Abstract:
In a method for manufacturing active fixation helices for the stimulation and/or sensing of organs, an elongated helix precursor body is produced that has one or more electrical conductors surrounded by an insulating material. This helix precursor body is then shaped into a helix, material removed in predetermined places in order to expose the areas of the conductors which will be used as electrodes in the final product. The body is coated with an electrically conducting biocompatible coating which is subsequently partly removed in continuous loops from around the electrodes in order to electrically insulate them from each other and to ensure that the electrically active areas of the electrodes are of the correct dimensions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to methods for manufacturing active fixation electrodes for electrical medical leads, in particularly helix electrodes intended to be screwed into body tissue. 
         [0003]    2. Description of the Prior Art 
         [0004]    Implantable medical electrical stimulation and/or sensing leads (also called “leads” or “electrode leads”) are well known in the fields of tissue and organ stimulation and monitoring. Such fields include cardiac pacing. Leads may be attached to an organ by an active fixation means which is designed to penetrate the surface of the organ that is to be stimulated or sensed. A common active fixation means employs a helix which has a sharpened tip and is mounted at the end of the electrode lead. The fixation helix typically has an outside helix diameter which is slightly less than that of the lead body and extends in axial alignment with the lead body. The sharpened tip of the helix can be screwed into the organ by being rotated. Typically the helix is electrically connected to one or more conductors in the electrode lead. These conductors can be electrically connected to one or more exposed surfaces of the helix which then can be used as stimulating and/or sensing electrodes. A fixation helix therefore may contain one or a plurality of conductors. Typically the outer surface of the helix, including the exposed surfaces used as electrodes, is partly covered with a biocompatible coating to minimize interference with the tissue to which it is to be attached. Typically the biocompatible coating is electrically conducting and it is arranged in a predetermined pattern with continuous gaps on the insulating material und the exposed electrode surfaces in order to prevent the different electrodes from being in electrical contact with each other. The sizes of the surface areas of the exposed electrodes are set at levels which are compatible with the organ they are attached to United States Patent Application Publication 2006/0122682 describes an active fixation helix for an electrical medical leads and methods of making such active fixation helixes. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates methods for manufacturing active helices suitable for use as active fixation electrodes for electrical medical leads, in particularly helix electrodes intended to be screwed into body tissue. Such helices are made of thin electrical conductors, encased in an insulating material—usually treated to be biocompatible, and twisted into the shape of a helix. The portions of the conductors are exposed to form electrically active surfaces which can be used for stimulating or sensing. 
         [0006]    A first embodiment of a method in accordance with the present invention for making a helix includes a first step of producing an elongated helix precursor body having one or more electrical conductors surrounded by an insulating material. This helix precursor body is then shaped into a helix, material removed in predetermined places in order to expose the areas of the conductors which will be used as electrodes in the final product and coated with an electrically conducting biocompatible coating which is subsequently partly removed in continuous loops from around the electrodes in order to electrically insulate them from each other and to ensure that the electrically active areas of the electrodes are of the correct dimensions. 
         [0007]    An alternative embodiment of a method in accordance with the present invention for making a helix comprises a first step of producing an elongated helix precursor body comprising one of more electrical conductors surrounded by an insulating material. Material is then removed at predetermined places from the helix precursor body in order to expose the areas of the conductors which will be used as electrodes in the final product. The body is coated with an electrically conducting biocompatible coating which is then removed in continuous loops from around the electrodes in order to electrically insulate them from each other and to ensure that the electrically active areas of the electrodes are of the correct dimensions. The body is then formed in to the shape of a helix. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
           [0009]      FIG. 1  shows schematically an example of an electrical medical lead provided with active fixation. 
           [0010]      FIG. 2  shows schematically an embodiment of electrically active helix having a single conductor. 
           [0011]      FIG. 3  shows schematically an embodiment of a multi-conductor electrically active helix. 
           [0012]      FIGS. 4   a )- 4   e ) show schematically steps in a first method in accordance with the present invention for making an active fixation means. 
           [0013]      FIGS. 5   a )- 5   f ) show schematically stages in the manufacture of a multi-conductor helix precursor body. 
           [0014]      FIGS. 6   a )- 6   e ) show schematically steps in a second method in accordance with the present invention for making an active fixation. 
           [0015]      FIGS. 7   a )- 7   c ) show schematically cross-sections through examples of possible helix precursor bodies. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  shows schematically an example of an electrical medical lead  1  provided with an active fixation means  3 . The active fixation means is formed by an electrically active helix  5  having a proximal end  7  in electrical connection with a conductor (not shown) inside said electrical medical lead  1  and a sharpened distal end  9 . A number of helix revolutions  11  are arranged between said proximal end  7  and said distal end  9 . The helix  5  is attached to the lead  1  by a sleeve  12  which surrounds the end of the lead and one or more revolutions  11  of the helix  5 . 
         [0017]      FIG. 2  shows schematically an embodiment of electrically active helix having a single conductor. The helix body  13  surrounds a longitudinally extending lumen  15  and is comprised of an electrically conducting core  17  which is at least partially surrounded by an insulating sheath  21  such that a continuous portion of the surface  23  said electrically conducting core  17  is exposed. The exposed surface  23  is coated with an electrically conducting biocompatible coating  27  and preferably the insulating sheath is also covered with a biocompatible coating. In order to electrically insulate the exposed surface  23  of the core  17  from the rest of the surface of the helix body, a continuous loop of the surface of the helix surrounding said exposed surface  17  must be free of electrically conducting material. 
         [0018]      FIG. 3  shows schematically an embodiment of a multi-conductor electrically active helix. The helix body  33  surrounds a longitudinally extending lumen  35  and is comprised of electrically conducting cores  37 ,  39  each of which is at least partially surrounded by an insulating sheath  41  such that a continuous portion of the surface  43 , respectively  45 , of each the electrically conducting cores  37 ,  39  is exposed. Each exposed surface  43 ,  45  of the cores and the insulating sheath  41  is coated with an electrically conducting biocompatible coating  47  but the exposed surfaces  43 ,  45  are electrically insulated from each other and the sheath  41  by being surrounded by a continuous loop of insulating material. This is described in more detail below. 
         [0019]    A first embodiment of a method for producing an active fixation means in the form of a multi-conductor electrically active helix will now be described in connection with  FIGS. 4   a )- 4   e ). In a first step an elongated cylindrical helix body precursor  51  is formed. This helix body precursor  51  has a proximal end  53  and a distal end  55  and comprises first and second elongated electrically conducting cores  37 , and  39 , surrounded by a sheath  41  of insulating material  42 . The cores  37 ,  39  can be made of any suitable conducting material, for example a metal such as platinum. 
         [0020]    An example of such a helix body precursor  51  is shown in  FIG. 4   a ). In this example the first core  37  is arranged along the central longitudinal axis of the helix body precursor  51  and the second core  39  is arranged parallel to the first core  37  and between the first core  37  and the outer surface  57  of the helix body precursor. This can be achieved for example by co-extruding the cores  37 ,  39  inside an insulating sheath material. 
         [0021]    In the next step of the method a predetermined length of second core  39  and the insulating material surrounding it are removed from distal end  55 , leaving a shoulder  58  in the helix body precursor  51 , said shoulder extending over a portion of the first core  37  which is still surrounded by insulating material  42  as shown in  FIG. 4   b ). 
         [0022]    In a third step, as shown in  FIG. 4   c ) shoulders  59 , resp.  61 , are formed in the insulating sheath  41  by selectively removing insulating material from the distal end  55  of the helix body precursor  51  in order to expose resp. a surface  43  of the first electrically conducting core  37 , and a surface  45  of the second electrically conducting core  39 . In this example shoulder  59  is a continuation of shoulder  58  in a direction towards the first electrically conducting core  37  but it is possible to place shoulder  59  further away from the distal end  55  than shoulder  58 , thereby removing or undercutting shoulder  58 . In this embodiment of the present invention part of exposed first core  37  nearest the distal end  55  of the helix body precursor  51  is leveled so that the exposed surface  43  is coplanar with the longitudinally extending surface  62  of shoulder  59 . Similarly part of exposed second core  39  nearest the distal end  55  of the helix body precursor  51  is removed so that its exposed surface  45  is coplanar with the longitudinally extending surface  64  of shoulder  61 . As alternatives one or more of the exposed surfaces of the cores can be left standing proud of the surrounding longitudinally extending surface e.g. with a convex exposed surface, or, conversely, one or more exposed cores surfaces can be sunk into the surrounding longitudinally extending surface, e.g. with a concave exposed surface. While this step has been described as following the preceding step it is of course possible to perform these two steps substantially simultaneously. 
         [0023]    Subsequently, as shown in  FIG. 4   d ) a continuous electrically conducting biocompatible coating  47  can be applied to the exposed surface of said helix body precursor so that it covers the insulating sheath, shoulders  59 ,  61  and the exposed surfaces  43 ,  45  of the electrically conducting cores  37 ,  39 . 
         [0024]    Finally, as shown in  FIGS. 4   e ) and  4   f ) a continuous loop  71 , resp.  73  of said electrically conducting biocompatible coating  47  on the insulating sheath surrounding each of the exposed surfaces  43 ,  45  of the electrically conducting cores  37 ,  39  is removed. The result of this is that each electrically conducting coating on the exposed surface  43 ,  45  of each core  37 ,  39  is not in electrical contact with the remaining electrically conducting coating  47  on the insulating sheath. This limits the electrically-effective surface area of each exposed core surface which will subsequently be used as sensing or stimulating electrodes. The biocompatible coating can be removed by, for example, cutting, polishing, grinding or similar methods. The elongated helix body precursor can now be formed into a helical shape comprising an internal lumen by winding around a cylindrical former or by any other known way in order to form a helix body comprising a number of revolutions separating a distal end and a proximal end. Preferably the forming of the helical shape is performed so that the exposed surface of each core is orientated in a predetermined direction, for example toward the exterior of the helix. As in this embodiment of the present invention the forming of the helix revolutions takes place after the electrically conducting biocompatible coating has been applied to the insulating sheath, it is preferable that the bonding of the biocompatible coating to the underlying sheath and exposed surface of the electrically conducting core is sufficiently strong that the biocompatible coating is not disturbed or moved during forming of these revolutions. Examples of coatings which exhibit such strong bonding are titanium oxide, platinum black, and metal oxides formed from the conducting wire or lead. 
         [0025]      FIGS. 5   a )- 5   f ) show stages in the manufacture of a multi-conductor electrically active helix in which each conductor has a number of active electrode in accordance with the above first embodiment of a method for producing active fixation. In these figures the reference numerals used in  FIGS. 4   a )- 4   f ) have been repeated when they correspond to similar features. As can be seen from  FIGS. 5   a )- 5   f ) the stages in this method are substantially the same as those described above except that in the third step, as shown in  FIG. 5   c ), a number of cuts are made in the insulating sheath and insulating material removed from between alternating pairs of cuts in order to form slits  42 ′,  42 ″,  42 ″ and  44 ′,  44 ″,  44 ′″ which expose a number of longitudinally extending surfaces  43 ′,  43 ″,  43 ″ of the first electrically conducting core  37 , and a number of longitudinally extending surfaces  45 ′,  45 ″,  45 ′″ of the second electrically conducting core  39 . In this embodiment of the present invention exposed portions of first core  37  nearest the distal end  55  of the helix body precursor  51  are not levelled, i.e. the exposed surfaces  43 ′,  43 ″,  43 ′″ project above the longitudinally extending surfaces  62  of the slits  42 ′,  42 ″,  42 ′″ formed in shoulder  59 . Similarly the exposed portions of second core  39  nearest the distal end  55  of the helix body precursor  51  are not levelled, i.e. the surfaces of its exposed surfaces  45 ′,  45 ″,  45 ′″ project above the longitudinally extending surfaces  64  of the slits  44 ′,  44 ″,  44 ′″ formed in shoulder  61 . As alternatives one or more of the exposed surfaces  43 ′- 43 ′″,  45 ′- 45 ′″ of the cores can made level with the surrounding longitudinally extending slit&#39;s surface or, one or more exposed cores surfaces can be sunk into the surrounding longitudinally extending slit&#39;s surface, e.g. with a concave exposed surface. While this step has been described as following the preceding step it is of course possible to perform these two steps substantially simultaneously. 
         [0026]    Subsequently, as shown in  FIG. 5   d ) a continuous electrically conducting biocompatible coating  47  can be applied to the exposed surface of said helix body precursor so that it covers the insulating sheath, shoulders  59 ,  61  and the exposed surfaces  43 ′- 43 ′″,  45 ′- 45 ′″ of the electrically conducting cores  37 ,  39 . 
         [0027]    Finally, as shown in  FIGS. 5   e ) and  5   f ) a continuous loop  71 ′- 71 ′″, resp.  73 ′- 73 ′″ of said electrically conducting biocompatible coating  47  on the insulating sheath surrounding each of the exposed surfaces  43 ′- 43 ′″,  45 ′- 45 ′″ of the electrically conducting cores  37 ,  39  is removed. The result of this is that each electrically conducting coating on the exposed surfaces of each core  37 ,  39  is not in electrical contact with the remaining electrically conducting coating  47  on the insulating sheath. This limits the electrically-effective surface area of each exposed core surface which will subsequently be used as sensing or stimulating electrodes. The biocompatible coating can be removed by, for example, cutting, polishing, grinding or similar methods. The elongated helix body precursor can now be formed into a helical shape having an internal lumen by winding around a cylindrical former or by any other known way in order to form a helix body comprising a number of revolutions separating a distal end and a proximal end. Preferably the forming of the helical shape is performed so that the exposed surface of each core is orientated in a predetermined direction, for example towards the exterior of the helix. 
         [0028]    In a second embodiment of a method for producing an active fixation in the form of an electrically active helix, the helix body precursor is formed into a helical shape before the surfaces of the conducting core or cores are exposed. Thus this method is similar to the first embodiment of the invention except that the forming of the helix is performed before the application of coatings. In more detail an example of a second embodiment of the present invention includes the steps of: 
         [0029]    a) forming a helix body having a proximal end and a distal end connected by a number of helical revolutions, said body comprising at least one electrically conducting core partially surrounded by an insulating sheath whereby a continuous portion of the surface of each electrically conducting core extending from the distal end toward the proximal end and facing in a predetermined direction is exposed; 
         [0030]    b) applying a continuous electrically conducting, biocompatible coating to surface of the insulating sheath and each exposed surface of each electrically conducting core; 
         [0031]    c) removing a portion of the electrically conducting biocompatible coating on the insulating sheath surrounding each continuous portion of the surface of each electrically conducting core such that the electrically conducting coating on the exposed surface of each electrically conducting core is not in electrical contact with the remaining electrically conducting coating on the insulating sheath. 
         [0032]    In the above examples, the exposed surfaces  43 - 45 ′″, and  45 - 45 ′″ which are to act as sensing or stimulating electrodes, are quadratic when seen from a view perpendicular to the exposed surface and extend longitudinally, but it is possible for them to made in any shape. 
         [0033]    There are several possible ways of forming an elongated helix body precursor. For example, as shown in  FIGS. 6   a ) and  6   b ) a electrically conducting core  81  and an insulating sheath  83  can be extruded simultaneously, the insulating sheath  83  being formed with a longitudinal slit  85  such that a continuous longitudinally extended portion of the surface  87  of the electrically conducting core  81  is exposed and not surrounded by the insulating sheath  83 . 
         [0034]    Such an elongated helix body precursor can be formed into a helix  89  as shown in  FIG. 6   c ), for example by winding around a former. The complete helix  89  can then be coated with a biocompatible conductive material  91  such as titanium nitride by, for example, vapor deposition as shown in  FIG. 6   d ). In order to isolate the exposed surface  87  of the core  81  which is intended to be electrically active during use from the surface of the insulating sheath  83  which is intended to be inactive during use, continuous strips  93  of the biocompatible conductive material  91  on the insulating sheath  83  can be removed, by polishing, cutting or other suitable methods, leaving a continuous non-conducting gap  93  between the core  85  and the major part of the visible surface of the insulating sheath, as can be seen in  FIG. 6   e ). 
         [0035]      FIGS. 7   a )- 7   c ) show schematically examples of further possible helix body precursors in cross-section.  FIG. 7   a ) shows a cross-section through a co-extruded or co-formed precursor body  101  containing two symmetrically-positioned conducting cores  103 ,  105  of circular cross-section surrounded by a circular insulating sheath  107 . 
         [0036]      FIG. 7   b ) shows a cross-section through a co-extruded or co-formed precursor body  109  containing three conducting cores  111 ,  113 ,  115  each of circular cross-section surrounded by a circular insulating sheath  117 . The cores are arranged with the two cores positioned at 90° either side of a middle core—thereby leaving a gap of approximately 180° of insulating material without any cores. Preferably this gap is arranged to be facing towards the interior of the helix when the precursor is formed into a helix. 
         [0037]      FIG. 7   c ) shows a cross-section through a co-extruded or co-formed precursor body  119  containing an asymmetrically-positioned core  121  of quadratic cross-section positioned inside an insulating sheath  125  of C-shaped cross-section, with a surface  125  of core  121  exposed. 
         [0038]    The above suggested cross-sections are merely examples of conceivable cross-sections—the skilled person would understand that in the event that a lead, precursor body or helix has a plurality of conductors it is always possible to remove selectively insulating material in predetermined positions so that when in use in a patient conductors can come into contact with tissue and thereby be used as a stimulating and/or sensing electrode. 
         [0039]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.