Abstract:
A stent-graft system comprising a graft member and a stent having a connection end interconnected with the graft member and a free end opposed thereto. The stent includes a plurality of struts extending between the connection end and the free end and at least two of the struts having different lengths such that the free end has a nonuniform profile. A method of securing at least one end of a stent-graft within a vessel is also provided.

Description:
RELATED PATENT APPLICATION 
       [0001]    This patent application is a continuation and claims the benefit of U.S. patent application Ser. No. 11/861,828, filed Sep. 26, 2007, naming Michael V. Chobotov as inventor, entitled ASYMMETRIC STENT APPARATUS AND METHOD, and having attorney docket no. TRI-0656-UT, which is incorporated by reference herein in its entirety, including all text and drawings. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a system for the treatment of disorders of the vasculature. More specifically, the invention relates to a system for the treatment of disease or injury that potentially compromises the integrity of a flow conduit in the body. For example, an embodiment of the invention is useful in treating indications in the digestive and reproductive systems as well as indications in the cardiovascular system, including thoracic and abdominal aortic aneurysms, arterial dissections (such as those caused by traumatic injury), etc. that include a curved lumen. 
         [0003]    Medical devices for placement in a human or other animal body are well known in the art. One class of medical devices comprises endoluminal devices such as stents, stent-grafts, filters, coils, occlusion baskets, valves, and the like. A stent typically is an elongated device used to support an intraluminal wall. In the case of a stenosis, for example, a stent provides an unobstructed conduit through a body lumen in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside and/or outside thereof. A covered stent is commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), a stent-graft, or endograft. 
         [0004]    An endograft may be used, for example, to treat a vascular aneurysm by removing or reducing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an endograft 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 endograft, typically restrained in a radially compressed configuration by a sheath, crocheted or knit web, catheter or other means, is delivered by an endograft delivery system or “introducer” to the site where it is required. The introducer may enter the vessel or lumen from an access location outside the body, such as purcutaneously through the patient&#39;s skin, or by a “cut down” technique in which the entry vessel or lumen is exposed by minor surgical means. The term “proximal” as used herein refers to portions of the endograft, stent or delivery system relatively closer to the end outside of the body, whereas the term “distal” is used to refer to portions relatively closer to the end inside the body. 
         [0005]    After the introducer is advanced into the body lumen to the endograft deployment location, the introducer is manipulated to cause the endograft to be deployed from its constrained configuration, whereupon the stent is expanded to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion typically is effected by spring elasticity, balloon expansion, and/or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration. 
         [0006]    Among the many applications for endografts is that of deployment in lumen for repair of an aneurysm, such as a thorasic aortic aneurysm (TAA) or an abdominal aortic aneurysm (AAA). An AAA is an area of increased aortic diameter that generally extends from just below the renal arteries to the aortic bifurcation and a TAA most often occurs in the descending thoracic aorta. AAA and TAA generally result from deterioration of the arterial wall, causing a decrease in the structural and elastic properties of the artery. In addition to a loss of elasticity, this deterioration also causes a slow and continuous dilation of the lumen. 
         [0007]    The standard surgical repair of AAA or TAA is an extensive and invasive procedure typically requiring a week long hospital stay and an extended recovery period. To avoid the complications of the surgical procedure, practitioners commonly resort to a minimally invasive procedure using an endoluminal endograft to reinforce the weakened vessel wall, as mentioned above. At the site of the aneurysm, the practitioner deploys the endograft, anchoring it above and below the aneurysm to relatively healthy tissue. The anchored endograft diverts blood flow away from the weakened arterial wall, minimizing the exposure of the aneurysm to high pressure. 
         [0008]    Intraluminal stents for repairing a damaged or diseased artery or to be used in conjunction with a graft for delivery to an area of a body lumen that has been weakened by disease or damaged, such as an aneurysm of the thorasic or abdominal aorta, are well established in the art of medical science. 
         [0009]    While intraluminal stents are advantageous in anchoring the device, an improved system for aligning stents in curved vessels or lumens is desired. 
       SUMMARY OF THE INVENTION 
       [0010]    In one aspect, the invention provides a stent-graft system comprising a graft member and a stent having a connection end interconnected with the graft member and a free end opposed thereto. The stent includes a plurality of struts extending between the connection end and the free end and at least two of the struts having different lengths such that the free end has a nonuniform profile. 
         [0011]    In another aspect, the invention provides a method of securing at least one end of a graft within a vessel. The method comprises: positioning within the vessel a stent-graft comprising a stent and a graft with a connection end of the stent connected to an end of the graft, the stent having a free end opposite the connection end, the stent including a plurality of nonuniform struts such that the free end has at least one short strut and at least one long strut; positioning the stent-graft within the vessel such that the at least one short strut is aligned with an inner radial curvature of the vessel; and deploying the stent. 
         [0012]    Other aspects and advantages of the present invention will be apparent from the detailed description of the invention provided hereinafter. 
     
    
     
         [0013]    The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
           [0014]      FIG. 1  shows a prior art endovascular graft portion fully deployed within an angulated internal vasculature of the patient. 
           [0015]      FIG. 2  shows an endovascular graft portion in accordance with an embodiment of the present invention fully deployed within an angulated internal vasculature of the patient. 
           [0016]      FIG. 3  shows a flat pattern of an embodiment of a stent in accordance with an embodiment of the present invention. 
           [0017]      FIG. 4  shows a flat pattern of another alternative embodiment of a stent in accordance with the present invention. 
           [0018]      FIG. 5  shows a portion of an endovascular graft according to an embodiment of the present invention partially deployed within an angulated internal vasculature of the patient. 
           [0019]      FIG. 6  shows the endovascular graft portion of  FIG. 5  fully deployed within the internal vasculature of the patient. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
         [0021]    Unless otherwise stated, the term “graft” or “endovascular graft” is used herein to refer to a prosthesis capable of repairing and/or replacing diseased vessels or portions thereof, including generally tubular and bifurcated devices and any components attached or integral thereto. For purposes of illustration, the graft embodiments described herein may be used in the endovascular treatment of abdominal aortic aneurysms (AAA) or thoracic aortic aneurysms, however, other applications are within the scope of the present invention. For the purposes of this application, with reference to endovascular graft devices, the term “proximal” describes the end of the graft that will be oriented towards the oncoming flow of bodily fluid, typically blood, when the device is deployed within a body passageway. The term “distal” therefore describes the graft end opposite the proximal end. Finally, while the drawings in the various figures are accurate representations of the various embodiments of the present invention, the proportions of the various components thereof are not necessarily shown to exact scale within and among or between any given figure(s). 
         [0022]    Referring to  FIG. 1 , a prior art stent graft  110  is illustrated deployed within an angulated vessel  1  of a patient. The stent graft  110  includes a stent  140  connected to a graft  113  as is known in the art. The stent  140  includes a plurality of struts  141  which each have a uniform length to define a uniform free end  142  with all of the struts  141  terminating in a common plane P. With such a stent  140  positioned in an angulated vessel  1 , the stent  140  may not align properly. For example, an inner strut  141   a  may liftoft from an inner radial curvature  3  of the vessel  1  as indicated at arrow A. Alternatively, an outer strut  141   b  may penetrate the vessel wall at an outer radial curvature  5  of the vessel  1 . 
         [0023]    Referring to  FIGS. 2 and 3 , a stent graft  10  in accordance with a first embodiment of the invention will be described. An end of the graft  10  is illustrated and may represent the proximal or distal end of the graft  10 . The graft  10  includes a generally tubular structure or graft body section  13  comprised of one or more layers of fusible material, such as expanded polytetrafluoroethylene (ePTFE). An inflatable cuff  16  is disposed at or near the end  14  of graft body section  13 . A neck portion  23  is disposed in the vicinity of graft body section end  14  and serves as an additional means to help seal the deployed graft against the inside of a body passageway. Graft body section  13  forms a longitudinal lumen  22  configured to confine a flow of fluid therethrough. 
         [0024]    An attachment ring  24  is affixed to or integrally formed in graft body section  13 , or as shown in  FIG. 2 , at or near graft body section end  14  and neck portion  23 . In the embodiment of  FIG. 1 , attachment ring  24  is a serpentine ring structure comprising apices  28 . Other embodiments of attachment ring  24  may take different configurations. Attachment ring  24  may be made from any suitable material that permits expansion from a constrained state, most usefully a shape memory alloy having superelastic properties such as nickel titanium (NiTi). Other suitable attachment ring  24  materials include stainless steel, nickel-cobalt alloys such as MP35N, tantalum and its alloys, polymeric materials, composites, and the like. Attachment ring  24  (as well as all stents and attachment rings described herein) may be configured to self-expand from the illustrated radially constrained state. 
         [0025]    Some apices  28  may also comprise a attachment ring connector element (not shown). The number of connector elements may vary and can be distributed, for example, on every apex, every third or fourth apex, or any other pattern are within the scope of the present invention. 
         [0026]    Graft  10  further comprises one or more stents  40  having, in the deployed state, a generally free end  42  and a connection end  44 .  FIG. 2  illustrates a proximal stent  40 , but the stents  40  may additionally or alternatively be provided on the distal end of the graft  10 . In the case of a bifurcated graft, a stent  40  may be provided on the distal end of each leg of the bifurcated graft. 
         [0027]    As shown in  FIG. 2 , stent  40  is typically, though not necessarily, made a part of graft  10  by having the connection end  44  affixed or connected to attachment ring  24  via connector elements as described in detail below. The connection end  44  of stent  40  may also be affixed or embedded directly to or in neck portion  23  and/or other portions of graft body section  13 . In addition, the attachment ring and the stent may not be mechanically or otherwise fastened to one another but rather unified, formed of a monolithic piece of material, such as NiTi. 
         [0028]    This configuration of stent  40 , attachment ring  24 , neck portion  23 , and cuff  16  helps to separate the sealing function of cuff  16 , which requires conformation and apposition to the vessel wall within which graft  10  is deployed without excessive radial force, from the anchoring function of stent  40  (attachment ring  24  and neck portion  23  play intermediate roles). 
         [0029]    Referring to  FIGS. 2 and 3 , each stent  40  of the present invention generally comprises a series of interconnected struts  41  which will be described in more detail hereinafter. Each stent  40  further comprises stent connector elements  48  at the connection end  44  thereof. The stent connector elements  48  are configured to be affixed or otherwise connected to attachment ring connector elements  30  via coupling members (not shown), for example, threads or wires. The stents  40  may be manufactured from any suitable material, including the materials suitable for attachment ring  24 . When manufactured from a shape memory alloy having superelastic properties such as NiTi, the stents  40  may be configured to self-expand upon release from the contracted state. The strut structure is often formed as a flat structure, as illustrated in  FIGS. 3-4 , and thereafter, wrapped and connected in a cylindrical or other configuration, as illustrated in  FIG. 2 . 
         [0030]    Each stent  40  may include one or more barbs  43 . A barb  43  can be any outwardly directed protuberance, typically terminating in a sharp point that is capable of at least partially penetrating a body passageway in which graft  10  is deployed (typically the initial and medial layers of a blood vessel such as the abdominal aorta). The number of barbs, the length of each barb, each barb angle, and the barb orientation may vary from barb to barb within a single stent  40  or between multiple stents  40  within a single graft. Although the various barbs  43  may be attached to or fixed on the stent struts  41 , it is preferred that they be integrally formed as part of the stent struts  41 , as shown in the various figures. 
         [0031]    As illustrated, the struts  41  can have various configurations and lengths. In the present invention, the struts  41  have differing lengths such that the stent  40  has a nonuniform free end  42 . That is, the ends of all different struts  41  do not lie along a single plane. In the present embodiment, the short struts  41   a  define the distal most portions of the free end  42  while the long struts  41  c define the proximal most portions of the free end  42  and the intermediate struts  41   b  define portions therebetween. In the present embodiment, the free end  42  has a sinusoidal configuration as illustrated in  FIG. 3 . For some embodiments, the strut lengths slope to a pair of short struts offset approximately ninety degrees relative to the long struts. For some embodiments, the short struts are configured to be aligned with an inner radial curvature and outer radial curvature of an angulated vessel. 
         [0032]    Referring to  FIG. 2 , in a preferred deployment, the stent  40  is preferably aligned within an angulated vessel such that a pair of the short struts  41   a  are positioned against an inner radial curvature  3  of the vessel  1  and a second pair of the short struts  41   a  are positioned against an outer radial curvature  5  of the vessel  1 . To facilitate alignment, one or more of the struts  41  may be provided with a radiopaque marker  50  or the like. In this orientation, the long struts  41   c  are along the sides of the vessel  1  and do not cause liftoff or penetration. 
         [0033]    Referring to  FIGS. 4-6 , a second embodiment of the invention is illustrated. The stent graft  10 ′ is similar to in the previous embodiment, but the stent  70  includes a portion which is generally the same as the stent  40  of the previous embodiment and a secondary stent portion  80  connected thereto. The secondary stent portion  80  has a plurality of struts  81  which have a uniform length such that the secondary stent  80  has a generally uniform free end  82 , i.e. each of the struts  81  terminating in generally the same plane P. The connection end  84  is desirably connected to the long struts  41   c  of the stent portion  40 . 
         [0034]    In use, the stent  70  is preferably deployed in a multistage manner. The stent  70  is positioned within the vessel  1  with the secondary stent portion  80  aligned with a generally straight portion  7  of the vessel  1  and deployed. The secondary stent portion  80  may connect to the straight portion  7  of the vessel  1 , for example, via barbs or the like, and anchor the stent graft  10 ′ in position. Since the vessel portion  7  is straight, the uniform struts  81  are not subject to liftoff or penetration. At this time, the nonuniform stent portion  40  remains in a constrained state via belt  35  or the like. 
         [0035]    The staged deployment of the stent  70  also facilitates self-alignment of the stent portion  40  and graft  10 . Upon deployment of the secondary stent portion  80 , the graft  13  is free to expand and distal fluid flow flows into the graft  13  and creates a “windsock” effect. That is, the distal fluid flow applies a slight distal force upon the graft  13 . This distal force helps to align the graft  13  and the stent  40  within the vessel  1 , which is particularly advantageous during deployment of the stent graft within the angulated vessel  1 , for example, which is an aortic arch. 
         [0036]    The stent portion  40  may thereafter be deployed by release of the belt  35  whereby the stent portion  40  deploys in a manner similar to described above. As shown in  FIG. 6 , the stent  40  is preferably aligned within the angulated vessel  1  such that a pair of the short struts  41  a are positioned against the inner radial curvature  3  of the vessel  1  and a second pair of the short struts  41  a are positioned against the outer radial curvature  5  of the vessel  1 . Again, to facilitate orientation, one or more of the struts  41  may be provided with a radiopaque marker  50  or the like. Orientation is preferably performed prior to deployment of the secondary stent portion  80 . As in the previous embodiment, in this orientation, the long struts  41   c  are along the sides of the vessel  1  and do not cause liftoff or penetration. 
         [0037]    While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.