In vitro studies of temporary vena cava filters

Comparison of the in vitro clot-capturing efficiencies of commercially available retrievable inferior vena cava filters

OBJECTIVE

We compared the in vitro clot-capturing efficiencies (CCEs) of commercially available retrievable inferior vena cava (IVC) filters.

METHODS

Four types of commercially available retrievable IVC filters were included in the present study: Denali (BD, Franklin Lakes, NJ), OptEase (Cordis Corp, Hialeah, Fla), Celect (Cook Medical, Bloomington, Ind), and Option (Argon Medical Devices, Frisco, Tex). The CCE of each IVC filter for 10 different size clots, ranging from 2 mm × 10 mm to 6 mm × 20 mm, was analyzed using a venous flow simulator.

RESULTS

When ≥4 × 10-mm clots were used, the CCEs were 100% for all four types of IVC filters in a 20-mm-diameter simulated IVC filter. However, when ≤3 × 20-mm clots were used, the CCEs were significantly different among the four types of filters in a 20-mm-diameter simulated IVC, with the Denali showing the highest CCE, followed by the OptEase, Celect, and Option. When ≥6 × 10-mm clots were used, the CCEs were 100% for all four types of IVC filters in the 25-mm-diameter simulated IVC. However, when ≤5 × 20-mm clots were used, the CCEs were significantly different among the four types of filters in the 25-mm-diameter simulated IVC, with the Denali showing the highest CCE. When ≤5 × 10-mm clots were used, the CCEs were significantly lower in the 25-mm-diameter simulated IVC than in the 20-mm-diameter simulated IVC for all four types of IVC filters, with Option showing the greatest change in CCEs, followed by the Celect, OptEase, and Denali.

CONCLUSIONS

The CCEs were significantly different among the four IVC filters and were significantly lower for the smaller size clots than for the larger size clots and for the larger diameter simulated IVC than for the smaller diameter simulated IVC.

In Vitro Clot Trapping Efficiency of the FDA Generic Inferior Vena Cava Filter in an Anatomical Model: An Experimental Fluid-Structure Interaction Benchmark

PURPOSE

Robust experimental data for performing validation of fluid-structure interaction (FSI) simulations of the transport of deformable solid bodies in internal flow are currently lacking. This in vitro experimental study characterizes the clot trapping efficiency of a new generic conical-type inferior vena cava (IVC) filter in a rigid anatomical model of the IVC with carefully characterized test conditions, fluid rheological properties, and clot mechanical properties.

METHODS

Various sizes of spherical and cylindrical clots made of synthetic materials (nylon and polyacrylamide gel) and bovine blood are serially injected into the anatomical IVC model under worst-case exercise flow conditions. Clot trapping efficiencies and their uncertainties are then quantified for each combination of clot shape, size, and material.

RESULTS

Experiments reveal the clot trapping efficiency increases with increasing clot diameter and length, with trapping efficiencies ranging from as low as approximately 42% for small 3.2 mm diameter spherical clots up to 100% for larger clot sizes. Because of the asymmetry of the anatomical IVC model, the data also reveal the iliac vein of clot origin influences the clot trapping efficiency, with the trapping efficiency for clots injected into the left iliac vein up to a factor of 7.5 times greater than that for clots injected into the right iliac (trapping efficiencies of approximately 10% versus 75%, respectively).

CONCLUSION

Overall, this data set provides a benchmark for validating simulations predicting IVC filter clot trapping efficiency and, more generally, low-Reynolds number FSI modeling.

Effects of reverse deployment of cone-shaped vena cava filter on improvements in hemodynamic performance in vena cava

BACKGROUND

Cone-shaped vena cava filters (VCFs) are widely used to treat venous thromboembolism. However, in the long term, the problem of occlusion persists even after the filter is deployed. A previous study hypothesized that the reverse deployment of a cone-shaped VCFs may prevent filter blockage.

METHODS

To explore this hypothesis, a comparative study of the traditional and reverse deployments of VCFs was conducted using a computational fluid dynamics approach. The distribution of wall shear stress (WSS) and shear stress-related parameters were calculated to evaluate the differences in hemodynamic effects between both conditions. In the animal experiment, we reversely deployed a filter in the vena cava of a goat and analyzed the blood clot distribution in the filter.

RESULTS

The numerical simulation showed that the reverse deployment of a VCF resulted in a slightly higher shear rate on the thrombus, and no reductions in the oscillating shear index (OSI) and relative residence time (RRT) on the vessel wall. Comparing the traditional method with the reversely deployed cases, the shear rate values is 16.49 and 16.48 1/s, respectively; the minimal OSI values are 0.01 and 0.04, respectively; in the vicinity of the VCF, the RRT values are both approximately 5 1/Pa; and the WSS is approximately 0.3 Pa for both cases. Therefore, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. However, it is effective in capturing thrombi in the short term, as demonstrated via animal experiments. The reversely deployed cone-shaped filter captured the thrombi at its center in the experiments.

CONCLUSIONS

Thus, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. Therefore, we would not suggest the reverse deployment of the cone-shaped filter in the vena cava to prevent a potentially fatal pulmonary embolism.

Improvement of hemodynamic performance using novel helical flow vena cava filter design

We propose a vena cava filter in which helical flow is created in the filter’s working zone to minimize filter blockage by trapped clots and facilitate the lysis of trapped clots. To validate this new design, we compared five helical flow inducers with different thread pitches in terms of blood flow patterns in the filter. The vena cava was reconstructed based on computed tomography images. Both the numerical simulation and in vitro experiment revealed that the helical flow inducer can effectively create a helical flow in the vessel, thereby subduing the filter structure’s adverse disruption to blood flow, and increasing flow-induced shear stress in the filter center. In addition, the smaller thread pitch helical flow inducer reduced the oscillating shear index and relative residence time on the vessel wall. Moreover, we observed that the helical flow inducer in the vena cava could induce flow rotation both in clockwise and counterclockwise directions. In conclusion, the new design of the filter with the smaller thread pitch inducer is advantageous over the traditional filter in terms of improving local hemodynamics, which may reduce thrombosis build-up after deployment.

In Vitro Evaluation of Optionally Retrievable and Permanent IVC Filters

PURPOSE

To systematically evaluate different optionally retrievable and permanent inferior vena cava (IVC)-filters with respect to their capture rates.

MATERIAL AND METHODS

Seven optionally retrievable and permanent IVC filters were tested in an in vitro flow model with a tube size of 22 mm in horizontal and vertical positions. To analyze the capture efficiency the IVC filters were implanted in concentric and eccentric positions and subsequently exposed to single and multiple blood clots of different sizes (3x5, 3x10, 5x10, 5x20, 7x20, 10x24 mm). Capture rates and pressure changes were measured and compared between the different IVC filters.

RESULTS

There were significant differences between the tested IVC filters. In general, the capture rate improved with increasing clot size (P<0.0001). In the single-clot exposure the highest mean capture rate was achieved with the Celect filter (90.4%+/-15.7%), whereas the Günther Tulip filter achieved best results in the multi-clot exposure (76.7%+/-12.5%). Capture rates differed significantly between the various IVC filters (single-clot: P<0.0001; multi-clot: P=0.0016). The position (horizontal or vertical) did not show a significant influence, whereas capture rates significantly decreased in the multi-clot test with eccentric filter positions (P=0.0299). In this study optionally retrievable IVC filters were more efficient than the tested permanent IVC filters (single-clot: P<0.0001; multi-clot: P=0.0002).

CONCLUSIONS

Optionally retrievable IVC filters are efficient. Clot size, IVC filter type, and position significantly influence capture rate. Deliberate selection of the most efficient IVC filter and concentric positioning are important to ensure optimal results.

Double-filter technique for deployment of a permanent inferior vena cava filter while avoiding the risk of pulmonary embolism from a thrombus trapped by a temporary filter

Because temporary caval filters have not been associated with any long-term complications, their use seems practical as long as indications are accurately assessed. However, problems about further dealing with the emboli trapped in a temporary filter remain. This case report describes a new approach to managing a thrombus captured by a temporary filter during the exchange for a permanent filter. We applied the Anthéor temporary filter (Boston Scientific, Natick, MA, USA) as the device for thrombus capturing, then successfully placed the permanent filter with no clinical evidence of pulmonary embolism. Intravascular ultrasound was also useful for monitoring the entire procedure.

Massive Pulmonary Thromboembolism in Pregnancy Rescued Using Transcatheter Thrombectomy

We report a rescued 37-year-old woman in her 30(th) week of gestation with massive pulmonary thromboembolism who was admitted to our cardiac care unit with progressive dyspnea and 2 episodes of syncope. Helical chest CT showed massive pulmonary thromboembolism of both pulmonary arteries. Although 26,000 U/day of heparin was administered following insertion of a temporary filter, hemodynamic evaluation documented no improvement. Since pulmonary artery (PA) pressure increased from 62/22 mmHg to 80/24 mmHg just after an emergency cesarean section on day 2, an emergency transcatheter thrombectomy was performed and it showed decreased PA pressure following extensive thrombus aspiration. Mother and baby were discharged with no complications.

Clinical outcome and complications of temporary inferior vena cava filter placement

OBJECTIVE

We evaluated the current clinical experience of temporary inferior vena cava (IVC) filter placement and its related complications.

METHODS

From January 2000 to December 2005, we enrolled 33 patients (8 men and 25 women) who underwent percutaneous insertion of a temporary IVC filter in the Department of Vascular Surgery of Tokyo University Hospital. Deep vein thrombosis (DVT) was proven in 78.8% of the patients. The indications for filter insertion were contraindication to anticoagulation therapy (9.1%), thrombolytic therapy (12.1%), perioperative prophylactic implantation (84.8%), pregnancy with DVT (3.0%), and prophylactic implantation in the absence of DVT (15.2%). A Neuhaus Protect was used in 13 patients, and an Antheor was used in 20 patients.

RESULTS

The mean +/- SD duration of filter placement was 10.6 +/- 7.0 days. There was no case of pulmonary embolism during filter protection and retraction. Filter thrombosis (capture of thrombus) was observed in four patients (12.1%), who then received additional thrombolytic therapy. Thrombi were dissolved by thrombolysis in three, one of whom had replacement with a permanent filter. The thrombus was not dissolved in one patient and was removed under venotomy at the insertion site. Major filter-related complications occurred in nine patients (27.3%), including filter dislocation in four patients (12.1%), catheter fracture in three (9.1%), and catheter-related infection in one (3.0%). In a patient with giant ovarian cancer, the IVC was nearly occluded with massive thrombus around the filter 2 days after operation, and the vena cava was then ligated under open laparotomy. No patients died during filter protection and retraction.

CONCLUSIONS

Temporary IVC filters were effective for the prevention of fatal pulmonary embolism. However, our experience of a high incidence of complications related to temporary filters suggests that this device has limited indications and supports the need for innovative design of temporary filters.

Avaliação in vitro de um novo filtro de veia cava

OBJETIVO: O objetivo do estudo foi avaliar a eficácia de um novo filtro de veia cava, de baixo perfil, na retenção de coágulos em modelo in vitro. MÉTODO: O filtro consiste em dois cones opostos pelo ápice. O cone distal é formado por oito hastes de aço inoxidável, que têm a função de retenção dos êmbolos. O cone proximal é constituído de quatro hastes, cuja função é ancorar e centralizar. Os filtros foram introduzidos e fixados no interior de um tubo de PVC transparente de 25, 30 e 35 mm de diâmetro interno, em posição vertical, e conectados com um sistema pulsátil de fluxo (bomba peristáltica). Foi utilizado, para veículo, um reservatório com solução salina (0,9%) com 40% de glicerina, mantido em temperatura ambiente. Confeccionaram-se trombos com sangue bovino em tubos plásticos de 3, 4,5 e 6 mm de diâmetro e, posteriormente, foram segmentados nas medidas de 10, 15, 20 e 30 mm de comprimento, totalizando 12 diferentes tamanhos. Realizaram-se 100 liberações para cada tipo de êmbolo e tamanho das cânulas, totalizando 3.600 eventos. Foram feitos lançamentos seqüenciais com cinco êmbolos, sendo 10 para cada tamanho de êmbolo e cânulas, totalizando 360 eventos. Fez-se avaliação da capacidade de retenção dinâmica utilizando os três diferentes tamanhos de cânulas com 100 eventos cada, totalizando 300 eventos. RESULTADOS: Detectou-se que o diâmetro e comprimento dos êmbolos, assim como diâmetros da cânula, podem comprometer a eficácia do filtro. A média de captura de êmbolos pelos filtros foi de 80,5% nas cânulas de 35 mm, 88,7% para cânulas de 30 mm e 86,6% para cânulas de 25 mm. CONCLUSÃO: Conclui-se que a eficácia desse filtro sofre interferência relacionada ao tamanho dos êmbolos e diâmetro da cânula.

Clinical experience with retrievable Günther Tulip vena cava filters

PURPOSE

To report clinical experience with retrievable Günther Tulip filters from implantation to retrieval and their status in nonretrieved situations.

METHODS

Seventy-five Günther Tulip filter implantations were performed in 71 patients (43 women; mean age 55 years). Indications for filter placement were pulmonary embolism (PE) or iliofemoral deep vein thrombosis (DVT) in patients with a contraindication to anticoagulation (43, 61%) or perioperative PE prophylaxis (28, 39%) in patients with confirmed iliofemoral DVT. Retrieval procedures were planned for each patient. Patients with nonretrieved filters were followed with plain radiography and duplex sonography.

RESULTS

Technical success of filter insertion was 97.3% (73/75). Eighteen (25%) patients died from unrelated causes prior to retrieval attempts, and 6 other patients were too critically ill for a retrieval procedure. Of 49 (67%) planned retrieval attempts, 14 (19%) filters could not be removed owing to large trapped thrombi. The mean implantation period for the 35 (48%) retrieved filters was 8.2 days (range 1-13). Delivery tilt was observed in 12 (16%) filters and during retrieval attempts in 1 more case. For 9 nonretrieved filters, tilt and migration were observed in 22% at a mean follow-up of 30 months, but no venous thrombosis was assessed.

CONCLUSIONS

Our data confirm the clinical efficacy of the Günther Tulip filter during implantation and the feasibility of its retrieval. Further long-term follow-up should be conducted on nonretrieved filters to confirm our 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.

Current practice of temporary vena cava filter insertion: a multicenter registry

PURPOSE

To evaluate the current practice of temporary vena cava filter placement and its complications.

MATERIALS AND METHODS

A multicenter registry was conducted from May 1995 until May 1997 using a standardized questionnaire. One hundred eighty-eight patients were evaluated. Patient characteristics, filter indications, filter characteristics, and complications were registered.

RESULTS

Deep vein thrombosis was proven in 95.2% of the patients. Main filter indication was thrombolysis therapy (53.1%). Average filter time was 5.4 days. An Antheor filter was inserted in 56.4%, a Guenther filter in 26.6%, and a Prolyser filter in 17.%. Transfemoral filter implantation was slightly preferred (54.8%). Four patients died of pulmonary embolism (PE) during filter protection. Major filter problems were filter thrombosis (16%) and filter dislocation (4.8%). When thrombus was found in or at the filter before explantation, additional thrombolysis was performed in 16.7%, additional filter implantation in 10%, and thrombus aspiration in 6.7%; 4.8% of filters were replaced with permanent filters.

DISCUSSION

Temporary vena cava filters are placed to prevent PE in a defined patient population. Despite their presence, PEs still occur in a small percentage. Problems of filter thrombosis and dislocation have to be solved.

CONCLUSION

The results of this multicenter registry support the need for innovative filter design, as well as a randomized, prospective study.

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.