U.S. patent application number 15/923489 was filed with the patent office on 2018-09-27 for pressure-sensitive flexible polymer bipolar electrode.
The applicant listed for this patent is St. Jude Medical, Atrial Fibrillation Division, Inc.. Invention is credited to Hong Cao, Saurav Paul, Harry A. Puryear, Riki Chou Thao.
Application Number | 20180271593 15/923489 |
Document ID | / |
Family ID | 40799407 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180271593 |
Kind Code |
A1 |
Paul; Saurav ; et
al. |
September 27, 2018 |
PRESSURE-SENSITIVE FLEXIBLE POLYMER BIPOLAR ELECTRODE
Abstract
The present invention is directed to bipolar ablation systems. A
bipolar electrode system for ablation therapy is disclosed,
including a pressure-sensitive conducting composite layer and a
pair of electrodes in electrical conductive contact or
communication with the pressure-sensitive conducting composite
layer. Energy (e.g., ablation energy) is delivered via the
pressure-sensitive conductive composition when sufficient pressure
is applied to transform the pressure-sensitive conductive composite
to an electrical conductor. An electrically insulative flexible
layer, which may include a passageway for a fill material is also
disclosed. In some embodiments, the systems can also be used for
targeted delivery of compounds, such as drugs, using a bipolar
electrode.
Inventors: |
Paul; Saurav; (Minneapolis,
MN) ; Puryear; Harry A.; (Shoreview, MN) ;
Thao; Riki Chou; (Maplewood, MN) ; Cao; Hong;
(Savage, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Atrial Fibrillation Division, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
40799407 |
Appl. No.: |
15/923489 |
Filed: |
March 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13555929 |
Jul 23, 2012 |
9949792 |
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15923489 |
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11968044 |
Dec 31, 2007 |
8226648 |
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13555929 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2018/00875
20130101; A61B 2018/00023 20130101; A61B 18/1492 20130101; A61B
18/1206 20130101; A61B 2018/00577 20130101 |
International
Class: |
A61B 18/14 20060101
A61B018/14 |
Claims
1.-33. (canceled)
34. A catheter, comprising: a catheter shaft comprising a distal
portion and a proximal portion; and an electrode assembly coupled
to the distal portion, the electrode assembly comprising an
exterior configured to engage target tissue and configured to bend
and conform to a compliant tissue wall of the target tissue, first
and second electrodes on the exterior; first and second channeling
members configured to be transformed from an insulator to a
conductor in response to a respective applied pressure; a pair of
electrical wires in electrical contact with the first and second
channeling members; wherein the first channeling member is disposed
radially inward of and in electrical communication with the first
electrode and the second channeling member is disposed radially
inward of and in electrical communication with the second
electrode; wherein the electrode assembly is configured to channel
electrical energy with respect to a first portion of the exterior
of the electrode assembly while not channeling electrical energy
with respect to a second portion of the exterior of the electrode
assembly when the first portion is in contact with the target
tissue and the second portion is not in contact with the target
tissue.
35. The catheter of claim 34 wherein at least one of said first and
second channeling members comprise pressure-sensitive conductive
composite (PSCC) layers.
36. The catheter of claim 34 wherein at least one of said first and
second channeling members comprise a quantum tunneling composite
member.
37. The catheter of claim 34, wherein the electrode assembly is
further configured to allow a fluid to exit from the electrode
assembly between the first electrode and the second electrode.
38. The catheter of claim 34, wherein the electrode assembly is
further configured to allow a fluid to exit from the electrode
assembly adjacent the first electrode and the second electrode.
39. The catheter of claim 34, wherein the electrode assembly
comprises a porous material such that a fluid may pass
therethrough.
40. The catheter of claim 34, wherein ablative energy from an
ablative energy source coupled to the pair of electrical wires is
channeled to the first portion of the exterior via a corresponding
first portion of the first and second channeling members when
sufficient pressure is applied thereto and thereby transform said
corresponding first portion of the first and second channeling
members into electrical conductors.
41. The catheter of claim 34 further comprising: an electrically
insulative flexible layer adjacent the first and second channeling
members.
42. The catheter of claim 41 further comprising: a sensor located
in the electrically insulative flexible layer configured to monitor
a temperature.
43. The catheter of claim 41 further comprising: a heat sink
thermally coupled to one of the channeling members and the
electrically insulative flexible layer.
44. The catheter of claim 34 wherein the first electrode comprises
a circumferentially-extending ring of electrically-conductive
material having a first outside surface, said second electrode
comprises a circumferentially-extending ring of
electrically-conductive material having a second outside surface,
the exterior of the electrode assembly including the first and
second outside surfaces.
45. The catheter of claim 34 wherein the first and second channel
members comprises at least a first annular portion
radially-inwardly of the first electrode and a second annular
portion radially-inwardly of the second electrode, the first
electrode being longitudinally offset from the second
electrode.
46. The catheter of claim 34 further comprising a tip electrode at
a distal end of the catheter shaft and located distal of the first
and second electrodes, said catheter further comprising a further
electrical wire coupled to the tip electrode.
47. The catheter of claim 34 wherein electrical energy at a first
portion of at least one of the first and second electrodes in
contact with the target tissue is channeled to at least one of the
first and second wires via a corresponding first portion of the
first and second channeling members when sufficient pressure is
applied thereto and thereby transform said corresponding first
portion of the first and second channeling members into electrical
conductors.
48. The catheter of claim 46 wherein the electrical energy
comprises electrical characteristics of the target tissue.
49. A catheter, comprising: a catheter shaft comprising a distal
portion and a proximal portion; and an electrode assembly coupled
to the distal portion including: first and second electrodes whose
outside surfaces are configured to engage target tissue; first and
second channeling members disposed radially inward of said first
and second electrodes, respectively, and configured as electrical
insulators in an absence of a predetermined applied pressure and
further configured as electrical conductors in a presence of the
predetermined applied pressure; and pair of electrical conducting
wires in contact with the first and second channeling members and
coupled to one of an ablative energy source and a measuring device;
said electrode assembly includes (i) a conductive zone
corresponding to a portion of said outside surfaces of said first
and second electrodes that are subject to said predetermined
applied pressure when in contact with the target tissue and in
which one of ablative energy and electrical energy corresponding to
electrical characteristics of the target tissue are delivered and
(ii) a complementary insulative zone where neither the ablative
energy nor the electrical energy is delivered when said
complementary insulative zone is not subject to said predetermined
applied pressure when it is not in contact with the target tissue;
wherein one of (i) the ablative energy from the ablative energy
source and (ii) the electrical energy corresponding to electrical
characteristics of the target tissue is channeled through the
conductive zone via a corresponding first portion of said first and
second channeling members when the predetermined pressure is
applied thereto to transform the corresponding first portion of
said first and second channeling members into electrical
conductors.
50. The catheter of claim 49 further comprising a tip electrode
coupled with a further electrical conducting wire.
51. The catheter of claim 49 wherein said first and second
channeling members comprises quantum tunneling composite
members.
52. A catheter, comprising: a catheter shaft comprising a distal
portion and a proximal portion; and an electrode assembly coupled
to the distal portion including first and second electrodes having
respective outside surfaces configured to engage target tissue;
first and second channeling members being arranged relative to said
first and second electrodes, respectively; and first and second
electrical conducting wires extending to a proximal end of said
catheter and are configured for connection to an electrical
apparatus, wherein the first and second electrical wires are in
contact with the first and second channeling members, respectively;
said first channeling member being configured to selectively couple
said first electrical conducting wire to said first electrode when
said outside surface of said first electrode experiences a
predetermined pressure applied thereto and configured to not
selectively couple said first electrical conducting wire to said
first electrode when said outside surface of said first electrode
does not experience said predetermined pressure applied thereto,
said second channeling member being configured to selectively
couple said second electrical conducting wire to said second
electrode when said outside surface of said second electrode
experiences said predetermined pressure applied thereto and
configured to not selectively couple said second electrical
conducting wire to said second electrode when said outside surface
of said second electrode does not experience said predetermined
pressure applied thereto.
53. The catheter of claim 52 wherein said first and second
channeling members are configured as electrical insulators in
absence of the predetermined applied pressures and electrical
conductors in the presence of the predetermined applied pressures.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 13/555,929 (the '929 application), filed 23
Jul. 2012, presently pending, which is a continuation of U.S.
application Ser. No. 11/968,044 (the '044 application), filed 31
Dec. 2007, now U.S. Pat. No. 8,226,648. The '929 application and
the '044 application are both hereby incorporated by reference in
their entirety as though fully set forth herein.
BACKGROUND OF THE INVENTION
a. Field of the Invention
[0002] The present invention pertains generally to an
electrophysiological device and method for providing energy to
biological tissue and, more particularly, to an ablation apparatus
that includes a bipolar electrode that uses a flexible polymer
electrode. The present invention is also directed to an
electrophysiological device that can be used for drug delivery to a
target tissue.
b. Background Art
[0003] In a normal heart, contraction and relaxation of the heart
muscle (myocardium) takes place in an organized fashion as
electrochemical signals pass sequentially through the myocardium
from the sinoatrial (SA) node located in the right atrium to the
atrial ventricular (AV) node and then along a well defined route
which includes the His-Purkinje system into the left and right
ventricles. Sometimes abnormal rhythms occur in the atrium, a
condition known as atrial arrhythmia. Three of the most common
arrhythmia are: (1) ectopic atrial tachycardia, (2) atrial
fibrillation, and (3) atrial flutter. Arrhythmia can result in
significant patient discomfort and even death because of a number
of associated problems, including: (1) an irregular heart rate,
which causes a patient discomfort and anxiety; (2) loss of
synchronous atrioventricular contractions which compromises cardiac
hemodynamics resulting in varying levels of congestive heart
failure; and (3) blood flow stasis, which increases the
vulnerability to thromboembolism. It is sometimes difficult to
isolate a specific pathological cause for the arrhythmia, although
it is believed that the principal mechanism is one or a multitude
of stray circuits within the left and/or right atrium. These
circuits or stray electrical signals are believed to interfere with
the normal electrochemical signals passing from the SA node to the
AV node and into the ventricles. Efforts to alleviate these
problems in the past have included administering various drugs. In
some circumstances, drug therapy is ineffective and frequently is
plagued with side effects, such as dizziness, nausea, vision
problems, and other difficulties.
[0004] For example, an increasingly common medical procedure for
the treatment of certain types of cardiac arrhythmia and atrial
arrhythmia involves ablation of heart tissue to cut off the path
for stray or improper electrical signals. Such procedures may be
performed by catheters that incorporate ablation electrodes.
Typically, the catheter is inserted in an artery or vein in the
leg, neck, or arm of the patient and threaded, sometimes with the
aid of a guidewire or introducer, through the vessels until a
distal tip of the catheter reaches the desired location for the
ablation procedure in the heart. During the ablation procedure, the
electrode of the ablation catheter is placed in contact with the
target tissue and therapeutic substance is applied to the tissue
via the electrode. Therapeutic substance may be a chemical
substance; energy, such as thermal energy (heating or cooling);
electrical energy, such as radiofrequency (RF) current;
electromagnetic energy, such as light; and acoustic energy, such as
ultrasound. Upon delivery of sufficient therapeutic substance to
the tissue, the ablation procedure kills and/or irreversibly
modifies the target tissue, and produces lesions. The lesion
partially or completely blocks the stray electrical signals to
lessen or eliminate arrhythmia.
[0005] Efficacious delivery of therapeutic substance from the
electrode to the target tissue requires that the electrode to be in
optimal contact with the target tissue. Ensuring optimal contact
between the electrode and the tissue is not readily achieved using
rigid electrodes, such as metal electrodes. Several factors that
may contribute to suboptimal contact include: (i) the remote
manipulation of the catheter from the electrode, typically over
four feet away; (ii) the constant movement of the heart wall; (iii)
the variable compliance of the heart wall, and (iv) the highly
contoured nature of the heart wall. Flexible polymer electrodes are
designed to provide superior conformance with tissue than metal
electrodes.
BRIEF SUMMARY OF THE INVENTION
[0006] In a first aspect, the invention is directed to a bipolar
electrode system for ablation therapy, comprising a
pressure-sensitive conducting composite layer and at least a pair
of electrodes in electrical conductive contact or communication
with the pressure-sensitive conducting composite layer. The bipolar
electrode system may include a catheter base that is coupled to the
conductive element and/or the pressure-sensitive conductive
composite. An energy source may be coupled to the pair of
electrodes, such that energy (e.g., ablation energy) is delivered
via the pressure-sensitive conductive composition when sufficient
pressure is applied to transform the pressure-sensitive conductive
composite to an electrical conductor. An electrically insulative
flexible layer, which may include a passageway for a fill material,
may be found adjacent to the pressure-sensitive conductive layer.
Sensors may also be located in the electrically insulative flexible
layer for monitoring temperature, such as at an outlet coupled to a
passageway for a fill material, or elsewhere. In those cases where
an outlet is present, the outlet may permit flowable filler
material to flow from the passageway. Additionally, a heat sink may
be thermally coupled to the pressure-sensitive conductive composite
member and/or to the electrically insulative flexible layer. In
those electrodes where a passageway is found in the insulative
flexible layer, there may also be found a wall such that flowable
fill material circulates in the insulative flexible layer. The
electrically insulative flexible layer itself may be permeable or
non-permeable. In those bipolar electrode systems that include a
passageway for a filler material and where the filler material
cools the electrode during ablation, the passageway can be a loop
such that a cooling fluid travels from a proximal end of the
electrode through a distal end of the electrode and returns to the
proximal end of the electrode via the passageway.
[0007] In another aspect, the present invention is direct to a
bipolar electrode for ablation therapy that comprises a
pressure-sensitive conducting composite layer, an electrically
insulative flexible tube adjacent the pressure-sensitive conducting
composite layer, at least a pair of electrodes in electrical
conductive contact or communication with the pressure-sensitive
conducting composite layer, and a passageway for a filler material
in the electrically insulative flexible tube.
[0008] In yet another aspect, the invention is directed to methods
of treating a target tissue. A bipolar electrode system having a
pair of electrodes for conducting RF energy and a layer of
pressure-sensitive conductive composite that is in electrical
contact or communication with at least a portion of the pair of
electrodes are coupled to an RF energy supply; the bipolar
electrode system is operatively contacted with a target tissue of a
subject; pressure is exerted upon the target tissue through the
electrode such that the pressure-sensitive conductive composite
becomes conductive, delivering energy to the target tissue. The
method can include communicating with a heat sink thermally coupled
to the bipolar electrode system.
[0009] In another aspect, the invention is directed to a bipolar
electrode for ablation therapy that includes a catheter having a
proximal end and a distal end, at least a pair of electrodes for
conducting energy, and a layer of quantum tunneling composite that
is in electrical communication with the pair of electrodes, where
the layer is located at least in part at a distal end of the
catheter. The bipolar electrode can also include an electrically
insulative flexible tube thermally adjacent to the
pressure-sensitive conducting composite layer. The electrode can
also include at least one sensor to measure the temperature of the
electrically insulative flexible tube, and/or a heat sink that is
coupled to at least the quantum tunneling composite layer or the
electrically insulative flexible tube.
[0010] In yet another aspect, the invention is directed to a
bipolar electrode assembly for conducting ablative energy, where
the assembly comprises a pair of electrodes for conducting the
ablative energy, a quantum tunneling composite member, and an
energy source coupled to the quantum tunneling composite member,
wherein the pair of electrodes is disposed relative to the quantum
tunneling composite member such that pressure that is applied to
the pair of electrodes is transferred to the quantum tunneling
composite member and causes the quantum tunneling composite member
to become electrically conductive such that it conducts electrical
energy to the electrode. The electrode assembly can also include a
conductor that is in electrical contact or communication with the
quantum tunneling composite member, where the conductor is
configured to conduct electrical energy sufficient to cause
ablation. The electrode may be located on a distal end of the
electrode assembly, and the quantum tunneling composite member may
be disposed in physical contact or communication with the electrode
along the longitudinal axis of the electrode assembly. The
electrode assembly can also include at least one pressure transfer
member disposed between the quantum tunneling composite member and
the electrode, such that pressure applied to the electrode is
transferred through at least one pressure transfer member to the
quantum tunneling composite member. A processor that can sense the
degree of contact between the electrode and the surface of a tissue
to be ablated can also be included in the assembly. A processor
that monitors for a change in impedance of the quantum tunneling
composite member can also be included with the electrode assembly,
where the processor is coupled to a generator to control the energy
being generated based on a change in impedance of the quantum
tunneling composite member.
[0011] In another aspect, the invention is directed to a method of
delivering a compound to a target tissue, where a bipolar electrode
system that has a pair of electrodes for conducting DC and RF
energy and a layer of pressure-sensitive conductive composite that
is in electrical contact or communication with at least a portion
of the pair of electrodes is coupled to a DC energy supply to the
pair of electrodes and with a circulating a flowable filler
material that includes the compound to be delivered to the target
tissue. The system is operatively contacted to the bipolar
electrode system with a target tissue of a subject; the DC energy
supply is engaged, and then an effective amount of pressure is
exerted upon the target tissue through the electrode such that the
pressure-sensitive conductive composite becomes conductive and
delivers DC energy to the target tissue. The method can also
include coupling an RF energy supply to the pair of electrodes. The
method can also include the steps of, after delivering DC energy to
the target tissue, disengaging the DC energy supply, engaging a RF
energy supply coupled to the pair of electrodes, and exerting an
effective amount of pressure upon the target tissue through the
electrode such that the pressure-sensitive conductive composite
becomes conductive and delivers RF energy to the target tissue.
Compounds that can be delivered include those that are
electrophoretic and photosensitive, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1A-1B show a general scheme of a pressure-sensitive
conductive composite (PSCC) electrode as applied to a target
tissue.
[0013] FIGS. 2A-2B depict an embodiment of a PSCC electrode that
includes an outlet.
[0014] FIGS. 3A-3B show another embodiment of a PSCC electrode that
does not include an outlet.
[0015] FIGS. 4A-4B show direction of ablative energy from the
embodiment of a PSCC electrode shown in FIGS. 3A-3B.
[0016] FIGS. 5A-5B illustrate an embodiment of a PSCC electrode
than can be used for both ablation and targeted drug delivery.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Pressure-sensitive conductive composite (PSCC) electrodes
are disclosed, along with methods for using an electrode for tissue
ablation and targeted drug delivery.
[0018] As used herein, "pressure-sensitive polymer,"
"pressure-sensitive composite" and "PSCC" generally mean a
pressure-sensitive conductive composite that has unique electrical
properties wherein the electrical resistance of the PSCC varies
inversely in proportion to the pressure that is applied to the
PSCC. Useful PSCCs commonly have a high electrical resistance when
quiescent (not under pressure), and become conductive under
pressure, where the electrical resistance may fall, for example, to
less than one ohm. When quiescent, the PSCC material can have a
resistance that is greater than 100,000 ohms to greater than 1M
ohms, and as a non-conductor (e.g., having a resistance greater
than 10M ohms).
[0019] The present invention can use various pressure-sensitive
conductive composite materials. For example, U.S. Pat. No.
6,999,821 discloses conductor-filled polymers that can include
presently available materials approved for implantation in a human
body such as silicone rubber with embedded metallic, carbon or
graphite particles or powder. For example, silver-filled silicone
rubbers, such as NuSil R2637 (NuSil; Carpinteria, Calif.) and
similar products from Specialty Silicone Products (Ballston Spa,
N.Y.) can be used. Other insulating or weakly conductive materials
(e.g., non-conductive elastomers) can be embedded with conductive
materials, conductive alloys and/or reduced metal oxides (e.g.,
using one or more of gold, silver, platinum, iridium, titanium,
tantalum, zirconium, vanadium, niobium, hafnium, aluminum,
silicone, tin, chromium, molybdenum, tungsten, lead, manganese,
beryllium, iron, cobalt, nickel, palladium, osmium, rhenium,
technetium, rhodium, ruthenium, cadmium, copper, zinc, germanium,
arsenic, antimony, bismuth, boron, scandium and metals of the
lanthanide and actinide series and, if appropriate, at least one
electroconductive agent). The conductive material can comprise a
powder, grains, fibers or other shaped forms. The oxides can be
mixtures comprising sintered powders of an oxycompound. The alloy
can be conventional, such as, for example, titanium boride.
[0020] Other examples of PSCCs that can be suitable for use in
connection with embodiments of the present invention include
quantum tunneling composites ("QTC"), such as those available
through Peratech Ltd. (Darlington, UK), and include the QTC pill,
the QTC substrate and the QTC cables. QTC materials can have
variable resistance values that range from >10 M ohms (in the
absence of stress) to <1 ohm when under pressure.
[0021] Other examples of PSCC materials that can be used in the
present invention include the conductive polymers disclosed in U.S.
Pat. Nos. 6,646,540, 6,495,069, and 6,291,568. These materials can
have a variable resistance of >10.sup.12 ohms before any stress
is applied to less than 1 ohm when finger pressure is applied.
[0022] As a result of this unique property, PSCC materials have the
ability to transform from an effective insulator to a metal-like
conductor when deformed by compression, twisting, or stretching.
The electrical response of a PSCC can be tuned appropriately to the
spectrum of pressures being applied. Its resistance range often
varies from greater than 10 M ohms to less than 1 ohms. The
transition from insulator to conductor often follows a smooth and
repeatable curve, with the resistance dropping monotonically to the
pressure applied. Moreover, the effect is reversible once the
pressure is removed, restoring electrical resistance. Thus, a PSCC
may be transformed from an insulator to a conductor, and back to an
insulator, simply by applying the appropriate pressure. PSCCs can
conduct large currents (up to 10 Amps) and support large voltages
(40 V and higher).
[0023] The PSCC can transform from an insulator (that is,
conducting little or no current) to an effective conductor simply
by applying a small change in pressure to the PSCC. For example, by
applying pressure with a hand, or more particularly, with a finger,
a surgeon can transform the PSCC from an insulator to a conductor
to permit contact sensing.
[0024] The PSCC can also be chosen or customized to have a specific
pressure sensitivity such that the insulator-conductance transition
occurs over a wide or narrow range. For example, highly sensitive
PSCCs, which register a sharp change in resistance with a finite
amount of applied pressure, may be preferred for soft contact
applications such as the atrial wall. Less-sensitive PSCCs, which
require more pressure to register the same amount of change in
resistance, may be preferred for hard contact applications such as
ablation in ventricular walls.
[0025] Because a PSCC's resistance drops monotonically as pressure
increases, a PSCC electrode is able to deliver energy for ablation
gradually, and then increasingly as pressure increases.
[0026] In an embodiment of the present invention, the electrode is
fabricated with a PSCC that differentiates between a soft and a
hard push. Such a device can be used to switch, for example, an
ablation electrode in response to a concentrated pressure while
ignoring the general background pressure. Alternatively, such a
device can "turn on" and deliver electrical energy that is already
present within the device.
[0027] Because PSCC electrode devices and systems may be used to
deliver ablation with a "soft start," the PSCC electrode devices
and systems of the present invention may be used in direct contact
with the target tissue, thereby eliminating the physical gap that
sometimes exists with other ablation electrodes. Eliminating the
gap can reduce the possibility of arcing, and thereby can improve
the safety and efficacy of ablation.
[0028] In some embodiments, the PSCC electrode device can contain a
filler material that can be used, for example, to cool the device
and surrounding tissues, or to carry desired compounds. "Filler
material" (e.g., as shown as element 12 in FIGS. 2B-4B) comprise
flowable fillers, such as water, saline, silicone oil; solid
fillers, gel fillers, or structured solid-fillers, such as a bundle
of acoustics-carrying glass or metal fibers. In the case of
flowable and gel fillers, the material need not be physiologically
compatible if the filler is isolated from, or briefly contacts, the
target and surrounding tissues when using the PSCC electrode
device.
[0029] FIGS. 1A and 1B illustrate an overall scheme of the present
teaching. PSCC electrode system 10 includes a catheter shaft 42 and
a contact surface 100 that extends from catheter shaft 42. The PSCC
electrode 40 is flexible such that when it comes into contact with
a target tissue 28, PSCC electrode 40 is deflected in direction 50
(e.g., as illustrated in FIG. 1B), and the deflection permits
activation of PSCC electrode 40 based on a degree of contact
between PSCC electrode 40 and the target tissue 28.
[0030] FIGS. 2A-2B show a PSCC electrode system 120 as a first
bipolar electrode according to the present teaching. FIGS. 2A and
2B show two cross-sectional drawings taken along the reference
lines of A-A (longitudinal) and B-B (cross-sectional) of FIG. 1A.
As depicted in FIGS. 2A and 2B, the PSCC bipolar electrode system
120 comprises a PSCC electrode 40 that extends from a catheter
shaft 42. The PSCC electrode 40 comprises an electrically
insulative flexible tube 14 located centrally in the electrode 40
and extending into the catheter shaft 42. The electrically
insulative flexible tube 14 may include a filler material 12. An
efflux outlet 32 may be connected to the electrically insulative
flexible tube 14 and, in the case of flowable filler material 12,
can allow such filler material 12 to flow from the system 120 to
the surrounding area (including the surrounding tissue 30 and the
target tissue 28). Returning to the PSCC electrode 40, a PSCC
substrate layer 22 may be mechanically connected to the
electrically insulative flexible tube 14 and be electrically and
mechanically coupled to electrodes 24, such as gold-loaded
conductive polymer electrodes. The PSCC substrate 22 may be
functionally and electrically connected to one end of electrical
conducting element 34. The electrical conducting element 34 is
substantially contained within the catheter shaft and is connected
at the other end to a current source 16 (e.g., RF current source)
or an electrical ground 18. A heat sink 20 may thermally
encapsulate, at least partially, the electrically insulative
flexible tube 14. The PSCC substrate layer 22 is capable of bending
and conforming to a compliant tissue wall of a target tissue
28.
[0031] The PSCC bipolar electrode system 120 ablates tissue by
delivering ablation energy, depicted in FIG. 2A as electric field
26, via the electrodes 24 when the pressure applied to the PSCC
substrate layer 22 as a result of electrode-tissue contact is
sufficient to engender or provide an electrical response that is
transmitted to the electrodes 24. The applied pressure can be
provided and manipulated directly by an operator (such as an
operating physician), or indirectly through a mechanical device
operably linked to the PSCC electrode 40. The ablation energy 26 is
delivered substantially to the target tissue 28 and not to
surrounding tissue 30 (e.g., blood) by virtue of activating the
PSCC adjacent to the target tissue 28. The pressure sensitivity of
the PSCC substrate layer 22 may be adjusted to match the compliance
target tissue 28, such that the electrical conductivity of the
electrode and the electric field from the electrode is directed
substantially to the target tissue 28. The filler material 12 may
be in contact with the tissue via outlet 32. In the case of
flowable filler material 12, the outlet allows for the flowable
filler material 12 to enter the surrounding tissues, e.g., 28,
30.
[0032] Having an open system for a flowable filler material 12,
shown in FIGS. 2A and 2B, is useful especially for those procedures
wherein the flow of the filler material 12 can be easily managed,
or may be beneficial to the procedure. An example of such a
procedure is endocardial RF ablation. Notably, the filler material
12 can be used to help control the temperature of the electrode
system 120 and the target tissue 28 by providing enhanced cooling
effects in addition to the cooling effects of the surrounding
tissues such as the flowing blood (e.g., a depicted as 30).
[0033] FIGS. 3A-3B show a PSCC electrode system 130 as a second
bipolar electrode according to the present teaching. FIGS. 3A and
3B show two cross-sectional views taken along the reference lines
of A-A (longitudinal) and B-B (cross-sectional) of FIG. 1A. The
PSCC bipolar electrode system 130 comprises a PSCC electrode 40
that extends from a catheter shaft 42. The PSCC electrode 40
comprises an electrically insulative flexible tube 14 located
centrally in the electrode 40 and extending into the catheter shaft
42. The electrically insulative flexible tube 14 may include a
filler material 12. A PSCC substrate layer 22 may be mechanically
connected to the electrically insulative flexible tube 14, and be
electrically and mechanically coupled to electrodes 24, such as
gold-loaded conductive polymer electrodes. The PSCC substrate 22
may be functionally and electrically connected to one end of an
electrical conducting element 34. The electrical conducting element
34 is substantially contained within the catheter shaft and is
connected at the other end to a current source 16 (e.g., RF current
source) or an electrical ground 18. A heat sink 20 may thermally
encapsulate, at least partially, the electrically insulative
flexible tube 14. The PSCC substrate layer 22 is capable of bending
and conforming to a compliant tissue wall of a target tissue
28.
[0034] Unlike the first bipolar electrode, as depicted in FIGS.
2A-2B, the electrically insulative flexible tube 14 in the second
bipolar electrode, as depicted in FIGS. 3A-3B, does not contain an
efflux outlet 32. Consequently, any filler material 12 present
within the electrically flexible tube 14 does not come in contact
with either the target tissue 28 or the surrounding tissue 30. The
filler material, if flowable, can then circulate through the
thermally insulative flexible tube, which can be aided by the
introduction of irrigation channels 14'. Thus, the second bipolar
electrode in FIGS. 3A-3B comprises a closed-cooling system as
opposed to an open-cooling system of the first bipolar electrode in
FIGS. 2A-2B.
[0035] The PSCC bipolar electrode system 130 ablates tissue by
delivering ablation energy, depicted in FIG. 3A as electric field
26, via the electrodes 24 when the pressure applied to the PSCC
substrate layer 22 as a result of electrode-tissue contact is
sufficient to engender or provide an electrical response that is
transmitted to the electrodes 24. The applied pressure can be
provided and manipulated directly by an operator (such as an
operating physician), or indirectly through a mechanical device
operably linked to the PSCC electrode 40. The ablation energy 26 is
delivered substantially to the target tissue 28 and not to
surrounding tissue 30 (e.g., blood) by virtue of activating the
PSCC adjacent to the target tissue 28. The pressure sensitivity of
the PSCC substrate layer 22 may be adjusted to match the compliance
target tissue 28, such that the electrical conductivity of the
electrode and the electric field from the electrode is directed
substantially to the target tissue 28. In this embodiment, filler
material 12 may circulate within the inner flexible core 14 or may
be stationary there within. Alternatively, if the filler material
12 is flowable and circulates within the inner flexible core, the
filler material may be circulated once and then dispersed or
disposed of, or may be re-circulated within a loop that is within,
or even exterior to the PSCC bipolar electrode system 10 itself. In
the case of a filler material 12 that is flowable, such filler
material 12 does not enter the surrounding tissues, e.g., 28, 30
when the embodiment shown in FIGS. 3A-3B is used.
[0036] The PSCC electrode 40 having a closed-cooling system for a
flowable filler material 12, as shown in FIGS. 3A-3B, is useful
especially for those procedures wherein the flow of the filler
material 12 to the target tissue 28 or other surrounding tissue 30
may be detrimental to the ablation procedure or difficult to
manage. An example of such difficulty during a procedure may occur
during epicardial RF ablation where, e.g., saline (a flowable
filler material 12) may flow through the efflux outlet of the
electrode 40 into the pericardial sac and conduct ablation energy
to non-targeted tissues. A critical aspect of epicardial ablation
is the functional nature of the surrounding tissue 30; as opposed
to flowing blood in endocardial ablation procedures, the
pericardial fluid with the pericardial sac does not provide
significant additional (convective) cooling of electrode and the
target tissue. Thus, the filler material 12 within a closed-cooling
system can be used to help control the temperature of the electrode
system 130. Additionally, the closed-loop irrigation system can
provide interfacial cooling as well as cooling of the adjoining
tissues, thus minimizing risk of collateral damage. Furthermore, a
cooled interface allows high energy applications during ablation
without causing may be used also allow for creating deeper lesions
as is customarily required in treating ventricular tachycardia.
[0037] FIGS. 4A-4B show yet another embodiment of the present
invention, which can be used for ablation as well as for
electroporation for delivery of chemicals, for example,
electrophoretic compounds, such as drugs, to a targeted tissue. The
main difference from this embodiment when compared to those shown
in FIGS. 2A-2B and 3A-3B is that the heat sink 20 and the
electrically insulative flexible tube 14 are porous or otherwise
permeable, allowing molecules of the chemicals to pass through the
walls. The molecules can be loaded with a filler material 12.
[0038] FIGS. 4A-4B show a PSCC electrode system 140 as a third
bipolar electrode according to the present teaching. FIGS. 4A and
4B show two cross-sectional views taken along the reference lines
of A-A (longitudinal) and B-B (cross-sectional) of FIG. 1A. The
PSCC bipolar electrode system 140 comprises a PSCC electrode 40
that extends from a catheter shaft 42. The PSCC electrode itself 40
comprises a electrically insulative flexible tube 14 located
centrally in the electrode 40 and extends into the catheter shaft
42; the electrically insulative flexible tube 14 may include a
filler material 12 which may contain compounds to be delivered to a
target tissue 28. Optionally, an efflux outlet 32 can be connected
to the electrically insulative flexible tube 14 and, in the case of
flowable filler material 12, can allow such filler material 12 to
flow from the system 140 to the surrounding area (including the
surrounding tissue 30 and the target tissue 28). Returning to the
PSCC electrode 40, a PSCC substrate layer 22 may be mechanically
connected to the electrically insulative flexible tube 14 and may
be electrically and mechanically coupled to electrodes 24, such as
gold-loaded conductive polymer electrodes and wet porous polymer
electrodes. The PSCC substrate 22 may be functionally and
electrically connected to one end of electrical conducting element
34. The electrical conducting element 34 is substantially contained
within the catheter shaft and is connected at the other end to a
current source 16' (e.g. RF and/or direct current source) or an
electrical ground 18. The PSCC substrate later 22 may be connected
functionally and electrically to electrical conducting element 34
and can also be connected to an electrical ground 18. A heat sink
20 may thermally encapsulate, at least partially, the electrically
insulative flexible tube 14. The PSCC substrate layer 22 is capable
of bending and conforming to a compliant tissue wall of a target
tissue 28.
[0039] During electroporation, the bipolar electrodes 26 are
energized with direct current 16 to create tissue ablation via
cellular necrosis or apoptosis. In other applications, the bipolar
electrodes 26 are energized with direct current 16 while the porous
distal portion carries electrophoretic agents, such as
photosensitive drugs for photodynamic therapy. This electroporation
technique therefore provides in situ drug delivery. Such techniques
may be used for tissue conditioning as precursor to ablative
therapies, such as radiofrequency catheter ablation, ultrasound,
and photodynamic therapy. After conditioning the tissue with a
drug, the electrodes can be energized in a bipolar setting using RF
current.
[0040] FIGS. 5A-5B demonstrate how the PSCC becomes electrically
conductive only at the electrode-target tissue wall due to contact
pressure. In this case, the ablation energy 26 only flows between
the electrodes 24 and into the target tissue 28, but not into
surrounding tissue 30. Furthermore, the bipolar configurations, as
shown in FIGS. 2A-2B, 3A-3B and 4A-4B, limit the path of the
ablation energy 26 to localized areas in the target tissue 28 near
the electrodes 24, thereby preventing the current from escaping
into adjacent tissue 30 and causing collateral damage. The
electrode shown in FIGS. 5A-5B has a conductive core 52, and
insulative zone 54. As generally illustrated in the embodiment
shown in FIG. 5A, when the PSCC electrode 40 is in a relatively
contact-free environment, such as air, or in the flowing blood
stream while inside a blood vessel or heart chamber, the PSCC
electrode 40 can be effectively an insulator. When used for an
ablation application, however, the PSCC bipolar electrode system 40
can be placed against a target tissue 28, such as shown in FIG. 5B.
As the contact pressure increases, the PSCC electrode 40 becomes
conductive, having a conductive zone 56 and permits the degree of
contact to activate and/or control operation of PSCC electrode 40,
transmitting ablation energy 26 into the adjacent target tissue 28.
Because of the unique properties of a PSCC electrode 40, only that
portion of the PSCC electrode 40 that is in contact with the target
tissue 28 becomes conductive. Those portions not in direct contact
with the target tissue 28, such as the region facing the
surrounding tissue 30, remain non-conductive, thereby mitigating
current leakage that may cause undesired coagulum and thrombus
formation in untargeted regions.
[0041] The present teachings permit the construction of a flexible,
pressure-sensitive ablation electrode that can be used in a wide
variety of different tissue environments, including for example,
tissues having varying degrees of elasticity and contour. The
present teachings further permit the construction of a flexible
electrode that responds to pressure that is applied to the
electrode, for example, pressure that may be applied to the
electrode by the myocardium. Such electrodes may be used to respond
to pressure that is applied directly to the PSCC component (for
example, when the PSCC component is located at the most distal
portion of a catheter), or to pressure that is applied indirectly
to the PSCC (for example, when an electrode tip is disposed between
the PSCC component and the tissue). When used in conjunction with
an electrode tip, it is desired that the electrode tip be formed of
an electrically conductive material that is relatively stiffer than
the PSCC. This will permit the electrode tip to transfer pressure
from the electrode tip to the PSCC component. Optionally, one or
more additional pressure transfer elements may be used, for
example, between the electrode tip at a distal end and the PSCC
component located at a more proximal end. In the case where a PSCC
component is positioned within a catheter, the PSCC component can
be used to respond to pressure that is applied axially to catheter.
Of course, the PSCC component could be oriented in order to respond
to pressure that is applied transversely to the catheter.
[0042] While the embodiments disclosed in the attached figures
disclose an electrode that is generally cylindrical in shape, the
present invention also contemplates that the electrode may be
formed into various shapes to better fit the contour of the target
tissue. In one embodiment, for example, the electrode can be made
long enough to strap around and form a noose around the pulmonary
veins in epicardial applications. For example, electrical conductor
16 that is coupled to the energy source may be formed into a
desired shape, and then the PSCC layer can be formed over the
conductive element in the preferred shape. For example, the
electrode may be shaped like a spatula for certain applications,
including for example, minimally invasive sub-xyphoid epicardial
applications, where the spatula shape will permit directional
placement and navigation in the pericardial sac. Because PSCC can
be made as a flexible material, it can be used for electrodes
having a great variety of shapes, including a spatula.
[0043] Generally, flexibility is a very desirable characteristic in
a catheter. Some applications, however, may require a less flexible
and/or rigid catheters. Thus, as an alternative to the flexible
embodiments discussed above, it is contemplated that the same
structural design may be used to produce a less flexible (or even
rigid or partially rigid) ablation device. For example, the PSCC
electrode may use a rigid core, instead of a flexible core. It may
be solid conductive core of varying degrees of rigidity, or a
non-conductive core coated with a conductive layer such that the
combination achieves a desired degree of rigidity. A PSCC substrate
layer may then be applied to the core such that when the electrode
is pressed against tissue, the PSCC becomes a conductor and
electrically couples the conductive core (or layer, as the case may
be) to the tissue via the PSCC. In this alternative embodiment, the
PSCC may be coated with one or more outer electrically-conductive
layers (which may be rigid or flexible). In this further
modification, the PSCC layer can be sandwiched between at least two
conductive coatings, and thus under pressure, RF energy may be
delivered to the tissue via the compressible PSCC layer.
[0044] The electrically conductive element may be mounted on an
electrically insulative but thermally conductive shaft. The
thermally conductive shaft can improve the cooling of the electrode
and the electrode-tissue interface temperature during ablation by
thermally conducting heat from the interface to the ambient flowing
blood in endocardial applications. In addition, the thermally
conductive shaft can be equipped with thermal sensors that can be
used for temperature controlled RF ablation. The thermally
conductive shaft may be made of an electrically insulative,
thermally conductive material, including, for example,
COOLPOLY.RTM. thermally conductive, electrically insulative
plastic. In an embodiment, the thermally conductive shaft is made
of a biocompatible, thermally conductive, electrically insulative
material.
[0045] The heat sink can comprise a material with high thermal
conductivity. The use of a heat sink can be particularly useful for
small electrodes typically around 10 mm or less, or for sectioned
electrodes that may give rise to hot spots. The heat sink may be
made of an electrically insulative, thermally conductive material,
including, for example, thermally conductive polyurethane (e.g.,
polyurethane with thermally conductive ceramic powder embedded
therein), diamond, aluminum nitride, boron nitride, silicone,
thermal epoxy and thermally conductive, electrically insulative
plastics. In an embodiment, the thermally conductive shaft is made
of a biocompatible, thermally conductive, electrically insulative
material.
[0046] The electrically insulative member 20 may provide one or
more passageways for carrying filler materials 12 that are flowable
(e.g. saline solution) to the distal end of the electrode and/or
the electrode-tissue interface 100. The passageways include an
inlet to the electrode, and an outlet at the distal end of the
electrode. Moreover, one or more thermal sensors may be placed in
the passageway, for example, to measure the temperature of the
coolant at the inlet and at the outlet. The temperature difference
between the inlet and outlet during ablation could be used to
monitor the efficacy of the electrode-tissue interface cooling and
also to perform temperature-controlled ablation. One or more of the
passageways may be alternatively defined as a cooling tube, which
may comprise the same material as, or a material different from,
the electrically insulative member.
[0047] The electrically insulative tube inside the catheter shaft
may be thermally insulative or may contain a thermally insulative
layer. Such thermal insulation helps minimize the degree to which
the flowable filler material is heated to body temperature as the
result of thermal conduction through the catheter shaft wall as the
fluid travels from the outside fluid source through the catheter
shaft and to the electrode. The thermally conductive tube inside
the electrode, on the other hand, can cool the electrode and the
electrode-tissue interface during ablation by thermally conducting
the heat from the interface to the flowing fluid inside the tube
catheter.
[0048] In an optional embodiment, the electrodes may be combined
with a processor that monitors the current that is being delivered
by the power source. Thus, a computer processor (not shown)
monitors the maximum current being delivered and use this
information to help control the ablation process. Because a PSCC's
resistance drops monotonically as pressure increases, the amount of
current being delivered can be used to assess a degree of contact
between the contact surface and target tissue. Using this
information, the computer processor (not shown) may decrease or
increase the power level of the power source. By way of example
only, the computer processor (not shown) may be used to limit the
total amount of energy that is delivered to a target tissue.
Depending on the nature of the tissue, the power level and the
total energy delivered to the electrode and the tissue may be
increased or decreased to improve the safety and efficacy of lesion
creation.
[0049] The PSCC used in the present invention may be chosen to have
a specific pressure sensitivity. For example, highly sensitive
PSCCs, which register a sharp change in resistance with a finite
amount of applied pressure, may be preferred for soft contact
applications such as the atrial wall. Less sensitive PSCCs, which
require more pressure to register the same amount of change in
resistance, may be preferred for hard contact applications such as
ablation in ventricular walls.
[0050] The RF source to be used with the present invention is
preferably within the radio frequency range of 100-1000 kHz, and
more preferably with 250 kHz-550 kHz. The electrical energy source
(RF and/or direct current source) is preferably capable of
delivering up to 150 Watts of electrical power.
[0051] It is contemplated that each of the embodiments discussed
above may optionally be used in connection with one or more
electrically-conductive, outer coverings. Preferably, the outer
covering is electrically conductive, such as a flexible wire mesh,
a conductive fabric, a conductive polymer layer (which can be
porous or nonporous), or a metal coating. The outer covering may be
used to not only increase the mechanical integrity, but to enhance
the PSCC device's ability to assess the tissue contact (for
example, in the when measuring electrical characteristics using a
reference electrode connected to the target tissue). In some
embodiments, the outer covering may be made using a biocompatible
material in order to help make the overall assembly biocompatible.
Preferably the outer covering is flexible, though certain
applications may prefer a medium to high degree of rigidity.
[0052] One of ordinary skill will appreciate that while the PSCC
materials may be designed to respond to a variety of stresses, the
principles and embodiments herein may be adapted to respond to
specific stress forces, for example, axial forces, orthogonal
forces, twisting, compressing, stretching, etc., without deviating
from the scope of the present invention.
[0053] Although multiple embodiments of this invention have been
described above with a certain degree of particularity, those
skilled in the art could make numerous alterations to the disclosed
embodiments without departing from the spirit or scope of this
invention. All directional references (e.g., upper, lower, upward,
downward, left, right, leftward, rightward, top, bottom, above,
below, vertical, horizontal, clockwise, and counterclockwise) are
only used for identification purposes to aid the reader's
understanding of the present invention, and do not create
limitations, particularly as to the position, orientation, or use
of the invention. Joinder references (e.g., attached, coupled,
connected, and the like) are to be construed broadly and may
include intermediate members between a connection of elements and
relative movement between elements. As such, joinder references do
not necessarily infer that two elements are directly connected and
in fixed relation to each other. It is intended that all matter
contained in the above description or shown in the accompanying
drawings shall be interpreted as illustrative only and not
limiting. Changes in detail or structure may be made without
departing from the spirit of the invention as defined in the
appended claims.
* * * * *