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 (Cmax) 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 Cmax (+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.

Vein graft thrombi, a niche for smooth muscle cell colonization - a hypothesis to explain the asymmetry of intimal hyperplasia.

UNLABELLED: Essentials Vein graft failure is the most frequent late onset complication of coronary artery bypass grafting. Cuff technique-based interposition mouse model including new anticoagulation regime was conducted. Early vein graft thrombi may serve as a niche for smooth muscle cell colonization. The focal character of early thrombi may form the basis for the asymmetry of intimal hyperplasia. SUMMARY: Background Autologous saphenous veins are widely used in coronary artery bypass grafting; however, 10 years after surgery, 40% of grafts are completely occluded, and another 30% show reduced blood flow. Objective In the past, the central processes and signaling pathways responsible for this loss of patency have been identified. However, one central finding in the process of graft failure is so far not understood: the asymmetric character of intimal hyperplasia. It was the goal of the present study to address this aspect. Methods By the use of a cuff technique-based vein interposition mouse model with a new anticoagulation regime, alterations in vein grafts were analyzed 1 h, 1 day, 2 days, 3 days, 7 days and 21 days after reperfusion by means of immunolabeling, histochemistry, and high-resolution ultrasound. Results The novel and major finding of this study is that the vein graft thrombus may serve as a niche that is infiltrated and colonized by smooth muscle cells (SMCs). Fibroblast growth factor-1 and platelet-derived growth factor-B may be the SMC-attracting factors in the thrombus. The focal character of early thrombi may define the focal and asymmetric character of vein graft intimal hyperplasia. Conclusions Inhibiting the formation and reducing the size of early thrombi is an old concept for reducing vein graft failure. However, in light of the present new findings obtained under a clinic-like anticoagulation regime, early vein graft thrombus prevention/size reduction should be revisited in the prevention of graft failure.

Novel point mutation in fibrinogen (Innsbruck; BßArg44Gly). Phenotypic differences compared to another mutation (fibrinogen Nijmegen) at the same position.

This is a report of a novel fibrinogen point mutation (fibrinogen Innsbruck), a C/G point mutation at position 220 of exon two of the fibrinogen Bß-chain leading to BßArg44Gly. The heterozygous mutation was found in a 16-year-old adolescent, hospitalized for the management of juvenile depression, who suffered from multiple epistaxis episodes during his stay at the university hospital in Innsbruck, Austria. Fibrinogen (based on the Clauss method) and fibrinogen antigen levels were highly discrepant (86 vs. 223 mg/dl) with thrombin time and reptilase time being in the respective upper reference ranges. Densitometric analysis of electrophoretic band pattern showed a reduction of α-polymers, indicating an impaired fibrin polymerization. This is in agreement with structural analysis, which showed a disturbance of the flexibility and structure of the region surrounding the fibrinoeptide B cleavage site. Fibrinogen Nijmegen, a mutation at the same position, is causative for thrombosis, whereas fibrinogen Innsbruck appears to lead to a bleeding tendency, illustrating that even mutations at the same position can cause contrary symptoms.