WO1999037227A1

WO1999037227A1 - Tissue resection using resistance heating

Info

Publication number: WO1999037227A1
Application number: PCT/US1999/001519
Authority: WO
Inventors: Barry N. Gellman; Gordon Minns; Aaron Perlmutter
Original assignee: Boston Scientific Limited
Priority date: 1998-01-26
Filing date: 1999-01-26
Publication date: 1999-07-29
Also published as: AU2469499A

Abstract

A resistive heating (RH) system for use in medical procedures (e.g., resecting prostate tissue in the context of treating benign prostatic hyperplasia (BPH) or uterine tissue in treating cancer) includes an electrode through which passes electrical current to heat the electrode via the electrode's resistance to the flow of the electrical current. The electrode can be coupled to a source of the electrical current. The source can include a controller, or controlling equipment can be provided as one or more pieces of equipment separate from the source.

Description

TISSUE RESECTION USING RESISTANCE HEATING

Cross-Reference to Related Application

This is based on and claims priority to and the benefit of provisional U.S. patent application serial number 60/072,620 filed on January 26, 1998.

Technical Field

This invention relates to resecting, cutting, cauterizing, desiccating, vaporizing, coagulating, and/or imposing hemostasis on living tissue and, more particularly, performing one or more of these operations using thermal energy transferred from a resistance heated (RH) electrode that contacts the tissue.

Background Information

Known electro surgical procedures employ electrodes energized by monopolar or bipolar radio frequency (RF) currents. The difference between monopolar and bipolar RF is in the proximity of the return electrode to the active electrode. With monopolar devices, a grounding pad (i.e., the return electrode) is placed against the skin of the patient, and it is used as a sink for all of the RF energy that emanates from the active electrode (e.g., a cutting tool). Low current and high voltage (e.g., 1000 Volts) are associated with RF systems and techniques, as such low currents and voltages generally are required to complete the circuit from the active electrode to the return electrode. RF systems utilize the electrical resistance of the tissue to generate heat as the current passes from the active electrode, through the tissue, and heads to the return electrode. As the tissue dries or carbonizes, the tissue becomes less conductive and the applied RF energy radiates to less resistive tissue until the impedance of the tissue inhibits any further current flow. Bipolar devices operate in a similar manner except the return electrode typically is not a grounding pad, and the return electrode generally is much closer physically to the active electrode. With bipolar devices, as with monopolar devices, low current and high voltage are used, and shocks to the patient and/or physician are possible. RF systems have been used to resect tissue. An RF system can be used to treat benign prostatic hyperplasia (BPH) by resecting prostate tissue using a monopolar RF electrode. The use of a monopolar RF electrode generally requires the operating environment to be non-conductive to assure that the current travels from the active electrode to the grounding pad. Any conductive material in the environment could result in stray currents and possible damage to non-targeted and/or healthy tissue. For example, to treat BPH by resecting prostate tissue using a monopolar RF electrode, a resectoscope is usually present and stray RF current could travel from the active electrode to the resectoscope (instead of going to the grounding pad where it should be going) and possibly burn the urethra as the resectoscope is metal and will conduct the current.

RF systems used in resecting prostate tissue to treat BPH generally include an active electrode, a grounding pad, and an RF generator/controller unit. The RF generator could be separate from the RF controller but, whatever the configuration, RF energy is supplied in some manner to the active electrode and usually controlled (e.g., based on temperature) to provide enough RF energy to complete the circuit from the active electrode to the grounding pad and to cut through the prostate tissue.

Alternatively, a laser can also be used to perform electro surgery. A pulse of laser light having a selected wavelength and amplitude can be applied to tissue to remove and/or ablate tissue. As the laser beam can be focused to a pinpoint size, a procedure can be performed very precisely. Alternatively, in a contact laser system, the laser light heats a contact element which burns tissue. A laser system typically includes complex optical instruments including a laser light source and a lens.

Summary of the Invention

Instead of an RF or a laser system, a resistance heating (RH) system can be used according to the invention to resect, cut, cauterize, desiccate, vaporize, coagulate, and/or impose hemostasis on living tissue. In accordance with the invention, an RH system can be used in a variety of procedures and areas including but not limited to urology, endoscopy, gynecology, neurology, and cardiology. For example, an RH system can be used to resect prostate tissue in the treatment of BPH, or to resect a fibroid tumor in the uterus. In such an applications, an RH - 3 -

system has many advantages over existing systems including: resection with an RH system can be accomplished in a saline environment as well as a glycine environment (glycine typically is used when a monopolar RF electrode is used, and glycine is more expensive than saline); stray current is not an issue when using an RH system as there is no current passing through the patient from one electrode to another as in an RF system and thus no related danger to the patient such as stray current traveling to the resectoscope and burning the patient's urethra; no need for a grounding pad with an RH system and thus problems with the use of a grounding pad such as added cost to the system and skin burns due to poor pad/skin contact are eliminated by the use of an RH system; and an RH system uses much lower voltages than an RF system (e.g., 5 Volts for an RH system versus 1000 Nolts for an RF system) and thus the possibility of a dangerous shock to the patient and/or physician is essentially eliminated.

An RH system according to the invention generally includes an electro surgical device having a resistive electrode and a controller. The controller can include an electrode interface circuit, a variable current/voltage source, and a microcomputer. The electrode can be a high- resistance electrode made of a strand of rhenium or tungsten with a ceramic coating to handle the high temperatures (e.g., 500-800 degrees C) needed to coagulate and/or resect tissue. The electrode can be is a wire in a half-circle shape or loop shape through which the current passes and heats the wire because of the wire's resistance to electrical current flow. The heated wire is used to resect and or to coagulate tissue. The controller supplies and controls the current applied to the resistive electrode.

An RH system according to the invention requires high current but low voltage such as about 5 Volts or less (unlike an RF system which uses a very high voltage such as about 1000 Volts). The use of low voltage helps to resist passage of current to the patient. In one embodiment, the RH system uses a voltage of 5 Volts and a current of 50 to 55 Amps. The voltage and current selection is based on the desired target temperature and associated heat loss from the surrounding.

An RH system of the invention can use DC power instead of AC power. There are safety issues associated with the use of AC that are not a problem when DC is used. - 4 -

An electrosurgical device of the invention includes a positive lead, a negative lead, and a an RH electrode coupled to distal ends of the leads. The electrical resistance of the electrode is greater than the electrical resistance of the leads. A cross section of the leads can have a semicircular shape for attachment to a standard resectoscope used in urological and/or gynecological applications.

The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.

Brief Description of the Drawings

In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

FIG. 1A shows one embodiment of an electrosurgical device comprising a resistive heating (RH) electrode according to the invention.

FIG. 1AA illustrates a cross sectional view of a lead of the device of FIG. 1 A, taken along line A- A' of FIG. 1A.

FIG. IB illustrates a perspective view of one embodiment of an electrosurgical device comprising an RH electrode according to the invention.

FIG. 1C illustrates one method of assembling an electrosurgical device comprising an RH electrode according to the invention.

FIG. ID shows another embodiment of an electrosurgical device comprising an RH electrode according to the invention.

FIG. 2 shows a controller for use with an electrosurgical device comprising an RH electrode.

Description Referring to FIG. IN an electrosurgical device 10 includes a pair of leads 12, 14, and a resistive heating (RH) electrode 16 electrically coupled to the distal ends of the pair of leads 12, 14. The pair of leads 12, 14 are conductive leads formed of a material having a low resistance. The RH electrode 16 is formed of a material having a higher resistance than the conductive leads 12, 14. When current is applied to the electrosurgical device, current flows from a current source (not shown), through lead 12, through the RH electrode 16, and through lead 14. Since the resistance of the RH electrode 16 is higher than that of the pair of leads 12, 14, heat is generated at the RH electrode 16 when current passes through the RH electrode 16. The RH electrode 16 functions as both working and return electrode. Heat generated at the RH electrode 16 can achieve a temperature sufficient to resect and/or cauterize tissue. For example, heat generated at the RH electrode 16 can achieve a temperature near 900°F-1400°F (500°C-800°C).

Examples of suitable materials for forming the pair of leads 12, 14 include but are not limited to, copper, aluminum, and silver. Examples of suitable materials for forming the RH electrode 16 include but are not limited to, refractory metals such as Rhenium, tungsten, nickel- chromium alloy, and stainless steel, or alloys comprising any of these metals. In one embodiment, the RH electrode 16 is coated with a ceramic coating. The size and shape of the RH electrode 16 is a function of the performance needed. However, an RH electrode 16 having a larger cross sectional area will require higher current flow through the electrode 16 to obtain or maintain the desired heat temperature. Therefore, a smaller cross sectional area may be desired for the electrode 16. A cross sectional area of the leads 12, 14 also affects heat generation. A lead having a smaller cross section has a higher resistance than a lead having a larger cross section made of the same material. When resistance of the lead is high, heat can be generated in non- critical, less desirable location reducing the effects of the of the electrode 16. Therefore, a larger cross section area may be desired for the leads 12, 14. In one embodiment, the RH electrode 16 is a substantially U-shaped wire loop. In another embodiment, the RH electrode 16 is a substantially U-shaped ribbon-like structure having a broad surface. Such an electrode is described in U.S. Patent No. 5,569,244 which is incorporated in its entirety herein by reference. The RH electrode can still have other configurations. In one embodiment, the cross section of the leads 12, 14 has a semi-circular shape as shown in FIG. 1 AA. In another embodiment, the cross section of the leads 12, 14 has a circular shape.

The RH electrode 16 can be connected to the distal ends of the pair of leads 12, 14 in any one of a number of ways. Examples of suitable connection methods include but are not limited to, soldering, (e.g., silver soldering,) welding, brazing, crimping, swaging, and screwing. The connection method selected is dependent on the material of the RH electrode 16 and the leads 12, 14. An important factor, however, is that no matter which connection method is employed, the connection must result in a low electrical resistance joint. FIG. IB shows an electrosurgical device 20 where the RH electrode 26 is connected to the pair of leads 22, 24 using soldering or welding. FIG. IC illustrates an electrosurgical device 30 where the RH electrode 36 is connected to the pair of leads 32, 34 mechanically. In this embodiment, the RH electrode 36 has a substantially U-shaped portion 35 and straight parallel portions 37. The parallel portions 37 couple to the pair of leads 32, 34. In the embodiment of FIG. IC, when current is applied to the RH electrode 36, the parallel portions 37 are cooler than the U-shaped portion 35, as they are nearer to the low resistance leads 32, 34. Thus, tissue near the cooler parallel portions 37 are less affected by application of current to the RH electrode 36.

In one embodiment, an electrosurgical device 40 according to the invention is constructed in a manner shown in FIG. ID to adapt to existing resectoscopes. The electrosurgical device 40 has a positive lead 42 and a negative lead 44. The positive and negative leads 42, 44 together form a tubular body. The positive and negative leads 42,44 are separated with an insulator 48. The insulator 48 can comprise teflon. In one detailed embodiment (not shown), the insulator 48 encapsulates the leads 42, 44. Each lead 42, 44 can have a D shape or semi-circular cross section, and such a cross sectional configuration of the leads 42, 44 maximizes the cross sectional area of the leads positioned within a passageway of the resectoscope (not shown). A larger cross sectional area of the leads 42, 44, results in lower resistance. The positive and negative leads 42, 44 branch apart at a distal end to form a pair of leads 46, 47 and accommodate an RH electrode 50. The RH electrode 50 is electrically coupled to the distal ends of the pair of leads 46, 47. The electrosurgical device 40 has a cradle 52 for mounting the device 40 to the resectoscope. The electrosurgical device 40 has a positive connector 54 electrically coupled to the positive lead 42, and a negative connector 56 electrically coupled to the negative lead 44. The positive and negative connectors 54, 56 are designed to plug into an adapter for connection to a power source (not shown).

Referring to FIG. 2, a controller 60 for use with the electrosurgical device having an RH electrode described above includes an electrode interface circuit 62, a variable current/voltage source 64, and a microcomputer 66. The controller 60 measures resistance at the RH electrode. The resistance at the RH electrode changes as heat is withdrawn from the electrode by various thermal masses including tissue, irrigants, and surrounding fluids. The controller 60 adjusts current applied to the RH electrode to maintain a predetermined resistance at the RH electrode. In the embodiment of FIG. 2, the electrode interface circuit 62 provides information about the voltage drop across and current flow through the RH electrode to the microcomputer 66. In one detailed embodiment, the electrode interface circuit 62 includes off-the shelf differential and operational amplifiers.

The variable current /voltage source 64 supplies a low-voltage DC power to heat the RH electrode. For example, the voltage applied to the RH electrode can be about 5 V volts. The output level of the power applied to the RH electrode can be controlled based on the resistance of the RH electrode and from calculations performed by the microcomputer 66. The variable current/voltage source 64 can be implemented using either linear or switching regulator technology. In either case, the output of the current/voltage source must be ohmically isolated from earth ground to meet surgical instrument electrical safety standards.

The microcomputer 66 reads input from a user interface (not shown). The input, for example, can include power settings and cut/coagulation control. The microcomputer 66 also receives input from the electrode interface 62. The microcomputer 60 converts analog signals of the voltage and current measurements of the RH electrode to digital signals. The microcomputer 66 controls heating of the electrode according to the following algorithm. When the surgeon calls for a cutting or a coagulation procedure, for example by stepping on a foot control, the resistance of the electrode is measured. To measure the resistance, the current/voltage source 64 energizes the RH electrode with a small, known current. A voltage drop across the electrode is measured, and the electrode resistance when the electrode is positioned at the body temperature is determined using Ohm's law. This preliminary measurement of the electrode resistance is used to automatically calibrate the RH electrode, such that the electrode can be manufactured with less stringent resistance tolerance. The microcomputer 66 uses stored information about temperature and resistance relationship of the electrode material to generate a resistance to temperature conversion formula. This formula is used to determine the temperature of the RH electrode during heating of the electrode. This formula also provides the current level necessary to achieve a desired temperature at the RH electrode.

During a cutting or coagulation procedure, the microcomputer 66 reads the user-specified power setting from the control panel and commands the current/voltage source 64 to heat the RH electrode. The power applied for heating the RH electrode is controlled using an algorithm included in the microcomputer 66 to achieve an effective cutting/coagulation temperature in the face of widely varying thermal loads and losses due to variations in electrode position, saline or irrigant flow, and tissue characteristics.

In one embodiment, the controller is a single piece of equipment comprising the power source, the electrode interface, and the microcomputer. In another embodiment, the power source, the electrode interface, and the microcomputer comprise separate pieces of equipment linked with each other to control the RH electrode.

An RH system in accordance with the description provided herein was used successfully to resect chicken parts in a saline environment. The RH system used to resect the chicken parts in the saline bath was DC powered by 2 Volts and 26-32 Amps. The RH system has also been used successfully to resect and provide hemostasis in live canine prostate tissue in a saline environment. The RH system was DC powered by 5 volts and 50-55 amps. An RH system according to the invention can be used to resect, cut, cauterize, desiccate, vaporize, coagulate, and/or impose hemostasis on tissue generally including resecting prostate tissue to treat benign prostatic hyperplasia (BPH) or resecting uterine tissue such as a fibroid tumor in the uterus to treat cancer in a living patient. - 9 -

Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.

What is claimed is:

Claims

- 10 -Claims

1. A resistive heating system for use in medical procedures, comprising:

a source of electrical current;

an electrosurgical device comprising a pair of leads each having a distal end and a proximal end and an electrode coupled to the distal ends of the pair of leads, the proximal ends of the pair of leads coupled to the source such that the electrical current passes through the electrode and heats the electrode due to the electrode's resistance to the flow of the electrical current; and

a controller for controlling the electrical current provided to the electrode by the source to maintain the electrode at a temperature sufficient to resect tissue.

2. The system of claim 1 wherein the electrode comprises a refractory metal.

3. The system of claim 2 wherein the electrode comprises rhenium.

4. The system of claim 1 wherein the electrode comprises tungsten.

5. The system of claim 1 wherein the electrode includes a ceramic coating.

6. The system of claim 1 wherein the electrode is used to resect prostate tissue.

7. The system of claim 1 wherein the electrode is used to resect uterine tissue.

8. The system of claim 1 wherein the electrode comprises a substantially u-shaped loop.

9. The system of claim 1 wherein the controller comprises a power source, an electrode interface, and a microcomputer.

10. The system of claim 1 wherein the controller controls the electrical current provided to the electrode based on a resistance and a temperature of the electrode.

11. The system of claim 9 wherein the electrode interface provides information about a voltage drop across the electrode to the microcomputer. - 11 -

12. The system of claim 1 wherein the controller adjusts the electrical current provided to the electrode to compensate for any heat loss by the electrode.

13. A method of treating tissue, comprising:

providing a resistance heating system comprising an electrode through which electrical current passes to heat the electrode due to the electrode's resistance to the flow of the electrical current and a controller for controlling the electrical current provided to the electrode to maintain the electrode at a temperature sufficient to resect tissue; and

treating tissue with the electrode.

14. The method of claim 13 wherein the treating step comprises resecting tissue.

15. The method of claim 13 wherein the treating step comprises resecting prostate tissue.

16. The method of claim 13 wherein the treating step comprises resecting uterine tissue.

17. The method of claim 13 wherein the providing step further comprises providing a source of the electrical current coupled to the electrode and to the controller.

18. The method of claim 13 wherein the electrical current is a DC signal.

19. The method of claim 13 wherein the providing step comprises providing the electrode which comprises a refractory metal.

20. The method of claim 19 wherein the electrode comprise rhenium.

21. The method of claim 13 wherein the providing step comprises providing the electrode which comprises a tungsten element which includes a ceramic coating.

22. The method of claim 13 wherein the providing step comprises providing a loop electrode.

23. The method of claim 13 further comprising calibrating the resistance heating system. - 12 -

24. The method of claim 23 wherein the calibrating step comprises determining a relationship between resistance and temperature of the electrode.

25. An electrosurgical device comprising: a positive lead having a proximal end and a distal end; a negative lead having a proximal end and a distal end; an electrode coupled to the distal ends of the positive and negative leads, an electrical resistance of the electrode being greater than an electrical resistance of the positive and negative leads, and a cross section of the positive and negative leads having a semi-circular shape.

26. The electrode of claim 25 wherein the positive and the negative leads comprise copper.

27. The electrode of claim 25 wherein the electrode comprises a refractory metal.

28. The electrode of claim 27 wherein the electrode comprises rhenium.

29. The electrode of claim 25 wherein the electrode comprises tungsten.

30. The electrode of claim 25 further comprising an insulator disposed between the positive and the negative leads.

31. The electrode of claim 30 wherein the insulator also encapsulates the positive and negative leads.

32. The electrode of claim 25 wherein the positive and negative leads form a substantially tubular structure.