U.S. patent application number 09/824910 was filed with the patent office on 2002-03-14 for temporary vascular filter.
Invention is credited to Finander, Brian V., Kusleika, Richard S..
Application Number | 20020032460 09/824910 |
Document ID | / |
Family ID | 23582456 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020032460 |
Kind Code |
A1 |
Kusleika, Richard S. ; et
al. |
March 14, 2002 |
Temporary vascular filter
Abstract
The present invention provides a method of deploying a medical
filter within a channel in a patient's body and filter systems
which can be used in such a method. Such a filter may include a
radially expandable body 52 having an opening 56 in a proximal
length thereof. In one method, the filter is urged along a length
of the channel with the filter body in a radially reduced
configuration. This body is expanded to substantially fill the
lumen of the vessel and orient the opening in the body proximally.
Body fluid is permitted to enter the filter body through the
proximally oriented opening and pass distally through the distal
length of the body so that the distal length of the body filters
from the body fluid particulate material entrained therein. The
proximal length of the body can be drawn into the retrieval
catheter, thereby effectively closing the proximally oriented
opening within the catheter to retain the particulate material
within the enclosure. In a preferred embodiment, the filter body 52
is formed of a porous, resilient fabric having pores therein and
the proximal opening 56 is at least five times the size of such
pores.
Inventors: |
Kusleika, Richard S.; (Eden
Prairie, MN) ; Finander, Brian V.; (Vadnais Heights,
MN) |
Correspondence
Address: |
Edward S. Hotchkiss
1100 International Centre
900 Second Ave. S.
Minneapolis
MN
55402-3397
US
|
Family ID: |
23582456 |
Appl. No.: |
09/824910 |
Filed: |
April 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09824910 |
Apr 3, 2001 |
|
|
|
09400159 |
Sep 21, 1999 |
|
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Current U.S.
Class: |
606/200 |
Current CPC
Class: |
A61F 2002/018 20130101;
A61F 2230/0006 20130101; A61B 17/221 20130101; A61F 2230/0069
20130101; A61B 2017/2212 20130101; A61F 2/0108 20200501; A61F
2002/016 20130101; A61F 2/013 20130101 |
Class at
Publication: |
606/200 |
International
Class: |
A61M 029/00 |
Claims
What is claimed is:
1. A method of deploying a medical filter within a channel in a
patient's body, the method comprising: a) providing a filter having
a radially expandable body having proximal and distal ends and
defining an enclosure, the body having a distal length and a
proximal length which has an opening therein; and a retrieval
catheter having a lumen with a diameter less than a maximum
dimension of the body's expanded configuration; b) urging the
filter along a length of the channel with the filter body in a
radially reduced configuration; c) radially expanding the body to
its expanded configuration such that it substantially fills the
lumen of the vessel and the opening in the body is oriented
proximally; d) permitting body fluid to enter the enclosure through
the proximally oriented opening and pass distally through the
distal length of the body, the distal length of the body filtering
from the body fluid particulate material entrained therein; and e)
drawing the proximal length of the body within the lumen of the
retrieval catheter, thereby effectively closing the proximally
oriented opening within the catheter to retain said particulate
material within the enclosure.
2. The method of claim 1 wherein the proximal length of the
filter's body tapers proximally to a narrow proximal end which is
smaller than the lumen of the catheter, the step of drawing the
proximal length within the catheter comprising receiving a narrow
proximal end of the body in the lumen of the catheter then
retracting the filter until the internal surface of the catheter
engages the body of the filter distally of the opening to
effectively create a particulate seal therebetween.
3. The method of claim 2 wherein the narrow proximal end of the
body is spaced from a wall of the vessel when the filter is
expanded into its expanded configuration.
4. The method of claim 3 wherein a wall of the catheter is
positioned between the narrow proximal end of the body and the wall
of the vessel as the proximal length of the body is drawn into the
lumen of the catheter.
5. The method of claim 1 wherein a wall of the catheter urges the
filter's body radially inwardly toward said radially reduced
configuration as the body is drawn into the lumen thereof.
6. The method of claim 1 wherein the filter is urged along the
channel in said radially reduced configuration within a deployment
catheter.
7. The method of claim 6 wherein the same catheter is used as both
the deployment catheter and the retrieval catheter.
8. The method of claim 6 wherein the deployment catheter's wall
constrains the filter body in said radially reduced configuration
when the body is received in the lumen thereof, body being radially
expanded by deploying the filter out of the distal end of the
catheter, whereupon the body resiliently expands radially outwardly
upon removal of the constraint.
9. The method of claim 1 wherein the retrieval catheter is held
substantially stationary as the proximal length of the filter's
body is drawn therewithin.
10. The method of claim 1 wherein the proximal length of the
filter's body is drawn into the catheter's lumen by holding the
body substantially stationary and advancing the catheter distally
over the proximal length thereof.
11. The method of claim 1 wherein the filter is carried by a
mandrel, the catheter being advanced along the mandrel prior to
drawing the body of the filter into the lumen thereof.
12. A collapsible filter system comprising: a) a mandrel having a
distal end and a proximal end; and b) a filter carried along the
mandrel, the filter comprising a radially expandable body having a
proximal end and a distal end, the body being formed of a porous,
resilient fabric having pores therein through which a body fluid
may pass, but which restrict passage therethrough of particulate
material entrained in the body fluid; c) a proximally oriented hole
passing through the fabric along a proximal length of the filter's
body, the hole being spaced distally of the proximal end of the
body and being at least about ten times the size of said pores.
13. The medical filter of claim 12 wherein the proximal length of
the body tapers toward the body's proximal end.
14. The medical filter of claim 12 wherein one of the proximal end
and the distal end of the body is secured to the mandrel at a fixed
location therealong while the other end of the body is slidably
carried by the mandrel.
15. The medical filter of claim 12 wherein the proximal end of the
body is secured to the mandrel at a fixed location therealong while
the distal end of the body is slidably carried by the mandrel.
16. The medical filter of claim 12 wherein the mandrel includes a
stop spaced proximally of its distal end and positioned between the
proximal and distal ends of the body, a proximal length of the
mandrel extending proximally of the stop and a distal length of the
mandrel extending distally of the stop.
17. The medical filter of claim 16 wherein the proximal end of the
body is slidably carried along the proximal length of the mandrel
and the distal end of the body is slidably carried along the distal
length of the mandrel, the proximal and distal ends being slidable
along the mandrel independently of one another such that the
distance between the proximal and distal ends can be varied to
effect different configurations of the filter.
18. The medical filter of claim 12 wherein the proximal end of the
body is affixed to the mandrel adjacent a distal end thereof.
19. The medical filter of claim 12 wherein the proximal length of
the filter's body includes a plurality of proximally oriented holes
through the fabric.
20. The medical filter of claim 12 wherein the filter body defines
an enclosure for retaining particulate material therein, the
mandrel extending through the enclosure.
21. The medical filter of claim 20 wherein the enclosure has a
central axis, the mandrel being spaced radially outward from the
central axis and extending closer to one side of the body than to
an opposite side of the body.
22. A method of using the medical filter of claim 12 wherein the
radially expandable body is placed in a radially reduced
configuration for deployment; the body is radially expanded to an
expanded configuration at a treatment site; and a retrieval sheath
is urged distally with respect to the filter, the retrieval sheath
receiving therewithin the proximal length of the filter's body
while engaging a periphery of the body distally of the opening,
thereby effectively closing the proximally oriented opening within
the retrieval sheath.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to filters for body
passageways, and has particular utility in connection with
temporary vascular filters.
BACKGROUND OF THE INVENTION
[0002] Filters can be deployed in channels or vessels in patient's
bodies in a variety of medical procedures or in treating certain
conditions. For example, rotating burrs are used in removing
atheroma from the lumen of patients' blood vessels. These burrs can
effectively dislodge the atheroma, but the dislodged material will
simply float downstream with the flow of blood through the vessel.
Filters can be used to capture such dislodged material before it is
allowed to drift too far downstream, possibly occluding blood flow
through a more narrow vessel.
[0003] Some researchers have proposed various traps or filters for
capturing the particulate matter released or created in such
procedures. However, most such filters generally have not proven to
be exceptionally effective in actual use. These filters tend to be
cumbersome to use and accurate deployment is problematic because if
they are not properly seated in the vessel they can drift to a more
distal site where they are likely to do more harm than good. In
addition, these filters are generally capable of only trapping
relatively large thrombi and are not effective for removing smaller
embolic particles from the blood stream.
[0004] The problems with most temporary filters, which are intended
to be used only during a particular procedure then retracted with
the thrombi trapped therein, are more pronounced. Even if the trap
does effectively capture the dislodged material, it has proven to
be relatively difficult or complex to retract the trap back into
the catheter through which it was delivered without simply dumping
the trapped thrombi back into the blood stream, defeating the
purpose of the temporary filter device. For this reason, most
atherectomy devices and the like tend to aspirate the patient's
blood during the procedure to remove the dislodged material
entrained therein.
[0005] One promising filter design which overcomes many of these
difficulties is shown in International Publication No. WO
96/01591(the publication of PCT International Application No.
PCT/US95/08613), the teachings of which are incorporated herein by
reference. Generally, this reference teaches a trap which can be
used to filter particles from blood or other fluid moving through a
body vessel. In one illustrated embodiment, this trap includes a
basket 270 which can be deployed and retracted through a catheter
or the like, making it particularly suitable for use in minimally
invasive procedures such as angioplasty or atherectomy procedures.
The fact that this trap is optimally carried on a mandrel 260
further enhances its utility as most common angioplasty balloons
and atherectomy devices are used in conjunction with such mandrels.
While this trap is very useful and shows great promise in many
common procedures, it may be possible to better retain the thrombi
collected in the filter during retrieval of the filter.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method of deploying a
medical filter within a channel in a patient's body and devices
which are well suited for use in such procedures. In accordance
with one method of the invention, a filter and retrieval catheter
are provided. This filter has a radially expandable body having
proximal and distal ends and which defines an enclosure. The
expandable body has a distal length and a proximal length which
includes an opening therein. The retrieval catheter has a lumen
with a diameter less than the maximum dimension of the body's
expanded configuration. This filter is urged along a length of the
channel in the patient's body with the filter body in a radially
reduced configuration. The body is radially expanded to its
expanded configuration such that it substantially fills the lumen
of the vessel and the opening in the body is oriented proximally.
Body fluid is permitted to enter the enclosure through this
proximally oriented opening and is permitted to pass through the
distal length of the body. In so doing, the distal length of the
body filters from the body fluid particulate material entrained
therein (assuming, of course, that there is any such particulate
material of an appropriate size). The proximal length of the body
is drawn within the lumen of the catheter, thereby effectively
closing the proximally oriented opening within the retrieval sheath
to retain said particulate material within the enclosure.
[0007] Further refinements of this method are envisioned. For
example, in one embodiment, the filter has a narrow proximal end
which is smaller than the lumen of the catheter. In drawing the
proximal length of the filter within the catheter, this narrow
proximal end may be introduced into the distal end of the
catheter's lumen. The filter may then be retracted until the
internal surface of the catheter engages the body of the filter
distally of the opening to effectively create a particulate seal
therebetween.
[0008] As noted above, the present invention also encompasses a
device well suited for use in such procedures. In one embodiment,
such a device comprises a collapsible filter system including a
mandrel and a filter. The mandrel has proximal and distal ends and
the filter is carried along the mandrel between these ends. The
filter has a radially expandable body having proximal and distal
ends of its own. The body is formed of a porous, resilient fabric
having pores therein through which a body fluid may pass, but which
are small enough to restrict passage of particulate material over a
certain, predetermined size entrained in the body fluid. A
proximally oriented hole passes through the fabric along a proximal
length of the filter's body. This hole is spaced distally of the
proximal end of the body and being at least about five times the
size of said pores.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view of a medical filter in
accordance with one embodiment of the present invention;
[0010] FIG. 2 is a side elevation view of the filter of FIG. 1;
[0011] FIG. 3 is a cross sectional view of the medical filter of
claim 1, taken along line 3-3 of FIG. 2;
[0012] FIG. 4 is a schematic side view in partial cross section
illustrating a filter of an alternative embodiment of the invention
in a radially reduced configuration within a catheter;
[0013] FIG. 5 is a schematic side view illustrating the filter of
FIG. 4 deployed in a vessel in a patient's body;
[0014] FIG. 6 is a schematic side view of the filter of FIGS. 4 and
5 with collected particulate material trapped within the
filter;
[0015] FIG. 7 is a schematic side view of the filter of FIGS. 4-6
drawn far enough into the catheter to effectively close the
proximally oriented opening within the catheter; and
[0016] FIG. 8 is a schematic side view of the filter of FIGS. 4-7
withdrawn completely within the lumen of the catheter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIGS. 1-3 illustrate a filter system 10 in accordance with
one embodiment of the invention. This filter system can be used in
any channel in a patient's body, including blood vessels, the
urinary tract or biliary tract and airways. This filter system 10
is optimally designed to be deployed in a patient's vessel in a
minimally invasive procedure, such as by introducing the filter
system into a blood vessel through a catheter (as described in
greater detail below).
[0018] The filter system 10 of the invention generally includes a
mandrel 20 and a filter 50. Conceptually, the mandrel 20 can be
thought of as having a primary function of positioning and
controlling the deployment of the filter 50 while the filter can be
considered the primary therapeutic or functional element of the
system 10.
[0019] The mandrel 20 should be fairly flexible to allow the device
to be deployed in a curving body passageway without kinking or
otherwise inhibiting suitable deployment of the filter 50. While
the mandrel can be formed of any material having any dimension
suitable for the task for which the filter system 10 is to be
employed, in most circumstances, the mandrel 20 will comprise an
elongate metal wire. In one particularly preferred embodiment, the
mandrel 20 is formed of nitinol, a roughly stoichiometric alloy of
nickel and titanium having excellent "superelastic" properties. The
use of nitinol in medical guidewires and related applications is
well known in the art and need not be discussed in detail here. If
so desired, the distal-most length of the mandrel may include a
flexible helically wound coil 22 extending thereover. The use of
such helical coils to enhance flexibility of the distal tip is well
known in the guidewire art.
[0020] The mandrel 20 shown in FIGS. 1-3 has an enlarged diameter
stop 40 attached thereto. The stop 40 is spaced proximally from the
distal tip 25 of the mandrel 20. Desirably, the stop 40 is spaced
proximally of the proximal end of the helical coil 22 of the
mandrel. This permits the distal slider 60 of the filter 50 to
slide relatively freely and unencumbered along the length of the
mandrel distally of the stop.
[0021] The stop 40 can be formed of any desired material and can be
attached to the mandrel 20 in any desired fashion. The stop should
be attached to the mandrel relatively securely, though, as the stop
will be used to urge the filter 50 within the lumen of the vessel
in which the system 10 is to be deployed. As an example, the stop
40 may comprise a standard radiopaque marker band which has been
securely crimped on the mandrel 20 and/or attached to the mandrel
using an adhesive or solder. The precise length and shape of the
stop 40 is not critical. The drawings illustrate the stop 40 as a
relatively short cylindrical body attached about the circumference
of the mandrel. However, the stop 40 may have a more bulbous shape
and could, in theory, even be formed integrally with the
mandrel.
[0022] The stop 40 effectively divides the mandrel into distal and
proximal lengths. The distal length 30 of the mandrel can be
thought of as that length which extends distally from the stop 40
to the distal tip 25 of the mandrel. Likewise, the proximal portion
35 of the mandrel 20 can be thought of as comprising the length of
the mandrel extending proximally from the stop 40 to the proximal
end of the mandrel.
[0023] The filter 50 shown in FIGS. 1-3 has an elongate, generally
tubular body 52 which extends from a distal slider 60 proximally to
a proximal slider 65. The body 52 of the filter can be formed of
any material suitable for the application at hand. In many
applications, e.g., filtering blood within a patient's vasculature,
the filter body 52 typically comprises a length of a braided
tubular fabric. The use of a tubular braid of nitinol to make
medical devices is described in some detail in International
Publication No. WO 96/01591, the teachings of which were
incorporated above by reference. Briefly speaking though, this
process can employ a tubular braid of a fabric comprising two sets
of nitinol wires wrapped helically about a mandrel, with one set of
wires being wrapped spirally about the mandrel in one direction and
the other set being wrapped in the other direction. This braid is
then placed in contact with a molding surface of a molding element
which defines the shape of the desired functional element. By heat
treating the fabric in contact with the molding surface of the
molding element, one can create a functional element having
virtually any desired shape.
[0024] The body 52 of the filter 50 desirably is made of a fairly
flexible, resilient material. In particular, the filter 52
desirably has a radially expanded configuration, e.g., the shape
shown in FIGS. 1-3, which the device will tend to resiliently
assume in the absence of any countervailing biasing force. A body
52 formed of a nitinol tubular braid which has been heat set into
the desired shape should suit this purpose well.
[0025] In the filter system 10 shown in FIGS. 1-3, the body 52 of
the filter 50 assumes a generally tubular shape having tapered
proximal and distal ends. The maximum outer diameter of the middle
length of the body 52 should be sized to substantially fill the
lumen of a vessel to ensure that the filter will effectively
preclude any emboli (or other particulate material which may be
entrained in the patient's bloodstream) from passing around the
filter.
[0026] The body of the filter includes a distal length 53 and a
proximal length 54, each of which tapers from the middle of the
body's length to their respective ends. In particular, the distal
length 53 tapers distally toward a narrow distal end adjacent the
distal slider 60 while the proximal length 54 of the filter body
tapers toward its proximal end adjacent the proximal slider 65. The
rate of this tapering can be varied as desired. While FIGS. 1-3
illustrate a fairly gradual taper, the change in diameter may be
more abrupt. The filter body 52 of FIGS. 1-3 is also fairly
symmetrical, with the tapers of the proximal and distal lengths
being about the same. In some circumstances it may be advantageous
to have the two lengths taper differently, e.g. where the proximal
length tapers more gradually while the distal length changes
diameter more abruptly.
[0027] The proximal length 54 of the filter body has at least one
proximally oriented opening 56 therein. This opening passes through
the flexible, resilient fabric of which the body 52 desirably is
formed. The fabric has pores therein which allow fluids to pass
therethrough, but the pores are small enough to prevent passage of
particles larger than a predetermined size. If the body is formed
of a metallic tubular braid as mentioned above, the maximum sizes
of these pores can be controlled by adjusting the number of wires
in the braid and the pick and pitch of the braid. For example, if
the filter 50 is to be employed as a vascular filter, a pore size
of 20-1500 microns is desirable. If such a filter body has a
maximum diameter of about 4 mm, it may be formed of 48 wires each
having a diameter of about 0.002 inches (about 50 microns) and a
pick rate of about 90 per inch (about 35 per centimer).
[0028] The size of the proximally oriented opening 56 should be
sufficient to permit body fluid with particulate material entrained
therein to enter the enclosure within the body 52 of the filter. At
a minimum, it is expected that the opening will be at leas five
times the maximum pore size of the fabric of which the body is
formed, with an opening of at least ten times the maximum pore size
being preferred.
[0029] The opening 56 can be formed in any suitable fashion. If the
filter is formed from a preformed flat sheet of fabric wrapped into
the desired shape, the opening can be cut through the fabric before
the fabric is shaped into the filter body. If the body 52 is formed
of a tubular metallic braid, it may instead be cut through the
fabric after the braid is heat set in the desired shape.
[0030] In one particularly preferred method of forming the filter
(which method comprises another embodiment of the invention), a
tubular metal braid is provided. The distal and proximal sliders
60, 65 are attached to the braid a suitable distance from one
another. The braid is trimmed at the distal end of the distal
slider 60 and at the proximal end of the proximal slider 65. A
forming mandrel (not shown) is passed between the wire strands of
the braid and positioned within the tubular braid.
[0031] The forming mandrel has an external molding surface which
generally coincides with the desired shape of the filter body. The
forming mandrel may have a larger diameter than the inner diameter
of the tubular braid and the braid may be drawn down against the
forming mandrel by applying axial tension to the braid. This
structure may be heated at an elevated temperature to heat-set the
filter body 52 in this shape and the forming mandrel may be
removed.
[0032] The forming mandrel includes a proximal projection having a
periphery the size and shape of the desired proximal opening 56.
This projection extends through the wire mesh of the tubular braid
during heat treatment, forcing the wire strands to extend about the
periphery of the projection. As a consequence of the heat
treatment, when the forming mandrel is removed, the wires will
retain the proximal opening without requiring cutting the
fabric.
[0033] In FIGS. 1-3, the filter 50 is shown as having a single
opening 56 extending over only one side of the proximal length 54
of the filter body (i.e., above the mandrel 20 in FIG. 2). To
increase the percentage of body fluid which passes into the
enclosure of the filter body, the number of openings or the shape
of the opening(s) can be adjusted to maximize the cross sectional
area of the vessel covered by the openings. For example, a
plurality of openings can be spaced equiangularly about the
proximal length 54, such as three openings arranged about 120
degrees from one another.
[0034] The opening 56 in FIGS. 1-3 is generally elliptical with a
major axis extending generally in a plane which contains the axis
of the mandrel 20. If one were to increase coverage of the opening
56 by adjusting its shape, the strength of the filter and its
connection to the proximal slider 65 should not be compromised. One
way to accomplish this is to offset the filter 50 with respect to
the mandrel 20. In FIGS. 1-3, the body 52 of the filter is
generally symmetrical about a central longitudinal axis and this
axis generally coincides with the axis of the mandrel. One could
instead make the filter asymmetrical, with the axis of the mandrel
20 spaced radially outwardly from the central axis of the body 52.
In such a design, the mandrel could extend adjacent to one side of
the body and the opposite side of the body would extend farther
from the mandrel. By positioning the opening 56 on the larger side
of the body, the opening can be made larger and cover more of the
cross sectional area of the vessel in which the filter is
deployed.
[0035] While the opening 56 can extend up to or even into the
proximal slider 65, in a preferred embodiment the opening 56 is
spaced distally from the slider 65 and the proximal end of the body
52. This will enable a more secure connection between the slider 65
and the body. The distal end of the opening desirably terminates
proximally of the location where the filter body has its maximum
diameter. This will minimize the chance that body fluid could slip
between the filter and the wall of the vessel in which the filter
is deployed. This will also provide a more effective seal between
the filter body 52 and the catheter in which it is retrieved. (Such
retrieval is discussed below in connection with FIGS. 7 and 8.)
[0036] The filter 50 is attached to or carried by the mandrel 20 by
means of a proximal slider 65 attached to the body 52 adjacent its
proximal end and a distal slider 60 attached adjacent the distal
end of the body 52. The distal slider 60 should be free to slide
along at least a proximal portion of the distal length 30 of the
mandrel while the proximal slider 65 should be free to slide along
at least a distal portion of the proximal length 35 of the mandrel.
In use, the stop 40 of the mandrel effectively defines a limit on
the range of motion of these sliders 60, 65.
[0037] While each of the sliders 60, 65 should be slidable along
its respective length of the mandrel, the sliders can take any
desired shape. In the illustrated embodiments, each slider
comprises a relatively thin ring which is carried about the
mandrel. The thin ring can be attached to the body 52 in any
desired fashion, such as by crimping or swaging the fabric of the
body between two layers of the ring or soldering, welding or
otherwise adhering the fabric to the ring.
[0038] The stop 40 of the mandrel is positioned within the body 52
of the filter and is not exerting any biasing force on either of
the sliders 60, 65. In this configuration, the mandrel 20 can be
moved proximally and distally with respect to the filter 50 without
substantially affecting the shape or position of the filter. The
limits of this range of free movement of the mandrel with respect
to the filter are generally defined by the relationship between the
stop 40 and the sliders 60, 65. In particular, the mandrel can be
moved from a distal position wherein the stop 40 abuts but does not
exert any force on the distal slider 60 and a proximal position
wherein the stop 40 abuts, but does not exert any significant force
on, the proximal slider 65. This allows the filter 50 (or any other
functional element which is carried by the mandrel) to be fairly
precisely positioned within a patient's vessel and retain that
position even if the guidewire is moved slightly during use. This
can be advantageous in circumstances where other devices are
exchanged over the guidewire (e.g., during angioplasty and
atherectomy procedures).
[0039] The inner diameter of the generally annular collars defining
the sliders 60, 65 is desirably larger than the outer diameter of
the mandrel, but should be smaller than the outer diameter of the
stop 40. In this fashion, the stop serves as an effective limit on
proximal movement of the distal slider 60 and distal movement of
the proximal slider 65. Apart from this relationship with the
slider 40 and the fact that both sliders are indirectly linked to
one another by the body 52 of the filter, the proximal and distal
sliders are slidable along the mandrel essentially independently of
one another.
[0040] When the mandrel 20 is urged distally (to the left in FIGS.
2 and 3) against the distal slider 60, the stop will exert a distal
biasing force against the distal end of the body 52 of the filter.
In theory, if the filter were used in a frictionless environment,
the filter would travel with the mandrel without any appreciable
alteration in the shape of the body 52. In most clinical
applications, though, this is not the case. Instead, there is
typically some force restraining completely free movement of the
filter within the channel of the patient's body. Typically (and as
suggested in FIGS. 5 and 6, for example), the body 52 of the filter
will resiliently expand into physical contact with the interior
surface of the vessel within which it is deployed. This contact
with the vessel wall will tend to hold the filter 50 in place as
the stop of the mandrel slides proximally and distally between the
two sliders 60, 65. When the mandrel is urged distally until it
exerts a distal force against the distal slider 60, this force will
tend to axially elongate the body 52.
[0041] Resilient tubular braids tend to assume a radially reduced
profile upon axial elongation. (This property and some of its
implications are discussed in International Publication No. WO
96/01591, mentioned previously.) As a consequence, when the mandrel
20 is urged distally to push distally against the distal slider 60,
this distal force acts against the restorative force of the
resilient braid, which would otherwise bias the braid into its
expanded configuration (FIGS. 1-3). By overcoming this restorative
force with a countervailing distal force, the body 52 will tend to
both axially elongate and assume a radially reduced profile. This,
in turn, reduces the force with which the body engages the wall of
the vessel or catheter in which the filter is positioned and
reduces friction between the filter 50 and the vessel or catheter.
Hence, urging the mandrel distally to move the filter 50 distally
will, at the same time, reduce friction between the filter and the
vessel wall to further facilitate advancement of the filter along
the vessel's lumen. This requires less force to push the filter
distally, enabling the mandrel to be smaller and reducing the outer
diameter of the collapsed device, making deployment in smaller
vessels feasible. In addition, the reduced friction between the
filter and the vessel wall limits damage to the intima of the
vessel, permitting the filter to be deployed and moved with a
minimum of trauma.
[0042] When the mandrel is retracted proximally, the stop 40 of the
mandrel will abut against, and exert a proximal biasing force on,
the proximal slider 65 of the filter 50. This proximal biasing
force will act against the restorative force of the body 52 to
axially elongate and radially reduce that body. This permits the
device to be withdrawn proximally along the lumen of the vessel
either for repositioning at a more proximal location or for
withdrawal from the patient's body at the end of the procedure.
[0043] In the embodiment of FIGS. 1-3, the proximal and distal
sliders 60, 65 are free to move relatively independently of one
another, limited primarily by their indirect link to one another
through the body 52 of the filter. For example, when the mandrel 20
is urged distally against the distal slider 60 (FIG. 4), the
proximal slider will slide proximally along the proximal length 35
of the mandrel. Similarly, when the mandrel is withdrawn proximally
to urge proximally against the proximal slider 65, the distal
slider will be free to drift distally along the distal length 30 of
the mandrel. Ideally, there should be a sufficient distance between
the distal shoulder of the stop 40 and the proximal end of the
helical coil 22 at the distal end of the mandrel.
[0044] FIGS. 4-8 schematically depict one method of the invention
utilizing an alternative filter design. Most of the elements of the
filter 50' in FIGS. 4-8 are essentially the same as like elements
in FIGS. 1-3, so the same reference numbers have been used for most
elements in both sets of drawings. The primary differences between
the filter 50' of FIGS. 4-8 and the filter 50 described above is
that the stop 40 has been omitted in FIGS. 4-8 and the proximal
slider 65' has been secured to the mandrel 20 at a fixed location.
The distal slider 60 remains free to slide along the mandrel.
[0045] The body 52' of the filter 50' is shaped a little
differently from the filter body 52 of FIGS. 1-3. This difference
is not crucial and does not yield significantly different
properties. Instead, the differences in the fully deployed shapes
of the two filters 50, 50' are intended to highlight that the shape
can vary without compromising the filter's function.
[0046] FIG. 4 schematically illustrates the filter 50' collapsed
within the lumen of a catheter C. The body 52' of the filter has
been collapsed under the biasing force of the catheter walls into
an axially elongated, radially reduced configuration. This catheter
and filter combination may be advanced through a patient's body as
a unit until a specific treatment site has been reached, but this
combined unit may be dificult to steer through a more tortuous
path. For many applications (e.g., deployment at a remote site
within a patient's vasculature), the catheter will first be
positioned adjacent the treatment site. Only then will the filter
system be introduced into the distal end of the catheter C and
urged along the catheter's lumen and the vessel V until the distal
end 25 of the mandrel and the distal slider 65 are positioned
adjacent the distal end of the catheter, as shown in FIG. 4.
[0047] Regardless of how the system reaches the state illustrated
in FIG. 4, once the catheter is in place the filter 50' can be
deployed out the distal end of the catheter. In particular, the
filter 50' may be urged out of the distal end of the catheter,
e.g., by holding the catheter C still and urging the mandrel 20
distally or by holding the mandrel 20 stationary and withdrawing
the catheter C proximally.
[0048] Upon exiting the distal end of the catheter C, the flexible
body 52 will resiliently expand radially outwardly, desirably until
it engages the wall of the vessel V or, less desirably, is
positioned adjacent to the vessel wall. (Such a configuration is
shown in FIG. 5.) This will help ensure that all fluid passing
along the vessel V will have to pass through the filter body
52'.
[0049] A substantial portion (ideally, all or at least a vast
majority) of the body fluid in the vessel should pass through the
proximally oriented opening 56 in the filter body. Since the
opening is fairly large, it is anticipated that any particulate
material entrained in the body fluid travelling through the vessel
will enter the interior of the filter through the opening 56. The
pores in the distal length 53 of the filter body are significantly
smaller, though, so most oversized particles will be trapped within
the enclosure of the filter body. FIG. 6 schematically depicts such
a situation, with a number of individual particles P being shown
trapped within the filter body. If the filter 50 or 50' is to be
used in a vascular procedure, the pores should be large enough to
permit red blood cells to pass therethrough, but small enough to
trap thrombi or emboli above a certain predetermined size.
[0050] A wide variety of vascular filters are known in the art and
thee with which such filters can be deployed varies. One of the
primary distinguishing characteristics between these various filter
designs is the ease with which the filters can be withdrawn from or
repositioned within the patient's body. For example, most
commercially available vena cava filters are provided with sharp
barbs or other structures which firmly seat the devices in a wall
of the vessel, but which effectively preclude retraction of the
device. Temporary filters avoid such tenacious attachments to the
vessel wall, permitting them to be retracted or moved after initial
deployment. As noted above, though, one of the primary difficulties
encountered in using such temporary filters is the risk of dumping
the captured particulate material back into the vessel from which
it was filtered. Many designs require that the physician first
aspirate the particulate material or, in the case of thrombi
captured in vascular procedures, use drugs which help break down
the particles to clinically acceptable sizes.
[0051] International Publication No. WO 96/01591, mentioned
previously, provides a particularly useful filter. This filter,
which may be generally dome-shaped and have a proximally-facing
lip, enables a physician to close the filter prior to retraction,
keeping the captured particles within the filter during removal or
repositioning. Unfortunately, this design is mechanically complex.
In one embodiment disclosed therein, the filter is provided with a
drawstring which can be used to draw the proximal edge of the
filter down toward the wire on which it is carried, minimizing the
risk of losing the particles. A second design proposed in this
reference employs a separately deployable cover which can be
brought into sealing engagement with the filter. While this may
further reduce the risk of dumping particles back into the vessel,
the increased mechanical complexity makes it difficult to provide a
highly reliable, cost-effective device.
[0052] The present invention provides an elegant solution to these
difficulties which minimizes mechanical complexity and promises to
provide very effective containment of filtered particles. FIG. 7
shows the filter 50' of FIGS. 4-6 partially retracted into the
catheter C. If the filter is being used for only a short period of
time, the catheter C may be the same catheter used to initially
deploy the filter in the vessel. If the filter is to be left in
place for a longer period of time, though, it may be preferred to
remove the deployment catheter (FIG. 4) from the patient's body and
later introduce a separate retrieval catheter by advancing-the
retrieval catheter along the mandrel 20.
[0053] The lumen of the retrieval catheter C in FIG. 7 has a
diameter smaller than the maximum cross-sectional dimension of the
body's expanded configuration. The lumen is larger than the narrow
proximal end of the filter body 52' adjacent the proximal slider
65', though, and the illustrated filter body is spaced from the
vessel wall about its entire periphery. As a consequence, the
distal tip of the catheter can be positioned between the proximal
end of the body 52' and the wall of the vessel V before the
catheter engages the body of the filter adjacent the slider. This
can be done by holding the catheter in place and withdrawing the
mandrel proximally, by holding the mandrel stationary and moving
the catheter distally, or moving both the catheter and the
mandrel.
[0054] Once the proximal end of the body 52' is introduced into the
catheter's lumen, the rest of the body can be drawn into the lumen
of the catheter. Again, the body can be drawn into the catheter by
advancing the catheter distally or retracing the filter proximally.
At some point, the wall of the catheter C will engage the larger
diameter body 52. Ideally, the lumen of the catheter is notably
smaller than the deployed diameter of the filter body. As shown in
FIG. 7, in this case the walls of the catheter will exert a biasing
force to urge the body toward the radially reduced configuration in
which it was initially deployed (FIG. 4).
[0055] Perhaps more importantly, though, the internal surface of
the catheter engages the body of the filter distally of the
filter's proximally oriented opening 56. While the opening may
still be open to the lumen of the catheter, the engagement between
the filer body and the catheter wall distally of the opening
effectively creates a particulate seal therebetween. As a
consequence, simply by advancing the catheter C with respect to the
filter 50', one can seal within the combined catheter and filter
all of the captured particles above the predetermined minimum size.
This combination can then be moved as a unit either to remove it
from or reposition it within the patient's body with minimal risk
of losing any of the captured particles.
[0056] If the filter is to be completely withdrawn from the vessel,
it is preferred that the filter body 52' be completely withdrawn
into the lumen of the catheter (as shown in FIG. 8) rather than
leaving a distal section of the filter extending out of the
catheter (as shown in FIG. 7). This will reduce friction against
the vessel wall, making withdrawal easier and reducing trauma to
the intima of the vessel.
[0057] While a preferred embodiment of the present invention has
been described, it should be understood that various changes,
adaptations and modifications may be made therein without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *