Abstract:
A device-to-lead terminal connector for an implantable medical device is designed to positively lock the proximal lead terminal within a lead bore formed in the connector of the implantable device. Rather than using a conventional setscrew locking arrangement, first and second latching members are insertable through side ports in the device connector that intersect with the lead bore and that contain an elastomeric sleeve. When the latching members are squeezed together, they cooperate to expand the elastomeric sleeve against the proximal lead terminal to press it into intimate electrical and mechanical engagement with a contact in the lead bore of the device connector. The need for a tool to effect locking of the lead terminal in place is dispensed with.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     I. Field of the Invention  
         [0002]     This invention relates generally to implantable medical devices for stimulating target tissue, and more particularly to, implantable pulse generators connecting to one or more elongated, electrode bearing leads and incorporating a locking mechanism for retaining a proximal end of the said lead in electrical and mechanical engagement with the input/output contacts of the pulse generator.  
         [0003]     II. Discussion of the Prior Art  
         [0004]     Dating back to the late 1950&#39;s and early 1960&#39;s, advances have been made in the treatment of patients through the application of electrical stimulation to target tissue from a pulse generator that is surgically implanted, subcutaneously or submuscellarly, within a patient. A medical lead, comprising an elongated, flexible, insulating lead body and having surface electrodes thereon at a distal end and flexible conductors extending through the lead body for connecting the electrodes to a proximal terminal, is used to deliver electrical stimulation from the device to tissue abutting the electrodes and, in the case of cardiac rhythm management devices, to convey depolarization signals picked up by the electrodes back to the pulse generator.  
         [0005]     In a typical prior art design, the proximal terminal of the medical lead comprises a rigid, straight pin having one or more electrical contacts disposed along its length. The pulse generator, in turn, has a molded plastic or epoxy connecter affixed to a hermetically sealed housing containing a battery power supply and electronic circuitry for delivering pulses in accordance with control signals provided by a microprocessor-based controller. The input and output nodes of the electronic circuitry are connected by feed-through wires that pass through suitable seals and connect to contact rings in a terminal receiving bore formed in the connector. The contact rings in the connector are adapted to mate with the electrical contacts of the lead terminal when the lead terminal is properly inserted and locked in place in the connector.  
         [0006]     In the beginning, the implantable pulse generators were generally the size of a hockey puck. With improvements in circuit design and integrated circuitry, cardiac pacemakers and spinal cord stimulators are presently about the size of a silver dollar and about four times as thick. Efforts are still underway to further reduce the size and thickness of the implantable devices to render them less noticeable cosmetically. One design feature that has made it difficult to reduce the thickness dimension of such devices is the lead securing mechanism used in the header of the pulse generator.  
         [0007]     In a typical prior art design, the lead locking mechanism comprises a block or blocks of metal disposed in the connector and having a longitudinal bore(s) for receiving the proximal end portion of the lead&#39;s proximal terminal therein. A threaded, transversely-extending bore that intersects with the longitudinal bore is also provided in the block for receiving a set screw. Once the proximal lead terminal is inserted into the longitudinal bore of the block comprising the locking mechanism, the setscrew is tightened down against the terminal in one or more locations. This forces the terminal pin into intimate contact with the wall of the longitudinal bore. Such a locking device mandates a connector whose thickness must be sufficient to contain the block of the locking member, the setscrew and a seal plug assembly used to prevent ingress of bodily fluids through the threaded bore. Such a construction typically drives a connector thickness of at least 7 mm. The prior art design also requires the use of a torquing tool to advance the setscrew.  
         [0008]     It is also advantageous that one be able to replace a pulse generator without also having to replace the medical lead. Industry standards have been established for lead terminals in terms of their size (diameter and length), the location of contacts and location of insulation and seals. Therefore, any lead locking mechanism in a pulse generator should be such that it cooperates with a portion of the terminal that is in compliance with the standard, such as the proximal tip portion of the lead.  
         [0009]     The present invention offers a lead lock mechanism that allows for a thinner connector than has heretofore been possible to achieve using setscrew technology. Moreover, the lead lock mechanism of the present invention does not require any special tools to effect locking. Also, the lead lock mechanism of the present invention is designed to accommodate any medical leads conforming to a given international standard.  
       SUMMARY OF THE INVENTION  
       [0010]     The instant invention provides a tool-less connector for an implantable medical device. The device may include an implantable pulse generator contained within a hermetically sealed housing and that has a connector affixed to a predetermined surface of the housing. The header includes first and second side surfaces and a front surface. At least one longitudinally extending bore is formed inwardly from the front surface and is adapted to receive a proximal terminal of a medical lead therein. The proximal terminal of the lead has a conductive pin at a proximal end thereof. At least one electrical contact is disposed in the connector. It is positioned to cooperate with the conductive pin of the lead terminal when the proximal terminal of the lead is fully inserted into the longitudinal bore in the header. First and second side ports extend inwardly from the first and second side surfaces of the connector and the side ports intersect with the longitudinal bore at a location that is in general alignment with the electrical contact. An elastomeric tube is inserted through one of the first and second side ports. In accordance with the present invention, a first latch member is adapted to be inserted through the first side port. The first latch member includes a pair of bifurcated legs that extend into the lumen of the elastomeric tube. Completing the arrangement is a second latch member that is insertable through the second side port into the lumen of the elastomeric tube. The second latch member has a tapered wedge surface that is adapted to spread the bifurcated legs of the first latch member apart and thereby press the elastomeric tube against the conductive pin of the lead. The force applied is sufficient to hold that conductive pin in place against the electrical contact when the first and second latch members are squeezed together, such as by being pinched between the physician&#39;s thumb and forefinger. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts.  
         [0012]      FIG. 1  is a side elevation of a prior art implantable tissue-stimulating device over which the present invention is an improvement;  
         [0013]      FIG. 2  is an isometric view of an implantable tissue stimulator device incorporating the tool-less lead locking mechanism of the present invention in an exploded form;  
         [0014]      FIG. 3  is an isometric view of a first latch member shown in  FIG. 2 ;  
         [0015]      FIG. 4  is a side elevation of the first latch member of  FIG. 3 ;  
         [0016]      FIG. 5  is an isometric view of a second latch member shown in  FIG. 2 ; and  
         [0017]      FIG. 6  is a greatly enlarged transverse cross-section taken through the header of the implantable tissue stimulator incorporating the novel lead locking mechanism of the present invention illustrating the locking engagement of the first and second latching members. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Referring to  FIG. 1 , there is indicated generally by numeral  10  a prior art tissue stimulating device, such as a cardiac rhythm management device or a nerve stimulator. It is seen to comprise a hermetically sealed housing  12  which will typically contain a battery and electronic circuitry for producing pulses of preprogrammed amplitude, duration and repetition rate dictated by a microprocessor-based controller forming a part of the electronic circuit contained within the hermetically sealed housing  12 . The tissue-stimulating device  10  has a molded plastic connector  14  affixed to it and formed longitudinally in the connector is a lead receiving bore  16  into which the terminal portion  18  of a medical lead  20  is inserted.  
         [0019]     As is well known in the art, the lead  20  comprises an elongated, flexible, plastic lead body  22  having one or more electrodes, as at  24  and  26 , proximate its distal end. These electrodes are connected by elongated flexible conductors (not shown) that extend through the lead body  24  and are insulated from one another. The conductors connect to contacts as at  28  and  30 , disposed on the proximal terminal  18  of the lead. Sealing rings on the lead, as at  32  and  34 , interface with the wall of the bore  16  to prevent ingress of body fluids into the bore of the connector  14 .  
         [0020]     In accordance with the prior art, the implantable device  10  will include a locking mechanism in the connector for preventing disengagement of the contact areas  28  and  30  on the lead terminal  18  from mating contacts contained in the bore  16 . A typical prior art lead lock comprises a block of metal  36  having a longitudinal bore  38  formed therethrough, that bore being intersected by a transversely extending threaded bore  40 . Fitted into the threaded bore  40  is a setscrew  42 . An elastomeric plug is fitted into the bore  40 , again to prevent ingress of body fluids into the interior of the connector. At the time of implant, the setscrew is tightened using a torquing tool inserted through the elastomeric plug so as to tightly press the contact  30  on the lead against the wall of the bore  38 . Once the setscrew has been tightened down,  
         [0021]     It can be appreciated from what has thus far been described that this prior art approach mandates a relatively wide connector, i.e., about 8 mm, in order to accommodate the locking block  36  a predetermined number of threads of the setscrew and a seal plug. Moreover, as mentioned, the implanting physician must be provided with an appropriate torquing tool, such as an Allen wrench, for tightening the setscrew.  
         [0022]     Referring next to  FIG. 2 , there is shown an implantable tissue-stimulating device incorporating the novel lead locking mechanism of the present invention. Again, the pulse generator  50  includes a hermetically sealed housing  52  having a molded plastic connector  54  affixed to a planar surface  56  of the housing. The connector  54  has a front surface  58  and opposed side surfaces  60  and  62 . Formed inward from the front surface  58  are lead receiving bores  64  and  66  which, as in the prior art design, are adapted to receive the proximal terminal of a pair of medical leads therein.  
         [0023]     A first side port  68  extends inwardly from the side surface  60  of the connector to intersect with the longitudinal bores  64  and  66 . In a similar fashion, a second side port  70  ( FIG. 6 ) is formed inwardly of the side surface  62  of the connector to also intersect with the longitudinal bores  64  and  66 . An elastomeric tube or sleeve, preferably formed from silicon rubber and of one piece continuous construction is identified by numeral  72 . It is inserted through one of the first and second side ports to be centered crosswise in the connector and the tube  72  includes a lumen  74 . When the elastomeric tube is inserted in the manner shown in  FIG. 2 , its outer periphery does not appreciably occupy the bores  64  and  66 .  
         [0024]     With continued reference to  FIG. 2 , associated with each of the bores  64  and  66  is a metal contact. More particularly, a metal contact  76  is associated with the bore  66  and a metal contact  78  is provided in the bore  64 . Each of the contacts  76  and  78  has a semicircular recess formed therein whose radius is only slightly larger than the radius of the terminal contact  30  on the medical lead  20  ( FIG. 1 ). As such, upon insertion of the lead terminals into the longitudinal bores  64  and  66 , the contact  30  of the lead terminal inserted into the bore  64  will fit into the semicircular recess of the contact  78  and slightly depress the elastomeric sleeve  72 . Likewise, as a lead terminal is inserted into the bore  66 , its contact  30  will fit into the semicircular recess of the contact  76  while again slightly compressing the elastomeric sleeve  72 .  
         [0025]     To lock the leads in place against their respective contacts  76 - 78  and thereby prevent the leads from coming loose in the connector, a first latching member  80  is inserted into the lumen  74  from the side  60  of the connector and a second latching member  82  is inserted into the lumen  74  of the sleeve from the side  62 . Retention features on lumen  74 , latching members  80  and  82 , and on header  54  allow the device  50  to be shipped with  80  and  82  partially engaged. This minimizes any assembly by the physician. As will be explained in greater detail herein below, when the first and second latching members are squeezed together against the respective side surfaces  60  and  62 , the elastomeric sleeve  72  is radially expanded to thereby firmly press the contacts  30  of the medical lead against the respective contacts  76  and  78  located in the connector. This provides electrical connection between the lead and connector. Additionally, the resulting frictional forces are such that the lead terminal contacts are able to remain in place even when substantial pulling forces are applied to the leads. Moreover, the elastomeric sleeve  72  forms a seal with the latching members  80 ,  82  and connector  54  to prevent ingress of body fluids into the interior of the header.  
         [0026]     Referring next to  FIG. 3 , there is shown an isometric view of the first latching member  80  shown in  FIG. 2 . It is seen to comprise a molded plastic part having a head member  84  in the form of a oval disk with a slightly convex face  86  and generally flat base  88 . Integrally formed with the head member  84  and projecting generally perpendicular from the base  88  are legs  90  and  92 . The legs  90  and  92  have a somewhat flat outer surface  94  with radiused side edges  96  and  98 . Projecting outward from the surfaces  94  at the end of each of the legs is a protuberance  100  and  102 . Also rising from the surface  94  of each of the legs is a series of elongated knobs as at  104 . An aperture  106  is formed through the thickness dimension of the head  84  at the center thereof and longitudinally aligned with this aperture and projecting inwardly from each of the legs  90  and  92  are latches  108  and  110  ( FIG. 5 ).  
         [0027]     Turning next to  FIG. 5 , there is an isometric view of the second latching member  82 . It, too, comprises a generally oval-shaped head member  112  having a slightly convex outer face  114  and a generally flat interface  116 . Integrally molded with and projecting outwardly from the interface  116  is a wedge member  118  that tapers in thickness (from thicker to thinner) in progressing from the head  112  to the free ends of the wedge member  120 . Formed inwardly from the free end  120  is a cut-out that defines first and second arms  122  and  124  that are spaced from one another and positioned on either side of a center post  126 . Each of the arms  122  and  124  has a beveled surface  127  terminating in a shoulder  128  to form a barb. The cut-out in the wedge member  118  also defines inwardly projecting fingers  130  and  132  that are directed toward one another but separated by a gap. The fingers thereby result in the formation of latch surfaces  134  and  136 .  
         [0028]      FIG. 6  is a transverse cross-section view taken through the locking mechanism with the latching members  80  and  82  fully engaged and latched. it can be seen that the wedge-shaped center post  126  serves to spread the legs  90  and  92  of the latching member  80  apart, thus compressing the elastomeric sleeve  72  against the lead terminals  30  to bring the lead terminals  30  in firm engagement with the contacts  76  and  78 . The protuberances  100  and  102  of the latching member  80  engage a shoulder formed in the lumen  74  of the sleeve  72  and that the barbs on fingers  130  and  132  mate with latches  108  and  110  of the member  80 , inhibiting separation of the latching members. The two pieces  80  and  82  may then be dismayed by a physician by inserting a tool or common torque wrench through orifice  106  in member  80 . During insertion of the tool or torque wrench, tabs  130  and  132  are separated by the tool and flexing of legs  122  and  124 . With the locking tabs spread apart, further insertion of the tool brings it into contact with center post  126 , thus allowing the user to push out latching member  82  and disengage the latch. Barbs  128  and protuberances  100  and  102  prevent the latching mechanisms  80  and  82 , respectively, from coming out.  
         [0029]     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.