Experimental Model of Large Pulmonary Embolism Employing Controlled Release of Subacute Caval Thrombus in Swine

Purpose: To develop a catheter-based model of large pulmonary embolism (PE) in swine based on in situ venous thrombus formation. Materials and Methods: Ten Yorkshire swine underwent transjugular implantation of a retrievable inferior vena cava (IVC) filter. A thrombin and collagen mixture was injected into a confined space created by two balloons inflated proximal and distal to the IVC filter. Animals were left to survive for 7 days +/- 3 to allow thrombus to organize in situ. The caval thrombus was released on transcatheter retrieval of the IVC filter and embolized into the main and branch pulmonary arteries. The severity of PE was scored based on digital subtraction angiography with the Miller index. At necropsy, thrombi were recovered and analyzed histopathologically. Results: Large PE was induced in all animals (Miller index score of 15 +/- 5). Two animals developed saddle embolus with bilateral pulmonary artery occlusion, and five developed proximal occlusion of the left or right pulmonary artery. Nevertheless, no animal exhibited significant hemodynamic compromise. Large tubular thrombi were explanted in the size range of 5-10 cm long and 0.5-1 cm wide. Histologic analysis indicated an organized thrombus with infiltration of white blood cells and fibrin deposition. Conclusions: Large caval thrombi can be formed in vivo and released at a predetermined time to induce large PE in a large animal model. This may help in the development and testing of new therapeutic approaches for PE.