U.S. patent application number 10/689846 was filed with the patent office on 2004-12-30 for embolic protection device.
This patent application is currently assigned to SALVIAC Limited. Invention is credited to Brady, Eamon, Gilson, Paul, Gilvarry, Michael.
Application Number | 20040267302 10/689846 |
Document ID | / |
Family ID | 26320277 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040267302 |
Kind Code |
A1 |
Gilson, Paul ; et
al. |
December 30, 2004 |
Embolic protection device
Abstract
A collapsible filter element for a transcatheter embolic
protection device, the filter element comprises a collapsible
filter body of polymeric material which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filer element. A proximal inlet portion of the filter body has
one or more inlet openings sized to allow blood and embolic
material enter the filter body. A distal outlet portion of the
filter body has a plurality of generally circular outlet openings
sized to allow through-passage of blood, but to retain embolic
material within the filter body. The distal outlet portion of the
filter body in the region of the outlet openings has means for
reducing shear stress on blood passing through the outlet openings.
The shear stress reducing means includes lead-in and lead-out
radiussed portions of the filter body leading to the outlet holes.
The porosity of the distal portion of the filter body decreases
towards the distal end. A blind portion extends for at least 5% of
the length of the body. Preferably there are between 200 and 300
outlet opening with an average diameter of approximately 150
microns.
Inventors: |
Gilson, Paul; (Moycullen,
IE) ; Brady, Eamon; (Elphin, IE) ; Gilvarry,
Michael; (Ballina, IE) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Assignee: |
SALVIAC Limited
|
Family ID: |
26320277 |
Appl. No.: |
10/689846 |
Filed: |
October 22, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10689846 |
Oct 22, 2003 |
|
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|
09986064 |
Nov 7, 2001 |
|
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|
6726701 |
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09986064 |
Nov 7, 2001 |
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PCT/IE00/00055 |
May 8, 2000 |
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Current U.S.
Class: |
606/200 ;
606/127 |
Current CPC
Class: |
A61F 2002/018 20130101;
A61F 2230/0006 20130101; A61F 2/01 20130101; A61F 2230/0067
20130101 |
Class at
Publication: |
606/200 ;
606/127 |
International
Class: |
A61B 017/22; A61M
029/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 1999 |
WO |
PCT/IE99/00033 |
May 7, 1999 |
WO |
PCT/IE99/00036 |
Claims
1. A collapsible filter element for a transcatheter embolic
protection device, the filter element comprising: a collapsible
filter body which is movable between a collapsed stored position
for movement through a vascular system and an expanded position for
extension across a blood vessel such that blood passing through the
blood vessel is delivered through the filter element; a proximal
inlet portion of the filter body having one or more inlet openings
sized to allow blood and embolic material enter the filter body; a
distal outlet portion of the filter body having a plurality of
outlet openings sized to allow through-passage of blood, but to
retain embolic material within the filter body; the distal outlet
portion of the filter body in the region of the outlet openings
having means for reducing shear stress on blood passing through the
outlet openings.
2-73. (Canceled)
Description
[0001] The term "STROKE" is used to describe a medical event
whereby blood supply to the brain or specific areas of the brain is
restricted or blocked to the extent that the supply is inadequate
to provide the required flow of oxygenated blood to maintain
function. The brain will be impaired either temporarily or
permanently, with the patient experiencing a loss of function such
as sight, speech or control of limbs. There are two distinct types
of stroke, haemorrhagic and embolic. This invention addresses
embolic stroke.
[0002] Medical literature describes caroitid artery disease as a
significant source of embolic material. Typically, an
atherosclerotic plaque builds up in the carotid arteries. The
nature of the plaque varies considerably, but in a significant
number of cases pieces of the plaque can break away and flow
distally and block bloodflow to specific areas of the brain and
cause neurological impairment. Treatment of the disease is
classically by way of surgical carotid endarterectomy whereby, the
carotid artery is cut and the plaque is physically removed from the
vessel. The procedure has broad acceptance with neurological
complication rates quoted as being low, somewhere in the order of
6% although claims vary widely on this.
[0003] Not all patients are candidates for surgery. A number of
reasons may exist such that the patients could not tolerate
surgical intervention. In these cases and an increasing number of
candidates that are surgical candidates are being treated using
transcatheter techniques. In this case, the evolving approach uses
devices inserted in the femoral artery and manipulated to the site
of the stenosis. A balloon angioplasty catheter is inflated to open
the artery and an intravascular stent is sometimes deployed at the
site of the stenosis. The action of these devices as with surgery
can dislodge embolic material which will flow with the arterial
blood and if large enough, eventually block a blood vessel and
cause a stroke.
[0004] It is known to permanently implant a filter in human
vasculature to catch embolic material. It is also known to use a
removable filter for this purpose. Such removable filters typically
comprise umbrella type filters comprising a filter membrane
supported on a collapsible frame on a guidewire for movement of the
filter membrane between a collapsed position against the guidewire
and a laterally extending position occluding a vessel. Examples of
such filters are shown in U.S. Pat. No. 4,723,549, U.S. Pat. No.
5,053,008, U.S. Pat. No. 5,108,419, WO97/17100 and WO 98/33443.
Various deployment and/or collapsing arrangements are provided for
the umbrella filter. However, as the filter collapses, the captured
embolic material tends to be squeezed outwardly towards an open end
of the filter and pieces of embolic material may escape from the
filter with potentially catastrophic results. More usually, the
filter umbrella is collapsed against the guidewire before removal
through a catheter or the like. Again, as the filter membrane is
collapsed, it will tend to squeeze out the embolic material.
Further, the umbrella filter is generally fixed to the guidewire
and any inadvertent movement of the guidewire during an
interventional procedure can dislodge the filter.
[0005] The insertion of such known filters in the human vasculature
which comprises very small diameter blood vessels may result in
inappropriate haemodynamics which can exacerbate damage to the
flowing blood and may result in haemolysis.
[0006] This invention is therefore directed towards providing an
embolic protection device which will overcome these major
problems.
STATEMENTS OF INVENTION
[0007] According to the invention there is provided a collapsible
filter element for a transcatheter embolic protection device, the
filter element comprising:
[0008] a collapsible filter body which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filter element;
[0009] a proximal inlet portion of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body;
[0010] a distal outlet portion of the filter body having a
plurality of outlet openings sized to allow through-passage of
blood, but to retain embolic material within the filter body;
[0011] the distal outlet portion of the filter body in the region
of the outlet openings having means for reducing shear stress on
blood passing through the outlet openings.
[0012] In a preferred embodiment of the invention the shear stress
reducing means includes lead-in radiussed portions of the filter
body leading to the outlet holes.
[0013] In a particular embodiment of the invention the shear stress
reducing means includes lead-out radiussed portions of the filter
body leading from the outlet holes.
[0014] Most preferably the outlet holes are generally circular.
[0015] In another preferred embodiment of the invention the
proximal inlet portion of the filter body in the region of the
inlet openings has means for reducing shear stress on blood passing
through the inlet openings. Preferably the shear stress reducing
means includes lead-in radiussed portions of the filter body
leading to the inlet holes. Ideally, the shear stress reducing
means includes lead-out raduissed portions of the filter body
leading from the inlet holes.
[0016] In a particularly preferred embodiment the filter is of a
polymeric material. Preferably the filter body defines a three
dimensional matrix. Most preferably, the filter body is of a
resilient elastomeric material. The filter body may be of a
polyurethane elastomer. Most preferably the filter body is of a
polycarbonate urethane material.
[0017] In an especially preferred embodiment of the invention the
filter body is covered with a hydrophilic coating, the openings
being provided in the coating.
[0018] Preferably the filter is of a polymeric material and the
raduissed portions are formed by solvent polishing of the polymeric
material.
[0019] In a preferred embodiment the porosity of the distal portion
of the filter body decreases towards the distal end of the filter.
Ideally, the overall porosity of the distal portion of the filter
element is from 5% to 40%. Preferably the overall porosity of the
distal portion of the filter element is form 8% to 21%.
[0020] In a preferred embodiment in the transverse cross sectional
areas at longitudinally spaced-apart locations of the distal
portion are substantially the same.
[0021] Preferably the distal portion is of generally conical shape
having a radial dimension which decreases towards a distal end of
the filter element.
[0022] In one embodiment the distal portion includes a blind
section adjacent to the distal end of the filter element.
Preferably the blind portion extends longitudinally for at least 5%
of the length of the distal portion, ideally for less than 30% of
the length of the distal portion.
[0023] In a preferred arrangement the number of outlet holes
increases towards an outer edge of the distal outlet portion of the
filter body.
[0024] Most preferably there are between 200 and 1000 outlet
openings with an average diameter of between 50 and 200 microns.
Ideally, there are between 200 and 300 outlet openings with an
average diameter of approximately 150 microns. There may be at
least 200 outlet openings with an average diameter of no more than
200 microns.
[0025] Preferably there are less than 1000 openings with an average
diameter of at least 50 microns.
[0026] In a particularly preferred embodiment the openings are
sized such that shear stress imparted to blood flowing through the
filter body at physiological flow rates is less than 800 Pa, most
preferably less than about 400 Pa and ideally less than about 200
Pa.
[0027] The openings are ideally generally circular openings.
[0028] In a preferred embodiment said filter body, when in a
deployed configuration includes a generally cylindrical
intermediate section between said proximal and distal portions. The
filter body is generally tapered when in a deployed configuration.
Preferably said distal section of said filter body comprises at
least a portion of the filter element. Ideally said intermediate
section of said filter body comprises at least a portion of the
filter element.
[0029] In a preferred embodiment the intermediate section of said
filter body includes a circumferential groove.
[0030] In a particularly preferred embodiment said filter body,
when in a deployed configuration is defined by a generally
elongated shape, having an intermediate section with an axial
dimension and a transverse dimension, the ratio of the axial
dimension to the transverse dimension being at least 0.5, ideally
at least 1.0.
[0031] In one embodiment of the invention the filter body includes
a guidewire lumen extending co-axially of a longitudinal axis of
the filter body.
[0032] In another aspect the invention provides a collapsible
filter element for a transcatheter embolic protection device, the
filter element comprising:
[0033] a collapsible filter body which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filter element, the filter body having a proximal end, a
longitudinal axis and a distal end;
[0034] a proximal inlet portion of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body;
[0035] a distal outlet portion of the filter body having a
plurality of outlet openings sized to allow through-passage of
blood, but to retain embolic material within the filter body;
[0036] the porosity of the distal portion of the filter body
decreasing towards the distal end of the filter.
[0037] In a further aspect the invention provides a collapsible
filter element for a transcatheter embolic protection device, the
filter element comprising:
[0038] a collapsible filter body which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filter element;
[0039] a proximal inlet portion of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body;
[0040] a distal outlet portion of the filter body having a
plurality of outlet openings sized to allow through-passage of
blood, but to retain embolic material within the filter body;
[0041] the filter body comprising a membrane of polymeric
material;
[0042] wherein there are between 200 and 1000 outlet openings with
an average diameter of between 50 and 200 microns.
[0043] The invention also provides a collapsible filter element for
a transcatheter embolic protection device, the filter element
comprising:
[0044] a collapsible filter body which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filter element;
[0045] a proximal inlet portion of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body;
[0046] a distal outlet portion of the filter body having a
plurality of outlet openings sized to allow through-passage of
blood, but to retain embolic material within the filter body;
[0047] the filter body comprising a membrane of polymeric
material;
[0048] wherein the openings are sized such that shear stress
imparted to blood flowing through the filter body at physiological
flow rates is less than 800 Pa, preferably less than about 400
Pa.
[0049] In a further aspect the invention provides a collapsible
filter element for a transcatheter embolic protection device, the
filter element comprising:
[0050] a collapsible filter body which is movable between a
collapsed stored position for movement through a vascular system
and an expanded position for extension across a blood vessel such
that blood passing through the blood vessel is delivered through
the filter element;
[0051] the filter body having a longitudinal axis a proximal inlet
portion, a distal outlet portion and an intermediate section
extending between the proximal portion and the distal portion;
[0052] a proximal inlet portion of the filter body having one or
more inlet openings sized to allow blood and embolic material enter
the filter body;
[0053] a distal outlet portion of the filter body having a
plurality of outlet openings sized to allow through-passage of
blood, but to retain embolic material within the filter body;
[0054] the filter body having a guidewire lumen co-axial with the
longitudinal axis;
[0055] wherein in a deployed configuration the intermediate section
is generally cylindrical with an axial dimension and a transverse
dimension, the ratio of the axial dimension to the transverse
dimension being at least 0.5, preferably at least 1.0.
[0056] In yet another aspect the invention provides a transcatheter
embolic protection device including:
[0057] a delivery system comprising:
[0058] a tubular member having a longitudinal axis, distal and
proximal portions, said distal portion of the tubular member being
removably advanceable into the vasculature of a patient;
[0059] a medical guidewire longitudinally axially movable in said
tubular member and having distal and proximal portions;
[0060] and a filter element of any aspect of the invention the
filter body having;
[0061] a first collapsed, insertion and withdrawal configuration an
a second expanded, deployed configuration;
[0062] a proximal inlet section and a distal outlet section, said
proximal inlet section including inlet openings which are operable
to admit body fluid when the filter body is in the second expanded
configuration;
[0063] a plurality of outlet openings disposed on at least a
portion of the filter element adjacent to the distal outlet
section;
[0064] wherein said filter body is moved between said first and
second configurations by displacement of said delivery system.
[0065] Preferably the filter body has a collapsible filter frame
operably coupled thereto. Said frame may comprise a plurality of
support arms having proximal and distal ends. Preferably the arms
are formed of an elastic shape memory material.
[0066] In a preferred embodiment said frame is constructed such
that filter body is biased toward said second, deployed
configuration.
[0067] In one embodiment of the invention said inlet openings are
defined at least partially by said arms. Preferably proximal
portions of said arms extend generally outwardly and distally from
said guidewire when said filter body is in said second, deployed
configuration.
[0068] In one embodiment distal portions of said arms extend
generally outwardly and proximally from said guidewire when said
filter body is in said second, deployed configuration.
[0069] Preferably the distal portion of the tubular member further
includes a pod for receiving therein the filter body when in said
first, collapsed configuration. Preferably said filter body is
urged into said first, collapsed configuration by said pod when the
guidewire is moved proximally.
[0070] In one embodiment said guidewire is solid.
[0071] In one arrangement said filter body comprises a sleeve
slidably disposed on said guidewire. The device may further
comprise stops for limiting the range of longitudinal movement of
the sleeve on said guidewire. The sleeve may comprise a guidewire
member distal to the filter body tapering distally.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] The invention will be more clearly understood from the
following description thereof given by way of example only with
reference to the accompanying drawings in which:
[0073] FIG. 1 is partially sectioned elevational view of an embolic
protection device according to the invention;
[0074] FIG. 2 is a schematic sectional elevational view of the
embolic protection device of FIG. 1;
[0075] FIG. 3 is a sectional view of the distal end of the device
of FIG. 1 shown in its loaded condition within its delivery
catheter;
[0076] FIG. 4 is a longitudinal cross sectional view of the device
of FIG. 1;
[0077] FIG. 5 is a cross sectional view of a distal end of the
device of FIG. 1;
[0078] FIG. 6 is a view on the line A-A in FIG. 4;
[0079] FIG. 7 is a perspective view of a filter body of the device
of FIGS. 1 to 6;
[0080] FIG. 8 is a side elevational view of the filter body of FIG.
7;
[0081] FIG. 9 is a view on a proximal end of the filter body;
[0082] FIG. 10 is a perspective view of a support frame;
[0083] FIG. 11 is a side elevational view of the support frame;
[0084] FIG. 12 is a perspective view illustrating the manufacture
of the support frame;
[0085] FIG. 13 is a view of the support frame and filter body
assembly;
[0086] FIGS. 14A to 14E are developed views of the distal end of a
filter body illustrating different arrangements of outlet holes for
filter sizes 6 mm, 4 mm, 4.5 mm, 5 mm, and 5.5 mm respectively;
[0087] FIG. 15 is a side elevational view of another filter body of
the invention;
[0088] FIG. 16 is a developed view of the distal end of the filter
body of FIG. 15 illustrating an arrangement of outlet holes;
[0089] FIGS. 17(a) and 17(b) are perspective partially cut-away
cross sectional views of a filter body before and after solvent
polishing respectively;
[0090] FIG. 18 is a graph of shear stress with outlet hole size and
hole number;
[0091] FIG. 19 is a longitudinal cross sectional view of a filter
body according to the invention;
[0092] FIGS. 20 to 25 are longitudinal cross sectional views of
different embodiments of the filter body according to the
invention;
[0093] FIGS. 26 to 28 are longitudinal cross sectional views of
further embodiments of the filter body according to the
invention;
[0094] FIG. 29 is a schematic perspective view of a filter element
according to another aspect of the invention;
[0095] FIGS. 30 to 33 are schematic perspective views of different
embodiments of the filter element according to the invention;
[0096] FIG. 34 is a schematic perspective view of a filter element
according to a further aspect of the invention; and
[0097] FIGS. 35(a) to 35(d) are longitudinal side views of another
filter according to the invention in different configurations of
use.
DETAILED DESCRIPTION
[0098] Referring to FIGS. 1 to 13 there is illustrated an embolic
protection device as described in our WO-A-9923976 indicated
generally by the reference number 100. The device 100 has a
guidewire 101 with a proximal end 102 and a distal end 103. A
tubular sleeve 104 is slidably mounted on the guidewire 101. A
collapsible filter 105 is mounted on the sleeve 104, the filter 105
being movable between a collapsed stored position against the
sleeve 104 and an expanded position as shown in the drawings
extended outwardly of the sleeve 104 for deployment in a blood
vessel.
[0099] The sleeve 104 is slidable on the guidewire 101 between a
pair of spaced-apart end stops, namely an inner stop 106 and an
outer stop which in this case is formed by a spring tip 107 at the
distal end 103 of the guidewire 101.
[0100] The filter 105 comprises a filter body 110 mounted over a
collapsible support frame 111. The filter body 110 is mounted to
the sleeve 104 at each end, the body 110 being rigidly attached to
a proximal end 112 of the sleeve 104 and the body 110 being
attached to a collar 115 which is slidable along a distal end 114
of the sleeve 104. Thus the distal end of the body 110 is
longitudinally slidable along the sleeve 104. The support frame 111
is also fixed at the proximal end 112 of the sleeve 104. A distal
end 116 of the support frame 111 is not attached to the sleeve 104
and is thus also free to move longitudinally along the sleeve 104
to facilitate collapsing the support frame 111 against the sleeve
104. The support frame 111 is such that it is naturally expanded as
shown in the drawings and can be collapsed inwardly against the
sleeve 104 for loading in a catheter 118 or the like.
[0101] The filter body 110 has large proximal inlet openings 117
and small distal outlet openings 119. The proximal inlet openings
117 allow blood and embolic material to enter the filter body 110,
however, the distal outlet openings 119 allow through passage of
blood but retain undesired embolic material within the filter body
110.
[0102] An olive guide 120 is mounted at a distal end of the sleeve
104 and has a cylindrical central portion 121 with tapered ends
122, 123. The distal end 122 may be an arrowhead configuration for
smooth transition between the catheter and olive surfaces. The
support frame 111 is shaped to provide a circumferential groove 125
in the filter body 110. If the filter 105 is too large for a
vessel, the body 110 may crease and this groove 125 ensures any
crease does not propagate along the filter 105.
[0103] Enlarged openings are provided at a proximal end of the
filter body 110 to allow ingress of blood and embolic material into
an interior of the body 110.
[0104] Referring in particular to FIGS. 10 to 13 the collapsible
support frame 111 has four foldable arms 290 which are collapsed
for deployment and upon release extend outwardly to expand the
filter body 110.
[0105] The support frame 111 can be manufactured from a range of
metallic or polymeric components such as a shape memory alloy like
nitinol or a shape memory polymer or a shaped stainless steel or
metal with similar properties that will recover from the
deformation sufficiently to cause the filter body 110 to open.
[0106] The support frame 111 may be formed as illustrated in FIG.
12 by machining slots in a tube 291 of shape memory alloy such as
nitinol. On machining, the unslotted distal end of the tube 291
forms a distal collar 293 and the unslotted proximal end of the
tube 291 forms a proximal collar 294. In use, as described above,
the distal collar 293 is slidably movable along the tubular sleeve
104 which in turn is slidably mounted on the guidewire 101 for
deployment and retrieval. The proximal collar 294 is fixed relative
to the tubular sleeve 104.
[0107] To load the filter 105 the sub assembly of the support frame
111 and filter body 110 is pulled back into the catheter 118 to
engage the distal stop 107. The support arms 290 are hinged
inwardly and the distal collar 293 moves forward along the tubular
sleeve 104. As the support arms 290 enter the catheter 118 the
filter body 110 stretches as the filter body collar 115 slides
along the tubular sleeve 104 proximal to the olive 120. On
deployment, the catheter 118 is retracted proximally along the
guidewire 101 initially bringing the collapsed filter assembly with
it until it engages the proximal stop 106. The catheter sleeve then
begins to pull off the filter 105 freeing the support arms 290 to
expand and the filter body 110 apposes the vessel wall.
[0108] For retrieval, a retrieval catheter is introduced by sliding
it over the guidewire 101 until it is positioned at the proximal
end of the filter body 110 and support frame 111. Pulling the
guidewire 101 will initially engage the distal stop 107 with the
filter element and begin to pull it into the retrieval catheter.
The initial travel into the retrieval catheter acts to close the
proximal openings 117 of the filter element, thus entrapping the
embolic load. As the filter 105 continues to be pulled back the
filter body 110 and the support frame 111 are enveloped in the
retrieval catheter. The collapsed filter 105 may then be removed
from the patient.
[0109] Conveniently the tip of the catheter which forms a housing
or pod for reception of the filter is of an elastic material which
can radially expand to accommodate the filter with the captured
embolic material. By correct choice of material, the same catheter
or pod can be used to deploy and retrieve the filter. For
deployment, the elastic material holds the filter in a tightly
collapsed position to minimise the size of the catheter tip or pod.
Then, when retrieving the filter, the catheter tip or pod is
sufficiently elastic to accommodate the extra bulk of the filter
due to the embolic material.
[0110] Also, the filter is not fast on the guidewire and thus
accidental movement of the guidewire is accommodated without
unintentionally moving the filter, for example, during exchange of
medical devices or when changing catheters.
[0111] It will also be noted that the filter according to the
invention does not have a sharp outer edge as with many umbrella
type filters. Rather, the generally tubular filter shape is more
accommodating of the interior walls of blood vessels.
[0112] Conveniently also when the filter has been deployed in a
blood vessel, the catheter can be removed leaving a bare guidewire
proximal to the filter for use with known devices such as balloon
catheter and stent devices upstream of the filter.
[0113] The outer filter body 110 is preferably of a resilient
biocompatible elastomeric material. The material may be a
polyurethane based material. There are a series of commercially
available polyurethane materials that may be suitable. These are
typically based on polyether or polycarbonate or silicone
macroglycols together with diisocyanate and a diol or diamine or
alkanolamine or water chain extender. Examples of these are
described in EP-A461,375 and U.S. Pat. No. 5,621,065. In addition,
polyurethane elastomers manufactured from polycarbonate polyols as
described in U.S. Pat. No. 5,254,622 (Szycher) are also
suitable.
[0114] The filter material may also be a biostable polycarbonate
urethane article an example of which may be prepared by reaction of
an isocyanate, a chain extender and a polycarbonate copolymer
polyol of alkyl carbonates. This material is described in our WO
9924084.
[0115] The filter body may be manufactured from a block and cut
into a desired shape. The filter may be preferably formed by
dipping a rod of desired geometry into a solution of the material
which coats the rod. The rod is then dissolved. The final geometry
of the filter may be determined in the dipping step or the final
geometry may be achieved in a finishing operation. Typically the
finishing operations involve processes such as mechanical machining
operations, laser machining or chemical machining.
[0116] The filter body is of hollow construction and may be formed
as described above by dipping a rod in a solution of polymeric
material to coat the rod. The rod is then dissolved, leaving a
hollow body polymeric material. The rod may be of an acrylic
material which is dissolved by a suitable solvent such as
acetone.
[0117] The polymeric body thus formed is machined to the shape
illustrated in FIGS. 1 to 13. The final machined filter body
comprises an inlet or proximal portion 210 with a proximal neck
212, and outlet or distal portion 213 with a distal neck 214 and an
intermediate portion 215 between the proximal and distal
portions.
[0118] Alternatively the filter body may be formed by a blow
moulding process using a suitably shaped mould. This results in a
filter body which has thin walls.
[0119] The inlet holes 117 are provided in the proximal portion 210
which allow the blood and embolic material to flow into the filter
body. In this case the proximal portion 210 is of generally conical
shape to maximise the hole size.
[0120] The intermediate portion 215 is also hollow and in this case
is of generally cylindrical construction. This is important in
ensuring more than simple point contact with the surrounding blood
vessel. The cylindrical structure allows the filter body to come
into soft contact with the blood vessel to avoid damaging the
vessel wall.
[0121] The intermediate portion 215 is provided with a radial
stiffening means, in this case in the form of a radial
strengthening ring or rim 220. The ring 220 provides localised
stiffening of the filter body without stiffening the material in
contact with the vessel. Such an arrangement provides appropriate
structural strength so that line apposition of the filter body to
the vessel wall is achieved. It is expected that other geometries
of stiffening means will achieve a similar result.
[0122] The tubular intermediate portion 215 is also important in
maintaining the stability of the filter body in situ to retain
captured emboli and to ensure that flow around the filter is
minimised. For optimum stability we have found that the ratio of
the axial length of the intermediate portion 215 of the filter body
to the diameter of the intermediate portion 215 is preferably at
least 0.5 and ideally greater than 1.0.
[0123] The outlet holes 119 are provided in the distal portion 213
which allow blood to pass and retain embolic material in the filter
body.
[0124] The purpose of the filter is to remove larger particulate
debris from the bloodstream during procedures such as angioplasty.
In one case the filter is used to prevent ingress of embolic
material to the smaller blood vessels distal to a newly-deployed
carotid stent. A known property of the filter is that it will
present a resistance to the blood flow. The maximum blood pressure
in the arterial system is determined by the muscular action of the
heart. The cardiovascular system is a multiple-redundant network
designed to supply oxygenated blood to the tissues of the body. The
path from the heart through the site of deployment of the filter
and back to the heart can be traced through the system. In the
absence of the filter this system has a resistance, and the flow
through any part of it is determined by the distribution of
resistance and by the pressure generated by the heart.
[0125] The introduction of the filter adds a resistance on one of
the paths in the network, and therefore there will be a reduced
blood flow through this part of the circuit. It is reasonable to
assume that the flow along the restricted carotid will be inversely
proportional to the resistance of this branch of the circuit. For
laminar flow in a tube the resistance is independent of the flow
rate.
[0126] The performance of vascular filters and particularly
vascular filters for smaller blood vessels is determined by the
relationship between the filter and the media being filtered. Blood
is a complex suspension of different cell types that react
differently to different stimuli. The defining geometric attributes
of the filter structure will establish the filter's resistance to
flow in any blood vessel. Ideally, all flow will be through the
filter and will be exposed to minimal damage.
[0127] All filters that do not have a sealing mechanism to divert
flow only through it and will have some element of flow around it.
We have configured the filter geometry such that flow through the
filter is maximised and flow around the filter is minimised.
Pressure drop across the face of the filter when related to the
pressure drop through the alternate pathway will determine the
filter efficiency.
[0128] Related to the pressure drop, is the shear stress
experienced by the blood elements. Red cells have an ability to
deform under the influence of shear stresses. At low stresses
(physiological) this deformation is recoverable. Additionally, a
percentage of the red cell population is fragile and will fragment
at low shear stress even in patients with "healthy" cell
populations. While the body can deal with the rupture and
fragmentation of small numbers of red blood cells, gross red blood
cell damage are likely to be problematic clinically. Consideration
must be given to the effects of the shear stresses, both the
intensity and duration, on the constituent blood particles and the
haemostatic mechanisms. It is the effects on the red blood cells
and platelets that are of primary importance.
[0129] Shear stresses can cause red cell destruction which is more
pronounced in patients with red cell disorders, such as sickel cell
disease. Haemolysis can lead to amaenia, which can impede oygen
transportation around the body, and in extreme cases causes damage
to the kidneys, but this would be unlikely given the relatively
short duration of deployment of vascular filters.
[0130] More importantly though, shear stress also causes damage to
the platelets themselves. Platelets play a key role in haemostasis
and help orchestrate the complex cascade of events that lead to
blood clot formation. The damage to the platelets causes
communication chemicals to be released, and these "activate" other
platelets in the vicinity. Once activated, the platelets swell and
their surfaces become sticky, and this causes them to aggregate
together and on available surfaces to form a "clump". The released
chemicals attract and activate other platelets in the area such
that the clump grows in size. Fibrous proteins are also created and
together a blood clot (thrombus) is formed. Depending on its size
and position, the thrombus may occlude some of the holes in a
vascular filter. It is also possible for the thrombus to become
detached, particularly on removal of the device, and float freely
away downstream to become an embolus. Should the embolus be large
enough to become trapped in a narrow arterial vessel further along
the system, flow in that vessel would be compromised and this could
lead directly to stroke. Platelet aggregation occurs most
effectively in stagnant and re-circulating flow regions.
[0131] It is also known that activated platelets can coat foreign
bodies in the blood, such as intravasculature catheters. The
foreign material surface then becomes sticky and therefore a site
for further aggregation. This in turn could affect the local
geometry of the device and the local flow characteristics.
[0132] Shear may be expressed as follows:
Wall shear stress: .tau.=4 .mu.Q/.pi.R.sup.3
[0133] Where .mu. is the blood viscosity
[0134] Q is the mass flow rate
[0135] R is the vessel radius
[0136] In FIG. 18 we show the relationship under specific flow
conditions in a stated diameter of vessel. This plot assumes a
Newtonian fluid, equal flow rate through each hole, a flow rate of
270 ml/min and a 4 mm blood vessel.
[0137] The relationship shows that as hole size decreases, then the
required number of holes increases significantly.
[0138] This representation of shear is a good general
representation however, local conditions at the filter pores can
have significant impact on the shear with flow irregularities
generating the possibility of shear levels increasing by an order
of magnitude. The location of the maximum shear stress is at the
edges of the filter holes at their downstream side. The filter
element of the invention has local radii and the filter entrance
and exit holes to minimise the shear stress levels. Holes may be
drilled using mechanical drilling or laser cutting. However, these
processes can produce dimensionally repeatable holes but will
impart surface conditions that are not suitable for small vessel
filtration. Any fraying of edges due to mechanical cutting will
certainly cause flow disruptions and form sites for platelet
aggregation. Similarly laser cutting due to its local intense
heating and vaporisation of the substrate will lead to pitting,
surface inclusions, rough edges and surface imperfections.
[0139] In the invention the holes are post processed to modify the
surfaces and to radius the edges. A preferred embodiment of the
filter element is manufactured using a medial grade polyurethane
such as Chronoflex.TM. supplied by Cardiotech Inc. The filter holes
are post-processed by solvent polishing using acetone or other
suitable solvent.
[0140] Referring in particular to FIG. 17(a) there is illustrated a
section of a polymeric filter body with a number of machined outlet
holes 119. After solvent polishing the hoes are surface treated
providing radiused lead-in and lead-out portions.
[0141] Solvent polishing of the membrane is achieved by softening
the material in the surface layers of the membrane such that a
local reflow process is facilitated. This reflow is achieved using
one of two classes of solvent.
[0142] Solvents that have an ability to dissolve the polymer.
[0143] Solvents that have an ability to swell the polymer.
[0144] The process for the first class of solvents involves
exposing the membrane to a limited amount of the solvent. This is
achieved by dipping the membrane in the solvent for a short time or
exposing the membrane to concentrated vapours of the solvent for a
time. The solvent is absorbed into the surface layers and they
become solubilised. The solubilised surface layers act like a
viscous liquid and they adopt configurations of lowest surface
energy. The lowest energy configuration for a liquid is a sphere.
The sharp edges and corners become rounded by the solubilisation of
the surface. The solvent is dried to reveal a smooth solvent
polished surface.
[0145] Swelling solvents act slightly differently in that they
cannot dissolve the material. However their ability to swell the
material allows similar reflow processes to occur. The key
difference is that the membrane is immersed in the solvent for a
longer period of time, preferably in excess of 30 minutes. The
solvent swelling process is most effective when the membrane
material is a two phase polymer such as a polyuerthane or a PEBAX,
as the solvent can be selected to match either phase.
[0146] Solvents will dissolve polymers when their solubility
parameters are similar. Solvents will swell a polymer when their
solubility parameters are slightly different. Preferably the
swelling solvent swells the material by less than 30%. Above this
level the solvent should be considered dissolving solvent.
[0147] Having reduced the local shear stresses as described above,
it is then desirable to minimise the propensity for the activated
platelets to adhere to the filter substrate. The more preferred
embodiment of filter is one where the polished polymeric surface is
combined with a coating on the substrate.
[0148] The swelling of the polymer matrix reduces residual stresses
that may have developed during the coated core drying or lasering
processes. During the lasering process, the material in the
immediate proximity of the lasered holes will have been exposed to
heat. This heat will disrupt hard segment crystallites and they
will reform to lower order meta-stable structures or be completely
dissolved in the soft phase. The heat will also induce the soft
segments to contract, however, the re-arrangement of the hard
segments imposes new restrictions on the recovery of the soft
segments to an equilibrium (relaxed) state. Thus, on removal of the
heat source (laser), the morphology of the block coploymer will
have changed, in the sense that the new configurations of the hard
segments and soft segments will have been frozen in. After
lasering, the holes have sharp and well-defined geometries. After
exposing the coated material to the solvent, the solvent uncoils
the soft segment chains and disassociates low ordered hard segment
that are dissolved in the soft segment phase, so on removal of the
solvent, the polymer matrix dries in a more relaxed state. In so
doing, the sharp, well-defined walls of the lasered holes are
transformed to a more contoured relaxed state.
[0149] Such applicable solvents for this application, but not
limited to, are 2-propanone, methyl ethyl ketone or
trichloroethylene.
[0150] The solvent characteristics are described as follows at room
temperature:
[0151] The solvent is organic, colourless and in a liquid
state.
[0152] The overall solubility parameter of the solvent is quoted
between 16 to 26 Mpa.sup.0.5.
[0153] The solvent is polar and is also capable of hydrogen bond
interactions.
[0154] On partitioning the overall solubility parameter of the
solvent into dispersion. polar and hydrogen bonding components, the
hydrogen bonding value (in its own solution) is quoted between 3
Mpa.sup.0.5 to 8.5 Mpa.sup.0.5
[0155] The solvent is infinitely misible in water.
[0156] The solvent is aprotic (proton acceptor) towards the
formation of hydrogen bonding between it and the polymer.
[0157] We have found that the optimum average diameter of the
outlet holes in the polymeric membrane is from 100 to 200 microns,
ideally approximately 150 microns. The number of holes in the
distal portion 213 is from 200 to 500, ideally about 300. This hole
size and number of holes misses shear levels by reducing localised
flow rates. Thus, we have found that shear can be maintained below
800, preferably below 500 and ideally below 200 Pa at a blood flow
rate of up to 270 mi/min in a 4 mm blood vessel. Ideally the holes
are circular holes.
[0158] We have found that by maintaining blood shear below 800,
preferably below 500 and ideally below 200 Pa, the filter provides
appropriate haemodynamics to minimise turbulence and inappropriate
shear stress on native arteries and veins. Damage to flowing blood
such as haemolysis which involves the destruction of red blood
cells by rupture of the cell envelope and release of contained
hemoglobin is avoided. The outlet hole size and number of holes is
optimised in order to capture embolic material, to allow the
embolic material to be entrapped in the filter body and to be
withdrawn through a delivery device such as a delivery catheter on
collapsing of the filter body.
[0159] Shearing of red blood and damage to platelets during
filtration is a problem easily solved in extra-corporeal circuits
by providing large filter areas with consequent low flow rates
through individual pores controlled to flow rates such that the
shear is maintained in ranges that are below known threshold levels
with clinical relevance.
[0160] However, as shear stress increases in inverse proportion to
the cube of the radius, small blood vessels do not provide space in
which to control shear levels by reducing localised flow rates. At
flow rates up to 270 ml/min in a 4 mm blood vessel we have found
that we can maintain shear at levels below 200 Pa with 150 micron
holes.
[0161] We have also found that the porosity of the distal end of
the filter membrane and the arrangement of outlet holes is
important in optimising capture of embolic material without
adversely effecting blood shear characteristics and the material
properties of the filter body which allow it to be collapsed for
delivery, expanded for deployment and collapsed for retrieval.
[0162] Referring in particular to FIGS. 7, 8 and especially 14(a)
to 14(e) we have found that the overall porosity of the filter
element is preferably between 5% and 40% and ideally between 8% and
21%. The transverse cross sectional areas of the filter body at
longitudinally spaced-apart locations of the distal portion are
substantially the same. Most importantly we have found that the
porosity of the distal portion of the filter body should decrease
towards the distal end. Arrangements of distal holes 119 for
different filter diameters are shown in FIGS. 14(a) to 14(e). F IG.
14(a) shows an arrangement for a 6 mm filter, 14(b) for a 4 mm
filter, FIG. 14(c) for a 4.5 mm filter, FIG. 14(d) for a 5 mm
filter and FIG. 14(e) for a 5.5 mm filter. The number of outlet
holes 119 also increases towards an outer edge of the distal
portion of the filter body.
[0163] In addition we have found that for optimum capture of
embolic material while facilitating retrieval of the filter with
entrapped embolic material into a retrieval catheter the distal
portion of the filter element includes a blind section 130 adjacent
the distal end of the filter element. Ideally the blind portion 130
extends longitudinally for at least 5% and preferably less than 30%
of the length of the distal portion.
[0164] In order to reduce the profile of the filter body we have
significantly reduced the thickness of the filter membrane to
typically in the order of 25 microns. This reduction in thickness
however means that the membrane used must have a relatively high
stiffness to achieve a comparable strength. However, we have found
that such an increase in stiffness results in poor memory
performance and is therefore undesirable.
[0165] We have surprisingly found that by providing a filter body
of laminate construction in which a membrane is coated with a
coating to a thickness of from 5% to 40% of the thickness of the
membrane we have been able to provide a filter body which has a low
profile but which has good memory characteristics.
[0166] In particular, we have found that hydrophilic coatings and
hydrogels are highly suitable coatings as they have a similar
surface to the endothelial lining of a blood vessel and are not
perceived by the body's immune system as foreign. This results in
at least reduction and in some cases substantial elimination of
platelet adhesion and fibrin build up which could otherwise occlude
the filter and/or create a harmful thrombus. The coating also
provide a relatively low friction surface between the filter body
and the delicate endothelial lining of a vessel wall and therefore
minimise the trauma and injury to a vessel wall caused by
deployment of the filter body in the vasculature.
[0167] A hydrogel will absorb water swelling its volume. The
swelling of the hydrogel will exert an expansion force on the
membrane helping to pull it into its recovered or deployed
shape.
[0168] A coating that expands on contact with blood will exert an
expansion force on the membrane helping to pull it into its
recovered or deployed shape.
[0169] A coating that expands when subjected to body temperature
will exert an expansion force on the membrane helping to pull it
into its recovered or deployed shape.
[0170] Hydrophilic coatings can be classified by their molecular
structure:
[0171] Linear Hydrophilic polymers can dissolve or be dispersed in
water
[0172] Cross-linked hydrophilic polymers, which include hydogels,
can swell and retain water.
[0173] Hydrophilic coatings may be also synthetic or natural.
Synthetic hydrophilic polymers include the following:
[0174] Poly(2-hydroxy ethyl methacrylate)--(PHEMA)
[0175] Poly(vinyl alcohol)--(PVA)
[0176] Poly (ethylene oxide)--(PEO)
[0177] Poly (carboxylic acids) including:
[0178] Poly (acrylic acid)--(PAA)
[0179] Poly (methacrylic acid)--(PMAA)
[0180] Poly (N-vinyl-2-pyrollidone)--(PNVP)
[0181] Poly (sulfonic acids), poly (acrylonitrile), poly
(acrylamides)
[0182] Natural Hydrophylics Include:
[0183] Cellulose ethers
[0184] Collagen
[0185] Carrageenan
[0186] Commercially available hydrophylic coatings suitable for
coating filter membrane include, but are not limited to the
following:
[0187] Aquamer (Sky Polymers Inc.)
[0188] Phosphorylcholine (PC) (Biocompatibiles Ltd)
[0189] Surmodics (Surmodics Inc. BSI)
[0190] Hydak (Biocoat Inc)
[0191] Hydomer (Hydormer Inc)
[0192] Hydrogels as stated are cross-linked hydrophilic molecules.
The molecular mobility of hydrogels is constant and extensive,
giving ceaseless molecular motion, which contributes to the
property of biocompatibility by inhibiting protein absorption.
[0193] The extent to which a hydrogel imparts properties of
biocompatibility, wettability and lubricity is directly related to
the amount of water it absorbs into its molecular matrix, which is
referred to as the "degree of swelling".
W=[(Wsw-Wo)/Wsw].times.100
[0194] Where Wsw=Weight of swollen gel
[0195] Wo=Weight of dry gel
Water uptake=U[(Wsw-Wo)/Wsw].times.100
[0196] A typical hydrogel will absorb up to 20% of their dry weight
of water Superabsorbant hydrogels will absorb up to 2000% of their
dry weight of water.
[0197] Hydrogel strength is directly related to cross link density
(.mu.) and molecular weight between cross-links (Mc).
[0198] Hydrophilic coatings may be typically applied by dipping,
spraying and/or brushing. The coatings may also be applied by
solution or by colloidal dispersion.
[0199] The membrane surface to be coated may be prepared by
cleaning with a solvent and/or ultrasonic cleaning. Plasma or
corona discharge may also be used to increase the surface energy
and thus provide for better adhesion.
[0200] Alternatives to Hydrophilics include low friction
fluoropolymer, i.e. PTFE & FEP coatings that are chemically
inert and have low coefficients of friction, which also helps
prevent adhesion of platelets.
[0201] Other coatings that rely on being chemically inert
include.
[0202] Poly-para-xylylene (Paralene N, C & D) made by Novatron
Limited.
[0203] Diamond like carbon.
[0204] TetraCarbon (Medisyn Technologies Ltd.).
[0205] Both diamond like carbon & tetracarbon also provide very
thin hard surface layers, which help reduce the dynamic coefficient
of friction for elastomers.
[0206] The coating may be typically applied by dipping, spraying
and/or brushing. The coatings may also be applied by solution or
colloidal dispersion.
[0207] Typically, to produce a filter according to the invention a
polymeric filter membrane is first produced by machining a core of
a desired shape from an inert material such as perspex. The perspex
core is then dipped in a solution of a polymeric material as
described above. Alternatively the membrane is formed by blow
moulding. Holes are then laser machined in the dipped core. The
perspex core is removed by dissolving in acetone. Residual acetone
is washed out with water.
[0208] A filter frame of gold plated Nitinol is mounted on a filter
carrier in the form of a polyimide tube. The filter membrane is
then slid over the filter support frame to provide an uncoated
filter assembly.
[0209] The filter assembly is dipped in a solvent such as propan
2-ol to clean the assembly. The cleaned assembly is then dipped in
a solution of a coating material. A vacuum is applied to remove
excess coating material prior to drying in an oven. The coating
material is typically of Aquamer in a water/ethanol solution. The
thickness of the coating is typically 2 to 10 microns.
[0210] Preferably the filter body contains regions of varying
stiffness and durometer hardness. The change in filter stiffness
along its geometry can be achieved by varying the material
properties or by modifications to the thickness or geometry of the
membrane. The change in material hardness is achieved by varying
the material properties. The polymer material may be one of the
following: polyamides, polyurethanes, polyesters, a polyether block
amide (PEBAX), olefinic elastomer, styrenic elastomer. Ideally the
filter body has a durometer of between 60 D and 70 A Shore
hardness
[0211] Referring to FIG. 19 there is illustrated a filter element
comprising a filter body 2 according to the invention. In this
case, the filter body 2 has a proximal section 3 and a distal
section 4 interconnected by an intermediate section 5. Both the
proximal section 3 and the distal section 4 are made from a
relatively stiff grade of polyurethane material which enables a low
wall thickness to be achieved, thus advantageously minimising the
bulk of the filter when it is in a collapsed position so that it
has a low crossing profile while at the same time providing
adequate strength. The intermediate section 5 is made from a soft
elastic grade of polyurethane having good shape memory
characteristics which will help the filter maintain the desired
expanded shape during use of the filter. This soft portion also
allows one filter size to accommodate a range of vessel sizes
conforming closely to the vessel wall to prevent blood and embolic
material bypassing the filter.
[0212] In the filter body 2 illustrated in FIG. 19 the body is of
generally uniform thickness in cross section. However, to achieve
any desired variation in the properties of the filter body the
thickness may be variable such as in the filter body 10 illustrated
in FIG. 20.
[0213] Referring to FIGS. 21 to 25, any required structural
properties may also be provided by a filter body, which is at least
partially of a laminate construction. The layers of the laminate
may be of the same or different materials. In the illustration of
FIG. 21 the distal section 4 and part of the intermediate section 5
are of a two layer 21, 22 construction. The layers 21, 22 may be of
the same or different materials.
[0214] The layers 21, 22 are keyed together by mechanical or
chemical means, the holes in the distal section 4 are then formed
by boring through the two layers 21, 22.
[0215] In the illustration of FIG. 22 the entire filter body 30 is
of a three layer 31, 32, 33 construction. Layer 31 is a structural
layer made from a material such as polyether block amide (PEBAX),
polyester, polyethylene, polyurethane, terephthalate (PET), or
nylon. Layers 32, 33 are coating layers made from a material such
as a hydrophilic, hydrogel, non-thrombogenic, or non-stick
material. Layers 32, 33 may be of the same or different materials.
The holes at the distal end 4 are also lined with the coating
layers 32, 33.
[0216] When coating layers 32, 33 are of different materials, they
are applied to structural layer 31 as follows. A temporary
protective film is first sealed to the outer most surface of layer
31. Then coating layer 33 is applied to the inner most surface of
layer 31 by immersing the body formed by layer 31 in a coating
solution. Excess coating solution is sucked out and the protective
film is removed from the outer most surface of layer 31. Another
temporary protective film is then sealed to the inner most surface
of layer 33. The body formed by layers 31, 33 is completely
immersed in a coating solution. Excess coating solution is drawn
out and the protective film is removed from the innermost surface
of layer 33.
[0217] If the coating layers 32, 33 are of the same material, both
layers 32, 33 may be applied to the structural layer 31 in one step
without the use of protective films.
[0218] In the illustration of FIG. 23 the entire filter body 45 is
of a three layer 46, 47, 48 construction. Layers 46, 47, 48 are
structural layers and layers 47, 48 are of the same material. The
holes at the distal end 4 are also lined with the structural layers
47, 48.
[0219] In the illustration of FIG. 24 the entire filter body 50 is
of a three layer 51, 52, 53 construction. Layers 51, 52, 53 are
structural layers, and in this embodiment layers 52, 53 are of
different materials.
[0220] In the illustration of FIG. 25 the entire filter body 55 is
of a four layer 56, 57, 58, 59 construction. Layers 56, 57 are
structural layers and may be of the same or different materials.
Layers 58, 59 are coating layers and may be of the same or
different materials. The holes at the distal end 4 are also lined
with the coating layers 58, 59.
[0221] Referring to FIG. 26 there is illustrated another filter
element 60 according to the invention, which is similar to part of
the distal section 4 of filter element 2 of FIG. 19. But having no
proximal webbing members thus maximising the size of the inlet
opening.
[0222] FIG. 27 illustrates a filter element 61, which is similar to
the distal section 4 and part of the intermediate section 5 of
filter element 20 of FIG. 21, having the advantages of the laminate
structure previously described, combined with the large inlet
opening of FIG. 26 and the variable distal geometry of FIG. 19
(enabling the filter to accommodate a range of vessel sizes).
[0223] FIG. 28 illustrates a further filter element 65, which
includes a support ring 66 to maintain the intermediate section 5
open to advancing blood flow. Support ring 66 may be arranged
perpendicular to the direction of the blood flow or inclined at an
angle, as illustrated in FIG. 28. The support ring 66 may be of an
elastic, super elastic or shape memory material, and may be either
actuated remotely to appose the vessel wall in a perpendicular or
close to perpendicular position, or fixed in circumference so that
its inclination and shape are controlled by the diameter of the
vessel.
[0224] A different layer structure may be provided at any desired
location of the filter body to achieve required properties.
[0225] Referring now to FIG. 29 there is shown another filter
element according to the invention, indicated generally by the
reference 70. The filter element 70 has a filter body 72 of
generally similar construction to the filter element described
previously, the body having a proximal section 73 and a distal
section 74 interconnected by an intermediate section 75. In this
case, the distal section 74 is of a relatively hard polyurethane
material whilst the proximal section 73 and intermediate section 75
are of a softer grade polyurethane material. A number of
longitudinal ribs 76 are provided around a circumference of the
proximal section 73. Advantageously, this construction facilitates
close engagement of an outer circumference of the proximal section
73 against a vessel wall to minimise the risk of embolic material
bypassing the filter element 70. An internal support frame, as
described above, urges the proximal section 73 outwardly so that it
expands against and closely conforms with the wall of the blood
vessel in which the filter element 70 is mounted in use.
[0226] Conveniently, the corrugations or ribs 76 allow the proximal
section 73 of the filter element 70 to accommodate a wider range of
vessel sizes whilst maintaining good contact between the outer
circumference of the proximal section 73 and the vessel wall and
providing improved filter body integrity.
[0227] Referring to FIG. 30 there is illustrated another filter
element 80 according to the invention. In this case corrugations 81
are provided for improved filter body integrity.
[0228] Referring to FIG. 31 there is illustrated another filter
element 82 according to the invention. In this case the cross
section of the filter element 82 is of a flower petal shape with a
plurality of longitudinally extending ribs 83 for improved
apposition. As explained in reference to FIG. 29, the "petal
shaped" cross section (as for corrugations) increase the
circumference of the filter body, thus enabling the body to be
apposed closely against the vessel wall by a supporting structure
in a wide range of vessel sizes.
[0229] Referring to FIG. 32 there is illustrated another filter
element 85 according to the invention. In this case slits 86 are
provided in the place of the corrugations or "petal shapes" shown
above. The slits 86 enable the body of the filter to conform to a
range of vessel diamters by overlapping and preventing creasing in
small diamater vessels, or allowing the body to expand with the aid
of a supporting structure in larger diameter vessels. In both
instances close engagement of the outer circumference with the
vessel wall is facilitated, thus minimizing the risk of embolic
material bypassing the filter.
[0230] Referring to FIG. 33 there is illustrated another filter
element 88 according to the invention. In this case ribs 89 are
provided to prevent creases forming along the filter element 88 in
the longitudinal direction, and also to allow expansion of the
filter element 88.
[0231] Referring to FIG. 34 there is illustrated a further filter
element 90 according to the invention, which is of a
concertina-like shape with two circumferentially extending grooves
91, 92. This circumferential grooves or ribs have several
advantages. They add to the integrity of the filter body, assisting
it in maintaining its shape in the vessel after deployment. They
inhibit the propagation of creases between the varying diameter
body segments, so that one filter can be designed for a range of
vessel sizes. They enable the filter to extend in length to greatly
increase its effective volume without adding to the length of the
deployed device in use. This provides the benefit of safe retrieval
of large embolic loads as explained with reference to stretchable
membranes below.
[0232] Referring to FIGS. 35(a) to 35(d) there is illustrated
another embolic protection system according to the invention
incorporating a filter element 94 according to the invention which
is similar to those described above. The protection system includes
a guidewire 95 and a retrieval catheter 96 which is advanced over
the guidewire to retrieve the filter containing trapped embolic
material 97. In this case the filter body includes an intermediate
98 and distal 99 membrane, one or both of which are stretchable to
facilitate the retrieval of the captured embolic material 97. The
stretching of the membrane during the retrieval process is
illustrated in FIGS. 35(b) to 35(d).
[0233] The use of such a stretchable filter membrane allows larger
volumes of captured embolic material to be retrieved than would be
possible with a stiffer membrane. This is possible because if a
filter is to be retrieved by withdrawing it into or through a
catheter of a given internal diameter, the maximum volume of
material that can be retrieved is directly proportional to the
length of the filter and the internal diameter of the catheter. The
stretchable membrane allows the filter to increase in length upon
retrieval, thus increasing the space available for retention of
captured embolic material. This is particularly significant in the
case of large volumes of captured embolic material, which will be
more difficult to safely retrieve with a non-stretchable
device.
[0234] The stretchable section may include some or all of the
filter body, and may not necessarily include the distal cone. The
distal cone containing the outlet pores may be formed from a non
stretch material, while the inter mediate filter body is
stretchable. This provides the advantage of filter extension during
retrieval while preventing the problem of release of captured
material through expanding distal pores.
[0235] Another advantage of the stretchable section is that the
crossing profile can be reduced as the filter can be loaded into a
delivery pod in a stretched, rather than bunched or folded,
configuration. This reduces the volume of filter material contained
in any given cross section of the loaded delivery pod.
[0236] In addition the use of a stretchable filter material in the
intermediate section can also be advantageous by providing a
section of the filter body which can be circumferentially expanded
by a support frame to appose the wall of a wide range of vessel
sizes.
[0237] The invention is not limited to the embodiments hereinbefore
described which may be varied in detail.
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