U.S. patent application number 16/117706 was filed with the patent office on 2019-02-21 for design of ablation electrode with tactile sensor.
The applicant listed for this patent is St. Jude Medical, Atrial Fibrillation Division, Inc.. Invention is credited to Hong Cao, Saurav Paul, Riki Thao.
Application Number | 20190053848 16/117706 |
Document ID | / |
Family ID | 39585041 |
Filed Date | 2019-02-21 |
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United States Patent
Application |
20190053848 |
Kind Code |
A1 |
Cao; Hong ; et al. |
February 21, 2019 |
Design of Ablation Electrode with Tactile Sensor
Abstract
A catheter assembly for assessing contact between the catheter
assembly and tissue is disclosed. The assembly includes a catheter
shaft and a pressure sensitive conductive composite member whose
electrical resistance varies with pressure applied to the catheter
assembly. The assembly also includes at least one measurement
terminal to permit the measurement of changes in the electrical
characteristics of the pressure sensitive conductive composite
member. The assembly may optionally include a measurement device to
measure resistance, impedance and/or other electrical
characteristics. The assembly may utilize a reference electrode
secured to the patient's tissue, which permits the measurement
device to measure changes between the reference electrode and the
at least one measurement terminal. Optionally, the assembly may
include a conductive outer layer. Also disclosed are sensor
assemblies, contact sensor, methods of contact sensing, and methods
of manufacturing relating to the use of pressure sensitive
conductive composites.
Inventors: |
Cao; Hong; (Savage, MN)
; Thao; Riki; (Brooklyn Park, MN) ; Paul;
Saurav; (Shoreview, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Atrial Fibrillation Division, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
39585041 |
Appl. No.: |
16/117706 |
Filed: |
August 30, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11647279 |
Dec 29, 2006 |
10085798 |
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16117706 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/6852 20130101;
A61B 18/1492 20130101; A61B 5/6885 20130101; A61B 2090/065
20160201 |
International
Class: |
A61B 18/14 20060101
A61B018/14; A61B 5/00 20060101 A61B005/00 |
Claims
1-27. (canceled)
28. A catheter, comprising: a catheter shaft comprising a distal
portion and a proximal portion, wherein the catheter shaft
comprises at least one tactile sensor that extends longitudinally
along at least a portion of the catheter shaft, and at least one
electrode, wherein the at least one tactile sensor comprises an
inner non-conductive shaft surrounded by a flexible conductive
coil, wherein the flexible conductive coil is operably connected to
an electrical conductor.
29. The catheter of claim 28, wherein the electrical conductor
comprises a plurality of conductive wires.
30. The catheter of claim 28, wherein the at least one tactile
sensor comprises a pressure sensitive conductive composite sensor,
a capacitance sensor, or a piezoelectric sensor.
31. The catheter of claim 28, wherein the at least one electrode
comprises a second tactile sensor.
32. The catheter of claim 31, wherein the second tactile sensor is
a capacitance sensor.
33. The catheter of claim 28, wherein the at least one tactile
sensor is contained entirely within a portion of the catheter shaft
and proximal of the distal portion, and wherein the electrode is an
ablation electrode.
34. The catheter of claim 33, wherein the at least one tactile
sensor is located between the distal portion of the catheter shaft
and the ablation electrode.
35. An electrode assembly, comprising: a thin elongate catheter
shaft having a distal tip and a proximal portion; at least one
tactile sensor contained entirely within a portion of the catheter
shaft and proximal of the distal tip; and an ablation electrode
disposed at the distal end of the electrode assembly; wherein the
at least one tactile sensor is located between the distal tip of
the catheter shaft and the ablation electrode, such that the at
least one tactile sensor detects forces that are applied to the
ablation electrode, and wherein the at least one tactile sensor
comprises a plurality of tactile sensors positioned substantially
in a common plane such that they detect force applied both axially
to the electrode assembly and force applied laterally to the
electrode assembly.
36. The electrode assembly of claim 35 further comprising: an
analysis device coupled to the at least one tactile sensor to
receive respective output signals therefrom, wherein the analysis
device provides information regarding an angle defined between the
ablation electrode and the longitudinal axis of the catheter
shaft.
37. The electrode assembly of claim 36 wherein: the at least one
tactile sensor generates an output signal with a magnitude that is
proportional to the force applied thereto; and the analysis device
provides information regarding a magnitude and direction of the
forces that are applied to the electrode.
38. An electrode assembly, comprising: a thin elongate catheter
shaft having a distal end and a proximal end, wherein the thin
elongate catheter shaft comprises at least one tactile sensor,
wherein the at least one tactile sensor comprises a flexible
conductive coil; and at least one ablation electrode disposed at
the distal end of the thin elongate catheter shaft; wherein the at
least one tactile sensor is located between the distal end of the
catheter shaft and the at least one ablation electrode, such that
the at least one tactile sensor detects forces that are applied to
the at least one ablation electrode, and wherein the flexible
conductive coil is connected to at least one electrical
conductor.
39. The electrode assembly of claim 38, wherein the at least one
electrical conductor comprises a plurality of conductive wires.
40. The electrode assembly of claim 38, wherein the at least one
tactile sensor comprises a pressure sensitive conductive composite
sensor, a capacitance sensor, or a piezoelectric sensor.
41. The electrode assembly of claim 38, wherein the at least one
ablation electrode comprises a second tactile sensor.
42. The electrode assembly of claim 41, wherein the second tactile
sensor is a capacitance sensor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/647,279 filed Dec. 29, 2006, which is related to U.S.
application Ser. No. 11/647,314 filed 29 Dec. 2006, now U.S. Pat.
No. 9,579,483; Ser. No. 11/647,316 filed Dec. 29, 2006, now U.S.
Pat. No. 7,955,326; Ser. No. 11/647,294 filed Dec. 29, 2006, now
U.S. Pat. No. 7,883,508; and Ser. No. 11/553,965 filed 27 Oct.
2006, now U.S. Pat. No. 8,021,361, all of which are hereby
incorporated by reference 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 a contact sensor that
is capable of being using with an ablation apparatus to provide
greater contact sensitivity.
b. Background Art
[0003] Many medical procedures, including for example, creating
lesions with electrical energy, rely on good contact between the
medical device and the tissue. In some catheter applications, the
point of electrode-tissue contact is as far as about 150 cm away
from the point of application of force. This gives rise to
functional and theoretical challenges associated with conventional
devices, and thus, the ability to accurately assess tissue contact
is increasingly important.
[0004] There is a need for contact sensing devices that provide
greater contact sensitivity for control of medical treatments.
[0005] There is a need for improved sensor devices that provide
greater contact sensitivity, especially in connection with RF
ablation treatments.
BRIEF SUMMARY OF THE INVENTION
[0006] Disclosed herein is an electrode assembly having a catheter
shaft, at least one tactile sensor; and an electrode at a distal
end of the electrode assembly. The at least one tactile sensor is
located between the catheter shaft and the electrode such that the
tactile sensor will detect force that is applied to the electrode.
The at least one tactile sensor may comprise two sensors, namely, a
first tactile sensor that detects forces applied axially to the
electrode assembly and a second tactile sensor that detects forces
applied laterally to the electrode assembly. Further, each tactile
sensor may be one that detects compression and stretching forces
and generates an output signal that distinguishes a compression
force applied to the tactile sensor from a stretching force applied
to the tactile sensor. The assembly may include an analysis device
coupled to the first and second tactile sensors such that it
provides directional content information regarding the forces that
are applied to the electrode. The output signal of each tactile
sensor may be a signal with a magnitude that is proportional to the
force applied to the tactile sensor. Optionally, the analysis
device may provide information regarding the magnitude and
direction of the forces that are applied to the electrode. The
tactile sensor may be selected from the group consisting of: a
pressure sensitive conductive composite sensor; a capacitance
sensor; and a piezoelectric sensor. The tactile sensor may use a
pressure sensitive conductive composite material.
[0007] Also disclosed is an electrode assembly having a catheter
shaft, an ablation electrode at a distal end of the electrode
assembly, and a plurality of tactile sensors located between the
ablation electrode and the catheter shaft. Each of the plurality of
tactile sensors may be in a plane that passes transverse to an axis
of the electrode assembly. The plurality of sensors may detect
longitudinal compression forces and transverse bending forces
applied to the ablation electrode. Preferably, each of the
plurality of tactile sensors generates a signal that is indicative
of a characteristic selected from the group consisting of:
resistance; capacitance; voltage; impedance; and combinations
thereof. Preferably, the tactile sensors are selected from the
group consisting of: a pressure sensitive conductive composite
sensor; a capacitance sensor; a piezoelectric sensor; and
combinations thereof. In a particular embodiment, each of the first
and second tactile sensors may be a quantum tunneling conductive
composite sensor. Of course, the tactile sensors may comprise a
piezoelectric wire. In an optional embodiment, each of the
plurality of tactile sensor generates an output signal in
proportion to the compression force applied to the tactile sensor,
and an output device may provide an indication of a direction of
the force applied to the ablation electrode. For example, the
output device may provide information on a direction and magnitude
of the force applied to the ablation electrode.
[0008] Also disclosed is an ablation catheter for ablating tissue.
The catheter has a catheter shaft, an ablation electrode at a
distal end of the ablation catheter, and a plurality of tactile
sensors located between the ablation electrode and the catheter
shaft. The plurality of tactile sensors may be spaced evenly about
a circumference of the ablation catheter, wherein each of the
plurality of tactile sensor generates an output signal in
proportion to the compression force applied to a portion of the
ablation electrode. The catheter may include a controller
configured to receive each of the output signals from the plurality
of tactile sensors, wherein the controller analyzes the output
signals and assesses a degree of contact between the ablation
electrode and the tissue to be ablated. The ablation electrode is
preferably electrically coupled to an ablation energy source such
that the controller generates a control signal to activate the
ablation energy source when the controller determines that the
degree of contact between the ablation electrode and the tissue
exceeds a preset contact threshold. Of course, the controller may
also generate a control signal to deactivate the ablation energy
source when the controller determines that the degree of contact
between the ablation electrode and the tissue exceeds a preset
maximum value. The sensor may be a pressure sensitive conductive
composite sensor; a capacitance sensor; a piezoelectric sensor;
and/or combinations thereof. For example, the tactile sensor may be
made of quantum tunneling conductive composite material. In one
embodiment, the ablation catheter may comprises at least four
tactile sensors which are arranged in opposing pairs and are spaced
evenly about a circumference of the electrode assembly.
[0009] Also disclosed is a method of sensing contact between a
catheter and a tissue. For example, the method may include
providing a catheter having a catheter shaft; an ablation
electrode; and at least one tactile sensor located between the
catheter shaft and the electrode. The catheter may be placed in
contact with the tissue such that at least one force is exerted on
the ablation electrode. The applied force may generate an output
signal from each of the at least one tactile sensors; and further,
may generate a signal that is indicative of a degree of contact
between the catheter and the tissue. The control signal may be used
to inhibit delivery of ablation energy if the degree of contact is
below a preset contact threshold. Alternatively, the control signal
may generate a control signal that activates delivery of ablation
energy if the degree of contact is above a preset contact
threshold. The method may also generate a control signal that
deactivates delivery of ablation energy if the degree of contact is
above a preset maximum value. When two sensors are used, the
outputs can be compared such that an assessment may be made to
determine whether the force is a lateral force. More particularly,
the outputs may be compared in terms of impedance; resistance;
capacitance; current and/or voltage. Multiple reference points may
also be recorded. For example, the devices being used may be
subjected to a first known amount of pressure such that the
resulting output signal may be measured. This may be repeated for
additional known forces. Then, if a unknown force is applied, the
measurement information stored in data may be used to assess the
degree of contact.
[0010] An object of the present invention is to provide a contact
sensor assembly that can assess contact with tissue based on the
degree of pressure that is exerted on the sensor.
[0011] Another object of the present invention is to provide a
flexible contact sensor that measures pressure that is being
exerted on the sensor based on direct or indirect contact between
the sensor and another mass, such as tissue.
[0012] Yet another object of the present invention is to provide a
method of contact sensing.
[0013] Yet another object of the present invention is to provide a
method of manufacturing a contact sensor.
[0014] An objective of the present invention is to provide a
pressure-sensitive, conductive composite-based sensor that may be
used in connection with RF ablation treatment.
[0015] Another objective of the present invention is to provide a
catheter having at least one tactile sensor that can assess whether
sufficient contact exists between an ablation electrode and tissue
to be ablated before ablation begins.
[0016] Yet another objective of the present invention is to provide
a catheter having multiple tactile sensors that can assess a
direction and magnitude of the forces being applied to the
catheter.
[0017] Still another objective of the present invention is to
provide a tactile force sensor that can measure the force asserted
on an electrode by soft tissue.
[0018] Still another objective of the present invention is to
provide a tactile force sensor that can assess contact based on
resistance measurements using a PSCC sensor.
[0019] Still another objective of the present invention is to
provide a tactile force sensor that can assess contact based on
capacitance measurements using a capacitance sensor.
[0020] Still another objective of the present invention is to
provide a tactile force sensor that can assess contact based on
measurements using a piezoelectric sensor.
[0021] An objective of the present invention is to provide a
QTC-based sensor that may be used in connection with RF ablation
treatment.
[0022] Another object of the present invention is to provide a
flexible, contact-sensitive sensor that can be used in a wide
variety of tissue environments.
[0023] Yet another objective of this invention is to provide a
method for practicing medical procedures using a
pressure-sensitive, conductive polymer-based sensor in accordance
with the teachings herein.
[0024] An advantage of using a PSCC in a contact sensor is that the
design may be significantly less complicated, which permits reduced
manufacturing costs and increased reliability.
[0025] The foregoing and other aspects, features, details,
utilities, and advantages of the present invention will be apparent
from reading the following description and claims, and from
reviewing the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIGS. 1A and 1B are perspective views of a representative
embodiment of the present invention, illustrating how the present
invention may be used to assess contact with tissue.
[0027] FIG. 2 is a side view drawing of an exemplary catheter
having a PSCC sensor.
[0028] FIGS. 3A and 3B are cross sectional views that demonstrate
the contact pressure at the sensor-tissue interface.
[0029] FIGS. 4A and 4B are cross-sectional views of a preferred
embodiment of a catheter having a PSCC sensor.
[0030] FIGS. 5A and 5B are cross-sectional views of a preferred
embodiment in which the PSCC sensor is in the shape of a helix.
[0031] FIGS. 6A and 6B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is located about an
inner conductive core.
[0032] FIGS. 7A and 7B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is in the shape of a
mesh.
[0033] FIGS. 8A and 8B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is formed as an outer
substrate layer.
[0034] FIGS. 9A and 9B are cross-sectional views of a preferred
embodiment of a catheter having a PSCC sensor.
[0035] FIGS. 10A and 10B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is in the shape of a
helix.
[0036] FIGS. 11A and 11B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is located about an
inner conductive core.
[0037] FIGS. 12A and 12B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is in the shape of a
mesh.
[0038] FIGS. 13A and 13B are cross-sectional views of another
preferred embodiment in which the PSCC sensor is formed as an outer
substrate layer.
[0039] FIG. 14 is a cross-sectional view of a preferred embodiment
having a single tactile sensor.
[0040] FIGS. 15 and 16 are cross-sectional views of a preferred
embodiment having two tactile sensors.
DETAILED DESCRIPTION OF THE INVENTION
[0041] An ablation electrode having at least one tactile sensor is
disclosed, together with a method of using and a method of
manufacturing the ablation electrode. The present invention
utilizes tactile sensors of three basic types: pressure sensitive
conductive composite sensors; capacitance sensors; and
piezoelectric sensors.
[0042] When used in this application, the terms "pressure sensitive
conductive composite" and "PSCC" mean a pressure sensitive
conductive composite that has unique electrical properties as
follows: the electrical resistance of the PSCC varies inversely in
proportion to the pressure that is applied to the PSCC. The PSCC
material that is most useful with the present invention has a high
electrical resistance when not under stress (that is, in a
quiescent state), and yet the same PSCC material starts to become
conductive under pressure, and indeed, the electrical resistance
may fall to less than one ohm (11) when under sufficient pressure.
When in a quiescent state, the PSCC material preferably has a
resistance that is greater than 100,000 ohms, and more preferably,
greater than about 1M ohms, and most preferably, the PSCC material
is a non-conductor in its quiescent state (e.g., having a
resistance greater than 10M ohms). Preferably, the PSCC material
will also meet cytotoxity, hemolysis, systemic toxicity and
intracutaneous injection standards.
[0043] The present invention will work with different PSCC
materials. For example, U.S. Pat. No. 6,999,821 (which is
incorporated by reference herein as if fully set forth below)
discloses a conductor-filled polymer that may be useful in the
present invention. As disclosed therein, conductor-filled polymers
may include presently available materials approved for implantation
in a human body such as silicone rubber with embedded metallic,
carbon or graphite particles or powder. Silver filled silicone
rubbers of the kind manufactured by NuSil or Specialty Silicone
Products, modified so as to be approved for implantation, are of
potential utility. An example is silver-coated, nickel-filled
silicone rubber sold as NuSil R2637. The substrate need not be
silicone; for example, it is contemplated that other insulating or
weakly conductive materials (e.g., non-conductive elastomers) may
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 may be in the form of powder, grains, fibers or
other shaped forms. The oxides can be mixtures comprising sintered
powders of an oxycompound. The alloy may be conventional or for
example titanium boride.
[0044] Other examples of an acceptable PSCCs for use in the present
invention include quantum tunneling composites ("QTC"), such as
those available through Peratech Ltd. (of Darlington, UK),
including the QTC pill, the QTC substrate and the QTC cables. The
QTC materials designed by Peratech Ltd. have variable resistance
values that range from greater than 10M ohms (in the absence of
stress) to less than 1 ohm when under pressure. Ideally, the QTC
would meet cytotoxity, hemolysis, systemic toxicity and
intracutaneous injection standards.
[0045] Other examples of PSCC materials that may be used in the
present invention include the conductive polymers described and
disclosed in U.S. Pat. No. 6,646,540 ("Conductive Structures");
U.S. Pat. No. 6,495,069 ("Polymer Composition"); and U.S. Pat. No.
6,291,568 ("Polymer Composition"); all of the foregoing patents are
incorporated by reference as if set forth below in their
entireties. These materials are described as having a variable
resistance of greater than 10.sup.12 Ohms before any stress is
applied to less than 1 ohm when finger pressure is applied.
[0046] As a result of this unique property, PSCC materials may be
described as having an 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.OMEGA. to less
than 1.OMEGA.. 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 in the sense that once the pressure is removed, the
electrical resistance is also restored. Thus, a PSCC may be
transformed from an insulator to a conductor, and back to an
insulator, simply by applying the appropriate pressure. PSCCs have
been known to carry large currents (up to 10 Amps) and support
large voltages (40 V and higher).
[0047] Preferably, the PSCC being used in connection with the
present invention 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.
[0048] The PSCC used in the present invention may also be chosen or
customized to be of a specific pressure sensitivity such that the
transformation from an insulator to a conductor occurs over a wide
or narrow range of pressure. For example, highly sensitive PSCCs,
which register a sharp change in resistance with a small 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.
[0049] The unique properties of a PSCC permit the creation of novel
and pressure-sensitive current-control devices for evaluating
tissue contact. The unique properties also permit the creation of
novel and pressure-sensitive sensors to assess contact between the
sensors and tissue that may be the subject of ablation.
[0050] Capacitance sensors utilize a probe that senses changes in
capacitance to assess contact. Typically, driver electronics are
used to convert the changes in capacitance into voltage changes,
such that a device can indicate and/or record the resulting voltage
change. In its most basic form, a capacitor consists of two
conductive plates separated by a dielectric medium. The capacitor
stores energy in the form of an electric field, and the ability to
store energy is measured in capacitance. A capacitance sensor
monitors capacitance which will vary in response to a stimuli such
as touch. A force on a capacitance sensor typically reduces the
sensor's ability to store energy, resulting in a measurable change.
With a capacitance sensor, the sensor surface is the electrified
plate and when pressure is applied, the resulting change in
capacitance can be measured and quantified.
[0051] Piezoelectric sensors utilize a piezoelectric material,
which generates an electrical voltage when the material is placed
under stress. A piezoelectric sensor can be used to measure the
voltage that results when a piezoelectric material is placed under
strain. Piezoelectric materials can be made in a variety of forms,
including for example, piezoelectric wire, piezoelectric film, and
piezoelectric tubes.
[0052] FIGS. 1A and 1B illustrate a sample embodiment of the
present invention. As illustrated in FIGS. 1A and 1B, PSCC contact
sensor 105 includes a catheter shaft 90 and a contact surface 100
that extends from catheter shaft 90. In this embodiment, contact
sensor 105 is flexible such that when it comes into contact with
tissue 12, contact sensor 105 is deflected in direction 18 as
illustrated in FIG. 1b, and the deflection permits the degree of
contact between contact sensor 105 and tissue 12 to be
assessed.
[0053] FIG. 2 is a close-up of the sample embodiment depicted in
FIGS. 1A and 1B. FIG. 2 illustrates cross-sectional reference lines
A-A and B-B, which will be used to illustrate preferred embodiment
of the present invention.
[0054] As illustrated in FIG. 3A, when the PSCC sensor 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 is an insulator. When used for a sensing application, however,
the PSCC sensor is placed against tissue as illustrated in FIG. 3B.
As the contact pressure increases, the PSCC becomes conductive and
permits the degree of contact to be assessed by the sensing device.
Because of the unique properties of a PSCC, only that portion of
the PSCC sensor that is in contact with the tissue becomes
conductive. Those portions which are not in direct contact with the
tissue, such as the region facing the blood, remain non-conductive,
thereby mitigating any current leakage that may cause coagulum and
thrombus formation.
[0055] The resistance of a PSCC sensor changes anisotropically,
based on the variation of the contact pressure on the PSCC sensor.
Thus, as illustrated in FIG. 3B, the contact pressure at the
sensor-tissue interface is maximum at the point (or line) of normal
incidence and gradually decreases along the arc of contact to zero
at the edge of the contact. Because of its ability to detect stress
forces in any direction, the sensor can be designed to be
omni-directional in use.
[0056] FIGS. 4A and 4B illustrate a preferred embodiment of the
present invention, revealing two cross sectional drawings taken
along the reference lines of A-A and B-B as labeled in FIG. 2.
[0057] In FIGS. 4A and 4B, PSCC contact sensor 110 includes a
catheter shaft 90 and a contact surface 100 that extends from
catheter shaft 90. Catheter shaft 90 may be either conductive or
non-conductive, and preferably, catheter shaft 90 is
non-conductive. In this embodiment, the PSCC forms the working
surface of the sensor that is used for contact assessment. As
depicted in FIGS. 4A and 4B, PSCC sensor 110 comprises: flexible
inner conductive core 111; and an outer PSCC substrate layer 112,
which is mechanically and electrically coupled to the flexible
inner conductive core 111. Flexible inner conductive core 111 may
include a flat top (like the top of a right cylinder), or
optionally it may include a portion of a sphere on its distal end
as illustrated in FIG. 4A. Flexible inner conductive core 111 may
be connected to an electrical conductor 114, which may be connected
to an analyzer (not shown). In use, this preferred embodiment is
used to assess contact between PSCC sensor 110 and tissue (not
shown) to which a reference electrode (not shown) has been
attached. PSCC sensor 110 assesses the contact between contact
surface 100 and the subject tissue by monitoring the electrical
characteristics between two nodes, namely, the reference electrode
(not shown) and the flexible inner conductive core 111 (which is
preferably measured using electrical conductor 114). By way of
example, an analyzer (such as an impedance, resistance, capacitance
or other electrical measurement device) may be used to measure the
electrical characteristics present on electrical conductor 114
relative to the reference electrode (not shown) secured to the
tissue being contacted with PSCC sensor 110. Preferably, the
reference electrode is grounded to an electrical ground reference
signal.
[0058] FIGS. 5A and 5B illustrate another preferred embodiment of
the present invention, revealing two cross sectional drawings taken
along the reference lines of A-A and B-B as labeled in FIG. 2. PSCC
sensor 120 extends from a catheter shaft 90, and PSCC sensor 120
comprises: flexible inner conductive coil 121 in the shape of a
helix; and a PSCC substrate layer 122 within which the inner
conductive coil 121 is located. Flexible inner conductive coil 121
is connected to an electrical conductor 114, which may be connected
to an analyzer (not shown). In use, this preferred embodiment is
used to assess contact between PSCC sensor 120 and tissue (not
shown) to which a reference electrode (not shown) has been
attached. PSCC sensor 120 assesses the contact between contact
surface 100 and the subject tissue by monitoring the electrical
characteristics between two nodes, namely, the reference electrode
(not shown) and the flexible inner conductive coil 121 (which is
preferably measured using electrical conductor 114). By way of
example, an analyzer (such as an impedance, resistance, capacitance
or other electrical measurement device) may be used to measure the
electrical characteristics present on electrical conductor 114
relative to the reference electrode (not shown) secured to the
tissue being contacted with PSCC sensor 120. Preferably, the
reference electrode is grounded to an electrical ground reference
signal.
[0059] FIGS. 6A and 6B illustrate yet another preferred embodiment
of the present invention, revealing two cross sectional drawings
taken along the reference lines of A-A and B-B as labeled in FIG.
2. PSCC sensor 130 extends from a catheter shaft 90, and PSCC
sensor 130 comprises: flexible inner conductive coil 131 in the
shape of a helix; an outer PSCC substrate layer 132; and an
electrically insulative flexible shaft 133 located within the helix
of the flexible inner conductive coil 131. Flexible shaft 133 may
optionally include a portion of a sphere on its distal end as shown
in FIG. 6A. Flexible inner conductive coil 131 is connected to an
electrical conductor 114, which may be connected to an analyzer
(not shown). In use, this preferred embodiment is used to assess
contact between PSCC sensor 130 and tissue (not shown) to which a
reference electrode (not shown) has been attached. PSCC sensor 130
assesses the contact between contact surface 100 and the subject
tissue by monitoring the electrical characteristics between two
nodes, namely, the reference electrode (not shown) and the flexible
inner conductive coil 131 (which is preferably measured using
electrical conductor 114). By way of example, an analyzer (such as
an impedance, resistance, capacitance or other electrical
measurement device) may be used to measure the electrical
characteristics present on electrical conductor 114 relative to the
reference electrode (not shown) secured to the tissue being
contacted with PSCC sensor 130. Preferably, the reference electrode
is grounded to an electrical ground reference signal.
[0060] FIGS. 7A and 7B illustrate yet another preferred embodiment
of the present invention, revealing two cross sectional drawings
taken along the reference lines of A-A and B-B as labeled in FIG.
2. PSCC sensor 140 extends from a catheter shaft 90, and PSCC
sensor 140 comprises: flexible inner conductive sheath 141 formed
of a mesh; an outer PSCC substrate layer 142; and an electrically
insulative flexible shaft 143 located interiorly of the flexible
inner conductive sheath 141. Flexible shaft 143 may optionally
include a portion of a sphere at its distal end as shown in FIG.
7A. Flexible sheath 141 is connected to an electrical conductor
114, which may be connected to an analyzer (not shown). In use,
this preferred embodiment is used to assess contact between PSCC
sensor 140 and tissue (not shown) to which a reference electrode
(not shown) has been attached. PSCC sensor 140 assesses the contact
between contact surface 100 and the subject tissue by monitoring
the electrical characteristics between two nodes, namely, the
reference electrode (not shown) and the flexible sheath 141 (which
is preferably measured using electrical conductor 114). By way of
example, an analyzer (such as an impedance, resistance, capacitance
or other electrical measurement device) may be used to measure the
electrical characteristics present on electrical conductor 114
relative to the reference electrode (not shown) secured to the
tissue being contacted with PSCC sensor 140. Preferably, the
reference electrode is grounded to an electrical ground reference
signal.
[0061] FIGS. 8A and 8B illustrate yet another preferred embodiment
of the present invention, revealing two cross sectional drawings
taken along the reference lines of A-A and B-B as labeled in FIG.
2. PSCC sensor 150 extends from a catheter shaft 90, and PSCC
sensor 150 comprises: an electrically insulative flexible shaft
153; a flexible inner conductive layer 151 (formed, for example, as
a coating and/or wrap around flexible shaft 153); and an outer PSCC
substrate layer 152. Electrically insulative flexible shaft 153 and
flexible inner conductive layer 151 may optionally include a
portion of a sphere at their respective distal ends (as illustrated
in FIG. 8A). Flexible inner conductive core 151 is connected to an
electrical conductor 114, which may be connected to an analyzer
(not shown). In use, this preferred embodiment is used to assess
contact between PSCC sensor 150 and tissue (not shown) to which a
reference electrode (not shown) has been attached. PSCC sensor 150
assesses the contact between contact surface 100 and the subject
tissue by monitoring the electrical characteristics between two
nodes, namely, the reference electrode (not shown) and the flexible
inner conductive core 151 (which is preferably measured using
electrical conductor 114). By way of example, an analyzer (such as
an impedance, resistance, capacitance or other electrical
measurement device) may be used to measure the electrical
characteristics present on electrical conductor 114 relative to the
reference electrode (not shown) secured to the tissue being
contacted with PSCC sensor 150. Preferably, the reference electrode
is grounded to an electrical ground reference signal.
[0062] FIGS. 9A and 9B illustrate a preferred embodiment of the
present invention, revealing two cross sectional drawings taken
along the reference lines of A-A and B-B as labeled in FIG. 2. FIG.
9A is a variation of the preferred embodiment illustrated in FIG.
4A. In FIGS. 9A and 9B, PSCC contact sensor 110' includes a
catheter shaft 90 and a contact surface 100 that extends from
catheter shaft 90. Catheter shaft 90 may be either conductive or
non-conductive, and preferably, catheter shaft 90 is
non-conductive. As depicted in FIG. 9A, PSCC sensor 110' comprises:
flexible inner conductive core 111; and an outer PSCC substrate
layer 112, which is mechanically and electrically coupled to the
flexible inner conductive core 111. Flexible inner conductive core
111 may optionally include a portion of a sphere on its distal end,
as illustrated in FIG. 9A. Flexible inner conductive core 111 may
be connected to an electrical conductor 114, which may be connected
to an analyzer (not shown). PSCC substrate layer 112 is covered by
a conductive outer layer 119, which may be connected to an
electrical conductor 116; conductive outer layer 119 may be
flexible, rigid, or it may offer an intermediate degree of
flexibility. In use, this preferred embodiment is used to assess
contact between PSCC sensor 110' and tissue by monitoring the
electrical characteristics between two nodes, namely, the
conductive outer layer 119 (which is preferably measured using
electrical conductor 116) and the flexible inner conductive core
111 (which is preferably measured using electrical conductor 114).
By way of example, an analyzer (such as an impedance, resistance,
capacitance or other electrical measurement device) may be used to
measure the electrical characteristics present on electrical
conductor 114 relative to electrical conductor 116.
[0063] FIGS. 10A and 10B illustrate another preferred embodiment of
the present invention, revealing two cross sectional drawings taken
along the reference lines of A-A and B-B as labeled in FIG. 2. FIG.
10A is a variation of the preferred embodiment illustrated in FIG.
5A. PSCC sensor 120' extends from a catheter shaft 90, and PSCC
sensor 120' comprises: flexible inner conductive coil 121 in the
shape of a helix; and a PSCC substrate layer 122 within which the
inner conductive coil 121 is located. Flexible inner conductive
coil 121 is connected to an electrical conductor 114, which may be
connected to an analyzer (not shown). PSCC substrate layer 112 is
covered by a conductive outer layer 119, which may be connected to
an electrical conductor 116; conductive outer layer 119 may be
flexible, rigid, or it may offer an intermediate degree of
flexibility. In use, this preferred embodiment is used to assess
contact between PSCC sensor 120' and tissue by monitoring the
electrical characteristics between two nodes, namely, the
conductive outer layer 119 (which is preferably measured using
electrical conductor 116) and the flexible inner conductive coil
121 (which is preferably measured using electrical conductor 114).
By way of example, an analyzer (such as an impedance, resistance,
capacitance or other electrical measurement device) may be used to
measure the electrical characteristics present on electrical
conductor 114 relative to electrical conductor 116.
[0064] FIGS. 11A and 11B illustrate yet another preferred
embodiment of the present invention, revealing two cross sectional
drawings taken along the reference lines of A-A and B-B as labeled
in FIG. 2. FIG. 11A is a variation of the preferred embodiment
illustrated in FIG. 6A. PSCC sensor 130' extends from a catheter
shaft 90, and PSCC sensor 130' comprises: flexible inner conductive
coil 131 in the shape of a helix; an outer PSCC substrate layer
132; and an electrically insulative flexible shaft 133 located
within the helix of the flexible inner conductive coil 131.
Flexible shaft 133 may optionally include a portion of a sphere on
its distal end as shown in FIG. 11A Flexible inner conductive coil
131 is connected to an electrical conductor 114, which may be
connected to an analyzer (not shown). PSCC substrate layer 112 is
covered by a conductive outer layer 119, which may be connected to
an electrical conductor 116; conductive outer layer 119 may be
flexible, rigid, or it may offer an intermediate degree of
flexibility. In use, this preferred embodiment is used to assess
contact between PSCC sensor 130' and tissue by monitoring the
electrical characteristics between two nodes, namely, the
conductive outer layer 119 (which is preferably measured using
electrical conductor 116) and the flexible inner conductive coil
131 (which is preferably measured using electrical conductor 114).
By way of example, an analyzer (such as an impedance, resistance,
capacitance or other electrical measurement device) may be used to
measure the electrical characteristics present on electrical
conductor 114 relative to electrical conductor 116.
[0065] FIGS. 12A and 12B illustrate yet another preferred
embodiment of the present invention, revealing two cross sectional
drawings taken along the reference lines of A-A and B-B as labeled
in FIG. 2. FIG. 12A is a variation of the preferred embodiment
illustrated in FIG. 7A. PSCC sensor 140' extends from a catheter
shaft 90, and PSCC sensor 140' comprises: flexible inner conductive
sheath 141 formed of a mesh; an outer PSCC substrate layer 142; and
an electrically insulative flexible shaft 143 located interiorly of
the flexible inner conductive sheath 141. Flexible shaft 143 may
optionally include a portion of a sphere at its distal end as shown
in FIG. 7A. Flexible sheath 141 is connected to an electrical
conductor 114, which may be connected to an analyzer (not shown).
PSCC substrate layer 112 is covered by a conductive outer layer
119, which may be connected to an electrical conductor 116;
conductive outer layer 119 may be flexible, rigid, or it may offer
an intermediate degree of flexibility. In use, this preferred
embodiment is used to assess contact between PSCC sensor 140' and
tissue by monitoring the electrical characteristics between two
nodes, namely, the conductive outer layer 119 (which is preferably
measured using electrical conductor 116) and the flexible sheath
141 (which is preferably measured using electrical conductor 114).
By way of example, an analyzer (such as an impedance, resistance,
capacitance or other electrical measurement device) may be used to
measure the electrical characteristics present on electrical
conductor 114 relative to electrical conductor 116.
[0066] FIGS. 13A and 13B illustrate yet another preferred
embodiment of the present invention, revealing two cross sectional
drawings taken along the reference lines of A-A and B-B as labeled
in FIG. 2. FIG. 13A is a variation of the preferred embodiment
illustrated in FIG. 8A. PSCC sensor 150' extends from a catheter
shaft 90, and PSCC sensor 150' comprises: an electrically
insulative flexible shaft 153; a flexible inner conductive layer
151 (formed, for example, as a coating and/or wrap around flexible
shaft 153); and an outer PSCC substrate layer 152. Electrically
insulative flexible shaft 153 and flexible inner conductive layer
151 may optionally include a portion of a sphere at their
respective distal ends (as illustrated in FIG. 13A). Flexible inner
conductive core 151 is connected to an electrical conductor 114,
which may be connected to an analyzer (not shown). PSCC substrate
layer 112 is covered by a conductive outer layer 119, which may be
connected to an electrical conductor 116; conductive outer layer
119 may be flexible, rigid, or it may offer an intermediate degree
of flexibility. In use, this preferred embodiment is used to assess
contact between PSCC sensor 150' and tissue by monitoring the
electrical characteristics between two nodes, namely, the
conductive outer layer 119 (which is preferably measured using
electrical conductor 116) and the flexible inner conductive core
151 (which is preferably measured using electrical conductor 114).
By way of example, an analyzer (such as an impedance, resistance,
capacitance or other electrical measurement device) may be used to
measure the electrical characteristics present on electrical
conductor 114 relative to electrical conductor 116.
[0067] Electrical conductors 114 and 116 may be implemented using a
single conductive wire or multiple strands of wire. Preferably, the
wires may be made of flexible conductive materials which allow the
surface contacting area to be bent and formed into various shapes
to provide better contact to the tissue. Acceptable materials
include, but are not limited to, stainless steel, nickel titanium
(nitinol), tantalum, copper, platinum, iridium, gold, or silver,
and combinations thereof. Preferably, the material used to
manufacture the conductive element is a bio-compatible electrically
conductive material, such as platinum, gold, silver, nickel
titanium, and combinations thereof. Other electrically conductive
materials coated with bio-compatible materials may also be
employed, including for example, gold-plated copper. Finally, it is
also contemplated that electrically conductive polymers may also be
used provided they are bio-compatible or coated with a
bio-compatible material.
[0068] A further embodiment of the present invention is disclosed
in connection with FIG. 14, namely, an ablation electrode assembly
200, which includes catheter shaft 290, ablation electrode 280 and
tactile sensor 270 positioned there between. Catheter shaft is
typically formed with a non-electrically conductive outer layer and
may have one or more lumens internally of the shaft. Ablation
electrode 280 may be formed of a wide variety of materials
including, but not limited to, stainless steel, nickel titanium
(nitinol), tantalum, copper, platinum, iridium, gold, or silver,
and combinations thereof. Preferably, the material used to
manufacture the ablation electrode is a bio-compatible electrically
conductive material, such as platinum, gold, silver, nickel
titanium, and combinations thereof. Other electrically conductive
materials coated with bio-compatible materials may also be
employed, including for example, gold-plated copper. Finally, it is
also contemplated that electrically conductive polymers may also be
used provided they are bio-compatible or coated with a
bio-compatible material.
[0069] In a typical operation, ablation assembly 200 may be used to
ablate cardiac tissue, and thus, ablation electrode 280 may be
pressed into contact with the myocardium. When the ablation
electrode 280 is in sufficient contact with the myocardium, the
myocardium exerts a force 210 to the ablation electrode 280, mostly
along the longitudinal axis. The force is delivered by ablation
electrode 280 to tactile sensor 270, which is preferably soft and
sufficiently sensitive to measure the small force applied to
ablation electrode 280.
[0070] Tactile sensor 270 may be one of three types of sensors: a
pressure sensitive conductive composite sensor; a capacitance
sensor; and a piezoelectric sensor. A PSCC sensor may utilize any
number of the PSCC materials and embodiments described above.
Preferably the sensor includes, or may be coupled to, a device for
measuring the resistance of the tactile sensor 270. Of course, a
capacitance sensor and/or a piezoelectric sensor may be used, in
which case the sensor preferably includes, or may be coupled to, a
device for measuring the capacitance and/or voltage of the tactile
sensor 270. As described above, the three types of sensors work on
different physical principles. For example, a PSCC material
responds to pressure such that its resistance (or impedance)
changes, and may transform from a non-conductor to a conductor. A
capacitance sensor changes it capacitance based on pressure, and
similarly a piezoelectric sensor varies its output voltage based on
the degree of pressure applied to the surface of the sensor.
[0071] In many applications, the ablation catheter 200 will be
placed in contact with a tissue surface such that the ablation
catheter is orthogonal to the tissue surface, resulting in an axial
force 210 being applied to the ablation electrode 280. When the
force is axial, a single tactile sensor 270 will often be
sufficient to assess the contact between ablation electrode 280 and
the tissue to be ablated.
[0072] For example, if tactile sensor 270 is a PSCC sensor, then
the force 210 will cause the resistance of tactile sensor 270 to
drop, and the extent to which it decreases may be used to assess
the degree of contact between ablation electrode 280 and the tissue
being treated. Similarly, if tactile sensor 270 is a capacitance
sensor, then the force 210 will cause the capacitance of tactile
sensor 270 to drop, and the extent to which it decreases may be
used to assess the degree of contact between ablation electrode 280
and the tissue being treated. If tactile sensor 270 is a
piezoelectric sensor, then the force 210 will cause the voltage
generated by tactile sensor 270 to change (depending on the
configuration, it may increase or decrease), and the extent of the
change may be used to assess the degree of contact between ablation
electrode 280 and the tissue being treated.
[0073] In other applications, it is possible that the force applied
to the catheter is a transverse force, in which case a single
tactile sensor 270 as illustrated in ablation electrode 200 may be
inadequate to assess the contact.
[0074] FIGS. 15-16 depict an ablation electrode 300 with two
tactile sensors 371, 372. First tactile sensor 371 and second
tactile sensor 372 are positioned side by side, which is very
useful in practice. When axial force 310 is applied as illustrated
in FIG. 15, both tactile sensors 371, 372 are compressed by
compressing forces 315, 316, and if axial force 310 is perfectly
axial, then tactile sensors will experience approximately equal
compressing forces.
[0075] When transverse force 311 is applied as illustrated in FIG.
16, tactile sensors 371, 372 are affected differently. As
illustrated, first tactile sensor 371 will experience a pulling or
stretching (that is, tensile) force 317, whereas second tactile
sensor 372 will experience a compression force 318. Depending on
the type of tactile sensor being used, the compression and
stretching forces could result in changes that move in opposite
directions, and a measurement device (such as a computer or other
processor) can deduce useful information about these changes. For
example, as illustrated in FIG. 16, detecting a tensile force 317
on first tactile sensor 371, while simultaneously detecting a
compression force 318 on second tactile sensor 372, will permit the
measurement device to determine that a lateral force 311 is being
applied (based on opposite forces being detected) and further that
the direction is downward (or more particularly, in a direction of
travel from first tactile sensor 371 to second tactile sensor 372.
Thus, the use of two tactile sensors permits the device to
distinguish between an upward lateral force, a downward lateral
force, as well as an axial force (relatively equal forces being
applied to both tactile sensors).
[0076] Applying the teachings herein, one of ordinary skill would
appreciate that additional tactile sensors could be employed in the
ablation electrode, in which case, the electrode could glean
additional directional content out of the applied forces. By way of
example, and without limiting the number of tactile sensors to be
used with the present invention, a catheter may be implemented
using four tactile sensors, each arranged to be located within a
quadrant of the electrode (or in other words, being spaced about a
circumference and about 90 degrees apart). Such an arrangement
would permit the assessment of forces in at least three
directions.
[0077] Of course, the tactile sensors used by the present
inventions will also permit one to determine the magnitude of
forces being applied to the ablation electrode. Generally, the
change effected in the electrical characteristics of the tactile
sensor will vary proportionately with the force being applied. When
used in this context, the term "proportional" in intended to be
construed broadly to encompass all proportionality relationships
and constants.
[0078] It is also contemplated that the present invention may
monitor the impedance of a tactile sensor, for example, in the
event that a measurement device applied an alternating voltage to a
PSCC sensor. The teachings above would be easily applied to
impedance measurements.
[0079] In operation, any of the devices above could be used to
effect an ablation treatment. For example, the ablation device
depicted in FIG. 14 would be placed in contact with a tissue
surface to permit the degree of contact to be assessed by measuring
one of the resistance, capacitance, voltage, and/or impedance.
Based on the measured electrical characteristic, the device could
readily generate a signal that is indicative of a degree of contact
that exists between the catheter and the tissue. Further, if the
measured characteristics were deemed to be associated with a
pressure that is below a minimum pressure threshold, a control
signal could be generated to preclude ablation (e.g., inhibit the
generator's output of ablation energy). Similarly, if the pressure
were deemed to be above a particular threshold (for example,
because the resistance of a PSCC material had dropped too low),
then a signal could be generated that would inhibit ablation.
[0080] In some circumstances it may be permissible to preclude
ablation based on the orientation of the ablation electrode to the
tissue. For example, if it is determined that a bending force is
being applied to the ablation electrode, then the electrode may not
have a desired angle of contact with the surface to be ablated. At
such an angle, ablation may not create the proper lesion. Thus,
ablation could be inhibited until a proper angle of contact is
detected.
[0081] The present invention permits the construction of a
flexible, pressure sensitive contact assessment device that can be
used in a wide variety of different tissue environments, including
for example, tissues having varying degrees of elasticity and
contour.
[0082] The present invention permits the construction of a flexible
sensor to measure pressure that is applied to the sensor, for
example, pressure that may be applied to the sensor by the
myocardium. Such sensors may be used to measure the pressure that
is applied directly to the sensor, or depending on the
configuration of the sensor, it may measure the pressure that is
applied to a component that is in contact with the sensor (as may
be the case when an additional element is disposed between a
PSCC-based sensor and tissue that is exerting pressure on the
additional element). In the case where a PSCC-based sensor is
positioned within a catheter, the PSCC-based sensor is preferably
used to measure pressure that is applied axially to catheter. Of
course, the PSCC based sensor could be oriented in order to measure
pressure that is applied transversely to the catheter.
[0083] While the preferred embodiments disclosed in the attached
figures disclose a contact sensor that is generally cylindrical in
shape, the present invention also contemplates that the contact
sensor may be formed into various shapes to better fit the contour
of the target tissue. In one embodiment, for example, the contact
sensor can be made long enough to strap around and form a noose
around the pulmonary veins in epicardial applications.
Particularly, the conductive element that is coupled to the PSCC
(for example, reference numbers 111, 121, 131, 141, and 151) may be
formed into a desired shape and then the PSCC layer will be formed
over the conductive element in the preferred shape. For example,
the contact sensor may be shaped like a spatula for certain
applications, including for example, minimally invasive sub-xyphoid
epicardial applications, where the spatula shape will permit easy
placement and navigation in the pericardial sac. Because PSCC can
be made to be a flexible material, it can be used to form
electrodes having a great variety of shapes, including a
spatula.
[0084] Alternatively, the conductive element that is coupled to the
PSCC may be formed using shape-memory retaining material, such as
nitinol, which would permit the electrode to be fitted to specific
preset geometries, such as the ostium of a pulmonary vein, such
that the electrode is shaped to provide a desired contact pressure
pattern on the tissue due to the deformation of the wire when
pressed against the tissue.
[0085] Similarly, while the reference to insulative shaft (for
example, 133, 143, and 153) is generally used in connection with a
generally cylindrical member, it is contemplated by the present
invention that the insulative shaft could be in a geometric shape
other than a cylinder, including, for example, a noose, a spatula,
or the shape of the ostium of a pulmonary vein. For purposes of
this application, the term "insulative shaft" is intended to
encompass shapes in addition to a cylindrical shaft.
[0086] Whenever it is desired that the conductive element that is
coupled to the PSCC may be formed in the shape of a helix, such as
is the case with elements 121, and 131, the coil may be chosen to
be of a specific stiffness (i.e., having a characteristic spring
constant) that would allow the coil to exert a desired amount of
pressure on the PSCC when the electrode bends or deflects upon
contact with the tissue. One of skill in the art would understand
that the degree of desired contact pressure would depend in part
upon the elastic property of the tissue being contacted with the
electrode. For example, the atrial wall may require less contact
pressure than the ventricular wall. Thus, electrodes of varying
stiffness can be designed for application in different tissues and
different regions of the heart.
[0087] In some embodiments, for example, as depicted in FIGS. 5, 6
and 7, the conductive element may be mounted on an insulative
shaft. The conductive element can be shaped in any number of ways,
including for example, a coil, mesh, coating or wrap. The
insulative shaft provides additional mechanical support in
applications that require greater amounts of axial pressure and
torque. The insulative shaft may be made of any electrically
insulative material, including, for example, polyurethane.
Preferably, the insulative shaft is made of a biocompatible,
electrically insulative material.
[0088] The embodiments described above can be used with a processor
such that the processor may provide more precise information about
the pressures being encountered by the embodiment. In particular,
any of the sensors described above may be used with a memory device
to record information regarding one or more forces that are applied
to the sensor. For example, a first known pressure may be applied
to the contact sensor and a first measurement of an electrical
characteristic may be made such that the first known pressure may
be associated with the first measurement. Similarly, a second known
pressure may be applied to the contact sensor and a second
measurement of an electrical characteristic may be made such that
the second known pressure may be associated with the second
measurement. Additional known pressures may be applied and
additional corresponding measurements may be made and associated.
Then, if an unknown pressure is applied, the processor may use the
known pressures and their respective associated measurements to
help quantify the unknown pressure, for example by interpolating or
extrapolating the value of the unknown pressure from the known
pressures.
[0089] While the embodiments above are discussed in the context of
applied pressure, the embodiments above can also be used to assess
forces relative to contact between tissue and the contact sensor.
Pressure is simply a measurement of the force per unit area, and
thus, to assess force, the surface area of a contact surface must
be known or be capable of being determined or calculated. The force
information may be derived from the information available on forces
and the contact surface area.
[0090] Though not depicted, it is contemplated that each of the
embodiments discussed above may optionally be used in connection
with one or more electrically-conductive, outer protective
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 contact sensor's
ability to assess the tissue contact (for example, when measuring
electrical characteristics using a reference electrode connected to
the target tissue). In some cases, the outer covering may be made
using a biocompatible material in order to help make the overall
assembly biocompatible.
[0091] Though not depicted, it is also contemplated that in certain
sensor configurations, it may be desirable to optionally use an
electrically non-conductive outer protective covering. In such
cases, an outer covering that is electrically insulative, such as a
non-conductive polymer layer (which can be porous or nonporous),
may be used to increase the mechanical integrity. In some cases,
the outer covering may be made using a biocompatible material in
order to help make the overall assembly biocompatible. Such an
electrically-non-conductive covering may also serve as a pressure
transfer element to more evenly distribute pressure to the pressure
sensitive conductive composite member.
[0092] 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 forces, compressing forces, stretching forces,
etc., without deviating from the scope of the present
invention.
[0093] While many of the embodiments above are discussed in the
context of a PSCC sensor, the same principles can be applied to
devices having tactile sensors of a non-PSCC material.
[0094] 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.
* * * * *