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The postthrombotic syndrome (PTS) is chronic venous insufficiency secondary to a prior deep vein thrombosis (DVT). It is the most common complication of venous thromboembolism (VTE) and, while not fatal, it can lead to chronic, unremitting symptoms as well as societal and economic consequences. The cornerstone of PTS treatment lies in its prevention after DVT. Specific PTS preventative measures include the use of elastic compression stockings and pharmacomechanical catheter-directed thrombolysis. However, the efficacy of these treatments has been questioned by large randomized controlled trials (RCTs). So far, anticoagulation, primarily prescribed to prevent DVT extension and recurrence, appears to be the only unquestionably effective treatment for the prevention of PTS. In this literature review we present pathophysiological, biological, radiological, and clinical data supporting the efficacy of anticoagulants to prevent PTS and the possible differential efficacy among available classes of anticoagulants (vitamin K antagonists [VKAs], low molecular weight heparins [LMWHs] and direct oral anticoagulants [DOACs]). Data suggest that LMWHs and DOACs are superior to VKAs, but no head-to-head comparison is available between DOACs and LMWHs. Owing to their potentially greater anti-inflammatory properties, LMWHs could be superior to DOACs. This finding may be of interest particularly in patients with extensive DVT at high risk of moderate to severe PTS, but needs to be confirmed by a dedicated RCT.

ARTS will be the first trial to compare anticoagulation with a direct oral anticoagulant (apixaban) versus no anticoagulation among patients undergoing intra-abdominal, gynecologic, or urologic surgery at sufficiently similar risk of deep vein thrombosis or pulmonary embolism and major bleeding.

Background Multimerin 1 (human: MMRN1, mouse: Mmrn1) is a homopolymeric, adhesive, platelet and endothelial protein that binds to von Willebrand factor and enhances platelet adhesion to fibrillar collagen ex vivo. Objectives To examine the impact of Mmrn1 deficiency on platelet adhesive function, and the molecular motifs in fibrillar collagen that bind MMRN1 to enhance platelet adhesion. Methods Mmrn1‐deficient mice were generated and assessed for altered platelet adhesive function. Collagen Toolkit peptides, and other triple‐helical collagen peptides, were used to identify multimerin 1 binding motifs and their contribution to platelet adhesion. Results MMRN1 bound to conserved GPAGPOGPX sequences in collagens I, II, and III (including GPAGPOGPI, GPAGPOGPV, and GPAGPOGPQ) that enhanced activated human platelet adhesion to collagen synergistically with other triple‐helical collagen peptides (P

Due to lack of data, direct oral anticoagulants are not considered by guidelines for venous thromboembolism (VTE) prophylaxis after cancer surgery. Adherence to low-molecular-weight heparin injections in this setting is sometimes poor.Analysis of adherence to oral apixaban for extended thromboprophylaxis.Consecutive patients discharged after major surgery for abdominal/pelvic cancer and considered eligible for extended prophylaxis were offered apixaban 2.5 mg twice daily. Primary outcomes were adherence metrics-proportion of prescriptions filled, persistence (not prematurely discontinued), proportion of days covered (PDC) based on apixaban pill counts, and modified Morisky medication adherence scale at Days 28-30. Secondary outcomes were bleeding, VTE, and serious adverse events until Day 90.We included 53 patients, 51 were analyzed. Of 45 patients with prescriptions all had it filled (95% confidence interval [CI], 92%-100%). Persistence was 98% (95% CI, 90%-100%). PDC was ≥80% for 48 patients (94%; 95% CI, 84%-99%). We found good adherence (0/6 answers "yes") in 75% and moderate (1/6 answers "yes") in 25%. No major bleed or VTE occurred while on apixaban.Our results support good adherence with apixaban for VTE prophylaxis up to 28 days after major abdominal or pelvic cancer surgery.

Background Surgical bleeding is associated with postoperative cardiovascular complications. The efficacy and safety of tranexamic acid (TXA) in noncardiac surgery are still uncertain. Statins may prevent perioperative cardiovascular complications. We conducted a pilot to assess the feasibility of a perioperative trial of TXA and rosuvastatin. Methods Using a factorial design, we randomized patients at cardiovascular risk undergoing noncardiac surgery to intravenous TXA (1 g at the start and end of surgery) or placebo, and oral rosuvastatin (40 mg before and 20 mg daily for 30 days after surgery) or placebo. Feasibility outcomes included recruitment rates, follow-up, and compliance to interventions. Clinical outcomes were secondarily explored. Results After 3 months, we changed the design to a partial factorial due to the difficult recruitment of statin-naive patients. Over 6 months, 100 patients were randomized in the TXA trial (49 TXA, 51 placebo), 34 in the rosuvastatin trial (18 rosuvastatin, 16 placebo). Ninety-two percent (95% CI 80–98) of TXA and 86% (95% CI 74–94) of TXA-placebo patients received the 2 study doses. Thirty-three percent (95% CI 13–59) of rosuvastatin patients and 37% (95% CI 15–65) of rosuvastatin-placebo patients discontinued the study drug. A major cardiovascular complication occurred at 30 days in 1 TXA and 6 TXA-placebo patients, and 1 rosuvastatin and no rosuvastatin-placebo patients. Conclusions Our pilot study supports the feasibility of a perioperative TXA trial in noncardiac surgery. Feasibility of a perioperative rosuvastatin trial is uncertain because of a high prevalence of statin use in the target population and concerns about compliance. Trial registration ClinicalTrials.govNCT02546648.

Background: Cancer is an important yet understudied risk factor for ischemic stroke. We sought to examine the relationship between previous stroke and risk for future stroke in individuals newly diagnosed with cancer. Methods: Using a provincial administrative database, we conducted a population-based matched cohort study of adults in Ontario, Canada, from 2010-2019. Individuals with a new diagnosis of cancer and a history of ischemic stroke were matched (1:4) by age, sex, year of cancer diagnosis, cancer stage, and cancer site to cancer patients without a history of stroke. The cohort was followed until death, stroke, or March 31, 2020, whichever occurred first. Cumulative incidence function (CIF) curves were created for the incidence of stroke (primary outcome), with the date of cancer diagnosis as the index date. Sub-distribution adjusted hazard ratios (aHR) and 95% confidence intervals (CI) were calculated, where death was treated as a competing event. We further stratified those with a history of stroke by the timing of their most recent stroke: 0-1 years, 1-2 years, 2-5 years, or 5-10 years. Regression analyses were adjusted for baseline characteristics. Results: We examined 65,525 individuals with a new diagnosis of cancer, including 13,105 with a history of ischemic stroke and 52,420 without; the incidence of stroke outcome following cancer diagnosis was 5.5% and 1.8%, respectively. Cancer patients with a history of previous stroke had an increased risk for stroke after cancer diagnosis compared to those without a history of stroke (aHR 2.70 95%CI [2.42-3.00]). Individuals with stroke within the preceding 1 year of the cancer diagnosis had the highest risk of recurrent stroke with aHR 3.64 (95%CI 3.17-4.17). Conclusion: Individuals who have a history of stroke prior to a diagnosis of cancer were more likely to suffer stroke after cancer diagnosis, especially if that stroke had occurred within the year preceding the cancer diagnosis. This finding has potentially important implications for advancing strategies to prevent stroke in patients with cancer.

BACKGROUND Perioperative bleeding is common in patients undergoing noncardiac surgery. Tranexamic acid is an antifibrinolytic drug that may safely decrease such bleeding. METHODS We conducted a trial involving patients undergoing noncardiac surgery. Patients were randomly assigned to receive tranexamic acid (1-g intravenous bolus) or placebo at the start and end of surgery (reported here) and, with the use of a partial factorial design, a hypotension-avoidance or hypertension-avoidance strategy (not reported here). The primary efficacy outcome was life-threatening bleeding, major bleeding, or bleeding into a critical organ (composite bleeding outcome) at 30 days. The pri- mary safety outcome was myocardial injury after noncardiac surgery, nonhemor- rhagic stroke, peripheral arterial thrombosis, or symptomatic proximal venous thromboembolism (composite cardiovascular outcome) at 30 days. To establish the noninferiority of tranexamic acid to placebo for the composite cardiovascular out- come, the upper boundary of the one-sided 97.5% confidence interval for the hazard ratio had to be below 1.125, and the one-sided P value had to be less than 0.025. RESULTS A total of 9535 patients underwent randomization. A composite bleeding outcome event occurred in 433 of 4757 patients (9.1%) in the tranexamic acid group and in 561 of 4778 patients (11.7%) in the placebo group (hazard ratio, 0.76; 95% confi- dence interval [CI], 0.67 to 0.87; absolute difference, −2.6 percentage points; 95% CI, −3.8 to −1.4; two-sided P

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with coagulopathic bleeding. Impaired thrombin generation may be an important cause of coagulopathic bleeding but is poorly measured by existing hemostatic assays. We examined thrombin generation during cardiac surgery, using calibrated automated thrombography, and its association with bleeding outcomes.We conducted a prospective observational study in 100 patients undergoing cardiac surgery with CPB. Calibrated automated thrombography parameters were expressed as a ratio of post-CPB values divided by pre-CPB values. The association of thrombin generation parameters for bleeding outcomes was compared with conventional tests of hemostasis, and the outcomes of patients with the most severe post-CPB impairment in thrombin generation (≥ 80% drop from baseline) were compared with the rest of the cohort.All 100 patients were included in the final analysis, with a mean age of 63 (12) yr, 31 (31%) female, and 94 (94%) undergoing bypass and/or valve surgery. Post-CPB, peak thrombin decreased by a median of 73% (interquartile range [IQR], 49-91%) (P0.001) and total thrombin generation, expressed as the endogenous thrombin potential (ETP), decreased 56% [IQR, 30-83%] (P0.001). In patients with ≥ 80% decrease in ETP, 21% required re-exploration for bleeding compared with 7% in the rest of the cohort (P = 0.04), and 48% required medical or surgical treatment for hemostasis compared with 27% in the rest of the cohort (P = 0.04).Thrombin generation is significantly impaired by CPB and associated with higher bleeding severity. Clinical studies aimed at the identification and treatment of patients with impaired thrombin generation are warranted.RéSUMé: CONTEXTE: La chirurgie cardiaque avec circulation extracorporelle (CEC) est associée à des saignements sur coagulopathie. L’altération de la génération de thrombine peut constituer une cause importante de saignement sur coagulopathie, mais elle est mal mesurée par les tests d’hémostase existants. Nous avons examiné la génération de thrombine pendant la chirurgie cardiaque à l’aide d’une thrombographie automatisée calibrée ainsi que son association avec les issues hémorragiques. MéTHODE: Nous avons réalisé une étude observationnelle prospective portant sur 100 patients bénéficiant d’une chirurgie cardiaque sous CEC. Les paramètres de thrombographie automatisée calibrée ont été exprimés sous forme du rapport entre les valeurs post-CEC divisées par les valeurs pré-CEC. L’association des paramètres de génération de thrombine pour les issues hémorragiques a été comparée aux tests conventionnels de l’hémostase, et les issues des patients présentant l’altération post-CEC la plus prononcée dans la génération de thrombine (baisse ≥ 80 % par rapport aux valeurs de base) ont été comparées au reste de la cohorte. RéSULTATS: Les 100 patients ont tous été inclus dans l’analyse finale, avec un âge moyen de 63 (12) ans, 31 (31 %) femmes et 94 (94 %) subissant une chirurgie de pontage et / ou une chirurgie valvulaire. Après la CEC, le pic de thrombine a diminué d’une médiane de 73 % (écart interquartile [ÉIQ], 49 à 91 %) (P0,001) et la génération de thrombine totale, exprimée en potentiel de thrombine endogène (PTE), a diminué de 56 % [ÉIQ, 30–83 %] (P0,001). Chez les patients présentant une diminution ≥ 80 % du PTE, 21 % ont nécessité une nouvelle exploration pour dépister les saignements, comparativement à 7 % dans le reste de la cohorte (P = 0,04), et 48 % ont nécessité un traitement médical ou chirurgical pour l’hémostase, comparativement à 27 % dans le reste de la cohorte (P = 0,04). CONCLUSION: La génération de thrombine est significativement altérée par la CEC et associée à des saignements plus graves. Des études cliniques visant à identifier et à traiter les patients présentant une altération de la génération de thrombine sont recommandées.

Aim Patients with inflammatory bowel disease (IBD) are at increased risk of postoperative venous thromboembolism (VTE) following major abdominal surgery. The pathogenesis is multifactorial and not fully understood. A combination of pathophysiology, patient and surgical risk factors increase the risk of postoperative VTE in these patients. Despite being at increased risk, IBD patients are not regularly prescribed extended pharmacological thromboprophylaxis following colorectal surgery. Currently, there is a paucity of evidence-based guidelines. Thus, the aim of this review is to evaluate the role of extended pharmacological thromboprophylaxis in IBD patients undergoing colorectal surgery. Method A search of Ovid Medline, EMBASE and PubMed databases was performed. A qualitative analysis was performed using 10 clinical questions developed by colorectal surgeons and a thrombosis haematologist. The Newcastle-Ottawa Scale was utilized to assess the quality of evidence. Results A total of 1229 studies were identified, 38 of which met the final inclusion criteria (37 retrospective, one case-control). Rates of postoperative VTE ranged between 0.6% and 8.9%. Patient-specific risk factors for postoperative VTE included ulcerative colitis, increased age and obesity. Surgery-specific risk factors for postoperative VTE included open surgery, emergent surgery and ileostomy creation. Patients with IBD were more frequently at increased risk in the included studies for postoperative VTE than patients with colorectal cancer. The risk of bias assessment demonstrated low risk of bias in patient selection and comparability, with variable risk of bias in reported outcomes. Conclusion There is a lack of evidence regarding the use of extended pharmacological thromboprophylaxis in patients with IBD following colorectal surgery. As these patients are at heightened risk of postoperative VTE, future study and consideration of the use of extended pharmacological thromboprophylaxis is warranted.

Background Deep vein thrombosis (DVT) can lead to pulmonary embolism (PE), but the mechanisms responsible for this progression are unknown. Previously, we showed that inhibition of thrombin-mediated activation of factor (F) XIII promotes venous thrombus stability in a murine model. Aim In this study, we investigate the consequence of attenuating fibrinolysis, using FXIII, α2-antiplasmin (α2-AP) or ε-aminocaproic acid (EACA) supplementation, on clot lysis and venous thrombus stability using the same mouse model. Methods In vitro plasma clot lysis assay shows that EACA and α2-AP but not FXIII, inhibit fibrinolysis. Ferric chloride induced thrombi in the femoral vein of mice. After thrombus formation, mice received saline, EACA, α2-AP or FXIII, with or without dalteparin or dabigatran. Thrombus sizes and embolization over 2 hours were visualized using intravital videomicroscopy. Lungs were sectioned to quantify emboli presence via histology. Results The change in thrombus size over time was significantly greater after EACA treatment, but not FXIII or α2-AP supplementation, compared with saline. α2-AP-supplementation did not alter thrombus stability. Thrombi were more stable following EACA treatment and FXIII supplementation as evidenced by less embolic events and PE burden, even when they were anticoagulated with either dalteparin or dabigatran. Conclusion FXIII supplementation stabilized venous thrombi, even in the presence of anticoagulants, and did not alter thrombus size. Supplemental FXIII may be useful to stabilize DVT and be an alternative adjunctive treatment to minimize PE, even when anticoagulants are used.

Background Tolvaptan is the only approved drug for the treatment of autosomal dominant polycystic kidney disease (ADPKD) and causes significant polyuria with secondary polydipsia. Up to now, there is no study that examines tolvaptan adherence and satisfaction with information about tolvaptan in ADPKD patients on tolvaptan long-term therapy. Methods This non-interventional study includes 12 ADPKD patients that were formerly enrolled in the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes trial (TEMPO 3:4), in the subsequent extension trial (TEMPO 4:4) and have continued to use tolvaptan thereafter. Data were collected via questionnaires on patients’ self-reported adherence (MARS-D: Medication Adherence Report Scale - German version) and satisfaction with the information received about tolvaptan (SIMS-D: Satisfaction with Information about Medicines Scale - German version). In addition, serum creatinine levels and clinical data were collected. Results The duration of tolvaptan treatment amounted to 10.2 ± 0.3 years at a daily dosage of 90.0 ± 28.6 mg. The evaluation of MARS-D demonstrated strong adherence to tolvaptan (range of possible score: 5–25; median: 23.5; range of individual results: 5). The analysis of SIMS-D showed a high level of satisfaction with the information received about the action and usage of tolvaptan (SIMS-D AU subscore; range of possible score: 0–9; median: 9, range of individual results: 1), but also revealed clearly measureable dissatisfaction regarding the information received about potential problems of tolvaptan in 42 % of the patients (SIMS-D PP subscore; range of possible score: 0–8; median: 8, range of individual results: 6). During treatment with tolvaptan, the mean eGFR decreased from 78.8 ± 15.9 ml/min/1.73 m2 to 48.3 ± 19.4 ml/min/1.73 m2 (P

Background Direct oral anticoagulants (DOACs) are prescribed for over 80% of patients who start anticoagulant therapy for a new diagnosis of atrial fibrillation (AF). Inappropriate DOAC prescriptions are associated with increased mortality. However, limited data exist as to what proportion of primary care physicians (PCPs) initiate anticoagulation in patients with new AF and the extent of their DOAC knowledge. Material and methods We conducted a telephone survey of randomly selected PCPs in Ontario, Canada. Our primary objective was to determine the percentage of PCPs who initiate anticoagulation in new AF patients and the proportion of patients they initiate on DOACs. Our secondary objectives were to assess PCPs' knowledge about DOACs and to identify educational opportunities to address any knowledge gaps. Results Our survey included 50 respondents. After making a new AF diagnosis, 66% of PCPs stated that they usually initiate anticoagulation themselves and 84% prescribed a DOAC at least 75% of the time. Potential DOAC knowledge gaps included: administration considerations, off-label dosing, concomitant use of acetylsalicylic acid (ASA) in stable coronary artery disease (CAD) and use in valvular AF. Conclusion Most PCPs initiate anticoagulants for AF and prescribe DOACs for the vast majority of new patients. PCPs were well versed in certain aspects of DOAC prescribing, however, a number of knowledge gaps were identified. PCPs may benefit from targeted education in these areas to improve patient outcomes in AF.

Statins, a family of FDA-approved cholesterol-lowering drugs that inhibit the rate-limiting enzyme of the mevalonate metabolic pathway, have demonstrated anticancer activity. Evidence shows that dipyridamole potentiates statin-induced cancer cell death by blocking a restorative feedback loop triggered by statin treatment. Leveraging this knowledge, we develop an integrative pharmacogenomics pipeline to identify compounds similar to dipyridamole at the level of drug structure, cell sensitivity and molecular perturbation. To overcome the complex polypharmacology of dipyridamole, we focus our pharmacogenomics pipeline on mevalonate pathway genes, which we name mevalonate drug-network fusion (MVA-DNF). We validate top-ranked compounds, nelfinavir and honokiol, and identify that low expression of the canonical epithelial cell marker, E-cadherin, is associated with statin-compound synergy. Analysis of remaining prioritized hits led to the validation of additional compounds, clotrimazole and vemurafenib. Thus, our computational pharmacogenomic approach identifies actionable compounds with pathway-specific activities.

Background: Mortality from COVID-19 is high among hospitalized patients and effective therapeutics are lacking. Hypercoagulability, thrombosis and hyperinflammation occur in COVID-19 and may contribute to severe complications. Therapeutic anticoagulation may improve clinical outcomes through anti-thrombotic, anti-inflammatory and anti-viral mechanisms. Our primary objective is to evaluate whether therapeutic-dose anticoagulation with low-molecular-weight heparin or unfractionated heparin prevents mechanical ventilation and/or death in patients hospitalized with COVID-19 compared to usual care. Methods: An international, open-label, adaptive randomized controlled trial. Using a Bayesian framework, the trial will declare results as soon as pre-specified posterior probabilities for superiority, futility, or harm are reached. The trial uses response-adaptive randomization to maximize the probability that patients will receive the more beneficial treatment approach, as treatment effect information accumulates within the trial. By leveraging a common data safety monitoring board and pooling data with a second similar international Bayesian adaptive trial (REMAP-COVID anticoagulation domain), treatment efficacy and safety will be evaluated as efficiently as possible. The primary outcome is an ordinal endpoint with three possible outcomes based on the worst status of each patient through day 30: no requirement for invasive mechanical ventilation, invasive mechanical ventilation or death. Conclusion: Using an adaptive trial design, the Anti-Thrombotic Therapy To Ameliorate Complications of COVID-19 trial will establish whether therapeutic anticoagulation can reduce mortality and/or avoid the need for mechanical ventilation in patients hospitalized with COVID-19. Leveraging existing networks to recruit sites will increase enrollment and mitigate enrollment risk in sites with declining COVID-19 cases.

Oral factor Xa inhibitors are increasingly used for anticoagulation, but there is no approved reversal agent. Prothrombin complex concentrate (PCC) for the management of Xa-inhibitor–associated bleeding has been described in small case series and one cohort study. Patients on apixaban or rivaroxaban, suffering a major bleed, were treated at nine Canadian hospitals as per existing hospital protocol with a fixed dose of PCC 2,000 units and subsequently recruited for a 30-day follow-up. The treating physician evaluated the haemostatic effectiveness as observed during the first day as good, moderate or poor/none, using an assessment guide. Safety outcomes were thromboembolism or death. We recruited 66 patients with major bleeding who were treated with PCC and who were receiving rivaroxaban (56%) or apixaban (44%). The effectiveness was assessed as good in 65% (95% confidence interval [CI], 53–77), moderate in 20% (95% CI, 10–30) and poor/none in 15% (95% CI, 6–24). For the 36 patients with intracranial haemorrhage, the corresponding ratings were 67, 17 and 17%, and for 16 patients with gastrointestinal bleeding they were 69, 12 and 19%, respectively. There were nine deaths (14%) by 30 days, and five (8%) major thromboembolic events. In a post hoc analysis, according to International Society on Thrombosis and Haemostasis criteria, reversal was effective in 68% and ineffective in 32%. For major bleeding associated with oral Xa inhibitors, PCC may have a beneficial effect. The risk of thromboembolism after reversal of anticoagulation in patients with a prothrombotic background has to be taken into account.

Supplemental Digital Content is available in the text., Objective— Rosuvastatin has been widely used in the primary and secondary prevention of coronary heart disease. However, its antiatherosclerotic properties have not been tested in a mouse model that could mimic human coronary heart disease. The present study was designed to test the effects of rosuvastatin on coronary artery atherosclerosis and myocardial fibrosis in SR-B1 (scavenger receptor class B type 1) and apoE (apolipoprotein E) double knockout mice. Approach and Results— Three-week-old SR-B1−/−/apoE−/− mice were injected daily with 10 mg/kg of rosuvastatin for 2 weeks. Compared with saline-treated mice, rosuvastatin-treated mice showed increased levels of hepatic PCSK9 (proprotein convertase subtilisin/kexin type-9) and LDLR (low-density lipoprotein receptor) message, increased plasma PCSK9 protein but decreased levels of hepatic LDLR protein and increased plasma total cholesterol associated with apoB (apolipoprotein B) 48-containing lipoproteins. In spite of this, rosuvastatin treatment was associated with decreased atherosclerosis in both the aortic sinus and coronary arteries and reduced platelet accumulation in atherosclerotic coronary arteries. Cardiac fibrosis and cardiomegaly were also attenuated in rosuvastatin-treated SR-B1−/−/apoE−/− mice. Two-week treatment with rosuvastatin resulted in significant decreases in markers of oxidized phospholipids in atherosclerotic plaques. In vitro analysis showed that incubation of bone marrow-derived macrophages with rosuvastatin substantially downregulated cluster of differentiation (CD)36 and inhibited oxidized LDL-induced foam cell formation. Conclusions— Rosuvastatin protected SR-B1−/−/apoE−/− mice against atherosclerosis and platelet accumulation in coronary arteries and attenuated myocardial fibrosis and cardiomegaly, despite increased plasma total cholesterol. The ability of rosuvastatin to reduce oxidized phospholipids in atherosclerotic plaques and inhibit macrophage foam cell formation may have contributed to this protection.

Background: Hemophilia A and B are recessive X-linked bleeding disorders characterized by the deficiency in coagulation factor VIII and factor IX. Patients with the severe form of the disease can experience bleeding into the joints and muscle either spontaneously or after provoking events including sporting injuries of different degree. Patients are prone to bleeding in the musculoskeletal system. While most research is focused on hemarthrosis, muscle hematomas are not well studied although being the second most common complication of hemophilia, accounting for 10-25% of diagnosed bleeding episodes. There is limited consensus regarding optimal diagnosis and treatment of muscle hematomas in patients with hemophilia. We are investigating the effect of physical activity on muscle and joint bleeds in mouse models of hemophilia. Aim: The objective of this study was to compare the severity of exercise-induced skeletal bleedings in two mouse models of hemophilia A and B. Methods: Hemophiliac F8-KO and F9-KO mice, aged from 8-12 weeks old, were subjected to either mild or moderate daily treadmill exercise for 5 days. The speed was set at 10 meters per minute for the mild intensity group and 15 meters per minute for the moderate intensity group; and the animals were exercised for 30 minutes daily. Mechanical stimulus with a brush was used to encourage the animals to run. Animals were monitored daily and on day 6 (24 hours after the treadmill exercise) the animals were sacrificed to assess bleeding events. The mice skin was carefully removed and the body was macroscopically evaluated for presence of bleeds. If muscle bleedings were present, they were assigned a score in accordance with a previously published protocol (Tranholm M et al., JTH 2015 Jan;13(1):82-91) with minor modifications. Results: The animals were closely monitored during the study periods, and all completed the study. Normal behaviour and appearances were observed. No external bleeding was recorded. No muscle hematoma was observed in the wild-type C57-strain, thus the group received the bleeding score of 0. For the mild exercise group, the mean muscle bleeding score of F8-KO strain was 5.50 (standard error = 2.81), while the mean muscle bleeding score of F9-KO strain was 1 (standard error: 2). The two-tailed P value between the hemophilia A and B group was significant (p Discussions: The preliminary analysis of our data showed that musculoskeletal bleeding induced by exercise appears to be more severe in hemophilia A mice than hemophilia B. This is in accordance with previous observations that hemophilia B may be clinically milder than hemophilia A. In our study, there appears to be a more significant difference between the hemophilia A and B mice when the mice were subject to milder form of exercise. No statistical significance was found between the two groups when moderate exercise was given. Overall, this exercise model can be a useful tool to study the pathophysiology of musculoskeletal bleeding as well as to evaluate new therapeutic strategies in the prevention and management of muscle hematomas in hemophilia. Figure 1 Figure 1. Disclosures Gross: Leo Pharma: Honoraria; Bayer: Honoraria; BMS-Pfizer: Honoraria; Valeo: Honoraria. Matino: Bayer: Membership on an entity's Board of Directors or advisory committees, Other: research grants and personal fees; Pfizer: Membership on an entity's Board of Directors or advisory committees, Other: research grants and personal fees; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees, Other: research grants and personal fees; Sanofi: Membership on an entity's Board of Directors or advisory committees, Other: research grants and personal fees; Spark: Other: research grants; Octopharma: Membership on an entity's Board of Directors or advisory committees, Other: research grants and personal fees; Sobi: Membership on an entity's Board of Directors or advisory committees, Other: personal fees.

Cancer is a risk factor for thrombosis, but unlike venous thrombosis, its association with ischemic stroke, and its impact on stroke management and post-stroke outcomes are not well characterized. The primary objective of this study was to measure and compare the risk of ischemic stroke in individuals with a new diagnosis of cancer and those without a history of cancer in two separate matched cohorts based on the absence (Matched Cohort 1) or presence (Matched Cohort 2) of a prior diagnosis of ischemic stroke (Figure 1). Methods: We conducted a population-based matched cohort study of adults ≥18 years using linked clinical and administrative health databases in Ontario, Canada (2010 to 2019). Individuals with a new diagnosis of cancer were matched (1:1) to cancer-free controls by age and sex. Cancer diagnoses were determined using ICD-O-3 diagnostic codes (basal and squamous cell carcinoma and primary central nervous system tumors were excluded). For cancer patients, the index date was the diagnosis date and a corresponding dummy index date was assigned to the matched cancer-free control. The primary outcome was the incidence of ischemic stroke (time to ischemic stroke following index) determined using validated ICD-9 or -10 diagnostic codes from hospitalizations or emergency department visits. Analyses were conducted separately, in parallel, for each cohort. Standardized differences were used to compare the distributions of baseline characteristics. Cumulative incidence function (CIF) curves were generated for ischemic stroke and all-cause mortality. Competing risk methods were used to calculate sub-distribution adjusted hazard ratios (aHR) and 95% confidence intervals (CI) for ischemic stroke, where death was treated as a competing event. Interactions with the timeline at 1.5 years after index were incorporated to assess if the hazard ratio for the main exposure (cancer vs cancer-free) varied before and after the 1.5-year mark. Regression analyses were adjusted using baseline characteristics for which there was imbalance between groups. Results: Matched Cohort 1 included 620,647 individuals with cancer and 620,647 controls. Matched Cohort 2 included 13,924 individuals with cancer and 13,924 controls. Baseline characteristics were generally well balanced (Table 1). Use of antithrombotic medications (prior to index) among individuals ≥66 years was similar between the groups (data not shown). CIF curves for ischemic stroke and mortality are shown in Figure 2. In Matched Cohort 1 (no history of stroke), the risk of ischemic stroke was increased in cancer patients compared to cancer-free controls 1.5 years post-index (aHR 1.40, 95%CI 1.34-1.47). From 1.5 years to 5 years, the risk of ischemic stroke was lower in cancer patients compared to controls (aHR 0.72, 95%CI 0.69-0.74). In Matched Cohort 2 (prior history of ischemic stroke), the risk of ischemic stroke was similar at 1.5 years after the index date in individuals with and without cancer (aHR 1.00, 95%CI 0.88-1.14). From 1.5 to 5 years, the risk of ischemic stroke was reduced (aHR 0.53, 95%CI 0.46-0.62) in cancer patients compared to controls. Conclusions: Compared to cancer-free controls, the risk of ischemic stroke among individuals with a new cancer diagnosis depended on the presence or absence of prior history of ischemic stroke, a novel finding not previously reported. In individuals without a prior history of stroke, those with cancer had a 1.5-fold higher risk of ischemic stroke at 1.5 years compared to controls. In individuals with a prior history of stroke, those with cancer had a similar risk of stroke compared to controls. At 5 years post-index, the risk of ischemic stroke was lower in cancer patients in both cohorts which may reflect high early mortality rates and lower stroke risk among long-term survivors of cancer. The risk of death among cancer patients was highest during the first 1.5 years after the index date in both cohorts. However, the magnitude of the risk increase was higher in individuals without a prior history of stroke (10-fold) compared to those with a prior history of cancer (5-fold). Limitations include unknown causes of death and unavailability of some covariates (e.g. smoking and antithrombotic use in individuals aged Figure 1 Figure 1. Disclosures Siegal: BMS-Pfizer: Honoraria; Leo Pharma: Honoraria; Novartis: Honoraria; Portola: Honoraria; Servier: Honoraria. Carrier: Pfizer: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Servier: Honoraria; Leo Pharma: Honoraria, Research Funding; Bayer: Honoraria; Sanofi: Honoraria. Gross: Valeo: Honoraria; Leo Pharma: Honoraria; Bayer: Honoraria; BMS-Pfizer: Honoraria.

Using data collected from 2 national atrial fibrillation (AF) primary care physician chart audits (Facilitating Review and Education to Optimize Stroke Prevention in Atrial Fibrillation [FREEDOM AF] and Co-ordinated National Network to Engage Physicians in the Care and Treatment of Patients With Atrial Fibrillation [CONNECT AF]), we evaluated the frequency of, and factors associated with, the use of cardiovascular (CV) evidence-based therapies in Canadian AF outpatients with at least 1 CV risk factor or co-morbidity. Of the 11,264 patients enrolled, 9,495 (84.3%) were eligible for one or more CV evidence-based therapies. The proportions of patients with AF receiving all eligible guideline-recommended therapies were 40.8% of patients with coronary artery disease, 48.9% of patients with diabetes mellitus, 40.2% of patients with heart failure, 96.7% of patients with hypertension, and 55.1% of patients with peripheral arterial disease. Factors that were independently associated with nonreceipt of all indicated evidence-based therapies included sinus rhythm rather than AF at baseline and liver disease. In conclusion, although most Canadian outpatients with AF have CV risk factors or co-morbidities, a substantial portion of these patients did not receive all guideline-recommended therapies. These findings suggest that there is an opportunity to improve the quality of care for patients with AF in Canada.

According to recent literature, tolvaptan ameliorates the natural decline of renal function in autosomal dominant polycystic kidney disease. Tolvaptan is an orally available vasopressin V2 receptor antagonist. We describe herein the remaining questions and problems: it is unclear from the published work what influence tolvaptan has on total kidney volume. The consequences of hepatotoxicity for the subsequent dosing of tolvaptan have not been reported. A vasopressin V2 antagonist will cause polyuria and polydipsia and tolvaptan may influence quality of life (QOL), however, there are no QOL data. The cost-effectiveness of tolvaptan is borderline. It is unknown at which stage of renal failure tolvaptan therapy may have to be stopped. There are no established criteria to determine the ineffectiveness of tolvaptan. It is presently undecided whether a steady high water intake is able to imitate the renal effects of tolvaptan. Finally, the cause of worsening glomerular filtration rate after the start of tolvaptan is unknown.

Humans carrying the factor V Leiden (FVL) variant have a fivefold increased risk for venous thrombosis. However, incidence of deep vein thrombosis (DVT) is proportionally greater than that of pulmonary embolism (PE) in these individuals. This is known as the FVL paradox. We hypothesized that the rate of initial DVT development is similar in FVL and noncarriers, but thrombi in FVL carriers are more stable and develop into a clinically significant DVT more often than in noncarriers. To test this, we induced thrombi in the femoral vein of wild-type (WT), heterozygous (F5(L/+)), and FVL homozygous (F5(L/L)) mice. Using intravital microscopy, thrombus size and embolization were visualized and emboli in the lungs were quantified. Compared with WT, femoral vein thrombi in F5(L/+) and F5(L/L) mice were larger and embolized less. Total and large embolic events, the percentage of thrombus that embolized, and PE burden were significantly decreased in F5(L/L) mice. This suggests that in noncarriers (reflected by WT), a minor injury initially resulting in a small DVT tends to remain small and asymptomatic because of the embolization of the otherwise growing thrombus. Alternatively, the same insult in people with FVL (reflected by F5(L/L)) leads to thrombus growth as a result of less embolization, and thus symptomatic DVT development.

BACKGROUND: Thrombin-activated platelets can promote fibrinolysis by binding plasminogen in a fibrinogen-dependent manner and enhancing its activation by tissue-type plasminogen activator (t-PA). Whether t-PA also binds to activated platelets and the mechanism for regulation of platelet-dependent fibrinolysis remain unknown. OBJECTIVES: Determine the mechanism of plasminogen and t-PA binding on thrombin-activated platelets and its regulation by activated thrombin-activatable fibrinolysis inhibitor (TAFIa). METHODS: Plasminogen and t-PA binding with or without TAFIa treatment was quantified using flow cytometry. Plasmin generation on platelets was quantified using a plasmin-specific substrate. Mass spectrometry analyses identified fibrinogen as a potential target of TAFIa. Thrombus formation was studied in mice lacking fibrinogen (Fg(−/−)) using intravital microscopy. RESULTS: Plasminogen and t-PA bind to platelets activated by thrombin but not by other agonists, including protease-activated receptor agonists (PAR-AP). Plasminogen binds via its kringle domains because ε-aminocaproic acid eliminates binding, whereas t-PA binds via its finger and kringle domains. Plasminogen binding is fibrinogen-dependent because it is abolished on (a) Fg(−/−) platelets, and (b) thrombi in Fg(−/−) mice. Binding requires thrombin-mediated fibrinogen modification because addition of batroxobin to PAR-AP activated platelets has no effect on plasminogen binding but induces t-PA binding. TAFIa reduces plasminogen and t-PA binding to thrombin-activated platelets and attenuates plasmin generation in a concentration-dependent manner. Mass spectrometry identified K556 on the fibrinogen alpha-chain as a potential thrombin cleavage site that generates a TAFIa sensitive C-terminal lysine residue. CONCLUSION: These findings provide novel mechanistic insights into how platelets activated by thrombin at sites of vascular injury can influence fibrinolysis.

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.RéSUMé: Ce compte rendu narratif discute du rôle de la génération de thrombine dans la coagulation et le saignement en chirurgie cardiaque, des méthodes de laboratoire pour le dépistage clinique d’une génération de thrombine altérée et des interventions hémostatiques disponibles qui peuvent être utilisées pour améliorer la génération de thrombine. Une coagulopathie après la circulation extracorporelle (CEC) est associée à des pertes de sang excessives et à des complications pour les patients. La thrombine joue un rôle essentiel d’hémostase primaire, et une génération de thrombine altérée peut constituer une cause importante de coagulopathie post-CEC. Les analyses de coagulation existantes comportent d’importantes limites en ce qui touche à l’évaluation de la génération de thrombine, mais des analyses de sang complet conçues pour mesurer la génération de thrombine au chevet sont en cours d’élaboration. En attendant, les cliniciens pourraient devoir amorcer un traitement de manière empirique pour prendre en charge les saignements non chirurgicaux dans un contexte de valeurs de coagulation mesurées normales. Les traitements disponibles pour une génération de thrombine altérée comprennent l’administration de plasma, de concentrés de complexe prothrombinique, et d’agents de contournement (bypass) (facteur VII recombinant activé et activité de contournement de l’inhibiteur du facteur VIII). Des expériences in vitro ont exploré l’activité thérapeutique relative de ces traitements, mais les études cliniques manquent. L’intégration potentielle d’analyses de génération de thrombine dans la pratique clinique et d’algorithmes de traitement pour une génération de thrombine altérée doit attendre des développements cliniques plus poussés.

Arterial and venous thromboembolism are both more common in older adults. The use of anticoagulants, the mainstay to prevent thromboembolism, requires consideration of the balance between risk and benefit. Such consideration is even more important in the very elderly in whom the risk of anticoagulant-related bleeding and thrombosis are higher. This review will focus on the challenges of implementing and managing anticoagulant therapy in older patients in an era when the options for anticoagulants include not only vitamin K antagonists (VKAs), but also direct-acting oral anticoagulants (DOACs).

The fragment 2 domain (F2) of prothrombin and its interaction with factor (F) Va is known to contribute significantly to prothrombinase-catalyzed activation of prothrombin. The extent to which the F2-FVa interaction affects the overall thrombin generation, however, is uncertain. To study this interaction, nuclear magnetic resonance spectroscopy of recombinant F2 was used to identify seven residues within F2 that are significantly responsive to FVa binding. The functional role of this region in interacting with FVa during prothrombin activation was verified by the FVa-dependent inhibition of thrombin generation using peptides that mimic the same region of F2. Because six of the seven residues were within a 9-residue span, these were mutated to generate a prothrombin derivative (PT6). These mutations led to a decreased affinity for FVa as determined by surface plasmon resonance. When thrombin generation by an array of FXa containing prothrombinase components was monitored, a 54% decrease in thrombin generation was observed with PT6 compared with the wild-type, only when FVa was present. The functional significance of the specific low-affinity binding between F2 and FVa is discussed within the context of a dynamic model of molecular interactions between prothrombin and FVa engaging multiple contact sites.

Patients with active cancer have an increased risk of venous thromboembolism, which results in substantial morbidity, mortality, and health care expenditures. The Khorana score (range, 0 to 6, with higher scores indicating a higher risk of venous thromboembolism) has been validated to identify patients with cancer at elevated risk for this complication and may help select those who could benefit from thromboprophylaxis.We conducted a randomized, placebo-controlled, double-blind clinical trial assessing the efficacy and safety of apixaban (2.5 mg twice daily) for thromboprophylaxis in ambulatory patients with cancer who were at intermediate-to-high risk for venous thromboembolism (Khorana score, ≥2) and were initiating chemotherapy. The primary efficacy outcome was objectively documented venous thromboembolism over a follow-up period of 180 days. The main safety outcome was a major bleeding episode.Of the 574 patients who underwent randomization, 563 were included in the modified intention-to-treat analysis. Venous thromboembolism occurred in 12 of 288 patients (4.2%) in the apixaban group and in 28 of 275 patients (10.2%) in the placebo group (hazard ratio, 0.41; 95% confidence interval [CI], 0.26 to 0.65; P0.001). In the modified intention-to-treat analysis, major bleeding occurred in 10 patients (3.5%) in the apixaban group and in 5 patients (1.8%) in the placebo group (hazard ratio, 2.00; 95% CI, 1.01 to 3.95; P = 0.046). During the treatment period, major bleeding occurred in 6 patients (2.1%) in the apixaban group and in 3 patients (1.1%) in the placebo group (hazard ratio, 1.89; 95% CI, 0.39 to 9.24).Apixaban therapy resulted in a significantly lower rate of venous thromboembolism than did placebo among intermediate-to-high-risk ambulatory patients with cancer who were starting chemotherapy. The rate of major bleeding episodes was higher with apixaban than with placebo. (Funded by the Canadian Institutes of Health Research and Bristol-Myers Squibb-Pfizer Alliance; AVERT ClinicalTrials.gov number, NCT02048865.).

Importance: Patients with atrial fibrillation (AF) who use a direct oral anticoagulant (DOAC) and request elective surgery or procedure present a common clinical situation yet perioperative management is uncertain. Objective: To investigate the safety of a standardized perioperative DOAC management strategy. Design, Setting, and Participants: The Perioperative Anticoagulation Use for Surgery Evaluation (PAUSE) cohort study conducted at 23 clinical centers in Canada, the United States, and Europe enrolled and screened patients from August 1, 2014, through July 31, 2018. Participants (n = 3007) had AF; were 18 years of age or older; were long-term users of apixaban, dabigatran etexilate, or rivaroxaban; were scheduled for an elective surgery or procedure; and could adhere to the DOAC therapy interruption protocol. Interventions: A simple standardized perioperative DOAC therapy interruption and resumption strategy based on DOAC pharmacokinetic properties, procedure-associated bleeding risk, and creatinine clearance levels. The DOAC regimens were omitted for 1 day before a low-bleeding-risk procedure and 2 days before a high-bleeding-risk procedure. The DOAC regimens were resumed 1 day after a low-bleeding-risk procedure and 2 to 3 days after a high-bleeding-risk procedure. Follow-up of patients occurred for 30 days after the operation. Main Outcomes and Measures: Major bleeding and arterial thromboembolism (ischemic stroke, systemic embolism, and transient ischemic attack) and the proportion of patients with an undetectable or minimal residual anticoagulant level (

Surgery exposes patients to a risk of venous thromboembolism (VTE) and bleeding. VTE includes deep vein thrombosis (DVT) and pulmonary embolism (PE), which represent serious and sometimes fatal consequences of surgery. Therefore, optimizing treatment plans to reduce VTE risk while also minimizing bleeding risk is important to patients and the healthcare system. The goal of this Canadian Urological Association (CUA) guideline is to provide a structured approach to the prevention of perioperative thromboembolic events that may be applied in Canada. In this guideline, two forms of perioperative VTE prophylaxis are considered. The first is prophylaxis used for primary prevention VTE for patients undergoing surgery. The second is management of an anticoagulant or antiplatelet agent used for treatment or as a form of secondary prevention during the perioperative period. The CUA thromboprophylaxis guideline panel feels that it is important for urologists to be engaged in the discussion and management in each of these situations. The panel recognizes that in many clinical contexts, other specialists, including internists, cardiologists, neurologists, and hematologists, may also be involved in this aspect of patient care. The guidance provided in this document is intended to help urologists engage with their patients and colleagues in a collaborative context. The guidance provided in this document is intended to reflect best practice for the usual case for a specific surgery and patient population. This guideline is not intended for unusual conditions or circumstances, which are typically rare, and should be addressed involving appropriate specialists on a case-by-case basis. Decisions regarding thromboprophylaxis involve a tradeoff, in which the intended purpose is to decrease the risk of VTE while recognizing that thromboprophylaxis also increases the risk of bleeding. A systematic review and meta-analysis of randomized placebo-controlled trials performed for the American College of Chest Physicians VTE guideline reported that VTE prophylaxis decreases the relative risk of VTE by 50% and increases the relative risk of bleeding by 50%.1 In cases where the risk of VTE is high and the bleeding risk is low, VTE prophylaxis is usually warranted because the net benefit is favourable. When the risk of VTE is low and the bleeding risk is high, VTE prophylaxis may be harmful and is usually not warranted. In many cases, the tradeoff between VTE prevention and bleeding risk may be close and the “most favourable” approach to VTE prophylaxis is less clear. In these situations, individual patient values and preferences must be considered to determine the best management plan (Fig. 1). Open in a separate window Fig. 1 Graphical depiction of evaluating the tradeoffs of venous thromboembolism (VTE) and bleeding.

Thrombosis is a leading cause of morbidity and mortality worldwide. Animal models are used to understand the pathological pathways involved in thrombosis and to test the efficacy and safety of new antithrombotic drugs. In this review, we will first describe the central role a variety of animal models of thrombosis and hemostasis has played in the development of new antiplatelet and anticoagulant drugs. These include the widely used P2Y 12 antagonists and the recently developed orally available anticoagulants that directly target factor Xa or thrombin. Next, we will describe the new players, such as polyphosphate, neutrophil extracellular traps, and microparticles, which have been shown to contribute to thrombosis in mouse models, particularly venous thrombosis models. Other mouse studies have demonstrated roles for the factor XIIa and factor XIa in thrombosis. This has spurred the development of strategies to reduce their levels or activities as a new approach for preventing thrombosis. Finally, we will discuss the emergence of zebrafish as a model to study thrombosis and its potential use in the discovery of novel factors involved in thrombosis and hemostasis. Animal models of thrombosis from zebrafish to nonhuman primates are vital in identifying pathological pathways of thrombosis that can be safely targeted with a minimal effect on hemostasis. Future studies should focus on understanding the different triggers of thrombosis and the best drugs to prevent each type of thrombotic event.

ESSENTIALS: It is not known if D-dimer testing alone can safely exclude pulmonary embolism (PE). We studied the safety of using a quantitative latex agglutination D-dimer to exclude PE in 808 patients. 52% of patients with suspected PE had a negative D-dimer test and were followed for 3 months. The negative predictive value of D-dimer testing alone was 99.8%, suggesting it may safely exclude PE. Background Strategies are needed to exclude pulmonary embolism (PE) efficiently without the need for imaging tests. Although validated rules for clinical probability assessment can be combined with D-dimer testing to safely exclude PE, the rules can be complicated or partially subjective, which limits their use. Objectives To determine if PE can be safely excluded in patients with a negative D-dimer without incorporating clinical probability assessment. Patients/methods We enrolled consecutive outpatients and inpatients with suspected PE from four tertiary care hospitals. All patients underwent D-dimer testing using the MDA D-dimer test, a quantitative latex agglutination assay. PE was excluded in patients with a D-dimer less than 750 μg FEU L(-1) without further testing. Patients with D-dimer levels of 750 μg FEU L(-1) or higher underwent standardized imaging tests for PE. All patients in whom PE was excluded had anticoagulant therapy withheld and were followed for 3 months for venous thromboembolism (VTE). Suspected events during follow-up were adjudicated centrally. Results Eight hundred and eight patients were enrolled, of whom 99 (12%) were diagnosed with VTE at presentation. Four hundred and twenty (52%) patients had a negative D-dimer level at presentation and were not treated with anticoagulants; of these, one had VTE during follow-up. The negative predictive value of D-dimer testing for PE was 99.8% (95% confidence interval, 98.7-99.9%). Conclusions A negative latex agglutination D-dimer assay is seen in about one-half of patients with suspected PE and reliably excludes PE as a stand-alone test.

Essentials Direct oral anticoagulants (DOAC) are used for stroke and venous thromboembolism prevention. We report a new assay that measures anti-factor Xa DOAC levels in plasma and whole blood. Rivaroxaban and apixaban can be accurately quantified below trough levels. The ease and accuracy of the assay demonstrate its potential for point-of-care applications. Background Rivaroxaban and apixaban are the most commonly used anti-factor (F) Xa direct oral anticoagulants (DOAC), with indications for prevention of stroke in nonvalvular atrial fibrillation as well as treatment and prevention of venous thromboembolism. However, lacking is accessibility to a detection method that is able to quantify low levels of anti-FXa DOACs. Objective We report a new assay that measures anti-FXa DOAC levels in plasma and whole blood. Methods This is achieved by the use of a prothrombin derivative that is labeled with a fluorescent probe (Flu-II), which then acts as the macromolecular substrate to measure residual FXa activity. The Flu-II cleavage is then initiated by the addition of a solution containing FXa, FVa, and phospholipid vesicles composed of 75% PC and 25% PS (PCPS) vesicles with calcium, in the presence of hirudin to prevent feedback activity by the native thrombin generated. The Flu-II cleavage is monitored by fluorescence in real time where the initial rate of fluorescence change is inversely proportional to DOAC levels. Results In plasma systems, the assay demonstrates dose-response between 0 and 5 nmol/L rivaroxaban and between 0 and 10 nmol/L apixaban. Corn trypsin inhibitor did not affect this assay. With individual plasma samples, the assay showed excellent consistency and reproducibility. From 2 μL of whole blood, the assay showed dose-response between 0 and 2 nmol/L of DOACs in the final mixture of 100 μL, thus representing up to 100 nmol/L in circulating blood. Conclusion The assay is ideal for rapidly and accurately measuring DOAC levels in plasma and blood, demonstrating its potential for point-of-care applications.

Objective— Dual-antiplatelet therapy with acetylsalicylic acid and a P2Y 12 antagonist, such as clopidogrel, is the standard of care for acute coronary syndromes. However, the drugs have divergent effects on the formation of cAMP, an inhibitory second messenger. Thus, by inhibiting the synthesis of prostacyclin, acetylsalicylic acid reduces cAMP formation, whereas clopidogrel potentiates it. Therefore, with higher doses of acetylsalicylic acid, the potentiation of cAMP production by clopidogrel may be attenuated, which could limit the antithrombotic potential of the drug combination. The purpose of this study was to examine this possibility in vivo. Approach and Results— Mice were given oral acetylsalicylic acid at varying doses, oral clopidogrel (5 mg/kg body weight), or both. At doses of 0.15 and 0.6 mg/kg, acetylsalicylic acid inhibited arachidonic acid–induced platelet aggregation, but only 0.6 mg/kg acetylsalicylic acid, or higher, decreased the plasma levels of 6-keto-prostaglandin-F 1α , the stable metabolite of prostacyclin. When given with clopidogrel, laser injury–induced arterial thrombi were significantly larger with the 0.6 mg/kg dose of acetylsalicylic acid than with the 0.15 mg/kg dose. Thrombi in mice treated with clopidogrel and the 0.15 mg/kg dose of acetylsalicylic acid were smaller than in mice treated with clopidogrel alone, suggesting that acetylsalicylic acid can add to the antithrombotic effect of clopidogrel but that higher doses of acetylsalicylic acid blunt the antithrombotic effect of clopidogrel. Conclusions— These findings support the use of lower, prostacyclin-preserving, doses of acetylsalicylic acid in conjunction with clopidogrel.

Background Physicians treating nonvalvular atrial fibrillation (AF) assess stroke and bleeding risks when deciding on anticoagulation. The agreement between empirical and physician-estimated risks is unclear. Furthermore, the association between patient and physician sex and anticoagulation decision-making is uncertain. Methods We pooled data from 2 national primary care physician chart audit databases of patients with AF (Facilitating Review and Education to Optimize Stroke Prevention in Atrial Fibrillation and Coordinated National Network to Engage Physicians in the Care and Treatment of Patients with Atrial Fibrillation Chart Audit) with a combined 1035 physicians (133 female, 902 male) and 10,927 patients (4567 female and 6360 male). Results Male physicians underestimated stroke risk in female patients and overestimated risk in male patients. Female physicians estimated stroke risk well in female patients but underestimated the risk in male patients. Risk of bleeding was underestimated in all. Despite differences in risk assessment by physician and patient sex, > 90% of patients received anticoagulation across all subgroups. There was modest agreement between physician estimated and calculated (ie, CHADS2 score) stroke risk: Kappa scores were 0.41 (0.35-0.47) for female physicians and 0.34 (0.32-0.36) for male physicians. Conclusions Our study is the first to examine the association between patient and physician sex influences and stroke and bleeding risk estimation in AF. Although there were differences in agreement between physician estimated stroke risk and calculated CHADS2 scores, these differences were small and unlikely to affect clinical practice; further, despite any perceived differences in the accuracy of risk assessment by sex, most patients received anticoagulation.

Clinical trials and meta-analyses have suggested that aspirin may be effective for the prevention of venous thromboembolism (proximal deep-vein thrombosis or pulmonary embolism) after total hip or total knee arthroplasty, but comparisons with direct oral anticoagulants are lacking for prophylaxis beyond hospital discharge.We performed a multicenter, double-blind, randomized, controlled trial involving patients who were undergoing total hip or knee arthroplasty. All the patients received once-daily oral rivaroxaban (10 mg) until postoperative day 5 and then were randomly assigned to continue rivaroxaban or switch to aspirin (81 mg daily) for an additional 9 days after total knee arthroplasty or for 30 days after total hip arthroplasty. Patients were followed for 90 days for symptomatic venous thromboembolism (the primary effectiveness outcome) and bleeding complications, including major or clinically relevant nonmajor bleeding (the primary safety outcome).A total of 3424 patients (1804 undergoing total hip arthroplasty and 1620 undergoing total knee arthroplasty) were enrolled in the trial. Venous thromboembolism occurred in 11 of 1707 patients (0.64%) in the aspirin group and in 12 of 1717 patients (0.70%) in the rivaroxaban group (difference, 0.06 percentage points; 95% confidence interval [CI], -0.55 to 0.66; P0.001 for noninferiority and P=0.84 for superiority). Major bleeding complications occurred in 8 patients (0.47%) in the aspirin group and in 5 (0.29%) in the rivaroxaban group (difference, 0.18 percentage points; 95% CI, -0.65 to 0.29; P=0.42). Clinically important bleeding occurred in 22 patients (1.29%) in the aspirin group and in 17 (0.99%) in the rivaroxaban group (difference, 0.30 percentage points; 95% CI, -1.07 to 0.47; P=0.43).Among patients who received 5 days of rivaroxaban prophylaxis after total hip or total knee arthroplasty, extended prophylaxis with aspirin was not significantly different from rivaroxaban in the prevention of symptomatic venous thromboembolism. (Funded by the Canadian Institutes of Health Research; ClinicalTrials.gov number, NCT01720108 .).

Background The risk of recurrent venous thromboembolism (VTE) in cancer patients despite anticoagulant therapy is high. Clinical factors and pro-coagulant markers may identify high-risk patients and guide decisions about intensifying anticoagulation therapy. Aims To evaluate whether serial measurements of pro-coagulant markers can identify patients at high risk of recurrent VTE. Methods In this multicenter, prospective cohort study, patients with active cancer and acute deep vein thrombosis or pulmonary embolism were enrolled. Patients received standard low-molecular-weight heparin therapy and were followed for 6 months. D-dimer and soluble P-selectin levels were measured at baseline and 1, 4, 5, 12, and 24 weeks post treatment initiation. The association between recurrent VTE and a previously developed risk score, baseline values of the biomarkers, and individual relative changes from baseline were assessed. Results We enrolled 117 cancer patients (22% lung, 21% colorectal, 9% breast) with a mean age of 63 years; 62% had metastatic cancer. Eleven patients (9.4%) developed recurrent VTE, including two cases of fatal pulmonary embolism. VTE recurrence rates were 7.8% (95% CI, 3.1–18) in patients with a risk score of ≤0 points compared to 11% (95% CI, 5.2–20) for those with a score of ≥1 point (hazard ratio 1.3; 95% CI, 0.39–4.5). Baseline P-selectin levels but not D-dimer levels were significantly associated with a high risk of recurrence; the risk was four-fold higher in patients with elevated P-selectin levels than in those with normal levels (hazard ratio 4.0; 95% CI, 1.1–14). Changes in biomarker levels during treatment were not associated with recurrent VTE. Conclusion Baseline P-selectin but not D-dimer levels predict recurrent VTE and may be a valuable addition to clinical prediction rules to select patients for more intensive therapy or closer observation.

Background Factor V Leiden (FVL) is an inherited autosomal dominant condition that is identified in 20%-50% of patients with venous thromboembolic diseases and 5-8% of the population in Canada. People with FVL are often called hypercoagulable, and have a five-fold increase in the risk of venous thrombosis. There is a low prevalence of FVL among patients with fatal pulmonary embolism (PE) and a higher incidence of deep vein thrombosis (DVT) than PE in patients with FVL. This has been referred to as the FVL paradox in thrombosis. We wished to test whether FVL and normal patients are at the same risk of initial thrombus formation, expect FVL patients present with symptomatic DVT while normal patients do not present, because the small asymptomatic DVT in normal patients embolizes to become an asymptomatic PE. Aim Therefore, to explain why patients with FVL are more likely to present with a DVT rather than a PE we will study DVT stability in FVL mice using a modification of our previously published mouse model of venous thrombus stability. Methods Platelets were fluorescently labeled using CD41 fab fragments conjugated to an Alexa Fluor 488. DVT was induced using a ferric chloride saturated filter paper on the femoral vein of female mice. We chose conditions such that only a small thrombus developed in wild type (WT) mice, and then compared them to thrombi in FVL heterozygous (F5L/+) and FVL homozygous (F5L/L) mice. Intravital videomicroscopy recorded embolic events leaving the thrombus and the thrombus sizes every 10 minutes for 2 hours. Lungs were harvested sectioned and stained for presence of PE. Results Although thrombus size remained small in WT mice, it significantly increased over time in F5L/+ and F5L/L mice. The number of total and large embolic events, and the percent of thrombus that embolized was significantly decreased in F5L/+ and F5L/L mice compared to WT mice. Previously we have correlated increased large embolic events with increased PE burden. FVL mice had significantly reduced PE burden compared to WT mice. Mice with F5L had higher F1.2 levels than in WT, consistent with increased thrombin generation. Conclusion This suggests that in noncarriers (reflected by WT), a minor insult initially resulting in a small DVT tends to remain small and asymptomatic, due to the embolization. Alternatively, the same insult in people with FVL (reflected by F5L/L) leads to thrombus growth due to less embolization and thus development of symptomatic DVT, but no PE.

At sites of vessel injury, thrombin acts as the central mediator of coagulation through catalyzing fibrin clot formation and platelet activation. Thus, numerous commercially available small molecule chromogenic and fluorogenic substrates have been developed to evaluate thrombin activity. These substrates are limited in that they detect both active thrombin and thrombin bound to its inhibitor α2-macroglobulin, have limited specificity for thrombin and can only be used in plasma samples because of signal quenching. But plasma is not reflective of physiological settings because of the lack of red blood cells which can promote coagulation. Furthermore, assays of plasma require anticoagulation using chelating agents followed by recalcification using supraphysiological concentrations of calcium to initiate coagulation. In addition to calcium ions, chelating agents used as anticoagulants also sequester magnesium and zinc ions which alter coagulation. Thus, divalent cations present in physiological settings are removed in plasma assays. Thus, we designed a novel thrombin substrate that allows for thrombin activity assessment in whole blood. The thrombin substrate consists of a mAmetrine and tTomato fluorescence resonance energy transfer (FRET) pair linked by a thrombin recognition sequence (LVPRGVNL). In addition, the thrombin recognition sequence is flanked by short, antiparallel beta sheets that are linked to the FRET pair through a zipper made of arginine and glutamic acid residues. This design allows it to accommodate long thrombin recognition sequences that enhance specificity and ignore inactive thrombin bound to α2-macroglobulin. Thrombin activity is assessed by evaluating for the loss of FRET. Expressed in E.coli, the thrombin substrate contains two hexahistidine tags on its N-terminus and a calmodulin binding protein tag on its C-terminus. Purification based on these tags ensures that only intact substrate is purified; the tags are then removed by a specific bacterial protease. The purity and integrity of the substrate was confirmed using SDS-PAGE and FRET efficiency assessment. The purified substrate demonstrated specificity for thrombin over factor Xa and activated protein C in buffer containing calcium. To determine whether this thrombin substrate can be used as a point-of-care test of thrombin generation, blood (20 µL) obtained from separate finger pricks from the same healthy donor was incubated with the thrombin substrate and reagents (vehicle, APTT reagent, dabigatran) and evaluated in a portable fluorometer. The fluorometer (StellarCase-Fluoro analyzer) uses a 405 nm LED as excitation, a diffraction grating, a PC tablet and is powered by a lithium battery and enclosed in a rugged case. The change in fluorescence emission was analyzed with Excel to obtain a thrombin generation curve. Compared to blood alone, APTT reagent significantly shortened the time to peak thrombin generation. When dabigatran was added to the blood simultaneously with APTT reagent, the time to peak thrombin generation was increased. These results are consistent with published literature using plasma assays that require larger amounts of blood and centrifugation, suggesting that our substrate can be used as a point-of-care thrombin generation test using a single drop of blood. In conclusion, we have developed a thrombin sensor that has specificity for thrombin compared to related proteases and can measure thrombin activity in whole blood. This sensor is currently being developed into a point-of-care test of anticoagulants and has potential to help our understanding of hemostasis through evaluating thrombin generation in whole blood in varied scenarios.

Background The perioperative management of patients who take a direct oral anticoagulant (DOAC) for atrial fibrillation and require treatment interruption for an elective surgery/procedure is a common clinical scenario for which best practices are uncertain. The Perioperative Anticoagulant Use for Surgery Evaluation (PAUSE) study is designed to address this unmet clinical need. We discuss the rationale for the PAUSE design and analysis plan as well as the rationale supporting the perioperative DOAC protocol. Methods PAUSE is a prospective study with three parallel cohorts, one for each DOAC, to assess a standardized but patient-specific perioperative management protocol for DOAC-treated patients with atrial fibrillation. The perioperative protocol accounts for DOAC type, patient's renal function and surgery/procedure-related bleeding risk. The primary study aim is to demonstrate the safety of the PAUSE protocol for the perioperative management of each DOAC. The secondary aim is to determine the effect of the pre-procedure interruption on residual anticoagulation when measured by the dilute thrombin time for dabigatran and anti-factor Xa levels for rivaroxaban and apixaban. The study hypothesis is that the perioperative management protocol for each DOAC is safe for patient care, defined by expected risks for major bleeding of 1% (80% power to exclude 2%), and for arterial thromboembolism of 0.5% (80% power to exclude 1.5%) in each DOAC group. Conclusion The PAUSE study has the potential to establish a standard-of-care approach for the perioperative management of DOAC-treated patients. The PAUSE management protocol is designed to be easily applied in clinical practice, as it is standardized and also patient specific.