U.S. patent number 3,835,864 [Application Number 05/073,809] was granted by the patent office on 1974-09-17 for intra-cardiac stimulator.
This patent grant is currently assigned to Rasor Associates, Inc.. Invention is credited to Ned S. Rasor, Joseph William Spickler.
United States Patent |
3,835,864 |
Rasor , et al. |
September 17, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
INTRA-CARDIAC STIMULATOR
Abstract
A stimulator device for insertion in a living body and having
particular advantage for intra-cardiac use comprising a structure
having a body form of a size and configuration to enable its
transvenous or transarterial insertion, the surface of said body
form providing electrode means for contact with a portion of the
living body to be stimulated by said electrode means, and means
mounted to project outwardly of and peripherally of said body form
including anchor portions locating in a position displaced from
said electrode means and providing means for engaging in portions
of said living body to establish said electrode means in a required
position of use, said electrode means having in connection
therewith means to energize the same once said body form is located
in its required position of use.
Inventors: |
Rasor; Ned S. (Dayton, OH),
Spickler; Joseph William (Dayton, OH) |
Assignee: |
Rasor Associates, Inc. (Dayton,
OH)
|
Family
ID: |
22115924 |
Appl.
No.: |
05/073,809 |
Filed: |
September 21, 1970 |
Current U.S.
Class: |
607/36; 607/126;
607/35 |
Current CPC
Class: |
A61N
1/0573 (20130101); A61N 1/37512 (20170801); A61N
1/37518 (20170801); A61N 1/3785 (20130101) |
Current International
Class: |
A61N
1/372 (20060101); A61N 1/375 (20060101); A61N
1/05 (20060101); A61N 1/378 (20060101); A61n
001/36 () |
Field of
Search: |
;128/404,418,419P,421,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Hopps et al., "Surgery," Vol. 36, No. 4, Oct., 1954, pp. 833-849
(only p. 834 relied on). .
Frei et al. "Medical Research Engineering," 4th Quarter, 1956, pp.
11-18..
|
Primary Examiner: Kamm; William E.
Claims
What is claimed is:
1. A stimulator device for insertion in a living body and having
particular advantage for intracardiac use comprising a structure
having a body form for transvenous or transarterial insertion,
electrode means on the surface of said body form for contact with a
portion of the living body to be stimulated by said electrode
means, and means mounted to project outwardly of and peripherally
of said body form including anchor portions locating in a position
displaced from said electrode means and providing means for
engaging in portions of said living body to establish said
electrode means in a required position of use, said electrode means
having in connection therewith means to energize the same once said
body form is located in its required position of use.
2. A stimulator device as in claim 1 wherein said means to energize
said electrode means includes a power source positioning in a
location remote from said body form.
3. A stimulator device as in claim 1 wherein said means to energize
said electrode means includes a power source embodied within said
body form.
4. A stimulator device as in claim 1 wherein spaced surface
portions of said body form define separate electrode means.
5. A structure as in claim 1 wherein said anchor portions are
defined by wire like segments connected with and biased to normally
project outwardly from said body form to facilitate the
establishment of a connection thereof with said living body in an
area displaced from said electrode means.
6. A stimulator device as in claim 1 wherein said electrode means
have a fixed positioning in respect to said body form and comprise
at least two electrodes, and said body form includes insulator
means separating said electrodes.
7. A stimulator device as in claim 1 characterized by said body
form being a unitized structure having means for guiding the same
for transvenous or transarterial insertion.
Description
BACKGROUND OF THE INVENTION
Implanted Pacemaker devices are now commonly employed for the
long-term treatment of atrio-ventricular (A-V) block. Such
Pacemaker devices commonly employ flexible leads which connect a
remotely positioned power pack with electrodes which are placed in
contact with or attached to the myocardium. The techniques of
implanting and using such Pacemakers, and many Pacemaker which have
been used experimentally and in practice, are described by Siddons
and Sowton, Cardiac Pacemakers (1967), published by Charles C.
Thomas, Springfield, Illinois, Library of Congress Card No.
67-12042. Pacemakers having energy sources responsive to heart
movement are shown in U.S. Pat. Nos. 3,358,690 and 3,486,506.
Such Pacemakers, or other biological stimulators working on these
principles, have inherently suffered from certain disadvantages.
The leads to the electrodes are commonly routed through veins
leading into the heart itself. The movement of the heart and normal
activity of the individual tend to put a strain on these leads and
may result in lead breakage or dislodgement of the electrodes. The
leads themselves, retained in situ, are frequently a source of
irritation and infection. Further, since the electrical contact
with the heart is made at the point or region of mechanical support
or implantation, the normal fibrosis of tissue at these regions
often results in a marked increase power required to pace, known as
an increase in threshold. For example, the threshold has been found
to increase on the order of ten times its original value until a
plateau is reached over a period of two to three weeks. This
requires a correspondingly greater power input to the electrodes,
in the minimum of 3:1 over threshold, in order to achieve
consistent pacing.
The remote power pack itself is a cause of discomfort and often a
cause of difficulty. It is commonly implanted in a subcutaneous
pocket beneath the pectoralis major or within the abdomen. Again,
this provides a further opportunity for infection. Difficulty has
been encountered in preventing migration of the power pack.
Further, surgery is required from time to time to expose and
replace the power pack due to exhaustion of the mercury cells.
Prior pacing devices which derive their energy from the heart
movement or pressures have commonly required thoracic surgery for
attachment to the epicardium, and have employed flexible leads to
the electrodes.
SUMMARY OF THE INVENTION
The present invention is directed to a wholly selfcontained
stimulator which is particularly adapted for use as a Pacemaker. It
is contained within a package or housing which is sufficiently
small to be implanted by catheter insertion (transvenous or
transarterial) into a chamber of the heart where it is attached to
the endocardium. The stimulating electrodes are formed integrally
with the unit, without external leads, and thus make contact with
the endocardium. As used herein, "catheter" refers to an inserting
device embodying a sheath-like element of small bore tube form.
A Pacemaker device made according to the present invention is
intended primarily for long-term use. It can be used without
discomfort to the user. The likelihood of a failure due to
dislodgement of electrode contact, increase of threshold, or
occurrence of infection is substantially reduced. Failure due to
electrode lead breakage is eliminated entirely. The device can be
implanted by a catheter device and technique which require only
minor surgery and temporary discomfort to the patient. It can be
recovered if desired or, if failure should occur it may simply be
left in place and a new device inserted.
In one form of the invention a nucleonic battery is employed for
providing a power source to the pulse generator circuits contained
within the housing. This arrangement provides for an overall life
which may be well beyond the normal life expectancy of the patient.
For example, Pu-238 has a half life of 86 years, while Pm-147,
which may be preferred because of lower costs, has a half life of
2.7 years. Suitable electronics in the converting and pulse
generating portion are available which operate efficiently over
three or more half lives. Operation over such a large power range
is made possible in part by the fact that the device of the present
invention does not cause a material or significant increase in
threshold, and therefore can continue to operate after decay to
very low power levels.
Three forms of the invention are disclosed which employ a
biologically energized power source and thus derive their power
requirements from the body itself. Prior attempts have obtained
insufficient power from normal heart activity to provide reliable
and continuous pacing. However, the apparatus of the present
invention is one which does not result in a significant increase in
threshold power and accordingly reliable pacing may be affected
over an extended period of time with modest lower power
requirements. The energy required for each stimulation pulse may be
in the order of one microjoule or less, corresponding to a total
power input to the electronics on the order of six microwatts or
less. The mechanical work which is available substantially exceeds
this.
In one form of the invention, a movable wall or diaphragm
transforms hemodynamic pressure into electric energy by means of a
suitable transducer. In other forms of the invention, a mass is
suspended in such a manner that movements of the heart set up a
sympathetic or harmonic movement of the mass, and this movement may
be electromechanically coupled to produce energy. For example, the
transducer may comprise a permanent magnet in combination with a
non-moving electric coil. In another form, the mass may be
connected to stress a piezoelectric crystal.
The body or housing structure of the present invention may also be
used as the electrode structure for existing Pacemakers, as it
offers certain advantages over the endocardial electrodes which are
presently in use.
Another important object of the invention is the provision of a
bioelectric stimulator which is fully self-contained and
implantable at the site of stimulation, and an improved electrode
structure therefor.
A further object of the invention is the provision of a stimulator,
heart Pacemaker, or an electrode structure for a Pacemaker, in
which the region of attachment is spaced from the region of
stimulation to avoid the adverse effects of tissue fibrosis at the
region of attachment.
A further object of the invention is a provision of a catheter for
inserting the Pacemaker or electrode assembly therefor, as
described above, and the further provision of the combination of a
novel catheter and Pacemaker or electrode assembly therefor. The
catheter is preferably a triaxial arrangement in which one of three
concentric elements is removably secured to the body of the device,
a second element forms a torque tube which may be used to assist in
implanting the device and for removing the first element from the
device, and the third element comprises an outer removable sheath
which preferably extends at least partially over the body of the
device during transvascular passage and may be employed to retain
the body-attaching members on the device in a retracting or
inoperative position until the device has been positioned, as
desired. Thereafter, the sheath may be retracted to expose the body
of tissue-attaching members, or extended to cover these members for
removal of the device from the heart.
These and other objects and advantages of the invention will be
apparent from the following description, the accompanying drawings
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded view of the stimulator and catheter devices
of the invention;
FIG. 2 shows parts of FIG. 1 in an assembled condition;
FIG. 3 is an enlarged sectional view, partially in diagrammatic
form, of the stimulator of FIG. 1 adapted particularly for use as a
heart pacer;
FIG. 4 is an end view of the device of FIG. 3;
FIGS. 5a, 5b and 5c are, respectively, diagrams illustrating the
method of implanting the pacer using the catheter device of this
invention;
FIG. 6 is a schematic drawing showing a pulsing circuit which may
be used with this invention;
FIG. 7 is a diagram of a modified form of the circuit of FIG. 6
particularly adapted for use with a nucleonic or other varying
power source;
FIG. 8 shows a modified form of the invention adapted to respond to
hemodynamic pressure changes;
FIG. 9 is a block diagram of the pacer of FIG. 8;
FIG. 10 is a further modification showing a biologically powered
pacer according to the present invention;
FIG. 11 is a still further modification showing another form of the
biologically powered pacer; and
FIG. 12 is a modified catheter and an improved Pacemaker electrode
assembly according to the teachings of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIGS. 1-4, a self-contained stimulator 10,
particularly is adapted as a heart pacer, and a catheter 11 is
adapted for use with such pacer. The pacer 10 is formed with an
elongated capsule-like, generally cylindrical body 12. Preferably,
the body 12 is formed exclusively on its outer surfaces of
biologically compatable materials, the major portion of which may
be stainless steel. While the outer surface of the body 12 is shown
in the drawings as being formed essentially of smooth inert
material, such as stainless steel, it is within the scope of this
invention to provide the body with a compatible flocking material,
such as a dacron weave to promote the formation of neointima once
the unit has been implanted.
The device can be implanted in any of the four chambers of the
heart where patho-physiology would be optimum for a particular
patient. However, the preferred embodiment herein will emphasize
implantation within the right ventricle where the greatest clinical
and experimental experience has been concentrated to date. When the
stimulator, or pacer 10, is adapted for implantation directly
within a heart ventricle, it should have a maximum overall length
not substantially exceeding 30mm and preferably in the order of
18mm or less. The diameter of the body 12 should not substantially
exceed 10mm and is preferably 8mm or less. Such dimensions provide
a self-contained Pacemaker which is sufficiently small to permit
catheter transvascular insertion into a ventricle, and permit it to
be received within such ventricle without disturbing the proper
function of the heart.
The forward end of the body 12 is provided with means for attaching
the pacer 10 to the myocardium. A preferred form of the attachment
comprises a pair of oppositely directed spiral stainless steel
attaching points or wires 15 and 16, as best shown in FIG. 4. The
wires have inner ends attached to the circumference of the body 12
and free outer ends. These attaching wires are adapted to be
retained in a retracted position in closely surrounding relation to
the circumference of the body 12, but when released, spring out to
the expanded or operative position, as shown.
Catheter means for transvenous implanting of the Pacemaker 10
preferably consists of the triaxial device illustrated generally at
11 in FIGS. 1 and 2. This arrangement comprises a central rod 22
which is formed with a threaded end 23 which is adapted to be
attached or received with a suitable internally threaded nut 24
formed on the rear wall 24' of the body 12, as shown in FIG. 3. A
torque tube 25 is slidably received over the rod 22 and, at its
forward end, is formed with an internal socket portion 26 adapted
to be received over the nut 24 in driving engagement with the
Pacemaker 10. The catheter is further provided with an axially
slidable sheath 27 which has a forward metallic end portion 28 of a
diameter sufficiently to be received at least partially over the
body of the Pacemaker 10. In use, the sleeve 28 substantially
covers the Pacemaker and retains the attaching wires 15 and 16 in
their retracted position substantially as shown in FIG. 2. The use
of the catheter 11 is further described in connection with the
illustration of FIGS. 5a-c.
This entire catheter system may be rigid with defined bends or may
be flexible or may be steerable. In the preferred form, a central
rod 22 and the torque tube 25 are flexible, while the forward end
of the sheath 27 is formed with a predetermined bend as indicated
at 27' in FIG. 5a. The bend which may be formed within 2-4 inches
of the end of the catheter assembly, may have an angle of
approximately 30.degree. in order to permit the catheter and the
attached Pacemaker to be steerable around corners and bends.
Referring particularly to FIG. 3, the Pacemaker 10 is shown as
including a forward body portion 12a and a cylindrically continuous
rear body portion 12b. The forward portion 12a is hollow and
contains the electronic pulsing circuit 30, illustrative examples
of which are shown in FIGS. 6 and 7. It has been found that
relatively simple circuits are totally satisfactory and are in fact
preferred over the more complicated circuits shown, for example, in
the reference text referred to under the Background section of the
specification. The simpler circuits generally have lower losses and
greater overall reliability. Such circuits can easily be fitted
within the activity defined with the body section 12a without the
necessity of reverting to microminiature or integrated circuits.
However, such circuits permit even further miniaturization, but the
overall size of the stimulator of this invention is dictated not so
much by the circuit requirements but by the space requirements of
the power source.
The body sections 12a and 12b may be threaded together and sealed
as shown at 31, but it is within the scope of this invention to
make the body 12 of simple one-piece construction. The rear wall
24' is preferred welded to the case 12b by electron beam welding.
There is some advantage in the two-piece body construction of FIG.
3 in that it permits the body parts to be separated and adjustments
to be made to the circuit prior to insertion.
One of the important advantages of the stimulator of the present
invention resides in the fact that the pacing electrodes are formed
integrally with outer surfaces of the body 12. To this end, the
body portions 12a and 12b themselves define the positive pulsing
electrode which, as previously noted, may be formed preferably of
stainless steel. The negative pulsing electrode 32 is formed
preferably of platinum and supported on a forwardly extending
dielectric pedestal 33. The pedestal is preferably formed of an
inert ceramic, defining a hollow co-axial insulator. The insulator
33 may thus have an outer curved surface 34 leading smoothly from
the electrode end 32 and flaring outwardly at the body 12a to
assist in guiding the device during insertion. A tubular portion 35
extends into the interior of the body 12a. The forward end of the
body 12a is formed with an annular ledge 36 to provide support for
the insulator and for the electrode 32.
The stimulating electrode 32 may also be of the differential
current density type, known as the "Parsonnet Electrode" and
described by George H. Myers and Victor Parsonnet in Engineering in
the Heart and Blood Vessels, (1969) John Wiley & Sons, New
York, N.Y.
The arrangement as shown has several important advantages. In the
first place, it will be noted that, unlike prior devices, the
electrodes do not themselves form or comprise the attaching
devices. Rather, the pacing electrodes are well spaced axially from
the barbs 15 and 16. Thus, once these electrodes have made reliable
pacing contact with the heart tissue, they do not transmit the
destructive forces of attachment and retention to this tissue, and
they remain free of the adverse affects of fibrosis which
invariably occurs at the regions of attachment or forcible
retention. In devices where the electrodes themselves are directly
attached or are forcibly retained by pressing against the tissue,
an approximately 10 times increase in the threshold is not
uncommon. This occurs over approximately a two to three week period
subsequent to implanting and then reaches a plateau. Such a
substantial increase in threshold requires a corresponding increase
in power requirements simply to overcome the threshold and to
effect reliable stimulation. The elimination of the cause of
threshold rise permits reliable pacing with substantially lower
power consumption.
Another important advantage of the construction of FIG. 3 is the
total elimination of external flexible leads between the pacing
circuit and the tissue to be stimulated. This then results in the
elimination of the lead placement and breakage difficulties which
are inherently associated with remotely positioned pacer
circuit.
A further important advantage of the pacer of this invention is the
fact that it can be reliably powered from a suitable nucleonic
power source 40. There are available in the present state of the
art a number of nucleonic conversion devices which may be contained
within the physical dimensions of the body portion 12b, and
suitably shielded and sealed therein. A preferred form of such
device is a betavoltaic converter which is, in effect, a stack of
semiconductor photocells which are coated with a radioactive
material and which are irradiated by beta particles to produce an
unidirectional current electric output. Beta sources may include
Pm-147 which has a 2.7 years half life. It is within the state of
the art to provide an electronic circuit which will operate
effectively over more than three half-lives of such power sources
within the volume available. The use of tritium, with a half life
of 12.6 years, is also possible.
A power source 40 using radioisotope fuel may also be of the
thermionic type, the thermoelectric type or the double conversion
type. In the thermionic and thermoelectric types, heat from the
radioisotopic fuel is transformed into electric power by electron
transport through a thermionic diode or thermocouple respectively.
In the double conversion type, radiation from the radiosotope fuel
is employed to excite a light-emitting phosphor, and the photons in
turn excite a semiconductor photocell. All three of these types can
use Pu-238, which is a desirable fuel for biological applications
and has a half life of 86 years. The choice of fuel and type of
convertor will depend upon the cost of the source material and
fabrication, the half life, and the efficiency of conversion as
well as the shielding required. Suitable radioisotope-fueled
batteries are made by Donald W. Douglas Laboratories, 2955 George
Washington Way, Richland, Washington and sold under the tradenames
"Betacel" and "Isomite," representing beta-voltaic and thermionic
types respectively. While nucleonic power sources are preferred by
reason of long life, it is within the scope of the invention to
employ rechargeable batteries, or mercury cells. The latter may be
satisfactory for short term pacing, in view of the relatively high
overall efficiency of the device.
As shown in FIG. 3, an insulated plate 41 in contact with the power
source is hermetically sealed by an insulator 42, and leads 43
extend to the circuit contained within the body section 12a. The
case 12 is negative with respect to the power source but is
positive with respect to the biological load.
The diagram of FIG. 6 illustrates one form of the pulsing circuit
in which a power source 40 is shown as providing an output voltage
of approximately 39 volts. This output is applied through charging
resistor 44 and through the load 45 to a capacitor 46. The time
required to charge the capacitor will depend upon the charging time
constant of the circuit, and since the biological load 45 is
normally less than 1,000 ohms it forms a small part of the total
resistance in the charging circuit. However, as long as the load 45
is present the circuit will charge.
The transistors 48 and 49 comprise a transistor switch. This switch
automatically becomes conductive to connect one side of the
capacitor 46 to ground at some predetermined potential during the
charging of the capacitor 46, and thus provides a low impedence
grounding circuit permitting a discharge of the capacitor through
the load 45. The peak load voltage may be 1.3 volts, and the
transistor switch may be conductive for 3ms. Thereafter, the
current through the switching circuit drops to the point where it
becomes non-conductive, and recharging of the capacitor 46 resumes
through resistor 44, at a repetitive rate depending on the R-C
constant.
It might also be noted that since the capacitor 46 is charged
through the biological load a current reversal takes place between
the negative pulsing electrode 32 and the case 12 which has the
effect of reducing or eliminating polarization which otherwise
occurs when electrodes are pulsed in the same direction in an
electrolytic solution.
The diagram of FIG. 7 is essentially for the same circuit as shown
in FIG. 6 except for the addition of a constant current element 50
which may comprise a constant current transistor. This circuit is
useful to maintain a constant pulse height and rate when the
pulsing circuit is used with nucleonic power source whose output
decays with time, or with biologically activated power sources
whose output varies with the amount of biological activity.
The method of implanting the Pacemaker of the present invention
using the improved catheter is illustrated diagrammatically in FIG.
5. The Pacemaker is assembled with the catheter 11 as shown in FIG.
2. The catheter is formed with a fixed or predetermined bend 27'
about two to three inches from the end, of about
20.degree.-40.degree. to enable it to turn corners while it is
being inserted. The insertion technique itself is essentially the
same as currently in use for the transvenous implantation of
endocardiac electrodes and other cardiac catherization procedures.
The Pacemaker may, for instance, be inserted in the right external
jugular vein and advanced through the superior vena cava and
through the right atrium into the apex of the right ventricular
cavity. This is the position illustrated in FIG. 5a. This is
accomplished, of course, under fluoroscopic observation.
Prior to attaching the Pacemaker, the effectiveness of its resting
position may first be observed with an electrocardiograph to assure
that it is functioning normally and that it has captured the heart.
The end 28 of the sheath 27 is preferably made of conductive
material, such as stainless steel, so that the electrode formed on
the body 12 will conduct through the sheath.
Having determined a proper position, the sheath may be partially
retracted as shown in FIG. 5b to expose the barbs, and the torque
tube 25 rotated clockwise to imbed the barbs in the myocardium. The
entire Pacemaker, in this condition, will be wedged into the
trabeculae making contact both with the case and with the tip
electrode 32.
Once attachment in this manner is made, the torque tube 25 may be
held against rotation and the rod 23 unscrewed from the internal
threads in the nut 24. The entire catheter may then be extracted
leaving the Pacemaker imbedded essentially as shown in FIG. 5c. The
Pacemaker can be extracted from the heart by reversing the
foregoing procedure.
The invention is not limited to heart pacing as such. Other
examples of the direct implantation of the self-contained
stimulator at the site of the stimulation without separate
electrical leads include baropacing (stimulation of the
baroreceptors in the neck or aortic arch), stimulation of the
diaphragm for breathing (stimulation of the phrenic nerve),
stimulation of the numerous sphincter muscles which control the
flow of various body fluids and solids (at the sphincter site), and
other such functions which have been shown to respond to electrical
stimulation and which small size and absence of electrical leads
would render feasible or more practical. In most such cases the
self-contained stimulator described in FIG. 3 would deliver a pulse
approximately every 20 milliseconds during activation of the
biological function instead of about one pulse per second as in the
cardiac Pacemaker. Activation of the pulse train could be
accomplished by external command via an electromagnetic or magnetic
signal from outside the body.
The invention is not limited to an arrangement which contains an
internal source of power. In FIG. 8 there is illustrated an
embodiment of the invention which is responsive to hemodynamic
pressure. The body section 12b is replaced by a flexible or movable
section which incorporates a rubber diaphragm or metal bellows 60
which moves under the influence of pressure changes within the
heart cavity. Forces and motions arising from such pressure changes
are applied to an electromechanical transducer 62 the output of
which may be applied to a suitable energy storing circuit 63. The
transducer may be of the magnetic induction type or may be a
piezoelectric generator. The storage device 63 may be a
diode-isolated full-wave rectifier with capacitor storage. The
energy thus stored is available for subsequent release to the
stimulation electrodes by a pulse forming circuit substantially as
previously described. The storage device will be kept charged by
the succession of heart beats and therefore serves the function of
the power source previously described.
For example, if the effective area of the movable section 65 is
about 1/2cm.sup.2, and moves 1mm under the influence of a 20 torr
average pressure pulse, each beat would produce about 130
microjoules of mechanical work. Since less than 10 microjoules of
electric energy is required for each pulse, a large margin of
reserve power is available.
A circuit diagram at FIG. 9 shows an arrangement of the pacer of
FIG. 8 adapted as a synchronous pacer, to obtain the benefits from
synchronous pacing by slaving the unit to the atriol systole. After
storing the large power pulse generated by the transducer during
the ventricular contraction, the pulse-forming circuit is "armed;"
i.e. it reaches a condition in which the next significant
electrical signal from the transducer will cause the circuit to
"fire" and deliver an electrical pulse to the stimulating
electrodes. Therefore, the pressure impulse from the next atrial
contraction is transmitted through the tricuspid valve to generate
an electrical signal from the transducer which fires the circuit.
The stimulated ventricular contractions thereby become synchronized
with the atrial contractions. It may be desirable to construct the
circuit so that "arming" is delayed until after the refractory
period of the heartbeat to avoid premature firing by reverberations
from the ventricular contraction. Also it may be desirable
physiologically to provide a delay between the signal from the
atrial contraction and the Pacemaker output pulse, similar to the
delay in the A-V node.
FIGS. 10 and 11 illustrate additional arrangements by means of
which the heart movement itself can be used to provide a suitable
source of energy. Observation has shown that an implanted Pacemaker
undergoes transient displacements of about 1cm within a 24th of a
second. Assuming constant acceleration, a 5mm displacement relative
to the capsule over 1/24th second of an armature weighing 4 grams
would produce a force of about 2500 dynes acting over this
distance, to produce about 120 microjoules of work per beat, again
substantially in excess of the requirements of the Pacemaker.
Referring to FIG. 10, a mass 70 is mounted in the manner of a
pendulum on the end of a leaf spring 72. The natural oscillation
rate of the mass 70 on the spring 72 may be that of the paced heart
rate. The lower end of the spring 72 is joint with a magnetic
armature 75 received between the poles 76 and 77 of a permanent
magnet 78.
The lower end of the armature is retained in a V-shaped recess 79
by the magnetic attraction and is correspondingly formed with a
knife or V-edge 80 to provide a pivotal movement. The poles 76 and
77 are spaced apart so that the armature 75 can assume either one
of two stable positions, as shown by the full lines and broken
lines. In one position, the flux is induced through the armature in
one direction while in the other position it is induced in the
opposite direction.
Since the pendulum formed by the mass 70 and spring 72 oscillates
in resonance with the sinus rate of the heart, the bending moment
of the spring 72 lifts the armature 75 from one pole face whereupon
it abruptly moves to the opposite pole face, resulting in a sudden
reversal of the flux and inducing an electric current in the
surrounding coil 82. The coil output may be applied to the storage
device 63, as described in connection with FIG. 8. FIG. 11 is
similar to FIG. 10 except that the mass 70' and the spring 72' are
connected to stress a piezoelectric crystal 85. In this embodiment,
the periodic rate of the mass and spring may be substantially
greater than that of the heart, to produce a "ringing" effect with
each beat.
Certain of the teachings and advantages of the present invention
may be used to improve the performance of existing pacemakers which
presently use endocardinal electrodes. The body Pacemaker 10 may be
modified for this purpose to perform the function of the electrodes
only and an arrangement for this purpose is illustrated at 100 in
FIG. 12. In this case, the cartridge body 112 is made similarly to
the body 12 except that it does not contain any pulsing circuitry
or power source, but merely comprises means for making electrical
contact. Thus, the body 112 may conveniently be made to a smaller
length and/or diameter than that which has previously been
described. The outer surface of the body 112 thus comprises one of
the electrodes, while stimulating electrode 132 may be made and
supported on a ceramic pedestal spaced from the body 112 in the
manner which has been described in connection with the electrode 32
of FIG. 3.
The electrode assembly 100 will be connected by flexible leads to a
conventional remote pacer by means of a flexible electrical conduit
or lead 122. The lead 122 may be a coaxial conductive cable, which
has one of its leads connected to the case or body 112 and the
other connected to the electrode 132. The assembly 100 may be used
with remote pacers which employ a single electrode lead or a pair
of leads. Where a single lead is used, it would be connected inside
the body 112 to the electrode 132.
The electrode assembly of this invention is provided with a
somewhat modified form of attachment comprising a pair of generally
axially extending retaining wires 115 and 116. The forward ends of
the wires are attached or secured to the body 12. The wires extend
rearwardly and outwardly, and are movable between a retracted
position in which the wires lie adjacent to the outer surface of
the body, to a spread apart position, substantially as shown.
The general technique of inserting and implanting the electrode
assembly 100 does not differ substantially from that described in
connection with the pacemaker 10. The torque tube 25 and the sheath
27 may be used, with the rod 22 removed. The cylindrical conductive
end 28 would be received partially over the body 112 with the
attaching wires 115 and 116 collapsed and retained within end 28.
The electrical lead 122 is threaded through the hollow torque tube
25.
It would be expected that the electrode assembly would be inserted
well into the apex of the ventricle cavity accompanied by some
stretching of the heart muscle. The torque tube 25 could be
employed to provide axial forces as well as rotational alignment.
The sheath 27 would then be retracted exposing the ends of the
attachment wires 115 and 116, and when the axial force is released
the ends of the wires would tend to imbed themselves within the
heart muscle. If necessary, some pull could be placed on the lead
122 to complete the attachment, and then the catheter may be
extracted leaving the electrode assembly 100 in place.
The electrode assembly 100 provides to a remote Pacemaker certain
of the advantages of the present invention. Principally, the
electrodes, which are formed as integral and discrete surface
portions of the assembly, are not prone to dislodgement, movement,
penetration or breakage. Further, they define regions of
stimulation which are spaced from the region of attachment, as in
the case of the Pacemaker 10, and thus remain free of the adverse
affects of fibrosis.
It is accordingly seen that this invention provides a novel
self-contained biological stimulator, which is particularly adapted
for use as a Pacemaker, and an electrode assembly useful with
existing Pacemakers. It is intended for long-term treatment of
partial or complete A-V block. Synchronous pacing may be used, as
desired, and the circuit can be modified as known in the art for
demand pacing. For synchronous pacing of devices of the types of
FIGS. 3, 10 or 11, a short sensing or trigger electrode wire may
extend axially from the rear wall 24' of the body 12b through the
tricuspid valve into the right atrium to pick up the atrium pulse
as a control signal for the circuit 30. For demand pacing, the
surface electrode 32 may be used to pick up the ventricle pulse and
suppress the trigger circuit in the manner taught for example by
Keller U.S. Pat. No. 3,431,912 or Greatbatch U.S. Pat. No.
3,478,746. The physical size of the capsules which form the bodies
is sufficiently small to permit long-term treatment, such as in the
case of a child. The apparatus and method of the attachment and
implanting is one which results in minimum discomfort to the
patient. In the event of failure, the size of the Pacemaker is
sufficiently small to make it feasible to simply leave it in place
and to insert a new one, although intervenous removal by catheter
also is possible.
While the forms of apparatus herein described constitute preferred
embodiments of the invention, it is to be understood that the
invention is not limited to these precise forms of apparatus, and
that changes may be made therein without departing from the scope
of the invention.
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