Evaluation of the LGM Vena-Tech infrarenal vena cava filter in an ovine venous thromboembolism model.

Purpose: To validate a new percutaneous model of venous thrombosis in sheep and evaluate the use of the LGM Vena-Tech vena cava filter with use of this model.

Materials And Methods: After implantation of a LGM Vena-Tech filter in the infrarenal vena cava (IVC), thrombus was obtained by blocking the iliac vein with an inflated balloon (Wedge catheter) for 15 minutes and simultaneously injecting 20 mL of fresh thrombus into the femoral vein. Clot migration of the thrombus was induced by balloon deflation and injection of contrast medium. Migration and capture of the thrombus by the filter were filmed under fluoroscopy at 1 frame/sec. Euthanasia followed by pathologic examination of the IVC, heart, and lungs was performed immediately after the procedure in five sheep (group 1). Sheep in groups 2, 3, and 4, (five in each group), were killed at 2, 4, and 8 weeks, respectively, after vena cavography. Histologic examination was performed to analyze the evolution of the thrombus captured, the incorporation of the filter in the caval wall, and the physical and mechanical effects of captured thrombi on the filter.

Results: The Vena-Tech filter captured a large amount of thrombus in all cases except one, in which the filter captured a small strand of thrombus, related to incomplete occlusion of the iliac vein during the clot formation procedure. In the 15 animals in which follow-up was performed, fibrous evolution of the thrombus was observed at gross examination in 14, leading to the formation of fibrous webs between the filter and the IVC wall in eight. These observations were not related to the incidence of filter retraction (n = 4), caudal migration (n = 2), tilt (n = 2), or caval perforation (n = 1). Heart and lung thrombi were present in six animals. Histologic results confirmed the fibrous evolution of the thrombus and its organization during follow-up. Neointima increases significantly (P <.02) during follow-up, from 135.7 microm +/- 13.4 at 2 weeks to 192.2 microm +/- 125.7 at 4 weeks and 334.2 microm +/- 144.1 at 8 weeks.

Conclusion: The model used is suitable for the formation of a large amount of venous thrombus and analysis of its migration and capture by the LGM Vena-Tech filter. Fibrous evolution of the thrombus, including development of webs and changes in filter shape and position, were the main outcomes observed.