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.

A combined surgical-endovascular device concept for giant aneurysm neck occlusion.

PURPOSE: In this report, we describe a new multimodality device concept for occluding giant aneurysms. The device is designed to exploit the advantages, and avoid the disadvantages, of conventional microneurosurgery and interventional neuroradiology methods. CONCEPT: Our device concept involves surgically placing small permanent magnets, incorporated into a partially occluded magnetic clip, about the extraluminal neck without mechanically compromising the perforating vessels. These magnets serve as optimally positioned anchor points for ferromagnetic materials subsequently introduced via the endovascular route. RATIONALE: Currently, neurosurgical extraluminal obliteration of giant aneurysms is achieved by mechanically closing the aneurysm neck with metal clip blades, which is a technique that risks inadvertent occlusion of critical perforating vessels. Perforating vessel strokes can largely be avoided using endovascular aneurysm occlusion methods. However, in the setting of the giant aneurysm, these endovascular techniques are associated with high rates of incomplete occlusion. DISCUSSION: Preliminary feasibility tests of this concept were conducted using a simple prototype constructed in our laboratories.

A retrievable nitinol vena cava filter: experimental and initial clinical results.

PURPOSE: The authors describe the properties of a new retrievable nitinol vena cava filter and report experimental and initial clinical results. MATERIALS AND METHODS: The filters, made of nitinol monofilament wire that forms a spiral cone and retrieval wire, were introduced through an indwelling 5.5-F transfemoral sheath into the infrarenal portion of the inferior vena cava in 10 sheep. In seven animals, four 4 x 30-mm radiopaque clots were injected below the filter to test its thrombus-trapping efficacy. Aspiration thrombectomy was then attempted, and the filter was removed. Follow-up venography was performed 1 week after placement in three other animals. After successful preclinical testing, the filter was implanted and retrieved in two patients. RESULTS: All 10 filters were successfully and easily placed in sheep. All filters were thrombus-free at follow-up venography. All clots injected in the iliac veins were trapped by the filter and successfully removed by means of aspiration thrombectomy. All 10 filters were retrieved without difficulty. Temporary filter implantation and retrieval were accomplished in two patients for 5 and 7 days. In one patient, infrafilter thrombus was aspirated. Perisheath thrombosis occurred in both patients. One patient subsequently underwent permanent filter placement. CONCLUSION: Temporary vena cava filtration is feasible. Potential advantages include easy placement, surveillance, and retrieval. One current limitation is pericatheter thrombosis, which may be eliminated by a less thrombogenic sheath.

Nitinol intravascular stent: results of preclinical evaluation.

PURPOSE: To test an expandable nitinol intraluminal stent for hoop strength, biocompatibility, corrosion resistance, and patency. MATERIALS AND METHODS: Forty-four stents were implanted in the iliac arteries of 22 sheep. Follow-up was performed with angiography and histologic examination for up to 6 months. RESULTS: All but one stent remained widely patent during the follow-up period. Two stents in two sheep were placed incorrectly early in the study; these sheep were not followed up. Hoop strength was found to be superior to that of a similar, commercially available, self-expanding stent. Minimal corrosion was seen at 6 months, and the stent appears to be biocompatible. The stent has good radiopacity and deploys with minimal foreshortening. CONCLUSION: The stent can be reliably and safely deployed in the vascular system. Clinical trials in humans are warranted.

Thrombus-trapping efficiency of the Greenfield filter in vivo.

A total of 100 radiopaque blood clots were injected into seven adult sheep under fluoroscopic observation to assess the clot-trapping efficiency of the Greenfield vena caval filter. Eleven percent of the clots passed through the filter, with all failures limited to the two smallest clot sizes: 4 x 10 mm (five of 25) and 4 x 30 mm (six of 25). The Greenfield filter was 100% efficient in trapping larger clots (8 x 10 mm and 8 x 30 mm). There was a tendency toward poorer clot-trapping performance when the Greenfield filter was tilted within the vena cava, but this was not significant. There were no significant differences in hemodynamic measurements obtained immediately before and after injection of each clot, and no significant changes were noted in the animal's hemodynamic status or in blood gas measurements in those cases in which the clots passed through the filter. Since the caval diameter in sheep approximates that in humans, the authors conclude that the Greenfield filter in the clinical setting is capable of stopping large, likely fatal, emboli and a large number of smaller, possibly less clinically significant, emboli.