# Patent

## Title
Fuse-electrode electrosurgical apparatus

## Abstract

An electrosurgical apparatus for performing a surgical procedure on a target site, comprising a shaft having a distal end portion, the distal end portion comprising an active electrode including a fuse leg, the fuse leg adapted to break and disable the instrument upon applying a voltage differential between the active electrode and a return electrode for a predetermined amount of time. In another embodiment, the present invention is a method of performing an electrosurgical procedure on a target tissue, comprising: placing an electrosurgical instrument in close proximity to the target tissue, the electrosurgical instrument comprising an active electrode having a pre-selected portion adapted to break and disable the instrument upon applying a voltage differential thereto for a working time; and applying the voltage differential.

## Background
BACKGROUND
1. Field of the Invention
This invention relates to an electrosurgical apparatus, in particular an electrosurgical apparatus comprising an electrode assembly including an electrode leg adapted to break and disable the apparatus upon expiration of a predetermined amount of use of the apparatus.
2. Description of the Prior Art
In electrosurgical instruments, as illustrated for example in FIG. 1, a pair of electrodes maintained at differential voltages and with dissimilar charge densities are used to conduct current to a target site to treat tissue. Treatment may include ablating, heating, cutting, removing, puncturing, probing, and otherwise stimulating tissue at the target site. The target site may include any part of a patient's body including the skin, knee, nose, spine, neck, hip, heart and the throat. See for example, U.S. Pat. No. 6,149,620 and U.S. patent application Ser. No. 09/457,201 herein fully incorporate by reference for descriptions of procedures for treating tissue at target sites using electrosurgical instruments, including procedures and instruments readily adaptable for use in accordance with the present apparatus and method.
On these instruments, the electrode with the higher charge density, referred to as the active electrode, conducts current to the target site whereas the electrode at the lower charge density, referred to as the return electrode, conducts current away from the target site. Depending on the instrument's design both electrodes may be positioned on the distal end of a shaft of the instrument in which case the instrument is referred to as a bipolar instrument. Alternatively, where only the active electrode is positioned on the shaft of the instrument and the return electrode is placed elsewhere off the instrument but in an electrical circuit with the active electrode and the target site, the instrument is referred to as monopolar instrument. In both designs, however, regardless of where the electrodes are located, for the instrument to work, it is necessary to maintain a closed electrical circuit comprising the electrodes, the target site that including a conductive media, and a high-frequency alternating voltage source.
In electrosurgical procedures, whether a monopolar or a bipolar instrument is used, treatment of the target site is effected in one of three ways: passing current through the tissue at the site; passing current through a conductive fluid on the site; or generating plasma by passing current through a conductive fluid near the target site and directing the plasma to the site. Conductive fluid includes saline and lactated ringers solution. See for example, U.S. Pat. No. 6,149,620, and U.S. patent application Ser. No. 09/457,201, supra, for description of methods of treating tissue in accordance with one or more of these procedures.
In treating a target site, an important consideration is to limit the time that the tissue is exposed to current so as to avoid unintended damage to the tissue. Another consideration is to prevent accidental reuse of disposable components of the instruments, such as the electrodes, to reduce the risk of infection. A further consideration is to avoid using an instrument having electrodes that are worn or eroded to a state such that their mechanical structures are weakened to an unacceptable level and are likely to break.
One approach to limit exposure of the tissue to excessive current, and or control wear on the electrode is to rely on the operator to monitor the time that the instrument is in use and stop treatment at an appropriate time. This may be done, for example, either manually or automatically using various timing devices on the power supply.
However, while monitoring the power supply is feasible to track the time that the tissue is exposed to current, merely monitoring the power does not indicate to the operator the extent of erosion and wear occurring on the electrodes. In this regard the applicant has discovered that as the instrument is used, the active electrode erode and wear and are likely to break. Further, depending on the material used, the dimensions of the active electrode, the type of conductive fluid used, the location of the connection to the power supply and the voltage applied to the electrodes, erosion may occur to the extent where the electrodes undesirably breaks causing bits of fragments to become lodged in the tissue. Thus, while it is possible to monitor the power to prevent over-exposure of the tissue to current, it is a problem to decide when to stop use of the instrument to avoid the undesirable consequences of erosion and wear on the electrodes and or a break on the electrodes.
One approach to monitoring the instrument for electrode erosion and wear is to visually check the physical condition of the electrodes. A problem with this approach is that because the electrodes are almost invisible to an unaided eye, it very difficult to visually determine erosion and wear. A further practical problem is that during the exigencies of a surgical procedure, a practitioner may overlook the need to periodically check the electrodes for erosion wear in time to stop using the instrument before wear becomes a problem and or the electrode breaks.
Accordingly, there is need for a more reliable way to prevent unintended and or prolonged use of the equipment, excessive exposure of the tissue to current, the consequences of a deteriorated electrode, and or the unintended reuse of disposable components of the instrument. It is thus an object of the present invention to address at least these needs.
SUMMARY OF THE INVENTION
An electrosurgical apparatus for performing a surgical procedure on a target site, comprising an active electrode assembly including a fuse leg adapted to break and disable the apparatus upon expiration of a predetermined amount of use of the apparatus. In one embodiment the electrosurgical instrument, comprises a shaft having a distal end portion, the distal end portion comprising an active electrode including a fuse leg, the fuse leg adapted to break and disable the instrument upon applying a voltage differential between the active electrode and a return electrode for a predetermined amount of time. In another embodiment, the present invention is a method of performing an electrosurgical procedure on a target tissue, comprising: placing an electrosurgical instrument in close proximity to the target tissue, the electrosurgical instrument comprising a return electrode, and an active electrode having a pre-selected portion adapted to break and disable the instrument upon applying a voltage differential between the active and return electrodes for a working time; and applying said voltage differential.
Advantageously, with the present instrument and method, a target tissue may be treated with reduced risk and consequences of a random instrument failure since the instrument is adapted to fail upon expiration of a predetermined amount of use. In various embodiments, failure is intentional due to a planned break in the electrode to incapacitate the instrument and disclosed herein.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an electrosurgical apparatus in accordance with an embodiment of the invention.
FIG. 2 is a side view of a target site in a patient being treated by an electrosurgical apparatus in accordance with an embodiment of the invention.
FIG. 3 is a perspective view of the distal end an electrosurgical apparatus with an intact active electrode in accordance with an embodiment of the invention.
FIG. 4 is a perspective view of the distal end an electrosurgical apparatus with an eroded active electrode in accordance with an embodiment of the invention.
FIG. 5 is a perspective view of insulator adapted for receiving an active electrode in accordance with an embodiment of the invention.
FIG. 6 is a perspective view of an active electrode being installed on an insulator in accordance with an embodiment of the invention.



DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
With reference to FIGS. 1-6, the present invention in one embodiment is an electrosurgical instrument (10) for performing a surgical procedure on a target site. The surgical procedure includes volumetric removal of soft tissue from the target site, for example volumetric removal of soft tissue in the throat as illustrated schematically in FIG. 2, or soft tissues at other target sites including the skin, knee, nose, spine, neck, hip, and heart.
In one embodiment as shown schematically in FIGS. 3 and 4, the instrument comprises an active electrode assembly (12) located at the distal end (18) of a shaft (14) and includes a fuse leg (16a) sized to preferentially erode and break before a break occurs on any of the anchor legs (16b and 16c) upon expiration of a predetermined amount of use of the instrument.
In another embodiment, the invention is a method of performing an electrosurgical procedure using the instrument such that the procedure is automatically stopped after a predetermined amount of use of the instrument, due to failure on the fuse-electrode leg. In various embodiments, a predetermined amount of use includes tracking the accumulative current passing through the electrode assembly while treating a target site, as well as anticipating the erosion and wear on the fuse leg and designing the leg using appropriate materials and dimensions such that the leg will break upon a predetermined amount of use. In another embodiment, anticipation of a break on the fuse leg includes designing and adapting the leg based on the operating voltage and the conductive fluid in contact with the electrodes.
In various embodiments of the invention, the applicant is capitalizing on an observation that when the instrument is in use, erosion and wear on the active electrode occur to the extent that the erosion and wear cause a break in the electrode. Thus, the applicant is using this observation to plan for a break in an electrical circuit such that the break is used to control how much the instrument is useable, as described herein. In particular the applicant by designating a portion of the active electrode as a fuse leg, and selectively choosing the material, the operating voltage, the conductive fluid, and sizing the designated leg to conduct current through the electrode, the applicant can predetermine when to incapacitate the instrument.
While not admitting to any theory as to the cause of the erosion and or wear on the electrodes during use, it is believed that erosion and wear are attributable to an electrochemical action on the electrode due in part to the presence of a conductive fluid at the target site, and the passage of a current through the electrode in the presence of this conductive fluid. In particular, during use of the instrument, as a result of the current passing through the conductive fluid and the electrodes, plasma is formed in the vicinity of the electrodes when a voltage difference is applied between the electrodes. In one embodiment, the formation of plasma and the action of the active electrode contacting tissue at the site are correlated to the observed erosion and wear on the electrode.
In one embodiment an active electrode assembly (12) as illustrated in FIGS. 3, 4 and 6, is made of a conductive material such as platinum, tungsten, molybdenum, titanium, and corrosion resistant stainless steel. In this embodiment, the active electrode comprises a fuse leg (16a), and one or more anchor legs (16b, 16c) that together support the electrode assembly (12) on the insulator (22).
In various embodiments, the fuse electrode leg (16a) is the input path for current into the electrode assembly, and is thus electrically connected to a high frequency voltage source (not shown). To selectively promote erosion and wear on the fuse leg, several factors are controlled including: the material of the electrode, the dimensions of the electrode, the shape of the electrode, the range of voltage applied to the electrode, and the number of fuse and anchor legs. Further, it will be appreciated that the shape of the electrode assembly may vary and may take the form of a screen, a wire loop or another suitable shape; similarly, the cross-section of the electrode may vary and can be circular, cylindrical, square, oblong, disc, and or variations of these shapes.
In one embodiment the dimension of the fuse leg is selected for a width of about 0.008 inch to 0.015 inch, and a thickness of about 0.004 to about 0.007 inch. For this range of dimensions, a suitable operating voltage is about 50 volts to about 1000 volts, in particular about 200 volts to 350 volts. However it will be appreciated by one skilled in the art that in view of the description, these parameters may be varied to achieve a particular design. Similarly, the choice of material can vary; for example, a material such as platinum, tungsten, molybdenum, titanium and corrosion resistant stainless steel may be used. Similarly, the design is influenced by the desired operating time of the instrument which may vary from one hour to about 2 minutes to about 30 minutes or to about 7 minutes to about 10 minutes depending the procedure used, the amount of contact that the electrode makes with the tissue, and the flow characteristics of the conductive fluid that includes saline and lactated ringers solution.
Desirably, anchor-legs (16b, 16c) are larger than the fuse-electrode leg (16a), however as is illustrated in FIGS. 5 and 6, the actual size of each type of legs is constrained by the physical limitations of the electrode assembly (12), and the surface area (24) on the insulator to receive the electrode assembly. In designing the fuse leg to be smaller than the anchor legs it will be recognized by one skilled in the art that the fuse leg will generate a higher current density than a current density on any of the anchor legs and therefore will desirably erode at a faster rate than the anchor legs during use.
In various embodiments, the size, location, material of the fuse leg, the presence of a conductive material and the intended use of the instrument are factored together to optimize the design. Regarding size, in one embodiment a properly placed tungsten fuse of width 0.10 inches and thickness 0.007 inches will have a useful life of 7-10 minutes. Regarding location, in one embodiment the fuse leg is located in a position more likely to wear such as where power is inputted to the electrode or where the electrode is more likely to come in contact with tissue, or where the electrodes is located close to a suction lumen. On the other hand, examples of positions where the electrode is less likely to wear are those regions centrally located (most dispersed) from the return electrode, regions protected from high fluid velocity streams, and region not generally in constant contact with tissue during normal use.
As illustrated in FIGS. 3 and 4, the before-and-after effects of designing the fuse-electrode leg (16a) in accordance with the invention can be seen, for example in FIG. 3 which depicts an intact active: electrode assembly (12) anchored onto the insulator (22) prior to using the instrument, and FIG. 4 which depicts the active electrode (16a) after it has been eroded and broken, while the anchor electrodes (16b and 16c) are still intact. In the embodiment shown in FIGS. 3-6, an active electrode assembly having a fuse-electrode leg is configured to disable the instrument after a predetermined amount of use.
In one embodiment as shown in FIGS. 3-6, insulator (22) is formed of a ceramic material that defines holes (24a, 24b and 24c) in the surface for receiving fuse-electrode leg (16a) and anchor-electrode legs (16b, 16c). Additionally, insulator defines an axial aperture (26) for facilitating deployment on the distal end of shaft (14).
In one embodiment, as shown in FIG. 1, the shaft (14) includes an axial lumen (30) opened at said distal end (18) of the shaft. In this embodiment as illustrated in FIGS. 3, 4 and 6, the electrode assembly (12) comprises openings in the form of a sieve for restricting passage of materials into the lumen resulting from ablation of tissue at the distal end of the shaft (14).
In an embodiment illustrated in FIG. 1, shaft (14) further comprising an aspiration tube (32) disposed partly on the shaft for aspirating material away from the distal end. Also illustrated in FIG. 1 is a fluid supply system disposed (34) on the shaft for supplying conductive fluid to the distal end. Examples of aspiration tubes and fluid supply systems that are useable with the present apparatus are described in U.S. Pat. No. 6,149,620, and U.S. patent application Ser. No. 09/457,201, supra, and incorporated herein by reference.
As illustrated in the embodiments of FIGS. 3 and 4, return electrode (20) is provided on the shaft (14), as in a bipolar instrument, for completing the electrical connection to the voltage supply. However, return electrode may be positioned elsewhere for connection to the voltage supply as with monopolar instruments.
In another embodiment, the invention is a method of performing an electrosurgical procedure on a target location using the present apparatus. In one method the procedure involves placing the instrument proximally to a target location, and treating the target tissue with the electrode assembly until a failure at the fuse-leg incapacitates said instrument. In the method, treatment includes applying a high frequency voltage to the electrode assembly to facilitate failure at the fuse-leg during the procedure. In treating the target site, depending on whether current is passing through the target site, it may be required to direct a conductive fluid to the electrode assembly during the procedure to complete the electrical path.
As will be appreciated, the method can be used to treat target tissue includes ablating, puncturing, and cutting the target tissue. Depending on the tissue being treated, in one procedure a voltage of about 50 volts to 1000 volts can be applied; in other procedures, a voltage in the range of 200 volts to 350 volts can be applied. Also, depending on the tissue, treatment may last up to about one hour; in other procedures, treatment is about 2 minutes to about 30 minutes, more narrowly in the range of about 7 to 10 minutes. In various embodiment treatment may also include directing a conductive fluid to the target tissue so as to ablate, puncture, and cut tissue.
While the invention is described with reference to the present Figures and methods, it will be appreciated by one ordinarily skilled in the art that features of different embodiments may be combined for a particular instrument and or procedure in accordance with the present invention. Thus, alternative combination is to be considered to be within the scope of the present invention unless one feature or aspect mutually excludes the other. Accordingly, the scope of the invention should not be limited to the embodiments as described herein, but is limited only by the scope of the appended claims.

## Claims

1. An electrosurgical apparatus for performing a surgical procedure on a target site, comprising an active electrode assembly electrically connected to a high frequency voltage source, the active electrode assembly including a fuse leg and one or more anchor legs, wherein said fuse leg is electrically connected to the high frequency voltage source and is smaller than the one or more anchor legs, said fuse leg configured, sized, and located such that use of the apparatus causes said fuse leg to break prior to the one or more anchor legs and upon expiration of a predetermined amount of use of said apparatus, thereby disabling said apparatus.

2. The electrosurgical apparatus of claim 1, wherein said break is controlled by optimizing a parameter selected from the group consisting of a dimension of said fuse leg, a high frequency voltage applied to said fuse leg, a material comprising said fuse leg, and a conductive fluid in contact with said fuse leg.

3. The electrosurgical apparatus of claim 2, wherein said dimension of said fuse leg is preferably a width of about 0.008 inch to 0.015 inch.

4. The electrosurgical apparatus of claim 2, wherein said high frequency voltage preferably is about 200 volts to 350 volts.

5. The electrosurgical apparatus of claim 2, wherein said material is selected from the group consisting of platinum, tungsten, molybdenum, titanium and corrosion resistant stainless steel.

6. The electrosurgical apparatus of claim 2, wherein said dimension of said fuse leg is preferably a thickness of about 0.004 to about 0.007 inch.

7. The electrosurgical apparatus of claim 1, wherein said predetermined use is about 7 minutes to about 10 minutes.

8. The electrosurgical apparatus of claim 1, wherein said fuse leg is adapted for a higher current density compared with the current density on said anchor legs.

9. The electrosurgical apparatus of claim 1, further comprising:
a shaft having a distal end wherein said electrode assembly is disposed on said distal end;
a return electrode disposed on said shaft proximally to said electrode assembly; and
an insulator positioned between said return electrode and said electrode assembly for electrically insulating said return electrode from said electrode assembly.

10. The electrosurgical apparatus of claim 9, wherein said electrode assembly and said fuse leg comprise an active electrode.

11. The electrosurgical apparatus of claim 9, wherein said fuse leg is partially embedded in said insulator.

12. The electrosurgical apparatus of claim 9, wherein said shaft defines an axial lumen opened at said distal end of said shaft.

13. The electrosurgical apparatus of claim 9, further comprising an aspiration tube disposed partly on said shaft for aspirating material away from said distal end.

14. The electrosurgical apparatus of claim 13, wherein the fuse leg is located proximate to a distal opening of the aspiration tube.

15. The electrosurgical apparatus of claim 9, further including a fluid supply system disposed partly on said shaft for supplying conductive fluid to said distal end.

16. The electrosurgical apparatus of claim 15, wherein the fuse leg is located proximate to a distal opening of the fluid supply system.

17. An electrosurgical instrument, comprising: a shaft having a distal end portion, said distal end portion comprising an active electrode electrically connected to a high frequency voltage source, the active electrode including a fuse leg and one or more anchor legs, wherein said fuse leg is electrically connected to the high frequency voltage source and is smaller than the one or more anchor legs, said fuse leg configured, sized, and located to break prior to the one or more anchor legs and upon applying a voltage differential between said active electrode and a return electrode for a predetermined amount of time, thereby disabling said instrument.

18. The electrical instrument of claim 17, the one or more anchor legs for securing said active electrode on said shaft.

19. The electrical instrument of claim 17, wherein a return electrode is positioned on said shaft proximally to said active electrode; and
an insulator is interposed between said return electrode and active electrode on said shaft for electrically isolating said return electrode from said active electrode.