U.S. patent application number 17/200457 was filed with the patent office on 2021-09-02 for multi-electrode ablator tip having dual-mode, omni-directional feedback capabilities.
The applicant listed for this patent is St. Jude Medical, Cardiology Division, Inc.. Invention is credited to Don Curtis Deno, John A. Hauck, Zhenyi Ma, Stephen A. Morse, John W. Sliwa.
Application Number | 20210267671 17/200457 |
Document ID | / |
Family ID | 1000005594751 |
Filed Date | 2021-09-02 |
United States Patent
Application |
20210267671 |
Kind Code |
A1 |
Sliwa; John W. ; et
al. |
September 2, 2021 |
MULTI-ELECTRODE ABLATOR TIP HAVING DUAL-MODE, OMNI-DIRECTIONAL
FEEDBACK CAPABILITIES
Abstract
Electrode assemblies include segmented electrodes disposed on a
catheter. The segmented electrodes can be constructed at the tip of
the catheter. Tip electrodes can be constructed from an
electrically insulative substrate comprising an inner lumen, an
external tip surface, and a plurality of channels extending from
the inner lumen to the external tip surface, a plurality of
segmented electrodes, and a plurality of spot electrodes. Each of
the plurality of segmented electrodes and each of the plurality of
spot electrodes can be laterally separated from each other by an
electrically non-conductive substrate portion and each of the spot
electrodes and each of the segmented electrodes can be electrically
coupled to at least one wire or conductor trace.
Inventors: |
Sliwa; John W.; (San Jose,
CA) ; Ma; Zhenyi; (Santa Clara, CA) ; Morse;
Stephen A.; (Menlo Park, CA) ; Hauck; John A.;
(Shoreview, MN) ; Deno; Don Curtis; (Andover,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Cardiology Division, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
1000005594751 |
Appl. No.: |
17/200457 |
Filed: |
March 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15355201 |
Nov 18, 2016 |
10980598 |
|
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17200457 |
|
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62258281 |
Nov 20, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2018/1417 20130101;
A61B 2018/00875 20130101; A61B 2018/00577 20130101; A61B 2018/00351
20130101; A61B 18/1492 20130101; A61B 2018/1497 20130101; A61B
2218/002 20130101; A61B 2018/1467 20130101; A61B 2018/00797
20130101; A61B 2018/00869 20130101; A61B 2018/00892 20130101; A61B
2018/00083 20130101; A61B 2018/00839 20130101 |
International
Class: |
A61B 18/14 20060101
A61B018/14 |
Claims
1.-26. (canceled)
27. A tip electrode comprising: an electrically insulative
substrate comprising an inner lumen and an external tip surface,
wherein the electrically insulative substrate comprises a rigid
material; a plurality of segmented ablation electrodes disposed on
the electrically insulative substrate; and a plurality of wire or
conductor traces, wherein each of the plurality of segmented
ablation electrodes is coupled to at least one of the plurality of
wire or conductor traces and wherein each of the plurality of
segmented ablation electrodes are laterally separated from each
other by an electrically insulative gap.
28. The tip electrode according to claim 27 further comprising a
plurality of channels extending from the inner lumen to the
external tip surface.
29. The tip electrode according to claim 27, further comprising a
plurality of thermal sensors, wherein at least one of the plurality
of wire or conductor traces comprises a conductor pair and wherein
one of the plurality of thermal sensor is electrically coupled to
the conductor pair.
30. The tip electrode according to claim 27, further comprising a
plurality of spot electrodes disposed on the electrically
insulative substrate.
31. The tip electrode according to claim 30, wherein each of the
plurality of spot electrodes are laterally separated from the
plurality of segmented ablation electrodes by an electrically
insulative gap.
32. The tip electrode according to claim 31, wherein each of the
spot electrodes are electrically coupled to at least one of the
plurality of wire or conductor traces.
33. The tip electrode according to claim 31, wherein at least one
of the plurality of spot electrodes is disposed within the lateral
confines of at least one of the plurality of segmented ablation
electrodes.
34. The tip electrode according to claim 31, further comprising a
thermal sensor disposed adjacent one of the plurality of spot
electrodes such that the thermal sensor can be electrically
connected to a conductor pair electrically connected to the spot
electrode.
35. The tip electrode according to claim 31, wherein each of the
spot electrodes is disposed within a separate segmented ablation
electrode.
36. The tip electrode according to claim 27, wherein each of the
plurality of segmented ablation electrodes extend in a longitudinal
direction along a length of the tip electrode.
37. A system for ablating tissue comprising: a tip electrode
comprising: an electrically insulative substrate comprising an
inner lumen and an external tip surface; and a plurality of
segmented ablation electrodes, wherein at least one of the
plurality of segmented ablation electrodes is disposed on the
electrically insulative substrate, wherein each of the plurality of
segmented ablation electrodes are laterally separated from each
other by an electrically insulative gap and wherein each of the
segmented ablation electrodes are electrically coupled to at least
one wire or conductor; and an electronic control unit configured to
control the plurality of segmented ablation electrodes to bipolar
ablate cardiac tissue.
38. The system according to claim 37, wherein the electronic
control unit is configured to bipolar ablate cardiac tissue.
39. The system according to claim 37, further comprising a
plurality of spot electrodes disposed on the electrically
insulative substrate.
40. The system according to claim 39, wherein the electronic
control unit is further configured to use the plurality of spot
electrodes for at least one of: orientation independent sensing,
pacing, location sensing/tracking, and local impedance sensing.
41. The system according to claim 39, wherein at least one of the
spot electrodes is disposed within one of the plurality of
segmented ablation electrodes.
42. The tip electrode according to claim 39, further comprising a
thermal sensor disposed adjacent one of the plurality of spot
electrodes such that the thermal sensor can be electrically
connected to a conductor pair electrically connected to the spot
electrode.
43. A tip electrode comprising: an electrically insulative
substrate comprising an inner lumen and an external tip surface; a
plurality of segmented ablation electrodes; and a plurality of wire
or conductor traces, wherein at least one of the plurality of
segmented ablation electrodes is disposed on the electrically
insulative substrate, wherein each of the plurality of segmented
ablation electrodes are laterally separated from each other by an
electrically insulative gap, and wherein each of the segmented
ablation electrodes are electrically coupled to at least one of the
plurality of wire or conductor traces.
44. The system according to claim 43, further comprising a
plurality of spot electrodes disposed on the electrically
insulative substrate.
45. The system according to claim 44, wherein at least one of the
spot electrodes is disposed within one of the plurality of
segmented ablation electrodes.
46. The tip electrode according to claim 44, further comprising a
thermal sensor disposed adjacent one of the plurality of spot
electrodes such that the thermal sensor can be electrically
connected to a conductor pair electrically connected to the spot
electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/355,201, filed 18 Nov. 2016 (the '201 application), which
claims the benefit of U.S. provisional application No. 62/258,281,
filed 20 Nov. 2015 (the '281 application). The '201 application,
and '281 application are both hereby incorporated by reference as
though fully set forth herein.
BACKGROUND
[0002] a. Field
[0003] The instant disclosure relates to ablation tips that have
feedback capability. In one embodiment, the instant disclosure
relates to ablation tips that provide dual-mode, omni-directional
feedback so that lesion, mapping and/or force assessments can be
made regardless of the orientation of the tip.
[0004] b. Background Art
[0005] Electrophysiology catheters are used in a variety of
diagnostic and/or therapeutic medical procedures to diagnose and/or
correct conditions such as atrial arrhythmias, including for
example, ectopic atrial tachycardia, atrial fibrillation, and
atrial flutter. Arrhythmias can create a variety of conditions
including irregular heart rates, loss of synchronous
atrioventricular contractions and stasis of blood flow in a chamber
of a heart which can lead to a variety of symptomatic and
asymptomatic ailments and even death.
[0006] A medical procedure in which an electrophysiology catheter
is used includes a first diagnostic catheter deployed through a
patient's vasculature to a patient's heart or a chamber or vein
thereof. An electrophysiology catheter that carries one or more
electrodes can be used for cardiac mapping or diagnosis, ablation
and/or other therapy delivery modes, or both. Once at the intended
site, treatment can include, for example, radio frequency (RF)
ablation, cryoablation, laser ablation, chemical ablation,
high-intensity focused ultrasound-based ablation, electroporation
ablation or microwave ablation. An electrophysiology catheter
imparts ablative energy to cardiac tissue to create one or more
lesions in the cardiac tissue and oftentimes, a contiguous, and
transmural lesion. This lesion disrupts undesirable cardiac
activation pathways and thereby limits, corrals, or prevents errant
conduction signals that can form or sustain arrhythmias.
BRIEF SUMMARY
[0007] The instant disclosure, in at least one embodiment, relates
to a tip electrode of a catheter comprising an
electrically-insulative substrate.
[0008] In one embodiment, tip electrode can comprise an
electrically insulative substrate comprising an inner lumen, an
external tip surface, and a plurality of channels extending from
the inner lumen to the external tip surface, a plurality of
segmented electrodes, and a plurality of spot electrodes. Each of
the plurality of segmented electrodes and each of the plurality of
spot electrodes can be laterally separated from each other by an
electrically non-conductive substrate portion and each of the spot
electrodes and each of the segmented electrodes can be electrically
coupled to at least one wire or conductor trace.
[0009] In another embodiment of the disclosure, a system for
ablating tissue can comprise a tip electrode comprising an
electrically insulative substrate comprising an inner lumen, an
external tip surface, and a plurality of channels extending from
the inner lumen to the external tip surface, a plurality of
segmented electrodes, and a plurality of spot electrodes. Each of
the plurality of segmented electrodes and each of the plurality of
spot electrodes can be laterally separated from each other by an
electrically non-conductive substrate portion and each of the spot
electrodes and each of the segmented electrodes can be electrically
coupled to at least one wire or conductor. The system can further
comprise an electronic control unit configured to control the
plurality of spot electrodes and the plurality of segmented
electrodes to bipolar pace cardiac tissue.
[0010] In yet another embodiment of the disclosure, a system for
determining a tissue characteristic can comprise an electronic
control unit configured to measure a pre-lesion impedance at a
known temperature of a target site, measure an impedance at a known
temperature of the target site after ablation has occurred, and
utilize a model of lesion impedance behavior to determine a state
of the target site.
[0011] In yet another embodiment of the disclosure, a system for
determining a tissue characteristic can comprise an electronic unit
configured to measure a heat flow ability of a target site before
ablation has occurred, measure a heat flow ability of the target
site after ablation has occurred, and use a thermal model of the
target site to deduce at-least a depthwise temperature profile of
the target site based on the before and after heat flow ability.
The heat flow ability can be measured by changing a rate of heat
accumulation in the target site and observing the corresponding
change in a tissue surface temperature.
[0012] In yet another embodiment of the disclosure, a system for
determining a tissue characteristic can comprise an electronic
control unit configured to measure a pre-lesion impedance at a
known temperature of a target site, measure an impedance at a known
temperature of the target site after some ablation has occurred,
utilize a model of lesion impedance behavior to determine a state
of the target site, measure a heat flow ability of the target site
before some ablation has occurred, measure a heat flow ability of
the target site after some ablation has occurred, utilize a thermal
model of the target site to obtain at-least a depthwise temperature
profile of the target site based on the before and after heat flow,
and employ both results via a weighting of the two results to
determine a weighted lesion state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a diagrammatic depiction of an exemplary
intracardiac mapping and navigation system for use with various
medical devices that are capable of utilizing an electrode assembly
with dual-mode, omni-directional feedback capabilities of the
present disclosure.
[0014] FIGS. 2A-2D are schematic diagrams of exemplary bipole pairs
of driven body patch electrodes suitable for use with the
intracardiac mapping and navigation system of FIG. 1.
[0015] FIG. 3 is a schematic diagram of one embodiment of a medical
apparatus incorporating an electrode assembly.
[0016] FIG. 4 is an isometric view of an embodiment of a catheter
assembly comprising a plurality of segmented tip electrodes and a
plurality of spot electrodes.
[0017] FIG. 5 an isometric view of another embodiment of a catheter
assembly comprising a plurality of segmented tip electrodes and a
plurality of spot electrodes.
[0018] FIG. 6 is an isometric view of an embodiment of a tip
assembly comprising a plurality of segmented tip electrodes and a
plurality of spot electrodes.
[0019] FIG. 7 is an isometric, cross-sectional view of an
embodiment of a tip assembly comprising a plurality of segmented
tip electrodes and a plurality of spot electrodes.
[0020] FIG. 8 is an isometric, cross-sectional view of another
embodiment of a catheter assembly comprising a plurality of
segmented tip electrodes and a plurality of spot electrodes.
[0021] FIG. 9 is an isometric, cross-sectional view of another
embodiment of a catheter assembly.
[0022] FIG. 10 is a close-up cross-sectional view of an embodiment
of a tip electrode.
[0023] FIG. 11 is a diagrammatic view of a system that can be used
for combining the independent impedance and calorimetry feedback
from the electrodes on a catheter.
[0024] FIGS. 12A-12D are flowcharts for a method to utilize
impedance feedback and/or heat flow feedback methods to determine a
lesion state.
DETAILED DESCRIPTION
[0025] Various embodiments are described herein to various
apparatuses, systems, and/or methods. Numerous specific details are
set forth to provide a thorough understanding of the overall
structure, function, manufacture, and use of the embodiments as
described in the specification and illustrated in the accompanying
drawings. It will be understood by those skilled in the art,
however, that the embodiments may be practiced without such
specific details. In other instances, well-known operations,
components, and elements have not been described in detail so as
not to obscure the embodiments described in the specification.
Those of ordinary skill in the art will understand that the
embodiments described and illustrated herein are non-limiting
examples, and thus it can be appreciated that the specific
structural and functional details disclosed herein may be
representative and do not necessarily limit the scope of the
embodiments, the scope of which is defined solely by the appended
claims.
[0026] Reference throughout the specification to "various
embodiments," "some embodiments," "one embodiment," or "an
embodiment", or the like, means that a particular feature,
structure, or characteristic described in connection with the
embodiment is included in at least one embodiment. Thus,
appearances of the phrases "in various embodiments," "in some
embodiments," "in one embodiment," or "in an embodiment", or the
like, in places throughout the specification are not necessarily
all referring to the same embodiment. Furthermore, the particular
features, structures, or characteristics may be combined in any
suitable manner in one or more embodiments. Thus, the particular
features, structures, or characteristics illustrated or described
in connection with one embodiment may be combined, in whole or in
part, with the features structures, or characteristics of one or
more other embodiments without limitation given that such
combination is not illogical or non-functional.
[0027] It will be appreciated that the terms "proximal" and
"distal" may be used throughout the specification with reference to
a clinician manipulating one end of an instrument used to treat a
patient. The term "proximal" refers to the portion of the
instrument closest to the clinician and the term "distal" refers to
the portion located furthest from the clinician. It will be further
appreciated that for conciseness and clarity, spatial terms such as
"vertical," "horizontal," "up," and "down" may be used herein with
respect to the illustrated embodiments. However, surgical
instruments may be used in many orientations and positions, and
these terms are not intended to be limiting and absolute.
[0028] It can be desirable to monitor and/or control the
temperature of ablation electrode assemblies. It can also be
desirable to use ablation electrode assemblies to provide
irrigation fluid during RF ablation. RF ablation catheters can be
configured to provide temperature feedback during RF ablation via a
thermal sensor such as a thermocouple or thermistor. Typically, the
temperature reading provided by a single thermal sensor inside an
irrigated tip ablation electrode cannot accurately represent the
temperature of the electrode/tissue interface. One reason is
because a portion of the electrode that is in direct contact with
the targeted tissue can have a higher temperature than the interior
of the electrode where a single thermocouple typically resides
because tip irrigation forms a thermal gradient from the tip
external surface to the tip interior.
[0029] Secondly, even properly knowing the surface interface
temperature of the tip/tissue interface, the irrigation fluid can
cause at-least the near surface of the target tissue to be
subcooled relative to deeper tissues beyond the reach of the
cooling effect but still within the RF affected heated zone. Thus
the hottest spot of an irrigated lesion can be below the target
tissue surface by a millimeter or two. So for better thermal
control one can at-least get rid of the in-tip temperature gradient
error such as by placing the thermocouple on the tip exterior
surface as this invention teaches. The in-tissue temperature
gradient which remains may be modeled or estimated such as by this
disclosure.
[0030] Thus, if the tip thermal sensor is in direct contact with
the targeted surface tissue such as by being situated on a tip
surface facing that tissue, then the thermal sensor can provide a
temperature reading generally corresponding to the actual
temperature of the targeted tissue surface albeit that surface
temperature is still suppressed by irrigation-cooling relative to
deeper subsurface tissue within the RF treatment zone as stated
above. Furthermore, multiple thermal sensors positioned at
different tip surface locations on the electrode can be used to
assure that at least one of them is directly facing the juxtaposed
tissue to be lesioned no matter the rotational state of the tip
relative to the tissue. For example and without limitation, the
highest measured temperature of all these temperature sensing
locations is likely the one facing the ablating tissue.
[0031] The ability to assess lesion formation during ablation is a
desirable feature. This is achieved in today's practice by
monitoring electrograms (EGM's) and pacing from electrodes before,
during and after RF ablation. Closely spaced electrodes, either at
or near the ablation tip can potentially provide highly local
information that can be used to assess the effectiveness of the
ablation therapy. That is to say that multiple electrodes facing a
lesion on a catheter tip can be employed as bipolar pairs such that
the electrical impedance between such nearby pairs and thereby also
selectively through the intervening adjacent target-tissue and
resulting lesion itself can be measured. The additional sensing
electrodes can also be used to individually characterize the
electrophysiology of the local substrate. This can help to diagnose
the arrhythmia, determine the site for ablation and judge the
resulting lesion size/depth.
[0032] FIG. 1 is a diagrammatic depiction of an exemplary
intracardiac mapping and navigation system 10 for use with various
medical devices that are capable of utilizing an ablating catheter
electrode assembly with dual-mode, omni-directional feedback
capabilities of the present disclosure. Dual-mode, omni-directional
feedback capabilities can comprise thermal and electrical sensing
modes that include temperature and calorimetry. Dual-mode,
omni-directional feedback capabilities can further include pacing,
impedance, and omnipolar electrograms as described herein. In other
embodiments, dual-mode, omni-directional feedback capabilities can
refer to electrograms and impedance sensing, extending the single
mode electrogram approach of OIS as described herein. The system 10
may include various visualization, mapping and navigation
components as known in the art, including, for example, an
EnSite.TM. Velocity.TM. system commercially available from St. Jude
Medical, Inc., or as seen generally, for example, by reference to
U.S. Pat. No. 7,263,397, or U.S. Pat. No. 7,885,707, both of which
are hereby incorporated by reference in their entireties as though
fully set forth herein. With reference to the present disclosure,
the system 10 is configured to, among other things, collect
cardiologic data, particularly impedance and temperature
information, from intra-tip electrodes and sensors, respectively,
mounted to the medical device to thereby provide accurate, reliable
and complimentary lesion information without regard to the
orientation of the medical device. Such information can be used to
perform real-time lesion assessment, in addition to providing
orientation independent mapping. Further discussion of orientation
independent mapping can be found in PCT Application no.
PCT/US2014/037160, filed 7 May 2014 (the '160 reference), PCT
Application no. PCT/US2015/017576, filed 25 Feb. 2015 (the '576
reference), and PCT Application no. PCT/US2015/017582, filed 25
Feb. 2015 (the '582 reference), which are each incorporated by
reference in their entirety as though fully set forth herein. As
such, users of the system 10, such as clinicians, doctors, or
cardiologists, may be able to more readily perform ablation
procedures for remedying cardiac arrhythmia.
[0033] The system 10 may include an electronic control unit (ECU)
12, an analog-to-digital converter (A-to-D) 14, a low-pass filter
(L.P.) 16, a switch 18, a signal generator 20, and a plurality of
body surface patch electrodes 22. The system 10 may be
electronically and/or mechanically coupled with an elongate medical
device, such as, in one embodiment, a contact or non-contact
mapping catheter (e.g., a cardiac mapping catheter 24). The
catheter 24 includes a distal end portion 26 and a proximal end
portion 28. The distal end portion 26 includes an electrode
assembly 32 and extends into a heart 36 of a patient 38. The
proximal end portion 28 connects the catheter 24 to a switch 18 and
to an irrigation pump (not shown).
[0034] The system 10 may be configured to provide, among other
things, mapping of patient tissue, such as one or more chambers of
the heart 36 of the patient 38, and a 3D model bearing the surface
geometry of the mapped cardiac tissue. Accordingly, the ECU 12 may
be configured to receive electrical measurements from one or more
electrodes coupled to the electrode assembly 32 on the mapping
catheter 24 and, based on those measurements, to assess one or more
electrical characteristics of tissue surrounding the distal end of
the mapping catheter 26. In an embodiment, the ECU 12 may be
configured to determine a voltage distribution of an endocardial
surface according to electrical measurements from mapping catheter
electrode assembly 32. The ECU 12 may be further configured to
determine that voltage distribution with respect to an anatomical
model, such as a model of one or more chambers, features, and/or
surfaces of the heart 36.
[0035] The ECU 12 may include a non-volatile memory 40 and a
processor 42 configured to perform many of the functions and
operations described herein--i.e., a memory 40 may store
instructions for performing portions of one or more methods or
processes described herein, and a processor 42 may be configured to
execute those instructions to perform the methods or processes. The
memory 40 may also be configured to store an anatomical model, such
as a cardiac chamber model, a plurality of measurements from the
mapping catheter 24, a plurality of terms and values for the
methods described below, and other data and information. In an
embodiment, the ECU 12 may additionally or alternatively comprise a
field-programmable gate array (FPGA) and/or other known computing
device. In some embodiments, and as discussed further below, the
ECU 12 may be configured to perform a method of computing a 2D
projection and/or a partially unfolded surface of a 3D model in
order to better facilitate visualization of the model and features
of the model. The ECU may also include models of the impedance
behavior or heat-flow (calorimetry) behavior of forming
lesions.
[0036] In addition to (and as a part of) electrophysiology mapping,
the system 10 may be configured to determine the position and
orientation (P&O) of the mapping catheter 24 (e.g.,
particularly of the distal end portion 26) within the patient 38.
Accordingly, the ECU 12 may be configured to control generation of
one or more electrical fields and determine the position of one or
more electrodes (e.g., the electrode assembly 32) within those
fields. The ECU 12 may thus be configured to the control signal
generator 20 in accordance with predetermined strategies to
selectively energize various pairs (bipoles) of the body surface
patch electrodes 22, as described in greater detail below. In
operation, the ECU 12 may (1) obtain raw patch data (i.e., voltage
readings) via the filter 16 and the A-to-D converter 14 and (2) use
the raw patch data (in conjunction with electrode measurements) to
determine the raw, uncompensated, electrode location coordinates of
the electrode assembly 32 positioned inside the heart 36 or a
chamber thereof in three-dimensional space. The ECU 12 may be
further configured to perform one or more compensation and
adjustment functions, and to output a location of the electrode
assembly 32. Motion compensation may include, for example,
compensation for respiration-induced patient body movement, as
described in U.S. Publication No. 2012/0172702, which is hereby
incorporated by reference in its entirety for all purposes.
[0037] The body surface patch electrodes 22 may be used to generate
axes-specific electric fields within the patient 38, and more
specifically within the heart 36. Three sets of patch electrodes
may be provided: (1) electrodes 22.sub.X1, 22.sub.X2, (X-axis); (2)
electrodes 22.sub.Y1, 22.sub.Y2, (Y-axis); and (3) electrodes
22.sub.Z1, 22.sub.Z2, (Z-axis). Additionally, a body surface
electrode ("belly patch") 22B, may be provided as an electrical
reference. Other surface electrode configurations and combinations
are suitable for use with the present disclosure, including fewer
electrodes 22, more electrodes 22, or different physical
arrangements, e.g. a linear arrangement instead of an orthogonal
arrangement.
[0038] Each patch electrode 22 may be independently coupled to the
switch 18, and pairs of the patch electrodes 22 may be selected by
software running on the ECU 12 to couple the patch electrodes 22 to
the signal generator 20. A pair of electrodes, for example the
Z-axis electrodes 22.sub.Z1, 22.sub.Z2, may be excited by the
signal generator 20 to generate an electrical field in the patient
38 and, more particularly, within the heart 36. In one embodiment,
this electrode excitation process occurs rapidly and sequentially
as different sets of the patch electrodes 22 are selected and one
or more of the unexcited surface electrodes 22 are used to measure
voltages. During the delivery of the excitation signal (e.g.,
current pulse), the remaining (unexcited) patch electrodes 22 may
be referenced to the belly patch 22B and the voltages impressed on
these remaining electrodes 22 may be measured. In this fashion, the
patch electrodes 22 may be divided into driven and non-driven
electrode sets. The low pass filter 16 may process the voltage
measurements. The filtered voltage measurements may be transformed
to digital data by the analog to digital converter 14 and
transmitted to the ECU 12 for storage (e.g. in the memory 40) under
the direction of software. This collection of voltage measurements
may be referred to herein as the "patch data." The software may
have access to each individual voltage measurement made at each
surface electrode 22 during each excitation of each pair of surface
electrodes 22.
[0039] The patch data may be used, along with measurements made at
the electrode assembly 32, to determine a relative location of the
electrode assembly 32. The patch data may also be used along with
measurements made at the electrode assembly 32 and/or other
electrodes on the catheter 24, such as a tip electrode, or on
another device to determine a relative location of the electrode
assembly 32 and/or the other electrodes. The discussion above and
below describes determining the location of the electrode assembly
32, but it should be understood to apply to a tip electrode and
other electrodes, as well. In some embodiments, potentials across
each of the six orthogonal patch electrodes 22 may be acquired for
all samples except when a particular surface electrode pair is
driven. In some embodiments, sampling a voltage with a particular
patch electrode 22 while a surface electrode 22 acts as a source or
sink in a driven pair may be avoided, as the potential measured at
a driven electrode during this time may be skewed by the electrode
impedance and the effects of high local current density. In an
alternate embodiment, however, sampling may occur at all patch
electrodes 22, even those being driven.
[0040] Generally, in an embodiment, three nominally orthogonal
electric fields may be generated by a series of driven and sensed
electric bipoles in order to determine the location of the catheter
24 (i.e., of the electrode assembly 32). Alternately, these
orthogonal fields can be decomposed and any pair of surface
electrodes (e.g., non-orthogonal) may be driven as bipoles to
provide effective electrode triangulation.
[0041] FIGS. 2A-2D show a plurality of exemplary non-orthogonal
bipoles, designated D.sub.0, D.sub.1, D.sub.2 and D.sub.3. In FIGS.
2A-2D, the X-axis surface electrodes are designated X.sub.A and
X.sub.B, the Y-axis surface electrodes are designated Y.sub.A and
Y.sub.B, and the Z-axis electrodes are designated Z.sub.A and
Z.sub.B. For any desired axis, the potentials measured across an
intra-cardiac electrode assembly 32 resulting from a predetermined
set of drive (source-sink) configurations may be combined
algebraically to yield the same effective potential as would be
obtained by simply driving a uniform current along the orthogonal
axes. Any two of the patch electrodes 22 may be selected as a
bipole source and drain, as noted above, with respect to a ground
reference, e.g., the belly patch 22B, while the unexcited body
patch electrodes 22 measure voltage with respect to the ground
reference. The electrode assembly 32 placed in the heart 36 is also
exposed to the field from a current pulse, and voltages on
electrode assembly 32 are individually and separately measured with
respect to ground, e.g., the belly patch 22B.
[0042] Referring again to FIG. 1, data sets from each of the patch
electrodes 22 and the electrode assembly 32 are all used to
determine the location of the electrode assembly 32 within the
heart 36. After the voltage measurements are made for a particular
set of driven patch electrodes 22, a different pair of patch
electrodes 22 may be excited by the signal generator 20 and the
voltage measurement process of the remaining patch electrodes 22
and the electrode assembly 32 takes place. The sequence may occur
rapidly, e.g., on the order of one hundred times per second in an
embodiment. To a first approximation the voltage on the electrode
assembly 32 within the heart 36 bears a linear relationship with
position between the patch electrodes 22 that establish the field
within the heart 36, as more fully described in U.S. Pat. No.
7,263,397 referred to above.
[0043] Some or all of the conventional twelve (12) ECG leads,
coupled to additional body patches and designated collectively by
reference numeral 44, may be provided to support the acquisition of
an electrocardiogram (ECG) of the patient. As shown, the ECG leads
44 may be coupled directly to the ECU 12 for acquisition and
subsequent processing to obtain the phase of the heart in the
cardiac cycle. Cardiac phase information may be used, in an
embodiment, in mapping of electrical activity of the heart 36, as
described below.
[0044] In summary, FIG. 1 shows an exemplary system 10 that employs
seven body patch electrodes 22, which may be used for injecting
current and sensing resultant voltages. Current may be driven
between two patches 22 at any time. Measurements may be performed
between the non-driven patch 22 and, for example, the belly patch
22B as a ground reference. A patch bio-impedance, also referred to
as a "patch impedance", may be computed according to the following
equation:
B .times. i .times. o .times. Z .function. [ n .fwdarw. m ]
.function. [ k ] = V k I n .fwdarw. m ##EQU00001##
[0045] where V.sub.k is the voltage measured on patch k and
I.sub.n.fwdarw.m is a known constant current driven between patches
n and m. The position of the electrode assembly 32 may be
determined by driving current between different sets of patches and
measuring one or more patch impedances. In one embodiment, time
division multiplexing may be used to drive and measure all
quantities of interest. Position determining procedures are
described in more detail in, for example, U.S. Pat. Nos. 7,263,397
and 7,885,707 referred to above. To perform an electrophysiology
(e.g., mapping) procedure, the distal end portion 26 of the
catheter 24 or multiple such catheters 24 may be manually guided to
a desired location by a user such as a physician.
[0046] In addition to determining the positions of the electrode
assembly 32, the system 10 may also be configured to characterize
and assess the tissue of the heart, including lesions. Accordingly,
the ECU 12 may be further configured to perform one or more steps
in one or more complimentary methods of determining a voltage
distribution on a cardiac surface, such as determining the
impedance between intra-tip electrodes facing the lesion and
sensing the temperature at multiple locations facing the lesion on
electrode assembly 32. Because these methods employ entirely
different signal types (electrical voltage and temperature) they
provide a more sound answer as to lesion size by using two entirely
independent lesion-assessment mechanisms. In the case of the
temperature aspect, the use of temperature sensing over time can be
used in response to an RF power change. The temporal temperature
response can be fitted to a thermal model of the tissue in manners
of thermal modeling both inside and outside catheter ablation. One
embodiment employs the intra-tip impedance measurements and the
complimentary and independent temporal temperature responses to RF
power changes (which temporal responses are referred to as thermal
calorimetry). Both pieces of information can be utilized such as by
averaging them or weighing one somewhat more than the other in
accordance with the user's confidence in each.
[0047] FIG. 3 illustrates a schematic diagram of a medical
apparatus incorporating an electrode assembly as described below.
In the illustrated embodiment, the medical apparatus can comprise a
catheter 100. The catheter 100 can comprise a control handle 102,
and an elongated catheter body 104 having a distal region 106 with
an electrode assembly 108. The distal region 106 can comprise any
of the catheter tips shown and described below. The catheter 100
can be connected to an ECU as described below.
[0048] In one embodiment, the electrode assembly discussed herein
can comprise a multi-electrode RF ablator tip having dual-mode (the
bipolar electrical impedance mode and the complimentary independent
calorimetry mode embodiment discussed above) omnidirectional lesion
feedback capability, mapping and orientation independent sensing
capability and optionally shared interconnects. An electrode tip
assembly as discussed herein can have these characteristics while
still leaving physical room for a force feedback sensor. Lesion
feedback can be assessed omnidirectionally, this means the catheter
tip is able to be used to acquire information with any rotational
orientation or regardless which tip surface is actually facing the
cardiac tissue, using one or both complimentary feedback methods
(both simultaneously, sequentially, or independently used)
practiced from a multi-electrode tip with an
electrically-insulative substrate. As a result, in some
embodiments, no rotation of the electrode tip is required to ensure
that the minimum needed tissue-facing electrodes (for lesion
impedance feedback) and thermocouples (for lesion thermal or
calorimetric feedback) are, by-default, always facing the tissue of
interest.
[0049] To explain further, two different methods can be used
together, either simultaneously or sequentially in a complimentary
fashion, to provide more reliable lesion feedback than previous
methods. The first method is in-tip cross-electrode (bipolar) or
single electrode (unipolar) electrical impedance measurement(s).
Bipolar measurements can be done using one or more in-tip
subelectrode pairs, with the utilized bipolar-driven pair facing
the lesion and showing the major known local impedance changes
accompanying lesion formation. An RF body patch is not required for
these lesion-local measurements and the real time local temperature
can be taken into account as it has a known effect on impedance
also. Unipolar measurements can be done using a 3-terminal
impedance measurement. These two methods can result in more
specific ablation or pacing segment activation. The second
complimentary and independent method is "calorimetry" which can
comprise monitoring real time local surface-tissue lesion
temperature in response to a known ablation energy input rate
changes (input rate increases or decreases such as momentary
turning on or off of power) injected into an assumed model-volume
of tissue of known thermal properties adjacent the known
electrodes. Another method to change (e.g. momentarily reduce)
effective heat energy input is to change (e.g. momentarily reduce)
the irrigant flow rate which essentially leaves more heat in the
lesion tissue region.
[0050] In this second calorimetry method a simple thermal model of
the tissue (temperature versus depth) is employed. Essentially
widely known tissue thermal models can predict the buildup or
relaxation of a temperature-vs depth profile as a function of time
after a heat input at the tissue surface is started or stopped.
Other than the input lesion energy and irrigant heat removal the
other assumptions that can be made are that the initial tissue is
at 37 Deg C. (body temperature) and that the target tissue is
blood-perfused (further cooled by perfusing blood). Thus, since we
can detect the tissue surface temperature and we can predetermine
at what time ablating heat (or irrigation) is turned on or off or
step-changed in magnitude, we can observe the changing surface
temperature upon such a heating change and deduce a lesion
temperature depth profile and lesion tissue thermal conductivity
versus depth during that observation period. There is a unique
solution for the temperature and thermal conductivity profile for
each observed surface temperature response to a heating change.
Thus knowing the deduced temperature profile and thermal
conductivity profile allows judgement of the lesion extent based
purely on thermal considerations. For example lesioned tissue has
markedly lower thermal conductivity than unlesioned tissue. For
example the presence of a high temperature (e.g 60 deg C.) at a
known depth allows an estimate of the time-to-necrosis to be
estimated (less than a second to necrosis at 60 deg C.). Further
discussion relating to thermal models can be found in Berjano,
Enrique J., Theoretical modeling for radiofrequency ablation:
state-of-the-art and challenges for the future, BioMedical
Engineering OnLine 2006, 5:24, which is hereby incorporated by
reference as though fully set forth herein.
[0051] In one embodiment, the tip can have a thermally and
electrically-insulative substrate such as a ceramic substrate and a
plurality of thin electrodes on an outside substrate surface such
that the thermal response of the tissue results in the thin metal
surface electrode portions, and any thermally connected thermal
sensors, closely and rapidly follow the detectable tissue surface
temperature. By placing thermal sensors around the tip such as
under small isolated discs of such thin film electrodes, the
thermal sensors can measure that tissue surface tissue temperature
in real time because those thermal sensors have a thermally
insulating base, i.e. a ceramic base, and virtually no depth-wise
or lateral heat transfer. In ceramic tips of low thermal
conductivity, the tip can have a significant irrigant flow
(recirculating or passed into the bloodstream) to maintain tip
surface temps below blood thrombosis temperatures. Alternatively or
additionally the tips can ablate in a pulsed RF mode wherein time
is allowed for the tip surfaces to cool between such repeated
ablation power pulses.
[0052] In some embodiments, the thermal sensor (e.g thermocouple or
thermistor) wires and the isolated disc sub-electrode wires can be
cross-shared to perform one or more of the following: tissue
temperature measurement, tissue impedance measurement, tissue
electrical potential mapping or pacing, and electric-field spatial
navigation or even ablation itself. Since these embodiments can
optionally perform several functions with very few wires, thereby
retain compatibility with tip-force sensor usage by limiting the
required space for wired interconnections within the catheter body
and catheter tip and reserving space for a tip-force sensor which
has its own interconnections. The tip electrodes, as described
above and below, can take on a range of configurations ranging from
several large electrodes with small gaps to a single large
electrode with smaller separate electrically isolated electrodes
embedded in it. The actual ablation electrodes may or may not be
shared or included in the feedback electrodes. In one embodiment,
it is desired to have the feedback electrodes and the feedback
thermal sensors provide lesion-specific feedback which means that
the feedback electrodes and thermal sensors will be within the
area-wise confines of the ablating electrode.
[0053] The tip electrodes described herein can lead to reduced
manufacturing costs. The ceramic tips can be precisely green-molded
and then fully fired to have fine features and surface finishes and
even electrical and irrigant vias or ports to route
interconnections and/or irrigant from the tip interior to the tip
outer surfaces. The metallization of the electrode tips can be done
in several different ways depending on the desired product and
cost. In one embodiment, the ceramic tip substrates can comprise
one of aluminum oxide (alumina) or zirconium oxide (zirconia) or
zirconia toughened alumina. In one embodiment, all of the
metallization processes can be batched and several hundred
electrode tips can be co-deposited. The metallization techniques
can include one or more of wet plating, PVD, and CVD vapor
deposition methods for metals such as platinum or other exposed
noble metals. The patterned electrodes can also be patterned
additively or subtractively. A modified laser developed for
machining stents can be used to pattern the narrow kerfs through a
metallic ceramic overcoat to define such separated electrodes down
to an underlying isolating ceramic base layer. An exemplary method
such as sputtering may be used to deposit a well-adhering
underlayer and then a second process such as electroplating may be
used to thicken the electrode at a much lower processing cost.
Subtractive etching or lasering might be done on the underlayer or
on the dual layer sandwich. Screen printing or other mechanical
printing methods for surface film conductors can be used if the
needed electrode pattern resolution is loose enough. Inkjet
printing of conductor films can likewise be used.
[0054] Vias or irrigant ports may be molded or drilled into the
ceramic tips such that interconnections from the surface electrodes
can be routed into the tip interior and irrigant may pass outwards
from the tip. Those via interconnections might electrically and
physically comprise plated vias or discrete wires routed through
the vias. Presuming the vias are metallized or plated, at least
near their outside tip-surface as by electroless plating,
electroplating, CVD or sputtering for example, then the
metallurgical joint between a discrete via wire and the via
metallization can be hidden beneath the tip surface and covered
over with a localized coating or plug of biocompatible epoxy or the
like. The hidden metallization joint may comprise, for example, a
soldered joint, laser welded joint or a silver-epoxy joint for
example. In another embodiment, a via/port can deliver both
irrigant and route an electrode or thermocouple interconnection to
the tip surface.
[0055] An embodiment of a catheter assembly 200 is generally shown
in FIG. 4. The catheter assembly 200 can comprise a tip electrode
group 201 and a catheter shaft 203. In the illustrated embodiment,
the tip electrode group 201 can comprise a first segmented tip
electrode 205, a second segmented tip electrode 207, a third
segmented tip electrode 209, a fourth segmented tip electrode 211,
a first spot electrode 215, a second spot electrode 217, a third
spot electrode 219, a fourth spot electrode (not shown), an
irrigation through-hole 221, a first exposed non-conductive segment
227, a second exposed non-conductive segment 229, a third exposed
non-conductive segment 231, and a fourth exposed non-conductive
segment 233. Each of the plurality of spot electrodes can be
separated from other conductive portions of the tip electrode group
201 by a spot non-conductive portion 239. In the illustrated
embodiment, each of the plurality of spot electrodes 215,217,219 is
generally circular in shape and the spot non-conductive portion
that surrounds each of the plurality of spot electrodes is
generally circular in shape. Each of the plurality of spot
electrodes can further be coupled to a thermal sensor. The thermal
sensor can comprise a thermistor, a thermocouple, or other thermal
sensor as would be known to one of skill in the art. In one
embodiment, the thermal sensor can be electrically and thermally
coupled to the spot electrode. In another embodiment, the spot
electrode can comprise a thermal sensor. In one embodiment, the
spot non-conductive portion 239 is of equal diameter around each of
the spot electrodes. The plurality of non-conductive segments can
be of equal diameter around each of the spot electrodes. The
non-conductive segments can comprise various methods of separating
the electrodes via a process such as one or more of the above
mentioned subtractive or additive processes. In some embodiments,
the non-conductive segments can comprise electrode-layer gaps
between adjacent electrodes. In one such embodiment, the gap
between adjacent electrodes can comprise an exposed portion of an
inner electrically-insulative ceramic substrate of the tip
electrode. In another such embodiment, the gap can comprise an
electrically and thermally insulative ceramic material. In another
such embodiment, the gap can comprise an electrically or thermally
insulative material. The catheter assembly 200 can comprise part of
an irrigated or non-irrigated catheter system for examination,
diagnosis, and/or treatment of internal body tissues (e.g. targeted
tissue areas). In an exemplary embodiment, the catheter assembly
200 can comprise an ablation catheter (e.g. radio frequency (RF),
cryoablation, ultrasound, etc.). The instant disclosure refers to
RF ablation electrodes and electrode assemblies, but it is
contemplated that the instant disclosure is equally applicable to
any number of other ablation electrodes and electrode assemblies.
The vias mentioned above can be routed to the spot electrodes
215,217 and/or to the larger electrodes 205,207. In FIG. 4 the vias
are not visible as they are hidden by their overlying surface
electrodes or by the above-mentioned via plug material. In any
event such vias can be used to route surface connections to the tip
interior through the tip wall thickness.
[0056] The tip electrode group 201 can comprise multiple segmented
tip subelectrodes that can be configured to perform directed
ablation toward selected tissue, and the spot electrodes can act
not only as localized thermal sensors, but can also act as
electrodes for locally sensing or pacing tissue, measuring local
impedance such as between different spot electrodes. The spot
electrodes can also further be configured to act as e-field
navigation electrodes. The spot electrodes can further be used with
the segmented tip electrodes of the tip electrode 201 for
orientation independent sensing as described in the '160 reference,
the '576 reference, and the '582 reference incorporated by
reference above. In one embodiment, where a conductor pair coupled
to the thermal sensor is electrically connected to a spot
electrode, the shared functions as described herein can be used to
decrease the total number of wires within the tip electrode. In
another embodiment, the tip electrode can comprise five segmented
tip electrodes around the tip circumference. The five segmented tip
electrodes can be used such that an assumption can be made that at
least two of the segmented tip electrodes and associated spot
electrodes face tissue for a majority of their longitudinal length.
In some embodiments, the larger electrodes surround smaller or spot
electrodes as shown in FIG. 4. However, in other embodiments, the
smaller or spot electrodes are not surrounded by larger electrodes.
In further embodiments, an electrode overlaying the distal tip
comprise can comprise one contiguous electrode. A common feature of
the preferred embodiments herein is that vias can be employed
through the ceramic tip material to route interconnections from the
tip outer surface to an interior hollow core of the tip such that
such interconnections may pass out of the tip proximally toward the
catheter control handle as discrete wires or flex circuit traces.
In some embodiments, the vias are metallurgically coupled to
tip-interior discrete wires or flex circuit traces in a manner
wherein any nonbiocompatable metallurgy or conductive epoxy
employed to electrically join the vias and wires or traces is
masked or hidden from blood exposure at the tip outer surface. In
one embodiment, at least one of the vias can serve as an irrigation
port and some irrigation ports disposed within the tip can have no
electrical interconnection function.
[0057] In another embodiment, the spot non-conductive portions can
be removed or filled such that an individual segmented tip
electrode and the associated spot electrode can be thermally and
electrically coupled. As a result, the thermal sensor and
associated spot electrode cannot be used as a separate electrode
from the segmented tip electrode, however, the thermal sensor can
still be used for calorimetry purposes. Calorimetry is the
monitoring of the temperature of a tissue mass during calibrated
heat-input or heat-output such that a thermal property of the
tissue mass can be deduced.
[0058] In simplest terms, as a tissue dehydrates and lesions
develop, the tissue's thermal conductivity and specific heat drop
significantly. As a result, a pulse of injected heat before such a
lesion is made will result in a smaller depth-wise temperature
gradient than after the lesion is present and cooled back to a
starting temperature. Use of the disclosure can involve calorimetry
measurement before, during, and after a lesion is formed when the
calorimetry method is employed. Tissue impedance can be a function
of tissue dehydration but also of tissue temperature. Thus
measuring such temperature facing the lesion also results in a more
accurate temperature-corrected lesion impedance reading. Given a
pair of electrodes or spot electrodes which both face tissue, the
bipolar impedance can be measured between such pairs of intra-tip
electrodes. This impedance can be affected by the electrode
spacing, which will determine the penetrating depth of fringe
fields, and electrode size which is fixed and can be a design
choice. The two techniques, bipolar impedance lesion feedback and
calorimetry each depend on different lesion physical
properties--i.e. electrical conductivity versus thermal
conductivity/specific heat. The electrical impedance depends
primarily on the electrical conductivity of the lesion and has a
depth limit dictated by the shape of the electrical fringing fields
whereas thermal calorimetry depends on the thermal conductivity and
specific heat of tissue and has a deeper depth limit from which
residual heat may leak toward the tissue surface. Thus,
complimentary techniques can improve accuracy.
[0059] FIG. 5 depicts an isometric view of another embodiment of a
catheter assembly 300. The catheter assembly 300 can comprise a tip
electrode group 301 and a catheter body 303. The catheter body can
comprise a catheter shaft 305 and a ring electrode 307. The ring
electrode 307 can be coupled to a distal portion of the catheter
shaft 305. The tip electrode group 301 can comprise a distal
electrode portion(s) or subelectrodes 311 and a proximal portion(s)
or subelectrodes 313. In the illustrated FIG. 5 embodiment, the
proximal portion 313 can comprise a mostly cylindrical single
electrode shape, and the distal portion 311 can comprise a rounded
dome. In the depicted case the distal dome electrode 311 portion(s)
comprises five separate subelectrodes around the circumference.
Thus the tip electrode or electrode group 301 can comprise a
plurality of individual electrodes or electrode subgroups. The type
and placement of the individual electrodes on the tip electrode can
vary depending on the desired use of the tip electrode or other
design reasons. In the illustrated FIG. 5 embodiment, the tip
electrode 301 can comprise a proximal tip ring electrode 321, a
plurality of distal segmented subelectrodes 323, and a plurality of
spot electrodes 325,341. The tip ring electrode 321 in the
illustrated embodiment is located on a proximal portion 313 of the
tip electrode 301. Each of the individual electrodes of the tip
electrode 301 can be separated from other electrically conductive
portions of the tip electrode and the ring electrode by a
non-conductive portion or gap in the deposited electrode layer upon
the electrically insulating ceramic substrate. In the illustrated
FIG. 5 embodiment, the tip ring electrode 321 can be bordered by a
first circumferential non-conductive gap portion 327 at a proximal
end of the tip ring electrode 321 and a second circumferential
non-conductive gap portion 329 at a distal end of the tip ring
electrode 321. The gap portions 327,329 comprise exposed
electrically insulating tip ceramic substrate material for example.
Such gap portions may comprise lasered gaps in the electrode layer.
In other embodiments one or both of the circumferential
non-conductive portions can be removed from the catheter
assembly.
[0060] A plurality of subelectrodes 323 can also be located on the
catheter assembly 300. Each of the subelectrodes 323 can be
separated from the tip ring electrode and other subelectrodes by a
non-conductive gap portion of the tip electrode 301. In the
illustrated embodiment, each of the segmented subelectrodes can
extend longitudinally from the second circumferential
non-conductive portion 329 to a distal end 333 of the tip electrode
301. In the illustrated embodiment, each of the plurality of
segmented subelectrodes 323 can be separated by a longitudinally
extending non-conductive gap portion 335. FIG. 5 illustrates a tip
electrode with 6 discrete longitudinally extending non-conductive
gap portions delineating six separate segmented subelectrodes.
Other embodiments of a tip electrode according to this disclosure
can have varying numbers of longitudinally extending non-conductive
portions and varying numbers of segmented electrodes. The tip
electrode 301 can further comprise a plurality of spot electrodes
325. In the illustrated embodiment of FIG. 5, an individual spot
electrode is disposed within each of the segmented tip
subelectrodes and can be located on and equally spaced around the
distal portion 311 of the tip electrode 301. Each of the plurality
of spot electrodes 325 can be surrounded by a spot non-conductive
portion 337. The spot non-conductive portion 337 can electrically
isolate each of the spot electrodes from the rest of the tip
electrode 301. Note that both the spot electrodes and larger
surrounding electrodes are both situated upon the electrically
insulating tip substrate material. In other embodiments, the spot
electrodes can be in other configurations. In one embodiment, each
of the spot electrodes can be located on the proximal portion of
the tip electrode 301 and can also be evenly spaced around an outer
circumference of the tip electrode 301. In another embodiment, each
of the spot electrodes can be located adjacent the segmented tip
electrodes. In other embodiments, each of the spot electrodes can
be located within the longitudinal non-conductive portion of the
tip electrode. In on embodiment, each of the spot electrodes can be
located within the longitudinal non-conductive portion of the tip
electrode and each of the spot electrodes can be further surrounded
by a spot non-conductive portion.
[0061] The tip electrode can further comprise at least one ring
spot electrode 341. The at least one ring spot electrode 341 can be
disposed within the tip ring electrode 321. In the illustrated
embodiment, the at least one ring spot electrode 341 can be
disposed evenly between a proximal edge of the tip ring electrode
and a distal edge of the tip ring electrode. The at least one ring
spot electrode 341 can be surrounded by a ring spot non-conductive
portion 343. The ring spot non-conductive portion 343 can
electrically isolate the ring spot electrode 341 from the tip ring
electrode 321 and can also electrically isolate the ring spot
electrode 341 from the rest of the electrodes on the tip electrode
301. In other embodiments, the at least one ring spot electrode can
comprise a first ring spot electrode and the electrode tip can
comprise additional ring spot electrodes spaced apart from the
first ring spot electrode. In one embodiment, the tip electrode can
comprise a second ring spot electrode disposed around 180 degrees
around a circumference of the tip ring electrode from the first
ring spot electrode. In another embodiment, the tip electrode can
comprise four separate ring spot electrodes evenly spaced at 90
degrees around a circumference of the ring electrode 321. The tip
electrode 301 can further comprise one or more irrigation
through-holes 345. The irrigation through-hole(s) 345 can be
fluidly coupled to an irrigation source to supply an irrigant or
other fluid to an exterior of the distal portion 311 of the
electrode tip 301. In other embodiments, the irrigation
through-hole can comprise one of a plurality of irrigation
through-holes. In the illustrated embodiment, each of the
longitudinally extending non-conductive portions 335 can extend
from the second circumferential non-conductive portion 329 to a
non-conductive portion surrounding the irrigation through-hole 345.
This results in each of the segmented tip electrodes being bound on
a proximal end by the second circumferential non-conductive portion
329, on each side by a separate longitudinally extending
non-conductive portion, and at a distal end by the irrigation
through-hole 345. In another embodiment, each of the segmented
electrodes can abut the irrigation through-hole. In some
embodiments, an irrigation via 345 including a metallized interior
diameter metallized also is also configured to act as an electrical
connection or via from the tip surface to the tip interior such as
to both RF-power and irrigate a surface electrode.
[0062] FIG. 6 illustrates an embodiment of a tip assembly 400
comprising a tip electrode group 401 and a conductor assembly 403.
The tip electrode group 401 can comprise a base portion 407, a
plurality of individual electrodes and a non-conductive portion
surrounding each electrode. In the illustrated embodiment, the
plurality of individual electrodes can comprise a first segmented
tip electrode 409, a second segmented tip electrode 411, a third
segmented tip electrode 413, a fourth segmented tip electrode 415,
a fifth segmented tip electrode (not shown), a sixth segmented tip
electrode (not shown), a first spot electrode 419, a second spot
electrode 421, a third spot electrode 423, a fourth spot electrode
425, a fifth spot electrode (not shown), a sixth spot electrode
(not shown), a tip ring electrode 449, a first ring spot electrode
429, and a second ring spot electrode (not shown). The tip
electrode 401 can further comprise a proximal circumferential
non-conductive portion 431, a distal circumferential non-conductive
portion 433, a plurality of longitudinal non-conductive portions
437, and a distal end non-conductive portion 439. Each of the
segmented tip electrodes can be separated from adjacent segmented
tip electrodes by one of the plurality of longitudinal
non-conduction portions 437. Each of the segmented tip electrodes
can extend longitudinally from the distal circumferential
non-conductive portion 433 to the distal end non-conductive portion
439. The distal end non-conductive portion 439 can be disposed on a
distal end 451 of the tip electrode 401. Each of the spot
electrodes can be electrically and thermally isolated from the
other electrodes on the tip electrode 201 by a spot non-conductive
portion 455. The base portion 407 can be sized and configured to
fit within a catheter body to couple the tip assembly 400 to the
catheter body. The base portion 407 can further comprise a tip
anchor 441. The tip anchor 441 can be used to further secure the
tip assembly 400 to a catheter shaft. The conductor assembly 403
can comprise a plurality of individual conductors or conductor
pairs. Each of the conductor pairs can be coupled to an individual
thermocouple disposed within the tip electrode 401. Each of the
conductor pairs can electrically couple one or more electrodes to a
connector or other device to allow for signals to be measured from
the various electrodes of the tip electrode 401 or to deliver
energy through the various electrodes to a target area or tissue.
In one embodiment, the thermocouple leads (one or both) can be used
as interconnection wires to also power the sensing or ablating
electrodes. In some embodiments, the conductor pairs can also be
coupled to a thermal sensor or form a thermal sensor or
thermocouple in which case the wire pair may be thermocouple alloy
wires such as a copper wire and a constantin wire. This can be an
example of wire-sharing where two wires form a tip-surface
thermocouple but can also power a surface electrode or detect
electrical signals on a surface electrode. The thermal sensors
(e.g. thermocouples or thermistors having two wires) can be
disposed adjacent an outer tissue exposed surface of the tip
electrode and can transfer temperature and other data to a proximal
end of a conductor pair. The illustrated embodiment shows at least
a first conductor pair 443, a second conductor pair 445, and a
third conductor pair 447. In one embodiment, a separate conductor
pair is electrically connected to each of the discrete electrodes
disposed on the tip electrode. In another embodiment, each of the
conductor pairs can be electrically connected to one or more of the
discrete electrodes disposed on the tip electrode. In another
embodiment, such as that shown in FIG. 5, the conductor assembly
can comprise a plurality of conductor pairs and an irrigation
lumen. The irrigation lumen can be configured to be coupled to an
irrigation source. It will be appreciated that with so many
electrodes and thermal sensors such wire-sharing can be very
beneficial.
[0063] FIG. 7 illustrates an isometric, cross-sectional view, of an
embodiment of a tip assembly 500 comprising a tip electrode group
501 and a conductor assembly 503. The tip has a base portion 507
and can also comprise an electrically-insulative substrate 505 and
which mates with a polymer lumen. The electrically-insulative
substrate 505,507 can either be made of ceramic materials or
polymers of various durometers. The electrically-insulative
substrate can be an injection molded component. Injection molded
describes molded with a polymer to a final shape or with a ceramic
molded to a green shape which is then fired in a furnace. The
electrically-insulative substrate can be formed in various
configurations according to the desired use of the catheter. These
configurations can include irrigation lumens, irrigation flow
holes, sensor channels, and/or conductive channels (metallized
electrical vias or holes for discrete wires) as well as structures
for mechanical attachment, alignment, or stabilization. The
conductive material can be selectively bonded to, deposited, or
coated onto the electrically-insulative substrate by various
techniques, including low temperature print manufacturing (with or
without sintering), screen-printing, die-embossing, inkjet
deposition, electroplating, electroless plating, sputter
deposition, heat, mechanical deformation, cathodic arc deposition,
diffusion bonding, evaporative deposition and pulsed laser
deposition or combinations thereof.
[0064] The tip electrode group 501 can comprise and be formed
within a thin layer of conductive material clad or deposited onto
the electrically-insulative substrate 505,507. The thin layer of
conductive material deposited onto the electrically-insulative
substrate can improve temperature correlation between the electrode
and tissue interface because it is configured as a thin layer of
heat and electrically conducting material, and itself has a low
thermal capacity to modulate heat in the tissue itself. The thin
metal layer on the electrically and thermally insulating substrate
505,507 can also therefore preserve important thermal gradients
seen along the tissue surface. The thin layer of conductive
material (one or more electrodes thereof) can be at-least
temporarily if not permanently electrically connected to an
ablation system to allow for the delivery of ablative energy or the
like. The thin layer of conductive material can be electrically
connected to the ablation system in any manner conventional in the
art. For example, a conductor wire can be provided. The conductor
wire can extend through a lumen within the catheter shaft. The
patient may also utilize a ground-return patch in the case of a
single wire fed monopolar RF tip. Groups of such electrodes may be
employed to perform ablation and/or perform impedance feedback from
lesions or to perform electrical sensing or pacing.
[0065] In some embodiments the electrically-insulative substrate
can comprise a thermally insulative material. Alumina, zirconia
toughened alumina and zirconia are all poor thermal conductors but
have been proven in dental and medical implants. Silicon nitride is
a better thermal conductor than the others but still electrically
insulative and also proven in medical implants. Silicon nitride has
the same order of thermal conductivity as platinum iridium which is
a very poor metallic thermal conductor. For this reason silicon
nitride can thermally act similarly to existing platinum-iridium
tips and remove substantial heat from the tissue by having the tip
irrigated.
[0066] In such embodiments the electrically-insulative substrate
can provide an insulated internal flow path for ionically
conductive saline or other irrigation fluid. The
electrically-insulative substrate can thermally isolate the
multiple thermal sensors located within the tip electrode 203. By
thermally isolating the temperature sensors, the tip electrode 203
can have an improved ability to measure the temperature at the
tip-tissue interface during lesion formation. i.e. Using the
thermally insulating substrate 505 the tip can accurately and more
importantly rapidly detect the true tissue surface temperature
without suppressing it to a large degree due to tip-induced tissue
cooling. The listed ceramics above allow placement of temperature
sensors on the tip surface.
[0067] The tip electrode group 501 of FIG. 7 can further comprise
at least one segmented subelectrode 511, a tip ring electrode 513,
a first via or wire channel 515, a second via or wire channel 517,
a third via or wire channel 519, a first spot electrode 521, a
second spot electrode (not shown), a third spot electrode 523, a
first spot non-conductive portion 527, a second spot non-conductive
portion (not shown), a third spot non-conductive portion 529, and
an inner tip surface 531. While not shown, other electrodes can be
present on the tip electrode 501 as described throughout the
disclosure. The inner tip surface 531 can define an inner lumen 533
that extends from a proximal end of the tip electrode 501 to a more
distal portion of the tip electrode 501. The inner lumen 533 can be
configured to allow for wires, irrigation lumens, or other desired
components to be placed or routed through an inner portion of the
tip electrode 501. The first channel 515, the second channel 517,
and the third channel 519 can extend from the inner tip surface 531
to an exterior tip surface. In the illustrated embodiment, each of
the channels extends from an inner channel opening 537 to an outer
surface opening 539. Each of the channels (electrical
interconnection vias or water irrigation ports or both) can
comprise various sizes depending on the components designed to be
placed within. In the illustrated embodiments, each of the channels
can comprise a cylindrical hole within the electrically-insulative
substrate 505 of the tip electrode 501. In other embodiments, each
of the channels can comprise other shapes and sizes as may be
warranted by design considerations or ease of manufacturing. As
seen in the illustrated embodiment, the inner channel opening is
located proximally from the outer surface opening. This results in
the outer surface opening 539 being located in a distal direction
of the inner channel opening 537. In other embodiments the inner
channel opening and the outer surface opening of one or more of the
channels can be located along the same portion of a longitudinal
axis of the tip electrode. This placement of the channel can result
in a roughly 90 degree angle between the channel and the inner
lumen of the tip electrode. In yet other embodiments, the inner
surface opening can be located in a distal position in relation to
the outer surface opening. This results in the outer surface
opening being located in a proximal direction of the inner channel
opening. In other embodiments, a plurality of channels located
within a tip electrode can comprise one or more of the embodiments
listed above. In other embodiments, one or more of the channels can
extend in a radial direction from an inner lumen or other interior
portion of the tip electrode.
[0068] The illustrated embodiment in FIG. 7 shows a first spot
electrode 521 adjacent an outer surface of the tip electrode 501.
The first spot electrode 521 can comprise a thermal sensor. The
first spot electrode 521 can be secured within the first channel
515 with the first spot non-conductive portion 527. The first spot
non-conductive portion 527 can be used to secure the first spot
electrode 521 in a desired position in relation to the rest of the
electrodes on the tip electrode 501. Similarly, the third spot
non-conductive portion 529 can be used to secure the third spot
electrode 523 in a desired position in relation to the rest of the
electrodes on the tip electrode 501. The base portion 507 can also
comprise at least one tip anchor 543. The at least one tip anchor
543 can be used to further secure the tip assembly 500 to a
catheter shaft. The conductor assembly 503 can comprise a first
conductor pair 545, a second conductor pair 547, and a third
conductor pair 549. Each conductor pair can be electrically coupled
to a spot electrode. In the illustrated embodiment, the first
conductor pair 545 can be electrically coupled to the first spot
electrode 521, the second conductor pair 547 can be electrically
coupled to the second spot electrode (not shown), and the third
conductor pair 549 can be electrically coupled to the third spot
electrode 523. Each conductor pair can enter the tip electrode 501
through the inner lumen 533 and then travel through one of the
channels in the tip electrode 501. In one embodiment, the tip
assembly can comprise a plurality of conductor pairs, with an
individual conductor pair for each electrode on the tip electrode.
It will be appreciated that the vias or channels may be completely
metallized (as by interior wall coating or complete filling) in
their interiors thus serving as conductive vias without discrete
wires being placed therein. Alternatively they may be metallized
therein only at the outer tip surface region during the deposition
of the tip electrode conductive layer. Such partial channel or via
metallization at the outer entry channel region allows for a wire
to be soldered inside the channel near the tip surface-said wire
being thus also connected to the adjacent surface electrode via the
electrode layer metallization which also coats the tip surface in
the form of defined electrodes.
[0069] FIG. 8 illustrates an isometric cross-sectional view of
another embodiment of a catheter assembly 600. The catheter
assembly can comprise a tip electrode 601 and a flexible catheter
lumen body 603. The catheter body 603 can comprise a catheter shaft
605 and a ring electrode 607. The ring electrode 607 can be coupled
to a distal portion of the catheter shaft 605. The tip electrode
601 can comprise a base portion 611 and can also comprise an
electrically-insulative substrate 613. The tip electrode 601 can
further comprise at least one segmented electrode 615, a tip ring
electrode 617, a first spot electrode (not shown), a second spot
electrode 619, a ring spot electrode 621, a first channel 625, a
second channel 627, a third channel 629, a fourth channel 631, a
proximal circumferential non-conductive portion 635, a distal
circumferential non-conductive portion 637, a longitudinal
non-conductive portion 639, and an inner tip surface 641. While not
shown, other electrodes can be present on the tip electrode 601 as
described throughout the disclosure. The inner tip surface 641 can
define an inner lumen 645 that extends from a proximal end of the
tip electrode 601 to a more distal portion of the tip electrode
601. The inner lumen 645 can be configured to allow for wires,
irrigation lumens, or other desired components to be placed or
routed through an inner portion of the tip electrode 601. The first
channel 625, the second channel 627, the third channel 629, and the
fourth channel 631 can extend from the inner tip surface 641 to an
exterior tip surface. In the illustrated embodiment, each of the
channels extends from an inner channel opening 645 to an outer
surface opening 647. As seen in the illustrated embodiment, the
channels (electrical vias, water ports or both) can be formed in
various, different directions. The first channel 625 and the second
channel 627 can extend in a distal direction from the inner tip
surface 641 to the exterior tip surface. The third channel 629 can
extend in a roughly 90 degree angle from the inner tip surface 641.
The fourth channel 631 can extend from a distal end of the inner
lumen 645 to a distal end of the tip electrode. In one embodiment,
the fourth channel 631 can be sized and configured to couple to an
irrigation lumen. In another embodiment, the fourth channel can be
configured to fluidly couple to an irrigation source and can
deliver an irrigant or other fluid to an exterior portion of the
electrode tip. The base portion 611 of the electrode tip 601 can be
configured to fit within the distal end of the catheter shaft 605.
The base portion 611 can also comprise at least one tip anchor 649.
In one embodiment, an adhesive can be used to couple the base
portion 611 and the catheter shaft 605. In another embodiment, an
adhesive can be used along with at least one anchor coupled to the
at least one tip anchor 649. The catheter assembly 600 can further
comprise a first conductor pair 651, a second conductor pair 653,
and a third conductor pair 655. Each conductor pair can be
electrically coupled to a thermocouple or spot electrode. For a
spot electrode only one of the conductors can be used. For a
thermocouple (or ablating electrode) both conductors can be used.
For both a spot electrode and thermocouple in the same channel two
conductors serve the thermocouple and at least one (or both)
conductors serves the spot electrode. The necessary switching
between the thermocouple function and electrode function can happen
in the supporting system--conductor wires or metalized traces can
be shared among functions. In the illustrated embodiment, the first
conductor pair 651 can be electrically coupled to the first spot
electrode (not shown), the second conductor pair 653 can be
electrically coupled to the second spot electrode 619, and the
third conductor pair 655 can be electrically coupled to the ring
spot electrode 621. Each conductor pair can enter the tip electrode
601 through the inner lumen 645 and then travel through one of the
channels in the tip electrode 601. In one embodiment, the tip
assembly can comprise a plurality of conductor pairs, with an
individual conductor pair for each electrode on the tip electrode.
The second spot electrode 619 can be secured within the second
channel 627 with a second spot non-conductive portion 659. The
second spot non-conductive portion 659 can be used to secure the
second spot electrode 619 in a desired position in relation to the
rest of the electrodes on the tip electrode 601. Similarly, the
ring spot electrode 621 can be secured within the third channel 629
with a ring spot non-conductive portion 661. The ring spot
non-conductive portion 661 can be used to secure the ring spot
electrode 621 in a desired position in relation to the rest of the
electrodes on the tip electrode 601.
[0070] FIG. 9 illustrates an isometric, cutaway view of an
embodiment of a catheter assembly 700. The catheter assembly can
comprise a tip electrode 701, a conductor assembly 705, and a
catheter body 703. The catheter body 703 can comprise a catheter
shaft 707 and one or more ring electrodes 709 (one shown). The ring
electrode(s) 709 can be coupled to a distal portion of the catheter
shaft 707. The conductor assembly 705 can comprise a plurality of
conductor pairs 713 or individual conductors. As stated above, a
thermocouple or thermistor can use a pair of such conductors (e.g.
copper and constantin conductors) whereas a spot electrode or RF
ablation electrode needs at least one wire--preferably a copper or
other high conductivity metal conductor. The tip electrode 701 can
be coupled to the catheter body 703. The tip electrode 701 can
comprise a proximal circumferential non-conductive portion 717, a
tip ring electrode 719, an electrically-insulative substrate 721,
an inner tip surface 723, an inner lumen 725, and a first channel
727. While not shown, other electrodes can be present on the tip
electrode 701 as described throughout the disclosure. The inner tip
surface 723 can define the inner lumen 725 that extends from a
proximal end of the tip electrode to a more distal portion of the
tip electrode. The channel 727 can extend from an inner channel
opening 729 to an outer surface opening 731 and can extend from the
inner tip surface 723 at a roughly 90 degree angle. A ring thermal
sensor 733 can be secured within the third channel 727 with a ring
sensor non-conductive portion 735. Each channel 72 can optionally
support both an irrigation function and a thermocouple or electrode
function.
[0071] FIG. 10 illustrates a diagrammatic cross-sectional view of
another embodiment of a tip electrode 750. The tip electrode 750
can comprise an electrically-insulative substrate 751, an ablation
electrode 753, a spot electrode 755 situated within the ablation
electrode 753 yet isolated from it by an insulative circular gap
761, a thermal sensor 763, and a conductor pair 765. The thermal
sensor 763 is coupled to the conductor pair 765 and both can be
electrically and thermally coupled to the spot electrode 755. The
conductor pair 765 can transfer signals from the spot electrode 755
(via the copper wire) and the thermal sensor 763 (via both the
copper and constantin wires) to a proximal end of a device as
described above. The conductor pair 765 can also transfer energy to
the thermal sensor 763 or spot electrode 755 if it is also employed
to ablate as well as sense. The spot electrode 755 can be separated
from the electrode 753 by the electrically insulative gap 761.
[0072] FIG. 11 is a diagrammatic view of a system 770 that can be
used for combining the independent impedance and calorimetry lesion
feedback from the electrodes on a catheter to deduce a lesion state
and/or a temperature depth-profile if both feedback methods
described above are employed. The lesion state can comprise a
volume of the lesion, a depth of the lesion, a surface area of the
lesion, a circumference of the lesion, or other states known to one
of ordinary skill in the art. A weighting and/or combining
algorithm can be used to make these determinations. Separate
algorithms can be employed for the impedance and calorimetry
methods themselves. Weighting can also be simple averaging (equal
weight).
[0073] Again for intra-lesion bipolar electrical impedance feedback
one connects across any two electrodes which both face the lesion.
These may be two spot electrodes or a spot electrode and a larger
ablating electrode surrounding it for example.
[0074] For pace and ablate feedback the split tip implementations
of FIGS. 4, 5, and 6 can be bipolar paced in a novel manner that
can utilize an even number of distal pacing electrodes. A pair of
stimulator channels can be set for simultaneous pacing at the same
duration and current strength such that pacing anodes and cathodes
alternate. When adjusted to the pacing threshold, only the pair of
electrodes in contact with cardiac tissue can be responsible for
achieving capture. The pacing pulse strength may be set to an
appropriate margin over the pacing threshold and thus catheter
orientation independent pacing information quickly obtained. Pacing
immediately prior to, during, and after RF application provides
feedback on lesion effectiveness in a manner that complements
electrogram signal reduction, tissue impedance changes, and
calorimetry. Pace and ablate strategies can be valuable aids in the
identification of lesion gaps. The pace and ablate procedure can be
further seen in Eitel, C., Hindricks, G., Sommer, P. et al.,
Circumferential pulmonary vein isolation and linear left atrial
ablation as single catheter technique to achieve bidirectional
conduction block: the "pace-and-ablate" approach. Heart Rhythm.
2010; 7: 157-164, which is hereby incorporated by reference in its
entirety as though fully set forth herein. In one embodiment, an
electronic control unit can be configured to pace cardiac tissue by
utilizing the segmented electrodes and spot electrodes disclosed
herein.
[0075] Again, for calorimetry, we have thermocouples which face
tissue and themselves sit on a thermally insulating tip material
such as ceramic or polymer. We also have an adjacent or surrounding
ablation electrode facing (and causing) the lesion. Using known RF
thermal modeling techniques (earlier reference) we can make a
depth-wise thermal profile model which incorporates decreasing
thermal conductivity (and specific heat) of the tissue with extent
of necrosis or lesioning. In this manner a bolus of injected heat
(as by an RF power pulse), when stopped, will result in a thermal
temperature decay at the tissue surface detectable by the surface
contacting thermocouple(s). This decay curve is fitted to an
assumed temperature and thermal conductivity profile that caused
it. The initial starting assumption (before any lesion formation)
is a decreasing temperature with depth and no thermal conductivity
change (initially no necrosis has occurred). As the lesion
progresses decreased thermal conductivity and specific heat is
assumed (as caused by lesioning necrosis progressing downwards)
such that the surface temperature decay curve is matched by the
models current temperature and conductivity profile. Increasing
degrees of tissue thermal exposure can result in increasing loss of
thermal conductivity and specific heat as dewatering occurs. Full
necrosis is the final state. Thus the changes are gradual which can
allow for a feedback loop to automatically control ablation.
[0076] In another embodiment, the use of combined electrical
impedance and calorimetry lesion-feedback tools can be configured
to be acquired by impedance and calorimetry sensors that can be
built upon an electrically and thermally insulating substrate.
These two insulating qualities (electrical and thermal) can assure
that the two feedback methods are sampling only the adjacent facing
and underlying forming lesion. A number of possible calorimetric
algorithms can be employed whether based on the incorporated
references cited above, or using a new algorithm. This disclosure
is not limited to a particular algorithm. Further, the two outputs,
the electrical impedance, and the calorimetric information can have
their corresponding presumed lesion depths be weighted in any
desired manner such as 50/50 or equally wherein they are
averaged.
[0077] It can be further noted that navigation magnetic coils (not
shown) can easily be embedded or contained within the ceramic tip
and that the navigation magnetic coil connecting wires can also
perform shared duty as optionally might the thermal sensors.
[0078] In some embodiments, the system can comprise an ECU. FIG. 11
depicts a very generalized schematic of an overall system for
performing EP procedures while taking benefit of the disclosure
herein. The tip electrodes depicted above can be mounted on a
catheter shaft which can in turn be connected to a catheter control
handle. A variety of power, data and fluid lines can connect the
catheter to the system 770. In the illustrated embodiment, the
system 770 can comprise a computing module 771 (such as for
impedance modeling, calorimetric modeling, heart chamber mapping
and modeling), a spatial navigation module 773, an organ modeling
module 775, an impedance assessment module 777, a calorimetry
assessment module 779, a GUI module 781, an irrigation control
module 783, an ablation module 787, and a communication module 785.
In some embodiments the modules of the system 770 can be packaged
together or share the same circuitry or software. In other
embodiments, the modules of the system 770 can be separate. The
computing module 771 can comprise the computational and logic means
supporting the system 770 and can allow the system 770 to
communicate to the outside world. Such computations and logic can
be performed in software, firmware, or hardware. The spatial
navigation module 773 can comprise the circuitry needed to create
and sense navigation electric fields and/or magnetic fields. The
spatial navigation module 773 can also comprise known magnetic or
electromagnetic coils or body patches outside the spatial
navigation module itself. The organ modeling module 775 can
comprise software which can be employed to create a 3D/4D heart
model. It may take navigation data, such as position and
orientation, from the spatial navigation module 773 to do so. The
impedance assessment module 777 can comprise circuitry and sensing
such that the electrical impedance between desired pairs of
catheter tip electrodes or sub-electrodes can be measured from
within the single multi-electrode tip from electrodes touching the
lesion and being at a known real time temperature. The calorimetry
module 779 can comprise circuitry and sensing components such that
select electrodes or sub-electrodes can be heated and or cooled (or
irrigant flow can be step-changed) and resulting changing surface
temperature detected in a manner that subsurface tissue heat flow
can be deduced from at least one such reading and preferably from
dual readings from tissue-facing adjacent electrodes. Dual adjacent
readings can allow the module to better determine the rotational
alignment of the tip to the lesion and a more accurate heat flow
model can be made. In one embodiment, the employed electrodes face
the tissue and their real time temperatures are known. The GUI
module 781 can comprise circuitry to allow a user to communicate
with and control the system 770. In this manner the GUI module 781
can provide system controls, system outputs, heart models showing
the overlaid catheter and lesioning-extent, EP waveforms, patient
info, lesion maps, EP Mapping data, etc. The irrigation control
module 783 can comprise circuitry comprising a pump, logic for
turning an irrigation or saline pump on/off or for varying its flow
rate in support of ablation and feedback methods. In one
embodiment, the irrigation control module can further comprise an
irrigation or saline pump. The ablation module 787 can comprise an
existing standalone RF generator as well as a supporting irrigation
pump. In other embodiments, the ablation module can comprise a
modularized co-packaged RF generator. In yet other embodiments,
other ablative energy sources are included in the scope such as
laser, microwave, ultrasonic ablation, electroporation and cryo.
The communication module 785 can comprise a data/signal/power bus
that can allow the various modules to be powered, share the CPU,
share navigation feedback, share temperature feedback, share power
supplies, and share sensing circuitry. In some embodiments, the
power supplies and sensing circuitry can be shared between only
portions of the system and in other embodiments the power supplies
and sensing circuitry can be shared between the entire system. In
yet other embodiments, the power supplies and the sensing circuitry
can be shared between none of the modules in the system.
[0079] FIG. 12A depicts a flowchart for applying a method to
utilize both impedance feedback and heat flow (calorimetry)
feedback methods to determine a lesion state as described above.
Step 801 comprises placing a catheter tip at a target tissue
location at a desired lesion site. Step 803 comprises measuring a
pre-lesion impedance of the target tissue location at a known
cardiac starting temperature of about 37 deg C. Step 805 comprises
measuring a pre-lesion heat-flow ability of the target tissue
location at a known starting and peak temperatures wherein the peak
temperature is below lesioning temperature, for example 40 or 41
deg C. Step 807 comprises incrementally ablating the target tissue
location for a desired incremental time and at a desired power.
Step 809 comprises measuring a post-lesion (post lesion increment)
impedance of the target tissue location at a known starting
achieved peak temperature. Step 811 comprises measuring a
post-lesion heat-flow ability of the target tissue location at a
known starting achieved peak surface temperature. Step 813
comprises obtaining a state of the lesion temperature profile and
depth profile. The state of the lesion temperature profile and the
depth profile can be determined by using the impedance and the heat
flow values (scalar quantities) in to a tissue model. The states
can be determined at the moment when power was temporarily
discontinued. Step 815 comprises determining whether to further
ablate the target tissue location. In one embodiment of step 815
the impedance feedback and the calorimetric feedback can be
combined to determine whether further ablation of the target tissue
location is desired.
[0080] FIG. 12B depicts a flowchart for applying a method to
utilize an impedance feedback method to determine a lesion state as
described above. Step 821 comprises placing a catheter tip at a
target tissue location at a desired lesion site. Step 823 comprises
measuring a pre-lesion impedance of the target tissue location at a
known temperature. Step 825 comprises incrementally ablating the
target tissue location for a desired time and at a desired power.
Step 827 comprises measuring a post-lesion impedance of the target
tissue location at a known temperature such as at the achieved peak
temperature. Step 829 comprises obtaining a state of the lesion
temperature profile and depth profile. The state of the lesion
temperature profile and the depth profile can be determined by
using the impedance and the heat flow values (scalar quantities) in
to a tissue model. The states can be determined at the moment when
power was temporarily discontinued. Step 831 comprises determining
whether to further ablate the target tissue location.
[0081] FIG. 12C depicts a flowchart for applying a method to
utilize a heat flow feedback method to determine a lesion state as
described above. Step 841 comprises placing a catheter tip at a
target tissue location at a desired lesion site. Step 843 comprises
measuring a pre-lesion heat-flow ability of the target tissue
location at a known temperature. Step 845 comprises incrementally
ablating the target tissue location for a desired time and at a
desired power. Step 847 comprises measuring a post-lesion heat-flow
ability of the target tissue location at a known achieved peak
starting temperature. Step 849 comprises obtaining a state of the
lesion temperature profile and depth profile. The state of the
lesion temperature profile and the depth profile can be determined
by using the impedance and the heat flow values (scalar quantities)
in to a tissue model. The states can be determined at the moment
when power was temporarily discontinued. Step 850 comprises
determining whether to further ablate the target tissue
location.
[0082] FIG. 12D depicts a flowchart for applying a method to
utilize a pacing capture feedback method to determine a lesion
state as described above. Step 851 comprises placing a catheter tip
at a target tissue location at a desired lesion site. Step 853
comprises adjusting pacing outputs to a predetermined margin over
the pacing threshold which just maintains capture. Step 855
comprises incrementally ablating the target tissue location for a
desired time and at a desired power. Step 857 comprises observing
for post lesion pacing capture. Step 859 comprises determining
whether to further ablate the target tissue location.
[0083] In other embodiments, any of the methods listed in FIGS.
12A-12D can be used, but ablation at the target tissue can be
stopped at least once during ablation to assess lesioning progress.
In other embodiments, any of the methods listed in FIGS. 12A-12D
can be used, and OIS assessments of electrogram signals as
discussed above can also be performed while the method is being
performed. In other embodiments, where the spot electrodes as
discussed above are present on the catheter, the spot electrodes
can monitor impedance throughout the ablation or at certain
sampling times before, during, or after ablation. This can occur
separate from the electrodes that are ablating the target tissue.
In one embodiment, calorimetry can also be performed. In other
embodiments, irrigation can be provided adjacent the catheter tip.
In one embodiment, the irrigant is flow-excluded from the
tissue-facing tip surface, but can still maintain a desired max
temperature around the tip. In another embodiment, the irrigant
flow can be provided at a temperature or flow rate which can
deliver a desired cooling, warming, or temperature stabilizing
effect on at least a portion of the tip. This effect can be caused
for purposes of controllably practicing one or both lesion feedback
methods. In on embodiment, the catheter can comprise 5 or 6 major
electrodes running from the distal tip partway up the tip. This
multi-electrode distal tip region can be guaranteed to contain a
good tissue, high-percentage contact region-particularly if a
minimum tip force is maintained. In this embodiment, the major
electrodes are not present all the way up the tip such that that
none of the feedback electrodes have significant blood flow around
them such as at the proximal tip region which may sit off the
tissue surface. In some embodiments, that flow can significantly
affect both feedback methods.
* * * * *