Abstract:
A prosthesis ( 10 ) having a variable size or stretchable fenestration ( 14 ) in the graft material ( 37 ) of a biocompatible tubular graft ( 11 ). An expandable frame ( 16 ) is disposed about the fenestration, and a portion ( 17 ) of the graft material about the fenestration is folded back over the frame to cover the frame. Additional grafts or prosthesis of varying size can be inserted through the frame and fenestration with the stretched frame and folded portion compressing on the inserted graft forming a seal therewith.

Description:
This application claims priority of provisional application Serial No. 60/510,243, filed Oct. 10, 2003. 
    
    
     TECHNICAL FIELD 
     This invention is related to medical devices and, in particular, to a prosthesis having a fenestration. 
     BACKGROUND OF THE INVENTION 
     Prostheses such as stent grafts as used for stenting or repairing aneurysms as in the abdominal or thoracic aorta are usually fairly effective at excluding the aneurysm from exposure to blood pressure and therefore protect the patient from the dangers of aneurysm rupture. However, these stent grafts frequently block the flow of blood to the side branch vessels that carry blood to other organs and anatomy. The occlusion of the side branch vessels can result in damage to the tissue perfused by the blood flow from the side branch vessel. 
     Attempts to deal with these occlusions have been such things as by-pass vessels placed surgically to restore blood flow from a region of the aorta that is not stented and the placement of holes or fenestrations in the stent grafts that are aligned with the side branch vessel so asto allow blood to continue to flow into the side branch vessel. The fenestration approach is the preferred method since it does not involve major vascular surgery. Patients receiving stent grafts usually do so because they are too weak or sick to endure surgery. Once the fenestrated stent graft is deployed, the stent graft is anchored to the ostium of the side branch with a balloon expanded stent. This stent is placed so that the bulk of the stent length is in the side branch with 1 or 2 mm extending into the lumen of the stent graft. The 1 or 2 mm segment is then over expanded, or flared slightly, to hold the stent graft to the aortic wall and effect a seal that prevents blood from flowing into the aneurysm. 
     While this balloon stenting through a fenestration process is fairly effective, it is deficient in that the connection between the balloon expanded stent and the stent graft at the fenestration is never completely snug or tight. As a result, leaks often occur between the stent graft and aortic wall. The reason this connection can never truly be a tight, zero clearance fit is because balloon expandable stents always have some amount of recoil after they are expanded by the delivery balloon. This recoil is usually 4% to 10% of the stent diameter attained prior to balloon deflation. As a result, the fit between the balloon expandable stent and the stent graft fenestration is never truly tight. The eventual endothelialization of the area around the fenestration and the ostium or origin of the side branch is the only hope of an eventual complete seal and exclusion of the aneurysm. Before endothelialization occurs, the patient is still at risk of a ruptured aneurysm. In some cases, where the gap between the stent graft and aortic wall is large, a seal at the fenestration may never occur, leaving the patient with minimal or no protection from a ruptured aneurysm. 
     Other exemplary prostheses including stents, grafts, and stent grafts with, for example, fenestrations are disclosed in U.S. Pat. Nos. 6,524,335; 5,984,955; 6,395,018; 6,325,826; 6,077,296; 6,030,414; 5,617,878; 5,425,765; and 4,580,569, all of which are incorporated herein by reference in their entirety. 
     SUMMARY OF THE INVENTION 
     The foregoing problems are solved and a technical advance is achieved in an illustrative embodiment of a stretchable prosthesis fenestration including a variable size fenestration in the stent graft of the present invention. This invention provides a variable size fenestration or hole in the stent, graft or stent graft that is stretchable or elastic. By being stretchable, a balloon expandable stent can be advantageously expanded beyond the diameter of the fenestration without damaging the stent, graft or stent graft and will recoil along with the balloon expanded stent and maintain a close, snug fit to it. An expandable frame is disposed at least partially about the fenestration and at least partially controls the variable size of the fenestration to advantageously accommodate a close or snug fit with another prosthesis such as a stent, graft or stent graft positioned therethrough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a segment of stent graft with a fenestration of the present invention; 
         FIG. 2  shows a stretchable fenestration frame of the present invention made from coil spring material; 
         FIG. 3  shows an expandable fenestration frame of the present invention made from solid wire; 
         FIGS. 4A and 4B  depict cross sectional views through the stretchable fenestration of the present invention using the coil spring frame in the relaxed and stretched conditions; 
         FIGS. 5A and 5B  depict cross sectional views of another stretchable fenestration frame of the present invention where the coil frame is an oval or flat coil spring in the relaxed and stretched conditions; and 
         FIG. 6  depicts the stent graft of the present invention with a side branch graft connected to the main graft and fenestration; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a pictorial view of a segment of an illustrative prosthesis  10  such as a stent graft of the present invention in which a variable size fenestration  14  is disposed in tubular graft  11 ,  36 . Biocompatible tubular graft  11  or elongated tubular member  36  of graft material  37  includes a lumen  12  extending longitudinally therethrough. 
     The fenestration  14  can be made by first cutting a round hole in the graft material  37  that is considerably smaller than the desired finished hole. An expandable frame  16  such as a stretchable coil loop  23  as in  FIG. 2  is laid on the graft material, around the hole, then the graft material is everted through the coil loop and out over the loop back onto the graft material. The edge can then be sutured or sewn to the graft material using well-known sutures  38  and capturing the coil loop at the resulting hole or fenestration. The result is prosthesis  10 , tubular graft  11 , or elongated tubular member  36  depicted in  FIG. 1 . A tubular graft sleeve can also be positioned and attached to the hole to facilitate the eversion or fold back. 
     The folded portion  17  of the graft that is everted through the coil frame and back out onto the graft material needs to be stitched far enough away from the coil frame so as to allow a space for the coil frame to expand. The variable size  15  of the fenestration  14  is depicted in  FIGS. 4A ,  4 B,  5 A, and  5 B.  FIGS. 4A ,  4 B,  5 A, and  5 B illustrate how variable size  15  of the opening or fenestration  14  expands as the coil loop frame is stretched. Diameter  39  is the relaxed, un-stretched diameter, and diameter  40  is the maximum stretched or expanded diameter. From the diameter  40  or the expanded diameter, the coil loop frame will cause the fenestration to be tight or snug around the stent that is positioned through the fenestration and into the side branch artery. 
     The coil loop shown in  FIGS. 5A and 5B  is an alternative form of the coil loop frame. The coil from which the loop is made is made in an oval shape  24 . This will result in a fenestration that has a flange or protrusion that will seat in the ostium of the side branch vessel and improve the seal between the stent graft and aorta. The oval shaped coil will also increase the amount of surface area in contact with a balloon expandable stent or stent graft, further improving the seal between the stent graft and aorta. 
       FIG. 3  shows an alternate form of fenestration frame  16  that uses a solid wire frame  41 . It is simply a loop wherein the ends overlap. The overlap portion allows the loop to expand and contract a small amount. The expansion and contraction allows the fenestration to expand as needed when the balloon expandable stent is expanded in it and contract with the balloon expanded stent as the balloon is deflated, thus maintaining a tight fit to the balloon expanded stent. 
     The materials used to make the fenestration frames can be any springy, biocompatible material, such as stainless steel, nitinol, Elgiloy, MP35N, platinum and many other materials including polymers. Platinum would have the added advantage of providing improved radiopacity of the fenestration, making it easier for the physician to accurately place the fenestration in the side branch vessel. 
     In addition to the wire and spring fenestration loops described, it is also possible to make stretchable fenestration frames using elastic bands, such as Silicone rubber “O” rings  25 , or any other biocompatible elastomer  26 . 
     In addition to using the radiopacity of the fenestration frame to aid in the placement and orientation of the stent graft, separate radiopaque markers  21  can be added to the stent graft as depicted in  FIG. 1  in the vicinity of or around the periphery of the fenestration. These markers can be radiopaque material  22  such as gold, platinum, tungsten, and any other high density material  27  such bands or wires and can be shaped and/or oriented in such a way so as to indicate rotational orientation fluoroscopically. 
     The size of a fenestration can typically vary over a range of about 2 to 10 mm diameter. The wire used to make the coil frames would be in the 0.002 to 0.006 in. diameter range. Flat, square, rectangular and oval wire could also be used to make the coil loop frames  16 . The diameter of the coil in the coil loop frame would be in the 0.010 to 0.050 in. range. The long and short axis of the oval coil loop frame would be in the 0.005×0.010 inch to 0.020×0.050 inch range. The long axis dimension could be greater if a longer or taller flange protrusion around the fenestration is desired. The wire in the wire loop frame could be in the 0.010 to 0.060 inch diameter range. 
     The coil loop frame  16  can be made by first coiling the wire to the desired coil diameter by any number of well known coil spring winding techniques and then joining the ends of a length of the coil to form a loop frame  23  of the desired diameter. The ends of the coil could be welded, soldered or glued together to form the continuous coil loop. The ends of the coil could also be stretched slightly over a distance of about 1 mm so that the two ends could be threaded or screwed together to form a mechanical connection. The oval coil loop  24  can be made in much the same manner except that the original coil would be pressed or flattened to form the short diameter of the oval. 
     The shape of stents  13  used to make the stent graft could be altered to accommodate the inclusion of the fenestrations and frames. For example, the most common stent in a stent graft is the Gianturco “Z” stent (U.S. Pat. No. 4,580,568). The straight struts  28  of the Z stent that are adjacent to the fenestration could be curved as depicted in  FIG. 1  so that a larger space is provided for the fenestration. The Z stents can also just be spaced far enough apart as with strut spacing  31  as opposed to lesser spacing  32  so as to allow the formation of a fenestration between them. The length  29  of the straight struts can also be reduced in the area of the fenestration as opposed to longer strut length so as to allow the stents to remain close together while providing a space for the fenestration. 
     In addition to a separate stretchable fenestration frame, a side branch graft  33  can be attached to the fenestrated area in the main stent graft that is made of a “stretch fabric,” similar to the tops of stockings and the like that has an unstretched diameter smaller than the side branch vessel diameter that allows it to be easily maneuvered into the side branch, and then another stent  42  such as a Z stent is placed inside it that would stretch the side branch portion up to the diameter of the side branch vessel and create a long fluid tight seal between the side branch vessel and the main stent graft. This is depicted in  FIG. 6 . 
     The graft material can be any biocompatible material such as any biocompatible polymer such as Dacron, commercially available Thoralon™ material and the like and biological materials such as extracellular matrix (ECM) material, for example, small intestine submucosa (SIS) of porcine, bovine and the like. This ECM material is described and claimed in the patents of Purdue University and Cook Biotech, which are all incorporated by reference herein. This SIS and other ECM material is commercially available from Cook Biotech, West Lafayette, Ind. 
     The following list of figure elements is provided only for informational purposes and is not intended to limit the claims in any manner. 
     ELEMENT LIST 
     
         
           10 . prosthesis 
           11 . biocompatible tubular graft 
           12 . lumen of  11   
           13 . expandable stent 
           14 . fenestration of  11   
           15 . variable size of  14   
           16 . expandable frame 
           17 . folded portion of  11   
           18 . second tubular graft 
           19 . second lumen of  18   
           20 . covered portion of  17   
           21 . radiopaque marker 
           22 . radiopaque material of  21   
           23 . coil loop frame (round cross-sectional shape) 
           24 . oval-shaped coil loop frame (oval cs shape) 
           25 .  0 -ring 
           26 . silicone rubber and any other elastic polymer material of  25   
           27 . gold, platinum, and any other high density material of  22   
           28 . struts 
           29 . first strut length 
           30 . second strut length 
           31 . first strut spacing 
           32 . second strut spacing 
           33 . side branch graft 
           34 . internal to lumen  12   
           35 . external to lumen  12   
           36 . elongated tubular member 
           37 . graft material 
           38 . sutures 
           39 . diameter (relaxed) 
           40 . diameter (stretched) 
           41 . solid wire frame ( 16 ) 
           42 . branch stent