U.S. patent application number 10/219598 was filed with the patent office on 2002-12-19 for microwave ablation instrument with flexible antenna assembly and method.
This patent application is currently assigned to AFX, INC.. Invention is credited to Berube, Dany, Gauthier, Jules, Nguyen, Hiep.
Application Number | 20020193783 10/219598 |
Document ID | / |
Family ID | 23924610 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020193783 |
Kind Code |
A1 |
Gauthier, Jules ; et
al. |
December 19, 2002 |
Microwave ablation instrument with flexible antenna assembly and
method
Abstract
A flexible microwave antenna assembly for a surgical ablation
instrument capable of conforming to a tissue surface for ablation
thereof. The ablation instrument includes a transmission line
having a proximal portion suitable for connection to an
electromagnetic energy source. The antenna assembly includes a
flexible antenna coupled to the transmission line for radially
generating an electric field sufficiently strong to cause tissue
ablation. A flexible shield device is coupled to the antenna to
substantially shield a surrounding area of the antenna from the
electric field radially generated therefrom while permitting a
majority of the field to be directed generally in a predetermined
direction. A flexible insulator is disposed between the shield
device and the antenna which defines a window portion enabling the
transmission of the directed electric field in the predetermined
direction. The antenna, the shield device and the insulator are
formed for selective manipulative bending thereof, as a unit, to
one of a plurality of contact positions to generally conform the
window portion to the biological tissue surface to be ablated.
Inventors: |
Gauthier, Jules; (Laval,
CA) ; Berube, Dany; (Fremont, CA) ; Nguyen,
Hiep; (Milpitas, CA) |
Correspondence
Address: |
Ross M. Carothers
AFx inc.
47929 Fremont Blvd.
Fremont
CA
94538
US
|
Assignee: |
AFX, INC.
47929 FREMONT BLVD.
FREMONT
CA
94538
|
Family ID: |
23924610 |
Appl. No.: |
10/219598 |
Filed: |
August 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10219598 |
Aug 14, 2002 |
|
|
|
09484548 |
Jan 18, 2000 |
|
|
|
Current U.S.
Class: |
606/17 ; 128/898;
343/841 |
Current CPC
Class: |
A61B 2018/1861 20130101;
A61B 18/18 20130101; A61B 2018/1807 20130101; A61B 18/1492
20130101; A61B 18/1815 20130101; H05B 6/702 20130101 |
Class at
Publication: |
606/17 ; 128/898;
343/841 |
International
Class: |
A61B 018/18 |
Claims
1. A method of ablating tissue at a target tissue site, comprising
the steps: providing a flexible ablation device defining an outer
ablation surface and comprising a means for directionally
controlling ablation energy emitted therefrom; manipulating the
distal portion of the ablation device to generally conform the
ablation surface to a tissue surface at the target tissue site;
applying ablation energy sufficient to ablate tissue at the target
tissue site.
2. The method of claim 1, wherein the ablation device comprises at
least one ablation element.
3. The method of claim 2, wherein the at least one ablation element
is an antenna.
4. The method of claim 1, wherein the ablation energy is one or
more energies from the group consisting of: radiofrequency,
microwave, and cryogenic.
5. The method of claim 1, wherein the means for directionally
controlling the ablation energy is a shield device adapted to
direct the ablation energy in a single direction along a
longitudinal axis of the ablation device, whereby the step of
applying ablation energy results in the creation of a continuous
lesion.
6. The method of claim 6, wherein the step of applying ablation
energy results in the isolation of at least one pulmonary vein from
the epicardial surface of a patient's heart.
7. A method for treatment of a heart comprising: providing an
ablation instrument having a flexible antenna assembly defining a
window portion enabling the transmission of a directed electric
field therethrough in a predetermined direction; selectively
bending the flexible antenna assembly to one of a plurality of
contact positions to generally conform the shape of said window
portion to the targeted biological tissue surface to be ablated;
manipulating the ablation instrument to strategically position the
conformed window portion into contact with the targeted biological
tissue surface; and generating the electric field sufficiently
strong to cause tissue ablation to the targeted biological tissue
surface.
8. The method of claim 7, wherein said flexible antenna assembly
includes: a flexible antenna for radially generating the electric
field; a flexible shield device coupled to said antenna to
substantially shield a surrounding area of the antenna from the
electric field radially generated therefrom while permitting a
majority of the field to be directed generally in the predetermined
direction; and a flexible insulator disposed between the shield
device and the antenna, and defining said window portion enabling
the transmission of the directed electric field in the
predetermined direction.
9. The method of claim 8, further including: repeating the bending,
manipulating and generating events to form a plurality of
strategically positioned ablation lesions.
10. The method of claim 9, wherein the lesions are formed to create
a predetermined conduction pathway in the muscular tissue wall of
the targeted biological tissue and/or to divide the left and/or
right atria to substantially prevent reentry circuits.
11. The method of claim 8, further including: an elongated,
bendable, retaining member coupled longitudinally therealong to
said insulator in a manner enabling the insulator to retain the one
contact position after manipulative bending thereof for said
conformance of the window portion to the biological tissue surface
to be ablated.
12. The method of claim 1, wherein said retaining member is
embedded in the flexible insulator.
13. The method of claim 7, wherein the heart remains beating
throughout the bending, manipulating and generating events.
14. The method of claim 7, further including: arresting the
patient's heart.
15. The method of claim 7, further including: temporarily arresting
the patient's heart.
16. The method of claim 7, wherein said ablation instrument is a
microwave ablation instrument.
17. A method for ablating medically refractory atrial fibrillation
of the heart comprising: providing an ablation instrument having a
flexible antenna assembly adapted to generate an electric field
sufficiently strong to cause tissue ablation, said antenna assembly
defining a window portion enabling the transmission of the electric
field therethrough in a predetermined direction; selectively
bending and retaining the flexible antenna assembly in one of a
plurality of contact positions to generally conform the shape of
said window portion to the targeted biological tissue surface to be
ablated; manipulating the ablation instrument to strategically
position the conformed window portion into contact with the
targeted biological tissue surface; and forming an elongated lesion
in the targeted biological tissue surface through the generation of
the electric field by the antenna assembly.
18. The method of claim 17, wherein said flexible antenna assembly
includes: a flexible antenna for radially generating the electric
field; a flexible shield device coupled to said antenna to
substantially shield a surrounding area of the antenna from the
electric field radially generated therefrom while permitting a
majority of the field to be directed generally in the predetermined
direction; and a flexible insulator disposed between the shield
device and the antenna, and defining said window portion enabling
the transmission of the directed electric field in the
predetermined direction.
19. The method of claim 18, further including: repeating the
bending, manipulating and generating events to form a plurality of
strategically positioned ablation lesions and/or to divide the left
and/or right atria to substantially prevent reentry circuits.
20. The method of claim 19, wherein the lesions are formed to
create a predetermined conduction pathway between a sinoatrial node
and an atrioventricular node of the heart.
21. The method of claim 19, wherein said repeating the bending,
manipulating and generating events are applied in a manner
isolating the pulmonary veins from the epicardium of the heart.
22. The method of claim 18, further including: an elongated,
bendable, retaining member coupled longitudinally therealong to
said insulator in a manner enabling the insulator to retain the one
contact position after manipulative bending thereof for said
conformance of the window portion to the biological tissue surface
to be ablated.
23. The method of claim 22, wherein said retaining member is
embedded in the flexible insulator.
24. The method of claim 17, wherein the heart remains beating
throughout the bending, manipulating and generating events.
25. The method of claim 23, wherein said biological tissue surface
includes the epicardium of the heart during a minimally invasive
heart procedure.
26. The method of claim 17, further including: arresting the
patient's heart.
27. The method of claim 17, further including: temporarily
arresting the patient's heart.
28. The method of claim 26, wherein said biological tissue surface
includes the endocardium of one of the left atrium and the right
atrium during an open-heart procedure.
29. The method of claim 17, wherein said ablation instrument is a
microwave ablation instrument.
30. The method of claim 17, wherein said ablation instrument
includes an elongated flexible gripping member having a distal grip
portion and an opposite proximal portion coupled to a distal
portion of said antenna assembly, and a handle member coupled to a
proximal portion of said antenna assembly; and said manipulating
includes manually gripping said flexible gripping member and said
handle member to cooperatively and selectively bend said antenna
assembly to selectively urge the window portion in abutting contact
with the biological tissue surface to be ablated.
31. The method of claim 30, wherein said handle member is a
flexible elongated member.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/484,548, filed Jan. 18, 2000, entitled "A
MICROWAVE ABLATION INSTRUMENT WITH FLEXIBLE ANTENNA ASSEMBLY AND
METHOD," a copy of which is hereby incorporated herein by
reference, in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates, generally, to ablation
instrument systems that use electromagnetic energy in the microwave
frequencies to ablate internal bodily tissues, and, more
particularly, to antenna arrangements and instrument construction
techniques that direct the microwave energy in selected directions
that are relatively closely contained along the antenna.
[0004] 2. Description of the Prior Art
[0005] It is well documented that atrial fibrillation, either alone
or as a consequence of other cardiac disease, continues to persist
as the most common cardiac arrhythmia. According to recent
estimates, more than two million people in the U.S. suffer from
this common arrhythmia, roughly 0.15% to 2.0% of the population.
Moreover, the prevalence of this cardiac disease increases with
age, affecting nearly 8% to 17% of those over 60 years of age.
[0006] Atrial arrhythmia may be treated using several methods.
Pharmacological treatment of atrial fibrillation, for example, is
initially the preferred approach, first to maintain normal sinus
rhythm, or secondly to decrease the ventricular response rate.
Other forms of treatment include chemical cardioversion to normal
sinus rhythm, electrical cardioversion, and RF catheter ablation of
selected areas determined by mapping. In the more recent past,
other surgical procedures have been developed for atrial
fibrillation, including left atrial isolation, transvenous catheter
or cryosurgical ablation of His bundle, and the Corridor procedure,
which have effectively eliminated irregular ventricular rhythm.
However, these procedures have for the most part failed to restore
normal cardiac hemodynamics, or alleviate the patient's
vulnerability to thromboembolism because the atria are allowed to
continue to fibrillate. Accordingly, a more effective surgical
treatment was required to cure medically refractory atrial
fibrillation of the heart.
[0007] On the basis of electrophysiologic mapping of the atria and
identification of macroreentrant circuits, a surgical approach was
developed which effectively creates an electrical maze in the
atrium (i.e., the MAZE procedure) and precludes the ability of the
atria to fibrillate. Briefly, in the procedure commonly referred to
as the MAZE III procedure, strategic atrial incisions are performed
to prevent atrial reentry and allow sinus impulses to activate the
entire atrial myocardium, thereby preserving atrial transport
function postoperatively. Since atrial fibrillation is
characterized by the presence of multiple macroreentrant circuits
that are fleeting in nature and can occur anywhere in the atria, it
is prudent to interrupt all of the potential pathways for atrial
macroreentrant circuits. These circuits, incidentally, have been
identified by intraoperative mapping both experimentally and
clinically in patients.
[0008] Generally, this procedure includes the excision of both
atrial appendages, and the electrical isolation of the pulmonary
veins. Further, strategically placed atrial incisions not only
interrupt the conduction routes of the common reentrant circuits,
but they also direct the sinus impulse from the sinoatrial node to
the atrioventricular node along a specified route. In essence, the
entire atrial myocardium, with the exception of the atrial
appendages and the pulmonary veins, is electrically activated by
providing for multiple blind alleys off the main conduction route
between the sinoatrial node to the atrioventricular node. Atrial
transport function is thus preserved postoperatively as generally
set forth in the series of articles: Cox, Schuessler, Boineau,
Canavan, Cain, Lindsay, Stone, Smith, Corr, Change, and D'Agostino,
Jr., The Surgical Treatment Atrial Fibrillation (pts. 1-4), 101
THORAC CARDIOVASC SURG., 402-426, 569-592 (1991).
[0009] While this MAZE III procedure has proven effective in
ablating medically refractory atrial fibrillation and associated
detrimental sequelae, this operational procedure is traumatic to
the patient since substantial incisions are introduced into the
interior chambers of the heart. Consequently, other techniques have
thus been developed to interrupt and redirect the conduction routes
without requiring substantial atrial incisions. One such technique
is strategic ablation of the atrial tissues through ablation
catheters.
[0010] Most approved ablation catheter systems now utilize radio
frequency (RF) energy as the ablating energy source. Accordingly, a
variety of RF based catheters and power supplies are currently
available to electrophysiologists. However, radio frequency energy
has several limitations including the rapid dissipation of energy
in surface tissues resulting in shallow "burns" and failure to
access deeper arrhythmic tissues. Another limitation of RF ablation
catheters is the risk of clot formation on the energy emitting
electrodes. Such clots have an associated danger of causing
potentially lethal strokes in the event that a clot is dislodged
from the catheter.
[0011] As such, catheters which utilize electromagnetic energy in
the microwave frequency range as the ablation energy source are
currently being developed. Microwave frequency energy has long been
recognized as an effective energy source for heating biological
tissues and has seen use in such hyperthermia applications as
cancer treatment and preheating of blood prior to infusions.
Accordingly, in view of the drawbacks of the traditional catheter
ablation techniques, there has recently been a great deal of
interest in using microwave energy as an ablation energy source.
The advantage of microwave energy is that it is much easier to
control and safer than direct current applications and it is
capable of generating substantially larger lesions than RF
catheters, which greatly simplifies the actual ablation procedures.
Such microwave ablation systems are described in the U.S. Pat. Nos.
4,641,649 to Walinsky; 5,246,438 to Langberg; 5,405,346 to Grundy,
et al.; and 5,314,466 to Stern, et al, each of which is
incorporated herein by reference.
[0012] Most of the existing microwave ablation catheters
contemplate the use of longitudinally extending helical antenna
coils that direct the electromagnetic energy in a radial direction
that is generally perpendicular to the longitudinal axis of the
catheter although the fields created are not well constrained to
the antenna itself. Although such catheter designs work well for a
number of applications, such as radial output, they are
inappropriate for use in precision surgical procedures. For
example, in MAZE III surgical procedures, very precise and
strategic lesions must be formed in the heart tissue which the
existing microwave ablation catheters are incapable of
delivering.
[0013] Consequently, microwave ablation instruments have recently
been developed which incorporate microwave antennas having
directional reflectors. Typically, a tapered directional reflector
is positioned peripherally around the microwave antenna to direct
the waves toward and out of a window portion of the antenna
assembly. These ablation instruments, thus, are capable of
effectively transmitting electromagnetic energy in a more specific
direction. For example, the electromagnetic energy may be
transmitted generally perpendicular to the longitudinal axis of the
catheter but constrained to a selected angular section of the
antenna, or directly out the distal end of the instrument. Typical
of these designs are described in the U.S. patent application Ser.
Nos. 09/178,066, filed Oct. 23, 1998; and 09/333,747, filed Jun.
14, 1999, each of which is incorporated herein by reference.
[0014] In these designs, the of the microwave antenna is preferably
tuned assuming contact between the targeted tissue and a contact
region of the antenna assembly extending longitudinally adjacent to
the antenna longitudinal axis. Hence, should a portion of, or
substantially all of, the exposed contact region of the antenna not
be in contact with the targeted tissue during ablation, the
adaptation of the antenna will be adversely changed and the antenna
will be untuned. As a result, the portion of the antenna not in
contact with the targeted tissue will radiate the electromagnetic
radiation into the surrounding air. The efficiency of the energy
delivery into the tissue will consequently decrease which in turn
causes the penetration depth of the lesion to decrease.
[0015] This is particularly problematic when the tissue surfaces
are substantially curvilinear, or when the targeted tissue for
ablation is difficult to access. Since these antenna designs are
generally relatively rigid, it is often difficult to maneuver
substantially all of the exposed contact region of the antenna into
abutting contact against the targeted tissue. In these instances,
several ablation instruments, having antennas of varying length and
shape, may be necessary to complete just one series of
ablations.
SUMMARY OF THE INVENTION
[0016] Accordingly, a flexible microwave antenna assembly is
provided for a surgical ablation instrument adapted to ablate a
surface of a biological tissue. The ablation instrument includes a
transmission line having a proximal portion suitable for connection
to an electromagnetic energy source. The antenna assembly includes
a flexible antenna coupled to the transmission line for radially
generating an electric field sufficiently strong to cause tissue
ablation. A flexible shield device is coupled to the antenna to
substantially shield a surrounding area of the antenna from the
electric field radially generated therefrom while permitting a
majority of the field to be directed generally in a predetermined
direction. A flexible insulator is disposed between the shield
device and the antenna which defines a window portion enabling the
transmission of the directed electric field in the predetermined
direction. In accordance with the present invention, the antenna,
the shield device and the insulator are formed for selective
manipulative bending thereof, as a unit, to one of a plurality of
contact positions to generally conform the window portion to the
biological tissue surface to be ablated.
[0017] In one configuration, a longitudinal axis of the antenna is
off-set from a longitudinal axis of the insulator to position the
antenna substantially proximate to and adjacent the window portion.
The shield device is in the shape of a semi-cylindrical shell
having a longitudinal axis generally co-axial with a longitudinal
axis of the insulator.
[0018] In another embodiment, the insulator defines a receiving
passage formed for sliding receipt of the antenna longitudinal
therein during manipulative bending of the antenna assembly.
Moreover, a polyimide tube device may be positioned in the
receiving passage proximate the distal end of the antenna. The tube
provides a bore formed and dimensioned sliding longitudinal
reciprocation therein of at least the distal end of the
antenna.
[0019] Another embodiment of the present invention provides an
elongated, bendable, retaining member adapted for longitudinal
coupling therealong to the insulator. This bendable retaining
member enables the insulator to retain the one contact position
after manipulative bending thereof for the conformance of the
window portion to the biological tissue surface to be ablated. The
retaining member is preferably disposed longitudinally along the
insulator, and on one the of the shield device, while the antenna
is preferably disposed on an opposite side of the shield device,
longitudinally along the insulator, and between the shield device
and the window portion.
[0020] In another aspect of the present invention provides a
microwave ablation instrument, adapted to ablate a surface of a
biological tissue, is provided having a handle member formed for
manual manipulation of the ablation instrument. An elongated
transmission line is provided coupled to the handle member. A
proximal portion of the transmission line is suitable for
connection to an electromagnetic energy source. The ablation
instrument further includes a flexible antenna assembly coupled to
the handle member which is formed for selective manipulative
bending thereof. The antenna assembly includes a flexible antenna
coupled to the transmission line for radially generating an
electric field sufficiently strong to cause tissue ablation. A
flexible shield device of the antenna assembly is employed to
substantially shield a surrounding radial area of the antenna from
the electric field radially generated therefrom, while permitting a
majority of the field to be directed generally in a predetermined
direction. A flexible insulator is disposed between the shield
device and the antenna, and defines a window portion enabling the
transmission of the directed electric field in the predetermined
direction. The antenna, the shield device and the insulator are
formed for selective manipulative bending thereof, as a unit, to
one of a plurality of contact positions to generally conform the
window portion to the biological tissue surface to be ablated.
[0021] In this configuration, the ablation instrument may include a
bendable, malleable shaft having a proximal portion coupled to the
handle member, and an opposite a distal portion coupled to the
antenna assembly. The shaft is preferably a semi-rigid coaxial
cable, but may also include a tubular shaft where the transmission
line may be disposed therethrough from the proximal portion to the
distal portion thereof. The shaft is preferably conductive having a
distal portion conductively coupled to the proximal end of the
shield device, and another portion conductively coupled to the
outer conductor of the transmission line.
[0022] In another embodiment, a restraining sleeve is adapted to
limit the bending movement of the bendable antenna assembly at the
conductive coupling between the shield device and the shaft. The
restraining sleeve is formed and dimensioned to extend peripherally
over the conductive coupling to limit the bending movement in a
predetermined direction to maintain the integrity of conductive
coupling. The restraining sleeve includes a curvilinear transverse
cross-sectional dimension extending past the conductive coupling
longitudinally therealong by an amount sufficient to maintain the
integrity.
[0023] In still another configuration, an elongated grip member is
included having a distal grip portion and an opposite proximal
portion coupled to a distal portion of the antenna assembly. The
grip member and the handle member cooperate to selectively bend the
antenna assembly and selectively urge the window portion in
abutting contact with the biological tissue surface to be ablated.
The gripping member is preferably provided by an elongated flexible
rod having a diameter smaller than a diameter of the insulator. A
longitudinal axis of the flexible rod is off-set from the
longitudinal axis of the insulator to position the rod in general
axial alignment with the antenna, and adjacent the window
portion.
[0024] In still another aspect of the present invention, a method
is provided for ablating medically refractory atrial fibrillation
of the heart including the step of providing a microwave ablation
instrument having a flexible antenna assembly adapted to generate
an electric field sufficiently strong to cause tissue ablation. The
antenna assembly defines a window portion enabling the transmission
of the electric field therethrough in a predetermined direction.
The method further includes selectively bending and retaining the
flexible antenna assembly in one of a plurality of contact
positions to generally conform the shape of the window portion to
the targeted biological tissue surface to be ablated, and
manipulating the ablation instrument to strategically position the
conformed window portion into contact with the targeted biological
tissue surface. The next step includes forming an elongated lesion
in the targeted biological tissue surface through the generation of
the electric field by the antenna assembly.
[0025] These bending, manipulating and generating events are
preferably repeated to form a plurality of strategically positioned
ablation lesions. Collectively, these lesions are formed to create
a predetermined conduction pathway between a sinoatrial node and an
atrioventricular node of the heart.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The assembly of the present invention has other objects and
features of advantage which will be more readily apparent from the
following description of the best mode of carrying out the
invention and the appended claims, when taken in conjunction with
the accompanying drawing, in which:
[0027] FIG. 1 is a diagrammatic top plan view of a microwave
ablation instrument system with a bendable directional reflective
antenna assembly constructed in accordance with one embodiment of
the present invention.
[0028] FIG. 2 is an enlarged, fragmentary, top perspective view of
the antenna assembly of FIG. 1 mounted to a distal end of a handle
member of the ablation instrument.
[0029] FIG. 3 is an enlarged, fragmentary, top perspective view of
the antenna assembly of FIG. 1 illustrated in a bent position to
conform to a surface of the tissue to be ablated.
[0030] FIG. 4 is an enlarged, fragmentary, top perspective view of
the antenna assembly of FIG. 2 illustrated in another bent position
to conform to a surface of the tissue to be ablated.
[0031] FIG. 5 is an enlarged, fragmentary, top plan view of the
antenna assembly of FIG. 2 illustrating movement between a normal
position (phantom lines) and a bent position (solid lines).
[0032] FIG. 6 is a fragmentary side elevation view of the antenna
assembly of FIG. 5.
[0033] FIG. 7 is an enlarged, front elevation view, in
cross-section, of the antenna assembly taken substantially along
the plane of the line 7-7 in FIG. 6.
[0034] FIG. 8 is an enlarged, fragmentary, side elevation view of
the antenna assembly of FIG. 2 having a restraining sleeve coupled
thereto.
[0035] FIG. 9 is an enlarged, front elevation view, in
cross-section, of the antenna assembly taken substantially along
the plane of the line 9-9 in FIG. 8.
[0036] FIG. 10 is a diagrammatic top plan view of an alternative
embodiment microwave ablation instrument system constructed in
accordance with one embodiment of the present invention.
[0037] FIG. 11 is a reduced, fragmentary, top perspective view of
the antenna assembly of FIG. 10 illustrated in a bent position to
conform to a surface of the tissue to be ablated.
[0038] FIG. 12 is a reduced, fragmentary, top perspective view of
an alternative embodiment antenna assembly of FIG. 10 having a
flexible handle member.
DETAILED DESCRIPTION OF THE INVENTION
[0039] While the present invention will be described with reference
to a few specific embodiments, the description is illustrative of
the invention and is not to be construed as limiting the invention.
Various modifications to the present invention can be made to the
preferred embodiments by those skilled in the art without departing
from the true spirit and scope of the invention as defined by the
appended claims. It will be noted here that for a better
understanding, like components are designated by like reference
numerals throughout the various Figures.
[0040] Turning now to FIGS. 1-4, a microwave ablation instrument,
generally designated 20, is provided which is adapted to ablate a
surface 21 of a biological tissue 22. The ablation instrument 20
includes a handle member 23 formed to manually manipulate the
instrument during open surgery. An elongated transmission line 25
is provided coupled to the handle member 23 at a distal portion
thereof, and having a proximal portion suitable for connection to
an electromagnetic energy source (not shown). The ablation
instrument 20 further includes a flexible antenna assembly,
generally designated 26, coupled to the handle member 23 and to the
transmission line 25 to generate an electric field. The antenna
assembly 26 is adapted to transmit an electric field out of a
window portion 27 thereof in a predetermined direction sufficiently
strong to cause tissue ablation. The antenna assembly is further
formed for selective manipulative bending to one of a plurality of
contact positions (e.g., FIGS. 3 and 4) to generally conform the
window portion 27 to the biological tissue surface 21 to be
ablated.
[0041] More specifically, the flexible antenna assembly 26 includes
a flexible antenna 28 coupled to the transmission line 25 for
radially generating the electric field substantially along the
longitudinal length thereof. A flexible shield device 30
substantially shields a surrounding radial area of the antenna wire
28 from the electric field radially generated therefrom, while
permitting a majority of the field to be directed generally in a
predetermined direction toward the window portion 27. A flexible
insulator 31 is disposed between the shield device 30 and the
antenna 28, and defines the window portion 27 enabling the
transmission of the directed electric field in the predetermined
direction. The antenna 28, the shield device 30 and the insulator
31 are formed for selective manipulative bending thereof, as a
unit, to one of a plurality of contact positions to generally
conform the window portion 27 to the biological tissue surface 21
to be ablated.
[0042] Accordingly, the microwave ablation instrument of the
present invention enables manipulative bending of the antenna
assembly to conform the window portion to the biological tissue
surface to be ablated. This ensures a greater degree of contact
between the elongated window portion and the targeted tissue. This
is imperative to maintain the radiation efficiency of the antenna,
and thus, proper tuning for more efficient microwave transmission.
Such manipulative bending also substantially increases the
versatility of the instrument since one antenna assembly can be
configured to conform to most tissue surfaces.
[0043] Briefly, the ablation instrument 20 includes a handle member
23 coupled to the antenna assembly 26 through an elongated tubular
shaft or semi-rigid coaxial cable, hereinafter referred to as shaft
32. By manually manipulating the handle, the window portion 27 of
the antenna assembly 26 may be oriented and positioned to perform
the desired ablation. As mentioned, the shaft 32 is preferably
provided a semi-rigid coaxial cable or by a conductive material
such as a metallic hypotube which is mounted to the components of
the antenna assembly 26 through brazing paste, welding or the like,
as will be discussed. Accordingly, when the shaft 32 is provided by
the semi-rigid coaxial cable, the braided outer conductor 29 of the
semi-rigid coaxial cable 32, peripherally surrounding the center
conductor 33, is preferably conductively coupled to the outer
conductor of the transmission line 25. Similarly, the inner
conductor 33 of the semi-rigid coaxial cable 32 is conductively
coupled to the inner conductor of the transmission line 25.
[0044] In contrast, when the shaft 32 is provided by the tubular,
such as a conductive hypotube, the solid cylindrical shell outer
conductor 29 thereof is preferably conductively coupled to the
outer conductor of the transmission line 25. In this configuration,
the inner conductor and the insulator of the transmission line
extend through the cylindrical shell outer conductor 29 of the
conductive hypotube 32 to provide the inner conductor 33 thereof.
In this manner, the metallic hypotube itself functions as the outer
conductor of the transmission line 25 for shielding along the
length of the shaft.
[0045] Moreover, the shaft 32, whether the hypotube or the
semi-rigid coaxial cable, is preferably bendable and malleable in
nature to enable shape reconfiguration to position the antenna
assembly at a desired orientation relative the handle. This permits
the surgeon to appropriately angle the window portion toward the
targeted region for tissue ablation. It will be appreciated,
however, that the material of the shaft 32 is further sufficiently
rigid so that the shaft is not easily deformed during operative
use. Such materials for the hypotube, for example, include
stainless steel or aluminum having diameters ranging from about
0.090 inches to about 0.200 inches with wall thickness ranging from
about 0.010 inches to about 0.050 inches. When the semi-coaxial
cable is applied as the shaft 32, the outer diameter of the outer
conductor ranges from about 0.090 inches to about 0.200 inches,
with wall thickness ranging from about 0.010 inches to about 0.050
inches; while the inner conductor includes a diameter in the range
of about 0.010 inches to about 0.050 inches.
[0046] The transmission line 25 is typically coaxial, and is
coupled to a power supply (not shown) through connector 35 (FIG.
1). As best illustrated in FIGS. 2 and 5-7, the microwave ablation
instrument 20 generally includes an elongated antenna wire 28
having a proximal end attached to center conductor 33 of
transmission line 25. These linear wire antennas radiate a
cylindrical electric field pattern consistent with the length
thereof It will be appreciated, however, that the antenna may be
any other configuration, as well, such as a helical or coiled
antenna.
[0047] The electrical interconnection between the antenna wire 28
and the distal end of the center conductor 33 may be made in any
suitable manner such as through soldering, brazing, ultrasonic
welding or adhesive bonding. Moreover, the antenna wire 28 may be
an extension of the center conductor of the transmission line
itself which has the advantage of forming a more rugged connection
therebetween. Typically, the antenna wire 28 is composed of any
suitable material, such as spring steel, beryllium copper, or
silver-plated copper.
[0048] As will be discussed in greater detail below, the diameter
of the antenna wire may vary to some extent based on the particular
application of the instrument. By way of example, an instrument
suitable for use in an atrial fibrillation application may have
typical diameter in the range of approximately 0.005 to 0.030
inches. More preferably, the diameter of antenna wire may be in the
range of approximately 0.013 to 0.020 inches.
[0049] The antenna 28 is designed to have a good radiation
efficiency and to be electrically balanced. Consequently, the
energy delivery efficiency of the antenna is increased, while the
reflected microwave power is decreased which in turn reduces the
operating temperature of the transmission line. Moreover, the
radiated electromagnetic field is substantially constrained from
the proximal end to the distal end of the antenna. Thus, the field
extends substantially radially perpendicularly to the antenna and
is fairly well constrained to the length of the antenna itself
regardless of the power used. This arrangement serves to provide
better control during ablation. Instruments having specified
ablation characteristics can be fabricated by building instruments
with different length antennas.
[0050] Briefly, the power supply (not shown) includes a microwave
generator which may take any conventional form. 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. Food and Drug Administration 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. 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).
[0051] Referring back to FIGS. 1-5, the microwave ablation
instrument 20 of the present invention will be described in detail.
As above-mentioned, the antenna wire 28, the shield device 30 and
the insulator 31 of the antenna assembly cooperate, as a unit, to
enable selective manipulative bending thereof to one of a plurality
of contact positions to generally conform the window portion 27 to
the biological tissue surface 21 to be ablated. Thus, FIGS. 3 and 4
illustrate two particular contact positions where the window
portion 27 may be configured to maintain contact for substantially
curvilinear tissue surfaces 21. Consequently, due to the proper
impedance matching between the medium of the insulator 31 and that
of the biological tissue, contact therebetween along the window
portion 27 is necessary to maintain the radiation efficiency of the
antenna.
[0052] As above-mentioned, a flexible shield device 30 extend
substantially along the length of the antenna substantially
parallel to the longitudinal axis of the antenna in a normal unbent
position (shown in solid lines in FIG. 2 and phantom lines in FIG.
5). The shield device 30 is formed and dimensioned to shield
selected surrounding areas radially about the antenna wire 28 from
the electric field radially generated therefrom, while reflecting
the field and permitting the passage of the field generally in a
predetermined direction toward the strategically located window
portion 27 of the insulator 31. As best viewed in FIGS. 2, 7 and 9,
the shield device 30 is preferably semi-cylindrical or
arcuate-shaped in the transverse cross-sectional dimension to
reflect the impinging field back toward the antenna thereof.
[0053] Tissue ablation can thus be more strategically controlled,
directed and performed without concern for undesirable ablation of
other adjacent tissues which may otherwise be within the
electromagnetic ablation range radially emanating from the antenna.
In other words, any other tissues surrounding the peripheral sides
of the antenna which are out of line of the window portion of the
cradle will not be subjected to the directed electric field and
thus not be ablated. This ablation instrument assembly is
particularly suitable for ablation procedures requiring accurate
tissue ablations such as those required in the MAZE III procedure
above-mentioned.
[0054] Briefly, it will be appreciated that the phrase "peripheral
area immediately surrounding the antenna" is defined as the
immediate radial transmission pattern of the antenna which is
within the electromagnetic ablation range thereof when the shield
assembly is absent.
[0055] The shield device 30 is preferably composed of a high
conductivity metal to provide superior microwave reflection. The
walls of the shield device 30, therefore, are substantially
impenetrable to the passage of microwaves emanating from the
antenna 28 to protect a backside of the antenna assembly from
microwave exposure. More specifically, when an incident
electromagnetic wave originating from the antenna reaches the
conductive shield device, a surface current is induced which in
turn generates a responsive electromagnetic field that will
interfere with that incident field. Consequently, this incident
electromagnetic field together with the responsive electromagnetic
field within the shield device 30 of the antenna assembly 26 cancel
and are thus negligible.
[0056] FIGS. 2 and 5 best illustrate that the shield device 30 is
preferably provided by a braided conductive mesh having a proximal
end conductively mounted to the distal portion of the outer
conductor of the coaxial cable. This conductive mesh is preferably
thin walled to minimize weight addition to the shield assembly yet
provide the appropriate microwave shielding properties, as well as
enable substantial flexibility of the shield device during bending
movement. One particularly suitable material is stainless steel,
for example, having mesh wires with a thickness in the range of
about 0.005 inches to about 0.010 inches, and more preferably about
0.007 inches.
[0057] As mentioned, an elongated microwave antenna normally emits
an electromagnetic field substantially radially perpendicular to
the antenna length which is fairly well constrained to the length
of the antenna wire regardless of the power used. However, to
assure proper shielding, the longitudinal length of the shield may
be longer than and extend beyond the distal and proximal ends of
the antenna wire 28.
[0058] To maintain the electromagnetic field characteristics of the
antenna during operative use, even with a flexible antenna, it is
important to maintain the position of a transverse cross-sectional
segment of shield device 30 relative a corresponding transverse
cross-sectional segment of the antenna wire 28. Relative position
changes between the segments may alter the radiation pattern and
the radiation efficiency of the antenna. Accordingly, to stabilize
these transverse cross-sectional segments of the shield device
relative to the corresponding transverse cross-sectional segments
of the antenna wire 28, the antenna assembly 26 includes the
flexible insulator 31 preferably molded over and disposed between
the shield device 30 and the antenna wire 28.
[0059] The insulator 31 is preferably further molded to the distal
portion of the metallic tubular shaft, and is preferably
cylindrical shaped having an axis generally coaxial with that of
the shield device 30. The insulator 31 further performs the
function of decreasing the coupling between the antenna 28 and the
flexible shield device 30. Should the antenna 28 be too close to
the conductive shield device 30, a strong current may be induced at
the surface thereof. This surface current will increase the
resistive losses in the metal and the temperature of the cradle
device will increase. On the other hand, direct conductive contact
or substantially close contact of the antenna with the metallic
cradle device will cause the reflective cradle device to become
part of the radiative structure, and begin emitting electromagnetic
energy in all directions.
[0060] The insulator 31 is therefore preferably provided by a good,
low-loss dielectric material which is relatively unaffected by
microwave exposure, and thus capable of transmission of the
electromagnetic field therethrough. Moreover, the insulator
material preferably has a low water absorption so that it is not
itself heated by the microwaves. Finally, the insulation material
must be capable of substantial flexibility without fracturing or
breaking. Such materials include moldable TEFLON.RTM., silicone, or
polyethylene, polyimide, etc.
[0061] In the preferred embodiment, the insulator 31 defines an
elongated window portion 27 extending substantially adjacent and
parallel to the antenna wire 28. Thus, as shown in FIGS. 5 and 7-9,
a longitudinal axis of the antenna wire 28 is off-set from, but
parallel to, the longitudinal axis of insulator 31 in a direction
toward the window portion. This configuration positions the antenna
wire 28 actively in the window portion 27 to maximize exposure of
the targeted tissue to the microwaves generated by antenna, as well
as further space the antenna sufficiently away from the shield
device to prevent the above-mentioned electrical coupling.
[0062] In a normal unbent position of the antenna assembly 26
(shown in solid lines in FIG. 2 and phantom lines in FIG. 5), the
window portion 27 is substantially planar and rectangular in shape.
Upon bending thereof, however, the face of the window portion 27
can be manipulated to generally conform to the surface of the
tissue 22 to be ablated. Thus, a greater degree of contact of a
curvilinear surface 21 of a tissue 22 with full face of the window
portion 27 is enabled. The radiation pattern along the antenna,
therefore, will not be adversely changed and the antenna will
remain tuned, which increases the efficiency and the penetration
depth of the energy delivery into the tissue 22.
[0063] In accordance with the present invention, the window portion
27 is strategically sized and located relative the shield device to
direct a majority of the electromagnetic field generally in a
predetermined direction. As best viewed in FIGS. 2, 5 and 7, the
window portion 27 preferably extends longitudinally along the
insulator 31 in a direction substantially parallel to the
longitudinal axis thereof The length of the ablative radiation is
therefore generally constrained to the length of the antenna wire
28, and may be adjusted by either adjusting the length of the
antenna wire 28. To facilitate the coupling between the coaxial
cable and the antenna wire, the proximal end of the window portion
27 generally extends proximally a little longer than the proximal
end of the antenna 28 (about 2-5 mm). On the distal end, however,
the window portion 27 is configured to approximate the length of
the distal end of the shield device 30. Incidentally, as will be
described in greater detail below, the distal portion of the shield
device 30 extends well beyond the distal end of the antenna to
accommodate for bending of the antenna assembly 26.
[0064] FIGS. 7 and 9 best illustrate that the radiation pattern of
the electromagnetic field delivered from the window portion 27 may
extend radially from about 120.degree. to about 180.degree., and
most preferably extend radially about 180.degree., relative the
longitudinal axis of the insulator. Thus, a substantial portion of
the backside of the antenna is shielded from ablative exposure of
the microwaves radially generated by the antenna in directions
substantially perpendicular to the longitudinal axis thereof. The
circumferential dimension of window portion 27, hence, may vary
according to the breadth of the desired ablative exposure without
departing from the true spirit and nature of the present invention.
Moreover, while a small percentage of the electromagnetic field,
unshielded by the shield device, may be transmitted out of other
non-window portions of the insulator, a substantial majority will
be transmitted through the window portion. This is due to the
impedance matching characteristics which are turned to contact
between the tissue and the window portion.
[0065] Accordingly, the predetermined direction of the ablative
electromagnetic field radially generated from the antenna may be
substantially controlled by the circumferential opening dimension,
the length and the shape of the window portion 27. Manipulating the
shape of the antenna assembly 26 to conform the window portion
generally to the shape of the targeted tissue surface, and
positioning of window portion 27 in the desired direction for
contact with the tissue, thus, controls the direction of the tissue
ablation without subjecting the remaining peripheral area
immediately surrounding the antenna to the ablative electromagnetic
field.
[0066] In a preferred embodiment of the present invention, an
elongated, bendable, retaining member, generally designated 36, is
provided which is adapted for longitudinal coupling therealong to
the insulator 31. Once the window portion 27 is manually
manipulated for conformance to the biological tissue surface to be
ablated, this bendable retaining member 36 functions to retain the
insulator 31 in the one position for operative ablation thereof. As
best viewed in FIGS. 2, 5 and 7, the retaining member 36 is
preferably positioned behind the shield device 30 so as to be
shielded from exposure to the microwaves transmitted by antenna 28.
The retaining member preferably extends along the full length of
the shield device in a direction substantially parallel to the
longitudinal axis of the insulator 31.
[0067] This retaining member 36 must be a ductile or bendable
material, yet provide sufficient rigidity after being bent, to
resist the resiliency of the insulator to move from a bent position
(e.g., FIGS. 3 and 4) back toward the normal position (FIG. 2).
Moreover, both the retaining member 36 and the antenna wire 28 must
not be composed of a material too rigid or brittle as to fracture
or easily fatigue tear during repeated bending movement. Such
materials for the retaining member include tin or silver plated
copper or brass, having a diameter in the range of about 0.020 inch
to about 0.050 inches.
[0068] In a preferred form, retaining member 36 is molded or
embedded in the moldable insulator. This facilitates protection of
the retaining member 36 from contact with corrosive elements during
use. It will be appreciated, however, that retaining member 36
could be coupled to the exterior of the insulator longitudinally
therealong.
[0069] As shown in FIGS. 2 and 5, a proximal portion of the
retaining member 36 is positioned adjacent and substantially
parallel to a distal portion of the shaft 32. Preferably, the
proximal portion of the retaining member 36 is rigidly affixed to
the distal portion of the shaft 32 at a coupling portion 41 thereof
to provide relative stability between the shaft and the antenna
assembly 26 during bending movement. While such rigid attachment is
preferably performed through soldering, brazing, or ultrasonic
welding, the coupling could be provided by a rigid, non-conductive
adhesive or the like.
[0070] Preferably, the retaining member 36 is cylindrical-shaped,
having a substantially uniform transverse cross-sectional
dimension. It will be appreciated, however, that other geometric
transverse cross-sectional dimensions may apply such as a
rectangular cross-section. As shown in FIG. 9, this retaining
member 36 is in the form of a thin metallic strip embedded atop the
shield device 30. In this configuration, due to the relative
orientation of the antenna and the shield device 30 bending in
vertical direction, will be permitted while movement in a lateral
side-to-side direction will be resisted. Moreover, the retaining
member 36 may not be uniform in transverse cross-sectional
dimension to permit varied rigidity, and thus variable bending
characteristics, longitudinally along the antenna assembly.
[0071] In another alternative configuration, the retaining member
36 may be incorporated into the shield device or the antenna itself
In either of these configurations, or a combination thereof, the
shield device and/or the antenna must provide sufficient rigidity
to resist the resiliency of the insulator 31 to move from the bent
position (e.g., FIGS. 3 and 4) back toward the normal position
(FIG. 2).
[0072] In accordance with the present invention, the insulator 31
defines a receiving passage 37 formed for sliding receipt of the
antenna wire 28 longitudinally therein during manipulative bending
of the antenna assembly 26. As best viewed in FIGS. 5 and 6, this
sliding reciprocation enables bending of the antenna assembly 26
without subjecting the antenna 28 to compression or distension
during bending movement of the antenna which may ultimately fatigue
or damage the antenna, or adversely alter the integrity of the
electromagnetic field.
[0073] Such displacement is caused by the bending movement of the
antenna assembly pivotally about the retaining member 36. For
example, as shown in FIG. 7, during concave bending movement (FIGS.
2 and 5) or convex bending movement (FIG. 8) of the window portion
27 of the antenna assembly 26, the pivotal or bending movement will
occur about the longitudinal axis of the retaining member 36.
Accordingly, upon concave bending movement of the window portion 27
(FIGS. 2 and 5), the length of the receiving passage 37 shortens.
This is due to the fact that the insulator 31 compresses at this
portion thereof since the receiving passage 37 is positioned along
the radial interior of the retaining member. Essentially, the
radius of curvature of the receiving passage 37 is now less than
the radius of curvature of the outer retaining member 36. However,
the longitudinal length of the antenna 28 slideably retained in the
receiving passage 37 will remain constant and thus slide distally
into the receiving passage.
[0074] In contrast, upon convex bending movement of the window
portion 27 (FIG. 8), the length of the receiving passage 37
distends since the receiving passage 37 will be positioned on the
radial exterior of the retaining member 36. In this situation, the
radius of curvature of the receiving passage 37 will now be greater
than the radius of curvature of the outer retaining member 36.
Consequently, the distal end of the antenna slides proximally in
the receiving passage 37.
[0075] Preferably, the diameter of the receiving passage is about
5% to about 10% larger than that of the antenna wire 28. This
assure uninterfered sliding reciprocation therein during bending
movement of the antenna assembly 26. Moreover, the proximal end of
the receiving passage 37 need not commence at the proximal end of
the antenna wire 28. For instance, since the displacement at the
proximal portion of the antenna wire 28 is substantially less than
the displacement of the antenna wire 28 at a distal portion
thereof, the proximal end of the receiving passage 37 may commence
about 30% to about 80% from the proximal end of the antenna wire
28. The distal end of the receiving passage 37, on the other hand,
preferably extends about 30% to about 40% past the distal end of
the antenna wire 28 when the antenna assembly is in the normal
unbent position. As above-indicated, this space in the receiving
passage 37 beyond the distal end of the antenna 28 enables
reciprocal displacement thereof during concave bending
movement.
[0076] To assure that the distal end of the antenna 28 does not
pierce through the relatively soft, flexible insulating material of
the insulator 31, during bending movement, the tip portion thereof
may be rounded or blunted. In another configuration, the receiving
passage 37 may be completely or partially lined with a flexible
tube device 38 (FIGS. 2 and 5-7) having a bore 39 formed and
dimensioned for sliding longitudinal reciprocation of the antenna
distal end therein. The walls of tube device 38 are preferably
relatively thin for substantial flexibility thereof, yet provide
substantially more resistance to piercing by the distal end of the
antenna 28. Moreover, the material composition of the tube device
must have a low loss-tangent and low water absorption so that it is
not itself affected by exposure to the microwaves. Such materials
include moldable TEFLON.RTM. and polyimide, polyethylene, etc.
[0077] Referring now to FIGS. 8 and 9, a restraining sleeve,
generally designated 40, is provided which substantially prevents
convex bending movement of the retaining member 36 at the proximal
portion thereof. At this coupling portion 41, where the retaining
member 36 and the shield device 30 are mounted to the distal
portion of the shaft 32, repeated reciprocal bending in the convex
direction may cause substantial fatigue of the bond, and ultimately
fracture. The restraining sleeve 40, thus, preferably extends
longitudinally over the coupling portion 41 to maintain the
integrity of the coupling by preventing strains thereon.
Essentially, such convex bending movement will then commence at a
portion of the antenna assembly 26 distal to the coupling
portion.
[0078] The restraining sleeve 40 includes an arcuate shaped base
portion 42 removably mounted to and substantially conforming with
the circumferential cross-sectional dimension of the proximal
portion of the insulator 31 (FIG. 9). The base portion 42 is
rigidly affixed to the antenna assembly and/or the shaft to provide
protective stability over the coupling portion 41.
[0079] A finger portion 43 extends distally from the base portion
42 in a manner delaying the commencement of convex bending of the
antenna assembly to a position past the distal end of the finger
portion 43. Consequently, any strain upon the coupling portion 41
caused by convex bending movement of the antenna assembly is
eliminated.
[0080] In another embodiment of the present invention, the
microwave ablation instrument 20 includes an elongated grip member
45 having a distal grip portion 46 and an opposite proximal portion
47 coupled to a distal portion of the antenna assembly 26. As best
illustrated in FIGS. 10 and 11, the grip member 45 and the handle
member 23 of the ablation instrument 20 cooperates to selectively
bend the flexible antenna assembly 26 and selectively urge the
window portion 27 into abutting contact with the biological tissue
surface to be ablated. For example, this application is
particularly useful when the targeted tissue surface is located at
a rear portion of an organ or the like. FIG. 11 illustrates that,
during open procedures, the elongated grip member 45 may be passed
around the backside of the organ until the window portion 27 of the
antenna assembly is moved into abutting contact with the targeted
tissue surface 21. Subsequently, the handle member 23 at one end of
the ablation instrument, and the grip member 45 at the other end
thereof are manually gripped and manipulated to urge the window
portion 27 into ablative contact with the targeted tissue
surface.
[0081] This configuration is beneficial in that the window portion
27 is adapted to conform to the tissue surface upon manual pulling
of the grip member 45 and the handle member 23. As the flexible
antenna assembly 26 contacts the targeted tissue 22, the window
portion 27 thereof is caused to conform to the periphery of the
tissue surface. Continued manipulation of the grip member 45 and
the handle member 23 further urge bending contact. Accordingly,
this embodiment will not require a retaining member for shape
retention.
[0082] The elongated grip member 45 is provided by a substantially
flexible rod having a diameter smaller than the diameter of the
insulator 31. Such flexibility enables manipulation of the rod to
position its distal end behind a targeted biological tissue 22.
Once the distal grip portion 46 of the grip member 45 is strung
underneath organ 22 or the like, the distal grip portion 46 may be
gripped to pull the antenna assembly 26 behind the organ 22 for
ablation of the targeted tissue.
[0083] It will be appreciated, however, that the rod 45 should not
be substantially more flexible than that of the antenna assembly.
This assures that the window portion 27 of the insulator 31 will be
caused to conform to the curvilinear surface of the targeted tissue
22, as opposed to the mere bending of the flexible rod 45. Such
materials for the flexible rod 45 includes Pebax filled with
silicone and polyethylene, polyurethane, etc.
[0084] To mount flexible rod 48 to the ablation instrument 20, the
antenna assembly 26 includes a mounting portion 48 extending
distally from the insulator 31. This mounting portion 48 is
preferably integrally formed with the insulator 31 and is of a
sufficient length to enable the proximal portion of flexible rod 45
to be integrally molded thereto without interference with the
shield device 30 and/or the antenna wire 28.
[0085] In the preferred embodiment, a longitudinal axis of the
flexible rod 45 is off-set from the longitudinal axis of the
insulator 31 in the direction toward the window portion 27. As
viewed in FIG. 11, this off-set preferably positions the
longitudinal axis of the flexible rod proximately in co-axial
alignment with the antenna. This arrangement facilitates alignment
of the window portion 27 against the targeted tissue 22 as the grip
member 45 and the handle member 23 are manipulated to conform the
window portion 27 with and against the tissue surface 21. Due to
the off-set nature of the flexible rod 45, when the antenna
assembly and the rod are tightened around the biological tissue 22,
the antenna assembly 26 is caused to rotate about its longitudinal
axis toward an orientation of least resistance (i.e., a position
where the flexible rod 45 is closest to the biological tissue
22).
[0086] Additionally, as shown in FIG. 12, the handle member 23 may
be elongated and substantially flexible in a manner similar to the
elongated grip member 45. In another embodiment of the present
invention, the handle member 23 includes a proximal grip portion 50
and an opposite distal portion 51 coupled to a proximal portion of
the antenna assembly 26. Thus, the flexible handle member 23 and
the flexible grip member 45 cooperate to selectively bend the
flexible antenna assembly 26 and selectively urge the window
portion 27 into abutting contact with the biological tissue surface
to be ablated. As another example, this application is particularly
useful for creating long continuous linear lesions (E.g., to
enclose the pulmonary veins when treating atrial fibrillation or
the like). The flexible handle member 23 at one end of the ablation
instrument, and the flexible grip member 45 at the other end
thereof are manually gripped and manipulated to urge the window
portion 27 into ablative contact with the targeted tissue surface.
This can be performed by simply sliding the antenna assembly 26 by
pulling either the flexible grip member 45 or the flexible handle
member 23 to position the widow portion 27 against the tissue.
Moreover, this can be used to slightly overlap the lesions to
generate a long continuous lesion without gaps. easily end the
targeted tissue surface is located at a rear portion of an organ or
the like.
[0087] The elongated flexible handle member 23 is preferably
provided by a substantially flexible coaxial cable appropriately
coupled to the transmission line. In some instances, the handle
member 23 may simply be an extension of the transmission line.
[0088] Preferably, the flexible coaxial cable handle member 23 is
covered by a plastic sleeve such as Pebax, PE Polyolifin, etc. Such
dual flexibility enables increased manipulation of both the
gripping member and the handle member. To mount flexible handle
member 23 to the antenna assembly 26, the distal portion thereof is
preferably integrally formed with the insulator 31
[0089] Similar to the gripping member 45, a longitudinal axis of
the flexible handle member 23 is off-set from the longitudinal axis
of the insulator 31 in the direction toward the window portion 27.
As viewed in FIG. 12, this off-set, together with the same off-set
of the gripping member, preferably positions the longitudinal axis
of the handle member proximately in co-axial alignment with the
antenna. This arrangement facilitates alignment of the window
portion 27 against the targeted tissue 22 as the grip member 45 and
the handle member 23 are manipulated to conform the window portion
27 with and against the tissue surface 21. Due to the off-set
nature of the flexible rod 45, when the antenna assembly and the
rod are tightened around the biological tissue 22, the antenna
assembly 26 is caused to rotate about its longitudinal axis toward
an orientation of least resistance (i.e., a position where the
flexible rod 45 is closest to the biological tissue 22).
[0090] In still another aspect of the present invention, a method
is provided for treatment of a heart including providing a
microwave ablation instrument 20 having a flexible antenna assembly
26 defining a window portion 27 enabling the transmission of a
directed electric field therethrough in a predetermined direction.
By selectively bending the flexible antenna assembly 26 to one of a
plurality of contact positions, the window portion 27 can be
generally conformed to the shape of the targeted biological tissue
22 surface to be ablated. The method further includes manipulating
the ablation instrument 20 to strategically position the conformed
window portion 27 into contact with the targeted biological tissue
surface 21; and generating the electric field sufficiently strong
to cause tissue ablation to the targeted biological tissue surface
21.
[0091] More preferably, this method is directed toward medically
refractory atrial fibrillation of the heart. By repeating the
bending, manipulating and generating events, a plurality of
strategically positioned ablation lesions can be accurately formed
in the heart. Collectively, these lesions are formed to create a
predetermined conduction pathway between a sinoatrial node and an
atrioventricular node of the heart, or to divide the left and/or
right atrium in order to avoid any reentry circuits.
[0092] These techniques may be preformed while the heart remains
beating, such as in a minimally invasive heart procedure, while the
heart is temporarily arrested, such as when the heart is stabilized
for about 20 or 30 seconds during a cabbage procedure, or while the
heart is arrested, such as in an open heart surgery. Moreover,
these procedures may be applied to ablate the endocardium as well
as the epicardium in order to treat atrial fibrillation. throughout
the bending, manipulating and generating events. Moreover, the
repeated events of bending, manipulating and generating are applied
in a manner isolating the pulmonary veins from the epicardium of
the heart.
[0093] Although only a few embodiments of the present inventions
have been described in detail, it should be understood that the
present inventions may be embodied in many other specific forms
without departing from the spirit or scope of the inventions.
Particularly, the invention has been described in terms of a
microwave ablation instrument for cardiac applications, however, it
should be appreciated that the described small diameter microwave
ablation instrument could be used for a wide variety of non-cardiac
ablation applications as well.
[0094] It should also be appreciated that the microwave antenna
need not be a linear antenna. The concepts of the present invention
may be applied to any kind of radiative structure, such as a
helical dipole antenna, a printed antenna, a slow wave antenna, a
lossy transmission antenna or the like. Furthermore, it should be
appreciated that the transmission line does not absolutely have to
be a coaxial cable. For example, the transmission line may be
provided by a stripline, a microstrip line, a coplanar line, or the
like.
* * * * *