Strut interlocking of titanium Greenfield vena cava filters and its effect on clot capturing: an in vitro study

Inferior vena cava filter – comprehensive overview of current indications, techniques, complications and retrieval rates

Summary: Inferior vena cava (IVC) filter has been used to manage patients with pulmonary embolism and deep venous thrombosis. Its ease of use and the expansion of relative indications have led to a dramatic increase in IVC filter placement. However, IVC filters have been associated with a platitude of complications. Therefore, there exists a need to examine the current indications and identify the patient population at risk. In this paper, we comprehensively reviewed the current indications and techniques of IVC filter placement. Further, we examined the various complications associated with either permanent or retrievable IVC filters. Lastly, we examined the current data on filter retrieval.

Complications of inferior vena cava filters

Inferior vena cava (IVC) filter placement is a relatively low risk alternative for prophylaxis against pulmonary embolism in patients with pelvic or lower extremity deep venous thrombosis who are not suitable for anticoagulation. There is an increasing trend in the number of IVC filter implantation procedures performed every year. There are many device types in the market and in the early 2000s, the introduction of retrievable filters brought an additional subset of complications to consider. Modern filter designs have led to decreased morbidity and mortality, however, a thorough understanding of the limitations and complications of IVC filters is necessary to weight the risks and benefits of placing IVC filters. In this review, the complications associated with IVC filters are divided into procedure related, post-procedure, and retrieval complications. Differences amongst the device types and retrievable filters are described, though this is limited by a significant lack of prospective studies. Additionally, the clinical presentation as well as prevention and treatment strategies are outlined with each complication type.

Impact of unilateral common iliac vein occlusion on trapping efficacy of the Greenfield filter: an in vitro study

RATIONALE AND OBJECTIVES

The purpose of this study was to assess the effect of unilateral common iliac vein occlusion on the capturing efficacy of the Greenfield filter in vitro.

MATERIALS AND METHODS

A stainless steel over-the-wire Greenfield filter was placed in the Silastic inferior vena cava module of a pulsatile circuit. Three 30-mm blood clots in sets of five were injected through the module's right iliac limb with the circuit in four experimental conditions: vertical position, both iliac limbs patent (VP); vertical position, left iliac limb occluded (VOC); horizontal position, both iliac limbs patent (HP); and horizontal position, left iliac limb occluded (HOC). Each experiment was repeated 15 times, resulting in 75 clots per condition and a total of 300 clot introductions.

RESULTS

Clot trapping efficacy was 36 of 75 (48%) for VP, 41 of 75 (55%) for VOC, 32 of 75 (43%) for HP, and 26 of 75 (35%) for HOC. Cross comparisons of the four conditions revealed a marginally significant difference (P = .0138 with a corrected test-wise alpha = .0125) only between horizontal and vertical positions with unilateral common iliac limb occlusion.

CONCLUSION

Unilateral common iliac vein occlusion decreases the capturing efficacy of the Greenfield filter in the horizontal position in vitro. In patients with unilateral common iliac vein occlusion, use of inferior vena cava filters with higher capturing efficacy may be considered.

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.