Abstract:
A modular header and method of fabricating same for making electrical connection between an array of feed-through pins extending through a wall of a hermetically sealed enclosure of an implantable medical device and lead connector receptacles within the header in which the header is fabricated using a pre-formed molded header module, together with a set or harness of interconnected flexible conductors incorporated and sealed by an overlayer of medical grade polymer material. The assembled header modular is capable of complete pre-testing prior to assembly onto an implantable medical device.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    I. Field of the Invention  
           [0002]    The present invention relates generally to implantable medical devices having external electrical connections and electrical feed-throughs and, more particularly, to the provision of a pre-built modular sub-assembly interconnect system for a header module such as are found in implantable pulse generators (IPG&#39;s) associated with cardiac rhythm management and other hermetically sealed implantable medical devices.  
           [0003]    II. Related Art  
           [0004]    Implantable medical devices of a class having electrical circuit components are well known in the medical field. These include cardiac rhythm management devices which commonly include a pacemaker unit which, in turn, includes sensing and control circuitry, together with a power supply, protectively housed in a hermetically sealed case or can in combination with one or more conductive electrical leads designed to connect to the patient&#39;s heart muscle tissue, the activity of which is to be sensed and stimulated. To maintain the integrity of the components in the sealed case, provision must be made for hermetically sealed passage of electrical conductors to the exterior for connection to the leads and ultimately to tissue of interest. This has been typically accomplished by using connector blocks and associated feed-through conductors located external to the IPG housing which, themselves, are typically placed within a sealed header structure of medical grade polymer material.  
           [0005]    While great strides have been made in improving the sophistication of the pacemaker devices themselves, the assembly and testing of the devices has remained relatively dependent on the skill of the assembly workers. Attempts have been made in the art to simplify the assembly process and to improve the acceptance rate of completed devices which undergo rigorous testing once assembled. In U.S. Pat. No. 5,282,841, for example, a ribbon conductor set or harness is provided to facilitate connection of feed-through terminal conductors to corresponding connector blocks in the header in which the individual ribbon conductors leads can be shaped to a three-dimensional geometry for ease of assembly. The assembled or fully interconnected unit is thereafter subjected to an over molding or coating step in which an entire epoxy head is cast over the assembly to encapsulate and seal the connecting components. That system, however, still depends on the skill of workers for assembly and requires extensive over molding. Furthermore, the electrical integrity of the unit cannot be tested until it is completely assembled.  
           [0006]    U.S. Pat. No. 6,205,358 B1 discloses a pre-formed header module in combination with a ribbon connector harness which is assembled and placed between feed-through pins on the side of the sealed enclosure and the header module and thereafter captured in an over molding or backfilling step using medical grade polymer. This system also suffers from similar drawbacks to those described above.  
         SUMMARY OF THE INVENTION  
         [0007]    By means of the present invention there is provided a module header sub-assembly for assembly to in connection with a hermetically sealed implantable medical device which solves many of the above problems and overcomes the drawbacks of previous versions of such devices. The present invention provides the desired electrical feed-through, but, unlike previous header units, the header of the present invention is a sufficiently complete sub-assembly such that it can be tested for functional integrity prior to assembly onto the hermetically sealed medical device. The present header also facilitates assembly and reduces the amount of necessary backfill.  
           [0008]    The modular header sub-assembly of the present invention eliminates the routing of individual feed-through wires to the respective connector blocks by providing an array of metallic conductors incorporated into the sub-assembly itself and molding in either the primary, secondary or even a tertiary mold operation. In this manner, one end of each of the flexed conductors is connected to the appropriate connector block and the other end aligned with the remaining traces to be connected to corresponding feed-through pins in the hermetically sealed IPG unit. In this manner, an array of aligned connectors are arranged to match an array of aligned feed-through pins such that connection between them can be made through a small window readily backfilled after connecting and welding operations. This enables additional site connectors to be implemented while maintaining an actually decreasing header size when compared to conventional wire routings. The flex or trace design further allows all weld locations to be in a minimal number of weld access planes and therefore readily adaptable to process automation. Furthermore, pre-fabricated wire terminations provide repeatable attached locations on conductor sites making feasible alternate welding techniques such as programmable micro-laser welding.  
           [0009]    The reduction of the volume required to be backfilled after welding operations also eliminates concerns with respect to the sealing integrity of the backfill which is currently dependent on the technique and skill of the operator in the subsequent inspection. The pre-fabricated wire terminations further eliminates a major manufacturing step involved in routing and backfilling of the wire channels in the header and further allows testing of the integrity of each conductor in the header prior to assembly of the header to the hermetically sealed device. Since the flex/conductor system can be an integral part of the header, mold/sealing operations requiring high pressures are now possible since the header does not have to be connected to the device prior to these primary or secondary mold/seal operations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    In the drawings:  
         [0011]    [0011]FIG. 1 is a schematic representation of an implantable medical device in the form of an IPG of a class suitable for including the header interconnect system of the present invention;  
         [0012]    [0012]FIG. 2 is a greatly enlarged perspective view of a primary molding of a pre-formed header module showing pre-formed patterned conductor channels and including connector blocks adapted to receive a corresponding connected array system or harness of flexible connector in accordance with the present invention;  
         [0013]    [0013]FIG. 3 is a perspective view similar to that of FIG. 2 as it is being addressed and fitted with a pre-formed harness of flexible conductors in accordance with the invention;  
         [0014]    [0014]FIG. 4 depicts the pre-formed header module of FIGS. 2 and 3 with the connector system assembled in place;  
         [0015]    [0015]FIG. 5A is a view of the pre-formed header module of FIG. 4 after the application of a secondary overlayer of medical grade polymer;  
         [0016]    [0016]FIG. 5B is a view similar to FIG. 5A with the header module rotated to better depict the array of connecting terminals adapted to receive the feed-through pins of a corresponding hermetically sealed device;  
         [0017]    FIGS.  6 - 8  depict views of assembly steps characteristic of an alternative embodiment of an inline connector design using a side connection system in the modular header; and  
         [0018]    [0018]FIG. 9 shows an assembled device with parts cut away exposing the connection and greatly enlarged fragment views of a typical connection mode in accordance with the assembly of the header of the invention onto the hermetically sealed implantable unit. 
     
    
     DETAILED DESCRIPTION  
       [0019]    It will be appreciated that the present invention enables the header to be built as a complete modular sub-assembly capable of being tested for circuit integrity prior to attachment to the feed-through pins of the hermetically sealed pacer, other IPG or other implanted unit. The present invention also greatly simplifies the connection process and reduces the amount of backfilling required to complete the header/hermetically sealed IPG assembly. While the detailed description which follows is limited to one or two embodiments, it will also be understood that these are intended as examples only and are not intended to limit the scope of the inventive concept in any manner.  
         [0020]    [0020]FIG. 1 depicts a simplified schematic view of an implantable medical device  20  of a class suitable for utilizing the header of the present invention including a pre-formed, pre-assembled header module  22  attached to a hermetically sealed enclosure  24 . A plurality of leads  26 , which typically include atrial and ventricle pacing/sensing leads, for example, are connected to the header using elongated lead connectors  28  and receptacles as at  30 . The leads are further connected to feed-throughs using feed-through pins extending through the hermetically sealed enclosure  24 . These are beneath the backfilled surface and so are not shown in the figure.  
         [0021]    Generally, the hermetically sealed enclosure  24  contains a power source in the form of an electrochemical cell which may be a lithium battery, control and sensing circuitry which controls the operation of the device and senses and records data according to programmed instructions which may be fixed or timed variable and microprocessor controlled. Telemetry transceiver system is provided to enable the device to communicate with an external programmer.  
         [0022]    It will be appreciated that particular electronic features may vary considerably from device to device and the practice of the present invention is not dependent or based on any particular embodiment of such a unit, but is based on a common need for pass-through connections.  
         [0023]    [0023]FIG. 2 is a greatly enlarged perspective view of a pre-formed molded header module  40  having a plurality of elongated external lead connector receptacles as at  42 . The pre-formed primary header module is provided with a plurality of recessed conductor channels as at  44  and  46  which connect with corresponding connector blocks as at  48  and  50 . The lead connector receptacles  42  also connect with corresponding connector blocks  48  and  50  through internal passages (not shown) in a well known manner.  
         [0024]    As shown in FIG. 3, the pre-formed flex conductor system or harness  51  is provided with leads or conductors represented by even reference characters  52  through  66  configured to fit into the corresponding recessed channels  44 ,  46  and to have corresponding free ends designed to attach to corresponding connector block as at  48  or  50 , or otherwise (not shown) each flexible connector further having a second end fixed in spaced relation along a removable common member  68  provided for production of the harness and ease of assembly onto the primary molded module  40 .  
         [0025]    [0025]FIG. 4 depicts the molded module  40  of FIGS. 2 and 3 with the flexible conductors, which may be constructed of a conducting foil, or the like, situated in place in the corresponding relevant receiving channels  44 ,  46 . The material of the flexible conductors  52 - 66  is one easily deformed to fit the relevant recessed channel  44 ,  46  yet is sufficiently rugged to withstand the manufacture, assembly and a subsequent over-molding operation while remaining in tact. The material conductive of the traces or harness is preferably a stainless steel, but other bio-compatible materials which adapt themselves to the manufacturing and assembly steps satisfactorily in accordance with the invention may be used.  
         [0026]    [0026]FIGS. 5A and 5B illustrate the pre-molded or primary molded header modules  40  of FIGS.  2 - 4  after application and routing of the conductive traces in the channels  44 ,  46  and connection of them to the corresponding connector blocks, some of which are illustrated at  48  and  50 , and after a secondary molding or first over-molding step has been performed and the common member  68  has been removed. The over-molding layer  70  seals the conductors within the modular header exposing only the external connection sites as at  42 ,  48  and  50  and an array of terminal spade connectors  72  adapted to be connected to corresponding feed-through pin  74  shown in FIG. 9. As shown particularly in the enlarged fragment views of FIG. 9, the spade connectors  72  can readily and automatically be crimped about feed-through pins  74  and the connection welded as at  76 .  
         [0027]    FIGS.  6 - 8  depict an alternative embodiment utilizing an inline external connector configuration including a pre-molded header module  80  having an array of inline external connection openings as at  82  adapted to receive external leads (not shown) in the usual well known manner. An array of possible side co-planar terminals or block connection sites as at  84  are provided and these are addressed by a pre-formed flex conductor system or harness  86  containing an array of leads or traces as at  88  not unlike those previously discussed and connected for manufacturing and assembly purposes by one or more stabilizing members as at  90 , as shown in FIG. 7. In FIG. 7, the free ends of the traces  88  are shown in place on the side of module  80  and connected to the sites  84 . Here, as in the case of the embodiment earlier described, connection is readily achieved by an assembler. These traces also are provided with spade connectors  72 .  
         [0028]    [0028]FIG. 8 depicts the modular header  80  after the application of an overlayer  92  of medical grade polymer on the connection side which seals in the conductors  88  leaving only the array of terminal spade connectors  72  conveniently configured in an inline arrangement corresponding feed-through terminal pins  74  as depicted in FIG. 9 in the manner previously described.  
         [0029]    Note that the remaining recess volume  75  in FIGS. 5A and 5B and  94  in FIG. 8 is quite small in relation to the size of the header module  40  or  80  such that the amount of backfilling after final connection to fill out and streamline the structure remains relatively minor.  
         [0030]    The embodiments, once assembled, can easily be tested as by plugging the header module into a test stand and attaching any desired external leads. The use of the harness in combination with predetermined separate paths for the conductors precludes shorts and eliminates the need for using insulated conductors.  
         [0031]    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.