We reported in our previous study that the main component of thrombus in acute venous thrombosis was fibrinogen and albumin and cytoskeletal proteins accounted for only a minor fraction of the thrombus (29) . The thrombus composed of fibrinogen is unstable, which makes the delayed thrombolysis feasible and also explain the therapeutic effectiveness of transcatheter thrombolysis not long after APE. Findings support that the formation of thrombus in VTE is not due to the comprehensive activation of coagulation factors as in traditional theory.