United States Patent 3738369

An implantable body organ stimulator such as an electronic cardiac pacer has a magnetic reed switch and a switch operator embedded in its encapsulation. The state of the reed switch may be changed to alter any one of several functional characteristics of the stimulator with a switch operator which controls the operating state. The operator comprises a magnet which is movable between two positions in a guide tube which is adjacent the reed switch. The magnet may be urged from one position to another with a needle that enters the interior of the guide tube through an aperture in a plate that is embedded in the encapsulation. Means are provided in one embodiment for preventing restoration of the magnet to its original position.

Adams, Theodore P. (Wauwatosa, WI)
Bowers, David L. (Wauwatosa, WI)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
335/153, 335/157, 335/169, 335/170
International Classes:
A61N1/375; H01H36/00; (IPC1-7): A61N1/36
Field of Search:
128/419C,419E,419P,419R,421,422 335
View Patent Images:
US Patent References:
3311111Controllable electric body tissue stimulators1967-03-28Bowers
3260821Push switch1966-07-12Yokeo
3204059Magnetically latched relay1965-08-31Saaty

Primary Examiner:
Kamm, William E.
We claim

1. An implantable body organ stimulator comprising:

2. The invention set forth in claim 1 including:

3. The invention set forth in claim 1 wherein:

4. The invention set forth in claim 1 wherein:

5. The invention set forth in claim 4 including:

6. The invention set forth in claim 1 including:

7. The invention set forth in claim 1 wherein:

8. The invention set forth in claim 1 including:

9. A body implantable organ stimulator which has optionally selective operating characteristics, comprising:

10. An implantable body organ stimulator which has optionally selective operating characteristics, comprising: switching

11. The invention set forth in claim 10 wherein:


The present invention relates to electric body organ stimulators such as electronic cardiac pacers. The most prevalent current practice is for manufacturers to provide stimulators in which the operating characteristics such as output voltage and current, pulse energy, pulse rate and pulse width are fixed. Unfortunately, the physiological requirements of some patients may dictate that one or more of these characteristics by something other than a standard or fixed value. This has compelled manufacturers to make and stock a variety of stimulators with different characteristics in order to meet the requirements of different classes of patients. This situation is problematical for hospitals and cardiologists too because they are compelled to stock a variety of stimulators in order to be sure of having the right type on hand when needed. It is readily apparent that having to make and stock a limited number of models or styles of stimulators would be beneficial to patients, manufacturers, hospitals, and physicians from the economic as well as the medical point of view.

Some progress has been made in improving the versatility of stimulators. One approach has been to incorporate a magnetic reed switch in the stimulator. The switch is variously connected in the electronic circuitry to switch capacitors, inductors, resistors or other circuit elements and thereby change the functional characteristics of the stimulator. The patient or the physician or both were provided with a permanent magnet that could be placed in proximity with the stimulator over intervening body tissue and the magnetic reed switch would respond by changing states in which case a functional characteristic, usually stimulus pulse rate, was changed. Moreover, on a subsequent occasion, the magnet could be applied again to restore the reed switch and the functional characteristic to its original state. Experience has taught, however, that it is usually undesirable to adapt a stimulator for being switched back and forth between functional states because such switching might be done by the patient to his disadvantage. It is preferred at the time of implantation that the physician determine those functional characteristics which are appropriate to the particular patient and then set the stimulator to operate and remain in the most desirable state or mode. On the other hand, it is advantageous to enable the physician to test various modes of operation at the time of implantation in order to determine the best operating mode for the patient. This suggests the need for a switch operator which will permit performing test switching but which can be locked in a fixed state after the best operating mode is determined. Heretofore, no suitable switch operator has been available that could operate reliably in the body environment.

Requirements of a switch operator for use in body organ stimulators is that it be reliable, durable, compact, inexpensive, not subject to inadvertent operation or tampering, not adversely affected by body fluids and that it be adapted for effective sterilization. In addition, it must permit test switching of the functional characteristics of the stimulator by the physician and not the patient.


It is a general object of this invention to overcome the above-noted disadvantages by providing a body organ stimulator with a function selection switch operator.

A further object of this invention is to provide a switch operator which is compact, reliable from the mechanical and electrical point of view, subject to effective sterilization and can be switched either before, during or after implantation by the physician.

Other more specific objects are to provide a switch operator which has at least two states either of which may be established as a stable state at the option of the physician at the time of implantation or sometime after implantation with minimum discomfort to the patient. A corollary to this object is to provide an operator which is adapted for remote magnetic operation and which will latch in a stable state.

How the foregoing and other more specific objects are achieved will appear from time to time throughout the course of the description of illustrative embodiments of the invention which will be set forth hereinafter.

In general terms, the new switch operator may be characterized as a casing having a magnet holder or magnet guide tube inside of and substantially coextensive with the casing. There is a permanent magnet inside of the guide tube. In one embodiment, the permanent magnet is retained in one position or state by silicone grease with which the guide tube is filled. When the magnet is shifted manually, it passes through the grease and is magnetically retained thereby in a second stable position in the guide tube. In another embodiment, the magnet may be shifted past resilient tabs which are mechanically urged out of the way by the magnet to permit its passage and which spring back behind it to preclude restoration of the magnet to its original position, thereby making the switch unidirectional. In both embodiments there is a reed switch outside of the casing which is in one state or another depending on whether the magnet is shifted. The magnet is accessible for being shifted with a needle which is admitted through a small aperture in an indifferent electrode plate which forms part of the stimulator. All parts are of materials which will not be adversely affected by body fluids or other chemicals likely to be encountered in stimulator applications.

A more detailed description of embodiments of the invention will now be set forth in reference to the drawings.


FIG. 1 is a plan view of a body implantable stimulator in which some of the parts that are essential to explaining the invention are shown in dashed lines;

FIG. 2 is a view of the right side of FIG. 1;

FIG. 3 is a schematic diagram of a stimulator in which the invention is incorporated;

FIG. 4 is an assembly view of one version of the new switch operator and an associated switch, some of the parts being shown in section;

FIG. 5 is an exploded view of the assembly shown in FIG. 4;

FIG. 6 is a plan view of a locking element; and

FIG. 7 depicts in section an alternative embodiment of the switch operator.


A typical implantable stimulator in which the invention may be incorporated is shown in FIG. 1. This may be an electronic cardiac pacer, for instance. The shape of the stimulator is determined by an insulating medium 10 in which a battery and the electronic components of the device are encapsulated. The battery is shown as a dashed line circle 11 to which rigid conductors 12 and 13 are suitably attached. Conductors 12 and 13 are rigid and serve to deliver electric power to a printed circuit board 14 and to support the same prior to encapsulation of the whole unit. The electronic circuitry which usually comprises a pulse timing circuit and a pulse generating circuit is not shown in detail but it will be understood to be encompassed in the broken line rectangle identified by the reference numeral 15. Mounted on printed circuit board 14 is a connector assembly generally indicated by the numeral 16 and having one part 17 embedded in encapsulation 10 and another part 18 extending therefrom.

As can bee seen in FIG. 2, part 18 of connector assembly 16 is cylindrical and surrounds an insulating block 19 in which there are two output terminals comprising connector pin sockets 20 and 21. As shown in FIG. 1, sockets 20 and 21 are connected to printed circuit board 14 by means of conductors 24 and 25. Conductor 25 connects with the printed circuit board by means of a jumper 26 which junctions with 25 at 27. An extension of conductor 25, namely 28, connects at junction 27 and to the casing of the new switch operator which is generally designated by numeral 31. The details of the switch operator will be described later. Adjacent operator 31 is a reed switch which has one conductor 32 connecting with conductor 28 and operator 31. Two conductors 34 and 35 connect the reed switch to printed circuit board 14 in this example.

In this device, electric pulses at a suitable width, repetition rate and energy are delivered from pulse generator 15 and its associated circuit board 14 to pin sockets 20 and 21 by way of conductors 24 and 25. The output characteristics or other functions of the pulse generator are changed by operation of reed switch 33 with operator 31 as will be described more fully hereinafter. Note also in FIGS. 1 and 2 that in the side of encapsulation 10 there is embedded a metal plate 36 which serves as an optionally usable indifferent electrode. The same signal which is applied to pin socket 20 by way of conductors 25 and 26 is also applied to indifferent electrode 36 by reason of it being connected with operator 31 by way of conductor 28.

In some cases indifferent electrode plate 36 may be covered with an insulating strip 37 as can be seen in FIG. 2. This strip is adhered to electrode plate 36 and is capable of being peeled off by the implanting physician to expose the indifferent electrode and activate it if desired for unipolar stimulation Indifferent electrode 36 is only exposed and activated and in contact with body tissue if the preferred treatment of the patient is to stimulate with a single conductor lead extending from connector 16 to the organ which is to be stimulated as is true of the unipolar mode. In such case, the connector of the single conductor lead, not shown, would join with the pin socket 21 which is fed from the printed circuit board through conductor 24 and current would flow from the end of the lead through the organ and return through body tissue to the indifferent electrode plate 36. The return circuit to the pulse generator is completed through the casing of switch operator 31 and conductor 28, as is evident in FIG. 1. If, instead of the unipolar mode of stimulation just described bipolar stimulation is desired by the physician, the plastic insulating strip 37 is permitted to remain in place and a two-conductor lead, not shown, is connected between connector 16 and the organ which is to be stimulated. Stimulating signals are then delivered from pulse generator 15 across the ends of the leads which are in contact with the organ.

Before discussing the new switch operator in detail, its general applicability to implantable stimulators will be discussed in connection with the schematic diagram of a stimulator shown in FIG. 3. In this case, the encapsulating resin may be considered as being within the boundaries of dash-dot line 10. The output terminals 20 and 21 are schematically represented as extending out of the encapsulation. Within encapsulation 10 there is generally some form of timing and signal generating circuit which is marked 40 in FIG. 3. Output signals from circuit 40 are delivered to output terminals 20 and 21. The parameters of the signal generator such as output voltage, output current, output signal energy, pulse width, pulse amplitude and pulse repetition rate are dependent on the choice of circuit elements as is well known to skilled electronic circuit designers. Any one of the parameters mentioned can usually be changed by appropriate selection of or switching of inductors, capacitors, resistors, or active elements such as transistors. Thus, any circuit elements such as those just mentioned may be connected with conductors such as 34 and 35 to a reed switch 38 or any appropriate magnetically operable switch. One or more reed switches 33 and one or more operators 31 may be present to allow alteration of one or more of the above-mentioned parameters. One parameter on which the physician usually desires some choice is stimulating pulse energy. Stimulating with the lowest energy pulses to which the heart will respond but still provide an adequate margin of safety is usually preferred both for physiological reasons an to extend battery life.

The signal generator 40 may be adapted to produce output signals at two different energy levels such as thirty or sixty microjoules. This may be achieved by incorporating a voltage doubler circuit and a voltage tripler circuit, neither of which is shown, in the signal generator 40. A lead such as 35 may be brought out from the voltage doubler and connected to one contact of reed switch 33 and another lead 34 from the tripler may be connected to the other contact of the reed switch. A lead 41 may interconnect the common reed of the reed switch 33 to a line which supplies output terminal 21 and is in common with the voltage doubler and tripler circuits. Thus, when reed switch 33 is in one position or state, low energy signals may be applied to output terminal 21, and when it is in the other state, high energy signals may be applied. Note also that the reed switch 33 may be connected to switch operator 31 and to indifferent electrode plate 36 so that when the latter is activated and terminal 21 is not in use, either high or low energy stimulation will be available, by virtue of operating reed switch 33, for the unipolar mode as was true in connection with operating in the bipolar mode. In this particular example, reed switch 33 is under the control of operator 31. The state of the operator, and hence the reed switch, may be changed by inserting a thin narrow instrument such as needle 42 through an aperture 43 in indifferent electrode plate 36 which is sealingly engaged with the operator 31 as will be described.

In FIG. 4, one embodiment of the new switch operator 31 is shown assembled and in section. An exploded view of the operator is shown in FIG. 5. The operator is adapted to mount next to any suitable surface such as indifferent electrode plate 36. The construction and steps involved in assembling the operator will be considered in connection with FIGS. 5 and 6 concurrently.

Operator 31 comprises a tubular guide or magnet holder 50 which has a flared end 51 and is preferably made of non-magnetic stainless steel. Intermediate the ends of the guide are two resilient tabs 52 and 52' which are depressed inwardly and serve as magnet retainer means. There is a clearance space such as 53 contiguous with each tab so that the tabs 52 and 52' are free to spring radially outwardly and to return to the position in which they are shown. A cylindrical permanent magnet 54 is inserted in guide 50 as shown in FIG. 4. The flared end 51 of guide 50 is then placed against plate 36 surrounding aperture 43. The flared part 51 is spot-welded to plate 36 at four circumferentially spaced apart points two of which 55 and 56 being visible in FIG. 4. A silicone plug 57 haVing a conically shaped body and a mushroom shaped head may be inserted in aperture 43 of electrode plate 36. Plug 57 prohibits contaminants from entering switch operator 31 but it is permeable to the gas which is used for sterilizing the stimulator. Thus, even though switch operator 31 is otherwise totally enclosed as will appear, its interior is accessible to sterilizing gas.

A cylindrical casing 58, preferably of non-magnetic stainless steel, constitutes the exterior of the switch operator 31 assembly. Casing 58 is enlarged diametrally at its end 59 to create a recess and there are annular shoulders 60 and 61 within the recess. A reed switch 33 is in proximity with casing 58. It has a flexible lead 62 which is welded at 63 to casing 58. The welding of the reed switch lead 62 is accomplished before the reed switch and casing 58 are encapsulated. To secure the glass body of reed switch 33 against casing 58 prior to encapsulation, a thin shrinkable plastic sleeve 64 is used. Reed switch 63 is provided with two stationary contacts 66 and 67 which might be connected to conductors 34 and 35 leading to the signal generator 40 as shown in FIG. 3.

It is contemplated that in most cases, casing 58 and its associated reed switch 33 will be encapsulated in the same encapsulation that holds the other electronic circuit components of the stimulator prior to the insertion of guide tube 50, its magnet 54 and plate 36 to which the guide tube is attached. The enlarged portion 59 of casing 58 must, in the last analysis, have good electrical continuity with the circuit including reed switch 33, casing 58, guide tube 50 and plate 36. Casing 58 should also be mechanically secure with respect to guide tube 50 when the latter is inserted within the former.

To enhance the mechanical and electrical integrity of the device, a split ring 69 is provided. This ring is initially flat as can be seen in FIGS. 5 and 6. In a commercial embodiment the ring is about 9 mils thick and has an unstressed outside diameter about 50 mils greater than the largest inside diameter of enlarged portion 59 on casing 58. The ring as may be seen in FIG. 6 is slotted at 70 and has an inside hole 71 whose initial diameter is about 2 mils less than the outside diameter of guide tube 50. Split ring 69 serves as a means for locking casing 58 to guide tube 50. During assembly, ring 69 is inserted in the enlarged portion 59 on casing 58 and then the guide tube 50 is inserted in the hole 71 of split ring 69, continuing into the bore of casing 58. When the face of the ring 69 strikes shoulder 60 in the casing, the oversize ring is caused to flex and curve as shown in FIG. 4. The inner and outer edges of the ring then make firm gripping contact with the inside of the casing and the outside of the guide tube. Prior to insertion of guide tube 50 into casing 58 as just described, a quantity of conductive plastic material 73 is deposited around the flared end 51 of guide tube 50 and the indifferent plate 36. This conductive material occupies most of the recess within the enlarged casing portion 59 and further assures positive and lasting electric continuity from reed switch 33 to indifferent electrode plate 36, by virtue of the conductive material contacting guide tube 50, casing 58, split ring 69, and plate 36.

When switch operator 31 and plate 36 are assembled as shown in FIG. 4 and encapsulated in resin 10, for instance, plate 36 will remain exposed from the outside of the stimulator. If a magnet of adequate strength is brought in proximity with the stimulator, reed switch 33 will change its contact state. A change of switch state may correspond with a change in output energy or in some other functional characteristic of the stimulator. For instance, stimulators are usually set by the manufacturer to operate in the low energy mode. At the time of implantation, the physician may desire to have a choice as to whether the particular patient should be stimulated with high or low energy. Thus, after the implantations is completed except for closing the incision where the stimulator is located, the patient will be stimulated with low energy pulses. The physician may then want to determine whether high energy stimulation is indicated in the particular case. He may do so by bringing a magnet, not shown, of suitable strength in proximity with the stimulator and thereby cause reed switch 33 to change its state and temporarily, at least, cause stimulation in the high energy mode. If the final decision is for high energy stimulation, the physician may insert needle 42 through silicone rubber plug 57 and force magnet 54 down guide tube 50 past tabs 52 and 52'. As the magnet 54 travels it deflects spring tabs 52 and 52' and passes them. Thereafter the tabs spring inwardly again as shown in FIG. 4 and serve as a latch or retainer means to positively prevent magnet 54 from returning to the position in which it is initially shown. When magnet 54 is positioned at the left end of guide tube 50, it, of course, is magnetically coupled with reed switch 33 and influences it to switch to another state which corresponds with high energy stimulation. The magnet continues to influence the reed switch for the life of the stimulator. If tabs 52 and 52' are omitted the magnet 54 will be movable bidirectionally.

An alternative switch operator embodying the principles of the one just described is shown in FIG. 7 and is generally designated by the reference numeral 31'. Parts which are similar to those described in connection with the previous embodiment will be given the same reference numeral except that a prime mark will be added. Thus, the reed switch is marked 33' and the plastic sleeve which surrounds it and holds it to the operator is marked 64'. The stationary contacts of the reed switch are marked 66' and 67'. Silicone plug 57' which may be operated by a needle 42' have their counterparts in the previous embodiment as does the indifferent electrode plate 36'.

Operator 31' also has a slidable magnet 54' which is in a magnet holder or guide tube 80 which is given a different reference numeral because of its structural dissimilarity with its counterpart in the previous embodiment. Guide tube 80 is preferably non-magnetic stainless steel and has a part of its outer surface length diametrally reduced such as at 81 extending to its right end in FIg. 7. The reduced portion 81 is surrounded by a cylindrical shell 82 of magnetic material which constitutes a magnetic shield for magnet 54'. Shield 82 has a flange 83 which is spot-welded at 101 to electrode plate 36' and then electrically and mechanically bonded with conductive epoxy resin 100 to the guide tube 80 and outer tube 88.

A ring-shaped magnetic keeper 84 is placed within cylindrical magnetic shield 82 and there is another magnetic keeper 85 fit within the internally shouldered left end 86 of the guide tube 80. Magnet 54', therefore, will adhere to one keeper 84 or the other 85 depending upon which keeper the magnet is in contact with originally. A space 86 is filled with silicone grease to serve as magnet position retainer means in this embodiment. The bore of guide tube 80 is somewhat larger than the outside diameter of magnet 54' in which case the grease will flow along the sides of the magnet and occupy the space which it formerly occupied when the magnet is urged to the left in FIG. 7 by inserting the needle 42'.

When the magnet 54' is in the position in which it is shown in FIG. 7, it has no influence on magnetic reed switch 33'. When magnet 54' is shifted to the left, however, the shielding effect of shield 82 is removed and the magnet causes the reed switch to change states. The magnet is kept in the operative position under the influence of the silicone grease and by magnetic attraction with keeper 85 which is retained in place by an end cap 87 and is preferably made of magnetic stainless steel. The end cap fits tightly within guide tube 80 and is further secured in place and sealed by conductive epoxy resin which is spread on its periphery before insertion.

Guide tube 80 is surrounded by an outer cylindrical sleeve 88 which fits tightly around guide tube 80 and is secured thereto with epoxy resin at the interfaces of these elements. Sleeve 88 is preferably stainless steel of a non-magnetic type. One flexible lead 62' from the reed switch may be welded as at 63' to the outside of outer cylindrical sleeve 88. The cylindrical interspace 89 surrounding magnetic shield 82 may also be filled with conductive epoxy resin so that there is good electric continuity from the reed switch to the keeper plate 36' by way of the switch operator assembly.

As described earlier, during assembly magnetic shield 82 is first spot-welded to electrode plate 36' and magnetic keeper ring 84 is inserted within shield 82 as shown. The whole assembly shield 82 and plate 36 are inserted into cavity 89 with epoxy placed on the outside surface of shield 82 and 83. Before assembly, parts 80 and 88 are usually previously embedded in a resinous insulating material such as encapsulation 10. Before final assembly, movable magnet 54' is inserted within guide tube 80 which has been filled to a suitable depth with silicone grease. Upon assembly, the magnet will adhere to keeper ring 84. Conductive epoxy resin is used between interfaces of all the metal parts to avoid relying on press fits and to augment electric continuity of the operator.

As in connection with the previous embodiment, the patient's response to different stimulus energy levels may be tested by placing a suitably strong test magnet, not shown, in proximity with the reed switch 33' to cause it to switch and the stimulator to respond by delivering signals of different energy level. When the test magnet is removed, the reed switch returns to its original state. If low stimulating energy is indicated for the particular patient, magnet 54' be allowed to remain in the position in which it is shown. If high energy stimulation is indicated, a needle 42' will be perforated through silicone plug 57' and the magnet 54' will be shifted through grease 86 which will transpose and contribute toward holding the magnet in its operative position in cooperation with keeper 85. It should be appreciated that one of the purposes for occupying the interior of guide tube 80 with silicone grease is to provide an impediment for shifting of magnet 54' in the event the stimulator is subjected to a mechanical shock which would be sufficient to move the magnet 54'. Also the grease will occupy the space surrounding the magnet in the guide tube 80, reducing the chance of body fluid entrapment. Unless magnet 54' is moved a considerable distance from keeper 84 by use of needle 42', the magnet will always return to its rest position against the keeper. Of course, the end cap 87 adjacent the other keeper 85 may be provided with a perforation that would enable shifting the magnet 54' to its original position once it was switched to the left. If the silicone grease is omitted, the magnet 54' can be shifted bidirectionally with an external magnet. Such modification is usually not advantageous when the operator is used in a stimulator to accomplish the purposes hereinabove discussed.

In summary, both embodiments of the new operator have a sealed chamber in which a magnet is disposed for unidirectional movement by application of a manual force. The magnet will be retained in one chosen state or the other in either embodiment. The operator is adapted to cooperate with a switch which is also entirely sealed and not subject to deterioration by oxidation or permeation by fluids from the body or even possibly from a leaky battery. How the operator may be modified to make it bidirectional has been discussed. The device is useful in cardiac stimulators as well as other body organ stimulators. Although emphasis has been placed on controlling stimulus energy levels with the new operator, it will be understood that various other functional characteristics of the stimulator may be controlled or selected likewise.

Equipping stimulators with a means for controlling the stimulus energy levels has some additional advantages which have not been mentioned heretofore. For instance, if low energy mode is chosen initially, that energy may be inadequate for stimulation when the batteries are near depletion. On the other hand, it may be that the attending physician is aware of impending failure of the stimulator because of battery depletion although it may be impossible for the convenience of the patient or because of inability to make a hospital reservation to replace the stimulator power supply immediately. An emergency situation can easily be avoided in those cases where the low energy mode is in effect, since the physician can extend the life of the stimulator for a reasonable period by switching it to the high energy state, possibly at the expense of a slightly lower stimulus pulse rate. This can be achieved by locating the switch assembly behind electrode plate 36 or 36' under an X-ray fluoroscope so a needle may be inserted through the tissue and perforate the silicone plug to transfer the magnet and hence switch the stimulator to the high energy mode. The residual battery capacity will usually be sufficient to stimulate the patient at the increased energy and at an acceptable rate until replacement of the stimulator is possible.

Another important advantage of the invention described above is that it enables the manufacturer to maintain good quality control by getting better data on the life of the stimulator when operated in either the high energy or low energy mode but not both. This results from the fact that the magnetic switch operator cannot be shifted back to its original state in which case the manufacturer upon receipt of a returned stimulator will know the mode of operation which the stimulator has been in and will be able to make a judgment as to whether its life was appropriate for that mode. Moreover, a different warranty period is applicable to each mode.

Although embodiments of the invention have been described in detail such description is to be considered illustrative rather than limiting, for the invention may be variously embodied and is to be limited only by the claims which follow.