Abstract:
An implantable medical device, which is connected or is to be connected to at least two elongated electric function conductors for the transmission of treatment signals or diagnostic signals or both, and at least one electrode pole connected to at least one of the function conductors, via which electrode pole electric current can be delivered in the case of use to surrounding tissue of the body or with which electric potentials can be sensed in the surrounding tissue or both. Includes a wave transfer module connected to the function conductor and which is embodied to transform waves arriving via a function conductor and to switch them as transformed waves onto another function conductor or the same function conductor in such a controlled manner that the waves are destructively superimposed at the electrode pole.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application 61/425,249 filed on 21 Dec. 2010, the specification of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    At least one embodiment of the invention relates to a permanently or temporarily implantable device having an elongated electric conductor. 
         [0004]    2. Description of the Related Art 
         [0005]    Devices of this type, for example, electrode lines for electrostimulation, have the disadvantage that the electric conductor thereof can heat up in an MRI scanner because the alternating magnetic fields prevailing in the MRI scanner induce not inconsiderable electric currents in the electric conductor. Induced currents of this type can also be emitted via electrode poles of the electrode line to surrounding tissue and thus, for example, lead to undesirable heating of the tissue. For this reason, nowadays patients with cardiac pacemakers usually cannot be examined, or can be examined only to a limited extent, in an MRI scanner. 
         [0006]    At least one stimulation electrode line is typically connected to implantable cardiac pacemakers or defibrillators (also referred to below jointly as cardiac stimulators or IPG (implantable pulse generator)), which stimulation electrode line has a standardized electrical connection at its proximal end provided for connection to the cardiac pacemaker or defibrillator and has one or more electrode poles on its distal end provided for placement in the heart. An electrode pole of this type is used to deliver electric pulses to the tissue (myocardium) of the heart or to sense electric fields, in order to be able to sense an activity of a heart within the scope of the so-called sensing. For these purposes, electrode poles typically form electrically conductive surface sections of an electrode line. Electrode poles are typically provided as an annular electrode in the form of a ring around the electrode line or in the form of a point electrode or tip electrode at the distal end of the electrode line. The electrode poles are connected in an electrically conductive manner via one or more electric conductors to contacts of the electric connection of the electrode line at the proximal end thereof. Thus one or more electric conductors run between the contacts of the electrical connection the electrode lines at the proximal end thereof and the electrode poles at the distal end of the electrode line, which conductors electrically connect one or more of the electrode poles to one or more of the contacts. These electric conductors can be used, on the one hand, to transmit stimulation pulses to the electrode poles and, on the other hand, to transmit electric signals recorded by means of the electrode poles to the proximal end of the electrode line and are also respectively referred to as a function line in the course of the further description. Function lines of this type are electric conductors necessary for the functions of the respective electrode line and as such are exposed to the risk of electric currents being induced in them through external alternating magnetic fields, which currents can lead, for example, to an undesirable heating up of the function lines or of the electrode poles connected to them or which can lead to the delivery of corresponding currents via the electrode poles to surrounding tissue and thus to a heating of the surrounding tissue. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    At least one embodiment of the invention is based on the object of creating a device that solves the problem described above. 
         [0008]    According to at least one embodiment of the invention, this object is attained by a temporarily or permanently implantable medical device, which is connected or is to be connected to at least two elongated electric function conductors for the transmission of treatment signals or diagnostic signals or both, and at least one electrode pole connected to at least one of the function conductors, via which electrode pole electric current can be delivered in the case of use to surrounding tissue of the body or with which electric potentials in the case of use can be sensed in the surrounding tissue or both. 
         [0009]    According to at least one embodiment of the invention, the medical device has a wave transfer module that is connected or is to be connected to the function conductor and which is embodied to transform waves arriving via a function conductor and to switch them as transformed waves onto another function conductor or the same function conductor in such a controlled manner that the waves are destructively superimposed at the electrode pole. 
         [0010]    A medical device for which the invention is particularly relevant is an electrode line, e.g., for a cardiac stimulator, in which the function conductors are electric conductors of the electrode line, wherein the electrode line has electrode poles, which are electrically connected via the function connectors to the wave transfer module. 
         [0011]    The medical device, for example, an implantable cardiac stimulator connected to an electrode line, can have a housing, which is embodied in an electrically conductive manner or has an electrode pole via which electric current in case of use can be transmitted to surrounding body tissue or with which electric potentials in surrounding tissue can be sensed or both. 
         [0012]    Preferably, the medical device has an interference field recognition device, which is embodied to detect a presence of strong electromagnetic fields and in the case of the presence to generate a corresponding output signal, and which is connected to a control unit for controlling the wave transfer module. 
         [0013]    The interference field recognition device can have a temperature sensor, which is arranged such that it can detect a heating of an electrode pole. In this manner, the interference field recognition device detects a heating as the result of high-frequency interference fields and thus interference fields indirectly via their effect. The temperature sensors are located at the electrode poles or other locations that can heat up due to the interactions with electromagnetic fields. 
         [0014]    Alternatively or additionally, the interference field recognition device can have a sensor for currents or voltages induced in a function conductor and thus be embodied to directly detect induced currents or voltages. 
         [0015]    According to a preferred embodiment, the wave transfer module has a delay line, which delays and or damps electromagnetic waves, so that in the case of operation a transformed wave is produced, which is destructively superimposed with an induced wave on the same or a different function conductor and in this manner compensates for the induced wave. The delay line can have an impedance that causes this effect. 
         [0016]    According to an embodiment variant, the delay line is realized by one or more, preferably discrete electronic components from a group that comprises coils, capacitors, ohmic resistances and transducers. These form, for example, an LC circuit, optionally also with an ohmic resistance, in order to adjust the damping. 
         [0017]    Additionally or alternatively, the delay line can have three-dimensional structures which, due to their physical properties, have a wave-delaying and/or damping effect. Three-dimensional structures of this type are not necessarily discrete electronic components but e.g., a waveguide, a coaxial line, a strip line, with optionally lossy materials in order to adjust the damping. The wave transfer module is hereby preferably adjustable with respect to its effect, in particular with respect to its delaying effect and/or its damping effect, e.g., in that the adjustable elements are operated electrically, mechanically, optically, etc. The adjustment of the controllable delay lines can also be carried out by an external programming device. 
         [0018]    Expediently, the wave transfer module has a switching unit which is arranged and embodied to switch transformed waves on a function conductor determined by the switching unit or not. This makes it possible to use the wave transfer module only when it is necessary and furthermore to adapt it to the respective case of use. The adjustment of the switching unit can also be carried out by an external programming device. 
         [0019]    According to a preferred embodiment variant, a delay line of the wave transfer module connects at least two function conductors, wherein the connection is to be produced via the switching unit. The switching unit can have the form of a switching matrix in which every cross point in the switching matrix is occupied by a switch. 
         [0020]    According to a further embodiment, the medical device can have a terminal impedance unit and the wave transfer module can have a switching unit, which is arranged and embodied to connect a function conductor to a terminal impedance unit. The terminal impedance can cause a phase shift of a wave on a function conductor and thus likewise contribute to the desired effect of a wave cancellation. For this purpose, preferably at least one impedance value of the terminal impedance unit can be electrically, mechanically or optically controlled. The terminal impedances can be realized discretely or physically. The adjustment of the controllable terminal impedances can also be carried out through an external programming device. 
         [0021]    The control device is preferably embodied to control the controllable delay lines and/or the controllable terminal impedances and/or the switching unit depending on an output signal of the interference field recognition device such that in case of use a heating induced by interference fields at the electrode poles is minimized. 
         [0022]    Particularly preferably, a battery operated electronic implant with 
         [0000]    An electrically conductive housing or a housing with at least one electrode pole,
 
Electric function conductors that connect the electrode poles of electric feed-through of the implant in order to be able to conduct electric signals from the respective electrode pole into the implant,
 
An interference field recognition device for detecting the presence of strong electro-magnetic fields, in particular MRI fields, and
 
A wave transfer module, which is controlled by the interference field recognition device via a control device and transforms waves reaching the implant via at least one function conductor and switches them onto at least one other function conductor such that the waves are destructively superimposed on the distal electrode poles so that there the heating due to MRT is minimized.
 
         [0023]    Alternatively to a controllable terminal impedance, a controllable generator can also be provided which is embodied to actively feed a compensation signal into a function conductor. The compensation signal to be fed in has the same frequency as the interference signal and a certain phase position, wherein the frequency is determined via the interference field recognition device and the phase position and amplitude are adjusted after evaluation of the temperature signals such that the interference field induced heating at the electrode poles (optionally generally the temperature measurement points) is minimized. 
         [0024]    In addition to the embodiments described herein other alternative embodiments may include some or all of the disclosed features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    At least one embodiment of the are now explained in more detail with reference to the Figures. The figures show the following: 
           [0026]      FIG. 1  shows as implantable medical devices an implantable cardiac stimulator  10  and an implantable electrode line  20  connected thereto. 
           [0027]      FIG. 2  shows in very diagrammatic representation the inner structure of a cardiac stimulator according to the invention. 
           [0028]      FIG. 3  shows in very diagrammatic representation a structure of a delay line. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The implantable cardiac stimulator  10  can be a cardiac pacemaker or a cardioverter/defibrillator (ICD). In the exemplary embodiment shown, the cardiac stimulator  10  is a ventricular cardiac pacemaker and defibrillator. Other known cardiac stimulators are dual-chamber cardiac pacemakers for the stimulation of the right atrium and of the right ventricle or biventricular cardiac pacemakers that, in addition to the right ventricle, can also stimulate the left ventricle. 
         [0030]    Stimulators of this type typically have a housing  12 , which is generally composed of metal and is thus electrically conductive and can be used as a large-area electrode pole. A terminal housing  14  is typically attached to the outside of the housing  12 , which terminal housing is also referred to as a header. A header of this type typically has female contacts to accommodate plug contacts. The female contacts have electric contacts  16 , which are connected via corresponding conductors to an electronic system arranged in the housing  12  of the cardiac stimulator  10 . 
         [0031]    In one or more embodiments, the electrode line  20  also represents an implantable medical device. Electrode poles in the form of a point electrode or tip electrode  22  and an annular electrode  24  arranged in their vicinity are arranged in a manner known per se at the distal end of the electrode line  20 . The electrode poles  22  and  24  are embodied such that, depending on the function of a cardiac stimulator to which the electrode line  20  is connected, are used to sense electrical potentials of the cardiac tissue (myocardium) or are embodied to transmit electrical signals, for example, to deliver stimulation pulses to the cardiac tissue surrounding them.  FIG. 1  shows how the electrode poles, that is, the tip electrode  22  and the annular electrode  24 , in case of use the electrode line  20 , are located in the apex of a right ventricle of a heart. 
         [0032]    The tip electrode  22  as well as the annular electrode  24  are electrically connected via respectively at least one electric conductor  26  to a plug contact  28  at the proximal end of the electrode line  20 . The plug contact  28  has electrical contacts that correspond to the electrical contacts  16  of the female contact in the terminal housing  14  of the implantable cardiac stimulator. The electric conductors  26  in the electrode line  20  can be embodied as approximately elongated cable pull conductors or as helically coiled conductors. Conductors of this type, which connect the functional electrode poles to electric contacts of the plug contact at the proximal end of the electrode line  20  in an electrically conductive manner, are also referred to as function conductors within the scope of this text, since they, for example, transmit electric signals for the purpose of treatment from the plug contact to the respective electrode pole or guide signals representing sensed electric potentials from the respective electrode pole to the plug contact and thus serve the elementary function of the medical device. 
         [0033]    The electric conductors  26 , which connect the electrode poles  22  and  24  respectively to the electric contacts of the plug connector  28  of the electrode line  20 , are surrounded by an insulating sheath over the major part of their length, so that an electric contact to the tissue of the heart is produced in targeted manner via the electrode poles. 
         [0034]    In addition to the electrode poles  22  and  24 , which are typically used for the (in this case ventricular) stimulation of the cardiac tissue, the electrode line  20  also has two larger-area electrode poles  30  and  32 , which serve as defibrillation electrodes and are formed by at least one uninsulated helically coiled wire. 
         [0035]    It should be pointed out that within the scope of this exemplary embodiment the invention is explained on the basis of a right ventricular cardiac pacemaker and defibrillator. However, an ablation electrode line, for example, can basically also be used as a medical device for the purposes of the invention, which ablation electrode line in the case of use likewise projects into the heart of a patient and which is controlled by a device arranged outside the patient and is connected thereto for this purpose. 
         [0036]      FIG. 2  shows a diagrammatic representation of the inner structure of a medical device according to an embodiment the invention. The medical device has an electrically conductive housing  100 , which corresponds to the housing  12  from  FIG. 1 . Two electrode lines  102  and  104 , which respectively have a tip electrode  106  and an annular electrode  108 , are connected to the housing. Each of the tip electrodes  106  and of the annular electrodes  108  respectively forms an electrode pole. Each electrode pole is connected via a separate feed line  110  to an electronic system in the interior of the housing  100 . The feed lines  110  respectively form a function conductor. Temperature sensors  112  are respectively arranged in the immediate vicinity of the electrode poles  106  and  108 , which are connected via signal lines  114  to a control unit  116  in the interior of the housing  100 . 
         [0037]    Instead of the temperature sensors  112 , other sensors can also be for detecting electromagnetic interference fields or currents or voltages induced into the feed lines  110 . 
         [0038]    The feed lines  110  (function conductors) and the signal lines  114  are guided into the housing  100  via plug connectors not shown in  FIG. 2  and via housing feed-throughs  140 . The function conductor  110  is thereby connected to the typical components of a cardiac stimulator as well as sensing units or stimulation units. This is shown overall in  FIG. 2  by the block  118  which represents the sensory and therapeutic cardiac pacemaker electronic system. 
         [0039]      FIG. 2  shows that the function conductors  110  on the one hand are guided to the cardiac pacemaker electronic system  118  and on the other hand to switching units  120  and  122 , which are embodied as switching matrices. A wave transfer module  124  is connected to the switching matrices  120  and  122 , which wave transfer module has (in the case shown three) adjustable delay lines  126 . The delay lines  126  are adjustable with respect to their delaying effect and/or their damping effect. For this purpose they are connected via control lines  128  to the control unit  116 . In this manner they can be received by the control unit  116  depending on the signals that the control unit  116  receives via the signal lines  114  from the sensors  112  in the electrode lines  102  and  104 . Concretely, the control device  116  is embodied to receive the switching matrices  120  and  122  as well as the delay lines  126  depending on the signals received via the signal lines  114  such that the signals entering via the signal lines  114  as far as possible do not show any heating of the electrode poles  106  and  108 . In this context, the control unit  116  can also be seen as an operator control. 
         [0040]    The latter effect is obtained with the aid of the adjustable delay lines  126  in that waves entering via the function conductors  110  are switched on the adjustable delay lines  126  and the delay lines  126  are adjusted such that the waves are transformed and are switched on the same or different function conductors in a manner such that they are destructively superimposed with induced waves and thus cancel the effect of the induced waves. 
         [0041]    A terminal impedance unit  130 , which in the concrete case has three adjustable terminal impedances  132 , also alternatively or additionally serves this purpose. The adjustable impedances  132  can be adjusted by the control unit  116  via control lines  134 . Through the adjustable terminal impedances  132 , the reflection of the waves on the function conductors  110  at the proximal ends thereof defined by the terminal units can be adjusted with respect to phase position and damping in order in this manner to likewise achieve a destructive superposition of waves in the region of the electrode poles of the respective function conductors. 
         [0042]    Instead of the terminal impedance unit  130 , a compensation signal generator can also be provided, which generates compensation signals actively and controlled by the control unit  116  and feeds them into the respective function conductor. 
         [0043]    It should be pointed out that the housing  100  of the cardiac stimulator represents a pole of its own, which likewise is electrically connected (see reference number  136 ) to the switching matrices  120  and  122  as well as the cardiac stimulator electronic system  118 . 
         [0044]    The control unit and thus the behavior of the switching units  120  and  122  as well as the adjustments of the delay lines  126  and of the terminal impedances  132  can be programmed externally. This is indicated by the arrow  300 . 
         [0045]    The structure of an exemplary delay line is shown diagrammatically in  FIG. 3 . In  FIG. 3  the reference numbers are used as follows:
     200 : Conductive implant housing     210 : Line of an electrode     211 : Line of an electrode (the same electrode as  110  or a different one)     220 : Wave transfer module     230 : Conductor of the delay line     240 : Reference conductor of the delay line     250 : Connection of the reference conductor of the delay line to the implant housing     260 ,  261 : Switch     270 ,  271 : Connection to the electronic system   
 
         [0055]    Upon recognition of a strong electromagnetic field (in particular HF fields, such as occur in MR scanners and which represent a risk potential for patient and implant) by the temperature sensors  112  and the control unit  116 , which in this context form a interference field recognition unit, the switching of the electrode inputs in the implant is automatically reconfigured. This is caused by the control unit  116 , which is correspondingly programmed or structured. This switching is carried out only temporarily while the interference occurs, in the day-to-day operation of the implant the high-resolution and broadband signal recording, in particular also the impedance determination for a hemodynamic sensor, is not impaired. The electrode lines then run directly (as usual) into the electronic system  118  of the cardiac stimulator. In a preferred realization, during the interference and switching according to the invention with delay lines, the electronic system  118  is switched away at some or all inputs. A switch provided for this purpose and controlled by the control unit  116  is not shown in  FIG. 2 . 
         [0056]      FIG. 2  shows an optional additional interference field recognition unit  150  which reacts to interference fields in general and in this case actives the control unit  116 , as described above, for the duration of the interference fields or for a predetermined period. 
         [0057]    In a preferred implementation, the coupling of the feed lines is carried out by means of the switching matrices  120  and  122  such that, e.g., the center conductor of a first electrode is switched (coaxially) on the outer conductor of a second electrode. In a further realization, at the same time the center conductor of the second electrode is switched on the outer conductor of the first electrode (cross connection). In a further realization, the delay is thereby virtually 0 seconds, i.e. it is switched directly without the use of delay lines. 
         [0058]    In the interconnection of the electrodes, for optimization with respect to heating it is additionally ensured that the areas enclosed between the electrodes are minimal. The currents induced by MRI gradient fields are thus minimized and the risk of undesirable cardiac stimulation (induced by the MR scanner) is reduced. In particular, a connection is not produced to the housing potential. 
         [0059]    It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teaching. The disclosed examples and embodiments are presented for purposes of illustration only. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention.