WO2010038178A1

WO2010038178A1 - Electrode for implantable medical device

Info

Publication number: WO2010038178A1
Application number: PCT/IB2009/054199
Authority: WO
Inventors: Pieter G. Blanken; Dirk W. Harberts; Michel M. J. Decre; Hubert C. F. Martens
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-10-02
Filing date: 2009-09-25
Publication date: 2010-04-08

Abstract

An electrode (10, 20) for an implantable medical device is provided. The electrode comprises at least one electrically conducting electrode wire (11, 21, 31, 41, 51, 61, 67) surrounded by a shield (32, 42, 52, 56, 62, 66) for shielding the electrode wire (11, 21, 31, 41, 51, 57, 61, 67) against electromagnetic radiation. The shield (32, 42, 52, 56, 62, 66) comprises multiple shielding layers (12, 14) with electrically conductive material alternated with dielectric layers (13). Additionally, an implantable medical device (200, 300, 400, 500, 600) is provided, which device (200, 300, 400, 500, 600) comprise such an electrode (10, 20). Also, a method for producing said electrode (10, 20) is provided.

Description

Electrode for implantable medical device

FIELD OF THE INVENTION

This invention relates to an electrode for an implantable medical device comprising at least one electrically conducting electrode wire surrounded by a shield for shielding the electrode wire against electromagnetic radiation. This invention further relates to implantable medical device comprising such an electrode and to a method for producing such an electrode.

BACKGROUND OF THE INVENTION

Such an electrode is, e.g., known from US patent number 5,217,010. The US patent describes a pacemaker or ECG monitor for implantation in a patient. The device comprises an electronic circuit in a metal shielding case. A lead runs from the electronic circuitry through the patient's body tissue. The lead is a relatively robust wire which is designed to withstand continuous movements of body tissue. In the US patent it is described that the electromagnetic radiation caused by an MRI system may impede the proper functioning of the pacemaker or ECG monitoring device. In an MRI system, the electrode will function as an antenna for the electromagnetic radiation and a resulting voltage over the electrode may harm the device electronics of the pacemaker or ECG monitor. To ensure safe operation in an MRI system, the device electronics are shielded by a metal case and the lead is also surrounded by a shield. In order to prevent excessive heating of the case, the case shield may contain multiple alternating metal and insulating layers.

In some situations, it may be desirable to use a more flexible electrode. For example, in implantable deep brain stimulation devices it is important to use a flexible electrode to prevent damage of the electrode in the body.

OBJECT OF THE INVENTION

It is an object of the invention to provide an electrode as described in the opening paragraph, which electrode has an improved flexibility while maintaining a sufficient level of shielding. SUMMARY OF THE INVENTION

According to a first aspect of the invention, this object is achieved by providing an electrode according to the opening paragraph, wherein the shield comprises multiple shielding layers with electrically conductive material alternated with dielectric layers.

The thin layers provide the flexibility which is important for, e.g., electrodes of implantable deep brain stimulation devices. By using multiple shielding layers, the shield is enabled to provide sufficient shielding of the electrode against the electromagnetic radiation of, e.g. an MRI scanner or a cellular phone. It is to be noted that the shielding case in the above mentioned US patent also uses a multi-layered shield. It is however not obvious for a skilled person to apply that multi- layered shield to the electrode. The shield of the case in the US patent is multi-layered in order to prevent the case from heating caused by currents produced by the electromagnetic field of the MRI system. Such induced currents increase linearly with the flux which is a product of magnetic field and surface area. The heat generation depends on the square of the currents. Therefore, cases with large surfaces heat up much more than electrodes. This heating problem caused by currents induced in the shield does not exist for electrodes. Consequently, a skilled person would have no reason to also apply a multi-layered shield to the electrode. Furthermore, the inventors of the now claimed invention sought for a way to provide a flexible shield for electrodes. Flexibility is not an issue for a shield of a case.

According to a second aspect of the invention an implantable medical device is provided, comprising at least one electrode as described above and device electronics coupled to the electrode wire. The implantable medical device may, e.g., be a pacemaker, a defibrillator, a urinary implant, a neurostimulation device, a spinal cord stimulator or a muscle stimulator.

Preferably, the device electronics is surrounded by a shielding case for shielding the device electronics against electromagnetic radiation, the shielding case being electrically coupled to at least one of the shielding layers of the shield surrounding the electrode wire. By coupling the electrode shielding to the shielding of the device electronics, electrical potential differences between the electrode shielding and the shielding case are eliminated.

One of the advantages of using an electrode according to the invention is that its flexibility allows for producing implantable medical devices with attached thereto one or more electrodes of a standard length. Such medical devices and their electrodes can be implanted into the human body and any excess of electrode length may thereafter be rolled up or folded up and hidden under the skin or within the medical device, e.g. in a special compartment which is provided for that purpose.

According to a third aspect of the invention a method is provided for producing an electrode for an implantable medical device, the method comprising using thin film deposition and/or photolithography for applying multiple shielding layers with electrically conductive material alternated with dielectric layers, thereafter applying at least one electrically conducting electrode wire, and thereafter applying multiple shielding layers with electrically conductive material alternated with dielectric layers. Thin film deposition and photolithography allow manufacturing of an electrode with accurately positioned and very thin layers of shielding material, dielectric layers and electrode wire. As a result a very flexible electrode is provided with optimal shielding properties. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

Figure 1 shows a cross section of an embodiment of an electrode according to the invention, Figure 2 schematically shows an implantable medical device with a shielded electrode,

Figure 3 schematically shows an implantable medical device with three separately shielded electrodes,

Figure 4 schematically shows an implantable medical device with three jointly shielded electrodes,

Figure 5 schematically shows a further embodiment of an implantable medical device with three electrodes,

Figure 6 schematically shows an implantable medical device with a twisted electrodes pair, and Figure 7 shows a flow diagram of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a cross section of an embodiment of an electrode 10 according to the invention. The electrode comprises four electrode wires 11 of an electrically conducting material, such as platinum, iridium, gold or silicon. The electrode wires 11 are surrounded by multiple layers of shielding material 12 and dielectric material 13. The shielding layers 12 may, e.g., comprise platinum, iridium, gold, silicon or titanium. The dielectric layers 13 comprise, e.g., polyurethane, polyimide, silicon oxide or silicon nitride. In this embodiment, each electrode wire 11 is surrounded by a separate shielding layer 12. A common shielding layer 14 surrounds two electrodes 11. Different shielding layers 12, 14 are separated by dielectric layers 13. The shielding 12, 14 shield the electrode wire 11 against electromagnetic radiation from, e.g., an MRI scanner or mobile communication devices, thereby preventing that the electrode wire will operate as a large antenna. Alternatively, a single wire may be surrounded by multiple shielding layers that only enclose that single wire. Then the second shielding layer is not a common shielding layers surrounding two electrodes.

Figure 2 schematically shows an implantable medical device with a shielded electrode 20. The medical device may, e.g., be a pacemaker, an ECG monitor, a defibrillator, a neurostimulating device or a urinary implant. In this figure, the shield 22 is displayed as a simple cylinder. However, according to the invention, the shield 22 does comprise multiple shielding layers alternated with dielectric layers. The tip of the electrode wire 21 is not shielded, because it should be able to make contact with the body tissue in which the medical device is implanted. One end of the electrode wire 21 is coupled to the device electronics 27. The device electronics 27 are powered by a small battery 26. Preferably, also the battery 26 and the device electronics 27 are shielded against electromagnetic radiation from, e.g., an

MRI scanner or mobile communication devices. Therefore, the device electronics 27 and the battery 26 are comprised in a shielding case 24. Because flexibility is not an issue for the shielding case 24, the shielding case 24 may be made of a single conductive plate which is thick enough to provide sufficient shielding. However, also a layered shielding case 24 may be used in order to avoid excessive heating of the shielding case 24. Coupling of the shielding case 24 to the shield 22 of the electrode wire 21 may be provided for avoiding potential differences between different parts of the implantable medical device. In the event that the shielding case 24 also comprises layered shielding, different shielding layers of the electrode shield 22 may be coupled to specific layers in the shielding case 24. Figure 3 schematically shows an implantable medical device with three separately shielded electrodes. Each electrode wire 31 is surrounded by its own multi-layered shielding 32. Preferably the shields 32 are all coupled to a shielding 34 of the device electronics. Figure 4 schematically shows an implantable medical device with three jointly shielded electrodes. All three electrode wires 41 are jointly surrounded by a common multi- layered shielding 42. Preferably the shield 42 is coupled to a shielding 44 of the device electronics. Figure 5 schematically shows a further embodiment of an implantable medical device with three electrodes. One electrode wire 51 is surrounded by its own multi-layered shielding 52. Two other electrode wires 57 are jointly surrounded by a common multi-layered shielding 56. Preferably the shields 52, 56 are both coupled to a shielding 54 of the device electronics. Figure 6 schematically shows an implantable medical device with a twisted pair of electrodes 67. One electrode wire 61 is surrounded by its own multi-layered shielding 62. Two other electrode wires 67 are joined as a twisted pair and are jointly surrounded by a common multi-layered shielding 66. Preferably the shields 62, 66 are both coupled to a shielding 64 of the device electronics. Figure 7 shows a flow diagram of the method according to the invention. The method comprises three steps 71, 72, 73. In a first step 71 multiple shielding layers with electrically conductive material are provided which shielding layers are alternated with dielectric layers. For forming these layers, thin film deposition and photolithography may be used. In this first step 71, multiple shielding layers and dielectric layers are stacked. Preferably this first step 71 begins and ends with applying a dielectric layer for avoiding contact between shielding layers and the electrode wire or between shielding layers and the body tissue in which the device is implanted.

Thereafter, in a second step 72, at least one electrically conducting electrode wire is put upon the available shielding layers and dielectric layers. In order to complete the electrode, in a third step 73, the first step 71 of applying shielding layers and dielectric layers is repeated. Preferably, the shielding layers applied in the third step 73 are coupled to the shielding layers applied in the first step in order to ensure that the at least one electrode wire is shielded against electromagnetic radiations from all sides. Finally, the resulting electrode may then be applied to a unit with device electronics for completing the implantable medical device.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. An electrode (10, 20) for an implantable medical device (200, 300, 400, 500, 600) comprising at least one electrically conducting electrode wire (11, 21, 31, 41, 51, 61, 67) surrounded by a shield (32, 42, 52, 56, 62, 66) for shielding the electrode wire (11, 21, 31, 41, 51, 57, 61, 67) against electromagnetic radiation, the shield (32, 42, 52, 56, 62, 66) comprising multiple shielding layers (12, 14) with electrically conductive material alternated with dielectric layers (13).

2. An electrode (10, 20) as claimed in claim 1, wherein the electrode (10, 20) comprises at least two electrically conducting electrode wires (11, 31) and wherein each one of the at least two electrode wires (11, 31) is individually surrounded by at least one of the shielding layers (12).

3. An electrode (10, 20) as claimed in claim 1, wherein the electrode (10, 20) comprises at least two electrically conducting electrode wires (11, 41, 57, 67) and wherein the at least two electrode wires (11, 41, 57, 67) are jointly surrounded by at least one of the shielding layers (14).

4. An electrode as (10, 20) claimed in claim 1, wherein at least one of the shielding layers and/or at least one of the dielectric layers is obtained by using thin film deposition.

5. An electrode as (10, 20) claimed in claim 1, wherein at least one of the shielding layers (12, 14) and/or at least one of the dielectric layers (13) is obtained by using photolithography.

6. An implantable medical device (200, 300, 400, 500, 600) comprising at least one electrode (10, 20) as claimed in claim 1 and device electronics (27) coupled to the electrode wire (11, 21, 31, 41, 51, 57, 61, 67).

7. An implantable medical device (200, 300, 400, 500, 600) as claimed in claim

6, wherein the implantable medical device (200, 300, 400, 500, 600) is a pacemaker, a defibrillator, a urinary implant or a neurostimulation device.

8. An implantable medical device (200, 300, 400, 500, 600) as claimed in claim

6, wherein the device electronics (27) are surrounded by a shielding case (24, 34, 44, 54, 64) for shielding the device electronics (27) against electromagnetic radiation, the shielding case (24, 34, 44, 54, 64) being electrically coupled to at least one of the shielding layers (12, 14) of the shield (32, 42, 52, 56, 62, 66) surrounding the electrode wire (11, 21, 31, 41, 51, 57, 61, 67).

9. A method for producing an electrode for an implantable medical device, the method comprising using thin film deposition and/or photolithography for:

(71) applying multiple shielding layers with electrically conductive material alternated with dielectric layers, thereafter

(72) applying at least one electrically conducting electrode wire, and thereafter

(73) applying multiple shielding layers with electrically conductive material alternated with dielectric layers.