Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1998-08-14
2002-02-19
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C606S198000
Reexamination Certificate
active
06348066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an implantable prosthesis. In particular, the invention relates to endoluminal grafts and stent-grafts which are deployed in a blood vessel which has a varying diameter. The invention is particularly suited for repairing the aortic artery and daughter arteries, although it is not limited thereto.
2. State of the Art
An endoluminal stent-graft typically includes tubular graft material which is affixed to the inside or outside of a woven metallic stent and is delivered to the damaged site of a blood vessel via a catheter. Endoluminal stent-grafts are most often used to repair blood vessels affected by a variety of lesions such as stenoses or aneurysms. A typical prior art stent, shown in
FIGS. 1-6
, is a metallic structure
10
made of braided wire
12
such as stainless steel, cobalt-chromium-nickel super alloys and combinations, co-extrusions or braised combinations of the above with tantalum, gold, platinum and the like. Stents are also made from memory alloys such as nitinol and the like. Typical stents are disclosed in U.S. Pat. Nos. 4,655,771 and 4,954,126 to Wallsten, the complete disclosures of which are hereby incorporated herein by reference, and in U.K. Patent Number 1,205,743 to Didcott, the complete disclosure of which is also hereby incorporated herein by reference. Generally, the wires
12
are braided with a large pick size, i.e. with relatively large interstices
14
between the wires, so that axial expansion of the stent causes a diametrical compression of the stent. Most often the braiding and/or the metal chosen for the wires yields a resilient stent which is self-expanding. However, some stents are not self-expanding and are expanded with the use of a balloon catheter. In the case of self-expanding stents, the proximal and distal ends
16
,
18
of the stent are usually flared when expanded.
While endoluminal stents have been used without any graft material when repairing stenoses, it is now generally preferred to use a graft material in combination with the stent when repairing stenoses as well as when repairing aneurysms. The graft material most often used in endoluminal grafts is a PET or polytetrafluroethylene (PTFE) material which is folded to reduce its size and which is attached to one or both ends of a radially expandable stent by means of sutures. When the stent self-expands or is balloon expanded, the graft unfolds around the stent. The above-referenced parent application discloses a stent-graft which incorporates an improved self-expanding graft material.
While the primary use of endoluminal stents is to treat stenoses, stents are also sometimes used in conjunction with graft material to bridge aneurysms. The advantage of using a stent in bridging aneurysms is that the expanded stent helps to fix the graft in place, can eliminate the need for sutures, and may provide some additional resistance to hoop stress. Prior art
FIGS. 2-5
illustrate the deployment of a stent-graft to bridge an aneurysm.
Referring now to
FIGS. 2-5
, the ends of the stent
10
are axially displaced inside an introducer
20
which includes an inner catheter
22
having a soft (dilator) tip
24
and an outer sheath
26
. The introducer
20
is delivered through a blood vessel
28
with the aid of a guide wire
30
which is inserted through the lumen of the inner catheter
22
. The introducer
20
is guided over the guide wire
30
to the site of an aneurysm, in this case two adjacent aneurysms, namely distal aneurysm
32
and proximal aneurysm
34
. With the aid of fluoroscopy, the introducer
20
is positioned so that the soft tip
24
is located distally relative to the distal aneurysm
32
. The outer sheath
26
is drawn proximally while the inner catheter
22
is held stationary. This releases the distal end
18
of the stent
10
which self-expands to the inner diameter of the vessel
28
as shown in FIG.
3
. Continued proximal movement of the outer sheath
26
releases the remainder of the stent
10
as shown in
FIG. 4
until the proximal end
16
of the stent
10
expands to the inner diameter of the vessel
28
proximal of the proximal aneurysm
34
as shown in
FIG. 5
, after which the introducer
20
and the guide wire
30
are removed from the vessel
28
.
From the foregoing, it will be appreciated that by using an appropriately sized stent-graft, the aneurysms
32
,
34
in
FIGS. 2-5
are effectively bridged utilizing the procedure described above. In particular, the stent-graft must be long enough so that its proximal and distal ends extend beyond the aneurysms and expand into healthy areas of the blood vessel. Moreover, the stent-graft must be chosen to have the appropriate expanded diameter so that a good seal is made between the stent-graft and the inner wall of the blood vessel. However, the diameter should not be so large that when the stent expands, the outward pressure of the expanding stent damages the wall of the blood vessel.
Because of the above considerations, it is difficult or impossible to bridge an aneurysm with a stent-graft when the diameter of the blood vessel on either side of the aneurysm differs by any significant amount. For example, as shown in
FIG. 6
, the distal end
18
of a stent-graft
10
is greatly compressed as compared to the proximal end
16
when the stent-graft is used to bridge aneurysms
32
,
34
where the diameter of the vessel
28
on the proximal side
28
a
of the aneurysms
32
,
34
is substantially greater than the diameter of the vessel on the distal side
28
b
of the aneurysms
32
,
34
. Depending on the nature of the particular stent-graft, this can cause damage to the vessel on the distal side
28
b
or can result in an inward tapering of the distal end
18
of the graft to a “cigar shape”. In the former situation, the damage can result in an additional aneurysm or rupture of the vessel. In the latter situation, the distal end
18
of the graft can obstruct the flow of blood, or jeopardize the seal between the distal end
18
and the inner wall of the vessel
28
b.
In the case of obstruction, occlusion of the vessel may occur which can be catastrophic to the patient. In the case of seal weakening, blood will enter into the aneurysmal sac and promote continued growth of the aneurysm.
More often than not the vessels of the vascular tree especially in the abdominal aortic artery exhibit the joining of vessels having very different diameters. For example, as shown in
FIG. 7
, the abdominal aortic artery
50
is the trunk from which the renal arteries, right
52
, left
54
and the iliac arteries, right
56
, left
58
proceed. An aortic aneurysm
60
between the renal arteries and the iliac arteries is very difficult to bridge since the diameter of the aortic artery is approximately 25 mm, whereas the diameter of the iliac artery is about 12 mm. A stent-graft having a diameter of 27 mm will fit well in the aortic artery, but will be too large for the iliac artery. A 13 mm diameter stent-graft will fit well in the iliac artery, but will be too small for the aortic artery.
The above-referenced parent application discloses a bifurcated stent-graft which is useful in repairing an abdominal aortic aneurysm and iliac aneurysm. The bifurcated graft is located in the abdominal aortic artery just above the iliac arteries with its bifurcated end closest to the iliac arteries. The bifurcated stent-graft effectively bypasses an aneurysm in the aortic artery and provides a radiopaque bifurcated guide to the iliac arteries. Once the bifurcated graft is deployed, an additional graft may be deployed in each of the iliac arteries. The additional grafts are deployed through the legs of the bifurcated stent-graft. The bifurcated legs provide separate fluid couplings for the two additional grafts so that blood can flow from the aortic artery to both iliac arteries.
Subsequent to the development of the bifurcated stent-graft of the parent application, additional discoveries have been made regarding the use of multiple stent-grafts to bridge vessels o
Dereume Jean-Pierre
Pinchuk Leonard
Corvita Corporation
Prebilic Paul B.
Ratner & Prestia
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