U.S. patent number 5,431,649 [Application Number 08/113,441] was granted by the patent office on 1995-07-11 for method and apparatus for r-f ablation.
This patent grant is currently assigned to Medtronic, Inc.. Invention is credited to Michael F. Hoey, Peter M. J. Mulier.
United States Patent |
5,431,649 |
Mulier , et al. |
July 11, 1995 |
Method and apparatus for R-F ablation
Abstract
An ablation catheter and a method of performing cardiac
ablation. The catheter is provided with a hollow, helical
electrode, which is screwed into cardiac tissue at a desired
ablation site and connected to a source of R-F electrical energy to
ablate the tissue adjacent the electrode. Prior to ablation, a
conductive fluid may be injected through the hollow needle, both to
provide for cooling of the tissue adjacent the needle and to
increase the conductivity of the tissue in the area of the
electrode.
Inventors: |
Mulier; Peter M. J. (St. Paul,
MN), Hoey; Michael F. (Shoreview, MN) |
Assignee: |
Medtronic, Inc. (Minneapolis,
MN)
|
Family
ID: |
22349430 |
Appl.
No.: |
08/113,441 |
Filed: |
August 27, 1993 |
Current U.S.
Class: |
606/41; 600/374;
606/45; 607/127; 607/120 |
Current CPC
Class: |
A61B
18/1492 (20130101); A61B 18/1477 (20130101); A61M
25/0084 (20130101); A61B 2090/064 (20160201); A61B
2017/00292 (20130101); A61B 2090/3925 (20160201); A61B
2018/00029 (20130101); A61B 2018/1253 (20130101); A61B
18/14 (20130101); A61B 2018/00011 (20130101); A61B
2018/00452 (20130101); A61M 2230/08 (20130101); A61M
2025/0089 (20130101); A61B 2018/00547 (20130101); A61B
2018/1435 (20130101); A61B 2017/22077 (20130101); A61B
2018/00351 (20130101); A61B 2017/00097 (20130101); A61B
2018/00023 (20130101); A61B 2018/0022 (20130101); A61B
2018/1425 (20130101); A61B 2218/002 (20130101); A61B
10/02 (20130101); A61B 2018/126 (20130101); A61B
2018/00476 (20130101); A61B 2018/1472 (20130101); A61B
2018/00821 (20130101); A61B 2018/00065 (20130101); A61B
2018/00577 (20130101); A61B 2017/00274 (20130101) |
Current International
Class: |
A61B
18/14 (20060101); A61B 17/22 (20060101); A61M
25/00 (20060101); A61B 17/00 (20060101); A61M
3/02 (20060101); A61M 3/00 (20060101); A61B
017/39 () |
Field of
Search: |
;606/32,41,45-49
;607/119,120,122,126,127,130,131 ;128/642 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0013605 |
|
1980 |
|
EP |
|
93/0472 |
|
Mar 1993 |
|
WO |
|
Primary Examiner: Pellegrino; Stephen C.
Assistant Examiner: Peffley; Michael
Attorney, Agent or Firm: Duthler; Reed A. Patton; Harold
R.
Claims
In conjunction with the above specification, we claim:
1. An ablation catheter system, comprising:
an elongated catheter body having a proximal end, a distal end and
an internal longitudinal lumen;
an elongated electrical conductor, mounted within said catheter
body;
a hollow helical conductive needle mounted to the proximal end of
said catheter body and having an internal lumen coupled to the
internal lumen of said catheter body, said hollow needle coupled to
said electrical conductor;
fluid delivery means coupled to the internal lumen of said catheter
body for delivering a conductive fluid to said internal lumen of
said catheter body; and
a source of R-F electrical energy, coupled to said electrical
conductor.
2. A catheter system according to claim 1 wherein said conductive
fluid delivering means comprises means for delivering Ringer's
solution.
3. A catheter system according to claim 1 wherein said conductive
fluid delivering means comprises a reservoir containing said
conductive fluid and a means for controlling fluid flow.
4. A catheter system according to claim 1 wherein said catheter
body comprises a torque transfer cable, extending longitudinally
along said catheter body.
5. A catheter system according to claim 1 wherein said catheter
comprises a conductive torque transfer cable, extending
longitudinally along said catheter body, coupled to said hollow
needle and to said source of R-F electrical energy.
6. A catheter system according to claim 1 wherein said catheter
comprises a conductive tube, extending longitudinally along said
catheter body, coupled to said hollow needle and to said source of
R-F electrical energy.
7. A catheter system according to claim 1 wherein said catheter
comprises a plastic tube, extending longitudinally along said
catheter body, coupled to said hollow needle and to said fluid
delivery means.
8. A method of catheter ablation, comprising:
advancing an elongated catheter having a proximal end, a distal
end, an internal longitudinal lumen, an electrical conductor and a
hollow helical conductive needle mounted to the proximal end of
said catheter body, coupled to the internal lumen of said catheter
and to said electrical conductor, to a desired site within a
heart;
screwing said helical needle into heart tissue at said desired
site;
delivering a conductive fluid through the internal lumen of said
catheter to said helical needle;
coupling said electrical conductor to a source of R-F electrical
energy; and
delivering R-F electrical energy to said helical needle.
9. A method according to claim 8 wherein said step of screwing said
helical needle into heart tissue comprises rotating said
catheter.
10. A method according to claim 8, further comprising the step of
connecting said electrical conductor to ECG monitoring
apparatus.
11. A method according to claim 8 wherein said catheter comprises a
torque transfer cable, extending longitudinally along said catheter
and coupled to said helical needle and wherein said step of
screwing said helical needle into heart tissue comprises rotating
said torque transfer cable.
12. A method according to claim 8 wherein said catheter comprises a
plastic tube, extending longitudinally along said catheter body,
coupled to said helical needle and further comprising the step of
delivering said conductive fluid through said plastic tube prior to
said step of screwing said needle into said heart tissue.
13. A method according to claim 8 wherein said step of delivering
said conductive fluid comprises delivering Ringer's solution.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to the field of devices for
cardiac surgery, and more specifically to devices for R-F ablation
of cardiac tissue.
The present invention is directed toward treatment of
tachyarrhythmias, which are heart rhythms in which an chamber or
chamber of the heart exhibits an excessively fast rhythm. In
particular, the present invention is directed toward treatment of
tachycardias, which are due to the presence of ectopic foci within
the cardiac tissue or due to the presence of aberrant condition
pathways within the cardiac tissue.
Therapies have been developed for treating tachycardias by
destroying cardiac tissue containing identified ectopic foci or
aberrant conduction pathways. A variety of approaches have been
taken, including application of electrical energy or other forms of
energy to destroy the undesired cardiac tissue. As examples,
ablation of cardiac tissue has been accomplished by means of radio
frequency electrical current, microwave energy, heat, electrical
pulses, cryothermy, and lasers. At present, ablation using R-F
energy is perhaps the most widely practiced in the context of
ablation procedures that can be carried out by means of a catheter,
inserted into the closed heart.
Most R-F ablation catheters employ electrodes which are intended to
contact the endocardium of the heart, or, in some cases as in U.S.
Pat. No. 5,083,565, are intended to penetrate the endocardium, and
enter the myocardium. In general, R-F ablation catheters are
effective to induce small lesions in heart tissue including the
endocardium and inner layers of myocardium, in the immediate
vicinity of the electrode. However, the medical community has
expressed a desire for devices which produce larger lesions, to
reduce the number of applications of R-F energy (burns) required to
effectively ablate the cardiac tissue associated with the
tachycardia.
R-F ablation causes tissue in contact with the electrode to heat
through resistance of the tissue to the induced electrical current
therethrough. The actual extent of heating is somewhat
unpredictable. However, temperature tends to rise as the duration
and amplitude of the R-F signal increase. Heating of the tissue
beyond a certain point can cause dissection or charring of the
tissue, resulting in a high impedance between the R-F electrode and
the return electrode, which in turn leads to cessation of the
heating process, and, in some cases, sticking of the electrode to
the charred tissue. One response to this phenomenon has been the
inclusion of thermocouple within the ablation electrode, in
conjunction with feedback control to modulate the R-F signal to
maintain the electrode temperature at a set parameter. One such
system is disclosed in U.S. Pat. No. 5,122,137.
SUMMARY OF THE INVENTION
The present invention is directed toward improving the consistency
and efficacy of R-F ablation, and to increase the overall size and
extent of the lesions induced by R-F ablation. These goals are
pursued by means of an ablation catheter employing a helical
electrode intended to be screwed into the myocardium at the site
intended for ablation. The helical electrode provides an enlarged
surface are as compared to relatively straight or needle-like
electrodes for insertion into the endocardium, and also serves to
stabilize the location of the catheter during the application of
the R-F signal. In addition, there is essentially no bleeding
following removal of the helical electrode, so it can safely be
placed in multiple locations for mapping and ablation purposes.
An additional aspect of the invention in its preferred embodiment
is the provision of a non-toxic, non-arrhythmogenic, conductive
solution such as Ringer's solution to the area of the electrode,
before and during application of R-F energy. In its preferred
embodiment, the helical electrode is hollow, and the conductive
solution is applied through one or more apertures in the electrode.
The conductive solution injected prior to application of the R-F
signal is believed to displace blood in the vicinity of the
electrode. Ringer's solution, for example, has a much higher
conductivity than blood (approximately 3-4.times.) or cardiac
muscle (approximately 7.times.), overall resistance to the induced
electrical current is reduced, which is believed to assist in
expanding the size of the lesion, by spreading the effective area
of application of the electrical current over a wider area.
Application of the conductive solution during the burn further
assists by preventing overheating of the tissue, allowing for a
prolonged application of the R-F signal, extending beyond the point
at which burning or charring would otherwise normally occur. Both
of these factors are believed to contribute to an increase in the
overall size of the lesion produced by application of R-F energy at
a particular location.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a catheter adapted to perform the improved
method of R-F ablation, according to the present invention.
FIG. 2 is a cutaway view through the distal end of the catheter
illustrated in FIG. 1.
FIGS. 3, 4, and 5 illustrate alternative embodiments of the helical
electrode of the catheter illustrated in FIGS. 1 and 2.
FIG. 6 illustrates the associated apparatus for administration of
conductive solution before and during application of R-F energy to
the helical electrode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a plan view of a catheter specifically designed for
performing R-F ablation according to the present invention. The
catheter includes an elongated catheter body 10, comprising an
insulative outer sheath 12, which may be made of polyurethane,
teflon, or other biocompatible plastic. A hollow, helical electrode
14 is located at the distal end of the catheter and is coupled to
the distal end of an internal tube, running the length of the
catheter. At the proximal end of the catheter a fitting 16 is
located, to which luer lock 18 is coupled. Luer lock 18 is coupled
to the proximal end of the internal tube. A swivel mount 20 is
mounted to luer lock 18, allowing rotation of the catheter relative
to luer lock 22. Luer lock 22 is intended to be coupled to a source
of conductive fluid such as Ringer's solution, and allows for
application of the Ringer's solution through the catheter and
through electrode 14, while electrode 14 is being screwed into
heart tissue. An electrical connector 24 exits fitting 16, and is
coupled to electrode 14, allowing for the use of electrode 14 to
apply R-F energy to heart tissue. Electrode 14 may also be employed
for other related functions such as measurement of electrograms
within the 15 heart and pacing of heart tissue by application of
low energy pulses appropriate for cardiac pacing. In use, the
catheter is advanced to the desired site for ablation, which
preferably has been previously identified by means of cardiac
mapping in a fashion similar to cardiac mapping presently employed
with R-F ablation procedures. The catheter may be guided to the
desired location by being passed down a steerable or guidable
catheter, for example, as disclosed in U.S. Pat. No. 5,030,204,
issued to Badger et al., or by means of a fixed configuration guide
catheter, for example in U.S. Pat. No. 5,104,393, issued to Isner,
both of which patents are incorporated herein by reference in their
entireties. Alternatively, the catheter may be advanced to the
desired site within a heart by means of a deflectable stylet, as
disclosed in PCT Patent Application WO 93/04724, published Mar. 18,
1993, or a deflectable guidewire as disclosed in U.S. Pat. No.
5,060,660, issued to Gambale, et al., both of which patents are
incorporated herein by reference in their entireties. When the
hollow needle 14 is located at the desired location it is screwed
into heart tissue by rotating the catheter body. A torque cable
within the catheter body provides for 1:1 torque transfer from the
proximal end of the catheter to the hollow needle 14.
When advanced to the desired location, luer lock 22 is coupled to a
pressurized source of Ringer's solution. An appropriate source is
discussed in more detail in conjunction with FIG. 6 below. However,
for purposes of the present invention, a source of Ringer's
solution capable of delivering 1 cc per minute of solution at
atmospheric pressure has been found to be adequate. Delivery of
Ringer's solution should begin before or at the time at which the
electrode 14 is screwed into the tissue to be ablated. In animal
experimentation, the inventors have found that delivery of Ringer's
solution for a period of two minutes prior to the delivery of R-F
energy assists in producing a larger but still controlled, regular
lesion.
After the electrode has been located, and Ringer's solution has
been administered for the desired period of time, electrical
connector 24 is coupled to an R-F electrosurgical power source, of
the type commercially available and employed for cutting an
electro-coagulation. The present inventors have employed a
Blendtome brand electrosurgical generator, Model No. 755,
coagulation setting number 7, cutting setting number 1. At these
settings, a prolonged application of R-F energy, e.g., one minute
or so, may be employed to produce a large, controlled lesion.
Greater or lesser time periods may be employed, however, time
periods less than 20 seconds may be counter-indicated, as it
appears that the cooling effect of the Ringer's solution, in such
shorter R-F application times, may actually decrease the effective
size of the lesion.
After R-F ablation, the electrode 14 may be coupled to a cardiac
pacemaker, and cardiac pacing energy may be delivered to the lesion
site in an attempt to measure the pacing threshold. Pacing
threshold may be measured by delivering pacing pulses at differing
energy levels, e.g. by altering pulse amplitude or width, and
determining the minimum energy level effective to cause a
depolarization of cardiac tissue. The inventors believe that the
higher the pacing threshold, assuming a relatively homogenous
lesion, the greater lesion size. As such, the electrode 14 can be
used to derive a rough estimate of overall lesion size. The
electrode 14 may also be coupled EKG monitoring equipment to assist
in determining whether the tachycardia persists and whether the
tissue in the vicinity of the electrode is still participating in
aberrant conduction or ectopic activity, associated with the
tachycardia.
The helical configuration of electrode 14 is believed to be
particularly beneficial in the context of an ablation electrode.
Because the electrode is screwed into and completely located within
the heart tissue, out of the bloodstream, application of R-F energy
is limited to the tissue itself. This differs from traditional R-F
ablation electrodes, which simply contact the endocardium, with the
result that a substantial portion of the energy applied is
dissipated in the blood within the heart adjacent the electrode
site. Moreover, R-F energy applied to the bloodstream may cause
clotting of the blood adjacent the electrode, and raise the risk of
clots breaking loose of the electrode.
The helical electrode also provides a substantially increased
surface area as compared to the needle-like electrodes proposed in
the above cited Parins patent, and also serves to anchor the
catheter reliably during application of the R-F energy. In
addition, the helical shape of the electrode prevents the
application of conductive solution through the electrode from
causing the electrode to be backed out of its insertion site due to
hydraulic pressure, as might occur if a straight, hollow electrode
were employed. The elongated path defined by the helical electrode
also reduces the possibility of leakage of conductive fluid along
the needle and out of the heart tissue.
FIG. 2 illustrates a cutaway version through the end of the
catheter illustrated in FIG. 1. In this view, it can be seen that
helical electrode 14 is provided with an internal lumen 26 which is
in communication with the internal lumen of a tube 30. Tube 30
extends to the proximal end of the catheter and is in full
communication with luer lock 18, as discussed above, tube 30 may be
fabricated of polyimide tubing or of stainless steel tubing. In the
present invention, the stainless steel tubing serves as an
additional conductor, coupling electrode 14 to electrical connector
24 and enhancing the overall conductivity of the catheter. The use
of polyimide tubing, while reducing the overall conductivity of the
catheter enhances the flexibility somewhat, and may be beneficial
in some cases. It is recommended to apply a steady flow of Ringer's
solution through the tubing to electrode 14 during passage catheter
through the vascular system to the electrode site, if possible. The
flow of Ringer's solution in this case assists in maintaining the
patency of the lumen of tubing 30, and prevents plugging of the
exit ports of the electrode as it is advanced into the cardiac
muscle.
Surrounding tube 30 are two coils 32 and 34, which are wound in
opposite directions, to provide a torque cable. In the case of the
specific devices employed by the inventors, a torque cable as
manufactured by Lake Region Manufacturing Company of Chaska, Minn.
was employed, which torque cable is described in U.S. Pat. No.
5,165,421, incorporated herein by reference in its entirety. Coils
32 and 34 also serve as conductors. As illustrated, tubing 30 is
between metal coils 32 and 34 and helical electrode 14. However, if
polyimide tubing is used, the coils 32 and 34 will serve as the
only conductor and thus will be electrically coupled to electrode
14 by means of welding, soldering or mechanical interconnection.
Insulative sleeve 12 serves both to provide a smooth exterior for
the catheter and to insulate the metal coils 32 and 34, along the
length of the catheter.
FIGS. 3, 4 and 5 illustrate alternate embodiments of the helical
electrode illustrated in FIG. 2. The electrode in FIG. 2 comprises
a hollow tube having a single exit port located as its distal end.
Electrode 36, illustrated in FIG. 3, corresponds to electrode 14
with the exception that additional exit ports 38, 40 and 42 have
been added, allowing for dispensing of the Ringer's solution along
the length of the helix. Ports 38, 40 and 42 may be laser drilled,
and may be spaced in any desired fashion around the circumference
of electrode 36 and along the length of electrode 36. Preferably,
it is believed desirable to have ports spaced around the full
circumference of the electrode, to provide for an even dispensing
and dispersing of Ringer's solution.
Electrode 44, illustrated in FIG. 4 is a second alternative
embodiment of a helical electrode corresponding to electrode 14,
but with the addition of an insulative sleeve 46, which covers the
proximal portion of the electrode. Sleeve 46 limits the application
of R-F energy to the distal portion of the electrode. Optionally,
additional exit ports corresponding to ports 38, 40 and 42
illustrated in FIG. 43 may also be employed in conjunction with
electrode 44. These additional exit ports may be limited to the
exposed, uninsulated portion of electrode 44, or may extend along
the entire length of electrode 44.
Electrode 48, illustrated in FIG. 5 is a third alternative
embodiment corresponding generally to electrode 14. However, in
this case, electrode 48 is provided with a thermocouple 50 located
in the distal end of electrode 48. Thermocouple wires 52 and 54
extend backwards through the lumen within electrode 48 and are used
to monitor the temperature at the tip of the electrode, for use in
feedback control of power applied to the electrode as described in
the above-cited patent issued to Lennox et al. Only one of
thermocouple wires 54 and 52 is insulated, and the other is simply
coupled to the interior of electrode 48. In order to employ the
electrode of FIG. 4B, an additional electrical connector would have
to be added to the embodiment illustrated in FIG. 5, in order to
allow connection to the thermocouple wire not connected to
electrode 48. Alternatively, both thermocouple wires may be
insulated, requiring two additional electrical connectors at the
proximal end of the device, each coupled to one of the thermocouple
wires. It should be noted that the thermocouple 50 effectively
blocks the distal opening of the lumen within electrode 48, so that
Ringer's solution will be dispensed only by means of side ports 56,
58 and 60.
FIG. 6 illustrates a pressurized source for Ringer's solution which
may be employed in conjunction with catheter illustrated in FIG. 1.
A reservoir 100 is provided, which is commercially manufactured by
Block Medical Inc., and sold under the brand name "Home Pump". The
reservoir contains Ringer's solution and provides Ringer's solution
at one atmosphere pressure to flow control 102, via filter 104.
Flow control 102 may, for example, provide a flow limit of 20 drops
or 1 cc per minute. Flow control 102 is coupled to a second flow
control element 104, which, in the experimental apparatus employed
by the inventors allows for additional adjustability of flow rates.
Flow control 104 is coupled to the luer lock 22, illustrated in
FIG. 1, which in turn is in fluid communication with electrode 14
(FIG. 1 ), allowing delivery of Ringer's solution to the electrode.
An electrosurgical generator 200 for providing R-F electrical
energy is illustrated in functional block form, coupled to
electrical connector 24 and to a ground plate electrode 202 (not
drawn to scale). All other labeled elements correspond to those
illustrated in FIG. 1.
Wile the embodiment illustrated above requires a second element
(e.g. a guide catheter or guide wire) for advancing and positioning
the catheter at its desired location, it is anticipated that the
basic apparatus disclosed above may also be incorporated into
catheters which themselves are steerable or deflectable, similar to
R-F ablation catheters presently in clinical investigation.
Similarly, it is anticipated that in commercial embodiments,
alternative mechanisms (e.g. precision pumps) for controlling the
flow of Ringer's solution may be employed. Similarly, while the
inventors have employed Ringer's solution, other alternative fluids
may be workable as well. As such, the embodiment discussed above
should be considered exemplary, rather than limiting, in
conjunction with the following claims.
* * * * *