JP3090945B2 - 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 atrium or right ventricle and is left in place, and then the pacemaker body is connected to the end of a lead wire led out of the body through the catheter from the pacing electrode.

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.

In addition, the potential generated between the two electrodes in the right ventricle includes not only the intracardiac electrocardiogram but also a slowly changing fluctuation, that is, a baseline fluctuation, and a large and long potential called an after potential generated after giving a pacing pulse. A residual potential over time, that is, a residual potential exists 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. 12, 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. 12 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 that detects intracardiac electrocardiography, first, remove the baseline fluctuation as an AC coupling with a cutoff frequency of 10 to 30 Hz on the input side, and then amplify it by several hundred times with an amplifier or remove high frequency noise. To this end, only a signal emphasizing the R wave of the intracardiac electrocardiogram is passed through a low-pass filter, and this signal 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 output side of 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. 15, 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 after-potential is input at the moment of the switching, and the amplifier circuit is saturated for, for example, several hundred milliseconds. During this time, the intracardiac electrocardiogram cannot be detected.

In order to avoid such saturation, the switch should not be switched to the input side until the after 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 FIG. 18 and FIG. The circuit shown in FIG. 18 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 residual potential is sufficiently lowered by the operation of the switch 21, the input / output terminal often does not become 0 due to the fact that it does not become completely 0 and there is a base line fluctuation. Next, the switch 23 is closed. This enables the input of an intracardiac electrocardiogram, but since the aforementioned slightly remaining after-potential and baseline fluctuating potential are rapidly charged in the capacitor 18, the amplifier circuit 14
, A pulsed potential as shown in FIG. 20 (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. 19, 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, it is possible to solve the problem of the open circuit shown in FIG. However, since it is necessary to control the opening and closing of the four switches with high precision, the control is complicated, so that the circuit is composed of many electronic circuits (electronic parts), and the size of the equipment is increased and the reliability is reduced. And the current consumption is increased, so that the battery life is shortened.

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 that sends an output signal from the pacing pulse generation circuit toward the electrode while sending the signal toward the detection circuit, wherein a pacing pulse generation circuit and the input / output terminal are provided. An output circuit having a characteristic of actively outputting a voltage up to approximately OV or a power supply voltage, and a pair of diodes reversely connected in parallel to each other, It is characterized in that towards the entry output terminal are connected in this order.

The output circuit has a characteristic that a minimum output voltage can output a voltage of 0 ± 0.6 V or less, or a maximum output voltage of a power supply voltage−0.6 V or more. Preferably it is a diode.

Further, the diodes connected in reverse may be silicon Schottky barrier diodes.

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 the range of ± 20 mV, which is a relatively low voltage range around 0 V. The input / output terminal is set to high impedance by the action of the connected diode. Therefore, the intracardiac electrocardiogram is input to the R-wave detection circuit without attenuation. Immediately after the pacing pulse is output from the input / output terminal, the after-potential is in a very high voltage range as compared with the intracardiac electrocardiogram. Since the impedance is set, the after-potential is rapidly attenuated within the intracardiac electrocardiogram voltage range near the forward voltage determined by the characteristics of the diode, 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.

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.

1 and 7 are block diagrams of a pacemaker according to one embodiment of the present invention, FIGS. 2 to 6 are circuit diagrams showing modified examples of the output circuit shown in FIG. 1, and FIGS. FIG. 11 is a schematic diagram showing a signal waveform in the middle of the circuit, and FIG. 11 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 is the position of the electrode at the tip of the catheter and will depend on the position 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. 8 and 9B show waveforms obtained by differentiating this waveform and inputting it to the amplifier circuit 14. FIG. The waveform shown in FIG. 9 is a waveform in which the polarity of the waveform shown in FIG. 8 is reversed. As described above, it is not known which waveform enters the input / output terminal 4 depending on the mounting position of the catheter.

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 paces are 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 forward / 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. 9 is input to the comparison circuit, Causes a detection time delay t as compared with the case where a waveform as shown in FIG. 8 is input. Since the detection time delay t is about 30 to 50 milliseconds,
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 S 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 pacing pulse generation circuit 54 is a circuit that generates a pacing pulse at a predetermined time period that can be adjusted. When the R-wave detection circuit 52 serving as a comparison circuit detects an R-wave, a 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
If the R-wave detection circuit 52 does not detect the R-wave within a predetermined time after the detection of the R-wave and the next R-wave should be detected, the pacing pulse generation circuit 54 sends the signal to the input / output terminal 4 in a predetermined time period. A pacing pulse is output toward the camera. Thereafter, during a predetermined time, the R-wave detection circuit 52
If the R-wave is not detected in step (3), 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, the after-potential generated at the input / output terminal 4 following the pacing pulse is attenuated in a short time by the action of the output circuit 56 and the reversely connected diodes 37 and 38 described later. The circuit interruption time can be set to a short time. As the circuit interruption time, specifically, 50 to 150 milliseconds after pacing pulse output,
Preferably it is 50 to 80 milliseconds.

As the switching circuit 50, for example, a switching circuit as shown in FIGS. 15 to 19 or another circuit may be used. Note that such a switching circuit 50 may be provided on the input side of the amplifier circuit 14.

In the present invention, a pair of diodes 57 and 58, which are mutually connected to the output circuit 56, are provided between the pacing pulse generating circuit 54 and the input / output terminal 4.
The output circuit 56 has a characteristic of actively outputting a voltage up to approximately OV or a power supply voltage. The circuit capable of actively outputting is referred to as a circuit having a function of discharging and sinking current in the output voltage range.

As an example of such an output circuit 56, for example, as shown in FIG. 2, there is a circuit constituted by six transistors 30 to 35. This circuit is a class B operation emitter follower complementary push-pull circuit. Since this circuit is often used in the output circuit of an operation amplifier, a sufficiently low impedance can be realized on the output side even near OV.

When a pacing pulse is output as a driving pulse to the base terminal of the transistor 35 via the resistor 36, the pacing pulse is output via the diode 37 of the diodes connected in parallel with opposite polarities to each other with the driving pulse. Is done. At this time, the impedance between the input and output terminals on the output side is made low through the diode 38. Further, when an intracardiac electrocardiogram is input to the input / output terminal 4 other than at the time of pacing pulse output, the diodes 37, 38 and the output circuit 56, which are reverse-connected in parallel with each other, reduce the forward voltage of the diodes 37, 38. The voltage range is set to high impedance. As a result, in the weak voltage range exhibited by the intracardiac electrocardiography, the reversely connected diodes 37 and 38 and the output circuit 56 have characteristics such that they exhibit high impedance. Therefore, in this case, the intracardiac electrocardiogram is input to the R-wave detection circuit 52 without attenuation.

The circuits shown in FIG. 3 and FIG.
40 is a source grounded complementary circuit (CMOS) constituted by 40. In the circuit shown in FIG. 3, if one power supply terminal is set to 0 potential, it is possible to actively output up to OV. The circuit shown in FIG. 4 can actively output from a negative power supply voltage to OV.

In the circuits shown in FIG. 3 and FIG.
When a pacing pulse is output as a driving pulse to the and 40, a pulse is output through the diode 37 of the diodes connected in parallel with opposite polarities to each other in accordance with the driving pulse. At this time, the impedance on the output side is made low through the diode 38.

The circuit shown in FIG. 5 and FIG.
This is a collector output circuit constituted by four transistors of .about.44. In the circuit of Fig. 5, OV at positive output
It can output near (about 20mV). Sixth
In the circuit shown in the figure, negative output can be output up to near OV.

In both circuits, when a driving pulse as a pacing pulse is output to the base terminals of the transistors 43 and 44 via the resistor 45, the diode 37 of the diodes connected in parallel with opposite polarities to each other with the driving pulse.
A pulse is output via the. At this time, the impedance on the output side is made low through the diode 38.

As described above, according to the circuit in which the output circuit 56 capable of actively outputting approximately OV or approximately the power supply voltage is connected to the input / output terminal 4 through the diodes 37 and 38 connected in reverse, the input / output terminal 4 If the potential of the signal being transmitted is within a predetermined range within the forward voltage of the diode, the input / output terminal is set to a high impedance of at least 5 kΩ or more, preferably 10 kΩ or more, while the potential of the signal is If it is out of the predetermined range, it is set to low impedance. Here, the predetermined range around 0 V is −
The range is narrower than the range of 600 mV + 600 mV, and preferably within a range around ± 20 mV (−20 to +20 mV) which is a voltage range of intracardiac electrocardiogram.

The range in which the output impedance is high can be changed by selecting the type of the diodes 37 and 38 connected in reverse in parallel. In other words, if a normal silicon diode is used as the diode to be used, ± 0.
In the 7V output range (the range of -0.7 to + 0.7V), a very high impedance region can be obtained.
A very high output impedance region can be obtained in the output range of 0.2V to ± 0.5V.

In addition to the circuits described above, various types of output circuits capable of actively outputting OV or almost the power supply voltage are conceivable. Of course, these circuits can also be applied as the output circuit of the present invention.

However, an open collector, an open drain, a switch, or the like cannot be used because the off-state impedance is extremely high and there is no ability to discharge an after potential. In addition, a complementary push-pull with a grounded emitter has a high impedance unless a current is constantly supplied, and is not suitable for a pacemaker.

According to the output circuit 56 and the reversely connected diodes 37 and 38 according to the present invention, the R wave can be efficiently detected from the input / output terminal 4 while the pacing pulse is not generated, and the pacing pulse is input / output. When output from the terminal 4, the after potential of the pacing pulse is rapidly attenuated, and the time during which the input to the R-wave detection circuit must be stopped due to the after-potential becomes extremely short. Decrease. 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, in the pacemaker according to the present invention, the circuit configuration other than the output circuit 56 and the diodes 37 and 38 is not particularly limited, and may have a circuit configuration as shown in FIG. 7, for example.

The circuit shown in FIG. 7 does not include the switching pulse generating circuit 55 and the switching circuit 50 shown in FIG. 1, but includes an absolute value circuit 60 and a pulse lowering 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

If the output signal from the absolute value circuit 60 has a positive polarity,
10 A negative pulse having a positive polarity and a negative polarity as shown in FIG. 10B is input to the input side of the R-wave detection circuit 52. The pulse width (time) T of the negative polarity must be equal to or greater than the influence time of the pacing pulse input from the input / output terminal 4 and the after potential thereof.
Milliseconds. 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, as shown in FIG. 10A, and the maximum waveform potential of the after-potential pacing pulse. V ₂
It is preferably larger than. Then, on the input side of the R-wave detection circuit 52, the pulse shown in FIG. 10B is added to the waveform shown in FIG. 10A corresponding to the pacing pulse and its after potential, and FIG. 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 appears).

Also in such a pacemaker circuit, if the output circuit 56 and the diodes 57 and 58 according to the present invention are connected between the pacing pulse generation circuit 54 and the input / output terminal 4, the same as the embodiment shown in FIG. It has a great effect. 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. 7 is shown in FIG.

In FIG. 11, reference numeral 4a denotes an input / output terminal, and 14a denotes 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 comparator 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. 11 indicates that after detecting an intracardiac electrocardiogram,
This is a one-shot multivibrator for stopping detection for up to 300 milliseconds. This multivibrator 53
In response to the output signal of the comparison circuit 52a, the signal a also has a function of sending a reset signal to the pacing pulse generation circuit 54a and resetting a timer for calculating the pulse interval of the pacing pulse 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 clear from the above description, according to the present invention,
Simply when the intracardiac electrocardiogram is input to the input / output terminal, because the intracardiac electrocardiogram is in the range of ± 20 mV, which is a relatively low voltage range around 0 V, by the action of the output circuit and the reverse-connected diode, The input / output terminals are set to high impedance. Therefore, 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 in a much higher voltage range than the intracardiac electrocardiogram. The output terminal is set to low impedance. As a result, the after-potential is rapidly attenuated within the intracardiac electrocardiogram voltage range around 0 V determined by the forward voltage characteristics of the diode, 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. A circuit having the configuration shown in FIG. 2 was used as the output circuit 56 shown in FIG.
Transistors 30, 32, 33, and 35 use 2SC2459, and transistors 31 and 34 use 2SA1049, and a diode.
37, 38 are Schottky barrier diodes (IS218
1) was used, and a resistor 36 having a resistance of 100 kΩ was used.

A dummy load circuit 2 as shown in FIG. 13 was connected to the input / output terminal 4 of this circuit, and an evaluation test was performed. The output pulse height of the pacing pulse output to 3.
8 V and an output pulse width of 2 ms was obtained. 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 only 55 milliseconds after the output of the pacing pulse. For this reason, an input inhibition time of about 70 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.

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]

1 and 7 are block diagrams of a pacemaker according to one embodiment of the present invention, FIGS. 2 to 6 are circuit diagrams showing modified examples of the output circuit shown in FIG. 1, and FIGS. FIG. 11 is a schematic diagram showing a signal waveform in the middle of the circuit, FIG. 11 is a circuit diagram further embodying the block diagram shown in FIG. 7, FIG. 12 is a graph showing a pacing pulse waveform, and FIG. FIG. 14 is a schematic diagram of an electrocardiogram, FIG. 15 to FIG. 19 are circuit diagrams of a switching circuit used in a pacemaker, FIG.
The figure is a graph showing the influence of the after potential in the circuit of the conventional pacemaker. 4,4a I / O terminal, 37,38 Diode, 50 Switching circuit, 52 R-wave detection circuit, 60 Absolute value circuit, 54 Pacing pulse generation circuit, 55 Switching pulse Generating circuit, 56 ... Output circuit, 62 ... Pulse pull-down circuit.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61N 1/365 A61B 5/0402

Claims (1)

(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 for outputting a pacing pulse from the electrode when the 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 between the pacing pulse generation circuit and the input / output terminal, approximately up to OV or An output circuit having a characteristic of actively outputting a voltage up to a source voltage, and a pair of diodes reversely connected in parallel to each other are connected in this order toward the input / output terminal. pacemaker.