U.S. patent application number 09/848535 was filed with the patent office on 2002-03-14 for signal delivery through the right ventricular septum.
Invention is credited to Mika, Yival, Shemer, Itsik.
Application Number | 20020032467 09/848535 |
Document ID | / |
Family ID | 22749645 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020032467 |
Kind Code |
A1 |
Shemer, Itsik ; et
al. |
March 14, 2002 |
Signal delivery through the right ventricular septum
Abstract
Apparatus for applying a signal to a heart of a human subject is
provided. The apparatus includes a set of one or more electrodes,
adapted to be coupled to the right ventricular septum of the heart.
A control unit of the apparatus is adapted to drive the electrode
set to apply an Excitable-Tissue Control (ETC) signal to the
septum. Preferably, the control unit is adapted to configure the
signal to be capable of modifying contractility of a portion of the
heart.
Inventors: |
Shemer, Itsik; (Zichron
Yaakov, IL) ; Mika, Yival; (Shmurat Zichron Yaako,
IL) |
Correspondence
Address: |
William H. Dippert
Cowan, Liebowitz & Latman, P.C.
1133 Avenue of the Americas
New York
NY
10036
US
|
Family ID: |
22749645 |
Appl. No.: |
09/848535 |
Filed: |
May 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60202382 |
May 4, 2000 |
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Current U.S.
Class: |
607/2 |
Current CPC
Class: |
A61N 1/3628 20130101;
A61B 2017/00247 20130101; A61N 1/36842 20170801; A61N 1/36557
20130101; A61B 2017/0243 20130101; A61B 2017/00243 20130101; A61B
5/6858 20130101; A61N 1/36585 20130101; A61N 1/36564 20130101; A61B
5/145 20130101; A61N 1/3627 20130101; A61N 1/056 20130101; A61B
5/6859 20130101; A61B 5/287 20210101; A61B 5/6853 20130101; A61B
5/029 20130101; A61B 5/6843 20130101; A61B 2018/00392 20130101;
A61B 5/6856 20130101; A61B 18/20 20130101; A61B 5/0215 20130101;
A61N 1/36843 20170801; A61B 5/6852 20130101; A61N 1/36514 20130101;
A61N 1/36542 20130101 |
Class at
Publication: |
607/2 |
International
Class: |
A61N 001/36 |
Claims
1. A method for applying a signal to a heart of a human subject,
comprising applying an Excitable-Tissue Control (ETC) signal to a
site on the right ventricular septum of the heart.
2. A method according to claim 1, wherein applying the ETC signal
comprises configuring the signal to be capable of modifying
contractility of a portion of the heart.
3. A method according to claim 2, wherein configuring the ETC
signal comprises configuring the signal to be capable of modifying
contractility of the left ventricle of the heart.
4. A method according to claim 2, wherein configuring the ETC
signal comprises configuring the signal to be capable of modifying
contractility of the septum.
5. A method according to claim 2, wherein configuring the ETC
signal comprises configuring the signal to be capable of modifying
contractility of the right ventricle of the heart.
6. A method according to claim 2, wherein configuring the ETC
signal comprises configuring the signal to be capable of increasing
contractility of the portion of the heart.
7. A method according to claim 2, wherein configuring the ETC
signal comprises configuring the signal to be capable of decreasing
contractility of the portion of the heart.
8. A method according to claim 7, wherein configuring the ETC
signal to be capable of decreasing the contractility comprises
configuring the signal to be capable of decreasing contractility of
the septum.
9. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of biphasic pulses.
10. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of generally square pulses.
11. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of pulses at a rate greater than about
50 Hz.
12. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of pulses at a rate less than about 100
Hz.
13. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of pulses at a rate between about 50 Hz
and 100 Hz.
14. A method according to claim 1, wherein applying the ETC signal
comprises applying a series of pulses which are greater than about
8 mA.
15. A method according to claim 14, wherein applying the ETC signal
comprises applying a series of pulses which are greater than about
10 mA.
16. A method according to claim 1, wherein applying the ETC signal
comprises applying the ETC signal to a site at or adjacent to an
intersection of the septum and the right ventricular free wall.
17. Apparatus for applying a signal to a heart of a human subject,
comprising: a set of one or more electrodes, adapted to be coupled
to the right ventricular septum of the heart; and a control unit,
adapted to drive the electrode set to apply an Excitable-Tissue
Control (ETC) signal to the septum.
18. Apparatus according to claim 17, wherein the control unit is
adapted to configure the signal to be capable of modifying
contractility of a portion of the heart.
19. Apparatus according to claim 18, wherein the control unit is
adapted to configure the signal to be capable of modifying
contractility of the left ventricle of the heart.
20. Apparatus according to claim 18, the control unit is adapted to
configure the signal to be capable of modifying contractility of
the septum.
21. Apparatus according to claim 18, wherein the control unit is
adapted to configure the signal to be capable of modifying
contractility of the right ventricle of the heart.
22. Apparatus according to claim 18, wherein the control unit is
adapted to configure the signal to be capable of increasing
contractility of the portion of the heart.
23. Apparatus according to claim 18, wherein the control unit is
adapted to configure the signal to be capable of decreasing
contractility of the portion of the heart.
24. Apparatus according to claim 23, wherein the control unit is
adapted to configure the signal to be capable of decreasing
contractility of the septum.
25. Apparatus according to claim 17, wherein the control unit is
adapted to drive the elect rode s et to apply a series of biphasic
pulses.
26. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply a series of generally
square pulses.
27. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply a series of pulses at a
rate greater than about 50 Hz.
28. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply a series of pulses at a
rate less than about 100 Hz.
29. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply a series of pulses at a
rate between about 50 Hz and 100 Hz.
30. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply a series of pulses
which are greater than about 8 mA.
31. Apparatus according to claim 30, wherein the control unit is
adapted to drive the electrode set to apply a series of pulses
which are greater than about 10 mA.
32. Apparatus according to claim 17, wherein the control unit is
adapted to drive the electrode set to apply the ETC signal to a
site at or adjacent to an intersection of the septum and the right
ventricular free wall.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to invasive devices
and methods for treatment of the heart, and specifically to devices
and methods for improving cardiac performance.
BACKGROUND OF THE INVENTION
[0002] The heart requires precise coordination of its mechanical
and electrical behavior to function optimally. The human body
normally regulates cardiac output in response to body needs by
changing the heart rate, as during physical exercise, and/or by
adapting the stroke volume. Under pathological conditions, however,
some of the normal regulatory mechanisms may be damaged. For
example, heart tissue damaged due to myocardial infarct typically
cannot sustain normal pumping function. Alternatively or
additionally, normal electrical signals are not generated, or are
impaired in their propagation, such that cardiac output and cardiac
efficiency (stroke work divided by oxygen consumption) are
correspondingly compromised. Standard pacemakers known in the art
are able to control the rate of the heart, e.g., to accelerate the
heart rate after detecting bradycardia, but are not able to
increase contraction strength over the long-term without producing
adverse side-effects.
[0003] PCT Patent Publication WO 97/25098, to Ben-Haim et al.,
entitled "Electrical muscle controller," and the corresponding U.S.
patent application Ser. No. 09/101,723, which are assigned to the
assignee of the present patent application and are incorporated
herein by reference, describe methods for modifying the force of
contraction of at least a portion of a heart chamber by applying a
non-excitatory electric signal to the heart at a delay after
electrical activation of the portion. The non-excitatory signal is
such as does not induce action potentials in cardiac muscle cells,
but rather modifies the cells' response to the activation. In the
context of the present patent application, the use of such a
non-excitatory signal is referred to as Excitable-Tissue Control
(ETC). The non-excitatory signal may be applied in combination with
a pacemaker or defibrillator, which applies an excitatory signal
(i.e., pacing or defibrillation pulses) to the heart muscle.
[0004] PCT Patent Publication WO 98/10832, to Ben-Haim et al.,
entitled "Cardiac output enhanced pacemaker," and the corresponding
U.S. patent application Ser. No. 09/254,900, which are assigned to
the assignee of the present patent application and incorporated
herein by reference, describe a pacemaker that gives cardiac output
enhancement. This pacemaker applies both excitatory (pacing) and
non-excitatory (ETC) electrical stimulation pulses to the heart. By
applying non-excitatory pulses of suitable strength, appropriately
timed with respect to the heart's electrical activation, the
contraction of selected segments of the heart muscle can be
increased or decreased, thus increasing or decreasing the stroke
volume of the heart.
SUMMARY OF THE INVENTION
[0005] It is an object of some aspects of the present invention to
provide improved methods and apparatus for stimulating cardiac
tissue.
[0006] It is a further object of some aspects of the present
invention to provide improved methods and apparatus for enhancing
cardiac performance.
[0007] It is still a further object of some aspects of the present
invention to provide improved methods and apparatus for increasing
cardiac output.
[0008] In preferred embodiments of the present invention, an
electrical cardiac stimulator for improving the performance of the
heart of a human subject applies an Excitable-Tissue Control (ETC)
signal to the interventricular septum via one or more electrodes
passed by catheter into the right ventricle. Preferably, but not
necessarily, at least one electrode is screwed or otherwise fixed
to the septum, and delivers the ETC signal during a refractory
period of excitable tissue of the septum, so as to modify a
characteristic of the mechanical behavior thereof.
[0009] It is noted that these embodiments of the present invention
simplify the procedure of applying electrical signals to modulate
cardiac contraction. It is known in the art to apply pacing signals
to the left ventricle by the difficult procedure of passing a
catheter through the coronary veins. It is also known in the art to
make an incision in a patient's chest so as to implant pacing
electrodes on the heart. It is further known in the art to pace
both ventricles via an electrode placed on the interventricular
septum, whereby pacing pulses generated by the electrode cause an
activation wave to propagate through the septum, through normal
conduction pathways of the heart. These prior art techniques differ
from preferred embodiments of the present invention in that the
prior art is directed towards stimulating one or both ventricles to
contract, while these embodiments of the present invention provide
means for modulating the mechanical behavior of the septum itself,
substantially without inducing new action potentials.
[0010] Typically, each electrode conveys a particular waveform to
the septum, which may differ in certain aspects from the waveforms
applied to other electrodes. The particular waveform to be applied
to each electrode is preferably determined by a control unit,
initially under the control of a physician during a calibration
period of the unit. Further preferably, the cardiac stimulator (or
elements thereof) is implanted in the patient in a manner similar
to that used to implant pacemakers or defibrillators known in the
art. After the initial calibration period, the unit is generally
able to automatically modify the waveforms as needed to maintain a
desired level of performance of the stimulator. In many
applications, standard pacing, cardioversion, and/or defibrillation
capabilities are additionally incorporated into the stimulator.
[0011] In a preferred embodiment, one or more mechanical sensors,
e.g., force transducers, strain gauges, pressure gauges, and/or
motion sensors, are positioned in a vicinity of the heart, and are
coupled to send mechanical-sensor signals to the control unit
indicative of aspects of the heart's functioning. Alternatively or
additionally, one or more physiological sensors, e.g., for
measuring mixed venous oxygen saturation (SvO2) or thoracic
electrical impedance, send physiological-sensor signals to the
control unit. The various sensor signals serve as feedback to
enable the control unit to iteratively adjust the ETC signal
applied to the septum, so as to cause the sensor signals to
converge to desired values. Alternatively or additionally, other
sensors, such as sensing electrodes, blood pressure sensors, or
flow transducers, are coupled to the heart or elsewhere on the
patient's body, and send signals to the control unit which are used
in determining modifications to parameters of the energy applied to
the heart.
[0012] Further alternatively or additionally, the control unit
analyzes the sensor signals to detect an onset of arrhythmia, for
example, an ectopic heartbeat. In this case, the control unit
preferably modifies or terminates application of the ETC signal
responsive to the detection.
[0013] There is therefore provided, in accordance with a preferred
embodiment of the present invention, a method for applying a signal
to a heart of a human subject, including applying an
Excitable-Tissue Control (ETC) signal to a site on the right
ventricular septum of the heart.
[0014] Typically, applying the ETC signal includes configuring the
signal to be capable of modifying contractility of a portion of the
heart. For example, configuring the ETC signal may include
configuring the signal to be capable of modifying contractility of
the left ventricle of the heart, the septum, or the right ventricle
of the heart.
[0015] Preferably, configuring the ETC signal includes configuring
the signal to be capable of increasing contractility of the portion
of the heart. Alternatively, configuring the ETC signal includes
configuring the signal to be capable of decreasing contractility of
the portion of the heart. In a preferred embodiment, configuring
the ETC signal to be capable of decreasing the contractility
includes configuring the signal to be capable of decreasing
contractility of the septum.
[0016] For some applications, applying the ETC signal includes
applying a series of biphasic pulses. Alternatively or
additionally, applying the ETC signal includes applying a series of
generally square pulses. Further alternatively or additionally,
applying the ETC signal includes applying a series of pulses at a
rate greater than about 50 Hz. Still further alternatively or
additionally, applying the ETC signal includes applying a series of
pulses at a rate less than about 100 Hz.
[0017] Preferably, applying the ETC signal includes applying a
series of pulses which are greater than about 8 mA. For some
applications, applying the ETC signal includes applying a series of
pulses which are greater than about 10 mA.
[0018] In a preferred embodiment of the present invention, applying
the ETC signal includes applying the ETC signal to a site at or
adjacent to an intersection of the septum and the right ventricular
free wall.
[0019] There is also provided, in accordance with a preferred
embodiment of the present invention, apparatus for applying a
signal to a heart of a human subject, including:
[0020] a set of one or more electrodes, adapted to be coupled to
the right ventricular septum of the heart; and
[0021] a control unit, adapted to drive the electrode set to apply
an Excitable-Tissue Control (ETC) signal to the septum.
[0022] The present invention will be more fully understood from the
following detailed description of the preferred embodiments
thereof, taken together with the drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1A, 1B, and 1C are schematic, sectional illustrations
of a heart, showing the placement of electrodes therein, in
accordance with preferred embodiments of the present invention;
[0024] FIG. 2 is a schematic block diagram of a control unit, which
generates signals to be applied to the electrodes shown in FIGS.
1A, 1B, and/or 1C, in accordance with a preferred embodiment of the
present invention; and
[0025] FIGS. 3, 4, and 5 are graphs showing experimental results
from the application of an ETC signal to an animal heart, in
accordance with a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] FIG. 1A is a schematic illustration of cardiac control
apparatus 18, which applies electrical energy to improve the
performance of the heart 20 of a patient, in accordance with a
preferred embodiment of the present invention. Apparatus 18
preferably comprises an implantable or external control unit 90,
which applies an ETC signal through a set of one or more electrodes
98 to the heart. (For clarity, connections between control unit 90
and the various electrodes are not shown.)
[0027] Preferably, a catheter 68 is used to convey a screw
electrode 65, or other type of electrode, through the right
ventricle 30 to a site on the interventricular septum 22 to which
the electrode is attached. Alternatively or additionally, a
catheter 66 conveys an electrode 69 through the right ventricle to
be fixed to the septum, and/or conveys an electrode 67 into the
right ventricle, where it is in electrical contact with electrodes
65 and 69 through the blood in the right ventricle. In a preferred
embodiment, one or more electrodes are placed at or adjacent to the
intersection of the septum and the right ventricular free wall.
[0028] Preferably, at least some of the electrodes have a coating
applied thereto which increases the electrodes' capacitance. A
preferred coating comprises iridium oxide (IROX). Alternatively or
additionally, at least some of the electrodes comprise coils, a
mesh, or other means for increasing the effective application area
of the ETC signal.
[0029] As described hereinbelow, control unit 90 drives one or more
of the electrodes to apply an ETC signal to the septum, so as to
modify an aspect of the heart's contractility. For example, the
signal may be applied so as to increase or decrease contractility
of the right ventricle, the left ventricle, or the septum.
Optionally, the control unit is implanted in the patient's body,
and a metal case of the control unit serves as a return electrode
for current driven through the electrodes in right ventricle
30.
[0030] Preferably, aspects of ETC signal application are performed
in accordance with techniques described in the above-referenced
U.S. patent applications Ser. Nos. 09/101,723 and 09/254,900.
Typically, the ETC signal is applied subsequent to an artificial
pacing pulse, as described hereinbelow. Alternatively, the ETC
signal is applied responsive to natural electrical activity of the
heart, for example, after a designated delay following a detected
activation of the atrium. For these applications, it is preferable
to use apparatus and methods described in Israel Patent Application
129,257, entitled "Trigger-based regulation of excitable tissue
control in the heart," which is assigned to the assignee of the
present invention and is incorporated herein by reference.
[0031] Control unit 90 is optionally coupled to one or more local
sense electrodes 74, which are placed in the right ventricle or
elsewhere on or in the heart. Local sense electrodes 74 preferably
convey electrical signals to the control unit responsive to cardiac
electric activity. Alternatively or additionally, one or more of
electrodes 98 and any other electrodes coupled to control unit 90
may also serve as sense electrodes. Optionally, one or more
mechanical sensors 70 (e.g., accelerometers, force transducers,
strain gauges, or pressure gauges), coupled to the control unit,
are placed on the right ventricle or elsewhere on the heart.
Alternatively or additionally, one or more supplemental sensors 72
(e.g., blood pressure, thoracic electrical impedance, pH, SvO2,
pCO2 or pO2 sensors) are coupled to the control unit and are placed
on or in the heart or elsewhere on or in the patient's body. The
control unit modifies the energy applied through electrodes 98
responsive to signals from sensors 70 and 72 and local sense
electrodes 74, as described hereinbelow.
[0032] The number of electrodes and sensors, as well as the
positions thereof, are shown in FIG. 1A by way of example, and
other sites on heart 20 or in a vicinity thereof are appropriate
for placement of some of the electrodes and sensors in other
applications of the present invention.
[0033] Preferably, control unit 90 is implanted in the patient in a
manner similar to that used to implant pacemakers or defibrillators
known in the art, such that after an initial calibration period,
described hereinbelow, the unit is generally able to automatically
modify the ETC signal it applies to the heart as needed, so as to
maintain a desired level of performance. In many applications,
standard pacing, cardioversion, and defibrillation capabilities are
additionally incorporated into apparatus 18.
[0034] FIGS. 1B and 1C are schematic illustrations of other
preferred configurations of cardiac control apparatus 18, in
accordance with respective preferred embodiments of the present
invention. FIG. 1B shows a catheter 166, which conveys a plurality
of electrodes 165, 167, and 169 to respective sites on the right
ventricular septum, while FIG. 1C shows a catheter 266, which
conveys a different arrangement of electrodes 265, 267, 269, and
271 to the septum. In another preferred embodiment (not shown), a
catheter passes a basket electrode into the right ventricle, so as
to apply the ETC signal to the septum as well as to other right
ventricular sites. Preferably, but not necessarily, all of the
electrodes shown in FIGS. 1A, 1B, and 1C are independently
controlled by control unit 90.
[0035] FIG. 2 is a schematic block diagram of control unit 90, in
accordance with a preferred embodiment of the present invention.
Mechanical sensors 70, supplemental sensors 72, local sense
electrodes 74, and electrodes 98 are preferably coupled to provide
feedback signals to a cardiac function analysis block 80 of control
unit 90. The feedback signals generally provide information about
various aspects of the heart's performance to block 80, which
analyzes the signals and actuates control unit 90 to modify the
electrical energy applied to the heart responsive to the analysis.
Preferably, the ETC signal is adjusted by the control unit
responsive to the feedback signals in order to yield a desired
response, e.g., a predetermined blood pressure, blood oxygen level,
cardiac output and/or cardiac electrical or motion profile.
[0036] Preferably, block 80 conveys results of its analysis to a
"parameter search and tuning" block 84 of control unit 90, which
iteratively modifies characteristics of the electrical energy
applied to the heart in order to attain a desired response.
Preferably, operating parameters of block 84 are entered by a human
operator of the control unit using operator controls 71, which
typically comprise a keyboard or mouse (not shown) coupled to the
control unit. Block 84 typically utilizes multivariate optimization
and control methods known in the art in order to cause one or more
of the aforementioned mechanical, electrical, chemical and/or other
measured parameters to converge to desired values.
[0037] In general, each one of electrodes 98 may convey a
particular waveform to heart 20, differing in certain aspects from
the waveforms applied by the other electrodes. The particular
waveform to be applied by each electrode is determined by control
unit 90, preferably under the control of the operator. Aspects of
the waveforms which are set by the control unit, and may differ
from electrode to electrode, typically include parameters such as
time shifts between application of waveforms at different
electrodes, waveform shapes, amplitudes, DC offsets, durations, and
duty cycles. For example, although the waveforms applied to some or
all of electrodes 98 usually comprise a biphasic square wave signal
following a natural or applied pacing pulse, other waveforms, such
as a sinusoid, a series of monophasic square waves, or a waveform
including an exponentially-varying characteristic, could be applied
to other electrodes. Generally, the shape, magnitude, and timing of
the waveforms are optimized for each patient, using suitable
optimization algorithms as are known in the art.
[0038] For the purposes of this embodiment of the present
invention, block 84 typically modifies a set of controllable
parameters of the ETC signal, responsive to the measured
parameters, in accordance with values in a look-up table and/or
pre-programmed formulae stored in an electronic memory of control
unit 90. The controllable parameters may comprise, for example, ETC
signal timing, magnitude and offset. Preferably, the controllable
parameters are conveyed by block 84 to a signal generation block 86
of control unit 90, which generates, responsive to the parameters,
electrical signals that are applied by electrodes 98 to the heart.
Block 86 preferably comprises amplifiers, isolation units, and
other standard circuitry known in the art of electrical signal
generation.
[0039] In the initial calibration procedure, parameter search and
tuning block 84 preferably modifies a characteristic (e.g., timing,
magnitude, or shape) of the ETC signal applied through one of
electrodes 98, and then determines whether a predetermined cardiac
functional response generally improves following the modification.
For example, the electrode may be used to sense the duration of the
refractory period of heart tissue to which the electrode is
coupled, and block 84 may subsequently determine time points during
the refractory period which are optimal for application of the ETC
signal by that electrode to the tissue. In a series of similar
calibration steps, block 84 repeatedly modifies characteristics of
the energy applied through each of the electrodes, such that those
modifications that improve the response are generally maintained,
and modifications that cause it to worsen are typically eliminated
or avoided.
[0040] When apparatus 18 is calibrated in the presence of a
physician, it is often desirable to have the patient perform
increasing levels of exercise (e.g., walk on a treadmill), in order
to derive a broader range of operating parameters, which are stored
in control unit 90 and can be accessed responsive to signals from
the sensors and electrodes coupled to the control unit. Preferably,
the calibration procedure is subsequently performed by the
physician at intermittent follow-up visits, and/or by unit 90
automatically during regular use of the apparatus (e.g.,
daily).
[0041] Preferably, during the initial calibration procedure, the
locations of one or more of electrodes 98 are varied while the ETC
signal is applied therethrough, so as to determine optimum
placement of the electrodes. Preferably, methods for measuring the
heart's response to the applied signal include electrocardiography,
echocardiography, and/or methods having as inputs the outputs of
mechanical and supplemental sensors 70 and 72. In subsequent steps,
the electrode is moved over an area of the interventricular septum,
and the response of the heart is measured. After the physician
considers that a sufficient number of sites have been investigated,
the electrode is returned to the site yielding the best response.
Subsequently, other electrodes are moved according to the same
protocol, so as to achieve substantially optimum placement of some
or all of the electrodes.
[0042] In a preferred embodiment, the ETC signal is applied in a
vicinity of a site where standard pacing pulses are applied.
Preferably, the ETC signal is applied through the same electrode as
that through which the standard pacing pulse is applied,
approximately 1-250 ms thereafter. Further preferably, the ETC
signal is applied approximately 20-250 ms after the pacing
pulse.
[0043] Alternatively, the sinoatrial node generates the cardiac
rhythm, substantially without artificial pacing. In such modes,
local sense electrodes 74 and, optionally, some or all of
electrodes 98, convey electrical signals to control unit 90, so as
to enable parameter search and tuning block 84 to synchronize the
electrical signals applied by electrodes 98 with the natural
electrical activity of the heart. It will be understood that
although electrodes 74 and 98 are shown for clarity of explanation
as separate entities, a single set of electrodes may be used to
perform both functions.
[0044] In a preferred embodiment, the ETC signal is applied at one
or more sites as a series of pulses, e.g., biphasic square pulses,
typically having a frequency between about 50 and 100 Hz. The
current applied during each pulse is preferably greater than 8 mA,
and, further preferably, greater than 10 mA.
[0045] Most preferably, during calibration and during regular
operation of control unit 90, an arrhythmia detection block 82 of
control unit 90 receives inputs from sensors 70 and 72 and
electrodes 74 and 98, and/or other electrodes and sensors (not
shown), and evaluates these inputs to detect imminent or actual
cardiac arrhythmia, e.g., an ectopic heartbeat, fibrillation,
bradycardia or heart block. Preferably, block 82 employs techniques
known in the art for detecting arrhythmias, so that parameter
search and tuning block 84 can treat or terminate the arrhythmia by
applying, for example, regular pacing pulses or defibrillation
pulses.
[0046] FIGS. 3, 4, and 5 are graphs showing experimental results
obtained during application of an ETC signal to a 30 kg
anesthetized pig, in accordance with a preferred embodiment of the
present invention. In this experiment, local sense electrodes
comprised two stitch electrodes, which were placed at the
mid-anterior wall of the left ventricle. The animal was paced in
DDD mode at 120 beats per minute through an active fixation screw
electrode, placed in the apical third of the right ventricular
septum. At 20 ms following the onset of electrical activity as
measured by the local sense electrodes, a biphasic electrical
signal, composed of a 15 ms, +14 mA pulse immediately followed by a
15 ms, -14 mA pulse, was applied to the septum through the screw
electrode implanted therein. In FIG. 3, results are shown following
application of the ETC signal between the screw electrode implanted
in the septum and a ring electrode in a vicinity thereof. FIGS. 4
and 5 show results following application of the ETC signal between
the screw electrode and a stitch electrode at the mid-anterior left
ventricular free wall.
[0047] In FIG. 3, an increase of approximately 5% in the measured
d(LVP)/dt is seen to begin upon initiation of a 2 minute ETC signal
application period. The dP/dt levels gradually return to baseline
upon termination of the ETC signal. FIGS. 4 and 5 show bipolar ETC
application periods lasting over 3 and over 4 minutes,
respectively, in which the measured dP/dt increased to
approximately 20% above baseline, and remained at this level for
the duration of signal application.
[0048] It is believed that at least some of the results displayed
in FIGS. 3, 4, and 5 derive from a change in contractility of the
left ventricle induced by the application of the ETC signal to the
interventricular septum.
[0049] It is also believed that similar results can be obtained in
humans, mutatis mutandis. It is further believed that these
embodiments of the present invention can produce, at least to some
extent, long-term effects which are likely to alleviate or cure
aspects of some common cardiac pathologies, such as congestive
heart failure (CHF). These effects are expected to derive from more
effective use of the heart muscle, whereby systemic demands on the
heart are reduced. Moreover, damage to other organs of the body is
reduced, because of the increase in blood perfusion.
[0050] It is believed that other signal application protocols would
also be successful in enhancing cardiac performance, in combination
with or in the absence of some of the stimulation and sensing
protocols described hereinabove. In a preferred embodiment, the ETC
signal is applied at a plurality of sites on the interventricular
septum, for example, on an anterior and a posterior aspect thereof.
Alternatively or additionally, the ETC signal is applied generally
simultaneously, or in alternation, at one or more of the following
sites: the posterior septum, the anterior septum, the anterior wall
of the right ventricle, the free wall of the right ventricle, and
the posterior-inferior left ventricular free wall.
[0051] Alternatively or additionally, the ETC signal is applied
through the right ventricular septum so as to decrease regional
contractility of the heart, preferably using techniques described
in one or both of the above-referenced U.S. patent applications. In
particular, the ETC signal may be used to decrease septal
contractility, which may be appropriate in treating conditions such
as idiopathic hypertrophic subaortic stenosis (IHSS). It is
believed that reduced septal contractility reduces functional
subaortic stenosis, thereby improving left ventricular
performance.
[0052] It will be appreciated by persons skilled in the art that
the present invention is not limited to what has been particularly
shown and described hereinabove. Rather, the scope of the present
invention includes both combinations and sub-combinations of the
various features described hereinabove, as well as variations and
modifications thereof that are not in the prior art which would
occur to persons skilled in the art upon reading the foregoing
description.
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