Abstract:
A medical device that filters thrombi in a body vessel is disclosed. After the need for filtering passes, the device maintains patency in the body vessel without requiring additional steps of percutaneous retrieval or introduction into the patient.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to medical devices. More particularly, the invention relates to a temporary vena cava filter that can be percutaneously placed in the vena cava of a patient and further take on the shape of a stent. 
         [0002]    Filtering devices that are percutaneously placed in the vena cava have been available for over thirty years. A need for filtering devices arises in trauma patients, orthopedic surgery patients, neurosurgery patients, or in patients having medical conditions requiring bed rest or non-movement. During such medical conditions, the need for filtering devices arises due to the likelihood of thrombosis in the peripheral vasculature of patients wherein thrombi break away from the vessel wall, risking downstream embolism or embolization. For example, depending on the size, such thrombi pose a serious risk of pulmonary embolism wherein blood clots migrate from the peripheral vasculature through the heart and into the lungs. 
         [0003]    A filtering device can be deployed in the vena cava of a patient when, for example, anticoagulant therapy is contraindicated or has failed. Typically, filtering devices are permanent implants, each of which remains implanted in the patient for life, even though the condition or medical problem that required the device has passed. In more recent years, filters have been used or considered in preoperative patients and in patients predisposed to thrombosis which places the patient at risk for pulmonary embolism. 
         [0004]    The benefits of a vena cava filter have been well established, but improvements may be made. For example, when the condition that required the filter has passed, there are situations where the body vessel is in need of a stent to maintain the body vessel open or the patency thereof. Retrieval of the filter and percutaneous introduction of a stent would take additional steps to accomplish. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a medical device that filters thrombi in a body vessel and, after the need for filtering passes, maintains patency in the body vessel without additional steps of percutaneous retrieval or introduction into the patient. 
         [0006]    In one embodiment, the present invention provides a filter device for capturing thrombi in a body vessel and transformable to a stent to maintain the body vessel open. The device comprises a plurality of biodegradable threads comprising proximal and distal portions. Each proximal portion has a first end. The first ends are attached together along a longitudinal axis. Each distal portion extends from the proximal portion to a distal end. The distal portions are expandable in the body vessel to engage the body vessel and the first ends are free of contact with the body vessel. Each biodegradable thread is comprised of biodegradable material that degrades at a predetermined time period after the device is deployed in the body vessel. 
         [0007]    The device further comprises a radial strut attached to each of the distal ends of the biodegradable threads. The radial strut is radially expandable in the body vessel to engage the distal ends with the body vessel. The radial strut is a z-wire formed into a closed zig-zag configuration including a series of straight sections and a plurality of bends. The straight sections are joined by the bends to form the radial strut. 
         [0008]    The device further comprises a biodegradable stabilizer attaching the first ends together and extending radially outwardly to contact the body vessel for balance to the device so that the first ends are free of contact with the body vessel. The biodegradable stabilizer is comprised of bio-absorbable material that degrades at a predetermined time period after the device is deployed in the body vessel. 
         [0009]    The device is depressible into a smaller first shape wherein the straight sections are arranged side by side and closely adjacent one another for insertion into the body vessel and the bends store stress therein. The device is expandable, by the release of the stress stored in the bends of the radial strut, into a second shape wherein the straight sections press against the wall of the body vessel. The device is transformable to the stent, by the degradation of the biodegradable stabilizer and threads at the predetermined time period, defining the stent. 
         [0010]    In another example, the present invention provides a method for capturing thrombi in a body vessel and for maintaining the body vessel open. The method comprises depressing the device  10  into the first configuration mentioned above. The method further comprises moving the depressed device into a sheath and locating the distal end of the sheath in a blood vessel with the depressed device within the distal end of the sheath. The method further comprises removing the sheath from the blood vessel while holding the stent in place whereby the stress in the second radial strut causes it to expand in the blood vessel to expand the distal portions of the biodegradable threads for engaging the anchoring hooks with the body vessel. The method further comprises degrading the biodegradable stabilizer and threads at the predetermined time period whereby the device takes on a third configuration to maintain the body vessel open. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1   a  is a side environmental view a device in an expanded configuration for capturing thrombi and transformable to a stent for maintaining patency of a body vessel in accordance with one embodiment of the present invention; 
           [0012]      FIG. 1   b  is a side environmental view of a device in an expanded configuration in accordance with another embodiment of the present invention; 
           [0013]      FIG. 2  is an enlarged view of a radial strut of the device in section  1  of  FIG. 1   a;    
           [0014]      FIG. 3  is an enlarged view of a biodegradable stabilizer of the device in  FIG. 1   a;    
           [0015]      FIG. 4   a  is a side view of the device in the third configuration for maintaining patency of a blood vessel; 
           [0016]      FIG. 4   b  is a cross-sectional view of the vena cava in which the device is in the third configuration; 
           [0017]      FIG. 5  is a side view of the device in a collapsed configuration; and 
           [0018]      FIG. 6  is a flow chart of one method for capturing thrombi in a body vessel and maintaining patency of the body vessel in accordance to one example of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1   a  illustrates a device  10  implanted in a body vessel for capturing thrombi in the body vessel in accordance with one embodiment of the present invention. Preferably, the device  10  is transformable to a stent to maintain patency or openness of the body vessel. As will be described in greater detail below, the device  10  may have a first (compressed) configuration for delivery thereof in a body vessel, a second (expanded) configuration for capturing thrombi in a body vessel, and a third (degraded) configuration for maintaining patency or openness of the body vessel. As shown, the device  10  is in the expanded configuration and comprises a plurality of biodegradable threads  12  having proximal and distal portions  16 , 17 . Each proximal portion  16  has a first end. The first ends  14  are attached together along a longitudinal axis. Each distal portion  17  extends from the proximal portion  16  to a distal end  18  having an anchoring hook. The distal portions are expandable in the body vessel to engage the anchoring hooks  19  with the body vessel. As shown, the first ends  14  are free of contact with the body vessel. 
         [0020]      FIG. 1   a  depicts the device  10  expanded after being deployed in inferior vena cava  52 . As shown, the inferior vena cava  52  has been broken away so that the device  10  can be seen. The direction of the blood flow BF is indicated in  FIG. 1   a  by the arrow that is labeled BF. The anchoring hooks  19   17  at the ends of the biodegradable threads  12  are shown as being anchored in the inner lining of the inferior vena cava  52 . The anchoring hooks  19   17  include barbs  29  that, in one embodiment, project toward the hub  11  of the filter. The barbs  29  function to retain the device  10  in the location of deployment. 
         [0021]    The spring biased configuration of the radial strut  20  causes the anchoring hooks  19  to engage the vessel wall and anchor the device at the location of deployment. After initial deployment, the pressure of the blood flow on the device  10  contributes in maintaining the barbs  29  anchored in the inner lining of the inferior vena cava  52 . 
         [0022]    Each biodegradable thread  12  is comprised of biodegradable material that degrades at a predetermined time period after the device  10  is deployed in the body vessel. Preferably, the biodegradable thread  12  is a biodegradable suture wire that may be made of any suitable material, such as polylactide or polyglycolide. The predetermined time period may be any suitable time period for the device  10  to effectively filter thrombi in the body vessel and begin to maintain the patency of the body vessel. For example, the time period may be between about two to ten weeks, preferably between about three to six weeks. However, any other time period may be acceptable without falling beyond the scope or spirit of the present invention. 
         [0023]    As shown in  FIG. 1   a,  the device  10  further comprises a radial strut  20  attached to each of the distal ends  18  of the biodegradable threads  12 . The radial strut  20  is disposed about the distal portions of the biodegradable threads  12  and is expandable therewith in the body vessel. The radial strut  20  is radially expandable in the body vessel to engage the anchoring hooks  19  of the distal ends  18  with the body vessel. Preferably, the radial strut  20  is formed from a superelastic material, stainless steel wire, Nitinol, cobalt-chromium-nickel-molybdenum-iron alloy, or cobalt chrome-alloy, or any other suitable material that will result in a self-opening or self-expanding device  10 . 
         [0024]    The radial strut  20  is preferably a z-wire formed into a closed zig-zag configuration including a series of straight sections and a plurality of bends. The straight sections are joined by the bends to form the radial strut. Of course, the radial strut  20  may be comprised a plurality of z-wires without falling beyond the scope or spirit of the present invention. As shown in  FIGS. 2 and 4   a - 4   b,  the radial strut  20  includes a length  40  of wire formed in a closed zig-zag configuration. The wire is closed by a sleeve  41  which is welded to or tightly squeezed against the ends of the wire to produce the endless configuration. Referring to  FIG. 5 , the radial strut  20  is shown in a resiliently compressed first configuration wherein the straight sections  42  are arranged side-by-side and closely adjacent one another. The straight sections of the stent are joined by bends  43  which are relatively sharp. 
         [0025]    Referring to  FIG. 1   a,  the device  10  further comprises a biodegradable stabilizer  22  that attaches the first ends  14  together in a closed position. In this embodiment, the biodegradable stabilizer  22  is a biodegradable thread  12  having a pair of contact ends. As shown, the biodegradable stabilizer  22  ties the first ends  14  together and extends radially outwardly to contact the contact ends with body vessel for balance to the device  10 . Thus, the biodegradable stabilizer  22  is preferably configured or made of material more rigid than the biodegradable threads  12 . This may be accomplished by diameter size or material or both. This allows the first ends  14  to be free of contact with the body vessel. The biodegradable stabilizer  22  is thus comprised of bio-absorbable material that is degrades at a predetermined time period after the device  10  is deployed in the body vessel. Preferably, the biodegradable stabilizer  22  is made of any suitable material, such as polylactide or polyglycolide. 
         [0026]      FIG. 1   b  illustrates a device  80  for capturing thrombi in a body vessel and further maintaining patency in the body vessel. As shown, the device  10  comprises similar components to the device  10  in  FIG. 1   a  such as the biodegradable threads  82 , first ends  84  and stabilizer  85 . However, the device  80  further includes a plurality of radial struts  86  connected about the biodegradable threads and spaced apart from each other along the longitudinal axis of the device  80 . As shown, the radial struts  86  are longitudinally spaced apart from each other. The placement of the radial struts provides support to the body vessel to maintain a relatively larger area of a body vessel open where needed. 
         [0027]    As mentioned above, the device  10  is depressible into a collapsed or first configuration (shape) as shown in  FIG. 5 . As such, the straight sections are arranged side by side and closely adjacent one another for insertion into the body vessel and the bends store stress therein. The device  10  is expandable, by the release of the stress stored in the bends of the radial strut, into an expanded or second configuration wherein the straight sections press against the wall of the body vessel. After degradation of the biodegradable threads  12  and the stabilizer  22 , the device  10  is take on a third (degraded) configuration having the shape of a stent. This is accomplished by the degradation of the biodegradable stabilizer  22  and threads  12  at the predetermined time period, defining the stent. In one embodiment, the radial strut  20  may be comprised of one or a plurality of z-wires connected about the biodegradable threads  12  and spaced apart from each other along the longitudinal axis of the device  10  as mentioned above and shown in  FIG. 1   b.    
         [0028]      FIG. 4   b  illustrates the device  10  in the third configuration implanted in vena cava  50 . As shown, the device  10  takes on the shape of a stent for maintaining patency of the vena cava degradation of the biodegradable member. As mentioned, the biodegradable threads  12  and stabilizer  22  defines the second configuration ( FIG. 1   a ) of the device  10  and degrades after deployment in the body vessel. Upon degradation, the device  10  transforms to the third configuration mentioned above and takes on the shape of a stent to maintain patency of the body vessel. 
         [0029]      FIG. 3   b  illustrates a cross-sectional view of the device  10  of  FIG. 3   a  at hub area  11 . As shown, the hub area  11  is formed of a bundle of first ends  14  of the longitudinal threads  12  attached together by the biodegradable stabilizer  22 . The threads  12  may be attached together by the biodegradable stabilizer  22  by any suitable manner such as by tying, sonic welding, or biodegradable adhesives. 
         [0030]      FIG. 6  illustrates one method  110  for capturing thrombi in a body vessel and for maintaining the body vessel open in accordance with one example of the present invention. As shown, the method comprises depressing the device  10  to the first configuration in box  112  and introducing or “loading” the device  10  into a delivery catheter in box  114 . For deployment of the device  10 , the delivery tube is percutaneously inserted through the patient&#39;s vessel such that the distal end  18  of the delivery tube is at the location of deployment. In this embodiment, a wire guide is preferably used to guide the delivery tube to the location of deployment. 
         [0031]    The method further comprises locating the distal end  18  of the sheath in a body vessel in box  116  wherein the device  10  in the first configuration is disposed within the distal end  18  of the sheath. The method further comprises removing the sheath from the body vessel while holding the device  10  in place in box  118 . The stress in the radial strut  20  causes it to expand the distal portions of the biodegradable threads  12  to the second configuration for engaging the anchoring hooks  19  with the body vessel. 
         [0032]    When the device  10  is expanded in the vena cava, the anchoring hooks  19   17  of the biodegradable threads  12  are in engagement with the vessel wall. The anchoring hooks  19   17  of the biodegradable threads  12  have anchored the device  10  at the location of deployment in the vessel, preventing the device  10  from moving with the blood flow through the vessel. The method further comprises degrading the biodegradable threads  12  and the stabilizer  22  at the predetermined time period in box  120  whereby the device  10  takes on a shape of a stent in the third configuration to maintain the body vessel open. 
         [0033]    While the present invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made to those skilled in the art, particularly in light of the foregoing teachings.