Patent Publication Number: US-2007118200-A1

Title: Bifurcation stent delivery system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      Not Applicable  
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
      Not Applicable  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      In some embodiments this invention relates to implantable medical devices, their manufacture, and methods of use. Some embodiments are directed to delivery systems, such as catheter systems of all types, which are utilized in the delivery of such devices.  
      2. Description of the Related Art  
      A stent is a medical device introduced to a body lumen and is well known in the art. Typically, a stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent in a radially reduced configuration, optionally restrained in a radially compressed configuration by a sheath and/or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. The introducer may enter the body from an access location outside the body, such as through the patient&#39;s skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means.  
      Stents and similar devices such as stent, stent-grafts, expandable frameworks, and similar implantable medical devices, 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, fallopian tubes, coronary vessels, secondary vessels, etc. Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or a combination of self-expanding and balloon expandable (hybrid expandable).  
      Stents may be created by methods including cutting or etching a design from a tubular stock, from a flat sheet which is cut or etched and which is subsequently rolled or from one or more interwoven wires or braids.  
      Within the vasculature 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.  
      The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.  
      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 invention contemplates a new apparatus and method that simplifies placement of a stent at the bifurcation of a vessel. The invention results in a reduced stent delivery system profile. The present system may improve trackability of the stent delivery system.  
      At least one of the embodiments of the present invention includes a medical device with a balloon catheter shaft such as described in U.S. patent application Ser. No. 10/747,546, filed Dec. 29, 2003 entitled Rotating Balloon Expandable Sheath Bifurcation Delivery System and U.S. patent application Ser. No. 10/226,362, filed Aug. 22, 2002 entitled Rotating Stent Delivery System For Side Branch Access And Protection And Method Of Using Same, the entire content of both incorporated herein by reference.  
      In at least one embodiment there are two guidewire housings positioned on the exterior of the balloon catheter. The guidewire housings can be formed in a number of different shapes, all of which are constructed and arranged to allow passage of a guidewire through the housing. For example, in a preferred embodiment, a guidewire housing can be substantially cylindrical, like a tubular sheath. Or, a guidewire housing can be formed as rail. In other embodiments, the guidewire housing can be crescent-shaped. Alternatively, the guidewire housing could be designed such that a cross-section of the guidewire housing is semi-circular.  
      Rotating a stent delivery system delivered to a site within the body is difficult. In order to rotate the stent delivery system, the torque applied must be large enough to exceed the torsional stiffness of the stent delivery system. The torque with respect to the stent delivery system is maximized if the radial distance between the guidewire housings, and thus the guidewires, is maximized.  
      In a preferred embodiment, the radial distance between the guidewire housings, and necessarily the guidewires themselves, is maximized. Specifically, in this embodiment, the two guidewire housings are positioned on substantially opposite portions of the balloon. Thus, in this embodiment, the torque about the stent delivery system is maximized.  
      In at least one embodiment, the guidewire housings are not attached to the balloon. Rather, a stent is disposed about the balloon, with the guidewire housings loosely placed in between the stent and balloon, and then the stent is crimped over the guidewire housings, securingly engaging the guidewire housings to the balloon and stent. In some embodiments, the guidewire housing is, however, attached to the proximal end of the catheter shaft. By attaching the guidewire housing to the catheter shaft, and only crimping the guidewire housing underneath the stent, the stent delivery system can be maneuvered within the lumen of a vessel.  
      In another advantageous embodiment, the catheter shaft includes an opening that allows inflation fluid to flow into the balloon, thereby causing the balloon to inflate.  
      A primary feature of some embodiments is the inclusion of a support tube within the catheter shaft. In a preferred embodiment, the support tube is not connected to the catheter shaft. Instead, the catheter shaft is disposed loosely about the support tube. By including a support tube within the catheter shaft, the catheter shaft will rotate around the support tube when the stent delivery system is rotated, thereby preventing the catheter shaft from forming a kink. As the catheter shaft forms the path in which any inflation fluid is delivered to the balloon, any kinks within the catheter shaft would detrimentally interfere with the fluid delivery. In a preferred embodiment, the support tube is hollow, allowing inflation fluid to flow through the support tube, as well as around it within the catheter shaft. Other embodiments include a support tube that is solid rather than hollow.  
      In a preferred embodiment, the support tube is formed in the shape of a spiral. It is also envisioned that in some embodiments the support tube is substantially cylindrical. The support tube could be formed in a number of other shapes, such as with a square or rectangular cross section.  
      These and other embodiments which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for further understanding of the invention, its advantages and objectives obtained by its use, reference should be made to the drawings which form a further part hereof and the accompanying descriptive matter, in which there is illustrated and described embodiments of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of an embodiment of the invention, comprising a stent, balloon catheter, and guidewire housings.  
       FIG. 2  is a perspective view of an embodiment of a guidewire housing with circular cross-section.  
       FIG. 3  is a perspective view of an embodiment of a guidewire housing with semi-circular cross-section.  
       FIG. 4  is a perspective view of an embodiment of a guidewire housing with crescent-shaped cross-section.  
       FIG. 5  is a perspective view of an embodiment of a guidewire housing formed as a rail wherein the lumen is partially formed by the balloon.  
       FIG. 6  is a transverse cross-sectional view of the embodiment depicted in  FIG. 1 .  
       FIG. 7   a  is a side view of an embodiment of the invention, with guidewire housings engaged to the proximal end of a catheter shaft.  
       FIG. 7   b  is a side perspective view of a stent wherein a side branch opening is shown formed from the enlargement of a cell opening in the stent wall.  
       FIG. 7   c  is a cross-sectional view of the stent of  FIG. 7   b.    
       FIG. 7   d  is a side view of a stent wherein the stent has been delivered from the catheter assembly, by balloon expansion and the assembly subsequently withdrawn from the vessel(s).  
       FIG. 8  is a side view of an embodiment of the invention, shown with a spiral support tube.  
       FIG. 9  is a side view of an embodiment of the invention, shown with a support tube of substantially elongate shape. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.  
      For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.  
      Depicted in the figures are various aspects of the invention. Elements depicted in one figure may be combined with, and/or substituted for, elements depicted in another figure as desired.  
      Referring now to the drawings, wherein the showings are for the purposes of illustrating the preferred embodiments of the invention and not for purposes of limiting same,  FIG. 1  shows a stent delivery system or assembly  5 . Assembly  5  shows a catheter  10  comprising catheter shaft  15 . Disposed about catheter shaft  15  is balloon  20 . Disposed about balloon  20  is stent  25 . There is a primary guidewire housing  30  and a secondary guidewire housing  35  positioned on the exterior of balloon  20 . The primary guidewire housing  30  and secondary guidewire housing  35  can be formed in a number of different shapes, all of which are constructed and arranged to allow passage of a guidewire through the guidewire housing. Primary guidewire  40  passes through primary guidewire housing  30  and secondary guidewire  45  passes through secondary guidewire housing  35 . Catheter shaft  15  also includes an opening  50 , positioned underneath balloon  20 . Opening  50  allows an inflation fluid (not shown) to be injected into balloon  20  through catheter shaft  15 .  
      In some embodiments, the secondary guidewire housing may not be external to the balloon, as shown in  FIG. 1 . Instead, the secondary guidewire housing may be incorporated with the balloon. For example, the secondary guidewire may be placed such that the balloon is folded about the secondary guidewire during manufacture. The balloon itself would thereby define a secondary guidewire lumen. In another example, the balloon material could be manufactured such that a cavity, defining a secondary guidewire lumen, is incorporated within the balloon wall thickness, thereby allowing a secondary guidewire to be inserted therethrough.  
      In some embodiments the stent, the delivery system or other portion of the assembly may include one or more areas, bands, coatings, members, etc. that is (are) detectable by imaging modalities such as X-Ray, MRI, ultrasound, etc. In some embodiments at least a portion of the stent and/or adjacent assembly is at least partially radiopaque.  
      In some embodiments the at least a portion of the stent is configured to include one or more mechanisms for the delivery of a therapeutic agent. The agent can be in the form of a coating or other layer (or layers) of material placed on a surface region of the stent, which is adapted to be released at the site of the stent&#39;s implantation or areas adjacent thereto. In some embodiments, a therapeutic agent may be delivered from the catheter and/or stent via a lumen, opening, or other delivery mechanism.  
      A therapeutic agent may be a drug or other pharmaceutical product such as non-genetic agents, genetic agents, cellular material, etc. Some examples of suitable non-genetic therapeutic agents include but are not limited to: anti-thrombogenic agents such as heparin, heparin derivatives, vascular cell growth promoters, growth factor inhibitors, Paclitaxel, etc. Where an agent includes a genetic therapeutic agent, such a genetic agent may include but is not limited to: DNA, RNA and their respective derivatives and/or components; hedgehog proteins, etc. Where a therapeutic agent includes cellular material, the cellular material may include but is not limited to: cells of human origin and/or non-human origin as well as their respective components and/or derivatives thereof. Where the therapeutic agent includes a polymer agent, the polymer agent may be a polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS), polyethylene oxide, silicone rubber and/or any other suitable substrate.  
       FIG. 2  shows a preferred embodiment of primary guidewire housing  30 , defining guidewire lumen  80 , in substantially cylindrical form. In another embodiment,  FIG. 3  shows the primary guidewire housing  30 , defining guidewire lumen  80 , with a design that has a semi-circular cross-section.  FIG. 4  shows the primary guidewire housing  30 , defining guidewire lumen  80 , with a design that has a crescent-shaped cross-section.  FIG. 5  shows the primary guidewire housing  30  formed as a rail, such that the guidewire lumen  80  is at least partially defined by the external surface of the balloon  20 . Although reference number  30  has been used in  FIGS. 2 through 5 , it should be pointed out that each of these designs applies to secondary guidewire housing  35 , or any other guidewire housing, as well.  
       FIG. 6  depicts a transverse cross-section of the assembly  5  of  FIG. 1 . Primary guidewire housing  30  and secondary guidewire housing  35  are crimped between balloon  20  and stent  25 . In this embodiment, guidewire housings  30  and  35  are not attached to balloon  20 . Rather, a stent  25  is disposed about balloon  20 , with guidewire housings  30  and  35  placed in between stent  25  and balloon  20 , and then stent  25  is crimped over guidewire housings  30  and  35 , securingly engaging guidewire housings  30  and  35  to balloon  20  and stent  25 .  
      While advancing assembly  5  to the bifurcation site, assembly  5  is rotatable in order to align the stent with the bifurcation.  FIG. 6  depicts a preferred embodiment, wherein the radial distance between the guidewire housings  30  and  35 , and necessarily guidewires  40  and  45 , is maximized. Specifically, as shown in  FIG. 6 , guidewire housings  30  and  35  are positioned on substantially opposite portions of balloon  20 . Thus, in this embodiment, the torque about the stent delivery system is maximized. Once assembly  5  is delivered to the bifurcation site, balloon  20  is expanded which, as a result, will expand stent  25 .  
      Referring now to  FIG. 7   a , the guidewire housings ( 30  and  35 ) are engaged to the proximal end of catheter shaft  15 . Primary guidewire housing  30 , having distal end  31 , is engaged to catheter shaft  15  at engagement region  55 . Likewise, guidewire housing  35 , having distal end  36 , is engaged to catheter shaft  15  at engagement region  60 . By fixedly engaging guidewire housings  30  and  35  to catheter shaft  15 , the trackability of stent delivery system is improved, allowing the stent delivery system to be maneuvered within the lumen of a vessel. The guidewire housings can be fixedly engaged to the catheter shaft by a number of methods, including chemical welding, heat welding, adhesives, as well as mechanical engagement. Furthermore, catheter shaft  15  includes an opening  50  that allows inflation fluid (not shown) to flow into balloon  20 , thereby causing balloon  20  to inflate.  
      Referring to  FIGS. 7   a  and  7   b , stent  25  may be at least partially constructed of a plurality of interconnected struts, connectors, or members  52 . The stent  25  defines a proximal opening  61 , a distal opening  62 , and a flow path  63  therebetween. The cell openings  51  are in fluid communication with the flow path  63 .  
      When the secondary guidewire  45  and/or the secondary guidewire housing  35  is threaded through one of cell openings  51  when the stent  25  is positioned onto balloon  20 , such as shown in  FIG. 7   a , the members  52  that define a selected cell opening  51   a , may bend or flex. This bending or flexing of members  52  may result in an expansion of the shape of cell opening  51   a , relative to other cell openings  51 .  
      Referring now to  FIGS. 7   a  and  7   b , the modified cell opening  51   a , hereinafter referred to as secondary opening  51   a , is positioned on the stent  25  between the proximal opening  61  and the distal opening  62 . The manner in which the secondary opening  51   a , the members  52  adjacent thereto, and to an extent the stent  25  itself, are expanded relative to other cell openings  51  by the position of the secondary guidewire and/or secondary guidewire housing is depicted in  FIGS. 7   b  and  7   c.    
      It should be noted that when the stent  25  is placed on the balloon  20  in the manner described above, there is minimal flexing of members  52  and therefore substantially no expansion of cell opening  51   a  relative to other cell openings  51 . Furthermore, the expansion of cell opening  51   a , relative to other cell openings  51  is provided only to allow sliding passage of the secondary guidewire  45 , and if desired, a distal portion  36  of the secondary guidewire housing  35 , through the secondary opening  51   a . Therefore, the actual size of the secondary opening  51   a  may be substantially similar to, or only marginally different from, that of the surrounding cell openings  51 .  
       FIG. 7   d  shows stent  25 , with proximal end  61  and distal end  62 , positioned within body lumen  100  of a vessel  101 , defined by vessel wall  105 , at bifurcation site  115 . Primary guidewire  40  extends through distal end  62  along first branch  110 . Secondary guidewire  45  extends through secondary opening  51   a  along second branch  120 .  
      An advantageous feature of some embodiments is shown in  FIG. 8 . Support tube  65  is included within catheter shaft  15 . In a preferred embodiment, support tube  65  is not connected to catheter shaft  15 . Instead, catheter shaft  15  is disposed loosely about support tube  65 . Including support tube  65  within catheter shaft  15  allows catheter shaft  15  to rotate around support tube  65  when the assembly  5  is rotated, thereby preventing any kinks from forming in catheter shaft  15 . As catheter shaft  15  forms the path in which any inflation fluid (not shown) is delivered to balloon  20  through opening  50 , any kinks within catheter shaft  15  would detrimentally interfere with fluid delivery. In a preferred embodiment, support tube  65  is hollow, allowing inflation fluid to flow through support tube  65 , as well as around it within catheter shaft  15 . Other embodiments include a support tube  65  that is solid rather than hollow.  
       FIG. 8  depicts a preferred embodiment of support tube  65 , formed in the shape of a spiral. It is also envisioned that in some embodiments the support tube  65  is a substantially elongate shape which extends substantially parallel to the longitudinal axis  70  of catheter shaft  15 , as shown in  FIG. 9 . The support tube  65  could be formed in a number of other shapes, such as with star-shaped, square, or rectangular cross-sections.  
      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.