Abstract:
A stent system is provided for stenting a bifurcated vessel structure having a parent vessel and a daughter vessel. The stent system has a parent vessel stent and a daughter vessel stent. The parent vessel stent has a substantially tubular body that is configured to be deployed into the parent vessel. This body has an angular flap that is openable to extend into the daughter vessel. The daughter vessel stent has a substantially tubular body that is configured to be deployed through the flap in the parent vessel stent into the daughter vessel. The daughter vessel stent has an angled tail portion that is configured to overlap with the flap of the parent vessel stent when both stents are deployed in the vessel structure. A method of stenting using this system is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/962,276, filed Nov. 5, 2013 and entitled “Bifurcated Stent and Delivery System,” which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The field of invention is generally related to medical stents and related delivery systems. More specifically, the invention relates to specifically designed stents and techniques for deploying these stents into vessel bifurcations, allowing for better coverage of the atherosclerotic lesion and preservation of the side-branch ostium with proper stent strut apposition to the vessel walls. The invention overcomes many of the limitations of the previous art. 
       BACKGROUND 
       [0003]    A stent is a mesh ‘tube’ inserted into a natural passage/conduit in the body to remove or counteract a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow access for surgery. 
         [0004]    Most of the time, stents are used to treat conditions that result when arteries become narrow or blocked. When a stent is placed into the body, the procedure is called stenting. A stent is placed in an artery as part of a procedure called angioplasty. Angioplasty restores blood flow through narrow or blocked arteries. A stent helps support the inner wall of the artery after angioplasty. 
         [0005]    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. Almost all stents used in the treatment of coronary atherosclerosis are balloon expandable. Self-expandable stents are generally used in larger blood vessel in the limbs and periphery. 
         [0006]    There are different kinds of stents. Stents usually are made of metal mesh of various metals and alloy combinations. Some stents are a plastic mesh-like material, and some stents are a combination of metal and synthetic lining material (for example PTFE-Polytetrafluoroethylene) and are called stent grafts and are used in larger arteries. 
         [0007]    An intraluminal coronary artery stent is a small, balloon-expandable, metal mesh tube that is placed inside a coronary artery to prevent the artery from re-closing. The metal portion of the structure is called a strut and the open portion of the mesh between struts is called a cell. Re-narrowing of arteries at the site of stent deployment has been addressed with medicine coated stents, called drug-eluting stents. Like other coronary artery stents, it is left permanently in the artery. 
         [0008]    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. 
         [0009]    Repair of coronary 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. 
         [0010]    Currently employed techniques have results that are less favorable than stenting results for lesions that do not involve bifurcations. The most commonly employed technique is to introduce guide-wires into the main blood vessel (parent-vessel) and the side branch (daughter-vessel). The ostium of the daughter-vessel is treated with balloon angioplasty and then a stent is deployed in the parent-vessel as if there was no bifurcation involvement. The hope is to have a stent cell line up with the ostium of the daughter-vessel resulting in unobstructed flow. However, in reality this is not always the case and stent struts usually are left in the ostium increasing the risk of acute and subacute stent thrombosis. Also promotion of neointimal growth onto the unopposed struts can result in renarrowing. A daughter-vessel is in effect “jailed” by the stent and blood flow can continue to be compromised results in inadequate treatment. 
         [0011]    Another phenomenon that is of concern in treatment of bifurcations is plaque shift. When a balloon or a stent is deployed in an artery, the plaque is compressed against the vessel wall. However, if there is a side branch ostium that is being stented across, plaque just beyond the bifurcation moves and shifts into the side branch resulting in worsening of the narrowing in this vessel. Plaque shift is of greatest concern when the plaque is located on the carina or the apex of the bifurcation. 
         [0012]    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 vessel 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. The deformation of the contralateral struts has been addressed by doing a simultaneous inflation with two balloons, one being placed in the parent and the other in the daughter-vessel. 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, resulting in myocardial infarction or even cardiac arrest. 
         [0013]    Other methods employed include a “T-stent” procedure. This involves implanting a stent in the daughter-vessel ostium followed by stenting of the parent-vessel across the daughter-vessel. Subsequently deforming the struts as previously described, to allow blood flow and access into the daughter-vessel. Alternatively, a stent is deployed in the parent-vessel followed by subsequent strut deformation as previously described, and finally a stent is placed into the daughter-vessel. Stent deployment in the ostium of the daughter-vessel may be necessary if there is a significant plaque burden at the bifurcation and involves the ostium of the daughter-vessel. Conversely stenting of the daughter-vessel may be required to treat a possible dissection created by the initial angioplasty. T-stenting would theoretically be useful in situations where the angle between the parent and daughter vessels is 90-degrees. This is rarely the case in real life and the alignment of the stent in the daughter-vessel with the apex of the carina results in inadequate coverage of the ostium. Alignment of the stent to the beginning of the side branch ostium results in protrusion of stent struts into the parent-vessel lumen. Both scenarios increase the risk of subsequent complications and renarrowing. 
         [0014]    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 main branch so that its proximal end overlaps with the already-stented side branch 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 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. 
         [0015]    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. 
         [0016]    All of the above-mentioned examples of stent deployment techniques suffer from the same problems and limitations. There can be uncovered intimal surface segments on the daughter-vessel between the stented segment and the parent-vessel or there is excessive coverage in the parent vessel proximal to the bifurcation. An uncovered intimal surface with a possible dissection flap or uncompressed plaque will increase the 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 is increased also. 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. 
         [0017]    Prior art Tryton bifurcation stent with trizone technology suffers from the same limitation of requiring to recross the stent struts of the parent-vessel stent with an arbitrary selection of a cell and subsequent deformation along with all its limitations as previously described. 
         [0018]    One prior art stent that is specifically designed for bifurcations in the petal stent from Boston Scientific. This has a specifically designed collar which expands radially into the ostium of the daughter vessel. The collar is designed as radially placed struts covering the entire perimeter of the ostium. The symmetry of the collar is believed to be a drawback as most bifurcations have non-90° take off angles, and so the collar would create an unnecessary and excessive crowding or deformation of struts in the ostium. 
         [0019]    The key element in the successful treatment of bifurcation with current art/technology is the simultaneous “kissing” balloon inflation. Successful placement of a guide-wire through the struts of the stent in the parent-vessel is essential for this to occur. Inability to cross with a guide-wire into the daughter-vessel would leave stent struts in the ostium and unopposed to the intimal surface. The present invention solves these and other problems as will be shown. 
       SUMMARY 
       [0020]    The prior art deficiencies and other problems associated with bifurcated stents and related delivery systems are overcome by the disclosed invention. It is an objective of the present invention to provide a bifurcated stent system that is easily delivered and deployed with precise positioning at a bifurcation. The invention simplifies the bifurcation stent delivery system eliminating the crucial and often failed step of recrossing with a guide-wire. It also eliminates the issue of uncovered intimal surface in the daughter-vessel and strut protrusion in the parent-vessel. 
         [0021]    The preferred embodiment of the invention provides a bifurcated stent and related delivery system that allows retaining the guide wire in the daughter branch during the stent deployment in the parent vessel. It provides for coverage of the area of the ostium of the daughter vessel with precise placement of the parent vessel stent. The system provides for precise placement of the daughter vessel stent as well. 
         [0022]    In another embodiment of the invention, the side branch (daughter vessel) stent could be used for placement in the ostial location of a single vessel. 
         [0023]    Other embodiments of the invention with variation in length and diameter in conjunction with other standard stents can be utilised for treatment of plaque in the left main artery location effectively dealing with the ostial placement of the left main stent and as well as the left main/left anterior descending and left circumflex coronary artery bifurcation. 
         [0024]    In summary the preferred embodiment of the invention provides a bifurcated stent and related delivery system that is deliverable and effectively overcomes the limitations of the prior art. Accurate placement, proper strut apposition, adequate coverage of intimal surfaces and preservation of the geometry of the side branch ostium will result in proper treatment of plaque at or near bifurcations. Part of the system can be used for accurate placement of stents in the ostial location. 
         [0025]    According to a first aspect of the invention, a stent system is provided for stenting a bifurcated vessel structure having a parent vessel and a daughter vessel. The stent system has a parent vessel stent and a daughter vessel stent. The parent vessel stent has a substantially tubular body that is configured to be deployed into the parent vessel. This body has an angular flap that is openable to extend into the daughter vessel. The daughter vessel stent has a substantially tubular body that is configured to be deployed through the flap in the parent vessel stent into the daughter vessel. The daughter vessel stent has an angled tail portion that is configured to overlap with the flap of the parent vessel stent when both stents are deployed in the vessel structure. 
         [0026]    Preferably, the parent vessel stent includes an introduction site proximate to a leading edge of the body of the parent vessel stent, which allows for passage of a daughter vessel guide wire on the inside of the stent along a luminal side thereof. 
         [0027]    Preferably, the parent vessel stent includes a radio-opaque marker proximate to this introduction site. 
         [0028]    The parent vessel stent may be pre-loaded (or later wired with) a parent vessel guide wire disposed substantially coaxially inside the body of the parent vessel stent. 
         [0029]    Preferably, the flap includes at least one radio-opaque marker. 
         [0030]    In the preferred embodiment, the flap has struts allowing opening of the flap in one direction. Preferably, the struts extend only on one side and do not form a collar around an ostium of the daughter vessel when opened. Preferably, the flap has struts forming a periphery around the flap. The flap is preferably a specially designed area in the parent vessel stent with a strut configuration that is different from the strut configuration of the main body of the parent vessel stent. The strut configuration allows the segment to be opened up as a flap providing coverage along a proximal end of the daughter vessel. Preferably, there are no struts along the distal edge of the ostium of the daughter vessel with the edge of the flap segment of the patient&#39;s vessel being aligned to it. 
         [0031]    In the preferred embodiment, the parent vessel stent has a spine which also extends along a central portion of the flap. 
         [0032]    The parent vessel stent may be pre-loaded (or may be later provided) with a balloon for deployment of the parent vessel stent. 
         [0033]    In certain embodiments, at least one of the parent vessel stent or the daughter vessel stent may contain a drug, or may be configured to elute a drug. 
         [0034]    Preferably, the daughter vessel stent includes a side hole proximate to a trailing edge of the body of the daughter vessel stent for passage of a parent vessel guide wire. Preferably, the side hole is defined radially opposite the angled tail portion of the daughter vessel stent. 
         [0035]    Preferably, the daughter vessel stent includes a radio-opaque marker proximate to the side hole. 
         [0036]    The daughter vessel stent may be pre-loaded (or later wired with) a daughter vessel guide wire disposed substantially coaxially inside the body of the daughter vessel stent. 
         [0037]    According to a second aspect of the invention, a method is provided for stenting a bifurcated vessel structure having a parent vessel and a daughter vessel and where the daughter vessel branches from the parent vessel at an angle. The daughter vessel has an ostium where it joins the parent vessel. The ostium in turn has a proximal edge and a distal edge. The method comprises: 
         [0038]    (1) inserting a parent vessel guide wire and a daughter vessel guide wire into the parent and daughter vessels, respectively; 
         [0039]    (2) loading a parent vessel stent on both wires, such that the parent vessel guide wire is substantially coaxial with the parent vessel stent; and such that the daughter vessel guide wire runs generally inside the parent vessel stent along its daughter vessel luminal side and emerges at a side hole in the parent vessel stent; 
         [0040]    (3) positioning the parent vessel stent with the daughter vessel guide wire at the distal edge of the daughter vessel ostium; 
         [0041]    (4) deploying the parent vessel stent with a first balloon; 
         [0042]    (5) deploying a side flap formed in the parent vessel stent into the ostium of the daughter vessel using a second balloon mounted on the daughter vessel guide wire; 
         [0043]    (6) loading a daughter vessel stent on the daughter vessel guide wire and inserting the parent vessel guide wire such that the parent vessel guide wire runs through a side hole in the daughter vessel stent, the daughter vessel guide wire being generally coaxial with the daughter vessel stent; 
         [0044]    (7) positioning the daughter vessel stent with the parent vessel guide wire at the distal edge of the ostium of the daughter vessel; and 
         [0045]    (8) deploying the daughter vessel stent with a third balloon. 
         [0046]    Importantly, once deployed, the flap of the deployed parent vessel stent and an angled side wall of the deployed daughter vessel stent overlap and are apposed at least in part with the proximate edge of the ostium. 
         [0047]    The method may further include predilating one or both vessels prior to inserting the parent vessel guide wire. 
         [0048]    The method may further include removing plaque from one or both vessels prior to inserting the parent vessel guide wire. 
         [0049]    The method may further include performing a kissing balloon inflation with a fourth balloon after deploying the daughter vessel stent for further shaping of the bifurcation. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0050]      FIG. 1  is a simplified vessel diagram showing deployment of a parent vessel stent with jailing effect across side branch (prior art). 
           [0051]      FIG. 2   a  is a simplified vessel diagram showing deployment of a daughter vessel stent with protrusion into parent vessel (prior art). 
           [0052]      FIG. 2   b  is a simplified vessel diagram showing deployment of a daughter vessel stent with uncovered daughter vessel intima (prior art). 
           [0053]      FIG. 3  is a simplified vessel diagram showing deployment using stent culotte technique (prior art). 
           [0054]      FIG. 4  is a simplified vessel diagram showing deployment using stent crush technique (prior art). 
           [0055]      FIG. 5  is a schematic diagram of a parent vessel stent system according to an embodiment of the present invention. 
           [0056]      FIG. 6  is a simplified sectional view of the parent vessel stent system of  FIG. 5  showing guide wires and deployment balloon. 
           [0057]      FIG. 7  is a top view of the flap portion of the parent vessel stent shown in  FIG. 5 . 
           [0058]      FIG. 8  is a diagram showing stent in parent vessel with flap extended, showing strut arrangement. 
           [0059]      FIG. 9  is a diagram showing stent in parent vessel with flap extended. 
           [0060]      FIG. 10  is a schematic diagram of a daughter vessel stent system according to an embodiment of the present invention. 
           [0061]      FIG. 11  is a simplified vessel diagram showing deployed side branch (daughter vessel) stent in relation to parent vessel. 
           [0062]      FIG. 12  is a simplified vessel diagram showing a first stage of deployment process according to an embodiment of the present method (positioning of parent vessel stent). 
           [0063]      FIG. 13  is a simplified vessel diagram showing a second stage of the deployment process (balloon inflation of parent vessel stent in the parent vessel). 
           [0064]      FIG. 14  is a simplified vessel diagram showing a third stage of the deployment process (balloon opening of flap in parent vessel stent into daughter vessel). 
           [0065]      FIG. 15  is a simplified vessel diagram showing a fourth stage of the deployment process (positioning of daughter vessel stent through flap in parent vessel stent). 
           [0066]      FIG. 16  is a simplified vessel diagram showing a fifth stage of the deployment process (balloon inflation of daughter vessel stent in daughter vessel). 
           [0067]      FIG. 17  is a simplified vessel diagram showing a sixth and final stage after removal of balloon and guide wires (showing overlap between daughter vessel stent and parent vessel stent to provide complete coverage of the bifurcation area without unopposed struts or jailing across the ostium). 
       
    
    
     DETAILED DESCRIPTION 
       [0068]    Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the examples set forth in the following descriptions or illustrated drawings. The invention is capable of other embodiments and of being practiced or carried out for a variety of applications and in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The system includes balloon expandable stents. 
         [0069]    The preferred embodiment of the invention provides a bifurcated stent and related delivery system that is deliverable and effectively overcomes the limitations of the prior art. Accurate placement, proper strut apposition, adequate coverage of intimal surfaces and preservation of the geometry of the side branch ostium will result in proper treatment of plaque at or near bifurcations. Part of the system can be used for accurate placement of stents in the ostial location. 
         [0070]    In the preferred embodiment of the invention, the following steps are taken for the deployment of the bifurcation stents of the invention: 
         [0071]    1. Wire both vessels.
       2. Predilate both lesions. Calcified lesions may require debulking/atherectomy.   3. Backload “main vessel stent” on the wires, with the wire from the daughter-vessel being introduced through the side-hole in the flap area ( FIGS. 5 ,  6  and  7 ).   4. Position the stent in the parent-vessel with daughter-vessel wire at the distal edge of its ostium ( FIG. 12 ).   5. Deploy stent ( FIG. 13 ) and remove stent delivery balloon.   6. Deploy the “side-flap” further by using a balloon on the side-branch wire ( FIG. 14 ).   7. Load “side branch stent”, this time with the wire from the parent vessel in the “side-hole” ( FIG. 10 ).   8. Position the stent with the wire from the “side-hole” (parent branch) at the edge of the ostium of the side branch ( FIG. 15 ).   9. Deploy stent ( FIG. 16 ) and remove the stent delivery balloon.   10. Perform “kissing” balloon inflation if needed for further shaping of the bifurcation.       
 
         [0081]      FIGS. 1 through 4  demonstrate the various shortcomings of the prior art that are overcome by the present invention. Please note that not all permutations of prior art are presented here. However, the common issues with prior art include: 
         [0082]    1. Inadequate coverage of vessel intima (extent dependant on technique employed). 
         [0083]    2. Strut protrusion into adjacent vessel lumen.
       3. Need to cross cells of a stent with a guide wire after its deployment. This is a very crucial and often limiting step in the treatment of bifurcation lesions with prior art.       
 
         [0085]    Note that in the present system, wires cross through a flap of a deployed stent and through a marked introduction site, but do not need to be inserted through cells (between struts). 
         [0086]      FIG. 1  shows prior art with deployment  100  of a stent  103  in the parent vessel  101 , across the ostium of the side branch  102 . This has the problems of jailing of the side branch  102  and also leaving unopposed stent struts  104 . These result in poor long term outcomes. 
         [0087]      FIG. 2   a  shows deployment  200   a  of a stent  203   a  in the daughter vessel (side branch)  202   a . The stent is aligned to the proximal edge of the ostium and has the problem of stent struts  204   a  protruding into the lumen of the parent vessel (main branch)  201   a.    
         [0088]      FIG. 2   b  shows deployment  200   b  of a stent  203   b  in the daughter vessel (side branch)  202   b . The stent is aligned to the distal edge of the ostium and has the problem of leaving part of the intima of the daughter vessel uncovered  204   b.    
         [0089]      FIG. 3  shows deployment  300  using the stent culotte technique (a suboptimal two-stent prior art technique for bifurcated vessels). Stents  303  and  304  are placed simultaneously in the daughter  302  and parent  301  vessels respectively. This results in unopposed stent struts  305  in the parent (main) vessel  301 . 
         [0090]      FIG. 4  shows deployment  400  using the stent crush technique (another suboptimal two-stent prior art technique for bifurcated vessels). In this technique stent  404  is placed in the daughter vessel  402  first with the stent deliberately left protruding in the parent vessel. This stent is then crushed with deployment of a stent  403  in the parent vessel  401 . This results in a double layer of stent struts  405  across the daughter vessel ostium. It also has the problem of making it difficult to navigate the wire into the daughter vessel (side branch) through the struts of not one but two stents. 
         [0091]      FIGS. 5 through 11  show at least one embodiment of the present system with the salient features of its various components, primarily the parent vessel stent (main artery) with the “flap” area and the daughter vessel (side branch) stent with the angled proximal edge. 
         [0092]      FIG. 5  shows the basic design of the parent vessel system  500  with parent vessel stent  501  with “flap” area  502 . Advantages include keeping the daughter vessel guide wire  503  on the luminal side  504  of the stent thereby eliminating the need of trying to recross the struts of the stent in the parent vessel. Also location of the introduction site of the daughter vessel wire  505  in conjunction with the radio-opaque markers on the stent  506  allows positioning of the “flap” area at the ostium of the daughter vessel. The “flap”  502  in combination with the angled proximal edge of the daughter vessel (side branch) stent (not shown in  FIG. 5 ) eliminates the uncovered intimal portion of the daughter vessel (i.e. the problem shown in  FIG. 2   b , at  204   b ). 
         [0093]      FIG. 6  shows a schematic of the cross section of the parent vessel stent catheter/stent system  600 . This cross section is proximal to the introduction site (reference character  505  in  FIG. 5 ) of the daughter vessel guide wire  601 , showing its location on the luminal side of the stent  602 . The parent vessel guide wire  604  is coaxial in the center. The daughter vessel guide wire  601  is not coaxial and is in between the stent  602  and the deployment balloon  603 . 
         [0094]      FIG. 7  shows the top view of the flap area  700  ( FIG. 5  at  502 ). The daughter vessel guide wire is introduced at introduction site  701  just proximal to the radio-opaque marker  702 . The folded struts and spine of the “flap”  704  are deployed by a balloon in the daughter vessel and provide coverage for the proximal edge of the ostium of the daughter vessel. Strut  703  forms a perimeter around the ostium of the daughter vessel. Some of these structures are shown again in  FIGS. 8 and 9  below. 
         [0095]      FIG. 8  shows parent vessel stent system  800  with stent deployed in the parent vessel  801  with flap extended into the ostium of the daughter vessel  802 . Struts  803  and  804  provide coverage to the ostium of the daughter vessel and strut  805  forms the perimeter around the ostium. 
         [0096]      FIG. 9  shows parent vessel stent system  900  with parent vessel  901  stent  903  deployed with flap extended  904  into the ostium of the daughter vessel  902 . 
         [0097]      FIG. 10  shows the basic structure of the daughter vessel (side branch) system  1000  with daughter vessel stent  1002 . Here the guide wire from the daughter vessel  1001  is coaxial in the center. The proximal edge of the stent is angled  1003  for coverage of the ostium in conjunction with the flap of the parent vessel stent. The guide wire from the parent vessel  1004  is introduced at side hole  1005  just proximal to the short side of the stent (i.e. opposite angled edge  1003 ). The radio-opaque marker  1006  helps with positioning of the stent. 
         [0098]      FIG. 11  shows the daughter vessel system  1100  with deployed side branch (daughter vessel)  1102  stent  1103  in relation to the parent vessel  1101 . 
         [0099]    Following  FIGS. 12 through 17  show the deployment sequence of current system. 
         [0100]      FIG. 12  shows positioning  1200  of parent vessel (main vessel)  1203  stent  1205  across the daughter vessel  1202 . The parent vessel guide wire  1204  is coaxial and guide wire from the daughter vessel  1201  is introduced through the flap in the parent vessel stent (region  502  shown in  FIG. 5 ). The stent is then advanced till the daughter vessel guide wire  1201  is against the distal edge of the ostium  1207 . Placement is also assisted by observing and placing the radio-opaque marker  1206  just beyond the ostium of the daughter vessel. 
         [0101]      FIG. 13  shows the deployment  1300  of parent vessel  1301  stent  1304  coaxially over the guide wire  1303  with balloon inflation  1302 ; the daughter vessel  1305  guide wire  1306  is retained and, being on the inside of the stent in area  1307 , is not trapped. 
         [0102]      FIG. 14  shows a further deployment  1400  of the parent vessel stent using standard angioplasty balloon  1401  which is used in this case to raise/extend the flap portion  1402  of the parent vessel  1405  stent  1406 . The balloon is placed coaxially over the guide wire  1403  in the daughter vessel  1404 . The guide wire  1407  in the parent branch is retained. The radio-opaque marker  1408  on the edge of the flap shows the area of coverage on the proximal edge of the ostium of the daughter branch. 
         [0103]      FIG. 15  shows positioning  1500  of the daughter vessel  1501  (side-branch) stent  1506  at the ostium, using the parent vessel guide wire  1503  and radio-opaque marker  1505  on the stent as guides. The parent vessel guide wire  1503  is introduced through the “side-hole” in the stent catheter located just proximal to the short side of the stent ( 1005   FIG. 10 ). The daughter vessel stent  1506  is advanced through the flap of the parent vessel stent  1504 , as far as permitted by the guide wire in the parent vessel. Positioning is also assisted by the radio-opaque marker  1505 . 
         [0104]      FIG. 16  shows deployment  1600  of the daughter vessel  1601  stent  1606 . Parent vessel guide wire  1603  is retained. The overlap  1605  of the angled edge with the flap  1607  of the parent vessel stent  1604  provides total coverage of the proximal edge of the ostium. 
         [0105]      FIG. 17  shows the final deployed state of the bifurcation stent system  1700 . The overlap segment  1705  between the flap  1706  of the parent vessel  1701  stent  1703  and the angled proximal edge  1707  of the daughter vessel  1702  stent  1704  allows for adequate coverage of the ostium of the daughter vessel. The system provides such coverage over a wide range of “take-off” angles between the parent and daughter vessels. 
         [0106]    The intent of the application is to cover all practical combinations and permutations. The above examples are not intended to be limiting, but are illustrative and exemplary. 
         [0107]    The examples noted here are for illustrative purposes only and may be extended to other implementations. While several embodiments are described, there is no intent to limit the disclosure to the embodiment(s) disclosed herein. On the contrary, the intent is to cover all practical alternatives, modifications, and equivalents.