Stent graft sealing zone connecting structure

Abstract

An endoluminal prosthesis useful for treatment of an abdominal aortic aneurysm includes a main body portion and two leg portions. The main body portion includes a graft material coupled to stents. The stents include an upper supra renal stent and sealing stents. The sealing length between the top of the graft material and the bottom of the uppermost sealing stent is minimized while avoiding stent overlap or otherwise compromising the crimped profile by connecting the apexes of the supra renal and sealing stents with a tether that is free to slide within the apexes. In addition, a pleat is provided at the top of the graft material at the attachment of the suprarenal and upper sealing stents to improve sealing. The tether and pleat also redistribute the downward force from blood flow to minimize the force carried by the attachment sites between the stent and graft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an expanded view of an exemplar endoprosthesis designed by the inventors for the purpose of describing certain issues with respect to prior art endoprosthesis designs;

FIG. 2 is a side elevation of an endoprosthesis according to the invention;

FIG. 3 is an enlarged broken schematic section of an upper portion of an endoprosthesis according to the invention, shown in an expanded state;

FIG. 4 is an enlarged broken schematic section of an upper portion of an endoprosthesis according to the invention, shown in a crimped state;

FIG. 5 is graph of a the change in the gap between the supra renal and upper sealing stent as a result of increasing the diameter of the main body portion of the stent;

FIG. 6 is a partial section of an upper interior wall of an endoprosthesis according to the invention, shown in an expanded state; and

FIG. 7 is a schematic broken section view through an portion of an endoprosthesis according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIGS. 2 through 4, a vascular endoprosthesis 110 suitable for treatment of an abdominal aortic aneurysm (AAA) includes a main body portion 112 and two smaller leg portions 114, 116 coupled thereto in a generally inverted Y-configuration. Each portion includes graft material 118 and a plurality of expandable stents coupled at the interior of the graft material, preferably with stitching 119. The graft material is preferably made of polyethylene terephthalate (sold under the trademark Dacron®), which is thrombogenic. The stents, described in more detail below, are preferably self-expanding, formed from a superelastic, shape memory material such as Nitinol or other nickel-titanium alloy, but may be pressure expandable such as with a balloon catheter. When the stents are expanded, they provide outward force of the graft material 118 against the body tissue.

The main body portion 112 preferably includes several discrete stents: an upper supra renal stent 120 preferably extending in a circular cylindrical form (i.e., preferably non-helical) above a portion of the graft material 118 and typically provided with tissue anchors 120a, one or more sealing stents 122, 124 generally extending circumferentially about the graft in a repeating Z-shape (also preferably extending non-helically) and providing outward force against the graft to seal between the graft and the body tissue, and a tapered stent 126 that leads into the legs 114, 116.

According to one aspect of the invention, the supra renal and upper sealing stents 120, 122 are connected together with a preferably fixed length tether 130 that is free to slide within the adjacent apexes 132, 134 of such stents. The cylindrical arrangement of the stents provides that the apexes 132, 134 define points that lie on respective circles. The tether 130 is preferably comprised of Dyneema synthetic fiber available from DSM of The Netherlands, or another flexible, lubricious, high strength, high fatigue resistance, and high wear resistance material such as an HDPE fiber. When the endoprosthesis 110 is crimped and thus the stents are compressed from the expanded diameter D₁ (FIG. 3) to the crimped diameter D₂ (FIG. 4) for loading into a delivery device, the tether 130 has a length sufficient to allow the supra renal and upper sealing stents to be displaced relative to each other by a large enough gap G₂ to prevent compromising the crimped profile. As will be described hereinafter, a pleat 140 helps accommodate displacement of the stents 120, 122 relative to each other. When the stents are again increased in diameter to D₂ once the endoprosthesis is expanded, the tether 130, which is free to move between the apexes 132, 134 through which it extends, is pulled taut, drawing the stents 120, 122 toward each other to significantly reduce or even completely eliminate the gap to G1 and decrease the length of the endoprosthesis required to achieve full circumferential apposition against the vessel wall, i.e., the minimum sealing length 136 (defined as the distance between the top 142 of the graft material 118 and the bottom 143 of the first sealing stent 122) relative to prior art endoprostheses suitable for treatment of abdominal aortic aneurism.

FIG. 5 illustrates the change in gap length as the diameter of the stents are increased in diameter from a crimped state (D₁) to an expanded state (D₂). For a device having a 30 mm expanded diameter (i.e., an endoprosthesis sized for treatment of an abdominal aortic aneurism), the plotted points can be curve fit to the following equation:

$\mathrm{Gap}\left(y\right)=\sqrt{34.7-{\left(\frac{\mathrm{diameter}\left(\theta \right)*\pi }{16}\right)}^2}$

where the Gap(y) is the gap length between the lower apexes of the supra renal and upper apexes of the upper sealing stent, and the diameter(Θ) is the diameter of such respective stents.

By decreasing the minimum sealing length, the outward force of the metal stent material of the supra renal and sealing stents 120, 122, 124 is maximized in the region most subject to leakage. In addition, the endoprosthesis of the invention has high flexibility given that the tether 130 is free to move between the apexes 132, 134 of stents 120, 122. Such freedom of motion allows the main body portion 112 of the endoprosthesis 110 to maintain flexibility across the minimum sealing length 136.

Referring to FIGS. 2 through 4, 6 and 7, according to another aspect of the invention, and as previously mentioned, additional graft material is heat set into a pleat 140 at the top of the graft 118. The lower apex 132 of the supra renal stent 120 is stitched to an inner fold material 144 of the pleat 140, whereas the upper apex 134 of the upper sealing stent 122 is stitched to an outer fold material 148 of the pleat. As such, pleat material 150 is interposed between the respective lower and upper apexes 132, 134 of the supra renal and upper sealing stent 120, 122. The tether 130 is thread in and out of this pleat 140 as it is extends through the apexes of the supra renal and upper sealing stents. When the endoprosthesis 110 is crimped, the pleat 140 is preferably at least partially unfolded to accommodate stent separation. After expansion of the endoprosthesis, the heat set of the pleat 140 results in at least partial automatic re-gathering of the material into the pleat. The additional graft material at the pleat 140 provides multiple layers of graft material to increase bulk of the graft material at the location thereof and tissue contact thereat. This increased thickness of graft material provides better sealing at a critical location, and such double layer of graft material at the pleat 140 is contacted against the body tissue without any gap (or any significant gap) between the supra renal and upper sealing stents 120, 122.

According to another aspect of the invention, after implantation, the loading on the supra renal and sealing stents 120, 122 is shared between the tether 130 and the stitches 119 that couple the stents to the graft material 118. Such stitches 119 are preferably at or adjacent the apexes of the stents and/or along the struts of the stent. Initially substantially all the downward force of blood flow through the endoprosthesis (particularly as the endoprosthesis narrows into the legs 114, 116) is carried by the tether 130 rather than on the stitches that operate to attach the graft material 118 to the stents 120, 122. Upon being subject to such force, the tether is tensioned and loaded incrementally. If the tether is fully loaded, the pleat 140 in the graft material 118 then absorbs force and may partially unfold. Only thereafter is the stitching 119 supporting the graft material 118 to the stents 120, 122 loaded and subject to force.

The endoprosthesis of the invention has high flexibility because the tether is free to move between the apexes of the stents. Such freedom of motion allows the main body portion of the endoprosthesis to main flexibility across the minimum sealing length.

There have been described and illustrated herein embodiments of an endoluminal prosthesis, particularly suitable for an AAA device. However, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, the tether and pleat may be used on endoluminal prostheses having no branches and/or intended for other purposes. In addition, while shape memory alloys, and preferably Nitinol have been disclosed as preferred materials for use in practicing the invention, it will be understood that other shape memory alloys and other shape set materials including biocompatible plastics may be used as well. Also, while the preferred graft material is the synthetic material polyethylene terephthalate, other graft materials including synthetic and natural materials can be used. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its scope as claimed.

Claims

1. An endoluminal device, comprising: a) a first stent including a first plurality of apexes;b) a discrete second stent including a second plurality of apexes;c) a tether extending through and freely movably relative to said first and second plurality of apexes, wherein when said first and second stents are crimped to a first diameter, slack in said tether permits the first and second stents to be longitudinally displaced to provide a gap therebetween, and wherein when said first and second stents are expanded to a second diameter, said tether draws said first and second stents together to reduce or eliminate said gap.

2. A device according to claim 1, further comprising: tubular graft material, wherein said second stent is coupled to said graft material.

3. A device according to claim 2, wherein: said graft material is provided external said second stent.

4. A device according to claim 2, wherein: said first plurality of apexes of said first stent are coupled to said graft material and said first stent longitudinally extends out of said graft material.

5. A device according to claim 4, wherein: said first stent includes anchors for anchoring said device to body tissue.

6. A device according to claim 5, further comprising: two tubular leg portions, wherein said graft material includes first and second ends, said first stent coupled to said first end of said graft material and said two leg portions coupled to said second end of said graft material so that said device has a Y-configuration.

7. A device according to claim 2, wherein: said graft material defines a pleat at a junction of said first and second stents.

8. A device according to claim 2, wherein: said first and second plurality of apexes are coupled to an interior surface of said graft material.

9. A device according to claim 1, wherein: said first plurality of apexes are arranged about points on a first circle, and said second plurality of apexes are arranged about points on a second circle.

10. An endoluminal prosthesis, comprising: a) a tubular graft comprising a graft material, said graft material including a pleat defining an inner fold material, an outer fold material, and an interposed material between said inner and outer fold materials, said pleat increasing the thickness of said graft material at the location of said pleat;b) a first stent including a first plurality of apexes in contact with said inner fold material; andc) a second stent including a second plurality of apexes in contact with said outer fold material, wherein said pleat can be at least partially unfolded to accommodate stent separation.

11. An endoluminal prosthesis according to claim 10, wherein: said pleat is heat set into said graft material.

12. An endoluminal prosthesis according to claim 10, wherein: said pleat is at an end of said tubular graft.

13. An endoluminal prosthesis according to claim 10, wherein: said second stent is coupled to an interior surface of said tubular graft.

14. An endoluminal prosthesis according to claim 10, wherein: a portion of said first stent is coupled to an interior surface of said tubular graft.

15. An endoluminal prosthesis according to claim 10, further comprising: a tether extending through and freely movably relative to said first and second plurality of apexes, wherein when said first and second stents are crimped to a first diameter slack in said tether permits the first and second stents to be longitudinally displaced to provide a gap therebetween and wherein when said first and second stents are expanded to a second diameter said tether draws said first and second stents together to reduce or eliminate said gap.

16. An endoluminal prosthesis according to claim 15, wherein: said first stent is coupled to said tubular graft at attachment sites and when said prosthesis is loaded by the flow of blood therethrough, the loading on said first stent is shared between said tether and said attachment sites.

17. An endoluminal prosthesis according to claim 16, wherein: said attachment sites are loaded only after said pleat has been longitudinally loaded.

18. An endoluminal prosthesis according to claim 10, further comprising: two tubular leg portions, wherein said tubular graft includes first and second ends, with said first stent coupled to said first end and said two leg portions coupled to said second end so that said prosthesis assumes a Y-configuration.

19. An endoluminal prosthesis, comprising: a) a tubular graft main body comprising a graft material including inner and outer surfaces and first and second ends;b) a first stent coupled at said inner surface of said graft material at said first end and extending out thereof;c) a second stent coupled at said inner surface of said graft material and extending completely therewithin; andd) two tubular leg portions extending from said second end of said main body such that said prosthesis assumes a Y-configuration, wherein said graft material is multiple layers thick at a junction of said first and second stents when said main body portion is in an expanded state.

20. An endoluminal prosthesis according to claim 19, wherein: at said junction, said graft material is folded back on itself lengthwise to be three layers thick when said main body portion is in an expanded state.

21. An endoluminal prosthesis according to claim 19, further comprising: a tether, wherein: said first and second stents include respective sets of apexes which are nearest each other and said tether extends through and is freely movable within said apexes.