Patent Publication Number: US-2011071606-A1

Title: Bifurcated lead system and apparatus

Description:
FIELD 
     The present disclosure relates to implantable medical devices; more particularly to medical leads capable of delivering electrical signals to two discrete anatomical locations, such as a left and a right occipital nerve. 
     BACKGROUND 
     Headaches, such as migraines, and occipital neuralgia are often incapacitating and may lead to significant consumption of drugs to treat the symptoms. However, a rather large number of people are unresponsive to drug treatment, leaving them to wait out the episode or to resort to coping mechanisms. For refractive occipital neuralgia, nerve ablation or separation may effectively treat the pain. 
     Occipital nerve stimulation may serve as an alternative for treatment of migraines or occipital neuralgia. For example, a dual channel implantable electrical generator may be implanted subcutaneously in a patient. A distal portion of first and second leads may be implanted in proximity to a left and right occipital nerve such that one or more electrode of the leads are in electrical communication with the occipital nerves. The proximal portions of the leads may then be connected to the signal generator such that electrical signals can be delivered from the signal generator to the electrodes to apply therapeutic signals to the occipital nerves Alternatively, two single channel implantable electrical generators may be employed, where the first lead is connected to one signal generator and the second lead is connected to the second signal generator. In either case, the lead is typically tunneled subcutaneously from site of implantation of the signal generator to the occipital nerve or around the base of the skull. Such tunneling can be time consuming and is invasive. 
     BRIEF SUMMARY 
     The present disclosure, among other things, describes leads, systems and methods for applying electrical signals to occipital nerves. In some embodiments, bifurcated leads are described. By using bifurcated leads, only one tunneling procedure is needed to tunnel a proximal portion of a lead between a location near the occipital nerves and the implantation site of the electrical signal generator. Such leads and procedures may reduce surgery time and invasiveness associated with occipital nerve stimulation. 
     In an embodiment, a method for applying electrical signals to a left occipital nerve and a right occipital nerve of a subject are described. The method includes providing a lead including (i) a proximal portion having first and second contacts and (ii) first and second distal arms. The first distal arm includes a first electrode, and the second distal arm includes a second electrode. The first electrode is electrically coupled to the first contact, and the second electrode is electrically coupled to the second contact. The method further includes placing the first electrode in electrical communication with the right occipital nerve, and placing the second electrode in electrical communication with the left occipital nerve. The method also includes generating a first electrical signal in an electrical signal generator implanted in the subject. The electrical signal generator is operably coupled to the lead via the first contact. The method additionally includes applying the first electrical signal to the right occipital nerve via the first electrode. The method also includes generating a second electrical signal in an electrical signal generator implanted in the subject. The electrical signal generator is operably coupled to the lead via the second contact. The method further includes applying the second electrical signal to the left occipital nerve via the second electrode of the lead. The first and second electrical signals are the same or different. It will be understood that a signal may be delivered between the first and second electrodes to apply the signal to the left or right occipital nerve in some circumstances. 
     In an embodiment, a bifurcated lead is described. The lead includes a proximal portion having first and second contacts, and includes a first distal arm having a first electrode electrically coupled to the first contact and having a first engagement element distal the electrode. The engagement element is configured to cooperate with an advancement tool such that advancement of the tool distally relative to the engagement element pushes the engagement element distally. The lead further includes a second distal arm having a second electrode electrically coupled to the second contact and having a second engagement element distal the electrode. The engagement element is configured to cooperate with an advancement tool such that advancement of the tool distally relative to the engagement element pushes the engagement element distally. The lead also includes a branch region where the lead transitions from the proximal portion to the first and second distal arms. In addition, the lead includes a tissue anchoring element attached to the branch region. 
     The leads, systems and methods described herein provide one or more advantages over prior leads, extensions, signal generators, systems and methods. Such advantages will be readily understood from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an implantable system including a signal generator, lead extension and lead. 
         FIGS. 2A-B  are schematic diagrams showing distal portions of bifurcated leads implanted in a subjects and positioned to apply an electrical signal to left and right occipital nerves. 
         FIG. 3A  is a schematic side view of a representative bifurcated lead. 
         FIGS. 3B-D  are schematic cross-sections of alternative embodiments of the proximal portion of the lead shown in  FIG. 3A  taken through line  3   b - 3   b.    
         FIG. 3E  is a schematic side view of an embodiment of the branch region of the lead depicted in  FIG. 3A , showing conductors running through the branch region. 
         FIG. 4  is a schematic side view of representative bifurcated leads. 
         FIGS. 5A-C  are schematic drawings of lines running in a plane, showing embodiments of angles at which the receptacles of a connector portion of an extension may enter a body of the connector. 
         FIGS. 6-9  are schematic side views of representative bifurcated leads. 
         FIGS. 10A-E  are schematic side views of representative bifurcated leads having extensible portions. 
         FIGS. 11A-F  are schematic side views of representative bifurcated leads having attached anchors. 
         FIGS. 12A-B ,  13 ,  14 A-B,  15 , and  16 A-B are various views of schematic diagrams of embodiments of distal portions of leads having an engagement element. 
         FIGS. 17-19  are schematic side views of tools for engaging engagements elements, such as those depicted in  FIGS. 12A-B ,  13 ,  14 A-B,  15 , and  16 A-B, to facilitate placement of a lead in a patient. 
         FIGS. 20A-C ,  21 A-B,  22 A-D, and  23 A-D are schematic views of engagement tools pushing leads via interaction with an engagement element. 
     
    
    
     The drawings are not necessarily to scale. Like numbers used in the figures refer to like components, steps and the like. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. In addition, the use of different numbers to refer to components is not intended to indicate that the different numbered components cannot be the same or similar. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments of devices, systems and methods. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     As used herein, “have”, “having”, “include”, “including”, “comprise”, “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to”. 
     “Exemplary” or “representative” is used herein in the sense of “for example” or “for the purpose of illustration”, and not in a limiting sense. 
     The present disclosure describes, inter alia, bifurcated lead that may simplify implantation procedures associated with electrical single therapy at two distinct anatomical locations, such as a left and a right occipital nerve. 
     Nearly any implantable medical device or system employing leads may be used in conjunction with the leads, extensions or adaptors described herein. Representative examples of such implantable medical devices include hearing implants, cochlear implants; sensing or monitoring devices; signal generators such as cardiac pacemakers or defibrillators, neurostimulators (such as spinal cord stimulators, brain or deep brain stimulators, peripheral nerve stimulators, vagal nerve stimulators, occipital nerve stimulators, subcutaneous stimulators, etc.), gastric stimulators; or the like. For purposes of occipital nerve stimulation, electrical signal generators such as Medtronic, Inc.&#39;s Restore® or Synergy® series of implantable neurostimulators may be employed. 
     Referring to  FIG. 1 , a schematic side view of a representative electrical signal generator system  100  is shown. In the depicted system  100 , the electrical signal generator  10  includes a connector header  15  configured to receive a proximal portion of lead extension  20 . The proximal portion of lead extension  20  contains a plurality of electrical contacts  22  that are electrically coupled to internal contacts (not shown) at distal connector  24  of lead extension  20 . The connector header  15  of the signal generator  10  contains internal contacts (not shown) and is configured to receive the proximal portion of the lead extension  20  such that the internal contacts of the connector header  15  may be electrically coupled to the contacts  22  of the lead extension  20  when the lead extension  20  in inserted into the header  15 . 
     The system depicted in  FIG. 1  further includes a lead  30 . The depicted lead  30  has a proximal portion that includes a plurality of contacts  32  and a distal portion that includes a plurality of electrodes  34 . Each of the electrodes  34  may be electrically coupled to a discrete contact  32 . The distal connector  24  of the lead extension  20  is configured to receive the proximal portion of the lead  30  such that the contacts  32  of the lead  30  may be electrically coupled to the internal contacts of the connector  24  of the extension  20 . Accordingly, a signal generated by the signal generator  10  may be transmitted to a patient by an electrode  34  of lead  30  when lead is connected to extension  20  and extension  20  is connected to signal generator  10 . 
     It will be understood that lead  30  may be coupled to signal generator  10  without use of an extension  20 . Any number of leads  30  or extensions  20  may be coupled to signal generator  10 . Typically, one or two leads  30  or extensions  20  are coupled to signal generator  10 . While lead  20  is depicted as having four electrodes  34 , it will be understood that lead  30  may include any number of electrodes  34 , e.g. one, two, three, four, five, six, seven, eight, sixteen, thirty-two, or sixty-four. Corresponding changes in the number of contacts  32  in lead  30 , contacts  22  and internal contacts in connector  24  of lead extension, or internal contacts in connector  15  of signal generator  10  may be required or desired. 
     Referring to  FIGS. 2A-B , bifurcated leads  300  are shown implanted in a patient to provide bilateral therapy to left and right occipital nerves  200 . As used herein, occipital nerve  200  includes the greater occipital nerve  210 , the lesser occipital nerve  220  and the third occipital nerve  230 . The greater and lesser occipital nerves are spinal nerves arising between the second and third cervical vertebrae (not shown). The third occipital nerve arises between the third and fourth cervical vertebrae. The portion of the occipital nerve  200  to which an electrical signal is to be applied may vary depending on the disease to be treated and associated symptoms or the stimulation parameters to be applied. In various embodiments, the lead distal portions  350 ,  351  that contain electrodes are placed to allow bilateral application of electrical signals to the occipital nerve  200  at a level of about C1 to about C2 or at a level in proximity to the base of the skull. The position of the electrode(s) may vary. It will be understood that the electrode need not, and in various embodiments preferably does not, contact the nerve to apply the signal to the nerve. It will be further understood that a signal may be applied to any suitable portion of an occipital nerve, whether at a trunk, branch, or the like. In various embodiments, one or more electrodes are placed between about 1 cm and about 8 cm from the midline to effectively provide an electrical signal to the occipital nerve  200 . 
     As shown in  FIG. 2A , a bifurcated lead  300  may include a paddle shaped distal portion  350  containing electrodes. Such paddle shaped leads are often referred to as surgical leads. Examples of surgical leads that may be used or modified to form leads as described herein include Medtronic Inc.&#39;s Resume, SymMix, On-Point, or Specify series of leads. Surgical leads typically contain electrodes that are exposed through one face of the paddle, providing directional stimulation. The depicted bifurcated lead  200  also includes a single proximal portion  310  that allows for only one tunneling procedure to the signal generator (not shown) implant site. In addition, the bifurcated lead  300  contains a branch region  340  and first  320  and second  330  distal arms. As shown in  FIG. 2B , the bifurcated lead may include distal portion  350  that include electrodes that are generally cylindrically shaped. Such leads are often referred to percutaneous leads. Examples of percutaneous leads that may be used or modified to form leads as described herein include Medtronic Inc.&#39;s Quad Plus, Pisces Quad, Pisces Quad Compact, or 1×8 SubCompact, 1×8 Compact, and 1×8 Standard leads. Such percutaneous leads typically contain ring electrodes that apply an electrical stimulation signal to tissue in all directions around the ring. Accordingly, the amplitude of the signal (and thus the energy required from the signal generator) applied may be greater with percutaneous leads that surgical leads for occipital nerve therapies. 
     Various embodiments of lead or system configurations are described below with reference to the figures discussed below. However, it will be understood that any bifurcated lead may be employed to apply an electrical signal to an occipital nerve; e.g., as described above with regard to  FIGS. 2A-B . It will be further understood that, while the lead and system configurations described below may be useful for applying electrical signals to occipital nerves, they may be employed to apply electrical signals to other tissues of a subject or may be used to record signals from tissue of a subject. 
     Referring now to  FIG. 3A , a schematic side view of a representative bifurcated lead  400  is shown. The lead  400  includes a proximal portion  410  that includes a plurality of contacts  450  for electrically coupling to an electrical signal generator, lead extension, adaptor, or the like. The lead  400  also includes first  420  and second  430  distal arms that contain electrodes  424 ,  434 . The electrodes  424 ,  434  are electrically coupled to contacts  450  via conductors that run within lead  400  from the contacts  450  to the electrodes  424 ,  434 . The lead  400  further includes a branch region  440  where the lead  400  transitions from the proximal portion  410  to the distal arms  420 ,  430 . The branch region  440  may be of any suitable size and shape. In various embodiments, the branch region  440  has a volume of less than about 10 cubic centimeters; e.g., less than about 5 cubic centimeters. 
     Referring now to  FIG. 3B-D , which are schematic cross sectional views of embodiments of the proximal portion  410  of the lead  400  depicted in  FIG. 3A  taken along line  3   b - 3   b . As shown in  FIG. 3B , the proximal portion of the lead includes a lead body  412 . The lead body  412  may include two lumens or tubes  414 A,  414 B (or any number of tubes or lumens, e.g. one for each conductor) through which or around which conductors (not shown) may run to connect proximal contacts with electrodes of the first and second distal arms. Of course, the lumens or tubes  414 A,  414 B may be solid and the conductors can run in separate tracks along the length of the proximal portion of the lead until connecting with the distal arms. Alternatively, as shown in  FIG. 3C , the lead body  412  in the proximal portion may include a single lumen  416  or solid core (not shown) and the conductors (not shown) may run in a single track along the along the length of the proximal portion of the lead. Alternatively, as shown in  FIG. 3D , the proximal portion of the lead may include two attached lead bodies  412 A,  412 B through which separate channels of conductors (not shown) run. Of course, the lead body of the proximal portion of lead body may be configured in any other suitable manner. 
     Referring now to  FIG. 3E , a representative example of a branch region  440  is shown in which the branch region  440  is transparent for purposes of illustration. In the depicted embodiment, a set of conductors  470  exit a lead body from the proximal portion  410  of the lead. The set of conductors  470  are separated into subsets  470   a ,  470   b  that independently enter lead bodies of the first  420  and second  430  distal arms. Any suitable manner of forming branch region  440  and separating conductors  470  for entry of subsets  470   a ,  470   b  into distal arms  420 ,  430  may be employed. For example, a lead body containing conductors  470  in proximal portion  410  may be formed. Additional lead bodies containing conductor subsets  470   a ,  470   b  forming distal arms  420 ,  430  may be formed. The conductor subsets  470   a ,  470   b  may be appropriately electrically coupled to the set of conductors  470  and branch region  440  may be overmolded over conductors  470 ,  470   a ,  470   b , resulting in branch region  440  as depicted. Of course, any other suitable process may be employed to form branch region  440  and appropriately electrically couple proximal portion  410  of the lead to the distal arms  420 ,  430 . 
     Referring now to  FIG. 4 , a schematic side view of a representative lead  400  is shown. The lead  400  includes a proximal portion  410  including contacts  450 , a first distal arm  420  having a paddle-shaped region  422  containing electrodes  424 , a second distal arm  430  having a paddle-shaped region  432  containing electrodes  434 , and a branch point  440  where the lead  400  transitions from the proximal portion  410  to the first  420  and second  430  distal arms. The distal arms  420 ,  430  exit the branch region  440  at second  444  and third  446  entry regions, respectively. The proximal portion  410  enters the branched region  440  at the first entry region  442 . The distal arms  420 ,  430  exit the branch point  440  substantially perpendicular to the angle of entry of the proximal portion  410  in the depicted embodiment. Of course, the distal arms  420 ,  430  may exit the branch region  440  at any suitable angle. 
     For example and with reference to  FIGS. 5A-C , representative configurations are shown where the distal arms  420 ,  430  exit the branch region at various angles are shown. In  FIGS. 5A-C , a plane  900  is shown. The plane  900  is defined by the geometric centers of the first entry region  442  where the proximal portion of the extension enters the connector, the second entry region  444  where the first distal arm exits the branch region, and the third entry region  446  where the second distal arm exits the branch region. Several lines  962 ,  964 ,  964  are shown running in the plane. Line  962  represents a line running through the geometric center of the entry point  442 , along the axial center of the proximal portion of the extension as it enters the branch region. Line  964  represents a line running through the geometric center of the second entry point  444 , along the axial center of the first distal arm as it exits the branched region. Line  966  represents a line running through the geometric center of third entry region  446 , along the axial center of the second distal arm as it exits the branched region. In various embodiments, lines  962  and  964  or lines  962  and  966  intersect at angles (indicated by “A”) of between about 90 degrees and about 180 degrees. In some embodiments, the angles are between about 110 degrees and about 160 degrees. 
     With reference to  FIG. 6 , an alternative configuration of an exemplary lead  400  is shown. In the embodiment depicted in  FIG. 6 , the distal portions  422 ,  432  containing the electrodes are substantially cylindrical (e.g., percutaneous-type). Of course, distal portions containing the electrodes may have any suitable shape. 
     Referring now to  FIG. 7 , a schematic side view of a representative lead  400  is shown. The lead includes a proximal portion  410  containing contacts  450  and a distal portion  450  substantially perpendicular to the proximal portion  410 . The distal portion  450  includes first  452  and second  454  sets of electrodes that are electrically coupled to the contacts  450 . The first  452  and second  454  sets of electrodes are spaced apart from one another. In the embodiment depicted, the distal portion  450  can be considered to include two arms with one being to one side of the midline of the proximal portion  410  and the other being to the other side of the midline. 
     Referring now to  FIG. 8 , a lead  400  may include one or more anchors  460  for facilitating retention of the lead to tissue into which it is implanted. The anchors  460  may include suture holes or tines as depicted, but the anchors may take any suitable form. In various embodiments, an anchor  460  is attached to branch region  440 . That is, the anchor  460  is secured in place on the branch region  460  prior to implantation. As used herein, “attached”, as it relates to an anchor and a branch region or the like, means the anchor is affixed to the branch region. The anchor is affixed well in advance of implantation; e.g., during manufacture of the lead. By way of example, the anchor may be fastened to, adhered to, integrally formed with, etc. the branch region. In various embodiments, the anchor is permanently attached to the branch region. For application of therapies to an occipital nerve, where proximal portion  410  is tunneled through the neck region of a subject, it may be desirable to securely anchor branch region  440  to tissue of the subject to prevent stress and strain placed on the proximal portion  410  of the lead from transferring to the distal arms  420 ,  430  through the branch region  440 . In addition, it may be desirable for proximal portion to contain a strain relief feature to allow for stretching and movement of the neck (and thus proximal portion  410 ) without transferring excessive force to branch region  440 . For example, proximal portion  410  may include a sigma shaped portion  470 , may be looped (not shown), or may be extensible. One or more anchors  460  may be attached to first  420  or second  430  distal arms or to portions thereof, such as the distal portions containing electrodes as depicted. 
     As depicted in  FIG. 9 , an unattached anchor  500 , such as the wing-shaped suture loop anchor depicted, may be disposed about the proximal portion  410  of the lead  400  to prevent or inhibit strain on the lead  400  experienced proximal the anchor  500  from transferring to the branch region  440  and thus to the distal arms  420 ,  430 . An unattached anchor  500  may be employed in addition to or alternatively to an attached anchor (e.g. as shown in  FIG. 8 ). 
     Referring now to  FIGS. 10-11 , various representative configurations of bifurcated leads are shown. While T-shaped configurations are depicted, it will be understood that such configurations are readily applicable to Y- or other shaped configurations. In the embodiments depicted in  FIGS. 10A-E , the bifurcated leads include a proximal portion  410  containing contacts (not shown), a branch region  440  and first  420  and second  430  distal arms containing electrodes (not shown). The squiggly lines depicted in  FIGS. 10B-E  represent extensibility of the lead that the squiggly portion. Extensibility may include a sigma shaped section, loops, or may otherwise be configured to be extensible. As depicted, proximal portion  410  or distal arms  420 ,  430  or portions thereof may be extensible. 
     As shown in  FIGS. 11A-F , in which circles represent anchors  460  that may be attached or unattached, a bifurcated lead may include one or more anchor at nearly any location of the lead, such as the distal portion or along the length of a distal arm  420 ,  430 , at a branch region  440 , or anywhere along the proximal portion  410 . It will be understood that possible combinations of the configurations shown in  FIGS. 10-11  are contemplated, as are combinations of other figured depicted and discussed herein. 
     Referring now to  FIGS. 12-16 , various schematic views of distal portions of distal portions  320  (which correspond to distal arms  420 ,  430  in the figures described above) having engagement elements  1010  are shown. As shown in  FIG. 12A , the distal portions  320  having one or more electrodes  34 . As further shown in  FIG. 12A , the depicted distal portions  320  may include paddle-shaped portions  330 . The paddle shaped portion  330  includes the one or more electrodes  34  and the engagement element  1010 . The engagement element  1010  is distal to the distal most electrode. The engagement element  1010  may be integrally formed with the paddle-shaped portion  330  or attached to the paddle-shaped portion (e.g., adhered, fastened, or otherwise secured). 
     With reference to  FIGS. 12A ,  13 , and  14 A, schematic top-down views of representative distal portions  320  of leads having a variety of engagement element  1010  configurations are shown. As depicted in  FIG. 13 , the engagement element  1010  may form a hole that may be engaged by a lead advancement tool tool, such as a tool having a hook. In the embodiment depicted in  FIG. 14A , the engagement element  1010  includes or consists of a slit in the paddle-shaped portion  330  of the lead. A lead advancement tool may be inserted into the body of the paddle  330  to push the paddle to a desired implant location. In the embodiments depicted in  FIGS. 12A and 14A , the engagement element  1010  extends from or is on the surface of the paddle  330  through which the electrodes are exposed. Typically paddle-shaped leads have electrodes exposed through one surface of the paddle, but not through the opposing surface. As shown in the embodiments depicted in  FIGS. 12B and 14B , an engagement element  1010  may alternatively or additionally extends from, or may be on, the opposing surface of the paddle  330  through which the electrodes are not exposed. 
     Referring now to  FIGS. 15 and 16A , schematic side views of alternative embodiments the distal portion of the lead depicted in  FIG. 12B  are show. The engagement element  1010  extends from a major surface of the paddle  330 . As depicted in  FIG. 15 , the engagement element  1010  forms a cavity  1020  configured to receive an engagement tool. 
     Referring to  FIG. 16B , a schematic perspective view of an embodiment of the paddle-shaped portion  330  of the lead depicted in  FIG. 16A  is shown. As with the engagement element depicted in  FIG. 15 , the engagement element  1010  depicted in  FIG. 16A  forms a cavity configured to receive an engagement tool. The cavity  1020  depicted in  FIG. 16A  is formed by first  1210 , second  1220 , and third  1230  side walls, a floor  1110 , which may be even with the major surface of the paddle  330  or may be recessed relative to the major surface, and a ceiling  1100 . The cavity  1020  depicted in  FIG. 16B , or other similar cavities, allow the portion of an engagement tool received by the cavity  1020  to engage a variety of surfaces  1100 ,  1110 ,  1210 ,  1220 ,  1230  to allow for steering or guiding of the distal portion of the lead as it is pushed through tissue of a patient by the tool. 
     It will be understood that the engagement elements  1010  depicted in  FIGS. 12-16  are merely examples engagement elements that may be employed in accordance with the teaching presented herein. Any other engagement element having a suitable configuration for engaging a portion of an engagement tool such that, when engaged by the tool, distal advancement of the tool pushes the distal portion of the lead distally. 
     It will be further understood that a lead engagement element may be positioned at any suitable location of the distal portion of the lead. Placing the engagement element distal to the distal most electrode or at or near the distal end of the lead allows for the remainder of the lead to be pulled through the patient&#39;s tissue by the pushing force applied to the distally located engagement element. However, if the lead is suitably designed (e.g., sufficiently rigid) to be pushed from a more proximal location, the engagement element may be place in a location more proximal than at or near the distal end of the lead. It will be further understood that the percutaneous leads, having generally cylindrical distal portions, or leads other that surgical or paddle leads may include engagement elements and may be implanted as described herein. 
     Engagement elements may be formed of any suitable material. In various embodiments, an engagement element is formed of material that forms the body of the paddle, such as polymeric material. Reinforcing elements may be included in the engagement members to provide sufficient structural rigidity to allow the lead to be pushed through tissue of the patient. 
     Referring now to  FIGS. 17-19 , schematic side views of alternative embodiments of engagement tools  700  are shown. The tools  700  have a lead engagement feature  720  configured to engage an engagement element of a lead. The tools  700  also include elongate members  710  that extend proximally from the lead engagement feature  720 . In various embodiments, the lead engagement feature  720  is the distal end of the elongate member  710 . As shown in  FIGS. 18-19 , the elongate members may include a curved portion  730 . In some embodiments, the tools  700  are preformed to include the curved portion  730 . In some embodiments, the elongate members  710  are configured to be manually bent to include a curve portion  730 , as needed or desired, by a physician or other health care provider during the implant procedure. The tool  700  depicted in  FIG. 19  is bent in a manner such that pulling on a portion, such as the loop  740 , of the elongate member  710  distal to the engagement feature  720  cause a portion of the elongate member  710  proximal to the engagement feature  720  to push the engagement feature. 
     It will be understood that  FIGS. 17-19  depict only some examples of suitable configurations for engagement tools that may be employed as described herein. Any other suitable form or configuration of engagement tool may be employed. 
     An engagement tool may be formed from any suitable material, such as a rigid polymeric material, a metallic material, combinations thereof, or the like. Preferably, the engagement tool is formed of material sufficiently stiff to push a lead through subcutaneous tissue of a patient, yet flexible enough to bend as may be needed during implantation. 
     Referring now to  FIGS. 20A-C , side views illustrating a tool pushing a distal portion of a lead (only distal portion shown for purposes of brevity, simplicity, and clarity). As shown in  FIG. 20A-B , the elongate member  710  in proximity to the engagement feature  720  of a tool may be advanced distally relative to the lead until the engagement feature engages the engagement member  1010  of the paddle-shaped portion  330  of the lead. As shown in  FIGS. 20B-C , further distal advancement of the elongate member  710  relative to the lead, when the tool is engaged with the engagement element  1010 , causes the distal portion of the lead (including the paddle  330  in the depicted embodiment) to move distally. Position “X” indicated in  FIGS. 20B-C  is intended to mark a stationary position to reflect movement of the paddle portion  330  of the lead, and the elongate member  710  is pushed against the engagement feature  1010 . 
       FIGS. 21A-B  illustrate another example of a tool  700  moving a lead (only the distal portion  320  is shown for the purposes of brevity, simplicity, and clarity). The elongate member  710  distal to the engagement element  720  is pulled, e.g. by pulling on loop  740 , to cause the elongate member  710  in proximity to the engagement feature  720  of the tool  700  to push the engagement feature  720 . When the engagement feature  720  engages the engagement element  1010  at the distal portion  320  of the lead, distal advancement of the tool, causes the distal portion  320  of the lead to be moved distally. 
     Referring now to  FIGS. 22A-D  and  FIGS. 23A-D , schematic drawings illustrating the advancement of a distal portion  320  of a lead  30  through tissue of a subject are shown.  FIGS. 23A-D  are substantially the same as  FIGS. 22A-D , except that the orientation of the lead  30  is slightly different. It will be understood that only the distal portion  320  of the lead is shown in  FIGS. 22B-D  and  FIGS. 23B-D  for purposes of brevity, simplicity and clarity. As in  FIGS. 20-21 , the distal portion  320  of the lead includes and engagement element  1010  configured to cooperate with a tool  700  to advance the distal portion  320  of the lead through tissue  800  of a patient. The distal portion  320  of the lead  30  may be inserted through an incision  820  made in the patient. In the depicted embodiment, the incision  820  is through the skin  810  allowing advancement and implantation of the lead  30  in subcutaneous tissue  800  of the patient. A tool  700  (e.g. as described above) may be used to facilitate initial insertion into the subcutaneous tissue  800  (see, e.g.,  FIG. 22B ,  23 B) and is used to advance the distal portion  320  of the lead through the tissue  300  (see, e.g.,  FIGS. 22C-D ,  23 C-D). As the distal portion  320  of the lead enters the tissue  800  and is pushed through the tissue  800 , the angle of the tool  700  (compare  FIGS. 22B-D ,  23 B-D) is manipulated to implant the distal portion  320  of the lead at the appropriate angle and depth within the tissue  800 . In the depicted embodiment, the tool  700  is pre-bent or curved. However, in various embodiments, the tool  700  may be bent or curved manually as needed or desired. Once the distal portion  320  of the lead is advanced to the desired location within the tissue  800 , the tool  700  may be removed. 
     In some embodiments, the tool may be removed simply by withdrawing the tool from the tissue. However, in some embodiments, the engagement element of the lead and the engagement feature of the tool may be configured such that a significant amount of force is needed to disengage the tool from the engagement element of the lead (e.g., a compression fit, interference fit, snap fit, or the like). In such embodiments, it may be necessary to employ another tool to hold the distal portion on the lead in place while the engagement tool is disengaged to prevent movement of the distal portion of the lead from its desired implant location. Any suitable additional tool, such as forceps, pliers or the like to hold the paddle portion or the like, may be employed. 
     Thus, embodiments of BIFURCATED LEAD SYSTEM AND APPARATUS are disclosed. One skilled in the art will appreciate that the leads, extensions, connectors, devices such as signal generators, systems and methods described herein can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation.