JP2999253B2 - pacemaker - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pacemaker which detects an intracardiac electrocardiogram by an electrode placed in the heart and outputs a pacing pulse from the electrode.

BACKGROUND OF THE INVENTION At present, for example, in a patient with acute myocardial infarction, a patient after cardiac surgery or a patient who has fallen into shock, it is called a pacemaker when it is necessary to normalize the heart function of the patient. Equipment is commonly used.

In such patients, an extracorporeal pacemaker is used if the need for normalizing cardiac function is transient, while an implantable pacemaker is used if permanent.

For example, the installation of an external pacemaker is
A catheter having two pacing electrodes is inserted into the right ventricle and is left in place, and then the pacemaker body is connected to the end of a lead led from the pacing electrode to the outside of the body through the catheter.

In this extracorporeal pacemaker, a pacemaker of a type called a demand type, which performs pacing when the heartbeat of a living body falls below a set number of beats and does not perform pacing when the heartbeat exceeds the set number of beats, is used. Therefore, the intracardiac electrocardiogram (peak value 2 to 20 mV) generated between the two electrodes of the catheter placed in the right ventricle was detected by a pacemaker, and the period interval between the R wave of the electrocardiogram and the next R wave was set. If it is longer than the time corresponding to the number of beats, a pacing pulse (peak value 2 to 4 V, pulse width 1 to 3 mS) is applied between the same two electrodes, and this is made to cause contraction of the heart muscle through the heart muscle. . Therefore, at the time of pacing, the heart forcibly repeats the beat at the set heart rate.

The input and output of this pacemaker are the same, and it must input a weak voltage at one time and output a high voltage at another time.

Further, the potential generated between the two electrodes in the right ventricle is not only an intracardiac electrocardiogram, but also has a slowly changing fluctuation, that is, a baseline fluctuation, and a large and long potential called an after potential generated after applying a pacing pulse. There is a residual potential over time, that is, a residual potential as if a large capacitor (capacitance) is connected in parallel between the electrodes, and this potential is input to the input / output terminal. This residual potential is indicated by reference symbol A in FIG. 11, and a pseudo load circuit 2 capable of reproducing the residual potential in a pseudo manner is shown in FIG. The symbol B in FIG. 11 is a pacing pulse.

In a circuit for detecting an intracardiac electrocardiogram, unless the pacing pulse B and the after-potential A are prevented from entering the detection circuit, these potentials are detected and cannot be discriminated as an intracardiac electrocardiogram.

In the circuit for detecting intracardiac electrocardiography, first, the input side is removed by AC coupling with a cutoff frequency of 10 to 30 Hz to remove baseline fluctuations, and then amplified by an amplifier by several hundred times, or high-frequency noise is removed. To this end, only the R wave of the intracardiac electrocardiogram is passed through a low-pass filter, and the signal is emphasized. This is detected by a comparator when an R wave having a certain amplitude or more is input.

Also, usually, after the detection circuit detects the intracardiac electrocardiogram,
A function to stop detection for 00 milliseconds is provided. this is,
S wave, T following R wave of intracardiac electrocardiogram as shown in FIG.
This is to prevent the detection of waves, extraordinary contractions, and the like. Therefore, if a pacing pulse or the like is erroneously detected, there is a disadvantage that the intracardiac electrocardiogram cannot be detected for 250 to 300 milliseconds thereafter.

Therefore, in order to avoid the influence of the pacing pulse and the after potential, conventionally, the following circuit is provided at the input / output terminal of the pacemaker.

First, the first circuit is a circuit as shown in FIG. In this circuit, when inputting intracardiac electrocardiogram,
A switch 12 is provided to completely separate the input and the output when outputting the pacing pulse. This switch 12
Is set to the input side, that is, the position of the solid line in FIG.
The signal is passed through 12 to an amplifier circuit 14, where it is amplified and output to a detection circuit for detecting the R wave of the intracardiac electrocardiogram. On the other hand, when outputting the pacing pulse, the switch 12 is set to the output side, that is, the position indicated by the dotted line in FIG. If the input and output are completely switched in this way, the influence of the pacing pulse can be avoided.

As a circuit that performs the same operation as the first circuit,
There is also a second circuit as shown. In this circuit, an open collector or open drain connection output means is provided, and, similarly to the first circuit, the input and output are completely completed when inputting an intracardiac electrocardiogram and outputting a pacing pulse. A switch 15 for separation is provided.

Further, as a third circuit, there is a circuit as shown in FIG. This circuit basically has substantially the same configuration as the circuit shown in FIG. 14, and the switch 17 in the figure operates in the same manner as the switch 12 in FIG. The only difference is that
The input path from the switch 17 to the amplifier circuit 14 is provided with an RC filter having a cutoff characteristic of 1 Hz or more, which is composed of a capacitor 18 and a resistor 19. This filter is provided in order to remove a slow change, that is, a baseline change. If the input terminal of the amplifier is directly connected to the input / output terminal without providing this filter, the amplifier may be saturated due to the baseline fluctuation.

As described above, if any of the three exemplified circuits is provided at the input / output terminal of the pacemaker, the influence of the pacing pulse can be avoided to some extent. Side, the residual potential (after potential) is input at the moment of switching, for example,
The amplifier circuit saturates for several hundred milliseconds,
During this time, there is no detection of intracardiac electrocardiogram.

In order to avoid such saturation, the switch may not be switched to the input side until the residual potential is sufficiently attenuated, but in this case, the intracardiac electrocardiogram detected by the pacing electrode is not input until the switch is switched. So it is not a fundamental solution.

Therefore, after outputting the pacing pulse, the input / output side is kept at a low impedance for a while, and the residual potential is forcibly discharged to a potential at which the intracardiac electrocardiogram can be detected. A circuit for detecting intracardiac electrocardiography was considered.

Such a circuit is shown in FIGS. 17 and 18. The circuit shown in FIG. 17 includes a switch 21 for connecting a resistor 20 for after-potential discharge to the input / output terminal 4,
Switch 22 that closes for the duration of pacing pulse output
And a switch 23 for inputting an intracardiac electrocardiogram from the input / output terminal 4 to the amplifier circuit 14 through a filter constituted by the capacitor 18 and the resistor 19. The function of the filter and the function of the amplifier circuit 14 are the same as those of the circuit described above. By operating these three switches as follows, the influence of the after potential can be reduced. That is, when outputting the pacing pulse, the switch 22 is closed for about 2 milliseconds, and a pulse having a relatively high potential is output to the input / output terminal. At this time, switch
21 and the switch 23 are open. After the output of this pacing pulse, switch 21 is almost simultaneously opened with switch 22.
Is closed, and the residual potential due to the after potential is forcibly attenuated via the resistor 20. This switch 21
Is closed (several tens of milliseconds) until the residual potential decays to such an extent that it does not affect the detection of intracardiac electrocardiogram. At this time, the switch 23 is open. Although the after potential is sufficiently lowered by the operation of the switch 21,
In many cases, the input / output terminal does not become 0 because it does not completely become 0 and there is also a baseline fluctuation. Next, the switch 23 is closed. This enables the input of an intracardiac electrocardiogram, but since the aforementioned slightly remaining after-potential is rapidly charged to the capacitor 18, the amplifier circuit 14
, A pulse-like potential as shown in FIG. 19 (B) is input. When the peak value of this pulse is large, it cannot be distinguished from the intracardiac electrocardiogram and is erroneously detected. In order to eliminate such a problem, in the circuit of FIG. 18, a switch 24 is connected in parallel with the resistor 19 between the connection point of the capacitor 18 and the resistor 19. The switch 24 is closed for a time longer than the time constant determined by the capacitor 18 and the resistor 19 just before the switch 21 is opened.
In this way, the problem of the opening shown in FIG. 19 can be solved. However, since it is necessary to control the opening and closing of the four switches with high accuracy, the control is complicated, so that it is composed of many electronic circuits (electronic parts), and the equipment becomes large and the reliability decreases. Battery life is shortened because of increased current consumption.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems associated with the prior art as described above, and to minimize the adverse effect of the after-potential by a circuit which operates extremely simply and simply, thereby pacing pulses and after-pulses. An object of the present invention is to provide a pacemaker that does not erroneously detect a potential or the like as an intracardiac electrocardiogram.

SUMMARY OF THE INVENTION The present invention for achieving the above object provides an electrode placed in the heart for detecting an intracardiac electrocardiogram, detecting an R wave of the intracardiac electrocardiogram input from the electrode, and
When a wave is detected, an R-wave detection circuit that generates an output signal, and a cycle of the R-wave is determined based on an output signal of the R-wave detection circuit, and the R-wave is detected at a cycle equal to or less than a predetermined interval. In such a case, a pacing pulse is not output from the electrode, and a pacing pulse generation circuit that outputs a pacing pulse from the electrode when an R wave is not detected for a predetermined interval or more, and an input signal from the electrode is the R wave. A pacemaker having an input / output terminal for sending an output signal from the pacing pulse generation circuit toward the electrode while sending the signal to a detection circuit, wherein the pacemaker is connected between the input / output terminal and the pacing pulse generation circuit. When the potential of the input signal transmitted via the input / output terminal is within a predetermined range, the high input voltage is at least 5 kΩ or more. An output circuit that is set to a low impedance when the potential of the signal is out of the range while being set to the impedance, wherein the predetermined range is a range narrower than a range of −600 mV to +600 mV. Features.

Preferably, the output circuit is a complementary push-pull circuit of an emitter follower, and the emitter terminals of two transistors forming the push-pull circuit are both connected to the input / output terminal, and are connected to the two transistors. Is 20 to more than the bias value that conducts between the base and the emitter of each transistor.
Preferably, a bias of 600 mV lower is applied.

The bias applied to the two transistors forming the complementary push-pull circuit of the emitter follower may be applied using a forward drop voltage of a diode connected between the bases of both transistors. This bias current may be provided by a constant current circuit.

According to the pacemaker of the present invention, when the intracardiac electrocardiogram is simply input to the input / output terminal, the intracardiac electrocardiogram is -600 mV to +6.
Since it is within the range of ± 20 mV, which is narrower than the range of 00 mV, the input / output terminal is set to high impedance by the operation of the output circuit. Therefore, an intracardiac electrocardiogram having a signal source impedance of 1 kOhm or less is not attenuated and R
Input to the wave detection circuit. Immediately after the pacing pulse is output from the input / output terminal, the after-potential is out of the range of -600 mV to +600 mV, and the input / output terminal is set to low impedance by the action of the output circuit. The after potential is rapidly attenuated within at least the range of -600 mV to +600 mV, and thereafter gradually attenuated according to the time constant. Therefore,
The time during which the input to the R-wave detection circuit must be stopped due to the after potential is extremely short, and the detection omission of the R-wave is reduced. Moreover, since the output circuit does not use a switch, there is no sudden change in potential caused by turning on / off the switch.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, a pacemaker according to the present invention will be described in detail based on an embodiment shown in the drawings.

FIGS. 1 and 6 are block diagrams of a pacemaker according to one embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing modified examples of the output circuit shown in FIG. 1, and FIGS. 7 to 9 are schematic diagrams showing signal waveforms on the way of the circuit according to the present invention, and FIG. 10 is a circuit diagram further embodying the block diagram shown in FIG. .

The circuit configuration of a pacemaker according to one embodiment of the present invention shown in FIG. 1 is applied to, for example, an extracorporeal pacemaker.

The input / output terminal 4 is connected to a pacing catheter having electrodes implanted in the heart, for example, through a lead wire.

An intracardiac electrocardiogram collected by a pacing catheter implanted in the heart is an R wave having a peak value of 2 to 20 mV, and its polarity may be + or-. This depends on the location of the electrode at the tip of the catheter and the location of the endocardium with which it has contacted.

Therefore, the intracardiac electrocardiographic detection circuit needs to detect both polarities. Normally, in an extracorporeal pacemaker, the input / output terminal 4 is AC-coupled in order to escape from the baseline fluctuation of the intracardiac electrocardiogram, and attenuates about 20 Hz or less. To be bipolar.

An amplification circuit 14 is connected to the input / output terminal 4. The amplifier circuit 14 amplifies the weak electrocardiogram input from the input / output terminal 4 several hundred times. The waveform of the intracardiac electrocardiogram input to the input / output terminal 4 is shown in FIGS. FIGS. 7 and 8 (B) show the waveform before this waveform is differentiated and input to the amplifier circuit 14. The waveform shown in FIG. 8 is a waveform in which the polarity of the waveform shown in FIG. 7 is reversed, and it is not known which waveform enters the input / output terminal 4 depending on the attachment position of the catheter as described above.

A switching circuit 50, a filter circuit 51, and an R-wave detection circuit 52 are sequentially connected to the amplification circuit 14. The switching circuit 50 sends the R-wave detection circuit 52 based on the output signal from the switching pulse generation circuit 55 when the intracardiac electrocardiogram is input from the input / output terminal 4 and when the pacing pulse is output from the input / output terminal. It is a circuit that connects or cuts off the path that leads.

The filter circuit 51 includes a low-pass filter, a high-pass filter, and the like, and extracts an R-wave component. This R
The wave is directly input to the R wave detection circuit 52. The output signal of the R wave from the filter circuit 51 has a waveform as shown in FIGS.

The R-wave detection circuit 52 may be anything as long as it can detect the R-wave, and is composed of, for example, a comparison circuit. In the R-wave detection circuit 52 as a comparison circuit, for example, a slight threshold is provided on the positive electrode side. Therefore, when the R-wave is not input, since the level is below the comparison level, the comparison circuit does not trigger, and when the R-wave is input and exceeds the comparison level, the comparison circuit is inverted to generate a trigger pulse. Output to the trigger control circuit 53. The waveform of the R-wave input to the R-wave detection circuit 52 as a comparison circuit is inverted according to the forward / reverse of the waveform of the R-wave input to the input / output terminal 4, as shown in FIG. In any case, if an R wave is input, a positive polarity wave higher than the comparison level is input to the comparison circuit.
Waves can be detected. However, since a waveform that changes inversion in accordance with the normal or reverse of the waveform of the R wave input to the input / output terminal 4 is input to the comparison circuit, when an inverted waveform as shown in FIG. Causes a detection time delay t as compared with the case where a waveform as shown in FIG. 7 is input. Since the detection time delay t is about 30 to 50 milliseconds, there is no problem.

The trigger control circuit 53 stops the detection by the R-wave detection circuit 52 for a predetermined time after the detection, based on the output signal, when the R-wave of the intracardiac electrocardiogram is detected by the R-wave detection circuit 52 as a comparison circuit. And has the function of resetting the timer of the pacing pulse from the pacing generation circuit 54 as described later. The predetermined time after the detection of the R wave is the time following the R wave of the intracardiac electrocardiogram as shown in FIG.
This is a time sufficient to prevent detection of a wave, T-wave, or extra-systole, and is generally 250 to 300 milliseconds. The trigger control circuit 53 is connected to a pacing pulse generation circuit 54, and the pacing pulse generation circuit 54 is connected to the input / output terminal 4 via an output circuit 56.

In the present embodiment, the pace singles generation circuit 54 is a circuit that generates a pacing pulse at a predetermined time period that can be adjusted, and when an R wave is detected by the R wave detection circuit 52 as a comparison circuit, trigger control is performed. The circuit 53 resets the timer for calculating the predetermined time period, so that no pacing pulse is output to the input / output terminal 4 within the predetermined time period after the input of the R wave. And R
If the R-wave detection circuit 52 does not detect the R-wave within a predetermined time after the detection of the wave and the next R-wave should be detected, the pacing pulse generation circuit 54 sends the signal to the input / output terminal 4 after a predetermined time period. Thus, a pacing pulse is output. Thereafter, if the R wave is not detected by the R wave detection circuit 52 within a predetermined time, a pacing pulse is further output, and the operation continues until the R wave detection circuit 52 detects the R wave. As described above, since the input / output terminal 4 is connected to the catheter having the electrode implanted in the heart, the heart can be paced by the pacing pulse output from the input / output terminal 4.

The pacing pulse generation circuit 54 is also connected to the switching pulse generation circuit 55. The switching pulse generation circuit 55 is synchronized with the case where the pacing pulse is output from the pacing pulse generation circuit 54.
It is a circuit that outputs a pulse for driving the switches in 50. That is, when the pacing pulse is being output, the switch of the switching circuit 50 is turned off to cut off the path to the R-wave detection circuit 52 for a predetermined time, while when the pacing pulse is not being output, the switching circuit 50 is turned off. Has the effect of keeping the path to the R-wave detection circuit 52 in the connected state by turning on the switch. Alternatively, the switching circuit may be of a type in which a signal is short-circuited to cut off a path leading to the R-wave detection circuit 52. In the present invention, since the after-potential generated at the input / output terminal 4 following the pacing pulse is attenuated in a short time by the operation of the output circuit 56 described later, the circuit interruption time by the switching circuit 50 is set to a short time. It becomes possible. As the circuit interruption time, specifically, after outputting the pacing pulse,
It is 50 to 150 ms, preferably 50 to 80 ms.

As the switching circuit 50, for example, a switching circuit as shown in FIGS. 16 to 19 or another circuit may be used. Note that such a switching circuit 50 may be on the input side of the amplifier circuit 14.

In the present invention, an output circuit 56 is provided between the pacing pulse generation circuit 54 and the input / output terminal 4. This output circuit 56 is at least 5 kOhm or more, preferably 10 kOhm or more, when the potential of the signal transmitted via the input / output terminal 4 is within a potential narrower than the range of -600 mV to +60 mV. Is set to a high impedance, while when the potential of the signal is out of the range, the circuit is set to a low impedance.

As a specific example of this circuit, there is a complementary push-pull circuit of an emitter follower as shown in FIG. In this circuit, the emitter terminals of two transistors 30 and 31 are connected to each other,
Are connected by diodes 32, 33 which are forward-connected to the base of one transistor 31, and further, the bases of the respective transistors 30, 31;
Between the collectors, resistors 34 and 35 are connected and diodes 32 and 33
, And a circuit that supplies current to the diodes 32 and 33 to make them conductive. The emitters of the transistors 30 and 31 are connected to the input / output terminal 4, and the connection point of the diodes 32 and 33 is connected to the pacing pulse generation circuit 54.

In this circuit, the conduction voltage between the base and the emitter of the NPN transistor 30 is 20 mV or more, preferably 20 mV or more.
A bias current is applied via a resistor 34 to a diode 32 having a forward drop voltage of about 600 mV lower. This bias current is set to a current larger than a value obtained by dividing the current required for pacing pulse output by the current amplification factor of the transistor 30. The same applies to the PNP transistor 31, the diode 33, and the resistor 35. According to such an output circuit 56,
In a range narrower than the range of 600 mV to +600 mV, preferably in the range of -20 mV to +20 mV, which is the range of intracardiac electrocardiography, the output impedance is higher than 5 kOhm, preferably higher than 10 kOhm, and extremely high in other ranges. Lower.
The range in which the output impedance becomes high can be changed by selecting the forward voltage of the bias diodes 32 and 33 connected in series and by selecting the type of the diodes. In other words, when a normal silicon diode having a low forward voltage drop is used as a diode to be used, a range of about ± 70 mV (−70 to +70 mV) is used.
In the range of about 70 mV), a high impedance region can be obtained.

The output circuit 56a shown in FIG. 2 connects a constant current circuit composed of a transistor 40 and a resistor 41 or a transistor 42 and a resistor 43 instead of the resistors 34 and 35 of the circuit shown in FIG. I have. A constant current circuit composed of the transistor 40 and the resistor 41 generates a bias current on the positive side of the transistor 30, and a constant current circuit composed of the transistor 42 and the resistor 43 generates a bias current on the negative side of the transistor 31. Give each. In this circuit, since the bias current is made constant, it is possible to operate with a power supply voltage lower than the power supply voltages V _CC and V _EE shown in FIG.

In these circuits, if a silicon Schottky barrier diode is used, in the range of about ± 0.25V,
A region with a high output impedance can be obtained.

In the above two circuits, there is only a current amplification effect,
There is no voltage amplification effect, and the voltage of the drive pulse to be applied to the connection point of the diode needs to be equal to or higher than the output pulse voltage. Further, in this circuit, if the drive pulse voltage is applied in reverse polarity, an output pulse of reverse polarity, that is, a pacing pulse can be output.

In the output circuit 56b shown in FIG. 3, a voltage amplifying means comprising a resistor 46 and a transistor 45 is connected to the resistor 40 of the circuit shown in FIG. 2, and a drive pulse is applied to the resistor 46. Things. Since this circuit has a voltage amplification function, there is an advantage that the voltage of the drive pulse can be freely selected to some extent. Further, by changing the emitter potential of the transistor 45, the potential of the drive pulse voltage can be changed. Further, if the transistor 45 is a PNP transistor, the collector terminal of which is connected to the base of the transistor 42, and the driving voltage is applied with the opposite polarity, an output pulse of the opposite polarity, that is, a pacing pulse can be output. In this circuit, a region with a high output impedance is obtained in a range of about ± 100 mV.

In the circuit exemplified above, if the forward voltage of the bias diode connected in series is selected, or if a zener diode exhibiting an appropriate forward voltage is selected, the region where the output impedance becomes high is reduced to about ± 20 mV. It is also possible to set.

Such circuits are not used in ordinary electronic circuits because they cause waveform distortion. That is, it is common sense that the bias always gives a bias higher than the conduction voltage between the base and the emitter of the transistor.
In order to realize the above-described characteristics, the circuit configuration is dared. It is also conceivable to use a source follower complementary push-pull circuit using a field-effect transistor instead of a transistor as an output circuit. However, the field-effect transistor is not industrial because the variation in gate-source voltage is large. But,
If relatively accurate field-effect transistors are developed,
It can be used in the present invention.

It should be noted that a common emitter output circuit as shown in FIG. 4 cannot create a high-impedance region near zero potential, and an emitter follower using one transistor as shown in FIG. It cannot absorb the after potential which has the same polarity as.

According to such output circuits 56a and 56b according to the present invention,
While the pacing pulse is not generated, the R wave can be efficiently detected from the input / output terminal, and when the pacing pulse is output from the input / output terminal, the after potential of the pacing pulse is rapidly attenuated, and the after potential of the after potential is reduced. Therefore, the time during which the input to the R-wave detection circuit must be stopped becomes extremely short, and the detection omission of the R-wave decreases. Moreover, since the output circuit does not use a switch, there is no sudden change in potential caused by turning on / off the switch.

It should be noted that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

For example, the pacemaker according to the present invention includes the output circuits 56, 5
The circuit configuration other than 6a and 56b is not particularly limited, and may be, for example, a circuit configuration as shown in FIG.

The circuit shown in FIG. 6 does not include the switching pulse generation circuit 55 and the switching circuit 50 shown in FIG. 1, but includes an absolute value circuit 60 and a pulse pull-down circuit 62 instead.

The absolute value circuit 60 converts the signal waveform input thereto into a wave of either positive or negative polarity. Thereafter, a signal of either positive or negative polarity is applied to the R-wave detection circuit 52 to detect the R-wave. For example, the output of the absolute value circuit 60 is set to be positive, and the positive-polarity wave is detected by the R-wave detection circuit 52 as a comparison circuit having a slight threshold on the positive side. Then, when the R-wave is not input, since the level is below the comparison level, the R-wave detection circuit 52 does not trigger, and when the R-wave is input and exceeds the comparison level, the R-wave detection as the comparison circuit is performed. The circuit 52 inverts and outputs a trigger pulse to the trigger control circuit 53. The output waveform of the absolute value circuit 60 that converts the wave into a positive wave is shown in, for example, FIG. As shown in these figures, if the signal passes through the absolute value circuit, the output waveform of the absolute value circuit 60 becomes the same even if a waveform of the opposite polarity is input to the input / output terminal 4.

When the pacing pulse is output to the input / output terminal 4, the pulse lowering circuit 62
The input signal of a predetermined value or more is applied to the R-wave detection circuit 52 for a predetermined period of time by applying, to the unipolar input signal input to the wave detection circuit 52, a pull-down pulse having a polarity opposite to that of the polarity and higher in potential than the input signal. Has the function of preventing

When the output signal from the absolute value circuit 60 has a positive polarity, a negative pulse having a positive and negative polarity as shown in FIG. 9B is input to the input side of the R-wave detection circuit 52. The pulse width (time) T of the negative polarity needs to be a width longer than the influence time of the pulse singles input from the input / output terminal 4 and the after-potential thereof, and is generally 20 to 150 milliseconds. is there. The pulse potential V is input from the input / output terminal 4 and passes through the amplifier circuit 14, the filter circuit 51, and the absolute value circuit 60, and the pacing pulse as shown in FIG. it is preferably larger than V _2. Then, the R-wave detection circuit
At the input side of 52, the pacing pulse and the waveform shown in FIG.
The pulse shown in FIG. 7B is applied, resulting in the waveform shown in FIG.

Even if the waveform shown in FIG. 4C is input to the R-wave detection circuit 52, the pacing pulse and the waveform corresponding to the after potential are sufficiently lowered by the down-pulse, so that a signal of a predetermined value or more is detected. The R-wave detection circuit 52 as a comparison circuit that performs
There is no false detection of a wave. In the above description of the operation, the case where the output of the absolute value circuit 60 is positive is described. However, even if the output of the absolute value circuit 60 is made negative and the polarity thereafter is completely reversed, the circuit operates in exactly the same manner.

With this configuration, even if the switching circuit is not used, the pacing pulse and its after potential are not erroneously detected as the R wave by the R wave detection circuit 52 as the comparison circuit. Even if a switch element is used, a pulse due to a leakage current or the like does not affect the detection of the R wave. This is because this switch operation is performed on the negative side (no positive noise is generated).

Also in such a pacemaker circuit, if the output circuits 56, 56a, 56b according to the present invention are connected between the pacing pulse generating circuit 54 and the input / output terminal 4, the same as the embodiment shown in FIG. Has an action. In particular, in this embodiment, even if a switching circuit is not used, the pacing pulse and its after potential are not erroneously detected as an R wave by the R wave detection circuit 52 as a comparison circuit, and the pulse reduction by the pulse reduction circuit 62 is performed. This is convenient because the time T can be shortened.

A more specific circuit diagram of a pacemaker as shown in FIG. 6 is shown in FIG.

In FIG. 10, reference numeral 4a is an input / output terminal, and 14a is an amplifier circuit, which is constituted by an operational amplifier and has an amplification factor of several hundred times. Reference numeral 51a denotes a filter, which is, for example, a low-pass filter and has an operational amplifier buffer. Reference numeral 60a denotes an absolute value circuit, which is a typical form using two operational amplifiers, and outputs a positive output signal. Reference numeral 52a denotes a comparison circuit which operates an operational amplifier comparator and finely adjusts the comparison potential to the positive side before use. The comparison circuit 52a outputs a positive output signal when a potential higher than the comparison potential is input, and outputs a negative output signal otherwise. The output from the absolute value circuit 60a is connected to the input terminal of the comparing means 52a via the resistor 64.

Reference numeral 62a denotes a switch signal generator that operates on a negative power supply. The switch signal generator shifts the level of the pacing output to a negative level, synchronizes with the rise of the pacing output, and outputs 0 from the output "". It is composed of a one-shot multivibrator that can output more negative and can output from negative to 0 from the output "Q", output starts in synchronization with the rising of the pacing pulse, and outputs several tens of milliseconds Is to stop. The output side of the switch signal generator 62a is connected to a comparison circuit 52a via a resistor 66.
Connected to the input terminal of These switch signal generators 62
The resistor a and the resistor 66 constitute a pulse pull-down circuit 62 as shown in FIG. Instead of the resistor 66, an FET 68 may be used. Also, an open collector or open drain transistor is connected to the input terminal of the comparison circuit 52a from the output of the signal generator 62a, their emitter or source is connected to a negative power supply, and their base or gate is connected to negative. It is also possible by switching with a potential.

Reference numeral 53a in FIG. 10 indicates that after detecting an intracardiac electrocardiogram,
This is a one-shot multivibrator for stopping detection for up to 300 milliseconds. This multivibrator 53a
Receives the output signal of the comparison circuit 52a, sends a reset signal to the pacing pulse generation circuit 54a, and resets the timer for calculating the pacing pulse interval from the pacing pulse generation circuit 54a. That is, the multivibrator 53a corresponds to the trigger control circuit 53 shown in FIG.

Incidentally, the pacing pulse generator circuit 54 is adapted to determine the pulse interval and the pulse width between t ₁ and t _2. Sign 56
Is a pacing pulse output circuit.

Effects of the Invention As is apparent from the above description, according to the pacemaker of the present invention, when the intracardiac electrocardiogram is simply input to the input / output terminal, the intracardiac electrocardiogram is in a range narrower than the range of -600 mV to +600 mV. Since it is within the range of ± 20 mV, the input / output terminal is set to high impedance by the action of the output circuit, and the intracardiac electrocardiogram is input to the R-wave detection circuit without attenuation.
When the pacing pulse is output from the input / output terminal, the after potential is from −600 mV to +600 mV.
The input / output terminal is set to a low impedance by the action of the output circuit because the input / output terminal is out of the range narrower than the range of mV.
As a result, the after potential is at least -60.
It is rapidly attenuated within the range of 0 mV to +600 mV, and thereafter gradually attenuated according to the time constant. Therefore, the time during which the input to the R-wave detection circuit must be stopped due to the after-potential becomes extremely short, and the detection omission of the R-wave is reduced. Moreover, since the output circuit does not use a switch, there is no sudden change in potential caused by turning on / off the switch.

EXAMPLES Hereinafter, the present invention will be described with more specific examples, but the present invention is not limited to these examples.

 A circuit as shown in FIG. 1 was created.

2SC2459 is used as the transistor 30, 2SA1049 is used as the transistor 31, and diodes 32 and 33 are
1S953 was used, and the resistors 34 and 35 used were 200 kOhm.

A pseudo load circuit 2 as shown in FIG. 12 was connected to the input / output terminal 4 of this circuit, and when an evaluation test was performed, when a potential of ± 9 V was applied as a power supply, the output was actually output to the input / output terminal. The output pulse height of the pacing pulse was 3.2 V, and the output pulse width was 2 milliseconds. When the after-potential at this time was measured at point C in FIG. 1, the time until the after-potential became 5 mV or less was only 85 milliseconds after the output of the pacing pulse. For this reason, the input inhibition time of about 100 milliseconds by the switching circuit 50 is sufficient. In addition to the input prohibition time, the intracardiac electrocardiogram could be detected without any problem between 2 and 20 mV. When the above data was obtained, the conduction voltage between the emitter and the base of the transistor was 625 mV, and the forward voltage drop of the diode was 555 mV (at 0.7 mA). The high impedance region of this output circuit was in the range of ± 70 mV. Incidentally, data obtained under the same conditions as above using the output circuits of FIGS. 4 and 5 instead of the output circuit 56 of FIG. But
The time required to reach 5 mV or less was 240 milliseconds after the output of the pacing pulse, and was 280 milliseconds in the circuit of FIG.

Similarly, a circuit evaluation test was performed using the output circuit shown in FIG.

2SC2459 is used as the transistor 30, 2SA1049 is used as the transistors 31 and 40, 2SC2459 is used as the transistor 42, and 1S is used as the diodes 32 and 33.
A 953 resistor was used as the resistor 41, and a 30 Mohm resistor was used as the resistor 43.

As a power source for this circuit, when a potential of ± 4.5 V is applied, the output pulse wave height of the pacing pulse actually output to the input / output terminal 4 is 3.7 V, and the output pulse width is 2 ms. Was. When the after potential at this time was measured at point C in the figure, the time required for the after potential to become 5 mV or less was 55 milliseconds after the output of the pacing pulse. Switching circuit for this
An input prohibition time of 50 is sufficient if about 70 milliseconds. In addition to the input prohibition time, the intracardiac electrocardiogram could be detected without any problem at a sensitivity of 20 mV. The high impedance area of this output circuit 56a is ± 200mV
Was in the range.

As described above, if the above circuit is inserted into the output stage of the pacemaker, after the pacing pulse is output, the after-potential generated by the pacing pulse can be rapidly attenuated. It is possible to reliably detect without being buried in the after potential.

[Brief description of the drawings]

FIGS. 1 and 6 are block diagrams of a pacemaker according to one embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing modified examples of the output circuit shown in FIG. 1, and FIGS. FIGS. 7 to 9 are schematic diagrams showing signal waveforms on the way of the circuit according to the present invention, FIG. 10 is a circuit diagram further embodying the block diagram shown in FIG. 11 is a graph showing the waveform of a pacing pulse, FIG. 12 is a circuit diagram of a pseudo load circuit, FIG. 13 is a schematic diagram of an electrocardiogram, FIGS. 14 to 18 are circuit diagrams of a switching circuit used in a pacemaker, and FIG. 19
The figure is a graph showing the influence of the after potential in the circuit of the conventional pacemaker. 4, 4a: input / output terminal, 50: switching circuit, 52: R-wave detection circuit, 60: absolute value circuit, 54: pacing pulse generation circuit, 55: switching pulse generation circuit, 56, 56a, 56b …… Output circuit, 62 …… Pull down circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61N 1/365

Claims (2)

(57) [Claims] An electrode placed in the heart for detecting an intracardiac electrocardiogram, an R wave of the intracardiac electrocardiogram input from the electrode is detected, and an output signal is generated when the R wave is detected. An R-wave detection circuit, and a period of the R-wave is determined based on an output signal of the R-wave detection circuit. When the R-wave is detected at a period equal to or less than a predetermined interval, a pacing pulse is output from the electrode. A pacing pulse generating circuit that outputs a pacing pulse from the electrode when an R wave is not detected for a predetermined interval or more, and an input signal from the electrode is sent to the R wave detecting circuit, and the pacing pulse is generated. A pacemaker having an input / output terminal for sending an output signal from a circuit toward the electrode, wherein the pacemaker is connected between the input / output terminal and the pacing pulse generation circuit; When the potential of the input signal transmitted via the input terminal is within a predetermined range, the impedance is set to a high impedance of at least 5 kΩ or more, and when the potential of the signal is out of the range, Further comprising an output circuit set to low impedance,
A pacemaker wherein the predetermined range is a range narrower than a range of -600 mV to +600 mV. 2. The output circuit is an emitter-follower complementary push-pull circuit. Emitter terminals of two transistors forming the push-pull circuit are both connected to the input / output terminal, and are connected to the two transistors. Wherein a bias of 20 to 600 mV lower than a bias value for conducting between the base and the emitter of each transistor is applied.
The pacemaker described in the section.