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

Retrievability of Uncoated Versus Paclitaxel-coated Günther-Tulip IVC Filters in an Animal Model

PURPOSE

To compare in a pilot study, the retrievability and inferior vena cava (IVC) wall reaction elicited by uncoated and paclitaxel-coated Günther-Tulip filters in the animal model.

MATERIALS AND METHODS

Three groups with five pigs each underwent infrarenal IVC implantation of Günther-Tulip filters. Paclitaxel-coated filters were used in Groups A and B and uncoated filters were used in Group C. Filters were removed at 14, 19, 22, 26, and 30 days after implantation. A laparotomy was performed to remove filters from animals in group A and filters from animals in groups B and C that could not be retrieved via the right transjugular approach. Filter-induced venous wall changes were evaluated by examination of IVC venography, feasibility of filter removal at different implantation times, and laparotomy and microscopic findings. Feasibility of filter retrieval and venous wall changes were correlated.

RESULTS

IVC cavography showed no abnormality. Filters in animals in group B were uneventfully removed by a right jugular approach. Uncoated filter removal was not feasible in three of five animals in group C (19, 22, and 26 days). Microscopically, animals in group A had absent filter-induced IVC wall changes at 14, 19, 22, and 26 days and minimal changes at 30 days post implantation; animals in group B had absent filter-induced IVC wall changes at 14, 19, and 22 days and minimal changes at 26 and 30 days; animals in group C had moderate filter-induced IVC wall changes at 14 days and severe changes at 19, 22, 26, and 30 days.

CONCLUSIONS

This pilot study suggests that endothelial reaction to the presence of IVC filters in the porcine model is diminished by addition of paclitaxel coating to these filters. Further studies are necessary to substantiate these results.

Evaluation of a spiral nitinol temporary inferior vena caval filter

RATIONALE AND OBJECTIVES

The authors performed this study to evaluate the (a) ability of a prototype temporary inferior vena caval (IVC) filter to trap and retain emboli in an ex vivo flow circuit, (b) feasibility of filter placement and removal via a superficial vein in sheep, and (c) intermediate-term effects of the filter on the insertion vein and at the filter site.

MATERIALS AND METHODS

In an iliocaval circuit, embolus capture with the prototype filter was compared to that with a Greenfield filter. In addition, prototype filters were placed into the infrarenal IVC in six sheep. Placement via a superficial venous route was initially attempted. Inferior vena cavography was performed weekly, and filters were removed after 2, 3, or 4 weeks (n = 2 each). Two weeks after the filters were removed, vena cavograms were obtained, the animals were sacrificed, and the IVC was evaluated at pathologic examination.

RESULTS

The prototype filter captured all emboli, and the Greenfield filter captured 70%-100% of emboli. Successful placement via a superficial venous route was accomplished in only two sheep owing to small vein caliber; four filters were placed via a deep vein. Adverse events included perifilter thrombus, insertion site infection, and caudal migration. Two sheep died before filter removal owing to sepsis and anesthetic complications. The filters in the remaining four sheep were easily and successfully removed. Five sheep had stenosis at the filter site, and fibrosis with acute and chronic inflammation was seen at microscopic examination.

CONCLUSION

The prototype filter trapped emboli as well as the Greenfield filter. Insertion via a superficial route, however, is possible only if the access vein is of an adequate size.

Günther Tulip filter: preliminary clinical experience with retrieval

PURPOSE

The Günther Tulip filter is a permanent filter that has a hook to permit retrieval. The authors report their preliminary clinical evaluation of the filter with regard to feasibility and safety of retrieval.

MATERIALS AND METHODS

Nine men and six women who ranged in age from 17 to 79 years (mean, 51 years) underwent treatment with use of the Günther Tulip filter. Patients judged to require caval interruption for < 14 days were selected to receive the filter and retrieval was planned for all patients. Indications for filter placement were: recent pulmonary embolism (PE) or proximal deep vein thrombosis (DVT) with a contraindication to anticoagulation (11 patients), massive PE treated with thrombolytic therapy (one patient), PE with heparin-induced thrombocytopenia (one patient), and prophylaxis after major trauma (two patients). Patients were followed for inferior vena cava (IVC) thrombosis, bleeding, and recurrent DVT or PE.

RESULTS

In all nine patients in whom it was attempted, the filter was successfully snared and retrieved via a jugular approach. The mean implantation period was 8.6 days (range, 5-13 days). Retrieval required 2.2-13 minutes (mean 5.3 minutes) of fluoroscopy. No caval injuries occurred as a result of retrieval. All retrieved filters had strands of organized thrombus on the filter struts. The patients were followed for 52-285 days (mean, 115 days) after retrieval. One patient developed a recurrent DVT 230 days after retrieval. No other patients developed a recurrent DVT and no patients developed IVC thrombosis, bleeding, or PE. Six filters were not retrieved: five because of an ongoing contraindication to anticoagulation and one because the patient died of causes unrelated to the filter.

CONCLUSION

This preliminary study confirms the feasibility and safety of retrieval of the Günther Tulip filter up to 13 days after implantation.

Fatal outcome in atrial migration of the Tempofilter

PURPOSE

To report the risk of fatal atrial migration with the Tempofilter.

METHODS

Among temporary filters, the high safety profile Tempofilter has been marketed as offering protection for up to 6 weeks. We implanted about 60 Tempofilters to prevent pulmonary embolism. The main indications were temporary thromboembolic risk, recurrent pulmonary embolism, and contraindication to or failure of anticoagulant therapy. Follow-up was performed regularly by plain abdominal film and Doppler ultrasound. Filters were removed about 4 weeks after placement.

RESULTS

We encountered three cases (5%) of atrial migration and one case of 5-cm cephalad displacement of the filter. Of the three patients with atrial migration, two died within 3 days of implantation, one from a massive pulmonary embolism and the other with cardiac tamponade. One patient did not show any serious complications.

CONCLUSIONS

The Tempofilter may actively migrate cranially and become dangerous in the case of migration within the heart.

Retrievable IVC square stent filter: experimental study

PURPOSE

In vitro and in vivo evaluation of a new retrievable, home-made, inferior vena cava (IVC) Square stent filter (SSF) with two trapping levels.

METHODS

In vitro, the SSF was compared in a flow model with the stainless steel Greenfield filter (SGF) for emboli-trapping efficiency by serially passing 300 emboli of 3 and 6 mm in diameter and 15-30 mm in length in each type of filter. Nine swine were used for the in vivo testing of the SSF for deployment and retrievability, emboli-trapping efficiency, stability, and self-centering ability and two were used (total of 11 swine) for testing repositioning and retrievability of the SSF at 2 weeks and for gross and histologic IVC changes at 2 months.

RESULTS

In vitro, the SSF and SGF had similar efficiency in trapping large emboli but the SSF had significantly better efficiency than the SGF for trapping all sizes of emboli (91.7% vs 81%), medium size emboli (93% vs 80%), and small emboli (86% vs 69%). Efficiency decreased in both filters from the first to the fifth embolus in each series but was still significantly better for the SSF. With the SSF, 89% of emboli were caught at the primary and 11% at the secondary filtration level. In the nine animals used for acute studies, the SSF was easily placed in all 27 attempts, assumed a central position 26 times, and was easily retrieved in 21 of 22 attempts. One tilted filter needed additional manipulation for retrieval. During emboli injection in five swine, the SSF had 97.2% emboli-trapping efficiency and demonstrated good stability. In the two animals used for longer-term evaluation, the filters were easily retrieved 2 weeks after implantation. Histologic evaluation at 2 months showed neointimal proliferation around the SSF wires in contact with the IVC wall, which was otherwise normal.

CONCLUSION

The SSF is a promising filter. It is easy to place and retrieve, is stable after placement, and has high efficiency for trapping emboli. Promising results justify further experimental and eventual clinical studies with a commercially manufactured SSF.

Clinical experience with temporary vena caval filters

PURPOSE

To look at the benefits and complications of different vena caval filters inserted prophylactically. Three temporarily implantable caval filter systems were used in 67 patients.

MATERIALS AND METHODS

Twelve Cook filters (six transjugular, six transfemoral), 11 Angiocor filters (one transjugular, 10 transbrachial), and 44 Antheor filters (three transjugular, four transfemoral, 37 transbrachial) were successfully implanted. In known iliac vein or caval thrombosis, the prophylactic filters were placed during thrombolytic therapy in 46 cases, surgery in 17 cases, thrombosis in pregnancy in three cases, and high-dose heparinization without lysis in one case.

RESULTS

One patient had a fatal pulmonary embolism during treatment; seven thrombi were detected in the filter. Other complications were caused either by the underlying therapy alone (one fatal outcome of abdominal aorta aneurysmal surgery, two cases of cerebral hemorrhage, two cases of retroperitoneal hematomas, two cases of streptokinase fever reactions, one compartment syndrome, two cases of macrohematuria), by the combination of therapy and caval filter implantation (three cases of groin hematomas, three cases of arm hematomas), or by filter implantation alone (two cases of subclavian vein thrombosis, one catheter infection, one dislocation, one air embolism, one basket rupture). The bleeding complications were related to the aggressive thrombolytic therapy and would have occurred without filter implantation.

CONCLUSION

Because temporary caval filters have no long-term complications per se, their use seems sensible as long as there are stringent indications, including the presence of iliac vein or caval thrombosis and risk of thrombus mobilization. The Antheor filter system was the most convenient system for implantation.

The Günther temporary inferior vena cava filter for short-term protection against pulmonary embolism

PURPOSE

To evaluate clinically the Günther temporary inferior vena cava (IVC) filter.

METHODS

Eleven IVC filters were placed in 10 patients. Indications for filter placement were surgical pulmonary embolectomy in seven patients, pulmonary embolism in two patients, and free-floating iliofemoral thrombus in one patient. Eight filters were inserted from the right femoral approach, three filters from the left. Follow-up was by plain abdominal radiographs, cavography, and duplex ultrasound (US). Eight patients received systemic heparinization. Follow-up, during 4-60 months after filter removal was by clinical assessment, and imaging of the lungs was performed when pulmonary embolism (PE) was suspected. Patients received anticoagulation therapy for at least 6 months.

RESULTS

Ten filters were removed without complications 7-14 days (mean 10 days) after placement. One restless patient pulled the filter back into the common femoral vein, and a permanent filter was placed. In two patients a permanent filter was placed prior to removal. One patient developed sepsis, and one an infection at the insertion site. Clinically no recurrent PE developed with the filter in place or during removal. One patient had recurrent PE 7 months after filter removal.

CONCLUSION

The Günther temporary IVC filter can be safely placed for short-term protection against PE. The use of this filter is not appropriate in agitated or immunocompromised patients.

Experimental impeller fragmentation of iliocaval thrombosis under tulip filter protection: preliminary results

PURPOSE

To assess the efficacy of catheter fragmentation of massive caval thrombosis and of filter protection against procedure-related pulmonary embolism.

METHODS

In 10 sheep, a self-expanding tulip-shaped filter made from Wallstent mesh (diameter 25 mm) was introduced from the right jugular approach into the proximal inferior vena cava. Experimentally induced massive iliocaval thrombosis was fragmented by an impeller catheter (expanded diameter 14 mm), which was advanced coaxially through the sheath of the expanded filter. Post-procedural cavography and pulmonary angiography were performed to document the extent of caval recanalization and pulmonary embolism.

RESULTS

In all cases, impeller fragmentation cleared the inferior vena cava and the iliac veins of thrombi completely. Fragments washed downstream were trapped in the filter. In two of the first cases, parts of the clots caused pulmonary embolism before the filter was in place. Further events were avoided by a modification of the experimental setup. Except for some small peripheral perfusion defects in two cases, pulmonary angiograms did not show any incidence of pulmonary embolism.

CONCLUSION

Our preliminary results suggest that impeller fragmentation of iliocaval thrombi under tulip filter protection is effective and does not cause significant pulmonary embolism.

Preliminary investigation of the Irie inferior vena caval filter

PURPOSE

In vitro and in vivo investigations were performed to evaluate the Irie retrievable inferior vena caval (IVC) filter.

MATERIALS AND METHODS

The clot capturing performance of the Irie and five other IVC filters were assessed in both horizontal and vertical orientations within a pulsed-flow circuit with 240 clot challenges for each filter. Subjective comparisons of the flow disturbance characteristics of the Irie and three other filters were also performed. In vivo studies consisted of 13 Irie filter insertions and eight attempted retrievals in 11 pigs. Histologic evaluation of the IVC was performed with the Irie filter in situ and following retrieval.

RESULTS

In vitro testing demonstrated the clot capturing capability and flow disturbance characteristics of the Irie filter to be similar to those of other IVC filters. Filter deployment problems occurred during three of the 13 insertions. Six of the eight retrieval procedures were successful; four filters were retrieved 1 month after insertion. Follow-up cavography demonstrated two tilted filters and three caval perforations.

CONCLUSION

The performance of the Irie filter is similar to that of other currently available IVC filters. The filter can be retrieved after neointimal incorporation of the struts into the IVC wall.

Use of a temporary caval filter to assist percutaneous iliocaval thrombectomy: experimental results

PURPOSE

To test a new filter design that allows coaxial insertion of thrombectomy devices and active clot removal.

MATERIALS AND METHODS

A prototype filter system was used in animal experiments. It is a transjugularly inserted coaxial system with a 16-F outer sheath and an inner tube that is covered by a tulip-shaped meshwork with a 22-mm diameter at its inserted end. The inner tube allows insertion of instruments up to 8 F. The filter was developed to assist with percutaneous mechanical thrombectomy in the iliofemoral and caval veins. The filter has been used as an assisting tool in nine sheep and eight pigs. It was combined with an impeller system in nine sheep for caval thrombectomy and with a hydrodynamic catheter for iliac thrombectomy in eight pigs after artificial induction of iliac or caval thrombosis.

RESULTS

The filters captured emboli from the intervention in six of nine sheep. The amount of captured emboli was reduced within the filter cone by the impeller instrument in five of six instances. Residual thrombus was removed by closing the filter in five of six sheep. In pigs, the filter captured emboli in three cases during hydrodynamic embolectomy. Pulmonary embolization did not occur with the filter in place. After filter removal, minor pulmonary clot embolization occurred in one case.

CONCLUSION

The temporary tulip filter was effective in these animal models in capturing and removing thrombus material that may dislodge from iliocaval veins during mechanical thrombectomy.

Temporary inferior vena cava filters: in vitro comparison with permanent IVC filters

PURPOSE

An in vitro comparison of clot-trapping abilities of permanent and temporary inferior vena cava (IVC) filters.

MATERIALS AND METHODS

A flow model was used to simulate the IVC. Two permanent IVC filters, the titanium Greenfield and LG-Medical (LGM), were compared with two temporary filters, the Filcard International and Gunther. Clot sizes used were 2.5 x 2.5 mm, 2.5 x 5 mm, 5 x 5 mm, 5 x 10 mm, and 5 x 20 mm. Individual clots were presented to the filters with the simulated IVC in a horizontal or vertical orientation. Clot-trapping dynamics and pressure gradient changes during the injection of multiple, sequential clots were also examined.

RESULTS

As clot size diminished, all filters trapped fewer clots; however, the temporary filters trapped more small clots than the permanent filters. Very little difference was observed in clot-trapping abilities among the filters for clots of 5 x 10 mm or greater. In the horizontal orientation, the permanent filters trapped 38% of all clots delivered, while the temporary filters trapped 73%, chi 2 = 24.8 (P < .001). In the vertical orientation, the overall clot-trapping abilities of the filters improved, with the permanent filters trapping 73% of all clots delivered, while the temporary filters trapped 95%, chi 2 = 18 (P < .001). During trapping of multiple clots, the temporary filters allowed fewer clots to pass.

CONCLUSION

The temporary filters performed better than the permanent filters in both individual clot-trapping orientations. During multiple clot-trapping experiments, fewer clots were allowed to pass by the temporary filters. The temporary filters demonstrated the ability to capture clots both inside and outside the wire struts.

Retrievable IVC filter: preliminary in vitro and in vivo evaluation

PURPOSE

To develop an inferior vena cava (IVC) filter that is retrievable even after neointimal formation and incorporation into the caval wall.

MATERIALS AND METHODS

Eight filters were placed percutaneously in the infrarenal IVC of eight dogs. Four weeks after placement, percutaneous retrieval of the filters was attempted. Vena cavograms were obtained before and immediately after retrieval. Three dogs were killed immediately after the retrieval procedure was completed. In the other five dogs, follow-up vena cavography was performed 4-14 weeks after retrieval, and autopsy was performed.

RESULTS

The filters were placed and retrieved successfully in all eight dogs. No migration, caval penetration, or tilting occurred. The IVCs were completely patent both before and immediately after retrieval in all eight dogs. In the three dogs killed immediately after retrieval, neointimal hyperplasia was seen around the struts, but there was no detachment. Delayed stenosis was not seen in any of the five dogs that were followed up, and the inner surface of the caval wall was smooth.

CONCLUSION

This IVC filter can be easily placed and safely retrieved percutaneously, even after neointimal formation.

Preliminary clinical experience with the Gunther temporary inferior vena cava filter

PURPOSE

The authors describe their preliminary clinical experience with the Gunther temporary inferior vena cava (IVC) filter.

PATIENTS AND METHODS

Seven women and 10 men, mean age 52 years (range, 19-85 years), were treated with the temporary IVC filter. Indications for filter placement were pulmonary embolism (PE) in four patients and iliofemoral deep venous thrombosis in six. In these patients anticoagulation was contraindicated because of planned major surgery. Filters were placed in four patients following massive PE and in three for prophylaxis following cranial trauma. Four patients had underlying malignant disease. Filters were introduced through the right common femoral vein in 14 patients, the left common femoral vein in two, and the left internal jugular vein in one.

RESULTS

No patient developed recurrent PE with the filter in place. All filters were removed without complication 3-14 days (mean, 7 days) after placement. Two of the patients with underlying malignant disease required placement of a permanent filter. Two patients developed IVC thrombosis with the filter in place, and both developed recurrent PE after filter removal. Two patients developed insertion vein thrombosis. One patient developed a bleeding disorder that caused a massive hematoma at the insertion vein site, which may have contributed to her death.

CONCLUSION

The Gunther temporary filter can be used in selected patients; however, patients with underlying malignant disease may be more appropriately treated with a permanent filter. The temporary filter does not appear to reduce the rate of insertion vein and IVC thrombosis.