Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
2001-04-19
2003-01-21
Lazarus, Ira S. (Department: 3749)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
C607S116000, C607S126000
Reexamination Certificate
active
06510347
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an implanted tissue stimulator system and catheters.
The concept of using electronic stimulation systems for the purpose of controlling nerves or muscles is well known. These systems typically utilize an implantable or an external pulse generator. The external systems consist of a transmitter and antenna which transmits energy and/or stimulation signals transcutaneously through a patient's skin to an implanted receiver. The receiver provides signal processing of the received pulses and transmits the energy derived therefrom to activate electrodes implanted adjacent to specific types of tissue to be stimulated. A system like the one described above has been disclosed previously in U.S. Pat. No. 3,727,616. It is also known in prior art where more than one pair of electrodes are activated such as U.S. Pat. No. 3,449,768.
Problems arise in these prior art systems where electrode placement fails to provide the desired physical response. It may also occur later if a change in patient condition or electrode position occurs. This failure may also be caused by improper polarity of the stimulated electrodes relative to one another. Furthermore, it is often required that the electrodes be implanted surgically adjacent to one or more nerve fibers. This type of procedure involves inherent risks due to the fact that it is often performed in close proximity to the brain or spinal cord or other sensitive nerves or tissues. It is therefore desirable to perform the electrode implantation only once to minimize the surgical risks to the patient as well as the financial burdens. Moreover, even when a plurality of electrodes have been utilized, such that repeated surgical procedures are not required, the prior art systems did not provide for dynamic programming and reprogramming of different electrodes after surgery until U.S. Pat. No. 4,459,989 to Borkan.
The Borkan patent '989 disclosed an external stimulator system which allowed noninvasive programming of the stimulated electrodes. Each electrode was capable of assuming a positive, negative or open circuit status with respect to the other electrodes. This effectively allowed the electrodes to be “repositioned” non-invasively. That same programming ability (plus/minus/off) was later applied to totally implantable systems as well. The system had mono/biphasic control also. Further improvements are described in U.S. Pat. No. 4,612,934 also to Borkan.
The application of spinal cord stimulation has shown itself to be effective in the treatment of pain and is under study for various other medical conditions. Initially, the leads were implanted by laminectomy and applied to the dura in the epidural space. The next generation of electrodes were positioned by percutaneous implantation. These were either placed into the intrathecal space or the epidural space
An example of a mutlielectrode catheter assembly for spinal cord stimulation is shown in U.S. Pat. No. 4,379,462 to Borkan.
The recent use of totally implantable stimulator systems with an implanted power source have resulted in increased emphasis on the amount of power required to deliver an effective stimulation regimen. In addition, use of multi-electrode systems has put an even greater strain on the limited resources of an implanted power cell.
Various stimulation catheters are disclosed to lie along and stimulate tissue. The electrodes on the leads are various sizes to conserve the battery as well as allowing a more defined area of stimulation. It may also include multiple channels or passages for delivery of drugs, thermal or photonic energy.
One embodiment envisions epidural, nerve root or intrathecal stimulation leads that include a sheath having at least three in-line electrodes spaced along the exterior of a distal end of the sheath to lie in-line along the tissue. In this embodiment, the electrodes extend no greater than 270° about the exterior of the sheath. The electrodes can extend anywhere in the range of 30 °-270°. The radius of the electrode maybe smaller than the radius of the sheath This reduces the surface area of the electrodes and therefore the power required by the battery. It also allows the electrodes to have a more defined or localized stimulation. Wherein the electrodes extend less than 360° about the exterior of the sheath, the length of the each electrode along the sheath should be typically at least three millimeters. If the electrode contact extends 360° about the sheath, the length of the electrodes along the sheath typically would be three millimeters or less. The energy delivered to each electrode is distributed over the entire surface area of the electrode.
In epidural spinal cord stimulation, a great deal of energy is wasted since the target neural tissue lies in only one direction. Use of an electrode with a limited circumferential electrode contact will allow better use and direction of stimulation energy. The currently preferred electrode contact length is two to four millimeters. Use of an electrode with, for instance, a 180 degree electrode allows the same stimulation field to be generated at one half the power required for a standard electrode contact of the same length. Alternatively, it allows the longer (4 mm) electrode contact to be used at the same power consumption as a smaller (2 mm) electrode. The larger electrodes are more forgiving in terms of precise positioning and are more desirable but often not chosen due to the tradeoff between implant battery life and lead size.
In another embodiment, an additional electrode spaced along the length of the sheath from at least three in-line electrodes at the distal end of the sheath. By positioning the additional lead on the sheath it is closer to the distal electrodes and thereby reduces the current path compared to using the stimulator casing as the additional lead in a monopolar mode. The additional electrode has a surface area on the sheath greater than the surface area on the sheath of each the at least three electrodes. The additional electrode is typically at least twice the surface area of each of the at least three electrodes and may be spaced, for example, at least 10 millimeters from the other electrodes. The increase in surface area can be by varying the electrode length along the sheath or diminishing the circumference around the sheath of the electrodes. The lead may be activated in either a bipolar mode using two of the at least three electrodes and in a monopolar mode using the additional electrode as a common anode and at least one of the other electrodes as a cathode.
The sheath may include a fixing element configured to fix the electrode in place along the tissue. The fixing element may include at least one of the following: inflatable balloons, nitinol, tines and the sheath shape.
The invention also anticipates an embodiment Wherein the electrodes extend no greater than 60° about the exterior of the sheath, the electrodes are positioned along the nerve root where it enters the spinal cord(dorsal root entry zone). Alternatively, where the electrodes extend no greater than 90° about the exterior of the sheath, the electrodes may be positioned along the mid-line of the spinal cord to stimulate only the longitudinal and not the bending nerve fibers.
The sheath may also include a passage extending from an inlet at the proximal end of the sheath to one or more outlets at the distal end of the sheath. The outlets may be located at one or more locations including, but not limited to the tip of the distal end, the area between the electrodes and on the electrodes. This passage may be used for dispensing of drugs or other fluids, for example, adhesive. It may also be an optical channel or for a stilet to be used during positioning of the lead. This may be used without fixing elements.
Alternatively, one or more optical channels can be provided extending from a port at the proximal end of the sheath to a port at the distal end of the sheath. The port for the optical channel at the distal end may located at one or more
Barnes & Thornburg
Lazarus Ira S.
Rinehart K. B.
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