Abstract:
A plug includes a pin having an axial contact at its opposite end with a mounting rod connected to a center conductor. At the interface between the pin and the inner wall of the plug body, a support sleeve mounted on the shaft and bearing axially against a collar formed on said rod is provided. Axially, a locking ring is secured to the shaft so that the support sleeve is clamped between the collar of the rod and the locking ring, if necessary, leaving a degree of freedom of rotation between the sleeve and the pin. Radially, the outer surface of the sleeve comes into direct contact with the inner wall of the bore of the plug body, to which it is directly secured. The direct attachment of the sleeve to the plug body may be obtained by a snap-in connection with notches cooperating with a counterpart groove.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    The present application claims the benefit of and priority to France Priority Application No. 1253103, filed Apr. 4, 2012, under 35 U.S.C. §119. The entirety of France Priority Application No. 1253103 is incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of active implantable medical devices as defined by Directive 90/385/EEC issued Jun. 20, 1990, by the Council of European Communities. 
         [0003]    This field includes implants that continuously monitor the cardiac rhythm and, if necessary, deliver to the heart electrical pulses of stimulation, cardiac resynchronization, cardioversion and/or defibrillation. This field also includes neurological devices, cochlear implants, drug diffusion pumps, implantable biological sensors, and the like. 
       BACKGROUND 
       [0004]    Active implantable devices generally include a housing commonly referred to as the generator. The generator is typically electrically and mechanically connected to one or more intracorporeal “leads.” These intracorporeal leads are electrodes which are intended contact the bodily tissues (e.g., myocardium tissue, nerve tissue, muscle tissue, etc.) to which electrical stimulation pulses are applied and/or from which an electrical signal is collected. 
         [0005]    Standardized connection systems exist to ensure interchangeability of the leads and generators produced by different manufacturers. For example, “IS-1” and “IS-4” standards define a number of dimensional and electrical characteristics relating to pacing or resynchronization pulse delivery leads. For defibrillation leads, wherein the electrical stresses are most severe in view of the high energy to be channeled from the generator to the lead, the “DF-1” and “DF-4” standards define dimensional and electrical characteristics of the connection system. 
         [0006]    The present invention more particularly relates to a multipolar electrical connection plug for a lead for an active implantable medical device. A multipolar electrical connection plug is a single-body lead including both stimulation and shock electrodes. The complexity of these leads, which is high due to specific constraints in terms of power related to one or the other uses (i.e., stimulation or shock), is further enhanced by the development of multisite devices and intracardiac sensors such as endocardial acceleration (EA) sensors. 
         [0007]    Some leads have a single plug and a plurality of electrical contacts. The plurality of electrical contacts simultaneously connect to various terminals of the generator (e.g. for various energy levels). For example, each of the plurality of electrical contacts may connect to a different generator terminal for the collection of depolarization signals, for the application of pacing pulses, for the delivery of a defibrillation shock energy, or for the transmission of signals collected by a sensor. An advantage of leads having a single plug is that single-plug leads can be subject to single standard. In this context, a single “multipolar” and “isodiameter” connector (e.g., having multiple contacts and a smooth cylindrical shape) to be inserted in a counterpart cylindrical cavity of the connector head of the generator is in compliance with the IS-4/DF-4 standard (ISO 27186-2010). 
         [0008]    European Patent Application No. 1641084 A1 and its U.S. counterpart U.S. Patent Application Publication No. 2006/0068645 describe an example of such a four-pole connection plug. Connection plugs of those applications are of the isodiameter type having an axial electrical contact pin at one end. Connection plugs of those applications also have three annular electrical contact areas on the body of the plug. The annular electrical contact areas are made by consecutive cylindrical rings and are alternately separated by intercalary insulating cylindrical areas. The insulating cylindrical areas electrically isolate the electrical contact areas from one another. Accordingly, it is possible to simultaneously perform all the necessary electrical connections between the generator and the lead pins in a single movement by inserting the connection plug into the cavity of the connector head of the generator. 
         [0009]    However, the realization of such a connection plug raises many manufacturing problems and challenges. ISO standards constrain the outer diameter to merely 3.2 mm (e.g., according to ISO 27186), thereby limiting design possibilities. The impact of compliance with such tight dimensional tolerances in an industrial manufacturing process can be significant in terms of time and cost. 
         [0010]    A further difficulty arises with respect to “coaxial configuration” leads. Coaxial configuration leads include a mobile central conductor housed in an axial lumen of the lead body and a plurality of other conductors extending from a periphery of the lead body. The axial contact pin is connected to the central conductor. The pin-conductor assembly has a rotational degree of freedom relative to the outer body of the plug and relative to the lead body. 
         [0011]    Coaxial configuration leads are mainly used to allow an anchoring screw deployment mechanism (e.g., located at a distal end of the lead) to be driven by manipulation of the proximal end of the lead (e.g., wherein the plug is). For example, a surgeon may hold the proximal end of the lead body with its plug connection with one hand and rotate the pin extending from the plug with the other hand. The torque applied to the pin is transmitted via the inner conductor to the deployment and driving mechanism of the anchoring screw, which allows control of the penetration of the latter into the heart wall. Such a pin-driven lead structure is described, for example, in U.S. Pat. No. 7,241,180 B1 and U.S. Patent Application Publication No. 2010/0211144 A1. 
         [0012]    The presence of a movable element in the plug of coaxial configuration leads causes additional difficulties in the design and manufacturing thereof. One difficulty in the design of coaxial configuration leads is attributable to the need to maintain specific dimensional tolerances (e.g., specified by ISO standards) while achieving a minimum functional space necessary for free rotation of the axial pin. Another difficulty is attributable to sealing requirements. In some cases it is advantageous to provide sealing between the external environment and the internal regions of the plug and of the lead body (e.g., including the central lumen which receives the mobile axial conductor). Such sealing functions to prevent the penetration of body fluids between the mobile parts and in the inner areas of the plug and of the lead body. Sealing can be important in the case of a lead with defibrillation electrodes, given the important electrical energy and the high voltage passing through the plug during the application of the defibrillation shock. The structure of such a plug and the method of assembly of the mobile axial pin are challenging and difficult aspects of both the plug design and the implementation of the manufacturing method. 
         [0013]    U.S. Patent Application Publication No. 2010/0211144 A1 discloses a pin mounting assembly having two concentric members. The disclosed assembly has a ring-shaped part mounted around the shaft of the pin (e.g., acting as a bearing if the pin is mobile in rotation) and a circumferential collar surrounding the ring around its periphery. The circumferential collar acts as a coupler with the plug body and is encapsulated or screwed during manufacturing. This configuration allows a rotational degree of freedom between the pin and the plug body if necessary. However, the pin mounting assembly disclosed in Publication No. 2010/0211144 leads to a relatively complex and expensive manufacturing process, requiring the production of parts with very tight tolerances in order to meet the imposed dimensional constraints. More importantly, the disclosed configuration fails to provide a satisfactory solution to the issue of very narrow tolerances despite the presence of mobile parts (e.g., the pin possibly being handled without axial or radial clearance with respect to the lead body). Additionally, the disclosed configuration fails to adequately provide absolute tightness of the internal regions of the plug and of the lead body with respect to the external environment. 
       SUMMARY 
       [0014]    The present invention provides solutions to the problems described above by providing new plug configurations. The plug configurations of the present invention can be made by a manufacturing method having relatively few steps, thereby reducing manufacturing costs, while respecting constraints of dimensional tolerances and sealing. 
         [0015]    Industrial implementation of the plug according to the present invention is facilitated by the use of parts having basic shapes. Such parts are consequently easy and inexpensive to machine. Industrial implementations of the plugs according to the present invention are further facilitated by reducing the number of parts to be assembled. 
         [0016]    The particular configurations of the plugs described herein provide an improved protection of the connection between the central pin and the inner conductor to which the central pin is welded. The described configurations protect the connection against various stresses and reduces the risk of rupture by material fatigue at the pin-conductor interface. 
         [0017]    Moreover, although the invention is particularly advantageous in the context of a pin-driven type lead with mobile axial pin, it should be noted that embodiments can also be applied to fixed axial pin leads, given the benefits mentioned above, including ease of industrial implementation. 
         [0018]    One implementation of the present disclosure is an electrical connection plug for a multipolar lead of an active implantable medical device (e.g., of a type as disclosed by U.S. Pat. No. 7,241,180 B1 above). That is, a plug having a cylindrical outer surface with a plurality of axially distributed annular contacts and an axial contact at its free end. 
         [0019]    In some embodiments, the plug includes an axial pin forming said axial contact at its free end. The end of the axial pin may be made of a conductive material. The plug may further include a mounting pin at its opposite end for connecting to an internal central conductor of the lead. In some embodiments, the plug includes a plug body having a central bore which accommodates the central conductor and the pin rod. The plug body may be made of an insulating material. In some embodiments, the plug body carries the annular contacts at its outer surface and houses the connection conductors to the respective annular contacts. 
         [0020]    In some embodiments, the plug further comprises a means of connecting the pin to the plug body. The connecting means may form a connection interface between the pin rod and the inner wall of the bore of the plug body in the vicinity of its outlet. The connection means of the pin to the plug body may include a holding sleeve mounted on the pin rod. An end face of the sleeve may axially abut against a flange formed on the rod. An outer surface of the sleeve may directly radially contact the inner wall of the bore of the plug body at the outlet thereof. The sleeve may be made of a biocompatible polymer material. 
         [0021]    In some embodiments, the connection means of the pin to the plug body further includes a locking ring. The locking ring may be secured to the pin rod such that the retaining sleeve is axially clamped between the rod collar and the locking ring. In some embodiments, such clamping leaves a rotational degree of freedom between the sleeve and the pin. The connection means of the pin to the plug body may further include a means for directly securing the sleeve to the plug body at the location of its contact with the inner wall of the bore. 
         [0022]    In some embodiments, the means for directly securing the sleeve to the plug body comprises a snap connection with teeth cooperating with an homologous groove. In some embodiments, the snap connection which can be welded or glued. 
         [0023]    In some embodiments, the plug further comprises a seal mounted on the pin rod. The seal may be axially clamped between the locking ring and a shoulder of the central bore of the plug body. 
         [0024]    One embodiment relates to an electrical connection plug for multipolar lead of an active implantable medical device, said plug having a cylindrical outer surface having a plurality of axially distributed annular contacts ( 110 ,  120 ,  130 ), and carrying at its free end an axial contact ( 210 ), this plug comprising: 
         [0025]    An axial pin end ( 200 ) of conductive material, forming at its free end said axial contact ( 210 ) and having at its opposite end a mounting rod ( 230 ) adapted to be connected to an inner central conductor ( 240 ) of the lead; 
         [0026]    A plug body ( 140 ) of insulating material, comprising a central bore ( 142 ) housing the central conductor and the pin rod and carrying at its outer surface the annular contacts ( 110 ,  120 ,  130 ), the plug body also housing of the connection conductors ( 112 ,  122 ,  132 ) to the respective annular contacts, and 
         [0027]    Means of connection of the pin to the plug body, forming a connection interface between the pin rod and the inner wall of the bore of the plug body in the vicinity of its outlet, wherein the connection means of the pin to the plug body comprises: 
         [0028]    (I) A retaining sleeve ( 300 ) mounted on the pin rod ( 230 ) so that: (a) axially, the end face ( 310 ) of this sleeve abuts against a collar ( 260 ) formed on the rod, and (b) radially, the outer surface of the sleeve comes into direct contact with the inner wall of the bore of the plug body ( 140 ) at the outlet thereof; 
         [0029]    (II) A locking ring ( 400 ), secured to the pin rod ( 230 ) so that, axially, the retaining sleeve ( 300 ) is clamped between the collar of the rod and the locking ring, if necessary leaving a degree of freedom in rotation between the plug and the pin, and 
         [0030]    (III) Means for directly securing the sleeve ( 300 ) to the plug body ( 140 ) at the point of its contact with the inner wall of the bore, wherein the direct securing means of the sleeve to the plug body comprises a snap-in connection with notches ( 380 ) cooperating with a counterpart groove ( 160 ). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Further features, characteristics and advantages of the present invention will become apparent to a person of ordinary skill in the art from the following detailed description of preferred embodiments. The present invention is described with reference to the following drawings made in which like reference characters refer to like elements and in which: 
           [0032]      FIG. 1  is an exploded perspective view of a connection plug showing the various components thereof, according to an exemplary embodiment. 
           [0033]      FIG. 2  is a perspective view in section through an axial plane of the same plug, with its various components assembled, according to an exemplary embodiment. 
           [0034]      FIG. 3  shows, separately, in perspective and in axial section, the center pin of the plug shown in  FIG. 2  with its retaining sleeve and locking ring, according to an exemplary embodiment. 
           [0035]      FIGS. 4 and 5  show perspective views of the annular contacts and the connections formed between such contacts and their respective conductors, according to an exemplary embodiment. 
           [0036]      FIG. 6  is a perspective view of the plug body obtained after overmolding the annular contacts of  FIG. 5 , according to an exemplary embodiment. 
           [0037]      FIG. 7  is a perspective view and an axial plan view of the plug body shown in  FIG. 6 , according to an exemplary embodiment. 
           [0038]      FIGS. 8 ,  9  and  10  show three successive steps of the assembly method of the set associated with the axial pin and its the connection conductor, and of introduction of this assembly into the overmolded plug body of  FIG. 6 , according to an exemplary embodiment. 
           [0039]      FIG. 11  shows the final state of the plug obtained after execution of the various steps of methods of  FIGS. 4 to 10 , according to an exemplary embodiment. 
           [0040]      FIGS. 12   a  and  12   b  illustrate a first exemplary embodiment of the retaining sleeve of the plug of the invention. 
           [0041]      FIGS. 13   a  and  13   b  illustrate a second exemplary embodiment of the retaining sleeve of the plug of the invention. 
           [0042]      FIGS. 14   a  and  14   b  illustrate a third exemplary embodiment of the retaining sleeve of the plug of the invention. 
           [0043]      FIG. 15  is an enlarged, perspective and section view through an axial plane of the end of the plug incorporating a retaining sleeve according to the second embodiment shown in  FIGS. 13   a  and  13   b , according to an exemplary embodiment. 
           [0044]      FIG. 16  is an enlarged perspective view, of the plug end of  FIG. 15 , according to an exemplary embodiment. 
           [0045]      FIG. 17  is an enlarged view in perspective and in section through an axial plane, of the end of the plug incorporating a retaining sleeve according to the third embodiment shown in  FIGS. 14   a  and  14   b , according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Referring to  FIGS. 1 ,  2  and  11 , a proximal end of an “isodiameter” multipolar lead is shown. The illustrated isodiameter mulitpolar lead is an example of a lead compliant to the IS-4/DF-4 standard (i.e., ISO 27186). The tip of the lead is a plug to be inserted into a connector head of an implantable generator (e.g. a pacemaker, a defibrillator, a resynchronizer, etc.).  FIG. 1  is an exploded view of this plug showing various elements thereof. In  FIG. 11 , the plug is shown in assembled form, as it appears at the end of the manufacturing process.  FIG. 2  shows in more detail the internal structure of this same plug with the configuration of the different parts in their final assembled state. 
         [0047]    The illustrated plug is shown to include a plug body  100  having a plurality of annular contacts  110 ,  120 , and  130 . The remainder of the plug body may be formed by a piece of insulating material  140 . The assembly is shown having an “isodiameter” type. In other words, the assembly is in the form of a smooth cylindrical body. Plug body  100  is shown carrying at its proximal side (i.e., the left side in the figures) an axial pin  200 . Pin  200  has an end made of an electrically conductive material. Pin  200  has a free end emerging from a proximal side of the plug body  100  and having an axial contact  210 . 
         [0048]    The plug is shown as a quadripolar plug (e.g., having three annular contacts and one axial contact). This configuration includes the functionality of a bipolar lead to collect depolarization waves and to apply stimulation pulses between the axial electrode  210  and the ring electrode  110  (e.g., according to the standard IS-4). Additionally, this configuration may be used to apply a defibrillation shock between the two ring electrodes  120  and  130  (e.g., according to the standard DF-4). Alternatively, the electrodes  120  and/or  130 , or other additional ring electrodes may be used for connecting to a supply line and/or for the control of circuits incorporated in the lead (e.g., to a sensor located at the end of lead, an endocardial acceleration sensor, etc.). The configuration shown is of course not exhaustive and the invention is applicable to a plug with any number of annular contacts. 
         [0049]    Pin  200  is shown to include lumen  220  at the center of pin  200 . Lumen  220  may be used for introducing a stylet (i.e. slender probe). A surgeon may use the stylet to guide the lead at the time of implantation into a patient. 
         [0050]    Pin  200  is shown to further include a cylindrical mounting rod  230 . Mounting rod  230  may be located at the opposite end of the axial contact  210  (e.g., the part located inside the plug body when the plug is assembled). An end of cylindrical mounting rod  230  (e.g., the distal side end, right in the figure) is designed to connect (e.g., physically and electrically) with an internal central conductor  240 . The distal end of cylindrical mounting rod  230  may connect to the proximal end  242  of central conductor  240 . Conductor  240  may be accommodated in a central bore  142  (as shown in  FIG. 2 ) of plug body  100 . Conductor  240  may optionally be free to rotate within central bore  142 . In some embodiments, conductor  240  is coated along its length with a sleeve  250  of material having a low friction coefficient (e.g., PTFE). Central bore  142  opens proximally at end  144 . 
         [0051]    Pin  200  may be a unitary member made of a conductive material (e.g., stainless steel MP35N). Insulating portion  140  of plug body  100  may be made of a biocompatible polymer. In some embodiments, insulating portion  140  may be made of, an insulating material such as polyetheretherketone (PEEK) or a thermoplastic aromatic polyurethane such as tecothane. Such materials are thermoplastic materials which can be easily overmolded with the annular contacts  110 ,  120 , and  130 . Such thermoplastic materials can also be easily overmolded with the connection conductors to these rings (e.g., conductor  132  visible in  FIG. 2 ). Contacts  110 ,  120 , and  130  may be made of stainless steel (e.g., stainless steel MP35N). 
         [0052]    The connection between pin  200  and plug body  100  may be formed by an assembly including a retaining sleeve  300 . Sleeve  300  may be clamped between a flange  260  on the proximal side and a locking ring  400  on the distal side. Flange  260  may be formed on pin  200  between free end  210  and mounting rod  230 . These elements are shown separately in  FIG. 3 , mounted on pin  200 . 
         [0053]    This configuration provides substantially zero axial space between sleeve  300  and the assembly formed of the pin  200  and ring  400 . In some embodiments, ring  400  may be secured to pin  200  so as to constitute a rigid assembly therewith. This configuration provides a degree of freedom in rotation between pin  200  and sleeve  300  (which may be advantageous for a pin-driven type lead). The possibility of rotation is shown by arrow  270 . In some embodiments, sleeve  300  has a shoulder  310  on the proximal side thereof. Shoulder  310  defines a face  320  on the distal side thereof. Face  320  may be sized, shaped, and/or oriented to come into contact with a counterpart shoulder  146  located at the outlet of the inner lumen  144  of the plug body. Shoulder  310  also defines a face  330  on the proximal side thereof. Face  330  may come into direct contact with collar  260  of pin  200 . 
         [0054]    Sleeve  300  is directly secured to plug body  100  at the point of its contact with the inner wall of the inner bore. This allows a very simple mounting, thereby ensuring compliance with dimensional tolerances. Sleeve  300  can form a seal with the central bore  142  of the plug body  100 . With respect to the seal, it is also possible to provide a ring seal  500  (e.g., as shown in  FIG. 2 ). Ring seal  500  may be made, for example, of silicone compressed between the distal face of the ring  400  and a shoulder  148  via central bore  142  of plug body  100 . Ring seal  500  may be provided in the case of a pin-driven type lead. 
         [0055]    Ring  400  may be made of a material that can be easily secured to plug assembly  230  of pin  200 . For example, ring  400  may be made of stainless steel MP35N. Support sleeve  300  may be made of a material that can be easily secured to the insulating portion  140  of the plug body. For example, sleeve  300  may be made of PEEK or Tecothane. 
         [0056]    Referring now to  FIGS. 4 to 11 , a process for manufacturing the described plug is shown, according to an exemplary embodiment. The first step in the manufacturing process is the realization of the plug body  100 , overmolded with its annular contacts  110 ,  120 ,  130 . The annular contacts may be prepared separately (as shown in  FIG. 4 ). The annular contacts may be prepared, for example, by welding a terminal  114  to the inside of a contact  110 . Terminal  114  may also be welded or crimped to a corresponding conductor  112 . In some embodiments, contact  110  and terminal  114  may be two components of a single unitary piece. 
         [0057]    As shown in  FIG. 5 , the various annular contacts  110 ,  120 ,  130  provided with their respective conductors  112 ,  122 ,  132  are then positioned relative to each other based on the configuration that they will have on the plug body in its final state. The insulating portion  140  of the plug body (e.g., made of biocompatible polymer) may then be overmolded with the contacts  110 ,  120 ,  130  as shown in  FIG. 6 , leaving a central lumen  142 . 
         [0058]    Referring to  FIG. 6  and  FIG. 7 , the sub-assembly thus obtained is shown in section view. Note in particular that at the outlet  144  of central bore  142 , there is no overmolded part or insert. Rather, only the outlet  144  with the shoulder  146  is provided to further receive the support sleeve. In other words, the part obtained at this stage of the method is a part made entirely of insulating material, with the exception of the annular contacts and of their connection conductors. 
         [0059]    Referring to  FIGS. 8 ,  9 , and  10 , the pin and the parts serving to form the connection interface are assembled as shown. The pin and parts shown in  FIGS. 8 ,  9 , and  10  may be assembled separately from the sub-assembly shown in  FIGS. 6 and 7 . The first step in assembling the connection interface (shown in  FIG. 8 ) is to place the support sleeve  300  on mounting rod  230  of pin  200 . When sleeve  300  is placed on rod  230 , face  330  of this sleeve abuts against collar  260 . Locking ring  400  is then also threaded on mounting rod  230  so as to press ring  300  against collar  260 . Then ring  400  is secured to pin  200  in the position shown in  FIG. 9 . Ring  400  may be secured to bin  200  by laser welding  410 , gluing, screwing, crimping, or other suitable fastening means. 
         [0060]    Referring specifically to  FIG. 9 , an optional seal  500  may be placed around mounting rod  230  and against ring  400 . After placing seal  500 , the next step is to weld end  242  of axial conductor  240  on the end of mounting rod  230  (e.g., using laser welding  270  as shown in  FIG. 10 ). The sub-assembly thus obtained is shown in  FIG. 10  in its final state. 
         [0061]    Referring specifically to  FIG. 10 , the next step is to introduce (e.g., shown by arrow  280 ) this sub-assembly within the inner lumen of plug body  100 . The sub-assembly may be introduced to plug body  100  from the proximal end of plug body  100  until face  320  of support sleeve  300  proximally abuts against the plastic material of body  140 . These two elements are then joined together using, for example laser welding  340  as shown in  FIG. 11 , gluing, ultrasonic welding, chemical welding or another suitable method. 
         [0062]    In some embodiments, axial conductor  240  is prepared concurrently with plug body  100  and combines with plug body  100  to form an assembly. Axial conductor  240  may then be mounted on another assembly (e.g., shown in  FIG. 8 ), thereby including pin  200 , retaining sleeve  300 , and locking ring  400 , as assembled together. In some embodiments seal  500  may be inserted onto the rod of the pin prior to welding. Axial conductor  240  may be welded to mounting rod  230 , resulting in the configuration illustrated in  FIG. 10 . 
         [0063]    Referring now to  FIG. 11 , the final state of the plug obtained after execution of the various method steps of  FIGS. 4 to 10  is shown, according to an exemplary embodiment. It is emphasized that the connection of the two subassemblies (e.g., the plug body resulting from steps of  FIGS. 5 to 7  and the pin provided with the various associated elements resulting from steps of  FIGS. 8 and 9 ) is direct without intermediary components. Note in particular that sleeve  300  and polymer  140  of the plug body may be made of identical or similar materials (e.g., two biocompatible polymers). This material selection may facilitate joining and securing the two subassemblies while guaranteeing compliance with dimensional tolerances and sealing requirements without requiring the implementation of complex manufacturing techniques. These requirements may be met even in a configuration of the pin-driven type with one degree of freedom in rotation between pin end  210  and plug body  100 . For example, these requirements are met even in a configuration in which rotation  270  imparted to axial pin  210  is transmitted (as shown at  290  in  FIG. 11 ) over the entire length of the central conductor  240 . 
         [0064]    Referring now to  FIGS. 12-17 , various exemplary embodiments of retaining sleeve  300  are illustrated.  FIGS. 12   a  and  12   b  correspond to a first embodiment, which is illustrated in  FIGS. 1-11  as described above. The first embodiment is shown to include a smooth outer surface  350  inserted into a recess (in conjugated form) located at the outlet of the plug body. Ring  310  may be glued or welded to the plug body. 
         [0065]    Referring now to  FIGS. 13   a  and  13   b , a second embodiment of retaining sleeve  300  is shown. The second embodiment is shown in assembled form in  FIGS. 15 and 16 . In the second embodiment, the outer surface of sleeve  300  is provided with a thread  360 . Thread  360  may engage a homologous thread  150  formed in plug body  100  (as shown in  FIG. 15 ). On the apparent front face, a footprint  370  (e.g., a slot, notch, indentation, etc.) may be provided for an appropriate tool to achieve screwing of sleeve  300  in the plug body (see also  FIG. 16 ). In some embodiments, sleeve  300  and plug body  100  may be glued or welded together can be done in addition to securing via threads  360  and  150 . 
         [0066]    Referring to  FIGS. 14   a  and  14   b , a third embodiment of retaining sleeve  300  is shown. The third embodiment is characteristic of the invention illustrated in  FIGS. 14   a ,  14   b  and  17 . In the third embodiment, an outer surface  350  of sleeve  300  is provided with notches  380 . Notches  380  may cooperate with a counterpart groove  160  (as shown in  FIG. 17 ) formed in the plug body. This cooperation allows placement of sleeve  300  by direct snapping into the plug body. In some embodiments, gluing or welding of these two elements may be performed to enhance the connection therebetween.