Abstract:
A method of removing an implanted vessel filter by a femoral approach comprising the steps of providing a catheter with a curved tip, inserting a straightening device into the catheter to move the catheter tip from a curved position to a more straightened position, advancing the catheter tip through the femoral vein and past a cranial end of the filter, withdrawing the straightening device to enable the catheter tip to return to the curved condition, and inserting a filter grasping device though the catheter and a curved catheter tip to exit a distal portion to grasp the filter.

Description:
This application is a continuation of application Ser. No. 12/499,887, filed Jul. 9, 2009, (now U.S. Pat. No. 8,715,313), which is a continuation of application Ser. No. 11/801,547, filed May 10, 2007, (now U.S. Pat. No. 7,976,562), which claims priority from provisional application Ser. No. 60/818,202, filed Jun. 30, 2006, and is a continuation-in-part of application Ser. No. 10/899,429, filed Jul. 12, 2004 (now U.S. Pat. No. 7,704,266) which claims priority from provisional application Ser. No. 60/572,274, filed May 18, 2004, and is a continuation-in-part of application Ser. No. 10/805,796 filed Mar. 22, 2004, (now U.S. Pat. No. 7,338,512), which claims priority from provisional application Ser. No. 60/538,379, filed Jan. 22, 2004. The entire contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     This application relates to a vascular filter and more particularly to a method of removing a vein filter from the vessel. 
     2. Background of Related Art 
     Passage of blood clots to the lungs is known as pulmonary embolism. These clots typically originate in the veins of the lower limbs and can migrate through the vascular system to the lungs where they can obstruct blood flow and therefore interfere with oxygenation of the blood. Pulmonary embolisms can also cause shock and even death. 
     In some instances, blood thinning medication, e.g. anticoagulants such as Heparin, or sodium warfarin can be given to the patient. These medications, however, have limited use since they may not be able to be administered to patients after surgery or stroke or given to patients with high risk of internal bleeding. Also, this medication approach is not always effective in preventing recurring blood clots. 
     To avoid invasive surgery, less invasive surgical techniques involving placement of a mechanical barrier in the inferior vena cava have been developed. These barriers are in the form of filters and are typically inserted through either the femoral vein in the patient&#39;s leg or the right jugular vein in the patient&#39;s neck or arm under local anesthesia. The filters are then advanced intravascularly to the inferior vena cava where they are expanded to block migration of the blood clots from the lower portion of the body to the heart and lungs. 
     These prior filters take various forms. One type of filter is composed of coiled wires such as disclosed in U.S. Pat. Nos. 5,893,869 and 6,059,825. Another type of filter consists of legs with free ends having anchors for embedding in the vessel wall to hold the filter. These filters are disclosed, for example, in U.S. Pat. Nos. 4,688,553, 4,781,173, 4,832,055, and 5,059,205, 5,984,947 and 6,007,558. Another type of filter is disclosed in U.S. Pat. No. 6,214,025 consisting of wires twisted together to form a cylindrical anchoring portion conforming to the inner vessel wall surface to exert a radial force and a conical filtering portion. 
     Co-pending commonly assigned U.S. application Ser. No. 10/889,429 (the “&#39;429 application”), the entire contents of which is incorporated herein by reference, discloses other forms of vein filters. These filters can be permanently implanted or removed minimally invasively, e.g. intravascularly. The &#39;429 application discloses various configurations of the cranial end of the filter to facilitate removal. The filters of the &#39;429 application are generally designed to be removed from a jugular approach since the retrieval hook portion is located on the cranial end. It would be advantageous to provide a method for retrieving these filters utilizing a femoral approach as well. Such femoral approach could advantageously also be utilized to retrieve other filters. 
     SUMMARY 
     The present invention provides a method of removing an implanted vessel filter by a femoral approach comprising the steps of: providing a catheter with a curved tip; inserting a straightening device into the catheter to move the catheter tip from a curved position to a more straightened position; advancing the catheter tip through the femoral vein and past a cranial end of the implanted filter; withdrawing the straightening device to enable the catheter tip to return to the curved position; and inserting a filter grasping device through the catheter and curved catheter tip to exit a distal portion to grasp the filter. 
     The step of inserting the filter grasping device preferably includes the step of inserting a snare to engage a hook portion at the cranial end of the filter. Preferably the method includes the step of pulling the filter into a lumen of the catheter after grasping of the filter. The step of advancing the catheter tip preferably includes the step of advancing the catheter and straightening device over a guidewire. Subsequent to the step of withdrawing the filter, the catheter tip is preferably moved to a more straightened position to facilitate removal of the catheter. The method steps may also include advancing the catheter after grasping the filter to disengage filter hooks from the vessel wall. 
     The present invention also provides a method of removing an implanted vessel filter by a femoral approach comprising the steps of providing a catheter with a tip; inserting a curved device into the catheter to a position proximal of the tip; advancing the catheter tip through the femoral vein and past a cranial end of the implanted filter; inserting the curved device into the catheter tip to move the catheter tip from a first more straightened position to a second more curved position; and inserting a filter grasping device though the curved device, catheter and curved catheter tip to exit a distal portion to grasp the filter. 
     The step of inserting the filter grasping device may include the step of inserting a snare to engage the filter. The catheter may have a first hardness at an intermediate portion and a second hardness less than the first hardness at the tip such that in the step of inserting the curved device, the first hardness maintains the curved device in a more straightened position and the second hardness allows the curved device to move to a more curved position to thereby move the catheter tip to the more curved position. 
     The method may further include the step of pulling the filter into a lumen of the curved device after grasping of the filter. 
     The method may further comprise the step of withdrawing the filter and grasping device through the catheter, wherein subsequent to the step of withdrawing the filter, the method includes the step of withdrawing the curved device from the catheter tip to move the catheter tip to a more straightened position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiment(s) of the present disclosure are described herein with reference to the drawings wherein: 
         FIG. 1  is a broken perspective view of the retrieval catheter with a dilator positioned therein to straighten the catheter tip; 
         FIG. 2  is a broken perspective view of the catheter of  FIG. 1  with the dilator removed and the catheter tip in the curved position; 
         FIGS. 3-14  illustrate the method steps of the present invention for retrieving a filter by a femoral approach, wherein 
         FIG. 3  illustrates initial insertion of the guidewire through the femoral vein; 
         FIG. 4  illustrates the retrieval catheter being advanced over a guidewire toward the inferior vena cava just below (upstream) the juncture of the renal arteries to where the filter has been implanted; 
         FIG. 5  illustrates the tip of the retrieval catheter being advanced beyond the implanted filter with the dilator still positioned in the catheter to maintain the catheter tip in the straightened position; 
         FIG. 6  illustrates the dilator being withdrawn to enable the catheter tip to return to its normally curved position; 
         FIG. 7  illustrates a filter retrieval snare being inserted into the retrieval catheter; 
         FIG. 8  illustrates the filter retrieval snare advanced through the retrieval catheter, the snare shown exiting the distal tip of the catheter and engaging the cranial end of the filter; 
         FIG. 9  is a close up view of the area of detail of  FIG. 8  showing the snare engaging the retrieval hook at the cranial end of the filter; 
         FIG. 10  is a close up view similar to  FIG. 9  except showing the snare tightened around the retrieval hook of the filter; 
         FIG. 11  illustrates movement of the retrieval catheter distally to disengage the filter retention hooks from the vessel wall; 
         FIG. 11A  illustrates an alternate embodiment to aid movement of the retrieval catheter distally by the use of a wire; 
         FIG. 12  illustrates retraction of the retrieval snare to remove the filter from the vessel and pull it through the retrieval catheter; 
         FIG. 13  illustrates reinsertion of the dilator into the retrieval catheter; and 
         FIG. 14  illustrates removal of the catheter after advancement of the dilator to the distal tip to straighten the tip. 
         FIG. 15A  is a perspective view of one embodiment of a vein filter that can be removed using the retrieval catheter; 
         FIG. 15B  is an enlarged developed view of the retention hooks of the filter of  FIG. 15A ; 
         FIG. 16  is a perspective view of an alternate embodiment of a retrieval hook of a filter; 
         FIG. 17A  is a broken perspective view of a retrieval catheter with a straight tip and showing a dilator being inserted therein; 
         FIG. 17B  is a broken perspective view of the retrieval catheter of  FIG. 17A  with the dilator fully inserted to move the catheter tip to the curved position; 
         FIG. 18  is a perspective view of a cranial end of a filter have a dome shaped end; and 
         FIG. 19  is a perspective view of a cranial end of a filter having a dome shaped end with a notch formed therein. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the drawings, wherein like reference numerals identify similar or like components throughout the several views, a method for retrieving vein filters utilizing a femoral approach is described. In co-pending commonly assigned patent application Ser. No. 10/899,429, filed Jul. 12, 2004, various embodiments of filters are described with various structures, e.g. hooks, to facilitate removal. The &#39;429 application also describes retrieval of the filter through the catheter. Being that the retrieval structure of the filters is at the cranial end, the method of the present invention provides a way to retrieve those filters from the inferior vena cava, as well as other filters with retrieval hook or structure on the cranial end, utilizing a femoral approach. 
     Turning initially to  FIG. 1 , the retrieval catheter or sheath  10  of the present invention has a body  12  and a distal tip  14 . The distal tip  14  has a curved shape as shown in  FIG. 2  (the straightened shape is shown in phantom). The curved shape is the normal condition of the catheter tip  14  and the curve shown is about 180 degree turn although other curves are also contemplated. The curved catheter tip  14  is sufficiently flexible to be straightened by insertion of dilator  20  through lumen  16  as shown in  FIG. 1 . 
     The retrieval method is illustrated by the method steps of  FIGS. 3-14 . After insertion of the guidewire  30  through the right femoral vein “f” (or alternatively the left), the guidewire  30  is maneuvered past the cranial end  54  of filter  50 . Retrieval catheter  10 , with dilator  20  positioned therein, is then inserted through the femoral vein “f” and advanced through the iliac veins into the inferior vena cava. (Tubing  104  and valve assembly  106  enable saline injection described below.) That is, dilator  20  is positioned in the lumen  16  of the retrieval catheter  10  during insertion to move and maintain the tip  14  in the substantially straightened position (or more straightened position) to enable advancement of the catheter through the vascular system. Retrieval catheter  10  and dilator  20  are inserted over guidewire  30  past the caudal end  52  of the filter  50  and beyond the cranial end  54  as shown in  FIG. 5 . 
     Dilator  20  (and guidewire  30 ) is then withdrawn as shown by the arrow in  FIG. 6 , which enables the distal tip  14  of catheter  10  to return to its normal more curved configuration. In this curved configuration, the distal opening  18  of catheter  10  faces the cranial end of the filter and is maneuvered so opening  18  is above the hook  56  of filter  50 . It could also be placed to substantially align with the hook. 
     Snare catheter  40  is inserted through the lumen  16  of the retrieval catheter  10 , as shown by the arrow of  FIG. 7 , and extends around the curved distal tip  14  of catheter  10  as shown in  FIGS. 8 and 9 , exiting distal opening  18 . 
     The snare  42 , movably positioned in a lumen of the snare catheter  40 , is placed around hook  56  of filter  50 , and then tightened around the hook as shown in  FIG. 10 , by retraction of the snare wire to grasp the filter. Once tightened, the catheter  10  is preferably moved distally (shown in phantom) in the direction of the arrow of  FIG. 11  to disengage the filter retention hooks  58  from the vessel wall. To facilitate such distal advancement and hook disengagement, a wire can be used as shown in the alternate embodiment of  FIG. 11A . In this embodiment, catheter  10 ′ has a side opening  15  through which wire  17  extends from the catheter lumen, either the lumen for the snare or another lumen adjacent to the snare lumen. This stiffening wire  17  is pushed forward along with the retrieval catheter  10 ′ to help move the catheter distally by providing additional force on the catheter. 
     Once the filter retention hooks  58  are disengaged from the vessel wall, the snare catheter  40  is withdrawn, pulling the filter  50  into the retrieval catheter  10  as shown in  FIG. 12 . The snare catheter  40  and filter  50  are then removed through the proximal end of the catheter  10 . Next, the dilator  20 , preferably with guidewire  30 , is reinserted through the catheter lumen  16  ( FIG. 13 ) to straighten the distal tip  14  (or move it to more straightened position). The retrieval catheter  10 , with the straightened tip, along with the dilator  20  and guidewire  30 , are then withdrawn from the body in the direction of the arrow of  FIG. 14 . 
       FIGS. 17A and 17B  illustrate an alternate retrieval catheter. Retrieval catheter or sheath  110  has a substantially straight tip  114  and distal opening  118 . The tip portion  115  of catheter  110  has a first hardness and the intermediate portion  117  (or portion proximal of tip portion  115 ) has a second hardness greater than the first hardness. A dilator or stylet  120  has a curved tip  122 . The dilator  120  has a third hardness greater than the first hardness of the tip portion  115  but less than the second hardness of the intermediate portion  117 . When the dilator  120  is inserted in the catheter  110  and the tip  122  is in the intermediate portion  117 , the tip is restrained in a more straightened position due to the greater hardness of portion  117 . When the dilator  120  is further inserted so the tip  122  is in the tip portion  115 , it is enabled to return to its normally curved position since its hardness is greater than that of tip portion  115 , thereby forcing the distal tip  114  of retrieval catheter  110  into a more curved position as shown in  FIG. 17B . 
     Thus, in use, after insertion of the guidewire as described above, retrieval catheter  110 , with dilator  120  positioned partially therein, is inserted through the femoral vein “f” and advanced through the iliac arteries into the inferior vena cava. Retrieval catheter  110  and dilator  120  are inserted over the guidewire past the caudal end  52  of the filter  50  and beyond the cranial end  54 . (Alternatively, the dilator  120  can be inserted into catheter  110  after the catheter is inserted). 
     Dilator  120  is then fully inserted into the catheter  110  (and the guidewire withdrawn either prior to or after full insertion) to force the distal tip  114  of catheter  110  to its curved configuration. In this more curved configuration, the distal opening  118  of catheter  110  faces the cranial end of the filter and preferably is maneuvered so opening  18  is above the hook  56  of filter  50 . 
     Snare catheter  40  is inserted through the lumen of the dilator  120  and extends around curved tip  122  of dilator  120  and curved distal tip  114  of catheter  110 , exiting the distal opening of the dilator and the distal opening  118  of the catheter  110 . 
     The snare  42  is placed around hook  56  of filter  50 , and then tightened as described above. Once tightened, the catheter  10  is preferably moved distally, also as described above, to disengage the filter retention hooks  58  from the vessel wall. After the filter  50  is withdrawn, the dilator  120  is retracted to straighten the tip of catheter  110 . 
       FIG. 15A  shows an example of a filter that could be withdrawn using the retrieval method of the present invention. The filter  50  is shown in the expanded placement configuration. It should be appreciated that other filters, including those described in the &#39;429 application, could be retrieved using the femoral approach method described herein. The filter  50  (and other filters described therein) can be inserted through the jugular vein in the neck of the patient or through the femoral vein in the leg of the patient or the arm. The filters can also be placed in the superior vena cava. 
     Filter  50  is preferably made from a shape memory nitinol tube and has a flared region  57  and a converging region  51  at the filtering region  59 . 
     Filtering region  59  has six struts  61  (only some of which are labeled for clarity) curving outwardly from tubular portion  64 . Each filter strut or strut portion  61  extends radially from tubular portion  64  and divides into two connecting filter struts or strut portions  61   a ,  61   b  (preferably of equal width) that angle way from each other (in different directions) to extend to the connecting strut portion of an adjacent strut  61 . After convergence of strut portions  61   a ,  61   b  at joining region  61   d , it transitions into elongated mounting strut portions  61   c  which form flared mounting or anchoring region  57 . The struts  61  terminate in hooks  58 , of two different sizes as described in the &#39;429 application. Hooks  58  include a series of teeth  58   a  ( FIG. 15B ) to engage the vessel wall to provide additional retention to prevent movement of the implanted filter in the caudal direction. A heel  59  extends past the hook to function as a stop to prevent the filter strut portions from going through the vessel wall. 
     The tubular portion  64  is preferably in the form of a retrieval hook as described in the &#39;429 application. Hook  56  has a curved hook  72  at the proximalmost end which is configured to receive a retrieval snare or other retrieval device. A portion of the wall of the hook  56  is cut out to expose the annular interior surface  74 . The interior surface  74  accommodates a portion of a tubular snare sheath. That is, the outer wall of the snare sheath (tube) can partially fit within the cut out region. This enhances removal as the snare pulls the filter hook into collinear arrangement with the sheath tube. 
     Engagement of the retrieval hook  56  and its retraction into the snare sheath or tube, including the collinear arrangement are described in detail and shown in  FIGS. 13H-13N  of the &#39;429 application. When the filter  50  is pulled into the retrieval sheath  10  it is collapsed for removal. 
       FIG. 16  shows an alternate embodiment of a retrieval hook  170  having a longer hook  172  to increase the snare engagement area and provide a more closed area to retain the snare.  FIGS. 18 and 19  illustrate alternative cranial ends of the filter which can be achieved using the method of the present invention. In  FIG. 18 , a rounded dome-shaped tip  210  can be engaged by a grasping device to retrieve the filter. The grasping device can be inserted around the curved catheter tip in the same manner as described above for the snare retrieval device. In  FIG. 19 , a notch  222  is formed in dome-shaped tip  220  to receive a retrieval snare or other grasping device inserted through the curved retrieval catheter (sheath) tip. 
     To facilitate removal of the filter from the vessel, cold saline can be injected onto the implanted filter to change the temperature of the filter to move it to a relatively softer condition to facilitate the filter being drawn in to the retrieval sheath. That is, injection of cold saline will cause the filter to approach its softer martensitic state, bringing the filter to a more flexible condition. The flexible condition facilitates the collapse and withdrawal of the filter into the retrieval sheath by decreasing the frictional contact between the filter and the inner surface of the retrieval sheath. 
     While the above description contains many specifics, those specifics should not be construed as limitations on the scope of the disclosure, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto.