Effects of recombinant human activated protein C on the coagulation system: a study with rotational thromboelastometry

Ex vivo reversal of effects of rivaroxaban evaluated using thromboelastometry and thrombin generation assay

Background

In major bleeding events, the new direct oral anticoagulants pose a great challenge for physicians. The aim of the study was to test for ex vivo reversal of the direct oral anticoagulant rivaroxaban with various non-specific reversal agents: prothrombin complex concentrate (PCC), activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and fibrinogen concentrate (FI).

Methods

Blood was obtained from healthy volunteers and from patients treated with rivaroxaban. Blood samples from healthy volunteers were spiked with rivaroxaban to test the correlation between rivaroxaban concentration and coagulation tests. Patient blood samples were spiked with various concentrations of the above-mentioned agents and analysed using thromboelastometry and thrombin generation.

Results

When added in vitro, rivaroxaban was significantly (P<0.05) correlated with ROTEM^® thromboelastometry EXTEM (extrinsic coagulation pathway) clotting time (CT), time to maximal velocity (MaxV−t), and with all measured thrombin generation parameters. In vivo, CT, MaxV−t, lag time, and peak thrombin generation (C_max) were significantly correlated with rivaroxaban concentrations. Regarding reversal of rivaroxaban, all tested agents significantly (P<0.05) reduced EXTEM CT, but to different extents: rFVIIa by 68%, aPCC by 47%, PCC by 17%, and FI by 9%. Only rFVIIa reversed EXTEM CT to baseline values. Both PCC (+102%) and aPCC (+232%) altered overall thrombin generation (area under the curve) and increased C_max (+461% for PCC, +87.5% for aPCC).

Conclusions

Thromboelastometry and thrombin generation assays do not favour the same reversal agents for rivaroxaban anticoagulation. Controlled clinical trials are urgently needed to establish doses and clinical efficacy of potential reversal agents.

Clinical trial registration

EudracCT trial no. 213-00474-30.

Inducing Acute Traumatic Coagulopathy In Vitro: The Effects of Activated Protein C on Healthy Human Whole Blood

INTRODUCTION

Acute traumatic coagulopathy has been associated with shock and tissue injury, and may be mediated via activation of the protein C pathway. Patients with acute traumatic coagulopathy have prolonged PT and PTT, and decreased activity of factors V and VIII; they are also hypocoagulable by thromboelastometry (ROTEM) and other viscoelastic assays. To test the etiology of this phenomenon, we hypothesized that such coagulopathy could be induced in vitro in healthy human blood with the addition of activated protein C (aPC).

METHODS

Whole blood was collected from 20 healthy human subjects, and was "spiked" with increasing concentrations of purified human aPC (control, 75, 300, 2000 ng/mL). PT/PTT, factor activity assays, and ROTEM were performed on each sample. Mixed effect regression modeling was performed to assess the association of aPC concentration with PT/PTT, factor activity, and ROTEM parameters.

RESULTS

In all subjects, increasing concentrations of aPC produced ROTEM tracings consistent with traumatic coagulopathy. ROTEM EXTEM parameters differed significantly by aPC concentration, with stepwise prolongation of clotting time (CT) and clot formation time (CFT), decreased alpha angle (α), impaired early clot formation (a10 and a20), and reduced maximum clot firmness (MCF). PT and PTT were significantly prolonged at higher aPC concentrations, with corresponding significant decreases in factor V and VIII activity.

CONCLUSION

A phenotype of acute traumatic coagulopathy can be induced in healthy blood by the in vitro addition of aPC alone, as evidenced by viscoelastic measures and confirmed by conventional coagulation assays and factor activity. This may lend further mechanistic insight to the etiology of coagulation abnormalities in trauma, supporting the central role of the protein C pathway. Our findings also represent a model for future investigations in the diagnosis and treatment of acute traumatic coagulopathy.

Utility of thromboelastography and/or thromboelastometry in adults with sepsis: a systematic review

Introduction

Coagulation abnormalities are frequent in sepsis. Conventional coagulation assays, however, have several limitations. A surge of interest exists in the use of point-of-care tests to diagnose hypo- and hypercoagulability in sepsis.

We performed a systematic review of available literature to establish the value of rotational thromboelastography (TEG) and thromboelastometry (ROTEM) compared with standard coagulation tests to detect hyper- or hypocoagulability in sepsis patients. Furthermore, we assessed the value of TEG/ROTEM to identify sepsis patients likely to benefit from therapies that interfere with the coagulation system.

Methods

MEDLINE, EMBASE, and the Cochrane Library were searched from 1 January 1980 to 31 December 2012. The search was limited to adults, and language was limited to English. Reference lists of retrieved articles were hand-searched for additional studies. Ongoing trials were searched on http://www.controlled-trials.com and http://www.clinicaltrials.gov. Studies addressing TEG/ROTEM measurements in adult patients with sepsis admitted to the ICU were considered eligible.

Results

Of 680 screened articles, 18 studies were included, of which two were randomized controlled trials, and 16 were observational cohort studies. In patients with sepsis, results show both hyper- and hypocoagulability, as well as TEG/ROTEM values that fell within reference values. Both hyper- and hypocoagulability were to some extent associated with diffuse intravascular coagulation. Compared with conventional coagulation tests, TEG/ROTEM can detect impaired fibrinolysis, which can possibly help to discriminate between sepsis and systemic inflammatory response syndrome (SIRS). A hypocoagulable profile is associated with increased mortality. The value of TEG/ROTEM to identify patients with sepsis who could possibly benefit from therapies interfering with the coagulation system could not be assessed, because studies addressing this topic were limited.

Conclusion

TEG/ROTEM could be a promising tool in diagnosing alterations in coagulation in sepsis. Further research on the value of TEG/ROTEM in these patients is warranted. Given that coagulopathy is a dynamic process, sequential measurements are needed to understand the coagulation patterns in sepsis, as can be detected by TEG/ROTEM.