Title:
BODY IMPLANTABLE LEAD
United States Patent 3788329
Abstract:
A flexible, body-implantable lead section which can be employed as an integral part of a monoplanar electrode system or alternatively as a separate means used to convert bipolar electrode system to a monopolar system. The lead section has at least one electrical conductor. The conductor is covered substantially over its entire length with an insulating material substantially inert to body fluids and tissue. The distal end of the conductor is adapted to be connected to an active electrode adapted to be located at a selected location inside the body. Indifferent electrode means are also provided. The indifferent electrode means are secured to at least a portion of the length along the surface of the inert material. In the preferred embodiment the indifferent electrode means is securely wrapped around at least a portion of the length of the inert material. This lead section with the indifferent electrode means can be employed with various configurations active electrodes for monitoring electrical activity and/or stimulating various types of tissue, including muscle and nerve tissue.
US Patent References:
Diathermy electrode
Kazdin - January 1952 - 2583853
Method and apparatus for measuring bioelectronic parameters
Woodhouse - May 1966 - 3249103
Cardiac pacer electrode system
Murphy et al. - May 1966 - 3253595
Conductive catheter
Fisher et al. - December 1968 - 3416533
IMPLANTABLE ELECTRODE FOR NERVE STIMULATION
Schwartz et al. - January 1969 - 3421511
Diathermy electrode
Kazdin - January 1952 - 2583853
Method and apparatus for measuring bioelectronic parameters
Woodhouse - May 1966 - 3249103
Cardiac pacer electrode system
Murphy et al. - May 1966 - 3253595
Conductive catheter
Fisher et al. - December 1968 - 3416533
IMPLANTABLE ELECTRODE FOR NERVE STIMULATION
Schwartz et al. - January 1969 - 3421511
Application Number:
05/244842
Publication Date:
01/29/1974
Filing Date:
04/17/1972
View Patent Images:
Export Citation:
Assignee:
Medtronic, Inc. (Minneapolis, MN)
Primary Class:
Other Classes:
607/118, 607/117
International Classes:
A61N1/05; A61N1/04
Field of Search:
128/418,419P,419C,417,416,410,411,DIG.4,2.1E,2.6E,404
US Patent References:
| 3472234 | BODY ORGAN ELECTRODE | October 1969 | Tachick | |
| 3478746 | CARDIAC IMPLANTABLE DEMAND PACEMAKER | November 1969 | Greatbatch | |
| 3485247 | CARDIAC CATHETERIZATION APPARATUS AND METHOD | December 1969 | Ackerman | |
| 3580242 | FETAL SCALP ELECTRODE UNIT | May 1971 | La Croix | |
| 3596662 | ELECTRODE FOR CARDIAC STIMULATOR | August 1971 | Bolduc | |
| 3650276 | METHOD AND APPARATUS, INCLUDING A FLEXIBLE ELECTRODE, FOR THE ELECTRIC NEUROSTIMULATION OF THE NEUROGENIC BLADDER | March 1972 | Burghele | |
| 3654933 | IMPLATABLE ELECTRODE | April 1972 | Hagfors | |
| 3664347 | ELECTRIC HEART STIMULATION METHOD AND ELECTRODE | May 1972 | Harmjanz |
Other References:
electrode Fixation Using a Plastic Adhesive, Methyl-2-Cyanoacrylate, Electroencephalography and Clinical Neurophysiology, 1964, Vol. 17, p. 696-697..
Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Cohen, Lee S.
Attorney, Agent or Firm:
Rappaport, Irving Schwartz Lew Sivertson Wayne S.
Claims:
I claim
1. A body implantable lead comprising:
2. The lead of claim 1 wherein the exposed portion of said indifferent electrode conductor means has sufficient area to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
3. The lead of claim 2 wherein said indifferent electrode conductor means is wrapped and exposed for more than one turn around the periphery of said lead section.
4. A lead as set forth in claim 3 further including means for inserting in and guiding said lead through a selected body vessel.
5. A lead as set forth in claim 3 wherein said last mentioned means includes a coil spring embedded in the material and defining a lumen therein, said spring being adapted to receive a stylet to provide said lead with sufficient rigidity to facilitate its insertion and guidance through the selected body vessel.
6. A lead as set forth in claim 3 wherein said active electrode means is configured to provide electrical energy to cardiac tissue.
7. A lead as set forth in claim 3 wherein said active electrode means is configured to provide electrical energy to selected nerve tissue.
8. In combination with a body implantable lead, an indifferent electrode forming lead section which comprises:
9. The combination of claim 8 wherein the surface area of the exposed portion of said indifferent electrode conductor means has sufficient area to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
10. The combination of claim 9 wherein said indifferent electrode conductor means is exposed and wrapped for more than one turn around the periphery of said encapsulating means.
11. A flexible, body implantable lead section for converting a bipolar electrode system to a monopolar system comprising:
12. The lead section of claim 11 wherein the exposed portion of said indifferent electrode means has a surface area sufficient to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
13. The lead section of claim 12 wherein the exposed portion of said indifferent electrode means is wrapped more than one turn around the periphery of said encapsulating means.
1. A body implantable lead comprising:
2. The lead of claim 1 wherein the exposed portion of said indifferent electrode conductor means has sufficient area to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
3. The lead of claim 2 wherein said indifferent electrode conductor means is wrapped and exposed for more than one turn around the periphery of said lead section.
4. A lead as set forth in claim 3 further including means for inserting in and guiding said lead through a selected body vessel.
5. A lead as set forth in claim 3 wherein said last mentioned means includes a coil spring embedded in the material and defining a lumen therein, said spring being adapted to receive a stylet to provide said lead with sufficient rigidity to facilitate its insertion and guidance through the selected body vessel.
6. A lead as set forth in claim 3 wherein said active electrode means is configured to provide electrical energy to cardiac tissue.
7. A lead as set forth in claim 3 wherein said active electrode means is configured to provide electrical energy to selected nerve tissue.
8. In combination with a body implantable lead, an indifferent electrode forming lead section which comprises:
9. The combination of claim 8 wherein the surface area of the exposed portion of said indifferent electrode conductor means has sufficient area to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
10. The combination of claim 9 wherein said indifferent electrode conductor means is exposed and wrapped for more than one turn around the periphery of said encapsulating means.
11. A flexible, body implantable lead section for converting a bipolar electrode system to a monopolar system comprising:
12. The lead section of claim 11 wherein the exposed portion of said indifferent electrode means has a surface area sufficient to insure an energy density sufficiently low to substantially eliminate local tissue stimulation.
13. The lead section of claim 12 wherein the exposed portion of said indifferent electrode means is wrapped more than one turn around the periphery of said encapsulating means.
Description:
BACKGROUND OF THE INVENTION
In the field of implantable electromedical devices, and in particular, in pulse generators used for muscle and nerve stimulation, the leads used to transmit the stimulating pulse from the pulse generator to the selected portion of the body to be stimulated may employ monopolar or bipolar electrode configurations. In a bipolar electrode configuration the electrical stimulating impulse occurs between a pair of fairly closely spaced active electrodes, both located generally near the distal end of the lead. In a monopolar electrode configuration, often used with body implantable pulse generators, there is a single active electrode near the distal end of the lead. An indifferent electrode, often in the form of a relatively large, flat, metal plate, is located on the exterior of the pulse generator. The electrical impulses in such a monopolar system occur between the single electrode at the distal end of the lead and the plate on the outer surface of the pulse generator. In these systems a bipolar lead must be used with a pulse generator designed to operate with a bipolar lead and a monopolar lead must be used with a pulse generator having the plate and designed to operate with a monopolar lead. Therefore, it is difficult to interchange monopolar and bipolar systems without changing both the pulse generator and the corresponding lead.
The present invention overcomes the above cited shortcomings of prior art systems by providing a lead of monopolar construction which may be employed with a pulse generator designed to operate with a bipolar lead so as to form a monopolar system. The lead of the present invention eliminates the need for employing the plate on the outer surface of a body implantable monopolar pulse generator and permits a bipolar pulse generator to be easily converted to a monopolar operating system. By eliminating the indifferent plate, the problems currently associated with bonding the plate to the implantable pulse generator's expoxy covering and of welding or bonding leads to the plate are avoided. Also, with the use of the lead of the present invention the problem of muscle stimulation occurring at the edges of the plate are substantially eliminated. A sufficient length of indifferent electrode in accordance with the present invention, properly arranged and exposed, insures against a high energy density which could otherwise cause local tissue stimulation. The present invention provides a monopolar electrode lead which can be used with single or multi-channel nerve stimulators. The lead configuration of the present invention can also be employed for physiological monitoring, such as, for example, monitoring the electrical activity of the heart such as used in cardiac pacemaking, as well as various types of tissue stimulation.
SUMMARY OF THE INVENTION
The above features, advantages and objects of the present invention, as well as others, are accomplished by providing a flexible body-implantable lead section comprising: at least one electrical conductor; and adapted to be connected at its distal end to an active electrode, which is adapted to be located at a selected location inside the body, the conductor being substantially covered over its length with an insulating material inert to body fluids and tissue; and indifferent electrode means, the indifferent electrode means being secured to at least a portion of the length along the surface of the inert material.
The lead section of the present invention can be employed in various leads with different, active electrode configurations. This is accomplished by constructing the lead section as an integral part of a flexible body-implantable lead comprising: at least one electrical conductor, the conductor being substantially covered over its length with an insulating material substantially inert to body fluids and tissue; active electrode means electrically connected at substantially the distal end of the electrical conductor, the electrode means adapted to be located at a selected location inside the body; and indifferent electrode means, the indifferent electrode means being secured to at least a portion of the length along the surface of the inert material.
Other features, advantages and objects of the present invention will hereinafter become more fully apparent from the following description of the drawings, which illustrate several embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a section of a lead in accordance with the present invention.
FIG. 2 shows a lead of the present invention for use as an endocardial lead with a monopolar pulse generator or for converting a bipolar pulse generator of a cardiac pacemaker system to a monopolar configuration.
FIG. 3 is a diagram of another embodiment of a lead in accordance with the present invention for use in a nerve stimulating system; and
FIG. 4 shows another embodiment of a lead in accordance with the present invention for use in a system for stimulating the dorsal column of the spine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before describing the present invention in detail, the meaning of certain terminology used herein should be clearly understood. The terminology "distal end" is used in referring to that portion of the lead toward the end to which the active electrode is attached. The terminology "proximal end" is used in referring to that portion of the lead toward the end which is connected to the source of electrical energy or monitoring equipment. The term "active electrode" as used herein generally refers to the electrode at which stimulation is desired to be achieved (most often of negative polarity) or the electrode at whose location electrical activity of tissue is to be monitored. The term "indifferent electrode" as used herein is intended to refer to that electrode which is common to a system or at system ground. For a tissue stimulation system the indifferent electrode will often be of positive electrical potential with respect to the active electrode.
FIG. 1 shows section 10 of a flexible lead which may be used with an electro-medical device for implantation in the body. Section 10 comprises an electrical conductor 12 having a distal end 14, which is adapted to connect to an active electrode which may be used to supply electrical energy to or monitor electrical activity at a selected portion of the body. A proximal end 16 is provided, which is adapted to be connected to a source of electrical energy or monitoring equipment. Electrical conductor 12 is embedded in an insulating covering material 18 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Another electrical conductor 20, which serves as an indifferent electrode, is partially embedded in the outer surface of material 18 to hold conductor 20 in fixed position. Conductor 20 is wrapped in a helical configuration around material 18. The proximal end 22 of conductor 20 is adapted to be connected to a source of electrical energy or monitoring equipment. The distal end 24 of conductor 20 is terminated by projecting inside material 18 at a point 26 on the outer surface of material 18.
Conductors 12 and 20 are made of a conductive material which is substantially inert to body fluids and tissue, such as, for example, platinum or platinum-iridium alloy. Conductors 12 and 20 may, for example, be made in a configuration and of a construction the same as that of the lead described in U.S. Pat. No. 3,572,344. This lead construction has excellent mechanical strength and flex characteristics and at the same time is an excellent electrical conductor.
Section 10 may, for example, be used in converting a bipolar lead and pulse generator to a monopolar system without having to replace the lead or the pulse generator. Both ends of section 10 may be fitted with appropriate male and female adapters (not shown), to permit section 10 to be electrically connected distally to a bipolar lead and proximally to an electrical energy source or monitoring equipment. Conductor 12 of section 10 is adapted to be connected at its distal end 14 to a conductor connected to the active electrode of a bipolar lead and specifically, if for tissue stimulation, at its proximal end 16 to a source of electrical energy, generally to the negative polarity signal. Conductor 20 serves as an indifferent electrode and is adapted to be connected at its proximal end 22 to a common or ground potential. Conductor 20 should be of sufficient length and surface area and the helical turns adequately spaced from one another such as to insure sufficiently low energy density to substantially eliminate local tissue stimulation. Conductor 20 should have the same properties so as to avoid picking up local tissue electrical activity when adapted for use in certain monitoring systems.
FIG. 2 shows a flexible, body-implantable endocardial lead 30 for use with a bipolar pulse generator or for converting a bipolar generator to a monopolar system. Lead 30 has an electrical conductor 32 which is embedded in an insulating convering material 34 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Conductor 32 projects through the outer surface of material 34 at point 36. From point 36, conductor 32 is closely wrapped for several turns in a helical configuration around material 34 to form the active electrode of monopolar lead 30. The wrapped turns of conductor 32 are partially embedded in the outer surface of material 34 so as to maintain the turns in fixed position. Distal end 38 of conductor 32 is terminated by projecting into material 34 at point 40. Proximal end 42 of conductor 32 is connected to a connector pin 44 which projects beyond material 34 and is adapted to be connected to a source of electrical energy, such as, for example, a pulse generator. The active electrode formed near the distal end of conductor 32 may simultaneously serve to monitor electrical activity of the heart in a demand pacemaker.
Also embedded in material 34 is a closely wound helical coil spring 46 which defines a lumen therein. Spring 46 is open at its proximal end 48 so as to permit a stylet (not shown) to be inserted therein so as to provide lead 30 with sufficient rigidity to be inserted into and guided through a body vessel to a desired location inside the body. Spring 46 is closed at its distal end 50 to limit the distance of insertion of the stylet.
Lead 30 also is provided with another electrical conductor 52 having a proximal portion 54 which is embedded in material 34 and is connected to a connector pin 56. Conductor 52 projects through the outer surface of material 34 at a point 58 and is wrapped for several spaced turns in a helical configuration around material 34. The wrapped turns of conductor 52 are partially embedded in the outer surface of material 34 so as to maintain them in fixed position. Distal end 60 of conductor 52 is terminated by projecting inside material 34 at a point 62. The wrapped turns of conductor 52 may, for example, extend for approximately 21/2 inches or so along the length of material 34 and the turns are approximately three-eighths inch between centers. The exposed length and surface area and the spacing between the helical turns of conductor 52 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1.
Conductors 32 and 52 are made of materials which are substantially inert to body fluids and tissue, such as, for example, platinum or a platinum-iridium alloy. Pins 44 and 56 and spring 46 may, for example, be made of stainless steel alloys. The construction and configuration of conductors 32 and 52 may be that of the lead described in U.S. Pat. No. 3,572,344.
FIG. 3 shows a flexible, body-implantable lead 70 for use in a multi-channel nerve stimulator. Lead 70 has a pair of electrical conductors 72 and 74 spaced from one another and embedded in an insulating covering material 76 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Distal ends 78 and 80 of conductors 72 and 74 are terminated in such a way as to form monopolar electrodes 82 and 84 respectively. Electrodes 82 and 84 are partially exposed and partially embedded in base portions 86 and 88 respectively which are formed integrally with material 76. Electrodes 82 and 84 and corresponding base portions 86 and 88 are adapted to be wrapped around the nerves which are to be stimulated as, for example, the carotid sinus nerves. Conductors 72 and 74 are connected to connector pins 90 and 92 respectively which are adapted to be connected to a body-implantable receiver (not shown). The receiver is designed to receive stimulating pulses from an RF coupled external transmitter and apply these pulses to the nerves through electrodes 82 and 84.
Lead 70 is provided with a third electrical conductor 94 which is embedded in material 76 at its proximal end 96 where it is connected to a connector pin 98. Conductor 94 projects through the outer surface of material 76 at point 100 and is wrapped for several turns around material 76 in a helical configuration similar to that of conductor 52 in FIG. 2. The spaced turns of conductor 94 are partially embedded in material 76 so as to maintain them in fixed position. Material 76 has a somewhat greater cross section near its proximal end in the section where the spaced turns of conductor 94 are partially embedded. The distal end 102 of conductor 94 terminates in material 76 by projecting through the outer surface at point 104.
In lead 70, electrodes 82 and 84 form the active electrodes and are connected via conductors 72 and 74 and pins 90 and 92 respectively to the implantable receiver. The spaced turns of conductor 94 form an indifferent electrode which is connected via pin 98 to either an electrical common or ground. The exposed length and surface area and the spacing between the turns of conductor 94 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1.
FIG. 4 shows a flexible, body-implantable lead 110 incorporating the present invention and particularly designed for stimulating the dorsal column of the spine. Lead 110 has a conductor 112 embedded in an insulating covering material 114 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Conductor 112 is terminated at its distal end in a spiral configuration to form an active electrode 116 which is partially embedded in a base portion 118 which is formed integrally with covering material 114. Material 114 is shown to intersect the base portion 118 at some angle other than 90° because such a configuration has been found easier to work with in attaching the active electrode 116 formed by the spiral configuration to the dorsal column. Spiral configuration 116 is partially embedded in base portion 118 to maintain the spiral configuration in fixed position. Although configuration 116 is shown to be a spiral, other configurations for the active electrode are possible. Proximal end 120 of conductor 112 is connected to a connector pin 122 which is adapted to be connected to a body implantable receiver (not shown) which may receive pulses which are RF coupled from an external transmitter. Active electrode 116 is generally connected to a negative polarity signal through conductor 112 and pin 122.
A second conductor 124 is provided with its proximal end 126 embedded in material 114 and connected to a connector pin 128 which is adapted to be connected to the receiver (not shown). Proximal end 126 of conductor 124 projects through the outer surface of material 114 at point 130 and is wrapped in a helical configuration for several spaced turns around material 114. The exposed length and surface area and the spacing between the turns of conductor 124 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1. The turns of conductor 124 are partially embedded in the outer surface of material 114 to maintain the turns in fixed position. The distal end 132 of conductor 124 is terminated by projecting into material 114 at point 134. Conductor 124 forms an indifferent electrode which is generally connected via pin 128 to ground potential which commonly is of positive polarity.
Conductors 112 and 124 may be made in the structure and configuration of the lead described in U.S. Pat. No. 3,572,344. Conductors 112 and 124 and pins 122 and 128 are made of a material substantially inert to body fluids and tissue. Although electrode 116 has been shown and described as having a spiral configuration, other configurations for the active electrode could be employed.
Also, it should be understood that although the four embodiments shown have the indifferent electrode wrapped around the covering material, the indifferent electrode could be partially embedded in the outer surface of the covering material in any desired configuration. Instead of having the indifferent electrode wrapped around the inert material containing one or more electrical conductors, the inert material could be securely wrapped around the indifferent electrode. In a broad sense the indifferent electrode and at least a portion of the length of the inert material are securely wrapped relative to one another. It should also be understood that although the preferred embodiments of the invention show the indifferent electrodes securely wrapped around the inert material in a helical configuration, any other means of securing the indifferent electrode to the surface of the inert material would be satisfactory. Although the indifferent electrode is shown located near the proximal end of the lead, it could be secured anywhere along the length of the lead.
FIGS. 1-4 show several embodiments of body-implantable leads which can be used in various applications. It should be understood, of course, that the foregoing disclosure relates to only a few configurations which the present invention may take and that numerous modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.
In the field of implantable electromedical devices, and in particular, in pulse generators used for muscle and nerve stimulation, the leads used to transmit the stimulating pulse from the pulse generator to the selected portion of the body to be stimulated may employ monopolar or bipolar electrode configurations. In a bipolar electrode configuration the electrical stimulating impulse occurs between a pair of fairly closely spaced active electrodes, both located generally near the distal end of the lead. In a monopolar electrode configuration, often used with body implantable pulse generators, there is a single active electrode near the distal end of the lead. An indifferent electrode, often in the form of a relatively large, flat, metal plate, is located on the exterior of the pulse generator. The electrical impulses in such a monopolar system occur between the single electrode at the distal end of the lead and the plate on the outer surface of the pulse generator. In these systems a bipolar lead must be used with a pulse generator designed to operate with a bipolar lead and a monopolar lead must be used with a pulse generator having the plate and designed to operate with a monopolar lead. Therefore, it is difficult to interchange monopolar and bipolar systems without changing both the pulse generator and the corresponding lead.
The present invention overcomes the above cited shortcomings of prior art systems by providing a lead of monopolar construction which may be employed with a pulse generator designed to operate with a bipolar lead so as to form a monopolar system. The lead of the present invention eliminates the need for employing the plate on the outer surface of a body implantable monopolar pulse generator and permits a bipolar pulse generator to be easily converted to a monopolar operating system. By eliminating the indifferent plate, the problems currently associated with bonding the plate to the implantable pulse generator's expoxy covering and of welding or bonding leads to the plate are avoided. Also, with the use of the lead of the present invention the problem of muscle stimulation occurring at the edges of the plate are substantially eliminated. A sufficient length of indifferent electrode in accordance with the present invention, properly arranged and exposed, insures against a high energy density which could otherwise cause local tissue stimulation. The present invention provides a monopolar electrode lead which can be used with single or multi-channel nerve stimulators. The lead configuration of the present invention can also be employed for physiological monitoring, such as, for example, monitoring the electrical activity of the heart such as used in cardiac pacemaking, as well as various types of tissue stimulation.
SUMMARY OF THE INVENTION
The above features, advantages and objects of the present invention, as well as others, are accomplished by providing a flexible body-implantable lead section comprising: at least one electrical conductor; and adapted to be connected at its distal end to an active electrode, which is adapted to be located at a selected location inside the body, the conductor being substantially covered over its length with an insulating material inert to body fluids and tissue; and indifferent electrode means, the indifferent electrode means being secured to at least a portion of the length along the surface of the inert material.
The lead section of the present invention can be employed in various leads with different, active electrode configurations. This is accomplished by constructing the lead section as an integral part of a flexible body-implantable lead comprising: at least one electrical conductor, the conductor being substantially covered over its length with an insulating material substantially inert to body fluids and tissue; active electrode means electrically connected at substantially the distal end of the electrical conductor, the electrode means adapted to be located at a selected location inside the body; and indifferent electrode means, the indifferent electrode means being secured to at least a portion of the length along the surface of the inert material.
Other features, advantages and objects of the present invention will hereinafter become more fully apparent from the following description of the drawings, which illustrate several embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a section of a lead in accordance with the present invention.
FIG. 2 shows a lead of the present invention for use as an endocardial lead with a monopolar pulse generator or for converting a bipolar pulse generator of a cardiac pacemaker system to a monopolar configuration.
FIG. 3 is a diagram of another embodiment of a lead in accordance with the present invention for use in a nerve stimulating system; and
FIG. 4 shows another embodiment of a lead in accordance with the present invention for use in a system for stimulating the dorsal column of the spine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before describing the present invention in detail, the meaning of certain terminology used herein should be clearly understood. The terminology "distal end" is used in referring to that portion of the lead toward the end to which the active electrode is attached. The terminology "proximal end" is used in referring to that portion of the lead toward the end which is connected to the source of electrical energy or monitoring equipment. The term "active electrode" as used herein generally refers to the electrode at which stimulation is desired to be achieved (most often of negative polarity) or the electrode at whose location electrical activity of tissue is to be monitored. The term "indifferent electrode" as used herein is intended to refer to that electrode which is common to a system or at system ground. For a tissue stimulation system the indifferent electrode will often be of positive electrical potential with respect to the active electrode.
FIG. 1 shows section 10 of a flexible lead which may be used with an electro-medical device for implantation in the body. Section 10 comprises an electrical conductor 12 having a distal end 14, which is adapted to connect to an active electrode which may be used to supply electrical energy to or monitor electrical activity at a selected portion of the body. A proximal end 16 is provided, which is adapted to be connected to a source of electrical energy or monitoring equipment. Electrical conductor 12 is embedded in an insulating covering material 18 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Another electrical conductor 20, which serves as an indifferent electrode, is partially embedded in the outer surface of material 18 to hold conductor 20 in fixed position. Conductor 20 is wrapped in a helical configuration around material 18. The proximal end 22 of conductor 20 is adapted to be connected to a source of electrical energy or monitoring equipment. The distal end 24 of conductor 20 is terminated by projecting inside material 18 at a point 26 on the outer surface of material 18.
Conductors 12 and 20 are made of a conductive material which is substantially inert to body fluids and tissue, such as, for example, platinum or platinum-iridium alloy. Conductors 12 and 20 may, for example, be made in a configuration and of a construction the same as that of the lead described in U.S. Pat. No. 3,572,344. This lead construction has excellent mechanical strength and flex characteristics and at the same time is an excellent electrical conductor.
Section 10 may, for example, be used in converting a bipolar lead and pulse generator to a monopolar system without having to replace the lead or the pulse generator. Both ends of section 10 may be fitted with appropriate male and female adapters (not shown), to permit section 10 to be electrically connected distally to a bipolar lead and proximally to an electrical energy source or monitoring equipment. Conductor 12 of section 10 is adapted to be connected at its distal end 14 to a conductor connected to the active electrode of a bipolar lead and specifically, if for tissue stimulation, at its proximal end 16 to a source of electrical energy, generally to the negative polarity signal. Conductor 20 serves as an indifferent electrode and is adapted to be connected at its proximal end 22 to a common or ground potential. Conductor 20 should be of sufficient length and surface area and the helical turns adequately spaced from one another such as to insure sufficiently low energy density to substantially eliminate local tissue stimulation. Conductor 20 should have the same properties so as to avoid picking up local tissue electrical activity when adapted for use in certain monitoring systems.
FIG. 2 shows a flexible, body-implantable endocardial lead 30 for use with a bipolar pulse generator or for converting a bipolar generator to a monopolar system. Lead 30 has an electrical conductor 32 which is embedded in an insulating convering material 34 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Conductor 32 projects through the outer surface of material 34 at point 36. From point 36, conductor 32 is closely wrapped for several turns in a helical configuration around material 34 to form the active electrode of monopolar lead 30. The wrapped turns of conductor 32 are partially embedded in the outer surface of material 34 so as to maintain the turns in fixed position. Distal end 38 of conductor 32 is terminated by projecting into material 34 at point 40. Proximal end 42 of conductor 32 is connected to a connector pin 44 which projects beyond material 34 and is adapted to be connected to a source of electrical energy, such as, for example, a pulse generator. The active electrode formed near the distal end of conductor 32 may simultaneously serve to monitor electrical activity of the heart in a demand pacemaker.
Also embedded in material 34 is a closely wound helical coil spring 46 which defines a lumen therein. Spring 46 is open at its proximal end 48 so as to permit a stylet (not shown) to be inserted therein so as to provide lead 30 with sufficient rigidity to be inserted into and guided through a body vessel to a desired location inside the body. Spring 46 is closed at its distal end 50 to limit the distance of insertion of the stylet.
Lead 30 also is provided with another electrical conductor 52 having a proximal portion 54 which is embedded in material 34 and is connected to a connector pin 56. Conductor 52 projects through the outer surface of material 34 at a point 58 and is wrapped for several spaced turns in a helical configuration around material 34. The wrapped turns of conductor 52 are partially embedded in the outer surface of material 34 so as to maintain them in fixed position. Distal end 60 of conductor 52 is terminated by projecting inside material 34 at a point 62. The wrapped turns of conductor 52 may, for example, extend for approximately 21/2 inches or so along the length of material 34 and the turns are approximately three-eighths inch between centers. The exposed length and surface area and the spacing between the helical turns of conductor 52 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1.
Conductors 32 and 52 are made of materials which are substantially inert to body fluids and tissue, such as, for example, platinum or a platinum-iridium alloy. Pins 44 and 56 and spring 46 may, for example, be made of stainless steel alloys. The construction and configuration of conductors 32 and 52 may be that of the lead described in U.S. Pat. No. 3,572,344.
FIG. 3 shows a flexible, body-implantable lead 70 for use in a multi-channel nerve stimulator. Lead 70 has a pair of electrical conductors 72 and 74 spaced from one another and embedded in an insulating covering material 76 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Distal ends 78 and 80 of conductors 72 and 74 are terminated in such a way as to form monopolar electrodes 82 and 84 respectively. Electrodes 82 and 84 are partially exposed and partially embedded in base portions 86 and 88 respectively which are formed integrally with material 76. Electrodes 82 and 84 and corresponding base portions 86 and 88 are adapted to be wrapped around the nerves which are to be stimulated as, for example, the carotid sinus nerves. Conductors 72 and 74 are connected to connector pins 90 and 92 respectively which are adapted to be connected to a body-implantable receiver (not shown). The receiver is designed to receive stimulating pulses from an RF coupled external transmitter and apply these pulses to the nerves through electrodes 82 and 84.
Lead 70 is provided with a third electrical conductor 94 which is embedded in material 76 at its proximal end 96 where it is connected to a connector pin 98. Conductor 94 projects through the outer surface of material 76 at point 100 and is wrapped for several turns around material 76 in a helical configuration similar to that of conductor 52 in FIG. 2. The spaced turns of conductor 94 are partially embedded in material 76 so as to maintain them in fixed position. Material 76 has a somewhat greater cross section near its proximal end in the section where the spaced turns of conductor 94 are partially embedded. The distal end 102 of conductor 94 terminates in material 76 by projecting through the outer surface at point 104.
In lead 70, electrodes 82 and 84 form the active electrodes and are connected via conductors 72 and 74 and pins 90 and 92 respectively to the implantable receiver. The spaced turns of conductor 94 form an indifferent electrode which is connected via pin 98 to either an electrical common or ground. The exposed length and surface area and the spacing between the turns of conductor 94 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1.
FIG. 4 shows a flexible, body-implantable lead 110 incorporating the present invention and particularly designed for stimulating the dorsal column of the spine. Lead 110 has a conductor 112 embedded in an insulating covering material 114 which is substantially inert to body fluids and tissue, such as, for example, silicone rubber. Conductor 112 is terminated at its distal end in a spiral configuration to form an active electrode 116 which is partially embedded in a base portion 118 which is formed integrally with covering material 114. Material 114 is shown to intersect the base portion 118 at some angle other than 90° because such a configuration has been found easier to work with in attaching the active electrode 116 formed by the spiral configuration to the dorsal column. Spiral configuration 116 is partially embedded in base portion 118 to maintain the spiral configuration in fixed position. Although configuration 116 is shown to be a spiral, other configurations for the active electrode are possible. Proximal end 120 of conductor 112 is connected to a connector pin 122 which is adapted to be connected to a body implantable receiver (not shown) which may receive pulses which are RF coupled from an external transmitter. Active electrode 116 is generally connected to a negative polarity signal through conductor 112 and pin 122.
A second conductor 124 is provided with its proximal end 126 embedded in material 114 and connected to a connector pin 128 which is adapted to be connected to the receiver (not shown). Proximal end 126 of conductor 124 projects through the outer surface of material 114 at point 130 and is wrapped in a helical configuration for several spaced turns around material 114. The exposed length and surface area and the spacing between the turns of conductor 124 should be determined according to the same criteria as described regarding the characteristics of conductor 20 in FIG. 1. The turns of conductor 124 are partially embedded in the outer surface of material 114 to maintain the turns in fixed position. The distal end 132 of conductor 124 is terminated by projecting into material 114 at point 134. Conductor 124 forms an indifferent electrode which is generally connected via pin 128 to ground potential which commonly is of positive polarity.
Conductors 112 and 124 may be made in the structure and configuration of the lead described in U.S. Pat. No. 3,572,344. Conductors 112 and 124 and pins 122 and 128 are made of a material substantially inert to body fluids and tissue. Although electrode 116 has been shown and described as having a spiral configuration, other configurations for the active electrode could be employed.
Also, it should be understood that although the four embodiments shown have the indifferent electrode wrapped around the covering material, the indifferent electrode could be partially embedded in the outer surface of the covering material in any desired configuration. Instead of having the indifferent electrode wrapped around the inert material containing one or more electrical conductors, the inert material could be securely wrapped around the indifferent electrode. In a broad sense the indifferent electrode and at least a portion of the length of the inert material are securely wrapped relative to one another. It should also be understood that although the preferred embodiments of the invention show the indifferent electrodes securely wrapped around the inert material in a helical configuration, any other means of securing the indifferent electrode to the surface of the inert material would be satisfactory. Although the indifferent electrode is shown located near the proximal end of the lead, it could be secured anywhere along the length of the lead.
FIGS. 1-4 show several embodiments of body-implantable leads which can be used in various applications. It should be understood, of course, that the foregoing disclosure relates to only a few configurations which the present invention may take and that numerous modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.