18 * Effect of warfarin and rivaroxaban on clot structure

Abstract

Introduction: In atrial fibrillation (AF), oral anticoagulant (OAC) is the mainstay treatment in prevention of stroke. However, the various OAC confers one with different level of protection against thrombosis and bleeding risk, possibly due to different effect on fibrin clot structure. Coagulation and clot lysis can be assessed by Thrombelastography (TEG). Methods: Blood samples from 29 warfarin patients (Mean INR 2.41, SD 0.58), 18 Rivaroxaban patients (dose 20mg daily) and 18 patients on Antiplatelet agent (such as Aspirin 75mg) were collected and analysed by Thromboelastography (TEG). Demographics of these 65 AF patients were also collected. All results are analysed by statistical methods involving one-way analysis of variance (ANOVA). Results: Using TEG, the ability of warfarin and Rivaroxaban to delay fibrin clot formation was confirmed, with similar R-time between Warfarin and Rivaroxaban user as opposed to antiplatelet user (8.3 minutes vs 9.1 minutes vs 5.9, p = 0.039). No significant differences were seen in Maximum Amplitude or strength of clot, G (kd/sc), between all three groups. However, Rivaroxaban and antiplatelet agent resulted in a steeper a-angle when compared to warfarin (65.58 vs 65.88 vs 59.08, p = 0.026), a greater percentage of fibrin clot autolysis at 60 minutes (3.8% vs 4.2% vs 2.1%, p = 0.002) and a tendency to allow for shorter K-time (1.8 min vs 1.7 min vs 2.4 min, p = 0.051). There is no significant difference in age, gender, body mass index, body weight between all three groups. Conclusions: Rivaroxaban efficacy in impeding coagulation is demonstrated by the delay fibrin clot formation. However it does not appear to reduce the rate of fibrin build-up like warfarin, as demonstrated by steeper a-angle and shorter K-time, possibly due to its unique inhibitory action specifically on Factor Xa. Warfarin use in this cohort resulted in formation of clots which are less responsive to fibrinolysis (lower lysis at 60 minutes). This might possibly explain why Rivaroxaban has reduced serious bleeding risks (intracranial bleeding, life threatening bleeding) as compared to Warfarin. TEG Indices of Warfarin vs Rivaroxaban vs Antiplatelet agent. (Table Presented).