GB1598793A

GB1598793A - Cardiac pacemakers

Info

Publication number: GB1598793A
Application number: GB891978A
Authority: GB
Original assignee: Needle Industries Ltd
Current assignee: Needle Industries Ltd
Priority date: 1977-03-10
Filing date: 1978-03-07
Publication date: 1981-09-23

Description

(54) IMPROVEMENTS IN OR RELATING TO CARDIAC PACEMAKERS (71) We, NEEDLE INDUSTRIES LI MITED, a British Company, of Arrow Works, Studley, Warwickshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a cardiac pacemaker suitable for implantation in a human or animal body as a part of a complete cardiac pacemaker system. A complete cardiac pacemaker system may additionally comprise a plug and socket connector (such as is described and claimed in our co-pending Application Serial No. 1598791 [Application No. 10,280/ 77]) and an electrode catheter to carry electric pulses to the heart, (such as is described and claimed in our co-pending Applications Serial Nos. 1598792 and 1598794 [Applications Nos. 8918/78 and 8026295]).

In a cardiac pacemaker system, the implanted pacemaker itself, which supplies pulses at regular intervals to stimulate the heart via an electrode catheter, must have a long and reliable life because surgery is required to correct any fault and of course in an extreme case the consequence of a pacemaker failure may be fatal. It is therefore most important that the case within which the power source and electronic components for generating the train of electric pulses are housed must be totally hermetically sealed and resistant to the body fluids present at the site of implantation.

Cases have been made of metals such as stainless steel and titanium, but in the environment within a body, these metals suffer from electrolytic corrosion, especially if used as an electrode for return electric current. This corrosion may effect the biocompatibility after a period of time. Plastics materials such as epoxy resins, have been employed for implantation pacemaker cases, but moisture from the body can cause the resins to swell, leading eventually to cracking. Plastics cases thus have a typical life of 3 years. Polypropylene is another plastics material currently often employed for implant cases, but moisture tends to diffuse through polypropylene over a period of time and this can lead to premature failure of the contained electronic components. Also, when using a plastics material, it is necessary to provide a contact on the outer surface of the case to form an "earth return" for the electric circuit and this also can cause problems. In the first place, electrolytic corrosion may take place, but also if the plastics material is liable to change its physical structure or dimensions over a period of years, the security of attachment of the contact pad and the hermetic seal of-a wire leading thereto through the case may fail.

In view of all of the above difficulties, there has been no commercially successful implant case which has been entirely free of problems for the life of the contained components. It has been appreciated that because platinum is relatively inert in a human or animal body and is biocompatible, it would be a suitable material for a case, but in view of the cost of platinum it is not practical to make a case thereof. Platinum with a sufficient degree of purity to ensure bio-compatibility is relatively soft and this means that a case made of platinum must have a considerable wall thickness, thus putting up the cost yet more. Moreover, the weight of a sufficiently strong case can cause difficulties when the case has been implanted.

According to this invention, there is provided a case for implantation in a human or animal body, comprising a rigid substrate of a plastics material defining a chamber and a skin of platinum fitted over the substrate so as to be supported thereby, the skin being formed of two or more pieces of platinum each having a thickness lying in the range of from 0.1875 mm to 0.5 mm and being welded together along mating edges to form a hermetically closed case.

As mentioned above, it has been found that platinum is essentially inert when implanted in a human or animal body, even if in the body for a considerable number of years, and very little - if any - corrosion, pitting or other deterioration takes place.

Whereas a case made from thick-walled platinum of a strength sufficient to protect contained electronics would be prohibitively expensive and very heavy, the strength of the case of this invention is provided by a plastics material substrate which supports only a skin of platinum. The skin thickness lies in the range from 0.1875 mm to 0.5 mm, and preferably is 0.25 mm thick. In this way, the high strength and low weight of a plastics construction can be combined with the corrosion resistance of platinum, and moreover the platinum can provide the "earth return" electrode for the casing.

Though the rigid plastics material substrate could be in the form of a framework for supporting the platinum skin, it is preferred for the substrate to have continuous walls defining a closed chamber.

Such a substrate advantageously is moulded from polypropylene. Preferably, the substrate is in the form of two mating parts which may be mated after the required power source and electronic package have been located therewithin. Preferably also the skin of platinum is in two pre-formed parts which respectively fit over the two parts of the substrate when mated, with the join between the two platinum parts overlying the join between the two parts of the substrate. The two parts of the platinum skin either may overlap slightly, or may more simply abut, as is more appropriate for the welding technique to be employed to join the two parts together. Advantageously, an electron beam but-welding technique is used.

It will be appreciated that no separate contact pad need be provided with a case of this invention to serve as an earth return, because the platinum skin itself may perform this function. However, a suitable connector must be provided for an electrode catheter or similar device to carry the electric pulses to the site of stimulation - and normally the heart. To this end, it is preferred for the case of this invention to incorporate a socket member allowing electrical connection of an electrode catheter to the interior of the case, the catheter carrying an appropriate plug member which may be fitted into the socket member. Conveniently, the socket member comprises a ceramic body defining a bore for receiving the plug member, the ceramic body having a metallic flange around the opening to the bore. By providing an aperture in the platinum skin, corresponding in shape and position to the metallic flange, the skin can be welded to the flange so as to form a hermetic seal therewith. The flange can be made of platinum, but by careful design, titanium can be used if the flange is not, or is only to a very small extent, exposed to the body fluids.

According to another aspect of this invention, there is provided pacemaker apparatus comprising a case for implantation in a body and containing the required power source and electronic package to generate timed electrical pulses, the case being constructed as described above in accordance with this invention and including a socket member allowing electrical connection to be made to the electronic package, whereby an electrode catheter carrying an appropriate plug member at the proximal end thereof may be connected to the pacemaker apparatus.

The plug member for use with the apparatus just-described may have an insulating body portion and a conducting spigot projecting therefrom and to which the conductors of the catheter are connected, and the socket member defines a bore for sealingly receiving the body portion of the plug member and having a block of resilient rubber material located within the bore, there being an electrical contact provided through the wall of the socket member defining the bore and making electrical connection with the rubber material, and the block of rubber material having a recess for receiving the spigot of the plug member, the recess having a smaller cross-sectional dimension than that of the spigot, whereby the block is deformed by insertion of the spigot into the recess to make an electrical connection therebetween.

It is also preferred for the electrode catheter for use with the pacemaker apparatus to comprise a flexible core of insulating plastics material, a plurality of conducting carbon-fibre monofilaments laid over the core to lie along the length thereof from the proximal end to the distal end, and a flexible sleeve of bio-compatible insulating material covering the carbon-fibre monofilaments.

By way of example only, a specific embodiment of this invention will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is a cross-sectional view through an electrical socket member used in a pacemaker casing of this invention; Figure 2 is a side view of an electrode catheter including a plug member for use with the socket member shown in Figure 1: Figure 3 is a cross-sectional view, but on an enlarged scale, through the plug member of Figure 2, when fitted to an electrode catheter; Figure 4 is a cross-sectional view through part of an electrode catheter for use with the plug member of Figure 3; Figure 5 is a diagram showing the fabrication of the catheter of Figure 4; Figure 6 is a cross-sectional view, but on an enlarged scale, through the distal end portion of the electrode catheter shown in Figure 2; Figure 7 is a perspective view of a cardiac pacemaker casing constructed in accordance with this invention and incorporating the socket member shown in Figure 1; Figure 8 is a cross-section through the pacemaker casing of Figure 7; and Figure 9 is a cross-section through the wall of the pacemaker casing of Figure 7, but on an enlarged scale.

Referring initially to Figures 1 to 3, there is shown a plug and a socket connector intended for connecting an electrode catheter of a cardiac pacemaker system to a pacemaker casing. The connector comprises a plug member 10 and a socket member 11, the plug member 10 being moulded directly on the end of the electrode catheter 12 and the socket member 11 being adapted for incorporation in the casing of the pacemaker itself.

The socket member 11 (Figure 1) comprises a main body 13 made from a ceramics material and defining a blind circular bore 14. An inwardly directed annular rib 15 is provided within the bore 14, spaced slightly from the open end thereof and upstanding from the wall defining the bore by about 0.1 mm. A circular metallic flange 16 (for instance of titanium) is provided on the ceramics body portion 13 around the open end of the bore 14 during the manufacture of the socket member, so that the flange 16 is hermetically bonded to the main body 13.

Similarly, a conducting contact 17 is provided through the blind end wall of the main body 13 so as to project into the bore 14.

The contact is conveniently of platinum, and is also hermetically sealed to the main body.

Within the bore 14, the contact 17 has an enlarged head 18, provided with barbs 19 directed towards the blind end of the bore.

Located within the bore 14 is a block 20 of relatively soft, resilient conducting silicone rubber material, loaded with carbon particles to render the block electrically conducting. The block 20 is of circular cross-section to fit closely within the bore 14, and has a circular recess 21 opening co-axially towards the open end of the bore 14. A second co-axial recess is provided for receiving the head 18 of the contact 17, the block 20 being deformed to fit over the head and engage with the barbs 19, thereby making a good electrical connection therebetween. An annular channel 22 is provided partwaybetween the ends of the block 20 of conducting silicone rubber material.

The conducting silicone rubber material is known per se and comprises relatively soft, resilient silicon rubber which has been loaded with carbon black. Such material displays reasonable electrical conductivity, though the resistance offered depends to some extent upon the degree of compression of the material. A typical material is that known as Dow-Corning Q4-1602 Silastic (Registered Trade Mark).

The plug member 10 (Figures 2 and 3) comprises a body portion 23 of circular cross-section and is provided with three annular ribs 24, each having the general cross-sectional shape of a barb directed generally away from the free end of the plug member 10. The body portion 23 is moulded from insulating silicone rubber, and is thus flexible, relatively soft and resilient. The material is similar to that of the block 20, except that it has not been loaded with carbon black; as such the material displays excellent insulating properties. A typical material for this purpose is that known as Dow-Corning MDX-4-4210 Clean-Grade Elastomer. The body portion 23 is moulded around a metal spigot 25, which projects from the free end of the body portion for connection with the socket member of Figure 1. The diameter of the spigot 25 should be slightly greater than that of the recess 21 when the block of silicone rubber is located in the bore 14 of the socket member 11.

As shown in Figure 3, the body portion 23 is moulded directly on to an electrode catheter 12, which is described in detail below. The catheter 12 includes an outer insulating silicone rubber protective sleeve 26, conductors 27 and a plastics core 28. The spigot 25 is shaped to receive in a first counterbore 29 the conductors 27, to make electrical connection therewith, and in a second, smaller counterbore 30 the plastics core 28. The body portion 23 bonds during the moulding operation to the sleeve 26, and if required the spigot 25 can lightly be crimped on the conductors 27 to ensure a reliable electrical connection thereto.

In use, when the plug member 10 is fitted into the socket member 11, the spigot 25 enters the recess 21 in the block 20 of conducting silicone rubber located within the bore 14 and makes an electrical connection therewith. By arranging the diameter of the recess 21 to be of slightly smaller size than that of the spigot 25, the rubber is compressed and resiliently urged into engagement with the spigot, as the spigot enters the recess 21 and a good electrical connection is thereby achieved. The annular channel 22 allows the rubber to distort and deform as required to allow accommodation of the spigot 25 in the recess 21. The annular ribs 24, shaped as barbs, allow the body portion 23 of the plug member easily to enter bore 14 of the ceramic body 16 but restrain withdrawal of the plug member owing to their barb-like shape. The rib 24 nearest the catheter 12 rides over and engages behind rib 15 of the socket member 11, and further assists in the retention of the plug member within the socket member.

Moreover, the ribs 24 of the plug member 10 effect a hermetic seal between the body portion 23 of the plug member and the main body 13 of the socket member, whereby the electrical connection between the spigot 25 and the block 20 of conducting silicone rubber material is isolated from the surrounding environment.

Referring now to Figures 3 to 6, there is shown an electrode catheter 12 intended for use in a cardiac pacemaker system, connectible by means of the plug and socket connector described above to a pacemaker casing, and having an electrode for heart stimulation at its distal end. The catheter comprises a flexible, hollow core 28 of insulating plastics material such as polypropylene over which is laid a plurality of carbon-fibre monofilament conductors 27, each of approximately 101l diameter. The carbon-fibre monifilament conductors 27 are assembled together into two groups 32 and 33 each containing several hundred such monofilaments randomly-oriented - and typically from 200 to 1000 - and the two groups are then wave-wound around the core 28 as shown in Figure 5. In this way, the groups are interwoven around the core 28 to form an open net-like tubular structure extending along the plastics core 28.

Extruded over the core 28 carrying the wave-wound groups of monofilament conductors 27 is a protective, insulating sleeve 26, of insulating silicone rubber material. By extruding the silicone rubber sleeve 26 directly as a tube over the carbon-fibre monofilament conductors 27, the sleeve is moulded around the groups of filaments as well as the filaments themselves such that they are partially embedded in the sleeve. In this way, the sleeve serves to retain the conductors 27 in the required position, as well as protecting the conductors against damage and insulating the conductors from the surroundings.

The electrode catheter described above has a relatively low impedance with good flexibility, whilst displaying excellent torsional rigidity (owing to the plastics core 28) allowing the catheter to be inserted where required within an animal or human body.

The silicone rubber sleeve is virtually inert and is essentially bio-compatible within human or animal bodies.

The catheter may be terminated at the proximal end with the plug described above, or instead may be terminated with one of the more usual plug or other connectors used with known cardiac pacemaker systems or other equipment in which an electrode catheter must be inserted or implanted in a body. The distal end of the catheter should be terminated in an appropriate manner for the intended use of the catheter, and such terminations - for instance for cardiac stimulation - are well known in the art.

Figure 6 shows the electrode 34 provided at the distal end of the electrode catheter.

This electrode comprises a platinum tip 35 having a rounded free end, there being an axial bore extending into the tip from its other end. In this bore are received the plastics core 28 and the carbon-fibre conductors 27 such that the conductors are connected electrically to the tip 35. The silicone rubber sleeve 26 is moulded directly over part of the tip 35 so as to insulate the greater part thereof and to hold the tip on the core and conductors. A silicone rubber flange 36 is provided at the end of the sleeve 26 so as to assist retention of the electrode in the required position.

Figures 7 to 9 show a cardiac pacemaker implant case 40, embodying a socket member generally similar to that shown in Figure 1 and for use with a catheter electrode having a plug member as shown in Figure 3.

The case for the pacemaker comprises two separate moulded plastics chamber parts 41 and 42, which mate together at 43 to define a complete chamber. Part 41 is fitted with a socket member 44, comprising a ceramic body 45 defining a bore in which is located a conducting silicon rubber block 46, connected to an electronic package 47 contained within chamber part 41 by means of contact 48 extending through the ceramic body 45. Within the chamber part 42 is a battery pack 49, connected to the electronic package 47 by means of wires 50. A continuous ring 51 of resilient silicone rubber material is positioned between the electronic package 47 and the battery pack 49 so as to urge the package and pack 47 and 49 respectively apart, into firm engagement with the associated chamber parts 41 and 42.

The ring 51 moreover is engaged with the chamber parts 41 and 42 immediately under the mating region 43 of the chamber parts.

If required, as shown in Figure 9, a layer 52 of silicone rubber can be provided between the inner wall of a chamber part and the package or pack therewithin. The two chamber parts 41 and 42 can be glued together once all the components have been assembled therewithin, by means of an adhesive selected for the plastics material of the chamber parts. For instance, the parts can be of an epoxy resin, and a similar resin used for glueing the parts together.

The entire moulded plastics chamber parts 41 and 42 are covered by a platinum skin 53, also formed in two separate parts which abut in the mating region 43 of the two chamber parts. The skin is shaped from platinum sheet of about 0.25 mm thickness, so as to fit closely over the chamber parts.

An aperture 54 is provided in the skin around the opening into the bore of the socket member 44. The abutting edges of the two separate parts of the skin 53 are welded together by an electron beam welding technique and the skin is also welded around the aperture 54 to a metal flange 55 around the socket member 44 by the same technique, whereby a continuous hermetical seal is formed around the entire casing.

The two parts of the platinum skin conveniently are formed by a deep drawing operation from a flat sheet of platinum, using the chamber parts themselves as the male drawing tool. Pure platinum is relatively soft and lends itself to such a forming operation, especially when in a relatively thin sheet, particularly because the material displays virtually no spring-back. However, the skin could be formed separately and then fitted to the assembled chamber parts prior to the welding operation.

An electrical connection must be provided to the platinum skin, to allow a current return from the distal end of a catheter used with the pacemaker case.

Conveniently, this is effected by means of the flange 55 of the socket member 44, connected internally back to the electronic package 47 within chamber part 41.

In use, an appropriate electrode catheter fitted with a plug member at its proximal end for insertion into socket member 44 is introduced into the body so that the distal end is within the heart where stimulation is required, and the proximal end is adjacent the site of implanting of the pacemaker case. If a catheter such as is described above is used, excellent torsional control of the distal end can be achieved by operation and principally rotation - of the proximal end during positioning of the distal end.

Next, the plug member 10 of the catheter is inserted into the socket 40 of the pacemaker casing, and the pacemaker is positioned suitably at the implantation site, whereafter the surgery is completed in the usual way.

It is found that the platinum skin, even though serving as a contact for the earth return. is not prone to corrosion or other deterioration. for platinum proves to be virtually inert within the environment of a human or animal body at the usual sites of implantation. Thus the life of the implanted pacemaker will be dictated by the battery pack 49, rather than by the life of the pacemaker casing or the life of the electrode catheter - and battery packs are currently being produced which should call for preventative replacement only every 5 years, even though the actual life may be yet longer.

WHAT WE CLAIM IS: 1. A case for implantation in a human or animal body, comprising a rigid substrate of a plastics material defining a chamber and a skin of platinum fitted-over the substrate so as to be supported thereby, the skin being formed of two or more pieces of platinum each having a thickness lying in the range of from 0.1875 mm to 0.5 mm and being welded together along mating edges to form a hermetically closed case.

2. A case as claimed in claim 1, wherein the thickness of the platinum skin is substantially 0.25 mm.

3. A case as claimed in any of the preceding claims, wherein the rigid substrate of plastics material has continuous walls defining a closed chamber.

4. A case as claimed in claim 3, wherein the substrate is in the form of two mating parts which may be mated to form the closed chamber after the required components have been located therewithin.

5. A case as claimed in claim 4, wherein the skin of platinum is in two pre-formed parts which respectively fit over the two parts of the substrate when mated, with the join between the two platinum parts overlying the join between the two parts of the substrate.

6. A case as claimed in any of the preceding claims, wherein the parts of the platinum skin are welded together by means of an electron beam butt-welding technique.

7. A case as claimed in any of the preceding claims, wherein the case has a socket member provided therein allowing electrical connection to be made to the interior of the case, whereby an electrode catheter carrying an appropriate plug member may electrically be connected to the case.

8. A case as claimed in claim 7, wherein the socket member comprises a ceramic body defining a bore for receiving a plug member, the ceramic body having a metallic flange around the opening to the bore.

9. A case as claimed in claim 8, wherein the platinum skin is provided with an aperture corresponding in shape and position to the metallic flange, and the skin is welded to the flange so as to form a hermetic seal therewith.

10. A case as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in Figures 6, 7 and 8 of the accompanying drawings.

11. Pacemaker apparatus, comprising a case as claimed in any of claims 7 to 9 for

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. used for glueing the parts together. The entire moulded plastics chamber parts 41 and 42 are covered by a platinum skin 53, also formed in two separate parts which abut in the mating region 43 of the two chamber parts. The skin is shaped from platinum sheet of about 0.25 mm thickness, so as to fit closely over the chamber parts. An aperture 54 is provided in the skin around the opening into the bore of the socket member 44. The abutting edges of the two separate parts of the skin 53 are welded together by an electron beam welding technique and the skin is also welded around the aperture 54 to a metal flange 55 around the socket member 44 by the same technique, whereby a continuous hermetical seal is formed around the entire casing. The two parts of the platinum skin conveniently are formed by a deep drawing operation from a flat sheet of platinum, using the chamber parts themselves as the male drawing tool. Pure platinum is relatively soft and lends itself to such a forming operation, especially when in a relatively thin sheet, particularly because the material displays virtually no spring-back. However, the skin could be formed separately and then fitted to the assembled chamber parts prior to the welding operation. An electrical connection must be provided to the platinum skin, to allow a current return from the distal end of a catheter used with the pacemaker case. Conveniently, this is effected by means of the flange 55 of the socket member 44, connected internally back to the electronic package 47 within chamber part 41. In use, an appropriate electrode catheter fitted with a plug member at its proximal end for insertion into socket member 44 is introduced into the body so that the distal end is within the heart where stimulation is required, and the proximal end is adjacent the site of implanting of the pacemaker case. If a catheter such as is described above is used, excellent torsional control of the distal end can be achieved by operation and principally rotation - of the proximal end during positioning of the distal end. Next, the plug member 10 of the catheter is inserted into the socket 40 of the pacemaker casing, and the pacemaker is positioned suitably at the implantation site, whereafter the surgery is completed in the usual way. It is found that the platinum skin, even though serving as a contact for the earth return. is not prone to corrosion or other deterioration. for platinum proves to be virtually inert within the environment of a human or animal body at the usual sites of implantation. Thus the life of the implanted pacemaker will be dictated by the battery pack 49, rather than by the life of the pacemaker casing or the life of the electrode catheter - and battery packs are currently being produced which should call for preventative replacement only every 5 years, even though the actual life may be yet longer. WHAT WE CLAIM IS:

1. A case for implantation in a human or animal body, comprising a rigid substrate of a plastics material defining a chamber and a skin of platinum fitted-over the substrate so as to be supported thereby, the skin being formed of two or more pieces of platinum each having a thickness lying in the range of from 0.1875 mm to 0.5 mm and being welded together along mating edges to form a hermetically closed case.

implantation in a body and containing the required power source and electronic package to generate timed electrical pulses, the case including a socket member allowing electrical connection to be made to the electronic package, whereby an electrode catheter carrying an appropriate plug member at the proximal end thereof may be connected to the pacemaker apparatus.

12. Pacemaker apparatus as claimed in claim 11, in combination with the plug member of a plug and socket connector the plug member of which has an insulating body portion and a conducting spigot projecting therefrom and to which the conductors of an electrode catheter can be connected, and the socket member defines a bore for sealingly receiving the body portion of the plug member and having a block of conducting resilient rubber material located within the bore, there being an electrical contact provided through the wall of the socket member defining the bore and making electrical connection with the rubber material, and the block of rubber material having a recess for receiving the spigot of the plug member the recess having a smaller cross-sectional dimension than that of the spigot, whereby the block is deformed by insertion of the spigot into the recess to make an electrical connection therebetween.

13. Pacemaker apparatus as claimed in claim 11 or claim 12, in combination with an electrode catheter comprises a flexible core of insulating plastics material, a plurality of conducting carbon-fibre monofilaments laid over the core to lie along the length thereof from the proximal end to the distal end, and a flexible sleeve of bio-compatible insulating material covering the carbon-fibre monofilaments, connectible to the socket of the core by means of an appropriate plug on the proximal end of the catheter.

14. A pacemaker system substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.