U.S. patent number 3,595,242 [Application Number 04/810,519] was granted by the patent office on 1971-07-27 for atrial and ventricular demand pacer.
This patent grant is currently assigned to American Optical Corporation. Invention is credited to Barouh V. Berkovits.
United States Patent |
3,595,242 |
Berkovits |
July 27, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
ATRIAL AND VENTRICULAR DEMAND PACER
Abstract
An atrial and ventricular (bifocal) demand pacer. A device is
disclosed for providing electrical stimulation to the atrium after
a first predetermined time, and to the ventricle after a second
predetermined time, where both predetermined times are measured
from the last natural heartbeat. The pacer monitors the ventricular
endocardial electrogram and programs both the atrial and the
ventricular stimulation accordingly. In patients with atrial
bradycardia but normal atrio-ventricular (AV) conduction, only the
atria are stimulated. When the condition is complicated with AV
block, both the atria and the ventricles are pacer controlled. The
interval between the atrial and ventricular stimulation is selected
to facilitate the proper atrio-ventricular timing sequence. The
pacer does not compete with spontaneous ventricular
contractions.
Inventors: |
Berkovits; Barouh V. (Newton
Highlands, MA) |
Assignee: |
American Optical Corporation
(Southbridge, MA)
|
Family
ID: |
25204045 |
Appl.
No.: |
04/810,519 |
Filed: |
March 26, 1969 |
Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61N
1/368 (20130101) |
Current International
Class: |
A61N
1/368 (20060101); A61n 001/36 () |
Field of
Search: |
;128/2.06,419--424,419P |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
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
the beating of said patient's heart, means for generating an
electrical stimulus on said atrial terminal means following a first
predetermined time interval after the detection of the last beating
of said patient's heart, and means for generating an electrical
stimulus on said ventricular terminal means following a second
predetermined time interval after the detection of the last beating
of said patient's heart.
2. A pacer in accordance with claim 1 wherein said second
predetermined time interval is longer than said first predetermined
time interval.
3. A pacer in accordance with claim 2 wherein said first
predetermined time interval is shorter than the normal interval
between successive R-waves in the electrocardiographic waveform of
said patient and is longer than the normal interval between an
R-wave and the next P-wave in the electrocardiographic waveform of
said patient.
4. A pacer in accordance with claim 3 wherein said second
predetermined time interval is longer than the normal interval
between successive R-waves in the electrocardiographic waveform of
said patient.
5. A pacer in accordance with claim 4 wherein said second
predetermined time interval is longer than said first predetermined
time interval by 160--250 milliseconds.
6. A pacer in accordance with claim 4 wherein said atrial and
ventricular terminal means together include only three
electrodes.
7. A pacer in accordance with claim 2 wherein said second
predetermined time interval is longer than the normal interval
between successive R-waves in the electrocardiographic waveform of
said patient, and further including means for disabling the
operation of said detecting means during the generation of an
electrical stimulus on said atrial terminal means.
8. A pacer in accordance with claim 7 further including means for
controlling said atrial and ventricular generating means to
generate said respective electrical stimuli independent of the
operation of said detecting means in the presence of noise which
would otherwise be confused with the beating of said patient's
heart.
9. A pacer in accordance with claim 7 wherein said second
predetermined time interval is longer than said first predetermined
time interval by 160--250 milliseconds.
10. A pacer in accordance with claim 4 wherein said detecting means
is connected to said ventricular terminal means, and further
including means for disabling the operation of said detecting means
during the generation of an electrical stimulus on said atrial
terminal means.
11. A pacer in accordance with claim 2 wherein said detecting means
is connected to said ventricular terminal means.
12. A pacer in accordance with claim 11 wherein said atrial and
ventricular terminal means together include only three
electrodes.
13. A pacer in accordance with claim 2 further including means for
controlling said atrial and ventricular generating means to
generate said respective electrical stimuli independent of the
operation of said detecting means in the presence of noise which
would otherwise be confused with the beating of said patient's
heart.
14. 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, a first timing circuit
including first means for generating an electrical impulse on said
atrial terminal means, a second timing circuit including second
means for generating an electrical impulse on said ventricular
terminal means, means for detecting a beating action of said
patient's heart, and means responsive to the operation of said
detecting means for resetting said first and said second timing
circuits.
15. A pacer in accordance with claim 14 wherein said detecting
means is operative to detect a ventricular contraction of said
patient's heart.
16. A pacer in accordance with claim 14 wherein the period of said
first timing circuit is shorter than the normal interval between
two successive R-waves in the electrocardiographic waveform of said
patient.
17. A pacer in accordance with claim 16 wherein the period of said
first timing circuit is longer than the normal interval between an
R-wave and the next P-wave in the electrocardiographic waveform of
said patient.
18. A pacer in accordance with claim 17 wherein the period of said
second timing circuit is longer than the normal interval between
successive R-waves in the electrocardiographic waveform of said
patient.
19. A pacer in accordance with claim 16 wherein the period of said
second timing circuit is longer than the normal interval between
successive R-waves in the electrocardiographic waveform of said
patient.
20. A pacer in accordance with claim 14 wherein the period of said
second timing circuit is longer than the normal interval between
successive R-waves in the electrocardiographic waveform of said
patient.
21. A pacer in accordance with claim 18 further including means for
preventing the resetting of said first and second timing circuits
responsive to the operation of said detecting means in the presence
of noise which would otherwise be confused with a beating action of
said patient's heart.
22. A pacer in accordance with claim 14 further including means for
preventing the resetting of said second timing circuit responsive
to the operation of said detecting means in the presence of noise
which would otherwise be confused with a beating action of said
patient's heart.
23. A pacer in accordance with claim 21 wherein said atrial and
ventricular terminal means together include only three
electrodes.
24. A pacer in accordance with claim 14 wherein said atrial and
ventricular terminal means together include only three
electrodes.
25. A pacer in accordance with claim 18 wherein the period of
second timing circuit exceeds the period of said first timing
circuit by 160--250 milliseconds.
26. 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 a
beating action of said patient's heart, means for applying an
electrical impulse to said atrial terminal means following a first
predetermined time interval after the detection of the last beating
action of said patient's heart, and means for applying an
electrical impulse to said ventricular terminal means following a
second predetermined time interval after the application of said
electrical impulse to said atrial terminal means only in the
absence of the detection of a beating action of said patient's
heart following the generation of said electrical impulse on said
atrial terminal means during said second predetermined time
interval.
27. A pacer in accordance with claim 26 wherein said detecting
means is operative to detect a ventricular contraction of said
patient's heart, and further including means for disabling the
operation of said detecting means during the application of an
electrical impulse to said atrial terminal means.
28. A pacer in accordance with claim 27 wherein said first
predetermined time interval is longer than the normal interval
between an R-wave and the next P-wave in the electrocardiographic
waveform of said patient.
29. A pacer in accordance with claim 28 wherein said first and
second predetermined time intervals are within respective ranges
such that with the proper beating of said patient's heart an R-wave
in said electrocardiographic waveform will occur between the
termination of said first predetermined time interval and the
termination of said second predetermined time interval.
30. A pacer in accordance with claim 26 wherein said first
predetermined time interval is shorter than the normal interval
between successive R-waves in the electrocardiographic waveform of
said patient and said second predetermined time interval is longer
than said normal interval.
31. A pacer in accordance with claim 30 wherein said first
predetermined time interval is longer than the normal interval
between an R-wave and the next P-wave in the electrocardiographic
waveform of said patient.
32. A pacer comprising terminal means for connection to a patient's
heart for atrial and ventricular stimulation, means for detecting
the beating of said patient's heart, means controlled by the
operation of said detecting means for generating electrical stimuli
in a predetermined timing sequence on said terminal means for
stimulating said atrium and said ventricle.
33. A pacer as recited in claim 32, and wherein said detecting
means includes means for preventing erroneous detection of an
atrial contraction as an apparent ventricular contraction.
Description
BIFOCAL DEMAND PACEMAKER
This invention relates to pacers, and more particularly to demand
pacers for use with patients exhibiting symptomatic atrial
bradycardia and unpredictable AV block.
The electrical activity of a normal heart begins with a nerve
impulse generated by a bundle of fibers located in the sinoatrial
node. The impulse spreads across the two atria while they contract
and speed the flow of blood into the ventricles underneath them.
The atrial activity of the heart corresponds to the P-wave in an
electrocardiogram trace. The electrical impulse continues to spread
across the atrioventricular (AV) node, which in turn stimulates the
left and right ventricles. Typically, an interval of approximately
120--160 milliseconds elapses between atrial and ventricular
stimulation. The ventricular activity corresponds to the QRS
portion of the electrocardiogram, and typically has a duration of
80 milliseconds. Toward the end of each heartbeat, the ventricular
muscles repolarize, and this portion of the electrical activity of
the heart corresponds to the T-wave in the electrocardiogram.
Of the two types of contractions, the ventricular is far more
important than the atrial. The atrial contractions cause the
ventricular contractions to be more efficient; the ventricular
contractions are more effective if the ventricles are first filled
with blood. While a patient can survive without proper atrial
action, he cannot survive without ventricular contractions. With an
AV block, that is, an AV node which is opencircuited, life cannot
be sustained (unless the ventricles somehow beat on their own
without AV stimulation, and even in such a case the heartbeat rate
is generally far too slow). With proper ventricular contractions, a
patient can live even with atrial fibrillation. For this reason,
early pacers were generally used to protect against ventricular
asystole. These pacers stimulated the ventricles continuously at a
fixed rate to control their contractions.
Following the use of this type of pacer for many years, the demand
pacer was introduced. In a demand pacer, electrical
heart-stimulating impulses are provided only in the absence of
natural heartbeats. If only a single natural heartbeat is absent,
only a single electrical impulse is generated. 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 previous natural heartbeats--as would be the
case if they were all natural heartbeats. The result is an overall
"integrated" operation, i.e., a mutually exclusive cooperation of
natural heartbeats and stimulating impulses. The demand pacer of
this type is disclosed in my U.S. Pat. No. 3,345,990 issued on Oct.
10, 1967.
Generally, a demand pacer is primed to generate an impulse at a
predetermined time after the last natural heartbeat. If another
natural heartbeat occurs during the timeout interval of the pacer,
an impulse is not generated and the timeout period starts all over
again. On the other hand, if a natural heartbeat does not take
place by the end of timeout period a stimulating impulse is
generated. For the proper operation of a demand pacer, the
pacemaker circuitry must determine if a natural heartbeat has
occurred. The largest magnitude electrical signal generated by the
heart activity is the QRS complex corresponding to ventricular
contraction. To determine whether a natural heartbeat has occurred,
an electrode is generally coupled to a ventricle. Since in most
cases ventricular stimulation is required, the same electrode can
be used for both stimulating the ventricles and detecting a natural
heartbeat, as disclosed in my aforesaid patent.
In the presence of noise, erroneous operation of a demand pacer of
this type can take place. The noise may result in the generation of
an electrical signal on the ventricular electrode, and the pacer
circuitry may treat this noise as indicative of a natural heartbeat
and inhibit the generation of a stimulating impulse even if one is
required. In my copending application Ser. No. 727,129 filed on
Apr. 11, 1968, which was issued on Sept. 15, 1970, as U.S. Pat. No.
3,528,428, an improved demand pacer is disclosed. In this improved
demand pacer, in the presence of noise the pacemaker timeout period
is not interrupted. Continuous stimulating impulses are generated,
even if they are not required. It is better to provide an impulse
even if it is not required than it is not to provide an impulse if
it is required.
There are many patients with symptomatic atrial bradycardia even
though they have normal AV conduction. In such a patient, the slow
atrial rate causes the ventricular rate to slow down. Ventricular
pacer stimulation has been used in the past to treat this disorder.
For such patients, however, it would be better to provide atrial
stimulation to thus control both the atrial and ventricular rates,
with the additional benefit of the natural atrioventricular
sequence. But such atrial stimulation would leave the patient
unprotected from unpredictable AV block. Thus, provision should
also be made for ventricular stimulation if it becomes
necessary.
Both types of pacing could be accomplished with the use of two
individual pacers. But even if they are combined in a single
package many problems must be overcome, especially if a demand-type
operation is desired. One of the most obvious problems concerns the
timing sequence of the two types of pacing.
It is a general object of my invention to provide a bifocal pacer
for atrial as well as ventricular stimulation, which preferably is
of the demand type.
In accordance with the principles of my invention the first
function of the pacer is to generate an atrial-stimulating impulse.
After a predetermined time interval, the pacer functions to
generate a ventricular-stimulating impulse. Three electrodes are
provided--a neutral electrode, an electrode for atrial stimulation
and an electrode for ventricular stimulation. In the illustrative
embodiment of the invention, the ventricular electrode also serves
to detect the occurrence of a ventricular contraction.
The pacer exhibits two timeout or escape intervals. The ventricular
escape interval is 160--250 milliseconds longer than the atrial
escape interval. The ventricular escape interval is greater than
the normal interval between two heartbeats (as in a conventional
demand pacer). The atrial escape interval is greater than the
normal interval between atrial and ventricular beats (P to R), but
less than the normal interbeat interval (R to R). Both timeout
periods begin with the generation of the last heartbeat (natural or
stimulated). If another ventricular contraction does not occur
within the atrial timeout period, that is, in the absence of a
premature ventricular contraction, the atrial-stimulating impulse
is generated. The atria contract and fill the ventricles with
blood. In the event the ventricles contract (i.e., there is no AV
block), the detected EGG signal on the ventricular electrodes
resets both timeout circuits and the ventricular impulse is not
generated. In the event the ventricular contraction does not occur,
a ventricular impulse is generated at the end of the ventricular
timeout interval.
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 is the same as FIG. 1 in my copending application Ser. No.
727,129 and depicts a preferred demand pacer for ventricular
stimulation, and further shows in heavy lines the additional
circuit elements and the five conductors 80--84 which are required
to connect the demand pacer of FIG. 1 to the atrial-stimulating
circuit of FIG. 3;
FIG. 2 depicts a typical electrocardiogram;
FIG. 3 depicts an atrial-stimulating circuit which, when used with
the circuit of FIG. 1, provides bifocal stimulation in accordance
with the preferred embodiment of the present invention;
FIG. 4 depicts the arrangement of FIGS. 1 and 3; and
FIG. 5 is a timing diagram which will be helpful in understanding
the present invention.
Except for the elements and conductors shown in heavy lines, the
circuit of FIG. 1 is identical to that disclosed in my copending
application Ser. No. 727,129. (In said application, conductor 11
extends directly from electrode E1 to capacitor 17--there is no FET
switch 92 in the signal path.) Electrodes E1 and E2 are implanted
in the patient's heart, electrode E2 being the neutral electrode
and electrode E1 being positioned to stimulate the ventricles of
the patient's heart. When switch S is closed, the pacer functions
to continuously supply electrical impulses at a fixed rate. When
the pacer is operated in the demand mode, however, switch S is
open. Current flows between electrodes E1 and E2 to stimulate the
ventricles only when an electrical stimulus is required.
Capacitor 65 serves to provide a source of current when an impulse
is required. At that time, transistor T9 conducts and the capacitor
discharges through the electrodes. Capacitor 57 charges through
potentiometers 35 and 37 until the voltage across it causes
transistors T7 and T8 to conduct. At that time, capacitor 57
discharges through transistors T7 and T8, transistor T9 conducts,
and an impulse is delivered to the patient's heart from capacitor
65. The setting of potentiometer 37 controls the time taken for
capacitor 57 to discharge, that is, the width of each impulse. The
setting of potentiometer 35 controls the time required for
capacitor 57 to charge to that level which causes conduction in
transistors T7 and T8, that is, the interpulse interval.
Ordinarily, in the absence of conduction of transistor T6,
capacitor 57 would continuously charge and discharge, and impulses
would be supplied to the patient's heart at fixed intervals
determined by the setting of potentiometer 35.
Electrode E1 is coupled over conductor 11 to the base of transistor
T1. A typical ECG. is shown in FIG. 2, and transistors T1 and T2
conduct when electrode E1 detects a ventricular contraction which
results in the generation of an R wave. (Excessive signals are
shorted through Zener diode 67 to prevent damage to transistor T1.)
With the conduction of these transistors, a positive pulse is
delivered to the base of transistor T6. Transistor T6 conducts and
capacitor 57 discharges through it. Thus, although the capacitor
was previously charging to the level which would have resulted in
the generation of an impulse, it is discharged and a new timeout
interval begins. This arrangement ensures that an impulse is not
generated if a natural heartbeat has occurred. The timeout interval
is such that impulses are generated with an interpulse interval
slightly in excess of the desired natural interbeat interval. Only
if a natural heartbeat is missing is a stimulating impulse
generated.
The remaining transistors in the circuit serve to prevent
conduction of transistor T6 in the presence of noise. In the
presence of noise it would otherwise be possible for transistor T6
to conduct and prevent the generation of an impulse even though one
is required. For this reason, when the pacer detects extraneous
noise, transistor T6 is prevented from operating and impulses are
delivered at a fixed rate. A more complete description of the
operation of the circuit of FIG. 1 is set forth in my
above-identified application.
The illustrative embodiment of the invention is derived by adding
the circuit elements and conductors shown in heavy lines in FIG. 1,
and combining the circuits of FIGS. 1 and 3, as shown in FIG. 4.
The circuit of FIG. 3 is in almost all respects identical to the
circuitry on the right side of FIG. 1. The various elements in the
circuit of FIG. 3 are designated by the same numerals as the
equivalent elements in FIG. 1 with the addition of prime symbols.
Conductor 80 couples potentiometer 35' and resistor 59' to a
terminal of battery 7 just as potentiometer 35 and resistor 59 are
coupled to the same terminal in FIG. 1. Conductor 81 couples the
base of transistor T7' to the other terminal of battery 7 just as
the base of transistor T7 in FIG. 1 is coupled to this terminal.
Conductor 82 couples the base of transistor T6' to the right side
of capacitor 53, just as the base of transistor T6 in FIG. 1 is
coupled to the right side of the capacitor. Conductor 83 serves to
provide a common neutral for the circuits of FIGS. 1 and 3.
Finally, conductor 84 serves to extend a signal to disable FET
switch 92, as will be described below.
Electrode E3 in FIG. 3 is implanted in the patient's heart to
stimulate his atria. The circuit of FIG. 3 functions just as does
the circuit on the right side of FIG. 1, except that each
stimulating impulse results in an atrial contraction rather than a
ventricular contraction. Capacitor 57' charges through
potentiometers 35' and 37'. After a predetermined interval, when
the capacitor voltage has reached the level required to control
conduction of transistors T7' and T8', the two transistors conduct
and forward bias the base-emitter junction of transistor T9'. The
charge on capacitor 65' flows through transistor T9' and electrodes
E2 and E3. The width of each pulse is determined by the setting of
potentiometer 37' which determines the time required for capacitor
57' to discharge through transistors T7' and T8'. The interpulse
interval is determined by the setting of potentiometer 35' which
determines the time required for capacitor 57' to charge to the
level which causes transistors T7' and T8' to conduct.
Any pulse delivered through capacitor 53 as a result of the
detection of an R-wave causes transistor T6' to conduct along with
transistor T6. At the same time that capacitor 57 discharges
through transistor T6, capacitor 56' discharges through transistor
T6'. In such an event, the timeout period of the circuit of FIG. 3
is not concluded and an atrial-stimulating pulse is not generated.
Instead, the timeout begins once again.
FIG. 5 depicts a timing sequence which will be helpful in
understanding the present invention. Two R-waves are shown and
represent two successive beats (ventricular contractions) of the
patient's. heart. Typically, the time interval between them is less
than 760 milliseconds. The P-wave associated with the second R-wave
is shown occurring before it.
Potentiometer 35' has a value such that capacitor 57' charges to
the level required for the conduction of transistors T7' and T8'
after 600 milliseconds have elapsed since the last capacitor
discharge. The atrial-stimulating pulse E3 is thus shown occurring
600 milliseconds after the first R-wave. It should be noted that
the atria are stimulated following the P-wave during a normal
heartbeat. Actually, if a P-wave has been generated it is an
indication that the atria have contracted and an atrial-stimulating
impulse on electrode E3 is not required. However, if such an
impulse is generated following the atrial contraction, that is,
during the refractory interval of the atria, it has no effect on
the beating action of the patient's heart. (The generation of an
atrial-stimulating impulse prior to the natural atrial contraction
can induce an atrial premature beat which is not desirable.)
Potentiometer 35 in FIG. 1 has a value such that the timeout
interval for the ventricular stimulation is 800 milliseconds. Thus,
the pulse designated E1 in FIg. 5 is shown occurring 800
milliseconds after the first R-wave, which is slightly after the
second R-wave should it be present. If the second R-wave is
detected on electrode E1, both timeout circuits are reset and an
impulse is not generated on electrode E1. This is the desired
demand-type operation. If a natural heartbeat does not occur within
800 milliseconds after the last heartbeat, and impulse is generated
on electrode E1 to stimulate the ventricular contraction.
It should be noted that if the heart beats naturally, there will be
no ventricular stimulation by the pacer. However, there will be
atrial stimulation because the 600 millisecond timeout interval of
the circuit of FIG. 3 is less then the natural interpulse interval.
But in the event a natural atrial contraction does not take place,
the atrial stimulation is required in order that the heart function
more efficiently. The ventricular stimulation, of course, is
provided to correct any AV block. A normal ventricular contraction
can occur approximately 120--160 milliseconds after the atrial
stimulation. The ventricular timeout period in the circuit of FIg.
3 is 200 milliseconds longer than the atrial timeout period in the
circuit of FIg. 1; sufficient time is allowed for a natural
ventricular contraction before a ventricular-stimulating impulse is
generated. In general, the ventricular timeout period should exceed
the atrial timeout period by 160--250milliseconds.
It should also be noted that the operation of the circuit of FIG. 3
is keyed to the detection of a ventricular contraction by the
circuit of FIG. 1. It is highly desirable to key the circuit of
FIG. 3 to the beating of the patient's heart--were a free-running
generator provided to stimulate the atria, the timing of the
beating of the patient's heart might be seriously affected. While
the natural timing might change, the circuitry timing would be
invariant. For this reason, capacitor 57' is discharged following
any beating of the patient's heart. Theoretically, it might be
possible to detect an atrial contraction, that is, to detect the
P-wave, and to discharge capacitor 57' before its timeout is
completed so that an atrial-stimulating impulse would not be
generated if it is not required. However, it is exceedingly
difficult to detect the P-wave due to its small magnitude as
compared to the R-wave. For this reason, in the illustrative
embodiment of the invention it is the detection of the R-wave which
also serves to reset the timeout period of the circuit of FIG. 3.
Of course, this results in the continuous generation of impulses at
electrode E3 if the heart is beating normally (even though impulses
at electrode E1 are not generated) because each R-wave is detected
after the impulse at electrode E3 has been generated. However, the
generation of an atrial-stimulating impulse during the refractory
interval of the atria has been found not to interfere with the
normal beating of a patient's heart. (The same is not true of the
generation of a ventricular-stimulating impulse following a
ventricular contraction, and this is the reason for the use of the
demand-type pacers in the first place.)
It is possible in some cases that the atrial contraction will
generate an electrical signal on electrode E1 which will cause
transistor T1 to conduct and restart the two timeout periods. For
this reason, FET switch 92 is inserted in conductor 11 between
electrode E1 and capacitor 17 in the base circuit of transistor T1.
The switch is normally conducting due to its connection through
resistor 94 to neutral conductor 9. The negative pulse generated at
electrode E3 is transmitted over conductor 84 and through diode 95
to capacitor 93. The capacitor charges and turns off the FET
switch. When the atrial-stimulating pulse terminates (after a
typical duration of 2 milliseconds), capacitor 93 discharges
through resistor 94. The time constant of the capacitor-resistor
combination is such that the FET switch remains off for
approximately an additional 6 milliseconds to prevent erroneous
detection of a ventricular contraction for a few additional
milliseconds until after all transients have died down. In this
manner, the heartbeat detection circuit is disabled during each
atrial stimulation and for a short interval thereafter. Capacitor
91 is provided to short high frequency transients, arising from the
FET switching, to conductor 9.
The timeout intervals of 600 milliseconds and 800 milliseconds
shown in FIG. 5 are not critical. Considerable flexibility is
possible. Generally, the timeout interval for the circuit of FIG. 3
should be such that an impulse is generated at electrode E3 some
time between the P and R-waves following a previous R-wave. The
timeout interval for the circuit of FIG. 1 should be such that an
impulse is generated at electrode E1 at a time after the last
R-wave which exceeds the desired period between natural
heartbeats.
It is thus seen that the pacer of the invention serves to correct
for the condition known as atrial bradycardia at the same time that
it protects against ventricular asystole. 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.
* * * * *