U.S. patent application number 14/194570 was filed with the patent office on 2014-09-18 for medical systems and methods for modulating nerves.
This patent application is currently assigned to Boston Scientific Scimed, Inc.. The applicant listed for this patent is Boston Scientific Scimed, Inc.. Invention is credited to HONG CAO, HUISUN WANG.
Application Number | 20140276755 14/194570 |
Document ID | / |
Family ID | 50290307 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140276755 |
Kind Code |
A1 |
CAO; HONG ; et al. |
September 18, 2014 |
MEDICAL SYSTEMS AND METHODS FOR MODULATING NERVES
Abstract
Medical devices and methods for making and using medical devices
are disclosed. An example medical device may include a medical
device for modulating nerves. The medical device may include an
elongate shaft having a distal region. Two or more electrodes may
be positioned adjacent to the distal end region of the elongate
shaft. A control unit may supply power and control algorithms to
the electrodes. The control algorithm may allow the electrodes to
be operated simultaneously and individually.
Inventors: |
CAO; HONG; (MAPLE GROVE,
MN) ; WANG; HUISUN; (MAPLE GROVE, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boston Scientific Scimed, Inc. |
Maple Grove |
MN |
US |
|
|
Assignee: |
Boston Scientific Scimed,
Inc.
Maple Grove
MN
|
Family ID: |
50290307 |
Appl. No.: |
14/194570 |
Filed: |
February 28, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61777744 |
Mar 12, 2013 |
|
|
|
Current U.S.
Class: |
606/33 ; 607/101;
607/102 |
Current CPC
Class: |
A61B 18/1492 20130101;
A61B 18/1206 20130101; A61B 2018/00577 20130101; A61B 2018/1467
20130101; A61B 18/1815 20130101; A61B 18/1233 20130101; A61B
2018/00821 20130101; A61N 5/00 20130101; A61B 2090/3966 20160201;
A61B 2090/065 20160201; A61B 2018/00375 20130101; A61B 2018/00827
20130101; A61B 2018/00815 20130101; A61B 2018/141 20130101; A61B
2018/00702 20130101; A61B 2018/00547 20130101; A61B 18/16 20130101;
A61B 2018/00434 20130101; A61B 2018/00875 20130101; A61B 2018/00642
20130101 |
Class at
Publication: |
606/33 ; 607/101;
607/102 |
International
Class: |
A61B 18/18 20060101
A61B018/18; A61N 5/00 20060101 A61N005/00 |
Claims
1. A nerve modulation system, comprising: an elongate member having
a proximal end and a distal end region; two or more electrodes
positioned adjacent to the distal end region of the elongate
member; a ground pad; a control unit in electrical communication
with each of the two or more electrodes, the control unit
positioned adjacent to the proximal end of the elongate shaft; an
electrical conductor extending between each electrode and the
control unit, each electrical conductor comprising an electrical
switch and a current sensing circuit; wherein the control unit
includes a control algorithm configured to selectively control
power applied to the two or more electrodes.
2. The nerve modulation system of claim 1, wherein the control unit
applies power to the two or more electrodes simultaneously.
3. The nerve modulation system of claim 1 wherein the control unit
applies power to fewer than all of the two or more electrodes.
4. The nerve modulation system of claim 1, further comprising a
temperature sensor disposed adjacent to each of the two or more
electrodes.
5. The nerve modulation system of claim 1, wherein the control unit
is configured to monitor electrical parameters of each circuit
created by the control unit, electrode and ground pad.
6. The nerve modulation system of claim 5, wherein the control unit
is configured to terminate ablation upon reaching a predetermined
temperature or electrical parameter.
7. A method for performing nerve modulation, the method comprising:
providing a nerve modulation system, the nerve modulation system
comprising: an elongate member having a proximal end and a distal
end region; two or more electrodes positioned adjacent to the
distal end region of the elongate shaft; a ground pad; and a
control unit positioned adjacent to the proximal end of the
elongate member; advancing the nerve modulation system through a
lumen such that the two or more electrodes are adjacent to a target
region; applying power to the two or more electrodes; measuring a
temperature adjacent to each of the two or more electrodes; and
monitoring an impedance between each of the two or more electrodes
and the ground pad; wherein the control unit includes a control
algorithm for controlling a power level and a duration power is
applied to each of the two or more electrodes.
8. The method of claim 7, wherein applying power to the two or more
electrodes comprises applying power to the two or more electrodes
simultaneously.
9. The method of claim 7, wherein applying power to the two or more
electrodes comprises applying power to less than all of the two or
more electrodes.
10. The method of claim 7, wherein applying power to the two or
more electrodes comprises selectively applying power to the two or
more electrodes simultaneously and applying power to less than all
of the two or more electrodes.
11. The method of claim 10, wherein the control algorithm is
configured to discontinue applying power to at least one of the two
or more electrodes when the at least one electrode achieves a
predetermined modulation criteria.
12. The method of claim 11, wherein the predetermined modulation
criteria comprises measuring a predetermined temperature for a
predetermined time period or a predetermined drop in monitored
impedance.
13. A method for performing nerve modulation, the method
comprising: providing a nerve modulation system, the nerve
modulation system comprising: an elongate member having a proximal
end and a distal end region; two or more electrodes positioned
adjacent to the distal end region of the elongate member; at least
one temperature sensor positioned adjacent to each of the two or
more electrodes; a ground pad; and a control unit including a
controller and a radiofrequency generator positioned adjacent to
the proximal end of the elongate member; advancing the nerve
modulation system through a lumen such that the two or more
electrodes are adjacent to a target region; applying power at a
predetermined maximum power to the two or more electrodes;
measuring a temperature adjacent to each of the two or more
electrodes; and monitoring an impedance between each of the two or
more electrodes and the ground pad; wherein the control unit
includes a control algorithm for controlling a power level and a
duration power is applied to each of the two or more electrodes and
discontinuing power to at least one of the two or more electrodes
when the at least one electrode achieves a predetermined modulation
criteria.
14. The method of claim 13, wherein the control unit is configured
to reduce the power applied to the two or more electrodes to a
power less than the predetermined maximum power if a temperature
adjacent to at least one of the two or more electrodes is greater
than a predetermined maximum temperature.
15. The method of claim 14, wherein the predetermined modulation
criteria comprises measuring a predetermined temperature for a
predetermined time period.
16. The method of claim 15, wherein the predetermined temperature
is at least 55.degree. C.
17. The method of claim 15, wherein the predetermined time period
is at least 25 seconds.
18. The method of claim 13, wherein the predetermined modulation
criteria comprising a predetermined drop in monitored
impedance.
19. The method of claim 18, wherein the predetermined drop in
monitored impedance is at least 20%.
20. The method of claim 13, wherein the control unit is configured
to reduce the power applied to the two or more electrodes to a
power less than the predetermined maximum power once one or more of
the two or more electrodes have achieved the predetermined
modulation criteria.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
to U.S. Provisional Application Ser. No. 61/777,744, filed Mar. 12,
2013, the entirety of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present disclosure pertains to medical devices, and
methods for using medical devices. More particularly, the present
disclosure pertains to elongated medical devices for modulating
nerves.
BACKGROUND
[0003] A wide variety of intracorporeal medical devices have been
developed for medical use, for example, intravascular use. Some of
these devices include guidewires, catheters, and the like. These
devices are manufactured by any one of a variety of different
manufacturing methods and may be used according to any one of a
variety of methods. Of the known medical devices and methods, each
has certain advantages and disadvantages. There is an ongoing need
to provide alternative medical devices as well as alternative
methods for manufacturing and using medical devices.
BRIEF SUMMARY
[0004] This disclosure provides design, material, manufacturing
method, and use alternatives for medical devices. An example
medical device may include a medical device for modulating nerves.
The medical device may include an elongated shaft having a proximal
end and a distal end. Two or more electrodes may be positioned
adjacent to the distal end of the elongate shaft. The medical
device may further include a ground pad and a control unit in
electrical communication with each of the two or more electrodes.
The control unit may be positioned adjacent to the proximal end of
the elongate shaft and may be configured to selectively control
power applied to the electrodes. The control unit may allow the
electrodes to be simultaneously powered or powered individually, as
desired.
[0005] An example use of an example medical device may include a
method for performing nerve modulation. The method may include
providing a nerve modulation system. The nerve modulation system
may include an elongate shaft having a proximal end and a distal
end and two or more electrodes positioned adjacent to the distal
end of the elongate shaft. The nerve modulation system may further
include at least one temperature sensor positioned adjacent to each
of the two or more electrodes and a ground pad. A control unit
including a controller and a radiofrequency generator may be
positioned adjacent to the proximal end of the elongate shaft. The
nerve modulation system may be advanced through a lumen such that
the two or more electrodes are adjacent to a target region. Power
may then be applied at a predetermined maximum power to the two or
more electrodes. A temperature adjacent to each of the two or more
electrodes may be measured. The impedance between each of the two
or more electrodes and the ground pad may also be monitored. The
control unit may include a control algorithm for controlling a
power level and a duration power is applied to each of the two or
more electrodes and discontinuing power to at least one of the two
or more electrodes when the at least one electrode achieves a
predetermined modulation criteria.
[0006] The above summary of some embodiments is not intended to
describe each disclosed embodiment or every implementation of the
present disclosure. The Figures, and Detailed Description, which
follow, more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The disclosure may be more completely understood in
consideration of the following detailed description in connection
with the accompanying drawings, in which:
[0008] FIG. 1 is a schematic view illustrating a renal nerve
modulation system in situ;
[0009] FIG. 2 is an illustrative multi-electrode nerve modulation
system;
[0010] FIG. 3 is a schematic of the electrical connections of an
illustrative renal nerve modulation system;
[0011] FIG. 4 is a flow chart of an illustrative method of
operating a renal nerve modulation system; and
[0012] FIG. 5 is another illustrative multi-electrode nerve
modulation system; and
[0013] FIG. 6 is another illustrative multi-electrode nerve
modulation system.
[0014] While the disclosure is amenable to various modifications
and alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
disclosure.
DETAILED DESCRIPTION
[0015] For the following defined terms, these definitions shall be
applied, unless a different definition is given in the claims or
elsewhere in this specification.
[0016] All numeric values are herein assumed to be modified by the
term "about," whether or not explicitly indicated. The term "about"
generally refers to a range of numbers that one of skill in the art
would consider equivalent to the recited value (i.e., having the
same function or result). In many instances, the terms "about" may
include numbers that are rounded to the nearest significant
figure.
[0017] The recitation of numerical ranges by endpoints includes all
numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,
3.80, 4, and 5).
[0018] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the content clearly dictates otherwise. As used in this
specification and the appended claims, the term "or" is generally
employed in its sense including "and/or" unless the content clearly
dictates otherwise.
[0019] It is noted that references in the specification to "an
embodiment", "some embodiments", "other embodiments", etc.,
indicate that the embodiment described may include one or more
particular features, structures, and/or characteristics. However,
such recitations do not necessarily mean that all embodiments
include the particular features, structures, and/or
characteristics. Additionally, when particular features,
structures, and/or characteristics are described in connection with
one embodiment, it should be understood that such features,
structures, and/or characteristics may also be used in connection
with other embodiments whether or not explicitly described unless
clearly stated to the contrary.
[0020] The following detailed description should be read with
reference to the drawings in which similar elements in different
drawings are numbered the same. The drawings, which are not
necessarily to scale, depict illustrative embodiments and are not
intended to limit the scope of the invention.
[0021] Certain treatments require the temporary or permanent
interruption or modification of select nerve function. One example
treatment is renal nerve ablation, which is sometimes used to treat
conditions related to hypertension, congestive heart failure,
diabetes, or other conditions impacted by high blood pressure or
salt retention. The kidneys produce a sympathetic response to
congestive heart failure, which, among other effects, increases the
undesired retention of water and/or sodium. Ablating some of the
nerves running to the kidneys may reduce or eliminate this
sympathetic function, which may provide a corresponding reduction
in the associated undesired symptoms.
[0022] While the devices and methods described herein are discussed
relative to renal nerve modulation, it is contemplated that the
devices and methods may be used in other treatment locations and/or
applications where nerve modulation and/or other tissue modulation
including heating, activation, blocking, disrupting, or ablation
are desired, such as, but not limited to: blood vessels, urinary
vessels, or in other tissues via trocar and cannula access. For
example, the devices and methods described herein can be applied to
hyperplastic tissue ablation, cardiac ablation, pulmonary vein
isolation, tumor ablation, benign prostatic hyperplasia therapy,
nerve excitation or blocking or ablation, modulation of muscle
activity, hyperthermia or other warming of tissues, etc. In some
instances, it may be desirable to ablate perivascular renal nerves
with radiofrequency ablation.
[0023] Some ablation devices may be provided with multiple
electrodes or modulation elements. Multi-electrode catheters may be
powered such that all electrodes are activated simultaneously
(single-shot) or the electrodes are activated sequentially one
after another (multi-shot). In a single-shot application,
radiofrequency (RF) power may be delivered to all of the electrodes
at the same time. It is contemplated that in a single-shot
application, the electrodes may also be directly connected on one
another. A single-shot device may treat each electrode equally and
thus cannot adjust power to specific electrodes to address issues
such as electrode-to-tissue contact or underlying tissue structure
and/or properties. Multi-shot devices may deliver RF power to one
electrode at a time and may generate lesions sequentially. This may
take longer to complete an ablation procedure than a single-shot
device and may lengthen the procedure time. Further, while an RF
generator may be designed to have multiple channels, each
configured to power an individual electrode, there may be
challenges to separating the channels in frequency or interference
of electrical current distribution when all of the channels are
powered simultaneously. It may be desirable to have a device which
can perform ablation in both a single-shot mode and a sequential
mode without the use of separate channels.
[0024] FIG. 1 is a schematic view of an illustrative renal nerve
modulation system in situ. System 10 may include one or more
conductive element(s) 16 for providing power to a renal ablation
system including a renal nerve modulation device 12 and,
optionally, within a delivery sheath or guide catheter 14. A
proximal end of conductive element(s) 16 may be connected to a
control and power unit 18, which may supply the appropriate
electrical energy to activate one or more electrodes disposed at or
near a distal end of the renal nerve modulation device 12. In
addition, control and power unit 18 may also be utilized to
supply/receive the appropriate electrical energy and/or signal to
activate one or more sensors disposed at or near a distal end of
the renal nerve modulation device 12. When suitably activated, the
electrodes are capable of ablating tissue as described below and
the sensors may be used to sense desired physical and/or biological
parameters. The terms electrode and electrodes may be considered to
be equivalent to elements capable of ablating adjacent tissue in
the disclosure which follows. In some instances, return electrode
patches 20 may be supplied on the legs or at another conventional
location on the patient's body to complete the circuit. A proximal
hub (not illustrated) having ports for a guidewire, an inflation
lumen and a return lumen may also be included.
[0025] The control and power unit 18 may include monitoring
elements to monitor parameters such as power, voltage, pulse size,
temperature, force, contact, pressure, impedance and/or shape and
other suitable parameters, with sensors mounted along renal nerve
modulation device 12, as well as suitable controls for performing
the desired procedure. In some embodiments, the power unit 18 may
control a radiofrequency (RF) electrode. The electrode may be
configured to operate at a suitable frequency and generate a
suitable signal. It is further contemplated that other ablation
devices may be used as desired, for example, but not limited to
resistance heating, ultrasound, microwave, and laser devices and
these devices may require that power be supplied by the power unit
18 in a different form.
[0026] FIG. 2 is an illustrative embodiment of a distal end of a
renal nerve modulation system 100 that may be utilized to ablate or
otherwise modulate renal nerves while minimizing damage to
surrounding tissue. As shown, the renal nerve modulation system 100
may be disposed within a body lumen or vessel 102 having a wall
104. The outer surface of the vessel wall 104 may be surrounded by
local body tissue. The local body tissue may comprise adventitia
and connective tissues, nerves, fat, fluid, etc. in addition to the
muscular vessel wall 104. The system 100 may include a catheter
shaft 106 having a distal end region 108. The catheter shaft 106
may extend proximally from the distal end region 108 to a proximal
end configured to remain outside of a patient's body. The proximal
end of the catheter shaft 106 may include a hub attached thereto
for connecting other treatment devices or providing a port for
facilitating other treatments. It is contemplated that the
stiffness of the catheter shaft 106 may be modified to form a
modulation system 100 for use in various vessel diameters and
various locations within the vascular tree. In some instances, the
proximal portion of the catheter shaft 106 may be flexible to
enable consistent torque transmission. The catheter shaft 106 may
further include one or more lumens extending therethrough. For
example, the catheter shaft 106 may include a guidewire lumen
and/or one or more auxiliary lumens. The lumens may have a variety
of configurations and/or arrangements. For example, the guidewire
lumen may extend the entire length of the catheter shaft 106 such
as in an over-the-wire catheter or may extend only along a distal
portion of the catheter shaft 106 such as in a single operator
exchange (SOE) catheter. These examples are not intended to be
limiting, but rather examples of some possible configurations.
While not explicitly shown, the modulation system 100 may further
include temperature sensors/wire, an infusion lumen, radiopaque
marker bands, fixed guidewire tip, a guidewire lumen, external
sheath and/or other components to facilitate the use and
advancement of the system 100 within the vasculature. It is further
contemplated that the modulation system 100 may include one or more
centering baskets, expandable framework, and/or expandable balloons
to center or otherwise position the modulation system 100 within
the body lumen 102. In some embodiments, the catheter shaft 106 may
include push and/or pull wires to deflect a distal end region 108
of the catheter shaft 106. For example, a push and/or pull wire may
be attached adjacent to the distal end of the catheter shaft 106
and then extend along an outer surface of the catheter shaft 106 or
along an interior passageway formed in the shaft 106 to a position
where it is accessible to a user. In other embodiments, the
catheter shaft 106 may incorporate a planar deflection mechanism,
such as a rib and spine mechanism. However, it is contemplated that
the catheter shaft 106 may be deflected in any desired manner.
[0027] The system 100 may include an elongate member 110 extending
within a lumen of the catheter shaft 106. In some instances, the
elongate member 110 may extend the entire length of the catheter
shaft 106 while in other instances, the elongate member 110 may be
attached to the catheter shaft 106 adjacent the distal end region
108 thereof. In some instances, the distal end region 112 of the
elongate member 110 may form a ring or lasso type structure. The
distal end region 112 may be configured to be advanced to the
desired treatment region within the catheter shaft 106. Once
adjacent to the desired treatment region, the distal end region 112
of the elongate member 110 may be advanced distally such that it
exits the lumen of the catheter shaft 106. In some instances, the
distal end region 112 may be configured to self-expand from a
collapsed position into a ring while in other instances, actuation
mechanisms may be employed to expand the distal end region 112. It
is contemplated that the distal end region 112 may form a unitary
structure with the elongate member 110. In other instances, the
distal end region 112 may be formed of a separate structure and
fixedly secured to the elongate member 110.
[0028] The system 100 may include one or more distal ablation
electrodes 114a, 114b, 114c, 114d (collectively 114) positioned
adjacent the distal end region 112 of the elongate member 110.
While the ablation electrodes 114 are described as radiofrequency
electrodes, it is contemplated that other methods and devices for
raising the temperature of the nerves may be used, such as, but not
limited to: ultrasound, microwave, or other acoustic, optical,
electrical current, direct contact heating, or other heating. While
the system 100 is illustrated as including four ablation electrodes
114, it is contemplated that the modulation system 100 may include
any number of ablation electrodes 114 desired, such as, but not
limited to, one, two, three, or more. The ablation electrodes 114
may be longitudinally and/or radially and/or circumferentially
spaced as desired. The ablation electrodes 114 may be spaced about
the distal end region 112, although this is not required. In some
instances, the electrodes 114 may be positioned about the distal
end region 112 such that not all of the electrodes 114 contact the
vessel wall 104 simultaneously when the distal end region 112 is in
the expanded state. In other instances, the electrodes 114 may be
arranged such that all of the electrodes 114 are configured to
contact the vessel wall 104 simultaneously when the distal end
region 112 is in the expanded state.
[0029] In some embodiments, the electrodes 114 may include wire
wrapped coils, generally solid shapes, ball-type electrodes, etc.
In some embodiments, the ablation electrodes 114 may be formed of a
separate structure and attached to the distal end region 112. For
example, the ablation electrodes 114 may be machined or stamped
from a monolithic piece of material and subsequently bonded or
otherwise attached to the distal end region 112. In other
embodiments, the ablation electrodes 114 may be formed directly on
the surface of the distal end region 112. For example, the ablation
electrodes 114 may be plated, printed, or otherwise deposited on
the surface. It is contemplated that the ablation electrodes 114
may take any shape desired, such as, but not limited to, square,
rectangular, circular, elliptical, etc. In some instances, the
ablation electrodes 114 may be a radiopaque marker band. The
ablation electrodes 114 may be formed from any suitable material
such as, but not limited to, platinum, gold, stainless steel,
cobalt alloys, or other non-oxidizing materials. In some instances,
titanium, tantalum, or tungsten may be used.
[0030] While not explicitly shown, the ablation electrodes 114 may
also include other structures and/or features associated typically
associated with ablation (e.g., thermal ablation) such as a
temperature monitoring member, which may take the form of a
thermocouple or thermistor. In at least some embodiments, a
thermistor including two thermistor wires may be disposed adjacent
to one or more of the ablation electrodes 114. In some embodiments,
the wires are not physically connected to ablation electrodes
114.
[0031] The modulation system 100 may be advanced through the
vasculature in any manner known in the art. For example, system 100
may include a guidewire lumen to allow the system 100 to be
advanced over a previously located guidewire. In some embodiments,
the modulation system 100 may be advanced, or partially advanced,
within a guide catheter such as the guide catheter 16 shown in FIG.
1. Once the ablation electrodes 114 of the modulation system 100
have been placed adjacent to the desired treatment area,
positioning mechanisms may be deployed, if so provided. As
discussed above, in some embodiments, the catheter shaft 106 and/or
elongate member 110 may include push and/or pull wires to deflect a
distal end region 108 of the catheter shaft 106 and/or a distal end
region 112 of the elongate member 110. In some instances, the
modulation system 100 may be structured such that an operator may
have the ability to deflect the catheter shaft 106 and/or elongate
member 110 such that the force with which the ablation electrodes
114 contact the vessel wall 104 may be controlled.
[0032] In some instances, multiple treatments may be used to
achieve the desired tissue modulation. In some instances, the
catheter shaft 106 and/or elongate member 110 may be rotated and
additional ablation can be performed at multiple locations around
the circumference of the vessel 102. The number of times the
catheter shaft 106 and/or elongate member 110 is rotated at a given
longitudinal location may be determined by the number and size of
the ablation electrodes 114 on the distal end region 112. Once a
particular location has been ablated, it may be desirable to
perform further ablation procedures at different longitudinal
locations. If necessary, the catheter shaft 106 and/or elongate
member 110 may be rotated to perform ablation around the
circumference of the vessel 102 at each longitudinal location. This
process may be repeated at any number of longitudinal locations
desired. In some instances, the treatment may be performed in a
helical pattern such that each treatment region is longitudinally
and radially spaced from the adjacent treatment region.
[0033] Turning now to FIG. 3, the ablation electrodes 114 may be
connected to a control unit 120 or to separate control units by
electrical conductors 126a, 126b, 126c, 126d (collectively 126).
While the electrical conductors 126 are illustrated as connecting
to the control unit 120 by a single line, it is contemplated that
the conductors 126a, 126b, 126c, 126d may each be separately
connected to the control unit 120, if so desired. Control unit 120
may provide power for operating the electrodes 114 as well as
provide control logic for controlling the energy supplied to the
electrodes 114. In some instances, an RF generator and a control
unit may be supplied separately. As will be explained in more
detail below, the control unit 120 may apply power to all
electrodes 114 simultaneously with a single RF power source at the
beginning of the ablation and switch on/off each electrode 114
based on ablation response. It is further contemplated that power
may be delivered to a specific electrode or electrodes if so
desired. Due to the nature of renal denervation, each ablation
electrode 114 may require a small amount of power, for example,
less than 10 Watts (W). A common RF generator design may have a
maximum output of 50 to 75 W without any technical issues.
[0034] The first electrical conductor 126a may be provided with an
electrical switch 118a and a current sensing circuit 116a. The
electrical switch 118a may be selectively opened and closed to
complete the electrical circuit. The current sensing circuit 116a
may include a small value resistor (such as, but not limited to 1
ohm) and one or more amplifiers. Another example of a current
sensing circuit may include a current sensing coil and one or more
amplifiers. The current sensing circuit may measure the current to
the electrode 114a and may also be used to calculate the impedance
between the electrode 114a and the ground pad electrode 122. The
calculated impedance may be used as a contact indicator (for
example, whether or not the electrode 114a is contacting the vessel
wall 104) as well as an indication of ablation progress. In
general, the resistance of the surrounding tissue may decrease as
the temperature of the tissue increases until a point where the
tissue begins to denature or irreversibly change, for example, at
approximately 50-60.degree. C. Once the tissue has begun to
denature the resistance of the tissue may increase. As the target
tissue is ablated, the change in impedance may be analyzed to
determine how much tissue has been ablated. The power level and
duration of the ablation may be adjusted accordingly based on the
impedance of the tissue. Electrical conductors 126b, 126c, 126d may
also include electrical switches 118b, 118c, 118d and current
sensing circuits 116b, 116c, 116d. The electrical switches 118b,
118c, 118d and current sensing circuits 116b, 116d, 116d may be
similar in form and function to electrical switch 118a and current
sensing circuit 116a previously discussed.
[0035] While not explicitly shown, the ablation electrodes 114 may
each include a temperature sensor, such as, but not limited to a
thermistor or thermocouple, positioned adjacent to the electrode.
The temperature sensor may measure the temperature response of the
adjacent tissue during the ablation procedure. The temperature
response may also be used to monitor the progress of the ablation
procedure (for example, temperature may be used as an indication of
lesion size).
[0036] The control unit 120 may be configured to monitor the
electrical parameters from each electrical conductor 126a, 126b,
126c, 126d as well as the temperature from each temperature sensor.
The control unit 120 may control the voltage of the power source to
adjust the power supplied to each electrode 114a, 114b, 114c, 114d
separately. It is further contemplated the electrical switches
118a, 118b, 118c, 118d may be selectively opened and closed to
selectively include or exclude electrodes 114a, 114b, 114c, 114d
during the ablation procedure. For example, an individual electrode
may be excluded from the ablation procedure during the initial
ablation. Power may be delivered to the excluded electrode at a
later time, if so desired. This may allow a physician to avoid
certain sites due to position or contact. For example an electrode
with poor contact, as indicated by an initial impedance reading,
may be excluded from the initial ablation. The control unit 120 may
include a control algorithm, such as algorithm 200 shown in FIG. 4,
for determining how much power should be applied to each electrode
114 and/or for determining when electrodes should be turned
on/off.
[0037] The control unit 120 may first apply power 202 to all of the
electrodes 114a, 114b, 114c, 114d included with the modulation
system 100. It is contemplated that the power may be increased or
ramped 204 from zero to the maximum power over a predetermined
length of time. In some instances, the ramp time may be 5 seconds
or less, 10 seconds or less, 15 seconds or less, or greater than 15
seconds as desired. The maximum power may be determined by the
number of electrodes 114 and the amount of power supplied to each
electrode. For example, a modulation system, such as system 100,
including four electrodes 114 each receiving 8 Watts would have a
maximum power of 32 Watts. During the ramp time and/or once the
maximum power has been reached, the control unit 120 may monitor
the electrical parameters from each electrical conductor 126a,
126b, 126c, 126d as well as the temperature from each temperature
sensor. If a maximum temperature, for example, but not limited to
65.degree. C., if reached at any one of the electrodes 114a, 114b,
114c, 114d, the power delivered to the electrode that has reached
the maximum temperature may be reduced 206. The maximum temperature
may be any temperature desired, such as, but not limited, to
greater than 50.degree. C. It is contemplated that each of the
electrodes 114a, 114b, 114c, 114d may reach a different temperature
during the procedure.
[0038] The control unit 120 may also monitor the electrical
parameters from each electrical conductor 126a, 126b, 126c, 126d as
well as the temperature from each temperature sensor to determine
if predetermined completion criteria have been met 208. For
example, the procedure may be considered complete for a region
adjacent an electrode 114 when a target temperature (for example,
but not limited to, at least 55.degree. C.) has been sustained for
a given time period (for example, but not limited to, at least 25
seconds). The target temperature and time periods are just
examples. The target temperature and/or time period may be any
temperature or time period desired. Alternatively, or additionally,
the procedure may be considered complete for a region adjacent an
electrode 114 when a calculated impedance drops by a predetermined
amount (such as, but not limited to 20%). The calculated impedance
drop is just an example. The calculated impedance drop may be any
impedance drop desired. If an electrode 114 has not met the
completion criteria, the control unit 120 may continue to
supply/regulate power to and/or monitor the parameters of the
electrode 114, as shown in step 206. If an electrode 114 has met
the completion criteria, the control unit 120 may turn off the
power supply 210 to that particular electrode 114. This may be
accomplished via electrical switch 118.
[0039] The control unit 120 may also monitor how many electrodes
114 have met the completion criteria 212. If all of the electrodes
114 have not met the completion criteria, the maximum power
supplied may be reduced based on the number of electrodes still
active in the procedure 214. The control unit 120 may continue to
supply/regulate power to and/or monitor the parameters of the
electrode 114, as shown in step 206. This procedure may be iterated
until all of the electrodes 114 have reached the completion
criteria. Once all of the electrodes 114 have met the completion
criteria, the procedure is complete 216 and power supply is
terminated. It is contemplated that the control algorithm 200 may
also terminate the procedure even if the completion criteria have
not been met at all of the electrodes 114. For example, ablation
may be terminated if the completion criteria have not been met
after a predetermined time period. The control algorithm 200 may
allow the catheter to create multiple lesions at the same time and
to apply power to specific electrodes that need more ablation time
or power to achieve the desired tissue modulation. This may short
the ablation time and total procedure time. The control algorithm
may be further illustrated in example procedures enclosed
herein.
[0040] FIG. 5 illustrates a distal end region of another
illustrative renal nerve modulation system 300 that may be similar
in form and function to other system disclosed herein. The system
300 may include a catheter shaft 302 having a distal end region
304. The catheter shaft 302 may extend proximally from the distal
end region 304 to a proximal end configured to remain outside of a
patient's body. The proximal end of the catheter shaft 302 may
include a hub attached thereto for connecting other treatment
devices or providing a port for facilitating other treatments. It
is contemplated that the stiffness of the catheter shaft 302 may be
modified to form a modulation system 300 for use in various vessel
diameters and various locations within the vascular tree. The
catheter shaft 302 may further include one or more lumens extending
therethrough. For example, the catheter shaft 302 may include a
guidewire lumen and/or one or more auxiliary lumens. The lumens may
be configured in any way known in the art. While not explicitly
shown, the modulation system 300 may further include temperature
sensors/wire, an infusion lumen, radiopaque marker bands, fixed
guidewire tip, a guidewire lumen, external sheath and/or other
components to facilitate the use and advancement of the system 300
within the vasculature.
[0041] The system 300 may include an elongate member 306 extending
within a lumen of the catheter shaft 302. In some instances, the
elongate member 306 may extend the entire length of the catheter
shaft 302 while in other instances, the elongate member 306 may be
attached to the catheter shaft 302 adjacent the distal end region
304 thereof. In some instances, the elongate member 306 may include
a first portion 308 and a second portion 310. The first and second
portions 308, 310 may run side by side or be secured to one another
along a proximal region 314, although this is not required. The
first and second portions 308, 310 may separate at a distal end of
the elongate member 306 to form a looped distal end region 316. The
looped distal end region 316 of the elongate member 306 may be
configured to be advanced to the desired treatment region within
the catheter shaft 302. Once adjacent to the desired treatment
region, the distal end region 316 of the elongate member 306 may be
advanced distally such that it exits the lumen of the catheter
shaft 302. In some instances, the distal end region 316 may be
configured to self-expand into a ring while in other instances,
actuation mechanisms may be employed to expand the distal end
region 316.
[0042] The system 300 may include one or more distal ablation
electrodes 312a, 312b, 312c, 312e, 312e (collectively 312)
positioned adjacent the distal end region 316 of the elongate
member 306. The electrodes 312 may be similar in form and function
to electrodes 114 described above. While the ablation electrodes
312 are described as a radiofrequency electrode, it is contemplated
that other methods and devices for raising the temperature of the
nerves may be used, such as, but not limited to: ultrasound,
microwave, or other acoustic, optical, electrical current, direct
contact heating, or other heating. While the system 300 is
illustrated as including five ablation electrodes 312, it is
contemplated that the modulation system 300 may include any number
of ablation electrodes 312 desired, such as, but not limited to,
one, two, three, four, or more. The ablation electrodes 312 may be
longitudinally and/or radially and/or circumferentially spaced as
desired. The ablation electrodes 312 may be spaced about the distal
end region 316, although this is not required. In some instances,
the electrodes 312 may be positioned about the distal end region
316 such that not all of the electrodes 312 contact the vessel wall
at the same time when the distal end region 316 is in the expanded
state. In other instances, the electrodes 312 may be arranged such
that all of the electrodes 312 are configured to contact the vessel
wall simultaneously when the distal end region 316 is in the
expanded state.
[0043] While not explicitly shown, the ablation electrodes 312 may
also include other structures and/or features associated typically
associated with ablation (e.g., thermal ablation) such as a
temperature monitoring member, which may take the form of a
thermocouple or thermistor. In at least some embodiments, a
thermistor including two thermistor wires may be disposed adjacent
to one or more of the ablation electrodes 312. In some embodiments,
the wires are not physically connected to ablation electrodes
312.
[0044] FIG. 6 illustrates a distal end region of another
illustrative renal nerve modulation system 400 that may be similar
in form and function to other system disclosed herein. The system
400 may include a catheter shaft 402 having a distal end region
404. The catheter shaft 402 may extend proximally from the distal
end region 404 to a proximal end configured to remain outside of a
patient's body. The proximal end of the catheter shaft 402 may
include a hub attached thereto for connecting other treatment
devices or providing a port for facilitating other treatments. It
is contemplated that the stiffness of the catheter shaft 402 may be
modified to form a modulation system 400 for use in various vessel
diameters and various locations within the vascular tree. The
catheter shaft 402 may further include one or more lumens extending
therethrough. For example, the catheter shaft 402 may include a
guidewire lumen and/or one or more auxiliary lumens. The lumens may
be configured in any way known in the art. While not explicitly
shown, the modulation system 400 may further include temperature
sensors/wire, an infusion lumen, radiopaque marker bands, fixed
guidewire tip, a guidewire lumen, external sheath and/or other
components to facilitate the use and advancement of the system 400
within the vasculature.
[0045] The system 400 may include an elongate member 406 extending
within a lumen of the catheter shaft 402. In some instances, the
elongate member 406 may extend the entire length of the catheter
shaft 402 while in other instances, the elongate member 406 may be
attached to the catheter shaft 402 adjacent the distal end region
404 thereof. In some instances, the elongate member 406 may include
a first portion 408 and a second portion 410. The first and second
portions 408, 410 may run side by side or be secured to one another
along a proximal region 420, although this is not required. The
first and second portions 408, 410 may separate to form a first
looped region 416 and a second looped region 418 adjacent a distal
end of the elongate member 406. The first portion 408 may cross
over the second portion 410 at an intersection point 412 to define
the first and second looped regions 416, 418. The looped regions
416, 418 of the elongate member 406 may be configured to be
advanced to the desired treatment region within the catheter shaft
402. Once adjacent to the desired treatment region, the looped
regions 416, 418 of the elongate member 406 may be advanced
distally such that it exits the lumen of the catheter shaft 402. In
some instances, the looped regions 416, 418 may be configured to
self-expand into a two looped structure while in other instances,
actuation mechanisms may be employed to expand the distal end
region 416.
[0046] The system 400 may include one or more distal ablation
electrodes 414a, 414b, 414c, 414d, 414e (collectively 414)
positioned adjacent the distal end region 416 of the elongate
member 406. The electrodes 414 may be similar in form and function
to electrodes 114 described above. While the ablation electrodes
414 are described as a radiofrequency electrode, it is contemplated
that other methods and devices for raising the temperature of the
nerves may be used, such as, but not limited to: ultrasound,
microwave, or other acoustic, optical, electrical current, direct
contact heating, or other heating. While the system 400 is
illustrated as including five ablation electrodes 414, it is
contemplated that the modulation system 400 may include any number
of ablation electrodes 414 desired, such as, but not limited to,
one, two, three, four, or more. The ablation electrodes 414 may be
longitudinally and/or radially and/or circumferentially spaced as
desired. The ablation electrodes 414 may be spaced about the looped
regions 416, 418, although this is not required. In some instances,
the electrodes 414 may be positioned about the distal end region
416 such that not all of the electrodes 414 contact the vessel wall
at the same time when the looped regions 416, 418 are in the
expanded state. In other instances, the electrodes 414 may be
arranged such that all of the electrodes 414 are configured to
contact the vessel wall simultaneously when the looped regions 416,
418 are in the expanded state.
[0047] While not explicitly shown, the ablation electrodes 414 may
also include other structures and/or features associated typically
associated with ablation (e.g., thermal ablation) such as a
temperature monitoring member, which may take the form of a
thermocouple or thermistor. In at least some embodiments, a
thermistor including two thermistor wires may be disposed adjacent
to one or more of the ablation electrodes 414. In some embodiments,
the wires are not physically connected to ablation electrodes
414.
[0048] The materials that can be used for the various components of
devices/systems 12, 100, 300, 400 (and/or other medical devices
disclosed herein) may include those commonly associated with
medical devices. For simplicity purposes, the following discussion
makes reference to device 12. However, this is not intended to
limit the devices and methods described herein, as the discussion
may be applied to other similar medical devices disclosed
herein.
[0049] Device 12 may be made from a metal, metal alloy, polymer
(some examples of which are disclosed below), a metal-polymer
composite, ceramics, combinations thereof, and the like, or other
suitable material. Some examples of suitable metals and metal
alloys include stainless steel, such as 304V, 304L, and 316LV
stainless steel; mild steel; nickel-titanium alloy such as
linear-elastic and/or super-elastic nitinol; other nickel alloys
such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such
as INCONEL.RTM. 625, UNS: N06022 such as HASTELLOY.RTM. UNS: N10276
such as HASTELLOY.RTM. C276.RTM., other HASTELLOY.RTM. alloys, and
the like), nickel-copper alloys (e.g., UNS: N04400 such as
MONEL.RTM. 400, NICKELVAC.RTM. 400, NICORROS.RTM. 400, and the
like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035
such as MP35-N.RTM. and the like), nickel-molybdenum alloys (e.g.,
UNS: N10665 such as HASTELLOY.RTM. ALLOY B2.RTM.), other
nickel-chromium alloys, other nickel-molybdenum alloys, other
nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper
alloys, other nickel-tungsten or tungsten alloys, and the like;
cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g.,
UNS: R30003 such as ELGILOY.RTM., PHYNOX.RTM., and the like);
platinum enriched stainless steel; titanium; combinations thereof;
and the like; or any other suitable material.
[0050] As alluded to herein, within the family of commercially
available nickel-titanium or nitinol alloys, is a category
designated "linear elastic" or "non-super-elastic" which, although
may be similar in chemistry to conventional shape memory and super
elastic varieties, may exhibit distinct and useful mechanical
properties. Linear elastic and/or non-super-elastic nitinol may be
distinguished from super elastic nitinol in that the linear elastic
and/or non-super-elastic nitinol does not display a substantial
"superelastic plateau" or "flag region" in its stress/strain curve
like super elastic nitinol does. Instead, in the linear elastic
and/or non-super-elastic nitinol, as recoverable strain increases,
the stress continues to increase in a substantially linear, or a
somewhat, but not necessarily entirely linear relationship until
plastic deformation begins or at least in a relationship that is
more linear that the super elastic plateau and/or flag region that
may be seen with super elastic nitinol. Thus, for the purposes of
this disclosure linear elastic and/or non-super-elastic nitinol may
also be termed "substantially" linear elastic and/or
non-super-elastic nitinol.
[0051] In some cases, linear elastic and/or non-super-elastic
nitinol may also be distinguishable from super elastic nitinol in
that linear elastic and/or non-super-elastic nitinol may accept up
to about 2-5% strain while remaining substantially elastic (e.g.,
before plastically deforming) whereas super elastic nitinol may
accept up to about 8% strain before plastically deforming. Both of
these materials can be distinguished from other linear elastic
materials such as stainless steel (that can also can be
distinguished based on its composition), which may accept only
about 0.2 to 0.44 percent strain before plastically deforming.
[0052] In some embodiments, the linear elastic and/or
non-super-elastic nickel-titanium alloy is an alloy that does not
show any martensite/austenite phase changes that are detectable by
differential scanning calorimetry (DSC) and dynamic metal thermal
analysis (DMTA) analysis over a large temperature range. For
example, in some embodiments, there may be no martensite/austenite
phase changes detectable by DSC and DMTA analysis in the range of
about -60 degrees Celsius (.degree. C.) to about 120.degree. C. in
the linear elastic and/or non-super-elastic nickel-titanium alloy.
The mechanical bending properties of such material may therefore be
generally inert to the effect of temperature over this very broad
range of temperature. In some embodiments, the mechanical bending
properties of the linear elastic and/or non-super-elastic
nickel-titanium alloy at ambient or room temperature are
substantially the same as the mechanical properties at body
temperature, for example, in that they do not display a
super-elastic plateau and/or flag region. In other words, across a
broad temperature range, the linear elastic and/or
non-super-elastic nickel-titanium alloy maintains its linear
elastic and/or non-super-elastic characteristics and/or
properties.
[0053] In some embodiments, the linear elastic and/or
non-super-elastic nickel-titanium alloy may be in the range of
about 50 to about 60 weight percent nickel, with the remainder
being essentially titanium. In some embodiments, the composition is
in the range of about 54 to about 57 weight percent nickel. One
example of a suitable nickel-titanium alloy is FHP-NT alloy
commercially available from Furukawa Techno Material Co. of
Kanagawa, Japan. Some examples of nickel titanium alloys are
disclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which are
incorporated herein by reference. Other suitable materials may
include ULTANIUM.TM. (available from Neo-Metrics) and GUM METAL.TM.
(available from Toyota). In some other embodiments, a superelastic
alloy, for example a superelastic nitinol can be used to achieve
desired properties.
[0054] In at least some embodiments, portions or all of device 12
may also be doped with, made of, or otherwise include a radiopaque
material. Radiopaque materials are generally understood to be
materials which are opaque to RF energy in the wavelength range
spanning x-ray to gamma-ray (at thicknesses of <0.005''). These
materials are capable of producing a relatively dark image on a
fluoroscopy screen relative to the light image that non-radiopaque
materials such as tissue produce. This relatively bright image aids
the user of device 12 in determining its location. Some examples of
radiopaque materials can include, but are not limited to, gold,
platinum, palladium, tantalum, tungsten alloy, polymer material
loaded with a radiopaque filler, and the like. Additionally, other
radiopaque marker bands and/or coils may also be incorporated into
the design of device 12 to achieve the same result.
[0055] In some embodiments, a degree of Magnetic Resonance Imaging
(MRI) compatibility is imparted into device 12. For example, device
12 or portions thereof may be made of a material that does not
substantially distort the image and create substantial artifacts
(i.e., gaps in the image). Certain ferromagnetic materials, for
example, may not be suitable because they may create artifacts in
an MRI image. Device 12 or portions thereof may also be made from a
material that the MRI machine can image. Some materials that
exhibit these characteristics include, for example, tungsten,
cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as
ELGILOY.RTM., PHYNOX.RTM., and the like),
nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as
MP35-N.RTM. and the like), nitinol, and the like, and others.
[0056] Some examples of suitable polymers for device 12 may include
polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene
(ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene
(POM, for example, DELRIN.RTM. available from DuPont), polyether
block ester, polyurethane (for example, Polyurethane 85A),
polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for
example, ARNITEL.RTM. available from DSM Engineering Plastics),
ether or ester based copolymers (for example,
butylene/poly(alkylene ether) phthalate and/or other polyester
elastomers such as HYTREL.RTM. available from DuPont), polyamide
(for example, DURETHAN.RTM. available from Bayer or CRISTAMID.RTM.
available from Elf Atochem), elastomeric polyamides, block
polyamide/ethers, polyether block amide (PEBA, for example
available under the trade name PEBAX.RTM.), ethylene vinyl acetate
copolymers (EVA), silicones, polyethylene (PE), Marlex high-density
polyethylene, Marlex low-density polyethylene, linear low density
polyethylene (for example REXELL.RTM.), polyester, polybutylene
terephthalate (PBT), polyethylene terephthalate (PET),
polytrimethylene terephthalate, polyethylene naphthalate (PEN),
polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI),
polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly
paraphenylene terephthalamide (for example, KEVLAR.RTM.),
polysulfone, nylon, nylon-12 (such as GRILAMID.RTM. available from
EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene
vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene
chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (for
example, SIBS and/or SIBS 50A), polycarbonates, ionomers,
biocompatible polymers, other suitable materials, or mixtures,
combinations, copolymers thereof, polymer/metal composites, and the
like.
Example 1
[0057] An example of control algorithm 200 is provided herein. This
example is merely exemplary and is not intended to limit the
control algorithm to the example scenario provided. It is
contemplated the times, temperature, impedance drops, power levels,
and number of electrodes active will vary from procedure to
procedure. A modulation system including four electrodes is
provided. The electrodes are positioned adjacent to a desired
treatment region. A maximum temperature for the system is set at
65.degree. C. At the start of the modulation procedure (time
(t)=0), power is delivered to all four electrodes with a 5 second
ramp to a power limit of 32 Watts. Each electrode receives 8 Watts.
At t=5 seconds, power is being delivered at a full 32 Watts. The
temperature of a first, second, and third electrodes reaches
55.degree. C. at t=5 seconds. The fourth electrode reaches
55.degree. C. at t=15 seconds. The impedance of each electrode
drops by more than 20%. At t=30 seconds the first, second, and
third electrodes achieve the ablation criteria (for example,
T=55.degree. C. for at least 25 seconds). The first, second, and
third electrodes are turned off. The total power supplied to system
is reduced to 8 Watts, the maximal power for one electrode. At t=40
seconds, the fourth electrode achieves the ablation criteria (for
example, T=55.degree. C. for at least 25 seconds) and is turned
off. The ablation procedure is terminated.
Example 2
[0058] Another example of control algorithm 200 is provided herein.
This example is merely exemplary and is not intended to limit the
control algorithm to the example scenario provided. It is
contemplated the times, temperature, impedance drops, power levels,
and number of electrodes active will vary from procedure to
procedure. A modulation system including four electrodes is
provided. The electrodes are positioned adjacent to a desired
treatment region. A maximum temperature for the system is set at
65.degree. C. At the start of the modulation procedure (time
(t)=0), power is delivered to all four electrodes with a 5 second
ramp to a power limit of 32 Watts. Each electrode receives 8 Watts.
At t=5 seconds, the temperature of the first electrode reaches
65.degree. C. and the total power is reduces to 24 Watts, each
electrode receiving 6 Watts. The temperature of the second and
third electrodes reaches 55.degree. C. and the temperature of the
fourth electrode remains at 45.degree. C. because 6 Watts is not
enough to bring the temperature to 55.degree. C. The impedance of
the first, second, and third electrodes drops by more than 20%. The
impedance of the fourth electrode drops by 5%. At t=30 seconds the
first, second, and third electrodes achieve the ablation criteria
(for example, T=55.degree. C. for at least 25 seconds). The first,
second, and third electrodes are turned off. The total power
supplied to system is reduced to 6 Watts for the fourth electrode.
The system may then adjust the power to the fourth electrode to
approximately 8 Watts. At t=32 seconds, the fourth electrode
reaches 55.degree. C. and impedance drops by more than 20%. At t=57
seconds, the fourth electrode achieves the ablation criteria (for
example, T=55.degree. C. for at least 25 seconds) and is turned
off. The ablation procedure is terminated.
[0059] It should be understood that this disclosure is, in many
respects, only illustrative. Changes may be made in details,
particularly in matters of shape, size, and arrangement of steps
without exceeding the scope of the disclosure. This may include, to
the extent that it is appropriate, the use of any of the features
of one example embodiment being used in other embodiments. The
invention's scope is, of course, defined in the language in which
the appended claims are expressed.
* * * * *