Abstract:
The present invention is drawn to a system and/or device for deploying a stent at a bifurcation. In one embodiment, the system and/or device for deploying a stent at a bifurcation may include a dual balloon catheter may include an elongate catheter body. Some dual balloon catheters may have a first proximal balloon and a second balloon bonded to at least a portion of the elongate catheter body. In some cases, a guide wire port may be positioned between the first and second balloons.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 10/626,794, now U.S. Pat. No. 7,476,243, filed Jul. 22, 2003, titled “BIFURCATION STENT DELIVERY SYSTEM”, which is a divisional of U.S. application Ser. No. 09/490,808, filed Jan. 26, 2000, now abandoned, which claims priority to U.S. Provisional Application No. 60/117,351, filed Jan. 27, 1999, all of which are hereby incorporated by reference in their entirety. 
     U.S. Pat. No. 4,950,227 issued Aug. 21, 1990 to Savin et al. entitled “STENT DELIVERY SYSTEM” and assigned to Boston Scientific Corporation is hereby incorporated by reference. 
     Reference is hereby made to the following U.S. issued patents:
     U.S. Pat. No. 6,258,534 (Ser. No. 09/035,652) filed Mar. 5, 1998, entitled “DILATATION AND STENT DELIVERY SYSTEM FOR BIFURCATION LESIONS”;   U.S. Pat. No. 6,096,073 (Ser. No. 09/028,792) filed Feb. 24, 1998, entitled “STENTS AND STENT DELIVERY AND DILATATION SYSTEM FOR BIFURCATION LESIONS”;   U.S. Pat. No. 6,143,002 (Ser. No. 09/129,472) filed Aug. 4, 1998, entitled “SYSTEM FOR DELIVERING STENTS TO BIFURCATION LESIONS”; and   U.S. Pat. No. 6,514,281 (Ser. No. 09/148,179) filed Sep. 4, 1998, entitled “SYSTEM FOR DELIVERING BIFURCATION STENTS”.   

    
    
     BACKGROUND 
     The present invention relates to a system for treating vascular disease. More specifically, the present invention relates to a system for deploying a stent in a bifurcation lesion. 
     Vascular disease currently represents a prevalent medical condition. Typical vascular disease involves the development of a stenosis in the vasculature. The particular vessel containing the stenosis can be completely blocked (or occluded) or it can simply be narrowed (or restricted). In either case, restriction of the vessel caused by the stenotic lesion results in many well known problems caused by the reduction or cessation of blood circulation through the restricted vessel. 
     A bifurcation is an area of the vasculature where a first (or parent) vessel is bifurcated into two or more branch vessels. It is not uncommon for stenotic lesions to form in such bifurcations. The stenotic lesions can affect only one of the vessels (i.e., either of the branch vessels or the parent vessel) two of the vessels, or all three vessels. 
     Vascular stents are also currently well known. Vascular stents typically involve a tubular stent which is movable from a collapsed, low profile, delivery position to an expanded, deployed position. The stent is typically delivered using a stent delivery device, such as a stent delivery catheter. In one common technique, the stent is crimped down to its delivery position over an expandable element, such as a stent deployment balloon. The stent is then advanced using the catheter attached to the stent deployment balloon to the lesion site under any suitable, commonly known visualization technique. The balloon is then expanded to drive the stent from its delivery position to its deployed position in which the outer periphery of the stent frictionally engages the inner periphery of the lumen. In some instances, the lumen is predilated using a conventional dilatation catheter, and then the stent is deployed to maintain the vessel in an unoccluded, and unrestricted position. 
     Self-expanding stents can also be used. Self-expanding stents are typically formed of a resilient material. The resilient material has sufficient resilience that it can be collapsed to the low profile position and inserted within a delivery device, such as a catheter. Once the catheter is placed at the site of the stenotic lesion, the stent is pushed from within the catheter such that it is no longer constrained in its low profile position. The stent, driven by the resilience of the material, expands to a higher profile, deployed position in which its outer periphery frictionally engages the walls of the stenosed vessel, thereby reducing the restriction in the vessel. 
     While there have recently been considerable advances in stent design and stent deployment techniques, current methods of treating bifurcation lesions are suboptimal, particularly where both downstream branch vessels are affected by the lesion Current techniques of dealing with such lesions typically require the deployment of a slotted tube stent across the bifurcation. However, this compromises the ostium of the unstented branch. 
     Further, once the first stent is deployed, the treating physician must then advance a dilatation balloon between the struts of the stent already deployed in order to dilate the second branch vessel. The physician may then attempt to maneuver a second stent through the struts of the stent already deployed, into the second branch vessel for deployment. This presents significant difficulties. For example, dilating between the struts of the stent already deployed tends to distort that stent. Further, deploying the second stent through the struts of the first stent is not only difficult, but it can also distort the first stent. Thus, the current systems used to alternately deploy stents in a bifurcated lesion have significant disadvantages. 
     Also, since two guidewires are often used to deploy stents at a bifurcation, the guidewires can become crossed, or somewhat entangled. The deployment systems which are advanced along such guidewires can become caught on the wires, where they cross over one another. This can require additional time and manipulation of the stent deployment system in order to properly deploy the stent at the bifurcation. 
     Further, some branch vessels can have somewhat smaller diameter lumens than the parent vessels from which they branch. Therefore, stents of different sizes need to be deployed in the parent vessel and the branch vessel. Alternatively, a single stent having a larger diameter portion, and one or more smaller diameter portions, can be deployed at the bifurcation. However, this can lead to difficulty in deployment. For instance, a balloon which is sized to fit within the smaller diameter stent portion, and deploy that portion, may not be large enough to deploy the larger diameter stent portion. Therefore, a plurality of balloon catheters must be used to deploy such stents. 
     SUMMARY 
     The present invention is drawn to a system and/or device for deploying a stent at a bifurcation. In one embodiment, a dual balloon catheter may include an elongate catheter body that may having a distal end, at least one guide wire lumen therethrough and an inflation lumen therein. The dual balloon catheter may also include a first proximal balloon that may have a proximal portion bonded to the catheter and a second distal balloon that may have a distal portion bonded to the catheter distally of the first balloon, the proximal and distal balloons in fluid communication with the inflation lumen. A guide wire port may be positioned between the first and second balloons and in communication with the at least one guide wire lumen. 
     The preceding summary is provided to facilitate a general understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a typical bifurcation lesion; 
         FIGS. 2 and 3  illustrate a stent having two different deployed diameters; 
         FIG. 4  illustrates the stent shown in  FIGS. 2 and 3  deployed in a bifurcation; 
         FIG. 5  illustrates a dual-balloon stent deployment system; 
         FIGS. 6A and 6B  illustrate deployment of the stent deployment system illustrated in  FIG. 5 ; 
         FIG. 7  illustrates another embodiment of a dual-balloon stent deployment system; 
         FIGS. 8A and 8B  illustrate catching of a distal portion of a stent deployment system on crossed or tangled guidewires; 
         FIGS. 9A-9C  illustrate a stent deployment system with a distal sleeve disposed thereabout; 
         FIG. 10  illustrates another embodiment of a dual-balloon stent deployment system; 
         FIGS. 10A-10C  illustrate another embodiment of a dual-balloon stent deployment system; 
         FIGS. 11A and 11B  illustrate another embodiment of a dual-balloon stent deployment system; 
         FIGS. 12A-12C  illustrate a stepped-balloon stent deployment system; 
         FIGS. 13A-13C  illustrate a retractable stent deployment system; 
         FIGS. 14A-14C  illustrate a collapsible embodiment of a stepped balloon stent deployment system; and 
         FIGS. 15A-15C  illustrate stiffening and torquing systems for use with a stent deployment system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates bifurcation  10  which includes parent vessel  12 , first branch vessel  14  and second branch vessel  16 .  FIG. 1  also illustrates that a bifurcation lesion  18  has developed in bifurcation  10 . As illustrated, lesion  18  extends into both branch vessels  14  and  16 , and extends slightly into parent vessel  12  as well. Lesion  18  may also be located on only one side of the branch vessel  14  or  16 . In either case, it is preferable to stent both branch vessels  14  and  16  to avoid collapsing one. In order to treat bifurcation lesion  18 , it may commonly first be predilated with a conventional angioplasty balloon catheter dilatation device. 
       FIG. 2  is a side view of a stent  20  which can be used to treat a portion of bifurcation  10 . Stent  20  includes a first portion  22  and a second portion  24 . First portion  22  has a relatively large deployed diameter, while second portion  24  has a somewhat smaller deployed diameter. 
       FIG. 3  is an end view of stent  20  taken as indicated by arrows  3 - 3  in  FIG. 2 . In one illustrative embodiment, portions  22  and  24  of stent  20  are simply discrete stents which have been interwoven, or attached, to one another. Alternatively, stent  20  can be formed by one integral stent formed with portions  22  and  24  being integral with one another. In either case, stent  20  can preferably be deformed to a low profile, collapsed (or deployment) position in which it can be inserted through parent vessel  12  to bifurcation  10 . Stent  20  is then deployed, either using its own resilience, or using a balloon deployment system, to its expanded, deployed position illustrated in  FIG. 2 . 
       FIG. 4  illustrates stent  20  deployed in bifurcation  10 . In  FIG. 4 , first and second guidewires  26  and  28  are first inserted, through parent vessel  12 , to bifurcation  10  such that guidewire  26  has a distal end residing in branch vessel  14  while guidewire  28  has a distal end residing in branch vessel  16 . Using a stent deployment system, such as any of those described in greater detail later in the specification, stent  20  is advanced in a low profile, insertion position to the location illustrated in  FIG. 4 . Stent  20  is then deployed by expanding portions  22  and  24  to the deployed positions illustrated in  FIG. 4 . In one illustrative embodiment, portion  24  has an outer diameter which, when deployed, frictionally engages the inner diameter of branch vessel  14 . Similarly, portion  22  has an outer diameter which, when deployed, is sufficient to frictionally engage the inner diameter of parent vessel  12 , to remain in place in bifurcation  10 . 
       FIG. 5  is a side view of a dual-balloon stent deployment system  30  in accordance with one aspect of the present invention. System  30  is shown with a cross-section of stent  20 , in the deployed position, disposed thereon. System  30  includes a proximal catheter  32  having a lumen  34  disposed therein. First and second guidewire lumens (or tubes)  36  and  38  extend from within lumen  34  and extend to distal ends  40  and  42 . System  30  also includes a first, proximal balloon  44  and a second, distal balloon  46 . Balloon  44  has a proximal end  48  which is sealed to the distal end of catheter  32 . While proximal end  48  of balloon  44  can be sealed to either the outer or inner side of catheter  32 , it is illustrated in  FIG. 5  as being sealed to the outer surface of catheter  32 , using, for example, an adhesive. Balloon  44  also has a distal end  50  which is sealed, with a fluid tight seal, about guidewire tube  36  and a portion of the proximal end  52  of balloon  46 . 
     Balloon  46  includes a proximal end  52  which is also fluidly sealed partially to an inside surface of the distal waist of balloon  44  and partially to guidewire lumen  38 . However, an inflation lumen  54  extends from the interior of balloon  44 , through the proximal end  52  of balloon  46 , and communicates with the interior or balloon  46 . Balloon  46  further includes a distal end  56  which is sealed to the outer surface of guidewire lumen  42 . Therefore, an inflation lumen for inflating balloons  44  and  46  is defined by lumen  34  of catheter  42 , and lumen  54  disposed about at least a portion of guidewire tubes  36  and  38 . 
     Guidewire lumen  38  extends from lumen  34  distally through both balloons  44  and  46 , and protrudes out the distal end  56  of balloon  46 . Guidewire lumen  36 , on the other hand (and as will be disclosed in greater detail later in the specification) is used to track a guidewire which extends down a branching vessel. Guidewire lumen  38  has a distal end  40  which extends out from within the distal end  50  of balloon  44 , and extends to a position outside of balloon  46 . Both balloons  44  and  46  can preferably be collapsed to a low profile, insertion position. However, balloon  44  has a relatively large inflated diameter for driving deployment of the larger diameter portion  22  of stent  20 . Balloon  46 , on the other hand, has a smaller inflated diameter for driving deployment of the smaller diameter stent portion  24  of stent  20 . 
       FIGS. 6A and 6B  illustrate the deployment of stent  20  utilizing system  30  illustrated in  FIG. 5 .  FIG. 6A  illustrates system  30  in the insertion position. First, guidewires  26  and  28  are advanced through the vasculature to bifurcation  10 , such that they reside within branch vessels  14  and  16 , respectively. It should be noted that system  30  can be backloaded onto guidewires  26  and  28 . In that case, prior to inserting guidewires  26  and  28 , system  30  is loaded onto the guidewire such that guidewire  26  resides within guidewire tube  36  while guidewire  28  resides within tube  30 . Alternatively, system  30  can be loaded onto guidewires  26  and  28  from the proximal end of the guidewires. In either case, after the guidewires are positioned appropriately, system  30  is advanced using catheter  32  through the vasculature (and may be advanced through a guide catheter  58 ) to bifurcation  10 . System  30  is then further advanced such that stent portion  24  follows guidewire  26  and resides within branch vessel  14 . 
     Once in the position illustrated in  FIG. 6A , fluid is introduced into balloons  44  and  46  through catheter  32 , to inflate the balloons. This drives stent portions  22  and  24  of stent  20  into the deployed position illustrated in  FIG. 6B . In the deployed position, the outer diameter of stent portions  22  and  24  are sufficient to frictionally engage the interior vessel walls of parent vessel  12  and branch vessel  14 , respectively, such that stent  20  is frictionally held in place in bifurcation  10 . The lumens  44  and  46  are then deflated, and system  30  is removed from within stent  20 . Guidewires  26  and  28  are then removed from bifurcation  10 , leaving stent  20  deployed in place. 
     System  30  preferably employs balloons  44  and  46  which have steep proximal and distal cone angles in order to reduce any gap between the balloons this increases the ability to exert adequate deployment force on stent portions  22  and  24 . Similarly, post delivery dilatation may be used in order to further dilate the lesion from within the deployed stent  20 . 
       FIG. 7  illustrates a side view of another embodiment of a dual-balloon stent deployment system  60  in accordance with one aspect of the present invention. System  60  has a number of items which are similar to system  30  shown in  FIG. 5 , and those items are similarly numbered in  FIG. 7 . System  60  includes a proximal balloon  62  which has a proximal end  64  and a distal end  66 . The proximal end  64  in balloon  62  is sealed about the distal end of catheter  32 . The interior of balloon  62  communicates with lumen  34  of catheter  32 . The distal end  66  of balloon  62  is formed in a cone configuration. A radially interior portion is sealed about guidewire tubes  36  and  38 , leaving an inflation lumen  68  therebetween, which communicates with the interior of balloon  46 . The radial outward portion of the distal end  66  of balloon  62 , when inflated, assumes an outer diameter which is substantially the same as the maximum diameter of the remainder of balloon  62 . However, the distal end  66  is formed in a reverse cone shape such that the radial outward portion of the distal end  66  is substantially tubular in shape. The balloon tapers proximally along a portion  70  to the inner diameter portion of balloon  62 . 
     In this way, the outer diameter of balloon  62  obtains a substantially greater size, at its extreme distal end, than balloon  44  in system  30 . This assists in deploying portion  22  of stent  20 . Again, post-delivery dilatation may be used to further advance stent portions  22  and  24  toward the wall of vessels  12  and  14 , respectively. Stent deployment system  60  is deployed in a similar fashion as stent deployment system  30 , illustrated with respect to  FIGS. 6A and 6B . 
       FIGS. 8A and 8B  illustrate a problem which can be encountered in deploying a stent in a bifurcation.  FIG. 8A  illustrates a stent deployment system  72  located just proximally of bifurcation  10 . Stent deployment system  72  includes a distal stent portion  74  which has a distal end  76 .  FIG. 8A  also illustrates that guidewires  26  and  28  are crossed over one another in a cross-over region  78 . As deployment system  72  is advanced distally, the distal end  76  of stent portion  74  encounters cross over region  78 .  FIG. 8B  illustrates that the distal end  76  of stent portion  74  can actually catch, and hang up on, a portion of guidewire  28  which is crossed over guidewire  26 . This makes it very difficult, if not impossible, to continue to advance stent deployment system  72  distally over guidewires  26  and  28 . Instead, system  72  must be withdrawn proximally, and the guidewires  26  and  28  must be remanipulated or deployment system  72  must be torqued (rotated about its longitudinal axis) or otherwise maneuvered, in an attempt to loosen guidewire  28  from the distal end  76  of stent portion  74 . 
       FIG. 9A  illustrates stent deployment system  60 , as discussed with respect to  FIG. 7 , but with the addition of a distal sleeve  80  or a proximal sleeve  82  or both disposed about the distal end of stent portion  24  and the proximal end of stent portion  22 , respectively. Distal sleeve  80  and proximal sleeve  82  are provided in order to minimize the likelihood that the longitudinal ends of stent  20  will catch or engage any unwanted obstacles, such as tissue or guidewires. The sieves  80  and  82  are described in greater detail in U.S. Pat. No. 4,950,227, which is fully incorporated herein by reference. Briefly, sleeves  80  and  82  are illustratively formed of silicone and are approximately 2 cm in length. Sleeve  80  is fixed to the distal end  42  of guidewire lumen  38  using adhesive or welding. Similarly, the proximal end of sleeve  82  is fixed to the distal end of catheter  32 , using a suitable adhesive. Such adhesive may, for example, be comprised of a urethane bead. Sleeves  80  and  82  overlap stent portions  24  and  22 , respectively, by a distance which is approximately 3 mm. Further, in one embodiment, sleeves  80  and  82  have tapered distal edges. In a further embodiment, sleeves  80  and  82  have tapered distal and proximal edges. This facilitates the transfer of system  60  within the vasculature, while decreasing the tendency to catch or engage undesired obstacles. 
       FIGS. 9B and 9C  illustrate the deployment of stent portion  24  and the interaction of stent portion  24  with sleeve  80 . A similar interaction is obtained between sleeve  82  and the proximal end of stent portion  22 . As stent portion  24  is deployed, balloon  46  is inflated and the distal end of stent portion  24  is released from within sleeve  80 . This is illustrated in  FIG. 9B . Then, after stent portion  24  is deployed and balloon  46  is deflated (and thus radially retracted) sleeve  80  contracts about the distal end of balloon  46 . The deflation of balloon  46  facilitates removal of balloon  46 , as well as sleeve  80 , from within the deployed stent portion  24 , as deployment system  60  is axially removed from the vasculature. It should be noted that sleeves  80  and  82  can be used on substantially any of the embodiments described herein. 
       FIG. 10  illustrates another dual-balloon stent deployment system  90  in accordance with one aspect of the present invention. System  90  includes an outer sheath  92 , an inner sheath  94  defining an inflation lumen  96 , a plurality of guidewire lumens  98  and  100 , each having distal ends  102  and  104 , respectively. System  90  also includes first balloon  106  and second balloon  108 . First balloon  106  has a distal end  110  which is sealed about the outer surface of guidewire lumen  102 . Balloon  106  also has a proximal end  112  which is sealed within a disc  114  which is sealed (such as through adhesive) to the inside of the distal end of catheter  94 . Balloon  108  has a distal end  116  which is sealed about the outer surface of guidewire lumen  104 , and a proximal end  118  which is sealed within disc  114 . The interior of balloons  106  and  108  are in fluid communication with the lumen  96  formed by inner catheter  94 . This provides an arrangement to provide fluid under pressure to inflate balloons  106  and  108 . It should be noted that, instead of using disc  114 , the inside of the distal end of catheter  94  can simply be filled with adhesive using a technique commonly referred to as potting. 
     Balloons  106  and  108  can either have the same, or different, deployed diameters. However, balloon  108  may have a greater longitudinal length than balloon  106 . Therefore, stent portion  22  of stent  20  can be deployed by inflating both balloons  106  and  108  to drive stent portion  22  into its higher profile, deployed position. By contrast, stent portion  24  is disposed only about the distal part of balloon  108 , distal of balloon  106 . Thus, stent portion  24  is deployed by the inflation of balloon  108 . System  90  is used to deploy stent  20  in a similar fashion to that described with respect to system  30  in  FIGS. 6A and 6B . 
       FIGS. 10A-10C  illustrate another stent deployment system  120 . System  120  is similar to system  90  illustrated in  FIG. 10 , and similar items are similarly numbered. However, rather than having a disc  114  disposed at the distal end of catheter  94 , system  120  has a plug member  122  (which is also illustrated in  FIGS. 10B and 10C ). Plug member  122  has an exterior surface which snugly fits within the interior of the distal end of catheter  94 , and is secured therein, such as by frictional fit or suitable adhesive. Plug member  122  also has generally tubular extensions  124  and  126  which extend from a body  128  thereof. A pair of lumens  130  and  132  extend through body  128  and through extension members  124  and  126 , respectively. Lumens  130  and  132  are larger than guidewire lumens  98  and  100  such that guidewire lumens  98  and  100  can pass therethrough, and still leave an area which provides fluid communication between lumen  96  of catheter  94  and the interior of balloons  106  and  108 , respectively. This provides a mechanism by which balloons  106  and  108  can be inflated through the infusion of pressurized fluid through lumen  96  in catheter  94 . 
     In addition, the proximal ends  112  and  118  of balloons  106  and  108  are illustratively fastened about the exterior of extension members  124  and  126 , respectively. Such fastening can take any suitable form, such as through adhesive. 
       FIGS. 11A and 11B  illustrate yet another embodiment of a stent deployment system  138  in accordance with another aspect of the present invention. System  138  includes a first balloon  140  and a second balloon  142 . Each balloon is disposed about a guidewire lumen  144  and  146 , respectively. A proximal catheter  148  is provided with two separate inflation lumens  150  and  152 . Inflation lumen  150  is provided to inflate balloon  140  while inflation lumen  152  is provided to inflate balloon  142 . The proximal end of balloons  140  and  142  are sealably connected about inflation lumens  150  and  152  and guidewire lumens  144  and  146 . 
     Similarly, catheter  148  is also provided with a stiffening member  154 . Stiffening member  154  is preferably a stiffening wire (or a pair of stiffening wires or a hypotube) which runs at least through a distal portion of catheter  148 , and is fastened thereto, to provide increased pushability, and increased torquability. 
       FIG. 11B  is a cross-sectional view of catheter  148  taken along section lines  11 B- 11 B shown in  FIG. 11A .  FIG. 11B  shows that, in one illustrative embodiment, catheter  148  includes a pair of stiffening members  154 A and  154 B which are either embedded within, or fixedly secured to, the wall of catheter  148 . Similarly,  FIG. 11B  better illustrates that inflation lumens  150  and  152  are generally kidney-shaped (or shaped in a generally hemispherical shape) and extend partially about the guidewire lumens  144  and  146 , respectively System  138  is used to deploy stent  20  in a fashion similar to system  30  illustrated in  FIGS. 6A and 6B . 
       FIG. 12A  is a side view of another embodiment of a stent deployment system  160  in accordance with one aspect of the present invention. System  160  includes a catheter  162  with a lumen  164  therein. A guidewire lumen  166  extends through lumen  164  to a distal end  168  of the guidewire lumen. System  160  also includes a stepped balloon  170 . Stepped balloon  170  has a distal end  172  sealably connected about the outer surface of guidewire lumen  168 . Balloon  170  also has a proximal end  174  sealably connected about the external surface of catheter  162 . In addition, balloon  170  has a first portion  176  which has a first inflated outer diameter and a second portion  178  which has a second inflated outer diameter, less than the first inflated outer diameter of portion  176 . Balloon  170  has a step region  180  which defines the transition between portion  176  and  178 . The step region  180 , in the embodiment illustrated in  FIG. 12A , is simply a steeply tapering portion which extends from the inflated outer diameter of balloon portion  178  to the inflated outer diameter of balloon portion  176 . Balloon  170  is preferably formed of a conventional balloon material preformed into the stepped shape illustrated generally in  FIG. 12A . 
     Thus, stent  20  can be deployed using only a single balloon  170 . The smaller diameter stent portion  24  is disposed over balloon portion  178 , while the larger diameter balloon stent portion  22  is disposed over balloon portion  176 . 
       FIG. 12B  illustrates another stepped balloon  182 . Balloon  182  also includes first and second portions  184  and  186 . However, the step in balloon  182  is generally concentric, rather than eccentric as described with respect to  FIG. 12A .  FIG. 12C  illustrates balloon  182  disposed within bifurcation  10 . In one illustrative embodiment, stent  20  has section  22 , which is weaker than section  24 . Due to the strength of stent  20 , the step in balloon  182  moves or shifts from being concentric, to being non-concentric, as illustrated in  FIG. 12C . The eccentricity shifts towards the open cell (or weaker section) of stent  22 . 
       FIGS. 13A-13C  illustrate another stent deployment system  190  in accordance with one aspect of the present invention. Deployment system  190  includes stepped balloon  182  with a guidewire lumen  192  extending therethrough. Stent  20  is disposed about balloon  182 . In addition, within stent portion  22 , and on the exterior of balloon  182 , is provided a second guidewire lumen  194 . A proximal catheter  196  is coupled to fluidly communicate with the interior of balloon  182 . A pull wire  198  is coupled to the proximal end of guidewire lumen  194  and to a pull sleeve  200  slidably disposed about catheter  196 , generally at the proximal end of catheter  196 . 
       FIGS. 13A and 13B  illustrate the insertion of system  190  for deployment of stent  20 .  FIG. 13B  illustrates that system  190  is advanced through the vasculature over guidewires  26  and  28  such that the distal end of balloon  182  (and stent portion  24 ) resides within branch vessel  14 . Stent  20  is deployed under relatively low pressure to pre-dilate the stent. Next, guidewire lumen  194  is withdrawn proximally in the direction indicated by arrow  202 , by user withdrawal of sleeve  20  proximally over catheter  196 . 
     Balloon  182  is then further inflated to a relatively high pressure to post-dilate the stent, as illustrated in  FIG. 13C . This acts to deploy stent  20  outwardly causing the outer surface of stent  20  to frictionally engage the interior surface of parent vessel  12  in branch vessel  14 . Balloon  182  is then deflated and the system is withdrawn from the vasculature, leaving stent  20  in place in bifurcation  10 . 
       FIGS. 14A-14C  illustrate another stent deployment system  210  in accordance with one aspect of the present invention. System  210  is similar to system  190  described with respect to  FIGS. 13A-13C , and similar items are similarly numbered. However, system  210  allows guidewire lumen  194  to remain in place, adjacent balloon  182 , during deployment of stent  20 . Therefore, rather than having a removable guidewire lumen  194 , system  210  includes guidewire lumen  212 . As in system  190 , guidewire lumen  212  resides within portion  22  of stent  20 , but on the exterior of balloon  182 . 
       FIG. 14B  illustrates that system  210  is inserted within bifurcation  10  in a manner similar to system  190  (illustrated in  FIG. 13B ) However, guidewire lumen  212  remains in place during inflation of balloon  182 , as shown in  FIG. 14C . In one preferred embodiment, at least the distal portion  214  of guidewire lumen  212  is collapsible. Therefore, as balloon  182  is inflated, the distal portion  214  (which resides within stent  20 ) of guidewire lumen  212  collapses against the inner wall of stent portion  22 , about guidewire  28 . The exterior periphery of balloon  182  drives deployment of stent portion  22 , by exerting pressure on the collapsible portion  214  of guidewire lumen  212 . 
     In another embodiment, the distal portion  214  of guidewire tube  212  is substantially rigid. When balloon  182  is inflated, tube  212  stays in place. Therefore, inflation of balloon  182  exerts pressure on tube  212  causing stent portion  22  to deploy radially outwardly. 
       FIGS. 15A-15C  illustrate another embodiment of the present invention. For purposes of the present discussion, system  210  illustrated with respect to  FIGS. 14A-14C  is illustrated in  FIG. 15A , along with a torquing system  220 . However, it will be appreciated that torquing system  220  can be used with substantially any of the other embodiments discussed herein. 
     Torquing system  220  includes a shaft  222  disposed about guidewire lumen  212  and catheter  196 . System  220  also includes a slidable sleeve  224  which is slidably engageable with the exterior surface of shaft  222 . Sleeve  224  is preferably substantially rigid when compared with, for example, catheter  196 . When sleeve  224  slidably engages the surface of shaft  222 , the user can torque or rotate sleeve  222  and thus substantially increase the torquability (or rotatability) of stent deployment system  210 . 
       FIG. 15B  is a rear perspective view of one embodiment of shaft  222  and sleeve  224 . In one embodiment, shaft  222  is a relatively flexible and resilient shaft, made of suitable polymer material which is commercially available and conventionally used to make percutaneous catheters. However, shaft  222  includes flattened wall surfaces  226  disposed on generally opposite sides thereof. Sleeve  224  is either a full hypotube, or a portion thereof, which also has flattened sides  228  which are spaced from one another just far enough to slidably receive the flattened surfaces  226  of shaft  222 . Therefore, when the user advances sleeve  224  distally such that the sides  228  engage surfaces  226 , the user can more easily torque system  210 . 
       FIG. 15C  illustrates an alternative embodiment of shaft  222  and sleeve  224 . In the embodiment illustrated in  FIG. 15C , shaft  222  has one or more slots  230  defined about the perimeter thereof. Similarly, sleeve  224  has corresponding radially inwardly directed protrusions  232  disposed thereabout. Protrusions  232  are sized just smaller than slots  230 . Therefore, as the user slides sleeve  224  distally, protrusions  232  slidably engage, and slide within, slots  230 . Since sleeve  224  is made of a relatively rigid material, it can be used to torque, or steer, system  210  within the vasculature. 
     Thus, it can be seen that the present invention provides a system for deploying a stent at a bifurcation. The system includes a variety of dual-balloon delivery and deployment systems. In another embodiment, the system includes a stepped balloon arrangement. Further, in another embodiment, the system includes a mechanism by which torquability can be increased to make positioning of the stent delivery system within the vasculature much easier. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.