U.S. patent application number 09/914547 was filed with the patent office on 2002-12-12 for field delivery safety system using detection of atypical ecg.
Invention is credited to Mika, Yuval, Policker, Shai, Prutchi, David, Shemer, Itzhak.
Application Number | 20020188322 09/914547 |
Document ID | / |
Family ID | 26869127 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020188322 |
Kind Code |
A1 |
Policker, Shai ; et
al. |
December 12, 2002 |
FIELD DELIVERY SAFETY SYSTEM USING DETECTION OF ATYPICAL ECG
Abstract
Apparatus for applying a non-excitatory signal to a heart,
comprising: at least one electrode; a power source; a wide-field
ECG sensor that receives a wide-field ECG signal containing
contributions from non-local sized portions of the heart; a
controller for selectively electrifying said at least one electrode
with a non-excitatory signal from said power source; and a safety
filter that inhibits said electrifying responsive to said
wide-field ECG signal.
Inventors: |
Policker, Shai; (Tzur-Moshe,
IL) ; Mika, Yuval; (Zichron-Yaacov, IL) ;
Prutchi, David; (Lake Jackson, TX) ; Shemer,
Itzhak; (Zichron-Yaacov, IL) |
Correspondence
Address: |
William H Dippert
Cowan Liebowitz & Latman
1133 Avenue of the Americas
New York
NY
10036-6799
US
|
Family ID: |
26869127 |
Appl. No.: |
09/914547 |
Filed: |
August 28, 2001 |
PCT Filed: |
December 28, 2000 |
PCT NO: |
PCT/IL00/00873 |
Current U.S.
Class: |
607/1 |
Current CPC
Class: |
A61N 1/40 20130101; A61N
1/3622 20130101; A61N 1/368 20130101; A61N 1/32 20130101 |
Class at
Publication: |
607/1 |
International
Class: |
A61N 001/00 |
Claims
1. Apparatus for applying a non-excitatory signal to a heart,
comprising: at least one electrode; a power source; a wide-field
ECG sensor that receives a wide-field ECG signal containing
contributions from non-local sized portions of the heart; a
controller for selectively electrifying said at least one electrode
with a non-excitatory signal from said power source; and a safety
filter that inhibits said electrifying responsive to said
wide-field ECG signal.
2. Apparatus according to claim 1, wherein said wide-field ECG
sensor detects electric field contributions from at least two heart
chambers.
3. Apparatus according to claim 1, wherein said wide-field ECG
sensor detects electric field contributions from an area of at
least 5 cm.sup.2 of the heart.
4. Apparatus according to claim 1, wherein said wide-field ECG
sensor detects electric field contributions from an area of at
least 15 cm.sup.2 of the heart.
5. Apparatus according to claim 1, wherein said wide-field ECG
sensor detects electric field contributions from at least one
quarter of a heart chamber.
6. Apparatus according to claim 1, wherein said wide-field ECG
sensor detects electric field contributions from at least one third
of a heart chamber.
7. Apparatus according to any of claims 1-6, wherein said
wide-field ECG sensor detects electric field contributions from
parts of the heart that are expected to be activated prior to said
electrifying.
8. Apparatus according to any of claims 1-7, wherein said
wide-field ECG sensor detects electric field contributions from
parts of the heart that are expected to be activated after to said
electrifying.
9. Apparatus according to any of claims 1-8, wherein said
wide-field ECG sensor includes at least one component shared with a
sensor used for timing said electrifying.
10. Apparatus according to claim 9, wherein said wide-field ECG
sensor shares said at least one electrode.
11. Apparatus according to any of claims 1-10, wherein said
non-excitatory signal increases a contractility of at least a
portion of said heart.
12. Apparatus according to any of claims 1-11, wherein said safety
filter includes a template matcher that matches said ECG trace to
at least one template.
13. Apparatus according to claim 12, wherein said template matcher
matches said ECG trace to at least one template suitable for a
paced heart and at least one template suitable for an unpaced
heart.
14. Apparatus according to claim 12 or claim 13, wherein said at
least one template includes at least two templates, each designated
for different heart rates.
15. Apparatus according to claim 12 or claim 13, wherein said at
least one template includes a single template suitable for multiple
heart rates.
16. Apparatus according to any of claims 12-15, wherein said at
least one template includes at least two templates, each designated
for a different non-excitatory signal.
17. Apparatus according to any of claims 12-16, wherein said at
least one template includes at least two templates, each designated
for a wide-field ECG sensing area.
18. Apparatus according to any of claims 12-17, wherein said at
least one template includes an ECG portion corresponding to a
period between a right ventricle pacing or sensing event and a time
for application of a non-excitatory signal.
19. Apparatus according to any of claims 12-18, wherein said at
least one template is continuously updated.
20. Apparatus according to claim 19, wherein said at least one
template is updated to be a weighted average of a current template
and a current ECG signal.
21. Apparatus according to claim 19, wherein said at least one
template is updated with both normal and abnormal ECG signals.
22. Apparatus according to any of claims 12-21, wherein said filter
ignores templates that did not match for a considerable period of
time.
23. Apparatus according to any of claims 1-22, wherein said filter
prevents said electrification from starting.
24. Apparatus according to any of claims 1-22, wherein said filter
stops an ongoing electrification from continuing.
25. Apparatus according to any of claims 1-24, wherein said filter
is configured to prevent arrhythmia to be caused by said
non-excitatory signal.
26. Apparatus according to any of claims 1-24, wherein said filter
is configured to prevent inefficient non-excitatory signal to be
applied to said heart.
27. Apparatus according to any of claims 1-26, wherein said
wide-field ECG sensor comprises two electrode portions spaced apart
at least 3 centimeters.
28. Apparatus according to claim 27, wherein said wide-field ECG
sensor comprises two electrode portions spaced apart at least 5
centimeters.
29. Apparatus according to claim 27 or claim 28, wherein at least
one of said two electrode portions is adapted to be placed
distanced from the heart.
30. Apparatus according to any of claims 27-29, wherein at least
one of said two electrode portions is adapted to be in contact with
the heart's inner surface.
31. Apparatus according to any of claims 27-30, wherein at least
one of said two electrode portions is adapted to be in contact with
the heart's outer surface.
32. Apparatus according to any of claims 27-31, wherein at least
one of said two electrode portions is adapted to float in the
heart's volume.
33. Apparatus according to any of claims 27-32, wherein said two
electrodes are mounted on a same elongate lead.
34. A method of determining if to inhibit the application of a
non-excitatory signal to the heart, comprising: detecting a
non-local ECG trace; determining if said trace indicates a normal
activation of the heart; and inhibiting the application of a
non-excitatory signal responsive to a negative determination of
said trace.
Description
RELATED APPLICATIONS
[0001] This application is related to and claims the benefit under
35 USC 119(e) of U.S. Ser. No. 60/173,422 filed on Dec. 29, 1999,
the disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present relates to inhibition of delivery of
inappropriate controlling currents to a heart.
BACKGROUND
[0003] The application of a non-excitatory field to the heart, in
order to modify its contractility and/or have another desirable
controlling effect on the heart is described, for example in
PCT/IL97/00012, the disclosure of which is incorporated herein by
reference.
[0004] Such non-excitatory signals can cause, in some cases, an
arrhythmia, which may be potentially fatal, for example if it is
applied to excitable tissue. The signal is applied, in some
devices, in a time window determined based on a locally sensed
depolarization event. Such a window will also tend to prevent
pro-arrhythmic effects, at least in some cases. However, if an
arrhythmia exists, the applied non-excitatory signal can cause a
further arrhythmia.
[0005] However, in spite of these and other safety measures that
may be applied, there remains the danger that an applied
non-excitatory signal will inadvertently cause or interact with an
arrhythmia.
SUMMARY OF THE INVENTION
[0006] An aspect of some embodiments of the invention relates to
using a wide-field ECG signal to determine when to inhibit the
application of a non-excitatory control signal (ETC). The
application of an ETC signal may be prevented or an ETC signal
being applied may be stopped and/or modified. In an exemplary
embodiment of the invention, the ETC signal is designed to increase
contractility, decrease contractility, change an activation profile
(e.g., conduction velocity or heart rate) and/or prevent
propagation of arrhythmia.
[0007] In an exemplary embodiment of the invention, the wide-field
ECG signal contains contributions from a significant portion of the
heart and is used to determine if the heart, as a whole (or a
significant portion thereof) is experiencing a normal activation
profile (e.g., one for which the ETC signal is suitable). In an
exemplary embodiment of the invention, the wide-field ECG includes
contributions from two or more chambers and/or from a heart portion
having a surface area of over 3, 5 or 15 cm.sup.2.
[0008] In an exemplary embodiment of the invention, the wide-field
ECG is compared to one or more templates of suitable or unsuitable
heart ECGs. In an exemplary embodiment of the invention, the ECG
comprises a trace of the ECG from the start of the beat until when
the ETC signal is applied. Alternatively other methods of matching
an ECG signal to stored signal parameters are used.
[0009] An aspect of some embodiments of the invention relates to a
method of acquiring and/or maintaining a "normal" template of heart
ECG activation. In an exemplary embodiment of the invention, a
plurality of ECG traces are accumulated for heart cycles. The ECG
traces may be accumulated separately for different states, for
example, for machine-paced cycles and for autonomous-paced cycles.
In an exemplary embodiment of the invention, a dispersion (and/or
other variation-related parameter) of the ECG traces is calculated.
Possibly, the dispersion is used when matching an ECG trace to the
template, to determine if the trace "fits" the template or not.
[0010] In an exemplary embodiment of the invention, the template is
continuously updated, possibly also with "abnormal" ECG traces. In
an exemplary embodiment of the invention, this type of updating
allows the template to track changes in the normal activation of
the heart.
[0011] Alternatively or additionally, when a template is not
matched for a considerable period of time (e.g. 120 beats), it is
dropped. Revival may be automatic, for example if the template
matches at least a threshold amount over a threshold period.
Alternatively or additionally, revival may be manual, for example,
by a physician that programs an ETC controller that delivers the
non-excitatory signal.
[0012] There is thus provided in accordance with an exemplary
embodiment of the invention, apparatus for applying a
non-excitatory signal to a heart, comprising:
[0013] at least one electrode;
[0014] a power source;
[0015] a wide-field ECG sensor that receives a wide-field ECG
signal containing contributions from non-local sized portions of
the heart;
[0016] a controller for selectively electrifying said at least one
electrode with a non-excitatory signal from said power source;
and
[0017] a safety filter that inhibits said electrifying responsive
to said wide-field ECG signal. Optionally, said wide-field ECG
sensor detects electric field contributions from at least two heart
chambers. Alternatively or additionally, said wide-field ECG
detects electric field contributions from an area of at least 5 cm2
of the heart. Alternatively or additionally, said wide-field ECG
detects electric field contributions from an area of at least 15
cm2 of the heart.
[0018] In an exemplary embodiment of the invention, said wide-field
ECG sensor detects electric field contributions from at least one
quarter of a heart chamber. Alternatively or additionally, said
wide-field ECG sensor detects electric field contributions from at
least one third of a heart chamber.
[0019] In an exemplary embodiment of the invention, said wide-field
ECG sensor detects electric field contributions from parts of the
heart that are expected to be activated prior to said electrifying.
Alternatively or additionally, said wide-field ECG sensor detects
electric field contributions from parts of the heart that are
expected to be activated after to said electrifying. Alternatively
or additionally, said wide-field ECG sensor includes at least one
component shared with a sensor used for timing said electrifying.
Optionally, said wide-field ECG sensor shares said at least one
electrode.
[0020] In an exemplary embodiment of the invention, said
non-excitatory signal increases a contractility of at least a
portion of said heart.
[0021] In an exemplary embodiment of the invention, said safety
filter includes a template matcher that matches said ECG trace to
at least one template. Optionally, said template matcher matches
said ECG trace to at least one template suitable for a paced heart
and at least one template suitable for an unpaced heart.
Alternatively or additionally, said at least one template includes
at least two templates, each designated for different heart rates.
Alternatively, said at least one template includes a single
template suitable for multiple heart rates.
[0022] In an exemplary embodiment of the invention, said at least
one template includes at least two templates, each designated for a
different non-excitatory signal. Alternatively or additionally,
said at least one template includes at least two templates, each
designated for a wide-field ECG sensing area. Alternatively or
additionally, said at least one template includes an ECG portion
corresponding to a period between a right ventricle pacing or
sensing event and a time for application of a non-excitatory
signal. Alternatively or additionally, said at least one template
is continuously updated. Optionally, said at least one template is
updated to be a weighted average of a current template and a
current ECG signal. Alternatively, said at least one template is
updated with both normal and abnormal ECG signals.
[0023] In an exemplary embodiment of the invention, said filter
ignores templates that did not match for a considerable period of
time. Alternatively or additionally, said filter prevents said
electrification from starting.
[0024] In an exemplary embodiment of the invention, said filter
stops an ongoing electrification from continuing. Alternatively or
additionally, said filter is configured to prevent arrhythmia to be
caused by said non-excitatory signal. Alternatively or
additionally, said filter is configured to prevent inefficient
non-excitatory signal to be applied to said heart.
[0025] In an exemplary embodiment of the invention, said wide-field
ECG sensor comprises two electrode portions spaced apart at least 3
centimeters. Optionally, said wide-field ECG sensor comprises two
electrode portions spaced apart at least 5 centimeters.
Alternatively or additionally, at least one of said two electrode
portions is adapted to be placed distanced from the heart.
Alternatively or additionally, at least one of said two electrode
portions is adapted to be in contact with the heart's inner
surface. Alternatively or additionally, at least one of said two
electrode portions is adapted to be in contact with the heart's
outer surface. Alternatively or additionally, at least one of said
two electrode portions is adapted to float in the heart's volume.
Alternatively or additionally, said two electrodes are mounted on a
same elongate lead.
[0026] There is also provided in accordance with an exemplary
embodiment of the invention, a method of determining if to inhibit
the application of a non-excitatory signal to the heart,
comprising:
[0027] detecting a non-local ECG trace;
[0028] determining if said trace indicates a normal activation of
the heart; and
[0029] inhibiting the application of a non-excitatory signal
responsive to a negative determination of said trace.
BRIEF DESCRIPTION OF THE FIGURES
[0030] Non-limiting exemplary embodiments of the invention will be
described in following description of exemplary embodiments, read
in conjunction with the accompanying figures. Identical structures,
elements or parts that appear in more than one of the figures are
labeled with a same or similar numeral in all the figures in which
they appear.
[0031] FIG. 1 is a schematic illustration of an ETC controller
including a safety filter in accordance with an exemplary
embodiment of the present invention; and
[0032] FIG. 2 is a flowchart of a method of determining if to
inhibit an ETC signal, in accordance with an exemplary embodiment
of the invention.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
[0033] FIG. 1 is a schematic illustration of an ETC controller 101
including a safety filter 104 in accordance with an exemplary
embodiment of the present invention. ETC controller 101 includes an
ETC logic module 102 that generates a non-excitatory signal to be
applied to a heart 100 via one or more electrodes, such as
electrodes 106 and 108. Apparatus for such generation of
non-excitatory control signals and various types of such signals,
are described, for example, in PCT/IL97/00012 and in PCT
publications WO 97/25098, WO 98/10831, WO 98/10832 and U.S. patent
application Ser. No. 09/260,769, the disclosures of which are
incorporated herein by reference.
[0034] As used herein the term non-excitatory is used to describe a
pulse that does not generate a new propagating action potential,
but may modify an existing or future potential. This behavior may
be, for example, a result of the pulse amplitude, frequency
application location and/or pulse envelope, and generally also
depends on the timing of the pulse application. It is noted that a
single pulse may have excitatory and non-excitatory parts. For
example a 100 ms pacing pulse, may cease to have a pacing effect
after 20 ms and have real non-excitatory effects after 40 ms.
[0035] In an exemplary embodiment of the invention, module 102
generates a contractility enhancing signal. However, if such a
signal is applied at an inappropriate timing relative to the
refractory period of the heart tissue to which it is applied, the
signal will be excitatory and generate a propagating action
potential. This action potential can be the cause of a fatal
arrhythmia.
[0036] In an exemplary embodiment of the invention, a safety filter
104 is provided, to inhibit ETC signals that might cause
arrhythmia. In an exemplary embodiment of the invention, as
described below, filter 104 operates by comparing a currently
acquired a non-local ECG trace with allowed values for such a
trace. Such a non-local ECG trace while possibly less suitable for
detecting local events, may be used to detect area-wide activation
profiles, or at least whether such a profile is normal or not.
Optionally, the trace is acquired using a plurality of ECG
electrodes 110. This comparison serves as an overall reasonableness
test. If the test fails, meaning that the heart cycle is not
proceeding "normally", the ETC is not applied. Optionally, as
described below, a template of allowed traces is used to match the
trace.
[0037] In an exemplary embodiment of the invention, filter 104 is
provided as a watchdog, that is applied separately from other logic
used to decide whether to apply an ETC signal and what that signal
should be. Alternatively, the logic of filter 104 is integrated
with the logic of ETC logic 102.
[0038] In an exemplary embodiment of the invention, filter 104 is a
logic filter, in that it inhibits a "go-ahead" signal for
delivering an ETC signal or it provides a "no-ETC" signal to ETC
logic 102. Alternatively, filter 104 is a power filter, that
prevents the current applied by ETC logic 102 from reaching
electrodes 106 and 108. Optionally, this current is used for
operating filter 104. Therefore, filter 104 may optionally be
provided as a stand alone device or upgrade, alternatively to being
provided integrally with ETC logic 102 in a single casing.
[0039] FIG. 2 is a flowchart 200 of a method of determining if to
inhibit an ETC signal, in accordance with an exemplary embodiment
of the invention.
[0040] At 202, a wide field ECG trace is acquired using ECG
electrodes 110. Electrodes 110 may be dedicated electrodes or they
may be part of controller 101, for example, spaced apart
electrification electrodes, that are read as ECG electrodes, for
example using methods known in the art or pairs of ECG sensing
electrodes used by ETC logic 102, or a set comprising an ECG
sensing electrode and a ETC electrification electrode. Optionally,
the wide-field ECG sensor has shared components with ETC logic 102,
for example, one or more electrodes, switch(es) and/or a processing
circuit.
[0041] In an exemplary embodiment of the invention, different
electrodes are placed on different heart chambers. In an exemplary
embodiment of the invention, one of the electrodes comprises the
casing of controller 101. Alternatively or additionally, the
electrodes are spaced-apart ring electrodes on a catheter.
Alternatively or additionally, at least one of the ECG electrodes
is located on an electrification or ECG electrode lead, distanced a
short distance form the heart. Alternatively, other implantable
electrode configurations may be used.
[0042] Alternatively or additionally, electrodes 110 are external
electrodes, for example, 12-lead ECG electrodes. Such external
electrodes may communicate with filter 104 and/or ETC logic 102,
using wired or wireless means, for example as known in the art.
Alternatively, controller 101 may be an external controller, for
example one used after cardiac-affecting surgery.
[0043] At 204, the acquired trace is compared to one or more
templates. Alternatively, other matching methods, as described
below may be used. The templates may include one or more "normal"
templates, which indicate a suitable cardiac cycle and/or one or
more "abnormal" templates, which indicate an abnormal cardiac
cycle.
[0044] At 206, a decision is made to inhibit the ETC signal, based
on the comparisons of 204. For example, if no "normal" template was
matched or if an "abnormal" template was matched, an inhibition
signal is generated to ETC logic 102 (208).
[0045] In an exemplary embodiment of the invention, the inhibition
signal prevents an ETC signal from being applied to the heart, in
this cycle. Alternatively or additionally, the inhibition signal is
applied to a later cycle. Alternatively or additionally, a current
ETC signal is terminated, at once, or with a suitable tailing end,
as a result of detecting an abnormal cardiac condition.
Alternatively or additionally, an ongoing sequence of ETC pulses is
stopped or modified. In an exemplary embodiment of the-invention,
an ETC sequence to be applied to the heart can be defined to be
conditional, with different sub-sequences being applied, depending
on the detection of an abnormal condition. Optionally, the tailing
end depends on the abnormal condition detected by the template
matching, for example, the tailing end including a
counter-arrhythmia signal.
[0046] In an exemplary embodiment of the invention, at least two
templates are provided, one for matching a self-paced condition and
one for matching an artificially paced condition. An indication may
or may not be provided to filter 104, regarding which condition is
current If controller 101 and/or a pacemaker (not shown) can apply
multiple pacing schemes, multiple templates may be provided,
optionally at least to the extent that different pacing schemes
have markedly different normal wide-field ECG traces. Optionally,
filter 104 and/or controller 101 include an input for receiving
various parameters that can affect "normal" activation, for
example, the ingestion of a pharmaceutical or the continuing
activity of a multi-cycle cardiac control sequence, that is
expected to affect the heart in a known manner, for example, each
stage of the sequence having a different normal ECG.
[0047] Alternatively or additionally, different ETC pulses and/or
sequences may have different danger conditions and/or danger levels
associated with them. In an exemplary embodiment of the invention,
different templates and/or different matching parameters are used
depending on the type of ETC signal to be applied and/or depending
on the sensitivity of the patient and/or depending on the
importance of actually applying an ETC pulse periodically, at
least.
[0048] Alternatively or additionally, an ETC signal is selected to
be applied based on which templates were matched and which not. In
one example, a list of ETC pulses (with a similar, general
function) is ordered in order of desirability of application. The
most desirable ETC pulse whose "normal" template matches the
current ETC trace is applied. Alternatively or additionally, if a
sequence of ETC signals is to be applied, those signals that do not
have a matching "normal" template, are inhibited. Optionally, ETC
logic 102 may prevent the application of an ETC signal, if a
previous or later (e.g., in same cycle) signal is inhibited, even
if the instant ETC signal may be applied. This mechanism may be
used to prevent partial application of sequences, where the partial
sequence is not effective and/or possibly damaging.
[0049] Optionally, template matching is used to detect a change in
the state of the heart, for example, the completion of a remodeling
process or a transition from a sleep pattern to an exercise
pattern. As such, the template matching of filter 104 may provide
an input to ETC logic 102 and/or be mirrored in ETC logic 102.
[0050] Referring again to ECG electrodes 110, their placement may
reflect contingency, for example, the placement location of local
sensing and/or electrifying electrodes, or it may be selected to
have a certain wide-filed view of the heart. In one example, one
electrode is on the right ventricle and one on the left ventricle.
In another example, one electrode is at each end of the heart. In
another example, the electrodes are arranged in a grid, and
selectively coupled to yield a desirable ECG trace. Different ECG
traces may be sensed for different ETC signal applications and/or
locations.
[0051] In an exemplary embodiment of the invention, the wide-field
covers parts of at least two chambers, for example the two
ventricles. Alternatively or additionally, the field covers a
significant part of the left ventricle or of the right ventricle.
Alternatively or additionally, the field is aimed to cover a
portion of the heart that is known or expected to activate
abnormally, for example the right atrium. Alternatively or
additionally, the field is aimed to include contributions from two
parts of the heart, whose activation order is expected to change as
a result of abnormal activation. Optionally, multiple wide-area
ECGs are sensed, for example for matching templates to multiple
areas, for a single or multiple pulse applications. Alternatively
or additionally, the size and/or location of the field may be
varied as part of a calibration process, for example per patient,
per condition to be careful of and/or per ETC signal type.
[0052] In an exemplary embodiment of the invention, the portion of
the heart viewed includes an area that is expected to be activated
(hopefully correctly) before the ETC signal is to be applied.
Alternatively or additionally, the portion includes an area that is
expected not to be activated before the ETC signal is to be
applied. Alternatively or additionally, the portion includes an
area that is expected to be activated just as or just before the
ETC signal is to be applied. Exemplary areas that may be viewed
include areas where incorrect conduction pathways exist.
Alternatively or additionally, the area may include parts where a
normal conduction and activation profile is expected.
[0053] Different ECG sensing areas will generally affect the
content of templates that are considered "normal". Conversely,
different sensing areas may be useful for detecting different types
of potential arrhythmia, for example, for different ETC
signals.
[0054] In an exemplary embodiment of the invention, the wide-field
includes significant contribution from at least 3, 5, 10, 15
cm.sup.2 or more of the heart's surface. Alternatively or
additionally, the field width may be measured in percentages, for
example, being at least 10%, 20%, 40% or 60% of the heart's muscle
volume.
[0055] In an exemplary embodiment of the invention, the matching of
a current ECG trace to previously stored ECG parameters is by
template matching. In an exemplary embodiment of the invention, the
template defines a portion of the ECG trace to be matched and one
or more matching parameters define an allowed variation between the
trace and the template.
[0056] In an exemplary embodiment of the invention, the portion of
ECG trace used for the matching is selected to include
contributions from the parts of the heart that are of interest. As
noted above, in some cases, the part of the heart that is being
viewed is expected not to have an activation, at least for some of
the time.
[0057] In an exemplary embodiment of the invention, the wide field
ECG sensor covers part of the right ventricle and part of the left
ventricle (e.g., near the apex) and the temporal potion used for
the match is between a right ventricle sensing event and a latest
reasonable left ventricle ETC application event. When the right
ventricle is paced, the trace may start slightly after the pacing
event. Optionally, the template also includes portions from after
the application of the ETC signal.
[0058] In other examples, the trace includes parts of the atrial
activation and/or SA pacing.
[0059] Alternatively or additionally, the temporal portion is
selected to include parts of the trace that are expected to be less
affected by normal changes in the heart's activation, such as
exercise events and changes in heart rate. For example, the
inter-beat period may not be included in the template.
[0060] In an exemplary embodiment of the invention, the template
matching uses a Woody filter, in which the ECG trace is temporally
shifted to find a maximum correlation with the template.
Alternatively or additionally, dynamic time warping methods may be
applied to allow the trace to be compressed or expanded. The trace
may be allowed to be flexible or it may be required to be expanded
or shrunk by a certain fixed factor or according to fixed rules
(e.g., one part of ECG should shrank half as much as a second
part). The template matching may be fixed or may use a floating
point representation.
[0061] Alternatively or additionally, different templates may be
provided for different heart rate conditions.
[0062] Although a template may be limited to one cardiac cycle, in
some embodiments of the invention, a multi-cycle template is
provided, for example to detect arrhythmia that are characterized
by beat-to-beat variations or by a periodic behavior. In an
exemplary embodiment of the invention, such a template includes
multiple ECG trace portions. Alternatively, such a template
includes only parts (same or different) from ECG traces of
consecutive beats. Possibly, filter 104 compares only the relevant
parts of the acquired ECG signal to the template. Possibly, the
template is designed to match spaced apart beats (e.g., skip beats)
and/or to compare averaged ECG traces to the template.
[0063] In an exemplary embodiment of the invention, the distance
function used for calculating the difference between the trace and
the template is a simple linear distance. Alternatively or
additionally, some parts of the template may have different weight
than other parts. Alternatively or additionally, at least some
parts of the template may define an RMS, quadric or exponential
distance function. Alternatively or additionally, time offsets also
affect the matching score. Alternatively or additionally, energy
scaling may also affect the score.
[0064] Optionally, some limitation is imposed on the allowed
beat-to-beat variation. For example, two consecutive beats are
expected to match or not match the template in substantially
similar manners. Thus, consecutive beats in which one is different
from the template in one way and the other is different in another
way may be used to inhibit an ETC signal, even though they both
match the template, within defined parameters.
[0065] The matching parameters may be defined depending on the type
of matching performed. For example, the parameters may include only
an allowed variation. Alternatively or additionally, the parameters
may define a dispersion, that a set of consecutive beats must
maintain (or be lower). Alternatively or additionally, the
parameters may include a method of calculating the distance or
different weights for different parts of the template.
Alternatively or additionally, the parameters may define the type
of matching to be performed, for example template or
non-template.
[0066] In an exemplary embodiment of the invention, an initial
template may be provided with controller 101. Alternatively, a
short learning process may be applied when controller 101 is
installed and/or recalibrated. In an exemplary embodiment of the
invention, the learning process includes acquiring a plurality of
relevant ECG traces from the patient and defining a template(s)
based on the average trace and an allowed deviation based on the
disparity between the traces. A human operator may view the traces
and/or the template and reject and/or modify them. In some cases, a
single template may need to be split into two due to the
distribution of ECG traces in a patient. Such programming may be,
for example, by wired connection, or by wireless connection of a
programmer with controller 101.
[0067] In an exemplary embodiment of the invention, if a template
is not matched for a considerable period of time, for example, 120
beats, 1200 beats or 12000 beats, the template is dropped. Such
lack of use may imply that the activation of the heart changed
enough so that what was once normal activation, is now abnormal
activation. An alert may be generated to the patient and/or a
physician, using means known in the art, or the status may be
retrieved when controller 101 is next reprogrammed/debriefed.
[0068] In an exemplary embodiment of the invention, the templates
are continuously updated (210). Optionally, even abnormal traces
are used for updating "normal" templates. On the one hand, what was
once considered abnormal may now be normal. On the other hand, if
such abnormal beats are infrequent enough, they will not markedly
affect the template. In addition, many arrhythmia will not be
repetitive, so their effect is negligible. Optionally, ETC logic
102 provides an arrhythmia signal to filter 104, so filter 104 can
ignore or otherwise take into account ECG traces that are detected
by ETC logic 102 to be arrhythmic.
[0069] In an exemplary embodiment of the invention, the template is
updated to be a weighted average of the current template and the
instant ETC trace. Thus, old traces have a smaller weight than
newer ones and the template can adapt to current conditions.
Alternatively, other averaging or updating methods may be used.
[0070] In an exemplary embodiment of the invention, this type of
template updating takes into account the long term effects of
changes in the cardiac activation profile as a result of the ETC
treatment and/or health changes. Also, the ETC application profile
may change when the cardiac activity changes in time. For example,
the template and/or template matching method may be used to select
which ETC signal or sequence to apply and/or which anti-arrhythmia
signal to apply.
[0071] In an exemplary embodiment of the invention, templates are
stored as sequences of samples, that match the samples acquired by
the wide-field ETC sensor. Alternatively or additionally, other
template storage methods may be used.
[0072] Alternatively to template matching, other matching methods
may be used, for example, feature based matching, where certain
features of the ECG trace are searched for and compared in shape
and/or relative position to a template (or set of features and
distances otherwise stored).
[0073] In an exemplary embodiment of the invention, a filtering
algorithm is applied by a real-time device. In such a device it is
usually desirable to reduce the computational load and/or memory
load. Optionally, the template should be matched as ECG samples are
acquired. Table I lists an exemplary algorithm, in which T0 is, for
example 17 ms and T1 is automatically calculated as shown in step
1. This algorithm is to be applied to an ETC device that paces or
senses a right-ventricle activation and applies an ETC signal to
the left ventricle. In operation, an INHIBIT signal is updated by
thresholding the value of a mean-absolute-distance between the
current ECG trace and the relevant template (pacing or sensing). If
INHIBIT is active when the ETC signal is to be applied, the signal
is inhibited. The template is updated using a pseudo-coherent
averager that averages the last NumBeats traces (of sense type
beats or of pace type beats).
1TABLE 1 1. Set T1 to be RV to LV time + worst-case ETC delay 2.
Set T0 to be 10 samples (17 ms) 3. Set TH from GUI 4. Set
updateOnInhibit from GUI (TRUE or FALSE) 5. Set staleNum = 120 6.
Set NumBeats from GUI (default 4 and must be power of 2 in this
implementation) 7. Set TemplatePace = vector zeros(T1) (vector of
T1 zeros) 8. Set TemplateSense = vector zeros(T1) (vector of T1
zeros) 9. Set lastUpdatePace = 0 10. Set IastUpdateSense = 0; 11.
Set Inhibit = 1 12. Set accTH = 0 13. Set MSE = 0; 14. Wait for
Vpace or Vsense 15. Set Inhibit = 1 16. Set Invect = zeros(T1) 17.
Set t = 0; 18. Acquire new sample --> Invect(t) 19. t = t + 1;
20. accTH = accTH + TH 21. if t > T0 22. A = Invect(t) 23. If
Vpace 24. B = TemplatePace(t) 25. Else 26. B = TemplateSense(t) 27.
EndIf 28. If A > B 29. MSE = MSE + A - B 30. Else 31. MSE = MSE
+ B - A 32. EndIf 33. If MSE < accTH 34. Set Inhibit = 0 35.
EndIf 36. EndIf 37. if CCM detected or t > T1 38. if Vpace &
(INHIBIT = 0 .vertline. updateOnInhibit = TRUE) 39. if
lastDetectedPace < staleNum 40. TemplatePace = =
((NumBeats-1)*TemplatePace + Invect)/NumBeats 41. Else 42.
TemplatePace = vector zeros(T1) 43. EndIf 44. Last DetectedPace =
0; 45. LastDetectedSense = LastDetectedSense + 1 46. ElseIf INHIBIT
= 0 .vertline. updateOnInhibit = TRUE 47. If lastDetectedSense <
staleNum 48. TemplateSense = ((NumBeats-1)*TemplateSense +
Invect)/NumBeats 49. Else 50. Templatesense = vector zeros(T1) 51.
EndIf 52. LastDetectedSense = 0; 53. LastDetectedPace =
LastDetectedPace + 1 54. EndIf 55. Goto 11 56. ELSE 57. Goto 18 58.
EndIf
[0074] Although ETC logic 102 may operate independently of the
existence of filter 104, in some embodiments of the invention, ETC
logic 102 is modified to take the inhibition into account. ETC
logic 102 may be applying ETC signals to achieve a long term
effect, an average increase in blood flow and/or control of other
bodily parameters. By inhibiting some of the ETC signals, such
goals may be confounded. In an exemplary embodiment of the
invention, the rate of application of ETC pulses is increased to
compensate for inhibited pulses. Alternatively or additionally, the
ETC signal is inhibited (by ETC logic 102 and/or filer 104) for one
or more cycles following a true inhibition (e.g., due to a detected
arrhythmia), for example, based on the degree of template match or
mismatch, based on preset values and/or based on a delay while at
least a certain percentage of the cycles match an "abnormal"
template. Alternatively or additionally, the treatment sequence may
be changed, if, in the particular heart, the sequence cannot be
reliably applied. Possibly, such changes are automatically
performed by ETC logic 102. Alternatively, a human operator reads
indications of lack of application from ETC logic 102 and modifies
the programming accordingly.
[0075] It should be noted that calibration information, matching
parameters and/or other operational parameters of filter 104 can be
learned by experience, for example by tracking the effect of the
operation (or lack thereof) of filter 104 on a same or a different
patient.
[0076] Filter 104 is expected to detect various abnormal
conditions, for example, some types of premature ventricular
contractions (PVC). In an exemplary embodiment of the invention,
the arrhythmic condition to be detected comprises a beat from a
non-sinus source that reaches the left-ventricle activation sensor
slightly before (e.g., 10-20 ms) or slightly after the activation
from the right ventricle reaches it. Alternatively or additionally,
other safety mechanisms may be used to inhibit ETC signals, for
example, one or more of:
[0077] (a) the detection of noise on local sensing ECG channels,
for example, a right-ventricle channel;
[0078] (b) detecting a PVC using a right-heart sequence
detector;
[0079] (c) detecting a left ventricle event during a right heart AV
segment;
[0080] (d) detecting an abnormally short AV delay;
[0081] (e) detecting beats conducted from an atrium, especially a
tachyarrhythmic atrium; and
[0082] (f) inhibiting ETC signals for several cycles after a
current ETC signal is inhibited and/or after an arrhythmia is
detected.
[0083] Some of these mechanisms and/or mechanisms for determining a
timing window during which an ETC pulse may be safely and/or
usefully applied to a heart are described in U.S. patent
application Ser. Nos. 09/276,460, 09/378,776, 09/572,482 and
09/338,649, and in PCT applications PCT/IL00/00321 and
PCT/IL00/00493 and PCT publication WO 00/57952, the disclosures of
which are incorporated herein by reference.
[0084] Optionally, the templates are used to associate different
locally sensed danger conditions (and/or sequences) with wide-field
ECG signals, for example, for later use. Alternatively or
additionally, windowing parameters for applying ECG signals may be
associated with wide-field ECG templates.
[0085] Although the above application has focused on ETC signals,
in some embodiments of the invention, filter 104 is used to inhibit
excitatory signals generated by controller 101. In an exemplary
embodiment of the invention, controller 101 may generate an
excitatory signal which is not expected to cause an arrhythmia.
However, due to an abnormal activation of the heart, the ETC signal
will cause an arrhythmia. The abnormality of the ECG is detected
and the excitatory signal is stopped. In another example, a second,
ETC, signal may be designated to block the propagating of the
excitatory signal. However, due to the abnormal activation, such
blocking may not work and/or the application of the ETC signal
itself may cause an arrhythmia.
[0086] It should be noted that in some cases, the inhibited signal
might have directly caused an arrhythmia. In other cases, the
signal would only have prepared the grounds for a later arrhythmia,
for example, by depressing a portion of the heart for several
cycles. In other case, as noted above, it is an existing arrhythmia
(possibly self-limiting) that prepare the grounds for the
non-excitatory signal to cause an arrhythmia (possibly non-self
limiting).
[0087] Alternatively or additionally to preventing signals that are
dangerous, in an exemplary embodiment of the invention, filter 104
is used to prevent ineffective signals. An ETC signal may have one
or more associated templates and/or matching parameter sets that
indicate conditions of lesser effectiveness. Such ineffective
signals may have, for example, one or more of the following
undesirable effects:
[0088] (a) weaken the heart;
[0089] (b) waste power;
[0090] (c) have a counter-desired effect (e.g., reduce
contractility);
[0091] (d) undo a desired long term effect of the ETC signals
(e.g., modeling); and
[0092] (e) cause pain to the patient.
[0093] Optionally, the effectiveness of an ETC signal is defined
parametricly, for example based on the instant level of cardiac
reserve ability. Such an instant level may be provide, for example,
by a model that tracks the response of the heart to previously
applied ETC signals, under various conditions. Inefficient effect
of an ETC signal may also be detected using non-electrical sensors,
for example pressure sensors. Optionally, a pressure or a tension
sensor in an earlier activated part of the heart (e.g., an earlier
activated chamber) may be used to generate a trace for matching to
a template, for detecting abnormal activation of the heart.
[0094] The present invention has been described using non-limiting
detailed descriptions of embodiments thereof that are provided by
way of example and are not intended to limit the scope of the
invention. It should be understood that features and/or steps
described with respect to one embodiment may be used with other
embodiments and that not all embodiments of the invention have all
of the features and/or steps shown in a particular figure or
described with respect to one of the embodiments. Variations of
embodiments described will occur to persons of the art.
[0095] It is noted that some of the above described embodiments may
describe the best mode contemplated by the inventors and therefore
include structure, acts or details of structures and acts that may
not be essential to the invention and which are described as
examples. Structure and acts described herein are replaceable by
equivalents which perform the same function, even if the structure
or acts are different, as known in the art. Therefore, the scope of
the invention is limited only by the elements and limitations as
used in the claims. When used in the following claims, the terms
"comprise", "include", "have" and their conjugates mean "including
but not limited to".
* * * * *