Desenvolvimento e avaliação de filtro para veia cava inferior stent-filtro

Abstract

Implantation of an inferior cava vena filter is recommended for the prevention of pulmonary embolism when anticoagulation fails or is contra-indicated. The aim of this study was to develop and evaluate a new low-cost model of inferior cava vena filter. In reality in this case it is a combination of a inferior cava vena filter with a vascular stent. The material utilized in the fabrication of the stent-filter was AISI-302 stainless steel with both 3.5 mm and 4.0 mm of diameter. The filter was tested in vitro and in vivo in an experiment involving animals. In vitro the efficiency of the stent-filter was assessed using a semi-open circuit with pulsating flow, into which it was positioned. Thrombi of sheep blood of 3 mm of diameter and 30 mm of length were produced within a silicon tube. The test circuit was filled with isosmotic fluid comprising of 0.9% saline solution with 40% glycerin. The a total of 150 emboli were introduced into the circuit divided in three stages with 50 each. In the first stage the flow rate of the solution in the circuit was 1.0 L/min, in the second 1.5 L/min and in the third 2.0 L/min. In the live experiment, stent-filters were implanted in three female and two male adult Australian Merino Sheep with weights between 32 and 40 kg. Macroscopic evaluations were made of the vein walls adjacent to the stent-filters after sacrificing the sheep. After portions of the vein walls were embedded in paraffin, sliced with a thickness of 5 microns, fixed on slides and stained using hematoxylin and eosin for histologic examination. For statistical evaluation, the percentage of emboli captured in the circuit was considered. The total length of the stent-filter is 48 mm, 18 mm being the stent and 30 mm the filter. The diameter is 28 mm with the parts of the filter joined using rings located at the end of the individual arms. In-vitro the filter captured a total of 92% of the emboli in all the events. The macroscopic evaluation demonstrated that the filter was pervious, fixed into and restrained by the vein walls without any signs of perforations or fractures of the structure. The histologic examination showed complete formation of the endothelium in the region of the stents and areas lacking endothelium in the region adjoining the filter with hyperplasia of the intima. In conclusion, it was possible to develop a new low-cost stent-filter efficient in the capture of 3-mm emboli. The anchoring of which, in the vascular walls, was satisfactory. The greater quantity of material used in its production can be compensated for by the advantage of formation of endothelium seen in the region of the stent. However regions of injured endothelium in the region of the filter were observed suggesting a mechanical trauma caused by the filter on the vessel walls.