WO2007123443A1

WO2007123443A1 - A medical implantable lead and a method for manufacturing the same

Info

Publication number: WO2007123443A1
Application number: PCT/SE2006/000478
Authority: WO
Inventors: Rolf Hill; Bengt-Åke NOREN
Original assignee: St. Jude Medical Ab
Priority date: 2006-04-25
Filing date: 2006-04-25
Publication date: 2007-11-01

Abstract

The invention relates to a medical implantable lead, being adapted to be inserted into a human or animal body, comprising two electrical conductors and a helix (4) , which is adapted to serve as an attachment for the lead to the tissue as well as to serve as a first electrode for one of the conductors for transmitting of electrical signals to and/or from the tissue. The helix is movable between a retracted position located inside a tubular header (1) and an extended position projecting from the header. The distal end portion of the header is provided with a marker (12) of a radiopaque material. The header is manufactured of an electrically insulating material and the marker is arranged in the header, such that the marker does not present any electrically conducting surface towards the outer circumference of the header. The invention also relates to a method for manufacturing of such a medical implantable lead.

Description

A MEDICAL IMPLANTABLE LEAD AND A METHOD FOR MANUFACTURING

THE SAME

The invention relates to a medical implantable lead, being adapted to be inserted into a human or animal body, comprising two electrical conductors and a helix, which is adapted to serve as an attachment for the lead to the tissue as well as to serve as a first electrode for one of the conductors for transmitting of electrical signals to and/or from the tissue, and which is movable between a retracted, inactive position located inside a tubular- header of the lead and an extended, active position, by screw rotating of the helix in relation to the header, in which the distal end portion of the helix is projecting from the distal end of the header, the header being provided with a marker of a radiopaque material in a distal end portion thereof, for being visible in an image generating process of the inner of the tissue, as well as a second electrode for the other conductor.

The invention also relates to a method for manufacturing of an embodiment of such a medical implantable lead.

Background of the invention

A medical implantable lead of the above kind may be used for different purposes. E.g. connected to a pacemaker for monitoring and pacing the activity of a human heart, as a nerve stimulator or connected to a device for monitoring and/or pacing the activity of any other arbitrary organ in a human or animal body.

Leads of the kind indicated above, are of a so called bipolar type. An unipolar lead comprises only one electrode, whereas a bipolar lead, according to the invention, comprises two electrodes having different electrical potential and being connected to separate electrical conductors inside the lead. The technical development goes towards increasing use of bipolar leads, since they can be made to function with good performance in terms of e.g. accuracy, sensitivity and energy efficiency. Both of the electrodes of a bipolar lead can be positioned on the helix if they are separated by an intermediate electrically insulated portion. However, since the technical development goes towards smaller and smaller dimensions on leads of this kind, for example having a helix length in the order of only about 2 mm, the electrodes will in such case usually be positioned too close together to achieve satisfactory performance. Therefore it is in most cases desirable, as in the present invention, to have one electrode positioned on the helix and the other electrode on a tubular tip portion, a so called helix protector or header, to obtain sufficient separation between the electrodes .

When mounting such a medical implantable lead into body tissue, e.g. inside a heart, it is desirable for a physician, performing the mounting, to be able to visually follow the mounting procedure to see when the helix has been fully extended from the tubular header to be assured that the helix has been attached properly. This monitoring is in pacemaker applications done by means of x-ray imaging of the actual region of the body, but could in other applications be performed by some other means, e.g. by means of magnetic resonance imaging. Therefore it is necessary that the components to be seen in the imaging process, are radiopaque for the chosen imaging process, i.e. that they are impenetrable or at least difficult to penetrate for the radiation.

Consequently, the distal end of the header as well as the helix are preferably radiopaque. However, in many cases the helix is so small that it might be hard to see by the chosen imaging method and therefore it is advisable to make also a shaft assembly, which is located inside the header and adapted to mount and rotate the helix inside the header, of a radiopaque material in order to see and monitor also the movement of the shaft assembly. For this reason the entire header can not be manufactured of a radiopaque material since this would make it impossible to see and monitor the shaft assembly. As a consequence of the circumstances reviewed above, the leads used today are usually provided with a metallic, radiopaque marker ring, of for example platinum and/or iridium, in case of x-ray imaging, which is located in a distal end of the header, and an electrode ring in a proximal end or an intermediate portion of the header. The electrode ring is normally of a non- radiopaque material .

However, it has been found that it is advantageous to position the electrode ring closer to the distal end of the header than it normally has been done before. In this way an advantageous balance may be achieved between sensitivity and selectivity such that relevant signals can be distinguished and received but irrelevant signals sorted out when monitoring the tissue, as well as achieve a suitable balance between distribution and concentration of signals when pacing the tissue, i.e. when sending electrical signals to the tissue. In pace-maker applications the preferred distance of the electrode ring from the distal end of the header has been found to be between 1,0 to 1,5 mm, preferably about 1,2 mm. However, this will also result in a very close positioning of the electrode ring in relation to the marker ring. One disadvantage of moving the electrode ring closer to the marker ring, is however that the marker ring will disturb the emitting and receiving of the very weak signals involved, which will result in a deteriorated performance of the lead.

One way to overcome this problem is to do as is disclosed in a hereinafter described prior art lead, namely to position the marker ring on the inside of the tubular bore of the header. However, in this way the marker ring will come into contact with the helix and hence it is necessary to connect the marker ring to the same electrical potential as the helix. Otherwise the marker ring might act as a capacitor and disturb the transmitting and receiving of signals. In the disclosed prior art lead, the electrical connection of the marker ring is accomplished by a metallic, electrically conductive sleeve in the header which is, in its proximal end, connected to the same conductor as the helix.

Moreover, available leads are often assembled of many different components, which result in high costs for manufacturing and assembling of the leads . It is therefore a need for simplifying the structure and assembling process of the leads in order to reduce costs.

Summary of the invention

An object of the present invention is to eliminate or reduce the above problems associated with prior art leads. More precisely, it is an object to provide a medical implantable lead having good performance characteristics, which is possible to manufacture and assemble in a simple and cost reducing way. At least this object is achieved by a lead according to claim 1.

The invention also relates to a method for manufacturing of a preferred embodiment of a medical implantable lead having essentially the same object as above. At least this object is achieved by a method according to claim 7.

Accordingly, the present invention is based on the insight that the above object may be achieved by a medical implantable lead, the tip portion or header of which comprises a header sleeve which is formed, preferably by moulding, of an electrically insulating material, preferably plastics, e.g. PEEK, and that the radiopaque marker is arranged in the header in such a way that the marker does not present any electrically conducting surface towards the outer circumference or towards the inner bore of the header. Within this general idea, the invention may be realized in many different ways. In one embodiment the marker may be in form of a radiopaque substance, which is mixed or doped in at least a distal end portion of the header sleeve at the same time as moulding of the same. The radiopaque substance should be of an electrically insulating material such that radiopaque material which, after moulding, will be positioned in the surface layer of the header sleeve, should not affect the signal transmission between the electrodes and the tissue. An example of such a material is barium sulphate. However, as a rule it is, as mentioned before, desirable to provide only the distal end portion of the header sleeve with a radiopaque substance in order to be able to see also a shaft assembly, which supports and rotates the helix, during the imaging process. This may be achieved by techniques known in the art, e.g. by so called double casting of the header sleeve.

In another embodiment the marker may be a solid body, e.g. a metallic ring, which is embedded into the header, either by being moulded into the header or by being inserted into a recess in the header, for example in a slot in the distal end of the header. However, the solid body need not be in form of a ring, but could also be e.g. radiopaque pins positioned in the header. It is to be understood that the scope of the invention also comprises the use of a marker which is formed as a separate component, preferably in form of a ring, of a material being electrically non-conductive, for example plastics doped with barium sulphate, which is exposed to the outside and/or the inside of the header. One disadvantage with such a solution is however that the marker will be a separate component which has to be manufactured separately, stock-kept and mounted on the header sleeve.

A header according to the invention, can be assembled of fewer components and fewer manufacturing steps, which is cost-saving as mentioned before. However, a consequence of fewer components also is that the overall header can be made with smaller dimensions with regard to width as well as length. One advantage with a decreasing length is that the rigid and stiff length of the lead, represented by the header, will decrease in favour of a corresponding increase of the flexible part of the lead. This is advantageous for i.a. increased flexibility and reduced forces on the tissue at the area of attachment.

Preferred embodiments of the invention, as well as a detailed description of the closest state of the art, will now be described by way of example.

Brief description of the drawings In the drawings is shown in: Fig 1 a cross section of a distal portion of a lead according to prior art;

Fig 2 a cut through perspective view of a distal portion of a lead according to the present invention;

Fig 3 a cross section of the lead according to fig 2 showing a first embodiment of a header according to the invention; Fig 4 a cross section of a header according to a second embodiment of the invention; and Fig 5 a cross section of a header according to a third embodiment of the invention.

Detailed description of closest prior art and preferred embodiments of the invention

Reference is first made to fig 1, in which an embodiment of a prior art medical implantable lead is illustrated in a cross section of a distal portion of the lead. By reference number 1 is indicated a tip portion, a so called helix protector or header, which comprises a metallic tube or sleeve 2, of e.g. titanium, which has been provided with a cap 3 of an insulating material, e.g. plasties, in its distal end. The header 1 is hollow and adapted to serve as a carrier for the components necessary for performing of attachment of the medical lead to the tissue as well as transmitting of signals between the lead and the tissue. The header constitutes a rigid portion of the lead which is connected to a flexible portion comprising at least two electrically separated conductors. Inside the header is indicated, by reference number 4, a helix, which is mounted on and rotatable by means of a shaft assembly 5. When rotating the helix 4 by means of the shaft assembly 5, the helix can be extended out from the bore of the header 1 through engagement of the helix with a post 6 arranged on the inside of the header sleeve 2. When extending the helix from the inner bore of the header, also the shaft assembly 5 will be displaced forward in the header. Arranged on the outer circumference of the header 1 is a metallic ring 7, which serves as an electrode for one of the conductors 7' inside the lead. The helix 4 functions as an electrode for another conductor 4' via the shaft assembly 5. On the inside of the insulating cap 3 is provided a ring 8 of a metallic, radiopaque material, e.g. of platinum and/or iridium, which serves as a marker for the distal end of the header when generating an image of the body tissue by means of for example x-ray imaging.

The medical implantable lead depicted in fig 1, presents several disadvantages. Since it comprises many separate components of different materials, the costs to manufacture and assemble the components will be considerable. I. a. since the ring electrode 7 is applied outside of the electrically conducting, metallic header sleeve 2, a first insulating layer 9 has to be provided over the header 1 before mounting of the ring electrode 7, in order to electrically insulate them from each other. Moreover, since the ring electrode 7 is connected to the conductor 7' , a second insulating layer 10 has to be arranged over the first insulating layer sandwiching the conductor 7' between the insulating layers 9 and 10. Because the electrode ring 7 is arranged so close to the distal end of the header 1, the outermost tip of the header 1 is provided with the electrically insulating cap 3 and the marker ring 8 is arranged on the inner circumference of the cap to eliminate any interfering influence, from the electrically conducting marker ring 8 or the header sleeve 2, on emitting and/or receiving of signals from or to the electrodes in form of the electrode ring 7 and the helix 4, respectively. Furthermore, when forming the header sleeve 2 of a metallic material, it is difficult or even impossible to form the post 6 as an integrated part of the header to a reasonable cost. Accordingly, it is necessary to form the post 6 as a separate component which is connected to the header in a separate assembling step, e.g. by welding of the post in an aperture through the wall of the header. Now reference is made to figs 2 and 3, wherein an embodiment of the medical implantable lead, according to the invention, is shown in a cut through perspective view and a cross section of the distal portion, respectively. In the following description the same reference numbers is used for components which are substantially equivalent to the components described in connection with the prior art lead in fig 1.

Accordingly, the lead in fig 2 and 3 comprises a helix 4, which is mounted on and rotatable by means of a shaft assembly 5. On the outer circumference of the lead in close proximity to the distal end, the lead is provided with an electrically conducting electrode 7, in this case in form of a metallic ring, which is connected to a conductor 1' .

However, according to the invention, a header sleeve 11 is manufactured as a unitary component of an electrically insulating material, e.g. plastics. This has to effect that no insulating layer has to be provided between the header sleeve 11 and the electrode 7. Instead the electrode may be arranged directly against the header sleeve 11, which means that this insulating layer and manufacturing step can be avoided in relation to prior art. Also a separate cap (reference number 3 in fig 1) can be dispensed with, since a marker 12 is arranged directly in a distal end portion of the header sleeve 11.

The marker 12 may be arranged in different ways in the header and in figs 3-5 are shown, in cross sections of the header sleeve 11, three different embodiments for arranging the marker in the distal end of the header. The header sleeve is in these figures shown as a half-tube. However, this is done only for purpose of clarity and in reality the entire header sleeve is preferably formed as a complete tube in one single forming process, including forming of a marker section 12 and the post 6 for engagement with the helix.

In fig 3 is shown a first embodiment of the marker arrangement in the distal end of the header. In this embodiment the header sleeve 11 is during moulding provided with an annular recess opening towards the distal end face, and subsequently a marker in form of a ring 12, is inserted into the recess from the end face and sealed therein by means of for example a thin layer of silicone 13. If a marker of an electrically conducting material is used, the marker 12 can not be positioned in the definite outermost end of the header, since there must be provided a sufficient space for the sealing layer 13 such that no electrically conducting surface of the marker ring 12, which can disturb the emitting and/or receiving of signals at the electrodes, is exposed to the outside. In practice it is in most cases sufficient if a space of about 0,2 mm is provided from the distal end of the marker ring 12 to the distal end of the header sleeve.

In fig 4 is shown a second embodiment where the marker is in form of a doped, radiopaque substance, e.g barium sulphate, in a marker section 12 of the outermost distal end of the header sleeve 11. The radiopaque substance is mixed into the cast compound when moulding the header sleeve. One advantage with this embodiment is that the marker will be positioned at the very end of the header such that the outermost end of the header will be visible when generating an image, e.g. by x-ray imaging, of the inside of the body during mounting of the lead. Another advantage is that a marker in form of a separate detail, involving manufacturing, stock-keeping and assembling, can be dispensed with.

In fig 5 is shown a third embodiment of the marker arrangement in the distal end of the header. Here the marker is in form of a ring 12 of a radiopaque material, e.g. platinum and/or iridium, which is embedded into the marker section during moulding of the header sleeve. Also in this embodiment the marker can not be positioned in the definite outermost end of the header. In an actual embodiment, the marker will be positioned about 0,2 mm from the end face.

Claims

1. A medical implantable lead being adapted to be inserted into a human or animal body, comprising two electrical conductors and a helix (4) , which is adapted to serve as an attachment for the lead to the tissue as well as to serve as a first electrode for one of the conductors for transmitting of electrical signals to and/or from the tissue, and which is movable between a retracted, inactive position located inside a tubular header (1) and an extended, active position, by screw rotating of the helix in relation to the header, in which the distal end portion of the helix is projecting from the distal end of the header, the header being provided with a marker (12) of a radiopaque material in a distal end portion thereof, for being visible in an image generating process of the inner of the tissue, as well as a second electrode (7) for the other conductor, c h a r a c t e r i z e d in that the header (1) comprises a header sleeve (11) , which is manufactured of an electrically insulating material, and the marker (12) is arranged in the header, such that the marker does not present any electrically conducting surface towards an outer circumference or an inner bore of the header.

2. A medical implantable lead according to claim 1, c h a r a c t e r i z e d in that the marker (12) is in form of a radiopaque material which is doped into the header sleeve (11) .

3. A medical implantable lead according to claim 2, c h a r a c t e r i z e d in that the doped material is barium sulphate.

4. A medical implantable lead according to claim 1, c h a r a c t e r i z e d in that the marker (12) is in form of at least one body of a radiopaque material which is embedded into the header sleeve (11) .

5. A medical implantable lead according to claim 4, c h a r a c t e r i z e d in that the marker (12) is in form of at least one body of a radiopaque material which is moulded into the header sleeve (11) .

6. A medical implantable lead according to claim 4, c h a r a c t e r i z e d in that the marker (12) is in form of at least one body of a radiopaque material which is inserted into a recess in the distal end surface of the header sleeve (11) .

7. A method for manufacturing of a medical implantable lead of the kind which is adapted to be inserted into a human or animal body and which comprises two electrical conductors and a helix (4) , which is adapted to serve as an attachment for the lead to the tissue as well as to serve as a first electrode for one of the conductors for transmitting of electrical signals to and/or from the tissue, and which is movable between a retracted, inactive position located inside a tubular header (1) and an extended, active position, by screw rotating of the helix in relation to the header, in which the distal end portion of the helix is projecting from the distal end of the header, the header being provided with a marker (12) of a radiopaque material in the distal end portion thereof, for being visible in an image generating process of the inner of the tissue, as well as a second electrode (7) for the other conductor for conducting of electrical signals to and/or from the tissue, c h a r a c t e r i z e d by the step to mould a header sleeve (11) of an electrically insulating material and to dope the material with a radiopaque, electrically insulating substance before moulding and solidification.

8. A method according to claim 7, c h a r a c t e r i z e d by using barium sulphate as the radiopaque substance.