Patent Publication Number: US-7713296-B2

Title: Catheter system for stenting bifurcated vessels

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Utility Application Ser. No. 11/107,393, filed Apr. 15, 2005, which is a continuation-in-part of U.S. Utility Application Ser. No. 10/833,494, filed Apr. 27, 2004, which claims the benefit of U.S. Provisional Application, Ser. No. 60/512,259, filed Oct. 16, 2003, and U.S. Provisional Application, Ser. No. 60/534,469, filed Jan. 5, 2004, the disclosures of which are incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to catheters and catheter systems for performing angioplasty and vascular stenting. More particularly it relates to a catheter system and method for stenting a vessel at a bifurcation or sidebranch of the vessel. 
     BACKGROUND OF THE INVENTION 
     The following patents and patent applications relate to catheters and catheter systems for performing angioplasty and stenting of bifurcated vessels. These and all patents and patent applications referred to herein are incorporated by reference in their entirety.
     U.S. Pat. No. 6,579,312 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,540,779 Bifurcated stent with improved side branch aperture and method of making same   U.S. Pat. No. 6,520,988 Endolumenal prosthesis and method of use in bifurcation regions of body lumens   U.S. Pat. No. 6,508,836 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,494,875 Bifurcated catheter assembly   U.S. Pat. No. 6,475,208 Bifurcated catheter assembly   U.S. Pat. No. 6,428,567 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,387,120 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,383,213 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,371,978 Bifurcated stent delivery system having retractable sheath   U.S. Pat. No. 6,361,544 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,325,826 Extendible stent apparatus   U.S. Pat. No. 6,264,682 Bifurcated stent delivery system having retractable sheath   U.S. Pat. No. 6,258,073 Bifurcated catheter assembly   U.S. Pat. No. 6,254,593 Bifurcated stent delivery system having retractable sheath   U.S. Pat. No. 6,221,098 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,210,380 Bifurcated catheter assembly   U.S. Pat. No. 6,165,195 Stent and catheter assembly and method for treating bifurcations   U.S. Pat. No. 6,142,973 Y-shaped catheter   U.S. Pat. No. 6,117,117 Bifurcated catheter assembly   U.S. Pat. No. 6,086,611 Bifurcated stent   U.S. Pat. No. 5,720,735 Bifurcated endovascular catheter   U.S. Pat. No. 5,669,924 Y-shuttle stent assembly for bifurcating vessels and method of using the same   U.S. Pat. No. 5,613,980 Bifurcated catheter system and method   U.S. Pat. No. 6,013,054 Multifurcated balloon catheter   U.S. Pat. No. 4,896,670 Kissing balloon catheter   U.S. Pat. No. 5,395,352 Y-adaptor manifold with pinch valve for an intravascular catheter   U.S. Pat. No. 6,129,738 Method and apparatus for treating stenoses at bifurcated regions   U.S. Pat. No. 6,544,219 Catheter for placement of therapeutic devices at the ostium of a bifurcation of a body lumen   U.S. Pat. No. 6,494,905 Balloon catheter   U.S. Pat. No. 5,749,825 Means method for treatment of stenosed arterial bifurcations   U.S. Pat. No. 5,320,605 Multi-wire multi-balloon catheter   U.S. Pat. No. 6,099,497 Dilatation and stent delivery system for bifurcation lesions   U.S. Pat. No. 5,720,735 Bifurcated endovascular catheter   U.S. Pat. No. 5,906,640 Bifurcated stent and method for the manufacture and delivery of same   U.S. Pat. No. 5,893,887 Stent for positioning at junction of bifurcated blood vessel and method of making   U.S. Pat. No. 5,755,771 Expandable stent and method of delivery of same   US 20030097169A1 Bifurcated stent and delivery system   US 20030028233A1 Catheter with attached flexible side sheath   US 20020183763A1 Stent and catheter assembly and method for treating bifurcations   US 20020156516A1 Method for employing an extendible stent apparatus   US 20020116047A1 Extendible stent apparatus and method for deploying the same   US 20020055732A1 Catheter assembly and method for positioning the same at a bifurcated vessel   WO 9944539A2 Dilatation and stent delivery system for bifurcation lesions   WO 03053507 Branched balloon catheter assembly   WO 9924104 Balloon catheter for repairing bifurcated vessels   WO 0027307 The sheet expandable trousers stent and device for its implantation   FR 2733689 Endoprosthesis with installation device for treatment of blood-vessel bifurcation stenosis   

     SUMMARY OF THE INVENTION 
     The present invention relates generally to catheters and catheter systems for performing angioplasty and vascular stenting. More particularly it relates to a catheter system and method for stenting a vessel at a bifurcation or sidebranch of the vessel. 
     In a first aspect, the invention comprises a catheter system for stenting bifurcated vessels. The catheter system includes a first balloon catheter, a second balloon catheter and a linking device for holding the first and second balloon catheters in a side-by-side configuration and aligned with one another along a longitudinal axis. The catheter system may include one or more vascular stents of various configurations mounted on the first and/or second balloon catheters. The linking device allows the catheter system to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent from the catheters. Typically, the catheter system will also include a first and second steerable guidewire for guiding the first and second balloon catheters within the patient&#39;s blood vessels. Optionally, the linking device may also be configured to hold one or both of the guidewires stationary with respect to the catheter system. The catheter system may be arranged with the inflatable balloons in a side-by-side configuration for stenting the bifurcated vessels using a method similar to the “kissing balloons” technique. Alternatively, the catheter system may be arranged with the inflatable balloons in a low-profile staggered or tandem configuration for stenting the bifurcated vessels using a modified “kissing balloons” technique. When arranged in the staggered or tandem configuration, the second balloon catheter may optionally be constructed with a flexible tubular extension that extends the guidewire lumen distally from the inflatable balloon. 
     In one preferred embodiment of a catheter system for stenting bifurcated vessels, a first balloon catheter and a second balloon catheter are held together with a linking device with the first and second dilatation balloons arranged in a low-profile tandem configuration. The second balloon catheter has an elongated flexible tubular extension extending distally from the second dilatation balloon. The balloon material of the first dilatation balloon mounted on the first balloon catheter is folded around the flexible tubular extension of the second balloon catheter with only the distal tip of the flexible tubular extension exposed. A stent is crimped over the first dilatation balloon of the first balloon catheter and the flexible tubular extension of the second balloon catheter. Preferably, the distal tip of the flexible tubular extension emerges from the folds of the balloon material at an intermediate position on the dilatation balloon and extends through an open cell between two struts on the crimped stent. This configuration provides a smoother, more consistent surface for crimping the stent onto, which results in a smoother crossing profile for the catheter system. Optionally, any of the described embodiments of the catheter system may be provided with a chromium-cobalt alloy stent with a strut configuration optimized for stenting bifurcations. 
     In a second aspect, the invention comprises a linking device for holding the first and second balloon catheters of the system in a side-by-side configuration and aligned with one another along a longitudinal axis. The linking device allows the catheter system to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent from the catheters. Optionally, the linking device may also be configured to hold one or both of the guidewires stationary with respect to the catheter system. The linking device is preferably releasable so that one or both of the balloon catheters and/or the guidewires can be released from the linking device and maneuvered separately from the rest of the catheter system. In one embodiment the linking device is self-releasing in the sense that the linking device demounts itself from the first and second balloon catheters as the catheter system is advanced into the patient&#39;s body. 
     In a third aspect, the invention comprises a method for stenting bifurcated vessels utilizing the described catheter system. In a first variation of the method, the inflatable balloons are arranged in a side-by-side configuration for stenting the bifurcated vessels in a method similar to the “kissing balloons” technique, but utilizing a linking device for holding the first and second balloon catheters in a side-by-side configuration and aligned with one another along a longitudinal axis. In a second variation of the method, the inflatable balloons are arranged in a staggered or tandem configuration for stenting the bifurcated vessels using a modified “kissing balloons” technique that also utilizes a linking device for holding the first and second balloon catheters in a side-by-side configuration and aligned with one another along a longitudinal axis. When desired, the linking device may be released so that one or both of the balloon catheters and/or the guidewires can be maneuvered separately from the rest of the catheter system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first embodiment of a catheter system for stenting bifurcated vessels according to the present invention. 
         FIG. 2  shows the catheter system of  FIG. 1  in use for stenting a bifurcated vessel with a bifurcated stent. 
         FIG. 3  shows a variation of the catheter system of  FIG. 1  for stenting a bifurcated vessel. 
         FIG. 4  shows the catheter system of  FIG. 3  in use for stenting a bifurcated vessel. 
         FIG. 5  shows a second embodiment of a catheter system for stenting bifurcated vessels. 
         FIGS. 6A-9  show various embodiments of a linking device for use with the catheter system of the present invention. 
         FIGS. 10-13  show the catheter system of  FIG. 5  in use for stenting a bifurcated vessel using a main stent and a sidebranch stent. 
         FIG. 14  shows a third embodiment of a catheter system for stenting bifurcated vessels. 
         FIG. 15  shows a cross section of a split-tube linking device for the catheter system of  FIG. 14 . 
         FIG. 16  shows an alternate cross section of a split-tube linking device for the catheter system of  FIG. 14 . 
         FIG. 17  shows the catheter system of  FIG. 14  in use. 
         FIG. 18  shows a distal portion of a catheter system for stenting bifurcated vessels. 
         FIG. 19  shows a bifurcated vessel after stenting with the catheter system of  FIG. 18 . 
         FIG. 20  shows a distal portion of a fourth embodiment of a catheter system for stenting bifurcated vessels prior to mounting a stent on the first balloon catheter. 
         FIGS. 21A ,  21 B and  21 C show cross sections of the catheter system for stenting bifurcated vessels taken along section lines A, B and C in  FIG. 20 . 
         FIG. 22  shows the catheter system for stenting bifurcated vessels of  FIG. 20  with a main vessel stent mounted on the dilatation balloon of the first balloon catheter. 
         FIG. 23  illustrates a stent configured for stenting bifurcated vessels shown with the stent laid out flat to show the strut configuration of the stent. 
         FIGS. 24A ,  24 B and  24 C are detail drawings of three portions of the stent of  FIG. 23 . 
         FIG. 25  illustrates another stent configured for stenting bifurcated vessels shown with the stent laid out flat to show the strut configuration of the stent. 
         FIGS. 26A ,  26 B and  26 C are detail drawings of three portions of the stent of  FIG. 25 . 
         FIG. 27  illustrates a two-part stent configured for stenting bifurcated vessels shown with the stent mounted on a stent delivery catheter. 
         FIG. 28  is an enlarged detail drawing showing the non-linked zone of the two-part stent shown in  FIG. 27 . 
         FIG. 29  shows the two-part stent of  FIG. 27  in an expanded state. 
         FIG. 30  shows the two-part stent of  FIG. 27  expanded in a bifurcated vessel. 
         FIG. 31  shows the bifurcated vessel after stenting with the two-part stent of  FIG. 27 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a first embodiment of the catheter system  100  of the present invention for stenting bifurcated vessels. The catheter system  100  includes a first balloon catheter  102  and a second balloon catheter  104 . An inflatable balloon  130 ,  132  is mounted on each of the first and second balloon catheters  102 ,  104  near the distal end of the catheters. A balloon-expandable vascular stent  150  is mounted on the catheter system  100 , typically by crimping or swaging the stent  150  over both of the inflatable balloons  130 ,  132 . The stent structure is shown generically and is not intended to be limited to any particular strut geometry. Typically, the catheter system  100  will also include a first and second steerable guidewire  140 ,  142  for guiding the first and second balloon catheters  102 ,  104  within the patient&#39;s blood vessels. The first and second steerable guidewires  140 ,  142  will typically have a diameter of 0.010-0.018 inches (approximately 0.25-0.46 mm), preferably 0.014 inches (approximately 0.36 mm). A linking device  160  releasably joins the first balloon catheter  102  and the second balloon catheter  104  together near the proximal ends of the catheters. The linking device  160  holds the first and second balloon catheters  102 ,  104  in a side-by-side configuration and aligned with one another along a longitudinal axis. The linking device  160  allows the catheter system  100  to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent  150  from the catheters. Optionally, the linking device  160  may also be configured to hold one or both of the guidewires  140 ,  142  stationary with respect to the catheter system  100 . 
     The first and second balloon catheters  102 ,  104  may be of any known construction for balloon angioplasty or stent delivery catheters, including rapid exchange and over-the-wire catheter constructions. In a particularly preferred embodiment, the first and second balloon catheters are constructed as rapid exchange catheters, wherein a proximal section  106 ,  108  of each catheter is constructed of hypodermic tubing, which may be formed from stainless steel, a superelastic nickel-titanium or titanium-molybdenum alloy or the like. The exterior of the proximal section  106 ,  108  is preferably coated with PTFE or another highly lubricious coating. A proximal connector  122 ,  124 , such as a luer lock connector or the like, is attached at the proximal end of the proximal section  106 ,  108  and communicates with a balloon inflation lumen that extends through the hypodermic tubing. Each catheter includes a flexible distal section  110 ,  112  joined to the proximal section  106 ,  108 . Typically, the flexible distal section  110 ,  112  has two lumens that extend through most of its length, including a guidewire lumen that extends from a proximal guidewire port  114 ,  116  to a distal port  118 ,  120  at the distal end of the catheter, and a balloon inflation lumen that connects from the balloon inflation lumen of the proximal section  106 ,  108  to the interior of the inflatable balloon  130 ,  132 , which is mounted near the distal end of the flexible distal section  110 ,  112 . The first and second inflatable balloons  130 ,  132  may have the same length and diameter and pressure compliance or they may have different lengths, diameters and/or pressure compliances, depending on the geometry of the target vessel that the catheter system  100  is intended for. The inflatable balloons  130 ,  132  may be made from a variety of known angioplasty balloon materials, including, but not limited to, PVC, polyethylene, polyolefin, polyamide, polyester, PET, PBT, and blends, alloys, copolymers and composites thereof. The first and second inflatable balloons  130 ,  132  may be made from the same material or different materials. The flexible distal section  110 ,  112  is typically constructed of flexible polymer tubing and may have a coaxial or multilumen construction. Preferably, one, two or more radiopaque markers are mounted on the flexible distal section  110 ,  112  to indicate the location of the inflatable balloons  130 ,  132  under fluoroscopic imaging. A transition element may be included to create a gradual transition in stiffness between the proximal section  106 ,  108  and the flexible distal section  110 ,  112 , and to avoid a stress concentration at the juncture between the two sections. The transition element may be constructed as a tapered or spiral wound element that is formed as an extension of the hypodermic tubing or from a separate piece of wire or tubing. 
     In this illustrative example, the catheter system  100  is configured for delivering a Y-shaped bifurcated stent  150 . The bifurcated stent  150  has a main trunk  152  connected to first and second sidebranches  154 ,  156  of the stent. The catheter system  100  is prepared for use by inserting the inflatable balloons  130 ,  132  in a deflated and folded state through the main trunk  152  of the bifurcated stent  150 , with one balloon extending into each of the first and second sidebranches  154 ,  156 . The bifurcated stent  150  is then crimped or swaged over the inflatable balloons  130 ,  132 . A support wire may be inserted into each of the guidewire lumens to support them during the crimping or swaging step. The proximal sections  106 ,  108  of the catheters are inserted into the linking device  160  to hold the first and second balloon catheters  102 ,  104  in a side-by-side configuration and aligned with one another along a longitudinal axis. This preparation may be carried out at the manufacturing facility or it may be performed at the point of use by a medical practitioner. 
       FIG. 2  shows the catheter system  100  of  FIG. 1  in use for stenting a bifurcated vessel. The catheter system  100  is inserted into a body lumen that is desired to be stented and advanced to the point of the bifurcation. For stenting coronary arteries or carotid arteries, the catheter system  100  is typically inserted through a guiding catheter that has been previously positioned at the ostium of the target vessel. For stenting in peripheral arteries or other body lumens, the catheter system  100  may be inserted directly into the vessel, for example using the Seldinger technique or an arterial cutdown, or it may be inserted through an introducer sheath or guiding catheter placed into the vessel. The first and second balloon catheters  102 ,  104  are maneuvered with the help of the steerable guidewires  140 ,  142  so that the first and second inflatable balloons  130 ,  132 , with the first and second sidebranches  154 ,  156  of the stent  150  mounted thereon, extend into the respective first and second sidebranches of the bifurcated vessel. The first and second inflatable balloons  130 ,  132  are inflated separately and/or together to expand the stent  150  and to seat it securely within the vessel, as shown in  FIG. 2 . This is similar to the “kissing balloons” technique that has been previously described in the literature. An advantage of the present invention over prior methods is that the linking device  160  allows the catheter system  100  to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent  150  from the catheters. 
     Once the stent  150  has been deployed, both balloons  130 ,  132  are deflated and the catheter system  100  is withdrawn from the patient. Alternatively, one or both of the balloon catheters  102 ,  104  can be released from the linking device  160  and used separately for dilating and/or stenting other vessels upstream or downstream of the stent  150 . 
       FIG. 3  shows a variation of the catheter system  100  of the present invention for stenting a bifurcated vessel. The construction of the catheter system  100  is very similar to the catheter system described above in connection with  FIG. 1  with the exception that the system utilizes a straight, i.e. non-bifurcated, stent  170 . The stent structure is shown generically and is not intended to be limited to any particular strut geometry. In one particularly preferred embodiment, the stent  170  is in the form of an open-cell stent, having a cylindrical body  174  with one or more side openings  172  that are suitable for placement at a bifurcation or sidebranch of the vessel without hindering blood flow into the sidebranch. Because of their flexibility and open structure, open-cell stents are well suited for stenting bifurcated vessels. The side openings  172  can be expanded or remodeled with a dilatation balloon inserted through the side opening or with two dilatation balloons, using the “kissing balloons” technique. A closed-cell stent with large side openings and/or expandable side openings may also be utilized. Alternatively, the catheter system may utilize a side-hole stent intended for stenting bifurcations or for stenting a main vessel at the location of a sidebranch vessel. In this case, the stent has an approximately cylindrical body with a side hole intended to be positioned at the site of a sidebranch vessel. The side hole may be preformed in the stent or it may be a slit or a potential hole that can be expanded to form a side hole. 
     The catheter system  100  is prepared for use by inserting the inflatable balloons  130 ,  132  in a deflated and folded state into the stent  170 , with the first balloon  130  extending all the way through the cylindrical body  174  and the second balloon  132  exiting the cylindrical body  174  at the side opening  172  that is intended to be positioned at the bifurcation or sidebranch vessel. Alternatively, the second balloon  132  may be positioned proximal to the side opening  172  so that only the distal tip of the catheter  104  or only the guidewire  142  exits the cylindrical body  174  at the side opening  172  to decrease the distal crossing profile of the catheter system  100 . The stent  170  is then crimped or swaged over the inflatable balloons  130 ,  132 . A support wire may be inserted into each of the guidewire lumens to support them during the crimping or swaging step. The proximal sections  106 ,  108  of the catheters are inserted into the linking device  160  to hold the first and second balloon catheters  102 ,  104  in a side-by-side configuration and aligned with one another along a longitudinal axis. This preparation may be carried out at the manufacturing facility or it may be performed at the point of use by a medical practitioner. 
       FIG. 4  shows the catheter system  100  of  FIG. 3  in use for stenting a bifurcated vessel. The catheter system  100  is inserted into a body lumen that is desired to be stented and advanced to the point of the bifurcation. For stenting coronary arteries or carotid arteries, the catheter system  100  is typically inserted through a guiding catheter that has been previously positioned at the ostium of the target vessel. For stenting in peripheral arteries or other body lumens, the catheter system  100  may be inserted directly into the vessel, for example using the Seldinger technique or an arterial cutdown, or it may be inserted through an introducer sheath or guiding catheter placed into the vessel. The first and second balloon catheters  102 ,  104  are maneuvered with the help of the steerable guidewires  140 ,  142  so that the first and second inflatable balloons  130 ,  132 , with the stent mounted thereon, extend into the respective first and second sidebranches of the bifurcated vessel. The first inflatable balloon  130  will typically be positioned in the larger of the two sidebranches or in the main lumen of the vessel at the location of a smaller sidebranch vessel. The first inflatable balloon  130  is inflated to expand the stent and to seat it securely within the vessel, as shown in  FIG. 4 . Then, the first inflatable balloon  130  is deflated and the second inflatable balloon  132  is inflated to expand the side opening  172  at the location of the second sidebranch vessel. Optionally, the first and second inflatable balloons  130 ,  132  may be inflated simultaneously using the “kissing balloons” technique. 
     Once the stent  170  has been deployed, both balloons  130 ,  132  are deflated and the catheter system  100  is withdrawn from the patient. Alternatively, one or both of the balloon catheters  102 ,  104  can be released from the linking device  160  and used separately for dilating and/or stenting other vessels upstream or downstream of the stent  170 . Optionally, a sidebranch stent may be placed in the second sidebranch vessel before or after deployment of the stent  170 . 
       FIG. 5  shows a second embodiment of the catheter system  100  for stenting bifurcated vessels. The construction of the catheter system  100  is very similar to the catheter system described above in connection with  FIGS. 1 and 3 , with the exception that the second balloon catheter  104  is constructed with a flexible tubular extension  134  connected to the distal end of the catheter. The guidewire lumen extends through the flexible tubular extension  134 . The flexible tubular extension  134  allows the first and second inflatable balloons  130 ,  132  to be assembled together in a staggered or tandem initial position. This variation of the catheter system  100  utilizes a main stent  170 , which is typically a straight, i.e. non-bifurcated, stent, as described above. In addition, the catheter system  100  may optionally utilize a sidebranch stent  178 . The stent structures are shown generically and are not intended to be limited to any particular strut geometry. These distal features of the catheter system  100  can be seen in greater detail in the enlarged view of  FIG. 10 . 
     The catheter system  100  is prepared for use by first inserting the second inflatable balloon  132  in a deflated and folded state through the optional sidebranch stent  178  and crimping or swaging the sidebranch stent  178  over the second inflatable balloon  132 . Alternatively, the sidebranch stent  178  may be mounted on a separate balloon catheter for use with the catheter system  100 . The first inflatable balloon  130  is then inserted in a deflated and folded state into the main stent  170 , with the first balloon  130  extending all the way through the cylindrical body  174 . The flexible tubular extension  134  of the second balloon catheter  104  is inserted into the main stent  170  alongside the first balloon  130  with the flexible tubular extension  134  exiting the cylindrical body  174  at the side opening  172  that is intended to be positioned at the bifurcation or sidebranch vessel. Preferably, the flexible tubular extension  134  terminates at the side opening  172  of the main stent  170  to reduce the crossing profile of the distal portion of the stent  170 . Alternatively, the flexible tubular extension  134  may extend distally from the side opening  172  if desired. The main stent  170  is then crimped or swaged over the first inflatable balloon  130  and the flexible tubular extension  134 . A support wire may be inserted into each of the guidewire lumens to support them during the crimping or swaging step. The proximal sections  106 ,  108  of the catheters are inserted into the linking device  160  to hold the first and second balloon catheters  102 ,  104  in a side-by-side configuration and in a desired alignment with one another along the longitudinal axis. This preparation may be carried out at the manufacturing facility or it may be performed at the point of use by a medical practitioner. 
     In an alternate embodiment of the catheter system  100  of  FIG. 5 , the second balloon catheter  104  may be constructed without a flexible tubular extension  134 . In this case, the distal tip of the second balloon catheter  104  would be positioned proximal to the main stent  170  and the second steerable guidewire  142  would be inserted into the main stent  170  alongside the first balloon  130  with the guidewire  142  exiting the cylindrical body  174  at the side opening  172 . This would provide an even lower crossing profile for the catheter system  100 . 
       FIGS. 6A-9  show various embodiments of a linking device  160  for use with the catheter system  100  of the present invention.  FIG. 6A  shows an end view and  6 B shows a front view of a first embodiment of a linking device  160 . The linking device  160  has a body  162  with a first channel  164  and a second channel  166  extending along a surface of the body in a side-by-side configuration, preferably with the first and second channels  164 ,  166  approximately parallel to one another. The first and second channels  164 ,  166  are preferably undercut and sized to have a captive interference fit with the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104 . The linking device  160  is preferably molded of a flexible polymer or elastomer with a high coefficient of friction so that it effectively grips the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  when they are inserted into the first and second channels  164 ,  166 . In use, the linking device  160  holds the first and second balloon catheters  102 ,  104  arranged in a side-by-side configuration and aligned with one another along a longitudinal axis. The linking device  160  allows the catheter system  100  to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent from the catheters. When it is desired, one or both of the balloon catheters  102 ,  104  can be released from the linking device  160  and maneuvered separately from the rest of the catheter system  100 . 
     Optionally, the linking device  160  of  FIG. 6B  may also be configured to hold one or both of the guidewires  140 ,  142  stationary with respect to the catheter system  100 . In this case, the body  162  of the linking device  160  would include one or two slots  168 , shown in dashed lines in  FIG. 6B , that are sized and configured to create a captive interference fit with the proximal section of the guidewires  140 ,  142 .  FIG. 6C  shows an end view of the linking device  160  with optional slots  168  for holding the guidewires  140 ,  142 . When it is desired, the guidewires  140 ,  142  can be released from the linking device  160  and maneuvered separately from the rest of the catheter system  100 . 
     In an alternative embodiment, the linking device  160  of  FIGS. 6A-6B  may be permanently attached to one of the balloon catheters and releasably attached to the other. In another alternative embodiment, the linking device  160  may be configured to attach instead to the proximal connectors  122 ,  124  of the balloon catheters  102 ,  104  or it may be molded into the proximal connectors  122 ,  124 . 
       FIG. 7A  shows an end view and  7 B shows a front view of a second embodiment of the linking device  160 . The linking device  160  has a body  162  with a first channel  164  and a second channel  166  extending along one surface of the body in a side-by-side configuration, preferably with the first and second channels  164 ,  166  approximately parallel to one another. The first and second channels  164 ,  166  are preferably undercut and sized to have a captive sliding fit with the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104 . A first locking device  180  is associated with the first channel  164 , and a second locking device  182  is associated with the second channel  166 . The first and second locking devices  180 ,  182  are configured to releasably lock the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  in a desired alignment with one another along the longitudinal axis. Each of the locking devices  180 ,  182  will typically include a spring or other biasing member to hold the locking device in a locked position and a push button or other actuating member to release the locking device. The linking device  160  allows the catheter system  100  to be advanced as a unit and helps prevent premature or inadvertent dislodgement of the stent from the catheters. When it is desired, one or both of the locking devices  180 ,  182  can be released to allow one of the balloon catheters  102 ,  104  to be advanced or retracted with respect to the other to adjust their longitudinal alignment. In addition, one or both of the balloon catheters  102 ,  104  can be released completely from the linking device  160  and maneuvered separately from the rest of the catheter system  100 . 
     Optionally, the linking device  160  of  FIGS. 7A-7B  may also be configured to hold one or both of the guidewires  140 ,  142  stationary with respect to the catheter system  100 . In this case, the body  162  of the linking device  160  would include one or two additional locking devices, or slots or other structures configured to grip the proximal section of the guidewires  140 ,  142 . When it is desired, the guidewires  140 ,  142  can be released from the linking device  160  and maneuvered separately from the rest of the catheter system  100 . 
     In an alternative embodiment, the linking device  160  of  FIGS. 7A-7B  may be permanently attached to one of the balloon catheters and releasably attached to the other. 
       FIG. 8A  shows an end view and  8 B shows a front view of a third embodiment of the linking device  160 . The linking device  160  has a first linking member  184  attached to the proximal section  106  of the first balloon catheter  102  and a second linking member  186  attached to the proximal section  108  of the second balloon catheter  104 . The first linking member  184  and the second linking member  186  have interlocking features so that the two catheters can be releasably attached to one another. In the example shown, the interlocking features are corresponding male  187  and female  185  elements that can be attached and detached to one another in the manner of a snap or zip-lock device.  FIG. 8C  shows an end view of the linking device  160  with the first linking member  184  and the second linking member  186  detached from one another. Optionally, the linking device  160  can be configured so that the balloon catheters  102 ,  104  can be attached to one another in different longitudinal alignments. In other embodiments, the linking device  160  of  FIGS. 8A-8C  may utilize alternative interlocking features such as clamps, snaps, hook-and-loop fasteners, a releasable adhesive, a repositionable adhesive, etc. 
     Optionally, the linking device  160  of  FIGS. 8A-8C  may also be configured to hold one or both of the guidewires  140 ,  142  stationary with respect to the catheter system  100 . In this case, one or both of the linking members  184 ,  186  would include a locking device, slot or other structure configured to hold the proximal section of one of the guidewires  140 ,  142 . This configuration would allow each guidewire and balloon catheter pair to be moved as a unit separately from the rest of the catheter system  100  when the linking members  184 ,  186  are separated. When it is desired, one or both of the guidewires  140 ,  142  can be released from the linking members  184 ,  186  and maneuvered separately from the rest of the catheter system  100 . 
       FIG. 9  shows a fourth embodiment of the linking device  160  that utilizes a peel-away sheath  190  for attaching the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  together. The peel-away sheath  190  may be made from heat shrink polymer tubing that is heat shrunk onto the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  to lock them together in a desired alignment with one another along the longitudinal axis. The peel-away sheath  190  has tabs or handles  196  to facilitate peeling the peel-away sheath  190  apart to release the balloon catheters  102 ,  104  so that they can be maneuvered separately from one another. The peel-away sheath  190  may utilize features, such as polymer orientation, perforations and/or an incised groove, to assure that the peel-away sheath  190  will peel apart along a longitudinal dividing line. 
       FIGS. 10-13  show the catheter system  100  of  FIG. 5  in use for stenting a bifurcated vessel using a main stent  170  and a sidebranch stent  178 . The catheter system  100  is inserted into a body lumen that is desired to be stented and advanced to the point of the bifurcation. For stenting coronary arteries or carotid arteries, the catheter system  100  is typically inserted through a guiding catheter that has been previously positioned at the ostium of the target vessel. For stenting in peripheral arteries or other body lumens, the catheter system  100  may be inserted directly into the vessel, for example using the Seldinger technique or an arterial cutdown, or it may be inserted through an introducer sheath or guiding catheter placed into the vessel. The staggered or tandem initial position of the first and second inflatable balloons  130 ,  132  provides a very low crossing profile. The low crossing profile allows the catheter system  100  with a 3.0 or 3.5 mm (expanded diameter) coronary stent  170  mounted on it to be delivered through a 6 French (approximately 2 mm external diameter) guiding catheter, which will typically have an internal diameter of 0.066-0.071 inches (approximately 1.68-1.80 mm internal diameter). 
     The catheter system  100  is maneuvered with the help of the steerable guidewires  140 ,  142  so that the first inflatable balloon  130 , with the main stent  170  mounted on it, extends into the first sidebranch of the bifurcated vessel and the second steerable guidewire  142  extends into the second sidebranch, as shown in  FIG. 10 . The first inflatable balloon  130  will typically be positioned in the larger of the two sidebranches or in the main lumen of the vessel at the location of a smaller sidebranch vessel. 
     When advancing the catheter system  100 , the second steerable guidewire  142  may be positioned with its distal tip withdrawn into the flexible tubular extension  134  of the second balloon catheter  104  until the catheter system  100  reaches the bifurcation so that it will not be inadvertently damaged or interfere with advancement of the catheter system  100 . This can be facilitated by inserting the proximal section of the second guidewire  142  into the optional slot or locking device  168  on the linking device  160 . When the distal tip of the second balloon catheter  104  is in the vicinity of the sidebranch vessel, the second steerable guidewire  142  can be released from the linking device  160  and advanced with its distal tip extending from the flexible tubular extension  134  to engage the sidebranch vessel. 
     Once the main stent  170  is in the desired position, the first inflatable balloon  130  is inflated to expand the main stent  170  and to seat it securely within the vessel, as shown in  FIG. 11 . Then, the first inflatable balloon  130  is deflated and the linking device  160  is released so that the second balloon catheter  104  can be advanced into the second sidebranch. The second inflatable balloon  132  is inflated to expand the sidebranch stent  178  and to seat it securely within the second sidebranch vessel, while simultaneously opening the side opening  172  in the main stent  170 , as shown in  FIG. 12 . Alternatively, if a sidebranch stent is not used or if it is to be delivered on a separate balloon catheter, the second inflatable balloon  132  is inflated to open the side opening  172  in the main stent  170  at the location of the second sidebranch vessel. Optionally, the first and second inflatable balloons  130 ,  132  may be inflated simultaneously using the “kissing balloons” technique. 
     Once the stents  170 ,  180  have been deployed, both balloons  130 ,  132  are deflated and the catheter system  100  is withdrawn from the patient. Alternatively, one or both of the balloon catheters  102 ,  104  can be released from the linking device  160  and used separately for dilating and/or stenting other vessels upstream or downstream of the main stent  170 . Optionally, a sidebranch stent  178  may be placed in the second sidebranch vessel using a separate balloon catheter before or after deployment of the main stent  170 . 
       FIG. 14  shows a third embodiment of a catheter system  100  for stenting bifurcated vessels utilizing a linking device  160  constructed of an elongated split-tube  200 . The split-tube  200  of the linking device  160  is configured to hold the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  arranged in a side-by-side configuration and aligned with one another along a longitudinal axis. A longitudinal split  202  extends the length of the split-tube  200 . The longitudinal split  202  allows the split-tube  200  to be placed over the proximal sections  106 ,  108  of the catheters  102 ,  104  during catheter preparation and to be removed from the catheters  102 ,  104  at the appropriate time during the stenting procedure. The length of the split-tube  200  can vary. Good results were obtained with a catheter system  100  having a split-tube  200  that extends along most of the proximal sections  106 ,  108  of the balloon catheters  102 ,  104  between the proximal hubs  122 ,  124  and the proximal guidewire ports  114 ,  116  of the rapid exchange catheters. Preferably, the split-tube  200  of the linking device  160  is configured with a distal pull-tab  210  or other feature to facilitate lifting the distal part of the split-tube  200  to remove the linking device  160  and release the balloon catheters  102 ,  104  so that they can be maneuvered separately from one another. The pull-tab  210  is preferably located on a side of the split-tube  200  opposite to the longitudinal split  202 . The pull-tab  210  can be formed by skiving or cutting away part of the tube  200  as shown. 
       FIG. 15  shows a cross section of one embodiment of the split-tube  200  of the linking device  160  for the catheter system  100  of  FIG. 14 . The split-tube  200  has an inner lumen  204  that is sized and configured to hold the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  together with sufficient friction that the catheter system  100  can be advanced as a unit without any relative movement of the two catheters. In one particularly preferred embodiment, the split-tube  200  is manufactured as an extruded profile with an approximately circular outer profile and an approximately oval inner lumen  204 . The longitudinal split  202  connects the inner lumen  204  with the exterior of the split-tube  200  at a thin part of the wall that coincides with the major axis of the oval inner lumen  204 . The longitudinal split  202  is preferably formed during the extrusion of the split-tube  200 . Alternatively, the tube  200  can be extruded without the longitudinal split  202  and then slitted along the length to form the longitudinal split  202  in a secondary operation. Suitable materials for the split-tube  200  include polyamide copolymers (e.g. PEBAX 6333 or PA 8020 from ATOFINA), polypropylene, and any extrudable medical grade polymer with a suitable combination of strength, flexibility and friction characteristics. 
     The split-tube  200  of the linking device  160  can be made with many other possible configurations, including single-lumen and multiple-lumen configurations, and may include one or more longitudinal splits  202 . By way of example,  FIG. 16  shows an alternate cross section of a split-tube  200  of the linking device  160  for the catheter system  100  of  FIG. 14 . In this embodiment, the split-tube  200  has a first inner lumen  206  that is sized and configured to hold the proximal section  106  of the first balloon catheter  102  and a second inner lumen  208  that is sized and configured to hold the proximal section  108  of the second balloon catheter  104 . The inner lumens  206 ,  208  are sized and configured to hold the proximal sections  106 ,  108  of the first and second balloon catheters  102 ,  104  with sufficient friction that the catheter system  100  can be advanced as a unit without any relative movement of the two catheters. Two longitudinal splits  202  connect the inner lumens  206 ,  208  with the exterior of the split-tube  200 . The two longitudinal splits  202  are preferably located on the same side of the split-tube  200  opposite to the distal pull-tab  210  to facilitate removal of the linking device  160  from both catheters  102 ,  104  simultaneously. The longitudinal splits  202  are preferably formed during the extrusion of the split-tube  200 . Alternatively, the tube  200  can be extruded without the longitudinal splits  202  and then slitted along the length to form the longitudinal splits  202  in a secondary operation. Optionally, the linking device  160  in  FIG. 15  or  FIG. 16  can include additional lumens, slots or other structures to hold one or both of the guidewires  140 ,  142  stationary with respect to the catheter system  100 . 
       FIG. 17  shows the catheter system  100  of  FIG. 14  in use. The linking device  160  with the split-tube  200  has the advantage that, once it is started, the split-tube  200  will demount itself as the catheter system  100  is advanced so that the physician does not need to unpeel, remove or displace a linking member that would otherwise require a “third hand”. The catheter system  100  is prepared for use by aligning the first and second balloon catheters  102 ,  104  in the desired longitudinal alignment and then pressing the longitudinal split  202  of the split-tube  200  against the proximal sections  106 ,  108  of the catheters until they are enclosed within the inner lumen  204  (or lumens  206 ,  208 ) of the split-tube  200 , as shown in  FIG. 14 . A stent or stents may then be crimped or mounted on the balloons  130 ,  132  in the desired configuration. This preparation may be carried out at the manufacturing facility or it may be performed at the point of use by a medical practitioner. The distal ends of the catheters  102 ,  104  with the stent or stents mounted thereon are inserted into the patient in the usual manner through a guiding catheter with a Y-fitting  220  or other hemostasis adapter on the proximal end of the guiding catheter. The distal pull-tab  210  is pulled toward the side to start demounting the split-tube  200  from the balloon catheters  102 ,  104 , and then the first and second balloon catheters  102 ,  104  are advanced as a unit. As shown in  FIG. 17 , when the split-tube  200  encounters the Y-fitting  220 , the split-tube  200  will peel away or demount itself from the proximal sections  106 ,  108  of the balloon catheters  102 ,  104 . The stent or stents can be deployed in the vessel bifurcation using the methods described herein. 
       FIG. 18  shows a distal portion of a catheter system  100  for stenting bifurcated vessels. The catheter system  100  is similar to that shown in  FIG. 5  with a first balloon catheter  102  having a first inflatable balloon  130  and a second balloon catheter  104  having a second inflatable balloon  132  and a flexible tubular extension  134  extending distally from the balloon  132 . The first and second inflatable balloons  130 ,  132  are assembled together in a staggered or tandem initial position as shown to provide a low crossing profile. The catheter system  100  can use any of the linking devices  160  described herein to maintain the longitudinal alignment of the catheters  102 ,  104  during insertion. A distal stent  122  is mounted on a distal portion of the first inflatable balloon  130  and a proximal stent  124  is mounted on a proximal portion of the first inflatable balloon  130  and the flexible tubular extension  134  of the second balloon catheter  104 . Preferably, only a small space is left between the distal and proximal stents  122 ,  124 . The distal stent  122  is configured to fit the distal main branch diameter and proximal stent  124  is configured to fit the proximal main branch diameter and the bifurcation itself. Preferably, the proximal stent  124  is configured so that it can be overdilated if necessary to fit the vessel at the bifurcation. In addition, the catheter system  100  may optionally utilize a sidebranch stent  178  mounted on the second balloon  132 , as illustrated in  FIG. 5 . 
     The distal stent  122  and the proximal stent  124  are deployed using sequential and/or simultaneous inflation of the first and second inflatable balloons  130 ,  132  using the methods described herein.  FIG. 19  shows a bifurcated vessel after stenting with the catheter system  100  of  FIG. 18 . Using separate distal and proximal stents  122 ,  124  allows the stents to be independently sized to fit the target vessel and it allows independent expansion of the two stents without any links between them that could cause distortion of one or both stents during deployment. 
       FIGS. 20-22  illustrate a distal portion of a fourth embodiment of a catheter system  100  for stenting bifurcated vessels. The catheter system  100  is similar in structure and configuration to the catheter system of  FIG. 5  with a first balloon catheter  102  having a first inflatable balloon  130  and a second balloon catheter  104  having a second inflatable balloon  132  and a flexible tubular extension  134  extending distally from the second inflatable balloon  132 . The first and second inflatable balloons  130 ,  132  are assembled together in a staggered or tandem initial position, as shown in  FIG. 5 , to provide a low crossing profile. The catheter system  100  can use any of the linking devices  160  described herein to maintain the longitudinal alignment of the catheters  102 ,  104  during insertion. In a particularly preferred embodiment, the catheter system  100  will utilize a linking device  160  in the form of an auto-release sheath constructed of an elongated split-tube  200 , as illustrated in  FIGS. 14-17 . 
       FIG. 20  shows a distal portion of the catheter system  100  prior to mounting a stent on the first balloon catheter  102 . The flexible tubular extension  134  of the second balloon catheter  104  extends distally from the second dilatation balloon  132  (see  FIG. 5 ) to an intermediate position between the proximal and distal ends of the first inflatable balloon  130 . The balloon material of the first inflatable balloon  130  is folded around the flexible tubular extension  134  of the second balloon catheter with only the distal tip  135  of the flexible tubular extension  134  exposed. This configuration provides a smoother, more consistent surface for crimping a stent onto the first inflatable balloon  130  and the flexible tubular extension  134 , which results in a smoother crossing profile for the catheter system  100 . 
       FIGS. 21A ,  21 B and  21 C show cross sections of the catheter system  100  taken along section lines A, B and C in  FIG. 20 .  FIG. 21A  shows a cross section of the catheter system  100  taken through a distal portion of the first inflatable balloon  130  along section line A in  FIG. 20 . This distal portion of the first inflatable balloon  130  may be folded in any convenient low-profile balloon folding configuration, such as the three-wing folding configuration shown. Alternatively, the distal portion of the first inflatable balloon  130  may be folded in a two-wing or four-wing folding configuration or other balloon folding configuration known in the industry.  FIG. 21C  shows a cross section of the catheter system  100  taken through a proximal portion of the first inflatable balloon  130  and the flexible tubular extension  134  along section line C in  FIG. 20 . In this proximal portion of the first inflatable balloon  130 , the balloon material is wrapped around the flexible tubular extension  134  completely enclosing it. Preferably, the proximal portion of the first inflatable balloon  130  is folded in a two-wing folding configuration as shown, although other folding configurations may also be used.  FIG. 21B  shows a cross section of the catheter system  100  taken through a transition point intermediate between the proximal and distal portions of the first inflatable balloon  130  along section line B in  FIG. 20 . At this transition point, the first inflatable balloon  130  makes a transition from the two-wing folding configuration of the proximal portion to the three-wing folding configuration of the distal portion. At this transition point, the distal tip  135  of the flexible extension tube  134  emerges from the folds of the balloon material of the first inflatable balloon  130 , as shown in  FIG. 20 . Optionally, the first inflatable balloon  130  may be heat set in this folded configuration to facilitate mounting a stent on the folded balloon in the next assembly step. 
     Next, a main vessel stent  170  is mounted over the first inflatable balloon  130  of the first balloon catheter  102  and the flexible tubular extension  134  of the second balloon catheter  104 , as shown in  FIG. 22 , for example by crimping or swaging. The distal tip  135  of the flexible extension tube  134  emerges from the folds of the balloon material of the first inflatable balloon  130  and extends through an open cell or side opening  172  between two struts on the crimped stent  170 . This configuration provides a smoother, more consistent surface for crimping the stent onto, which results in a smoother crossing profile for the catheter system  100 . Optionally, the first inflatable balloon  130  may be heat set after mounting the main vessel stent  170  onto the first inflatable balloon  130 . This provides a smoother surface on the balloon and stent assembly and increases stent retention force, which helps to prevent accidental dislodgement of the stent from the balloon. Optionally, a side branch stent  178  may be mounted on the second inflatable balloon  132  of the second balloon catheter  104 , as illustrated in  FIG. 5 . 
     In an alternate embodiment of the catheter system  100 , the flexible tubular extension  134  may be a distal portion of a single or multiple lumen non-balloon catheter, which is wrapped in the balloon material of the first inflatable balloon  130 . In another alternate embodiment of the catheter system  100 , the flexible tubular extension  134  may be a sidebranch of the first balloon catheter  102 , which is wrapped in the balloon material of the first inflatable balloon  130 . The sidebranch of the first balloon catheter  102  may or may not have a second inflatable balloon mounted on it. 
     Optionally, any of the described embodiments of the catheter system  100  may be provided with a stent with a strut configuration optimized for stenting bifurcations.  FIGS. 23-26  illustrate stents  240  configured for stenting bifurcated vessels shown with the unexpanded stent laid out flat to show the strut configuration of the stent  240 . Preferably, the stent  240  is fabricated from a seamless metal tube, for example by laser cutting, annealing and electropolishing. In a particularly preferred embodiment, the stent  240  is made from a high-strength biocompatible chromium-cobalt alloy, such as alloy L605 (ASTM F90-01). Alternatively, the stent  240  may be made from other biocompatible metals or alloys, including, but not limited to,  316  stainless steel, Elgiloy or Carpenter MP35. The stent  240  is preferably configured with a multiplicity of struts  250  that are joined together along the length of the stent  240  by links  252  in an open cell configuration. The struts  250  are preferably configured as sinuous or undulating rings extending circumferentially around the stent  240 . Each strut  250  has a predetermined number of undulations or cells  254  around the circumference of the stent  240 . In the embodiment shown, the cells  254  are shown as simple sinusoidal undulations, however other configurations of cells including open cells and closed cells are also possible. 
     The stent  240  is divided into a distal area  242 , a carina area  244  and a proximal area  246 . The strut configuration in each area is preferably optimized for the portion of the vessel in which it will be placed. The number of cells  254  in each strut  250 , along with other factors, determines how much the strut  250  will be able to expand circumferentially. In a particularly preferred embodiment, the struts  250  in the carina area  244  will have a greater number of cells  254  than the struts  250  in the distal area  242  and the proximal area  246 . Preferably, the struts  250  in the proximal area  246  will also have a greater number of cells  254  than the struts  250  in the distal area  242 . This configuration allows the carina area  244  to be expanded more than the distal area  242  and the proximal area  246 , and allows the proximal area  246  to be expanded more than the distal area  242 . The differential expansion properties of the different areas allow the stent  230  to conform closely to the typical geometry of a bifurcated vessel, where the vessel proximal to the bifurcation typically has a greater diameter than the vessel distal to the bifurcation, and where the vessel in the carina area immediately proximal to the carina of the bifurcation has a diameter greater than the vessels proximal or distal to the bifurcation. This configuration of the stent  240  also allows the crush resistance or hoop strength of the expanded stent to be optimized for each of the areas despite the different stent expansion ratios in each area. 
     An example of a 3.0 mm (expanded diameter) stent  240  is shown in  FIG. 23 . The stent  240  is shown with the unexpanded tubular stent laid out flat to show the strut configuration of the stent as it is manufactured and prior to crimping. The stent  240  may be formed, for example, from a seamless tube with nominal dimensions of approximately 1.60 mm diameter, with a wall thickness of approximately 0.11 mm. The stent  240  has six struts  250  in the distal area  242  each having six cells  254  and joined together by two links  252 , except for the most distal strut  250 , which is joined by three links  252 , three struts  250  in the carina area  244  each having eight cells  254  and joined together by four links  252 , and five struts  250  in the proximal area  246  each having seven cells  254  and joined together by two links  252 , except for the most proximal strut  250 , which is joined by three links  252 . A single link  252  joins the distal area  242  to the carina area  244 , and three links  252  join the proximal area  246  to the carina area  244 . 
       FIGS. 24A ,  24 B and  24 C are detail drawings of three portions of the stent of  FIG. 23 .  FIG. 24A  shows one cell  254  of two adjacent struts  250  in the distal area  242  joined by a link  252 .  FIG. 24B  shows one cell  254  of two adjacent struts  250  in the carina area  244  joined by a link  252 .  FIG. 24C  shows one cell  254  of two adjacent struts  250  in the proximal area  246  joined by a link  252 . It will be noted that the length of the arms  256  in each cell  254  is slightly longer and more divergent in the distal area  242 , of intermediate length and divergence in the proximal area  246  and shortest length and least divergence in the carina area  244  in order to accommodate the different numbers of cells  254  in the struts  250  of these three different areas. Alternatively or in addition, other means may be used to accommodate the different numbers of cells  254  in the struts  250  of the three different areas. For example, the radius of the U-shaped bends  258  that join the arms  256  of the cells  254  together may be varied to accommodate the different numbers of cells  254  around the circumference of the stent  240 . 
     Another example of a 3.5 mm (expanded diameter) stent  240  is shown in  FIG. 25 . The stent  240  is shown with the unexpanded tubular stent laid out flat to show the strut configuration of the stent as it is manufactured and prior to crimping. The stent  240  may be formed, for example, from a seamless tube with nominal dimensions of approximately 1.60 mm diameter, with a wall thickness of approximately 0.11 mm. The stent  240  has six struts  250  in the distal area  242  each having eight cells  254  and joined together by two links  252 , except for the most distal strut  250 , which is joined by four links  252 , three struts  250  in the carina area  244  each having ten cells  254  and joined together by five links  252 , and five struts  250  in the proximal area  246  each having nine cells  254  and joined together by three links  252 , except for the most proximal strut  250 , which is joined by five links  252 . A single link  252  joins the distal area  242  to the carina area  244 , and three links  252  join the proximal area  246  to the carina area  244 . 
       FIGS. 26A ,  26 B and  26 C are detail drawings of three portions of the stent of  FIG. 25 .  FIG. 26A  shows one cell  254  of two adjacent struts  250  in the distal area  242  joined by a link  252 .  FIG. 26B  shows one cell  254  of two adjacent struts  250  in the carina area  244  joined by a link  252 .  FIG. 26C  shows one cell  254  of two adjacent struts  250  in the proximal area  246  joined by a link  252 . Again, it will be noted that the length of the arms  256  in each cell  254  is slightly longer and more divergent in the distal area  242 , of intermediate length and divergence in the proximal area  246  and shortest length and least divergence in the carina area  244  in order to accommodate the different numbers of cells  254  in the struts  250  of these three different areas. As mentioned above, other means may also be used to accommodate the different numbers of cells  254  in the struts  250  of the three different areas. 
       FIGS. 23 and 25  represent only two examples of the many possible configurations for stents made according to the principles of the present invention. For example, the dimensions of the stent, the number and configuration of the struts, cells and links, and other parameters of the stent can be varied greatly, while adhering to the general principles of the stent design that allow it to accommodate the particular geometry of a bifurcated vessel. 
       FIG. 27  illustrates a two-part stent  300  configured for stenting bifurcated vessels. The two-part stent  300  is shown mounted on a stent delivery catheter  304  in an unexpanded condition. Preferably, the stent delivery catheter  304  is configured with a step balloon  302  having a proximal portion  306  and a distal portion  308  that expand to different diameters. Typically, the proximal portion  306  will have a larger expanded diameter than the distal portion  308 , as shown in  FIG. 29 . However, it should be noted that the proportions of the proximal portion  306  and the distal portion  308  can be reversed, for example for stenting a bifurcated vessel using a retrograde approach rather than a standard antegrade approach. The proximal portion  306  of the step balloon  302  may be cylindrical or conical, as appropriate for the geometry of the bifurcation in the target vessel.  FIG. 29  shows an example of a step balloon  302  with a conical proximal portion  306  that increases in diameter from the proximal end of the balloon to the distal end of proximal portion  306  and is largest in diameter adjacent to the step in the balloon. 
     The two-part stent  300  has a proximal part  310  and a distal part  314  and a non-linked zone  312  between the proximal part  310  and the distal part  314 .  FIG. 28  is an enlarged detail drawing showing the non-linked zone  312  of the two-part stent  300 . The proximal part  310  and the distal part  314  of the two-part stent  300  are typically formed by cutting a metallic tube to form zigzag or undulating stent struts  316 . Alternatively, the stent struts  316  can be formed from wire. Optionally, the proximal part  310  and the distal part  314  of the two-part stent  300  can be made with different strut configurations, according to the principles described above, to accommodate expansion to different diameters in the portions of the vessel proximal and distal to the carina region. 
     In a preferred configuration, the stent struts  316  form circumferential rings that are joined to one another by one or more links similar to the stent embodiments described above. However, there are no links in the non-linked zone  312  between the proximal part  310  and the distal part  314 . The absence of links in the non-linked zone  312  allows greater freedom of movement between the proximal part  310  and the distal part  314  of the two-part stent  300 . This effectively eliminates any difficulties in alignment of the two parts relative to one another during placement of the two-part stent  300  in a bifurcated vessel. 
     In one particularly preferred embodiment, the undulations of the stent struts  316  extend like fingers  316 ,  318  from the distal end of the proximal part  310  and the proximal end of the distal part  314 . The fingers  316 ,  318  interdigitate with one another to create an overlap of the proximal part  310  and the distal part  314  in the non-linked zone  312 , as shown in  FIG. 28 , in order to provide strut coverage in the carina region of the bifurcated vessel equivalent to or greater than a typical one-part stent. 
     The stent delivery catheter  304  with the two-part stent  300  can be used as a stand-alone catheter for stenting bifurcated vessels. Alternatively, it can be used as the first balloon catheter  102  in a two-catheter stenting system for bifurcated vessels similar to those shown in  FIGS. 1-5 ,  18  and  20 - 22  for ease and simplicity in performing a kissing-balloon technique. The tandem balloon configurations shown in  FIGS. 5 ,  18  and  20 - 22  would provide the additional benefit of a lower crossing profile, as compared to the side-by-side balloon configurations shown in  FIGS. 1-4 . (or two-catheter system) 
     When used as a stand-alone catheter, the stent delivery catheter  304  with the step balloon  302  and the two-part stent  300  allow simple stenting of a bifurcation using a provisional stenting technique. The stent delivery catheter  304  is introduced into the patient&#39;s vascular system and navigated with the aid of a guidewire to the vessel bifurcation to be stented. The step balloon  302  is maneuvered so that the non-linked zone  312  of the two-part stent  300  is positioned at the carina region of the bifurcation just proximal to the takeoff of the sidebranch vessel. Optionally, a second guidewire (not shown) may be introduced into the sidebranch vessel to maintain access to the sidebranch vessel using the “jailed wire” technique. The step balloon  302  is inflated with fluid to expand the two-part stent  300 .  FIG. 30  shows the two-part stent  300  of  FIG. 27  expanded in a bifurcated vessel. The proximal portion  306  of the step balloon  302  expands the proximal part  310  of the two-part stent  300  to larger diameter appropriate to the size of the vessel proximal to the bifurcation, and the distal portion  308  of the step balloon  302  expands the distal part  314  of the two-part stent  300  to smaller diameter appropriate to the size of the vessel distal to the bifurcation. It may be preferable to overdilate the vessel slightly, as shown in  FIG. 30 , because there will be some elastic recovery of the vessel wall and the stent  300  when the balloon  302  is deflated. After deflating and withdrawing the step balloon  302  the proximal part  310  of the two-part stent  300  will shift into the ostium of the side branch  304  creating an access to the side branch  304 .  FIG. 31  shows the bifurcated vessel after stenting with the two-part stent  300  of  FIG. 27 . 
     According to the provisional stenting technique, the procedure may be terminated with a kissing balloon inflation and/or by deploying a stent within the sidebranch vessel. A third guidewire is now crossed from within the proximal part  310  of the two-part stent  300  through the non-linked zone  312  at the distal end of the proximal part  310  of the two-part stent  300  into the lumen of the sidebranch vessel. The edges of the expanded stent are designed to facilitate guidewire crossing. After withdrawing the jailed wire, the procedure can be completed with classical kissing balloons technique. 
     While the present invention has been described herein with respect to the exemplary embodiments and the best mode for practicing the invention, it will be apparent to one of ordinary skill in the art that many modifications, improvements and subcombinations of the various embodiments, adaptations and variations can be made to the invention without departing from the spirit and scope thereof. Although the present invention has been primarily described in relation to angioplasty and stenting of bifurcated blood vessels, the apparatus and methods of the invention can also be used for other applications as well. For example, the catheter system can be used for stenting bifurcated lumens in other organ systems of the body. In addition, the linking devices described herein can be used in other applications where it is desired to hold two or more catheters or similar devices arranged in a side-by-side configuration and aligned with one another along a longitudinal axis. The principles of the invention can also be applied to catheters other than balloon catheters.