Patent Publication Number: US-2012035714-A1

Title: Stent Graft Having A Marker And A Reinforcing And Marker Ring

Description:
FIELD OF INVENTION 
     This invention relates to a medical device and more particularly to a reinforcing ring used in a stent graft device. 
     BACKGROUND OF THE INVENTION 
     Stent grafts are used to bridge a defect in the vasculature of a patient and can be deployed into the vasculature endovascularly. This requires that the device can be constrained into a small diameter delivery device and be able to expand, or be expanded, when released within the vasculature. 
     Where there are side branches to the vasculature it may be necessary to provide an aperture in the stent graft, known as a fenestration, to enable access from a deployed stent graft to that side branch. Such a fenestration may be reinforced with a peripheral circular ring stitched to the graft material around the fenestration. 
     PCT Publication WO 2005/034808 entitled “Fenestrated Stent Graft” describes the use of resilient reinforcing rings around peripheries of fenestrations in stent grafts and the teachings therein are incorporated herein in their entirety. 
     To obtain a good seal of a branch stent graft within the fenestration an inflatable balloon can be used to expand the branch stent graft into the fenestration and for this purpose the reinforcing ring must be able to resist expansion of its diameter. At the same time the ring must be resilient so that it can be distorted into its constrained deployment configuration but when released expand back to its circular configuration. In this specification the term resilient, when used in relation to a wire used to manufacture a reinforcing ring, refers to a wire which is substantially inextensible but which has a spring function so that when distorted and released returns to substantially its original configuration. 
     This invention will be discussed in relation to the application of a reinforcing ring to a fenestration within the wall of a stent graft and a reinforcing ring to the end of a stent graft but such a ring may have greater applicability such as a peripheral reinforcement of a scalloped end of a stent graft. 
     Generally such reinforcing rings are manufactured from a metal known as a superelastic metal such as, but not restricted, to a nickel titanium alloy known as nitinol. To form a ring of a superelastic metal the desired final shape is formed from a wire on a former and then the wire on the former is heated above a temperature which sets the wire in the new shape. Upon cooling the ring holds it formed shape and can be distorted and resiliently returns to the formed shape. As a result of the poor radiopacity of nickel-titanium alloys, however, reinforcing rings made from fine nitinol wires can be difficult to visualize from outside the body using non-invasive imaging techniques, such as x-ray fluoroscopy. Consequently, a clinician may not be able to accurately place and/or manipulate a stent graft with a reinforcing ring to a desired position within a body vessel. 
     PCT Publication WO 2005/034808 referred to above also discloses the use of gold marker beads to assist with providing the necessary visualisation. However, such beads do not precisely indicate the position of fenestrations or other openings. 
     It is the object of this invention to provide a reinforcing ring, or stent graft and reinforcing ring, to overcome the above problem or to at least provide the practitioner with a useful alternative. 
     Throughout this discussion the term “stent graft” is intended to mean a device which has a tubular body of biocompatible graft material and at least one stent fastened to the tubular body to define a lumen through the stent graft. The stent graft may be bifurcated and have fenestrations, side arms or the like. Other arrangements of stent grafts are also within the scope of the invention. 
     Definition Proximal &amp; Distal 
     Throughout this specification the term distal with respect to a portion of the aorta, a deployment device or a prosthesis such as a stent graft is intended to mean the end of the aorta, deployment device or prosthesis such as a stent graft further away in the direction of blood flow from the heart and the term proximal is intended to mean the portion of the aorta, deployment device or end of the prosthesis nearer to the heart. For other lumens within the human or animal body the terms caudal and cranial respectively should be understood. 
     DESCRIPTION OF THE INVENTION 
     According to a first aspect of the invention there is provided a stent graft comprising:
         a wall defining a generally tubular lumen, the wall defining an opening, the opening having a circumferential periphery;   a resilient reinforcing wire curved to follow the periphery of the opening; and   a marker winding wound helically around the reinforcing wire,   whereby the marker winding is viewable on an image display system employing electromagnetic radiation so as to indicate the location of the periphery of the opening.       

     According to a second aspect of the invention there is provided a stent graft comprising:
         a wall defining a generally tubular lumen, the wall defining a fenestration for providing fluid communication between the lumen and a branch vessel, the fenestration having a circumferential periphery;   a resilient reinforcing wire curved to follow the periphery of the fenestration thereby defining a reinforcing ring;   a marker winding wound helically around the reinforcing wire of the reinforcing ring,   whereby the marker winding is viewable on an image display system employing electromagnetic radiation so as to indicate the location of the periphery of the fenestration.       

     In one form the marker winding defines a curved passageway around the resilient wire of the reinforcing ring, the curved passageway having an internal diameter D, wherein the marker winding is helically wound with a pitch providing at least one winding per length D along the reinforcing wire of the reinforcing ring. 
     In one form the marker winding is helically wound with a pitch of greater than 60 degrees and in a further form the marker winding is helically wound with a pitch of greater than 75 degrees. 
     In one form the resilient reinforcing wire is nitinol. 
     In one form the marker winding is radiopaque. 
     In one form the marker winding comprises gold wire. 
     In one form gold wire has a diameter of less than 0.4 mm. 
     In one form the reinforcing ring is stitched to the wall. 
     In one form the wound marker winding defines a curved passageway around the resilient wire, the curved passageway having an internal diameter, and the resilient wire having a diameter, the internal diameter of the curved passageway being at least twice the diameter of the resilient wire. 
     According to a third aspect of the invention there is provided a reinforcing and marker ring for a stent graft, the reinforcing and marker ring comprising:
         a plurality of turns of a substantially inextensible resilient wire in a circular shape and terminal ends at each end of the wire, the terminal ends each comprising a loop, each loop attachable to a stent graft having an opening or a fenestration so as to substantially lock a peripheral length of the circular shape; and   a marker winding wound helically around the reinforcing wire, the marker winding being viewable on an image display system employing electromagnetic radiation so as to indicate the location of a periphery of the fenestration, wherein the circular shape of the resilient wire, with the marker winding wound around it, is collapsible under radial pressure to form a squashed circular shape for loading into a delivery device, the squashed circular shape self-expanding back to a substantially circular shape upon release from the delivery device.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This then generally describes the invention but to assist with understanding reference will now be made to the accompanying drawings which show preferred embodiments of the invention. 
       In the drawings: 
         FIG. 1  shows a stent graft having reinforcing rings in a side wall. 
         FIG. 2   a  shows a reinforcing ring for use around the fenestration within the stent graft of  FIG. 1 . 
         FIG. 2   b  shows an alternative embodiment of the reinforcing ring shown in  FIG. 2   a.    
         FIG. 3   a  shows an enlarged view of the reinforcing ring of  FIG. 2   a  and a portion of the stent graft of  FIG. 1 . 
         FIG. 3   b  shows an enlarged view of the alternative embodiment of the reinforcing ring shown in  FIG. 2   b  and portion of the stent graft of  FIG. 1 . 
         FIG. 4   a  shows the reinforcing ring of  FIG. 2   a  in a squashed condition. 
         FIG. 4   b  shows the reinforcing ring of  FIG. 2   b  in a squashed condition. 
         FIG. 5  shows an enlarged view of the portion of the helically wound marker winding of  FIGS. 2   b  and  3   b.    
         FIG. 6  shows an alternative stent graft having a reinforcing ring at a proximal end. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 ,  2   a ,  3   a  and  4   b  show an embodiment of a reinforcing ring according to the present invention. 
     Referring first to  FIG. 1 , a pair of reinforcing and marker rings  60  around a pair of fenestrations  24  of a stent graft  10 , are shown. The stent graft  10  has a tubular body  20  with three stents  50 ,  52  and  54  stitched onto the tubular body  20  by means of stitches  51 . The tubular body has a wall  22  of biocompatible material. Within the wall of the stent graft  10 , two reinforcing and marker rings  60  are provided (one, three or any number of reinforcing rings may be provided instead). 
     The reinforcing and marker rings  60  are shown separate from the stent graft and in an enlarged view in  FIG. 2   a . Each reinforcing and marker ring  60  comprises a plurality of turns of a substantially inextensible resilient wire  71 , such as nitinol wire, in a substantially circular shape. Terminal ends at each end of the wire  71 , each comprising a loop  72 ,  78  are provided. Each loop  72 ,  78  is attachable to the stent graft  10  so as to substantially lock a peripheral length of the circular shape. This provides the reinforcing and marker ring  60  with a fixed diameter into which, for instance, a self-expanding or balloon expandable stent graft can expanded. A marker winding  80  wound helically around the reinforcing wire is provided. This is shown in  FIGS. 2   a  and  3   a . The marker winding  80  is viewable on an image display system employing electromagnetic radiation so as to indicate the location of a periphery of the fenestration  24 . 
     The circular shape of the resilient wire  71 , with the marker winding  80  helically wound around it, is collapsible under radial pressure to form a squashed circular shape, such as is shown in  FIG. 4   a , for loading into a delivery device. The squashed circular shape self-expands back to a substantially circular shape upon release from the delivery device. 
     It will be particularly noted that in the region  82  as shown in  FIG. 4   a  the resilient wire  71  has a sharp bend but in that region the radiopaque marker wire  80  is substantially transverse to the resilient wire and will not, therefore, affect the resiliency of that wire. 
     The self-expanding property of the reinforcing and marker ring  60  is achieved by the shape memory properties of the wire  71 , such as nitinol wire. 
     Referring now to  FIG. 3   a , it can be seen that the reinforcing and marker ring  60  is attached to the stent graft body  20  by stitching  90 . 
       FIGS. 2   b ,  3   b  and  4   b  show an alternative embodiment in which the marker winding  80  is wound with a larger pitch. 
       FIG. 5  shows an enlarged view of a portion of the helically wound marker winding  80 . The marker winding  80  defines a passageway around the resilient wire  71 . The passageway has an internal diameter D and is curved to follow the reinforcing wire  71  (not shown in  FIG. 5 ). The marker winding  80  is helically wound with a pitch providing about two windings per length D along the reinforcing wire in a direction X. The wire  80  can have a diameter d in the range of from 0.2 to 0.5 mm. 
     Various pitches can be used, but pitches providing at least one winding per length D along the reinforcing wire have been found to be particular effective in providing a viewable image on an image display system employing electromagnetic radiation so as to indicate the location of a periphery of the fenestration  24 , while at the same time not substantially inhibiting the expansion of the squashed circular shape back to a substantially circular shape upon release from a delivery device. 
     Pitches of greater than about 60 degrees, and especially greater than 75 degrees, (as is shown in  FIG. 5  as P) have been found to provide a good viewable image while at the same time not substantially inhibiting the expansion of the squash circular shape back to a substantially circular shaped upon release from a delivery device. 
     Various materials can be used for the marker winding. For instance, gold has been found to be particularly effective as a radio opaque material suitable for use with x-ray imaging. Gold is also ductile and is readily formed from fine wire into the helical shape required as described above. Various gold wire diameters maybe used, with diameters of less than 0.4 mm being particularly effective. In the embodiment illustrated in the drawings, the diameter of the gold wire is approximately 0.2mm and the re-enforcing wire  71  has a diameter of approximately 0.15 mm. 
     In order to assemble a re-enforcing ring such as that illustrated in  FIG. 3   a  or  3   b , fine gold wire (having a diameter of about 0.2 mm) is wound tightly around a 0.5 mm wire so as to form a helical winding. The helical winding is then placed onto the loops of nitinol wire  71  to form a complete radiopaque reinforcing and marker ring  60  as is illustrated in  FIG. 2   b . The reinforcing and marker ring  60  is then attached to the wall  22  of the tubular body  20  around the fenestration  24  as is shown in  FIG. 3   b.    
       FIG. 6  shows the construction of an alternative stent graft with a proximal reinforcing ring. The same reference numerals as used in  FIG. 1  are used for  FIG. 6  for the corresponding components. The tubular body  20  of the stent graft  10  has a proximal-most external stent  50  stitched onto the tubular body by means of stitches  51 . At the proximal end  21  of the stent graft  10  a reinforcing and marker ring  60  is provided. The reinforcing and marker ring  60  comprises two turns of a shape memory wire  71 , such as nitinol wire, around the proximal end  21  and loops  72  and  78  at each terminal end of the nitinol wire  71 . The loops  72  and  78  prevent the ends of the nitinol wire causing damage to the vasculature in which they are deployed. The two turns of nitinol wire  71  are stitched by means of stitching  90  to the proximal end  21  the tubular body  20 . 
     Marker winding  80 , shown in  FIG. 6 , is helically wound around the reinforcing wire  71 . The marker winding  80 , in the form of gold for instance, is viewable on an image display system employing electromagnetic radiation so as to indicate the location of the proximal end  21  of the stent graft  10 . 
     The marker winding  80  described above is provided to assist in visualising position using x-ray fluoroscopy. It should be understood that other non-invasive imaging techniques, such as Magnetic Resonance Imaging (MRI) may also be used and, depending on the type of imaging technique used, different materials can be used for the marker winding  80 . While gold is radiopaque and is highly suitable for x-ray fluoroscopy imaging, other material may be used where MRI is to be used. 
     It will be understood that the term “comprise” and any of its derivatives (e.g. comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied. 
     Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.