U.S. patent application number 14/461670 was filed with the patent office on 2015-11-19 for wearable cardioverter defibrillator components discarding ecg signals prior to making shock/no shock determination.
The applicant listed for this patent is Physio-Control, Inc.. Invention is credited to David P. Finch, Robert P. Marx, JR., Joseph L. Sullivan.
Application Number | 20150328472 14/461670 |
Document ID | / |
Family ID | 54537669 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150328472 |
Kind Code |
A1 |
Sullivan; Joseph L. ; et
al. |
November 19, 2015 |
WEARABLE CARDIOVERTER DEFIBRILLATOR COMPONENTS DISCARDING ECG
SIGNALS PRIOR TO MAKING SHOCK/NO SHOCK DETERMINATION
Abstract
Components of wearable cardiac defibrillator (WCD) systems,
software, and methods are provided. A WCD system includes a support
structure that a patient can wear and electrodes that can capture
at least two of the patient's ECG signals. A component includes an
energy storage module that can store an electrical charge, a
discharge circuit, and a processor that can make a shock/no shock
determination, and cause the discharge circuit to discharge the
stored charge, if the determination is to shock. In some
embodiments, the processor discards at least one of the ECG signals
prior to making the shock/no shock determination. The determination
can be made from the remaining one or more ECG signals. In some
embodiments, the processor makes an aggregate shock/no shock
determination from two or more of the ECG signals.
Inventors: |
Sullivan; Joseph L.;
(Kirkland, WA) ; Marx, JR.; Robert P.; (Kent,
WA) ; Finch; David P.; (Bothell, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Physio-Control, Inc. |
Redmond |
WA |
US |
|
|
Family ID: |
54537669 |
Appl. No.: |
14/461670 |
Filed: |
August 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61992841 |
May 13, 2014 |
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Current U.S.
Class: |
607/7 |
Current CPC
Class: |
A61N 1/025 20130101;
A61N 1/046 20130101; A61B 5/0464 20130101; A61N 1/3904 20170801;
A61N 1/3987 20130101; A61N 1/3925 20130101; A61B 5/6805 20130101;
A61N 1/3918 20130101; A61B 5/7221 20130101; A61N 1/0484
20130101 |
International
Class: |
A61N 1/39 20060101
A61N001/39; A61N 1/02 20060101 A61N001/02 |
Claims
1. A component of a wearable cardiac defibrillation system, the
system including a support structure configured to be worn by a
patient and electrodes configured to capture at least three ECG
signals of the patient and transport electrical charge, the
component comprising: an energy storage module configured to be
coupled to the support structure and to store an electrical charge;
a discharge circuit coupled to the energy storage module; and a
processor configured to: decide whether at least one of the at
least three ECG signals meets a reliability criterion and, if not,
to discard it, make a shock/no shock determination from one of the
ECG signals that is not the discarded ECG signal, and cause, if the
determination is to shock, the discharge circuit to discharge the
electrical charge through at least two of the electrodes so as to
defibrillate the patient.
2. The component of claim 1, in which the reliability criterion is
that the ECG signal has a reliability value that is higher than a
threshold.
3. The component of claim 1, in which the reliability criterion is
that the ECG signal has a reliability value that is higher than the
reliability value of another of the ECG signals.
4. The component of claim 1, in which all the ECG signals are
discarded except one.
5. The component of claim 4, in which the reliability criterion is
that the ECG signal that is not discarded is the one that has a
higher reliability value than the other ECG signals.
6. The component of claim 4, in which the shock/no shock
determination is not made if the non-discarded ECG signal has a
reliability value that is less than a threshold.
7. The component of claim 1, in which the component or the wearable
cardiac defibrillation system further includes an implement
configured to detect an ECG common voltage signal, and the
reliability criterion for a certain ECG signal is derived from a
mathematical correlation between the ECG common voltage signal and
the certain ECG signal.
8. The component of claim 7, in which the mathematical correlation
includes a cross-correlation, and the ECG common voltage signal and
the certain ECG signal are simplified before the
cross-correlation.
9. The component of claim 1, in which an impedance signal of the
patient is also captured, and the reliability criterion for a
certain ECG signal is derived from a mathematical correlation
between the impedance signal and the certain ECG signal.
10. The component of claim 9, in which the mathematical correlation
includes a cross-correlation, and the impedance signal and the
certain ECG signal are simplified before the cross-correlation.
11. The component of claim 9, in which the component or the
wearable cardiac defibrillation system further includes an
accelerometer configured to generate an acceleration signal, and
the reliability criterion for a certain ECG signal is derived from
a mathematical correlation between the acceleration signal and the
certain ECG signal.
12. The component of claim 11, in which the mathematical
correlation includes a cross-correlation, and the acceleration
signal and the certain ECG signal are simplified before the
cross-correlation.
13. The component of claim 1, in which the decision is made from a
patient heart rate detected in the ECG signal.
14. The component of claim 1, in which a mathematical correlation
is taken between two of the ECG signals.
15. The component of claim 1, in which the reliability criterion is
not met if two others of the ECG signals have an aspect similar to
each other.
16. A component of a wearable cardiac defibrillation system, the
system including a support structure configured to be worn by a
patient and electrodes configured to capture at least two ECG
signals of the patient and transport electrical charge, the
component comprising: an energy storage module configured to be
coupled to the support structure and to store an electrical charge;
a discharge circuit coupled to the energy storage module; and a
processor configured to: decide whether at least one of the ECG
signals meets a reliability criterion from a measured amplitude of
at least one of the ECG signals and, if not, to discard it, make a
shock/no shock determination from one of the ECG signals that is
not the discarded ECG signal, and cause, if the determination is to
shock, the discharge circuit to discharge the electrical charge
through at least two of the electrodes so as to defibrillate the
patient.
17. The component of claim 16, in which the reliability criterion
is met depending on how well the measured amplitude matches a
reference amplitude.
18. The component of claim 17, in which the reference amplitude has
been measured in advance for the patient.
19. The component of claim 16, in which the reliability criterion
is met depending on how large is a ratio of a peak value to a
median value of the ECG signal.
20. A non-transitory computer-readable storage medium storing one
or more programs which, when executed by at least one processor of
a wearable cardiac defibrillation system, the system including a
support structure configured to be worn by a patient, electrodes
configured to capture at least three ECG signals of the patient and
transport electrical charge, an energy storage module configured to
be coupled to the support structure and to store an electrical
charge, and a discharge circuit coupled to the energy storage
module, they result in: deciding whether at least one of the at
least three ECG signals meets a reliability criterion and, if not,
discarding it; making a shock/no shock determination from one of
the ECG signals that is not the discarded ECG signal, and causing,
if the determination is to shock, the discharge circuit to
discharge the electrical charge through at least two of the
electrodes so as to defibrillate the patient.
21-34. (canceled)
35. A non-transitory computer-readable storage medium storing one
or more programs which, when executed by at least one processor of
a wearable cardiac defibrillation system, the system including a
support structure configured to be worn by a patient, electrodes
configured to capture at least two ECG signals of the patient and
transport electrical charge, an energy storage module configured to
be coupled to the support structure and to store an electrical
charge, and a discharge circuit coupled to the energy storage
module, they result in: deciding whether at least one of the ECG
signals meets a reliability criterion from a measured amplitude of
the at least one of the ECG signals and, if not, discarding it;
making a shock/no shock determination from one of the ECG signals
that is not the discarded ECG signal, and causing, if the
determination is to shock, the discharge circuit to discharge the
electrical charge through at least two of the electrodes so as to
defibrillate the patient.
36-38. (canceled)
39. A method for a component of a wearable cardiac defibrillation
system, the system including a support structure configured to be
worn by a patient, electrodes configured to capture at least three
ECG signals of the patient and transport electrical charge, an
energy storage module configured to be coupled to the support
structure and to store an electrical charge, and a discharge
circuit coupled to the energy storage module, the method
comprising: deciding whether at least one of the at least three ECG
signals meets a reliability criterion and, if not, discarding it;
making a shock/no shock determination from one of the ECG signals
that is not the discarded ECG signal, and causing, if the
determination is to shock, the discharge circuit to discharge the
electrical charge through at least two of the electrodes so as to
defibrillate the patient.
40-53. (canceled)
54. A method for a component of a wearable cardiac defibrillation
system, the system including a support structure configured to be
worn by a patient, electrodes configured to capture at least two
ECG signals of the patient and transport electrical charge, an
energy storage module configured to be coupled to the support
structure and to store an electrical charge, and a discharge
circuit coupled to the energy storage module, the method
comprising: deciding whether at least one of the ECG signals meets
a reliability criterion from a measured amplitude of the at least
one of the ECG signals and, if not, discarding it; making a
shock/no shock determination from one of the ECG signals that is
not the discarded ECG signal, and causing, if the determination is
to shock, the discharge circuit to discharge the electrical charge
through at least two of the electrodes so as to defibrillate the
patient.
55-93. (canceled)
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application claims priority from U.S.
Provisional Patent Application Ser. No. 61/992,841, filed on May
13, 2014, the disclosure of which is hereby incorporated by
reference for all purposes.
BACKGROUND
[0002] When people suffer from some types of heart arrhythmias, the
result may be that blood flow to various parts of the body is
reduced. Some arrhythmias may even result in a Sudden Cardiac
Arrest (SCA). SCA can lead to death very quickly, e.g. within 10
minutes, unless treated in the interim.
[0003] Some people have an increased risk of SCA. People at a
higher risk include individuals who have had a heart attack, or a
prior SCA episode. These people receive the recommendation to
receive an Implantable Cardioverter Defibrillator ("ICD"). The ICD
is surgically implanted in the chest, and continuously monitors the
person's electrocardiogram ("ECG"). If certain types of heart
arrhythmias are detected, then the ICD delivers an electric shock
through the heart.
[0004] After being identified as having an increased risk of an
SCA, and before receiving an ICD, these people are sometimes given
a wearable cardiac defibrillator ("WCD") system. A wearable
defibrillator system typically includes a harness, vest, or other
garment for wearing by the patient. The system includes a
defibrillator and external electrodes, which are attached on the
inside of the harness, vest, or other garment. When the person
wears the system, the external electrodes may then make good
electrical contact with the person's skin, and therefore can help
monitor the person's ECG. If a shockable heart arrhythmia is
detected, then the defibrillator delivers the appropriate electric
shock through the person's body, and thus through the heart.
BRIEF SUMMARY
[0005] The present description gives instances of components of
wearable cardiac defibrillator systems, software, and methods, the
use of which may help overcome problems and limitations of the
prior art.
[0006] In embodiments, a component of a wearable cardiac
defibrillation system is provided. The system includes a support
structure that a patient can wear and electrodes that can capture
at least two of the patient's ECG signals. The component includes
an energy storage module that can store an electrical charge, a
discharge circuit, and a processor that can make a shock/no shock
determination, and cause the discharge circuit to discharge the
stored charge, if the determination is to shock.
[0007] In some embodiments, the processor discards at least one of
the ECG signals prior to making the shock/no shock determination.
The determination can be made from the remaining one or more ECG
signals.
[0008] In some embodiments, the processor makes an aggregate
shock/no shock determination from two or more ECG signals.
[0009] An advantage over the prior art is that the shock/no shock
determination can be made with better information, and therefore
have a better chance of being correct for the occasion. These and
other features and advantages of this description will become more
readily apparent from the Detailed Description, which proceeds with
reference to the associated drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram of components of a sample wearable
defibrillator system, made according to embodiments.
[0011] FIG. 2 is a diagram showing sample components of an external
defibrillator, such as the one in the system of FIG. 1, and which
is made according to embodiments.
[0012] FIG. 3 is a conceptual diagram for illustrating an example
how different electrodes may capture ECG signals along different
vectors according to embodiments.
[0013] FIG. 4 is a conceptual diagram for illustrating that
different possible ECG signals can be used to arrive at a shock/no
shock determination according to embodiments.
[0014] FIG. 5 is a conceptual diagram for illustrating different
types of processes according to embodiments.
[0015] FIG. 6 is a flowchart for illustrating methods according to
embodiments.
[0016] FIG. 7 is a conceptual diagram for illustrating an example
of how a decision can be made to discard at least one ECG signal
according to embodiments.
[0017] FIG. 8 is a conceptual diagram for illustrating an example
of how a decision can be made to discard all except one ECG signal
according to embodiments.
[0018] FIG. 9 is a flowchart for illustrating methods according to
embodiments.
[0019] FIG. 10 is a conceptual diagram for illustrating how a
sample combination can be made from individual decisions according
to embodiments.
DETAILED DESCRIPTION
[0020] As has been mentioned, the present description is about
components of wearable cardiac defibrillator systems, software, and
methods. Embodiments are now described in more detail.
[0021] A wearable cardiac defibrillator (WCD) system made according
to embodiments has a number of components. These components can be
provided separately as modules that can be interconnected, or can
be combined with other components, etc.
[0022] A component of a WCD system can be a support structure,
which is configured to be worn by the patient. The support
structure can be any structure suitable for wearing, such as a
harness, a vest, one or more belts, another garment, and so on. The
support structure can be implemented in a single component, or
multiple components. For example, a support structure may have a
top component resting on the shoulders, for ensuring that the
defibrillation electrodes will be in the right place for
defibrillating, and a bottom component resting on the hips, for
carrying the bulk of the weight of the defibrillator. A single
component embodiment could be with a belt around at least the
torso. Other embodiments could use an adhesive structure or another
way for attaching to the person, without encircling any part of the
body. There can be other examples.
[0023] FIG. 1 depicts components of a wearable defibrillator system
made according to embodiments, as it might be worn by a person 82.
A person such as person 82 may also be referred to as a patient
and/or wearer, since that person wears components of the wearable
defibrillator system.
[0024] In FIG. 1, a generic support structure 170 is shown relative
to the body of person 82, and thus also relative to his or her
heart 85. Structure 170 could be a harness, a vest, one or more
belts, or a garment, etc., as per the above. Structure 170 could be
implemented in a single component, or multiple components, and so
on. Structure 170 is wearable by person 82, but the manner of
wearing it is not depicted, as structure 170 is depicted only
generically in FIG. 1.
[0025] A wearable defibrillator system is configured to
defibrillate the patient, by delivering electrical charge to the
patient's body in the form of an electric shock delivered in one or
more pulses. FIG. 1 shows a sample external defibrillator 100, and
sample defibrillation electrodes 104, 108, which are coupled to
external defibrillator 100 via electrode leads 105. Defibrillator
100 and defibrillation electrodes 104, 108 are coupled to support
structure 170. As such, many of the components of defibrillator 100
can be therefore coupled to support structure 170. When
defibrillation electrodes 104, 108 make good electrical contact
with the body of person 82, defibrillator 100 can administer, via
electrodes 104, 108, a brief, strong electric pulse 111 through the
body. Pulse 111, also known as a defibrillation shock or therapy
shock, is intended to go through and restart heart 85, in an effort
to save the life of person 82. Pulse 111 can also be one or more
pacing pulses, and so on.
[0026] A prior art defibrillator typically decides whether to
defibrillate or not based on an electrocardiogram ("ECG") signal of
the patient. However, defibrillator 100 can defibrillate, or not
defibrillate, also based on other inputs.
[0027] The wearable defibrillator system may optionally include an
outside monitoring device 180. Device 180 is called an "outside"
device because it is provided as a standalone device, for example
not within the housing of defibrillator 100. Device 180 can be
configured to monitor at least one local parameter. A local
parameter can be a parameter of patient 82, or a parameter of the
wearable defibrillation system, or a parameter of the environment,
as will be described later in this document.
[0028] Optionally, device 180 is physically coupled to support
structure 170. In addition, device 180 can be communicatively
coupled with other components, which are coupled to support
structure 170. Such a component can be a communication module, as
will be deemed applicable by a person skilled in the art in view of
this disclosure.
[0029] FIG. 2 is a diagram showing components of an external
defibrillator 200, made according to embodiments. These components
can be, for example, included in external defibrillator 100 of FIG.
1. The components shown in FIG. 2 can be provided in a housing 201,
which is also known as casing 201.
[0030] External defibrillator 200 is intended for a patient who
would be wearing it, such as person 82 of FIG. 1. Defibrillator 200
may further include a user interface 270 for a user 282. User 282
can be patient 82, also known as wearer 82. Or user 282 can be a
local rescuer at the scene, such as a bystander who might offer
assistance, or a trained person. Or, user 282 might be a remotely
located trained caregiver in communication with the wearable
defibrillator system.
[0031] User interface 270 can be made in any number of ways. User
interface 270 may include output devices, which can be visual,
audible or tactile, for communicating to a user. User interface 270
may also include input devices for receiving inputs from users. For
example, interface 270 may include a screen, to display what is
detected and measured, provide visual feedback to rescuer 282 for
their resuscitation attempts, and so on. Interface 270 may also
include a speaker, to issue voice prompts, etc. Sounds, images,
vibrations, and anything that can be perceived by user 282 can also
be called human perceptible indications. Interface 270 may
additionally include various controls, such as pushbuttons,
keyboards, touchscreens, a microphone, and so on. In addition,
discharge circuit 255 can be controlled by processor 230, or
directly by user 282 via user interface 270, and so on.
[0032] Defibrillator 200 may include an internal monitoring device
281. Device 281 is called an "internal" device because it is
incorporated within housing 201. Monitoring device 281 can monitor
patient parameters, patient physiological parameters, system
parameters and/or environmental parameters, all of which can be
called patient data. In other words, internal monitoring device 281
can be complementary or an alternative to outside monitoring device
180 of FIG. 1. Allocating which of the system parameters are to be
monitored by which monitoring device can be done according to
design considerations.
[0033] Patient physiological parameters include, for example, those
physiological parameters that can be of any help in detecting by
the wearable defibrillation system whether the patient is in need
of a shock, plus optionally their medical history and/or event
history. Examples of such parameters include the patient's ECG,
blood oxygen level, blood flow, blood pressure, blood perfusion,
pulsatile change in light transmission or reflection properties of
perfused tissue, heart sounds, heart wall motion, breathing sounds
and pulse. Accordingly, the monitoring device could include a
perfusion sensor, a pulse oximeter, a Doppler device for detecting
blood flow, a cuff for detecting blood pressure, an optical sensor,
illumination detectors and perhaps sources for detecting color
change in tissue, a motion sensor, a device that can detect heart
wall movement, a sound sensor, a device with a microphone, an SpO2
sensor, and so on. Pulse detection is taught at least in
Physio-Control's U.S. Pat. No. 8,135,462, which is hereby
incorporated by reference in its entirety. In addition, a person
skilled in the art may implement other ways of performing pulse
detection.
[0034] In some embodiments, the local parameter is a trend that can
be detected in a monitored physiological parameter of patient 82. A
trend can be detected by comparing values of parameters at
different times. Parameters whose detected trends can particularly
help a cardiac rehabilitation program include: a) cardiac function
(e.g. ejection fraction, stroke volume, cardiac output, etc.); b)
heart rate variability at rest or during exercise; c) heart rate
profile during exercise and measurement of activity vigor, such as
from the profile of an accelerometer signal and informed from
adaptive rate pacemaker technology; d) heart rate trending; e)
perfusion, such as from SpO2 or CO2; f) respiratory function,
respiratory rate, etc.; g) motion, level of activity; and so on.
Once a trend is detected, it can be stored and/or reported via a
communication link, along perhaps with a warning. From the report,
a physician monitoring the progress of patient 82 will know about a
condition that is either not improving or deteriorating.
[0035] Patient state parameters include recorded aspects of patient
82, such as motion, posture, whether they have spoken recently plus
maybe also what they said, and so on, plus optionally the history
of these parameters. Monitoring device 180 or monitoring device 281
may include a motion detector, which can be made in many ways as is
known in the art. For example, accelerometers make good motion
detectors. Or, one of these monitoring devices could include a
location sensor such as a Global Positioning System (GPS), which
informs of the location, and the rate of change of location over
time. Many motion detectors output a motion signal that is
indicative of the motion of the detector, and thus of the patient's
body. Patient state parameters can be very helpful in narrowing
down the determination of whether SCA is indeed taking place.
[0036] System parameters of a wearable defibrillation system can
include system identification, battery status, system date and
time, reports of self-testing, records of data entered, records of
episodes and intervention, and so on.
[0037] Environmental parameters can include ambient temperature and
pressure. A humidity sensor may provide information as to whether
it is likely raining. Presumed patient location could also be
considered an environmental parameter. The patient location could
be presumed if monitoring device 180 or 281 includes a GPS
sensor.
[0038] Defibrillator 200 typically includes a defibrillation port
210, such as a socket in housing 201. Defibrillation port 210
includes electrical nodes 214, 218. Leads of defibrillation
electrodes 204, 208, such as leads 105 of FIG. 1, can be plugged in
defibrillation port 210, so as to make electrical contact with
nodes 214, 218, respectively. It is also possible that
defibrillation electrodes 204, 208 are connected continuously to
defibrillation port 210, instead. Either way, defibrillation port
210 can be used for guiding, via electrodes, to the wearer the
electrical charge that has been stored in energy storage module
250. The electric charge will be the shock for defibrillation,
pacing, and so on.
[0039] Defibrillator 200 may optionally also have an ECG port 219
in housing 201, for plugging in sensing electrodes 209, which are
also known as ECG leads. It is also possible that Sensing
electrodes 209 can be connected continuously to ECG port 219,
instead. Sensing electrodes 209 can help sense an ECG signal, e.g.
a 12-lead signal, or a signal from a different number of leads,
especially if they make good electrical contact with the body of
the patient. Sensing electrodes 209 can be attached to the inside
of support structure 170 for making good electrical contact with
the patient, similarly as defibrillation electrodes 204, 208.
[0040] Optionally a wearable defibrillator system according to
embodiments also includes a fluid that it can deploy automatically
between the electrodes and the patient skin. The fluid can be
conductive, such as by including an electrolyte, for making a
better electrical contact between the electrode and the skin.
Electrically speaking, when the fluid is deployed, the electrical
impedance between the electrode and the skin is reduced.
Mechanically speaking, the fluid may be in the form of a
low-viscosity gel, so that it does not flow away, after it has been
deployed. The fluid can be used for both defibrillation electrodes
204, 208, and sensing electrodes 209.
[0041] The fluid may be initially stored in a fluid reservoir, not
shown in FIG. 2, which is can be coupled to the support structure.
In addition, a wearable defibrillator system according to
embodiments further includes a fluid deploying mechanism 274. Fluid
deploying mechanism 274 can be configured to cause at least some of
the fluid to be released from the reservoir, and be deployed near
one or both of the patient locations, to which the electrodes are
configured to be attached to the patient. In some embodiments,
fluid deploying mechanism 274 is activated responsive to receiving
activation signal AS from processor 230, prior to the electrical
discharge.
[0042] It will be appreciated, then, that the electrodes of a WCD
system include both the defibrillation electrodes that can
transport the electrical charge for defibrillation purposes, and
also the sensing electrodes that are configured to capture the ECG
signals of the patient. Moreover, with proper design, a single
electrode can perform both functions.
[0043] FIG. 3 is a conceptual diagram for illustrating how
electrodes of a WCD system may capture ECG signals along different
vectors according to embodiments. A section of a patient 382 having
a heart 385 is shown. There are four electrodes 304, 306, 307, 308,
attached to the torso, each with a wire lead 305. Any pair of these
electrodes defines a vector across with an ECG signal may be
measured. The four electrodes 304, 306, 307, 308 therefore can
define six vectors, across which six respective ECG signals 311,
312, 313, 314, 315, 316 can be captured. FIG. 3 thus illustrates a
multi-vector situation. In FIG. 3 it will be understood that
electrodes 304, 306, 307, 308 are drawn on the same plane for
simplicity, while that is not necessarily the case. Accordingly,
the vectors of ECG signals 311, 312, 313, 314, 315, 316 are not
necessarily on the same plane, either.
[0044] Any one of ECG signals 311, 312, 313, 314, 315, 316 might
provide sufficient data for making a good shock/no shock
determination. The effort is to shock when needed, and not shock
when not needed. The problem is that, at any given point in time,
some of these ECG signals may include noise, while others not. The
noise may be due to patient movement or how the electrode contacts
the skin. The noise problem for a WCD may be further exacerbated by
the desire to use dry, non-adhesive monitoring electrodes. Dry,
non-adhesive electrodes are thought to be more comfortable for the
patient to wear, but may produce more noise than a conventional ECG
monitoring electrode that includes adhesive to hold the electrode
in place and an electrolyte gel to reduce the impedance of the
electrode-skin interface. In order make the best shock/no-shock
determination as correctly as possible, a WCD may assess which of
ECG signals 311, 312, 313, 314, 315, 316 is best for rhythm
analysis and ECG interpretation.
[0045] Returning to FIG. 2, defibrillator 200 also includes a
measurement circuit 220. Measurement circuit 220 receives
physiological signals from ECG port 219, if provided. Even if
defibrillator 200 lacks ECG port 219, measurement circuit 220 can
obtain physiological signals through nodes 214, 218 instead, when
defibrillation electrodes 204, 208 are attached to the patient. In
these cases, the patient's ECG signal can be sensed as a voltage
difference between electrodes 204, 208. Plus, impedance between
electrodes 204, 208 and/or the connections of ECG port 219 can be
sensed. Sensing the impedance can be useful for detecting, among
other things, whether these electrodes 204, 208 and/or sensing
electrodes 209 are not making good electrical contact with the
patient's body. These physiological signals can be sensed, and
information about them can be rendered by circuit 220 as data,
other signals, etc.
[0046] Defibrillator 200 also includes a processor 230. Processor
230 may be implemented in any number of ways. Such ways include, by
way of example and not of limitation, digital and/or analog
processors such as microprocessors and digital-signal processors
(DSPs); controllers such as microcontrollers; software running in a
machine; programmable circuits such as Field Programmable Gate
Arrays (FPGAs), Field-Programmable Analog Arrays (FPAAs),
Programmable Logic Devices (PLDs), Application Specific Integrated
Circuits (ASICs), any combination of one or more of these, and so
on.
[0047] Processor 230 can be considered to have a number of modules.
One such module can be a detection module 232. Detection module 232
can include a ventricular fibrillation ("VF") detector. The
patient's sensed ECG from measurement circuit 220 can be used by
the VF detector to determine whether the patient is experiencing
VF. Detecting VF is useful, because VF results in SCA.
[0048] Another such module in processor 230 can be an advice module
234, which generates advice for what to do. The advice can be based
on outputs of detection module 232. There can be many types of
advice according to embodiments. In some embodiments, the advice is
a shock/no shock determination that processor 230 can make, for
example via advice module 234. The shock/no shock determination can
be made by executing a stored Shock Advisory Algorithm.
[0049] The shock/no shock determination can be made from one or
more of the captured ECG signals according to embodiments. An
example is now described.
[0050] FIG. 4 shows the time waveforms 411, 412 of two sample ECG
signals. Waveform 411 is from an ECG signal of a heart in a normal
sinus rhythm. Waveform 412 is from an ECG signal of a heart
undergoing asystole with compression artifact. According to
embodiments, processor 230 can make a shock/no shock determination
495 from such ECG signals, and any other available ones, as is
described later in this document. In FIG. 4, waveforms 411, 412 are
chosen because they make good samples individually; however, the
exact situation of FIG. 4 does not necessarily occur often, as
either one of waveforms 411, 412 could be further distorted by
noise, etc.
[0051] Returning to FIG. 2, if the determination is to shock,
processor 230 can cause discharge circuit 255 to discharge the
electrical charge stored in energy storage module 250 through at
least two of the electrodes 204, 208 so as to defibrillate the
patient. Discharging is also called delivering the electrical
charge. Discharging can be also for pacing instead of for
defibrillation, and so on.
[0052] Processor 230 can include additional modules, such as other
module 236, for other functions. In addition, if internal
monitoring device 281 is indeed provided, it may be operated in
part by processor 230, etc.
[0053] Defibrillator 200 optionally further includes a memory 238,
which can work together with processor 230. Memory 238 may be
implemented in any number of ways. Such ways include, by way of
example and not of limitation, volatile memories, nonvolatile
memories (NVM), read-only memories (ROM), random access memories
(RAM), magnetic disk storage media, optical storage media, smart
cards, flash memory devices, any combination of these, and so on.
Memory 238 is thus a non-transitory storage medium. Memory 238, if
provided, can include programs for processor 230, which processor
230 may be able to read, and execute. More particularly, the
programs can include sets of instructions in the form of code,
which processor 230 may be able to execute upon reading. Executing
is performed by physical manipulations of physical quantities, and
may result in the functions, processes, actions and/or methods to
be performed, and/or the processor to cause other devices or
components or blocks to perform such functions, processes, actions
and/or methods. The programs can be operational for the inherent
needs of processor 230, and can also include protocols and ways
that decisions can be made by advice module 234. In addition,
memory 238 can store prompts for user 282, if they are a local
rescuer. Moreover, memory 238 can store data. The data can include
patient data, system data and environmental data, for example as
learned by internal monitoring device 281 and outside monitoring
device 180. The data can be stored in memory 238 before it is
transmitted out of defibrillator 200, or stored there after it is
received by it.
[0054] Defibrillator 200 may also include a power source 240. To
enable portability of defibrillator 200, power source 240 typically
includes a battery. Such a battery is typically implemented as a
battery pack, which can be rechargeable or not. Sometimes a
combination is used of rechargeable and non-rechargeable battery
packs. Other embodiments of power source 240 can include an AC
power override, for where AC power will be available, an energy
storage capacitor, and so on. In some embodiments, power source 240
is controlled by processor 230.
[0055] Defibrillator 200 additionally includes an energy storage
module 250, which can thus be coupled to the support structure of
the wearable system. Module 250 is where some electrical energy is
stored in the form of an electrical charge, when preparing it for
sudden discharge to administer a shock. Module 250 can be charged
from power source 240 to the right amount of energy, as controlled
by processor 230. In typical implementations, module 250 includes a
capacitor 252, which can be a single capacitor or a system of
capacitors, and so on. As described above, capacitor 252 can store
the energy in the form of electrical charge, for delivering to the
patient.
[0056] Defibrillator 200 moreover includes a discharge circuit 255.
Circuit 255 can be controlled via processor 230 or user interface
270. When so controlled, circuit 255 can permit the energy stored
in module 250 to be discharged to nodes 214, 218, and thus also to
defibrillation electrodes 204, 208. Circuit 255 can include one or
more switches 257. Switches 257 can be made in a number of ways,
such as by an H-bridge, and so on.
[0057] Defibrillator 200 can optionally include a communication
module 290, for establishing one or more wired or wireless
communication links with other devices of other entities, such as a
remote assistance center, Emergency Medical Services (EMS), and so
on. Module 290 may also include an antenna, portions of a
processor, and other sub-components as may be deemed necessary by a
person skilled in the art. This way, data and commands can be
communicated, such as patient data, event information, therapy
attempted, CPR performance, system data, environmental data, and so
on.
[0058] Defibrillator 200 can optionally include other
components.
[0059] Moreover, methods and algorithms are described below. These
methods and algorithms are not necessarily inherently associated
with any particular logic device or other apparatus. Rather, they
are advantageously implemented by programs for use by a computing
machine, such as a general-purpose computer, a special purpose
computer, a microprocessor, etc.
[0060] Often, for the sake of convenience only, it is preferred to
implement and describe a program as various interconnected distinct
software modules or features, individually and collectively also
known as software. This is not necessary, however, and there may be
cases where modules are equivalently aggregated into a single
program, even with unclear boundaries. In some instances, software
is combined with hardware, in a mix called firmware.
[0061] This detailed description includes flowcharts, display
images, algorithms, and symbolic representations of program
operations within at least one computer readable medium. An economy
is achieved in that a single set of flowcharts is used to describe
both programs, and also methods. So, while flowcharts described
methods in terms of boxes, they also concurrently describe
programs.
[0062] Methods are now described.
[0063] FIG. 5 is a conceptual diagram for illustrating embodiments
of processes according to embodiments. These processes may start
from at least two ECG signals, such as a set 510 of the previously
described ECG signals 311, 312, 313, 314, 315, 316. These processes
aim at using the most appropriate ECG signals for rhythm analysis
and making a determination of whether to shock or not.
[0064] In embodiments of FIG. 5, one may optionally use one of
discarding processes 525, in which one or more of the ECG signals
of set 510 is discarded. In the example of FIG. 5, ECG signal 313
is shown as discarded; in other examples, other sets of the ECG
signals may be discarded. Discarding according to one of processes
525 is described in more detail later in this document. If, after
discarding, only one of the ECG signals remains, then a shock/no
shock determination 535 can be made.
[0065] In embodiments of FIG. 5, one may optionally use one of
combination processes 545 for the ECG signals of set 510. One of
combination processes 545 may be used whether one of discarding
processes 525 has been used first or not. In combination processes
545 two or more of the ECG signals of set 510, or their results,
are combined to make an aggregate shock/no shock determination 555.
Accordingly, combination processes 545 may be performed directly
from the ECG signals 311, 312, 313, 314, 315, 316 of set 510. Or,
combination processes 545 may be performed from the ECG signals
remaining after processes 525, if there are two or more of them
remaining. Combination according to one of processes 545 is
described in more detail later in this document.
[0066] FIG. 6 shows a flowchart 600 for describing methods
according to embodiments. The methods of flowchart 600 may also be
practiced by embodiments described elsewhere in this document.
[0067] In flowchart 600, the group of operations 610, 620, 630, 640
can implement embodiments for discarding processes 525. According
to an operation 610, it can be inquired whether there is another
ECG signal to consider, for example from set 510. If yes, then
according to another operation 620, then a next one of the ECG
signals may be input. According to another operation 630, it can be
decided whether the input ECG signal meets a reliability criterion,
as will be described later in this document. If not, then according
to another operation 640, the input ECG signal may be discarded,
i.e. no longer considered.
[0068] Once all appropriate signals have been considered, execution
may proceed from operation 610 to another operation 650, where it
is inquired whether one or more than one ECG signals remain after
the discarding. This number of remaining ECG signals may depend
both on circumstances and also on the methodology of discarding
according to a reliability criterion, as will be understood from
the examples below.
[0069] In some embodiments, the reliability criterion is that the
ECG signal has a reliability value that is higher than a threshold.
The reliability value may be computed as a mathematical statistic
to decide whether the reliability criterion is met or not.
Accordingly, it will not be known in advance whether any, some, or
all of the ECG signals in set 510 will be discarded, and therefore
whether there will be any remaining signals for making the shock/no
shock determination. If no ECG signals remain, then a shock/no
shock determination might not be made, and the WCD system may
instead prompt for better sensing conditions, e.g. ask that
movement stops, etc.
[0070] For instance, FIG. 7 shows an example where ECG signals 314,
315, 311 meet the reliability criterion, while ECG signals 316,
312, 313 do not and are thus shown as discarded. In the example of
FIG. 7, meeting the reliability criterion is determined by the fact
that ECG signals 314, 315, 311 have a reliability value that is
higher than threshold T, while the rest do not. Accordingly, in
this instance, the ECG determination can be made from the
non-discarded ECG signals 314, 315, 311 according to one of
processes 545.
[0071] In other embodiments, the reliability criterion can be that
the ECG signal has a reliability value that is higher than the
reliability value of another of the ECG signals. In other words,
the criterion can be relative, among the ECG signals. In such
embodiments, discarding may continue until all the ECG signals are
discarded except a specified number, such as one, two, three, etc.
For implementing these embodiments, flowchart 600 would have to be
modified accordingly. For example, the reliability criterion can be
that the ECG signal that is not discarded is the one that has a
higher reliability value than the other ECG signals. The advantage
is that only one ECG signal remains, and thus making a shock/no
shock determination 535 can be done more simply, as is known.
[0072] For instance, FIG. 8 shows an example of where ECG signal
314 remains, while all other ECG signals 315, 311, 316, 312, 313
are discarded. In the example of FIG. 8, ECG signal 314 is not
discarded because it was the one that has the higher reliability
value. A shock/no shock determination 535 can be made from single
remaining ECG signal 314.
[0073] In these embodiments, discarding can proceed regardless of
whether any threshold is met or not. Accordingly, the risk is that
the single remaining ECG signal 314, while deemed the best
available, will have a reliability value that is not higher than a
threshold. Optionally, it can be further determined whether the
remaining non-discarded ECG signal has a reliability value that is
less than a threshold and, if so, not making a shock/no shock
determination.
[0074] Returning to FIG. 6, therefore, at operation 650, if more
than one non-discarded ECG signals remain, execution can proceed to
processes 545. If only one non-discarded ECG signal remains, then,
execution can proceed to another operation 660.
[0075] According to operation 660, a shock/no shock determination
535 can be made from one of the ECG signals that is not a discarded
ECG signal. That ECG signal may be the only remaining ECG signal.
The determination can be made as is known in the art.
[0076] According to another operation 670, it may be inquired if
the determination of operation 660 is to shock. If so, then
according to another operation 680, a discharge circuit can be
caused to discharge a stored electrical charge through at least two
electrodes so as to defibrillate a patient.
[0077] Selective discarding of ECG signals is now described in more
detail. In some instances, the reliability criterion is related to
a noise of the ECG signal.
[0078] In some embodiments, the component or the wearable cardiac
defibrillation system includes an implement (not shown). The
implement can be configured to detect an ECG common voltage signal.
In such embodiments, the reliability criterion for a certain ECG
signal can be derived from a mathematical correlation between the
ECG common voltage signal and the certain ECG signal. This may
help, because a common-mode signal may cause artifacts to appear on
the ECG signals that are differential, i.e. between electrodes. A
perfect differential amplifier in a circuit that detects an ECG
signal would not have this problem, but real-life differential
amplifiers have a limited common-mode rejection. The reliability
criterion could be that the mathematical correlation is less than a
threshold, and the reliability values would be inverted from what
is suggested in FIGS. 7 and 8. If ECG signals were ranked, the one
with the lowest correlation would be considered to have the lowest
noise and would thus be chosen for rhythm monitoring.
[0079] In some embodiments, an impedance signal of the patient is
captured along with the ECG signals. In such embodiments, the
reliability criterion for a certain ECG signal can be derived from
a mathematical correlation between the impedance signal and the
certain ECG signal. Again, the reliability criterion could be that
the mathematical correlation is less than a threshold.
[0080] Impedance could be monitored in a number of contexts. In
some embodiments, impedance along multiple vectors is monitored,
even all the vectors that would correspond to the ECG signals, if
available. In some embodiments, the impedance signal could be
derived from a single vector impedance measurement made between two
electrodes, or it could be an impedance measurement found by a
combination between different sets of electrodes. The combination
could be a root of the sums of the squares (RSS). In some
embodiments, the impedance of the electrode-skin interface of each
electrode is also monitored.
[0081] In some embodiments, the component or the wearable cardiac
defibrillation system includes an accelerometer, which could be
within outside monitoring device 180 or internal monitoring device
281. The accelerometer can be configured to generate an
acceleration signal. In such embodiments, the reliability criterion
for a certain ECG signal can be derived from a mathematical
correlation between the acceleration signal and the certain ECG
signal. The accelerometer can be, for example, a three-axis
accelerometer, each axis providing a channel. The correlation could
be performed separately against each of the three channels, or it
could be performed on a mathematical combination of the three
channels, such as an RSS combination.
[0082] As described above, the mathematical correlation could be a
cross-correlation. The cross-correlation could be a mathematically
literal cross-correlation, or it may be a pseudo cross-correlation,
an association of some sort. A literal cross-correlation would
involve taking a point by point product of the two signals, and
then taking the sum.
[0083] A pseudo cross-correlation could be any function that
associates activity on one channel with activity on another
channel. In some embodiments, signals could be simplified before
the point-by-point multiplication of the cross-correlation is
performed. For example, the absolute value of the signals could be
taken. For another example, each signal could be low-pass filtered.
A pseudo cross-correlation may also look for similarities in the
frequency domain. This might be done by taking a Fast Fourier
Transform (FFT) of each signal and examining the amount of overlap.
Or, it is possible that alignment between the peak frequency of
each signal might be sufficient to indicate noise on a particular
channel. Yet another possibility is to look at the coherence
between the two signals.
[0084] In embodiments, the decision of whether to discard an ECG
signal or not is made based on whether a cardiac feature is
recognized in one of the ECG signals, which would make that ECG
signal a more reliable indicator. For example, either one of
waveforms 411, 412 corresponds to a signal of high reliability.
[0085] In embodiments, the decision of whether to discard an ECG
signal or not is made from a measured amplitude of the ECG signal.
This can be performed in a number of ways.
[0086] For one example, the reliability criterion can be met
depending on how well the measured amplitude matches a reference
amplitude. The reference amplitude can be known in advance--for
example it may be the amplitude of a QRS complex that is typical
for a patient, or has been measured in advance for specific patient
82, perhaps at the time that the WCD system was fitted to them.
[0087] For another example, the reliability criterion can be met
depending on how large is a ratio of a peak value to a median value
of the ECG signal. This works because it takes advantage of the
characteristics of a QRS complex, such as is shown in waveform 411.
QRS complexes have a high such ratio; sinusoidal noise tends to
have a lower ratio. It has the advantage that it would bias the
channel selection toward the channel with the highest apparent QRS
complexes.
[0088] In some embodiments, at least a certain one of the ECG
signals is analyzed for a detected patient heart rate. Of course, a
patient heart rate will not always be detected but if it is, such
as in waveform 412, it is a rather good indication. Then the
individual shock/no shock recommendation from the certain ECG
signal can be to shock, if the detected patient heart rate is above
a threshold, and not to shock otherwise. That threshold could be,
for example, 200 bpm.
[0089] In some embodiments, the ECG signals can be compared to each
other, for example by taking a mathematical correlation between two
of them in pairs. If two of them show cardiac features
concurrently, that can be evidence that they are both reliable,
only one of them need be used, and the rest can be discarded. Of
course, similarity can be while allowing for different amplitude
scale, different other aspects for different placement of
electrodes, etc. Plus, sometimes noise artifacts can be temporally
similar along different vectors especially if they share the same
electrode, and should not be allowed to confuse the analysis. In
these embodiments, therefore, the reliability criterion for an ECG
signal might not be met, if two others of the ECG signals have an
aspect similar to each other, because these two other signals may
be preferred.
[0090] Combination processes 545 of FIG. 5 are now described in
more detail. An embodiment of these processes can be used for
making an aggregate shock/no shock determination 555 from two or
more ECG signals.
[0091] FIG. 9 shows a flowchart 900 for describing methods
according to embodiments. The methods of flowchart 900 may also be
practiced by embodiments described elsewhere in this document.
Flowchart 900 can implement embodiments for combination processes
545.
[0092] According to an operation 960, an aggregate shock/no shock
determination 555 can be made from at least two of the ECG signals,
as described later. According to another operation 970, it may be
inquired whether the aggregate determination of operation 960 is to
shock. If so, then according to another operation 980, a discharge
circuit can be caused to discharge a stored electrical charge
through at least two electrodes so as to defibrillate a
patient.
[0093] Making the aggregate shock/no shock determination is now
described in more detail. There are a number of ways this may be
performed. In many embodiments, an individual shock/no shock
recommendation is made from the respective ECG signals, for example
is if each of them were the only ECG signal. Then the aggregate
shock/no shock determination can be made from the individual
recommendations, by combining them. There are many such ways to
combine, and examples are described.
[0094] In some embodiments, the aggregate shock/no shock
determination is to shock if any of the individual recommendations
is to shock. This can be implemented if it is desirable to bias the
WCD system in favor of shocking, e.g. to ensure a very high
sensitivity. These embodiments can be complemented with those
described above, e.g. where the heart rate is detected to be above
a threshold.
[0095] In some embodiments, the aggregate shock/no shock
determination is to not shock if any of the individual
recommendations is to not shock. This can be implemented if it is
desirable to bias the WCD system against shocking, e.g. to avoid
disturbing the patient with shocks, some of which might not be
needed. These embodiments can be complemented with those described
above, e.g. where the heart rate is detected to be below a
threshold, and/or where ECG signals can be discarded based on
amplitude. For example, at least one of the ECG signals can be
discarded if its measured amplitude does not meet a reliability
criterion, which would bias leaving in ECG signals with a possible
QRS complex as described above, especially where the reliability
criterion is met depending on how large is a ratio of a peak value
to a median value of the ECG signal. In these cases, the ECG
signals used to make the aggregate shock/no shock determination do
not include the discarded ECG signal.
[0096] In some embodiments, the aggregate shock/no shock
determination is made from a statistic of the individual shock/no
shock recommendations. The statistic could be a simple majority
voting. In such cases, all ECG signals might be discarded except an
odd number, such as the top three most reliable ones.
[0097] In some embodiments, individual shock/no shock
recommendations are made in the form of respective certainty values
from the ECG signals. For example, these certainty values, instead
of a simple shock/no-shock result. Such algorithms might, for
example, produce a result in which a positive number is shockable,
a negative number is non-shockable, and zero is indeterminate. In
these embodiments, the aggregate shock/no shock determination can
be made from a numeric combination of the certainty values. An
example is now described.
[0098] FIG. 10 is a conceptual diagram for illustrating how a
sample combination can be made from individual decisions according
to embodiments. Three ECG signals have been analyzed, and have
resulted in making three individual shock/no shock recommendations
in the form of numerical certainty values that are plotted as
vectors 1011, 1014, 1015. Within a combination process 1045, the
three vectors are added into a resultant vector 1018. Since it is
positive, the aggregate determination will be to shock.
[0099] There are other ways for combining the certainty values. For
example, the median value may be consulted. In the example of FIG.
10, the median value would be vector 1015, resulting in an
aggregate shock determination. In addition, at least one of them
can be multiplied by a confidence coefficient before the aggregate
shock/no shock determination is made. The confidence coefficient
can be implemented in a number of ways.
[0100] In some embodiments, the confidence coefficient is learned
from parameters of the signal itself, such as the amplitude as
described above. In particular, at least one of the ECG signals can
be discarded if its measured amplitude does not meet a reliability
criterion, and the ECG signals used to make the aggregate shock/no
shock determination do not include the discarded ECG signal.
[0101] In some embodiments, the confidence coefficient is learned
from a history of the ECG signal. This could be done by running
multiple successive analyses on each channel that generates an ECG
signal. If one channel produces a consistent result over time,
either shock or no-shock, then it might be considered more reliable
than a channel that produces an inconsistent result over time. If a
numerical value is calculated for the shock decision, then the
channel with the least numerical spread might be considered the
most reliable. The numerical spread might be estimated, for
example, by examining the range of values, by examining the
variance of the data, or by examining the standard deviation.
[0102] In the methods described above, each operation can be
performed as an affirmative step of doing, or causing to happen,
what is written that can take place. Such doing or causing to
happen can be by the whole system or device, or just one or more
components of it. In addition, the order of operations is not
constrained to what is shown, and different orders may be possible
according to different embodiments. Moreover, in certain
embodiments, new operations may be added, or individual operations
may be modified or deleted. The added operations can be, for
example, from what is mentioned while primarily describing a
different system, apparatus, device or method.
[0103] A person skilled in the art will be able to practice the
present invention in view of this description, which is to be taken
as a whole. Details have been included to provide a thorough
understanding. In other instances, well-known aspects have not been
described, in order to not obscure unnecessarily the present
invention. Plus, any reference to any prior art in this description
is not, and should not be taken as, an acknowledgement or any form
of suggestion that this prior art forms parts of the common general
knowledge in any country.
[0104] This description includes one or more examples, but that
does not limit how the invention may be practiced. Indeed, examples
or embodiments of the invention may be practiced according to what
is described, or yet differently, and also in conjunction with
other present or future technologies. Other embodiments include
combinations and sub-combinations of features described herein,
including for example, embodiments that are equivalent to:
providing or applying a feature in a different order than in a
described embodiment; extracting an individual feature from one
embodiment and inserting such feature into another embodiment;
removing one or more features from an embodiment; or both removing
a feature from an embodiment and adding a feature extracted from
another embodiment, while providing the features incorporated in
such combinations and sub-combinations.
[0105] In this document, the phrases "constructed to" and/or
"configured to" denote one or more actual states of construction
and/or configuration that is fundamentally tied to physical
characteristics of the element or feature preceding these phrases.
This element or feature can be implemented in any number of ways,
as will be apparent to a person skilled in the art after reviewing
the present disclosure, beyond any examples shown in this
example.
[0106] The following claims define certain combinations and
subcombinations of elements, features and steps or operations,
which are regarded as novel and non-obvious. Additional claims for
other such combinations and subcombinations may be presented in
this or a related document. When used in the claims, the phrases
"constructed to" and/or "configured to" reach well beyond merely
describing an intended use, since such claims actively recite an
actual state of construction and/or configuration based upon
described and claimed structure.
* * * * *