GB1598792A - Electrode catheters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRODE CATHETERS (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 an electrode catheter, and in particular to such a catheter which is suitable for implantation in a human or animal body. The electrode catheter of this invention may be used as a part of a cardiac pacemaker system for a human body, the catheter being connected by means of a plug and socket connector (such as is described and claimed in our copending Applications Serial Nos. 1598791 and 1598794 [Applications Nos. 10,280/77 and 8026295]) to a cardiac pacemaker (such as one described and claimed in our copending Application No. 1598793 [Application No. 8919/78]).

In a cardiac pacemaker system, the pacemaker itself is usually implanted some distance from the heart, and an electrode catheter feeds current pulses to the site where stimulation is required. The electrode catheter must be resistant to the environment within the body in which it is implanted, as well as being flexible and totally reliable. Furthermore, it is important that the catheter has considerable torsional rigidity in order that the distal end may be moved to and located in the required position within the heart solely by moving the proximal end of the electrode catheter.

Known forms of electrode catheters for use with cardiac pacemakers usually comprise one or more spirally wound strands of stainless steel wire, the whole being covered with a relatively inert and flexible insulating sleeve. Though this construction is satisfactory for short-term operation - and typically 4 to 5 years - it nevertheless offers a fairly high resistance to the flow of electric current (approximately 45 ohms for a 90 cm long electrode catheter) and furthermore allows only relatively poor torsional control of the catheter distal end as the catheter is being inserted in position from its proximal end.

This is on account of the spring-like properties of the sprially wound stainless steel wires which are unable accurately to transmit torque applied to the proximal end. Such a catheter also suffers from problems of electrolytic corrosion and mechanical fatigue.

According to this invention, there is provided an electrode catheter comprising 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 biocompatible insulating material covering the carbon-fibre monofilaments.

The core of plastics material is preferably hollow and serves to give the electrode catheter torsional and tensile rigidity, as well as serving as a support for the carbonfibre monofilaments which are relatively fragile. By suitable adjustment of the material and dimensions of the core of plastics material, the electrode catheter can be given any required properties regarding flexibility, torsional resistance and tensile strength.

A typical material is polypropylene, and may have an inner diameter of t/2 mm., and an outer diameter of 1 mm.

The carbon-fibre monofilaments are preferably assembled together into two groups each containing several hundred such monofilaments. For instance, from 200 to 1000 monofilaments may be assembled into two randomly-oriented groups. Though the two groups could each simply be laid along the plastics material core, it is greatly preferred for the two groups to be wound helically in opposite senses on the core so that the groups are interwoven in the form of a tubular net - that is, the two groups are wave-wound on the core. This has the advantage that when the electrode catheter is flexed, strains on the monofilaments are much reduced and are relatively uniformly distributed, the strains being less for finer pitches of winding. The reduction in strain and the protection of the monofilaments against damage can be enhanced by applying a layer of material relatively soft as compared to the carbon-fibre monofilaments - such as soft silicone rubber - over the core of plastics material and for the carbon-fibre monofilaments to be laid thereover or at least partially embedded therein.

The sleeve covering the carbon-fibre monofilaments may be made of any flexible insulating material which is biocompatible that is to say, inert to the environment in a body in which the catheter is to be implanted, and insulating silicone rubber advantageously can be used for this purpose, or an appropriate grade of natural rubber. Preferably, the rubber is extruded directly on to the monofilaments when these have been laid on the core, and in this way the rubber serves securely to hold the monofilaments in the required relative disposition, by virtue of the rubber at least partially bonding to and surrounding the monofilaments.

The proximal end of the electrode catheter of this invention may be fitted with a plug member of a plug and socket electrical connector, to allow the catheter to be plugged into a cardiac pacemaker provided with an appropriate socket. Such a plug member may be moulded directly on to the proximal end of the catheter. The distal end of the catheter is preferably formed with an electrode element for stimulating the heart when the electrode catheter has been implanted in a body.

A specific construction of an electrode catheter of this invention employing carbonfibre monofilaments of 101l diameter and arranged in two groups of 500 filaments shows a very low electrical resistance - and typically 3 ohms for a 90 cm length as compared with known stainless steel catheters having a typical resistance of 45 ohms.

Moreover, the electrode catheter of this invention displays high tensile strength and good flexibility characteristics, as well as allowing excellent torsional control of the distal end by manipulation solely of the proximal end.

Though especially suitable for use in a cardiac pacemaker system, for carrying electric pulses from the pacemaker to a heart, the catheter of this invention may be used in other applications where an electrode catheter is to be inserted into or implanted within an animal or human body for transferring electric current from one point to another.

Of course, such an electrode catheter may be employed for measurement purposes as well as for stimulation purposes.

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 a socket member of a plug and socket connector suitable for use with an electrode catheter of this invention; Figure 2 is a side view of an electrode catheter of this invention, and including a plug member for insertion in the socket of Figure 1; Figure 3 is a cross-sectional view, but on an enlarged scale, through the plug member shown in Figure 2, as fitted to an electrode catheter constructed in accordance with this invention; Figure 4 is a cross-sectional view through part of the electrode catheter shown in Figure 2; Figure 5 is a diagram showing the fabrication of the electrode 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 for connection to the electrode catheter of Figure 2; 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 partway between 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 10y diameter. The carbon-fibre monofilament 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. It 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.

Ir is found that the platinum skin, even through serving as a contact for the earth return, is not prone to corrosion or other deterioration, or 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. An electrode catheter comprising 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 biocompatible insulating material covering the carbon-fibre monofilaments.

2. An electrode catheter as claimed in claim 1, wherein the core of plastics material is hollow.

3. An electrode catheter as claimed in claim 1 or claim 2, wherein the carbon-fibre monofilaments are assembled together into two groups, the two groups being laid along the plastics material core.

4. An electrode catheter as claimed in claim 3, wherein the two groups are wound helically in opposite senses on the plastics material core so that the groups are interwoven in the form of a tubular net.

5. An electrode catheter as claimed in any of the preceding claims, wherein a layer of soft material relative to the carbon-fibre monofilaments is applied over the core of plastics material and the carbon-fibre monofilaments are laid over said layer.

6. An electrode catheter as claimed in claim 5, wherein the relatively soft material comprises silicone rubber.

7. An electrode catheter as claimed in any of the preceding claims, wherein the sleeve of insulating material covering the carbon-fibre monofilament is a silicon rubber sleeve.

8. An electrode catheter as claimed in claim 7, wherein the silicone rubber is extruded directly on to the monofilaments when these have been laid on the core so as to form an insulating sleeve thereover.

9. An electrode catheter as claimed in any of the preceding claims, wherein the proximal end of the electrode catheter is fitted with a plug member of a plug and socket electrical connector.

10. An electrode catheter as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in Figures 2 to 6 of the accompanying drawings.

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

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. 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. Ir is found that the platinum skin, even through serving as a contact for the earth return, is not prone to corrosion or other deterioration, or 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. An electrode catheter comprising 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 biocompatible insulating material covering the carbon-fibre monofilaments.

2. An electrode catheter as claimed in claim 1, wherein the core of plastics material is hollow.

3. An electrode catheter as claimed in claim 1 or claim 2, wherein the carbon-fibre monofilaments are assembled together into two groups, the two groups being laid along the plastics material core.

4. An electrode catheter as claimed in claim 3, wherein the two groups are wound helically in opposite senses on the plastics material core so that the groups are interwoven in the form of a tubular net.

5. An electrode catheter as claimed in any of the preceding claims, wherein a layer of soft material relative to the carbon-fibre monofilaments is applied over the core of plastics material and the carbon-fibre monofilaments are laid over said layer.

6. An electrode catheter as claimed in claim 5, wherein the relatively soft material comprises silicone rubber.

7. An electrode catheter as claimed in any of the preceding claims, wherein the sleeve of insulating material covering the carbon-fibre monofilament is a silicon rubber sleeve.

8. An electrode catheter as claimed in claim 7, wherein the silicone rubber is extruded directly on to the monofilaments when these have been laid on the core so as to form an insulating sleeve thereover.

9. An electrode catheter as claimed in any of the preceding claims, wherein the proximal end of the electrode catheter is fitted with a plug member of a plug and socket electrical connector.

10. An electrode catheter as claimed in claim 1 and substantially as hereinbefore described, with reference to and as illustrated in Figures 2 to 6 of the accompanying drawings.