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Hypercoagulability and endothelial dysfunction are hallmarks of coronavirus disease 2019 (COVID-19) and appear to predict disease severity. A high incidence of thrombosis despite thromboprophylaxis is reported in patients with moderate to severe COVID-19. Recent randomized clinical trials suggest that therapeutic-intensity heparin confers a survival benefit in moderate-severity COVID-19 compared to standard-intensity heparin, potentially by harnessing heparin-mediated endothelial-stabilizing and anti-inflammatory effects.We hypothesized that patients with moderate-severity COVID-19 exhibit enhanced hypercoagulability despite standard-intensity thromboprophylaxis with low molecular weight heparin (LMWH) compared to non-COVID-19 hospitalized patients.Patients with moderate COVID-19 and a control group (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]-negative hospitalized patients) receiving LMWH thromboprophylaxis were recruited. Markers of endothelial damage and plasma thrombin generation parameters were assessed.Tissue plasminogen activator levels were significantly increased in the COVID-19 group (8.3 ± 4.4 vs. 4.9 ± 2.4 ng/ml; P = .02) compared to non-COVID-19-hospitalized patients. Despite thromboprophylaxis, mean endogenous thrombin potential was significantly increased among COVID-19 patients (1929 ± 448 vs. 1528 ± 460.8 nM*min; P = .04) but lag time to thrombin generation was significantly prolonged (8.1 ± 1.8 vs. 6.2 ± 1.8 mins; P = .02). While tissue factor pathway inhibitor (TFPI) levels were similar in both groups, in the presence of an inhibitory anti-TFPI antibody, the difference in lag time between the groups was abrogated.Collectively, these data demonstrate that COVID-19 of moderate severity is associated with increased plasma thrombin generation and endothelial damage, and that hypercoagulability persists despite standard LMWH thromboprophylaxis. These findings may be of clinical interest given recent clinical trial data which suggest escalated heparin dosing in non-severe COVID-19 may be associated with improved clinical outcomes.

Objective The aim of this study was to evaluate infants, born to women with SARS-CoV-2 detected during pregnancy, for evidence of haematological abnormalities or hypercoagulability in umbilical cord blood. Study design This was a prospective observational case-control study of infants born to women who had SARS-CoV-2 RNA detected by PCR at any time during their pregnancy (n = 15). The study was carried out in a Tertiary University Maternity Hospital (8,500 deliveries/year) in Ireland. This study was approved by the Hospital Research Ethics Committee and written consent was obtained. Umbilical cord blood samples were collected at delivery, full blood count and Calibrated Automated Thrombography were performed. Demographics and clinical outcomes were recorded. Healthy term infants, previously recruited as controls to a larger study prior to the outbreak of COVID-19, were the historical control population (n = 10). Results Infants born to women with SARS-CoV-2 had similar growth parameters (birth weight 3600 g v 3680 g, p = 0.83) and clinical outcomes to healthy controls, such as need for resuscitation at birth (2 (13.3%) v 1 (10%), p = 1.0) and NICU admission (1 (6.7%) v 2 (20%), p = 0.54). Haematological parameters (Haemoglobin, platelet, white cell and lymphocyte counts) in the COVID-19 group were all within normal neonatal reference ranges. Calibrated Automated Thrombography revealed no differences in any thrombin generation parameters (lag time (p = 0.92), endogenous thrombin potential (p = 0.24), peak thrombin (p = 0.44), time to peak thrombin (p = 0.94)) between the two groups. Conclusion In this prospective study including eligible cases in a very large population of approximately 1500 women, there was no evidence of derangement of the haematological parameters or hypercoagulability in umbilical cord blood due to COVID-19. Further research is required to investigate the pathological placental changes, particularly COVID-19 placentitis and the impact of different strains of SARS-CoV-2 (particularly the B.1.1.7 and the emerging Delta variant) and the severity and timing of infection on the developing fetus.

BACKGROUND Rivaroxaban, a direct oral factor Xa inhibitor, mediates anti-inflammatory and cardiovascular-protective effects besides its well-established anticoagulant properties; however, these remain poorly characterized. Extracellular vesicles (EVs) are important circulating messengers regulating a myriad of biological and pathological processes and may be highly relevant to the pathophysiology of atrial fibrillation as they reflect alterations in platelet and endothelial biology. However, the effects of rivaroxaban on circulating pro-inflammatory EVs remain unknown. OBJECTIVES We hypothesized that rivaroxaban's anti-inflammatory properties are reflected upon differential molecular profiles of circulating EVs. METHODS Differences in circulating EV profiles were assessed using a combination of single vesicle analysis by Nanoparticle Tracking Analysis and flow cytometry, and proteomics. RESULTS We demonstrate, for the first time, that rivaroxaban-treated non-valvular atrial fibrillation (NVAF) patients (n=8) exhibit attenuated inflammation compared with matched warfarin controls (n=15). Circulating EV profiles were fundamentally altered. Moreover, quantitative proteomic analysis of enriched plasma EVs from six pooled biological donors per treatment group revealed a profound decrease in highly pro-inflammatory protein expression and complement factors, together with increased expression of negative regulators of inflammatory pathways. Crucially, a reduction in circulating levels of soluble P-selectin was observed in rivaroxaban-treated patients (compared with warfarin controls), which negatively correlated with the patient's time on treatment. CONCLUSION Collectively, these data demonstrate that NVAF patients anticoagulated with rivaroxaban (compared with warfarin) exhibit both a reduced pro-inflammatory state and evidence of reduced endothelial activation. These findings are of translational relevance toward characterizing the anti-inflammatory and cardiovascular-protective mechanisms associated with rivaroxaban therapy.

Premature infants are at high risk of haemorrhage and thrombosis. Our understanding of the differences between the neonatal and adult haemostatic system is evolving. There are several limitations to the standard coagulation tests used in clinical practice, and there is currently a lack of evidence to support many of the transfusion practices in neonatal medicine. The evaluation of haemostasis is particularly challenging in neonates due to their limited blood volume. The calibrated automated thrombogram (CAT) is a global coagulation assay, first described in 2002, which evaluates both pro- and anti-coagulant pathways in platelet-rich or platelet-poor plasma. In this review, the current applications and limitations of CAT in the neonatal population are discussed.Conclusion: CAT has successfully elucidated several differences between haemostatic mechanisms in premature and term neonates compared with adults. Moreover, it has been used to evaluate the effect of a number of haemostatic drugs in a pre-clinical model. However, the lack of evidence of CAT as an accurate predictor of neonatal bleeding, blood volume required and the absence of an evidence-based treatment algorithm for abnormal CAT results limit its current application as a bedside clinical tool for the evaluation of sick neonates. What is Known:• The Calibrated automated thrombogram (CAT) is a global coagulation assay which evaluates pro- and anti-coagulant pathways.• CAT provides greater information than standard clotting tests and has been used in adults to evaluate bleeding risk. What is New:• This review summarises the physiological differences in haemostasis between neonates and adults described using CAT.• The haemostatic effect of several drugs has been evaluated in neonatal plasma using CAT.

Preeclampsia complicates up to 8% of pregnancies and is a leading cause of fetomaternal morbidity andmortality. Treatment options are limited, with supportive care and delivery of the placenta representing the cornerstone of current management strategies. Derangements in blood coagulation are wellrecognised in this disorder and appear to favour an increased risk of venous thromboembolism among affected women. This risk appears to be most significant in the postpartum period. The mechanisms underlying this increased thrombosis risk remain to be fully elucidated although increased expression of procoagulant factors, endothelial dysfunction, attenuation of endogenous anticoagulant activity and increased platelet activity have been implicated in the prothrombotic tendency. Preeclampsia is also occasionally complicated by life-threatening haemorrhagic events and current evidence suggests that in some severe manifestations of this disease a coagulopathy with a clinical bleeding tendency may be the predominant haemostatic abnormality. Identifying affected women at significant risk of thrombosis and managing the competing thrombotic and haemorrhagic risks continue to be a significant clinical challenge. Derangements in blood coagulation are also implicated in the pathogenesis of preeclampsia; however, the role of antiplatelet or anticoagulant drugs in the prevention and treatment of this disorder remains a source of considerable debate. In addition, the potential role of specific haemostatic markers as diagnostic or screening tools for preeclampsia has also yet to be determined. Further characterisation of the underlying molecular mechanisms would likely be of major translational relevance and could provide insights into the pathogenesis of this disease as well as the associated haemostatic dysfunction.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare and under-recognised complication of acute pulmonary embolism. Information regarding the characteristics of CTEPH in Ireland is limited, and the aim of this retrospective cohort study was to address this knowledge gap. Seventy-two cases of CTEPH were diagnosed in the National Pulmonary Hypertension Unit (NPHU) in Ireland between 2010 and 2020. This accounted for 6% of all referrals to the unit and translates to an estimated annual incidence of 1.39 per million population (95% confidence interval, 0.33-2.46). The prevalence of diagnosed CTEPH in Ireland in 2020 was estimated at 12.05 per million population (95% CI 9.00-15.10). The average duration of symptoms prior to CTEPH diagnosis was 23 (±22) months. Patients with CTEPH were more likely to be male (n = 40, 56%), older (60 ± 17 years) and have identifiable risk factors for CTEPH (n = 61, 85%) at diagnosis. Regarding treatment, pulmonary hypertension (PH) vasodilator therapy was prescribed in 75% (n = 54) within 12 months of diagnosis, inferior vena cava filters were placed in 24% (n = 17) and 97% (n = 70) of cases were anticoagulated. Pulmonary endarterectomy was performed in 35% (n = 25), balloon pulmonary angioplasty in 6% (n = 4). One-, three- and five-year survival was 93%, 80% and 65% from the time of diagnosis, and this was significantly better in patients who underwent pulmonary endarterectomy (p = 0.01). This is the first study describing the characteristics of CTEPH in Ireland and highlights suboptimal disease recognition and referral for the assessment for pulmonary endarterectomy.

Background Decompensated cirrhosis is associated with coagulation abnormalities that can increase the risk of thrombosis and bleeding. It is unclear precisely when these abnormalities arise and whether they are exacerbated as compensated cirrhosis progresses. Transient elastography using FibroScan generates liver stiffness measurements (LSM) that associate with portal hypertension, clinical outcomes and provides prognostic information at an earlier stage than traditional liver function scores eg, MELD score. Objective To characterize thrombin generation in patients with compensated cirrhosis and to determine whether parameters of coagulation change throughout compensated cirrhosis, staged using LSM. Patients/Methods Blood samples were collected from well‐compensated cirrhotic patients n = 61, All Child Pugh A stage) attending the Mater Misericordiae University Hospital, Ireland. Comprehensive clinical staging of liver disease, including LSM, was performed. Tissue Factor‐stimulated thrombin generation was measured by calibrated automated thrombography. Results Using LSM to stage well‐compensated cirrhotic patients, we demonstrate a significant decrease in the rate of propagation, the rate of attenuation, and total thrombin generation as LSM increase. LSM correlated with endogenous thrombin potential, peak thrombin generation, the rate of propagation, and the rate of attenuation. This association between thrombin generation and LSM was still evident in sub‐analyses excluding patients with ongoing alcohol use, active HCV infection, or a history of decompensation. In contrast, there was no significant correlation between thrombin generation, prothrombin times, Child‐Pugh scores, or MELD scores. Conclusion Liver stiffness measurements identify differences in parameters of thrombin generation within a cohort of compensated cirrhotic patients before changes in clotting times occur.

Pulmonary arterial hypertension is a rare disease of the pulmonary vasculature, characterised pathologically by proliferation, remodelling and thrombosis in situ . Unfortunately, existing therapeutic interventions do not reverse these findings and the disease continues to result in significant morbidity and premature mortality. A number of haematological derangements have been described in pulmonary arterial hypertension which may provide insights into the pathobiology of the disease and opportunities to explore new therapeutic pathways. These include quantitative and qualitative platelet abnormalities, such as thrombocytopaenia, increased mean platelet volume and altered platelet bioenergetics. Furthermore, a hypercoagulable state and aberrant negative regulatory pathways can be observed, which could contribute to thrombosis in situ in distal pulmonary arteries and arterioles. Finally, there is increasing interest in the role of extracellular vesicle autocrine and paracrine signalling in pulmonary arterial hypertension, and their potential utility as biomarkers and novel therapeutic targets. This review focuses on the potential role of platelets, extracellular vesicles and coagulation pathways in the pathobiology of pulmonary arterial hypertension. We highlight important unanswered clinical questions and the implications of these observations for future research and pulmonary arterial hypertension-directed therapies.

Recurrent venous thromboembolism (VTE, or deep vein thrombosis and pulmonary embolism) is associated with mortality and long-term morbidity. The circumstances in which an index VTE event occurred are crucial when personalized VTE recurrence risk is assessed. Patients who experience a VTE event in the setting of a transient major risk factor (such as surgery associated with general anesthesia for >30 minutes) are predicted to have a low VTE recurrence risk following discontinuation of anticoagulation, and limited-duration anticoagulation is generally recommended. In contrast, those patients whose VTE event occurred in the absence of risk factors or who have persistent risk factors have a higher VTE recurrence risk. Here, we review the literature surrounding VTE recurrence risk in a range of clinical conditions. We describe gender-specific risks, including VTE recurrence risk following hormone- and pregnancy-associated VTE events. Finally, we discuss how the competing impacts of VTE recurrence and bleeding have shaped international guideline recommendations.

Introduction Temporarily immobilising an injured lower limb is a recognised predisposing factor for the development of venous thromboembolism (VTE). We aim to conduct a prospective study to measure the incidence of VTE after temporary lower limb immobilisation. The study will also measure VTE risk factors in this patient cohort and identify those risk factors that are predictors of developing VTE. Finally, this study will validate the Thrombosis Risk Prediction for patients with cast immobilisation (TRiP (cast)) risk assessment model. Methods The planned study design will be prospective and multicentre, including 15 participating sites within the Irish Network for VTE Research (INViTE). Consecutive patients aged 18 years and older with an immobilised injured lower limb will be eligible for inclusion. We will collect the relevant clinical variables at the index emergency department (ED) visit. The primary outcome will be the incidence of symptomatic VTE within three months after the injury. We will include VTE predictors in a multivariable logistic regression model, with VTE occurrence as the outcome variable. The TRiP (cast) model will be prospectively validated for first time using the Thrombosis In patients with Lower Limb Injuries Requiring Immobilisation (TiLLIRI) cohort. Discussion The association between lower limb immobilisation and VTE has been documented for over seventy-five years. However, the benefits of pharmacological thromboprophylaxis are still unclear. Identifying patients at a higher risk of VTE after immobilising an injured lower limb will help patient-focused benefit-risk analysis to inform clinical decision making and treatment decisions. The TiLLIRI study will address this critical clinical knowledge gap in the first-ever large prospective multicentre observational study of its kind. The results of this study are likely to inform future clinical trials and prospective management studies and to impact upon patient safety positively.

Coronavirus Disease 2019 (COVID-19), caused by the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has affected over 30 million globally to date. Although high rates of venous thromboembolism and evidence of COVID-19-induced endothelial dysfunction have been reported, the precise aetiology of the increased thrombotic risk associated with COVID-19 infection remains to be fully elucidated. Therefore, we assessed clinical platelet parameters and circulating platelet activity in patients with severe and nonsevere COVID-19. An assessment of clinical blood parameters in patients with severe COVID-19 disease (requiring intensive care), patients with nonsevere disease (not requiring intensive care), general medical in-patients without COVID-19, and healthy donors was undertaken. Platelet function and activity were also assessed by secretion and specific marker analysis. We demonstrated that routine clinical blood parameters including increased mean platelet volume (MPV) and decreased platelet:neutrophil ratio are associated with disease severity in COVID-19 upon hospitalisation and intensive care unit (ICU) admission. Strikingly, agonist-induced ADP release was 30- to 90-fold higher in COVID-19 patients compared with hospitalised controls and circulating levels of platelet factor 4 (PF4), soluble P-selectin (sP-selectin), and thrombopoietin (TPO) were also significantly elevated in COVID-19. This study shows that distinct differences exist in routine full blood count and other clinical laboratory parameters between patients with severe and nonsevere COVID-19. Moreover, we have determined all COVID-19 patients possess hyperactive circulating platelets. These data suggest abnormal platelet reactivity may contribute to hypercoagulability in COVID-19 and confirms the role that platelets/clotting has in determining the severity of the disease and the complexity of the recovery path., The reason for the increased thrombotic risk associated with SARS-CoV-2 infection remains unclear. This study reveals that disease severity is associated with increased mean platelet volume and decreased platelet:neutrophil ratio; moreover, all COVID-19 patients possess hyperactive circulating platelets, with agonist-induced ADP release 30-to-90 fold higher than controls.

While recent advances in recombinant DNA technology, gene therapy and the discovery of novel non-substitutional agents have revolutionised the management of haemophilia A, plasma-derived clotting factor concentrates continue to be used and are likely to remain an important therapeutic option for the foreseeable future. The administration of plasma-derived products is associated with a risk of pathogen transmission. However, this risk has been greatly reduced, if not virtually eliminated, by modern manufacturing techniques. Moreover, FVIII inhibitor formation (which has overtaken pathogen transmission as the major modern complication of factor replacement therapy) may occur less frequently with the use of plasma-derived FVIII concentrates relative to recombinant alternatives, although this remains a source of considerable debate. In addition, plasma-derived FVIII concentrates remain the primary replacement therapy for haemophilia A in the developing world, where access to recombinant therapy is more limited. The future role of plasma-derived concentrates globally will be determined by several factors including the ability of manufacturers to continue to provide safe and affordable product, the potential for plasma-derived concentrates to confer lower a risk of inhibitor formation in previously untreated patients with haemophilia and the impact of novel therapies on the market for plasma-derived products both in the developed and developing world.

Introduction Pulmonary embolism (PE) is a leading cause of cardiovascular morbidity worldwide. The risk of early death in the setting of untreated PE may be as high as 30%. However, diagnostic and therapeutic advances in recent years have led to a progressive decline in global PE-related mortality and recent data describing rates of in-hospital death following PE suggest a mortality rate of approximately 5-15%. Moreover, strategies directed at stratification of PE severity have been shown to safely identify a sub-group of low-risk patients (up to 30-50% of all patients) for whom outpatient management is feasible without the need for hospital admission. Avoiding hospitalisation for low-risk PE patients is associated with improved patient satisfaction and avoids exposing patients to the risks associated with hospital admission. Ambulatory PE management would also be predicted to lead to significant healthcare cost-savings. However ambulatory care models for low-risk PE appear to be under-utilised despite these potential benefits. Barriers to implementation include access to outpatient follow-up services and the perceived risks associated with this model of care. The Ireland East Hospital Group (IEHG) is the largest hospital network in the Republic of Ireland, consisting of 11 hospitals (including large academic centres, community general hospitals and the national maternity hospital). The IEHG serves a population of over 1.1 million individuals. We sought to determine the frequency of admissions to hospital with PE and to assess key outcomes, including length-of-stay (LOS) and in-hospital mortality within this population. Methods Data pertaining to PE diagnosis from January 2018 to December 2020 were obtained from NQAIS Clinical (National Quality Assessment and Improvement System; an electronic reporting tool which is populated with anonymised data extracted from the hospital in-patient enquiry system). This system compiles diagnostic data on all patients by ICD-10 code at the time of discharge. For the purposes of this analysis the ICD-10 codes I26.0 and I26.9 were used to identify patients with PE and only admission episodes where PE was the primary diagnosis were included; cases of 'secondary PE' (historical PE or hospital-acquired) were excluded. Projected population figures, extrapolated from Census 2016 data, were obtained from Health Atlas Ireland (an open-source application providing access to datasets developed by the Health Intelligence Unit of the Health Service Executive of Ireland). Results During the 3-year study period, 958 in-patient episodes occurred where PE was recorded as the primary diagnosis, corresponding to an incidence of 0.37 per 1000 adults per annum (95% CI 0.35 to 0.40). The incidence was highest in the over 85 years age-group (1.07 per 1000 per annum; 95% CI 0.80 to 1.33). PE was more common in women in all age-groups apart from the 46-65 years age group [males: 0.51 (95% CI 0.44-0.51) vs females: 0.36 (95% CI 0.3-0.42) per 1000]. In 82.7% of episodes, the ultimate discharge destination was to home. In 5.3% the discharge destination was a nursing home and 4.6% were transferred to another hospital. The all-cause in-hospital mortality rate was 3.1% (30 fatalities; 18 females, 12 males). Most deaths occurred in the 66-85 years age-group (n=14), with 9 fatalities in the age >85 years group and 7 fatal PE events in the 46-65 years age-group. Average hospital LOS was 7.8 days. 8.9% of inpatient episodes resulted in same-day discharge. In 55.9% of episodes, discharge occurred after day 4. Those discharged to home had an average length of stay of 6.31 days, while patients awaiting nursing home facilities averaged 26.5 days. Conclusion The incidence of acute presentation with PE within this population is consistent with international reports. The rate of in-hospital mortality compares favourably with these international standards. The mortality rate may reflect improvements in PE care but may also reflect the inclusion of a significant number of 'low-risk' individuals in the analysis (many of whom may have been suitable for outpatient management). The mortality rate might also reflect increased detection of small, low-risk distal PE (as a result of advances in diagnostics). In any event, these data suggest that more widespread implementation of outpatient PE management is likely to be feasible and would represent an opportunity for improved resource utilisation. Disclosures Ni Ainle: Leo Pharma: Research Funding; Actelion: Research Funding; Daiichi-Sankyo: Research Funding; Bayer Pharma: Research Funding. Kevane: Leo Pharma: Research Funding.

Introduction Infants born very preterm ( Extracellular vesicles, comprising of lipid-bound nanoparticles released from cells (including platelets), may potentially play a role in modulating neonatal haemostasis. We aimed to characterize phospholipid (PL)-dependent plasma thrombin generation in platelet-rich (PRP) and platelet-poor plasma (PPP) in premature infants in both umbilical cord blood & peripheral neonatal blood using calibrated automated thrombography (CAT). Methods In this prospective observational study, PRP and PPP was prepared by centrifugation from citrated umbilical cord blood and peripheral neonatal blood collected from premature infants (24 - 31 weeks) and healthy term controls (>37 weeks). No samples were collected from heparinised lines. Parameters of plasma thrombin generation in PRP were assessed using CAT, with thrombin generation stimulated by tissue factor only (TF; final concentration 1pM). CAT was also repeated in PPP using only TF and no exogenous PL (rendering the assay dependent upon the endogenous PL content of plasma). Results In the analysis of umbilical cord blood PRP, plasma thrombin generation was accelerated in the preterm infant group with a significantly shorter time to peak TG observed. The other parameters of TG were similar in both groups (Table 1). In the subset of infants from whom peripheral blood samples were available, there was further evidence of enhanced plasma TG in preterm PRP relative to term infants (Table 2). In this subgroup, the lag time and time to peak thrombin were significantly shorter in the preterm group and peak thrombin was significantly higher. TG was also assessed in both PPP and PRP prepared from umbilical cord blood samples in a subgroup of infants (n=10 term, n=6 preterm) using 1pM TF only, rendering the assay dependent on the phospholipid content of plasma. No difference was observed in any CAT parameters, suggesting that neonatal PPP phospholipid content (potentially from circulating extracellular vesicles) is sufficient to support thrombin generation in the absence of exogenous phospholipid. Conclusion These preliminary data suggest that neonatal PRP, measured in both umbilical cord blood and peripheral neonatal blood, has similar thrombin generation or may even be hypercoagulable, compared with healthy term controls. Moreover, neonatal plasma phospholipid appears to support thrombin generation in the absence of exogenous phospholipid. This ongoing prospective study aims to further characterize the platelet-dependency of neonatal thrombin generation and evaluate the potential role of extracellular vesicles in neonatal haemostasis. Figure 1 Figure 1. Disclosures Maguire: Actelion: Research Funding; Bayer Pharma: Research Funding. Ni Ainle: Leo Pharma: Research Funding; Actelion: Research Funding; Daiichi-Sankyo: Research Funding; Bayer Pharma: Research Funding.

Background Hospitalised patients with severe COVID-19 (requiring critical care level support) appear to be at increased risk of thrombosis despite standard pharmacological thromboprophylaxis. The magnitude of thrombotic risk in patients with COVID-19 of moderate severity (not requiring critical care) is less clear. The optimal approach to thromboprophylaxis (and the role of intensified thromboprophylaxis) remains to be determined. Evidence of endothelial dysfunction has been widely reported in COVID-19 (particularly in severe COVID) and this may contribute to hypercoagulability. Aim To assess differences in patterns of hypercoagulability and endothelial dysfunction between a group of patients with moderate COVID-19 and a group of age-matched hospitalized patients (SARS-CoV-2 PCR negative) receiving low molecular weight heparin (LMWH) thromboprophylaxis. Methods Blood was collected from individuals admitted to hospital with COVID-19 of moderate severity (not requiring critical care level support) and a group of age-matched patients admitted with infective/inflammatory illness (SARS-CoV-2 PCR negative). All subjects received standard-dose LMWH thromboprophylaxis, with blood drawn at 12 hours post-dose (and with measurement of anti-FXa activity levels). Circulating levels of endothelial & fibrinolytic markers including ICAM, PAI-1, VCAM, soluble thrombomodulin (sTM), and tissue plasminogen activator (tPA) were determined by ELISA. Thrombin generation (TG) in platelet-poor plasma was assessed by calibrated automated thrombography in the presence of tissue factor (Final concentration, 1pM & 5pM), thrombomodulin (TM) (Final concentration, 6.25nM), and an inhibitory anti-tissue factor pathway inhibitor antibody (anti-TFPI; Final concentration 100μg/mL). Results 14 COVID-19 positive subjects and 11 hospitalized controls were recruited. There were no differences in mean age (69.7±4.5 vs 61.6±4.7 years; p= 0.2) or mean Body mass index (25.7±1.1 vs 22.7±1.2 Kg/m2; p=0.1) between groups. No COVID-19 patient or control required critical care support. In the COVID group, radiological evidence of pneumonitis [diffuse (n=3) or peripheral infiltrates (n=7)] was present in the majority of cases. None of the COVID-19 cases were requiring supplemental oxygen at the time of recruitment. All controls were admitted with either respiratory or urinary infection [radiological evidence of pneumonia in 4/11; supplemental oxygen requirement in 2/11, (28-36% FiO2 via nasal cannula)]. Plasma levels of sTM, ICAM, PAI-1 & VCAM were similar in both groups. Levels of t-PA were significantly higher in the COVID group (8.31±4.35 vs 4.91±2.37 ng/mL; p= 0.005). Despite similar plasma anti-Xa activity in both groups (0.06 vs 0.04 IU/mL; p=0.2), mean endogenous thrombin potential (ETP) was significantly higher in the COVID group (1929±119.7 vs 1528±138.9 nM*min; p=0.02), although peak thrombin was similar (173.6±26 vs 161.5±31nM). ETP-TM ratio was similar between groups (0.3±0.1 vs 0.2±0.1; p=0.3). Despite increased ETP, the lag time to thrombin generation was significantly prolonged in the COVID group (8.3±0.6 vs 5.8±0.5 mins, p= 0.006). This pattern has previously been observed in vascular diseases associated with altered plasma tissue factor pathway inhibitor (TFPI) activity. In the presence of an anti-TFPI antibody, the difference in lagtime between groups was attenuated (4.7±0.2 vs 3.5±0.1 mins; p= 0.002) and the difference in overall thrombin generation (delta TG) between both groups became significantly increased (Fig.1). Conclusion Plasma thrombin generation is enhanced in patients with non-severe COVID-19 despite pharmacological thromboprophylaxis. Endothelial dysfunction is also observed in this group and appears to modulate parameters of plasma thrombin generation. The clinical implications of these observations are not known although clinical studies of intensified thromboprophylaxis in attenuating thrombotic risk and other complications are ongoing. Fig 1. Inhibition of TFPI activity enhances thrombin generation in COVID-19. In the presence of an inhibitory anti-TFPI antibody, peak plasma thrombin generation was enhanced in COVID-19 in contrast to that observed among SARS-CoV-2 PCR negative hospitalised patients (339.6+25.2 vs 247.4+10.1, p=0.01). Figure 1 Figure 1. Disclosures Maguire: Actelion: Research Funding; Bayer Pharma: Research Funding. Ni Ainle: Daiichi-Sankyo: Research Funding; Actelion: Research Funding; Leo Pharma: Research Funding; Bayer Pharma: Research Funding. Kevane: Leo Pharma: Research Funding.

Venous Thromboembolism (VTE) remains a significant cause of morbidity and mortality worldwide. Rivaroxaban, a direct oral factor Xa inhibitor, mediates anti-inflammatory and cardiovascular-protective effects besides its well-established anticoagulant properties, however, these remain poorly characterized. Extracellular vesicles (EVs) are important circulating messengers regulating a myriad of biological and pathological processes and may be highly relevant to the pathophysiology of VTE as they reflect alterations in platelet and endothelial biology. However, the effects of Rivaroxaban on circulating pro-inflammatory EVs in VTE patients remain unknown. We hypothesized that rivaroxaban's anti-inflammatory properties are reflected upon differential molecular profiles of circulating EVs. Single-episode VTE patients anticoagulated with 20 mg Rivaroxaban or warfarin at a target INR of 2.0-3.0, respectively, who had commenced therapy no sooner than 3 months previously were recruited following informed written consent at the Mater Misericordiae University Hospital, Dublin, Ireland. Patient data including age, sex, BMI, prevalent risk factors and comorbidities were collected. Patients on warfarin therapy had a time in therapeutic range of at least 55% and an INR in target range at time of blood sampling. Exclusion criteria included known pro-inflammatory conditions, active malignancy, recurrent VTE, antiphospholipid syndrome, bleeding or platelet function disorders, use of anti-platelet drugs, and thrombocytopenia. To address the hypothesis, we firstly used a combination of Nanoparticle Tracking Analysis (NTA) and flow cytometry to comprehensively characterise differences in the concentration and size of small (0-200 nm) and large (200-1000 nm) circulating EVs, respectively. Statistical analysis revealed a trend towards reduced levels of circulating small and large EVs in Rivaroxaban-treated VTE patients compared with matched warfarin controls. Moreover, small and large EVs measured in the patients plasma correlated strongly and highly significantly (r=0.804, p Collectively, we established that EV proteomic signatures are powerful biological sensors of Rivaroxaban's anti-inflammatory potential. Moreover, Rivaroxaban therapy may ameliorate endothelial dysfunction relative to warfarin. These findings are of translational relevance towards characterizing the anti-inflammatory and cardiovascular-protective mechanisms associated with Rivaroxaban therapy. Disclosures Kevane: Leo Pharma: Research Funding. Murphy: Bayer Pharma: Research Funding. Ni Ainle: Daiichi-Sankyo: Research Funding; Actelion: Research Funding; Leo Pharma: Research Funding; Bayer Pharma: Research Funding. Maguire: Bayer Pharma: Research Funding; Actelion: Research Funding.

Essentials Inhibition of tumor cell trans-endothelial migration inhibits metastasis formation. Low molecular weight heparin (LMWH)-mediated endothelial barrier protection was investigated. LMWH enhanced endothelial barrier activity and attenuated tumor cell transmigration. The cytoprotective activity of LMWH did not appear to be dependent on anticoagulant activity. Background One of the key events in the progression of cancer metastasis is the trans-endothelial migration of circulating tumor cells. Moreover, inhibition of tumor-induced vascular permeability has been shown to inhibit metastasis in vivo. Low molecular weight heparin (LMWH) appears to confer a survival benefit in cancer but the underlying mechanisms are poorly understood. Objective To characterise LMWH-mediated endothelial barrier protection and to explore strategies to limit the LMWH-associated haemorrhagic risk in this setting. Methods Endothelial barrier function was assessed using in vitro assays of endothelial permeability and tumor cell trans-endothelial migration. Thrombin-mediated activation of PAR-1 signalling was assessed by flow cytometry and western blotting. LMWH anticoagulant activity was assessed by calibrated automated thrombography and plasma anti-factor Xa activity assay. Results LMWH tinzaparin enhanced endothelial barrier function and reduced tumor cell trans-endothelial migration (73.9±5.7% of baseline; P

Background Ambulatory management of isolated acute deep venous thrombosis (DVT) is the recommended standard of care in selected populations. However, in practice a significant number of patients continue to be managed as in-patients. Objectives In this study we aimed to evaluate acute DVT treatment pathways in our emergency department (ED) in practice and to identify barriers to outpatient management. Methods This study was a cross-sectional analysis of prospectively collected data pertaining to consecutive patients presenting to the ED of a large, city center, academic teaching hospital over a 46 week period who were diagnosed with DVT. Results Implementation of an outpatient care pathway led to the majority of patients presenting with DVT in our institution being treated without hospital admission. Forty percent (31/78) of patients with DVT were treated with a direct oral anticoagulant (DOAC) as an outpatient in line with international best practice guidelines. Conclusion The study provides a clear picture of the clinical profile and management of patients in clinical practice. Due to the lack of resources and supported infrastructure it is difficult to effectively implement outpatient venous thromboembolism (VTE) management to its full potential. Directing resources towards strategies which facilitate outpatient DVT treatment among vulnerable patient groups could represent a means of reducing hospital admissions for DVT in urban centers. Our study highlights the success and clinical limitations of the outpatient treatment model, which should become standard as part of wider VTE care.

ObjectivesTo determine the incidence of venous thromboembolism (VTE) and the incidence of hospital-acquired VTE (HA-VTE) arising within the population served by the Ireland East Hospital Group (IEHG).Design/home/user/Documents/Sathish Kumar G/RFO/June/21-06-2019/bmjopen_iss_9_7_20190621_1/ A retrospective observational study was conducted using hospital discharge data obtained from the hospital inpatient enquiry data reporting system. In this system, VTE events recorded as ‘primary diagnosis’ represented the reason for initial hospital admission, whereas VTE recorded as a ‘secondary diagnosis’ occurred following admission and were therefore used as an approximation of HA-VTE. These data were used to estimate the overall incidence of VTE and the proportion of these events which were hospital-acquired.SettingThe IEHG is the largest hospital group in the Irish healthcare system and serves a population of over 1 million individuals.ParticipantsData were generated from records pertaining to the 2727 patient admission episodes where a diagnosis of VTE was made during the 22-month study period.ResultsDuring the study period, 2727 VTE events were recorded within the IEHG (which serves a population of 1 036 279) corresponding to an incidence of 1.44 (95% CI 1.36 to 1.51) per 1000 per annum. 1273 (47%) of VTE events were recorded as secondary VTE. The incidence of VTE was highest among individuals over 85 years of age (16.03 per 1000;95% CI 12.81 to 19.26) and was more common following emergency hospital admission.ConclusionThese data suggest that HA-VTE accounts for at least 47% of all VTE events arising within a hospital group serving a population of over 1 million individuals within the Ireland. Given that HA-VTE is a well-recognised source of (potentially preventable) hospital deaths, these findings provide a compelling argument for prioritising strategies directed at reducing the risk of VTE among hospital patients served by the IEHG and within the Ireland as a whole.

Objective ; Early-onset preeclampsia is a rare pregnancy-specific disorder associated with significantly increased maternal and fetal morbidity and mortality. Whilst it is known that even normotensive pregnancies are associated with changes in clot formation and dissolution, the nature of how these changes differ in those with early onset preeclampsia has not been well established. We sought to evaluate parameters of fibrin formation and fibrinolysis in individuals with early onset preeclampsia in comparison to both pregnant and non-pregnant controls. Furthermore, such parameters were correlated with markers of disease severity in this patient cohort, including the presence of multiorgan involvement, the rate of disease progression and the extent of the anti-angiogenic state in this condition. Study design ; Patients with early onset preeclampsia (N = 20) and both pregnant (N = 16) and non -pregnant (N = 16) controls were recruited from the cohort at a large urban maternity hospital which saw over 15,000 deliveries during the study period. Platelet poor plasma was prepared from collected whole blood and analysed for parameters of fibrin formation and fibrinolysis (lagtime to and rate of fibrin formation; PAI-1; PAI-2; D-dimer; plasmin-antiplasmin; tPA) in addition to markers of angiogenesis (sFLT-1; Endoglin) using commercially available specific immunoassays. Results ; The maximum rate of fibrin formation as well as PAI-1, PAI-2 and D-dimer levels were all significantly increased in those with early onset preeclampsia and pregnant controls when compared to non-pregnant controls without significant differences between the 2 former groups. Plasmin-antiplasmin levels were significantly reduced in a similar manner. tPA levels were significantly elevated in EOP compared to both pregnant and non-pregnant controls. EOP was associated with significantly increased anti-angiogenic factors (sFLT-1; Endoglin) when compared to both pregnant and non-pregnant controls. Conclusion ; Markers of fibrin formation and fibrinolysis are significantly alerted in early onset preeclampsia; furthermore, certain markers correlate with disease severity in this patient cohort.

Venous thromboembolism (VTE) remains a leading cause of maternal morbidity and mortality in the developed world. Low molecular weight heparins (LMWH) are routinely used to provide therapeutic anticoagulation during pregnancy for women with VTE, with measurement of plasma anti-FXa activity used to guide dosing in certain patient groups. There is limited evidence to support the use of anti-FXa monitoring in pregnant patients. This study seeks to ascertain whether anti-FXa monitoring of pregnant patients with VTE influences patient outcomes. We performed a single-centre case series including two consecutive groups of pregnant patients treated with LMWH for VTE sustained in the index pregnancy with and without monitoring of anti-FXa levels. 35,394 patients delivered during the study period in a large urban stand-alone maternity hospital, with 26 cases of VTE eligible for inclusion. There was no significant difference between the two groups in any clinical outcome; including maternal blood loss at delivery, recurrent thromboembolic events or rates of planned delivery. These data provide clinical evidence to support current international guideline recommendations that measurement of plasma anti-FXa activity in the majority of patients receiving therapeutic-intensity antenatal LMWH is not warranted.

In this prospective review of cancer screening in unselected patients with unprovoked venous thromboembolism (VTE) presenting to a large teaching hospital in the Republic of Ireland, we aimed to determine the effects of the implementation of the National Institute for Health and Care Excellence screening policy in a “real-world” population. Within our institution, 64 individuals presented with unprovoked VTE during the study period, of whom 47 underwent a screening computed tomography (CT) scan. Two cases of previously undiagnosed cancer were identified. However, in both cases, the clinical history provided by the affected individuals would have prompted a CT scan regardless of the recommendations of the screening policy. The screening CT scans identified 18 incidental lesions within the cohort, which required further diagnostic studies. None of the additional investigations completed to date have detected any lesion of clinical significance. These findings support the view that cancer screening with CT imaging in unselected individuals with unprovoked VTE is not justified or cost-effective.

Cirrhosis is a consequence of prolonged liver injury and is characterised by extensive tissue fibrosis: the deposition of collagen-rich extracellular matrix. The haemostatic balance is disordered in cirrhosis and coagulation activation appears to promote fibrosis. In spite of recent studies demonstrating a role for anticoagulant therapy in preventing cirrhosis progression, there has not been a change in clinical practice, suggesting that physicians are reluctant to anticoagulate patients with cirrhosis due to bleeding risks. Platelets play an important role in facilitating coagulation. Glycoprotein VI (GPVI) is a platelet-specific collagen receptor that is shed from the platelet surface in a metalloproteinase-dependent manner in response to GPVI ligation and coagulation activation. Our aim was to use soluble GPVI levels to determine whether there was evidence for collagen and coagulation-induced platelet activation in early, well-compensated cirrhosis. Plasma soluble GPVI levels were quantified in 46 patients with mixed aetiology cirrhosis and 55 healthy controls using an immunoassay. In the cirrhosis group, soluble GPVI levels were significantly increased (5.8 ± 4.4 ng/ml, n = 46) compared to healthy controls (3.3 ± 3.4 ng/ml, n = 55, p

The etiology of the prothrombotic state in myeloma has yet to be definitively characterized. Similarly, while recent evidence suggests that patients with monoclonal gammopathy of undetermined significance (MGUS) may also be at increased risk of thrombosis, the magnitude and the etiology of this risk have also yet to be defined. The present study aims to characterize patterns of plasma thrombin generation and sensitivity to the anticoagulant activity of activated protein C (APC) at the time of initial diagnosis of myeloma and in response to therapy in comparison to that observed among patients with MGUS and matched, healthy volunteers. Patients presenting with newly diagnosed/newly relapsed myeloma (n = 8), MGUS (n = 8), and matched healthy volunteers (n = 8) were recruited. Plasma thrombin generation was determined by calibrated automated thrombography. Peak thrombin generation was significantly higher in patients with myeloma (383.4 ± 33.4 nmol/L) and MGUS (353.4 ± 16.5 nmol/L) compared to healthy volunteers (276.7 ± 20.8 nmol/L; P < .05). In the presence of APC, endogenous thrombin potential was significantly lower in control plasma (228.6 ± 44.5 nmol/L × min) than in either myeloma (866.2 ± 241.3 nmol/L × min, P = .01) or MGUS plasma (627 ± 91.5 nmol/L × min, P = .003). Within the myeloma cohort, peak thrombin generation was significantly higher at diagnosis (353.2 ± 15.9 nmol/L) than following completion of the third cycle of therapy (282.1 ± 15.2 nmol/L; P < .005). Moreover, sensitivity to APC increased progressively with each cycle of chemotherapy. Further study of the etiology and evolving patterns of hypercoagulability among patients with these conditions is warranted and may have future implications for thromboprophylaxis strategies.

Summary Background Very premature infants are at high risk of bleeding complications; however, few data exist on ranges for standard coagulation tests. Objectives The primary objective of this study was to measure standard plasma coagulation tests and thrombin generation in very premature infants compared with term infants. The secondary objective was to evaluate whether an association existed between coagulation indices and intraventricular hemorrhage (IVH). Patients/Methods Cord and peripheral blood of neonates < 30 weeks gestational age (GA) was drawn at birth, on days 1 and 3 and fortnightly until 30 weeks corrected gestational age. Prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen and coagulation factor levels were measured and tissue factor-stimulated thrombin generation was characterized. Control plasma was obtained from cord blood of term neonates. Results One hundred and sixteen infants were recruited. Median (range) GA was 27.7 (23.7–29.9) weeks and mean (SD) birth weight was 1020 (255) g. Median (5th–95th percentile) day 1 PT, APTT and fibrinogen were 17.5 (12.7–26.6) s, 78.7 (48.7–134.3) s and 1.4 (0.72–3.8) g L−1, respectively. No difference in endogenous thrombin potential between preterm and term plasma was observed, where samples were available. Levels of coagulation factors II, VII, IX and X, protein C, protein S and antithrombin were reduced in preterm compared with term plasma. Day 1 APTT and PT were not associated with IVH. Conclusion In the largest cross-sectional study to date of very preterm infants, typical ranges for standard coagulation tests were determined. Despite long clotting times, thrombin generation was observed to be similar in very preterm and term infants.

Essentials Eisenmenger syndrome is characterised by thrombotic and hemorrhagic risks of unclear aetiology. Calibrated automated thrombography was used to assess these coagulation derangements. Platelet activity supported abnormalities in procoagulant and anticoagulant pathway function. Endothelin-1 antagonism appeared to ameliorate these derangements. Summary Aims The mechanisms underlying the competing thrombotic and hemorrhagic risks in Eisenmenger syndrome are poorly understood. We aimed to characterize derangements of blood coagulation and to assess the effect of dual endothelin-1 receptor antagonism in modulating hemostasis in this rare disorder. Methods In a 10-month recruitment period at a tertiary cardiology referral center, during which time there were over 14 000 outpatient consultations, consecutive subjects with Eisenmenger syndrome being considered for macitentan therapy (n = 9) and healthy volunteers (n = 9) were recruited. Plasma thrombin generation in platelet-rich and platelet-poor plasma was assessed by calibrated automated thrombography prior to and following therapy. Results Median peak plasma thrombin generation was higher in platelet-rich plasma obtained from Eisenmenger syndrome subjects relative to controls (median peak thrombin [25th-75th percentile]: 228.3 [206.5-258.6] nm vs. 169.9 [164.3-215.8] nm), suggesting a critical mechanistic role for platelets in supporting abnormal hypercoagulability in Eisenmenger syndrome. Abnormal enhanced sensitivity to the anticoagulant activity of activated protein C was also observed in platelet-rich plasma in Eisenmenger syndrome, suggesting that derangements of platelet activity may influence the activity of anticoagulant pathways in a manner that might promote bleeding in this disease state. Following 6 months of macitentan therapy, attenuations in the derangements in both procoagulant and anticoagulant pathways were observed. Conclusions Abnormal platelet activity contributes to derangements in procoagulant and anticoagulant pathways in Eisenmenger syndrome. Therapies targeting the underlying vascular pathology appear to ameliorate these derangements and may represent a novel strategy for the management of the competing prothrombotic and hemorrhagic tendencies in this disorder.

Objective: To characterise Mean platelet volume (MPV) in patients with early onset preeclampsia (EOPE) and unaffected controls from time of first antenatal visit until the postpartum. Materials and methods: Retrospective secondary analysis of an observational study in an Irish tertiary referral centre with 9000 deliveries annually. The MPV of 27 women with EOPE was compared to 19 unaffected controls. The inclusion criteria for the disease state was the development of EOPE defined by the National Institute for Health and Care Excellence (NICE) guideline, as new onset hypertension presenting after 20 weeks and prior to 34 weeks with significant proteinuria. Between October 2013 and July 2015 we recruited 27 women with EOPE and 19 pregnant controls. Statistical analysis was performed using paired T-test of Mann-Whitney test where appropriate and a P-value Results: At time of diagnosis and late in the third trimester MPV was significantly increased to 9.0 (±0.3) fL in cases of EOPE in comparison to 8.5 (±0.6) fL in normotensive controls (P Conclusion: Despite an increased MPV at time of diagnosis of EOPE this study did not demonstrate a potential use for increased MPV as a first trimester screening tool.

Background: beta-thromboglobulins are derived from the cleavage of the CXC chemokine platelet basic protein and are released in high concentrations by activated platelets. Platelet-derived beta-thromboglobulins (beta TG) share 70% homology with platelet factor 4 (PF4), another CXC chemokine released by activated platelets. PF4 modulates coagulation by inhibiting heparin-antithrombin interactions, promoting protein C activation, and attenuating the activity of activated protein C. In contrast, the effect of beta TG on coagulation is unknown.Aim/Methods: Clotting times, thrombin generation, chromogenic clotting factor assays, and surface plasmon resonance (SPR) were used to assess the effect of purified beta TG on coagulation.Results: In normal pooled plasma, beta TG shortened the lagtime and time to peak thrombin generation of tissue factor (TF)-dependent and TF-independent thrombin generation. In factor VIII and factor IX-deficient plasmas, beta TG induced thrombin generation in the absence of a TF stimulus and in the presence of anti-TF and factor VIIa inhibitory antibodies. The procoagulant effect was not observed when thrombin generation was independent of factor X activation (supplementation of factor X-deficient plasma with factor Xa). Cleavage of a factor Xa-specific chromogenic substrate was observed when beta TG was incubated with factor X, suggesting a direct interaction between beta TG and factor X. Using SPR, beta TG were found to bind to immobilised factor X in a dose dependent manner.Conclusion: beta TG modulate coagulation in vitro via an interaction with factor X. (C) 2017 Elsevier Ltd. All rights reserved.

Background: Pregnant patients with cardiac disease have significantly higher predicted maternal morbidity and mortality compared to the general obstetric population. Published guidelines on optimal management of these patients recommend multidisciplinary care provision. There are few published data on the incidence of haematological complications in pregnant women with cardiac disease, although the data that does exist suggests a relatively high rate of bleeding and thrombotic events. Aims: To determine the outcomes in terms of haematological morbidity occurring within a cohort of pregnant women with cardiac disease in the setting of multidisciplinary care provision. Methods: Patients were identified from a database compiled by the obstetric cardiology service listing all cardiac patients managed in the Rotunda maternity hospital during the period from 2004 to 2011. Data were obtained from the medical and obstetric case notes relating to details of perinatal care and the occurrence of antenatal and postnatal complications. Results: During the 8-year review period, 451 women with cardiac disease were assessed. Fifty-nine were determined to have moderate to high-risk disease. Each received consultant-delivered multidisciplinary care, where written management strategies were agreed by collaborating senior colleagues either preconceptually or in early pregnancy. No venous thromboembolic events occurred and a modest rate of post-partum haemorrhage (approximately 5%) was recorded. There were no maternal deaths. Conclusion: The relatively favourable outcomes observed within our institution highlight the importance of a multidisciplinary approach to the management of pregnant women with cardiac disease, particularly in scenarios where limited published evidence exists to guide management.