Abstract:
Systems and techniques for explanting implantable devices are described. In one aspect, a device includes an explant tool configured to explant an implantable device from a body. The explant tool includes an elongate shank comprising a forward portion defining a longitudinal passage and a front tip attached to the forward portion and defining an opening to the longitudinal passage defined by the forward portion. The front tip comprises a slanted surface that slopes in a direction so as to spread tissue during forward penetration of the front tip into the body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 61/024,527 filed Jan. 29, 2008, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     This disclosure relates to explanting implantable devices. 
     Devices that are implanted in a body can perform any of a number of different activities, including diagnostic, therapeutic, monitoring, and other activities. At times, it may be desirable to explant (i.e., remove) an implanted device from the body. For example, the lifespan of an implanted device may have come to an end, a medical condition may have been cured, and/or alternative approaches to performing the activities of an implanted device may have been developed. 
     SUMMARY 
     Systems and techniques for explanting implantable devices are described. In one aspect, a device includes an explant tool configured to explant an implantable device from a body. The explant tool includes an elongate shank comprising a forward portion defining a longitudinal passage and a front tip attached to the forward portion and defining an opening to the longitudinal passage defined by the forward portion. The front tip comprises a slanted surface that slopes in a direction so as to spread tissue during forward penetration of the front tip into the body. 
     This and other aspects can include one or more of the following features. The elongate shank can include a rear portion that is more flexible than the forward portion. The device can also include a positioning member dimensioned to slide along at least a portion of the elongate shank. The elongate shank can include a longitudinal cutout positioned to open the longitudinal passage. The positioning member can include a tooth dimensioned to fill at least a portion of the longitudinal cutout. 
     The front tip further can include a cutting element arranged to cut through a tissue upon forward penetration of the front tip into the body. The front tip can also include a recess to hold the cutting element. The front tip can also include a cutting, a serrated, or an abrasive element arranged to cut through a tissue upon rotation of the front tip. 
     In another aspect, a method includes locating a flexible tail of an implantable device that is implanted in a body, inserting the flexible tail into a forward tip of an elongate explant tool, advancing the forward tip into the body, following the flexible tail; and withdrawing the implantable device from the body. 
     This and other aspects can include one or more of the following features. The implantable device can be art implantable pulse generator. The method can include maintaining a tension on the flexible tail while advancing the forward tip into the body, e.g., by pulling on a terminal portion of the flexible tail from outside the body. The flexible tail can be inserted into the forward tip by threading the flexible tail through a passage through the forward tip. The forward tip can be advanced by reaching a device body of the implantable device with the forward tip. The method can also include cutting or serrating a tissue capsule around the device body. 
     The implantable device can be withdrawn from the body through a tissue passage formed by advancement of the forward tip into the body. The forward tip can include a slanted surface beside the passage. The forward tip can be advanced by spreading tissue around the tail using the slanted surface to pass the forward tip. An active element can be removed from the flexible tail of the implantable device prior to the insertion of the flexible tail into the forward tip. The forward tip can be advanced by sliding a positioning member along a shank connected to the forward tip, wherein sliding the positioning member maintains the positioning member outside the body. 
     In another aspect, a system includes an implantable device comprising a device body attached to a flexible tail and an explant tool comprising a tip mounted on a shank, wherein the tip defines a passage dimensioned to pass the sectional area of the flexible tail of the implantable device. The flexible tail has a sectional area over at least a portion of its length. 
     This and other aspects can include one or more of the following features. The implantable device can include a first dimension lateral to a site at which the device body is attached to the tail. The shank can include a second dimension in a vicinity of the tip. The second dimension can be lateral to the shank. The second dimension can be the same size or larger than the first dimension. 
     The implantable device can include an implantable pulse generator. The flexible tail can include an active element configured to participate in a performance of activities by the implantable device. The implantable device can also include a positioning member dimensioned to slide along at least a portion of the shank. The shank can also define the passage defined by the tip. The positioning member can be configured to maintain a portion of the flexible tail in a portion of the passage defined by the shank. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 and 2  are schematic representations of implantable devices that may have occasion to be explanted. 
         FIGS. 3 and 4  are schematic representations of tails of implantable devices that include active components. 
         FIG. 5  is a sectional representation of the active component of the tail of  FIG. 4 . 
         FIG. 6  is a schematic representation of one example of an implantable device that may have occasion to be explanted. 
         FIG. 7  is a schematic representation of an explant tool. 
         FIGS. 8-10  are schematic representations of implementations of tips of the explant tool of  FIG. 7 . 
         FIGS. 11-17  schematically represent an illustrative example of the use of the explant tool of  FIG. 7  to explant an implantable device from a body. 
         FIG. 18  is a schematic representation of another implementation of an explant tool. 
         FIG. 19  is a diagrammatic view of a positioning member. 
         FIG. 20  is a view of the positioning member of  FIG. 19  from above. 
         FIG. 21  is a schematic representation of the reception of a portion of an explant tool in the positioning member of  FIG. 19 . 
         FIG. 22  schematically represents the use of a positioning member and an explant tool to explant an implantable device from a body. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  are schematic representations of implantable devices  100  that may have occasion to be explanted. Each implantable device  100  includes a device body  105  and a tail  110 . Each device body  105  includes a biocompatible housing that houses elements configured to perform activities when the corresponding implantable device  100  is implanted in a body. For example, each device body  105  can include mechanical, electrical, chemical, biological, and/or optical components that perform, e.g., diagnostic, therapeutic, monitoring, and/or other activities after implantation. 
     In some implementations, implantable devices  100  are implantable pulse generators. An implantable pulse generator (IPG) is an implantable device that delivers electrical pulses to cells or tissue. The electrical pulses can be delivered for therapeutic, functional, diagnostic, or other purposes. When implantable device  100  is an implantable pulse generator, the elements housed in device body  105  can include, e.g., one or more power storage devices such as a battery, one or more electrodes for delivery of the electrical pulses, and/or control circuitry for managing the delivery of the electrical pulses. 
     Tails  110  are generally flexible, elongate members that are each attached to a corresponding device body  105  at an attachment site  115 . Each attachment site  115  is found on a surface  120  of device body  105  of a corresponding implantable device  100 . Surface  120  extends laterally outward from attachment site  115 . Tails  110  are thus thinner than device bodies  105  in that at least a portion of device bodies  105  have a larger cross-section than tails  110 . In some implementations, the cross-sections of tails  110  are generally uniform along their entire length. In other implementations, the cross-sections of tails  110  are not uniform along their entire length but may include elements that can be detached or otherwise removed to achieve a uniform cross-section. Each tail  110  extends longitudinally from attachment site  115  to an end  135 . 
     Tails  110  can be formed from one or more flexible polymeric, ceramic, or metallic biocompatible materials, such as nylon, polytetrafluoroethylene, silicone, polyurethane, polyester, polypropylene, titanium, carbon fiber, stainless steel, noble metals, glass fibers, and the like. In some implementations, tails  110  can be formed from bioresorbable materials if the expected duration of implantation is shorter than the time for resorbtion. The material forming tails  110  can be shaped into wires or other elongate strands. In some implementations, the wires or strands can be woven or threaded to form a stranded tails  110 . In other implementations, tails  110  can be solid. 
     Tails  110  can be completely passive or can include one or more active components. Active tails  110  can include one or more mechanical, electrical, chemical, biological, and/or optical components that contribute to the performance of activities by implantable device  100 . For example, active tails  110  can include active components such as optical fibers, fluid conduits, and/or electrical leads that are covered by one or more electrical insulators. 
     In operation, device bodies  105  of implantable devices  100  can be implanted at relatively “deep” sites, while tails  110  can extend to relatively superficial sites closer to the skin or other surface. This arrangement can have a number of different advantages. For example, a tail  110  can guide medical personnel from a superficial site to a device body  105  of an implanted device  100  that it implanted at a deeper site with minimal collateral tissue damage, as discussed further below. As another example, if an active tail  110  includes a charging element that contributes to the conversion of energy from outside a body into potential energy, the charging element can be positioned close to the skin surface so that a relatively small amount of the energy from outside the body is dissipated by transmission through the body. 
       FIG. 3  is a schematic representation of a tail  110  that includes active components, namely, one or more leads  305  and one or more electrodes  310 . Leads  305  are wires that place electrodes  310  in electrical contact with components in device body  105  of an implantable device  100 . The conducting path formed by leads  305  and electrodes  310  traverses an outer surface  315  of tail  110  so that electrodes  310  can deliver electrical pulses originating in device body  105  to sites that are relatively remote from device body  105 . 
       FIG. 4  is a schematic representation of a tail  110  that includes active components, namely, a pair of leads  405  and a charging element  410 .  FIG. 5  is a sectional representation of charging element  410  along the line  5 - 5  of  FIG. 4 . 
     Charging element  410  includes a coiled conductor  415  that is housed in a biocompatible casing  420 . Leads  405  are wires that place coiled conductor  415  in electrical contact with components in device body  105  of implantable device  100 . Coiled conductor  415  can respond to a magnetic or electric field generated outside the body in which implantable device  100  is implanted. The motion of electrons in coiled conductor  415  under the influence of such a magnetic or electric field can be converted into potential energy and stored, e.g., at a rechargeable battery or other energy storage device in device body  105  of implantable device  100 . 
     The conducting path formed by leads  405  to coiled conductor  415  allows charging element  410  to be positioned close to the skin surface while device body  105  is implanted at a deeper site. Such a positioning can reduce the dissipation of the magnetic or electric field from outside the body while allowing the motion induced by such a field in coiled conductor  415  to be efficiently conveyed to device body  105 . 
       FIG. 6  is a schematic representation of one example of an implantable device  100 , namely, an implantable microstimulator  600 . Implantable pulse generator  600  includes a generally cylindrical device body  105  and tail  110  that is attached to a surface  120  which caps device body  105 . Device body  105  can be dimensioned to be implantable through the cannula of a closed surgical device. Device body  105  houses electrical circuitry, power storage devices, and other components for the delivery of electrical stimuli to cells or tissue. 
     Implantable pulse generator  600  also includes a stimulating electrode  605  and a counter electrode  610  that are separated by an insulator  615 . Stimulating electrode  605  is positioned on a cap  620  of device body  105 . Counter electrode  610  and insulator  615  are generally cylindrical members with the same circumferential outer surface geometry. Counter electrode  610  and insulator  615  are joined at a seam  625  with their outer surfaces aligned. 
       FIG. 7  is a schematic representation of an explant tool  700 . Explant tool  700  includes a handle  705  that is fixed to an elongate shank  710  at a site  712 . Shank  710  extends longitudinally away from handle  705  to terminate in a tip  715 . Tip  715  can have a truncated conical shape (as shown), a blunted, bullet shape, a truncated pyramidal shape, or other shape that includes one or more slanted surfaces that slope to spread tissue during forward penetration of tip  715  into the body.  FIG. 8  is a schematic representation of the truncated conical implementation of tip  715  in additional detail. In the vicinity of tip  715 , shank  710  includes an outer circumference  720 . The truncated cone of tip  715  includes a slanted surface  725  that slopes inward from outer circumference  720  to an end  730  of tip  715 . Outer circumference  720  can be dimensioned to be the same size or larger than a lateral size an implantable device that is to be explanted, as discussed further below. 
     Tip  715  and at least a portion of shank  710  define a passage  735 . Passage  735  extends longitudinally into the truncated cone of tip  715  and through the forward portion of shank  710 . Shank  710  includes a cutout  740  that communicates with end  730  via passage  735 . Cutout  740  ends the generally circular outer diameter  720  of shank  710  in a rounded edge  745 . Passage  735  can be dimensioned to receive the tail of an implantable device that is to be explanted, as discussed further below. 
     In some implementations, end  730  of tip  715  can include one or more elements to aid in the penetration of tip  715  into a body. For example, end  730  can include a blade or other sharpened edge for cutting through tissue. As another example, end  730  can be serrated or include abrasive elements for sawing through tissue upon rotation. 
       FIG. 9  is a schematic representation of another implementation of tip  715 . In the illustrated implementation, slanted surface  725  defines one or more lateral depressions  905 . A blade  910  or other cutting element is recessed in each depression  905 . Blade  910  is oriented laterally relative to shank  710  and can cut tissue that moves into depression  905  during the forward penetration of tip  715  into a body. 
       FIG. 10  is a schematic representation of another implementation of tip  715 . In the illustrated implementation, slanted surface  725  defines one or more longitudinal depressions  1005 . A blade  1010  or other cutting element is recessed in each depression  1005 . Blade  1010  is oriented longitudinally along shank  710  and can cut tissue that moves into depression  905  upon rotation of tip  715  during the penetration of a body. 
       FIGS. 11-17  schematically represent an illustrative example of the use of explant tool  700  to explant an implantable device  100  from a body  1100 . With reference to  FIG. 11 , body  1100  includes a body surface  1105  by which medical personnel can access implantable device  100 . Body surface  1105  is generally the skin. 
     Implantable device  100  is implanted in body  1100  with device body  105  positioned at a relatively deep site  1110  and with tail  110  extending to a superficial site  1115  closer to surface  1105 . Thus, superficial site  1115  is at a depth D 1  beneath surface  1105  and surface  120  of device body  105  is at a depth D 2  beneath surface  1105 . Depth D 1  is smaller than depth D 2 . 
     With reference to  FIGS. 12-13 , after a sufficiently long implantation term, implantable device  100  will often become encased in a tissue capsule  1205 . Medical personnel can make an incision  1305  in the vicinity of end  135  of tail  110  using a scalpel  1210  or other device. The exposed portion of tissue capsule  1205  can also be cut and the terminal portion  1310  of tail  110  can be teased out from body  1100 . Since superficial site  1115  is at a depth D 1  beneath body surface  1105 , incision  1305  is relatively shallow despite the implantation of device body  105  of device  100  at a deeper location. 
     In implementations where tail  110  includes one or more active components, such as charging element  410 , that are relatively large, the active components can be detached or otherwise removed from the remainder of tail  110 . For example, tail  110  can be cut to remove charging element  410 . 
     With reference to  FIGS. 14 and 15 , the terminal portion  1310  of tail  110  can be inserted into end  710  of explant tool  700  by threading tail  110  through passage  735  and out into cutout  740 . The terminal portion  1310  of tail  110  can then be grasped between the jaws  1505  of hemostat or other pliers  1510 . Explant tool  700  can be advanced into incision  1305  by medical personnel manipulating handle  705  (not shown). Pliers  1510  can maintain tension on tail  110  while explant tool  700  is advanced. 
     With reference to  FIGS. 15 and 16 , while maintaining grip on terminal portion  1310  of tail  110 , further manipulation can be used to advance tip  715  along tail  110  and deeper into body  1100  toward device body  105  of implantable device  100 . If necessary, explant tool  700  can be pushed or rotated using handle  705  to aid in the penetration of tip  715  through tissue capsule  1205  that surrounds tail  110 . Such manipulation can bring blades, serrated edges, and/or abrasive elements to bear on tissue capsule  1205 . As tip  715  penetrates into body  1100  along tail  110 , slanted surface  725  spreads tissue capsule  1205  to create a channel  1605 . Channel  1605  can thus pass solid objects with diameters that are the same size or smaller than outer circumference  720  of shank  710 . 
     With reference to  FIG. 17 , following tail  110 , tip  715  of explant tool  700  can reach site  1110  where device body  105  of implantable device  100  is implanted. If necessary, tip  715  of explant tool  700  can be used to penetrate any tissue capsule  1205  around surface  120  of device body  105  to clear the way for withdrawal of device body  105  through channel  1605 . Implantable device  100  can be explanted through channel  1605  by pulling explant tool  700 , along with the gripped terminal portion  1310  of tail  110 , away from body  1100 . 
       FIG. 18  is a schematic representation of another implementation of explant tool  700 . In the illustrated implementation, shank  710  of explant tool  700  includes a relatively flexible portion  1810  and a relatively inflexible portion  1805  that is joined to tip  715 . Relatively inflexible portion  1805  is less flexible than relatively flexible portion  1810  and hence better suited for penetrating into a body. In particular, a relatively less flexible and harder dissection tip can facilitate penetration of the tissue and decrease deformation of the dissection tip. 
     The different flexibilities of relatively inflexible portion  1805  and relatively flexible portion  1810  can be achieved in a number of different ways. For example, portion  1805  can be made from a first, relatively inflexible, polymer and portion  1810  can be made from a second, relatively flexible, polymer. As another example, portion  1805  and portion  1810  can have identical compositions but different structures. For example, passage  735  can be larger in portion  1810  than in portion  1805 . As yet another example, the materials used to form portions  1805 ,  1810  can be handled in different ways and/or include different compositions. 
     In some implementations, portions  1805 ,  1810  are joined at a seam  1815 . In other implementations, shank  710  can be formed as a unitary structure and portions  1805 ,  1810  can be separated by a gradient or other transition in flexibility. 
       FIG. 19  is a diagrammatic view of a positioning member  1900 .  FIG. 20  is a view of positioning member  1900  from above. Positioning member  1900  is a generally planar member that includes an interior wall  1920 . Interior wall  1920  extends from a first face  1910  to a second face  1915  of positioning member  1900  to define a passage  1905  therethrough. Interior wall  1920  also defines a lateral tooth  1925  that extends toward the interior of passage  1905 . 
     Positioning member  1900  is dimensioned to slidably receive the portion of shank  710  that includes cutout  740 .  FIG. 21  is a schematic representation of the reception of this portion of shank  710  in positioning member  1900 . As shown, cutout  1905  is dimensioned to pass this portion of shank  710  with lateral tooth  1925  extending into cutout  740 . In extending into cutout  740 , lateral tooth  1925  can prevent the entry of a tail  110  into cutout  740 . Lateral tooth  1925  does not however, extend into passage  735 . Rather, passage  735  can pass a tail  110  of an implantable device  100 . The Portion of shank  710  that includes cutout  740  can be slid forward and backward (i.e., in and out of the page) through positioning member  1900 . 
       FIG. 22  schematically represents the use of positioning member  1900  and explant tool  700  to explant an implantable device  100  from a body  1100 . As shown, the portion of shank  710  that includes cutout  740  is received in positioning member  1900 . Positioning member  1900  is maintained outside of body  1100  and can rest against body surface  1105 . Tail  110  is threaded into tip  715  and follows passage  735  past positioning member  1900  and out of body  1100 . Positioning member  1900  thus prevents the entry of tail  110  into cutout  740  before tail  110  exits body  1100 . 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, other charging elements, including optical (e.g., photovoltaic cells) and mechanical (e.g., piezoelectric devices) elements, can be used. As. another example, a tail  110  need not be teased out from the body before insertion into passage  735  of an explant tool  700 . As yet another example, a positioning member  1900  need not include a tooth  1925 . Accordingly, other implementations are within the scope of the following claims.