Pacer With Magnetic Coupling Means For External Rate Adjustment

Abstract

There is disclosed a pacer rate adjustment mechanism which utilizes magnetic coupling. In one embodiment of the invention, a diametrically magnetized disc magnet, mounted on a bearing, is fixed to the shaft of a small rate-controlling potentiometer in the pacer. The pacer rate can be adjusted by rotating a strong bar magnet external of the patient, thereby rotating the pacer magnet and turning the potentiometer shaft; continuous rate adjustment is possible without requiring skin puncture. In another embodiment of the invention, two flux-linked diametrically magnetized disc magnets are provided in the pacer. One of them is fixed to the potentiometer shaft and the other is connected to a needle port. The latter magnet is turned by use of a Keith or other needle extended through the skin of the patient; the turning of this magnet causes the potentiometer magnet to rotate and the pacer rate to be varied. Although this embodiment of the invention requires skin puncture to change the pacer rate, it still offers one of the main advantages of the first embodiment, namely, a total hermetic seal with no possibility of fluid penetration into the pacer circuit itself. This is accomplished by mounting the needle magnet external of the enclosure in which the circuitry is potted, and then covering the external magnet and needle port with the conventional epoxy coating and/or silicone rubber boot.

Description

This invention relates to pacer rate adjustment mechanisms, and more particularly to such mechanisms which allow a continuous adjustment of pacer rate.

In a conventional heart pacer there is usually provided a potentiometer whose setting controls the rate at which stimulating pulses are generated. An illustrative pacer circuit is disclosed in Berkovits U.S. Pat. No. 3,528,428 issued on Sept. 15, 1970 and entitled "Demand Pacer." In the case of an external pacer, the adjustment of the potentiometer allows hospital personnel to change the pacer rate. In the case of an implantable pacer, the potentiometer is usually set on the production line to provide a predetermined rate, and that rate cannot be changed after the pacer circuit is potted in the conventional encapsulating epoxy compound.

There are many occasions, however, when a physician desires to change the pacer rate after implantation. In the prior art, two types of rate adjustment mechanisms for implantable pacers have been proposed. In one, the pacer circuit includes a reed switch, or some other type of magnetically actuated switch, which controls one of two pacer rates depending upon the switch position. The pacer rate can be switched by properly positioning a magnet pole of the correct polarity near the skin of the patient in the vicinity of the pacer. The disadvantage of this type of pacer rate control is that the number of pacer rates is limited; continuous rate control is not possible.

With the other type of pacer rate control mechanism, a continuous adjustment of the rate is possible. A needle receptacle or port is mounted on the exterior of the pacer, the receptacle being capable of rotational movement. The receptacle is coupled through the pacer epoxy package to the shaft of the pacer potentiometer. A Keith or some other type of needle can be extended through the patient's skin with the tip of the needle being positioned in the receptacle. If the needle is then turned, the rotational motion is transmitted through the epoxy package to the potentiometer shaft and the pacer rate can be adjusted accordingly. There are two main disadvantages with this type of continuous pacer rate control. First, to adjust the pacer rate it is necessary to puncture the patient's skin. Second, because of the mechanical coupling between the needle receptacle and the internal pacer mechanism, there is a danger that body fluids will flow along the coupling mechanism into the pacer circuit and possibly cause it to become inoperative.

It is a general object of our invention to provide a pacer capable of continous rate adjustment without danger of body fluids gaining access to the pacer mechanism.

It is another object of our invention, in one embodiment thereof, to provide such a continuous rate adjustment without requiring skin puncture.

In accordance with the principles of our invention, the shaft of the pacer rate potentiometer is fixed to a small diametrically magnetized disc magnet. When the pacer is potted, the magnet along with the rest of the mechanism is completely contained within a sealed enclosure. The magnet is positioned near a surface of the pacer, and it can be turned by positioning a strong external magnet near the skin of the patient in the vicinity of the pacer magnet and then turning the bar magnet. (The external magnet may be a bar magnet, a horseshoe magnet, etc. In fact, any source of an external rotating magnetic field can be used.) As the magnets turn, the physician can observe the pacer rate on an oscilliscope until the desired rate is achieved. This arrangement allows continuous rate adjustment without skin puncture, and it also eliminates the possibility of fluid penetration into the pacer mechanism. To ensure that the potentiometer shaft does not turn inadvertently as a result of its connection to the pacer magnet--which inadvertent motion might be possible if the patient moves violently as a result of the additional mass of the magnet -- a small bar of soft magnetic material may be placed on the exterior of the assembly which houses the pacer magnet. (The bar of magnetic material is also inside the enclosure.) This bar locks the magnet once it has been positioned by the physician. The locking mechanism cannot be overcome by violet movement of the patient and the only way to change the pacer rate is to use a strong external magnet as described.

In the second embodiment of the invention, a similar magnet (without the bar-locking mechanism) is utilized and the entire pacer mechanism is housed in an enclosure as described above. A second diametrically magnetized disc magnet is positioned in face-to-face relationship with the first, but external to the enclosure. A needle receptacle extends in the axial direction from the second magnet and the magnet and the needle mechanism are covered by the conventional silicone rubber boot which is applied to the exterior of an implantable pacer. The second magnet can be rotated by inserting a needle through the patient's skin into the receptacle and then turning it. The magnetic coupling of the two magnets (through the enclosure) causes the magnet attached to the potentiometer shaft to turn with the needle magnet. The magnetic coupling in this case also prevents fluid penetration into the pacer, although with this pacer it is necessary to puncture the skin of the patient in order to effect a rate adjustment.

It is a feature of our invention to mount on the shaft of the pacer rate potentiometer a small magnet which can be turned under the influence of a magnet external of the pacer epoxy package.

It is another feature of our invention, in one illustrative embodiment thereof, to mount a second magnet having a needle port in face-to-face relationship with the potentiometer shaft magnet external of the pacer package.

Further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description in conjunction with the drawing, in which:

FIG. 1 is a representation, partly in section, of the first illustrative embodiment of our invention;

FIG. 2 is a view of the internal disc magnet incorporated in the pacer of FIG. 1;

FIG. 3 is a cross-sectional view of the elements within housing 20 of the pacer of FIG. 1;

FIG. 4 is a representation, partly in section, of the second illustrative embodiment of our invention; and

FIG. 5 depicts the face-to-face relationship of the two diametrically magnetized disc magnets utilized in the embodiment of the invention illustrated in FIG. 4.

FIG. 1 depicts a pacer 10, with only those elements being shown which are necessary for an understanding of the present invention. In the interior of the pacer, there is a magnetically permeable closed can 12 (for example, made of brass) which contains the pacer circuit. Although not shown in the drawing, around the can there are disposed several batteries with wired connections from the batteries to the circuit inside the can. A receptacle 14 is provided into which a plug can be inserted at the time the pacer is implanted in a patient. Two connectors 18 are provided for connection to pins which extend from the plug, each of the pins being extended from the plug along a lead to an electrode for attachment to heart tissue. The two connectors are coupled to the pacer circuit by wires not shown in the drawing. The entire pacer is potted in an epoxy compound 22. Thereafter, a silicone rubber boot 24 is formed around the entire pacer except that the receptacle 14 is left open for insertion of the electrode plug.

The pacer is depicted only symbolically in FIG. 1. The details of the pacer itself are unimportant insofar as the present invention is concerned. What must be understood is the function of potentiometer 16 and the mechanism inside housing 20. The potentiometer includes a shaft which when turned controls the pacer rate. As will be described below, the shaft is coupled to a magnet inside housing 20, and on the outside of the housing there is a bar 40 of soft magnetic material. The potentiometer and the housing are included with the rest of the pacer circuitry within can 12. The can and housing 20 are magnetically permeable so that magnetic flux lines can flow through the silicone rubber boot 24, the epoxy package 22, the can and the housing to the magnet inside the housing. The housing and the magnet inside it are disposed near a surface of the pacer so that the pacer can be positioned in the patient with the magnet as close as possible to the patient's skin for maximum coupling of flux lines from the external bar magnet to the magnet inside the housing.

FIG. 2 simply shows the shape of the magnet 30 included in housing 20. The magnet is in the form of a disc with a central hole, and it is magnetized diametrically. That is, the north and south poles of the magnet are at opposite ends of one of its diameters.

FIG. 3 is a cross-sectional view of potentiometer 16 and the mechanism contained in housing 20. The potentiometer includes a bushing 16b through which the end of shaft 16a extends. The end of the shaft has a screw slot, and as ordinarily used the shaft can be turned by using a screwdriver to change the potentiometer setting. A typical potentiometer of this type is that marketed under the name Trimpot by Bourns, Inc. The housing consists of two parts 32 and 36. The bottom of can 32 is cemented to the top of the potentiometer, and after the elements in can 32 are assembled cover 36 is placed over it and an adhesive filler 38 is formed to seal the cover to the can.

A bearing 44 is placed on can 32 in the position shown and then plastic molded rotor 34 is placed on the bearing with projection 34a extending into the screw slot of shaft 16a. The disc magnet 30 is placed on top of the rotor 34. An adhesive layer is first placed on the rotor on that part which holds the magnet so that the magnet is rigidly secured to the rotor; the two of them rotate together around the axis of shaft 16a and turn the shaft with them. After the magnet is placed on the rotor, another bearing 42 is placed on top of the rotor after which the cover is attached to the can as described above. The entire unit is relatively small, with the magnet having a diameter in the order of one-half of an inch and being 3/16ths of an inch thick.

Rotor 34 can slide slightly in the axial direction, but at all times at least a part of projection 34a is within the screw slot of the shaft so that a positive drive condition is always obtained. The purpose of the bearings on both sides of the rotor is to ensure that low friction rotation is possible when the potentiometer shaft is to be rotated.

The dimensions of the external magnet which can be used to cause the internal magnet to rotate are 3 inch .times. 1-1/2 inch .times. 3/4inch with the north and south poles being at opposite ends of the 3-inch dimension. Alnico material is used for both magnets, and both are magnetized to saturation. With such magnets, the internal magnet can be rotated by placing the external magnet on the patient's skin in the vicinity of the pacer and then rotating it. Preferably, the potentiometer which should be used is a multi-turn device so that a single rotation of the internal magnet does not drastically change the pacer rate; instead the rate should change only slowly with each complete turn of the internal magnet. In one embodiment of the invention, a 20-turn potentiometer was used.

It is possible if the pacer is subject to vibrations, for example, during exercise by the patient, that the additional mass coupled to the potentiometer shaft may cause it to rotate. To prevent this from happening, a small bar of soft unmagnetized magnetic material, for example, made of cold rolled steel, is cemented, as shown at 46, to the top of cover 36. Typically, the bar may be 1/32 inch in width with relative length and height dimensions as shown. The flux which flows out of the two poles of magnet 30 flows upward through the cover 36 and through the steel bar. This has the effect of locking or braking the magnet so that it does not move if it is vibrated. The steel bar is used for making a rate setting more stable. The effect of steel bar 40 is overcome by the strong external magnet which diverts the flux from the bar. It is only in the absence of the external magnet that the steel bar functions to brake the rotor.

The embodiment of the invention depicted in FIG. 4 is similar to that depicted in FIG. 1 except that bar 40 is omitted. Also, there is an indentation in the surface of the epoxy package into which brass can 54 is fitted. The brass can is secured to the epoxy package by means of an adhesive. Before the can is secured to the epoxy package, molded epoxy disc 56 is placed on the epoxy package with the can being placed over it. Embedded in the disc is a diametrically magnetized disc magnet 52. The epoxy disc contains an axial bore 56a into which a needle can be fitted so that when the needle is turned the disc and the embedded magnet turn with it. The can is provided with an entrance port 54a for guiding the needle into the bore of the epoxy disc. After the can is secured to the package, they are covered with a conventional silicone boot 58. Although not shown in the drawing, the boot can cover port 54a since a conventional needle used for adjusting a pacer rate can penetrate through the rubber boot.

Magnets 30 and 52 are shown in FIG. 5, and it is apparent that because the north and south poles of different magnets are disposed adjacent to each other, the flux lines flow in a loop through the two magnets. If magnet 52 is turned, magnet 30 turns with it. Consequently, by inserting a needle and turning disc 56 within can 54, magnet 30 rotates to change the pacer rate.

Locking bar 40 is not included on housing 20 in the embodiment of FIG. 4. A brake is not necessary because magnet 30 is locked to magnet 52, and magnet 52 is contained within an epoxy disc 56 which is not mounted on bearings. Consequently, there is friction between disc 56 and can 54, and disc 56 cannot rotate as a result of vibrations. Magnet 52 thus serves as a lock for magnet 30. The only way that the two magnets can be rotated is with the use of an adjusting needle; by rotating the needle the frictional forces are overcome and both magnets turn with it.

Although the embodiment of FIG. 4 does require skin puncture in order to change the pacer rate, a continuous rate adjustment is possible without any danger of fluid penetration into the pacer circuit. This is because the pacer circuit is completely enclosed by the sealed enclosure 12, and magnetic coupling is provided through the wall of the enclosure for rotating the potentiometer magnet.

Although the invention has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

Claims

What we claim is:

1. An implantable heart pacer for stimulating the heart of a patient, said pacer comprising a pacer circuit including a multi-turn potentiometer, said potentiometer including a shaft which when turned controls a continuous change in the rate at which stimulating pulses are generated by the pacer circuit, magnet means fixed to the potentiometer shaft for controlling the turning thereof as the magnet is rotated, said magnet means being rotated by rotating magnetic flux lines emanating external of said patient, a magnetically permeable, hermetically sealed, package encapsulating said pacer circuit for allowing rotating magnetic flux lines which flow through said package to said magnet means to cause said magnet means to rotate, a magnetically permeable can for housing said magnet means, and bar means electrically disconnected from said circuit and made of soft magnetic material disposed on said can for braking said magnet means from rotating more than one half-turn in the absence of externally emanating rotating flux lines.

2. A heart pacer in accordance with claim 1 wherein said can includes bearing means for mounting said magnet means therein.

3. A heart pacer in accordance with claim 2 wherein said magnet means is a diametrically magnetized disc magnet whose axis is in line with the axis of said potentiometer shaft.

4. A heart pacer in accordance with claim 1 wherein said magnet means is rotated by rotating magnetic flux lines emanating external of a patient and said pacer circuit further includes a magnetically permeable can for housing said magnet means.

5. A heart pacer in accordance with claim 4 wherein said can includes bearing means for mounting said magnet means therein.

6. A heart pacer in accordance with claim 1 wherein said magnet means is a diametrically magnetized disc magnet whose axis is in line with the axis of said potentiometer shaft.

7. A heart pacer in accordance with claim 6 further including magnet means mounted for rotation external of said magnetically permeable package, said potentiometer shaft magnet means and said external magnet means being fluxlinked to each other, and means responsive to the insertion and rotation therein of a needle tool for rotating said external magnet means.

8. A heart pacer in accordance with claim 7 wherein said external magnet means is a diametrically magnetized disc magnet whose axis is in line with the axis of said potentiometer shaft.

9. A heart pacer in accordance with claim 8 further including a can for housing said external magnet means in a plane parallel with said potentiometer shaft magnet means.

10. A heart pacer in accordance with claim 1 further including magnet means mounted for rotation external of said magnetically permeable package, said potentiometer shaft magnet means and said external magnet means being fluxlinked to each other, and means responsive to the insertion and rotation therein of a needle tool for roating said external magnet means.

11. A heart pacer in accordance with claim 10 further including a can for housing said external magnet means in a plane parallel with said potentiometer shaft magnet means.