Abstract:
A long-term retrievable, permanent blood filtration unit is to be implanted in a vessel of a patient&#39;s body, particularly for capturing blood clots, comprising a filter, a stent and a locking mechanism for releasably attaching the filter to the stent.

Description:
REFERENCE TO EARLIER FILED APPLICATION  
       [0001]    The present application claims the benefit of the filing date under 35 U.S.C. § 119(e) of Provisional U.S. Patent Application Serial No. 60/410,236, filed Sep. 12, 2002, which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a blood filtration unit which is to be implanted inside a vessel of a patient&#39;s body.  
           [0003]    Currently known filtration units are formed by at least one filter which is implanted intravenously, generally into the inferior vena cava, to capture blood clots which could migrate towards the heart, in order to avoid the risk of embolism.  
           [0004]    Traditionally, blood filters have been classified in two categories: permanent filters and temporary, or retrievable, filters.  
           [0005]    Permanent filters are designed to be implanted permanently in patients where the risk of embolism is chronic. Some conventional permanent filters have, for example, a frustoconical structure comprising a series of branches terminated by barbs, anchors or similar structures which enable the filter to be secured permanently to the vessel wall. Long-term risks associated with implantation of a permanent vena cava filter include venous stasis due to caval occlusion and its related complications. Although long term complication rates with permanent filters in patients are low, these can be avoided with the use of retrievable or temporary filters in patients with indications such as after severe trauma, and prior to extensive orthopedic or pelvic surgery.  
           [0006]    Temporary filters are designed to be implanted temporarily in patients where the risk of blood clot migration lasts only for a brief period, usually a few weeks. Temporary filters differ from permanent filters basically in that they do not comprise hooks for securing to the vessel wall. The branches of the filter simply engage the vessel wall without hooking into it. Several temporary filtering devices have been developed for insertion into the inferior vena cava (IVC) by transcatheter technique.  
           [0007]    Temporary filters are further classified as either tethered temporary or retrievable filters. Tethered temporary filters are modified catheters or intraluminal devices attached to a tethering catheter or a wire for retrieval one to six weeks after implantation. Tethered filters remain connected throughout the entire period of implantation to prevent the filter from migrating in the vessel. They are implanted in the infrarenal vena cava with the tethering catheter extending out of the puncture site in the neck or groin, or buried subcutaneously within the soft tissues in the patient&#39;s neck. The tether remains coupled to the filter after deployment and is later used to retrieve the filter. The potential for septic complications associated with the tethering catheter exiting the neck or groin require removal of such devices within fourteen days of placement. Risk periods for pulmonary embolism in such patients, however, can extend up to twenty-one weeks.  
           [0008]    Retrievable filters are usually self-expanding and self-attaching devices which can be removed or, if desired, left in place permanently. Typically, these filters have a construction similar to some versions of permanent filters. A hook or similar grasping structure is provided to allow a snare to engage the filter during the retrieval procedure. The filter in its entirety is then retrieved using a snare by drawing it into a catheter. However, to ensure the filter does not migrate within the vessel, barbs, anchors or similar structures must be used to engage the filter with the interior wall of the vessel for retaining the filter in place. These anchors make removal without injuring the vessel difficult. Percutaneous retrieval of these devices requires a new jugular and/or femoral vein catheterization. There is approximately a two week period for removal or repositioning of the filter before it becomes fixed to the caval wall by endothelization. Most existing filters are not easily or safely removable after they have remained in place for more than two weeks, and consequently longer term temporary filters which do not result in the likelihood of injury to the vessel wall upon removal are not available.  
           [0009]    In some patients, the risk of embolism remains great and continues over time contrary to what was expected. If a temporary filter has been implanted first, it is generally necessary to remove the filter in order to replace it by a permanent filter if the two week time period for removal or repositioning of the filter has been exceeded.  
           [0010]    These problems are overcome through the use of a filter having a broad range of clinical utility with a long-term implantation period and at the same time a long-term retrievability option.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    In a first aspect, the invention is a long-term retrievable, permanent filter for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel, said filter having two parts: a first part comprising a stent for positioning, engaging the vessel walls, and becoming incorporated by endothelial tissue; and a second part comprising a filter, said filter releasably coupled to said stent by a locking mechanism. After the risk of embolism has passed, the filter part may be retrieved using a catheter and snare. Alternatively, the filter may be left in place permanently if desired.  
           [0012]    In another aspect, the invention is a long-term retrievable, permanent filter for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel comprising: (1) a stent for positioning, engaging the vessel walls, and becoming incorporated by endothelial tissue; (2) a filter; and (3) a locking mechanism for releasably coupling said stent to said filter; wherein said filter further comprises an apical hub, a plurality of divergent legs, at least one of said plurality of divergent legs secured at one end to said hub, at least one of said plurality of divergent legs releasably secured at another end, which is distally located with respect to said hub, to said stent by said locking mechanism. wherein said locking mechanism further comprises a stent attachment means and a filter attachment means.  
           [0013]    In another aspect, the invention is a long-term retrievable, permanent filter for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel comprising: (1) a stent for positioning, engaging the vessel walls, and becoming incorporated by endothelial tissue; (2) a filter; and (3) a locking mechanism for releasably attaching said stent to said filter; wherein said filter further comprises an apical hub, a plurality of filter legs having an upstream end and a downstream end, at least one of said plurality of filter legs secured at the downstream end to said hub, at least one of said plurality of filter legs releasably secured at the upstream end to said stent by said locking mechanism.  
           [0014]    In yet another aspect, the invention is a long-term retrievable, permanent filter for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel comprising: (1) a stent for positioning, engaging the vessel walls, and becoming incorporated by endothelial tissue; (2) a filter; and (3) a locking mechanism for releasably attaching said stent to said filter; wherein said filter further comprises an apical hub, a plurality of divergent legs having an upstream end and a downstream end, at least one of said plurality of divergent legs secured at the downstream end to said hub, at least one of said plurality of divergent legs releasably secured at the upstream end to said stent by said locking mechanism; wherein said locking mechanism further comprises stent attachment means attached to the downstream end of at least one of said plurality of divergent legs and at least one filter attachment means attached to said stent.  
           [0015]    In yet another aspect, the invention is a long-term permanent retrievable filter for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel of a mammal comprising: (1) a filter comprising a plurality of divergent legs each having an upstream end and a downstream end, each of said plurality of divergent legs further comprising a cannula and a lumen; (2) an apical hub connecting each of said downstream ends of said plurality of divergent legs; (3) a stent configured to engage a wall of said generally tubular vessel and become incorporated by endothelial tissue; (4) a locking mechanism comprising a stent attachment means attached to said filter and a filter attachment means attached to said stent, said stent attachment means is releasably secured to said filter attachment means for releasably securing said filter to said stent, said stent attachment means further comprising at least one attachment wire, said at least one attachment wire extends through at least one lumen of said plurality of divergent legs and is attached at a retrieval connection point; wherein an upward motion applied to said retrieval connection point disengages said at least one attachment wire of said stent attachment means from said filter attachment means. 
       
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 depicts a perspective view of one embodiment of the long-term retrievable, permanent filter of the present invention.  
         [0017]    [0017]FIG. 2 depicts one preferred embodiment of the long-term retrievable, permanent filter of FIG. 1.  
         [0018]    [0018]FIG. 3 depicts a plan view of one exemplary embodiment of the stent part of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0019]    [0019]FIG. 3A depicts a plan view and enlarged, partial cross sectional view of the stent part of the long-term retrievable, permanent filter of FIG. 3.  
         [0020]    [0020]FIGS. 4-4 b  depicts a plan view and enlarged, partial cross sectional views of a second embodiment of the stent part of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0021]    [0021]FIG. 5 depicts an enlarged, partial view of the embodiment of FIGS. 3 and 4- 4   b.    
         [0022]    [0022]FIG. 6 depicts a side view of one preferred embodiment of the filter part of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0023]    [0023]FIG. 6A depicts an enlarged, partial, side-view of a stent attachment means of the filter part of FIG. 6.  
         [0024]    [0024]FIG. 7 depicts an enlarged, partial, side-view of one preferred embodiment of locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0025]    [0025]FIG. 8 depicts an end view of the filter part of FIG. 6.  
         [0026]    [0026]FIG. 9 depicts an alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0027]    [0027]FIG. 10 depicts another alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0028]    [0028]FIG. 11 depicts another alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0029]    [0029]FIG. 11A depicts another alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0030]    [0030]FIG. 12 depicts another alternative preferred embodiment of a stent attachment means of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0031]    [0031]FIG. 13 depicts another alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0032]    [0032]FIG. 14 depicts another alternative preferred embodiment of a locking mechanism of the long-term retrievable, permanent filter of FIGS. 1 and 2.  
         [0033]    [0033]FIG. 15 depicts a partial, side-view of the long-term retrievable, permanent filter of FIGS. 1 and 2 retracted within an introduction catheter.  
         [0034]    [0034]FIG. 16 depicts a side, partial cross-section view of another alternative preferred embodiment of the filter part of the long-term retrievable, permanent filter of FIG. 1.  
         [0035]    [0035]FIG. 17 depicts a side, partial cross-section view of another alternative preferred embodiment of the filter part of the long-term retrievable, permanent filter of FIG. 1.  
         [0036]    [0036]FIG. 18 depicts a side, partial cross-section view of an alternate preferred embodiment of the filter part of the long-term retrievable, permanent filter of FIGS.  1  partially within a collapsing sheath.  
         [0037]    [0037]FIG. 19 depicts an enlarged, partial side view of the long-term retrievable, permanent filter of FIGS. 1 and 2 within a vein wall.  
         [0038]    [0038]FIG. 19A depicts a partial, cross-sectional view of the long-term retrievable, permanent filter of FIG. 19.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    As noted above, the present invention relates to a number of different aspects of a long-term, retrievable, permanent filter. Schematic illustrations of the preferred embodiments are provided in FIGS. 1-19A.  
         [0040]    Referring to the drawings in detail, the invention as illustrated is embodied in a long-term retrievable, permanent filter  100  for filtering solid and semi-solid materials from a liquid moving axially in a generally tubular vessel  700  having two parts: a first part comprising a stent part  200  for positioning and engaging the vessel walls and becoming incorporated by endothelial tissue; and a second part comprising a filter part  300 . A locking mechanism  500  releasably attaches the filter part  300  to the stent part  200 . Preferably, locking mechanism  500  is a two part locking mechanism comprising a filter attachment means  510  and a stent attachment means  520 , as described in further detail herein.  
         [0041]    The stent part  200  of long-term retrievable, permanent filter  100  most preferably comprises a square stent as described herein. It is also anticipated that stents of the type described in U.S. Pat. No. 6,200,336, the disclosure of which is incorporated herein by reference, stents such as the Cook Z® Stent, stents of the type disclosed in U.S. Pat. Nos. 5,035,706 and 4,580,568, the disclosures of which are incorporated herein by reference, and other stents may be used in the alternative.  
         [0042]    In the preferred embodiment shown in FIG. 3, stent part  200  comprises a multiple-sided stent comprising a frame  11  of resilient material, preferably metal wire made of stainless steel or a superelastic material (e.g., nitinol). Although the embodiments shown depict a round wire, other types of wire, e.g., flat, square, or triangular, may be used to form the frame. In the illustrative embodiment, the frame  11  comprises a closed circumference  62  of a single piece of material  59  that is formed into a multiple-sided stent having a plurality of sides  13  interconnected by a series of bends  12 . The preferred and depicted embodiment includes four sides  13  of approximately equal length. The square stent design provides optimal radial pressure and conformity to the vein wall with the least amount of metal and therefore achieves good anchoring and minimizes inflammatory responses. Alternative embodiments include forming a frame into any polygonal shape, for example a pentagon, hexagon, octagon, etc. In the preferred embodiments of FIG. 3 and  5 , the bends  12  interconnecting sides  13  comprise a coil  14  of approximately one and a quarter turns. The coil bend is spring-like and reduces stress and metal fatigue. When using stainless steel wire, the size of the wire depends on the size of the device and the application. In one preferred embodiment of stent part  200 , the wire is metal and, the wire is stainless steel and round. In such an embodiment, the diameter of the wire is between about 0.005 and about 0.020 inch, more preferably between about 0.012 and about 0.016 inch, and most preferably is about 0.012 inch. The frame  11  ranges in sizes from about 10 mm and about 50 mm, more preferably between about 30 and about 45 mm, and most preferably is about 35 mm. Wire that is too stiff can damage the vessel, not conform well to the vessel wall, and increase the profile of the device.  
         [0043]    Returning to FIG. 3, the single piece  59  of material comprising frame  11  is formed into the closed circumference by securing the first and second ends  60 ,  61  with an attachment mechanism  15  such as a piece of metal cannula. The ends  60 ,  61  of the single piece  59  are then inserted into the cannula  15  and secured with solder  25 , a weld, adhesive, or crimping to form the closed frame  11 . The ends  60 ,  61  of single piece  59  can be joined directly without addition of a cannula  15 , such as by soldering, welding, or other methods to join ends  60  and  61 . Besides joining the wire, the frame could be fabricated as a single piece of material  59 , by stamping or cutting the frame  11  from another sheet (e.g. with a laser), fabricating from a mold, or some similar method of producing a unitary frame.  
         [0044]    Preferably, stent part  200  further includes one or more barbs  16  to anchor stent part  200  following deployment as shown in FIG. 4. As will be understood, a barb can be a wire, hook or any structure attached to the frame and so configured as to be able to anchor the stent part  200  within a lumen of a human or veterinarian patient. The illustrative embodiment includes a first barb  17  with up to three other barbs  18 ,  71 ,  72 , indicated in dashed lines, representing alternative embodiments. As depicted in detail view  4 A, each barb  17  and  18  of the barb combination  38  that comprises barbs  17  and  18  is an extension of the single piece  59  of material of the frame  11  beyond the closed circumference  59 . The attachment cannula  15  secures and closes the single piece  59  of material into the frame  11  as previously described, while the first and second ends  60 ,  61  thereof, extend from the cannula  15 , running generally parallel with the side  13  of the frame  11  from which they extend. Preferably, each end  60 ,  61  terminates around or slightly beyond respective bends  20 ,  23  to form barbs  17 ,  18 , which anchors the stent  100  following deployment. More preferably, each barb  17 ,  18  extends about 1-2 mm over frame  11  on opposing bends  20 ,  23 . To facilitate anchoring, the distal end  19  of barb  17  in the illustrative embodiment contains a bend or hook. Optionally, the tip of the distal end  19  can be ground to a sharpened point for better tissue penetration. Most preferably additional barbs  71 ,  72  are added to opposing corners  21 ,  22 . To add a third and fourth barb as shown, a double ended barb  39  comprising barbs  71  and  72  is attached to the opposite side  13  as defined by bends  21  and  22 . Unlike barb combination  38 , the double barb  39 , as shown in detail view  4 B, comprises a piece of wire, usually the length of barb combination  38 , that is separate from the single piece  59  comprising the main frame  11 . It is secured to the frame by attachment mechanism  15  using the methods described for FIG. 3. While this embodiment describes up to a four barb system, more than four barbs can be used.  
         [0045]    The stent part  200  further includes a filter attachment means  510  for attaching the filter part  300  to the stent part  200  to form the long-term retrievable, permanent filter  100 . Preferably, the filter attachment means  510  comprises at least one cannulae  510  attached to the frame  11  as shown in FIGS. 3 and 4. Most preferably, the filter attachment cannulae  510  are about 20 gauge (“G” ) or about  21  G.  
         [0046]    The filter part  300  of the long-term retrievable, permanent filter  100  may be a filter of the type described in U.S. Pat. Nos. 4,580,568, 5,035,706, 5,133,733, the disclosures of which are incorporated herein by reference, filters such as the Cook Günther-Tulip™ Vena Cava filter as well as other vena cava filters.  
         [0047]    [0047]FIG. 6 shows one preferred embodiment the filter part  300  in the expanded position. In this embodiment, the filter part  300  comprises a plurality of elongated legs. Preferably, each of the plurality of elongated legs, of which there are four for example, is of equal length and is identically configured to the others. The legs  310 ,  320 ,  330  and  340  are collectively arrayed in a conical geometric configuration so that the legs converge to the apical hub  350  and are symmetrically spaced about a central axis extending through an apical hub  350 . The apical hub, or end ferrule,  350  may be of the kind disclosed in U.S. Pat. No. 4,691,246. Alternatively, other apical hubs as known in the art are contemplated. Preferably, the apical hub points upstream in the direction of blood flow in the blood vessel of a patient. Preferably, the apical hub  350  comprises a retrieval connection point  355  at the apex of the filter part  300 .  
         [0048]    The filter legs  310 - 340  may be flexible wire and, in one preferred embodiment, the wires are metallic and round. In such an embodiment, the diameter of the wire may be between about 0.2 and about 0.4 millimeter, for example about 0.3 or about 0.35 millimeter.  
         [0049]    Each leg comprises a central element  310   a ,  320   a ,  330   a ,  340   a  as well as two generally symmetrical curved side elements  310   b ,  320   b ,  330   b  and  340   b  and  310   c ,  320   c ,  330   c  and  340   c  extending on either side of each central element as best shown in FIG. 8. Each leg is distributed in a generally equally spaced angular manner so as to ensure the axial stability of the filter. As best seen in FIG. 6, preferably, the curvature of the four central wires is a flared, or trumpet shape, and the bends of the legs are aligned with one another around the periphery of the filter. The length and curvature of the legs  310 - 340  preferably are chosen such that after insertion into the blood vessel, the legs  310 - 340  are positioned to avoid contact with the wall of the blood vessel.  
         [0050]    In the embodiment shown the two side elements of each leg  310 - 340  are formed from one piece of wire, the ends of which are held together in hub  350 . At the middle of its length the wire piece may form an eyelet  310   e ,  320   e ,  330   e ,  340   e  surrounding the leg to be freely slidable along a part of the length thereof. Preferably, the side elements of each leg are formed from one piece of wire without the eyelet  310   e - 340   e  with the middle of the wire length attached to the leg as known in the art. By removing the eyelet  310   e - 340   e , the potential that the wire crossing will be covered with neointima and potentially prevent retrieval is minimized. Preferably, the side elements of each leg have a length and a curvature such that, in the unfolded trumpet-like configuration of the filter part  300 , the maximum distance between the side elements is of the same order as the distance between the neighboring side elements of two adjacent legs as shown in FIG. 8.  
         [0051]    As shown in FIG. 6, at least one filter leg  310 - 340  further comprises a stent attachment means  520  for releasably engaging the filter attachment means  510  of the filter part  300 .  
         [0052]    In alternate embodiments, the filter part  300  may be formed without curved side elements  310   b - 340   b ,  310   c - 340   c  and may comprise a plurality of elongated legs with different lengths, thicknesses and flexibilities.  
         [0053]    Coatings, such as biocompatible polymeric coatings, and surface treatments, such as metallization with a noble metal can be applied to the legs  310 - 340 . Also, each of the legs  310 - 340  may be coated with a polymeric, synthetic resin material having anti-thrombogenic properties.  
         [0054]    The locking mechanism  500  comprises a filter attachment means  510  located on the stent part  200  and a stent attachment means  520  located on the filter part  300 . The filter attachment means  510  releasably engages the stent attachment means  520 , thereby releasably attaching the filter part  300  to the stent part  200 . The locking mechanism  500  is sized to be large enough to remain locked during normal conditions, but small enough such that the force necessary to remove the filter part  300  does not damage the vessel during removal. It is believed that about 800 to about 1000 grams of force is the optimal force needed to remove the filter part  300  from the stent part  200 . Preferably, locking mechanism directs the filter away from the wall of the lumen, as shown in FIGS. 1, 2,  19  and  19 A. As shown in FIGS. 19 and 19A, preferably filter attachment means  510  protrudes into the lumen and away from the vein wall. The stent frame  11  and filter attachment means  510  are positioned adjacent to vein wall  700  such that stent attachment means  520  is positioned in an open area away from the vein wall  700 . This configuration minimizes the risk of tissue in-growth at the connection points between the filter part  300  and anchor part  200 .  
         [0055]    In the embodiments shown in FIGS. 6-7,  9 - 13 , the locking mechanism  500  may comprise an interference-fit locking mechanism. In these embodiments, the stent attachment means  520  comprises an attachment wire  521  and the filter attachment means  510  comprises a cannula  511 . The attachment wire  521  may be an extension of the filter leg  310 - 340  or a separate piece of wire attached to the filter leg  310 - 340 . Many different configurations have been contemplated for the attachment wire  521  of the stent attachment means  520  and the cannula  511  of the filter attachment means  510 . For example, in the embodiment shown in FIG. 9, the attachment wire  521  of the stent attachment means  520  comprises a bend  522 . In this embodiment, the bend  522  comprises an angle that provides a locking force when the filter part  300  is in the open or expanded configuration. When the filter part  300  is collapsed, however, the bend straightens and the locking force is reduced, thereby releasing the filter part  300  from the anchor part  200 .  
         [0056]    In the embodiment shown in FIG. 10, the attachment wire  521  of stent attachment means  520  comprises a ball  523  extending from the filter leg  310 - 340  and the cannula  511  of the filter attachment means  510  comprises a slot  512 . In this embodiment, filter leg  310  is removed by sliding ball  523  through cannula slot  512 . As shown in FIG. 11, the cannula  511 , alternatively, may be crimped to form ball recess  513 . FIG. 11 also shows that the ball  523  forms an interference fit with the cannula  511 . FIG. 11 A shows an alternate embodiment of filter leg  310  secured in place within cannula  511  of the filter attachment means  510 . In this embodiment, filter leg is removed by sliding ball  523  into the ball recess  513  and away from cannula  511 , as indicated by arrow  710 . Preferably, the cannula slot  512  of the filter attachment means  510  coincides with the direction of blood flow (indicated by arrow  720  in FIGS. 11 and 11A) in the vessel. These configurations achieve a greater retention force in the direction of the blood flow than the amount of force required to push the filter into the cannula such that ball  523  of the stent attachment means  520  engages then ball recess  513  of the filter attachment means  510 .  
         [0057]    In the embodiment shown in FIGS. 6 and 7, the attachment wire  521  of the stent attachment means  520  comprises a Y-shaped adapter and the filter attachment means  510  comprises a cannula  511 . Preferably, the Y-shaped adapter further comprises a Y-shaped prong  524  attached to a cannula  525 . The Y-shaped prong  524  was formed from 0.010 inch stainless steel wire. The stent attachment means  520  of the Y-shaped locking mechanism  500  is attached to the filter leg  310 - 340  at the end opposite the apical hub  350  by attaching the free end of the cannula  525  to the filter leg  310 - 340  by any means known in the art such as brazing, welding, soldering, crimping, mechanical fasteners, twisting, gluing and the use of adhesives etc.  
         [0058]    In an alternate embodiment shown in FIG. 12, the attachment wire  521  of the stent attachment means  520  comprises a looped adapter and the filter attachment means  510  comprises a cannula  511 . Preferably, the looped adapter further comprises a looped wire  526  attached to a cannula  525 . The looped adapter  526  forms an interference fit with the cannula  511 .  
         [0059]    In yet another alternate embodiment shown in FIG. 13, the attachment wire  521  of the stent attachment means  520  comprises a coiled adapter and the filter attachment means  510  comprising a cannula  511 . Preferably, the coiled adapter further comprises a coil  527  attached to a cannula  525 .  
         [0060]    Still yet other embodiments of the locking mechanism  500  have been contemplated. In an alternate embodiment shown in FIG. 14, the locking mechanism  500  comprises a coiled locking mechanism. In this embodiment, the filter leg  310 - 340  comprises at least one coil  527  that attaches to a portion of the stent part  200 . The coil  527  may releasably and directly engage a side of stent part  200 . Alternatively, the coil  527  may releasably engage a loop  514  on the stent part  200  as shown in FIG. 14. In another embodiment, multiple coils may be used to vary the force required for removal. For removal, the filter part  300  is pulled by the retrieval connection point  355  and the coil  527  straightens and releases the stent part  200 . In another embodiment, if the coil is formed from a shape memory alloy, the coil may be straightened by using localized heating or cooling.  
         [0061]    Other locking mechanisms may be used to fix the free ends of the filter part  300  to the stent part  200  to form the long-term retrievable, permanent filter  100  of the present invention without departing from the spirit or scope of the present invention. For example, brazing, welding, soldering, crimping, mechanical fasteners, twisting, gluing and the use of adhesives etc. may be suitable for some applications. Alternatively, at least one leg  310 - 340  of filter part  300  can be modified to releasably attach to stent part  200  directly. In yet alternative embodiments, filter attachment means  510  may comprise an attachment wire and stent attachment means  520  may comprise a cannula. Any structure capable of directing the filter part  300  away from the wall of the lumen is contemplated.  
         [0062]    From the unfolded trumpet-like configuration illustrated in FIGS. 1 and 2, the long-term retrievable, permanent filter  100  may be collapsed into a slender and very narrow bundle of filter elements as shown in FIG. 15, the cross-sectional dimension of which is approximately equal to the sum of the thicknesses of the central and side elements of all four legs. The locking mechanism  500  is designed such that the structure of filter part  300  remains in tact during the retrieval process. Therefore, in the collapsed configuration, the collected blood clots are retained within the filter part  300  as the filter part  300  is withdrawn into a collapsing sheath during the retrieval process. The locking mechanism  500  is also designed so that in the expanded configuration, the long-term retrievable, permanent filter  100  of the present invention provides a large retention force in the direction of the blood flow to retain the filter part  300  in place but is easily collapsed and retrieved without damaging the vein wall.  
         [0063]    [0063]FIGS. 16-18 show alternative preferred embodiments of the long-term, retrievable, permanent filter  100 ′. In these embodiments, the long-term retrievable, permanent filter  100 ′ has been adapted such that the user can decrease the force required to unlock the filter part  300 ′ from the stent part  200 ′ to remove the filter part  300 ′. As seen in FIG. 16, at least one filter leg  3   10 ′- 340 ′ comprises a cannula and a lumen  310   d ,  320   d ,  330   d ,  340   d . An apical hub  350 ′ connects the filter legs  310 ′- 340 ′ to form the filter part  300 ′. The attachment wires  521 ′ extend through lumens  310   d ,  320   d ,  330   d ,  340   d  and are attached at the retrieval connection point  355 ′ of the filter part  300 ′. The retrieval connection point  355 ′ may align with, or be positioned above, the apical hub  350 ′. As shown in FIG. 17, the apical hub  350 ′ may further comprise an outer hook  360  and the retrieval connection point  355 ′ may comprise an inner hook  365 . The two hooks  360 ,  365  may be snared with a retrieval loop and squeezed together such that the upward motion of the inner hook  365  disengages attachment wires  521 ′ of the stent attachment means  520  from the filter attachment means  510 .  
         [0064]    In the alternate preferred embodiment shown in FIG. 18, the apical hub  350 ′ comprises a locking ring  351  ′ and retrieval connection point  355 ′ comprises a snare hook  356 ′. To disengage attachment wires  521 ′ of the stent attachment means  520 ′ from the filter attachment means  510 ′. A retrieval loop  600  is used to withdraw the snare hook  356 ′ into a snare catheter  610  and in so doing secures the snare hook  356 ′. Next, an unlocking catheter  620  is advanced towards and positioned against the locking ring  351 ′. The retrieval loop  600  is then withdrawn to pull attachment wires  521 ′ through filter legs  310 ′- 340 ′ and unlock the attachment wires  521 ′ of the stent attachment means  520  from the filter attachment means  510 . As the retrieval loop  600  is retracted, the filter part  300 ′ is pulled within a collapsing sheath  630  and collapses.  
         [0065]    In accordance with the invention, both the stent part  200  and the filter part  300  may be made of various materials, which can differ from each other, and can have different sizes and strengths. Preferably, the material is metal. Although the wire used in the preferred embodiments has a round cross-section, other shapes are also functional. In the preferred embodiment, the wire is preferably a radiopaque and non-ferromagnetic metal which has been certified for use in permanently implanted medical devices by the International Standards Organization (ISO). In particular, the wire may be made of a 316L stainless steel wire, or of a suitable grade of stainless steel such as that known as AFNOR K 13C20 N16 Fe15. Alternatively, the wire may be a high cobalt, low ferrous alloy, such as that known as and sold under the registered trademarks of “PHYNOX,” “ELGILOY” or “Conichrome” which may have the composition, by weight percent: cobalt 42%, chromium 21.5%, nickel 18%, iron 8.85%, molybdenum 7.6%, manganese 2% with the balance made up of carbon and beryllium having a maximum of 0.15% carbon and 0.001% beryllium. Also, the wire may be a nickel-chromium alloys, such as “MP35N” or that known as and sold under the registered trademark of “Inconel.” The wire may also be formed from titanium, titanium alloy, nickel titanium alloy known to be shape-memory metals which are sold and manufactured under the trademark “NITINOL”, an alloy of tantalum or any other biocompatible material with elasticity may in certain circumstances be employed to advantage. When a nickel titanium alloy is used, the wires are operating in the linear portion of the stress/strain curve of the alloy, though it is possible to employ wires operating in the super-elastic region while obtaining benefits of the invention. Likewise, thermally responsive shape-memory metal can be employed with the geometric and spatial constraints provided by the invention. Alternatively, the wire may be formed from various polymers. It is also anticipated that new materials, as they are developed, will be useful.  
         [0066]    Preferably, the long-term retrievable, permanent filter  100  of the present invention is preferably constructed from materials that will preferably withstand twelve million respiratory cycles without mechanical failure and will be non-thrombogenic.  
         [0067]    A long-term retrievable, permanent filter  100  according to the invention is positioned in a blood vessel according to the conventional process which is facilitated by the flexibility of the filter. For percutaneous insertion of long-term retrievable, permanent filter  100 , a vein is punctured with a needle, and a guidewire is advanced into the blood vessel through the needle beyond the desired implantation site. A catheter consisting of an inner, dilating cannula within an outer sheath, up to 14 French in diameter, is then advanced into the vein, over the guidewire. When the desired implantation site is reached, the inner dilating cannula and guidewire are removed, leaving the sheath behind. The sheath acts as a conduit to permit the insertion of the filter. The long-term retrievable, permanent filter  100 , in a collapsed configuration, is introduced into the sheath and advanced to the implantation site as shown in FIG. 15. Once long-term retrievable, permanent filter  100  is in an appropriate position, the long-term retrievable, permanent filter  100  is pushed out of the sheath or uncovered using a pushing catheter. Upon discharge, the filter part  300  and the stent part  200  open, the stent part  200  positions the long-term retrievable, permanent filter  100  in the blood vessel and engages the interior wall of a blood vessel of a patient.  
         [0068]    A long-term retrievable, permanent filter  100  according to the invention is retrieved from a blood vessel by advancing a guidewire into the blood vessel to the implantation site. Then, advancing a catheter over the guidewire to the retrieval connection point  355  of the filter part  300 . The guidewire is withdrawn and a retrievable loop is advanced through the collapsing catheter to the retrieval connection point  355  of filter part  300 . The retrieval connection point  355  is grasped by the retrievable loop. As the retrievable loop is withdrawn, locking mechanism  500  releases filter part  300  from stent part  200  and filter part  300  is collapsed within the collapsing catheter.  
         [0069]    Whereas the long-term retrievable, permanent filter  100  of the present invention has been described and illustrated with reference to a specific embodiment comprising four legs and a square stent it will be understood that various modification, e.g., with respect to the number of legs and/or the configuration of the stent can be made without departing from the scope of the following claims.