Implantable medical device and assembly therefor

Abstract

The invention is directed to an implantable medical device (60) and an electrode assembly for such medical device that can correctly and reliably be positioned at a pre-defined target location by a simple and cost-effective implantation procedure. The electrode assembly (180) comprises: - a lead body (70) extending in a longitudinal direction (79), - a helical member (90) connected to a distal end of the lead body (70), configured to convert rotational movement into linear movement in a feed direction (793) during implantation, - a stop surface (71) forming a distal end face of the lead body (70) in a stimulation condition upon completion of the implantation process, wherein the stop surface (71) has a greater diameter (D) transverse the feed direction (793) than the implantation cross section of the helical member (90), and - a differential electrode (72) at the lead body (70) or at the helical member (90), wherein the differential electrode (72) is located at a predefined distance (L) in longitudinal direction to the stop surface (71).

Description

[0001] Implantable medical device and assembly therefor

[0002] The invention generally relates to an implantable medical device, for example an implantable lead, electrode, actuator, sensor or leadless pacemaker for therapy in connection with electrical stimulation or based on received electrical signals or for electrical sensing of bodily parameters. Further, the invention relates to an electrode assembly for such medical device. Examples for such medical devices may be a pacemaker (with leads), an implantable cardiac monitor (ICM), an Implantable Leadless Pacer (ILP), an Implantable Leadless Pressure Sensor (ILPS), an Implantable Cardiac Defibrillator (ICD), a Shockbox, a device that delivers spinal cord stimulation (SCS), deep brain stimulation (DBS) or neurostimulation or a device that delivers one or more therapeutic substances, e.g. a drug pump, or contains sensors that collect physiological signals to monitor the health status of the patient.

[0003] Medical leads, e.g. for pacemakers, or leadless pacemakers implanted in a patient’s body for cardioversion or pacing of the heart are generally known in the art. In particular, electrically conducting stimulating assemblies may be implanted in or about the heart to reverse (i.e., defibrillate or cardiovert) certain life-threatening arrhythmias or to stimulate contraction (pacing) of the heart. Electrical energy is transmitted from a pulse generator which is electrically connected to the lead. Such transmitted electrical energy is applied to the heart via electrodes to return the heart to normal rhythm or to stimulate the heart. Leads have also been used to sense conditions, materials or events (generally referred to as "sense" or "sensing") in the body, e.g. as electrical potential in an atrium or ventricle of the heart. The sensed electrical signals are transmitted to a processing unit for monitoring the health status of the patient or for providing therapeutic actions on the basis of the sensed signals.

[0004] Electrodes accommodated at the surface of the implantable medical device form the electrical link between the stimulation signal generator or processing unit and the patient’s body tissue which is to be treated or sensed. Accordingly, the medical device must be reliably mechanically and electrically connected to the patient’s body tissue at a pre-defined target location. For that, the medical device often comprises a helical member mounted at its distal end, wherein the helical member is configured to move a distal section of the device within the patient’s tissue to the pre-defined target location. For example, in case of a pacemaker, such helical member penetrates the heart’s septum when a lead tip is pressed against the septum and rotated.

[0005] To receive best results for stimulation or sensing, a high degree of precision is necessary, when an electrode shall be placed at the pre-defined target location for different patients. One example is the stimulation of the left bundle of the heart, because the thickness and structure of the cardiac septum varies greatly from patient to patient. In this example, usually an electrode assembly of an electrode lead for stimulating the left bundle currently is pushed from the right side via a guide catheter into a suitable position at the cardiac septum. The electrode is then screwed into the tissue with the distal helix. Since the septum thickness varies from patient to patient, the distance between the right septum wall and the left bundle is difficult to predict and adjust. Accordingly, the suitable stimulation site can often be found by trial and error only. This is a lengthy process and requires a great deal of experience of the healthcare practitioner (HCP). It is currently estimated that HCPs may need to perform up to 100 implantations to learn the procedure. Electrode assemblies may be damaged during unsuccessful attempts and repositioning so that they must be replaced. If an electrode assembly is damaged without the HCP realizing it and then implanted, it may not function properly. Damaging septal perforation may also occur during implantation. To improve this situation, different methods for iterative evaluation of different parameters were already used for positioning of the electrode assembly. For example, parameters or methods such as sensing of the heart signals, searching for extrasystoles during screwing when the left bundle is reached, determining an injury potential, stimulating and determining of QRS width, stimulation threshold, stimulation impedance or ECG morphology were assessed or used.

[0006] Accordingly, it is an object of the present invention to provide an electrode assembly and a corresponding implantable medical device that enables correct positioning of the electrode assembly at a pre-defined target location reliably and by a simple implantation procedure.

[0007] The above-mentioned object is solved by an electrode assembly with the features of claim 1, by a medical device with the features of claim 13 and by an implantation method with the features of claim 15.

[0008] In particular, the problem is solved by a medical electrode assembly comprising:

[0009] - a lead body extending in a longitudinal direction,

[0010] - a helical member connected to a distal end of the lead body, configured to convert rotational movement into linear movement in a feed direction during implantation, - a stop surface forming a distal end face of the lead body in a stimulation condition upon completion of the implantation process, wherein the stop surface has a greater diameter D transverse the feed direction than the implantation cross section of the helical member, and

[0011] - a differential electrode at the lead body or at the helical member, wherein the differential electrode is located at a predefined distance L in longitudinal direction to the stop surface.

[0012] The lead body of the above electrode assembly may form the distal end section of the electrode lead. The longitudinal direction of the lead body is the direction having the greatest dimension. The lead body may comprise a cylindrical outer shape, wherein in this case its axial direction is referred to as longitudinal direction. In one embodiment, the lead body comprises an electrically insulating outer layer and an internal lumen configured to provide space for at least one motion element and / or at least one electrically conducting member for electrically connecting the electrode. The lumen may contain, for example, a mandrel wire configured to rotate and / or pull the helical member connected to the distal end of the lead body. The lumen may be configured to cover the helical member during advancing the electrode assembly within the vasculature towards the target position or after implantation.

[0013] The helical member is configured to convert rotational movement into linear movement in the feed direction thereby screwing the electrode assembly comprising the electrode or the medical device comprising the electrode assembly in the patient’s tissue thereby implanting the electrode member at the target position. The helical member is connected to the distal end of the lead body. In one embodiment the helical member protrudes from the distal tip of the lead body during implantation. In one embodiment, the feed direction is parallel or identical to the longitudinal direction. In another embodiment, the feed direction runs at a small angle (less than 50°) with regard to the longitudinal direction.

[0014] The differential electrode is used for stimulating at the target location and / or receiving electrical signals (i.e. sensing) from the target location of the patient’s tissue. The differential electrode is therefore electrically connected through the electrode assembly to a respective signal generator or processing unit. Further electrodes such as an indifferent electrode may be provided.

[0015] The medical electrode assembly defined above is particularly suitable for stimulation and / or sensing in a septum-like or wall-like structure of patient’s body. The inventors have found that helical member can be used to drive the electrode assembly at an entry area into and within the tissue of the septum / wall thereby penetrating the septum / wall until the helical member fully protrudes from the septum / wall at the opposite side so that the pull-effect of the helical member is ceased. Accordingly, the electrode assembly then stops moving and is no longer advancing into the feed direction. Hence, implantation process is completed. During implantation the helical member has created a through- hole / channel within the tissue. The diameter of such through-hole / channel depends on the implantation cross section of the helical member and the specific tissue. The implantation cross section is the effective cross-section of the helical member which displaces patient’s tissue during penetration. Upon completion of the implantation, the lead body seals the through-hole or channel created by the penetration of the helical member through the wall / septum. In particular, the stop surface formed at the distal end face of the lead body seals the end of the through-hole / channel opposite the entry area. This is because the stop surface has a greater diameter D transverse the feed direction than the implantation cross section of the helical member, i.e. transverse the feed direction (e.g. perpendicular the feed direction) the diameter of the stop surface is greater than the diameter of the implantation cross section of the helical member, wherein the diameter of the stop surface may include any element that protrude from this stop surface and also extends across this element’s cross section. In one embodiment, if the diameter of the stop surface and / or the diameter of the implantation cross section varies along the respective surface / cross section, the stop surface is dimensioned such that the smallest diameter of the stop surface is greater than the greatest diameter of the implantation cross section (this also refers to the specific dimensional relations explained below). Further, from above-explained procedure follows that upon completion of the implantation process the stop surface of the lead body is located at or in close proximity to the end of the through-hole / channel within the patient’s tissue opposite the entry area of the electrode assembly. Furthermore, the inventors found that the position of the differential electrode at the lead body can be chosen such that the differential electrode has a predefined distance L in longitudinal direction to the stop surface. The differential electrode may be positioned distally or proximally from the stop surface. In one embodiment, an end face of the differential electrode forms the stop surface. The distance of the differential electrode to the stop surface is adapted to the expected position of the target position for stimulation and / or sensing within the patient’s tissue for the specific use case relative to the end of the through- hole / channel opposite the entry area, e.g. the position of the left bundle within the heart’s septum. The differential electrode according to the invention includes an electrode for stimulation and / or sensing in a bipolar and unipolar arrangement.

[0016] In one embodiment, the medical electrode assembly is used to be implanted into the heart’s septum for stimulation of the left bundle. In this case, the electrode assembly may be introduced from the right ventricle at an entry area within the right side of the heart’s septum. It is screwed by the helical member through the septum until the helical member fully penetrates the septum and protrudes from the left side of the septum thereby automatically ceasing movement. The stop surface of the lead body seals the through-hole created by the helical member at the left endocardium and, at the same time, provides a reference point for positioning of the differential electrode. The distance of the differential electrode from the stop surface and thereby from the left endocardium is chosen such that the electrode is located at the left bundle for left bundle stimulation and / or sensing.

[0017] According to the invention, the implantation movement of the electrode member within the patient’s tissue can be automatically and reliably controlled such that it ceases at a pre-defined position (namely when the helical member fully protrudes from the patient’s septum / wall). At the same time, the sensing and / or stimulation position of the differential electrode is automatically and accurately as well as reproducibly set, wherein the position of the electrode can be adapted to the specific use case by its distance to the stop surface. Therein, the distance of the differential electrode to the stop surface is the distance of the electrode’s distal end to the stop surface in longitudinal direction if the differential electrode is located proximally from the stop surface and the distance of the electrode’s proximal end to the stop surface in longitudinal direction if the differential electrode is located distally from the stop surface. At the same time, the through-hole / channel created by the helical member within the patient’s tissue is permanently and reliably sealed.

[0018] The lead body may have an essentially cylindrical and / or conical shape and extend along a longitudinal axis. It may comprise a continuous surface or may comprises steps at its surface. The helical member (formed, for example, from a wire or a solid body) has a helical shape and is connected to the distal end of the lead body. The helical member may be rotatably attached to the distal front end of the lead body such that it distally projects from the distal front end of the lead body.

[0019] The terms “axial” / ”longitudinal”, “radial” and “circumferential” describe the special relationship and / or movement of elements assuming an essentially cylindrical shape of the lead body.

[0020] In one embodiment the electrode assembly is implanted into the septal tissue by externally rotating the helical member by a mandrel wire. As pointed out above, the helical member converts the rotational motion into forward feed thereby moving the electrode assembly into the patient’s tissue for fixating the electrode assembly. In one embodiment, the helical member may be configured rotatable and / or movable in longitudinal direction (distally and / or proximally). In one embodiment, the helical member may be retractable into the lead body upon completion of the implantation process.

[0021] In one embodiment the helical member is attached to a driving element, e.g. a mandrel wire, such that it is movable (rotatable and / or movable in the longitudinal direction) within the lumen of the lead body. The helical member may be moved in distal direction prior and / or during the implantation process, for example, by rotating the driving element. A rotational movement of the driving element in the opposite direction upon completion of the implantation process may retract the helical member back into the lumen of the lead body.

[0022] As indicated above, the helical member may be formed from a wire or a solid body. In case the helical member is formed from a wire the wire has a three-dimensional, spiraling curve that wraps around an imagined cylinder or cone (circular helix or conic helix). The helical member’s axis may be straight or curved. The pitch of such helical member is the height of one complete helix turn, measured parallel to the helix’ axis. Such helical member may be a uniform helix (i.e. its pitch is constant). Alternatively, the helical member may be a variable pitch helix where the pitch of the helix changes along its length. The helical member may be right-handed or left-handed. The helical member may be a variable pitch helix where the pitch of the helix changes along its length. The wire cross section may be circular, square, triangular or any other suitable form.

[0023] In one embodiment, the helical member may have a sharp distal end. The sharp distal end causes the through-hole / channel in the patient’s tissue to be small and centered with respect to the feed direction.

[0024] In one embodiment, the helical member may be formed from a solid body comprising at least one helical thread at its surface so that a three-dimensional spiraling structure revolving around the axis of the full body is created. Each thread may exhibit a constant or a variable radius. The helical thread’s pitch may vary in feed direction similar to the wire-like helical member.

[0025] The implantation cross section of the helical member may depend on the shape of the helical member and the type and condition of the patient’s tissue. The diameter of the implantation cross section corresponds to the diameter of the through-hole / channel within the patient’s tissue created by the helical member during implantation (including, if applicable, a helical section and a straight and proximal section forming a shaft, e.g. a rotatable shaft). In one embodiment, for a wire-like helical member, the implantation cross section may be equal to the cross section of the wire of the helical member. For another wire-like helical member, the implantation cross section may be greater than this wire cross section, because the radial extension of the helical member causes tearing of the patient’s tissue such that the implantation cross section is greater than the diameter of the wire. In other words, depending on the type of tissue, the specific shape of the helical member and the feed direction the implantation cross section may be greater than the wire cross section if, e.g. by the helical form of the wire or the tissue type, a through-hole / channel in the tissue is created during implantation which is greater than the wire diameter. With regard to a helical member type produced from a solid body the implantation cross section may correspond to the cross section of the helical member perpendicular to the feed direction.

[0026] In one embodiment, the stop surface is formed by the distal front surface of the lead body, with its diameter exceeding the diameter of implantation cross section. Alternatively, the stop surface may be formed by a front surface of an electrode located at the surface of the lead body or by a separate element located at the distal end of the lead body.

[0027] In one embodiment, the stop surface may be perpendicular or slightly tilted with respect to the longitudinal direction, depending on the feed direction during implantation.

[0028] In one embodiment, the stop surface may exhibit a circular circumference, maximizing the contact area between electrode assembly and the penetrated tissue thereby enhancing the sealing effect. Alternatively, the circumference of the stop surface may be square or rectangular or may have any other continuous form.

[0029] In one embodiment, the lead body may comprise a collar, e.g. a disc-shaped collar, at its distal end that has a greater diameter D than the lead body. The distal front surface of this collar forms the stop surface upon completion of the implantation process. This is a simple embodiment realizing the greater diameter D at the stop surface.

[0030] In one embodiment, the distance of the differential electrode from the stop surface is from 3 mm to 15 mm, for example from 5 mm to 10 mm, for example in distal direction. In proximal direction, the distance is, for example, less than 5 mm. The differential electrode may have a length in longitudinal direction from 1 mm to 10 mm, for example from 2 mm to 8 mm. These parameters are especially suitable for a differential electrode provided for left bundle stimulation or similar use cases.

[0031] In one embodiment, the differential electrode may be formed by a metallic sleeve securely fixed at the lead body having an outer diameter in the range from 0.25 mm to 3.6 mm. Such differential electrode may be cost-effectively produced.

[0032] In one embodiment, the helical member comprises a straight shaft, e.g. a rotatable shaft, at its proximal end which is formed integrally or is fixedly attached to a helical section of the helical member, wherein the shaft is aligned with the feed direction and configured to rotate with the helical member during implantation such that on and upon completion of the implantation process the shaft distally protrudes from the stop surface. The shaft may rotate in the through-hole / channel created by the helical member within the patient’s tissue without further expanding or damaging the inner diameter of the through-hole / channel when the helical member fully protrudes from the side opposite the entry area. The shaft may rotate with respect to the lead body and may be connected to a mandrel that drives the rotation of the helical member. The shaft may rotate with the helical section of the helical member. The shaft is rotation symmetric with regard to the rotation axis of the helical member. The diameter of the stop surface transverse the feed direction is greater than the diameter of the shaft. In one embodiment the shaft is formed by a proximal portion of the spiral wire with the radius decreasing toward the distal front surface of the lead body. In one embodiment, the helical section of the helical member continuously merges or merges via a step into the shaft. In particular, the shaft may be formed by a straight portion of the spiral wire protruding perpendicular from the distal front surface of the lead body. This is an embodiment which can be cost-effectively produced.

[0033] In one embodiment, the diameter of the shaft is less than or equal to 0.5 times the diameter transverse the feed direction of the stop surface, for example less than or equal to 0.3 times the diameter transverse the feed direction of the stop surface. Accordingly, the stop surface has a significantly greater diameter than the shaft so that the through-hole / channel is reliably sealed.

[0034] In one embodiment, the helical member is electrically insulated against the differential electrode located at the lead body. An electrically insulated helical member ensures that the pre-defined location is stimulated by the differential electrode only and avoids leakage current. In this embodiment, the helical member does not function as an electrode but as a drive member only that pulls the electrode assembly (and the medical device or part thereof that includes that electrode member) through the patient’s tissue.

[0035] In one embodiment, a distal tip section of the helical member is electrically connected to a receiver for electrical signals during implantation. After implantation the electrical connection may be disconnected or not used anymore. This configuration enables the helical member to be used as a sensing electrode for bodily parameters, which helps the HCP to identify an appropriate implantation location, e.g. by mapping. Accordingly, sensing during implantation is enabled in a simple manner so that no additional technical equipment is required that would increase the volume of the electrode assembly and, accordingly, the outer dimensions of the electrode assembly that would make implantation more complex.

[0036] In one embodiment, the diameter transverse the feed direction of the stop surface is greater than or equal to 1.3 times the diameter of the implantation cross section of the helical member upon completion of the implantation process. For example, the diameter transverse the feed direction of the stop surface is greater than or equal to 1.5 times the diameter of the implantation cross section of the helical member upon completion of the implantation process. In another example, the diameter transverse the feed direction of the stop surface is greater than or equal to 1.8 times the diameter of the implantation cross section of the helical member upon completion of the implantation process. The dimensions of the stop surface are such that it is significantly greater than the dimensions of the implantation cross section. As indicated above, the implantation cross section is the effective crosssection of the helical member displacing patient’s tissue during penetration. The above defined diameter of the stop surface guarantees a reliable closure of the through-hole / channel in the tissue upon completion of the implantation process. For example, within the heart’s septum, the stop surface may be located adjacent the comparable tough endocardium and reliably seals the channel in the endocardium created by penetration of the helical member.

[0037] The stop surface may have identical dimensions before and during implantation as well as upon completion of the implantation and correspondingly identical diameter. However, in some embodiments, the diameter is increased during implantation, e.g. towards the end of the implantation process, or upon completion of the implantation process. Such embodiments are explained in the following.

[0038] In one embodiment, the stop surface is formed by at least one elastic element configured to bend towards the surface of the lead body by surrounding tissue during implantation. The elastic element may be formed as a collar-like member located at the distal end of the electrode body. Bending of the elastic element is provided by the compressive force provided by the surrounding tissue during movement of the electrode assembly within the tissue driven by the helical member. In one embodiment, at least one section of the lead body extending proximally from the elastic collar-like member may have a reduced diameter thereby forming a recess. The length of the reduced diameter section in longitudinal direction is, for example, from 0.3 mm to 3 mm, the diameter reduction (in radial direction) is, e.g., from 0.1 to 1.3 mm. During implantation the elastic element may bend such that it is accommodated within the recess thereby reducing the space the electrode assembly occupies during implantation.

[0039] In one embodiment, the electrode assembly comprises a flanged sleeve and a first sleeve-like collar, wherein the first collar is located at the distal end of the lead body and is configured to interact with the flanged sleeve such that the collar expands on and upon the completion of the implantation process thereby increasing the diameter of the stop surface. For example, the first collar essentially has a form comprising a first base ring and a first hollow cylindrical sleeve, wherein the transition area between the first base ring and the first hollow cylindrical sleeve is bent around the outer circumference of the lead body such that the first base ring covers the outer surface of the lead body, wherein the first base ring forms the distal end face of the lead body. The flanged sleeve may be moved in longitudinal direction in an end phase or upon completion of the implantation process. As shown below in detail, the flanged sleeve is configured such that the flanged sleeve may be moved within the lumen of the lead body in longitudinal direction. The movement may be configured such that in the end phase of implantation or upon completion of the implantation process the flange of the first flanged sleeve interacts with the first collar, for example with the first base ring. The interaction causes a radial extension of the first collar such that its diameter increases thereby increasing the area of the stop surface. For example, the flange of the flanged sleeve forces the base ring outwards in radial direction for increasing the area of the stop surface.

[0040] In one embodiment, the electrode assembly comprises a second sleeve-like collar, wherein the second collar is located at the distal end of the lead body and is configured to interact with the helical member such that the second collar expands when the helical member is retracted upon completion of the implantation process. For example, the second collar essentially has a form comprising a second base ring and a second hollow cylindrical sleeve, wherein the transition area between the second base ring and the second hollow cylindrical sleeve is bent around the outer circumference of the lead body such that the second base ring covers the outer surface of the lead body, wherein the second base ring forms the distal end face of the lead body. The helical member may be moved in proximal longitudinal direction upon completion of the implantation process, for example during retraction of the helical member into the inner lumen of the lead body. As shown below in detail, the helical member and the second collar are configured such that the movement causes an interaction with the second collar upon completion of the implantation process, for example with the second base ring. The interaction effects, e.g., a radial extension of the second collar such that its diameter increases thereby increasing the area of the stop surface. For example, the helical member forces the second base ring outwards in radial direction for increasing the area of the stop surface.

[0041] In one embodiment, the electrode assembly further comprises an extractable member, wherein the extractable member is retracted within the lead body prior implantation and configured to be extracted from the distal end of the lead body during implantation or during traversing of the helical member in distal direction beyond the distal end of the lead body such that it forms the stop surface upon completion of the implantation process. In one embodiment the deformable member is initially contained within the lumen of the lead body and may have the shape of a circular ring. For example, upon rotation of the helical member, the extractable member moves distally through the lumen of the lead body. When its most distal section reaches the distal edge of the lead body, the deformable member everts from the inside to the outside of the lead body and forms a stop surface whose diameter is greater than the diameter of the lead body. The above mechanism prevents dislocation of the electrode assembly and perforation of the endocardium and may be activated by the HCP.

[0042] In one embodiment, at least one indifferent electrode is provided at the lead body, wherein the distal end of the nearest indifferent electrode is located at a predefined longitudinal distance from the proximal end of one differential electrode. The indifferent electrode provides the counter electrode for bipolar stimulation. In one example, the proximal end of the differential electrode and the distal end of the nearest indifferent electrode exhibit a longitudinal distance from 5 mm to 15 mm, for example from 8 mm to 12 mm.

[0043] In one embodiment, the differential electrode is a ring electrode encompassing an electrically insulating outer layer of the lead body. This configuration allows the differential electrode to be securely fixed at the lead body. In a further embodiment, the differential electrode is formed as a sleeve such that it at least partly forms the stop surface of the lead body.

[0044] In one embodiment, the lead body comprises at least one protruding element of the group comprising tines, fins, nubs and scales. This at least one protruding element anchors the lead body within the patient’s tissue, for example, upon completion of the implantation process. This can be of advantage because the helical member fully protrudes from the tissue or is retracted within the lead body so that the helical member does not contribute to anchorage of the electrode assembly within the tissue.

[0045] The above object is further solved by an implantable medical device, for example an electrode lead, an actuator, a sensor or a leadless pacemaker, wherein the medical device comprises the above explained electrode assembly at its distal end. For example, the implantable medical device is a leadless pacemaker comprising a housing and at least one fixation element connected to the housing, wherein the fixation element comprises the electrode assembly. An indifferent electrode is formed by the housing or is fixed at the housing. The implantable medical device may be reliably and cost- effectively fixed to the patient’s tissue using the electrode assembly described above. In particular, a leadless pacemaker may use such electrode assembly in an easy manner. A complex assessment of different sensor information is not necessary because fixing of the electrode assembly and its correct positioning is provided automatically.

[0046] In one embodiment, the lead body may comprise or consist of at least one material of the group comprising Silicones, Polyurethanes (TPU) and PU-based materials, Polyester Urethanes (PEU), Polyether Urethanes (PEEU), Polycarbonate Urethanes (PCU), Silicone-based Polycarbonate Urethanes (PCU), Polycarbonate-Polyurea Urethanes (PCHU), Polydimethylsiloxane Urethanes (PSU), Polyisobutylene Urethanes (PIU), Polyisobutylene-based Copolymers (PIC), Polyether Block Amides (PEBA, such as PEBAX), Polyimides (PI), Fluorinated Hydrocarbons, Ethylene- Tetrafluoroethylene Copolymer (ETFE), Polytetrafluoroethylene, Polysulfone (PSU), Polyethylene (PE), Polypropylene (PP), Polyamides (PA), Polyimides (PI), Fluorinated Hydrocarbons, Ethylene- Tetrafluoroethylene Copolymers (ETFE), Polytetrafluoroethylene (PTFE), Tetrafluoroethylene (TFE), Perfluoro(ethylene-propylene) (FEP), Perfluoroalkoxy Polymers (PFA), Polyaryletherketone (PAEK), Polyetheretherketone (PEEK), Polyethylene Terephthalate (PET); the stop surface (e.g. provided as a first collar or a second collar or an elastic element, the extractable member) may comprise or consist of at least one material of the group comprising the materials of the lead body above and / or metals like Titanium, MP35N, Stainless steel or (preferred) Platinum resp. Platinum / Iridium, Tantalum, Rhodinium, Palladium and Gold; the differential and / or the indifferent electrode may comprise or consist of at least one electrically conducting material of the group comprising steel (MP35N), silver alloy, Titanium, Platinum, Platinum / Iridium, Iridium, Tantalum, Rhodinium, Palladium and Gold. The electrically insulating material of the helical member and / or of the lead body may comprise or consist of at least one biocompatible material of the group comprising silicone, polyurethane (PU), polytetrafluoroethylene (PTFE), glass, ceramics and polyetheretherketone (PEEK); the helical member may comprise or consist of at least one material of the group comprising Nitinol, Pt, Pt / Ir, Steel and MP35N; the rod-shaped member and / or the fixing element and / or the rod-shaped electrode member may comprise at least one material of the group comprising Pt / Ir and MP35N. In one embodiment, the helical member may comprise an electrically insulating coating, wherein the material of the coating may comprise at least one material of the group comprising the materials of the lead body above. In one embodiment, the helical member may comprise or consist of a degradable material comprising at least one material of the group comprising Magnesium and plastic like materials as starch-based materials, Cellulose, Proteins and Polysaccharides, Lignin, Polylactic acid (PLA), Polyhydroxyalkanoates (PHA), Polybutylene adipate terephthalate (PBAT) and Biodegradable polyurethanes (PU).

[0047] The above object is further solved by an implantation method for an electrode assembly described above and comprising the following steps:

[0048] - Advancing the electrode assembly to a pre-defined entry area for implantation at a pre-defined tissue within the patient’s body, and

[0049] - Penetrating the pre-defined tissue by the helical member at the pre-defined entry area and simultaneously rotating the helical member until the helical member fully protrudes from a side of the tissue that is opposite the entry area. As indicated above, this method automatically and precisely moves the differential electrode to a pre-defined stimulation and / or sensing position. Once, the helical member fully protrudes from the tissue opposite the entry area, the penetration movement of the electrode assembly caused by the helical member is automatically stopped. At this position, the electrode assembly is fixedly located within the pre-defined tissue at the pre-defined stimulation and / or sensing position.

[0050] The present invention will now be described in further detail with reference to the accompanying schematic drawings, wherein:

[0051] Fig. 1 shows a first embodiment of an electrode assembly in a side view implanted in a heart’s septum in a cross-sectional view,

[0052] Fig. 2 depicts an enlargement of Fig. 1,

[0053] Fig. 3 shows a second embodiment of an electrode assembly in a side view implanted in a heart’s septum in a cross-sectional view,

[0054] Fig. 4 shows a third embodiment of an electrode assembly in a side view in a first state,

[0055] Fig. 5 illustrates the embodiment of Fig. 4 in a side view in a second state,

[0056] Fig. 6 shows a fourth embodiment of an electrode assembly in a side view,

[0057] Fig. 7 illustrates a fifth embodiment of an electrode assembly in a side view,

[0058] Fig. 8 shows a sixth embodiment of an electrode assembly in a side view implanted in a heart’s septum in a cross-sectional view,

[0059] Fig. 9 shows a seventh embodiment of an electrode assembly in a side view implanted in a heart’s septum in a cross-sectional view,

[0060] Fig. 10 illustrates an eighth embodiment of an electrode assembly in a side view and a heart’s septum in a cross-sectional view during implantation in the heart’s septum,

[0061] Fig. 11 depicts the embodiment of Fig. 10 implanted in a heart’s septum in a cross-sectional view, Fig. 12 shows a longitudinal section of a ninth embodiment of an electrode assembly in a first state,

[0062] Fig. 13 illustrates the embodiment of Fig. 12 in a longitudinal section in a second state,

[0063] Fig. 14 shows a longitudinal section of a tenth embodiment of an electrode assembly in a first state,

[0064] Fig. 15 illustrates the embodiment of Fig. 14 in a longitudinal section in a second state,

[0065] Fig. 16 shows a longitudinal section of an eleventh embodiment of an electrode assembly in a first state,

[0066] Fig. 17 illustrates the embodiment of Fig. 16 in a longitudinal section in a second state,

[0067] Fig. 18 shows a twelth embodiment of an electrode assembly in a side view implanted in a heart’s septum in a cross-sectional view,

[0068] Fig. 19 depicts an implantation step of a first embodiment of an implantable electrode lead having an electrode assembly similar to the embodiment of Fig. 18 in a side view within a heart’s septum in a cross-sectional view, and

[0069] Fig. 20 illustrates an implantation step of an embodiment of an implantable leadless pacemaker in a side view within a heart’s septum in a cross-sectional view.

[0070] The following embodiments of an electrode lead assembly are explained with respect to an electrode lead forming a lead 60 for a pacemaker, wherein the electrode lead assembly is located at the distal end of the electrode lead 60.

[0071] The first embodiment of the electrode lead assembly is shown in Fig. 1 and 2 in a position upon completion of the implantation. The electrode lead assembly is implanted in a septum 40 between a right ventricle 20 and left ventricle 30 of a patient’s heart 10.

[0072] The electrode lead assembly comprises a cylindrical lead body 70 having an electrically insulated outer surface with a ring-like differential electrode 72 and a ring-like indifferent electrode 73 located one after another at the outer surface of the lead body 70 with a distance along the longitudinal direction (bipolar structure). The longitudinal direction is depicted in Fig. 2 by the dot-dashed line 79. A helical member 90 formed as a wire-like helix is connected distally with the distal end of the lead body 70. The helical member 90 is connected via a shaft 91, in particular a rotatable shaft 91, to a mandrel (not shown) extending within an inner lumen of the lead body 70. The helical member 90 with its shaft 91 is made of an electrically insulating material, such as Peek or with parylene insulated MP35N. The inner lumen of the lead body 70 may further comprise electrically conducting conductors configured to electrically connect the electrodes 72, 73 to a signal generator and / or a processing unit for providing stimulation signals and / or receiving and processing received electrical signals. At the distal end of the lead body 70 a disc-like collar 76 is provided. The collar 76 distally provides a stop surface 71 at its front surface . The stop surface 71 has a greater diameter (see diameter D in Fig. 4) than the implantation cross section of the helical member. The implantation cross section is, in this case, the diameter of the shaft 91 since the channel within the created by the helical section of the helical member 90 is smaller than the channel created by the shaft 91. For example, the diameter of the rotatable shaft 91 is 0.6 mm, the diameter of the wire of the helical member 90 is 0.23 mm and the diameter of the stop surface 71 is 1.8 mm perpendicular a feed direction. Additionally, the diameter of the collar 76 and of the stop surface 71 perpendicular the feed direction are equal. The differential electrode 72 is located directly proximally from the collar 76, i.e. 0.3 mm from the stop surface 71. As one can derive from Fig. 1 and 2 the differential electrode 72 is located such that it is in direct electrical contact with the left bundle 44 for stimulation of the left bundle 44. Accordingly, it is in a predefined distance from the right bundle 56. The indifferent electrode 73 is located outside the septum 40 within the right ventricle 20 of the patient’s heart 10.

[0073] The implantation procedure of the electrode lead assembly shown in Fig. 1 and 2 is explained in the following. It is also referred to Fig. 10 and 11 showing the implantation process for another embodiment and to Fig. 4 for the dimensions D (diameter) and L (distance).

[0074] For implantation, the electrode lead assembly is advanced to the right ventricle 20 to a suitable position at the right side of septum 40. This position is referred to as entry area in the following. Then, the helical member 90 is rotated and pressed against the tissue for penetration into the tissue. During continuous rotation the helical member 90 screws the electrode lead assembly through the right endocardium 42, the myocardium and through the left endocardium 44 in the feed direction (see Fig. 10, arrow 793), wherein the right and the left endocardium 42, 44 is tougher than the myocardium. The helical member 90 is screwed fully through the left endocardium 44 at the side of the septum 40 opposite the entry area. When the helical member fully protrudes from the side of the septum 40 opposite the entry position, driving the electrode lead assembly in the feed direction is ceased. The helical member 90 just rotates such that its shaft 91 rotates in a channel of the left endocardium 44 but does not further advance the electrode lead assembly through the septum 40. Thereby automatically, the large stop surface 71 of the collar 76 with its greater diameter than diameter of the shaft 91 seals the channel created by implantation of the electrode lead assembly to the left ventricle 30. Additionally, the stop surface 71 prevents the electrode lead assembly from exiting the septum 40. Further automatically, the differential electrode having a length of 1.2 mm in longitudinal direction directly electrically contacts the left bundle 54 for stimulation because it exhibits a distance L of 0.2mm from the stop surface 71 (see Fig. 4). Accordingly, the differential electrode 72 is automatically at the correct position for stimulation and therefore stimulates the left bundle 54 reliably. The indifferent electrode 73 having a distance of 12 mm from the differential electrode 72 is located outside the septum 40 within the right ventricle 20 of the patient’s heart 10.

[0075] In the following, further embodiments of the electrode lead assembly are discussed. Elements having a reference number with the similar ones and tens digit correspond to the respective element of the first embodiment. The reference numbers of the embodiments differ in their hundreds and thousands digit, only. It is therefore referred to the first embodiment with regard to these elements and mainly the differences to the first or any further embodiment is explained below.

[0076] The second embodiment of an electrode lead assembly comprises a disc-shaped collar 176 that has approximately the same diameter than the lead body 170. The collar 176 may be formed integrally with the lead body 170. However, as shown in Fig. 3, the stop surface 171 seals the channel at the left endocardium 44 because the stop surface 171 has a diameter of 1.4 mm and the diameter of the shaft 191, in particular the rotatable shaft 191, is 0.6 mm. Similar to the first embodiment, helical member 190 with its rotatable shaft 191 is made of an electrically insulating material, such as PEEK, insulated Pt / Ir. The differential electrode 172 has a distance of 0.3 mm from the stop surface 171.

[0077] Fig. 4 and 5 show a third embodiment of an electrode lead assembly having a collar forming an elastic element 276, for example, made of Silicone. Further, the section of the lead body 270 directly proximal from the elastic element 276 and supporting the differential electrode 272 has a reduced cross sectional diameter of, e.g., 0.4 mm compared with the remaining part of the lead body 270 having a diameter of, e.g., 1.4 mm. Due to its elasticity, the elastic element 276 is bent against the outer surface of the lead body 270 by the surrounding tissue during implantation as shown in Fig. 5 thereby reducing the occupied space. In the fully implanted position (similar to Fig. 1 and 2) the collar relaxes and bents back as shown in Fig. 4. The stop surface 271 has a greater diameter D of, e.g., 0.2 mm than the lead body 270 (e.g. 1.6mm) and the shaft 291, in particular the rotatable shaft 291, (e.g. 0.6 mm). Fig. 6 depicts an embodiment of an electrode lead assembly having a disc-shaped collar 376 with a diameter of the stop surface 371 of, e .g . , 1.4 mm that is between the diameter of the stop surface 171 of the collar 176 of the second embodiment and of the diameter of the stop surface 71, 271 of collar 76, 276 of the first and third embodiment. Further, the shaft 391, in particular the rotatable shaft 391, is formed directly from the helical section of the helical member 390. In the following, the helical member is also referred to as a helix.

[0078] The embodiment of Fig. 7 is another embodiment of an electrode lead assembly having a straight shaft 491, in particular a rotatable shaft 491, that merges from the helical section of the helical member 490. Additionally, the electrode member 490 has a sharp distal tip for easier penetration into the patient’s tissue at the entry area. Additionally, the helical member 490 forms an electrode and therefor comprises electrically conducting material, for example at its distal or proximal end section. The helical electrode member 490 may be used for sensing, for example, during implantation or for stimulation. Accordingly, the electrically conducting section of the electrode member 490 is electrically connected to a conductor extending within the inner lumen of the lead body 470. The diameter of the helix 490 is changing - it starts with a grinded sharp tip and a small helix diameter (e.g. 0.5mm) then the helix diameter grows to 1.8 mm and then the helix diameter shrinks again to until the wire reaches the middle axis of the helix. The wire is than bent in axial direction. This last axial end of the wire is the middle axis of the helix.

[0079] For all versions the helix may be thought as a conductive helix, which may be used form mapping during implantation. As soon as the helix is in the left ventricle it cannot stimulate effective anymore because it is no longer in the tissue. Then a ring electrode like 472 is needed.

[0080] Exception: The helix wire may be also the axis of the helix (Fig. 7-9). So, the helix wire may replace the (normally nonconductive) rod-component. Since the helix wire is conducive and is perforating the bundles, it may stimulate or sense.

[0081] Further, the helix shaft may be connected to the inner conductor, which connects it to the pacemaker.

[0082] The embodiment of an electrode lead assembly of Fig. 8 comprises a helical member 590 comprising an electrically conducting material at its proximal section, i.e. at the end of the helical section and the shaft 591, in particular the rotatable shaft 591. The distal end of the helical member 590 is electrically insulated. The proximal section of the helical member 590 is provided for stimulation of the left bundle 54 which is possible as it runs through and is therefore in direct contact with the left bundle 54. Accordingly, the proximal section of the helical member 590 forms the differential electrode. The diameter of the helix 590 is changing - it starts with a grinded sharp tip and a small helix diameter (e.g. 0.5mm) then the helix diameter grows to 1.8 mm and then the helix diameter shrinks again to until the wire reaches the middle axis of the helix. The wire is than bent in axial direction. This last axial end of the wire is the middle axis of the helix.

[0083] For all versions the helix may be thought as a conductive helix, which may be used form mapping during implantation. As soon as the helix is in the left ventricle it cannot stimulate effective anymore because it is no longer in the tissue. Then a ring electrode like 472 is needed.

[0084] Fig. 9 depicts an embodiment of an electrode lead assembly similar to the one of Fig. 8 but comprising additionally an electrically conducting section at the distal tip of the helical member 690. Accordingly, the proximal section (including the shaft 691, in particular the rotatable shaft 691) of the helical member 690 and the distal tip of the helical member 690 are electrically conducting but electrically insulated from each other. In the central section of the helical member 690 shown as a grey area in Fig. 9, the helical member 690 is electrically insulated. The electrically conducting distal tip of the helical member 690 may be used, for example, for sensing (mapping) during implantation. The tip of the helix 690 may be conductive to provide the ability to map during implantation (stimulating and sensing). Since this section will be in the left ventricular blood pool and is no longer needed but loses energy during stimulation, the area is reduced. But the shaft of the helix is not insulated but conductive, to provide an electrode, which is still in the left bundle and can stimulate after implantation. So the coating is made to reduce the unnecessary electrode surface to safe energy during stimulation.

[0085] The embodiment of an electrode lead assembly shown in Fig. 10 and 11 comprises a retractable helical member 790. Fig. 10 shows the electrode lead assembly during implantation. The helical member 790 protrudes from the distal end of the lead body 770 and its rotation screws the electrode lead assembly into the septum 40 of the patient. Upon completion of implantation, the helical member 790 is fully retracted into the lead body 770 (see Fig. 11). This may be facilitated by an internal mechanism that allows free rotation of the helical member 790 in one direction and a screwing of the helical member 790 into the lead body if the helical member 790 is rotated in the opposite direction.

[0086] The two embodiments shown in Fig. 12 to 15 comprise a sleeve-like collar 876, 976. Each sleevelike collar 876, 976 is composed of a sleeve-like (hollow cylindrical) section 876a, 976a at its proximal end and a base ring section 876b, 976b at its distal end and a transition area between the base ring and the hollow cylindrical section that is bent around the outer circumference of the lead body 870, 970. The stop surface 871, 971 is formed by the base ring section 876b, 976b, respectively. Upon completion of the implantation process, each collar 876, 976 is deformed such that the stop surface 871, 971 is increased. Accordingly, Fig. 12 and 14 show the position and shape of the sleevelike collar 876, 976 prior finishing the implantation process and Fig. 13 and 15 show the position upon completion of the implantation process and deformation. The deformation of the sleeve-like collar 876, 976 is effected by a flanged sleeve 874 or the helical member 990. In the embodiment shown in Fig. 12, 13, the flanged sleeve 874 is initially covered by the lead body 870 and upon completion of the implantation process moved distally such that the distal flange section of the flanged sleeve 874 interacts with the ring section 876b. The flange section of the flanged sleeve 874 presses the ring section 876b radially to the outside such that the diameter of the stop surface 871 increases (see arrows in Fig. 13 depicting the movements). Similarly, in the embodiment shown in Fig. 14 and 15 the helical member 990 interacts with the ring section 976b when the helical member 990 is retracted into the lead body 970 thereby deforming the ring section 976b such that it is forced radially to the outside and the diameter of the stop surface 971 is increased (see arrows in Fig. 15 depicting the movements). For that, the sleeve-like collars 876, 976 are elastically or plastically deformable, e.g. at the transition area between the base ring 876b, 976b and the hollow cylindrical section 876a, 976a, respectively.

[0087] The embodiment of an electrode assembly shown in Fig. 16 and 17 comprises a cup-shaped extractable member 1075 that is initially covered by the lead body 1070 (see Fig. 16). Further, the extractable member 1075 is coupled to the helical member 1090 such that by distal movement of the helical member 1090 (see arrow in Fig. 16) the extractable member 1075 is drawn in distal direction, as well. After full extraction of the extractable member 1075 it forms a collar-like element and a stop surface 1071 of the lead body 1070 having a greater diameter than the diameter of the implantation cross section. Upon completion of the implantation, the helical member 1090 may be retracted into the inner lumen of the lead body 1070 but the extractable member 1075 remain stationary.

[0088] Fig. 18 shows a unipolar embodiment of an electrode assembly comprising a helical member 1190 with shaft 1191, in particular with rotatable shaft 1191, formed from a solid body, wherein the helical section has helical threads at its outer surface. Additionally, a sleeve-like electrode 1172 forms a distal section of the lead body 1170, wherein the distal front surface of the sleeve-like electrode 1172 forms the stop surface 1171. The diameter of the stop surface 1171 is 1 mm, i.e. greater than the implantation cross section of the helical member 1190 (i.e. its cross section perpendicular to the longitudinal and feed direction) having a diameter of 0.8 mm. The lead body 1170 comprises a twisted rope 1181 as a conductor that is electrically connected to the electrode 1172 and covered by an electrically insulating shell. The electrically insulating shell may extend through the sleeve-like electrode 1172 forming the shaft 1191. Alternatively, the twisted rope 1181 may be guided within a helical guiding element. The electrode 1172 may be configured for stimulation and / or for providing shocks, e.g. for defibrillation.

[0089] The embodiment of an electrode assembly depicted in Fig. 18 is identified in Fig. 19 by the reference number 180. The electrode assembly 180 is used for anchoring at and electrically connecting an electrode lead 160 to a predefined position within the septum 40 of the patient’s heart 10.

[0090] Alternatively, as shown in Fig. 20, the electrode assembly 180 may be used for anchoring and stimulating using an implantable leadless pacemaker as a medical device according to the invention. The electrode 1172 of the electrode assembly 180 is used as differential electrode for the leadless pacemaker. The leadless pacemaker further comprises a housing 200 with a ring-like indifferent electrode 101 at the surface of housing 200. Furthermore, the leadless pacemaker is coupled to an electrode lead having an electrode lead assembly 180 at its distal end. An additional fixation of the leadless pacemaker is provided by tines 100.

[0091] Implantation of the leadless pacemaker starts with implantation of an electrode lead comprising the electrode assembly 180 as explained above, wherein the length of the electrode lead is a multiple of the length of the electrode assembly 180. Then, the differential electrode may be temporarily electrically connected and electrically checked at the proximal end of the electrode lead. In the next step, the main part (housing 200 with, e.g., ring-like indifferent electrode, electrical components, voltage source, tines 100) of the leadless pacemaker is pushed over the electrode lead in longitudinal and distal direction. The main part of the leadless pacemaker is then fixed in the septum 40 using tines 100. The electrode lead is then contacted by a pre-defined element of the main part of the leadless pacemaker when it reaches its final position at the septum 40. Once the main part of the leadless pacemaker is in correct position, the electrode lead is contacted and cut off in the leadless pacemaker using an internal (not shown) mechanically acting clamping member that mechanically grips the electrode lead. The cut off proximal end of the electrode lead is removed from the patient’s body afterwards. Accordingly, the leadless pacemaker has a reliable and exactly positioned electrode for stimulation of the left bundle 54. Additionally, the implantation process is simple and cost- effective.

Claims

Claims1. A medical electrode assembly (180) comprising- a lead body (70, 170, 270, 370, 470, 570, 670, 770, 870, 970, 1070, 1170) extending in a longitudinal direction (79),- a helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) connected to a distal end of the lead body (70, 170, 270, 370, 470, 570, 670, 770, 870, 970, 1070, 1170), configured to convert rotational movement into linear movement in a feed direction (793) during implantation,- a stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071, 1171) forming a distal end face of the lead body (70, 170, 270, 370, 470, 570, 670, 770, 870, 970, 1070, 1170) in a stimulation condition upon completion of the implantation process, wherein the stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071, 1171) has a greater diameter (D) transverse the feed direction (793) than the implantation cross section of the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190), and- a differential electrode (72, 172, 272, 372, 472, 590, 591, 690, 691, 772, 1172) at the lead body (70, 170, 270, 370, 470, 570, 670, 770, 870, 970, 1070, 1170) or at the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190), wherein the differential electrode (72, 172, 272, 372, 472, 590, 591, 690, 691, 772, 1172 ) is located at a predefined distance (L) in longitudinal direction to the stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071, 1171).

2. The electrode assembly (180) of claim 1, wherein the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) comprises a straight shaft (91, 191, 291, 391, 491, 591, 691, 891, 991, 1091, 1191), in particular a rotatable shaft, at its proximal end which is formed integrally or is fixedly attached to a helical section of the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190), wherein the shaft (91, 191, 291, 391, 491, 591, 691, 891, 991, 1091, 1191) is aligned with the feed direction and configured to rotate with the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) during implantation such that on and / or upon completion of the implantation process the shaft (91, 191, 291, 391, 491, 591, 691, 891, 991, 1091, 1191) distally protrudes from the stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071, 1171).

3. The electrode assembly (180) of any one of the previous claims, wherein the helical member (90, 190, 290, 390, 490, 790, 890, 990, 1090, 1190) is electrically insulated against thedifferential electrode (72, 172, 272, 372, 472, 772, 1172) located at the lead body (70, 170, 270, 370, 470, 770, 870, 970, 1070, 1170).

4. The electrode assembly (180) of any one of claims 1 to 2, wherein a distal tip section of the helical member (690) is electrically connected to a receiver for electrical signals during implantation.

5. The electrode assembly (180) of any one of the previous claims, wherein the diameter (D) transverse the feed direction of the stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071, 1171) is greater than or equal to 1.3 times the diameter of the implantation cross section of the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) upon completion of the implantation process.

6. The electrode assembly (180) of any one of the previous claims, wherein the stop surface (271) is formed by at least one elastic element (276) configured to bend towards the surface of the lead body (270) by surrounding tissue during implantation.

7. The electrode assembly (180) of any one of the claims 1 to 5, further comprising a flanged sleeve (874) and a first collar (876), wherein the first collar (876) is located at the distal end of the lead body (870) and is configured to interact with the flanged sleeve (874) such that the first collar (876) expands on and upon the completion of the implantation process thereby increasing the diameter of the stop surface (871).

8. The electrode assembly (180) of any one of the claims 1 to 5, further comprising a second collar (976), wherein the second collar (976) is located at the distal end of the lead body (970) and is configured to interact with the helical member (990) such that the second collar expands when the helical member (990) is retracted upon completion of the implantation process.

9. The electrode assembly (180) of any one of the claims 1 to 5, further comprising an extractable member (1075), wherein the extractable member (1075) is retracted within the lead body (1070) prior implantation and configured to be extracted from the distal end of the lead body (1070) during implantation or during traversing of the helical member (1090) in distal direction beyond the distal end of the lead body (1070) such that it forms the stop surface (1071) upon completion of the implantation process.

10. The electrode assembly (180) of any one of the previous claims, wherein at least one indifferent electrode (73, 173, 273, 373, 473, 573, 673, 773) is provided at the lead body (70, 170, 270, 370, 470, 570, 670, 770), wherein the distal end of the nearest indifferent electrode (73, 173, 273, 373, 473, 573, 673, 773) is located at a predefined proximal distance from the proximal end of one differential electrode (72, 172, 272, 372, 472, 590, 591, 690, 691, 772, 1172 ).

11. The electrode assembly (180) of any one of the claims 2 to 10, wherein the diameter of the shaft (91, 191, 291, 391, 491, 591, 691, 891, 991, 1091) is less than or equal to 0.5 times the diameter (D) transverse the feed direction of the stop surface (71, 171, 271, 371, 471, 571, 671, 771, 871, 971, 1071).

12. The electrode assembly (180) of any one of the previous claims, wherein the helical member (790, 1090) is retractable into the lead body (770, 1070) upon completion of the implantation process and / or wherein the differential electrode (72, 172, 272, 372, 472, 772) is a ring electrode encompassing an electrically insulating outer layer of the lead body (70, 170, 270, 370, 470, 770) and / or wherein the lead body (1170) comprises at least one protruding element of the group comprising tines (100), fins, nubs and scales.

13. An implantable medical device, for example an electrode lead (60, 160), an actuator, a sensor or a leadless pacemaker, wherein the medical device comprises an electrode assembly (180) of any one of the previous claims at its distal end.

14. The implantable medical device of claim 13, wherein the device being a leadless pacemaker comprising a housing (200) and at least one fixation element connected to the housing (200), wherein the fixation element comprises the electrode assembly (180).

15. An implantation method for an electrode assembly (180) of any one of the claims 1 to 12 comprising the following steps:- Advancing the electrode assembly (180) to a pre-defined entry area for implantation at a pre-defined tissue within the patient’s body, and- Penetrating the pre-defined tissue by the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) at the pre-defined entry area and simultaneously rotating the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) until the helical member (90, 190, 290, 390, 490, 590, 690, 790, 890, 990, 1090, 1190) fully protrudes from a side of the tissue that is opposite the entry area.

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