Abstract:
A medical filter retrieval system for retrieval of a medial filter from placement inside a body passage of a patient has a medical filter with a ferromagnetic head at one end thereof and a retrieval catheter. Located coaxially within the retrieval catheter are an elongated central probe having a ferromagnetic end. The medical filter is retrieved from the body passage by bringing the magnetic end of the central probe into proximity of the filter head which attracts and aligns the probe end to the filter head and magnetically attaches the probe end and head. Optionally, a snare device can be coaxially located within the retrieval catheter to engage the filter after the probe has been aligned with the filter head.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    The present invention relates to a system and method for retrieval of a medical filter. More specifically, the present invention relates to a system and method using magnetic force for alignment and retrieval of a medical filter. 
         [0002]    Medical filters, including vena cava filters, are emplaced inside blood vessels or other body passages for the purpose of intercepting thrombus or particles while allowing free flow of blood in the vessels or other body fluid in the body passages. Medical filters often are emplaced and never retrieved, remaining effective during their time in place, and remaining permanently in place. However, in some cases it may be desirable to remove or retrieve a medical filter after it has been in place for a period of time. 
         [0003]    Generally speaking, it is known to use catheters to emplace or deliver medical filters in a vein or bodily passage as well as to remove medical filters following their implantation. Retrieval of medical filters can be challenging. One method of retrieval involves use of a catheter with a loop which is pushed out of the catheter and used to snare a hook on the end of a filter. One of the most difficult aspects of vascular and other medical filter retrievals is locating or aligning the correct part of the filter with the operative end or loop of the retrieval catheter. The surgeon is often working through a long catheter extending through a tortuous anatomy while viewing a shadowy image of the filter and retrieval catheter loop in a two dimensional fluoroscopy image. Fluid flow within the vein or body passage may further increase the challenge. 
         [0004]    In light of these challenges, it would be beneficial to have an improved device and method for removal or retrieval of vascular and other medical filters. It would also be desirable to have a practical and economical system and method which facilitate removal of medical filters after implantation. It would be further desirable to have a retrieval system and method which can reduce the time required for retrieval and which can be used even under view of a shadowy, two dimensional image. Furthermore it would be desirable to have a retrieval system and method which can be used from either a femoral or jugular approach and which can be adapted for use with a wide variety of medical filter designs. 
         [0005]    Accordingly, the present invention provides an improved system and method using magnetic force for retrieving a medical filter inside a body passage of a patient. The filter retrieval system comprises:
       a medical filter having a retrieval section with a head which is ferromagnetic head at least at one longitudinal end thereof; and   a retrieval catheter having a probe with an end which is ferromagnetic and is attracted to the head of the medical filter by magnetic force when proximate thereto.
 
In accordance with the method of the present invention, a medical filter in a body passage is retrieved by use of magnetic force where the medical filter has a retrieval section with a head which is ferromagnetic by:
   advancing a retrieval catheter having a probe with an end which is ferromagnetic through the body passage until the ferromagnetic end of the probe is proximate to said ferromagnetic head of said filter and is brought into alignment and contacting relationship therewith by said magnetic force;   withdrawing the ferromagnetic end of the probe and the medical filter into the retrieval catheter.       
 
         [0010]    Further understanding of the present invention will be had from the following description taken in conjunction with the accompanying drawings and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view, broken away, of a preferred embodiment of a system of the present invention, showing a medical filter and a retrieval catheter; 
           [0012]      FIG. 2  is a side elevation view, broken away, of the medical filter and retrieval catheter of  FIG. 1  in operative relationship and illustrating an initial step of carrying out a preferred method of the present invention; 
           [0013]      FIG. 3  is a side elevation view, broken away, illustrating another step of the preferred method of  FIG. 2  in which the medial filter and retrieval catheter come into contacting and attaching relationship; 
           [0014]      FIG. 4  is a side elevation view, broken away, illustrating a further step of the preferred method of  FIG. 2  in which the medical filter and retrieval catheter are brought into alignment; 
           [0015]      FIG. 5  is a side elevation view, broken away, illustrating a further step of the preferred method of  FIG. 2  in which the arms of the snaring device of the retrieval catheter are advanced over the head of the medical filter; 
           [0016]      FIG. 6  is a side elevation view, broken away, illustrating the step of the preferred method of  FIG. 2  in which the arms of the snaring device of the retrieval catheter are urged radially inwardly as they are brought into the sheath of the retrieval catheter; 
           [0017]      FIG. 7  is a side elevation view, broken away, illustrating the step of the preferred method of  FIG. 2  of pulling the filter into the retrieval sheath; and 
           [0018]      FIG. 8  is a side elevation, broken away, showing an alternative preferred embodiment of a retrieval catheter of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The following description of the preferred embodiments of the present invention is intended to be merely illustrative in nature, and as such, is not intended to limit in any way the present invention, its application, or uses. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, the present invention may be used in veins but is also useful in other body passages. 
         [0020]    Now referring to  FIG. 1 , a preferred embodiment of a medical filter retrieval system of the present invention is shown and indicated generally by the numeral  10 . System  10  comprises a medical filter  12  and a retrieval catheter  14  operatively associated therewith as will be further understood from the following description of this preferred embodiment of the present invention. Medical filter  12  and retrieval catheter  14  are designed to cooperate with each other to be self aligning and to facilitate using retrieval catheter  14  to remove filter  12  from a vein or other bodily passage where it has been implanted. 
         [0021]    Medical filter  12  is made of a resilient material which tends to expand to the form illustrated in  FIG. 1  but can be compressed to a smaller diameter form such as when inside a suitable delivery catheter or withdrawn into a retrieval catheter. Medical filter  12  has a body  16  with a longitudinal axis  18  and carries a plurality of radially and axially extending struts  20 . The plurality of struts  20  define a filter basket  22 . It will be appreciated by those skilled in the art that struts  20  and body  16  may be modified within the scope of the present invention and that body  16  may carry additional struts and have an opposing filter basket not shown in the figure. Filter  12  may be symmetrical or asymmetrical in form. 
         [0022]    In accordance with the present invention, medical filter  12  has a retrieval section  23  at one end thereof. Retrieval section  23  is an elongated body having a longitudinally centered head  24  at its rightward end as shown in  FIG. 1 . Filter head  24  is characterized by having a ferromagnetic nature, a convex curved forwardly facing surface  26 , and a rearward shoulder with a generally flat rearward facing surface  28 . Filter head  24  thus has a generally semi-spherical shape, which term as used herein includes semi-spherical, semi-ellipsoidal, and semi-parabloid shapes, and provides forward facing surface  26 . 
         [0023]    Filter head  24  is provided with a ferromagnetic feature to cooperate with retrieval catheter  14  as described in more detail below. Thus, filter head  24  may be made of a ferromagnetic material or it may incorporate or encapsulate a ferromagnetic material. Rare earth magnetic materials such as samarium cobalt or neodymium iron boron are preferred magnetic materials because of their strong magnetic force relative to their size. The rare earth magnetic material may be encapsulated in traditional biocompatible materials in sufficient concentrations for sufficient magnetic force. Other suitable ferromagnetic materials for head  24  include, but are not limited to, duplex austenitic-ferritic stainless steel and ferritic stainless steel. Alternatively, head  24  may have a ferromagnetic material welded or glued thereon. Also alternatively, filter head  24  may be tubular with ferromagnetic material placed inside the tube. 
         [0024]    The remainder of filter  12  may be made of any suitable material using a variety of methods. Suitable conventional materials and methods are well known in the art. Nitinol and stainless steel are examples of suitable materials but other materials may be used so long as the material has the desired characteristics of strength, resilience, flexibility, biocompatibility and endurance and is suitable for the particular manufacturing technique employed. It is, of course, required that the material employed be capable of expanding to the desired shape upon ejection from the delivery catheter and reduction in diameter when withdrawn into the lumen of the retrieval catheter. Thus, the material must also be sufficiently resilient to accomplish both compression and expansion. 
         [0025]    Suitable methods of manufacture of body filter  12  include cutting a pattern into a tube to enable expansion of the tube into the desired body and struts. Another suitable method is forming the struts and body from separate strips or wires and then joining the respective parts together by suitable methods which are well known in the art. 
         [0026]    Retrieval catheter  14  has an elongated sheath  40  coaxially encompassing central probe  42  and snaring device  44 . Probe  42  has a forward end  46  which is magnetically attracted to head  24  and which comprises a ferromagnetic material or a magnetic material. The forward face  48  of forward end  46  of probe  42  is a generally hemispherical surface  48  to facilitate alignment of forward end  46  with head  24  as described in more detail hereinafter. Snaring device  44  has a plurality of somewhat flexible arms  51  which are spring biased radially outwardly and which have reentrantly bent ends  52 . Snaring device  44  has a tubular portion  50  which is coaxially located within lumen  56  of retrieval catheter  14 . Tubular portion  50  is slidably located within lumen  56  so that, with respect to  FIG. 2 , it may be moved rightwardly with respect to sheath  40  to thereby draw arms  51  and ends  52  radially inwardly or it may be moved leftwardly with respect to sheath  40  to the position shown in  FIG. 2  thereby allowing arms  51  and ends  52  to expand radially outwardly. 
         [0027]    Having described a preferred system of the present invention, further understanding of the unique character and advantages of the present invention will be had by an understanding of the method for retrieval of filter  12 . It will be further appreciated that the present method relates to a method for retrieval of a medical filter which has been previously position within a vein or body passage. For example and not by way of limitation, filter  12  is intended to be initially deployed in the lumen of a delivery catheter as is conventional in the art. Insertion of filter  12  into a delivery catheter can be by any conventional method including by simply pushing filter  12  into the lumen at the distal end of a delivery catheter. Alternatively, filter  12  may be inserted into the proximal end of a delivery catheter and pushed by means of a push wire or the like to the distal end of the catheter. Emplacement of filter  12  in a vein or other body passage may also be done by conventional means well known in the art. For example, a delivery catheter carrying a radially compressed filter  12  may be inserted along a body vessel in a patient until its distal end is near the desired site for treatment. The delivery catheter may be inserted using either a femoral approach or a jugular approach. A push wire may be used to eject filter  12  from the lumen of the delivery catheter by pushing filter  12 . As filter  12  is ejected, arms  20  expand radially outwardly until contacting the walls of the vessel. 
         [0028]    Once emplaced in a body passage such as a vein, in many cases there will be no desire to retrieve filter  12  from the vessel and there will be no need for the present invention. However, is some cases there will be a desire to retrieve filter  12  from the vessel and is such cases the present invention provides an advantageous system and method for this purpose. Now referring to  FIGS. 2-9 , further understanding can be had of the method of the present invention using the system of the present invention. 
         [0029]      FIG. 2  illustrates the initial step of the method of retrieving filter  12  in accordance with this invention. Filter  12  is shown in place in vessel  60 . Retrieval catheter  14  is shown having been advanced through vessel  60  to a location proximate to filter  12 . As will be appreciated by the skilled artisan, such advancement may be from either a femoral or jugular approach but must be made toward an appropriate head  24  of medical filter  12 . If medical filter  12  has a head  24  at either of its longitudinal ends, then medical filter  12  can be approached from either direction. Of course, if medical filter  12  has a head  24  at only one end, then it must be approached toward the end that has head  24 . Snare  44  is preferably withdrawn into lumen  56  of retrieval catheter  14  during advancement of catheter  14  through vessel  60  to facilitate the advancement of the catheter through the vessel. However, when proximate to medical filter  12 , tubular portion  54  of snaring device  44  is extended beyond sheath  40  of retrieval catheter  14  (leftwardly as viewed in  FIG. 2 ) to allow arms  51  to flex radially outwardly into position to capture head  24  of medical filter  12  for retrieval thereof. As illustrated in  FIG. 2 , head  24  of medical filter  12  and forward end  46  of probe  42  are attracted to each other by magnetic force  62  and as retrieval system  14  is advanced toward medical filter  12 , magnetic force  62  urges forward face  48  of end  46  of probe  42  into contacting relationship with forward facing surface  26  of head  24 . This contacting relationship is shown in  FIG. 3  and represents the step of probe  42  magnetically attaching to medical filter  12 . 
         [0030]    It is contemplated that head  24  and probe  42  will not be initially in exact alignment but will be nearly aligned as shown in  FIG. 3 . Substantial alignment or centering of head  24  and probe  42  as shown in  FIG. 4  can be achieved by pulling rightwardly as shown in  FIG. 4  to utilize the round ends of each surface  26  and  48  to align the axis of probe  42  with the axis of medical filter  12 . Then snaring device  44  can be advanced to the left as viewed in  FIGS. 5 and 6 . 
         [0031]    As shown in  FIG. 6 , after probe  42  and head  24  are aligned, coaxial snaring device  44  is advanced, if necessary, leftward as shown in the  FIG. 6 , so that hooks  52  are positioned radially outwardly from shoulder  28  of head  24 . Then, tubular portion  54  of snaring device  44  is manipulated rightwardly with respect to sheath  40  which urges arms  50  radially inwardly and into neck portion  29  of medical filter  12  as shown in  FIG. 7 . 
         [0032]      FIG. 7  illustrates the step of pulling medical filter  12  into lumen  56  of retrieval catheter  14  by pulling snaring device into lumen  56 . Hooks  52  abut against shoulder  28  when retrieval catheter  14  is manipulated rightwardly and struts  20  are compressed radially inwardly by sheath  40  as medical filter  12  is pulled into lumen  56 . Finally,  FIG. 9  illustrates the step of retrieving catheter  14  which now encompasses medical filter  12  from vessel  60 . 
         [0033]    Now referring to  FIG. 8 , an alternative preferred embodiment of a retrieval catheter of the present invention is shown and indicated generally by the numeral  100 . Retrieval catheter  100  is generally analogous to retrieval catheter  14 , but does not have snaring device  44 . Thus, retrieval catheter  100  carries probe  142  which has forward end  146  which is comprised of a magnetic material. The magnetic material of end  146  serves to align probe  142  with head  24  of medical filter  12  and is characterized by a magnetic force at least sufficient to remain attached to head  24  while probe  142  is withdrawn into the sheath of retrieval catheter  100 . 
         [0034]    While preferred embodiments of the present invention have been specifically described above, it will be appreciated by those skilled in the art that the present invention is subject to variations and modifications. For example, the filter may be cut from a single tube and have end rings which are integral, i.e., one piece, with the spine and struts. The filter may have wire struts and end rings which are tubular.