DE2061182A1 - Bifunctional demand-driven pacemaker - Google Patents

Description

Priority; Dec 15, 1969; V. St. A .; Mr. 884 825

The invention relates to cardiac pacemakers, and more particularly on demand-controlled pacemakers for those patients suffering from atrial bradycardia and unpredictable Atrial ventricular obstruction (AV obstruction).

The electrical activity of a normal heart begins with a nerve impulse going through one in the sinus node located fiber bundle is generated. The impulse spreads through the two atria as they contract and accelerate the flow of blood into the heart chambers below them. The atrial activity of the heart corresponds to the P wave of the ECG. The electrical impulse spreads extends to the atrial node, which in turn stimulates the left and right ventricles. Usually a period of 120-160 msec elapses between the atrial stimulation and the ventricular stimulation. The heart-

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chamber activity corresponds to the QRS signal of the ECG and has usually a duration of 80 msec. Towards the end of each heartbeat, the ventricular muscles repolarize, and this one Part of the heart's electrical activity corresponds to the T-wave of the EKG.

Of the two types of contraction, the ventricular contraction is much more important than the atrial contraction. the Atrial contraction causes the ventricular contractions are more effective; the ventricular contractions are more effective when the ventricles are initially filled with blood be filled. A patient can do without proper atrial activity survive; but it cannot survive without ventricular contractions. In the presence of atrioventricular block, i. H. with electrically loosened atrial nodes, life cannot be sustained unless the ventricles are active beat independently without AV stimulation; even in one In such a case, however, the heart rate is usually far too low. With proper ventricular contractions a patient can even live with atrial fibrillation. Because of this they became the state of the art Corresponding pacemakers are generally used to protect against failure of the ventricular contractions. These pacemakers stimulated the heart chambers continuously at a predetermined pulse rate to initiate their contractions to control.

After this type of pacemaker had been used for many years, the on-demand pacemaker was introduced. At a On-demand pacemakers will only generate the electrical impulses that stimulate the heart when the natural ones No heartbeats. If only a single natural heartbeat is absent, only one becomes electrical

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Impulse generated. If more than one natural heartbeat is absent, the pacemaker will provide stimulation pulses at the pacemaker repetition rate for as long as the natural heartbeats are absent. Regardless of how many electrical stimulus pulses are generated, these appear essentially at the same time interval from one another and from previous natural heartbeats, as would be the case if all natural heartbeats were involved. The result is an "integrated" mode of operation; h _e a mutually exclusive \ cooperation of natural heartbeats and stimulation impulses. A consumer pacemaker of this type is described in U.S. Patent 3,345 published October 10, 1967.

Typically, an on-demand pacemaker is designed to generate a pulse a predetermined time after the last natural heartbeat. If another natural heartbeat occurs within this period of the pacemaker, no pulse is generated and the pacemaker's clocking period begins again. Alternatively, if a natural heartbeat called until the end of the overall period of time g does not occur, a stimulation pulse is generated. For a convenience pacemaker to operate properly, the circuitry of the pacemaker must determine whether a natural heartbeat has occurred. The electrical signal of the greatest amplitude that arises during cardiac activity is the QRS signal, which corresponds to the ventricular contraction. To determine whether a natural heartbeat has occurred, an electrode is typically coupled to a heart chamber. Since ventricular stimulation is desired in most cases, the same electrode can be used to stimulate the cardiac -

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chambers as well as for registering a natural heartbeat can be used, as in the above-mentioned US patent is described.

When interfering signals occur, this type of utility pacemaker may malfunction. The interfering signal can result in the generation of an electrical signal at the ventricular electrode, and the circuit arrangement of the pacemaker can interpret this interfering signal as a natural heartbeat and prevent the generation of a stimulation pulse, even if such a stimulus is actually required. An improved demand pacemaker is described in copending US patent application Ser. No. 727,129 filed April 11, 1968. With this improved need pacemaker, the pacemaker's clock period is not interrupted in the presence of an interfering signal. Continuous stimulation pulses are generated even when they are not needed. It is more likely to generate a pulse, even if it is not needed, than to not generate a pulse when one is needed.

There are many patients with atrial bradycardia, and that too those with normal AV conduction (atrium-ventricle conduction). For such a patient, the slow atrial beat rate is beneficial a decrease in the heart rate. The stimulation of the ventricle by the Pacemaker has heretofore been used to remedy this deficiency. For such patients, however, it would be better provide atrial stimulation so as to increase both the atrial beat rate and the ventricular beat rate control, additionally taking advantage of the natural

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Time sequence between atrial activity and ventricular activity would fare. However, such atrial stimulation would do not protect the patient from unpredictable atrioventricular blockage. Care must therefore also be taken that ventricular stimulation is given if necessary.

Both types of pacing could be achieved using two separate pacemakers. However, even if these are combined in a single housing könn- λ th, many problems must be overcome, especially when an on-demand mode is desired. An obvious difficulty is e.g. B. the chronological sequence of the workflow of the two pacemakers. A bifunctional demand-driven pacemaker for both atrial stimulation and cardiac stimulation is described in our own pending patent application P 20 10 724.8, filed on March 6, 1970. The first puncture of the pacemaker is to generate an atrial stimulation pulse. After a predetermined period of time, the pacemaker causes a ventricular pacing pulse to be generated. Three electrodes are provided, a neutral electrode, an electrode for atrial stimulation and an electrode for ventricular stimulation. The ventricular electrode also serves to register the occurrence of a ventricular contraction

The pacemaker has two heartbeat intervals. The ventricular heart rate interval is 160-250 msec longer than the atrial beat interval. The ventricular heart rate interval is greater than the normal length of time between two heartbeats, as in a standard on-demand pacemaker. The forecourt interval HAst greater than the normal time interval between ventricular and atrial beats (from R to P), but shorter

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than the normal cardiac pause (from R to R). Both clock intervals begin with the generation of the last heartbeat (natural or stimulated). If another ventricular contraction does not occur within the atrial stroke interval, d. H. in the absence of premature ventricular contraction, the atrial stimulation pulse is generated. The atria contract and fill the heart chambers with blood. In the event that the ventricles contract, d. H. that there is no AV blockage, the EKG signal received from the ventricular electrode cancels both of them Clock circuits, and the ventricular pace will not generated. In the event that ventricular contraction does not occur, a ventricular stimulus is provided at the end of the ventricular pacing interval generated.

The atrial stimulation pulse has a relatively large amplitude of the order of 5 V and causes an electrical signal to appear on the ventricular electrode. if treating this signal as if it resulted from a ventricular contraction would the ventricular clock circuit will be cleared, and no ventricular stimulation pulse would be generated, even if a ventricular contraction occurs did not occur after the atrial contraction. For this reason it is necessary to prevent the pacemaker from receiving a signal which is present on the ventricular electrode at the time of a Electrical stimulation of the atrium appears to be misinterpreted as ventricular contraction. The one in the pending German patent application P 20 10 724.8 described bifunctional pacemaker is the detector circuit to register the heartbeat during a short

unresponsive time period following the generation of each atrial stimulation pulse. Usually

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the atrial stimulation pulse has a duration of 2 msec, and the detector circuit for registering the heartbeat is blocked for 8 msec, which begins with the start of the atrial stimulation pulse kick off. In this way, the ventricular heart rate circuit cannot be cleared when the atrial stimulation pulse is produced. The ventricular clock circuit sets their usual functioning continues, and when the ventricular contraction does not occur as planned, a ventricular stimulation pulse is generated.

However, it sometimes happens that a ventricular contraction coincides with or follows an atrial contraction within 8 msec. In the case of the bifunctional demand pacemaker described in the above-mentioned German patent application, such a ventricular contraction cannot be registered because the detector circuit for registering the ventricular contractions is blocked during the generation of each atrial stimulation pulse and immediately thereafter. If a ventricular contraction during the unresponsive period occurs, the chamber clock circuit is not deleted, and it will generate a ventricular pacing pulse at the end of the clock period, although a contraction A tion of the ventricle has already taken place.

The object of the invention is to provide a bifunctional need s-controlled pacemaker, in which an electrical signal is sent to the ventricular electrode, which is transmitted by originates from the generation of an atrial stimulation pulse, is not interpreted as a ventricular contraction, so that an unresponsive period of the pacemaker is not required after the atrial stimulation and a ventricular contraction, which during atrial stimulation or immediately occurs thereafter, can be registered.

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© he bifunctional pacemaker according to the invention is based based on an analysis of the signal frequencies used in the various Waveforms, including the atrial stimulation pulse and the QRS group. The atrial clock circuit and the ventricular clock circuit are from each other isolated by using a different pair of electrodes for each of the two punctures instead of using of a total of three electrodes for the two punctures, one of the electrodes being assigned to both punctures in common is. This isolation sets the magnitude of the electrical signal that is generated due to the generation of atrial stimulation appears on the ventricular electrode. However, the signal amplitude is not small enough to allow the detector circuit of the pacemaker from viewing the signal as an indication of ventricular contraction. It will additional circles are provided to distinguish between the two palls, with the difference of the prequences of the two signals that appear on the ventricular electrode is used. This way there is none Need to disable the detector circuit after generating an atrial stimulation pulse and when there is a ventricular contraction actually occurs during or immediately after atrial stimulation, this event can occur be registered.

An essential feature of the invention is that separate and isolated atrial and ventricular electrodes in the bifunctional demand pacemaker are provided, with a detector circuit for registering the ventricular contraction being provided at the same time capable of doing so, that of atrial stimulation to suppress originating signals.

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A bifunctional artificial cardiac pacemaker is characterized according to the invention by a first pair of electrodes for connection to the human heart for the purpose of atrial stimulation, a second pair of electrodes for connection to the human heart for the purpose of ventricular stimulation, a detector circuit which is coupled to the second pair of electrodes and scans electrical signals that based on the heartbeat of the patient, a pulse generator circuit for generating electrical Stimulationsim__pulse on the said g electrode pairs in accordance with the time at which the said heartbeat signals are sampled, and electrical blocking devices to prevent the response of the said detector circuit to the occurrence of an electrical signal on the second Pair of electrodes resulting from the generation of a stimulation pulse on the first pair of electrodes.

An exemplary embodiment of the invention is explained in more detail below in connection with the drawings. In the Drawings show:

Figure 1 shows the bifunctional demand-controlled heart f

pacemaker according to the earlier patent application P 20 10 724.8;

FIG. 2 shows the course of a typical EKG;

Figure 3 is a timing diagram for illustration the operation of the pacemaker of FIGS

4 shows the preferred embodiment of the invention.

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The one in Pig. 1, the electrode E2 is neutral - the conductor 9 is grounded -, the electrode El is the ventricular stimulating electrode and electrode E3 is the atrial stimulating electrode. The clock circuit for stimulating the ventricle is located between the switch S and the electrodes in the drawing El and E2. The capacitor 65 is initially charged by a current drawn from the batteries 3, 5 and 7 Flows through the resistor 59, the electrodes E1 and E2 and the patient's heart in a period of time that is much is shorter than the interval between successive ones Heartbeats. The value of the resistor 59 is chosen to be low enough to allow the capacitor to be charged quickly 65 to allow, and at the same time high enough to significantly weaken the at the electrodes E1 and E2 To prevent received signal, the electrodes E1 and E2 are implanted. When the transistor T9 in When its conductive state is set, the capacitor discharges through it, taking the current from the capacitor through the collector-emitter path of the transistor, via a cable to the electrode E2, via the heart, via the electrode E1 and another cable to the capacitor flows. The discharge of the capacitor 65 via the electrodes causes the stimulation of the heart chamber if necessary required stimulus. As soon as the transistor T9 switches off, the capacitor 65 charges up again in order to be prepared for the next cycle. The condenser So it simply serves as a power source for the moment when a pulse is needed. The capacitor 65 is not involved in the various clocking operations used to control the selective generation of pulses will.

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The capacitor always charges to the maximum battery voltage. Since he is about an essentially closed course When the transistor discharges, there is no variation in the size of the pulses with increasing resistance of the battery due to signs of aging. Furthermore, no energy is wasted between manufacture and implantation; as long as the electrodes are not closed in a circuit, the capacitor 65 cannot discharge, even if the transistor T9 is switched to its conductive state during each cycle. ™

The charging and discharging of the capacitor takes place via the Heart instead of so that the total direct current flowing through the electrodes from the pacemaker is equal to zero. Otherwise electrolytic processes in the heart cells could dissolve the electrodes »

The transistors T7 and T8, which are connected according to FIG. 1, represent the equivalent of a standard silicon-controlled rectifier. Both are normally non-conductive. When the emitter electrode of the transistor T7 becomes sufficiently positive, the transistors conduct and a current flows through the emitter circuit of transistor T8. The current flow continues until the potential at the emitter of the Transistor T7 falls below a predetermined vert.

The transistor T9 is a simple current amplifier that is normally non-conductive. When the transistor T8 is conductive the current flowing through the resistors 61 and 63 causes the potential at the base of the to increase Transistor T9. At this time, the transistor T9 is in its conductive state and the capacitor 65 can turn discharged over him in the manner described above.

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The arrangement can be used in the free-running mode, that is, it can e.g. B ₀ a pulse with a pulse rate of 72 pulses per minute regardless of the occurrence of natural heartbeats. In such a case the switch S is closed and the base of the transistor T6 is connected to the negative terminal of the battery 3. The transistor T6 therefore remains in its switched-off state. The pulses transmitted via the capacitor 53, which will be described later, are short-circuited via the switch so that they do not reach the transistor. Initially, the capacitor 57 is discharged and the transistors T7 and T8 are non-conductive. The current flows from the batteries 3, 5 and 7 via the resistors 37 and 37, the capacitor 57 and the resistors 61 and 63 «The current via the resistors 61 and 63 is not sufficient to switch on the transistor T9. When the capacitor charges, the potential at the junction between the capacitor and the resistor 37 increases. This increases the potential of the transistor T7. Finally, the potential is sufficient to trigger the relaxation of the oscillator consisting of transistors T7 and T8. The capacitor 57 discharges through the resistor 37 and through these two transistors. At the same time, current flows from the batteries 3 and 5 via the collector-emitter path of the transistor T8 and the resistors 61 and 63. The transistor T9 becomes conductive and the capacitor 65 discharges through it, so that a pulse is sent to the ventricles is given. As soon as the capacitor 57 has discharged sufficiently and the potential of the emitter of the transistor T7 has fallen to a sufficiently low value, the transistors T7, T8 and T9 switch off and the pulse is ended. The capacitor 65 will immediately recharge and the capacitor 57 will begin charging again in preparation for the next pulse.

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The charging period of the capacitor 57, i. H. the time interval between the pulses is determined by the dimensioning of the capacitor and the resistors 35 »37, 61 and 63. The resistors 37, 61 and 63 are very small in relation to the size of the resistor 35. Hence the size of the Pulse pause essentially determined by resistor 35. By adjusting the size of the resistor 35 can the repetition rate of the impulses can be set «,

Furthermore, it may also be desirable to adapt the width of each to the ^ The heart delivered impulse. The capacitor discharges through the resistor 37 and the transistors T7 and T8. The width of the pulse supplied to the capacitor 65 is determined by the discharge time of the capacitor 57, d. ho by the period of time during which the transistors T7 and T8 conduct and therefore turn on transistor T9. By varying the size of the resistor 37 the width of each pulse can be adjusted. In the case of an implantable pacemaker, the values of the Resistances 35 and 37 are adjusted before the device is implanted in the body «,

When the switch S is open, i. H. in the case of an on-demand pacemaker mode, they became the same Play processes as in the free-running operating mode, when no input signal was made to the base of transistor T6 via capacitor 53. The transistor T6 would remain in the non-conductive state and would not affect the charging of the capacitor 57. However, at open switch S transmitted via the capacitor 53 Impulse not short-circuited in front of the base-emitter path of the Vranaistor T6 via the switch. When the Rather, every pulse via the switch is

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capacitor 53 transferred to the base of transistor T6 and puts the transistor in its conductive state. The capacitor 57 discharges through the collector-emitter path of the transistor. In this case, the clock cycle is interrupted, und.das the potential of the junction of the capacitor 57 and the resistor 37 does not increase to the point where transistors T7 and T8 are put into their conductive state. When the arrangement works as an on-demand pacemaker, each contraction of the heart chamber causes a pulse to be transmitted through the Capacitor 53 for the purpose of switching on the transistor T6. The transistor T6 is discharged while the capacitor 57 conductive, just before the point in time when the capacitor 57 is discharged through the transistors T7 and T8 would trigger the generation of a pulse. After the capacitor 57 has discharged through the transistor T6, the transistor switches off. The capacitor then starts charging again. The new cycle begins immediately after the last ventricular contraction occurred, so that the next pulse, if needed, immediately after the next natural heartbeat is registered in the case of a properly functioning heart, is produced"

Similar circuitry is provided for generating an atrial stimulating pulse. The different Circuit components to the right of the electrodes E1 and E2 are provided with the same reference numerals as circuit components equivalent to them in the clock circuit for the ventricles, with only dashes appended are. Except for the sizing of the circuit components, the timing circuit for the atria is the same as those for the ventricles.

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The electrode E3 "is implanted in the patient's heart in order to stimulate its atria. The capacitor 57 'is discharged via the potentiometers 35' and 37 '. After a predetermined time interval, namely, when the capacitor voltage to the switching on of transistors T7 ¹ and T8 'has reached the required value, the two transistors become conductive and bias the base-emitter junction of the transistor T9' in the forward direction. The charge on the capacitor 65 'flows through the transistor T9' and the electrodes E2 and E3. The width of each The pulse is determined by the setting of the potentiometer 37 ', which determines the time that the capacitor 57' needs to discharge through the transistors T7 'and T8'. The length of the pulse pauses is determined by the setting of the potentiometer 35 ', the 'is required in order to charge to the value ^f the conduction state of the transistors T7 and T8' of the capacitor 57 causes which determines the time.

Any pulse delivered through the capacitor 53 as a result of the registration of an R-wave causes the Transistor T6 'as well as transistor T6 becomes conductive. At the same time that the capacitor 57 is across the Transistor T6 discharges, the capacitor 57 'discharges through the transistor T6'. In this case the clock period becomes of the circuit of Fig. 3 is not completed, and no pulse is generated to stimulate the courts. Instead of this Another clock period begins.

Fig. 3 illustrates the timing and is used to understand the operation of the pacemaker. It will two R waves shown representing two consecutive heartbeats (Ventricular contractions). Usually the time interval between these is less than

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760 msec. The P wave assigned to the second R wave occurs before this, as shown.

The potentiometer 35 'is dimensioned so that the capacitor 57 * is charged to the value which ^{is necessary for the conductivity of the transistors T7' and T8 1} after 600 msec have passed since the last capacitor discharge. The pulse E3 for stimulating the atria occurs, as shown, 600 msec after the first R wave. It should be noted that with a normal heartbeat, the atria are stimulated after the P wave occurs. Indeed, the fact that a P-wave has been generated is an indication that a contraction of the atria has occurred and an impulse to stimulate the atria at electrode E3 is not needed. However, if such a pulse is generated after the atrial contraction, that is, during the non-receptive period of the atria, it has no effect on the patient's heartbeat. The generation of an atrial stimulation pulse prior to natural atrial contraction can trigger premature atrial activity, which is undesirable.

The potentiometer 35 in FIG. 1 is dimensioned so that the time interval up to the ventricular stimulation is 800 msec amounts to. The pulse labeled E1 in FIG. 3 occurs, as shown, 800 msec after the first R-wave; H. some after the second R wave, if this occurs. If the second R-wave is registered on the electrode El, will be both clock circuits are cleared and no pulse is applied generated by the electrode El. This is the desired on-demand mode. When a natural heartbeat is not within occurs from 800 msec after the last heartbeat, a pulse is generated at the electrode El to activate the ventricular

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to stimulate contraction. It should be noted that with a natural heartbeat, no ventricular stimulation occurs the pacemaker takes place. However, an atrial stimulation occurs because the atrial pacing interval of 600 msec is shorter is than the natural length of the pause. If, however, a natural atrial contraction does not take place, the Atrial stimulation is needed for the purpose of being more effective Cardiac activity is achieved. Ventricular stimulation is of course provided to prevent atrial ventricular blockage to correct. A normal atrial contraction can be approximately Occur 120-160 msec after atrial stimulation. The chamber cycle period is 200 msec longer than the atrial cycle period; there is therefore sufficient time for natural ventricular contraction before a ventricular stimulation pulse is produced. In general, the chamber cycle period should be 160-250 msec longer than the atrial cycle period.

It should also be pointed out that the operation of the atrial clock circuit depends on the registration of a ventricular contraction at the electrode E1. It is highly desirable to relate the atrial pacing circuit to the patient's heartbeat; if a free-running generator were provided to stimulate the atria, the timing of the patient's heartbeat would be seriously affected. Namely, while the timing of the natural heart activity can change, the timing of the circuit would remain unchanged. For this reason, the capacitor 57 ^f discharges after each heartbeat of the patient. Theoretically it is possible to register an atrial contraction, i. to register the P-wave, and to discharge the capacitor 57 'before it ends its clock period, so that no advance

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Hof stimulation pulse is generated when this is not required will. However, it is extremely difficult to register the P wave because of its small size in comparison to the R wave. For this reason, the Pig pacemaker is used. 1 the registration of the R wave to it, too to delete the atrial clock circuit. Of course this has one Continuous generation of pulses at electrode E3 when the heart beats normally - even when at the Electrode El no pulses are generated - because every R-wave is registered after the pulse at the electrode E3 has been generated. However, it has been found that the generation of an atrial stimulation pulse during the insensitive period of the atrium the normal heartbeat does not bother the patient. However, this does not apply to the generation of a ventricular stimulation pulse which follows ventricular contraction, and this is the primary reason that demand pacemakers are used.

The puncture of the circuit part to the left of the switch S. is to register a natural heartbeat (ventricular contraction), excluding other unwanted signals should be, and then a positive pulse to the base of transistor T6 for the purpose of interruption of the charging cycle of the capacitors 57 and 57 '.

The natural heartbeat generates electrical signals necessary for the sequence of certain processes during characteristic of each heartbeat. A heart beating in a normal rhythm (sinus rhythm) produces electrical ones Signals, commonly called P, Q, R, S, and T waves according to Pig. 2 are designated

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It is generally accepted that it is preferable to record the QRS portion of an EKG for the purpose of registering a natural one Heartbeat τοη to distinguish the P- and T-waves. at ximplantable pacemaker is indeed the electrogram of the cells in the area of the electrodes is important and not the skin ECG, as the pacemaker is based on the Electrical signals generated by cells at the level of the electrodes. The electrogram from these cells is generally considerably different from the skin EKG. The latter is namely the integral over the total Cell electrograms generated by the heartbeat will. Because the different cells generate their signals at different times during each heartbeat the integral, d. H. the EKG, different in some ways from a single cell electrogram. However as well as the BKG shows a sharply rising R-wave, this is also the case with the cell electrograms. These sharply rising point of the electrogram is the most reliable indication of a natural heartbeat. If also the QRS complex of an EKG is referred to below, one should keep in mind that for the electrodes implanted in the patient's heart the sharply rising The momentum of the cell electrogram is important. It has become common to focus on the QRS complex of the EKG to concentrate instead on the individual cell electrograms, mainly because the R-wave in the EKG is predominantly the sharply rising impulse of the Cell electrograams.

Using frequency analysis, it can be shown that the R-wave contains frequency components that are predominantly fall in the range of 20-30 Hz. The P and T waves contain mostly lower frequencies. To get an

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Solution of the transistor T6 by the P- and T-waves To avoid this, various filters are provided in the arrangement in order to filter out the frequencies below 20 Hz. It is of course advantageous to provide additional filters to filter out the frequencies above 30 Hz, and in particular signals at 60 Hz. Such filters are provided in the pacemaker shown in FIG. 1 However, it has been found that such filters are effective in preventing the transistor T6 from being triggered by 60 Hz stray signals are not fully effective. For this reason there are not only different filters in the amplifier stages T1 and T2 are provided, but there is also a pulse rate filter circuit, consisting of the transistors T3, T4 and T5, the resistors 45 and 47 and the capacitors 49 and 53, provided in order to prevent the transistor T6 from being triggered by 60 Hz stray signals. This pulse rate filter circuit is described further below after first considering the frequency filter circuit.

The transistor Tl is normally conductive, the emitter electrode of the transistor via the resistor 19 and the conductor 9 is connected to the negative terminal of the battery 3 and the base of the transistor via the resistor 15 and conductor 13 is connected to the positive terminal of the battery. The electrodes implanted in the heart recorded electrical signals are via the capacitor 17 and a resistor 15 in the base circuit of the Coupled transistor Tl. Signals from both poles can be

from

ritäten «et the transistor Tl are amplified. The transistor is biased so that it is in mode A works because the received signals can be of either polarity depending on the way in which the electrodes are implanted are.

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It should be noted that the Zener diodes 67 and 67 * bridge the electrodes E1 and E2 or E3 and E2. It is possible that very high voltages will appear on the electrodes. ' If z. B, a defibrillation device is used, a very high voltage can be applied to the patient's heart. To prevent damage to the pacemaker circuit, large voltage signals are short-circuited through the Zener diodes. Each mode conducts in its forward direction at voltages slightly above Λ a few tenths of a volt and in the reverse direction at voltages above the breakdown voltage of 10 V.

The capacitor 17 and the resistor 15 emphasize the step in the cell electrogram. These two circuit components form a differentiator which emphasizes the frequency components above about 20 Hz. For such signals creates a significant voltage drop across resistor 15, and the input signal to the transistor Tl is relatively large. For signals of lower frequency, however, the voltage drop across capacitor 17 is much greater, and it is connected to the base-emitter junction of the transistor "

Tl placed a smaller input signal,

The resistor 19 and the capacitor 21 in the emitter circuit of the transistor Tl have a similar function. The impedance the parallel connection grows with decreasing frequency. The emitter impedance causes negative feedback of the Transistor, and the overall gain of the transistor drops therefore with decreasing frequency.

The amplified signal at the collector of the transistor Tl is applied to the base-emitter junction of the transistor T2,

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this transistor also being biased to operate in A mode. The transistor T2 causes a further amplification of the received signals. The capacitor 25 and the resistor 27 in the emitter circuit of the transistor T2 have the same function as the resistor 19 and the capacitor 21 in the emitter circuit of the transistor Tl. This third differentiating element causes a further limitation of the response sensitivity of the detector circuit to low frequencies, so that the P- and T-waves and other frequencies below 20 Hz are suppressed will,,

The resistor 29 and the capacitor 23 serve as an integrator to reduce the high frequency noise components which are above 30 Hz. The higher the frequency, the lower the impedance of the capacitor 23 _} and the lower the total collector impedance of the transistor Tl, and the lower the gain of the stage. The resistor 31 and the capacitor 43 in the collector circuit of the transistor T2 have the same function. Indeed, these four elements serve to attenuate frequencies above 60 Hz and have little effect on 60 Hz signals. In the embodiment shown, the pulse rate filter circuit separates the 60 Hz stray signals from the desired signals.

AC signals at the collector of transistor T2 become the base of transistor T3 via capacitor 41 and coupled to the base of transistor T4. The overall gain of the stages T1 and T2 from the electrodes E1 and E2 to the collector of the transistor T2 and to the conductor 9 is such that signals in the range of 20-30 Hz are strongest Degree to be reinforced. The gain curve falls below

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of 20 Hz decreases very quickly, so that the frequency components the P and T waves are not amplified enough to put the transistors T3 and T4 in their conductive state steer. For frequency components above 30 Hz, for example for 60 Hz signals, the gain is only slightly lower than the maximum gain. For signals of much higher frequency, e.g. B. over 150 Hz, is the gain low enough to prevent incorrect activation of transistors T3 and T4.

When transistors T3 and T4 need a signal of about 1V to turn on and the maximum gain of stages T1 and T2 is above 50, it is evident that signals of 20 mV are in the range of 20-30 Hz at the electrodes can control the transistors T3 and T4 in their conductive state. The one from the heartbeat Electrical signals generated in the vicinity of the electrodes usually contain components of 20-30 Hz above 20 mV. The frequency components characteristic of the P and T waves do not have just one two to three times lower amplitude than that for the R-waves characteristic components; the reinforcement of the stages T1 and T2 in the range around 5 Hz is also only a fraction of the maximum gain, so that these signals do not put the transistors T3 and T4 in their conduction state steer"

The pulse rate filter circuit contains three transistors T3> T4 and T5, which together form a two-phase switch that has two functions. First, the switch serves to provide unipolar current pulses for charging the capacitor 49. However, the switch is because of it second function no real rectifier. This second

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Function is to generate unipolar pulses of constant size, regardless of the size of the above a limit value lying input signals. Every signal through the capacitor 41 "be it negative or positive, that exceeds a limit value (usually 1 V) results in a unipolar current pulse of a predetermined size, which charges the capacitor 49 via the resistor 45.

The emitter of the transistor T4 is connected to the positive terminal of the battery 5, while the base of the transistor is connected via the bias resistor 39 to the same potential. The transistor T4 is normally non-conductive. If, however, a negative signal is transmitted via the capacitor 41, the transistor becomes conductive and a current flows from the battery 5 via the emitter-collector path of the transistor, via the resistor 45 and via the parallel connection of the resistor 47 and the capacitor 49. As a result, the capacitor charges to a maximum voltage that is determined by batteries 3 and 5, the voltage drop across transistor T4 and resistors 45 and 47. If the emitter-collector path of the transistor is viewed as a conductor of negligible impedance, the charging current is determined solely by the size of the batteries and the dimensions of the elements 45, 47 and 49. The size of the negative input signal has no influence. As long as this is above the limit value that is required to control the transistor T4 in its conduction state, a current pulse of a predetermined size is provided to charge the capacitor 49.

A positive signal appearing across capacitor 41 on the other hand has no effect on transistor T4. However

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this signal controls the transistor T3 in its conduction state, so that a current from the battery 7 through the resistor 33 and the collector-emitter path of the transistor T3 flows. It is necessary that the positive signal appearing on capacitor 41 also be unipolar Pulse of the same polarity to charge the capacitor 49 results. The collector output of the transistor T3 cannot be used for this purpose because its potential drops when the transistor T3 conducts current. For this reason, the transistor T5 is provided as a phase inverter. While the emitter of this transistor with the negative terminal of the battery 7 is connected, the base of the transistor is connected to the junction of the resistors 51 and 69 connected. Usually the transistor is non-conductive. However, if the transistor T3 is conductive and its collector voltage drops, so also falls the base potential of the transistor T5. Then the transistor T5 becomes conductive and a current flows from the positive one Terminal of the battery 5 via the emitter-collector path of the transistor T5 to the resistor 45. One can see so that each transmitted through the capacitor 41 is changing signal above a limit value results in a unipolar pulse delivered to the charging circuit.

If we now consider the unipolar pulses supplied by transistor T4 or transistor T5 or by both, which occur with a very slow repetition rate, each such pulse causes the capacitor to charge 49> whereby the current flows through the resistor 45 and the capacitor. Part of the current flows through it the resistor 47} but the capacitor 49 is charged in the meantime, and the voltage applied to it grows. At the end of the pulse, capacitor 49j begins

10 9 3 2 6/1036

to discharge through resistor 47. Assuming that each charging pulse is sufficient to fully charge capacitor 49, the capacitor voltage is equal to the sum of the voltages of batteries 3 and 5 multiplied by the voltage divider ratio of resistors 47 and 45 minus a voltage drop at transistor T4. The exceptional case of narrow high-frequency input pulses is described below. At the end of each unipolar pulse, capacitor 49 begins to discharge through resistor 47. If the capacitor is completely discharged by the time the next charge pulse is delivered, the capacitor will then recharge to the maximum voltage, after which it will completely discharge again. The voltage across the capacitor 49 is coupled in terms of alternating current via the capacitor 53 to the base of the transistor T6 and to the base of the transistor T6 ^1. Each charging pulse increases the voltage on capacitor 49 from zero to the maximum value. This positive step is sufficient to switch the transistors T6 and T6 'into their conduction state, as a result of which the capacitors 57 and 57' discharge and thereby prevent the generation of the next stimulus pulses.

Let us now consider charging pulses that occur with a higher repetition rate, e.g. B. at a rate of 72 per minute, which can be expected with natural heartbeats. Each charging pulse charges the capacitor 49 to its own maximum tension. The capacitor then begins to discharge through resistor 47; however, before this discharge is completed, another charging pulse occurs. The capacitor charges immediately to the maximum voltage and then begins to discharge again. The capacitor never fully discharges; but the one attached to him minimum voltage, namely at the end of the discharge cycle,

1 09826/1 086

AO 2818 ~ 27 -

when the next charge pulse is reached is low enough so that the increase in capacitor voltage when occurring each charging pulse is still sufficient to control the transistors T6 and T6 'in their conduction state every charging impulse, which comes from a natural heartbeat, causes a cancellation of both clock circuits.

Consider the effect of 60 Hz signals on the circuit. If a stray signal of 60 Hz is fed to the base of the transistor T3 and the base of the transistor T4, each of these transistors conducts during each Viechseistromperiode, namely the transistor T3 conducts for a certain time during the positive half cycle, and the transistor T4 conducts for a certain time the negative half-period. As a result, the capacitor 49 charge pulses are supplied at an rate of 120 per second. This rate is considerably greater than 72 per minute. Each pulse fully charges capacitor 49 and the next pulse is delivered before the capacitor has had an opportunity to discharge it to any appreciable extent. Although each pulse fully charges the capacitor, the resulting increase in capacitor voltage is negligible because the capacitor voltage never drops significantly below the maximum voltage. As a result, voltage steps of negligible amplitude are fed via the capacitor 53 to the base of the transistor T6 and the base of the transistor T6 ¹ . Each transistor requires a signal of approximately 0.5 volts for its conduction state, and the voltage steps provided across capacitor 53 are well below this value due to the fact that the unipolar pulses occur at a rate of 120 per second.

10982G / 1 086

AO 2818 - 28 -

Activation of the transistors T3 or T4 with a repetition rate of 40 per second corresponding to a pulse spacing of 25 msec is sufficient for a noticeable discharge of capacitor 49 and triggering of the transistor T6 to prevent. It is obvious that in the case in which signals of 60 Hz or signals of a higher frequency occur, voltage steps are sent through the capacitor 53 whose size is no longer sufficient to control the transistors T6 and T6 'in the conduction state. The transistors T6 and T6 'remain non-conductive and the pacemaker then operates in its free-running mode. Even if natural heartbeats occur at this time, they will have no effect. Every natural heartbeat results in a charge pulse applied to capacitor 49; but this has no effect, since the Capacitor is constantly almost at a maximum value. Only in the absence of undesired high-frequency signals the capacitor has ample opportunity to unwind prior to delivering one resulting from a natural heartbeat Discharge current pulse. Only then does every natural heartbeat have a line of transistors T6 and T6 ' and result in an erasure of the clock circuits. With regard to their mode of operation, the resistors 45 and 47 and capacitor 49 can be thought of as a large inertia switch. This switch cannot respond to control signals respond above a pulse rate of 40 per second. Any signal with a repetition rate greater than 40 per second is not able to block the circuits for generating the stimulus pulses.

Of course, during the time when 60 Hz signals or other unwanted signals occur, the Pacemaker in its free-running mode together

10 9 8 2 6/1086

with the patient's natural heartbeat. This can be disadvantageous, but it is much cheaper than if the pacemaker would fail completely, what then deadly danger if at that time the patient's heart stops working.

While very high-frequency signals have the same effect on the capacitor 49 as signals of 60 Hz, there is one type of signal which, due to the lack of discharge of the capacitor _Λ

gate 49 cannot be prevented from incorrectly controlling the transistors ™ T6, T6 '. More precisely, individual pulses of very small width can drive one of the transistors T3 or T4 into the conduction state and cause a charging pulse to be supplied to the capacitor 49. If capacitor 49 is discharged at this time, as is normally the case at the end of each cycle, the positive voltage step across capacitor 49 can cause ^{transistors T6 and T6 1 to falsely trip.} In order to rule out this possibility, the resistor 45 is provided. Each charging pulse generates a rapid rise in the voltage on capacitor 49, but this rise is not an exact step function, since resistor 45 |

causes an increase in the time constant of charging. In the case of a very narrow pulse, the pulse ends at the time in which the capacitor 49 has just started noticeably to charge. The capacitor 49 therefore does not charge sufficient to trigger transistors T6 and T6 *, i.e. H. to control in their conduction state

The transistors T1 and T2 have a different function than the transistors T5, T4, T5. The first two transistors are used together with the differentiation associated with them and integrators as a frequency filter circuit. Higher fre-

1 0 9 B 2 fi / 1 0 Ü 6

AO 2818 - 30 -

sequences are weakened somewhat; What is particularly important, however, is the weakening of the lower frequencies below 20 Hz. By weakening these signal frequencies and by secreting certain peaks in the heart muscle signal, it is possible to switch off any influence of the P and T peaks on the control of the transistors T6 and T6 ¹ . The frequency filter circuit attenuates signals below 20 Hz, but this must not be confused with heartbeats with a repetition rate of 72 per minute. It is precisely the emphasis on the signal frequencies in the range of 20-30 Hz that ensures that heartbeats appear at a repetition rate of 72 per minute at the base of transistor T3 and at the base of transistor T4, namely due to the R waves below Exclusion of the other signals. As far as the signals sent by capacitor 41 are concerned, it is more convenient to analyze the operation of the pacemaker by considering the pacing rates. Once the signal has passed through capacitor 41, the frequency components of any signal are not determinative. From this point on, the essential importance lies in the number of excitations of the transistor T3 or T4 during a predetermined period of time. Since the two-phase switch delivers a current pulse of a predetermined size to the circuit charging the capacitor for every signal, it is the pulse rate filter circuit that prevents the pacemaker from being switched off by sinusoidal interference signals or by any other interfering signals that occur with a repetition rate that is greater than the minimum value is. The pacemaker of Figure 1 prevents interference from any signals occurring at a repetition rate greater than 40 per second.

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In some cases it is possible that the atrial stimulation pulse generates an electrical signal at the electrode E1 which, after amplification, results in the two clock circuits being deleted. For this reason, the FET switch 92 is connected in the conductor 11 between the electrode El and the capacitor 17 and thus in the base circuit of the transistor Tl. The switch is normally conductive due to its connection through resistor 94 to ground conductor 9. The negative pulse generated at electrode E3 is brought to capacitor 93 via conductor 84 and diode 95. The capacitor charges and turns off the FET switch 2 msec -, the capacitor 93 discharges through the resistor 94. The time constant of the capacitor-resistor circuit is such that the FET switch remains switched off for about 6 additional msec, thus preventing an incorrect registration of a ventricular contraction for an additional millisecond. until all voltage spikes decayed. in this way, the circle is stimulation for the registration of the heartbeat during each atrium and un- for a short period of time thereafter ä receptive made. the capacitor 91 is provided for high-frequency voltage spikes from the switching of the FET Switch can result to short-circuit to the conductor 9.

It is possible, however, that there is a possible ventricular contraction occurs within the deadline period of 8 msec controlled by the FET switch 92. In which Pacemaker of Fig. 1, such a ventricular con-

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traction not discovered because the signal at the electrode E1 does not pass through the switch and the capacitor 17 to the The base of the transistor Tl arrives. It is desirable that the ventricular contraction be registered in order for the ventricular clock circuit to be registered is deleted. The atrial clock circuit starts again, as long as the capacitor 57 'discharges, to generate the atrial pulse first. But the capacitor 57 continues to charge when the transistor T6 not turned on when ventricular contraction occurs will.

Pig's pacemaker. 4 is similar to Pig. I, except that the trap circuit including FET switch 92 is omitted. The pacemaker's chamber clock circuit of Fig. 4 can be erased if a ventricular contraction occurs during or immediately after generation an atrial stimulation pulse occurs. Simultaneously In the absence of such a ventricular contraction, the atrial stimulation pulse cannot turn on the transistor T6 and thus a deletion of the chamber clock circuit cause"

The circuit arrangement of FIG. 4 has a number of differences from that of FIG. 1. First are in place a single atrial stimulation electrode E3> the ground electrode E2 with the ventricular stimulation electrode El has in common two separate atrial stimulation electrodes E3 and E4 provided. The collector circuit of the transistor T9 'in FIG. 4 is therefore different from that of FIG. Second, instead of the FET switch 92 of FIG. 1, the circuitry of FIG. 4 includes filter circuits for attenuating of the signal at the electrode El, which is from the

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Generation of the atrial stimulation pulse results. Third, instead of a direct connection between the top terminals of the resistor 47 and the capacitor, Pig. 1 a parallel connection of the resistor 38 and the diode 42 is provided in the circuit arrangement of FIG. Fourth, the arrangement of the switch S is somewhat different in the circuit arrangement of FIG. 4, and two separate capacitors 53 and 54 are provided in place of the single capacitor 53 of FIG. Ä

In the pacemaker of Fig. 1, the atrial stimulation pulse can at the electrode E3 a considerable signal at the electrode E1, which register the ventricular contraction should cause. This is due to the fact that the ground electrode E2 is common to the other two electrodes is. Each of the electrodes E1 and E3 is connected to the electrode E2 via the heart. The electrode E2 has a certain Impedance, and it is evident that when an atrial stimulation pulse and current flow are generated between the electrodes E3 and E2 the potential at the electrode E2 due to a occurring at this electrode Voltage drop increases. The risen Po- " potential is in turn supplied via the heart of the electrode E1.

In order to eliminate the insensitivity period of the pacemaker after the atrial stimulation pulse, it is first necessary to attenuate the signal which occurs at the electrode E1 and which originates from the generation of an atrial stimulation pulse. This is accomplished in the pacemaker of Figure 4 by providing a separate pair of electrodes E3 and E4 for the atrial stimulation circuit. When an atrial stimulation pulse is generated, flows

1 0 9 S 2 B / 1 C 'o 6

²⁰⁶¹

a current between electrodes E3 and E4. Because the electrode E2 is not assigned to the electrodes E1 and E3 together is, the electrode E1 is not communicated any noticeable increase in potential.

The capacitor 65 'is no longer used to store charge in preparation for the generation of each atrial stimulation pulse. Instead, the current conduction of transistor T9 ¹ causes a pulse to be delivered via transformer 44 to electrodes E3 and E4. When the transistor becomes conductive, a current flows from the batteries 3, 5 and 7 via the primary winding of the transformer 44 and the collector-emitter path of the transistor T9 ¹ to the Srdleiter 9. The current pulse through the primary winding of the transformer 44 causes a Voltage pulse appears on the secondary winding of the transformer. This pulse passes through capacitor 48. Electrode E3 goes positive with respect to electrode E4 and a current flows through the atrium to which the electrodes are connected.

The capacitor 48 is provided to prevent a direct current flow in the event that the electrodes polarize will. The Zener diode 52 is in Pig instead of the Zener diode 67 '. 1 provided. The diode is polarized that it is reverse biased when the stimulating current pulse is generated. In the case of excessive Signal amplitude at the electrodes, which comes from an external source, conducts the diode in its forward direction, when the signal exceeds a few tenths of a volt, and it conducts in its reverse direction when that Signal exceeds 10 V. In either case, the size of the can in reverse through the transformer 44 too

1 09826/1 086

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The impulses reaching the collector circuit of the transistor T9 ¹ do not cause any damage.

The diode 46 is provided so that the current through the primary winding of the transformer is destroyed when the transistor T9 ^! switches off at the end of each pulse. The current then continues to flow in the same direction through the primary winding; however, it then flows through the diode 46 instead of through the transistor 19 '. ^{When the transistor T9 1} is conducting, the diode is polarized in the reverse direction, so that it has no influence on the operation of the circuit during the generation of the stimulus pulse. The use of the diode in this way enables the magnetic field generated by the current flow through the primary winding to disappear rapidly at the end of the Yorhof stimulation pulse.

Since the current path for the atrial stimulation pulse runs through the heart tissue between electrodes E3 and E4 and the electrodes El and Ξ2 or the heart tissue in which these are planted, - does not include, the potential at the electrode E2 and the potential at the electrode El, -

which through the heart tissue between the electrodes El and ™ E2 is reflected, much less than the potential that is applied to the same electrode in the pacemaker of FIG is being developed. In practice, however, the potential can

still
of the electrode El / be sufficient to cause a deletion of the chamber clock circuit after amplification by the transistors Tl and T2. For this reason, the pacemaker of Figure 4 contains additional circuit components to prevent deletion of the chamber clock circuit.

The atrial stimulation pulse usually has a permanentron 2 msec. Due to its narrow width, the impulse is

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determined primarily by relatively high-frequency components ". In the pacemaker of FIG. 1, the electrode E1 is connected directly to the capacitor 17 via the FET switch 92. If the FET switch is omitted, it is obvious that the electrode El is directly connected to the base of the transistor Tl is coupled via the capacitor. In the pacemaker of Fig. 4, the electrode El is on the Resistor 32 coupled to capacitor 17. An end to the Resistor is connected to ground line 9 via capacitor 91. The capacitor 91 in the pacemaker of Fig. 1 is used to high-frequency switching voltage peaks of the FET switch 92 to short to ground. at In the pacemaker of FIG. 4, resistor 32 and capacitor 91 form a low-pass filter which controls the voltage spike weakens, which passes through the capacitor 17 to the base of the transistor Tl when an atrial stimulation pulse is produced. A typical value for the cut-off frequency of the resistor 32 and the capacitor 91 The low-pass filter is 15 Hz. The low-pass filter has only a small influence on the QRS signal that is sent to the electrode El is received because the QRS wave is predominantly through Frequencies above 15 Hz is determined. The low-pass filter, however, weakens the relatively high-frequency signals on line 11, when generating an atrial stimulation pulse appear.

In the pacemaker of FIG. 1, the potential for biasing the base of the transistor T1 is derived from the connection of the line 13 to the connection point between the batteries 3 and 5 and to the resistor 15. In the ideal case, batteries have no internal resistance; in practice, however, an internal resistance of the batteries is always noticeable. Is generated Menn the atrial stimulation pulse,

10982 6/1086

20G11S2

AO 2818 - 37 -

the current flowing through the battery causes the voltage across each battery to change. So although the use of a separate pair of electrodes in the atrial stimulation circuit and the inclusion of an additional low-pass filter reduces the size of the voltage peak reaching the base of the transistor Tl through the capacitor 17 when an atrial stimulation pulse is generated, the change in the voltage of the battery during the flow of the atrial stimulation current can cause ä that the base potential of the transistor Tl changes. This change in the base potential has the same effect as the transmission of a voltage peak through the capacitor 17; namely, the amplified signal can cause a deletion of the ventricular clock circuit. In order to keep changes in the base potential of the transistor Tl due to the internal resistance of the battery to a minimum, the resistor 36 and the capacitor 34 are provided «

This is because these two circuit components form a further low-pass filter. The atrial stimulation pulse, the flows through the battery 3, the result is that a voltage peak of 2 msec duration is generated at the battery terminals

appears. This pulse is characterized by relatively high frequencies, and these are determined by the low-pass filter weakened, so that the still resulting and reached through the resistor 15 to the base of the transistor Tl Voltage surge is minimal. The cutoff frequency of the low-pass filter, which consists of the resistor 36 and the capacitor 34 can be much higher than the cutoff frequency of the resistor 32 and capacitor 91 Low-pass filter, which is 15 Hz. The latter filter should not weaken the frequencies that are used for

109826/1086

the QRS waveform are characteristic, and from this The reason is the cutoff frequency of this filter is only 15 Hz. Since there is no need for the QRS signal To send via the resistor 15 to the base of the transistor Tl, the resistor 36 and the capacitor 34 can Attenuate even higher frequencies that are characteristic of the QRS waveform. Because of this, the

of

Cutoff frequency / low-pass filter switched into line 13 be orders of magnitude higher than the cutoff frequency of the low-pass filter switched into line 11.

However, even with these changes from the arrangement of FIG. 1, it is possible that the signal at the electrode El, that of the generation of an atrial stimulation pulse arises, is large enough that after amplification one of the transistors T4 and T5 becomes conductive. In such a In this case, the increase in voltage across capacitor 49 would cause transistor T6 to become conductive and the chamber clock circuit is deleted. For this reason a further change is made from the pacemaker of FIG made to reduce the likelihood of false triggering of transistor T6.

The brief atrial stimulation pulse (2 msec) causes Although one of the transistors T4 and T5 becomes conductive, the conductivity of this transistor only causes 2 msec. This brief impulse is similar to an RF voltage spike, for their attenuation, the circuit arrangement includes the resistor 45, the V / resistor 47 and the capacitor 49 contains. Resistor 45 causes capacitor 49 to be compared to the width of an RF voltage spike charges slowly. Only a relatively broad voltage spike, such as that which occurs when receiving a QRS

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AO .2818. - 39 -

Signal at the Elektro-de El occurs, the capacitor 49 is charged to a value sufficient to trigger the transistor T6. In order to further reduce the probability that a voltage spike occurring during the generation of an atrial stimulation pulse charges the capacitor 49 to a value sufficient to trigger the transistor T6, the resistance value of the resistor 45 can be increased. With a sufficiently large resistance, the capacitor 49 can be prevented from being caused by a voltage spike of

2 msec to a sufficient amount to trigger the transistor. However, if the resistance of resistor 45 is increased, the voltage spike resulting from the receipt of a QRS signal may not be sufficient to charge capacitor 49 to an extent sufficient to trip transistor T6. This is based on the fact that the resistor 45 and the resistor 47 form a voltage divider and that the voltage available for charging the capacitor 49 is smaller, the larger the resistor 45 is. Even a voltage spike resulting from the occurrence of a QRS signal may then possibly not be able to charge the capacitor 49 to an extent sufficient to trigger the transistor T6 "if the resistance value of the resistor 45 is increased significantly.

In the circuit arrangement according to FIG. 4, instead of the direct connection of the capacitor 49 to the connection point of the resistors 45 and 47 of the capacitor with said junction via the resistor 38 and the parallel circuit containing diode 42 is connected. The current flowing from the collector of one of the transistors T4 and T5 comes, flows through resistor 45 and resistor

10932 6/1086

BAD ORKSiNAl,

58 in the charging section for charging the capacitor. the Inclusion of the resistor 38 in the circuit arrangement is equivalent to an increase in the resistance 45, as far as the delay in the charging of the capacitor 49 is affected. However, as a result of the measure, the resistor 38 with the connection point of the resistors 45 and 47 increases instead of increasing the size of the resistor 45, the maximum charge of the capacitor 49 will not be so great Measure affects. Accordingly, although the resistor 38 delays the charging of the capacitor 49, so that the relative narrow voltage spike resulting from the generation of an atrium Stimulation pulse originates, the capacitor 49 is not sufficient to trigger the transistor T6 charges; the relatively broad voltage spike caused by the Registration of a ventricular contraction originates, but charges the capacitor 49 in one to trigger the transistor sufficient measure.

The use of the resistor 38 influences the operation of the circuit arrangement, however, also in another Way. Recall that the voltage spike resulting from each QRS signal drives capacitor 49 of FIG charges and the capacitor then discharges through resistor 47. The capacitor must be on during the pause in the heartbeat sufficiently discharged for the voltage spike resulting from each QRS signal to be able to lower the voltage to increase on the capacitor. If the capacitor does not discharge sufficiently, the voltage rise is across the capacitor due to the conduction of the transistors T4 or T5 not sufficient to bring the transistor T6 into its conduction state to control. Indeed, the pulse rate filter circuit works in such a way that pulses with too high a repetition rate do not allow the capacitor to discharge sufficiently, so that each pulse only slightly charges the capacitor.

10 9 8 2 6/1086

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loads and the transistor T6 is not triggered. When including the resistor 38 in the circuit arrangement from Fig. 4 it is evident that the unloading path this resistor as well as the resistor 47 contains. the Increased time constant of the discharge path can possibly lead to the capacitor 49 between does not discharge the heartbeats sufficiently. The Tran sistor T6 will not be activated when receiving a QRS signal become a leader.

For this reason, the diode 42 is provided in the circuit. The diode is only conductive when the capacitor 49 discharges and the current flows in the forward direction through the diode. In such a case the resistor 38 is practically short-circuited by the diode, the impedance of which is negligible. Accordingly, the pacemaker's discharge path of FIG. 4 is basically the same as that of FIG. 1, since resistor 38 is virtually eliminated from the discharge path. The resistor is only effective during the charging cycle of the capacitor 49, since when current flows from one of the transistors T4 and T5, this current flows through the resistor 38 from left to right and the diode 42 is then polarized in the reverse direction. The inclusion of the diode 42 in the circuit enables the resistor 38 to be used to increase the charge time constant of the pulse rate filter circuit without at the same time influencing the discharge time constant. The circuit can e.g. B. be set so that one of the transistors T4 and T5 must conduct at least 10 msec at intervals that correspond to a normal heartbeat, so that the voltage rise across the capacitor 49 is sufficient to trigger the transistor T6. The atrial stimulation pulse, which is only 2 msec.

1 0 9 °. ■ 'Π / i "8 6 BATH ORIGINAL

206118?

AO 2818 - 42 -

transistors T4 and T5 put in its conduction state, none enable sufficient charging to trigger the transistor T6.

Recall that in the pacemaker of Figure 1, at the end of the atrial clock period, when transistors T7 'and T8 ¹ conduct, the voltage drop across resistors 61' and 63 * increases. This voltage rise is fed back to line 82 via resistor 55 ′. Of course, it is necessary that the increased voltage on the line 82, which is connected to the base of the transistor T6, is not sufficient to make the transistor T6 conductive, which in turn would result in the deletion of the ventricular clock circuit. In the circuit of FIG. 1, the transistor T6 does not become conductive because the resistor 55 'and the capacitors 53 and 49 form an integrating circuit. The potential at the connection point of the capacitor 53 and the resistor 55 ', i.e. at the base of the transistor T6, cannot suddenly rise if the potential at the junction of the resistors 55 'and 61' rises when an atrial stimulation pulse is generated. The atrial stimulation pulse is sufficiently short that the voltage at the base of the transistor T6 does not rise in a hatred sufficient to control the conductivity of the transistor at the point in time at which the atrial stimulation pulse has ended.

It has, however, been shown that it is possible to obtain a better insulation between the two clock se do hai / ^1: provide s, and this is achieved by using an additional capacitor 54 in the circuit of Fig. 4. The line 82 is used additional capacitor connected to the junction of the capacitor 53 and the capacitor 49 overall

109826/1086
BATH ORIGINAL

AO 2818 - 43 -

couples. The increase in voltage on capacitor 49 when one of the transistors T4 and T 5 is conducting now has the consequence that a pulse passes through the capacitor 53 when the switch S is closed to the base of the transistor T6 and a pulse passes through the capacitor 54 to the base of the transistor T6 'arrived. Each transistor conducts as required when a QRS signal is received. However, if the atrial pacing impulse is generated, the reflected along the line 82 pulse is now given by the capacitor 54 to the g junction of capacitors 59 and 53, instead of directly coupled to the base of transistor T6 as in the circuit arrangement according to Mg. 1 to will. The capacitor 49 has a larger capacitance than the capacitor 53j so that the pulse sent by the capacitor 53 to the base of the transistor T6 is reduced even more in its amplitude in order to prevent conduction of the transistor T6. Using an additional capacitor 54 in this way isolates the two clock circuits from one another.

Note that switch S in the Pig. 4 is in series with the base of the transistor T6, instead of being in parallel therewith, as is the case with the circuit arrangement of FIG. In the circuit arrangement of FIG. 1, when the switch S is closed, the base of the transistor T6 and the base of the transistor T6 ^{1 are} short-circuited to ground, and both clock circuits operate in their continuous mode of operation. When the switch S is open, both clock circuits operate in the demand mode. A somewhat different arrangement is used in the circuit arrangement of FIG. 4, the switch S being in series with the base of the transistor T6. When the switch is open, works

1098 26/1086

AO 2818 - 44 -

the ventricular clock circuit in the continuous operating mode, since no pulses pass through the capacitor 53 in order to trigger the transistor T6 and to discharge the capacitor 57. On the other hand, when the switch is closed, the ventricular clock circuit operates in the demand mode. As far as the atrial clock circuit is concerned, it works constantly in the on-demand mode. Even when switch S is open and the ventricular clock circuit is operating in continuous mode, every ventricular contraction is registered and causes a pulse to pass through capacitor 54 and render transistor T6 'conductive. The atrial cycle period therefore begins anew with each ventricular contraction. This arrangement is very useful because it enables the two clock circuits to be synchronized with one another, even when the ventricular clock circuit is operating in the continuous mode.

Claims;

1 0 9 G λ '■ / ι ::: 8 6

Claims (11)

Claims ly'Bifunctional artificial cardiac pacemaker, characterized by a first pair of electrodes (E'3, E4) for connection to the human heart for the purpose of atrial stimulation, a second pair of electrodes (El, E2) for connection to the human heart for the purpose of ventricular stimulation, a detector circuit (Tl to T5 , 41, 49, "53), which is coupled to the second pair of electrodes (El, E2) and scans electrical signals based on the heartbeat of the patient, a pulse generator circuit (57, T7, T8, 65, 57 ', T7 ¹ , T8 ¹ , 65 ») for generating electrical stimulation pulses at the said pairs of electrodes in accordance with the point in time at which the said heartbeat signals are sampled, and electrical blocking devices (32, 91; 34, 36; 38, 42) to prevent the aforementioned from responding Detector circuit to the occurrence of an electrical signal at the second Slectrodenpaa (El, E2), which from the generation of a stimulation pulse on the first electrode pair r (E3, E4). Ä 2. pacemaker according to claim 1, characterized in that the stimulation pulses on the first pair of electrodes (E3, E4) generated after time intervals that are shorter than the normal time interval between successive R-waves of the EKG and which are longer than the normal time between an R-wave and the next following P-wave in the EKG, and that at the second pair of electrodes (E1, E2) stimulation pulses are generated at time intervals which are longer than the normal time interval between successive ones R waves of the EKG. 10 9 8 7 8/1086 AO 2818 - ^ jT- Hfc 3. A pacemaker according to claim 1 or 2, characterized in that the means for generating the stimulation pulses for the first pair of electrodes (E3, E4) have a pulse generator (57 ', T7 ¹ , T8 ^!, T9 ¹ ) and a transformer (44) for Coupling of the pulse generator to the first pair of electrodes included. 4. Pacemaker according to one of the preceding claims, characterized in that the electrical stimulation pulses applied to the first pair of electrodes (E3, £ 4) are much narrower than a common QRS signal, and that the aforementioned blocking devices a low-pass filter (32, 91) for attenuating the Contain relatively high-frequency signal components that are in that appearing on the second pair of electrodes (El, E2) electrical signal are included, which is from the generation of an electrical stimulation pulse to the first Electrode pair (E3, E4) originates. 5. Pacemaker according to one of the preceding claims, characterized in that a Control stage is provided, which takes place above a predetermined pulse rate operation of the detector circuit responds and the generation of stimulation pulses on the second pair of electrodes (E1, E2) with a pulse rate controls which of the sampling of the patient's heartbeats is independent, and that the control stage has a capacitor (49), a first resistor (45) in series with the capacitor (49), one on the operation of the Detector circuit responsive switching stage (T3, 24, T5) for Feeding a current pulse to the first resistor (45) for the purpose of charging the capacitor (49), a second resistor (38) between the first resistor (45) and the 1 0 9 S 7 6 / 1Ü G 6 206118? AO 2818 -Jb-- HV Capacitor (49) is connected to the capacitor in the pauses between the successive current pulses discharged, with the pulse generator circuit in a Voltage rise across the capacitor (49) responds when one of the current pulses is supplied if the voltage rise is greater is as a predetermined value, and means (42) for reducing the discharge time constant of the capacitor (49) contains. 6. pacemaker according to claim 5, characterized in that that said means for reducing the discharge time constant from a diode (42) exist, which is connected in parallel to said second resistor (38) and whose forward direction in the direction of the discharge current coming from the capacitor (49). 7. Pacemaker according to one of the preceding claims, characterized in that the pulse generator circuit has a first clock circuit (57 ¹ , T7 ', T8 ¹ , T9') for generating the stimulation pulse to be supplied to the first pair of electrodes (E3, E4) and a second clock f circuit (57, T7, T8, T9) for generating the stimulation pulse to be supplied to the second pair of electrodes (E1, E2) and that the detector circuit responds to a signal that is scanned by the second pair of electrodes (E1, E2) and indicates a ventricular contraction, and then deletes it causes the second clock circuit and that said blocking devices prevent the deletion of the second clock circuit when a signal resulting from the generation of an atrial stimulation pulse appears on the second pair of electrodes (E1, E2). 109 & 2R / 1GÖ6 AO 2818 H* 8. pacemaker according to claim 5, characterized that said second resistor (38) both in the charging section (45, 38) and in the discharge path (38, 42) of the capacitor (49) and that the means for reducing the discharge time constant of the capacitor (49) reduce the resistance of the discharge path. 9. Pacemaker according to one of claims 5 to 8, characterized characterized in that the switching stage (T3, T4, T5) generated and the capacitor (49) have a duration which is equal to the duration of the current pulses applied to the second pair of electrodes (El, E2) received signal, and that the charging path and the discharging path of the capacitor (49) in common Resistor (38) is large enough to cause a potential increase across the capacitor that is above a predetermined value (49) to prevent when the supplied current pulse has a length below a predetermined value. 10. pacemaker according to claim 9, characterized in that the discharge resistance through Elimination of the resistance (38) common to the charging path and the discharging path has such a low value, that a discharge of the capacitor (49) is enabled to a sufficiently low value so that the next supplied Current pulse causes a voltage rise on the capacitor which is above said predetermined value has the consequence, if the next current pulse occurs a specified time span after the previous current pulse, wherein the predetermined period of time is the reciprocal of the pulse rate to be suppressed. 1 0 9 8 2 6/1 : e 6 AO 2818 11. Pacemaker according to one of claims 1 to 6, characterized in that the pulse generator circuit has a first clock circuit (57 ', T7 ^f , T8', 19 ') for generating a stimulation pulse to be supplied to the first pair of electrodes (E3, E4) and a second clock circuit (57, T7, T8, Τ9) for generating a simulation pulse to be supplied to the second pair of electrodes (El, E2) and that the detector circuit responds to the ventricular contraction of the patient and then clears the first clock circuit and the second clock circuit and that a switch (S) is provided to prevent the deletion of only the second clock circuit. 109 S26 / 1086