AN ELECTRODE TERMINAL FIXATION APPLIANCE

Abstract: An appliance for fixation of a proximal end terminal (16) of an electrode cable to a connector member of an implantable device, such as a heart stimulator, comprising a connector insert (12) having a hole (14) for receiving the terminal (16), and a member (20) for clamping fixation of the terminal (16) in the insert (12), said clamping member (20) being axially movable in a shaft (18) in said insert (12) which adjoins and crosses said hole (14). The clamping member has the shape of an unthreaded pin (20) which is hold captive and movable axially within limits in the shaft (18) and biased by a spring means (32) towards a position therein such that an inner end of the pin (20) is capable of engaging a side of the terminal (16) being exposed in the shaft (18). The inner end of the pin (20) having a diametrically extending recess (46) to be aligned with the terminal (16) during insertion thereof into said hole (14). According to the invention the inner end of the pin (20) has two diametrically aligned depressions (48) at a right angle to said recess (46), the pin (20) being capable of fixating the terminal (16) by clamping action after rotating the pin for aligning the depressions with the terminal.

Description: AN ELECTRODE TERMINAL FIXATION APPLIANCE BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to an appliance for fixation of a proximal end terminal of an electrode cable to a connector member of an implantable medical device, e.g. a heart stimulator, such as a pacemaker or a defibrillator. More particularly, the appliance of the present invention comprises a connector insert having a hole for re- ceiving the terminal, and a member for clamping fixation of the terminal in the insert, said clamping member being axially movable in a shaft in said insert which adjoins and crosses said hole, wherein said clamping member has the shape of an unthreaded pin which is hold captive and movable axially within limits in the shaft and biased by a spring means towards a position therein such that an inner end of the pin is capable of engaging a side of the terminal being exposed in the shaft, said inner end of the pin having a diametrically extending recess to be aligned with the terminal during insertion thereof into said hole. 2. Related prior art In a most general and simple type of lead fixation appliance the proximal terminal of the electrode cable is axially fixated in the connector member by means of a set screw, which is screwed into a transverse threaded shaft in order to radially press the electrode terminal against contact surfaces of the connector member to thereby achieve a clamping fixation of the terminal. The use of screws requires accurate as- sembly instructions and a precise tightening torque to be applied to the screw. Various kinds of screwless electrode fixation devices have been developed. For example, US-A-4 860 750 discloses a wedge element for fixating a lead in an asymmetrical manner which does not ensure a constant clamping force within the toler- ance range of the lead. Also, achievement of safe body fluid sealing of the wedge element need careful efforts. US-A-4 848 346 discloses two circular springs which could be expanded to allow insertion of a heart lead by depressing a straight end portion of the springs protruding from the outer surface of the connector block. However, such protruding end portions may cause unintentional release of the heart lead. US-A-6 112 120 discloses an apparatus for connecting a bipolar proximal end ter- minal of an electrode cable to a connector member of an implantable medical device. The apparatus comprises two connection outputs, each having a spring-biased electrical contact element exerting a radial pressure on a respective terminal portion. The terminal is fixated in the medical device by means of a separate locking wedge. SUMMARY OF THE INVENTION An object of the present invention is to provide an improved electrode terminal fixation appliance having an unthreaded fixation pin which is capable of safely snap-lock the terminal in the connector insert only by turning the pin a quarter of a revolution. This object is achieved in the appliance stated in the introduction above in that the inner end of the pin has two diametrically aligned depressions at a right angle to said recess, said depressions having a less depth than the recess so that the pin is capable of fixating the terminal by clamping action after rotating the pin for aligning the depressions with the terminal. Other features and structural details of the appliance of the present invention are disclosed in the following description and set forth in the accompanying dependent claims with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged side view of an electrode terminal fixation appliance of the present invention in an inactive position, in which it is ready for receiving a proximal end terminal of a heart stimulator electrode to be fixated in a connector member of the stimulator; Fig. 2 is a side view similar to fig. 1 but showing the appliance in an active position in which a spring-biased captive fixation pin has been rotated 90° and is securely holding a proximal end terminal having been inserted into a through-hole in a con- nector insert piece; Fig. 3 is a further enlarged perspective view of the fixation pin; and Fig. 4 is a side view of a second embodiment of the appliance of the present invention, using an elastic O-ring as a combined spring-biasing and sealing means. DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 shows an electrode terminal fixation appliance 10 of the present invention intended for use in an implantable medical device (not shown), in particular a pace- maker or defibrillator. The appliance 10 is adapted to be mounted in a connector member of the medical device which connects an electronic unit of the device with a proximal end terminal of an electrode cable which is adapted to be inserted through veins and to be fixated at a distal end thereof in the heart. The fixation appliance 10 comprises a connector insert block 12 having a bore or through-hole 14 for receiv- ing the proximal end terminal 16 (fig. 2) of the electrode cable (not shown). A stepped blind hole or shaft 18 extending transversely to the through-hole 14 houses an unthreaded clamping pin 20 in a captive manner such that it can move axially within certain limits and rotate 90° between a terminal receiving position (fig. 1) and a terminal fixating position (fig. 2). The pin 20 has a first cylindrical part 22 which is guided in a wider section 24 of the stepped shaft 18, and a second cylindri- cal part 26 that is guided in a narrow section 28 of the shaft 18. Between the two cylindrical parts 22, 26 of the pin there is a recess 30 for holding a spring unit 32 for biasing the pin 20 towards a first axial position (fig. 1). The spring unit 32 comprises a first washer 34, which is axially secured in a circular groove 36 in the wider section of the shaft 18, and a second washer 38 which is biased against a shoulder 40 of the recess 30 by a helical compression spring element 42. In said first axial position of the pin 20, as shown in fig. 1, the second washer 38 rests against a step 44 between the wider and narrow sections of the shaft 18. A concave recess 46 (fig. 2 and 3) having a perimeter or profile corresponding to the cross-section of the proximal end terminal 16 is formed at the inner end of the pin 20 and is aligned with the through-hole 14 in the position shown in fig. 1 so as to allow for unobstructed insertion of the terminal 16 into the insert block 12. As shown in fig. 1 and 3, two diagonally opposed, notch-like depressions 48 are formed transversely to the concave recess 46 at the end of the pin 20 and are adapted to form pressure seats which engage and fixate the proximal terminal 16 in the connector block 12 in a second axial position of the pin 20, as shown in fig. 2. In order to make it possible to bring the pin 20 from its first axial, terminal receiving position in fig. 1 to its second axial, terminal fixating position in fig. 2, the pin 20 has to be rotated 90° by a tool, such as a screw driver, key wrench or the like, engaging with a corresponding slot or the like (not shown) in the outer end 50 of the pin 20. To facilitate the rotation of the pin 20 there are formed diagonally opposed, inclined circumferential cam surfaces 52 at the inner end of the pin 20, so that the pin 20 is smoothly lifted against the action of the compression spring element 42 during the rotation of the pin and the notch-like depressions 48 snap-fits into engagement with the periphery of the terminal 16. The spring element 42 has an appropriate stiffness to cause the pin 20 to exert a sufficient clamping pressure on the terminal 16 to safely lock the same in the connector block 12. It is conceivable to form the washers 34, 38 as integral end parts of the spring element 42 in order to minimize the number of components. According to a second embodiment of the fixation appliance of the present inven- tion shown in fig. 4, the spring unit biasing the pin 20 towards a clamping position on the terminal 16 may be formed as a stiff O-ring 54 which also acts as a sealing ring preventing body fluids from reaching the respective contact surfaces between the terminal 16 and the connector block 12.

Claims: CLAIMS 1. An appliance for fixation of a proximal end terminal (16) of an electrode cable to a connector member of an implantable device, such as a heart stimulator, com- prising a connector insert (12) having a hole (14) for receiving the terminal (16), and a member (20) for clamping fixation of the terminal (16) in the insert (12), said clamping member (20) being axially movable in a shaft (18) in said insert (12) which adjoins and crosses said hole (14), wherein said clamping member has the shape of an unthreaded pin (20) which is hold captive and movable axi- ally within limits in the shaft (18) and biased by a spring means (32) towards a position therein such that an inner end of the pin (20) is capable of engaging a side of the terminal (16) being exposed in the shaft (18), said inner end of the pin (20) having a diametrically extending recess (46) to be aligned with the terminal (16) during insertion thereof into said hole (14), characterized in that the inner end of the pin (20) has two diametrically aligned depressions (48) at a right angle to said recess (46), said depressions (48) having a less depth than the recess (46) so that the pin (20) is capable of fixating the terminal (16) by clamping action after rotating the pin for aligning the depressions with the terminal . 2. An appliance according to claim 1, characterized in that the inner end of the pin (20) has two diagonally opposed, circumferentially extending, inclined ramp surfaces (52) allowing rotation of the pin (20) a quarter of a revolution while displacing, against the action of the spring means (32), the pin (20) away from its inner position to a clamping position in which the terminal (16) is supported by said two diametrically aligned depressions (48). 3. An appliance according to claim 2, characterized in that the pin (20) is provided with means for delimiting the rotation thereof. 4. An appliance according to any one of claims 1-3, characterized in that said spring means (32) comprises a helical compression spring member (42) acting between axially facing surfaces of respective cut-outs (36, 30) in the shaft (18) and the pin (20). 5. An appliance according to claim 4, characterized in that the compression spring member (42) is engaging said axially facing surfaces via a respective washer (34, 38). 6. An appliance according to any one of claims 1-3, characterized in that said spring means comprises an elastic annular member (54) acting between axially facing surfaces of respective cut-outs in the shaft and the pin. 7. An appliance according to claim 6, characterized in that said annular member is 8. An appliance according to any one of claims 1-7, characterized in that a screw driver slot aligned with the terminal receiving hole (14) is provided in an outer end of the pin (20).

Inventors: LOEFSTEDT CHARLOTTE, LOEFSTEDT, CHARLOTTE
Applicants: LOEFSTEDT CHARLOTTE, ST JUDE MEDICAL, LOEFSTEDT, CHARLOTTE, ST. JUDE MEDICAL AB
Application year: 2001
Main classification: A61N1
IPC codes: A61N1