U.S. patent application number 11/860514 was filed with the patent office on 2008-02-28 for stent for treating vulnerable plaque.
This patent application is currently assigned to ADVANCED CARDIOVASCULAR SYSTEMS INC.. Invention is credited to E. TINA CHENG, DANIEL L. COX.
Application Number | 20080051878 11/860514 |
Document ID | / |
Family ID | 31976126 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080051878 |
Kind Code |
A1 |
CHENG; E. TINA ; et
al. |
February 28, 2008 |
STENT FOR TREATING VULNERABLE PLAQUE
Abstract
An intravascular stent assembly for implantation in a body
lumen, such as a coronary artery, is designed to treat a lesion
with vulnerable plaque by reducing the fibrous cap stresses. The
stent includes distal, proximal, and center sections where the
center section is configured to treat the vulnerable plaque. The
stent consists of radially expandable cylindrical rings generally
aligned on a common longitudinal stent axis and either directly
connected or interconnected by one or more interconnecting links
placed so that the stent is flexible in the longitudinal direction
while providing high degrees of radial strength and vessel
scaffolding.
Inventors: |
CHENG; E. TINA; (Union City,
CA) ; COX; DANIEL L.; (Palo Alto, CA) |
Correspondence
Address: |
FULWIDER PATTON, LLP (ABBOTT)
6060 CENTER DRIVE
10TH FLOOR
LOS ANGELES
CA
90045
US
|
Assignee: |
ADVANCED CARDIOVASCULAR SYSTEMS
INC.
3200 Lakeside Drive S314
Santa Clara
CA
95054-2807
|
Family ID: |
31976126 |
Appl. No.: |
11/860514 |
Filed: |
September 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10462984 |
Jun 17, 2003 |
7273492 |
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11860514 |
Sep 24, 2007 |
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10228850 |
Aug 27, 2002 |
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10462984 |
Jun 17, 2003 |
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Current U.S.
Class: |
623/1.16 ;
623/1.17 |
Current CPC
Class: |
A61F 2002/91533
20130101; A61F 2/91 20130101; A61F 2/915 20130101; A61F 2002/91525
20130101; A61F 2002/825 20130101; A61F 2230/0013 20130101; A61F
2250/0018 20130101; A61F 2250/0029 20130101; A61F 2002/91558
20130101; A61F 2002/91575 20130101 |
Class at
Publication: |
623/001.16 ;
623/001.17 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. An intravascular stent, comprising: a plurality of a first set
of cylindrical rings and a plurality of a second set of cylindrical
rings, each set of cylindrical rings being radially expandable,
longitudinally aligned, and each with a first delivery diameter and
a second implanted diameter; a plurality of links connecting a
plurality of adjacent cylindrical rings; wherein the stent includes
a distal section, a center section, and a proximal section; wherein
the first set of rings are formed with a first cross-sectional
width and the second set of rings are formed with a second,
relatively smaller cross-sectional width.
2. The stent of claim 1, wherein the first set of rings are located
within the proximal section and the distal section of the stent and
the second set of rings are located within the center section of
the stent.
3. The stent of claim 1, wherein the links comprise a first set
with a first cross-sectional width and a second set with a second,
relatively smaller cross-sectional width than the width of the
first set of links.
4. (canceled)
5. The stent of claim 1, wherein a plurality of the links are
formed with W-shaped undulations.
6. The stent of claim 1, wherein the first set of rings are formed
with V-shaped and U-shaped undulations and wherein the second set
of rings are formed with V-shaped undulations.
7. The stent of claim 1, wherein the second set of rings is formed
with U-shaped undulations.
8. The stent of claim 1, wherein the first set of rings and the
second set of rings are formed with substantially U-shaped
undulations.
9. The stent of claim 1, wherein adjacent rings are connected with
three links.
10. The stent of claim 1, wherein the first set of rings and the
second set of rings are located with the proximal section and the
distal section of the stent and the links are located within the
center section of the stent.
11. The stent of claim 10, wherein there are six links connecting
two rings.
12. The stent of claim 10, wherein twelve links connect two
rings.
13. The stent of claim 10, wherein a plurality of the first set of
rings and a plurality of the second sets of rings are directly
connected.
14-22. (canceled)
23. The stent of claim 1, wherein the stent is self-expanding.
24. The stent of claim 23, wherein the material forming the
cylindrical rings embodies shape memory characteristics.
25. The stent of claim 24, wherein the shape memory material is a
superelastic material.
26. The stent of claim 25, wherein the superelastic material is
nickel-titanium.
27-46. (canceled)
47. An intravascular stent, comprising: a first set of cylindrical
rings and a plurality of a second set of cylindrical rings, each
set of cylindrical rings being radially expandable, longitudinally
aligned, and each with a first delivery diameter and a second
implanted diameter; a plurality of links connecting a plurality of
adjacent cylindrical rings; wherein the stent includes a distal
section, a center section, and a proximal section; wherein the
first set of rings are formed with first undulations having a first
cross-sectional width and the second set of rings are formed with
non-overlapping undulations having a second, relatively smaller
cross-sectional width, and the second set of rings having a higher
concentration of undulations than the first section.
48. The stent of claim 47, wherein the first set of rings are
located within the proximal section of the stent and the second set
of rings are located within the center section of the stent.
49. The stent of claim 48, further comprising a third set of
cylindrical rings are located within the distal section of the
stent, wherein the third set of cylindrical rings are formed with
undulations having the first cross-sectional width.
50. The stent of claim 47, wherein the links comprise a first set
with a first cross-sectional width and a second set with a second,
relatively smaller cross-sectional width than the width of the
first set of links, and the first set of links connect the first
set of rings together and a plurality of the second set of links
connect a plurality of the second set of rings together.
51. The stent of claim 47, wherein the first set of links are
formed with W-shaped undulations, and the second set of links are
straight.
52. The stent of claim 47, wherein the first set of rings are
formed with V-shaped and U-shaped undulations and wherein the
second set of rings are formed with V-shaped and U-shaped
undulations.
53. A method for delivering an intravascular stent in an artery
having vulnerable plaque, comprising: providing an intravascular
stent delivery assembly comprising an elongated catheter for
delivering the intravascular stent having a distal section, a
proximal section, and a center section, each section having links
and rings with undulations, wherein the undulations of the center
section are non-overlapping and wherein the center section has a
higher undulation concentration than the distal section and
proximal section so that less stress is effected on the tissue of
the artery by the center section than by the distal and proximal
sections; advancing the stent delivery assembly into an
atherosclerotic artery within the patient's body lumen; positioning
the stent in a region of the artery containing vulnerable plaque;
implanting the stent in the artery such that only the center
section of the stent apposes and contacts a region of the artery
containing vulnerable plaque; withdrawing the stent delivery
catheter assembly from the patient.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to vascular repair devices,
and in particular to intravascular stents, which are adapted to be
implanted into a patient's body lumen, such as a blood vessel or
coronary artery, for the treatment of unstable or vulnerable, human
atherosclerotic plaque.
[0002] Currently, the treatment of unstable or vulnerable plaque
presents a significant therapeutic challenge to medical
investigators. Vulnerable plaque is characterized by a basic lesion
which is a raised plaque beneath the innermost arterial layer, the
intima. Atherosclerotic plaques are primarily composed of varying
amounts of long chain extracellular matrix (ECM) proteins that are
synthesized by smooth muscle cells. The other primary lesion
component of atherosclerotic plaque includes lipoproteins, existing
both extracellularly and within foam cells derived primarily from
lipid-laden macrophages. In a more advanced lesion, a necrotic core
may develop, consisting of lipids, foam cells, cell debris, and
cholesterol crystals, and myxomatous configurations with
crystalline lipid forms. The necrotic core is rich in tissue factor
and quite thrombogenic, but in the stable plaque it is protected
from the luminal blood flow by a robust fibrous cap composed
primarily of long chain ECM proteins, such as elastin and collagen,
which maintain the strength of the fibrous cap. The aforementioned
plaque represents the most common form of vulnerable plaque, known
as a fibroatheroma. Histology studies from autopsy suggest this
form constitutes the majority of vulnerable plaques in humans. A
second form of vulnerable plaque represents a smaller fraction of
the total, and these are known as erosive plaques. Erosive plaques
generally have a smaller content of lipid, a larger fibrous tissue
content, and varying concentrations of proteoglycans. Various
morphologic features that have been associated with vulnerable
plaque, include thinned or eroded fibrous caps or luminal surfaces,
lesion eccentricity, proximity of constituents having very
different structural moduli, and the consistency and distribution
of lipid accumulations. With the rupture of fibroatheroma forms of
vulnerable plaque, the luminal blood becomes exposed to tissue
factor, a highly thrombogenic core material, which can result in
total thrombotic occlusion of the artery. In the erosive form of
vulnerable plaque, mechanisms of thrombosis are less understood but
may still yield total thrombotic occlusion.
[0003] Although rupture of the fibrous cap in a fibroatheroma is a
major cause of myocardial infarction (MI) related deaths, there are
currently no therapeutic strategies in place to treat lesions that
could lead to acute MI. The ability to detect vulnerable plaques
and to treat them successfully with interventional techniques
before acute MI occurs has long been an elusive goal. Numerous
finite element analysis (FEA) studies have proved that, in the
presence of a soft lipid core, the fibrous cap shows regions of
high stresses. Representative of these studies include the
following research articles, each of which are incorporated in
their entirety by reference herein: Richardson et al. (1989),
Influence of Plaque Configuration and Stress Distribution on
Fissuring of Coronary Atherosclerotic Plaques, Lancet, 2 (8669),
941-944; Loree et al. (1992), Effects of Fibrous Cap Thickness on
Circumferential Stress in Model Atherosclerotic Vessels,
Circulation Research, 71, 850-858; Cheng et al. (1992),
Distribution of Circumferential Stress in Ruptured and Stable
Atherosclerotic Lesions: A Structural Analysis With
Histopathological Correlation, Circulation, 87, 1179-1187; Veress
et al. (1993), Finite Element Modeling of Atherosclerotic Plaque,
Proceedings of IEEE Computers in Cardiology, 791-794; Lee et al.
(1996), Circumferential Stress and Matrix Metalloproteinase 1 in
Human Coronary Atherosclerosis: Implications for Plaque Rupture,
Atherosclerosis Thrombosis Vascular Biology, 16, 1070-1073; Vonesh
et al. (1997), Regional Vascular Mechanical Properties by 3-D
Intravascular Ultrasound Finite-Element Analysis, American Journal
of Physiology, 272, 425-437; Beattie et al. (1999), Mechanical
Modeling: Assessing Atherosclerotic Plaque Behavior and Stability
in Humans, International Journal of Cardiovascular Medical Science,
2 (2), 69-81; and Feezor et al. (2001), Integration of Animal and
Human Coronary Tissue Testing with Finite Element Techniques for
Assessing Differences in Arterial Behavior, BED-Vol. 50, 2001
Bioengineering Conference, ASME 2001. Further, these studies have
indicated that such high stress regions correlate with the observed
prevalence of locations of cap fracture. Moreover, it has been
shown that subintimal structural features such as the thickness of
the fibrous cap and the extent of the lipid core, rather than
stenosis severity are critical in determining the vulnerability of
the plaque. The rupture of a highly stressed fibrous cap can be
prevented by using novel, interventional, therapeutic techniques
such as specially designed stents that redistribute and lower the
stresses in the fibrous cap.
[0004] One of the avenues to reduce cap rupture is to reinforce the
strength and increase thickness of the fibrous cap. Studies have
shown that placement of the intravascular stent at a lesion site
can induce neointimal thickening. Using the same reasoning, placing
an intravascular stent at the vulnerable plaque site can induce
neointimal thickening, which in turn will increase the cap
thickness. However, a special stent pattern, rather than the
traditional workhorse stent, should be used to stent these lesions.
A pattern which induces less shear stress upon expansion, less
point stress upon the vessel wall and delayed neointimal thickening
should be used for stent vulnerable plaques.
[0005] Stents are generally tubular-shaped devices which function
to hold open a segment of a blood vessel, coronary artery, or other
body lumen. They are particularly suitable for use to support and
hold back a dissected arterial lining which can occlude the fluid
passageway therethrough.
[0006] Various means have been described to deliver and implant
stents. One method frequently described for delivering a stent to a
desired intraluminal location includes mounting the expandable
stent on an expandable member, such as a balloon, provided on the
distal end of an intravascular catheter, advancing the catheter to
the desired location within the patient's body lumen, inflating the
balloon on the catheter to expand the stent into a permanent
expanded condition and then deflating the balloon and removing the
catheter. One of the difficulties encountered using prior art
stents involved maintaining the radial rigidity needed to hold open
a body lumen while at the same time maintaining the longitudinal
flexibility of the stent to facilitate its delivery. Once the stent
is mounted on the balloon portion of the catheter, it is often
delivered through tortuous vessels, including tortuous coronary
arteries. The stent must have numerous properties and
characteristics, including a high degree of flexibility, in order
to appropriately navigate the tortuous coronary arteries. This
flexibility must be balanced against other features including
radial strength once the stent has been expanded and implanted in
the artery. While other numerous prior art stents have had
sufficient radial strength to hold open and maintain the patency of
a coronary artery, they have lacked the flexibility required to
easily navigate tortuous vessels without damaging the vessels
during delivery.
[0007] Generally speaking, most prior art intravascular stents are
formed from a metal such as stainless steel, which is balloon
expandable and plastically deforms upon expansion to hold open a
vessel. The component parts of these types of stents typically are
all formed of the same type of metal, i.e., stainless steel. Other
types of prior art stents may be formed from a polymer, again all
of the component parts being formed from the same polymer material.
These types of stents, the ones formed from a metal and the ones
formed from a polymer, each have advantages and disadvantages. One
of the advantages of the metallic stents is their high radial
strength once expanded and implanted in the vessel. A disadvantage
may be that the metallic stent lacks flexibility which is important
during the delivery of the stent to the target site. With respect
to polymer stents, they may have a tendency to be quite flexible
and are advantageous for use during delivery through tortuous
vessels, however, such polymer stents may lack the radial strength
necessary to adequately support the lumen once implanted into an
occlusive fibromuscular lesion of 70% stenosis or greater.
[0008] What has been needed and heretofore unavailable is a stent
that can be used to treat a vulnerable plaque by reducing the cap
stresses. The present invention satisfies this need and others.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to an intravascular stent
assembly that can be used to treat a lesion with vulnerable plaque
by reducing the cap stresses. The invention also includes methods
of using the stent assembly for the treatment of the same.
[0010] The stent assembly embodying features of the invention can
be readily delivered to the desired body lumen, such as a coronary
artery (peripheral vessels, bile ducts, etc.), by mounting the
stent assembly on an expandable member of a delivery catheter, for
example a balloon, and advancing the catheter and stent assembly
through the body lumen to the target site. Generally, the stent is
compressed or crimped onto the balloon portion of the catheter so
that the stent assembly does not move longitudinally relative to
the balloon portion of the catheter during delivery through the
arteries, and during expansion of the stent at the target site. The
stent is relatively flexible along its longitudinal axis to
facilitate delivery through tortuous body lumens yet is stiff and
stable enough radially in an expanded condition to maintain the
patency of a body lumen such as an artery when implanted
therein.
[0011] In one embodiment, the stent assembly of the invention
includes a series of cylindrical rings formed with undulations and
located within distal, center, and proximal sections of the stent.
The undulations of the rings located in the center section may have
either smaller or larger cross-sectional widths than the
undulations of the rings in the distal and proximal sections in
order to accommodate the vulnerable plaque section of the artery.
Links are incorporated to connect all the cylindrical rings
together into the stent assembly. The center section may be coated
with a polymer to increase surface area.
[0012] In another embodiment, the stent assembly of the present
invention includes a series of cylindrical rings with undulations
and also located within distal, center, and proximal sections of
the stent. Similarly, the undulations of the rings located in the
center section may have either smaller or larger cross-sections
than the undulations of the rings in the distal and proximal
sections in order to accommodate the vulnerable plaque section of
the artery. The rings are directly connected to each other,
generally without the need for separate links. The center section
may also be coated with a polymer to increase surface area.
[0013] The resulting stent structures are a series of radially
expandable cylindrical rings which are configured so that
vulnerable plaque and small dissections in the wall of a body lumen
may be pressed back into position against the luminal wall, while
maintaining the longitudinal flexibility of the stent both when
being negotiated through the body lumens in their unexpanded state
and when expanded into position. The rings within the center
section are arranged to provide the section with a high surface
area density to reduce the likelihood of plaque rupture by creating
less stress on the plaque. The high surface area also helps to
reduce the scissoring affect the center section rings may have upon
expansion. Undulations within the cylindrical rings allow for an
even expansion around the circumference by accounting for the
relative differences in stress created by the radial expansion of
the cylindrical rings. Each of the individual cylindrical rings may
rotate slightly relative to their adjacent cylindrical rings
without significant deformation, cumulatively providing stents
which are flexible along their length and about their longitudinal
axis, but which are still very stable in the radial direction in
order to resist collapse after expansion.
[0014] Each of the embodiments of the invention can be readily
delivered to the desired luminal location by mounting them on an
expandable member of a delivery catheter, for example a balloon,
and passing the catheter-stent assembly through the body lumen to
the implantation site. A variety of means for securing the stents
to the expandable member on the catheter for delivery to the
desired location is available. It is presently preferred to
compress the stent onto the unexpanded balloon. Other means to
secure the stent to the balloon include providing ridges or collars
on the inflatable member to restrain lateral movement, using
bioabsorbable temporary adhesives, or a retractable sheath to cover
the stent during delivery through a body lumen.
[0015] The presently preferred structures for the expandable
cylindrical rings which form the stents of the present invention
generally have a plurality of circumferential undulations
containing a plurality of alternating peaks and valleys. The peaks
and valleys are formed in generally U- and V-shaped patterns and
aligned along the longitudinal axis.
[0016] While the cylindrical rings and links generally are not
separate structures, they have been conveniently referred to as
rings and links for ease of identification. Further, the
cylindrical rings can be thought of as comprising a series of U-
and V-shaped structures in a repeating pattern. While the
cylindrical rings are not divided up or segmented into U's and V's,
the pattern of cylindrical rings resemble such configuration. The
U's and V's promote flexibility in the stent primarily by flexing
and may tip radially outwardly as the stent is delivered through a
tortuous vessel.
[0017] The undulations of the cylindrical rings can have different
degrees of curvature and angles of adjacent peaks and valleys to
compensate for the expansive properties of the peaks and valleys.
The cylindrical rings of the stents are plastically deformed when
expanded (except with NiTi alloys) so that the stents will remain
in the expanded condition and therefore they must be sufficiently
rigid when expanded to prevent the collapse thereof in use.
[0018] With stents formed from super-elastic nickel-titanium (NiTi)
alloys, the expansion occurs when the stress of compression is
removed. This allows the phase transformation from martensite back
to austenite to occur, and as a result the stent expands.
[0019] After the stents are expanded some of the peaks and/or
valleys may, but not necessarily, tip outwardly and embed in the
vessel wall. Thus, after expansion, the stents may not have a
smooth outer wall surface, rather they have small projections which
embed in the vessel wall and aid in retaining the stents in place
in the vessel.
[0020] The links which interconnect adjacent cylindrical rings can
have a cross-section similar to the cross-sections of the
undulating components of the expandable cylindrical rings. The
links may be formed in a unitary structure with the expandable
cylindrical rings formed from the same intermediate product, such
as a tubular element, or they may be formed independently and
mechanically secured between the expandable cylindrical rings. The
links may be formed substantially straight or with a plurality of
undulations. They may also be used primarily to support the
vulnerable plaque region or primarily to connect adjacent
rings.
[0021] Preferably, the number, shape and location of the links can
be varied in order to develop the desired vulnerable plaque
coverage and longitudinal flexibility. These properties are
important to minimize alteration of the natural physiology of the
body lumen into which the stent is implanted and to maintain the
compliance of the body lumen which is internally supported by the
stent. Generally, the greater the longitudinal flexibility of the
stents, the easier and the more safely they can be delivered to the
implantation site, especially where the implantation site is on a
curved section of a body lumen, such as a coronary artery or a
peripheral blood vessel, and especially saphenous veins and larger
vessels.
[0022] The stent may be formed from a tube by laser cutting the
pattern of cylindrical rings and undulating links in the tube, by
individually forming wire rings and laser welding them together,
and by laser cutting a flat metal sheet in the pattern of the
cylindrical rings and links, and then rolling the pattern into the
shape of the tubular stent and providing a longitudinal weld to
form the stent.
[0023] Other features and advantages of the present invention will
become more apparent from the following detailed description of the
invention, when taken in conjunction with the accompanying
exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is an elevational view, partially in section, of a
stent embodying features of the invention which is mounted on a
delivery catheter and disposed within a damaged artery.
[0025] FIG. 2 is an elevational view, partially in section, similar
to that shown in FIG. 1 wherein the stent is expanded within a
damaged or diseased artery.
[0026] FIG. 3 is an elevational view, partially in section,
depicting the expanded stent within the artery after withdrawal of
the delivery catheter.
[0027] FIG. 4 is a perspective view of the center section of the
stent of FIG. 3 in its expanded state depicting the serpentine
pattern along the peaks and valleys that form the cylindrical
rings.
[0028] FIG. 5 is a schematic of a process of fibrous cap rupture in
a fibroatheroma form of vulnerable plaque leading to a thrombotic
occlusion of an artery.
[0029] FIG. 6 is a plan view of a flattened section of one
embodiment of a stent of the invention including undulating links
and U- and V-shaped ring undulations.
[0030] FIG. 6a is a cross-sectional view of an undulation within a
center ring taken along line 6a-6a of FIG. 6.
[0031] FIG. 6b is a cross-sectional view of an undulation within a
distal ring taken along line 6b-6b of FIG. 6.
[0032] FIG. 7 is a plan view of a flattened section of one
embodiment of a stent of the invention including two sets of rings,
each with U-shaped undulations.
[0033] FIG. 7a is a cross-sectional view of an undulation within a
center ring taken along line 7a-7a of FIG. 7.
[0034] FIG. 7b is a cross-sectional view of an undulation within a
distal ring taken along line 7b-7b of FIG. 7.
[0035] FIG. 8 is a plan view of a flattened section of one
embodiment of a stent of the invention including two sets of rings
with U-shaped undulations where the rings are directly connected to
each other.
[0036] FIG. 8a is a cross-sectional view of an undulation within a
center ring taken along line 8a-8a of FIG. 8.
[0037] FIG. 8b is a cross-sectional view of an undulation within a
distal ring taken along line 8b-8b of FIG. 8.
[0038] FIG. 9 is a plan view of a flattened section of one
embodiment of a stent of the invention including two sets of rings
with U-shaped undulations where a center set consists of two
rings.
[0039] FIG. 9a is a cross-sectional view of an undulation within a
center ring taken along line 9a-9a of FIG. 9.
[0040] FIG. 9b is a cross-sectional view of an undulation within a
distal ring taken along line 9b-9b of FIG. 9.
[0041] FIG. 10 is a plan view of a flattened section of one
embodiment of a stent of the invention including a center set
consisting of four rings.
[0042] FIG. 10a is a cross-sectional view of an undulation within a
center ring taken along line 10a-10a of FIG. 10.
[0043] FIG. 10b is a cross-sectional view of an undulation within a
distal ring taken along line 10b-10b of FIG. 10.
[0044] FIG. 11 is a plan view of a flattened section of one
embodiment of a stent of the invention including six links within a
center section.
[0045] FIG. 11a is a cross-sectional view of an undulation within a
center link taken along line 11a-11a of FIG. 11.
[0046] FIG. 11b is a cross-sectional view of an undulation within a
distal ring taken along line 11b-11b of FIG. 11.
[0047] FIG. 12 is a plan view of a flattened section of one
embodiment of a stent of the invention including twelve links
within a center section.
[0048] FIG. 12a is a cross-sectional view of an undulation within a
center link taken along line 12a-12a of FIG. 12.
[0049] FIG. 12b is a cross-sectional view of an undulation within a
distal ring taken along line 12b-12b of FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Before describing in detail an exemplary embodiment of a
stent for the treatment of a vulnerable plaque in accordance with
the present invention, it is instructive to briefly describe a
typical stent implantation procedure and the vascular conditions
which are typically treated with stents.
[0051] Turning to the drawings, FIG. 1 depicts a metallic stent 10
incorporating features of the invention mounted on a catheter
assembly 12 which is used to deliver the stent and implant it in a
body lumen, such as a coronary artery, peripheral artery, or other
vessel or lumen within the body. The stent generally includes a
plurality of radially expandable cylindrical rings 11,13 disposed
generally coaxially and interconnected by undulating links 15 and
straight links 17 disposed between adjacent cylindrical rings. The
stent as shown in FIG. 2 generally includes distal 21, center 23,
and proximal 25 sections. The catheter assembly shown in FIG. 1
includes a catheter shaft 13 which has a proximal end 14 and a
distal end 16. The catheter assembly is configured to advance
through the patient's vascular system by advancing over a guide
wire by any of the well known methods of an over the wire (OTW)
system (not shown) or a well known rapid exchange (RX) catheter
system, such as the one shown in FIG. 1.
[0052] Catheter assembly 12 as depicted in FIG. 1 is of the well
known rapid exchange type which includes an RX port 20 where the
guide wire 18 will exit the catheter. The distal end of the guide
wire exits the catheter distal end 16 so that the catheter advances
along the guide wire on a section of the catheter between the RX
port and the catheter distal end. As is known in the art, the guide
wire lumen which receives the guide wire is sized for receiving
various diameter guide wires to suit a particular application. The
stent is mounted on the expandable member 22 (balloon) and is
crimped tightly thereon so that the stent and expandable member
present a low profile diameter for delivery through the
arteries.
[0053] As shown in FIG. 1, a partial cross-section of an artery 24
is shown with a small amount of plaque 25 that has been previously
treated by an angioplasty or other repair procedure. Stent assembly
10 of the present invention is used to repair a diseased or damaged
arterial wall which may include the plaque as shown in FIG. 1, or a
dissection, or a flap which are commonly found in the coronary
arteries, peripheral arteries and other vessels.
[0054] In a typical procedure to implant stent assembly 10, the
guide wire 18 is advanced through the patient's vascular system by
well known methods so that the distal end of the guide wire is
advanced past the plaque or diseased area 26. Prior to implanting
the stent assembly, the cardiologist may wish to perform an
angioplasty procedure or other procedure (i.e., atherectomy) in
order to open the vessel and remodel the diseased area. Thereafter,
the stent delivery catheter assembly 12 is advanced over the guide
wire so that the stent assembly is positioned in the target area.
The expandable member or balloon 22 is inflated by well known means
so that it expands radially outwardly and in turn expands the stent
assembly radially outwardly until the stent assembly is apposed to
the vessel wall. The expandable member is then deflated and the
catheter withdrawn from the patient's vascular system. The guide
wire typically is left in the lumen for post-dilatation procedures,
if any, and subsequently is withdrawn from the patient's vascular
system. As depicted in FIG. 2, the balloon is fully inflated with
the stent expanded and pressed against the vessel wall, and in FIG.
3, the implanted stent remains in the vessel after the balloon has
been deflated and the catheter assembly and guide wire have been
withdrawn from the patient.
[0055] The stent 10 serves to hold open the artery 24 after the
catheter is withdrawn, as illustrated by FIG. 3. Due to the
formation of the stent from an elongated tubular member, the
undulating components of the stent are relatively flat in
transverse cross-section, so that when the stent is expanded, it is
pressed into the wall of the artery and as a result does not
interfere with the blood flow through the artery. The stent is
pressed into the wall of the artery and will eventually be covered
with endothelial cell growth which further minimizes blood flow
interference. The rings 11,13 and links 15,17 of the stent will
eventually become endothelialized. It is this endothelialization
and subsequent neointimal growth that will integrate the device
into the fibrous cap portion of the vulnerable plaque along with
the remainder of the stented portion of the artery. This
integration will yield lower fibrous cap stresses overall. The
undulating portion of the stent provides good tacking
characteristics to prevent stent movement within the artery.
Furthermore, the closely spaced cylindrical rings at regular
intervals provide uniform support for the wall of the artery, and
consequently are well adapted to tack up and hold in place small
flaps or dissections in the wall of the artery.
[0056] The stent patterns shown in FIGS. 1-3 are for illustration
purposes only and can vary in size and shape to accommodate
different vessels or body lumens. Further, the stent 10 is of a
type that can be used in accordance with the present invention.
[0057] The first set of links and second set of links 15,17 which
interconnect adjacent first sets of cylindrical rings and adjacent
second sets of cylindrical rings 11,13 may have cross-sections
similar to the cross-sections of the undulating components of
either set of expandable cylindrical rings. In one embodiment, all
of the links are joined at either the peaks or the valleys of the
undulating structure of adjacent cylindrical rings. In this manner
there is little or no shortening of the stent assembly upon
expansion.
[0058] The number and location of the first set of links and the
second set of links 15,17 connecting the first set of rings and
second set of rings 11,13 can be varied in order to vary the
desired longitudinal and flexural flexibility in the stent assembly
structure both in the unexpanded as well as the expanded condition.
These properties are important to minimize alteration of the
natural physiology of the body lumen into which the stent assembly
is implanted and to maintain the compliance of the body lumen which
is internally supported by the stent assembly. Generally, the
greater the longitudinal and flexural flexibility of the stent
assembly, the easier and the more safely it can be delivered to the
target site.
[0059] With reference to FIG. 4, which illustrates the center
section 23 of the stent 10, the cylindrical rings 13 are in the
form of undulating portions. The undulating portion is made up of a
plurality of V-shaped members 31 having radii that more evenly
distribute expansion forces over the various members. After the
cylindrical rings have been radially expanded, outwardly projecting
edges 34,36 may be formed. That is, during radial expansion some of
the V-shaped members may tip radially outwardly thereby forming
outwardly projecting edges. These outwardly projecting edges can
provide for a roughened outer wall surface of the stent and assist
in implanting the stent in the vascular wall by embedding into the
vascular wall. In other words, the outwardly projecting edges may
embed into the vascular wall, for example arterial vessel 24, as
depicted in FIG. 3. Depending upon the dimensions of the stent and
the thickness of the various members making up the serpentine
pattern, any of the U-shaped members can tip radially outwardly to
form the projecting edges. The rings within the distal section and
proximal section 21,25 of the stent can be configured similarly to
tip outwardly.
[0060] Cylindrical rings 13 can be nested such that adjacent rings
slightly overlap in the longitudinal direction so that one ring is
slightly nested within the next ring and so on. The degree of
nesting can be dictated primarily by the length of each cylindrical
ring, the number of undulations in the rings, the thickness of the
rings, and the radius of curvature, all in conjunction with the
crimped or delivery diameter of the stent. If the rings are
substantially nested one within the other, it may be difficult to
crimp the stent to an appropriate delivery diameter without the
various struts overlapping. It is also contemplated that the rings
may be slightly nested even after the stent is expanded, which
enhances vessel wall coverage. In some circumstances, it may not be
desirable to nest one ring within the other, which is also
contemplated by the invention. As mentioned above, the distal
section and proximal section 21,25 can be configured similarly.
[0061] FIG. 5 illustrates a schematic of a process of fibrous cap
rupture in a fibroatheroma form of vulnerable plaque leading to a
thrombotic occlusion of an artery 24 (FIG. 1). A patent lumen 42 at
the lesion site is separated from a lipid core 44 of the lesion by
the fibrous cap 40. When the fibrous cap is ruptured 46, the
lumenal blood becomes exposed to tissue factor, a highly
thrombogenic core material, which can result in total thrombotic
occlusion 48 of the artery. The intravascular stent assembly of the
present invention is a novel, interventional, therapeutic technique
that redistributes and lowers the stresses in the fibrous cap.
[0062] In one embodiment shown in FIG. 6, the stent assembly 10 of
the present invention has a plurality of a first set and second set
11,13 of flexible undulating cylindrical rings being expandable in
a radial direction, with each of the rings having a first delivery
diameter and a second implanted diameter and being aligned on a
common longitudinal axis. The first set of rings have a
cross-section shown in FIG. 6b with a width 128 and height 130. The
first set of links have a similar cross-section. At least one first
set link 15 is attached between adjacent first set rings to form
the distal section and proximal section 21,25 of the stent. The
first set of links are formed with W-shaped undulations which add
to the stent's flexibility. Preferably, each of the rings is formed
of a metallic material. However, the stent assembly of the present
invention is not limited to the use of such metallic materials as
non-metallic materials are also contemplated for use with the
invention. The center section 23 has a plurality of a second set of
rings with V-shaped undulations 13 and a second set of
substantially straight links 17. The second set of rings have a
cross-section shown in FIG. 6a with a width 124 and height 126. The
second set of links have a similar cross-section. The length of a
characteristic vulnerable plaque region is generally in the range
of about 3 to 30 mm, and it is preferable that the length of the
center section is slightly longer than the vulnerable plaque
region. In any event, the center section should be long enough to
cover the vulnerable plaque region. Thus, for some applications,
the center section may be longer or shorter than the disclosed
range. The center section can be fabricated in a multiplicity of
sizes in order to accommodate multiple lengths of lesions
containing vulnerable plaque that require treatment. The width 124
of the rings and links within the center section is smaller than
the width 128 of the rings and links within the distal and proximal
sections and can vary depending on the severity of vulnerable
plaque to be treated.
[0063] The stent assembly of the present invention is placed in an
artherosclerotic artery such that upon deployment the center
section 23 apposes the region containing the vulnerable plaque.
With further reference to FIG. 6, the center section 23 of the
stent assembly apposes the treatment site (not shown) within the
body lumen while the rings are in the implanted diameter (FIG. 3).
This configuration could be applicable for at least two reasons.
First, given that previous studies have suggested that many
vulnerable plaques are not occlusive prior to the thrombotic event,
these plaques could require less scaffolding strength than typical
metallic stents are designed to provide. Second, in the event of
cap rupture within the plaque, the dense center section could
provide high coverage and focal drug delivery to the rupture
region. For purposes of this invention, the treatment site is
preferably an artery 24 having at least one lesion containing
vulnerable plaque 25 (FIG. 1).
[0064] The stent 50 shown in FIG. 7 includes a distal section 51,
center section 53, and proximal section 55. A first set of
undulating rings 56 with a first cross-section shown in FIG. 7b
with a width 136 and height 138 and a first set of substantially
straight links 57 also with a similar cross-section are located
within the distal and proximal sections. The links connect adjacent
rings in both sections.
[0065] The center section 53 includes a second set of undulating
rings 58 with a second, relatively smaller cross-section shown in
FIG. 7a with a width 132 and height 134 and a second set of
substantially straight links 59 with a similar cross-section
connecting adjacent rings. The undulations 52 of the three center
section rings are substantially U-shaped and have a smaller width
132 than the width 136 of the U-shaped undulations 54 in the first
set of rings. In addition, the second set of links are shorter than
the first set of distal and proximal links 57 and also have a
smaller width 132. The smaller dimensions and higher undulation
concentrations of the second set of rings and links helps to
redistribute and lower stresses in the fibrous cap of the
artery.
[0066] The stent 70 shown in FIG. 8 also includes a distal section
71, center section 73, and proximal section 75. A first set of
undulating rings 76 with a first cross-section shown in FIG. 8b
with a width 144 and height 146 and located within the distal and
proximal sections are directly, adjacently connected through
attachment points 77.
[0067] The center section 73 includes a second set of undulating
rings 78 with a second, smaller cross-section shown in FIG. 8a with
a width 140 and height 142. Like the first set of rings 76, the
second set of three rings are directly, adjacently connected
through attachment points 79. Similar to FIG. 7, the undulations 72
of the center section are substantially U-shaped and the rings
incorporate more undulations per ring and have a smaller width 140
than the width 144 of the rings within the distal and proximal
sections, also with U-shaped undulations 74. As in FIG. 7, the
smaller dimensions of the second set of rings helps to redistribute
and lower stresses in the fibrous cap.
[0068] The stent 80 shown in FIG. 9 also includes distal section
81, center section 83, and proximal section 85. A first set of
undulating rings 86 with a first cross-section shown in FIG. 9b
with a width 152 and height 154 and located within the distal and
proximal sections are directly, adjacently connected through
attachment points 87.
[0069] The center section 83 includes a second set of undulating
rings 88 with a second, smaller cross-section shown in FIG. 9a with
a width 148 and height 150. Like the first set of rings 86, the
second set of two rings are directly adjacently connected through
attachment points 89. Similar to FIGS. 7 and 8, the undulations 82
of the center section are substantially U-shaped and the rings have
more undulations per ring than the first set of rings 86 located
within the distal section 81 and proximal 85 section. The second
set of rings are also longer from peak 121 to valley 122 than the
first set of rings. The increase in length helps flexibility within
the center section. As in FIGS. 7 and 8, the relatively smaller
width 148 and larger number of U-shaped undulations within the
center section help to redistribute and lower stresses in the
fibrous cap.
[0070] The stent 90 shown in FIG. 10 includes a distal section 91,
center section 93, and proximal section 95. A first set of
undulating rings 96 located within the distal and proximal sections
and with a first cross-section shown in FIG. 10b with a width 160
and height 162 are directly, adjacently connected through
attachment points 97.
[0071] The center section 93 includes a second set of undulating
rings 98 with a second, wider cross-section shown in FIG. 10a with
a width 156 and height 158. Like the first set of rings 96, the
second set of four rings are directly adjacently connected through
attachment points 99. The undulations 92 of the center section are
substantially U-shaped and the rings incorporate more undulations
per ring and are shorter from peak 180 to valley 182 than the
distal and proximal rings 96, which also incorporate U-shaped
undulations 94. When compared to the stent shown in FIG. 8, the
stent of FIG. 10, allows a greater fibrous cap coverage area due to
the higher number of second set rings and due to the larger ring
cross-sectional width 156.
[0072] The stent 100 shown in FIG. 11 also includes a distal
section 101, center section 103, and proximal section 105. A first
set of undulating rings 106 located within the proximal section and
a second set of undulating rings 104 located within the distal
section, each with a first cross-section shown in FIG. 11b with a
width 168 and height 170 and second cross-section, respectively,
are each directly, adjacently connected through attachment points
107. In this particular embodiment, the first and second set of
rings are identically configured and share the same cross-section
shown in FIG. 11b.
[0073] The center section 103 differs from previous embodiments
because it incorporates a series of six links 109 to cover the
fibrous cap of an artery. The links incorporate U-shaped
undulations 102 which are arranged perpendicular to the stent
longitudinal axis and connect to the U-shaped undulations 102b
within the rings 104,106. The undulations allow the links to cover
more surface area and have greater flexibility than would a similar
straight link. The links also incorporate a cross-section shown in
FIG. 11a with a relatively smaller width 164 and height 166 for
added flexibility.
[0074] The stent 110 shown in FIG. 12 also includes a distal
section 111, center section 113, and proximal section 115. Similar
to FIG. 11, a series of links 119 form the center section of the
stent of the present embodiment.
[0075] A first set of undulating rings 116 located within the
proximal section and a second set of undulating rings 114 are
located with the distal section, each with a first cross-section
shown in FIG. 12b with a width 176 and height 178 and second
cross-section, respectively, are each directly, adjacently
connected through a first set of links 117. In this particular
embodiment, the first and second set of rings are identically
configured and share the same cross-section shown in FIG. 12b. The
first set of links are configured with a cross-section identical to
the rings.
[0076] The center section 113 incorporates a second set of twelve
links 119 to cover the fibrous cap of an artery. The second set of
links, like the links 109 shown in FIG. 11, incorporate U-shaped
undulations 112 which are arranged perpendicular to the stent
longitudinal axis. The second set of links also incorporate
straight portions 118 that fit within the U-shaped undulations
112b, 112c of the rings 116,114. The links also incorporate a
cross-section shown in FIG. 12a with a relatively smaller width 172
and height 179.
[0077] The stents of the present invention can be made in many
ways. However, the preferred method of making the stent is to cut a
thin-walled tubular member, such as stainless steel tubing to
remove portions of the tubing in the desired pattern for the stent,
leaving relatively untouched the portions of the metallic tubing
which are to form the stent. It is preferred to cut the tubing in
the desired pattern by means of a machine-controlled laser, which
is well known in the art.
[0078] The stent tubing may be made of suitable biocompatible
material such as stainless steel, titanium, tungsten, tantalum,
vanadium, cobalt chromium, gold, palladium, platinum, and iradium,
super-elastic (nickel-titanium) NiTi alloys and even high strength
thermoplastic polymers. The stent diameters are very small, so the
tubing from which it is made must necessarily also have a small
diameter. For PCTA applications, typically the stent has an outer
diameter on the order of about 1.65 mm (0.065 inches) in the
unexpanded condition, the same outer diameter of the hypotubing
from which it is made, and can be expanded to an outer diameter of
5.08 mm (0.2 inches) or more. The wall thickness of the tubing is
about 0.076 mm (0.003 inches). For stents implanted in other body
lumens, such as PTA applications, the dimensions of the tubing are
correspondingly larger. While it is preferred that the stents be
made from laser cut tubing, those skilled in the art will realize
that the stent can be laser cut from a flat sheet and then rolled
up in a cylindrical configuration with the longitudinal edges
welded to form a cylindrical member.
[0079] In the instance when the stents are made from plastic, the
implanted stent may have to be heated within the arterial site
where the stents are expanded to facilitate the expansion of the
stent. Once expanded, it would then be cooled to retain its
expanded state. The stent may be conveniently heated by heating the
fluid within the balloon or the balloon itself directly by a known
method.
[0080] The stents may also be made of materials such as
super-elastic (sometimes called pseudo-elastic) nickel-titanium
(NiTi) alloys. In this case the stent would be formed full size but
deformed (e.g. compressed) to a smaller diameter onto the balloon
of the delivery catheter to facilitate intraluminal delivery to a
desired intraluminal site. The stress induced by the deformation
transforms the stent from an austenite phase to a martensite phase,
and upon release of the force when the stent reaches the desired
intraluminal location, allows the stent to expand due to the
transformation back to the more stable austenite phase. Further
details of how NiTi super-elastic alloys operate can be found in
U.S. Pat. Nos. 4,665,906 (Jervis) and 5,067,957 (Jervis),
incorporated herein by reference in their entirety.
[0081] The stent of the invention also can be coated with a drug or
therapeutic agent. Further, it is well known that the stent (when
made from a metal) may require a primer material coating such as a
polymer to provide a substrate on which a drug or therapeutic agent
is coated since some drugs and therapeutic agents do not readily
adhere to a metallic surface. The drug or therapeutic agent can be
combined with a coating or other medium used for controlled release
rates of the drug or therapeutic agent. Examples of therapeutic
agents or drugs that are suitable for use with the polymeric
materials include sirolimus, everolimus, actinomycin D (ActD),
taxol, paclitaxel, or derivatives and analogs thereof. Examples of
agents include other antiproliferative substances as well as
antineoplastic, antiinflammatory, antiplatelet, anticoagulant,
antifibrin, antithrombin, antimitotic, antibiotic, and antioxidant
substances. Examples of antineoplastics include taxol (paclitaxel
and docetaxel). Further examples of therapeutic drugs or agents
that can be combined with the polymeric materials include
antiplatelets, anticoagulants, antifibrins, antithrombins, and
antiproliferatives. Examples of antiplatelets, anticoagulants,
antifibrins, and antithrombins include, but are not limited to,
sodium heparin, low molecular weight heparin, hirudin, argatroban,
forskolin, vapiprost, prostacyclin and prostacyclin analogs,
dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin),
dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor
antagonist, recombinant hirudin, thrombin inhibitor (available from
Biogen located in Cambridge, Mass.), and 7E-3B.RTM. (an
antiplatelet drug from Centocor located in Malvern, Pa.). Examples
of antimitotic agents include methotrexate, azathioprine,
vincristine, vinblastine, fluorouracil, adriamycin, and mutamycin.
Examples of cytostatic or antiproliferative agents include
angiopeptin (a somatostatin analog from Ibsen located in the United
Kingdom), angiotensin converting enzyme inhibitors such as
Captopril.RTM. (available from Squibb located in New York, N.Y.),
Cilazapril.RTM. (available from Hoffman-LaRoche located in Basel,
Switzerland), or Lisinopril.RTM. (available from Merck located in
Whitehouse Station, N.J.); calcium channel blockers (such as
Nifedipine), colchicine, fibroblast growth factor (FGF)
antagonists, fish oil (omega 3-fatty acid), histamine antagonists,
Lovastatin.RTM. (an inhibitor of HMG-CoA reductase, a cholesterol
lowering drug from Merck), methotrexate, monoclonal antibodies
(such as PDGF receptors), nitroprusside, phosphodiesterase
inhibitors, prostaglandin inhibitor (available from GlaxoSmithKline
located in United Kingdom), Seramin (a PDGF antagonist), serotonin
blockers, steroids, thioprotease inhibitors, triazolopyrimidine (a
PDGF antagonist), and nitric oxide. Other therapeutic drugs or
agents which may be appropriate include alpha-interferon,
genetically engineered epithelial cells, and dexamethasone.
[0082] While the foregoing therapeutic agents have been used to
prevent or treat restenosis, they are provided by way of example
and are not meant to be limiting, since other therapeutic drugs may
be developed which are equally applicable for use with the present
invention. The treatment of diseases using the above therapeutic
agents are known in the art. Furthermore, the calculation of
dosages, dosage rates and appropriate duration of treatment are
previously known in the art.
[0083] While the invention has been illustrated and described
herein in terms of its use as intravascular stents, it will be
apparent to those skilled in the art that the stents can be used in
other instances in all vessels in the body. Since the stents of the
present invention have the novel feature of enhanced longitudinal
flexibility due to their angulated undulations, they are
particularly well suited for implantation in almost any vessel
where such devices are used. This feature, coupled with limited
longitudinal contraction of the stent when radially expanded,
provides a highly desirable support member for all vessels in the
body. Other modifications and improvements may be made without
departing from the scope of the invention.
* * * * *