Abstract:
The present invention relates to 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 performance, including deployment, filtration and position stability at the desired site, as well as retrievability. The filter may preferably have a hook structure that provides multiple retrieval surfaces, or may be provided with anchors for removably retaining the filter in position. A filter may be designed with one end being customized for retrieval and the other end being customized for position retention, in which case a cartridge may be provided to ensure proper orientation of the filter during delivery.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application is a continuation-in-part of Ser. No. 10/285,218, entitled “Vascular Filter with Improved Anchor or Other Position Retention,” filed Oct. 31, 2002. 

   BACKGROUND AND SUMMARY OF THE INVENTION 
   1. Technical Background 
   The present invention relates to a medical filter which can be placed inside a blood vessel or other body passage for the purpose of intercepting thrombus or particles, which may be optionally retrieved at a later time. 
   2. Discussion 
   Some basic types of medical filters are generally known, wherein a single filter element, mesh or member extends across the direction of flow inside a blood vessel. Several features are desirable for medical filters, including non-surgical or percutaneous delivery of the filter to a desired site, and expansion from a preferably small initial size to an expanded working size that matches the vascular anatomy at the desired site. Also, a medical filter should of course preferably capture a sufficient percentage of thrombus, while allowing blood to flow freely through the filter. 
   Another desirable feature is a capability to remain in the desired position for treatment through a period of time, and also to offer the physician the option during that time of leaving the filter in place permanently, or retrieving the filter when no longer needed. 
   In addition, a medical filter should preferably have a design whereby the filter is stable in the vessel, such that the filter has little or no tendency to “tilt” and may become less effective in capturing thrombus. Some medical filters may be used in the vena cava, and may be described in such event as a “vena cava filter.” 
   Prior medical filters may consist of a network of interconnected ribs, which extend substantially in a radial direction in relation to the blood vessel. Unfortunately, an entire filter may shift position if one of the ribs were to break. In addition, the free ends of the ribs, which may be positioned under a certain pressure against the internal wall of the blood vessel, may cause trauma to the vessel wall, or may become embedded within. 
   Another possible design is essentially a screen placed across a transverse dimension of a vessel. Again, it is important to take measures to resist “tilting” by this screen type of filter. 
   A disadvantage of some known medical filters may be a possibility of shifting position or tilting inside the blood vessel, even when the filter maintains its proper shape, if a prior filter may have been incorrectly placed in a blood vessel which is too wide. In such an event, a medical filter may not grab sufficient hold on the internal wall of the blood vessel. 
   A medical filter may be delivered through a catheter in a compressed shape, where it tends to resiliently expand within the blood vessel. The medical filter may tend to trap thrombus or particles, and resist their movement further downstream. The filter may include, in a position of use, an outer shape corresponding to the internal diameter of the blood vessel transverse to the longitudinal direction hereof. 
   A medical filter which may also be implanted permanently or temporarily. It is preferable to implant the filter initially without deciding at that time whether the filter will eventually be retrieved or is to remain permanently. It is also desirable that if the filter is retrieved, then it should be retrieved as easily as possible. 
   To help in successful retrieval, a desirable factor is to avoid endothelialization or in-growth of the vessel wall around the structural members of the filter. 
   On a retrievable filter, it is also desirable to provide releasable temporary position stabilizers, to resist a possibility of tilting and to enhance position retention. 
   Some medical filters provide anchors or small barbs, which extend at various angles in radial directions outward from the ribs. One successful design which is sufficient for a variety of applications is shown in the commonly owned U.S. Pat. No. 6,443,972, entitled “Vascular Filter” which issued to at least one of the co-inventors of the present invention on Sep. 3, 2002. This patent shows many desirable features for filters, including a longitudinally stable central body section, and two filter sections providing multiple filtering action. Other advantageous features are that it is preferably made of a single piece of resilient material, and can be implanted through a catheter without requiring surgery. 
   A filter may be provided with barbs or anchors for increasing position retention. The barbs tend to gently hold the filter in place inside the blood vessel, and so it is of course desirable to avoid endothelialization of the filter components, to facilitate its retrieval. 
   Also, medical filters of the present invention that are retrievable, rather than permanent filters, may provide an additional advantage. When a medical filter is retrieved from a blood vessel, the entire filter is resiliently compressed to a relatively small diameter, for extraction through a catheter. 
   The filter may preferably have a hook structure at one or both ends, of a design that preferably provides multiple hook surfaces for increasing ease of retrieval. 
   A filter according to the present invention may also preferably have one or more small barbs or anchors. An additional design is to provide a filter with a hook structure at one end, and cooperating barbs for holding the filter in position, that are arranged to pull out gently if the filter is retrieved in a retrieval direction by pulling on the hook structure with a retrieval snare or other retrieval device. 
   With a medical filter according to the present invention, a tubular section may tend to resiliently exert slight pressure along a large section of contact area on the wall of the blood vessel or other body passage, which tends to hold itself in place. The medical filter will consequently tend not to shift position. 
   The term “tubular” is used in its broadest sense, to encompass any structure arranged at a radial distance around a longitudinal axis. Accordingly, tubular includes any structure that (i) is cylindrical or not, such as for example an elliptical or polygonal cross-section, or any other regular or irregular cross-section; (ii) has a different or changing cross-section along its length; (iii) is arranged around a straight, curving, bent or discontinuous longitudinal axis; (iv) has an imperforate surface, or a periodic or other perforate, irregular or gapped surface or cross-section; (v) is spaced uniformly or irregularly, including being spaced varying radial distances from the longitudinal axis; (vi) has any desired combination of length or cross-sectional size. 
   In addition, the medical filter according to the present invention tends not to rotate transversely or tilt over, which is another advantage of the present invention. In a possible embodiment, a medical filter according to the present invention may preferably be formed out of one single piece, which provides advantages including simplicity of manufacture. 
   In a preferred embodiment, a medical filter according to the present invention includes a first and second filter section, arranged on either side of a central body section. The body section and the filter sections thus enclose a space. Due to the elongated shape of the medical filter according to the present invention, and the arranging of the first and second section on either side of the body member, the present filter has an enhanced filtering effect. In other words, two filtering structures have been created for intercepting thrombus, particulates or other matter moving inside the blood vessel or other body passage. 
   Another possible embodiment of the filter according to the present invention is that, when seen in an axial or longitudinal direction, the filter sections have the shape of a regular polygon, and provide several smaller filtering “cells.” The purpose of these filtering cells is to intercept thrombus moving inside a blood vessel, and the smaller filtering cells tend to capture more thrombus. 
   The filter sections, as arranged according to an embodiment described above on either side of the tubular body section, may be identical in shape, thereby enhancing the simplicity of the medical filter according to the present invention. 
   Another possible benefit of the present invention relates to endothelialization, which is the healing of the vessel inner surface by endothelial cells. It is desirable not to damage these endothelial cells when removing a retrievable medical filter, and the improved designs of the present invention tend to minimize any impact during retrieval. 
   Some medical filters may have been made of a braiding of wire-like elements, or a tubular element also having a series of cuts at places corresponding to the positions of passages. It is thus possible to build various medical filters according to the present invention, by various techniques and of various materials to obtain the ultimate shape and desired design. Possible junctions of filter components may be formed by melting or welding free ends together, or by employing such a cutting pattern that the basic shape of the medical filter according to the present invention is obtained. 
   It should be noted that the present invention also relates to methods for using implantable filters as described herein. 
   These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. The invention will be explained in greater detail below with reference to the attached drawings of a number of examples of embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side elevation view of a filter arranged according to the principles of the present invention, in an expanded shape; 
       FIG. 2  illustrates an end elevational view along a longitudinal axis of a filter according to the principles of the present invention, in an expanded configuration; 
       FIGS. 3 and 4  show partial elevation views of a hook structure of a filter according to the principles of the present invention; 
       FIGS. 5–8  show partial views of shoulder portions of a medical filter, according to the principles of an embodiment of the present invention; 
       FIG. 9  is a diagrammatic view of a filter in an initial compressed shape and an expanded deployed shape; 
       FIGS. 10–11  and  20 – 22  show accessory devices that may be used to deliver implantable filters of the present invention; 
       FIGS. 12–13  show side elevational views of a storage and insertion cartridge for a medical filter; 
       FIGS. 14–19  show diagrammatic views of methods for delivering and deploying a filter of the present invention; and 
       FIGS. 23–24  show cross-sectional views of a medical filter according to the present invention, alone and implanted in a body passage of a patient. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments of the present invention is merely illustrative in nature, and as such it does not 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. 
   A medical filter according to the present invention is illustrated in  FIGS. 1–8 . The filter  10  is preferably made of a resilient material, and tends to expand from an initial compressed shape to an expanded shape, as depicted diagrammatically in  FIG. 9 . 
   In the expanded shape, the filter  10  preferably has a series of longitudinal ribs  12 , aligned essentially parallel with a longitudinal axis of the filter  10 . A plurality of members preferably define a first and second filter section  14  and  16 , arranged near a retrieval end of the filter and an insertion end, respectively. A pair of central collars  18  and  20  are also preferably positioned at the retrieval end and the insertion end, respectively. A hook structure  22  is attached to the retrieval collar  18 . 
   In addition, a series of apertures  24  and a corresponding series of anchoring barbs  26  are preferably positioned at shoulders or transitions between a central body section  15  defined by the longitudinal ribs  12  and the filter sections  14  and  16 , respectively. In other words, the apertures  24  are located between the ribs  12  and the filter section  14  at the retrieval end, and the barbs  26  are located between the ribs  12  and the filter section  16  at the insertion end of the filter  10 . 
   The filter  10  is preferably delivered to a desired site for treatment by a delivery catheter  28 , which preferably defines a lumen  30  extending between a proximal hub  32  having a hemostatic valve (not shown) and a distal lumen opening  34 . The proximal hub  32  also preferably has a flush lumen tube  36  and a stopcock  38 , which may be used for various therapeutic purposes, including flushing the lumen  30  of the delivery catheter  28 , injecting radiopaque contrast fluid for viewing on an x-ray video screen, or delivering medications. 
   The filter  10  is preferably initially packaged in a compressed state in a filter cartridge  40 , shown in  FIGS. 12 and 13 . The cartridge  40  defines a lumen  42 , in which the compressed filter is stored. If the filter  10  is to be used in a blood vessel, the physician should preferably be able to easily determine which end of the cartridge  40 , and thus which end of the filter  10 , should be inserted first. The filter  10  can accordingly be correctly arranged in the body passage or blood vessel  72 , as shown in  FIG. 24 . The cartridge  40  shown in  FIGS. 12 and 14  also preferably has a femoral jack  44  and a jugular jack  46 , which preferably have different shapes, to correspond with matching femoral and jugular access delivery catheter systems, respectively. Such different shapes may for example include, when viewed from an end of the cartridge  40 , a circle, a square or a triangle. The cartridge also preferably has femoral arrows  48  with a label (not shown) indicating that the femoral jack  44  is to be used for inserting the filter  10  from a femoral access direction, as well as jugular arrows  50  with a label (not shown) indicating that the jugular jack  46  is to be used for inserting the filter  10  from a jugular access direction. 
   The hook structure  22  of filter  10  may have a T-shape, as shown in  FIGS. 3 and 4 , with twin hooks. It is possible that this twin hook structure  22  may improve the ease of retrieving the filter  10 . 
   The barbs or anchors  26  extend in a longitudinal direction, and are exposed when the filter  10  is in an expanded shape. As shown in  FIGS. 1 ,  5  and  9 , the anchors  26  and the second filter section  16  define an acute angle. They may be formed as shown in  FIGS. 5 and 6 , in which a series of cuts in the ribs  12  both shape the anchor  26  and define an aperture for the anchor  26  when the filter is in a compressed shape. 
   The apertures  24  may tend to balance stresses in the filter. In other words, anchors  26  may be formed by cutting them out of the ribs, which will tend to bend and define the center section  15  and the filter section  16 . Similarly, the presence of apertures  24  may tend to balance stresses in the ribs, causing them to bend in a complementary manner and define the center section  15  and the filter section  14 . 
   In use, delivery catheter  28  is inserted along a body passage in a patient until distal end  34  is near a desired site for treatment. After filter  10  is disposed within lumen  30  of catheter  28 , a push wire  52  may be used to eject the filter  10  from the distal tip  34  of the catheter  28 . Push wire  52  shown in  FIGS. 10 and 11  has a proximal hub  54 . and a distal end  56 . Filter  10  is introduced into the body passage, where the medical filter  10  will resiliently expand after being released from the catheter  28 , under the influence of expansive forces inherent to the material of which the medical filter has been made, into the illustrated shape. 
   Of course, several methods are possible for placing the filter inside lumen  30  of the catheter  28 . The filter may simply be placed inside the lumen  30  distal end  34 , providing a relatively short distance the filter  10  must be pushed before exiting the catheter  28 . 
   Another possible method for inserting filter  10  at the desired site is to insert it into the lumen  30  proximal end, and then push the filter  10  with a push wire  52  along the entire length of the catheter  28 , after the catheter, after the catheter distal end has been advanced to the desired position for treatment. 
   Another possible aspect is to provide positive feedback on which the end of the filter  10  is inserted first into lumen  30 . In other words, it may be desirable to insert one end of the filter into the catheter first, for example when approaching from a femoral access point, and the other end of the first being inserted first at a different access point, for example when approaching a jugular access point. The cartridge  40  shown in  FIGS. 12 and 13  may facilitate arranging the filter  10 , including a first series of arrows  48  having a first label or indicator such as “Femoral”, and a second series of arrows  50  having a second label or indicator such as “Jugular”. 
   For example, with reference to  FIGS. 14–16 , if a jugular approach is selected by the physician (or any other access point where it is desirable that the filter  10  be inserted with to hook structure  22  lead in first), the physician may refer to the “Jugular” arrows  50  and insert the corresponding jugular jack  46  at one end of the cartridge  40  into the proximal hub and hemostatic valve  32  of the catheter  28 . Next, push wire  52  is advanced into to other end of the cartridge  40 , and through to lumens of the cartridge  40  and to catheter  28  until a marker  58  reaches the hemostatic valve, This marker  58  may be provided at a position such that to push wire distal end will have positioned the filter  10  to a point where it has reached the distal end of the catheter  28 . At this arrangement, the physician may re-position the assembly to refine the location of the filter  10  just before deploying the filter. 
   As another example, the physician may choose a femoral access point (or any other access point where the physician desires to insert the filter  10  with the collar  20  end first). In this kind of situation, the physician may choose a catheter  28  having a length suitable for such desired site for treatment, as shown in  FIGS. 17-19 . 
   Accordingly, the physician would in such a case refer to the “Femoral” arrows  48 , and insert the corresponding femoral jack  44  on the cartridge  40  into the proximal hub  32 . The push wire  52  is used to advance and deploy the filter  10  as described above. 
   Optional devices that may be used, in particular for example before the catheter  28  is inserted and advanced to the desired site for treatment, are a guidewire  68  and a complementary introducer  70  as shown in  FIG. 22 . The dilator  60  shown in  FIG. 20  has a proximal hub  62  and spiral sideholes  66 , flanked by markers  64 . Another optional device that may be used, in particular when the catheter  28  is inserted and advanced to the desired site for treatment, is a dilator  60 . The dilator  60  shown in  FIG. 20  has a proximal hub  62  and spiral sideholes  66 , flanked by markers  64 . 
   Medical filters according to the present invention may be made of any suitable material using a variety of methods. One material having the desired characteristics of strength, resilience, flexibility, biocompatibility and endurance is nitinol. Other materials having the desired characteristics may be used, such as stainless steel. Likewise, the manufacturing methods may include providing a tube, and then cutting a pattern into the tube to enable expansion into the desired shape. Various other methods are of course possible, including forming the filter of discrete members and then joining or connecting the members. 
   In addition to the nitinol mentioned so far, many other materials may also be used for manufacturing a medical filter according to the present invention. By way of alternative, various metals may for instance be used, in which case it is essential that the medical filter assumes the intended shape hereof after having been ejected from the catheter for the purpose of introduction hereof. The medical filter, during introduction, is of course kept in a compressed state, by the catheter. To this end, a configuration may be used decompressing the filter metal due to the elastic properties hereof. 
   In the axial view, the filter sections on either side of the ribs of the medical filters according to the present invention described above display diamond or polygon shapes. It is also possible to suffice with medical filters of which the filter sections display in axial view a star shape, or any other suitable shape, as long as they intercept blood clots or thrombus successfully. An advantage of this feature is that, after passing the first filter section and the tubular section or the elongated body member, a second chance at interception in the form of an additional filter section has been provided. Also, other shapes of the filter sections in axial view are possible, which shapes will occur to those skilled in the field after reading the present description. The shapes of the filter sections in axial view need not be symmetrical, and may have in principle any suitable appearance. 
   It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion describes merely exemplary embodiments illustrating the principles of the present invention, the scope of which is recited in the following claims. Those skilled in the art will readily recognize from the description, claims, and drawings that numerous changes and modifications can be made without departing from the spirit and scope of the invention.