Atrial And Ventricular Demand Pacer With Separate Atrial And Ventricular Beat Detectors

Abstract

An atrial and ventricular pacer in which competition between spontaneous atrial activity and atrial stimulation is prevented. In the conventional type atrial and ventricular pacer, the detection of a QRS wave re-starts both the atrial and ventricular timing circuits, but spontaneous atrial activity does not inhibit the generation of an atrial stimulating pulse. In the description of an illustrative embodiment contained herein, by preventing the generation of such a pulse when a spontaneous atrial beat is detected the batteries have a longer life.

Parent Case Text

This application is a continuation-in-part of my co-pending application, Ser. No. 884,825, filed on Dec. 15, 1969 and which has matured into U.S. Pat. No. 3,661,158.

Description

This invention relates to atrial and ventricular pacers, and more particularly to such pacers in which competition between spontaneous atrial activity and atrial stimulation is prevented.

There are many patients who require an atrial and ventricular pacer, as opposed to the more usual ventricular pacer. In demand pacers of the latter type, a detector monitors the spontaneous ventricular beating of the heart; if too long a time interval has elapsed since the last beat, a stimulating pulse is generated to trigger the ventricular beat. In pacers of the former type, an additional circuit is provided for generating atrial stimulating pulses to compensate for irregular atrial activity. To maintain synchronism between the two pulsing circuits, as disclosed in my above-identified application, every ventricular beat -- whether natural or stimulated -- causes the atrial timing period to re-start together with the (longer) ventricular timing period. Following any ventricular beat, an atrial stimulating pulse is generated a short time after the next atrial beat should occur. The atrial stimulating pulse is generated even if a natural atrial beat occurs. Thereafter, a ventricular stimulating pulse is generated, but only if a natural ventricular beat does not occur within a predetermined time interval subsequent to the previous ventricular beat.

As explained in my co-pending application, if an atrial stimulating pulse is generated following an atrial contraction, that is, during the refractory interval of the atria, it has no effect on the beating action of the patient's heart. It is only the generation of a ventricular stimulating pulse during the refractory interval of the ventricles that can be dangerous. For this reason, the detection of a spontaneous ventricular beat inhibits the generation of the ventricular stimulating pulse which would otherwise soon occur. But atrial stimulating pulses are not inhibited. In fact, even if the heart beats perfectly, in the conventional type atrial and ventricular pacer, an atrial stimulating pulse is generated during every heartbeat cycle. Of course, the timing of the atrial pulse generator is keyed to the ventricular beats so that at all times both pulsers and the natural heart activity remain in synchronism.

In my co-pending application, I described the possibility of detecting an atrial contraction and in response thereto re-starting the atrial timing period. However, it was believed to be difficult to detect an atrial contraction (or, more accurately, the atrial depolarization signal), and for that reason an atrial beat detector was not provided in my earlier pacer.

It is a general object of my invention to provide an atrial and ventricular pacer of the prior art type but in which the detection of an atrial beat inhibits the generation of the atrial stimulating pulse which otherwise would be generated soon thereafter.

In accordance with the principles of my invention, a conventional type ECG wave detector is provided to detect atrial depolarization signals in the prior art type atrial and ventricular pacer. The detection of a ventricular beat still re-starts the timing of the atrial pulse generating circuit (along with that of the ventricular pulse generating circuit), but now the atrial pulse generator is also inhibited from producing an atrial simulating pulse whenever a spontaneous atrial beat is detected. The major advantage of this design is that atrial stimulating pulses are not generated when they are not needed; the drain on the battery is reduced and the pacer has to be replaced less frequently. (Although some atrial contractions may not be detected, that simply results in the type of operation described in my co-pending application. It is for each atrial beat which is detected that the drain on the battery is reduced.)

It is a feature of my invention to provide an atrial beat detector in an atrial and ventricular pacer, the detection of an atrial beat resulting in the re-starting of the atrial timing period and the inhibition of the generation of the atrial stimulating pulse which otherwise would be generated.

Further objects,features, and advantages of my invention will become apparent upon consideration of the following detailed description in conjunction with the drawing in which:

FIG. 1 depicts schematically the atrial and ventricular pacer disclosed in my co-pending application;

FIG. 2 consists of timing waveforms which will be helpful in understanding the operation of the circuit of FIG. 1;

FIG. 3 depicts schematically the illustrative embodiment of the invention; and

FIG. 4 consits of timing waveforms which will be helpful in understanding the operation of the circuit of FIG. 3.

FIG. 1 depicts three circuit blocks, the details of which are disclosed in my co-pending application. Ventricular demand stimulator 10 applies a ventricular stimulating pulse, on ventricular electrodes E1 and E2, 800 milliseconds after the previous ventricular beat, whether spontaneous or stimulated. A ventricular beat also results in the appearance of a pulse on the electrodes which is extended to ventricular beat (VB) detector 20. The VB detector extends a signal over conductor 40 to the ventricular demand stimulator, in response to the detection of a ventricular beat, to inhibit the generation of the next ventricular pulse which otherwise would be generated and to control the start of a new 800-millisecond timing interval. Atrial demand stimulator 30 is provided to extend an atrial stimulating pulse to electrodes E3 and E4. The atrial stimulator timing period starts together with the ventircular stimulator timing period, the VB detector output being extended to both pulse generators. However, the timing period of the atrial stimulator is 600 milliseconds rather than 800 milliseconds.

FIG. 2 depicts the operation of the pacer during seven heartbeat cycles. The letters R and P indicate respectively spontaneous ventricular and atrial contractions which occur during the seven cycles. The letters VS and AS identify respectively the generations of ventricular and atrial stimulating pulses. Since the detection of a ventricular beat re-starts the atrial timing period, and the atrial timing period is 600 milliseconds, the time interval between each spontaneous ventricular beat and the next atrial stimulating (AS) pulse is 600 milliseconds as shown. The notation 600(F) is used to indicate that the interval separating any spontaneous ventricular contraction and the next atrial stimulating pulse is fixed. Similarly, since each stimulating ventricular beat (VS) results in VB detector 20 energizing its output 40 to re-start both timing periods, the interval between each VS pulse and the next AS pulse is similarly 600 milliseconds and is shown by the notation 600(F).

In the absence of a spontaneous ventricular beat, a ventricular stimulating pulse is generated 800 milliseconds after the previous ventricular beat under control of ventricular demand stimulator 10. Since the interval is always 800 milliseconds, the notation 800 (F) is used to indicate the time between a spontaneous ventricular beat (R) and the next ventricular stimulating (VS) pulse if such a pulse is generated, and the time interval between one ventricular stimulating pulse and the next ventricular stimulating pulse in the absence of an intervening spontaneous ventricular beat. Finally, in the example shown in the drawing, it is assumed that a spontaneous ventricular beat (R) occurs 700 milliseconds after a previous ventricular beat, whether spontaneous (R) or stimulated (VS). Consequently, 700 milliseconds separate each R--R pair or VS-R pair. Since each of these time intervals is not fixed, and instead is a function of the condition of the patient, the letter F is not used together with the 700 -millisecond designations.

In the circuit of FIG. 1, as shown in FIG. 4 of my copending application, two capacitors are provided to control the 600-millisecond atrial timing period and the 800-millisecond ventricular timing period. Each capacitor charges from an initial value toward a respective firing level. It takes 600 milliseconds for the atrial capacitor (57') in my co-pending application to reach the atrail firing level, at which time an atrial stimulating pulse is generated, the capacitor is discharged and a new timing interval begins; it requires 800 milliseconds for the ventricular timing capacitor (57) in my co-pending application to reach the ventricular firing level, at which time a ventricular stimulating pulse is generated, the capacitor is discharged and a new ventricular timing period begins. Both capacitors are discharged and new timing periods begin when either a spontaneous ventricular beat (R) is detected or a ventricular stimilating (VS) pulse is generated. The two sawtooth waveforms depict the respective capacitor voltage waveforms. The little arrows directly above the peaks of the waveforms indicate when, for the seven illustrative cycles, atrial and ventricular stimulating pulses are generated as a result of the voltages of the respective capacitors rising to the respective firing levels.

With respect to the ventricular capacitor voltage waveform, the voltage across the capacitor has sufficient time to rise to the ventricular firing level only in the absence of a spontaneous ventricular beat. Consequently, it is only at the end of each of cycles 3 and 4 that a ventricular stimulating pulse is generated. In the case of the atrial capacitor, however, the voltage across it always reaches the atrial firing level 600 milliseconds after the detection of a spontaneous ventricular beat (R) or the generation of a ventricular stimulating (VS) pulse. Consequently, an atrial stimulating pulse is shown as occuring during every cycle. Immediately after the generation of an AS pulse, the atrial capacitor voltage starts to rise. But the QRS detector causes the capacitor to be discharged at the end of each cycle when a spontaneous ventricular beat (R) is detected, or a ventricular stimulating (VS) pulse is generated. The capacitor then starts to charge again and the atrial firing level is reached 600 milliseconds later.

The circuit of FIG. 3 is similar to that of FIG. 1 except that atrial beat (AB) detector 50 is provided. The atrial electrodes E3 and E4 are connected to inputs of the AB detector. The AB detector is similar to the VB detector 20, and may in fact be identical. Although it was believed to be difficult to detect atrial beats (that is, the atrial depolarization signal), this is no longer always true. The problem in the past was that the atrial electrodes would shift slightly after implantation. But newer atrial electrodes which have become available commercially permit far more reliable detection of atrial depolarization signals.

The output of AB detector 50 and the output of VB detector 20 are both extended to respective inputs or OR gate 60, the output of which is extended to atrial demand stimulator 30. The only difference between the pacers of FIGS. 1 and 3 is that in the latter circuit the timing period of the atrial demand stimulator is re-started whenever a spontaneous atrial beat is detected, as well as when a spontaneous ventricular beat is detected or a ventricular stimulating pulse is generated.

FIG. 4 shows the capacitor waveforms for the same seven heartbeat cycles depicted in FIG. 2. The major difference between the two timing sequences is that with the circuit of FIG. 3 each spontaneous atrial beat (P) re-starts the atrial timing period. It is only in the absence of a spontaneous atrial beat, during heartbeat cycles 4, 5 and 7, that atrial simulating (AS) pulses are generated. While the ventricular sawtooth waveforms are thus the same in FIGS. 2 and 4, the atrial sawtooth waveforms are considerably different. In FIG. 4, the atrial firing level is reached during only three of the seven heartbeat cycles. In general, because an atrial stimulating pulse is not generated by the pacer of FIG. 3 when a spontaneous atrial beat is detected, there is reduced battery dissipation. This contributes to extended life of the pacer.

Although the invention has been described with reference to a particular embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

Claims

What I claim is:

1. A pacer comprising terminal means for connection to a patient's heart for atrial stimulation, terminal means for connection to said patient's heart for ventricular stimulation, means for detecting an atrial beat of said patient's heart, means for detecting a ventricular beat of said patient's heart, means responsive to the operation of said ventricular detecting means for generating an electrical stimulus on said ventricular terminal means following a first predetermined time interval after the last detected ventricular beat only of said patient's heart, means for generating an electrical stimulus on said atrial terminal means following a second predetermined time interval after the last ventricular beat only of said patient's heart, and means for preventing the generation of an electrical stimulus on said atrail terminal means responsive to the detection of an atrial beat of said patient's heart during said second predetermined time interval.

2. A pacer in accordance with claim 1 wherein said first predetermined time interval is longer than said second predetermined time interval.

3. A pacer in accordance with claim 2 wherein said second predetermined time interval is shorter than a probable minimum interval between successive ventricular beats of said patient's heart and is longer than a probable maximum interval between a ventricular beat and the next atrail beat of said patient's heart.

4. A pacer in accordance with claim 3 wherein said first predetermined time interval is longer than the usually-occurring interval between successive ventricular beats of said patient's heart.

5. A pacer comprising terminal means for connection to a patient's heart for ventricular stimulation, terminal means for connection to said patient's heart for atrial stimulation, a first timing circuit means for generating an electrical impulse on said ventricular terminal means, a second timing circuit means for generating an electrical impulse on said atrial terminal means, means for detecting a ventricular beat of said patient's heart and responsive thereto for resetting both of said first and second timing circuit means, and means for detecting an atrial beat of said patient's heart and responsive thereto for resetting said second timing circuit.

6. A pacer in accordance with claim 5 wherein the period of said first timing circuit means is longer than a probable maximum interval between two successive ventricular beats of said patient's heart.

7. A pacer in accordance with claim 6 wherein the period of said second timing circuit means is longer than a probable maximum interval between a ventricular beat and the next atrail beat of said patient's heart.