Abstract:
A pacemaker has a metallic housing with a connector arrangement adapted to receive a contact plug, with contact surfaces, at the proximal end of an electrode lead. The connector arrangement includes a metallic tubular member with opposite ends which are welded or bonded to respective openings in the metallic housing. The metallic tubular member is substantially continuous along its length between the opposite ends. All components which are needed for making electrical contact with the contact surfaces of the lead are contained within the interior of the metallic tubular member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to pacer housings and more particularly to those parts of the housing intended for connection to the electrode leads. 
   2. Description of the Prior Art 
   Implantable pacers normally have a pacer housing (also called can) containing electronic circuitry and a unit for electric power as well as different electrodes which are connected to the interior parts in the pacer housing and which are to be implanted in or in the vicinity of the heart. The electrodes are connected to the pacer by means of leads. The internal parts of the pacers have to be well protected against the internal environment, especially the body fluids in the body for a long period of time, which places strict requirements on all entries into the interior of the can and especially on the connections of the leads to the housing. At the same time it should be possible to disconnect the pacer from the implanted leads for replacement or servicing of the pacer. The connective parts of the pacer and the leads have largely been standardized so as to encompass a relatively deep female socket having a number of contact surfaces whereas the leads are provided with a male part comprising one or several corresponding peripheral, generally circular contact surfaces. 
   At present the connective part of the pacer housing containing the female socket is made of a transparent material, normally of epoxy resin, which is molded onto the housing and onto contacts extending outwardly from the housing. The male part of the leads is normally locked by means of set screws, although other fastening means have been suggested. The positioning and alignment of the different contact surfaces and of the fastening means or metallic threads for the set screws prior to the molding of the connective part is, however, complicated and the delay in the manufacturing process incurred by the curing of the epoxy resin is considerable. 
   It would thus be desirable if the molding procedure could be dispensed with. 
   It has been discussed that these complexities could be avoided by designing the pacer with a socket located inside the metal housing. This kind of sockets, sometimes termed “black holes”, are not used at present. 
   U.S. Pat. No. 4,934,366 and U.S. Pat. No. 5,324,311, both of which are incorporated by reference, describe two interior sockets or black holes for pacers. Both designs employ a tubular member formed by a number of longitudinally alternating sections respectively made of metal and insulating ceramics. An end section of metal can be welded or bonded to an opening in the pacer housing by means of a flange. The use of different materials, however, sets high standards in regard to precision and durability of the components as well as in the assembly procedure thereof. This is especially important since the interior sockets must meet very high standards regarding the integrity of the interior of the pacer housing during long times of implantation in a demanding environment. The manufacture of these known sockets thus is relatively complicated. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to avoid the aforementioned molding procedure and to simplify the design of an interior socket of a pacer connector while still meeting the required high standards for a pacer housing. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a conventional pacer housing with a transparent, molded connective part. 
       FIG. 2  shows a known lead with a male connective part. 
       FIGS. 3-6  show a preferred embodiment of the connective part in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a conventional pacer housing  1  having a  15  molded, transparent connective part  2 . The connective part  2  includes a female socket  3 . The inner end of the socket  3  is provided with a longitudinal bore  7  having a relatively small diameter. The bore  7  is provided with a contact surface  4  adjacent to which threads  5  for a set or lock screw are located in a bore  6  oriented orthogonally relative to the female socket. The housing is hermetically sealed also in relation to the molded part  2  and the contact between the interior electronics and the contact surface  4  is achieved by means of a feed-through. The feed-through is formed by a ceramic plug, typically made of alumina, into which one or more leads have been soldered. This lead is bonded (e.g. ultrasonically welded) to the electronics and to the contact surface  4 . The ceramic plug is soldered or brazed by means of gold into a sleeve made of titanium. This operation may be made at any time before the assembly of the pacer housing. The sleeve is welded into an opening in the housing in a sealing manner during the assembly of the pacer housing that normally consists of two halves. Before the connective part is molded onto the housing, these halves are welded together and sealed. 
     FIG. 2  illustrates a lead  15  comprising a proximal connecting plug  10  and a distal, transvenous, intracardial electrode  16  as well as an attachment arrangement  17  for suturing the proximal end of the lead in the body of the patient. The connecting plug  10  is designed to be received in the socket  3  and the end thereof is provided with a longitudinally projecting contact pin  11  as well as a cylindrical body  17  provided with sealing rings  12 ,  13 ,  14  intended to engage and seal against the corresponding inner cylindrical surface of the female socket  3 . The shape of the pin  11  corresponds to the shape of the bore  7 . When the plug  10  is inserted into the socket  3  the pin  11  engages the contact surface  4  and the set-screw in the bore  6  can be tightened against the pin  11  in order to securely lock the plug  10  in the socket  3 . The complexities involved in holding the bores, contact surfaces and threads in position and keeping them open and free from the molding material during the molding process are evident. 
   For simplicity, the above known device has  20  been illustrated as unipolar. A bipolar embodiment naturally will be more complex to manufacture. The preferred embodiments of the invention described below will relate to bipolar embodiments. 
     FIGS. 3-5  show a preferred embodiment of the invention comprising a tubular member  20 . For clarity, the reference signs not repeated throughout all drawings. 
   The tubular member  20  is a tube  21  with two open ends  22 ,  23 . Each end is to be welded into a respective opening in the pacer housing. The tube  21  is made of the same metal as the pacer housing, in this case titanium. The mid-section of the tube  21  is provided with two relatively small lateral openings  24 ,  25 . The openings  24 ,  25  are sealed by means of a ceramic plug  26  fitting snugly in the tube  21  and soldered with gold against the inside of the tube  21 . Two contact rings  27 ,  28  plug overlapping the lateral openings. The ceramic plug also originally could consist of several separate parts with the contact rings held between and soldered to these parts, thus uniting the parts of the plug to a unitary unit. The soldered junctions then would form an efficient seal. 
   It should be noted that the size of the openings  24 ,  25  which are necessary to allow the bonding of the leads to the parts of the contact rings accessible through the openings  24 ,  25  and  31 ,  32  is small, in relation to the entire circumference and to the length of the tube  21 . The openings thus do not affect the structural integrity of the tube  21 . The contact rings  27 ,  28 , moreover, overlap the openings and are bonded thereto by means of the intermediate layer of ceramics, in this way strengthening the area in which said openings are located. 
   Typical dimensions for a tube intended to house a standard IS-1 male connector are for instance an inner diameter of 20 mm, a wall thickness of 0.3 mm (i.e. the same as the thickness of typical pacer housing walls) and a diameter of the holes  24 ,  25  of about 2 mm. A minimum area of about 4 mm 2  is necessary for the equipment presently used for bonding leads to metallic surfaces. The length of the tube  21  is of course adapted to the specific housing into which it is to be placed, but might typically be about 25 mm. 
   These dimensions of course can be varied as long as the tube remains structurally intact, i.e. as long as the tube has a strength and rigidity that is sufficient to prevent loads, including thermal stresses, on the housing and/or the connector to be transferred as tensile forces to the ceramic parts. Of course, low tensile forces not exceeding the tensile strength of the ceramic could be accepted. Since there are standards regarding the loads a pacer housing and connector should be able to withstand and regarding the dimensions only would involve standard stress calculations and dimensioning well within the scope of the man in the art. It should be noted that this also could take the degree of soldering between ceramic plug and tube into account, since this would determine the extent to which tube and ceramic would function as a composite without going outside the ordinary skill of the man skilled in the art. 
   The ceramic plug is provided with an interior bore  10  corresponding to the shape of the male connector in the same way as the molded prior art female connector described above and thus includes interior sealing surfaces  52 ,  53  for engagement with the sealing rings on the male connector. 
   A part  30 ,  31  of the inside of the contact rings is not covered with the ceramic material. In this way two inner circumferential grooves are obtained in the inner bore of the ceramic plug. The bottom of the grooves consists of the metal in the contact rings. Two openings  32 ,  33  are also provided in the outer surface of the ceramic plug that may be made to coincide with the lateral openings  24 ,  25  in the tube wall. These openings give access to the contact rings  27 ,  28  when the ceramic plug has been mounted correctly in the tube  21 . 
   Thus, when the ceramic plug  26  has been soldered or bonded into place, the openings  24 ,  25  will be completely sealed by the plug  26  although allowing electrical connection to the interior of the tube  21  via the contact rings  27 ,  28 . 
   To this extent the tubular member  20  can be manufactured in advance as desired. 
   Both ends of the prefabricated tube  21  can be welded to the pacer housing and the housing parts can be welded together after the connection of interior leads from the interior electronics to the contact rings  27 ,  28 , should this be desired. 
   The remaining parts, i.e. the structures for achieving the contact between the contact rings and the contact surfaces on the male connector part on the lead, and for locking or fixating the male connector part in the socket, can easily be inserted afterwards. This means, for instance, that these parts would not interfere with the standard helium-based procedures for testing the housing with connector for leaks or that these parts would not be affected by the leak testing procedure. 
     FIG. 3  shows the main components of the tubular member  20 , the tube  21  with openings  24 ,  25 , the ceramic plug  26 , a fixation part  40  and two circular spring contacts  57 ,  58 . The spring contacts are similar to the spring contacts used in U.S. Pat. No. 4,934,366. 
   The fixation part  40 , shown in more detail in  FIG. 4 , is designed in the same way as the lead locking device disclosed in U.S. Pat. No. 4,784,141, incorporated herein by reference, and has a hollow cylindrical part  41  fitting into the end of the tube  21 . The inner end of the cylindrical part  41  is provided with an interior flange  42  with an inner conical surface  43 . The locking device further comprises a resilient locking ring  44  located adjacent the flange  42 . One side of the ring has a conical surface  45  that is complementary to the conical surface  43 . The other side of the ring also has a conical surface  46  that is complementary to a conical surface  47  on a plug  48  provided with exterior threads  49  fitting into interior threads  50  on the inside of the cylindrical part  41 . The outside of the plug  48  is provided with an O-ring  51  that is located in a peripheral groove  52  and sealingly engages the inside of the cylindrical part  41 . When the plug  48  is screwed into the cylindrical part  41 , the resilient ring  44  will be forced inwardly into contact with the contact pin of the male connector part by means of the interaction of the different conical surfaces, thus locking the contact pin inside the tube  21 . 
   The tube  21  preferably is of the same material as the pacer housing, which normally is made of titanium. The ceramic plug may for instance be made of alumina, Al 2 O 3 , and the contact rings may for instance be made of stainless steel or of titanium. 
   In the above embodiment the ceramic plug has been illustrated as extending from the end of the tube and past the openings in the side of the tube. It is, however, only necessary that the ceramic plug cover the openings. The remaining part can be designed as a separate part inserted and bonded to the tube after the assembly of the pacer housing in a similar way as the fixation part  40 . 
     FIG. 4  shows the tube  21  with all component parts mounted. 
     FIG. 5  shows how the tube  21  has been mounted in a pacer housing  60  and welded to openings  61 ,  62  in the openings via flanges located on the outside of the tube ends.  FIG. 5  also shows a male connector plug  110  inserted in the tubular member. The plug has a contact pin  111 , a contact surface  118  and four sealing rings  112 ,  113 ,  114 ,  117 . The resilient ring  44  grips the pin  111  and the sealing rings  112 - 114 ,  117  are in engagement with the interior sealing surfaces  52 ,  53 . 
   The connector can be achieved in a simple way compared  30  with the known molded connector means. 
   As mentioned above, the ceramic part can be soldered into the tube  21  in advance by similar methods as used when obtaining the feed-through in the prior art. The tube  21  then is placed in the openings in one of the pacer housing halves and conductors  55 ,  56  are bonded (typically by means of the electronic board  54  and to the parts of the contact rings that are accessible via the openings in the tube. The housing halves then are assembled and the two halves and the ends of the tube are welded together by means of a laser beam to form a sealed unit. This unit then is tested for leakage, for instance by means of standard helium-based procedures. It should be noted that no other kinds of work operations than those already used in the prior art are necessary. 
   The pacer then is finished by slipping the resilient spring contacts into the respective interior grooves in the ceramic plug and by inserting and bonding the lead locking mechanism into place in the corresponding open end of the tube. 
   The new connective part thus is very simple to manufacture and to mount in the pacer housing. The welding and sealing of the housing only includes the additional step of welding the ends of the tube to the edges of the openings in the housing, which is done in the same operation as the welding of the two housing halves. After the welding operation, no further operations are necessary, except for the simple insertion of contact rings and lead locking mechanism. 
   Since the tube after the welding operation in principle forms an integral, load-carrying part of the pacer housing, a high degree of tightness and integrity is obtained. The tube will ensure a high strength and a high durability of the connective part, whilst the ceramic plug will ensure a high degree of tightness in view of the large contact area between ceramic plug and tube that can used for soldering, i.e. sealing. 
   Although a pacer housing with one tubular member has been  35  illustrated, the housing of course can contain several members. The housing also wholly or partly could be made of openings holding the tube  21  are of metal or of a material allowing a bond of sufficient strength to the metal tube  21 . Furthermore, although the tube  21  has been illustrated as having a circular cross-section, other cross-sections are possible. 
   An important advantage with the connector according to the invention is that the connecting pin  111  on the end of the lead can be reached from the outside through the end of the tube containing the lead locking mechanism. This will facilitate the removal of the male connector from the female socket since the pin  11  can be pushed outwardly through said second end by means of a tool if the male connector proves to be difficult to pull out. In the above, preferred embodiment it is sufficient to unscrew the threaded plug  48 , thus exposing the end of the contact pin  111 . Furthermore, in this state a stylet could be introduced into the longitudinal channel, for instance for repositioning the electrode with the aid of the internal electronics in the pacer. The plug  48  could also contain a sealable, longitudinal bore, for instance sealed by a screw, for this purpose. 
   Another important feature of the invention is the possibility of achieving a high capacitance between contact ring and tube by allowing the ceramic plug and one of the contact rings to extend all the way to one end of the tube. The ring and the tube will be separated by the ceramic, which is chosen to be insulating and thus is a dielectric. Connecting a small capacitor between the ring and the tube can increase the capacitance further. 
   Another important advantage of a high capacitance is that it helps avoid interference. 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.