Abstract:
An implantable lead and an improved method of manufacture is disclosed that is highly automated and simplified over prior art techniques. An implantable lead is disclosed having a flexible tubing member, a central coil member having a first portion having differing pitches, and a least one contact sleeve having a through radial hole for receipt of the wire member. A method for manufacture of the lead is disclosed by providing a coil member having a fixed pitch portion and a variable pitch portion, extending at least one filar member radially from the coil member, placing a lead body over the coil member, providing a contact sleeve over a portion of the lead body, the contact sleeve having a slot for receipt of the filar member, and welding the filar member to the contact sleeve.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to implantable devices and more particularly relates to the design and manufacture of implantable leads. 
     2. Description of the Related Art 
     An increasingly popular technique for therapeutically treating neurological disorders and chronic pain is providing electrical stimulation to neural tissue within the brain, the spinal cord, and/or a peripheral nerve. Thus, for example, physicians may surgically implant leads having electrode contacts near the spinal column of the human body and deliver electrical energy, using a signal generator, to these contacts to stimulate targeted neural tissue and elicit the desired therapeutic relief. 
     Implantable leads now also provide electrical stimulation via more than one electrode. This significantly increases the functionality of the implantable lead. For example, a multiple electrode lead allows the physician to adjust the treatment therapy to target different neural tissue, or to direct the stimulation more precisely to the neural tissue of interest. This is particularly useful where the implanted lead migrates along the spinal cord after it has been implanted. By subsequently adjusting the electrical stimulation delivered by the multi-electrode lead, the need for a second surgery is avoided. 
     A commonly-used implantable lead is a Pisces-style lead. As depicted in FIGS. 1A and 1B, this lead is a long and narrow tube, typically polyurethane, having an outside diameter of 0.050″ and an inside diameter of 0.030″. Along the distal end  120  of the lead are one or more electrodes  105  that wrap around the circumference of the lead body and have a certain width. These electrodes  105  are coupled to respective wires  110  that run from within a lumen  117  of the lead tubing to corresponding connectors  115  along the proximal end  125  of the lead. Most implantable leads utilized today are based on a coiled-spring design. In such leads, the wires that are used to connect the lead to the electrodes are wrapped around a mandrel with enough tension to cause the wires to exceed their yield point and thus to hold a coiled shape. The coiled wires are insulated from each other and typically have a fixed pitch, namely a fixed number of revolutions per inch. Each coiled wire is coupled to a corresponding electrode along the lead body. This is achieved by having the distal end of the wire (the filar) exit tangentially from the coil along the distal end of the lead and then be connected to an electrode located at that portion of the lead. 
     The coiled-spring design of the implantable leads, however, is limiting in its difficulty of assembly with the electrodes. In particular, the coiled-spring wires are unwound along the distal end of the lead and extended tangentially from the coil at along the desired portion of the lead where the corresponding electrode for each wire is to be placed. The tangentially extending wires are typically referred to as filars. This unwinding process, however, is inaccurate resulting in the filars extending unevenly from the coil. This results in non-coplanar weld placement of the electrode contacts over the filars. 
     After placement of the electrodes, the filars are positioned and trimmed while maintaining contact with the corresponding electrodes. A filar for the wire corresponding to an electrode is placed within a slot of the electrode and put in contact with that electrode and welded. The resulting weld, however, often protrudes from the surface of the lead, potentially causing interference during implant. 
     Further inefficiencies result in the overall manufacture of the Pisces-style lead. Known procedures for manufacturing implantable leads require considerable steps and operator involvement. Multiple cure processes must be performed requiring as much as 2-3 days of cure time. The greater the number of leads, the greater time and cost required in manufacturing the lead. Further, manufacture of these leads requires skilled technicians to perform some of these manufacturing steps. 
     It is therefore desirable to provide a design for and a method of manufacture of an implantable lead that can overcome these and other disadvantages. 
     SUMMARY OF THE INVENTION 
     A preferred form of the invention is an implantable lead and a method of manufacture of the lead. The implantable lead has flexible tubing impressions, contact sleeves positioned over the impressions and having openings, and a wire coil member running along a central lumen portion of the lead. The wire coil has radially extending filars that extend in a substantially perpendicular axis relative to the surface of the wire coil. Further, the wire coil has fixed and variable pitch portions to provide accurate positioning of the radially extending filars. 
     The method of manufacture includes the steps of forming a coil having at least one wire member having fixed and variable pitches, each wire member having a filar member, extending the filar member of at least one of the wire members radially from the coil member at a predetermined portion along the variable pitch portion of the coil member, heat forming a flexible lead body over the coil member, providing a contact sleeve over a portion of the lead body, the contact sleeve having a opening for receipt of the filar member, and welding the filar member to the contact sleeve. 
     The design and process of the implantable lead of the present invention provides a number of advantages over leads of the prior art. By way of examples, the present invention provides a wire coil design that provides improved accuracy in distances between the filars and improved assembly with the electrodes. In addition, the present invention reduces the direct build time of the lead, reduces the required level of operator training to manufacture the lead, and requires less manufacturing floor space. The applicant estimates that each of these variables may be reduced by as much as 50% over prior art techniques. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages and features of the invention will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which: 
     FIGS. 1A and 1B front views of an implantable lead of the prior art; 
     FIG. 2 is a front view of an implantable lead in accordance with a preferred embodiment of the present invention; 
     FIG. 3 is a front view of a coiled loop along the proximal end in accordance with a preferred embodiment of the present invention; 
     FIG. 4 is a front view of the coiled loop of FIG. 3 along the main body; 
     FIG. 5 is a front view of a coiled loop of FIG. 3 along the distal end; 
     FIG. 6 is a close-up sectional view of a filar of the coiled loop of FIG. 3; 
     FIG. 7 is another close-up sectional view of the filar of the coiled loop of FIG. 3; 
     FIG. 8 is a front view of a lead body in accordance with a preferred embodiment of the present invention; 
     FIGS. 9-11 are sectional views of the lead body of FIG. 8; 
     FIG. 12 is flow chart illustrating a manufacturing process for an implantable lead in accordance with a preferred embodiment of the present invention; and 
     FIGS. 13A and 13B are front and cross-sectional views, respectively, of an implantable lead having a concentric catheter in accordance with another preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, a preferred form of the invention basically includes an implantable lead  10  having an outer tubing  205 , a helical coil (not shown) within the tubing  205 , and a plurality of electrodes  210  along the distal end  215  of the lead and a plurality of conductors  290  along the proximal end  295 . Outer tubing  205  is preferably a polyurethane tubing having a 0.050″ outside diameter and a 0.030″ inside diameter. Other tubing materials such as silicon rubber or thermoform are also suitable. FIGS. 8-11 depict the outer tubing  205  in accordance with a preferred embodiment of the present invention. Outer tubing  205  has one or more notches  225  on the distal end, one for each electrode to be placed along the lead  10 . Similarly, outer tubing  205  has one or more notches  220  on the proximal end  295 , one for each connector  290  to be placed along the lead  10 . Notches  220  are of variable length typically in the range from 0.06 inch to 0.24 inch, for example 0.09 inch, and have an outside diameter of approximately 0.040 inch. Similar notches  225  are positioned along the proximal end for coupling to a power source (not shown). 
     Referring back to FIG. 2, electrodes  210  are preferably formed electrodes  210  having an aperture along its body. The diameter of the aperture is closely matched to the diameter of the filar  235  (discussed below) of its associated wire to allow the filar  235  to be inserted within the aperture and to allow proper welding of the filar  235  to the electrode  210 . Electrodes  210  are placed over the notches  220  and formed on to the lead  10 . 
     FIGS. 3-7 depict the helical coil  230  fitted within the outer tubing  205 . Helical coil  230  consists of a plurality of wound wires providing electrical connection to each of the electrodes  210 . Each wire within the coil  230  contacts and provides electrical energy to a corresponding electrode  210  on the lead  10 . As shown in FIG. 5, the distal end of each wire, or the filar  235 , terminates at a designated portion of the lead  10  where the corresponding electrode  210  is located. The coils  230  are preferably wound having a portion having a fixed pitch and a portion along the electrodes  210  having a variable pitch. The variable pitch allows the filars  235  of each of the wires to be coplanar and allows the filars  235  to have the necessary spacing between each other. As preferred and as illustrated in FIGS. 6 and 7, filars  235  extend in a substantially perpendicular manner from the coil  230 . Coil  230  may be formed using a programmable coil winder, which is generally known in the art. The variable pitch in the coil  230  may be formed using techniques generally understood in the art. Similarly, the proximal end of each wire terminates in filar  235  as shown in FIG.  3 . 
     The outside diameter of coil  230  is approximately in the range of .026 inch to 0.030 inch. The pitch angle of the revolutions is in the range of 10 degrees to approaching  90  degrees. At 10 degrees, the helical coil  230  approaches a straight or linear wire whereas when it approaches 90 degrees the helical coil  230  would be considered tight or close wound. 
     In an alternative embodiment, shown in FIGS. 13A-B, coil  230  may be fabricated to form a hollow lumen  34  within the coil  230 . A stylet may then be inserted in the lumen, and drugs may be infused through the lumen and out through microporous portions  27 - 29 . Alternatively, a thin walled tube could be placed within coil to provide a closed conduit from proximal to distal ends of body  12 . The core revolutions would “float” on the inner conduit formed by the thin walled tube. Drugs may be infused through the thin walled tube to exit the distal end of the lead or along a side wall portion. The structure of the lumen may be similar to that disclosed in U.S. Pat. Nos. 5,702,437 and 5,713,923, both of which are incorporated herein by reference in their entireties. 
     FIG. 12 depicts a flow chart illustrating the method of manufacture of an implantable lead in accordance with a preferred embodiment of the present invention. At step  505 , a plurality of wires that are wrapped to form a coil of wires are cleaned and inspected. As discussed above, any number of techniques can be used to form the coil  230  and typically entails wrapping the wires around a mandrel. The coil  230  preferably has a constant pitch along the body of the coil  230 . Approaching the distal end  215  of the coil  230 , near the placement of the electrodes  210 , the coil  230  has a variable pitch. As stated before, coil  230  may be formed using a programmable coil winder, which is generally known in the art. 
     At step  507 , notches  220  and  225  are provided along the distal and proximal ends of the lead body  205  using any number of techniques, including but not limited to, grinding or laser etching. The notches  220  and  225  extend circumferentially around the lead body and serve to accommodate placement of the electrodes  210  and connectors  290  along the lead body  205 . The notches  220  and  225  are preferably in the range of 0.005 inch deep. 
     At step  508 , a polyurethane split lead body  205  is slid over the coil  230 . The lead body  205  has distal and proximal slits along the distal  215  and proximal  290  ends, respectively, to receive the radially protruding filars  235  discussed below. 
     At step  510 , each wire is extended radially away from the coil member along the distal end of the coil at the point of contact with the electrode  210  corresponding to each wire. The distal ends of the wires, known as the filars  235 , extend substantially perpendicularly from the surface of the coil  230 , thereby providing each of placement of the electrodes  210 . In addition, the filars  235  are preferably coplanar with each other and also have a predetermined distance between the filars  235 . Accordingly, pitch of the coil  230  may be calculated as a function of the distance between the filars  235 . The predetermined distance between the filars  235  allows the electrode  210  to be positioned at the desired portion of the lead  10 . During this process, the lead body  205  may be slid toward the proximal end  295  and away from the distal end  215  to allow unwinding of the coil member  230 . After the coil  230  is unwound, the lead body  205  may slide back over the distal end  215  with the filars  235  extending through the distal slit on lead body  205 . 
     At step  515 , a similar procedure is performed at the proximal end  295  for placement of the conductors  290 . Again, during this process, the lead body  205  may be slid toward the distal end  215  and away from the proximal end  295  to allow unwinding of the coil members  230 . After the coil  230  is unwound, the lead body  205  may slide back over the proximal end  295  with the filars  235  extending through the proximal slit on lead body  205 . 
     At step  520 , the lead  10  is placed in a mold to heat seal the slits and to provide a final dimension for the notches  220  and  225 . Advantageously, this process eliminates a number of the steps and detail required to fabricate a lead under the prior art, including, for example, eliminating the step of using a solvent and the need for a curing process. 
     At step  525 , electrodes  210  are formed over the notches  220  of the lead body  205 . The electrodes  210  have an aperture for receipt of the filars  235 . Advantageously, a formed electrode  210  is easier to install than a machined electrode of the prior art and required less operator time. Similarly, at steps  530 , connectors  290  are assembled and positioned in a similar manner as that described above in step. Connectors  290  also have an aperture for receipt of the filars  235 . 
     At step  535 , the filars  235  are trimmed and spot welded to their corresponding electrodes  210  and connectors  290 . Alternatively, the filars  235  may be attached or connected as part of a seam weld. Advantageously, spot welds provide a convenient way of assuring that the filars  235  are in contact with the electrodes  210  and connectors  290 . In particular, if the filar  235  is in contact with the electrode  210  or connector  290 , the aperture of the electrode  210  or connector  290  will be filled in by the weld. If the filar  235  is not in contact with the electrode  210  or connector  290 , the aperture will not be filled in. Additionally, this welding process results in a flush surface over the contact sleeve, and avoids interference during implant. 
     Finally, at step  540 , a tip  240  is formed on the distal end  215  of the lead I  0 . The lead tip  240  is inserted into a heated mold where the tip  240  is formed from the mold. The tip  240  is then cooled and withdrawn from the mold. Alternatively, the tip  240  may be heat-butt-jointed to the lead  10 . 
     Advantageously, this process of the present invention has many advantages over prior art techniques. For example, the present technique may be automated. Further, the present technique significantly reduces the manufacture time for leads and avoids the need for lengthy cure processes. 
     Those skilled in the art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention, as defined in the accompanying claims.