Patent Publication Number: US-6709440-B2

Title: Stent and catheter assembly and method for treating bifurcations

Description:
This application is a division of application Ser. No. 09/861,473 file May 17, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to stents and stent delivery and deployment assemblies for use at a bifurcation and, more particularly, one or more stents for repairing bifurcations, blood vessels that are diseased, and a method and apparatus for delivery and implantation of the stents. 
     Stents conventionally repair blood vessels that are diseased. Stents are generally hollow and cylindrical in shape and have terminal ends that are generally perpendicular to their longitudinal axis. In use, the conventional stent is positioned at the diseased area of a vessel and, after deployment, the stent provides an unobstructed pathway for blood flow. 
     Repair of vessels that are diseased at a bifurcation is particularly challenging since the stent must be precisely positioned, provide adequate coverage of the disease, provide access to any diseased area located distal to the bifurcation, and maintain vessel patency in order to allow adequate blood flow to reach the myocardium. Therefore, the stent must provide adequate coverage to the diseased portion of the bifurcated vessel, without compromising blood flow, and extend to a point within and beyond the diseased portion. Where the stent provides coverage to the vessel at the diseased portion, yet extends into the vessel lumen at the bifurcation, the diseased area is repaired, but blood flow may be compromised in other portions of the bifurcation. Unapposed stent elements may promote lumen compromise during neointimal formation and healing, producing restenosis and requiring further procedures. Moreover, by extending into the vessel lumen at the bifurcation, the stent may block access to further interventional procedures. 
     Conventional stents are designed to repair areas of blood vessels that are removed from bifurcations, and, therefore are associated with a variety of problems when attempting to use them to treat lesions at a bifurcation. Conventional stents are normally deployed so that the entire stent is either in the parent vessel or the proximal portion of the stent is in the parent vessel and the distal portion is located in the side branch vessel. In both cases, either the side branch vessel (former case) or the parent vessel (later case), would become “jailed” by the stent struts. This technique repairs one vessel at the bifurcation at the expense of jailing or obstructing the alternate vessel. Blood flow into the jailed vessel would be compromised as well as future access and treatment into the distal portion of the jailed vessel. 
     Alternatively, access into a jailed vessel can be attained by carefully placing a guide wire through the stent, and subsequently tracking a balloon catheter through the stent struts. The balloon could then be expanded, thereby deforming the stent struts and forming an opening into the previously jailed vessel. The cell to be spread apart must be randomly and blindly selected by re-crossing the deployed stent with a guide wire. The drawback with this approach is that there is no way to determine or guarantee that the main-vessel stent struts are properly oriented with respect to the side branch or that an appropriate stent cell has been selected by the wire for dilatation. The aperture created often does not provide a clear opening and creates a major distortion in the surrounding stent struts. A further drawback with this approach is that there is no way to tell if the main-vessel stent struts have been properly oriented and spread apart to provide a clear opening for stenting the side branch vessel. This technique also causes stent deformation to occur in the area adjacent to the carina, pulling the stent away from the vessel wall and partially obstructing flow in the originally non-jailed vessel. Deforming the stent struts to regain access into the previously jailed strut is also a complicated and time consuming procedure associated with attendant risks to the patient and is typically performed only if considered an absolute necessity. Vessels which supply a considerable amount of blood supply to the myocardium and may be responsible for the onset of angina or a myocardial infarct would necessitate the subsequent strut deformation in order to reestablish blood flow into the vessel. The risks of procedural complications during this subsequent deformation are considerably higher than stenting in normal vessels. The inability to place a guide wire through the jailed lumen in a timely fashion could restrict blood supply and begin to precipitate symptoms of angina or even cardiac arrest. In addition, platelet agitation and subsequent thrombus formation at the jailed site could further compromise blood flow into the side branch. 
     Plaque shift is also a phenomena which is of concern when deploying a stent across a bifurcation. Plaque shift occurs when treatment of disease or plaque in one vessel causes the plaque to shift into another location. This is of greatest concern when the plaque is located on the carina or the apex of the bifurcation. During treatment of the disease the plaque may shift from one side of the carina to the other thereby shifting the obstruction from one vessel to the alternate vessel. 
     In another prior art method of implanting stents, a “T” stent procedure includes implanting a stent in the side branch ostium of the bifurcation followed by stenting the main vessel across the side branch and subsequently deforming the struts as previously described, to allow blood flow and access into the side branch vessel. Alternatively, a stent is deployed in the parent vessel and across the side branch origin followed by subsequent strut deformation as previously described, and finally a stent is placed into the side branch vessel. T stenting may be necessary in some situations in order to provide further treatment and additional stenting in the side branch vessel. This is typically necessitated when the disease is concentrated at the origin of the jailed vessel. This procedure is also associated with the same issues and risks previously described when stenting only one vessel and deforming the struts through the jailed vessel. In addition, since a conventional stent generally terminates at right angles to its longitudinal axis, the use of conventional stents to treat the origin of the previously jailed vessel (typically the side branch vessel) may result in blocking blood flow of the originally non-jailed vessel (typically the parent vessel) or fail to provide adequate coverage of the disease in the previously jailed vessel (typically a side branch vessel). The conventional stent might be placed proximally in order to provide full coverage around the entire circumference of the side branch, however this leads to a portion of the stent extending into the pathway of blood flow of the parent vessel. The conventional stent might alternatively be placed distally to, but not entirely overlaying the circumference of the origin of the side branch to the diseased portion. Such a position of the conventional stent results in a bifurcation that does not provide full coverage or has a gap on the proximal side (the origin of the side branch) of the vessel and is thus not completely repaired. The only conceivable situation that the conventional stent, having right-angled terminal ends, could be placed where the entire circumference of the ostium is repaired without compromising blood flow, is where the bifurcation is formed of right angles. In such scenarios, extremely precise positioning of the conventional stent is required. This extremely precise positioning of the conventional stent may result with the right angled terminal ends of the conventional stent overlying the entire circumference of the ostium to the diseased portion without extending into a side branch, thereby repairing the right-angled bifurcation. 
     To circumvent or overcome the problems and limitations associated with conventional stents in the context of repairing diseased bifurcated vessels, a stent that consistently overlays most of the diseased area of the bifurcation and provides adequate access to distal disease without subjecting the patient to any undue risks may be employed. Such a stent would have the advantage of providing adequate coverage at the proximal edge of the origin of the side branch such that a conventional stent which terminates at right angles to its longitudinal axis can be deployed in the side branch or alternate vessel without leaving a significant gap at the origin of the side branch. In addition, such a stent would allow access to all portions of the bifurcated vessel should further interventional treatment be necessary. 
     In another prior art method for treating bifurcated vessels, commonly referred to as the “Culotte technique,” the side branch vessel is first stented so that the stent protrudes into the main or parent vessel. A dilatation is then performed in the main or parent vessel to open and stretch the stent struts extending across the lumen from the side branch vessel. Thereafter, a stent is implanted in the side branch so that its proximal end overlaps with the parent vessel. One of the drawbacks of this approach is that the orientation of the stent elements protruding from the side branch vessel into the main vessel is completely random. In addition excessive metal coverage exists from overlapping strut elements in the parent vessel proximal to the carina area. Furthermore, the deployed stent must be recrossed with a wire blindly and arbitrarily selecting a particular stent cell. When dilating the main vessel the stent struts are randomly stretched, thereby leaving the possibility of restricted access, incomplete lumen dilatation, and major stent distortion. 
     In another prior art procedure, known as “kissing” stents, a stent is implanted in the main vessel with a side branch stent partially extending into the main vessel creating a double-barrelled lumen of the two stents in the main vessel distal to the bifurcation. Another prior art approach includes a so-called “trouser legs and seat” approach, which includes implanting three stents, one stent in the side branch vessel, a second stent in a distal portion of the main vessel, and a third stent, or a proximal stent, in the main vessel just proximal to the bifurcation. 
     All of the foregoing stent deployment assemblies suffer from the same problems and limitations. Typically, there is uncovered intimal surface segments on the main vessel and side branch vessels between the stented segments or there is excessive coverage in the parent vessel proximal to the bifurcation. An uncovered flap or fold in the intima or plaque will invite a “snowplow” effect, representing a substantial risk for sub-acute thrombosis, and the increased risk of the development of restenosis. Further, where portions of the stent are left unapposed within the lumen, the risk for subacute thrombosis or the development of restenosis again is increased. The prior art stents and delivery assemblies for treating bifurcations are difficult to use and deliver making successful placement nearly impossible. Further, even where placement has been successful, the side branch vessel can be “jailed” or covered so that there is impaired access to the stented area for subsequent intervention. The present invention solves these and other problems as will be shown. 
     In addition to problems encountered in treating disease involving bifurcations for vessel origins, difficulty is also encountered in treating disease confined to a vessel segment but extending very close to a distal branch point or bifurcation which is not diseased and does not require treatment. In such circumstances, very precise placement of a stent covering the distal segment, but not extending into the distal side branch, may be difficult or impossible. The present invention also offers a solution to this problem. 
     SUMMARY OF THE INVENTION 
     The invention provides for improved stent designs and stent delivery catheter assemblies for repairing a main vessel and side branch-vessel forming a bifurcation, without compromising blood flow, thereby allowing access to all portions of the bifurcated vessels should further interventional treatment be necessary. The present invention includes a trap-door stent pattern, a stent delivery catheter assembly, an apparatus for crimping the stent and the method for crimping the stent onto the catheter, and the method for delivering and implanting the stent in a bifurcated vessel. 
     The Stent Pattern 
     The stent of the present invention includes a cylindrical body having rings aligned along a longitudinal axis, where each ring has a delivered diameter in which it is crimped or compressed tightly onto the balloon catheter, and an implanted diameter where the stent is implanted in a bifurcated vessel. Each ring also includes a number of first peaks that are configured to spread apart to permit the rings to be greatly expanded outwardly or to be compressed radially inwardly onto the balloon portion of a delivery catheter. In one embodiment, the cylindrical body includes a proximal section, a distal section, and a central section. The proximal section includes between one and fifteen rings, the distal section includes between one and fifteen rings, and the central section includes between one and ten rings. In one embodiment, the number of first peaks in the central section differs from the number of first peaks in the proximal section and the distal section. In another embodiment, the rings of the proximal section have between four and twelve first peaks, the rings of the distal section have between four and twelve first peaks, and the rings of the central section have between five and fifteen first peaks. In another embodiment of the stent, the rings of the proximal section have seven first peaks, the rings of the distal section have six first peaks, and the rings of the central section have eight first peaks. In another embodiment, the number of first peaks in the rings or ring of the central section is greater than the number of first peaks in any of the rings of either the proximal section or the distal section. In each of the embodiments, the rings are connected by at least one link between adjacent rings. 
     In one embodiment of the stent of the invention, the proximal section, the distal section, and the central section each have only one ring. In this embodiment, the stent is highly deliverable since it will typically be substantially shorter than a stent having a greater number of rings, so that it can pass through tortuous anatomy more easily and rotational position of the stent is easily achieved by applying torque to the delivery system or manipulating the guide wires. 
     In one embodiment of the stent of the invention, the rings in the central section of the stent have a corresponding set of nested peaks that are nested within the first peak of the rings of the central section. The nested peaks, when expanded, will appose the opening to the side branch vessel and provide additional support and vessel wall coverage. With the addition of the nested peaks, the central section of the stent can expand to an even greater diameter than a similar stent without the nested peaks because the nested peaks provide more material to expand. 
     The links connecting the rings can have various embodiments including straight segments, curved segments, undulating segments, and non-linear segments. 
     The tubular body of the stent of the invention has a distal opening, a proximal opening, and a central opening. The distal opening and the proximal opening are aligned along the stent longitudinal axis and typically would be implanted in the main vessel, while the central opening is radially offset relative to the alignment of the distal opening and the proximal opening. The stent is implanted so that the central opening provides access to the side branch (or alternative vessel) and the ring or rings proximal to the central opening provide support and coverage to the origin of the side branch and to the area immediately proximal to the carina. 
     Each ring of the stent of the present invention has at least one second peak where at least some of the at least one second peaks is connected to a link. 
     The stent of the present invention includes struts that make up the rings and links, the struts having either uniform cross-sections, or cross-sections having various widths and thicknesses. 
     The Stent Delivery Catheter 
     The present invention also includes a stent delivery catheter assembly for repairing bifurcated vessels including an elongated catheter body which has a proximal catheter shaft, an intermediate section or mid-section, and a distal section. The catheter assembly contains an over-the-wire (OTW) guide wire lumen extending from the proximal catheter hub to one of the distal tips of the distal end of the catheter. The catheter assembly also includes a rapid exchange (Rx) guide wire lumen which extends from the proximal end of the mid-section to one of the distal tips of the distal end of the catheter. The proximal catheter shaft also contains an inflation lumen which extends from the proximal hub of the proximal catheter shaft to the mid-section of the catheter and is in fluid communication with the inflation lumen contained within the midsection. The mid-section contains lumens for both an OTW and an Rx guide wire lumen. The Rx guide wire lumen begins at about the proximal section of the intermediate shaft and extends to one of the distal tips of the distal catheter shaft. The OTW guide wire lumen extends through the intermediate section of the catheter and extends proximally to the catheter hub connected to the proximal catheter shaft and extends distally to one of the tips of the distal section of the catheter. The distal section of the catheter consists of two shafts extending from the distal end of the mid-shaft to the distal end of the catheter tips. Each shaft has a balloon connected adjacent the distal end followed by a tip connected to the distal end of the balloon. Each shaft contains a guide wire lumen and an inflation lumen. The inflation lumen of each shaft is in fluid communication with the inflation lumen of the mid-shaft. One of the shafts of the distal section contains an Rx guide wire lumen, which extends proximally through the mid-section of the catheter and exits at about the proximal end of the midsection of the catheter, the Rx guide wire lumen also extends distally to one of the tips of the distal section of the catheter. The second shaft of the distal section contains an OTW guide wire lumen, which extends proximally through the mid-section and proximal section of the catheter and exits at the proximal hub connected to the distal end of the proximal catheter section, the OTW guide wire lumen also extends distally to one of the tips of the distal section of the catheter. The distal section of the catheter includes two balloons. One balloon is longer and is connected to one of the shafts of the distal catheter section. The long balloon is connected to the catheter shaft such that the inflation lumen of the shaft is in fluid communication with the balloon and the guide wire lumen contained within the shaft extends through the center of the balloon. The proximal section of the balloon is sealed to the distal end of the shaft and the distal end of the balloon is sealed around the outside of the guide wire lumen or inner member running through the center of the balloon. The proximal and distal seals of the balloon allow for fluid pressurization and balloon inflation from the proximal hub of the catheter. The short balloon is connected in the same manner as the long balloon described above to the alternate shaft of the distal section of the catheter. Each balloon has a tip extending from their distal ends. The tips are extensions of the inner members extending through the center of the balloon and contain a lumen for a guide wire associated with each guide wire lumen. The distal end of the catheter has two tips associated with their respective balloons and the guide wire lumen or inner member. One tip is longer and contains a coupler utilized for joining the tip during delivery of the previously described stent. 
     The stent of the present invention is crimped or compressed onto the long balloon and the short balloon such that the long balloon extends through the distal opening and the proximal opening in the stent, while the short balloon extends through the proximal opening and the central opening of the stent. 
     In one embodiment of the bifurcated catheter assembly, the OTW guide wire lumen extends through the short balloon and the short tip. The OTW guide wire and short balloon are configured for treating the side branch or alternate vessel. The Rx guide wire lumen extends through the long balloon and the long tip and coupler. The Rx guide wire and the long balloon and long tip are configured for treating the parent or main vessel. The coupler consists of a joining lumen adjacent to and connected to the long tip. The lumen extends from the proximal end of the long tip and extends between 1 mm to about 20 mm to the end of the long tip where it terminates. The proximal end of the joining lumen is located distal to the position of the short tip. A joining wire extends through the proximal hub and distally exits the short tip and then enters the joining lumen of the coupler on the long tip thereby joining the two tips. The proximal hub has a mechanism which locks the joining wire into position while the catheter and stent are tracked into position. The wire can then be released or unlocked at the appropriate time and retracted to release or uncouple the tips. The locking mechanism on the proximal hub is similar to a Rotating Hemostatic Valve (RHV) mechanism which consists of a two part housing with an O ring inside. The two part housing has one piece with male threads and another with female threads. The housing is screwed together until compression is applied to the O ring causing the inside diameter of the O ring to continually decrease until it locks onto the joining wire. Alternatively, the OTW guide wire can be used as the joining wire. 
     In another embodiment of the bifurcated catheter assembly, the long tip contains a series of holes on the distal section of the long tip and the short tip contains a series of holes on the distal section of the short tip. The holes are aligned and spaced on the long and short tip such that a staggered relationship between hole pairs is created between the holes on the long and short tip. The tips are then coupled by a joining wire which is threaded through the staggered hole pairs in the distal section of the long and short tips. The joining wire extends proximally through the OTW guide wire lumen to the proximal hub where it is locked in place as previously described. The Rx guide wire extends through the Rx guide wire lumen proximally through the center of the long balloon and exits the Rx notch located on the mid-section of the catheter and extends distally through the long tip and into the distal anatomy. The diameter of the joining wire is such that it occupies minimal space in the Rx guide wire lumen and does not create interference with the Rx guide wire. The tips are uncoupled at the appropriate time by unlocking the joining wire and removing it from the anatomy. 
     In another embodiment of the bifurcated catheter assembly, the OTW guide wire lumen extends through the long tip and coupler, and the long tip is connected to the short balloon. The OTW guide wire lumen and short balloon are configured for treatment of the side branch or alternate vessel. The OTW guide wire lumen extends to the proximal hub of the proximal section of the catheter. The Rx guide wire lumen extends through the long balloon and short tip distally and extends proximally to the exit notch located on the mid-section of the catheter. The Rx guide wire lumen and long balloon are configured to treat the parent or main vessel. The coupler consists of a joining lumen adjacent to and attached to the distal end of the long tip. The proximal end of the joining lumen is located distal to the short tip and the distal end of the joining lumen extends slightly beyond the long tip. The end of the joining lumen is open and the Rx guide wire extends distally through the joining lumen and into the distal anatomy and extends proximally through the short tip and long balloon to the exit notch located on the mid-section of the catheter. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the coupling lumen located in the distal section of the Rx tip. 
     In another embodiment of the bifurcated catheter assembly, the long tip contains a slit used for coupling the two tips together. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through the slit. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip. 
     In another embodiment of the bifurcated catheter assembly, the long tip contains two slits on the distal section of the long tip. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through one of the slits. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. The tips are uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip. Before the tips are uncoupled, the OTW guide wire is advanced through the long tip and exits the alternate slit and continues into the distal anatomy. Advancement of the OTW guide wire before retracting the Rx guide wire for uncoupling always ensures wire placement in the distal and diseased anatomy. Maintaining a wire in the distal and diseased anatomy ensures access to the vessel in the event of vessel closure due to vessel dissection or spasm. 
     In another embodiment of the bifurcated catheter assembly, the long tip contains a slit in the distal section of the long tip and is configured to allow the inner diameter of the lumen to expand when an outward radial force is applied (by a guide wire pushed from the proximal end) and contract to its original shape when the guide wire is removed. The tip is formed from a material having elastic and retractable properties such as found in a variety of elastomers. An expandable pattern such as minute cuts or slits, can then be cut (with a laser) in the distal section of the long tip. The expandable pattern contains elements which deform when an outward radial force is applied to the inside of the lumen. The elements then return to their original shape when the outward radial force is removed. An alternate method of creating an expandable tip would be to utilize a more conventional tip or inner member material, and then subsequently cut an expandable pattern (slits) in the distal section of the tip. An additional material with the appropriate elastic and retractable properties can then be coated or bonded over the distal section of the long tip to impart the expandable properties of the tip. The Rx guide wire extends through the Rx guide wire lumen contained in the short tip and extends proximally through the center of the long balloon and exits the Rx guide wire exit notch located on the mid-section of the catheter. The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of long tip through the slit. The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire extends from the distal end of the long tip to the proximal hub located on the proximal section of the catheter. During delivery of the stent, the distal end of the OTW guide wire remains in the distal section of the long tip just proximal of the slit. Before the tips are uncoupled, the OTW guide wire is advanced through the long tip which will expand upon advancement of the OTW guide wire since both of the guide wires will exit through the portion of the long tip distal of the slit. The tips are then uncoupled at the appropriate location and time during the procedure by retracting the Rx guide wire such that the tip of the wire exits the slit located in the distal section of the long tip. 
     The present invention also includes a stent delivery catheter assembly for repairing bifurcated vessels including an elongated catheter body which has a proximal end and a distal end and a proximal catheter shaft and an over-the-wire (OTW) guide wire lumen extending therethrough. The catheter assembly also includes a rapid exchange (Rx) catheter portion attached to the distal end of the proximal catheter shaft, the Rx catheter portion having a distal end and a proximal end with an Rx guide wire lumen extending therethrough and a coupler associated with the distal end of the Rx catheter portion. The catheter body also includes an OTW catheter portion attached to the distal end of the proximal catheter shaft, where the OTW catheter portion includes an OTW guide wire lumen that corresponds with and aligns with the OTW guide wire lumen in the proximal catheter shaft. A long balloon is associated with the Rx catheter portion and a short balloon is associated with the OTW catheter portion. The Rx catheter portion is configured for treating the main vessel of a bifurcation and the OTW catheter portion is configured for treating a side branch vessel of the bifurcation. Alternatively, the OTW catheter portion is configured for treating the main vessel of a bifurcation, while the Rx catheter portion is configured for treating a side branch vessel of the bifurcation. The stent of the present invention is crimped or compressed onto the long balloon and the short balloon such that the long balloon extends through the distal opening and the proximal opening in the stent, while the short balloon extends through the proximal opening and the central opening of the stent. 
     In another embodiment of the bifurcated catheter assembly of the invention, the bifurcated catheter can be used for a variety of procedures such as dilatation, drug delivery, and delivering and deploying the stent of the invention in a body lumen. The bifurcated catheter assembly includes an elongated shaft having a proximal shaft section with a first inflation lumen and a multifurcated distal shaft section with a first branch and at least a second branch. The first branch has a second inflation lumen with at least a portion thereof in fluid communication with the first inflation lumen. An intermediate shaft section joins the proximal and distal sections together and defines a fourth inflation lumen in fluid communication with the first, second and third inflation lumens. A joining wire lumen extends within the proximal section, the intermediate section, and the first branch of the multifurcated distal section. The guide wire lumen extends within the intermediate section and the second branch of the multifurcated distal section. The guide wire lumen extends within the intermediate section and the second branch of the multifurcated distal section. A first balloon is positioned on the first branch and a second balloon is positioned on the second branch, with interiors of the balloons in fluid communication with the inflation lumens. A coupler is associated with the second branch, distal to the second balloon, and is configured for releasably coupling the first and second branches together to form a coupled configuration. 
     The Stent Crimping Method 
     The stent of the present invention can be tightly crimped or compressed onto the catheter assembly so that the stent remains firmly in place until the balloons are expanded, thereby expanding the stent at the site of the bifurcation. In keeping with the invention, a mold assembly is provided for use in progressively crimping the stent in a tighter and tighter configuration until it is tightly crimped or compressed onto the long and short balloons of the catheter assembly. In one embodiment, the crimping assembly or mold assembly includes three sections, including a tapered section, a straight section, and a finish section, through which the stent, which has been premounted on the balloons, is advanced for the purpose of progressively compressing the stent onto the balloons. The tapered section of the mold assembly has a tapered lumen and an opening or first end in which its cross-section is larger than the cross-section of the uncrimped stent premounted on the balloons of the catheter assembly. The tapered section has a second end having a smaller cross-section than the first end so that as the stent and balloons are advanced through the tapered section and its tapered lumen, the stent will be progressively compressed onto the balloons so that the stent will take substantially the same shape as the cross-section of the second end of the tapered section. The straight section has a first end cross-section that is basically the same size cross-section as the second end of the tapered section, and the straight section also has a second end cross-section that is substantially the same size cross-section as the first end. The stent and balloons are advanced through the straight section to provide a uniform crimp along the stent surface so that any unevenness created by the tapered lumen of the tapered section is removed, thereby providing a smooth and uniform stent outer surface having a configuration shaped substantially like the lumen defined by the second end of the straight section. The stent and balloons are then advanced through the finish section which has a first end cross-section that is substantially the same cross-sectional shape as the second end of the straight section. As the stent and balloons are advanced through the finish section, they are progressively compressed or crimped into the cross-sectional configuration of the second end of the finish section. After the stent and catheter have been successfully inserted into the mold, the balloons can be pressurized and heat can be applied to the mold to further enhance the stent retention. The result is a tightly crimped stent on the long and short balloons so that the stent will remain firmly attached to the long and short balloons during delivery of the stent through tortuous vessels such as the coronary arteries. Once the stent and long balloons are positioned at the bifurcations, the balloons can be inflated as will be hereinafter described, to expand the stent and implant it at the bifurcation. 
     Delivering and Implanting the Stent 
     The method of delivering and implanting the stent mounted on the catheter assembly are contemplated by the present invention. The bifurcated catheter assembly of the present invention provides two separate balloons in parallel which are advanced into separate passageways of an arterial bifurcation and the balloons are inflated either simultaneously or independently (or a combination thereof) to expand and implant the stent. More specifically, and in keeping with the invention, the catheter assembly is advanced through a guiding catheter (not shown) until the distal end of the catheter assembly reaches the ostium to the coronary arteries. An Rx guide wire is advanced out of the Rx shaft and into the coronary arteries to a point distal of the bifurcation or target site. In a typical procedure, the Rx guide wire will already be positioned in the main vessel after a pre-dilatation procedure. The catheter assembly is advanced over the Rx guide wire so that the catheter distal end is just proximal to the opening to the side branch vessel. Up to this point in time, the OTW guide wire (or mandrel or joining wire) remains within the catheter assembly and within the coupler so that the long balloon and the short balloon of the catheter assembly remain adjacent to one another to provide a low profile. As the catheter assembly is advanced to the bifurcated area, the coupler moves axially relative to the distal end of the OTW guide wire (or mandrel or joining wire) a small distance (approximately 0.5 mm up to about 5.0 mm), but not pull completely out of the coupler, making it easier for the distal end of the catheter to negotiate tortuous turns in the coronary arteries. Thus, the slight axial movement of the coupler relative to the OTW guide wire (or mandrel or joining wire) distal end allows the tips to act or move independently, thereby increasing flexibility over the tips joined rigidly and it aids in the smooth tracking of the catheter assembly over the Rx guide wire. The proximal end of the OTW guide wire is releasably attached to the proximal hub as previously described. The OTW guide wire (or mandrel or joining wire) is removed or withdrawn proximally from the coupler, thereby uncoupling the long balloon and the short balloon. Thereafter, the OTW guide wire is advanced distally into the side branch vessel so that the catheter assembly can next be advanced distally over the Rx guide wire in the main vessel and the OTW guide wire in the side branch vessel. The separation between the Rx guide wire and the OTW guide wire allows the long balloon and the short balloon to separate slightly as the catheter assembly is further advanced over the Rx guide wire and the OTW guide wire. The catheter assembly advances distally until it reaches a point where the central opening on the stent is approximately adjacent to the opening to the side branch vessel, so that the catheter assembly can no longer be advanced distally since the stent is now pushing up against the opening to the side branch vessel. One or more radiopaque markers are placed on the distal portion of the catheter assembly to aid in positioning the stent with respect to the bifurcation or target site. Once the long and short balloons with the stent mounted thereon are positioned in the main vessel just proximal to the side branch vessel, the long balloon and the short balloon are next inflated simultaneously or independently (or a combination thereof), to expand the stent in the main vessel and the opening to the side branch vessel. The central section of the stent is expanded into contact with the opening to the side branch vessel and the central opening should substantially coincide with the opening to the side branch vessel providing a clear blood flow path through the proximal opening of the stent and through the central opening into the side branch vessel. By inflating the long balloon and the short balloon substantially simultaneously, plaque shifting is avoided and better vessel wall coverage results. 
     As the catheter assembly is advanced through tortuous coronary arteries, over the Rx guide wire, the central opening of the stent may or may not always be perfectly aligned with the opening to the side branch vessel. If the central opening of the stent is in alignment with the opening to the side branch vessel it is said to be “in phase” and represents the ideal position for stenting the main branch vessel and the opening to the side branch vessel. When the central opening of the stent and the opening to the side branch vessel are not aligned it is said to be “out of phase” and depending upon how many degrees out of phase, the stent may require repositioning or reorienting so that the central opening more closely coincides with the opening to the side branch vessel. The orientation of the central opening of the stent with respect to the opening to the side branch vessel can range anywhere from a few degrees to 360°. If the central opening of the stent is more than 90° out of phase with respect to the opening to the side branch vessel, it may be difficult to position the radiopaque marker, and thus the linear or longitudinal position of the stent. When the central opening is in the out of phase position, the stent of the invention still can be implanted and the central opening will expand into the opening of the side branch vessel and provide adequate coverage. In cases where the system is more than 90° out of phase, the Rx and OTW guide wires will be crossed causing a distal torque to be applied to help the system to rotate in phase. In the event rotation does not occur, the system can be safely deployed with adequate coverage and support as long as the radiopaque markers located on the distal end of the catheter reach the proper positioning as can be detected under fluoroscopy. The unique and novel design of the catheter assembly and the stent of the present invention minimizes the misalignment so that the central opening of the stent generally aligns with the opening to the side branch vessel, and is capable of stenting the opening to the side branch vessel even if the central opening is out of phase from the opening of the side branch vessel. 
     After the stent of the present invention has been implanted at the bifurcation, if necessary a second stent can be implanted in the side branch vessel so that the second stent abuts the central opening of the stent of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a bifurcation in which a prior art “T” stent is in a side branch ostium followed by the stenting of the main vessel across the branch ostium. 
     FIG. 2 is an elevational view of a bifurcation in which “touching” prior art stents are depicted in which one stent is implanted in the side branch, a second stent implanted in a proximal portion of the main vessel next to the branch stent, with interrupted placement of a third stent implanted more distally in the main vessel. 
     FIG. 3 is an elevational view of a bifurcation depicting “kissing” stents where a portion of one stent is implanted in both the side branch and the main vessel and adjacent to a second stent implanted in the main vessel creating a double-barreled lumen in the main vessel distal to the bifurcation. 
     FIG. 4 is an elevational view of a prior art “trouser legs and seat” stenting approach depicting one stent implanted in the side branch vessel, a second stent implanted in a proximal portion of the main vessel, and a close deployment of a third stent distal to the bifurcation leaving a small gap between the three stents of an uncovered luminal area. 
     FIG. 5A is an elevational view of a bifurcation in which a prior art stent is implanted in the side branch vessel. 
     FIG. 5B is an elevational view of a bifurcation in which a prior art stent is implanted in the side branch vessel, with the proximal end of the stent extending into the main vessel. 
     FIGS. 6A-6E are perspective views depicting different embodiments of the stent of the present invention in an unexpanded configuration. 
     FIGS. 7A-7E are flattened elevational views of the stents of FIGS. 6A-6E respectively, depicting different embodiments of the stent of the present invention in a flattened configuration. 
     FIG. 8 is a flattened elevational view of one embodiment of the stent of the present invention. 
     FIG. 9 is a flattened elevational view of one embodiment of the stent of the present invention. 
     FIG. 10 is a flattened elevational view of one embodiment of the stent of the present invention. 
     FIG. 11 is a flattened elevational view of one embodiment of the stent of the present invention. 
     FIG. 12 is a flattened elevational view of one embodiment of the stent of the present invention. 
     FIG. 13 is a flattened elevational view depicting a central section of the stent having a nested ring portion. 
     FIG. 14 is a partial elevational view of the stent of FIG. 13 in a cylindrical configuration and depicting an enlarged view of the nested ring portion. 
     FIG. 15 is an elevational view depicting the central opening of the stent of the invention. 
     FIG. 16 is an enlarged partial elevational view of the stent of FIG. 15 depicting the central section and the central opening. 
     FIG. 17 is a flattened elevational view of one embodiment of the stent of the invention depicting a nested ring portion. 
     FIG. 18 is a flattened elevational view of one embodiment of the stent of the invention depicting a nested ring portion. 
     FIG. 19 is a flattened elevational view of one embodiment of the stent of the invention depicting a nested ring portion. 
     FIG. 20 is a flattened elevational view depicting one embodiment of the stent of the present invention. 
     FIG. 21 is a flattened elevation view depicting one embodiment of the stent of the present invention in which at least some of the links have an undulating portion. 
     FIG. 22A is a portion of the stent pattern of the invention depicting struts of variable thickness. 
     FIG. 22B is a portion of the stent pattern of the invention depicting struts of variable width. 
     FIG. 23 is an elevational view of the catheter assembly for delivering and implanting the stent of the invention. 
     FIG. 23A is an elevational view of the catheter assembly configured for independent inflation. 
     FIG. 23B is a cross-sectional view taken along lines  23 B— 23 B depicting the cross-section of the proximal shaft of the independent inflation catheter. 
     FIG. 23C is a cross-sectional view taken along lines  23 C— 23 C depicting the cross-section of the mid-shaft of the independent inflation catheter. 
     FIG. 23D is a cross-sectional view taken along lines  23 D— 23 D depicting the cross-section of the Rx shaft of the independent inflation catheter. 
     FIG. 23E is a cross-sectional view taken along lines  23 E— 23 E depicting the cross-section of the OTW shaft of the independent inflation catheter. 
     FIG. 24 is a cross-sectional view taken along lines  24 — 24  depicting the cross-section of the proximal shaft of the catheter. 
     FIG. 25 is a cross-sectional view taken along lines  25 — 25  depicting the cross-section of a portion of the catheter shaft. 
     FIG. 26A is a cross-sectional view taken along lines  26 A— 26 A depicting the cross-section of the Rx catheter shaft. 
     FIG. 26B is a cross-sectional view taken along lines  26 B— 26 B depicting the cross-section of the over-the-wire shaft. 
     FIG. 27 is a longitudinal cross-sectional view of the coupler. 
     FIG. 28A is a longitudinal cross-sectional view depicting a portion of the catheter distal end including the radiopaque markers. 
     FIG. 28B is a transverse cross-sectional view taken along lines  28 B— 28 B depicting the inner member and long balloon. 
     FIG. 29 is an elevational view of one embodiment of the catheter assembly for delivering and implanting the stent of the invention. 
     FIG. 30 is a transverse cross-sectional view taken along lines  30 — 30  depicting the proximal shaft section of the catheter. 
     FIG. 31 is a transverse cross-sectional view taken along lines  31 — 31  depicting the mid or intermediate shaft section of the catheter. 
     FIG. 31A is a transverse cross-sectional view taken along lines  31 A— 31 A depicting the first distal outer member. 
     FIG. 31B is a transverse cross-sectional view taken along lines  31 B— 31 B depicting the second distal outer member. 
     FIG. 32 is a transverse cross-sectional view taken along lines  32 — 32  depicting the multifurcated distal section of the catheter. 
     FIG. 33 is a longitudinal cross-sectional view of the coupler depicting a guide wire slidably positioned in the dead-end lumen of the coupler. 
     FIG. 34 is an elevational view and a partial longitudinal cross-sectional view of the crimping mold assembly. 
     FIG. 35 is an elevational view of the catheter assembly being advanced into the main vessel. 
     FIG. 36 is an elevational view of the catheter assembly in the main vessel prior to advancement into the side branch vessel. 
     FIG. 37 is an elevational view of the catheter assembly as the over-the-wire guide wire is being advanced into the side branch vessel. 
     FIG. 38 is an elevational view of the catheter assembly positioned in the main vessel and the over-the-wire guide wire advanced and positioned in the side branch vessel. 
     FIG. 39 is an elevational view of the catheter assembly advanced so that the long balloon is in the main vessel and a portion of the short balloon is positioned in the side branch vessel. 
     FIG. 40 is an elevational view of a bifurcation depicting the stent of the invention implanted in the main vessel and the opening to the side branch vessel. 
     FIG. 41 is an elevational view of a bifurcation in which the stent of the present invention is implanted in the main vessel, and a second stent is implanted in the side branch vessel. 
     FIG. 42 is an elevational view depicting the catheter assembly positioned in the main vessel and the over-the-wire guide wire advancing out of the catheter. 
     FIG. 43 is an elevational view of the catheter assembly positioned in the main vessel and the over-the-wire guide wire wrapping around the coupler. 
     FIG. 44 is an elevational view showing the catheter assembly positioned in the main vessel and the over-the-wire guide wire wrapped over the coupler and positioned in the side branch vessel. 
     FIG. 45 is an elevational view of the catheter assembly advanced toward the carina or bifurcation junction but unable to advance further due to the over-the-wire guide wire wrapped over the coupler and/or the long tip. 
     FIG. 46 is an elevational view of an alternative embodiment of the catheter assembly. 
     FIG. 47 is a transverse cross-sectional view taken along lines  47 — 47  depicting the proximal shaft of the catheter. 
     FIG. 48 is a transverse cross-section view taken along lines  48 — 48  depicting the mid-shaft portion of the catheter. 
     FIG. 49A is a transverse cross-section view taken along lines  49 A— 49 A depicting the Rx distal shaft of the catheter. 
     FIG. 49B is a transverse cross-sectional view taken along lines  49 B— 49 B depicting the inner member associated with the Rx shaft portion of the catheter. 
     FIG. 50 is a transverse cross-sectional view taken along lines  50 — 50  depicting the OTW shaft portion of the catheter. 
     FIG. 51 is a partial schematic view depicting one embodiment of the coupler of the catheter assembly. 
     FIG. 52 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 53 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 54 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 55 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 56 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 57 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 58 is a partial schematic view depicting another embodiment of the coupler of the catheter assembly. 
     FIG. 59 is a partial schematic view depicting another embodiment for coupling the distal end of the catheter assembly. 
     FIG. 60 is a partial schematic view depicting another embodiment for coupling the distal end of the catheter assembly. 
     FIG. 61 is a partial schematic view depicting another embodiment for coupling the distal end of the catheter assembly. 
     FIG. 62 is a partial schematic view depicting another embodiment for coupling the distal end of the catheter assembly. 
     FIG. 63 is a partial schematic view depicting another embodiment for coupling the distal end of the catheter assembly. 
     FIG. 64 is an elevational view of one embodiment of the catheter assembly configured for independent inflation of the balloons. 
     FIG. 65 is a transverse cross-sectional view taken along lines  65 — 65  depicting the proximal shaft section of the catheter. 
     FIG. 66 is a transverse cross-sectional view taken along lines  66 — 66  depicting the mid or intermediate shaft section of the catheter. 
     FIG. 67 is a transverse cross-sectional view taken along lines  67 — 67  depicting the multifurcated distal section of the catheter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention includes a stent and stent delivery catheter assembly and method for treating bifurcations in, for example, the coronary arteries, veins, peripheral vessels and other body lumens. Prior art attempts at implanting intravascular stents in a bifurcation have proved less than satisfactory. For example, FIGS. 1-4 depict prior art devices which include multiple stents being implanted in both the main vessel and a side branch vessel. In FIG. 1, a prior art “T” stent is implanted such that a first stent is implanted in the side branch near the origin of the bifurcation, and a second stent is implanted in the main vessel, into the side branch. With this approach, portions of the side branch vessel are left uncovered, and blood flow to the side branch vessel must necessarily pass through the main vessel stent, causing possible obstructions or thrombosis. 
     Referring to FIG. 2, three prior art stents are required to stent the bifurcation. In FIG. 3, the prior art method includes implanting two stents side by side, such that one stent extends into the side branch vessel and the main vessel, and the second stent is implanted in the main vessel. This results in a double-barreled lumen which can present problems such as thrombosis, and turbulence in blood flow. Referring to the FIG. 4 prior art device, a first stent is implanted in the side branch vessel, a second stent is implanted in a proximal portion of the main vessel, and a third stent is implanted distal to the bifurcation, thereby leaving a small gap between the stents and an uncovered luminal area. 
     All of the prior art devices depicted in FIGS. 1-4 have various drawbacks which have been solved by the present invention. 
     In treating side branch vessel  5 , if a prior art stent is used in which there is no acute angle at the proximal end of the stent to match the angle of the bifurcation, a condition as depicted in FIGS. 5A and 5B will occur. That is, a stent deployed in side branch vessel  5  will leave a portion of the side branch vessel exposed, or as depicted in  5 B, a portion of the stent will extend into main vessel  6 . 
     The stent of the present invention can be implanted in the main or side branch vessels to treat a number of disease configurations at a bifurcation, but not limited to, the following: 
     1. Treatment of a parent or main vessel and the origin of the side branch at a bifurcation with any angle associated between the side branch and parent vessel. 
     2. Treatment of a parent vessel proximal to the carina and the side branch vessel simultaneously. 
     3. Treatment of the proximal vessel extending only into the origin of the side branch and the origin of the distal parent at the bifurcation. 
     4. Treatment of the area at the bifurcation only. 
     5. The origin of an angulated posterior descending artery. 
     6. The origin of an LV extension branch just at and beyond the crux, sparing the posterior descending artery. 
     7. The origin of a diagonal from the left anterior descending. 
     8. The left anterior descending at, just proximal to, or just distal to the diagonal origin. 
     9. The origin of a marginal branch of the circumflex. 
     10. The circumflex at, just proximal to, or just distal to the marginal origin. 
     11. The origin of the left anterior descending from the left main. 
     12. The origin of the circumflex from the left main. 
     13. The left main at or just proximal to its bifurcation. 
     14. Any of many of the above locations in conjunction with involvement of the bifurcation and an alternate vessel. 
     15. Any bifurcated vessels within the body where conventional stenting would be considered a therapeutic means of treatment proximal or distal to the bifurcation. 
     The present invention solves the problems associated with the prior art devices by providing a stent which adequately covers the main branch vessel and extends partially into the side branch vessel to cover the origin of the side branch vessel as well. The invention also includes a stent delivery catheter assembly and the method of crimping the stent on the catheter and delivering and implanting the stent in the body, especially the coronary arteries. 
     The Stent Pattern 
     The stent pattern of the present invention is novel in that it provides for vessel wall coverage of the main branch vessel and at least partial coverage of the origin of the side branch vessel. More specifically, in FIGS. 6-20, several embodiments of trap-door stent  20  are shown. The stent is characterized as a “trap door” since the stent pattern is configured so that as the stent is expanded, a portion of the stent flares radially outwardly and opens to a greater diameter than the remainder of the stent, like a trap door, seemingly hidden until opened. The trap door portion, as will be further described herein, expands or opens to cover the opening to the side branch vessel. Once stent  20  is implanted in the main branch vessel and the opening to the side branch vessel, a second, conventional stent can be implanted in the side branch vessel, essentially abutting the trap door portion of the stent. 
     The intravascular stent  20  of the present invention is referred to as a “trap door” stent since the central portion of the stent is somewhat hidden during delivery and opens like a trap door to treat a bifurcated vessel when the stent is expanded. The stent of the present invention has a cylindrical body  21  that includes a proximal end  22  and a distal end  23 . The stent has an outer surface  24  which contacts the vascular wall when implanted and an inner surface  25  through which blood flows when the stent is expanded and implanted. The stent can be described as having numerous connected rings  30  aligned along a common longitudinal axis of the stent. The rings are formed of undulating portions which include first peaks  34  that are configured to be spread apart to permit the stent to be expanded to a larger diameter or compressed tightly toward each other to a smaller diameter onto a catheter. The rings are connected to each other by at least one link  31  between adjacent rings. Typically, there are three links that connect adjacent rings and the links of one ring are circumferentially offset by about 60° from the links of an adjacent ring. While the links  31  typically are offset as indicated, this is not always the case, especially in the area of the trap door. Further, in order to enhance the expandability and the diameter of the ring or rings in the trap door area, long links  33  are about twice the length of the straight links  32 . The number of links between adjacent rings does vary, however, in view of the trap door configuration. 
     The cylindrical body of the stent has a proximal section  26 , a distal section  29  and a central section  28  where the proximal section can have between one and fifteen rings  30 , the distal section can have between one and fifteen rings, and the central section will have between one and ten rings. The number of first peaks  34  in the central section generally will differ from the number of first peaks  34  in the proximal section and the distal section. 
     The central section  28  is essentially the trap door portion of the stent and is enlarged to appose the entrance to the side branch vessel when the stent is expanded. By way of example only, in one embodiment the rings  30  of the proximal section  26  have seven first peaks, the rings of the distal section  29  have six first peaks, and the rings of the central section  28  have eight first peaks. Thus, when expanded, the ring or rings of the central section will expand and the first peaks will spread apart to appose the entrance to the side branch vessel. The rings of the proximal section and distal section will expand into apposition with the walls of the main branch vessel. The number of peaks per section is a matter of choice depending upon the application and the type of bifurcated vessel to be treated. Each of the rings has at least one second peak  35 , which is connected to link  31 . The peaks are spaced on the rings in such a fashion as to provide uniformity after final expansion, since a bifurcated stent does not necessarily expand coaxially inside the vessel. 
     In one embodiment of the invention, a standard 18 mm-long stent  20  will have eight rings  30  in the proximal section  26 , one ring in the central section  28 , and six rings in the distal section  29 . Each of the rings has a length that is substantially the same as the rest of the rings. In another embodiment, there is one ring in the proximal section, one ring in the central section, and one ring in the distal section. In this latter embodiment, the stent is much easier to navigate through a tortuous vessel because it is very short in its overall length (generally between about 2.0 mm to about 8.0 mm in overall length) and the distal end  23  of the stent tracks easily through the vessel in which it is to be implanted, such as a coronary artery. In addition, the short stent is more capable of rotating if it arrives at the bifurcation out of phase, whereby distal torque can be applied from the OTW and Rx guide wires to properly orient the stent. 
     A central opening  40  in the proximal section  26  of the stent allows the passage of a balloon contained on the delivery system. The stent is to be crimped tightly onto two separate expandable members of a catheter. Typically, and as will be described in more detail below, the expandable portions of the catheter will be balloons similar to a dilatation-type balloon for conventional dilatation catheters. In the present invention, the trap door stent  20  is configured such that the stent has a distal opening  36  and a proximal opening  38  that are in axial alignment and through which a longer balloon extends, and the central opening  40  which is adjacent the central section  28  or “trap door,” through which a shorter balloon extends. The stent is crimped tightly onto both the long and short balloons as will be described. 
     In another embodiment, as shown in FIGS. 13-14 and  17 - 19 , the ring  30  or rings in the central section  28  of the stent  20  have a corresponding set of nested peaks  39  nested within the first peaks  34  of the ring or rings of the central section. The nested peaks, when expanded, will appose the opening to the side branch vessel and provide additional support as well as vessel wall coverage. With the addition of the nested peaks, the central section can expand to an even greater diameter than a similar stent without the nested peaks because the extra peaks provide more material to expand. 
     With all of the embodiments of the trap door stent  20  disclosed herein, the rings  30  can be attached to each other by links  31  having various shapes, including straight links  32  or non-linear links  33  having curved portions. The non-linear links, as shown in FIG. 21, can have undulating portions  37  that are perpendicular (or offset) to the longitudinal axis of the stent and act as a hinge to enhance the flexibility of the stent. The links are not limited by any particular length or shape and can be a weld, laser fusion, or similar connection. Welds or laser fusion processes are particularly suited to stent patterns that are out of phase (the peaks point toward each other) as opposed to the in phase pattern (the peaks point in the same direction) shown in the drawings. 
     Each embodiment of the stent  20  also can have rings  30  and links  31  that have variable thickness struts  48 A and  48 B, as shown in FIG. 22A, at various points in order to increase the radial strength of the stent, provide higher radiopacity so that the stent is more visible under fluoroscopy, and enhance flexibility in the portions where the stent has the thinnest struts. The stent also can have variable width struts  49 A and  49 B, as shown in FIG. 22B, to vary flexibility, maximize vessel wall coverage at specific points, or to enhance the stent radiopacity. The variable thickness struts or variable width struts, which may be more radiopaque than other struts, can be positioned along the stent to help the physician position the stent during delivery and implantation in the bifurcated vessel. 
     The trap door stent  20  can be formed in a conventional manner typically by laser cutting a tubular member or by laser cutting a pattern into a flat sheet, rolling it into a cylindrical body, and laser welding a longitudinal seam along the longitudinal edges of the stent. The stent can also be fabricated using conventional lithographic and etching techniques where a mask is applied to a tube or flat sheet. The mask is in the shape of the final stent pattern and is used for the purpose of protecting the tubing during a chemical etching process which removes material from unwanted areas. Electro-discharge machining (EDM) can also be used for fabricating the stent, where a mold is made in the negative shape of the stent and is used to remove unwanted material by use of an electric discharge. The method of making stents using laser cutting processes or the other described processes are well known. The stent of the invention typically is made from a metal alloy and includes any of stainless steel, titanium, nickel-titanium (NiTi or nitinol of the shape memory or superelastic types), tantalum, cobalt-chromium, cobalt-chromium-vanadium, cobalt-chromium-tungsten, gold, silver, platinum, platinum-iridium or any combination of the foregoing metals and metal alloys. Any of the listed metals and metal alloys can be coated with a polymer containing fluorine-19 ( 19 F) used as a marker which is visible under MRI. Portions of the stent, for example some of the links, can be formed of a polymer impregnated with  19 F so that the stent is visible under MRI. Other compounds also are known in the art to be visible under MRI and also can be used in combination with the disclosed metal stent of the invention. 
     The stent of the invention also can be coated with a drug or therapeutic agent to assist in repair of the bifurcated vessel and may be useful, for example, in reducing the likelihood of the development of restenosis. Further, it is well known that the stent (usually made from a metal) may require a primer material coating to provide a substrate on which a drug or therapeutic agent is coated since some drugs and therapeutic agents do not readily adhere to a metallic surface. The drug or therapeutic agent can be combined with a coating or other medium used for controlled release rates of the drug or therapeutic agent. Examples of therapeutic agents that are available as stent coatings include rapamycin, actinomycin D (ActD), or derivatives and analogs thereof. ActD is manufactured by Sigma-Aldrich, 1001 West Saint Paul Avenue, Milwaukee, Wis. 53233, or COSMEGEN, available from Merck. Synonyms of actinopmycin D include dactinomycin, actinomycin IV, actinomycin I 1 , actinomycin X 1 , and actinomycin C 1 . Examples of agents include other antiproliferative substances as well as antineoplastic, antinflammatory, antiplatelet, anticoagulant, antifibrin, antithomobin, antimitotic, antibiotic, and antioxidant substances. Examples of antineoplastics include taxol (paclitaxel and docetaxel). Examples of antiplatelets, anticoagulants, antifibrins, and antithrombins include sodium heparin, low molecular weight heparin, hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogs, dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole, glycoprotein, IIb/IIIa platelet membrane receptor antagonist, recombinant hirudin, thrombin inhibitor (available from Biogen), and 7E-3B® (an antiplatelet drug from Centocore). Examples of antimitotic agents include methotrexate, azathioprine, vincristine, vinblastine, fluorouracil, adriamycin, and mutamycin. Examples of cytostatic or antiproliferative agents include angiopeptin (a somatostatin analog from Ibsen), angiotensin converting enzyme inhibitors such as Captopril (available from Squibb), Cilazapril (available from Hoffman-LaRoche), or Lisinopril (available from Merck); calcium channel blockers (such as Nifedipine), colchicine fibroblast growth factor (FGF) antagonists, fish oil (omega 3-fatty acid), histamine antagonist, Lovastatin (an inhibitor of HMG-CoA reductase, a cholesterol lowering drug from Merck), monoclonal antibodies (such as PDGF receptors), nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor (available from Glazo), Seramin (a PDGF antagonist), serotonin blockers, steroids, thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist), and nitric oxide. Other therapeutic substances or agents which may be appropriate include alpha-interferon, genetically engineered epithelial cells, and dexamethasone. 
     It should be understood that any reference in the specification or claims to a drug or therapeutic agent being coated on the stent is meant that one or more layers can be coated either directly on the stent or onto a primer material on the stent to which the drug or therapeutic agent readily attaches. 
     The Stent Delivery Catheter Assembly 
     In keeping with the invention, as shown in FIGS. 23-28A, the stent  20  is mounted on catheter assembly  101  which has a distal end  102  and a proximal end  103 . The catheter assembly includes a proximal shaft  104  which has a proximal shaft over-the-wire (OTW) guide wire lumen  105  and a proximal shaft inflation lumen  106  which extends therethrough. The proximal shaft OTW guide wire lumen is sized for slidably receiving an OTW guide wire. The inflation lumen extends from the catheter assembly proximal end where an indeflator or similar device is attached in order to inject inflation fluid to expand balloons or expandable members as will be herein described. The catheter assembly also includes a mid-shaft  107  having a mid-shaft OTW guide wire lumen  108  and a mid-shaft rapid-exchange (Rx) guide wire lumen  109 . The proximal shaft OTW guide wire lumen  105  is in alignment with and an extension of the mid-shaft OTW guide wire lumen  108  for slidably receiving an OTW guide wire. The mid-shaft also includes a mid-shaft inflation lumen  110  which is in fluid communication with the proximal shaft inflation lumen  106  for the purpose of providing inflation fluid to the expandable balloons. There is an Rx proximal port or exit notch  115  positioned on the mid-shaft such that the Rx proximal port is substantially closer to the distal end  102  of the catheter assembly than to the proximal end  103  of the catheter assembly. While the location of the Rx proximal port may vary for a particular application, typically the port would be between 10 and 50 cm from the catheter assembly distal end  102 . The Rx proximal port or exit notch provides an opening through which an Rx guide wire  116  exits the catheter and which provides the rapid exchange feature characteristic of such Rx catheters. The Rx port  115  enters the mid-shaft such that it is in communication with the mid-shaft Rx guide wire lumen  109 . 
     The catheter assembly  101  also includes a distal Rx shaft  111  that extends from the distal end of the mid-shaft and which includes an Rx shaft Rx guide wire lumen  112 , to the proximal end of the inner member  111 A inside balloon  117 . The distal Rx shaft  111  also contains an Rx shaft inflation lumen  114 . The Rx shaft Rx guide wire lumen  112  is in alignment with the Rx guide wire lumen  109  for the purposes of slidably carrying the Rx guide wire  116 . The Rx shaft inflation lumen  114  is in fluid communication with the mid-shaft inflation lumen  110  for the purposes of carrying inflation fluid to the long expandable member or long balloon. 
     The catheter assembly also contains an Rx inner member  111 A that extends from the distal end of the distal Rx shaft  111  to the Rx shaft distal port  113 . The Rx inner member  111 A contains an Rx guide wire lumen  111 B. The Rx inner member guide wire lumen  111 B is in alignment with the Rx shaft Rx guide wire lumen  112  for the purpose of slidably carrying the Rx guide wire  116 . The Rx guide wire will extend through the Rx proximal port  115  and be carried through Rx guide wire lumen  109  and Rx shaft Rx guide wire lumen  112 , and through Rx guide wire lumen  111 B and exit the distal end of the catheter assembly at Rx shaft distal port  113 . 
     The catheter assembly further includes a long balloon  117  positioned adjacent the distal end of the catheter assembly and a distal tip  118  at the distal end of the Rx shaft. Further, a coupler  119  is associated with distal Rx shaft  111  such that the Rx shaft Rx guide wire lumen  112  extends through the coupler, with the distal port  113  being positioned at the distal end of the coupler. The coupler has an Rx guide wire lumen  120  that is an extension of and in alignment with Rx lumen  111 B. The coupler  119  further includes a blind lumen  121  for receiving and carrying an OTW guide wire (or joining mandrel)  125 . The blind lumen includes a blind lumen port  122  for receiving the distal end of the OTW guide wire (or joining mandrel)  125  and a dead-end lumen  124  positioned at the coupler distal end  123 . The coupler blind lumen  121  will carry the distal end of a guide wire (either the distal end of the OTW guide wire (or joining mandrel)  125  or an Rx guide wire (or joining mandrel)  116  as will be further described herein) during delivery of the catheter assembly through the vascular system and to the area of a bifurcation. The blind lumen is approximately 3 to 20 mm long, however, the blind lumen can vary in length and diameter to achieve a particular application or to accommodate different sized guide wires having different diameters. Since the coupler moves axially relative to the shaft it is not connected to, the guide wire that resides in the blind lumen  121  of the coupler slides axially relative to the coupler during delivery of the catheter assembly through the vascular system and tortuous anatomy so that, additional flexibility is imported to the tips making it easier to track through tortuous circuitry. A distance “A” should be maintained between the distal end  126  of the OTW guide wire  125  and the dead end  124  of the blind lumen. The distance “A” can range from approximately 0.5 to 5.0 mm, however, this range may vary to suit a particular application. Preferably, distance “A” should be about 0.5 mm to about 2.0 mm. 
     In further keeping with the invention, the catheter assembly  101  also includes an OTW shaft  128  which extends from the distal end of mid-shaft  107 . The OTW shaft carries a short balloon  129  that is intended to be shorter than long balloon  117  and positioned substantially adjacent to the long balloon. The OTW shaft  128  also includes an OTW lumen  130  that is in alignment with the mid-shaft OTW guide wire lumen  108  and proximal shaft OTW guide wire lumen  105 . Thus, an OTW lumen extends from one end of the catheter assembly to the other and extends through the OTW shaft  128 . An OTW shaft distal port  131  is at the distal end of the OTW lumen  130  and the OTW shaft  128  also includes an OTW shaft inflation lumen  132 . Inflation lumen  132  is in alignment and fluid communication with inflation lumens  110  and  106  for the purpose of providing inflation fluid to the long balloon  117  and the short balloon  129 . In this particular embodiment, an OTW guide wire  125  would extend from the proximal end  103  of the catheter assembly and through proximal shaft OTW guide wire lumen  105 , mid-shaft OTW guide wire lumen  108 , OTW lumen  130  and out distal port  131  where it would extend into the coupler  119 , and more specifically into blind lumen  121  through blind lumen port  122 . 
     In order for the catheter assembly  101  to smoothly track and advance through tortuous vessels, it is preferred that the OTW lumen  130  be substantially aligned with the blind lumen  121  of coupler  119 . In other words, as the OTW guide wire extends out of the OTW lumen  130 , it should be aligned without bending more than about ±10° so that it extends fairly straight into the coupler blind lumen  121 . If the OTW lumen  120  and the coupler blind lumen  121  are not substantially aligned, the pushability and the trackability of the distal end of the catheter assembly may be compromised and the physician may feel resistance as the catheter assembly is advanced through tortuous vessels, such as the coronary arteries. 
     In an alternative embodiment, as will be explained more fully herein, a mandrel (stainless steel or nickel titanium wire is preferred) resides in the OTW guide wire lumens  105 , 108 , 130 , and extends into blind lumen  121 . The mandrel is used in place of an OTW guide wire until the catheter assembly has been positioned near the bifurcated vessel, at which time the mandrel can be withdrawn from the vascular system and the OTW guide wire advanced through the OTW guide wire lumens to gain access to the side branch vessel. This will be described more fully in the section related to delivering and implanting the stent. 
     The catheter assembly  101  of the present invention can be dimensioned for various applications in a patient&#39;s vascular system. Such dimensions typically are well known in the art and can vary, for example, for various vessels being treated such as the coronary arteries, peripheral arteries, the carotid arteries, and the like. By way of example, the overall length of the catheter assembly for treating the coronary arteries typically is approximately 135 to 150 cm. Further, for stent delivery in the coronary arteries at a bifurcated vessel, the working surface or the stent carrying surface of the long balloon  117  can be about 18.5 mm for use with an 18 mm-long stent. The short balloon  129  typically will be about 6 to 9 mm, depending on the type of trap door stent  20  that is being implanted. The lengths of the various shafts, including proximal shaft  104 , mid-shaft  107 , distal Rx shaft  111 , and OTW shaft  128  are a matter of choice and can be varied to suit a particular application. 
     FIGS. 23A-23E illustrate an alternative embodiment of the bifurcated catheter assembly  101  which is configured to inflate the expandable portion or balloons either simultaneously or independently. For example, it may be advantageous to partially inflate the balloon in the main vessel and to fully inflate the balloon in the side branch vessel to avoid plaque shifting or to make sure that the central opening in the stent is fully opened and covers the opening to the side branch vessel. The present invention catheter assembly provides for independent balloon inflation and is shown in FIGS. 23A-23E. The reference numbers are primed to indicate like structure shown in FIGS. 23-27. The description of the catheter assembly set forth in FIGS. 23A-23E is essentially the same as for FIGS. 23-27 except for the independent inflation lumen and associated structure which is described as follows. 
     As shown in FIGS. 23A-23E, an inflation lumen  135 ′ is located at the distal end of catheter assembly  101 ′ and extends from the proximal end of the catheter into the proximal shaft  104 . Inflation lumen  135 ′ will connect to either inflation lumen  106 A′ or inflation lumen  106 B′, and it is a matter of choice as to which inflation lumen  106 A′ or  106 B′ is used. Inflation lumen  135 ′ has a proximal port  136 ′ that will be in fluid communication with an inflation source such as an indeflator. The other inflation port  137 ′ will connect to a separate inflation source so that independent inflation occurs between ports  136 ′ and into inflation lumen  135 ′ and  137 ′ which connects into either inflation lumen  106 A′ or inflation lumen  106 B′, whichever one is not connected to inflation lumen  135 ′. Inflation lumens  106 A′ and  106 B′ are in fluid communication with lumens  110 A′ and  110 B′ respectively and extend through mid-shaft section  107 ′ and split, one extending into the Rx shaft  111 ′ and the other extending into the OTW shaft  128 ′. With the inflation lumen separated, the long balloon  117 ′ can be inflated independently of short balloon  129 ′. Alternatively, the balloons can be inflated simultaneously, or they can be inflated independently at different pressures, depending upon a particular application. 
     In an alternative embodiment of the independent inflation catheter  101 ′ of FIGS. 23A-23E, both guide wires within the catheter assembly extend proximally to the catheter proximal end  103 ′ and function as OTW guide wires. In this embodiment, lumen  135 ′ is an OTW guide wire lumen and is in communication with lumen  106 B′ of the proximal section of the catheter  104 ′. Guide wire lumen  106 B′ is then in communication with either lumens  108 ′ or  109 ′ in the mid-section of the catheter and extends distally to tip branch  111 A′. Guide wire  125 ′ extends from the catheter proximal end through lumen  106 A′ in the proximal section of the catheter  104 ′ and into lumen  108 ′ or  109 ′ whichever is not occupied by the other OTW guide wire previously described. Wire  125 ′ then extends distally into lumen  130 ′ located in branch  128 ′ and into the coupler  122 ′ to join the two tips. 
     As shown in FIG. 28A, radiopaque markers  135  are placed on the catheter assembly to help the physician identify the location of the distal end of the catheter in relation to the target area for stent implantation. While the location of the radiopaque markers is a matter of choice, preferably the long balloon  117  will have three radiopaque markers on the inner shaft of the guide wire lumen  112  and the short balloon  129  will have one radiopaque marker on the inner member of the OTW guide wire lumen  130 . Preferably, the middle radiopaque marker on the inner shaft of the long balloon is aligned with the opening of the trap door. One or more of the radiopaque markers may coincide with the alignment of the stent on the balloons which will be described more fully herein. 
     FIG. 29 illustrates another embodiment of a bifurcated catheter  140  which embodies features of the invention. As with catheter  101 , the bifurcated catheter  140  can be used for a variety of procedures such as dilatation, drug delivery, and delivering and deploying a stent, including a stent of the invention, in a body lumen. Bifurcated catheter  140  generally comprises an elongated shaft  142  having a proximal shaft section  144  with a first inflation lumen  146 , and a multifurcated distal shaft section  148  with a first branch  150  and at least a second branch  152 . The first branch  150  has a second inflation lumen  154  within at least a portion thereof in fluid communication with the first inflation lumen  146  and the second branch  152  has a third inflation lumen  156  within at least a portion thereof in fluid communication with the first inflation lumen  146 . An intermediate shaft section  158  joins the proximal and distal sections together and defines a fourth inflation lumen  160  in fluid communication with the first, second, and third inflation lumens  146 / 154 / 156 . A joining wire lumen  162  extends within the proximal section, the intermediate section, and the first branch  150  of the multifurcated distal section  148 . The guide wire lumen  164  extends within the intermediate section  158  and the second branch  152  of the multifurcated distal section  148 . A guide wire lumen  164  extends within the intermediate section  158  and the second branch  152  of the multifurcated distal section  148 . A first balloon  166  is on the first branch  150  and a second balloon  168  is on the second branch  152 , with interiors in fluid communication with the inflation lumens. An adapter  169  on the proximal end of the catheter is configured to direct inflation fluid into the inflation lumens and to provide access to joining wire lumen  162 . A coupler  170  on the second branch, distal to the second balloon  168 , is configured for releasably coupling the first and second branches  150 / 152  together to form a coupled configuration, as discussed in more detail below. The bifurcated catheter  140  is illustrated in the coupled configuration in FIG.  29 . 
     In the embodiment illustrated in FIG. 29, the joining wire lumen  162  is defined by a first inner tubular member  172 , and the guide wire lumen  164  is defined by a second inner tubular member  174 . In a presently preferred embodiment, the first inner tubular member  172  is formed of a single tubular member, which may comprise one or more layers as is conventionally known in the art. However, in alternative embodiments, the first inner tubular member  172  may be formed of separate longitudinal members joined together, end to end, along the length of the first inner tubular member  172 . Similarly, the second inner tubular member  174  is preferably a single or multi-layered, single tubular member, although a plurality of separate members may be joined together to form the second inner tubular member  174 . 
     FIGS. 30-32 illustrate transverse cross sections of the catheter illustrated in FIG. 29, taken along lines  30 — 30 ,  31 — 31 , and  32 — 32 , respectively. In the embodiment illustrated in FIG. 29, the proximal shaft section  144  comprises a proximal outer tubular member  145  defining the first inflation lumen  146 , as best illustrated in FIG.  30 . Similarly, the first branch  150  of the multifurcated distal shaft section  148  is formed in part by a first distal outer tubular member  155 , and the second branch  152  is formed in part by a second distal outer tubular member  157 . The intermediate shaft section  158  comprises an intermediate outer tubular member  159  defining the fourth inflation lumen  160 . In the embodiment illustrated in FIG. 29, the intermediate outer tubular member is a separate tubular member secured to the distal end of the proximal outer tubular member. However, in alternative embodiments, the intermediate section  158  (or intermediate outer tubular member) may be an integral, one piece unit with the proximal section  144 , formed by a distal end portion of the proximal section  144 . In a presently preferred embodiment, the distal end of the proximal outer tubular member  145  is tapered to form a truncated distal end which provides improved kink resistance, pushability, and a smooth junction transition. The tapered distal end of the proximal outer tubular member is preferably formed by cutting the end at an angle to form a truncated end. In one embodiment the taper is about 4 to about 10 mm in length. In a presently preferred embodiment, the proximal end of the intermediate outer tubular member  159  is expanded or flared to allow the proximal end to overlap around the outer surface of the distal end of the proximal outer tubular member  145 . The intermediate outer tubular member  159  has a single distal end as illustrated in FIG. 29, which is disposed about both the proximal end of the first distal outer tubular member  155  and the proximal end of the second distal outer tubular member  157 . The first inner tubular member  172  and the second inner tubular member  174  extend within the fourth inflation lumen  160  in the intermediate outer tubular member  159  in a side-by-side, radially spaced apart relation, as illustrated in FIG.  31 . In the embodiment illustrated in FIG. 31, the intermediate outer tubular member  159  has a circular transverse cross sectional shape. In an alternative embodiment, the intermediate outer tubular member  159  has an oblong transverse cross sectional shape (not shown). FIGS. 31A and 31B detail the structure of first and second outer tubular members  155  and  157  respectively. Inner tubular member  172 , which carries joining wire  180 , is in coaxial relationship with first distal outer tubular member  155 , with inflation lumen  154  between the two shaft members. Similarly, inner tubular member  174 , which carries guide wire  194 , is in coaxial relationship with second distal outer tubular member  157 , with inflation lumen  146  between the two shaft members. As shown in FIG. 32, which illustrates the multifurcated distal shaft section with the proximal view of the intermediate tubular member  159  shown in phantom, the first inner tubular member  172  is coaxially disposed in the first distal outer tubular member  155 , and second inner tubular member  174  is coaxially disposed in the second distal outer tubular member  157 . The first inner tubular member  172  is configured as an OTW member, to slidably receive a joining wire  180  or guide wire in the joining wire lumen  162  therein, with the distal end of the joining wire extending out the port and into the distal end of the first branch  152  and into the coupler  170  to form the coupled configuration. The joining wire  180  is preferably a flexible, typically metal, member. In one embodiment, the joining wire  180  comprises a guide wire, and preferably a guide wire having a distal tip coil configured for use in crossing chronic total occlusions and which consequently provides a desired level of stiffness for improved retractability of the joining wire  180  proximally into the joining wire lumen  162  during uncoupling of the first and second branches  150 / 152 . The joining wire  180  preferably performs similar to a guide wire by providing support at the proximal end of the catheter  140  and the ability to track the patient&#39;s tortuous anatomy. In one embodiment, the joining wire  180  has a proximal section with a 0.014 inch outer diameter, and two tapered sections distal thereto tapering to a smaller outer diameter, providing a smooth distal transition. In a presently preferred embodiment, the joining wire  180  has a soft distal tip comprising a polymeric tube (not shown) around the distal end of the wire  180 . The polymeric tube, preferably formed of a polyether block amide adhesively bonded to the distal end of the joining wire  180 , provides an atraumatic distal end and improved, secure placement of the distal end of the joining wire  180  in the coupling lumen  184  of the coupler  170 , discussed below. The second inner tubular member  174  is configured as an Rx member, to slidably receive a guide wire (not shown) in the guide wire lumen  164  therein. The second inner tubular member  174  has a proximal end which is located at the intermediate section  158 , with the guide wire lumen  164  therein extending between and in fluid communication with a distal port in the distal end of the second branch  152  and a proximal port in a side wall of the intermediate outer tubular member  159 . The proximal port in the intermediate outer tubular member  159  is spaced a relatively short distance from the distal end of the second branch and a relatively long distance from the proximal end of the catheter. Although the proximal end of the guide wire lumen  164  is at the intermediate section  158  in the presently preferred embodiment, in alternative embodiments, the proximal end of the guide wire lumen may be at locations other than the intermediate section, such as within the proximal section  144  or within the second branch  152  of the multifurcated distal section  148 . 
     Coupler  170  is shown in more detail in FIG. 33, illustrating an enlarged, longitudinal cross-sectional view of the distal end of the second branch  152  of the catheter illustrated in FIG. 29, taken within circle  33 . The coupler  170  comprises a tubular sleeve disposed around at least a section of the second inner tubular member  174 . A coupling lumen  184  is defined at least in part by the tubular sleeve, and is configured to slidably receive the distal end of the joining wire  180 , to thereby releasably couple the first and second branches  150 / 152  together. In the embodiment illustrated in FIG. 33, the coupling lumen  184  is a blind lumen having a closed distal end and an open proximal end. In the illustrated embodiment, the coupler is formed by placing a polymeric tubular sleeve, which has a uniform inner lumen extending from the proximal end to the distal end thereof, over the distal end of the second inner tubular member, with a mandrel on one side of second tubular member between an inner surface of the tubular sleeve and an outer surface of the second outer tubular member. The mandrel has a distal taper in order to form the distal taper of the coupler  185 . The tubular sleeve is preferably fusion bonded to the second inner tubular member by applying heat and optionally a radially contracting force. The mandrel is then removed, to thereby form the coupling lumen  184 . As a result, the coupling lumen  184  is at least in part defined by an outer surface of the inner tubular member  174  and an inner surface of the tubular sleeve  170 . Thus, the coupling lumen  184  is defined in part by a radially enlarged proximal portion of the inner lumen of the tubular sleeve  170  in which the second inner tubular member is disposed. In alternative embodiments, the coupler  170  may comprise a single lumen extrusion secured in parallel to the distal end of the guide wire lumen  164  at the distal end of the second branch  152 , two single lumen extrusions with one extruded lumen defining the coupling lumen  184  and bonded to the second extruded lumen which is disposed around the distal end of the tubular member defining the guide wire lumen  164  at the distal end of the second branch  152 , a dual lumen extrusion with the first lumen defining the coupling lumen  184  and the second lumen either defining the distal end of the guide wire lumen  164  or disposed around the distal end of the tubular member defining the guide wire lumen  164  at the distal end of the second branch  152 , or a lumen created in the tubular member defining the guide wire lumen  164  at the distal end of the second branch  152 . In the embodiment illustrated in FIG. 29, the section of the second inner tubular member  174  disposed in the tubular sleeve  170  has an outer diameter not greater than an outer diameter of a section of the second inner tubular member proximally adjacent to the tubular sleeve  170 . 
     The location of the distal end of the first branch  150  relative to the coupler  170  on the second branch  152  is selected to provide improved catheter performance, such as improved advanceability of the catheter through the tortuous anatomy, and improved retractability of the joining wire  180  proximally into the joining wire lumen  162 . Specifically, the distal end of the first branch  150  is proximally spaced from a distal port of the coupling lumen  184  to avoid disadvantageous affects on advanceability of the catheter around turns in the body lumen which are caused by the first branch  150  being too far distally forward. However, the distal end of the first branch  150  is distally spaced from the second balloon  168  working length to avoid having a disadvantageously long length of joining wire  180  exposed and unsupported between the first and second branches  150 / 152 . In the illustrated embodiment, in the coupled configuration, the distal end of the first branch is radially aligned with a proximal section of the coupler  170 . 
     In another embodiment, the distal end of the tubular sleeve  170  is proximal to the distal end of the second branch. In the embodiment illustrated in FIG. 29, a distal tip member  186  defining a lumen is secured (preferably butt joined) to the distal end of the first inner tubular member  172  and forms the distal end of the first branch  150 , and a distal tip member  188  defining a lumen is secured (preferably butt joined) to the distal end of the second inner tubular member  174  and forms the distal end of the second branch  152 . The distal tip members  186 / 188  are typically tubular members formed of a relatively low durometer polymeric material to provide a soft, atraumatic distal tip. The tubular sleeve  170  is thus disposed about and secured to a distal section of the second inner tubular member  174  and a proximal section of the distal tip member  188 . Consequently, in the embodiment illustrated in FIG. 33, the coupling lumen  184  is defined by an outer surface of the distal section of the second inner tubular member  174 , an outer surface of the proximal section of the distal tip member  188 , and an inner surface of the tubular sleeve  170 . 
     The first balloon  166  on the first branch  150  has a proximal end sealingly secured to a distal section of the first distal outer tubular member  155 , and a distal end sealingly secured to a distal section of the first inner tubular member  172 , so that the first balloon  166  can be expanded by delivery of inflation medium to the interior of the first balloon  166  from the second inflation lumen  154 . Similarly, second balloon  168  on the second branch  152  has a proximal end sealingly secured to a distal section of the second distal outer tubular member  57 , and a distal end sealingly secured to a distal section of the second inner tubular member  174 , so that the second balloon  168  can be expanded by delivery of an inflation medium to the interior of the second balloon  168  from the third inflation lumen  156 . In the embodiment illustrated in FIG. 29, the first and second balloons  166 / 168  are both in fluid communication with a common proximal inflation lumen (e.g., the first inflation lumen  146 ), and thus are not inflated separate from one another. However, in alternative embodiments, separated or valved inflation lumens may be present to provide for independent inflation of the first and second balloons  166 / 168 , so that the first inflation lumen  146  is in fluid communication with at least one of the second and third inflation lumens  154 / 156 . In one embodiment, the first balloon  166  has a shorter length than the second balloon  168 , and an elongated proximal tapered section having a length not less than a length of the cylindrical working length of the first balloon  166 , for improved stent delivery in a main branch vessel and at the opening of a side branch vessel. In another embodiment, the length of the elongated proximal tapered section of the first balloon  166  is greater than the length of the cylindrical working length of the first balloon  166 , and in one embodiment is about 5 to about 7 mm, preferably about 6 mm. However, a variety of suitable balloon sizes and configurations may be used depending on the application. Specifically, the configuration of the proximal tapered section of the first balloon  166  will vary depending on the shape of the patient&#39;s bifurcated vessel. Although illustrated as two separate balloons, it should be understood that in an alternative embodiment the first and second balloons  166 / 168  may comprise a bifurcated balloon (not shown) on the multifurcated distal shaft section  148 . In the embodiment illustrated in FIG. 29, the first balloon  166  has an elongated proximal skirt section, with the proximal end of the first balloon  166  being radially aligned with a proximal section of the second balloon  168 , in the coupled configuration. Preferably, the proximal end of the first balloon  166  is radially aligned with the junction between the proximal tapered section and the proximal skirt section of the second balloon  168 , which are proximal to the working length of the second balloon  168 . A variety of suitable balloon configurations can be used for the second balloon  168 , including conventional stent delivery balloons, and the balloon having multiple tapered sections disclosed in U.S. Pat. No. 6,200,325, incorporated in its entirety by reference herein. 
     Although the first and second balloons  166 / 168  are illustrated in FIG. 29 in an inflated configuration with the joining wire  180  disposed in the coupling lumen  184 , it should be understood that in use, the joining wire  180  is typically retracted proximally out of the coupling lumen  184  and into the joining wire lumen  162  before inflation of the balloons  166 / 168 . Additionally, the joining wire  180  is typically releasably secured in place in the bifurcated catheter  140  during advancement of the catheter  140  in the patient&#39;s vasculature, preferably by locking a proximal portion of the joining wire  180  to the catheter  140 . In one embodiment, a locking member (not shown), is provided on the proximal end of the catheter  140  to releasably lock the joining wire  180  in place. The locking member preferably comprises a modified Touhy Borst adapter having a body which screws onto the proximal adapter  169  at the guide wire port thereof, such that silicon tubing inside the locking member compresses onto the joining wire  180 , and a cap which is screwed onto the body of the locking member. The proximal end of the joining wire  180  is then trimmed flush with the cap of the locking member, and an adhesive is used to fill the cap hole to provide securing of the joining wire  180 . Subsequent to securing the joining wire  180  in place, a plastic tamper-proof seal may be provided over the body of the locking member and the guide wire port of the proximal adapter  169  to ensure that the joining wire  180  remains in place before use. 
     FIG. 29 illustrates expanded stent  20 , in dashed lines, mounted on the first and second balloons  166 / 168 , to form a catheter assembly. The method of deploying the stent  20  at a bifurcated body lumen of a patient is similar to the method disclosed herein for the embodiment of the catheter assembly  101 . Generally, the catheter  140  in the coupled configuration is introduced into the patient&#39;s body lumen and advanced therein, typically over a guide wire already in position in the lumen. Specifically, the proximal end of the guide wire extending outside of the body lumen is introduced into the distal end of the guide wire lumen  164 , and the catheter  140  advanced over the guide wire until the distal end of the catheter is in a desired location at the body lumen bifurcation. The joining wire  180  is then proximally retracted from the coupling lumen  184  to uncouple the first and second branches  150 / 152 . The catheter is then advanced over the guide wires to position the stent at the bifurcation. The first and second balloons  166 / 168  are inflated to expand the stent  20  in the main branch vessel and at the opening to the side branch vessel. The first and second balloons  166 / 168  are deflated and the catheter  140  withdrawn, leaving the stent  20  implanted in the body lumen. A second stent can be implanted in the side branch vessel, as discussed herein. 
     In the embodiment illustrated in FIG. 29, three radiopaque marker bands are provided on the second inner tubular member  174 , to facilitate positioning the distal end of the catheter  140  in place in the patient&#39;s vasculature. In an alternative embodiment (not shown), a single radiopaque marker is provided on the first or second inner tubular member  172  or  174  as a carina marker band. The single radiopaque marker is secured to the first or second inner tubular member  172  or  174 , preferably by adhesive bonding or crimping, such that it is aligned with the proximal end of the first balloon  166  or preferably aligned on the trap door opening of the stent. The single radiopaque marker provides improved manufacturability and flexibility compared to multiple markers. 
     Bifurcated catheter  140  is similar in many respects to the catheter assembly  101  disclosed herein, and it should be understood that the disclosure and individual features of the bifurcated catheter  140  and catheter assembly  101  discussed and illustrated with respect to one of the embodiments applies to the catheter assembly  101  discussed and illustrated with respect to one of the embodiments applies to the other embodiment as well. To the extent not discussed herein, the various components of catheter  140  can be formed of conventional materials used in the construction of catheters, and joined together using conventional methods such as adhesive bonding and fusion bonding. In one embodiment, the proximal outer tubular member is formed of a relatively high strength material such as a relatively stiff nylon material or a metal hypotube. The intermediate tubular member and distal outer tubular members are preferably formed of a polymeric material including polyamides such as nylon or urethanes. The inner tubular members preferably have at least an outer layer which is fusion bondable (i.e., compatible) with the polymeric material of the balloons and the coupler. In one embodiment, the coupler and distal tip members are formed of a polyamide such as polyether block amide (PEBAX) or blend thereof. 
     The materials used to construct the catheter assembly  101  or  140  are known in the art and can include for example various compositions of PEBAX, PEEK (polyetherketone), urethanes, PET or nylon for the balloon materials (polyethylene terephathalate) and the like. Other materials that may be used for the various shaft constructions include fluorinated ethylene-propylene resins (FEP), polytetrafluoroethylene (PTFE), fluoropolymers (Teflon), Hytrel polyesters, aromatic polymers, block co-polymers, particularly polyamide/polyesters block co-polymers with a tensile strength of at least 6,000 psi and an elongation of at least 300%, and polyamide or nylon materials, such as Nylon 12, with a tensile strength of at least 15,000 psi. The various shafts are connected to each other using well known adhesives such as Loctite or using heat-shrink tubing over the joint of two shafts, of which both methods are well known in the art. Further, any of the foregoing catheter materials can be combined with a compound that is visible under MRI, such as  19 F, as previously discussed herein. 
     The Stent Crimping Method 
     Since the present invention stent and catheter assembly are used in bifurcated vessels, and most likely in bifurcations occurring in the coronary arteries, the stent must be tightly crimped onto the catheter assembly during delivery so that the stent remains firmly in place until the balloons are expanded thereby implanting the stent at the site of the bifurcation. Due to the unique and novel design of trap door stent  20 , and the particular balloon arrangement of a long balloon  117  and a short balloon  129 , the apparatus and method of crimping are unique. 
     In keeping with the invention a crimping assembly or mold assembly  200  is provided in order to tightly crimp the stent  20  onto the catheter assembly  101 , and more particularly onto long balloon  117  and short balloon  129 . As illustrated in FIG. 34, the mold assembly preferably has three sections, tapered section  201 , straight section  202 , and finish section  203 , through which the stent mounted on the balloons is advanced for the purpose of crimping or compressing the stents onto the balloons. While in the preferred embodiment there are three sections used to compress the stent, more or fewer sections may be appropriate to suit a particular application. With respect to tapered section  201 , it includes a first end  204  shown by way of cross-section immediately under the tapered section depicted in FIG.  34 . The tapered section also has second end  205  and a tapered lumen  206  such that the lumen created by first end  204  is larger than the lumen created by second end  205 . The lumen created by first end  204  is large enough to accommodate the catheter assembly with the stent premounted on the long balloon  117  and the short balloon  129 . The premounting procedure can include slightly compressing the stent onto the balloons using the operator&#39;s fingers to lightly compress the stent so that it remains on the balloons prior to insertion into the mold assembly. As the catheter assembly with the stent mounted on the balloon is advanced from left to right in FIG. 34, the tapered lumen  206  progressively compresses the stent onto the two balloons and begins to shape the stent into the cross-section shown at second end  205 . The stent and balloons are then advanced into straight section  202  which has a first end  207  and a second end  208  that have identical cross-sectional configurations. As the stent and balloons are advanced through straight lumen  209 , the stent is uniformly compressed and any unevenness created by the tapered lumen  206  is removed, thereby providing a smooth and uniform stent outer surface having a configuration shaped like the lumen defined by second end  208 . The stent and balloons are then advanced from left to right in FIG.  34  through finish section  203 . Finish section  203  has a first end  210  that has substantially the same cross-sectional shape as the second end  208  of straight section  202 . As the stent and balloons are advanced through finish section  203 , they are progressively compressed or crimped into the cross-sectional configuration of second end  211 . The finish lumen  212  gradually and progressively (moving left to right) compresses the stent onto the balloons from the cross-sectional shape of first end  210  into the cross-sectional shape of second end  211 . The catheter is advanced such that the proximal portion of the stent up through the trap door resides in section  202  and the portion of the stent and catheter distal to the trap door reside in section  203 . Sections  202  and  203  are shaped to accommodate the natural shape of the catheter and balloons as they change along their lengths. The balloons can be pressurized and the molds heated while the balloons (and stent) and catheter are constrained in the mold in order to compress the stent into the balloon material so that when the balloon is deflated after the stent is expanded, there is an imprint of the stent pattern on the balloon. Pressurization and heating provide additional stent retention. Cross-section  214  represents the main body of the stent that expands and is implanted in the main branch vessel. 
     After the stent and balloons are advanced through finish section  203 , the catheter assembly can be pulled back through the mold assembly  200  without damaging or dislodging the stent, since its profile is substantially smaller in its crimped state than when it entered the mold assembly prior to crimping. The mold assembly can be made from any type of material that is compatible with the metal alloy of the stent being crimped. For example, the mold assembly can be made from stainless steel, a hardened plastic, or glass that will not scratch or cause any surface irregularities to the stent or damage the balloons or catheter in any way during the crimping process. 
     Delivering and Implanting the Stent 
     Referring to FIGS. 35-41, the bifurcated catheter assembly of the present invention provides two separate balloons in parallel which can be advanced into separate passageways of an arterial bifurcation and inflated either simultaneously or independently to expand and implant a stent. As shown in the drawings, bifurcation  300  typically includes a main vessel  301  and a side branch vessel  302  with the junction between the two referred to as the carina  304 . Typically, plaque  305  will develop in the area around the junction of the main vessel and the side branch vessel and, as previously described with the prior art devices, is difficult to stent without causing other problems such as portions of the stent extending into the blood flow path jailing a portion of the side branch vessel, or causing plaque to shift at the carina and subsequently occlude the vessel. 
     In keeping with the invention, the catheter assembly  101  or  140  is advanced through a guiding catheter (not shown) in a known manner. Once the distal end  102  of the catheter reaches the ostium to the coronary arteries, the Rx guide wire  310  is advanced distally into the coronary arteries (or any other bifurcated vessel) so that the Rx guide wire distal end  311  extends past the opening to the side branch vessel  303 . (In most cases, the main vessel will have been predilated in a known manner prior to delivery of the trap door stent. In these cases, the Rx guide wire will have been left in place across and distal to the target site prior to loading the catheter assembly onto the Rx guide wire for advancement to the target site.) After the distal end of the Rx guide wire is advanced into the main vessel past the opening to the side branch vessel, the catheter is advanced over the Rx guide wire so that the catheter distal end  102  is just proximal to the opening to the side branch vessel. Up to this point in time, the OTW guide wire  312  (or mandrel) remains within the catheter and within coupler  119  keeping the tips and balloons joined. More specifically, the OTW guide wire remains within the OTW guide wire lumens  105 , 108 , and  130  as previously described. The distal end of the OTW guide wire  313  is positioned within coupler blind lumen  121  during delivery and up to this point in time. As the catheter is advanced through tortuous coronary arteries, the OTW guide wire distal end  313  should be able to slide axially a slight amount relative the coupler blind lumen to compensate for the bending of the distal end of the catheter. As the catheter distal end moves through tight twists and turns, the coupler moves axially relative to the balloon shaft that it is not attached to thereby creating relative axial movement with the OTW guide wire. Stated differently, the coupler moves axially a slight amount while the OTW guide wire remains axially fixed (until uncoupled) relative to the catheter shaft. If the OTW guide wire were fixed with respect to the coupler at the distal end, it would make the distal end of the catheter stiffer and more difficult to advance through the coronary arteries, and may cause the distal end of the catheter to kink or to be difficult to push through tight turns. Thus, the coupler moves axially relative to the distal end of the OTW guide wire in a range of approximately 0.5 mm up to about 5.0 mm. Preferably, the coupler moves axially relative to the OTW guide wire distal end  313  about 0.5 mm to about 2.0 mm. The amount of axial movement will vary depending on a particular application and the severity of the tortuousity. The proximal end of the OTW guide wire (or joining wire or mandrel) should be removably fixed relative to the catheter shaft during delivery so that the distal end of the OTW guide wire does not prematurely pull out of the coupler. The distal end of the OTW guide wire still moves axially a small amount within the coupler as the distal end of the catheter bends and twists in negotiating tortuous anatomy. 
     As previously disclosed and as shown in FIG. 28A, radiopaque markers  140  are positioned on the inner shaft and coincide or align with the long balloon  117  and the short balloon  129 . The radiopaque markers will assist the position in positioning the catheter assembly  101 , and more specifically the long balloon and short balloon with respect to the opening to the side branch vessel  303 . Typically, it is desirable to have one radiopaque marker centered with respect to the length of the long balloon, and perhaps several other radiopaque markers defining the overall length of the long balloon, or defining the length of the unexpanded or expanded stent  20 . Similarly, a radiopaque marker associated with the short balloon is preferably aligned with the center radiopaque marker of the long balloon. 
     As shown for example in FIG. 36, the OTW guide wire  312  next is withdrawn proximally so that the OTW guide wire distal end  313  is removed from the coupler blind lumen  121 . As shown in FIG. 37, the OTW guide wire next is advanced distally into the side branch vessel  302 , extending past the opening to the side branch vessel  303  and advancing distally into the vessel for a distance as shown in FIG.  38 . Once the Rx guide wire  310  is in position in the main vessel, and the OTW guide wire  312  is in position in the side branch vessel, this will have a tendency to impart a slight separation between the long balloon  117  and the short balloon  129 . As shown in FIG. 39, the catheter assembly  101  is advanced distally over the Rx guide wire and the OTW guide wire and, as the assembly is further advanced, the long balloon  117  continues to separate from the short balloon  129  as each advances into the main vessel  301  and the side branch vessel  302  respectively. As the assembly continues to advance distally, it will reach the point where central opening  40  on the stent  20  is adjacent the opening to the side branch vessel  303 . At this point, the catheter assembly can no longer be advanced distally since the stent is now pushing up against the opening to the side branch vessel. The long balloon  117  and the short balloon  129  are next inflated simultaneously to expand the stent  20  into the main vessel and into the opening to the side branch vessel. As shown in FIG. 40, a portion of the central section  28  of the stent will expand into contact with the opening to the side branch vessel and the central opening  40  of the stent should coincide with the opening to the side branch vessel providing a clear blood flow path through the proximal opening of the stent  38  and through the central opening  40  into the side branch vessel. The expanded stent  20  is shown in FIG. 40 covering a portion of the main vessel and the opening to the side branch vessel. 
     In keeping with the invention, as the catheter assembly is advanced through tortuous coronary arteries, the central opening  40  of the stent  20  may or may not always be perfectly aligned with the opening to the side branch vessel  303 . If the central opening of the stent is in rotational alignment with the opening to the side branch vessel the stent is said to be “in phase” and represents the ideal position for stenting the main branch vessel and the opening to the side branch vessel. When the opening and the opening to the side branch vessel are not rotationally aligned it is said to be “out of phase” and depending upon how may degrees out of phase, may require repositioning or reorienting the central opening with respect to the opening to the side branch vessel. More specifically, the mis-alignment can range anywhere from a few degrees to 360°. If the central opening is in excess of 90° out of phase with respect to the opening to the side branch vessel, it may be difficult to position the stent with respect to the longitudinal axis. When the out of phase position is approximately 270° or less, the stent  20  still can be implanted and the central opening will expand into the opening to the side branch vessel and provide adequate coverage provided that the stent and radiopaque markers can be positioned longitudinally. Due to the unique and novel design of the catheter assembly and the stent of the present invention, this misalignment is minimized so that the central opening  40  generally aligns with the opening to the side branch vessel, even if the central opening is out of phase approximately 90° from the opening of the side branch vessel  303 . Typically, the alignment between the central opening and the opening to the side branch vessel will be less than perfect, however, once the OTW guide wire  312  is advanced into the side branch vessel  302 , as previously described, the assembly will slightly rotate the central opening  40  into better alignment with the opening to the side branch vessel. As can be seen in FIGS. 35-39, after the stent has been properly oriented, it is expanded into contact with the main branch vessel and the central opening expanded to contact with the opening to the side branch vessel. 
     As shown in FIG. 41, a second stent  320  can be implanted in the side branch vessel  302  such that it abuts central opening  40  of stent  20 . The second stent can be delivered and implanted in the following manner. After implanting stent  20 , the long balloon  117  and the short balloon  119  are deflated and catheter assembly  101  (or  140 ) are removed from the patient by first withdrawing the Rx guide wire  310  and then withdrawing the catheter assembly over the in-place OTW guide wire  312  (an extension guide wire which is known in the art may be required), which remains in the side branch vessel  302 . Alternatively, the catheter assembly can be withdrawn from the patient while leaving both the Rx and OTW guide wires in place in their respective vessels. Next, a second catheter assembly (not shown) on which second stent  320  is mounted, is backloaded onto the proximal end of the OTW guide wire  312 . The catheter assembly is next advanced through the guiding catheter and into the coronary arteries over the OTW guide wire, and advanced such that it extends into proximal opening  38  of the expanded and implanted stent  20 . The second catheter assembly is advanced so that it extends through the opening to the side branch vessel and advances over the OTW guide wire  312  and into the side branch vessel where second stent  320  can be expanded and implanted in the side branch vessel to abut the trap door portion of stent  20 . Alternatively, the catheter assembly  101  can be withdrawn to just proximal of the bifurcation, the Rx guide wire  310  withdrawn proximally into the catheter, and then the catheter assembly advanced into the side branch vessel over the in-place OTW guide wire  312 . The Rx guide wire can then be advanced into the side branch vessel, the OTW guide wire safely withdrawn into the catheter assembly, and the catheter assembly then safely removed in an Rx exchange over the Rx guide wire which remains in place in the side branch vessel. Thereafter the second catheter assembly can be advanced over the in-place Rx guide wire  310  and into the side branch vessel where the second stent is implanted as previously described. Care must be taken in this approach to avoid wire wrapping, that is avoiding wrapping the Rx and OTW guide wires in the side branch vessel. 
     In another alternative embodiment for implanting second stent  320 , the long balloon  117  and the short balloon  119  are deflated and catheter assembly  101  is removed from the patient by first withdrawing OTW guide wire  312  so that it resides within the catheter assembly, and then withdrawing the catheter assembly over the in-place Rx guide wire  310 , which remains in the main vessel  301 . Next, a second catheter assembly (not shown) on which second stent  320  is mounted, is back loaded onto the proximal end of Rx guide wire  310 , advanced through the guiding catheter into the coronary arteries, and advanced such that it extends into the proximal opening  38  of the expanded and implanted stent  20 . The Rx guide wire is then withdrawn proximally a short distance so that the Rx guide wire distal end  311  can be torqued and rotated so that it can be advanced into the side branch vessel  302 . Once the Rx guide wire is advanced into the side branch vessel, the second catheter is advanced and the second stent  320  is positioned in the side branch vessel where it is expanded and implanted in a conventional manner as shown in FIG.  41 . The second catheter assembly is then withdrawn from the patient over the Rx guide wire. 
     In an alternative method of deploying and implanting stent  20 , the catheter assembly  101  as shown in FIGS. 35-41 can be adapted to carry a mandrel (not shown) instead of the OTW guide wire. For example, during delivery and positioning of the stent in the main branch vessel  301 , a mandrel resides in the OTW guide wire lumens  105 , 108 , and  130 , and the distal end of the mandrel extends into and resides in coupler blind lumen  121 . As the catheter assembly is positioned just proximal to the bifurcation, such as shown in FIGS. 35 and 36, the mandrel is withdrawn proximally from the catheter assembly allowing the long balloon  117  and the short balloon  129  to slightly separate. Thereafter, an OTW guide wire  312  is frontloaded into the proximal end of the catheter assembly and advanced through the OTW guide wire lumens and into the side branch vessel  302  as shown in FIGS. 37 and 38. After this point, the delivery and implanting of the stent is the same as previously described. 
     In an alternative method of delivering and implanting the stent of the invention, the catheter assembly  101  or  140  is advanced through a guiding catheter (not shown) in a known manner. Once the distal end  102  of the catheter reaches the ostium to the coronary arteries, the Rx guide wire  310  is advanced out of the Rx shaft  111  and advanced distally into the coronary arteries (or any other bifurcated vessels) so that the Rx guide wire distal end  311  extends through the opening to the side branch vessel  303 . (As noted above, the Rx guide wire may already be positioned in the main vessel or side branch vessel as a result of a pre-dilatation procedure). After the distal end of the Rx guide wire is advanced into the side branch vessel, the catheter is advanced over the Rx guide wire so that the catheter distal end  102  is positioned distal to the opening to the side branch vessel and partially within the side branch vessel. More specifically, the short tip of the short balloon  129  should be distal to the carina  304 . Up to this point in time, the OTW guide wire  312  remains within the catheter and within coupler  119 . More specifically, the OTW guide wire remains within the OTW guide wire lumens  105 , 108 , 130  as previously described. The distal end of the OTW guide wire  313  is positioned within coupler blind lumen  121  during delivery and up to this point in time. As the catheter is advanced through tortuous coronary arteries, for example, the OTW guide wire distal end  313  should be able to move axially a slight amount within the coupler blind lumen to compensate for the bending of the distal end of the catheter. If the OTW guide wire were fixed with respect to the catheter shaft and the coupler at the distal end, it would make the distal end of the catheter stiffer and more difficult to advance through the coronary arteries, and may cause the distal end of the catheter to kink or be more difficult to push through tight turns. Thus, the distal end of the OTW guide wire will move axially in a range of approximately 0.5 mm up to about 5.0 mm. Preferably, the OTW guide wire distal end  313  will move back and forth axially about 0.5 mm to about 2.0 mm. The amount of axial movement depends on a particular application or vessel tortuousity. The proximal end of the OTW guide wire should be removably fixed relative to the catheter shaft during delivery so that the distal end of the OTW guide wire does not prematurely pull out of the coupler. The distal end of the OTW guide wire still moves axially a small amount within the coupler as the distal end of the catheter bends and twists in negotiating tortuous anatomy. 
     The OTW guide wire  312  next is withdrawn proximally so that the OTW guide wire distal end  313  is removed from the coupler blind lumen  121 . The OTW guide wire next is advanced distally into the side branch vessel  302  a short distance. The catheter assembly is next withdrawn proximally so the long balloon  117  and the short balloon  129  are in the main vessel just proximal of the opening of the side branch vessel. More specifically, the coupler distal tip is proximal to vessel carina  304 . As the catheter assembly is withdrawn from the side branch vessel, the long balloon and short balloon will begin to separate slightly. Thereafter, the Rx guide wire  310  is withdrawn proximally until it is clear of the opening to the side branch vessel, whereupon it is advanced distally into the main branch vessel for a distance. The catheter assembly next is advanced distally over the Rx guide wire in the main branch vessel and the OTW guide wire in the side branch vessel. As the catheter advances distally, the long balloon and short balloon will separate at least partially until the short balloon enters the side branch vessel and the long balloon continues in the main branch vessel. As the balloons and stent push up against the ostium of the bifurcation, the catheter assembly cannot be advanced further and the stent is now in position to be expanded and implanted. At this point the radiopaque markers should be appropriately positioned. The central opening  40  on the stent  20  should be approximately adjacent the opening to the side branch vessel  303 . The long balloon  117  and the short balloon  129  are next inflated simultaneously to expand the stent  20  into the main vessel and into the opening into the side branch vessel respectively. A portion of the central section  28  of the stent will expand into contact with the opening to the side branch vessel and the central opening  40  of the stent should coincide to the opening of the side branch vessel providing a clear blood flow path through the proximal opening of the stent  38  and through the central opening  40  into the side branch vessel. When fully expanded, stent  20  should cover at least a portion of the main vessel and the opening to the side branch vessel. After the stent has been expanded and implanted, the balloons are deflated and the assembly is withdrawn from the vascular system over the Rx and OTW guide wires. The Rx and OTW guide wires remain in place in the main and side branch vessels for further procedures. 
     The above procedures can also be performed with a spare safety wire placed in the alternate vessel. The safety wire is removed from the patient after the OTW guide wire has been advanced into the side branch vessel (first case) or the Rx guide wire has been advanced into the distal main vessel (second case). The safety wire allows access to the vessel should closure from a dissection or spasm occur. 
     As can be seen in FIGS. 42-45, the OTW guide wire  312  on occasion can be inadvertently torqued in the wrong direction and wrap around the distal end  102  of the catheter or around the coupler  119  prior to advancing into the side branch vessel  302 . If this occurs, and the OTW guide wire is advanced into the side branch vessel, the catheter assembly can be advanced distally only a certain distance before the crossed wires reach the junction or carina of the main vessel and the side branch vessel and the catheter can no longer be advanced distally. At this point, the physician knows that the wires are wrapped or that the central opening is severely out of alignment with the opening of the side branch vessel, in which cases the OTW guide wire  312  is withdrawn proximally into the catheter and the catheter assembly is reoriented by rotating the assembly to better position the central opening  40  with respect to the opening to the side branch vessel prior to advancing the OTW guide wire  312 . Thus, as shown in FIG. 45, once the guide wires are wrapped, the OTW guide wire must be withdrawn proximally, and then readvanced into the side branch vessel taking care to avoid wrapping. The catheter assembly would then be readvanced in an effort to reorient the central opening  40  with the opening to the side branch vessel. 
     If it becomes impossible to deliver the stent for whatever reason, including that described above with respect to the wrapped guide wires, the catheter assembly  101  can be withdrawn into the guiding catheter and removed from the patient. Typically, the OTW guide wire  312  would be withdrawn proximally into the catheter and the catheter assembly would be withdrawn proximally over the Rx guide wire which remains in place in the main vessel  301 . Alternatively, as the catheter assembly is withdrawn, the stent can be safely implanted proximal to the bifurcation. If desired, a second catheter assembly can be backloaded over in-place Rx guide wire  310  and advanced through the guiding catheter and into the coronary arteries as previously described to implant another stent. 
     Alternative Catheter Assemblies 
     In keeping with the invention, as shown in FIGS. 46-50, the stent  20  is mounted on alternative catheter assembly  401  which has a distal end  402  and a proximal end  403 . The catheter assembly includes a proximal shaft  404  which has a proximal shaft over-the-wire (OTW) guide wire lumen  405  and a proximal shaft inflation lumen  406  which extends therethrough. The proximal shaft OTW guide wire lumen is sized for slidably receiving an OTW guide wire. The inflation lumen extends from the catheter assembly proximal end where an indeflator or similar device is attached in order to inject inflation fluid to expand balloons or expandable members as will be herein described. The catheter assembly also includes a mid-shaft  407  having a mid-shaft OTW guide wire lumen  408  and a mid-shaft rapid-exchange (Rx) guide wire lumen  409 . The proximal shaft OTW guide wire lumen  405  is in alignment with and an extension of the mid-shaft OTW guide wire lumen  408  for slidably receiving an OTW guide wire. The mid-shaft also includes a mid-shaft inflation lumen  410  which is in fluid communication with the proximal shaft inflation lumen  406  for the purpose of providing inflation fluid to the expandable balloons. There is an Rx proximal port or exit notch  415  positioned on the mid-shaft such that the Rx proximal port is substantially closer to the distal end  402  of the catheter assembly than to the proximal end  403  of the catheter assembly. While the location of the Rx proximal port may vary for a particular application, typically the port would be between  10  and  50  cm from the catheter assembly distal end  402 . The Rx proximal port or exit notch provides an opening through which an Rx guide wire  416  exits the catheter and which provides the rapid exchange feature characteristic of such Rx catheters. The Rx port  415  enters the mid-shaft such that it is in communication with the mid-shaft Rx guide wire lumen  409 . 
     The catheter assembly  401  also includes a distal Rx shaft  411  that extends from the distal end of the mid-shaft and which includes an Rx shaft Rx guide wire lumen  412 , to the proximal end of the inner member  411 A inside balloon  417 . The distal Rx shaft  411  also contains an Rx shaft inflation lumen  414 . The Rx shaft Rx guide wire lumen  412  is in alignment with the Rx guide wire lumen  409  for the purposes of slidably carrying the Rx guide wire  416 . The Rx shaft inflation lumen  414  is in fluid communication with the mid-shaft inflation lumen  410  for the purposes of carrying inflation fluid to the long expandable member or long balloon. 
     The catheter assembly also contains an Rx inner member  411 A that extends from the distal end of the distal Rx shaft  411  to a blind lumen port  422  of coupler  419 . The Rx inner member  411 A contains an Rx guide wire lumen  411 B. The Rx inner member guide wire lumen  411 B is in alignment with the Rx shaft Rx guide wire lumen  412  for the purpose of slidably carrying the Rx guide wire  416 . The Rx guide wire will extend through the Rx proximal port  415  and be carried through Rx guide wire lumen  409  and Rx shaft Rx guide wire lumen  412 , and through Rx guide wire lumen  411 B and into coupler  419 . 
     The catheter assembly further includes a long balloon  417  positioned adjacent the distal end of the catheter assembly and a distal tip  418  at the distal end of the Rx shaft. Further, coupler  419  is associated with distal Rx shaft  411  such that the Rx shaft Rx guide wire lumen  412  extends into the coupler. The coupler  419  includes a blind lumen  421  for receiving and carrying the Rx guide wire  416 . The blind lumen includes a blind lumen port  422  for receiving the distal end of the Rx guide wire  416 . The coupler blind lumen  421  will carry the distal end of the Rx guide wire  416  during delivery of the catheter assembly through the vascular system and to the area of a bifurcation. The blind lumen is approximately 3 to 20 mm long, however, the blind lumen can vary in length and diameter to achieve a particular application or to accommodate different sized guide wires having different diameters and length. The guide wire that resides in the blind lumen  421  should be able to slide axially in the coupler as the coupler moves during delivery of the catheter assembly through the vascular system and tortuous anatomy so that the guide wire does not get jammed into the dead end portion of the blind lumen, which may cause the distal end of the catheter assembly to bind or kink as it travels along tight curves. A distance should be maintained between the distal end of the Rx guide wire  416  and the dead end of the blind lumen. The distance can range from approximately 0.5 to 5.0 mm, however, this range may vary to suit a particular application. Preferably, the distance between the Rx guide wire distal end and the dead end of the blind lumen should be about 0.5 mm to about 2.0 mm. 
     In further keeping with the invention, the catheter assembly  401  also includes an OTW shaft  428  which extends from the distal end of mid-shaft  407 . The OTW shaft carries a short balloon  429  that is intended to be shorter than long balloon  417  and positioned substantially adjacent to the long balloon. The OTW shaft  428  also includes an OTW lumen  430  that is in alignment with the mid-shaft OTW guide wire lumen  408  and proximal shaft OTW guide wire lumen  405 . Thus, an OTW lumen extends from one end of the catheter assembly to the other and extends through the OTW shaft  428 . An OTW shaft distal port  431  is at the distal end of the OTW lumen  430  and the OTW shaft  428  also includes an OTW shaft inflation lumen  432 . Inflation lumen  432  is in alignment and fluid communication with inflation lumens  410  and  406  for the purpose of providing inflation fluid to the long balloon  417  and the short balloon  429 . In this particular embodiment, an OTW guide wire  425  would extend from the proximal end  403  of the catheter assembly and through proximal shaft OTW guide wire lumen  405 , mid-shaft OTW guide wire lumen  408 , OTW lumen  430  where it would extend through the coupler  419 , and more specifically through the coupler through lumen  426  and out distal port  413 . 
     In order for the catheter assembly  401  to smoothly track and advance through tortuous vessels, it is preferred that the Rx lumen  411 B be substantially aligned with the blind lumen  421  of coupler  419 . In other words, as the Rx guide wire  416  extends out of the Rx lumen  411 B, it should be aligned without bending more than about ±10° so that it extends fairly straight into the coupler blind lumen  421 . If the Rx lumen  411  and the coupler blind lumen  421  are not substantially aligned, the pushability and the trackability of the distal end of the catheter assembly may be compromised and the physician may feel resistance as the catheter assembly is advanced through tortuous vessels, such as the coronary arteries. 
     There are numerous alternative embodiments of the catheter assembly  101 , 140  and  401  which includes different arrangements for coupling the long and short balloons together during delivery over either the Rx guide wire or the OTW guide wire. These embodiments are disclosed in FIGS. 51-58. 
     In the embodiment disclosed in FIG. 51, the long balloon  500  is adjacent the short balloon  501  with the stent  20  mounted thereon. An Rx guide wire lumen  502  extends through the long balloon and through coupler  506  which has a through lumen  507 . An OTW guide wire lumen  503  extends through the short balloon and carries the OTW guide wire  505 . The Rx guide wire  504  extends through the Rx guide wire lumen  502  in the long balloon and exits the coupler through lumen  507 . A distal end of the OTW guide wire  505  extends into a blind or dead end lumen  508  in the coupler  506  and is adjacent to through lumen  507 . Thus, the coupler  506  has dual lumens that are side by side, one of which is a through lumen  507  and the other is a blind lumen  508 . In this embodiment, the catheter assembly tracks over the Rx guide wire to the target site or the bifurcation area while the OTW guide wire remains in blind lumen  508 , thereby coupling the long balloon and the short balloon during delivery. Once positioned at the bifurcation area, the OTW guide wire is withdrawn proximally to uncouple the short balloon from the long balloon so that the stent can be deployed and implanted. 
     In an alternative embodiment, the OTW guide wire lumen extends through the long balloon and the Rx guide wire lumen extends through the short balloon, as shown in FIG.  52 . Thus, long balloon  500  is mounted adjacent short balloon  501  and the long balloon carries the OTW guide wire lumen  503 , while the short balloon carries the Rx guide wire lumen  502 . A coupler  506  has a through lumen  507  which carries the OTW guide wire  505  and a blind lumen  508  which contains the distal end of Rx guide wire  504 . During delivery, the catheter assembly tracks over the OTW guide wire  505  until the catheter assembly reaches the target site or bifurcation. Thereafter, the Rx guide wire  504  is withdrawn proximally to uncouple the short balloon from the long balloon so that the catheter assembly can be advanced over the Rx guide wire and the OTW guide wire to further position and implant the stent as previously described. In this embodiment, a locking mechanism to releasably lock the proximal portion of the Rx guide wire will be located on the proximal catheter shaft as previously described. 
     In another embodiment, the catheter assembly is delivered over the Rx guide wire which extends through the short balloon and the coupler through lumen. As shown in FIG. 53, the long balloon  500  and the short balloon  501  are adjacent to each other with the stent  20  mounted thereon. Rx guide wire lumen  502  extends through the short balloon and OTW guide wire lumen  503  extends through the long balloon. The Rx guide wire  504  extends through the Rx guide wire lumen and through coupler  506  and through coupler through lumen  507  to extend out of the catheter assembly. The OTW guide wire  504  extends through the OTW guide wire lumen and into blind lumen  508  in coupler  506 . During delivery, the catheter is advanced over the Rx guide wire  504  until the target site or bifurcation is reached, whereupon the OTW guide wire is withdrawn proximally from the blind lumen  508  of the coupler  506  so that the short balloon  501  is uncoupled from the long balloon  500 . Thereafter, the catheter assembly can be advanced over the guide wire as previously discussed so that the stent can be further delivered and implanted at the bifurcation. 
     In FIG. 54, an alternative embodiment is shown in which the long balloon  500  is adjacent the short balloon  501  with a stent  20  mounted thereon. In this embodiment, the Rx guide wire lumen  502  extends through the long balloon while the OTW guide wire lumen  503  extends through the short balloon. The Rx guide wire  504  extends through the Rx guide wire lumen in the long balloon and extends into coupler  506  so that the distal end of the Rx guide wire is positioned in blind lumen  508 . The OTW guide wire extends through the short balloon and through coupler through lumen  507  to extend into the vascular system. The catheter assembly is delivered over the OTW guide wire  505  until the assembly reaches the target site or bifurcation, whereupon the Rx guide wire is withdrawn proximally to uncouple the short balloon from the long balloon. Thereafter, the catheter is further advanced over the guide wires to further position the stent so that the stent can be implanted at the bifurcation. In the embodiments disclosed in FIGS. 51 and 53, the OTW guide wire can be substituted with a joining wire or mandrel for the purpose of coupling the short balloon to the long balloon. Once the catheter assembly has been positioned at the bifurcation by advancing the catheter over the Rx guide wire, the mandrel or joining wire can be removed from the catheter assembly, and the OTW guide wire  505  can be backloaded into the catheter and advanced through the catheter assembly and into the side branch vessel so that the catheter assembly can be further advanced and the stent implanted. 
     In another embodiment, as shown in FIGS. 55-58, the coupler has side-by-side dual lumens, both of which are through lumens. 
     In the embodiment disclosed in FIG. 55, the long balloon  500  is positioned adjacent the short balloon  501  with a stent  20  mounted thereon. An Rx guide wire lumen  502  extends through the long balloon and an OTW guide wire lumen  503  extends through the short balloon. The coupler  506  is mounted on the distal tip of the short balloon and has side-by-side dual lumens, including a first through lumen  509  and a second through lumen  510  adjacent thereto. The first through lumen  509  is in alignment with the OTW guide wire lumen  503  while the second through lumen  510  is in alignment with the Rx guide wire lumen  502 . Rx guide wire  504  extends through the Rx guide wire lumen and the second through lumen, while the OTW guide wire  505  extends through the OTW guide wire lumen  503  and the first through lumen  509 . During delivery, the catheter assembly is advanced over the Rx guide wire  504  while the OTW guide wire  505  remains within second through lumen  510 . The catheter assembly is advanced over the Rx guide wire  504  until the catheter assembly is positioned at the bifurcation, whereupon the OTW guide wire can be advanced distally out of through lumen  509  and into the side branch vessel, and the Rx guide wire can then be withdrawn proximally to uncouple the short balloon from the long balloon. The Rx guide wire is then advanced into the main vessel and the catheter assembly advanced over the guide wires as previously described to further position and implant the stent. 
     In another embodiment, as shown in FIG. 56, the catheter assembly tracks over the OTW guide wire. In this embodiment, the long balloon  500  is adjacent the short balloon  501  with the stent  20  mounted thereon. An Rx guide wire lumen  502  extends through the short balloon while an OTW guide wire lumen  503  extends through the long balloon. An Rx guide wire  504  extends through the Rx guide wire lumen  502  while an OTW guide wire  505  extends through the OTW guide wire lumen  503 . The coupler  506  is attached to the distal end of the short balloon and has a first through lumen  509  which aligns with the Rx guide wire lumen  502 . The second through lumen  510  extends through the coupler and is substantially in alignment with the OTW guide wire lumen  503 . In this embodiment, the OTW guide wire  505  extends through the second through lumen  510  to couple the long balloon to the short balloon. During delivery, the catheter assembly tracks over the OTW guide wire  505  while the Rx guide wire  504  remains in the Rx guide wire lumen and in the first through lumen  509  of the coupler. When the catheter assembly is positioned at the bifurcation, the Rx guide wire  504  is extended distally into the side branch vessel, whereupon the OTW guide wire  505  is withdrawn proximally to uncouple the long balloon and the short balloon. Thereafter, the catheter assembly is advanced over the guide wires so that the stent may be further positioned and implanted as previously described. 
     In another embodiment, as shown in FIG. 57, the coupler has side-by-side through lumens and the catheter assembly tracks over the Rx guide wire while the OTW guide wire remains in the catheter assembly during delivery. More specifically, as shown in FIG. 57, the long balloon  500  and the short balloon  501  are adjacent to each other with the stent  20  mounted thereon. An Rx guide wire lumen  502  extends through the short balloon while an OTW guide wire lumen  503  extends through the long balloon. An Rx guide wire  504  extends through the Rx guide wire lumen and into and through coupler  506  and through second through lumen  510 . The OTW guide wire  505  extends through OTW guide wire lumen  503  and into the coupler where the distal end of the OTW guide wire resides in through lumen  509 , but does not extend out of lumen  509  until after the catheter assembly has initially been positioned at the bifurcation. During stent delivery, the catheter assembly is advanced over the Rx guide wire  504  until the distal end of the catheter assembly is positioned at the bifurcation, whereupon the OTW guide wire  505  is advanced distally out of first through lumen  509  and into the main vessel. The Rx catheter  504  is withdrawn proximally from the second through lumen and the coupler  506  to uncouple the long balloon and the short balloon. The Rx guide wire is next advanced into the side branch vessel and the catheter assembly advanced over the guide wires as previously described to further position and implant the stent. 
     In another embodiment, as shown in FIG. 58, a catheter assembly is advanced over the OTW guide wire which is positioned in a coupler having side-by-side through lumens. More specifically, a long balloon  500  is positioned adjacent a short balloon  501  with a stent  20  mounted thereon. An Rx guide wire lumen  502  extends through the long balloon and carries the Rx guide wire  504 . An OTW guide wire lumen  503  extends through the short balloon and carries an OTW guide wire  505 . The OTW guide wire couples the short balloon to the long balloon by extending through coupler  506  and more specifically through second through lumen  510 . The Rx guide wire  504  resides in first through lumen  509  of coupler  506 . During delivery of the stent, the catheter assembly is advanced distally over the OTW guide wire  505  until the catheter assembly reaches the target site or bifurcation. Thereafter, the Rx guide wire  504 , which has to this point resided in the first through lumen  509  of the coupler is advanced distally out of the first through lumen  509  and into the main vessel. The OTW guide wire  505  is withdrawn proximally from the coupler and the second through lumen  510  to uncouple the short balloon from the long balloon. The OTW guide wire lumen  505  is next advanced into the side branch vessel as previously described, and the catheter assembly is advanced over the guide wires to further position and implant the stent. 
     A number of alternative embodiments are available for coupling the long balloon to the short balloon as disclosed herein, and particularly as disclosed in embodiments shown in FIGS. 51-58. As described below, alternative coupler embodiments include a sewn tip, a slit tip, a double slit tip, and an expandable slit tip. 
     As shown in FIG. 59, the so-called sewn tip design is shown in which long balloon  530  is coupled to short balloon  531  with the stent (not shown) mounted thereon. Long tip  532  is adjacent short tip  533  and the long tip has holes  534  and the short tip has holes  535 . The holes are aligned and spaced on the long and short tips such that a staggered relationship exists between the hole pairs along the long tip and the short tip. The tips are coupled by a joining wire  536  which is threaded through the staggered holes in the distal section of the long and short tips. The proximal end of the joining wire (not shown) extends proximally through the guide wire lumen to the proximal hub where it is locked into place as previously described by a suitable locking mechanism. A guide wire  537  (either an OTW or Rx guide wire) extends through a guide wire lumen  538 . The diameter of the joining wire  536  is such that it occupies minimal space in the guide wire lumen  538  and does not create frictional interference with the guide wire  537 . For example, the joining wire can be a nitinol wire having a diameter of approximately 0.006 inch and is flexible enough to extend through the holes  534 , 535 , yet remain rigid enough to couple the long tip  532  to the short tip  533 . As previously described, the catheter assembly is advanced over the guide wire  537  until it reaches the target site or bifurcation, whereupon the joining wire  536  is withdrawn from the catheter assembly thereby uncoupling the tips and uncoupling the short balloon from the long balloon. 
     In an alternative embodiment for coupling the balloons, as shown in FIG. 60, a long balloon  550  is coupled to short balloon  551 . A long tip  552  is attached to the short balloon while a short tip  553  is attached to the long balloon. A slit  554  is formed in a distal section of the long tip  552 . An Rx guide wire lumen  555  extends through the long balloon and through the section of the long tip  552  that is distal to the slit  554 . An OTW guide wire lumen  556  extends through the catheter assembly and through the short balloon and extends into the long tip  552 . An Rx guide wire  557  extends through the Rx guide wire lumen and through slit  554  to couple the two balloons together. An OTW guide wire  558  resides in the OTW guide wire lumen and extends into the long tip  552  to a point just proximal of slit  554 . During delivery, the catheter assembly is advanced over the Rx guide wire  557  until the assembly reaches the bifurcation, whereupon the tips are uncoupled by withdrawing the Rx guide wire proximally through the slit. The Rx guide wire is next advanced into the main vessel and the OTW guide wire is advanced through the long tip  552  and into the side branch vessel where the catheter assembly is advanced over the guide wires to further position the stent and implant it at the bifurcation. 
     In an alternative embodiment that is similar to that shown in FIG.  60  and referring to FIG. 61, a first slit  554  is formed in the long tip  552  and has a second slit  559  that is positioned 180° opposite the first slit  554  on the distal end of the long tip  552 . In this embodiment, the Rx guide wire  557  extends through the Rx guide wire lumen  555  contained in the short tip  553  and extends proximally through the center of the long balloon  550 . The Rx guide wire extends distally through the Rx guide wire lumen and exits the short tip then enters the distal section of the long tip through first slit  554 . The Rx guide wire exits the long tip and continues distally through the anatomy. The OTW guide wire  558  extends from the distal end of the long tip just proximal of the first slit  554  and extends through the short balloon  551 . During the delivery of the stent in this embodiment, the catheter assembly is advanced over the Rx guide wire  557  until the distal end of the catheter assembly reaches the bifurcation. Before the tips are uncoupled, the OTW guide wire is advanced distally through the long tip and exits second slit  559  and continues into the distal anatomy. Advancing the OTW guide wire before retracting the Rx guide wire for uncoupling will ensure wire placement in the distal and diseased anatomy. Maintaining a wire in the distal and diseased anatomy insures access to the vessel in the event of vessel closure due to dissection or spasm. In order to uncouple the balloons, the Rx guide wire  557  is withdrawn proximally through first slit  554  only after the OTW guide wire  558  has been advanced through second slit  559 . After the Rx guide wire is retracted out of first slit  554 , the long balloon separates from the short balloon and the catheter assembly can be further advanced over the guide wires for further positioning and implanting the stent. 
     In another embodiment of the bifurcated catheter assembly, the long tip contains a slit in the distal section and also is configured such that the inner diameter of the lumen of the long tip is allowed to expand when two guide wires are advanced simultaneously therethrough. In this embodiment, as shown in FIGS. 62 and 63, the long balloon  570  is positioned adjacent short balloon  571  with the stent (not shown) mounted thereon. A long tip  572  extends from the short balloon and a short tip  573  extends from the long balloon  570 . The long tip has an expandable section  574  that is capable of expanding when more than one guide wire is advanced therethrough. The expandable section  574  also has a slit  575  for receiving the Rx guide wire  578 . An Rx guide wire lumen extends through the long balloon and the short tip and carries the Rx guide wire  578 . An OTW guide wire lumen  577  extends through the short balloon and the long tip  572  and extends all the way to the distal end of the long tip. The Rx guide wire  578  extends distally through the Rx guide wire lumen and exits the short tip and then enters the distal section of the long slit  575 . The Rx guide wire exits the long tip and continues distally through the anatomy. During delivery of the stent, the catheter assembly is advanced over the Rx guide wire until it is positioned at the bifurcation. Before the tips are uncoupled, the OTW guide wire  579  is advanced distally through the long tip  572  which will expand upon advancement of the OTW guide wire into the distal and diseased anatomy. The expandable section  574  of the long tip is formed of a material that will easily expand as the OTW guide wire  579  advances through the section in a side-by-side relationship with the Rx guide wire  578 , and it will contract after the guide wires are pulled back through the section. The expandable section  574  may have numerous small slits in it, made by a laser for example, to enhance expandability. The expandable section should be formed from an elastomeric material known in the art. After the OTW guide wire is advanced distally through the expandable section, the Rx guide wire  578  is withdrawn proximally through the expandable section and out of slit  575  to uncouple the long balloon from the short balloon. Thereafter, the Rx guide wire is advanced distally and the catheter assembly is advanced over the guide wires to further position the stent for implanting at the bifurcation as previously described. 
     In FIGS. 51-63, the joining wire (whether in Rx or OTW guide wire or joining wire) is not bent as shown in the drawings. Rather, the joining wire should be substantially straight (or just slightly curved) and the angle between the coupler and the joining tip should be less than about 10° for optional performance in smoothly tracking through the vascular system. The drawings are illustrations only, and it is preferred that the joining wires be generally straight. 
     It may be advantageous to provide a catheter assembly that is capable of inflating the expandable portions or balloons either simultaneously or independently. For example, it may be advantageous to partially inflate the balloon in the main vessel and fully inflate the balloon in the side branch vessel to avoid plaque shifting or to make sure the stent opening to the side branch vessel is fully opened. The present invention catheter assembly provides for independent balloon inflation and is shown in FIGS. 64-67. The reference numbers are primed to indicate like structure shown in FIGS. 29-33. The description of the catheter assembly set forth for FIGS. 29-33 is essentially the same as for FIGS. 64-67 except for the independent inflation lumen and associated structure of the latter drawings. 
     In keeping with the invention, as shown in FIGS. 64-67, the catheter assembly  140 ′ includes a proximal shaft section  144 ′, an intermediate shaft section  158 ′, and a multifurcated distal shaft section  148 ′ connected together as previously disclosed. Adapter  169 ′ on the proximal end of the catheter assembly has a fifth inflation lumen  190 ′ that extends through first inflation lumen  146 ′ in the proximal shaft section  144 ′. Fifth inflation lumen  190 ′ extends distally from the adapter, through proximal shaft section  144 ′, through intermediate shaft section  158 ′ and fourth inflation lumen  160 ′, and terminates at the distal end of the intermediate or mid-shaft section  158 ′. The distal end  191 ′ of the fifth inflation lumen extends into and is in fluid communication with second inflation lumen  154 ′ which extends into first branch  150 ′. Alternatively, (not shown) the distal end  191 ′ of the fifth inflation lumen can extend into and be in fluid communication with the third inflation lumen  156 ′ which extends into the second branch  152 ′. 
     With the distal end  191 ′ of the fifth inflation lumen connected to the second inflation lumen  154 ′, independent balloon inflation is easily achieved by injecting inflation fluid from one source (usually an indeflator) through first proximal port  192 ′ to inflate first balloon  166 ′, and injecting inflation fluid from a second source through second proximal port  193  to inflate second balloon  168 ′. The balloons  192 ′ and  193 ′ be inflated independently at any pressure or simultaneously at equal pressure. 
     The delivery of the catheter assembly  140 ′ through the vascular system over the Rx guide wire  194 ′ and the OTW guide wire  180 ′ is substantially the same as previously described for FIGS. 29-33. 
     While particular forms of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.