Effect of anticoagulation on the lysis of filter entrapped thromboembolism in dogs.

Resolution of thrombi entrapped in Greenfield vena caval filters is a primary mechanism for maintenance of caval patency with this device following an embolic event. In order to determine if anticoagulation is beneficial in this setting, thrombus was harvested from 65 mongrel dogs with infrarenal IVC thrombosis after phenolization. These thrombi were weighed and embolized into Greenfield filters placed above the renal veins. The infrarenal IVCs were then ligated and the animals allowed to recover. Beginning the first postoperative day, animals were given either oral coumadin daily to elevate the prothrombin time above 1.5 normal, subcutaneous heparin 500 u/kg/day divided into two doses, or received no treatment. They were sacrificed either 1, 2, 3, or 4 weeks after embolism and the residual thrombi weighed. Initial thrombus weights were similar for each period (differences NS). Comparison of initial with final weights revealed that both coumadin and heparin-treated animals had a significantly increased resolution in the first week when compared to controls. By 2 weeks, however, there were no significant differences between the groups, and controls proceeded to a mean of 95% resolution by 4 weeks. A general linear model used to separate the effects of treatment, time, and initial thrombus weight showed that resolution was primarily a function of initial thrombus weight, and of time. Coumadin was marginally beneficial. Thrombus resolution proceeds rapidly in this model without anticoagulation. These data suggest that prevention of deep vein thrombosis and its sequelae remain the sole indication for anticoagulation after filter placement.