Evaluation of migration forces of a retrievable filter: Experimental setup and finite element study

Calibration of interface properties and application to a finite element model for predicting vena cava filter-induced vein wall failure

We present a computational framework that integrates experimental techniques and finite element modeling to calibrate material fracture parameters of the vena cava and the interaction properties between a retrievable filter (Günther Tulip) and the vena cava wall. The fitted parameters were then used to analyze the interaction of the inferior vena cava filter with the vena cava during the deployment process. An idealized cava finite element model was then developed including residual stresses and physiological pressure conditions. Filter deployment was simulated, and a comprehensive study of tissue-filter interaction was performed by cohesive surface modeling. Simulations predict that there are no fracture areas for either model, so we can conclude that there is no penetration of the anchor into the vena cava. This suggests there are other physiological situations, such as the Valsalva maneuver, which could produce this penetration observed on some patients.

Influence of a Commercial Antithrombotic Filter on the Caval Blood Flow During Neutra and Valsalva Maneuver

Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva maneuver. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work, we analyzed the response of the vena cava during normal breathing and Valsalva maneuver, for a healthy vena cava and after insertion of a commercial Günther-Tulip® filter. Validated computational fluid dynamics (CFD) and patient specific data are used for analyzing blood flow inside the vena cava during these maneuvers. While during normal breathing, the vena cava flow can be considered almost stationary with a very low pressure gradient, during Valsalva the extravascular pressure compresses the vena cava resulting in a drastic reduction of the vein section, a global flow decrease through the cava but increasing the velocity magnitude. This change in the section is altered by the presence of the filter which forces the section of the vena cava before the renal veins to keep open. The effect of the presence of the filter is investigated during these maneuvers showing changes in wall shear stress and velocity patterns.

Failure properties of vena cava tissue due to deep penetration during filter insertion

In this work, we use an in-vitro mechanical test to explore the resistance of biaxially stretched vena cava tissue against deep perforation and a methodology which integrates experimental and numerical modeling to identify constitutive fracture properties of the vena cava. Six sheep vena cava were harvested just after killing, and cyclic uniaxial tension tests in longitudinal and circumferential directions and biaxial deep penetration tests were performed. After that, we use a nonlinear finite element model to simulate in vitro penetration of the cava tissue in order to fit the fracture properties under penetration of the vena cava by defining a cohesive fracture zone. An iterative process was developed in order to fit the fracture properties of the vena cava using the previously obtained experimental results. The proposed solutions were obtained with fracture energy of 0.22 or 0.33 N/mm. In comparison with the experimental data, the simulation using [Formula: see text], [Formula: see text], and [Formula: see text] parameters ([Formula: see text]) is in good agreement with results from penetration experiments of cava tissue. It is noticeable that the parameter estimation process of the fracture behavior is more accurate than the estimation process of the elastic behavior for the toe region of the curve.

Clinical course and predictive factors for complication of inferior vena cava filters

RATIONALE

The use of inferior vena cava (IVC) filters is associated with various complications. We aimed to elucidate the clinical course and predictive factors for complications of IVC filters, especially IVC penetration

METHODS

A retrospective observational study was performed in 45 adult patients with retrievable IVC filters and follow-up computed tomography (CT) between January 2003 and December 2012. Primary outcomes were the prevalence and predictive factors of IVC penetration. Secondary outcome was other complications of IVC filters.

RESULTS

IVC penetration following filter placement occurred in 87.6% of patients, and 57.8% of those involved significant penetration. Embedding of filter tips, suggestive of lateral tilting, was observed in 51.1%. Both Vertebral body erosions and aortic penetrations were seen in 4.4%, but they were asymptomatic. Longer indwelling duration of the IVC filter was significantly associated with a higher grade of IVC penetration, and the risk of significant IVC penetration increased in patients with the filter indwelling time of more than 20 days and an IVC diameter of less than 24.2mm.

CONCLUSIONS

In patients with a retrievable IVC filter, IVC penetration on CT was common, and significant IVC penetration was associated with a longer indwelling time of the IVC filter and a lesser IVC diameter.