Abstract:
A removable vascular filter system for capture and retrieval of emboli while allowing continuous perfusion of blood during a carotid endarterectomy procedure, comprising a porous filter membrane with variable diameter holes, and a filter membrane support structure. The system may minimize the incidence of stroke, or other clinical complications that may be associated with carotid endarterectomy procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This patent application is a continuation-in-part of pending U.S. patent application Ser. No. 09/365,146, filed Jul. 30, 1999, which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    I. Field of the Invention  
           [0003]    The present invention relates to the treatment of vascular disease by carotid endarterectomy. More particularly, the present invention relates to a system that reduces macro- and micro-embolization during the carotid endarterectomy procedure.  
           [0004]    II. Discussion of the Related Art  
           [0005]    A variety of surgical and non-surgical angioplasty procedures have been developed for removing obstructions from blood vessels. Balloon angioplasty utilizes a balloon-tipped catheter, which may be inserted within a stenosed region of the blood vessel. By inflation of the balloon, the stenosed region is dilated. Stenting involves the permanent implantation of a metallic scaffold in the area of the obstruction, following balloon dilatation. The stent is often delivered on an angioplasty balloon, and is deployed when the balloon is inflated. Another alternative is the local delivery of medication via an infusion catheter. Other techniques, such as atherectomy, have also been proposed. In atherectomy, a rotating blade is used to shave plaque from an arterial wall. Surgery involves either removing the plaque from the artery or attaching a graft to the artery so as to bypass the obstructing plaque. In the carotid artery, an arteriotomy is made, and plaque removal, or endarterectomy, is routinely performed.  
           [0006]    One problem common to all of these techniques is the potential inadvertent release of portions of the plaque or thrombus, resulting in emboli, which can lodge elsewhere in the vascular system. Such emboli may be dangerous to the patient, and may cause severe impairment of the distal circulatory bed. Depending upon the vessel being treated, this may result in a stroke or myocardial infarction or limb ischemia.  
           [0007]    Vascular filters or embolism traps for implantation into the vena cava of a patient are well known, being illustrated by, for example, U.S. Pat. Nos. 4,727,873 and 4,688,533. Additionally, there is a substantial amount of medical literature describing various designs of vascular filters and reporting the results of the clinical and experimental use thereof. See, for example, the article by Eichelter &amp; Schenk entitled “Prophylaxis of Pulmonary Embolism,” Archives of Surgery, Vol. 97, August 1968, pp. 348 et seq. See, also, the article by Greenfield, et al., entitled “A New Intracaval Filter Permitting Continued Flow and Resolution of Emboli”, Surgery, Vol. 73, No. 4, pp. 599-606 (1973).  
           [0008]    Vascular filters are used, often during a postoperative period, when there is a perceived risk of a patient encountering a pulmonary embolus resulting from clots generated at the surgical site. Typically, the filter is mounted in the vena cava to catch large emboli passing from the surgical site to the lungs.  
           [0009]    The vascular filters of the prior art are usually permanently implanted in the venous system of the patient, so that even after the need for the filter has abated, the filter remains in place for the lifetime of the patient, absent surgical removal. U.S. Pat. No. 3,952,747 describes a stainless steel filtering device which is permanently implanted transvenously within the inferior vena cava. The filtering device is intended to treat recurrent pulmonary embolism. U.S. Pat. No. 4,873,978 describes a catheter device comprising a catheter body having a strainer mounted at its distal end. The strainer is shiftable between an opened configuration where it extends substantially across the blood vessel to entrap passing emboli, and a closed configuration where it retains the captured emboli during removal of the catheter. A mechanism actuable at the proximate end of the catheter body allows selective opening and closing of the strainer. Typically, the strainer is a collapsible cone having an apex attached to a wire running from the distal end to the proximate end of the catheter body.  
           [0010]    Permanent implantation may be deemed medically undesirable, but it has been done because vascular filters are implanted in patients primarily in response to potentially life threatening situations. Accordingly, the potential disadvantages of permanent implantation of a vascular filter are often accepted.  
           [0011]    Notwithstanding the usefulness of the above-described methods, a need still exists for an apparatus and method for substantially reducing the risk of embolization associated with carotid endarterectomy. In particular, it would be desirable to provide a device which could be located within the vascular system between the operative site and the brain to collect and retrieve portions of plaque and thrombus which have dislodged during the endarterectomy procedure.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides a vascular filter system which may be used to address the clinical problem of preventing embolization associated with carotid endarterectomy, which may result in a major or minor stroke, as briefly described above.  
           [0013]    An objective of the present invention is to provide a vascular filter system for reducing macro- and micro-embolization. Another objective of the present invention is to provide a vascular filter system which is readily removable from the vascular system, or elsewhere, of a patient when the filter is no longer needed. It is a further objective of the present invention to provide a vascular filter system having a configuration which does not require hooks to penetrate and grip the blood vessel walls, so that the implantation results in less blood vessel injury. It is yet a further objective of the invention to capture thrombus or emboli generated during a carotid endarterectomy procedure. It is yet a further objective of the invention to provide a filter membrane with variable-sized holes to allow distal perfusion while capturing embolic particulates.  
           [0014]    In one exemplary embodiment, the vascular filter of the present invention comprises a thin membrane attached to a guidewire and supported by fine metal spines. Attachment of the filter membrane to the guidewire allows expansion of the filter membrane with a firm fit inside the artery. The attachment also allows for collapse of the filter membrane at the end of the procedure so that it fits tightly against the guidewire and may be withdrawn through a guide catheter. In another exemplary embodiment, the filter membrane rests upon or is attached to a basket-like structure, at least one end of which is attached to the guidewire. The filter membrane has a hole size such that blood flow is not impeded when the filter membrane is expanded, but micro and macro emboli may be captured. Expansion of the filter membrane is aided by the forward flow of blood against the filter.  
           [0015]    In another aspect of the invention, a filter system is useful to capture thrombi or emboli generated during a surgical procedure such as carotid endarterectomy. The system comprises a device having inflatable proximal and distal balloons, wherein a guidewire-based collapsible filter basket extends through a lumen in the distal balloon. The balloons are inflated on either side of a stenosis in a carotid artery to maintain blood flow to the brain through the filter while the stenosis is surgically removed.  
           [0016]    An advantage of the present invention is that it provides the benefits of filtration and capture of embolic particulates, temporarily, during a surgical procedure. Another advantage of the present invention is that it provides a filter membrane with variable-sized holes to allow distal perfusion while capturing embolic particulates.  
           [0017]    Given the following enabling description of the drawings, the apparatus should become evident to a person of ordinary skill in the art.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which the reference characters refer to like parts throughout, and in which:  
         [0019]    [0019]FIG. 1 illustrates a lateral, partial cross-sectional view of one exemplary embodiment of the present invention with the filter membrane in an open position.  
         [0020]    [0020]FIG. 2 illustrates a lateral, partial cross-sectional view of the exemplary embodiment of the present invention illustrated in FIG. 1 with the sheath closed.  
         [0021]    [0021]FIG. 3 illustrates a schematic representation of a portion of a filter membrane in accordance with the present invention.  
         [0022]    [0022]FIG. 4 illustrates a lateral view of a core wire in accordance with the present invention.  
         [0023]    [0023]FIG. 5 illustrates a cross-sectional view across section line  5 - 5  of a portion of the core wire as illustrated in FIG. 4.  
         [0024]    [0024]FIG. 6 illustrates a lateral, cross-sectional view of an alternate basket structure for the exemplary embodiment illustrated in FIG. 1.  
         [0025]    [0025]FIG. 7 illustrates a lateral, partial cross-sectional view of another exemplary embodiment of the present invention.  
         [0026]    [0026]FIG. 8 illustrates a lateral, partial cross-sectional view of a further exemplary embodiment of the present invention.  
         [0027]    [0027]FIG. 9 illustrates a schematic, partial cross-sectional view of another exemplary embodiment of the present invention where the distal section of the filter basket is inverted.  
         [0028]    [0028]FIG. 10 illustrates a schematic, partial cross-sectional view of the exemplary embodiment illustrated in FIG. 9 where the filter basket is collapsed.  
         [0029]    [0029]FIG. 11 illustrates a schematic partial cross-sectional view of a filter system in situ in accordance with the present invention.  
         [0030]    [0030]FIG. 12 illustrates cross-sectional view along line  12 - 12  as illustrated in FIG. 11. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    The present invention relates to a vascular filter system for use in carotid endarterectomy, which may substantially reduce the risk of distal embolization during surgical procedures, while still allowing perfusion of distal tissue.  
         [0032]    The system comprises a thin, porous filter membrane with variable-sized openings which is capable of blocking emboli and which is attached to the distal end of a guidewire. In one exemplary embodiment of the invention, a thin, flexible, perforated membrane is supported by four or more supports that form a distally extending basket. At least one end of the basket is attached to the guidewire, and the other, slidable end may be moved to cause the membrane to open or close.  
         [0033]    The present invention may be better appreciated by reference to the drawings. FIG. 1 illustrates a lateral, cross-sectional view of a distal end of a guidewire  160  with a filter membrane  170  attached thereto. FIG. 1 shows guidewire  160  with a shapeable soft “floppy” tip  162  at its extreme distal end which provides flexibility and maneuverability to guidewire  160 . The filter membrane  170  in FIG. 1 is illustrated in an open position.  
         [0034]    Guidewire  160  comprises a core wire  164 , which extends into floppy tip  162 , and a sheath  166 . Filter membrane  170  is supported by a basket  169  comprising two or more filter basket wires  168 , having distal ends  172  and proximal ends  174 . The distal ends  172  of basket wires  168  are fixedly attached by distal radiopaque marker or crimp band  176  to core wire  164 , and the proximal ends  174  of basket wires  168  are attached to proximal radiopaque marker or crimp band  178 , which is slidable over core wire  164 , optionally with a polymeric, such as polyimide, or metallic sleeve between core wire  164  and proximal ends  174 . Preferably, proximal marker  178  is fixedly attached to core wire  164 , and distal marker  176 , with a polymeric or metallic sleeve, is slidable over core wire  164 .  
         [0035]    The flow of blood in FIG. 1 is toward the distal end of guidewire  160 . As such, the force of the flow of blood pushes on deployed filter membrane  170  and helps to maintain filter membrane  170  in the deployed position.  
         [0036]    A sheath member  180  is attached to the distal end of sheath  166 , sheath member  180  having a lumen  182  with a diameter and length sufficient to receive or slide over proximal marker  178 . Sheath  166  and sheath member  180  can be either separate pieces bonded together or a continuous, integral structure. Sheath  166  and sheath member  180  are each made from low friction polymeric material, preferably polytetrafluoroethylene, polyethylene, nylon, or polyurethane.  
         [0037]    Filter membrane  170  may comprise a number of different metallic and non-metallic permeable membranes having sufficient porosity to facilitate blood flow but having sufficiently small openings to capture emboli. Filter membrane  170  is preferably affixed at least at its distal portion  184  to core wire  164  and/or basket wire distal ends  172  and, optionally, to basket wires  168 . The remainder of filter membrane  170  may be unattached or, preferably, attached to basket wires  168 , such as by a suitable adhesive. Preferably basket wires  168  are encapsulated in membrane  170 .  
         [0038]    Basket  169  may be somewhat cylindrical in its middle with tapered, conical, proximal and distal portions. Alternately, basket  169  may be slightly spherical, optionally with a flat, cylindrical middle portion. Preferably, basket  169  is from about five to about forty mm in length and from about two to about thirty mm, or from about two to about twenty mm, in diameter at its widest.  
         [0039]    The proximal end of the sheath  180  is attached to a control handle or guidewire torquer  186 . Control handle  186  has an opening  188  for core wire  164  so that sheath  180  can move slidably over core wire  164 . For example, when sheath  180  is moved distally toward basket wires  168 , filter membrane  170  collapses. Also, there may be instances where sheath  180  will be removed proximally so that other catheters or other vascular devices can be introduced over core wire  164 . Control handle  186 , which functions as a torque device, also primarily functions to lock sheath  180  to core wire  164  during insertion.  
         [0040]    There are a number of known, commercially available guidewire torquers that may be modified to function as control handle  186 . Modification includes, but is not limited to, providing a slightly larger central lumen.  
         [0041]    In FIG. 2 sheath  166  and sheath member  180  are shown advanced distally so that basket wires  168  and filter member  170  are collapsed against core wire  164 . The distal end  192  of sheath member  180  may optionally be slightly tapered to provide a better profile for insertion.  
         [0042]    In an exemplary embodiment of the present invention, as shown in FIG. 3, filter membrane  170  comprises a polymeric material such as polyurethane or silicone elastomer that has openings or holes  190  that vary in diameter with one another. Alternately, the filter membrane may comprise fabric or non-fabric meshes, such as those used in known hemodialysis filters or heart-lung bypass machine filters. Suitable materials include polymers or physiologically acceptable metals or alloys. The openings or holes  190  may be created in the material through a laser drilling or other suitable process, or they may be naturally-occurring openings or holes in the material itself.  
         [0043]    Holes  190  of filter membrane  170 , a pattern for which can be seen in FIG. 3, are preferably only on the conical portion of filter membrane  170 . The holes  190  may be from about twenty to about three hundred microns in diameter, and may vary in diameter as compared with one another. The holes  190  may also comprise fibers attached to the circumference of the holes  190 , which can serve to increase embolic capture. The vertical row separation of holes  190  may be from about 1.2 to 1.4 times the hole diameter and the center-to-center diameter of holes  190  may be from about 1.4 to 1.6 times the hole diameter, or in an exemplary embodiment the vertical and horizontal spacing of the holes is such that the center-to-center spacing of the holes is from about 1.2 to 2.0 times the hole diameter. Preferably the open area of the holes represents from about ten to fifty percent, more preferably from about ten to forty percent of the filter surface. Alternatively, the holes may be non-uniformly spaced. The mesh should have holes of a size sufficient to block and capture any micro- and macro-emboli which may flow downstream from the site where the stenosis or other problem is being treated, but large enough such that blood flow is not substantially impeded. The mesh used in the filter device of the present invention can have a hole size of from about twenty to about three hundred microns, preferably from about fifty to about one hundred fifty microns. Moreover, the size of filter membrane  170  is such as to allow a firm fit between filter membrane  170  and an artery wall. The diameter of filter membrane  170  will be directly related to the artery being treated, with typical diameters ranging from about two millimeters to about forty millimeters, most preferably from about two millimeters to about twenty millimeters.  
         [0044]    Referring back to FIGS. 1 and 2, basket wires  168  may comprise a suitable, physiologically acceptable metal. Stainless steel or nitinol are preferred, although titanium or other metal alloys could be used.  
         [0045]    Core wire  164 , illustrated in greater detail in FIG. 4, where the proximal and middle portions  200  and  202  are substantially uniform in diameter, and then the distal portion  204  tapers to an end point  206 . In fact, distal portion  204  could taper uniformly or, more preferably, non-uniformly, as shown in FIG. 4. Typically core wire  164  is from about two hundred fifty to three hundred centimeters in length, with an initial diameter of from about 0.009 to 0.038 inches, preferably from about 0.014 to 0.018 inches. Distal section  204  is typically from about eight to ten centimeters. With a diameter that tapers from about 0.001 to about 0.005 inches, core wire  164  may optionally have a thin polymeric coating  207  for friction reduction. Preferably end point  206  is a solid, squat cylinder, as shown in FIGS. 4 and 5.  
         [0046]    Referring back to FIG. 1, floppy tip  162  preferably comprises a radiopaque helical spring  210  that is fixedly attached, e.g., by welding, brazing, or soldering, to end point  206  and, optionally, attachment point  208 . Optionally, spring coil  210  may have a polymeric or lubricious coating  212 .  
         [0047]    [0047]FIG. 6 represents an alternate design of the filter system of the present invention, where basket wires  220  are substantially helical in shape. Filter member  222  covers or encompasses the distal portion of basket wires  220 , and the proximal and distal portions of basket wires  220  are secured by proximal radiopaque marker or crimp band  224  and distal radiopaque marker or crimp band  226 , respectively. Markers  224  and  226  are fixed or slidable on core wire  228  as described above. Preferably there are from four to eight basket wires  220 , each with a rotation of from about forty-five degrees to three hundred sixty degrees.  
         [0048]    Additional exemplary embodiments of the present invention are illustrated in FIGS. 7 and 8. The schematic representation in FIG. 7 depicts a filter membrane  280  supported by strut wires  282 . The distal ends  284  of strut wires  282  are attached to the distal portion of a tubular member  286 . A movable core wire  290  extends through a lumen  292  in tubular member  286  to a distal floppy section  294 , where a helical spring coil  296  surrounds the distal portion  298  of core wire  290  and is attached to end point  300 . There is an attachment point  302  of weld or solder or other suitable material at the proximal portion of spring coil  296  where the distal portion  304  of sheath member  306  is also attached to core wire  290 . A lumen  308  of sheath member  306  is large enough so that as core wire  290  is pulled proximally, or tubular member  286  is advanced distally, the distal ends  284  of strut wires  282  move into lumen  308  and collapse filter membrane  280 .  
         [0049]    Moveable core wire  250  of the structure shown in FIG. 8 comprises a floppy tip  252  where a helical spring coil  254  encompasses the distal portion  256  of core wire  250 . A basket wire structure component of two or more basket wires  258  supports a filter membrane  260  on the distal portion  262  of the basket structure. Distal ends  264  of the basket wires  258  are encompassed by a radiopaque marker or crimp band  266  that is attached to core wire  250  and/or spring coil  254 . The proximal ends  268  of basket wires  258  are attached to the distal portion of a sheath  270  that surrounds core wire  250 . Sheath  270  moves slidably over core wire  250  so that when sheath  270  is pulled proximally into core wire  250 , filter membrane  250  collapses.  
         [0050]    In FIG. 9, a basket  320  comprising from four to eight strut wires  322  is secured by a distal fixed grommet  324  and a proximal slidable grommet  326 . Grommet  326  is slidable over core wire  328 . Filter membrane  330  is attached to or arranged upon basket  320 , with a proximal section  332  of the membrane  330  being open to flow, represented by arrows  334 . A distal portion  336  of membrane  330  forms a conical shape  340  that extends proximally. The filter may be deployed by, for example, a sheath or a tube fixed to the proximal slidable grommet  326 . This design is optimized for perfusion and emboli collection. For example, as more emboli is collected, it tends to collect in outer, non-filter areas, leaving the holes open for perfusion.  
         [0051]    Membrane  330  preferably has holes only in distal section  336 / 340 , which holes are arranged as described above. It is believed that under normal, substantially laminar flow conditions, debris or emboli  342  will tend to collect in annular recesses  344 .  
         [0052]    To close and capture emboli, as shown in FIG. 10, slidable grommet  326  is moved proximally to collapse basket  320  and membrane  330 . This may be accomplished with, for example, sheath  350  or a fixed tubular member or other apparatus that is preferably slidable over the core wire.  
         [0053]    The wires, membrane, and other materials of this exemplary embodiment are consistent with those described above.  
         [0054]    In the exemplary embodiment of the invention shown in FIG. 11, a filter system  360  comprises a proximal section  362  having a proximal balloon  364 , a distal section  366  having a distal balloon  368 , and a middle connecting section  370 . Each of proximal section  362  and distal section  366  has at least two lumens, one for inflation of a balloon and one for blood flow. See, for example, the cross section of FIG. 12, wherein distal section  366  has inflation lumen  372  and blood flow lumen  374 .  
         [0055]    Middle section  370  comprises a lumen  376  to connect the blood flow lumen of proximal section  362  and distal section  366 , as well as lumen  378  to connect to respective inflation lumens. Lumen  378  is in turn in fluid connection through inflation catheter  380  with an inflation hub  382 , which in turn can be connected to known inflation means. Inflation hub  382  may have an inflation cuff  383  to assist the operator in determining or monitoring the extent of inflation. Middle section  370  also has a port  384  for insertion or removal of a guidewire-based filter  386  with filter basket  388 . The proximal end of guidewire  390  extends proximal from port  384 .  
         [0056]    In the exemplary embodiment described above, the vascular filter system is advanced through blood flow lumen  374  of distal section  366 . It is within the scope of the present invention that distal section  366  may comprise an additional lumen through which the vascular filter system would be advanced.  
         [0057]    It is within the scope of the present invention that there may be an additional member with an inflatable balloon and lumen in fluid connection with the middle section. The additional member would have a lumen for insertion of a vascular filter through a port in the middle section. This arrangement would facilitate placing balloons and vascular filters in the internal and external carotid arteries.  
         [0058]    During a carotid endarterectomy, filter system  360  is positioned prior to the surgical procedure. First, an incision  402  would be made in the internal carotid artery  390  distal to a stenosis  392  and distal section  366  would be inserted through the incision, with distal balloon  368  in deflated condition. Next, proximal section  362  with balloon  364  deflated would be inserted into an incision  404  in the common carotid artery  394 . Then, balloons  364  and  368  would be inflated essentially simultaneously (although optionally the apparatus could be configured for separate inflation). Once the balloons are inflated, an incision  400  is made adjacent stenosis  392 . Vascular filter  386  may be inserted either with filter system  360  or later, preferably prior to incision  400 .  
         [0059]    Subsequent to this procedure, after incision  400  has been closed, balloons  364  and  368  are deflated. Then, filter basket  388  would be collapsed and withdrawn proximally through port  384 .  
         [0060]    The preceding specific exemplary embodiments are illustrative of the practice of the invention. It is to be understood, however, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the spirit of the invention or the scope of the appended claims.