Abstract:
In one embodiment, a medical lead comprises a lead body for conducting electrical pulses and a paddle. The paddle includes an intermediate metal layer, at least an insulative polymer backing layer, and an insulative polymer covering layer. The intermediate metal layer comprises a plurality of features defined by gaps in the metal material in the metal layer such that each feature is electrically isolated from each other feature, wherein each feature includes a respective connector element that is electrically coupled to at least one conductor within the lead body, wherein a portion of the insulative polymer covering layer is exposed above each feature to define a respective electrode for the corresponding feature. Also, the paddle possesses shape memory to cause the paddle to assume a substantially planar orientation when the shape memory is in a relaxed state.

Description:
RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/772,321, filed Feb. 10, 2006, entitled “SELF-FOLDING PADDLE LEAD AND METHOD OF FABRICATING A PADDLE LEAD,” which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application is generally related to a paddle lead that is self-folding for insertion in a patient using an insertion tool or catheter and that returns to an extended state upon exiting the insertion tool or catheter within the epidural space. 
       BACKGROUND 
       [0003]    Application of electrical fields to spinal nerve roots, spinal cord, and other nerve bundles for the purpose of chronic pain control has been actively practiced for some time. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated nerve tissue. Specifically, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Thereby, paresthesia can effectively mask the transmission of non-acute pain sensations to the brain. 
         [0004]    It is known that each exterior region, or each dermatome, of the human body is associated with a particular longitudinal spinal position. Thus, electrical stimulation of nerve tissue must occur at a specific longitudinal location to effectively treat chronic pain. Additionally, it is important to avoid applying electrical stimulation of nerve tissue associated with regions of the body that are unaffected by chronic pain. Positioning of an applied electrical field relative to a physiological midline is also important. 
         [0005]    Percutaneous leads and laminotomy leads are the two most common types of lead designs that provide conductors that deliver stimulation pulses from an implantable pulse generator (IPG) to distal electrodes adjacent to the nerve tissue. As shown in  FIG. 1A , conventional percutaneous lead  100  includes electrodes  101  that substantially conform to the body of the body portion of the lead. Due to the relatively small profile of percutaneous leads, percutaneous leads are typically positioned above the dura layer through the use of a Touhy-like needle. Specifically, the Touhy-like needle is passed through the skin, between desired vertebrae to open above the dura layer for the insertion of the percutaneous lead. 
         [0006]    As shown in  FIG. 1B , conventional laminotomy or paddle lead  150  has a paddle configuration and typically possesses a plurality of electrodes  151  (commonly, two, four, eight, or sixteen) arranged in one or more columns. Multi-column laminotomy leads enable reliable positioning of a plurality of electrodes. Also, laminotomy leads offer a more stable platform that tends to migrate less after implantation and that is capable of being sutured in place. Laminotomy leads also create a uni-directional electrical field and, hence, can be used in a more electrically efficient manner than conventional percutaneous leads. Due to their dimensions and physical characteristics, conventional laminotomy leads require a surgical procedure for implantation. The surgical procedure (a partial laminectomy) is evasive and requires the resection and removal of certain vertebral tissue to allow both access to the dura and proper positioning of a laminotomy lead. 
       SUMMARY 
       [0007]    In one embodiment, a medical lead comprises a lead body for conducting electrical pulses and a paddle. The paddle includes an intermediate metal layer, at least an insulative polymer backing layer, and an insulative polymer covering layer. The intermediate metal layer comprises a plurality of features defined by gaps in the metal material in the metal layer such that each feature is electrically isolated from each other feature, wherein each feature includes a respective connector element that is electrically coupled to at least one conductor within the lead body, wherein a portion of the insulative polymer covering layer is exposed above each feature to define a respective electrode for the corresponding feature. Also, the paddle possesses shape memory to cause the paddle to assume a substantially planar orientation when the shape memory is in a relaxed state. 
         [0008]    The foregoing has outlined rather broadly certain features and/or technical advantages in order that the detailed description that follows may be better understood. Additional features and/or advantages will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the appended claims. The novel features, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIGS. 1A and 1B  depict a conventional percutaneous lead and a conventional paddle lead, respectively. 
           [0010]      FIG. 2  depicts a self-folding flexible paddle according to one representative embodiment. 
           [0011]      FIG. 3  depicts a flowchart for fabricating the paddle shown in  FIG. 2  according to one representative embodiment. 
           [0012]      FIG. 4A  depicts a cross-sectional view of a paddle lead including the paddle shown in  FIG. 2  according to one representative embodiment.  FIGS. 4B-4D  depict the “sliding” folding progression of the paddle of the paddle lead shown in  FIG. 4A  according to one representative embodiment. 
           [0013]      FIGS. 5A-5H  depict placement of a paddle lead within the epidural space of a patient according to one representative embodiment. 
           [0014]      FIG. 6  depicts a foldable paddle lead coupled to an implantable pulse generator according to one representative embodiment. 
           [0015]      FIG. 7  depicts a foldable paddle lead that folds in a manner similar to a page being turned in a book. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 2  depicts a schematic representation of flexible paddle  200  according to one representative embodiment. Flexible paddle  200  is preferably fabricated using laminated layers of biocompatible polymer(s) and one or several thin layers of suitable conductive material. The conductive material may cover almost all of the surface area of the polymer backing. Specifically, the various structures (electrodes, guides, connector elements) are preferably defined by scribing or etching borders or edges between these structures. In such embodiments, the conductive material provides sufficient shape memory to cause the paddle structure to assume a planar shape in a relaxed state. In alternative embodiments, one or more layers of the polymer may be utilized to provide the desired mechanical characteristic. 
         [0017]    The width of paddle  200  is sufficient to provide suitable spacing between the two sets of electrodes  203  to enable stimulation of the pertinent nerve fibers across the physiological midline of the patient. The design of paddle  200  enables paddle  200  to be substantially maintained at a desired position within the patient&#39;s epidural space. Moreover, the design of paddle  200  ensures that electrodes  203 - 1  through  203 - 8  will remain in fixed relative positions, e.g., electrodes  203 - 1  through  203 - 4  cannot be offset longitudinally from electrodes  203 - 5  through  203 - 8 . 
         [0018]    Paddle  200  includes guide structures  202 - 1  and  202 - 2  which are proximate to distal end  201  of the paddle. Guide structures  202 - 1  and  202 - 2  cause paddle  200  to fold upon itself when the guide structures  200  contact the lumen of an insertion tool. In some embodiments, the guide structures  202 - 1  and  202 - 2  are implemented by scribing longitudinal elements in the conductive material. When paddle  200  contacts the inner surface of the insertion tool, the longitudinal elements distribute force into the body of paddle  200  according to the shape of the respective longitudinal elements. Additionally, guide structures  202 - 1  and  202 - 2  are preferably implemented to possess different amounts of rigidity (e.g., due to the shape of the respective guide structures  202 , the thickness of their respective longitudinal members, etc.). The difference in the amount of rigidity controls the manner in which paddle  200  folds. As will be discussed in greater detail below, one side of paddle  200  folds over the other side in a substantially lateral manner thereby minimizing the amount of open space within the epidural space required for paddle  200  to unfold. 
         [0019]    In the embodiment shown in  FIG. 2 , paddle  200  includes slit  204  in the middle of the lead paddle to provide a portion of the paddle with a very small modulus. Slit  204  may be defined by removing at least the conductive material. If the outer insulative material provides an undue amount of rigidity at this point, the insulative material may also be removed or replaced with a lower modulus material with improved elasticity. When distal end  201  is initially inserted within a suitable insertion tool, guide structures  202 - 1  and  202 - 2  experience force associated with the contact with the inner wall of the insertion tool. The force associated the contact and the presence of slit  204  cause segment  210  of paddle  200  to fold over segment  220 . In one embodiment, after paddle  200  has been folded, the entire width of paddle  200  is fit within the insertion tool. Thus, the paddle can be advanced through the tool into the patient&#39;s epidural space. Also, once the paddle is pushed through the insertion tool, the shape memory characteristics of the laminate structure cause paddle  200  to unfold thereby exposing electrodes  203 - 1  through  203 - 8  to the spinal tissue. Preferably, the shape memory provides sufficient force to displace fibrous tissue or scar tissue within the epidural space. However, the expansive force of the shape memory is also preferably limited to avoid damage to other tissue. In some embodiments, one or more laminate film layers and/or the conductive material cause paddle  200  to possess memory or a spring characteristic. 
         [0020]    In a similar manner, if paddle  200  needs to be removed from the patient, distal end  205  and guide structures  202 - 2  and  202 - 3  are provided. Specifically, proximal end  205  can be pulled by lead body  410  into the same or similar tool as used to insert paddle lead  200 . When guide structures  202 - 2  and  202 - 3  experience force due to contact of paddle  200  with the inner wall of the tool, segment  210  once again folds over segment  220  thereby enabling paddle  200  to be withdrawn from the patient&#39;s epidural space through the tool. Accordingly, it is not necessary to perform a partial laminectomy procedure for the insertion or removal of paddle  200 . 
         [0021]    Numerous variations upon the design shown in  FIG. 2  are possible. For example, paddle  200  need not include slit  204 . The center portion of paddle  200  could be rigid and both of segments  210  and  220  could fold when paddle  200  is inserted into an insertion tool. Alternatively, slit  204  could be moved from the middle of the paddle. Also, multiple slits  204  could be used to create multiple folding segments. Also, slit  204  need not necessarily remain as a void between the front and back sides of paddle  200 . Instead, the conductive material and/or the original insulative material may be removed and a relatively thin portion of highly elastic polymer or hydrogel material, as examples, may be provided at slit  204  to prevent tissue growth from occurring through paddle  200 . 
         [0022]    Also, paddle  200  could include more than two segments with all or some of the segments folding when inserted into a suitable tool. Although eight electrodes are shown in  FIG. 2 , any suitable number of electrodes could be employed. Additionally, any suitable pattern of electrodes could be formed. In some embodiments, multiple (three, four, five, etc.) columns of electrodes are employed to enable “field steering” which is known in the art to facilitate selective stimulation of nerve tissues. Also, although folding is the preferred mechanism to reduce the width of paddle  200  during insertion procedures, other deformations could be alternatively employed. For example, paddle  200  could be adapted to “curl” into a cylindrical structure upon entry into the insertion tool and “uncurl” upon exiting the tool. 
         [0023]      FIG. 3  depicts a flowchart for fabricating paddle  200  according to one representative embodiment. In step  301 , a rectangle or other suitable portion of conductive material is provided. Although the following discussion only refers to fabrication of a single paddle  200 , multiple paddles can be fabricated in parallel on suitably sized portion of conductive material according to the present invention. The conductive material can be medical grade stainless steel, platinum iridium, and/or the like. The thickness of the conductive material is selected to allow the conductive material to be relatively flexible while possessing a degree of memory or spring characteristic. In one embodiment, the thickness of the conductive material is selected to equal approximately 25.4 microns (1 mil). 
         [0024]    In step  302 , a coating of urethane (or a similar polymer) is spin coated on one side of the conductive material for the purpose of achieving a surface with greater adhesive qualities. In step  303 , a urethane film (or any other suitable biocompatible polymer) is applied to the same side as the spin coat and is laminated to the conductive material. The urethane film and coating provide an insulative layer to electrically isolate the conductive material. The urethane film preferably has a thickness of preferably 25.4 to 152.4 microns (one to six mils). 
         [0025]    In step  304 , the paddle form is created by scribing the paddle form in the conductive material using a suitable laser (e.g., a programmable YAG laser system). A separate strip or “feature” of conductive material is defined in a pattern definition for each electrode that extends from a respective connector element  206  (shown collectively as  206 - 1  through  206 - 8  in  FIG. 2 ) to the area where the corresponding electrode will be formed (as will be discussed below). In addition to defining the conductive paths, the laser scribing defines the guide structures that facilitate the self-folding functionality of paddle  200 . It shall be appreciated that the guide structures (as well as any structure providing spring-like properties) need not be conductive. 
         [0026]    The pattern definition is preferably provided to a programmable laser system. The programmable laser system then applies pulses of energy according to the defined pattern to ablate the conductive material between each strip of conductive material. The application of laser pulses is controlled to ablate the conductive material at the defined locations without cutting completely through the urethane film behind the ablated conductive material. The lamination between the urethane film and the conductive material holds the separate strips or features of conductive material at the defined locations. Also, upon completion of the application of laser pulses to paddle  200 , each strip of conductive material is electrically isolated from every other strip or feature due to the laser scribed separations between them and the insulative characteristic of the urethane film. In an alternative embodiment, photo-etching techniques could be employed to create the paddle form. For example, the paddle form could be created using a photoresist and chemical etching in lieu of laser scribing. In another alternative embodiment, micro-printing is employed to create the paddle form. 
         [0027]    In step  305 , a spin coat of urethane is applied over the conductive material on the side opposite to the urethane laminate layer. The coating of the urethane material electrically insulates the top of paddle  200 . In step  306 , electrodes  203  are defined by removing the urethane material of the applied coating at the respective locations thereby exposing the conductive material at those locations. The removal of the urethane material may occur using the programmable laser. Alternatively, a separate CO 2  laser could be utilized for exposure of the conductive material and/or masked plasma etching. In step  307 , connector elements  206  are exposed on one or both sides of paddle  200 . 
         [0028]    After the completion of paddle  200  according to the flowchart of  FIG. 3 , paddle  200  is ready to be mechanically integrated with and electrically coupled to a medical lead. To provide electrical connections between an implantable pulse generator and electrodes  203  of paddle  200 , the medical lead provides a plurality of conductors (e.g., wires) which are typically spirally wound around a mandrel. Each conductor is contained within an insulative material to ensure that the plurality of conductors are electrically isolated from each other. Also, the plurality of conductors are typically enclosed within a protective flexible body of biocompatible and biostable polymer. On a proximal end of the medical lead, a plurality of terminals are provided for coupling a pulse generator device to the various conductors. 
         [0029]    On the distal end of a medical lead, openings in the outer body and in the insulative coating of the conductors are made at suitable locations. Conductive material can be provided within the openings to provide an electrical path from the conductors to the surface of the lead. The exposed connector elements  206  of paddle  200  are preferably coupled to the lead conductors at these locations to create the electrical connection between the conductors of the lead and electrodes  203 . Alternatively, a wire connection could be employed between each conductor of the lead and a respective connector element  206 . Additional details regarding specific medical leads and lead fabrication methods are available in U.S. Pat. No. 6,216,045 entitled “Implantable lead and method of manufacture,” which is incorporated herein by reference. It shall be appreciated that paddle designs according to the present invention can be implemented with any type of suitable medical lead. 
         [0030]      FIG. 4A  depicts a cross-sectional view of paddle lead assembly  400  according to one representative embodiment. Medical lead  410  is shown at the bottom of the assembly. Block  420  is utilized to facilitate the lead assembly process and as shown in  FIG. 4A , is affixed to medical lead  410 . Block  420  can be implemented using an extrusion of bio-compatible polymer. Block  420  could also be implemented as an injection molded structure. Paddle  200  is coupled to block  420 . Block  420  may optionally include recess  430  that facilitates the folding of segment  210 . It shall be appreciated that other shapes and designs could be employed for block  420 . Also, in an alternative embodiment, paddle  200  could be directly attached to a stimulation lead. 
         [0031]    One advantage of assembly  400  is the minimization of volume displacement associated with the folding and unfolding of the paddle. Reference is made to  FIG. 7  for comparison, where foldable lead  700  folds in a manner similar to turning pages in a book. As shown in  FIG. 7 , this type of folding requires free space  750  to accomplish the folding and unfolding. Specifically, if foldable lead  700  were inserted into the epidural space of a patient, space  750  must be free of tissue to allow foldable lead  700  to unfold. However, assembly  400  is adapted to fold in a different manner that requires significantly less volume displacement. Recess  430  and the slit  204  enables portion  210  of paddle  200  to fold over portion  220  in a “sliding” or substantially lateral manner. Slit  204  provides a degree of flexibility to the paddle and recess  430  guides portion  210  during the folding process. As shown in the progression of  FIGS. 4B through 4D , the upward displacement of portion  210  of paddle  200  during folding (and, similarly, during unfolding) is relatively minimal. That is, a “bend” develops in portion  210  which is moved across the portion of the paddle  200  during the folding and unfolding process. Accordingly, assembly  400  can be unfolded within a much smaller volume than foldable lead  700 . 
         [0032]      FIGS. 5A-5H  depict various steps of a method for placement of a paddle lead within the epidural space of a patient according to one representative embodiment. As shown in  FIG. 5A , an epidural needle is inserted into the epidural space. The initial insertion of the epidural needle typically occurs an angle that is offset relative to the spinal column. Also, the location for insertion of the needle is typically two to five vertebrae below the spinal tissue associated with the pain to be treated by the electrical neuromodulation. Using fluoroscopic guidance, a guide wire is inserted with the stylet slightly withdrawn as shown in  FIG. 5B . Once the tip of the guide wire is fully within the epidural space and slightly beyond the distal tip of the needle, the stylet is fully re-inserted and the guide wire is advanced to the desired target location as shown in  FIG. 5C . 
         [0033]    As shown in  FIG. 5D , the needle is removed using the “hold-and-push” technique leaving the guide wire in the epidural space. The insertion tool  500  is inserted over the proximal end of the guide wire and advanced into the epidural space under fluoroscopy to appropriate position ( FIG. 5E ) and the guide wire is removed. For the purpose of the present application, an insertion tool refers to any catheter-like structure, having a lumen or an open channel, that can be inserted between the vertebrae into the epidural space without a partial laminectomy. The insertion tool may or may not comprise a sharp distal end. The insertion tool preferably expands the tissue surrounding the guide wire thereby enabling the insertion of the paddle lead. In practice, the insertion tool is preferably a flexible hollow plastic tube. The flexibility of the tube accommodates an offset insertion angle into the vertebrae used for the initial insertion of the epidural needle. An example of an introduction tool can be found in U.S. Patent Publication No. 20050288758A1, which is incorporated herein by reference. If appropriate, a segment of the epidural space could be opened to accommodate paddle  200  (step not shown). For example, a cutting tool (e.g., having dual blades or scissor-like elements) could be advanced through insertion tool  500  to open tissue to allow paddle  200  to be received and unfolded. 
         [0034]    The distal end of paddle  200  of lead assembly  400  is inserted within insertion tool  500  as shown in  FIG. 5F . Preferably, a guide wire is inserted within the lumen of the lead coupled to paddle  200  to facilitate the advancement of the lead and paddle. The contact of paddle  200  with the interior of insertion tool  500  causes paddle  200  to fold upon itself thereby fitting paddle  200  within the insertion tool as shown in  FIG. 5G . Paddle  200  is advanced through insertion tool  500  by advancing lead body  410  as shown in  FIG. 5H . When paddle  200  exits insertion tool  500 , paddle  200  resumes its extended state to expose electrodes  203  to the target spinal tissue for stimulation. In an alternative embodiment, the lead could be mated to the insertion tool using a suitable mating component and the lead could be advanced concurrently with the placement of the insertion tool. 
         [0035]      FIG. 6  depicts foldable paddle lead  400  coupled to implantable pulse generator (IPG)  600  according to one representative embodiment. An example of a commercially available IPG is the Eon® Rechargeable IPG available from Advanced Neuromodulation Systems, Inc. As shown in  FIG. 6 , paddle lead  400  is coupled to one of the headers  610  of generator  600 . Each header  610  electrically couples to a respective lead  410  or an extension lead. Also, each header  610  electrically couples to internal components contained within the sealed portion  620  of IPG  600 . The sealed portion  620  contains the pulse generating circuitry, communication circuitry, control circuitry, and battery (not shown) within an enclosure to protect the components after implantation within a patient. The control circuitry controls the pulse generating circuitry to apply varying pulses to the patient via electrodes  203  of paddle  200  according to multiple parameters (e.g., amplitude, pulse width, frequency, etc.). The parameters are set by an external programming device (not shown) via wireless communication with IPG  600 . 
         [0036]    Although some representative embodiments have been discussed in terms of neurostimulation applications, alternative representative embodiments could be employed for other medical applications. For example, in one alternative embodiment, a paddle structure could be adapted for any suitable type of cardiac stimulation such as defibrillation and pacing. The paddle structure could be inserted through the vascular system of the patient using a suitable catheter and introduced within a suitable cardiac region. The paddle structure then could be adapted to unfold upon exiting the catheter to contact the cardiac tissue to be stimulated. In other alternative embodiments, the paddle could be utilized for cardiac mapping and/or tissue ablation. 
         [0037]    Some representative embodiments may provide a number of advantages. Some representative embodiments provide a paddle that can be inserted into and removed from the epidural space of a patient without requiring a partial laminectomy. Furthermore, some representative embodiments provide a method of fabricating a paddle design that is highly repeatable and efficient. The fabrication method further does not necessarily require the use of any overly caustic chemicals. 
         [0038]    Although representative embodiments and advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from this disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized without departing from the scope of the appended claims. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.