Abstract:
A method of delivering a stent comprising providing an elongate guide having a stent coaxially supported on the guide for placement and movement by the guide, providing a tubular sheath member, advancing the elongate guide into the body to provide initial access to a preselected treatment site within the body and to carry and deliver the stent to position the stent at the treatment site, and exposing the stent from the tubular sheath member to enable the stent to move from a first reduced diameter position to a second expanded position.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to catheters and intravascular medical procedures. More particularly, it relates to methods and apparatus for delivering a stent through a catheter by way of a guidewire delivery device.  
       BACKGROUND ART OF THE INVENTION  
       [0002]     Intravascular stents are well known in the medical arts for the treatment of vascular stenoses. Stents are prostheses which are generally tubular and which expand radially in a vessel or lumen to maintain its patency. For deployment within the body&#39;s vascular system, most stents are mounted onto a balloon angioplasty catheter for deployment by balloon expansion at the site of a dilated stenosis or an aneurysm. Self-expanding stents, which typically expand from a compressed delivery position to its original diameter when released from the delivery device, generally exert a radial force on the constricted portion of the body lumen to re-establish patency. One common self-expanding stent is manufactured of Nitinol, a nickel-titanium shape memory alloy, which can be formed and annealed, deformed at a low temperature, and recalled to its original shape with heating, such as when deployed at body temperature in the body.  
         [0003]     To position a stent across an area of stenosis or an aneurysm, a guiding catheter having a preformed distal tip is percutaneously introduced into the vascular system of a patient by way of, e.g., a conventional Seldinger technique, and advanced within the vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired artery. A guidewire is then positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire must first be advanced out of the distal end of the guiding catheter into the patient&#39;s coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated, then the catheter having a stent positioned on the distal portion is advanced into the patient&#39;s vasculature over the previously introduced guidewire until the stent is properly positioned across the lesion. Once in position, the stent may be released accordingly.  
         [0004]     It is generally desirable to have catheters which present small cross sectional diameters to enable access into small sized vessels. However, conventional techniques and apparatus typically require the use of a guidewire for the desirable placement of the catheter and stent within the vasculature. Thus, conventional catheters typically require a separate lumen within the catheter body to allow for the passage of a guidewire therethrough. This separate lumen necessarily adds to the cross sectional profile of the device. Yet vasculature having a tortuous path and/or a small diameter, such as the intracranial vasculature, present problems for the conventional stenting catheter. Accordingly, a highly flexible stenting apparatus which is capable of accessing tortuous regions and which presents a small cross section is needed.  
       SUMMARY OF THE INVENTION  
       [0005]     A highly flexible stent delivery assembly is described below. The assembly has the desirable characteristics of guidewires in traversing tortuous vasculature, including small cross sectioned vessels. The stent delivery assembly of the present invention is thus able to deliver and place a stent anywhere in the vasculature or within the body that is readily accessible by a guidewire but is not normally accessible by a stenting catheter body which would ride over such a guidewire.  
         [0006]     The stent delivery assembly may typically comprise a guidewire body which is preferably covered at least in part by a retractable sheath. A radially expandable stent is disposed directly in contact about the guidewire preferably near or at the distal end of the guidewire. The retractable sheath preferably covers the entire stent during deployment and placement, and is retractable proximally to uncover or expose the stent for radial expansion. A pair of optionally placed radio-opaque marker bands may be located on either side (distally or proximally) or both sides of the stent on the guidewire body.  
         [0007]     The sheath may have a flush port, which is in fluid communication with the distal end of the assembly, located near the proximal end of the sheath. The flush port enables a fluid, e.g., saline, to be passed through the assembly prior to insertion into the vasculature for flushing out air or debris trapped between the sheath and guidewire. It may also be used to deliver drugs or fluids within the vasculature as desired.  
         [0008]     Because the guidewire body, rather than a catheter body, carries and delivers the stent through the vasculature, the stent may be placed almost anywhere in the body accessible by a conventional guidewire. This may include, e.g., the tortuous intracranial vasculature as well as, e.g., the more accessible coronary vasculature. Furthermore, the assembly, which may include the guidewire, sheath, and stent, may be introduced into a wide variety of conventional catheters. This portability allows for flexibility in using the same type of assembly in an array of conventional catheters depending upon the desired application and the region of the body to be accessed.  
         [0009]     The sheath may be made from various thermoplastics, e.g., PTFE, FEP, Tecoflex, etc., which may optionally be lined on the inner surface of the sheath or on the outer surface of the guidewire or on both with a hydrophilic material such as Tecoflex or some other plastic coating. Additionally, either surface may be coated with various combinations of different materials, depending upon the desired results. It is also preferably made to have a wall thickness of about, e.g., 0.001 in., thick and may have an outer diameter ranging from about 0.0145 to 0.016 in. or greater. The sheath may be simply placed over the guidewire and stent, or it may be heatshrinked to conform closely to the assembly.  
         [0010]     The guidewire body may be made of a conventional guidewire or it may also be formed from a hypotube having an initial diameter ranging from 0.007 to 0.014 in. Possible materials may include superelastic metals and alloys, e.g., Nitinol, or metals such as stainless steel, or non-metallic materials, e.g., polyimide. The hypotube may be further melted or ground down, depending upon the type of material used, into several sections of differing diameters. The distal end of the guidewire may be further tapered and is preferably rounded to aid in advancement through the vasculature. Radio-opaque coils may be placed over a portion of distal end to aid in radiographic visualization.  
         [0011]     The stent may be configured to be self expanding from a constrained first configuration when placed upon guidewire to a larger expanded second configuration when deployed. When the sheath is retracted proximally, the stent preferably self expands to a preconfigured diameter of, e.g., about 0.060 in. (1.5 mm), and up to a diameter of about 0.315 in. (8 mm). Various materials may be used to construct the stent such as platinum, Nitinol, other shape memory alloys, or other self expanding materials.  
         [0012]     Other variations may include a guidewire which defines a stepped section near the distal end of the guidewire. The stepped section outer diameter is less than the uniform diameter defined by the remainder of the guidewire. The stent may be placed over this section while maintaining a flush outer diameter which may facilitate delivery of the stent-guidewire assembly not only through catheter body but within the vasculature. The guidewire may be further formed into tapered section distally of the stepped section.  
         [0013]     When in use in tortuous pathways, such as intracranial vessels, the guidewire assembly may be used with the sheath alone or in combination with a delivery catheter. The catheter body may be advanced within the vessel to a treatment location such as an aneurysm. Once the catheter is near the treatment site, the guidewire may be advanced out of the catheter and adjacent the treatment site. The sheath may then be retracted proximally to expose the stent to radially expand into contact with the walls of the vessel. Alternatively, the sheath may be held stationary while the guidewire and stent are advanced to expose the stent, e.g., as when deploying a coil stent. The stent may be self expanding or configured to expand upon the application of an electric current with or without the sheath. In either case, once the stent has been released from the guidewire and expanded, both the guidewire and sheath may be withdrawn into the catheter body and removed from the vicinity. The catheter may be left within the vessel to allow for the insertion of additional tools or the application of drugs near the treatment site.  
         [0014]     Other variations may include an expandable balloon section preferably located distally of the stent. In this case, treatment preferably includes the expansion of the balloon first to mitigate any occlusions within the vessel. The stent may then be released in a manner similar to that described above. Once the balloon has been deflated and the stent expanded, the assembly may be removed from the vicinity. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1A  shows a variation on the stent delivery assembly where a guidewire has a stent disposed on the wire near its distal end.  
         [0016]      FIG. 1B  shows another variation on the assembly where the guidewire may have an expandable balloon located near the distal end of the wire.  
         [0017]      FIG. 2  shows a representative illustration of the guidewire and stent assembly which is insertable within a catheter; the assembly shows the guidewire surrounded by a partially retracted sheath which exposes the stent.  
         [0018]      FIG. 3  shows a cross sectioned side view of a variation of the stent delivery assembly placed within a catheter body lumen.  
         [0019]      FIG. 4  shows a cross sectioned side view of another variation of the stent delivery assembly also placed within a catheter body lumen.  
         [0020]      FIG. 5  shows a cross sectioned side view of yet another variation of the stent delivery assembly having an expandable balloon section.  
         [0021]      FIGS. 6A  to  6 C illustrate an example of one method of placing a stent within a hollow body organ using the guidewire assembly.  
         [0022]      FIGS. 7A  to  7 C illustrate an example of another method of placing a stent within the hollow body organ in combination with an expandable balloon. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     A stent delivery assembly having a small cross section and which is highly flexible is described herein. As shown in  FIG. 1A , catheter assembly  10  is comprised of a conventional catheter body  12  having a distal end  14  and a proximal end  16 . A fitting assembly  18  is attached to the proximal end  16  and may preferably have various attachments, e.g., Luer lock  20 , to allow for access to catheter body  12  or the use of other instruments. Conventional catheter body  12  shows guidewire assembly  22  being slidably positioned therewithin. Assembly  22 , which is described in further detail below, is shown in this variation as having a guidewire body  24  preferably covered at least in part by a retractable sheath  26 . A radially expandable stent  28  is preferably disposed near the distal end of guidewire  24 . Stent  28  may also be placed between an optional pair of radio-opaque marker bands  30 ,  32 . One or both marker bands  30 ,  32  may be used or they may be left off the assembly entirely. The use of radio-opaque material allows for the visualization of the assembly during placement within the vasculature. Such visualization techniques may include conventional methods such as fluoroscopy, radiography, ultrasonography, magnetic resonance imaging, etc.  
         [0024]      FIG. 1B  shows the distal portion of catheter body  12  with another guidewire variation  34  which has an optional angioplasty balloon  36 . As shown in this variation, balloon  36  is preferably located distally of stent  28  and may be sufficiently deflated such that sheath  26  may be placed over both stent  28  and balloon  36 .  
         [0025]      FIG. 2  shows a representative illustration of the stent delivery assembly  40  removed entirely from the delivery catheter body with guidewire  24  covered by sheath  26 . Stent  28  is preferably placed directly over guidewire body  24  and is covered by sheath  26 . Sheath  26  may have a flush port  42  located near the proximal end of the sheath  26 . Flush port  42  is preferably in fluid communication with the distal end of the assembly  40  so that a fluid, e.g., saline, may be passed through the assembly  40  prior to insertion into the vasculature for flushing out air or debris trapped between the sheath  26  and guidewire  24 . Flush port  42  may also be used to deliver drugs or fluids within the vasculature as desired.  
         [0026]     Because the guidewire body  24 , rather than a catheter body, carries and delivers stent  28  through the vasculature, the stent  28  may be placed almost anywhere in the body accessible by a conventional guidewire. This may include, e.g., the tortuous intracranial vasculature as well as, e.g., the more accessible coronary vasculature. Furthermore, assembly  40 , which may include the guidewire  24 , sheath  26 , and stent  28 , may be introduced into a wide variety of conventional catheters. This portability of assembly  40  allows for flexibility in using the same type of assembly  40  in an array of conventional catheters depending upon the desired application and the region of the body to be accessed.  
         [0027]     The sheath  26  may be made from various thermoplastics, e.g., PTFE, FEP, Tecoflex, etc., which may optionally be lined on the inner surface of the sheath or on the outer surface of the guidewire or on both with a hydrophilic material such as Tecoflex or some other plastic coating. Additionally, either surface may be coated with various combinations of different materials, depending upon the desired results. Sheath  26  is preferably made to have a wall thickness of about 0.001 in. thick, and optionally thicker, and may have an outer diameter ranging from about 0.0145 to 0.016 in., or greater. Sheath  26  may also be placed over guidewire body  24  having a diameter of about 0.038 in. When placed over guidewire body  24  and stent  28 , it may be simply placed over to slide along wire  24  or it may also be heatshrinked over the wire  24  and stent  28  to conform closely to the assembly.  
         [0028]     A more detailed view of the guidewire assembly is shown in the cross sectioned side view in  FIG. 3 . As seen, the distal end of guidewire body  24  is shown loaded within sheath lumen  60  of sheath  26  and this assembly is shown as being disposed within catheter lumen  62  of catheter body  12 . As previously discussed, because stent  28  is placed upon a guidewire body rather than a catheter body, the assembly may be introduced into any part of the body which is accessible by a conventional guidewire but which is not normally accessible for stenting treatments.  
         [0029]     The guidewire body  24  may be made of a conventional guidewire and it may also be formed from a hypotube having an initial diameter ranging from 0.007 to 0.014 in. The hypotube or guidewire may be made from a variety of materials such as superelastic metals, e.g., Nitinol, or it may be made from metals such as stainless steel. During manufacture, a proximal uniform section  50  of the hypotube may be made to have a length of between about 39 to 87 in. (100 to 220 cm), preferably between about 63 to 71 in. (160 to 180 cm), having the initial diameter of 0.007 to 0.022 in., preferably 0.008 in. The hypotube may be further melted or ground down into a tapered section  52 , depending upon the type of material used, which is distal to the proximal uniform section  50 . Tapered section  52  may have a length of about 4 in. (10 cm) to reduce the diameter down to about 0.002 to 0.003 in. The hypotube may be further formed to have a distal uniform section  54  of about 2 in. (5 cm) in length over which the stent  28  is preferably placed. Radio-opaque marker bands may optionally be placed either distally  30  or proximally  32  of stent  28  to visually aid in the placement of the stent  28 , as is well known in the art. Alternatively, distal and proximal marker bands  30 ,  32  may be eliminated altogether. Marker bands  30 ,  32  may be used as blocks or stops for maintaining the stent in its position along guidewire body  24 . Alternatively, if bands  30 ,  32  are omitted from the device, stops or blocks may be formed integrally into the guidewire body  24  or they may be separately formed from material similar to that of guidewire body  24  and attached thereto.  
         [0030]     Distal end  56  may be further tapered beyond distal uniform section  54  to end in distal tip  58 , which is preferably rounded to aid in guidewire  24  advancement. A coil, preferably made from a radio-opaque material such as platinum, may be placed over a portion of distal end  56 . Alternatively, a radio-opaque material, e.g., doped plastics such as bismuth or tungsten, may be melted down or placed over a portion of distal end  56  to aid in visualization. Stent  28  is preferably made to be self expanding from a constrained first configuration, as when placed upon guidewire  24  for delivery, to a larger expanded second configuration as when deployed within the vasculature. Stent  28  may be constrained by sheath  26  to a diameter of, e.g., 0.014 in., while being delivered to a treatment site within the body, but when sheath  26  is retracted proximally, stent  28  preferably self expands to a preconfigured diameter of, e.g., about 0.060 in. (1.5 mm), and up to a diameter of about 0.315 in. (8 mm). Various materials may be used to construct stent  28  such as platinum, Nitinol, other shape memory alloys, or other self expanding materials. Sheath  26  may also have drainage ports or purge holes  64  formed into the wall near the area covering stent  28 . There may be a single hole or multiple holes, e.g., three holes, formed into sheath  26 . Purge holes  64  allow for fluids, e.g., saline, to readily escape from inbetween sheath  26  and guidewire  24  when purging the instrument, e.g., to remove trapped air or debris.  
         [0031]      FIG. 4  shows a cross sectioned side view of another variation  70  of the stent delivery assembly. As shown, guidewire variation  70  is shown as being surrounded by sheath  26  and the sheath-guidewire assembly is shown as being placed within catheter lumen  62  prior to delivery of the stent. In this variation, the guidewire may have a uniform section  72  like that described in  FIG. 3  above. However, there is also a stepped section  74  defined in the guidewire outer diameter near the distal end of the guidewire. Within this section  74 , the stepped outer diameter is less than the uniform diameter defined by the guidewire uniform section  72 . It is over this stepped section  74  that stent  84  may be placed along with optional distal and/or proximal marker bands  80 ,  82 , respectively, such that sheath  26  remains flush over this section. Maintaining a flush outer diameter may facilitate delivery of the stent-guidewire assembly not only through catheter body  12  but within the vasculature. The guidewire may be further formed into tapered section  76  distally of stepped section  74 . And the guidewire may be finally formed into a distal tip  78  over which coil  86  may be optionally placed. Coil  86  may optionally be covered by a covering  88 , e.g., a polymer or other plastic material, placed or heatshrinked over the coil  86  and distal tip  78  to provide a smooth section.  
         [0032]      FIG. 5  shows a cross sectioned side view of yet another variation of the stent delivery assembly having an expandable balloon section. As shown, much of the guidewire is similar to variations described above but with the addition of an expandable balloon  36  which may be inflated to an expanded balloon  36 ′. The variation shown may have a uniform section  90  which similarly tapers down  92  into a distal uniform section  94 , over which stent  28  may be placed. Although balloon  36  may be placed proximally of stent  94 , it is preferably located distally of stent  94 , as shown. When deflated, retractable sheath  26  may also be placed over balloon  36  to provide a uniform profile. To accommodate the inflation and deflation of balloon  36 , a small inflation lumen (not shown) may be defined within the body of the guidewire for the passage of fluids into and out of the balloon  36 . A coil may also be optionally placed over distal end  96 ; alternatively, a radio-opaque material may be melted down or placed over distal end  96 .  
         [0033]     In operation, the stent delivery guidewire may be used with or without the catheter body to deliver the assembly intravascularly. It is preferable that a catheter be used to provide a pathway close to the treatment site. However, in tortuous pathways, such as intracranial vessels, the guidewire device may be used with the sheath alone if the catheter body presents too large a cross section for delivery purposes.  FIGS. 6A  to  6 C show an example of the deployment of the guidewire assembly. Catheter body  12  may first be advanced within the lumen  102  of vessel  100  to a treatment location, e.g., aneurysm  104 . Once catheter body  12  has reached a position near aneurysm  104 , guidewire  24  may be advanced through and out of catheter  12  with sheath  26  covering stent  28 , as seen in  FIG. 6A . As guidewire  24  is advanced, stent  28  located on guidewire  24  may be positioned via radio-opaque marker bands  30 ,  32  to the desired location, such as over the neck  106  of aneurysm  104 . Once guidewire  24  and stent  28  have been properly positioned, sheath  26  may be retracted proximally to expose stent  28  to the vascular environment, as shown in  FIG. 6B .  
         [0034]     Stent  28 , as shown in  FIG. 6C , may be left to radially self expand into gentle contact with the walls of vessel  100  to occlude the neck  106  of aneurysm  104  (as is well known in the art). Stent  28  may also be configured to expand upon the application of an electric current actuated from a location external of the patient. The current may be delivered to stent  28  via an electrical connection or line (not shown) disposed within the body of guidewire  24 . Once the stent  28  has been released from the guidewire body  24  and expanded into contact with vessel  100 , guidewire  24  and sheath  26  may be withdrawn into catheter body  12  and removed entirely from catheter  12  or the catheter  12  itself may then be removed entirely from the body of the patient. If guidewire  24  and sheath  26  are removed only, catheter  12  may be left in position within vessel  100  to allow for the insertion of additional tools or the application of drugs near the treatment site.  
         [0035]     Treatment may also be accomplished with the guidewire variation having an expandable balloon section.  FIG. 7A  shows vessel  110  which is stenosed with an obstruction  112 . Once catheter body  12  has been positioned within vessel  110 , guidewire body  34  may be advanced out of catheter  12  while still covered by sheath  26 . Balloon  36  may then be positioned adjacent to the obstruction  112  optionally guided by marker bands  30 ,  32 . Once positioned, balloon  36  may be expanded to balloon  36 ′, as shown in  FIG. 7B , to open the stenosed vessel. After the obstruction  112  has been opened, balloon  36  may be deflated and the guidewire body  34  may be advanced distally to position sheath  28  adjacent to obstruction  112 . Sheath  26  may then be retracted to expose stent  28  to expand, as described above, into contact against obstruction  112  and vessel  110 .  FIG. 7C  shows the placement of guidewire  34  and expanding stent  28  over obstruction  112 .  
         [0036]     The applications of the guidewire assembly and methods of use discussed above are not limited to the deployment and use within the vascular system but may include any number of further treatment applications. Other treatment sites may include areas or regions of the body such as organ bodies. Modification of the above-described assemblies and methods for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the scope of the claims.