U.S. patent application number 11/953151 was filed with the patent office on 2008-04-17 for brush electrode and method for ablation.
Invention is credited to Kedar Ravindra Belhe, Hong Cao, Saurav Paul, Chou Thao.
Application Number | 20080091192 11/953151 |
Document ID | / |
Family ID | 34753060 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080091192 |
Kind Code |
A1 |
Paul; Saurav ; et
al. |
April 17, 2008 |
Brush electrode and method for ablation
Abstract
A brush electrode and a method for using the brush electrode for
tissue ablation are disclosed. The brush electrode comprises a
plurality of flexible filaments or bristles for applying ablative
energy (e.g., RF energy) to target tissue during the formation of
spot or continuous linear lesions. Interstitial spaces are defined
among the filaments of the brush electrode, and the interstitial
spaces are adapted to direct conductive or nonconductive fluid,
when present, toward the distal ends of the brush filaments. The
brush electrode facilitates electrode-tissue contact in target
tissue having flat or contoured surfaces. The flexible filaments
may be selectively trimmed to give a desired tip configuration or a
desired standoff distance between the tissue and the conductive
filaments in the brush electrode. Also, the filaments may be
grouped into clusters. A shielded-tip brush electrode, including a
flexible boot, is also disclosed.
Inventors: |
Paul; Saurav; (Minneapolis,
MN) ; Belhe; Kedar Ravindra; (Minnetonka, MN)
; Cao; Hong; (Savage, MN) ; Thao; Chou;
(Brooklyn Park, MN) |
Correspondence
Address: |
ST. JUDE MEDICAL, ATRIAL FIBRILLATION DIVISION
14901 DEVEAU PLACE
MINNETONKA
MN
55345-2126
US
|
Family ID: |
34753060 |
Appl. No.: |
11/953151 |
Filed: |
December 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10808919 |
Mar 24, 2004 |
7326204 |
|
|
11953151 |
Dec 10, 2007 |
|
|
|
60537092 |
Jan 16, 2004 |
|
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|
Current U.S.
Class: |
606/41 |
Current CPC
Class: |
A61B 18/1402 20130101;
A61B 2018/143 20130101; A61B 2018/1472 20130101 |
Class at
Publication: |
606/041 |
International
Class: |
A61B 18/14 20060101
A61B018/14 |
Claims
1. A wet-brush electrode that facilitates electrode-tissue contact
in target tissue having contoured surfaces, the wet-brush electrode
comprising a plurality of flexible filaments adapted to transfer
ablative energy to target tissue, said plurality of flexible
filaments defining interstitial spaces among said plurality of
flexible filaments, wherein said interstitial spaces are adapted to
carry conductive fluid; a primary conductor operatively connected
to, and adapted to transfer ablative energy to, said plurality of
flexible filaments; and a fluid-delivery means adapted to deliver
conductive fluid to said interstitial spaces.
2. The catheter of claim 1, wherein at least one flexible filament
comprising said plurality of flexible filaments has a distal end,
and wherein at least one of said plurality of flexible filaments
taper, towards said distal end of said at least one of said
flexible filaments.
3. The catheter of claim 1, wherein said plurality of flexible
filaments comprises a conductive filament and a nonconductive
filament.
4. The catheter of claim 1, further comprising an embedded device
selected from the group consisting of a thermocouple, a pressure
sensor, and an ultrasound sensor.
5. The catheter of claim 1, further comprising an outer sheath.
6. The catheter of claim 5, wherein said outer sheath comprises a
concentric ring of sub-channels around a main channel, and wherein
at least a portion of said plurality of flexible filaments resides
in said main channel.
7. A catheter for ablating tissue inside a human body, the catheter
comprising an outer sheath having a distal sheath end; a conforming
electrode adapted to apply ablative energy to target tissue, said
conforming electrode comprising an embedded portion and an exposed
portion, wherein said exposed portion has a distal electrode end,
wherein a working surface is present at said distal electrode end
of said exposed portion, and wherein said exposed portion extends
from said distal electrode end of said outer sheath; and a primary
conductor in direct electrical contact with said conforming
electrode and adapted to carry ablative energy from an energy
source to said conforming electrode.
8. The catheter of claim 7, wherein said conforming electrode
comprises a brush electrode having a plurality of flexible
filaments.
9. The catheter of claim 8, wherein said plurality of flexible
filaments comprises conductive filaments having longitudinal axes,
and wherein said conductive filaments have varying conductivity
along said longitudinal axes.
10. The catheter of claim 9, wherein said filaments are coated with
materials having different electrical conductivity at different
locations along said conductive filaments.
11. The catheter of claim 9, wherein said conductivity varies
continuously.
12. The catheter of claim 11, wherein said brush electrode
comprises tapered filaments.
13. The catheter of claim 12, wherein at said distal sheath end,
said tapered filaments have larger cross-sectional areas than said
tapered filaments have at said distal electrode end.
14. The catheter of claim 13, wherein said outer sheath further
comprises a lumen adapted to carry a conductive fluid from a fluid
supply to interstitial gaps among said plurality of flexible
filaments, and wherein said conductivity of said plurality of
flexible filaments is adapted to match a conductivity of said
conductive fluid at said distal ends of said filaments.
15. The catheter of claim 8, wherein said outer sheath further
comprises a circumferential ring of sub-channels around a main
channel, and wherein said plurality of flexible filaments extends
in said main channel.
16. The catheter of claim 15, wherein said sub-channels are adapted
to carry fluid.
17. The catheter of claim 8, wherein said outer sheath surrounding
said plurality of flexible filaments is porous adjacent to an
exposed portion of said brush electrode.
18. The catheter of claim 8, wherein a threaded sheath surrounds
said plurality of flexible filaments, said threaded sheath having
an outer surface and a spiral ridge on said outer surface.
19. The catheter of claim 18, wherein said catheter further
comprises a covering around at least a portion of said threaded
sheath, thereby defining a helical flow channel between said
threaded sheath and said covering, wherein said helical flow
channel is adapted to deliver fluid to tissue adjacent to said
brush electrode.
20. The catheter of claim 8, wherein a grooved sheath surrounds
said plurality of flexible filaments of said brush electrode, said
grooved sheath having an outer surface and at least one
longitudinally-extending groove formed on said outer surface of
said grooved sheath.
21. The catheter of claim 20, wherein said catheter further
comprises a covering around at least a portion of said grooved
sheath, thereby defining at least one longitudinally-extending flow
channel between said grooved sheath and said covering, wherein said
longitudinally-extending flow channel is adapted to deliver fluid
to tissue adjacent to said brush electrode.
22. The catheter of claim 8, wherein said outer sheath provides
mechanical support for said plurality of flexible filaments and
provides electrical shielding for said plurality of flexible
filaments.
23. The catheter of claim 8, wherein said outer sheath further
comprises a lumen adapted to carry conductive fluid from a fluid
source to said brush electrode.
24. The catheter of claim 23, wherein said lumen has a
configuration selected from the group consisting of a single,
embedded channel; a plurality of sub-channels; a helical channel;
and at least one longitudinally-extending groove.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/808,919, filed 24 Mar. 2004 (the '919 application), now
pending. This application also claims priority to U.S. application
Ser. No. 10/856,925, filed 27 May 2004 (the '926 application) and
U.S. application Ser. No. 10/856,926, filed 27 May 2004, (the '926
application). The '919 application, the '925 application, and the
'926 application are hereby incorporated by reference as though
fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] a. Field of the Invention
[0003] The instant invention is directed toward a brush electrode
and a method for using the brush electrode for tissue ablation. In
particular, the brush electrode of the present invention comprises
a plurality of flexible filaments or bristles for applying ablative
energy (e.g., RF energy) to target tissue during the formation of
spot or continuous linear lesions.
[0004] b. Background Art
[0005] It is well known that benefits may be gained by forming
lesions in tissue if the depth and location of the lesions being
formed can be controlled. In particular, it can be desirable to
elevate tissue temperature to around 50.degree. C. until lesions
are formed via coagulation necrosis, which changes the electrical
properties of the tissue. For example, when sufficiently deep
lesions are formed at specific locations in cardiac tissue via
coagulation necrosis, undesirable atrial fibrillations may be
lessened or eliminated. "Sufficiently deep" lesions means
transmural lesions in some cardiac applications.
[0006] Several difficulties may be encountered, however, when
attempting to form adequately-deep lesions at specific locations
using some existing ablation electrodes. For example, when forming
lesions with RF energy, high temperature gradients are often
encountered in the vicinity of the electrode. At the edges of some
existing electrodes are regions of very high current density,
leading to large temperature gradients and hot spots. These "edge
effects" may result in the formation of undesirable coagulum and
charring of the surface tissue. For example, undesirable coagulum
may begin to form when blood reaches around 80.degree. C. for an
appreciable length of time, and undesirable tissue charring and
desiccation may be seen when tissue reaches around 100.degree. C.
for an appreciable length of time. There two types of undesirable
coagulum: coagulum that adheres to and damages the medical device;
and coagulum blood clots or curds that may enter a patient's
bloodstream, possibly resulting in other health problems for the
patient. Charring of the surface tissue may also have deleterious
effects on a patient.
[0007] As the temperature of the electrode is increased, the
contact time required to form an adequately-deep lesion decreases,
but the likelihood of charring surface tissue and forming
undesirable coagulum increases. As the temperature of the electrode
is decreased, the contact time required to form an adequately-deep
lesion increases, but the likelihood of charring surface tissue and
forming undesirable coagulum decreases. It is, therefore, a
balancing act trying to ensure that tissue temperatures are
adequately high for long enough to create deep lesions, while still
preventing or minimizing coagulum formation and/or charring of the
surface tissue. Active temperature control may help, but the
placement of thermocouples, for example, is tricky and setting the
RF generator for a certain temperature becomes an empirical
exercise as actual tissue temperatures are generally different from
those recorded next to the electrode due to factors such as
convection and catheter design.
[0008] Another difficulty encountered with existing ablation
electrodes is how to ensure adequate tissue contact. Current
techniques for creating continuous linear lesions in endocardial
applications include, for example, dragging a conventional catheter
on the tissue, using an array electrode, or using pre-formed
electrodes. All of these devices comprise rigid electrodes that do
not always conform to the tissue surface, especially when sharp
gradients and undulations are present, such as at the ostium of the
pulmonary vein in the left atrium and the isthmus of the right
atrium. Consequently, continuous linear lesions are difficult to
achieve. When forming lesions in a heart, the beating of the heart
further complicates matters, making it difficult to keep adequate
contact between the electrode and the tissue for a sufficient
length of time to form a desired lesion. With a rigid electrode, it
can be quite difficult to maintain sufficient contact pressure
until an adequate lesion has been formed. This problem is
exacerbated on contoured or trabeculated surfaces. If the contact
between the electrode and the tissue cannot be properly maintained,
a quality lesion is unlikely to be formed.
[0009] Catheters based upon a virtual electrode may address some of
the difficulties, but these catheters often require high flow rates
of conductive fluid (e.g., typically around 70 milliliters per
minute) to maintain effective cooling for high-power RF
applications. The introduction of a large amount of conductive
fluid into a patient's bloodstream may have detrimental effects on
the patient.
[0010] Thus, there remains a need for an ablation catheter that
address these issues with the existing designs and that permits the
formation of uniform, transmural spot and continuous linear lesions
on smooth or contoured surfaces.
BRIEF SUMMARY OF THE INVENTION
[0011] It is desirable to be able to form adequately-deep spot or
continuous linear lesions in tissue while reducing the formation of
undesirable coagulum and charring of the surface tissue, while
applying a reasonable amount of RF energy, while mitigating
electrode-tissue contact problems, and/or while reducing the amount
of conductive fluid (e.g., isotonic saline) possibly entering a
patient's bloodstream during the procedure. The present invention
is an improved ablation electrode.
[0012] In one form, the present invention comprises a wet-brush
electrode that facilitates electrode-tissue contact in target
tissue having contoured surfaces. The wet-brush electrode comprises
a plurality of flexible filaments adapted to transfer ablative
energy to target tissue, the flexible filaments having longitudinal
axes and defining interstitial spaces among the plurality of
filaments, wherein the interstitial spaces are adapted to direct
conductive fluid predominantly parallel to the filament
longitudinal axes. This wet-brush electrode also comprises a
primary conductor operatively connected to, and adapted to transfer
ablative energy to, the plurality of flexible filaments; and a
fluid-delivery means adapted to deliver conductive fluid to the
interstitial spaces.
[0013] In another form, the present invention comprises a catheter
for tissue ablation. The catheter comprises an outer sheath having
a distal end and a brush electrode, the brush electrode comprising
(a) a plurality of flexible filaments adapted to transfer ablative
energy to target tissue during lesion formation, wherein the
flexible filaments extend from the distal end of the outer sheath;
and (b) a primary conductor in electrical contact with the
plurality of filaments. Although the brush electrode may be merely
frictionally engaged with the distal end of the outer sheath, the
catheter may also comprises an attachment means for physically
securing the brush electrode to the distal end of the outer sheath.
The filaments may be conductive filaments and/or nonconductive
filaments, and the filaments may have nonuniform cross-sectional
configurations (e.g., the may be tapered). Further, nonconductive
tips may be present at the distal ends of at least some of the
flexible filaments.
[0014] In yet another form, the present invention comprises a
catheter for ablating tissue inside a human body. The catheter
comprises an outer sheath having a distal end; a conforming
electrode adapted to apply ablative energy to target tissue, the
conforming electrode comprises an embedded portion and an exposed
portion, wherein the exposed portion has a distal end, wherein a
working surface is present at the distal end of the exposed
portion, and wherein the exposed portion extends from the distal
end of the outer sheath; and a primary conductor in direct
electrical contact with the conforming electrode and adapted to
carry ablative energy from an energy source to the conforming
electrode. The conforming electrode may comprise a dry or wetted
brush electrode having a plurality of flexible filaments. The
flexible filaments may be trimmed to give a desired tip
configuration or a desired standoff distance between the tissue and
the conductive filaments in the brush electrode. Also, the
filaments may be grouped into clusters.
[0015] In still another form, the present invention comprises a
catheter for tissue ablation, wherein the catheter includes a
shielded-tip brush electrode. In particular, the catheter comprises
an outer sheath having a distal end; a shielded-tip brush electrode
at the distal end of the outer sheath, the shielded-tip brush
electrode comprising (a) a bundle of filaments adapted to transfer
ablative energy to target tissue during the formation of a lesion,
wherein the bundle of filaments extend from the distal end of the
outer sheath, and wherein the bundle of filaments has an outer
surface; and (b) a primary conductor having an uninsulated portion,
wherein the uninsulated portion is in electrical contact with the
plurality of filaments. Attachment means may be present to secure
the shielded-tip brush electrode to the distal end of the outer
sheath.
[0016] In another form, the present invention comprises a catheter
having an outer sheath with a distal end; an inner sheath with a
distal end; an annular channel defined between the outer sheath and
the inner sheath, wherein the annular channel is adapted to carry
fluid; a mechanical interface supported at least in part by the
distal end of the inner sheath; a flexible electrode adapted to
apply ablative energy to target tissue, wherein the flexible
electrode is supported by the mechanical interface, wherein the
flexible electrode comprises an embedded portion and an exposed
portion, and wherein the exposed portion extends from the distal
end of the outer sheath and comprises a working surface; a primary
conductor adapted to carry ablative energy from an energy source to
the flexible electrode, wherein the primary conductor comprises an
uninsulated portion in electrical contact with the flexible
electrode; and a flexible boot at the distal end of the outer
sheath, the flexible boot defining an annular fluid jacket around a
booted portion of the flexible electrode, wherein the booted
portion comprises at least a portion of the exposed portion of the
flexible electrode, and wherein the annular fluid jacket is adapted
to carry fluid that is in fluid communication with the annular
channel.
[0017] The present invention also comprises a method of ablating
tissue inside a human body using a flexible brush electrode affixed
at a distal end of an outer sheath of a catheter. The method
comprising the steps of placing an exposed portion of the brush
electrode adjacent to tissue to be treated; applying ablative
energy to the exposed portion of the brush electrode; and forming a
lesion in the tissue via coagulation necrosis.
[0018] In each of the brush electrode embodiments described above,
the filaments comprising the brush have interstitial gaps between
them. The interstitial gaps are adapted to direct fluid, when
present, toward the tissue being treated.
[0019] In each of the brush electrodes described above, a secondary
lead may also be present and may have a device (e.g., a
thermocouple, a pressure sensor, and an ultrasound sensor)
operatively connected with it.
[0020] The foregoing and other aspects, features, details,
utilities, and advantages of the present invention will be apparent
from reading the following description and claims, and from
reviewing the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is an isometric view of one embodiment of a catheter
having a brush electrode according to the present invention, and
depicts the filaments comprising the brush electrode extending from
a distal end of an outer sheath.
[0022] FIG. 2 is an enlarged view of the circled region of FIG.
1.
[0023] FIG. 3 is similar to FIG. 2, but depicts an alternative
embodiment where the brush electrode is secured at the distal end
of the outer sheath by at least one suture that is covered by a
section of shrink tube.
[0024] FIG. 4 is similar to FIG. 3, but a portion of the shrink
tube has been broken away to reveal two sutures through the outer
sheath.
[0025] FIG. 5 is an isometric, cross-sectional view of the catheter
depicted in FIGS. 3 and 4, taken along line 5-5 of FIG. 3,
revealing a primary conductor making electrical contact with the
filaments comprising the brush electrode, and depicting a secondary
lead (e.g., for a thermocouple) extending adjacent to the primary
conductor and becoming embedded within the brush filaments.
[0026] FIGS. 6 and 7 depict steps that may be used to form the
brush electrode depicted in, for example, FIG. 5.
[0027] FIG. 8 is similar to FIG. 5, but is a cross-sectional view
of an alternative embodiment of the brush electrode, wherein
conductive filaments are interspersed among relatively longer
nonconductive filaments.
[0028] FIG. 9 is a cross-sectional view taken along line 9-9 of
FIG. 8.
[0029] FIG. 10 is an enlarged view of the circled region of FIG.
8.
[0030] FIGS. 1-14 depict alternative shapes for the filaments
comprising the tip of the brush electrode.
[0031] FIG. 15 depicts an alternative embodiment of the filaments
comprising the brush electrode, wherein the individual filaments
gradually taper toward their distal ends.
[0032] FIG. 16 depicts an alternative embodiment of the filaments
comprising the brush electrode, wherein the individual filaments
have nonconductive tips at their distal ends creating a stand-off
distance.
[0033] FIG. 17 is a fragmentary, isometric view of an embodiment of
the outer sheath having a concentric ring of sub-channels around a
main or central channel through which the brush filaments
extend.
[0034] FIG. 18 is a fragmentary, isometric view of an embodiment
wherein the sheath surrounding the filaments of the brush electrode
is porous adjacent to the exposed portion of the brush
electrode.
[0035] FIG. 19 is a fragmentary, isometric view of an embodiment
wherein the sheath surrounding the filaments of the brush electrode
is a threaded sheath, having a spiral or helical ridge on its outer
surface, adjacent to the exposed portion of the brush
electrode.
[0036] FIG. 20 is a fragmentary view of a section of the threaded
sheath depicted in FIG. 19, surrounded by a covering shown in
phantom and cross-section to create a helical flow channel between
the threaded sheath and the covering.
[0037] FIG. 21 is a fragmentary, isometric view of an embodiment
wherein the sheath surrounding the filaments of the brush electrode
is a grooved sheath, having a plurality of longitudinally-extending
grooves or cuts on its outer surface, adjacent to the exposed
portion of the brush electrode.
[0038] FIG. 22 is a fragmentary view of a section of the grooved
sheath depicted in FIG. 21, surrounded by a covering (shown
cross-section) to create a plurality of longitudinally-extending
flow channels between the grooved sheath and the covering.
[0039] FIG. 23 is a cross-sectional view taken along line 23-23 of
FIG. 21, with the covering shown in phantom and with the
longitudinally-extending flow channels clearly visible.
[0040] FIG. 24 is similar to FIG. 5, but depicts an isometric,
cross-sectional view of a catheter wherein the primary conductor
makes electrical contact with the filaments via an energy transfer
coil or spring surrounding at least the embedded portion of the
brush electrode.
[0041] FIG. 25 is similar to FIGS. 5 and 24, but depicts an
isometric, cross-sectional view of a catheter wherein the primary
conductor makes electrical contact with the filaments via an energy
transfer mesh or fabric surrounding at least the embedded portion
of the brush electrode.
[0042] FIG. 26 is a cross-sectional view of a first embodiment of a
shielded-tip brush electrode, wherein an uninsulated portion of the
primary conductor is looped around the outer surface of the brush
electrode.
[0043] FIG. 27 is similar to FIG. 26, but depicts a second
embodiment of a shielded-tip brush electrode.
[0044] FIGS. 28-35 depict different cross-sectional configurations
for brush electrodes according to the present invention.
[0045] FIG. 36 is a cross-sectional view of a brush electrode
wherein some of the filaments comprise hollow or porous
members.
[0046] FIG. 37 is a cross-sectional view of a brush electrode
having devices (e.g., a thermocouple or other temperature sensor, a
pressure sensor, or an ultrasound sensor) embedded among the
conductive and nonconductive filaments.
[0047] FIG. 38 is an isometric view of a catheter having a brush
electrode according to the present invention forming a spot or
point lesion on a section of tissue.
[0048] FIG. 39 is an isometric view of a catheter having a brush
electrode according to the present invention forming a linear or
drag lesion on a section of tissue.
[0049] FIGS. 40-42 depict a brush electrode according to the
present invention forming different-sized lesions based in part
upon the amount of splay of the brush electrode.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Several embodiments of a brush electrode 10 according to the
present invention are depicted in the figures. As described further
below, the brush electrode of the present invention provides a
number of advantages, including, for example, the ability to form
deep lesions in tissue while reducing the formation of undesirable
coagulum and charring of the surface tissue, while applying a
reasonable amount of RF energy, while mitigating electrode-tissue
contact problems, and/or while reducing the amount of conductive
fluid (e.g., saline) possibly entering a patient's bloodstream
during the procedure. The present invention facilitates the
formation of a deep lesion in a shorter period of time than
required by other ablation devices, and it provides the ability to
create lesions in highly perfused tissue or in fluid-rich
environments. The brush electrode 10 facilitates enhanced tissue
contact in difficult environments (e.g., during ablation of a
contoured or trabeculated surface inside a beating heart), whether
creating a spot lesion 12 (e.g., FIG. 38) or a continuous linear
lesion 14 (e.g., FIG. 39), by readily conforming to surface
contours.
[0051] FIG. 1 is an isometric view of one embodiment of a catheter
16 having a brush electrode 10 according to the present invention.
As depicted in this figure, the catheter comprises a catheter shaft
with an outer sheath 18. In the embodiment depicted in FIG. 1, the
outer sheath is formed from sections of different material (e.g.,
in the embodiment depicted FIG. 1, five different sections comprise
the outer sheath). These sections of different material enable the
catheter 16 to have, for example, different mechanical properties
(e.g., flexibility) at different locations along the catheter
shaft. The outer sheath 18 may or may not comprise these sections
of different material depending upon the intended application for
the catheter. Although the outer sheath 18 depicted in FIG. 1 has a
circular cross section, the cross-section of the outer sheath may
be other than circular.
[0052] As also shown in FIG. 1, the brush electrode 10, which
comprises an exposed portion 20 and an embedded portion 22 (see,
e.g., FIG. 5), is present at a distal end 24 of the outer sheath
18. In particular, at the distal end of the outer sheath, the
exposed portion 20 of the brush electrode 10, comprising a
plurality of filaments 26, may be seen (see, e.g., FIG. 2). The
exposed portion of the brush electrode may project a few
millimeters from the distal end of the outer sheath. The distance
that the exposed portion of the brush electrode extends from the
distal end of the outer sheath varies depending upon a number of
factors including the composition of the filaments comprising the
brush and the particular area to be treated with the brush
electrode 10. The distal end 24 of the outer sheath 18 may include
a conductive or nonconductive base 28. As explained further below,
the flexible brush electrode provides enhanced tissue contact,
particularly for use on contoured or trabeculated surfaces.
[0053] FIG. 2 is an enlarge view of the circled region of FIG. 1.
As clearly shown in FIG. 2, the brush electrode 10 according to
this embodiment has a relatively flat working surface 30 at the
distal end 32 of the brush electrode 10. In other words, in this
depicted embodiment, all of the filaments 26 comprising the brush
electrode 10 extend approximately the same distance from the distal
end 24 of the outer sheath 18. Thus, the brush tip provides a
relatively flat working surface 30 comprising the longitudinal ends
of the filaments. The outer sheath of the catheter provides
mechanical support for the filaments and may also provide
electrical shielding. As explained further below, the brush
electrode comprises a bundle of bristles or filaments that each may
be constructed from a variety of different materials, including
nonconductive materials, semi-conductive materials, and conductive
materials. For example, the filaments may be formed from metal
fibers, metal plated fibers, carbon-compound fibers, and other
materials. Very thin, carbon fibers may be used, or relatively
thicker but less conductive Thunderon.RTM. acrylic fibers may be
used for the brush electrode filaments. Thunderon.RTM. is
manufactured by Nihon Sanmo Dyeing Company Ltd. of Kyoto, Japan.
Nylon fibers coated with conductive material may also be used.
Filaments 26 constructed from metal plated fibers, like coated
nylon fibers, may comprise flattened areas around their outer
surfaces, resulting in the filaments having noncircular
cross-sectional shapes. The brush filaments may be insulated from
each other, or they may be in electrical contact with each other.
As explained further below, conductive or nonconductive fluids 34
may flow within the filaments themselves (see, e.g., FIG. 36) or
along the outer surface of the filaments (see, e.g., FIG. 5).
[0054] Once the distance that the filaments extend from the distal
end 24 of the other sheath 18 is set to a desired length, the
bundle of filaments comprising the brush electrode 10 may be fixed
to the outer sheath 18. FIGS. 3-5 depict one technique for fixing
or anchoring the brush electrode 10 relative to the outer sheath
using sutures. In FIG. 3, a rearward suture 36 and a forward suture
38 are shown in phantom under a section of shrink tube 40
surrounding the outer surface of the outer sheath 18. The shrink
tube protects the sutures and makes it easier to insert the
catheter by mitigating possible snags that may occur due to the
presence of the sutures. FIG. 4 is similar to FIG. 3, but depicts a
portion of the shrink tube 40 broken away to reveal a portion of
the two sutures 36, 38. The suture knots 42 are clearly visible in
FIG. 4.
[0055] FIG. 5 is an isometric, cross-sectional view of the catheter
16 depicted in FIGS. 3 and 4, taken along line 5-5 of FIG. 3. In
FIG. 5, it is apparent that the rearward suture 36 may be used to
set the depth that the brush electrode 10 may be inserted into the
distal end 24 of the outer sheath 18. In this figure, the forward
suture 38 pierces the filaments 26 comprising the embedded portion
22 of the brush electrode 10 and thereby help prevent movement of
the brush electrode relative to the outer sheath of the catheter.
In the embodiment depicted in FIG. 5, conductive fluid 34 is shown
flowing through a lumen 44 of the outer sheath (depicted as a
single, embedded channel) from a fluid source (not shown) to the
brush electrode 10. When the conductive fluid 34 flows through the
brush electrode, it creates a wet-brush electrode in which
impinging jets of fluid traveling interstitially impact the tissue
46 (see, e.g., FIGS. 38 and 39) at the tissue-electrode interface,
which makes it easier to control temperature rises at the
interface. Wet-brush electrodes are discussed further below. In an
alternative embodiment, the lumen 44 depicted in FIG. 5 may
comprise a plurality of separate lumen.
[0056] FIG. 5 also clearly depicts a primary conductor 48 having an
insulated portion 50 and an uninsulated portion 52. The primary
conductor carries ablative energy (e.g., RF current) from an energy
source (not shown) to the brush electrode 10. As depicted in FIG.
5, the primary conductor 48 extends within the fluid-carrying lumen
44 of the catheter, along a longitudinal axis 54 of the catheter
16. The primary conductor may comprise, for example, insulated
copper wire with an uninsulated portion in electrical contact with
the brush electrode. In this embodiment, the uninsulated portion 52
of the primary conductor is looped or noosed around the filaments
comprising the brush electrode at a connection point 56 (FIG. 7).
At the loop or noose 58, ablative energy is transferred from the
primary conductor to the conductive filaments comprising part of
the brush electrode 10. In this embodiment, the uninsulated portion
52 of the primary conductor 48 is connected to the embedded portion
22 of the brush electrode 10 so that the connection between the
primary conductor and the brush electrode is protected within the
outer sheath 18 of the catheter 16.
[0057] Also clearly visible in FIG. 5 is an embedded or secondary
lead 60, which extends substantially parallel to the primary
conductor 48. A distal end 62 of the secondary lead 60 becomes
embedded with the filaments 26 comprising the brush electrode 10.
As discussed further below in connection with, for example, FIG.
37, the secondary lead 60, when present, may be operatively
connected to some type of sensor embedded in the brush electrode
(e.g., a thermal sensor 64, an ultrasound sensor 66, or a pressure
sensor 68). The brush electrode depicted in FIG. 5 acts as a
surface-cooled electrode 10.
[0058] FIGS. 6 and 7 depict possible steps for forming the brush
electrode 10 depicted in FIGS. 1-5. In FIG. 6, a bundle 70 of
conductive filaments 72 and nonconductive filaments 74 is being
formed by using the uninsulated portion 52 of the primary conductor
48 to bind or tie together the filaments. In FIG. 6, the
uninsulated portion has been noosed around the bundle of filaments
70, but has not been tightened or snugged against the bundle. In
FIG. 7, the uninsulated portion 52 of the primary conductor has
been snuggly noosed around the connection point 56 at approximately
the mid-section of the bundle of filaments that will ultimately
form the brush electrode 10. The conductive filaments 72 and the
nonconductive filaments 74 are then bent around the connection
point 56 in the direction of the arrows 76, 78 depicted in FIG. 7.
Once the filaments are folded upon themselves about the connection
point 56, they are inserted into the distal end 24 of the outer
sheath 18 and positioned relative to the distal end 24 of the outer
sheath 18 so that the desired amount of the filaments extends from
the distal end of the sheath and comprises the exposed portion 20
of the brush electrode 10. The ends of the filaments may then be
trimmed, if desired, to create a desired shape for the working
surface 30 at the distal end 32 of the brush electrode 10 (see,
e.g., FIGS. 11-14).
[0059] FIGS. 8, 9, and 10 depict an alternative embodiment of the
brush electrode. This standoff brush electrode 10' includes an
exposed portion 20' with a working surface 30' wherein the
longitudinal ends of the conductive filaments 72 are not flush with
the longitudinal ends of the nonconductive filaments 74. As shown
to better advantage in FIG. 10, which is an enlarged view of the
circled region of FIG. 8, in this alternative embodiment of the
brush electrode, the conductive filaments 72 are interspersed among
relatively longer nonconductive filaments 74. The relatively longer
nonconductive filaments prevent the conductive filaments from
directly touching the tissue 46 (see, e.g., FIG. 40) when the
working surface 30' of the brush electrode is placed normal to the
tissue being treated. With this brush configuration and
substantially perpendicular orientation of the brush working
surface 30' relative to the tissue being treated, the brush
electrode acts as a virtual electrode. If the perpendicular
orientation can be maintained, there is no direct contact between
the conductive filaments and the tissue, and the conductive fluid
34 (see FIG. 5) flowing through the lumen 44 of the outer sheath 18
makes the electrical contact at the brush-tissue interface.
Although FIGS. 8 and 10 depict each of the conductive filaments 72
as being shorter than each of the nonconductive filaments 74, the
electrical characteristics of the brush electrode may be adjusted
by having some conductive filaments that extend to the working
surface at the tip of the brush electrode, if desired.
[0060] FIG. 9 is a cross-sectional view taken along line 9-9 of
FIG. 8 and clearly depicts the bundled filaments 70 at the
connection point 56 between the filaments and the uninsulated
portion 52 of the primary conductor. The secondary lead 60 is also
visible in FIG. 9. In this embodiment, it is possible to adjust the
fluid and electrical contact at the brush-tissue interface through
appropriate selection of the conductive and nonconductive
filaments. Since this configuration of the brush electrode performs
most effectively when placed normal or perpendicular to the tissue,
a relatively short exposed portion 20' for the brush electrode 10'
may be desirable with relatively stiff filaments (e.g.,
Thunderon.RTM. filaments).
[0061] FIGS. 11-14 depict alternative shapes for the filaments 26
comprising the tip of the brush electrode. The various tip
configurations may provide advantages for special applications of
brush electrodes. FIG. 11 depicts a blade-shaped distal tip 80
creating a line of contact with the longest filaments of the brush
electrode. As depicted in FIG. 11, the line of contact at the most
distal end of the brush electrode extends perpendicularly into the
page. In FIG. 12, the working surface of the electrode tip has a
concave portion or channel 82. The concave-tip embodiment depicted
in FIG. 12 is beneficial for wrap-around applications and provides
advantages when ablating curved surfaces like the outer surface of
a blood vessel. FIG. 13 depicts a convex, trough-shaped tip 84.
This particular configuration is beneficial, for example, when
reaching into troughs or depressions on a contoured surface. The
distal tip could also be domed or hemispherical rather than having
the trough-shaped contact surface shown in FIG. 13. In FIG. 14, the
brush electrode has a wedge-shaped tip 86. The wedge-shaped tip
facilitates angular placement and increases the area of the working
surface 30''. The distal tip could also be conical (not shown),
coming nearly to a point at the most distal end of the brush
electrode, with its longest filaments proximal to the longitudinal
axis 54 of the catheter 16 (see FIG. 5). This latter configuration
may be advantageous for point applications of ablative energy. The
brush electrodes are depicted in many of the drawings with circular
cross sections, but may have different cross-sectional
configurations.
[0062] FIG. 15 depicts an example of a brush electrode 10'' having
continuously varying conductivity along the longitudinal axes of
the filaments. In particular, the brush electrode comprises tapered
filaments 26'. In this alternative embodiment, at least a portion
of the individual filaments 26' comprising the brush electrode 10''
gradually taper toward their distal or free ends 88. In other
words, at the distal end 24 of the outer sheath 18, the filaments
26' have larger cross-sectional areas than they have at their
distal ends 88, adjacent to the working surface 30''' of the brush
electrode 10''. The filaments 26' are thus more conductive adjacent
to the distal end of the outer sheath and less conductive at the
distal ends of the filaments. Since the filaments are more
conductive adjacent to the distal end of the outer sheath, this
minimizes current flow to the less conductive fluid wetting the
brush from the lumen of the outer sheath. When less of the ablative
energy flows into the conductive fluid adjacent to the distal end
of the outer sheath, this minimizes the energy transfer into the
conductive fluid and the concomitant heating of the conductive
fluid before it contacts the surface of the tissue. At the distal
ends 88 of the filaments 26' depicted in FIG. 15, the conductivity
of the filaments may be matched to the conductivity of the fluid to
create a relatively uniform electric field at the brush-tissue
interface.
[0063] The taper depicted in FIG. 15 could be an inverse taper,
which may be advantageous for certain applications. It should be
noted that, in order to vary the conductivity along the length of
the filaments, the filaments may also be coated or plated with
materials having different or varying electrical conductivity. For
example, the filaments, whether tapering or not, could be coated
with conductive material. The conductive material coating the
filaments in the region most closely adjacent to the distal end 24
of the outer sheath 18 may be more conductive than the coating on
the portion of the filaments most closely adjacent to the distal
end of the filaments themselves. Thus, the conductivity of the
filaments would be greater near the distal end of the outer sheath
than near the distal ends of the filaments, even though the
cross-sectional areas of the filaments may not be changing
substantially as one moves longitudinally along the filaments
toward their distal ends. Although not specifically shown in the
figures, the conductivity of all of the disclosed filaments may
also vary radially rather than, or in addition to, varying
longitudinally. In other words, the conductivity of the filaments
may vary as one moves from the center of the filaments to the
surface of the filaments.
[0064] FIG. 16 depicts a brush electrode 10''' in which the
conductivity of the filaments varies discontinuously. In
particular, FIG. 16 depicts filaments 26'' that are conductive
except at their distal ends. The distal end of each filament
includes a nonconductive tip 90. These nonconductive tips provide a
stand-off distance when the working surface of the brush electrode
is placed substantially perpendicular to the tissue being treated
since the conductive portions of the filaments do not actually
touch the tissue in this embodiment. Similar to what occurs in the
embodiment depicted in FIGS. 8-10, the conductive fluid would pass
through the lumen of the catheter and wet the brush. The conductive
fluid would carry the current over the stand-off distance and to
the tissue, thereby acting as a virtual electrode. It should be
noted that, although the embodiment depicted in FIG. 16 shows each
of the conductive filaments 26'' having a nonconductive tip 90,
some of the conductive filaments 26'' may extend all the way to the
working surface 30'''' of the brush electrode and thus would, in
fact, contact the tissue during use of the brush electrode.
[0065] FIG. 17 depicts an embodiment of the outer sheath 18' having
a concentric ring of sub-channels 92 around a main or central
channel 94 through which the brush filaments 26 extend. The
circumferential ring of sub-channels around the brush-carrying
central channel may be used to carry conductive or nonconductive
fluid, including therapeutic fluid or medicine. The embedded
sub-channels depicted in this figure could define spiral or helical
paths toward the distal end 24' of the outer sheath, similar to the
paths or channels 104 described below in connection with FIG. 19
and FIG. 20.
[0066] FIG. 18 depicts an embodiment wherein the sheath 18''
surrounding the filaments of the brush electrode 10 is porous
adjacent to the exposed portion 20 of the brush electrode. An outer
covering (not shown) may be placed around the outer cylindrical
surface of the porous sheath, possibly leaving an angular ring of
material 96 exposed at the distal end 24'' of the sheath 18''
adjacent to the brush electrode 10.
[0067] FIG. 19 is a fragmentary, isometric view of an embodiment
wherein a threaded sheath 98 surrounds the filaments of the brush
electrode 10. The threaded sheath 98 has a spiral or helical ridge
100 on its outer surface. As shown to good advantage in FIG. 20,
when the threaded sheath is inserted into a covering 102 (shown in
phantom and cross-section), a helical flow channel 104 is created
between the threaded sheath 98 and the covering 102. Conductive
fluid, nonconductive fluid, or medication may be delivered to the
tissue adjacent to the brush electrode via this flow channel.
[0068] FIG. 21 is a fragmentary, isometric view of another
embodiment, wherein the sheath surrounding the filaments of the
brush electrode is a grooved sheath 106. The grooved sheath has a
plurality of longitudinally-extending grooves or cuts 108 formed on
its outer surface, adjacent to the exposed portion of the brush
electrode 10. As shown to best advantage in FIG. 23, when the
grooved sheath 106 is inserted into a covering 102' (shown in
phantom and cross-section), a plurality of longitudinally-extending
flow channels 110 are created between the grooved sheath 106 and
the covering 102'. Again, conductive fluid, nonconductive fluid, or
medication may be delivered to the tissue adjacent to the brush
electrode via these flow channels. FIG. 22 is a fragmentary view of
a section of the grooved sheath 106 depicted in FIG. 21, surrounded
by a covering 102' (shown in cross-section) to create the plurality
of longitudinally-extending flow channels 110 between the grooved
sheath and the covering.
[0069] FIGS. 24 and 25 depict alternative mechanical interfaces
between the filaments 26 of the brush electrode 10 and the primary
conductor 48. FIG. 24 is similar to FIG. 5, but depicts an
isometric, cross-sectional view of a catheter 16' wherein the
exposed portion 52 of the primary conductor 48 makes electrical
contact with the brush filaments 26 via an energy transfer coil or
spring 112 surrounding at least the concealed or embedded portion
22 of the brush electrode 10. In this embodiment, the ablative
energy is transferred to the brush electrode 10 over a large
surface area (i.e., over the entire inner surface area of the coil
112). Thus, less damage to the filaments may occur in this
embodiment than may occur in the embodiment depicted in FIG. 5,
wherein all of the ablative energy is transferred from the
uninsulated portion 52 of the primary conductor to the brush
electrode at the single connection point 56. As depicted in FIG.
24, a loop of wire 114 may be present to help collect and stabilize
the filaments 26 during assembly of the catheter 16'. This loop of
wire 114 may be anchored to, for example, the inner surface 116 of
the outer sheath 18. As previously described, a secondary lead 60
may also be present in the lumen 44 of the outer sheath 18.
[0070] FIG. 25 is similar to FIGS. 5 and 24, but depicts an
isometric, cross-sectional view of a catheter 16'' wherein the
primary conductor 48 makes electrical contact with the filaments of
the brush electrode 10 via an energy transfer mesh or fabric 118
surrounding at least the concealed or embedded portion 22 of the
brush electrode 10. This embodiment has the same advantages that
were just described for the embodiment depicted in FIG. 24. In
another embodiment, the primary conductor 48 makes electrical
contact with the filaments of the brush electrode 10 via an energy
transfer wrap (not shown), which is similar to the mesh or fabric
118, but comprises a solid or porous sheet of conductive
material.
[0071] FIG. 26 is a cross-sectional view of a first embodiment of a
shielded-tip brush electrode 120. In this embodiment, the
uninsulated portion 52 of the primary conductor 48 is looped around
the outer surface of the brush electrode after passing through a
mechanical interface 122 supporting the filaments 26 of the brush
electrode adjacent to the distal end 124 of an inner sheath 126.
Since fluid may or may not travel through the lumen 128 of the
inner sheath 126, the mechanical interface 122 may or may not be
porous. In the embodiment depicted in FIG. 26, there is an outer
sheath 130 surrounding the inner sheath 126. The inner sheath
houses the primary conductor 48 and supports the mechanical
interface 122 for the filaments 26 of the brush electrode 120. The
primary conductor again includes an uninsulated portion 52 that
transfers ablative energy 150 (e.g., RF energy) to the conductive
filaments in the brush electrode 120. As mentioned, in this
embodiment the uninsulated portion 52 of the primary conductor
forms loops or coils 132 around the circumference of the brush.
These loops or coils increase the surface area through which the
ablative energy is transferred, thereby providing for more
effective, and potentially less destructive, energy transfer to the
brush electrode 120.
[0072] As shown in FIG. 26, the outer sheath, which may be a
typical braided sheath, is placed around the inner sheath 126, but
is radially and longitudinally offset from the inner sheath. The
radial offset creates an annular gap or channel 134 between the
inner sheath 126 and the outer sheath 130 through which conductive
fluid may, for example, be introduced to the sides of the brush
electrode filaments. The conductive fluid, if present, would flow
through the annular channel 134 in the direction of the arrows 136
shown at the top of FIG. 26. The longitudinal offset between the
inner sheath 126 and the outer sheath 130 ensures that the channel
134 for the conductive fluid extends past the distal end 124 of the
inner sheath 126 to the sides of the brush electrode filaments. In
this embodiment, the conductive fluid would flow through the
annular channel between the inner sheath and the outer sheath, past
the coils 132 of uninsulated conductive wire, into an annular fluid
jacket 138 surrounding a region of the brush electrode adjacent to
the distal ends of the inner and outer sheaths, and then into the
sides of the brush electrode itself and through the interstitial
gaps between the filaments comprising the brush electrode. The
ablative energy (e.g., the RF energy 150) is thus carried by the
conductive fluid into the core of the brush electrode and toward
its working surface 140. In this embodiment, a flexible polymer
nipple or boot 142, defining an outer wall of the annular fluid
jacket 138, also supports the filaments in a ring 144 of direct
contact extending around the perimeter of the filament bundle. The
flexible boot or nipple may be porous. Finally, a smooth outer wall
146 to facilitate easier insertion and manipulation of the catheter
in a patient may cover the outer sheath 130 and abut a
corresponding edge 148 of the flexible polymer nipple or boot 142.
Alternatively, the outer wall material may actually form the nipple
or boot in addition to forming a parametric covering around the
outer sheath. An annular layer of porous material or mesh fabric
(not shown) may be placed in the annular fluid jacket 138 to keep
the brush wetted and to help prevent splaying (see FIGS. 40-42) of
the brush electrode.
[0073] FIG. 27 is similar to FIG. 26, but depicts a second
embodiment of a shielded tip brush electrode 120'. The only
differences between the embodiment depicted in FIG. 26 and the
embodiment depicted in FIG. 27 are the size of the fluid jacket
138' and the configuration of the flexible polymer nipple or boot
142' that supports the brush filaments. In the embodiment depicted
in FIG. 27, an alternative flexible polymer nipple or boot 142'
defines a smaller fluid jacket 138' and supports the filaments in a
band of direct contact extending around the perimeter of the
filament bundle. The band of direct contact 152 supports the
filaments over a larger section of the outer surface of the brush
electrode than does the ring of direct contact 144 depicted in FIG.
26. By adjusting the configuration of the flexible polymer nipple
or boot in this manner, the amount of conductive fluid flowing into
the brush electrode and the overall flexibility of the brush
electrode can be manipulated.
[0074] It should be noted that, although the filaments depicted in
FIGS. 26 and 27 are shown as extending just into the distal end 124
of the inner sheath 126, the filaments may extend further into the
inner sheath and may even extend all the way to the proximal end
(not shown) of the catheter.
[0075] FIGS. 28-35 depict different cross-sectional configurations
for brush electrodes according to the present invention.
Interstitial spaces 156 are clearly visible in each of these
figures. In FIGS. 28-31, the brush electrode 10 has a conductive
core 154. In these four figures, the conductive filaments 72 are
shown with cross hatching, and the nonconductive filaments 74 are
shown without cross hatching. Thus, the brush electrode depicted in
FIG. 28 is fully conductive and does not comprise any nonconductive
filaments. In each of the embodiments depicted in FIGS. 29-31, a
conductive core 154 is shielded by a barrier of nonconductive
filaments 74. In particular, FIG. 29 depicts a core of relatively
large conductive filaments surrounded by two rings of nonconductive
filaments of approximately the same size. In FIG. 30, a core 154 of
relatively small conductive filaments 72 is surrounded by two rings
of relatively large nonconductive filaments 74. In FIG. 31, a
conductive core 154 of relatively large conductive filaments 72 is
surrounded by two rings of relatively small nonconductive filaments
74.
[0076] FIGS. 32 and 33 depict cross-sectional configurations for
brush electrodes that have conductive perimeters 158. Thus, in the
embodiments depicted in FIGS. 32 and 33, a nonconductive core 160
of nonconductive filaments 74 is surrounded by conductive filaments
72. FIG. 32 depicts a core of relatively small nonconductive
filaments surrounded by two rings of relatively large conductive
filaments. In FIG. 33, a core of relatively large nonconductive
filaments is surrounded by two rings of relatively small conductive
filaments.
[0077] In FIG. 34, conductive clusters 162 of relatively small
filaments are interspersed among relatively large nonconductive
filaments 74. The interspersed conductive clusters may be
interspersed in a specific pattern, pseudo randomly, or randomly
among the nonconductive filaments in order to achieve a desired
electric field from the resulting brush electrode. In FIG. 35,
nonconductive clusters 164 of relatively small filaments are
interspersed among relatively large conductive filaments 72.
[0078] FIG. 36 is a cross-sectional view of a brush electrode
wherein some of the filaments are hollow or porous 166. Such hollow
or porous filaments 166 may be used as conduits for conductive
fluid, they may be used to supply therapeutic chemicals, and/or
they may provide suction ports at the brush-tissue interface to
control field smearing on the tissue surface. If the filaments are
porous, they may retain a small amount of fluid in pores that are
oriented at various angles to the longitudinal axis of the
filaments. During an ablation procedure, some of the ablative
energy may dehydrate the porous filaments before affecting the
surrounding blood, particularly when the conductivity of the tissue
lessens as the ablation progresses. Thus, if excess ablative energy
is present during an ablation procedure, that energy may harmlessly
dehydrate the porous filaments rather than negatively affecting the
tissue being ablated or the blood in the area of that tissue. In
one embodiment (not shown), some of these hollow filaments 166 do
not extend to the distal end 32 (labeled on, for example, FIG. 2)
of the brush electrode. For example, some of the hollow filaments
166 may only extend part way into the exposed portion 20 (labeled
on, for example, FIG. 3) of the brush electrode. These shortened
hollow filaments may deliver conductive fluid or therapeutic
chemicals, for example, to an interior region of the bundle of
brush filaments. In the embodiment depicted in FIG. 36, the other
filaments 26 may be conductive or nonconductive filaments.
[0079] FIG. 37 is a cross sectional view of a brush electrode
having devices 64, 66, 68 embedded among the conductive and
nonconductive filaments 26. The devices may include, for example,
pressure sensors 68 to measure contact pressure between the brush
electrode and the tissue, thermal sensors 64 (e.g., a thermocouple)
at the tip of the brush electrode to sense the brush-tissue
interface temperature, or fiber optic or ultrasound sensors 66 for
in situ lesion identification and characterization. The devices may
be operatively connected to equipment (not shown) at the proximal
end of the catheter by secondary leads like the secondary lead 60
depicted in, for example, FIGS. 5 and 8-16.
[0080] FIG. 38 is a fragmentary, isometric view of a catheter 16
having a brush electrode 10 according to the present invention
forming a spot or point lesion 12 on a section of tissue 46. As
shown in this figure, the brush electrode is placed against the
tissue with its filaments in contact with or in close proximity to
the tissue. The conductive filaments are connected to, for example,
an RF source (not shown) and serve as the active electrode. When
present, conductive fluid from a fluid source (not shown) flows
through the lumen 44 (e.g., FIG. 5) of the catheter and through the
brush filaments to the working surface at the brush tip, thereby
creating a wet-brush electrode. Rather than being localized on the
tissue to create a spot or point lesion 12 as shown in FIG. 38, the
brush electrode 10 may be dragged along the surface of the tissue
46 to create a continuous linear lesion 14, as shown in FIG. 39.
FIG. 39 is a fragmentary, isometric view of a catheter 16 having a
brush electrode according to the present invention forming a linear
or drag lesion on a section of tissue.
[0081] FIGS. 40-42 depict a brush electrode 10 according to the
present invention forming different size spot lesions 12 based in
part upon the amount of splay of the brush electrode. In FIG. 40,
relatively light contact pressure is being used to press the brush
electrode 10 against the tissue 46 while forming a lesion 12. This
application of light pressure results in minimal splaying of the
filaments comprising the brush electrode, and thus a relatively
small lesion is formed. In FIG. 41, more pressure is being used to
press the brush electrode 10 into contact with the tissue 46,
resulting in relatively more splaying of the brush electrode. As
long as the efficiency of the brush electrode is not degraded too
greatly by the splaying, a relatively larger lesion 12 may thus be
formed by applying additional pressure to press the brush electrode
toward the tissue. Finally, in FIG. 42, even more contact pressure
is being applied to the brush electrode 10 than is being applied in
FIGS. 40 and 41, resulting in even more splaying of the brush
electrode and the formation of a relatively larger lesion 12 on the
tissue 46 than is being formed in FIGS. 40 and 41.
[0082] The brush electrode according to the present invention
delivers ablative energy to the tissue via the conductive filaments
alone, via the conductive fluid alone, or via both the conductive
filaments and the conductive fluid. In the latter two
configurations, the brush electrode is referred to as a wet-brush
electrode. Since it is possible for the conductive fluid to escape
from the exposed portion of the wet-brush electrode prior to
reaching the working surface at the distal tip of the wet-brush
electrode, there is some ablative energy leakage to the surrounding
blood. The leakage of ablative energy to the surrounding blood is
in part due to direct contact between the blood and the conductive
filaments and in part due to the conductive fluid escaping between
the filaments to the surrounding blood, particularly when
substantial splaying of the filaments occurs (see, e.g., FIG.
42).
[0083] The design parameters for the brush electrode include both
filament and brush parameters. The filament parameters include, for
example, the material and structural properties of the individual
filaments (e.g., what material(s) each individual filament is
constructed from, whether the filaments are hollow or solid,
whether the filaments are porous, and how flexible or stiff the
filaments are), the shape and cross-sectional areas of the
individual filaments, and the electrical conductivity of the
individual filaments. The electrical conductivity of the individual
filaments may be constant along the length of the filaments or may
vary along the length of the filaments. Also, if the conductivity
of a filament varies along its length, it may vary continuously or
discontinuously. The filament design parameters may be different
for each filament.
[0084] The design parameters for the brush electrode include, for
example, the overall shape and cross-sectional area of the brush
(i.e., the overall shape and size of the filament bundle forming
the brush electrode), the tip length of the brush itself (i.e., the
length of the portions of the filaments that extend the farthest
from the distal end of the outer sheath), the shape of the brush
tip, the length of the individual filaments relative to each other,
the packing density of the filaments comprising the brush, and the
overall electrical resistance of the brush. When both nonconductive
and conductive filaments are present, the conductive filaments may
be distributed evenly, randomly, or pseudo-randomly among the
nonconductive filaments comprising the brush electrode.
[0085] By controlling, among other things, the cross-sectional
shapes of the filaments, the cross-sectional areas of the
filaments, the flexibility or stiffness of the filaments, the
packing density of the filaments, the ratio of the nonconductive
filaments to the conductive filaments, and the placement of the
nonconductive and conductive filaments relative to each other, it
is possible to obtain brush electrodes having desired electrical
and thermal characteristics, which ultimately determine the types
of lesions that may be obtained when using the brush electrodes for
ablation. As mentioned above, it is even possible to vary the
mechanical and electrical properties of each individual filament,
if necessary, to achieve desired results.
[0086] The shapes and cross-sectional areas of the individual
filaments and the packing density of the brush electrode affect the
interstitial spaces between the filaments. The interstitial spaces
between the filaments determine the flow path of the conductive or
nonconductive fluid when the brush electrode is being used as a
wet-brush electrode. The flow path of the conductive or
nonconductive fluid determines to a great extent the electrical and
thermal characteristics of the wet-brush electrode. The use of a
large number of individual filaments defining interstitial spaces
among the filaments results in efficient and effective cooling of
the brush electrode and of the tissue surface. The effective
cooling of the brush electrode achieved by the present invention
reduces the formation of coagulum on the electrode, and the
effective cooling of the tissue surface achieved by the present
invention allows for the application of high-power ablation energy
for long durations, ultimately resulting in the formation of better
lesions.
[0087] During use of a brush electrode, the following operating
parameters may be taken into account: the incidence angle between
the brush electrode and the tissue, the stand-off distance between
the brush electrode and the tissue, the power being applied, the
rate of fluid flow when present, and the duration of contact
between the electrode and the tissue.
[0088] In one set of tests, Thunderon.RTM. filaments were used
favorably in a wet-brush electrode having a circular cross section
with an overall diameter of 6-8 French, a tip length of 2-3
millimeters, and electrical resistance of 100-150 ohms. In this
embodiment, the size of the Thunderon.RTM. filaments was 40
decitex. When using this brush electrode with zero stand-off
distance, 30 watts of power, saline flowing at 12 milliliters per
minute, and contact between the wet-brush electrode and the tissue
occurring for 60 seconds, 5-to-6 millimeter deep lesions were
formed with an incidence angle of 90.degree. between the wet-brush
electrode and the tissue. Four millimeter deep lesions were formed
when the incidence angle between the wet-brush electrode and the
tissue was 0.degree.. When a stand-off distance of 1 millimeter was
used during tests with similar operating parameters, a slightly
less deep (on the order of 3 millimeters deep) lesion was
formed.
[0089] In another set of tests, lesions 3-13 millimeters deep were
created using 20-50 watts of power and flow rates of 3-18
milliliters per minute with wet-brush electrodes made from
commercially available carbon fibers (e.g., carbon fibers available
through Cytec Carbon Fibers LLC of South Carolina, United States of
America. Isotonic saline infusion was used in these tests. Isotonic
saline is generally about twice as conductive as the surrounding
blood. In other tests, linear lesions 20-42 millimeters long and
3-8 millimeters deep were created by applying 20-50 watts of power
for 60 seconds in the presence of flow rates of 3-18 milliliters
per minute using wet-brush electrodes produced with conductive
filaments made from Thunderon.RTM..
[0090] As already mentioned, when conductive fluid is used, the
brush electrode becomes a wet-brush electrode. In a wet-brush
electrode, the conductive fluid serves both thermodynamic functions
and electrical functions. Thermodynamically, the conductive fluid
cools both the electrode and the tissue surface. As previously
mentioned, effective cooling of the electrode inhibits or prevents
coagulum formation on the electrode; and effective cooling of the
tissue surface permits longer application of relatively high
ablative energy, resulting in the formation of the deeper lesions.
Electrically, the conductive fluid serves as a virtual electrode.
The conductive fluid also insulates the conductive brush filaments
from the surrounding blood, which helps prevent the formation of
coagulum. The conductive fluid also creates a conductivity gradient
resulting from a concentration gradient. The conductive fluid
flowing through the brush interstitium has a field homogenizing
effect. The conductive fluid flowing through the working surface at
the distal tip of the wet-brush electrode thus helps to mitigate
hot spots resulting from edge effects. Further, since the number of
edges present in a brush electrode greatly exceeds the number of
edges present in many existing electrodes, the energy build up at
each filament edge in a brush electrode is less than it would be
for existing electrodes, assuming the same power setting. This
results in less severe edge effects when using the brush electrode
of the present invention. The conductive fluid, when used, further
smoothes or reduces the undesirable edge effects.
[0091] In the wet-brush electrode, the filaments serve both
mechanical and electrical functions. Mechanically, the filaments
create a flexible electrode that provides improved tissue contact.
The filaments also create interstitial spaces, which not only
provide effective fluid channeling, but also prevents the "virtual
electrode" from being washed away by the surrounding blood, and
helps to smooth the concentration gradient of the conductive fluid.
Electrically, the filaments serve as a conductive electrode.
[0092] Again, it should be noted that although the filaments are
depicted in nearly all of the figures as having circular
cross-sections for visual simplicity, the individual filaments may
intentionally or unintentionally have a wide variety of
cross-sectional configurations and areas, and need not be circular.
Manufacturing irregularities may result in various cross-sectional
configurations, or filaments having a variety of different
cross-sectional configurations may be intentionally selected to
achieve a desired electric field at the brush-tissue interface. The
filaments also may not be perfectly aligned longitudinally.
Further, the filaments may comprise a yarn of braided or twisted
groups of fibers, or the filaments may comprise a roving pattern of
untwisted, longitudinally-extending, substantially-parallel,
conductive and nonconductive fibers.
[0093] Although several embodiments of this invention have been
described above with a certain degree of particularity, those
skilled in the art could make numerous alterations to the disclosed
embodiments without departing from the spirit or scope of this
invention. All directional references are only used for
identification purposes to aid the reader's understanding of the
present invention, and do not create limitations, particularly as
to the position, orientation, or use of the invention. It is
intended that all matter contained in the above description or
shown in the accompanying drawings shall be interpreted as
illustrative only and not limiting. Changes in detail or structure
may be made without departing from the spirit of the invention as
defined in the appended claims.
* * * * *