U.S. patent application number 11/497542 was filed with the patent office on 2007-07-05 for distributed cardiac activity monitoring with selective filtering.
This patent application is currently assigned to CardioNet, Inc.. Invention is credited to Dave Churchville, Zach Cybulski, Lev Korzinov.
Application Number | 20070156054 11/497542 |
Document ID | / |
Family ID | 34838678 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070156054 |
Kind Code |
A1 |
Korzinov; Lev ; et
al. |
July 5, 2007 |
Distributed cardiac activity monitoring with selective
filtering
Abstract
System and techniques for distributed monitoring of cardiac
activity include selective T wave filtering. In general, in one
implementation, a distributed cardiac activity monitoring system
includes a monitoring apparatus, with a selectively activated T
wave filter, and a monitoring station. The monitoring apparatus can
include a communications interface, a real-time QRS detector, a T
wave filter, and a selector that activates the T wave filter to
preprocess a cardiac signal provided to the real-time QRS detector
in response to a message. The monitoring station can
communicatively couple with the monitoring apparatus, over a
communications channel, via the communications interface and can
transmit the message to the monitoring apparatus to activate the T
wave filter based at least in part upon a predetermined criteria
(e.g., abnormal T waves for an individual, as identified by a
system operator).
Inventors: |
Korzinov; Lev; (San Diego,
CA) ; Churchville; Dave; (San Diego, CA) ;
Cybulski; Zach; (San Diego, CA) |
Correspondence
Address: |
FISH & RICHARDSON, PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
CardioNet, Inc.
|
Family ID: |
34838678 |
Appl. No.: |
11/497542 |
Filed: |
July 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10781045 |
Feb 17, 2004 |
7099715 |
|
|
11497542 |
Jul 31, 2006 |
|
|
|
Current U.S.
Class: |
600/509 |
Current CPC
Class: |
Y10S 128/901 20130101;
A61B 5/0006 20130101; A61B 5/349 20210101 |
Class at
Publication: |
600/509 |
International
Class: |
A61B 5/04 20060101
A61B005/04 |
Claims
1. A machine-implemented method comprising: identifying heart beats
in a sensed cardiac signal; activating a T wave filter, used in
said identifying heart beats, in response to a message from a
monitoring station generated at least in part based upon discovery
of a predetermined characteristic in the sensed cardiac signal; and
outputting information corresponding to the identified heart beats
to a communications channel of a distributed cardiac activity
monitoring system.
2. The method of claim 1, wherein said identifying heart beats
comprises identifying R waves in the sensed cardiac signal.
3. The method of claim 1, further comprising sending at least a
portion of the sensed cardiac signal to the monitoring station, and
wherein the discovery of the predetermined characteristic comprises
identification of a tall T wave in the at least a portion of the
sensed cardiac signal by an operator at the monitoring station.
4. The method of claim 1, wherein said activating the T wave filter
comprises activating a filter that reduces signal amplitude at low
frequencies of the sensed cardiac signal.
5. The method of claim 4, wherein the filter has a frequency
response of about 0 dB or more at frequencies above ten Hertz.
6. The method of claim 5, wherein the filter has a frequency
response of about -10 dB or less in a low frequency range of zero
to five Hertz.
7. The method of claim 6, wherein the filter has a frequency
response of about +2 dB or more in a high frequency range of twenty
to twenty five Hertz.
8. The method of claim 1, wherein said outputting information
comprises outputting heart rate data to a wireless communications
channel.
9. The method of claim 1, further comprising: determining that an
abnormal T wave is possible based on signal morphology analysis;
and notifying a system operator of the possible abnormal T
wave.
10. The method of claim 1, further comprising deactivating the T
wave filter in response to a second message.
11. A distributed cardiac activity monitoring system comprising: a
monitoring apparatus including a communications interface, a
real-time QRS detector, a T wave filter, and a selector that
activates the T wave filter with respect to the real-time QRS
detector in response to a message, wherein the activated T waver
filter preprocesses a cardiac signal provided to the real-time QRS
detector; and a monitoring station that communicatively couples
with the monitoring apparatus via the communications interface and
transmits the message to the monitoring apparatus to activate the T
wave filter based at least in part upon a predetermined
criteria.
12. The system of claim 11, wherein the communications interface
comprises a wireless communications interface.
13. The system of claim 11, wherein the T wave filter comprises a
filter that reduces signal amplitude at low frequencies.
14. The system of claim 13, wherein the filter has a frequency
response of about -10 dB or less in a low frequency range of zero
to five Hertz.
15. The system of claim 13, wherein the filter has a frequency
response of about 0 dB or more at frequencies above ten Hertz.
16. The system of claim 15, wherein the filter has a frequency
response of about +2 dB or more in a high frequency range of twenty
to twenty five Hertz.
17. The system of claim 11, wherein the selector comprises analog,
selective activation circuitry.
18. The system of claim 11, wherein the monitoring apparatus
further comprises additional logic that determines if an abnormal T
wave is possible based on signal morphology analysis, and notifies
a system operator of the possible abnormal T wave.
19. The system of claim 11, wherein the monitoring station further
comprises additional logic that determines if an abnormal T wave is
possible based on signal morphology analysis, and notifies a system
operator of the possible abnormal T wave.
20. A cardiac monitoring apparatus comprising: a communications
interface; a real-time heart beat detector; a T wave filter; and a
selector that activates the T wave filter with respect to the
real-time heart beat detector in response to a message, wherein the
activated T waver filter preprocesses a cardiac signal provided to
the real-time heart beat detector.
21. The apparatus of claim 20, wherein the communications interface
comprises a wireless communications interface.
22. The apparatus of claim 20, wherein the real-time heart beat
detector comprises an analog heart beat detector, the T wave filter
comprises an analog T wave filter, and the selector comprises
analog, selective activation circuitry.
23. The apparatus of claim 20, wherein the T wave filter comprises
a filter that reduces signal amplitude at low frequencies.
24. The apparatus of claim 23, wherein the filter has a frequency
response of about -10 dB or less in a low frequency range of zero
to five Hertz.
25. The apparatus of claim 24, wherein the filter has a frequency
response of about 0 dB or more at frequencies above ten Hertz.
26. The apparatus of claim 25, wherein the filter has a frequency
response of about +2 dB or more in a high frequency range of twenty
to twenty five Hertz.
27. The apparatus of claim 20, further comprising additional logic
that determines if an abnormal T wave is possible based on signal
morphology analysis, and notifies a system operator of the possible
abnormal T wave.
28. A method comprising: receiving at least a portion of a sensed
cardiac signal from a monitoring apparatus in contact with a living
being under active cardiac monitoring; identify an abnormal T wave
in the received cardiac signal; and sending a message to the
monitoring apparatus over a communications channel, the message
causing the monitoring apparatus to activate a T wave filter used
in identifying heart beats of the living being under active cardiac
monitoring.
29. The method of claim 28, further comprising: determining that an
abnormal T wave is possible based on signal morphology analysis;
and notifying a system operator of the possible abnormal T wave,
wherein the system operator performs said identifying the abnormal
T wave.
30. The method of claim 28, wherein said sending the message
comprises sending the message over a wireless communications
channel.
31. The method of claim 28, further comprising installing the T
wave filter into the monitoring apparatus, which comprises a
preexisting beat detector.
32. A system comprising: means for identifying heart beats in a
sensed cardiac signal; means for filtering the sensed cardiac
signal to reduce T waves in the sensed cardiac signal; and means
for selectively activating the means for filtering in response to
discovery of a predetermined characteristic in the sensed cardiac
signal.
33. The system of claim 32, further comprising means for alerting a
system operator of a possible abnormal T wave.
34. The system of claim 32, wherein the means for filtering
comprises means for generally highpass filtering.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation, and claims the benefit
of priority under 35 USC 120, of U.S. application Ser. No.
10/781,045, filed Feb. 17, 2004. The disclosure of the prior
application is considered part of, and is incorporated by reference
herein, the disclosure of this application.
BACKGROUND
[0002] The present application describes systems and techniques
relating to monitoring cardiac activity, for example, processing
cardiac electrical activity to determine heart rate.
[0003] The electrical activity of the heart can be monitored to
track various aspects of the functioning of the heart. Given the
volume conductivity of the body, electrodes on the body surface or
beneath the skin can display potential differences related to this
activity. Anomalous electrical activity can be indicative of
disease states or other physiological conditions ranging from
benign to fatal.
[0004] Cardiac monitoring devices can sense the cardiac electrical
activity of a living being and identify heart beats. Frequently,
identification of heart beats is performed by identifying the R
waves in the QRS complex, as can be seen in an electrocardiogram
(ECG). The R wave is the first positive deflection in the QRS
complex, representing ventricular depolarization. The typically
large amplitude of this positive deflection in the QRS complex is
useful in identifying a heart beat.
SUMMARY
[0005] In general, in one aspect, a distributed cardiac activity
monitoring system includes a monitoring apparatus, with a
selectively activated T wave filter, and a monitoring station. The
monitoring apparatus can include a communications interface, a
real-time QRS detector, a T wave filter, and a message-activated
selector that activates the T wave filter with respect to the
real-time QRS detector to preprocess a cardiac signal provided to
the real-time QRS detector. The monitoring station can
communicatively couple with the monitoring apparatus, over a
communications channel, via the communications interface and can
transmit the message to the monitoring apparatus to activate the T
wave filter based at least in part upon a predetermined criteria
(e.g., abnormal T waves for an individual, as identified by a
system operator).
[0006] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features and
advantages will become apparent from the description, the drawings,
and the claims.
DRAWING DESCRIPTIONS
[0007] FIG. 1 illustrates a distributed cardiac activity monitoring
system in which a cardiac signal is monitored for medical
purposes.
[0008] FIG. 2 illustrates an example cardiac monitoring apparatus
used with a living being.
[0009] FIG. 3 illustrates an example ECG of a normal patient.
[0010] FIG. 4 illustrates an example ECG of a patient with abnormal
T waves.
[0011] FIG. 5 illustrates a process of selectively activating a T
wave filter.
[0012] FIG. 6 illustrates a frequency response of an example T wave
filter.
[0013] FIG. 7 illustrates an impulse response of an example T wave
filter.
[0014] FIG. 8 illustrates an example distributed process for
selectively activating a T wave filter.
DETAILED DESCRIPTION
[0015] FIG. 1 illustrates a distributed cardiac activity monitoring
system 100 in which a cardiac signal is monitored for medical
purposes. A living being 110 (e.g., a human patient, including
potentially a healthy patient for whom cardiac monitoring is
nonetheless deemed appropriate) has a cardiac monitoring apparatus
120 configured to obtain cardiac signals from the patient's heart.
The cardiac monitoring apparatus 120 can be composed of one or more
devices, such as a sensing device 122 and a processing device 124.
The cardiac monitoring apparatus 120 can communicate with a
monitoring station 140 (e.g., a computer in a monitoring center)
via a communications channel 130. The cardiac monitoring apparatus
120 can include one or more sensing, calibration, signal
processing, control, data storage, and transmission elements
suitable for generating and processing the cardiac signal, as well
as for relaying all or a portion of the cardiac signal over the
communications channel 130. The communications channel 130 can be
part of a communications network and can include any suitable
medium for data transmission, including wired and wireless media
suitable for carrying optical and/or electrical signals.
[0016] The cardiac monitoring apparatus 120 can communicate sensed
cardiac signals (e.g., ECG data), cardiac event information (e.g.,
real-time heart rate data), and additional physiological and/or
other information to the monitoring station 140. The cardiac
monitoring apparatus 120 can include an implantable medical device,
such as an implantable cardiac defibrillator and an associated
transceiver or pacemaker and an associated transceiver, or an
external monitoring device that the patient wears. Moreover, the
cardiac monitoring apparatus 120 can be implemented using, for
example, the CardioNet Mobile Cardiac Outpatient Telemetry (MCOT)
device, which is commercially available and provided by CardioNet,
Inc of San Diego, Calif.
[0017] The monitoring station 140 can include a receiver element
for receiving transmitted signals, as well as various data
processing and storage elements for extracting and storing
information carried by transmissions regarding the state of the
individual 110. The monitoring station 140 can be located in the
same general location (e.g., in the same room, building or health
care facility) as the monitoring apparatus 120, or at a remote
location. The monitoring station 140 can include a display and a
processing system, and a system operator 150 (e.g., a doctor or a
cardiovascular technician) can use the monitoring station 140 to
evaluate physiological data received from the cardiac monitoring
apparatus 120. The system operator 150 can use the monitoring
station 140 to change operational settings of the cardiac
monitoring apparatus 120 remotely during active cardiac monitoring
of the living being 110. Moreover, the cardiac monitoring apparatus
120 can selectively activate a T wave filter in response to
discovery of a predetermined characteristic in the sensed cardiac
signal, such as described further below. For example, the system
operator can determine that the patient has consistently abnormal T
waves and cause the monitoring station 140 to send a message to the
monitoring apparatus 120 to activate the T wave filter.
[0018] FIG. 2 illustrates an example cardiac monitoring apparatus
200 used with a living being. The apparatus 200 can include a
sensor 210, a signal amplifier 220, a T wave filter 230, a selector
240, a beat detector 250, additional logic 260, and a
communications interface 270. The sensor 210 can include two or
more electrodes subject to one or more potential differences that
yield a voltage signal, such as the signals illustrated in FIGS. 3
and 4. The electrodes can be body surface electrodes such as
silver/silver chloride electrodes and can be positioned at defined
locations to aid in monitoring the electrical activity of the
heart. The sensor 210 can also include leads or other conductors
that form a signal path to the signal amplifier 220. The signal
amplifier 220 can receive and amplify the voltage signals.
[0019] Furthermore, the signal amplifier 220 can include additional
processing logic. For example, the additional processing logic can
perform filtering and analog-to-digital conversion; the T wave
filter 230 can be integrated into the signal amplifier 220.
Additional processing logic can also be implemented elsewhere in
the apparatus 200, and the amplification and other additional
processing can occur before or after digitization. The signal
amplifier 220 can provide an amplified and processed signal to the
T wave filter 230 and to the selector 240. Moreover, some of the
additional processing logic discussed in connection with FIG. 2 can
also be implemented in the monitoring station 140.
[0020] The various components of the apparatus 200 can be
implemented as analog or digital components. For example, the
selector 240 can be analog, selective activation circuitry that
selects one of its two inputs (from the signal amplifier 220 and
from the T wave filter 230) to be provided to the beat detector
250. Alternatively, the selector 240 can enable and disable the T
wave filter 230 (e.g., the T wave filter 230 can be integrated into
the beat detector 250 and turned on and off as needed). In general,
the selector 240 activates the T wave filter 230 with respect to
the heart beat detector 250, to preprocess the signal, in response
to a message (e.g., a message received from the monitoring station
140 or a message generated within the apparatus 200).
[0021] The beat detector 250 is a component (e.g., analog circuitry
or digital logic) that identifies the time period between
ventricular contractions. For example, the beat detector 250 can be
a real-time QRS detector that identifies successive QRS complexes,
or R waves, and determines the beat-to-beat timing in real time
(i.e., output data is generated directly from live input data). The
beat-to-beat timing can be determined by measuring times between
successive R-waves. The beat detector 250 can provide information
regarding the time period between ventricular contractions to
additional logic 260. The additional logic 260 can include logic to
determine if an abnormal T wave potentially is occurring based on
signal morphology analysis, an atrial fibrillation/atrial flutter
(AF) detector, AF decision logic, and an event generator. The heart
rate information can be transmitted using the communications
interface 270, which can be a wired or wireless interface.
Moreover, the sensed cardiac signal, or portions thereof, can be
sent to a monitoring station, periodically, upon being interrogated
and/or in response to identified events/conditions.
[0022] The morphology of a cardiac signal can vary significantly
from patient to patient. Sometimes, the patient's ECG has a very
tall T wave, which might result in false classification of this T
wave as an R wave. When this happens, the heart rate reported by
the apparatus may be twice the real heart rate, and the morphology
of beats may not be detected correctly. The T wave filter 230 can
reduce the amplitude of T waves, while preserving or slightly
increasing the amplitude of R waves.
[0023] FIG. 3 illustrates an example ECG 300 of a normal patient.
The heart cycle has four generally recognized waveforms: the P
wave, the QRS complex, the T wave, and the U wave. The relative
sizes of a QRS complex 310 and a T wave 320 represent the signal
from a typical heart. FIG. 4 illustrates an example ECG 400 of a
patient with abnormal T waves. As shown, a T wave 420 is tall in
comparison with a normal T wave 320, and the rest of the cardiac
cycle looks the same. In general, abnormal T waves can result in
misclassification of T waves as R waves. In these cases, the T wave
filter can be selectively applied to improve cardiac monitoring
performance. The reduction in amplitude of the T wave may be up to
80% (five times) and can thus create a significant increase in the
accuracy of QRS detection in patients with abnormal T waves.
[0024] FIG. 5 illustrates a process of selectively activating a T
wave filter. Heart beats are identified in sensed cardiac signals
at 500. A T wave filter is selectively activated in response to
discovery of a predetermined characteristic in the sensed cardiac
signal at 510. The discovery of the predetermined characteristic
can involve an operator's identification of a tall T wave in at
least a portion of the sensed cardiac signal, and activating the T
wave filter can improve the cardiac monitoring. After filter
activation, heart beats are identified in sensed cardiac signals
using the activated T wave filter at 520. The T wave filter can be
a custom highpass-like filter. The filter can be such that it
reduces signal amplitude at low frequencies of the sensed cardiac
signal and increases signal amplitude at high frequencies of the
sensed cardiac signal.
[0025] FIG. 6 illustrates a frequency response 600 of an example T
wave filter. As shown, the filter's frequency response can be less
than or equal to -10dB in the low frequency range of 0-5 Hertz
(Hz). This frequency range is where T wave power spectrum is
predominantly located. At higher frequencies, the filter can
preserve and/or increase the amplitude of the signal (e.g., modify
the signal by 0 dB or more for frequencies above 10 Hz), which can
increase the amplitude of the R wave and make the beat detection
more reliable. As shown, the filter's frequency response can be +2
dB or more in a high frequency range of 20-25 Hz. FIG. 7
illustrates an impulse response 700 of the example T wave filter
illustrated in FIG. 6.
[0026] FIG. 8 illustrates an example distributed process for
selectively activating a T wave filter. Heart beats are identified
in a sensed cardiac signal at 800. The cardiac signal can be from a
monitoring apparatus in contact with a living being under active
cardiac monitoring, as described above. A possibly abnormal T wave
can be determined in a post-processing operation that analyzes
signal morphology, and a system operator can be notified of the
possible abnormal T wave at 805; this operation can alternatively
be done at the monitoring station, as mentioned below. This can
assist the operator in identifying patients that may benefit from
having the T wave filter activated in their monitors. Additionally,
the operator can proactively check the sensed cardiac signal from
the monitor to assess the T waves.
[0027] At least a portion of the sensed cardiac signal can be sent
to a monitoring station at 810. This can involve continuously or
periodically sending the cardiac signal, or sending the cardiac
signal in response to identified events/conditions, such as the
identification of the possible abnormal T wave at 805. The sensed
cardiac signals are received from the monitoring apparatus at 815.
A possibly abnormal T wave can be determined using a signal
morphology analyzer, and a system operator can be notified of the
possible abnormal T wave at 820.
[0028] An abnormal T wave can be identified, such as by a system
operator, in the received cardiac signal at 825, and a message can
be sent to the monitoring apparatus over a communications channel
at 830. The message causes the monitoring apparatus to activate a T
wave filter used in identifying heart beats of the living being
under active cardiac monitoring. The T wave filter is activated in
response to the message at 835. Information corresponding to the
heart beats identified using the T wave filter (e.g., heart rate
data) can be output to the communications channel at 840. This
information can be received at the monitoring station at 845.
[0029] Moreover, if the system operator subsequently determines
that the T wave filter is not needed for the patient, a message to
deactivate the T wave filter can be sent at 850, and the T wave
filter can be deactivated in response to this second message at
855. The T wave filter may not distinguish morphology of the beat.
Therefore, slow ventricular beats, such as premature ventricular
contractions (PVCs), or some ectopic beats may also be reduced in
amplitude when the filter is applied. In cases where multiple PVCs
are monitored, the T wave filter may reduce the amplitude of these
beats, and thus a pause or asystole event may be generated, which
generally should alert the system operator to deactivate the T wave
filter. However, this may not be relevant in the particular
application as many cardiac monitoring applications do not require
monitoring of PVCs or ectopic beats.
[0030] Fast ventricular beats (with a rate over 100 beats per
minute) may be left unchanged by the T wave filter because their
power spectrum is usually above 10 Hz. The T wave filter described
can be installed into a monitoring apparatus that includes a
preexisting beat detector. The T wave filter can preprocess the
input provided to the preexisting beat detector, improving the
functioning of the beat detector for individuals with abnormal T
waves, even though the preexisting beat detector was designed
without a T wave filter in mind. The T wave filter can be in a
disabled state by default and may be turned on only for the
monitors used with those individuals with abnormal T waves (e.g.,
patients whose cardiac signal features constant tall T waves).
[0031] The systems and techniques described and illustrated in this
specification can be implemented in analog electronic circuitry,
digital electronic circuitry, integrated circuitry, computer
hardware, firmware, software, or in combinations of the forgoing,
such as the structural means disclosed in this specification and
structural equivalents thereof. Apparatus can be implemented in a
software product (e.g., a computer program product) tangibly
embodied in a machine-readable storage device for execution by a
programmable processor, and processing operations can be performed
by a programmable processor executing a program of instructions to
perform functions by operating on input data and generating output.
Further, the system can be implemented advantageously in one or
more software programs that are executable on a programmable
system. This programmable system can include the following: 1) at
least one programmable processor coupled to receive data and
instructions from, and to transmit data and instructions to, a data
storage system; 2) at least one input device; and 3) at least one
output device. Moreover, each software program can be implemented
in a high-level procedural or object-oriented programming language,
or in assembly or machine language if desired; and in any case, the
language can be a compiled or an interpreted language.
[0032] Also, suitable processors include, by way of example, both
general and special purpose microprocessors. Generally, a processor
will receive instructions and data from a read-only memory, a
random access memory, and/or a machine-readable signal (e.g., a
digital signal received through a network connection). Generally, a
computer will include one or more mass storage devices for storing
data files. Such devices can include magnetic disks, such as
internal hard disks and removable disks, magneto-optical disks, and
optical disks. Storage devices suitable for tangibly embodying
software program instructions and data include all forms of
non-volatile memory, including, by way of example, the following:
1) semiconductor memory devices, such as EPROM (electrically
programmable read-only memory); EEPROM (electrically erasable
programmable read-only memory) and flash memory devices; 2)
magnetic disks such as internal hard disks and removable disks; 3)
magneto-optical disks; and 4) optical disks, such as CD-ROM disks.
Any of the foregoing can be supplemented by, or incorporated in,
ASICs (application-specific integrated circuits).
[0033] To provide for interaction with a user (such as the system
operator), the system can be implemented on a computer system
having a display device such as a monitor or LCD (liquid crystal
display) screen 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 system. The
computer system can be programmed to provide a graphical user
interface through which computer programs interact with users and
operational settings can be changed in the monitoring system.
[0034] Finally, while the foregoing system has been described in
terms of particular implementations, other embodiments are within
the scope of the following claims.
* * * * *