Retrievable IVC filter: preliminary in vitro and in vivo evaluation

In vitro evaluation of clot capture efficiency of an absorbable vena cava filter

OBJECTIVE

The purpose of this study was to determine the in vitro clot capture efficiency (CCE) of an investigational absorbable inferior vena cava filter (IVCF) vs the Greenfield IVCF.

METHODS

Investigational absorbable and Greenfield filters were challenged with polyacrylamide clot surrogates ranging from 3 × 5 to 10 × 24 mm (diameter × length) in a flow loop simulating the venous system. Filters were challenged with clots until CCE standard error of 5% or less was achieved under binomial statistics. Pressure gradients across the filters were measured for the largest size clot, enabling calculation of forces on the filter.

RESULTS

The in vitro CCE of the absorbable IVCF was statistically similar to that of the Greenfield filter for all clot sizes apart from the 3 × 10-mm clot, for which there was statistically significant difference between filter CCEs (absorbable filter, 59%; Greenfield filter, 31%; P = .0001). CCE ranged from an average 32% for the 3 × 5-mm clot to 100% for 7 × 10-mm and larger clots for the absorbable IVCF. Pressure gradient across the absorbable filter with 10 × 24-mm clot averaged 0.14 mm Hg, corresponding to a net force on the filter of 2.1 × 10(-3) N, compared with 0.39 mm Hg or 5.8 × 10(-3) N (P < .001) for the Greenfield filter.

CONCLUSIONS

CCE of the absorbable filter was statistically similar to or an improvement on that of the Greenfield stainless steel filter for all clot sizes tested. CCE of the Greenfield filter in this study aligned with data from previous studies. Given the efficacy of the Greenfield filter in attenuating the risk of pulmonary embolism, the current study suggests that the absorbable filter may be a viable candidate for subsequent human testing.

A modified technique to minimize filter tilting during deployment of the Günther Tulip filter: in vitro study

With an in vitro model of the inferior vena cava, it was demonstrated that slight tension on the introducer during quick release of the jugular Günther Tulip filter led to less tilting of the filter compared with the technique recommended by the manufacturer. This technique may be useful to minimize significant filter tilting that may be associated with decreased filtration efficiency, and difficulty or impossibility of future filter retrieval.

Long-term optional retrievability of a new inferior vena cava filter in an ovine model

Long-term retrievability of a new optional retrieval inferior vena cava (IVC) filter composed of a modified square stent and a modified Günther Tulip filter was tested in eight sheep. Eleven filters were placed into the IVC and eight were successfully retrieved 3-5 months after implantation. Incorporation of the filter struts into the IVC wall prevented its retrieval in three sheep at 3, 4, and 5 months after placement.

The Günther Tulip Retrievable Filter: Prolonged Temporary Filtration by Repositioning within the Inferior Vena Cava

PURPOSE

To report experience with the retrievable Günther Tulip filter (GTF) as a means of temporary caval filtration for the prevention of pulmonary embolism (PE) with use of a technique that prolongs filter dwell time beyond 14 days.

MATERIALS AND METHODS

Eighty-eight GTFs were implanted in 87 patients. The GTFs were placed with the intention of retrieval in all patients within 14 days after initial implantation. In 23 of the 87 patients (26%), there was a need to prolong temporary caval filtration beyond the recommended period of 14 days. This was successfully achieved with use of percutaneous techniques from the right internal jugular vein whereby the filter was repositioned to a different location within the inferior vena cava (IVC) before definitive device removal.

RESULTS

Of 88 GTFs implanted in 87 patients, 70 were successfully retrieved and 18 were left in place permanently. Forty-seven filters in 46 patients were removed after initial implantation with no need for percutaneous repositioning within the IVC to prolong dwell time (mean dwell time, 13 days). In the 23 patients who required repositioning of 23 GTFs within the IVC to prolong temporary caval filtration, the mean dwell time was 34.8 days; the mean number of repositioning procedures was 1.5, the mean time between repositioning procedures was 13.8 days, and the mean fluoroscopy time was 4.4 minutes in patients in whom filter retrieval was attempted. One patient underwent placement and subsequent removal of the GTF twice for perioperative prophylaxis against PE on two separate occasions. No filters were misplaced in an unintended location or tilted (>15 degrees ) in relation to the main caval axis after deployment. In one patient, a GTF became permanently fixed in the IVC 16 days after initial implantation and could not be removed percutaneously. Nine patients had mild or moderate-sized cervical hematomas. One patient had recurrent asymptomatic PE 2 months after filter insertion.

CONCLUSION

Dwell times of 14 days can be achieved in most patients before device removal. Prolongation of the dwell time beyond 14 days can be safely and easily achieved by performing percutaneous repositioning of the device within the IVC via a jugular approach.

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.

In vitro model for the evaluation of inferior vena cava filters: effect of experimental parameters on thrombus-capturing efficacy of the Vena Tech-LGM filter

PURPOSE

To determine the experimental parameters in an in vitro model that influence the thrombus-capturing efficacy of the Vena Tech-LGM filter.

MATERIALS AND METHODS

The Vena Tech-LGM filter was evaluated in an in vitro model of the vena cava with a computer-controlled flow system with a total of 5,200 thrombi. The influences of the following experimental parameters on the capture rate were analyzed with a multiple logistic regression model: type of testing (single, double, and multiple shot testing), thrombus diameter and length, IVC diameter and orientation, flow quality and quantity, flow velocity, and the length of the prepositioned thrombus.

RESULTS

A significant influence on the capture rate could be demonstrated for the type of testing, the thrombus diameter and length, the IVC diameter, and with double shot testing for the length of the prepositioned thrombus and the IVC orientation. The flow quality and the peak velocity were not significant. Based on these results, a protocol for in vitro testing of IVC filters was designed.

CONCLUSIONS

Experimental parameters influence the thrombus-capturing efficacy of the Vena Tech-LGM filter and should be taken into account when in vitro testing is performed.

A physiologic in vitro model of the inferior vena cava with a computer-controlled flow system for testing of inferior vena cava filters

RATIONALE AND OBJECTIVES

The authors develop a physiologic in vitro model of the inferior vena cava (IVC) for testing of filters.

METHODS

The model is driven by a centrifugal pump. A computer-controlled electromagnetic valve is used for generation of different flow patterns. Limitation of the pressure increase in case of IVC occlusion is achieved by a bypass circuit. A glycerin solution is used for perfusion. Artificial clots are made from polyacrylamide gel. Data acquisition includes continuous monitoring of flow and difference pressure over the filter and video recording of the testing events.

RESULTS

The model can generate constant and pulsatile flows. The pressure increase can be limited to 70 mm Hg in case of occlusion. Calculation of the flow velocities in the IVC is possible. A classification of thrombus capturing is presented. The testing of most of the results are reproducible.

CONCLUSIONS

The in vitro model simulates the physiologic conditions in the IVC. It can be used for comparative testing of different filters and the evaluation of new filter designs.

Caval incorporation of the LGM Vena Tech filter: an experimental study

PURPOSE

To analyze LGM Vena Tech filter incorporation and the rapidity of the process.

MATERIALS AND METHODS

A filter was inserted into the infrarenal inferior vena cava (IVC) of 15 ewes assigned to one of three groups depending on the length of follow-up (2, 4, or 8 weeks). Radiologic data concerning IVC diameter and filter patency, stability, and incorporation were obtained before and after insertion and before euthanasia. Histopathologic analysis concerned wall thickness and smooth muscle cell area (SMCA) at three levels of the filter and at one point outside the filter.

RESULTS

All filters remained patent during follow-up. Incorporation of struts was dependent on time (P = .006), level of the filter (P = .0001), and strut surface (P < .0001). Neointimal thickness increased during follow-up (P = .0002), being more marked in the midportion of the filter (P = .0037). Adventitial thinning was observed (P = .0001), corresponding to a significant decrease in SMCA (P < .0001) above the struts as a function of the length of the follow-up period (P = .0021).

CONCLUSIONS

The LGM Vena Tech filter was well tolerated and is suitable for incorporation into the IVC wall of normal animals without risk of any deleterious reactions due to biological incompatibility.

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.

Results of a multicenter study of the retrievable Tulip Vena Cava Filter: early clinical experience

PURPOSE

To evaluate clinically a new, retrievable vena caval filter in a multicenter study.

METHODS

The Tulip filter is a stainless steel half-basket that is suitable for antegrade or retrograde insertion via an 8.5 Fr introducer sheath. The filter can be retrieved via the jugular approach using an 11 Fr coaxial retrieval system. Forty-eight filters were implanted via the femoral approach and 38 via the jugular approach in 83 patients. Follow-up examinations (plain films, colorcoded duplex sonography) were performed up to 3 years after filter insertion (mean 136 days) in 75 patients. Twenty-seven patients were screened by colorcoded duplex sonography for insertion site thrombosis.

RESULTS

An appropriate filter position was achieved in all cases. Insertion problems occurred in 3 cases; these were not due to the filter design but to an imperfect prototype insertion mechanism that has now been modified (n = 2) or a manipulation error (n = 1). In 2 of these cases the filters were replaced percutaneously; 1 patient required venotomy for filter removal. No further complications due to filter insertion occurred. Two filters were used as temporary devices and were successfully removed after 6 and 11 days, respectively. There was 1 fatal recurrent pulmonary embolism (PE) and 2 non-fatal PE, 5 complete and 3 partial caval occlusions, and 3 caudal migrations of the filter. Insertion site venous thrombosis was not seen in the 27 patients monitored for this complication.

CONCLUSION

Precise placement of the Tulip filter is feasible by either access route and the device appears mechanically stable. Further observations are needed to confirm that safe filter removal is practical up to 10 days after its insertion.