Abstract:
Embodiments include an implantable electronic device with at least one electromagnetic field detection unit and at least one antenna, wherein the at least one electromagnetic field detection unit is connected to the at least one antenna. The at least one electromagnetic field detection unit responds to electromagnetic fields that occur or are present in an environment surrounding a patient outside an environment of an MRI device and electromagnetic fields that are shielded in the environment of the MRI device. The at least one electromagnetic field detection unit indicates an absence of the electromagnetic fields that typically occur in the environment surrounding a patient outside an MRI device and that are shielded in the environment of an MRI device.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application 62/085,259 filed on 27 Nov. 2014, the specification of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the invention generally relate to a magnetic resonance imaging (MRI) sensor for an implantable electronic device, wherein the sensor is configured to detect when the implantable electronic device is operated within or in a direct vicinity of an MRI device, such as a magnetic resonance scanner. In addition, embodiments of the invention generally relate to an implantable electronic device that includes an MRI sensor and that is configured to be used in an MRI scanner, in particular one or more of an implantable heart therapy device, a heart monitoring device a cardiac pacemaker and a cardioverter/defibrillator. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, implantable heart therapy and/or heart monitoring devices include for example heart stimulators in the form of cardiac pacemakers or cardioverters/defibrillators. Such heart stimulators are generally connected to electrode lines, which have stimulation electrodes and optionally additional defibrillation electrodes in a chamber of a heart or in the immediate vicinity thereof. Typically, a cardiac pacemaker may deliver an electric stimulation pulse to the muscle tissue of a heart chamber via a stimulation electrode (more specifically one or more stimulation electrode poles) in order to thus cause a stimulated contraction of the heart chamber, provided the stimulation pulse has a sufficient intensity and the heart muscle tissue (myocardium) is not in a refractory phase at that precise moment. A contraction of a heart chamber stimulated as such may be referred to herein as a stimulated event. A stimulation pulse having sufficient intensity to cause a stimulated contraction of a heart chamber may be referred to herein as “above-threshold”. Should a natural contraction of the heart chamber occur, such a contraction may be referred to herein as an autonomous action or as a natural or intrinsic event. A contraction, for example of the right atrium of a heart, may be referred to herein as an atrial event, which for example may be a natural atrial event or, in the case of an atrial cardiac pacemaker, may also be a stimulated atrial event. Generally, natural (intrinsic) and stimulated left-ventricular and right-ventricular events may be distinguished in a similar manner. 
         [0006]    Typically, a local excitation of the myocardium spreads, starting from the location of excitation, via stimulus conduction in the myocardium and leads to a depolarization of the muscle cells and therefore to a contraction of the myocardium. Generally, after a short period of time, this causes a repolarization of the muscle cells and therefore a relaxation of the myocardium. Typically, during the phase of depolarization, the heart muscle cells are insensitive to excitation, that is to say are in a refractory state. This time is generally referred to as the refractory period. Typically, the electric potentials accompanying the depolarization and repolarization may be sensed, and the course thereof over time (referred to as an electrocardiogram) may be evaluated. 
         [0007]    In an electrocardiogram, generally, action potentials accompanying a contraction of the ventricle and reflecting a depolarization of the heart muscle cells may be identified as a Q-wave, whereas the repolarization of the heart muscle cells accompanying the relaxation of the myocardium is reflected as a T-wave. 
         [0008]    In healthy individuals, typically, the respective heart rhythm is determined by the sinus node, which is controlled by the autonomous nervous system. Generally, the sinus node excites the right atrium of a human heart by stimulus conduction and also excites the (right) ventricle of the heart via the atrioventricular (AV) node. Typically, a natural heart rhythm starting from the sinus node may be referred to as the sinus rhythm and leads to natural contractions of the respective heart chamber, which may be detected as natural (intrinsic) events. 
         [0009]    Generally, such natural (intrinsic) events are detected by recording the electric potentials of the myocardium of the respective heart chamber with the aid of sensing electrodes, which are part of a corresponding electrode line. Typically, the sensing electrode poles may simultaneously be the stimulation electrode poles and may be used alternately as a stimulation electrode pole and as a sensing electrode pole. Generally, a sensing electrode pole pair, which is formed by two adjacent electrode poles, specifically a point electrode (tip electrode) and a ring electrode, the point electrode also serving as a stimulation electrode pole, is typically provided for the sensing, that is to say the sensing of intrinsic events. Generally, a bipolar recording of an intracardial electrocardiogram (IEGM) is thus provided. Typically, intrinsic events and the stimulation in the ventricle are sensed with the aid of a ventricular electrode line, and the stimulation and the sensing of intrinsic events in the atrium (in the right atrium) are implemented with an atrial electrode line, which electrode lines are connected separately to the respective heart stimulator. In addition, generally, a left-ventricular electrode line may also be provided, which typically protrudes via the coronary sinus and a lateral vein branching off therefrom into the vicinity of the left ventricle, where it may have a small-area stimulation and/or sensing electrode. 
         [0010]    Typically, to be able to satisfy the different needs of various patients, implantable heart stimulators may be operated in various operating modes. The various stimulation and sensing modes are generally referred to in a standardized manner using a three-letter code, of which the first letter denotes the location of stimulation (V=ventricle, A=atrium, D=ventricle and atrium), the second letter denotes the location of the sensing (V=ventricle, A=atrium, D=ventricle and atrium), and the third letter denotes the type of operation (I=inhibited, T=triggered, D=both inhibited and triggered). In particular for dual-chamber cardiac pacemakers in DDD mode, generally, a ventricular stimulation may be performed synchronously with an atrial heart rate that is as natural as possible. Typically, should it be impossible to sense any healthy natural heart rate in the atrium, for example in the case of atrial tachycardia or atrial fibrillation, cardiac pacemakers that are atrium-synchronous in principle often have a mode-switching capability in order to switch from an atrium-synchronous ventricular stimulation to an atrium-asynchronous stimulation in VVI mode, should a perceived atrial rate lie outside permissible limits. Generally, ventricular tachycardias within the scope of cardioversion therapy may be treated by stimulation with a stimulation rate above the tachycardia rate. 
         [0011]    Typically, the stimulation modes may be set by corresponding control programs, which for example process or ignore detected events, or by control parameters. By way of example, generally, the detection of events in the atrium and/or ventricle may thus be activated or deactivated by a control parameter. 
         [0012]    With regard to the references used herein, it is noted that the terms stimulation electrode or sensing electrode within the scope of the invention may include a respective electrode pole on an electrode line, for example the part of an electrode line via which stimulation pulses are delivered or electric potentials are received. It should also be noted that an electrode line used for stimulation may be referred to herein as a “stimulation electrode”. 
         [0013]    Generally, the sensing electrode poles are connected during operation of the heart stimulator to corresponding sensing units, which may evaluate a respective electrocardiogram recorded via a sensing electrode pole (or a sensing electrode pole pair) and in particular may detect intrinsic atrial or ventricular events, that is to say natural atrial or ventricular contractions. Typically, this is achieved by way of example using a threshold value comparison, wherein an intrinsic event is detected when a respective intracardial electrocardiogram exceeds a threshold value predefined as suitable. 
         [0014]    Generally, the respective intrinsic atrial heart rate (atrial frequency) or ventricular heart rate (ventricle frequency) may be derived from the frequency with which atrial or ventricular events follow one another, and for example tachycardias may thus be detected. 
         [0015]    Typically, the detection of natural events is additionally used in demand pacemakers to suppress (inhibit) the delivery of stimulation pulses to a corresponding heart chamber should the natural event be detected in a time window prior to the planned delivery of a stimulation pulse to this heart chamber. In the case of rate-adaptive cardiac pacemakers, generally, the moment in time of the delivery of a respective stimulation pulse is planned in accordance with a respective stimulation rate, which is to correspond to the physiological demand of a patient, that is to say for example is higher with greater exertion. Generally, a heart stimulator may be equipped with one or more activity sensors, which for example may be a CLS (closed loop stimulation) sensor. 
         [0016]    Typically, it is problematic that the function of such implantable electric medical devices, such as heart stimulators, may be severely adversely affected by strong electromagnetic fields or magnetic fields as occur for example in a magnetic resonance imaging (MRI)_scanner (or magnetic resonance scanner or MRI device). Generally, many individuals who carry an active implantable medical device (also referred to hereinafter as an implant or IMD) are therefore contraindicated for MRI examinations, although MRI examinations are becoming increasingly important in the field of diagnostic medicine. 
         [0017]    In order to still enable MRI examinations for individuals carrying active implantable medical devices, typically, various approaches are used, which are based either on the execution of the MRI examination or on the implantable medical device. 
         [0018]    Generally, technologies for identifying magnetic fields are used, which are based on conventional methods for magnetic field detection. For example, United States Patent Application Publication US 2008/0154342, entitled “Implantable Medical Device Comprising Magnetic Field Detector”, to Digby et al., appears to describe a method for using a GMR (giant magnetic resistance) sensor in order to detect magnetic fields of MRI devices. 
         [0019]    In addition, generally, other MRI sensors are used, in particular magnetic field sensors, gradient field sensors, high-frequency field sensors, position sensors, noise or (Lorentz) vibration sensors or voltage profile sensors, which monitor characteristic voltage profiles. 
         [0020]    Typically, for example, an implantable cardioverter/defibrillator (ICD) is set by a cardiologist prior to an MRI examination into an operating mode that is not adversely affected by the magnetic fields prevailing in the MRI scanner. Following the MRI examination by a radiologist, generally, a cardiologist has to set the ICD back into an operating mode corresponding to the needs of the patient. 
         [0021]    In view of the above, there is a need for a supplement or an alternative to prior art MRI sensors, for example an implantable electronic device including an MRI sensor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0022]    One or more embodiments of the invention include an implantable electronic device that includes at least one electromagnetic field detection unit and at least one antenna, wherein the at least one electromagnetic field detection unit is connected to the at least one antenna. In at least one embodiment, the field detection unit may respond to electromagnetic fields that occur, or are present, in an environment surrounding a patient outside an environment of an MRI device, and to electromagnetic fields that are shielded in the environment of the MRI device. In one or more embodiments, the field detection unit may display or indicate an absence of the electromagnetic fields that occur in the environment surrounding the patient outside the environment of the MRI device and that are shielded in the environment of the MRI device. 
         [0023]    By way of at least one embodiment, the field detection unit may include at least one receiver that adapts to the electromagnetic fields that occur in the environment surrounding the patient outside the environment of the MRI device and that are shielded in the environment of the MRI device. In one or more embodiments, the field detection unit may include a plurality of receivers. In at least one embodiment, the electronic device may include a control unit connected to the at least one receiver. In one or more embodiments, when none of the at least one receiver indicates, in a respective receiving range, a field strength above a predefined limit field strength, the control unit connected to the at least one receiver signals the absence of the electromagnetic fields. 
         [0024]    According to one or more embodiments, the field detection unit may include a tunable receiver, such as a broadband frequency identification unit, that scans a wider frequency range and that may be connected to a field characteristic memory or may include a field characteristic memory. In at least one embodiment, the field characteristic memory may include characteristic features of electromagnetic fields that occur outside the environment of the MRI device and that are shielded in the environment of the MRI device. In one or more embodiments, the characteristic features may be or may include, for example, frequencies or frequency ranges of electromagnetic fields. 
         [0025]    In at least one embodiment, the field detection unit may identify the absence of one or more electromagnetic fields present in the patient environment and may indicate the MRI environment if all fields have “disappeared” or are not present. 
         [0026]    By way of at least one embodiment, the electronic implantable device may include an MRI sensor that may automatically identify the environment of the MRI device, for example to improve the suitability of an active implantable medical device, such as the electronic implantable device, even under the influence of magnetic fields of a magnetic resonance imaging (MRI) scanner. 
         [0027]    In one or more embodiments, the electronic implantable device may include the MRI sensor, wherein the electronic implantable device may be a heart stimulator. In at least one embodiment, the heart stimulator may include a stimulation control unit and a memory unit. In one or more embodiments, program information corresponding to control programs and/or control parameters may be stored in the memory unit. In at least one embodiment, the program information may control the function of the stimulation control unit. In one or more embodiments, the stimulation control unit may, when the at least one field detection unit indicates the absence of the electromagnetic fields, in the environment surrounding a patient outside the environment of an MRI device, select a control program or control parameters, from the control programs and control parameters stored in the memory unit, that allow safe operation of the implantable electronic device in the environment of the MRI device. In at least one embodiment, the control programs or control parameters to be selected, for example, are control programs or control parameters that fix the sensing and/or stimulation modes to V00 or A00, to switch off the sensing. 
         [0028]    In one or more embodiments, the stimulation control unit may maintain the selected control program or the selected control parameters until the at least one field detection unit indicates the absence of the electromagnetic fields that typically occur in the environment surrounding a patient outside the environment of an MRI device and that are shielded in the environment of an MRI device. 
         [0029]    By way of at least one embodiment, the control programs or control parameters may determine the operating mode, such as the respective operating mode of the implantable electronic device, which may be controlled by the stimulation control unit. In one or more embodiments, the control programs or control parameters stored in the memory unit may influence the mode of operation of the stimulation control unit. In at least one embodiment, the stimulation control unit may control the operation of the implantable electronic device, including a delivery of therapy for example, such as the heart stimulation. In one or more embodiments, the control unit may select a control program to be applied or control parameters to be applied, which may define the delivery of therapy, for example. 
         [0030]    Embodiments of the invention may allow the safe operation of the electronic implant in the MRI scanner, without the need to reprogram or adapt the MRI program immediately before the examination. 
         [0031]    In at least one embodiment, the electronic implantable device may be or may include one or more of an implantable pulse generator (IPG), an implantable cardioverter/defibrillator (ICD), a heart stimulator that provides cardial resynchronization therapy (CRT), and a neurostimulator. In one or more embodiments, the electronic implantable device may be or may include one or more of a heart therapy device, a heart monitoring device, an implantable biventricular cardiac pacemaker and a cardioverter/defibrillator. In at least one embodiment, cardial resynchronization therapy (CRT) may be carried out with a biventricular cardiac pacemaker. 
         [0032]    By way of one or more embodiments, the memory unit may include a control program that may be selected by the control unit, wherein the control program is configured to suppress a triggering of stimulation pulses. In at least one embodiment, the memory unit may include at least one program that causes an operation mode that is without stimulation. 
         [0033]    In one or more embodiments, the implantable electronic device may be or may include a cardiac pacemaker, wherein the memory unit may include a control program or control parameters selectable by the control unit. In at least one embodiment, the control program or control parameters may prompt the control unit to cause an asynchronous stimulation in an asynchronous stimulation mode, such as V00 or D00. In at least one embodiment, in accordance with the three-letter code described above, the stimulation modes may manage without sensing of intrinsic events, and may not include inhibition or triggering of stimulation pulses by detected intrinsic events. In one or more embodiments, due to alternating magnetic or electromagnetic fields, a heart stimulator may incorrectly detect signals induced by the alternating magnetic or electromagnetic fields as intrinsic events, wherein such incorrectly detected signals are considered by the stimulation modes. In a pure stimulation mode, by way of at least one embodiment, which manages without the detection of intrinsic events, incorrectly detecting signals induced by the alternating magnetic or electromagnetic fields may be absent or avoided. 
         [0034]    According to one or more embodiments, the implantable electronic device may be or may include a cardiac pacemaker, wherein the memory unit may store a control program that may be selected by the control unit. In at least one embodiment, the control program may cause an asynchronous stimulation in an asynchronous stimulation mode, such as V00 or D00. 
         [0035]    In at least one embodiment, the control programs or control parameters to be selected may be selected such that they ensure a fundamentally safe operation of the implantable electronic device in a magnetic resonance scanner, for example the deactivation of the shock delivery in an ICD. 
         [0036]    In one or more embodiments, the MRI sensor may include one or more of a magnetic field sensor, a gradient field sensor, a high-frequency field sensor, a position sensor, a vibration sensor (such as a Lorentz vibration sensor), and a voltage profile sensor, which monitors characteristic voltage profiles, for example in the electrode lines of the implantable medical device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The above and other aspects, features and advantages of at least one embodiment of the invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings, wherein: 
           [0038]      FIG. 1  shows a system with a heart therapy and/or heart monitoring device, as an implantable electronic device, including a three-chamber ICD system; 
           [0039]      FIG. 2  shows main components of the heart therapy and/or heart monitoring device of  FIG. 1 ; 
           [0040]      FIG. 3  shows a typical course of an MRI examination of an ICD patient with an implantable electronic device without an MRI sensor; and 
           [0041]      FIG. 4  shows a block diagram of an MRI sensor, according to one or more embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    The following description is of the best mode presently contemplated for carrying out at least one embodiment of the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
         [0043]      FIG. 1  shows a heart therapy and/or heart monitoring device and system, including a three-chamber ICD system as an example of an active implantable medical device, according to one or more embodiments of the invention. In at least one embodiment, the implantable medical device may include a generator  100 , or a heart stimulator  100 , for example as the heart therapy and/or heart monitoring device, connected to a number of implantable electrode lines  110 ,  112  and  114 . One or more embodiments may include a right-ventricular (RV) electrode line  110  that provides right-ventricular sensing and delivers stimulation, which may include a right-ventricular (RV) tip electrode  121  and a right-ventricular (RV) ring electrode  122  at the distal end thereof. During operation, in at least one embodiment, right-ventricular stimulation pulses may be delivered as necessary to deliver biventricular CRT stimulation via the RV tip electrode  121 . One or more embodiments may include shock electrodes or coils  123 , such as a distal shock coil  123  and/or a proximal shock coil (not illustrated), attached to the RV electrode line  110 , to deliver shock. In at least one embodiment, the generator housing of the generator  100  may be a counter electrode. 
         [0044]    In one or more embodiments, electrode line  112  may be a right-atrial electrode line  112 , which, at the distal end thereof, may include a bipolar sensing and stimulation pole with a right-atrial tip electrode  131  and a right-atrial ring electrode  132 . In one or more embodiments, the right-atrial electrode line  112  may sense the atrial rhythm and may stimulate the atrium. 
         [0045]    In at least one embodiment, the system may include a left-ventricular coronary sinus (CS) electrode line to deliver left-ventricular stimulation pulses that provide CRT via one or more of four left-ventricular (CS) stimulation electrode poles  141 ,  142 ,  143  and  144 . 
         [0046]    One or more embodiments may include a wireless bidirectional telemetry unit, for example in the generator  100 , to communicate with one or more of external programming devices, control devices, and data transfer devices  160 . 
         [0047]      FIG. 2  shows the main components of the heart stimulator  100  of  FIG. 1 , according to one or more embodiments of the invention. As shown in  FIG. 2 , at least one embodiment may include electrical terminals that correspond to the various electrodes  121 ,  122 ,  131  and  132 , as illustrated on the left-hand side of  FIG. 2 . In one or more embodiments, the shock electrodes  123  may be connected to a right-ventricular shock pulse generator  50 . In at least one embodiment, the shock pulse generator  50  may be connected to a stimulation control unit  54 , wherein the stimulation control unit  54  activates the shock pulse generator  50  as required in order to generate and deliver a defibrillation shock. 
         [0048]    In one or more embodiments, the terminal of the right-ventricular tip electrode  121  (RV tip) and the connection of the right-ventricular ring electrode  122  (RV ring) may each be connected both to a right-ventricular stimulation unit  56  and to a right-ventricular sensing unit  58 . In at least one embodiment, the right-ventricular stimulation unit  56  and the right-ventricular sensing unit  58  may each be connected to the stimulation control unit  54 . 
         [0049]    By way of one or more embodiments, the right-ventricular stimulation unit  56  may generate a right-ventricular stimulation pulse in response to an actuation signal of the stimulation control unit  54 , and may deliver the right-ventricular stimulation pulse via the right-ventricular ring electrode  122  (RV ring) and the right-ventricular tip electrode  121  (RV tip). In at least one embodiment, the housing of the generator  100  may form a neutral electrode, and the right-ventricular stimulation unit  56  may be connected to the terminal of the right-ventricular ring electrode  122  (RV tip) and the housing as another electrode to deliver a stimulation pulse. In one or more embodiments, a right-ventricular stimulation pulse may be distinguished from a defibrillation shock in the that the stimulation pulse may include a much lower pulse intensity, such that the stimulation pulse does not excite the entire heart tissue (myocardium) of a heart chamber all at once, compared to a defibrillation shock, but excites the heart muscle cells in the immediate vicinity of the right-ventricular tip electrode  121  (RV tip). In at least one embodiment, the excitation may spread by natural stimulus conduction over the entire right ventricle and may ensure a stimulated contraction of the right ventricle. 
         [0050]    In one or more embodiments, the right-ventricular sensing unit  58  may amplify and may filter, initially by an input amplifier, electric potentials applied to the terminal of the right-ventricular ring electrode  122  (RV ring) and the right-ventricular tip electrode  121  (RV tip). In at least one embodiment, the right-ventricular sensing unit  58  may evaluate the profile of the electric signals applied to the inputs of the sensing unit  58 , such that the right-ventricular sensing unit  58  may automatically detect a natural (intrinsic) event, for example an automatic contraction of the right ventricle. In one or more embodiments, such detection may be implemented for example such that the profile of the signal applied to the inputs of the right-ventricular sensing unit  58  is compared with a threshold value. In at least one embodiment, the greatest amplitude of the signal is the R-wave, which defines a natural contraction of the right ventricle, and which may be detected by threshold value comparison. In one or more embodiments, the right-ventricular sensing unit  58  may output a corresponding output signal to the stimulation control unit  54 , wherein the output signal indicates a natural contraction of the right ventricle. In at least one embodiment, the moment in time at which the threshold value is exceeded may include the moment of detection for the respective event. 
         [0051]    At least one embodiment may include one or more sensing units (not illustrated in  FIG. 2 ) for the shock electrodes. In one or more embodiments, the one or more sensing units may detect signals between the shock electrodes, between the shock electrode  123  and the housing of the generator  100 , or between the other shock electrode (the proximal shock electrode or coil) and the housing of the generator  100 . 
         [0052]    In at least one embodiment, the terminal of the right-atrial tip electrode  131  (RA tip) and the terminal of the right-atrial ring electrode  132  (RA ring) may be both connected to a right-atrial stimulation unit  60  and to a right-atrial sensing unit  62 , which are each in turn connected to the stimulation control unit  54 . In one or more embodiments, the right-atrial stimulation unit  60  may generate stimulation pulses, of which the intensity is sufficient to excite the right-atrial myocardium. In at least one embodiment, the right-atrial stimulation pulses may include a pulse intensity that differs from the right-ventricular stimulation pulses. In one or more embodiments, the right-atrial sensing unit  62  may detect a P-wave from the course of the differential signal applied to the inputs of the sensing unit  62 , wherein the P-wave defines a natural (intrinsic) contraction of the right atrium. In at least one embodiment, when the right-atrial sensing unit  62  detects a corresponding P-wave, the right-atrial sensing unit  62  may generate an output signal and may forward the output signal to the stimulation control unit  54 , which defines a natural contraction of the right atrium. 
         [0053]    By way of one or more embodiments, the terminal of the left-ventricular tip electrode  141  (LV tip) and the terminals of the left-ventricular ring electrodes  142 ,  143  and  144  may be connected in a similar manner to a left-ventricular stimulation unit  64  and a left-ventricular sensing unit  66 . In at least one embodiment, the left-ventricular stimulation unit  64  and the left-ventricular sensing unit  66  may be connected to the stimulation control unit  54 . In one or more embodiments, the left-ventricular stimulation unit  64  and the left-ventricular sensing unit  66  may function similarly to the stimulation units  56  and  60  and sensing units  58  and  62  as described above. 
         [0054]    According to at least one embodiment, the heart stimulator  100  may include an acceleration sensor  72  connected to the stimulation control unit  54 , wherein the acceleration sensor  72  may be integrated into the housing of the heart stimulator  100 . In one or more embodiments, the acceleration sensor  72  may detect a movement signal dependent on a physical activity of a patient and may output a corresponding first accelerometer output signal to the stimulation control unit  54 , indicating the physical activity of the patient. As such, in one or more embodiments, the stimulation control unit  54  may adapt the timing of the stimulation pulse to the need of the patient (hemodynamic need). In at least one embodiment, the accelerometer output signal may be used to determine rest phases, in which a dislocation thereof may be detected. 
         [0055]    In one or more embodiments, the generator  100  may include a memory unit  80  connected to the stimulation control unit  54 . In at least one embodiment, the memory unit  80  may store signals generated or evaluated by the stimulation control unit  54 . In one or more embodiments, the memory unit  80  may store control programs for the stimulation control unit  54 , wherein the control programs may be modified. 
         [0056]    In at least one embodiment, the stimulation control unit  54  may be connected to an MRI sensor  200 . In one or more embodiments, the MRI sensor  200  may include a field detection unit, as will be described further below regarding  FIG. 4 . In at least one embodiment, the MRI sensor  200  may include one or more of a magnetic field sensor, a gradient field sensor, a high-frequency field sensor, a position sensor, a vibration sensor (such as a Lorentz vibration sensor), and a voltage profile sensor. 
         [0057]    In one or more embodiments, the memory unit  80  may be connected to a telemetry unit  84 , wherein the telemetry unit  84  may one or more of wirelessly transfer data stored in the memory unit  80  to the external device  160 , transfer program commands from the external device  160  to the heart stimulator  100 , and store the transfer program commands in the memory unit  80 . 
         [0058]    In at least one embodiment, the implantable electronic device may allow an automatic MRI detection and switchover into a safe state during an MRI examination, wherein at least two patient-tailored MRI program settings may be stored in the implantable electronic device and may be selected automatically in accordance with a patient status detected by the implant prior to the MRI examination. 
         [0059]      FIG. 3  illustrates a typical course of an MRI examination of an ICD patient without a device according to embodiments of the invention. As shown in  FIG. 3 , an ICD patient  300  may include an aftercare consultation with a cardiologist  310  before the planned MRI examination, wherein the ICD is switched off. The MRI examination may be carried out by a radiologist  320  after a temporal delay lasting from hours to a few days. After a further delay, the patient may again be treated by the cardiologist  330  and the ICD may be switched back on. During the entire period starting with the MRI examination by a radiologist  320  to the renewed switching-on of the ICD by the cardiologist  330 , the patient is without the protection of the implanted defibrillator and may be without rhythm monitoring. The remaining residual risk, for example, which may be measured in proportion to the benefit of the MRI examination, is generally accepted. 
         [0060]    By way of one or more embodiments, with the use of an MRI sensor  200 , the illustrated sequence of  FIG. 3  may be changed such that the MRI setting may only be effective directly during the MRI examination and the subsequent aftercare by the cardiologist  330  for reprogramming may be spared. Typically, the moment of the first aftercare consultation by the cardiologist  310  in order to determine the MRI program cannot take place arbitrarily prior to the actual MRI examination by the radiologist  320 , since the conditions of the patient may change, and therefore an adaptation of the MRI program may be necessary. 
         [0061]    At least one embodiment of the invention provides an anti-bradycardia stimulation. In one or more embodiments, patients who do not require any stimulation may be examined in principle in the OFF mode in the MRI scanner to avoid the risk of arrhythmia induction. In at least one embodiment, patients who require stimulation, however, may be stimulated in an asynchronous operating mode (such as V00, D00) in the MRI scanner. In one or more embodiments, the respective pacemaker dependency may change over the course of time. 
         [0062]      FIG. 4  shows a block diagram of an MRI sensor  200  of the electronic implant  100 , according to one or more embodiments of the invention. In at least one embodiment, the MRI sensor  200  may include at least one antenna  210 , connected to an antenna matching network/amplifier  220 . In one or more embodiments, the antenna matching network/amplifier  220  may be connected to a tunable low-current broadband frequency identification unit  230 , which may scan the field strengths of the defined ambient frequencies cyclically and may signal the field strengths to a control unit  240 . In at least one embodiment, the control unit  240  may compare all ambient frequencies received from the broadband frequency identification unit  230  having a field strength above a (respective) predefined limit field strength with previously stored field characteristics. For example, in at least one embodiment, previously stored field characteristics may include previously stored frequency ranges of the ambient frequencies, which may be present in the environment of the implantable electronic device outside the environment of the MRI device. By way of one or more embodiments, when the control unit  240  does not identify any of the previously stored ambient frequencies, the control unit  240  may signal an MRI environment. In at least one embodiment, the broadband frequency identification unit  230  may form a field detection unit together with the control unit  240 . 
         [0063]    In one or more embodiments, suitable frequencies may be selected from the frequency bands between 30 kHz to 30 GHz. 
         [0064]    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. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention.