Patent Publication Number: US-2010114271-A1

Title: Shielded conductor filar - stimulation leads

Description:
FIELD 
     The present disclosure relates generally to medical devices and, more specifically, to a shielded conductor filar for a stimulation lead. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Various elongate, conductive leads have been proposed for transmitting a signal for a medical device. For example, conductive leads have been proposed for functioning as a heart pacemaker lead, as a defibrillation lead, as a neural lead, and the like. For example, in the case of the pacemaker lead, the lead transmits a pacing signal from a pacemaker device to corresponding heart tissue to maintain proper heart function. 
     Conventional leads, typically include a single conductive wire (i.e., filar) or coil with a protective coating thereon. These conventional leads typically function within an independent circuit. As such, the usefulness of these leads may be somewhat limited. Furthermore, these leads may be prone to fracture, which can prevent proper signal transmission. Additionally, an electromagnetic field can leak into the lead and add noise to the signal. For example, a patient with an implanted pacemaker lead may not be able to undergo an MRI imaging procedure because the resultant electromagnetic field may detrimentally effect operation of the signal transmission within the lead. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A lead for a medical device is disclosed. The lead includes an elongate filar core member having an axis, which is operable for transmitting a lead signal. Furthermore, the lead includes an insulating layer disposed directly on the elongate filar core member and that extends along the axis. The lead also includes an electrically conductive layer disposed directly on the insulating layer and that extends along the axis. 
     In addition, a method of manufacturing a lead for a medical device is disclosed. The method includes coating an elongate filar core member with an insulating layer, wherein the elongate filar core member is operable for transmitting a lead signal. The method also includes depositing an electrically conductive layer directly on the insulating layer. 
     Moreover, a method of operating a medical device is disclosed. The method includes operatively connecting a medical lead in a predetermined anatomical location. The medical lead includes an elongate filar core member having an axis, an insulating layer disposed directly on the elongate filar core member and extending along the axis, and an electrically conductive layer disposed directly on the insulating layer and extending along the axis. Furthermore, the method includes transmitting a lead signal via the elongate filar core member. 
     Additionally, a lead for a medical device is disclosed that includes an elongate filar core member. The elongate filar core member is operable for transmitting a lead signal. The elongate filar core member has an axis, a cross section of the elongate filar core member substantially perpendicular to the axis is substantially solid, and the elongate filar core member is made of silver, MP35N, MP35N-clad silver, platinum, platinum clad tantalum, silica, or a combination thereof. Also, the lead includes an insulating layer disposed directly on the elongate filar core member and extends along the axis. The insulating layer is made of soluble imide (SI) polyimide or Ethylene Tetrafluoroethylene (ETFE) insulating polymer. The insulating layer substantially surrounds an outer surface of the elongate filar core member. The lead also includes an electrically conductive layer disposed directly on the insulating layer and extends along the axis. The electrically conductive layer is made of gold, platinum, carbon, carbon nanotubes, or a combination thereof. The electrically conductive layer is operable for transmitting the lead signal, transmitting a secondary signal that is different from the lead signal, and/or providing shielding for transmission of the lead signal. Also, the electrically conductive layer substantially surrounds an outer surface of the insulating layer. Still further, the lead includes a protective layer that substantially surrounds an outer surface of the electrically conductive layer. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic view of a medical device with a lead according to the teachings of the present disclosure; 
         FIG. 2  is a perspective view of the lead of  FIG. 1  shown partially exposed; 
         FIG. 3  is a sectional view of the lead of  FIG. 1 ; 
         FIG. 4  is a sectional view of a lead according to another embodiment; 
         FIG. 5  is a sectional view of a lead according to still another embodiment; 
         FIG. 6  is a longitudinal sectional view of the lead of  FIG. 1 ; 
         FIG. 7  is a schematic electrical diagram that includes the lead of  FIG. 1  according to an exemplary embodiment; and 
         FIG. 8  is a schematic electrical diagram that includes the lead of  FIG. 1  according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring initially to  FIG. 1 , an exemplary embodiment of a medical device  10  is schematically illustrated. In this embodiment, the medical device is a pacemaker device  12  or other cardiac rhythm management device. The pacemaker device  12  can be of a known type. 
     A lead  14  is operatively connected to the medical device  10 . The lead  14  is generally elongate and extends between the pacemaker device  12  and biological tissue  15 , such as tissue of a heart  16 , at a predetermined location. Thus, the lead  14  is operatively coupled to the pacemaker device  12  and the tissue  15  to transmit a lead signal (e.g., a stimulation signal or sensing signal to/from the heart). 
     It will be appreciated that the medical device  10  and the signals transmitted by the lead  14  could be of any suitable type without departing from the scope of the present disclosure. For instance, the lead  14  could stimulate and/or sense neural signals to/from brain tissue, the lead  14  could transmit signals for heart defibrillation, or any other type. Furthermore, the lead  14  could be an implantable lead for longer term use, or the lead  14  could be temporarily coupled to tissue  15  without departing from the scope of the present disclosure. 
       FIGS. 2 and 3  illustrate an exemplary embodiment of the lead  14  of  FIG. 1  in greater detail. It will be appreciated that  FIG. 2  shows the lead  14  with certain outer layers removed for clarity; however, these layers could extend over the entire axial length of the lead  14  without departing from the scope of the present disclosure. 
     As shown, the lead  14  includes an elongate filar (i.e., thread-like) core member  18 . The filar core member  18  defines an axis X. In some embodiments, the filar core member  18  is flexible. Also, in some embodiments, the filar core member  18  has a cross section that is substantially solid. For instance, the filar core member  18  can have a diameter of approximately 0.004 inches. Furthermore, in some embodiments, the filar core member  18  can include a lumen that extends along the axis X. 
     The filar core member  18  can be made out of any suitable material. For instance, in some embodiments, the filar core member  18  is made out of an electrically conductive material. Also, in some embodiments, the filar core member  18  is made out of an optical fiber for transmitting an optic signal (i.e., light). Accordingly, the filar core member  18  can be made out of silver, MP35N stainless steel, MP35N-clad silver, platinum, platinum-clad tantalum, silica, or a combination of two or more of these materials. However, it will be appreciated that the filar core member  18  could be made out of any suitable material without departing from the scope of the present disclosure. Furthermore, in cases in which the filar core member  18  is made out of an optical fiber, the filar core member  18  can be coated with a reflective material to enhance the transmission of optical signals (i.e., light) therethrough. 
     In addition, in the embodiments represented in  FIGS. 2 and 3 , the lead  14  includes an insulating layer  20 . In some embodiments, the insulating layer  20  is generally hollow and cylindrical and is disposed directly on an outer surface  22  of the core member  18  to cover and surround the outer surface  22 . The insulating layer  20  can extend over the majority of the axial length of the filar core member  18 . Also, in some embodiments, the insulating layer  20  can leave a portion of the outer surface  22  exposed for operative and electrical connection of the filar core member  18  to the medical device  10  and/or the tissue  15 . 
     The insulating layer  20  can have any suitable thickness. For example, in some embodiments, the insulating layer  20  has a substantially constant wall thickness of approximately 0.0002 inches. 
     In some embodiments, the insulating layer  20  is made out of an electrically insulating material, such as an insulating polymeric material. For example, in some embodiments, the insulating layer  20  can be formed of polyimide, such as a Soluble Imide (SI) polyimide material as described in U.S. Pat. No. 5,639,850, issued to Bryant on Jun. 17, 1997, and incorporated herein by reference in its entirety. In other embodiments, the insulating layer  20  is made out of Ethylene Tetrafluoroethylene (ETFE) insulating polymer. As such, the insulating layer  20  can effectively insulate and protect the filar core member  18 . Also, manufacturing of the lead  14  can be facilitated due to the insulating layer  20  as will be discussed. 
     Moreover, the lead  14  can also include an electrically conductive layer  24 . In some embodiments, the conductive layer  24  is generally hollow and cylindrical and is disposed directly on an outer surface  26  of the insulating layer  20  to cover and surround the outer surface  26 . As such, the conductive layer  24  is supported by the filar core member  18 , and the insulating layer  20  is disposed between the filar core member  18  and the conductive layer  24 . The conductive layer  24  can extend over the majority of the axial length of the insulating layer  20 . Also, in some embodiments, the insulating layer  20  can leave a portion of the outer surface  22  of the filar core member  18  exposed for operative and electrical connection of the filar core member  18  to the medical device  10  and/or the tissue  15 . 
     The conductive layer  24  can have any suitable thickness. For example, in some embodiments, the conductive layer  24  has a substantially constant wall thickness of approximately 0.0002 inches. 
     The conductive layer  24  can be made out of any suitable material, such as an electrically conductive material. For example, in some embodiments, the conductive layer  24  can be formed of gold, platinum, carbon, carbon nanotubes, or a combination of two or more of these materials. 
     As will be discussed in greater detail below, the conductive layer  24  can be operable for transmitting the same signal (i.e., the lead signal) as the filar core member  18 , can transmit a separate signal (i.e., a secondary signal) from the filar core member  18 , or can provide shielding of the core member  18  from signal leakage for improved transmission of the lead signal by the core member  18 . Furthermore, manufacturing of the lead  14  can be facilitated due to the conductive layer  24  as will be discussed. 
     Additionally, in the embodiments represented in  FIGS. 2 and 3 , the lead  14  includes a protective layer  28 . In some embodiments, the protective layer  28  is generally cylindrical and hollow and is disposed directly on an outer surface  30  of the conductive layer  24  to cover and surround the outer surface  30 . The protective layer  28  can extend over the majority of the axial length of the lead  14 . Also, in some embodiments, the protective layer  28  can leave a portion of the outer surface  22  of the filar core member  18  and/or the outer surface  30  of the conductive layer  24  exposed for operative and electrical connection to the medical device  10  and/or the tissue  15 . 
     The protective layer  28  can have any suitable thickness. For example, in some embodiments, the protective layer  28  has a substantially constant wall thickness of approximately 0.0002 inches. 
     The protective layer  28  can be made out of any suitable material, such as an electrically insulative material. For example, in some embodiments, the protective layer  28  can be made out of Si polyimide, similar to the insulating layer  20 . In other embodiments, the protective layer  28  is made out of ETFE insulating polymer similar to the insulating layer  20 . Accordingly, the protective layer  28  can protect the other components of the lead  14  from abrasion or other damage. Furthermore, the protective layer  28  can facilitate manufacturing of the lead  14  as will be discussed. 
     To manufacture the lead  14 , in some embodiments, the insulating layer  20  is first coated on the filar core member  18 . For example, in some embodiments, the material of insulating layer  20  is combined with a solvent, such as Naptha or petroleum ether, into a liquid, and the filar core member  18  is exposed to the solvent-based combination. Then, heat (e.g., 650° to 750° F.) is applied to drive out the solvent, thereby curing the insulating layer  20 . In some embodiments, this process is repeated multiple times in order to build up the insulating layer  20  in layers until insulating layer  20  has the desired wall thickness. For instance, the core member  18  can exposed to the solvent-based combination and cured between fifteen times and twenty times, and in some embodiments, a total of eighteen times. However, it will be appreciated that the insulating layer  20  can be formed in any suitable fashion. 
     After the insulating layer  20  has cured, material of the conductive layer  24  can be deposited thereon. In some embodiments, the conductive layer  24  is formed by a known sputtering process, in which the insulating layer  20  is bombarded by atomized particles of the material of the conductive layer  24 . In other embodiments, such as where the conductive layer  24  is made out of carbon nanotubes, the carbon nanotubes are mixed with polyimide in a liquid state, and the lead  14  is dipped into the liquid mixture to deposit the mixture on the insulating layer  20 . However, it will be appreciated that the conductive layer  24  can be formed in any suitable fashion. 
     Next, the protective layer  28  is formed on the conductive layer  24 . In some embodiments, the protective layer  28  is formed in a manner that is substantially similar to that of the insulating layer  20 . 
     The lead  14  can be operatively connected to the medical device  10  and/or the tissue  15  using any suitable fastener. Also, the core member  18  and the conductive layer  24  of the lead  14  can be electrically connected to the medical device  10  and/or tissue  15  in order to create one or more circuits therewith. For instance, the core member  18  and/or the conductive layer  24  can include specific electrodes (not shown) (e.g., exposed areas) for operatively connecting with the medical device  10  and/or the tissue  15 . Also, in some embodiments represented in  FIG. 6 , an aperture  25  can be formed in the insulating layer  20  such that the core member  18  and conductive layers  24  abut so as to electrically connect together. 
     Thus, as represented in  FIG. 7 , the core member  18  can be incorporated into a first circuit  27  that transmits a lead signal, and the conductive layer  24  can be incorporated into a separate, independent second circuit  29  for transmitting a secondary signal. Also, as represented in  FIG. 8 , the core member  18  and conductive layers  24  can be connected in a circuit  31  with the medical device  10  and the tissue  15  such that the core member  18  operates as a cathode within the circuit, and the conductive layers  24  operates as an anode within the circuit, or vice versa. Furthermore, the conductive layer  24  can be electrically connected to the core member  18  and operate to redundantly transmit the same signal as the core member  18 . Similarly, the conductive layer  24  can operate as a shunt to the core member  18  in the event that the core member  18  fractures, builds up excessive resistance, and the like. 
     Moreover, in some embodiments, the conductive layer  24  can shield the core member  18  from signal leakage. For instance, in some embodiments, the conductive layer  24  is electrically connected to ground, and the core member  18  transmits the lead signal. Because the conductive layer  24  is substantially continuous (i.e., does not include any substantial gaps), because the conductive layer  24  covers substantially the entire axial length of the core member  18 , and because the conductive layer  24  is spaced from the core member  18  by the thickness of the insulating layer  20 , the conductive layer  24  can substantially reduce leakage of the signal into and/or out of the core member  18 . Accordingly, the signal is less likely to be detrimentally effected by signal noise and/or the signal is more likely to transmit at a sufficient strength. In some embodiments, the conductive layer  24  shields the core member  18  against electromagnetic fields due to MRI imaging procedures. Also, in some embodiments, the lead  14  can be operatively connected to a sensor (not shown) for transmitting signals to and/or from the tissue  15 , and the conductive layer  24  shields the core member  18  from signal leakage for more accurate operation of the sensor. 
     Thus, the lead  14  can be used in a wide variety of ways and for a wide variety of functions. Because of the conductive layer  24 , the lead  14  can be more versatile for transmitting a wider variety of signals. Also, the conductive layer  24  can enable the lead  14  to transmit signals even if the core member  18  fails. Moreover, the conductive layer  24  can provide shielding for improving signal transmission. Additionally, the lead  14  can be manufactured relatively quickly and in a relatively inexpensive manner as compared to some conventional leads. 
     Referring now to  FIG. 4 , another embodiment of the lead  114  is illustrated. Components that are similar to those of  FIGS. 1-3  are identified with corresponding reference numerals increased by  100 . 
     As shown, the lead  114  includes a core member  118 , a first insulating layer  120   a,  and a first conductive layer  124   a  similar to the embodiment of  FIG. 3 . However, the lead  114  additionally includes a second insulating layer  120   b  disposed over and covering the first conductive layer  124   a  and a second conductive layer  124   b  disposed over and covering the second conductive layer  124   b.  Also, the lead  114  includes a protective layer  128  disposed over and substantially covering the second conductive layer  124   b.    
     It will be appreciated that the core member  118  and the first and second conductive layers  124   a,    124   b  can each be operatively connected to the medical device  10  and/or the tissue  15  for signal transmission as discussed above. Also, it will be appreciated that the first and/or second conductive layers  124   a,    124   b  can provide shielding for the signal transmission within the core member  118 . Moreover, the lead  114  can include any number of conductive layers  124   a,    124   b  for increasing the versatility of the lead  114  and/or for increasing the shielding capability of the lead  114 . 
     Referring now to  FIG. 5 , another embodiment of the lead  214  is illustrated. Components that are similar to those of  FIGS. 1-3  are identified with corresponding reference numerals increased by  200 . 
     As shown, the lead  214  includes a core member  218  and an insulating layer  220  similar to the embodiment of  FIGS. 1-3 . The lead  214  also includes a first conductive layer  224   a  and a second conductive layer  224   b.  The first conductive layer  224   a  is a layer of conductive material that extends along the axis of the lead  214  and, as shown in the cross section of  FIG. 5 , the first conductive layer  224   a  covers only a portion of the core member  218 . Similarly, the second conductive layer  224   b  is a layer of conductive material that extends along the axis of the lead  214  and, in cross section, the second conductive layer  224   b  covers only a portion of the core member  218 . In some embodiments, the first and second conductive layers  224   a,    224   b  are disposed in spaced relationship on opposite sides of the core member  218  so as to be substantially symmetrically disposed about the axis X. Thus, gaps  235  are defined between the first and second conductive layers  224   a,    224   b  as shown. In some embodiments, the first conductive layer  224   a  covers approximately one hundred and seventy degrees about the circumference of the core member  218  and the second conductive layer  224   b  extends approximately one hundred and seventy degrees about the circumference of the core member  218 , leaving gaps  235  totaling approximately twenty degrees. 
     Furthermore, the lead  214  can include a protective layer  228 . The protective layer  228  encapsulates and surrounds the other components of the lead  214  and fills the gaps  235  between the first and second conductive layers  224   a,    224   b.    
     It will be appreciated that the lead  214  could include any number of conductive layers  224   a,    224   b  without departing from the scope of the present disclosure. It will also be appreciated that the core member  218  and the conductive layers  224   a,    224   b  could be operatively coupled to the medical device  10  and tissue  15  for signal transmission as discussed above. 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper,” “lower,” “above,” “below,” “top,” “upward,” and “downward” refer to directions in the drawings to which reference is made. Terms such as “front,” “back,” “rear,” and “side,” describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first,” “second,” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
     When introducing elements or features and the exemplary embodiments, the articles “a,” “an,” “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.