Patent Description:
The present disclosure relates to lead for an active implantable medical device (AIMD) for implanting into tissue of a patient.

Medical devices having one or more active implantable components, generally referred to herein as active implantable medical devices (AIMDs), have provided a wide range of therapeutic benefits to patients over recent decades. AIMDs often include an implantable, hermetically sealed electronics module, and a device that interfaces with a patient's tissue, sometimes referred to as a tissue interface. The tissue interface may include, for example, one or more instruments, apparatus, sensors or other functional components that are permanently or temporarily implanted in a patient. The tissue interface is used to, for example, diagnose, monitor, and/or treat a disease or injury, or to modify a patient's anatomy or physiological process.

In particular applications, an AIMD tissue interface includes one or more conductive electrical contacts, referred to as electrodes, which deliver electrical stimulation signals to, or receive signals from, a patient's tissue. The electrodes are typically disposed in a biocompatible electrically non-conductive member, and are electrically connected to the electronics module. The electrodes and the non-conductive member are collectively referred to herein as an electrode assembly.

For neuro-stimulators, the tissue interface is a stimulating lead <NUM> which delivers electrical pulse to a specific nerve or tissue. This lead <NUM> may consist of a long thin non-conductive (and insulating) body <NUM> and a number of conductive rings <NUM>, <NUM> at both ends <NUM>, <NUM> of the body <NUM>. Referring to <FIG>, <FIG>, the rings <NUM> at a therapeutic end <NUM> are known as electrodes and the rings <NUM> at the connector end <NUM> are known as contacts, where the electrodes are connected to the contacts along the long thin non-conductive body <NUM>. An example of the long thin non-conductive body <NUM> is shown in the cross-section in <FIG> that shows conductive wires <NUM> surrounded by a non-conductive body <NUM>. These conductive wires <NUM> are sized to have lengths to conduct signals between corresponding conductive rings, such as the length of conductive wire <NUM>' that spans between <NUM>' and <NUM>' in <FIG>. A different length of conductive wire <NUM>" spans between conductive rings <NUM>" and <NUM>".

Patients with an implanted neuro-stimulator and associated lead may have issues undergoing magnetic resonance imaging (MRI). The MRI uses three types of fields to create an image: a static magnetic field; a radiofrequency (RF) magnetic field; and a gradient magnetic field. Exposure to these fields may cause heating to the leads. This heating may result in tissue burns and damage (which may not be immediately felt by the patient). Another potentially damaging effect is damage to the implant due to radiofrequency energy being transmitted from the lead. This can lead to reprogramming, damage to the implant or explant of the implant. Additionally, the MRI could cause a temporary unintended stimulation due to induced voltage through the assembly and system. <CIT> discloses a medical device including a resonance tuning module located in the housing of the medical device, connected to a lead. The resonance tuning module further includes a control circuit, the control circuit acting to determining a resonant frequency for the device, and an adjustable impedance circuit to change the combined resonant frequency of the medical device and lead. <CIT> discloses an electrical implantable lead, with a elongated body including a plurality of lumens. At least one non-linear lumen extends longitudinally along a portion of the lead body and includes a plurality of crests and troughs.

There have been attempts to provide designs for MRI safe leads. US patent publication <CIT> illustrates a method of reducing the heat caused by MRI conditions. This document suggests coiling conductors in a multi-layer structure, with each coil layer electrically connected to the next to provide parallel conductive paths. However, this method may result in high inductance when exposed to MRI radiation. US patent publication <CIT> uses a similar approach with a lead body and multi-layer coil conductor within the length of the lead body. The stiffness of the multi-layer coil conductor is similar to the lead body, ensuring consistent mechanical properties of the lead. US patent publication <CIT> uses a different approach with the lead body providing an additional path for containing conductive material. This path spans at least a section of the length of the lead for conducting the induced RF energy away from the conductive wire of the lead.

In light of the above mentioned issues, it would be advantageous to have an electrode assembly, such as one used in an implantable medical device, that may be implanted in a patient whilst the patient is undergoing magnetic resonance imaging. This may include providing an implantable electrode assembly which, when exposed to an MRI environment, does not generate significant heat in the leads due to electromagnetic currents. In may be further advantageous for an implantable medical device that can operate during magnetic resonance imaging without, or with reduced, side effects described above.

There is disclosed a lead for an active implantable medical device comprising: an elongated, biocompatible, electrically non-conductive body having a centre section between a first portion at a proximal end and a body extension at a distal end; a plurality of electrical connectors at the first portion; a plurality of electrodes at a second portion of the elongated body, wherein the second portion is between the centre section and the body extension ; and a plurality of electrically conductive filaments inside the elongated body to connect the electrical connectors to corresponding electrodes, wherein each of the plurality of electrically conductive filaments include corresponding filament extension sections in the body extension that extends towards the distal end beyond a most distal electrode of the plurality of electrodes at the second portion.

In some examples, a length of each of the filament extension sections is <NUM> or more. In yet further examples, the length of each of the filament extension sections is in the range of <NUM> to <NUM>.

In some examples, the lead further comprises a biocompatible, electrically non-conductive seal at the body extension to insulate the filament extension sections.

In some examples of the lead, each of the plurality of conductive filaments have a common physical and/or electrically equivalent overall length.

In further examples, each electrical distance between each electrical connector and corresponding electrode is shorter that the common overall length.

In some examples of the lead, each of the plurality of electrical connectors are located separately along a first length of the first portion.

In some examples of the lead, each of the plurality of electrodes are located separately along a length of the second portion.

In some examples of the lead, the electrical connectors and/or electrodes are ring shaped.

In some examples, the lead further comprises a central lumen to receive a stylet.

There is also provided a method of manufacturing a lead for an active implantable medical device, comprising: forming a multi-lumen elongated biocompatible, electrically non-conductive body, the elongated body having a centre section between a first portion at a proximal end and a body extension at a distal end; locating a plurality of electrically conductive filaments through the lumens of the elongated body, wherein the plurality of electrically conductive filaments include corresponding filament extension sections that extend into the body extension beyond a most distal electrode of the plurality of electrodes at the second portion; forming a plurality of electrical connectors at the first portion, wherein each of the electrical connectors are electrically connected to respective electrically conductive filaments; forming a plurality of electrodes at a second portion of the elongated body, wherein the second portion is between the centre section and the body extension, and the plurality of electrodes are connected, via corresponding electrically conductive filaments, to corresponding electrical connectors.

In some examples, the method further comprises: sizing each of the plurality of electrically conductive filaments to a common overall length.

In some examples, the elongated body is formed by extruding the biocompatible, electrically non-conductive material with the multi-lumens.

In some examples, the method further comprises sealing an end of the body extension to insulate the filament extension sections.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the scope of the present invention which is defined by the appended claims.

Aspects of the present disclosure are generally directed to an electrode assembly for an active implantable medical device (AIMD). An AIMD may include an implantable electronics module and a tissue interface. The electrode assembly that, at least in part, forms the tissue interface.

The electrode assembly may be used with one type of AIMD, a neuro stimulator, and more specifically a deep brain stimulator or spinal cord stimulator. Deep brain stimulators are a particular type of AIMD that deliver electrical stimulation to a patient's brain, while spinal cord stimulators deliver electrical stimulation to a patient's spinal column. As used herein, deep brain stimulators and spinal cord stimulators refer to devices that deliver electrical stimulation alone or in combination with other types of stimulation. It should be appreciated that embodiments of the present disclosure may be implemented in any brain stimulator (deep brain stimulators, cortical stimulators, etc.), spinal cord stimulator or other neuro stimulator now known or later developed, such as cardiac pacemakers/defibrillators, functional electrical stimulators (FES), pain stimulators, etc. Embodiments of the present disclosure may also be implemented in AIMDs that are implanted for a relatively short period of time to address acute conditions, as well in AIMDs that are implanted for a relatively long period of time to address chronic conditions.

The electrode assembly in accordance with embodiments of the present disclosure are not limited to devices that deliver electrical stimulation signals to a patient. For instance, in certain embodiments, the electrode assembly may be used to receive, record or monitor the physiological response of a patient's tissue to, for example, a therapy. In such embodiments, the electrodes receive a signal from the patient's tissue representing the physiological response. An electrode assembly of the present disclosure that delivers electrical stimulation signals to, or receives signals from, a patient's tissue may also include one or more other components, such as therapeutic agent delivery systems, sensors, etc., that interface with the patient's tissue.

An example of a lead <NUM> for an active implantable medical device <NUM> is illustrated in <FIG> (which show opposite ends of the same lead <NUM>). The lead <NUM> includes an elongated, biocompatible, electrically non-conductive body <NUM>. The elongated body <NUM> extends from a first portion <NUM>, to a centre section <NUM>, to a second portion <NUM>, and finally to a body extension <NUM>.

A plurality of electrical connectors <NUM> are at the first portion <NUM> near a proximal end whereby the connectors <NUM> are used to electrically connect to the active implantable medical device <NUM>. A plurality of electrodes <NUM> are at the second portion <NUM> near a distal end of the elongated body <NUM>, such that the electrodes <NUM> are between the centre section <NUM> and the body extension <NUM>. The electrodes <NUM> deliver therapy to the patient.

A plurality of electrically conductive filaments <NUM> (represented by broken lines) are located inside the elongated body <NUM> to connect the electrical connectors <NUM> to corresponding electrodes <NUM>. Furthermore, the plurality of electrically conductive filaments <NUM> include corresponding filament extension sections <NUM> in the body extension <NUM>.

The filament extension sections <NUM> in the body extension <NUM> moves the reflection point <NUM> of the electromagnetic waves along the elongated body <NUM> away from the most distal electrode <NUM> at the second portion <NUM>. Such electromagnetic waves are excited along the lead <NUM> during MRI scans.

An example of the specific components of the lead <NUM> will now be described in detail.

The first portion <NUM>, including the plurality of connectors <NUM>, are configured to be inserted into the AIMD <NUM>, whereby the connectors <NUM> are in electrical connection with respective connectors inside the AIMD. In one example, the connectors <NUM> are configured to be received in medical grade connector/contact systems such as those under the trade name "Bal Conn" offered by "Bal Seal Engineering". The connectors <NUM> are substantially annular (i.e. ring-shaped) and typically constructed of a biocompatible and electrically conductive material. The annular construction permits good electrical contact with the receiving contact in the AIMD. Suitable material for the connectors <NUM> may include, but is not limited to, platinum, iridium, and/or alloys thereof. In other examples, the connectors <NUM> can include a core of high conductance material such as cobalt, chromium, molybdenum or alloys thereof with a coating of metals such as platinum, tantalum, niobium, titanium or alloys thereof.

The connectors <NUM> are located separately along axis length L<NUM> of the first portion <NUM>. In <FIG>, this includes three connectors <NUM> spaced along the first portion <NUM> for illustrative purposes. However, it is to be appreciated that additional connectors <NUM>, for additional channels, can be used. In some examples, this can include up to a dozen or more channels (with a corresponding dozen connectors <NUM>, electrically conductive filaments <NUM>, and electrodes <NUM>). The whole length L1 of the first portion <NUM> is typically inserted into the AIMD.

In addition to the connectors <NUM>, the first portion <NUM> includes non-conductive part(s) that support the connectors <NUM>. In some examples, this includes the same material, and can be part of, the elongated, biocompatible, electrically non-conductive body <NUM>.

A particular example will now be described with reference to <FIG> which is a cross-section of the first portion <NUM> through one of the connectors <NUM>, of a twelve channel lead <NUM>. This includes the biocompatible, electrically non-conductive body <NUM> with a central lumen <NUM>, and a dozen outer lumens <NUM>. The central lumen <NUM> is provided to receive a stylet to aid insertion and implantation of the lead <NUM> after which the stylet is withdrawn. The outer lumens <NUM> house the electrically conductive filaments <NUM>, which in this case includes a dozen electrically conductive filaments <NUM>.

A particular example of electrically connecting the connector <NUM>' to an electrically conductive filament <NUM>' will now be described with reference to <FIG>. Part of the electrically non-conductive body <NUM> is thinned <NUM> or removed to expose a particular outer lumen <NUM>'. This allows an electrically conductive filament <NUM>'inside the outer lumen <NUM>' to be in electrical contact with the electrical conductor <NUM>' located around the periphery of the body <NUM>. It is to be appreciated that the order of assembling these components can be varied.

In one example, the electrically conductive filaments <NUM> are inserted into the outer lumens <NUM> (such as by a drawn filled tubing process) and the connectors <NUM> are subsequently attached to the first portion <NUM> of the body <NUM>. In other examples, the connectors <NUM> are positioned on the body <NUM> before the electrically conductive filaments <NUM> are inserted in the outer lumens <NUM>.

In the above example, the body <NUM> and electrical conductive filaments <NUM> extend into, and are part of, the first portion <NUM>. In alternative examples, separate material or components can form the first portion <NUM>. This can include a separate electrical conductive filament in the first portion <NUM> that is electrically connected to the electrically conductive filament <NUM> in the centre portion <NUM>. Similarly, a body of the first portion <NUM> can be separately made, but connected to, the centre portion <NUM> of the body <NUM>.

The centre section <NUM> of the body <NUM> includes the biocompatible, electrically non-conductive body <NUM> and the electrically conductive filaments <NUM> in the outer lumens <NUM>. In examples where a stylet is used, the centre section <NUM> also has a central lumen <NUM> to receive the stylet.

The centre section <NUM> has a length L<NUM>, which is typically the longest portion of the elongated body <NUM>. In typical examples, the centre section <NUM> encloses the electrically conductive filaments <NUM> to minimise conduction between the electrically conductive filaments <NUM> to tissue immediately surrounding the centre section <NUM>.

The body <NUM> is made of biocompatible, electrically non-conductive material that can include thermoplastic polyurethanes (TPUs) such as those under the trade name "pellethane" offered by "The Lubrizol Corporation". In some examples, the body <NUM> is made from an extrusion of a flexible material with multiple lumens. In some examples, the body <NUM> and the electrically conductive filaments <NUM> are mated together with a drawn filled tubing process.

The electrically conductive filaments <NUM> is preferably selected from a configuration of biocompatible materials. This can include single core or multi strand wires. In another example, this can include a composite of a medical grade alloy, with the trade name "35N LT" offered by Fort Wayne Metals, having a silver core. In another specific example, the conductive filaments <NUM> include a wire jacket of 35N LT (Nickel-Cobalt-Chromium alloy) per ASTM F562 and of a composition which includes ≤ <NUM>. 01wt% titanium, and a wire core of silver <NUM>% of the cross-sectional area of the electrically conductive filament <NUM>.

The second portion <NUM> includes a plurality of electrodes <NUM>, <NUM> to deliver therapy to the patient. In some examples, the number of electrodes <NUM> are the same as the number of corresponding connectors <NUM>, and in turn, the same number of electrically conductive filaments <NUM> that form the electrical connection.

The size and spacing of the electrodes <NUM> located along length L<NUM> is selected based on the anticipated therapy to the patient. Typically, each electrode <NUM> has a longer axial length than the corresponding connector <NUM>.

The electrodes <NUM>, in some examples, can be assembled to the lead <NUM> in a similar way to the connectors <NUM> in the first portion <NUM>. Thus in some examples, the structure shown in <FIG> similarly reflects the structure in the second portion <NUM>. Furthermore, the electrodes <NUM> can be made of the same, or a similar, biocompatible electrically conductive material.

The non-conductive part(s) of the second portion <NUM> can be integrally formed with the body <NUM> of the centre section <NUM> and the first portion <NUM>. Similarly, the electrically conductive filaments <NUM> are integrally formed and extend from the centre section <NUM> into the second portion <NUM>. The electrically conductive filaments <NUM> continue through the second portion <NUM> and to the body extension <NUM> discussed below.

It is to be appreciated that in alternative examples, the electrically conductive filaments <NUM> in the second portion <NUM> can be separately formed, but electrically connected, to the electrically conductive filaments <NUM> in the centre section <NUM>. Similarly the non-conductive part(s) of the second portion may, in an alternative example, be separately formed but connected to the centre section <NUM>.

Referring to <FIG> and <FIG>, the body extension <NUM> is at the distal end of the lead <NUM> and adjacent the second portion <NUM>. The purpose of the body extension <NUM> is to extend the electrically conductive filaments <NUM>, by a Length L<NUM> of the filament extension section <NUM>, past the most distal electrode <NUM> of the plurality of electrodes <NUM>. The Length L<NUM> moves the reflection point <NUM> of an electromagnetic wave propagating along the lead <NUM> away from the most distal electrode <NUM>.

In some examples, the body extension <NUM> is formed as part of the biocompatible, electrically non-conductive body <NUM> that makes up the first portion <NUM>, centre section <NUM>, and second portion <NUM>. This can include an extrusion of flexible material with a multi-lumens, whereby the end is sealed with an electrically non-conductive seal <NUM>. The seal <NUM> insulates (to an extent) the filament extension section <NUM> from the immediate surrounding tissue.

In some examples, this seal <NUM> can be a plug of material injected into the lumens <NUM>, <NUM>. In other examples, the end of the body extension <NUM> can be dipped into a sealing material. In yet another examples, the seal <NUM> is formed by closing the lumens <NUM>, <NUM> in the electrically non-conductive body <NUM> material by welding, such as heat, ultrasonic welding, resistance welding, laser welding, etc. A similar seal may be provided at the first portion to close off the ends of the outer lumens <NUM> at the proximal end.

In some examples, the filament extension section <NUM> has a Length L<NUM> of <NUM> or more. In some examples, the Length L<NUM> is in the range of <NUM> to <NUM> (inclusive).

In some examples, each of the electrically conductive filaments <NUM> are sized to have a common overall length. In some examples, this common overall length is a physical overall length. In other examples, the common overall length is an electrically equivalent overall length. In yet further examples, the electrically conductive filaments share both common physical and electrically equivalent overall length. The common overall length may assist in minimising the generation of differential electromagnetic modes and induced differential voltages propagating between the filaments <NUM> in the body <NUM>.

In some examples, the common overall length of the electrically conductive filament <NUM> is the sum of L<NUM>, L<NUM>, L<NUM>, and L<NUM>.

In some examples, the electrical distance between each electrical connector <NUM> and the corresponding electrode <NUM> is shorter than the common overall length. This difference in length is typically at least Length L<NUM> of the filament extension section <NUM>.

The leads <NUM> are selected from a length suitable for the therapy and patient characteristics. In some examples, the leads <NUM> are in the range of <NUM> to <NUM> in length. In yet other examples, the lead are in the range of <NUM> to <NUM> in length.

<FIG> illustrate complex electric field magnitudes at a distal end (i.e. body near the second portion <NUM>) for a <NUM> long lead <NUM> with a dozen of electrodes <NUM> (and corresponding dozen of electrically conductive filaments <NUM> and electrical connectors <NUM>). The diagram <NUM> in <FIG> illustrates the magnitude of complex electric fields at the distal end without a body extension <NUM>. In particular, the highest magnitude corresponds to the first electrode <NUM> located at the most distal portion (i.e. around <NUM> from the proximal end), with a magnitude of approximately14 V/m. The other electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have a smaller magnitude, with the twelfth electrode <NUM> (closer to the proximal end) having the smallest magnitude.

The diagram <NUM> in <FIG> illustrates the magnitude of complex electric field at the distal end with a body extension <NUM> ranging from <NUM> to <NUM>. These different lengths are represented by the different lines in the diagram. The highest magnitude corresponds to the first electrode <NUM> located at the most distal portion (i.e. around <NUM> from the proximal end), with a magnitude of approximately <NUM> V/m. The other electrodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have a smaller magnitude, with the twelfth electrode <NUM> (closer to the proximal end) having the smallest magnitude.

In both scenarios (i.e. with and without the body extension <NUM>), a plane electromagnetic wave with an axiolateral electric field of 1V/m at <NUM> was used to excite the distal end. The leads and AIMD (in the form of an implanted pulse generator) were embedded in a gelled saline solution to simulate tissue. In this test, the lead <NUM> with the body extension <NUM> at the distal end a decrease in complex electric field magnitude by more than <NUM>%.

Referring to <FIG>, there is also disclosed a method of manufacturing a lead <NUM> for an active implantable medical device <NUM>. This includes forming <NUM> a multi-lumen <NUM> elongated biocompatible, electrically non-conductive body <NUM>, wherein the elongated body <NUM> has a centre section <NUM> between a first portion <NUM> and a body extension <NUM>. In some examples, this includes extruding the elongated body <NUM> with multiple lumens. The method also includes locating <NUM> a plurality of electrically conductive filaments <NUM> through the lumens <NUM> of the elongated body <NUM>, wherein the plurality of electrically conductive filaments <NUM> include corresponding filament extension sections <NUM> that extend into the body extension <NUM>. As noted above, some examples of include locating and securing the electrically conductive filaments <NUM> using a drawn filled tubing technique. The method further includes forming <NUM> a plurality of electrical connectors <NUM> at the first portion <NUM>, wherein each of the electrical connectors <NUM> are electrically connected to respective electrically conductive filaments <NUM>. The method <NUM> also includes forming <NUM> a plurality of electrodes <NUM> at a second portion <NUM> of the elongated body <NUM>, wherein the second portion <NUM> is between the centre section <NUM> and the body extension <NUM>, and the plurality of electrodes <NUM> are connected, via corresponding electrically conductive filaments <NUM>, to corresponding electrical connectors <NUM>.

In some examples, it may be possible to perform some of these steps in other sequences. For example, the step of forming the electrodes <NUM> can precede the step of forming the connectors <NUM>.

The method <NUM> may also include additional steps. For example, this can include steps of sealing one or more ends of the lead and or sizing the length of the electrically conductive filaments <NUM>.

Claim 1:
A lead (<NUM>) for an active implantable medical device (<NUM>) comprising:
- an elongated, biocompatible, electrically non-conductive body (<NUM>) having a centre section (<NUM>) between a first portion (<NUM>) at a proximal end and a body extension (<NUM>) at a distal end;
- a plurality of electrical connectors (<NUM>) at the first portion (<NUM>);
- a plurality of electrodes (<NUM>) at a second portion (<NUM>) of the elongated body (<NUM>),
wherein the second portion (<NUM>) is between the centre section (<NUM>) and the body extension (<NUM>); and
- a plurality of electrically conductive filaments (<NUM>) inside the elongated body (<NUM>) to connect the electrical connectors (<NUM>) to corresponding electrodes (<NUM>),
- wherein each of the plurality of electrically conductive filaments (<NUM>) include corresponding filament extension sections (<NUM>) in the body extension (<NUM>) that extends towards the distal end beyond a most distal electrode (<NUM>) of the plurality of electrodes (<NUM>) at the second portion (<NUM>).