U.S. patent application number 14/496153 was filed with the patent office on 2015-03-12 for system and method for measuring force and torque applied to a catheter electrode tip.
The applicant listed for this patent is St. Jude Medical, Atrial Fibrillation Division, Inc.. Invention is credited to Gleb V. Klimovitch, John W. Sliwa.
Application Number | 20150073245 14/496153 |
Document ID | / |
Family ID | 42285798 |
Filed Date | 2015-03-12 |
United States Patent
Application |
20150073245 |
Kind Code |
A1 |
Klimovitch; Gleb V. ; et
al. |
March 12, 2015 |
System and method for measuring force and torque applied to a
catheter electrode tip
Abstract
A contact sensing assembly including a catheter including an
electrode having a base portion mounted adjacent a head portion of
the catheter body. A sensor is disposed adjacent the base portion
for measuring compression or tensile forces applied to an electrode
tip portion, and includes a predetermined sensitivity. The base and
head portions include predetermined rigidity so that forces applied
to the electrode tip portion are determinable as a function of the
sensitivity and a sensor output. A contact sensing assembly also
includes an electrode pipe operatively connected to the catheter
body for movement and bending with the catheter body, and an
electrode wire disposed in the electrode pipe and including
isolation. A change in capacitance resulting from movement of the
electrode wire toward the electrode pipe or contact of the
electrode wire with the electrode pipe during bending of the
catheter correlates to a force applied to the catheter.
Inventors: |
Klimovitch; Gleb V.; (Santa
Clara, CA) ; Sliwa; John W.; (Los Altos Hills,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Atrial Fibrillation Division, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
42285798 |
Appl. No.: |
14/496153 |
Filed: |
September 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12347607 |
Dec 31, 2008 |
8864757 |
|
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14496153 |
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Current U.S.
Class: |
600/373 ;
600/459; 606/41; 607/119 |
Current CPC
Class: |
A61N 1/05 20130101; A61B
2218/002 20130101; A61B 8/12 20130101; A61B 18/1492 20130101; A61B
18/24 20130101; A61B 5/6885 20130101; A61B 18/02 20130101; A61N
7/022 20130101; A61B 2090/065 20160201; A61B 5/042 20130101 |
Class at
Publication: |
600/373 ; 606/41;
600/459; 607/119 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61N 1/05 20060101 A61N001/05; A61B 8/12 20060101
A61B008/12; A61B 18/14 20060101 A61B018/14; A61B 5/042 20060101
A61B005/042 |
Claims
1-39. (canceled)
40. A contact sensing assembly comprising: a catheter comprising a
body having a proximal end, a distal end, and a head portion; an
electrode comprising a tip portion and a base portion, wherein the
base portion is adjacent to the head portion of the catheter body;
a gap separating the base portion of the electrode and the head
portion of the catheter body; and three individual sensors, each
individual sensor being attached in the gap between the base
portion of the electrode and the head portion of the catheter so
that each of the sensors is configured to experience the following
forces: (i) a compressive force when a part of the base portion
adjacent the particular individual sensor is forced toward a part
of the head portion adjacent the particular individual sensor, and
(ii) a tensile force when the part of the base portion adjacent the
particular sensor is forced away from the part of the head portion
adjacent the particular sensor; wherein each of the three sensors
is adapted to provide an output signal corresponding to a
compressive or tensile force across the gap experienced by each
respective sensor; and wherein a contact force applied to the
electrode is a function of an aggregation of the output signals
from the three sensors.
41. The contact sensing assembly of claim 40, wherein the output
signals are voltage output signals.
42. The contact sensing assembly of claim 40, wherein each of the
three sensors has a predetermined sensitivity; and wherein the base
and head portions of the electrode include a predetermined rigidity
so that an axial component of the contact force applied to the
electrode is determinable as a sum of the output signals from the
three sensors divided by the predetermined sensitivity of each of
the three sensors, respectively.
43. The contact sensing assembly of claim 42, wherein torque
applied to the electrode is determinable as a function of the
output signals from the three sensors divided by the predetermined
sensitivity of each of the three sensors, respectively, and a
distance of the three sensors from a central axis of the
electrode.
44. The contact sensing assembly of claim 43, wherein for an
electrode having a central axis disposed along a z-direction,
torque applied to the electrode is determinable as follows:
T_y=3/4*D*(V_c/.alpha..sub.--c-V_a/.alpha._a-V_b/.alpha._b), where
T_y is the torque applied to the electrode in a y-direction, D is a
diameter of a circle passing through the center of each of the
three sensors, V is a voltage output of each respective individual
sensor, and .alpha. is the predetermined sensitivity of each
respective individual sensor.
45. The contact sensing assembly of claim 43, wherein for an
electrode having a central axis disposed along a z-direction,
torque applied to the electrode is determinable as follows:
T_x=sqrt(3)/2*D*(V_a/.alpha._a-V_b/.alpha._b), where T_x is the
torque applied to the electrode in a x-direction, D is a diameter
of a circle passing through the center of each of the three
sensors, V is a voltage output of each respective individual
sensor, and .alpha. is the predetermined sensitivity of each
respective individual sensor.
46. The contact sensing assembly of claim 40, further comprising a
coupling member connecting the electrode to the catheter body.
47. The contact sensing assembly of claim 46, wherein the coupling
member comprises an elastic material.
48. The contact sensing assembly of claim 40, wherein the
individual sensors are emplaced in the gap between at least two
annular or circular rings.
49. The contact sensing assembly of claim 40, wherein the tip
portion of the electrode comprises a temperature sensor.
50. The contact sensing assembly of claim 49, wherein the tip
portion of the electrode comprises an irrigation port.
51. The contact sensing assembly of claim 40, wherein the electrode
comprises one of an RF ablation electrode, a HIFU ablation
transducer, a laser ablation assembly, a cryogenic ablation
assembly, an ultrasonic imaging apparatus, an electrical cardiac
pacing electrode, and an electrical cardiac sensing electrode.
52. The contact sensing assembly of claim 40, wherein the three
sensors are fabricated using at least one of flex circuit
technology, lithographic technology, thin-film technology, and
thick film technology.
53. The contact sensing assembly of claim 40, wherein the contact
force applied to the electrode is utilized for at least one of: a)
automatically limiting a maximum force; b) warning of a high or
unacceptable force; c) giving visual or audible feedback to a
practitioner regarding a tissue contact force; d) warning of a loss
of contact force or contact; and e) warning of a contact force
which is too low.
54. A contact sensing assembly comprising: a catheter comprising a
body having a proximal end, a distal end, and a head portion; an
electrode comprising a tip portion and a base portion, wherein the
base portion is adjacent to the head portion of the catheter body;
a gap separating the base portion of the electrode and the head
portion of the catheter body; and three individual sensors, each
individual sensor being attached in the gap between the base
portion of the electrode and the head portion of the catheter, each
of the three individual sensors including the following: A) a first
sensor located at a first position between the base portion of the
electrode and the head portion of the catheter body, wherein said
first sensor is configured for outputting a first signal related to
a first compressive or tensile force applied to the first sensor by
movement of the electrode relative to the catheter, and (B) a
second sensor located at a second position between the base portion
of the electrode and the head portion of the catheter body, wherein
the second position is different from the first position, and
wherein said second sensor is configured for outputting a second
signal related to a second compressive or tensile force applied to
the second sensor by movement of the electrode relative to the
catheter; wherein the base and head portions at the first and
second positions include predetermined rigidities so that an axial
component of a contact force applied to the electrode is
determinable as a function of the predetermined sensitivities of
the first and second sensors and the first and second output
signals from the first and second sensors, respectively.
55. The contact sensing assembly of claim 54, wherein a torque
applied to the electrode is determinable as a function of a sum of
the first and second output signals of each of the three individual
sensors divided by, respectively, the predetermined sensitivity of
each individual sensor, and a distance of the individual sensors
from a central axis of the electrode.
56. The contact sensing assembly of claim 55, wherein for an
electrode having a central axis disposed along a z-direction, a
torque applied to the electrode is determinable as follows:
T_y=3/4*D*(V_c/.alpha._c-V_a/.alpha._a-V_/.alpha._b), where T_y is
the torque applied to the electrode in a y-direction, D is a
diameter of a circle passing through the center of each individual
sensor, V is a voltage output of each respective individual sensor,
and a is the predetermined sensitivity of each respective
individual sensor.
57. The contact sensing assembly of claim 55, wherein for an
electrode having a central axis disposed along a z-direction, a
torque applied to the electrode is determinable as follows:
T_x=sqrt(3)/2*D*(V_a/.alpha._a-V_b/.alpha._b), where T_x is the
torque applied to the electrode in a x-direction, D is a diameter
of a circle passing through the center of each individual sensor, V
is a voltage output of each respective individual sensor, and
.alpha. is the predetermined sensitivity of each respective
individual sensor.
58. The contact sensing assembly of claim 54, further comprising a
coupling member connecting the electrode to the catheter body.
59. The contact sensing assembly of claim 58, wherein the coupling
member comprises an elastic material.
60. The contact sensing assembly of claim 54, wherein the
individual sensors are emplaced in the gap between at least two
annular or circular rings.
61. The contact sensing assembly of claim 54, wherein the tip
portion of the electrode comprises a temperature sensor.
62. The contact sensing assembly of claim 54, wherein the tip
portion of the electrode comprises an irrigation port.
63. The contact sensing assembly of claim 54, wherein the electrode
comprises one of an RF ablation electrode, a HIFU ablation
transducer, a laser ablation apparatus, a cryogenic ablation
assembly, an ultrasonic imaging transducer, a cardiac pacing
electrode, and a cardiac sensing electrode.
64. The contact sensing assembly of claim 54, wherein the
individual sensors are fabricated using at least one of flex
circuit technology, lithographic technology, thin-film technology,
and thick film technology.
65. The contact sensing assembly of claim 54, wherein the
determined contact force applied to the electrode is utilized for
at least one of: a) automatically limiting a maximum force; b)
warning of a high or unacceptable force; c) giving visual or
audible feedback to a practitioner regarding a tissue contact
force; d) warning of a loss of contact force or contact; and e)
warning of a contact force which is too low.
66. The contact sensing assembly of claim 54, wherein each sensor
of the individual sensors is one of a resistive force sensor and a
capacitive force sensor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/347,607, filed 31 Dec. 2008, now pending, which is hereby
incorporated by reference as though fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] a. Field of the Invention
[0003] This invention relates to a system and method for assessing
the force and torque between an electrode and tissue in a body. In
particular, the instant invention relates to a system and method
for assessing the force and torque between an electrode tip on a
diagnostic and/or therapeutic medical device such as a mapping or
ablation catheter and tissue, such as cardiac tissue. The instant
invention also relates to a method for sensing and calculating
contact force exerted by another component on a tissue, and
generally, a method for sensing and calculating contact force on an
elongate member when in contact with another component or
structure, for medical or non-medical purposes.
[0004] b. Background Art
[0005] Electrodes are used on a variety of diagnostic and/or
therapeutic medical devices. For example, electrodes may be used on
cardiac mapping catheters to generate an image of the internal
geometry of a heart and electrical potentials within the tissue.
Electrodes are also used on ablation catheters to create tissue
necrosis in cardiac tissue to correct conditions such as atrial
arrhythmia (including, but not limited to, ectopic atrial
tachycardia, atrial fibrillation, and atrial flutter). Arrhythmia
can create a variety of dangerous conditions including irregular
heart rates, loss of synchronous atrioventricular contractions and
stasis of blood flow which can lead to a variety of ailments and
even death. It is believed that the primary cause of atrial
arrhythmia is stray electrical signals within the left or right
atrium of the heart. The ablation catheter imparts ablative energy
(e.g., radiofrequency energy, cryoablation, lasers, chemicals,
high-intensity focused ultrasound, etc.) to cardiac tissue to
create a lesion in the cardiac tissue. This lesion disrupts
undesirable electrical pathways and thereby limits or prevents
stray electrical signals that lead to arrhythmias.
[0006] The safety and effectiveness of many of diagnostic and/or
therapeutic devices is often determined in part by the proximity of
the device and the electrodes to the target tissue. In mapping
catheters, the distance between the electrodes and the target
tissue affects the strength of the electrical signal and the
identity of the mapping location. The safety and effectiveness of
ablation lesions is determined in part by the proximity of the
ablation electrode to target tissue and the effective application
of energy to that tissue. If the electrode is too far from the
tissue or has insufficient contact with the tissue, the lesions
created may not be effective. On the other hand, if the catheter
tip containing the electrode contacts the tissue with excessive
force, the catheter tip may perforate or otherwise damage the
tissue (e.g., by overheating). Therefore, to successfully ablate
live tissue, the electrode should be applied to the tissue with
proper force. When ablating and moving an electrode, in addition to
the magnitude of the force, knowledge of direction of the force
(i.e. multi-axial measurement) and further the torque acting on the
electrode tip are important for estimating the distribution of
pressure and stress over an electrode tip surface.
[0007] Contact force between a catheter electrode and tissue has
typically been determined using one or more of the following
methods: clinician sense, fluoroscopic imaging, intracardiac echo
(ICE), atrial electrograms (typically bipolar D-2), pacing
thresholds, evaluation of lesion size at necropsy and measurement
of temperature change at the energy delivery site. Each of these
methods has disadvantages, however.
[0008] For example, although a clinician can evaluate contact force
based on tactile feedback from the catheter and prior experience,
the determination depends largely on the experience of the
clinician and is also subject to change based on variations in the
mechanical properties of catheters used by the clinician. The
determination is particularly difficult when using catheters that
are relatively long (such as those used to enter the left atria of
the heart).
[0009] Because fluoroscopic images are two-dimensional projections
and blood and myocardium attenuate x-rays similarly, it can be
difficult to quantify the degree of contact force and detect when
the catheter tip is not in contact with the tissue.
[0010] Intracardiac echo can be time consuming and it can be
difficult to align the echo beam with the ablation catheter.
Further, intracardiac echo does not always permit the clinician to
confidently assess the degree of contact and can generate
unacceptable levels of false positives and false negatives in
assessing whether the electrode is in contact with tissue.
[0011] Atrial electrograms do not always correlate well to tissue
contact and are also prone to false negatives and positives. Pacing
thresholds also do not always correlate well with tissue contact
and pacing thresholds can be time-consuming and also prone to false
positives and negatives because tissue excitability may vary in
hearts with arrhythmia. Evaluating lesion size at necropsy is
seldom available in human subjects, provides limited information
(few data points) and, further, it is often difficult to evaluate
the depth and volume of lesions in the left and right atria.
Finally, temperature measurements provide limited information (few
data points) and can be difficult to evaluate in the case of
irrigated catheters.
[0012] The inventors herein have thus recognized a need for a
system and method for determining the contact force and torque upon
an electrode tip, both during RF ablation and when driving the RF
electrode to the ablation site, that will minimize and/or eliminate
one or more of the above-identified deficiencies.
BRIEF SUMMARY OF THE INVENTION
[0013] It is desirable to provide a system and method for
determining the degree of coupling between an electrode and a
tissue in a body. In particular, it is desirable to be able to
determine a degree of electrical coupling between electrodes on a
diagnostic and/or therapeutic medical device such as a mapping or
ablation catheter and tissue, such as cardiac tissue.
[0014] A system for assessing a degree of coupling between an
electrode and a tissue in a body in accordance with one embodiment
of the invention may include a contact sensing assembly including a
catheter having a body having a proximal end and a distal end, and
an electrode including a tip portion and a base portion mounted
adjacent a head portion of the catheter body. One or more force and
torque sensors may be disposed generally adjacent the base portion
and may include one or more pressure sensors for measuring pressure
applied to the electrode tip portion and providing a pressure
signal related to the measured pressure, with the pressure sensor
including a predetermined sensitivity. The base and head portions
may include a predetermined rigidity so that force applied to the
electrode tip portion may be determinable as a function of the
predetermined sensitivity and the pressure signal.
[0015] For the assembly described above, in an embodiment, the
assembly may include a plurality of pressure sensors, and the
individual pressure sensor output signals allow a vector
reconstruction of a net tip contact force using a vector addition
algorithm or relationship. In an embodiment, the assembly may
further include a plurality of pressure sensors, and the force
applied to the electrode tip portion may be determinable as a sum
of a voltage output signal of each pressure sensor respectively
divided by the predetermined sensitivity of each pressure sensor.
In an embodiment, the assembly may further include a plurality of
pressure sensors, and torque applied to the electrode tip portion
may be determinable as a function of a voltage output signal of
each pressure sensor respectively divided by the predetermined
sensitivity of each pressure sensor, and a distance of the pressure
sensors from a central axis of the electrode.
[0016] For the assembly described above, in an embodiment, the
assembly may include three symmetrically disposed pressure sensors,
and for an electrode having a central axis disposed along a
z-direction, torque applied to the electrode tip portion may be
determinable as follows:
T_y=3/4*D*(V_c/.alpha._c-V_a/.alpha._a-V_b/.alpha._b), where T_y
may be the torque applied to the electrode tip portion in a
y-direction, D may be a diameter of a circle passing through the
centers of each pressure sensor, V may be a voltage output of each
respective pressure sensor, and .alpha. may be the predetermined
sensitivity of each respective pressure sensor. In an embodiment,
the assembly may include three symmetrically disposed pressure
sensors, and for an electrode having a central axis disposed along
a z-direction, torque applied to the electrode tip portion may be
determinable as follows:
T_x=sqrt(3)/2*D*(V_a/.alpha._a-V_b/.alpha._b), where T_x may be the
torque applied to the electrode tip portion in a x-direction, D may
be a diameter of a circle passing through the centers of each
pressure sensor, V may be a voltage output of each respective
pressure sensor, and a may be the predetermined sensitivity of each
respective pressure sensor.
[0017] For the assembly described above, in an embodiment, the
generally distal end of the catheter may include a coupling member
connecting the electrode to the catheter body. In an embodiment,
the coupling member may include an elastic material. In an
embodiment, the pressure sensors may be emplaced in an interface
between two or more annular or circular rings. In an embodiment,
the tip portion of the electrode may include an irrigation port.
The electrode may include an RF ablation electrode, a HIFU ablation
transducer, a laser ablation assembly, a cryogenic ablation
assembly, an ultrasonic imaging apparatus, an electrical cardiac
pacing electrode, or an electrical cardiac sensing electrode. The
pressure sensors may be fabricated using flex circuit technology,
lithographic technology, thin-film technology, and/or thick film
technology. In an embodiment, the assembly may further include a
proximal control handle including one or more catheter deflection
or articulation controls, and one or more switches for controlling
a diagnostic or therapeutic function of the electrode. The force
applied to the electrode tip may be utilized for automatically
limiting a maximum force, warning of a high or unacceptable force,
giving visual or audible feedback to a practitioner regarding a
tissue contact force, warning of a loss of contact force or
contact, and/or warning of a contact force which may be too
low.
[0018] In an embodiment, a system for assessing a degree of
coupling between an electrode and a tissue in a body may include a
contact sensing assembly including a catheter including a body
having a proximal end and a distal end, and an electrode including
a tip portion and a base portion mounted adjacent a head portion of
the catheter body. One or more sensors may be disposed generally
adjacent the base portion for measuring compression or tensile
forces applied to the electrode tip portion and providing an output
signal related to the measured forces, with the sensor including a
predetermined sensitivity. The base and head portions may include a
predetermined rigidity so that the compression or tensile forces
applied to the electrode tip portion are determinable as a function
of the predetermined sensitivity and the output signal.
[0019] For the assembly described above, in an embodiment, the
assembly may include a plurality of sensors, and the individual
sensors each generate an output signal that together provide a
vector reconstruction of a net tip contact force using a vector
addition algorithm or relationship. In an embodiment, the assembly
may include a plurality of sensors, and the compression or tensile
forces applied to the electrode tip portion may be determinable as
a sum of the output signals of each sensor respectively divided by
the predetermined sensitivity of each sensor. In an embodiment, the
assembly may include a plurality of sensors, and torque applied to
the electrode tip portion may be determinable as a function of the
output signal of each sensor respectively divided by the
predetermined sensitivity of each sensor, and a distance of the
sensors from a central axis of the electrode.
[0020] For the assembly described above, in an embodiment, the
assembly may include three symmetrically disposed sensors, and for
an electrode having a central axis disposed along a z-direction,
torque applied to the electrode tip portion may be determinable as
follows: T_y=3/4*D*(V_c/.alpha._c-V_a/.alpha._a-V_b/.alpha._b),
where T_y may be the torque applied to the electrode tip portion in
a y-direction, D may be a diameter of a circle passing through the
centers of each sensor, V may be a voltage output of each
respective sensor, and .alpha. may be the predetermined sensitivity
of each respective sensor. In an embodiment, the assembly may
include three symmetrically disposed sensors, and for an electrode
having a central axis disposed along a z-direction, torque applied
to the electrode tip portion may be determinable as follows:
T_x=sqrt(3)/2*D*(V_a/.alpha._a-V_b/.alpha._b), where T_x may be the
torque applied to the electrode tip portion in a x-direction, D may
be a diameter of a circle passing through the centers of each
sensor, V may be a voltage output of each respective sensor, and a
may be the predetermined sensitivity of each respective sensor.
[0021] For the assembly described above, in an embodiment, the
generally distal end of the catheter may include a coupling member
connecting the electrode to the catheter body. In an embodiment,
the coupling member includes an elastic material. In an embodiment,
the sensors may be emplaced in an interface between two or more
annular or circular rings. In an embodiment, the tip portion of the
electrode may include an irrigation port. The electrode may include
an RF ablation electrode, a HIFU ablation transducer, a laser
ablation apparatus, a cryogenic ablation assembly, an ultrasonic
imaging transducer, a cardiac pacing electrode, or a cardiac
sensing electrode. The sensors may be fabricated using flex circuit
technology, lithographic technology, thin-film technology, and/or
thick film technology. In an embodiment, the assembly may include a
proximal control handle including one or more catheter deflection
or articulation controls, and one or more switches for controlling
a diagnostic or therapeutic function of the electrode. The
compression or tensile force applied to the electrode tip may be
utilized for automatically limiting a maximum force, warning of a
high or unacceptable force, giving visual or audible feedback to a
practitioner regarding a tissue contact force, warning of a loss of
contact force or contact, and/or warning of a contact force which
may be too low. The sensor may be a resistive force sensor, a
capacitive force sensor, or an optical force sensor.
[0022] In an embodiment, a system for assessing a degree of
coupling between an electrode and a tissue in a body may include a
contact sensing assembly including a catheter having a body having
a proximal end and a distal end, an electrode pipe disposed in the
catheter body, and an electrode wire disposed in the electrode pipe
and including isolation thereon. A change in capacitance resulting
from movement of the electrode wire toward the electrode pipe or
contact of the electrode wire with the electrode pipe during
bending of the catheter may directly correlate to a force applied
to the catheter.
[0023] For the assembly described above, in an embodiment, the
electrode wire and electrode pipe may be mechanically coupled
toward a distal end thereof An electrode operatively connected to
the catheter may include an RF ablation electrode, a HIFU ablation
transducer, a laser ablation apparatus, a cryogenic ablation
assembly, an ultrasonic imaging transducer, a cardiac pacing
electrode, or a cardiac sensing electrode. In an embodiment, the
assembly may further include a proximal control handle including
one or more catheter deflection or articulation controls, and one
or more switches for controlling a diagnostic or therapeutic
function of an electrode operatively connected to the catheter. The
compression or tensile force applied to the electrode tip may be
utilized for automatically limiting a maximum force, warning of a
high or unacceptable force, giving visual or audible feedback to a
practitioner regarding a tissue contact force, warning of a loss of
contact force or contact, and/or warning of a contact force which
may be too low.
[0024] In an embodiment, a system for assessing a degree of
coupling between an electrode and a tissue in a body may include a
contact sensing assembly including a catheter having a body having
a proximal end and a distal end, an electrode pipe operatively
connected to the catheter body for movement and/or bending with the
catheter body, and an electrode wire disposed in the electrode pipe
and including isolation thereon. A change in capacitance resulting
from movement of the electrode wire toward the electrode pipe or
contact of the electrode wire with the electrode pipe during
bending of the catheter may directly correlate to a force applied
to the catheter.
[0025] The foregoing and other aspects, features, details,
utilities and advantages of the invention will be apparent from
reading the following description and claims, and from reviewing
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a partial perspective view of a catheter assembly
in accordance with an embodiment of the invention;
[0027] FIG. 2 is an isometric diagrammatic view of an electrode
area according to the invention, illustrating exemplary force and
torque sensors;
[0028] FIG. 3 is a top view of the electrode area of FIG. 2, with
the electrode removed for clarity;
[0029] FIG. 4 is a partial diagrammatic view of a catheter assembly
in accordance with another embodiment of the invention;
[0030] FIGS. 5a-5d are partial isometric diagrammatic views of a
catheter structure in accordance with another embodiment of the
invention; and
[0031] FIGS. 6a-6f are schematic overviews of a system for
measuring force and torque in accordance with alternate embodiments
of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0032] Referring now to the drawings wherein like reference
numerals are used to identify like components in the various views,
FIG. 1 illustrates an exemplary embodiment of a contact sensing
assembly 10 as provided by the invention. In a general form,
referring to FIGS. 1 and 2, contact sensing assembly 10 may include
a catheter 12, an electrode 14 connected to the catheter, and a
force and torque sensor 16 for interacting with base 18 of
electrode 14 or alternatively with head 20 of catheter body 22 if
sensor 16 is mounted on base 18. In another embodiment, contact
sensing assembly 10 may include a first interactive component and a
second interactive component. The contact sensing assembly may be
used in the diagnosis, visualization, and/or treatment of tissue
(such as endocardial tissue) in a body. Contact sensing assembly 10
may be used in a number of diagnostic and therapeutic applications,
such as for example, the recording of electrograms in the heart,
the performance of cardiac ablation procedures, and/or various
other applications. The catheter assembly can be used in connection
with a number of applications that involve humans, or other
mammals, for tissue observation, treatment, repair or other
procedures. Moreover, the invention is not limited to one
particular application, but rather may be employed by those of
ordinary skill in the art in any number of diagnostic and
therapeutic applications, and for medical or non-medical purposes.
For example, the contact sensing assemblies disclosed herein may be
usable in combination with a robotic catheter system (e.g.
disclosed in commonly owned and copending applications titled
"Robotic Catheter System," "Robotic Catheter Manipulator Assembly,"
"Robotic Catheter Device Cartridge," "Robotic Catheter Rotatable
Device Cartridge," "Robotic Catheter Input Device," "Robotic
Catheter System Including Haptic Feedback," and "Robotic Catheter
System with Dynamic Response," the respective disclosures of which
are incorporated herein by reference in their entirety), for
example, for coupling to a computer controlled catheter or surgical
instrument for real-time feedback and precise control during a
procedure.
[0033] Referring to FIGS. 1-4, catheter 12 of the invention may
include body 22 having a distal end 24 and a proximal end 26. Body
22 of catheter 12 is generally tubular in shape, although other
configurations of the catheter may be used as known in the
industry. If desired, the outer portion of catheter 12 may have a
braided outer covering therein providing increased flexibility and
strength. The catheters of the invention vary in length and are
attached to a handle or other type of control member that allows a
surgeon or operator of the catheter to manipulate the relative
position of the catheter within the body from a remote location, as
recognized by one of ordinary skill in the art.
[0034] An embodiment of a system and method for measuring force and
torque applied to the tip of electrode 14, namely contact sensing
assembly 10, will now be described in detail.
[0035] As shown in FIG. 3, body 22 of catheter 12 may generally
include sensors 28, 30, 32 of force and torque sensor 16 mounted on
head 20 in a tri-axial arrangement. Alternatively, sensors 28, 30,
32 may be generally located between a "neck" area of electrode 14
and a support portion on the body. The body of electrode 14,
particularly near base 18 and the area of body 22 adjacent head 20,
may be sufficiently rigid to permit any forces (axial or
transverse) applied to distal end 24 to be measured by force and
torque sensor 16. The sensor arrangement of FIGS. 2 and 3 may
specifically measure force along the electrode axis F.sub.z, and
two components of torque in a plane perpendicular to the electrode
axis, namely T.sub.x and T.sub.y. If needed, the force in the x and
y directions may be determined from the torque components.
[0036] The method of calculating force and torque from sensors 28,
30, 32 will now be described in detail.
[0037] Without loss of generality, all three sensors 28, 30, 32 may
be presumed to have the same sensitivity ".alpha." (.alpha. is the
proportionality constant between force applied to a sensor and the
sensor's electrical output, and represents a predetermined value
for each sensor). Given forces in the z-direction applied to each
sensor F_a, F_b, F_c (e.g. forces applied to sensors 28, 30, 32),
the sensor outputs will be V_a=.alpha. F_a, V_b=.alpha. F_b,
V_c=.alpha. F_c, respectively. It should be noted that the term
"forces in the z-direction" does not imply force and torque sensor
16 only measures forces in the z-direction. Namely, if a force is
applied in the y-direction in FIG. 2, while sensors 28, 32 may
measure a negative (e.g. tensile) force, sensor 30 would measure a
positive (e.g. compression) force, with force and torque sensor 16
determining the force in the z-direction based on the respective
measurements at each sensor 28, 30, 32.
[0038] The force/torque components may be given by the following
equations:
F.sub.--z=(V_a+V.sub.--b+V.sub.--c)/.alpha.,
T.sub.--y=sqrt(3)/(2*.alpha.)*D*(V.sub.--c-V.sub.--a/2-V.sub.--b/2),
and
T.sub.--x=sqrt(3)/(2*.alpha.)*D*(V.sub.--a-V.sub.--b),
where "D" is the diameter of circle 34 in the x-y plane passing
through the centers of sensors 28, 30, 32.
[0039] If each sensor 28, 30, 32 has a different sensitivity
.alpha. (e.g. .alpha._a, .alpha._b, .alpha._c), then the sensor
outputs would be:
V.sub.--a=.alpha._aF_a,
V_b=.alpha._bF_b,V_c=.alpha..sub.--cF_c.
[0040] The force and torque components may be given by the
following equations:
F.sub.--z=V.sub.--a/a.sub.--a+C.sub.--b/a.sub.--b+V.sub.--c/a.sub.--c,
T.sub.--y=3/4*D*(V.sub.--c/a.sub.--c-V.sub.--a/a-C.sub.--b/a.sub.--b),
and
T.sub.--x=sqrt(3)/2*D*(V.sub.--a/a.sub.--a-V.sub.--b/a.sub.--b)
[0041] Thus the sensor arrangement of FIGS. 2 and 3 may
specifically measure force along the electrode axis F.sub.z, and
two components of torque in the plane perpendicular to the
electrode axis, namely T.sub.x and T.sub.y, with the force and
torque being determined as discussed above.
[0042] Referring to FIG. 4, electrode 14 and body 22 may optionally
be connected by an elastic hermetic neck, with elastic hermetic
neck 38 further allowing only predetermined relative movement of
electrode 14 and body 22, and thus force and torque determination
by sensors 28, 30, 32. It should be noted that while neck 38 is
illustrated as including ridges, neck 38 may optionally be a smooth
structure, or another elastic coupling element such as those
disclosed in commonly owned and copending application titled
"Optic-Based Contact Sensing Assembly and System."
[0043] Thus by measuring the z-directional forces applied to each
sensor 28, 30, 32, force and torque sensor 16 provides feedback on
the amount of force of electrode 14 onto a tissue (e.g. F.sub.z),
as well as the torque applied to electrode 14 (e.g. T.sub.x and
T.sub.y).
[0044] Referring next to FIGS. 5a-5d, another embodiment of a
system and method for measuring force applied to the tip of an
electrode, namely contact sensing assembly 100, will be described
in detail.
[0045] Generally, contact sensing assembly 100 of FIGS. 5a-5d may
estimate the lateral (x-y) force of an electrode tip (e.g.
electrode 14) onto tissue (e.g. heart or other tissue) from the
bending curvature of a catheter 102 near the tip of an electrode.
Such a sensor of curvature may be either resistive or capacitive.
If capacitive, an inner electrode wire 104 (made for example of
stainless steel) may be disposed inside a coaxial outer electrode
pipe 106, with wire 104 and electrode pipe 106 being mechanically
connected at bottom area 108. Outer electrode pipe 106 may be made
of a flexible plastic, with the interior surface thereof covered
with a thin metal film (e.g. gold). Electrode wire 104 may be
covered with a thin layer of isolation 110 made of, for example,
Teflon.RTM., to prevent shorts, and may also include isolation at
the mechanical coupling at bottom area 108. Outer electrode pipe
106 may be mechanically coupled to catheter body 112 so that they
both bend similarly.
[0046] In operation, as shown in FIG. 5c, when electrode pipe 106
bends together with catheter body 112, the capacitance between
electrode wire 104 and electrode pipe 106 increases as electrode
wire 104 (which has isolation thereon) begins to move toward
electrode pipe 106. As shown in FIG. 5d, as electrode pipe 106
bends more together with catheter body 112, the contact area
between electrode wire 104 and electrode pipe 106 increases, to
thus further increase the capacitance between electrode wire 104
and electrode pipe 106. The increase in capacitance is measured and
correlated to the amount of force on the tip of the electrode (e.g.
electrode 14) based on the degree of bending of catheter body 112.
For example, for a catheter body having a predetermined flexibility
based on the application of a predetermined force, the capacitance
may be directly correlated to the amount of force being applied to
catheter body 112. Likewise, for any given catheter body having a
predetermined flexibility based on the application of a
predetermined force, a capacitance factor may be provided to
determine the amount of force being applied to the catheter body
based on measured capacitance.
[0047] As discussed above, contact sensing assembly 100 may be
either resistive or capacitive. For an assembly 100 based on
changes in resistivity, a resistive solution may be injected inside
electrode pipe 106 and anti-short standoffs (not shown) may be used
instead of isolation 110. The resistive solution, such as saline,
may be used to fill assembly 100 right before or during
surgery.
[0048] Thus by measuring the change in capacitance or resistivity
between inner electrode wire 104 and outer electrode pipe 106,
contact sensing assembly 100 provides feedback on the amount of
force of an electrode (e.g. electrode 14) onto tissue.
[0049] Those skilled in the art would appreciate in view of this
disclosure that various modifications may be made to the
aforementioned force and torque sensors without departing from the
scope of the invention.
[0050] For example, for force and torque sensor 16, more components
of force and torque may be measured by using more sensors 28, 30,
32. Sensors 28, 30, 32 may be positioned differently than the
arrangement of FIGS. 2 and 3 (e.g. asymmetrically relative to the
central axis of the electrode), or the sensors may be positioned so
that their axes of sensitivity are not parallel to the electrode
central axis.
[0051] Further, electrode 14 may also be configured to include a
means for irrigating. For example, without limitation, as shown in
FIG. 1, the incorporation of at least one irrigation port 36 within
electrode 14 may provide an irrigated electrode tip. An irrigated
electrode tip allows for the cooling of electrode 14, for instance,
through the transporting of fluid through electrode 14 and around
the surface of the tissue. A number of different types of
electrodes, irrigated and non-irrigated, may be connected and
incorporated for use of an electrode 14 according to embodiments of
the invention depending on the type of procedures being done. Such
irrigated electrodes include, but are not limited to, those
disclosed in U.S. patent application Ser. Nos. 11/434,220 (filed
May 16, 2006), 10/595,608 (filed Apr. 28, 2006), 11/646,270 (filed
Dec. 28, 2006) 11/647,346 (filed Dec. 29, 2006) and 60/828,955
(filed Oct. 10, 2006), each of which is hereby incorporated by
reference as though fully set forth herein.
[0052] The invention further discloses a force-based catheter
system 200, as shown in FIGS. 6A-6F, that includes assemblies 10 or
100 (note: only assembly 10 illustrated) of the invention connected
to a signal converter 210 (such as an analog to digital converter)
and an operator interface 220, which may further include a computer
and display, for processing the force signals received from
assemblies 10 or 100 in connection with positioning and contact
with tissue, such as myocardial tissue 205. This force-based
information is processed to determine the contact force exerted on
electrode 14 or the electrode for assembly 100. A calibration
system 230 (i.e., calibration software) may be further provided to
readily correlate the pressure or capacitance measurements to the
external force or torque on the electrode. A mapping system 240,
such as the Ensite system, also known as NavX.RTM., may be
integrated with system 200 to provide a visualization and mapping
system for use in connection with assemblies 10 or 100 of the
invention. In an alternate embodiment, as shown in FIGS. 6D-6F,
signal converter 210 may be integrated with assemblies 10, 100,
such that the force or torque signal is directly processed and
provided on operator interface 220. Overall, each of these
components may be modified and/or integrated with one another
depending on the design of the force/torque system as recognized by
one of ordinary skill in the art.
[0053] Although several 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 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
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 as limiting. Changes in detail or
structure may be made without departing from the invention as
defined in the appended claims.
* * * * *