Abstract:
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. A belt retaining structure is provided at the stent free end. A belt is releasably retained in the belt retaining structure and is configured to constrain the stent free end independent of the stent connection end. A method of securing at least one end of a stent-graft within a vessel is also provided.

Description:
RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 13/277,117, titled “System and Method of Pivoted Stent Deployment”, filed Oct. 19, 2011, by Isaac J. Zacharias et al., which is a continuation of U.S. patent application Ser. No. 11/861,716, now U.S. Pat. No. 8,066,755, titled “System and Method of Pivoted Stent Deployment”, filed Sep. 26, 2007, by Isaac J. Zacharias et al., which are both incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     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. 
     For indications such as abdominal aortic aneurysms, traditional open surgery is still the conventional and most widely-utilized treatment when the aneurysm&#39;s size has grown to the point that the risk of aneurysm rupture outweighs the drawbacks of surgery. Surgical repair involves replacement of the section of the vessel where the aneurysm has formed with a graft. An example of a surgical procedure is described by Cooley in Surgical Treatment of Aortic Aneurysms, 1986 (W. B. Saunders Company). 
     Despite its advantages, however, open surgery is fraught with high morbidity and mortality rates, primarily because of the invasive and complex nature of the procedure. Complications associated with surgery include, for example, the possibility of aneurysm rupture, loss of function related to extended periods of restricted blood flow to the extremities, blood loss, myocardial infarction, congestive heart failure, arrhythmia, and complications associated with the use of general anesthesia and mechanical ventilation systems. In addition, the typical patient in need of aneurysm repair is older and in poor health, facts that significantly increase the likelihood of complications. 
     Due to the risks and complexities of surgical intervention, various attempts have been made to develop alternative methods for treating such disorders. One such method that has enjoyed some degree of success is the catheter-based delivery of a stent-graft via the femoral arteries to exclude the aneurysm from within the aorta. Illustrative stent-grafts and methods of delivery thereof are described in U.S. Patent Application Publication Nos. 2003/0125797A1, 2004/0138734A1 and U.S. Pat. No. 6,295,019, each of which is incorporated herein in its entirety by reference herein. 
     SUMMARY OF THE INVENTION 
     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. A belt retaining structure is provided at the stent free end. A belt is releasably retained in the belt retaining structure and is configured to constrain the stent free end independent of the stent connection end. 
     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 free end including a belt retaining structure with a belt releasably retained thereabout; deploying the stent connection end within the vessel; repositioning the stent-graft within the vessel; and releasing the belt to deploy the free end of the stent. 
     Other aspects and advantages of the present invention will be apparent from the detailed description of the invention provided hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  shows a portion of an endovascular graft according to an embodiment of the present invention in a contracted state for delivery through a catheter. 
         FIG. 2  shows a flat pattern of an embodiment of a stent in accordance with the present invention. 
         FIG. 3  shows a flat pattern of an alternative embodiment of a stent in accordance with the present invention. 
         FIG. 4  shows a flat pattern of another alternative embodiment of a stent in accordance with the present invention. 
         FIG. 5  shows a portion of an endovascular graft according to an embodiment of the present invention partially deployed within the internal vasculature of the patient. 
         FIG. 6  shows the endovascular graft portion of  FIG. 5  fully deployed within the internal vasculature of the patient. 
         FIG. 7  shows a portion of an endovascular graft according to an embodiment of the present invention partially deployed within an aortic arch of the patient. 
         FIG. 8  is an isometric view of a pivot fitting in accordance with another embodiment of the present invention. 
         FIG. 9  is an end view of the pivot fitting of  FIG. 8 . 
         FIG. 10  is a cross-sectional view along the line  10 - 10  in  FIG. 9 . 
         FIG. 11  is a cross-sectional view similar to  FIG. 10  illustrating schematically a stent thereon in a contracted state. 
         FIG. 12  is a cross-sectional view similar to  FIG. 10  illustrating schematically a stent thereon in a partially deployed state. 
         FIG. 13  is a perspective view illustrating a stent in the partially deployed state of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     Referring to  FIG. 1 , a portion of an illustrative endovascular graft  10  is shown in its contracted configuration. 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). 
     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. 
     A attachment ring  24  is affixed to or integrally formed in graft body section  13 , or as shown in  FIG. 1 , 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. 
     Some apices  28  may also comprise an attachment ring connector element  30  (see  FIGS. 5 and 6 ). The number of connector elements  30  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. 
     Graft  10  further comprises one or more stents  40  having, in the deployed state (see  FIG. 6 ), a generally free end  42  and a connection end  44 .  FIGS. 1 and 5-6  illustrate 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. 
     As shown in  FIGS. 1 and 5-6 , 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. 
     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). As will be described in more detail hereinafter, the stents  40  of the present invention permit improved positioning of the graft  10  prior to stent anchoring, thereby facilitating better placement and sealing of the graft  10 . 
     Referring to  FIGS. 2-4 , each stent  40  of the present invention generally comprises a series of interconnected struts  41 . As illustrated, the struts  41  can have various configurations and lengths. 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. 2-4 , and thereafter, wrapped and connected in a cylindrical or other configuration, as illustrated in  FIG. 1 . 
     Each stent  40  includes 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  (and tuck pads  45  discussed below) 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. 
     When stent  40  is deployed in the abdominal aorta, for example, typically in a location proximal to the aneurysm and any diseased tissue, barbs  43  are designed to work in conjunction with the distally-oriented blood flow field in this location to penetrate tissue and prevent axial migration of graft  10 . As such, the barbs  43  in the  FIG. 1  embodiment are oriented distally with respect to graft body section  13 . However, the number, dimensions, configuration and orientation of barbs  43  may vary significantly, yet be within the scope of the present invention. 
     Struts  41  may also comprise optional integral tuck pads  45  disposed opposite each barb  43 . During preparation of graft  10  (and therefore the stents  40 ) into its reduced diameter delivery configuration, each barb  43  is placed behind a corresponding strut  41  and/or optional tuck pad  45 , if present, to thereby prevent the barbs  43  from contacting the inside of a delivery sheath or catheter during delivery of the device and from undesired contact with the inside of a vessel wall. As described in U.S. Pat. No. 6,761,733 to Chobotov et al., the complete disclosure of which is incorporated herein by reference, an initial stage release belt  35  disposed about the struts  41  retain the stent  40  in this delivery configuration. The initial stage release belts  35  retain the contracted stent  40  on a guidewire chassis  12  or the like. 
     The number of initial stage belts  35  varies in accordance with the structure of the stent  40 . For example, the stents  40  as illustrated in  FIGS. 2 and 4  have proximal and distal segments and two corresponding initial stage belts  35 , one about the proximal segment and one about the distal segment, are used to secure the stent  40  as shown in  FIG. 1 . In shorter stents  40  having a single segment, like the stent  40  illustrated in  FIG. 3 , a single initial stage belt  35  is typically used to secure the stent  40 . Upon deployment of the stent  40 , by releasing the initial stage belt(s)  35 , the radial expansion of stent  40  results in a displacement of struts  41  so that the distance between them increases. As the struts  41  separate, the barbs  43  are freed from behind the struts  41  and optional tuck pads  45 , if present, and engage the wall of the vessel being treated. To enhance the engagement of the barbs  43  in the vessel wall  20 , the barbs  43  may be designed to work in conjunction with the distally-oriented blood flow field, that is, the barbs  43  are oriented distally, however, they do not have to be. In the illustrative embodiment, the barbs  43  at the proximal end are oriented distally, while the barbs  43  at the distal end are oriented proximally. 
     While secure engagement of the barbs  43  in the vessel wall  20  is desirable to prevent axial migration of graft  10 , such engagement is generally permanent and not subject to modification. Attempts to reposition the stent  40  or graft  10  after engagement of the barbs  43  in the vessel wall  20  may cause tearing or other damage to the vessel wall  20 . 
     Referring to  FIGS. 2-4 , each stent  40  of the present invention includes a belt retaining structure  50  provided along the crowns  47  at the free end  42  of the stent  40 . In the embodiments illustrated in  FIGS. 2 and 3 , the belt retaining structure  50  includes a plurality of mushroom shaped connectors  52  extending from the crowns  47 . The mushroom shaped connectors  52  may be provided at each crown  47 , as illustrated, or in any configuration with respect to the crowns  47 . Referring to  FIGS. 1 and 5 , a releasable secondary stage belt  53  is positionable about the mushroom shaped connectors  52  to retain the stent free end  42  in a contracted state until the secondary stage belt  53  is released, for example, via a release wire  55 . In the embodiment illustrated in  FIG. 4 , the belt retaining structure  50  includes a through hole  54  provided in a plurality of the crowns  47 . A releasable belt (not shown) is threaded through the through holes  54  and pulled tight to retain the stent free end  42  in a contracted state until the belt is released. Other belt retaining structures  50  along the stent free end  42  may also be utilized. 
     As shown in  FIG. 5 , upon release of the initial stage belts  35 , the stent connection end  44 , the attachment ring  24 , and the graft  10  expand while the secondary stage belt  53  engages the belt retaining structure  50  and retains the stent free end  42  in the generally contracted condition. The stent connection end  44  and the graft  10  expand based on the self expanding nature of the stent  40  and also the force of the distal fluid flow into the graft  10 . The struts  41  and barbs  43  are configured such that when the belt retaining structure  50  is in place and the stent free end  42  is restrained, the barbs  43  do not extend sufficiently radially to engage the vessel wall  20 , but instead remain spaced therefrom. As such, the graft  10  and stent  40  may be moved and repositioned without the barbs  43  engaging and damaging the vessel wall  20 . In at least one embodiment of the invention, the barbs  43  are axially positioned closer to the stent free end  42  than the stent connection end  44  to further ensure the barbs  43  will not contact the vessel wall  20  in the partially deployed state. 
     Once the stent  40  and graft  10  are positioned as desired, the release wire  55  may be pulled to release the secondary stage belt  53  from the belt retaining structure  50 , thereby allowing the stent  40  to fully deploy as illustrated in  FIG. 6 . Upon full deployment, the struts  41  are free to fully radially expand such that the barbs  43  engage the vessel wall  20  in a normal manner. 
     In addition to facilitating manual movement and repositioning of the graft  10  and stent  40 , the staged deployment of the stent  40  also facilitates self-alignment of the stent  40  and graft  10 . As explained above, upon release of the initial stage belts  35 , the graft  10  is free to expand and distal fluid flow flows into the graft  10  and creates a “windsock” effect. That is, the distal fluid flow expands the graft  10  and applies a slight distal force upon the graft  10 . This distal force helps to align the graft  10  and the stent  40  within the vessel. 
     This self alignment is particularly advantageous during deployment of a stent graft within an angulated vessel, for example, in the aortic arch. Referring to  FIG. 7 , the stent  40  is illustrated partially deployed in an aortic arch  25 . The delivery guidewire chassis  12  contacts the vessel wall  20  and does not remain coaxial with respect to the arch  25 . As such, in the initial delivery position, the stent  40  may be cocked or otherwise misaligned with respect to the vessel wall  20 . In a prior art single stage deployment, the stent would expand and the barbs would engage the vessel wall even if the stent was misaligned. With the stent  40  of the present invention, the initial stage belt(s)  35  are released and the stent  40  is partially deployed. The distal fluid flow flows into the graft  10  and creates the windsock effect, thereby pulling the graft  10  and stent  40  into alignment with the flow and thereby the vessel wall  20 . 
     Referring to  FIGS. 8-13 , a pivot fitting  100  configured to assist in the multi-staged deployment of stent  40  will be described. The pivot fitting  100  has a generally cylindrical body  102  with an axial through bore  104  configured to position the fitting  100  about the guidewire chassis  12  (see  FIG. 13 ) or the like. A transverse bore  106  is provided to facilitate positioning and attachment of the pivot fitting  100  about the guidewire chassis  12  and loading into the delivery catheter (not shown). 
     The pivot fitting  100  includes an area  108  of reduced cross section extending between a shoulder  110  and a radial belt support member  112 . The area  108  is configured to receive the free ends of the stent  40 , for example, the mushroom shaped connectors  52  or the crowns  47  with through holes  54 . To facilitate passage of the stent members, the radial belt support member  112  includes a plurality of radial slots  114 . In the embodiment illustrated in  FIG. 13 , each radial slot  114  receives the narrow neck portion of a respective mushroom shaped connector  52 . 
     A circumferential groove  116  is provided along the radial surface of the radial belt support member  112 . The circumferential groove  116  is configured to receive and maintain the secondary stage belt  53 . A belt radial slot  118  is provided in the radial belt support member  112  to facilitate passage of the secondary stage belt  53  from the guidewire chassis  12  or the like outward to the circumferential groove  116 . 
     Referring to  FIG. 11 , in the delivery stage, the stent  40  is compacted with the free end  42  passing through the radial slots  114  in the radial belt support member  112 . The secondary stage belt  53  is secured in the circumferential groove  116  and constrains the stent free end  42 . Turning to  FIGS. 12 and 13 , upon release of the initial stage release belts  35 , the connection end  44  of the stent  40  expands while the free end  42  is retained by the secondary stage belt  53 . The opening diameter of the connection end  44  can be controlled by the relation of the outer diameter of area  108  and the inner diameter of the circumferential groove  116  and the length of the portion of the stent free end  42  that extends into area  108 . In this partially deployed state, the stent free end  42  is securely retained by the pivot fitting  100 , which in turn is connected to the guidewire chassis  12 . As such, movement of the guidewire chassis  12  provides relatively precise control of the position of the stent  40 . Once the stent  40  is positioned in a desired position, the secondary stage belt  53  is released and the stent free end  42  disengages from the pivot fitting  100  and expands. The pivot fitting  100  remains connected to the guidewire chassis  12  and is removed upon removal thereof. 
     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.