U.S. patent application number 08/952175 was filed with the patent office on 2001-09-06 for system for simultaneous unipolar multi-electrode ablation.
Invention is credited to DALY, MICHAEL, HATZIANESTIS, KONSTADINOS, KOVOOR, PRAMESH, ROSS, DAVID.
Application Number | 20010020166 08/952175 |
Document ID | / |
Family ID | 3793886 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010020166 |
Kind Code |
A1 |
DALY, MICHAEL ; et
al. |
September 6, 2001 |
SYSTEM FOR SIMULTANEOUS UNIPOLAR MULTI-ELECTRODE ABLATION
Abstract
A system (2,4), method and splitter (6) for ablating tissue (15)
using radiofrequency (RF) energy is disclosed. The system (2,4)
ablates tissue (15) using unipolar RF energy simultaneously
delivered to multiple electrodes (22A-22D) in one or more probes
(20). This is carried out by the multiple channel RF splitter (6)
that can independently control the RF energy delivered through each
channel (18) to a respective electrode (22A-22D) in a continuous
manner. Each electrode (22A-22D) has a corresponding temperature
sensor or transducer (36A-36D) that is processed independently so
that the amount of RF energy delivered to each electrode (22A-22D)
can be varied dependent on the temperature of the electrode
(22A-22D) so that the lesion size produced by each electrode
(22A-22D) can be accurately controlled. Preferably, each probe (20)
has a needle-like structure with a number of electrodes (22A-22D)
separated by insulative material and is adapted to puncture tissue.
Each channel (18) of the splitter (6) has circuitry for
interrupting current delivered to the respective channel if a
predetermined temperature or current level is exceeded.
Inventors: |
DALY, MICHAEL; (EASTWOOD,
AU) ; KOVOOR, PRAMESH; (WENTWORTHVILLE, AU) ;
HATZIANESTIS, KONSTADINOS; (MCMAHONS POINT, AU) ;
ROSS, DAVID; (CHELTENHAM, AU) |
Correspondence
Address: |
LADAS & PARRY
26 WEST 61ST STREET
NEW YORK
NY
10023
|
Family ID: |
3793886 |
Appl. No.: |
08/952175 |
Filed: |
January 22, 1998 |
PCT Filed: |
April 30, 1997 |
PCT NO: |
PCT/AU97/00258 |
Current U.S.
Class: |
606/34 ;
606/41 |
Current CPC
Class: |
A61B 2018/00791
20130101; A61B 2018/126 20130101; A61B 2018/1467 20130101; A61B
2018/00654 20130101; A61B 18/12 20130101; A61B 2018/1273 20130101;
A61B 2018/124 20130101; A61B 2017/00084 20130101; A61B 2018/0066
20130101; A61B 18/1206 20130101; A61B 18/1477 20130101; A61B
2018/00797 20130101 |
Class at
Publication: |
606/34 ;
606/41 |
International
Class: |
A61B 018/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 1996 |
AU |
PN9572 |
Claims
1. A system for ablating tissue, comprising: means for generating
RF energy; probe means comprising N separate electrodes, each
having a corresponding means for sensing the temperature of said
electrode; splitter means for splitting said RF energy coupled to
said generating means and said probe means, said splitter means
having N separate channels each being coupled to a corresponding
one of said N electrodes and temperature sensing means; and means
for controlling said splitter means, whereby the ablation of tissue
at each electrode is independently controlled using closed loop
feedback of the temperature of said electrode by independently
regulating the amount of said RF energy delivered to each
electrode.
2. The system according to claim 1, comprising a plurality of probe
means and splitter means, wherein said controlling means separately
controls each of said probe means and said corresponding splitter
means.
3. The system according to claim 1 or 2, wherein said probe means
has an elongated needlelike structure with one end adapted to
puncture tissue and having sufficient rigidity to puncture said
tissue, wherein each of said electrodes consists of a metal
substantially circular surface separated one from another by
insulation means.
4. The system according to claim 1 or 2, wherein said probe means
is a catheter probe device.
5. The system according to any one of claims 1 to 4 wherein said RF
energy has a single phase.
6. The system according to any one of claims 1 to 5, further
comprising means for independently and continuously adjusting said
RF energy delivered to each electrode in response to a control
signal from said controlling means dependent on said temperature of
said electrode.
7. The system according to any one of claims 1 to 6, wherein said
controlling means is programmable.
8. The system according to any one of claims 1 to 7 wherein each
respective temperature sensing means comprises a thermocouple.
9. The system according to any one of claims 1 to 8, wherein said
splitter means comprises means for independently interrupting
current from said RF energy generating means to one or more of said
electrodes.
10. The system according to any one of claims 1 to 9, further
comprising means for independently sensing at least one of the
group consisting of the voltage, current, impedance and average
power of each electrode to provide a corresponding measurement
signal; and wherein said controlling means generates said control
signal to independently interrupt delivery of said RF energy to
said respective electrode when said meaurement signal exceeds a
predetermined threshold condition.
11. A medical apparatus for treatment by radiofrequency (RF)
ablation of tissue, said apparatus comprising: an RF energy
generator; one or more probes each comprising a plurality of
separate electrodes and corresponding temperature sensors for
sensing the temperature of said electrodes, each temperature sensor
connected to a respective one of said plurality of electrodes; a
splitter for splitting said RF energy provided by said RF energy
generator, said splitter having a plurality of separate channels,
wherein each of said electrodes is coupled to a respective one of
said plurality of channels; and a programmable controller coupled
to said RF splitter for independently controlling the ablation of
tissue at each electrode using closed loop feedback of the
temperature of said electrode, whereby the amount of said RF energy
delivered to each electrode is independently regulated by said
programmable controller.
12. The medical apparatus according to claim 11, comprising at
least two probes, and wherein said programmable controller
separately controls each of said probes.
13. The medical apparatus according to claim 11 or 12, wherein each
probe has an elongated needle-like structure with one end adapted
to puncture tissue and having sufficient rigidity to puncture said
tissue, wherein each of said electrodes consists of metal separated
one from another by insulative material.
14. The medical apparatus according to any one of claims 11 to 13
wherein said RF energy has a single phase.
15. The medical apparatus according to any one of claims 11 to 14,
further comprising means for independently and continuously
adjusting said RF energy delivered to each electrode in response to
said programmable controller dependent on said temperature of said
electrode.
16. The medical apparatus according to claim 11 or 12 wherein each
probe is a catheter device.
17. The medical apparatus according to any one of claims 11 to 16,
wherein each of said temperature sensors comprises a temperature
transducer.
18. The medical apparatus according to claim 17 wherein said
temperature transducer is a thermocouple at least partially
embedded in said respective electrode.
19. The medical apparatus according to any one of claims 11 to 18
wherein each channel of said splitter is coupled to means for
interrupting current delivered to the corresponding electrode.
20. The medical apparatus according to any one of claims 11 to 19
comprising means for independently interrupting the delivery of RF
energy to each electrode when at least one of the voltage, current,
impedance and average power measured at the respective electrode
exceeds a predetermined threshold.
21. A radio frequency (RF) energy splitter for use with one or more
probes in a system for RF ablation of tissue, each probe comprising
a plurality of separate electrodes and corresponding temperature
sensors for sensing the temperature of said electrode, said
splitter comprising: input means for receiving RF energy from an RF
energy generator; a plurality of channel modules for separately
delivering RF energy from said input means to a respective
electrode of said plurality of electrodes of said one or more
probes, each channel module comprising: means for variably
adjusting an amount of said RF energy delivered to said respective
electrode in response to a control signal, said variable adjusting
means being coupled between said input means and said respective
electrode; means for interrupting said RF energy delivered to said
respective electrode; output means coupled to said respective
temperature sensor for providing a temperature signal; means for
determining if said temperature at said respective electrode
exceeds a predetermined threshold and actuating said interrupting
means if said threshold is exceeded, whereby said RF energy is
interrupted from delivery to said respective electrode; wherein
each channel module is capable of receiving said respective control
signal from and providing said respective temperature signal to a
programmable controller so that the amount of said RF energy
delivered to each electrode can be independently regulated using
closed loop feedback of the temperature of each electrode.
22. The splitter according to claim 21, wherein said variable
adjusting means comprises a bridge rectifier including a
fast-switching variable resistance for controlling operation of
said bridge rectifier in response to said control signal.
23. The splitter according to claim 21 or 22, wherein said RF
energy interrupting means comprises means for interrupting a
current through said RF energy interrupting means and means for
limiting said current.
24. The splitter according to any one of claims 21 to 23, wherein
said determining means compares said temperature signal with said
predetermined threshold.
25. The splitter according to any one of claims 21 to 24 wherein
said one or more probes each has a needle-like structure with one
end adapted to puncture tissue and having sufficient rigidity to
puncture said tissue, wherein each of said electrodes conceits of
metal separated one from another by insulative material.
26. The splitter according to any one of claims 21 to 25 wherein
said one or more probes each comprise a catheter probe device.
27. The splitter according to any one of claims 21 to 25, wherein
each channel comprises means for sensing at least one of the group
consisting of the voltage, current, impedance and average power of
said respective electrode whereby said programmable controller can
interrupt delivery of said RP energy to said electrode dependent
upon the measurement provided by said sensing means.
28. A method for ablating tissue, comprising the steps of:
generating RF energy; providing probe means comprising N separate
electrodes, each having a corresponding means for sensing
temperature of said electrode; sensing the temperature of each
electrode using said temperature sensing means of said electrode;
splitting said RF energy to said probe means into N separate
channels each being coupled to a corresponding one of said N
electrodes and said temperature sensing means; and controlling the
splitting of said RF energy to said probe means, whereby the
ablation of tissue at each electrode is independently controlled
using closed loop feedback of the measured temperature of said
electrode by independently regulating the amount of said RF energy
delivered to each electrode.
29. The method according to claim 28, further comprising the step
of separately controlling the splitting of said RF energy to a
plurality of said probe means.
30. The method according to claims 28 or 29, wherein said probe
means has an elongated needle-like structure with one end adapted
to puncture tissue and having sufficient rigidity to puncture said
tissue, wherein each of said electrodes consists of a metal
substantially circular surface separated one from another by
insulation means.
31. The method according to any one of claims 28 to 30 wherein said
RP energy has a single phase.
32. The method according to any one of claims 28 to 31, further
comprising the step of independently and continuously adjusting
said RF energy delivered to each electrode in response to a control
signal from a programmable controlling means dependent on said
temperature of said electrode.
33. The method according to any one of claims 28 to 32, further
comprising the steps of: sensing at least one of the group
consisting of the voltage, current, impedance and average power of
the respective electrode; and independently interrupting the
delivery of said RP energy to said electrode if a predetermined
threshold is exceeded by the sensed value.
34. A method for treatment by radiofrequency (RP) ablation of
tissue, said method comprising the steps of: generating RF energy;
providing one or more probes each comprising a plurality of
separate electrodes and corresponding temperature sensors, each
temperature sensor connected to a respective one of said plurality
of electrodes; measuring the temperature of each electrode using
said respective temperature sensor; splitting said RF energy into a
plurality of separate channels, wherein each of said electrodes is
coupled to a respective one of said plurality of channels; and
programmably controlling the splitting of said RF energy so as to
independently control the ablation of tissue at each electrode
using closed loop feedback of the measured temperature of said
electrode, whereby the amount of said RF energy delivered to each
electrode is independently regulated.
35. The method according to claim 34, comprising the further steps
of using at least two probes, and programmably controlling each of
said probes separately.
36. The method according to claims 34 or 35, wherein each probe has
an elongated needle-like structure with one end adapted to puncture
tissue and having sufficient rigidity to puncture said tissue,
wherein each of said electrodes consists of metal separated one
from another by insulative material.
37. The method according to any one of claims 34 to 36 wherein said
RF energy has a single phase.
38. The method according to any one of claims 34 to 37, further
comprising the step of independently and continuously adjusting
said RF energy delivered to each electrode in response to said
temperature of said electrode.
39. The method according to any one of claims 34 to 38, further
comprising the step of independently interrupting the delivery of
RF energy to each electrode when at least one of the voltage,
current, impedance and average power measurement at the respective
electrode exceeds a predetermined threshold.
40. A method of splitting radio frequency (RF) energy delivered to
one or more probes in a system for RF ablation of tissue, each
probe comprising a plurality of separate electrodes and
corresponding temperature sensors for sensing the temperature of
said electrode, said method comprising the steps of: receiving RP
energy from an RF energy generator; providing a plurality of
channel modules for separately delivering said RF energy to a
respective electrode of said plurality of electrodes of said one or
more probes, further comprising, for each channel module, the
sub-steps of: variably adjusting an amount of said RF energy
delivered to said respective electrode in response to a control
signal; measuring the temperature of said respective electrode
using said corresponding temperature sensor to provide a
temperature signal; determining if said temperature at said
respective electrode exceeds a predetermined threshold and
interrupting delivery of said RF energy to said respective
electrode if said threshold is exceeded; wherein each channel
module is capable of receiving said respective control signal from
and providing said respective temperature signal to a programmable
controller so that the amount of said RF energy delivered to each
electrode can be independently regulated using closed loop feedback
of the temperature of each electrode.
41. The method according to claim 40, wherein said step of variably
adjusting said RF energy comprises the step of changing the
resistance of a fast-switching variable resistance incorporated in
a bridge rectifier in response to said control signal.
42. The method according to claim 40 or 41, wherein said step of
interrupting said RF energy comprises the steps of interrupting a
current to said respective electrode and limiting said current.
43. The method according to any one of claims 40 to 42, wherein
said step of determining comprises the step of comparing said
temperature signal with said predetermined threshold.
44. The method according to any one of claims 40 to 42, for each
channel module, further comprises the sub-steps of: sensing at
least one of the group consisting of the voltage, current,
impedance and average power of said respective electrode; and
independently interrupting delivery of said RF energy to said
electrode dependent upon the sensed value.
Description
BACKGROUND
[0001] The present invention relates to a system, method and
apparatus for ablating tissue under temperature control of each
electrode to control lesion dimensions, and in particular for
ablating myocardial tissue to treat Ventricular Tachycardia (VT) or
atrial fibrillation/flutter (AF).
[0002] Ventricular tachycardia is a disease of the heart which
causes the heart chambers to beat excessively fast and usually
degenerates to ventricular fibrillation where the heart chambers do
not effectively pump blood through the body's system and hence
leads to death. Ventricular tachycardia is the most common cause of
cardiac arrest and sudden death. Typical features of patients with
VT are (1) a history of myocardial infarction (heart attack), (2)
significant left ventricular dysfunction (the main chamber
effecting the pumping action), and (3) left ventricular aneurysm
(dilation, thinning and stretching of the chamber). Detailed
mapping studies of the electrical propagation within the myocardium
during VT have shown that a re entrant pathway within and around
the scarring (caused by infarction) is responsible for the
arrhythmia, These studies have shown that the critical area of
myocardium necessary to support reentry appears to be less than 2
to 4 cm.sup.2.
[0003] Atrial fibrillation (AF) and atrial flutter are diseases of
the heart which can cause the heart to beat excessively fast and
frequently in an erratic manner. This usually results in distress
for patients. This may also be associated with clot formation in
the atria, which may become dislodged and cause strokes. AF is
usually due to abnormal electrical activation of the atria.
Preliminary investigations have shown that linear lesions in the
atria using radiofrequency ablation can cure these arrhythmias.
[0004] A number of conventional techniques using radio frequency
(RF) energy have been used to treat VT or AF. Endocardial radio
frequency catheter ablation has been used in the treatment of
hemodynamically stable monomorphic ventricular tachycardia
secondary to coronary artery disease. The resulting lesions caused
in RF ablation using catheters however have been insufficient in
volume to destroy the area of tissue causing the arrhythmia.
[0005] Radiofrequency catheter ablation has been used for treatment
of AF, but has been limited by the number of separate ablations
required and the time required to perform the procedure.
[0006] In accordance with one conventional technique, RF energy is
delivered from an RF source, incorporating phase shift networks to
enable potential differences and hence current flow between
multiple, separate electrode structures. Also, multiple RF power
sources have been used connected to such electrodes. The
independent phases of the power source lead to multiple current
paths.
[0007] However, this conventional system lacks adequate temperature
control because the multiphase RF ablation cannot function
satisfactorily unless certain restrictions on the dimensions of the
electrode are adhered to. The ablation temperature can only be
maintained at an optimum predetermined level of approximately
80.degree. C. This is a significant shortfall of the technique.
SUMMARY
[0008] The present invention is directed to improving the efficacy
of producing radio frequency lesions using multiple temperature
controlled delivery by splitting high frequency current from a
single generator into a number of electrodes simultaneously.
Further, the system accurately measures the temperatures of these
electrodes which are then used as the feedback in the system,
allowing appropriate control strategies to be performed to regulate
the current to each electrode.
[0009] In accordance with a first aspect of the invention, a system
for ablating tissue comprises;
[0010] a device for generating RF energy;
[0011] a probe device comprising N separate electrodes, each having
a corresponding device for sensing the temperature of the
electrode;
[0012] a splitter device for splitting the RF energy coupled to the
generating device and the probe device, the splitter device having
N separate channels each being coupled to a corresponding one of
the N electrodes and temperature sensing device; and
[0013] a device for controlling the splitter device, whereby the
ablation of tissue at each electrode is independently controlled
using closed loop feedback of the temperature of the electrode by
independently regulating the amount of the RF energy delivered to
each electrode.
[0014] Preferably, the system comprises a plurality of the probe
devices and the splitter devices, and the controlling device
separately controls each of the probe devices and the corresponding
splitter device.
[0015] Preferably, the probe device has an elongated needle-like
structure with one end adapted to puncture tissue and having
sufficient rigidity to puncture the tissue, or a catheter which can
be advanced into the heart. Bach of the electrodes may consist of a
circular metal surface separated one from another by
insulation.
[0016] Preferably, the RF energy has a single phase.
[0017] Preferably, the system further comprises a device for
independently and continuously adjusting the RF energy delivered to
each electrode in response to a control signal from the controlling
device dependent on the temperature of the electrode.
[0018] Preferably, the controlling device is programmable.
[0019] Optionally, the probe device is a catheter probe device.
[0020] Preferably, each of the temperature sensing devices is a
thermocouple. Preferably, the splitter device comprises one or more
devices for independently interrupting current from the RF energy
generating device to a respective electrode.
[0021] In accordance with a second aspect of the invention, a
medical apparatus for treatment by radiofrequency ablation of
tissue comprises:
[0022] an RF energy generator;
[0023] one or more probes each comprising a plurality of separate
electrodes and corresponding temperature sensors for sensing the
temperature of the electrodes, each temperature sensor connected to
a respective one of the plurality of electrodes;
[0024] a splitter for splitting the RF energy provided by the RF
energy generator, the splitter having a plurality of separate
channels, wherein each of the electrodes is coupled to a respective
one of the plurality of channels; and
[0025] a programmable controller coupled to the RF splitter for
independently controlling the ablation of tissue at each electrode
using closed loop feedback of the temperature of the electrode,
whereby the amount of the RF energy delivered to each electrode is
independently regulated by the programmable controller.
[0026] In accordance with a third aspect of the invention, a radio
frequency energy splitter for use with one or more probes in a
system for RF ablation of tissue is provided. Each probe comprises
a plurality of separate electrodes and corresponding temperature
sensors for sensing the temperature of the electrode. The splitter
comprises:
[0027] an input device for receiving RF energy from an RF energy
generator;
[0028] a plurality of channel modules for separately delivering RP
energy from the input device to a respective electrode of the
plurality of electrodes of the one or more probes, each channel
module comprising:
[0029] a device for variably adjusting an amount of the RF energy
delivered to the respective electrode in response to a control
signal, the variable adjusting device being coupled between the
input device and the respective electrode;
[0030] a device for interrupting the RF energy delivered to the
respective electrode:
[0031] an output device coupled to the respective temperature
sensor for providing a temperature signal;
[0032] a device for determining if the temperature at the
respective electrode exceeds a predetermined threshold and
actuating the interrupting device if the threshold is exceeded,
whereby the RF energy is interrupted from delivery to the
respective electrode;
[0033] wherein each channel module is capable of receiving the
respective control signal from and providing the respective
temperature signal to a programmable controller so that the amount
of the RF energy delivered to each electrode can be independently
regulated using closed loop feedback of the temperature of each
electrode.
[0034] Preferably, the variable adjusting device or circuit
comprises a bridge rectifier including a fast-switching variable
resistance for controlling operation of the bridge rectifier in
response to the control signal.
[0035] Preferably, the RF energy interrupting device comprises a
circuit for interrupting a current through the RF energy
interrupting device and a circuit for limiting the current.
[0036] Preferably, the determining device compares the temperature
signal with the predetermined threshold.
[0037] In accordance with a fourth aspect of the invention, a
method for ablating tissue comprises the steps of:
[0038] generating RF energy;
[0039] providing a probe device comprising N separate electrodes,
each having a corresponding temperature sensing device;
[0040] measuring the temperature of each electrode using the
temperature sensing device of the electrode;
[0041] splitting the RF energy to the probe device into N separate
channels each being coupled to a corresponding one of the N
electrodes and temperature sensing device; and
[0042] controlling the splitting of the RF energy to the probe
device, whereby the ablation of tissue at each electrode is
independently controlled using closed loop feedback of the measured
temperature of the electrode by independently regulating the amount
of the RF energy delivered to each electrode.
[0043] Preferably, the method comprises the step of separately
controlling the splitting of the RF energy to a plurality of the
probe device.
[0044] Preferably, the probe device has an elongated needle-like
structure with one end adapted to puncture tissue and having
sufficient rigidity to puncture the tissue, wherein each of the
electrodes consists of a metal substantially circular surface
separated one from another by insulation.
[0045] Preferably, the RF energy has a single phase.
[0046] Preferably, the method further comprises the step of
independently and continuously adjusting the RF energy delivered to
each electrode in response to a control signal from a programmable
controlling device dependent on the temperature of the
electrode.
[0047] In accordance with a fifth aspect of the invention, a method
for treatment by radiofrequency (RF) ablation of tissue comprises
the steps of:
[0048] generating RF energy;
[0049] providing one or more probes each comprising a plurality of
separate electrodes and corresponding temperature sensors, each
temperature sensor connected to a respective one of the plurality
of electrodes;
[0050] measuring the temperature of each electrode using the
respective temperature sensor;
[0051] splitting the RF energy into a plurality of separate
channels, wherein each of the electrodes is coupled to a respective
one of the plurality of channels; and
[0052] programmably controlling the splitting of the RF energy so
as to independently control the ablation of tissue at each
electrode using closed loop feedback of the measured temperature of
the electrode, whereby the amount of the RF energy delivered to
each electrode is independently regulated.
[0053] Preferably, the method involves using at least two probes,
and comprises the step of programmably controlling each of the
probes separately.
[0054] In accordance with a sixth aspect of the invention, there is
provided a method of splitting radio frequency energy delivered to
one or more probes in a system for RF ablation of tissue. Each
probe comprises a plurality of separate electrodes and
corresponding temperature sensors for sensing the temperature of
the electrode. The method comprises the steps of:
[0055] receiving RF energy from an RF energy generator;
[0056] providing a plurality of channel modules for separately
delivering the RF energy to a respective electrode of the plurality
of electrodes of the one or more probes, further comprising, for
each channel module, the sub-steps of:
[0057] variably adjusting an amount of the RF energy delivered to
the respective electrode in response to a control signal;
[0058] measuring the temperature of the respective electrode using
the corresponding temperature sensor to provide a temperature
signal;
[0059] determining if the temperature at the respective electrode
exceeds a predetermined threshold and interrupting delivery of the
RF energy to the respective electrode if the threshold is
exceeded;
[0060] wherein each channel module is capable of receiving the
respective control signal from and providing the respective
temperature signal to a programmable controller so that the amount
of the RF energy delivered to each electrode can be independently
regulated using closed loop feedback of the temperature of each
electrode.
[0061] Preferably, the step of variably adjusting the RF energy
comprises the step of changing the resistance of a fast-switching
variable resistance incorporated in a bridge rectifier in response
to the control signal.
[0062] Preferably, the step of interrupting the RF energy comprises
the steps of interrupting a current to the respective electrode and
limiting the current.
[0063] Preferably, the step of determining comprises the step of
comparing the temperature signal with the predetermined
threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] Embodiments of the invention are described hereinafter with
reference to the drawings, in which
[0065] FIG. 1 is a block diagram of the RF ablation system
according to one embodiment;
[0066] FIG. 2. is a detailed schematic of a single channel of the
system of FIG. 1;
[0067] FIG. 3 is a detailed schematic of the system of FIG. 1,
wherein N=4; and
[0068] FIG. 4 is a detailed schematic of a single channel of an RF
ablation system according to another embodiment.
DETAILED DESCRIPTION
[0069] First Embodiment
[0070] The RF ablating system according to a first embodiment shown
in FIG. 1 comprises a programmable controller 2, an N-channel RF
splitter 6, an RF generator 8, a large conductive, dispersive plate
12, and an N-electrode probe 20. RF generators for RF ablation of
tissue are well known in the art. It will be appreciated by a
person skilled in the art that the present invention can be
practiced with any of a number of RF generators without departing
from the scope and spirit of the invention.
[0071] Preferably, the probe 20 has a needle-like structure wherein
each of the electrodes 22A to 22D has a tubular or ring shape. The
electrodes 22A to 22D are separated from each other by an
intervening insulative portion. Such a probe structure is disclosed
in International Publication No. WO 97/06727 published on Feb. 27,
1997 (International Application No. PCT/AU96/00489 by the
Applicant) and incorporated herein by cross-reference. The
structure of this probe 20 enables the electrodes 22A to 22D to be
inserted into the myocardium for use in the present system. While
this embodiment is described with reference to a single needle
probe 20, the system may be practiced with a plurality of such
needle probes 20 and one or more corresponding N-channel RF
splitters 6 that are controlled by the programmable controller 2.
It will be apparent to a person skilled in the art that the
embodiment is not limited to the use of such needle-like probes but
may be practiced with other types of ablating probes including
catheters.
[0072] Further, while this embodiment is discussed with reference
to ablation of reentrant pathways in relation to ventricular
tachycardia, the system is not limited to this particular
application, and instead can practiced in relation to a number of
other applications. For example, the system may be used to ablate
tissue causing atrial fibrillation or flutter, tumors, or for
coagulation treatment.
[0073] The programmable controller 2 may be implemented using a
general purpose computer executing a control algorithm to operate
the RF splitter 8 in response to measured temperatures of the
electrodes 22A to 22D, as described below. In this embodiment, the
programmable controller 2 is preferably implemented using an AMLAB
instrument emulator (published in International Publication No.
WO92/15959 on Sep. 17, 1992; International Application No.
PCT/AU92/00076), which comprises a general purpose computer having
a digital signal processor subassembly that is configurable using a
graphical compiler. The programmable controller 2 is connected to
the N-channel RF splitter 6 via N output control signals 14 and N
temperature signals 16 provided from the N-channel RF splitter 6 to
the programmable controller 2. The N-channel RF splitter 6, the RF
generator 8, the RMS-to-DC converter 10, the probe 20, and the
dispersive plate 12, shown as module 4, are provided so as to meet
electrical isolation barrier requirements in accordance with IEC
601 and AS3200.1 type CF standards.
[0074] The N-channel RF splitter 6 provides RF energy from the RE
generator 8 coupled to the splitter 6 via N electrical connections
18 to the corresponding electrodes 22A to 22D of the probe 20. In
addition, the N electrical connections 18 are connected to
corresponding thermocouples of each of the electrodes 22A to 22D.
While thermocouples are preferably employed, other temperature
transducers or sensing circuits/devices may be practiced without
departing from the scope and spirit of the invention. For example,
a temperature sensing device for a respective electrode of one or
more electrodes could include a thermistor or other temperature
transducer. The N temperature signals 16 provided to the
programmable controller 2 are obtained from the temperature sensing
devices of the electrodes 22A to 22D. The RF generator 8 is also
connected to the dispersive electrode 12 via the RMS-to-DC
converter 10.
[0075] This embodiment advantageously employs a single RF generator
in which the N-channel RF splitter 6 independently controls the
delivery of RF energy of a single phase to one or more of the
electrodes 22A to 22D of the probe 20. The temperature of each of
the electrodes 22A to 22D is independently monitored by the
programmable controller 2, which in turn provides the control
signals 14 to the N-channel RF splitter 6 to simultaneously control
the amount of RF energy delivered to the corresponding electrode
22A to 22D.
[0076] Using closed-loop feedback and independent, simultaneous
control of each electrode, the system is able to advantageously
regulate temperatures to occur at each electrode at the desired
temperature. This produces optimum lesion size, and avoids charring
and vaporisation associated with temperatures greater than
100.degree. C. This is in marked contrast to the prior art, since
the embodiment provides a margin of at least 20.degree. C.,
highlighting the lack of temperature control of all of the
electrodes in the conventional system. The prior art is able to
affect only the temperature of the electrode being monitored. As
lesions size is proportional to the temperature of the electrodes,
the system according to this embodiment is able to controllably
produce larger lesion. The ability to maintain all electrodes at a
desired temperature simultaneously and independently enables
contiguous uniform lesions, not as dependent on the size and
contact area of each electrode. Conversely, if it is desired to
deliver RF energy to only one particular electrode to minimise
thermal damage to "good" tissue, the system according to this
embodiment is able to ensure that adjacent electrodes have minimal
current. That is, the system according to this embodiment has the
ability to ensure precise temperature control of each electrode
individually and simultaneously.
[0077] FIG. 3 is a detailed schematic diagram of the system of FIG.
1. As shown in FIG. 3, the number of electrodes and separate
channels N is preferably four (4). However, this embodiment may be
practiced with a different number (e.g., N=3 or N=5) of electrodes
and channels without departing from the scope and spirit of the
present invention. Further, the splitter may be practiced with N
channels and a number of separate probes where the total number of
electrodes of the probes is less than or equal to N. A single
electrode 22A and corresponding channel of the N-channel RF
splitter 6 is described hereinafter with reference to FIG. 2. While
a single electrode 22A and corresponding channel are described, it
will be apparent to a person skilled in the art that the following
description applies equally to the three remaining electrodes 22B
to 22D and the corresponding channels of the splitter of FIG.
3.
[0078] In FIG. 2, the control signal 14A output by the programmable
controller 2 is provided to an isolation amplifier 42A which in
turn is connected to a fast-switching, full bridge rectifier 34A.
In particular, the output of the isolation amplifier 42A is
connected to a fast-switching variable resistance 48A used to
control operation of the rectifier bridge 34A. Preferably, the
variable resistance 48A is implemented using a power N-channel
enhancement MOSFET. The programmable controller 2 receives a
temperature signal 16A from the output of another isolation
amplifier 40A.
[0079] One terminal of the RF generator 8 is coupled via a
decoupling capacitor 9 to the dispersive electrode 12. The tissue
(e.g., myocardium) which the probe 20 is to be applied to is
generally represented by a block 15 between the dispersive plate 12
and an electrode 22A of the needle probe 20. In this embodiment,
the needle probe is inserted into the tissue. The electrode 22A is
generally represented by a tubular or ring-like structure in
accordance with the electrode structure employed in the needle
probe 20. However, again it will be appreciated that other
electrode structures may be practised dependent on the probe type
without departing from the scope and spirit of the invention. The
other terminal of the RF generator 8 is connected via a fail-safe
relay 38A and a thermal fuse, current limiter 39A to the rectifier
bridge 34A. The relay 38A consists of a fail-safe relay contact
38A' and a fail-safe relay winding 38A". These circuits act as
current interrupting and current limiting devices.
[0080] The output terminal of the fast-switching, full bridge
rectifier 34A is coupled via a decoupling impedance matching
capacitor 44A to a stainless steel conductor 47A, which is
connected to the stainless steel electrode 22A and a terminal of
the thermocouple junction 36A. The stainless steel conductor 47A is
also connected to a low pass filter 30A, preferably composed of
passive elements. A titanium conductor 46A is also coupled to the
stainless steel electrode 22A and the other terminal of the
thermocouple junction 36A embedded in the electrode 22A. The
titanium conductor 46A is further connected to the low-pass filter
30A. However, other conductive materials may be used for the
electrode 22A and the conductors 46A and 47A without departing from
the scope and spirit of the invention. The output of the low pass
filter 30A is provided to a thermocouple reference compensation
amplifier and alarm 32A. The amplifier 32A also provides a control
signal to the relay 38A. The output of the amplifier 32A is
provided to the isolation amplifier 40A, which in turn provides the
temperature signal 16A to the programmable controller 2. Again,
other temperature sensing devices and corresponding associated
circuits to provide equivalent functionality may be practiced
without departing from the scope and spirit of the invention.
[0081] The thermocouple 36A embedded in the electrode 22A produces
a temperature signal on conductors 46A and 47A in response to the
heat produced by the delivery of RF energy to the myocardium tissue
15. The signal produced by the thermocouple junction 36A is
low-pass filtered using the low-pass filter 30A, the output of
which is provided to the amplifier and alarm 32A. The alarm and
amplifier 32A produces an amplified temperature signal that is
provided to the isolation amplifier 40A. In addition, the amplifier
and alarm 32A provides a control signal to operate the relay 38A so
as to interrupt the delivery of RF energy from the RF generator via
the relay 38A when the measured or sensed temperature exceeds a
predetermined threshold level.
[0082] The programmable controller 2 uses the temperature signal
16A to produce a control signal 14A that is provided to the
variable resistance 48A of the full bridge rectifier 34A. This
control signal 14A is provided via the isolation amplifier 42A. The
control signal 14A operates the full bridge rectifier so as to
variably and continuously control the amount of RF energy delivered
to the stainless steel electrode 22A for ablation. Thus, this
embodiment is able to precisely and independently control the
electrodes 22A to 22D of the needle probe 20.
[0083] The heating in RF energy transfer occurs not from the
electrode 22A to 22D itself but from a small volume of tissue in
contact with the electrode 22A to 22D, This heating source is
directly proportional to the electrode surface area in contact with
the tissue, contact pressure and the electrical conductivity of the
tissue. Therefore, the system according to this embodiment
advantageously controls the RP energy in each electrode
independently of each other.
[0084] Thus, the system provides maximum control at each electrode
22A to 22D by minimising current flow between adjacent electrodes
22A to 22D. This is achieved by a single RF source (one phase) 8
using RF splitter 8 to regulate current flow to each electrode 22A
to 22D as a function of the temperature of each electrode.
[0085] The first embodiment illustrated in FIGS. 1 to 3 provides a
system for simultaneous unipolar, multi-electrode ablation using
simultaneous closed-loop control of temperature at each electrode
22A to 22D. This system advantageously enables multielectrode
ablation for ablating ventricular tachycardia and atrial
fibrillation. In contrast to conventional ablation systems which
cut off current to any electrode during ablation if a temperature
or impedance goes above a particular level and therefore cannot
produce reliable lesions because the electrode-tissue interface
surface area varies considerably during ablation, this embodiment
is able to overcome this disadvantage of conventional systems. In
this embodiment the control algorithm for generating the control
signals and operating the system in response to the temperature of
each of the electrodes is preferably implemented in software
carried out using a general purpose computer.
[0086] An experimental example of the use of the system is set
forth below outlining the use of another system in accordance with
that of this embodiment. ablation with simultaneous closed-loop
temperature control of each electrode is the optimum method for
simultaneous multi-electrode ablation.
[0087] Second Embodiment
[0088] Another embodiment of the invention is illustrated in FIG.
4, in which like elements of FIGS. I to 3 are indicated with the
same reference numerals, For the purpose of brevity only,
components of the second embodiment shared with the first
embodiment are not repeated hereinafter. However, those aspects of
the second embodiment will be readily understood by a person
skilled in the art in view of the description with reference to
FIGS. 1 to 3. Instead, the description hereinafter describes those
aspects of the second embodiment not set forth above.
[0089] A single channel of the system according to the second
embodiment is shown schematically in FIG. 4. The system comprises
the programmable controller 2 and the module 4', which comprises
the like numbered elements of FIG. 2, a voltage/current sensing
module 50A and the corresponding isolation amplifier 52A. Again,
while the RF generator 8 is illustrated within the module 4', it
will be apparent to a person skilled in the art that the RP
generator 8 can be equally applied to plural channels, as indicated
in FIG. 3.
[0090] The conductors 46A and 47A are also coupled to the input
terminals of the voltage and/or current sensing module 50A, which
preferably detects the root-mean-square (RMS) voltage and/or
current at the electrode 22A. The detected or measured voltage
and/or current signal is output by the sensing module 50A and
provided to isolation amplifier 52A. In turn the output of the
isolation amplifier 52A is provided to the programmable controller
2.
[0091] The voltage and/or current sensing module 50A measures the
RMS voltage and current delivered to the electrode 22A Thus, the
average power and impedance of each electrode 22A can be determined
independently as well. Thus, the module 50A independently senses at
least one of following: the voltage, current, impedance and average
power of each electrode. This is done to provide a corresponding
measurement
EXAMPLE
[0092] A system in accordance with the first embodiment was
implemented and tested to compare unipolar versus bipolar ablation
and single electrode temperature control versus simultaneous
multi-electrode temperature control during ablation.
[0093] Two types of 21 gauge needles, each with 2 cylindrical
electrodes were introduced from the epicardium at thoracotomy in 3
greyhounds, The proximal electrode measured 1 mm. The distal
electrode measured 1 mm in one needle and 1.5 mm in the other. The
inter electrode distance was 4 mm. Seventy four intramural RF
ablations were performed for 60 seconds through both the electrodes
of each needle simultaneously in an unipolar (Uni) or a bipolar
(Bi) fashion. During ablations the temperature of only one
electrode (proximal or distal) or both the electrodes
simultaneously were maintained at 80.degree. C. by closed loop
control. Lesion sizes were measured histologically.
[0094] The maximum.+-.SD temperature (temp) measured at the
proximal (P) and the distal (D) electrodes were
1 (electrode controlled = electrode at which temperature was
Controlled) Length of each electrode Uni Electrode Temp of P Temp
of D in needle or Bi controlled electrode electrode p value P = 1
mm, Bi P(1 mm) 82 .+-. 1 82 .+-. 2 0.7 D = 1 mm P = 1 mm, Uni P(1
mm) 83 .+-. 1 82 .+-. 2 0.01 D = 1 mm P = 1 mm, Bi P(1 mm) 81 .+-.
1 60 .+-. 2 <0.001 D = 1.5 mm P = 1 mm, Bi D(1.5 mm) 96 .+-. 2
80 .+-. 2 <0.001 D = 1.5 mm P = 1 mm, Uni Both 82 .+-. 2 81 .+-.
1 0.24 D = 1.5 mm
[0095] Simultaneous multi-electrode ablation without closed-loop
temperature control of each electrode results in higher temperature
at the smaller electrode-tissue interface and lower temperature at
the larger electrode-tissue interface. This results in varying
lesion sizes and potentially coagulum formation and impedance
rises. Unipolar RF signal which can be used by the programmable
controller so that additional safety features may be implemented in
the system. This preferably provides an increased level of safety
by enabling predetermined cut-off levels (eg, RMS voltage, RMS
current, impedance and average power) to be used to shut-down the
output of each electrode 22A. This is preferably carried out by the
programmable controller 2 which provides control signal 14A
dependent upon at least one of these criteria. Thus, the controller
2 generates the control signal 14A to independently interrupt
delivery of the RF energy to the respective electrode when the
meaurement signal exceeds a predetermined threshold condition.
Further control structures utilising RMS voltage and/or current may
also be applied to enhance the control and safety performance of
the system.
[0096] Thus, the second embodiment provides, in addition to the
advantages of the first embodiment, additional safety features.
[0097] While only a small number of embodiments of the invention
has been described, it will be apparent to a person skilled in the
art that modifications and changes thereto can be made without
departing from the scope and spirit of the present invention.
* * * * *