Abstract:
The invention provides an embolic filter, a support structure therefor, and methods for preparing said filter for retrieval.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to embolic filters, support structures therefor, and methods for preparing said filters for retrieval. 
     BACKGROUND 
     Human blood vessels often become occluded or blocked by plaque, thrombi, other deposits, or material that reduce the blood carrying capacity of the vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, and even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected. 
     Several procedures are now used to open these stenosed or occluded blood vessels in a patient caused by the deposit of plaque or other material on the walls of the blood vessels. Angioplasty, for example, is a widely known procedure wherein an inflatable balloon is introduced into the occluded region. The balloon is inflated, dilating the occlusion, and thereby increasing the intraluminal diameter. 
     Another procedure is atherectomy. During atherectomy, a catheter is inserted into a narrowed artery to remove the matter occluding or narrowing the artery, i.e., fatty material. The catheter includes a rotating blade or cutter disposed in the tip thereof. Also located at the tip are an aperture and a balloon disposed on the opposite side of the catheter tip from the aperture. As the tip is placed in close proximity to the fatty material, the balloon is inflated to force the aperture into contact with the fatty material. When the blade is rotated, portions of the fatty material are shaved off and retained within the interior lumen of the catheter. This process is repeated until a sufficient amount of fatty material is removed and substantially normal blood flow is resumed. 
     In another procedure, stenosis within arteries and other blood vessels is treated by permanently or temporarily introducing a stent into the stenosed region to open the lumen of the vessel. The stent typically includes a substantially cylindrical tube or mesh sleeve made from such materials as stainless steel or nitinol. The design of the material permits the diameter of the stent to be radially expanded, while still providing sufficient rigidity such that the stent maintains its shape once it has been enlarged to a desired size. 
     Such percutaneous interventional procedures, i.e., angioplasty, atherectomy, and stenting, can dislodge material from the vessel walls. This dislodged material can enter the bloodstream. Some existing devices and technology use a filter for capturing the dislodged material from the bloodstream. 
     SUMMARY 
     This disclosure pertains to an embolic filter and method. Such a filter can include a guide wire, a filter element and a bridle connected to a filter support structure. Displacing the bridle with respect to the filter can partially elongates the support structure in a dimension generally parallel to the guide wire and narrows the support structure in a dimension generally perpendicular to the guide wire. This allows the elongated support structure to be drawn substantially within the lumen of a sheath for removal. 
     The inclusion of a linkage between a support structure at the proximal mouth of a filter element and the guide wire or guide tube about which a filter is deployed may, when combined with a retrieval bridle, assist in effecting a smooth transition between the fully deployed state of the filter and an at least partially collapsed state suitable for retrieval. The linkage may be formed, for example, by a wire wound about the guide wire (forming a coil) at one end, and formed as one piece with, or otherwise attached to the support structure at the other end. Attachment of the coil to the guide wire, if desired, may be accomplished by ordinary means such as an adhesive, soldering, crimping, and the like. 
     The filter element can be attached to a support structure which maintains the mouth of the filter in an open, deployed configuration and which may tend to seal the mouth of the filter across the lumen of vessel in which the filter is deployed. The support structure can be a nominally circular ring of wire or polymer which may be deformed by moderate radial forces. The support structure may be an elastomeric ring including a NiTi alloy such as nitinol. 
     A bridle can be attached to the support structure at a point which generally does not coincide with the point of attachment of the linkage to the support structure. The bridle may comprise one or more wires or strings which may be manipulated from the proximal end of the guide wire to deform the support structure. The bridle is generally configured to act in cooperation with the linkage to elongate the support structure in a dimension generally parallel to the guide wire and to narrow the support structure in a dimension generally perpendicular to the guide wire. Displacing the bridle proximally at least partially tilts the support structure relative to the guide wire. Desirable deformation of the support structure may be facilitated by the inclusion of a deadeye or block having a through hole fixed to the guide wire proximal to the deployed support structure such that pulling on the bridle which passes through the hole of the deadeye tends to narrow the support structure ring into an ellipse as the support structure deforms. In some embodiments, the function of the deadeye may be provided by the mouth of a catheter or sheath into which the support structure will be drawn. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a fully deployed embolic filter slightly rotated out of the plane to more clearly show attachment of a bridle to the support structure. Details of the filter have been omitted for clarity. 
         FIGS. 2A-2F  are schematic representations of certain elements of the filter of  FIG. 1  in various stages of collapse.  FIGS. 2A ,  2 C, and  2 E are top views.  FIGS. 2B ,  2 D, and  2 F are side views. 
         FIG. 3  illustrates a variant fully deployed embolic filter slightly rotated out of the plane to more clearly show attachment of a bridle to the support structure. Details of the filter have been omitted for clarity. 
         FIGS. 4A-4F  are schematic representations of certain elements of the filter of  FIG. 3  in various stages of collapse.  FIGS. 4A ,  4 C, and  4 E are top views.  FIGS. 4B ,  4 D, and  4 F are side views. 
     
    
    
     DETAILED DESCRIPTION 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily to scale, are not intended to limit the scope of the claimed invention. The detailed description and drawings illustrate example embodiments of the claimed invention. 
     All numbers are herein assumed to be modified by the term “about.” The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include the plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The embolic filters disclosed herein can include a guide wire, or tube, and advanced through a blood vessel until they are positioned downstream of an obstruction to be treated. The filters are then deployed in various ways, such as by withdrawing a catheter or sheath in which they had been compressed. These filters include several structural elements such as struts or rings which tend to bias a filter element consisting of a porous sheet or mesh in the form of a cone or basket toward expansion to completely span the lumen of the vessel to be protected. When the procedure has been completed, the filter is withdrawn by at least partially collapsing the filter and reintroducing the filter into a catheter or sheath to contain any captured emboli or other debris while the filter is withdrawn from the vessel. 
       FIG. 1 , shows a filter  10  having a generally conical filter element  30  can be disposed about a guide wire or tube  20  having proximal and distal ends (not shown). A mouth  31  of the filter element  30  is generally circular and can be shaped by a support structure  42  in the form of a flexible ring which tends to expand the filter against a vessel wall. The ring may be formed from a NiTi alloy an biased to expand when exiting a delivery sheath (not shown). As illustrated, the detailed structure of the filter membrane has been omitted to allow the linkage  70  and its relationship with the guide wire  20  and the support structure  42  to be more clearly shown. It will be appreciated that the filter element  30  is generally formed from a sheet or mesh having holes large enough to allow blood cells to pass freely through the filter while emboli and other debris will remain trapped within the filter element. In this embodiment, the filter element  30  is supported proximally by support ring  42  and distally by a collar  32  which can be fixed to the guide wire  20  or linkage  70  is pivotably attached to the support structure  42  at a first point  74  and slideably attached to the guide wire  20  at a second point  72 . 
     Bridle  62  which can include  2  wires, is also attached to the support structure  42  at points about its perimeter which can be generally symmetrically situated 90 degrees or less from the attachment point  74  of the linkage  70 . The bridle  62  may slidably pass through a deadeye  50  attached to the guide wire  20 . If the deadeye  50  is employed, it tends to cause the bridle  62  to narrow the support structure  42  as the bridle is withdrawn proximally. The bridle wires  62  may extend to the proximal end of wire  20 . 
     Filter element  30  may be formed from a continuous sheet, a pre-perforated sheet, or a woven mesh. It may be formed of any material which is sufficiently flexible and compatible with bodily fluids such as blood. Examples of suitable materials include polyurethane, polyolefin, polyester, and silicone polymers. Assembly of the combined filter element as well as other structures which make up the filter may employ materials and methods such as adhesives, sewing, solvent welding, ultrasonic welding, crimping, and the like. 
     The entire sheet from which filter element  30  is formed may be perforated. The fabrication process punches or drills holes through at least the portion of the sheet which will form filter element  30  in order to provide fluid communication between the interior of the filter and the exterior of filter element  30 . 
     As shown in  FIG. 1 , collar  32  is fixed to guide wire  20  and the linkage  70  is slideably disposed about the guide wire. Since the relative displacement between the collar  32  and the most proximal part of the support structure  42  is limited by the elasticity of filter element  30 , pulling bridle  62  proximally, tends to pull point  74 , at which linkage  70  is attached to support structure  42 , toward guide wire  20  as the second end  72  of the linkage  70  slides distally. Second end  72  can be connected to a bushing or tube  75  slidably disposed on guide wire  20 . Paired  FIGS. 2A-2B ,  2 C- 2 D, and  2 E- 2 F provide schematic views of the stages of the collapse of the support ring  42  and the attendant changes in the relative positions of the linkage  70 , guide wire  20 , and collar  32 . The filter element has been omitted for clarity.  FIGS. 2A ,  2 C, and  2 E are top views of the elements.  FIGS. 2B ,  2 D, and  2 F are side views of the elements. As the bridle is moved proximally, the support structure ring narrows and elongates while second end  72  moves distally, facilitating withdrawal of the filter into a lumen of a catheter or sheath  76 . 
       FIG. 3 , shows a filter  110  which is similar to filter  110 . In this embodiment, however, filter element  30  is supported proximally by the support structure  42  and distally by a collar  132  which is free to move along guide wire  20 . Linkage  70  is pivotably attached to the support structure at first point  74  and fixed to the guide wire  20  at a second point  72  by a collar  175  or other device. Bridle  62  is also attached to the support structure  42  at points about its perimeter which can be generally symmetrically situated 90 degrees or more from the attachment point  74  of the linkage  70  but unlike filter  10 , these points are opposite point  74 . 
     As shown in  FIG. 3 , collar  132  of filter  110  is free to move along guide wire  20  and linkage  70  is fixed to guide wire  20 . Since the relative displacement between the collar  32  and the most proximal part of support structure  42  is limited by the elasticity of the filter element  30  (not shown in  FIGS. 2A-E ), pulling the bridle  62  proximally, tends to pull first point  74 , at which linkage  70  is attached, to the support structure  42 , toward the guide wire  20  as the second end  72  of the linkage  70  pivots about the fixed point of attachment to the guide wire. Paired  FIGS. 4A-4B ,  4 C- 4 D, and  4 E- 4 F provide schematic views of the stages of the collapse of the support ring  42  and the attendant changes in the relative positions of the linkage  70 , guide wire  20 , and collar  32 . The filter element has been omitted for clarity.  FIGS. 4A ,  4 C, and  4 E are top views of the elements.  FIGS. 4B ,  4 D, and  4 F are side views of the elements. As bridle  62  is withdrawn, the support structure ring narrows and elongates facilitating withdrawal of the filter into a lumen of a catheter or sheath  76 . 
     A number of option configurations of the filter can be made. For example, the bridle can include two or more wires or strings. A bridle comprising two or more strings may optionally extend the length of the guide wire without joining the wires or strings into a single unit or the two or more wires or strings may be consolidated proximal the support structure. Placement of the point(s) of attachment of the bridle to the support structure may advantageously be varied depending on the desired manner of retrieving the filter. If the linkage is attached to the top of the support structure and is fixed to the guide wire, attaching the bridle wire or string near the bottom of the support structure will facilitate tilting and elongation of the support structure such that the bottom of the support ring enters the a retrieval catheter or sheath before the top does. The distal end of the filter element will slide along the guidewire as the support structure collapses. Additionally, attaching two bridle wires to the support structure slightly below the widest part of the support structure and passing them through a deadeye located relatively close to the open mouth of the deployed support structure will tend to partially elongate the support structure in a dimension generally parallel to the guide wire and narrow the support structure in a dimension generally perpendicular to the guide wire bottom as the support structure distorts into a more elliptical configuration as the bridle is pulled proximately. 
     Although the illustrative examples described above relate to an embodiment in which the open mouth of the filter is directed proximally with respect to the guide wire, a reversal of the filter components is also contemplated. In such an embodiment, the deadeye would be mounted distally with respect to the mouth of the filter element and the bridle would be folded back at the deadeye to lie generally along the guide wire as it passes the filter element. 
     Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are herein incorporated by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.