-mediated ILT deposition with increased tissue levels of MMP-9 activity, increased inflammatory infiltrate, and decreased elastin and collagen content in stereotactically sampled human AAA, suggesting that ILT deposition is associated with local increases in proteolytic activity that may preferentially weaken and promote rupture at selected regions.

Outflow Through Aortic Side Branches Drives False Lumen Patency in Type B Aortic Dissection

Objective: Thoracic endovascular aortic repair (TEVAR) for type B aortic dissection (TBAD) aims to induce false lumen (FL) thrombosis by sealing intimal tears between the true (TL) and the FL, and blocking the inflow into the FL. Incomplete thrombosis of the FL is correlated with poor clinical outcome. We hypothesize that the number of major and minor branches arising from the FL affects FL patency and may negatively influence TEVAR induced FL thrombosis.

Methods: Computed tomography (CT)-scans from 89 patients diagnosed with TBAD [best medical treatment (BMT) n = 52, TEVAR n = 37] from two high-volume vascular surgery centers were analyzed retrospectively. Analysis included evaluation of the FL patency status, the number, location and size of intimal tears, and the presence of minor and major side branches originating from the FL. Multiple regression analysis was conducted to evaluate obtained parameters as predictors for FL thrombosis status.

Results: In univariate analysis, the strongest correlation for FL patency was found for the number of major (R = 0.79) and minor (R = 0.86) side branches originating from the FL. When applying a multiple linear regression model, the number of major (normalized beta 0.37; P < 0.001) and minor (normalized beta 0.41; P < 0.01) side branches arising from the FL were valid predictors for the axial length of the patent and non-patent FL, and additionally determined the length of the patent FL at 12-month follow-up in patients that underwent TEVAR.

Conclusions: Our data suggest that the number of minor side branches that originate from the FL in TBAD is an important determinant of FL patency, to a greater degree than previously assumed.

Blood Flow Velocimetry in a Microchannel During Coagulation Using Particle Image Velocimetry and Wavelet-Based Optical Flow Velocimetry

This article describes novel measurements of the velocity of whole blood flow in a microchannel during coagulation. The blood is imaged volumetrically using a simple optical setup involving a white light source and a microscope camera. The images are processed using particle image velocimetry (PIV) and wavelet-based optical flow velocimetry (wOFV), both of which use images of individual blood cells as flow tracers. Measurements of several clinically relevant parameters such as the clotting time, decay rate, and blockage ratio are computed. The high-resolution wOFV results yield highly detailed information regarding thrombus formation and corresponding flow evolution that is the first of its kind.

Ultrasound-Responsive Nanopeptisomes Enable Synchronous Spatial Imaging and Inhibition of Clot Growth in Deep Vein Thrombosis

Deep vein thrombosis (DVT) is a life-threatening blood clotting condition that, if undetected, can cause deadly pulmonary embolisms. Critical to its clinical management is the ability to rapidly detect, monitor, and treat thrombosis. However, current diagnostic imaging modalities lack the resolution required to precisely localize vessel occlusions and enable clot monitoring in real time. Here, we rationally design fibrinogen-mimicking fluoropeptide nanoemulsions, or nanopeptisomes (NPeps), that allow contrast-enhanced ultrasound imaging of thrombi and synchronous inhibition of clot growth. The theranostic duality of NPeps is imparted via their intrinsic binding to integrins overexpressed on platelets activated during coagulation. The platelet-bound nanoemulsions can be vaporized and oscillate in an applied acoustic field to enable contrast-enhanced Doppler ultrasound detection of thrombi. Concurrently, nanoemulsions bound to platelets competitively inhibit secondary platelet-fibrinogen binding to disrupt further clot growth. Continued development of this synchronous theranostic platform may open new opportunities for image-guided, non-invasive, interventions for DVT and other vascular diseases.

Role of Purinergic Signalling in Endothelial Dysfunction and Thrombo-Inflammation in Ischaemic Stroke and Cerebral Small Vessel Disease

The cerebral endothelium is an active interface between blood and the central nervous system. In addition to being a physical barrier between the blood and the brain, the endothelium also actively regulates metabolic homeostasis, vascular tone and permeability, coagulation, and movement of immune cells. Being part of the blood–brain barrier, endothelial cells of the brain have specialized morphology, physiology, and phenotypes due to their unique microenvironment. Known cardiovascular risk factors facilitate cerebral endothelial dysfunction, leading to impaired vasodilation, an aggravated inflammatory response, as well as increased oxidative stress and vascular proliferation. This culminates in the thrombo-inflammatory response, an underlying cause of ischemic stroke and cerebral small vessel disease (CSVD). These events are further exacerbated when blood flow is returned to the brain after a period of ischemia, a phenomenon termed ischemia-reperfusion injury. Purinergic signaling is an endogenous molecular pathway in which the enzymes CD39 and CD73 catabolize extracellular adenosine triphosphate (eATP) to adenosine. After ischemia and CSVD, eATP is released from dying neurons as a damage molecule, triggering thrombosis and inflammation. In contrast, adenosine is anti-thrombotic, protects against oxidative stress, and suppresses the immune response. Evidently, therapies that promote adenosine generation or boost CD39 activity at the site of endothelial injury have promising benefits in the context of atherothrombotic stroke and can be extended to current CSVD known pathomechanisms. Here, we have reviewed the rationale and benefits of CD39 and CD39 therapies to treat endothelial dysfunction in the brain.

The effect of Dean, Reynolds and Womersley numbers on the flow in a spherical cavity on a curved round pipe. Part 2. The haemodynamics of intracranial aneurysms treated with flow-diverting stents

The flow in a spherical cavity on a curved round pipe is a canonical flow that describes well the flow inside a sidewall aneurysm on an intracranial artery. Intracranial aneurysms are often treated with a flow-diverting stent (FDS), a low-porosity metal mesh that covers the entrance to the cavity, to reduce blood flow into the aneurysm sac and exclude it from mechanical stresses imposed by the blood flow. Successful treatment is highly dependent on the degree of reduction of flow inside the cavity, and the resulting altered fluid mechanics inside the aneurysm following treatment. Using stereoscopic particle image velocimetry, we characterize the fluid mechanics in a canonical configuration representative of an intracranial aneurysm treated with a FDS: a spherical cavity on the side of a curved round pipe covered with a metal mesh formed by an actual medical FDS. This porous mesh coverage is the focus of Part 2 of the paper, characterizing the effects of parent vessel Re, De and pulsatility, Wo, on the fluid dynamics, compared with the canonical configuration with no impediments to flow into the cavity that is described in Part 1 (Chassagne et al., J. Fluid Mech., vol. 915, 2021, A123). Coverage with a FDS markedly reduces the flow Re in the aneurysmal cavity, creating a viscous-dominated flow environment despite the parent vessel Re > 100. Under steady flow conditions, the topology that forms inside the cavity is shown to be a function of the parent vessel De. At low values of De, flow enters the cavity at the leading edge and remains attached to the wall before exiting at the trailing edge, a novel behaviour that was not found under any conditions of the high-Re, unimpeded cavity flow described in Part 1. Under these conditions, flow in the cavity co-rotates with the direction of the free-stream flow, similar to Stokes flow in a cavity. As De increases, the flow along the leading edge begins to separate, and the recirculation zone grows with increasing De, until, above De ≈ 180, the flow inside the cavity is fully recirculating, counter-rotating with respect to the free-stream flow. Under pulsatile flow conditions, the vortex inside the cavity progresses through the same cycle - switching from attached and co-rotating with the free-stream flow at the beginning of the cycle (low velocity and positive acceleration) to separated and counter-rotating as De reaches a critical value. The location of separation within the harmonic cycle is shown to be a function of both De and Wo. The values of aneurysmal cavity Re based on both the average velocity and the circulation inside the cavity are shown to increase with increasing values of De, while Wo is shown to have little influence on the time-averaged metrics. As De increases, the strength of the secondary flow in the parent vessel grows, due to the inertial instability in the curved pipe, and the flow rate entering the cavity increases. Thus, the effectiveness of FDS treatment to exclude the aneurysmal cavity from the haemodynamic stresses is compromised for aneurysms located on high-curvature arteries, i.e. vessels with high De, and this can be a fluid mechanics criterion to guide treatment selection.

Targeting Contrast Agents With Peak Near-Infrared-II (NIR-II) Fluorescence Emission for Non-invasive Real-Time Direct Visualization of Thrombosis

Thrombosis within the vasculature arises when pathological factors compromise normal hemostasis. On doing so, arterial thrombosis (AT) and venous thrombosis (VT) can lead to life-threatening cardio-cerebrovascular complications. Unfortunately, the therapeutic window following the onset of AT and VT is insufficient for effective treatment. As such, acute AT is the leading cause of heart attacks and constitutes ∼80% of stroke incidences, while acute VT can lead to fatal therapy complications. Early lesion detection, their accurate identification, and the subsequent appropriate treatment of thrombi can reduce the risk of thrombosis as well as its sequelae. As the success rate of therapy of fresh thrombi is higher than that of old thrombi, detection of the former and accurate identification of lesions as thrombi are of paramount importance. Magnetic resonance imaging, x-ray computed tomography (CT), and ultrasound (US) are the conventional non-invasive imaging modalities used for the detection and identification of AT and VT, but these modalities have the drawback of providing only image-delayed indirect visualization of only late stages of thrombi development. To overcome such limitations, near-infrared (NIR, ca. 700-1,700 nm) fluorescence (NIRF) imaging has been implemented due to its capability of providing non-invasive real-time direct visualization of biological structures and processes. Contrast agents designed for providing real-time direct or indirect visualization of thrombi using NIRF imaging primarily provide peak NIR-I fluorescence emission (ca. 700-1,000 nm), which affords limited tissue penetration depth and suboptimal spatiotemporal resolution. To facilitate the enhancement of the visualization of thrombosis via providing detection of smaller, fresh, and/or deep-seated thrombi in real time, the development of contrast agents with peak NIR-II fluorescence emission (ca. 1000-1,700 nm) has been recently underway. Currently, however, most contrast agents that provide peak NIR-II fluorescence emissions that are purportedly capable of providing direct visualization of thrombi or their resultant occlusions actually afford only the indirect visualization of such because they only provide for the (i) measuring of the surrounding vascular blood flow and/or (ii) simple tracing of the vasculature. These contrast agents do not target thrombi or occlusions. As such, this mini review summarizes the extremely limited number of targeting contrast agents with peak NIR-II fluorescence emission developed for non-invasive real-time direct visualization of thrombosis that have been recently reported.

Partitioning risk factors for embolic stroke of undetermined source using exploratory factor analysis

Background

Embolic stroke of undetermined source (ESUS) accounts for up to 25% of strokes. Understanding risk factors associated with ESUS is important in reducing stroke burden worldwide. However, ESUS patients are younger and present with fewer traditional risk factors. Significant global variation in ESUS populations also exists making the clinical picture of this type of stroke unclear.

Methods and results

ESUS patients were pair matched for age, sex, and ethnicity with a group of all other strokes (both n = 331). Exploratory factor analysis was applied in both groups to 14 risk and clinical factors to identify latent factors. In ESUS patients, two latent factors emerged consisting primarily of heart-related variables such as left ventricular wall motion abnormalities, reduced ejection fraction, and increased left atrial volume index, as well as aortic arch atherosclerosis. This is in comparison to the all other strokes group, which was dominated by traditional stroke risk factors.

Conclusions

Our findings support the existence of a unique pattern of risk factors specific to ESUS. We show that LVWMA and corresponding changes in left heart function are a potential source of emboli in these patients. In addition, the clustering of aortic arch atherosclerosis with left heart factors suggests a causal link. Through the application of exploratory factor analysis, this work contributes to a further understanding of stroke mechanisms in ESUS.

Large vessel cardioembolic stroke and embolic stroke of undetermined source share a common profile of matrix metalloproteinase-9 level and susceptibility vessel sign length

BACKGROUND

Embolic stroke of undetermined source (ESUS) accounts for up to 25% of ischemic strokes. Identification of biomarkers that could improve the prediction of stroke subtype and subsequently of stroke prevention still remains a major issue.

METHODS

The HIBISCUS-STROKE cohort includes ischemic stroke patients with large vessel occlusion treated with mechanical thrombectomy following admission magnetic resonance imaging. Presence and length of susceptibility vessel sign (SVS) were assessed by gradient-recalled echo T2*-weighted imaging. Matrix metalloproteinase-9 (MMP-9) was measured on sera collected at admission. A multiple logistic regression model was performed to detect independent markers distinguishing cardioembolic (CE) from large-artery atherosclerosis (LAA) subtype.

RESULTS

A total of 147 patients were included, of them the etiology was distributed as follows: 86 (58.5%) CE, 26 (17.7%) LAA, and 35 (23.8%) ESUS. The optimal cutoff for differentiating CE from LAA subtype was 14.5 mm for SVS length (sensitivity, 79.7%; specificity, 72.7%) and 1110 ng/ml for admission MMP-9 level (sensitivity, 85.3%; specificity, 52.2%). Multivariate analysis revealed that current smoking (odds ratio [OR] 0.07, 95% confidence interval [CI] 0.01-0.93), tandem occlusion (OR 0.01, 95% CI 0.01-0.21), SVS length (OR 0.78, 95% CI 0.63-0.97), and admission MMP-9 level (OR 0.99, 95% CI 0.99-1.00) were inversely associated with CE subtype. SVS length and MMP-9 level did not differ between ESUS and CE subtypes.

CONCLUSION

SVS length and admission MMP-9 level may improve the prediction of CE subtype whose profile is close to ESUS, thus suggesting a common cardiac embolic source.

Insight Into Pathological Integrin αIIbβ3 Activation From Safeguarding The Inactive State

The inhibition of physiological activation pathways of the platelet adhesion receptor integrin αIIbβ3 may fail to prevent fatal thrombosis, suggesting that the receptor is at risk of activation by yet an unidentified pathway. Here, we report the discovery and characterization of a structural motif that safeguards the receptor by selectively destabilizing its inactive state. At the extracellular membrane border, an overpacked αIIb(W968)-β3(I693) contact prevents αIIb(Gly972) from optimally assembling the αIIbβ3 transmembrane complex, which maintains the inactive state. This destabilization of approximately 1.0 kcal/mol could be mitigated by hydrodynamic forces but not physiological agonists, thereby identifying hydrodynamic forces as pathological activation stimulus. As reproductive life spans are not generally limited by cardiovascular disease, it appears that the evolution of the safeguard was driven by fatal, hydrodynamic force-mediated integrin αIIbβ3 activation in the healthy cardiovascular system. The triggering of the safeguard solely by pathological stimuli achieves an effective increase of the free energy barrier between inactive and active receptor states without incurring an increased risk of bleeding. Thus, integrin αIIbβ3 has evolved an effective way to protect receptor functional states that indicates the availability of a mechanical activation pathway when hydrodynamic forces exceed physiological margins.

Patient-Specific Modelling of Blood Coagulation

Blood coagulation represents one of the most studied processes in biomedical modelling. However, clinical applications of this modelling remain limited because of the complexity of this process and because of large inter-patient variation of the concentrations of blood factors, kinetic constants and physiological conditions. Determination of some of these patients-specific parameters is experimentally possible, but it would be related to excessive time and material costs impossible in clinical practice. We propose in this work a methodological approach to patient-specific modelling of blood coagulation. It begins with conventional thrombin generation tests allowing the determination of parameters of a reduced kinetic model. Next, this model is used to study spatial distributions of blood factors and blood coagulation in flow, and to evaluate the results of medical treatment of blood coagulation disorders.