Thrombin generation and fibrinolysis in anti-factor IX treated blood and plasma spiked with factor VIII inhibitor bypassing activity or recombinant factor VIIa

Improved outcome with individualised antifibrinolytic therapy: what is the evidence?

Viscoelastic haemostatic testing (VHT) has been used to determine hyperfibrinolysis and hypofibrinolysis. When modified by addition of tissue plasminogen activator (tPA), VHT has been suggested to assess responses to antifibrinolytic therapy and to estimate the concentration of tranexamic acid in patients undergoing cardiac surgery. Despite some evidence that tPA-modified VHT might allow individualisation of antifibrinolytic therapy, further studies are warranted to prove its clinical benefit for postsurgical bleeding, transfusion of blood products, and thromboembolic events.

Point-of-care testing for tranexamic acid efficacy: a proof-of-concept study in cardiac surgical patients

BACKGROUND

Low-dose tranexamic acid (TXA) has been recently recommended for cardiopulmonary bypass (CPB) to reduce associated complications. Although point-of-care laboratory tests for TXA concentrations are unavailable, a novel TPA-test on the ClotPro® system can measure TXA-induced inhibition of fibrinolysis. We evaluated the performance of the TPA-test in vitro and in patients undergoing surgery requiring CPB.

METHODS

Blood samples were obtained from six volunteers for in vitro evaluation of tissue plasminogen activator (tPA)-triggered fibrinolysis and the effects of TXA. This was followed by an observational study in 20 cardiac surgery patients to assess clinical effects of TXA on the TPA-test.

RESULTS

Hyperfibrinolysis induced by tPA was inhibited by TXA ≥2 mg L-1 in a concentration-dependent manner, and was completely inhibited at TXA ≥10 mg L-1. In patients undergoing CPB, antifibrinolytic effect was detectable on TPA-test parameters after a 0.1 g bolus of TXA at the end of CPB, and complete inhibition of fibrinolysis was obtained with TXA ≥0.5 g. The antifibrinolytic effects of 1 g TXA on TPA-test parameters were gradually attenuated over 18 h after surgery. However, the fibrinolytic inhibition continued in four patients with estimated glomerular filtration rate (eGFR) ≤30 ml min-1 1.73 m-2. The eGFR had strong correlations with TPA-test parameters at 18 h after surgery (r=0.86-0.92; P<0.0001).

CONCLUSIONS

The TPA-test is sensitive to low concentrations of TXA and serves as a practical monitoring tool for postoperative fibrinolytic activity in cardiac surgery patients. This test might be particularly useful in patients with severe renal impairment.

Clinical guideline on reversal of direct oral anticoagulants in patients with life threatening bleeding

BACKGROUND

Anticoagulation is essential for the treatment and prevention of thromboembolic events. Current guidelines recommend direct oral anticoagulants (DOACs) over vitamin K antagonists in DOAC-eligible patients. The major complication of anticoagulation is serious or life-threatening haemorrhage, which may necessitate prompt haemostatic intervention. Reversal of DOACs may also be required for patients in need of urgent invasive procedures. This guideline from the European Society of Anaesthesiology and Intensive Care (ESAIC) aims to provide evidence-based recommendations and suggestions on how to manage patients on DOACs undergoing urgent or emergency procedures including the treatment of DOAC-induced bleeding.

DESIGN

A systematic literature search was performed, examining four drug comparators (dabigatran, rivaroxaban, apixaban, edoxaban) and clinical scenarios ranging from planned to emergency surgery with the outcomes of mortality, haematoma growth and thromboembolic complications. The GRADE (Grading of Recommendations, Assessment, Development and Evaluation) methodology was used to assess the methodological quality of the included studies. Consensus on the wording of the recommendations was achieved by a Delphi process.

RESULTS

So far, no results from prospective randomised trials comparing two active comparators (e.g. a direct reversal agent and an unspecific haemostatic agent such as prothrombin complex concentrate: PCC) have been published yet and the majority of publications were uncontrolled and observational studies. Thus, the certainty of evidence was assessed to be either low or very low (GRADE C). Thirty-five recommendations and clinical practice statements were developed. During the Delphi process, strong consensus (>90% agreement) was achieved in 97.1% of recommendations and consensus (75 to 90% agreement) in 2.9%.

DISCUSSION

DOAC-specific coagulation monitoring may help in patients at risk for elevated DOAC levels, whereas global coagulation tests are not recommended to exclude clinically relevant DOAC levels. In urgent clinical situations, haemostatic treatment using either the direct reversal or nonspecific haemostatic agents should be started without waiting for DOAC level monitoring. DOAC levels above 50 ng ml-1 may be considered clinically relevant necessitating haemostatic treatment before urgent or emergency procedures. Before cardiac surgery under activated factor Xa (FXa) inhibitors, the use of andexanet alfa is not recommended because of inhibition of unfractionated heparin, which is needed for extracorporeal circulation. In the situation of DOAC overdose without bleeding, no haemostatic intervention is suggested, instead measures to eliminate the DOACs should be taken. Due to the lack of published results from comparative prospective, randomised studies, the superiority of reversal treatment strategy vs. a nonspecific haemostatic treatment is unclear for most urgent and emergency procedures and bleeding. Due to the paucity of clinical data, no recommendations for the use of recombinant activated factor VII as a nonspecific haemostatic agent can be given.

CONCLUSION

In the clinical scenarios of DOAC intake before urgent procedures and DOAC-induced bleeding, practitioners should evaluate the risk of bleeding of the procedure and the severity of the DOAC-induced bleeding before initiating treatment. Optimal reversal strategy remains to be determined in future trials for most clinical settings.

Fibrinolysis biomarker, thrombin, and activated protein C level alterations after coagulation activation depend on type of thrombophilia and clinical phenotype

Background

Recently, we have shown alterations in the anticoagulant response to recombinant activated factor VII (rFVIIa)-induced coagulation activation in patients with thrombophilia.

Objectives

This study aimed to extend this in vivo model to fibrinolysis biomarkers.

Methods

This interventional in vivo study included 56 patients with thrombophilia and previous venous thromboembolism (VTE+), 38 without VTE (VTE-), and 35 healthy controls. Plasma levels of D-dimer, plasmin-α2-antiplasmin (PAP) complex, and plasminogen activator inhibitor-1 (PAI-1) were monitored for over 8 hours after rFVIIa infusion (15 μg/kg) along with thrombin markers and activated protein C (APC).

Results

Throughout cohorts, median PAP increased by 40% to 52% (P < 3.9 × 10-10) and PAI-1 decreased by 59% to 79% (P < 3.5 × 10-8). In contrast to thrombin-antithrombin (TAT) complex, which also increased temporarily (44% to 115%, P < 3.6 × 10-6), changes in PAP and PAI-1 did not reverse during the observation period. The area under the measurement-time curves (AUCs) of PAP and TAT, which are measures of plasmin and thrombin formation, respectively, were each greater in the VTE+ cohort than in healthy controls (median PAP-AUC = 0.48 vs 0.27 ng·h/L [P = .003], TAT-AUC = 0.12 vs 0.03 nmol·h/L [P = 2.5 × 10-4]) and were correlated with one another (r = 0.554). As evidenced by the respective AUCs, asymptomatic factor (F)V Leiden carriers showed less PAP formation (0.22 vs 0.41 ng·h/L, P = 9 × 10-4), more pronounced PAI-1 decline (0.10 vs 0.18 ng·h/L, P = .01), and increased APC formation (28.7 vs 15.4 pmol·h/L, P = .02) than those within the VTE+ group (n = 19 each).

Conclusion

rFVIIa-induced thrombin formation is associated with fibrinolysis parameter changes outlasting the concomitant anticoagulant response. Both correlate with thrombosis history in FV Leiden and might help explain its variable clinical expressivity.

Interconnectedness of global hemostasis assay parameters in simultaneously evaluated thrombin generation, fibrin generation and clot lysis in normal plasma

BACKGROUND

Fluorogenic thrombin generation (TG) assays and turbidity-based fibrin generation (FG)- and fibrinolysis (FL)-resistance assays have been sought to assess bleeding and clotting disorders. Theoretically, TG, FG and FL tests should provide overlapping information because thrombin is responsible for FG and induces protection from FL. The relationships between TG, FG and FL parameters remain poorly investigated, partly because existing experimental systems do not permit simultaneous detection of both TG and FG in the same sample of plasma, and are instead tested in separate experiments.

OBJECTIVES AND METHODS

We evaluated the potential benefits of a combined TG/FG/FL assay by testing responses of normal plasma to a wide range of tissue factor (TF) and tissue plasminogen activator (tPA) concentrations. Correlations between multiple parameters extracted from the TG and FG/FL curves were also compared.

RESULTS

Rate of FG correlated well with TG peak height at all TF concentrations, but correlations between TG and FL parameters depended on the TF concentration. Without thrombomodulin, all FG/FL parameters at high TF could be predicted from TG parameters and no FL protection was observed. With thrombomodulin and high TF, TF-dependent FL protection did not correlate with TF-dependent TG. The fluorogenic thrombin substrate did not interfere with optical density readings, and meaningful tPA concentrations did not interfere with TG readings.

CONCLUSIONS

In normal plasma, TG, FG and FL parameters may provide interchangeable information. Evaluation of FL-resistance may provide additional data under special assay conditions, but the value of this information should be studied under disease conditions.