Abstract:
A basket for an embolic protection filtering device to be deployed within a body lumen for capturing embolic debris is disclosed. In one embodiment, a strut pattern forming the basket includes V-shaped struts having an internal radius at the apex with a kerf on each strut arm beginning at the radius and extending toward an opposite end of the strut. The apex may have a bulbous shape. In another embodiment, the strut arms of the basket include undulations. Also, the apices may be situated so that one apex is longitudinally staggered from an adjacent apex. The combination of features enables the basket to be crimped to a small profile while distributing stress away from the apices of the V&#39;s in the strut pattern.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to a device that can be used during an interventional procedure in a stenosed or occluded region of a blood vessel to capture embolic material that might be created and released into the bloodstream as a result of the procedure. The present invention is particularly useful when performing balloon angioplasty, stenting, laser angioplasty, or atherectomy procedures in critical vessels of a patient&#39;s body, such as the carotid arteries, where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain. The consequences to the patient of such an event are devastating.  
           [0002]    A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the walls of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The balloon catheter is initially inserted into the patient&#39;s arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the blood vessel.  
           [0003]    Another procedure is laser angioplasty which uses a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which a rotating cutting blade shaves the deposited plaque from the arterial wall. A vacuum catheter may be used to capture the shaved plaque or thrombus from the blood stream during this procedure.  
           [0004]    In another widely practiced procedure, the stenosis can be treated by placing a device known as a stent into the stenosed region to hold open and sometimes expand the diseased segment of blood vessel or other arterial lumen. Stents are particularly useful in the treatment or repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removal by atherectomy or other means. A stent is usually delivered in a compressed condition to the target site where it is deployed in an expanded condition to support the vessel and to help maintain patency of the lumen.  
           [0005]    Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter that expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or superelastic nickel-titanum (NiTi) alloys, that self-expands from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. The self-expansion of a NiTi stent is triggered either through thermally induced shape memory effect or by the stent&#39;s own superelastic properties.  
           [0006]    The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream which can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque, which become embolic debris that travel downstream and lodge somewhere in the patient&#39;s vascular system. While not a frequent occurrence, pieces of plaque can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often the particles are not fully vaporized and enter the bloodstream. Likewise, emboli created during an atherectomy procedure may enter the bloodstream.  
           [0007]    When any of the above-described procedures are performed in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although carotid percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.  
           [0008]    Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following treatment using any one of the above-identified procedures. One approach that has been attempted is cutting the debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient&#39;s vasculature. Yet it is often difficult to control the size of the fragments that are formed, and the risk of vessel occlusion still exists.  
           [0009]    Other techniques that have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source that provides temporary suction to remove embolic debris from the bloodstream. On the other hand, complications exist with such systems because the vacuum catheter may not remove all of the embolic material from the bloodstream, and a more powerful suction could cause problems to the patient&#39;s vasculature.  
           [0010]    Still other techniques that have had success include the placement of a filter assembly downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. The filter assembly is typically attached to the distal end of an elongated shaft or guide wire and is delivered to the deployment site via a delivery catheter. Such filters have proven successful in capturing embolic debris released into the bloodstream during treatment. Nevertheless, some filter assembly designs are difficult and/or time consuming to manufacture.  
           [0011]    Some existing embolic protection filters include a filter membrane and a basket or cage that supports the filter membrane. The basket can be fabricated from a longitudinal, small diameter hypotube by cutting a particular pattern into the hypotube thus forming the struts, ribs, or framework of the basket. The hypotube can be set to a particular expanded size using successive heat treatments. The heat treatments also relieve stress that can build up in the strut pattern particularly at locations where two or more struts or ribs are joined. Without the heat treatments, the basket can fracture because of the buildup of stress at that joint or at other key areas. Unfortunately, the successive heat treatments add to the cost of manufacturing the baskets. Moreover, the existing baskets may still have low fatigue resistance during use even after being subjected to multiple heat treatments.  
           [0012]    What has been needed is a basket for an embolic protection device that is not prone to fracturing during manufacture or use, thereby reducing the need for heat treatment and improving fatigue resistance over conventional filter baskets. The present invention disclosed herein satisfies these and other needs.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention is directed to an expandable basket for an embolic protection device used to filter embolic debris in a body lumen. In a preferred embodiment, the basket is comprised of a cylindrical body formed by a plurality of struts wherein adjacent struts are connected together at alternating ends in a zigzag pattern; an apex disposed at each of the connected ends of the struts; an internal radius at each apex; and a kerf formed in at least one strut extending from each internal radius toward an opposite end of the strut.  
           [0014]    In one preferred embodiment, the apices at a first end of the cylindrical body are substantially longitudinally aligned, as are the apices at a second end of the cylindrical body. The invention may include optional undulating pattern of curves along a length of the struts to increase the flexibility of the struts. Another embodiment includes apices having a bulbous shape. The flattened bulbous shape preferably contours into the body of the struts. Also, in an alternative embodiment, adjacent apices are staggered longitudinally to permit the struts to fit together more compactly when the basket is in a compressed state.  
           [0015]    In other alternative embodiments, the apices with a bulbous shape do not include the kerf adjacent the internal radii in the apices, but instead include struts having a smaller, constant cross-section. Moreover, the struts extending from the apices on one side of the basket are closer together than the struts extending from the apices on the opposite side of the basket. This pattern permits the struts to fit together even more compactly when compressed.  
           [0016]    These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 a  is a side elevational view of a pattern formed into tube stock for use in the present invention basket employed in an embolic protection device.  
         [0018]    [0018]FIG. 1 b  is a plan view of the tube of FIG. 1 a  in which the tube has been unrolled and flattened into two dimensions to illustrate the strut pattern.  
         [0019]    [0019]FIG. 1 c  is a perspective view of the basket from FIGS. 1 a  and  1   b  in the expanded state.  
         [0020]    [0020]FIG. 2 is a plan view of an alternative embodiment tube for use as a basket in an embolic protection device, wherein the tube is unrolled and flattened into two dimensions revealing internal radii at the apices with respective kerfs extending from the radii.  
         [0021]    [0021]FIG. 3 is a plan view of an alternative embodiment tube unrolled and flattened to depict an undulating wave formed into the struts.  
         [0022]    [0022]FIG. 4 is a plan view of an alternative embodiment tube unrolled and flattened to depict staggered apices.  
         [0023]    [0023]FIG. 5 is a plan view of an alternative embodiment tube unrolled and flattened to depict another strut pattern having more pronounced kerfs formed in the struts. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The present invention is directed to a novel basket for use in an embolic protection device, wherein the basket includes structure that decreases stress concentrations in critical areas, and has a strut pattern that enables tighter compaction of the struts when the basket is in a compressed state. Turning now to the drawings, in which like reference numerals represent like or corresponding elements in the drawings, FIGS. 1 a - 1   c  illustrate a preferred embodiment basket  20  used in an embolic protection device (not shown).  
         [0025]    In general, an embolic protection device filters embolic debris inside a body lumen. The embolic protection device is often used in the carotid artery during a stenting procedure in which the filter part of the device is deployed distal of the stent to capture friable embolic debris that might have been generated. Without such a filtering mechanism, the free floating embolic debris might cause a stroke in the patient during the procedure. After the procedure, the filter is collapsed to collect the debris, withdrawn into a recovery catheter, and removed from the patient&#39;s body.  
         [0026]    [0026]FIG. 1 a  is a side elevational view of a preferred embodiment basket  20  in a compressed state. The basket  20  includes expandable struts  22  and strut arms  24  possessing spring-like or self-expanding properties and can move from a compressed or collapsed position as shown in FIG. 1 a  to an expanded or deployed position as shown in FIG. 1 c . In FIG. 1 c , the basket  20  includes a body composed of an elongated cylindrical component  25  having a first end  26  and a second end  27 , a first truncated cone  28  that extends from the first end  26  of the cylindrical component  25 , and a second truncated cone  30  that extends from the second end of the cylindrical component. The first truncated cone  28  terminates at a first hollow, cylindrical guide wire collar  32 . Likewise, the second truncated cone  30  terminates at a second hollow, cylindrical guide wire collar  34 .  
         [0027]    Starting from the first collar  32 , the expanded basket  20  includes a plurality of individual arms  24  that taper upward to form the first truncated cone  28  of the basket  20 . The arms  24  merge with struts  22  that extend longitudinally to form the elongated, straight, center cylindrical component  25  of the basket  20 . Individual arms  24  extend from the struts  22  and taper downward forming the second truncated cone  30  of the basket  20 . The arms  24  of the second truncated cone  30  terminate at the second collar  34 .  
         [0028]    In a preferred embodiment, the basket  20  is manufactured in the unexpanded state from a small diameter hypotube  36 , shown in FIG. 1 a . The stock tubing used to make the basket  20  may be made of any biocompatible material, such as highly elastic stainless steel, a shape memory alloy such as nitinol, or the like. Of the shape memory or superelastic alloys, nitinol in the preferable range of 55% nickel-45% titanium is suitable. Typically, the preferred size tubing for making the present invention basket  20  in the compressed state has an outer diameter on the order of about 0.020-0.040 inch, with a wall thickness of about 0.003-0.006 inch. Of course, tubing size varies depending upon the application.  
         [0029]    The basket  20  may be machined from seamless tubing. Alternatively, the tubing for the basket  20  may be formed by rolling flat, sheet stock into a tube where the seam is then welded. Rolled sheet stock which has been drawn through a circular die can also be used for the tubing.  
         [0030]    The basket  20  has a strut pattern or framework that may be fashioned by several methods including electrical discharge machining (EDM) or chemical etching. A preferred method is to laser cut the hypotube  36 . In this procedure, a computer controlled laser cuts away portions of the hypotube  36  following a pre-programmed template to form the desired pattern for the struts  22  and arms  24 . Methods and equipment for laser machining small diameter tubing may be found in U.S. Pat. Nos. 5,759,192 and 5,780,807 to Saunders, whose contents are incorporated herein by reference.  
         [0031]    After the strut pattern has been formed into the stock tubing, the basket  20  is deformed into expanded configurations. One method of expanding the basket  20  is by mechanically stretching it over a mandrel (not shown). The mandrel may incorporate pins to maintain the desired curvature of the struts  22  and arms  24 . Because the preferred material is nitinol, once the desired expanded shape is set on the mandrel, the basket  20  is annealed at or above the martensite deformation temperature (M d ) of the material. This heat sets the new expanded shape into the basket  20 . Annealing can be accomplished by heating the basket  20  within a variety of media such as air, molten salt, inert gas, or vacuum. Annealing at 500-550° C. is preferred for nickel—titanium alloys. After heat setting, the basket  20  is cleaned again. This process of deforming, annealing, and cleaning can be repeated until the desired expanded configuration is obtained. Naturally, the cost of producing the basket increases with each repetition of the process.  
         [0032]    In an alternative embodiment, a basket may be formed from a tube (not shown) with a diameter that approximates the basket&#39;s size in the expanded configuration. In this configuration, the struts and arms are cut into the tube as they appear in the expanded configuration. This method eliminates the need to stretch and anneal the basket to achieve the expanded configuration. The basket may also be formed from a tube that is larger than the hypotube of FIG. 1 a , but not as large as the expanded configuration. In this third configuration, the tube must still be expanded, but the tube does not require as many expansion increments as the basket made from the hypotube. The reduction or elimination of the expansion step reduces the time and cost of manufacturing the basket.  
         [0033]    Referring again to FIG. 1 c , the expanded basket  20  can be rotatably secured to a shaft member, such as a guide wire (not shown). The basket  20  is slidably mounted onto the guide wire by threading the guide wire into the first  32  and second  34  collars. The expandable basket  20  is mounted between a tapered fitting (not shown) located proximal to the first collar and a band (not shown) located distal to the second collar  34 . This particular construction allows the expandable basket  20  to optionally rotate freely about the guide wire while allowing the basket to move longitudinally along the guide wire between the tapered fitting and the band. The above example is merely illustrative of one method of attaching the basket  20  to the guide wire. Other ways of attaching the basket  20  to the guide wire known in the art can be employed with the present invention.  
         [0034]    By rotatably mounting the basket  20  to the guide wire in the manner described, the basket lengthens longitudinally with the second collar  34  sliding along the guide wire when the basket  20  is compressed for insertion into a delivery sheath (not shown). Likewise, the basket  20  contracts longitudinally while it self-expands radially upon release from the delivery sheath for deployment within the body lumen (not shown). An advantage of rotatably mounting the basket  20  on the guide wire is that the basket remains stationary if the guide wire is rotated at its proximal end after the basket has been deployed within the patient&#39;s vasculature. If the basket  20  were to rotate after deployment, the seal of the filter against the wall of the body vessel might be disturbed and possibly allow unfiltered blood to bypass the filter. Additionally, rotation of the basket  20  within a body vessel could cause trauma to the wall of the vessel.  
         [0035]    Referring again to FIGS. 1 a - 1   c , a strut pattern  44  is shown formed into the tube. Specifically, FIG. 1 b  is a plan view of the strut pattern  44  unrolled and flattened into two dimensions. The strut pattern  44  includes a plurality of struts  22  in the central cylindrical component  25  of the basket  20 . The struts  22  are created by cutting slits  48  into the tube by the earlier described methods. The slits  48  alternate circumferentially with one slit starting from an opening  50  to the left of the first end  26  of the cylindrical component  25 , thereby creating an open end  52 , and extending longitudinally to a position prior to an opening  50  to the right of the second end  27  of the cylindrical component  25 , thereby creating a closed end  54 . The adjacent slit  48  on the circumference starts from an opening  50  to the right and extends longitudinally to a position prior to an opening  50  on the left. In this fashion, adjacent struts  22  are connected to each other at alternating ends.  
         [0036]    When the tube expands (see FIG. 1 c ), the struts  22  formed by the slits open up and create a zigzag pattern  56  with apices  58  forming in the closed ends  54 . Further, the apices  58  at the first end  26  of the cylindrical component  25  are optionally longitudinally aligned, as are the apices at the second end  27  of the cylindrical component. Between the openings  50  to the right and left sides of the struts  22  are the arms  24  that attach to the struts at the apices  58 . The arms  24  extend longitudinally from the struts  22  to the collar  32 ,  34  at either end of the basket  20 . The collars  32 ,  34  are portions of the tube that have not been cut longitudinally and are, therefore, not expandable. Alternatively, the collars  32 ,  34  can be separate from the basket  20  and the ends of the arms  24  can be coupled to the collars using bonding techniques that are known in the art, such as welding, brazing, and adhesive bonding.  
         [0037]    With the slits  48  embodying substantially straight cuts, the expanded struts  22  form V&#39;s. Each V has an amplitude and a vertex, the latter coinciding with what has been identified as an apex  58 . As seen in FIG. 1 c , the apices  58  have small internal radii  60  at the internal portions of the closed ends  54 . During expansion of the basket  20 , the small internal radii  60  oftentimes experience a high concentration of stress that exceeds the ultimate stress of the material. Therefore, in order to expand the basket  20  without fracturing the struts  22  at the apices  58 , the basket  20  is expanded in increments with each expansion increment followed by heat treatment to relieve the stress at the apices.  
         [0038]    One approach to reducing the amount of stress in the internal radii  60  of the closed ends  54  of the struts  22  is to increase the size of the internal radii, thereby reducing the stress concentration factor. For example, FIG. 2 is a plan view of a strut pattern  62  flattened into two dimensions. This exemplary embodiment strut pattern  62  has closed ends or apices  64  of the struts  66  that feature enlarged internal radii  68 . In addition, an optional kerf  70  extends from each enlarged internal radius  68  a distance towards the open end  72  of the slit  74 . The kerf  70  further expands the radius, thereby reducing stress concentrations during expansion of the basket  76 . By reducing the amount of stress in the basket  76 , the number of incremental expansions and heat treatments can be reduced, thereby reducing the manufacturing cost of the baskets. Another benefit of reducing the amount of stress in the basket  76  is improved fatigue resistance. As the stress experienced by the basket  76  decreases, the number of cycles the basket can withstand prior to failure increases.  
         [0039]    In addition to the enlarged internal radii  68  and kerfs  70  illustrated in FIG. 2, the stress within the internal radii can be further reduced, as shown in FIG. 3, by configuring the struts  78  with an undulating wave pattern of curves  80  along a length of the struts. The curves  80  create preferential bending points through a length of the struts  78 , thereby effectively distributing the stress along the length of the struts rather than concentrating the stress at the internal radii where fractures typically occur. For example, when the strut pattern  62  of FIG. 2 is expanded, all of the displacement occurs at the internal radii  68 . However, the struts  78  of FIG. 3 distribute this displacement among the various radii of the curves  80  within the wave pattern. Therefore, at any one curve  80  in FIG. 3, the strain is less than the strain experienced by the radius  68  of FIG. 2. Since stress and strain are linearly related, decreasing the strain in the radii of the curves  80  of FIG. 3 decreases the stress. Further, the undulating pattern of curves  80  reduces the amount of stress at any point along the length of the struts  78 .  
         [0040]    As seen in FIG. 4, another approach to relieving the stress in the internal radii  82 ,  84  of the apices  86 ,  88  is to longitudinally stagger or alternate the location of the apices on adjacent struts  90  of the basket  92 . That is, one apex  86  is a first distance  94  from the collar  96  and the adjacent apex  88  on the circumference of the basket  92  is a second, farther distance  98  from the collar, with the distance from the collar to adjacent apices alternating between the first distance and the second distance. Another way to look at it is that the location of the apex  86  is staggered in the longitudinal direction relative to an adjacent apex  86 . With staggered apices, there is more room in the same area of the strut pattern so that each apex  86  can have a larger radius, thereby reducing stress buildup.  
         [0041]    For example, the apices  86 ,  88  in FIG. 4 are configured with a preferably flattened, bulbous shape having a radius larger than the apices  64  that are longitudinally aligned as in FIG. 2. In addition, the struts  90  are fashioned such that the apices  88  at the second distance  98  have their largest width at the same distance from the collar  96  as the smallest width of the apices  86  at the first distance  94 . With the struts  90  including kerfs of removed material and the flattened bulbous shape of the apices  86 , the end result is that the struts  90  fit together in a highly compact arrangement while in the compressed state, yet the stress at the key points is reduced during expansion.  
         [0042]    [0042]FIG. 5 depicts another alternative embodiment basket  100  with apices  102 ,  104  having a flattened, bulbous shape. As with the basket  92  shown in FIG. 4, this alternative embodiment basket  100  includes apices  102 ,  104  that are longitudinally staggered. In addition, the apices  102 ,  104  shown in FIG. 5 curve inward, almost completing a circle, and contour into the length of the struts  106 .  
         [0043]    In this embodiment, the kerfs of the earlier described baskets are omitted. Rather, the cross sections of the struts  106  are reduced throughout. Further, as cut from a tube, the struts  106  extending from the apices  102  on the first end  108  of the cylindrical component  110  are closer together than the struts  106  extending from the apices  104  on the second end  112  of the cylindrical component.  
         [0044]    The apices  102 ,  104  are configured with internal radii  114 ,  116  that are about the same size as those on the apices of baskets having the apices longitudinally aligned, as depicted in FIGS. 2 and 3. The flattened bulbous shape of the apices  102 ,  104  increases the internal radii  114 ,  116 , thereby reducing the amount of stress within the internal radii. Also, the strut pattern of this basket  100  configuration enables the basket to be more highly compressed, thus allowing the basket to be easier to deliver within a patient.  
         [0045]    In view of the foregoing, it is apparent that the systems of the present invention substantially enhance the efficiency of producing baskets for supporting embolic protection filters. Further modifications and improvements may additionally be made to the system disclosed herein without departing from the scope of the present invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.