Abstract:
The housing of an implantable cardiac device is selectively made active or passive by an external connector member, such as a shorting plug or lead connector inserted in its header. Advantageously, the header, the shorting plug, and the lead connector all are constructed and arranged to conform to a pre-selected standard in the industry, such as IS-4. The header includes an access hole that is provided with several housing connector elements connected either to the conductive surface or to an internal electrical circuit. The external connector members each have a shaft with external conductor elements. Each shaft includes conductors such as wires. The housing is made active by inserting into the header an external connector element having two of its external connector elements connected by a shorting wire.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   This invention pertains to a cardiac system with an implantable housing that can be selectively rendered to be active or passive. More particularly, the invention describes a cardiac system including housing with a header, a plug and/or a connector with a lead terminating with one or more electrodes and adapted to be inserted into the housing. The structure of the plug or connector defines whether the housing is active or passive. 
   2. Description of the Prior Art 
   Implantable cardiac devices are used extensively to provide therapy to patients with various cardiac problems. The therapy from these types of devices usually consists of the application of electrical stimulation pulses to cardiac tissues. Typically, each such device typically consists of sensing circuitry used to sense intrinsic cardiac signals, generating circuitry used to generate electrical stimulation signals, control circuitry used to control the operation of the device, and various auxiliary circuitry used to perform other functions, such as telemetry, data logging, etc. This circuitry is contained in a housing suitable for implantation. The housing further includes a header used to connect the circuitry contained in the housing to one or more leads which extend into, or at least in the vicinity of, the patient&#39;s heart and terminate in one or more electrodes. Various header structures are disclosed in U.S. Pat. Nos. 5,545,189; 5,620,477; 5,899,930; 5,906,634; 6,167,314; 6,208,900; and 6,330,477, all incorporated herein by reference. 
   At least two electrodes are required for sensing, stimulation and some other functions of the device. In many instances, for example, when the housing is implanted pectorally, it is advantageous to have the housing act as one of the electrodes. In these instances, typically at least a portion of the housing&#39;s outer surface is exposed and is composed of a conductive material. This portion is then electrically connected to the circuitry within the housing and plays an active part in the operation of the circuitry (i.e., is used to provide stimulation, sensing and/or other functions). Such a housing is often referred to as an ‘active’ housing. 
   However, an active housing may not be desirable for all locations (e.g., abdominal) because it may be too distant from the heart to be effective, or because it may be, in some instances, adjacent to a muscle that is adversely affected by electrical stimulation. 
   A housing could be constructed from the start as an active or passive housing by providing an appropriate electrical link between the housing surface and its circuitry. However, this approach is impractical if the decision as to which kind of housing to use is made at the last minute, i.e., just prior to implantation. Since most cardiac devices are programmable, an electrically controlled switch could be used as the link and the decision as to whether to make a housing active or not could be another programming parameter. However, such electrically controlled switches use up space within the housing and add cost and complexity to the electrical circuitry. 
   U.S. Pat. No. 5,620,477 discloses a housing  12  that can be rendered selectively active and passive using a mechanical element. This housing makes use of a special header having two connector blocks  34 ,  36 . Connector block  34  is connected to an internal circuit while connector block  36  is connected to the conductive surface  16 . The housing  12  is rendered active by a plug inserted into the header and having a long connector pin  54  which is positively attached to the connector blocks  34 ,  36 , thereby effectively shorting the two connector blocks to each other. Alternatively, a lead connector is provided with its own connector pin  54 . The problem with this approach is that it requires a special design for both the housing header and the plug or lead connector. Thus, this housing cannot be used with standard multi-lead connectors conforming to specific standards, such as an IS-4 quadripolar lead connector. 
   SUMMARY OF THE INVENTION 
   The present invention provides a novel implantable cardiac housing that overcomes the deficiencies of such existing housings. More particularly, an implantable cardiac device is disclosed having a housing with a header. The header is structured to accept an external connector member such as a plug or a multiple conductor lead connector conforming to a pre-selected standard such as IS-4. The header includes a plurality of housing connector elements that come into contact with the external connector member. One of these housing connector elements is connected to a conductive portion of the housing. Another of the housing connector elements is connected to an internal electrical circuit disposed within the housing. 
   Each of the external connector members has a shaft with a plurality of external connector elements. The external connector elements are wired in a manner that connects distant electrodes to the internal electrical circuit. In addition, in certain embodiments of the present invention, the external connecting elements include a shorting wire to connect two housing connector elements, thereby rendering the housing active. Alternatively, If the housing is to remain passive, no shorting wire is provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side view of the housing of a cardiac device and a shorting plug constructed in accordance to this invention; 
       FIG. 2  shows a partial cross-sectional of the shorting plug of  FIG. 1 ; 
       FIG. 3  shows a partial cross-sectional view of a first lead connector similar to the connector of the shorting plug of  FIG. 2 ; 
       FIG. 4  shows a partial cross-sectional view of a second lead connector used for an passive housing; and 
       FIG. 5  shows a partial cross-sectional view of a third lead connector in which the housing is active and is electrically connected to a remote electrode. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, a cardiac system  10  constructed in accordance with this invention includes a housing  12  with an external surface  14 . A portion  16  of the external surface  14  is made of an electrically conductive material, such as stainless steel, a titanium alloy, or other electrically conductive materials known in the art. Alternatively, the entire surface of the housing  10  could be made conductive. The housing  12  holds a power supply (not shown) and various electrical circuits  17  used to sense intrinsic cardiac signals, generate stimulation pulses and perform other similar conventional functions. These electrical circuits are provided on one or more circuit boards  18 . The housing  12  is hermetically sealed and includes a header  20  made of an epoxy or other similar non-conductive material. 
   The header  20  is formed with one or more access holes  22  to provide a means of interfacing the housing  12  with one or more external connector members. Examples of external connector members include a shorting plug  30  and a lead connector  40 . Furthermore, the header  20  is formed to enable these external connector members to be electrically coupled to the circuits contained within the housing  12 . 
   Each access hole  22  may be used to provide one or more connections. More particularly, several housing connector elements  24 A,  24 B,  24 C,  24 D are disposed axially along the access hole  22 . These housing connector elements may comprise contacting blades, springs, screws or any other similar conventional connecting mechanisms known in the art. Housing connector elements  24 A,  24 B,  24 C are electrically coupled to one of the circuits  17  on board  18 . Housing connector element  24 D is electrically coupled to the conductive portion  16  of the housing  12 . 
   The header  20  is arranged and constructed to electrically couple the external connector members (such as a shorting plug  30  or a lead connector  40  for a multi-electrode lead) to the electrical circuits  17  when the external connector members are inserted into the access hole  22 . 
   The shorting plug  30  includes a head  32  and a shaft  34 . The head  32  portion of the shorting plug  30  is used to hold and manipulate the shorting plug  30  during its insertion into the access hole  22 . The shaft  34  portion of the shorting plug  30  is constructed in accordance with standard guidelines set for multi-electrode connectors, such as IS-4. 
   The external connector elements  36 A,  36 B,  36 C,  36 D are disposed about the shaft  34  of the shorting plug  30 . In the configuration shown in  FIG. 1 , the connecting element  36 A forms the tip of the shaft  34 , while the connector elements  36 B,  36 C,  36 D are ring-shaped and are axially spaced from the shaft tip. The external connector elements  36 A– 36 D are formed of a conductive biocompatible material. The regions between the connector elements on the shaft  34 , however, are made of an insulating or non-conductive material. 
   When the shaft of the external connecting member (in this case, the shorting plug  30 ) is properly positioned within the access hole  22 , the external connector elements  36 A– 36 D couple to the housing connector element  24 A– 24 D located within the header  20 . This subsequent union provides an electrical connection between the external connector member and the cardiac system  10 . 
   The lead connector  40  similarly has a proximal end consisting of a shaft  44 . Disposed along the proximal end of the shaft  44  are external connector elements  46 A,  46 B,  46 C,  46 D. External connector elements  46 A– 46 D are constructed and function to the external connector elements  36 A– 36 D described with reference to the shorting plug  30 . Lead connector  40  is attached to a lead  42  which includes a plurality of conductors  48 . The plurality of conductors  48  terminate and are connected distally to an electrode  50 . Proximally, the plurality of conductors  48  are connected to one of the external connector elements  46 A– 46 D. 
   In one embodiment, the lead  42  is implanted with the electrodes  50  disposed in the patient&#39;s cardiac chambers. In an alternative embodiment, the lead is implanted with the electrodes  50  disposed subcutaneously within the patient&#39;s anatomy. Similarly, particular embodiments of the present invention include a combination of electrodes  50  disposed subcutaneously around the patient&#39;s thorax and transvenously within the patient&#39;s heart. 
     FIG. 2  shows a cross-sectional partial view of the shaft of an external connecting member. In particular,  FIG. 2  depicts a portion of the shaft  34  of the shorting plug  30 . The shaft portion of the external connecting members is constructed to permit connections between external connector elements. For example, as depicted in  FIG. 2 , a shorting element  35  may be provided between external connector elements  36 C and  36 D. This design flexibility, in particular the electrical interactions between external connector elements, permits external connecting members to be used in mechanically programming a cardiac system  10  to have a housing that is active or passive. 
   In illustration, when the shorting plug  30  is fully inserted into the access hole  22 , the external connector elements  36 A– 36 D come into electrical contact with the respective housing connector elements  24 A– 24 D contained within the access hole  22 . If the housing connector elements  24 C and  24 D are coupled to the circuit board  18  and to the conductive portion  16  of the housing  12  respectively, when the shorting plug  30  depicted in  FIG. 2  is inserted into the access hole  22 , the conductive portion  16  of the housing  12  is connected to the board  18 , thereby rendering the housing  12  active. 
   External connecting members may be used to mechanically program a cardiac system  10  having a single access hole  22 , or alternatively, having multiple access holes. When the cardiac system  10  possesses a single access hole  22 , a lead connector  40  is utilized to mechanically program the cardiac system  10  as active or passive. Alternatively, when the cardiac system includes multiple access holes  22 , a combination of shorting plugs  30  and lead connectors  40  can be utilized to mechanically program the cardiac system  10  to a desired configuration. 
   In a cardiac system  10  having two access holes  22 , there are at least five different combinations in which to arrange the external connecting members to mechanically program the cardiac system  10  as active or passive. One grouping of combinations utilizes two lead connectors  40 . In this grouping, both lead connectors  40  may be constructed to mechanically render the cardiac system  10  passive. Alternatively, one lead connector  40  may be constructed to render a passive cardiac system  10 , whereas the second lead connector  40  may be constructed for rendering the cardiac system  10  active. The result of such a lead connector  40  arrangement would be an active cardiac system  10  having two distally positioned electrodes. 
   A second grouping utilizes a single lead connector  40  and a single shorting plug  30 . In this grouping, both lead external connecting members may be constructed for mechanically rendering a passive cardiac system  10 . Alternatively, the lead connector  40  may be constructed for rendering the cardiac system  10  passive, whereas the shorting plug  30  may be constructed to render the cardiac system  10  active. Another conceivable arrangement is to have the lead connector  40  render the cardiac system  10  active and the shorting plug  30  render the cardiac system  10  passive. Again, in either of the last two examples, the result of such external connecting member arrangements would be an active cardiac system  10  having a distally positioned electrode. 
     FIGS. 2–5  further illustrate how within a single external connecting member, the interactions between external connecting elements may be configured to provide an array of mechanical programming for the cardiac system  10 . 
     FIG. 3  shows the structure of the lead connection  40  if the housing  12  is to be an active housing. As shown in this Figure, conductors  48  are attached to external connector elements  46 A,  46 B and a shorting wire  45  is provided between external connector elements  46 C and  46 D. In this manner, the circuit board  18  is connected to the housing portion  16 . 
     FIG. 4  shows alternative construction for a lead connection  40 . As seen in this Figure, the external connector elements  46 A,  46 B,  46 C are all connected to a respective conductor  48  while the external connection element  46 D is not connected to a conductor  48 . As a result, when the lead connector  40 ′ is inserted into the housing  12 , the housing  12  is passive. 
     FIG. 5  shows yet another alternate construction for a lead connector  40 ″. In this embodiment the external connector elements  46 C,  46 D are connected to each other by a wire  45  and to a conductor  48 . This arrangement may be advantageous if multiple current paths are desired. 
   While the invention has been described with reference to several particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles of the invention. Accordingly, the embodiments described in particular should be considered as exemplary, not limiting, with respect to the following claims.