U.S. patent application number 12/703930 was filed with the patent office on 2010-06-10 for kink resistant bifurcated prosthesis.
Invention is credited to Randy S. Chan, Lilip Lau, Troy Thornton.
Application Number | 20100145434 12/703930 |
Document ID | / |
Family ID | 25094851 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100145434 |
Kind Code |
A1 |
Thornton; Troy ; et
al. |
June 10, 2010 |
KINK RESISTANT BIFURCATED PROSTHESIS
Abstract
The invention relates to an endoluminal prosthesis adapted for
placement at a bifurcation site within the body. The stent or
stent-graft may be constructed to have segments of differing
structural properties. A section of the stent-graft may be
constructed to have a single-lumen tubular stent member covering a
multilumen graft member. The stent-graft may comprise at least two
modular components adapted for in situ assembly. An extended
cylindrical interference fit may be used to seal the modular
components.
Inventors: |
Thornton; Troy; (San
Francisco, CA) ; Chan; Randy S.; (San Jose, CA)
; Lau; Lilip; (Sunnyvale, CA) |
Correspondence
Address: |
GORE ENTERPRISE HOLDINGS, INC.
551 PAPER MILL ROAD, P. O. BOX 9206
NEWARK
DE
19714-9206
US
|
Family ID: |
25094851 |
Appl. No.: |
12/703930 |
Filed: |
February 11, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10184989 |
Jul 1, 2002 |
7682380 |
|
|
12703930 |
|
|
|
|
08772372 |
Dec 23, 1996 |
6551350 |
|
|
10184989 |
|
|
|
|
Current U.S.
Class: |
623/1.16 ;
623/1.35 |
Current CPC
Class: |
A61F 2/06 20130101; A61F
2250/0098 20130101; A61F 2/07 20130101; A61F 2002/075 20130101;
A61F 2/89 20130101; A61F 2002/9586 20130101; A61F 2250/0039
20130101; A61F 2/91 20130101; A61F 2002/067 20130101 |
Class at
Publication: |
623/1.16 ;
623/1.35 |
International
Class: |
A61F 2/82 20060101
A61F002/82 |
Claims
1. An implantable endoluminal prosthesis adapted for placement at a
bifurcation site within a body, said device having at least two
segments, at least one of said segments having structural
properties different from another of said segments.
2. The endoluminal prosthesis of claim 1 wherein said device
comprises a main body component and a contralateral leg
component.
3. The endoluminal prosthesis of claim 1 wherein at least one of
said components has a segment having an axial stiffness that is
higher than adjacent segments.
4. The endoluminal prosthesis of claim 3 wherein said segment of
higher axial stiffness comprises at least one extended strut.
5. A stent section comprising a wire structure having undulations,
said undulations characterized by an alternating series of upper
apexes and lower apexes, said wire structure arranged in a helical
configuration having at least a first turn and a second turn, said
first turn having at least one lower apex which extends to
substantially meet a lower apex of said second turn.
6. The stent section of 5 wherein said upper and lower apexes of
said of said first turn are in-phase with said apexes of said
second turn.
7. The stent section of 5 wherein said stent section comprises
multiple turns, each one of said multiple turns having at least one
lower apex which extends to substantially meet a lower apex of an
adjacent turn.
8. The stent section of 7 wherein the extended apex of each turn is
spaced one undulation from the extended apex of a successive
turn.
9. A modular prosthesis adapted for placement at a bifurcation site
within a body, said prosthesis comprising: a main body component
having an extended cylindrical female receiving portion; and a leg
component having a mating cylindrical male portion, adapted for
attachment to said extended cylindrical female receiving
portion.
10. The modular prosthesis of claim 9 wherein said male portion is
attached within said female portion by an interference fit.
11. The modular prosthesis of claim 10 wherein cylindrical male
portion has a first diameter and said cylindrical female portion
has a diameter smaller than said first diameter.
12. The modular prosthesis of claim 10 wherein said female
receiving portion further comprises a zone of decreased diameter in
the vicinity of an anchoring ring, said anchoring ring being
attached to said female receiving portion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/184,989 filed Jul. 1, 2002, which is a continuation of U.S.
application Ser. No. 08/772,372 filed Dec. 23, 1996, now U.S. Pat.
No. 6,551,350 issued Apr. 22, 2003.
TECHNICAL FIELD
[0002] This invention relates generally to implants for repairing
ducts and passageways in a body. More specifically this invention
relates to an implant adapted for delivery to and repair of a
bifurcation site within the body. In one aspect, this invention
involves a modular, kink-resistant, bifurcated stent-graft
device.
BACKGROUND ART
[0003] Treatment or isolation of vascular aneurysms or of vessel
walls which have been thickened by disease has traditionally been
performed via surgical bypassing with vascular grafts. Shortcomings
of this invasive procedure include the morbidity and mortality
associated with major surgery, long patient recovery times, and the
high incidence of repeat intervention needed due to limitations of
the graft or of the procedure.
[0004] Minimally invasive alternatives involving stents or
stent-grafts are generally known and widely used in certain types
of treatments. Intralumenal stents, for example, are particularly
useful for treatment of vascular or arterial occlusion or stenosis
typically associated with vessels thickened by disease.
Intralumenal stents function to mechanically hold these vessels
open. In some instances, stents may be used subsequent to or as an
adjunct to a balloon angioplasty procedure.
[0005] Stent-grafts, which include a graft layer either inside or
outside of a stent structure, are particularly useful for the
treatment of aneurysms. An aneurysm may be characterized as a sac
formed by the dilatation of the wall or an artery, vein, or vessel.
Typically the aneurysm is filled with fluid or clotted blood. The
stent-graft provides a graft layer to reestablish a flow lumen
through the aneurysm as well as a stent structure to support the
graft and to resist occlusion or restenosis.
[0006] Treatment of a bifurcation site afflicted with such defects
as an occlusion, stenosis, or aneurysm is a particularly demanding
application for either stents or stent-grafts. A bifurcation site
is generally where a single lumen or artery (often called the
trunk) splits into two lumen or arteries (often called branches),
such as in a "Y" configuration. For example, one such bifurcation
site is found within the human body at the location where the
abdominal aortic artery branches into the left and right (or
ipsilateral and contralateral) iliac arteries.
[0007] When a defect, such as an aneurysm, is located very close to
the bifurcation of a trunk lumen into two branch lumens, treatment
becomes especially difficult. One reason for this difficulty is
because neither the trunk lumen nor either of the branch lumens
provides a sufficient portion of healthy, lumen wall on both sides
of the defect to which a straight section of single lumen stent or
stent-graft can be secured. The stent or stent-graft must span the
bifurcation site and yet allow undisturbed flow through each of the
branch and trunk lumens.
[0008] What is required then is a stent or stent-graft which may be
secured to each of the lumen wall a sufficient distance away from
the defect and yet is capable of allowing undisturbed flow into
each of the branch and trunk lumen. Such a configuration, at least
after implantation, generally must have the same Y-shape as
described for the bifurcation site. Prior to implantation, the
stent or stent-graft may have a Y-shape or may have a modular
construction which is assembled into the desired shape as it is
implanted.
[0009] As we shall see, deployment of implants adapted to meet
these needs is also problematic in that they must be deployed and
secured in three different lumen which are impossible to access
from a single direction. Further, to facilitate intralumenal
delivery through a body's tortuous vasculature, the implant must be
capable of being compressed into a very small diameter or
profile.
[0010] Prior devices that deal with treatment at a bifurcation site
within the body generally include grafts, stents, and stent-grafts
in either a single-piece or modular configuration as described
below.
[0011] The use of tubular grafts for treating defects at
bifurcation sites has been known for some time. Bifurcated grafts
have been disclosed, for example, in U.S. Pat. Nos. 3,029,819 to
Starks, 3,096,560 to Liebig, 3,142,067 to Liebig, and 3,805,301 to
Liebig. These grafts are typically made of woven fabric or other
synthetic material and, because they have no supporting stent
structure, typically involve excising the defected segment and
suturing the fabric graft in place using common surgical
procedures.
[0012] A number of bifurcated graft implants have been developed
which use some limited means of supporting the one-piece bifurcated
graft structure. Typically such means also provide a way to hold
the graft open and secure the graft to the lumen wall without the
need for sutures so that the graft may be suitable for translumenal
delivery via a remote site as opposed to the more invasive surgical
grafting techniques as described above.
[0013] One such implant is disclosed in U.S. Pat. No. 4,562,596 to
Kornberg. Kornberg discloses a bifurcated aortic graft constructed
for intraluminal delivery through the femoral artery. The graft
consists of a tubular graft material having a plurality of
longitudinal supporting struts or stays equipped with hooks or
barbs to facilitate attachment within the desired location of the
damaged artery. The graft is equipped with a resilient top ring for
snugging the upper end of the trunk portion against the aortic wall
upon deployment. The graft has a trunk portion and two legs, one of
which is shorter than the other. The graft is delivered in a
compressed state through a first branch artery with the shorter leg
folded against the longer. At some point, as the compressed implant
is advance through the first branch artery, the shorter leg clears
the bifurcation point and articulates into the luminal region of a
second branch artery. The entire implant is then moved in the
reverse direction to allow the shorter leg to progress down the
second branch. The implant is then expanded to its final shape
against the lumen walls by way of a balloon.
[0014] Instead of longitudinal struts, other devices have provided
the necessary support and securing means for the graft material by
employing sections of stent structure at selected locations along
the graft. Typically, stent rings may be placed at the trunk and/or
branch openings of the stent. Such stent rings are either
self-expanding or require balloon expansion.
[0015] U.S. Pat. No. 5,489,295 to Piplani et al., for example,
discloses a bifurcated graft having a main body and legs formed of
a flexible surgically implantable material. Expandable spring
attachments are secured to the main body adjacent to the trunk
opening and also to one of the legs adjacent to the branch leg
opening. Delivered compressed, these expandable spring attachments
urge the openings of the graft open upon deployment and serve as
anchoring means for securing the graft to the vessel wall. Lumen
wall engagement may be enhanced by the addition of barbs or hooks
at the apices of the spring attachments.
[0016] Another device involving a single-piece bifurcated graft
with limited supporting and securing means is disclosed in U.S.
Pat. Nos. 5,360,443 and 5,522,880 both to Barone et al. Barone et
al. disclose a tubular aortic graft for intraluminal delivery. The
graft is secured by the expansion and deformation of a thin-walled
tubular member. The thin walled tubular member has a first diameter
for delivery. Upon the application of an expanding force from a
balloon, the member has a second expanded and deformed diameter for
securing the graft to the lumen wall.
[0017] As with all such one-piece devices, the delivery of the
graft implant is complicated by the fact that each of the trunk and
two legs of the graft must be positioned into their respective
lumen and then secured into place. This requires the branch legs to
be compressed together for delivery through one of the lumen and
requires difficult maneuvering of the branch legs to get them
unfolded and untwisted into place within their respective branch
lumen. This type of delivery requires the graft sections to be
highly flexible so that its components may be manipulated as
required and requires a larger profile. This demand for high
flexibility often results in unsupported graft sections that may be
subject to kinking, folding, collapse or the like.
[0018] Bifurcated stent devices generally suffer from even greater
delivery problems because they are even less compressible and less
flexible than their unsupported graft counterparts discussed above.
U.S. Pat. No. 4,994,071 to MacGregor, for example, discloses a
single-piece bifurcated stent for insertion into a bifurcating
vessel. The stent includes a trunk portion constructed from a
series of generally parallel loops interconnected by a sequence of
half-hitch connections which extend along its length. The parallel
loops form a cylindrical lattice which define a flow passageway.
Two smaller cylindrical lattices are similarly constructed and
attached to the trunk portion to form the branch flow passageways.
The stent is designed to be delivered in one piece, over two
guidewires (one for each branch) from the direction of the trunk
vessel.
[0019] Another bifurcated stent example is found in U.S. Pat. No.
5,342,387 to Summers. Summers discloses a Y-shaped bifurcated stent
comprising three coil sections (a major coil section and two minor
coil sections), constructed of stent wire according to specific
coil patterns and joined so as to form an unobstructed support for
the trunk and branched vessels. To deploy the bifurcated stent, the
stent is compressed around an inflatable bifurcated balloon. The
compressed balloon/stent is delivered up one of the branch vessels
until one of the minor coils is clear of the bifurcation juncture.
Then the stent is backed down, positioning one of the minor coils
in each of the branches. The stent is then expanded by the
bifurcated "tri-wing" balloon and then the balloon is removed.
[0020] To alleviate these complicated delivery problems, some
implant devices have used a modular approach. An example of a
modular stent may be found in FR 2,678,508 A1. According to that
disclosure, in order to provide continuity at junctions, in
particular at vessel bifurcations, at least two helicoidal spring
elements comprised of self locking coils are used. A first element
is constructed to have a first coil diameter section corresponding
to the diameter of the aortic artery and a second coil diameter
section corresponding to one of the iliac arteries. A second
element similarly has two sections, one of which corresponds to the
diameter of the second iliac artery, the other equivalent to the
diameter of the aortic section of the first element so that the
corresponding coils of each element may be delivered separately and
locked together in situ.
[0021] Another type of modular approach involves using two separate
elongated tubes delivered through each of the branch lumen. The
tubes, which may consist of a tubular graft element supported by
unconnected stent segments, establish the required flow lumen in
each of the branch arteries, and in the trunk lumen, are forced
together in such a manner as to substantially seal around the
periphery. Generally, the shape of the two tubes in the trunk lumen
is that of two back-to-back, semi-circular "D" shapes. U.S. Pat.
No. 5,507,769 to Marin et al and EP 0 551,179 A1 to Palmaz et al.
disclose implants of the type which employ two separate tubes.
Palmaz further discloses the use of an expandable tubular member
which is secured to the trunk artery prior to delivery of the
separate tubes. The purpose of this additional member is to help
secure the two tubes to the trunk lumen.
[0022] Still another type of modular stent-graft device is
disclosed in WO 95/21592 (International Application number
PCT/US95/01466. In that publication, there is disclosed a modular
bifurcated stent or stent-graft comprising two separate modules for
delivery in a compressed state and connected together in situ. A
first module has a proximal part adapted to engage the trunk
artery, then bifurcating into a first distal portion adapted to
extend into one branched artery and a female receiving opening to
be positioned near the other branched artery. A male proximal
portion of a second module is connected to the female receiving
opening. According to the disclosure, to ensure the two modules
remain connected, it is preferred that the receiving opening has a
frustoconical section and the second module has a mating male
frustoconical section.
[0023] Further related modular stent-graft approaches may be found
for example in EP 0 686 379 A2, EP 0 696 447 A2, and U.S. Pat. No.
5,562,724 to Vorwerk et al. While these modular devices tend to
offer a measure of improved delivery, continuing problems may
include a certain amount of leakage around the openings of the
device, leakage at the modular connection, increased compressed
profiles, and not optimized flexibility, kink-resistance, and axial
stiffness.
[0024] Further it is generally important for any stent or
stent-graft to be accurately and quickly deployed so that it may be
properly positioned at a desired treatment location. This is
especially true with bifurcated devices using a modular approach
because, when deployed, the connecting feature must be properly
aligned rotationally over a branch artery.
[0025] From the foregoing discussion it is evident that it would be
desirable to have a self-expanding stent-graft device possessing
superior kink-resistance and flexibility to allow the device to
follow the natural geometry of the vasculature and, at the same
time, allow for sufficient axial stiffness to facilitate accurate
placement, resist movement, and prevent leakage. It would be highly
desirable to have such a stent or stent-graft device that also
provides for a reduced compressed profile for delivery through the
body's vasculature. It would be highly desirable for such a stent
or stent-graft to have the capability to ensure axial and
rotational alignment.
DISCLOSURE OF THE INVENTION
[0026] The present invention is an endoluminal prosthesis that
avoids the problems and disadvantages of the prior art. The
invention generally involves a construction which can be adapted
for placement at a bifurcation site within a mammalian body. In one
embodiment, the prosthesis is a bifurcated stent or
stent-graft.
[0027] In another embodiment an inventive stent-graft construction
may provide for at least two segments of the stent-graft to have
different structural properties from each other. The structural
properties may include flexibility and axial stiffness. With such a
construction, it is possible to optimize the performance
characteristics for ideal delivery and at the same time enhance the
device's kink resistance, its ability to maintain its deployed
position, and its conformability (which is helpful to effectuate
required sealing against the vessel wall). In a preferred
embodiment, the axial stiffness is varied according to the presence
or absence of extended strut features or the use of a tape member
of varying thickness or width.
[0028] According to another embodiment of the present invention,
the bifurcated stent-graft may be constructed to have a region of
single lumen stent covering a multilumen graft. This construction
provides for a reduced delivery profile and simplified
manufacturing. In one aspect of the present invention, the stent
construction is configured to cover a larger portion of periphery
of the bifurcated graft.
[0029] Another embodiment of the present invention involves a
modular stent-graft. A preferred embodiment includes an extended
region of cylindrical overlap between the modular components to
effectuate improved sealing between the components. In a preferred
embodiment the modular components in the area of the cylindrical
overlap are constructed to have a diametrical interference fit. In
alternate embodiments, sealing is enhanced by the addition of an
anchoring ring, a flap of graft material, or both. Certain sealing
defects may be further avoided by the use of a scalloping
construction graft material around the end openings of the
stent-graft.
[0030] In yet a further embodiment, the present invention involves
a method of forming a bifurcated graft member comprising the steps
of heat boding a first tube section to a second tube section such
that a common septum is formed and then removing the septum to form
a smooth bifurcation.
[0031] Another embodiment of the present invention involves a
prosthesis anchor for securing the prosthesis to the lumen wall.
The anchor may involve a pivotably coupled wire portion extending
angularly from the surface of the prosthesis. In one aspect of the
inventive anchor, the anchor further has a second wire portion in
angular relation to the surface of the prosthesis such that
displacement of the second wire toward the surface urges said first
wire away from the surface and into the lumen wall.
[0032] The above is a brief description of some deficiencies in the
prior art and advantages of the present invention. Other features,
advantages, and embodiments of the invention will be apparent to
those skilled in the art from the following description,
accompanying drawings, and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a perspective view of a mammalian implant that is
restrained in a collapsed state.
[0034] FIG. 2 is an end view of the restrained implant of FIG.
1.
[0035] FIG. 3 is a perspective view of the assembly of FIG. 1 with
the restraint released and the implant in an expanded state.
[0036] FIG. 4A is an end view of the assembly of FIG. 3.
[0037] FIG. 4B is a bottom plan view of the restraining member of
FIG. 4A.
[0038] FIG. 5A shows a restraining member retraction mechanism
where the mechanism is in an unactuated state.
[0039] FIG. 5B shows the mechanism of FIG. 5A in an actuated
state.
[0040] FIG. 5C shows an alternate construction of a retraining
member retraction mechanism where the mechanism is in an unactuated
state.
[0041] FIG. 5D shows the mechanism of FIG. 5C in an actuated
state.
[0042] FIG. 6A is a perspective view of another embodiment of the
implant in conjunction with the restraining member of FIG. 1.
[0043] FIG. 6B is a perspective view of a further embodiment of the
implant in conjunction with the restraining member of FIG. 1.
[0044] FIG. 7A illustrates the restraining and coupling member of
FIG. 1 and the pull direction for removing the coupling member from
the restraining member.
[0045] FIG. 7B shows the assembly of FIG. 7A with the coupling
member loosened to illustrate the chain knots.
[0046] FIG. 7C diagrammatically represents release of the assembly
of FIG. 7A or 7B as the coupling member is pulled in the direction
shown.
[0047] FIGS. 8A, 8B, 8C, 8D, 8E and 8F diagrammatically show a
procedure for loading an expandable stent-graft into a restraining
member prior to endolumenal delivery.
[0048] FIG. 9A diagrammatically shows delivering a restrained
implant to a desired site in a mammalian body lumen with the
coupling member configured as shown in FIGS. 7A-7C.
[0049] FIG. 9B is a sectional view of FIG. 9A taken along line
9B-9B.
[0050] FIG. 9C shows an alternate multiple restraining member
arrangement for that shown in FIG. 9A.
[0051] FIG. 10A diagrammatically shows partial deployment of the
implant assembly illustrated in FIG. 9A showing progressive
expansion in a direction away from the distal end of the
illustrated guidewire (i.e., toward the illustrated hub).
[0052] FIG. 10B is a sectional view of FIG. 10A taken along line
10B-10B.
[0053] FIG. 11A diagrammatically shows full deployment of the
implant assembly illustrated in FIG. 9A.
[0054] FIG. 11B is a sectional view of FIG. 11A taken along the
line 11B-11B.
[0055] FIGS. 12A, 12B, 12C and 12D diagrammatically show deployment
of a restrained implant where the coupling member configuration
provides release from the middle portion of the implant outward
toward the implant ends.
[0056] FIG. 13 illustrates one coupling member configuration for
deployment as shown in FIGS. 12A-12D.
[0057] FIG. 14A is a perspective view of a bifurcated stent-graft
in accordance with the principles of the present invention.
[0058] FIG. 14B is a top plan view of the bifurcated stent-graft of
FIG. 14A.
[0059] FIG. 14C is a cross-section view taken along section line
14C-14C depicted in FIG. 14A.
[0060] FIG. 14D is a cross-sectional view taken along section line
14D-14D depicted in FIG. 14A showing an alternate embodiment.
[0061] FIG. 15 is a front view of the assembled bifurcated
stent-graft of FIG. 14A placed at a bifurcation site within the
vasculature of a body.
[0062] FIG. 16 is a perspective break-away view showing a close-up
of one construction of stent anchors according to the present
invention.
[0063] FIG. 17 is a perspective break-away view showing a close-up
of a preferred construction of the stent anchors.
[0064] FIG. 18 is a cross-sectional view of the stent-graft of FIG.
14B taken along section line 18-18.
[0065] FIG. 19 is a cross-sectional view of the stent-graft of FIG.
14A taken along section line 19-19.
[0066] FIG. 20 is an enlarged partial cross-sectional view of an
alternative contralateral leg connection depicted in FIG. 19.
[0067] FIG. 21 and FIG. 22 are enlarged partial cross-sectional
views of more alternative constructions of the receiving lumen.
[0068] FIG. 23 is a partial perspective view of an alternate
scalloped construction of the proximal region of the contralateral
leg component.
[0069] FIGS. 24A and 24B are cross-sectional views taken along
section line 24A-24A as shown in FIG. 14A depicting a free state
and a forced state respectively.
[0070] FIGS. 25A and 25B are cross-sectional views taken along
section line 25A-25A as shown in FIG. 23 depicting a free state and
a forced state respectively.
[0071] FIG. 26A is a front view of graft components prior to
assembly.
[0072] FIGS. 26B and 26C are respectively the front view and top
view of the assembled graft of FIG. 26A.
[0073] FIG. 27A is a front view of the unassembled components of an
alternate construction of the graft element.
[0074] FIG. 27B is a front view of the assembled graft element
according to the alternative construction of FIG. 27A.
[0075] FIGS. 28A, 28B, 28C, 28D, and 28E diagrammatically show
deployment of a bifurcated stent-graft.
[0076] FIGS. 29A, 29B, 29C, and 29D diagrammatically show
deployment of a bifurcated stent-graft using an alternate delivery
system.
DETAILED DESCRIPTION
[0077] The following disclosure relating to the present invention
will use certain nomenclature as set forth below. The term distal,
as hereinafter used, is meant to refer to locations that are
furthest away from the catheter delivery hub. Proximal is meant to
refer to locations that are closer to the catheter delivery
hub.
[0078] Referring to the drawings in detail wherein like numerals
indicate like elements, the present invention generally involves
bifurcated implants such as stents or stent-grafts for delivery to
a desired site through a body's vasculature. This may involve
delivery systems that can be used in conjunction with such
implants. As this invention involves both bifurcated components as
well as non-bifurcated components, it is worthwhile to begin by
describing in detail the general prosthesis construction and
preferred manner of deployment that is applicable to both straight
and bifurcated stents or stent-grafts in accordance with FIGS.
1-13. The bifurcated prosthesis will be described with relation to
FIGS. 14-28.
[0079] Although the invention will be described with reference to
the delivery examples illustrated in the drawings, it should be
understood that it can be used in conjunction with other delivery
devices having constructions different than those shown.
[0080] For illustrative purposes, this invention will be described
with reference to the location in the human body where the
abdominal aorta bifurcates into the left and right (or ipsilateral
and contralateral) iliac arteries. It should be understood,
however, that the present invention may be used at many other
locations within the body.
[0081] Referring to FIGS. 1 through 13, delivery systems for
delivering implants or devices, such as stents or stent-grafts, to
a desired site in mammalian vasculature are shown. Such delivery
systems generally include a restraining member that is adapted and
configured for surrounding at least a portion of a collapsed or
compressed implant and a coupling member(s) for releasably coupling
portions of the restraining member to one another to maintain the
implant in its collapsed or compressed state.
[0082] Referring to FIGS. 1-4, an implant delivery system is shown.
Delivery system (100), generally includes a restraining member
(102), which as shown may be in the form of a sheet of material,
and a coupling member (104) for releasably coupling portions of the
restraining member to one another. The restraining member portions
that are coupled may differ than those illustrated, but preferably
are selected to maintain the implant, such as self-expanding
stent-graft (106), in a collapsed or compressed state as shown in
FIGS. 1 and 2 where the restraining member (102) is shown in the
form of a tube. In the illustrative embodiment, the coupling member
(104) is shown as a filament or thread-like element which prevents
the restraining member (102) from rearranging to a configuration
where the stent-graft (106) could expand to its expanded state.
[0083] The implant may be collapsed in any suitable manner for
placement within the restraining member (102). For example, the
implant may be folded or radially crushed before placement within
the restraining member (102) as will be described in more detail
below. As shown in FIGS. 9-11, a delivery assembly (108), which
includes the restraining member (102) and the stent-graft (106),
has relatively small cross-sectional dimensions which facilitate
endolumenal delivery of the assembly to a site where the natural
lumen diameter may be smaller than the expanded diameter of the
stent-graft (106).
[0084] Referring to FIGS. 3 and 4A, the assembly (108) is shown in
a deployed state after removal of the coupling member (104). The
restraining member (102) may be fixedly secured to the stent-graft
(106) so that the two components remain attached after expansion at
the desired deployment site. The attachment between the restraining
member and the implant preferably is made to prevent significant
movement between the restraining member and stent-graft after
deployment which could disrupt endovascular fluid flow. Referring
to FIGS. 4A and 4B multiple sutures (110) may be used to fixedly
attach the restraining member (102) to the stent-graft (106). More
specifically, the sutures can form loops that pass through the
restraining member and around portions of the stent as shown in
FIG. 4A. It is further noted that although one arrangement of the
sutures (110) is shown in FIG. 4B other arrangements may be
used.
[0085] Although other configurations of the restraining member
(102) can be used, a preferred configuration is a generally
rectangular one having constant width as shown in FIG. 4B. For
example, in the case where the restraining member is used in
conjunction with a modular bifurcated stent as will be described
below, the restraining member may have a similar rectangular
configuration as that shown in FIG. 4B. Alternatively, it may have
two differently sized rectangular portions arranged to mate with
the regions of different diameter (trunk and leg) or another
configuration that would maintain the implant in a collapsed stent
when secured. Returning to FIG. 4B, the restraining member may be
described as having side margins (112) that extend between the ends
(114) of the member. Eyelets (116) are disposed along the side
margins so that the coupling member (104) may be laced or threaded
therethrough. The eyelets may be in the form of through holes
(118), which may be formed by a uniform-diameter puncturing device
or by other means such as laser-drilling. Alternatively, the
eyelets may be formed by loops (120) which may be attached to the
side margins (112) or formed by other means as would be apparent to
one of ordinary skill in the art.
[0086] It is further desirable to have structural reinforcement at
the side margins (112) to minimize or eliminate the possibility of
the coupling member (104) from tearing the restraining member (102)
when under load. Reinforced side margins may be formed by folding a
portion of the restraining member (102) over a reinforcement member
(122), such as a small diameter suture, which may be heat bonded
between the two layers of sheet material. With this construction, a
relatively low profile bead of material along the side margins
(112) prevents or minimizes the possibility of tear propagation
and, thus, accidental uncoupling of the restraining member (102).
The small diameter suture (122) may comprise ePTFE, for
example.
[0087] As the restraining member (102) constrains a collapsed
self-expanding stent-graft, for example, forces resulting from
stored spring energy in the collapsed stent-graft (106) will be
acting on the restraining member (102) when it is configured for
delivery. Thus, the restraining member (102) may comprise a
material which is creep resistant and can withstand required loads
without stretching over time. The restraining member (102) may
comprise, for example, ePTFE, which is believed to provide suitable
creep resistance, flexibility, and biocompatibility in a thin sheet
form which can be heat bonded. Other materials also may be used
including polyethers such as polyethylene terephthalate
(DACRON.RTM. or MYLAR.RTM.) or polyaramids such as KEVLAR.RTM..
[0088] The thread-like coupling member (104) may also comprise
ePTFE. Sutures of polyethers such as polyethylene terephthalate
(DACRON.RTM. or MYLAR.RTM. or polyaramids such as KEVLAR.RTM. or
metal wire comprising nitinol, stainless steel or gold may also be
used for the coupling member (104). The coupling member (104) may
simply extend to form a remote pull line as will be discussed
below. Alternatively, a metallic pull line, such as one comprising
stainless steel may be coupled to a nonmetallic coupling member
(104) such as one comprising ePTFE. The coupling may be made by
folding the end of the metallic pull line back upon itself to form
an eyelet and threading the coupling member therethrough and
securing it to the eyelet with a knot.
[0089] It is further noted that the width of the restraining
member, when in a flat orientation as shown in FIG. 4A, preferably
is less than the diameter of the implant. Typically the restraining
member width will be less than about 40 mm (typically about 25-40
mm when the device is sized for thoracic aorta applications), and
typically less than about 15 mm in other applications where the
lumen is smaller. The sheet of material preferably has a thickness
less than 0.010 inch (0.254 mm) and more preferably less than 0.005
inch (0.127 mm). In addition, the length of the restraining member
preferably is less than or equal to that of the implant.
[0090] Additionally, a retraction assembly may be provided to
retract the restraining member during expansion of the implant, so
that the length of the restraining member is maintained to be about
equal to or less than that of the implant. The expandable portion
of the implant may undergo minor amounts of shortening along the
axial direction due to the expansion thereof in the radial
direction, which may lead to an overlap of the restraining member
at the ends of the implant, but for the use of some type of
retraction assembly in these situations. The retraction assembly
minimizes or eliminates the risk of the restraining member
extending beyond the implant and interfering with any channel
formed by the implant, or any fluid flowing therethrough after
expansion.
[0091] Referring to FIGS. 5A-5D, retraction assemblies or
mechanisms are shown. In FIG. 5A, a retraction assembly (340) is
shown including a biocompatible filament (342), which includes a
portion that is stitched, tied or otherwise fixed to the
restraining member (102), as shown at an attachment point (348),
adjacent to one end of the restraining member. Filament (342) is
passed underneath the members forming the first or end helical turn
of the stent (126) and looped under or otherwise slidably secured
to a portion of the second, third or another helical turn other
than the first helical turn such as an apex or bend portion (344)
in a second turn. The other end portion of filament (342) is
further fixed, by tying or other means, to a portion of the stent
that is circumferentially spaced from the attachment point (348) or
the apex or bend portion (344), for example, such as an apex or
bend portion (346) of the same helical turn. Preferably, the
filament (342) is looped through an apex portion (344) of the
second helical turn and tied to an apex portion (346) which is
adjacent to the apex portion (344) as shown in FIG. 5A.
[0092] FIG. 5A shows the stent in the compressed state. Upon
expansion of the stent, as mentioned above, the members of the
stent expand to effect the radial expansion of the stent, as shown
in FIG. 5B. Because the distance between apex portions (344) and
(346) becomes greater upon expansion of the stent, and because the
filament (342) is relatively unyieldable and inelastic, the
distance between the attachment point (348) and the apex portion
(344) necessarily decreases. The result is that the end of the
restraining member (102) is retracted with respect to the stent
(126), as shown in FIG. 5B. Thus, the retraction along the
longitudinal axis of the restraining member is driven by the
expanding distance between adjacent apexes of the stent (126) in
this embodiment. Although only one retraction mechanism is shown at
one end of the restraining member, another similarly configured and
arranged retraction mechanism may be used at the other end of the
restraining member.
[0093] FIGS. 5C and 5D show another embodiment for a retraction
assembly. The views of this assembly (as are those shown in FIGS.
5A and 5B) are taken from a location between the generally
cylindrical graft and stent looking radially outward. In contrast
to that shown above where one end portion of a filament is secured
to the restraining member and another to a portion of the stent
that circumferentially moves during stent expansion, the other end
of the filament is secured to a portion of a stent that moves
generally parallel to the longitudinal axis of the stent (axially)
as the stent expands. In this embodiment, at least one apex portion
(364) of an end helix of the stent member (126') (which differs
from stent (126) in that it includes eyelets or loops which may be
formed as shown in the drawings) is made shorter than the majority
of apex portions (366). However, the apex portions may be otherwise
configured such as those shown in FIGS. 4A and 4B. A filament (362)
is tied or otherwise fixed at one end to apex portion (364), and at
the other end, to one end portion of the restraining member (102).
As shown in FIG. 5D, upon radial expansion of the stent, inwardly
positioned apex portion (364) retracts to a greater extent in the
longitudinal or axial direction than the full height apex portions
(366) which are shown in the last or most outwardly positioned turn
of the stent. This relative greater retraction directly translates
through filament (362) such that the end of the restraining member
(102) is retracted relative to apex portions (366). As described
above, another similarly constructed retraction mechanism may be
provided at the other end of the restraining member.
[0094] Returning to FIG. 3, one stent-graft construction that may
be used in conjunction with the delivery systems disclosed herein
is shown. Stent-graft (106) generally includes a thin-walled tube
or graft member (124), a stent member (126), which can be a
self-expanding stent, and a ribbon or tape member (128) for
coupling the stent (126) and graft (124) members together. The
stent (126) and graft (124) members may be heat bonded together,
thus sealing in portions of the stent member (126) that are between
the tape member (128) and the graft member (124). The mechanical
properties of the stent-graft (106) may be customized, for example,
through materials selection, by varying the structural pattern of
the stent member, varying the thickness of the tape (128) and graft
(124) members, and varying the pattern with which the tape member
contacts the stent and graft members.
[0095] As shown in FIG. 1A, the tape member (128) may cover only a
portion of the stent member (126) as it follows the helical turns
of the undulating stent member. With this construction, regions of
the stent member do not interface with the tape member when the
stent-graft is in an uncompressed state, for example. This is
believed to advantageously reduce shear stresses between the stent
member (126) and the tape member (128) when the stent-graft
undergoes bending or compression, thereby reducing the risk of
tearing the graft (124) or tape (128) members or causing
delamination between the stent (126) and graft (124) members.
[0096] The tape member (128) also preferably has a generally broad
or flat surface for interfacing with the stent (126) and graft
(124) members as compared to filament or thread-like structures
such as sutures. This increases potential bonding surface area
between the tape member (128) and the graft member (124) to enhance
the structural integrity of the stent-graft. The increased bonding
surface area also facilitates minimizing the thickness of the tape
member (128). It has been found that a tape member in the form of a
generally flat ribbon as shown in the drawings provides desired
results.
[0097] Tape members having widths of 0.025, 0.050 and 0.075 inches
applied to a stent member having a peak-to-peak undulation
amplitude of about 0.075 inch are believed to provide suitable
results. However, it has been found that as the tape member band
width increases, the stent-graft flexibility generally is
diminished. It is believed that a tape member width of about
one-fourth to three-fourths the amplitude of the stent member
undulations, measured peak-to-peak, may be preferred (may be more
preferably about one-third to two-thirds that amplitude) to
optimize flexibility. It also has been found that by positioning
one of the lateral margins of the tape member adjacent to the
apexes, the tape member width may be reduced without significantly
sacrificing apex securement. Varying the width of the tape member
(e.g., varying width of the tape along the length of the stent
graft) can also result in the adjustment of other structural
properties. Increasing the width can also potentially increase the
radial stiffness and the burst pressure and decrease the porosity
of the device. Increasing band width can also diminish graft member
wrinkling between coupling member turns.
[0098] The tape member (or separate pieces thereof) also may
surround the terminal end portions of the stent-graft to secure the
terminal portions of the graft member to the stent member.
[0099] FIGS. 6A and 6B illustrate further stent-graft constructions
that may be used with the delivery systems described herein.
Referring to FIG. 6A, stent-graft (200) is the same as stent-graft
(106) with the exception that stent-graft (200) includes a filament
that couples stent undulations in adjacent turns. Filament (202) is
laced or interwoven between undulations of the stent member and
acquires a helical configuration (i.e., it forms a secondary helix)
in being laced as such. Such a configuration is disclosed in PCT
publication No. WO 95/26695 (International Application No.
PCT/US95/04000) the entirety of which is hereby incorporated herein
by reference. The stent-graft (300) shown in FIG. 6B is the same as
that shown in FIG. 6A with the exception that the filament (302) is
interwoven between undulations in the same helical turn of the
stent member.
[0100] The filaments (202, 302) are of the same construction and
may be of any appropriate filamentary material which is blood
compatible or biocompatible and sufficiently flexible to allow the
stent to flex and not deform the stent upon folding. Although the
linkage may be a single or multiple strand wire (platinum,
platinum/tungsten, gold, palladium, tantalum, stainless steel,
etc.), much preferred is the use of polymeric biocompatible
filaments. The flexible link may be tied-off at either end of the
stent-graft (200), for example, by wrapping its end portion around
the stent and tying it off at the point at the beginning of the
last turn as would be apparent to one of ordinary skill.
[0101] A percutaneously delivered stent-graft must expand from a
reduced diameter, necessary for delivery, to a larger deployed
diameter. The diameters of stent-grafts obviously vary with the
size of the body lumen into which they are placed. For instance,
the stents typically may range in size from 2.0 mm in diameter (for
neurological applications) to 40 mm in diameter (for placement in
the aorta). A range of about 2.0 mm to 6.5 mm (perhaps to 10.0 mm)
is believed to be desirable. Typically, expansion ratios of 2:1 or
more are required. These stents are capable of expansion ratios of
up to 5:1 for larger diameter stents. Typical expansion ratios, for
instance, typically are in the range of about 2:1 to about 4:1. The
thickness of the stent materials obviously varies with the size (or
diameter) of the stent and the ultimate required yield strength of
the folded stent. These values are further dependent upon the
selected materials of construction. Wire used in these variations
are typically of stronger alloys, e.g., nitinol and stronger spring
stainless steels, and have diameters of about 0.002 inches to 0.005
inches. For the larger stents, the appropriate diameter for the
stent wire may be somewhat larger, e.g., 0.005 to 0.020 inches. For
flat stock metallic stents, thicknesses of about 0.002 inches to
0.005 inches is usually sufficient. For the larger stents, the
appropriate thickness for the stent flat stock may be somewhat
thicker, e.g., 0.005 to 0.020 inches.
[0102] The following example is provided for purposes of
illustrating a preferred method of manufacturing a stent-graft as
shown in FIG. 3. It should be noted, however, that this example is
not intended to be limiting. The stent member wire is helically
wound around a mandrel having pins positioned thereon so that the
helical structure and undulations can be formed simultaneously.
While still on the mandrel, the stent member is heated to about
460.degree. F. for about 20 minutes so that it retains its shape.
Wire sizes and materials may vary widely depending on the
application. The following is an example construction for a
stent-graft designed to accommodate a 6 mm diameter vessel lumen.
The stent member comprises a nitinol wire (50.8 atomic % Ni) having
a diameter of about 0.007 inches. In this example case, the wire is
formed to have sinusoidal undulations, each having an amplitude
measured peak-to-peak of about 0.100 inch and the helix is formed
with a pitch of about 10 windings per inch. The inner diameter of
the helix (when unconstrained) is about 6.8 mm. (The filament when
used as shown in FIGS. 6A and 6B may have a diameter of about 0.006
inch.)
[0103] In this example, the graft member is porous expanded
polytetrafluoroethylene (PTFE), while the tape member is expanded
PTFE coated with FEP. The tape member is in the form of a flat
ribbon (as shown in the illustrative embodiments) that is
positioned around the stent and graft member as shown in FIG. 3.
The side of the tape member or ribbon that is FEP coated faces the
graft member to secure it to the graft member. The intermediate
stent-graft construction is heated to allow the materials of the
tape and graft member to merge and self-bind as will be described
in more detail below.
[0104] The FEP-coated porous expanded PTFE film used to form the
tape member preferably is made by a process which comprises the
steps of:
[0105] (a) contacting a porous PTFE film with another layer which
is preferably a film of FEP or alternatively of another
thermoplastic polymer;
[0106] (b) heating the composition obtained in step (a) to a
temperature above the melting point of the thermoplastic
polymer;
[0107] (c) stretching the heated composition of step (b) while
maintaining the temperature above the melting point of the
thermoplastic polymer; and
[0108] (d) cooling the product of step (c).
[0109] In addition to FEP, other thermoplastic polymers including
thermoplastic fluoropolymers may also be used to make this coated
film. The adhesive coating on the porous expanded PTFE film may be
either continuous (non-porous) or discontinuous (porous) depending
primarily on the amount and rate of stretching, the temperature
during stretching, and the thickness of the adhesive prior to
stretching.
[0110] In constructing this example, the thin wall expanded PTFE
graft was of about 0.1 mm (0.004 in) thickness and had a density of
about 0.5 g/cc. The microstructure of the porous expanded PTFE
contained fibrils of about 25 micron length. A 3 cm length of this
graft material was placed on a mandrel the same diameter as the
inner diameter of the graft. The nitinol stent member having about
a 3 cm length was then carefully fitted over the center of the thin
wall graft.
[0111] The stent-member was then provided with a tape coupling
member comprised of the FEP coated film as described above. The
tape member was helically wrapped around the exterior surface of
the stent-member as shown in FIG. 3. The tape member was oriented
so that its FEP-coated side faced inward and contacted the exterior
surface of the stent-member. This tape surface was exposed to the
outward facing surface of the thin wall graft member exposed
through the openings in the stent member. The uniaxially-oriented
fibrils of the microstructure of the helically-wrapped ribbon were
helically-oriented about the exterior stent surface.
[0112] The mandrel assembly was placed into an oven set at
315.degree. C. for a period of 15 minutes after which the
film-wrapped mandrel was removed from the oven and allowed to cool.
Following cooling to approximately ambient temperature, the mandrel
was removed from the resultant stent-graft. The amount of heat
applied was adequate to melt the FEP-coating on the porous expanded
PTFE film and thereby cause the graft and coupling members to
adhere to each other. Thus, the graft member was adhesively bonded
to the inner surface of the helically-wrapped tape member through
the openings between the adjacent wires of the stent member. The
combined thickness of the luminal and exterior coverings (graft and
tape members) and the stent member was about 0.4 mm.
[0113] Although the delivery systems have been described with
reference to the stent-graft examples illustrated in the drawings,
it should be understood that it can be used in conjunction with
other devices, stents or stent-grafts having constructions
different than those shown. For example, delivery systems described
herein may be used in conjunction with bifurcated stents or
stent-grafts as will be described in detail below. In addition,
although a self-expanding stent-graft has been described, balloon
expanding stent-grafts also may be used in conjunction with the
delivery systems described herein. These stent-grafts require a
balloon to expand them into their expanded state as opposed to the
spring energy stored in a collapsed self-expanding stent.
[0114] Referring to FIGS. 7A-C, one slip knot configuration that
may be used in conjunction with the thread-like coupling member
(104) will be described. The restraining member (102) is shown
without an implant positioned therein for purposes of
simplification. FIG. 7A illustrates the slip knot in a prerelease
or predeployment state. The series of knots are generally flush
with the restraining member (102) surface and add very little
profile to the construct which is preferred during implant
delivery. FIG. 7B shows the assembly of FIG. 7A with the
thread-like coupling member (104) loosened to illustrate how the
chain knots (130) may be formed. FIG. 7C diagrammatically
represents release of the assembly of FIG. 7A or 7B. The
illustrated stitch is releasable by pulling one end of the line
that results in releasing of the cylindrical or tubular restraining
member and then deployment of the device. This particular stitch is
called a chain stitch and may be created with a single needle and a
single line. A chain stitch is a series of loops or slip knots that
are looped through one another such that one slip knot prevents the
next slip knot from releasing. When the line is pulled to release a
slip knot, the following slip knot is then released and that
releases the next slip knot. This process continues during pulling
of the line until the entire line is pulled out of the restraining
member.
[0115] Referring to FIGS. 7A-C, as the unknotted portion or the
lead (132) of the thread-like coupling member (104) is pulled, such
as in the direction shown by reference arrow (134), each
consecutive chain knot (132) releases the next adjacent one. In the
preferred embodiment, the chain knots (130) of the coupling member
(104) are arranged to progressively release the collapsed implant
in a direction away from the distal portion of the delivery
catheter as shown in FIG. 10A and as will be discussed in detail
below.
[0116] Referring to FIGS. 8A through 8F, a method for making an
assembly comprising a restraining member with a collapsed or
compressed implant therein is shown for purposes of example. FIG.
8A shows the restraining member (102) with its side margins
releasably coupled to one another and its left end dilated by a
tapered mechanical dilator (402). A small funnel (404) is then
inserted into the restraining member (102) as shown in FIGS. 8B and
8C. The small funnel (404) and restraining member (102) are then
mounted onto a pulling frame (410), and a large funnel (406) is
fined into the small funnel (404) as shown in FIG. 8D. Traction or
pull lines (408), which have been sutured to one end of the
stent-graft, (106) are pulled through the large funnel (406), small
funnel (404), and restraining member (102) with a tapered mandrel
(416). As shown in FIG. 8F, the pull lines (408) are fastened to a
tie down post (412) located on a tension screw (414) and then are
pulled by the tension screw (414). The stent-graft (106) is then
pulled and collapsed sequentially through the large (406) and small
(404) funnels, and then into the restraining member (102). Once the
stent-graft (106) has been radially collapsed into the restraining
member (102), which has its side margins coupled together, the pull
lines (408) can be removed. The mandrel (416) may be inserted into
the restrained implant to facilitate introduction of another
component. In the preferred embodiment, a multilumen catheter (136)
(FIGS. 9-11) is introduced through the center of the compressed
stent-graft (106) and is used to deliver the radially restrained
stent-graft to the desired endolumenal site.
[0117] It also is noted that the funnels may be chilled to
facilitate compression of the stent when the stent is made of
nitinol. That is, when the stent is made of nitinol, the funnels
may be chilled below 0.degree. C. or below the transition
temperature (M.sub.f) where nitinol is in its martensitic state. In
addition, the stent-graft could be folded first and then reduced in
profile by pulling through the funnel and into the restraining
member. Cooling may be accomplished by spray soaking the
stent-graft with chilled gas such as tetrafluoroethane. Micro
Dust.TM. dry circuit duster manufactured by MicroCare Corporation
(Conn) provides suitable results. The spray canister preferably is
held upside down to discharge the fluid as a liquid onto the
stent-graft.
[0118] A method of deploying an implant will be described with
reference to FIGS. 9-11. In general, an implant may be delivered
percutaneously with the delivery systems described herein,
typically through the vasculature, after having been assembled in
the reduced diameter form (see e.g. FIG. 1). At the desired
delivery site, the implant may be released from the restraining
member, thus allowing the implant to expand or be expanded against
the lumen wall at the delivery site. Although other devices
including stents or stent-grafts may be used, such as balloon
expandable stents, the following example will be made with
reference to a self expanding stent-graft, which has the ability to
fully expand itself into its final predetermined geometry when
unconstrained. More particularly, the following example will be
made using a delivery system as shown in FIGS. 1 and 7A-C and a
stent-graft construction as shown in FIG. 3.
[0119] Referring to FIGS. 9A and 9B, an implant delivery assembly
including a collapsed stent-graft (106) that is confined within a
restraining member (102) and, which surrounds a distal portion of
the delivery catheter (136), is shown. The attending physician will
select a device having an appropriate size. Typically, the
stent-graft will be selected to have an expanded diameter of up to
about 20% greater than the diameter of the lumen at the desired
deployment site.
[0120] The delivery catheter preferably is a multilumen catheter.
The proximal portion of the catheter (136) is coupled to a hub
(140), which includes a guidewire port (142) for a guidewire (142),
and a deployment knob (144), which is coupled to the lead (132) of
the thread-like coupling member (104). Accordingly, when the knob
(144) is retracted, the restraining member (102) is released so
that the stent-graft may expand. The hub (140) also may include a
flushing port (146) as is conventional in the art. The stent-graft
(106) is held axially in place prior to deployment by a proximal
barrier (148) and distal barrier (150) which are positioned around
delivery catheter (136) adjacent to the proximal and distal
portions, respectively, of the restrained stent-graft. The proximal
and distal barriers (148, 150) may be fixedly secured to the
multilumen catheter (136) to restrict any axial movement of the
restrained stent-graft. The barriers preferably are positioned to
abut against the stent-graft or restraining member. The lead (132)
of the coupling member (104) is passed through an aperture (152) in
the proximal barrier (148) which is fluidly coupled to a lumen in
the delivery catheter (136) so that the coupling member lead (132)
can be coupled to the deployment knob (144). FIGS. 9A and 9B show
advancement of the catheter (136) and the restrained implant
through a vessel (154) toward a desired site. Referring to FIGS.
10A and 10B, once the restrained stent-graft reaches the desired
site (156), the deployment knob (144) is retracted so that the
stent-graft progressively expands as shown in the drawings as the
coupling member (104) is removed from the restraining member. The
coupling member preferably is arranged to facilitate stent-graft
expansion in a direction from the distal to proximal ends of the
stent-graft (i.e., in a direction from the catheter tip to the
catheter hub). FIGS. 11A and 11B show the stent-graft (106) and
restraining member (102) in their final implantation position after
the coupling member and catheter have been removed therefrom. In
another embodiment, multiple restraining members may be used as
shown in FIG. 9C. When the multiple coupling members (104) are
released simultaneously implant deployment time may be reduced.
[0121] A method for deploying a balloon expandable stent-graft may
be the same as that described above, with the exception that after
the coupling member (104) has been retracted from the eyelets
(116), the balloon, which may be positioned inside the stent-graft
prior to delivery, is inflated to expand the stent-graft (106) and
then deflated for removal through the catheter (136).
[0122] According to further embodiments, multidirectional coupling
member release or multiple coupling members may be used. These
configurations may facilitate more rapid deployment of the implant
than when a single unidirectional coupling member is used. FIGS.
12A-12D diagrammatically show multidirectional deployment of a
restrained implant where a coupling member arrangement is provided
to release the implant from its middle portion, preferably its
axial center, outward toward the implant ends. Although a
particular coupling member configuration is not shown in these
diagrammatic representations, one suitable coupling configuration
is shown in FIG. 13 where the leads (132) may be passed through the
aperture (152) and coupled to the deployment knob (144) as shown in
FIG. 9A and described above.
[0123] Referring to FIG. 12A, the restrained stent-graft, which is
positioned on the distal end portion of delivery catheter (136), is
advanced through a vessel (154) for deployment in an aneurysm
(158). The axial midpoint of the restraining member (102)
preferably is positioned at the center of the aneurysmal sac. As
the coupling member arrangement unlacing propagates from middle of
the construct toward the proximal and distal ends of the
restraining member (102) and the stent-graft (106), the stent-graft
(106) progressively expands from its axial midportion toward its
ends as shown in FIGS. 12B and 12C. This may be accomplished by
pulling the leads (132) shown in FIG. 13 simultaneously when the
arrangement in that figure is used. The stent-graft size is
selected so that when the restraining member is fully released and
the stent-graft fully deployed as shown in FIG. 12D, the proximal
and distal portions of the stent-graft are positioned against the
proximal and distal necks of the aneurysm. The delivery catheter
may then be retracted.
[0124] As is apparent from the drawings, this embodiment
advantageously allows fluid flow through the aneurysmal sac to
remain substantially unobstructed during the release of the
restraining member. For example, the stent-graft ends are still
constrained at the deployment time shown in FIG. 12C where the
aneurysm neck regions are shown minimally obstructed. In addition,
this simultaneous, multidirectional release of the restraining
member advantageously reduces the time in which fluid flow in the
vessel may disturb the implant position as it is deployed as
compared to a single directional release mechanism such as that
shown in FIGS. 9-11.
[0125] Referring to FIG. 13, a multiple coupling member
configuration is shown. The illustrated arrangement includes two
lacing configurations (150) and (152). Except for the placement of
the lead (132) of thread-like coupling member (104), configuration
(152) is the mirror image of configuration (150). Each of the
lacing configurations (151 & 153) is the same as that shown in
FIGS. 7A-C with the exception that each configuration (151 &
153) further includes two additional slip knots, generally
designated with reference numeral (504), and tuck or loop
arrangement (506). The additional slip knots are not interwoven in
the restraining member and provide a delay mechanism for release of
the coupling member, as is apparent from the drawings, when the
lead (132) is pulled in the direction of the arrow (134). Thus,
inadvertent pulling of the lead (132) will not immediately begin to
release the coupling member from the restraining member. The tuck
arrangement simply involves tucking the slack from lead (132) under
stitches at various intervals as shown so that the additional slip
knots (504) may be pulled out of the way for delivery. In addition,
the tuck or loop arrangement (506) provides an additional delay
mechanism for release of the slip knots.
Bifurcated Stent or Stent-Graft.
[0126] The following describes a modular bifurcated stent-graft
constructed [or treating a bifurcation site within a mammalian
body. The stent-graft components generally comprise a flexible
graft member attached to a wire stent member using a tape member
according to the principles discussed at length above. Preferably
the stent-graft components are designed for compressed delivery and
are self-expanding, in the manner described above.
[0127] The modular stent-graft of FIGS. 14A through 14D generally
has two principal components; a main body (700) and a contralateral
leg (730) each generally having a graft member attached to a stent
member according to the description above. The main body (700)
generally has a number of sections which have distinct overall
constructions. A distal trunk section (708) has a single lumen
structure beginning at a distal end (702) of the main body (700)
and continuing until a bifurcation point (728). The bifurcation
point (728) is the location within the prosthesis where the single
lumen of the distal trunk section (708) bifurcates into internal
two flow lumen.
[0128] An intermediate section (710) begins at the bifurcation
point (728) and continues to the receiving hole (704). In the
intermediate section (710), the stent-graft has an internal graft
structure which is bifurcated into two lumen surrounded by a
generally tubular, single-lumen stent structure. Finally, a
proximal section (712) is a single lumen structure for both the
stent member and the graft member and includes an ipsilateral leg
(726) which terminates at an ipsilateral leg hole (706).
[0129] The graft member of the intermediate section (710)
bifurcates the single lumen distal trunk section (708) into the
ipsilateral leg (726) and an internal female receiving lumen (703).
The receiving lumen (703) terminates at a receiving hole (704). The
receiving hole (704) and receiving lumen (703) accommodate delivery
and attachment of the contralateral leg component (730).
Preferably, the graft material at the distal end (734) of the
contralateral leg component (730) is scalloped as shown more
clearly in FIG. 23 discussed below.
[0130] The receiving hole (704) is supported by a wire structure
around a substantial portion of its periphery so that the receiving
hole (704) is held open after deployment. In a preferred embodiment
the wire structure that supports the receiving hole (704) is an
independent wire ring (714).
[0131] The independent wire ring (714) is located in the general
area of the receiving hole (704) in the intermediate section (710).
The independent wire ring (714) ensures that the graft material at
the receiving hole (704) is supported in an open position to
receive the distal end (734) of the contralateral leg (730). In
absence of such support, the receiving hole (704) may not reliably
open after delivery of the main body component (700) because within
the intermediate section (710) the bifurcated graft member in the
area of the receiving lumen (703) does not have full stent support
on its interior periphery. This may be better seen in FIG. 18 which
shows the absence of any internal stent support of the interior
graft periphery (785) in the area of the receiving lumen (703).
[0132] The independent wire ring (714) may be comprised of the same
materials as the other stent-graft sections discussed above and is
preferably self-expanding. In a preferred embodiment, the
independent wire ring comprises a single turn of an undulating wire
stent material surrounded by at least one layer of tape which is
heat bonded to the receiving hole (704). Alternatively, the
independent wire ring (714) could be formed as the last turn of the
main body (700).
[0133] A radiopaque marker may be used to make the receiving hole
(704) visible during implantation. Such a marker may include a
radiopaque wire adjacent to the independent wire ring (714). Such
markers make it easier to see the location of the receiving hole
(704) after deployment of the main body (700) within the mammalian
body.
[0134] This construction of the intermediate stent section (710) as
seen in cross-section in FIG. 14C is characterized by a
single-lumen stent member and bifurcated graft member and offers
both a smaller compressed profile as well as simplified
manufacturing over constructions which have discreet stented leg
features. The compressed profile is determined largely by the
physical amount of stent and graft material present in a given
section. This construction eliminates the stent material that would
normally support the inside periphery of the bifurcated graft
section resulting in less stent material to compress in that
region. As the main body component (700) is compressed for delivery
as discussed above, the compressed profile is significantly smaller
than would be a structure that had a section of bifurcated stent
over the section of bifurcated graft.
[0135] Even though bifurcated flow is supported, manufacturing is
simplified because there is no bifurcated stent section. Winding a
bifurcated stent section in one piece, for example, is a more
complex process. Likewise, winding separate cylindrical stent
structures and connecting them to form a bifurcated stent structure
is complicated and ultimately may be less reliable. The
intermediate section (710) allows the entire stent member that
covers the main body component (700) to be made from a single
undulating wire arranged in multiple helical turns. The result is a
bifurcated stent-graft device which is simple to manufacture,
easily compressible and which expands reliably upon deployment.
[0136] An alternate construction of the intermediate stent section
(710), is shown in FIG. 14D. The intermediate stent section (710)
has a shape characterized by the indented regions (727). The
cross-sectional shape could generally be described as a `figure-8`,
except that the area between the bifurcated graft member remains
unsupported at its centermost region. This construction is still a
single lumen stent construction and therefore maintains much of the
benefits of reduced profile and simplified manufacturability while
providing the bifurcated graft member with increased support around
a greater portion of its perimeter. Further, indented portions
(727) have less of a tendency to spring outward upon application of
external forces.
[0137] As mentioned above, the main body component (700) and the
contralateral leg component (730) are adapted for delivery in a
compressed state to a bifurcation site within a body. For this
purpose the main body component (700) is preferably equipped with a
restraining member (722) constructed as described above. Likewise,
the contralateral leg component (730) has an attached restraining
member (732). These restraining members are typically sutured to
the graft material at intervals down their length.
[0138] FIG. 15 shows an assembled bifurcated stent-graft (740)
after deployment at a bifurcation site within a bifurcated body
vessel afflicted with an aneurysm (758). Although not intended to
be so limited to any particular location, the inventive prosthesis
is shown at the location where the abdominal aortic artery (752)
bifurcates into the left iliac artery (756) and the right iliac
artery (754). So that the various features of the inventive implant
are more clearly shown, the restraining member is not shown in FIG.
15.
[0139] The assembled bifurcated stent-graft (740) is comprised of
the main body component (700) and the contralateral leg component
(730). The distal end (734) of the contralateral leg component
(730) has been inserted into the receiving leg hole (704) and the
female receiving lumen (703) of the main body component (700).
[0140] For best results in deploying any stent or stent-graft of
these types it is essential that they have the appropriate
structural properties such as axial stiffness, flexibility and
kink-resistance. With complicated structures, such as those
required for treating a bifurcated site, it is increasingly
difficult to obtain the desired structural properties because
optimizing one may negatively effect the other.
[0141] For instance, optimizing the global axial stiffness of a
stent or stent-graft will necessarily make the device significantly
less flexible and consequently impair its resistance to kinking and
lessen its ability to conform to the natural bends of curves the
body's vasculature. Conversely a device that has high flexibility
with little axial stiffness is difficult to properly deploy and
does not aid in anchoring the device in the desired location.
[0142] With these constraints in mind, it has been discovered that
having a bifurcated stent-graft which has segments constructed with
varying structural properties offers improved deployability, is
less susceptible to kinking, and favorably tends to maintain its
desired position after deployment while allowing sufficient
flexibility to accommodate movement by the body. The exact
structural properties desired may depend on the location where the
prosthesis is to be deployed.
[0143] For these reasons, it is preferable that the bifurcated
stent or stent-graft be constructed with at least two segments
having structural properties different from one another. For
example, in FIG. 14A, a length of the distal section (708) and the
intermediate section (710) may be constructed with a higher axial
stiffness for improved deployment and positional stability while
the proximal section (712) may be constructed to have higher
flexibility to accommodate the geometry of the iliac artery.
[0144] It may be further desirable to have a number of segments
that have different structural properties. Accordingly, the main
body component (700) and the contralateral leg component (730) of
the assembled stent-graft (740) have segments constructed with
structural properties different from adjacent segments. In one
preferred embodiment shown in FIG. 15, the main body component
(700) has four different segments constructed with different
structural properties. The distal segment (742) is constructed to
have higher axial stiffness than the more flexible proximally
adjacent segment (744). The proximal section (748) is constructed
to have a higher flexibility than that of its distally adjacent
segment (746). Likewise the contralateral leg component (730) has
an axially stiffer distal segment (750) and a more flexible
proximal segment (749).
[0145] There are a number of ways to alter the structural
properties of stent or stent-graft components. One way of
selectively altering the structural properties of a stent-graft
segment is to use a tape member for that segment that has different
physical dimensions. Such a tape member is discussed above with
reference to the tape member (128) of FIG. 3. For example the tape
member width, thickness or spacing may be increased, from the
preferred dimensions discussed above, in a segment where it is
desirable to have increased or decreased stiffness. For example,
the use of wider tape wound with closer spacing will increase the
stiffness in that area.
[0146] Another way of selectively altering the structural
properties of a stent or stent-graft segment is shown in FIGS. 14A
and 15. Extended struts (718) and (719) may be used to increase the
axial stiffness of a stent-graft segment. Extended struts are
formed by extending an apex on one turn of the undulating wire
until it contacts an apex on an adjacent turn. This contact between
an extended strut and the apex of an adjacent stent turn provides
an added amount of axial stiffness. In a preferred embodiment, a
layer of tape (not shown) is applied around the device in a helical
pattern that covers each of the apexes of the extended struts. This
additional layer of taping keeps the strut pairs together.
[0147] Referring to FIG. 14A, a first helical stent turn (720) and
a second helical stent turn (721) have a generally undulating shape
having apexes. An extended strut (718) of the stent turn (720) is
formed having its apex near or in contact with the apex of the
stent turn (721) directly below. The extended strut (719) is
similarly formed by extending an apex of the stent turn (721)
directly down to contact the apex in the turn below. This pattern
in continued, each time spacing the extended strut over one
undulation. This results in a helical pattern of extended struts
down the length of the device. Of course, the extended struts may
be arranged in patterns other than the helical configuration
described.
[0148] A number of these patterns may be employed in any one
segment or the extended strut pattern may be used in other segments
to increase axial stiffness. Preferably the distally adjacent
segment (746) on the main body component (700) and the axially
stiff distal segment (750) on the contralateral leg component are
constructed with extended struts as shown in FIG. 15.
[0149] Another important aspect of the present invention is
achieving a secure position against the walls of the vessel lumen
so that the deployed position is maintained and so that there is no
leakage of luminal flow. Referring now to FIG. 15, the distal end
(702) is sized to properly fit the inside diameter of the target
artery, in this case the abdominal aortic artery. Typically the
prosthesis is designed to have an unconstrained diameter slightly
larger than the inside of the target vessel.
[0150] The ipsilateral and contralateral legs of the assembled
bifurcated stent-graft (740) are typically the same size at their
distal ends (around 13 mm for example) regardless of the size of
the distal end (702) and undergo tapered sections (724) and (738)
that taper to a diameter which corresponds approximately to the
internal diameter of the iliac arteries. These tapered sections
(724) and (738) are preferable to abrupt changes in diameter as
they tend to produce superior flow dynamics.
[0151] After deployment, the assembled bifurcated stent-graft (740)
must establish sufficient contact with the healthy vessel lumen an
each side of the aneurysm (758) so that the device does not migrate
or dislodge when subjected to the relatively high fluid pressures
and flow rates encountered in such a major artery, especially when
the body again becomes mobile after recovery. Further, sufficient
contact must be made so that there is no leakage at the distal end
(702), the ipsilateral leg hole (706) or the proximal end (736) of
the contralateral leg.
[0152] Anchoring or staying features that allow the stent or
stent-graft exterior to anchor itself to the vessel lumen wall may
be provided to help the device seal to the vessel wall and maintain
its deployed position. For example, anchors (716) as seen in FIGS.
14A and 15 are provided on the main body component (700) and could
also be provided on the contralateral leg component (730).
Preferably the top stent portion (717) is directed angularly
outward. This flared stent portion works to force the anchors (716)
into the vessel wall as the top stent portion (717) expands under
force into radial interference with the vessel wall upon
deployment.
[0153] A preferred construction for an anchor (716) is shown in
FIG. 17. This construction involves extending two wires from the
upper stent turn (762) under an apex of an adjacent lower stent
turn (764). The two ends of stent wires (760 and 761) are then bent
out and away from the graft material (768). Extended struts (771)
are formed adjacent to each anchor in the manner described above
except the extended struts extend under the adjacent lower stent
turn (764) down to a third stent turn (765). This extended strut
arrangement provides support for the anchors (716) and provides for
low stresses in the wires (760 and 761) under the application of
bending forces encountered as the prosthesis expands into the
vessel wall. The extended struts (771) minimize the localized
deformation of the stent-graft structure in the area of the anchors
by providing broader support.
[0154] Another construction of the anchors (716') are shown in FIG.
16. An anchor (716') is formed in the same manner except the ends
of the anchor remain connected in a `U-shape` configuration as
shown. An anchor (716') may be formed at any location on the
stent-graft. Most preferably, the anchors are formed in an evenly
spaced pattern around the top stent portion (717) (FIG. 14A).
[0155] It should be apparent that the anchors as described above
are not limited in use to the stent-graft combination shown in the
figures but indeed could be used in any non-bifurcated or stent
only construction that require similar functionality.
[0156] Sealing at the vessel wall may also be enhanced by the
alternate construction shown in FIG. 17 by way of a sealing
mechanism. A sealing mechanism can be used with any type of
implant, including any of the implants discussed above. For
purposes of illustration, the sealing mechanism is shown with
reference to the bifurcated implant of FIG. 14 and comprises seal
member (772) as seen in detail in FIGS. 16 and 17. The sealing
mechanism described below can be used with any of the implants
discussed above.
[0157] One preferred construction for seal member (772) in the
variations shown in FIGS. 16 and 17 may be similar to the preferred
construction for the tape member used in constructing the
stent-graft tubular member, as is provided in reference to FIG. 1
and FIG. 3 above.
[0158] In general, a thin walled ePTFE tape is used for seal member
(772) similarly as that for tape member (128), shown variously in
the previous figures. The tape used for seal member (772) is
adhered to the outer surface of the stent-graft, including over
tape member (128), described previously for bonding the stent and
graft members. Seal member (772) has an inner surface constructed
of a similar material for either the outer surface of the tape
member (128) or the outer surface of the graft-member (124),
depending upon which surface the seal member is desirably
adhered.
[0159] First cuff end (767) is bonded to the stent-graft outer
surface and second cuff end (769) is not, in order to form the
unadhered flange to function as a one-way valve against
peri-stent-graft flow. Seal member (772) may be selectively adhered
along its length in this manner by providing a variable inner
surface to the seal member such that, upon heating, only the
surface in the region of first cuff end (767) bonds to the outer
surface of the stent-graft. For example, the inner surface of seal
member (772) may have an FEP liner in the region of first cuff end
(767) but not in the region of second cuff end (769). In this case,
upon contacting an outer surface of the stent-graft that has a
uniform FEP outer surface, only first cuff end (767) may be heat
secured thereon.
[0160] Alternatively, seal member (772) may have a uniform inner
surface, such as constructed of FEP, and a variable outer surface,
such as with a selective portion of FEP, may be provided either on
the tape member (128) or on the graft member (124) in the region
where the heat bonding of seal member (772) is desired. Still
further, seal member (772) may have a uniform surface and may be
positioned over tape member (128) and graft member (124) so that
variability between the outer surfaces of tape member (128) and
graft member (124) causes a selective bonding with the first cuff
end (767) over one of those surfaces.
[0161] Further to the construction of seal member (772), the
particular wall thickness of the tape which may be used for this
component should desirably be as thin as possible to functionally
provide the flange-one-way-valve function for that member. This is
because, since seal member (772) is over the outer surface of the
other stent and graft components of the stent-graft, seal member
(772) is believed to be the profile-limiting feature of the overall
assembly. Therefore, in a particular design, seal member (772) may
desirably be a thinner wall than for the tape member used to
construct the stent-graft described in reference to FIGS. 1 and
3.
[0162] Further referring to the particular constructions and
related methods just described for adhering seal member (772) to
the outer surface of the underlying stent-graft, it should be
apparent to one of ordinary skill in the art that the desired
construction and heat securing technique for seal member (772) is
premised upon the theory that, where one polymer meets a like
polymer (such as FEP meeting FEP), heating under proper conditions
will allow for a selected heat bond. The present invention,
however, should not be construed as limited to these particularly
described conditions, but instead should be considered to more
broadly encompass any suitable means for securing a seal member to
the outer surface of a given tubular member, as would be apparent
to one of ordinary skill, and as is provided previously with
reference to FIGS. 16 and 17.
[0163] Further there is a plurality of circumferential strut spaces
between the struts of the stent member. It is believed that these
spaces may provide a path for leakage flow around the outer surface
of the graft member and along the outside of the stent-graft.
Second cuff end (769), however, captures such leakage flow beneath
its flange, which can not propagate along the outer surface of the
stent-graft because first cuff end (767) is secured to the outer
surface of that stent-graft. In other words, flow over the
stent-graft and into an aneurysm is occluded.
[0164] Furthermore, when apex strut (716) is anchored into the wall
of abdominal aortic artery as shown in FIG. 15, it has been
observed that the portion of main body component (700) at and
adjacent to the apex strut (716) may be forced away from the artery
wall. This action causes a separation between the outer surface of
main body (700) and the artery wall, which separation is believed
to create a leakage flow path. The flange of seal member (772)
captures that flow and occludes it from propagating into the
aneurysm (758).
[0165] In addition to maintaining a good contact with the vessel
lumen walls, the components of the stent-graft must make sufficient
contact with each other such that the separate modules stay
attached and do not leak at their engagement interface. The
inventive stent-graft shown in FIG. 18 illustrates several
important features designed to effectuate a leak-free and
positionally stable seal at the interface between the receiving
lumen (703) of the main body component (700) and contralateral leg
component (730).
[0166] FIG. 18 shows a partial cross-section of the assembled
stent-graft. The contralateral leg component (730) has been
inserted into the receiving lumen (703) of the main body component
(700). This cross-sectional view shows clearly that the main body
component (700) includes a main body graft member (780) and a main
body stent member (782). The contralateral leg component (730)
includes a contralateral graft member (784) and a contralateral
stent member (786).
[0167] At the interface between the contralateral leg component
(730) and the receiving lumen (703), the assembly provides for an
extending sealing region (790). Preferably the extended scaling
region (790) consists of a generally cylindrical interfering
friction fit between the outside diameter of the contralateral leg
component (730) and the inside diameter of the receiving lumen
(703). That is, the natural or resting outside diameter of the self
expanding contralateral leg component (730) would be larger than
the natural inside diameter of the receiving lumen (703). Thus the
forces created by the interference act to seal the two components
and also serve to resist movement of the two components.
[0168] The type of generally cylindrical extended sealing region
just described has many advantages. First, it allows for the stent
and graft structures in the extended sealing region (790) to be
constructed of relatively simple generally cylindrical elements
that are easily manufactured. Because the extended sealing region
(790) extends over a large length it necessarily has a large
surface area to effectuate sealing between the components. This
larger sealing area typically provides that multiple turns of the
stent structures will be engaged in an interfering and thus scaling
relationship.
[0169] In one preferred embodiment, the extended sealing region has
a length in excess of one-half of the diameter of the receiving
lumen (703), more preferably the length is greater that the
diameter of the receiving lumen (703), and most preferably the
length is more than 2 times the diameter of the receiving lumen
(703).
[0170] Because the manufacturing tolerances of the simplified
shapes are easily controlled and because the engagement of the
extended sealing region (790) is quite large, a highly reliable
joint is formed between the modular components. Even so it may be
desirable to create one or more localized zones of increased
interference to increase the sealing capability and positional
stability.
[0171] Localized zones of interference may be created in a number
of ways. In a preferred embodiment, an annular ring of decreased
diameter is formed within the receiving lumen. Such a localized
decreased diameter causes a greater interference with the outside
diameter of the contralateral leg component in a localized area
while the remainder of the engagement with the receiving lumen is
subject to the general interference friction fit described
above.
[0172] One way of creating a localized decreased diameter is
illustrated in FIG. 20 which shows a partial cross-section of the
extended sealing region (790). A zone of reduced diameter (799) is
created by placing an anchoring ring (798) between the graft member
(780) and the stent member (782) of the receiving lumen (703). The
anchoring ring may be made from any polymeric or wire material,
preferably a material that will not inhibit the receiving lumen
from self-expanding to an open position. Most preferably the
material is a suture material, typically ePTFE.
[0173] Alternately, localized zones of decreased diameter may be
created as shown in FIGS. 21 and 22 by folding a portion of the
graft member (780) back up into the receiving lumen (703). In FIG.
21, the zone of reduced diameter (806) is formed by creating a
folded flap (808) of the graft material (780) around an anchoring
ring (802). The flap is heat bonded in place roughly at a location
(804) as shown. In FIG. 22, the zone of reduced diameter (809) is
formed of flap (808) and heat bonded roughly at a location (807) in
a similar manner but without any anchoring ring. The localized
interference using these methods tends to cover a larger area and
the flap (808) provides a more flexible member to seal against the
outside diameter of the contralateral leg component (730).
[0174] One further aspect of ensuring a good seal between the
stent-graft components involves the use of a scalloped stent-graft
construction at the distal end of the contralateral leg component
(810). To create this scalloped construction, the graft material
between the apexes of the stent member is removed on the last turn
of the stent. For example scallop (812) may be formed by removing
(or cutting and folding under) the graft material from between a
first apex (814) and an adjacent apex (816).
[0175] The advantage of using a scalloped arrangement are
illustrated in FIGS. 24A through 25B. FIG. 24A shows a
cross-section of the fully expanded contralateral leg component
(730) having an unscalloped construction. A first apex (822) and an
adjacent apex (824) have continuous graft material (784) in the
area between them. When the apex (822) and the adjacent apex (824)
are forced together in the directions of the arrows (820), the
graft material (784) forms a buckle or wrinkle (818) which is a
potential leak path or is a potential site for thrombogenic
material to build up as seen in FIG. 24B. The scalloped
construction shown in FIGS. 25A and 25B, on the other hand, have no
graft material between the first apex (814) and the adjacent apex
(816) and therefore when forced together do not form a graft
material wrinkle.
[0176] The wrinkle (818), mentioned above may also be formed when
the stent-graft is not allowed to expand to its complete diameter.
For instance it is quite common that the receiving lumen or vessel
wall internal diameter is smaller than the fully expanded
stent-graft outer diameter. This being the case, it should be clear
that the scalloped construction may alternately be used at any of
the terminal openings of the main body component or the
contralateral leg component. Preferably, the distal end (702) of
the main body component (700) also has this scalloped construction
as shown in FIGS. 14A and 14B.
[0177] In the previous discussion we have referred generally to a
stent-graft that includes a graft member. While the construction of
such straight stent grafts are discussed at length above, the
construction of a bifurcated graft member is illustrated in FIGS.
26, 27A and 27B. A bifurcated graft member suitable for
construction of the main body component (700) discussed above is
generally formed of two graft members: the ipsilateral tapered
graft (840) and the contralateral tapered graft (842). The separate
contralateral leg graft component (844) is a straight or tapered
section and may be formed according to the principles discussed in
the first section above.
[0178] The ipsilateral tapered graft (840) has three sections which
are separated by tapers. A top section (846), a middle section
(848), and a bottom section (850). The body component graft (854)
is formed by heat bonding the top section (846) of ipsilateral
tapered graft (840) to the top section (847) of contralateral
tapered graft (842). This heat bonding forms a common septum (856)
which in a preferred embodiment is subsequently cut away to produce
a smooth bifurcation (858). Cutting away the septum material
prevents fluid flow disturbance or blockage that could result from
deviation of the septum. Such deviation is caused by the fluid
pressure and is aggravated if the stent-graft is radially
compressed in a manner which causes the septum to become loose or
no longer taut.
[0179] In another embodiment, a graft section may be constructed in
the manner illustrated in FIGS. 27A and 27B. According to this
embodiment, the body component graft (867) is constructed from two
pieces. A tubular graft section (860) is bent into a `U-shape`. A
top hole (864) is formed by notching the top of the `U-shape`.
Upper graft section (862) is placed over the top hole (864) of
tubular graft section (860). The two pieces are bonded together at
the bonding interface (866). Preferably, the two graft pieces are
heat bonded while supported by interior mandrels (not shown) to
obtain the desired shape and smooth interior. However, upper graft
section (862) may be attached to the tubular graft section (860) at
the bond interface (866) in any manner that provides a sufficiently
leak free seal. For example the components may be sutured together
or adhesive bonded.
[0180] In use, the modular bifurcated stent-graft is typically
delivered percutaneously through the vasculature of the body.
Preferably the prosthesis is delivered by way of a restraining
member as described in detail above. FIGS. 28A though 28E
diagrammatically illustrate deployment of a bifurcated stent-graft
with a restraining member (902) using a percutaneous catheter
assembly. Referring to FIG. 28A, a multilumen catheter assembly
(928) has been inserted to a selected site within a body lumen. The
main body component (700) of a bifurcated stent-graft is held in a
compressed state about a guidewire (926) and a guidewire lumen
(929) by a restraining member (902) and a coupling member (906).
The collapsed main body component (700) is held axially in place
prior to deployment by a distal barrier (930) and a proximal
barrier (932). The distal (930) and proximal (932) barriers are
typically affixed to the guidewire lumen (929). The coupling member
(906) extends through the eyelets (920) of the restraining member
(902) forming chain knots and into the multilumen catheter
(928).
[0181] FIG. 28A shows advancement of the multilumen catheter (928)
with the distally located main body component (700) and the
restraining member (902) into implantation position, typically at
the bifurcation of a major vessel. During deployment it is critical
that the surgeon align the main body component (700) so that the
ipsilateral leg (726) will extend down one branch of the bifurcated
vessel, and so the receiving hole (704) and the receiving lumen
(703) will be lined up with the other branch of the bifurcated
vessel so as to receive the contralateral leg component (730).
[0182] One way of facilitating this alignment is to provide
radiopaque markers so that the surgeon may readily determine the
rotational position of the main body component (700) prior to
deployment or release from the restraining member (902). In a
preferred embodiment, a long marker (934) is located on the
contralateral side of the compressed assembly and a shorter marker
(936) is placed on the ipsilateral side. Preferably these markers
are placed on the stent prior to compression but may alternatively
be part of the restraining member. Having one marker of a different
length allows the surgeon to identify the orientation of both the
ipsilateral leg and the receiving lumen relative to the bifurcated
vessel.
[0183] Once the assembly is properly aligned and positioned for
implantation, the coupling member (906) is pulled and the
restraining member (902) begins to release the implant, typically
at the distal end first. In the preferred embodiment, the
restraining member (902) is located down the side as shown because
it is less likely to interfere with deployment of the receiving
lumen (703).
[0184] FIG. 28B shows the main body component (700) radially
expanding as the coupling member (906) is retracted through the
eyelets (920) of the restraining member (902) and into the catheter
assembly (928). In the preferred embodiment, the restraining member
(902) has been fixedly attached to the main body component (700)
with a number of sutures along the length of the main body
component to prevent any relative longitudinal movement between the
implanted prosthesis and the restraining member (902). The
restraining member may optionally employ a retracting or pull-down
mechanism as described at length above.
[0185] FIG. 28C shows the main body component (700) and the
restraining member (902) in final implantation position at the
vessel bifurcation after the guidewire (926) and the catheter
assembly (928) have been retracted.
[0186] FIG. 28D shows the contralateral leg component (730) being
delivered to the contralateral receiving hole using a restraining
member (942). The procedure for positioning and releasing the
contralateral leg component (730) is the same as that described
above for implantation of a generally cylindrical stent-graft
except that certain radiopaque markers may be employed to ensure
its proper position relative to the bifurcation point (728) of main
body component (700).
[0187] Radiopaque markers may be located, for example, to indicate
the position of the receiving hole (704), the distal end (734) of
the contralateral leg component (730), and the bifurcation point
(728) of the main body component (700). These markers serve to
indicate the position of the contralateral leg component as it
enters the receiving hole (704) and its ultimate position relative
to the receiving lumen (703) which begins at bifurcation point
(728). In a preferred embodiment illustrated in FIG. 19, the
radiopaque wires (794) may be heat bonded or imbedded into the
graft material (780) around the periphery of the receiving lumen.
Such radiopaque wires could be used in other places such as the
contralateral leg component lumen, the ipsilateral leg lumen or the
lumen at the distal end of the main body component (700).
[0188] FIG. 28E shows the assembled bifurcated stent-graft in its
final implantation state with the contralateral leg component
expanded into and engaged with the receiving lumen of the main body
component (700).
[0189] FIGS. 29A through 29D diagrammatically show the same stent
or stent-graft components being deployed except that the
restraining member (902) is released from the center out towards as
the coupling member (906) is retracted. This may provide more
accurate placement relative to the bifurcation point of the vessel
instead of relative to the distal end as with end release.
[0190] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention will be apparent to persons skilled in
the art upon reference to the description. It is therefore intended
that the appended claims encompass any such modifications or
embodiments.
* * * * *