Abstract WP269: Increased Sensitivity to recombinant Tissue Plasminogen Activator (rtPA)-induced Lysis in vitro of Thrombi Produced in Human Platelet Rich Plasma containing Dabigatran

Dabigatran is a direct thrombin inhibitor approved for the prevention of stroke in patients with atrial fibrillation. It significantly reduced ischemic and hemorrhagic stroke in these patients vs warfarin. However, in patients treated with dabigtran who developed a stroke, there remain unresolved issues regarding thrombolysis therapy, both in terms of timing of lytic treatment to minimize hemorrhage risk and also lytic dose. It is hypothesized that if the fibrin network in a thrombus formed in patients on dabigatran treatment is altered and is less compact, then it may be more sensitive to lysis at lower doses of rtPA. Thrombi were produced in human platelet rich plasma (PRP) in the presence of low conc. of dabigatran (0, 30, 75 ng/ml). PRP was supplemented with 594-Alexa fluorescent labelled human fibrinogen. Thromboplastin (Thromborel ® ) and 200mM CaCl 2 were added and this was incubated at 37°C for 60 min to allow clot formation. Thrombi were removed from PRP and washed twice in saline. They were then added to human plasma from the same subject containing increasing conc. (0-250 IU/ml) of rtPA (Actilyse ® ) and incubated for 2 hrs under continual stirring conditions at 37°C. Lysis was measured as amount of fluorescence released into plasma from the thrombus over 2hrs. Preformed thrombi added to plasma containing only dabigatran underwent no lysis. Lysis of preformed control thrombi (in the absence of dabigatran) occurred in a conc-dependent manner when incubated with rtPA and maximal lysis was achieved with 300 IU/mL. Thus further experiments were performed with ≤250 IU/ml rtPA to look for potential synergistic effects with dabigatran. Clots preformed in PRP containing either 30 or 75 ng/mL dabigatran were more susceptible to rtPA-induced lysis, with maximal lysis achieved with 100 IU/mL rtPA, and ~ 90% lysis was achieved with 50 IU/mL rtPA. These data provide evidence that thrombi preformed in low concentrations of dabigatran appear to be more susceptible to thrombolysis with rtPA than those preformed in the absence of dabigatran, thus lower concentrations of rtPA achieve a similar degree of thrombolysis under these experimental conditions. This may imply that in patients that suffer a stroke while on dabigatran therapy, lower doses of tPA may also be effective.