Recurrent venous thromboembolism patients form clots with lower elastic modulus than those with non-recurrent disease.

BACKGROUND:Venous thromboembolism (VTE) is associated with a high risk of recurrent events after withdrawal of anticoagulation. OBJECTIVES:The aim of this study was to determine the difference in plasma clot mechanical properties from patients having recurrent (r) versus non-recurrent (nr) VTE. METHODS:We previously developed a system for determining clot mechanical properties using an in-house magnetic tweezers system. This system was used to determine the mechanical properties of clots made from plasma of 11 patients with rVTE and 33 with nrVTE. Plasma was mixed with micrometre-sized beads followed by the addition of thrombin and calcium to induce clotting, then placed in small capillary tubes and allowed to clot overnight. Bead displacements upon manipulation with magnetic forces were analysed to determine clot elastic and viscous moduli. Fibrin clot structure was analysed by turbidimetry and confocal microscopy. FXIII was measured by pentylamine incorporation into fibrin. RESULTS:Clots from rVTE patients showed nearly two-fold less elastic and less viscous moduli than clots from nrVTE patients, regardless of male sex, unprovoked events, family history of VTE, fibrinogen concentration or BMI. No differences were observed in clot structure, fibrinolysis rates or FXIII levels. CONCLUSION:Using magnetic tweezers for the first time in patient samples, we found that plasma clots from rVTE patients demonstrated reduced elastic modulus and reduced viscous modulus when compared with nrVTE patients. These data indicate a possible role for fibrin clot visco-elastic properties in determining VTE recurrence.