U.S. patent application number 11/247736 was filed with the patent office on 2006-02-09 for local cardiac motion control using applied signals and mechanical force.
Invention is credited to Shlomo Ben-Haim, Nissim Darvish, Bella Felzen, Yuval Mika, Benny Rousso.
Application Number | 20060030889 11/247736 |
Document ID | / |
Family ID | 35758408 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060030889 |
Kind Code |
A1 |
Ben-Haim; Shlomo ; et
al. |
February 9, 2006 |
Local cardiac motion control using applied signals and mechanical
force
Abstract
Apparatus (18) for performing a medical procedure on a beating
heart (20) includes a mechanical stabilization element (25), a
surface (27) of which is adapted to be applied to a segment (24) of
the heart to reduce motion of the segment. One or more electrodes
(100) are fixed to the surface of the stabilization element, so as
to contact the segment when the stabilization element is applied to
the segment. Preferably, at least one of the one or more electrodes
is adapted to apply electrical signals to the segment so as to
further reduce motion thereof, while the heart continues to pump
blood.
Inventors: |
Ben-Haim; Shlomo; (Cessaria,
IL) ; Darvish; Nissim; (Haifa, IL) ; Mika;
Yuval; (Zichron Yaakov, IL) ; Rousso; Benny;
(Bat Yam, IL) ; Felzen; Bella; (Haifa,
IL) |
Correspondence
Address: |
WOLF, BLOCK, SHORR AND SOLIS-COHEN LLP
250 PARK AVENUE
10TH FLOOR
NEW YORK
NY
10177
US
|
Family ID: |
35758408 |
Appl. No.: |
11/247736 |
Filed: |
October 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09979937 |
May 20, 2002 |
6973347 |
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PCT/IL00/00303 |
May 25, 2000 |
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11247736 |
Oct 11, 2005 |
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09320090 |
May 26, 1999 |
6442424 |
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11247736 |
Oct 11, 2005 |
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Current U.S.
Class: |
607/3 |
Current CPC
Class: |
A61B 5/287 20210101;
A61B 2562/046 20130101; A61B 5/145 20130101; A61B 2562/043
20130101; A61B 2017/0243 20130101; A61B 5/1109 20130101; A61N
1/36514 20130101; A61B 5/0215 20130101; A61N 1/0587 20130101; A61B
2505/05 20130101; A61B 5/6869 20130101; A61B 2017/00039 20130101;
A61B 17/02 20130101; A61B 2017/00022 20130101; A61B 2017/306
20130101 |
Class at
Publication: |
607/003 |
International
Class: |
A61N 1/362 20060101
A61N001/362 |
Claims
1. Apparatus for use during performance of a surgical procedure on
a segment of a beating heart, comprising a surgical tool, which
comprises: a mechanical stabilization element, a surface of which
is adapted to be applied, during the surgical procedure, to the
segment of the heart to reduce motion of the segment; and one or
more electrodes, fixed to the surface of the stabilization element,
so as to contact the segment when the stabilization element is
applied to the segment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of commonly assigned,
co-pending U.S. patent application Ser. No. 09/979,937, filed May
20, 2002; which in turn is a U.S. National Phase of PCT Patent
Application No. PCT/IL00/00303, filed May 25, 2000, which in turn
is based upon U.S. patent application Ser. No. 09/320,090, filed
May 26, 1999, now U.S. Pat. No. 6,442,424, each of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to invasive devices
and methods for treatment of biological tissue, and specifically to
devices and methods for controlling tissue and muscle during
surgery.
BACKGROUND OF THE INVENTION
[0003] Heart surgery is often accompanied by the induction of
cardioplegia (elective stopping of essentially all cardiac activity
by injection of chemicals, selective hypothermia, mechanical
stabilization, or electrical stimuli). In humans, induced global
cardioplegia is nearly always practiced in conjunction with
cardiopulmonary bypass.
[0004] Recently, minimally-invasive methods of cardiac surgery have
been developed, in which the heart is approached through an
incision made between the ribs, without stemotomy. It is sometimes
preferred that, rather than inducing cardioplegia, the surgeon
mechanically restrains a portion of the heart on which a surgical
procedure, such as a bypass graft, is to be performed. Various
tools and methods have been developed for this purpose, such as:
(a) a suction cup-based stabilization platform (e.g., the Utrecht
Octopus); (b) mechanical stabilization devices, such as the Ultima
OPCAB System, produced by Guidant, Inc. (Indianapolis, Ind.); (c)
the Octopus 2 or the EndoOctopus device, both produced by
Medtronic, Inc. (Minneapolis, Minn.); (d) a U-shaped metal foot and
other stabilizers produced by Genzyme Surgical Products, Inc.
(Tucker, Ga.); (e) the Octopus Suction stabilizer, produced by
Medtronic GmbH, Germany; and (f) CardioVations mechanical
stabilizers produced by Ethicon Endo-Surgery (Cincinnati,
Ohio).
[0005] The ClearView Blower/Mister, produced by Medtronic, is used
during minimally-invasive cardiac surgery to spray a gas/saline
mist into the operative field, so as to remove blood therefrom. The
surgeon bends the device into a desired shape and places it near to
the operative field, so that only the target area will be sprayed.
In a product description on the World Wide Web (http: II
www.medtronic.com/cardiac/mics/prod clearview.html, Feb. 8, 2000),
Medtronic suggests that "generous tube length provides access to
the surgical site, while the user's hand remains outside the
surgical field."
[0006] An article entitled "Coronary artery bypass grafting without
cardiopulmonary bypass and without interruption of native coronary
flow using a novel anastomosis site restraining device
(`Octopus`)," by Borst et al., Journal of the American College of
Cardiology, 27(6) (May 1996), pp. 1356-1364, which is incorporated
herein by reference, describes use of the Octopus
suction-generating device during experimental surgery on in situ
pig hearts.
[0007] Such mechanical restraint of the heart muscle requires that
substantial force, e.g., pressure or vacuum, be applied, which can
cause tissue trauma. The effects of mechanical stabilization are
described in an article, "The effects of mechanical stabilization
on left ventricular performance," by Burfeind et al., European
Journal of Cardio-Thoracic Surgery, 14(1998), pp. 285-289, which is
incorporated herein by reference.
[0008] PCT Patent Publication WO 97/25098, to Ben-Haim et al., and
the corresponding U.S. National Phase patent application Ser. No.
09/101,723, entitled, "Electrical muscle controller," 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 electrical signal to the heart at a
delay after electrical activation of the portion. The signal may be
applied in combination with a pacemaker or defibrillator, which
also applies an excitatory signal (i.e., pacing or defibrillation
pulses) to the heart muscle.
[0009] PCT Patent Publication WO 98/10832 to Ben-Haim et al., and
the corresponding U.S. National Phase patent application Ser. No.
09/254,900, entitled, "Cardiac output enhanced pacemaker," which
are also assigned. to the assignee of the present patent
application and incorporated herein by reference, describe a
pacemaker that modifies cardiac output. This pacemaker applies both
excitatory (pacing) and non-excitatory electrical signals to the
heart. By applying non-excitatory signals 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. U.S. Pat. No. 5,651,378, to
Matheny et al., and an article entitled, "Vagus Nerve Stimulation
as a Method to Temporarily Slow or Arrest the Heart," by Matheny
and Shaar, Annals of Thoracic Surgery, 63(6) Supplement (June
1997), pp. S28-29, which are both incorporated herein by reference,
describe a method to stimulate the vagus nerve in order to slow or
stop a patient's heart during coronary artery bypass grafting
surgery. In addition, an article entitled "Right vagal nerve
stimulation during minimally invasive direct coronary artery bypass
grafting in dogs: A preliminary study," by Hayashi et al, Journal
of Cardiovascular Surgery (Torino), 39(4) August 1998, pp. 469-471,
which is incorporated herein by reference, describes a first set of
experiments, in which the vagal nerve was stimulated so as to slow
the heart rate. In a second set of experiments, the calcium channel
blocking agents diltiazem or verapamil were administered in
conjunction with the vagal nerve stimulation, and produced either
marked bradycardia or ventricular arrest. It is noted that
stimulation of the vagus nerve affects not only cardiac function,
but also the functioning of other parts of the patient's body, such
as the pharynx, larynx, trachea, lungs, and gastrointestinal
tract.
SUMMARY OF THE INVENTION
[0010] It is an object of some aspects of the present invention to
provide improved methods and apparatus for regulating the
heart.
[0011] It is a further object of some aspects of the present
invention to provide improved methods and apparatus for reducing
motion of the heart during minimally-invasive and open chest
surgery.
[0012] It is yet a further object of some aspects of the present
invention to provide improved methods and apparatus for applying
mechanical force to reduce motion of the heart during minimally
invasive and open chest surgery.
[0013] It is still a further object of some aspects of the present
invention to provide improved methods and apparatus for reducing
motion of the heart during minimally-invasive and open-chest
surgery, while minimizing or substantially eliminating injury to
the heart resulting from the motion reduction.
[0014] In preferred embodiments of the present invention, tissue
control apparatus inhibits motion of a segment of a patient's
heart, while allowing the heart to continue to pump blood. The
tissue control apparatus comprises a stabilization element, which
has a surface that is applied to the heart in order to reduce
motion thereof. Additionally, one or more electrodes are coupled to
the surface of the stabilization element. When the element is
applied to the segment of the heart, a control unit applies
electrical signals to the heart through at least one of the
electrodes, so as to reduce or substantially stop motion of the
segment for the duration of signal application. Alternatively or
additionally, the signals are applied through the element so as to
control other aspects of the mechanical behavior of the patient's
heart. Further alternatively or additionally, the control unit
detects electrical activity of the segment of the heart through the
electrodes coupled to the stabilization element. At generally the
same time, the stabilization element applies a mechanical
motion-restraining force to the segment of the heart, so as to
further reduce the segment's motion. Termination of signal and
force application allows the segment, as well as the heart as a
whole, to resume substantially normal motion.
[0015] The reduction in motion of the segment, as provided by these
embodiments of the present invention, is typically used to enable a
surgeon to perform minimally invasive surgery or open-chest
surgery, generally without inducing global cardioplegia or
requiring cardiopulmonary bypass. For some applications, the
electrical signals are used to reduce the force applied--and thus
the injury produced--by the stabilization element, while
maintaining a desired level of motion reduction. Purely mechanical
stabilization devices known in the art, by contrast, reduce motion
of a segment of the heart through application of a mechanical force
to the delicate tissue of the heart that is considerably larger
than that generated using these embodiments of the invention, and
therefore risk damaging the tissue which is being forced to be
substantially motionless.
[0016] In some preferred embodiments of the present invention, one
or more motion sensors, e.g., accelerometers, are coupled to the
stabilization element and/or to the heart, and send motion signals
to the control unit indicative of the segment's motion and,
optionally, of the motion of other areas of the heart. Preferably,
the motion signals serve as feedback to enable the control unit to
adjust the electrical signals applied to the heart, in order to
reduce or otherwise regulate the detected motion of the segment. In
a preferred embodiment, the control unit receives the motion
signals from the sensors, and actuates the electrodes to apply the
electrical signals in order to change contractility and/or
contraction timing of muscle in the segment, so as to reduce the
detected motion.
[0017] The electrical signals applied to the heart preferably
comprise one or more of: regular pacing pulses, rapid pulses, a
fencing signal (as described hereinbelow), and an enhancement
signal. The enhancement signal is typically similar to an
Excitable-Tissue Control (ETC) signal, as described in the
above-referenced PCT Patent Publication WO 97/25098, U.S. patent
application Ser. No. 09/101,723, and in U.S. patent application
Ser. No. 09/260,769, entitled "Contractility enhancement using
excitable tissue control and multi-site pacing," which is assigned
to the assignee of the present patent application and incorporated
herein by reference. While for some applications these signals are
applied so as to reduce motion of the heart, they may alternatively
or additionally be applied to modify the mechanical behavior of the
heart in other ways, such as those described in one or more of the
patent applications incorporated herein by reference. Most
preferably, the electrical signals are synchronized with the
overall heartbeat, and have timing, shape, and magnitude
characteristics which are determined during a calibration period of
the control unit. As a result of calibration of the tissue control
apparatus, a high degree of stabilization is preferably achieved,
while maintaining adequate safety margins, e.g., acceptable patient
vital signs, reduction in applied mechanical force, and avoidance
of fibrillation and arrhythmia.
[0018] Generally, motion of the segment is characterized by a sum
of (a) a first component, consisting of motion resulting from
general contraction and relaxation of the heart; and (b) a second
component, consisting of local motion due to stimulation of the
segment by the electrodes on the stabilization element, and due to
the motion-restraining force generated by the stabilization
element. It is a goal of this embodiment of the present invention
to apply electrical signals which alter the second component,
particularly with respect to the timing thereof, such that the net
motion of the segment, resulting from summing the two components,
is generally minimized and/or smoothed.
[0019] In some preferred embodiments of the present invention,
additional electrodes are placed at multiple sites on the
epicardium and/or endocardium of the segment of the heart.
Alternatively or additionally, the additional electrodes are placed
in blood vessels of the heart or in a vicinity of the heart, and,
optionally, on areas of the heart other than the segment.
Typically, each of the additional electrodes conveys a particular
waveform to the heart, 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 the unit
under the control or supervision of a human operator, in such a
manner as to regulate the first and/or the second component of the
segment's motion.
[0020] U.S. patent application Ser. No. 09/320,091, entitled,
"Induction of cardioplegia using applied electrical signals," which
is assigned to the assignee of the present invention and is
incorporated herein by reference, describes methods for applying
electrical signals to the heart to induce a global cardioplegic
state. Additionally, the above-mentioned U.S. patent application
Ser. No. 09/320,090 describes methods and apparatus for reducing
the motion of a segment of the heart. Aspects of the methods
described in these patent applications may also be used in
conjunction with the principles of the present patent application.
In particular, in a preferred embodiment of the present invention,
the electrical signals applied to the heart comprise rapid pulses
and/or fencing signals, as described hereinbelow, applied through
one or more of the electrodes coupled to the stabilization element,
in order to induce a state of generally constant and/or reduced
contraction of the segment. The use of such pulses is described
further in application Ser. Nos. 09/320,091 and 09/320,090.
Additionally, the signals may be applied to other regions of the
heart in order to modify contraction parameters in the other
regions (e.g., timing and strength), such that motion of the
segment is reduced. Alternatively or additionally, rapid pulses
and/or other signals are applied using methods and apparatus
described in a US patent application filed May 5, 2000, entitled
"High-frequency induction of cardioplegia," which is assigned to
the assignee of the present patent application and is incorporated
herein by reference.
[0021] In some preferred embodiments of the present invention, a
"fencing" signal is applied through one or more of the electrodes,
preferably in order to prevent or inhibit the propagation of an
action potential from one region of the heart to another. Fencing
may be applied in conjunction with any (or none) of the electrical
signals described hereinabove. Most preferably, the fencing signal
is applied in a vicinity of the segment. Such fencing is described
in PCT Patent Publication WO 98/10830 and U.S. patent application
Ser. No. 09/254,903, both of which are entitled, "Fencing of
cardiac muscles," assigned to the assignee of the present
invention, and incorporated herein by reference. Fencing is
typically used, according to these embodiments, to reduce motion
and/or a contraction force of the segment, generally by blocking or
reducing the normal propagation of signals, and sometimes by
applying the fencing signal to one or more sites within the
segment.
[0022] In some preferred embodiments of the present invention,
periods of mechanical force and electrical signal application are
separated by periods in which force and/or electrical signals are
not applied. Preferably, the durations of the application and
non-application periods are set to maximize the surgeon's time for
performing surgery, without unnecessarily extending the length of
time in which free motion of the segment is limited. It is noted,
however, that even in applications which utilize continuous
application to the segment of a stabilizing force and/or
motion-reduction signals, the level of functioning of the rest of
the heart is expected to be generally sufficient to support
systemic activity without the need for cardiopulmonary bypass.
[0023] For some applications, it may be desirable to partially
(and, in some cases, significantly) reduce the overall output of
the heart in order to attain a high degree of stabilization of the
segment for a short time. Suitable methods of electrical control of
the heart to reduce cardiac output are described in the
above-mentioned U.S. patent application Ser. Nos. 09/101,723 and
09/254,900 and in PCT Patent Publications WO 97/25098 and WO
98/10832. It is emphasized that in these embodiments, as in most
applications of the present invention, the patient's vital signs
are preferably monitored substantially continuously.
[0024] In some preferred embodiments of the present invention, an
automatic or semi-automatic feedback loop modifies the electrical
signals applied to the heart, so as to optimize the segment's
stabilization without undesirably changing measured physiological
parameters, such as, for example, pCO2, pO2, Left Ventricular
Pressure (LVP), ECG, and systemic blood pressure. Preferably, an
abnormal value of any of these parameters triggers an alarm,
responsive to which the operator and/or the control unit initiates
an appropriate response. Further preferably, arrhythmia and
fibrillation detection capabilities, as well as appropriate
treatment protocols, are incorporated into the control unit.
[0025] Preferably, application of the mechanical force and
electrical signals in accordance with the present invention
stabilizes the segment within a very short period, typically about
1 second, and can maintain the segment's stability for prolonged
periods. The heart typically returns to normal function within
about 2 seconds of removal of the electrical signals.
[0026] There is therefore provided, in accordance with a preferred
embodiment of the present invention, apparatus for performing a
medical procedure on a beating heart, including: [0027] a
mechanical stabilization element, a surface of which is adapted to
be applied to a segment of the heart to reduce motion of the
segment; and [0028] one or more electrodes, fixed to the surface of
the stabilization element, so as to contact the segment when the
stabilization element is applied to the segment.
[0029] Preferably, at least one of the one or more electrodes is
adapted to apply electrical signals to the segment so as to further
reduce motion thereof, while the heart continues to pump blood.
[0030] In a preferred embodiment, the one or more electrodes
include one or more local sense electrodes, and the apparatus
includes a control unit, coupled to the local sense electrodes.
Preferably, the local sense electrodes are adapted to convey to the
control unit a current responsive to electrical activity of the
heart, and the control unit is adapted to modify the electrical
signals responsive to the conveyed current.
[0031] Alternatively or additionally, the at least one of the one
or more electrodes is adapted to apply the signals so as to modify
contraction of muscle tissue of the heart.
[0032] Preferably, the at least one of the one or more electrodes
is adapted to apply the signals at a rate greater than about 5
Hz.
[0033] In a preferred embodiment, the at least one of the one or
more electrodes includes two electrodes, which are adapted to
concurrently apply to the segment respective first and second
electric fields at respective first and second frequencies, so as
to generate a field in the heart at a beat frequency of the first
and second frequencies which reduces motion of the segment.
[0034] Alternatively or additionally, the at least one of the one
or more electrodes is adapted to apply to the segment an electric
field having a carrier frequency in excess of about 500 Hz, an
amplitude of which electric field is modulated at a modulation
frequency, so as to reduce motion of the segment.
[0035] In a preferred embodiment, the one or more electrodes
include one or more fencing electrodes, which are adapted to apply
a fencing signal to the heart so as to block propagation of an
activation wave into the segment. Alternatively or additionally,
the one or more electrodes include one or more fencing electrodes,
which are adapted to apply a fencing signal to the heart so as to
reduce a contraction force thereof.
[0036] Optionally, the one or more electrodes include one or more
pacing electrodes, which are adapted to apply a pacing signal to
the heart. Further optionally, the one or more electrodes include
one or more enhancement electrodes, which are adapted to apply an
enhancement signal to the heart. Still further optionally, the one
or more electrodes include one or more local sense electrodes,
which are adapted to sense electrical activity of the heart.
[0037] Typically, the one or more electrodes include at least one
carbon electrode, stitch electrode, wire electrode, and/or needle
electrode.
[0038] In a preferred embodiment, the apparatus includes a
transport element, fixed to the stabilization element, which
transport element is adapted to convey a fluid between the segment
of the heart and the stabilization element, when the stabilization
element is applied to the segment.
[0039] There is further provided, in accordance with a preferred
embodiment of the present invention, a method for performing a
medical procedure on a beating heart, including: [0040] applying a
mechanical stabilization element to a segment of the heart, so as
to reduce motion of the segment; and [0041] conveying electrical
signals between the segment and the element.
[0042] Typically, performing the procedure includes performing a
treatment on the segment while motion of the segment is reduced.
Alternatively or additionally, performing the procedure includes
performing a diagnostic procedure while motion of the segment is
reduced.
[0043] Preferably, applying the signals includes applying bipolar
and/or unipolar signals, as well as calibrating the signals
intermittently during the procedure.
[0044] In a preferred embodiment, applying the signals includes:
[0045] applying a first signal, prior to performing the procedure,
so as to precondition a response of the heart; and [0046] applying
a subsequent signal, during the procedure, so as to reduce the
motion of the segment during the procedure.
[0047] Alternatively or additionally, applying the signals
includes: [0048] sensing electrical activity of the heart to detect
arrhythmia thereof; and [0049] applying electrical energy to the
heart to treat the arrhythmia.
[0050] Further alternatively or additionally, applying the signals
includes: sensing electrical activity of the heart; and [0051]
modifying the application of the electrical signals responsive to
the sensed electrical activity.
[0052] Preferably, the method includes sensing motion of the heart,
wherein applying the signals includes modifying a characteristic of
at least some of the signals applied to the heart responsive to the
sensed motion.
[0053] In a preferred embodiment, applying the signals includes
applying a fencing signal to the heart to block propagation of an
activation wave into the segment of the heart and/or to reduce a
contraction force thereof.
[0054] Typically, applying the signals includes applying the
signals so as to further reduce motion of the segment.
[0055] In a preferred embodiment, applying the signals includes
applying pulses at a rate greater than 5 Hz.
[0056] In a preferred embodiment, applying the electrical signals
includes applying to the segment first and second electric fields
at respective first and second frequencies, so as to generate a
field in the heart at a beat frequency of the first and second
frequencies which reduces motion of the segment. Alternatively or
additionally, applying the electrical signals includes applying to
the segment an electric field having a carrier frequency in excess
of about 500 Hz, an amplitude of which electric field is modulated
at a modulation frequency, so as to reduce motion of the
segment.
[0057] Typically, applying the signals includes applying pulses
and/or an enhancement signal to the segment.
[0058] In a preferred embodiment, applying the signals includes
applying the signals so as to modify contraction of muscle tissue
of the heart. Typically, modifying the contraction includes
inducing contraction of the muscle tissue. Alternatively or
additionally, applying the signals includes: [0059] determining an
aspect of the motion of the segment due generally to contraction of
muscle tissue outside the segment; and [0060] adjusting the signals
responsive to the determined aspect of the segment's motion, so as
to reduce the aspect of the segment's motion.
[0061] In a preferred embodiment, applying the signals includes
applying signals through the stabilization element to a plurality
of sites on the segment of the heart. For example, applying the
signals may include applying a first waveform at a first one of the
sites and applying a second waveform, which differs from the first
waveform, at a second one of the sites. Preferably, applying the
first and second waveforms includes controlling a timing
relationship of the waveforms so as to reduce the motion of the
segment.
[0062] There is still further provided, in accordance with a
preferred embodiment of the present invention, apparatus for
performing a medical procedure on a beating heart, including:
[0063] a stabilization element, a surface of which is adapted to be
applied to a segment of the heart to reduce motion of the segment;
and [0064] one or more transport elements, fixed to the
stabilization element, which are adapted to convey a fluid between
the segment of the heart and the stabilization element, when the
stabilization element is applied to the segment.
[0065] Preferably, one of the one or more transport elements is
adapted to apply a liquid and/or gas to the segment of the
heart.
[0066] Alternatively or additionally, one of the one or more
transport elements is adapted to apply suction, so as to remove
liquid from the surface of the heart.
[0067] There is yet further provided, in accordance with a
preferred embodiment of the present invention, a method for
performing a medical procedure on a beating heart, including:
[0068] applying a stabilization element to a segment of the heart,
so as to reduce motion of the segment; and [0069] conveying a fluid
between the segment and the element, when the stabilization element
is applied to the segment.
[0070] 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
[0071] FIG. 1 is a schematic illustration of the external surface
of a heart, showing the placement of a stabilization element
thereon, in accordance with a preferred embodiment of the present
invention;
[0072] FIG. 2A is a schematic illustration of the stabilization
element, in accordance with a preferred embodiment of the present
invention;
[0073] FIG. 2B is a schematic illustration of the stabilization
element, in accordance with another preferred embodiment of the
present invention;
[0074] FIG. 2C is a schematic illustration of the stabilization
element, in accordance with yet another preferred embodiment of the
present invention; and
[0075] FIG. 3 is a schematic block diagram of a control unit, which
generates signals to be applied to the heart through the
stabilization element, in accordance with a preferred embodiment of
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0076] Reference is made to FIGS. 1, 2A, 2B, and 2C. FIG. 1 is a
schematic illustration of apparatus 18, comprising a stabilization
element 25 for reducing the motion of a segment 24 of a patient's
heart 20, in accordance with a preferred embodiment of the present
invention. FIGS. 2A, 2B, and 2C are schematic illustrations of
stabilization element 25, in respective configurations thereof, in
accordance with preferred embodiments of the present invention. Two
techniques are typically utilized concurrently to modulate the
motion of segment 24, in order to enable surgery within the
segment:
[0077] Mechanical stabilization: A surface 27 of stabilization
element 25 is placed on segment 24, so as to apply a mechanical
force thereto. The force is typically derived from a positive
pressure exerted by surface 27 of the element on heart 20.
Alternatively or additionally, one or more optional vacuum ports 39
on surface 27 are coupled through a control unit 90 of apparatus 18
to a liquid-gas-vacuum source 92. The vacuum ports hold the surface
of the heart in contact with the stabilization element, thereby
reducing motion of segment 24. Typically, but not necessarily,
surface 27 is roughened or otherwise configured so as to reduce or
eliminate any slip between surface 27 and segment 24.
[0078] (2) Electrical Stimulation and/or sensing: One or more
electrodes 100 coupled to surface 27 are actuated by control unit
90 to apply electrical signals to heart 20 and/or to sense
electrical activity of the heart. Preferred parameters of the
signals are described hereinbelow with reference to FIG. 3. The
electrical signals typically reduce motion of the heart, but may,
alternatively or additionally, pace the heart or intermittently
enhance or otherwise modulate motion of the heart.
[0079] Typically, application of signals as provided by these
embodiments of the present invention enables the mechanical force
applied by element 25 to be reduced compared to forces applied
using strictly mechanical cardiac stabilizers known in the art.
Moreover, the reduced mechanical force is generally achieved while
maintaining at least the same level of motion reduction as is
yielded using the prior art stabilizers. The inventors believe that
reducing the applied force, as is enabled using these embodiments
of the present invention, minimizes injury to tissue of the heart
that may be produced using the prior art mechanical stabilizers.
Additionally, use of mechanical stabilization in conjunction with
the electrical signals may reduce motion of the segment to a level
below that which could safely be attained by applying mechanical
force or electrical signals separately.
[0080] Optionally, a handle 41 of stabilization element 25 has two
members 29 and 31, which are slidably coupled to each other. Lines
35 preferably pass through handle 41, to couple control unit 90 to
electrodes 100 and vacuum ports 39. For some applications, lines 35
couple additional electrodes, sensors, and actuated devices on the
stabilization element to control unit 90. To simplify the
performance of open-chest procedures, a connecting member 37
typically couples handle 41 to a chest retractor (not shown), so as
to keep the stabilization element generally stationary with respect
to the patient's chest.
[0081] An elevated portion 33 of stabilization element 25
preferably enables surface 27 of the element to be placed on
segment 24, without directly compressing a particular site within
the segment. Thus, for example, elevated portion 33 may be placed
over the left anterior descending artery 22 of heart 20, so as not
to restrict blood flow through the artery. Preferably, one or more
liquid/gas transport elements 62 on elevated portion 33 or
elsewhere on the stabilization element apply one or more materials,
such as physiological saline solution, gaseous CO.sub.2, and/or air
to the surface of heart 20, so as to keep the surgery site moist
and/or clear of blood. Further preferably, the flow of these
materials through transport elements 62 is regulated by control
unit 90, which is coupled to control flow from liquid-gas-vacuum
source 92. Alternatively or additionally, elements 62 apply suction
to the surgery site, so as to remove therefrom blood or other
liquids that may interfere with the surgeon's work.
[0082] In a preferred embodiment of the present invention,
transport elements 62 are coupled to stabilization element 25 in
the absence of electrodes coupled thereto. Prior art transport
elements, such as the ClearView Blower/Mister described in the
Background section of the present application, are entities unto
themselves, which must be deliberately placed in the operative
field, and subsequently maintained there, often by a person other
than the surgeon. In this embodiment of the present invention, by
contrast, transport elements 62 are coupled to the stabilization
element, which will in any case be placed and maintained in the
operative field (typically using connecting member 37).
[0083] Depending on the patient's condition and the site of the
surgery, a surgeon will typically select a stabilization element in
which electrodes 100 comprise one or more of the following types of
electrodes: carbon electrodes 34 (FIG. 2A), needle electrodes 52
(FIG. 2B), or wire electrodes 54 (FIG. 2C). As appropriate, other
types of electrodes may be incorporated into stabilization element
25, in addition to or instead of those shown. Alternatively or
additionally, more or fewer electrodes may be incorporated into the
stabilization element. In the preferred embodiment shown in FIG.
2A, for example, dedicated local sense electrodes 74 coupled to
stabilization element 25 convey electrical signals to control unit
90 responsive to cardiac electric activity. Alternatively or
additionally, some or all of electrodes 100 (FIGS. 2B and 2C)
convey signals to the control unit responsive to the heart's
electrical activity, without the use of dedicated local sense
electrodes.
[0084] The types and placement of electrodes and sensors in FIGS.
2A, 2B, and 2C are shown by way of example. Other sites on
stabilization element 25, or in and around the heart, are
appropriate for electrode or sensor placement in other applications
of the present invention. In particular, electrodes may be placed
in a manner similar to that described in the above-mentioned U.S.
patent application Ser. No. 09/320,090, entitled "Local cardiac
motion control using applied electrical signals." Additionally,
different numbers of electrodes or sensors (including no electrodes
or sensors in some areas) and different types and combinations of
sensors and coil, stitch, defibrillation, basket, screw, patch,
needle and wire electrodes may be used in applying the principles
of the present invention. It is noted that whereas specific types
and placements of electrodes are described herein and shown in the
figures, it is within the scope of the present invention to use, as
appropriate, substantially any electrodes known in the art of
tissue stimulation and bioelectrical sensing, and to place these
electrodes on stabilization element 25, at one or more locations on
or in a vicinity of the heart, or elsewhere on or in the patient's
body.
[0085] In addition to the electrodes described hereinabove, a
plurality of motion sensors 70 (e.g., accelerometers) and one or
more optional supplemental sensors 72 are preferably coupled to
stabilization element 25 (FIG. 2B), to the heart, or to another
site on or in the patient's body. Sensors 72 may comprise, for
example, a systemic blood pressure sensor, an LVP sensor, a p02
sensor, a pC02 sensor, a flow rate sensor, and/or a force sensor,
which measures a contact force between stabilization element 25 and
heart 20. The electrodes and sensors (optionally in combination
with other electrodes and sensors not coupled to the stabilization
element) provide substantially continuous monitoring of the
patient's vital signs, in order to ensure that all of the signs are
maintained within a safe range during the surgery. To the extent
that any of the vital signs is outside the range, control unit 90
will either take corrective action on its own and/or provide an
alarm to the surgeon, who will then be able to respond
appropriately.
[0086] FIG. 3 is a schematic block diagram of control unit 90,
which conveys electrical energy to stabilization element 25 in
order to reduce motion of segment 24, in accordance with a
preferred embodiment of the present invention. Alternatively or
additionally, the control unit conveys to the stabilization element
other forms of electrical energy, such as standard pacing pulses or
the enhancement signal described in the Summary section of this
application. Preferably, control unit 90 conveys the electrical
energy to one or more of electrodes 100 coupled to surface 27 of
stabilization element 25, in order to reduce or substantially stop
the motion of segment 24. In a preferred embodiment, local sense
electrodes 74 and/or electrodes 100 convey signals responsive to
the electrical activity of heart 20 to the control unit, and
substantially no signals are applied to the heart through the
stabilization element.
[0087] Motion sensors 70, described hereinabove with reference to
FIG. 2B, preferably send motion sensor signals to a motion analysis
block 80 of control unit 90. The motion sensor signals provide
feedback to the control unit, which modifies the electrical signals
applied to the heart responsive thereto. For example, the
electrical signals may include pulses, characteristics of which are
adjusted by the control unit responsive to the motion sensor
signals, in order to minimize motion of segment 24. Motion analysis
block 80 5 preferably comprises amplifiers to amplify low-level
signals generated by motion sensors 70, and a signal processing
block, coupled to the amplifiers, which determines respective
states of motion of the motion sensors. In some applications,
motion analysis block 80 additionally receives signals from one or
more of supplemental sensors 72, particularly those sensors that
detect mechanical phenomena such as blood flow rate and blood
pressure.
[0088] Preferably, motion analysis 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 signals in order to reduce the motion of segment 24. To
achieve this goal, block 84 typically utilizes multivariate
optimization and control methods known in the art (e.g., downhill
simplex, linear state variable feedback or extended Kalman
filters), in order to cause the measured motion and/or other
parameters to converge to a desired value. For the purposes of some
embodiments of the present invention, block 84 modifies a set of
controllable parameters to minimize and/or smooth motion of segment
24. 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 100 to segment 24.
[0089] As described hereinabove, motion sensors 70 are generally
attached to stabilization element 25 and/or directly to the heart.
Typically, the motion sensors are mechanically coupled to segment
24, and the element is placed adjacent to a surgical location
within the segment. In the embodiment shown in FIG. 1, for example,
the stabilization element is placed on the surface of left
ventricle 44, adjacent to the left anterior descending artery 22,
to enable a single-vessel coronary artery bypass graft to be
performed thereon. Alternatively, the stabilization element is
placed at another ventricular site, or, for some applications, at
an atnal site of heart 20. Typically, the control unit receives
motion signals from sensors 70 indicative of motion of the surgical
site, and actuates electrodes 100 to apply the electrical signals
in order to cause muscle in a vicinity of the site to contract in a
manner which generally reduces motion of the site.
[0090] Generally, motion of segment 24 is characterized by a sum
of: (a) a first component, consisting of global heart motion
resulting from beating of heart 20, and especially motion due to
contraction of heart regions not within segment 24; and (b) a
second component, consisting of motion resulting from the part of
the heart in segment 24 that is typically stimulated by electrodes
100. Control unit 90 generally applies the electrical energy to
electrodes 100 on the stabilization element so as to alter the
second component of the motion. In a preferred embodiment,
additional electrodes (not shown) are applied directly to the
heart, independent of stabilization element 25. These additional
electrodes apply other signals to the rest of the heart, so as to
alter the first component (and, particularly, to alter timing of
the first component), such that the net motion of segment 24,
resulting from summing the two components, is generally minimized
and/or smoothed. Electrodes suitable for direct placement on the
heart are described in the above-mentioned U.S. patent application
Ser. No. 09/320,090, entitled "Local cardiac motion control using
applied electrical signals."
[0091] Preferably, the electrical signals provided by some
embodiments of the present invention have some similarity to pacing
pulses, and/or are timed to correlate with pacing pulses. They are
typically synchronized with the overall heartbeat, and have timing,
shape, and magnitude characteristics which are determined during a
calibration period at the beginning of a surgical procedure and/or
at regular intervals during the procedure. For some applications,
the electrical signals applied to the heart comprise combinations
of signals described herein, including regular pacing, rapid
pulses, fencing, enhancement signals and other signals.
[0092] During the calibration period, parameter search and tuning
block 84 preferably executes an optimization algorithm, such as
"gradient descent," in which, for example, block 84 modifies a
characteristic (e.g., timing, duration, or magnitude) of the
electrical signals generated by one of the electrodes described
herein, and then determines whether the measured motion of segment
24 decreases, or changes in some other desired way, following the
modification. Typically, in a series of similar calibration steps,
block 84 modifies characteristics of the electrical signals applied
by each of the other electrodes, wherein those modifications that
reduce motion of segment 24 are generally maintained, and
modifications that increase the motion of the segment are
eliminated or avoided. In combination with the application of
limited mechanical force by stabilization element 25, motion of
segment 24 is gradually reduced to a point at which the surgeon can
safely and conveniently perform the surgical procedure. Optionally,
the surgeon does not use the stabilization element to apply
mechanical force until motion of segment 24 has already been
substantially reduced through the application of the electrical
signals.
[0093] In some cases, it is desirable to have a preconditioning
period of segment 24 and/or of the whole heart. During the
preconditioning period, electrodes 100 (or other electrodes placed
on the heart) apply the electrical signals for short periods
initially, followed by progressively longer periods. During the
preconditioning period, characteristics of the heart's response to
the signals change, so that substantially similar inputs will
engender different responses before and after the preconditioning
period. In a preferred embodiment, the control unit applies signals
for a 2 second period, followed by 4 second, 6 second, and longer
periods, until a desired motion-reduction period of 20 seconds is
attained. It is believed that the heart is preconditioned, or
trained, during this period, and that training the heart during the
preconditioning period may improve the response of the heart during
subsequent signal-application periods. Because the heart may change
its response to the applied signals throughout the surgical
procedure, i.e., it is continually being trained, it is generally
preferable to repeat the calibration at intermittent times during
the procedure.
[0094] Most preferably, during the calibration period and during
regular operation of control unit 90, an arrhythmia detection block
82 of control unit 90 receives inputs from motion sensors 70,
supplemental sensors 72, electrodes 74 and 100, and/or other
electrodes and sensors (not shown), and evaluates these inputs to
detect an onset of cardiac arrhythmia. Preferably, block 82 employs
techniques known in the art for determining arrhythmia, so that
control unit 90 can treat or terminate the arrhythmia by pacing or
by performing cardioversion or defibrillation. In a preferred
embodiment, control unit 90 applies a shockless defibrillation
technique, as described in U.S. Provisional Patent Application No.
60/136,092, entitled "Shockless defibrillation," which is assigned
to the assignee of the present patent application and is
incorporated herein by reference.
[0095] As described hereinabove, the motion sensor signals
typically provide feedback to enable the control unit to modify the
electrical signals applied to the heart, in order to reduce the
detected motion of the segment. Additionally or alternatively,
local sense electrodes 74, which optionally comprise some or all of
electrodes 100, convey electrical signals to control unit 90 to
enable parameter search and tuning block 84 to synchronize the
electrical signals applied by electrodes 100 with the natural
electrical activity of the heart and with propagation
characteristics of the applied electrical signals. Preferably,
parameter search and tuning block 84 assesses the output from local
sense electrodes 74 in conjunction with the motion sensor signals,
so as to determine appropriate parameters for the applied
electrical signals, which both minimize motion of segment 24 and
preserve the overall function of heart 20.
[0096] In a preferred embodiment of the present invention, some of
electrodes 100 apply rapid pulses to segment 24 which are generally
similar in form and intensity to pulses commonly used to pace the
heart. The pulses are believed to induce a reversible state of
generally constant contraction of the segment, without causing
fibrillation or other dangerous arrhythmic activity. In a preferred
rapid pulse application mode, control unit 90 generates a
regularly-spaced series of current pulses, injecting current
through the electrodes into underlying cardiac tissue. In this
mode, the pulses are preferably characterized by a frequency above
5 Hz, and are typically applied above 10 Hz. Pulses applied between
about 25 and 30 Hz have been found by the inventors to produce
generally desirable results. Other parameters typically
characterizing the pulses include a duty cycle between about 5 and
50%, a DC offset between about -10 and +10 mA, and an amplitude
between about -20 and +20 mA. An amplitude of between about 1 and 5
mA is typically sufficient. These values are cited by way of
example, however, and it will be understood that higher or lower
frequencies and amplitudes may also be used, depending on the type
and placement of the electrodes and on the specific condition of
the patient's heart. For example, a frequency higher than 100 Hz
was tested on rabbits and found to yield suitable results.
[0097] Alternatively or additionally, control unit 90 applies a
fencing signal to some of electrodes 100 (or to other electrodes,
not coupled to the stabilization element), generally in order to
inhibit the generation and propagation of an action potential from
one region of the heart to another. Fencing is typically used in
these applications to block or reduce the normal propagation of
signals and/or to reduce the contractility of affected muscle
tissue. Alternatively or additionally, the fencing signal generally
reduces the contraction strength of the muscle stimulated
thereby.
[0098] In a preferred embodiment, the electrical signals comprise
first and second electrical signals, which are respectively applied
to first and second sets of electrodes 100. Preferably, the first
and second signals have respective first and second frequencies
associated therewith, which generate electric fields in the heart
at the respective frequencies. Typically, the first and second
signals have frequencies between about 500 and 20,000 Hz, and the
difference between the first and second frequencies is between
about 4 and 25 Hz. It is believed that the segment's motion is
reduced responsive to a beat frequency generated by interference of
the first and second signals. Suitable methods and apparatus for
applying the first and second signals, mutatis mutandis, are
described in the above-mentioned US patent application, entitled
"High-frequency induction of cardioplegia."
[0099] Alternatively or additionally, the electrical signals
applied by stabilization element to segment 24 comprise an
amplitude-modulated (AM) signal, applied by control unit 90 to one
or more of electrodes 100. The AM signal comprises (a) a
high-frequency component, usually over 500 Hz, which generally
passes through cardiac tissue, substantially without affecting
cardiac function, and (b) a low-frequency component, generated by
modulation of the amplitude of the high-frequency component. The
low-frequency, similar to the beat frequency described above, is
preferably between about 4 and 25 Hz. Preferably, the AM signal is
applied in a manner generally similar to that described in the
application "High-frequency induction of cardioplegia."
[0100] In general, each one of electrodes 100 conveys a particular
waveform to heart 20, differing in certain aspects from the
waveforms applied by the other electrodes. The particular waveform
to be applied is determined by control unit 90, preferably under
the control of a human 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, frequencies, duty cycles, etc.
For example, although the waveforms applied to the electrodes
typically comprise a series of monophasic square wave pulses, other
waveforms, such as a sinusoid, a series of uniphasic and/or
biphasic square waves, or substantially any other shape known in
the art of applying electric signals to tissue, could be used in
the framework of the present invention. Additionally, in some
operational modes, the voltage applied by some or all of electrodes
100 is controlled, rather than the current, as described
hereinabove.
[0101] Generally, the shape, magnitude, and timing of the waveforms
are optimized for each patient, using suitable optimization
algorithms, as are known in the art, in order to attain a desired
level of stabilization of segment 24. Typically, the optimization
is performed continually, both during the calibration period and
during regular operation. However, during a surgical procedure, the
operational parameters are typically changed more gradually, so as
not to interrupt the surgeon's actions.
[0102] Preferably, application of the electrical signals in
accordance with the present invention increases the stability of
segment 24 within a very short period (e.g., several seconds), such
that the surgeon preferably applies mechanical force via
stabilization element 25 to the segment when the segment is already
at least partially stabilized. In this manner, a lower amount of
mechanical force is typically applied to the segment than would be
applied using prior art methods. It is believed that the lower
force is likely to induce substantially less trauma to the heart
compared with results obtained using prior art methods for cardiac
mechanical stabilization. The inventors have found that the heart
typically returns to normal function within about 2 seconds of
removal of the electrical signals. A short waiting time, typically
about 15 seconds, is preferably followed by recalibration before
signals are applied again. Although the initial calibration period
can take several minutes in order to determine appropriate signals
to be applied by electrodes 100, recalibration typically requires
less time. The method of this embodiment of the present invention
has been found to be generally spontaneously reversible, typically
without requiring cardioversion or defibrillation. (Cardioversion
and defibrillation capabilities are nevertheless typically provided
to enhance safety.)
[0103] Control unit 90 preferably comprises a flow control block
88, typically including valves and mechanical switches. Block 88
allows the control unit to regulate the flow of liquid and gas from
source 92 to the surface of heart 20, as described hereinabove,
and, additionally, to control the timing and/or strength of the
vacuum applied through ports 39. Depending on the nature of the
surgical procedure, the operation of flow control block 88 may be
regulated directly by operator controls 71 and/or by parameter
search and tuning block 84, responsive to the inputs thereto. In
another preferred embodiment (not shown), the strength of the
vacuum and/or the flow of liquid and gas to the heart is regulated
independent of the control unit.
[0104] Although preferred embodiments are described hereinabove
with reference to reducing motion of the segment of the heart in
order to enable surgery on the segment, it will be understood that
the present invention may be used for other purposes, such as to
enhance a physician's ability to perform diagnostic tests on the
segment. Furthermore, the principles of the present invention are
applicable not only to the heart, but also to controlling local
motion in segments of other types of tissue, such as smooth muscle
(e.g., the intestines) and skeletal muscle.
[0105] 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 subcombinations of the
various features described hereinabove and in the articles, patents
and patent applications incorporated herein by reference, 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.
* * * * *
References