Abstract:
An adaptation probe for insertion into implanted electrode devices of active medical implants to enable them for use in high-frequency magnetic alternating fields of MRI systems comprises an elongated, flexible probe body, and at least one electrical assembly, which has one or more electrical components connected to an interface, in the probe body, and which can be electrically connected to a supply lead of the electrode device such that the electrically properties of the electrode device can be adapted, in particular the frequency-dependent resistance, impedance, capacitance, or inductance thereof.

Description:
This application takes priority from German Patent Application DE 10 2010 000 368.9, filed 11 Feb. 2010, German Patent Application DE 10 2010 000 370.0, filed 11 Feb. 2010, German Patent Application DE 10 2010 000 371.9, filed 11 Feb. 2010, German Patent Application DE 10 2010 000 372.7, filed 11 Feb. 2010, the specifications of which are all hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One or more embodiments of the invention relates to an adaptation probe for insertion into implanted electrode devices of active medical implants to enable them for use in high-frequency magnetic alternating fields of MRI systems. Embodiments of the invention furthermore relate to a set composed of such an implantable electrode device and an adaptation probe that can be inserted therein. 
     2. Description of the Related Art 
     Regarding the background of the invention, it should be pointed out that the subject matter of one or more embodiments of the invention is relevant primarily in conjunction with cardiac pacemakers, implantable defibrillators, and other types of active implantable electromedical devices. The latter typically comprise at least one current/voltage-carrying supply lead in the electrode device—typically referred to simply as “electrode”—, the distal end of which is disposed e.g. in a ventricle and is used to measure cardiological potential signals or to transmit relevant therapeutic current signals. 
     The compatibility of such electrode devices in the case of implantable electromedical devices having high-frequency magnetic fields of the type used in imaging diagnostic methods in particular which are based on magnetic resonance—so-called MRI (magnetic resonance imaging) methods—is a serious problem. In the case of such MRI methods, a magnetic alternating field puled with radio frequency (RF) is superimposed on a strong static magnetic field, which is used to change the energy status of the protons in the tissue being investigated and to produce corresponding MRI signals from the tissue. 
     Due to the laws of electromagnetic induction, this magnetic alternating field induces alternative voltages in the supply lead of the electrode devices—under discussion here—of electromedical device implants, the energy of which is converted to heat at the electrically conductive contact poles, in particular, of the electrode device with human tissue. This can result in considerable heating e.g. of the tip contact of a cardiac electrode with corresponding impairment and even damage of the cardiac tissue in contact therewith or that surrounds it. 
     To prevent these problems, U.S. Pat. No. 7,363,090 B2 proposes the use of filters on the basis of oscillating circuits of parallel-connected coil and capacitor, which is assigned to the corresponding supply lead for the tip contact pole or a ring contact pole of a corresponding electrode of an implantable electromedical device. The filters disclosed in this known patent are designed—in practical application by the patent owner—as relatively voluminous components that reinforce the electrode device along a certain length and impart unfavorable mechanical properties to the electrode equipped therewith. Furthermore, the filter is accommodated in a closed housing that does not provide passage for the guide wires that are typically used when implanting an electrode. To this extent, the potential uses of this known electrode with filter devices is limited. 
     Document US 2009/0281592 A1 makes known filter components for reducing the heating of pacemaker electrodes of an electromedical implant due to the effect of high-frequency magnetic fields produced during MRI procedures, in which case an induction coil is installed around a non-conductive central section of a shank which connects a tip contact pole to an inner spiral conductor of the electrode device. By installing an induction coil on the shank, inductive signal filtering is achieved to reduce the electrode tip without the need for a relatively long, voluminous coil body along the length of the electrode. Capacitive elements can also be integrated in the shank to create an LC filter circuit. As an alternative thereto, a so-called “air coil” is disclosed in this publication as an inductive element, in the case of which the shank may be omitted. 
     A disadvantage of the prior art described is the fact that such electrode devices must be equipped individually, according to their design, with the appropriate circuits to implement a filter function at the production stage. Conventional electrode devices without such protective devices and, in particular, those that are already implanted in a patient without the appropriate filter devices pose a risk when introduced into a high-frequency magnetic field. 
     BRIEF SUMMARY OF THE INVENTION 
     Proceeding therefrom, the problem addressed by embodiments of the invention is that of providing a system which can be used to subsequently reinforce implantable electrode devices of active medical implants such that they are suitable for use in high-frequency magnetic alternating fields, in particular in regard to MRI systems. 
     This problem is solved by the adaptation probe claimed herein, which comprises an elongated, flexible probe body and an electrical assembly having at least one or more electrical components in the probe body, which are connected to an interface. After the probe body has been inserted into the electrode device that is present, this electrical assembly can be electrically coupled to one of the supply leads of the electrode device such that the electrical properties of the electrode device can be adapted, in particular the frequency-dependent resistance, impedance, capacitance, or inductance thereof. Such an electrode device is therefore subsequently equipped such that it can be used without reservation in a high-frequency magnetic alternating field. The prevention of high-frequency currents in the supply leads of the electrode device, which are induced accordingly by the alternating field, effectively prevents the electrode device, in particular the contact poles thereof, from heating up. The adaptation probe is typically installed after the electrode device has been implanted, in order to change the electrical properties thereof. This has the particular advantage that the electrode device itself is not stiffened locally by the filter elements. The electrode device can therefore be implanted in a particularly gentle manner. The lumen thereof, which is typically provided for a guide wire, can then be used to insert the adaptation probe therein. 
     According to a preferred embodiment, the probe body can be formed by an insulated wire or a plastic rod which may be optionally equipped with a wire core. Electronic components are then installed on this probe body and are mounted such that they form an electronic component at the functionally desired longitudinal position of the adaptation probe. It can be integrated into the probe body e.g. before the tip of the adaptation probe and/or at, at least two, or preferably several longitudinal positions of the probe body. The tip of the probe body can be designed to be electrically conductive or insulating. 
     According to a preferred embodiment, each of the electrical components can be coupled to the electrode device by way of one or more connection contacts. This can be a direct electrical contact, or a capacitative or inductive coupling to the supply lead or corresponding components of the electrode device is also feasible. 
     The contact connection can be designed according to various concepts, for example, the connection contact can be connected to a supply lead of the electrode device in a form-fit manner, or can be designed geometrically and physically as contact spring, sliding contact, or a similar contact tab. For a subsequent reinforcement of an implanted electrode device, a preferred embodiment is particularly advantageous in which one or more electrical assemblies are detachably fastened to the probe body, in particular on the tip thereof. Therefore, the electrical assembly can be “released” after the adaptation probe with the electrical assembly/assemblies thereof have been inserted into the electrode device and the suitable contact with the supply lead thereof has been established. In this regard, the actual probe body does not need to remain in the electrode device. Only the assembly that adapts the electrical properties of the electrode device remains permanently at the site. According to a related embodiment of the connection between electrical assembly and probe body, e.g. in the form of a bayonet connection, the electrical assembly can also be removed from the electrode device by reinserting the probe body and attaching the electrical assembly thereto. 
     Further preferred embodiments relate to the embodiment of the electrical assembly itself, which can comprise e.g. electrical contact pins with miniature electronic components connected therebetween. Contact pins and miniature components are all disposed together in a bonded manner in a filter housing applied by injection molding all around. According to another embodiment, a “barrel filter” is provided as the electrical assembly, in which the contact pins of the electrical assembly are designed as mutually insulated caps that face one another, in the interior of which the electrical components of the electrical assembly are disposed. 
     Since the adaptation probe can be used in various electrode devices, it is particularly advantageous if the electrical assembly can be adjusted individually by way of series- and/or parallel-connected filter elements by bridging them with separable short-circuit lines. The bridged element is activated by separating a particular line. 
     Finally, one or more embodiments of the invention relates to a set composed of an implantable electrode device of a medical implant and an adaptation probe which can be inserted therein is designed according to one of the embodiments described above. 
     In summary, the adaptation probe according to the invention is a particularly simple solution for enabling conventional electrical devices of active medical implants to be used in high-frequency magnetic alternating fields. The actual design of the electrode device does not need to be changed. The adaptation probe is a universal solution for different types of electrodes. Heating of the electrode device is reliably prevented nevertheless, and the cardiac muscle is not damaged by heating of the contact poles of the electrode device in the MR environment. Finally, a further advantage of the adaptation probe is that space that was previously left unused, namely the lumen provided only to receive the guide wire during implantation of the electrode device, is used to accommodate the electrical assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, details, and advantages of the invention will be apparent from the description of embodiments, which follows, and with reference to the attached drawings. In the drawings: 
         FIGS. 1 to 3  show schematic side views of sections of an adaptation probe to be inserted into an electrode device, in different embodiments, 
         FIG. 4  shows an adaptation probe in a state in which it has been inserted into an electrode device, 
         FIG. 5  shows a wiring diagram of an electrical assembly having an adjustable frequency behavior, 
         FIGS. 6 and 7  show views of the contacting between an electrical assembly of an adaptation probe and the electrode device in two variants thereof, 
         FIGS. 8 to 15  show highly schematicized depictions of electrical assemblies in the form of high-frequency filters in various embodiments, 
         FIGS. 16 and 17  show partial depictions of such high-frequency filters, and 
         FIGS. 18 to 26  show schematic coaxial longitudinal sectional views of electrical assemblies having integrated high-frequency filters in different embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The basic configuration of an adaptation probe  1 , which is also referred to as a “finishing wire”, will be explained in greater detail with reference to  FIG. 1 . A probe body  2  is formed of an elongated, flexible plastic rod equipped with a metal core which is not depicted. Shortly before distal tip  3 , which is likewise non-conductive in the case shown, an electrical assembly  4  which can be composed e.g. of a capacitor  5  having a related capacitance C is integrated into probe body  1 . This capacitor is to be electrically connected to a supply lead of the electrode device by way of connection contacts  6 ,  7  in a manner to be described in greater detail. 
     In the case of the embodiment shown in  FIG. 2 , tip  3  in front of electrical assembly  4  is conductive. 
       FIG. 3  shows an adaptation probe  1 , in the case of which a plurality of electrical assemblies  4  having electrical components  8 , such as capacitors or even more complex circuits, are integrated therein, being distributed over a plurality of longitudinal positions of probe body  2 . 
       FIG. 4  shows the basic principle of cooperation between adaptation probe  1  and electrode device  9  which is shown in sections in this drawing. Electrode device  9  is shown with electrode body  10  thereof and a spiral supply lead  11  which extends therein to a contact pole which is not shown. Adaptation probe  1  slid into lumen  12  of electrode device  9  and contacts spiral supply lead  11  at a suitable point. Between the two connection contacts  6 ,  7  of electrical assembly  4 , the spiral supply lead functions as inductance and, together with capacitor  5  in adaptation probe  1 , can therefore form an LC oscillating circuit having a typical frequency-dependent transmission behavior. When adapted accordingly, the currents induced in the supply lead, which occur in the electrode device due to a high-frequency alternating field in the MR environment, are filtered out. 
       FIG. 5  shows an electrical assembly in the form of an adjustable filter, in which a series circuit of inductances L is connected parallel to a series circuit of capacitances C. Each inductance L and capacitance C itself is short-circuited by jumpers  513  which—as indicated using dashed lines—can be separated individually. It is therefore possible to include the desired number of inductances L and/or capacitances C to the oscillating circuit with corresponding total inductance L ges  and total capacitance C ges . In this manner, a potential scattering of the filter characteristics can be compensated for during production. “Trimming” takes place by changing the capacitances and/or inductances. 
     Other alternatives for the contacting between electrical assembly  4  and supply lead  11  will be explained with reference to  FIGS. 6 and 7 .  FIG. 6  shows a form-fit contacting in which probe body  2  with annular connection contacts  6 ,  7  is slid into the lumen of spiral supply lead  11 , thereby contacting the corresponding winding of spiral supply lead  11  which is bare at this point. 
     In the embodiment shown in  FIG. 7 , contacts  6 ,  7  have geometric shapes e.g. in that a laterally projecting contact spring  514  establishes the electrical connection between connection contacts  6 ,  7  and spiral supply lead  11  at two different positions. 
       FIG. 7  also shows a bayonet connection  15 , which indicates that in this embodiment the distal end section of adaptation probe  1  was “released” in electrode device  9  and remaining probe body  2  was removed. 
       FIGS. 8 to 15  show different embodiments of how electrical assemblies  4  can be designed in the form of high-frequency filter  21  which is suitable for insertion into an electrode device for a cardiac pacemaker, defibrillator, neurostimulator or similar active medical implants. 
     Housings of aforementioned filters are typically composed of solid metal parts, and expensive ceramic components are usually used to build an insulation between housing and electrical components. The sealing of the housing is very elaborate, problematic, and therefore cost-intensive. The concepts shown in  FIGS. 8 to 11  make it possible to create a simply designed seal against fluids, thereby enabling high frequency filter  21  to be realized in a cost-favorable manner. Highly diverse electrical components can be embedded easily and in a variable manner since the housing is created mainly by providing a coating applied by injection molding, and possibly various pre- and post-handling steps. 
     In detail,  FIG. 8  shows contact pins  13 ,  14  of filter  21 , which are interspaced collinearly, between which one or more electrical components  25  are installed, being interconnected accordingly, and thereby being connected. The ends of contact pins  13 ,  14  are left exposed and this entire assembly is enclosed in a plastic body  26  applied by injection molding, which ensures that components  25  are sealed and electrically insulated. 
     If necessary, filter  21  produced in this manner can also be provided with a coating  27  which can be composed e.g. of a plastic, a ceramic, or another type of anorganic layer. Such a functional coating  27  is used to adapt the surface properties to particular usage conditions; for example, coating  27  can provide mechanical stabilization or form a vapor barrier. 
     The embodiment depicted in  FIG. 9  differs from that shown in  FIG. 8  in that a wire coil  28  is also wound around electrical components  25  between contact pins  13 ,  14 , which can generate inductance L of high frequency filter  21 . 
     To provide an adaptation probe  1  with a high frequency filter  21  and simultaneously enable the use of a guide wire,  FIG. 10  shows an embodiment in which contact pins  13 ,  14  are designed as conductive tubes  29 ,  30 , lumen  31  of which align with a corresponding passage  32  in plastic body  26  that forms filter housing  22 . A guide wire, mandrel, or the like can then pass through lumen  31  and passage  32 . As shown clearly in  FIG. 10 , electrical components  25  are embedded such that they are offset laterally relative to passage  32 . 
       FIG. 11  shows another outer view of the filter depicted in  FIG. 10 , in which case as well a coating  27  of metal, various plastics or anorganic or organic compounds depending on the desired functionality is applied to the housing. 
     Electrical contact pins  13 ,  14  or tubes  29 ,  30  can be composed of stainless steel, platinum, platinum/iridium alloy, or titanium. They may also be provided with one or more bores, grooves, engravings, or recesses to increase the mechanical strength of filter  21  after the coating is applied by injection molding, thereby stabilizing it overall. 
       FIGS. 12 to 17  which follow show embodiments of a high frequency filter  21  that do not require contact pins, and the housing of which can therefore be sealed in a simple manner. In the case of the above-described variants of filter  21 , contact pins  13 ,  14  increase the overall size of filter  21 , and additional passages must be insulated or sealed off. 
     As made clear from the view according to  FIG. 12  and the schematic sectional view according to  FIG. 13 , the contact pins are formed by two contact caps  33 ,  34  which are insulated from one another, and which are mechanically connected and electrically insulated by an insulator insert  35 . The two “semi-barrels” formed by contact caps  33 ,  34  are connected in a water-tight manner, and two electrically separated regions result. 
     Electrical components  25  are arranged in insulator insert  35  in an appropriate configuration so that they have e.g. a high-pass, low-pass, bandpass, or band-stop behavior. Electrical components  25  are electrically connected to the inside of contact caps  33  and  34 . As indicated in  FIG. 14 , this takes place via appropriate connecting lines  36 ,  37  which are formed by typical wires, litz wires, or wire cables, and can be welded, crimped, or lased to the inside of contact caps  33 ,  34 . An inductively or capacitively coupling connection of the connectors is also feasible. 
     The embodiment of high frequency filter  21  as a barrel filter described herein results in a shortening of the overall size and increases safety by reducing connection points. When installed in an adaptation probe, the region stiffened by the filter is therefore shortened as well. 
     As shown in  FIG. 15 , components  25  can also be electrically contacted via sliding contacts  38  or corresponding contact springs which are in electrical contact with the inner side of contact caps  33  and  34 . 
       FIG. 16  shows a special embodiment of insulator insert  35 , on which a welding disc  39  composed of metal has been placed. They extend radially beyond the jacket wall of cylindrical insulator insert  35  and are used to connect contact caps  33 ,  34  by welding. Furthermore, insulator insert  35  has a passage coaxially in the center, similar to a tube, in the form of a bore or the like, as a recess for components  25 . 
     Insulator insert  35 , as insulating intermediate piece, can be composed e.g. of ceramic or plastic, onto corresponding projections  41 ,  42  of which the contact caps—left contact cap  34  is shown in FIG.  21 —can be slid and fastened to insulator insert  35  by welding, soldering, bonding, crimping, or the like. 
     Instead of metal, the two semi-barrels of contact caps  33 ,  34  can also be made of a plastic, a conductive plastic, a ceramic, or another non-conductor. They must then be coated entirely or partially with a conductive material. 
     Finally,  FIGS. 18 to 26  relate to further integral designs of a high-frequency filter  21 . 
     For example,  FIG. 18  shows a high-frequency filter element  21  as pin unit  43 , in which a filter composed of two SMD components  44 ,  45  in the form of inductance L and capacitance C connected in parallel is formed. The design of SMD components  44 ,  45  need not be identical. They are integrated completely in the pin unit, which can therefore be manufactured isodiametrically. Connectors  46 ,  47  to the left and right are composed of conductive material. 
     As shown in  FIG. 19 , pin unit  43  can also be composed of a body  48  of dielectric material, which has corresponding connecting lines  36 ,  37  between SMD components  44 ,  45 , which form the filter components, and connectors  46 ,  47 . This design places less of a demand on the filter components since they are embedded in a homogeneous material. 
     In the embodiment shown in  FIG. 20 , high frequency filter  21  and SMD components  44 ,  45  thereof are integrated in a body  48  having a relatively thin structure. This installation between two conductive elements is omitted in this drawing. Entire pin unit  43  is therefore not necessarily isodiametrical. As described with reference to  FIG. 19 , this embodiment can also be composed of dielectric material having suitable lead structures. 
     To separate high frequency filter  21  itself from the surroundings, it is enclosed in a plastic body  26  applied by injection molding, a coating, a housing, or a similar measure, as shown in  FIG. 21 . 
     A further miniaturization for pin unit  43  is attained using the embodiment shown in  FIG. 22 . There, wire-wound coil  28  of high frequency filter  21  is placed around SMD component  44  which is designed as capacitor C. The required space is therefore markedly reduced compared to the above-described embodiments according to  FIGS. 18 to 21 . 
     In the embodiment of pin unit  43  depicted in  FIG. 28 , coil  24  and SMD component  44  for capacitance C are installed mechanically one behind the other, wherein interconnection  49  emphasized using solid lines is parallel. The pin unit can be isodiametric in design and comprise appropriate connectors  46 , 47  on the ends thereof. In the interior of the component, capacitance C is installed as capacitor SMD component  44 , and inductance L is installed as wire-wound coil. In  FIG. 24 , the supporting structure of the body of the pin unit is omitted for clarity. 
     Such a supporting structure is shown in  FIG. 25 . Furthermore, this embodiment comprises a metallization  50  which extends over wide subregions of pin unit  43  on the outer side thereof. The contacting of the components takes place via metallization  50 , namely that of wire-wound coil  28  and capacitor SMD component  44 , as shown in  FIG. 26 . Interconnection  49  can therefore be designed with shorter paths in the interior. 
     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. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Adaptation probe 
           2  Probe body 
           3  Tip-distal 
           4  Electrical assembly 
           5  Capacitor 
           6  Connection contact 
           7  Connection contact 
           8  Electrical component 
           9  Electrode device 
           10  Electrode body 
           11  Spiral supply lead 
           12  Lumen 
           13  Contact pin 
           14  Contact pin 
           15  Bayonett connection 
           25  Electrical components 
           26  Plastic body 
           27  Coating 
           28  Wire-wound coil 
           29  Tube 
           30  Tube 
           31  Lumen 
           32  Passage 
           33  Contact cap 
           34  Contact cap 
           35  Insulator insert 
           36  Connecting line 
           37  Connecting line 
           38  Sliding contact 
           39  Welding disc 
           40  Passage 
           41  Projection 
           42  Projection 
           43  Pin unit 
           44  SMD component 
           45  SMD component 
           46  Connector 
           47  Connector 
           48  Body 
           49  Interconnection 
           50  Metallization 
           513  Jumper 
           514  Contact spring