U.S. patent application number 14/736149 was filed with the patent office on 2015-12-10 for selecting energy escalation for defibrillation.
The applicant listed for this patent is ZOLL Medical Corporation. Invention is credited to Gary A. Freeman, Weilun Quan.
Application Number | 20150352369 14/736149 |
Document ID | / |
Family ID | 54834273 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150352369 |
Kind Code |
A1 |
Quan; Weilun ; et
al. |
December 10, 2015 |
SELECTING ENERGY ESCALATION FOR DEFIBRILLATION
Abstract
In an aspect, a system for treating a patient in cardiac arrest
is described and includes memory, one or more electronic ports for
receiving signals from sensors for obtaining indications of an
electrocardiogram (ECG) of the patient, one or more sensors for
obtaining a transthoracic impedance of the patient, and a patient
treatment module executable on one or more processing devices that
is configured to generate, from the ECG, transform values that
represent magnitudes of two or more frequency components of the
ECG, and modify, based on at least one transform value, at least
one shock delivery parameter.
Inventors: |
Quan; Weilun; (Dracut,
MA) ; Freeman; Gary A.; (Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZOLL Medical Corporation |
Chelmsford |
MA |
US |
|
|
Family ID: |
54834273 |
Appl. No.: |
14/736149 |
Filed: |
June 10, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62010202 |
Jun 10, 2014 |
|
|
|
Current U.S.
Class: |
607/7 |
Current CPC
Class: |
A61H 31/005 20130101;
A61B 5/0402 20130101; A61B 5/7257 20130101; A61N 1/3925 20130101;
A61B 5/04011 20130101; A61H 31/004 20130101; A61H 31/007 20130101;
A61H 31/006 20130101; A61N 1/3987 20130101; A61B 5/053 20130101;
A61N 1/3968 20130101; A61N 1/3993 20130101; A61H 2230/045 20130101;
A61N 1/3906 20130101; A61B 5/4836 20130101; A61N 1/3937
20130101 |
International
Class: |
A61N 1/39 20060101
A61N001/39 |
Claims
1. A system for treating a patient in cardiac arrest, the system
comprising: memory; one or more electronic ports for receiving
signals from sensors for obtaining indications of an
electrocardiogram (ECG) of the patient; one or more sensors for
obtaining a transthoracic impedance of the patient; and a patient
treatment module executable on one or more processing devices, the
patient treatment module configured to: generate, from the ECG,
transform values that represent magnitudes of two or more frequency
components of the ECG, and modify, based on at least one transform
value, at least one shock delivery parameter.
2. The system of claim 1, wherein the at least one shock delivery
parameter is current.
3. The system of claim 2, wherein the current is an average
defibrillation current.
4. The system of claim 1, wherein the at least one shock delivery
parameter is defibrillation waveform duration.
5. The system of claim 1, wherein the at least one shock delivery
parameter is defibrillation waveform rise time.
6. The system of claim 1, wherein the at least one shock delivery
parameter is shock energy.
7. The system of claim 1, wherein the at least one shock delivery
parameter is defibrillation peak voltage.
8. The system of claim 1, wherein generating the transform values
comprises applying one or more Fast Fourier Transforms (FFTs) to
data representing the ECG.
9. The system of claim 8, wherein the FFTs comprise vectorized FFTs
applied to vectors formed from data obtained by different leads for
the ECG.
10. The system of claim 8, wherein generating the transform values
comprises one or more amplitude spectrum area calculations applied
to the data representing the ECG.
11. The system of claim 1, wherein generating the transform values
comprises computing a mathematical transform from a time domain to
a frequency domain on a window of data.
12. The system of claim 11, wherein the window is between about one
second and about 2 seconds in width.
13. The system of claim 11, wherein the window is a tapered
window.
14. The system of claim 13, wherein the tapered window comprises a
Tukey window, Hahn window, Blackman Harris window or Flat Top
window.
15. The system of claim 1, wherein the system is programmed to
automatically charge one or more capacitors to an identified level
of energy to be delivered.
16. The system of claim 1, wherein the system is programmed to
present to a user an identified level of energy to be delivered,
and to permit the user to choose between using the identified level
of energy to be delivered or manually selecting a different level
of energy to be delivered.
17. The system of claim 16, further comprising a visible, audible,
or tactile output mechanism arranged to present, to the user, an
indication regarding the identified level of energy to be
delivered.
18. The system of claim 17, wherein the indication comprises
information about a current level, duration, or associated
waveform.
19. The system of claim 1, wherein the patient treatment module is
arranged to identify a level of energy to be delivered as a shock
to the patient based on a trans-thoracic impedance of the patient
and a value derived from a current ECG from the patient.
20. The system of claim 1, wherein the patient treatment module is
further arranged to use data representing a current ECG to
determine a likelihood of success from delivering a defibrillating
shock with one or more capacitors to the patient.
21. The system of claim 20, further comprising an interlock that
prevents a user from delivering a shock unless the determined
likelihood of success exceeds a determined value.
22. The system of claim 1, further comprising a visible, audible,
or tactile output mechanism arranged to present, to a user of the
system, an indication regarding the determined likelihood of
success from delivering a defibrillating shock with one or more
capacitors to the patient.
23. The system of claim 1, wherein the patient treatment module
comprises an ECG analyzer for generating an amplitude spectrum area
(AMSA) transform value using the transform values.
24. The system of claim 1, wherein generating the transform values
includes defining a region for employing one of escalating energy
levels for a plurality of shocks or a fixed energy level for a
plurality of shocks.
25. The system of claim 24, wherein an AMSA transform value of
about 12 mV-Hz defines the region.
26. A system for treating a patient in cardiac arrest, the system
comprising: memory; one or more electronic ports for receiving
signals from sensors for obtaining indications of an
electrocardiogram (ECG) the patient; one or more sensors for
obtaining a transthoracic impedance of the patient; and a patient
treatment module executable on one or more processing devices, the
patient treatment module configured to: generate transform values
that represent magnitudes of two or more frequency components of
the ECG, determine the viability of future therapeutic actions
based at least in part on the transform values and the
transthoracic impedance, and provide a treatment determination
based on the viability determination.
27. The system of claim 26, wherein determining the viability of
the future therapeutic actions comprises adjusting one or more
values derived from the transform values.
28. The system of claim 27, wherein the one or more values derived
from the transform values include AMSA values.
29. The system of claim 27, wherein adjusting comprises modifying
the one or more values derived from the transform values using a
multiplicative factor, linear regression or non-linear
regression.
30. The system of claim 27, wherein the adjusting comprises
modifying the one or more values derived from the transform values
using a table lookup.
31. The system of claim 26, wherein the treatment determination
identifies delivering a defibrillating shock to the patient.
32. The system of claim 26, wherein the treatment determination
identifies administering cardiopulmonary resuscitation (CPR).
33. The system of claim 26, wherein the treatment determination
identifies adjusting a cardiopulmonary resuscitation (CPR)
technique.
34. A system for monitoring the physiological status of a patient
in cardiac arrest, the system comprising: memory; one or more
electronic ports for receiving signals from sensors for obtaining
indications of a vectorcardiograph (VCG) for the patient; and a
patient treatment module executable on one or more processing
devices, the patient treatment module configured to: generate
transform values for a time segment of VCG, wherein the transform
values represent magnitudes of two or more frequency components of
the VCG, and are indicative of a likelihood of success of a future
therapeutic action.
35. The system of claim 34, wherein the VCG is represented in a
polar coordinate system and the transform is a polar Fourier
transform.
36. The system of claim 34, wherein the VCG is represented in a
spherical coordinate system and the transform is a spherical
Fourier transform.
37. The system of claim 34, wherein the transform is a Hankel
transform.
38. The system of claim 34, wherein the transform is a spherical
harmonic transform.
39. One or more machine-readable storage devices having encoded
thereon machine readable instructions for causing one or more
processors to perform operations comprising: receiving signals
indicative of an electrocardiogram (ECG) of a patient; obtaining a
transthoracic impedance of the patient; generating, from the ECG,
transform values that represent magnitudes of two or more frequency
components of the ECG; and modifying, based on at least one
transform value, at least one shock delivery parameter.
40. The one or more machine-readable storage devices of claim 39,
wherein the at least one shock delivery parameter is current.
41. The one or more machine-readable storage devices of claim 40,
wherein the current is an average defibrillation current.
42. The one or more machine-readable storage devices of claim 39,
wherein the at least one shock delivery parameter is defibrillation
waveform duration.
43. The one or more machine-readable storage devices of claim 39,
wherein the at least one shock delivery parameter is defibrillation
waveform rise time.
44. The one or more machine-readable storage devices of claim 39,
wherein the at least one shock delivery parameter is shock
energy.
45. The one or more machine-readable storage devices of claim 39,
wherein generating the transform values comprises applying one or
more Fast Fourier Transforms (FFTs) to data representing the
ECG.
46. The one or more machine-readable storage devices of claim 45,
wherein the FFTs comprise vectorized FFTs applied to vectors formed
from data obtained by different leads for the ECG.
47. The one or more machine-readable storage devices of claim 45,
wherein generating the transform values comprises one or more
amplitude spectrum area calculations applied to the data
representing the ECG.
48. The one or more machine-readable storage devices of claim 39,
wherein generating the transform values comprises computing a
mathematical transform from a time domain to a frequency domain on
a window of data.
49. The one or more machine-readable storage devices of claim 48,
wherein the window is between about one second and about 2 seconds
in width.
50. The one or more machine-readable storage devices of claim 48,
wherein the window is a tapered window.
51. The one or more machine-readable storage devices of claim 50,
wherein the tapered window comprises a Tukey window, Hahn window,
Blackman Harris window or Flat Top window.
52. The one or more machine-readable storage devices of claim 39,
further comprising instructions for automatically charging one or
more capacitors to an identified level of energy to be
delivered.
53. The one or more machine-readable storage devices of claim 39,
further comprising instructions for presenting to a user, an
identified level of energy to be delivered, and permitting the user
to choose between using the identified level of energy to be
delivered or manually selecting a different level of energy to be
delivered.
54. The one or more machine-readable storage devices of claim 53,
further comprising a visible, audible, or tactile output mechanism
arranged to present, to the user, an indication regarding the
identified level of energy to be delivered.
55. The one or more machine-readable storage devices of claim 54,
wherein the indication comprises information about a current level,
duration, or associated waveform.
56. The one or more machine-readable storage devices of claim 39,
further comprising instructions for identifying a level of energy
to be delivered as a shock to the patient based on a trans-thoracic
impedance of the patient and a value derived from a current ECG
from the patient.
57. The one or more machine-readable storage devices of claim 56,
further comprising instructions for using data representing the
current ECG to determine a likelihood of success from delivering a
defibrillating shock with one or more capacitors to the
patient.
58. The one or more machine-readable storage devices of claim 57,
further comprising instructions for implementing an interlock that
prevents a user from delivering a shock unless the determined
likelihood of success exceeds a determined value.
59. The one or more machine-readable storage devices of claim 39,
further comprising instructions for providing a visible, audible,
or tactile indication regarding the determined likelihood of
success from delivering a defibrillating shock with one or more
capacitors to the patient.
60. The one or more machine-readable storage devices of claim 39,
further comprising instructions for generating an amplitude
spectrum area (AMSA) transform value using the transform
values.
61. The one or more machine-readable storage devices of claim 39,
wherein generating the transform values includes defining a region
for one of employing escalating energy levels for a plurality of
shocks or a fixed energy level for a plurality of shocks.
62. The one or more machine-readable storage devices of claim 61,
wherein an AMSA transform value of about 12 mV-Hz defines the
region.
63. One or more machine-readable storage devices having encoded
thereon machine readable instructions for causing one or more
processors to perform operations comprising: receiving signals
indicative of an electrocardiogram (ECG) of a patient; obtaining a
transthoracic impedance of the patient; generating transform values
that represent magnitudes of two or more frequency components of
the ECG; determining the viability of future therapeutic actions
based at least in part on the transform values and the
transthoracic impedance; and providing a treatment determination
based on the viability determination.
64. The one or more machine-readable storage devices of claim 63,
wherein determining the viability of future therapeutic actions
comprises adjusting one or more values derived from the transform
values.
65. The one or more machine-readable storage devices of claim 64,
wherein the one or more values derived from the transform values
include AMSA transform values.
66. The one or more machine-readable storage devices of claim 64,
wherein adjusting comprises modifying the one or more values
derived from the transform values using a multiplicative factor,
linear regression or non-linear regression.
67. The one or more machine-readable storage devices of claim 64,
wherein the adjusting comprises modifying the one or more transform
values using a table lookup.
68. The one or more machine-readable storage devices of claim 63,
wherein the treatment determination identifies delivering a
defibrillating shock to the patient.
69. The one or more machine-readable storage devices of claim 63,
wherein the treatment determination identifies administering
cardiopulmonary resuscitation (CPR).
70. The one or more machine-readable storage devices of claim 63,
wherein the treatment determination identifies adjusting a
cardiopulmonary resuscitation (CPR) technique.
71. One or more machine-readable storage devices having encoded
thereon machine readable instructions for causing one or more
processors to perform operations comprising: receiving signals
indicative of a vectorcardiograph (VCG) for a patient; and
generating transform values for a time segment of VCG, wherein the
transform values represent magnitudes of two or more frequency
components of the VCG, and are indicative of a likelihood of
success of a future therapeutic action.
72. The one or more machine-readable storage devices of claim 71,
wherein the VCG is represented in a polar coordinate system and the
transform is a polar Fourier transform.
73. The one or more machine-readable storage devices of claim 71,
wherein the VCG is represented in a spherical coordinate system and
the transform is a spherical Fourier transform.
74. The one or more machine-readable storage devices of claim 71,
wherein the transform is a spherical Fourier transform or a polar
Fourier transform.
75. The one or more machine-readable storage devices of claim 71,
wherein the transform is a Hankel transform.
76. The one or more machine-readable storage devices of claim 71,
wherein the transform is a spherical harmonic transform.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application 62/010,202, filed on Jun. 10, 2014. This application is
also related to the co-filed utility application which claims
priority to U.S. Provisional Application 62/010,215, filed on Jun.
10, 2014, and U.S. Provisional Application 62/011,902, filed on
Jun. 13, 2014. The content of each of the above referenced
applications is incorporated herein by reference.
TECHNICAL FIELD
[0002] This document relates to cardiac resuscitation systems and
techniques.
BACKGROUND
[0003] Ventricular fibrillation (VF) is an abnormal heart rhythm
(arrhythmia) that causes the heart to lose pumping capacity. If
such a problem is not corrected quickly--typically within
minutes--the rest of the body loses oxygen and the person dies.
Therefore, prompt care of a person undergoing VF can be key to a
positive outcome for such a person.
[0004] One common way to treat ventricular fibrillation is through
the use of an electrical defibrillator that delivers a relatively
high-voltage shock to the heart in order to force it back to a
normal, consistent, and strong rhythm. People who have had previous
problems with ventricular fibrillation may be implanted with an
automatic defibrillator, or be provided a wearable defibrillator,
that constantly monitors the condition of their heart and applies a
shock when necessary. Other people may be treated using a portable
external defibrillator, such as in a hospital or by emergency
medical technicians, or via an automatic external defibrillator
(AED) of the kind that is frequently seen in airports, public
gymnasiums, and other public spaces. Defibrillation may be
delivered in coordination with cardiopulmonary resuscitation (CPR),
which centers around the provision of repeated compressions to a
victim's chest, such as by a rescuer pressing downward repeatedly
with the palms of the hands, or via an automatic mechanical
compression device.
SUMMARY
[0005] This document describes systems and techniques that may be
used to adjust the manner in which shocks are delivered to a person
suffering from VF. The techniques discussed here take into account
a number of input signals in determining whether a shock should be
delivered and how it should be delivered. Generally, the input
signals are patient-dependent, in that they are measured from a
patient at the time of a rescue event, e.g., by electrodes from a
portable defibrillator that have been attached to the patient's
skin. One such signal is an amplitude spectrum area (AMSA) value,
where the AMSA transform value is a numerical value that is based
on the sum of the magnitude of a weighted frequency distribution
from the signal, e.g., between 3 and 48 Hz. Such AMSA transform
value can be used, alone or in combination with other signals, to
determine a likelihood that a shock will succeed in defibrillating
a patient if it is currently delivered, and also to determine an
energy level to deliver with the shock.
[0006] As to delivered energy levels, generally, a patient's AMSA
transform values decrease as time goes on in a VF event without
achieving defibrillation, and energy needed for a successful
defibrillation goes up. Thus, a defibrillator may be programmed to
select energy levels for charging capacitors and delivering shocks,
where the energy levels increase as the measured AMSA level
decreases. In other implementations, the selected energy may be a
function of a ratio between AMSA of other electrocardiograph
predictor, and trans-thoracic impedance (TTI) measured for the
patient.
[0007] The energy level of delivered shocks may by increased
automatically by a defibrillator or higher energy levels may be
suggested to a rescuer who is selecting energy levels manually, as
a VF episode continues. In particular, shocks may be delivered with
fewer joules early in an event and may increase as time passes, or
increases with each shock that is delivered, or both. Whether the
energy increase is made automatically or as part of a suggestion to
the rescuer may depend on whether the defibrillator is operating in
a manual mode (where the rescuer is presumed to have expertise to
select his or her own energy level) or an automatic mode (where the
rescuer is presumed to need direct assistance).
[0008] Upon a defibrillator making a determination that a shock to
be delivered currently will succeed in defibrillating the patient
(i.e., determining a likelihood of future success for
defibrillating the patient), the defibrillator may provide an
indication to a rescuer about such a determination, and may also
provide an indication of a planned energy for the shock. For
example, the defibrillator may only allow a shock to be performed
when the indication is sufficiently positive (e.g., over a set
percentage of likelihood of success)--and may only provide a "ready
for shock" light or other indication in such a situation. Also, a
defibrillator may provide a display--such as a graphic that shows
whether defibrillation will likely succeed (e.g., above a
predetermined threshold level of likelihood of success) or provide
a number (e.g., a percentage of likelihood of success) or other
indication (e.g., a grade of A, B, C, D, or F) so that the rescuer
can determine whether to apply a shock. The display may also show
the energy level that the shock will be delivered at, and the
rescuer in appropriate circumstance may be able to change the
energy level before delivering the shock (and potentially before
charging the capacitor or capacitors, if such charging occurs late
in the process).
[0009] In certain implementations, such systems and techniques may
provide one or more advantages. For example, determinations of
whether a shock should be provided or what advice to provide a
rescuer based on AMSA transform values can be made from variables
that are measured for a patient for other purposes (e.g., TTI and
ECG readings). Also, energy levels can be selected that are
determined a priori to maximize that likelihood of successful
defibrillation. The AMSA transform values can be improved with
respective to their predictive qualities by actions such as
monitoring ECG vectors and performing vectorized FFT operations to
produce an improved AMSA value. As a result, a patient may avoid
receiving an ineffective shock, and then having to wait another
cycle for another shock (which may end up being equally
ineffective), and avoid the physical harm caused by any delivered
shocks. And a system may guide the rescuer in providing the actions
that are currently best for the patient, whether that involves
delivering a shock, providing deep chest compressions, providing
progressive chest compressions, or otherwise caring for the
patient. Alternatively, the techniques described here may be
implemented by a system that provides chest compressions
automatically and mechanically throughout the course of a cardiac
event. Such a process may, therefore, result in the patient
returning to normal cardiac function more quickly and with less
stress on his or her cardiac system, which will generally lead to
better patient outcomes.
[0010] In one implementation, a system for managing care of a
person is disclosed and comprises one or more capacitors arranged
to deliver a defibrillating shock to a patient; one or more
electronic ports for receiving a plurality of signals from sensors
for obtaining indications of an electrocardiogram (ECG) for the
patient; and a patient treatment module executable on one or more
computer processors using code stored in non-transitory media and
arranged to identify a level of energy to be delivered in a shock
to the patient by applying a mathematical computation to current
ECG data from the patient and data indicating a present level of
trans-thoracic impedance for the patient. The mathematical
computation may comprise applying one or more Fast Fourier
Transforms (FFTs) to the ECG data, and the FFTs may comprise
vectorized FFTs applied to vectors formed by different leads for
collecting the ECG data. The mathematical computation can also
comprise one or more amplitude spectrum area calculations applied
to the ECG data.
[0011] In certain aspects, the mathematical computation comprises a
mathematical transform from a time domain to a frequency domain on
a window of data. The window may be between about one second and
about 2 seconds in width, and may be a tapered window for example
Tukey, Hann, Blackman-Harris, or Flat Top. Also, the system can be
programmed to automatically charge the one or more capacitors to
the identified a level of energy to be delivered.
[0012] In other aspects, the system is programmed to present to a
user the identified level of energy to be delivered, and to permit
the user to choose between using the identified level of energy to
be delivered or manually selecting a different level of energy to
be delivered. The system can also include a visible, audible, or
tactile output mechanism arranged to present, to the user, an
indication regarding the identified level of energy to be
delivered. In addition, the patient treatment module can be
arranged to identify the level of energy to be delivered in the
shock to the patient by applying the mathematical computation to a
ratio correlating the present level of trans-thoracic impedance of
the patient and a value derived from the current ECG from the
patient. The patient treatment module can also be further arranged
to use the current ECG data to determine a likelihood of success
from delivering a defibrillating shock with the one or more
capacitors to the patient.
[0013] In yet other aspects, the system also includes an interlock
that prevents a user from delivering a shock unless the determined
likelihood of success exceeds a determined value. The system can
also include a visible, audible, or tactile output mechanism
arranged to present, to a user of the system, an indication
regarding the determined likelihood of success from delivering the
defibrillating shock with the one or more capacitors to the
patient. Moreover, the patient treatment module can comprise an ECG
analyzer for generating an amplitude spectrum area (AMSA) value
using the transform.
[0014] In another implementation, a method is disclosed for
managing care of a person. The method comprises monitoring, with an
external defibrillator, electrocardiogram (ECG) data from a person
receiving emergency cardiac assistance; performing a mathematical
transformation of the ECG data from a time domain to a frequency
domain using a window of the ECG data in the time domain; and
determining a level of energy to be delivered using at least the
mathematical transformation of the ECG data and data indicating a
present level of trans-thoracic impedance for the patient The
method can also comprise displaying to a user of the external
defibrillator a numeric value of the determined level of energy,
the mathematical transformation can comprise applying one or more
Fast Fourier Transforms (FFTs) to the ECG data, and the FFTs can
comprise vectorized FFTs applied to vectors formed by different
leads for collecting the ECG data.
[0015] In some aspects, the mathematical transformation comprises
one or more amplitude spectrum area calculations applied to the ECG
data. Also, the window of ECG data can comprise a window that is
between about one second and about two seconds in width, and the
window can be a tapered window selected from a group comprising
Tukey, Hann, Blackman-Harris, and Flat Top. The method can
additionally include automatically charging one or more capacitors
of the external defibrillator to the identified a level of energy
to be delivered. Moreover, the method can include presenting to a
user of the defibrillator the identified level of energy to be
delivered, and permitting the user to choose between using the
identified level of energy to be delivered or manually selecting a
different level of energy to be delivered.
[0016] In yet other aspects, the method can also include presenting
to the user a visual, audible, or tactile indication regarding the
identified level of energy to be delivered. In addition, the method
can comprise determining the level of energy to be delivered by
applying the mathematical transformation to a determined
trans-thoracic impedance of the patient. The method can also
comprise identifying the level of energy to be delivered by
applying the mathematical transformation to a ratio correlating the
determined trans-thoracic impedance of the patient and a value
derived from the current ECG from the patient, and using the
current ECG data to determine a likelihood of success from
delivering a defibrillating shock with the one or more capacitors
to the patient. In addition, the method can include preventing a
user of the defibrillator from delivering a shock with the
defibrillator unless the determined likelihood of success exceeds a
determined value.
[0017] In an aspect, a system for treating a patient in cardiac
arrest is described and includes memory, one or more electronic
ports for receiving signals from sensors for obtaining indications
of an electrocardiogram (ECG) of the patient, one or more sensors
for obtaining a transthoracic impedance of the patient, and a
patient treatment module executable on one or more processing
devices that is configured to generate, from the ECG, transform
values that represent magnitudes of two or more frequency
components of the ECG, and modify, based on at least one transform
value, at least one shock delivery parameter.
[0018] In another aspect, a system for treating a patient in
cardiac arrest is described and includes memory, one or more
electronic ports for receiving signals from sensors for obtaining
indications of an electrocardiogram (ECG) the patient, one or more
sensors for obtaining a transthoracic impedance of the patient, and
a patient treatment module executable on one or more processing
devices that is configured to generate transform values that
represent magnitudes of two or more frequency components of the
ECG, determine the viability of future therapeutic actions based at
least in part on the transform values and the transthoracic
impedance, and provide a treatment determination based on the
viability determination.
[0019] In a further aspect, a system for monitoring the
physiological status of a patient in cardiac arrest is described
and includes memory, one or more electronic ports for receiving
signals from sensors for obtaining indications of a
vectorcardiograph (VCG) for the patient, and a patient treatment
module executable on one or more processing devices that is
configured to generate transform values for a time segment of VCG,
wherein the transform values represent magnitudes of two or more
frequency components of the VCG, and are indicative of a likelihood
of success of a future therapeutic action.
[0020] In another aspect, one or more machine-readable storage
devices are described that have encoded thereon machine readable
instructions for causing one or more processors to perform
operations comprising receiving signals indicative of an
electrocardiogram (ECG) of a patient, obtaining a transthoracic
impedance of the patient, generating, from the ECG, transform
values that represent magnitudes of two or more frequency
components of the ECG, and modifying, based on at least one
transform value, at least one shock delivery parameter.
[0021] In a further aspect, one or more machine-readable storage
devices are described that have encoded thereon machine readable
instructions for causing one or more processors to perform
operations comprising receiving signals indicative of an
electrocardiogram (ECG) of a patient, obtaining a transthoracic
impedance of the patient, generating transform values that
represent magnitudes of two or more frequency components of the
ECG, determining the viability of future therapeutic actions based
at least in part on the transform values and the transthoracic
impedance, and providing a treatment determination based on the
viability determination.
[0022] In another aspect, one or more machine-readable storage
devices are described that have encoded thereon machine readable
instructions for causing one or more processors to perform
operations comprising receiving signals indicative of a
vectorcardiograph (VCG) for a patient, and generating transform
values for a time segment of VCG, wherein the transform values
represent magnitudes of two or more frequency components of the
VCG, and are indicative of a likelihood of success of a future
therapeutic action.
[0023] In another aspect, a method is described that includes
receiving signals indicative of an electrocardiogram (ECG) of a
patient, obtaining a transthoracic impedance of the patient,
generating, from the ECG, transform values that represent
magnitudes of two or more frequency components of the ECG, and
modifying, based on at least one transform value, at least one
shock delivery parameter.
[0024] In a further aspect, a method is described that includes
receiving signals indicative of an electrocardiogram (ECG) of a
patient, obtaining a transthoracic impedance of the patient,
generating transform values that represent magnitudes of two or
more frequency components of the ECG, determining the viability of
future therapeutic actions based at least in part on the transform
values and the transthoracic impedance, and providing a treatment
determination based on the viability determination.
[0025] In an additional aspect, a method is described that includes
receiving signals indicative of a vectorcardiograph (VCG) for a
patient, and generating transform values for a time segment of VCG,
wherein the transform values represent magnitudes of two or more
frequency components of the VCG, and are indicative of a likelihood
of success of a future therapeutic action.
[0026] Other features and advantages will be apparent from the
description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0027] FIG. 1 shows a relationship between AMSA and shock energy
that may be implemented by a portable defibrillator.
[0028] FIGS. 2A and 2B are graphs showing relationships between
sensitivity and specificity, and AMSA threshold values for groups
of patients.
[0029] FIG. 2C is a graph showing relationships between AMSA
transform values and the probability of defibrillation success.
[0030] FIG. 3 shows consideration by a system of multiple signals
in making shock determinations and recommendations.
[0031] FIG. 4 is a schematic diagram of a portable
defibrillator.
[0032] FIG. 5 is a flow chart of a process for determining an
energy level for a defibrillator.
[0033] FIG. 6 shows a defibrillator showing certain types of
information that can be displayed to a rescuer.
[0034] FIG. 7 shows a general computer system that can provide
interactivity with a user of a medical device.
DETAILED DESCRIPTION
[0035] In general, defibrillation is a common treatment for various
arrhythmias, such as VF. However, there can be undesired side
effects (e.g., heart tissue damage, skin burns, etc.) that follow
an electrical shock. Other undesired side effects include
unnecessary interruptions of chest compressions when a shock needs
to be delivered. Added to this, the effectiveness of defibrillation
can fall generally over the elapsed time of a VF episode--where an
episode may be measured from the time when a victim first starts
feeling symptoms of cardiac arrest or loses consciousness and falls
down. (Generally, the time from onset of a lethal VF episode and
unconsciousness is relatively short, on the order of less than
one-half minute.) It is therefore desirable to predict whether
defibrillation will be successful in restoring a regular heartbeat
following onset of an arrhythmic episode, determine a proper energy
level for a shock, and/or to determine how long it has been since a
cardiac event started or what stage of the event the patient is in
(e.g., a first, second, or third stage or phase).
[0036] Predictions about likely effectiveness of a shock (which may
be termed as an "indicator of success," a "success indication," or
a "determination" and "indication of a likelihood of success") may
cause a defibrillating shock to not be provided when the chance of
successful defibrillation is low. Instead, the shock may be
provided when its odds of succeeding are relatively high, and can
be provided at an energy level that maximizes those odds of
success.
[0037] FIG. 1 shows a relationship between AMSA and shock energy
that may be implemented by a portable defibrillator. In the figure,
a graph 100 shows identified relationships between AMSA transform
values (expressed as mV-Hz according to common practice) and energy
(expressed in Joules, as is also common practice) levels that have
been determined to be needed to successfully defibrillate a patient
at such corresponding AMSA transform values (e.g., above a
predetermined predicted likelihood of success value). The values
shown here may be programmed into a medical device like a
defibrillator, where the AMSA value is treated as an independent
variable (along with potentially other inputs, such as TTI), and
the energy level is the dependent variable. In particular, an AMSA
value or similar value (e.g., that is based on amplitudes in an ECG
signal for a patient) may be computed from a patient's ECG data,
and the medical device may select an energy level based on the
computed AMSA value (and perhaps based on additional values, such
as by blending the multiple inputs together in a weighted manner).
The energy value may be applied automatically in charging
capacitors for delivering a shock to a patient, or may be displayed
or otherwise presented to a rescuer, with the rescuer able to
override the suggested energy level with a manually entered energy
level, followed by the rescuer choosing to deliver the shock.
[0038] Three example relationships are shown between AMSA transform
values and energy output values in this example. Generally, each of
the representations indicate that the energy needed to achieve a
successful defibrillation falls as AMSA rises. The three examples
show programming for a defibrillator 102 by which the relationship
between computed AMSA transform values and the energy computed by
the defibrillator has different partially-linear relationships with
AMSA (though non-linear relationships may also be employed). Such
relationships may be determined by analyzing data collected by
defibrillators in-the-field for past rescue events, and identifying
AMSA for patients from such events (for both successful and
unsuccessful delivered shocks), energy levels for such events, and
defibrillation outcomes. Standard statistical techniques can then
be applied to determine relationships between AMSA and energy for
successful defibrillation and unsuccessful defibrillation. Other
factors, as indicated in more detail below, may also be used in
determining appropriate energy levels, such as trans-thoracic
impedance (TTI), patient body size (e.g., weight or surface area,
whether actual or estimated) and pharmacological history for the
patient, either outside of the present VF episode or as part of the
episode.
[0039] Stepped trace 108 generally shows increasing energy with
decreasing AMSA transform values. The increases in energy may be
stepped, such as in 1, 2, 5, or 10 Joule steps at appropriate AMSA
transform values (every 0.5, 1, 2, 3, 4, or 5 steps of AMSA
transform value). Such a trace 108 may be implemented by formula or
look-up table, where the look-up table correlates the particular
discrete values for AMSA shown here to an output for the multiple
discrete levels of energy shown here.
[0040] In certain implementations, the energy may be flat for a
range of AMSA transform values, but linearly changing for another
range of AMSA transform values. For example, the energy can be flat
at high and low AMSA transform values, and sloped in the middle.
Trace 104 shows such a relationship for energy that will be
computed by the defibrillator as changing by such a flat-slope-flat
function. In this example, energy is consistent for a large range
of AMSA transform values and then changes linearly for a mid-range
of AMSA transform values, and is steady again for another range of
AMSA transform values.
[0041] Trace 102 is similar to trace 104 in that it has a sloped
portion and a flat portion. However, trace 102 is sloped starting
immediately at low AMSA levels until it flattens at a particular
AMSA transform value (here, 20 mV-Hz).
[0042] The particular traces shown here are provided for
explication only, and other relationships may be programmed into a
medical device such as a defibrillator, and the computation of
appropriate energy may be based on multiple factors, in addition to
an AMSA or similar value derived from ECG data. For example, a
relationship may include both linear and non-linear portions if
such is what data from past usage indicates is the best approach to
having future defibrillators select output energy for shocks. Also,
as discussed further next, the computation of output energy may
depend on multiple inputs, in addition to AMSA or other ECG
amplitude-related criterion, and the relationship between inputs
and energy output may be determined in a variety of manners,
including multi-dimensional regression analysis that can then be
represented by data structure or formula for computing energy
output in future devices.
[0043] FIG. 2A shows a plot of sensitivity (%) versus AMSA
threshold (mv-Hz) for a first set of subjects having a
trans-thoracic impedance (TTI) measured greater than 150 ohms, and
a second set of subjects having a trans-thoracic impedance measured
less than 150 ohms. The data shows the influence of TTI on the
prediction accuracy of AMSA for shock success at different
threshold values as presented in sensitivity and specificity. Such
values may be incorporated with AMSA transform values so as to
select an output energy for a defibrillator, where the output
energy is both a function of AMSA (or other ECG based shock
prediction value) and of TTI. A gain factor may be used to adjust
for variations in TTI so as to maintain substantially equal levels
of performance of AMSA with regard to assessing the likelihood of
viability of future therapeutic actions, e.g., the viability of
delivering a defibrillating shock. For example, referring again to
FIG. 2A, the AMSA transform values for TTI<150 Ohms may be
multiplied by a gain factor of 1.17 so that the two curves overlap
more closely. In some implementations, a linear or non-linear
regression analysis may be performed to determine the relationship
between the optimal AMSA measure, which has as inputs to the
regression equation the TTI measure, and the raw AMSA reading. In
some implementations, the viability of a future therapeutic action
may be expressed as a probability, e.g. 0-100%, and the probability
may be adjusted by the TTI measure, for instance, using regression
methods, table lookup or neural networks. In some implementations,
complex relationships, such as depicted in FIG. 2B, may require
table lookup or non-linear regression to be adjusted for effects of
TTI.
[0044] The data was obtained by collecting data from defibrillators
used in real rescue events from multiple emergency medical services
in the United States through regular field case submission to ZOLL
Medical Corporation, and where individual personal identifying
information could not be determined from the gathered data. All
reporting parties used ZOLL automatic external defibrillators that
included current-based impedance compensation. The sampling rate
for ECG data was 250 Hz, and analysis was performed on a selection
of an episode of 2.05 seconds (512 data points) ending at 0.5
seconds before each shock attempt. Shock success was defined as an
organized rhythm for a minimum of 30 seconds, starting 60 seconds
after the delivered shock, and with a rate of 40 beats per minute
or greater. A total of 1292 shocks (305 successful) form 580
patients with VF were included in the analysis. AMSA. The TTI was
measure at shocking pads placed on each respective subject.
[0045] As shown by the comparative data, a patient's TTI affects
the predictability of AMSA by shifting the threshold upward for a
given sensitivity or specificity value. AMSA transform value was
significantly higher when the TTI was greater than 150 ohm
(11.6.+-.8.9 vs. 9.8.+-.7.1, p=0.002) as compared with those shocks
with TTI less than 150 ohm. The AMSA threshold value was increased
from 8.2 mvHz to 10.3 mvHz when sensitivity was set to 85%. Such
information can be used to provide a real-time adjustment
mechanism, like those discussed above, that adjusts an AMSA
threshold for predicting likelihood of shock success or otherwise
taking into account the real-time measured TTI so as to affect the
reported likelihood in a manner that makes it more accurate.
[0046] FIG. 2B shows a plot of specificity (%) versus AMSA
threshold (mv-Hz) for a first set of subjects having a
trans-thoracic impedance measured less than 150 ohms, a second set
of subjects having a trans-thoracic impedance greater than 150
ohms. The tested subjects and data collection were the same as for
the graph in FIG. 2A. As shown by the comparative data, AMSA
threshold generally increases, for a given specificity, with
increasing trans-thoracic impedance. For example specificity at a
threshold of 85% was 11.8 mvHz for TTI<150 ohms, and 14.2 mvHz
for TTI>150 ohms. Again, analysis of such data may be used in
programming devices to provide predictions of likelihood of shock
success, or to disable or enable the ability to shock a particular
patient, based on calculated AMSA transform values.
[0047] Thus, in an implementation, the data structure can be
established, and when a shockable rhythm is determined to exist for
a patient (e.g., via ongoing analysis of ECG data from the
patient), AMSA and other inputs or "signals" can be computed. Those
inputs may then be used to compute an energy level to charge the
defibrillator capacitor or capacitors to, in addition to other
computations (e.g., a computation of a likelihood that a shock, if
currently delivered, will succeed in defibrillating the
patient).
[0048] The likelihood of shock success can depend upon a number of
factors, relationships between or among factors, etc. For example,
shock energy levels, delivery techniques, etc. may be defined based
upon one or more quantities that use AMSA transform values. For
example, AMSA transform values may be used to define regions that
employ different energy levels, delivery techniques, etc. such as
escalating energy levels for subsequent shocks.
[0049] In one study data was collected and analyzed from 1219
shocks from 543 patients with VF. ECG recordings, sampled at 250
Hz, were digitized and reviewed. Episodes of approximately two
seconds (e.g., 2.05 seconds or 512 data points) that terminated a
half second before a shock attempt were analyzed. Shock success was
defined as an organized rhythm that was present for a minimum of 30
seconds, started within 60 seconds after the shock, and had a rate
of 40 beats per minute or larger.
[0050] Using an escalating defibrillation energy protocol (with
energy levels stepping from 120 Joules (J) to 150 J and to 200 J),
shock success increased with each step for AMSA transform values of
12 mV-Hz or greater (e.g., 50.0% success for 120 J, 64.6% success
for 150 J and 82.5% shock success for 200 J). For instances of
lower AMSA transform values, below 12 mV-Hz, shock success rates
did not significantly improve for the escalation steps (e.g., 9.3%
success for 120 J, 12.4% for 150 J and 10.4% for 200 J). Through
data analysis (e.g., using multivariable logistic regression),
shock success for higher AMSA transform values (e.g., 12 mV-Hz and
above) can depend upon the energy level (e.g., higher energy levels
may demonstrate improved success) while lower AMSA transform values
(e.g., below 12 mV-Hz) may solely depend on the AMSA transform
values and be somewhat independent of escalating energy levels.
Referring to FIG. 2C, for AMSA transform values larger than 12
mV-HZ, improvement in the probability of success is graphically
depicted.
[0051] One or more regions may be defined, for example using an
AMSA transform value, and different shock protocols can be employed
for each region. A single AMSA transform value (e.g., 12 mV-Hz) can
define the upper boundary of a lower AMSA transform value region
(e.g., values below 12 mV-Hz) and also provide the lower boundary
of another region that includes equivalent and larger AMSA
transform values (e.g., values of 12 mV-Hz and above). When
operating within the first region (e.g., for AMSA transform values
below 12 mV-Hz), a fixed low energy level protocol can be employed
(e.g., the energy level used for an initial shock is also used for
subsequent shocks). For operating in the second region (e.g., when
an AMSA value of 12 mV-Hz or larger is measured from a patient), an
escalating energy level protocol or a fixed maximum energy protocol
can be implemented. An escalating protocol may step the energy
levels by using one or more techniques, such as linearly increasing
the level with each successive shock (e.g., after an initial shock
of 120 J, energy levels of 150 J and then 200 J may sequentially be
used). Employing a fixed maximum energy level protocol, an energy
level larger than the energy level used for the fixed lower energy
level protocol can be implemented. After each shock, another AMSA
transform value may be calculated from measurements to determine if
the region of operation has changed. By using these regions defined
by the AMSA transform value (e.g., 12 mV-Hz), an escalating energy
protocol or a fixed maximum energy level protocol may improve
defibrillation results when the AMSA transform values is relatively
high (e.g., at or above 12 mV-Hz). When low (e.g., below 12 mV-Hz),
an escalating energy protocol may not improve defibrillation
results and a fixed low energy protocol may perform just as well as
the escalating energy protocol. Through real-time AMSA analysis
during a CPR, energy selection for defibrillation along with
defibrillation timing can be optimized.
[0052] In some implementations, other therapeutic and/or shock
delivery parameters can be modified based on the transform values.
Examples of such therapeutic and/or shock delivery parameters
include, but are not limited to: first phase average defibrillation
current, defibrillation waveform duration, defibrillation peak
voltage, defibrillation waveform rise time, and defibrillation
average current. The therapeutic parameters may also include
parameters that govern synchronized defibrillation. Synchronized
defibrillation is also known as synchronized cardioversion. At low
currents or energies, synchronized defibrillation may be beneficial
for ECG waveforms with AMSA transform values higher than a
threshold (e.g. AMSA transform values in excess of 18 to 20).
[0053] FIG. 3 shows consideration by a system of multiple signals
in making shock determinations and recommendations. As shown
conceptually here, various input signals for determining a
likelihood that a shock will be successful and for determining a
best energy level for the shock are shown in a circle around the
outputs that such signals may impact. In a particular
implementation, one of the signals may be used alone, or multiple
of the signals may be combined so as to create a composite energy
or likelihood--e.g., by giving a score to each type and a weight,
and combining them all to generate a weighted composite score for a
likelihood.
[0054] The relevant signals may be generated from inputs that may
obtain at least some of their data from signals generated by a pair
of electrodes 324 that may be adhered to a patient's torso--above
one breast and below the other, respectively, for example, in a
typical manner. The electrodes may include leads for obtaining ECG
data (e.g., via a 12-lead arrangement) and providing such data for
analysis for a number of purposes. In addition, a CPR puck 320 may
be placed on a patient's sternum and may deliver signals indicative
of acceleration of the puck, and thus of up-down acceleration of
the patient's sternum, which may be mathematically integrated so as
to identify a depth of compression (and presence or absence of
complete release) by the rescuer (and can also be used more simply
to identify whether the patient is currently receiving chest
compressions or not).
[0055] The electrodes 324 may be electrically connected to an ECG
unit 322, which may be part of a portable defibrillator and may
combine data from different leads (e.g., 8 or 12 leads) in a
familiar manner to construct a signal that is representative of the
patient's 326 ECG pattern. The ECG combination may also be
represented mathematically as a vector value, such as including
vector components in an XYZ representation. Such an ECG signal is
often used to generate a visual representation of the patient's 326
ECG pattern on a screen of the defibrillator. The ECG-related data
may also be analyzed in various ways to learn about the current
condition of the patient 326, including in determining what sort of
shock indication to provide in order to control the defibrillator
or to display to a rescuer.
[0056] As one such example, ECG data may be provided to an AMSA
analyzer 302, which may nearly continuously and repeatedly compute
an AMSA number or similar indicator that represents ECG amplitude
at particular different frequencies and/or frequency ranges in an
aggregated form (e.g., a numeral that represents a value of the
amplitude across the frequencies). The AMSA transform value may be
determined from vectorized versions of the ECG readings so as to
provide more predictive AMSA transform values. Similarly, power
spectrum area can be measured and its value can be used as an input
that is alternative to, or in addition to, an AMSA value for
purposes of making a shock indication.
[0057] As described in more detail above and below, a current AMSA
transform value (or a combination of multiple values over a short
period taken in different windows of time) can be used to determine
whether a shock is likely to be successful, and a plurality of
combined AMSA transform values, such as a running average computed
many times over a time period using a moving window may indicate
how much time has elapsed since a cardiac event began and thus
indicate which phase, of multiple phases during a VF event, the
victim is in, where each phase calls for a different most-effective
treatment sub-protocol. Also, when rescuers first arrive on a
scene, several seconds of ECG data may be used to provide them an
initial indication of the time since the event started and/or the
phase in which the victim currently is in--e.g., by displaying a
number of elapsed minutes or the name of one of multiple phases
(like the three phases discussed above) on a display screen of a
medical device such as a monitor or defibrillator/monitor.
[0058] The AMSA analyzer 302 may be programmed to perform the
analysis on the ECG inputs, and perhaps other inputs, so as to
maximize the predictive value of the AMSA readings, whether by
affecting inputs to the AMSA determination, and/or making an AMSA
determination and then adjusting the AMSA transform value that is
generated from that determination. As one example, the size of the
window in time from which ECG data is taken in making the
calculation may be set to maximize the predictive value, such as by
being about 1 second to about 1.5 seconds long. As another example,
the shape of the window may be tapered, such as by being in the
form of a Tukey or Hann window, rather than having vertical edges
like a boxcar window. Similarly, the coefficients for the window,
such as Chit and p may be set to maximize the expected predictive
value of the calculation.
[0059] The AMSA analyzer 302 may also be programmed to change such
parameter values dynamically over the course of a particular VF
incident, either by moving the values progressively as time elapses
so as to make the values match known expected values for maximizing
the predictive effect of the calculation, or to respond to
particular readings, e.g., to use particular window length, form,
or coefficients when an AMSA transform value is in a certain
defined range.
[0060] The predictive quality of the AMSA determination may also be
increased by performing the FFT or other transform in making the
calculation on a vector value rather than a scalar value from the
leads. Such an approach may provide a more complete picture of the
operation of the heart, such as by catching minimums and maximums
in the various signals more reliably and in capturing a picture of
a greater portion of the heart rather than a particular point on
the heart, where such point might be less representative of the
overall condition of the heart. The overall process may thus better
represent the actual condition of the heart, rather the
non-indicative random changes in the signals.
[0061] The combination of ECG data from different leads may also be
represented as a vector value in a three dimensional space. Such
representations are termed "Vectorcardiography" (VCG), and
represents the electrical activity of the heart as the motion of a
vector in three dimensional space. Various lead systems, including,
for example, the standard Frank XYZ lead system can be used for
obtaining vectorcardiographic representations. The techniques
described in this document can be adapted for data from such a
Cartesian XYZ lead system by computing multidimensional discrete
Fourier transforms (DFTs) on the data. In some implementations,
fast Fourier transform (FFT) processes can be used in computing the
multidimensional DFTs.
[0062] A multidimensional DFT is represented as:
X k = n = 0 N - 1 ? ##EQU00001## ? indicates text missing or
illegible when filed ##EQU00001.2##
[0063] Therefore, the multidimensional DFT transforms an array
x.sub.n with a d-dimensional vector of indices n=(n.sub.1, . . . ,
n.sub.d) by a set of d nested summations (over n.sub.j=0 . . .
N.sub.j-1 for each j), where the division n/N, defined as
n/N=(n.sub.1/N.sub.1, . . . , n.sub.d/N.sub.d), is performed
element-wise. The multidimensional DFT is therefore a composition
of a sequence of d sets of one-dimensional DFTs, performed along
one dimension at a time., The order in which the individual one
dimensional DFTs are performed does not affect the results of the
computation. Therefore, a multi-dimensional DFT can be computed,
for example, using a row-column process, by performing a sequence
of one-dimensional FFTs along one dimension (e.g., row-wise),
followed by a sequence of one-dimensional FFTs along another
dimension (e.g., column-wise). In some implementations, the
column-wise FFTs can precede the row wise FFTs. This process can be
extended for more than two dimensions for higher-dimension
data.
[0064] In some implementations, the VCG may be described using a
spherical coordinate system. For example, the spherical coordinates
(r, .theta., .phi.) can be used to represent radial distance r,
polar angle .theta. (theta), and azimuthal angle .phi. (phi). The
symbol .rho. (rho) is often used instead of r. In some cases,
Cartesian coordinate systems may not represent the activity of the
electrical vector of the heart with sufficient resolution. However,
because the activity is rotational in nature (with respect to a
fixed origin), representing the VCG using a polar or spherical
coordinate system may be of benefit in such cases.
[0065] In some implementations, because electrical activity is
often impacted by the physical structure of the heart itself, it
may be beneficial to align the spherical coordinate system with the
physical structure of the heart. This can be accomplished, for
example, by imaging of the heart at the time of VCG acquisition. By
using a portable ultrasound system, such as the NanoMaxx with P21N
probe (by Sonosite of Bothel Wash.), the location of the heart's
apex, along with the angular axis of the heart can be determined.
In some implementations, an inertial sensor system, such as the
Analog Devices ADIS164362 Tri-Axis Gyroscope, Accelerometer, may be
used to determine the position and angle of the ultrasound probe
with respect to the location of the VCG apex electrode. The
relative locations and angles of the heart's axis and apex position
with respect to the VCG electrode can be stored along with the VCG.
In some implementations, a rotational transform may align the zero
polar and azimuthal angles of the spherical coordinate system of
the VCG with the physical axis of the heart.
[0066] In some implementations, for example, when the VCG is
represented in a spherical coordinate system, a Spherical Fourier
Transform can be used as the transform. Examples of Spherical
Fourier Transforms are described by Wang, et al., in "Rotational
Invariance Based on Fourier Analysis in Polar and Spherical
Coordinates," IEEE Transactions on Pattern Analysis and Machine
Intelligence, VOL. 31, NO. 9, September 2009, and in Wang et al.,
"Fourier Analysis in Polar and Spherical Coordinates," Internal
Report, Albert-Ludwigs University Freiburg, 2008. Spherical Fourier
analysis can be defined as the decomposition of a function in terms
of eigenfunctions of the Laplacian with the eigenfunctions being
separable in the corresponding coordinates. The VCG can therefore
be decomposed into wave-like basic patterns that have clear radial
and angular structures. In some implementations, this decomposition
can be an extension of Fourier analysis and can, therefore, be
called Fourier analysis in the corresponding coordinates. In some
cases, the radius of the VCG vector may undergo very little change,
and the relevant changes occur primarily in the rotational dynamics
of the heart's electrical vector. In such cases, using conventional
Cartesian spectral analysis can cause the rotational dynamics to be
inadequately represented by the rectangular representation.
[0067] In some implementations, determining a likelihood of success
from delivering a future defibrillating shock can comprise
performing a mathematical transform on the ECG data. The
mathematical transform can be done using Fourier, discrete Fourier,
Hilbert, discrete Hilbert, wavelet, and discrete wavelet methods.
In some implementations, the determination of the likelihood of
success can include a zero-crossing-based analysis, an example of
which is described in Kedem, Spectral Analysis and Discrimination
by Zero-Crossings, Proceedings of the IEEE, Vol 74, No 11, November
1986. Zero-crossing counts in filtered time series may be referred
to as higher order crossings. In addition, determining a likelihood
of success from delivering a future defibrillating shock comprises
performing a calculation by an operation, such as logistic
regression, table look-up, neural network, and fuzzy logic.
[0068] A CPR chest compression module 304 provides another signal
and may receive signals about the motion of the puck 320 to
determine whether chest compressions are currently being applied to
the patient, and to determine the depth of such compressions and
whether full release is occurring. Such information may be used,
for example, in giving a rescuer feedback about the pace and depth
of the chest compressions (e.g., the defibrillator could generate a
voice that says "push harder"). The presence of current chest
compression activity may also signal the other components that a
shock is not currently advisable, or that ECG data should be
analyzed in a particular manner so as to remove residual artifacts
in the ECG signal from the activity of the chest compressions.
[0069] Information about pharmacological agents 306 provided to a
patient may also be identified and taken into account as another
signal in providing a shock indication to a rescuer and selecting
an energy level for any shock. Such information may be obtained
manually, such as by a rescuer entering, via a screen on a
defibrillator or on a tablet computer that communicates with the
defibrillator, identifiers for the type of agent administered to a
patient, the time of administration, and the amount administered.
The information may also be obtained automatically, such as from
instruments used to administer the particular pharmacological
agents. The device that provides a shock indication may also take
that information into account as yet another signal in identifying
the likelihood that a shock will be successful if provided to the
patient (e.g., by shifting up or down an AMSA threshold for
measuring shock success likelihood), and for other relevant
purposes such as determining an energy to apply in the shock.
[0070] A defibrillation history success module 308 tracks the
application of defibrillating shocks to the patient and whether
they were successful in defibrillating the patient, and/or the
level to which they were successful. For example, the module 308
may monitor the ECG waveform in time windows of various sizes for a
rhythm that matches a profile of a "normal" heart rhythm, and if
the normal rhythm is determined to be established for a
predetermined time period after the application of a defibrillating
shock, the module 308 may register the existence of a successful
defibrillating shock. If a shock is applied and a normal rhythm is
not established within a time window after the delivery of the
shock, the module 308 can register a failed shock. In addition to
registering a binary value of success/fail, the module may further
analyze the ECG signal to determine the level of the success or
failure and may, for example, assign a score to the chance of
success of each shock, such as a normalized score between 0 (no
chance of success) and 1 (absolute certainty).
[0071] With respect to modifying an AMSA or other shock prediction
algorithm (SPA) score, or affecting the manner in which such score
is computed based on prior success or failure in delivering
defibrillating shocks, it has been observed that victims of cardiac
fibrillation will successfully defibrillate for lower AMSA
threshold values if they have been previously successfully
defibrillated during the same rescue session. Such a determination
may also be combined with determinations about trans-thoracic
impedance (trans-thoracic impedance) of the patient, or other
measured factors, as discussed more fully below.
[0072] Particular techniques discussed here, including selection of
proper window size for the ECG data, proper window type, proper
coefficients, and the use of vectorized operations in calculating
the AMSA, may improve the quality of the AMSA scoring process. An
AMSA score may also be used to determine where, time-wise, a person
is in the process of suffering from cardiac arrest and
fibrillation, since defibrillating shocks may be much less
effective after a person has been fibrillating for several minutes,
and CPR (including forceful CPR) may be a preferred mode of
treatment instead. Such systems may also combine a current AMSA
transform value (e.g., for recommending a shock) with a trend in
AMSA transform value over time (e.g., for recommending chest
compressions instead of a shock), where some or all of the AMSA
transform values may be made from vector input.
[0073] A trans-thoracic impedance module 310 may also obtain
information from sensors provided with the electrodes 324, which
indicates the impedance of the patient between the locations of the
two electrodes. The impedance can also be a factor in determining a
shock indication, such as by taking into account an impedance in
altering the AMSA score that will trigger a recommendation for
providing a defibrillating shock. It would be understood that
mathematically, such additional factors such as TTI may be used as
inputs to an AMSA-related calculation, or may be used to modify a
result of an AMSA-related calculation.
[0074] One or more of the particular factors or signals discussed
here may then be fed to a shock indication module 312 and/or an
energy selection module 314, which may combine them each according
to an appropriate formula so as to generate a binary or analog
shock indication and a proposed energy level for a shock,
respectively. For example, any of the following appropriate steps
may be taken: a score may be generated for each of the factors, the
scores may normalized (e.g., to a 0 to 1 or 0 to 300 scale), a
weighting may be applied to each of the scores to represent a
determined relevance of that factor to the predictability of a
shock outcome or energy level to be delivered, the scores may be
totaled or otherwise combined, and an indication can be determined
such as a go/no go indication, a percentage of likely success, and
other such indications.
[0075] The results of such determinations may also be provided to a
display module 316, which may generate a presentation to be
provided to a rescuer who is operating the defibrillator. Such
presentation, may be visual, auditory, haptic, or a combination of
the three. For example, if a shock is determined to be likely to
succeed if it is provided, the display module 316 may cause a
screen on the defibrillator to display a binary indication such as
"Ready to deliver shock" or an analog indication such as "80%
likelihood of successful shock." Similarly, the display module may
cause a screen to show a message such as "200J." One or more of
these message may alternatively or additionally be spoken by
computer-generated voice into a speaker on the defibrillator or
into a wireless earpiece worn by a rescuer or rescuers.
[0076] In this manner then, the system 300 may take into account
one or a plurality of factors and treat them as input signals in
determining whether a shock to be delivered to a patient is likely
to be successful. The factors may take data measured from a
plurality of different inputs (e.g., ECG, TTI, delivered agents,
etc.), and may be combined to create a likelihood indication, such
as a numerical score that is to be measured against a predetermined
scale (e.g., 0 to 300% likelihood or A to F grade). They may also
be used to select an appropriate energy level for delivery of a
shock. In some implementations, different ones of the factors may
be used in the likelihood of success determination than in the
energy level determination. Additional determinations may also be
made with one or more of the signals. Such determinations may then
be used to control an automatically-operated system (e.g., that
delivers chest compressions mechanically), to limit operation of a
manually-operated system (e.g., by enabling a shock that is
triggered by a user pressing a button), or by simply providing
information to a system whose shock is determined solely by a
rescuer (e.g., for manual defibrillators in which the operator is a
well-trained professional, or a hybrid defibrillator that is set in
a manual mode).
[0077] FIG. 4 is a schematic diagram of a portable defibrillator
system 400. In this example, defibrillator 402, along with an
example electrode package 406 and compression puck 404, defines an
apparatus for administering care to a patient who requires cardiac
assistance (where the term patient addresses any human individual
in need of assistance, and is not limited to someone who has been
checked into a healthcare system already). Other components (not
pictured) may also be provided, including in-ambulance and
in-hospital display systems that can wirelessly communicate with
the defibrillator 402 and display information received from the
defibrillator 402; and wearable computing devices, such as
electronic glasses that provide visual annotations on a scene that
a user views, which may be worn by rescuers and provide critical
information about a patient visually or aurally, including each of
the types of information discussed here and with respect to FIG. 6
below.
[0078] Particular components of the defibrillator 402 are shown
here to indicate certain particular functionality provided by the
defibrillator 402, though additional features that are not shown
may also be provided. For example, defibrillator 402 includes a
switch 426 and at least one capacitor 422 for selectively supplying
or applying a shock to a patient. The defibrillator 402 further
includes an ECG analyzer module 412, a trans-thoracic impedance
module 414, a CPR feedback module 416 that controls frequency and
magnitude of chest compressions applied to a subject, a patient
treatment (PT) module 418 (which includes a defibrillation history
analyzer), a speaker, and a display 410.
[0079] In this example, the ECG analyzer module 412, trans-thoracic
impedance module 414, CPR feedback module 416, and patient
treatment (PT) module 418 are grouped together as a logical module
420, which may be implemented by one or more computer processors
executing software stored on one or more non-transient recordable
media. For example, respective elements of the logical module 420
can be implemented as: (i) a sequence of computer implemented
instructions executing on at least one computer processor of the
defibrillator 402; and (ii) interconnected logic or hardware
modules within the defibrillator 402.
[0080] In the example of FIG. 4, the electrode package 406 is
connected to the switch 426 via port 408 on the defibrillator 402
so that different packages may be connected at different times
(e.g., if a customer wants to buy different model numbers of
packages, or if the customer wants to replace a disposable package
that has been used or otherwise become ineffective). The electrode
package 406 may also be connected through the port 408 to ECG
analysis module 412, and TTI module 414, and may include A/D
conversion before being provided to the logical module 420. The
electrode package 406 includes electrodes for delivering a
defibrillating electrical pulse to a patient in addition to
capturing electrical signals from the heart that indicate ECG
functioning. In this example, there are a plurality of physical and
signal (pairs of physical) leads so that vector representations of
the ECG data may be collected and processed--e.g., to developed a
vectorized AMSA reading for the patient from the ECG data.
[0081] The compression puck 404 is connected, in this example, to
the CPR feedback module 416, also via port 408. In one embodiment,
the ECG analysis module 412 is a component that receives ECG
signals and produces a digital ECG representation form the signals,
where the produced ECG representation represents a current
streaming ECG representation capable of analysis and display in
familiar manners. Similarly, the TTI module 414 is a component that
receives TTI data that represents a current impedance across a
patient's torso where the electrodes 406 have been placed.
[0082] The patient treatment module 418 is configured to receive an
input from each one of the ECG analyzer module 412, TTI module 414,
and CPR feedback module 416. The patient treatment module 418 uses
inputs as received from at least the ECG analyzer module 412 and
trans-thoracic impedance module 414 to predict whether a
defibrillation event will likely terminate an arrhythmic episode,
and to identify an energy level (or at least a presumptive energy
level that can be overridden by an expert user) at which the shock
will be delivered. For example, ECG data can be used both to
determine AMSA transform values for a patient (including via
vectorized methods), and also determine whether shocks are
effective or not so that such information can be saved and used to
identify likelihoods that subsequent shocks will be effective. In
this manner, the patient treatment module 418 uses information
derived from both an ECG signal (both for AMSA and for adjusting
the AMSA value) and TTI measurement to provide a determination of a
likelihood of success for delivering a defibrillating shock to a
subject, and for selecting an energy level.
[0083] The patient treatment module 418 is further configured to
provide an input to each one of the speaker, display 410, and
switch 426, either directly or indirectly. In general, input
provided to the speaker and display 410 corresponds to either a
success indication or a failure indication regarding the likelihood
of success for delivering a shock to the patient, and display or
other presentation of an energy level at which the shock will be
delivered. In one embodiment, the difference between a success
indication and a failure indication is binary and based on a
threshold. For example, a success indication may be relayed to the
display 410 when the chances corresponding to a successful
defibrillation event is greater than 75%, and a "no shock"
indication when it is less then 75% (accompanied potentially by a
lock-out of the ability to deliver a shock with the defibrillator
402). In such example, the value "75%" (or some higher value) may
be rendered on the display 410 indicating a positive likelihood of
success. When a positive likelihood of success is indicated, the
patient treatment module 418 enables the switch 426 such that a
shock may be delivered to a subject.
[0084] The patient treatment module 418 may also implement an ECG
analyzer for generating an indication of heart rate for the patent,
for generating an indication of heart rate variability for the
patent, an indication of ECG amplitude for the patent, and/or an
indication of a first or second derivative of ECG amplitude for the
patient. The indication of ECG amplitude can include an RMS
measurement, measured peak-to-peak, peak-to-trough, or an average
of peak-to-peak or peak-to-trough over a specified interval. Such
indications obtained by the ECG analyzer may be provided to compute
an AMSA transform value for the patient and/or can be used in
combination with a computed AMSA transform value so as to generate
some derivative indication regarding whether a subsequent shock is
likely or unlikely to be effective (and the degree, e.g., along a
percentage scale, of the likelihood).
[0085] In another embodiment, likelihood of a successful
defibrillation event may be classified into one of many possible
groups such as, for example, low, medium, and high likelihood of
success. With a "low" likelihood of success (e.g., corresponding to
a successful defibrillation event is less than 50%), the patient
treatment module 418 disables the switch 426 such that a shock
cannot be delivered to a subject. With a "medium" likelihood of
success (e.g., corresponding to a successful defibrillation event
is greater than 50% but less than 75%), the patient treatment
module 418 enables the switch 426 such that a shock may be
delivered to a subject, but also renders a warning on the display
410 that the likelihood of success is questionable. With a "high"
likelihood of success (e.g., corresponding to a successful
defibrillation event is greater than or equal to 75%), the patient
treatment module 418 enables the switch 426 such that a shock may
be delivered to a subject, and also renders a cue on the display
410 indicating that the likelihood of success is very good. Still
other embodiments are possible.
[0086] Thus, the system 400 may provide, in a portable electric
device (e.g., a battery-operated device) the capability to analyze
a number of inputs and to identify a variety of factors from those
inputs, where the factors can then be combined to provide a
flexible, intelligent determination of likely success. As one such
example, an energy to be delivered (as a set value or a default
value that can be overridden).
[0087] FIG. 5 is a flow chart of a process for determining an
energy level for a defibrillator. In general, the process involves
collecting data from a patient who is being treated by rescuers and
using that data to identify an appropriate energy level to deliver
in a future shock to the patient, if it is determined that the
patient is in need of and susceptible to a defibrillating shock. In
particular, the data may include ECG data collected from electrodes
placed on the patient, and converted using a shock prediction
algorithm such as amps up. The process may be carried out using the
structures shown in FIGS. 3 and 4 above, and including use of the
patient treatment module 418 for determining energy levels for
delivery of a shock or shocks to a patient.
[0088] The process begins at box 500, where a patient is generally
monitored by a medical device such as a portable defibrillator at
the site of a rescue attempt. The monitoring may occur subsequent
to rescuers attaching electrodes to a patient, where the electrodes
may be configured both to provide a defibrillating shock and also
to collect lead information for generating ECG data. The monitoring
may occur substantially continuously, in a typical manner, and data
from the monitoring may be displayed on the medical device, such as
by displaying a continuous readout of the patient's pulse, ECG,
blood pressure, and other relevant medical information.
[0089] At box 502, a TTI for the patient is determined. Such
determination may be made by providing a small electric current
between the electrodes have been applied to the patient, measuring
voltage across the electrodes, and determining impedance by way of
homes law.
[0090] At box 504, the patient's AMSA is determined. Such
determination may occur, for example, by applying a fast Fourier
transfer (FFT) to multiple dimensions of the ECG data, and forming
an AMSA transform value out of such vectorized ECG data. Thus, the
transformations may occur via the use of vectorized FFTs applied to
vectors formed by different leads that have collected the ECG data,
The value may also, in addition to or alternatively to, being an
AMSA transform value, be a value computed from ECG data, including
amplitude data of an ECG representation, to determine a shock
success prediction level.
[0091] Rather than treating each shock as a discrete event in
analyzing the probability of success, the techniques described here
can take into account prior shock deliveries, and an observed
response of the patient to those deliveries, in determining an AMSA
transform value or other value that will indicate that a shock
currently applied to the patient will likely be successful (or not)
in defibrillating the patient. Such a determination may also be
combined with determinations about trans-thoracic impedance
(trans-thoracic impedance) of the patient, or other measured
factors, as discussed more fully below.
[0092] To obtain better predictive value for the AMSA transform
values, the time window from which the ECG data for an AMSA
determination is taken may be made relative small (e.g., between 3
and 4 seconds, between 2 and 3 seconds, and between 1 and 2
seconds), which will place the data as close to the current status
of the patient as possible. Smaller windows may suffer from edge
effects more-so than would larger windows, so the shape (e.g., a
tapered window) and coefficients for the windows may also be
selected to maximize predictive power of the method. For example, a
Tukey window having appropriate coefficients may be employed, and
the measurements may be made across multiple scalar lead values
with the data being processed as a vector representation of those
scalar values.
[0093] The techniques discussed here receive input from a plurality
of ECG leads (e.g., from a 12-lead system) and characterize that
input as a vector value, where the vector that may be made up of
three orthogonal (X, Y, and Z) vectors from the plurality of leads
and can be understood as rotating through a complex space with each
cycle of a heartbeat. A complex FFT operation may then be conducted
on the vector representation in order to compute a vectorized
amplitude spectrum area (AMSA) transform value, where the AMSA
transform value is a numerical value that is based on the sum of
the magnitude of a weighted frequency distribution from the signal,
e.g., between 3 and 48 Hz. Generally, the greater the AMSA, the
greater the probability that an applied shock will defibrillate the
heart successfully.
[0094] The particular parameters for computing the vectorized AMSA
value may be selected so as to maximize the predictive capabilities
of a medical device. For example, a tapering function may be
applied to the ECG data window (e.g., by using a Tukey window), so
as to improve the accuracy of the FFT applied to the data. Such a
tapered window may prevent the data from jumping immediately from a
zero value up the measured values, and then back down immediately
to a zero value at the end of a measured window. Various parameters
for the tapering function may also be applied, such as coefficients
to define the slopes of the starting and ending edges of the
function. Moreover, the length of the window may be selected to
provide better data, such as by using a relatively short window
having a duration shorter than 4 seconds, and in certain examples
of about 1 second, between 1 and 2 seconds, between 1 and 3
seconds, between 2 and 3 seconds, or between 3 and 4 seconds
long.
[0095] In certain other implementations, multiple different
tapering functions may be applied to the same data essentially
simultaneously, AMSA transform values may be determined from each
such applied function, and the resulting AMSA transform value from
one of the functions may be selected, or an AMSA transform value
may be generated that is a composite from multiple different
tapering functions. The window function that is used, the length of
the window, and the coefficients for the window may also be
adjusted dynamically, so that one or more of them change during a
particular incident, or deployment, with a particular patient. For
example, it may be determined from analysis of prior data that a
certain window shape, size, and/or coefficients are better earlier
in an episode of VF than later, so that a defibrillator may be
programmed to change such parameters over the course of an
event.
[0096] Such changes may be tied to an initial determination about
how long the patient has been in VF, which may be a function of
user input (e.g., when the emergency call was made) and parameters
measured by the defibrillator. Also, changes to the window type,
size, and coefficients may be made from readings dynamically made
from the patient under treatment. For example, AMSA transform
values in a particular range may be measured better by a particular
window type, size, or range of coefficients, so that an AMSA
measurement made at time n that shows such a value, may be measured
using the other parameters known to work best with that AMSA
transform value at time n+1. Other techniques for dynamically
adjusting the window type, window size, and/or coefficients may
also be employed.
[0097] With respect to indications of where a victim is in the
process of a VF episode--e.g., how many minutes since the victim's
episode has started--an average AMSA transform value (including as
a vectorized AMSA transform value) may be determined over a time
period so as to identify more generalized changes in the victim's
AMSA transform values, rather than AMSA at a particular point in
time or small slice of time. For example, AMSA transform values can
be computed for particular points in time or particular windows in
time and those values can be saved (e.g., in memory of a patient
monitor or defibrillator). After multiple such measurements and
computations have been made, an average may be computed across
multiple such values. Because AMSA generally falls (on average)
over time in an episode, if the average for a certain number of
readings (e.g., a moving average) falls below a particular value or
falls below the value over a minimum time period (so as to indicate
the general AMSA condition of the victim rather than just a
transient reading), the device may provide additional feedback to a
rescuer.
[0098] These general phases of cardiac arrest or VF may be
identified, in one representation, as three separate phases (though
there may be some overlap at the edges of the phases): electrical,
circulatory, and metabolic. The electrical phase is the first
several minutes of an event, and marks a period during which
electric shock can be particularly effective in defibrillating the
victim's heart and returning the victim to a relative satisfactory
condition. The circulatory phase appears to mark a decrease in
effectiveness for electric shock in defibrillating the victim, and
particularly in the absence of chest compressions performed on the
victim. As a result, a device such as a portable defibrillator may
be programmed to stop advising shocks during such a phase (or may
advise a shock only when other determinations indicate that a shock
would be particularly likely to be effective) and may instead
advise forceful CPR chest compressions. Such forceful compressions
may maximize blood flow through the heart tissue and other parts of
the body so as to extend the time that the victim may survive
without lasting or substantial damage.
[0099] In the metabolic phase, chest compressions may be relatively
ineffective as compared to the circulatory phase. For example,
where tissue has become ischemic, such as in circulatory phase, the
tissue may react favorably to the circulation of blood containing
some oxygen, but where tissue has become severely ischemic, such as
in the metabolic phase, the introduction of too much oxygen may be
harmful to the tissue. As a result, more gentle compressions for
the first period, such as 30 seconds, may need to be advised in the
metabolic phase before the rescuer (or a mechanical chest
compressor controlled to provide appropriate levels of compression
following the points addressed here) uses a full force.
[0100] Other treatments that may be useful in the metabolic phase
include extracorporeal circulation and cooling, either alone, in
combination with each other, or in combination with other
pharmacological treatments. In any event, observation of elapsed
time since an event has begun and/or observation of the phase in
which a victim is in, may be used to control a device or instruct a
rescuer to switch from a first mode of providing care to a second
mode of providing care in which the parameters of the provided care
differ (e.g., speed or depth of chest compressions may change,
temperature-based therapy may be provided or stopped, or
pharmaceuticals may be administered).
[0101] At box 506, a ratio of the TTI to AMSA is determined. The
ratio may be simple, such as by simply dividing the actual TTI
value by the AMSA transform value. The ratio may alternatively, or
in addition, be generated based on normalized values for TTI and
for AMSA, so as to provide a ratio that is more easily handled by
additional steps of the process. For example, the input values may
be scaled, so as to provide a linear output value for the
ratio.
[0102] At box 508, an energy level for a shock to be delivered is
determined. Such determination may occur by applying a value from a
shock prediction algorithm, such as an AMSA transform value, to a
predefined formula, to a lookup table, or by way of other
mechanisms for determining an energy level to supply. In other
implementations, a ratio between the TTI value and the AMSA
transform value may be used in a similar manner (e.g., by applying
it to a formula, look-up, etc.). The determination may also take
into account other variables, either as part of combining those
variables with the AMSA and TTI values, or by applying corrections
after an initial determination is made using AMSA, TTI, or
both.
[0103] At box 510, the capacitor or multiple capacitors in a
defibrillator may be charged to the determined energy level. Such
charging may occur automatically and at this point in the process,
or may occur at a later point in the process, such as after a
rescuer has indicated that they would like to provide a shock.
Also, the computed energy level and charging of capacitors may, in
certain circumstances, occur only after the process has determined
that the patient has a shockable heart rhythm, so that a shock is
advised at all. The determination of a shockable heart rhythm may
be part of determining a likelihood of success for applying a shock
or may be separate from such a determination. For example, the
determination of a shockable rhythm may be a threshold step before
making further calculations and may be a relative simple
determination to make. In contrast, the determination of a
likelihood of success may be more complex and may occur after a
shock a bowl rhythm is determined.
[0104] At box 512, shock indications are provided to the rescuer.
Such indications may include the energy level that has been
computed by the device as well as an indication of a likelihood of
a shock that is currently delivered being a success in
defibrillating the patient. Such presentation, as indicated above
and below, may include displaying a percentage likelihood of the
shock succeeding, displaying a letter grade, or displaying a binary
indication that a shock is or is not currently advised. The
presentation may also be audible or haptic. In certain
implementations, especially where the defibrillator is a manual or
professional defibrillator, or when the defibrillator is in a
manual mode, the computed energy may be overridden by the rescuer,
as may the determination of whether a shock is or is not currently
advisable, though the system may place a lower limit on a
likelihood of success even for manual mode, so that if the
likelihood is below that limit, even a skilled operator cannot
override the determination to not deliver a shock.
[0105] Additional information provided to a rescuer may take the
form of instructions, such as instructions to perform chest
compressions or some other action, where the action is selected
from among a plurality of possible treatments based on the current
phase for the victim. A system may also integrate both automatic
and manual approaches--e.g., locking out the ability to provide a
shock until a threshold level is reached, and then showing the
relative likelihood of success above that value. The likelihood of
success can be shown in various manners, such as by showing an
actual percentage, or showing two or more of a low, medium, or high
likelihood of success, e.g., on an electronic display of a
defibrillator.
[0106] At box 514, the process delivers the shock to the patient.
In such a situation, the information may have been provided to the
rescuer and the delivery of a shock enabled because the information
indicated that the likelihood of success was sufficient. In
response, the rescuer may have pushed a shock button to deliver the
shock, the device have waited a sufficient time for the rescuer to
remove his hand from the device, and then the device having closed
a switch automatically between the capacitors and the patient so as
to deliver the stored energy from the capacitors to the patient at
a level (e.g., in Joules) that was determined by the device or
entered by the rescuer. In certain implementations, the capacitor
may be pre-charged to a level that does not match the level
determined by the device or entered by a user when the shock is
going to be provided. In such circumstances, additional charge may
be provided to the capacitors or charge may be released from the
capacitors before delivering the shock, so that the energy level
that is determined or selected may be the appropriate energy level
delivered to the patient.
[0107] In this manner, the process allows a medical device such as
a defibrillator to deliver a shock at the time that is most
appropriate and most likely to defibrillator a patient, and any
energy level that is most likely to defibrillator the patient. As a
result, the patient may be more likely to be defibrillator from the
shock, and to be defibrillator with fewer shocks and plus less
damage from failed shocks.
[0108] FIG. 6 shows a defibrillator showing certain types of
information that can be displayed to a rescuer. In the figure, a
defibrillation device 600 with a display portion 602 provides
information about patient status and CPR administration quality
during the use of the defibrillator device. As shown on display
602, during the administration of chest compressions, the device
600 displays information about the chest compressions in a box on
the same display 602 as is displayed a filtered ECG waveform 610
and a CO2 waveform 612 (alternatively, an SpO2 waveform can be
displayed). The device 602 may be an implementation of the
defibrillator 402 shown schematically in FIG. 4 or similar forms of
devices. The presentation here is intended to show an example of a
typical device layout and information that can be presented to a
user of the device 600.
[0109] During chest compressions, the ECG waveform 610 is generated
by gathering ECG data points and accelerometer readings, and
filtering the motion-induced (e.g., CPR-induced) noise out of the
ECG waveform. Measurement of velocity or acceleration of chest
compression during chest compressions can be performed according to
the techniques taught by U.S. Pat. No. 7,220,335, titled "Method
and Apparatus for Enhancement of Chest Compressions During Chest
Compressions," the contents of which are hereby incorporated by
reference in its entirety.
[0110] Displaying the filtered ECG waveform helps a rescuer reduce
interruptions in CPR because the displayed waveform is easier for
the rescuer to decipher. If the ECG waveform is not filtered,
artifacts from manual chest compressions can make it difficult to
discern the presence of an organized heart rhythm unless
compressions are halted. Filtering out these artifacts can allow
rescuers to view the underlying rhythm without stopping chest
compressions.
[0111] Box 614 shows a rescuer information about the manner in
which they are and recently have been performing chest compressions
on the patient. The CPR information in box 614 is automatically
displayed when compressions are detected by the device 600. The
information about the chest compressions that is displayed in box
614 includes rate 618 (e.g., number of compressions per minute) and
depth 616 (e.g., depth of compressions in inches or millimeters).
The rate and depth of compressions can be determined by analyzing
accelerometer readings, e.g., mounted in a puck placed on a sternum
of the patient. Displaying the actual rate and depth data (in
addition to, or instead of, an indication of whether the values are
within or outside of an acceptable range) can also provide useful
feedback to the rescuer. For example, if an acceptable range for
chest compression depth is 1.5 to 2 inches, providing the rescuer
with an indication that his/her compressions are only 0.5 inches
can allow the rescuer to determine how to correctly modify his/her
administration of the chest compressions (e.g., he or she can know
how much to increase effort, and not merely that effort should be
increased some unknown amount).
[0112] A perfusion performance indicator (PPI) 620 is also
displayed to provide feedback to a rescuer or rescuers to help them
improve their performance with respect to the patient. The PPI 620
is displayed here as a shape (e.g., a diamond) with the amount of
fill that is in the shape (from 0 to 100%) differing over time to
provide feedback about both the rate and depth of the compressions.
When CPR is being performed adequately, for example, at a rate of
about 100 compressions per minute (CPM) with the depth of each
compression greater than 1.5 inches, the entire indicator will be
filled. As the rate and/or depth decreases below acceptable limits,
the amount of fill lessens. The PPI 620 provides a visual
indication of the quality of the CPR such that the rescuer can aim
to keep the PPI 620 completely filled.
[0113] The data displayed to the rescuer can change based on the
actions of the rescuer or rescue team. For example, the data
displayed can change based on whether the rescuer is currently
administering CPR chest compressions to the patient. Additionally,
the ECG data 610 displayed to the user can change based on the
detection of CPR chest compressions. For example, an adaptive
filter can automatically turn on or off based on detection of
whether CPR is currently being performed. When the filter is on
(during chest compressions), the filtered ECG data is displayed and
when the filter is off (during periods when chest compressions are
not being administered), unfiltered ECG data is displayed. An
indication of whether the filtered or unfiltered ECG data is
displayed can be included visually with the waveform (e.g., via an
indicative icon).
[0114] The display also shows a reminder 621 regarding "release" in
performing chest compression. Specifically, a fatigued rescuer may
begin leaning forward on the chest of a victim and not release
pressure on the sternum of the victim at the top of each
compression. This can reduce the perfusion and circulation
accomplished by the chest compressions. The reminder 621 can be
displayed when the system recognizes that release is not being
achieved (e.g., signals from an accelerometer show an "end" to the
compression cycle that is flat and thus indicates that the rescuer
is staying on the sternum to an unnecessary degree). Such a
reminder can be coordinated with other feedback as well, and can be
presented in an appropriate manner to get the rescuer's attention.
The visual indication may be accompanied by additional visual
feedback near the rescuer's hands, and by a spoken or tonal audible
feedback, including a sound that differs sufficiently from other
audible feedback so that the rescuer will understand that release
(or more specifically, lack of release) is the target of the
feedback.
[0115] Box 622 shows an indication of a likelihood that a shock, if
currently administered, will be effective in defibrillating the
patient. Here, the likelihood is indicated as being 75%, which is
above a threshold value, so the defibrillator 600 is recommending
that the rescuer press a button 624 that will operate a switch to
cause energy to be discharged into the patient. The likelihood
determination may have been made by a process that takes in vector
ECG values, and produces an AMSA transform value (repeatedly) for
the patients using such data as it arrives on a plurality of leads
that are connected to the patient via electrodes and to the
defibrillator 600 wire one or more ports into which the physical
ECG leads can be plugged in a familiar manner.
[0116] Box 622 also displays a value, in Joules, to indicate the
energy that will be delivered by the shock if it is delivered. Such
value may have been determined, as described above, using AMSA or
other ECG-derived values, including values that look to a weighting
of the ECG spectrum and/or that use transforms such as FFT's to
make such determination conveniently and efficiently. Energy
adjustment button 626 is a rocker button that allows the rescuer to
adjust the energy up or down from the values that is displayed, and
if the rescuer engages the button 626, box 622 may be updated,
e.g., to show 5 more or less Joules, depending on whether the
rescuer engaged the top or the bottom of the button 626,
respectively.
[0117] FIG. 6's particular displays may be implemented, as noted
above, with a system that uses particular techniques to improve the
accuracy of a prediction that an applied shock will be a success
and that uses AMSA or other SPA values in making such a prediction.
For instance, the feedback provided by the displays in the figures
can be determined by selecting an appropriate ECG window size for
calculating AMSA on vectorized values (e.g., one second or slightly
longer, such as 1.5 seconds or 2 seconds), a window type (e.g.,
Tukey), and particular coefficients for the window. Such factors
can also be changed over the time of a VF event, as discussed
above, so as to maintain a most accurate predictor of
defibrillation success.
[0118] While at least some of the embodiments described above
describe techniques and displays used during manual human-delivered
chest compressions, similar techniques and displays can be used
with automated chest compression devices such as the AUTOPULSE
device manufactured by ZOLL Medical Corporation of Chelmsford,
Mass.
[0119] The particular techniques described here may be assisted by
the use of a computer-implemented medical device, such as a
defibrillator that includes computing capability. The computing
portions of such defibrillator or other device is shown generally
in FIG. 7, and may communicate with and/or incorporate a computer
system 700 in performing the operations discussed above, including
operations for computing the quality of one or more components of
CPR provided to a victim and generating feedback to rescuers,
including feedback to change rescuers who are performing certain
components of the CPR. The system 700 may be implemented in various
forms of digital computers, including computerized defibrillators
laptops, personal digital assistants, tablets, and other
appropriate computers. Additionally the system can include portable
storage media, such as, Universal Serial Bus (USB) flash drives.
For example, the USB flash drives may store operating systems and
other applications. The USB flash drives can include input/output
components, such as a wireless transmitter or USB connector that
may be inserted into a USB port of another computing device.
[0120] The system 700 includes a processor 710, a memory 720, a
storage device 730, and an input/output device 740. Each of the
components 710, 720, 730, and 740 are interconnected using a system
bus 750. The processor 710 is capable of processing instructions
for execution within the system 700. The processor may be designed
using any of a number of architectures. For example, the processor
710 may be a CISC (Complex Instruction Set Computers) processor, a
RISC (Reduced Instruction Set Computer) processor, or a MISC
(Minimal Instruction Set Computer) processor.
[0121] In one implementation, the processor 710 is a
single-threaded processor. In another implementation, the processor
710 is a multi-threaded processor. The processor 710 is capable of
processing instructions stored in the memory 720 or on the storage
device 730 to display graphical information for a user interface on
the input/output device 740.
[0122] The memory 720 stores information within the system 700. In
one implementation, the memory 720 is a computer-readable medium.
In one implementation, the memory 720 is a volatile memory unit. In
another implementation, the memory 720 is a non-volatile memory
unit.
[0123] The storage device 730 is capable of providing mass storage
for the system 700. In one implementation, the storage device 730
is a computer-readable medium. In various different
implementations, the storage device 730 may be a floppy disk
device, a hard disk device, an optical disk device, or a tape
device.
[0124] The input/output device 740 provides input/output operations
for the system 700. In one implementation, the input/output device
740 includes a keyboard and/or pointing device. In another
implementation, the input/output device 740 includes a display unit
for displaying graphical user interfaces.
[0125] The features described can be implemented in digital
electronic circuitry, or in computer hardware, firmware, software,
or in combinations of them. The apparatus can be implemented in a
computer program product tangibly embodied in an information
carrier, e.g., in a machine-readable storage device for execution
by a programmable processor; and method steps can be performed by a
programmable processor executing a program of instructions to
perform functions of the described implementations by operating on
input data and generating output. The described features can be
implemented advantageously in one or more computer programs that
are executable on a programmable system including at least one
programmable processor coupled to receive data and instructions
from, and to transmit data and instructions to, a data storage
system, at least one input device, and at least one output device.
A computer program is a set of instructions that can be used,
directly or indirectly, in a computer to perform a certain activity
or bring about a certain result. A computer program can be written
in any form of programming language, including compiled or
interpreted languages, and it can be deployed in any form,
including as a stand-alone program or as a module, component,
subroutine, or other unit suitable for use in a computing
environment.
[0126] Suitable processors for the execution of a program of
instructions include, by way of example, both general and special
purpose microprocessors, and the sole processor or one of multiple
processors of any kind of computer. Generally, a processor will
receive instructions and data from a read-only memory or a random
access memory or both. The essential elements of a computer are a
processor for executing instructions and one or more memories for
storing instructions and data. Generally, a computer will also
include, or be operatively coupled to communicate with, one or more
mass storage devices for storing data files; such devices include
magnetic disks, such as internal hard disks and removable disks;
magneto-optical disks; and optical disks. Storage devices suitable
for tangibly embodying computer program instructions and data
include all forms of non-volatile memory, including by way of
example semiconductor memory devices, such as EPROM, EEPROM, and
flash memory devices; magnetic disks such as internal hard disks
and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM
disks. The processor and the memory can be supplemented by, or
incorporated in, ASICs (application-specific integrated
circuits).
[0127] To provide for interaction with a user, the features can be
implemented on a computer having an LCD (liquid crystal display) or
LED display for displaying information to the user and a keyboard
and a pointing device such as a mouse or a trackball by which the
user can provide input to the computer.
[0128] The features can be implemented in a computer system that
includes a back-end component, such as a data server, or that
includes a middleware component, such as an application server or
an Internet server, or that includes a front-end component, such as
a client computer having a graphical user interface or an Internet
browser, or any combination of them. The components of the system
can be connected by any form or medium of digital data
communication such as a communication network. Examples of
communication networks include a local area network ("LAN"), a wide
area network ("WAN"), peer-to-peer networks (having ad-hoc or
static members), grid computing infrastructures, and the
Internet.
[0129] The computer system can include clients and servers. A
client and server are generally remote from each other and
typically interact through a network, such as the described one.
The relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0130] Many other implementations other than those described may be
employed, and may be encompassed by the following claims.
* * * * *