Effects of direct oral anticoagulants on thromboelastographic parameters and fibrin clot properties in patients with venous thromboembolism.

Data concerning the impact of direct oral anticoagulants (DOACs) on the thromboelastography (TEG) indices in venousthromboembolism (VTE) patients are limited. The goal of this study was to compare the impact of DOACs on clot properties measured in whole blood using TEG kaolin test and in plasma obtained from real-life VTE patients. We assessed 53 patients, including 20 on rivaroxaban, 20 on apixaban, and 13 on dabigatran. Using the TEG® 5000, coagulation status was evaluated in whole blood samples, while plasma fibrin clot permeability (Ks) and its susceptibility to lysis (CLT) were assessed in citrated plasma. Plasma concentrations of rivaroxaban (99 [48 - 311] ng/ml) and apixaban (85 [40 - 105] ng/ml) were positively associated with Ks and inversely with CLT, while dabigatran concentrations (71 [39 - 98] ng/ml) correlated positively with Ks. Moreover, Ks was associated with clot formation times (R and K), time to maximum clot strength (TMA), coagulation index (CI) reflecting the overall coagulation status, and whole blood clot lysis time (TEG-CLT). Blood clot lysis index (CL30) was associated with plasma CLT in all patients on DOACs, while TMA correlated with CLT only in patients on apixaban. Higher DOAC concentrations were associated with longer retardation of whole blood clot formation and longer time needed to reach maximum level of its strength as well as with more permeable clots. We concluded that plasma fibrin clot properties correlate with corresponding TEG indices suggesting that TEG might be helpful in providing prognostic information about DOAC influence in VTE patients.

Viscoelastic properties of plasma fibrin clots are similar in patients on rivaroxaban and vitamin K antagonists.

Unfavorable fibrin clot features have been observed in patients with venous thromboembolism (VTE). We investigated whether rivaroxaban, a direct factor Xa inhibitor, and vitamin K antagonists (VKAs) can improve plasma clot viscoelastic properties. We studied four age- and sex-matched groups: 25 healthy controls, 15 VTE patients taking rivaroxaban 20 mg/day (blood concentration, 145 (67 - 217) ng/ml), 15 VTE patients taking VKA (INR: 2 - 3), and 15 VTE patients who stopped oral anticoagulant therapy (OAT). Using a hybrid rheometier the storage (G') and loss (G") moduli were evaluated in citrated plasma after addition of 5 pmol/l tissue factor. Fiber thickness within clots was assessed using scanning electron microscopy. Higher G' but not G" was observed for VTE patients taking rivaroxaban (+34%; post hoc, P = 0.029) compared to controls. As reflected by lower G' and G", patients taking rivaroxaban (-19% and -30%; post hoc, P = 0.0013 and P < 0.0001, respectively) formed less stiff and viscous clots compared to VTE patients after OAT withdrawal, also after adjustment for fibrinogen. VTE patients treated with rivaroxaban and VKA had similar clot viscoelastic properties (post hoc, P = 0.85 for G' and P = 0.29 for G"). G' and G" correlated with plasma rivaroxaban concentrations (r = -0.67, P = 0.005 and r = -0.59, P = 0.021, respectively), and the time from the last dose of rivaroxaban intake (r = 0.59, P = 0.02 and r = 0.58, P = 0.022, respectively). G' and G" showed no association with INR in patients on VKAs. G' or G" were not associated with fibrin diameter on scanning electron microscopy images in either group. Our preliminary study shows that both rivaroxaban and VKA improve clot viscoelastic properties in VTE patients, which might contribute to their antithrombotic effects. G' and G" may reflect specific clot physical features, beyond key plasma clot characteristics, which highlights benefits from comprehensive plasma clot analysis in patients with thrombotic diseases.