Plasma levels of direct oral anticoagulants in atrial fibrillation patients at the time of embolic stroke: a pilot prospective multicenter study.

BACKGROUND: Patients with atrial fibrillation (AF) who are on long-term direct oral anticoagulants (DOAC) with low anti-Xa or anti-IIa levels may be at higher risk of recurrent stroke. However, no prospective post-marketing study has investigated these DOAC plasma levels at the time of embolic stroke. The aim of this study was to assess the anti-Xa (rivaroxaban, apixaban) and anti-IIa (dabigatran) plasma levels in DOAC-treated AF patients at the time of acute embolic stroke. PATIENTS AND METHODS: We prospectively identified 43 patients with AF on long-term DOAC who experienced embolic strokes. We compared the DOAC plasma levels of these patients with a control sample of 57 patients who tolerated long-term therapeutic dose DOAC therapy without any adverse event. DOAC levels were assessed with drug-specific anti-Xa chromogenic analysis (rivaroxaban, apixaban) and with Hemoclot Thrombin Inhibitor assay (dabigatran). RESULTS: Dabigatran-treated patients with stroke had significantly lower anti-IIa levels when compared with the trough (40.7 ± 36.9 vs. 85.4 ± 57.2 ng/mL, p < 0.05) and peak samples of the controls (40.7 ± 36.9 vs. 138.8 ± 78.7 ng/mL, p < 0.001). Similarly, there were significantly lower anti-Xa levels in apixaban-treated patients with stroke compared to the trough control samples (72.4 ± 46.7 vs. 119.9 ± 81.7 ng/mL, p < 0.05), and in rivaroxaban- and apixaban-treated patients when compared to peak control samples (rivaroxaban: 42.7 ± 31.9 vs. 177.6 ± 38.6 ng/mL, p < 0.001; apixaban: 72.4 ± 46.7 vs. 210.9 ± 88.7 ng/mL, p < 0.001). CONCLUSION: This observational study showed significantly lower anti-IIa and anti-Xa plasma levels in AF patients with embolic stroke compared to those who tolerated long-term therapeutic dose DOAC therapy.

ROTEM Testing for Direct Oral Anticoagulants.

Direct oral anticoagulants (DOACs) are increasingly used worldwide for the prevention of stroke in patients with atrial fibrillation and to prevent or treat venous thromboembolism. In situations such as serious bleeding, the need for urgent surgery/intervention or the management of a thromboembolic event, the laboratory measurement of DOACs levels or anticoagulant activity may be required. Rotational thromboelastometry (ROTEM) is a viscoelastic hemostatic assay (VHA) which has been used in emergencies (trauma and obstetrics), and surgical procedures (cardiac surgery and liver transplants), but experience with this assay in DOACs-treated patients is still limited. This article reviews the use of ROTEM in the setting of DOACs therapy, focusing on DOACs-associated bleeding and the use of this VHA for the management of reversal strategies for DOACs-associated anticoagulation.

Direct Oral Anticoagulants Plasma Levels in Patients with Atrial Fibrillation at the Time of Bleeding: A Pilot Prospective Study.

ABSTRACT: Patients with atrial fibrillation (AF) on long-term direct oral anticoagulants (DOACs) may be at higher risk of bleeding because of higher anti-Xa or anti-IIa levels. However, there is no postmarketing study investigating these DOAC plasma levels at the time of bleeding. The aim of this study was to evaluate DOAC levels at the time of a bleeding emergency. We analyzed 5440 patients examined at our Emergency Department in from April 1, 2019, to September 30, 2019. During this period, we prospective identified 105 consecutive patients with bleeding while on long-term antithrombotic therapy; 49 patients had AF on DOACs. We compared DOAC levels in patients who bled against a control sample of 55 patients who tolerated long-term high dose DOAC therapy without any emergency. Samples of these patients were tested with drug-specific anti-Xa chromogenic analysis (rivaroxaban and apixaban) and with Hemoclot Thrombin Inhibitor assay (dabigatran). Dabigatran-treated patients who bled had significantly higher anti-IIa levels when compared with trough (261.4 ± 163.7 vs. 85.4 ± 57.2 ng/mL, P < 0.001) and peak samples of controls (261.4 ± 163.7 vs. 138.8 ± 78.7 ng/mL, P < 0.05). Similarly, there were significantly higher anti-Xa levels in rivaroxaban-treated and apixaban-treated patients with bleeding compared with trough control samples (rivaroxaban: 245.9 ± 150.2 vs. 52.5 ± 36.4 ng/mL, P <0.001 and apixaban: 311.8 ± 142.5 vs. 119.9 ± 81.7 ng/mL, P < 0.001), as well as in apixaban-treated patients when compared with peak control samples (311.8 ± 142.5 vs. 210.9 ± 88.7 ng/mL, P < 0.05). Finally, rivaroxaban anti-Xa levels in patients who bled tended to be higher compared with peak control samples (245.9 ± 150.2 vs. 177.6 ± 38.6 ng/mL, P = 0.13). This observational study showed a significant difference in anti-IIa and anti-Xa plasma levels in patients with AF with bleeding complications compared with those who tolerated long-term high-dose DOAC therapy without bleeding complications.

Apixaban: An Optimal Agent for the Treatment of Cancer-Associated Venous Thromboembolism?

BACKGROUND: Apixaban, a direct inhibitor of activated coagulation factor X (FXaI), is being frequently selected for treatment and prevention of venous thromboembolism (VTE). Several reports about possible use of oral FXaI in patients with cancer-associated VTE (CA-VTE) have been published recently. AREAS OF UNCERTAINTY: The efficacy/safety profile of oral FXaI anticoagulation in patients with CA-VTE seems promising; however, several problems remain unanswered. The pharmacologic profile of apixaban could prefer this agent for the treatment of CA-VTE. DATA SOURCES: Currently available medical literature was searched and reviewed to summarize data regarding the use of apixaban for the prevention and treatment of cancer-associated VTE. RESULTS: Apixaban therapy in patients with cancer and VTE is expected to increase as clinicians gain more experience and reassurance with data from real-world studies that are generally promising. Several studies demonstrated that apixaban exhibits noninferiority to warfarin and low molecular weight heparin in preventing recurrent thrombosis in cancer-associated VTE. Nevertheless, there are still concerns regarding the bleeding associated with apixaban therapy, and regarding the optimal management of these bleeding emergencies. THERAPEUTIC OPINION: Although currently available evidence confirms the noninferiority of apixaban for reduction of the risk of recurrent VTE in patients with cancer; there are still concerns regarding the safety, especially in selected subpopulations of these patients.

Use of Fibrinogen Determination Methods in Differential Diagnosis of Hypofibrinogenemia and Dysfibrinogenemia.

BACKGROUND: Fibrinogen plays an important role in hemostasis. The normal concentration of fibrinogen in blood plasma is between 1.8 - 4.2 g/L. Decreased fibrinogen levels are observed in congenital afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, disseminated intravascular coagulation, fibrinolytic therapy, some more severe hepatic parenchymal disorders, and increased blood loss. Elevated fibrinogen levels occur in inflammatory diseases and neoplastic diseases, in pregnancy, and postoperative conditions. Functional fibrinogen measurement is also one of the basic coagulation screening tests. The fibrinogen antigen assay is used to distinguish between qualitative and quantitative fibrinogen disorders. METHODS: The aim of the study was the use of fibrinogen determination methods in differential diagnosis of hypofibrinogenemia and dysfibrinogenemia, statistical evaluation and determine the relationship of fibrinogen Clauss assay, prothrombin time (PT) derived fibrinogen assay, and fibrinogen antigen in the group of 60 patients with congenital fibrinogen disorders (n = 40 dysfibrinogenemia; n = 20 hypofibrinogenemia). RESULTS: The results measured by the PT-derived fibrinogen assay were approximately four times higher compared to the fibrinogen Clauss assay in the group of patients with dysfibrinogenemia. In patients with hypofibrinogenemia, there is a correlation (r = 0.9016) between the fibrinogen Clauss assay and PT-derived fibrinogen assay with a statistical significance of p < 0.0001. Using a linear or quadratic interpolation function, we were able to determine the fibrinogen Clauss assay and the fibrinogen antigen assay before analysis. CONCLUSIONS: The higher level of the PT-derived fibrinogen assay compared to the fibrinogen Clauss assay in the group of patients with dysfibrinogenemia may pose a greater risk to asymptomatic patients who require diagnosis and treatment in case of bleeding. The fibrinogen value using the PT-derived fibrinogen assay could erroneously give a normal level. The use of the interpolation function is important to estimate the value of fibrinogen activity and antigen before the analysis itself by the Clauss assay or analysis by the fibrinogen antigen assay.

Genetic Background of von Willebrand Disease: History, Current State, and Future Perspectives.

Sequencing of the gene encoding for von Willebrand factor (VWF) has brought new insight into the physiology of VWF as well as its pathophysiology in the context of von Willebrand disease (VWD). Molecular testing in VWD patients has shown high variability in the overall genetic background of this condition. Almost 600 mutations and many disease-causing mechanisms have been described in the 35 years since the VWF gene was identified. Genetic testing in VWD patients is now available in many centers as a part of the VWD diagnostic algorithm. Molecular mechanisms leading to types 2 and 3 VWD are well characterized; thus, information from genetic analysis in these VWD types may be beneficial for their correct classification. However, the molecular basis of type 1 VWD is still not fully elucidated and most likely represents a multifactorial disorder reflecting a combined impact of environmental and genetic factors within and outside of VWF. Regarding sequencing methods, the previous gold-standard Sanger sequencing is gradually being replaced with next-generation sequencing methods that are more cost- and time-effective. Instead of gene-by-gene approaches, gene panels of genes for coagulation factors and related proteins have recently become a center of attention in patients with inherited bleeding disorders, especially because a high proportion of VWD patients, mainly those with low VWF plasma levels (type 1), appear to be free of mutations in VWF. Whole-exome sequencing (WES) and whole-genome sequencing (WGS) are accessible in a very limited number of laboratories. Results from these studies have presented several genes other than VWF or ABO possibly affecting VWF levels, and such findings will need further validation studies.

The Effect of Proton Pump Inhibitor Withdrawal on Dabigatran Etexilate Plasma Levels in Patients With Atrial Fibrillation: A Washout Study.

BACKGROUND: Several studies demonstrated that proton pump inhibitors (PPIs) co-administrated with dabigatran in patients with atrial fibrillation (AF) decreased dabigatran trough and peak plasma levels. However, it is still unknown whether this interaction is reversible or not, and whether the withdrawal of PPI would lead to normalization of dabigatran plasma levels. AIM OF STUDY: The aim of this study was to determine the effect of PPI withdrawal on dabigatran plasma levels in patients with AF. METHODS: This pilot prospective study enrolled 23 AF patients on long-term dabigatran and PPI therapy (omeprazole 20 mg twice daily or pantoprazole 40 mg once daily). Dabigatran trough and peak levels (ng/mL) were tested on PPI and after a 2-week period of PPI withdrawal with Hemoclot Thrombin Inhibitor Assay. RESULTS: The analysis of dabigatran plasma levels demonstrated significant elevation in trough dabigatran levels after 2 weeks of PPI withdrawal (97.2 ± 79.7 vs. 163.8 ± 105.5 ng/mL; P < 0.05). Moreover, significantly higher peak dabigatran levels were observed after 2 weeks of PPI withdrawal (142.4 ± 102.8 vs. 255 ± 129.5 ng/mL; P ≤ 0.001). CONCLUSIONS: This study showed that a 2-week period of PPI withdrawal lead to a significant increase in dabigatran trough and peak plasma levels in patients with AF.

Genetic Variants in the FGB and FGG Genes Mapping in the Beta and Gamma Nodules of the Fibrinogen Molecule in Congenital Quantitative Fibrinogen Disorders Associated with a Thrombotic Phenotype.

Fibrinogen is a hexameric plasmatic glycoprotein composed of pairs of three chains (Aα, Bß, and γ), which play an essential role in hemostasis. Conversion of fibrinogen to insoluble polymer fibrin gives structural stability, strength, and adhesive surfaces for growing blood clots. Equally important, the exposure of its non-substrate thrombin-binding sites after fibrin clot formation promotes antithrombotic properties. Fibrinogen and fibrin have a major role in multiple biological processes in addition to hemostasis and thrombosis, i.e., fibrinolysis (during which the fibrin clot is broken down), matrix physiology (by interacting with factor XIII, plasminogen, vitronectin, and fibronectin), wound healing, inflammation, infection, cell interaction, angiogenesis, tumour growth, and metastasis. Congenital fibrinogen deficiencies are rare bleeding disorders, characterized by extensive genetic heterogeneity in all the three genes: FGA, FGB, and FGG (enconding the Aα, Bß, and γ chain, respectively). Depending on the type and site of mutations, congenital defects of fibrinogen can result in variable clinical manifestations, which range from asymptomatic conditions to the life-threatening bleeds or even thromboembolic events. In this manuscript, we will briefly review the main pathogenic mechanisms and risk factors leading to thrombosis, and we will specifically focus on molecular mechanisms associated with mutations in the C-terminal end of the beta and gamma chains, which are often responsible for cases of congenital afibrinogenemia and hypofibrinogenemia associated with thrombotic manifestations.

Sticky Platelet Syndrome: 35 Years of Growing Evidence.

Since the identification of antithrombin deficiency by Egeberg in 1956, ongoing research in prothrombotic defects continues to progress. Interestingly, past research has predominantly focused on coagulation factors and not on other components of the hemostatic system. The possible role of platelet function defects in the development of thrombotic events was suggested for the first time in the late 1970s, when an increased platelet adhesiveness and aggregation after epinephrine (EPI) and adenosine diphosphate (ADP) was found in a group of patients with unexplained transient ischemic attack. Clinical evidence for other types of thrombotic events (e. g. myocardial infarction, ischemic stroke, optic neuropathy, and pregnancy-related complications) with similar laboratory findings was provided by several authors in the 1980s and 1990s, with Drs. Mammen and Bick undertaking key research. The familial occurrence was noted as well, and the term sticky platelet syndrome was introduced by Holliday in 1983 to describe the defect. The term in our present understanding describes a thrombophilic qualitative platelet disorder characterized by increased in vitro platelet aggregation after the addition of very low concentrations of ADP and/or EPI and an increased risk of thromboembolic (predominantly arterial) events. Although now recognized for 35 years, significant issues, namely its etiology, inheritance, epidemiology, and diagnostics, remain a matter of vigorous debate. The aim of this review is to summarize the history, key works, and present understanding of the syndrome and to outline present-day diagnostic and clinical problems and controversies.

Proton Pump Inhibitors and Dabigatran Therapy: Impact on Gastric Bleeding and Dabigatran Plasma Levels.

Dabigatran etexilate, a direct thrombin inhibitor, is now frequently used for long-term pharmacological prevention of stroke or systemic embolism in patients with atrial fibrillation. However, such long-term dabigatran therapy (DT) significantly increases the risk of upper gastrointestinal (GI) bleeding. This increased risk of gastric bleeds might be reduced with gastroprotective agents, such as proton pump inhibitors (PPIs). PPIs coadministrated with dabigatran reduce the risk of upper GI bleeding in patients on long-term oral DT. Nevertheless, there is heated discussion regarding interactions between PPI and dabigatran that lead to decreases in dabigatran plasma levels. This article reviews up to date data about the risk of gastric bleeding on dabigatran, the impact of PPI on the reduction of gastric bleeding, and the interaction between PPI and dabigatran leading to decreased dabigatran plasma levels.

The Impact of Proton Pump Inhibition on Dabigatran Levels in Patients With Atrial Fibrillation.

BACKGROUND: Proton pump inhibition (PPI) administrated together with dabigatran reduces the risk of gastrointestinal hemorrhage. However, there is a discussion regarding possible PPI-dabigatran interaction that may reduce the efficacy of this therapy. STUDY QUESTION: To determine the impact of concomitant PPI on dabigatran plasma levels in patients with nonvalvular atrial fibrillation (NV-AF). STUDY DESIGN: A pilot prospective study in patients with NV-AF on dabigatran therapy was performed; 31 patients were enrolled. PPI with either omeprazole or pantoprazole was administrated in 19 patients. MEASURES AND OUTCOMES: Blood samples were taken for the assessment of the dabigatran trough and peak levels. Dabigatran concentration was measured with the Hemoclot Thrombin Inhibitor Assay. RESULTS: There were significant differences in dabigatran trough level comparing patients treated with PPI and patients without PPI (58.86 ± 36.76 ng/mL vs. 110.72 ± 88.47 ng/mL, P < 0.05). Similarly, there were significant differences in dabigatran peak level between compared groups (88.0 ± 20.5 ng/mL vs. 174.4 ± 139.64 ng/mL, P < 0.05). CONCLUSIONS: This pilot study demonstrated the interaction between PPI and dabigatran levels in patients with NV-AF.

Apixaban: a novel agent to treat heparin induced thrombocytopenia and to prevent embolism in patient with atrial fibrillation after multiple valve replacement?

Very limited but promising experiences with the use of direct factor Xa inhibitors for the treatment of heparin-induced thrombocytopenia (HIT) have been reported. This contribution features our first experience with the use of apixaban (without a pre-treatment with parenteral anticoagulant) to treat a case of HIT which developed in a patient after multiple heart replacement surgery. Apixaban was effective, well tolerated and safe. An apixaban-calibrated chromogenic anti-Xa activity assessment was used to monitor apixaban activity throughout the therapy. Patient continued on apixaban for the prevention of thrombosis in the settings of atrial fibrillation. No ischemic or bleeding events occurred during the clinical follow up and the platelet count was stable. Our experience suggests that apixaban might be effectively used for the treatment of HIT and for the long-term prevention of embolism in patients after multiple valve replacement with biological prostheses and atrial fibrillation.

Does proton pump inhibition change the on-treatment anti-Xa activity in xabans-treated patients with atrial fibrillation? A pilot study.

Proton pump inhibition (PPI) reduces gastrointestinal bleeding on direct oral anticoagulants. However, PPI may affect dabigatran on-treatment levels; and there is no information regarding the effect of PPI on xabans on-treatment activity. Thus, the aim of this study was to determine the impact of PPI on therapeutic anti-Xa activity in rivaroxaban- and apixaban-treated patients with atrial fibrillation (AF). This single-centre pilot prospective study enrolled 77 consecutive xabans-treated patients (42 rivaroxaban-treated and 35 apixaban-treated patients) with AF. PPI was administrated in 44 patients. Trough and peak anti-Xa activity was assessed with factor Xa-calibrated anti-Xa chromogenic analysis. There were no significant differences in trough anti-Xa activity comparing PPI-treated patients and patients without PPI (80.5 ± 66.5 ng/mL in PPI group vs. 71.6 ± 64.1 ng/mL in non-PPI group, p = 0.57, Table 2). Similarly, there were no significant differences in peak anti-Xa activity between compared groups (175.2 ± 102.5 ng/mL in PPI group vs. 202.9 ± 84.1 ng/mL in non-PPI group, p = 0.21). This pilot study did not reveal significant changes in xabans on-treatment anti-Xa activity according the PPI status.

Proton Pump Inhibition in Patients Treated With Novel Antithrombotic Drugs: Should We Worry About Thrombosis?

Proton pump inhibition (PPI) administered together with antiplatelet and anticoagulant agents reduces the risk of gastrointestinal hemorrhage. Several novel antithrombotic agents have been recently introduced for patients with acute coronary syndrome (prasugrel and ticagrelor) or for patients requiring long-term anticoagulation (dabigatran, rivaroxaban, apixaban, edoxaban, and betrixaban). In fact, these agents might offer even stronger inhibition of platelets or coagulation compared with older agents; therefore, the need for gastroprotection might be even stronger when these new agents are used for long-term antithrombotic therapy. On the contrary, there are several reports regarding an adverse interaction between PPI and antithrombotic agents connected with a reduction in antithrombotic therapy on-treatment levels, implicating a higher risk of thrombosis. This interaction was demonstrated in clopidogrel-treated patients and more recently also in dabigatran-treated patients. This article discusses a possible novel antithrombotic therapy/PPI interaction leading to higher risk of thrombosis.

Progress in the Understanding of Sticky Platelet Syndrome.

The knowledge on the etiology of thrombosis has increased tremendously over the past decades. Nevertheless, Virchow triad is still traditionally invoked to explain mechanisms leading to thrombosis, alleging concerted roles for abnormalities in blood composition, vessel wall components, and blood flow in the development of arterial and venous thrombosis. Recent decades have been focused primarily on describing abnormalities in blood composition, including defects of coagulation proteins and platelets. Although defects of coagulation factors are relatively well-described in the literature, prothrombotic platelet disorders are still less understood. One such defect, the Wien-Penzing defect was first described in 1991. Another platelet defect is sticky platelet syndrome (SPS). In this article, we review information about SPS, and we propose a new definition and standardization of diagnostic criteria. We also attempt to explain the causes and consequences of this condition.

Platelet Aggregation in Direct Oral Factor Xa Inhibitors-treated Patients With Atrial Fibrillation: A Pilot Study.

BACKGROUND: Activated factor X (factor Xa) plays an important role in regulation of platelets. The aim of this study was to test the effect of direct oral factor Xa inhibitors-rivaroxaban and apixaban-on platelet aggregation in patients with nonvalvular atrial fibrillation. PATIENTS AND METHODS: This single-center pilot study enrolled 21 factor Xa inhibitors-treated (9 rivaroxaban-treated and 12 apixaban-treated) patients with nonvalvular atrial fibrillation. The trough and peak samples of these patients were tested for adenosine diphosphate (ADP)-induced, epinephrine-induced, and collagen-induced platelet aggregation with light transmission aggregometry, and with factor Xa-calibrated anti-Xa chromogenic analysis. RESULTS: The detected trough anti-Xa activity was 57.5 ± 43.4 µg/L. There was a significant increase in peak anti-Xa activity to 175.9 ± 119.6 µg/L (P < 0.001) observed. The platelet aggregation was reduced with reduced inductor concentration. However, no significant changes in ADP-induced, or in epinephrine-induced, or in collagen-induced platelet aggregation were seen comparing trough and peak sample. There were no significant differences in anti-Xa activity or in platelet aggregation comparing rivaroxaban-treated and apixaban-treated patients. CONCLUSIONS: This study showed that factor Xa inhibition does not affect ADP-induced, epinephrine-induced, and collagen-induced platelet aggregation.

Does Pantoprazole Affect the On-Treatment Platelet Reactivity in Patients With Acute STEMI Treated With ADP Receptor Blockers?-A Pilot Prospective Study.

BACKGROUND: Proton pump inhibition (PPI) administrated together with adenosine diphosphate (ADP) receptor blockers (ADPRB) significantly reduces the risk of gastrointestinal bleeding. Nevertheless, there is a heated discussion about an interaction between PPI and ADPRB that leads to high on-treatment platelet reactivity (HTPR). STUDY QUESTION: Is there a relationship between pantoprazole PPI and HTPR on ADPRB therapy in patients with acute ST-elevation myocardial infarction (STEMI). METHODS: Single center pilot study in patients with acute STEMI was performed. This study enrolled totally 87 patients (34 clopidogrel-treated and 53 new ADPRB-treated patients). Pantoprazole was administrated in 33 patients. HTPR was detected with ADP-induced light transmission aggregometry and vasodilator-stimulated phosphoprotein phosphorylation analysis. Samples were taken before coronary angiography (sample 1) and on the next day after the procedure (sample 2). RESULTS: No significant differences were found in pantoprazole-treated patients and patients without PPI neither in sample 1 (59.2 ± 29.5% vs. 54.9 ± 22.7%, P = 0.49) nor in sample 2 (43.8 ± 27.2% vs. 37.0 ± 22.9%, P = 0.30). Similarly, there were no significant differences in the platelet reactivity index of vasodilator-stimulated phosphoprotein phosphorylation in both samples (sample 1: 53.3 ± 29.8% vs. 65.0 ± 20.5%, P = 0.11; sample 2: 30.8 ± 27.1% vs. 40.6 ± 27.5%, P = 0.19). A comparison of clopidogrel and new ADP receptor blockers in patients on pantoprazole PPI did not reveal significant differences in on-treatment platelet reactivity. CONCLUSIONS: This study did not reveal interaction between pantoprazole and ADPRB in patients with acute STEMI.