Abstract:
A free standing filter is provided with a filter body having an elongate guidewire receiving member extending centrally therethrough to define an open ended channel configured to receive a plurality of different sized guidewires. An expandable and contractible frame surrounds the elongate guidewire receiving member and is connected at a proximal end to the elongate guidewire receiving member. A porous embolic capturing unit has an open end connected to the frame and a closed end connected to the elongate guidewire receiving member which extends through the porous embolic capturing unit.

Description:
This application is a continuation in part application of U.S. Ser. No. 60/125,134 filed Mar. 19, 1999. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to small filters for insertion into a vein or artery, and more particularly to a filter which, when expanded, is free standing in engagement with a body vessel without penetrating the vessel wall. 
     BACKGROUND OF THE INVENTION 
     In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a body vessel such as an arterial or vascular passageway and which are subsequently expandable into contact with walls of the passageway. These devices, among others, include stents, such as those shown by U.S. Pat. No. 5,540,712 and blood clot filters such as those shown by U.S. Pat. No. 5,669,933 which expand and are held in position by engagement with the inner wall of a vessel. It has been found to be advantageous to form such devices of a thermal shape memory material having a first, relatively pliable low temperature condition and a second, relatively rigid high-temperature condition. By forming such devices of temperature responsive material, the device in a flexible and reduced stress state may be compressed to fit within the bore of a delivery catheter when exposed to a temperature below a predetermined transition temperature, but at temperatures at or above the transition temperature, the device expands and becomes relatively rigid. 
     Known self expanding medical devices have been formed of Nitinol, an alloy of titanium and nickel which provides the device with a thermal memory. The unique characteristic of this alloy is its thermally triggered shape memory, which allows a device constructed of the alloy to be cooled below a temperature transformation level to a martensitic state and thereby softened for loading into a catheter in a relatively compressed and elongated state, and to regain the memorized shape in an austenitic state when warmed to a selected temperature, above the temperature transformation level, such as human body temperature. The two interchangeable shapes are possible because of the two distinct microcrystalline structures that are interchangeable with a small variation in temperature. The temperature at which the device assumes its first configuration may be varied within wide limits by changing the composition of the alloy. Thus, while for human use the alloy may be focused on a transition temperature range close to 98.6° F., the alloy readily may be modified for use in animals with different body temperatures. 
     In recent years advances have been made in the treatment of blood vessel stenosis or occlusion by plaque, thrombi, embolic, or other deposits which adversely reduce or block the flow of blood through a vessel. Balloon angioplasty or similar transluminal treatments have become common for some blood vessel lesions, but for all such procedures, plaque and emboli dislodged during the procedure are free to flow within the lumen of the vessel and possibly cause substantial injury to a patient. 
     In an attempt to contain and remove emboli and other debris, balloon angioplasty coupled with irrigation and aspiration has been performed as illustrated by U.S. Pat. No. 5,883,644 and International Publication No. WO 98/39046 to Zadno-Azizi et al. This procedure requires complete vessel occlusion cutting off all blood flow which imposes severe time constraints on the procedure. Additionally, the balloons involved in the procedure are affixed to elongate guidewires or small elongate catheters which extend for a substantial distance through blood vessels to the location of the stenosis or occlusion, and it is practically impossible to prevent some back and forth longitudinal motion of these elongate elements within a vessel during a procedure. This movement of the guidewire or catheter to which a balloon is attached causes the balloon to move back and forth and abrade emboli from the vessel wall downstream of the balloon containment area. 
     Angioplasty is often not a preferred treatment for lesions in the carotid artery because dislodged plaque can enter arterial vessels of the brain causing brain damage or even death. As indicated by U.S. Pat. No. 5,879,367 to Kaganov et al., carotid endarterectomy is a surgical procedure used to remove a lesion in the carotid artery, but this procedure also involves substantial risk of dislodged embolic material. 
     In an attempt to contain dislodged emboli during a procedure to clear blood vessel stenosis or occlusion, a variety of distal filters have been devised such as those shown by U.S. Pat. No. 5,814,064 and International Publication Nos. WO 98/38920 and WO 98/39053 to Daniel et al. as well as U.S. Pat. No. 5,827,324 to Cassell et al., U.S. Pat. No. 5,846,260 to Maahs and U.S. Pat. No. 5,876,367 to Kaganov et al. These filters are secured to the distal portion of a guidewire or catheter and are deployed distally from the stenosis or occlusion to capture embolic material. Once the distal filter is positioned and expanded into contact with the wall of the blood vessel, an angioplasty balloon, a stent, or other devices are introduced over the proximal end of the guidewire or catheter to which the filter is attached and moved into position in the area of the occlusion or stenosis spaced proximally from the filter. 
     Known guidewire or catheter attached distal filters have been subject to a number of disadvantages. First, since the elongate catheter or guidewire to which the filter is attached is used to guide over the wire devices during a subsequent procedure, it is extremely difficult if not impossible to prevent longitudinal movement of the wire or catheter after the filter has been deployed. This causes the filter to move back and forth within the vessel with resultant abrasion by the filter of the vessel wall, and such abrasion not only causes trauma to the vessel wall but also operates to dislodge debris which is free to flow distally of the filter. Thus filter movement after the filter is deployed somewhat defeats the purpose of the filter. Also, it is often desirable during a procedure to exchange guidewires, and such an exchange is not possible with an attached filter. 
     Finally the retrieval of known distal filters while retaining captured embolic material has proven to be problematic. Many cone shaped filters with wide, upstream proximal open ends tend to eject captured embolic material through the open end as the filter is collapsed. Also, many distal filters are formed by a mesh material which is expanded by a filter frame, and when the frame closes to collapse the filter for withdrawal through a catheter, the mesh folds creating outwardly projecting pleats. These pleats snag on the withdrawal catheter making retrieval of the filter difficult and often causing the filter to spill captured embolic material. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a novel and improved free standing filter for expansion within a blood vessel to capture dislodged embolic material. 
     Another object of the present invention is to provide a novel and improved free standing filter for use during a procedure to treat blood vessel stenosis or occlusion which does not cause trauma to the luminal wall during guidewire balloon and stent exchanges. 
     A further object of the present invention is to provide a novel and improved free standing filter for use during a procedure to treat blood vessel stenosis or occlusion which is formed to facilitate intra-procedural guidewire exchanges. 
     Yet another object of the present invention is to provide a novel and improved free standing filter for use during a procedure to treat blood vessel stenosis or occlusion which is formed to remain stationary after expansion independent of guidewire or catheter motion. 
     A further object of the present invention is to provide a novel and improved free standing filter for use during a procedure to treat blood vessel stenosis or occlusion which includes an elastomeric or knitted fiber mesh which collapses without pleating during the filter recovery process. 
     A still further object of the present invention is to provide a novel and improved free standing filter for use during a procedure to treat blood vessel stenosis or occlusion which is formed to capture and safely remove embolic material. The filter is provided with a proximal end designed for docking with a recovery system and which operates to positively close the open end of a filter mesh as the filter is collapsed during recovery. 
     These and other objects of the present invention are accomplished by providing a free standing filter with a filter body having an elongate guidewire receiving member extending centrally therethrough to define an open ended channel configured to receive a plurality of different sized guidewires. An expandable and contractible frame surrounds the elongate guidewire receiving member and is connected at a proximal end to the elongate guidewire receiving member. A porous embolic capturing unit has an open end connected to the frame and a closed end connected to the elongate guidewire receiving member which extends through the porous embolic capturing unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view in side elevation of the free standing filter of the present invention in the expanded configuration; 
     FIG. 2 is a partially sectional view in side elevation of a second embodiment of the free standing filter of the present invention; 
     FIG. 3 is a partially sectional view of the free standing filter of FIG. 2 within a delivery tube; 
     FIG. 4 is a sectional view of a positioning and recovery unit for the free standing filter of FIG. 2; 
     FIG. 5 is a sectional view of the positioning and recovery unit of FIG. 4 engaged with the free standing filter; and 
     FIG. 6 is a perspective view of the fine mesh filter of FIG. 1; and 
     FIG. 7 is a perspective view of the fine mesh filter of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the free standing filter  10  of the present invention is formed around a central tube  11  which forms the longitudinal axis for the filter  10  and slidingly receives a guidewire  12 . The frame of the filter is formed by a stent  14  which may be collapsed inwardly toward the tube  11  and which expands outwardly away from the tube to the substantially cylindrical open ended configuration shown in the drawings. Ideally, this stent is formed of thermal shape memory material and is of the type shown by U.S. Pat. No. 5,540,712, although other expandable stents can be used. The stent  14  is coupled at one end to the central tube  11  by elongate lead wires  16  which extend between an open proximal end  18  of the stent and a spaced coupling  20  which is secured to the central tube  11 . 
     Extending around the stent  14  and attached thereto is a flexible, fine mesh filter material  22  which opens at the proximal end  18  of the stent and covers the body of the stent. Ideally, the stent extends over this mesh filter material. At the distal end  24  of the stent, the fine mesh filter material projects outwardly to form a flexible conical section  26  with an apex  28  connected to a coupling  30  which slides on the tube  11  in spaced relation to the stent distal end  24 . Thus when the stent expands as shown in the drawings, the mesh filter material forms a substantially cylindrical section  32  which opens at the proximal end of the stent and a flexible, closed conical section  26  which extends beyond the distal end of the stent to catch and collect small particles. The mesh filter material therefore defines an enclosed chamber with a single open end  33  and a closed end  35 . The fine filter mesh may be formed of suitable biocompatible material such as polyester or a PTFE material and is coated with thromboresistant materials such as, for example, Phosphoral Choline or Hyaluronic Acid. The mesh is a braided material or elastomeric mesh which normally conforms to the exterior shape of the central tube  11 , but which stretches to expand outwardly away from the tube when the stent  24  expands. Thus the mesh is biased toward the tube  11 , and when the stent collapses inwardly toward the tube, the mesh contracts back to the exterior shape of the tube and does not form pleats. 
     In the operation of the filter  10 , the stent with the mesh filter material is inserted in a collapsed condition into a delivery tube  34  and guidewire  12  extends through the central tube  11 . Then the delivery tube is used to deliver the filter  10  over the guidewire  12  to a desired position within a body vessel whereupon the filter is ejected from the delivery tube. Now the previously collapsed stent  14  expands into contact with the walls  36  of the vessel (shown in broken lines) thereby expanding the flexible mesh filter material which was previously collapsed within the delivery tube with the stent. The guidewire  12  may now be used to guide other devices into the vessel, and since the guidewire can move freely in a longitudinal direction within the tube  11 , longitudinal movement of the guidewire will not result in movement of the expanded filter. 
     Once the stent  14  has expanded against the wall  36  of the vessel, the guidewire  12  can be removed and replaced with a new guidewire of a different size. The tube  11  is preferably formed of sufficient size to accept 0.014 inch diameter to 0.035 inch diameter guidewires. It may often be desirable to initially use a very fine guidewire (0.014″) to cross a lesion and position the filter  10  and to then exchange this fine guidewire for a thicker wire. 
     The fine mesh filter material  22 , when expanded, should have a pore size within a range of 50 μm to 300 μm to capture and retain embolic material sized in excess of the pore size while permitting blood flow in the direction of the arrow  38  line in FIG. 1 between the wires  16  and into the proximal end  18  of the stent  14 . The blood and embolic material flows through the and into the flexible conical section  26  of the fine mesh filter material where the embolic material is trapped while the blood passes through the filter material. 
     To remove the filter  10  with the captured embolic material, the stent  14  is collapsed against the tube  11  for withdrawal through a catheter or delivery tube  34 . Preferably the stent is formed of the thermal shape memory material such as nitinol or other materials, for example, including but not limited to Titanium, stainless steel, MP35N alloys or other similar materials and may be collapsed by cooling the stent to a temperature below a transition temperature. It is important to note that the embolic material has been captured within the conical section  28 , so that when the stent collapses against the tube  11 , it positively closes the mouth of the conical section preventing material from escaping as the filter is drawn into the tube  34 . The stent forces the entire longitudinal extent of the section  32  against the tube  11  to prevent the escape of material from the conical section  28 . 
     Referring now to FIGS. 2,  3  and  7 , a second embodiment of the free standing filter of the present invention is indicated generally at  40 . For unimpeded passage through a catheter or delivery tube  34 , it is beneficial to form a filter with a frame which completely surrounds and protects the filter mesh material. Thus the filter  40  includes a cellular frame  42  which is preferably formed of thermal shape memory material such as nitinol, and this frame when expanded includes a central section  44  having a substantially tubular configuration, a proximal end section  46  and a distal end section  48 , both having a substantially conical configuration. A central tube  50 , similar in size to the tube  11 , forms the central longitudinal axis for the filter  40  and extends through the filter and outwardly from the proximal and distal sections of the frame  42 . The distal end of the tube  50  is provided with a tapered atraumatic molded tip  52  configured to center and guide the filter within the delivery tube  34 . 
     The central section  44  of the frame  42  includes a plurality of interconnected cells  54  which are substantially equal in size and which are defined by spaced sidewalls  56  and  58  which extend substantially parallel to the tube  50  and the longitudinal axis of the filter. Adjacent cells  54  in a row of cells extending around the central tube  50  are connected together by their adjacent sidewalls  56  and  58 , and these sidewalls remain substantially parallel to the tube  50  in both the expanded and collapsed configuration of the filter  40  as illustrated in FIGS. 2 and 3. The opposite ends of each cell are formed by outwardly inclined endwall sections  60  and  62  which meet at an apex  64 . Extending in a distal direction from the apex  64  of alternate cells  54  at the proximal end of the central section  44  are short, straight stabilizers  66  which engage the vessel wall  36  when the filter is expanded and aid to preclude movement of the filter in a distal direction. 
     The proximal end section  46  and distal end section  48  of the frame  42  are formed of cells  68  with tapered sidewalls  70  and  72  which extend at an angle to the central tube  50  to form the tapered conical end sections of the frame. Proximal end section  46  of the frame is secured to the tube  50  by a coupling  74 , and distal end section  48  is secured to a coupling  76  which slides on the tube  50 . The couplings  74  and  76  are provided with radiopaque markers  78  and  80  respectively. 
     Fine mesh filter material  82  of the type previously described for the filter  10  is positioned within the central and distal sections of the frame  42 . This filter material is bonded to at least the first row of cells  54  in the proximal end of the central section  44  of the frame, and at the distal end of the frame the filter material is secured to the tube  50  adjacent to the coupling  76  by a coupling  84 . Thus the filter material forms a cone when the filter  40  is expanded, and the open proximal end of the cone is positively closed when the proximal end row of cells of the central section  44  collapse against the tube  50 . 
     As shown in FIG. 3, when the filter  40  moves along the guidewire  12  through the delivery tube  34 , the mesh filter material  82  is enclosed within the frame  42  which protects the filter material. Also, when an expanded filter is contracted and drawn back into the delivery tube, the frame engages the delivery tube and precludes the filter from catching or snagging on the delivery tube. 
     FIGS. 4 and 5 disclose a positioning and recovery system  84  for the filter  40 . This system includes an elongate, flexible, tubular member  86  having a docking end  88  for receiving the coupling  74  of the filter  40 . The docking end is provided with a plurality of longitudinally extending lumens  90 , two of which are shown in FIGS. 4 and 5, and an outwardly inclined hook  92  of flexible material, such as stainless steel, is mounted in each lumen to extend outwardly from the docking end of the tubular member  86 . 
     When the filter  40  is collapsed within the delivery tube  34  as shown in FIG. 3, the tubular member  86  with the hooks  92  engaged with the cells  68  extends over the guidewire  12  to move the filter through the delivery tube. When the filter is ejected from the delivery tube and the hooks  92  extend outwardly from the end of the delivery tube, the hooks spring open as illustrated in FIG. 4 releasing the filter. If desirable, the filter can be moved further from the delivery tube by the engagement between the filter and the stepped docking end of the tubular member  86  before the delivery tube and the docking and positioning system are withdrawn. 
     To recover the filter, the tubular member  86  with the hooks  92  compressed as shown in FIG. 5 is passed through the delivery tube and outwardly therefrom until the hooks spring open and are positioned over the cells  68  as shown in FIG.  4 . Now the delivery tube is moved over the hooks to compress and engage the hooks with the cells  68  as shown in FIG. 5, and once the hooks are engaged, the filter can be drawn back into the delivery tube by the tubular member  86 .