Abstract:
A filter device positionable within a blood vessel for trapping emboli in the vessel, the filter device having a head and a plurality of divergent legs each secured at a first end to the head; each leg having one or more hooks at a second end. The hooks can include an expandable and contractible sleeve or hook that provides securing means for the legs and which also allows for easy removal of the filter device.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention pertains to the field of intra vena cava filters. In particular, the present invention pertains to retrievable intra vena cava filters. Intra vena cava filters are commonly implanted either temporarily or permanently in patients at risk for blood clotting.  
       BACKGROUND OF THE INVENTION  
       [0002]     Blood clots (emboli) carried in the blood stream often constitute serious threats to health and in some instances, to life itself. The reduction of such clots, or their stabilization and arrest of further migration in the circulatory system of the body, is desiderata constantly motivating the development by the medical profession of new techniques and devices for this purpose. Although emboli moving in other portions of the circulatory system can also present serious problems, development of means for preventing emboli from migrating into the pulmonary circulation from the vena cava has received the primary attention.  
         [0003]     One method of capturing emboli is the utilization of filters emplaced in the major blood vessels such as the vena cava. U.S. Pat. No. 4,817,600 to Herms et al. discloses a titanium filter having a plurality of legs joined to a head or nose bead; the legs having a first straight portion, and sharply divergent legs extending therefrom.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention pertains to an intra vena cava filter implantable temporarily or permanently, and methods for removal thereof. The filter includes struts having tips that engage the wall of the vein or inner surface of another organ to provide positional stability of the filter.  
         [0005]     In one embodiment, the struts are made of multiple wires, with the end of each wire sharpened and bent into a hook shape facing a different direction. In another embodiment, the expandable hooks are removed with the filter by reducing the diameter of the hooks. In a further embodiment, the filter includes expandable hooks that fit over the ends of the struts. The hooks function to secure the filter in a vessel, but can be expanded to release the struts, allowing removal of the filter. Methods are provided for subsequent removal of the filters. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a front perspective view of an intra vena cava filter according to one embodiment of the invention;  
         [0007]      FIG. 2A  is a side view of one strut of the filter of  FIG. 1 ;  
         [0008]      FIG. 2B  is a side view of a strut of another embodiment of intra vena cava filter;  
         [0009]      FIG. 2C  is a cross-sectional view of the strut of  FIG. 2A ;  
         [0010]      FIG. 3A  is a front perspective view of an intra vena cava filter according to another embodiment of the invention.  
         [0011]      FIG. 3B  is a side view of a strut end and radially contractible sleeve of the filter of  FIG. 3A  embedded in a vessel wall;  
         [0012]      FIG. 3C  is a side view of the strut end of  FIG. 3B  with the radially contractible sleeve in an extended, radially contracted configuration as the strut is removed from a vessel wall;  
         [0013]      FIG. 4  is a side view of another embodiment of radially contractible sleeve;  
         [0014]      FIG. 5  is a side view of another embodiment of a strut with an expandable hook;  
         [0015]      FIG. 6  is a side view of the strut of  FIG. 5  with the expandable hook in the expanded configuration in position over the retaining member at the end of the strut;  
         [0016]      FIG. 7  is a side view of the strut of  FIG. 6  with the expandable hook in a radially contracted configuration secured to the end of the strut and embedded in the caval wall; and  
         [0017]      FIG. 8  is a side view of the strut of  FIG. 7  with the expandable hook in an expanded configuration to release the strut for removal of the filter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring now to the drawings wherein like reference numerals refer to like elements throughout the several views,  FIG. 1  is a front perspective view of a filter  10  including a hub  12  from which extends a plurality of legs  14 . Each leg can be straight or can include bends or curves along its length. Bends or curves in the legs may help catch thrombi that flow through the vessel. In one embodiment, all of the legs  14  are identical. In another embodiment, some or all of the legs  14  are differently shaped. Some legs  14  can be straight while others have one or more bends, and the legs with bends can have different numbers of bends and the angles of the bends can be different. The legs  14  can be biased to expand from a radially compressed configuration in which some or all of the legs  14  are touching within a delivery device to the expanded, cone shaped configuration shown in  FIG. 1 , when deployed in a blood vessel.  
         [0019]     The free end  13  of each leg  14  includes one or more barbs  16  for engagement with the vessel wall to stabilize filter  10  within a vessel. The barbs  16  can be integral with the legs  14  or the barbs  16  can be made separately and then attached to the free ends  13  of the legs  14 . In one embodiment, each leg  14  is made of a plurality of wires  18 . In the embodiment shown in  FIG. 1 , each leg  14  is made of three wires  18  attached to each other along their length. Each wire  18  has a barb  16  at the free end  13 . The barbs  16  face in opposing directions. In another embodiment, the barbs  16  can face in substantially the same direction but are spaced apart. In a further embodiment, each leg is formed of a single wire that is split or divided into a plurality of barbs at the free end. The barbs  16  are configured to anchor the filter to the vessel walls.  
         [0020]     The legs  14  and hub  12  can be made of the same material or can be made of different materials. Suitable materials include metals such as platinum, gold, tantalum, tungsten, titanium, or metal alloys such as stainless steel, Beta III Titanium, cobalt-chrome alloy, Elgiloy®, L605, MP35N, and Ta-10W. In one embodiment, the legs  14  and hub  12  are made of biocompatible titanium alloy beta III (ASTM grade 10, obtained from Ormco Corporation of Glendora, Calif., and designated Ti-11.5Mo-6Zr-4.5Sn, with major alloy elements molybdenum (10-13%), Zirconium (4.5-7.5%) and Tin (3.75-5.25%))  
         [0021]     The legs  14  can be made of a plurality of wires, ribbons, threads, rods, filaments, etc. In one embodiment, the legs  14  are made of a bundle of three wires. The wires  18  can be attached along their entire length, as shown in  FIGS. 1, 2A  and  2 C. In another embodiment the wires  18  are attached to each other at one or more discrete points  20  along their length. In the embodiment shown in  FIG. 2B , a leg  114  is formed of three wires  18  spaced apart between the attachment points  20 . The wires can be attached by adhesive, and solder. In one embodiment, legs  14  are made of wire having a diameter of about 0.018 inch (0.5 mm).  
         [0022]     The legs  14  extend outward from the hub  12  to define an imaginary cone. In one embodiment, the hub  12  is formed by fusing the legs  14  together. In a further embodiment, the hub  12  is a separate element attached to the legs  14 . The hub  12  can have any shape, including a sphere, cylinder, oval, polygon, etc. In some embodiments, the legs  14  include multiple angles, as shown in  FIG. 1 . In one embodiment, the diameter of the base of the filter is about 38 mm, and the overall length of the filter is about 50 mm.  
         [0023]     In a further embodiment, shown in  FIGS. 3A-3C  the filter  210  includes radially contractible sleeves  22  attached to one or more legs  214 . The radially contractible sleeve  22  fits over the barb  16  and is attached to the free end  113  of the leg  214 . The sleeve  22  can be made of a mesh, braid, net, or woven material. As used herein, woven material is intended to include a plurality of strands that are interlaced, twisted, knotted, braided, knitted, or otherwise interconnected to form a material that contracts and expands radially and in a lengthwise direction. In one embodiment, the sleeve  22  is made of Nitinol. In the radially expanded state, shown in  FIG. 3B , the sleeve  22  diameter is larger than the diameter of the barb  16 . In the radially contracted state, shown in  FIG. 3C , the sleeve  22  extends lengthwise and fits tightly around the barb  16 . In use, the filter  210  is delivered to the desired vessel location with the sleeves  22  in a radially expanded state covering barbs  16  of the legs  214 . The sleeve-covered barbs  16  are embedded in the vessel walls  50  to anchor the filter  210 , as shown in  FIG. 3B . When the filter  210  is to be retrieved, the legs  214  are pulled, causing the sleeves  22  to extend and radially contract around the extended barbs  16 , reducing their diameter and allowing the barbs  16  to be removed from the vessel wall  50 , as shown in  FIG. 3C . After a filter has been in place for a period of time, endothelial growth over the barbs often makes removal difficult. The ability of the sleeve  22  to radially contract reduces its diameter and allows the filter  210  to be removed even after endothelial growth occurs over the sleeve  22 .  
         [0024]     In a further embodiment, the radially contractible sleeve  122  has a plurality of projections  26 , as shown in  FIG. 4 . The projections  26  can be extensions of wires, threads, ribbons, etc. that form the net, mesh or woven radially contractible sleeve  122 . In another embodiment, the projections  26  are additional wires, threads, ribbons, etc. attached to the exterior of the sleeve  122 . The projections  26  may help anchor the sleeve within the vessel wall  50 .  
         [0025]     Another embodiment of the invention is shown in  FIGS. 5-8 . This embodiment is similar to the embodiment shown in  FIG. 3A  except that instead of a barb, the free ends  113  of the legs  414  have a retaining member  116 . An expandable hook  222  fits over and is secured to the retaining member  116 . The expandable hook  222  anchors the filter to the vessel wall  50 , as shown in  FIG. 7 . The retaining member  116  can be configured as a sphere, as shown in  FIGS. 5-8 , or any other shape that provides a surface to which the expandable hook  222  can be secured. Other such shapes include a square or other polygon, a triangle, an oval, etc.  
         [0026]     The expandable hook  222  is radially expandable and fits over the retaining member  116  at the free end  113  of each leg  414 . Once the expandable hook  222  is positioned over the retaining member  116 , the hook  222  is radially contracted around the retaining member  116  thereby securing the hook  222  to the leg  414 . The expandable hook  222  can be made of a mesh, braid, net, or woven material. In one embodiment, the expandable hook  222  is made of Nitinol. The expandable hook  222  can be expanded and contracted by changing the temperature of the hook. In another embodiment, the expandable hook  222  is mechanically expanded and contracted. In further embodiments, the expandable hook  222  is expanded and contracted via a chemical reaction.  
         [0027]     In the radially expanded state, shown in  FIGS. 5 and 6 , the diameter of the expandable hook  222  is larger than the diameter of the retaining member  116 . In the radially contracted state, shown in  FIG. 7 , the expandable hook  222  extends lengthwise and contracts tightly around the retaining member  116 . In use, expandable hooks  222  are attached to retaining members  116  at the free ends  113  of at least two filter legs  414 . See  FIGS. 5 and 6 . The hooks  222  are contracted around the retaining members  116 , and the filter is delivered to the desired vessel location where the expandable hooks  222  are embedded in the vessel walls  50 , as shown in  FIG. 7 . If the filter is to be retrieved, the hooks  222  are expanded, as shown in  FIG. 8 , thereby releasing the retaining members  116  and allowing the filter to be retrieved. The hooks  222  remain in the vessel wall  50 .  
         [0028]     The filter  10 ,  210  can be placed within a vessel by way of a jugular vein access point or other intravascular route as known to those skilled in the art. It is anticipated that the filter disclosed herein can be placed permanently in the vena cava or other organ, as well as being placed temporarily.  
         [0029]     Numerous characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size and ordering of steps without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.