Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1997-05-01
2001-02-06
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06185463
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates to a method and apparatus for providing a medical body implantable lead having a series of electrodes at its distal end which lead is resistant to “shorting” between the electrodes when the lead comes into contact with another medical body implantable lead.
2. DESCRIPTION OF THE PRIOR ART
The state of the art of implantable pulse generator and lead systems for stimulating human tissue has advanced to the point that such devices are being designed and used in increasing numbers to treat a wide variety of medical conditions. In addition to implantable pulse generator and lead systems for treating many different types of cardiac conditions (bradycardia, tachycardia, fibrillation, and the like), so called neurological pulse generator and lead systems have been provided for stimulating tissue in a patient's nervous system, in order to treat such diverse conditions as pain, motor impairment, incontinence, and impotence, to name only a few.
In most cases, electrical stimulation pulses are conveyed from an implanted pulse generator to the desired stimulation site by means of an implanted lead having exposed electrodes at its distal end. Typically, implantable spinal cord leads contain multiple electrodes. Two basic styles are available.
One style is the percutaneously inserted lead which is introduced through a Touhy needle. The implanting physician places the electrode in an appropriate location using fluoroscopic visualization. The procedure is done under a local anesthetic. Proper electrode placement is tested using a trial stimulation screening technique to assure that paresthesia is perceived in the affected area. An example of this type of lead is disclosed in U.S. Pat. No. 4,379,462 issued to Borkan.
A typical lead configuration of this percutaneous lead includes an insulated and flexible conductor having a circular cross section that is fitted with one or more ring electrodes. These ring electrodes usually have an the outer surface that is isodiametric with respect to the remainder of the lead. The isodiametric configuration minimizes the difficulty in passing the lead through a vein or through tissue. The smooth surface also minimizes the formation of potentially harmful thrombi when the lead is implanted.
That lead is designed to be inserted so that the electrodes lie inline along the spinal cord. Percutaneously inserted leads of this type provide focused stimulation patterns and are generally suited for unilateral pain problems. If the pain is bilateral it is often necessary to implant two leads, one on each side of the midline of the spinal cord. Both leads may be connected to one pulse generator or each lead may be connected to one of two separate pulse generators.
Isodiametric construction has been achieved in different ways. For example, Beranek, U.S. Pat. No. 4,592,372, discloses achieving an isodiametric configuration of an electrode assembly in a cardiac pacing lead by compressing a metallic sleeve which constitutes the ring electrode just far enough so that its outer diameter is the same as the outer diameter of the flexible body of the lead itself. Blake, et al., U.S. Pat. No. 3,995,623, proposes a construction for a lead useful in cardiac monitoring and temporary transvenous pacing which has multiple ring electrodes. Those ring electrodes are constructed from a coil strip of spring metal which appears to be crimped upon the electrode body with overlapping ends of the strip being joined to secure the ring electrode.
Beranek, U.S. Pat. No. 4,608,986, discloses a multiple lumen pacing lead having multiple ring electrodes. Although there appears to be minimal disclosure concerning the actual method of construction of the ring electrode, it would appear from the drawings that one of the crimping techniques discussed in the above patent is used to accomplish the construction.
In Peers-Trevarton, U.S. Pat. Nos. 4,437,474 and 4,458,695 a multipolar pacing lead construction having multiple ring electrodes in an isodiametric arrangement is again disclosed. In that construction, the ring electrodes appear to be received in annular slots formed between a series of insulators which are passed over the coiled conductor of the lead and presumably cemented in place with the spaces between these insulating elements defining the slots or annular spaces for the ring electrodes.
Likewise it has been known in the prior art to build an isodiametric lead with spaced ring electrodes by cementing or gluing short sections of precut tubing onto a lead body using the appropriate adhesives and using cylindrically shaped ring electrodes that are isodiametric with the tubing as the ring electrodes. Medtronic, Inc., the assignee of this application, has offered for sale a lead for spinal cord stimulation, the Model 3487A lead, fabricated in such a manner. Conductors from within the lead body can be led through to the underside of the ring electrodes and attached to the electrodes with a laser weld. Such a construction method is labor intensive and costly.
The Model 3487A lead utilizes a coiled conductor set to traverse the lead and provide the electrical path between the ring electrodes at the distal end of the lead and the connector block which connects the lead to the stimulator device. Such coiled conductors have long been used for such applications. However, improvements in noncoiled types of conductor wire afford various benefits including improved resistance to flex fatigue, improved flexibility, and better crush resistance. It has also been understood in the art that ring electrodes and isodiametric leads can be constructed with a multiple lumen interior with conductors from the various lumens being passed through the insulation covering the lead body to make contract with the underside of electrodes along the lead body, typically ring electrodes.
The second basic spinal cord stimulation lead type are commonly called “paddle” leads since they typically have a flat planar shape that resembles a paddle. This type of lead is usually surgically implanted through a laminotomy. An example of this type of “paddle” lead is the RESUME® lead manufactured by Medtronic, Inc. of Minneapolis, Minn., the assignee of the present invention. This lead has four axially aligned inline electrodes located on the outer surface of an elongate paddle at the distal end of the lead. The lead is normally implanted so that the electrodes are aligned with and lie over the midline of the spinal cord. Because leads of this type are surgically implanted, the size of the electrodes may be made larger than those of the percutaneously implanted leads.
With this type lead, various electrode combinations may be selected so that the area of stimulation may be moved along the midline of the spinal cord. The lead provides a broader stimulation pattern more suitable for midline and bilateral pain problems than the percutaneously inserted lead. An example of a surgically implanted lead is disclosed in U.S. Pat. No. 3,724,467 issued to Avery et al.
A problem with isodiametric electrodes occurs when using two or more isodiametric or paddle leads in any combination in a side by side arrangement. When two or more leads having electrodes on their outer surfaces are placed near each other, contact between an electrode on one lead and an electrode on another lead may cause one or both of the electrodes to be “shorted.” In other words, the electrodes on two different leads contact each other and become electrically “common.”
This “shorting” manifests itself in different ways depending on the type of implantable pulse generator used. For example, in a two channel constant voltage device where the two channels are alternately activated, touching electrodes have the effect of doubling the surface area of each electrode. This results in a reduction in impedance. Since the implantable pulse generator is programmed to maintain a constant voltage, more current will flow from the electrode and the patient will feel a stronger stimulation.
In a two channel constant voltage device where
Getzow Scott M.
Kindhorn Curtis D.
Medtronic Inc.
Patton Harold R.
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