Protector Circuit For Cardiac Apparatus

Abstract

A protector circuit having relay arrangement and gas discharge tubes coupled between first electrodes attached to a patient and the amplifier of an electrocardiograph, the relays comprising fast acting reed relays which break the circuit when a defibrillator is energized to apply a countershock voltage across second electrodes mounted on said patient, to prevent the countershock voltage from distorting the heartbeat waveform produced by the electrocardiograph. The gas discharge tubes prevent voltages in excess of a predetermined value from reaching the amplifier by conducting such voltages to ground, whether the relays are opened or closed.

Parent Case Text

The present application is a continuation of application, Ser. No. 653,201, filed July 13, 1967, and now abandoned.

Description

BACKGROUND OF THE INVENTION

The present invention may be used in conjunction with the defibrillating apparatus disclosed in application, Ser. No. 529,410, filed Feb. 23, 1966, in the name of Joseph H. McLaughlin, now U.S. Pat. No. 3,527,228.

The present invention relates to improved apparatus for treating a cardiac patient and more particularly to an improved protector circuit for preventing stray voltages from affecting the accuracy of the visual representation of the heartbeat produced by an electrocardiograph.

By way of background, multi-purpose electrocardiac apparatus is capable of performing a plurality of functions. One of the functions is to monitor the heartbeat of a patient and display this heartbeat in visual form on an oscilloscope, graph or the like. This is the conventional electrocardiograph apparatus, which obtains its intelligence through electrodes applied to the patient. Another function of the improved electrocardiac apparatus is to selectively apply defibrillating countershock voltage to a patient experiencing fibrillation, which is an irregular heartbeat. Broadly, this consists of applying a very high countershock voltage to the heart of the patient through electrodes placed in opposition to each other on the patient's back and chest to cause a current flow through the chest cavity. When the countershock voltage is applied, the patient acts as a conductor and this countershock voltage, which may be of extremely high magnitude, on the order of 7,500 volts, may be transmitted to the electrodes of the electrocardiograph apparatus and set up stray voltages which may completely distort the visual representation of the heartbeat for a period of as much as 20 to 30 seconds. It is extremely important that an accurate visual representation of the patient's heartbeat be obtained immediately after application of the countershock voltage, so that the effect of the countershock voltage can be readily observed. The reason for this is that many times additional countershock voltage must be applied immediately after the initial countershock application of voltage if the application of the first countershock voltage is ineffective. However, as can readily be seen, if the electrocardiograph is producing an inaccurate signal, or one which is objectionally distorted, there is no clear intelligence upon which to base the decision as to whether additional countershock voltage should be applied. It is with improved electrocardiac apparatus which overcomes the foregoing shortcoming that the present invention is concerned.

SUMMARY OF THE INVENTION

It is accordingly one object of the present invention to provide a protector circuit for electrocardiograph apparatus which prevents stray voltages above a predetermined magnitude from affecting the visual representation of the heartbeat on the electrocardiograph, thereby assuring that such representation remains undistorted and true.

Another object of the present invention is to provide improved electrocardiac apparatus for providing a visual representation of a patient's heartbeat and for providing countershock voltage to the patient's heart, with a protector circuit for preventing the countershock voltage which is applied to the patient from adversely affecting the visual representation on the electrocardiograph, thereby providing an accurate picture of the patient's heartbeat at all times regardless of the voltages to which a patient may be subjected.

A further object of the present invention is to provide improved electrocardiograph apparatus including a protector circuit having a first circuit which causes the display portion of the electrocardiograph apparatus to be disconnected from the patient during the application of a countershock voltage and in addition includes a second circuit which prevents any countershock voltage applied to the patient from being transmitted to the electrocardiograph apparatus in the event disconnecting is not fully completed by said first circuit or in the event the distorting voltage comes from any other source. Other objects and attendant advantages of the present invention will readily be perceived hereafter.

The improved electrocardiac apparatus of the present invention includes an electrocardiograph for providing a visual representation of the patient's heartbeat and a defibrillator for providing countershock voltage to the patient for treatment of either ventricular fibrillation or other arrhythmias. The electrocardiograph has electrodes coupled to the patient in the conventional manner. The defibrillator has electrodes coupled to the chest and back of the patient. A protector circuit interconnects the defibrillator and the leads leading to the electrocardiograph display device. When the defibrillator is actuated, the leads to the electrocardiograph are automatically disconnected prior to the application of the countershock voltage and automatically reconnected after the countershock voltage has been applied. Thus, during the period of applying the countershock voltage, which is only approximately 21/2 milliseconds, stray voltages produced incidental to the application of defibrillating voltage cannot affect the picture of the patient's heartbeat on the display device. After this brief period of disconnection, the picture reappears with complete accuracy. In addition, in the event that disconnecting should not be effected as required, or in the event the patient is subjected to a stray voltage from any source other than the defibrillator, the protector circuit includes circuit means for preventing such voltages from reaching the apparatus, thereby insuring an accurate picture thereon. By the use of the foregoing protector circuit an accurate representation of the patient's heartbeat on the electrocardiograph apparatus is always assured. The present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawing the improved apparatus is shown which includes an electrocardiograph 10, a defibrillator circuit 11, and a protector circuit 12 coupling the electrocardiograph and the defibrillator. The electrocardiograph apparatus 10 includes three sensor electrodes 13, 14 and 15, the latter being coupled to ground. Electrodes 13, 14 and 15 are attached to patient 18, as on his opposite wrists, and suitable electrical contact is made by the use of electrode jelly. Electrode 15 is attached to the leg of the patient. Electrodes 13 and 14 are coupled to protector circuit 12 through leads 16 and 17, respectively. Leads 19 and 20, leading from circuit 12, are coupled to amplifier 21 which effects suitable amplification of the heartbeat waveform. The amplified heartbeat is visually indicated on cathode ray oscilloscope 22 by feeding the amplified signal from amplifier 21 to vertical amplifier 23 through leads 24 and 25, the output of vertical amplifier 23 being applied to plates 24' and 25' through leads 26 and 27, respectively. This signal is used to modify the trace provided by horizontal free running sweep amplifier 28 which is coupled to plates 29 and 30 by leads 31 and 32, respectively. In lieu of oscilloscope 22 any other type of visual indicating device, such as a graph or an elongated paper tape or the like, may be used.

The heartbeat waveform comprises a QRS complex including the Q portion, R portion and S portion as shown on the scope in FIG. 1. The countershock voltage is applied across the chest cavity of the patient by electrodes 33 and 34 which are coupled to leads 35 and 36, respectively, leading from the defibrillator circuit 11. One of these electrodes is mounted on the chest and the other on the back of the patient 18.

Summarizing the following portion of the specification briefly at this point, it can be seen that the electrodes 33 and 34 leading from the defibrillating circuit 11 and the electrodes 13, 14 and 15 leading to the electrocardiograph 10 are both mounted on patient 18. The countershock voltage, which may be as high as 7,500 volts, or translated into energy, in excess of 400 joules, when applied to the patient 18, may also be transmitted through the patient, who thus acts as a conductor, to the electrocardiograph apparatus 10 in the absence of a protector circuit 12. This direct application to the electrocardiograph apparatus will set up stray voltages therein which will completely distort the picture of the heart waveform on oscilloscope 22 for as long as 20 to 30 seconds. During this period the oscilloscope 22 will be incapable of providing accurate information as to the heartbeat of the patient. It is during this period that accurate information is critical to determine whether additional countershock should be applied. The instant protector circuit 12 contains switch means which disconnect the electrocardiograph 10 from the defibrillator circuit 11 when the countershock voltage is being applied and automatically reconnects the electrocardiograph 10 to the patient 18 after the countershock voltage is no longer being applied, to thereby protect the electrocardiograph and insure accuracy of the pictorial representation of the heartbeat thereon. The mode of operation of the defibrillator circuit 11 and the interrelationship between the electrocardiograph 10 and the protector circuit 12 will be more fully understood from the ensuing portions of the description.

The instant defibrillator circuit 11 provides a synchronized countershock to a patient, that is, in timed relationship to the patient's heartbeat. This is explained in detail in the above noted copending application. However, a certain repetition will be made here for the purpose of completeness. It will be appreciated that the protector circuit 12 of the present invention can be used with any type of defibrillator circuit and any type of electrocardiograph.

The amplified heartbeat signal at lead 24 is also fed to Schmitt trigger 37 by lead 38 to produce waveform 39 which in turn is fed to single shot multivibrator 40 by lead 41. It is the multivibrator 40 which produces a usable signal 42 in synchronized relationship to the heartbeat. The lead portion 43 of signal 42 is initiated when the R portion of the heartbeat 17 reaches a predetermined magnitude. Lead 45 conducts waveform 42 from multivibrator 40 to the indicating device 44, which indicates whether multivibrator 40 is operating satisfactorily. The indicating device 44 may include a pulse form inverter (not shown) for inverting waveform 42, an amplifier (not shown) and an integrator (not shown) in series, with the integrator being coupled to a meter. As is well understood, the foregoing components level out the pulse 42 to provide a constant output which can be read on the meter forming a part of indicating device 44. The foregoing elements are shown in detail in the above mentioned copending application but are omitted from the instant drawing in the interest of brevity. The magnitude of the reading on the meter associated with device 44 is proportional to the heartbeat rate.

When a heart pattern is shown on scope 22 which indicates that countershock is necessary, the attending physician will close defibrillator switch 46 to establish contact between leads 47 and 48. Preferably, however, switch 46 should be in lead 53. The output of multivibrator 40 is fed to silicon control rectifier 49 by lead 50, which is connected to lead 45. The silicon control rectifier 49 will be energized whenever the lead portion 43 of square wave 42 reaches a predetermined magnitude to cause current to flow from B+ to ground through lead 51, slow acting relay coil 52, lead 53, silicon control rectifier 49, lead 47, defibrillation switch 46, and lead 48 to ground. Whenever the silicon control rectifier 49 is energized to complete the above circuit, relay coil 52 will be energized. At this point it is only necessary to understand the energization of coil 52 is synchronized with the patient's heartbeat and that the relay 55 of which coil 52 forms a part actuates the remainder of the circuit which supplies the countershock voltage.

An AC source 56 is coupled across leads 57 and 58 with sine wave 59 depicting the waveform at this point. The normally centered armature 60 of switch 61 is selectively movable from a normally open position to either contact 62 or 63. As can be seen, when armature 60 contacts contact 63, a circuit will be completed through the primary 64 of transformer 65, which in turn will induce a voltage in the secondary winding 66. As will become more apparent hereafter, a charge will be placed on capacitor 67. The magnitude of the charge depends on the length of time that armature 60 is held on contact 63. After armature 60 is released it will return to a normally open position and capacitor 67 will retain a charge thereon. If it is desired to cause a lower voltage to be induced on the secondary winding 66, it is merely necessary to move armature 60 into engagement with contact 62 to complete a circuit to primary winding 64 through resistor 69.

The charge is placed on capacitor 67 through the following circuit. The output of secondary winding 66 is rectified by diodes 70 which are coupled to one side of secondary 66 by lead 71. Diodes 70 are coupled in series to prevent a reverse discharge thereacross after a charge is placed on capacitor 67, which is coupled in series with diodes 70 and secondary 66 through lead 72, armature 73 of slow acting relay 55, lead 74, choke coil 75, lead 76 and lead 77. At this point it is to be noted that lead 77 is grounded at 82' to the chassis of the apparatus through resistor 78, armatures 79 and 80 of fast-acting relay and lead 82.

Relay 81 is of the normally open type. Armatures 79 and 80 of fast-acting relay 81 are in engagement whenever there is a B+ voltage applied at terminal 83. The foregoing engagement is effected because coil 88 is energized through the path consisting of lead 51, winding 52, lead 53, lead 84, voltage drop resistor 85, lead 86, lead 87, winding 88 of relay 81, lead 89 and lead 90 to ground. This energization of relay 81 occurs whenever the apparatus is turned on through its master switch (not shown). Otherwise, armatures 79 and 80 are not in engagement and line 77 is not grounded. Because of the parameters of the circuit, armatures 79 and 80 will move into contact to couple the circuit to chassis ground 82'. However, there will be an insufficient flow of current through slow-acting relay coil 52 to energize slow-acting relay 55 and therefore armature 73 thereof will occupy the position shown in the drawing. There is also a small current flow from lead 86 through lead 91, diode 92, lead 93, resistor 94 and lead 95 to ground. However, there will be a delay before there is a build-up of voltage across capacitor 96, which is coupled across leads 93 and 95 and it is only after voltage builds up of capacitor 96 that coil 88 will be energized.

The above described voltage which is applied to capacitor 67 is selectively discharged across the chest cavity of a patient to effect defibrillation. Quantitatively, this voltage may be as high as 7,500 volts, or translated into energy, in excess of 400 joules. The magnitude of this voltage depends upon the charging time through armature 60 and it can be read on meter 97 which is coupled across capacitor 67 through resistor 98. If for any reason it is desired to harmlessly discharge the voltage built up on capacitor 67, it is merely necessary to close switch 99 to thereby discharge capacitor 67 through resistor 100.

To apply the countershock voltage to the patient 18, electrodes 33 and 34, which are in the form of paddles, are coupled onto the opposite of the chest cavity of patient 18 by means of a suitable electrode jelly to establish good electrical contact. One paddle is mounted on the chest and the other paddle is mounted in opposition thereto on the back of the patient, with the heart essentially being located therebetween. Paddles 33 and 34 each include a conducting plate (not shown) which are electrically connected to leads 35 and 36. The remainder of paddles 33 and 34 are made out of a suitable non-conductive plastic material to confine the electrical countershock. Paddles 33 and 34 are conveniently provided with insulating handles 101 and 102.

As noted above, the capacitor 67, which provides the countershock voltage, is in charged condition while relay armature 73 is in the position shown in the drawing. In order to cause capacitor 67 to discharge across paddles or electrodes 33 and 34, armature 73 of slow-acting relay 55 must move from contact 103 to contact 104. However, in the absence of opening the connection to chassis ground 82' through lead 82 before armature 73 engages contact 104, there is the possibility that a person in contact with the patient 18 may form a leg of the circuit and thus receive an electrical shock. This would occur if he were grounded and touching either the patient or anything in electrical contact with him while the shock was being administered.

At this point it is to be noted that slow-acting relay 55 is a high voltage vacuum relay wherein armature 73 and contacts 103 and 104 are encased in a vacuum envelope (not shown) and coil 52 is mounted in encircling relationship to the envelope. This type of relay must be used to prevent arcing during the switching action. Fast-acting relay 81 is also a high voltage vacuum relay of the type having armatures 79 and 80 within a vacuum envelope 105 and a relay coil 88 surrounding the envelope.

In operation, the person administering the countershock closes switch 46 when he determines that countershock is necessary, as indicated by the picture of the heartbeat on oscilloscope 22. Upon the closing of switch 46, both sides of fast-acting relay coil 88 will be grounded, one side through leads 89 and 90, and the other side through leads 87 and 86, resistor 85, lead 84, silicon control rectifier 49, lead 47, switch 46 and lead 48. This grounding will occur only when silicon control rectifier 49 is conducting and it does so only when the proper voltage is supplied thereto from the single shot multivibrator 40 through lead 50. In other words, the silicon control rectifier 49 will conduct at portion 43 of waveform 42 produced by multivibrator 40. This occurs at the R portion of the heartbeat. It is approximately 2 milliseconds after this that armatures 79 and 80 of relay 81 will separate and this will disconnect the circuit from chassis ground. The foregoing is explained in greater detail in the above mentioned copending application.

Contact between armatures 79 and 80 must be broken to disconnect the circuit from chassis ground 82' before armature 73 of slow-acting relay 55 reaches contact 104 to thereby insure that the attendant cannot be subjected to the countershock voltage. Slow-acting relay 55 requires approximately 20 milliseconds for armature 73 to reach contact 104 after leaving contact 103. When armature 73 reaches contact 104, capacitor 67, which has countershock voltage stored thereon, will discharge through choke coil 75, armature 73 and leads 36 and 35, across paddles or electrodes 33 and 34, thereby establishing an electric discharge through the chest of the patient. The choke coil 75 causes the discharge to extend over a period of approximately 21/2 milliseconds (0.0025 seconds). The countershock voltage will be synchronized with the heartbeat and fall between the R and S waves.

The armature 73 will remain in engagement with contact 104 for as long as defibrillation switch 46 is held closed after contact is once made because once the silicon control rectifier 49 has been triggered by waveform 42, it will continue to conduct. Capacitor 67 provides only a single discharge each time switch 46 is closed. In other words, the attendant may maintain the defibrillation switch 50 closed for as long as he desires but he will get only a single shot of countershock voltage. Another shot can be obtained only after the capacitor 67 is again charged up in the manner described in detail above, and after switch 46 is again closed. After switch 46 has been released, it returns to a normally open position. The armature 73 of slow-acting relay 52 will move from contact 104 to contact 103 in a time period dependent on the inherent delay in the relay 55. This occurs because the opening of switch 46 terminates the flow of current through slow-acting relay coil 52.

However, armatures 79 and 80 of fast-acting relay 81 do not return into contact with each other before armature 73 leaves contact 104, to insure that an undesired countershock cannot be applied to either the patient or the attendant through ground. The circuit containing capacitor 96 achieves this function. More specifically, after both sides of fast-acting relay coil 88 were grounded by switch 46 incidental to initiating countershock, capacitor 96 is also discharged across resistor 94. However, after switch 46 is opened, relay coil 88 will not be energized until after capacitor 96 becomes energized and this takes a period of time depending on the time constant of the circuit consisting of capacitor 96 and resistor 94. The armature 73 of slow-acting relay 55 returns to contact 103 and it takes a period of time which is dependent on the inherent delay in the relay for this switching action to be completed. However, the switching action effected by fast-acting relay 81 is not completed until a time greater than 20 milliseconds because of the action of capacitor 96. This insures that the fast-acting relay 81 will not close until after the armature 73 of slow-acting relay 55 is no longer in contact with contact 104.

As noted above, when the countershock voltage is applied to the patient 18, he can act as a conductor to transmit this voltage to the electrocardiograph apparatus 10 and this would normally distort the picture on the scope 22 for a period of as much as 20 or 30 seconds, during which time it is important that the physician be able to monitor the patient's heartbeat accurately. In certain cases the foregoing voltage can permanently damage apparatus 10. In accordance with the present invention, a protector circuit 12 is supplied for preventing the foregoing by producing a selective switching action. More specifically, a reed relay 106 is provided having a glass envelope 107 containing armatures 108 and 109, and a coil 110. Envelope 107 is evacuated to prevent arcing between leads 108 and 109 as they open and close. Coil 110 is energized from a B+ source through lead 111, voltage drop resistor 112, lead 113 and lead 114, which is coupled to ground. In addition, a reed relay 115 is provided having armatures 116 and 117 in glass envelope 118 and a coil 119 wound around envelope 118. Coil 119 is coupled to the B+ source also through leads 111, 112, 113, 120 and 121 to ground. It is to be noted that whenever the B+ source connected to lead 111 is energized, that is, when the machine is connected to an electrical source and its master switch (not shown) is on, relay coils 110 and 119 will be energized to cause the respective armatures in the envelopes associated therewith to be in contact to thereby permit the amplifier 21 to be connected to electrodes 13 and 14. It will be appreciated that a single coil can be used around envelopes 107 and 111 instead of two coils 110 and 119.

Whenever defibrillator switch 46 is closed, transistor 122 will couple lead 113 to ground through leads 123 and 124. Both sides of relay coils 110 and 119 will thus be grounded when transistor 122 conducts, and it conducts only when defibrillator switch 46 is closed and there is a current flow from lead 48 to transistor 122 through lead 125. Reed relays 106 and 115 are of the fast-acting type which will open substantially simultaneously with the energization of fast-acting relay 81 to thereby insure that the leads to amplifier 21 are open before the countershock voltage is applied, that is, before armature 73 of slow-acting relay 55 engages contact 104. Relays 106 and 115 will close only after defibrillator switch 46 is released and returns to an open position shown in the drawing whereupon transistor 122 will cease to conduct. At this time the countershock voltage has already been applied to the patient and there is no danger of such voltage being applied to amplifier 21.

A neon lamp is associated with each of leads 16 and 17. More specifically, neon lamp 126 is coupled to lead 16 by lead 127 and said lamp in turn is coupled to ground by lead 128. In addition, a neon lamp 129 is connected between lead 17 and ground through leads 130 and 131. In the event that the voltage applied across leads 16 and 17 exceeds a predetermined value, for example, 50 volts, neon lamps 126 and 129 will conduct this voltage to ground while relays 106 and 115 are open. This prevents any residual voltage across leads 16 and 17 from being applied to electrocardiograph 10 after relays 106 and 115 are reclosed.

There may also be times when leads 16 and 17 are subjected to stray voltages when defibrillation is not being effected. Under these circumstances, relays 106 and 115 will be closed. If these stray voltages exceed a predetermined voltage, neon lamps 126 and 129 will conduct to ground, thereby preventing distortion of the picture on oscilloscope 22 or danger to amplifier 21. Lamps 126 and 129 will continue to conduct until such time as the voltage applied to leads 16 and 17 is below a certain value, at which time they will cease to conduct and leads 16 and 17, relays 106 and 115, and leads 19 and 20 will thereafter conduct normally to the amplifier 21.

It can thus be seen that an extremely simple protector circuit has been applied to electrocardiac apparatus, consisting of an electrocardiograph and a defibrillator circuit, for preventing countershock voltages applied to the patient from adversely affecting the electrocardiograph by either damaging the amplifier or distorting the visual representation of the heartbeat on the oscilloscope. In addition, the protector circuit includes an arrangement for preventing stray voltages which are not necessarily originated by the defibrillator from adversely affecting the electrocardiograph in the same manner. It will be appreciated that protector circuit 12 may be used with any type of electrocardiograph and any type of defibrillator or other electronic apparatus used in the treatment of a cardiac patient.

Claims

I claim:

1. An electrocardiograph circuit comprising electrode means adapted to be coupled to a patient for detecting a heartbeat, heartbeat signal amplifier means, display means for providing a visual indication of said patient's heartbeat, circuit means coupling said electrode means and said heartbeat signal amplifier means and said display means, circuit protector means in said circuit means coupled between said electrode means and said heartbeat signal amplifier means for effectively disconnecting said electrode means from said heartbeat signal amplifier means for selectively preventing distortion producing voltages from being conducted to said heartbeat signal amplifier means and thereby preventing distortions in said heartbeat signal amplifier means which can result in a distorted representation on said display means, said circuit protector means including relay means, defibrillator circuit means, switch means in said defibrillator circuit means for selectively energizing said defibrillator circuit means to apply a countershock voltage to a patient, second circuit means coupling said defibrillator circuit means to said circuit protector means and energizable incidental to the energization of said defibrillator circuit means for causing said circuit protector means to prevent distortion producing voltages produced incidental to defibrillation from being conducted to said heartbeat signal amplifier means, and third circuit means having voltage discharge means therein coupled between said electrode means and said relay means for conducting voltages in excess of a predetermined value applied to said electrode means away from said relay means and said heartbeat signal amplifier means, said relay means comprising fast acting reed relay means in said circuit means for opening said circuit means between said electrode means and said heartbeat signal amplifier means before said defibrillator circuit means apply said countershock voltage to said patient.

2. An electrocardiograph circuit comprising electrode means adapted to be coupled to a patient for detecting a heartbeat, heartbeat signal amplifier means in said electrocardiograph circuit for amplifying a heartbeat signal picked up by said electrode means, display means for providing a visual indication of said patient's heartbeat, first circuit means coupling said electrode means and said heartbeat signal amplifier means, second circuit means coupling said amplifier means and said display means, circuit protector means in said first circuit means coupled between said electrode means and said heartbeat signal amplifier means with said electrode means being in immediate preceding relationship to said circuit protector means which in turn are in immediate preceding relationship to said heartbeat amplifier means, said circuit protector means effectively disconnecting said electrode means from said heartbeat signal amplifier means for preventing distortion producing voltages from being conducted to any portion of said heartbeat signal amplifier means and thereby preventing distortions in said heartbeat signal amplifier means which can result in a distorted representation on said display means, said circuit protector means including relay means for disconnecting said electrode means from said heartbeat signal amplifier means, defibrillator circuit means, switch means in said defibrillator circuit means for selectively energizing said defibrillator circuit means to apply a countershock voltage to a patient, third circuit means coupling said defibrillator circuit means to said circuit protector means and energizable incidental to the energization of said defibrillator circuit means for causing said circuit protector means to prevent distortion producing voltages produced incidental to defibrillation from being conducted to said heartbeat signal amplifier means, means for causing said circuit protector means to automatically reconnect said electrode means to said heartbeat signal amplifier means after said switch means is released after the termination of said countershock voltage to cause said display means to provide said visual indication of said patient's heartbeat immediately after the termination of said countershock voltage, said relay means comprising fast acting reed relay means in said first circuit means for opening said first circuit means between said electrode means and said heartbeat signal amplifier means before said defibrillator circuit means apply said countershock voltage to said patient.

3. An electrocardiograph circuit comprising electrode means adapted to be coupled to a patient for detecting a heartbeat, heartbeat signal amplifier means in said electrocardiograph circuit for amplifying a heartbeat signal picked up by said electrode means, display means for providing a visual indication of said patient's heartbeat, first circuit means coupling said electrode means and said heartbeat signal amplifier means, second circuit means coupling said amplifier means and said display means, circuit protector means in said first circuit means coupled between said electrode means and said heartbeat signal amplifier means with said electrode means being in immediate preceding relationship to said circuit protector means which in turn are in immediate preceding relationship to said heartbeat amplifier means, said circuit protector means effectively disconnecting said electrode means from said heartbeat signal amplifier means for preventing distortion producing voltages from being conducted to any portion of said heartbeat signal amplifier means and thereby preventing distortions in said heartbeat signal amplifier means which can result in a distorted representation on said display means, said circuit protector means including relay means for disconnecting said electrode means from said heartbeat signal amplifier means, defibrillator circuit means, switch means in said defibrillator circuit means for selectively energizing said defibrillator circuit means to apply a countershock voltage to a patient, third circuit means coupling said defibrillator circuit means to said circuit protector means and energizable incidental to the energization of said defibrillator circuit means for causing said circuit protector means to prevent distortion producing voltages produced incidental to defibrillation from being conducted to said heartbeat signal amplifier means, and a fourth circuit means having voltage discharge means therein coupled between said electrode means and said relay means for conducting voltages in excess of a predetermined value applied to said electrode means away from said relay means and said heartbeat signal amplifier means, means for causing said circuit protector means to automatically reconnect said electrode means to said heartbeat signal amplifier means after said switch means is released after the termination of said countershock voltage to cause said display means to provide said visual indication of said patient's heartbeat immediately after the termination of said countershock voltage, said relay means comprising fast acting reed relay means in said first circuit means for opening said circuit means between said electrode means and said heartbeat signal amplifier means before said defibrillator circuit means apply said countershock voltage to said patient.