U.S. patent application number 11/332485 was filed with the patent office on 2006-10-26 for support frame for an embolic protection device.
This patent application is currently assigned to SALVIAC LIMITED. Invention is credited to Eamon Brady, Steven Horan, Ronald Kellly, Gerry McCaffrey, John Neilan, Gerard Rabitte, David Vale.
Application Number | 20060241681 11/332485 |
Document ID | / |
Family ID | 27541167 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060241681 |
Kind Code |
A1 |
Brady; Eamon ; et
al. |
October 26, 2006 |
Support frame for an embolic protection device
Abstract
A support 103 for an embolic protection device comprises round
wires 116 which may form one or more support hoops for a filter
body The circumferential hoop formed by the wires 116 ensures that
in the expanded position, the filter body 102 will be supported by
the support frame 103 in circumferential apposition with the
interior wall of the vasculature. The wires 116 may have a strain
distributing linkage element in the form of a loop 120 in. The loop
120 acts as a diameter or circumference adjuster allowing an
embolic protection device to adapt to different vessel contours and
sizes whilst maintaining apposition with the vessel wall. The
strain relieving geometry of the loops enhances the compliance of
the bend points without creating a weakened hinge point, thus
ensuring that there is no discontinuity in the circumferential seal
against the vessel wall.
Inventors: |
Brady; Eamon; (Elphin,
IE) ; Vale; David; (Clontarf, IE) ; Kellly;
Ronald; (Athlone, IE) ; Neilan; John; (Gort,
IE) ; Horan; Steven; (Athlone, IE) ; Rabitte;
Gerard; (Tuam, IE) ; McCaffrey; Gerry;
(Roslea, IE) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SALVIAC LIMITED
|
Family ID: |
27541167 |
Appl. No.: |
11/332485 |
Filed: |
January 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10325954 |
Dec 23, 2002 |
7037320 |
|
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11332485 |
Jan 17, 2006 |
|
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60341836 |
Dec 21, 2001 |
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60341805 |
Dec 21, 2001 |
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60373640 |
Apr 19, 2002 |
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60373641 |
Apr 19, 2002 |
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60377248 |
May 3, 2002 |
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Current U.S.
Class: |
606/200 |
Current CPC
Class: |
A61F 2230/0067 20130101;
A61B 2017/2215 20130101; A61F 2230/0093 20130101; A61F 2/0108
20200501; A61F 2002/016 20130101; A61B 2017/2212 20130101; A61F
2002/018 20130101 |
Class at
Publication: |
606/200 |
International
Class: |
A61M 29/00 20060101
A61M029/00 |
Claims
1. An embolic protection device comprising: a collapsible filter
element for delivery through a vascular system of a patient; the
filter element comprising a collapsible filter body and a filter
support for the filter body; the filter body having an inlet end
and an outlet end, the inlet end of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body, the outlet end of the filter body having a
plurality of outlet openings sized to allow through passage of
blood but to retain undesired embolic material within the filter
body; the filter support being movable between a collapsed position
for movement through the vascular system, and an extended outwardly
projecting position to support the filter body in an expanded
position; the filter support comprising a number of segments at
least some of which are interconnected by a strain distributing
linking element.
2. A device as claimed in claim 1 wherein at least some of the
segments are of wire.
3. A device as claimed in claim 1 wherein the linking element is of
wire.
4. A device as claimed in claim 3 wherein the linking element is of
the same wire as that of the support segments.
5. A device as claimed in claim 1 wherein the linking element
extends normally of adjacent segments.
6. A device as claimed in claim 1 wherein the linking element
extends longitudinally of the axis of the filter.
7. A device as claimed in claim 1 wherein the linking element
extends radially inwardly of the adjacent segments.
8. A device as claimed in claim 1 wherein the linking element
comprises a loop.
9. A device as claimed in claim 8 wherein the loop is of generally
omega shape.
10. A device as claimed in claim 1 wherein at least portion of the
linking element is radiopaque.
11. A device as claimed in claim 1 wherein at least portion of at
least some of the support segments are radiopaque.
12. A device as claimed in claim 1 wherein the linking element is
of multifilament construction.
13. A device as claimed in claim 1 wherein at least one of the
support segments is of multifilament construction.
14. A device as claimed in claim 1 wherein the support frame is
defined by at least two wire segments having terminations.
15. A device as claimed in claim 14 wherein the terminations of
adjacent segments extend generally parallel to one another.
16. A device as claimed in claim 14 wherein the terminations of
adjacent segments are fixed relative to one another.
17. A device as claimed in claimed in claim 1 wherein the support
frame is defined by at least two wire segments terminating
distally, the distal terminations of adjacent segments being fixed
relative to one another and extending generally parallel.
18. A device as claimed in claim 1 wherein the support frame is
defined by at least two wire segments terminating proximally, the
proximal terminations of adjacent segments being fixed relative to
one another and extending generally parallel.
19. A device as claimed in claim 1 wherein the support frame
comprises a support arm for one end of the filter body which
extends towards an opposite end of the filter body in the deployed
configuration.
20. A device as claimed in claim 1 wherein the device comprises a
carrier extending longitudinally of the frame.
21. A device as claimed in claim 20 comprising a flexible tether
extending between the carrier and the support frame.
22. A device as claimed in claim 20 wherein the carrier comprises a
tubular member.
23. A device as claimed in claim 20 wherein the carrier comprises a
guidewire.
24. A device as claimed in claim 1 wherein the support frame
comprises a support hoop.
25. A device as claimed in any of claim 1 wherein the filter
support comprises a support frame having at least two
longitudinally spaced-apart segments.
26. A device as claimed in claim 25 wherein the segments are
interconnected by at least one flexible linking element.
27. A device as claimed in claim 1 wherein the support frame
comprises a support arm for one end of the filter body which
extends towards an opposite end of the filter body in the deployed
configuration.
28. A device as claimed in claim 1 wherein the filter support
comprises a generally tubular support frame defined by at least one
wire.
29. A device as claimed in claim 1 wherein the wire element has a
round cross-section.
30. A device as claimed in claim 1 wherein the wire element has an
elongate cross-section with a long dimension and a short
dimension.
31. A device as claimed in claim 30 wherein the short dimension of
the wire element cross-section is aligned substantially along the
radial direction of the filter support.
32. A device as claimed in claim 1 wherein the wire element is
rectangular in cross-section.
Description
INTRODUCTION
[0001] This invention relates to an embolic protection device. In
particular, it relates to an embolic protection device of the type
comprising a collapsible filter body to capture embolic material,
and a support to maintain the filter body in an expanded position
when the embolic protection device is deployed in a
vasculature.
[0002] Embolic protection devices of this general type are
known.
[0003] However, there exist a number of problems with some of the
known devices. In particular, upon collapse of the filter support,
prior to delivery of the embolic protection device into and/or
retrieval from a vasculature, large, localised stresses may be
induced in the support. Solutions to this problem heretofore may
result in features which inhibit the optimum performance of the
device. In some systems flow paths for the blood can develop
between the filter body and the interior wall of the vasculature.
In general conventional devices are not highly trackable because of
their length in the wrapped delivery configuration.
[0004] There is therefore a need for an embolic protection device
which overcomes at least some of the disadvantages that exist with
some of the known devices.
STATEMENTS OF THE INVENTION
[0005] According to the invention there is provided an embolic
protection device comprising:
[0006] a collapsible filter element for delivery through a vascular
system of a patient;
[0007] the filter element comprising a collapsible filter body and
a filter support for the filter body;
[0008] the filter body having an inlet end and an outlet end, the
inlet end of the filter body having one or more inlet openings
sized to allow blood and embolic material enter the filter body,
the outlet end of the filter body having a plurality of outlet
openings sized to allow through passage of blood but to retain
undesired embolic material within the filter body;
[0009] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position;
[0010] the filter support comprising a number of segments at least
some of which are interconnected by a strain distributing linking
element.
[0011] In one embodiment at least some of the segments are of
wire.
[0012] The linking element may be of wire. The linking element may
be of the same wire as that of the support segments.
[0013] In one embodiment the linking element extends normally of
adjacent segments. The linking element may extend longitudinally of
the axis of the filter and/or the linking element extends radially
inwardly of the adjacent segments.
[0014] In a preferred embodiment the linking element comprises a
loop. The loop may be of generally omega shape.
[0015] In one embodiment at least portion of the linking element is
radiopaque. Alternatively or additionally at least portion of at
least some of the support segments are radiopaque.
[0016] In one embodiment the linking element is of multifilament
construction. Alternatively or additionally at least one of the
support segments is of multifilament construction.
[0017] In one embodiment the support frame is defined by at least
two wire segments terminating distally, the distal terminations of
adjacent segments being fixed relative to one another and extending
generally parallel.
[0018] The support frame may be defined by at least two wire
segments terminating proximally, the proximal terminations of
adjacent segments being fixed relative to one another and extending
generally parallel.
[0019] In one embodiment the support frame comprises a support arm
for one end of the filter body which extends towards on opposite
end of the filter body in the deployed configuration.
[0020] In one embodiment the device comprises a carrier extending
longitudinally of the frame. The carrier may be a tubular member,
sleeve or sleeves or may comprise a guidewire.
[0021] A flexible tether may extend between the carrier and the
support frame.
[0022] In one embodiment the support frame comprises a support loop
or hoop.
[0023] In another aspect the invention provides an embolic
protection device comprising:
[0024] a collapsible filter element for delivery through a vascular
system of a patient;
[0025] the filter element comprising a collapsible filter body and
a filter support for the filter body; the filter body having an
inlet end and an outlet end, the inlet end of the filter body
having one or more inlet openings sized to allow blood and embolic
material enter the filter body, the outlet end of the filter body
having a plurality of outlet openings sized to allow through
passage of blood but to retain undesired embolic material within
the filter body;
[0026] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position;
[0027] the filter support comprising a support frame having at
least two longitudinally spaced-apart segments which are
interconnected by at least one flexible linking element.
[0028] The support frame segments may be of wire.
[0029] In a further aspect the invention provides an embolic
protection device comprising:
[0030] a collapsible filter element for delivery through a vascular
system of a patient;
[0031] the filter element comprising a collapsible filter body and
a filter support for the filter body;
[0032] the filter body having an inlet end and an outlet end, the
inlet end of the filter body having one or more inlet openings
sized to allow blood and embolic material enter the filter body,
the outlet end of the filter body having a plurality of outlet
openings sized to allow through passage of blood but to retain
undesired embolic material within the filter body;
[0033] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position;
[0034] the filter support comprising a support frame defined by at
least two wire segments having terminations, the terminations of
adjacent segments being fixed relative to one another and extending
generally parallel.
[0035] The wire segments may terminate distally, the distal
terminations of adjacent segments being fixed relative to one
another and extending generally parallel. Alternatively or
additionally the wire segments terminate proximally, the proximal
terminations of adjacent segments being fixed relative to one
another and extending generally parallel.
[0036] The terminations may extend axially in relation to the
filter. The distal terminations may be free to move axially.
Alternatively or additionally the proximal terminations are free to
move axially.
[0037] In one embodiment the proximal terminations of adjacent wire
segments are configured to meet in a loop formation. The distal
terminations of adjacent wire segments may be configured to meet in
a loop formation.
[0038] In one embodiment the wire segments are of substantially the
same length.
[0039] The wire segments may be fixed relative to one another by
soldering, or welding, or bonding the wire segments to one another.
Alternatively or additionally the device comprises a clamp around
the wire segments to fix the wire segments relative to one another.
The clamp may comprise a tubular sleeve. The clamp may comprise a
clamp wire wound around the wire segments. The clamp may be at
least partially of radiopaque material.
[0040] In one embodiment the wire segments are provided by a single
wire bent back on itself.
[0041] Terminations may be located on an outer circumference of the
filter frame. Alternatively or additionally terminations are
located on an axis of the filter.
[0042] One of the proximal or distal terminations may be located on
an outer circumference of the filter frame and the other of the
proximal or distal terminations located on an axis of the
filter.
[0043] In one embodiment each wire element has a circumferentially
extending portion, and together the circumferentially extending
portions of the wire elements define a cell which forms a
substantially complete loop.
[0044] The wire elements may together define a number of cells
axially spaced-apart. The support frame may have a connector
between a first cell and a second cell.
[0045] The wire element may have an axially extending portion so
that the cell partially slopes axially.
[0046] The wire element may extend in an irregular path such as in
a substantially wave-like pattern.
[0047] In one embodiment the wire element extends in an arcuate
path.
[0048] In one embodiment the filter support comprises at least one
support leg extending radially inwardly from the support frame, the
leg being defined by at least one wire. The cross-sectional area of
the support leg may decrease radially inwardly.
[0049] In one embodiment at least part of the support leg is
integral with at least part of the support frame. The support leg
may be provided as an extension of one wire element and/or the
support leg is provided as an extension of two or more adjacent
wire elements.
[0050] In one embodiment the support leg extends at least partially
distally inwardly from the support frame.
[0051] The wire element may have a round cross-section.
[0052] Alternatively, the wire element has an elongate
cross-section with a long dimension and a short dimension. The
short dimension of the wire element cross-section may be aligned
substantially along the radial direction of the filter support. The
wire element may be rectangular in cross-section.
[0053] In one embodiment the filter body comprises a flap wrappable
around a wire element of the filter support to fix the filter body
to the filter support.
[0054] In another aspect the invention provides a method of
collapsing an embolic protection device for delivery and/or
retrieval of the device through a vascular system, the method
comprising the steps of: [0055] providing an embolic protection
device comprising a collapsible filter body and a filter support
for the filter body; and [0056] collapsing the filter support to a
low-profile configuration with an associated torqueing of at least
part of the filter support upon elongation of the filter
support.
[0057] In another aspect the invention, an embolic protection
device, comprises: [0058] a collapsible filter element for delivery
through a vascular system of a patient; the filter element
comprising a collapsible filter body and a filter support for the
filter body; [0059] the filter body having an inlet end and an
outlet end, the inlet end of the filter body having one or more
inlet openings sized to allow blood and embolic material enter the
filter body, the outlet end of the filter body having a plurality
of outlet openings sized to allow through passage of blood but to
retain undesired embolic material within the filter body; [0060]
the filter support being movable between a collapsed position for
movement through the vascular system, and an extended outwardly
projecting position to support the filter body in an expanded
position; the filter support comprising a support frame, [0061] a
carrier, and [0062] a flexible tether extending between the carrier
and the support frame.
[0063] In one embodiment the carrier extends longitudinally of the
frame. The carrier may be a tubular member or sleeve(s).
Alternatively the carrier is a guidewire. The filter support may
comprise a number of segments, at least some of which are
interconnected by a strain distributing element.
[0064] The filter support may comprise a loop.
[0065] In one embodiment at least some of the segments are of wire.
The linking element may be of wire. The linking element may be of
the same wire as that of the support segments. The linking element
may extend normally of adjacent segments, for example
longitudinally of the axis of the filter and/or radially inwardly
of the adjacent segments.
[0066] In one embodiment the linking element comprises a loop which
may be of generally omega shape.
[0067] At least portion of the linking element may be radiopaque.
At least some of the support segments may be radiopaque.
[0068] In one embodiment the linking element is of multifilament
construction.
[0069] In another embodiment at least one of the support segments
is of multifilament construction.
[0070] In one embodiment the support frame is defined by at least
two wire segments having terminations, the terminations of adjacent
segments being fixed relative to one another and extending
generally parallel. The support frame may be defined by at least
two wire segments terminating distally, the distal terminations of
adjacent segments being fixed relative to one another and extending
generally parallel. The support frame may be defined by at least
two wire segments terminating proximally, the proximal terminations
of adjacent segments being fixed relative to one another and
extending generally parallel.
[0071] In one embodiment the support frame comprises a support arm
for one end of the filter body which extends towards on opposite
end of the filter body in the deployed configuration.
[0072] In one embodiment the device comprises a carrier extending
longitudinally of the frame. A flexible tether may extend between
the carrier and the support frame.
[0073] In one embodiment the support frame comprises a support
loop.
[0074] In another aspect the invention provides an embolic
protection device comprising: [0075] a collapsible filter element
for delivery through a vascular system of a patient; [0076] the
filter element comprising a collapsible filter body and a filter
support for the filter body; [0077] the filter body having an inlet
end and an outlet end, the inlet end of the filter body having one
or more inlet openings sized to allow blood and embolic material
enter the filter body, the outlet end of the filter body having a
plurality of outlet openings sized to allow through passage of
blood but to retain undesired embolic material within the filter
body; [0078] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position; [0079] the filter support comprising a support
frame, [0080] a support arm for one end of the filter body which
extends towards an opposite end of the filter body in the deployed
configuration.
[0081] The support arm may be a proximal support arm that extends
distally in the deployed configuration. Alternatively or
additionally the support arm is a distal support arm that extends
proximally in the deployed configuration.
[0082] In a further aspect the invention provides an embolic
protection device comprising: [0083] a collapsible filter element
for delivery through a vascular system of a patient; [0084] the
filter element comprising a collapsible filter body and a filter
support for the filter body; [0085] the filter body having an inlet
end and an outlet end, the inlet end of the filter body having one
or more inlet openings sized to allow blood and embolic material
enter the filter body, the outlet end of the filter body having a
plurality of outlet openings sized to allow through passage of
blood but to retain undesired embolic material within the filter
body; [0086] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position; [0087] the filter support comprising a generally
tubular support frame defined by at least one wire.
[0088] The at least one wire of the tubular support frame becomes
torqued during collapse of the filter support. This torque induced
upon collapse is evenly distributed along the wire without
resulting in stress concentrations on the filter support. Thus, the
wires may be of a small cross-sectional area which advantageously
collapse down to a very low profile.
[0089] In addition, small wires enable greater flexibility for the
filter element, which allow for ease of advancement through the
vascular system.
[0090] The frame may comprise a number of cells, at least one of
the cells defining a segment of a tube. Each cell may define a
segment of a tube.
[0091] In one embodiment at least portion of an element of one cell
is connected to an element of another cell. The connection means
may be provided by an extension wire between the cells. At least
portion of an element of one cell may be directly fixed to an
element of another cell.
[0092] The or each cell may be defined by two wire elements. The
two wire elements may be of substantially the same length. The or
each wire element may have a proximal termination and a distal
termination, and the proximal terminations of adjacent wire
elements are fixed relative to one another, and/or the distal
terminations of adjacent wire elements are fixed relative to one
another.
[0093] The terminations of adjacent wire elements may extend
generally axially and parallel. The proximal terminations may be
circumferentially aligned with the distal terminations.
Alternatively the proximal terminations are circumferentially
offset from the distal terminations.
[0094] In one embodiment each wire element has an axially extending
portion and a circumferentially extending portion.
[0095] In one embodiment at least one wire element has an S-shaped
portion for distributed filter body support.
[0096] The wire elements may be provided by a single wire bent back
on itself. The single wire may have a strain relief means at the
bend in the wire. The wire may be treated to minimise stress at the
bend in the wire.
[0097] In one embodiment the filter support comprises at least one
support leg extending radially inwardly from the tubular support
frame, the leg being defined by at least one wire. At least part of
the support leg is integral with at least part of the tubular
support frame. The support leg may extend distally inwardly from
the support frame.
[0098] According to a further aspect of the invention, there is
provided an embolic protection device comprising:
[0099] a collapsible filter element for delivery through a vascular
system of a patient;
[0100] the filter element comprising a collapsible filter body and
a filter support for the filter body;
[0101] the filter body having an inlet end and an outlet end, the
inlet end of the filter body having one or more inlet openings
sized to allow blood and embolic material enter the filter body,
the outlet end of the filter body having a plurality of outlet
openings sized to allow through passage of blood but to retain
undesired embolic material within the filter body;
[0102] the filter support being movable between a collapsed
position for movement through the vascular system, and an extended
outwardly projecting position to support the filter body in an
expanded position;
[0103] the filter support comprising a support frame defined by at
least two wire elements, each wire element having a proximal
termination and a distal termination, the terminations of adjacent
elements extending generally axially and parallel.
[0104] According to the invention, there is provided a medical
device having a collapsed configuration for transport through a
body passageway, and an expanded configuration for deployment in a
body; the medical device comprising a support movable from the
collapsed configuration to the expanded configuration to support
the medical device in the expanded configuration;
[0105] the support comprising a radiopaque core.
[0106] The second moment of area of the radiopaque material is
proportional to the fourth power of its diameter. Therefore because
the radiopaque material is provided as the core of the support,
this greatly reduces the diameter and thus the second moment of
area of the radiopaque material. Correspondingly the forces
required to facilitate deployment of the medical device are also
greatly reduced.
[0107] In this manner the invention minimises the dampening effect
of the radiopaque material on the medical device.
[0108] By locating the radiopaque material as the core of the
support, this also results in a low-profile medical device.
[0109] In one embodiment of the invention the core is located
substantially along the neutral axis of bending of the support.
[0110] Preferably the support comprises at least one support
element. The support element may be of a superelastic material.
Ideally the radiopaque core is provided as a core embedded within
at least one support element. In one case the radiopaque core is in
powder form. In another case the radiopaque core is in liquid
form.
[0111] In a preferred embodiment the radiopaque core comprises a
radiopaque element amongst a plurality of support elements. The
element may comprise a wire. Ideally the elements are wound
together.
[0112] The radiopaque core may be of mercury, or gold, or
platinum.
[0113] In another aspect, the invention provides a medical device
having a collapsed configuration for transport through a body
passageway, and an expanded configuration for deployment in a
body;
[0114] the medical device comprising a support movable from the
collapsed configuration to the expanded configuration to support
the medical device in the expanded configuration;
[0115] the support comprising a reservoir enclosing a fluid, the
fluid being expandable upon an increase in temperature to bias the
support to the expanded configuration.
[0116] According to a further aspect of the invention, there is
provided a medical device having a collapsed configuration for
transport through a body passageway, and an expanded configuration
for deployment in a body;
[0117] the medical device comprising a support movable from the
collapsed configuration to the expanded configuration to support
the medical device in the expanded configuration;
[0118] the support comprising a reservoir enclosing a fluid, the
fluid being pressurised to bias the support to the expanded
configuration upon release of a constraint.
[0119] In one case the reservoir comprises an enclosed tube. The
tube may extend at least partially circumferentially around the
device. Ideally the ends of the tube meet to form an enclosed
loop.
[0120] The fluid may be of a radiopaque material. Preferably the
fluid is liquid mercury.
[0121] In a preferred embodiment of the invention the device is an
intravascular medical device for transport through a vasculature
and deployment in a vasculature. Most preferably the device is an
embolic protection filter. Ideally the filter comprises a filter
body supported by the support, the filter body having an inlet end
and an outlet end, the inlet end of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body, and the outlet end of the filter body having a
plurality of outlet openings sized to allow through passage of
blood but to retain undesired embolic material within the filter
body.
[0122] According to the invention, there is provided a medical
device having a collapsed configuration for transport through a
body passageway, and an expanded configuration for deployment in a
body;
[0123] the medical device comprising a support movable from the
collapsed configuration to the expanded configuration to support
the medical device in the expanded configuration;
[0124] at least part of the support being of a multifilament wire
construction.
[0125] In the multifilament wire construction of the invention,
each filament bends independently of the other filaments.
Correspondingly, the overall force required to bend the support is
a summation of the forces required to bend each filament. Because
the force required to bend a wire is proportional to the fourth
power of the diameter of the wire, the overall force required to
bend the multifilament support is much less than the force which
would be required to bend a single wire with the same overall
diameter as the multifilament support.
[0126] In this manner, the medical device of the invention achieves
enhanced trackability during transport through even tortuous body
passageways, while ensuring the medical device is moved by the
support from the collapsed configuration to the expanded
configuration upon deployment in the body.
[0127] The multifilament wire construction also provides the
medical device with greater deformability in the expanded
configuration. This enables the medical device to adapt to the
particular characteristics of the body passageway in which it is
deployed.
[0128] In one embodiment of the invention at least one filament is
wound around at least one other filament. By winding the filament,
the bending stress induced in the filament is reduced. Preferably
at least some of the filaments are braided together.
[0129] In a particularly preferred embodiment at least one filament
is of a radiopaque material. The radiopaque nature of the filament
provides visualisation of the medical device during transport
through and deployment in a body. The radiopaque filament is
ideally located substantially along the neutral axis of bending of
the support.
[0130] In another case at least one filament may comprise a
radiopaque core embedded within the filament.
[0131] In a further embodiment of the invention the support
comprises a jacket around the filaments. The jacket helps to
maintain the structure of the multifilament wire construction
intact and ensure the filaments move in a coordinated manner.
Preferably the filaments are embedded within the jacket. Ideally
the jacket is at least partially of a radiopaque material. The
jacket may be at least partially of a polymeric material.
[0132] Desirably the support is of the multifilament wire
construction at a point of high curvature in the expanded
support.
[0133] The device is preferably an intravascular medical device for
transport through a vasculature and deployment in a vasculature.
Ideally the device is an embolic protection filter. Most preferably
the filter has an inlet end and an outlet end, the inlet end having
one or more inlet openings sized to allow blood and embolic
material enter the filter, and the outlet end having a plurality of
outlet openings sized to allow through passage of blood but to
retain undesired embolic material within the filter.
[0134] In a preferred case the filter comprises a filter body
supported by the support, and the inlet openings and the outlet
openings are provided in the filter body to retain undesired
embolic material within the filter body. The filaments may define a
mesh. Ideally the inlet openings and the outlet openings are
provided by openings through the mesh.
BRIEF DESCRIPTION OF THE DRAWINGS
[0135] The invention will be more clearly understood from the
following description of some embodiments thereof, given by way of
example only, with reference to the accompanying drawings, in
which:
[0136] FIG. 1 is a perspective view of an embolic protection device
according to the invention;
[0137] FIGS. 2 and 3 are perspective views of a filter support of
the embolic protection device of FIG. 1;
[0138] FIG. 4 is an end view of the filter support of FIGS. 2 and
3;
[0139] FIGS. 5 to 7 are perspective views illustrating collapse of
the filter support of FIGS. 1 to 4;
[0140] FIG. 8a is an enlarged view of part of the filter support of
FIG. 5;
[0141] FIG. 8b is an enlarged view of part of the filter support of
FIG. 6;
[0142] FIG. 9 is a perspective view of the filter support of FIGS.
1 to 7;
[0143] FIGS. 10 to 20 are views of various alternative strain
distributing linkage elements;
[0144] FIG. 21 is a perspective view of another filter support;
[0145] FIG. 22 is an end view of the filter support of FIG. 21;
[0146] FIGS. 23 to 25 are perspective views of part of other filter
supports;
[0147] FIG. 26 is a perspective view of a further filter
support;
[0148] FIG. 27 is a perspective view of part of the filter support
of FIG. 26 in use;
[0149] FIG. 28 is a view along line A-A in FIG. 27;
[0150] FIGS. 29 and 30 are enlarged perspective views of part of
other filter supports;
[0151] FIG. 31 is a perspective view of another device of
invention;
[0152] FIG. 32 is a perspective view of the device of FIG. 31, in
use;
[0153] FIG. 33 is a cross sectional view on the line A-A in FIG.
31;
[0154] FIG. 34 is a cross sectional view on the line B-B in FIG.
31;
[0155] FIG. 35 is a cross sectional view similar to FIG. 34 of an
alternative embolic protection device.
[0156] FIGS. 36 and 37 are perspective views of other embolic
protection devices according to the invention;
[0157] FIG. 38 is a perspective view of another embolic protection
device;
[0158] FIG. 39 is a perspective view of an embolic protection
device;
[0159] FIG. 40 is a perspective view of a further embolic
protection device;
[0160] FIG. 41 is a perspective view of another embolic protection
device;
[0161] FIG. 42 is a longitudinal cross sectional view of the device
of FIG. 41;
[0162] FIG. 43 is a cross sectional view on the line A-A in FIG.
41;
[0163] FIG. 44 is a perspective view of another embolic protection
device;
[0164] FIG. 45 is a cross sectional view of the device of FIG.
44;
[0165] FIG. 46 is a perspective view of a support frame of the
invention;
[0166] FIG. 47 is an end view in the direction of the arrow A in
FIG. 46;
[0167] FIGS. 48 to 51 are views similar to FIGS. 46 and 47 of
further support frames;
[0168] FIGS. 52 to 62 are various views of linkage elements
rendered radiopaque;
[0169] FIG. 63 is a perspective view of portion of a frame element
or a linkage element;
[0170] FIG. 64 is a perspective view of the element of FIG. 63, in
use;
[0171] FIG. 65 and 66 are perspective views of alternative frame
elements or linkage elements;
[0172] FIG. 67 is a perspective view of portion of another frame
element or linkage element of the invention;
[0173] FIG. 68 is a perspective view of the element of FIG. 67, in
use;
[0174] FIGS. 69 to 77 are perspective views of portions of frame
elements or linkage elements;
[0175] FIGS. 78 to 81 are perspective views of portions of other
frame elements or linkage elements;
[0176] FIG. 82 is a perspective view of a support frame of the
invention;
[0177] FIG. 83 is a perspective view of another support frame of
the invention;
[0178] FIGS. 84 to 86 are perspective views of portions of other
frame elements or linkage elements;
[0179] FIGS. 87 to 99 are perspective views of various support
frames of the invention, most of which include tether elements;
[0180] FIGS. 100(a) to 100(d) are perspective views illustrating
one attachment of a tether to a support frame;
[0181] FIG. 101 is a perspective view of another support frame
including tethers;
[0182] FIG. 102 is a perspective view of partion of a further
support frame;
[0183] FIG. 103 is a perspective view of another embolic protection
device of the invention;
[0184] FIG. 104 is a perspective view of another support frame;
[0185] FIG. 105 is a perspective view of a further support
frame;
[0186] FIG. 106 is a perspective view of another embolic protection
device;
[0187] FIG. 107 is a perspective view of another support frame;
[0188] FIG. 108 is a perspective view of a further support
frame;
[0189] FIG. 109 is a perspective view illustrating the wrapping
down of the frame of FIG. 108;
[0190] FIGS. 110 and 111 are views similar to FIGS. 108 and 109 of
another support frame;
[0191] FIGS. 112 to 115 are perspective views illustrating
termination details;
[0192] FIG. 116 is a perspective view of another support frame;
[0193] FIG. 117 is a perspective view of another embolic protection
device;
[0194] FIG. 118 is a perspective view of a further embolic
protection device;
[0195] FIG. 119 to 125 are perspective views of various
terminations;
[0196] FIG. 126 is a perspective view of another embolic protection
device of the invention;
[0197] FIG. 127 is a perspective view of the support frame of FIG.
126;
[0198] FIG. 128 and 129 are perspective views illustrating the
wrap-down of the frame of FIG. 127.
[0199] FIG. 130 is a perspective view of another embolic protection
device;
[0200] FIG. 131 is a perspective view of a further embolic
protection device;
[0201] FIGS. 132 to 134 illustrate steps in the method for forming
embolic protection devices of FIG. 131;
[0202] FIG. 135 is a perspective view of another embolic protection
device;
[0203] FIG. 136 is a perspective view of an embolic protection
device;
[0204] FIG. 137 is a perspective view of another embolic protection
device;
[0205] FIG. 138 is a perspective view of a further embolic
protection device;
[0206] FIG. 139 is a perspective view of another embolic protection
device;
[0207] FIG. 140 is a perspective view of another support frame of
the invention;
[0208] FIG. 141 is a perspective view of another embolic protection
device;
[0209] FIG. 142 is a perspective view of a support frame of the
device of FIG. 141;
[0210] FIG. 142(a) is a detail view of portion of the support frame
of FIG. 142(b);
[0211] FIG. 142(b) is a plan view of an offset variant of the
support frame of FIG. 142;
[0212] FIG. 143 is a perspective view of an alternative support
frame;
[0213] FIG. 144 is a perspective view of an embolic protection
device with a single loop support frame;
[0214] FIG. 145 is a perspective view of another embolic protection
device;
[0215] FIGS. 146 to 148 are perspective views of support frames of
the invention;
[0216] FIG. 149 is a perspective view of another support frame;
[0217] FIGS. 150 is a view of a detail of the frame of FIG.
149;
[0218] FIG. 151 is a view of an alternative detail of the frame of
FIG. 149;
[0219] FIG. 152 and FIG. 153 are views of the frame of FIG. 149
being wrapped down;
[0220] FIG. 154 is a perspective view of another embolic protection
device;
[0221] FIG. 155 is a perspective view of a support frame of the
device of FIG. 154;
[0222] FIG. 156 is a perspective view of an alternative support
frame for the device of FIG. 155;
[0223] FIGS. 157 and 158 are perspective views of alternative
support frames;
[0224] FIG. 159 to 161 are side, plan and perspective views of
another embolic protection device;
[0225] FIG. 162 is a perspective view of an embolic protection
device according to the invention;
[0226] FIG. 163 is a cut-away, perspective view of the embolic
protection device of FIG. 162;
[0227] FIG. 164 is a perspective view from a side of a filter
support and an inner tube of the embolic protection device of FIG.
162;
[0228] FIG. 165 is a perspective view from an end of the filter
support and the inner tube of FIG. 164;
[0229] FIG. 166 is a perspective view of the filter support of FIG.
164;
[0230] FIG. 167 is a schematic side view illustrating collapse of
the embolic protection device of FIG. 162;
[0231] FIG. 168 is a schematic plan view illustrating collapse of
the embolic protection device of FIG. 162;
[0232] FIGS. 169(a) to 169(c) are perspective views illustrating
collapse of the embolic protection device of FIG. 162;
[0233] FIG. 170 is a perspective view of another filter support and
the inner tube of FIG. 164;
[0234] FIGS. 171 to 173 are plan, side and perspective views
respectively of a further filter support;
[0235] FIGS. 174 and 175 are side and perspective views
respectively of another filter support;
[0236] FIGS. 176 to 178 are plan, side and perspective views of a
further filter support;
[0237] FIG. 179 is a perspective view of another embolic protection
device according to the invention;
[0238] FIG. 180 is a schematic view of another filter support;
[0239] FIG. 181 is a development view of the filter support of FIG.
180;
[0240] FIG. 182 is an enlarged view of part of the filter support
of FIG. 181;
[0241] FIG. 183 is a perspective view of another filter support and
inner tube; and
[0242] FIG. 184 is a perspective view of the filter support of FIG.
183;
DETAILED DESCRIPTION
[0243] Referring to the drawings, there are illustrated several
embolic protection devices according to the invention. In general
the embolic protection devices comprise a collapsible filter
element for delivery through a vascular system of a patient. The
filter element comprises a collapsible filter body 102 and a filter
support 103 for the filter body 102, and a carrier which may
comprise a tubular member 108 to which the filter support 103 may
be mounted.
[0244] The filter body 102 has an inlet end 104 and an outlet end
105. The inlet end 104 has one or more large inlet openings 106
which are sized to allow blood and embolic material enter the
filter body 102. The outlet end 104 has a plurality of small outlet
openings 107 which are size to allow through passage of blood but
to retain undesired embolic material within the filter body 102. In
this way, the filter element captures and safely retains any
undesired embolic material in the blood stream within the filter
body 102 while facilitating continued flow of blood through the
vascular system. Emboli are thus prevented from flowing further
downstream through the vascular system, which could otherwise have
potentially catastrophic results.
[0245] The filter body 102 may be of an oriented polymeric
material, as described in WO 01/97714A and US 2002/0042627A, the
relevant contents of which are incorporated herein by
reference.
[0246] The filter support 103 is movable between a low-profile,
collapsed position for movement through the vascular system, and an
extended outwardly projecting position. In this outwardly
projecting position, the filter body 102 is supported in an
expanded position by the filter support 103, so as to maximise the
internal volume of the filter body 102 to capture and safely retain
as much embolic material as possible. The inner tube 108 has a
guidewire lumen 112 therethrough, through which a guidewire may
pass for exchange of the filter element 1 over the guidewire.
Alternatively, in all embodiments the carrier may comprise a
guidewire.
[0247] One embolic protection device 100 according to the invention
is illustrated in FIGS. 1 to 9. A proximal end of the filter
support 103 may be fixed to the inner tube 108.
[0248] Upon collapse of the filter element, the proximal end of the
filter support 103 may remain fixed relative to the inner tube 8,
and the filter support 103 collapses distally against the inner
tube 108. In this collapsed position, the filter support 103 is
axially elongated relative to the expanded position.
[0249] The filter support 103 in this case comprises two round
wires 116 which extend from the proximal end 109. The wires 116
extend together axially and radially outwardly in a leg 118 from
the proximal end 109, where the wires 116 are fixed to the inner
tube 108. The junction of the leg 118 with the support hoop is
referred to in this specification as the proximal termination point
119.
[0250] At a proximal termination point 119, the wires 116 separate,
and extend circumferentially around to form support hoops.
[0251] This arrangement of the circumferential hoop formed by the
wires 116 ensures that in the expanded position, the filter body
102 will be supported by the support frame 103 in circumferential
apposition with the interior wall of the vasculature.
[0252] The length of each wire 116 around the hoop is equal. At the
proximal termination point 19, the wires 116 are fixed to each
other, and extend generally axially and parallel in a bi-filar
arrangement.
[0253] As the filter support 103 collapses down against the inner
tube 108, the wires 116 become torqued. This torqueing action is
similar to the process of elongation of a coiled spring. Because
the support frame 103 is defined by round wires 116, the torque
developed in each wire 116 will be evenly distributed along the
length of each wire 116. In addition, the bi-filar connection of
the wires 116 to each other at the termination point 19, further
assists in torque distribution along the wires 116. Thus, collapse
of the filter support 103 does not induce high, localised stresses
in the filter support 103. In this way, the filter support 103 may
be constructed of wires 116 of a small cross-sectional area which
will collapse down to a very low profile. Furthermore, the
collapsed filter element with small wires 116 has greater
flexibility for ease of advancement of the filter element 1 through
the vascular system.
[0254] The wires 116 are preferably of a self-expanding material,
such as Nitinol.
[0255] The wires 116 may have a strain distributing linkage
element. In this case the linkage element comprises a loop 120 in
each wire. The loop 120 in this case extends axially and distally
of the wire hoop. The loop 120 is of generally omega shape as
illustrated and is formed integrally in a wire 116. The loop 120
acts as a strain reliever or distributor when the wires 116 are
wrapped down as illustrated in FIGS. 6, 7 and 8(b). The loop 120
has a relatively large radius resulting in highly efficient strain
distribution. Radii R1, R2, R3 are provided at key points in the
support frame to relieve strain as illustrated in FIG. 9. In
addition, the loop 120 allows the support frame to accommodate
varying vessel contours and sizes. In effect the loop 120 acts as a
diameter or circumference adjuster allowing an embolic protection
device to adapt to difference vessel contours and sizes whilst
maintaining apposition with the vessel wall. The strain relieving
geometry of the loops enhances the compliance of the bend points
without creating a weakened hinge point, thus ensuring that there
is no discontinuity in the circumferential seal against the vessel
wall.
[0256] The loops 120 can also be regarded as distal termination
points which have a pair of arms which extend axially and generally
parallel. The looped terminations 120 enhance the ability of the
filter support 103 to be wrapped down to a low profile.
[0257] In addition, the looped configuration of the distal
termination 120 spreads the force exerted by the filter support 103
on the filter body 102 over a greater area. In this way, the local
pressures applied by the filter support 103 on the filter body 102
and the walls of a vasculature are more evenly distributed, this
minimising the possibility of vessel trauma.
[0258] Another important advantage of the strain distributing
features such as loops 120 is that they provide an anchor to which
connecting elements such as tethers may be readily attached as
described in more detail below.
[0259] In use, the filter element is collapsed down and loaded into
a delivery catheter with an associated torqueing of the wires 116
around the hoop. The filter element is then delivered through a
vasculature fixed to or over a guidewire using the delivery
catheter until the filter element is located at a desired site in
the vasculature.
[0260] By moving the delivery catheter proximally relative to the
filter element 1, the element is deployed out of the delivery
catheter at the desired site in the vasculature. The filter support
103 expands radially outwardly to support the filter body 102 in
circumferential apposition with the interior wall of the
vasculature. In the fully expanded position, the wires 116 of the
support frame 103 are substantially free of torque.
[0261] The site of deployment of the filter element in the
vasculature is typically downstream of a treatment site, such as a
region of stenosis in the vasculature. During the performance of a
treatment procedure, the filter element captures and safely retains
any embolic material in the blood stream within the filter body
102.
[0262] After completion of the treatment procedure, the filter
element is collapsed down and retrieved into a retrieval catheter
with any retained embolic material within the filter body 2. The
wires 116 around the support frame 103 are again torqued during
collapse. The retrieval catheter is then withdrawn from the
vasculature with the filter element within the retrieval
catheter.
[0263] The delivery, deployment and retrieval of the embolic
protection device of the invention, as described above, is similar
to the described in our WO99/23976, WO01/80776A (US 2002-0052626A)
and WO01/80773A (US 2002-0049467A), the relevant contents of which
are incorporated herein by reference. The filter element may be
slidably exchanged over the guidewire without any attachment means
between the filter element and the guidewire. A distal stop on the
guidewire assists in retrieval of the filter element. The guidewire
may remain in the vasculature after retrieval of the filter
element.
[0264] The support comprises a segmented ring structure which may
have two circumferential wire segments. The wire segments may be
connected by a strain distributing linkage element at one end and
by a bifilar joint at the other end. The bifilar joint may be
coupled to the carrier by a single or multiple struts and/or
tethers. In one case the strut is attached to the carrier. The
connection may permit rotation relative to the carrier either
longitudinally distal or proximal to the point of attachement to
the segmented ring.
[0265] In some cases the attachment to the carrier is rigid, in
other csases a flexible joint is provided using a tether, a loop, a
thinned wire section or the like. A focal tether may be utilised. A
focal tether implies that the strut has tensile and compressive
integrity bu the joint is not rigid. The joint can thus flex in all
directions but it cannot translate.
[0266] Individual wires may taper towards the proximal or distal
end.
[0267] The support frames may have distal, proximal and/or
intermediate anchors. One anchor may be fixed and another
translatable and/or rotatable relative to the carrier. For example
a proximal anchor may be translatable or in arrangements in which
both proximal and distal anchors are provided both may be
translatable.
[0268] The support frame may comprise a segmented ring or hoop
which may have an elliptical cross-section in the free expanded
state. The support ring may be angulated relative to the axis of
the inner member.
[0269] Various strain distributing linkage elements are illustrated
in FIGS. 10 to 20. In FIG. 10 the strain distribution is provided
by a zig zag linkage element 130. The omega shape of the preferred
loop 120 will be apparent in FIG. 11 however the loop may
approximate to a curved V shape 131 as illustrated in FIG. 12.
Various arrangements in which a strain distributing element is
provided by a separate component defining a loop 135 are
illustrated in FIGS. 13 to 19. The loops 135 may be attached or
formed in a number of ways, as illustrated. Another strain
distributing diameter/adjusing feature 136 is illustrated in FIG.
20.
[0270] Referring to FIGS. 21 and 22, there is illustrated a further
filter support 140, which is similar to the filter support of FIGS.
1 to 9, and similar elements in FIGS. 21 and 22 are assigned the
same reference numerals. In this case the filter support 140
comprises two wires 141 which have an elongate cross-section, in
this case a rectangular cross-section, along their proximal section
118. The wires 141 are arranged such that the shorter dimension of
the rectangle is aligned along the radial direction of the filter
support, as illustrated in FIG. 22.
[0271] This flattened wire configuration provides for a filter
support 140 with enhanced flexibility. This is achieved because the
second moment of area of the wires 118 is reduced in the flattened
configuration.
[0272] In addition, the flattened wires 141 minimise the influence
of the support leg 118 on the outward radial force R1 exerted by
the support frame. This results in a filter support 140 which
exerts a relatively constant outward radial force R1 around the
circumference of the filter support (FIG. 22).
[0273] In FIG. 24, there is illustrated a filter support 145 in
which the cross-sectional area of the round wire 141 decreases
radially inwardly along the support leg 118 from the proximal
termination point 119 to the proximal end of the filter support
145. This tapered support leg 118 also achieves the enhanced
flexibility, and the relatively constant outward radial force R1
around the circumference of the filter support 145, similar to that
discussed previously with reference to FIGS. 21 and 22.
[0274] As illustrated in FIG. 23, the support leg 118 may be
provided by only one of the two round wires 116, with the other
round wire 116 terminating at the proximal termination point 119
where the wires 16 are fixed together. Another arrangement of this
type is illustrated in FIG. 25.
[0275] The configuration of a single wire support leg 118 also
achieves the enhanced flexibility, and the relatively constant
outward radial force R1 around the circumference of the filter
support 340, similar to that discussed previously with reference to
FIGS. 21 and 22.
[0276] FIGS. 26 to 28 illustrate another filter support 150, which
is similar to the filter support described above, and similar
elements are assigned the same reference numerals. In the filter
support 150, the round wires 116 extend circumferentially around
the support frame in an irregular, wave-like pattern. This
configuration increases the area of contact between the wires 116
and the filter body 102. As illustrated in FIG. 28 this increased
area of contact assists in more evenly distributing the radial
forces R1 from the support wires 116 to the filter body 102 and
hence to the vessel wall. In this way, the risk of vessel trauma
due to the forces exerted by the filter support 150 is
minimised.
[0277] The radial forces exerted by the filter support on the
filter body 102 and the walls of a vasculature depend on a number
of factors, such as the diameter of the round wires 116, the
material chosen for the wire 116 and the properties of that
material, the number of wires 116 in the filter support, the angle
of inclination a of the support leg 118 (FIG. 9), and the radii R1,
R2, R3 of the bends in the filter support. By suitably varying
these factors, the radial force exerted by the filter support 301
may be accurately controlled.
[0278] Another important influencing factor on the radial force
exerted by the filter support is the fixing of the wires 116
relative to one another at the proximal termination points 119
and/or at the distal termination points 120. It may be advantageous
to securely fix the wires 116 relative to one another at the
proximal termination point 119 to achieve the required radial force
perpendicular to the proximal termination point 119.
[0279] One means of fixing the two wires 116 of the filter support
relative to one another at the proximal termination point 119 is to
clamp the wire 116 together using a tubular polymeric sleeve 151,
as illustrated in FIG. 29. The sleeve 151 provides a durable means
of fixing the wires 116 together which will effectively resist
peeling of the wires 116 apart, thus resulting in a highly robust
filter element.
[0280] The sleeve 151 may be partially of a radiopaque material,
such as platinum, or iridium, to provide visualisation of the
filter element during use.
[0281] Alternatively the wires 116 may be clamped together by
winding a wire 152 around the support wires 16, and then bonding or
soldering the wire 152 in place around the clamped support wires
16, as illustrated in FIG. 30. The wire 152 may be radiopaque.
[0282] Another suitable means of fixing the two wires 116 together
is to directly solder, weld or bond the tow wires 116 together.
[0283] It will be appreciated that a variety of different means may
be used to effectively fix the wires 116 relative to one another at
the proximal termination point 119 and/or at the distal termination
point 120.
[0284] As illustrated in FIG. 32, the looped termination 120 may be
configured to fold radially inwardly upon collapse of the filter
160, so that the looped termination 120 will engage emboli 161
which have collected in the filter body 102. In this manner, the
looped terminations 120 will assist in holding the emboli 161 in
place within the filter body 2 and in preventing extrusion of the
emboli 161 out of the filter body 102 during retrieval of the
filter 160. Thus the filter 160 will safely retain the emboli 161
for removal from the vasculature.
[0285] Furthermore, as illustrated in FIGS. 31 to 35, the looped
termination 120 may be folded radially inwardly to engage against
the inner tube 108. This arrangement provides enhanced radial
support for the filter body 102.
[0286] Upon collapse of the filter 162, the looped terminations 120
slide over the inner tube 108 until the filter support is in the
fully collapsed, elongated configuration.
[0287] The loops 120 may be attached at 163 to constrain their
freedom of movement to the axis of the tube 108 (FIG. 35)
[0288] Another filter 170, is illustrated in FIG. 36, and similar
elements to those in previous drawing are assigned the same
reference numerals. The filter support comprises a single round
wire 116 which extends axially and radially outwardly in a single
leg 118 to the proximal termination point 119. The wire 116 extends
circumferentially around the support frame, looping at the distal
termination 120.
[0289] The filter body 102, has a single, large inlet opening 106
defined at the inlet end 104. This arrangement further minimises
the possibility of any embolic material becoming caught or hung-up
on any parts of the filter at the inlet end 104. This arrangement
also further reduces the overall longitudinal length of the filter
170.
[0290] In this case the filter body 102 is fixed directly to the
filter support at the inlet end 104 by wrapping two flaps 171 of
the filter body 102 around the support wires 116 and then fixing
the flaps 171 to the filter body 102 in this wrapped position (FIG.
36).
[0291] In the filter element 175 of FIG. 37, the support leg 118 is
fixed to the inner tube 108 at an inner foot section 176. The inner
section 176 is inverted to extend distally along the inner tube
108. In addition, the filter body 102 is configured to slide
distally over the inner tube 108 upon collapse by means of a sleeve
177 fixed to the filter body 102 at the distal end 105. The sleeve
117 is also inverted to extend proximally along the inner tube
108.
[0292] In this way, by inverting the inner section 176 of the leg
118 and the sleeve 177, the overall longitudinal length 6f the
filter support is minimised. This results in less "parking space"
in a vasculature being required to deploy the filter.
[0293] Furthermore, by extending the inner section 176 of the leg
118, distally, the possibility of embolic material becoming caught
or hung-up at the inlet end 104 of the filter element is
reduced.
[0294] Referring to FIG. 38 another filter 180 which has a more
enhanced transition to the foot 176 is illustrated.
[0295] The filter 185 of FIG. 39 has a proximal support leg 118
that extends distally to minimise the length and hence the parking
space of the filter. A support foot 176 is again provided for load
distribution.
[0296] The filter 190 of FIG. 140 has two proximal support legs
191, 192 which are axially offset.
[0297] Referring to FIGS. 41 to 43 another filter 195 has a single
proximal support arm 196 which terminates in an open collar 197
which is slidably engagable with the tubular member 108. This
arrangement provides a large single inlet opening on deployment.
The support frame is held in a lip 198 of the filter body/membrane
102.
[0298] Another filter 200 is illustrated in FIGS. 44 and 45 which
has a construction similar to that of FIG. 40 but with the support
frame having neither proximal nor distal support arms. Ths frame
design provides a very short wrapped length for superior
trackability. The stepped filter arms provide a large inlet opening
on deployment.
[0299] Various alternative support frames are illustrated in FIGS.
46 to 51. In each case, the support hoop is of generally elliptical
shape.
[0300] In the support 205 of FIGS. 46 and 47 the hoop is biased
towards an elliptical shape in its unconstrained state. When
constrained within a vessel the major axis of the elipse will be
compressed, which will tend to expand the minor axis. This action
may assist in the even distribution of radial force to the vessel
wall in the case where the support frame is inherently more
flexible at the loops than at the top of its proximal arms.
[0301] In the support 215 of FIGS. 48 and 49 the proximal arms of
the support frame are staggered so that the hoop is inclined at an
angle to the axis of the filter in side view.
[0302] Thus although the hoop is actually elliptical it appears
circular in end view as shown in FIG. 51.
[0303] In the support 210 of FIGS. 50 and 51 the loops of the
support frame are offset so that the hoop is inclined at an angle
to the axis of the filter in top view. Thus although the hoop is
actually elliptical it appears circular in end view as shown in
FIG. 51.
[0304] To enhance visualisation of the filter the wire segments
and/or the linkage elements may be rendered radiopaque. Referring
to FIG. 52 a section 250 is of a different material or has
different properties than that of the wire or linkage element 251.
The section 250 is ductile and radiopaque. In FIG. 53 the section
250 is formed by straight wires 252 some or all of which may be
radiopaque. In FIG. 54 the section 250 is of braided construction,
some or all of which may be radiopaque. A radiopaque coil 260 is
provided in FIG. 55. In FIG. 56 a linkage element 120 is rendered
radiopaque by using a radiopaque braid. The linkage element 120 may
be of different material and/or have a similar radiopacifying
arrangement as shown in FIGS. 52 to 55.
[0305] Methods of rendering terminations and/or linkage element
radiopaque are illustrated in FIGS. 57 to 62. In FIG. 57 a
radiopaque band or cup 270 may be used. A radiopaque solder 271 may
also be used (FIG. 58). Similarly a radiopaque band 275 may be
crimped around the heck of a loop 120 as illustrated in FIG. 59. A
coil 280 of radiopaque material may be wound around the loop 120 as
illustrated in FIG. 60 or across the loop as illustrated in FIGS.
61 and 62.
[0306] As illustrated in FIG. 63, at least part of the support may
be of a multifilament wire construction. In this case seven Nitinol
wires 300 are wound in a spiral around a single radiopaque wire
301, the radiopaque wire 301 being located substantially along the
axis of bending of the support. The support may have the
multifilament wire construction along the entire length of the
support in this instance.
[0307] During bending of the support (FIG. 64), for example upon
movement of the support to the expanded configuration, each wire
300, 301 bends independently of the other wires. As a result, the
force required to bend the multifilament support is minimised, and
thus the filter achieves enhanced trackability during transport
through a tortuous vasculature, such as in coronary
applications.
[0308] Because the Nitinol wires 300 are wound in a spiral around
the radiopaque wire 301, this configuration acts to decrease the
bending stresses induced in each wire 300, 301 upon bending. (FIG.
64)
[0309] The radiopaque wire 301 provides visualisation for a
clinician during transport of the filter 1 through a vasculature
and deployment of the filter in the vasculature. Because the
radiopaque wire 301 is located along the neutral axis of the
support, the forces required to plastically deform the radiopaque
wire 301 as the support moves from the collapsed configuration to
the expanded configuration, upon deployment of the filter 1, are
minimised. In this way the dampening effect of the radiopaque
material is minimised.
[0310] FIG. 65 illustrates portion of a support 310 of another
embolic protection filter according to the invention. In this case,
the support comprises two radiopaque wires 311 around which are
wound in a spiral a plurality of Nitinol wires 312.
[0311] A support 315 of a further embolic protection filter
according to the invention is illustrated in FIG. 65. The Nitinol
wires 318 and the radiopaque wire 317 are braided together to form
the multifilament wire support 35.
[0312] Referring to FIGS. 67 and 68 there is illustrated a support
320 of another embolic protection filter according to the
invention. The support comprises a single radiopaque wire 321 which
extends substantially longitudinally, and a single Nitinol wire 322
which is wrapped around the radiopaque wire 321 in a coil. As
illustrated in FIG. 68, the bending stress induced in the Nitinol
wire 322 upon bending is substantially less than the bending
stresses induced in a solid wire bent through the same angle.
[0313] A portion of a wire support 330 of another embolic
protection filter is illustrated in FIG. 69. In this case, a single
Nitinol wire 331 extends substantially longitudinally, and a single
radiopaque wire 332 is wrapped around the Nitinol wire 331 in a
coil.
[0314] FIG. 70 illustrated part of a support 340 of another embolic
protection filter according to the invention. The support 340 does
not have any radiopaque wire filaments, instead radiopacity is
achieved by a radiopaque core 341 embedded within at least one of
the wires 342. The radiopaque core 341 is located substantially
along the neutral axis of the Nitinol wire 342, and thus the force
required to plastically deform the radiopaque core during movement
of the support from the collapsed configuration to the expanded
configuration is minimised, and the dampening effect of the
radiopaque material is minimised.
[0315] Referring to FIGS. 71 to 72 a linking element loop 120 may
be provided with radiopacity in a similar manner.
[0316] Referring to FIGS. 73 or 74 a radiopaque material 345 may be
sandwiched between two outer layers. Such a frame could be
constructed by laser machining an entire frame (or portion thereof)
from a large diameter bi-metal or tri-metal tube. The frame cross
section could thus be square or rectangular as shown in FIG. 73, or
could be electropolished to create an elliptical or round wire
shape as shown in FIG. 74.
[0317] The support wire(s) may be of any suitable superelastic
material, or alternatively of a high strength material, such as
stainless steel.
[0318] Referring to FIG. 75, there is illustrated portion of a
support 350 of another embolic protection filter according to the
invention. In this case, the support 350 comprises a jacket 351 of
a polymeric material around multifilament wires 352, 353. The
Nitinol wires 352 and the radiopaque wire 353 are embedded within
the polymeric jacket 351. A variety of manufacturing procedures,
such as overmoulding, heat-shrinking, dipping, spraying, painting,
depositing may be used to fabricate the wires embedded within the
jacket 351. The jacket 351 acts to maintain the structure of the
multifilament wire construction intact, and ensures that the wires
move in a co-ordinated manner.
[0319] FIG. 76 illustrates a support 360 of another embolic
protection filter which comprises five Nitinol wires 361 wound
together in a spiral without any radiopaque wire filaments. A
radiopaque material, such as tungsten, bismuth subcarbonate, barium
sulphate, may be loaded into the polymeric jacket 362 to achieve
visualisation.
[0320] It will be appreciated that a jacket may be used with any of
support structure described previously. For example, FIG. 77
illustrated a support 370 of a further embolic protection filter in
which the Nitinol wires 371 and the radiopaque wire 372 are braided
together and embedded in the polymeric jacket 373.
[0321] Various ways of rendering a wire, linkage element or tubular
member of the embolic protection devices of the invention
radiopaque are illustrated in FIGS. 78 to 83. In general a
radiopaque material 390 is provided around the element or may
itself define the element such as in the case of the tubular member
of FIG. 83.
[0322] Referring to FIG. 84 a portion of a support 400 may be in
the form of one or more wires 401 of superelastic material, such as
Nitinol. A core of radiopaque material is embedded within at least
portion of at least one of the support wires 401. In this case, the
core is also in the form of a wire 402 of a suitable radiopaque
material, such as gold, or platinum, or mercury and extends along
the length of a support wire. The radiopaque wire 402 is located
substantially along the neutral axis of bending of the support wire
401. The radiopaque wire 402 provides visualisation for a clinician
during transport of the filter through a vasculature and deployment
of the filter in the vasculature. By providing the radiopaque wire
402 as the core of the support wire 401, this minimises the
diameter of the radiopaque wire 402 and its distance from the
neutral axis. Because the second moment of area of the radiopaque
wire 402 is proportional to the fourth power of its diameter, the
second moment of area of the radiopaque wire 402 is also minimised.
Correspondingly, the forces required to plastically deform the
radiopaque wire 402 as the support wire 401 moves from the
collapsed configuration to the expanded configuration, upon
deployment of the filter, are also minimised. In this manner, the
radiopaque core configuration of the invention acts to minimise the
dampening effect of the radiopaque material, which is necessary to
achieve visualisation of the filter.
[0323] The radiopaque material may also be provided in powder form
405, as illustrated in FIG. 85, or in liquid form 406, as
illustrated in FIG. 86. Because the radiopaque core 405, 406 is
embedded within the support wire 401, the radiopaque powder or
radiopaque liquid 26 will be safely retained and controlled within
the support wire 401.
[0324] By using a powder or liquid for the radiopaque material, the
yield stress of the radiopaque material is reduced. Thus the forces
required to move the support wire 401 from the collapsed
configuration to the expanded configuration are further
reduced.
[0325] The support may comprise a reservoir for enclosing a fluid,
the reservoir being provided, which extends circumferentially
around the filter at the inlet end 104 to form an enclosed loop
around the inlet opening.
[0326] The tube may enclose a fluid such as mercury. The
temperature of the fluid increases towards body temperature upon
deployment of the filter in a vasculature, which causes the fluid
to expand. This expansion of the fluid forces the support tube
towards the expanded configuration until the support tube is fully
expanded and the filter is supported in the expanded
configuration.
[0327] It will be appreciated that the expansile fluid may be of
any suitable material. By using a radiopaque material, such as
mercury, this provides the additional advantage that visualisation
of the filter will be possible during transport of the filter
through a vasculature and deployment of the filter in a
vasculature.
[0328] In another embolic protection filter according to the
invention, the fluid enclosed in the reservoir may be pressurised.
In this case, upon release of a constraint on the filter, such as
upon deployment of the filter out of the pod of the delivery
catheter, the pressurised fluid in the support reservoir forces the
support towards the expanded configuration until the filter is
supported in the fully expanded configuration.
[0329] It will be appreciated that the radiopaque core aspect of
the invention, and/or the temperature expansile fluid aspect of the
invention, and/or the pressurised fluid aspect of the invention may
be used in any suitable manner or combination with any appropriate
medical device.
[0330] It will further be appreciated that aspects of the invention
may be applied with any medical device for transport through a body
passageway and deployment in a body.
[0331] Referring to FIGS. 87 to 105 there are illustrated various
alternative support frames incorporating tethering features for
connecting the support frame distally and/or proximally and/or
intermediately to a carrier. Tethers may also be used additionally
or alternatively for connecting various elements of a support
frame.
[0332] In all cases the tethers may be of any suitable material
such as fine gauge wire, for example Nitinol wire, fibre or
polymers. The tethers may be of solid or braided construction, for
example.
[0333] Referring to FIGS. 87 to 89 two distal tethers 500, 501 are
used to connect a support hoop 503 to a tubular member 504. The
distal tethers provide added safety and stability to the frame
without any increase in the length of the device when wrapped down
as illustrated in FIG. 89.
[0334] FIG. 90 illustrates an alternative arrangement of distal
tethers 505.
[0335] The tethers may be connected to the support frame and
carrier in any suitable fashion. For example, the distal tethers
may be double stranded and looped around the support frame as shown
in FIG. 87.
[0336] Referring to FIGS. 91 to 96 there are illustrated various
constructions with proximal tethers, with FIG. 90 illustrating a
basic construction of two tethers 520 and a simple hoop support
frame.
[0337] FIG. 92 illustrates a similar frame to that shown in FIG. 9
previously, but with the proximal frame arms replaced with tethers
520. Additional strain relieving loops are provided at the tether
connection points to assist in the wrap down of the device as
discussed previously in relation to the distal loops. The use of
flexible tethers in place of wire arms enables the length and
stiffness of the wrapped down frame to be reduced, enhancing the
trackability of the device. The flexibility of the tethers also
enables an even radial force to be provided around the
circumference of the frame without interference from the proximal
arms.
[0338] In FIGS. 93 to 95 there are two tethers 521, 522 one 521 of
elastic and the other 522 of inelastic material. The elastic tether
acts to expand the filter and frame during deployment, but
stretches to enable the frame to collapse into two parallel wires
during retrieval/wrapping as shown in FIGS. 94 & 95. This mode
of collapse provides a longer wrapped frame than would be the cae
for FIG. 92. By varying the size, shape and position of the strain
relieving loops as shown benefits in the wrapped profile of the
frame support may be provided.
[0339] In FIG. 97 there are proximal tethers 530 and distal tethers
531. This construction provides the benefits described in relation
to FIG. 92 with the added benefit of the safety and stability
provided by the distal tethers. Again the tethers provide a means
of anchoring the support frame to the carrier without affecting the
stiffness or profile of the wrapped device.
[0340] In FIG. 98 an offset loop support 540 has a distal tether
541 to prevent the support frame from moving too far proximally and
outside the filter body.
[0341] In FIG. 99 another offset loop 550 has a proximal tether 551
to restrain the movement of the loop section of the frame and thus
reduce the overall length of the wrapped device.
[0342] Referring now to FIGS. 100(a) to 100(d) there is illustrated
one type of knot 600 in a tether 605 being tied to a linkage
element loop 601 of a support hoop 602.
[0343] Referring to FIG. 101 there is illustrated a support frame
with circumferentially extending tethers 610 which allows the frame
to move circumferentially to accommodate a broad vessel size range.
The tethers 610 also assist in providing added support to a filter
body, especially in large vessels. There is also an axially
extending tether 615 interconnecting elements of the support
frame.
[0344] Referring to FIG. 102, there is illustrated a filter support
620 comprising a hollow tube 605 which extends circumferentially
around the support frame to define a hoop. A tether 626 is looped
through the tube 605, passing out of the tube 605 at the proximal
termination point 119. The tether 626 extends proximally and
radially inwardly from the proximal termination point 119 to the
inner tube 108 to which the ends 627 of the wire 626 are fixed. The
tether 626 could be of wire and/or of a radiopaque material.
[0345] Torqueing of the tether 626 within the tube 605 is possible
during collapsing and expanding of the filter. In the filter
support, the tube 605 exerts the outward radial force to support
the filter body 102 in the extended outwardly projecting position,
and the element 626 acts as a flexible tether to maintain safe,
reliable control over the support tube 605.
[0346] The support tube 605 may be of any suitable material, such
as polyamide or a superelastic material, for example Nitinol. The
tube 605 may be flexible or rigid. The tube 605 strengthens the
proximal termination point 119 while permitting a degree of
flexibility at the proximal termination point 119.
[0347] One end of the tether 626 may terminate at the proximal
termination point 119 where the end is attached to the other side
of the looped tether 626, with the other end of the tether 626
fixed to the inner tube 605.
[0348] The invention incorporates circumferential wire angulation
into support structure design to give maximum circumferential
support to the filter membrane.
[0349] Referring now to FIG. 103 a filter 650 with a proximal
tether 651 extending from the support hoop is illustrated. Other
details of this filter are as described with reference of FIGS. 36
and 41.
[0350] Referring to FIG. 104 there is illustrated an alternative
support frame in which axially adjacent frame elements 660 are
interconnected by tethers 661 which provide additional support for
the filter body. The tethers 661 may be of light gauge thread or
wire to facilitate ease of wrapping down.
[0351] Referring to FIG. 105 there is illustrated another filter
support frame comprising two axially spaced-apart support hoops 670
interconnected by axially extending tethers 671. The tethers 671
provide membrane support but are of light and flexible material
which will add very little to the wrapped profile or stiffness of
the support frame. Referring next to FIG. 106, there is illustrated
another filter element 700. In this case, the filter support
comprises four round wires 116 which extend axially and radially
outwardly in two legs 118 from the proximal end to two opposed
proximal termination points 119.
[0352] The wires 116 separate at the proximal termination points
119 and extend circumferentially around the support frame 115 until
two opposed distal termination points 120 are reached. The wires
116 then regroup into legs 121 at the distal termination points
120, the legs 121 extending axially and radially inwardly to the
sleeve 111 to which the wires 116 are fixed.
[0353] In this case, the proximal termination points 119 are
90.degree. offset from the distal termination points 120.
[0354] FIG. 107 illustrates a support frame 710 of simpler
construction that than of FIG. 106.
[0355] FIGS. 108 and 109 illustrate the wrapping down of the
support frame of the filter of FIG. 106.
[0356] FIGS. 110 and 111 illustrate another support frame 720 in
which the sleeve 111 is located proximally resulting in a shorter
wrapped down configuration.
[0357] FIGS. 112 to 115 illustrate various terminations for the
wires in the wire frames of the invention which could be employed
to connect a single proximal or distal frame arm to the
circumferential hoop portion of the frame. A construction such as
that shown in FIG. 114 allows rotation of the hoop relative to the
arm, reducing the stresses induced during wrapping.
[0358] Referring to FIG. 116 there is illustrated another support
frame comprising a single hoop 800 with two strain distributing
loops 801. One of the loops 801 has an arm or tether 802 connecting
the hoop 800 to a tubular member 803. This arrangement provides a
support frame with a very short parking space in use. Thus, it can
be deployed even if only a short segment of vessel is available
downstream of a treatment location. The support can wrap down in
either direction for loading and/or retrieval.
[0359] It will be appreciated that the wires 116 may be slidably
mounted to the inner tube 108 at both the proximal support leg 118
and the distal support leg 121.
[0360] It will be further appreciated that by increasing the number
of wires 116 which define the complete looped cell 117 of the
support frame 115, the elongation of the overall filter support,
when collapsed down, will be reduced. For example, the filter
support of FIG. 117 comprises eight round wires 116 which extend
axially and radially outwardly in four legs 118. In this manner,
the space required in a vasculature to deploy and retrieve the
embolic protection device is correspondingly reduced.
[0361] Depending on the configuration of the filter element, the
inner tube may or may not be present. In this case the filter
support may be mounted directly onto a guidewire for exchange of
the filter element over the guidewire.
[0362] It will also be appreciated that the shape of one wire 116
of a cell 117 does not have to be symmetrical or similar to the
shape of the other wire 116 of the cell 117, provided that the
length of each wire 116 is equal.
[0363] Furthermore it will be appreciated that a single wire 116,
bent back on itself, may be used to define the support frame, in
which case the cells 117 of the support frame are defined by
elements of the single wire, as illustrated in FIG. 118.
[0364] FIGS. 119 to 121 illustrate possible means by which the
single wire 116 may be bent back on itself and wrapped around the
inner tube 108. This single wire arrangement enables ease of
attachment to the inner tube 108 without stress concentration
points occurring at the regions of looping of the wire 116 around
the inner tube 108.
[0365] The fixing of two separate wires 116 to each other in a
bi-filar arrangement is illustrated in FIG. 122. The fixing means
may be provided by, for example, welding, brazing, soldering, or an
adhesive joint at the point of fixation 820. In the case of a
single wire 116 bent back on itself to define the support frame, a
180.degree. U-bend at the end of the wire 116 may be formed in
multiple strain-temperature stages to prevent plastic deformation
of the wire 116 (FIG. 123). A strain relief means 821, such as
solder, braze or adhesive, may be provided at the base of the
U-bend, as illustrated in FIG. 124. Alternatively, a strain relief
tube 822 may be provided at the end of the single wire 116 (FIG.
125).
[0366] Referring to FIGS. 126 to 129 there is illustrated another
embolic protection filter 830. The wires 116 of the filter support
830 are connected to the inner tube 108 by two legs 121, in this
case, which are fixed directly to the inner tube 108. The four
round wires 116 of the filter support extend axially proximally and
radially outwardly in the two legs 121 to the two opposed distal
termination points 120. The wires 116 then separate and extend
circumferentially around the support frame until the two opposed
proximal termination points 119 are reached. Upon collapse of the
filter element, the support frame flips distally over the legs 121
until the filter support is fully collapsed against the inner tube
108 with the legs 121 at the proximal end of the filter
support.
[0367] By locating the support legs 121 distally of the inlet end
104 of the filter body 102, this arrangement minimises the
possibility of embolic material becoming caught or hung-up at the
inlet openings 106. In this manner, substantially all of the
embolic material is retained safely with the filter body 102 for
subsequent retrieval from the vascular system using a retrieval
catheter 832 as illustrated in FIGS. 128 and 129.
[0368] As illustrated with the filter 840 of FIGS. 130 and 131, a
proximal neck 841 of the filter body may be inverted to extend
distally rather than proximally, as is the case with the filter
element of FIG. 129. This arrangement reduces the overall
longitudinal length of the filter element, and thus the filter
element may be deployed and retrieved with a shorter "parking
space" in the vasculature.
[0369] FIGS. 132 to 134 illustrate the process of inverting the
proximal neck 841. The neck 841 is split along each side 842 (FIG.
133), and the neck 841 is then pushed distally into the interior of
the filter body (FIG. 134).
[0370] In addition, the longitudinal length of the filter element
of FIG. 130 is further shortened by providing a hemi-spherically
shaped proximal nose 845 instead of a conical nose, as is the case
with the filter element of FIG. 129. Furthermore, the overall
crossing profile of the filter element is reduced by means of the
hemi-spherical nose 845.
[0371] Referring to FIG. 135 there is illustrated a filter with a
proximally extending neck 847 which is split into two parts
847.
[0372] Referring to FIGS. 136 and 137 there is illustrated a filter
870 in which the filter body is connected directly to the frame by
means of folded filter seams.
[0373] FIG. 137 shows a variant filter 875 in which a second frame
provides additional body support to the filter.
[0374] Referring to FIG. 138, there is illustrated another filter
element 880, with a filter body which, in this case, has a single,
large inlet opening 881 defined at the inlet end 104. This
arrangement further minimises the possibility of any embolic
material becoming caught or hung-up on any parts of the filter
element at the inlet end 104. This arrangement also further reduces
the overall longitudinal length of the filter element.
[0375] FIGS. 139 and 140 illustrate a further filter element 885,
in which the proximal end 9 of the filter support is fixed to the
inner tube 108, while the distal end 110 of the filter support
remains unconnected to the inner tube 108. The filter support
comprises four round wires 116 which extend axially and radially
outwardly in two legs 118 from the proximal end 109 to the proximal
termination points 119. At the proximal termination points 119, the
wires 116 separate and extend circumferentially around the support
frame until the two distal termination points 120 are reached. The
proximal termination points 119 are circumferentially offset by
90.degree. from the distal termination points 120.
[0376] The proximal end 109 of the filter support 103 is fixed to
the inner tube 108, and the distal end I 10 of the filter support
103 is fixed to a sleeve 111 which is slidable over the inner tube
108. Upon collapse of the filter element, the proximal end 109 of
the filter support 103 remains fixed relative to the inner tube
108, and the distal sleeve 111 slides over the tube 108, until the
filter support 103 is fully collapsed against the inner tube 108.
In this collapsed position, the filter support 103 is axially
elongated relative to the expanded position.
[0377] The filter support 103 is illustrated in FIG. 142. The
filter support 103 comprises two round wires 116 which extend from
the proximal end 109 to the distal end 110. The wires 116 extend
together axially and radially outwardly in a leg 118 from the
proximal end 109, where the wires 116 are fixed to the inner tube
108, to a central support hoop 115. The junction of the leg 118
with the support hoop 115 is referred to in this specification as
the proximal termination point 119.
[0378] At the proximal termination point 119, the wires 116
separate, and extend circumferentially around the support hoop 115
until a symmetrical distal termination point 120 is reached. In
this way, the two wires 116 define the support hoop 115.
[0379] At the distal termination point 120, the wires 116 regroup
into a leg 121 which extends axially, and then axially and radially
inwardly to the sleeve 111 to which the wires 116 are fixed.
[0380] The path of the two wires 116 around the support hoop 115
together define a cell 116 which forms a complete loop, as
illustrated in FIG. 142. This arrangement of the circumferential
looped cell 117 ensures that in the expanded position, the filter
body 102 will be supported by the support hoop 115 in
circumferential apposition with the interior wall of the
vasculature.
[0381] The length of each wire 116 around the cell 117 is equal. At
the proximal and distal termination points 119, 120, the wires 116
are fixed to each other, and extend generally axially and parallel
in a bi-filar arrangement.
[0382] As the filter support 103 collapses down against the inner
tube 108, the wires 116 around the cell 117 become torqued. This
torqueing action is similar to the process of elongation of a
coiled spring.
[0383] Because the support frame 11 5 is defined by round wires
116, the torque developed in each wire 116 will be evenly
distributed along the length of each wire 116. In addition, the
bi-filar connection of the wires 116 to each other at the
termination points 119, 120 further assists in torque distribution
along the wires 116.
[0384] Thus, collapse of the filter support 103 does not induce
high, localised stresses in the filter support 103. In this way,
the filter support 103 may be constructed of wires 116 of a small
cross-sectional area which will collapse down to a very low
profile.
[0385] Furthermore the collapsed filter element with small wires
116 has greater flexibility for ease of advancement of the filter
element through the vascular system.
[0386] As illustrated in FIG. 142, the proximal termination point
119 is circumferentially offset by 180.degree. from the distal
termination point 120.
[0387] The wires 116 are preferably of a self-expanding material,
such as Nitinol, and the inner tube 108 is preferably of gold. This
arrangement provides for radiopacity.
[0388] In use, the filter element is collapsed down and loaded into
a delivery catheter with an associated torqueing of the wires 116
around the cell 117. The filter element is then delivered through a
vasculature fixed to or over a guidewire using the delivery
catheter until the filter element is located at a desired site in
the vasculature.
[0389] By moving the delivery catheter proximally relative to the
filter element, the filter element is deployed out of the delivery
catheter at the desired site in the vasculature. The filter support
103 expands radially outwardly to support the filter body 102 in
circumferential apposition with the interior wall of the
vasculature. In the fully expanded position, the wires 116 of the
support frame 115 are substantially free of torque.
[0390] The site of deployment of the filter element in the
vasculature is typically downstream of a treatment site, such as a
region of stenosis in the vasculature. During the performance of a
treatment procedure, the filter element captures and safely retains
any embolic material in the blood stream within the filter body
102.
[0391] After completion of the treatment procedure, the filter
element is collapsed down and retrieved into a retrieval catheter
with any retained embolic material within the filter body 102. The
wires 116 around the support frame 115 are again torqued during
collapse.
[0392] The retrieval catheter is then withdrawn from the
vasculature with the filter element within the retrieval
catheter.
[0393] Referring to FIGS. 142(a) and 142(b) there is illustrated a
lower portion and a top view of a modified support frame similar to
FIG. 142 in which the loops defined by the wires 115 are offset at
point 120. This offset could also be applied to point 119. Such a
design may be of benefit in broadening the area of circumferential
apposition and sealing provided by the filter.
[0394] Referring to FIG. 143 there is illustrated a support frame.
910 similar to that of FIG. 142 except that in this case the distal
and proximal legs 121, 118 are defined by a single wire, the second
wire extending only a short distance distally or proximally from
the distal and proximal termination points respectively.
[0395] Referring to FIG. 144 there is illustrated another embolic
protection filter 920 which comprises a single hoop support frame
921 with additional wire support arms 922, 923. In this case the
distal support leg is connected to the proximal end of the carrier.
Thus additional support is provided to the hoop without any impact
on the wrapped length of the device.
[0396] Referring to FIG. 145 there is illustrated a further embolic
protection filter 930 comprising support hoops 931, 932 which are
offset.
[0397] Referring to FIGS. 146 to 148 there are illustrated various
filter frames comprising a wire support hoops which may have strain
distribution features and/or tethers as described above.
[0398] The frame 935 of FIG. 146 comprises a single wire offset
hoop 936. The frame 938 of FIG. 147 is preferred because parking
space is minimised while facilitating wrap-down. It will be noted
the support comprises an offset wire support hoop 939 with an
axially extending proximally extending wire section 940 and an
inwardly extending support arm 941. The frame 945 of FIG. 148 is
similar to that of FIG. 147 except that there are two oppositely
directed offset hoops 946, 947 similar to the frame used in the
filter of FIG. 145.
[0399] Another support frame 950 is illustrated in FIGS. 149 to 150
which is again of wire and includes strain distributing loop
features 951 which may be of any suitable type as described above
and exemplified in FIGS. 150 and 151.
[0400] The support frame 960 of FIGS. 152 and 153 again has an
offset hoop 961 which can wrap down as illustrated in FIG. 153.
[0401] Referring to FIGS. 154 and 155, there is illustrated another
filter element 970, in which the filter support 972 comprises four
round wires 116. At the proximal termination point 119, two of the
wires 116 extend circumferentially around the support frame 115 to
define a first cell 117, and the other two wires 116 extend axially
and then extend circumferentially around the support frame to
define a second cell 117.
[0402] In this manner, the wires 116 define two axially
spaced-apart cells 117, each cell 117 forming a complete loop, as
illustrated in FIG. 155. This arrangement ensures that in the
expanded position, the filter body 102 will be supported by the
support frame in tubular apposition with the interior wall of the
vasculature. The tubular apposition further minimises the
possibility of any flow path for blood occurring between the filter
body 102 and the vasculature wall to bypass the filter element. At
the distal termination point 120, all four wires 116 regroup into
leg 121.
[0403] It will be appreciated that as the wires 116 extend
circumferentially around the support frame 115, the wires 116 may
also extend partially axially, so that the defined cell 117
partially slopes axially. Furthermore, the wires 116 may be at
least partially of an arcuate shape, as illustrated in the support
frame 973 of FIG. 156. In either case, the sloping or arcuate
configuration of the wires 116 increases the contact area between
the wires 116 and the filter body 102, and in this way, the
supporting force exerted by the wires 116 on the filter body 102 is
more evenly distributed. This arrangement minimises any trauma
experienced by the vasculature due to the apposition of the filter
element with the vasculature.
[0404] FIG. 157 illustrates another filter support 975, which is
similar to the filter support of FIGS. 154 and 155, and similar
elements in FIG. 157 are assigned the same reference numerals. In
this case, the filter support comprises six round wires 116. The
wires 116 extend axially and radially outwardly in two legs 118
from the proximal end 109 to two opposed proximal termination
points 119. As illustrated in FIG. 157, the wires 116 are arranged
to define two axially spaced-apart, complete loop cells 117. In
addition, two of the wires 116 act as axial bridges to connect the
two cells 117. At the distal termination points 120, the wires 116
regroup into two legs 121. The proximal termination points 119 are
circumferentially aligned with the distal termination points 120,
in this case.
[0405] The support frame 980 of FIG. 158 is similar to that of FIG.
157 except that in this case there are no proximal support arms
with consequential reduced filter length.
[0406] Referring to FIGS. 159 to 161, there is illustrated another
filter support 990, which is similar to the filter support of FIGS.
154 and 155, and similar elements are assigned the same reference
numerals. In this case, the filter support 990 comprises only two
round wires 116. The wires 116 extend together axially and radially
outwardly in a single leg 118 from the proximal end 109 to the
proximal termination point 119. The wires 116 then separate and
extend circumferentially around the support frame 115 to define the
first cell 117. The wires 116 extend axially, and then
circumferentially around the support frame 115 to define the second
cell 117. At the distal termination point 120, the wires 116
regroup into a single leg 121.
[0407] As illustrated in FIG. 161, the proximal termination point
119 is circumferentially aligned with the distal termination point
120.
[0408] Referring to the drawings, and initially to FIGS. 162 to 169
thereof, there is illustrated an embolic protection device
according to the invention. The embolic protection device comprises
a collapsible filter element I for delivery through a vascular
system of a patient.
[0409] The filter element 1 comprises a collapsible filter body 2
and a filter support 3 for the filter body 2, and an inner tube 8,
around which the filter support 3 is mounted.
[0410] The filter body 2 has an inlet end 4 and an outlet end 5.
The inlet end 4 has one or more, and in this case two, large inlet
openings 6 which are sized to allow blood and embolic material
enter the filter body 2. The outlet end 5 has a plurality of small
outlet openings 7 which are sized to allow through passage of blood
but to retain undesired embolic material within the filter body 2.
In this way, the filter element 1 captures and safely retains any
undesired embolic material in the blood stream within the filter
body 2 while facilitating continued flow of blood through the
vascular system. Emboli are thus prevented from flowing further
downstream through the vascular system, which could otherwise have
potentially catastrophic results. The filter body 2 may be of an
oriented polymeric material, as described in our WO 01/97714A and
US 2002/0042627A, the relevant contents of which are incorporated
herein by reference.
[0411] The filter support 3 is movable between a low profile,
collapsed position (FIG. 169(c)) for movement through the vascular
system, and an extended outwardly projecting position (FIG.
169(a)). As particularly illustrated in FIG. 2, in this outwardly
projecting position, the filer body 2 is supported in an expanded
position by the filter support 3 so as to maximise the internal
volume of the filter body 2 to capture and safely retain as much
embolic material as possible.
[0412] The inner tube 8 has a guidewire lumen 12 therethrough,
through which a guidewire may pass for exchange of the filter
element 1 over the guidewire.
[0413] The proximal end 9 of the filter support 3 is fixed to the
inner tube 8, and the distal end 10 of the filter support 3 is
fixed to a sleeve 11 which is slidable over the inner tube 8, as
illustrated in FIG. 164. As illustrated in FIGS. 167 to 169(c),
upon collapse of the filter element 1, the proximal end 9 of the
filter support 3 remains fixed relative to the inner tube 8, and
the distal sleeve 11 slides over the tube 8 (FIG. 169(b)), until
the filter support 3 is fully collapsed against the inner tube 8
(FIG. 169(c)). The partially and fully collapsed positions of the
filter support 3 are illustrated by dashed lines in FIGS. 167 and
168. In the fully collapsed position of (FIG. 169(c)), the filter
support 3 is axially elongated relative to the expanded
position.
[0414] The filter support 3 is illustrated in detail in FIGS. 164
to 166. The filter support 3 comprises eight round wires 16 which
extend from the proximal end 9 to the distal end 10. The wires 16
extend axially and radially outwardly in two legs 18 from the
proximal end 9, where the wires 16 are fixed to the inner tube 8,
to a central tubular support frame portion 15. The junction points
of the legs 18 with the tubular frame 15 are referred to in this
specification as the proximal termination points 19.
[0415] At each proximal termination point 19, the wires 16
separate, and then extend axially along and circumferentially
around the tubular frame 15 until symmetrical distal termination
points 20 are reached. At these distal termination points 20, the
wires 16 regroup into two legs 21 which extend axially and radially
inwardly to the sleeve 11, to which the wires 16 are fixed. In this
way, the wires 16 define the central tubular frame portion 15.
[0416] The path of the wires 16 around and along the tubular frame
portion 15 defines four cells 17, with each cell 17 forming a
segment of the tubular frame 15 (FIG. 166). Together the four cells
17 extend circumferentially around the tubular frame 15 in a
complete loop.
[0417] This arrangement of the tubular frame 15 ensures that in the
expanded position, the filter body 2 will be supported by the
tubular frame 15 in tubular apposition with the interior wall of
the vasculature. The tubular apposition further minimises the
possibility of any flow path for blood occurring between the filter
body 2 and the vasculature wall to bypass the filter element 1.
[0418] Each cell 17 is defined by two of the wires 16 which are
arranged, in the expanded position, in a generally parallelogram,
"hysteresis loop" shape. The length of each wire 16 around the cell
17 is equal. At the proximal and distal termination points 19, 20,
adjacent wires 16 are fixed to each other, and extend generally
axially and parallel in a bi-filar arrangement. Adjacent cells 17
within the tubular frame 15 are also connected together by fixing a
wire 16 in one cell 17 to a wire 16 in an adjacent cell 17.
[0419] As the filter support 3 collapses down against the inner
tube 8, the wires 16 around each cell 17 become torqued. This
torqueing action is similar to the process of elongation of a
coiled spring.
[0420] Because the tubular support frame 15 is defined by round
wires 16, the torque developed in each wire 16 will be evenly
distributed along the length of each wire 16. In addition, the
bi-filar connection of the wires 16 to each other at the
termination points 19, 20 further assists in torque distribution
along the wires 16.
[0421] Thus, collapse of the filter support 3 does not induce high,
localised stresses in the filter support 3. In this way, the filter
support 3 may be constructed of wires 16 of a small cross-sectional
area which will collapse down to a very low-profile. Furthermore
the collapsed filter element I with small wires 16 has greater
flexibility for ease of advancement of the filter element 1 through
the vascular system.
[0422] As illustrated in FIGS. 165 and 166, the proximal
termination points 19 are circumferentially offset by 90.degree.
from the distal termination points 20.
[0423] In use, the filter element 1 is collapsed down and loaded
into a delivery catheter with an associated torqueing of the wires
16 around the cells 17. The filter element 1 is then delivered
through a vasculature fixed to or over a guidewire using the
delivery catheter until the filter element 1 is located at a
desired site in the vasculature.
[0424] By moving the delivery catheter proximally relative to the
filter element 1, the filter element 1 is deployed out of the
delivery catheter at the desired site in the vasculature. The
filter support 3 expands radially outwardly to support the filter
body 2 in tubular apposition with the interior wall of the
vasculature. In the fully expanded position, the wires 16 of the
tubular support frame 15 are substantially free of torque.
[0425] The site of deployment of the filter element 1 in the
vasculature is typically downstream of a treatment site, such as a
region of stenosis in the vasculature. During the performance of a
treatment procedure, the filter element 1 captures and safely
retains any embolic material in the blood stream within the filter
body 2.
[0426] After completion of the treatment procedure, the filter
element 1 is collapsed down and retrieved into a retrieval catheter
with any retained embolic material within the filter body 2. The
wires 16 around the tubular wire support frame 15 are again torqued
during collapse.
[0427] The retrieval catheter is then withdrawn from the
vasculature with the filter element 1 within the retrieval
catheter.
[0428] The delivery, deployment and retrieval of the embolic
protection device of the invention, as described above, is similar
to that described in our WO 99/23976A; WO 01/80776A (US
2002-0052676A) and WO 01/80773A (US 2002-0049467A), the relevant
contents of which are incorporated herein by reference. The filter
element 1 may be slidably exchanged over the guidewire without any
attachment means between the filter element I and the guidewire. A
distal stop on the guidewire assists in retrieval of the filter
element 1. The guidewire may remain in the vasculature after
retrieval of the filter element 1.
[0429] FIG. 170 illustrates another filter support 30, which is
similar to the filter support 3 of FIGS. 162 to 168, and similar
elements in FIG. 170 are assigned the same reference numerals.
[0430] In this case, the filter support 30 comprises only six wires
16, which define only three tubular segment cells 17 as the wires
16 extend axially along and circumferentially around the tubular
frame 15. The three cells 17 do not form a complete 360.degree.
loop around the tubular frame 15. An extension wire 31 is provided,
in this case, to provide support to the filter body 2 between the
two circumferentially spaced-apart cells 17. The linkage element 31
may provide a diameter adjusting feature.
[0431] Referring to FIGS. 171 to 173, there is illustrated another
filter support 35, which is similar to the filter support 3 of
FIGS. 162 to 169, and similar elements in FIGS. 171 to 173 are
assigned the same reference numerals.
[0432] The wires 16 extend, in this case, circumferentially around
the tubular frame 15 in an "S-shape". The S-shape increases the
contact area between the wires 16 and the filter body 2, and in
this way, the supporting force exerted by the wires 16 on the
filter body 2 is more evenly distributed. This arrangement
minimises any trauma experienced by the vasculature due to the
apposition of the filter element 1 with the vasculature.
[0433] An alternative filter support 40 having wires 16 with a more
exaggerated S-shaped portion 41 is illustrated in FIGS. 174 and
175.
[0434] It will be appreciated that the shape of one wire 16 of a
cell 17 does not have to be symmetrical or similar to the shape of
the other wire 16 of the cell 17, provided that the length of each
wire 16 is equal.
[0435] Referring to FIGS. 176 to 178, there is illustrated another
filter support 45, which is similar to the filter support 3 of
FIGS. 162 to 169, and similar elements in FIGS. 176 to 178 are
assigned the same reference numerals.
[0436] In this case, the filter support 45 comprises only four
wires 16, which extend circumferentially around and axially along
the tubular support frame 15 to define two cells. The two cells
have a hexagonal, hysteresis loop shape, and together the two cells
17 extend circumferentially around the tubular frame 15 in a
complete loop.
[0437] The proximal termination points 19 are circumferentially
aligned with the distal termination points 20.
[0438] Another support frame 50, illustrated in FIG. 179, is
similar to the support frame 3 of FIGS. 161 to 169, and similar
elements if FIG. 179 are assigned the same reference numerals.
[0439] In this case, the wires 16 are fixed to inner tube 8 at a
point 51 distally of the tubular support frame portion 15. The
wires 16 extend from the fixation point 51 axially proximally and
radially outwardly in a single leg 52 to the tubular support frame
portion 15.
[0440] By providing a single proximal support leg 52, and by
locating this leg 52 distally of the inlet end 4 of the filter body
2, this arrangement minimises the possibility of embolic material
becoming caught or hung-up on the leg 18 at the inlet openings 6.
In this manner, substantially all of the embolic material is
retained safely within the filter body 2 for subsequent retrieval
from the vascular system.
[0441] The wires 16 are preferably of a self-expanding material,
such as Nitinol, and the inner tube 8 is preferably of gold. This
arrangement provides for radiopacity.
[0442] It will be appreciated that a plurality of cells 17 may be
defined by the wires 16 around the tubular support frame 15, as
illustrated in FIG. 18. Each wire 16 may be fixed to a wire 16 in
an adjacent cell 17 (FIG. 181) by welding, or by adhesive means 57
(FIG. 182), or by any other suitable means.
[0443] The wires 16 may be slidably mounted to the inner tube 8 at
both the proximal support leg 18 and the distal support leg 21.
[0444] By increasing the number of wires 16 which define the cells
17 of the tubular support frame 15, the elongation of the overall
filter support, when collapsed down, is reduced. In this way, the
space required in a vasculature to deploy and retrieve the embolic
protection device is also reduced.
[0445] Depending on the configuration of the filter element, the
inner tube may not be present. In this case the filter support will
be mounted directly onto the guidewire for exchange of the filter
element over the guidewire.
[0446] It will be appreciated that a single wire 16, bent back on
itself, may be used to define the tubular support frame 15, in
which case the cells 17 of the tubular support frame 15 are defined
by elements of the single wire 16, as illustrated in FIGS. 21 and
22. The support frame 90 of FIGS. 183 and 184 is similar to the
support frame 3 above, with the exception that the support frame is
defined by a single wire 16 bent back on itself.
[0447] A proximal neck of the filter body may be inverted to extend
distally rather than proximally. This arrangement reduces the
overall longitudinal length of the embolic protection device, and
thus the embolic protection device may be deployed and retrieved
with a shorter "parking space" in the vasculature. To invert the
proximal neck, the neck may be split along each side, and then the
pushed distally into the interior of the filter body.
[0448] In addition, the longitudinal length of the embolic
protection device may be further shortened by providing a
hemi-spherically shaped proximal nose instead of a conical nose.
Furthermore, the overall crossing profile of the embolic protection
device may be reduced by means of the hemi-spherical nose.
[0449] The invention incorporates circumferential wire angulation
into support structure design to give maximum circumferential
support to the filter membrane.
[0450] The angulated hysteresis structure/cell configuratons of the
invention are particularly suitable as support structures because
the strain energy is distributed over long lengths of the wire
structure. The wrapping/loading mechanisms of these hysteresis
structures are both a bending/straightening of the constituent
wires as well as a twisting/torsion of the wires. The energy
applied/introduced during the loading process is both bending and
torsional strain energy. These energies due to their nature and the
method by which the support structure folds/loads are distributed
over long lengths of the wire as opposed to concentrated focal
points so that the level of energy within the wire at any point
does not exceed the elastic strain energy limits. Hysteresis
designs optimise the strain distribution along the wire lengths.
With these designs there is distributed bending and torsional
strain along the wires. The component of radial force is converted
to torque strain energy. The corollary of this principle, that the
torsional strain energy provides radial stiffness, also
applies.
[0451] Angulated hysteresis structures also enable large radial
forces to be achieved from structures with small wire diameters.
The reason for this is that these designs use a greater proportion
of the wires' torsional strain resistance. The wires offer far
greater resistance to torsional strain than to bending strain and
therefore these designs optimise this feature. The angulated
hysteresis structure design arranges the wires so that the load
induces torsional strain and therefore delivers far higher
performance with small wire diameters than those designs that rely
on the bending strain/resistance.
[0452] The hysteresis support structure of the invention has
section/s of wire curvature that can be defined in 3D planes. These
sections of wire have geometrical properties such as a radius of
curvature and a centre of radius of curvature. As the hysteresis
structure designs are loaded and deployed, the geometrical
properties of these sections change--that is the radius of
curvature changes and the centre for the radius of curvature moves
in a path that can only be defined within a 3D plane.
[0453] Even relatively simple hysteresis designs are made up of
numerous sections of curvature with their corresponding radius of
curvature joined end to end to form a complete hysteresis loop.
These sections of curvature depending on the complexity of the
design may be combinations of concave and convex elements/segments.
The hysteresis loops themselves can be various shapes and there are
multitudes of hysteresis loop/cell geometries.
[0454] A wire or laser cut support structure design based on a
hysteresis cell type design typically may have four arms acting to
provide uniform radial force to give good vessel apposition. In
attempting to provide support over the complete body length
structure designs tend to have multiple arms/cells providing the
support. The problems with many of these designs is the excessive
elongation associated with them during loading. The advantage with
the invention in suit is that it only extends the same length
whether one/two or multiple arms are used. The invention also lends
itself to low wrapping profiles, because during loading it
contracts both radially and circumferentially leaving parallel
straight wires which often prove to be the easiest for loading.
[0455] Further advantages of the round wire arrangements
include:
[0456] Using a round wire allows for substantially more of the
strain energy induced during loading/wrapping down into a low
profile to be stored as torque along the wire lengths. This means
that the strain energy is more evenly distributed within the wires
than with conventional section designs, in which the strain energy
generally becomes concentrated around the bend points which can
cause problems such as exceeding the elastic strain energy limit at
these locations.
[0457] The invention also has the advantage of being more trackable
and flexible. This design achieves this by allowing the structure
to hinge at points. Planes through these points demonstrate that
bending at these hinge points is very easy.
[0458] Furthermore, the radial force may be altered by:
[0459] a) changing the wire diameter;
[0460] b) changing the proximal and distal cone angles.
[0461] Points of stress concentration can become strained
plastically and result in poor support structure performance.
[0462] Conventional approaches to dealing with these issues involve
designing in strain distributing geometric features to spread these
strains over a greater area of the structure. Another approach
involves the use of thinning out sections in the area of high
strain. At a given radius of curvature the strain in a thin section
is less than that of a thick section. Thinning however compromises
the overall support provided by the structure.
[0463] The filter support of the invention provides for torsional
strain and thus eliminates the need to use section thinning or
thickening to distribute strain.
[0464] When torque stresses are applied to members of an
approximately circular cross section the resulting strain becomes
distributed over the length of the section. In this situation it is
not possible to generate a corresponding torque phenomenon to the
cantilever bending phenomenon. The present invention provides
elements which are torsionally strained in the collapsed
configuration and which release these torsional strains as they
expand.
[0465] When collapse strains are evenly distributed, it is possible
that the overall level of strain in the system can be increased
without inducing plastic deformation. This makes it possible to
achieve a high level of radial support from small diameter support
members.
[0466] Designs that induce torque-strain into the support structure
during collapse are particularly advantageous. Bending strains tend
very often to have a strong cantilever effect with the strain
becoming localised at points of stress concentration.
[0467] The torque strain in the wire can be released in a variety
of expansion pathways. This means that the release of the torque is
not inhibited when uniaxial resistance is encountered. This feature
helps the support structure deliver good apposition to eccentric
vessels. This is an important aspect of the invention, especially
when the filter is placed in diseased vessel segments.
[0468] The geometric configuration of the filter support aligns the
wires of the cell in a substantially circumferential direction in
the expanded state. This ensures that radial pressure applied by
the vessel is initially transmitted as compressive hoop stress to
the structure.
[0469] The compressive component of applied stress decreases as the
system collapses, however the torsional resistance increases
resulting in a relatively flatter loading stress curve.
[0470] It will be appreciated that the body may be attached to or
independent of the support frame.
[0471] The invention is not limited to the embodiments hereinbefore
described which may be varied in detail.
* * * * *