An atrial-ventricular demand pacemaker having improved atrial pulse artifact rejection includes a blanking circuit (30, 100) connected in the signal path from the ventricular output terminal (17) to the sensing amplifier (21) to blank the signal during an atrial pulse. A holding circuit including a low-pass filter (46, 137) and a switching element (43, 112) stores a prior signal value at the sensing amplifier input during the blanking interval, and delays return to normal operation until after the blanking circuit has returned to normal. Artifact rejection is also improved by limiting atrial pulse output circuit recharge time and by limiting polarization current driven into the ventricular output circuitry by an atrial output pulse.
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1. A heart pacemaker comprising:
terminal means for connection to a patient's means for delivery atrial and ventricular stimulation thereto; generating means for delivering sequential atrial and ventricular electrical stimulation pulses to said terminal means at a predetermined repetition rate; a sensing amplifier for sensing electrical signals indicative of the patient's heartbeat; blanking means for normally connecting said terminal means to said sensing amplifier for conveying the patient's heartbeat signals thereto, and for selectively decoupling said sensing amplifier from said terminal means during delivery of an atrial stimulation pulse, said blanking means including holding circuit means operative during a blanking interval to hold a prior signal level at the input to the sensing amplifier, and timing means for sequentially returning the blanking means and the holding means to normal operation at the end of the atrial stimulation pulse.
2. A heart pacemaker comprising:
terminal means for connection to a patient's heart for delivering atrial and ventricular stimulation thereto; generating means for delivering sequential atrial and ventricular electrical stimulation pulses to said terminal means at a predetermined repetition rate; a sensing amplifier for sensing electrical signals indicative of the patient's heartbeat; demand control means connected to said sensing amplifier and operative for preventing delivering of said stimulating pulses if a heartbeat occurs within a predetermined time interval following a preceding heartbeat; means for providing a signal path from said terminal means to said sensing amplifier, said signal path means including a first switching means for selectively preventing the passage of signals along the signal path; signal holding means including a capacitor connected to said signal path means between said switching means and the sensing amplifier, and a second switching means operatively connected to selectively isolate said capacitor from said signal path and said first switching means and to thereby hold a prior signal at the input of said sensing amplifier; and timing means operatively connected for actuating said first and second switching means during delivery of an atrial pulse to block said signal path and hold a prior signal at said sensing amplifier, whereby atrial
pulse artifact is prevented from entering the sense amplifier. 3. A heart pacemaker according to
4. A heart pacemaker according to
5. A heart pacemaker according to
6. A heart pacemaker according to
7. A heart pacemaker comprising:
terminal means for connection to a patient's heart for delivering atrial and ventricular stimulation thereto; generating means for delivering sequential atrial and ventricular electrical stimulation pulses to said terminal means at a predetermined repetition rate; a sensing amplifier for sensing electrical signals indicative of the patient's heartbeat; demand control means connected to said sensing amplifier and operative for preventing delivery of said stimulating pulses if a heartbeat occurs within a predetermined time interval following a preceding heartbeat; blanking means for normally connecting said terminal means to said sensing amplifier for conveying the patient's heartbeat signals thereto, and for selectively decoupling said sensing amplifier from said terminal means during delivery from said terminal means during delivery of an atrial stimulation pulse, said blanking means including holding circuit means operative during a blanking interval to hold a prior signal level at the input to the sensing amplifier.
8. A heart pacemaker according to
the end of the atrial stimulation pulse. 9. A heart pacemaker comprising pulse generator means for generating electrical stimulation pulses in a first chamber of a heart; storage means for temporarily storing representations of natural electrical heartbeat signals occurring in a second chamber of a heart; sensing means coupled to said storage means for sensing said natural electrical heartbeat signals; circuit path means for coupling said signals to said storage means comprising capacitive coupling means associated with said path through which said signals are transmitted; terminal means for coupling said stimulation pulses from said pulse generator to the first chamber of the heart and for coupling said signals from the second chamber of the heart to said circuit path means; blanking means comprising timing means for timing out a first and a second period of time, means for preventing the transmission of signals through said circuit path means for said first period of time that begins prior to the generation of an electrical stimulation pulse and lasts until after the termination of said pulse, means for preventing further storage in said storage means for said second period of time which begins before the termination of said first period and lasts until after the termination of said first period; and discharging means for discharging said capacitive coupling means after the generation of a stimulation pulse before the termination of said first period of time. 10. A heart pacemaker as claimed in claim 9 wherein said circuit path means comprises resistive means coupled to said capacitive coupling means; said capacitive means and said resistive means are coupled together so as to provide signal differentiation for said signals, and said storage means provide signal integration. |
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This invention pertains to the field of electronic heart pacemakers. More specifically the invention pertains to improvements in atrial-ventricular demand pacemakers to improve their operation by decreasing the possibility that an atrial stimulation pulse artifact will be sensed as a ventricular depolarization by the sense amplifier of the ventricular demand circuitry of the pacemaker.
Of the numerous different types of electronic heart pacemakers and their corresponding various modes of operation which have been proposed in the art, the present invention is primarily directed to atrial-ventricular sequential pacemakers operating on a demand basis, either in an implantable or external device. In a demand type pacemaker, a predetermined minimum heart beat rate is established, with its corresponding maximum interval between successive heart beats. The minimum heart beat rate itself may be adjustable or programmable as is generally known in the art, but once it is set the pacemaker will operate in accordance with the selected or programmed rate. So long as the rate of the heart remains above the minimum rate, the stimulating pulse generating circuits are inhibited or reset and the pacemaker does not deliver any stimulating pulses to the heart. However, if the time interval between successive heart beats becomes greater than the selected amount corresponding to the minimum rate, the pacemaker delivers a stimulating pulse to the heart so as to support the heart at or above the preselected minimum rate. In order to provide the demand mode of operation, sensing means are provided for detecting a spontaneous ventricular depolarization. The sensing means generally includes a sense amplifier having an input connected to the ventricular stimulating electrode so that the electrical activity associated with a ventricular depolarization is picked up by the ventricular electrode and conveyed back to the pacemaker where it is applied to a sense amplifier. The sense amplifier generally contains electrical filtering networks which tailor the frequency of response of the amplifier for good sensitivity to the QRS wave complex of the electrocardiogram while rejecting other portions of the electrocardiogram.
Additionally, in the case of an atrial-ventricular pacemaker, the sense amplifier must be capable of rejecting the atrial stimulating pulse delivered by the pacemaker. The atrial stimulation pulse, delivered by the pacemaker through a separate lead to the atrium of the heart, may be conducted through body tissues and picked up by the ventricular lead, from which it is conducted to the sense amplifier. The magnitude of the atrial pulse thus picked up is typically many times that of the QRS wave, complicating the design of the sense amplifier discriminating circuits. Usually, a combination of electronic filtering to adjust the frequency response of the sense amplifier and establishing a minimum lead separation between the locations of the atrial and ventricular stimulation electrodes in the heart is required for proper operation. Unfortunately, this may require tuning the frequency response of the sense amplifier to less than optimum for the QRS wave in order to provide adequate rejection of the atrial pulse. A further disadvantage is that lead separation of electrodes within the heart may be difficult to achieve and maintain, especially if there is a possibility that a lead may be dislodged or moved slightly subsequent to the implantation.
In order to overcome these and other problems, the present invention provides for blanking the sense amplifier during delivery of an atrial pulse so that it will not be affected thereby. The blanking is achieved through switching circuits rcharge recharge resistor 87 was increased from 4.7 kilohms to 10 kilohms. Output capacitor 90 was reduced to hold the recharge time constant at a reasonable value of approximately 0.22 seconds. Further it has been found that a single output capacitor 90 can be used instead of back-to-back output capacitors that were used in a prior art circuit.
The presently preferred embodiment of the circuit of FIG. 4 includes the following components.
| ______________________________________ |
| R85 20 kilohm |
| R87 10 kilohm |
| C90, C83 22 microfarad |
| R101 30 kilohm |
| C102 .01 microfarad |
| R106 390 kilohm |
| C107 1000 picofarad |
| R110, R114 4.3 megohm |
| C113 390 picofarad |
| R115 750 kilohm |
| C117 6800 picofarad |
| R131, 133, 135 82 kilohm |
| 141, 143, 145 |
| C132, 137 .039 microfarad |
| C139 .33 microfarad |
| C142 .022 microfarad |
| C147, 155 0.1 microfarad |
| C149 .056 microfarad |
| C150 .02 microfarad |
| R152, 154 100 kilohm |
| R156 200 ohms |
| Transistors 103. |
| 112 2N 4338 |
| ______________________________________ |
Operational Amplifiers 104, 136, 146, 151; Texas Instruments TL064 or equivalent.
A circuit built according to the above preferred embodiment produces superior results in terms of atrial output pacing artifact rejection, even with large atrial output signals and minimum atrial and ventricular lead separation. While the above presently preferred embodiment gives satisfactory performance, it will be understood that additional circuit changes can be made depending upon the type of pacemaker, circuitry involved. For example, input blanking FET switch 103 and associated components could be eliminated, and sense output FET switch 112 would still provide blanking of the output from the preamplifier, to provide satisfactory operation. Also, the turn-on time delay to FET switch 112 could be shortened, and the changes in the values in the ventricular and atrial output circuits could also be varied while still maintaining satisfactory operation, and in any event improved operation over a pacemaker circuit with no atrial pulse blanking or recharge current limiting. While the preferred embodiment shown uses bipolar outputs of the pulse generators, the invention is applicable to pacemakers using unipolar outputs also.
As mentioned above, the invention can be used with a dual demand pacemaker, in which case an additional blanking circuit would be used between the atrial output terminal and the input to the additional sense amplifier that controls resetting of the atrial pulse generator in a dual demand pacemaker. The component values and time constants would be altered, of course, for the additional blanking circuit and sense amplifier, so that the desired result of sensing atrial depolarizations while rejecting ventricular pulse artifact would be achieved, along with the atrial artifact rejection as described above.
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