Patent Publication Number: US-2006015137-A1

Title: Retrievable intravascular filter with bendable anchoring members

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to devices for filtering blood clots within a blood vessel. More specifically, the present invention pertains to retrievable intravascular filter devices and associated methods for retrieving such devices within the body.  
     BACKGROUND OF THE INVENTION  
      Intravascular filters are used in combination with other thrombolytic agents to treat pulmonary embolism occurring within a patient. Such devices are generally inserted intravenously into a target location of the body (e.g. an artery or vein), and function by capturing blood clots (emboli) contained in the blood stream before they can reach the heart and/or lungs and cause permanent damage to the body. In the treatment of Deep Vein Thrombosis (DVT), for example, such filters can be placed in the vena cava to prevent further blood clotting in the large veins of the lower body. Placement of the filter is typically accomplished percutaneously via the femoral arteries or the jugular vein using a local anesthetic, or by performing a laparotomy with the patient under general anesthesia.  
      In certain procedures, an introducer sheath may be used to deliver the intravascular filter through the body. Such introducer sheaths are typically tubular in shape and include an internal lumen configured to transport the intravascular filter in a collapsed position through the body. Once advanced to a desired location within the vasculature (e.g. the inferior vena cava), the intravascular filter can then be removed from within the introducer sheath, allowing the device to spring open and engage the vessel wall. A needle, hook, barb, prong, wedge or other attachment means can be used to secure the intravascular filter to the vessel wall.  
      There are a number of situations in which it may be desirable for a physician to remove the intravascular filter once implanted within the body. In certain circumstances, for example, the risk of pulmonary embolism may be relatively short term (e.g. about two weeks), thus requiring insertion of the device for only a short period of time. Permanent implantation of the intravascular filter in such cases may unnecessarily impede the flow of blood within the vessel, and can lead to further thrombosis growth at the filter implantation site. In other circumstances, it may be desirable to reposition the intravascular filter within the vessel, or to replace the existing filter with a new filter.  
     SUMMARY OF THE INVENTION  
      The present invention relates generally to retrievable intravascular filters for filtering blood clots within the body. Devices and associated methods for retrieving the intravascular filter within a blood vessel are also discussed herein.  
      A retrievable intravascular filter in accordance with an illustrative embodiment of the present invention may include an apical head operatively coupled to a number of elongated filter legs that can be expanded within a blood vessel to collect blood clots contained in the blood stream. A bendable anchoring member coupled to or formed integrally with one or more of the elongated filter legs can be used to temporarily or permanently secure the filter legs to the inner wall of the blood vessel, thereby preventing the intravascular filter from migrating or tilting within the blood vessel. In certain embodiments, each of the bendable anchoring members can include a coiled member configured to bend from an initially curved shape when attached to the vessel wall to a substantially straight shape for retrieval within a retrieval catheter. In other embodiments, each of the bendable anchoring members can include a spiraled member having a pigtail configuration that can be configured to bend when detached from the vessel wall. A pointed tip portion oriented at an angle relative to the surface of the vessel wall can be used to releasably secure one or more of the filter legs to the vessel wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a retrievable intravascular filter in accordance with an illustrative embodiment of the present invention;  
       FIG. 2  is a top view showing the retrievable intravascular filter of  FIG. 1  disposed along the wall of a blood vessel;  
       FIG. 3  is an enlarged view showing the anchoring member of one of the elongated filter legs of  FIG. 1  in greater detail;  
       FIG. 4  is an enlarged view showing another illustrative anchoring member including a spiraled member having a pigtail configuration;  
       FIG. 5  is a partial cross-sectional view showing the retrievable intravascular filter of  FIG. 1  temporarily implanted within a blood vessel;  
       FIG. 6  is a partial cross-sectional view showing a retrieval apparatus advanced to the site of the retrievable intravascular filter of  FIG. 5 ;  
       FIG. 7  is a partial cross-sectional view showing the detachment of the retrievable intravascular filter using the retrieval apparatus of  FIG. 6 ; and  
       FIG. 8  is a partial cross-sectional view showing the retrievable intravascular filter of  FIG. 5  retracted into retrieval apparatus.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized.  
       FIG. 1  is a perspective view of a retrievable intravascular filter  10  in accordance with an illustrative embodiment of the present invention. Intravascular filter  10 , illustratively a vena cava filter, includes an apical head  12  operatively coupled to a number of elongated filter legs  14  each having a proximal section  16  and a distal section  18 . Each of the filter legs  14  may be configured identically with respect to each other, and may be symmetrically spaced about a central longitudinal axis L in a generally conical-shaped configuration when expanded. The filter legs  14  may be collectively arranged about the longitudinal axis L such that the proximal section  16  of each filter leg  14  converges at the apical head  12  to form an apex. In certain embodiments, the filter legs  14  can be biased to expand from a substantially straight position when radially constrained within a catheter or introducer sheath to an outswept position when deployed in a blood vessel.  
      The filter legs  14  can be formed from a wire, rod, tubing or other elongated member that can be cut and processed to form the general structure of  FIG. 1 . The dimensions of the filter legs  14  can vary depending on the particular location within the body in which the device is to be implanted. In applications involving the inferior vena cava, for example, the filter legs  14  can be dimensioned to collectively expand to a diameter of about 18 to 32 mm, which is the normal range for the human inferior vena cava. The dimensions of the filter legs  14  can vary, however, allowing the intravascular filter  10  to be implanted in other locations within the body such as the coronary arteries or the peripheral vasculature.  
      The filter legs  14  can be formed from a metal such as platinum, gold, tantalum, tungsten, titanium, or a metal alloy such as stainless steel (e.g. type 316L), Beta III Titanium, cobalt-chrome alloy, Elgiloy, L605, MP35N, Ta-10W, 17-4PH, or Aeromet 100. In certain embodiments, the filter legs  14  can be formed from a shape-memory material such as nickel-titanium alloy (Nitinol). A slight outward bend can be imparted to each filter leg  14  by heating the alloy beyond its final austenitic temperature, and then bending each filter leg  14  to a pre-defined shape. The filter legs  14  can be configured to revert to their pre-defined (i.e. bent) shape at or near body temperature (37° C.), allowing each individual filter leg  14  to maintain a straight position until deployed within the blood vessel.  
      A retrieval member  20  coupled to the apical head  12  can be provided to facilitate retrieval of the intravascular filter  10  from the body. The retrieval member  20  can include a hook, loop, clip, or other suitable fastening mechanism that can be used in conjunction with an optional retrieval device to retrieve the intravascular filter  10  from within the blood vessel, if desired. In certain embodiments, the retrieval member  20  can also be used to center the apical head  12  during deployment within the blood vessel to prevent the intravascular filter  10  from becoming off-centered or tilted.  
      The distal section  18  of one or more of the filter legs  14  can include a bendable anchoring member  22  that can be used to releasably secure the intravascular filter  10  to the wall of the blood vessel. The anchoring member  22  can be formed integral with or as a separate element from the wire, rod, tubing, etc. forming the filter legs  14 . In the illustrative embodiment of  FIG. 1 , for example, the anchoring members  22  are formed as separate members coupled to the distal section  18  of the filter leg  14  by adhesive, welding, crimping, or other suitable attachment method.  
       FIG. 2  is a top view showing the intravascular filter  10  of  FIG. 1  implanted within a blood vessel V. As can be seen in  FIG. 2 , the filter legs  14  can be configured to extend outwardly from the apical head  12  during deployment to anchor the intravascular filter  10  along the inner wall W of the blood vessel V. The filter legs  14  can be arranged at equidistant intervals such that the filter legs  14  are symmetrically spaced about the longitudinal axis formed by the apical head  12 . In the illustrative embodiment of  FIGS. 1-2 , the intravascular filter  10  is shown having six filter legs  14  arranged at 60° intervals. It should be understood, however, that any number or arrangement of filter legs could be employed, as desired.  
      When expanded within the blood vessel V, each anchoring member  22  can be configured to pierce the inner wall W of the vessel V as a result of the outwardly directed force exerted by the filter legs  14 . The amount of force exerted against the inner wall W can be made sufficient to prevent migration of the intravascular filter  10  within the vessel V without distending the blood vessel V. By altering various design factors such as the dimensions, material composition, and orientation of the filter legs  14 , the intravascular filter  10  can be configured to operate in a wide range of locations within the vasculature.  
      During implantation within the blood vessel V, the filter legs  14  provide a surface upon which blood clots (emboli) can be collected. To facilitate lysing of the collected blood clots, all or a portion of the intravascular filter  10  can include an anti-thrombogenic coating such as herapin (or its derivatives), urokinase, or PPack (dextrophenylalanine proline arginine chloromethylketone) to prevent insertion site thrombosis from occurring. An anti-inflammatory agent such as dexamethasone, prednisolone, corticosterone, budesonide, estrogen, sulfasalazine, mesalamine, or any suitable combination or mixture thereof can also be applied to all or a portion of the intravascular filter  10  to prevent inflammation caused by the engagement of the intravascular filter  10  along the vessel wall W. To prevent the further formation of blood clots within the blood vessel V, an anti-coagulant agent may also be delivered to the site of the intravascular filter  10 .  
       FIG. 3  is an enlarged view showing the anchoring member  22  of one of the elongated filter legs  14  of  FIG. 1  in greater detail. As shown in  FIG. 3 , each anchoring member  22  can include a coiled member  24  having a first end  26  coupled the distal section  18  of the filter leg  14 , and a second end  28  that is adapted to rest immediately adjacent to the inner wall of the blood vessel. A solder joint  30  or other suitable attachment means can be provided to secure the first end  26  of the coiled member  24  to the filter leg  14 . In an alternative embodiment, the coiled member  24  can be formed integrally with the distal section  18  of the filter leg  14 , obviating the need for a separate solder joint  30 .  
      The coiled member  24  can be formed from a spring coil wrapped about an imaginary arc  32  that curves upwardly in a direction towards the apex of the intravascular filter at or near the second end  28  thereof. The general shape of the anchoring member  22  can be formed by taking an elongated piece of wire or tubing, and then wrapping the wire or tubing about a curved mandrel having a shape approximating the imaginary arc  32  depicted in  FIG. 3 . In one illustrative embodiment, the anchoring member  22  can be formed from a piece of wire or tubing formed from superelastic and/or shape memory material such as nickel-titanium alloy (Nitinol) having a greater flexibility than the material forming the proximal and distal sections  16 , 18  of the filter legs  14 . The generally curved shape of the anchoring member  22  can be formed by wrapping the anchoring member  22  about a curved mandrel having a desired shape, heating the alloy beyond its final austenitic temperature to heat-set the shape, and then allowing the material to cool and revert back to its martensitic state. In use, the alloy can be configured to revert to its pre-defined (i.e. curved) shape at or near body temperature, allowing the anchoring member  22  to maintain a substantially straight position when loaded into the retrieval device.  
      A pointed tip portion  34  of each anchoring member  22  can be configured to pierce and secure the intravascular filter  10  to the inner wall of the blood vessel. The pointed tip portion  34  may be formed from an unraveled portion of the coiled member  24  that is ground down at section  36  to form a needle or other sharp edge for piercing the inner wall of the blood vessel. Alternatively, the pointed tip portion  34  of each anchoring member  22  can be formed by attaching a separate member such as a needle or barb to the second end  28  of the coiled member  24 . In certain embodiments, the pointed tip portion  34  of each anchoring member  22  can be configured to curve upwardly in the general direction of the imaginary arc  32  and at a slight angle relative to the inner surface of the vessel wall to facilitate removal.  
      During deployment within the blood vessel, the outwardly directed force exerted by the filter legs  14  causes the pointed tip portion  34  of each anchoring member  22  to pierce and secure to the inner wall of the blood vessel. A shoulder  38  formed from the distal-most coil turn of the coiled member  28  can be configured to act as a landing pad for the anchoring member  22 , if desired, limiting the engagement depth of the pointed tip portion  34  within the vessel wall.  
      The structure and material composition of the anchoring members  22  can differ from that of the elongated filter legs  14  to permit the anchoring members  22  to selectively bend when an external force is applied to the intravascular filter  10 . In certain embodiments, for example, each anchoring members  22  can be configured to bend from its initially curved shape to a substantially straight shape wherein each anchoring member  22  is aligned with the longitudinal axis of the corresponding filter leg  14 . A greater or lesser amount of bendability can be imparted to each anchoring member  22  by varying the size and spacing of the various coil turns  40  forming the coiled member  24 , and/or by the selection of materials forming the various components of the intravascular filter  10 .  
       FIG. 4  is an enlarged view showing another illustrative anchoring member  42  including a spiraled member  44  having a pigtail configuration. As shown in  FIG. 4 , the spiraled member  44  may extend from a first end  46  coupled to or formed integrally with the distal section  18  of the filter leg  14  to a second end  48  that is adapted to rest immediately adjacent to the inner wall of the blood vessel. Similar to the anchoring member  22  of  FIG. 3 , anchoring member  42  can be configured to selectively bend between a first position engaged along the inner wall of the blood vessel to a second position to facilitate retrieval within a retrieval catheter.  
      In a first (i.e. deployed) positioned depicted generally in  FIG. 4 , the spiraled member  44  can be oriented about a spiral axis  50  that is offset from the general longitudinal axis  52  of the filter leg  14 . The number of spirals and spacing between each adjacent spiral of the spiraled member  44  can be altered to provide a desired flexibility characteristic within the body. In the illustrative embodiment of  FIG. 4 , for example, the spiraled member  44  has a pigtail configuration wherein each successive spiral turn decreases in diameter towards the second end  48 . It should be understood, however, that the spiraled member  44  could have other configurations, if desired, to alter the flexibility characteristics to the anchoring member  42 .  
      The structure and material composition of the spiraled member  44  can also be altered to impart a greater or lesser amount of flexibility to the anchoring member  42 , if desired, allowing the anchoring member  42  to selectively bend when an external force is applied to the intravascular filter  10 . In certain embodiments, for example, the spiraled member  44  can be formed from a superelastic and/or shape memory material such as nickel-titanium alloy to permit the anchoring member  42  to easily bend or flex.  
      As can be further seen in  FIG. 4 , a pointed tip portion  54  of the spiraled member  44  can be oriented at an angle θ relative to the spiral axis  50 . In certain embodiments, the angle θ at which the pointed tip portion  54  departs from the spiral axis  50  can be selected to orient the pointed tip portion  54  at an angle relative to the surface of the vessel wall. A shoulder  56  formed by the distal-most spiral at the second end  48  of the spiraled member  44  can be configured to act as a landing pad for the anchoring member  42 , limiting engagement of the pointed tip portion  54  within the vessel wall.  
      Referring now to  FIGS. 5-8 , an illustrative method of retrieving the intravascular filter  10  within a blood vessel V will now be described. In a first position illustrated in  FIG. 5 , intravascular filter  10  is shown in a fully deployed position within a blood vessel V with each anchoring member  22  being temporarily secured to the inner wall W to prevent the movement of the intravascular filter  10  therein. In this position, the filter legs  14  of the intravascular filter  10  can be configured to collect and subsequently lyse blood clots contained in the bloodstream  58 .  
      As can be seen in a second position in  FIG. 6 , a retrieval catheter  60  having a proximal section (not shown), a distal section  62 , and an internal lumen  64  configured to collapse and receive the intravascular filter  10  can be advanced to a location adjacent to the apical head  12  of the intravascular filter  10 . An elongated member  66  having a hook  68  or other suitable means for engaging the retrieval member  20  can be inserted into the internal lumen  64  of the retrieval catheter  60  and advanced distally beyond the distal section  62  of the retrieval catheter  60 . Once advanced to the site of the apical head  12 , the elongated member  66  can then be manipulated to secure the hook  68  to the retrieval member  20  on the apical head  12 , as shown, for example, in  FIG. 6 . Once secured thereto, the elongated member  66  can then be pulled proximally while holding the retrieval catheter  60  stationary, causing the anchoring members  22  to detach from the inner wall W of the blood vessel V.  
      As can be seen in a third position in  FIG. 7 , each anchoring member  22  can be configured to bend and straighten in a direction substantially parallel with the longitudinal axis of the filter legs  14  as a result of the proximally exerted force applied by the elongated member  66 . When this occurs, a small pocket is created at the location where the pointed tip portion  34  engages the inner wall W of the blood vessel V, allowing the anchoring member  22  to be easily detached therefrom. Further retraction of elongated member  66  in the proximal direction causes the filter legs  14  to fold inwardly and collapse within the internal lumen  64  of the retrieval catheter  60 , as shown in a fourth position depicted in  FIG. 8 . Once retracted within the internal lumen  64 , the retrieval catheter  60 , elongated member  66  and collapsed intravascular filter  10  can then be removed from the body, if desired.  
      Having thus described the several embodiments of the present invention, those of skill in the art will readily appreciate that other embodiments may be made and used which fall within the scope of the claims attached hereto. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size and arrangement of parts without exceeding the scope of the invention.