US 3241556 A
Description (OCR text may contain errors)
Mrch 1966 F. ZACOUTO 3,241,556
CARDIAC STIMULATORS Filed May 15, 1963 2 Sheets-Sheet 1 //VVE/VTOR Free Zacouio $44M WM ATTORNEYS March 22, 1966 F. zAcouTo CARDIAC STIMULATORS 2 Sheets-Sheet 2 Filed May 13, 1963 Home y 0. IT... L i n Z n m y B United States Patent ,9 6 Claims. (Cl. 128421) It is known that certain patients with cardiac disorders are subject to ventricular, non-fibrillar heart failures which can be treated by periodic electrical pulses which cause the cardiac muscle to contract.
Proposals have already been made for the construction of external apparatus which transmit such electrical pulses from outside the body when a detector registers an unsatisfactory cardiac rhythm.
Such apparatus have the disadvantage that they submit the patient to unpleasant pulses and oblige him always to carry an apparatus liable to be faulty in ope-ration should there be a poor contact between the electrodes and the skin.
Chieiiy on account of this, cardiac stimulators to operate inside the body have recently been constructed. Such stimulators are attached to the patient by means of a surgical operation and are located entirely below the epidermis. These apparatuses generally comprise a pulse generator energised by a small electric battery, the generator supplying pulses to electrodes placed directly at the level of the heart.
Such devices have the disadvantage that they must operate permanently, which results both in a continuous run-down of the battery and also an electrolysis of the cardiac tissues in the neighborhood of the electrodes, whereas, for quite considerable periods of time, the patient has no need whatsoever of the help of the stimulator since his heart, during such periods, is spontaneously functioning with a satisfactory rhythm.
It is a particular object of the present invention to provide a device which enables a cardiac stimulator located inside the body to be automatically stopped when there is no need for it to operate.
Accordingly the invention provides a cardiac stimulator of the kind comprising electrodes for insertion in a patients heart, and a pulse generator adapted to be lo cated in the patients body, for feeding electrical pulses to said electrodes, said generator including a supply circuit, wherein said pulse generator comprises a switch circuit controlled by electrical means comprising an electrical coupling between an internal control circuit adapted to be located inside the body and an external control circuit for location outside the body, said external control circuit comprising an electrical member which is charged as a function of the cardiac rhythm of the user by means of a device for electrically detecting said cardiac rhythm and an amplifier, the said electrical member acting on the said external control circuit, which, via the said internal control circuit and the switch, stops the pulse generator when the average electrical charge exceeds a predetermined value.
In order that the invention may be more clearly understood, one embodiment thereof, by way of example, will 3,241,556 Patented Mar. 22, 1966 now be described with reference to the accompanying drawing, in which:
FIGURE 1 is a schematic view showing the different elements of a cardiac stimulator according to the invention, secured on a patient,
FIGURE 2 is a diagrammatic showing of one arrangement with the various elements of the stimulator,
FIGURE 3 shows an alternative arrangement in greater detail, and
FIGURE 4 shows another arrangement using an electromagnetic switch in the supply circuit of the pulse generator. The electrocardiograp'hic amplifier 1 amplifies the currents supplied by the detector electrodes 2 for electrically detecting the cardiac rhythm. Thus it is possible to charge a condenser 17 (FIGURE 3) from which the discharge may be regulated so as to actuate a control circuit comprising a part outside the body inductively coupled to a part inside the body for a given level (i.e. for a given minimum frequency of the heartbeats). In one advantageous embodiment of this control circuit, it also sets up high frequency oscillations coming from a radio transmitter 3, and the coupling members comprise a miniature transmitting device 4 located outside the body, and a miniature receiving aerial 7 located inside the body, the aerial 4 being located on the patients skin. It will hereinafter be assumed that the control is thus effected at high frequency.
The amplifier 1 and transmitter 3 may be of any kind well-known in the art and per se form no part of the present invention For example they preferably comprise solid-state devices such as transistors and crystal diodes as necessary, arranged in any of the well-known circuits available to those skilled in the art, for example in text books and manufacturers brochures. Thus, there is no need to describe such devices more fully herein.
To simplify the illustration, FIG. 2 shows the aerial loop 4 perpendicular to the epidermis, but in reality the loop lies flat on the skin. Elements 1 to 4 constitute the external control circuit.
A receiving aerial system 7 arranged inside the body and forming the internal control circuit, as near as possible to the epidermis, includes a coil which co-operates with an inductor 8 of a circuit 9 which also comprises a rectifying diode 10 and a capacitor 11. This circuit, biases the base of a transistor 12 which is also connected to the negative pole of a battery 13 via a resistor 16.
The positive pole of the battery 13 may be earthed, which in this case means that the said positive pole is not insulated from the body, whereas all the other parts of the device, which are not to be earthedf, are embedded in an insulating material such as polytetrafluoroethylene for insulation purposes.
When the transmitter 3 is not functioning due to the electrodes 2 not picking up heart beats, the circuit 9 produces no current and the base of the transistor 12 is biased with the negative potential of the battery 13 via the resistor 16.
As a result, the transistor 12 allows current to pass between its emitter and its collector, its resistance being about 2 ohms.
A pulse generator 14 is then supplied by the battery 13 and periodically sends pulses to the electrodes 15 embedded in the heart so as to stimulate it. The generator per se also forms no part of the invention and is not fur- 33 ther described. It may be constituted in any fashion known in the art but it will be apparent that it preferably employs solid-state devices and sub-miniature components, all well-known to those skilled in this art.
However, when the transmitter 3 is operating due to the electrodes picking up heart beats, the rectified current in the circuit 9 positively biases the base of the transistor 12, the effect of which is to interrupt the circulation of current between the emitter and the collector of the said transistor and to cause the pulse generator 14 to stop.
It will therefore be seen that when the electrodes 2 of the electrocardiographic detector I detect a satisfactory cardiac rhythm, they actuate the transmitter 3 which acts on the transistor I2 to interrupt the operation of the pulse generator/ stimulator 14 inside the body.
Under these conditions, i.e. when the patient has a substantially normal heart beat, the transmission of unnecessary electrical-pulses into the cardiac tissue is avoided and, what is more, the energy of the battery 13 is not wasted.
However, when the electrocardiographic detector detects either a heart failure or an unsatisfactory cardiac rhythm, the transmitter 3 stops transmitting, the effect of which is the immediate actuation, via the transistor 12, of .the pulse generator 14, and of the artificial stimulation of the heart which then becomes indispensable.
In the arrangement shown in FIGURE 3, as in that in FIGURE 2, the electrocardiographic amplifier 1 receives and amplifies the current pulses provided by the detector 2 which electrically detects the heartbeats in the cardiac rhythm. This amplifier charges a capacitor 17 which has a variable discharge to earth at 18, under the control of a variable resistor 19, in such a manner as to actuate a multi' vibrator circuit 20 for a given level (i.e. above a given minimum frequency of the heartbeats), the said multivibrator controlling the oscillations of a high frequency generator of which the radiation is transmitted by a coupling loop 4 constituting a miniature aerial, arranged flat on the patients skin. These elements constitute the external control circuit.
In the embodiment of FIGURE 3, the internal control circuit 8a to 12, the generator for feeding pulses to the electrodes 15 inserted in the patients heart 21 are similarly arranged to the corresponding elements in FIGURE 2, except for the introduction of a tuning capacitor 8a to make a resonant circuit out of the circuit 9, and the location of the battery, which in this case is located at 13a between the collector of the transistor 12 and the pulse generator I4.
In both these embodiments, the members or parts 8, 10, 11, 12, 13 (or 13a) and 14, are embedded in an insulating plastic material which the human body can readily tolerate, such as polytetrafluoroethylene. In this way, a small, compact assembly is formed which groups the various members or parts within the dotted rectangle which, in FIGURE 3, has been given the reference numeral 22.
It will be noted that the device according to the invention, of which the advantages are self-evident, provides a complete guarantee of safety for the patient since any breakdown either in the electrocardiographic detector of in the transmitter results in continuous operation of the stimulator which constitutes no particular danger for the patient.
Similarly, should one of the electrodes 2 of the electrocardiographic detector move and lose contact with the skin, there is no danger as the only result is to allow the stimulator inside the body to function.
It will be apparent that the embodiments described above are given only by way of example and that various modifications may be made to the specific details thereof without in any way departing from the scope of the invention.
In particular, it will be seen that it is possible to construct a stimulator to operate inside the body in accordance with the invention in which the oscillatory circuit 9 and the transistor 12 are replaced by an electromagnetic switch which is stable in the position closing the supply circuit to the pulse generator 14 and which is actuated by an electromagnetic field set up outside the body and controlled by the electrocardiographic detector.
In the arrangement shown in FIGURE 4, a number of the elements are identical with those which are designated by the same reference numeral in FIGURE 3. As in the previous embodiments, as long as an electrocardiographic detector 2 checks a satisfactory cardiac rhythm, the transmitter 3 delivers an alternating current. This current is rectified in a unit 24, thus enabling the operation of an electromagnetic relay 25 connected to the output terminals of the unit 24. When the relay 25 is energised, its contact 26 closes a circuit comprising a battery 27 and a winding 28, The winding 28 is wound around a magnetic core 29 which lies on the patients skin and outside his body, thus providing a magnetic field which is suitable to actuate a switch 23, for example a type of a pair of hermetically sealed magnetically operated switch contacts, which is located inside the patients body, and which is stable in the position closing the supply circuit to a pulse generator 14 identical with the apparatus designated by the same numeral in the previous embodiments.
Similarly, any other means could be used to interrupt the operation of the internal pulse generator when an apparatus located outside the body registers a satisfactory cardiac rhythm.
1. A cardiac stimulator comprising a plurality of electrodes for insertion in a patients heart, a pulse generator adapted to be located within the patients body and connected to said electrodes, a switching device adapted to be located inside the patients body for controlling the supply of energy to said pulse generator, an energy supply source adapted to be located wtihin the patients body and connected to said pulse generator via said switching device, an external control circuit comprising a detecting device for electrically detecting the cardiac rhythm of the patient, an amplifier for amplifying the output current of said detecting device, an electrical member chargeable by the output of said amplifier in dependence on said cardiac rhythm, an electrical means connected to said chargeable member for sensing the rate of charge of said chargeable member and for issuing an electrical output signal as long as the rate of charge of the chargeable member exceeds the predetermined value, coupling means for location on the patients body and fed with energy in response to the output signal of the external control circuit for bringing about the open circuit position of the switching device, as long as said external control circuit delivers an output signal causing energy to be fed into said coupling means, whereby the pulse generator starts operating and supplying pulses to the patients heart as soon as the detecting device detects that the cardiac rhythm drops below a pre-determined value.
2. A cardiac stimulator according to claim 1 in which said coupling means is an inductive coupling means.
3. A cardiac stimulator according to claim 1 in which said electrical means comprises a multivibrator circuit operating in dependence on the average charge of said chargeable member, a high-frequency oscillator controlled by said multivibrator circuit, and in which said coupling means is a high-frequency coupling means.
4. A cardiac stimulator according to claim 1, in which said electrically chargeable member comprises a rectifying element, a capacitator, chargeable through said rectifying element and a leakage line connected across said capacitator.
5. A cardiac stimulator according to claim 4 in which said electrically chargeable member includes manual charging rate adjustment means.
6. A cardiac stimulator according to claim 3, in which including an internal switching device is a transistor and said control circuit comprising means for biassing the,
base for said transistor including said supply source which also feeds said pulse generator, resonant circuit means and a diode joining said resonant circuit means to the base of the transistor in such a sense that said pulse generator is out of operation when said resonant circuit receives high frequency power via said coupling means between said internal control circuit and said external control circuit.
References Cited by the Examiner Senning, Dr. Ake: Journal of Thoracic and Cardiovascular Surgery, vol. 38, No. 5, page 5639, November 1959.
Eisenberg et al.: IRE Transactions on Bio-Medical Electronics, vol. BME-S, No. 4, pages 253-257, October 1961.
RICHARD A. GAUDET, Primary Examiner.