A new percutaneous vena cava filter

Usefulness of the Symphony Nitinol Stent for arteriosclerosis obliterans

The Symphony Peripheral Stent is a self-expanding stent made of thermal memory Nitinol wire. Stents were implanted in 39 lesions of 32 patients (26 men, 6 women) with atherosclerosis obliterans (ASO). The ankle-arm index (AAI), and vessel diameters evaluated by quantitative angiography were compared before and 6 months after treatment. Symphony Peripheral Stent implantation significantly improved the AAI from 0.50+/-0.4 to 0.9+/-0.2 (p<0.01), the minimum lumen diameter (MLD) from 2+/-1.5 to 5+/-1.4 mm (p<0.01) and percent diameter stenosis (% DS) from 69+/-20% to 16.5+/-8% (p<0.01). Re-evaluation of 33 of the 39 lesions 6 months after treatment revealed a low restenosis rate of 15%, an AAI of 0.8+/-0.3, MLD of 4.5+/-2 mm and %DS of 30+/-22%, so the Symphony Peripheral Stent is thus a promising choice for patients with ASO.

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.

A retrievable nitinol vena cava filter: experimental and initial clinical results

PURPOSE

The authors describe the properties of a new retrievable nitinol vena cava filter and report experimental and initial clinical results.

MATERIALS AND METHODS

The filters, made of nitinol monofilament wire that forms a spiral cone and retrieval wire, were introduced through an indwelling 5.5-F transfemoral sheath into the infrarenal portion of the inferior vena cava in 10 sheep. In seven animals, four 4 x 30-mm radiopaque clots were injected below the filter to test its thrombus-trapping efficacy. Aspiration thrombectomy was then attempted, and the filter was removed. Follow-up venography was performed 1 week after placement in three other animals. After successful preclinical testing, the filter was implanted and retrieved in two patients.

RESULTS

All 10 filters were successfully and easily placed in sheep. All filters were thrombus-free at follow-up venography. All clots injected in the iliac veins were trapped by the filter and successfully removed by means of aspiration thrombectomy. All 10 filters were retrieved without difficulty. Temporary filter implantation and retrieval were accomplished in two patients for 5 and 7 days. In one patient, infrafilter thrombus was aspirated. Perisheath thrombosis occurred in both patients. One patient subsequently underwent permanent filter placement.

CONCLUSION

Temporary vena cava filtration is feasible. Potential advantages include easy placement, surveillance, and retrieval. One current limitation is pericatheter thrombosis, which may be eliminated by a less thrombogenic sheath.

Surgical treatment of acute deep venous thrombosis

In patients with venous thrombotic disease and in whom anticoagulation or thrombolytic therapy is inappropriate, ineffective, or even contraindicated, insertion of vena caval filters or venous thrombectomy must be considered. The primary indication for the placement of vena caval filters is in patients who have developed a pulmonary embolus and in whom anticoagulation is either contraindicated or in whom anticoagulation must be discontinued because of the development of bleeding complications. At the present time, either the Greenfield filter placed through a jugular, femoral, or axillary venotomy or the bird's nest filter are appropriate and appear to be the most effective and least fraught with complications. The use of venous thrombectomy has waxed and waned over the last several decades. At the present time, the procedure is advocated mainly for lower limb venous thrombosis which is extensive enough to threaten limb viability. On occasion, it may be appropriate to extend the indications for venous thrombectomy to include femoral thrombosis of less than 10 days duration or iliac thrombosis of less than 3 weeks duration with floating thrombi at the level. Technical modifications which improve the patency of the obliterated veins which are predisposed to rethrombosis include the creation of a temporary arteriovenous fistula and meticulous care in removing the entire clot. The patient should be treated with anticoagulants postoperatively to prevent a recurrence of the problem. The main theoretical advantage of venous thrombectomy is a reduced incidence of postthrombotic syndrome. Objective data to support this contention do not exist.

First clinical results with a new caval filter

A new percutaneous inferior venacaval filter was used in 15 patients. The filter is constructed of stainless steel wires formed into a helical basket and anchoring legs. It can be inserted through a 10F catheter in an antegrade or retrograde fashion and can also be retrieved percutaneously. In a follow-up period of up to 13 months, the filter was well tolerated. One patient died of recurrent embolism despite filter protection. Local thrombogenicity was noted in 2 patients, but no other side effects were observed. Short-term heparinization following filter insertion is advisable. Heparin coating of the filter is under evaluation.