Cardiac pacer
First Claim
1. A heart pacing apparatus comprising a free-running means for generating a heart simulating electrical pulse stimulus having a predetermined interpulse period and pulse duration;
- electrode means comprising means for monitoring the beating action of the heart for detecting the presence of a naturally occuring R-wave and adapted to be positioned relative to the heart for directing said free-running pulse stimulus into the heart for stimulating heartbeat action;
coupling means for interconnecting said electrode means and said pulse stimulus generating means;
amplifier means operatively connected to said monitoring means for initially amplifying said detected R-wave to provide an initially amplified output signal having a predetermined level therefrom when said R-wave is received;
monostable multivibrator means operatively commected to said amplifier means for receiving said initially amplified output signal and generating a singleshot pulse therefrom having a predetermined pulse duration; and
means responsive to said single-shot pulse stimulus for inhibiting the generation of said free-running pulse stimulus to said heart until said one present interpulse period after the last naturally occurring detected R-wave, said monostable multivibrator means comprising at least a first transistor means and a second transistor means operatively connected together for generating said single-shot pulse, said first transistor means providing both additional amplification of said detected R-wave in said amplifier means and cooperating with said multivibrator means second transistor means for raising said level of said initially amplified output signal to a predetermined value to cause said multivibrator means to provide said single-shot pulse;
whereby said naturally occurring R-wave inhibits the generation of said stimulating pulse and synchronizes the timing of the next succeeding stimulating period.
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Abstract
An implantable demand cardiac pacer provides a stimulating pulse determined by a free-running multivibrator. The heartbeat is monitored to detect the presence of a naturally occurring R-wave in order to inhibit the generation of the pulse stimulus until one preset interpulse period after the last naturally occurring detected R-wave. A monostable multivibrator is responsive to the detection of the natural R-wave so as to cause the inhibition of the generation of the pulse stimulus provided by the free-running multivibrator to the heart, such as by preventing the passage of the pulse that closes a transistor switch in the output circuit of the pacer so as to prevent the passage of the generated stimulus to the heart or by injecting a charge in the firing circuit of the free-running multivibrator so as to duplicate the end-of-pulse condition of the free-running multivibrator and, thus, resynchronize the firing thereof. Such a stimulator may also utilize a tripolar arrangement of electrodes having a sensing anode, a stimulating anode and a common cathode so as to optimize the placement of the various electrodes with respect to the heart.
7 Citations
20 Claims
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1. A heart pacing apparatus comprising a free-running means for generating a heart simulating electrical pulse stimulus having a predetermined interpulse period and pulse duration;
- electrode means comprising means for monitoring the beating action of the heart for detecting the presence of a naturally occuring R-wave and adapted to be positioned relative to the heart for directing said free-running pulse stimulus into the heart for stimulating heartbeat action;
coupling means for interconnecting said electrode means and said pulse stimulus generating means;
amplifier means operatively connected to said monitoring means for initially amplifying said detected R-wave to provide an initially amplified output signal having a predetermined level therefrom when said R-wave is received;
monostable multivibrator means operatively commected to said amplifier means for receiving said initially amplified output signal and generating a singleshot pulse therefrom having a predetermined pulse duration; and
means responsive to said single-shot pulse stimulus for inhibiting the generation of said free-running pulse stimulus to said heart until said one present interpulse period after the last naturally occurring detected R-wave, said monostable multivibrator means comprising at least a first transistor means and a second transistor means operatively connected together for generating said single-shot pulse, said first transistor means providing both additional amplification of said detected R-wave in said amplifier means and cooperating with said multivibrator means second transistor means for raising said level of said initially amplified output signal to a predetermined value to cause said multivibrator means to provide said single-shot pulse;
whereby said naturally occurring R-wave inhibits the generation of said stimulating pulse and synchronizes the timing of the next succeeding stimulating period.
- electrode means comprising means for monitoring the beating action of the heart for detecting the presence of a naturally occuring R-wave and adapted to be positioned relative to the heart for directing said free-running pulse stimulus into the heart for stimulating heartbeat action;
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2. An apparatus in accordance with claim 1 wherein said free-running means comprises astable multivibrator means comprising resistance means and capacitance means, said multi-vibrator means having an associated RC time constant determining said interpulse period, said apparatus further comprising a DC source, said stimulus being dependent on said DC source value.
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3. An apparatus in accordance with claim 1 wherein said interpulse period is substantially within the range of 0.5 to 1.2 seconds.
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4. An apparatus in accordance with claim 1 wherein said free-running means comprises astable multivibrator means comprising resistance means and capacitance means for providing an associated RC time constant and at least one transistor means having an associated base-to-emitter voltage being present in said transistor means immediately after the termination of said free-running pulse stimulus, said RC time constant providing said interpulse period, said responsive inhibition means comprising means for injecting a charge onto said capacitance means in response to the generation of said single-shot pulse, said charge being equiValent to the charge present on said capacitance means immediately upon the completion of the generation of said free-running pulse stimulus;
- whereby said free-running pulse stimulus generation is inhibited at least until the subsequent expiration of one free-running interpulse period.
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5. An apparatus in accordance with claim 4 wherein said injection means injects said charge onto said capacitance means in response to the generation of said single-shot pulse each time a naturally occurring R-wave is detected, whereby the generation of said free-running pulse stimulus is inhibited until said one preset interpulse period after the last naturally occurring R-wave.
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6. An apparatus in accordance with claim 4 wherein said charge injection means comprises another capacitance means, said capacitance means being operatively connected to the output of said monostable multivibrator second transistor means, said other capacitance means being operatively connected to said associated astable multivibrator capacitance means for injecting said charge onto said capacitance means, said charge having been stored on said other capacitance means during said interpulse period, said stored charged being diminished each time said monostable multivibrator generates said single-shot pulse, said stored charge being replenished during a predetermined minimal charging interval to a predetermined value to enable said charge to be injected onto said capacitance means, said other capacitance means being coupled to said capacitance means through a gating means having a minimum bias potential, said charge not being injected when said stored charge is not replenished to at least said bias potential value, whereby said free-running pulse generation will not be inhibited.
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7. An apparatus in accordance with claim 1 wherein said apparatus further includes refractory means interposed between said amplifier means and said monostable multivibrator means for preventing said amplifier output signal from causing the generation of said single-shot pulse for a predetermined refractory period, said refractory period being dependent on an RC time constant associated with said refractory means.
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8. An apparatus in accordance with claim 1 wherein said apparatus further comprises means operatively connected to said amplifier means input for applying a gating signal thereto to obstruct said amplifier operation until the termination of a free-running generated pulse stimulus, whereby said monostable multivibrator single-shot pulse generation is inhibited until the conclusion of said free-running pulse stimulus.
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9. An apparatus in accordance with claim 1 wherein said free-running means comprises astable multivibrator means comprising resistance means and capacitance means for providing an associated RC time constant, said time constant determining said interpulse period;
- said capacitance means charging to a predetermined firing value for actuating said astable multivibrator means;
said apparatus further comprising rate sensitive triggering means interposed between said monostable multivibrator means and said astable multivibrator means for triggering said astable multivibrator means substantially at the beginning of said generated single-shot pulse irrespective of said astable multivibrator means time constant, said astable multivibrator means generating said stimulating pulse to charge said capacitance means to a value equivalent to said spontaneous firing value when triggered by said rate sensitive triggering means, whereby the timing of said astable multivibrator free-running interpulse period is synchronized with the detection of said naturally occurring R-wave.
- said capacitance means charging to a predetermined firing value for actuating said astable multivibrator means;
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10. An apparatus in accordance with claim 9 wherein said responsive inhibition means comprises means operatively connected between said astable multivibrator means and said coupling means to inhibit the passage of said free-running stimulating pulse to said electrode means in response to the generation of said single-shot pulse, said single-shot pulse being opposite in polarity to and greater in duration than said free-running stimulating pulse for inhibiting said coupling means from passing said generated free-running stimulating pulse to said electrode means.
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11. An apparatus in accordance with claim 10 wherein said coupling means comprises a transistor switch and said passage inhibition means comprises means for biasing said switch in an open condition wherein said electrode means and said free-running multivibrator means are uncoupled.
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12. An apparatus in accordance with claim 11 wherein said biasing means comprises means having an impedance of a value to assure that the potential of the output pulse of said free-running multivibrator is less than the level required to being said transistor switch into conduction, said switch coupling said electrode means to said free-running multivibrator only when in said conduction condition.
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13. An apparatus in accordance with claim 11 wherein said coupling means further comprises additional transistor amplifier means.
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14. An apparatus in accordance with claim 13 wherein said amplifier means is a Darlington type current amplifier means.
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15. An apparatus in accordance with claim 9 wherein said rate sensitive triggering means includes capacitance means chargeable to a predetermined value to trigger said astable multivibrator means during said single-shot pulse interpulse period, the recharging time constant of said capacitance means being longer than the discharge time constant thereof, said charge being diminished each time said monostable multivibrator means generates said single-shot pulse and being replenished during said interpulse period to a predetermined value to trigger said astable multivibrator means, said triggering value only being obtained when the charging interval is substantially equivalent to at least said interpulse period, said astable multivibrator means being free-running at a predetermined rate having the desired interpulse period.
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16. An apparatus in accordance with claim 1 wherein said electrode means comprises a sensing anode operatively connected to said amplifier means, for providing said detected R-wave to said amplifier means a stimulating anode operatively connected to said coupling means for providing said stimulus pulse to said heart and a common cathode connectable to said heart, said stimulating pulse being provided between said stimulating anode and said cathode and said detected R-wave being sensed between said sensing anode and said common cathode, whereby a tripolar R-inhibited demand pacer is provided.
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17. An apparatus in accordance with claim 1 wherein said amplifier means comprises a plurality of transistor means having gain.
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18. An apparatus in accordance with claim 17 wherein said amplifier means and said multivibrator means first transistor means comprises at least three stages of gain.
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19. An apparatus in accordance with claim 17 wherein said apparatus further comprises means for biasing said plurality of transistor means.
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20. An apparatus in accordance with claim 17 wherein each of said plurality of transistor means comprises a common emitter configuration.
Specification