Patent Publication Number: US-2023140180-A1

Title: Lead for an active implantable medical device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Australian Provisional Patent Application No 2019903747 filed on 4 Oct. 2019, the contents of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to lead for an active implantable medical device (AIMD) for implanting into tissue of a patient. 
     BACKGROUND 
     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&#39;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&#39;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&#39;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  1000  which delivers electrical pulse to a specific nerve or tissue. This lead  1000  may consist of a long thin non-conductive (and insulating) body  1004  and a number of conductive rings  1006 ,  1008  at both ends  1007 ,  1009  of the body  1004 . Referring to  FIGS.  5   a ,  5   b   ,  6  and  7 , the rings  1008  at a therapeutic end  1009  are known as electrodes and the rings  1006  at the connector end  1007  are known as contacts, where the electrodes are connected to the contacts along the long thin non-conductive body  1004 . An example of the long thin non-conductive body  1004  is shown in the cross-section in  FIG.  7    that shows conductive wires  1005  surrounded by a non-conductive body  1003 . These conductive wires  1005  are sized to have lengths to conduct signals between corresponding conductive rings, such as the length of conductive wire  1005 ′ that spans between  1006 ′ and  1008 ′ in  FIGS.  5   a  and  5   b   . A different length of conductive wire  1005 ″ spans between conductive rings  1006 ″ and  1008 ″. 
     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. 
     Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
     Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. 
     SUMMARY 
     There have been attempts to provide designs for MRI safe leads. US patent publication U.S. Pat. No. 8,798,767 B2 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 U.S. Pat. No. 9,050,457 B2 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 U.S. Pat. No. 9,302,101 B2 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 and a body extension; 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. 
     In some examples, a length of each of the filament extension sections is 10 mm or more. In yet further examples, the length of each of the filament extension sections is in the range of 10 mm to 50 mm. 
     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 and a body extension; 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; 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. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS.  1   a  and  1   b    illustrate an example of a lead for an active implantable medical device, whereby  FIG.  1   a    shows a distal end and  FIG.  1   b    shows a proximal end; 
         FIG.  2   a    is a perspective view of a distal end of the lead including a body extension with corresponding filament extension sections; 
         FIG.  2   b    illustrates a cross-section of the lead at the proximal end and through an electrical connector; 
         FIGS.  3   a  and  3   b    are test results showing, respectively, the magnitude of complex electric fields at a distal end with and without the body extension; 
         FIG.  4    is a flow diagram of a method of manufacturing a lead for an active implantable medical device; 
         FIGS.  5   a  and  5   b    illustrate an example of a prior art lead; 
         FIGS.  6    illustrates another view of a prior art lead; and 
         FIG.  7    illustrates a cross section of the prior art lead in  FIG.  6   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     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 broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     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&#39;s brain, while spinal cord stimulators deliver electrical stimulation to a patient&#39;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&#39;s tissue to, for example, a therapy. In such embodiments, the electrodes receive a signal from the patient&#39;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&#39;s tissue may also include one or more other components, such as therapeutic agent delivery systems, sensors, etc., that interface with the patient&#39;s tissue. 
     An example of a lead  1  for an active implantable medical device  99  is illustrated in  FIGS.  1   a  and  1   b    (which show opposite ends of the same lead  1 ). The lead  1  includes an elongated, biocompatible, electrically non-conductive body  3 . The elongated body  3  extends from a first portion  7 , to a centre section  4 , to a second portion  9 , and finally to a body extension  11 . 
     A plurality of electrical connectors  6  are at the first portion  7  near a proximal end whereby the connectors  6  are used to electrically connect to the active implantable medical device  99 . A plurality of electrodes  8  are at the second portion  9  near a distal end of the elongated body  3 , such that the electrodes  8  are between the centre section  4  and the body extension  11 . The electrodes  8  deliver therapy to the patient. 
     A plurality of electrically conductive filaments  5  (represented by broken lines) are located inside the elongated body  3  to connect the electrical connectors  6  to corresponding electrodes  8 . Furthermore, the plurality of electrically conductive filaments  5  include corresponding filament extension sections  13  in the body extension  11 . 
     The filament extension sections  13  in the body extension  11  moves the reflection point  16  of the electromagnetic waves along the elongated body  3  away from the most distal electrode  10  at the second portion  9 . Such electromagnetic waves are excited along the lead  1  during MRI scans. 
     An example of the specific components of the lead  1  will now be described in detail. 
     The First Portion  7   
     The first portion  7 , including the plurality of connectors  6 , are configured to be inserted into the AIMD  99 , whereby the connectors  6  are in electrical connection with respective connectors inside the AIMD. In one example, the connectors  6  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  6  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  6  may include, but is not limited to, platinum, iridium, and/or alloys thereof. In other examples, the connectors  6  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  6  are located separately along axis length Li of the first portion  7 . In  FIG.  1   b   , this includes three connectors  6  spaced along the first portion  7  for illustrative purposes. However, it is to be appreciated that additional connectors  6 , for additional channels, can be used. In some examples, this can include up to a dozen or more channels (with a corresponding dozen connectors  6 , electrically conductive filaments  5 , and electrodes  8 ). The whole length L 1  of the first portion  7  is typically inserted into the AIMD. 
     In addition to the connectors  6 , the first portion  7  includes non-conductive part(s) that support the connectors  6 . In some examples, this includes the same material, and can be part of, the elongated, biocompatible, electrically non-conductive body  3 . 
     A particular example will now be described with reference to  FIG.  2   b    which is a cross-section of the first portion  7  through one of the connectors  6 , of a twelve channel lead  1 . This includes the biocompatible, electrically non-conductive body  3  with a central lumen  35 , and a dozen outer lumens  15 . The central lumen  35  is provided to receive a stylet to aid insertion and implantation of the lead  1  after which the stylet is withdrawn. The outer lumens  15  house the electrically conductive filaments  5 , which in this case includes a dozen electrically conductive filaments  5 . 
     A particular example of electrically connecting the connector  6 ′ to an electrically conductive filament  5 ′ will now be described with reference to  FIG.  2   b   . Part of the electrically non-conductive body  3  is thinned  18  or removed to expose a particular outer lumen  15 ′. This allows an electrically conductive filament  15 ′inside the outer lumen  15 ′ to be in electrical contact with the electrical conductor  6 ′ located around the periphery of the body  3 . It is to be appreciated that the order of assembling these components can be varied. 
     In one example, the electrically conductive filaments  5  are inserted into the outer lumens  15  (such as by a drawn filled tubing process) and the connectors  6  are subsequently attached to the first portion  7  of the body  3 . In other examples, the connectors  6  are positioned on the body  3  before the electrically conductive filaments  5  are inserted in the outer lumens  15 . 
     In the above example, the body  3  and electrical conductive filaments  5  extend into, and are part of, the first portion  7 . In alternative examples, separate material or components can form the first portion  7 . This can include a separate electrical conductive filament in the first portion  7  that is electrically connected to the electrically conductive filament  5  in the centre portion  4 . Similarly, a body of the first portion  7  can be separately made, but connected to, the centre portion  4  of the body  3 . 
     The Body  3  and Centre Section  4   
     The centre section  4  of the body  3  includes the biocompatible, electrically non-conductive body  3  and the electrically conductive filaments  5  in the outer lumens  15 . In examples where a stylet is used, the centre section  4  also has a central lumen  35  to receive the stylet. 
     The centre section  4  has a length L 2 , which is typically the longest portion of the elongated body  4 . In typical examples, the centre section  4  encloses the electrically conductive filaments  5  to minimise conduction between the electrically conductive filaments  5  to tissue immediately surrounding the centre section  4 . 
     The body  3  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  3  is made from an extrusion of a flexible material with multiple lumens. In some examples, the body  3  and the electrically conductive filaments  5  are mated together with a drawn filled tubing process. 
     The electrically conductive filaments  5  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  5  include a wire jacket of 35N LT (Nickel-Cobalt-Chromium alloy) per ASTM F562 and of a composition which includes ≤0.01 wt % titanium, and a wire core of silver 28% of the cross-sectional area of the electrically conductive filament  5 . 
     The Second Portion  9   
     The second portion  9  includes a plurality of electrodes  8 ,  10  to deliver therapy to the patient. In some examples, the number of electrodes  8  are the same as the number of corresponding connectors  6 , and in turn, the same number of electrically conductive filaments  5  that form the electrical connection. 
     The size and spacing of the electrodes  8  located along length L 3  is selected based on the anticipated therapy to the patient. Typically, each electrode  8  has a longer axial length than the corresponding connector  6 . 
     The electrodes  8 , in some examples, can be assembled to the lead  1  in a similar way to the connectors  6  in the first portion  7 . Thus in some examples, the structure shown in  FIG.  2   b    similarly reflects the structure in the second portion  9 . Furthermore, the electrodes  8  can be made of the same, or a similar, biocompatible electrically conductive material. 
     The non-conductive part(s) of the second portion  9  can be integrally formed with the body  3  of the centre section  4  and the first portion  7 . Similarly, the electrically conductive filaments  5  are integrally formed and extend from the centre section  4  into the second portion  7 . The electrically conductive filaments  5  continue through the second portion  9  and to the body extension  11  discussed below. 
     It is to be appreciated that in alternative examples, the electrically conductive filaments  5  in the second portion  9  can be separately formed, but electrically connected, to the electrically conductive filaments  5  in the centre section  4 . Similarly the non-conductive part(s) of the second portion may, in an alternative example, be separately formed but connected to the centre section  4 . 
     The Body Extension  11   
     Referring to  FIGS.  1   a    and  2   a,  the body extension  11  is at the distal end of the lead  1  and adjacent the second portion  9 . The purpose of the body extension  11  is to extend the electrically conductive filaments  5 , by a Length L 4  of the filament extension section  13 , past the most distal electrode  10  of the plurality of electrodes  8 . The Length L 4  moves the reflection point  16  of an electromagnetic wave propagating along the lead  1  away from the most distal electrode  10 . 
     In some examples, the body extension  11  is formed as part of the biocompatible, electrically non-conductive body  3  that makes up the first portion  7 , centre section  4 , and second portion  9 . This can include an extrusion of flexible material with a multi-lumens, whereby the end is sealed with an electrically non-conductive seal  14 . The seal  14  insulates (to an extent) the filament extension section  13  from the immediate surrounding tissue. 
     In some examples, this seal  14  can be a plug of material injected into the lumens  15 ,  35 . In other examples, the end of the body extension  11  can be dipped into a sealing material. In yet another examples, the seal  14  is formed by closing the lumens  15 ,  35  in the electrically non-conductive body  3  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  15  at the proximal end. 
     Configurations of the Body Extension  11   
     In some examples, the filament extension section  13  has a Length L 4  of 10 mm or more. In some examples, the Length L 4  is in the range of 10 mm to 50 mm (inclusive). 
     In some examples, each of the electrically conductive filaments  5  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  5  in the body  3 . 
     In some examples, the common overall length of the electrically conductive filament  5  is the sum of L 1 , L 2 , L 3 , and L 4   4 . 
     In some examples, the electrical distance between each electrical connector  6  and the corresponding electrode  8  is shorter than the common overall length. This difference in length is typically at least Length L 4  of the filament extension section  13 . 
     The leads  1  are selected from a length suitable for the therapy and patient characteristics. In some examples, the leads  1  are in the range of 600 mm to 900 mm in length. In yet other examples, the lead are in the range of 500 mm to 1200 mm in length. 
     Test Data 
       FIGS.  3   a  and  3   b    illustrate complex electric field magnitudes at a distal end (i.e. body near the second portion  9 ) for a 600 mm long lead  1  with a dozen of electrodes  9  (and corresponding dozen of electrically conductive filaments  5  and electrical connectors  6 ). The diagram  300  in  FIG.  3   a    illustrates the magnitude of complex electric fields at the distal end without a body extension  11 . In particular, the highest magnitude corresponds to the first electrode  301  located at the most distal portion (i.e. around 600 mm from the proximal end), with a magnitude of approximately 14 V/m. The other electrodes  302 ,  303 ,  304 ,  305 ,  306 ,  307 ,  308 ,  309 ,  310 ,  311 ,  312  have a smaller magnitude, with the twelfth electrode  312  (closer to the proximal end) having the smallest magnitude. 
     The diagram  400  in  FIG.  3   b    illustrates the magnitude of complex electric field at the distal end with a body extension  11  ranging from 10 mm to 50 mm. These different lengths are represented by the different lines in the diagram. The highest magnitude corresponds to the first electrode  401  located at the most distal portion (i.e. around 600 mm from the proximal end), with a magnitude of approximately 9.5 V/m. The other electrodes  402 ,  403 ,  404 ,  405 ,  406 ,  407 ,  408 ,  409 ,  410 ,  411 ,  412  have a smaller magnitude, with the twelfth electrode  412  (closer to the proximal end) having the smallest magnitude 
     In both scenarios (i.e. with and without the body extension  11 ), a plane electromagnetic wave with an axiolateral electric field of 1V/m at 128 MHz 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  1  with the body extension  11  at the distal end a decrease in complex electric field magnitude by more than 30%. 
     Fabrication 
     Referring to  FIG.  4   , there is also disclosed a method of manufacturing a lead  1  for an active implantable medical device  99 . This includes forming  110  a multi-lumen  15  elongated biocompatible, electrically non-conductive body  3 , wherein the elongated body  3  has a centre section  4  between a first portion  7  and a body extension  11 . In some examples, this includes extruding the elongated body  3  with multiple lumens. The method also includes locating  120  a plurality of electrically conductive filaments  5  through the lumens  15  of the elongated body  3 , wherein the plurality of electrically conductive filaments  5  include corresponding filament extension sections  13  that extend into the body extension  11 . As noted above, some examples of include locating and securing the electrically conductive filaments  5  using a drawn filled tubing technique. The method further includes forming  130  a plurality of electrical connectors  6  at the first portion  7 , wherein each of the electrical connectors  6  are electrically connected to respective electrically conductive filaments  5 . The method  100  also includes forming  140  a plurality of electrodes  8  at a second portion  9  of the elongated body  3 , wherein the second portion  9  is between the centre section  4  and the body extension  11 , and the plurality of electrodes  8  are connected, via corresponding electrically conductive filaments  5 , to corresponding electrical connectors  6 . 
     In some examples, it may be possible to perform some of these steps in other sequences. For example, the step of forming the electrodes  140  can precede the step of forming the connectors  130 . 
     The method  100  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  5 . 
     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 broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.