U.S. patent application number 12/035865 was filed with the patent office on 2008-06-12 for implantable electrode assembly having reverse electrode configuration.
This patent application is currently assigned to CVRx, Inc.. Invention is credited to Mary L. Cole, Jeffrey J. Hagen, Martin A. Rossing.
Application Number | 20080140167 12/035865 |
Document ID | / |
Family ID | 37432180 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080140167 |
Kind Code |
A1 |
Hagen; Jeffrey J. ; et
al. |
June 12, 2008 |
IMPLANTABLE ELECTRODE ASSEMBLY HAVING REVERSE ELECTRODE
CONFIGURATION
Abstract
Methods and apparatus for generating an electric field inside a
patient include at least a first electrode and a second electrode
on a common implantable substrate. Each of the electrodes has a
respective proximal end and a respective distal end. Electrical
energy can be applied that causes electrical current to flow
simultaneously through the first and second electrodes
preferentially from the proximal end of one electrode to the distal
end of the other electrode.
Inventors: |
Hagen; Jeffrey J.;
(Plymouth, MN) ; Cole; Mary L.; (St. Paul, MN)
; Rossing; Martin A.; (Coon Rapids, MN) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
CVRx, Inc.
Minneapolis
MN
|
Family ID: |
37432180 |
Appl. No.: |
12/035865 |
Filed: |
February 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11133741 |
May 19, 2005 |
|
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|
12035865 |
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Current U.S.
Class: |
607/116 |
Current CPC
Class: |
A61N 1/0556 20130101;
A61N 1/3956 20130101; A61N 1/05 20130101 |
Class at
Publication: |
607/116 |
International
Class: |
A61N 1/05 20060101
A61N001/05 |
Claims
1. A method of generating an electric filed inside a patient, the
method comprising: providing at least a first electrode and a
second electrode on a common implantable substrate, wherein each of
the first and second electrodes has a respective proximal end and a
respective distal end, wherein the proximal end of the first
electrode is positioned closer to the distal end of the second
electrode than to the proximal end of the second electrode, wherein
the proximal end of the second electrode is positioned closer to
the distal end of the first electrode than to the proximal end of
the first electrode; implanting the implantable substrate inside
the patient; and applying electrical energy across the first and
second electrodes to cause electrical current to flow
simultaneously through the first and second electrodes
preferentially from the proximal end of one electrode to the distal
end of the other electrode.
2. The method of claim 1, and further comprising: implanting the
implantable electrode assembly such that each cathode electrode is
coupled to at least one anode electrode via electrically conductive
target tissue.
3. The method claim 2, wherein the target tissue provides a
generally uniform coupling along the lengths of the coupled
electrodes.
4. The method of claim 1, and further comprising: establishing a
generally uniform current density substantially through the length
of each electrode.
5. The method of claim 1, wherein the step of applying electrical
energy causes electrical current to flow preferentially from the
proximal end of the first electrode to the distal end of the second
electrode and preferentially from the distal end of the first
electrode to the proximal end of the second electrode.
6. An electrode assembly comprising: a generally flexible base
having a first surface region and an axially spaced-apart second
surface region; and at least three generally parallel elongate
electrode structures secured and axially aligned over a surface of
the base, each electrode structure having a proximal end and a
distal end; wherein an outer pair of the electrode structures is
electrically isolated from an inner electrode structure; wherein
the proximal ends of the outer pair of electrode structures and the
distal end of the inner electrode structure are disposed on the
first surface region of the vase, and the distal ends of the outer
electrode structures and the proximal end of the inner electrode
structure are disposed on the second surface region of the base
that is separate from the surface region.
7. The electrode assembly of claim 6, wherein the conductive lends
electrically coupled to the outer electrode structures are
electrically coupled to a first pole of an electrical signal
generator, and the conductive lead electrically coupled to the
inner electrode structure is electrically coupled to a second pole
of the electrical generator.
8. The electrode assembly of claim 6, wherein the base is adapted
to be attachable to an outside surface of a blood vessel.
9. The electrode assembly of claim 6, wherein the base includes a
plurality of finger-type extensions for facilitating securing the
base to target tissue.
10. The electrode assembly of claim 6, wherein each electrode
structure has a generally uniformly distributed impedance along its
length.
11. The electrode assembly of claim 6, wherein each electrode
structure includes a coiled portion adapted to make contact with
target tissue.
12. The electrode assembly of claim 6, wherein the electrode
structures are aligned to facilitate transmission of a generally
uniformly distributed electric field through target tissue situated
between the electrode structures.
13. An electrode assembly adapted for implantation at an
electrotherapy site in a patient, the electrode assembly
comprising: a substrate; and at least three elongate electrodes
secured to the substrate and electrically coupled to the
electrotherapy site, each electrode having a proximal end connected
to an electrically conductive lead and a distal end not connected
to a lead or other electrode; wherein a generally uniform charge
density is generated between an outer pair of the at least three
electrodes and an inner electrode when an electrical current is
applied to the electrodes.
14. The electrode assembly of claim 13, wherein the proximal ends
of the outer electrode structures and the distal end of the inner
electrode structure are disposed on the first surface region of the
base, and the distal ends of the outer electrode structures and the
proximal end of the inner electrode structure are disposed on the
second surface region of the base that is separate from the first
surface region.
15. The electrode assembly of claim 14, and further comprising: a
remote electrotherapy signal generator circuit electrically coupled
with the at least three electrodes and supplying electrotherapy
signaling to the electrotherapy site via the at least three
electrodes; and wherein at least the outer pair of the electrodes
is electrically coupled at the proximately situated region with a
lead to s first pole of the electrotherapy signal generator, and an
inner one of the electrodes is electrically coupled at the distally
situated region with a lead to a second pole of the electrotherapy
signal generator.
16. The electrode assembly of claim 14, wherein the at least three
electrodes include at least one anode and at least one cathode; and
wherein the at least one cathode is electrically coupled with at
least one corresponding lead at the proximally situated region, and
the at least one anode is electrically coupled with at least one
corresponding lead at the distally situated region.
17. The electrode assembly of claim 13, wherein the at least three
electrodes are situated generally coextensively.
18. An electrotherapy arrangement implanted at an electrotherapy
site, the electrotherapy arrangement comprising: an electrode
assembly, including: a substrate; and at least three adjacent
elongate electrodes secured to the substrate and electrically
coupled to the electrotherapy site, wherein each electrode is
situated such that proximal and distal ends of each successive
adjacent electrode's ends are longitudinally opposing; and an
electrotherapy signal generator circuit electrically coupled with
the at least three electrodes and applying electrotherapy signaling
to the electrotherapy site via the at least two electrodes; wherein
the electrotherapy signaling generates an electric field through
the electrotherapy site that is generally uniformly distributed
along a longitudinal reference axis located in the electrotherapy
site between an anode and a cathode of the at least three
electrodes.
19. The electrotherapy arrangement of clam 18, wherein the
electrotherapy signaling is adapted to stimulate baroreceptors.
20. The electrotherapy arrangement of claim 18, wherein the
electrotherapy signaling is adapted to stimulate at least one
nerve.
21. The electrotherapy arrangement of claim 18, wherein the
electrotherapy signaling is adapted to stimulate muscle tissue.
22. A method of generating an electric field inside a patient, the
method comprising: providing at least a first electrode, a second
electrode and a third electrode on a common implantable substrate,
wherein each of the first, second and third electrodes has a
respective proximal end and a respective distal end, wherein the
proximal end of the first electrode is positioned closer to the
distal end of the second electrode than to the distal end of the
second electrode than to the proximal end of the second electrode,
wherein the proximal end of the second electrode is positioned
closer to the distal end of the first electrode than to the
proximal end of the first electrode; implanting the implantable
substrate inside the patient; and applying electrical energy across
the first, second and third electrodes to cause electrical current
to flow simultaneously through the first and second electrodes
preferentially from the proximal end of one electrode to the distal
end of the other electrode and across the third electrode
preferentially from the proximal end of the third electrode to the
distal end of the second electrode and from the distal end of the
third electrode to the proximal end of the second electrode.
23. The method of claim 22, and further comprising: implanting the
implantable electrode assembly such that each cathode electrode is
coupled to at least one anode electrode via electrically conductive
target tissue.
24. The method of claim 23, wherein the target tissue provides a
generally uniform coupling along the lengths of the coupled
electrodes.
25. The method of claim 22, and further comprising: establishing a
generally uniform current density substantially through the length
of each electrode.
26. An electrode assembly comprising: a first electrode having a
first arcuate shape; and a second electrode having a second arcuate
shape; and wherein the second electrode at least partially
encircles the first electrode.
27. The electrode assembly of claim 26, further comprising: a third
electrode having a third arcuate shape; and wherein the third
electrode at least partially encircles the first and second
electrodes.
28. The electrode assembly of claim 27, wherein the second
electrode is electrically insulated from the first and third
electrodes.
29. The electrode assembly of claim 26, wherein the first and third
electrodes are electrically connected to one another.
30. The electrode assembly of claim 26, wherein each electrode
comprises a coil.
31. The electrode assembly of claim 26, wherein each electrode is
disposed on a common implantable substrate.
32. The electrode assembly of claim 26, wherein one of the
electrodes is electrically insulated from the other two
electrodes.
33. The electrode assembly of claim 26, wherein one of the
electrodes is electrically connected to one of the other two
electrodes.
34. The electrode assembly of claim 26, wherein each electrode has
a first end and a second end.
35. The electrode assembly of claim 26, further comprising a lead
electrically connected to a first end of the first electrode.
36. The electrode assembly of claim 26, further comprising a lead
electrically connected to a second end of the second electrode.
37. The electrode assembly of claim 26, further comprising a lead
electrically connected to a first end of the third electrode.
38. The electrode assembly of claim 26, further comprising an
electrotherapy signal generator electrically connected to at least
the first electrode and the second electrode, and delivering an
electrotherapy signal thereto.
39. The electrode assembly of claim 38, wherein a generally uniform
electric field is generated between the electrodes when the
electrotherapy signal is delivered thereto.
40. The electrode assembly of claim 38, wherein a generally uniform
current density is generated in a tissue when the electrodes are
placed in contact with the tissue and the electrotherapy signal is
delivered to the electrodes.
41. A method of generating an electric field inside a patient, the
method comprising: electrically contacting a target tissue of the
patient with a first electrode; electrically contacting the target
tissue along an arcuate path of a second electrode that least
partially encircles the first electrode; and applying electrical
energy across the first and second electrodes to establish a
generally uniform current density between the first and second
electrodes.
42. The method of claim 41, further comprising electrically
connecting the first electrode and the second electrode to a signal
source.
43. The method of claim 41, wherein contacting the target tissue
with the first electrode comprises contacting an exterior surface
of a wall of a blood vessel with the first electrode.
44. The method of claim 41, wherein the first electrode is fixed to
a flexible substrate and the method comprises conforming the
flexible substrate to the exterior surface of the wall of the blood
vessel.
45. The method of claim 41, further comprising delivering a signal
to the wall of the blood vessel to cause a change in the
patient.
46. The method of claim 45, wherein the change comprises a change
in blood pressure.
47. The method of claim 46, wherein the change comprises a
reduction in blood pressure.
48. The method of claim 45, wherein the change comprises an
increase in parasympathetic nervous system activity.
49. The method of claim 45, wherein the change comprises a decrease
in sympathetic system activity.
50. The method of claim 45, wherein the change comprises a change
in a radio of sympathetic nervous system activity to
parasympathetic nervous system activity.
51. The method of claim 45, wherein the change occurs in cells in
the wall of the blood vessel.
52. The method of claim 45, wherein the change occurs in nerve
fibers in the wall of the blood vessel.
53. The method of claim 45, wherein the change comprises a change
in receptors in the wall of the blood vessel.
54. The method of claim 53, wherein the change comprises a change
in baroreceptors in the wall of the blood vessel.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 11/122,741 (Attorney Docket No.
021433-001700US) filed May 19, 2005, the full disclosure of which
is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The invention relates generally to medical devices and
methods, and more particularly, to implantable electrodes for
applying electrotherapy/electrostimulation that utilizes at least a
pair of electrodes employing a reverse electrode configuration.
[0003] Implantable electrode assemblies for electrotherapy or
electrostimulation are well-known in the art. For example, various
configurations of implantable electrodes are described in U.S.
Patent Publication No. U.S. 2004/0010303, which is incorporated
herein by reference in its entirety. One type of electrode assembly
described therein is a surface-type stimulation electrode that
generally includes a set of generally parallel elongate electrodes
secured to, or formed on, a common substrate or base. Prior to
implantation in a patient, the electrodes are generally
electrically isolated from one another. Once the electrode assembly
is implanted, one or more of the electrodes are utilized as a
cathode(s), while one or more of the remaining electrodes are
utilized as an anode(s). The implanted cathode(s) and anode(s) are
electrically coupled via the target region of tissue to be treated
or stimulated.
[0004] One example of an application for this type of electrode
assembly is for implantation onto a surface of tissue to be the
target for electrotherapy or electrostimulation. The target tissue
may have an irregular or complex shape, such as the outer surface
of a blood vessel. The base or substrate and the electrodes of the
electrode assembly can be sufficiently flexible to conform to the
shape of the target tissue while maintaining a particular relative
positioning of the electrodes. The geometry of the electrode
assembly can be especially adapted for implantation at a particular
site. For example, an electrode assembly can be sized and shaped to
be implanted around the outside of the vascular wall such that the
electrotherapy or electrostimulation can be focused on a particular
target region.
[0005] One known problem associated with state of the art
implantable electrode arrangements of certain geometries is their
tendency to produce non-uniform electric fields or currents in the
target region under certain conditions. An example of such a
condition is when the implantation site has a low enough impedance
to approach that of the electrode materials. In such cases, the
internal resistance of the implanted electrodes becomes a
significant parameter in the electrical/electromagnetic model of
the implanted electrode arrangements. This problem can become
pronounced in electrode arrangements in which the size of the
electrodes approaches or exceeds the general size of the target
region, or in arrangements in which the electrodes have structural
geometries other than merely point electrodes.
[0006] Non-uniformity of electric field in the target region can
result in sub-optimal electrotherapy or electrostimulation. Another
consequence that occurs when the surface regions of implanted
electrodes operate with disparate charge densities is an increased
susceptibility of the electrodes to corrosion. Because corrosion is
a charge density based phenomenon, increased concentrations of
charge carriers in certain regions of the electrodes tends to focus
faradaic processes responsible for corrosion at those regions.
[0007] In U.S. Pat. No. 5,265,623, a defibrillation catheter is
described having generally linear electrode geometries (elongate
helical or spiral coils) that, when implanted, are both situated
generally longitudinally in the heart. The electrodes of the
defibrillation catheter are connected to the defibrillation energy
source from a center point of each electrode, rather than at the
ends thereof. This arrangement is intended to provide an improved
field distribution around the catheter electrode and avoid high
current densities at the electrode ends. The arrangement
nevertheless operates with a charge density gradient in each
electrode due to the construction and relative positioning of the
electrodes. Thus, the applied electric signaling is not likely to
be uniform along the length of the electrodes. Furthermore, the
multi-layer or multi-axial construction of the disclosed catheter
requires a complex and relatively expensive fabrication process.
Moreover, the catheter electrode assembly is not suitable for the
surface-type of implantation applications described above.
[0008] While techniques have been developed to improve the
distribution of electric field densities with respect to axial
defibrillation electrode leads, it would be desirable to provide
designs for implantable electrodes that improve the distribution of
electrical field densities with respect to surface-type implantable
electrodes.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention provides methods and apparatus for
generating an electric field inside a patient that enhances the
effective distribution of the density of the electric field. In one
embodiment, at least a first and a second electrode are arranged on
a common implantable substrate such that a proximal end of the
first electrode is closer to a distal end of the second electrode
and vice-versa. The electrodes are arranged and electrically
connected to an energy source via the proximal ends such that when
electrical energy is applied across the first and second
electrodes, electrical current preferentially flows simultaneously
through the first and second electrodes from the proximal end of
one electrode to the distal end of the other electrode. In one
aspect of the invention, the first and second electrodes are
situated proximate a surface of tissue to be stimulated such that
the electrodes are generally uniformly electrically coupled along
their lengths via the tissue.
[0010] A method of evenly distributing an electric field between at
least a pair of implanted electrodes according to another aspect of
the invention includes providing an implantable electrode assembly
that includes at least two electrodes on a common substrate,
wherein each electrode has an elongate shape and is situated
generally equidistantly along its length from at least one of the
other electrodes in a configuration where the proximal and distal
ends of the electrodes are reversed between an anode and a cathode.
Electrical energy is applied through the at least two electrodes
such that a generally uniform current density is established
between the anode and the cathode.
[0011] An electrode assembly according to another aspect of the
invention includes a generally flexible base and at least three
generally parallel elongate electrode structures secured over a
surface of the base, each electrode structure having a proximal end
and a distal end. An outer pair of the electrode structures is
electrically isolated from an inner electrode structure, and the
proximal end of each electrode structure is electrically coupled to
a conductive lead adapted to carry electrical energy. The proximal
ends of the outer electrode structures and the distal end of the
inner electrode structure are proximately situated at a first
surface region of the base, and the distal ends of the outer
electrode structures and the proximal end of the inner electrode
structure are proximately situated at a second surface region of
the base that is separate from the first surface region.
[0012] Another aspect of the invention is directed to an electrode
assembly implanted at an electrotherapy site in a patient, the
electrode assembly comprising a substrate; at least two elongate
electrodes secured to the substrate and electrically coupled to the
electrotherapy site, each electrode having opposing ends proximally
and distally situated; and an electrotherapy signal generator
circuit electrically coupled with the at least two electrodes and
supplying electrotherapy signaling to the electrotherapy site via
the at least two electrodes. The electrical coupling facilitates a
generally uniform charge density in the at least two
electrodes.
[0013] An electrotherapy arrangement implanted at an electrotherapy
site according to another aspect of the invention comprises an
electrode assembly that includes a substrate; and at least two
elongate electrodes secured to the substrate and electrically
coupled to the electrotherapy site, wherein each electrode is
situated such that its proximal ends are longitudinally opposing.
The electrotherapy arrangement further comprises an electrotherapy
signal generator circuit electrically coupled with the at least two
electrodes and applying electrotherapy signaling to the
electrotherapy site via the at least two electrodes. The
electrotherapy signaling generates an electric field through the
electrotherapy site that is generally uniformly distributed along a
longitudinal reference axis located in the electrotherapy site
between the anode and cathode of the at least two electrodes.
[0014] According to another aspect of the invention, an implantable
electrode assembly includes an implantable substrate and three
elongate electrodes secured to the substrate. Each electrode has
respective proximal and distal opposing ends, and the electrodes
are relatively situated such that each electrode is generally
uniformly spaced along its length with respect to its adjacent
electrode(s). The electrodes are also relatively spaced such that
an inner electrode is flanked on two sides by a pair of outer
electrodes. A first lead is connected to the inner electrode at the
inner electrode's proximal end positioned on one side of the
substrate, and second and third leads are connected to the outer
electrodes at the respective proximal ends positioned on an
opposite side of the substrate. In one embodiment, each of the
leads for the outer electrodes are positioned on one side and the
lead for the inner electrode is positioned on the opposite
side.
[0015] In an alternate embodiment, all of the leads are arranged on
one side and a portion of the lead to the inner electrode is routed
across the substrate within an insulator for the distal end of the
lead to connect to the proximal end of the electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0017] FIG. 1A is a top-view diagram illustrating an electrode
assembly according to one embodiment of the present invention.
[0018] FIG. 1B is a diagram illustrating one physical embodiment of
the electrode assembly of FIG. 1A.
[0019] FIG. 1C is a top-view diagram illustrating an electrode
assembly having a particular wiring arrangement according to one
embodiment of the invention.
[0020] FIG. 1D is a perspective view diagram illustrating an
example physical layout of the electrode assembly of FIG. 1C in
which the lead connecting one of the electrodes to the signal
generator runs along the bottom surface of the substrate.
[0021] FIG. 1E is a perspective view diagram illustrating another
example physical layout of the electrode assembly of FIG. 1C in
which at least one of the electrodes is formed around a portion of
the lead connected with the electrode.
[0022] FIG. 1F is a perspective view diagram illustrating one
example physical embodiment of a coiled outer electrode structure
formed around an inner coiled lead portion that is connected to the
electrode at a proximal end.
[0023] FIG. 1G is an end-view diagram of the electrode structure of
FIG. 1F.
[0024] FIG. 1H is a perspective view diagram illustrating another
example physical embodiment of a coiled outer electrode structure
formed around an inner coiled lead portion that is connected to the
electrode at a proximal end, in which an insulator is positioned
between the outer electrode and inner conductor portion.
[0025] FIG. 1i is a side-view diagram illustrating an example
coiled electrode structure of the type illustrated in FIG. 1H, in
which the outer and inner coils are generally helical in geometry
and in which the insulator is generally cylindrical in
geometry.
[0026] FIG. 1J is a side view diagram illustrating an example
coiled electrode structure of the type illustrated in FIG. 1H, in
which the inner coil has a spiral geometry wherein coil radius
decreases towards the proximal end, and in which the insulator has
a geometry wherein the walls have a profile of decreasing radius
that corresponds to the decreasing radius profile of the inner
coil.
[0027] FIG. 1K is a cross-sectional view diagram of the electrode
structure of FIG. 1J.
[0028] FIG. 2 is a schematic diagram illustrating functional
aspects of electrode assemblies known in the art.
[0029] FIG. 3 is a chart illustrating the current distribution
through target tissue during operation of the electrodes
represented in the schematic of FIG. 2.
[0030] FIG. 4 is a schematic diagram illustrating functional
aspects of an electrode assembly according to one embodiment of the
present invention.
[0031] FIG. 5 is a chart illustrating the current distribution
through target tissue during operation of the electrodes
represented in the schematic of FIG. 4.
[0032] FIG. 6 is a diagram illustrating an electrode assembly
according to one embodiment of the present invention in which the
electrodes are non-linear.
[0033] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0034] FIG. 1A is a diagram illustrating an implantable electrode
assembly 100 according to one example embodiment of the invention.
Electrode assembly 100 can be utilized in a variety of applications
including, but not limited to, electrotherapy or stimulation of the
patient. Tissue regions that are potential targets of
electrotherapy/electrostimulation include the patient's nervous
system (including nerve cells and synapses, and sensory receptors
such as baroreceptors), muscle tissue, organs, and blood vessels.
Electrode assembly 100 includes a base structure or substrate 102
that includes a flexible and electrically insulating material
suitable for implantation, such as silicone, optionally reinforced
with a flexible material such as polyester fabric. Base structure
or substrate 102 can be sized and shaped according to the
implantation site for the target tissue region (e.g., targeted
blood vessels, muscles, nerves, skin, bone, organs, cells, etc.),
and can have flexible and/or elastic properties. Thus, for example,
base structure or substrate 102 can have a length suitable to wrap
around all (360 degrees) or a portion (i.e., less than 360 degrees)
of the circumference of one or more blood vessels.
[0035] In one embodiment, electrode assembly 100 includes elongate
electrodes 104a-104c for making contact with the target tissue
region into which electrotherapy or electrostimulation is to be
applied. The electrodes can be un-insulated portions of larger
electrical conductors, dedicated un-insulated conductive
structures, or a combination thereof. While the elongate electrodes
104a-104c generally extend along a longitudinal axis, it will be
recognized that embodiments of the elongate electrodes can include
nonlinear geometries such as serpentine, curved or zig-zag, for
example, and that in some embodiments not all of an electrode
structure need be considered as part of the elongate electrode
geometry. In one example embodiment, as illustrated in FIG. 1A,
elongate electrodes 104a-104c are each about the same length, and
are situated generally parallel to one another such that proximal
ends 106a and 106c of outer electrodes 104a and 104c are positioned
on the same side 102a of base 102 as distal end 108b of center
electrode 104b. On the other side 102b of base 102, distal ends
108a and 108c of outer electrodes 104a and 104c are positioned
proximate to proximal end 106b of center electrode 104b on side
102b. For purposes of the present invention it will be understood
that proximal is used to reference a region proximate an end of a
structure that is electrically closer to the pulse generator and
that distal references a region proximate an end of a structure
that is further away electrically from the pulse generator as
compared to the proximal portion.
[0036] In a related type of embodiment, the electrodes are
generally co-extensive. Among electrode assemblies of this type,
the extent of co-extensiveness can vary according to the geometry
of the implantation site. For example, in one example embodiment,
the electrodes are co-extensive to within +/-25%. In another
embodiment, the electrodes are co-extensive to within +/-5%. While
this embodiment features one arrangement of three electrodes
104a-104c in accordance with the present invention, other
arrangements and configurations of electrodes 104 as described
hereinafter may also be utilized to enhance the uniform
distribution of the electric field delivered through the electrodes
to the target tissue region.
[0037] Electrodes 104a-104c are made from a suitable implantable
material, and are preferably adapted to have flexible and/or
elastic properties. Electrodes 104a-104c can comprise round wire,
rectangular ribbon or foil formed of an electrically conductive and
radiopaque material such as platinum. In one embodiment, the base
structure 102 substantially encapsulates the conductive material,
leaving only exposed electrode 104a-104c portions for electrical
connection to the target tissue. For example, each conductive
structure can be partially recessed in the base 102 and can have
one side exposed along all or a portion of its length for
electrical connection to target tissue. The exposed portions
constitute electrodes 104a-104c. In another embodiment, the
electrodes 104a-104c are made from conductive structures that can
be adhesively attached to the base 102 or can be physically
connected by straps, moldings or other forms of operably securing
them to the base 102. Electrical paths through the target tissue
are defined by anode-cathode pairs of the elongate electrodes
104a-104c. For example, in one embodiment, center electrode 104b is
a cathode, and outer electrodes 104a and 104c are both anodes, or
vice-versa. Thus, electrons of the electrotherapy or
electrostimulus signaling will flow through the target region
either into, or out of, electrode 104b.
[0038] Each electrode 104a-104c is connected at the corresponding
proximal end 106a-106c to an electrotherapy/electrostimulus source,
such as an implantable pulse generator (not shown) via a
corresponding lead 110a-110c. In one example embodiment, leads
110a-110c are each an insulated wire formed with, welded to, or
suitably interconnected with each corresponding electrode
104a-104c. Persons skilled in the art will appreciate that leads
110a-110c can be made of any suitable materials or geometries.
Furthermore, leads 110a-110c can each include a combination of
conductor types. Thus, for example, leads 110a-110c can each
include an insulated stranded wire portion, an un-insulated solid
wire portion, and/or a coiled wire portion having helical, spiral,
or other such coiled geometry.
[0039] FIG. 1B illustrates a physical embodiment of the example
electrode assembly 100 of FIG. 1A. The shape of base structure or
substrate 102 includes finger-type extensions 112, and reinforced
portions 114 for facilitating wrapping and securing the electrode
assembly 100 to the implantation site during implantation. Because
leads 110a and 110c are connected at opposite electrode ends from
lead 110b, leads 110a and 110c naturally extend in a different
direction away from the electrodes 104 than the direction of lead
110b. In certain applications, it may be desirable for the leads to
extend in the same direction away from the electrodes 104.
[0040] FIG. 1C is a diagram illustrating example electrode assembly
150 according to a related embodiment. Electrode assembly 150
includes a flexible and stretchable implantable substrate 152, to
which elongate electrodes 154a-154c are secured. Electrodes 154a
and 154c are connected respectively to leads 160a and 160c at
proximal ends 156a and 156c located on side 152a of substrate 152.
Electrode 154b is connected to lead 160b at proximal end 156b
located on side 152b of substrate 152. Distal ends 158a and 158c of
electrodes 154a and 154c, respectively, are located on side 152b
and are not connected to any leads. Distal end 158b of electrode
154b is located on side 152a and is not connected to any lead. Lead
160b extends along the length of electrode 154b towards distal end
156b, and further extends in the same direction as leads 160a and
160c, as illustrated in FIG. 1C. The leads 160a-160c are optionally
bundled and secured together by wire tie 161.
[0041] FIG. 1D illustrates a physical embodiment of example
electrode assembly 150. Electrodes 154a-154c are secured to
substrate 152, and are oriented along the reference z-axis.
Insulated leads 160a-160c are attached to their respective
electrodes as shown. Leads 160a and 160b are connected to
respective electrodes 154a and 154c at respective proximal ends
156a and 156c. Lead 160b is connected to electrode 154b at proximal
end 156b. Leads 160a and 160c extend in the -z direction away from
their corresponding electrodes 154a and 154c, and proceed in the -x
direction. Lead 160b extends away from electrode 154b in the +z
direction, then loops around substrate 152, and further proceeds in
the -z along the underside of substrate 152. Leads 160a-160c are
secured to substrate at various points by anchors 162 as shown.
Lead 162b is also secured at points along the underside surface of
substrate 152 by anchors 162 (not shown).
[0042] FIG. 1E illustrates another example physical layout of the
electrode assembly 150. In this embodiment, electrode 154b is
formed from an elongate structure having a hollow core 154b'. Lead
160b enters core 154b' at an opening at distal end 158b and passes
through core 154b' of the elongate structure to proximal end 156b,
at which point lead 160b connects with electrode 154b. In one
example embodiment, lead 160b includes a portion 160b' that is
specially adapted to be situated within core 154b'. Optionally,
electrodes 154a and 154c are adapted to be pliably compatible with
the structure of electrode 154b having a portion of lead 160b in
its core 154b'.
[0043] FIGS. 1F-1H illustrate various example electrode structures
that each include an elongate electrode portion in the shape of a
coil formed around a portion of a lead that is connected to the
electrode portion at the proximal end. Structure 164 of FIG. 1F is
an elongate structure having a length l. Structure 164 has an outer
coiled portion 166 made of non-insulated wire and generally helical
in its geometry. At least a portion of structure 164 can operate as
an electrode when in contact with target tissue. Structure 164
further includes a generally helical inner coiled portion 168
passing through the core 170 defined by the wire of outer coiled
portion 166. Inner coiled portion 168 is thus circumscribed along
at least a portion of its length by outer coil portion 166. One
type of wire material that can be suitable for certain implantable
applications is 80/20 Pt/Ir. However, persons skilled in the art
will recognize that other suitable materials may be used. Inner
coiled portion 168 enters core 170 at distal end 172, and helically
extends through core 170 towards proximal end 174, at which point
inner coiled portion 168 makes contact with outer coiled portion
166.
[0044] In one example embodiment, near proximal end 174, one or
more windings of outer coiled portion 166 have a progressively
reducing radius as they approach proximal end 174 such that, at
proximal end 174, windings of outer coiled portion 166 have
approximately the same radius as the windings of inner coiled
portion 168. This embodiment is illustrated in FIG. 1F. Outer
coiled portion 166 includes windings 167 having a relatively larger
radius, and windings 176 having a relatively smaller radius.
Reduced radius windings 176 are situated in a bifilar arrangement
at proximal end 174 with the windings of inner coiled portion 168.
FIG. 1G is an end view of structure 164 illustrating this
embodiment. Outer coiled portion 166 includes windings 167 having
larger radius r.sub.1, and windings 176 near the proximal end 174
having smaller radius r.sub.2. Winding 178 of outer coiled portion
166 integrally bridges the larger radius windings 167 with the
smaller radius windings 176. In one embodiment, at proximal end
174, the wire forming outer coiled portion 166 is welded to the
wire forming inner coiled portion 168. Persons skilled in the art
will appreciate that other suitable mechanisms of creating an
electrical contact between these wires, including, but not limited
to, soldering, crimping, twisting, or conductively adhesively
bonding, may be utilized.
[0045] In one embodiment, inner coiled portion 168 is positioned
relative to larger outer coiled portion 166's windings 167 such
that, in operation, the inner coiled portion 168 and outer coiled
portion 166 do not make contact at any point other than at the
proximal end 174. In one embodiment, inner coiled portion 168 is
formed from insulated wire. In another embodiment, inner coiled
portion 168 is formed from un-insulated wire, but inner surfaces of
windings 167 are insulated. In another embodiment, the radius of
the inner coiled portion's windings R.sub.2 is sized relatively to
the outer coiled portion's windings 167 having larger radius
r.sub.1 such that undesired contact points are not created when the
structure 164 is elastically flexed to a maximum limit.
[0046] In another type of embodiment, as illustrated in FIG. 1H,
structure 164' includes an insulating material 180 that is
coaxially situated between inner coiled portion 168' and
large-radius coils 167' of outer coiled portion 166'. According to
one example of this type of embodiment, as illustrated in the side
view diagram of FIG. 1I, the radii of inner coiled portion 168' and
of outer coiled portion 167' remain generally constant over the
length of the structure (disregarding the change in radius of the
outer portion near the proximal end). Insulator 180 has a generally
cylindrical outer wall that is adjacent to outer coiled portion
coils 167', and a generally cylindrical inner wall adjacent to
inner coiled portion 168'.
[0047] FIGS. 1J and 1K illustrate an example of a variation of the
embodiment of FIG. 1I. FIGS. 1J and 1K are, respectively, side view
diagrams of a structure in which large-radius coils 167'' of outer
coiled portion 166'' have a constant radius over length l, but
inner portion 168'' has a spiral geometry in which the coil radius
decreases towards the proximal end. The radii of outer and inner
walls of insulator 180' also have a profile of decreasing radius
that corresponds to the decreasing radius profile of inner coils
168''. According to one aspect of this embodiment, the geometry of
the structure of FIGS. 1J and 1K provides a benefit of securing in
place the insulator 180' by preventing it from sliding towards
either end of the structure.
[0048] In the configuration of electrodes 104a-104c (FIGS. 1A and
1B) and 154a-154c (FIGS. 1C, 1D, and 1E), having the electrode/lead
connections at opposite ends for electrodes of opposite polarity
provides improved electric field uniformity and improved corrosion
resistance as compared against equivalent configurations having the
connections at the same end. FIGS. 2-5, described in detail below,
illustrate these principles.
[0049] FIG. 2 is a diagram illustrating an electrical circuit model
of a state-of-the-art implanted electrode assembly. Distributed
resistance 202 represents one or more cathodes 203 connected to the
electrotherapy/electrostimulus signal generator. Likewise,
distributed resistance 204 represents one or more anodes 205
connected to the opposite pole of the
electrotherapy/electrostimulus generator. Distributed resistances
202 and 204 are each distributed over the length L and quantity of
their corresponding electrode(s), and are not necessarily equal in
magnitude. Target tissue impedance 206 represents the electrical
properties of the target tissue interconnecting the electrodes.
Target tissue impedance 206 is modeled as a set of parallel
resistor-capacitor pairs 206a-206f distributed over the aggregate
volume V that separates the cathode(s) from the anode(s). The
resistance of each electrode's distributed resistance 202 and 204
is generally evenly distributed over length L. With increasing
length L, the resistance component of impedance 206 decreases,
whereas the capacitance component increases.
[0050] Cathode 203 is connected to the signal generator at top end
208; anode 205 is connected to the opposite pole of the signal
generator at top end 210. When the electrotherapy/electrostimulus
signal is applied across electrodes 203 and 205, an aggregate
current I generally passes through the resistive component of the
target tissue having impedance 206. Also, an aggregate electric
field E generally exists across the electrodes 203 and 205 due to
the capacitive component of impedance 206. However, due to the
distributed resistances of the electrodes 203 and 205, as well as
the distributed target tissue impedance 206, the current I and
electric field E are also distributed over the length L and volume
V. The distribution of current I and electric field E depends on
the distribution of tissue impedance 206, and on the charge
distribution over the length L of each electrode 203 and 205.
[0051] Within each of the distributed electrode resistances 202 and
204, there exist a cathode current i.sub.cathode and i.sub.anode,
and corresponding voltage drops V.sub.cathode and V.sub.anode.
These currents and voltages occur within each elongate electrode
because the electrode resistances 202 and 204 create voltage and
current divisions with respect to signal paths through the target
tissue. Because the signal generator connections are located at the
top ends 208 and 210 of electrodes 203 and 205, respectively, the
cathode and anode currents and voltages have opposite directions
and polarities, as illustrated in FIG. 2.
[0052] As a result, the distributed current I and electric field E
through the target tissue region are not evenly distributed. By way
of example, discrete current components i.sub.1-i.sub.6 located
successively at greater distances from the top ends 208 and 210 are
successively lower in amplitude such that i.sub.1 has the greatest
amplitude while i.sub.6 has the lowest amplitude. FIG. 3
illustrates an example current distribution through volume V over
length L. The axis labeled L corresponds to the L dimension of FIG.
2, and the paths 1-6 correspond to the paths taken by example
current components i.sub.1-i.sub.6.
[0053] FIG. 4 illustrates an electrical diagram of an example
implanted electrotherapy/electrostimulation electrode assembly
according to one embodiment of the present invention. Distributed
resistances 402 and 404 represent aggregate elongate electrodes 403
and 405, respectively. Electrodes 403 and 405, and the target
tissue having impedance 406 are all correspondingly similar to
their respective analogues described above with reference to FIG.
2. The only difference in the arrangement between the example of
FIG. 2 and the example of FIG. 4 is the connection of the signal
generator to the cathode and anode. Cathode 403 is connected to the
signal generator at top end 408; whereas anode 405 is connected at
bottom end 411. As a result of this reversal, the bottom end 411 is
more negatively charged than the top end 410 of the anode 405. This
causes the charge density of the electrodes 403 and 405 to be
evenly distributed along the length L, which results in an even
distribution of aggregate current I' and aggregate electric field
E'. Thus, example discrete current components i.sub.1'-i.sub.6'
each pass through an equivalent impedance. For instance, current
component i.sub.2' passes through a smaller portion of cathode
impedance 402, through target tissue impedance component 406b, and
through a larger portion of anode impedance 404; whereas current
component i.sub.5' passes through a larger portion of cathode
impedance 402, an equivalent target tissue impedance component
406e, and through a smaller portion of anode impedance 404.
[0054] Another result of the electrode arrangement of FIG. 4 is
that the cathode current i.sub.cathode' is directed along the same
direction as the anode current i.sub.anode'. FIG. 5 illustrates the
uniform distribution of aggregate current I' over length L for the
example electrode assembly configuration of this embodiment.
[0055] By distributing the charge density evenly over each of the
electrodes 403 and 405, any faradaic processes are also distributed
over the surfaces of the electrodes. This effect results in an
increased corrosion threshold because electrode corrosion is based
on the charge density. Another effect is an increase in capacitance
seen by the electrotherapy or electrostimulation signaling. Because
the charge density is evenly distributed along length L, the
signaling sees a greater overall target tissue capacitance. With an
increased overall capacitance created by the charge balancing, more
of the activation current is used to charge the electrode double
layer and less is available for faradaic processes. The charging of
the electrode double layer results in an induced current in the
target tissue resulting in the desired stimulation or therapeutic
effect.
[0056] The present invention contemplates a variety of electrode
forms or shapes, not necessarily limited to straight linear
segments. FIG. 6 is a diagram illustrating an example electrode
assembly 600 according to another embodiment of the present
invention. Electrode assembly 600 includes a flexible substrate 602
to which arcing elongate electrodes 604a-604c are secured. Arcing
elongate electrodes 604a-604c each have a first end in a first
region A and a second end in a second region B such that the
electrodes 604a-604c arcuately extend between regions A and B.
Electrode 604a has a lead 610a electrically connected to its first
end 606a. Electrode 604b has a lead 610b electrically connected to
its second end 608b. Electrode 604c has a lead 610c electrically
connected to its first end 606c. For electrodes 604a and 604c,
respective second ends 608a and 608c have no leads connected
thereto. Conversely, for electrode 604b, first end 606b is free of
any lead connection. When implanted in a patient, electrodes
604a-604c are electrically interconnected by the target tissue. In
operation, the charge distribution in each of the electrodes is
approximately uniform, resulting in electric fields and currents
approximately uniformly distributed through the interconnecting
target tissue.
[0057] The invention may be embodied in other specific forms
without departing from the essential attributes thereof, therefore,
the illustrated embodiments should be considered in all respects as
illustrative and not restrictive.
* * * * *