Abstract:
A bifurcated stent includes a first stent section and a second stent section. The first stent section is balloon expandable, has an unexpanded configuration, an expanded configuration, and a tubular wall defining a secondary opening. The secondary stent section is self-expanding and an end of the secondary stent section is engaged to a portion of the tubular wall of the primary stent section defining the secondary opening. The secondary stent section has an unexpanded configuration with a first length and an expanded configuration with a second length where the first length is less than the second length. The secondary stent section is expanded to the expanded configuration after the primary stent section is expanded to the expanded configuration. The secondary stent section forms a portion of the tubular wall of the primary stent section in the unexpanded configuration.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of Ser. No. 11/028,754, filed Jan. 3, 2005, which is a continuation of Ser. No. 10/083,711, filed Feb. 26, 2006, which claims priority from U.S. provisional applications 60/271,506 filed Feb. 26, 2001; U.S. provisional application 60/271,602 filed Feb. 26, 2001; and U.S. provisional application 60/271,595 filed Feb. 26, 2001; the entire content of each being incorporated herein by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   Stents, grafts, stent-grafts, vena cava filters and similar implantable medical devices, collectively referred to hereinafter as stents, are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, etc. Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon. 
   Stents are generally tubular devices for insertion into body lumens. Balloon expandable stents require mounting over a balloon, positioning, and inflation of the balloon to expand the stent radially outward. Self-expanding stents expand into place when unconstrained, without requiring assistance from a balloon. A self-expanding stent is biased so as to expand upon release from the delivery catheter. Some stents may be characterized as hybrid stents which have some characteristics of both self-expandable and balloon expandable stents. 
   Stents may be constructed from a variety of materials such as stainless steel, Elgiloy, nitinol, shape memory polymers, etc. Stents may also be formed in a variety of manners as well. For example a stent may be formed by etching or cutting the stent pattern from a tube or section of stent material; a sheet of stent material may be cut or etched according to a desired stent pattern whereupon the sheet may be rolled or otherwise formed into the desired tubular or bifurcated tubular shape of the stent; one or more wires or ribbons of stent material may be braided or otherwise formed into a desired shape and pattern. 
   A vessel having a stenosis may be viewed as an inwardly protruding arcuate addition of hardened material to a cylindrical vessel wall, where the stenosed region presents a somewhat rigid body attached along, and to, the elastic wall. The stenosis presents resistance to any expansion of the vessel in the region bridged by the stenosis. Stenoses vary in composition, for example, in the degree of calcification, and therefore vary in properties as well. 
   A stent may be used to provide a prosthetic intraluminal wall e.g. in the case of a stenosis to provide an unobstructed conduit for blood in the area of the stenosis. An endoluminal prosthesis comprises a stent which carries a prosthetic graft layer of fabric and is used e.g. to treat an aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of embolism, or of the natural artery wall bursting. Typically, a stent or endoluminal prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm by so-called “minimally invasive techniques” in which the stent is compressed radially inwards and is delivered by a catheter to the site where it is required through the patient&#39;s skin or by a “cut down” technique in which the blood vessel concerned is exposed by minor surgical means. When the stent is positioned at the correct location, the catheter is withdrawn and the stent is caused or allowed to re-expand to a predetermined diameter in the vessel. 
   U.S. Pat. No. 4,886,062 discloses a vascular stent which comprises a length of sinuous or “zig-zag” wire formed into a helix; the helix defines a generally cylindrical wall which, in use, constitutes a prosthetic intraluminal wall. The sinuous configuration of the wire permits radial expansion and compression of the stent; U.S. Pat. No. 4,886,062 discloses that the stent can be delivered percutaneously and expanded in situ using a balloon catheter. 
   U.S. Pat. No. 4,733,665 discloses an expandable intraluminal graft which is constituted by a tubular member formed from a plurality of intersecting elongate members which permit radial expansion and compression of the stent. 
   EP-A-0556850 discloses an intraluminal stent which is constituted by a sinuous wire formed into a helix; juxtaposed apices of the wire are secured to one another so that each hoop of the helix is supported by its neighboring hoops to increase the overall strength of the stent and to minimize the risk of plaque herniation; in some embodiments the stent of EP-A-0556850 further comprises a tubular graft member to form an endoluminal prosthesis. 
   The devices cited above are generally satisfactory for the treatment of aneurysms, stenoses and other angeological diseases at sites in continuous unbifurcated portions of arteries or veins. 
   Within the vasculature however it is not uncommon for stenoses to form at a vessel bifurcation. A bifurcation is an area of the vasculature or other portion of the body where a first (or parent) vessel is bifurcated into two or more branch vessels. Where a stenotic lesion or lesions form at such a bifurcation, the lesion(s) can affect only one of the vessels (i.e., either of the branch vessels or the parent vessel) two of the vessels, or all three vessels. Many prior art stents however are not wholly satisfactory for use where the site of desired application of the stent is juxtaposed or extends across a bifurcation in an artery or vein such, for example, as the bifurcation in the mammalian aortic artery into the common iliac arteries. 
   In the case of an abdominal aortic aneurysm (“AAA”) in the infrarenal portion of the aorta which extends into one of the common iliac arteries, the use of one of the prior art prosthesis referred to above across the bifurcation into the one iliac artery will result in obstruction of the proximal end of the other common iliac artery; by-pass surgery is therefore required to connect the one iliac artery in juxtaposition with the distal end of the prosthesis to the other blocked iliac artery. It will be appreciated by a person skilled in the art that it is desirable to avoid surgery wherever possible; the requirement for by-pass surgery associated with the use of the prior art prosthesis in juxtaposition with a bifurcation in an artery therefore constitutes a significant disadvantage. 
   Another example of a vessel bifurcation is the left and right common carotid arteries. These arteries are the principal arteries of the head and neck. Both of the common carotid arteries are quite similar and divide at a carotid bifurcation or bulb into an external carotid artery and an internal carotid artery. In the region of the carotid bulb and the ostium of the internal carotid artery, stenoses present a particular problem for carotid stenting due to the large tapering of the vessel interior from the common carotid artery (both the left and the right) to the internal carotid artery. The region of the carotid bifurcation or bulb happens to be where stenoses most often occur, particularly in the region of the ostium to the internal carotid artery in both of the carotid arteries. 
   Embodiments of the present invention relate to endoluminal prosthesis (stents) that may be utilized in the region of a bifurcation of vessels. The present invention also embraces stent connecting means for connecting a stent (e.g. a stent which forms part of an endoluminal prosthesis or bifurcated stent) to another stent or portion thereof. Some embodiments of the invention are directed to designs of bifurcated stents and their method of manufacture, as well as apparatuses and methods for introducing prostheses to the vasculature and methods of treating angeological diseases. 
   All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety. 
   Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below. 
   A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention includes many different embodiments. Various embodiments of the invention are directed to designs of bifurcated stents and/or the methods and apparatuses utilized to deliver a bifurcated stent to a bifurcation site. 
   In at least one embodiment, the invention is directed to a bifurcated stent delivery system that includes a unique catheter assembly having a primary and secondary guide wire wherein the secondary guide wire diverges away from the primary guide wire through a split in the catheter housing. The split allows the catheter to deliver a bifurcated stent center first. 
   The bifurcated stent is an embodiment of the invention that comprises a primary stent section and a secondary stent section. When used with the above catheter, the primary section is delivered center first through the split in the catheter housing. The secondary stent section is then delivered into a secondary vessel according to the predelivery placement of the secondary guide wire. 
   The bifurcated stent may be a one piece design where the primary and secondary sections are engaged to one another prior to delivery or it may be a two-piece design where the primary and secondary sections are separate and distinct stent bodies that may be optionally engaged to one another during delivery. The primary and secondary stent sections are preferably self-expandable but may be either self-expandable or balloon expandable independent of one another. 
   In another embodiment of the invention a self-expandable bifurcated stent may be delivered by a catheter having a retractable outer sheath or sleeve that retains the bifurcated stent in a collapsed state. When the sheath is retracted the primary stent section is exposed to self-expand. In at least one embodiment the secondary stent section remains in the collapsed state within the expanded primary stent section until a pusher mechanism is actuated to cause the secondary stent section to self-expand. 
   In at least one embodiment of the invention, a catheter system is employed wherein two guide wires and at least two balloons are employed to deliver a single piece bifurcated stent. In at least one embodiment, the balloons are substantially parallel to one another and the bifurcated stent is placed over both balloons with a single balloon extending into each section of the bifurcated stent. As a result, the stent branches may be independently guided and expanded. Where a portion of the stent is disposed about both balloons, in some embodiments the balloons may be linked together with a restrictive collar or band of material that will limit the expandability of the balloons to prevent the stent from being over expanded, however in other embodiments the collar may be omitted. 
   In some embodiments of the invention the catheter may also employ two angioplasty balloons that are initially advanced to the bifurcation site prior to stent delivery. 
   In at least one embodiment of the invention the bifurcated stent to be delivered is a one piece bifurcation stent comprising a primary stent section and a secondary stent section, the secondary stent section is linked to the primary stent section with one or more flexible linkage members. In at least one embodiment at least four linkage members connect the stent sections. Preferably, the flexible members are substantially S-shaped and/or are selectively annealed. 
   In at least one embodiment, the invention is directed to a single piece bifurcated stent wherein the primary stent section and the secondary stent section are engaged together by a linkage which allows the bifurcated stent to form distinct support structures on either side of the carina of a bifurcation. Preferably, the linkage comprises at least one strut or connecting member that is shared by both stent sections. In at least one embodiment the linkage is constructed from a selectively annealed metal or other material. 
   In the various embodiments of the invention portions of a given catheter and/or stent may include radiopaque materials to aid in visual inspection and/or placement of the devices such as during fluoroscopy. 
   Additional details and/or embodiments of the invention are discussed below. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     A detailed description of the invention is hereafter described with specific reference being made to the drawings. 
       FIG. 1  is a side view of a distal portion of a stent delivery catheter positioned at a vessel bifurcation. 
       FIG. 2  is a side view of the catheter of  FIG. 1  shown during initial delivery of a primary stent section of a bifurcated stent. 
       FIG. 3  is a side view of the catheter and bifurcated stent of  FIG. 2  where the primary stent section is shown in the deployed state and a secondary stent section is shown in a predeployed state. 
       FIG. 4  is a side view of the catheter and bifurcated stent of  FIG. 3  shown during initial delivery of the secondary stent section. 
       FIG. 5  is an enlarged side view of the catheter and stent shown in  FIG. 4  wherein the primary and secondary stent sections are both shown in a deployed state. 
       FIG. 6  is a side view of a bifurcated stent delivery system that includes two substantially parallel balloons and guide wires. 
       FIG. 7  is a side view of a bifurcated stent delivery system wherein the catheter includes a restrictive band where the stent is disposed about both balloons. 
       FIG. 8  is a side view of a stent delivery system wherein the system includes a pair of angioplasty balloons. 
       FIG. 9  is a side view of the system of  FIG. 6  is shown being positioned at a bifurcation site prior to stent delivery. 
       FIG. 10  is a side view of the system of claim  9  wherein a first balloon is shown inflated and a primary stent section is shown in an expanded state. 
       FIG. 11  is a side view of the system of claim  10  wherein a second balloon is shown inflated and a secondary stent section is shown in an expanded state. 
       FIG. 12  is a side view of the system shown in  FIG. 11  wherein both balloons are inflated. 
       FIG. 13  is a side view of the system of claim  12  wherein the balloons are shown in an uninflated state prior to stent delivery and the sections of the bifurcated stent are shown in a deployed state. 
       FIG. 14  is an enlarged side view of a bifurcated stent wherein the stent sections are connected by one or more linkage members. 
       FIG. 15  is an enlarged side view of a bifurcated stent wherein the stent sections are connected by one or more linkage members. 
       FIG. 16  is a side view of a bifurcated stent wherein the stent sections are connected by an actuated linkage assembly. 
       FIG. 17  is a side view of a bifurcated stent wherein the primary stent section does not extend substantially beyond the carina when deployed. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As indicated above the present invention includes many different embodiments. In some embodiments the invention is directed to various designs of bifurcated stents, their delivery systems and methods of use. 
   In  FIG. 1  an embodiment of the invention is shown which comprises a bifurcated stent delivery system shown generally at  100 . System  100  includes a catheter  10  that is advanced to a bifurcation site  20  along a primary guide wire  12  and a secondary guide wire  14 . In use, the primary guide wire  12  and secondary guide wire  14  are advanced into a body lumen or vessel an advanced into the primary vessel  22 . At the bifurcation site  20  the secondary guide wire  14  is directed into a secondary vessel  24  causing the guide wires  12  and  14  to diverge about the carina  26 . Catheter  10  is advanced along the shared path of the guide wires  12  and  14  until it reaches the carina  26 . 
   In order to accommodate the divergent path of the secondary guide wire  14 , the catheter  10  includes a spilt area  30  where the secondary guide wire  14  exits the catheter  10 . The spilt area  30  is a gap between two portions of the outer housing  32  of the catheter  10 . The housing  32  may be characterized as a sheath, sleeve, sock or any other assembly suitable for retaining a stent in its collapsed state onto a stent receiving region of a catheter. Some examples of such stent retaining devices are described in U.S. Pat. No. 4,950,227 to Savin et al.; U.S. Pat. No. 5,403,341 to Solar; U.S. Pat. No. 5,108,416 to Ryan et al.; U.S. Pat. No. 5,968,069 to Dusbabek et al.; U.S. Pat. No. 6,068,634, to Cornelius et al.; U.S. Pat. Nos. 5,571,168; 5,733,267; 5,772,669; and 5,534,007 all of which are incorporated herein by reference in their entirety. 
   In the embodiment shown in  FIG. 1 , the housing  32  comprises a distal sleeve  34  and a proximal sleeve  36 . As is more clearly shown in  FIG. 2 , sleeves  34  and  36  overlay a stent retaining region  38  of the catheter  10 . Sleeves  34  and  36  may be self-retracting or include one or more pullback mechanisms (not-shown) such as are described in U.S. Pat. Nos. 5,571,135 and 5,445,646 both of which are incorporated herein by reference in their entirety. 
   In  FIG. 1 , the sleeves  34  and  36  overlay the bifurcated stent  50 , shown in  FIG. 2 , which is disposed about a stent retaining region  38 . Stent retaining region  38  may include a balloon or other inflatable area for use in expanding and/or seating stent  50 . Stent  50  may be balloon expandable, self-expanding or a hybrid type stent. 
   In the embodiments shown in  FIGS. 2-4 , the bifurcated stent  50  comprises a primary stent section  52  and a secondary stent section  54 . Preferably, both sections  52  and  54  are self-expanding stent bodies though the individual stent sections may have different expansion characteristics as desired. In addition, the sections  52  and  54  of the bifurcated stent  50  may be individual stent bodies that are separately advanced and deployed forming stent  50  once they are fully deployed, or they may be integrally formed or otherwise connected prior to their deployment. 
   In the embodiment shown in  FIG. 2 , the housing portions or sleeves  34  and  36  have been withdrawn from about the bifurcated stent  50 . As the sleeves  34  and  36  are withdrawn from the primary stent section  52  will begin to radially expand in a center first manner through the split area  30 . When the sleeves  34  and  36  are fully withdrawn, such as is shown in  FIG. 3  the primary stent section  52  is completely freed from the stent retaining region  38 . 
   If the stent section  52  and  54  are not integral to each other or otherwise linked prior to delivery, upon expansion of the primary section  52  the secondary section may be advanced along the secondary guide wire  14  and advanced to an opening  62  in the wall  64  of the primary stent section  52 . Opening  62  may be any diameter or shape but preferably is sized to accommodate the outer diameter of the secondary stent section  54  as well as the inner diameter of the secondary vessel  24 . 
   Whether the secondary stent section  54  is engaged to the primary stent section  52  or separate therefrom prior to deployment, when the secondary stent section  54  is in position at opening  62  and the primary section  52  has been expanded, the secondary stent section  54  is then deployed into the secondary vessel  24 , such as is shown in  FIG. 4 . The position of the stent  50  at the bifurcation site maybe visually established through the use of a radiopaque marker  90 , discussed in greater detail below. 
   In at least one embodiment, where the secondary stent section  54  is at least partially constructed from a shape memory material, such as nitinol, the secondary stent section  54  will self expand according to a preprogrammed shape memory, such that the section both radially and longitudinally expands into the secondary vessel  24 . In some embodiments, catheter  10  may include a pusher assembly  70  that is advanced along the secondary guide wire  14  to trigger expansion of the secondary stent section  54 . Pusher assembly  70  may provide a stimulus which causes the section  54  to expand. Such a stimulus may be in the form of a simple mechanical engagement; delivery of an electrical current; or delivery of a predetermined temperature and/or a predetermined pH, such as by the release of a heated saline bolus. In some embodiments, a separate balloon catheter or other inflation device may be advanced along the secondary guide wire  14  to fully expand and/or seat the secondary stent section  54 . 
   When both stent sections  52  and  54  are fully deployed, such as is shown in  FIG. 5 , the proximal end of the secondary stent section  54  is preferably engaged to the wall  64  of the primary stent section  52 . When fully deployed the primary stent section  52  defines a primary flow path  72  and the secondary stent section defines a secondary flow path  74  that is in fluid communication with the primary flow path via opening  62 . 
   In an alternative embodiment of the invention, such as is shown in  FIG. 6 , system  100  may be provided with catheter  10  that is equipped with at least two balloons, a primary balloon  80  and a secondary balloon  82 , which may be utilized for expansion and/or seating stent sections  52  and  54 . 
   In the embodiment shown in  FIG. 6 , the bifurcated stent  50  may be constructed from stainless steel or other material that necessitates or would benefit from balloon expansion. As with previous embodiments, the catheter  10  includes a pair of guide wires  12  and  14  which are advanced to the bifurcation site  20  and which diverge at the carina  26  with the secondary guide wire  14  advancing into the secondary vessel  24 . 
   In the embodiment shown in  FIG. 6 , during most of the advancement of the catheter  10  the balloons  80  and  82  are positioned together in the substantially parallel orientation shown. However, as the catheter  10  approaches the bifurcation site  20  the distal portion  86  of secondary balloon  82  and secondary stent section  54  are directed along the secondary guide wire  14  into the secondary vessel  24  as shown in  FIG. 9 . 
   In order to ensure that the bifurcated stent will provide adequate support to the vessels  22  and  24  of the bifurcation site, and particularly to the area of the carina  26 , the catheter  10  may include a radiopaque marker  90 . Marker  90  allows a practitioner to advance the catheter  10  to the bifurcation site  20  and visually determine through fluoroscopy or other means that the balloons  80  and  82  and stent sections  52  and  54  are properly positioned about the carina  26 . 
   Marker  90  may be constructed from any radiopaque material and is preferably part of the bifurcated stent  50 . 
   Once it is determined that the stent  50  is in proper position at the bifurcation site  20 , the primary balloon  80  is inflated to expand the primary stent section  52  as shown in  FIG. 10 . After the initial expansion of the primary stent section  52 , the secondary balloon  82  is inflated to initially expand the secondary stent  54  shown in  FIG. 11 . 
   In some embodiments it may be preferable to first deflate the primary balloon  80  before inflating the secondary balloon  82 . In some embodiments where balloon  80  is deflated prior to inflation of balloon  82 , balloon  80  may be subsequently inflated after inflation of balloon  82  to fully expand the stent and seat it in place within the bifurcation such as is shown in  FIG. 12 . Alternatively, balloons  80  and  82  may be inflated simultaneously. 
   Once both stent sections  52  and  54  are fully expanded, the balloons  80  and  82  are deflated and with drawn from the bifurcation site  20 , such as is depicted in  FIG. 13   
   Because some bifurcated stents may be subject to distortion or damage when over expanded or subjected to high radially outward acting pressure, in some embodiments, such as shown in  FIG. 7 , the proximal portion  88  of balloons  80  and  82 , where both balloons are contained within the primary stent section  52 , the catheter  10  may employ a circumferential band  92  that will limit the expandability of the proximal portion  88  of balloons  80  and  82 , thereby preventing over inflation and over expansion of the primary stent portion  54  when both balloons are inflated. Band  92  may be constructed from any minimally or non-expandable material such as polyethyleneterephthalate (PET) or stainless steel. 
   In some applications, it may be beneficial or necessary to conduct an angioplasty procedure prior to insertion of the bifurcated stent  50 . As a result, in at least one embodiment of the invention, an example of which is shown in  FIG. 8 , the catheter  10  may be equipped with a primary angioplasty balloon  94  and a secondary angioplasty balloon  96 . In practice balloons  94  and  96  may be initially advanced to the bifurcation site  20  along guide wires  12  and  14  respectively. Upon reaching the bifurcation site  20 , the balloons  94  and  96  may be inflated to reduce any stenosis or blockage  98  that may be present. After the blockage  98  is reduced, the balloons  94  and  96  may be deflated and advanced along the guide wires  12  and  14  into the respective vessels  22  and  24  thereby allowing balloons  80  and  82  to be positioned at the bifurcation site  20  to delivery the bifurcated stent  50 . 
   In the embodiments shown in  FIGS. 6-13 , the bifurcated stent  50  may be a single piece design, where sections  52  and  54  are engaged to one another prior to and after delivery; or the stent  50  may be a two-piece design where both sections  52  and  54  are independent stent bodies that are separate prior to delivery and which may continue to be separate or which may become engaged to one another during or after delivery. 
   In embodiments where the stent  50  is a one-piece design, the stent sections may be engaged together by one or more linkage member  102  such as are shown in  FIGS. 14-16 . In  FIGS. 14 and 15 , the sections  52  and  54  are connected by at least  4  linkage members  102 . In at least one embodiment, the sections  52  and  54  are connected by at least  8  linkage members  102 . Linkage members  102  may be characterized as struts or connecting members  104  that are shared between sections  52  and  54 . In a preferred embodiment, the members  102  are selectively annealed to provide the bifurcated stent  50  with improved flexibility between sections  52  and  54 . By selectively annealing the members  102 , the secondary stent section  52  may be articulated relative to the primary stent section  54  such that the bifurcated stent sections  52  and  54  may be provided with an angular relationship of about 90 degrees, indicated at reference numeral  106  in  FIG. 15 , or a more acute angle  108  shown in  FIG. 14 . By providing a bifurcated stent  50  that has sections  52  and  54  that may be oriented at a variety of angles, a single stent may be used to address a variety of different angular relationships between vessels of various bifurcation sites within a body. Preferably, the angular relationship between sections  52  and  54  defines an angle of about 10 degrees to about 120 degrees. 
   In at least one embodiment, the linkage members  102  are provided with a curvilinear or S-shaped configuration such as is best shown in  FIG. 15 . The S-shape of the linkage members aids in providing the bifurcated stent  50  with the ability to articulate about vessel junctions of various angles. 
   In at least one embodiment, shown in  FIG. 16 , the sections  52  and  54  of a bifurcated stent  50  are linked by a single linkage member  102 . When inserted at a bifurcation site  20 , the single linkage member is positioned at the carina  26  and acts as a hinge to allow the sections  52  and  54  to be disposed about the carina  26 . 
   In at least one embodiment of the invention shown in  FIG. 17 , stent  50  includes a primary stent section  52  which does not extend distally beyond the carina  26 . As a result the stent  50  may be advanced and positioned at the bifurcation site  20  by a singe guide wire  14  which extends into the secondary branch  24 . Use of a marker  90  allows a practitioner to position the stent  50  by abutting the marker adjacent to the carina  26  and deploying the stent as shown. The stent  50  may include sections that are either balloon expandable, self-expandable, or hybrid expandable as desired. In the embodiment shown, primary stent section  52  is balloon expandable, and secondary stent section  54  is self-expandable. 
   In addition to being directed to the specific combinations of features claimed below, the invention is also directed to embodiments having other combinations of the dependent features claimed below and other combinations of the features described above. 
   The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
   Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.