U.S. patent application number 11/796209 was filed with the patent office on 2007-08-30 for surgical microwave ablation assembly.
Invention is credited to Dany Berube, Roy Chin, Dinesh Mody, Nancy Norris.
Application Number | 20070203480 11/796209 |
Document ID | / |
Family ID | 24649648 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070203480 |
Kind Code |
A1 |
Mody; Dinesh ; et
al. |
August 30, 2007 |
Surgical microwave ablation assembly
Abstract
An ablation assembly capable of ablating tissues inside the
cavity of an organ is disclosed. The ablation assembly generally
includes an ablative energy source and an ablative energy delivery
device coupled to the ablative energy source. The ablative energy
delivery device is configured for delivering ablative energy
sufficiently strong to cause tissue ablation. The ablative energy
delivery device generally includes a penetration end adapted to
penetrate through a wall of an organ and an angular component that
is used to position the device inside the organ after the device
has penetrated through the wall of the organ.
Inventors: |
Mody; Dinesh; (Pleasanton,
CA) ; Berube; Dany; (Fremont, CA) ; Norris;
Nancy; (Fremont, CA) ; Chin; Roy; (Fremont,
CA) |
Correspondence
Address: |
LAW OFFICE OF ALAN W. CANNON
942 MESA OAK COURT
SUNNYVALE
CA
94086
US
|
Family ID: |
24649648 |
Appl. No.: |
11/796209 |
Filed: |
April 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09660466 |
Sep 12, 2000 |
7226446 |
|
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11796209 |
Apr 27, 2007 |
|
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09305143 |
May 4, 1999 |
6325796 |
|
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09660466 |
Sep 12, 2000 |
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Current U.S.
Class: |
606/33 |
Current CPC
Class: |
A61B 2018/00357
20130101; A61B 18/1815 20130101; A61B 2018/1425 20130101; A61B
2018/183 20130101; A61B 18/18 20130101; A61B 2018/1861 20130101;
A61B 18/1477 20130101; A61B 2017/00243 20130101 |
Class at
Publication: |
606/033 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. A method for ablating an interior region of an organ or duct
within a body of a patient comprising: providing an introducer
comprising a proximal end, a sharpened distal end, and at least one
lumen which is sized and dimensioned for slidable receipt of at
least a portion of an ablation device therethrough; penetrating a
wall of the organ or duct with the sharpened distal end of the
introducer; advancing at least an energy delivery portion of the
ablation device within the at least one lumen of the introducer
into the interior of the organ or duct; positioning at least a
portion of the energy delivery portion into at least close
proximity with a tissue region within the interior of the organ or
duct; applying energy to the energy delivery portion to effect
ablation of the tissue region.
2. The method of claim 1 wherein said penetrating comprises forming
an opening in a wall of the heart of a patient into an interior
chamber thereof.
3. The method of claim 2 wherein the interior chamber is selected
from a right atrium or a left atrium of the heart.
4. The method of claim 1 wherein said ablation device comprises a
steering mechanism associated with the proximal end of the device,
sand wherein said positioning further comprises manipulating said
steering mechanism to cause at least a portion of the energy
delivery portion to assume an angular orientation relative to a
longitudinal axis of the device.
5. The method of claim 4 wherein said angular orientation is
between about 0 and 90 degrees relative to the longitudinal axis of
the device.
6. The method of claim 4 wherein said angular orientation is
between about 45 and 135 degrees relative to the longitudinal axis
of the device.
7. The method of claim 1 wherein said energy delivery portion
comprises an antenna which is configured to be electrically coupled
to a source of microwave energy.
8. The method of claim 1 wherein said energy delivery portion is
preshaped to extend at an angle relative to a longitudinal axis of
the ablation device.
9. The method of claim 8 wherein said energy delivery portion
extends at an angle of between about 0 and 90 degrees relative to
the longitudinal axis of the ablation device.
10. The method of claim 8 wherein said energy delivery portion
extends at an angle of between about 45 and 135 degrees relative to
the longitudinal axis of the ablation device.
11. The method of claim 8 wherein said energy delivery portion
includes a biasing element which is configured to bias the energy
delivery portion into its preshaped angular orientation relative to
the longitudinal axis of the ablation device.
12. The method of claim 11 wherein said biasing element comprises a
nitinol wire.
13. The method of claim 1 wherein said organ or duct comprises a
beating heart.
14. The method of claim 1 wherein said ablation device is a
microwave probe.
15. The method of claim 1 wherein said ablation device is a
radiofrequency probe.
16. The method of claim 1 wherein said ablation device is a laser
probe.
17. The method of claim 1 wherein said ablation device is a
cryosurgical probe.
18. The method of claim 1 wherein said energy delivery portion is
configured to substantially make no contact with a tissue region to
be ablated within the interior of the organ or duct.
19. A method for ablating an interior region of an organ or duct
within a body of a patient comprising: providing an ablation device
comprising a proximal end, a sharpened distal end, and an energy
delivery portion located proximate to said distal end; penetrating
a wall of the organ or duct with the sharpened distal end of the
ablation device; advancing at least the energy delivery portion of
the ablation device into the interior of the organ or duct;
positioning at least a portion of the energy delivery portion into
at least close proximity with a tissue region within the interior
of the organ or duct; applying energy to the energy delivery
portion to effect ablation of the tissue region.
20. The method of claim 19 wherein said penetrating comprises
forming an opening in a wall of the heart of a patient into an
interior chamber thereof.
21. The method of claim 20 wherein the interior chamber is selected
from a right atrium or a left atrium of the heart.
22. The method of claim 19 wherein said ablation device comprises a
steering mechanism associated with the proximal end of the device,
sand wherein said positioning further comprises manipulating said
steering mechanism to cause at least a portion of the energy
delivery portion to assume an angular orientation relative to a
longitudinal axis of the device.
23. The method of claim 22 wherein said angular orientation is
between about 0 and 90 degrees relative to the longitudinal axis of
the device.
24. The method of claim 22 wherein said angular orientation is
between about 45 and 135 degrees relative to the longitudinal axis
of the device.
25. The method of claim 19 wherein said energy delivery portion
comprises an antenna which is configured to be electrically coupled
to a source of microwave energy.
26. The method of claim 19 wherein said energy delivery portion is
preshaped to extend at an angle relative to a longitudinal axis of
the ablation device.
27. The method of claim 26 wherein said energy delivery portion
extends at an angle of between about 0 and 90 degrees relative to
the longitudinal axis of the ablation device.
28. The method of claim 26 wherein said energy delivery portion
extends at an angle of between about 45 and 135 degrees relative to
the longitudinal axis of the ablation device.
29. The method of claim 26 wherein said energy delivery portion
includes a biasing element which is configured to bias the energy
delivery portion into its preshaped angular orientation relative to
the longitudinal axis of the ablation device.
30. The method of claim 29 wherein said biasing element comprises a
nitinol wire.
31. The method of claim 19 wherein said organ or duct comprises a
beating heart.
32. The method of claim 19 wherein said ablation device is a
microwave probe.
33. The method of claim 19 wherein said ablation device is a
radiofrequency probe.
34. The method of claim 19 wherein said ablation device is a laser
probe.
35. The method of claim 19 wherein said ablation device is a
cryosurgical probe.
36-99. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to apparatus and methods for
ablating biological tissues. More particularly, the present
invention relates to improved ablation devices that are capable of
penetrating through bodily organs.
[0002] Since their introduction at the end of the 80's, medical
ablation devices have become a standard tool for surgeons and
electrophysiologists. For example, ablation devices utilizing DC
shock, radio frequency (RF) current, ultrasound, microwave, direct
heat, cryothermy or lasers have been introduced and employed to
various degrees to ablate biological tissues. In some ablation
procedures, however, the ablation of the targeted tissues may be
difficult because of their location or the presence of
physiological obstacle. For example, in some coronary applications
where the ablation lines are done epicardially, the epicardium may
be covered by layers of fat that can prohibit the lesion formation
in the myocardial tissue.
[0003] Catheter devices are commonly used to perform the ablation
procedure. They are generally inserted into a major vein or artery
or through a bodily cavity such as the mouth, urethra, or rectum.
These catheters are then guided to a targeted location in the body
(e.g., organ) by manipulating the catheter from the insertion point
or the natural body's orifice. By way of example, in coronary
applications, a catheter is typically inserted transvenously in the
femoral vein and guided to a cardiac chamber to ablate myocardial
tissues. Although catheters work well for a number of applications,
in many applications it would be desirable to provide an ablation
assembly that can be used to position an ablation device during a
surgical procedure.
SUMMARY OF THE INVENTION
[0004] To achieve the foregoing and other objects of the invention,
methods and devices pertaining to the ablation of tissues inside
the cavity of an organ are disclosed. In general, the invention
pertains to an ablation assembly, and more particularly to a
surgical device, which includes an ablative energy source and an
ablative energy delivery device coupled to the ablative energy
source. The ablative energy delivery device is configured for
delivering ablative energy sufficiently strong to cause tissue
ablation. In most embodiments, the ablative energy is formed from
electromagnetic energy in the microwave frequency range.
[0005] The invention relates, in one embodiment, to an ablation
assembly that includes an ablation tool, which has a distal portion
configured for delivering ablative energy sufficiently strong to
cause tissue ablation, and a probe, which has a needle shaft with a
lumen extending therethrough. The needle shaft also has a proximal
access end and a distal penetration end that is adapted to
penetrate through a wall of an organ to an organ cavity. The lumen
is arranged for slidably carrying the ablation tool from an
un-deployed position, which places the distal portion of the
ablation tool inside the lumen of the needle shaft, to a deployed
position, which places the distal portion of the ablation tool past
the distal penetration end of the needle shaft.
[0006] In some embodiments, the distal portion of the ablation tool
is arranged to lie at an angle relative to a longitudinal axis of
the probe when the distal portion of the ablation tool is deployed
past the distal penetration end of the needle shaft. By way of
example, an angle of between about 45 to about 135 degrees may be
used. In related embodiments, the ablation assembly includes an
angular component for directing the distal portion of the ablation
tool to a predetermined angular position. By way of example, a
steering arrangement, a biasing arrangement or a curved probe
arrangement may be used.
[0007] The invention relates, in another embodiment, to an ablation
assembly that includes a probe, an antenna and a transmission line.
The probe is adapted to be inserted into a body cavity and to
penetrate an organ within the body cavity. The probe also has a
longitudinal axis. The antenna is carried by the probe for
insertion into a cavity within the organ, and the transmission line
is carried by the probe for delivering electromagnetic energy to
the antenna. Furthermore, the antenna and transmission line are
arranged such that when the antenna is deployed into the organ
cavity, the antenna lies at an angle relative to the longitudinal
axis of the probe. In some embodiments, when the antenna is
deployed into the organ cavity, the antenna lies proximate and
substantially parallel to the inner wall of the organ.
[0008] The invention relates, in another embodiment, to a microwave
ablation assembly that includes an elongated probe, a transmission
line and antenna device. The probe has a penetration end adapted to
penetrate into an organ and an opposite access end. The probe also
has a longitudinal axis and defines an insert passage extending
therethrough from the access end to the penetration end thereof.
The transmission line is arranged for delivering microwave energy,
and has a proximal end coupled to a microwave energy source. The
antenna device is distally coupled to the transmission line, and is
arranged for radiating a microwave field sufficiently strong to
cause tissue ablation. The antenna device further includes an
antenna and a dielectric material medium disposed around the
antenna. Furthermore, the antenna device and at least a portion of
the transmission line are each dimensioned for sliding receipt
through the insert passage of the elongated probe, while the
elongated probe is positioned in the organ, to a position advancing
the antenna device past the penetration end of the probe and at an
angle relative to the longitudinal axis of the probe.
[0009] In some embodiments, the transmission line is a coaxial
cable that includes an inner conductor, an outer conductor, and a
dielectric medium disposed between the inner and outer conductors.
In a related embodiment, a distal portion of the outer conductor is
arranged to be exposed inside the cavity of the organ. In another
related embodiment, the ablation assembly further includes a ground
plane configured for coupling electromagnetic energy between the
antenna and the ground plane. The ground plane is generally coupled
to the outer conductor of the transmission line and is positioned
on the transmission line such that when the antenna is advanced
into the organ cavity proximate the inner wall of the organ, the
ground plane is disposed outside the organ cavity proximate the
outer wall of the organ.
[0010] The invention relates, in another embodiment, to a method
for ablating an inner wall of an organ. The method includes
providing a surgical device that includes a probe and an ablation
tool. The probe is adapted to be inserted into a body cavity and to
penetrate an organ within the body cavity. The probe also has a
longitudinal axis. The ablation tool, which has a distal portion
for delivering ablative energy, is carried by the probe for
insertion into a cavity within the organ. The method further
includes introducing the surgical device into a body cavity. The
method additionally includes penetrating a wall of the organ with
the probe. The method also includes advancing the probe through the
wall of the organ and into an interior chamber thereof. The method
further includes deploying the distal portion of the ablation tool
inside the interior chamber of the organ at an angle relative to
the longitudinal axis of the probe, wherein the distal antenna is
positioned proximate an inner wall of the organ. Moreover, the
method includes delivering ablative energy that is sufficiently
strong to cause tissue ablation.
[0011] In most embodiments, the organ, which is being ablated, is
the heart. As such, the ablation assembly may be used to create
lesions along the inner wall of the heart. By way of example, these
lesions may be used treat atrial fibrillation, typical atrial
flutter or atypical atrial flutter.
[0012] The invention relates, in another embodiment, to an ablation
assembly that includes a needle antenna and a transmission line.
Both the needle antenna and the transmission line are adapted to be
inserted into a body cavity. The transmission line is arranged for
delivering electromagnetic energy to the needle antenna, and
includes a longitudinal axis. The needle antenna is arranged for
transmitting electromagnetic energy that is sufficiently strong to
cause tissue ablation. The needle antenna is also includes a
penetration end adapted to penetrate an organ within the body
cavity such that the needle antenna can be advanced through a wall
of the organ into a cavity within the organ. Furthermore, at least
one of the needle antenna or the transmission line is bent at an
angle relative to the longitudinal axis of the transmission line so
that the needle antenna can be positioned proximate an inner wall
of the organ.
[0013] The invention relates, in another embodiment, to a method
for ablating an inner wall of an organ. The method includes
providing a surgical device that has a needle antenna distally
coupled to a transmission line. The transmission line has a
longitudinal axis, and the needle antenna has a distal penetration
end that is adapted to penetrate through a wall of an organ. The
needle antenna is also adapted for delivering electromagnetic
energy. Furthermore, at least one of the needle antenna or the
transmission line is bent at an angle relative to the longitudinal
axis of the transmission line. The method further includes
introducing the surgical device into a body cavity. The method
additionally includes penetrating a wall of the organ with the
distal penetration end of the needle antenna. The method also
includes advancing the needle antenna through the wall of the organ
and into an interior chamber thereof. The method further includes
positioning the needle antenna inside the interior chamber of the
organ such that the needle antenna is proximate an inner wall of
the organ. Moreover, the method includes radiating electromagnetic
energy that is sufficiently strong to cause tissue ablation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawings and in which like reference numerals refer to similar
elements and in which:
[0015] FIG. 1 is a side elevation view, in cross section, of a
probe penetrating a body cavity and an organ, in accordance with
one embodiment of the present invention.
[0016] FIG. 2A is a top plan view of an ablation tool including an
antenna device and a transmission line, in accordance with one
embodiment of the present invention.
[0017] FIG. 2B is a side elevation view, in cross section, of the
antenna device of FIG. 2A, in accordance with one embodiment of the
present invention.
[0018] FIG. 2C is a front elevation view of the antenna device
taken substantially along the plane of the line 2-2' in FIG. 2B, in
accordance with one embodiment of the present invention.
[0019] FIG. 2D is a perspective view of the antenna device of FIG.
2A, in accordance with one embodiment of the present invention.
[0020] FIGS. 3A & 3B is a sequence of side elevation views, in
cross section, of the ablation tool of FIG. 2 being inserted and
advanced through the probe of FIG. 1, in accordance with one
embodiment of the present invention.
[0021] FIGS. 4A & 4B are side elevation views, in cross
section, of the ablation assembly of FIGS. 3A & 3B having acute
and obtuse angular positions, respectively, in accordance with one
embodiment of the present invention.
[0022] FIG. 5 is a side elevation view, in cross section, of an
alternative embodiment of the probe having a curved needle shaft,
in accordance with one embodiment of the present invention.
[0023] FIG. 6A is a side elevation view, in cross section, of
another embodiment of the antenna device.
[0024] FIG. 6B is a front elevation view of the antenna device
taken substantially along the plane of the line 6-6' in FIG. 6A, in
accordance with one embodiment of the present invention.
[0025] FIG. 7 is a perspective view of another embodiment of the
antenna device.
[0026] FIG. 8 is a perspective view of another embodiment of the
antenna device.
[0027] FIG. 9A is a side cross sectional view of the antenna device
of FIG. 2 while it is generating a concentrated electromagnetic
field, in accordance with one embodiment of the present
invention.
[0028] FIG. 9B is a front cross sectional view of the antenna
device of FIG. 2 while it is generating a concentrated
electromagnetic field, in accordance with one embodiment of the
present invention.
[0029] FIG. 10 is a perspective view of another embodiment of the
antenna device.
[0030] FIG. 11 is a perspective view of another embodiment of the
antenna device.
[0031] FIGS. 12A & 12B are side elevation views, in cross
section, of an ablation assembly, in accordance with one embodiment
of the present invention.
[0032] FIGS. 13A & 13B are side elevation views, in cross
section, of an ablation assembly, in accordance with one embodiment
of the present invention.
[0033] FIGS. 14A & 14B are side elevation views, in cross
section, of an ablation assembly, in accordance with one embodiment
of the present invention.
[0034] FIG. 15 is a side elevation view, in cross section, of
another embodiment of the ablation assembly, in accordance with one
embodiment of the present invention.
[0035] FIG. 16 is a side elevation view, in cross section, of a
probe inserted through an access device positioned in the body
cavity and penetrating a body an organ, in accordance with one
embodiment of the present invention.
[0036] FIG. 17 is a side elevation view showing a cardiac procedure
using the ablation assembly of FIGS. 1-3, in accordance with one
embodiment of the present invention.
[0037] FIG. 18 is a top plan view of an ablation assembly having a
needle antenna, in accordance with one embodiment of the present
invention.
[0038] FIG. 19 is a side elevation view of the needle ablation
assembly of FIG. 18 after penetrating an organ wall (in cross
section), in accordance with one embodiment of the present
invention.
[0039] FIG. 20 is a perspective view of the needle ablation
assembly of FIG. 18, in accordance with one embodiment of the
present invention.
[0040] FIG. 21 is a side elevation view, in cross section, of a
needle antenna, in accordance with one embodiment of the present
invention.
[0041] FIG. 22 is a side elevation view, in cross section, of a
needle antenna, in accordance with one embodiment of the present
invention.
[0042] FIG. 23 is a side elevation view, in cross section, of a
needle antenna, in accordance with one embodiment of the present
invention.
[0043] FIG. 24 is a side elevation view, in cross section, of a
needle antenna, in accordance with one embodiment of the present
invention.
[0044] FIGS. 25A & 25B are side elevation views of a needle
antenna having acute and obtuse angular positions, respectively, in
accordance with one embodiment of the present invention.
[0045] FIG. 26 is a perspective view of a needle antenna having a
gripping block, in accordance with one embodiment of the present
invention.
[0046] FIG. 27A is a perspective view of a needle antenna, in
accordance with one embodiment of the present invention.
[0047] FIG. 27B is a side elevation view of the needle antenna of
FIG. 27A, in accordance with one embodiment of the present
invention.
[0048] FIG. 27C is a side elevation view of the needle antenna of
FIG. 27A after penetrating an organ wall (in cross section), in
accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0049] The present invention will now be described in detail with
reference to a few preferred embodiments thereof and as illustrated
in the accompanying drawings. In the following description,
numerous specific details are set forth in order to provide a
thorough understanding of the present invention. It will be
apparent, however, to one skilled in the art, that the present
invention may be practiced without some or all of these specific
details. In other instances, well known process steps have not been
described in detail in order not to unnecessarily obscure the
present invention.
[0050] The present invention provides an ablation assembly that is
capable of ablating tissues inside the cavity of an organ (or
duct). More specifically, the present invention provides an
ablation assembly that is capable of producing lesions along an
interior wall of an organ. The ablation assembly generally includes
an ablative energy source and an ablative energy delivery device
coupled to the ablative energy source. The ablative energy delivery
device is configured for delivering ablative energy sufficiently
strong to cause tissue ablation. The ablative energy delivery
device generally includes an angular component that is used to
position the device inside the organ after the device has been
inserted through the wall of the organ. In one embodiment, a probe
(or introducer), which has a penetration end adapted to penetrate
through a wall of an organ, is used to help insert (or introduce)
the device through the wall of the organ. In another embodiment,
the device itself is arranged to include a penetration end that is
adapted to penetrate through a wall of an organ.
[0051] In accordance with one embodiment of the present invention,
the ablation assembly includes a probe and an ablation tool. The
ablation tool, which includes an antenna and a transmission line
coupled to the antenna, is adapted to be carried by the probe for
insertion within a cavity inside the organ. The transmission line
is arranged for delivering electromagnetic energy to the antenna.
The probe is adapted to be inserted into a body cavity and to
penetrate an organ within the body cavity. Furthermore, the
ablation assembly is arranged so that when the antenna is deployed
into the organ cavity, the antenna lies at an angle relative to the
longitudinal axis of the probe. In some embodiments, upon
deployment, the antenna is configured to assume a predetermined
position that substantially matches the shape and/or angular
position of the wall to be ablated.
[0052] Referring initially to FIGS. 1-3, an ablation assembly in
accordance with one embodiment of the invention will be described.
In this embodiment, the ablation assembly, generally designated 10
(illustrated in FIG. 3), includes a relatively thin, elongated
probe 12 (illustrated in FIG. 1), which works in combination with
an ablation tool 24 (illustrated in FIG. 2). The probe 12 has a
proximal access end 14 and an opposite distal penetration end 16
adapted to penetrate an organ 18 within a body cavity 20. The probe
12 also has a longitudinally extending lumen 22 that is sized
suitably for receiving the ablation tool 24 therethrough. The
ablation tool 24 includes a transmission line 28 that carries an
antenna device 30 at its distal end. The antenna device 30 is
designed to generate an electromagnetic field sufficiently strong
to cause tissue ablation. A proximal end 42 of the transmission
line 28 is coupled to an energy source (not shown).
[0053] The antenna device 30 and the transmission line 28 are sized
such that they are slidable through the lumen 22 while the
elongated probe 12 is positioned in a wall 35 of the organ 18. As
such, the ablation tool 24 may be advanced within the probe 12
until the antenna device 30 is moved into a cavity within the organ
18 at a position beyond the penetration end 16 of the probe 12. As
shown in FIG. 3B, the ablation tool 24 is configured so that when
it is extended beyond the penetration end 16 of the probe 12, the
antenna 30 lies at an angle 38 relative to the longitudinal axis 40
of the probe 12 (the axis taken from the proximal end 14 of the
probe). In many embodiments, the angle 38 is arranged such that
when the antenna device 30 is deployed into the organ cavity, the
antenna device 30 assumes a predetermined angular position that
matches the shape and/or angular position of the wall to be
ablated. By way of example, an angular position that places the
antenna device substantially parallel to the cavity wall may be
used.
[0054] Accordingly, an ablation assembly is provided which utilizes
a thin, elongated probe as a deployment mechanism to position an
antenna device within the organ targeted for ablation. Once the
probe is positioned in a wall of the organ, the antenna device and
the transmission line are inserted through the passage of the probe
as a unit until the antenna device is positioned inside the cavity
of the organ. Subsequently, an electromagnetic field is emitted
from the antenna device that is sufficiently strong to cause tissue
ablation. This arrangement is especially beneficial when the areas
targeted for ablation have obstructions along the outer wall of the
organ. For example, the ablation assembly may be used to bypass and
navigate around layers of fat or veins that surround the epicardial
surface (e.g., outer wall) of the heart. Additionally, the angular
component of the ablation assembly allows precise positioning and
placement of the antenna device at specific locations within the
cavity of a bodily organ. As a result, the ablative energy can be
accurately transmitted towards the tissue targeted for
ablation.
[0055] Referring to FIGS. 3A & 3B, the elongated probe 12
includes a rigid needle 43 having an elongated needle shaft 44
adapted to pierce through the organ 18 at its distal penetration
end 16. By way of example, the distal penetration end 16 may take
the form of a conventional beveled tipped needle or a beveled point
chamfered needle both of which form a sharp cutting edge. The lumen
22 extends longitudinally through the needle shaft 44, and includes
a proximal access opening 46 and an opposite distal penetration
opening 47 at the distal penetration end 16 thereof. As shown, a
handle 50 is disposed at the proximal end of the needle shaft 44 to
help facilitate the insertion and extraction of the antenna device
30 into and out of the proximal access opening 46 of the lumen
22.
[0056] In general, the needle shaft 44 is a thin walled rigid tube
having an outer diameter of about less than about 3 mm and an inner
diameter of about less than 1.5 mm. In addition, a wall thickness
in the range of between about 0.003 inches to about 0.007 inches,
and a lumen diameter (inner diameter) in the range of about 0.040
inch to about 0.060 inch may be used. In the embodiment shown, the
wall thickness is about 0.005 inches and the lumen diameter is
about 0.050 inches. This relatively small diameter size is
particularly suitable for use in highly vascularized organs, such
as the heart, so as to minimize the puncture diameter and, thus,
potential bleeding. It will be appreciated, of course, that the
present invention may be utilized to ablate the tissues of other
organs, and more particularly, the interior walls of other organs
as well. Furthermore, the needle shaft may be formed from any
suitable material that is rigid and bio-compatible. By way of
example, stainless steel may be used. Additionally, it should be
noted that the sizes are not a limitation, and that the sizes may
vary according to specific needs of each device.
[0057] In most embodiments, the probe is first positioned through
the skin or a body cavity, and then into the targeted organ or
tissues. Depending upon the depth of penetration, the wall of the
penetrated organ surrounding the needle shaft may be employed to
vertically and laterally position (and support) the probe during
tissue ablation. Referring to FIGS. 3A and 3B, once the probe 12 is
properly positioned and retained at the targeted penetration site,
and more particularly once the distal penetration end 16 of the
needle shaft 44 is placed at the proper selected depth (such as
that shown in FIGS. 3A & 3B), the antenna device 30 may be
advanced into the organ cavity.
[0058] In some embodiments, the probe 12 and the ablation tool 24
are formed as an integral unit, wherein the antenna device 30 is
moved into position by advancing the ablation tool 24 through the
probe from a first predetermined position to a second predetermined
position. For example, a handle, which is mechanically coupled to
the ablation tool 24, may be used to control the sliding movement
of the antenna tool 24 through the probe 12. As such, the first
predetermined position is configured to place the antenna device 30
in an un-advanced position (as shown in FIG. 3A) and the second
predetermined position is configured to place the antenna device 30
in a deployed position (as shown in FIG. 3B). In other embodiments,
the probe 12 and the ablation tool 24 are separate elements and
therefore the ablation tool 24 is inserted into the probe 12 after
the probe 12 has been positioned in the targeted area of the organ
18. After ablation tool 24 has been inserted into the probe 12, the
antenna device 30 can be advanced from the un-advanced position (as
shown in FIG. 3A) to the deployed position (as shown in FIG.
3B).
[0059] During deployment, the ablation tool 24 is moved through the
handle 50 and through the lumen 22. As best viewed in FIGS. 3A
& 3B the antenna device 30 and the associated transmission line
28 are advanced longitudinally through the lumen 22 of the needle
shaft 44 to the distal penetration end 16 thereof. Upon subsequent
advancement, the antenna device 30 may be manipulated to extend
through the penetration opening 47 of the insert passage 22 and
into the cavity of the organ 18. Such advancement allows the
antenna device 30 to assume a predetermined position having an
angle 38 relative to the longitudinal axis 40 of the probe 12. As
shown, the predetermined position is in a direction towards the
inner wall of the organ 18, and substantially parallel to the
tissue targeted for ablation thereof. In one embodiment, the
antenna device is arranged to move into the angled position during
advancement of the antenna tool through the probe. In another
embodiment, the antenna device is arranged to move into the angled
position after advancement of the antenna tool through the probe.
Deployment techniques will be discussed in greater detail
below.
[0060] As shown in FIGS. 3A & 3B, the probe 12 is
perpendicularly penetrating the organ 18, and the antenna device 30
is positioned about 90 degrees from the longitudinal axis 40 of the
probe 12. It is contemplated, however, that this position is not
always possible because some organs are particularly difficult to
access, and therefore the probe 12 may be inserted into the wall of
the organ 18 at different angles. Accordingly, the present
invention may be configured to provide a range of angled positions
to match the shape and/or angular position of the wall to be
ablated. By way of example, an antenna device position having an
angle in the range of between about 45 degrees to about 135 degrees
may be used. To illustrate this, FIG. 4A shows the antenna device
30 in an acute angular position having an angle 38 of about 60
degrees relative to the longitudinal axis 40, and FIG. 4B shows the
antenna device 30 in an obtuse angular position having an angle 38
of about 120 degrees relative to the longitudinal axis 40. These
angular positions are important parameters for ensuring that the
antenna device is properly positioned in a direction towards the
tissue targeted for ablation. Furthermore, although only three
angles have been shown, it should be noted that this is not a
limitation and that other angles may be used.
[0061] Several embodiments associated with angled positioning and
deployment of the antenna device will now be described in detail.
It should be appreciated, however, that the present invention may
be embodied in many other specific forms without departing from the
spirit or scope of the invention, and may be practiced without some
or all of these specific details.
[0062] In one embodiment, the ablation assembly may include a
biasing member that is specifically formed and shaped for urging
the antenna device to a predetermined bent position. That is, the
biasing member has a predetermined shape that corresponds to the
angled position of the antenna device. As soon as the antenna
device is advanced into the organ cavity the biasing member moves
to assume its predetermined shape and thus the antenna device moves
to the predetermined bent position. The biasing member generally
consists of one or more pre-shaped elastic or spring like strips or
rods that extend through the ablation arrangement in the area of
the antenna device. The strips or rods may be arranged to have a
circular, rectangular, or other cross section shape. By way of
example, stainless steels, plastics and shape memory metals may be
used.
[0063] In one implementation of this embodiment, the spring like
material is a shape memory metal such as NiTi (Nitinol). Nitinol is
a super elastic material that typically exhibits superb flexibility
and unusually precise directional preference when bending.
Accordingly, when the antenna device is positioned within the
cavity of an organ, the nitinol strip enables the antenna device to
conform to the inner wall of the organ. Similarly, when the antenna
device is withdrawn from the organ, the Nitinol strip facilitates
straightening to allow removal through the probe.
[0064] In another embodiment, the assembly may include a steering
system for bending the antenna device to a predetermined bent
position. The steering system generally includes one or more wires
that extend through the ablation arrangement. The wires are used to
pull the antenna device from an unbent position to a bent position
causing controlled, predetermined bending at the antenna device.
The pull wires are generally fastened to anchors, which are
disposed (attached to) at the proximal end of the antenna device.
In this type of arrangement, a steering element, located on the
handle 50, may be used to pull on the wires to facilitate the
bending. However, the actual position of the handle may vary
according to the specific needs of each ablation assembly. Steering
systems are well known in the art and for the sake of brevity will
not be discussed in greater detail.
[0065] In another embodiment, the needle shaft of the probe can be
pre-bent or curved to direct the antenna device to its advanced
position. Referring to FIG. 5, the needle shaft 44 of the probe 12
includes a curved section 55 which redirects the position of the
antenna device 30 in a manner skewed from the axis 40 of the
proximal end 14 of the probe 12. As the distal end of the antenna
device 30 contacts the curved wall 55 of the insert passage, the
antenna device 30 is urged toward the distal penetration opening 47
and into the cavity of organ 18 at an angle 38 relative to axis 40.
Although the probe is shown as having a substantially right angle,
it should be noted that the angle of the curved portion may vary
according to the specific needs of each ablation assembly. For
example, the angle 38 may also be configured to be acute or obtuse
(such as in FIGS. 4A & 4B) relative to the longitudinal axis
40.
[0066] Referring back to FIGS. 2 & 3, the ablation tool 24 is
illustrated having an elongated flexible transmission line 28 and
an antenna device 30 coupled to the distal end of the transmission
line 28. The transmission line 28 is adapted for insertion into the
probe 12 and is arranged for actuating and/or powering the antenna
device 30. In microwave devices, a coaxial transmission line is
typically used, and therefore, the transmission line 28 includes an
inner conductor 31, an outer conductor 32, and a dielectric
material 33 disposed between the inner and outer conductors 31, 32.
Furthermore, at the proximal end of the transmission line 28 is an
electrical connector 42 adapted to electrically couple the
transmission line 28, and therefore the antenna device 30, to the
energy source (not shown). The transmission line 28 may also
include a flexible outer tubing (not shown) to add rigidity and to
provide protection to the outer conductor 32. By way of example,
the flexible outer tubing may be made of any suitable material such
as medical grade polyolefins, fluoropolymers, or polyvinylidene
fluoride.
[0067] As shown in FIGS. 2B-D, the antenna device 30, which is also
adapted for insertion into the probe 12, generally includes an
antenna wire 36 having a proximal end that is coupled directly or
indirectly to the inner conductor 31 of the transmission line 28. A
direct connection between the antenna wire 36 and the inner
conductor 31 may be made in any suitable manner such as soldering,
brazing, ultrasonic or laser welding or adhesive bonding. As will
be described in more detail below, in some implementations, it may
be desirable to indirectly couple the antenna to the inner
conductor through a passive component in order to provide better
impedance matching between the antenna device and the transmission
line.
[0068] In another embodiment, the antenna device 30 can be
integrally formed from the transmission line 28 itself. This is
typically more difficult from a manufacturing standpoint but has
the advantage of forming a more rugged connection between the
antenna device and the transmission line. This design is generally
formed by removing the outer conductor 32 along a portion of the
coaxial transmission line 28. This exposed portion of the
dielectric material medium 33 and the inner conductor 31 embedded
therein define the antenna device 30 which enables the
electromagnetic field to be radiated substantially radially
perpendicular to the inner conductor 31. In this type of antenna
arrangement, the electrical impedance between the antenna device 30
and the transmission line 28 are substantially the same. As a
result, the reflected power caused by the low impedance mismatch is
also substantially small which optimizes the energy coupling
between the antenna and the targeted tissues.
[0069] The antenna wire 36 is formed from a conductive material. By
way of example, spring steel, beryllium copper, or silver plated
copper may be used. Further, the diameter of the antenna wire 36
may vary to some extent based on the particular application of the
ablation assembly and the type of material chosen. By way of
example, in coronary applications using a monopole type antenna,
wire diameters between about 0.005 inches to about 0.020 inches
work well. In the illustrated embodiment, the diameter of the
antenna is about 0.013 inches.
[0070] In an alternate embodiment, the antenna wire 36 can be
formed from a shape memory metal such as NiTi (Nitinol). As
mentioned, Nitinol is a super elastic material that typically
exhibits superb flexibility and unusually precise directional
preference when bending. Accordingly, when the antenna device 30 is
positioned within the cavity of an organ, the antenna wire 36
enables the antenna device 30 to conform to the inner wall of the
organ. Similarly, when the antenna device 30 is withdrawn from the
organ, the antenna wire 36 facilitates straightening to allow
removal through the probe 12. It should be noted, however, that the
electrical conductivity of the Nitinol is not very good, and as a
result, Nitinol can heat significantly when power (e.g., microwave)
is applied. In one implementation, therefore, a layer of good
conducting material is disposed over the Nitinol. For example,
silver plating or deposition may be used. The thickness of the good
conducting material can vary between about 0.00008 to about 0.001
inches, depending on the conductivity of the selected material.
[0071] The length of the ablative energy generated by the ablation
instrument will be roughly consistent with the length of the
antenna device 30. As a consequence, ablation devices having
specified ablation characteristics can be fabricated by building
ablation devices with different length antennas. By way of example,
in coronary applications, an antenna length between about 20 mm and
about 50 mm and more particularly about 30 mm may be used. In some
applications, the probe may be used to introduce a measuring tool
that is arranged to measure the ablative lesion distance needed for
a particular procedure. According to the measurements, the length
of the antenna device can be selected. For instance, in some
coronary applications, the tool may be used to measure the distance
between the mitral valve and the pulmonary veins.
[0072] As shown, the antenna wire 36 is a monopole formed by a
longitudinal wire that extends distally from the inner conductor
31. However, it should be appreciated that a wide variety of other
antenna geometries may be used as well. By way of example,
non-uniform cross-section monopole, helical coils, flat printed
circuit antennas and the like also work well. Additionally, it
should be understood that longitudinally extending antennas are not
a requirement and that other shapes and configurations may be used.
For example, the antenna may be configured to conform to the shape
of the tissue to be ablated or to a shape of a predetermined
ablative pattern for creating shaped lesions.
[0073] Furthermore, the antenna wire 36 is generally encapsulated
by an antenna enclosure 37. The antenna enclosure 37 is typically
used to obtain a smooth radiation pattern along the antenna device
30, and to remove the high electromagnetic field concentration
present when an exposed part of the antenna wire is in direct
contact with the tissue to be ablated. A high field concentration
can create a high surface temperature on the tissue to ablate which
is not desirable, especially for cardiac applications. The antenna
enclosure 37 may be made of any suitable dielectric material with
low water absorption and low dielectric loss tangent such as Teflon
or polyethylene. As will be described in greater detail below, in
some implementations, it may be desirable to adjust the thickness
of the antenna enclosure 37 in order to provide better impedance
matching between the antenna device 30 and the tissue targeted for
ablation. Although exposing the antenna wire is not typically done
because of the high field concentration, it should be noted that
the dielectric material forming the antenna enclosure 37 can be
removed to form an exposed metallic antenna.
[0074] As shown in FIG. 3B, the outer conductor 32 is arranged to
have a distal portion 39 that is exposed, beyond the penetration
end 16 of the probe 12, when the antenna device 30 is in its
advanced position. While not wishing to be bound by theory it is
generally believed that the radiated field tends to be more
confined along the antenna device 30 when the distal end of the
outer conductor 32 is extended in the organ cavity and exposed to
the surrounding medium. By way of example, an exposed outer
conductor having a length of about 1 mm to about 2 mm works well.
Although the outer conductor is shown and described as being
exposed it should be understood that this is not a limitation and
that the ablation arrangement can be made with or without an
exposed outer conductor.
[0075] In one embodiment, the antenna device and the outer
conductor are covered by a layer of dielectric. This layer of
dielectric helps to remove the high concentration of
electromagnetic field generated by the uncovered distal portion of
the outer conductor. This configuration is better suited for
cardiac applications because the high field concentration can
potentially generate coagulum or carbonization that can trigger an
embolic event. As shown in FIGS. 6A & 6B, the ablation tool 24
includes a protective sheath 45 that surrounds the outer periphery
of the antenna device 30 and a portion of the outer conductor 32 of
the transmission line 28. More specifically, the protective sheath
45 is arranged to cover at least a portion of the exposed distal
portion 39 of the outer conductor 32 and the antenna enclosure 37.
As shown, the protective sheath may also cover the distal end of
the antenna enclosure 37. By way of example, the protective sheath
may be formed from any suitable dielectric material such as Teflon
(PTFE), FEP, Silicon and the like.
[0076] In accordance with one embodiment of the present invention,
the ablation arrangement is arranged to transmit electromagnetic
energy in the microwave frequency range. When using microwave
energy for tissue ablation, the optimal frequencies are generally
in the neighborhood of the optimal frequency for heating water. By
way of example, frequencies in the range of approximately 800 MHz
to 6 GHz work well. Currently, the frequencies that are approved by
the U.S. FCC (Federal Communication Commission) for experimental
clinical work are 915 MHz and 2.45 GHz. Therefore, a power supply
having the capacity to generate microwave energy at frequencies in
the neighborhood of 2.45 GHz may be chosen. The power supply
generally includes a microwave generator, which may take any
conventional form. At the time of this writing, solid state
microwave generators in the 1-3 GHz range are expensive. Therefore,
a conventional magnetron of the type commonly used in microwave
ovens is utilized as the generator. It should be appreciated,
however, that any other suitable microwave power source could be
substituted in its place, and that the explained concepts may be
applied at other frequencies like about 434 MHz, 915 MHz or 5.8 GHz
(ISM band).
[0077] A frequent concern in the management of microwave energy is
impedance matching of the antenna and the various transmission line
components with that of the power source. An impedance mismatch
will cause the reflection of some portion of the incident power
back to the generator resulting in a reduction of the overall
efficiency. It is desirable to match the impedance of the
transmission line 28 and the antenna device 30 with the impedance
of the generator, which is typically fifty ohms.
[0078] The transmission line 28 is therefore provided by a
conventional fifty ohm coaxial design suitable for the transmission
of microwave energy at frequencies in the range of about 400 to
about 6000 megahertz. As shown in FIG. 2B, the coaxial transmission
line 28 includes an inner conductor 31 and a concentric outer
conductor 32 separated by a dielectric material medium 33. The
inner conductor 31 is formed from a solid metallic material core
having good electrical conductivity. The dielectric medium 33 is
formed from a semi-rigid dielectric material having a low loss
tangent. The outer conductor 32 is formed from a braided sleeve of
metallic wires that provide shielding and good flexibility
thereof.
[0079] To achieve the above-indicated properties from a relatively
small diameter ablation arrangement while still maintaining the
impedance match, the size of the inner conductor 31 and the outer
conductor 32, as well as the size, shape and material of the
dielectric material medium must be carefully selected. Each of
these variables, together with other factors related to the antenna
device, may be used to adjust the impedance and energy transmission
characteristics of the antenna device. Such preferable dielectric
materials include air expended TEFLON.TM., while the inner and
outer conductors are composed of silver or copper. The impedance of
the transmission line may be determined by the equation: Z 0 = 60
ln .function. ( b / a ) r ##EQU1##
[0080] where "b" is the diameter of the dielectric material medium,
"a" is the diameter of the inner conductor and .epsilon..sub.r is
the dielectric constant of the dielectric material medium 33. It
will be understood that a characteristic impedance other than fifty
ohms can also be used to design the microwave ablation system.
Also, in order to obtain good mechanical characteristics of the
coaxial cable assembly, it is important to consider the hardness or
malleability of the selected material.
[0081] As it was explained earlier, it is also important to match
the impedance of the antenna with the impedance of the transmission
line. As is well known to those skilled in the art, if the
impedance is not matched to the transmission line, the microwave
power is reflected back to the generator and the overall radiation
efficiency tends to be well below the optimal performance. Several
embodiments associated with tuning (e.g., improving or increasing
the radiation efficiency) the antenna device will now be described
in detail.
[0082] In one embodiment, an impedance matching device is provided
to facilitate impedance matching between the antenna device and the
transmission line. The impedance matching device is generally
disposed proximate the junction between the antenna and the
transmission line. For the most part, the impedance matching device
is configured to place the antenna structure in resonance to
minimize the reflected power, and thus increase the radiation
efficiency of the antenna structure. In one implementation, the
impedance matching device is determined by using a Smith Abacus
Model. The impedance matching device may be determined by measuring
the impedance of the antenna with a network analyzer, analyzing the
measured value with a Smith Abacus Chart, and selecting the
appropriate matching device. By way of example, the impedance
matching device may be any combination of serial or parallel
capacitor, resistor, inductor, stub tuner or stub transmission
line. An example of the Smith Abacus Model is described in
Reference: David K. Cheng, "Field and Wave Electromagnetics,"
second edition, Addison-Wesley Publishing, 1989, which is
incorporated herein by reference.
[0083] In another embodiment, as shown in FIG. 7, the antenna
device 30 includes a tuning stub 63 for improving the radiation
efficiency of the antenna device 30. The tuning stub 63 is a
circumferentially segmented section that extends distally from the
distal end 53 of the outer conductor 32. In some embodiments, the
tuning stub 63 is integrally formed from the outer conductor 32 and
in other embodiments, the tuning stub 63 is coupled to the outer
conductor 32. As shown, the tuning stub 63 is generally positioned
on one side of the antenna device 30, and more particularly to the
side which is closest to the tissue targeted for ablation (e.g.,
angular component side). The tuning stub 63 is also arranged to
partially cover or surround the antenna enclosure 37. By way of
example, the tuning stub 63 may cover between about 25% to about
50% of the perimeter of the antenna enclosure 37. Furthermore, the
length L of the tuning stub 63 may be adjusted to farther improve
the radiation efficiency of the antenna device 30. For example, by
increasing the length L, less power is reflected at the entrance of
the antenna device 30 and the radiation efficiency of the system is
increased. The radiation efficiency of the antenna device 30 is
maximized when the resonance frequency is the same as the
electromagnetic signal produced by the generator (2.45 GHz for
example).
[0084] In another embodiment, as shown in FIG. 8, the antenna
device 30 includes a pair of director rods 65 for improving the
radiation efficiency of the antenna device 30. As shown, the
director rods 65 are generally positioned on one side of the
antenna device 30, and more particularly to the side which is
closest to the tissue targeted for ablation (e.g., angular
component side). The director rods 65 are disposed on the periphery
of the antenna enclosure 37 and may be positioned anywhere along
the length of the antenna device 30. By way of example, one of the
director rods 65 may be positioned proximate the distal end of the
antenna device 30, while the other director rod 65 may be
positioned proximate the proximal end of the antenna device 30. The
position of the director rods may be adjusted to further improve
the radiation efficiency of the antenna device 30. The director
rods are generally formed from a suitable metallic material such as
silver, and may also be formed from any material, which is
silver-plated, for example, silver plated stainless steel or silver
plated copper. Furthermore, the size (length and width) of the
director rods 65 may be adjusted to further improve the radiation
efficiency of the antenna device 30. It should be appreciated that
a pair of rods is not a limitation and that a single rod or more
than a pair rods may be used.
[0085] One particular advantage of using microwave energy is that
the antenna device does not have to be in contact with targeted
tissue in order to ablate the tissue. This concept is especially
valid for cardiac ablation. For example, when a microwave antenna
is located in the atrium, the radiated electromagnetic field does
not see an impedance change between the blood and the myocardium
(since the complex permittivity of these two media are similar). As
a result, almost no reflection occurs at the blood-myocardium
interface and a significant part of the energy will penetrate in
the tissue to produce the ablation. In addition, the circulating
blood between the antenna device and the tissue to be ablated helps
to cool down the tissue surface. As such, the technique is
potentially safer since it is less prone to create coagulation
and/or carbonization. By way of example, a non-contact distance of
about 1 to about 2 mm may be used. Furthermore, although not having
contact provides certain advantages it should be noted that this is
not a limitation and that the antenna device, and more particularly
the antenna enclosure, may be positioned in direct contact with the
tissue to ablate.
[0086] Furthermore, as is well known to those skilled in the art,
it is more difficult to ablate tissues when the antenna device is
surrounded by air. That is, there is a strong difference in the
physical properties (the complex permittivity) between tissue and
air. Therefore, in one embodiment, when the antenna device is not
directly touching the tissue to be ablated, the surrounding cavity
is filled with a liquid before ablating the tissue. As a result of
filling the cavity with liquid, a better ablation may be achieved
that is potentially safer since it is less prone to create
coagulation and/or carbonization. By way of example, liquids such
as isotonic saline solution or distilled water may be used.
[0087] In some embodiments, as shown in FIGS. 9A & 9B, the
antenna device 30 is adapted to deliver electromagnetic energy
(e.g., microwave) in directions extending substantially radially
perpendicularly from the longitudinal axis 51 of the antenna wire
36 and through the antenna enclosure 37. That is, the antenna
device 30 generally produces a radial isotropic radiation pattern
41 wherein the generated energy is homogeneously distributed around
its volume. By way of example, the radiation pattern 41 generated
by the antenna device 30 generally has an ellipsoidal shape along
the length of the antenna device 30 (as shown in FIG. 9A), and a
circular shape around its width (as shown in FIG. 9B).
[0088] It should be appreciated, however, that other ablative
patterns may be needed to produce a particular lesion (e.g.,
deeper, shallower, symmetric, asymmetric, shaped, etc.).
Accordingly, the antenna device may be arranged to provide other
ablative patterns. For example, the antenna device may be arranged
to form a cylindrical ablative pattern that is evenly distributed
along the length of the antenna, an ablative pattern that is
directed to one side of the antenna device, an ablative pattern
that supplies greater or lesser energy at the distal end of the
antenna device and/or the like. Several embodiments associated with
adjusting the ablative pattern of the antenna device will now be
described in detail.
[0089] In one embodiment, the thickness of the antenna enclosure is
varied along the longitudinal length of the antenna device in order
to adjust the radiation pattern of the electromagnetic field to
produce a better temperature profile during ablation. That is, the
antenna enclosure thickness can be used to improve field
characteristics (e.g., shape) of the electromagnetic field. As a
general rule, a thicker enclosure tends to cause a decrease in
radiation efficiency, and conversely, a thinner enclosure tends to
cause an increase in radiation efficiency. Thus, by varying the
thickness along the length of the antenna, the amount of energy
being delivered to the tissue can be altered. As such, the
thickness can be varied to compensate for differences found in the
tissue being ablated. In some cases, the antenna device can be
configured to deliver a greater amount of energy to a specific area
and in other cases the antenna device can be configured to deliver
energy more uniformly along the length of the antenna. For
instance, if the delivered energy at the proximal end of the
antenna is greater than the energy at the distal end, then the
thickness of the dielectric material can be increased at the
proximal end to reduce the radiation efficiency and therefore
create a more uniform radiation pattern along the antenna.
Consequently, a more uniform heating distribution can be produced
in the tissue to ablate.
[0090] In an alternate implementation of this embodiment, as shown
in FIG. 10, the antenna device 30 includes a tuning sleeve 77 for
altering the radiation pattern of the antenna device 30. The tuning
sleeve 77 is formed from a suitable dielectric material and is
arranged to increase the thickness of the antenna enclosure 37. By
way of example, the tuning sleeve may be formed from the same
material used to form the antenna enclosure. In some embodiments,
the tuning sleeve 77 is integrally formed from the antenna
enclosure 37 and in other embodiments, the tuning sleeve 77 is
coupled to the antenna enclosure 37. Furthermore, the tuning sleeve
77 is disposed around the periphery of the antenna enclosure 37 and
may be positioned anywhere along the length of the antenna device
30. By way of example, the tuning sleeve may be positioned at the
proximal end or distal end of the antenna device, as well as
anywhere in between the proximal and distal ends of the antenna
device. As should be appreciated, the position and length of the
tuning sleeve 77 may also be adjusted to alter the radiation
pattern of the antenna device. Although the tuning sleeve is shown
as surrounding the antenna enclosure, it should be noted that it
may also be circumferentially segmented. In addition, it should
also be understood that a single sleeve is not a limitation and
that a plurality of sleeves may be used.
[0091] In some embodiments, the tip of the antenna wire can be
exposed to further alter the field characteristics. An exposed tip
generally produces "tip firing", which can be used to produce more
energy at the distal end of the antenna. In other embodiments, the
stub tuner may be used to alter the radiation pattern of the
antenna device. In other embodiments, the director rods may be used
to alter the radiation pattern of the antenna device.
[0092] In another embodiment, as shown in FIG. 11, the antenna
device 30 includes a reflector 71, which is arranged to direct a
majority of an electromagnetic field to one side of the antenna
wire 36 and thus to one side of the antenna device 30. In this
embodiment, the reflector 71 is positioned laterally to a first
side of the antenna wire 36 and is configured to redirect a portion
of the electromagnetic field that is transmitted towards the
reflector 71 to a second side of the antenna wire 36 opposite the
reflector 71. Correspondingly, a resultant electromagnetic field
including a portion of the generated and a portion of the
redirected electromagnetic field is directed in a desired direction
away from the second side of the antenna wire 36. The desired
direction is preferably in a direction towards the tissue to be
ablated and thus the reflector is disposed on the side of the
antenna device opposite the direction set for ablation.
Furthermore, the reflector is disposed substantially parallel to
the antenna to provide better control of the electromagnetic field
during ablation.
[0093] The reflector is generally coupled to the outer conductor of
the transmission line. Connecting the reflector to the outer
conductor serves to better define the electromagnetic field
generated during use. That is, the radiated field is better
confined along the antenna, to one side, when the reflector is
electrically connected to the outer conductor of the transmission
line. The connection between the reflector and the outer conductor
may be made in any suitable manner such as soldering, brazing,
ultrasonic welding or adhesive bonding. In other embodiments, the
reflector can be formed from the outer conductor of the
transmission line itself. This is typically more difficult from a
manufacturing standpoint but has the advantage of forming a more
rugged connection between the reflector and the outer conductor. In
other embodiments, metallization techniques are used to apply a
reflective surface onto the antenna enclosure.
[0094] As can be appreciated, by those familiar with the art, by
forming a concentrated and directional electromagnetic field,
deeper penetration of biological tissues may be obtained during
ablation and the biological tissue targeted for ablation may be
ablated without heating as much of the surrounding tissues and/or
blood. Further, since the radiated power is not lost in the blood,
less power is generally required from the power source, and less
power is generally lost in the transmission line. Additionally,
this arrangement may be used to form linear lesions that are more
precise.
[0095] Furthermore, the reflector 71 is typically composed of a
conductive, metallic mesh or foil. One particularly suitable
material is silver plated copper. Another suitable arrangement may
be a stainless steel mesh or foil that has a layer of silver formed
on its inner peripheral surface. However, it should be understood
that these materials are not a limitation. Furthermore, the actual
thickness of the reflector may vary according to the specific
material chosen.
[0096] The reflector 71 is configured to have an arcuate or
meniscus shape (e.g., crescent), with an arc angle that opens
towards the antenna wire 36. Flaring the reflector 71 towards the
antenna wire 36 serves to better define the electromagnetic field
generated during use. The arc angle is typically configured between
about 90.degree. to about 180.degree.. By way of example, an arc
angle of about 120.degree. works well. Additionally, it has been
found that if the arc angle 90 is greater than 180.degree. the
radiation efficiency of the antenna arrangement decreases
significantly.
[0097] Turning now to FIGS. 12A & 12B, an alternative
embodiment to the present invention is illustrated wherein a
metallic needle shaft 44 is used as an electrical continuation of
the outer conductor 32. In this embodiment, the outer conductor 32
includes a contact member 60 that is disposed at the distal end of
the outer conductor 32. The contact member 60 is arranged to
electrically couple the outer conductor 32 to the needle shaft 44
when the ablation tool is moved through the probe 12, and more
particularly when the ablation tool reaches its deployed position
(as shown in FIG. 12B). Furthermore, the distal portions of the
transmission line 28 are appropriately sized such that only the
dielectric material medium 33 and the inner conductor 31 are
slideably received in the lumen 22 of the metallic needle shaft 44.
That is, a distal portion of the outer conductor 32 has been
removed so that the outer conductor 32 is not carried by the lumen
22 of the needle shaft 44. As such, the contact member 60 is
adapted to contact the distal end 46 of the needle shaft 44. By
providing an electrical connection, the metallic needle shaft 44
can act as an extension of the outer conductor 32 of the
transmission line 28.
[0098] For ease of discussion, portions of the ablation tool 24
that are disposed proximally from the contact member 60 are
designated with an A, and portions of the ablation tool 24 that are
disposed distally from the contact member 60 are designated with a
B. Accordingly, the assembly comprising the inner conductor 31B,
the dielectric material 33B and the metallic needle shaft 44
creates a distal coaxial cable 28B. That is, the needle shaft 44
conductively functions as a shield for the transmission line 28
from the access opening 46 to the distal penetration opening 47 of
the probe 12. As best viewed in FIG. 122B, this shielding effect
commences when the outer conductor 32 of the transmission line 28
and the needle shaft 44 of the probe 12 are in conductive
communication with one another. The outer conductor 32 must
therefore be in conductive communication with the metallic needle
shaft 44 at least when the antenna device 30 is radiating
electromagnetic energy.
[0099] As shown in FIG. 12B, the contact member 60 is adapted to
electrically contact the proximal part 46 of the needle shaft 44
when the antenna device 30 is fully extended through the needle
shaft 44 and into the targeted organ 18. Thus, the contact member
60 not only operates as an electrical connector between the outer
conductor 32 and the needle shaft 44 but also as a stop device that
limits the amount of penetration into the organ. In most
configurations, the size of the contact member 60 is merely larger
than that of the access opening.
[0100] As it was explained earlier, it is also important to match
the impedance of the antenna with the impedance of the transmission
line. As is well known to those skilled in the art, if the
impedance is not matched to the transmission line, the microwave
power is reflected back to the generator and the overall radiation
efficiency tends to be well below the optimal performance.
Accordingly, the dimensions of the distal coaxial cable elements
are generally selected to match the impedance of the proximal
transmission line. As should be appreciated, the cross sectional
dimensions of 28B, 31B and 33B may be different from 28A, 31A and
33A.
[0101] With regards to the length of the antenna device 30, in the
configuration of FIGS. 12A&B, the length is generally defined
from the center of the distal penetration opening 47 to the distal
end of the antenna wire 36. Several important factors that will
influence the antenna length include the desired length of the
ablation, the antenna configuration, the frequency of the
electromagnetic wave and the impedance match of the antenna within
the tissue or the organ cavity. The matching of the antenna is
performed by adjusting its length so that the radiation efficiency
is adequate when the antenna is used in the tissue or in the organ
cavity. As an example, the radiation efficiency is generally
adequate when the return loss of the antenna is in the range of -10
dB to -13 dB at 2.45 GHz. Instruments having specified ablation
characteristics can be designed by varying the antenna length. For
example, in microwave coronary applications for treating atrial
fibrillation, the antenna device may have an antenna wire diameter
of about 0.013 inch, a dielectric material medium diameter of about
0.050 inch and a length in the range of approximately 20 mm to 30
mm.
[0102] The distal coaxial cable can also be used as a serial stub
tuner to match the impedance of the antenna device 30 and the
transmission line 28. This arrangement is advantageous since, while
maintaining the electrical continuation and the impedance match
between the generator and the antenna, the diameters of the inner
conductor 31 and the dielectric material medium 33 can be maximized
relative the insert passage 22. The larger diameters, consequently,
facilitate axial penetration into the organ due to the increased
lateral and axial rigidity without compromising the impedance
matching of about fifty (50) ohms.
[0103] Turning now to FIGS. 13A & 13B, an alternative
embodiment to the present invention is illustrated wherein the
ablation assembly 10 includes a clamping portion 79 for positioning
the antenna device 30 proximate the wall 82 of the organ 18. The
clamping portion 79 and the antenna device 30 are arranged to
facilitate linear positioning of the antenna device 30. The
clamping portion 79 generally includes a clamping finger 81 and a
bar slide 84 that is slidably coupled to the needle shaft 44 and is
configured to move relative to the probe 12. In general, the bar
slide 84 is configured to slide within at least one guide track 86
that is structurally attached to the needle shaft 44. The clamping
portion 79 is also arranged to be substantially aligned (in the
same plane) with the antenna device 30 when the antenna device 30
is in its angular position.
[0104] Accordingly, when the antenna device 30 is properly
positioned, the clamping portion 79 is moved in a direction towards
the organ 18 to pinch the organ wall between the antenna 30 and the
clamping finger 81. That is, the clamping finger 81 is moved to a
position that contacts the outer wall 88 of the organ 18, wherein
after contact and upon further finger movement the antenna device
30 is forced to move in a direction towards the probe 12. As a
result, the antenna device 30 and clamping finger 81 exert opposite
forces on opposite sides of the organ wall. By way of example, the
finger and the antenna device can be used to sandwich the
myocardium of the heart wherein the finger is applying a force to
the epicardial surface and the antenna device is applying an
opposing force to the endocardium. This particular approach tends
to create a more uniform ablating surface, which as result,
produces a better linear lesion.
[0105] The clamping finger is generally configured to be parallel
to the angular position of the deployed antenna device. By way of
example, if the antenna device is configured to have an angle of
about 60 degrees relative to the axis of the probe, then the finger
may be configured to have an angle of about 60 degrees relative to
the axis of the probe. In this manner, the antenna device and
clamping finger can pinch the organ wall evenly. Alternatively, the
clamping finger can be shaped to conform to the shape of the outer
wall. Further still, the clamping finger generally has a length
that is substantially equivalent to the length of the antenna
device. However, it should be noted that the length may vary
according to the specific design of each ablation assembly.
Additionally, the slide bar may be connected to a handle for
physically actuating the linear movement, a knob or jack for
mechanically actuating the linear movement, or an air supply for
powering the linear movement. A locking mechanism may also be used
to lock the engagement between the clamp finger and the antenna
device so that the antenna device does not move from the target
area during ablation.
[0106] Moreover, a seal may be used between the clamp finger and
the outer wall of the organ to seal the puncture site.
Additionally, a suction device may be disposed on the clamping
finger to anchor and temporarily position the clamping finger to
the outer organ wall. Alternatively, a balloon that is attached to
the probe may be used to pinch the organ wall between the inflated
balloon and the angularly positioned antenna device.
[0107] Turning now to FIGS. 14A & 14B, an alternative
embodiment to the present invention is illustrated wherein the
ablation assembly 10 includes a ground plane 89 for coupling
electromagnetic energy 90 through the organ wall 35. The ground
plane 89 generally provides a metallic surface that attracts the
electric field generated by the antenna device 30 and therefore a
more intense electromagnetic field 90 is produced between the
antenna device 30 and the ground plane 89. Accordingly, the
electromagnetic field 90 emitted by the antenna device 30 is more
constrained in the tissue 35 between the antenna device 30 and the
ground plane 89, which as a result helps to create the
ablation.
[0108] As will be appreciated by those familiar with the art,
inserting the tissue to ablate between the ground plane 89 and the
antenna 30 has several potential advantages over conventional
antenna structures. For example, by forming a concentrated
electromagnetic field, deeper penetration of biological tissues may
be obtained during ablation and the biological tissue targeted for
ablation may be ablated without heating as much of the surrounding
tissues and/or blood. Further, since the radiated power is not lost
in the blood, less power is generally required from the power
source, and less power is generally lost in the transmission line,
which tend to decrease its temperature. Additionally, this
arrangement may be used to form lesions that are more precise.
[0109] In this embodiment, the ground plane 89 is electrically
coupled to the outer conductor 32 of the transmission line 28. The
ground plane 89 is generally disposed on the needle shaft 44 of the
probe 12 at a predetermined distance Q away from the deployed
antenna device 30 (as shown in FIG. 14B). The predetermined
distance Q is arranged to place the ground plane 89 in close
proximity to the antenna device 30, and outside the outer wall of
the organ 18 when the needle shaft 44 is position inside the organ
wall 35. By way of example, in coronary applications, a distance
between about 1 mm and about 15 mm may be used.
[0110] Moreover, the ground plane 89 is generally configured to be
parallel to the angular position of the antenna device 30. By way
of example, if the antenna device 30 is configured to have an angle
of about 60 degrees relative to the axis of the probe, then the
ground plane may be configured to have an angle of about 60 degrees
relative to the axis of the transmission line. In this manner, the
antenna and the ground plane can couple energy more evenly.
Alternatively, the ground plane can be shaped to conform to the
shape of the outer wall. Further still, the ground plane generally
has a length that is substantially equivalent to the length of the
antenna device 30. By way of example, a ground plane length between
about 20 mm and about 50 mm works well. It should be noted,
however, that the length may vary according to the specific needs
of each ablation assembly. The ground plane is also arranged to be
substantially aligned (in the same plane) with the angular
component of the antenna device 30.
[0111] The ground plane 89 may be formed from a wire, strip or rod,
and may be arranged to have a circular, rectangular, or other cross
section shape. Furthermore, the ground plane 89 is formed from a
suitable conductive material such as stainless steel or silver. The
dimensions of the ground plane 89 may vary to some extent based on
the particular application of the ablation assembly and the type of
material chosen. Additionally, the ground plane may be printed on
or enclosed inside of a flexible dielectric substrate (such as
Teflon or polymide). Furthermore, the connection between the ground
plane 89 and the outer conductor 32 may be made in any suitable
manner such as soldering, brazing, ultrasonic welding or adhesive
bonding.
[0112] The ground plane 89 can be configured in a variety of ways.
In some embodiments, the ground plane may be rigidly or
structurally coupled to the needle shaft of the probe. In other
embodiments, the ground plane may be pivoted or slidably coupled to
the needle shaft of the probe. For example, the clamping finger, as
described above in FIG. 13, can be arranged to be a ground plane
for the antenna. In other embodiments, the ground plane may be
flexible in order to follow the natural curvature of the organ. In
other embodiments, the ground plane may be biased to contact the
tissue. Further still, in some embodiments, the ground plane may be
configured to act as a stop device that limits the amount of probe
penetration into the organ.
[0113] In an alternate embodiment, the ground plane may be properly
positioned across from the antenna device with a ground plane
positioner. The ground plane positioner generally includes tubular
member having passage therein. In this embodiment, the ground plane
is advanced longitudinally through the passage of the tubular
member to the distal opening of the passage. Upon subsequent
advancement, the ground plane may be manipulated to extend through
distal opening of the passage and to the outer wall of the organ.
Such advancement preferably allows the ground plane to assume a
predetermined position that is substantially aligned with the
deployed antenna device such that the organ wall is disposed
between the ground plane and the antenna device. In one embodiment,
the assembly may include a biasing member that is specifically
formed and shaped for urging the ground plane to a predetermined
bent position. In another embodiment, the assembly may include a
steering system for bending the ground plane to a predetermined
bent position. In another embodiment, the needle shaft of the
tubular member can be prebent or curved to direct the ground plane
to its advanced position.
[0114] Referring to FIG. 15, the ablation assembly 10 includes a
positioner 91 having a tubular member 92 and a passage 94 therein.
As mentioned above, the ground plane 96 is electrically coupled to
the outer conductor 32 of the transmission line 28. In this
particular embodiment, the tubular member includes a curved section
95 which redirects the position of the ground plane 96 in a manner
skewed from the axis 40 of the proximal end 14 of the probe 12. As
the distal end of the ground plane 96 contacts the curved wall 95
of the passage 94, the ground plane 96 is urged out of the distal
opening 97 and to an outer wall position that is substantially
aligned with the angled antenna device 30. Additionally, the ground
plane 96 may be fixed to the transmission line 28 such that when
the antenna device 30 is deployed so is the ground plane 96.
[0115] Turning now to FIG. 16, an alternative embodiment to the
present invention is illustrated wherein the ablation assembly 10
is inserted through an access device 70, which is positioned in the
body cavity 20. The access device 70 is generally disposed inside a
small incision that is made in the body cavity 20. The access
device includes a passage 72 that is appropriately sized for
receiving the ablation assembly 10 such that the needle shaft 44 of
probe 12 can be introduced into the body cavity 20. As can be
appreciated, the passage 72 allows access to the targeted organ 18.
Access devices are well known to those skilled in the art and
therefore they will not be described in detail herein.
[0116] Referring now to FIG. 17, the described ablation assembly 10
is used for ablating cardiac tissues, in accordance with one
embodiment of the present invention. The ablation assembly 10 is
especially beneficial in navigating around certain regions of the
heart 200. For example, the ablation assembly 10 may be used to
bypass the layers of fat 202 or veins 204 that surround the
epicardial surface 206 (e.g., outer wall) of the heart 200. By way
of example, the vein 204 may be the coronary sinus, which is
located just superior to the junction between the left atrium 240
and the left ventricle 246. As mentioned, fat 202 is a good
microwave absorber and a very poor thermal conductor. Furthermore,
veins 204 readily transfer heat through blood flow. As a result,
fat 202 and veins 204 are very difficult to ablate through from the
epicardial surface (not enough thermal energy to ablate).
Accordingly, by positioning the antenna device 30 inside a cavity
208 of the heart 200 (e.g., through the layer of fat), the ablative
energy can be supplied to the endocardium 210 rather than the
obstructed epicardial surface 206 thereby effectively ablating the
targeted tissue. By way of example, the cavity 208 may be the left
atrium 240, the right atrium 242, the left ventricle 246 or the
right ventricle 244.
[0117] The ablation assembly 10 may be used to treat a variety of
heart conditions. In one embodiment, the ablation assembly is used
to treat atrial fibrillation and in another embodiment the ablation
assembly is used to treat atrial flutter. Several implementations
associated with ablating cardiac tissues using the ablation
assembly 10 will now be described.
[0118] In one implementation, the ablation assembly 10 is used to
create lesions between any of the pulmonary veins 212 of the heart
200 in order to treat atrial fibrillation. In another
implementation, the ablation assembly 10 is used to create lesions
from one of the pulmonary veins 212 to the mitral valve 213 of the
heart 200 in order to avoid macro-reentry circuit around the
pulmonary veins in a lesion pattern used to treat atrial
fibrillation. In another implementation, the ablation assembly 10
is used to create lesions from one of the pulmonary veins 212 to
the left atrial appendage of the heart 200 also to avoid
macro-reentry circuit around the pulmonary veins in a lesion
pattern used to treat atrial fibrillation.
[0119] In one implementation, the ablation assembly 10 is used to
create lesions between the inferior caval vein 216 to the tricuspid
valve 214 of the heart 200, in order to treat typical or atypical
atrial flutter. In another implementation, the ablation assembly 10
is used to create lesions along the cristae terminalis in the right
atrium 242 of the heart 200 in order to treat typical or atypical
atrial flutter. In another implementation, the ablation assembly 10
is used to create lesions from the cristae terminalis to the fossae
ovalis in the right atrium 242 of the heart 200 in order to treat
typical or atypical atrial flutter. In yet another implementation,
the ablation assembly 10 is used to create lesions on the lateral
wall of the right atrium 242 from the superior 220 to the inferior
vena cava 216 in order to treat atypical atrial flutter and/or
atrial fibrillation.
[0120] Although a wide variety of cardiac procedures have been
described, it should be understood that these particular procedures
are not a limitation and that the present invention may be applied
in other areas of the heart as well.
[0121] A method for using the described microwave ablation assembly
in treating the heart will now be described with reference to FIG.
17. Although only a heart is shown and described, it should be
understood that other organs, as well as organ ducts, may be
treated with ablation assembly. The method includes providing an
ablation assembly such as any one of the ablation assemblies
described herein. More particularly, the method includes providing
a surgical device 10 having a probe 12 and an elongated microwave
ablation arrangement 24. The probe 12 includes a passage extending
therethrough from a proximal end 14 to an opposite distal end 16
thereof. The distal end 16 is adapted to penetrate through a
muscular wall 222 (e.g., myocardium) of the heart 200. Furthermore,
the elongated microwave ablation arrangement 24 includes a distal
antenna 30 coupled to a transmission line, which in turn is coupled
to a microwave energy source at a proximal end thereof. In
accordance with the present invention, the method includes
introducing the surgical device 10 into a body cavity 230. This may
be by penetration of the body 232 or through an access device 70.
Several surgical approaches are possible. For example, the surgical
device may be introduced through an open chest, a posterior
thoracotomy, a lateral thoracotomy (as shown in FIG. 10), or a
sternotomy. The surgical procedure can also use an endoscope in
order to visualize the ablation device during the placement. These
procedures are generally well known to those skilled in the art and
for the sake of brevity will not discussed in detail.
[0122] The method further includes penetrating the muscular wall
222 of the heart 200 with the distal end 16 of the elongated probe
12 and introducing the elongated probe 12 through the muscular wall
222 of the heart 200 and into an interior chamber 208 thereof. By
way of example, the surgical tool 10 can be introduced into the
left atrium 240, the right atrium 242, the right ventricle 244 or
the left ventricle 246. Furthermore, before penetration a purse
string suture may be placed in the heart wall proximate the area
targeted for penetration so as to provide tension during
penetration. Purse string sutures are well known in the art and for
the sake of brevity will not be discussed in more detail.
[0123] The method also includes introducing the elongated microwave
ablation device 24 into the passage of the elongated probe 12 and
advancing the antenna 30 past the distal end 16 of the probe 12
such that the antenna 30 is disposed inside the interior chamber
208 of the heart 200. Upon advancement, the antenna 30 preferably
assumes a predetermined position that substantially matches the
shape and/or angular position of the wall to be ablated. By way of
example, the position may place the antenna substantially parallel
to the interior surface 210 (e.g. endocardium) of the penetrated
muscular wall 222 and proximate the targeted tissue. Angled
advancement may be accomplished in a variety of ways, for example,
with a biasing member, a steering wire or a curved probe.
Furthermore, the method includes generating a microwave field at
the antenna that is sufficiently strong to cause tissue ablation
within the generated microwave field.
[0124] In accordance with another aspect of the present invention,
the ablation assembly includes a needle and a transmission line
having a longitudinal axis. The needle is adapted to be inserted
into a body cavity and to penetrate an organ (or duct) within the
body cavity. The needle is also configured for insertion into a
cavity within the organ and includes an antenna for transmitting
electromagnetic energy. The transmission line is coupled to the
antenna and configured for delivering electromagnetic energy to the
antenna. Furthermore, the ablation assembly is arranged so that
when the needle is finally inserted into the organ cavity, the
antenna lies at an angle relative to the longitudinal axis of the
transmission line. In most cases, the needle or the transmission
line is pre-shaped or bent at a predetermined position that is
arranged to substantially match the shape and/or angular position
of the wall to be ablated. In other cases, a biasing member or
steering system, in a manner similar to biasing member and steering
system described above, may be used to provide angled
positioning.
[0125] Turning now to FIGS. 18-21, an ablation assembly, generally
designated 100, is provided including a relatively thin needle 102
configured for emitting electromagnetic energy and having a
penetration end 104 adapted to penetrate an organ 106. The needle
102 is axially rigid to allow for tissue penetration and may be
longitudinally flexible to avoid damaging the organ 106 during
positioning. The ablation assembly 100 further includes a
transmission line 108 having a longitudinal axis 110 and a distal
end 112 that is coupled to the proximal end 114 of the needle 102
for generating an electromagnetic field sufficiently strong to
cause tissue ablation. At the proximal end 118 of the transmission
line 110 is an electrical connector 120 adapted to electrically
couple the antenna to an electromagnetic energy source (not shown).
As shown, the needle 102 is bent at an angle 116 relative to the
longitudinal axis 110 of the transmission line 108. In most
embodiments, the bend is arranged to easily position the antenna
parallel to the tissue to ablate by taking into consideration the
angle of approach (the angle used to insert the needle through the
organ).
[0126] Accordingly, the ablation assembly 100 utilizes the needle
102 to provide ablative energy within a cavity of the organ 106.
That is, the distal penetration end 104 is used to pierce through
an outer wall 122 of the organ 106 to position the needle 102
proximate and substantially parallel to an inner wall 124 of the
organ 106. Once the needle 102 is positioned, ablative energy that
is sufficiently strong to cause tissue ablation is emitted from the
needle 102 to ablate a portion of the inner wall 124. This
arrangement is especially beneficial when the areas targeted for
ablation have obstructions along the outer wall of the organ. For
example, the needle may be used to bypass and navigate around
layers of fat or veins that surround the epicardial surface (e.g.,
outer wall) of the heart. Furthermore, the angled position of the
needle assures that the ablative energy will be accurately
transmitted in the targeted ablation region.
[0127] Referring to FIG. 21, the needle 102 includes an elongated
antenna 130 and an antenna enclosure 132 that are adapted to pierce
through organ 106 at a distal penetration end 104. By way of
example, the distal penetration end 104 is in the form of a
conventional beveled tipped needle or a beveled point chamfered
needle which forms sharp cutting edge. As shown, the antenna 130 is
encapsulated by the antenna enclosure 132, which is generally
better suited to remove the high electromagnetic field
concentration that is normally obtained when the metallic part of
the antenna is in direct contact with the tissue. A high field
concentration can create a high surface temperature on the tissue
to ablate which is not desirable, especially for cardiac
applications. The antenna enclosure 132 may be made of any suitable
dielectric material (e.g., low loss tangent) with low water
absorption such as medical grade epoxy, polyethylene or Teflon type
products (e.g., bio compatible). As was described in great detail
above, it may be desirable to adjust the thickness of the antenna
enclosure in order to provide better impedance matching between the
antenna and the tissue targeted for ablation. It is contemplated,
however, that needle antenna enclosures having a thickness between
about 0.002 inches and about 0.015 inches, and more particularly
about 0.005 inches work well.
[0128] It should also be noted that the antenna enclosure may not
be required for all ablation assemblies. By way of example, FIGS.
22 & 24 show the ablation assembly 100 with an exposed antenna
130 having no antenna enclosure. However, it should be noted that
in most situations the antenna enclosure is configured to insulate
the antenna to avoid the charring and tissue destruction effects
that are commonly experienced when the ablative elements, and more
particularly, the metallic parts of the antenna, are directly in
contact with the body's tissue or fluid.
[0129] The antenna 130 is formed from a conductive material. By way
of example, spring steel, beryllium copper, or silver plated copper
work well. Further, the diameter of the antenna 130 may vary to
some extent based on the particular application of the ablation
assembly and the type of material chosen. By way of example, in
systems using a monopole type antenna, wire diameters between about
0.005 inch to about 0.020 inches work well. In the illustrated
embodiment, the diameter of the antenna is about 0.013 inches.
[0130] As mentioned, the field generated by the antenna will be
roughly consistent with the length of the antenna. That is, the
length of the electromagnetic field is generally constrained to the
longitudinal length of the antenna. Therefore, the length of the
field may be adjusted by adjusting the length of the antenna.
Accordingly, ablation arrangements having specified ablation
characteristics can be fabricated by building ablation arrangements
with different length antennas. By way of example, antennas having
a length between about 20 mm and about 50 mm, and more particularly
about 30 mm work well. Furthermore, the antenna shown is a simple
longitudinally extending exposed wire that extends distally from
the inner conductor. However it should be appreciated that a wide
variety of other antenna geometries may be used as well. By way of
example, helical coils, flat printed circuit antennas and other
antenna geometries will also work well. Additionally, it should be
understood that longitudinally extending antennas are not a
requirement and that other shapes and configurations may be used.
For example, the antenna may be configured to conform to the shape
of the tissue to be ablated or to a shape of a predetermined
ablative pattern for creating shaped lesions.
[0131] Referring back to FIG. 21, the transmission line 108
generally includes an inner conductor 134 and an outer conductor
136 separated by a dielectric material medium 138. An insulating
sheath 140 is typically disposed around the outer conductor 136.
Furthermore, the outer conductor 136 is generally arranged to have
a portion 136A that extends from the distal end of the insulating
sheath 140 so that it can be exposed. As mentioned, when the outer
conductor 136 is exposed, the generated electromagnetic field is
more constrained to the antenna and therefore the radiation
efficiency tends to be greater. By way of example, an exposed outer
conductor having a length of about 1 mm to about 2 mm works well.
Although the outer conductor is shown and described as being
exposed it should be understood that this is not a limitation and
that the ablation arrangement can be made with or without an
exposed outer conductor.
[0132] Furthermore, the transmission line 108 is provided by a
conventional fifty (50) ohm coaxial design suitable for the
transmission of microwave energy at frequencies in the range of
about 400 to about 6000 megahertz. In the preferred embodiment, the
inner conductor 134 is provided by a solid metallic material core
surrounded by a flexible semi-rigid dielectric material medium 138.
The outer conductor 136 includes a braided sleeve of metallic wires
surrounding the inner conductor 134 to provide shielding and good
flexibility thereof. Furthermore, the insulating sheath is
generally flexible and may be made of any suitable material such as
medical grade polyolefins, fluoropolymers, or polyvinylidene
fluoride. By way of example, PEBAX resins from Autochem of Germany
have been used with success.
[0133] In most embodiments, the proximal end 114 of the antenna 130
is coupled directly or indirectly to the distal end 112 of the
inner conductor 134 of the transmission line 108. A direct
connection between the antenna 130 and the inner conductor 134 may
be made in any suitable manner such as soldering, brazing,
ultrasonic welding or adhesive bonding. As was described in great
detail above, it may be desirable to indirectly couple the antenna
to the inner conductor through a passive component in order to
provide better impedance matching between the antenna device and
the transmission line. In other embodiments, the antenna 130 can be
integrally formed from the transmission line 108 itself. This is
typically more difficult from a manufacturing standpoint but has
the advantage of forming a more rugged connection between the
antenna and the transmission line.
[0134] The ablation assembly 100 is preferably thin having a
diameter in the range of between about 1.5 mm to about 3 mm, and
more preferably about 2 mm. This relatively small diameter size is
particularly suitable for use in most bodily organs, such as the
heart, so as to minimize the puncture diameter and, thus, potential
bleeding. It will be appreciated, however, that the present
invention may be used to ablate other organs or tissue as well.
Additionally, the ablation assembly must be sufficiently flexible
to accommodate normal operational use, yet be sufficiently rigid to
prevent buckling of the line during penetrative manipulation of the
needle into the targeted organ.
[0135] In one embodiment, the ablation assembly 100 includes a bend
150 that places the needle 102 at an angle relative to the
longitudinal axis 108 of the transmission line 110. As shown in
FIG. 21, the bend 150 is placed along a distal portion of the
transmission line. Alternatively, the bend 150 may be placed along
a proximal portion of the needle as shown in FIG. 23. In either
case, the bend 150 is arranged such that when the needle 102 is
introduced into the organ cavity, the needle is disposed at a
predetermined position that is arranged to substantially match the
shape and/or angular position of the wall to be ablated. That is,
the needle is bent in a direction towards the tissue targeted for
ablation. By way of example, the needle may be configured to be
bent in a direction that places the needle substantially parallel
and proximate the tissue to be ablated. Furthermore, bend 150 is
arranged to be sufficiently rigid to prevent buckling of the line
during penetrative manipulation of the needle into the targeted
organ.
[0136] In FIG. 19, the ablation assembly 100 is shown
perpendicularly penetrating the organ wall 106. It is contemplated,
however, that this position is not always possible because some
organs are particularly difficult to access, and therefore the
needle may be inserted into the wall of the organ at different
angles. Accordingly, the present invention may be configured to
provide a range of angled bends. By way of example, an antenna
position having an angle in the range of between about 45 degrees
to about 135 degrees with respect to the longitudinal axis of the
transmission line works well. However, it should be noted that this
is not a limitation and that other angles, as well as other bend
configurations, may be used. By way of example, the ablation
assembly can be configured to have multiple bends, curvilinear
bends, rectilinear bends, three dimensional bends or have a shape
that conforms to the shape of the tissue to be ablated or the
ablating line desired.
[0137] For ease of discussion, FIGS. 25A & 25B show a variety
of ablation assembly configurations. FIG. 25A shows the needle 102
in an acute angular position relative to longitudinal axis 110.
FIG. 25B shows the needle 102 in an obtuse angular position
relative to longitudinal axis 110. Again, these angular positions
are important parameters for ensuring that the antenna device is
properly positioned in a direction towards the tissue targeted for
ablation.
[0138] Turning now to FIG. 26, an alternative embodiment to the
present invention is illustrated wherein the ablation assembly 100
includes a handle 160 that provides gripping surfaces for
manipulating the needle 102 through the organ wall. The handle 160
is configured for receiving surgical tools such as forceps (not
shown). In this manner, the needle 102 may be positioned in the
organ by holding the handle 160 with forceps and maneuvering the
forceps such that the needle 102 penetrates through the organ wall.
Subsequently, the forceps may be used to position the needle 102
proximate the tissue targeted for ablation. The handle 160 is
disposed on the transmission line 108 at a predetermined distance X
away from the bent portion 150 of the assembly 100. The
predetermined distance X is arranged to place the handle 160 in
close proximity to the needle 102, and outside the outer wall of
the organ when the needle 102 is positioned inside the organ. By
way of example, in coronary applications, a distance between about
1 cm and about 3 cm works well. Furthermore, a handle formed from a
polymer having a width between about 5 mm and about 10 mm, a length
between about 2 mm and about 5 mm, and a height between about 5 mm
and about 10 mm works well. Although the handle is shown as being
rectangular it should be noted that this is not a limitation and
that the handle can be arranged with a plurality of different
shapes.
[0139] In one implementation, the handle is arranged to provide
additional support (rigidity and strength) at the junction between
the antenna and the inner conductor of the transmission line. In
another implementation, the handle is arranged to enclose an
impedance matching device located between the antenna and the inner
conductor. Furthermore, in a manner analogous to the clamping
portion (FIG. 13) described above, the handle can be arranged to be
slidably coupled to the transmission line such that the handle can
be used to clamp the wall of the organ between the bent needle and
the handle. Additionally, a seal may be used between the handle and
the outer wall of the organ to seal the puncture site. In another
implementation, the handle may include a balloon for biasing
contact between the handle and the bent antenna.
[0140] Turning now to FIGS. 27A-27C, an alternative embodiment to
the present invention is illustrated wherein the ablation assembly
100 includes a ground plane strip 170 for coupling electromagnetic
energy through the organ wall 106. The ground plane 170 generally
provides a metallic surface that attracts the electric field
generated by the antenna 130 and therefore a more intense
electromagnetic field 180 is produced between the antenna 130 and
the ground plane 170. As a result, a more efficient, controlled and
concentrated electric field can be used to ablate the targeted
tissue. Additionally, less power may be required from the power
source because of the more efficient use of the energy.
[0141] In this embodiment, the ground plane 170 is electrically
coupled to the outer conductor 136 of the transmission line 108.
The ground plane 170 is generally disposed on the transmission line
108 at a predetermined distance Y away from the antenna 130 of the
needle 102. The predetermined distance Y is arranged to place the
ground plane in close proximity to the needle 102, and outside the
outer wall of the organ 106 when the needle 102 is positioned
inside the organ 106. By way of example, in coronary applications,
a distance between about 1 mm and about 15 mm works well.
[0142] Additionally, the ground plane 170 must be sufficiently
flexible to accommodate needle maneuvering, normal operational use
and storage thereof, yet be sufficiently rigid to prevent buckling
or bends in the ground plane when the needle is positioned inside
the organ cavity. The ground plane 170 may be formed from a
metallic foil. By way of example, silver, stainless steal or gold
work well. The ground plane 170 can also be formed from a flexible
dielectric substrate with one or two metallic surface(s). By way of
example, Kapton.TM. or Teflon.TM. substrates work well. Further,
the thickness of the ground plane 170 may vary to some extent based
on the particular application of the ablation assembly and the type
of material chosen. By way of example, a strip thickness between
about 0.005 inch to about 0.040 inch works well. In the illustrated
embodiment, the thickness of the ground plane strip is about 0.010
inch. Furthermore, the connection between the ground plane 170 and
the outer conductor 136 may be made in any suitable manner such as
soldering, brazing, ultrasonic welding or adhesive bonding.
[0143] Although the ground plane is shown and described as a strip
it should be noted that this is not a limitation and that the
ground plane may vary in form according to the specific needs of
each assembly. By way of example, a metallic wire formed from
silver having a diameter between about 1 mm and about 2 mm works
well. Additionally, a plate formed from silver having a thickness
between about 0.005 inch and about 0.040 inch and a width between
about 2 mm and about 5 mm works well.
[0144] Moreover, the ground plane is generally configured to be
parallel to the angular position of the needle 102. By way of
example, if the needle is configured to have an angle of about 60
degrees relative to the axis of the transmission line, then the
ground plane may be configured to have an angle of about 60 degrees
relative to the axis of the transmission line. In this manner, the
antenna and the ground plane can couple energy more evenly.
Alternatively, the ground plane can be shaped to conform to the
shape of the outer wall. Further still, the ground plane generally
has a length that is substantially equivalent to the length of the
antenna 130. By way of example, a ground plane length between about
20 mm and about 50 mm works well. It should be noted, however, that
the length may vary according to the specific needs of each
ablation assembly. The ground plane is also arranged to be
substantially aligned (in the same plane) with the bent portion of
the needle 102.
[0145] Alternatively, in one implementation, the ground plane is
arranged to be part of the handle. In another implementation, the
electrode is movably coupled to transmission line. For example, the
ground plane may be pivotly or slidably coupled to the transmission
line. In another implementation, the ground plane is biased to
contact the tissue.
[0146] A method for using the described needle ablation assembly in
treating an organ will now be described. The method includes
providing a surgical device 100 having a needle 102 coupled to a
transmission line 108. The transmission line 108 is arranged to
have a portion with a longitudinal axis 110 and a proximal end 120
coupled to an electromagnetic energy source. By way of example, a
microwave energy source that generates energy in the microwave
frequency range works well. Furthermore, the needle 102 includes a
distal end 104 that is adapted to penetrate through a wall of an
organ 106 and an antenna 130 for generating a microwave field. By
way of example, the organ may be a human heart and the wall may be
the myocardium of the heart. The antenna 130 is also arranged to be
in an angular position relative to the longitudinal axis 110 of the
transmission line 108. By way of example, the needle or the
transmission line may be pre-shaped or bent at a predetermined
angular position.
[0147] In accordance with the present invention, the method
includes introducing the surgical device 100 into a body cavity.
This may be by penetration of the body or through an access device
inserted in the body. By way of example, in most coronary
applications, the introducing may be provided through the thorax
region of the body or through an opened chest. The method further
includes penetrating a wall of the organ 106 with the distal end
104 of the needle 102 and introducing the needle 102 through the
wall of the organ 106 and into an interior chamber thereof. By way
of example, the surgical tool 100 can be introduced into the left
atrium, the right atrium, the right ventricle, or the left
ventricle of the heart. Furthermore, before penetration a purse
string suture may be placed in the heart wall proximate the area
targeted for penetration so as to provide tension during
penetration. Purse string sutures are well known in the art and for
the sake of brevity will not be discussed in more detail.
[0148] The method also includes positioning the needle 102 inside
the interior chamber of the organ 106 such that the antenna 130
substantially matches the shape and/or angular position of the wall
to be ablated. By way of example, the position may place the
antenna substantially parallel to the interior surface of the
penetrated wall and proximate the targeted tissue. Furthermore, the
method includes generating a microwave field at the antenna that is
sufficiently strong to cause tissue ablation within the generated
microwave field.
[0149] Although only a few embodiments of the present invention
have been described in detail, it should be understood that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Particularly, the invention has been described in terms of a
microwave ablation assembly for cardiac applications. However, it
should be appreciated that the present invention could be used for
a wide variety of alternative applications as well. By way of
example, the present invention may be used in most procedures
relating to the ablation of internal biological tissues, and more
particularly, to the ablation of organs with cavities such as the
heart, the stomach, the intestines and the like. Further, although
the described assembly works extremely well for microwave
applications, it may be used to transmit electromagnetic energy at
other frequencies as well, for example, radio frequencies.
Additionally, it is contemplated that the present invention may be
practiced with other suitable ablative energy sources. By way of
example, the present invention may be practiced with electrical
current, ultrasound, electrical pulses, cryothermy, lasers, and the
like. In such configurations, the ablation element may be one or
several metallic electrodes, a laser transducer, a cryogenic
transducer, or an ultrasound transducer, while the transmission
element may be a metallic wire, a fiber optic or a tube carrying
cooling fluid.
[0150] Furthermore, while the invention has been described in terms
of several preferred embodiments, there are alterations,
permutations, and equivalents, which fall within the scope of this
invention. By way of example, the ablation assembly may also
include a series of mapping electrodes to detect
electrophysiological signals from the cardiac tissue. Such
electrodes can be used to map the relevant region of the heart
prior to or after an ablation procedure. The electrodes may also be
used to monitor the patient's condition and/or the nature of the
ablation process. The electrodes may be disposed along the antenna
device in the antenna region, along the transmission line, or along
the clamping finger. The electrode bands may optionally be divided
into a plurality of electrically isolated electrode segments. The
information obtained from the electrodes is transmitted via
electrode wires to external electronics such as an EP signal
monitoring device. Filtering of the signal may be provided as
necessary. In alternative embodiments, some of the external
electronics could be incorporated into the power supply and/or the
power supply could use information obtained from the electrodes in
its control scheme.
[0151] In addition, the ablation assembly may also include a series
of thermometry elements for measuring the temperature of the
tissue. The thermometry elements may take the form of thermocouple
wires, fiber optic sensor cables or any other suitable thermometry
devices. The thermometry elements may be disposed along the antenna
device, along the transmission line, or along the clamping
finger.
[0152] Moreover, although the ground plane has been shown and
described as being directly connected to the outer conductor of the
transmission line, it may be indirectly grounded through an
external conductor. This type of arrangement also creates a more
intense electromagnetic field, but not to the same degree as the
directly connected ground plane.
[0153] Further, it is also contemplated that the ablation assembly
may be widely modified without departing from the scope of this
invention. By way of example, balloons may be positioned at the
inner or outer penetration of the organ to seal the puncture site.
Additionally, the ablation assembly may include a chemical delivery
system for injecting chemical agents into the penetrated tissue.
Further still, purse string sutures may be used to help seal the
puncture site of the organ. It should also be noted that there are
many ways of implementing the methods and apparatuses of the
present invention. It is therefore intended that the following
appended claims be interpreted as including all such alterations,
permutations, and equivalents as fall within the true spirit and
scope of the present invention.
* * * * *