Stent or graft support structure for treating bifurcated vessels having different diameter portions and methods of use and implantation

A self-expanding stent structure is provided having a main portion that expands to a first diameter and a branch portion that expands to a second diameter, different the first diameter, the main portion having a link portion that forms a flexible linkage to, and forms part of, the branch portion. The self-expanding structure may be compressed to a reduced diameter for delivery, and resumes an expanded diameter during deployment. The self-expanding stent structure also may be advantageously incorporated in an asymmetric stent-graft system. Methods of use are also provided, wherein the main portion of the self-expanding structure, when deployed in a trunk vessel, may be used to anchor the branch portion in a branch vessel.

FIELD OF THE INVENTION 
The present invention relates generally to minimally invasive techniques 
for treating occlusive vascular disease, for example, in the carotid, 
renal, femoral and cerebral arteries, and for repairing aneurysms 
occurring in bifurcated organs or vessels, such as the abdominal aorta. 
BACKGROUND OF THE INVENTION 
In recent years a number of minimally invasive techniques have been 
developed to treat occlusive vascular disease, and to repair aneurysms 
occurring in organs and vessels. 
In occlusive vascular disease, such as arteriosclerosis, plaque accumulates 
within a vessel and gradually narrows the vessel to the degree that the 
vessel can no longer supply an adequate flow of blood. A number of 
vascular prostheses have been developed to re-expand and retain the 
patency of such afflicted vessels, for example, after atherectomy or 
angioplasty. U.S. Pat. No. 4,733,665 to Palmaz describes one type of 
balloon-expandable stent structure to treat occlusive disease. 
It is often desirable to support a tortuous vessel, or one having a 
diameter that changes along the length of the vessel. U.S. Pat. No. 
5,421,955 to Lau et al. describes a stent comprising a series of linked 
sinusoidal rings. That patent describes that the individual sinusoidal 
elements may be differentially expanded to accommodate diameter changes in 
the vessel. 
A drawback of the foregoing previously known devices, however, is that such 
devices are not readily deployable in bifurcated vessels, so that one 
portion of the stent may be deployed in a trunk vessel having a large 
diameter, and a second portion of the stent may be deployed in a branch 
vessel having a much smaller diameter. Moreover, because branch vessels 
often form an angle with trunk vessels, previously known devices cannot be 
readily employed in such environments. 
With respect to treatment of aneurysms, previously known minimally 
techniques generally seek to "re-line" a flow path through the organ, for 
example, by fixing a graft across the weakened tissue of the aneurysm. The 
graft is then held in place with one or more stents, which may be 
implanted, for example, using a balloon catheter. Such arrangements are 
described, for example, in Parodi U.S. Pat. No. 5,219,355, European 
Application No. 0 461 791, and Clouse U.S. Pat. No. 5,211,658. 
A number of techniques also have been developed for deploying graft systems 
in bifurcated anatomy, such as the aorto-iliac bifurcation. For example, 
U.S. Pat. No. 4,562,596 to Kornberg describes a graft comprising a main 
portion having first and second legs extending therefrom. The main portion 
is deployed in the aorta, while the first and second legs are deployed in 
the iliac arteries. U.S. Pat. No. 5,360,443 to Barone et al. and U.S. Pat. 
No. 5,489,295 to Piplani et al. describe similar devices. 
Other bifurcated graft systems, as described in U.S. Pat. Nos. 5,575,817 to 
Martin and 5,609,627 to Goicoechea et al., so called "asymmetric grafts," 
comprise a main portion having a long first leg, and a much shorter second 
leg. The grafts are deployed so that the long leg is disposed in the iliac 
artery used to gain access to the aorta, and so that the short leg does 
not extend into the contralateral iliac artery. In a separate step, an 
extension portion is then attached to the short leg, thus extending the 
second leg into the contralateral artery. 
In view of the foregoing, it would be desirable to provide a stent having 
first and second portions that may be deployed to different expanded 
diameters. 
It would further be desirable to provide a stent capable of being deployed 
in a bifurcated vessel that enables a first portion of the stent to be 
deployed in a trunk vessel having a first longitudinal axis, and a second 
portion of the stent to be deployed in a branch vessel having a second 
longitudinal axis, the second longitudinal axis forming an angle with the 
first longitudinal axis. 
It would be still further desirable to provide a stent structure suitable 
for use as a support element of a bifurcated graft system. 
It would be yet further desirable to provide methods of constructing and 
deploying a stent-graft system that overcome drawbacks of previously known 
stent and stent-graft systems. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide a stent having first and second portions that deploy to different 
expanded diameters. 
It is another object of this invention to provide a stent capable of being 
deployed in a bifurcated vessel, wherein a first portion of the stent is 
deployed in a trunk vessel having a first longitudinal axis, and a second 
portion of the stent is deployed in a branch vessel having a second 
longitudinal axis, the second longitudinal axis forming an angle with the 
first longitudinal axis. 
It is a further object of the present invention to provide a stent 
structure suitable for use as a support element of a bifurcated graft 
system. 
It is a still further object of the present invention to provide methods of 
constructing and deploying a stent-graft system that overcome drawbacks of 
previously known stent and stent-graft systems. 
These and other objects of the invention are accomplished by providing a 
self-expanding stent structure comprising a first portion having a first 
expanded diameter and a second portion having a second expanded diameter. 
The self-expanding stent structure comprises a main portion configured to 
be disposed in a trunk vessel having a first diameter and a branch portion 
configured to be disposed in a branch vessel having a second diameter 
different than the first diameter. A continuous flexible link extends from 
the main portion and forms part of the second portion. The self-expanding 
structure may be compressed to, and constrained at, a reduced diameter for 
delivery, and resumes an expanded shape during deployment. 
In accordance with the principles of the present invention, the stent 
structure also may be used to support a graft to treat aneurysms occurring 
in bifurcated organs or vessels, such as the abdominal aorta. Methods of 
deploying a stent and stent-graft system constructed in accordance with 
the present invention are also provided.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1A and 1B, stent 10 constructed in accordance with the 
principles of the present invention is described. Stent 10 comprises 
self-expanding structure having main portion 20 coupled to branch portion 
22 via flexible link 24. Each of main portion 20 and branch portion 22 are 
formed from a plurality of longitudinal wire segments 26 welded together 
at points of contact 28. Wire segments 26 preferably comprise a resilient 
material, such as a nickel-titanium alloy or stainless steel, and permit 
self-expanding structure 10 to be compressed to a reduced diameter, as 
described hereinafter. 
Flexible link 24 preferably comprises an extension of wire segments 26a and 
26b, and forms a part of main portion 20 and branch portion 22. Flexible 
link 24 permits branch portion 22 to bend out of alignment with 
longitudinal axis L of main portion 20, so that branch portion 22 is 
capable of bending to accommodate an angle at which a branch vessel 
connects to a trunk vessel. 
With respect to FIGS. 2A and 2B, each wire segment 26 comprises 
spaced-apart longitudinal segments 30 and 32 interconnected by connecting 
elements 34. As shown in FIG. 2A, connecting elements 34 are 
non-orthogonal to longitudinal segments 30 and 32 when self-expanding 
stent structure 10 assumes its fully expanded, deployed state (as in FIGS. 
1A and 1B). When a radially compressive load is applied to self-expanding 
structure 10, however, the angle a formed between the connecting elements 
34 and longitudinal segments 30 and 32 becomes more acute, thus reducing 
the circumferential distance between longitudinal segments 30 and 32, as 
depicted in FIG. 2B. Contraction of self-expanding stent structure 10 also 
causes apices 36 formed by the wire segments to move towards one another 
and foreshortens the length of stent 10. 
In accordance with the principles of the present invention, stent 10 may be 
compressed to reduced delivery diameter D.sub.c, depicted in FIG. 3B, 
wherein the diameters of main portion 20 and branch portion 22 are 
approximately equal. Stent 10 is then constrained at that reduced diameter 
for transluminal delivery using a delivery sheath. Once the stent is 
disposed at a desired position in a vessel, the delivery sheath is 
retracted, releasing the constraint. 
Upon release of the constraint imposed by the delivery sheath, the main and 
branch portions of self-expanding stent 10 resume expanded, deployed 
diameters D.sub.E1 and D.sub.E2, as depicted in FIG. 3A. Alternatively, 
the self-expanding stent structure may comprise a martensitic 
nickel-titanium alloy that expands to its deployed state by transitioning 
to the austenite phase upon being exposed to body temperature, as 
described in U.S. Pat. No. 4,503,569 to Dotter. 
Referring to FIGS. 4A and 4B, a method of using stent 10 to treat stenosis 
S in a patient's internal carotid artery ICA is described. In FIG. 4A, 
stent 10 is shown disposed within delivery sheath 40 at its reduced 
delivery diameter D.sub.C. Stent 10 is loaded in delivery sheath 40 so 
that branch portion 22 is located nearer to distal end 42 of the delivery 
sheath. 
Delivery sheath 40 has distal end 42 positioned within internal carotid 
artery ICA so that branch portion 22 is aligned with stenosis S. This may 
be accomplished, for example, by passing delivery sheath 40 in a 
retrograde fashion through a femoral artery, descending aorta A, and into 
common carotid artery CCA in aorta arch AA under fluoroscopic guidance. 
Push tube 44 is disposed within delivery sheath 40 so that its distal end 
abuts against the proximal end of stent 10. 
Once sheath 40 is positioned as shown in FIG. 4A, push tube 44 is held 
stationary while delivery sheath 40 is retracted in the proximal 
direction. As delivery sheath 40 is retracted proximally, first branch 
portion 22 expands to its expanded diameter D.sub.E1, and then main 
portion 20 expands to its expanded diameter D.sub.E2. As shown in FIG. 4B, 
flexible link 24 permits the main portion to the deployed in the common 
carotid artery CCA, which has a longitudinal axis disposed at an angle to 
the longitudinal axis of the internal carotid artery ICA. FIG. 4B also 
depicts second stent 15, constructed in accordance with the present 
invention, deployed with branch portion 15a disposed in subclavian artery 
SCA and main portion 15b anchored in the descending aorta A. 
As will be apparent from FIGS. 4A and 4B, a stent constructed in accordance 
with the present invention, such as stents 10 and 15, enable a first 
portion of the stent to be deployed in a trunk vessel at a first expanded 
diameter, and a second portion of the stent to be disposed in a branch 
vessel at a second expanded diameter, and wherein the axes of the first 
and second portions are not collinear. Consequently, the stent of the 
present invention may be employed in situations where only a short length 
of healthy tissue in the branch vessel is available, by using the main 
portion, deployed in a trunk vessel, to anchor the branch portion in 
place. The stent of the present invention therefore may be advantageously 
employed to treat occlusive disease in a number of other branched vessels, 
such as the femoral arteries and renal arteries. 
With respect to FIG. 5, use of stents 16 and 17 of the present invention in 
the carotid and cerebral arteries is described. Stents 16 and 17 are 
miniature versions of the stent of FIGS. 1A and 1B. In FIG. 5, stent 16 is 
disposed with branch portion 16a disposed in middle cerebral artery MCA 
just distal of the left anterior cerebral artery ACA, while main portion 
16b is disposed in left internal carotid artery LICA. Stent 17 is shown 
disposed with branch portion 17a disposed in a first branch of the middle 
cerebral artery B.sub.1 just distal of bifurcation of the middle cerebral 
artery BMCA, while main portion 17b is disposed in trunk of the middle 
cerebral artery MCA. 
Referring now to FIG. 6, stent-graft system 50 constructed in accordance 
with the present invention is described. Biocompatible graft material 52 
is affixed to, and supported by, self-expanding stent structure 10 of 
FIGS. 1A and 1B (the details of structure 10 are omitted from FIG. 6 for 
clarity). Graft material 52 may be affixed to either the interior or 
exterior of structure 10, using, for example, biocompatible sutures. 
Stent-graft system 50 includes main portion 54 covering main portion 20, 
branch portion 56 covering branch portion 22, and cuff 58 for accepting 
covered stent 60. 
Covered stent 60 may be constructed, for example, as described in allowed 
U.S. patent application Ser. No. 08/820,213 to Khosravi et al., which is 
incorporated herein by reference, and may comprise a coiled sheet stent, 
such as described in U.S. Pat. No. 5,443,500 to Sigwart, having graft 
material affixed to its outer surface. 
Graft material 52 preferably is a polyester fabric, such as DACRON.RTM., a 
registered trademark of the E.I. duPont de Nemours Company, Wilmington, or 
other biocompatible material, such as PTFE (polytetrafluoroethylene). One 
familiar with the art of graft technology will recognize that other 
suitable materials also may be used for graft 14. 
Referring to FIGS. 7A to 7C, deployment of graft 50 in abdominal aorta A to 
reline aorto-iliac bifurcation AIB having aneurysm AN in accordance with 
the methods of the present invention is described. In FIG. 7A, graft 50 is 
shown constrained to its reduced delivery diameter D.sub.c and contained 
within delivery sheath 65. Delivery sheath 65 is inserted along pre-placed 
guide wire 70 via a surgical cut-down in a femoral artery. Delivery sheath 
65 is then advanced through iliac artery I.sub.1 and into abdominal aorta 
A, so that graft 50 is disposed with main portion 54 in the aorta and 
branch portion 56 in iliac artery I.sub.1. Proper orientation of graft 50 
within aorta A may be determined, for example, using radio-opaque bands 
disposed on the graft or delivery sheath that are visible under a 
fluoroscope. 
Push tube 66 is held stationary and abuts against a proximal end of graft 
50 while delivery sheath 65 is withdrawn proximally. As delivery sheath 65 
is withdrawn, main portion 20 of self-expanding structure 10 expands to 
its deployed diameter D.sub.E1 into contact with the walls of aorta A, so 
that cuff 58 is aligned with iliac artery I.sub.2. As the delivery sheath 
is further withdrawn, branch portion 22 expands branch portion 56 of graft 
50 into contact with iliac artery I.sub.1. Delivery sheath 65 is then 
removed, leaving graft 50 in the state shown in FIG. 7B. Guide wire 75 is 
then inserted via the contralateral femoral artery, and advanced through 
iliac artery I.sub.2 so that the tip of guide wire 75 passes upward 
through cuff 58. 
A previously known delivery system containing a covered stent, such as 
described in allowed U.S. patent application Ser. No. 08/820,213 is then 
advanced along guide wire 75, and covered stent 60 is deployed with one 
end in cuff 58 and the other end extending into iliac artery I.sub.2, 
completing assembly of the stent graft system. Guide wire 75 is then 
retracted from the patient. 
The foregoing description of the present invention describes treating 
occlusive disease in the carotid, renal, femoral and cerebral arteries, 
and for excluding aneurysms occurring in the abdominal aorta. It should be 
understood, however, the methods and apparatus of the present invention 
are equally applicable elsewhere in the human body where it is desired to 
repair a birfucated vessel or organ, or "reline" a hollow-body organ or 
vessel. 
While preferred illustrative embodiments of the present invention are 
described above, it will be obvious to one skilled in the art that various 
changes and modifications may be made therein without departing from the 
invention and it is intended in the appended claims to cover all such 
changes and modifications which fall within the true spirit and scope of 
the invention.