Abstract:
An emboli filtration apparatus is provided including a guide wire having a filter element captured thereon, so that the guide wire is free to rotate and 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. In a preferred embodiment, the guide wire includes a proximal stop configured to reposition the filter element during a medical procedure without having to remove or insert additional interventional devices.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/037,881, filed Jan. 18, 2005, now U.S. Pat. No. 7,563,272, which is a continuation of U.S. patent application Ser. No. 10/278,172, filed Oct. 21, 2002 now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 09/774,197, filed Jan. 29, 2001, now U.S. Pat. No. 6,468,291, which is a continuation-in-part of U.S. patent application Ser. No. 09/354,897, filed Jul. 16, 1999, now U.S. Pat. No. 6,179,859. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and methods for removing emboli from the blood stream that are generated during treatment of vascular disease, such as angioplasty, atherectomy or stenting. More particularly, an emboli filtration device and methods are provided having a captured filter that enables movement of a guide wire associated with the filter without displacing the filter. 
     BACKGROUND OF THE INVENTION 
     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. 
     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 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 carotid arteries, and can result in infarction, stroke and even death. 
     Emboli filtration devices are known in which filter elements are deployed against the walls of a vessel distal of 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. 
     For example, U.S. Pat. No. 5,814,064 to Daniel et al. (Daniel) 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 of 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. 
     U.S. Pat. No. 4,723,549 to Wholey et al. (Wholey) 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 an interior wall of a vessel, distal of 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. 
     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 the filter will become temporarily dislodged or skewed, thereby permitting emboli to escape past 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 Daniel patent. 
     U.S. Pat. No. 6,336,934 to Gilson et al. (Gilson) describes an embolic protection device having a collapsible filter element that is mounted on a tubular sleeve, wherein the tubular sleeve is slidable and rotatable on a guide wire between proximal and distal stops. The filter element on the tubular sleeve is delivered in a collapsed state within a catheter and self-deploys when the catheter is retracted. In the deployed state, the tubular sleeve facilitates some manipulation of the guide wire while potentially reducing disruption of the filter element. 
     One drawback associated with the device described in the Gilson patent is that the guide wire is delivered into the patient&#39;s vessel with the filter element disposed in a collapsed state between the proximal and distal stops near the distal end of the guide wire. The placement of the filter element near the distal end of the guide wire during delivery may make it difficult for the guide wire to negotiate tortuous anatomy during delivery. It would be advantageous to deliver the guide wire in an unencumbered manner to the site of the occlusion, then subsequently deliver other interventional devices including the filter element. 
     In view of these drawbacks of previously known devices, it would be desirable to provide emboli filtration apparatus and methods having a filter element that remains stationary once deployed. 
     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. 
     It further would be desirable to provide emboli filtration apparatus and methods that reduce the risk of emboli escaping from a filter element. 
     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. 
     It still further would be desirable to provide emboli filtration apparatus and methods that enable a filter element to be repositioned during a medical procedure without having to remove or insert additional interventional devices. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide emboli filtration apparatus and methods having a filter element that remains stationary once deployed. 
     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. 
     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. 
     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. 
     It is still a further object of the present invention to provide emboli filtration apparatus and methods that enable a filter element to be repositioned during a medical procedure without having to remove or insert additional interventional devices. 
     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 translate while the filter element remains stationary. The apparatus thus allows for movement and 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. 
     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. 
     The filter element includes a proximal capture ring having a diameter that 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. 
     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. 
     In a further alternative embodiment of the present invention, the guide wire further comprises a proximal stop disposed proximal of the distal tip. The proximal stop is configured so that a filter element having an elastomeric capture ring may be advanced distally over the proximal stop during delivery of the filter element and locked distal of the proximal stop. As a further alternative, the proximal stop may be configured to permit the capture ring to pass distally over it, but prevent proximal passage. 
     During a medical procedure, the filter element is advanced to a central position between the proximal stop and distal tip. Advantageously, if it becomes necessary to advance the filter element distally during the medical procedure, the guide wire may be advanced distally to cause the proximal stop to abut the capture ring and urge the filter element distally. Using the proximal stop of the guide wire, it is not necessary to remove interventional devices or insert a push tube over the guide wire to reposition the filter element. 
     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 
       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: 
         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; 
         FIGS. 2A-2B  are, respectively, a perspective view and end view of the filter element of  FIG. 1 ; 
         FIGS. 3A-3E  are side sectional views showing deployment, use and removal of the apparatus of  FIG. 1  in accordance with the methods of the present invention; 
         FIGS. 4A-4B  are, respectively, side sectional views of an alternative embodiment of the apparatus of the present invention in deployed and contracted states; 
         FIGS. 5A-5B  are side sectional views depicting use of an alternative embodiment of the present invention having a proximal stop disposed on a guide wire; 
         FIGS. 6A-6C  are, respectively, a side view of an alternative embodiment of the proximal stop of  FIGS. 5A-5B , and enlarged views of the proximal stop in relaxed and contracted states; and 
         FIGS. 7A-7B  are side views of a further alternative embodiment of a proximal stop provided in accordance with principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 and 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. 
     Referring to  FIG. 1 , apparatus  10  of a first embodiment of the present invention comprises guide wire  11 , delivery sheath  20  and filter element  30 . 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 distal 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  11  may have a diameter of about 0.018 inches (0.46 mm) and the diameter of distal region  12  may be about 0.022 inches (0.56 mm). 
     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. 
     Referring now to  FIGS. 2A and 2B , filter element  30  comprises funnel-shaped filter sac  31  coupled to plurality of self-expanding struts  32  at proximal end  33  and soft elastomeric 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. 
     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. 
     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. 
     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. 
     Elastomeric 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. Elastomeric 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 elastomeric cone  34 . Cone  34  is sufficiently soft and flexible so that its lumen can expand to permit distal region  12  of guide wire  11  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. 
     Referring now to  FIG. 3 , preferred methods of using the apparatus of  FIG. 1  are 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 of stenosis S in the direction of blood flow (indicated by arrow F). 
     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 of the stenosis, as determined, for example, by fluoroscopy. Proximal end  26  of push tube  25  is then held stationary while catheter  21  is retracted in the proximal direction. 
     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  then is withdrawn proximally and removed from guide wire  11 . Guide wire  11  then may be advanced a short distal 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 . 
     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. 
     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. 
     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. 
     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  then is pulled proximally so that distal region  12  passes through elastomeric 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 . 
     When guide wire  11  is pulled further in the proximal direction, with catheter  21  held stationary, struts  32  are forced radially inward by the 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  then is removed from the vessel. 
     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.sub. 1  that is longer than the length of the filter element  60  in the contracted state. 
     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 hydrophilic 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 (not shown) to assist in visualization and placement of the guide wire. 
     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 . 
     Sleeve  63  and sac  64  filter blood passing through the vessel, and preferably 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, as shown in  FIG. 4A , 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. 
     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 , as shown in  FIG. 4B , thereby permitting 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 . 
     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 distal region  52  has crossed the stenosis, as confirmed by fluoroscopy, push tube  25  is held place and catheter  2  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. 
     Delivery sheath  20  then is removed, and one or more interventional devices may be serially employed on guide wire  50 . Like the embodiment of  FIG. 1 , motion imparted to guide wire  50  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. 
     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  52  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 . 
     Unlike the embodiment of  FIG. 1 , where the distal region passes through cone  34 , length L.sub. 1  is sufficiently long so that distal ring  65  is still disposed over the enlarged diameter of distal region  52  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  then are removed from the vessel with any emboli trapped within the contracted filter element. 
     In a preferred embodiment of the apparatus of  FIG. 4 , guide wire  50  has a suitable length for transluminal percutaneous applications and a diameter in a range of about 0.006 to 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 about 0.010 to 0.038 inches, more preferably 0.018 inches. 
     While filter element  60  may comprise 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.sub. 1  of distal region  52  preferably is 5.0 cm. For a guide wire having a diameter of 0.012 inches and distal region having a diameter 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. 
     Referring now to  FIG. 5 , apparatus  90  of an alternative embodiment of the present invention comprises guide wire  100  and filter element  102 . Filter element  102  preferably is constructed in accordance with filter element  30  of  FIGS. 1-3 . Specifically, filter element  102  comprises funnel-shaped filter sac  105  coupled to plurality of self-expanding struts  103  at a proximal end and elastomeric cone  106  at a distal end. Struts  103  are affixed to capture ring  104 , as described in detail hereinabove with respect to  FIG. 2 . Optionally, filter element  102  also may comprise cylindrical sleeve  63 , as described hereinabove with respect to  FIG. 4 , disposed between struts  103  and sac  105 . 
     Guide wire  100  comprises proximal stop  110  and distal region  112 . Distal region  112  serves as a distal stop that limits the distal movement of filter element  102  along guide wire  100 , as described hereinabove. Proximal stop  110  has proximal and distal ends  114  and  115  and taper  111  disposed therebetween, as shown in  FIG. 5A . Taper  111  of guide wire  110  spans from proximal end  114 , which preferably has a guide wire diameter of about 0.018 inches, to distal end  115 , which preferably has an enlarged diameter of about 0.022 inches. Proximal stop  110  and distal region  112  are spaced apart such a distance that filter element  102 , when deployed therebetween, will not be disturbed by incidental longitudinal movements of guide wire  100 . 
     Apparatus  90  of  FIG. 5  preferably is deployed in the manner described hereinabove with respect to apparatus  10  of  FIGS. 1-3 , except as noted below. In a first step, guide wire  100  is percutaneously and transluminally inserted into treatment vessel V under fluoroscopy, with proximal stop  110  preferably being disposed just distal of stenosis S. In a next step, filter element  102  is advanced along guide wire  100  in a contracted state, preferably being contracted within lumen  24  of catheter  21 , as described hereinabove with respect to  FIG. 3B . Push tube  25  of  FIG. 3B  then is advanced distally so that a distal end of push tube  25  abuts capture ring  104  and advances filter element  102  distally over guide wire  100 . 
     As push tube  25  advances filter element  102 , elastomeric cone  106  is pushed distally over proximal stop  110  of guide wire  100 . Elastomeric cone  106  is configured to be flexible enough to radially expand over the enlarged diameter of distal end  115  of proximal stop  110 . After being advanced over distal end  115 , elastomeric cone  106  then substantially seals itself about guide wire  100  to prevent emboli from subsequently escaping when a medical procedure is performed. 
     As push tube  25  further is advanced, capture ring  104  then is advanced over proximal stop  110 . Capture ring  104  also is compliant enough to expand over the enlarged diameter of distal end  115  when advanced distally, and then substantially seals itself about guide wire  100  after it passes over proximal stop  110 . Once filter element  102  is disposed between proximal stop  110  and distal region  112 , filter element  102  is deployed, e.g., by proximally retracting catheter  21  while holding push tube  25  stationary. The catheter and push tube then may be removed from the patient&#39;s vessel. 
     Once deployed, filter element  102  preferably is provided in a central position between proximal stop  110  and distal region  112 , as depicted in  FIG. 5A , either by proximally retracting or distally advancing guide wire  100  under fluoroscopy. In this central position, incidental movements of guide wire  100  will not substantially disturb filter element  102 . 
     If it becomes necessary to advance filter element  102  distally during the medical procedure, guide wire  100  may be advanced distally by a physician until distal end  115  of proximal stop  110  abuts capture ring  104  and gently urges filter element  102  distally, as shown in  FIG. 5B . Advantageously, this enables filter element  102  to be advanced distally without having to remove angioplasty or stenting apparatus, then having to advance a push tube over then length of guide wire  100 . Upon repositioning of filter element  102 , guide wire  100  preferably is repositioned to the central position depicted in  FIG. 5A , so that incidental movements of guide wire  100  do not disturb filter element  102 . 
     When treatment of the stenosis is completed and any emboli are captured within sac  105  of filter element  102 , delivery sheath  20  (with push tube  25  removed) may be advanced to a location just proximal of filter element  102 . Guide wire  100  then is retracted proximally so that distal region  112  passes through elastomeric cone  106  and bears against capture ring  104 , as described hereinabove with respect to  FIG. 3E . A lumen of cone  106  seals itself after distal region  112  passes through to prevent emboli from escaping downstream. Distal region  112  then abuts capture ring  104  and pulls filter element  102  in a proximal direction. With the catheter held stationary, struts  103  are forced radially inward by the distal edge of the catheter to cause filter element  102  and any emboli captured therein to be removed via the catheter. 
     Advantageously, the one-way stop feature of proximal stop  110  allows guide wire  100  to be advanced through a patient&#39;s vasculature without having filter element  102  disposed on the guide wire. This facilitates advancement of guide wire  100  through a patients tortuous vasculature. Then, when guide wire  100  is properly positioned in a vessel unencumbered, filter element  102  may be advanced distally over proximal stop  110 , and securely positioned between proximal stop  110  and distal region  112  during the medical procedure. 
     Referring now to  FIG. 6 , an alternative embodiment of proximal stop  110  of the embodiment of  FIG. 5  is described. In  FIG. 6A , guide wire  120  preferably is provided substantially in accordance with guide wire  11  of  FIG. 1 , and comprises enlarged diameter distal region  122 , which acts as a distal stop to limit travel of filter element  102  in the distal direction, as described hereinabove. Guide wire  120  further comprises proximal stop  130 , which includes at least one depressible tab  131  having proximal end  133  and distal end  134 , as shown in  FIGS. 6B-6C . 
     Proximal end  133  of depressible tab  131  is affixed to guide wire  120 , e.g., using a solder, while distal end  134  is biased to extend slightly radially outward from guide wire  120  in a relaxed state, as shown in  FIG. 6B . Depressible tab  131  may comprise a slight concave curvature to cause distal end  134  to be biased radially outward or, alternatively, proximal end  133  may be affixed to guide wire  120  in such a manner that allows distal end  134  to be biased radially outward in the relaxed state. 
     Depressible tab  131  is flexible so that it may be transformed between the relaxed state, shown in  FIG. 6B , and a contracted state, as shown in  FIG. 6C . In the contracted state, external compressive forces cause depressible tab  131  to be substantially flush with an exterior surface of guide wire  120 . Guide wire  120  optionally may comprise a shallow slot (not shown) disposed in a lateral surface that is adapted to receive depressible tab  131  in the contracted state. When depressible tab  131  is contracted, as shown in  FIG. 6C , the shallow slot serves to ensure that depressible tab  131  does not extend radially beyond guide wire  120 . 
     Apparatus  110  of  FIG. 6  preferably is deployed in the manner described hereinabove with respect to apparatus  10  of  FIGS. 1-3 , except as noted below. In a first step, guide wire  120  is percutaneously and transluminally inserted until proximal stop  130  is disposed just distal of a stenosis. In a next step, filter element  102  is advanced along guide wire  120  in a contracted state, preferably being contracted within lumen  24  of catheter  21 , as described hereinabove with respect to  FIG. 3B . Push tube  25  of  FIG. 3B  then is advanced distally so that a distal end of push tube  25  abuts capture ring  104  and advances filter element  102  distally. 
     As push tube  25  advances filter element  102 , elastomeric cone  106  is pushed distally over proximal stop  130 . Depressible tab  131  assumes the contracted state, depicted in  FIG. 6C , as filter element  102  is advanced distally to facilitate advancement of elastomeric cone  106  over proximal stop  130 . Elastomeric cone  106  also may radially expand over proximal stop  130 , if necessary, and then substantially seal itself about guide wire  120  after it passes over proximal stop  130 . As push tube  25  further is advanced, capture ring  104  then is advanced over proximal stop  130  in the same manner as elastomeric cone  106 . 
     After elastomeric cone  106  and capture ring  104  are advanced distally over proximal stop  130 , depressible tab  131  returns to the relaxed state, depicted in  FIG. 6B . Filter element  102  then is deployed between proximal stop  130  and distal region  122 , e.g., by proximally retracting catheter  21  while holding push tube  25  stationary. The catheter and push tube then may be removed from the patient&#39;s vessel. 
     Once deployed, filter element  102  preferably is provided in a central position between proximal stop  130  and distal region  122  by proximally retracting or distally advancing guide wire  120  under fluoroscopy. If it becomes necessary to advance filter element  102  distally during a medical procedure, guide wire  120  may be advanced distally to cause distal end  134  of depressible tab  131  to abut capture ring  104  and gently urge filter element  102  distally. Upon completion of the medical procedure, catheter  21  may be advanced distally over guide wire  120  to cause filter element  102  and any emboli captured therein to be removed via the catheter, as described in detail hereinabove with respect to  FIG. 3E . 
     Referring now to  FIG. 7 , a further alternative embodiment of the present invention is described, whereby guide wire  11  of  FIG. 1  is slightly bent to comprise a one-way proximal stop mechanism. Guide wire  150  of  FIG. 7A  comprises enlarged diameter distal region  152 , which acts as a distal stop to limit travel of filter element  102  in the distal direction. Guide wire  150  further comprises proximal stop  160 , which includes bent section  161  of guide wire  150  having proximal taper  163  and distal taper  164 . Proximal taper  163  comprises angle .alpha. with respect to longitudinal axis  170  of guide wire  150 , while distal taper  164  comprises angle .beta. with respect to longitudinal axis  170 , as depicted in  FIG. 7B . 
     Proximal stop  160  is configured to facilitate distal advancement of filter element  102  over bent section  161  of guide wire  150  via proximal taper  163 , while inhibiting movement of filter element  102  in a proximal direction over bent section  161  via distal taper  164 . In a preferred embodiment, angle .beta. is greater than angle .alpha., as illustratively shown in  FIG. 7B , to permit advancement of filter element  102  in a distal direction only. 
     Proximal stop  160  of guide wire  150  is flexible enough so that proximal and distal tapers  163  and  164  may assume substantially flat configurations, i.e., substantially parallel to longitudinal axis  170  of guide wire  150 , when elastomeric cone  106  and capture ring  104  are advanced distally over bent region  161 . Once filter element  102  is advanced distally over proximal stop  160 , proximal and distal tapers  163  and  164  return to the bent configurations depicted in  FIG. 7A . 
     Apparatus  140  of  FIG. 7  preferably is deployed in the manner described hereinabove with respect to apparatus  10  of  FIGS. 1-3 , except as noted below. In a first step, guide wire  150  is percutaneously and transluminally inserted until proximal stop  160  is disposed just distal of a stenosis. In a next step, filter element  102  is advanced along guide wire  150  in a contracted state, preferably being contracted within lumen  24  of catheter  21 , as described hereinabove with respect to  FIG. 3B . Push tube  25  of  FIG. 3B  then is advanced distally so that a distal end of push tube  25  abuts capture ring  104  and advances filter element  102  distally. 
     As push tube  25  advances filter element  102 , elastomeric cone  106  is pushed distally over proximal taper  163  of guide wire  150 . Proximal and distal tapers  163  and  164  may assume substantially flat configurations, i.e., substantially parallel to longitudinal axis  170 , to facilitate distal advancement of elastomeric cone  106 . As push tube  25  further is advanced distally, capture ring  104  then is advanced over proximal stop  160  in the same manner as elastomeric cone  106 . 
     Once filter element  102  is disposed between proximal stop  160  and distal region  152 , filter element  102  is deployed, as described hereinabove. Filter element  102  preferably is provided in a central position between proximal stop  160  and distal region  152 , as shown in  FIG. 7A , by proximally retracting or distally advancing guide wire  150  under fluoroscopy. If it becomes necessary to advance filter element  102  distally during a medical procedure, guide wire  150  may be advanced distally until distal taper  164  of proximal stop  160  abuts capture ring  104  and gently urges filter element  102  distally. Proximal stop  160  of guide wire  150  is configured to retain the bent shape depicted in  FIG. 7  as distal taper  164  urges filter element  102  distally. Upon completion of the medical procedure, catheter  21  may be advanced distally over guide wire  150  to cause filter element  102  and any emboli captured therein to be removed via the catheter, as described in detail hereinabove with respect to  FIG. 3E . 
     While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.