U.S. patent number 3,693,627 [Application Number 05/071,799] was granted by the patent office on 1972-09-26 for stimulator for treatment of tachycardia with a burst of stimuli having a continuously variable rate.
This patent grant is currently assigned to American Optical Corporation. Invention is credited to Barouh V. Berkovits.
United States Patent |
3,693,627 |
Berkovits |
September 26, 1972 |
STIMULATOR FOR TREATMENT OF TACHYCARDIA WITH A BURST OF STIMULI
HAVING A CONTINUOUSLY VARIABLE RATE
Abstract
An externally activated implantable heart stimulator. Apparatus
is disclosed for supplying to the heart of a patient a burst of
stimulating pulses having a repetition rate in excess of the
physiological heartbeat range of the patient. The stimulator
comprises terminals for connection to the heart, a controllable
electrical stimuli generator controlled internally by a discharging
capacitor and controlled externally by a magnet. The stimulator is
particularly applicable to the treatment of paroxysmal
supra-ventricular tachycardias, a rapid heartbeat condition
originating in the atrium. The stimulator can be temporarily
activated by anyone including the patient being stimulated.
Inventors: |
Berkovits; Barouh V. (Newton
Highlands, MA) |
Assignee: |
American Optical Corporation
(Southbridge, MA)
|
Family
ID: |
22103669 |
Appl.
No.: |
05/071,799 |
Filed: |
September 14, 1970 |
Current U.S.
Class: |
607/15 |
Current CPC
Class: |
A61N
1/3621 (20130101); A61N 1/362 (20130101); A61N
1/37 (20130101) |
Current International
Class: |
A61N
1/362 (20060101); A61n 001/36 () |
Field of
Search: |
;128/419P,421,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Bilqutay et al, "Journal of Thoracic & Cardiovascular Surgery,"
Vol. 56, No. 1, July, 1968, pp. 71-82. .
Cobbold et al, "Medical Electronics & Biological Engineering"
Vol. 3, No. 3, July, 1965, pp. 273-277..
|
Primary Examiner: Kamm; William E.
Claims
What is claimed is:
1. A heart stimulator for providing therapeutic treatment of
tachycardia by directly stimulating the heart of a patient and
interacting with the abnormal spread of an electrical impulse
generated in said heart, said stimulator comprising terminal means
for connection to the heart of said patient, and pulse generator
means for generating at least one burst of more than two electrical
stimuli at a continually changing rate above the normal
physiological heartbeat-rate range of said patient, said pulse
generator means including means for applying said stimuli to said
terminal means.
2. A heart stimulator as recited in claim 1 further comprising
control means for controlling duration of operation of said
generator means.
3. A heart stimulator as recited in claim 2 and wherein said
control means includes manually operable means for causing said
pulse generator means to initiate the generation of said stimuli
and for causing the termination of said stimuli.
4. A heart stimulator as recited in claim 3 and wherein said
manually operable means includes automatic means for automatically
terminating the generation of said stimuli after a predetermined
time, said automatic means comprising charged capacitor means for
discharging through said pulse generator means and for causing the
operation of said pulse generator means for the voltage of said
capacitor means exceeding a predetermined voltage, said charged
capacitor means including an electrically conductive recharge path,
and means for recharging said capacitor means via said path.
5. A heart stimulator as recited in claim 4 including means for
causing the voltage of said capacitor to exceed said predetermined
voltage for said predetermined time.
6. A heart stimulator as recited in claim 3 and wherein said
manually operable means comprises a reed switch and a magnet.
7. A heart stimulator as recited in claim 6 and wherein said
stimulator, except for said magnet, is implantable within said
patient and said magnet is operatively positioned external to said
patient.
8. A heart stimulator as recited in claim 6 and wherein said
manually operable means further comprises automatic means for
automatically terminating the generation of said stimuli after a
predetermined time, said automatic means comprising charged
capacitor means for discharging through said pulse generator means
and for causing the operation of said pulse generator means for the
voltage of said capacitor means exceeding a predetermined voltage,
said charged capacitor means including an electrically conductive
recharge path and means for recharging said capacitor means via
said path.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The subject matter of the present invention is related to the
following three copending applications: Ser. No. 727,129, filed
Apr. 11, 1968, which has matured into U.S. Pat. No. 3,528,428
entitled "Demand Pacer" Ser. No. 810,519, filed March 26, 1969,
which has matured into U.S. Pat. No. 3,595,242 entitled "Atrial and
Ventricular Pacemaker"; and Ser. No. 884,825, filed Dec. 15, 1969,
entitled Atrio-Ventricular Pacer with Atrial Stimuli
Discrimination. Information disclosed in these three patent
applications is incorporated herein by reference.
These applications were filed by the applicant of the present
invention. All of these applications, including the present
application, are assigned to the same assignee. Benefits of 35 USC
120 are claimed for the present invention with respect to the
earlier applications.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This present invention relates in general to electrical stimulation
of a heart. More particularly, the present invention relates to
electrical stimulation of the atria of the heart for treating
paroxysmal supra-ventricular tachycardia.
2. Description of Prior Art
The PQRST wave form complex depicted by electrocardiograms is well
known in the electro-medical art. The QRS portion of the wave form
complex is associated with the ventricular action of the heart. The
P wave is associated with the atrial action of the heart. 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.
A typical frequency of occurrence of the wave form complex, or
heartbeat rate, when the patient is at rest, is in the neighborhood
of 70 times per minute. However, the frequency of occurrence of the
wave form complex, due to improper heart functioning can exceed 160
occurrences per minute. This excessive rapidity of the heart's
action is known as "tachycardia." However, it should be understood
that the physiological range with regard to normal heartbeat rate
can vary considerably between individuals. For example, a child can
have a normal physiological range comprised of heartbeat rates
considerably higher than those of an adult.
"Atrial tachycardia" is the medical term assigned to the condition
in which rapid and regular succession of P waves of the wave form
complex occur. The rate of occurrence is in excess of the
physiological range of the particular patient.
"Paroxysmal supra-ventricular tachycardia" is the medical term
assigned to the condition in which there is a sudden attack of
rapid heart action in the atria or in the atrial-ventricular node.
The main characteristics are the same as those in atrial
tachycardia.
In normal heart operation the electrical activity begins with a
nerve impulse generated by a bundle of fibers located in the
sino-atrial node. The impulse spreads across the two atria while
they contract and speed the flow of blood into the ventricle
underneath them. The electrical impulse continues to spread across
the atrial-ventricular node, which in turn stimulates the left and
right ventricle.
During normal heart operation, tachycardia can arise when peculiar,
unique conditions occur unpredictably. These conditions are
associated with geometry of the atria, location of the nerve
impulse, timing of the beat and impulse conduction velocity within
the cardiac tissue. These conditions can set up a re-entry
mechanism in the atria, for example, whereby the impulse continues
to self-perpetuate. The self-perpetuation occurs at a rate above
the physiological rate and is self-sustaining even after the
"unique conditioning," (which permitted it to start), no longer
exists. The self-perpetuation must then be interrupted by outside
intervention interfering with the re-entry mechanism, thus
permitting the heart to resume normal sequency.
Presently, treatments of the condition of tachycardia include the
mechanical massage of the carotid sinus. This is an accepted
therapy, however it has several drawbacks. For example, it requires
a trained physician, who may not be readily available, to
administer the message.
Another treatment for tachycardia employs the use of drugs.
However, this therapy has toxic effects on the body.
The present invention treats the condition of paroxysmal
supra-ventricular tachycardia by application of a burst of
electrical stimuli to the heart and for example to the right atrium
to interrupt the self-perpetuating mechanism by interacting with
the abnormal spread of an electrical impulse generated in the right
atrium. The stimuli are generated at a rate above the normal
physiological heartbeat rate range. In a preferred embodiment, the
stimuli are generated at a rate in the neighborhood of 1,000 per
minute for a period of approximately 5 seconds duration. This
amounts to individual bursts of approximately 83 pulses. This
number of pulses occurring during a five second period is almost
always sufficient to alleviate the tachycardia condition. This has
been proven many times in practice. If necessary the application of
a burst of stimuli can be repeated over and over again.
In the prior art, pacers, (such as those disclosed in my copending
applications), are intended to provide and have been used to
provide electrical stimulation to the heart to control abnormally
slow heartbeats. Thus, pacer stimulation occurs at a rate which
falls within the normal physiological heartbeat rate range of the
particular patient being stimulated to induce heartbeats and thus
treat this physiological problem associated with the heart.
By comparison, although the present invention also provides
stimulation to the heart, the present invention is not intended to
induce heartbeats, but is intended to interfere with an abnormal
re-entry mechanism set up in the heart as previously described. To
accomplish this interference, the present invention provides
stimuli at a rate far in excess of the normal physiological
heartbeat rate range, for example, 1,000 stimuli per minute.
SUMMARY OF THE INVENTION
The present invention relates to an externally activated
implantable heart stimulator for providing a burst of stimulating
pulses to the heart of a patient to treat a condition of
tachycardia. The present invention incorporates an electrical
stimuli generator and a control for controlling the generator. The
stimuli are conducted to the heart via implantable terminals or
electrodes. The control incorporates an external magnet and an
implanted magnetic reed switch.
Advantages of the present invention include immediate and
self-initiated treatment. The patient can sense when tachycardia
occurs by his dizziness, perspiration and weakness. The patient can
recognize these symptoms readily. Instead of going to a hospital
for treatment, as is usually necessary at present, the patient can
apply stimulation himself via an externally controlled implanted
stimulator.
It is an object of the present invention to provide a new and
improved heart stimulator.
It is another object of the present invention to provide a new and
improved heart stimulator which generates therapeutic stimuli at a
rate above the normal physiological heartbeat-rate range of the
patient.
It is a further object of the present invention to provide a new
and improved heart stimulator which generates controllable bursts
of stimuli to the heart of a patient.
Other objects and advantages of the present invention will become
apparent to one having reasonable skill in the art after referring
to the detailed description of the appended drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an illustrative embodiment of the
present invention indicating the implantable stimulator and
external magnet; and
FIG. 2 is a schematic diagram of the circuit of an illustrative
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, a functional block diagram of an illustrative embodiment
of the present invention is depicted. Oscillator control 11
controls oscillator 12 as shown. Oscillator 12 triggers simuli
pulse generator 13 once with each oscillation. Stimuli pulse
generator 13 provides an electrical stimulus to heart 14 with each
oscillation. Heart 14 is stimulated in response thereto. Control
11, oscillator 12, generator 13, and heart 14 are depicted as
enclosed by phantom line 10. Phantom line 10 is intended to
represent the surface of a patient in whom the stimulator is
implanted. Magnet 15 is depicted as external to the patient. It is
positioned in close proximity to the oscillator control 11, and
dashed line 16 is intended to indicate the dependence of oscillator
control 11 on magnet 15.
FIG. 2 is a circuit diagram of an illustrative embodiment of the
present invention. Batteries 3 through 7 are connected in series
aiding. (The dashed line between batteries 3 and 7 indicated that
the exact number of batteries used may vary). The positive terminal
of battery 7 is connected to the junction of one end of resistor 23
and one end of resistor 24. The negative terminal of battery 3 is
connected to a junction comprised of one side of capacitor 28, the
emitter of transistor T9, electrode E2, one end of resistor 25, and
one end of resistor 63. The other end of resistor 23 is connected
to terminal 30 of reed switch 32. Reed element 31 makes contact
with terminal 30 in the normally closed position, and connects
terminal 30 with the other side of capacitor 28.
Terminal 29 is the normally open contact of reed switch 32, and is
connected to the junction consisting of one end of resistor 35 and
the anode of diode 27. The cathode of diode 27 is connected to the
anode of diode 26 whose cathode is connected to a junction
comprised of resistor 25, the base of transistor T7, and the
collector of transistor T8. The other end of resistor 35 is
connected to the emitter of transistor T7 and to one end of
resistor 37. The collector of transistor T7 is connected to the
base of transistor T8.
The other end of resistor 37 is connected to one side of capacitor
57 the other side being connected to a junction consisting of the
emitter of transistor T8 and one end of resistor 61. The other end
of resistor 61 is connected to a junction comprised of the other
end of resistor 63 and the base of transistor T9. The collector of
transistor T9 is connected to a junction comprised of the other end
of resistor 24, and one side of capacitor 65. The other side of
capacitor 65 is connected to electrode E1. Electrodes E1 and E2 are
both connected to heart 14.
In operation, consider reed switch 32 to initially be in its
normally closed position as depicted. In this position, capacitor
28 charges to a value of voltage equal to the sum of potentials of
the batteries or to full battery voltage. The charging circuit
includes resistor 23, the contact made between terminal 30 and reed
element 31, and capacitor 28.
When reed element 31 is in the position depicted, there is no
energization provided to the circuitry to the left of capacitor 28.
Thus, transistor T9 is non-conducting because of zero base current
and T9 behaves like an open switch. The open switch, transistor T9,
maintains capacitor 65 charged to full battery voltage. Resistor
24, capacitor 65, electrode E1, heart 14, electrode E2 and the
conductive path returning to the negative terminal of battery 3
comprise a charge path for capacitor 65. Capacitor 65 charges
through the heart. The relatively slow charging of capacitor 65,
(due to resistor 24,) through the heart does not cause any
stimulation to the heart. (It is the rapid discharge of capacitor
65, to be described later, which provides stimulation to the
heart.)
Thus, two charge paths exist, and capacitors 28 and 65 are each
charged to and for this condition remain at the total battery
potential. But, when reed element 31 is caused to make contact with
terminal 29, a different situation exists.
Consider magnet 15 to be brought in close proximity to magnetic
reed switch 32. This causes element 31 to move and to make contact
with fixed terminal 29. Circuit operation may best be understood by
assuming that magnet 15 is held in close proximity to switch 32 so
that element 31 is in contact with terminal 29 for a sufficient
period of time for capacitor 28 to substantially discharge to a
predetermined voltage.
Upon contact between element 31 and terminal 29 charged capacitor
28 becomes the effective D.C. power supply for the circuitry to its
left hand side in the diagram. However, the charged capacitor is an
unusual D.C. power supply in the sense that its "output" voltage is
a decreasing function of time rather than a fixed function of time.
Thus at some predetermined time during discharge of capacitor 28
through the circuitry to its left, the capacitor voltage will fall
below some predetermined voltage that is required to maintain
operation of the circuitry to its left.
Considering circuitry to the left of capacitor 28, the series
circuit of diode 27, 26 and resistor 25 establish a biasing network
for transistor T7 and T8. Current flow from capacitor 28 through
both diodes and resistor 25 establish a potential at the cathode of
diode 26 that is approximately one volt less than voltage at the
anode of diode 27. This voltage difference is due to the forward
voltage drop of diodes 26 and 27 being approximately 0.5 volts each
and being approximately constant for different forward current
values. (As voltage on capacitor 28 decreases, current through
resistor 25 decreases but the 1 volt drop across the diodes remains
approximately constant.). This voltage at the cathode of diode 26
is a threshold voltage which must be exceeded by voltage at the
emitter of transistor T7 by approximately 0.5 volts (since the
base-emitter junction of transistor T7 requires a forward bias
voltage similar to the 0.5 volt drop of the diodes) before
transistor T7 and T8 conduct.
Capacitor 57 charges through resistors 35 and 37 until the voltage
across it causes transistors T7 and T8 to conduct. Transistors T7
and T8, connected as shown, operate in a similar fashion to that of
a silicon controlled rectifier. Both are normally non-conducting.
When the emitter electrode of transistor T7 goes sufficiently
positive to exceed threshold voltage at the base of transistor T7
by approximately 0.5 volts the transistors conduct and current
flows through the emitter circuit of transistor T8. Current coming
from capacitors 28 and 57 continues to flow through the emitter of
transistor T8 until the potential difference between the emitter
and base of transistor T7 drops below approximately 0.5 volts due
to sufficient discharge of capacitor 57. Note that the current
drain from capacitor 28 during this operation contributes to its
discharge.
When transistors T7 and T8 stop conducting, capacitor 57 is made to
charge from the value of voltage across it at the time of turn off
of these transistors toward the "new" (and lower) value of voltage
on capacitor 28. When the voltage across capacitor 57 is
sufficiently positive, transistors T7 and T8 conduct once again and
the cycle is repeated. This circuitry comprises an oscillator and
can be thought of as a type of relaxation oscillator. The frequency
of oscillation varys due to the variation in the "power supply",
i.e., the variation in voltage on capacitor 28. In practice this
variation is in the neighborhood of 25 to 50 percent but is not
critical. It is important to stimulate above the normal
physiological rate, and as can be shown, frequency is increased
with decreasing voltage on capacitor 28. Therefore the lowest rate
is selected to be high enough.
Thus, voltage at the junction of resistors 35 and 37 varies with
voltage on capacitor 57. Capacitor 57 charge time is primarily
determined by resistors 35 and 37; its discharge time is primarily
determined by resistor 37. Resistors 35 and 37 are in the charge
path of capacitor 57 but only resistor 37 is in the discharge
path.
With each oscillation, the "power supply voltage" provided by
capacitor 28 is decreased in value. Thus after a predetermined
period of time, capacitor 28 will "run down" to a predetermined
voltage and there will be insufficient energy stored in capacitor
28, in view of the biasing constraints imposed by its " load"
circuitry, to provide another single oscillation. At this point
there will be no further energizations supplied to the heart unless
capacitor 28 is recharged.
When the magnet is removed, by spring action or other means,
element 31 moves back to its normally closed contact element 30.
Thus the position of magnet 15 controls the state of switch 32.
If magnet 15 were removed prior to capacitor 28 discharging to the
predetermined voltage (where it no longer acted like a power
supply), reed switch 31 would have been returned to its normally
closed contact earlier in time. Thus, the number of stimulations
supplied to the heart would have been reduced, and capacitor 28
would have been recharged.
Thus, there are two controls over the oscillator. First, if magnet
15 is held in position long enough, a finite number of oscillations
are allowed beyond which no further oscillations are permitted
unless the magnet is removed to allow capacitor 28 to recharge.
Second, the number of oscillations can be controlled or limited by
removing the magnet prior to discharge of capacitor 28 to the
predetermined voltage.
Transistor T9 is a simple current amplifier which is normally
non-conducting. When transistor T8 conducts the emitter current
flowing resistors 61 and 63 causes the potential at the base of
transistor 59 to increase.
At such a time transistor T9 is biased to conduction and capacitor
65 can discharge through it through the heart. Capacitor 65
discharges more rapidly than it charges since resistor 24 is not
involved in the discharge path. Capacitor 65 discharges through an
essentially short circuited transistor switch. Transistor T9
operates in response to each oscillation. The combination of the
oscillator, transistor T9, and capacitor 65 comprise a pulse
generator.
A typical minimum frequency of oscillation of an oscillator for a
stimulator of this type is in the neighborhood of 1,000 cycles per
minute. The predetermined time required for capacitor 28 to
discharge to the predetermined voltage is approximately 5 seconds
for this illustrative embodiment. Thus for each application of the
magnet one can achieve a "burst" of approximately 5/60 of 1,000 or
approximately a minimum of 83 stimulating pulses every 5
seconds.
After magnet 15 is removed, reed switch 32 assumes the depicted
state. Capacitor 28 is recharged and capacitor 65 is recharged as
previously described. Only if the patient or another person places
magnet 15 in proper position once again will there by another burst
of stimuli to the heart. The patient can perform this operation
himself in response to an uncomfortable feeling when he goes into
tachycardia. (Paroxysmal supra-ventricular tachycardia is a
disorder which is not lethal but which does cause temporary
discomfort to the patient.). When the magnet is in position once
again, capacitor 28 assumes its role as power supply and once again
a burst of stimuli is applied to the heart.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. For
example, the oscillator need not be of the relaxation variety, the
output could be transformer coupled, other biasing arrangements
could be used and other means for controlling turn on and turn off
of the oscillator could be employed. It should be understood that
the frequency of oscillation could have values greater than those
discussed herein, and that the duration of a burst of stimuli can
be greater or less than 5 seconds.
It should be understood that in the present invention the
oscillator need not be powered from a power supply that decreases
with time, but could be powered from a fixed power supply. Thus,
the oscillator would not turn off after a predetermined time, but
would provide continuous stimulation until the fixed supply and the
oscillator are disconnected from each other.
The present invention can, of course, be extra corporeal (external)
having the terminals implanted, or the entire mechanism, with the
exception of the control, can be implanted.
The atria are normally stimulated in treatment of tachycardia as
described herein, but the present invention may be used in the
treatment of other ventricular originated tachycardias by applying
ventricular stimulation. However, the possibility of inducing
ventricular fibrillation by application of this stimulation may
make this ventricular treatment somewhat hazardous at present.
The present embodiments are therefore to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description, and all changes which some within the
meaning and range of equivalency of the claims are therefore
intended to be embraced therein.
* * * * *