Abstract:
An emboli filtration apparatus is provided comprising a guide wire having a filter element captured thereon, so that the guide wire is free to rotate or translate while the filter element remains stationary. The apparatus allows for movement and rotation of the guide wire as devices are advanced over it to treat occlusive disease, substantially without dislodging the filter element.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part application of U.S. patent application Ser. No. 09/354,897, filed Jul. 16, 1999, now U.S. Pat. No. ______.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates apparatus and methods for removing emboli from the blood stream that are generated during treatment of vascular disease wherein a blood filter has a integral strut arrangement permitting reduced delivery profile and also enabling movement of a guide wire associated with the filter without displacing the filter.  
         BACKGROUND OF THE INVENTION  
         [0003]    Atherosclerosis and other vascular occlusive diseases are becoming prevalent today in many developed countries. In such diseases, the flow areas of blood vessels become narrowed or occluded by the buildup of plaque on the walls of the vessels, leading to ischemia, and depending upon the location of the vessel, damage to the organ or limb. A number of surgical and percutaneous procedures have been developed for treating stenosis in the coronary arteries and carotid arteries, including endarterectomy, angioplasty, atherectomy and stenting.  
           [0004]    One problem frequently encountered during such procedures is that pieces of plaque {“emboli”) often are dislodged from the stenosis or the vessel wall. Such emboli may travel into the smaller diameter regions of the vasculature, blocking blood vessels and causing ischemic injury. This problem is especially severe where the emboli are permitted to travel into the coronary arteries and cerebral arteries, and can result in infarction, stroke and even death.  
           [0005]    Emboli filtration devices are known in which filter elements are deployed against the walls of a vessel distal to a stenosis. Such filters typically comprise a polymer or wire sac mounted on a distal region of a guide wire or angioplasty catheter, and permit blood to flow through the filter while trapping emboli. Once treatment of the stenosis is completed, the filter containing the captured emboli is contracted and withdrawn from the vessel.  
           [0006]    For example, U.S. Pat. No. 5,814,064 to Daniel et al. describes an emboli capturing system having a radially expandable mesh filter disposed on the distal end of a guide wire. The filter is deployed distal to a region of stenosis, and any interventional devices, such as an angioplasty balloon or stent delivery system are advanced along the guide wire. The filter is designed to capture emboli generated during treatment of the stenosis while permitting blood to flow through the filter.  
           [0007]    U.S. Pat. No. 4,723,549 to Wholey et al. describes an angioplasty catheter having a filter element disposed on its distal end. The filter is supported on a plurality of circumferential struts, and is expanded against the interior wall of a vessel, distal to a stenosis, by an inflation balloon. An angioplasty balloon is disposed on the catheter proximal of the filter for dilating the stenosis. The filter captures emboli dislodged during the dilatation procedure, and then is contracted and removed from the vessel with the angioplasty catheter.  
           [0008]    A key disadvantage of previously known emboli filtration systems, such as described in the foregoing patents, is that the filters in those devices are fixedly attached to the guide wire or angioplasty catheter, respectively. If the catheter or guide wire is rotated, bumped or moved after the filter has been deployed, there is a substantial risk that filter will become temporarily dislodged or skewed, thereby permitting emboli to escape past the filter.  
           [0009]    Moreover, movement of the deployed filter against the vessel wall also may damage the endothelium, and/or dislodge emboli distal to the filter. Such motion is especially likely to occur when other devices such as an angioplasty balloon catheter are deployed along the guide wire after the filter is deployed, as in the Daniels et al. patent.  
           [0010]    In view of these disadvantages it would be desirable to provide emboli filtration apparatus and methods having a filter element that remains stationary once deployed.  
           [0011]    It also would be desirable to provide emboli filtration apparatus and methods having a filter that may be deployed along a guide wire, but is configured so that subsequent displacements or rotation of the guide wire will not dislodge the filter.  
           [0012]    It also would be desirable to provide emboli filtration apparatus and methods that self-center a filter element within a vessel, thereby preventing skewing or cocking of the filter element.  
           [0013]    It further would be desirable to provide emboli filtration apparatus and methods that reduce the risk of emboli escaping from a filter element.  
           [0014]    It still further would be desirable to provide emboli filtration apparatus and methods that reduce the risk of trauma to vessel endothelium resulting from movement transferred to the emboli filtration apparatus.  
           [0015]    It yet further would be desirable to provide emboli filtration apparatus having a reduced delivery profile, thereby enabling the filter to use in smaller vessels and to negotiate more tortuous anatomy.  
         SUMMARY OF THE INVENTION  
         [0016]    In view of the foregoing, it is an object of this invention to provide emboli filtration apparatus and methods having a filter element that remains stationary once deployed.  
           [0017]    It is another object of the present invention to provide emboli filtration apparatus and methods having a filter that may be deployed along a guide wire, but is configured so that subsequent displacements or rotation of the guide wire will not dislodge the filter.  
           [0018]    It is also an object of this invention to provide emboli filtration apparatus and methods that self-center a filter element within a vessel, thereby preventing skewing or cocking of the filter element.  
           [0019]    It is also an object of this invention to provide emboli filtration apparatus and methods that reduce the risk of emboli escaping from a filter element.  
           [0020]    It is a further object of the present invention to provide emboli filtration apparatus and methods that reduce the risk of trauma to vessel endothelium resulting from movement transferred to the emboli filtration apparatus.  
           [0021]    It is a yet further object of the present invention to provide emboli filtration apparatus having a reduced delivery profile, thereby enabling the filter to use in smaller vessels and to negotiate more tortuous anatomy.  
           [0022]    These and other objects of the present invention are accomplished by providing emboli filtration apparatus comprising a guide wire having a filter element captured thereon, so that the guide wire is free to rotate and/or translate while the filter element remains stationary. The apparatus thus allows for movement or rotation of the guide wire as devices are advanced over it to treat a stenosis, substantially without dislodging the filter element. Accordingly, the risk of permitting emboli to escape during temporary displacement or skewing of the filter element is reduced, as well as movement-induced trauma of the vessel endothelium.  
           [0023]    In a preferred embodiment, the apparatus comprises a guide wire having a filter element captured for rotation and translation on a distal end thereof. The filter element preferably comprises a wire or polymer sac affixed to a plurality of self-expanding struts. The filter element has a contracted state, suitable for transluminal insertion disposed inside a retractable sheath, and a deployed state, wherein an outer perimeter of the filter element engages the walls of a vessel when the sheath is retracted proximally. In a more preferred embodiment, the self-expanding struts comprise portions of a unitary strut arrangement.  
           [0024]    The filter element includes a proximal capture ring having a diameter which is larger than the diameter of the guide wire, but smaller than the diameter of the distal tip of the guide wire. The capture ring allows the guide wire to move freely relative to the filter element over a limited range, so that movement or rotation of the guide wire does not cause the filter to move or to scrape against the walls of the vessel. When it is desired to retract the filter element, the guide wire is pulled proximally so that the distal tip of the guide wire engages the capture ring and pulls the filter element back into a sheath to its contracted state.  
           [0025]    Optionally, the filter element may include a cylindrical sleeve that ensures that the filter forms an adequate seal against the walls of the vessel in the deployed state, thus preventing bypass flow around the filter. The sleeve also assists in orienting the axis of the filter element parallel to the axis of the vessel. As a further option, the strut arrangement of the filter element may be deployed on a tubular member that facilitates movement of the filter and enables the use of an elongated filter sac. A retrieval catheter suitable for use with such embodiments is also provided.  
           [0026]    Methods of using the apparatus of the present invention to remove emboli during a surgical or percutaneous transluminal procedure also are provided.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    Further features of the invention, its nature and various advantages will be apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which:  
         [0028]    [0028]FIG. 1 is a side view of the components of a first embodiment of apparatus constructed in accordance with the principles of the present invention;  
         [0029]    [0029]FIGS. 2A and 2B are, respectively, a perspective view and end view of the filter element of FIG. 1;  
         [0030]    FIGS.  3 A- 3 E are side sectional views showing deployment, use and removal of the apparatus of FIG. 1 in accordance with the methods of the present invention;  
         [0031]    [0031]FIGS. 4A and 4B are, respectively, side sectional views of an alternative embodiment of the apparatus of the present invention in the deployed and contracted states;  
         [0032]    FIGS.  5 A- 5 C are, respectively, perspective and side views of an alternative embodiment of the apparatus of the present invention;  
         [0033]    [0033]FIGS. 6A and 6B are side views of a further alternative embodiment of a filter constructed in accordance with the present invention in a contracted delivery state and deployed state;  
         [0034]    [0034]FIGS. 7A and 7B are side sectional views of the filter strut component of the apparatus of FIGS. 6;  
         [0035]    FIGS.  8 A- 8 D are, respectively, side sectional and side view of the apparatus of FIGS.  6  being use in conjunction with an angioplasty balloon to treat vascular disease;  
         [0036]    [0036]FIG. 9 is a side view of a further alternative embodiment of the apparatus of the present invention in the deployed state;  
         [0037]    [0037]FIGS. 10A and 10B are side views illustrating use of a retrieval catheter suitable for use in recovering the filter element of FIG. 9;  
         [0038]    [0038]FIG. 11 is a side view showing the filter element and retrieval catheter of FIGS.  10  in condition to be withdrawn from a vessel; and  
         [0039]    [0039]FIG. 12 is a side sectional view of yet another filter element constructed in accordance with the present invention that includes a coil to accommodate lateral displacement of the filter element.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    The present invention is directed to an emboli filtration system and methods that filter out emboli generated during surgical or percutaneous interventional procedures. In accordance with the principles of the present invention, a filter element is captured on a guide wire so that the guide wire is capable of rotation or translation, without disturbing the placement of the filter element. Because the filter element is captured on the guide wire, however, the filter element is readily removed by retracting the guide wire into a sheath.  
         [0041]    Referring to FIG. 1, apparatus  10  of the present invention comprises guide wire  11 , delivery sheath  20  and filter element  30 .  
         [0042]    In accordance with the principles of the present invention, guide wire  11  includes enlarged diameter distal region  12 . Guide wire  11  may be constructed of material commonly used in guide wire construction, such as stainless steel or a high strength polymer. Distal region  12 , which acts as a stop to limit travel of filter element  30  in the distal direction, comprises a soft metal or metal alloy coil or may be formed from a flexible polymer, such as polyethylene or nylon, molded onto the distal region of the guide wire. Alternatively, guide wire  11  and distal region  12  may comprise a mechanism, such as are known in the art, for steering distal region  12  through a patient&#39;s vasculature. Illustratively, guide wire may have a diameter of 0.018 inches (0.46 mm) and the diameter of distal region  12  may be 0.022 inches (0.56 mm).  
         [0043]    Delivery sheath  20  comprises flexible catheter  21  having proximal end  22 , distal end  23 , and interior lumen  24 . Push tube  25  is disposed within lumen  24 , and includes proximal end  26 , distal end  27  and guide wire lumen  28 , to permit catheter  21  and push tube  25  to be advanced along guide wire  11 . Proximal end  26  of push tube  25  extends through proximal end  22  of catheter  21 , so that push tube  25  may be translated in the distal and proximal directions relative to catheter  21 . Catheter  21  and push tube  25  preferably comprise flexible materials such as are commonly used in catheter construction, for example, polyethylene, polyurethane or nylon. Delivery sheath  20  preferably has an outer diameter of about  4  Fr.  
         [0044]    Referring now also to FIGS. 2A and 2B, filter element  30  comprises funnel-shaped filter sac  31  coupled to a plurality of self-expanding struts  32  at proximal end  33  and soft elastomer cone  34  at distal end  35 . Struts  32  are affixed to capture ring  36 , and self-expand from a contracted state, when filter element is disposed in lumen  24  of catheter  21 , and a deployed state, when filter element is ejected from delivery sheath  20 . In the deployed state, struts  32  extend outward to urge the perimeter of sac  31  into engagement with the walls of a vessel.  
         [0045]    Struts  32  may comprise a resilient metal or metal alloy, such as stainless steel or nickel-titanium, or a resilient polymer. It is expected that at least three struts  32  spaced equidistant apart around the perimeter of sac  31  should be employed to provide adequate expansion and control of the sac, although a greater number may be used. Alternatively, struts  31  may comprise flexible strands, and expansion of sac  31  may be accomplished by adding a flexible and resilient self-expanding nickel-titanium hoop along perimeter  38  of the sac.  
         [0046]    Particulate matter, such as emboli, pass through struts  32  and are trapped against sac  31 , which permits blood to pass freely through. The size of emboli trapped by sac  31  is determined by the pore size of the sac, and preferably is about 0.0012 inches ( 30  microns). Sac  31  may comprise a polymer sleeve affixed to struts  32  or a self-expanding wire mesh constructed from a resilient metal alloy, for example, nickel-titanium.  
         [0047]    Capture ring  36  has bore  37  with an inner diameter greater than the diameter of guide wire  11 , but smaller than the diameter of distal region  12 . This allows guide wire  11  to be rotated or translated distally relative to filter element  30 , without imposing a force on the filter element that might temporarily dislodge the filter element. Accordingly, various devices, such as angioplasty catheters, atherectomy devices or stent delivery systems may be exchanged on guide wire  11  without disturbing filter element  30  or causing it to scrape against the walls of the vessel. As will of course be understood, capture ring  36  need not be a tubular member, but may have any suitable shape that allows guide wire  11  to pass freely through it.  
         [0048]    Elastomer cone  34  is coupled to the distal end of sac  31  and includes a tapered central lumen that permits guide wire  11  to freely pass through cone  34  with minimal clearance. Elastomer cone  34  preferably comprises a non-stick or slick surface, such as polytetrafluoroethylene, and is designed so that emboli trapped in sac  31  are prevented from passing out of the filter element through the space between guide wire  11  and the lumen of elastomer cone  34 . Cone  34  is sufficiently soft and flexible so that its lumen can expand to permit distal region  12  of guide wire  12  to be pulled proximally through the cone, and then the lumen will seal itself to prevent emboli from escaping through the lumen, as described hereinafter.  
         [0049]    Referring now to FIGS. 3A to  3 E, methods of using the apparatus of FIG. 1 is described. In FIG. 3A, guide wire  11  first is percutaneously and transluminally inserted into vessel V, such as a coronary artery or common carotid artery, so that distal region  12  is disposed distal to stenosis S in the direction of blood flow (indicated by arrow F).  
         [0050]    In FIG. 3B, delivery sheath  20  with filter element  30  loaded in lumen  24  in the contracted state is advanced along guide wire  11  until the filter element is disposed at a desired location distal to the stenosis, as determined, for example, by fluoroscopy. Proximal end  28  of push tube  25  is then held stationary while catheter  21  is retracted in the proximal direction.  
         [0051]    As catheter  21  is retracted, struts  32  of filter element  30  expand outward to urge the perimeter of sac  31  into engagement with the walls of vessel V, as depicted in FIG. 3C. Delivery sheath  20  is then withdrawn proximally and removed from guide wire  11 . Guide wire  11  then may be advanced distally, so that any incidental movement of the guide wire associated with exchanging interventional instruments along guide wire  11  will not cause distal region  12  to contact filter element  30 .  
         [0052]    In FIG. 3D, angioplasty catheter  40  is illustratively advanced along guide wire  11  until balloon  41  is disposed across the stenosis. Balloon  41  then is inflated and deflated for one or several cycles, as in conventional, to dilate and disrupt the plaque comprising stenosis S and increase the diameter of vessel V. During this dilatation procedure, particles of plaque or emboli E are generated. These emboli are carried by blood flow in direction F into sac  31  of filter element  30 , where they become trapped.  
         [0053]    Insertion and advancement of angioplasty catheter  40  along guide wire  11  may cause the guide wire to be translated over a short range or rotated. Because filter element  30  is not affixed to guide wire  11 , however, such motion of the guide wire is not transferred to the filter element. Instead, filter element  30  remains stationary even though the guide wire rotates or translates relative to the filter element.  
         [0054]    Once balloon  41  has dilated stenosis S, angioplasty catheter  40  is withdrawn along guide wire  11  while leaving the guide wire in place. If desired, a stent delivery system (not shown) may be advanced along guide wire  11  and one or more stents deployed across the dilated stenosis to retain the patency of the dilated vessel.  
         [0055]    When treatment of the stenosis is completed, delivery sheath  20  (with push tube  25  removed) may again be advanced along guide wire  11  to a position just proximal of filter element  30 . Guide wire  11  is then pulled proximally so that distal region passes through elastomer cone  34  and bears against capture ring  36 . The lumen in cone  34  seals itself after distal region  12  passes through it so that emboli trapped in sac  31  do not escape through the lumen of cone  34 .  
         [0056]    When guide wire  11  is pulled further in the proximal direction, with catheter  21  held stationary, struts  32  are forced radially inward by distal edge of the catheter. This in turn causes sac  31  to disengage the vessel walls. As the guide wire continues to be pulled proximally, struts  32  cause sac  31  to collapse inward to its contracted position and the filter element is retracted into lumen  24  of catheter  21 . Emboli E are trapped and retained in filter element  30  throughout treatment of the stenosis, and are withdrawn from the vessel when the filter element is retracted within catheter  21 . Catheter  21  is then removed from the vessel.  
         [0057]    Referring now to FIGS. 4A and 4B, an alternative embodiment of the filter element and guide wire of the present invention is described. Guide wire  50  is similar in construction to guide wire  11  described with respect to FIG. 1, except that it includes flange  51  on enlarged diameter distal region  52  of guide wire  50 , and enlarged distal region  52  has length L 1  that is longer than the length of the filter element  60  in the contracted state.  
         [0058]    Distal region  52  may be formed from a malleable material, a coil spring, or a pliable thermoplastic material molded onto guide wire  50 , and preferably is covered with a smooth hydrophillic coating to facilitate movement of filter element  60  as described hereinafter. Alternatively, guide wire  50  and distal region  52  may comprise a mechanism, such as are known in the art, for steering distal region  52  through a patient&#39;s vasculature. Distal region  52  also may comprise a radiopaque material or may include a radiopaque band  53  to assist in visualization and placement of the guide wire.  
         [0059]    Filter element  60  comprises self-expanding struts  61  coupled to capture ring  62  and tubular sleeve  63 . Sleeve  63  is affixed at its distal end to funnel-shaped filter sac  64 , which in turn is coupled to distal ring  65 . Capture ring  62  has bore  66  with an inner diameter larger than the diameter of guide wire  50 , but smaller than the diameter of distal region  52 . Accordingly, guide wire  50  may freely translate and rotate through bore  66  of capture ring  62  while the filter element remains stationary. Distal ring  65  has bore  67  with a diameter slightly larger than the diameter of distal region  52 . This enables distal ring  65  to slide or rotate freely over distal region  52 , but with minimal clearance for emboli to escape from sac  64  through the annulus between distal ring  65  and distal region  52 . Distal region  52  includes flange  51 , which has a diameter that is larger than the diameter of bore  66  of capture ring  62 . Thus, filter element  60  is captured on guide wire  50  proximally by distal ring  65  abutting against flange  51 , and distally by capture ring  62  abutting against flange  51 .  
         [0060]    Sleeve  63  and sac  64  filter blood passing through the vessel, and have a pore size selected to filter out particles having a diameter greater than 0.0012 inches (30 microns). Sleeve  63  and sac  64  preferably comprise a flexible woven metal alloy, polymer tube, or perforated fabric, and are expanded to the deployed state by struts  61 . Advantageously, sleeve  63  is designed so that its perimeter conforms to the inner diameter of the vessel to seal against bypass flow, even in curved vessels. In addition, sleeve  63  tends to prevent skewing of the filter element and ensures that the filter is properly oriented parallel to the axis of the vessel when the filter element is deployed.  
         [0061]    Filter element  60  is suitable for delivery percutaneously and transluminally to a desired location in a vessel using delivery sheath  20  of FIG. 1. In particular, struts  61  may be radially compressed to collapse sleeve  63  and sac  64 , thereby permitting these the filter element to be loaded into lumen  24  of catheter  21  so that capture ring  62  abuts against distal end  27  of push tube  25 .  
         [0062]    Deployment of filter element  60  is similar to the method described with respect to FIGS. 3B and 3C. Specifically, delivery sheath  20  is advanced through a vessel with distal region  52  extending beyond distal end  23  of catheter  21 . Once the distal region has crossed the stenosis, as confirmed by fluoroscopy, push tube  25  is held place and catheter  21  is retracted proximally. Alternatively, push tube  25  may be omitted and guide wire  50  may be held stationary with filter element  60  held in position by flange  51 . Retraction of catheter  21  uncovers filter element  60 , allowing struts  61  to expand outward and urge the perimeter of sleeve  63  and sac  64  into engagement with the walls of the vessel.  
         [0063]    Delivery sheath  20  then is removed, and one of more interventional devices may be serially employed on guide wire  50 . As for the embodiment of FIG. 1, motion imparted to the guide wire during exchange of instruments along the guide wire causes the guide wire to slide through filter element  60  without causing skewing or displacement of the filter element. Advantageously, this prevents emboli from escaping sac  64  or damage to the endothelium caused by scraping of the filter element.  
         [0064]    Once treatment of the stenosis is completed, the treatment device (e.g., angioplasty catheter, etc.) is removed, and delivery sheath  20  is again advanced along guide wire  50 . When distal end  23  of catheter  21  is disposed adjacent to capture ring  62 , guide wire  50  is pulled proximally. As a result of this motion, distal region passes through filter element  60  until flange  51  abuts against capture ring  62 . Further proximal movement of guide wire  50  causes struts  61  to be urged inward, collapsing sleeve  63  and sac  64  so that they can be drawn into lumen  24  of catheter  21 .  
         [0065]    Unlike the embodiment of FIG. 1, where the distal region passes through cone  34 , length L 1  is sufficiently long so that distal ring  65  is still disposed over the enlarged diameter of distal region  51  when the filter element is in the contracted state. Accordingly, when filter element  60  is contracted for removal, emboli cannot escape through bore  67  of distal ring  65 , since the bore continues to be substantially blocked by distal region  52  of guide wire  50 . Delivery sheath  20 , guide wire  50  and filter element  60  are then removed from the vessel with any emboli trapped within the contracted filter element.  
         [0066]    In a preferred embodiment of the apparatus of FIGS.  4 , guide wire  50  has a suitable length for transluminal percutaneous applications and a diameter in a range of 0.006 and 0.025 inches, and more preferably 0.012 inches. Distal region  52  of guide wire  50  has a diameter larger than the diameter of guide wire  50 , and preferably in a range of 0.010 and 0.038 inches, more preferably 0.018 inches.  
         [0067]    While filter element  60  may any length suitable for an intended application, in one preferred embodiment, filter element  60  has a deployed length of 3.5 cm and a maximum deployed diameter of 12 mm. For this embodiment, length L 1  of distal region  52  preferably is 5.0 cm. For a guide wire having a diameter of 0.012 inches and proximal ring and distal region having equal diameters of 0.018 inches, capture ring  62  preferably has an inner diameter of 0.014 inches and an outer diameter of 0.018 inches. In this case distal ring  65  preferably has an inner diameter of 0.0181 inches and an outer diameter of 0.024 inches.  
         [0068]    Referring now to FIGS.  5 A- 5 C, another alternative embodiment of the present invention is described in which the capture ring, self-expanding struts and distal ring of the apparatus of FIGS.  4  are integrally formed from a slit tubular segment. In FIGS.  5 A- 5 C, filter element  70  is disposed on guide wire  71  and comprises tubular segment  72  having a plurality of through-wall longitudinal slits  73  defining struts  74 . Blood permeable sac  75  is affixed to the distal portion of the interior surface of tubular segment  72 , and filters blood passing therethrough when filter element  70  is deployed.  
         [0069]    In a preferred embodiment, tubular segment  72  comprises a shape-memory alloy, such as nitinol, which has been processed to assume an expanded, deployed state when ejected from a delivery sheath. As depicted in FIGS.  5 A- 5 C, tubular segment illustratively includes a plurality of longitudinal slits disposed circumferentially around tubular segment  71  to define a plurality of self-expanding struts  74 . The non-slitted proximal portion  76  and distal portion  77  form capture rings that correspond to capture ring  62  and distal ring  65  of the embodiment of FIGS. 4. Illustratively, tubular segment  72  includes nine slits defining ten self-expanding struts.  
         [0070]    Distal end  79  of guide wire  71  preferably includes a floppy or bendable tip, as is per se known in the art. In addition, distal stop  78  may be tapered where it joins guide wire  71  so that the distal stop serves as a nosecone, thereby facilitating passage of the guide wire and filter element through a vessel.  
         [0071]    When filter element  70  is unconstrained by a delivery sheath, i.e., ejected from a delivery sheath, struts  74  expand outwardly and the filter element foreshortens. As struts  74  expand outwardly, they carry sac  75  into apposition with the vessel wall, and create passages  78  that permit blood to flow into the sac, thereby filtering emboli from the blood stream. Sac  75  preferably comprises a biocompatible material that provides emboli filtration, as in the foregoing embodiments. In addition, sac  75  may comprise an elastomeric material that stretches to accommodate the degree of expansion of struts  74 , thereby permitting filter element  71  to be used in a range of vessel sizes while reducing the risk of bypass flow caused by incomplete apposition of the sac with the vessel wall.  
         [0072]    In accordance with the principles of the present invention, proximal portion  76  and distal portion  77  permit guide wire  71  to freely translate and rotate relative to filter element  70 , without disturbing the location of filter element within the vessel. Accordingly, guide wire  71  includes distal stop  78  against which capture ring  77  abuts to limit distal movement of the filter along guide wire  71 , and optionally may include a proximal stop (not shown) against which proximal capture ring  76  may abut to limit proximal movement. Filter element thus may be inserted along a previously-delivered guide wire, as depicted in FIGS.  3 , or may be delivered captured between proximal and distal stops and inserted with the guide wire itself, as described hereinafter.  
         [0073]    Advantageously, because struts  74  and capture rings  76  and  77  may be integrally formed from a single tubular segment, the overall diameter of the filter element in the contracted delivery diameter may be smaller that obtainable using separately-formed struts. Also, because a portion of the filter struts  74  lie flush against the vessel wall when the filter element is deployed, the struts facilitate self-centering and alignment of the filter element within a vessel, and provide stability and good apposition of the sac to the vessel wall. In addition, the number of separate parts employed in the design, and thus the assembly time and manufacturing cost of the device, are substantially reduced.  
         [0074]    While the embodiment of FIGS.  5  illustratively includes nine slits  73  defining ten struts  74 , more or less slits (and thus struts) may used, as will be apparent to one of ordinary skill in the art. Moreover, while in the depicted embodiment the longitudinal slits are spaced equi-distant apart around the circumference of tubular segment  72  to form equal-width struts, other arrangements may be desirable for specific applications.  
         [0075]    Referring now to FIGS. 6 and 7, a further alternative embodiment of the embolic filtration apparatus of the present invention is described. Filter element  80  is similar in construction to the embodiment of FIGS.  5 , and also employs tubular segment  81  having a plurality of longitudinally-extending circumferential slits  82  that define self-expanding struts  83 . Tubular segment  81  is disposed on tube  85 , which preferably is captured on guide wire  86  between optional proximal stop  87  and distal stop  88 . Blood permeable sac  89  is affixed to the exterior surface of struts  83  at proximal end  90  and to tube  85  at distal end  91 .  
         [0076]    [0076]FIG. 6A depicts filter element  80  in a contracted delivery state, as it might be disposed and constrained within a delivery sheath, while FIG. 6B shows filter element  80  deployed. Tubular segment  81  is processed (e.g., heat treated) so that, when unconstrained, struts  83  of deploy outwardly creating openings  84  through which emboli and debris from a vascular procedure enter blood permeable sac  89 . As will of course be understood, the distal end of guide wire  86  may terminate with a floppy tip, and tubular segment may include any number of longitudinal slits (and thus struts) as may be desired for a particular application.  
         [0077]    As depicted more clearly in FIGS. 7A and 7B, the non-slitted proximal portion of tubular segment  81  forms proximal collar  92 , and is affixed to tube  85 . The non-slitted distal portion of tubular segment  81  forms collar  93 , and is slidingly disposed on tube  85 , so that the collar  93  slides along tube  83  towards collar  92  when the filter element is deployed. Like the capture rings of the previously described embodiments, tube  85  serves as a linear bearing for filter element  80 .  
         [0078]    Tube  85  also corresponds to the capture ring of previous embodiments, because its proximal endface  94  abuts against proximal stop  87  to limit distally-directed motion of guide wire  86  while its distal endface  95  abuts against distal stop  88  to limit proximally-directed motion of guide wire  86 . Tube  85  preferably comprises a flexible material, such as polyimide or other plastic, and more preferably is lubricious or may include an internal coating of a lubricious material, such as PTFE, to facilitate movement of guide wire  86  relative to tube  85 .  
         [0079]    In accordance with the principles of the present invention, guide wire  86  is capable of rotation and/or a limited range of translation relative to tube  85 , and thus filter element  80 , without disturbing the position of the filter. Advantageously, arrangement of tubular segment  81  and sac  89  on tube  85  permits the filter sac to be elongated compared to the embodiment of FIGS. 5. This in turn provides greater surface area for the filter, and reduces the risk that the pores of sac  89  may become clogged if unexpectedly large amounts of emboli or other debris are captured by the filter. Filter element  80  of FIGS. 6 and 7 therefore provides structural simplicity, with enhanced filtration capacity.  
         [0080]    Referring now to FIGS. 8A to  8 D, methods of using the apparatus of FIGS.  6  is described. In FIG. 8A, delivery sheath  100  enclosing guide wire  86  and filter element  80  is percutaneously and transluminally inserted into vessel V, such as a coronary artery or common carotid artery, so that distal region  101  is disposed distal to stenosis S in the direction of blood flow (indicated by arrow F). A floppy tip disposed on the distal end of guide wire  86  extends (to the right in FIG. 8A) pass the location the filter element and is used to traverse the stenosis.  
         [0081]    In FIG. 8B, once the position of the filter element is disposed at a desired location distal to the stenosis, as determined, for example, by fluoroscopy, delivery sheath  100  is retracted while guide wire  86  is held stationary. Because filter element  80  can only move in the proximal direction until it abuts against proximal stop  87 , further retraction of delivery sheath  100  will cause filter element  80  to exit the distal end of the catheter.  
         [0082]    As soon as catheter  100  is removed, struts  83  of filter element  80  expand outward to urge the perimeter of sac  89  into engagement with the walls of vessel V, as depicted in FIG. 8B. Delivery sheath  100  then is withdrawn proximally and removed from guide wire  86 . Guide wire  86  then may be retracted a short distance proximally so that any incidental movement of the guide wire associated with exchanging interventional instruments along the guide wire will not cause proximal stop  87  to contact or disturb the position of filter element  80 .  
         [0083]    In FIG. 8C, angioplasty catheter  110  is illustratively advanced along guide wire  86  until balloon  112  is disposed across the stenosis. Balloon  112  then is inflated and deflated for one or several cycles, as in conventional, to dilate and disrupt the plaque comprising stenosis S and increase the diameter of vessel V. During this dilatation procedure, particles of plaque or emboli E are generated. These emboli are carried by blood flow in direction F into sac  89  of filter element  80 , where they become trapped.  
         [0084]    Insertion and advancement of angioplasty catheter  100  along guide wire  86  may cause the guide wire to be translated over a short range or rotated. Because filter element  80  is not affixed to guide wire  86 , however, such motion of the guide wire is not transferred to the filter element. Instead, filter element  80  remains stationary even though the guide wire rotates or translates relative to the filter element.  
         [0085]    Once balloon  112  has dilated stenosis S, angioplasty catheter  110  is withdrawn along guide wire  86  while leaving the guide wire in place. If desired, a stent delivery system (not shown) may be advanced along guide wire  86  and one or more stents deployed across the dilated stenosis to retain the patency of the dilated vessel.  
         [0086]    When treatment of the stenosis is completed, delivery sheath  100  may again be advanced along guide wire  86  to a position just proximal of filter element  80 . Guide wire  86  then held stationary while the distal region of sheath  100  contacts and translates the filter element slightly distally until it abuts against distal stop  88 . As the sheath is advanced further in the distal direction, struts  83  and sac  89  collapse and enter into distal end  101  of the delivery sheath. Because sac  89  is elongated, closing of struts  83  closes the mouth of the sac, and prevents emboli trapped in sac  89  from escaping into the bloodstream.  
         [0087]    Once filter element  80  is collapsed to its contracted position and retracted within the lumen of delivery sheath  100 , the delivery sheath, guide wire and filter element are removed from the vessel. Emboli E are trapped and retained in filter element  80  throughout treatment of the stenosis, and are withdrawn from the vessel when the filter element is retracted within sheath  100 .  
         [0088]    With respect to FIG. 9, a further alternative embodiment of an embolic filtration apparatus of the present invention is described. Filter element  120  comprises tubular segment  121  disposed on guide wire  122 , and comprises a slit tubular segment as described with respect to the embodiments of FIGS.  5 - 8 . Tubular segment  121  is processed so that struts  123  do not have a portion that lies flush against a vessel wall, as may be desirable for some situations, e.g., for short vessel lengths.  
         [0089]    As for the previous embodiments, struts  123  are self-expanding, and form a basket shape when unconstrained. Blood permeable sac  124  is affixed to the interior surfaces of struts  123  to span the vessel cross-section when the filter element is deployed. Sac  124  may comprise a microaggregate blood transfusion filter such as PALL SQ40SK, with a pore size of about 80-200 microns, or a woven material.  
         [0090]    Referring now to FIGS. 10A and 10B, use of filter element  120  with a retrieval catheter constructed in accordance with another aspect of the present invention is described. In FIG. 10A, filter element  120  is shown after completion of an interventional procedure, such as angioplasty, and is disposed on guide wire  122  between retrieval catheter  130  that includes recovery sock  132  and distal stop  126 . Recovery sock  132  comprises a material that is permeable to blood flow, but that has a pore size sufficiently small to prevent emboli from passing through it.  
         [0091]    As shown in FIG. 10B, with guide wire  122  first is withdrawn proximally (to the left in FIG. 10B) until distal stop  126  contacts the distal end of filter element  120 . With guide wire  122  held stationary, retrieval catheter  130  is advanced distally until sock  132  engages and covers the proximal end of filter element  120 . As retrieval catheter  130  is advanced further in the distal direction, struts  123  and sac  124  of filter element  120  collapse and are drawn into the lumen of the retrieval catheter. Recovery sock  132  thereby ensures that emboli captured in sac  124  do not escape into the blood stream during retrieval of filter element  120 .  
         [0092]    By advancing retrieval sheath  130  along guide wire  120  with the distal end of filter element  120  abutted against distal stop  126 , struts  123  are caused to collapse and enter the lumen of the retrieval catheter. Recovery sock  132  preferably contracts and continues to cover struts  123  as the filter element is collapsed, resulting in situation depicted in FIG. 11. Filter element  120 , guide wire  122  and retrieval catheter  130  now may be easily withdrawn from the vessel.  
         [0093]    Referring to FIG. 12, yet another alternative embodiment of the embolic filtration apparatus of the present invention is described. In the embodiment of FIG. 12, filter element  140  is similar to filter element  120  of FIG. 9, and includes slit tubular segment  141  forming struts  142  which form a basket and blood permeable sac  144  affixed to the interior surface of the struts. Tubular segment  141  is coupled at distal end  145  to flexible coil  146 . Coil  146  preferably comprises a flexible spiral coil, and is in turn connected to linear bearing  147  that is slidingly disposed on guide wire  150 .  
         [0094]    Guide wire  150  preferably has a smaller diameter than the diameter of tubular segment  141 , and includes distal stop  151  against which linear bearing  147  abuts to limit distally-directed travel of filter element  140 . Guide wire  150  extends through the interior lumen  148  of tubular segment  141  and interior lumen of coil  146  and linear bearing  147  to enable filter element  140  to rotate and/or translate freely relative to guide wire  150 .  
         [0095]    In accordance with another aspect of the present invention, the clearance between the guide wire and interior surface of tubular segment  141 , in combination with the presence of coil  146 , permits the proximal end of the filter to rotate relative to its distal end. This arrangement permits the filter element to accommodate some lateral displacement of the filter element from a position concentric with the guide wire, as indicated by the arrows X in FIG. 12.  
         [0096]    Moreover, depending upon the stiffness of coil  146 , the filter may also undergo a degree of lateral deflection (without end-to-end rotation) from the longitudinal axis of guide wire  150 . However, because emboli may pass through lumen  148  between guide wire  150  and the distal end of tubular segment  141  into the lumen of coil  146 , the spirals of coil  146  preferably are tightly packed so that emboli cannot escape through filter element  140  via coil  146 .  
         [0097]    One skilled in the art will appreciate that the present invention may be practiced by other than the described embodiments, which are presented for purposes of illustration and not limitation. It is intended that the present application cover such variations or modifications as may be apparent from the described embodiment as may fall within the scope of the appended claims.