U.S. patent application number 16/599393 was filed with the patent office on 2020-02-06 for method and apparatus for stenting.
The applicant listed for this patent is Medinol Ltd.. Invention is credited to Elazer R. EDELMAN, Yoram RICHTER.
Application Number | 20200038208 16/599393 |
Document ID | / |
Family ID | 23052210 |
Filed Date | 2020-02-06 |
United States Patent
Application |
20200038208 |
Kind Code |
A1 |
RICHTER; Yoram ; et
al. |
February 6, 2020 |
METHOD AND APPARATUS FOR STENTING
Abstract
A method and an apparatus to create a more favorable flow regime
in a lumen. An artificial shape in the lumen is created to at least
one of eliminate flow disturbances and enhance aspects of fluid
flow through a treatment site.
Inventors: |
RICHTER; Yoram; (Ramat
Hasharon, IL) ; EDELMAN; Elazer R.; (Brookline,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Medinol Ltd. |
Tel Aviv |
|
IL |
|
|
Family ID: |
23052210 |
Appl. No.: |
16/599393 |
Filed: |
October 11, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15291180 |
Oct 12, 2016 |
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16599393 |
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12541615 |
Aug 14, 2009 |
9492293 |
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15291180 |
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10484081 |
Jul 8, 2004 |
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PCT/US2002/007529 |
Mar 13, 2002 |
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12541615 |
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60275419 |
Mar 13, 2001 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2/90 20130101; A61M
25/1002 20130101; A61F 2230/0006 20130101; A61F 2250/0039 20130101;
A61F 2/958 20130101; A61F 2002/068 20130101; A61F 2/86 20130101;
A61F 2/06 20130101 |
International
Class: |
A61F 2/90 20060101
A61F002/90; A61F 2/958 20060101 A61F002/958; A61F 2/86 20060101
A61F002/86; A61F 2/06 20060101 A61F002/06 |
Claims
1. An expandable medical device for implantation in a body having a
longitudinal axis along a direction of blood flow, said device
comprising a first device segment directly connected around the
circumference to a second device segment, said device having two
tapers wherein the first device segment has a diverging
configuration and the second device segment has a converging
configuration.
2. The expandable medical device of claim 1, wherein the first
device segment has an opening having a first diameter and the
second device segment has an opening having a second diameter.
3. The expandable medical device of claim 2, wherein the first
diameter and the second diameter are the same.
4. The expandable medical device of claim 2, wherein the first
diameter is larger than the second diameter.
5. The expandable medical device of claim 1, wherein the device is
self-expanding.
6. The expandable medical device of claim 1, wherein the device is
balloon-expandable.
7. The expandable medical device of claim 1, wherein a
cross-section of any device segment in a plane normal to the
longitudinal axis thereof is circular.
8. The expandable medical device of claim 1, further comprising a
means for controlling a flow of blood.
9. The expandable medical device of claim 1, wherein the device is
configured to minimize a flow disturbance in the body.
10. The expandable medical device of claim 5, wherein the device is
re-positionable after delivery.
11. The expandable medical device of claim 1, wherein the device is
a stent structurally configured for implantation in a lumen of a
blood vessel.
12. The expandable medical device of claim 1, wherein the device
further comprises a first straight section located at a first end
of the device.
13. The expandable medical device of claim 12, wherein the device
further comprises a second straight section located at a second end
of the device.
14. The expandable medical device of claim 13, wherein the
cross-sectional diameter of each of the straight sections is
different.
15. The expandable medical device of claim 13, wherein the
cross-sectional diameter of each of the straight sections is the
same.
16. The expandable medical device of claim 1, wherein the first or
second stent segments or both have a frustoconical shape.
17. The expandable medical device of claim 1, wherein the envelope
is configured for substantially eliminating flow separation in a
lumen at the deployment site.
18. The expandable medical device of claim 1, wherein the device is
configured to change the shape of a lumen to an artificial tapered
shape.
19. The expandable medical device of claim 1, wherein the first
device segment, second device segment, or both, have a continuous
taper.
20. The expandable medical device of claim 1, wherein the first
device segment, second device segment, or both, have a stepped
taper.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to implantable
medical devices, and more particularly, to implantable stents for
maintaining the patency of a lumen.
BACKGROUND OFF THE INVENTION
[0002] Many factors are known that can contribute to and/or
exacerbate an occlusion of a bodily vessel or lumen. Such factors
include internally induced vascular injury, such as, for example,
vascular injury caused by an accumulation of plaque at the walls of
the lumen, or externally induced vascular injury, such as vascular
injury caused by the deployment of a stent and/or by angioplasty.
When a lumen is subjected to injury, white blood cells and other
substances tend to converge on the injured region of the lumen
bringing about inflammatory effects at that region. These
inflammatory effects tend to result in an occlusion of the lumen,
that is, an undesired narrowing of the lumen or a total blockage of
the lumen. In the case of an externally induced injury resulting
from a deployment of a stent, the inflammatory effects sometimes
tend to contribute to what is termed restenosis, or re-occlusion of
the lumen.
[0003] Moreover, in the lumen, there may be areas with flow
disturbances. The vasculature in the human body is a tree of
diverging lumens with typical dichotomous diverging patterns. The
dichotomous diverging patterns create bifurcations in the arterial
system where the mother lumen diverges into two daughter lumens. In
most cases one of the daughter branches is larger and is the
continuation of the mother vessel and the other one is smaller and
the side branch. (The venous system is basically the mirror image
of these bifurcations in which the flow is from smaller lumens into
larger ones, or in the direction of flow one can describe this
system as converging rather than diverging.) The present invention
is in part based on an observation that vascular injury may be
caused by or exacerbated by among other things flow disturbances in
the flow of blood at a given region of the lumen. These flow
disturbances include areas of "flow separation," in which vortices
are created next to the vessel wall, rendering the blood
essentially stagnant at those locations. Such areas of flow
separation are a particular problem in bifurcated lesions. However,
even lumens with a substantially constant diameter may have areas
with undesirable flow separation or other flow disturbances.
[0004] Such disturbances may work to increase the likelihood of
inflammation by increasing the residence time for inflammatory
cells near the walls of the lumen, and decreasing of flow forces
that might otherwise push those cells downstream. That, in turn,
may increase the probability that such white cells will penetrate
the wall and will initiate an inflammatory effect, which can result
in an undesirable narrowing of the lumen. Flow disturbance may also
be an instigator in endothelial cell dysfunction (whether due to
decreased fluid shear stress at the wall, imposition of
bi-directional shear stress, or otherwise) which then promotes the
occurrence of an inflammatory reaction. Finally, flow disturbance
may cause or exacerbate vascular injury by promoting particle
sedimentation and by inhibiting proper transport of waste materials
from the vessel wall into the lumen. Although the precise mechanism
or mechanisms by which flow disturbance accelerates the growth of
vascular lesions is not completely understood, it is believed that
avoiding flow disturbance will lessen the risk of vessels narrowing
or re-narrowing.
[0005] Moreover, a typical angioplasty procedure causes trauma to
the vessel wall. The angioplasty procedure is typically at the area
of highest constriction in a vessel, i.e., at the location of a
lesion. If a stent is implanted in this area, flow disturbances may
be present.
[0006] Without limiting the scope of the present invention, there
are at least three factors that may influence the presence of flow
disturbances at areas of constriction. First, it is unlikely that
the lesion formed by chance--lesions rarely do. There must be a
reason why the lesion is localized at a particular place. More than
likely, this place was a point of flow disturbance to begin with.
At best, stents according to the prior art do not alter the
geometry of a vessel but rather return it to the original geometry.
Hence there is a good chance that the stented geometry includes the
flow disturbance.
[0007] Thus, an angioplasty or stent procedure likely increase
inflammatory effects. First, as described above, any flow
disturbances may increase the residence times for inflammatory
cells near the walls of the vessel even in the absence of injury,
and/or adversely effect endothelial cell function. Second, the
vascular injury caused by the angioplasty and/or stent deployment
enhances the likelihood of inflammation, even in the absence of
flow disturbance.
[0008] Furthermore, as opposed to the optimal stent deployment
discussed above, stents often do not deploy optimally, thus
introducing a new flow disturbance into the system. This can be
because they are not adequately tapered (which is a particular
problem with conventional dedicated bifurcation stents), or because
they are deployed in a curving vessel and alter that curvature, or
because of sub-optimal support of a tough lesion or just because of
the nature of the stent design, or because most stents (and
particularly those that are dedicated bifurcation stents) do not
have an angle of taper.
[0009] There are known stents which are tapered. For example, U.S.
Pat. No. 5,827,321 to Roubin et al. discloses a tapered stent. The
stents disclosed in that patent, however, are tapered to provide an
optimized fit between the original geometry and the treated section
of the lumen, so as to minimize the stretch of the lumen wall when
treating a tapered section of a lumen. They are therefore
specifically designed not to alter the flow characteristics of a
lumen. Rather, they are specifically designed to conform to the
existing geometry of the lumen.
[0010] In view of this there is a need to minimize flow disturbance
and the concomitant probability of inflammatory cell
adhesion/infiltration where adhesion/infiltration is deemed to be a
problem. In particular there is a need to provide a method an
apparatus for reshaping a lumen to promote laminar flow and
minimize or eliminate any areas of flow separation, especially in
areas that were traumatized by the angioplasty procedure, in order
to minimize the effect of the trauma. This includes assuring the
proper shaping of the lumen when stenting a bifurcation or even to
creating an artificial geometry in a straight vessel where such
shape was non-existing prior to the treatment, in order to minimize
flow separation, that may happen if there is no shaping.
Preferably, this can be done by physicians using existing devices
that were not originally made to create an artificial geometry
SUMMARY OF THE INVENTION
[0011] Accordingly, the present invention provides stent
configurations that induce a more favorable flow regime (e.g., one
that minimizes or eliminates flow disturbance in the treatment
area) are provided. Specifically, a method and apparatus is
disclosed which enables a physician to tailor the flow
characteristics of the post-treatment site to avoid flow
disturbances, or otherwise enhance aspects of fluid flow through
the post-treatment site to avoid inflammatory effects.
[0012] Embodiments of the present invention utilize a shaped, e.g.,
tapered, stent such that the flow pattern, as it relates to the
probability of restenosis, is optimized relative to that which
would be induced by a stent that was either non-tapered or tapered
in such a way as to merely minimize the mechanical stress imposed
on the wall.
[0013] The aspects of the flow pattern that may be optimized by the
appropriate tapered geometry may include any one (or a combination)
of the following:
[0014] a. Reduction/elimination of regions of flow separation. Such
regions are most commonly found in bifurcated geometries.
[0015] b. Increase in the shear stress imposed on the vessel wall
by fluid flow.
[0016] c. Introduction/enhancement of acceleration of mean fluid
velocity along the length of the stent.
[0017] d. Reduction/elimination of the radial (perpendicular to the
vessel wall) component of fluid flow.
[0018] e. Replacement of bi-directional (forward and backward)
shear stress with a unidirectional shear stress.
[0019] f. Promotion of mass transport out of the vessel wall.
[0020] g. Transition of potentially non-laminar flow pattern to
laminar flow.
[0021] h. Other, as yet undescribed, aspects. The study of what
exactly is it about flow disturbance that enhances restenosis is
ongoing. The inventors do not know everything about how this
happens but have discovered that improving the flow regime
minimizes the probability of re-occlusion.
[0022] The optimization obtainable with embodiments of the present
invention can be achieved in vessel geometries that either:
[0023] 1. Include a region of flow disturbance (most commonly flow
separation); the most common examples of this would be
bifurcations. This region of flow disturbance which exists after
stenting with present devices predisposes the stent to re-occlusion
for any one of the factors mentioned above. Hence,
reduction/elimination of the region of disturbance minimizes the
probability of re-occlusion.
[0024] 2. May not include a region of flow disturbance; the most
common examples of this would be straight, tapered/non-tapered,
non-bifurcated vessel segments. The stent is still predisposed to
re-occlusion (as all stents are) due to a multitude of factors
including vessel wall injury, inflammatory response, foreign body
reaction etc, but the introduction of an artificial geometry in
these cases alters the flow pattern in such a way as to offset non
flow-disturbance related factors with the end result being a
minimization of the probability of restenosis.
[0025] Embodiments of stents with axially symmetric or asymmetric
tapers are disclosed. An axially asymmetric taper may be deployed
in geometries that include a region of flow disturbance (most
commonly flow separation; see 1 above). The stent would be deployed
such that the tapered part of its circumference would face the
region of flow disturbance. An axially symmetric taper would
typically be deployed in geometries that may not include a region
of flow disturbance (see 2 above). However, for considerations of
manufacturability, usability, marketing or otherwise, an axially
symmetric taper could still be used even in geometries that do
include regions of flow separation (see 1 above) with results that
would be expected to be superior to those that would be achieved
with a non-tapered stent.
[0026] The shape of the stent may be specifically designed to
improve the flow regime, e.g., by minimizing any flow disturbance,
and the resultant narrowing of the lumen. This may be accomplished
with a self-expanding stent that has, for example, at least two
sections with different cross-sectional areas, and a tapered
section connecting the two sections with different cross-sectional
areas to one another. Of course these sections will have different
cross-sectional areas.
[0027] In another embodiment, a balloon expandable stent may be
implanted with a delivery balloon which is shaped to cause it to
deploy to a predetermined shape. The shaped portion of the stent
may be positioned at the bifurcation or at the sensitive area
(e.g., a lesion site) in a straight vessel. This permits physicians
to use existing stents that were not originally designed to have a
non-uniform shape to carry out the present invention and create a
shaped, e.g., tapered geometry in a lumen. Of course, the stent may
be shaped and expanded to its predetermined shape by a balloon or
balloons of appropriate compliance to form the desired shape.
[0028] Thus, in a straight lumen, the stent may be configured to
introduce an artificial tapering. In some cases, for example at a
bifurcation, that tailoring may be accomplished by using a stent
with an axially asymmetric profile in the expanded shape. In other
cases, for example a vessel whose pre-diseased shape was generally
straight and of generally constant diameter, that tailoring may be
accomplished by inducing an artificially tapered section or
sections.
[0029] Thus, these embodiments provide a method and apparatus for
reshaping a lumen to promote more favorable flow regime, e.g.,
laminar flow, and minimize or eliminate any areas of flow
separation, especially in areas that were traumatized by the
angioplasty procedure in order to prevent restenosis. In general
terms, this is done using stents that are configured to minimize
flow disturbance. In the illustrated embodiments, these stents are
configured so that they have a taper which alters the flow
characteristics of the lumen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The present invention is illustrated by way of example and
not limitation in the figures in the accompanying drawings in which
like references indicate similar elements, and in which:
[0031] FIG. 1a is a particle image velocimetry representation of an
untapered bifurcation site in a lumen, showing the flow vector
field by way of arrows, and a highlighted region of flow
separation;
[0032] FIG. 1b is a particle image velocimetry representation
similar to FIG. 1a, showing the main branch of the bifurcation as
having been tapered to minimize and/or substantially eliminate flow
separation;
[0033] FIG. 2a is a perspective, schematic view of a profile of an
expanded stent according to a first embodiment of the present
invention;
[0034] FIG. 2b is a view similar to FIG. 2a showing the profile of
the stent in a perspective wire frame view;
[0035] FIG. 2c is a side elevational wire frame view of the stent
profile of FIGS. 2a and 2b;
[0036] FIG. 3a is a perspective, schematic view of a profile of an
expanded stent according to a second embodiment of the present
invention;
[0037] FIG. 3b is a view similar to FIG. 3a showing the profile of
the stent in a perspective wire frame view;
[0038] FIG. 3c is a side elevational wire frame view of the profile
of stent of FIGS. 3a and 3b;
[0039] FIG. 4a is a perspective, schematic view of a profile of an
expanded stent according to a third embodiment of the present
invention;
[0040] FIG. 4b is a side elevational wire frame view of the profile
of the stent of FIG. 4a;
[0041] FIG. 5a is a perspective, schematic view of a profile of an
expanded stent according to a fourth embodiment of the present
invention;
[0042] FIG. 5b is a side elevational wire frame view of the stent
of FIG. 5a;
[0043] FIG. 6a is a perspective, schematic view of a profile of an
expanded stent according to a fifth embodiment of the present
invention;
[0044] FIG. 6b is a side elevational wire frame view of the stent
profile of FIG. 6a;
[0045] FIG. 7a is a side elevational wire frame view of a profile
of an expanded stent according to a sixth embodiment of the present
invention;
[0046] FIG. 7b is a side elevational wire frame view of a profile
of an expanded stent according to a seventh embodiment of the
present invention;
[0047] FIG. 8 is a perspective view of an embodiment of a kit
according to the present invention showing a stent according to the
present invention disposed over a balloon on a catheter for
insertion into a lumen;
[0048] FIGS. 9a-9h are side-elevational views of deployment
balloons adapted to expand a balloon-expandable stent to the
configurations of FIGS. 2a, 3a, 4a, 5a, 6a, 7a, 7b, and 10,
respectively; and
[0049] FIG. 10 is a side elevational wire frame view of a profile
of an expanded stent according to an eighth embodiment of the
present invention.
DETAILED DESCRIPTION
[0050] The present invention is in part based on an observation
that vascular injury may be caused by or exacerbated by, among
other things, flow disturbances in the flow of blood at a given
region of the lumen. Flow disturbances in the form of flow
separation might work to increase the likelihood of inflammation by
increasing a residence time for inflammatory cells near the walls
of the lumen, by decreasing fluid shear stress at the wall, by
imposing bi-directional shear stress, by promoting particle
sedimentation and by decreasing mass transfer of waste products
from the wall into the lumen. Flow separation is manifested in
regions where flow vortices are created next to lumen walls, or
where blood is substantially stagnant next to the lumen walls. Flow
disturbances also may tend to adversely affect endothelial cell
function and hence prevent the endothelial cells from providing a
barrier to inflammatory cell infiltration. Although the precise
mechanism or mechanisms by which flow disturbance accelerates the
growth of vascular lesions is not completely understood, it is
believed that avoiding flow disturbance will lessen the risk of
vessels narrowing or re-narrowing.
[0051] In most general terms, embodiments of the present invention
are directed to disposing a stent, specifically designed to induce
a more favorable flow regime, in an area where an undesirable flow
disturbance would otherwise occur. This is done using a stent,
which, when expanded will have a non-uniform shape. In other words,
its shape deviates from the conventional longitudinally uniform
circular cross-section found in most stents.
[0052] In the following, exemplary shapes will be described. These
are only given as examples. Other shapes which, based on the
principles of fluid dynamics, will, in a particular instance, avoid
flow disturbances may be also used. Also described are the various
types of stents that may be used, such as self-expanding stents and
balloon-expandable stents along with ways of achieving the desired
stent profiles of shapes and delivering the stents.
Exemplary Shapes
[0053] FIGS. 2a-7b and 10 illustrate profiles of expanded stents
according to the present invention. It is noted that although FIGS.
2a-7b and 10 are sometimes referred to as showing a "stent," what
these figures actually show is a schematic view of the stent
envelope or profile, without showing cell patterns or other stent
configurations that would in turn contribute to form the shown
stent envelopes.
[0054] In general, the stent profiles illustrated in FIGS. 2a-7b
and 10 can be considered to comprise a first stent segment 12
configured to have at least a first stent cross-sectional area A1
in the expanded state of the stent as shown. A second stent segment
14 is longitudinally offset with respect to the first stent segment
12 and is configured to have a second stent cross-sectional area A2
in the expanded state of the stent as shown. The stent also
includes a third stent segment 16 configured to assume a tapered
stent segment configuration in the expanded state of the stent as
shown, the tapered stent segment configuration connecting the first
stent segment 12 to the second stent segment 14.
[0055] The stent may be configured such that, in an expanded state
thereof in a lumen, it manipulates a flow of blood in the lumen so
as to reduce or eliminate flow disturbances at the treatment site
after the stent is placed. In each of the illustrated embodiments,
the cross-sectional area of the stent varies as will be apparent
from the description that follows.
[0056] In the context of the present invention, a "stent segment"
refers to any portion of the stent envelope defined between two
boundary regions, such as boundary planes perpendicular to the
longitudinal axis of the stent. In particular, in embodiments of
the present invention, the first stent segment 12 is a stent
segment having a constant stent cross-sectional area A1 in a
deployed state of the stent, this first stent segment 12 being
defined between planes P1' and P1'', where P1' is a plane located
at the inlet opening I of the stent. The second stent segment 14 in
turn has a constant stent cross-sectional area A2 in a deployed
state of the stent, this second stent segment 14 being defined
between planes P2' and P2'', where P2'' is a plane located at the
outlet opening O of the stent. The third stent segment 16 is has a
tapered configuration in a deployed state defined between planes
P3' and P3'' and is tapered in a expanded state of the stent.
According to embodiments of the present invention, the tapering of
third stent segment may be either continuous, as shown in the
embodiments of FIGS. 2a-7b and 10, or stepped (not shown).
Referring in particular to embodiments of the present invention
shown in FIGS. 2b, 3b, 4b, 5b, 6b, 7a, 7b and 10, planes P1', P1'',
P2', P2'', P3', and P3'' are shown for respective ones of those
embodiments.
[0057] FIGS. 2a-2c show a stent profile 10 comprising a first
straight segment followed by a tapering segment leading to a final
straight segment. In the embodiment of FIGS. 2a-2c, the first stent
segment 12 is defined between planes P1' and P1'', where the latter
two planes are longitudinally offset with respect to one another,
defining a first stent segment 12 that is a right circular cylinder
therebetween. The second stent segment 14 is defined between planes
P2' and P2'', these two planes also being longitudinally offset
with respect to each other, defining a second stent segment 14 that
is also a right circular cylinder. In the embodiment of FIGS.
2a-2c, the respective ends of first, second and third stent
segments are congruent, that is, P1'' is coextensive with P3', and
P3'' is coextensive with P2' as clearly shown in FIG. 2b. In the
context of the present invention, when given boundary planes of two
stent segments are coextensive, it is said that those two stent
segments are "directly" connected to one another. The embodiment of
stent profile 10 shown in FIGS. 2a-2c may be used in a lumen having
a non-tapered original shape, and in this case would change the
shape of that lumen to an artificial, tapered shape.
[0058] The embodiment of stent 10 shown in FIGS. 2a-2c may also be
used in a lumen that had a natural taper in an original shape
thereof, in which case the first stent segment 12 may have a
cross-sectional area A1 corresponding to the original shape of a
proximal part of the lumen, the second stent segment 14 may have a
cross-sectional area A2 corresponding to the original shape of a
distal part of the lumen, and the third stent segment 16 has a
tapered configuration designed to minimize or eliminate flow
separation in that segment.
[0059] FIGS. 3a-3c show a stent profile 100 comprising one long
tapered segment 5. In the embodiment of FIGS. 3a-3c, boundary
planes P1' and P1'' are coextensive, meaning that the first stent
segment 12 is defined at the plane of the inlet I of stent 100.
Similarly, boundary planes P2' and P2'' are coextensive, meaning
that the second stent segment 14 is defined at the plane, of the
outlet O of stent 100. Additionally, P3' is coextensive with both
P1' and P1'', meaning that the third stent segment 16 is directly
connected to the first stent segment 12, and P3'' is coextensive
with both P2' and P2'', meaning that the third segment 16 is
likewise directly connected to the second stent segment 14. A
configuration such as the one described above results in a stent
100 having a stent envelope 20 that defines a frustoconical shape,
that is, a constant, symmetrical taper along the longitudinal axis
18 of the stent. The embodiment of FIGS. 3a-3c may be used
similarly to the embodiment of FIGS. 2a-2c.
[0060] Embodiments of the stent profiles according to the present
invention include within their scope stent configurations where the
stent envelope presents any number of diverging segments between
boundary planes P1'' and P3', and between boundary planes P3'' and
P2'. Examples of such diverging segments are provided in the
embodiments 4a-7b. Other such diverging segments may be tailored to
produce the desired flow characteristics, and are within the
purview of the present invention.
[0061] In particular, the stent profile 200 of the embodiment of
FIGS. 4a-4b is similar to that of FIGS. 2a-2c, except that it
further includes a fourth stent segment 22 having a diverging
configuration in an expanded state of the stent, the fourth stent
segment 22 being defined between boundary planes P4' and P4'' as
shown. In the shown embodiment, P4' is coextensive with P1'', and
P4'' is coextensive with P3', meaning that the fourth stent segment
22 is directly connected to both the first stent segment 12 and the
third stent segment 16. Here, the fourth stent segment 22
represents a diverging entrance segment.
[0062] Additionally, the stent profile 300 of the embodiment of
FIGS. 5a-5b is similar to the embodiment of FIGS. 4a-4b in that it
additionally includes a fifth stent segment 24 having a diverging
configuration with respect to an expanded state of the stent, the
fifth stent segment 24 being defined between boundary planes P5'
and P5'' as shown. In the shown embodiment, P5' is coextensive with
P3'', and P5'' is coextensive with P2', meaning that the fifth
stent segment 24 is directly connected to both the third stent
segment 16 and the second stent segment 14. Here, the fifth stent
segment 24 represents a diverging exit segment.
[0063] FIGS. 7a and 7b show two embodiments of stent profiles 500
and 600 according to the present invention, where the inlet
cross-sectional area A1 is the same as outlet cross-sectional area
A2. Stent profile 500 of FIG. 7a is similar to stent profile 200 of
FIG. 4b, except that in the embodiment of FIG. 4b, A2 is less than
A1. Moreover, stent profile 600 of FIG. 7b is similar to stent
profile 300 of FIG. 5b, except that in the embodiment of FIG. 5b,
A2 is likewise less than A1.
[0064] The embodiments of the stent that include one or more
diverging segments between first stent segment 12 and the second
stent segment 14 are useful in allowing the selection of tapering
angle despite the inlet cross-sectional area, or cross-sectional
area A1 of the first stent segment 12, or the outlet
cross-sectional area, or cross-sectional area A2 of the second
stent segment 14. One or more diverging segments can increase a
cross-sectional area of the stent at boundary plane P3' with
respect to cross-sectional area A1, and/or decrease a
cross-sectional area of the stent at boundary plane P3'' with
respect to outlet cross-sectional area A2, in this way allowing an
advantageous manipulation of the tapering angle in order to obtain
the desired flow characteristics without being limited by inlet
cross-sectional area A1 or outlet cross-sectional area A2, whether
A2 is less than A1, as in the case of the embodiments shown in
FIGS. 2a-5b and 10, or whether A2 is the same as A1, as in the case
of the embodiments shown in FIGS. 7a-7b.
[0065] Embodiments where two diverging segments 22 and 24 are used
in the stent of the present invention and where A1 and A2 are
substantially equal to one another, such as the embodiment shown in
FIGS. 7a-7b described above, are advantageous in that they allow a
taper in the stent while allowing the inlet cross-sectional area A1
and outlet cross-sectional area A2 to be identical. Again, however,
there is a variation in cross-sectional area along the length of
the stent.
[0066] Asymmetrical stent configurations are possible in accordance
with the principles of the present invention. For example, it is
possible to provide stents that are non-uniform about the axis of
the stent. This non-uniformity refers to the stent envelope, and
not necessarily to the actual cells of a stent (although modifying
the cells is one way to modify the stent envelope). Thus, in the
embodiment of FIGS. 6a-6b on the one hand, and of FIG. 10 on the
other hand, two respective examples of an asymmetrical stent
profile according to the present invention are provided, that is,
examples of a stent that is asymmetrical with respect to the
longitudinal axis 18 thereof.
[0067] In the shown embodiments of FIGS. 6a-6b, stent profile or
stent 400 has a stent envelope 20 that is configured such that, in
an expanded state of the stent 400, it defines a first portion 26
bounded by walls W1 and having a contour in a cross-sectional plane
including the longitudinal axis of the stent that is a curved line.
A contour of first portion 26 in the cross-sectional plane
including the longitudinal axis of the stent is provided for
example in FIG. 6b, where the contour of wall W1 in that
cross-sectional plane is curved line 30.
[0068] The stent envelope 20 in the embodiment of FIGS. 6a-6b
further includes a second portion 28 bounded by walls W2 and having
a contour in a cross-sectional plane including the longitudinal
axis of the stent that is a straight line parallel to the
longitudinal axis. This latter contour 32 is also shown in FIG. 6b.
The first portion and the second portion together define the stent
envelope 20 as shown. In the embodiment of FIGS. 6a and 6b, the
second portion is quonset-shaped, that is, has the shape of a right
cylinder cut in half along a plane that contains its longitudinal
axis.
[0069] Moreover, in the embodiment of FIG. 10, an example of an
asymmetrical stent profile or stent 700 is provided. In the shown
embodiment, the stent envelope 20 is configured such that, in an
expanded state of the stent 700, it defines a first portion 26
bounded by walls W1 and having a contour 30 in a cross-sectional
plane including a longitudinal axis of the stent that is a straight
line extending at an angle with respect to the longitudinal axis.
The stent envelope 20 in the embodiment of FIG. 10 further includes
a second portion 28 bounded by walls W2, and having a contour 32 in
a cross-sectional plane including the longitudinal axis of the
stent that is a straight line parallel to the longitudinal axis.
The first portion and the second portion together define the stent
envelope 20 as shown. In the embodiment of FIG. 10, the second
portion 28 is quonset-shaped. The embodiment of FIG. 10 is a
preferred embodiment of a stent profile according to the present
invention. It is to be understood, however, that asymmetrical
stents different from the one shown in the embodiments of FIGS.
6a-6b and 10 are within the purview of the present invention, as
long as they are configured to induce a favorable flow regime for
reducing a risk of restenosis.
[0070] The embodiments of the stent of the present invention shown
in FIGS. 2a-5b, 7a and 7b, are predominantly configured to change a
shape of the lumen to an artificial, tapered shape. On the other
hand, asymmetrical embodiments of the stent of the present
invention, that is, embodiments of stent that are asymmetrical with
respect to the longitudinal axis of the stent, such as the
embodiments of FIGS. 6a-6b and 10, are predominantly configured to
be used at a main branch of a bifurcation, either restoring the
shape of the main branch to its original shape, or changing the
shape of the main branch to an artificial, tapered shape.
[0071] The stent 500 and 600 of FIGS. 7a-7b may be used according
to embodiments of the present invention in a main branch of a
bifurcation. In the embodiments of FIGS. 7a-7b, A1 and A2 may
correspond to the actual cross-sectional area of the lumen, and,
despite A1 and A2, the shape of the lumen is changed to an
artificial tapered shape by virtue of the third stent segment 16,
and the fourth and fifth diverging segments 22 and 24.
[0072] Stents according to embodiments of the present invention,
such as the embodiments depicted in FIGS. 2a-7b and 10, may have,
in an undeployed state thereof, a tapered shape that mimics the
respective tapered shapes of the embodiments of FIGS. 2a-7b and 10,
or a non-tapered shape that is configured to assume a tapered shape
in a deployed state thereof according to embodiments of the present
invention as explained in more detail below.
[0073] According to the present invention, for example, one may
configure embodiments of the stent of the present invention for a
straight, either tapered or non-tapered, non-bifurcated lumen.
Although a non-tapered stent used at such a deployment location
would still be predisposed to restenosis due to a multitude of
factors, including lumen wall injury, inflammatory response,
foreign body reaction, providing the lumen instead with an
artificial, tapered shape according to embodiments of the present
invention would manipulate the flow regime in such a way as to at
least partially offset non-flow-disturbance related factors, an end
result being a reduction in the risk of restenosis.
[0074] The taper in the stent according to embodiments of the
present invention could be either symmetrical with respect to the
longitudinal axis 18 of the stent, such as, for example, shown by
way of example in the embodiments of FIGS. 2b-5b, 7a and 7b, or
asymmetrical with respect to the longitudinal axis of the stent, as
shown by way of example in the embodiments of FIGS. 6a-6b and 10.
It is noted that the present invention includes within its scope
symmetrical and asymmetrical tapered stents having configurations
other than those shown by way of example with respect to the
embodiments of FIGS. 2a-7b and 10, as long as the configuration of
the stent manipulates a flow regime at the deployment location
thereof to reduce a risk of restenosis at the deployment
location.
[0075] In general, but without limitation, an axially symmetric
taper, such as the one shown by way of example in the embodiments
of FIGS. 2a-5b, 7a and 7b, might be preferably deployed according
to embodiments of the present invention, in a vessel that is
generally straight, and not bifurcated. An axially asymmetric
taper, such as the one shown by way of example in the embodiments
of FIGS. 6a-6b and 10 might be deployed at a bifurcation site,
where the side branch is situated opposite the asymmetry, e.g.,
approximately at W2 in FIGS. 6a and 10.
[0076] Where the stent is configured to change a shape of the lumen
to an artificial shape, and, additionally, where the stent is used
in a lumen where flow separation either caused or exacerbated
vascular injury, the artificial shape, and hence the outer shape of
the stent envelope 20, are configured for substantially eliminating
such flow separation in the lumen at the deployment location of the
stent, thereby reducing a risk of restenosis at the deployment
location.
The Construction and Delivery of the Stents
[0077] In one embodiment of the stent, the stent is a
self-expanding stent. In one exemplary embodiment of the
self-expanding stent, the self-expanding stent has at least two
sections with different cross-sectional areas, and a tapered
section connecting the two sections with different cross sectional
areas to one another such as is shown in FIG. 2a-2c. The
configurations of the other embodiments described in FIGS. 3a-7b
and 10 may also be implemented as self-expanding stents.
[0078] The stent of the present invention may also be
balloon-expandable stent. A balloon-expandable stent in accordance
with the present invention is configured to introduce an artificial
taper to a lumen. The stent may be constructed so that when
expanded by a compliant balloon, for example, it will take a
predetermined shape, such as one of the shapes illustrated in FIGS.
2a-7b and 10.
[0079] In another embodiment of the present invention, as described
in detail below, a balloon-expandable stent is implanted with a
delivery balloon, which is tapered. Deploying a balloon-expandable
stent with a tapered delivery balloon will cause the stent to
deploy to the tapered shape of the balloon.
[0080] The present invention further contemplates a kit for
deploying the stent 1 of the present invention. As depicted in FIG.
8, the kit includes a stent according to any one of the embodiments
of the present invention, such as the embodiments described above,
and a delivery balloon 34, for example on a catheter C, configured
to be inflated for expanding the stent in a lumen such that, in an
expanded state of the stent, the stent has any one of the
configurations according to the present invention, such as those
described above with respect to FIGS. 2a-7b and 10.
[0081] In this connection, the tapered shape of the stent may be
produced by utilizing a balloon that has the desired profile when
expanded, or it may be produced by using a compliant or
semi-compliant balloon of regular profile along with a stent whose
wall design is preferentially expandable at some locations, in
order to produce the desired post-expansion shape.
[0082] In general terms, a balloon expandable stent and balloon are
together configured to produce a tapered shape after deployment.
The tapered portion or portions of the stent will be configured so
as to minimize or eliminate flow disturbances throughout the
treatment site. That may be accomplished with a tapered balloon
forming a conventional stent, or with compliant balloon(s),
semi-compliant balloon(s), or some combination of compliant,
semi-compliant, and/or non-compliant balloon(s), which would permit
physicians to use existing stents to carry out the present
invention and create a tapered geometry in a lumen. Alternatively,
it may be accomplished by configuring the stent and balloon
combination to produce the desired tapering geometry on
deployment.
[0083] Various embodiments of possible shaped balloons 34 according
to the present invention are depicted in FIGS. 9a-9h, those figures
corresponding, respectively, to balloons preferably adapted to be
used in balloon expandable versions of the stent embodiments of
FIGS. 2a-7b and 10.
[0084] Thus, with respect to shaped balloons, as shown by way of
examples in the embodiments of FIGS. 9a-9h, the balloon 34 on
catheter C includes a first balloon segment 112 configured to have
a first balloon segment cross sectional area in an inflated state
of the balloon for expanding the first stent segment 12 to the
first stent cross-sectional area A1. A second balloon segment 114
is longitudinally offset with respect to the first balloon segment
112 and is configured to have a second balloon segment
cross-sectional area in an inflated state of the balloon for
expanding the second stent segment 14 to the second stent
cross-sectional area A2, the second balloon segment diameter being
either different from the first balloon segment diameter, as in
FIGS. 9a-9e and 9h, or substantially equal to the first balloon
segment diameter, as in FIGS. 9f-9g. A third balloon segment 116 is
configured to assume a tapered balloon segment configuration in an
inflated state of the balloon, the tapered balloon segment
configuration connecting the first balloon segment 112 to the
second balloon segment 114.
[0085] The balloon 34 is configured such that, in an inflated state
thereof in a lumen, it expands the stent into an expanded shape
that minimizes or eliminates flow disturbances at the treatment
site. Optionally, balloon 34 may have one or more diverging
segments 122, 124 as shown in FIGS. 9c-9g. Optionally, balloon 34
is asymmetrical with respect to a longitudinal axis thereof, as
shown by way of example in FIGS. 9e and 9h, and includes a first
portion 126 that is tapered, and a second portion 128 that presents
a straight longitudinal contour. In such axially asymmetric
embodiments, a delivery system which provides the operator with
control over the rotational position of the stent about the
longitudinal axis may be used.
[0086] In another embodiment, a self-expandable stent may be
delivered in a conventional manner, and then reconfigured after
delivery with a tapered balloon to introduce an artificial taper in
the stent.
[0087] Thus, the present invention further provides a method of
deploying a stent comprising: delivering the stent to a deployment
location in a lumen; expanding the stent such that, in an expanded
state thereof; the stent is expanded into an expanded shape which
minimizes or eliminates flow disturbances at the treatment
site.
[0088] According to one embodiment of the present invention,
delivering the stent to the deployment location comprises
delivering the stent to a bifurcation site of the lumen, such as
the bifurcation site shown in FIG. 1a, the bifurcation site having
a main branch M and a side branch S and further corresponding to
the deployment location of the stent. Additionally, expanding the
stent comprises expanding the stent at the bifurcation site such
that: in an expanded state thereof, an envelope 20 of the stent is
asymmetrical with respect to a longitudinal axis thereof and
defines a first portion, such as first portion 26 of FIGS. 6a-6b
and 10 bounded by walls W1 and having a contour in a
cross-sectional plane including the longitudinal axis of the stent
that is either a curved line or a straight line angled with respect
to the longitudinal axis. A contour of first portion 26 of the
embodiment of FIGS. 6a-6b in the cross-sectional plane including
the longitudinal axis of the stent 400 is provided for example in
FIG. 6b, where the contour of wall W1 in that cross-sectional plane
is curved line 30. A contour of first portion 26 of the embodiment
of FIG. 10 in the cross-sectional plane including the longitudinal
axis of stent 700 is provided for example in FIG. 10, where the
contour of wall W1 is a straight line 30 angled with respect to the
longitudinal axis.
[0089] Expanding the stent 400 or stent 700 according to
embodiments of the present invention further comprises expanding
the stent at the bifurcation site such that the stent envelope 20
further includes a second portion such as second portion 28 bounded
by walls W2 of the embodiments of FIGS. 6a-6b and 10 bounded by
walls W2 and having a contour in a cross-sectional plane including
the longitudinal axis of the stent that is a straight line parallel
to the longitudinal axis of the stent. This latter contour 32 is
also shown in FIGS. 6b and 10. The first portion and the second
portion together define the stent envelope 20 as shown after
expansion of the stent 400 of FIGS. 6a-6b or stent 700 of FIG. 10
at the deployment site. According to an embodiment of the method
for deploying of the present invention, the side W1 containing
first portion 26 of the expanded stent with the taper is disposed
opposite the side branch of the bifurcation site, while the side W2
with the second portion 28 without a taper abuts the side branch,
that is, it is disposed adjacent to the side branch.
[0090] With respect to the delivery of an axially asymmetrical
stent, such as, for example, that shown in the embodiments of FIGS.
6a-6b and 10, one could use a balloon with a preferential shape, or
a delivery system such as those conventionally used in connection
with bifurcation stents that give the operator control with respect
to a rotational orientation of the stent relative to the
anatomy.
[0091] The present invention further provides a stent that
comprises a stent envelope adapted to be deployed at a deployment
location in a lumen; and means associated with the stent envelope
for controlling a flow of blood in the lumen when the stent
envelope is in its expanded state so as to induce a favorable flow
regime at the deployment location of the stent envelope relative a
flow regime that would have been generated had a straight stent
envelope been deployed at the deployment location for reducing a
risk of restenosis at the deployment location. An example of such
means has been provided with respect to embodiments of the present
invention depicted in FIGS. 2a-10. Other means would be within the
knowledge of a person skilled in the art.
[0092] It is to be understood, however, that stents of the present
invention may be configured to have any of the various known cell
and/or stent configurations, and may be made of any of the known
materials for forming stents, as would be readily recognized by one
skilled in the art. Any of the known materials, patterns and
configurations of the stent walls known for making stents would
benefit from the configuration of the stent envelope according to
embodiments of the present invention. As was discussed in detail
above, the stents may be self-expanding stents, balloon expandable
stents or combinations of the two.
[0093] A stent according to the present invention may be made by
any of the known methods of making stents, such as by a folding and
welding method as described in U.S. Pat. Nos. 5,836,964, 5,922,005,
6,156,052, 5,997,703, 6,197,048 B1, and 6,114,049, or by laser
cutting.
[0094] In addition, it is noted that the wire frame views in FIGS.
7a, 2b, 3b, 4b, 5b, 6b, 7b and 2c, 3c, 4c, and 5c, and 10 are not
meant to be interpreted as showing cell patterns, stent patterns,
or patterns of the actual walls of the stent itself, but rather as
showing contours of the stent envelope as shown by theoretical
lines that trace certain ones of those contours.
[0095] It is noted that the present invention permits physicians to
use existing stents that were not originally designed to be tapered
to carry out the present invention and to create a tapered geometry
in a lumen as described above. The taper in the stent can be
positioned at any desired treatment area in a lumen.
[0096] Although the present invention has been described using the
example of "tapered" stents and balloons, it should be understood
that configurations besides a taper are possible. Any configuration
or shape which is designed to alter the characteristics of a lumen
to induce a favorable flow regime that reduces a risk of restenosis
is within the scope of the present invention. The important aspect
is to tailor the stent to produce the desired geometry after
implantation.
[0097] It should be noted that it is possible that there are other
mechanisms of action which effect the lumen wall other than the
ones described above with respect to blood cells of the white
lineage. While we have proposed one mechanism of action, the
present application is not bound to only this mechanism of action.
Rather, the present application encompasses any shaped stent and
method for creating a shaped stent, which is designed to minimize
flow disturbances.
[0098] Moreover, while exemplary embodiments of a stent profile
according to the present invention have been described above with
respect to stent segments defined between respective boundary
planes, the present invention includes within its scope the
provision of stent configurations where transition regions between
respective segments of the stent are not necessarily defined in
planes, but are, for example, defined in a three-dimensional
region.
[0099] Furthermore, although FIGS. 6a-6b and 10 were described as
showing an axially asymmetric stent which may be used in a
bifurcated lumen, it should be understood that any of the
embodiments of the symmetric stent of the present invention, such
as those shown in FIGS. 2a-5b, 7a and 7b, can also be used in a
bifurcation geometry, and that any of the embodiments of an
asymmetric stent of the present invention, such as that shown in
FIGS. 6a-6b and 10, can also be used in a non-bifurcated
geometry.
[0100] The invention has been described with reference to specific
exemplary embodiments thereof. It will, however, be evident to
persons having the benefit of this disclosure, that various
modifications and changes may be made to these embodiments without
departing from the broader spirit and scope of the invention. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than in a restrictive sense.
* * * * *