Patent Publication Number: US-7210968-B1

Title: Dual-locking mechanism for lead and header attachment in pre-molded headers

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrical connector assemblies forming part of implantable medical devices (IMDs). Such connector assemblies have one or more electrical receptacles each adapted to receive an implantable lead and to connect the lead to electronic circuits within the IMD. More particularly, the invention relates to an electrical connector assembly which incorporates a fastener assembly for simultaneously releasably clamping a proximal end portion of the implantable lead within a receptacle of a header and firmly attaching the header to a casing of the implantable medical device. 
     BACKGROUND OF THE INVENTION 
     The present invention is applicable to a variety of IMDs utilizing pulse generators to stimulate selected body tissue. However, in this instance, the invention and its background will be described principally in the context of a specific example of such devices, namely, an implantable cardiac pacemaker and defibrillator unit having a connector assembly defining multiple lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein. 
     Cardiac pacemakers, and other implantable stimulation devices such as cardioverters and defibrillators, are hermetically sealed within a housing or casing (sometimes also referred to as a “can”) to isolate the electronic circuits contained within the device from the body environment. Such devices require that electrical signals be reliably passed between the hermetically sealed circuitry and external connectors without compromising the hermeticity of the device. Depending on the configuration of the implantable device there may be multiple electrical paths required between the device and its external connectors for delivering, for example, multi-chamber or multi-site stimulation and shock therapy, and for receiving sensed cardiac signals. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term connector assembly that does not compromise the hermetic package. 
     Typically, a hermetic housing feedthrough electrically couples the electronic circuits contained within the device housing or casing to the connector assembly. The feedthrough extends through the wall of the hermetically sealed casing into the connector assembly so as to couple the electronic circuits within the casing to lead-receiving receptacles within the connector assembly. Each lead has one or more electrical terminals on a proximal end thereof, typically in the form of a pin terminal and one or more conductive ring terminals. Typically, the pin is electrically coupled to a distal tip electrode and is therefore sometimes called the “tip terminal.” When the proximal end of the lead is inserted into the lead receptacle of a connector assembly, contacts within the receptacle come into contact with corresponding terminals on the lead so as to couple the lead to the electronic circuits within the implantable stimulation device via the feedthrough assembly. Needless to say, it is imperative that a completely dependable electrical connection be made and retained between the lead terminals and the corresponding connector assembly contacts. At the same time, the connector assembly must be capable of releasing the lead from the lead receptacle during explantation or other subsequent surgical procedure, and must also tightly seal against the entry of body fluids. 
     It is known in prior art connector assemblies to electrically and mechanically connect the proximal end of the lead within a receptacle of the connector assembly by means of a variety of expedients including captive fastening screw/collet arrangements and setscrews. In those prior art connector assemblies in which the lead is fixed within the lead receptacle using a setscrew, the setscrew is often threaded into an electrical connector block within the connector assembly. When the screw is advanced, it comes into contact with an associated terminal on the proximal end of the lead, mechanically and electrically coupling the lead and the connector assembly. However, the proximal end of a lead is sometimes damaged by an over-tightened setscrew and setscrews have a history of stripping out of the threaded connector block. To minimize or eliminate such problems, setscrews of a certain minimum physical size have been employed. The result is often a protrusion on the side of the connector assembly as the physical size of the pacemaker and its connector assembly is reduced. 
     A further problem of prior art setscrew type connector assemblies arises from the need to isolate the setscrew and the setscrew block from body fluids. One solution has been to use a silicone seal called a septum. The septum forms an insulation barrier between the setscrew and body fluids. However, the septum must permit a wrench to pass through it so that the screw can be tightened. Frequently, the septum is damaged by the wrench resulting in a loss of the insulation barrier. 
     One improvement is disclosed in U.S. Pat. No. 4,934,366 to Truex et al. which provides a feedthrough connector for a pacemaker, or other implantable medical device, that advantageously combines the connector function with the feedthrough function and eliminates the need for the cast epoxy connector previously used on prior art pacemakers. According to the Truex et al. patent, eliminating the external cast epoxy connector advantageously eliminates the need for septums, setscrews, and the feedthrough terminal and its associated platinum wires and connector blocks, as well as the whole time consuming casting process with its inherent propensity for cosmetic problems. In this patented instance, the feedthrough/connector includes a barrel assembly having an open end and a closed end. The open end of the assembly provides an opening into which the connecting end of a pacemaker lead, or other electrical lead, can be inserted. The barrel assembly includes metal (conductive) portions separated by ceramic (nonconductive) insulating portions. An overlap region of the conductive portions, separated by the nonconductive portion, advantageously provides structural strength as well as a capacitor structure which helps filter out unwanted electromagnetic interference (EMI) signals from passing through the connector. Spring contacts are mounted on the inside of the metal portions and are adapted to make electrical contact with the appropriate electrodes of the pacemaker or other electrical lead when the connecting end of the lead is inserted into the connector. 
     Another known improvement is disclosed in U.S. Pat. No. 5,252,090 to Giurtino et al. which discloses a connector assembly for an implantable stimulating device which employs a lead-locking spring clip to reliably provide a mechanical and electrical connection between the terminal pin of an electrode lead and the device, while reducing the user interaction required during implantation and disconnection. In this patented instance, no tools are required to establish the connection, nor is user action, other than inserting the lead into the connector, necessary to lock the lead into place. Disconnecting the lead requires only the application of a modest transverse compressing force to a release button on the connector assembly. In the event that a withdrawal force is applied to the lead without simultaneously applying the compressing force to the release button, the connector assembly increases its holding force on the electrode lead. 
     U.S. Pat. No. 5,951,595 to Moberg et al. discloses a connector assembly mounted on an implantable cardiac stimulation device having a side-actuated mechanism for fixing and tightly sealing electrical leads inserted into lead receptacles within an IMD connector assembly without the use of setscrews. In the Moberg et al. patent, fixing and sealing of the leads is accomplished by compressing resilient lead lock O-ring seals, disposed in annular recesses, with lip portions of a plunger drawn toward a molded support by the actuator mechanism. 
     It was in light of the foregoing that the present invention was conceived and has now been reduced to practice. 
     SUMMARY 
     An implantable medical device includes a casing and a header having a receptacle with an electrical contact for engageably receiving an electrical terminal on a proximal end of a lead and a fastener assembly for releasably clamping the lead to the header within the receptacle and firmly attaching the header to the casing. 
     In one embodiment, the header is mounted on the casing and has a distal notched region with an upper surface and a first channel in its upper surface aligned with, and being a partial extension of, the receptacle. The fastener assembly includes a lead-lock component engageably received within the notched region of the header and with a second channel therein which is aligned and juxtaposed with the first channel, the channels taken together being an extension of the receptacle. A fastener system firmly mounts the lead-lock component to the header at the notched region. 
     Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view illustrating the casing of a pacemaker representing a typical pulse generator containing an hermetically sealed electronic package and being prepared to receive a connector assembly embodying the present invention; 
         FIG. 2  is a perspective view of the pacemaker illustrated in  FIG. 1  after a subsequent intermediate step has been performed toward attachment of a connector assembly embodying the present invention; 
         FIG. 3  is a perspective view of the pacemaker illustrated in  FIGS. 1 and 2  after a all of the steps have been performed resulting in complete attachment of a connector assembly embodying the present invention; 
         FIG. 4  is a side elevation view of the pacemaker illustrated in  FIGS. 1 ,  2 , and  3 ; 
         FIG. 5  is a detail cross section view, in elevation, illustrating the connector assembly of the invention; 
         FIG. 6  is a detail exploded perspective view of the connector assembly of the invention; 
         FIG. 7  is a detail perspective view illustrating in greater detail a portion of the pacemaker illustrated in  FIG. 2 ; 
         FIG. 8  is detail perspective view illustrating in greater detail a portion of the pacemaker illustrated in  FIG. 3 ; 
         FIG. 9  is a cross section view taken generally along line  9 — 9  in  FIG. 4 ; 
         FIG. 10  is a cross section view taken generally along line  10 — 10  in  FIG. 4 ; 
         FIG. 11  is a cross section view taken generally along line  11 — 11  in  FIG. 4 ; 
         FIG. 12A  is a detail cross section view illustrating in greater detail an initial position of components illustrated in  FIG. 5 ; 
         FIG. 12B  is a detail cross section view illustrating in greater detail an intermediate position of components illustrated in  FIG. 5 ; 
         FIG. 12C  is a detail cross section view illustrating in greater detail a final position of components illustrated in  FIG. 5 ; 
         FIG. 12D  is a detail cross section view illustrating in still greater detail one of the components illustrated in  FIGS. 12A ,  12 B, and  12 C; 
         FIG. 13  is a detail perspective view illustrating in greater detail a portion of the pacemaker illustrated in  FIG. 3 , specifically, a casing and an associated header to which leads are being attached; 
         FIG. 14  is a detail perspective view similar to  FIG. 14  illustrating the leads already attached to the header; and 
         FIG. 15  is a detail perspective view similar to  FIG. 14  but with the leads now sealingly attached to the header and the header firmly attached to the casing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Refer now to the drawings and, initially, to  FIGS. 1 ,  2 ,  3 , and  4  which illustrate an implantable medical device (IMD)  20  in the form of a pulse generator such as a pacemaker or defibrillator intended to be introduced into an organ of a living body to provide stimulating pulses to selected body tissue, for example, into the heart. The device  20  represents an electronic package of a type to be hermetically sealed and enjoy the benefits of the present invention. Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms or embodiments. Any suitable size, shape or type of elements or materials may be used to practice the invention. 
     In order to appreciate the advantages of the present invention, it will help first to have a basic understanding of the construction of a known IMD. As seen in  FIG. 5 , the IMD  20  chosen for descriptive purposes to be a pacemaker includes a battery  22  that powers electronic circuitry  24  mechanically housed and hermetically sealed in a suitable casing  26 . Typically, this casing  26  is seen to include a first case half  28  and a second case half  30  which is matingly attachable to the first case half. When attached and properly sealed, the first and second case halves  28 ,  30  serve to encapsulate the electronic circuitry. 
     The casing  26  is shaped to include a primarily flat platform or mounting surface  32  to which a connector assembly  34  can be attached. At least one feedthrough terminal  36  ( FIGS. 1 and 5 ), electrically isolated from the casing  26 , is in electrical contact with the electronic circuitry  24 , passes through the casing  26 , and protrudes from the mounting surface  32 . Another component of note, though not part of the invention, is the outwardly protruding backfill port  38  through which, in a known manner, after the case halves  28 ,  30  are joined and welded together, all gases are evacuated from the casing and nitrogen introduced. 
     The manner of attachment of the connector assembly  34  to the outside of said casing will be described below but the connector assembly serves to releasably affix one or more leads  40  ( FIG. 13 ) having a proximal end portion  42  carrying at least one electrical terminal  44  for electrically coupling the feedthrough terminal  36  to the electronic circuitry  24  in a known manner. The receptacle may be variously configured, for example, to receive the proximal end portion of a pacing and/or sensing lead or of a cardioverting and/or defibrillating lead. 
     The connector assembly  34  includes a header  46  extending between proximal and distal ends  48 ,  50 , respectively, and has at least one elongated receptacle  52  ( FIGS. 7 and 10 ), although two receptacles are actually illustrated and there may be more receptacles, generally of circular cross section, with a longitudinal axis  54  for receiving the proximal end portion  42  of the lead  40 . In a known manner, the receptacle  52  carries an electrical contact positioned to engage the electrical terminal  44  and if there is more than one electrical terminal on the lead  40 , there would be a similar number of spaced electrical contacts in the receptacle to make contact with the electrical terminals, eventually coupling with appropriate components of the electronic circuitry  24 . 
     The connector assembly  34  also includes a fastener assembly  56  (see especially  FIGS. 5 and 6 ) for simultaneously releasably clamping the proximal end portion  42  of the lead  40  to the header  46  within the receptacle  52  and firmly attaching the header to the casing  26 . The header  46  has an undersurface  58  for mounting engagement on the mounting surface  32  of the casing  26  and a notched region  60  ( FIGS. 2 , and  5 – 7 ) at its distal end  50  having an upper surface  62  spaced from the undersurface  58  of the header. The notched region  60  has a first channel  64  (actually a pair of channels is illustrated) formed in its upper surface  62  aligned with, and being a partial extension of, the receptacle  52 . 
     The fastener assembly  56  includes a lead-lock component  66  for engageable reception with the notched region  60  of the header  46  and is formed with a second channel  68  ( FIGS. 6 and 8 ) which, when engageably received in the notched region, is aligned and juxtaposed with the first channel  64  of the header  46 , the first and second channels taken together being a full cylindrical extension of the receptacle  52  but having an inner diameter smaller than that of the receptacle when the connector assembly is firmly attached (as will be later explained) to the casing  26 . Viewing especially  FIGS. 2 ,  3 ,  5 , and  6 , the lead-lock component  66  includes a dovetail feature  70  at a location of engagement with the notched region  60  of the header  46 . The header has a corresponding dovetail cutout  72  for slidable engageable reception of the dovetail feature  70  to assure axial and lateral alignment of the lead-lock component  66  relative to the header. 
     The fastener assembly  56  also includes a fastener system  74  ( FIGS. 5 ,  6 ,  11 ,  12 A– 12 D) for firmly mounting the lead-lock component to the header  46  at the notched region  60 . Assisting the fastener system  74 , the header  46  has a mounting recess  76  (see  FIGS. 5 and 9 ) at its proximal end  48  and an outwardly projecting brace  78  is fixed, as by welding, to the mounting surface  32  of the casing  26  for engageable reception in the mounting recess. A first through bore  80  is formed in the header  46  proximate its distal end  50  and extending transverse of the longitudinal axis  54  of the receptacle  52  from the upper surface  62  to the undersurface  58 . The lead-lock component  66  has a second through bore  82  which is aligned with the first through bore  80  when the lead-lock component is firmly attached to the header  46  ( FIG. 5 ). 
     Not only does the fastener system  74  include the outwardly projecting brace  78  fixed to the mounting surface  32  of the casing  26  for engageable reception in the mounting recess  76  of the header  46 , but also an anchor  84  and a threaded fastener  86 . The anchor  84  has a base mounting flange  87  for attachment as by welding to the mounting surface  32  of the casing  26 . Also part of the anchor  84  is an upstanding mounting member  88  integral with the mounting flange  87  and containing an upwardly extending tapped bore  90  having first and second tapped regions  92 ,  94 , respectively, spaced by a smooth bore region  96 . 
     The threaded fastener  86  is received through the first and second through bores  80 ,  82 , respectively, ( FIG. 5 ) and is threadedly engaged with the anchor  84 . 
     Viewing  FIGS. 12A ,  12 B, and  12 C, the fastener  86  has a shank  98  and a head  100  and a threaded portion  102  of defined length adjacent its tip end. The lead-lock component  66  has a counter bore  104  ( FIGS. 5 and 6 ) axially aligned with the first through bore  82  for reception of the head  100  of the fastener  86 . The smooth bore region  96  ( FIG. 12D ) between the first and second tapped regions  92 ,  94  is longer than the defined length of the threaded portion  102  of the shank  98  of the fastener  86  such that as the fastener is tightened into engagement with the anchor, it is initially threaded through the first tapped region  92 , then is advanced through the smooth bore region  96 , then is threaded through the second tapped region  94  until the header  46  becomes firmly attached to the casing  26  and the lead-lock component  66  firmly clamps the proximal end portion  42  of the lead  40  to the header within the receptacle  52 . 
     With this construction, then, it can be understood that an active mechanical lock is achieved by a three-component assembly including the lead-lock component  66 , the anchor  84 , and the fastener  86 . The lead-lock component is molded of the same material as the pre-molded header, typically tecothane or other suitable biocompatible plastic material. The dovetail feature  70  fits into the corresponding dovetail cutout  72  in the header  46  to provide a tight axial and lateral alignment. The counter bored through bore  82  provides the opening for the fastener, aligning with the counter bored through hole  80  in the header  46  and the anchor  84 . By tightening the fastener  86  with one or more of the leads  40  installed, the lead-lock component  66  clamps down on each of the leads, locking them in place and sealing the receptacles  52 . 
     Also, as previously explained, the anchor  84  is designed so that the threaded portion  102  of the fastener  86  is captured within the anchor (see  FIGS. 12A ,  12 B,  12 C, and  12 D). The fastener is initially threaded through the first tapped region  92  on the top of the tapped bore  90 . Once through this tapped bore  90 , the fastener can engage the main, or second, tapped region  94  of the anchor to secure the lead-lock component  66  and header  46 . The fastener system  74  ensures that the fastener  86  cannot be easily disengaged from the anchor  84  using a torque wrench. An upward force on the fastener while turning it counterclockwise is needed to engage the first tapped region. Without this upward force, the fastener spins freely within the cavity of the smooth bore region  96 . The downward pressure required by a torque wrench ensures that the attending physician will not be able to inadvertently disassemble the fastener assembly  56 . 
     Also, as earlier noted, to fit the anchor design, the fastener has machined, protruding threads  102  with limited thread length to ensure it can spin freely in the anchor cavity of the smooth bore region  96 . 
     To assemble the components, with particular attention to  FIGS. 1 ,  2 ,  3 ,  7 , and  8 , the first step is the attachment of the anchor  84  and the brace  78  to the casing  26 . The anchor  84  is preferably welded along with the feedthrough terminal  36  during the welding of the case halves  28 ,  30 . Additional supports utilized to stabilize the header  46  on the casing  26  include the backfill port  38  and the feedthrough terminal  36  and additional bracing (not shown) may be welded above the feedthrough terminal after the case halves have been welded together. 
     After the anchor  84  and brace  78  have been welded to the mounting surface  32  of the casing  26 , the header is attached using the normal procedure: electrically connecting the header, followed by mechanically adhering the header using suitable medical adhesive ( FIG. 7 ). The final assembly step is the attachment of the dovetailed lead-lock component  66  onto the header ( FIG. 8 ). The dovetail feature  70  is slid into the corresponding dovetail cutout  72 , and the fastener  86  is inserted and engaged into the anchor  84 . The connector assembly is now completed, with the loosely tightened fastener adding header stability during shipping and initial period of the implantation procedure. 
     Finally, during implantation, the physician receives the medical device  20  with the fastener threads  102  captured in the anchor cavity of the smooth bore region  96  ( FIG. 12B ). The un-tightened fastener ensures that the physician can insert the leads without manipulation of the device. However, the encapsulation of the fastener within the anchor, along with the medical adhesive, will provide support for the header until it is fully secured. The physician inserts the leads  40 , testing to ensure a proper connection ( FIGS. 13 ,  14 ). The friction of the inserted leads within the receptacles  52  maintains the leads in the correct position. Then, the physician tightens the bolt using a torque wrench ( FIG. 15 ). This action compresses the leads between the lead-lock component  66  and the header  46 , resulting in a tight seal. This action also completes the mechanical attachment of the header to the casing, resulting in a solidly attached header. 
     This implantation procedure is preferred to the current method involving septums and the tightening of set-screws within the septum bores, for many reasons, including:
         ability to attach multiple leads using a single fastener;   improved access to the fastener to help visual verification of full engagement of a torque wrench to eliminate stripping of the head of the fastener; and   absence of septum use to reduce the possibility of damage to the medical device during implantation.
 
These improvements are achieved while retaining the familiar use of a torque wrench. The benefits will provide a quicker and more reliable implant procedure. An improved implant procedure means enhanced patient and physician satisfaction and fewer field returns. Combining these benefits with improved manufacturability results in a product with lower cost and higher sales potential.
       

     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.