US 3345990 A
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Oct. 10, 1967 a. v. BERKOVITS HEART-BEAT FACING APPARATUS Filed June 19, 1964 4 Sheets-Sheet l v m a 0 R 2 O E 2 2 0 P 1% D Ewm mm m w M w m 2 A w W 8 4 H L a M .2 w 0 R f G A 4 N m B a Em mg a N WMW 0 2 Dr I m w E T G W R S m Q F P L P lllllllllnlll m M 2 A T R S 2 Q P w 2 g T R ATTORNEY Oct. 10,1967 A B. v. BERKOVITS 3,345,990
HEART-BEAT FACING APPARATUS Filed June 19, 1964 4 Sheets-Sheet 2 ma M6 INVENTOR BAROU H V. BERKOVlTS ATTORNEY Oct. 10, 1967 s. v. BERKovrrS HEART-BEAT PAC ING APPARATUS Filed June 19, 1964 4 Sheets-Sheet 3 INVENTOR BAROUH v. BERKOVITS ATTORNEY Oct. 10, 1 967 B. v. BERKOVITS HEART-BEAT FACING APPARATUS Filed June 19, 1964 4 Sheets-Sheet 4 INVENTOR, BAROUH V. BERKOVITS 5W WA ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE A heart pacing apparatus which provides electrical heart-stimulating impulses to the patients heart only in the absence of natural heartbeats. If only a single natural heartbeat is absent only a single electrical impulse will be provided. If more than one natural heartbeat is missing, an equal number of electrical impulses will be provided. No matter how many electrical stimuli are generated, they occur at essentially the same time spacing from each other and from the last natural heartbeat as would be the case if they were all natural heartbeats. The apparatus is arranged normally to generate electrical impulses at predetermined time intervals approximately the rate of the heartbeat. Upon detection of a natural heartbeat the next electrical stimulus which would otherwise be generated is inhibited. At the same time, the apparatus restarts its timing cycle so that the next electrical impulse will be generated (it needed) after the predetermined time interval has elapsed, starting with the heartbeat just detected. The result is an overall integrated operation, i.e., a mutually exclusive cooperation of the natural heartbeats and stimulating pulses.
This invention relates to novel and improved electronic equipment for use in the treatment of persons suffering from cardiac disorders.
Electronic apparatus which can be operated in conjunction with electrocardiograph means for monitoring the heartbeat of persons suffering from cardiac disorders has been known for some time. Also, apparatus capable of providing electrical stimualtion of an abnormal heart to achieve a pacing or other corrective function with respect to the action of the heart has also been known. However, prior to the present invention, no heart pacing apparatus has been adapted to provide electrical stimulation of an abnormal heart in a manner which has satisfactorily integrated stimulated action of the heart with natural heart-beat action.
It is an object of this invention to provide a novel and advantageous apparatus for use in monitoring and pacing the heartbeat of persons suffering from cardiac disorders. It is also an object of this invention to provide electronic means for accurately monitoring the beating action of the human heart; to provide means which can effect corrective electrical stimulation of the beating action of an abnormal heart; and to provide such means which can antomatically effect such corrective heart stimulation only where required as determined by the heart-monitoring means. It is an important part of this invention to provide such an apparatus which can furnish heart-stimulating electrical impulses to an abnormal heart in such a manner that stimulated heartbeats can be closely integrated with natural heartbeats so that stimulated and natural heart action can each contribute to maintenance of a desirable heartbeat rate. A further object of this invention is to furnish stimulation to an abnormal heart in such a manner that heartbeats are individually stimulated and closely integrated with natural heartbeats so natural and stimulated heart action can each contribute to maintenance of a desirable heart-beat rate.
Patented Oct. 10, 1967 Other objects, advantages and details of the 'heart monitoring and pacing apparatus of this invention appear in the following detailed description of a preferred embodiment of the invention, the description referring to the drawings in which:
FIG. 1 is a block diagram illustrating basic components of the apparatus provided by this invention;
FIG. 2 is a graph indicating the shape of electrical waves produced by the heart during normal heart-beat action;
FIG. 3 is a schematic diagram of an amplifier means embodied in apparatus of FIG. 1;
FIG. 4 is a schematic diagram illustrating pulse generating means incorporated in the apparatus of this invention; and
FIG. 5 is a schematic diagram illustrating the heart stimulating means embodied in the apparatus of this invention.
Referring generally to FIG. 1, the heart pacing apparatus of this invention includes means 10 for monitoring the natural beating of a patients heart and also in cludes heart-stimulating means 12 adapted to provide electrical impulses to the heart for stimulating heart-beat action. Themonitoring means furnishes control signals in response to the occurrence of natural heartbeats, and the heart stimulating means are regulated by these control signals for stimulating the heart only when required for maintaining the heartbeat at a desired rate; That is, the heart stimulating means are regulated to provide an electrical impulse to stimulate an individual heartbeat on demand whenever an individual natural heartbeat does not occur at the proper interval thereby to closely integrate stimulated and natural heartbeats so that each can contribute to maintenance of the desired heart-beat rate.
As shown in FIG. 1, the monitoring means 10 includes means 14 for detecting electrical signals developed by the heart during natural heart-beat action and means 16 for amplifying these natural heart signals. The monitoring means also includes pulse generating means 18 which are responsive to said amplified signals for sending control signals to the heart stimulating means 12 at a frequency determined by the heart-beat rate. If desired, oscilloscope means 20 and audible signal means 22 can also be arranged to be responsive to said amplified signals or control signals for visually and audibly indicating the occurrence of natural and stimulated heartbeats. Similarly, a rate meter means 24 can be arranged to be responsive to said amplified or control signals for indicating the patients heart-beat rate. The monitoring means 10 and the heartstimulating means 12 are each connected to a suitable power source (not shown) in conventional manner.
It will be understood that natural beating action of the heart produces electrical signals or waves which are, respectively characteristic of successive steps in the occurrence of each heart beat. Thus a heart beating in normal or sinus rhythm produces electrical waves conventionally identified as P, Q, R, S and T waves as shown in FIG. 2, the R Wave for example being characteristic of ventricle contraction in the heart. In conventional practice, electrocardiograph means are adapted by means of electrodes attached to the wrists, ankles, chest or other parts of a patients body for detecting and for transmitting or recording these characteristic heart waves. In a similar way, the apparatus provided by this invention includes such an electrocardiograp-h means for deteeting a patients heart waves. Output leads 28 and 30 extending therefrom are arranged to transmit electrical signals corresponding to said heart waves. As the electrocardiograph means can be completely conventional, it is diagrammatically illustrated in FIG. 1 only by the block 14- but it will be understood that this block represents any conventional electrocardiograph means or the like which is adapted to detect heart waves and to provide electrical signals corresponding to said heart waves. In accordance with this invention as hereinafter described, a voltage peak such as that provided by the R wave is to be employed in actuating pulse generating means 18. Accordingly, simplified polarity-reversing switch means 32 are preferably interposed in leads 28, 30 for facilitating selection of a positive or negative voltage peak to be used for this purpose.
As indicated at 16 in FIG. 1, the signals received from the electrocardiograph means 14 through leads 28 and 30 are preferably amplified in conventional manner for the purposes of this invention. For example, in a preferred embodiment of this invention as shown in FIG. 3, the amplifier 16 includes a series of twin triodes 34, 36 and 38, each comprising a tube of the 12AX7 type. The cathodes of such tubes are heated by a conventional heater and heater energizing circuit (not shown). These twin triodes are arranged as push-pull amplifiers and are resistance-capacitance coupled to operate together as a cascade amplifier.
In the arrangement, the leads 28, 30 connect to the grids of the first twin triode 34 through resistors 40, 42 and also connect to ground through neon tubes 44, 46 and through resistors 50, 52 thereby to isolate the triode grids from undesirable transient voltages. The cathodes of tube 34 connect 'to the negative supply represented herein by the lead 54 through biasing resistors 56, 57 and 58 and a fixed bias means comprising the battery 60, switch 62 and resistors 64, 66 are connected between the cathodes. Each plate of triode 34 is connected to a positive plate supply represented herein by the lead 68 through respective plate load resistors 70, 72 and balancing potentiometer 74. Plate circuit decoupling is provided through by-' pass capacitors 76, 73. These plates are coupled to the grids of tube 36 through capacitors 80, 82 and resistors 84, 86. Appropriate grid bias potential is applied to said grids through resistors 88, 90, connected to ground while the cathodes of tube 36 are connected to the negative supply 54 through the common bias resistor 92. The plates of tube 36 connect to the positive supply 68 through plate load resistors 94, 96. Filter capacitor 98 is connected between the plates to discriminate against high frequency components in the amplified'wavesA neon bulb 100 is also preferably connected between the plates of tube 36 for limiting the output of the tube should potential difference between the plates rise above the breakdown potential of said bulb. The plates of tube 36 are coupled to the grids of tube 38 through capacitors 102, 104 and through parts of the variable potential dividers 1'06, 108 which are mechanically coupled together to serve as an amplifier gain control. Grids bias potential is applied through resistors 106, 108. The cathodes of tube 38 connect to the negative supply through common bias resistor 110 and the plates of the tube connect to the positive supply through plate load resistors 112, 114 and the variable voltage divider 116. Leads 118, 120 directly connect the plates of the triodes 38 to one pair of deflecting plates of the oscilloscope 22 for providing a visual display of the heart waves detected by the electrocardiograph means 14. The voltage divider 116 can serve as center control for the oscilloscope as will be understood. As operation of the oscilloscope can be completely conventional, details of the oscilloscope are not shown herein. It should also be understood that a particular amplifier has been described herein by way of illustration and that other conventional amplifier means could also be employed within the scope of this invention.
In a preferred embodiment according to this invention, the pulse generating means 18 includes a triode clipper 122 which preferably comprises a tube of the 12AX7 type as shown in FIG. 4. One grid of this tube shown at the left in the drawings is coupled to the output ofthe amplifier 16 through the lead 124 and capacitor 126,
operating grid bias being supplied through resistor 128. The plate of the left hand tube section connects to the positive supply 68 and the cathode connects to ground through the resistor 130. Since the value of resistor in the cathode-to-ground path of this section of tube 122 is high a small current therethrough develops sufficient bias which when applied to the grid through resistor 128 biases the tube substantially to cut off so that negative going pulses applied to the grid have substantially no effect on its anode current. However, a positive going pulse of sufiicient amplitude applied to the grid through capacitor 124 overcomes such bias and causes a current pulse of substantial magnitude to flow through resistor 130 developing a substantial positive pulse with respect to ground at point A which is coupled to the grid of the right hand section of tube 122 through series resistor 134 and coupling capacitor 132. As the maximum voltage peak developed by the heart may be either positive or negative, the switch 32 can be employed to select the desired voltage peak to render the left hand section of the tube 122 conductive for a brief period once during each heart beat.
The output of the left hand tube section is coupled to the grid of the right hand tube section through capacitor 132 and resistor 134. Resistors 136 and 138 provide a grid bias and a fixed bias is supplied to the grid from the negative supply 5-4 through resistor 140. The plate of the right hand tube section connects to the positive supply through the plate load resistor 142 and the cathode connects to ground through resistor 144. Preferably, diode 146 is employed for clamping the grid to a selected potential. The grid in the right hand tube section is normally biased beyond cut-off but this bias is reduced when the left hand tube section conducts to permit conduction through the right hand tube section, thereby to amplify the clipped wave formed by the left hand tube section.
In accordance with this invention, the output of the clipper .122 is coupled to a trigger circuit 148 through lead 150. The shunt combination of capacitor 152 and resistor 154 serially connected in said lead produces a high frequency boost to improve the triggering action of pulses coupled to trigger circuit 148, the trigger prefe'rably comprising a twin triode tube of the l2AT7 type. A fixed bias is supplied to the left hand grid of the trigger tube 148 from the negative supply 54 by means of the resistor 1 58. The plates of the trigger connect to the positive supply 68 through respective plate load resistors 162 and the cathodes connect to the negative supply through the common resistor 164. The left hand plate of the trigger tube also connects to right hand grid of the tube through capacitor 166 and resistor 168 and a resistor 170 serves to bias this grid above ground potential. In this arrangement, the left hand section of the trigger tube is normally biased below cut-oft and the right hand section of the tube is conducting. When a heartbeat signal passes the clipper .122, the left hand section of the trigger is momentarily rendered conductive to provide a large pulse on the plate of the left hand tube section. Preferably this plate can be clamped at a selected potentialabove ground by the zener diode 172. If desired, the output lead 174 from the left hand plate of the trigger can connect to audio signal means 22 through lead 175 shown in FIG. 1 for providing an audible signal correspondingin rate to the heartbeat. As the audio signal means can be conventional it will not be further described herein and it will be understood that any of various conventional audio means can be employed for this purpose. It should also be understood that although a particular pulse generator means has been described herein by way of illustration that other pulse generator means could also be used within the scope of this invention.
In accordance with this invention, the integrated heart stimulator 12 includes a double pole triple throw switch 177 which can be manually controlled for selecting the mode of operation for the heart stimulator. When the movable switch arms 178, 180 are set on the fixed contacts 182, 184, respectively, the heart stimulator will not be operative. On the other hand, when the movable arms are set on the fixed contacts 186, 188, the heart stimulator is adapted to provide a continuous series of heart stimulating electrical impulses at a predetermined rate which is independent of natural heartbeats occurring at the same time. Alternatively, when the movable arms are set on the fixed contacts 190, 192 as shown in the arrangement illustrated in FIG. 5, the heart stimulator is adapted to provide heart-stimulating electrical impulses only in closely integrated relation to natural heartbeats as hereinafter described so that stimulated and natural heartbeats can each contribute to maintenance of a predetermined heartbeat rate.
As shown in FIG. 5, the heart stimulator 12 is connected to the positive supply 68 through resistor 194 and through the variable resistor 196 to charge charge-storing means such as the capacitor 198. A diode 200 is also preferably connected to ground in parallel with the capacitor 198. As will be understood, the variable resistor 196 can be adjusted to regulate the time required for charging the capacitor 198 to a predetermined level.
In accordance with this invention, capacitor 198 is connected through the inductance 202 to the plate of a thyratron tube 204 and is also connected to the grid of the thyratron through the biasing resistor 206. The thyratron 204 preferably comprises a tube of the 2D21W type. The grid is also provided with a negative bias from the negative supply 54 through the resistor 208 so that the thyratron is not normally conductive. However the bias applied to the grid through the resistor 206 is adapted to render the thyratron conductive whenever the capacitor 198 has been charged to said predetermined level. The cathode of the thyratron 204 is connected to the thyratron screen and is also connected to ground through a variable resistor 210 and through a parallel neon lamp 211 and resistor 212.
In this arrangement, the capacitor 198 is charged to said predetermined level within a period of time selected by regulation of the variable resistor 196. As the capacitor becomes charged, the plate of tube 204 (normally cut off) becomes increasingly positive. This increasing positive potential is also applied to the tube grid through resistor 206 until the negative bias on that grid is eventually overcome. Then, as the capacitor reaches said predetermined charge level, the values of the anode and grid potential become adjusted relative to each other until the anode path abruptly becomes conductive for automatically discharging the capacitor 198 along a path through the variable resistor 210 and through the neon lamp 212. When the capacitor is substantially completely discharged, the grid of tube 204 again regains control and the tube is again cut-ofl? and rendered non-conductive. This cut-oft action is assisted by the collapse of the field in inductance 202 as the capacitor reaches the point where it is substantially discharged. That is, induced current fiow through the inductance and through diode 200 momentarily depresses the potential on the plate of tube 204 to an extent sufiicient to assure cut-off of the tube 204. This discharge of the capacitor 198 as above described may be considered to be in the nature of a breakdown or avalanche effect. When the thyratron 204 is again rendered non-conductive after discharge of the capacitor, recharging of the capacitor can again occur as will be understood.
Upon firing of the thyratron 204, an electrical impulse is supplied to the primary winding 214 of the transformer 216. Electrodes 218 of any conventional type connected to the primary winding can be employed for applying this electrical impulse to the patients heart or, alternatively, electrodes 220 connected to the secondary winding 222 of the transformer can be employed for applying a much smaller electrical impulse to the patients heart depending upon the turns ratio of the transformer. For example, the electrodes 218 can be employed for applying a relatively large heart stimulating pulse to the patients heart from outside the patients body whereas the electrodes 220 can be surgically connected to the patients heart for applying a relatively smaller electrical impulse directly to the patients heart when desired. The adjustable tap on resistor 210 can be varied to regulate the amplitude of the heart stimulating pulse to be applied through the electrodes 218 and 220. The neon lamp 211 is adapted to glow each time that the capacitor 198 is discharged through the thyratron 204 for indicating that a heartstimulating electrical impulse has been provided. The lamp also serves to limit the amplitude of the pulse applied through the electrodes 218 or 220.
Further in accordance with this invention, lead 174 connects the output of the pulse generator 18 through resistor 224 and capacitor 226 to the grid of a second thyratron 228, this thyratron also preferably comprising a conventional tube of the 2D21W type. As indicated in FIG. 5, the grid of this thyratron tube is also provided with a negative bias from the negative supply 54 by means of the resistors 230 and 232. Preferably, a by-pass capacitor 227 is also connected between the lead 1'74 and ground. The screen of the thyratron 228 is also connected to its cathode. In this arrangement, the second thyratron is disposed between the capacitor 198 and ground but is normally rendered non-conductive by the negative bias applied to its grid. However when an electrical impulse supplied by the pulse generator 18 in response to the occurrence of a natural heart beat is applied to the thyratron grid, the thyratron 228 is rendered conductive and provides another path for discharging the capacitor 198 to ground. The inductance 202 is common to the plate circuits of both thyratrons 204 and 228 and assures that, when either thyratron fires, the thyratron is promptly rendered non-conductive as soon as capacitor 198 is discharged, thereby permitting prompt recharging of the capacitor.
In this system, the capacitor 198 tends to be charged to a predetermined firing level within a selected period of time as determined by the resistance 196 and output characteristics of the power supply. If a natural heart-beat occurs during the time that the capacitor is being charged to this level, the capacitor is immediately discharged through the thyratron 228 without applying any stimulation to the heart. Recharging of the capacitor then begins again. If natural heart beats occur at the desired rate for an extended period of time, the capacitor 198 is repeatedly charged toward a selected level and is then discharged through the thyratron 228 just before the capacitor reaches said firing level. However, if no natural heart-beat occurs during the selected period of time that the capacitor 198 is being charged to the desired level, the capacitor is automatically discharged through the thyratron 204 to apply an electrical impulse to the patients heart through electrodes 218 or 220, thereby to stimulate a single heart beat. This stimulated heart beat will occur at the proper interval in place of the omitted natural heart beat. The capacitor is then recharged to be discharged through the thyratron 228 or the thyratron 204 as regulated by the occurrence or absence of natural heart beats. In this way, each electrical impulse applied to the patients heart occurs only at a predetermined time after the last natural or stimulated beat of the heart. If no natural heart beats occur for an extended period of time, the capacitor 198 is repeatedly charged and then discharged through the thyratron 204 for maintaining the patients heart beat at the desired rate. In this way it can be seen that, with the switch arms 178, 180 set on contacts 199, 192, the heart stimulator 12 is adapted to provide heart-stimulating electrical impulses to a patients heart in such a way that all stimulated heart beats are properly integrated with natural heart beats, whereby the stimulated and natural heart beats can cooperate in maintaining a desired heart beat rate. Of course when the switch arms 178, 180 are set on the contacts 186, 188 for selecting an alternate mode of operation, thyratron 228 cannot function to discharge the capacitor 198 and the heart stimulator 12 can provide a series of heartstimulating electrical impulses to a patients heart at a selected rate which is independent of the occurrence or absence of natural heart beats as will be understood.
In a practical embodiment of this invention, the components of the described apparatus can have the following values.
40, 42, 56, 58, 84, 86, 144 ohms 1K 164 do 18K 134 do 33K 110, 130, 160, 210 do 100K 116, 196 do 250K 140 do 820K 64, 66 do 1.25 158, 208 do 2.2 206 do 3.3 230 do 15 212 do K 194 do 22K 112, 114, 138, 162 do 47K 142 do 220K 57, 70, 72, 92 do 470K 74, 94, 96, 128, 224, 232 rnegohms 1 170 do 1.5 106, 108 do 2.5 50, 52, 88, 90, 136, 154, 168 do 10 Capacitors:
98 microfarads .0047 227 do .05 80, 82, 152, 166, 226 do .1 126 do .47 102, 104, 132 do 2 76, 78, 198 do- 10 Tubes (type):
44, 46, 100 105014 211 10501- 34, 36, 38, 122 12AX7 148 12AT7 146 IN2069 200 IN2071 177 2A22B 204, 228 2D21W Inductance: 202 microhenries 100 It should be understood that although a particular embodiment of this invention has been describedin detail by way of illustration, this invention includes all modifications and equivalents thereof which fall within the scope of the appended claims.
1. A heart pacing apparatus comprising means monitoring beating action of the heart, pulse generating means responsive to said monitoring means for providing an electrical impulse with the occurrence of each natural heartbeat, a capacitor, means repeatedly charging the capacitor to a predetermined level within a selected period of time, electrodes adapted to be positioned relative to the heart to direct a heart-stimulating electrical impulse into the heart for stimulating heart-beat action, thyratron means connected to the capacitor and coupled to said electrodes to automatically discharge the capacitor when the capacitor is charged to said predetermined level for directin a heartbeat stimulating electrical impulse to said heart through said electrodes, a second thyratron means connected between said capacitor and ground, said second thyratron means being rendered conductive by an electrical impulse from said pulse generating means for discharging said capacitor to ground without stimulating heart-beat action on the occurrence of a natural heartbeat.
2. A heart pacing apparatus comprising means monitoring the beating action of a patients heart, electrode means connected to the patient, charge-storing means, means charging said charge-storing means to a selected charge level within a predetermined period of time, thyratron means automatically responsive to charging of said charge-storing means to said selected charge level for discharging said charge-storing means along one path to apply a heart-stimulating electrical impulse to said patients heart through said electrode means and to immediately restore said charge-storing means to a discharged condition, and thyratron means responsive to said monitoring means when a natural beat of said patients heart occurs for discharging said charge-storing means along a second path to immediately restore said chargestoring means to said discharged condition without applying a heart-stimulating electrical impulse to said patients heart.
3. A heart pacing apparatus comprising electrode means for connection to a patient, pulse generating means normally operative to continuously supply electrical pulses to said electrode means, each pulse separated from the preceding pulse by a predetermined time interval, means for connection to said patient for monitoring the beating action of said patients heart, and means responsive to the detection of a heartbeat by said monitoring means for inhibiting the generation of only the next electrical pulse otherwise generated by said pulse generating means, said pulse generating means being operative to generate subsequent electrical pulses in time step with said detected heartbeat following the inhibiting of the generation of said only next otherwise generated pulse.
4. A heart pacing apparatus in accordance with claim 3 wherein said pulse generating means includes a charging circuit, means responsive to said charging circuit charging to a first predetermined level for deriving an electrical pulse and for discharging said charging circuit, and means responsive to the discharging of said charging circuit to a second predetermined level for initiating the charging of said charging circuit, and wherein said inhibiting means include an additional means for discharging said charging circuit.
5. A heart pacing apparatus comprising electrode means for connection to a patient, pulse generating means normally operative to continuously supply electrical pulses to said electrode means, each pulse separated from the preceding pulse by a predetermined time interval, means for connection to said patient for monitoring the beating action of said patients heart, and means responsive to the detection of a heartbeat by said monitoring means for controlling said pulse generating means to generate a pulse immediately, prior to the normal generation of the next pulse, and to thereafter generate said pulses separated by said predetermined time interval starting with said immediately generated pulse, said controlling means being further operative to prevent the supply of said immediately generated pulse to said electrode means.
6. A heart pacing apparatus in accordance with claim 5 wherein said predetermined time interval is slightly greater than the time interval between two normal heartbeats.
7. A heart pacing apparatus comprising electrode means for connection to a patient, means for connection to said patient for monitoring the beating action of said patients heart, a charging circuit including a capacitor and means for supplying charging current to said capacitor, first breakdown means normally operative for pcriodically discharging said capacitor and for coupling the discharge current of said capacitor to said electrode means, said first breakdown discharging means being operative to discharge said capacitor to a predetermined level and for thereafter allowing said charging current supplying means to initiate the charging of said capacitor, and second breakdown means responsive to the detection of a single heartbeat by said monitoring means for discharging said capacitor within a fraction of the time between natural heartbeats to a predetermined level and for thereafter immediately allowing said charging current supply means to initiate the charging of said capacitor, said second breakdown discharging means being operative to inhibit the operation of said first breakdown discharging means and the coupling of the capacitor discharge current to said electrode means.
8. A heart pacing apparatus comprising electrode means for connection to a patient, means for connection to said patient for monitoring the beating action of said patients heart, an electrical impulse generator operative to selectively supply heart-stimulating electrical impulses to said electrode means, and means for controlling the supply of each of said heart-stimulating electrical impulses the same predetermined time interval after either the last heartbeat as determined by said monitoring means or the last generated impulse, Whichever of said last heartbeat or last generated impulse occurred later.
9. A heart pacing apparatus in accordance with claim 8 wherein said controlling means includes means for preventing the generation of only the next electrical impulse which would otherwise be generated responsive to the detection of a natural heartbeat.
References Cited UNITED STATES PATENTS 3,241,556 3/1966 Zacouto 128-421 FOREIGN PATENTS 826,766 1/ 1960 Great Britain.
W. E. KAMM, Assistant Examiner.