U.S. patent application number 13/731908 was filed with the patent office on 2013-09-26 for endolumenal vascular prosthesis with neointima inhibiting polymeric sleeve.
This patent application is currently assigned to ENDOLOGIX, INC.. The applicant listed for this patent is ENDOLOGIX, INC.. Invention is credited to Myles S. Douglas, Brian C. Gray, Frank M. Zeng.
Application Number | 20130253638 13/731908 |
Document ID | / |
Family ID | 35061603 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130253638 |
Kind Code |
A1 |
Douglas; Myles S. ; et
al. |
September 26, 2013 |
ENDOLUMENAL VASCULAR PROSTHESIS WITH NEOINTIMA INHIBITING POLYMERIC
SLEEVE
Abstract
The present invention is related to a low profile endolumenal
prosthesis. The prosthesis comprises a radially expandable tubular
wire support and an expanded PTFE membrane. The density, wall
thickness and intranodal distance of the ePTFE are selected to
inhibit the formation and nourishment of a viable neointima on the
inner surface of the prosthesis, through the ePTFE membrane.
Inventors: |
Douglas; Myles S.;
(Gardnerville, NV) ; Zeng; Frank M.; (Irvine,
CA) ; Gray; Brian C.; (Orange, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENDOLOGIX, INC. |
Irvine |
CA |
US |
|
|
Assignee: |
ENDOLOGIX, INC.
Irvine
CA
|
Family ID: |
35061603 |
Appl. No.: |
13/731908 |
Filed: |
December 31, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10820455 |
Apr 8, 2004 |
8377110 |
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13731908 |
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Current U.S.
Class: |
623/1.46 |
Current CPC
Class: |
A61F 2220/0058 20130101;
A61F 2/06 20130101; A61F 2220/0075 20130101; A61F 2/856 20130101;
A61F 2/90 20130101; A61F 2002/072 20130101; A61F 2002/065 20130101;
A61F 2002/075 20130101; A61F 2220/005 20130101; A61F 2/07 20130101;
A61F 2/91 20130101 |
Class at
Publication: |
623/1.46 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. An endolumenal prosthesis having a lumenal surface and an
ablumenal surface, comprising: a tubular wire support with proximal
and distal ends and a central lumen extending therebetween, the
wire support comprising at least two axially adjacent tubular
segments, each segment comprising a series of proximal and distal
bends connected by a length of wire, wherein the wire support is
radially compressible into a first, reduced cross sectional
configuration for translumenal navigation to a treatment site in a
body lumen and self-expandable to a second, enlarged cross
sectional configuration for deployment at the treatment site in the
body lumen; and a uniform porous tubular ePTFE sheath on the wire
support, the tubular sheath having a sheath proximal end region and
a sheath distal end region, wherein the sheath is porous and
configured to inhibit sufficient cellular ingrowth through the wall
of the sheath that would permit the formation of a viable
neointimal layer on the lumenal surface of the sheath at the sheath
proximal and distal end regions without a coating on the sheath
that would inhibit cellular ingrowth.
2. The endolumenal prosthesis of claim 1, wherein the ePTFE sheath
wall thickness is no greater than about 0.2 mm.
3. The endolumenal prosthesis of claim 1, wherein the ePTFE sheath
has a density of at least about 0.75 grams per milliliter.
4. The endolumenal prosthesis of claim 3, wherein the ePTFE sheath
has a plurality of nodes, and the average distance between nodes is
within the range of from about 6 microns to about 80 microns.
5. The endolumenal prosthesis of claim 1, wherein the ePTFE sheath
has a density of at least about 0.5 grams per milliliter.
6. The endolumenal prosthesis of claim 1, wherein the ePTFE sheath
has a plurality of nodes, and the average distance between nodes is
within the range of from about 6 microns to about 80 microns.
7. The endolumenal prosthesis of claim 1, wherein the ePTFE sheath
has a water entry pressure in the range of from about 10 psi to
about 24 psi.
8. A prosthetic vascular graft, comprising: an expandable tubular
wire support; a uniform porous, tubular ePTFE layer carried by the
support, the ePTFE layer having: a wall thickness less than about
0.15 millimeters; an average density of greater than about 0.75
grams per milliliter; and an average distance between nodes in the
range of between about 6 to about 80 microns; so that the uniform
porous ePTFE layer prevents the formation and nourishment of a
viable neointimal layer therethrough along portions of the tubular
ePTFE layer's axial length, which are in contact with a vessel
wall.
9. The prosthetic vascular graft of claim 8, wherein the ePTFE
layer has a density within the range of from about 1.1 to about 1.5
grams per milliliter.
10. The prosthetic vascular graft of claim 8, wherein the ePTFE
layer has a water entry pressure in the range of from about 10 psi
to about 24 psi.
11. The prosthetic vascular graft of claim 8, wherein the ePTFE
layer is further configured to inhibit the formation of a viable
neointimal layer on the lumenal surface of the ePTFE layer at the
prosthetic vascular graft's distal end.
12. The prosthetic vascular graft of claim 8, wherein a proximal
end of the prosthetic vascular graft comprises a single opening and
a distal end of the prosthetic vascular graft comprises two
openings, such that the prosthetic vascular graft is configured for
implantation at a vascular bifurcation.
13. An artificial vascular prosthesis comprising an enlargeable
support structure having a uniform, porous, expanded
polytetrafluoroethylene (ePTFE) layer thereon, the layer having a
microstructure consisting of nodes interconnected by fibrils which
prevents tissue ingrowth through portions of the layer that contact
a vessel wall when the prosthesis is implanted to span an aneurysm,
in which either the ePTFE layer's density is greater than about 1
gram per milliliter or the ePTFE layer's wall thickness is less
than about 0.2 millimeters, or both.
14. The artificial vascular prosthesis of claim 13, wherein the
ePTFE layer's wall thickness is about 0.1 mm.
15. The artificial vascular prosthesis of claim 13, wherein the
ePTFE layer's wall thickness is within a range of from about 0.05
mm to about 0.15 mm.
16. The artificial vascular prosthesis of claim 15, wherein the
ePTFE layer has a density within a range of from about 1.1 to about
1.5 grams per milliliter.
17. The artificial vascular prosthesis of claim 15, wherein the
ePTFE layer has a plurality of nodes, and an average distance
between nodes is within a range of from about 6 microns to about 80
microns.
18. The artificial vascular prosthesis of claim 13, wherein the
ePTFE layer is further configured to inhibit the formation of a
viable neointimal layer on a lumenal surface of the ePTFE layer at
the artificial vascular prosthesis's distal end.
19. The artificial vascular prosthesis of claim 13, wherein a
proximal end of the artificial vascular prosthesis comprises a
single opening and a distal end of the artificial vascular
prosthesis comprises two openings, such that the artificial
vascular prosthesis is configured for implantation at a vascular
bifurcation.
20. The artificial vascular prosthesis of claim 13, wherein the
ePTFE sheath has a water entry pressure in a range of from about 10
psi to about 24 psi.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 10/820,455, filed Apr. 8, 2004, now U.S. Pat.
No. ______, which is expressly incorporated by reference in its
entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to an endolumenal vascular
prosthesis, and in particular, to a self-expanding low profile
prosthesis for use in the treatment of abdominal aortic aneurysms.
An ePTFE membrane on the prosthesis exhibits physical properties
which inhibit the formation of a thin viable neointima through the
membrane.
[0004] 2. Description of the Related Art
[0005] An abdominal aortic aneurysm is a sac caused by an abnormal
dilation of the wall of the aorta, a major artery of the body, as
it passes through the abdomen. The abdomen is that portion of the
body which lies between the thorax and the pelvis. It contains a
cavity, known as the abdominal cavity, separated by the diaphragm
from the thoracic cavity and lined with a serous membrane, the
peritoneum. The aorta is the main trunk, or artery, from which the
systemic arterial system proceeds. It arises from the left
ventricle of the heart, passes upward, bends over and passes down
through the thorax and through the abdomen to about the level of
the fourth lumbar vertebra, where it divides into the two common
iliac arteries.
[0006] The aneurysm usually arises in the infrarenal portion of the
diseased aorta, e.g., below the kidneys. When left untreated, the
aneurysm may eventually cause rupture of the sac with ensuing fatal
hemorrhaging in a very short time. High mortality associated with
the rupture led initially to transabdominal surgical repair of
abdominal aortic aneurysms. Surgery involving the abdominal wall,
however, is a major undertaking with associated high risks. There
is considerable mortality and morbidity associated with this
magnitude of surgical intervention, which in essence involves
replacing the diseased and aneurysmal segment of blood vessel with
a prosthetic device which typically is a synthetic tube, or graft,
usually fabricated of Polyester, Urethane, DACRON.RTM.,
TEFLON.RTM., or other suitable material.
[0007] To perform the surgical procedure requires exposure of the
aorta through an abdominal incision which can extend from the rib
cage to the pubis. The aorta must be closed both above and below
the aneurysm, so that the aneurysm can then be opened and the
thrombus, or blood clot, and arteriosclerotic debris removed. Small
arterial branches from the back wall of the aorta are tied off. The
DACRON.RTM. tube, or graft, of approximately the same size as the
normal aorta is sutured in place, thereby replacing the aneurysm.
Blood flow is then re-established through the graft. It is
necessary to move the intestines in order to get to the back wall
of the abdomen prior to clamping off the aorta.
[0008] If the surgery is performed prior to rupturing of the
abdominal aortic aneurysm, the survival rate of treated patients is
markedly higher than if the surgery is performed after the aneurysm
ruptures, although the mortality rate is still quite high. If the
surgery is performed prior to the aneurysm rupturing, the mortality
rate is typically slightly less than 10%. Conventional surgery
performed after the rupture of the aneurysm is significantly
higher, one study reporting a mortality rate of 66.5%. Although
abdominal aortic aneurysms can be detected from routine
examinations, the patient does not experience any pain from the
condition. Thus, if the patient is not receiving routine
examinations, it is possible that the aneurysm will progress to the
rupture stage, wherein the mortality rates are significantly
higher.
[0009] Disadvantages associated with the conventional, prior art
surgery, in addition to the high mortality rate include: the
extended recovery period associated with such surgery; difficulties
in suturing the graft, or tube, to the aorta; the loss of the
existing aorta wall and thrombosis to support and reinforce the
graft; the unsuitability of the surgery for many patients having
abdominal aortic aneurysms; and the problems associated with
performing the surgery on an emergency basis after the aneurysm has
ruptured. A patient can expect to spend from one to two weeks in
the hospital after the surgery, a major portion of which is spent
in the intensive care unit, and a convalescence period at home from
two to three months, particularly if the patient has other
illnesses such as heart, lung, liver, and/or kidney disease, in
which case the hospital stay is also lengthened. The graft must be
secured, or sutured, to the remaining portion of the aorta, which
may be difficult to perform because of the thrombosis present on
the remaining portion of the aorta. Moreover, the remaining portion
of the aorta wall is frequently friable, or easily crumbled.
[0010] Since many patients having abdominal aortic aneurysms have
other chronic illnesses, such as heart, lung, liver, and/or kidney
disease, coupled with the fact that many of these patients are
older, the average age being approximately 67 years old, these
patients are not ideal candidates for such major surgery.
[0011] More recently, a significantly less invasive clinical
approach to aneurysm repair, known as endovascular grafting, has
been developed. Parodi, et al. provide one of the first clinical
descriptions of this therapy. J. C. Parodi et al., Transfemoral
Intraluminal Graft Implantation for Abdominal Aortic Aneurysms, 5
Annals Vascular Surgery 491 (1991). Endovascular grafting involves
the translumenal placement of a prosthetic arterial graft within
the lumen of the artery.
[0012] In general, transluminally implantable prostheses adapted
for use in the abdominal aorta comprise a tubular wire cage
surrounded by a tubular sleeve made of polytetrafluoroethylene
(PTFE) or Dacron.RTM.. Both balloon expandable and self expandable
support structures have been proposed. Endovascular grafts adapted
to treat both straight segment and bifurcation aneurysms have also
been proposed.
[0013] Notwithstanding the foregoing, there remains a need for a
structurally simple, easily deployable endovascular prosthesis
having a low profile adapted for translumenal delivery. Moreover,
this need extends to prosthesis adaptable to span either a straight
or bifurcated abdominal aortic aneurysm. Preferably, the tubular
prosthesis can be self expanded at the site to treat the abdominal
aortic aneurysm, and exhibits flexibility to accommodate nonlinear
anatomies and normal anatomical movement.
SUMMARY
[0014] The present invention provides a tubular prosthesis for
spanning a defect in the vascular system, such as an abdominal
aortic aneurysm. The prosthesis comprises a support frame, and an
expanded polytetrafluoroethylene (ePTFE) membrane thereon. The
physical properties of the ePTFE membrane have been optimized to
enable the prosthesis to isolate the aneurysmic sack while at the
same time preventing tissue ingrowth through the wall sufficient to
form and nourish a thin viable neointimal layer along the inside
surface of the prosthesis. Due to the interplay of the wall
thickness, density, intranodal distance, and possibly other
physical characteristics of the ePTFE, the neointima inhibiting
ePTFE liner in accordance with the present invention cannot be
described in terms of a specific set of variables. To the contrary,
changes in any one variable may be offsetable by commensurate
changes in another variable, to produce a neointima inhibiting
ePTFE in accordance with the present invention. Such optimization
can be accomplished through routine experimentation by those of
skill in the art in view of the disclosure herein, and in view of
the objective of inhibiting the formation of a viable neointima on
the lumenal side of the ePTFE membrane, nourished through the
membrane.
[0015] In accordance with one aspect of the present invention,
there is provided a prosthetic vascular graft. The graft comprises
an expandable tubular support, and a tubular ePTFE layer carried by
the support. The ePTFE layer comprises a wall thickness of less
than about 0.15 mm, an average density of greater than about 0.75
gm/ml, and an average distance between nodes in the range of
between about 6 to about 80 microns. The ePTFE layer prevents the
formation and nourishment of a viable neointimal layer
therethrough.
[0016] There is provided in accordance with another aspect of the
present invention, a method of treating a patient. The method
comprises the steps of providing an implantable tubular prosthesis,
having an ePTFE layer thereon. The prosthesis is positioned across
a defect in a vessel, such that a first side of the layer is in
contact with the wall of the vessel. Formation of a viable
neointima on a second side of the layer, nourished through the
layer is inhibited, by providing the ePTFE layer with a density of
greater than about 0.75 gm/ml and a wall thickness of less than 0.2
mm.
[0017] In accordance with a further aspect of the present
invention, there is provided an endolumenal prosthesis having a
lumenal surface and an ablumenal surface. The prosthesis comprises
a tubular wire support with proximal and distal ends and a central
lumen extending therebetween. The wire support comprises at least
two axially adjacent tubular segments, each segment comprising a
series of proximal and distal bends connected by a length of wire.
The wire support is radially compressible into a first, reduced
cross-sectional configuration for transluminal navigation to a
treatment site in a body lumen, and self expandable to a second,
enlarged cross-sectional configuration for deployment at the
treatment site in the body lumen.
[0018] A tubular ePTFE sheath is provided on the wire support, the
sheath being configured to inhibit the formation of a viable
neointimal layer on the lumenal surface of the sheath.
[0019] The ePTFE sheath generally has a wall thickness of no
greater than about 0.2 mm, and often has a wall thickness within
the range of from about 0.05 mm to about 0.15 mm. In one
embodiment, the ePTFE sheath has a wall thickness of about 0.1
mm.
[0020] The ePTFE sheath generally has a density of at least about
0.5 gm/ml. In certain embodiments, the ePTFE sheath has a density
of at least about 0.75 gm/ml, and the ePTFE sheath in certain
embodiments has a density within the range of from 1.1 gm/ml to
about 1.5 gm/mm.
[0021] The ePTFE sheath has a plurality of nodes and the average
distance between nodes is generally within the range of from about
6 microns to about 80 microns.
[0022] In accordance with a further aspect of the present
invention, there is provided a prosthetic vascular structure. The
structure comprises expanded polytetrafluoroethylene, the expanded
polytetrafluoroethylene further comprising a macroscopically
tubular configuration with a proximal end, a distal end and an
inner surface, and a microscopic superstructure of irregularly
spaced nodes of various sizes and shapes interconnected by
fibrils.
[0023] The vascular structure further comprises an average wall
thickness of less than about 0.2 mm, and a substantially uniform
distribution of nodes throughout the tubular configuration.
[0024] The vascular structure additionally comprises an average
density of greater than about 0.5 gm/ml. The structure is
configured to provide for the smooth flow of blood between at least
two points in a living organism, while controlling cellular
ingrowth through the wall of the tubular configuration to
substantially prevent the formation of a thin, viable neointima
over the inner surface thereof.
[0025] Further features and advantages of the present invention
will become apparent to those of skill in the art in view of the
detailed description of preferred embodiments which follows, when
considered together with the attached drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic representation of a straight segment
vascular prosthesis in accordance with the present invention,
positioned within a symmetric abdominal aortic aneurysm.
[0027] FIG. 2 is an exploded view of an endolumenal vascular
prosthesis in accordance with the present invention, showing a self
expandable wire support structure separated from an outer tubular
sleeve.
[0028] FIG. 3 is a plan view of a formed wire useful for rolling
about an axis into a multi-segment support structure in accordance
with the present invention.
[0029] FIG. 4 is an enlarged detail view of a portion of the formed
wire illustrated in FIG. 3.
[0030] FIG. 5 is a schematic view of a portion of a wire cage wall,
illustrating folded link connections between adjacent apexes.
[0031] FIG. 6 is an exploded view of two opposing apexes
dimensioned for one embodiment of the folded link connection of the
present invention.
[0032] FIG. 7 is an enlarged view of a folded link, taken along the
lines 7-7 in FIG. 5.
[0033] FIG. 8 is a cross-sectional view taken along the line 8-8 in
FIG. 7.
[0034] FIGS. 6A, 7A, 8A, 7B, 8B, 7C, and 7D illustrate alternate
embodiments of a folded link constructed from an opposing apex
pair.
[0035] FIG. 9 is a partial view of a junction between two adjacent
tubular segments, illustrating oppositely oriented folded links in
accordance with the present invention.
[0036] FIG. 10 is a cross-section taken along the line 10-10 in
FIG. 9.
[0037] FIG. 11 is a schematic view of a portion of a wall of a
graft, laid out flat, illustrating an alternating folded link
pattern.
[0038] FIG. 12 is a wall pattern as in FIG. 11, illustrating a
multi-zone folded link pattern.
[0039] FIGS. 12A through 12C illustrate an alternate wall pattern,
which permits axially staggered links between adjacent graft
segments.
[0040] FIGS. 13A through 13D show alternative zig-zag wire or laser
cut sheet support configurations that vary from the support
illustrated in FIG. 3.
[0041] FIG. 13E is a detail view of a bend identified in FIG. 13D,
illustrating a varied filament width feature of the invention
[0042] FIG. 13F is a detail view of an integral link between
opposing apexes.
[0043] FIG. 14 is a cross-sectional view taken through a portion of
a prosthesis in which a wire support is embedded in an ePTFE
wall.
[0044] FIGS. 15A and 15B are schematic views of a portion of a wall
of a graft, laid out flat, illustrating two alternative wire
support configurations having spot welds between lumenal and
exterior layers of a polymeric membrane.
[0045] FIG. 15C is a cross-sectional view through the wall taken
along line C-C in FIGS. 15A and 15B.
[0046] FIG. 16 is a schematic illustration of a straight segment
delivery catheter in accordance with the present invention,
positioned within an abdominal aortic aneurysm.
[0047] FIG. 17 is an illustration as in FIG. 16, with the straight
segment endolumenal prosthesis partially deployed from the delivery
catheter.
[0048] FIG. 18 is a schematic representation of the abdominal
aortic anatomy, with an endolumenal vascular prostheses of the
present invention positioned within each of the right renal artery
and the right common iliac.
[0049] FIG. 19 is a schematic representation of a straight segment
graft in accordance with a further embodiment of the present
invention, with side openings to permit renal perfusion.
[0050] FIG. 20 is a schematic representation of a bifurcated
vascular prosthesis in accordance with the present invention,
positioned at the bifurcation between the abdominal aorta and the
right and left common iliac arteries.
[0051] FIG. 21 is an exploded view of the implanted graft of FIG.
20.
[0052] FIG. 22 is a cross sectional view of the bifurcated vascular
prosthesis in accordance with the present invention, taken along
the line 22-22 of FIG. 20.
[0053] FIG. 23 is a plan view of formed wire useful for rolling
about an axis into an aortic trunk segment and a first iliac branch
segment support structure in accordance with the present
invention.
[0054] FIG. 24 is a schematic representation of another embodiment
of the wire support structure for the bifurcated vascular
prosthesis of the present invention, showing a main body support
structure and separate branch support structures.
[0055] FIG. 25 is a schematic representation of the three-part wire
support structure as in FIG. 24, illustrating the sliding
articulation between the branch supports and the main body
support.
[0056] FIG. 26 is a plan view of formed wire useful to form a
branch support structure in accordance with the three-part support
embodiment of the present invention shown in FIG. 24.
[0057] FIGS. 27A, 27B and 27C are enlargements of the apexes
delineated by lines A, B and C, respectively, in FIG. 26.
[0058] FIG. 28 is a schematic representation of a polymeric sleeve
in accordance with one embodiment of the present invention.
[0059] FIG. 29 is a 1000.times. magnified view of a portion of the
polymeric sleeve of FIG. 28.
[0060] FIG. 30 is a cross-sectional view of a segment of a
polymeric sleeve after having been explanted from a medical
patient.
DETAILED DESCRIPTION
[0061] Referring to FIG. 1, there is disclosed a schematic
representation of the abdominal part of the aorta and its principal
branches. In particular, the abdominal aorta 30 is characterized by
a right renal artery 32 and left renal artery 34. The large
terminal branches of the aorta are the right and left common iliac
arteries 36 and 38. Additional vessels (e.g., second lumbar,
testicular, inferior mesenteric, middle sacral) have been omitted
for simplification. A generally symmetrical aneurysm 40 is
illustrated in the infrarenal portion of the diseased aorta. An
expanded straight segment endolumenal vascular prosthesis 42, in
accordance with one embodiment of the present invention, is
illustrated spanning the aneurysm 40.
[0062] The endolumenal vascular prosthesis 42 includes a polymeric
sleeve 44 and a tubular wire support 46, which are illustrated in
situ in FIG. 1. The sleeve 44 and wire support 46 are more readily
visualized in the exploded view shown in FIG. 2. The endolumenal
prosthesis 42 illustrated and described herein depicts an
embodiment in which the polymeric sleeve 44 is situated
concentrically outside of the tubular wire support 46. However,
other embodiments may include a sleeve 44 or sleeves 44 situated
substantially concentrically inside the wire support 46, or on both
the inside and the outside of the wire support 46. Alternatively,
the wire support 46 may be embedded within a polymeric matrix which
makes up the sleeve 44. Regardless of whether the sleeve 44 is
inside or outside the wire support 46, or both inside and outside,
the sleeve 44 may be attached to the wire support 46 by any of a
variety of methods or devices, including laser bonding, adhesives,
clips, sutures, lamination, dipping or spraying or others,
depending upon the composition of the sleeve or membrane 44 and
overall prosthesis design.
[0063] In one embodiment, the tubular wire support 46 is formed
from a continuous single length of round or flattened wire. As used
herein, "wire" includes its ordinary meaning, conventional wire, as
well as filaments having rectangular or other cross sections formed
by laser cutting or otherwise etching a support structure from a
sheet or tube stock. Alternatively, two or more wire lengths can be
secured together to produce the wire support 46. The wire support
46 is preferably formed in a plurality of discrete tubular segments
54, connected together and oriented about a common axis. Each pair
of adjacent segments 54 may be connected by a connector 66 as
illustrated in FIG. 3. The connectors 66 collectively produce a
generally axially extending backbone which adds axial strength to
the prosthesis 42. Adjacent segments can be connected both by the
backbone, as well as the interlocking junction disclosed below.
Additional structures, including circumferentially extending
sutures, solder joints, and wire loops may also be used.
Alternatively, in one embodiment, adjacent wire cage segments may
be held together by the polymeric sleeve in which the cage is
embedded. This embodiment is detailed below.
[0064] The segmented configuration of the tubular wire support 46
facilitates a great deal of flexibility. Each segment 54, though
joined to adjacent segments, may be independently engineered to
yield desired parameters. Each segment may range in axial length
from about 0.3 to about 5 cm or longer for certain applications.
Generally, the shorter the segment's length the greater its radial
strength. An endolumenal prosthesis may include from about 1 to
about 50 segments, preferably from about 3 to about 10 segments.
For example, while a short graft patch, in accordance with the
invention, may comprise only 2 segments and span a total of 2 to 3
cm, a complete graft may comprise 4 or more segments and span the
entire aortic aneurysm. In addition to the flexibility and other
functional benefits available through employment of different
length segments, further flexibility can be achieved through
adjustments in the number, angle, or configuration of the wire
bends associated with the tubular support.
[0065] In addition to having differing expanded diameters in
different zones of the prosthesis 42, different zones can be
provided with a different radial expansion force, such as ranging
from about 0.2 lbs to about 0.8 lbs. In one embodiment, the
proximal zone 55 is provided with a greater radial force than the
central zone 57 and/or distal zone 59. The greater radial force can
be provided in any of a variety of manners discussed elsewhere
herein, such as through the use of an additional one or two or
three or more proximal bends 60, distal bends 62 and wall sections
64 compared to a reference segment 54 in the central zone 57 or
distal zone 59. Alternatively, additional spring force can be
achieved in the proximal zone 55 through the use of the same number
of proximal bends 60 as in the rest of the prosthesis, but with a
heavier gauge wire.
[0066] The wire may be made from any of a variety of different
materials, such as elgiloy, Nitinol or MP35N, or other alloys which
include nickel, titanium, tantalum, or stainless steel, high Co--Cr
alloys or other temperature sensitive materials. For example, an
alloy comprising Ni 15%, Co 40%, Cr 20%, Mo 7% and balance Fe may
be used. The tensile strength of suitable wire is generally above
about 300 Ksi and often between about 300 and about 340 Ksi for
many embodiments. In one embodiment, a Chromium-Nickel-Molybdenum
alloy such as that marketed under the name Conichrom (Fort Wayne
Metals, Ind.) has a tensile strength ranging from 300 to 320 K psi,
elongation of 3.5-4.0%. The wire may be treated with a plasma
coating and be provided with or without additional coatings such as
PTFE, Teflon, Perlyne and drugs.
[0067] In addition to segment length and bend configuration,
discussed above, another determinant of radial strength is wire
gauge. The radial strength, measured at 50% of the collapsed
profile, preferably ranges from about 0.2 lb to 0.8 lb, and
generally from about 0.4 lb to about 0.5 lb or more. Preferred wire
diameters in accordance with the present invention range from about
0.004 inches to about 0.020 inches. More preferably, the wire
diameters range from about 0.006 inches to about 0.018 inches. In
general, the greater the wire diameter, the greater the radial
strength for a given wire layout. Thus, the wire gauge can be
varied depending upon the application of the finished graft, in
combination with/or separate from variation in other design
parameters (such as the number of struts, or proximal bends 60 and
distal bends 62 per segment), as will be discussed. A wire diameter
of approximately 0.018 inches may be useful in a graft having four
segments each having 2.5 cm length per segment, each segment having
six struts intended for use in the aorta, while a smaller diameter
such as 0.006 inches may be useful for a 0.5 cm segment graft
having 5 struts per segment intended for the iliac artery. In one
embodiment, the length of vascular prosthesis 42 is about 28
cm.
[0068] In one embodiment of the present invention, the wire
diameter is tapered from the proximal to distal ends.
Alternatively, the wire diameter may be tapered incrementally or
stepped down, or stepped up, depending upon differing radial
strength requirements along the length of the graft for each
particular clinical application. In one embodiment, intended for
the abdominal aortic artery, the wire has a cross-section of about
0.018 inches in the proximal zone 55 and the wire tapers down to a
diameter of about 0.006 inches in the distal zone 59 of the graft
42. End point dimensions and rates of taper can be varied widely,
within the spirit of the present invention, depending upon the
desired clinical performance.
[0069] The polymeric sleeve in accordance with the present
invention is illustrated, for example, in FIGS. 2, 20, 21 and 28.
Polymeric sleeve 44 is illustrated as a substantially cylindrical
tube of polymeric material, but may be manufactured in a variety of
shapes and sizes, as is well known to those of skill in the art.
For example, in one application, polymeric sleeve 44 is configured
for use at a bifurcation within the human body's vasculature, such
as polymeric sleeve 106 of FIGS. 20 and 21 described below. In
other embodiments, the polymeric sleeve 44 described below may be
used without a wire support or a wire support formed in a manner
not described herein.
[0070] Referring to FIG. 28, polymeric sleeve 44 includes an outer,
or ablumenal surface 252, an inner or lumenal surface 254, and a
wall thickness 256 therebetween. The inner surface 254 defines a
lumen 258 through which bodily fluid, such as blood, may flow. As
mentioned above, the polymeric sleeve 44 is adapted to be used as a
graft, without a support frame (as shown in FIG. 28), or may be
used in conjunction with a frame, such as described in greater
detail herein (e.g., wire cage 46 of FIGS. 1, 2 and 19, or wire
support 107 of FIG. 20). In one embodiment, the polymeric sleeve 44
is placed over at least a portion of a frame such that the inner
surface 254 of the polymeric sleeve 44 is adjacent the outer
surface of the frame, the polymeric sleeve 44 acting as a frame
cover. In another embodiment, the polymeric sleeve 44 is placed
inside at least a portion of a frame such that the outer surface
252 of the polymeric sleeve 44 is adjacent the inner surface of the
frame, the polymeric sleeve 44 acting as a frame liner. In another
embodiment, the frame is embedded or encapsulated between at least
two polymeric sleeves 44, as described elsewhere herein. An
adhesive bonding layer (not shown) may be used to adhere the
polymeric sleeve 44 to the frame, or to another polymeric sleeve
44. Other adhesive methods, such as sintering or laser welding, may
alternatively be used, as described below.
[0071] The polymeric sleeve 44 generally has a microscopic
superstructure of uniformly distributed nodes which are
interconnected by fibrils. The node-fibril superstructure of ePTFE
is generally well understood by those of skill in the art. One
example of prior art ePTFE is illustrated at approximately
1000.times. magnification in FIG. 29. The nodes 260 of ePTFE are
generally longitudinally aligned and extend along an axis
transverse to the axis of expansion of the ePTFE. The fibrils 262
of ePTFE span between the nodes 260, and are generally
longitudinally aligned and extend along an axis parallel to the
axis of expansion of the ePTFE.
[0072] In addition, the polymeric sleeve 44 may be characterized by
its wall thickness 256 (as illustrated in FIG. 28), an average
internodular distance (not shown), and an average density (not
shown). When these characteristics are properly selected, and
unlike prior art ePTFE sleeves, such as, for example, that
disclosed in U.S. Pat. No. 6,436,135, the polymeric sleeve 44 of
the present invention will prohibit the formation of a viable
neointimal layer through the wall of the sleeve and along the
sleeve's inner surface 254.
[0073] The term "neointimal layer" includes its ordinary meaning,
as is known to those of skill in the art, as well as a thin lining
of viable endothelial cells that would typically be less than ten
blood-cells thick. A neointimal layer is one that generally forms
along the inner surface of a medical device, such as the prosthetic
vascular structure taught by Goldfarb in U.S. Pat. No. 6,436,145,
incorporated by reference herein. The "neointima" is similar to the
inner surface of natural blood vessels, known to those of skill in
the art as the "intima." The intima is generally characterized by a
thin, delicate layer of endothelial cells whose function is to
provide a smooth interface between the blood stream and the vessel
wall. The natural intima serves to lessen the severity of irregular
vessel wall transitions, thereby helping to assure laminar blood
flow.
[0074] However, it has been found clinically useful in certain
settings to prevent the formation of a neointimal layer over the
inner surface of a prosthetic structure, such as a polymeric sleeve
44. Preventing the formation of a neointimal layer may have the
benefit of reducing the risk of excessive overgrowth, hyperplasia,
and occlusion of the vessel and other clinically adverse
events.
[0075] An ePTFE sleeve 44 in accordance with the present invention
generally will have a wall thickness 256 less than about 0.2 mm,
often no greater than about 0.15 mm or 0.125 mm, and in one
embodiment about 0.11 mm. The internodal distance is generally in
the range of between about 5 and about 100 .mu.m, often in the
range of between about 10 and 50 .mu.m, and in one embodiment is in
the range of between about 25 and 40 .mu.m. The average density is
generally greater than about 0.5 g/ml, often in excess of about
0.75 g/ml, and depending upon other variables, is at least about
1.0 or at least about 1.2. In one embodiment the average density is
in the range of about 1.0 g/ml to about 1.5 g/ml, and it generally
is no greater than about 2 g/ml.
[0076] The foregoing characteristics can be optimized in view of
each other to achieve a polymeric sleeve 44 that can function in
the abdominal aortic aneurysm environment to isolate the aneurysmic
sac while at the same time preventing tissue ingrowth through the
wall in the landing zones of the sleeve 44. The landing zones
include the locations generally in the proximal and distal end
region of the sleeve 44 where it is in contact with native healthy
intima of the vessel in which it is inserted.
[0077] Although the foregoing physical properties provide guidance
to the selection of a specific ePTFE material, one or more of the
characteristics described above may be selected outside the ranges
provided, and the sleeve 44 may still be capable of preventing the
formation and sustaining of a viable neointimal layer as long as
the other characteristics are selected to compensate. For example,
a wall thickness outside of the foregoing ranges will not
necessarily cause the sleeve 44 to allow the formation of a
neointimal layer as long as the density or one or more other
characteristics is properly selected. Routine experimentation, as
well as the methods taught by Goldfarb in U.S. Pat. No. 6,436,145,
incorporated by reference herein, may be used to optimize the
sleeve 44 characteristics in order to prevent neointima formation
for any given combination of selected sleeve 44
characteristics.
[0078] In another embodiment of the present invention a neointima
inhibiting polymeric sleeve is formed by treating or coating a
sleeve, such as a sleeve which would otherwise have allowed the
formation of a neointima, with a sealant. Neointima forming sleeves
are well known in the art. Examples of such sleeves are taught by
Goldfarb in U.S. Pat. No. 6,436,145. The sealant provides a
mechanical and/or chemical barrier to the migration of cells
through the polymeric sleeve 44 wall, thereby preventing the
formation of a neointimal layer on the luminal side of the sleeve's
44 wall.
[0079] In another embodiment, a coating having controlled
cytotoxicity is applied to a sleeve 44. The coating prevents the
migration of cells through the polymeric sleeve 44 wall, yet is not
sufficiently cytotoxic to cause clinically adverse events.
[0080] Neointima inhibiting polymeric sleeves 44 in accordance with
the present invention may upon explantation exhibit a structured
thrombus formation, or fibrin coating, or other proteinaceous layer
along the inner surface 254 thereof. However, these formations are
not a viable neointimal layer as contemplated herein, such as a
thin, viable neointima which is nourished through the sleeve 44
wall thickness 256. A thin, partial neointimal layer may also be
observed upon explantation to have climbed around the ends of the
sleeve 44 and adhere to the inner surface of the sleeve 44 for a
short distance from its ends. However, this growth also is not a
viable neointimal layer which is nourished through the sleeve 44
wall thickness 256.
[0081] Polymeric sleeves 44 within the contemplation of the present
invention may also allow partial tissue ingrowth into the polymeric
sleeve 44 wall thickness 256. Such partial tissue ingrowth may be
advantageous for anchoring of the polymeric sleeve 44 within the
body lumen. But the ePTFE sleeves within the present invention
inhibit further growth such as would support the formation of a
neointimal layer over the polymeric sleeve 44 inner surface 254.
The cross-sectional view of one such neointimal layer-inhibiting
polymeric sleeve 44 is schematically illustrated in FIG. 30
[0082] The polymeric sleeve 44 of FIG. 30 schematically represents
the expected finding in an abdominal aortic aneurysm bifurcation
graft explanted from a human recipient post mortem after an
implantation period of six months. A uniform, firmly attached
encapsulation of collagenous matter 264 is shown covering the outer
surface 252 of the polymeric sleeve 44. Some tissue ingrowth 266
may have occurred into a portion (e.g., approximately 40%) of the
wall thickness 256 of the polymeric sleeve 44. However, any tissue
ingrowth 266 is not sufficient to establish the formation of a
viable, neointimal layer over the inner surface 254 of the
polymeric sleeve 44. As shown in FIG. 30, the polymeric sleeve 44
prohibits the formation of a viable neointimal layer. Thrombus
formation and/or a fibrin coating may be present on the inner
(lumenal) surface 254 of tubular sleeve 44.
[0083] In one embodiment, the material of the polymeric sleeve 44
is expanded polytetrafluoroethylene (ePTFE). The process of
expanding polytetrafluoroethylene (PTFE) is well known to those of
skill in the art. In general, to expand PTFE, a resin is extruded
into a desired geometrical configuration, such as a sheet. As the
extrudate is stretched, the non-porous PTFE separates into solid
nodes of PTFE which are structurally interconnected by PTFE
fibrils. The fibrils are drawn from the nodes during expansion.
[0084] The extrudate is heated at a temperature below the sintering
temperature, which in one embodiment is 327.degree. C., and then
physically stretched or expanded along at least one direction. The
expanded material is then restrained against contraction, and is
sintered by brief exposure to temperatures in excess of the
sintering temperature. Sintering causes crystallization of the
expanded structure, and increased tensile strength of up to about
6500 psi.
[0085] The nodes are roughly ellipsoidal in shape, and are of
random, but generally uniform size, and are distributed in a
homogeneous pattern throughout the wall thickness 256. In addition,
in one embodiment, the nodes are typically less than a few times
the size of a normal fibroblast or red blood cell. Additional
details of the ePTFE production process are well known to those of
skill in the art. One example of such process is disclosed in U.S.
Pat. No. 4,187,390, which is incorporated in its entirety by
reference herein. Post processing steps such as compression to
increase density and/or reduce wall thickness may also be used.
[0086] The foregoing neointima inhibiting material may be used in
any of a variety of applications, such as for the tubular fabric
liner of a self expandable graft as is discussed below. Referring
to FIG. 3, there is illustrated a plan view of a single formed wire
used for rolling about a longitudinal axis to produce a four
segment straight tubular wire support. The formed wire exhibits
distinct segments, each corresponding to an individual tubular
segment 54 in the tubular support 46 (see FIGS. 1 and 2).
[0087] Each segment 54 has a repeating pattern of proximal bends 60
connected to corresponding distal bends 62 by wall sections 64
which extend in a generally zig-zag configuration when the segment
54 is radially expanded. Each segment 54 is connected to the
adjacent segment 54 through a connector 66, except at the terminal
ends of the graft. The connector 66 in the illustrated embodiment
comprises two wall or strut sections 64 which connect a proximal
bend 60 on a first segment 54 with a distal bend 62 on a second,
adjacent segment 54. The connector 66 may additionally be provided
with a connector bend 68, which may be used to impart increased
radial strength to the graft and/or provide a tie site for a
circumferentially extending suture.
[0088] Referring to FIG. 4, there is shown an enlarged view of the
wire support illustrating a connector 66 portion between adjacent
segments 54. In the embodiment shown in FIG. 4, a proximal bend 60
comprises about a 180 degree arc, having a radial diameter w1,
which in one embodiment ranges from 0.070 to 0.009 inches depending
upon the wire diameter. The proximal bend 60 is followed by a
relatively short length of parallel wire that spans an axial
distance d1. The parallel wires thereafter diverge outwardly from
one another and form the strut sections 64, or the proximal half of
a connector 66. At the distal end of the strut sections 64, the
wire forms a distal bend 62, preferably having identical
characteristics as the proximal bend 60, except being concave in
the opposite direction. The axial direction component of the
distance between the apexes of the corresponding proximal and
distal bends 60, 62 on a given strut section 64 is referred to as
(d) and represents the axial length of that segment. The total
expanded angle defined by the bend 60 and the divergent strut
sections 64 is represented by a. Upon compression to a collapsed
state, such as when the graft is within the deployment catheter,
the angle .alpha. is reduced to a'. In the expanded configuration,
a is generally within the range of from about 35.degree. to about
45.degree. for a six apex section having an axial length of about
1.5 cm or 2 cm and a diameter of about 25 mm or 28 mm. The expanded
circumferential distance between any two adjacent distal bends 62
(or proximal bends 60) is defined as (s).
[0089] In general, the diameter W of each proximal bend 60 or
distal bend 62 is within the range of from about 0.009 inches to
about 0.070 inches depending upon the wire diameter. Diameter W is
preferably as small as possible for a given wire diameter and wire
characteristics. As will be appreciated by those of skill in the
art, as the distance W is reduced to approach two times the
cross-section of the wire, the bend 60 or 62 will exceed the
elastic limit of the wire, and radial strength of the finished
segment will be lost. Determination of a minimum value for W, in
the context of a particular wire diameter and wire material, can be
readily determined through routine experimentation by those of
skill in the art.
[0090] As will be appreciated from FIGS. 3 and 4, the sum of the
distances (s) in a plane transverse to the longitudinal axis of the
finished graft will correspond to the circumference of the finished
graft cage in that plane. For a given circumference, the number of
proximal bends 60 or distal bends 62 is directly related to the
distance (s) in the corresponding plane. Preferably, the finished
graft in any single transverse plane will have from about 3 to
about 10 (s) dimensions, preferably from about 4 to about 8 (s)
dimensions and, more preferably, about 5 or 6 (s) dimensions for an
aortic application. Each (s) dimension corresponds to the distance
between any two adjacent bends 60-60 or 62-62 as will be apparent
from the discussion herein. Each segment 54 can thus be visualized
as a series of triangles extending circumferentially around the
axis of the graft, defined by a proximal bend 60 and two distal
bends 62 or the reverse.
[0091] In one embodiment of the type illustrated in FIG. 4, w is
about 2.0 mm.+-.1 mm for a 0.018 inch wire diameter. D1 is about 3
mm.+-.1 mm, and d is about 20 mm.+-.1 mm. Specific dimensions for
all of the foregoing variables can be varied considerably,
depending upon the desired wire configuration, in view of the
disclosure herein.
[0092] In one embodiment of the present invention, the apexes of
adjacent segments are joined by an integral linkage formed from the
wire. The form of the linkage may vary as detailed below including
various types of interlocking junctions. In other embodiments, the
apexes may be joined by independent structural elements such as
sutures and wire loops. In yet other embodiments, the apexes of
adjacent segments may not be joined at all. Rather, the formed wire
may be embedded in a polymeric membrane which acts both as the
graft sleeve and as a structure to join adjacent segments. Such a
design has the advantage that the profile of the stent graft may be
very low, since no overlapping, interlocking or external junctions
are employed to hold the wire segments together. Each of these
variations is discussed below.
[0093] Referring to FIGS. 5 and 6, one or more apexes 76 is
provided with an elongated axial length d2, which permits the apex
76 to be wrapped around a corresponding portion 78 such as an apex
of the adjacent segment to provide an interlocking link 70 between
two axially adjacent cage segments. In one embodiment of the link
70 produced by the opposing apexes 76 and 78 of FIG. 6, utilizing
wire having a diameter from 0.012'' to 0.018'', d1 is generally
within the range of from about 1 mm to about 4 mm and d2 is within
the range of from about 5 mm to about 9 mm. In general, a longer d2
dimension permits accommodation for greater axial travel of apex 78
with respect to 76, as will be discussed, thereby permitting
greater lateral flexibility of the graft. W1 is within the range of
from about 3 mm to about 5 mm, and W2 is sufficiently less than W1
that the apex 76 can fit within the apex 78. Any of a wide variety
of specific apex configurations and dimensions can be utilized, as
will be apparent to those of skill in the art in view of the
disclosure herein. Regardless of the specific dimensions, the end
of the apex 76 is advanced through the apex 78, and folded back
upon its self to hook the apex 78 therein to provide a link 70 in
accordance with the present invention.
[0094] The resulting link 70 (see FIGS. 7 and 8) comprises a wall
portion 71 extending in a first direction, substantially parallel
to the axis of the graft, and a transverse portion 72 extending
transverse to the axis of the graft. A return portion 73 extends
generally in the opposite direction from the wall portion 71 to
create a generally "U" shaped hook. In certain embodiments, a
closing portion 74 is also provided, to minimize the risk of
excessive axial compression of the wire cage. The forgoing
structure produces a functionally closed aperture 77 (illustrated
in FIGS. 8A and 8B), which receives the interlocking section 75 of
the adjacent graft segment. Alternatively, see FIG. 10.
[0095] In general, the aperture 77 preferably has a width (as
viewed in FIG. 8) in the radial graft direction of substantially
equal to the radial direction dimension of the interlocking section
75. In this embodiment, the interlocking section 75, as well as the
locking portion 71 and return portion 73 can be flattened in the
radial direction, to minimize the transverse cross-section of the
link 70. In the axial direction, the aperture 77 is preferably
greater than the axial direction dimension of the interlocking
section 75, to accommodate some axial movement of each adjoining
tubular segment of the graft. The axial length of the aperture 77
is at least about 2 times, and preferably at least about 3 or 4
times the cross-section of the interlocking section 75. The optimum
axial length of the aperture 77 can be determined through routine
experimentation by one of skill in the art in view of the intended
clinical performance, taking into account the number of links 70
per transverse plane as well as the desired curvature of the
finished graft.
[0096] FIGS. 6A, 7A and 8A illustrate an alternate configuration
for the moveable link 70. With this configuration, the radial
expansion force will be higher.
[0097] FIGS. 7B and 8B illustrate another alternate configuration.
This linkage has a better resistance to axial compression and
disengagement. Referring to FIGS. 7B and 8B, the apex extends
beyond closing portion 74 and into an axial portion 79 which
extends generally parallel to the longitudinal axis of the graft.
Provision of an axial extension 79 provides a more secure enclosure
for the aperture 77 as will be apparent to those of skill in the
art. The embodiments of FIGS. 7B and 8B also illustrate an enclosed
aperture 83 on the opposing apex. The aperture 83 is formed by
wrapping the apex in at least one complete revolution so that a
generally circumferentially extending portion 81 is provided.
Circumferential portion 81 provides a stop, to limit axial
compressibility of the graft. The enclosed aperture 83 can be
formed by winding the wire of the apex about a mandrel either in
the direction illustrated in FIG. 7B, or the direction illustrated
in FIG. 7C. The embodiment of FIG. 7C advantageously provided only
a single wire thickness through the aperture 77, thereby minimizing
the wall thickness of the graft. This is accomplished by moving the
crossover point outside of the aperture 77, as will be apparent
from FIG. 7C.
[0098] The link 70 in accordance with one embodiment of the present
invention is formed integrally with the wire that forms the cage of
the endovascular prosthesis. Alternatively, link 70 may be
constructed from a separate material that is secured to the wire
cage such as by soldering, suture, wrapping or the like.
[0099] The axial direction of the link 70 may also be varied,
depending upon the desired performance characteristics of the
graft. For example, the distal tips 76 of each link 70 may all face
the same direction, such as proximal or distal with respect to the
graft. See, for example, FIG. 5. Alternatively, one or more links
in a given transverse plane of apexes may face in a proximal
direction, and one or more links in the same transverse plane may
face in the opposite direction. See, for example, FIG. 9.
[0100] Regardless of the axial orientation of the link 70, at least
one and preferably at least two links 70 are provided per
transverse plane separating adjacent graft segments. In an
embodiment having six apexes per transverse plane, preferably at
least two or three and in one embodiment all six opposing apex
pairs are provided with a link 70. See FIG. 5.
[0101] The distribution of the interlocking link 70 throughout the
wire cage can thus vary widely, depending upon the desired
performance characteristics. For example, each opposing apex pair
between adjacent tubular segments can be provided with a link 70.
See FIG. 5. Alternatively, interlocking links 70 may be spaced
circumferentially apart around the graft wall such as by
positioning them at every second or third opposing apex pair.
[0102] The distribution of the links 70 may also be varied along
the axial length of the graft. For example, a first zone at a
proximal end of the graft and a second zone at a distal end of the
graft may be provided with a relatively larger number of links 70
than a third zone in the central portion of the graft. In one
embodiment, the transverse apex plane between the first and second
tubular segments at the proximal end of the graft may be provided
with a link 70 at each opposing apex pair. This has been determined
by the present inventors to increase the radial strength of the
graft, which may be desirable at the proximal (superior) end of the
graft and possibly also at the distal end of the graft where
resistance to leakage is an issue. A relatively lesser radial
strength may be necessary in the central portion of the graft,
where maintaining patency of the lumen is the primary concern. For
this reason, relatively fewer links 70 may be utilized in a central
zone, in an effort to simplify graft design as well as reduce
collapse profile of the graft. See FIG. 12.
[0103] In one straight segment graft, having four graft segments,
three transverse apex planes are provided. In the proximal apex
plane, each opposing pair of apexes is provided with a link 70. In
the central transverse apex plane, three of the six apex pairs are
provided with a links 70, spaced apart at approximately
120.degree.. Substantially equal circumferential spacing of the
link 70 is preferred, to provide relatively uniform resistance to
bending regardless of graft position. The distal transverse apex
plane may also be provided with a link 70 at each opposing apex
pair.
[0104] The foregoing interlocking link 70 in accordance with one
embodiment of the present invention can be readily adapted to both
the straight segment grafts as discussed above, as well as to the
bifurcated grafts discussed below.
[0105] The interlocking link 70 can be utilized to connect any of a
number of independent graft segments in axial alignment to produce
either a straight segment or a bifurcation graft. The interlocking
link 70 may be utilized as the sole component to secure adjacent
segments to each other, or may be supplemented by additional
attachment structures such as metal loops, sutures, welds and
others which are well understood in the art.
[0106] Referring to FIGS. 12A through 12C there is illustrated a
further wire layout which allows a smaller collapsed profile for
the vascular graft. In general, the embodiment of FIGS. 12A through
12C permits a series of links 70A and 70B to be staggered axially
from one another as seen in FIGS. 12A and 12B. In this manner,
adjacent links 70 do not lie in the same transverse plane, and
permit a tighter nesting of the collapsed wire cage. Preferably,
between each adjoining graft segment, at least a first group of
links 70A is offset axially from a second group of links 70B. In a
six apex graft, having a link 70 at each apex, for example, a first
group of every other apex 70A may be positioned slightly proximally
of a second group of every other apex 70B. Referring to FIG. 12C,
this may be accomplished by extending an apex 76A by a distance d3
which is at least about 1.2 times and as large as 1.5 times or 2
times or more the distance d2. The corresponding apexes 78 and 78A
are similarly staggered axially, to produce the staggered interface
between adjacent graft segments illustrated in FIG. 12A. Although a
loop apex is illustrated in FIG. 12C as apex 78, any of the
alternate apexes illustrated herein can be utilized in the
staggered apex embodiment of the invention. The zig-zag pattern
produced by axially offset links 70A and 70B can reside in a pair
of parallel transverse planes extending generally between adjacent
segments of the graft. Alternatively, the zig-zag relationship
between adjacent links 70A and 70B can spiral around the
circumference of a graft in a helical pattern, as will be
understood by those of skill in the art in view of the disclosure
herein. The precise axial offset between adjacent staggered links
70A and 70B can be optimized by one of ordinary skill in the art
through routine experimentation, taking into account the desired
physical properties and collapsed profile of the graft.
[0107] Additional details and embodiments of the wire layout for
the vascular graft described above can be found in U.S. Pat. No.
6,077,296, which is hereby incorporated by reference herein in its
entirety.
[0108] An alternative, low profile linkage between adjacent
segments may be provided by the polymeric sleeve or membrane. In
this embodiment, any of the variations of the wire cage illustrated
and described with respect to FIGS. 3-12C, may be coated on the
inside, the outside, or preferably, on both the inside and the
outside, by a polymeric sleeve, preferably of a laminated
structure, which creates a flexible polymeric linkage of very low
profile. In one embodiment, where the wire cage is embedded between
inner and outer layer(s) of polymeric material, the inner layer(s)
may be adhered to the outer layer(s) through the openings between
the adjacent wires of the support. The various mechanical linkages
between adjacent segments of previously disclosed embodiments may
be reduced in number or omitted when the embedding technology
described below is used. Instead the ePTFE layer retains the
desired spatial relationship between adjacent graft segments.
[0109] The sleeve or membrane that is used to cover the tubular
wire graft cage can be manufactured from any of a variety of
synthetic polymeric materials, or combinations thereof, including
DACRON.RTM., polyester, polyethylene, polypropylene,
fluoropolymers, polyurethane foamed films, silicon, nylon, silk,
thin sheets of super-elastic materials, woven materials,
polyethylene terephthalate (PET), or any other biocompatible
material. In one embodiment of the present invention, the membrane
material is a fluoropolymer, in particular, expanded
polytetrafluoroethylene (ePTFE) having a node-fibril structure. The
ePTFE membrane used in the present invention is manufactured from
thin films of ePTFE that are each approximately 0.0025 to 0.025 mm
in thickness. Thus, the films could be 0.0025, 0.0050, 0.0075,
0.0100, 0.0125, 0.0150, 0.0175, 0.0200, 0.0225, and 0.0250 mm
thick.
[0110] From 1 to about 200 plies (layers) of ePTFE film may be
stacked up and laminated to one another to obtain a membrane with
the desired mechanical and structural properties. The ePTFE
composite or stack may, if desired, exhibit the neointima
inhibiting properties described elsewhere herein. An even number of
layers are preferably stacked together (e.g., 2, 4, 6, 8, 10,
etc.), with approximately 2 to 20 layers being desirable.
Cross-lamination occurs by placing superimposed sheets on one
another such that the film drawing direction, or stretching
direction, of each sheet is angularly offset by angles between 0
degrees and 180 degrees from adjacent layers or plies. Because the
base ePTFE 15 thin, as thin as 0.0025 mm thick, superimposed films
can be rotated relative to one another to improve mechanical
properties of the membrane. In one preferred embodiment, the
membrane is manufactured by laminating between 4 to 8 plies of
ePTFE film, each film ply being about 0.0125 mm thick.
[0111] In this embodiment, the membrane is made by laminating 4
plies of ePTFE film, each film being about 0.0125 mm thick. The
laminated ePTFE sheets are then sintered together at temperatures
of about 370.degree. C., under vacuum to adhere the film layers to
one another. The resultant 8-ply laminate structure is typically
0.0375 mm thick. Additional details and variations on the ePTFE
laminating technology are disclosed in U.S. Pat. No. 5,925,075 to
Myers et al. the disclosure of which is herein incorporated in its
entirety by reference thereto.
[0112] Any of the variations of formed wire configurations
disclosed herein, particularly those described with reference to
FIGS. 13A-E, may be coated on the lumenal (inner) and/or external
surface, or embedded within a laminated ePTFE membrane in
accordance with the present invention. For example, as shown in
FIG. 13A, separate zig-zag segments, similar to those illustrated
in FIG. 3, but lacking the connector 66, may be positioned at a
substantially fixed axial distance from one another by embedding in
an ePTFE membrane. In the FIG. 13A variation, the adjacent segments
are rotationally positioned with respect to each other so that the
proximal bends 60 from one segment align with the distal bends 62
from the adjacent segment. Thus, the axial length of a graft or
graft portion formed by two adjacent segments is greater than or
equal to the sum of the axial length of each individual
segment.
[0113] The axial compressability, radial strength, and lateral
flexibility of a graft utilizing the structure illustrated in FIG.
13A will be influenced by the various factors discussed previously
herein, as well as by the spacing in an axial direction between
adjacent proximal bends 60 and corresponding distal bends 62 on the
adjacent segment. For example, as the axial spacing is increased,
greater lateral flexibility may be achieved. However, axial
compression of the graft may occur at a lower compressive force
level, depending upon the structural integrity of the embedded PTFE
wall. Specific axial spacings may be optimized for particular
applications, depending upon the desired performance. In general,
an axial separation between each proximal bend 60 and corresponding
distal bend 62 will be within the range of from about 0 to about 3
mm. Preferably, the spacing in a straight segment graft utilizing a
wire diameter of about 0.014'' will be within the range of from
about 0.5 mm to about 1.5 mm.
[0114] In another variation, shown in FIG. 13B, the separate
zig-zag segments are rotationally aligned. In the illustrated
configuration, adjacent segments 54 are nested within adjacent
segments, such that each proximal bend 60 from a distal segment
lies within angle .alpha. between two distal bends 62 of a proximal
segment. In this embodiment, the axial length formed by two
adjacent segments is less than the sum of the axial length 140 of
each individual segment. This design may be beneficial in
applications where greater radial support is desired.
[0115] Alternatively, a first segment 142 may be spaced axially
apart from a second segment 144, such that the axial distance
between a distal bend 62 on first segment 142 and distal bend 62 on
second segment 144 exceeds the axial length 140 of the segment.
Axial distances between two adjoining segments 142 and 144 may vary
within the range of from about 100% to about 200% of the length 140
of the adjacent segment 142, depending upon the desired radial
force and column strength of the resulting graft.
[0116] In the embodiment illustrated in FIG. 13B, ten segments are
illustrated in a nested configuration, in which no interconnecting
links are used to secure adjacent segments 54 to each other. Thus,
the spatial relationship between adjacent segments 54 is maintained
by the fabric or polymer layer or layers, to which the segments 54
are adhered and/or embedded.
[0117] In one nested embodiment having a 0.014'' filament and the
wall pattern illustrated in FIG. 13B, the circumferential distance
148 between any pair of adjacent distal bends 62 or proximal bends
60 is about 0.82''. The axial distance 146 between a proximal bend
60 and adjacent distal bends 62 is approximately 0.77''. The axial
length of the first leg 124 and second leg 126 between apex 122 and
first bend 128 or second bend 130 is approximately 0.10''. See FIG.
13E.
[0118] An alternative design is illustrated in FIG. 13C. In this
variation of the wire support, a single length of wire or laser cut
filament from sheet stock is formed into a zig-zag pattern which is
adapted to be rolled to form a spiral configuration, such as
disclosed by An et al., U.S. Pat. No. 5,545,211, which is herein
incorporated in its entirety by reference thereto. Unlike An,
however, axially adjacent apexes in the wire support do not need to
be interlinked. Thus, the present embodiment may be constructed
without interlinking axially adjacent apexes as disclosed, for
example, in U.S. Pat. No. 5,217,483 to Tower, the disclosure of
which is incorporated in its entirety herein by reference. The
resulting wire cage design is thus similar to that disclosed in
U.S. Pat. No. 5,665,115 to Cragg, the disclosure of which is
incorporated in its entirety herein by reference, after deletion of
the loop members 12. Deletion of loop members 12 from the Cragg
design is enabled by embedding the wire cage of the present
invention in the multi-layer ePTFE or other polymeric membrane as
disclosed herein.
[0119] Although previous embodiments have been described primarily
in the context of formed wire, the embodiments of FIGS. 13A-E may
conveniently be formed from a flat sheet or tube of material such
as Elgiloy, Nitinol, or other material having desired physical
properties. Sheets having a thickness of no more than about 0.025''
and, preferably, no more than about 0.015'' are useful for this
purpose. In one embodiment, the support structure is formed by
laser cutting the appropriate pattern on a 0.014'' thickness
Elgiloy foil or tube. Similarly, any of the other embodiments
disclosed previously herein can be manufactured by laser cutting,
chemical etching, or otherwise forming the wire cage support from a
flat sheet or tube of Elgiloy or other suitable material.
[0120] One advantage of forming the wire cage such as by laser
cutting is the ability to more precisely control the
cross-sectional area of the filament at different points in the
structure. For example, filament crossover points can be readily
manufactured having only a single filament thickness, compared to a
double filament thickness where the crossover is accomplished in a
wire structure. Referring to FIG. 13D, there is illustrated a side
wall pattern for a self-expandable vascular graft in which each
segment 54 comprises a plurality of diamond-shaped cells 152 each
having a proximal bend 60 and a distal bend 62. At junction 150,
the radial wall thickness of the support structure would be two
filament thicknesses if this structure were constructed from
preformed wire. However, by cutting the structure of FIG. 13D from
a solid walled tube or thin film sheet, the junction 150 may have
the same thickness as any other portion of the filament, thereby
minimizing the profile of the resulting graft. Adjacent segments 54
may be held with respect to each other by a polymeric layer such as
PTFE, as is described elsewhere herein.
[0121] Another example of design flexibility, which can be achieved
using the laser cutting technique of another embodiment of the
present invention, is illustrated in FIG. 13E. Referring to FIG.
13E, a detailed view is illustrated of either a proximal bend 60 or
distal bend 62 (as shown in FIG. 13F). In any embodiment having
only a few or no interconnecting links between adjacent segments
54, the radial strength in the finished product will tend to be
lower than the radial strength of a product with multiple
interconnecting links between adjacent segments 54 in an otherwise
comparable graft. As an alternate or supplement to adding
interconnecting links between adjacent segments 54, the
cross-sectional area of the filament 132 may be varied to affect
the radial strength.
[0122] For example, the plan view of the filament 132 in the area
of a bend 60 as seen in FIG. 13E has a first width in the
relatively straight sections thereof, and a second, greater width
in the bends, and a constant thickness throughout. In one
embodiment, the bend 60 comprises an apex 122 in which the filament
132 has a width 134 of about 0.020''. Each of a first leg 124 and
second leg 126 has a width at least one point of about 0.014''.
Thus, in the first and second leg sections, the transverse
cross-section of the filament 132 is approximately square since, in
this embodiment, it has been cut from a sheet having a thickness of
0.014''. A first bend 128 and a second bend 130 each have a maximum
width of approximately 0.020''. The width in a bend is preferably
at least about 110% and more preferably at least about 125% of the
average width in the adjacent filament. Bend widths of greater than
about 140% or 150% of the adjacent filament width may also be used.
The foregoing values can be readily converted to cross sectional
areas to apply the same concept where the filament enlargement in
the area of a bend occurs in whole or in part in the radial instead
of the circumferential direction.
[0123] By enlarging the cross-sectional area of the filament 132 in
the area of apex 122, first bend 128 and second bend 130,
particularly in the circumferential direction of the graft, the
inventors have determined that the relative radial strength of the
device can be increased while omitting or minimizing connecting
links between adjacent segments 54. In this embodiment, the apex
122 has an outside radius of curvature of about 0.027'', and an
inside radius of curvature of about 0.011''. The radius of
curvature of the concave surface of the filament 132 in the area of
first bend 128 or second bend 130 is approximately 0.15''. The
radius of the corresponding convex surface of each of the first
bend 128 and second bend 130 is approximately 0.05''. Any of the
foregoing dimensions or radii can be varied considerably, within
the scope of the present invention, to achieve particular physical
property characteristics, as will be apparent to those of skill in
the art.
[0124] If the foregoing floating segment embodiments exhibit
inadequate column strength or radial strength, one or more links
may be utilized to connect each adjacent pair of segments such as
142 and 144. Depending upon the degree of increased radial or
column strength desired in the finished product, two or three or
four or more links may be provided between each pair of segments
54. In one embodiment, at least one and as many as two or three or
more links may be utilized for each adjacent pair of segments.
[0125] In addition, where links are desired between adjacent
segments 54, links cut from a metal or other material tube or sheet
can also be integrally formed with the adjacent segments 54 without
adding wall thickness to the wire cage. See FIG. 13F.
[0126] Regardless of the particular configuration of wire cage, a
cross section of an the embedded support can be appreciated with
reference to FIG. 14. The wire 47 has a thin coating 48, which
comprises a thermoplastic polymer adhesive, such as for example,
FEP. In one embodiment, the coated wire is embedded within at least
two layers of polymer film 20, such as for example, ePTFE, one each
on the lumenal (inner) surface 30 and exterior surface 31. The
embedded support depicted in FIG. 14 is shown having two plies on
each of the lumenal and external surfaces. As detailed above,
however, preferably an even number of layers are stacked together
(e.g., 2, 4, 6, 8, 10, etc.), with approximately 2 to 20 layers
being desirable. Cross-lamination of superimposed sheets, each
sheet angularly offset by angles between about 0 degrees and about
180 degrees from adjacent sheet layers, may be desired in order to
improve mechanical properties of the membrane. As discussed in more
detail above, the membrane may be manufactured by laminating
between 4 to 8 plies of ePTFE film, each film ply being about
0.0125 mm thick. The laminated ePTFE sheets, fused together at
temperatures of about 370.degree. C. under vacuum, form a low
profile, flexible linkage between adjacent segments of the wire
cage.
[0127] Other graft configurations and methods of coating wire
stents with uniaxially and/or biaxially oriented ePTFE are
encompassed by the present invention. One such alternate method is
disclosed in U.S. Pat. No. 5,788,626 to Thompson, which is herein
incorporated in its entirety by reference thereto.
[0128] Another embodiment of the present invention may be
appreciated with reference to FIGS. 15 A-C. In FIG. 15A, a two
segment portion of the wire cage is shown in which the proximal 60
and distal 62 apexes from adjacent segments of the tubular member
are aligned in the longitudinal axis, thereby essentially abutting
one another as illustrated. In this variation, the wire cage is
surrounded by a polymeric sleeve 44, preferably at least two ePTFE
membranes, one along the lumenal surface and one along the exterior
surface of the stent. The membranes may comprises any number of
plies as discussed above. Alternatively, both surfaces of the cage
may be covered by a single tube of ePTFE membrane (1-200 plys)
extending through and folded over the wire cage resulting in a
layer of ePTFE along both the lumenal and exterior surfaces. In
either case, the PTFE envelope is spot welded in a pattern such as
that shown in FIG. 15A, wherein the lumenal and exterior membranes
are heat-fused in a plurality of spots 101. By spot-welding along
the proximal and distal edges of the tubular member, the sleeve is
closed around the support. Further, the pattern of four welding
spots surrounding each apical junction, acts as a flexible linkage,
thereby limiting movement of adjacent segments relative to one
another. In areas of the graft in between the welding spots, the
lumenal and exterior membranes are not necessarily fused.
[0129] As shown in end elevation from the distal margin of the
graft (along line C-C) in FIG. 15C, the inner 30 and outer 31
membranes are fused at the welding spots 101, whereas the membrane
layers can separate in between the welding spots. The sleeve is
also illustrated surrounding the wire apexes 62. This design, like
the previous variations in which the lumenal and exterior membranes
were fused in all areas between adjacent wires, presents a very low
profile, since the thickness of the PTFE membranes can be very
small, as detailed above.
[0130] An alternative configuration is illustrated in FIG. 15B,
wherein axially adjacent apexes of the support cage are
circumferentially offset, such that distal apexes 62 from the
adjacent segments are aligned with one another in the longitudinal
axis (and proximal apexes 60 from adjacent segments are aligned
with one another in the longitudinal axis). In this embodiment, the
distal apex 62 from a proximal segment is oriented between two
adjacent proximal apexes 60 of the distal segment. As in FIG. 15A,
the tubular wire segments are surrounded on both sides by a
polymeric sleeve 44. An identical pattern of welding spots 101 is
used to fasten the inner and outer membranes at the axial ends of
the tubular member. Thus, the thin end elevation wall profile
(shown in FIG. 15C) for the graft variation shown in FIG. 15B would
be the same as that presented by the graft of FIG. 15A. However,
along the length of the graft, at the junctions between adjacent
tubular wire segments, the pattern of welding spots is different
than that shown in FIG. 15B. In the inside angle of each apex, the
membranes are spot welded. Further, in a preferred variation, at
least alternating distal and proximal apexes and preferably all
apexes may be surrounded by several spot welds. The precise pattern
is not critical as long as the spot welds serve the purpose of
securing the inner and outer polymer layers together and minimizing
movement between adjacent segments in the longitudinal (or axial)
direction.
[0131] The spot welding of the two membrane layers may be
accomplished by any spot heating method or apparatus known in the
art. For example, a pointed heating iron, like a conventional
soldering iron, could be used as long as it was adapted to maintain
a membrane temperature sufficient to bond the layers of polymer
film together. Typically for ePTFE, a temperature of 370.degree.
for about 15 minutes would be sufficient to fuse the layers
together. In one preferred method of spot welding the lumenal and
exterior PTFE membranes, an RF chamber may be programmed to make
all of the necessary welds at once.
[0132] In one embodiment of the invention, the material of the
ePTFE membrane or sleeve is sufficiently porous to permit ingrowth
of endothelial cells into, but not through the sleeve wall. Such
controlled ingrowth may provide more secure anchorage of the
prosthesis and potentially reducing flow resistance, sheer forces,
and leakage of blood around the prosthesis.
[0133] The polymeric sleeve may be configured to prevent leakage of
fluid through the sleeve wall and into an aortic aneurysm sack. The
sleeve provides a seal across the aneurysm and substantially
prevents even micro amounts of leakage flow (i.e., the seeping of
fluid through the porous architecture of the sleeve membrane)
through the sleeve wall. Even micro amounts of leakage flow can
increase the pressure in the aneurysm sack, and over time may cause
the sack to grow and possibly rupture. Accordingly, in one
embodiment, the sleeve prevents fluids, including blood components
such as serum, from penetrating, leaking, or seeping through the
sleeve wall at standard anatomical pressures.
[0134] The ability of a sleeve to prevent micro leaks may be
assessed in vitro by pressurizing the sleeve from its luminal
surface with water, and observing the formation of water droplets
on the sleeve's abluminal or outer, low pressure surface. The
pressure at which water will form droplets visible to the unaided
eye on the low pressure side of the membrane is known as the water
entry pressure. In general, sleeves in accordance with the present
invention have a water entry pressure of at least about 3 psi, and
in another embodiment, the water entry pressure is at least about 5
psi or about 8 psi, and often at least about 10 psi. In some
applications the water entry pressure is at least about 15 psi. For
certain abdominal aortic aneurysm applications, the polymeric
sleeve will have a water entry pressure within the range of from
about 10 psi to about 24 psi.
[0135] The porosity characteristics of the polymeric sleeve may be
either homogeneous throughout the axial length of the prosthesis,
or may vary according to the axial position along the prosthesis.
For example, referring to FIGS. 1 and 2, different physical
properties will be called upon at different axial positions along
the prosthesis 42 in use. At least a proximal landing portion 55
and a distal landing portion 59 of the prosthesis 42 will seat
against the native vessel wall, proximally and distally of the
aneurysm. In these proximal and distal portions, the prosthesis may
be configured to encourage endothelial growth, or at least permit
endothelial growth to infiltrate portions of the prosthesis in
order to enhance anchoring and minimize leakage. A central portion
57 of the prosthesis spans the aneurysm, and anchoring is less of
an issue. Instead, maximizing lumen diameter and minimizing blood
flow through the prosthesis wall become more important. Thus, in a
central zone 57 of the prosthesis 42, the polymeric membrane or
sleeve 44 may either be nonporous, or provided with pores of
relatively lower porosity
[0136] A multi-zoned prosthesis 42 may also be provided in
accordance with the present invention by positioning a tubular
sleeve 44 on a central portion 57 of the prosthesis, such that it
spans the aneurysm to be treated, but leaving a proximal attachment
zone 55 and a distal attachment zone 59 of the prosthesis 42 having
exposed wires from the wire support 46. In this embodiment, the
exposed wires 46 are positioned in contact with the vessel wall
both proximally and distally of the aneurysm, such that the wire,
over time, may become embedded in cell growth on the interior
surface of the vessel wall.
[0137] In one embodiment of the prosthesis 42, the sleeve 44 and/or
the wire support 46 is tapered, having a relatively larger expanded
diameter at the proximal end 50 compared to the distal end 52. The
tapered design may allow the prosthesis to conform better to the
natural decreasing distal cross-section of the vessel, to reduce
the risk of graft migration and potentially create better flow
dynamics. The cage 46 can be provided with a proximal zone 55 and
distal zone 59 that have a larger average expanded diameter than
the central zone 57, as illustrated in FIG. 2. This configuration
may desirably resist migration of the prosthesis within the vessel
and reduce leakage around the ends of the prosthesis.
[0138] Referring to FIGS. 16 and 17, a straight segment deployment
device and method in accordance with a preferred embodiment of the
present invention are illustrated. A delivery catheter 80, having a
dilator tip 82, is advanced along guidewire 84 until the
(anatomically) proximal end 50 of the collapsed endolumenal
vascular prosthesis 88 is positioned between the renal arteries 32
and 34 and the aneurysm 40. The collapsed prosthesis in accordance
with the present invention has a diameter in the range of about 2
to about 10 mm. Generally, the diameter of the collapsed prosthesis
is in the range of about 3 to 6 mm (12 to 18 French). Preferably,
the delivery catheter including the prosthesis will be 16 F, or 15
F or 14 F or smaller.
[0139] The prosthesis 88 is maintained in its collapsed
configuration by the restraining walls of the tubular delivery
catheter 80, such that removal of this restraint would allow the
prosthesis to self expand. Radiopaque marker material may be
incorporated into the delivery catheter 80, and/or the prosthesis
88, at least at both the proximal and distal ends, to facilitate
monitoring of prosthesis position. The dilator tip 82 is bonded to
an internal catheter core 92, as illustrated in FIG. 17, so that
the internal catheter core 92 and the partially expanded prosthesis
88 are revealed as the outer sheath of the delivery catheter 80 is
retracted.
[0140] As the outer sheath is retracted, the collapsed prosthesis
88 remains substantially fixed axially relative to the internal
catheter core 92 and consequently, self-expands at a predetermined
vascular site as illustrated in FIG. 17. Continued retraction of
the outer sheath results in complete deployment of the graft. After
deployment, the expanded endolumenal vascular prosthesis 88 has
radially self-expanded to a diameter anywhere in the range of about
20 to 40 mm, corresponding to expansion ratios of about 1:2 to
1:20. In a preferred embodiment, the expansion ratios range from
about 1:4 to 1:8, more preferably from about 1:4 to 1:6.
[0141] In addition to, or in place of, the outer sheath described
above, the prosthesis 88 may be maintained in its collapsed
configuration by a restraining lace, which may be woven through the
prosthesis or wrapped around the outside of the prosthesis in the
collapsed reduced diameter. Following placement of the prosthesis
at the treatment site, the lace can be proximally retracted from
the prosthesis thereby releasing it to self expand at the treatment
site. The lace may comprise any of a variety of materials, such as
sutures, strips of PTFE, FEP, polyester fiber, and others as will
be apparent to those of skill in the art in view of the disclosure
herein. The restraining lace may extend proximally through a lumen
in the delivery catheter or outside of the catheter to a proximal
control. The control may be a pull-tab or ring, rotatable reel,
slider switch or other structure for permitting proximal retraction
of the lace. The lace may extend continuously throughout the length
of the catheter, or may be joined to another axially moveable
element such as a pull wire.
[0142] In general, the expanded diameter of the graft in accordance
with the present invention can be any diameter useful for the
intended lumen or hollow organ in which the graft is to be
deployed. For most arterial vascular applications, the expanded
size will be within the range of from about 10 to about 40 mm.
Abdominal aortic applications will generally require a graft having
an expanded diameter within the range of from about 20 to about 28
mm, and, for example, a graft on the order of about 45 mm may be
useful in the thoracic artery. The foregoing dimensions refer to
the expanded size of the graft in an unconstrained configuration,
such as on the table. In general, the graft will be positioned
within an artery having a slightly smaller interior cross-section
than the expanded size of the graft. This enables the graft to
maintain a slight positive pressure against the wall of the artery,
to assist in retention of the graft during the period of time prior
to endothelialization of the polymeric sleeve 44.
[0143] The radial force exerted by the proximal segment 94 of the
prosthesis against the walls of the aorta 30 provides a seal
against the leakage of blood around the vascular prosthesis and
tends to prevent axial migration of the deployed prosthesis. As
discussed above, this radial force can be modified as required
through manipulation of various design parameters, including the
axial length of the segment and the bend configurations. In another
embodiment of the present invention, radial tension can be enhanced
at the proximal, upstream end by increasing the wire gauge in the
proximal zone. Wire diameter may range from about 0.001 to 0.01
inches in the distal region to a range of from about 0.01 to 0.03
inches in the proximal region.
[0144] An alternative embodiment of the wire layout which would
cause the radial tension to progressively decrease from the
proximal segments to the distal segments, involves a progressive or
step-wise decrease in the wire gauge throughout the entire wire
support, from about 0.01 to 0.03 inches at the proximal end to
about 0.002 to 0.01 inches at the distal end. Such an embodiment
may be used to create a tapered prosthesis. Alternatively, the wire
gauge may be thicker at both the proximal and distal ends, in order
to insure greater radial tension and thus, sealing capacity. Thus,
for instance, the wire gauge in the proximal and distal segments
may about 0.01 to 0.03 inches, whereas the intervening segments may
be constructed of thinner wire, in the range of about 0.001 to 0.01
inches.
[0145] Referring to FIG. 18, there is illustrated two alternative
deployment sites for the endolumenal vascular prosthesis 42 of the
present invention. For example, an aneurysm 33 is illustrated in
the right renal artery 32. An expanded endolumenal vascular
prosthesis 42, in accordance with the present invention, is
illustrated spanning that aneurysm 33. Similarly, an aneurysm 37 of
the right common iliac 36 is shown, with a prosthesis 42 deployed
to span the iliac aneurysm 37.
[0146] Referring to FIG. 19, there is illustrated a modified
embodiment of the endovascular prosthesis 96 in accordance with the
present invention. In the embodiment illustrated in FIG. 19, the
endovascular prosthesis 96 is provided with a wire cage 46 having
six axially aligned segments 54. As with the previous embodiments,
however, the endovascular prosthesis 96 may be provided with
anywhere from about 2 to about 10 or more axially spaced or
adjacent segments 54, depending upon the clinical performance
objectives of the particular embodiment.
[0147] The wire support 46 is provided with a tubular polymeric
sleeve 44 as has been discussed. In the present embodiment,
however, one or more lateral perfusion ports or openings are
provided in the polymeric sleeve 44, such as a right renal artery
perfusion port 98 and a left renal artery perfusion port 100 as
illustrated.
[0148] Perfusion ports in the polymeric sleeve 44 may be desirable
in embodiments of the endovascular prosthesis 96 in a variety of
clinical contexts. For example, although FIGS. 1 and 19 illustrate
a generally symmetrical aneurysm 40 positioned within a linear
infrarenal portion of the abdominal aorta, spaced axially apart
both from bilaterally symmetrical right and left renal arteries and
bilaterally symmetrical right and left common iliacs, both the
position and symmetry of the aneurysm 40 as well as the layout of
the abdominal aortic architecture may differ significantly from
patient to patient. As a consequence, the endovascular prosthesis
96 may need to extend across one or both of the renal arteries in
order to adequately anchor the endovascular prosthesis 96 and/or
span the aneurysm 40. The provision of one or more lateral
perfusion ports or zones enables the endovascular prosthesis 96 to
span the renal arteries while permitting perfusion therethrough,
thereby preventing "stent jailing" of the renals. Lateral perfusion
through the endovascular prosthesis 96 may also be provided, if
desired, for a variety of other arteries including the second
lumbar, testicular, inferior mesenteric, middle sacral, and alike
as will be well understood to those of skill in the art.
[0149] The endovascular prosthesis 96 is preferably provided with
at least one, and preferably two or more radiopaque markers, to
facilitate proper positioning of the prosthesis 96 within the
artery. In an embodiment having perfusion ports 98 and 100 such as
in the illustrated design, the prosthesis 96 should be properly
aligned both axially and rotationally, thereby requiring the
ability to visualize both the axial and rotational position of the
device. Alternatively, provided that the delivery catheter design
exhibits sufficient torque transmission, the rotational orientation
of the graft may be coordinated with an indexed marker on the
proximal end of the catheter, so that the catheter may be rotated
and determined by an external indicia of rotational orientation to
be appropriately aligned with the right and left renal
arteries.
[0150] In an alternative embodiment, the polymeric sleeve 44
extends across the aneurysm 40, but terminates in the infrarenal
zone. In this embodiment, a proximal zone 55 (as illustrated in
FIG. 2) on the prosthesis 96 comprises a wire cage 46 but no
polymeric sleeve 44. In this embodiment, the prosthesis 96 still
accomplishes the anchoring function across the renal arteries, yet
does not materially interfere with renal perfusion. Thus, the
polymeric sleeve 44 may cover anywhere from about 50% to about 100%
of the axial length of the prosthesis 96 depending upon the desired
length of uncovered wire cage 46 such as for anchoring and/or
lateral perfusion purposes. In particular embodiments, the
polymeric sleeve 44 may cover within the range of from about 70% to
about 80%, and, in one four segment embodiment having a single
exposed segment, 75%, of the overall length of the prosthesis 96.
The uncovered wire cage 46 may reside at only a single end of the
prosthesis 96, such as for traversing the renal arteries.
Alternatively, exposed portions of the wire cage 46 may be provided
at both ends of the prosthesis such as for anchoring purposes.
[0151] In another embodiment, a two part polymeric sleeve 44 is
provided. A first distal part spans the aneurysm 40, and has a
proximal end that terminates distally of the renal arteries. A
second, proximal part of the polymeric sleeve 44 is carried by the
proximal portion of the wire cage 46 that is positioned superiorly
of the renal arteries. This leaves an annular lateral flow path
through the side wall of the vascular prosthesis 96, which can be
axially aligned with the renal arteries, without regard to
rotational orientation.
[0152] The axial length of the gap between the proximal and distal
segments of polymeric sleeve 44 can be adjusted, depending upon the
anticipated cross-sectional size of the ostium of the renal artery,
as well as the potential axial misalignment between the right and
left renal arteries. Although the right renal artery 32 and left
renal artery 34 are illustrated in FIG. 19 as being concentrically
disposed on opposite sides of the abdominal aorta, the take off
point for the right or left renal arteries from the abdominal aorta
may be spaced apart along the abdominal aorta as will be familiar
to those of skill in the art. In general, the diameter of the
ostium of the renal artery measured in the axial direction along
the abdominal aorta falls within the range of from about 7 mm to
about 20 mm for a typical adult patient.
[0153] Prior art procedures presently use a 7 mm introducer (18
French) which involves a surgical procedure for introduction of the
graft delivery device. Embodiments of the present invention can be
constructed having a 16 French or 15 French or 14 French or smaller
profile (e.g., 3-4 mm) thereby enabling placement of the
endolumenal vascular prosthesis of the present invention by way of
a percutaneous procedure. In addition, the endolumenal vascular
prosthesis of the present invention does not require a
post-implantation balloon dilation, can be constructed to have
minimal axial shrinkage upon radial expansion.
[0154] Referring to FIG. 20, there is disclosed a schematic
representation of the abdominal part of the aorta and its principal
branches as in FIG. 1. An expanded bifurcated endolumenal vascular
prosthesis 102, in accordance with one embodiment, is illustrated
spanning the aneurysms 103, 104 and 105. In addition, to the
description below, reference is made to U.S. Pat. Nos. 6,660,030,
6,187,036 and 6,197,049, which are hereby incorporated by reference
herein in their entirety. The illustrated endolumenal vascular
prosthesis 102 includes a polymeric sleeve 106 and a tubular wire
support 107, which are illustrated in situ in FIG. 20. The sleeve
106 and wire support 107 are more readily visualized in the
exploded view shown in FIG. 21 and the cross-sectional view of FIG.
22. The endolumenal prosthesis 102 illustrated and described herein
depicts an embodiment in which the polymeric sleeve 106 is situated
concentrically outside of the tubular wire support 107. However,
other embodiments may include a sleeve situated instead
concentrically inside the wire support or on both of the inside and
the outside of the wire support. Alternatively, the wire support
may be embedded within a polymeric matrix that makes up the sleeve.
Regardless of whether the sleeve 106 is inside or outside the wire
support 107, the sleeve may be attached to the wire support by any
of a variety of methods or devices, as has been previously
discussed.
[0155] The tubular wire support 107 comprises a primary component
108 for traversing the aorta and a first iliac, and a branch
component 109 for extending into the second iliac. The primary
component 108 may be formed from a continuous single length of
wire, throughout both the aorta trunk portion and the iliac branch
portion. See FIGS. 20 and 23. Alternatively, each iliac branch
component can be formed separately from the aorta trunk portion.
Construction of the graft from a three part cage conveniently
facilitates the use of different gauge wire in the different
components (e.g., 14 gauge main trunk and 10 gauge branch
components).
[0156] The wire support 107 is preferably formed in a plurality of
discrete segments, connected together and oriented about a common
axis. In FIG. 23, Section A corresponds to the aorta trunk portion
of the primary component 108, and includes segments 1-5. Segments
6-8 (Section B) correspond to the iliac branch portion of the
primary component 108.
[0157] In general, each of the components of the tubular wire
support 107 can be varied considerably in diameter, length, and
expansion coefficient, depending upon the intended application. For
implantation within a typical adult, the aorta trunk portion
(section A) of primary component 108 will have a length within the
range of from about 5 cm to about 12 cm, and, typically within the
range of from about 9 cm to about 10 cm. The unconstrained outside
expanded diameter of the section A portion of the primary component
108 will typically be within the range of from about 20 mm to about
40 mm. The unconstrained expanded outside diameter of the section A
portion of primary component 108 can be constant or substantially
constant throughout the length of section A, or can be tapered from
a relatively larger diameter at the proximal end to a relatively
smaller diameter at the bifurcation. In general, the diameter of
the distal end of section A will be on the order of no more than
about 95% and, preferably, no more than about 85% of the diameter
of the proximal end of section A.
[0158] The right and left iliac portions, corresponding to section
B on primary component 108 and section C will typically be
bilaterally symmetrical. Section C length will generally be within
the range of from about 1 cm to about 5 cm, and section C diameter
will typically be within the range of from about 10 mm to about 20
mm.
[0159] Referring to FIG. 21, the wire cage 107 is dividable into a
proximal zone 110, a central zone 111 and a distal zone 112. As has
been discussed, the wire cage 107 can be configured to taper from a
relatively larger diameter in the proximal zone 110 to a relatively
smaller diameter in the distal zone 112. In addition, the wire cage
107 can have a transitional tapered and or stepped diameter within
a given zone.
[0160] Referring to FIG. 23, there is illustrated a plan view of
the single formed wire used for rolling about a longitudinal axis
to produce a primary segment 108 having a five segment aorta
section and a three segment iliac section. The formed wire exhibits
distinct segments, each corresponding to an individual tubular
segment in the tubular support. Additional details of the wire cage
layout and construction can be found in co-pending U.S. patent
application Ser. No. 09/034,689 entitled Endolumenal Vascular
Prosthesis, filed Mar. 4, 1998, the disclosure of which is
incorporated in its entirety herein by reference.
[0161] Each segment has a repeating pattern of proximal bends 60
connected to corresponding distal bends 62 by wall sections 64
which extend in a generally zig-zag configuration when the segment
is radially expanded, as has been discussed in connection with FIG.
3. Each segment is connected to the adjacent segment through a
connector 66, and one or more links 70 as has been discussed in
connection with FIGS. 5-12. The connector 66 in the illustrated
embodiment comprises two wall sections 64 which connect a proximal
bend 60 on a first segment with a distal bend 62 on a second,
adjacent segment. The connector 66 may additionally be provided
with a connector bend 68, which may be used to impart increased
radial strength to the graft and/or provide a tie site for a
circumferentially extending suture.
[0162] In the illustrated embodiment, section A is intended for
deployment within the aorta whereas section B is intended to be
deployed within a first iliac. Thus, section B will preferably have
a smaller expanded diameter than section A. This may be
accomplished by providing fewer proximal and distal bends 60, 62
per segment in section B or in other manners as will be apparent to
those of skill in the art in view of the disclosure herein. In the
illustrated embodiment, section B has one fewer proximal bend 60
per segment than does each segment in section A. This facilitates
wrapping of the wire into a tubular prosthesis cage such as that
illustrated in FIG. 22, so that the iliac branch has a smaller
diameter than the aorta branch. At the bifurcation, an opening
remains for connection of the second iliac branch. The second
branch is preferably formed from a section of wire in accordance
with the general principles discussed above, and in a manner that
produces a similarly dimensioned wire cage as that produced by
section B. The second iliac branch (section C) may be attached at
the bifurcation to section A and/or section B in any of a variety
of manners, to provide a secure junction therebetween. In one
embodiment, one or two of the proximal bends 60 on section C will
be secured to the corresponding distal bends 62 on the distal most
segment of section A. Attachment may be accomplished such as
through the use of a circumferentially threaded suture, through
links 70 as has been discussed previously, through soldering or
other attachment method or device. The attachment method or device
will be influenced by the desirable flexibility of the graft at the
bifurcation, which will in turn be influenced by the method of
deployment of the vascular graft as will be apparent to those of
skill in the art in view of the disclosure herein.
[0163] Referring to FIG. 24, there is disclosed an exploded
schematic representation of a hinged or articulated variation in
the tubular wire support structure for a bifurcated graft in
accordance with present invention. The tubular wire support
comprises a main body, or aortic trunk portion 200 and right 202
and left 204 iliac branch portions. Right and left designations
correspond to the anatomic designations of right and left common
iliac arteries. The proximal end 206 of the aortic trunk portion
200 has apexes 211-216 adapted for connection with the
complementary apexes on the distal ends 208 and 210 of the right
202 and left 204 iliac branch portions, respectively. Complementary
pairing of apexes is indicated by the shared numbers, wherein the
right branch portion apexes are designated by (R) and the left
branch portion apexes are designated by (L). Each of the portions
may be formed from a continuous single length of wire. See FIG.
26.
[0164] Referring to FIG. 25, the assembled articulated wire support
structure is shown. The central or medial apex 213 in the
foreground (anterior) of the aortic trunk portion 200 is linked
with 213(R) on the right iliac portion 202 and 213(L) on the left
iliac portion 204. Similarly, the central apex 214 in the
background (posterior) is linked with 214(R) on the right iliac
portion 202 and 214(L) on the left iliac portion 204. Each of these
linkages has two iliac apexes joined with one aortic branch apex.
The linkage configurations may be of any of the variety described
above in FIG. 7A-D. The medial most apexes 218 (R) and (L) of the
iliac branch portions 202 and 204 are linked together, without
direct connection with the aortic truck portion 200.
[0165] The medial apexes 213 and 214 function as pivot points about
which the right and left iliac branches 202, 204 can pivot to
accommodate unique anatomies. Although the right and left iliac
branches 202, 204 are illustrated at an angle of about 45.degree.
to each other, they are articulable through at least an angle of
about 90.degree. and preferably at least about 120.degree.. The
illustrated embodiment allows articulation through about
180.degree. while maintaining patency of the central lumen. To
further improve patency at high iliac angles, the apexes 213 and
214 can be displaced proximally from the transverse plane which
roughly contains apexes 211, 212, 215 and 216 by a minor adjustment
to the fixture about which the wire is formed. Advancing the pivot
point proximally relative to the lateral apexes (e.g., apexes 211,
216) opens the unbiased angle between the iliac branches 202 and
204.
[0166] In the illustrated embodiment, the pivot point is formed by
a moveable link between an eye on apex 213 and two apexes 213R and
213L folded therethrough. To accommodate the two iliac apexes 213R
and 213L, the diameter of the eye at apex 213 may be slightly
larger than the diameter of the eye on other apexes throughout the
graft. Thus, for example, the diameter of the eye at apex 213 in
one embodiment made from 0.014'' diameter wire is about 0.059'',
compared to a diameter of about 0.020'' for eyes elsewhere in the
graft.
[0167] Although the pivot points (apexes 213, 214) in the
illustrated embodiment are on the medial plane, they may be moved
laterally such as, for example, to the axis of each of the iliac
branches. In this variation, each iliac branch will have an
anterior and a posterior pivot link on or about its longitudinal
axis, for a total of four unique pivot links at the bifurcation.
Alternatively, the pivot points can be moved as far as to lateral
apexes 211 and 216. Other variations will be apparent to those of
skill in the art in view of the disclosure herein.
[0168] To facilitate lateral rotation of the iliac branches 202,
204 about the pivot points and away from the longitudinal axis of
the aorta trunk portion 200 of the graft, the remaining links
between the aorta trunk portion 200 and the iliac branches 202, 204
preferably permit axial compression and expansion. In general, at
least one and preferably several links lateral to the pivot point
in the illustrated embodiment permit axial compression or
shortening of the graft to accommodate lateral pivoting of the
iliac branch. If the pivot point is moved laterally from the
longitudinal axis of the aorta portion of the graft, any links
medial of the pivot point preferably permit axial elongation to
accommodate lateral rotation of the branch. In this manner, the
desired range of rotation of the iliac branches may be accomplished
with minimal deformation of the wire, and with patency of the graft
optimized throughout the angular range of motion.
[0169] To permit axial compression substantially without
deformation of the wire, the lateral linkages, 211 and 212 for the
right iliac, and 215 and 216 for the left iliac, may be different
from the previously described apex-to-apex linkage configurations.
The lateral linkages are preferably slidable linkages, wherein a
loop formed at the distal end of the iliac apex slidably engages a
strut of the corresponding aortic truck portion. The loop and strut
orientation may be reversed, as will be apparent to those of skill
in the art. Interlocking "elbows" without any distinct loop may
also be used. Such an axially compressible linkage on the lateral
margins of the assembled wire support structure allow the iliac
branch portions much greater lateral flexibility, thereby
facilitating placement in patients who often exhibit a variety of
iliac branch asymmetries and different angles of divergence from
the aortic trunk.
[0170] Referring to FIG. 26, there is illustrated a plan view of a
single formed wire used for rolling about a longitudinal axis to
produce a four segment straight tubular wire support for an iliac
limb. The formed wire exhibits distinct segments, each
corresponding to an individual tubular segment in the tubular
supports 202 or 204 (See FIG. 24). The distal segment I, is adapted
to articulate with the aortic trunk portion 200 and the adjacent
iliac limb portion. The distal segment (I) has two apexes (e.g.,
corresponding to 211 and 212 on the right iliac portion 202 in FIG.
23) which form a loop adapted to slidably engage a strut in the
lateral wall of the aortic portion. These articulating loops (A)
are enlarged in FIG. 27A. As discussed above, the loops are
preferably looped around a strut on the corresponding apex of the
proximal aortic segment to provide a sliding linkage.
[0171] The apex 218 is proximally displaced relative to the other
four apexes in the distal segment (I). Apex 218 (R or L) is
designed to link with the complementary 218 apex on the other iliac
branch portion (See FIG. 25). The apex 218 in the illustrated
embodiment is formed adjacent or near an intersegment connector 66,
which extends proximally from the distal segment.
[0172] The other apexes on the distal segment (I) of an iliac limb
are designed to link with a loop on the corresponding apex of the
proximal aortic segment. Because many variations of this linkage
are consistent with the present invention (See FIGS. 7A-D), the
form of the corresponding apexes may vary. In a preferred
variation, the apexes (B) form a narrow U-shape, having an inside
diameter of about 0.019 inches in an embodiment made from 0.012
inch Conichrome wire (tensile strength 300 ksi minimum) as
illustrated in FIG. 27B. The U-shaped, elongated axial portion of
the apex shown in FIG. 25B permits the apex to be wrapped through
and around a corresponding loop apex of the proximal aortic
segment. This type of linkage is discussed in greater detail above
in connection with FIGS. 5 and 6.
[0173] In more general terms, the wire support illustrated in FIGS.
24 and 25 comprises a main body support structure formed from one
or more lengths of wire and having a proximal end, a distal end and
a central lumen extending along a longitudinal axis. The wire
support also comprises a first branch support structure formed from
one or more lengths of wire and having a proximal end, a distal end
and a central lumen therethrough. The first branch support
structure is pivotably connected to the proximal end of the main
body support structure. The tubular wire support further comprises
a second branch support structure formed from one or more lengths
of wire and having a proximal end, a distal end and a central lumen
extending therethrough. The distal end of the second branch support
structure is pivotably connected to the proximal end of the main
body support structure.
[0174] Further, the distal ends of the first and second branch
structures may be joined together by a flexible linkage, formed for
example between apexes 218(R) and 218(L) in FIG. 24. By
incorporating a medial linkage between the two branch support
structures and pivotable linkages with the main trunk, the first
and second branch support structures can hinge laterally outward
from the longitudinal axis without compromising the volume of the
lumen. Thus, the branches may enjoy a wide range of lateral
movement, thereby accommodating a variety of patient and vessel
heterogeneity. Additional corresponding apexes between the main
trunk and each iliac branch may also be connected, or may be free
floating within the outer polymeric sleeve. Axially compressible
lateral linkages, discussed above and illustrated in FIG. 25, may
optionally be added.
[0175] The proximal apexes (C) of the iliac limb portions are
adapted to link with the distal apexes of the next segment. These
proximal apexes preferably form loops, such as those illustrated in
FIG. 27C, wherein the elongated axial portions of the corresponding
proximal apex in the adjacent segment can wrap around the loop,
thereby providing flexibility of the graft, as discussed above for
FIGS. 5 and 6.
[0176] The wire may be made from any of a variety of different
alloys and wire diameters or non-round cross-sections, as has been
discussed. In one embodiment of the bifurcation graft, the wire
gauge remains substantially constant throughout section A of the
primary component 49 and steps down to a second, smaller
cross-section throughout section B of primary component 108.
[0177] A wire diameter of approximately 0.018 inches may be useful
in the aorta trunk portion of a graft having five segments each
having 2.0 cm length per segment, each segment having six struts
intended for use in the aorta, while a smaller diameter such as
0.012 inches might be useful for segments of the graft having 6
struts per segment intended for the iliac artery.
[0178] In one embodiment of the present invention, the wire
diameter may be tapered throughout from the proximal to distal ends
of the section A and/or section B portions of the primary component
108. Alternatively, the wire diameter may be tapered incremental or
stepped down, or stepped up, depending on the radial strength
requirements of each particular clinical application. In one
embodiment, intended for the abdominal aortic artery, the wire has
a cross-section of about 0.018 inches in the proximal zone 110 and
the wire tapers down regularly or in one or more steps to a
diameter of about 0.012 inches in the distal zone 112 of the graft
102. End point dimensions and rates of taper can be varied widely,
within the spirit of the present invention, depending upon the
desired clinical performance.
[0179] In general, in the tapered or stepped wire embodiments, the
diameter of the wire in the iliac branches is no more than about
80% of the diameter of the wire in the aortic trunk. This permits
increased flexibility of the graft in the region of the iliac
branches, which has been determined by the present inventors to be
clinically desirable.
[0180] The collapsed prosthesis in accordance with the present
invention has a diameter in the range of about 2 to about 10 mm.
Preferably, the maximum diameter of the collapsed prosthesis is in
the range of about 3 to 6 mm (12 to 18 French). Some embodiments of
the delivery catheter including the prosthesis will be in the range
of from 18 to 20 or 21 French; other embodiments will be as low as
19 F, 16 F, 14 F, or smaller. After deployment, the expanded
endolumenal vascular prosthesis has radially self-expanded to a
diameter anywhere in the range of about 20 to 40 mm, corresponding
to expansion ratios of about 1:2 to 1:20. In a preferred
embodiment, the expansion ratios range from about 1:4 to 1:8, more
preferably from about 1:4 to 1:6.
[0181] As described above in detail with respect to the linkage of
stent segments using the polymeric sleeve, the same construction
and methods are applicable to the flexible bifurcated wire cage
just described. Thus, the bifurcated stent can be coated on the
lumenal side, the external side, or preferably embedded within
layers of porous, expandable polymeric material, as described
above.
[0182] The self-expandable bifurcation graft of the present
invention can be deployed at a treatment site in accordance with
any of a variety of techniques as will be apparent to those of
skill in the art. One such technique is disclosed in co-pending
patent application Ser. No. 08/802,478 entitled Bifurcated Vascular
Graft and Method and Apparatus for Deploying Same, filed Feb. 20,
1997, the disclosure of which is incorporated in its entirety
herein by reference.
[0183] While a number of preferred embodiments of the invention and
variations thereof have been described in detail, other
modifications and methods of using and medical applications for the
same will be apparent to those of skill in the art. Accordingly, it
should be understood that various applications, modifications, and
substitutions may be made of equivalents without departing from the
spirit of the invention or the scope of the claims.
* * * * *