Abstract:
An appliance for fastening one or more electrode leads in a connector unit of an implantable medical device, for example a heart stimulator, is formed of a wire- or strip-shaped resilient locking member, which is arranged to be inserted and fixed in a cavity in a connector unit, and which is shaped to clampingly engage diametrically opposed circumferential parts of the casing of each electrode lead.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for fastening at least one electrode lead in an insertion hole in a connector unit of an implantable medical device, e.g. a heart stimulator, such as a pacemaker or defibrillator. 
     2. Description of the Prior Art 
     It is important during the connection of the proximal end of one or more electrode leads or conductors to the connector of a heart stimulator that each lead end is axially and radially securely held in the connector in order to ensure a good electrical contact and in order to prevent detaching of the electrode lead end from the connector. 
     In a known electrode lead fixing means, the electrode end is inserted into a hole in the connector which is adapted to the diameter of the end of the electrode, the end of the electrode being radially held fast in the hole. The axial locking or fastening of the end of the lead is achieved with the aid of a set screw, which is screwed into a transverse threaded hole in order to radially press a male plug part on the end of the electrode lead from one side against an opposing wall of a socket. This lamps the end of the lead and thus also serves to axial fasten the lead end in the hole. The use of a screw requires tools for the assembly and requires precise instructions and a precise tightening force on the screw. 
     U.S. Pat. No. 4,848,346 discloses a pacemaker connector system which eliminates problems associated with set screw systems. In this device the connector block firmly holds two circular springs which can be expanded to allow insertion of the heart lead by depressing a straight end portion of the spring which protrudes from the outer surface of the connector block. Such protruding end portions, however, may cause unintentional actuation of the springs and inadvertent release of the cardiac lead. 
     It has also been suggested to use a wedge element (U.S. Pat. No. 4,860,750) in order to fix the ends of the electrode conductors in the connector of the heart stimulator. Such a wedge element is insertable into a complementary channel which is orientated transversely and tangentially relative to the hole into which the electrode lead end is inserted, and has a cam profile with a concave seating surface in order to clamp the lead end through the lead casing when the wedge element is inserted. In this way the wedge element firmly holds the electrode lead in the hole from one side of the hole by means of elastic deformation of the lead end casing, which normally is made of a layer of silicon rubber. With this wedge-shaped embodiment of the locking or fixing element the fastening of the ends of the electrode leads is achieved by means of a single-sided, asymmetric type of fixing element which cannot guarantee a constant wedging force within the tolerance range for electrode leads. 
     European Application 0 590 756 describes a fixing arrangement for an electrode lead in a connector of a heart stimulator. The fixing arrangement is formed of a spring plate with opposing resilient gripping means cast in a connector, which is intended to cooperate with the contact pin on the lead and simultaneously prevent the end of the electrode lead from being pulled out of the connector. The retention force on the clamp increases when a withdrawing force is exerted on the electrode lead. The engagement of the gripping means on the contact pin of the lead end can be released when a force is exerted on opposing, projecting side tabs on the spring plate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved and simplified fixing means which can symmetrically clamp the end of the electrode lead on opposing sides with a constant force within the tolerance range for the lead, and which cannot be released if a clamping pressure is exerted upon the connector. 
     For this purpose the appliance of the present invention includes a resilient locking member insertable into a slot in the connector unit, the slot being formed to hold the locking member in a plane substantially normal to a longitudinal axis of the bore. The locking member is adapted, upon insertion thereof into the slot, to straddle and resiliently snap over an insulating cover of the electrode lead so as to firmly hold diametrically opposite portions thereof. 
     In a suitable embodiment of the fixing means according to the invention for fixing of two or more electrode leads arranged one above the other, the resilient locking member is shaped to be successively pushed over the casings of the leads along a path which connects the central axes of the leads with alternating inward and outward spring biasing of two opposing, preferably wave-shaped side branches of the resilient member. Such an embodiment provides a very simple mounting of the locking element as well as clamping the lead ends with a constant force from two opposing sides. 
     In another suitable embodiment of the fixing means according to the invention the resilient member is shaped so as to snap over the casing of the electrode lead in a direction which is essentially transverse to a line which connects the central axes of adjacent leads. In this way the electrode lead ends can be clamped by successively pushing locking sections of the resilient locking member over the lead ends from the side. Such an embodiment also makes it possible to fasten three or even more electrode ends in a connector where the insertion holes for the respective lead ends do not have to lie in a straight line. 
     In yet a further embodiment of the fixing means according to the invention for fixing two electrode leads, the resilient element is S-shaped with two arcuate portions which open in opposing directions and which are joined by a web part. The resilient member is rotatable around a transverse axis which is essentially parallel with the longitudinal axis of the electrode lead in the web part, in a cavity of the connector, from a passive position to a lead-clamping locking position, preferably inset in the connector. The resilient locking member is placed in this cavity before the ends of the electrode leads are pushed into their respective connection holes, following which the resilient member is rotated to the locking position simply by pressing each of the arcuate ends in opposing directions. 
     In a further embodiment for fixing of a single electrode lead the resilient locking member has an arcuate part, shaped in order to be able to clamp against diametrically opposing parts of an insulating casing on the electrode lead and rotatable in a cavity in the connector about an axis which is essentially parallel with the longitudinal axis of the electrode lead, from a passive position to a lead-clamping locking position, preferably inset in the connector. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows a side view of a pacemaker with an upper electrical connector unit for two bipolar electrode leads, the connecting ends of which being fixed by a fixing appliance according to the invention. 
     FIG. 2 is a schematic end view of the connector unit and a resilient locking member according to a first embodiment of the invention, before and after mounting. 
     FIG. 3 is a view corresponding to FIG. 2 but showing a second embodiment of the resilient locking member according to the invention, before and after mounting. 
     FIG. 4 is a view similar to FIGS. 2 and 3 but showing a third embodiment of the resilient locking member according to the invention, before and after mounting. 
     FIG. 5 is an end view of a pacemaker in FIG. 1 and shows a fourth embodiment of the resilient locking member according to the invention, in a position before fixing of the lead ends. 
     FIG. 6 is a view similar to FIG. 5 but showing the resilient locking member in the active locking position in the connector. 
     FIG. 7 shows a fifth embodiment of a resilient locking member according to the invention for mounting of a single electrode lead in a connector. 
     FIG. 8 is an end view of the resilient locking member in FIG. 7 in a position before fixing of the lead end. 
     FIG. 9 is a view similar to FIG. 8 but showing the resilient locking member in the active locking position in the connector. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an implantable pacemaker 10, having a casing 12, which encloses an electronic unit (not shown) with a pulse generator, and having a connector 14 in order to connect the electronic unit with, in this case, two proximal ends of bipolar electrical conductors 16 and 18, or so-called electrode leads. The leads are to be inserted through a peripheral vein and led via the upper carotid vein (vena cava superior) to the right side of the heart, where the electrodes at the distal lead end will come into contact with the heart muscle at a desired location. 
     There are two parallel blind holes 20 and 22 in the connector 14, which contain respective contact elements 24 and 26 for connection and contact with corresponding contact elements on the ends of the electrode leads 16 and 18, when these are inserted in the respective blind holes 20 and 22. 
     In order to attach the lead ends in the connector 14 according to the present invention to use a simple resilient locking member is used, which can partially surround diametrically opposing circumferential halves of the casing of the lead ends so as to clamp them with a constant force. 
     FIG. 2 shows a first embodiment of a simple resilient locking member 32 according to the invention for the simultaneous fastening of two electrode lead ends 16 and 18. The resilient member 32 is an elongated clip formed, for example, from a wire or a narrow strip of material suitable for the purpose, e.g. titanium, stainless spring steel or a plastic material, and has two essentially wave-shaped side branches 34a and 34b and a web part 34c joining them. The configuration of the side branches 34a and 34b and the web part 34c are therefore such that the casing of each of the lead ends 16 and 18 is subjected to symmetrical pressure forces directed toward each other, which are constant within the tolerance is range for the casing of the lead ends 16 and 18, when the resilient locking member 32 is mounted on them. In the embodiment in FIG. 2 the resilient locking member 32 is attached on the lead ends 16 and 18 is inserted in the connector 14 in the direction of arrow P in an exteriorly accessible slot 36 in the connector 14. The resilient member is pushed successively over the leads along a path which connects the central axes of the leads 16 and 18, with alternating springing in and out of the two opposing, wave-shaped side branches 34a and 34b on the resilient member 32. The slot 36 is shaped and dimensioned so that the resilient member 32 is held axially fixed therein. In this way, in the mounted condition, the lead ends 16 and 18 are radially held in the connector 14 through a tight fit in their respective holes 20 and 22, and axially fixed by means of the resilient member 32, of which the branches 32a and 32b are pressed somewhat into opposing side portions of the elastic outer casing, normally made of silicon rubber, of the electrode lead ends. In the active clamping position the resilient member 32 is enclosed within the outer contours of the connector 14, as shown in FIG. 2. 
     FIG. 3 shows a second embodiment of a resilient locking member 32a according to the invention for the simultaneous fastening of two electrode lead ends. Like the embodiment in FIG. 1 the resilient member 32a in this embodiment is formed of a wire- or strip-shaped resilient material, but it has a wavelike configuration. This configuration permits the resilient member to be pushed over the lead ends 16 and 18 in a lateral direction, essentially transverse to a line which connects the central axes of the leads, as is shown with arrow pr in FIG. 3. In this way the resilient member is first snapped over one lead end and subsequently over the other end while being inserted in the slot 36. In the mounted position the resilient member 32a is enclosed within the outer contour of the connector 14, as shown in FIG. 3, and presses into the opposing upper and lower portions of the elastic outer casing of the lead ends 16 and 18. 
     A third embodiment of a resilient member 32b according to the invention is shown in FIG. 4, where the ends of three electrode leads 16,18 and 19, which do not have to lie in the same vertical plane of the connector 14, are to be fastened in the connector 14. In principle, this embodiment is an extension of or an addition to the resilient member 32a in FIG. 3 with a further wave-shaped part. The snapping of the resilient member 32b over the lead ends occurs similarly in sequence in a slot 36 in the connector 14. 
     A fourth embodiment of a resilient member 32c according to the invention is shown in FIGS. 5 and 6, and consists of a wire or a strip element with two arcuate portions 38 facing in opposite directions and a straight web portion 40 connecting them. The resilient member 32c is inserted in a slot 36&#39; in the connector 14 and is rotatable therein about an imaginary transverse axis A in the web portion 40 from a passive position shown in FIG. 5, in which the lead ends 16 and 18 can be inserted without any resistance into the contact position with the corresponding contact elements 24 and 26 in the connector 14 (FIG. 1), to a lead end clamping position retracted in the connector as is shown more clearly in FIG. 6. The arcuate parts 38 can be equipped with small pressing plates 42 in order to facilitate a manual locking of the resilient member 32c. 
     FIG. 7 shows a connector 14 for a single electrode lead 17 with a locking resilient locking member 32d according to a fifth embodiment of the invention. The locking member 32d has an arcuate part which in similarity with the embodiment in FIGS. 5 and 6 can be rotated about an axle or pin between a position shown in FIG. 8, in which the electrode lead end can be inserted into the insertion hole in the connector 14, and a fixing position according to FIG. 9 partially surrounding an electrode lead end casing. A pressure plate 42 similar to the embodiment according to FIGS. 5 and 6 can be arranged on the arcuate part in order to facilitate the manual locking of the resilient member 32d. 
     The embodiments of the resilient member according to the invention do not require any tools for mounting of the resilient member. 
     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.