Electrosurgical catheter and method for resolving atherosclerotic plaque by radio frequency sparking

A method, and device utilized to practice it, for the resolution of tissue by radio frequency sparking. The device of the present invention having a distal end which is insertable within and along the lumen of a tubular body member and manipulated there through to desired position where the device will be operated. The device comprises an elongated flexible hollow tube having a distal end, a proximal end, and a diameter smaller than the diameter of the tubular, body member into which the device is being inserted; passage means within the tube; a plurality of electrodes adjacent the distal end of the device; and means for selectively supplying radio frequency electrical current to at least one of said electrodes.

FIELD OF THE INVENTION 
The present invention relates to a device and method for resolving or 
removing atherosclerotic plaque build-up in an artery in order to improve 
blood flow. The device consists of an electrosurgical catheter which has a 
plurality of electrode sites, each capable of resolving plaque via radio 
frequency ("RF") sparking between the electrodes and the plaque. The 
current generated at the selected electrode is modulated so that the fatty 
material of the plaque is resolved without creating significant amounts of 
residue. 
BACKGROUND OF THE INVENTION 
Various angioplasty techniques have been in use for several years. 
Typically, a catheter is introduced into the body through an artery in the 
leg or arm and threaded into the artery or blood vessel that has 
restricted blood flow due to the build-up of atherosclerotic plaque. The 
most common technique in current practice is balloon angioplasty. The 
catheter positioned within the subject artery has a deflated balloon at 
its tip. The balloon is inflated within the artery and the expansion of 
the balloon is designed to "press" the plaque into the artery wall, 
thereby minimizing blood flow restrictions. Balloon angioplasty generally 
just manipulates the form of the plaque, and does not create a significant 
problem of plaque residue flowing from the site. Unfortunately, balloon 
angioplasty has several failings and a relatively high complication rate. 
Atherosclerotic plaque build-up can exist in a number of different forms. 
The plaque can be quite hard and scaly or more fatty and pliable. The 
areas of plaque accumulation are generally not symmetrically located at a 
particular point in the artery, rather adhering to only portions of the 
artery walls. 
Considerable efforts have been directed toward finding improved means to 
perform angioplasty procedures. Numerous devices recently have been 
described that utilize the application of heat to resolve atherosclerotic 
plaque. See for example, U.S. Pat. Nos. 4,654,024 of Crittendon et al. and 
4,748,979 and 4,672,962 of Hershenson. The most extensive research 
concerning the use of heat to resolve atherosclerotic plaque has been 
directed toward the area of laser angioplasty techniques. In most laser 
angioplasty devices the laser is used simply to supply heat to the tip of 
the catheter. See for example, U.S. Pat. Nos. 4,784,133 of Mackin; 
4,685,458 of Lechrone; 4,770,653 of Shturman; 4,662,368 and 4,773,413 of 
Hussein; and 4,732,448 and 4,641,912 of Goldenberg. 
The various angioplasty techniques described in the literature uniformly 
fail to address the asymmetric disposition of the plaque within the 
artery. In most cases, the tip of the angioplasty catheter acts as if the 
plaque consists of a uniform symmetric coating on the interior wall of the 
artery. Particularly in those techniques which use something other than 
pressure to manipulate the plaque, the resolving forces are applied 
indiscriminately to the plaque and to the healthy tissue within the 
artery. 
Radio frequency sparking to cut or cauterize tissue as a medical procedure 
is common in the prior art. There are two basic classes of electrosurgical 
devices. Monopolar devices consist of a high-frequency electrical 
(generally RF) generator, a cutting or cauterizing electrode or needle, 
and a patient plate. The patient plate is attached to the body of the 
patient, and acts as the return electrode for completion of the RF 
circuit. Cutting occurs due to the heat generated by RF sparking from the 
electrode to the patient's body tissue. The shape of the electrode 
concentrates the RF energy, thus creating the high temperature spark. 
Appropriate modulation of the frequency determines whether cutting or 
cauterizing will occur. The relatively larger surface area of the patient 
plate, which is in contact with the patient's body, prevents the current 
flow from concentrating at one point. This prevents the RF current from 
burning the patient as the current exits the body. 
There are also several bipolar electrosurgical devices described in the 
prior art. Bipolar devices consist of a high frequency electrical 
generator and an instrument that contains both the delivery and return 
electrode. RF sparking occurs between the two self-contained electrodes of 
the instrument. The bipolar electrosurgical devices of the prior art are 
generally inadequate due to the conditions necessary to create bipolar 
sparking. The most fundamental difficulty is that bioactive electrodes 
must have a roughly equal voltage drop at both the delivery and return 
electrodes. The high power current required in order to achieve bipolar 
arcing often causes extraneous sparking, particularly when there is 
unequal contact with the surrounding tissue. 
The extension of known electrosurgical processes--utilizing RF sparking--to 
angioplasty techniques is relatively unexplored. A disclosure of a 
monopolar electrosurgical catheter for use in resolving atherosclerotic 
plaque is found in U.S. Pat. No. 4,682,596 of Bales. The mono and bipolar 
devices in Bales describe a hollow catheter with a hollow tip member. Only 
one potential electrode, at the catheter tip, is envisioned by the Bales 
patent. Bales briefly describes the utilization of variously modulated 
waveforms in order to resolve atherosclerotic plaque, and the application 
of high power levels while minimizing the creation of excessive amounts of 
heat. However, means are included for removing residue from the plaque 
destruction site, indicating that the modulation techniques employed have 
not been maximized. It should be possible to destroy the plaque in such a 
manner so as to eliminate significant residue formation. 
An article by Cornelius J. Slager et al. in the Journal of the American 
College of Cardiology entitled "Vaporization of Atherosclerotic Plaque by 
Spark Erosion" (Jun. 1985, pp. 1382-6) describes the use of a bipolar RF 
sparking catheter. Again, there is a single spark generating electrode. 
The sparking frequency is modulated, but not to optimize ablation. 
Synchronous transmission of energy with cardiac contraction is employed in 
order to minimize the disruption of electrical pathways in the heart. 
U.S. Pat. No. 4,643,186 of Rosen describes an "antenna" type bipolar RF 
sparking catheter for use in angioplasty. The delivery and return 
electrodes are configured in such a way that the electrodes terminate 
together to form an "antenna." 
When current is supplied to the antenna, RF sparking will occur. The 
addition of balloon means encapsulating the sparking antenna is also 
described. Rosen discloses coating the interior surface of such balloons 
in order to supply some control over the direction of sparking. Such 
directional manipulation can only be accomplished before the catheter is 
introduced into the patient's body. No means are disclosed for directing 
the random sparking of the "antenna" once introduced into the desired 
artery. 
An example of an asymmetrically shaped electrode or energy applicator is 
seen in U.S. Pat. No. 4,311,154 of Sterzer. The Sterzer patent discloses a 
device to be used in the treatment of a cancerous tumor with high 
temperatures, or hyperthermia. Sterzer describes a device for hyperthermic 
treatments utilizing microwave energy so that heat radiates 
nonsymmetrically from the surface of the instrument. Sterzer does not 
utilize RF sparking and, like the Rosen patent, does not contemplate the 
use of means for directing the energy once the device is in place within 
the body. 
The examples discussed above where RF sparking has been used for the 
resolution of atherosclerotic plaque employ relatively unsophisticated 
means. The RF spark is a very powerful and intense force to be let loose 
within the human body. Means for effectively harnessing the vast potential 
of RF sparking angioplasty have not been disclosed prior to this 
invention. 
SUMMARY OF THE INVENTION 
This invention relates to an improved device for the ablation or resolution 
of atherosclerotic plaque by use of RF sparking. The present invention 
adapts the electrosurgical electrode so that it may be incorporated into a 
catheter that may be manipulated to an arterial site of atherosclerotic 
plaque. The RF angioplasty catheter of the present invention has a 
segmented head, so that it is possible to control nonsymmetrical sparking 
from a plurality of electrodes. 
Combined with real time visualization techniques, the device of the present 
invention allows for greater control and precision when utilizing RF 
sparking to resolve atherosclerotic plaque. The RF spark is an extremely 
powerful and concentrated source of heat within the artery. By the use of 
a segmented catheter head, the somewhat random nature of the sparking may 
be actively directed towards the section of the artery surface containing 
the plaque build-up of interest. 
Controlling the direction of sparking from the electrode head makes it 
possible to increase the energy of the RF current utilized. By employing 
increased energy sparks, the material making up the atherosclerotic plaque 
may be almost totally disintegrated. The material constituting the plaque 
may be reduced to such fine particles that removal of residue from the 
plaque resolution site is not necessary. 
It is necessary to optimize the modulation of the RF current delivered to 
the sparking site. Even though the segmented catheter head greatly 
increases the specificity of the sparking action, it is still crucial to 
minimize temperature increases in the tissues surrounding the plaque. The 
higher energy sparks employed requires that pulsed modulation of the 
frequency be carefully controlled in order to allow the dissipation of 
heat to occur between the heat-generating spark pulses. 
The catheter device of the present invention may have an elongated flexible 
hollow body that has a single open cavity capable of delivering fluids to 
the site of plaque resolution. At the far, or distal end, of the device, 
there is a plurality of sparking sites or electrodes spaced about the 
exterior circumference of the generally cylindrical catheter device. The 
RF energy transmitted to the distal end of the catheter may be selectively 
applied to any one of the various electrodes. Visualization of the artery 
will determine which wall or walls of the artery contain the plaque 
build-up to be resolved and will determine which electrode should be 
activated.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows the distal end 20 of a atherosclerotic plaque resolving device 
constructed according to the teachings of the present invention. FIG. 3 
shows a cross-sectional view of the entire device, which is generally 
referred to, in total, as numeral 10. The device 10 is constructed, both 
by use of the appropriate size and materials, so that it may be inserted 
within and along the lumen of a blood vessel. Such devices are generally 
referred to as catheters, and may be manipulated to the desired location 
in the blood vessel or artery. The desired location is the site of 
atherosclerotic plaque build-up. Usually, the plaque site is causing 
reduced blood flow through the vessel or artery. 
The device and method of the present invention is particularly suited for 
the ablation of atherosclerotic plaque located within the arteries leading 
to the heart. The device and method disclosed herein has, however, 
significant advantages over the prior art that may be useful in a number 
of invasive surgical techniques. The device of the present invention may 
be used, for example, in the following procedures: the ablative treatment 
of fallopian tubes; the removal of colon obstructions, the removal of 
blood clots or tissue build-up within the blood vessels of the brain; and 
the removal of undesirable intestinal tissue. In each of these surgical 
procedures--and in the other invasive surgical techniques--a catheter is 
manipulated to the desired location within the body via the lumen of a 
tubular body member, and energy is applied to the distal end of the 
catheter in order to ablate or resolve tissue. 
Introduction of the device 10 to the appropriate site may be accomplished 
by use of a guidewire. A guidewire, with the appropriate bends and turns, 
is "threaded" through an arterial pathway to the desired point of plaque 
build-up. The device 10 may then be easily passed over the path of the 
guidewire to the correct arterial site. 
The device 10 includes an elongated hollow tubular body 12. The body 12 is 
usually flexible, and constructed of an electrically insulative material. 
Any of a number of polymeric or plastic materials may be employed for this 
purpose. The distal end 20 of the device 10 includes a plurality of 
electrodes 14. The electrodes 14 each constitute a monopolar 
electrosurgical electrode. The electrodes 14 may be constructed of any 
conductive metal or metallic alloy that is capable of retaining its form 
or shape when exposed to the extremely high temperatures generated by RF 
sparking. For example, the electrodes 14 may be composed of stainless 
steel, tungsten, platinum, titanium, zirconium or any of the other 
so-called refractory metals. Alloys of the refractory metals may also be 
employed. 
The distal end 20 of the device includes a generally flat end surface 22. 
The interior 16 of the tubular body 12 of the catheter 10 has a generally 
constant diameter throughout the axial length of the catheter. Each of the 
electrodes 14 is separated from each other by the insulative material of 
the tubular body 12, and exists in part on the circumference of the 
exterior surface of the tubular body 12 adjacent to the end surface 22, 
and in part planar to the end surface 22. Each electrode 14, therefore, 
consists of front 15 and radial 17 elements that are of unitary 
construction. The RF energy selectively delivered to each of the 
electrodes 14 will create sparking from the electrode 14 to the 
atherosclerotic plaque. 
In a monopolar device of the present invention as is schematically shown in 
FIG. 2, the return path for the RF current introduced into the body tissue 
is through a patient plate 92. The patient plate 92 is a relatively large 
dispersive plate that is attached to the body of the patient in order to 
establish contact with a significant amount of body surface area. The 
patient plate is typically placed onto the hip, thigh, buttock or belly of 
the patient. Conduction from the patient to the return electrode is 
maximized by applying electroconductive gel to the points of contact. 
The device 10 may also be constructed as a "bipolar" RF sparking source. In 
such an embodiment, a single return electrode may be included among the 
plurality of electrodes 14 at the distal end of the device 10. The RF 
sparking would thereby proceed from the selected electrode 14 to the 
return electrode. In such an embodiment a single return electrode may be a 
large conductive ring 93 distal to electrodes 14 with a surface area from 
5 to 20 times larger than that of any of the delivery electrodes 14. In 
another bipolar embodiment of the present invention, the power generator 
output and return may be adapted so that any one of the plurality of 
electrodes can serve as either the delivery or return electrode. For 
example, if the electrodes 14 in the device shown in FIG. 1 were numbered 
A-D and the plaque adjacent electrode A is twice that adjacent to 
electrodes B and C with the artery nearest electrode D containing no 
plaque, electrode A would be selected as the return electrode and B and C 
would be alternated as the delivery or anodic cathode. The plaque adjacent 
electrode A would receive twice the sparking energy as that adjacent 
electrodes B and C, and that adjacent electrode D would receive minimal 
amounts. In this embodiment, the directional specificity of sparking can 
be further controlled. 
The device 10 is attached to and activated by a high-frequency, high 
voltage power supply 98. There are several such power generators marketed 
for use in electrosurgery. Typically, the energy is radio-frequency. Each 
electrode 14 is coupled to the power supply via a wire conductor 40 that 
runs the entire length of the tubular body 12. Each wire 40 may be 
electrically insulated. 
The proximal end 50 of the catheter 10 has a "Y" shaped portion 52 that has 
a straight through passage 53 and a branch passage 54. The interior 16 of 
the tubular body 12 may be accessed from either the straight through 53 or 
the branch 54 passage. The wire conductors 40 are coupled to the 
generator, and prior to insertion into the catheter 10 via the branch 
passage 54 may be bundled together to form a single transmission wire 42, 
as shown in FIG. 9, or may remain separated. 
The RF generator 98 must be adapted via an electrode switching device 96 
such that the output of the generator may be selectively applied to one of 
the wire conductors 40, and therefore to one of the electrodes 14. Further 
modification of the generator via a device for waveform modulation 95 must 
be performed in order to create the optimized modulated waveform. The 
optimal waveform provides a RF pulse of energy strong enough to create a 
spark that will disintegrate the atherosclerotic plaque with minimum 
residue formation. At the same time, the waveform must be modulated such 
that there is not an excess heat build-up in the tissue adjacent to the 
plaque destruction site. Appropriate time periods in which heat may be 
dissipated between bursts of energy will enable adequate cooling periods 
for the adjacent tissues. 
It is thought that commonly available electrosurgery generator units may be 
adapted to provide the proper RF current; for example, a Bovie 
"Specialist" 75 Watt ES, Electro-Surgery Unit or similar Valleylabs unit. 
The frequency of the wave form employed will be between 0.05 and 200 
megahertz and the voltage will have a magnitude of several hundred volts. 
To achieve the optimum output modulation, a digital controller 93 will be 
connected in series with the generator to control pulse width of RF burst, 
on and off times and number of pulses. 
The transmission wire 42 or wire conductors 40 enter the catheter 10 via 
the branch passage 54 at the proximal end 50 of the catheter 10. In FIG. 
9, the embodiment of the invention utilizing a single transmission wire 
42, the transmission wire 42, which contains each of the wire conductors 
40, is constructed so that each of the wire conductors 40 is 
electronically insulated from each other. In addition, the exterior 
surface of the transmission wire 42 is coated with an insulating material. 
In the preferred embodiment of the invention, each of the wire conductors 
40 will be separately insulated, and will proceed separately through the 
catheter as seen in FIGS. 3, 5 and 6. 
FIG. 6 shows a radial sectional view of the catheter 10 at a point between 
its distal 20 and proximal 50 ends. As is shown, the wire conductors 40 
are located within the interior cavity 16 of the tubular body 12. The wire 
conductors 40 are designed so that they will not take up significant 
amounts of the interior 16 volume of the tubular body 12 and that the 
individual wires will not cross talk with each other. Room must be allowed 
for the passage of fluids to the plaque destruction site or to encompass 
the guide wire used to properly place the catheter 10. 
As can be seen in FIG. 3, the wire conductors 40 run nearly the full length 
of the tubular body 12. At some point 45 just adjacent the distal end 20 
of the catheter 10, the individual wire conductors 40 proceed through the 
tubular body 12 and are coupled to the electrodes 14. FIG. 5 is a radial 
sectional view of the catheter 10 at the point 45 where the wire 
conductors 40 each connect to its corresponding electrode 14. 
FIGS. 10 and 11 show an additional embodiment of the invention wherein the 
wire conductors 40 are separately contained within separate lumens within 
the tubular body of the cathode 10. 
The device 10 of the present invention is used for resolving or ablating 
atherosclerotic plaque or clots within the interior of vessels or 
arteries. The method of plaque resolution with such a device requires the 
use of some means for visualizing the interior of the vessel where plaque 
destruction is to occur. This can be accomplished by placing ultrasound 
transducers 85, as shown in FIG. 7 at the catheters distal end or under 
the electrodes 14. The transducers 85 send and receive ultrasonic signals 
which are processed using traditional ultrasonic processing means 100 and 
this displayed on video terminals 102 as shown in FIG. 2. Other 
visualization techniques would include, but would not be limited to, the 
following: the introduction of radionuclear dyes that allow for 
radiographic visualization use of other dyes suitable for introduction at 
the site of plaque destruction--or in the bloodstream generally--that are 
detectable by X-ray or other detection techniques, high resolution biplane 
angiography, and fiber optics introduced along the catheter pathway that 
provide an actual picture of the interior of the artery or vessel. 
Whatever means are used to determine the site of plaque build-up that 
requires treatment, the initial step is generally the placement of the 
catheter adjacent to the proposed destruction site. As described above, 
the appropriate positioning may be accomplished with the aid of a 
guidewire. Guidewires are constructed so that the wire will be introduced 
into an artery--either through the leg or arm--and threaded to the desired 
position. The placement of catheters is a well known and often performed 
procedure in connection with balloon angioplasty and other invasive 
surgical procedures. In the present invention the placement is critical 
not only with respect to the extension of the catheter distal end through 
an artery, but also with respect to the circumferential orientation of the 
catheter since the RF energy is applied differentially along the 
circumference to correspond to differential plaque build-up. 
When utilizing a guidewire to help manipulate the distal end 20 of the 
catheter 10 to the appropriate location, the end of the guidewire exiting 
the patient may be used to guide the catheter 10 by use of the hollow 
interior 16 of the tubular body 12. The guide wire can be removed from the 
interior of the catheter when resolution is to begin, or may be maintained 
in place if required by the attending physician. 
The interior cavity 16 of the catheter 10 may also be used to introduce 
fluids to the site of plaque destruction. For example, as an aid to 
visualization it may be desirable to flush the plaque destruction site. 
The introduction of dyes to aid the visualization process may also be 
accomplished via the interior cavity 16. 
The interior cavity may also be valuable in order to place a fiber optic 
element at the site of atherosclerotic plaque build-up. This could be 
accomplished by removal of the guidewire and introduction of the fiber 
optic--guided through the interior chamber--to the appropriate site. 
The electrodes 14 at the tip of the distal end 20 of the tubular body 12 
are shaped so that sparking may occur in both forward and radial 
directions. It is therefore possible to resolve plaque that has built up 
to such an extent that the catheter 10 is prevented from proceeding 
further along the arterial pathway. RF sparking from the front portions of 
the electrodes 14 will allow some forward directed sparking. Generally, 
the exterior diameter of the tubular body 12 is sized such that it is 
substantially smaller than the interior diameter of the arteries and 
vessels it will be encompassed by. Unless the atherosclerotic plaque 
build-up has progressed extremely far, it should be possible to place the 
distal end 20 of the catheter 10 in a position so that the plaque to be 
resolved will be generally planar to the side elements 17 of the electrode 
14 selected to ablate the plaque. 
Once the distal end 20 of the catheter 10 is properly placed, the operator 
must determine by consultation with the visualization technique utilized 
which surfaces of the artery or vessel require ablation. Rather than the 
random sparking delivered from the RF sparking electrodes of the current 
devices, it is possible to direct sparking towards those surfaces that 
require ablation. 
In an additional embodiment of the device 10 (shown in FIGS. 7 and 8), the 
electrodes 14 consist of a plurality of split rings spaced along the 
exterior surface of the distal end 20 of the catheter. Each of the split 
rings 80 are separated from each other by a relatively small amount of the 
insulative material that comprises the bulk of the catheter 10. Each ring 
80 is "split" into a plurality of separate electrodes by equally spaced 
portions of insulative material. In such an embodiment it may be useful to 
incorporate end electrodes 89 on the relatively flat end of the distal end 
20 of the catheter 10 as seen in FIG. 8. It would be possible to include a 
narrowed opening into the interior of the catheter to allow the expulsion 
of dyes or an interior catheter, as shown, or to "cap" the hollow catheter 
10. 
The embodiment of the invention shown in FIGS. 7 and 8, as can the 
embodiment shown in FIG. 1, may be adapted to serve as either monopolar or 
bipolar electrosurgical catheters. The embodiment shown in FIG. 7 has a 
total of 12 electrodes. When adapted to perform as a bipolar device in 
which each of the 12 electrodes may be selected to function as the anode 
or the cathode, the locational specificity for sparking at the site of 
plaque build-up is greatly enhanced. In such an embodiment, in addition to 
means for optimally modulating the wave form of the current flowing from 
the generator, the electrode switching means 96 must be adapted to select 
which of the electrodes will serve as the anode and which will serve as 
the cathode or return path.