Abstract:
A retrievable medical filter which can be placed in a blood vessel or other body passage. The filter has improved structural features for enhancing its filter effectiveness and to facilitate its retrieval from the body passage. The filter has a longitudinal spine with struts extending from each longitudinal to form filter baskets. The ends of the spine to which the struts are attached may be rings with serpentine cuts in the rings to make them expandable. The struts can extend circumferentially as well as radially outwardly to provide a structure which can be radially compressed without bending the struts in a tight radius.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    The present invention relates to medical filters which are intended to be placed inside a blood vessel or other body passage for the purpose of intercepting thrombus or particles. 
         [0002]    Medical filters, including vena cava filters, are generally known and used to intercept unwanted particulate material in blood vessels and the like. To function satisfactorily in a blood vessel, a filter must be effective to entrap thrombus, clots or other dangerous coagulations while allowing free flow of blood in the vessel. It has been found that certain features are desirable in such filters. It is important that the filter be emplaced with minimal trauma to the patient as by percutaneous delivery. It is also important that the filter be adapted to properly adjust to the size of the vessel. Of course, it is also important that the filter remain effective during its time in place. And, while the filter may be permanently emplaced, it is desirable if the filter can be easily retrieved if desired. 
         [0003]    Generally speaking, vena cava and other medical filters are known. It is also known to deliver filters in compressed shape by means of a catheter and to remove such filters following their implantation. However, difficulties may be encountered with presently known filters, and there remains room for improved designs of filters and methods of delivery and removal of filters. 
         [0004]    Accordingly, the present invention provides a medical filter which is suitable for permanent implantation but can be removed at any time after implantation if desired. The filter of the present invention can be implanted and retrieved from either femoral or jugular approaches. In a preferred embodiment of the present invention, retrieval is facilitated by a crossover design of the filter baskets which minimizes the diameter of the filter during retrieval. The filter matches the clot capture efficiency of a double-basket filter yet is readily implanted and retrieved. Furthermore, the design practical for manufacture and can be economically made. 
         [0005]    Thus, in accordance with the present invention, a medical filter for placement inside a body passage to treat a patient comprises:
       in a radially compressed state, a longitudinally extending spine having a plurality of struts secured at one longitudinal end of said spine and a plurality of struts secured at an opposite longitudinal end of said spine, each of said struts extending generally longitudinally along said spine and each of said struts being biased in a radially direction; and   in a radially expanded state, each of said struts extending in a direction generally radially outwardly and axially from said spine and each of said struts having a first bend proximate to said spine in a direction away from said spine and a second bend at each free end portion in a direction toward said spine.       
 
         [0008]    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 
         [0009]      FIG. 1  is a perspective view of a preferred embodiment of a filter of the present invention shown in expanded form; 
           [0010]      FIG. 2  is a longitudinal cross-sectional view of the filter of  FIG. 1  in place in a vein; 
           [0011]      FIG. 3  is a side elevation view of the filter of  FIG. 1  in compressed form and in an insertion cartridge; 
           [0012]      FIG. 4  is a longitudinal cross-sectional view of the filter of  FIG. 1  in association with a insertion cartridge illustrating emplacement of the filter from the vein; 
           [0013]      FIG. 5  is a longitudinal cross-sectional view of the filter of  FIG. 1  in association with a removal cartridge showing a step in removal of the filter from the vein; 
           [0014]      FIG. 6  is a longitudinal cross-sectional view of the filter of  FIG. 1  in association with a removal cartridge showing a further step in removal of the filter from the vein; 
           [0015]      FIG. 7  is a perspective view of an alternative preferred embodiment of a filter of the present invention; 
           [0016]      FIG. 8  is a perspective view of another alternative preferred embodiment of a filter of the present invention; 
           [0017]      FIG. 9  is a longitudinal cross-sectional view of the filter of  FIG. 8  in association with a removal cartridge and illustrating a step in retrieval of the filter of  FIG. 8 ; and 
           [0018]      FIG. 10  is a longitudinal cross-sectional view of the filter of  FIG. 8  in association with a removal cartridge and illustrating a further step in retrieval of the filter of  FIG. 8 . 
       
    
    
     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 preferred embodiments of the present invention are shown in use in a vein but may also be used in other body passages. 
         [0020]    Now referring to  FIGS. 1-3 , a preferred embodiment of a medical filter of the present invention is shown and indicated generally by the numeral  10 . Filter  10  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 as shown in  FIG. 2  where Filter  10  is shown inside a suitable delivery catheter  12 .  FIG. 3  shows filter  10  in place in a vein. 
         [0021]    Filter  10  has a body  14  which extends generally along the longitudinal axis of filter  10  and which carries a plurality of radially and axially extending struts  16  and  18 . Struts  16  combine to define a first filter basket  20  and struts  18  combine to define a second filter basket  22 . A first collar  24  with retrieval hook  26  attached thereto is located at one longitudinal end of filter  10 . A second collar  28  with retrieval hook  30  attached thereto is located at the other longitudinal end of filter  10 . Filter  10  is symmetric in form although it will be appreciated by those skilled in the art that asymmetric forms of filter  10  are within the broad scope of the present invention. For example filter  10  may have more or less struts  16  than struts  18  and filter  10  may have a retrieval hook at one end but not the other end thereof. It is, however, preferred that filter  10  is symmetrical and has retrieval hooks at both ends to allow it to be retrieved using a snare either from a femoral or jugular approach. 
         [0022]    Each strut  16  is attached to body  14  at a first end  32  thereof and is formed so as to extend, when not compressed, first generally axially along body  14  and then after bend  34  generally radially outwardly from body  14  for a distance slightly greater than the radius of a vena cava of intended use. The end portion  36  of each strut  16  is bent back slightly towards body  14  so that end  38  of strut  16  is radially inward with respect to bend radius  40 . 
         [0023]    Filter  10  may be made of any suitable material using a variety of methods. 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. Thus, the material must also be sufficiently resilient to accomplish both compression in the delivery catheter and expansion upon ejection from the catheter. 
         [0024]    Suitable methods of manufacture 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. 
         [0025]    Having described the structure of filter  10 , a preferred embodiment of the present invention, further understanding of the unique character and advantages of the present invention will be had by an understanding of its use. Now referring to  FIGS. 2-6 , filter  10  is intended to be initially deployed in the lumen  50  of a delivery catheter  12  as shown in  FIG. 3 . Insertion of filter  10  into delivery catheter  12  can be by any conventional method including by simply pushing filter  10  into the lumen at the distal end of a delivery catheter. Alternatively, filter  10  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. 
         [0026]    Emplacement of filter  10  is illustrated in  FIG. 4 . As shown in  FIG. 4 , delivery catheter  12  carrying radially compressed filter  10  in lumen  52  at distal end  54  of catheter  12  is inserted along body vessel  56  in a patient until distal end  54  is near the desired site for treatment. Catheter  12  may be inserted using either a femoral approach or a jugular approach. A push wire (not shown in the Figures) may be used to eject filter from lumen  52  by pushing filter  10  in the direction indicated by arrow  58 . As filter  10  is ejected, arms  16  expand radially outwardly until bend radius  40  of arm  16  contacts wall  60  of vessel  56 . After arms  16  are deployed, delivery catheter  12  is withdrawn slightly in the direction indicated in  FIG. 4  by arrow  62  whereupon filter  10  is completely ejected from lumen  52  and arms  18  expand into contacting relationship with wall  60  of vessel  56  and assume an operative filtering position within vessel  56  as is best illustrated in  FIG. 5 . 
         [0027]    Once emplaced in a body passage such as a vein and now referring to  FIG. 2 , filter  10  has struts  16  and  18  with ends  38  positioned proximal to wall  60  of vessel  56  but spaced therefrom so as to avoid piercing into vessel wall  60  and also to minimize any encapsulation by tissue growth. In operation, filter  10  provides a first filter basket  20  and a second filter basket  22  with basket openings facing each other so that the particular orientation of filter  10  with respect to flow of blood is not important. Furthermore, filter  10  as retrieval hooks  26  and  20  at opposite ends so that filter  10  can be retrieved from either direction. 
         [0028]    While filter  10  is suitable for permanent placement in vessel  56 , filter  10  may be readily removed or retrieved from vessel  56  if retrieval is desired. As is shown in  FIGS. 5 and 6 , the retrieval of filter  10  may be accomplished by means of a retrieval catheter  62  which may be inserted from either the femoral or jugular direction. After snaring retrieval hook  30  with snare  64  of retrieval catheter  62 , filter  10  is drawn into lumen  66  of retrieval catheter  62  as shown in  FIG. 5  whereupon struts  18  come into contact with distal end  68  of retrieval catheter  62  which contacting relationship urges the loose ends of struts  18  radially inwardly as shown in  FIG. 6 . Pulling of filter  10  rightward as shown in  FIG. 5  results in struts  16  reversely bending to the positions shown in  FIG. 6 . Further pulling of filter  10  into lumen  66  results in distal end  68  of retrieval catheter  62  coming into contact with struts  16  to urge struts  16  radially inwardly. Struts  16  thus are inverted as they are bent by the force exerted by end  68  of retrieval catheter  62  in a leftward direction as viewed in the figures and are ultimately bent radially inwardly as shown in  FIG. 6 . Because struts  16  and  18  have free ends  38 , they may be bent as shown in the figures to radially collapsed positions which can be compressed within lumen  66  for ready withdrawal from vessel  56 . 
         [0029]    Now referring to  FIG. 7 , an alternative preferred embodiment of a filter of the present invention is shown and indicated generally by numeral  100 . Filter  100  is similar in construction to filter  10 . But has a spine  114  with serpentine end rings  124  and  126 . Both spine  114  and serpentine end rings  124  and  126  compress radially for insertion into the lumen of a delivery catheter but expand to a relatively greater radius when deployed as shown in  FIG. 8 . Filter  100  is well adapted to be made from a tubular material by cutting the respective parts therefrom. Retrieval of filter  100  is analogous to retrieval of filter  10 . 
         [0030]      FIG. 8  shows another alternative embodiment of a filter of the present invention which is indicated generally by the numeral  200 . Filter  200  is a cross-over design wherein struts  216  and  218  extend from spine  214  initially in a generally circumferential direction.  FIG. 9  shows filter  200  in a deployed state. Filter  200  is substantially equivalent to filter  10  in filtering efficiency. And retrieval of filter  200  can be done in a manner analogous to retrieval of filter  10 . However, during retrieval, the somewhat circumferential orientation of struts  216  and  218  is advantageous because retrieval into the lumen of a retrieval catheter can be achieved with a greater bending radius of the struts as is illustrated in  FIGS. 9 and 10 . This feature allows use of a lumen with a small diameter because the cross-over design minimizes the size of the filter during retrieval. The filter size of filter  10  during retrieval is determined by the bend radius of struts  16 . The filter size of filter  200  during retrieval is reduced by the difference between the bend radius of the strut and the diameter of the end ring. 
         [0031]    A filter made in accordance with the present invention is retrievable at any time following implantation and may be retrieved from either femoral or jugular approaches. The cross-over design of the preferred embodiment shown in  FIG. 8  further reduces the size of the filter during retrieval. The filter has the clot capture efficiency of a double-basket filter. 
         [0032]    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 end rings may be tubular or cut into a serpentine pattern to allow the end rings to expandable to a larger diameter and subsequently compressible to a smaller diameter. This feature allows for very low profile filters when in the compressed state—an obvious advantage for insertion and removal. Of course, the filter may be tube-based or wire based or a combination.