Field steerable electrical stimulation paddle, lead system, and medical device incorporating the same

An implantable electrode paddle is adapted to receive an electrical signal from a medical device and generate an electrical field to stimulate selected body tissue. The paddle includes a housing including walls that define an interior space and a plurality of windows formed through at least a first one of the walls for transmitting the electrical field to the body tissue, an electrode array including a plurality of electrode groups, each electrode group including at least two electrodes individually secured in a respective window and spaced between about 0.1 mm and about 10 mm apart, and a plurality of wires, each of the wires being coupled to a respective electrode and routed within the interior space to receive the electrical signal. A lead assembly and an implantable medical device can include the paddle.

TECHNICAL FIELD

The present invention generally relates to medical leads for biological tissue therapy, and more particularly relates to systems and methods for steering a tissue stimulating electrical field using implantable medical leads.

BACKGROUND

Dorsal columns are long myelinated fibers oriented along the spinal cord axis and centrally located around the lumbar spine between the dorsal roots. Researchers have found that fibers enter the dorsal horn, and are arranged in approximately v-shaped layers. Fibers that enter at a higher vertebral level form a v-shaped layer covering the layers that originated at lower levels. The nerve fiber organization is less structured below the dorsal column surface, where the fibers are two or more vertebral levels away from their point of entry. M. C. Smith et al.,Topographical Anatomy of the Posterior Columns of the Spinal Cord in Man,107 Brain 671 (1984).FIG. 1is a cross sectional view of different vertebra through the spinal cord with symbols illustrating the spinal nerve pathways through the dorsal column.

Chronic pain originating in the lower back is quite common. Spinal cord stimulation is an accepted therapy for chronic pain. However, physicians have found that it can be difficult to properly position the spinal cord stimulation lead to achieve good pain relief for lower back pain. As illustrated inFIG. 1, nerve fibers associated with lower back pain (S4 to L5), are only close to the dorsal column surface for a short distance and are consequently difficult to locate. Physicians who consider properly treating lower back pain with SCS must develop an effective SCS technique and must learn to manipulate a stimulating lead with unusual skill and patience. Such a technique often involves implanting a stimulating device and carefully positioning at least one stimulating lead into a patient's spinal area. Even if the technique is performed properly, the leads may need to be repositioned over time. Repositioning the stimulating leads is typically an invasive surgical procedure that carries risks and requires great patience, care, and skill.

Accordingly, it is desirable to provide a system and method that physicians can readily adopt for stimulating the spinal cord, particularly areas of the spinal cord that have low surface concentrations of readily manipulated nerves such as those in the dorsal columns. In addition, it is desirable to provide a system and method for non-invasively relocating an electrical field after the system is implanted. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

An implantable electrode paddle is provided for receiving an electrical signal from a medical device and generating an electrical field to stimulate selected body tissue. The electrode paddle comprises a housing including walls that define an interior space and a plurality of windows formed through at least a first one of the walls for transmitting the electrical field to the body tissue, an electrode array including a plurality of electrode groups, each electrode group including at least two electrodes individually secured in a respective window and spaced between about 0.1 mm and about 10 mm apart, and a plurality of wires, each of the wires being coupled to a respective electrode and routed within the interior space to receive the electrical signal.

An implantable lead system is provided to transmit an electrical signal from a medical device and generate an electrical field to stimulate selected body tissue. The system comprises a first lead body comprising at least one conductor, and the electrode paddle described above.

An implantable medical device is also provided for generating an electrical field to stimulate selected body tissue. The device comprises a controlling device such as an electrical pulse generator having an electrical output for transmitting electrical signals, and the lead body and electrode paddle described above.

A method is provided for manufacturing an implantable electrode paddle that is adapted to receive an electrical signal from a medical device and generate an electrical field to stimulate selected body tissue. The method comprises the step of assembling an electrode array including a plurality of electrode groups, and a plurality of wires coupled to the electrode array, onto a first insulative substrate having a plurality of windows formed therethrough for transmitting the electrical field to the body tissue, and securing each electrode in a respective window with the electrodes in each group spaced between about 0.1 mm and about 10 mm apart.

DETAILED DESCRIPTION

While the following description is generally directed to treatments and systems involving a neurological stimulator in the form of an implantable pulse generator, the utility of the apparatus and method of the present invention is not limited to neurostimulatory pulse generating devices and can be adapted for use with a variety of implantable electrical devices that use multiple electrical leads to send electrical pulses to selected body parts.FIG. 2is an illustration of a patient110with an implantable pulse generator (IPG)10implanted in the patient's abdomen. The IPG10transmits independent stimulation pulses to the spinal cord120using an insulated lead12and electrodes32coupled thereto. The lead12is routed around the flank toward the spinal column120, and the electrodes32are placed in the epidural space next to the spinal column120. An extension (not shown), including a conductor, may also be used to electrically connect the IPG10to the lead12.

In order to manipulate the location of the electrical field produced by the electrodes32, the IPG10includes a plurality of outlets as necessary to selectively and independently control each electrode32to which the IPG10is coupled. According to one exemplary embodiment, the IPG10includes sixteen channels and respective outlets to control a field steerable stimulation lead including sixteen electrodes. In an alternative exemplary embodiment, the IPG10has fewer independent channels and respective outlets than the number of leads controlled thereby, and transmits coded address signals before each stimulation pulse to instruct which of the electrodes will transmit pulses to a patient. Electronics are disposed downstream from the IPG10on the lead to receive the coded address signals and, responsive thereto, to select and control the electrodes indicated by the coded signals.

The IPG10and the associated system typically utilize fully implantable elements, although it is within the scope of the invention to utilize partially implanted generators that employ wireless coupling technology such as electronic components sold by Medtronic, Inc. under the trademarks X-trel™ and Mattrix™. A wireless receiver in the IPG10can be adapted to receive instruction commands from a physician or another user, the instruction commands selecting stored pulse output commands from the IPG10or programming new pulse output commands. Also, according to either of the exemplary embodiments described above, the IPG10includes a memory for storing pulse output commands that can be programmed in advance of implantation and are tailored to a patient's needs. The output commands can be transmitted directly to the selected electrodes. In another embodiment, the output commands are encoded in address signals that are transmitted to a downstream electronic network that decodes and generates pulse output commands and transmits them to selected electrodes. The electrodes can be programmed individually, or controlling programs can generate commands that are transmitted to predetermined groups of electrodes depending on the patient's needs.

After the IPG10is implanted, the pre-programmed pulse output commands can be modified using an external programmer40that communicates wirelessly with the IPG10. The programmer40is equipped with an antenna41for wireless communication, and the IPG10is equipped with a receiver (not shown). The programmer40can communicate using any suitable known communication signals including but not limited to radio frequency signals. Wireless communication with the IPG10enables a physician or the patient to non-invasively relocate the electrical field after the IPG10is implanted, and to thereby adjust the dorsal column stimulation. Because specific fibers on the dorsal column can be electrically stimulated or not stimulated through post-surgical manipulation, the intricacy of implanting the IPG leads and electrodes32is substantially reduced. The physician performing the surgery can implant a lead body that houses the IPG electrodes32in a general area on the dorsal column and then later steer or alter the electrical field using the programmer40.

In a general sense, manipulating and adjusting the excitation locus can be performed using known techniques. Although the present invention is directed to fine tuning tissue stimulation, general techniques such as those described in U.S. Pat. No. 5,713,922, incorporated herein by reference, for neural tissue excitation adjustment in the spinal cord or brain can be used in combination with the present invention.

Steering or altering the IPG electrical field is further enabled according to the present invention by a fine tuning apparatus that secures and distributes the stimulating electrodes in the dorsal column vicinity.FIG. 3is a top view of an exemplary electrode paddle30. The electrode paddle30provides a hermetic encasement for circuitry and electronics, and also secures and supports many small and closely spaced electrodes32. The electrode paddle30and the electrodes32exposed thereon are formed using biostable materials, and the electrodes32are secured in the housing in a manner whereby corrosive body fluids are unable to contaminate the paddle interior and corrode or otherwise disrupt the electrode circuitry32. The electrode paddle30organizes the electrodes32into one or more groups31, and in an exemplary embodiment the electrodes32are organized into at least two groups31. The intra-group and inter-group electrode distribution on the electrode paddle30prevents the electrodes from contacting one another, and at the same time creates a dense electrode region33. The dense electrode region33permits the electrode paddle30to be small despite the large number of electrodes32secured thereon, and therefore to be positionable in the dorsal column vicinity with minimal impact on body tissues.

The exemplary electrode paddle30inFIG. 3includes two electrode groups31, with eight electrodes32in each group31. The groups31are spaced apart in the longitudinal direction A of the electrode paddle30, and the electrodes32within each group30are spaced apart in the lateral direction B. Although the number of electrodes and their precise configuration on the electrode paddle30can vary without varying from the scope of the present invention, the configuration illustrated inFIG. 3provides closely-spaced electrodes32that can be individually controlled to steer the electrical field that is therapeutically provided to a patient. In an exemplary embodiment the electrodes are each about 0.5 mm wide and are consistently spaced about 0.5 mm apart, although other electrode sizes and spacing may be suitable. For example, the electrodes can be spaced between about 0.1 mm and about 10 mm apart, and are preferably spaced between about 0.1 mm and about 0.5 mm apart.

When two electrodes are spaced about 0.5 mm apart, switching the electrical pulses from one electrode to the nearest laterally adjacent electrode laterally shifts the electrical field center about 0.5 mm. For an even more precise shift and a higher current, both of the two adjacent electrodes can be selected, causing the electrical field to be centered between the two electrodes and to have a larger current. Also, in some cases a high current may required to effectively stimulate a desired nerve fiber, and the voltage capability of the IPG10may be exceeded. The electrodes32are so closely spaced on the electrode paddle30that two or more electrodes32may be selected simultaneously to effectively function as a single larger electrode. With the electrode paddle30implanted in the dorsal column vicinity, selected nerve fibers can be carefully and precisely stimulated by steering the electrical field between the electrodes32in this manner.

The electrode paddle30can be used in combination with other known voltage divider systems as appropriate. U.S. Pat. Nos. 5,501,703 and 5,643,330, and Publication WO 95/19804, are incorporated herein in by reference. These references disclose, inter alia, an electric field steering process that involves individually controlling the voltage at each of a plurality of electrodes. More particularly, the references disclose individually manipulating the voltage of at least three electrodes that are incorporated in a multichannel apparatus for epidural spinal cord stimulation.

In an exemplary embodiment of the invention, electronics are provided on the lead between the electrode paddle30and the IPG10. A coded signal is sent from the IPG10to an electronics package that selectively activates the electrodes32in response.FIG. 4is a top view of a medical device assembly including the IPG10, a first lead body portion12a, an in-line hermetic encasement20, and a second lead body portion12bthat are electrically connected in sequence. Each lead body12a,12bmay include one or more leads that may be combined in one or more lead bodies. When the assembly is implanted, the first lead body portion12ais electrically coupled to the IPG10, and extends to another suitable location in the patient's body where it is electrically coupled to a hermetic electronic encasement20. The encasement20houses an electronic network that may include a memory for storing programs that, when carried out, enable the electronic network to communicate with and control multiple electrodes disposed on the electrode paddle30. The encasement20may further include at least one energy source such as a battery to power the electronic network and the electrode paddle30. An exemplary embodiment of the encasement20and its contents will be described in greater detail below.

A plurality of leads collectively identified as the lead body portion12bare electrically coupled to the encasement20at one end and are directly engaged or indirectly coupled with the electrode paddle30at an opposite end. Optionally, a connector block22can be fastened to the encasement20. The connector block22electrically connects one or more leads to the encasement20via connectors such as lead clamps (not shown) that hold the leads in place.

FIG. 5is an exploded view of a hermetic electronic encasement20disclosed in U.S. patent application Ser. No. 10/742,732 which is incorporated herein by reference. As mentioned above, the encasement20serves as the housing for electronic intelligence and other components such as at least one energy source21, and integrated electrical circuitry/components19. The encasement20is in-line with the lead body12a,12band consequently enables the electrode paddle30and, optionally, other stand-alone devices or components that may be controlled by the IPG10to be disposed downstream from and in direct communication with the IPG10.

Although the energy source21may be a simple battery, the hermetic encasement20may be powered by dedicated conductive lines from the IPG10. In another embodiment, the energy source21harvests or rectifies power from the IPG10stimulation pulses and stores the same in order to power the hermetic encasement20and the electrode paddle30. In yet another embodiment, the hermetic encasement20is temporarily powered via an external magnetic field or RF energy.

The electrical circuitry/components19are integrated into or mounted onto a multi-layered circuit board17formed of biostable materials. In an exemplary embodiment of the invention the circuit board17is a multi-layered ceramic structure that includes surface bonding pads18for coupling the circuitry/components19to the lead body12a,12b. The bonding pads18are deposited onto the circuit board17using any conventional depositing method and are formed from a biocompatible metal such as gold or platinum. Examples of depositing techniques include printing, chemical vapor deposition, or physical deposition such as sputtering.

The encasement assembly can include side walls15that combine to surround the mid-portion of the circuit board17, and end walls16that are attached to the side walls15to complete the encasement20. In an exemplary embodiment of the invention, the end walls16and side walls15are composed of a ceramic material. In order to protect and maintain the connections between the bonding pads18and the lead body12a,12ba flexible strain relief device14can be attached to one or both of the encasement ends. An adaptor13can be coupled to the strain relief device14to appropriately shape the device14and provide rigidity to the portion of the device14that interfaces with an endplate16.

In another exemplary embodiment of the invention, an integrated lead system is employed in which electronics are provided on the electrode paddle30, or on another lead extension in communication with the electrode paddle30, to allow use of large numbers of electrodes with a small number of conductors extending along the lead wire and/or extension. A coded signal is provided to the electrode paddle30from the IPG, and the electrode paddle electronics identify which electrodes to activate in response thereto. More particularly, the electronics on the electrode paddle30include a controller that responds to the coded signal and selectively activates the electrodes32. The electronics may be included within the paddle housing or may be separately housed adjacent to the electrode paddle30. The embodiments described above or within the scope of the invention as described herein can be used in combination with additional known electronics for selecting and controlling electrode arrays. See, for example, U.S. Pat. No. 6,038,480 (Hrdlicka et al) on living tissue stimulation and recording techniques with local control of active sites; U.S. Pat. No. 6,473,653 (Schallhom et al) on selective activation of electrodes within an implantable lead, and US Patent Application Publication No. US2003/0093130A and PCT Patent Publication No. WO2003/041795A (Stypulkowski) on multiplexed electrode array extensions, all three of which are incorporated herein by reference in their entirety.

Returning now to the functional aspects of the invention,FIGS. 6 to 9are images from a computer model of electrical fields, illustrating the effect of selecting different electrodes to supply stimulation to the spinal cord. More particularly, the figures illustrate the result of a computer modeling study of the electrical field generated by an electrode. Each figure is a cross section of the spinal cord120, with an eight-electrode paddle30located in the epidural space. The eight electrodes32are designated as electrodes32a,32b,32c,32d,32e,32f,32g, and32hprogressing upwardly from left to right with electrode32aon the far left. The electrode-generated electrical field is steerable about the spinal cord120as different electrodes32are selected. In the figures, the electrodes32are spaced 0.5 mm apart, although such spacing is merely exemplary and can be adjusted depending on the patient's needs. InFIG. 6, electrode32eis selected, generating an electrical field35eabout a spinal cord area. InFIG. 7, electrode32fis selected and the electrical field35fchanges its shape and position to stimulate a different spinal cord area. The fields35g,35hare shown inFIGS. 8 to 9, respectively, as electrodes32gand32hare selected.

Exemplary methods for manufacturing the electrode paddle30will now be discussed.FIG. 10is an exploded view of a substrate36and wire-electrode assemblies to be mounted thereon. The individual electrodes32are formed from any suitable conductive metal such as platinum-iridium. The wire-electrode subassemblies are then individually assembled onto a substrate36that includes a window37for each electrode32that exposes the electrode32to the spinal cord. The substrate36is typically polyurethane, but can be formed from a fiberglass, a polyimide, a thermoset elastomer such as silicone, another suitable polymer such as an injection molded polymer, or another suitable nonconductive material. The wire-electrode subassemblies are assembled onto the substrate36by a suitable technique. Alternatively, the electrodes32may be directly deposited onto the substrate36using a deposition process, or an etching process using a completely metallized surface as a starting material. One of the above processes is typically performed to first deposit or otherwise assemble the electrodes32, and thereafter form the wires34and join them to the electrodes32using a laser welding method, a crimping method, or other suitable joining process. Although not shown inFIG. 10, an insulative backing substrate may be adhered or otherwise joined to or be integral with the substrate36to shield and further isolate the electrodes32and wires34from the external environment and from each other.

In an exemplary embodiment, the substrate36includes two sheets36a,36b.FIG. 11is an exploded view of the substrate sheets36a,36bsecuring the electrodes32and routing the wires34. The sheets36a,36bare made from a resin such as polyurethane, or another suitable material as recited above. The electrode/wire assemblies are coupled using a process selected from those processes recited above, and are placed in slots37in sheet36a. The electrodes32may be temporarily retained using adhesive or a heated probe to melt small amounts of polyurethane over each electrode32. The other polyurethane sheet36bis then placed on top of the first sheet36aand the electrode/wire assemblies, trapping the wires and electrodes. Adhesive or heat staking may be used to temporarily retain the electrodes32and wires24for handling. The entire assembly36is then placed in a hot fixture, and a hot plate presses the sheets36a,36b. The heat allows the softened polyurethane to flow about any open spaces to encapsulate the electrode/wire assemblies and seal the sheets together with a fluid-impermeable seal.

FIG. 12is an isometric view of the substrate36being fit into a boot38. The boot38is made of silicone, polyurethane, or other suitable nonconductive material, and includes a receiving slot39in which the substrate36is received and then slidingly engaged. The slot39is of a depth that causes the top surface of sheet36ato be flush with the top surface of the boot38, and is sized to expose the electrodes32to the spinal cord to the boot exterior. Thus, the paddle30can be implanted with the electrodes32uniformly distanced from the spinal cord. After the substrate36is secured in the boot38, the wires34are routed into a connection tube40and joined to one or more lead bodies12. Adhesives such as silicone RTV or other sealants may be used to fill in any holes or to secure any panels that were installed during the manufacturing process.