Note: Descriptions are shown in the official language in which they were submitted.
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DISPLAY ARRANGEMENT FOR DIAGNOSIS OF CARDIAC RHYTHM DISORDERS
TECHNICAL FIELD
This application relates in general to electrocardiographic monitoring and, in
particular,
to a method for facilitating diagnosis of cardiac rhythm disorders with the
aid of a digital
computer.
BACKGROUND ART
An electrocardiogram (ECG) allows physicians to diagnose cardiac function by
visually
tracing the cutaneous electrical signals (action potentials) that are
generated by the propagation
of the transmembrane ionic currents that trigger the depolarization of cardiac
fibers. An ECG
trace contains alphabetically-labeled waveform deflections that represent
distinct features
within the cyclic cardiac activation sequence. The P-wave represents atrial
depolarization,
which causes atrial contraction. The QRS-complex represents ventricular
depolarization. The
T-wave represents ventricular repolarization.
The R-wave is often used as an abbreviation for the QRS-complex. An R-R
interval
spans the period between successive R-waves and, in a normal heart, is 600
milliseconds (ms)
to one second long, which respectively correspond to 100 to 60 beats per
minute (bpm). The
R-wave is the largest waveform generated during normal conduction and
represents the cardiac
electrical stimuli passing through the ventricular walls. R-R intervals
provide information that
allows a physician to understand at a glance the context of cardiac rhythms
both before and
after a suspected rhythm abnormality and can be of confirmational and
collaborative value in
cardiac arrhythmia diagnosis and treatment.
Conventionally, the potential of R-R interval context has not been fully
realized, partly
due to the difficulty of presentation in a concise and effective manner to
physicians. For
instance, routine ECGs are typically displayed at an effective paper speed of
25 millimeters
(mm) per second. A lower speed is not recommended because ECG graph resolution
degrades
at lower speeds and diagnostically-relevant features may be lost. Conversely,
a half-hour ECG
recording, progressing at 25 mm/s, results in 45 meters of ECG waveforms that,
in printed
form, is cumbersome and, in electronic display form, will require significant
back and forth
toggling between pages of waveforms, as well as presenting voluminous data
transfer and data
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storage concerns. As a result, ECGs are less than ideal tools for diagnosing
cardiac arrhythmia
patterns that only become apparent over an extended time frame, such as 30
minutes or longer.
R-R intervals have also been visualized in Poincare plots, which graph RR(n)
on the x-
axis and RR(n + 1) on they-axis. However, a Poincare plot fails to preserve
the correlation
between an R-R interval and the R-R interval's time of occurrence and the
linearity of time and
associated contextual information, before and after a specific cardiac rhythm,
are lost. In
addition, significant changes in heart rate, particularly spikes in heart
rate, such as due to sinus
rhythm transitions to atrial flutter or atrial fibrillation, may be masked or
distorted in a Poincare
plot if the change occurs over non-successive heartbeats, rather than over two
adjacent
heartbeats, which undermines reliance on Poincare plots as dependable cardiac
arrhythmia
diagnostic tools. Further, Poincare plots cannot provide context and immediate
temporal
reference to the actual ECG, regardless of paper speed. Events both prior to
and after a specific
ECG rhythm can provide key clinical information disclosed in the R-R interval
plot that may
change patient management above and beyond the specific rhythm being
diagnosed.
Therefore, a need remains for presenting R-R interval data to physicians to
reveal
temporally-related patterns as an aid to rhythm abnormality diagnosis.
DISCLOSURE OF THE INVENTION
R-R interval data is presented to physicians in a format that includes views
of relevant
near field and far field ECG data, which together provide contextual
information that improves
diagnostic accuracy. The near field (or short duration) ECG data view provides
a "pinpoint"
classical view of an ECG at traditional recording speed in a manner that is
known to and widely
embraced by physicians. The near field ECG data is coupled to a far field (or
medium
duration) ECG data view that provides an "intermediate" lower resolution, pre-
and post-event
contextual view.
Both near field and far field ECG data views are temporally keyed to an
extended
duration R-R interval data view. In one embodiment, the R-R interval data view
is scaled non-
linearly to maximize the visual differentiation for frequently-occurring heart
rate ranges, such
that a single glance allows the physician to make a diagnosis. All three views
are presented
simultaneously, thereby allowing an interpreting physician to diagnose rhythm
and the pre- and
post-contextual events leading up to a cardiac rhythm of interest.
The durations of the classical "pinpoint" view, the pre- and post-event
"intermediate"
view, and the R-R interval plot are flexible and adjustable. In one
embodiment, a temporal
point of reference is identified in the R-R interval plot and the ECG data
that is temporally
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associated with the point of reference is displayed in the near field and far
field ECG data
views. In a further embodiment, diagnostically relevant cardiac events can be
identified as the
temporal point of reference. For clarity, the temporal point of reference will
generally be
placed in the center of the R-R interval data to allow pre- and post-event
heart rhythm and ECG
waveform data to present in the correct context. Thus, the pinpoint "snapshot"
and
intermediate views of ECG data with the extended term R-R interval data allow
a physician to
comparatively view heart rate context and patterns of behavior prior to and
after a clinically
meaningful arrhythmia, patient concern or other indicia, thereby enhancing
diagnostic
specificity of cardiac rhythm disorders and providing physiological context to
improve
diagnostic ability.
One embodiment provides a system and method for facilitating diagnosis of
cardiac
rhythm disorders with the aid of a digital computer. Cutaneous action
potentials of a patient
are monitored and recorded. The cutaneous action potentials are retrieved as
electrocardiogram
(ECG) data for a set time period and a plurality of R-wave peaks in the ECG
data are identified.
A difference between recording times of successive pairs of the R-wave peaks
is calculated and
a heart rate associated with each time difference is determined. An extended
duration R-R
interval plot over the set time period is formed and includes each of the
recording time
differences and the associated heart rates. The extended duration R-R interval
plot is displayed
and a temporal point of reference in the extended duration R-R interval plot
is identified At
least part of the ECG data preceding and following the temporal point of
reference is displayed
as context in at least one accompanying ECG plot.
The foregoing aspects enhance the presentation of diagnostically relevant R-R
interval
data, reduce time and effort needed to gather relevant information by a
clinician and provide
the clinician with a concise and effective diagnostic tool, which is critical
to accurate
arrhythmia and cardiac rhythm disorder diagnoses.
Custom software packages have been used to identify diagnostically relevant
cardiac
events from the electrocardiography data, but usually require a cardiologist's
diagnosis and
verification. In contrast, when presented with a machine-identified event, the
foregoing
approach aids the cardiologist's diagnostic job by facilitating presentation
of ECG-based
background information prior to and after the identified event.
Still other embodiments will become readily apparent to those skilled in the
art from the
following detailed description, wherein are described embodiments by way of
illustrating the
best mode contemplated. As will be realized, other and different embodiments
are possible and
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the embodiments' several details are capable of modifications in various
obvious respects,
including time and clustering of events, all without departing from their
spirit and the scope
Accordingly, the drawings and detailed description are to be regarded as
illustrative in nature
and not as restrictive.
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a graph showing, by way of example, a single ECG waveform.
FIGURE 2 is a graph showing, by way of example, a prior art Poincare R-R
interval
plot.
FIGURE 3 is a flow diagram showing a method for facilitating diagnosis of
cardiac
rhythm disorders with the aid of a digital computer in accordance with one
embodiment
FIGURE 4 is a flow diagram showing a routine for constructing and displaying a
diagnostic composite plot for use in the method of FIGURE 3
FIGURE 5 is a flow diagram showing a routine for constructing an extended-
duration
R-R interval plot for use in the routine of FIGURE 4.
FIGURE 6 is a diagram showing, by way of example, a diagnostic composite plot
generated by the method of FIGURE 3.
FIGURE 7 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of sinus rhythm (SR) transitioning into atrial
fibrillation (AF)
FIGURE 8 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of 3:1 atrial flutter (AFL) transitioning into SR.
FIGURE 9 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of atrial trigeminy.
FIGURE 10 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of maximum heart rate in an episode of AF during
exercise.
FIGURE 11 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of SR transitioning into AFL transitioning into AF.
FIGURE 12 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of sinus tachycardia and palpitations that occurred
during exercise
accompanied by a jump in heart rate.
FIGURE 13 is a diagram showing, by way of example, a diagnostic composite plot
for
facilitating the diagnosis of bradycardia.
FIGURE 14 is a block diagram showing a system for facilitating diagnosis of
cardiac
rhythm disorders with the aid of a digital computer in accordance with one
embodiment.
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BEST MODE FOR CARRYING OUT THE INVENTION
A normal healthy cardiac cycle repeats through an expected sequence of events
that can
be visually traced through an ECG. Each cycle starts with cardiac
depolarization originating
high in the right atrium in the sinoatrial (SA) node before spreading leftward
towards the left
atrium and inferiorly towards the atrioventricular (AV) node. After a delay in
the AV node, the
depolarization impulse transits the Bundle of His and moves into the right and
left bundle
branches and Purkinje fibers to activate the right and left ventricles.
When a rhythm disorder is suspected, diagnostically-relevant arrhythmic events
in the
cardiac cycle can often be identified and evaluated with the assistance of an
ECG and R-R
interval tachography, such as Poincare plots. Routine ECG evaluation is
primarily focused
identifying changes to expected ECG waveform shapes. FIGURE 1 is a graph
showing, by
way of example, a single ECG waveform 10. The x-axis represents approximate
time in units
of tenths of a second and they-axis represents approximate cutaneous
electrical signal strength
in units of millivolts. By long-standing convention, ECGs are typically
printed or displayed at
an effective paper speed of 25 millimeters (mm) per second. Although in
practice an ECG may
be provided to a physician in traditional paper-printed form, in "virtual"
electronic display
form, or both, the term "effective paper speed" is nevertheless still widely
applied as a metric to
normalize the recorded ECG signal to a standardized grid of 1 mm squares
(omitted for the
sake of clarity in FIGURE 1), whereby each 1 mm horizontal box in the grid
corresponds to
0.04 s (40 ms) of recorded time. Other effective paper speeds, grid sizes and
units of display
are possible.
A full ECG consists of a stream of alphabetically-labeled waveforms 10 that
collectively cover cardiac performance over a period of observation. For a
healthy patient,
within each ECG waveform 10, the P-wave 11 will normally have a smooth,
normally upward,
positive waveform that indicates atrial depolarization. The QRS complex 17
will usually
follow, often with a downward deflection of a Q-wave 12, followed by a larger
upward
deflection of an R-wave 13, and be terminated with a downward waveform of the
S-wave 14,
which are collectively representative of ventricular depolarization. The T-
wave 15 will
normally be a modest upward waveform, representative of ventricular
repolarization, while the
U-wave 16, which is often not directly observable, will indicate the recovery
period of the
Purkinje conduction fibers.
Rhythm disorders often manifest through R-R interval variability and the
patterns
formed by R-R intervals over an extended time period are important tools in
the diagnosis of
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cardiac rhythm abnormalities. For example, atrial fibrillation (AF) is the
chaotic firing of the
atria that leads to an erratic activation of the ventricles. AF is initially
diagnosed by an absence
of organized P-waves 11 and confirmed by erratic ventricular rates that
manifest in an ECG R-
R interval plot as a cloud-like pattern of irregular R-R intervals due to an
abnormal conduction
of impulses to the ventricles. There is a Gaussian-like distribution to these
R-R intervals during
AF. Similarly, atrial flutter (AFL) is an abnormal heart rhythm in which
cardiac impulses
travel along pathways within the right atrium in an organized circular motion,
causing the atria
to beat faster than and out of sync with the ventricles. During AFL, the heart
beats quickly, yet
with a regular pattern. Although AFL presents in an electrogram (e-gram) as a
"sawlooth"
pattern, AFL can be confirmed in an ECG by characteristic R-R interval
patterns that usually
manifest as 2:1 atrioventricular (AV) conduction or 4:1 atrioventricular
conduction. On
occasion, the conduction through the AV node is variable and not fixed.
Conventionally, R-R intervals have been visualized using Poincare plots.
FIGURE 2 is
a graph showing, by way of example, a prior art Poincare R-R interval plot 18.
The x-axis
represents the duration of R-R interval n in units of milliseconds (ms). They-
axis represents
the duration of R-R interval n + 1 also in units of ms. Ordinarily, the x- and
y-axes use the
same units, so as to form a trend line 19 along the 45-degree angle. When an R-
R interval is
equal to the successive R-R interval, as often occurs when heart rhythm is
regular, the dot
representing the two intervals falls onto the 45-degree trend line 19.
Conversely, when an R-R
interval has changed since the preceding R-R interval, the dot representing
the two intervals
falls off the 45-degree trend line 19 and, as the difference between
successive R-R intervals
increases, the dots fall further away from the trend line 19.
The number of dots deviating from the trend line 19 in a Poincare plot can
indicate the
frequency of occurrence of irregular heartbeats when compared to the number of
dots on the
trend line 19. The distance of the dots to the trend line 19 can approximate
the extent of heart
rate change from one heartbeat to the next. However, as heart rate change is
limited to only
successively-occurring heartbeats, the linearity of time and associated
contextual information
over an extended time frame are lost. In addition, significant changes in
heart rate, particularly
spikes in heart rate, such as due to sinus rhythm transitions to atrial
flutter, may be masked,
distorted or even omitted in a Poincare plot if the change occurs over non-
successive
heartbeats. In summary, a Poincare plot is more useful as a mathematical tool
than a
physiological one, and therefore a Poincare plot cannot truly represent what
the heart is doing
serially over time with respect to changes in the heart's normal and abnormal
physiology.
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Despite the limitations of Poincate plots and related forms of R-R interval
tachography,
R-R interval data when presented in a format duplicating temporal
physiological events
remains a key tool that physicians can rely upon to identify temporally-
related cardiac
dysrhythmic patterns. Interpretation of R-R interval data can be assisted by
including multiple
temporal points of reference and a plot of R-R interval data that
comparatively depicts heart
rate variability in concert with R-R interval data. FIGURE 3 is a flow diagram
showing a
method 20 for facilitating diagnosis of cardiac rhythm disorders with the aid
of a digital
computer in accordance with one embodiment. The method 20 can be implemented
in software
and execution of the software can be performed on a computer, such as further
described infra
with reference to FIGURE 14, as a series of process or method modules or
steps.
As a precursor step, the cutaneous action potentials of a patient are
monitored and
recorded as ECG data over a set time period (step 21), which can be over a
short term or
extended time frame. ECG recordation, as well as physiological monitoring, can
be provided
through various kinds of ECG-capable monitoring ensembles, including a
standardized 12-lead
ECG setup, such as used for clinical ECG monitoring, a portable Holter-type
ECG recorder for
traditional ambulatory ECG monitoring, or a wearable ambulatory ECG monitor,
such as a
flexible extended wear electrode patch and a removable reusable (or single
use) monitor
recorder, such as described in commonly-assigned U S Patent application,
entitled "Method for
Providing Dynamic Gain over Electrocardiographic Data with the aid of a
Digital Computer,"
Serial No. 14/997,416, filed January 15, 2016,
the latter of which includes an electrode patch and monitor recorder that are
synergistically optimized to capture electrical signals from the propagation
of low amplitude,
relatively low frequency content cardiac action potentials, particularly the P-
waves, generated
during atrial activation. Still other forms of ECG monitoring assembles are
possible.
Upon completion of the monitoring period, the ECG and any physiological data
are
downloaded or retrieved into a digital computer, as further described infra
with reference to
FIGURE 14, with, for instance, the assistance of a download station or similar
device, or via
wireless connection, if so equipped, and a vector of the downloaded or
retrieved ECG data is
obtained (step 22). In one embodiment, the vector of ECG data represents a 40-
minute (or
.. other duration) time span that is used in constructing the plot of R-R
interval data, although
other pre-event and post-event time spans are possible Optionally, a
potentially-actionable
cardiac event within the vector of ECG data can be identified and the ECG data
during, prior to
and after the event is selected (step 23). The event could be identified with
the assistance of a
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software package, such as Holter LX Analysis Software, licensed by NorthEast
Monitoring,
Inc., Maynard, MA; IntelliSpace Cardiovascular Image and Infollnation
management system,
licensed Koninklijke Philips N.V., Amsterdam, Netherlands, MoMe System,
licensed by
InfoBionic, Lowell, MA; Pyramis ECG Management, licensed by Mortara Instrument
Inc.,
Milwaukee, WI; ICS Clinical Suite, licensed by Spacelabs Healthcare Inc.,
Snoqualmie, WA;
or a customized software package. Alternatively, the potentially-actionable
cardiac event could
be identified by a physician or technician during review of the ECG data.
To improve diagnosis of heart rate variability, a diagnostic composite plot is
constructed that includes one or more temporal points of reference into the
ECG data, which
provide important diagnostic context, and a plot of R-R interval data is
constructed based on
the vector of ECG data (step 24), as further described infra with reference to
FIGURE 4.
Briefly, both near field and far field contextual views of the ECG data are
constructed and
displayed. Both views are temporally keyed to an extended duration R-R
interval data view
that, in one embodiment, is scaled non-linearly to maximize the visual
differentiation for
frequently-occurring heart rate ranges, such that a single glance allows the
physician to make a
diagnosis. All three views are presented simultaneously, thereby allowing the
interpreting
physician to diagnose rhythm and the pre- and post-contextual events leading
up to a cardiac
rhythm of interest.
In a further embodiment, findings made through interpretation of heart rate
variability
patterns in the diagnostic composite plot can be analyzed to form a diagnosis
of a cardiac
rhythm disorder (step 25), such as the cardiac rhythm disorders listed, by way
of example, in
Table 1. For instance, the heart rate variability patterns in the diagnostic
composite plot could
be provided to a system that programmatically detects AF by virtue of looking
for the classic
Gaussian-type distribution on the "cloud" of heart rate variability formed in
the plot of R-R
interval data, which can be corroborated by the accompanying contextual ECG
data. Finally,
therapy to address diagnosed disorder findings can optionally be programmed
into a cardiac
rhythm therapy delivery device (step 26), such as an implantable medical
device (IMD) (not
shown), including a pacemaker, implantable cardioverter defibrillator (ICD),
or similar devices.
Cardiac Rhythm Disorders
Normal sinus rhythm
Sinus Bradycardia
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Cardiac Rhythm Disorders
Sinus Tachycardia
Premature atrial and ventricular beats
Ectopic atrial tachycardia
Atrial fibrillation
Atrial flutter
Atrial or ventricular bigeminy, trigeminy or quadrigeminy
Sinus Bradycardia
Fusion beats
Interpolated ventricular premature beats
Intraventricular conduction delay
Junctional rhythm
AV Nodal re-entrant tachycardia
AV re-entrant tachycardia
Wolff-Parkinson-White Syndrome and Pre-excitation
Ventricular tachycardia
Accelerated idioventricular rhythm
AV Wenckebach block
AV Type II block
Sinoatrial block
Table 1.
A diagnostic composite plot is constructed and displayed to help physicians
identify and
diagnose temporally-related cardiac dysrhythmic patterns. The diagnostic
composite plot
includes ECG traces from two or more temporal points of reference and a plot
of R-R interval
data, although other configurations of ECG data plots when combined with the R-
R interval
plot will also provide critical information. FIGURE 4 is a flow diagram
showing a routine 30
for constructing and displaying a diagnostic composite plot for use in the
method 20 of
FIGURE 3. Specific examples of diagnostic composite plots are discussed in
detail infra with
reference to FIGURES 7-13.
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In the diagnostic composite plot, R-R interval data is presented to physicians
in a format
that includes views of relevant near field and far field ECG data, which
together provide
contextual information that improves diagnostic accuracy. In a further
embodiment, other
views of ECG data can be provided in addition to or in lieu of the near field
and far field ECG
data views. The near field (or short duration) ECG data provides a "pinpoint"
classical view of
an ECG at traditional recording speed in a manner that is known to and widely
embraced by
physicians. The near field ECG data is coupled to a far field (or medium
duration) ECG data
view that provides an "intermediate" lower resolution, pre- and post-event
contextual view.
Thus, the extended-duration R-R interval plot is first constructed (step 31),
as further described
infra with reference to FIGURE 5. Optionally, noise can be filtered from the R-
R interval plot
(step 32), which is then displayed (step 33). Noise filtering can include low-
pass or high-pass
filtering or other forms of signal processing, including automatic gain
control, such as
described in commonly-assigned U.S. Patent application, Serial No. 14/997,416,
cited supra.
Rhythm disorders have different weightings depending upon the context with
which
they occur. In the diagnostic composite plot, the R-R interval data view and
the multiple views
of the ECG data provide that necessary context. Effectively, the short and
medium duration
ECG data that accompanies the extended-duration R-R interval plot represents
the ECG data
"zoomed" in around a temporal point of reference identified in the center (or
other location) of
the R-R interval plot, thereby providing a visual context to the physician
that allows temporal
assessment of cardiac rhythm changes in various complementary views of the
heart's behavior.
The durations of the classical "pinpoint" view, the pre- and post-event
"intermediate" view, and
the R-R interval plot are flexible and adjustable. In one embodiment, the
diagnostic composite
plot displays R-R interval data over a forty-minute duration and ECG data over
short and
medium durations (steps 34 and 35), such as four-second and 24-second
durations that provide
two- and 12-second segments of the ECG data before and after the R-R interval
plot's temporal
point of reference, which is generally in the center of the R-R interval plot,
although other
locations in the R-R interval plot could be identified as the temporal point
of reference. The
pinpoint "snapshot" and intermediate views of ECG data with the extended term
R-R interval
data comparatively depicts heart rate context and patterns of behavior prior
to and after a
clinically meaningful arrhythmia or patient concern, thereby enhancing
diagnostic specificity of
cardiac rhythm disorders and providing physiological context to improve
diagnostic ability. In
a further embodiment, diagnostically relevant cardiac events can be identified
and the R-R
interval plot can be constructed with a cardiac event centered in the middle
(or other location)
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of the plot, which thereby allows pre- and post-event heart rhythm data to be
contextually
"framed" through the pinpoint and intermediate ECG data views. Other
durations, intervals
and presentations of ECG data are possible.
The extended-duration R-R interval plot presents beat-to-beat heart rate
variability in a
.. format that is intuitive and contextual, yet condensed. The format of the R-
R interval plot is
selected to optimize visualization of cardiac events in a compressed, yet
understandable field of
view, that allows for compact presentation of the data akin to a cardiologists
understanding of
clinical events. FIGURE 5 is a flow diagram showing a routine 40 for
constructing an
extended-duration R-R interval plot for use in the routine 30 of FIGURE 4. The
duration of the
R-R interval plot can vary from less than one minute to the entire duration of
the recording.
Thus, a plurality of R-wave peaks is first selected out of the vector of ECG
data (step 41)
appropriate to the duration of the R-R interval plot to be constructed. For
successive pairs of
the R-wave peaks (steps 42-43), the difference between the recording times of
the R-peaks is
calculated (step 43). Each recording time difference represents the length of
one heartbeat.
.. The heart rate associated with the recording time difference is determined
by taking an inverse
of the recording time difference and normalizing the inverse to beats per
minute (step 44).
Taking the inverse of the recording time difference yields a heart rate
expressed in beats per
second, which can be adjusted by a factor of 60 to provide a heart rate
expressed in bpm.
Calculation of the differences between the recording times and the associated
heart rate
continues for all of the remaining pairs of the R-wave peaks (step 44)
The pairings of R-R intervals and associated heart rates are formed into a two-
dimensional plot. R-R intervals are plotted along the x-axis and associated
heart rates are
plotted along they-axis. The range and scale of they-axis (heart rate) can be
adjusted
according to the range and frequency of normal or patient-specific heart
rates, so as to increase
the visual distinctions between the heart rates that correspond to different R-
R intervals. In one
embodiment, they-axis of the R-R interval plot has a range of 20 to 300 beats
per minute and
R-R intervals corresponding to heart rates falling extremely outside of this
range are excluded
to allow easy visualization of 99+% of the heart rate possibilities.
In a further embodiment, they-axis has a non-linear scale that is calculated
as a function
of the x-axis (R-R interval), such that:
x ¨ min bpm \n
Y max bpm ¨ min bpm)
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where x is the time difference, min bpm is the minimum heart rate, max bpm is
the maximum
heart rate, and n < 1. The non-linear scale of the y-axis accentuates the
spatial distance
between successive heart rates when heart rate is low. For example, when n =
2, the spatial
difference between 50 and 60 bpm is 32% larger than the spatial difference
between 90 bpm
and 100 bpm, and 68% larger than the spatial difference between 150 bpm and
160 bpm. As a
result the overall effect is to accentuate the spatial differences in
frequently-occurring ranges of
heart rate and de-emphasize the spatial differential in ranges of heart rate
where a deviation
from norm would have been apparent, thus maximizing the spatial efficiency in
data
presentation. The goal is to show cardiac events in a simple, small visual
contextual format.
Larger scales and larger formats bely the practical limits of single-page
presentations for the
easy visualization at a glance by the busy physician. The visual distinctions
between the heart
rates that correspond to different R-R intervals stand out, especially when
plotted on a non-
linear scale. Other y-axis ranges and scales are possible as may be selected
by distinct clinical
needs and specific diagnostic requirements.
The diagnostic composite plot includes a single, long range view of R-R
interval data
and a pair of pinpoint ECG data views that together help to facilitate rhythm
disorder diagnosis
by placing focused long-term heart rate information alongside short-tet in
and medium-term
ECG information. Such pairing of ECG and R-R interval data is unique in its
ability to inform
the physician of events prior to, during and after a cardiovascular event.
FIGURE 6 is a
diagram showing, by way of example, a diagnostic composite plot 50 generated
by the method
of FIGURE 3. Note that the diagnostic composite plot can be tailored to
include more than
one view of R-R interval data and as many views of contextual ECG data as
needed. In a
further embodiment, a background information plot presenting an extended far
field of related
information can be included, such as activity amount, activity intensity,
posture, syncope
25 impulse detection, respiratory rate, blood pressure, oxygen saturation
(Sp02), blood carbon
dioxide level (pCO2), glucose, lung wetness, and temperature. Other forms of
background
information are possible. In a still further embodiment, background
information can be layered
on top of or keyed to the diagnostic composite plot 50, particularly at key
points of time in the
R-R interval data plot, so that the context provided by each item of
background information can
30 .. be readily accessed by the reviewing physician.
The diagnostic composite plot 50 includes an ECG plot presenting a near field
(short
duration) view 51, an ECG plot presenting an intermediate field (medium
duration) view 52,
and an R-R interval data plot presenting a far field (extended duration) view
53. The three
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views 51, 52, 53 are juxtaposed alongside one other to allow quick back and
forth referencing
of the full context of the heart's normal and abnormal physiology. Typically,
a temporal point
of reference, which could be a diagnostically relevant cardiac event, patient
concern or other
indicia, would be identified and centered on the x-axis in all three views.
The placement of the
temporal point of reference in the middle of all three x-axes enables the ECG
data to be
temporally keyed to the R-R interval data appearing in the center 60 of the R-
R interval data
view 53, with a near field view 51 of an ECG displayed at normal (paper-based)
recording
speed and a far field view 52 that presents the ECG data occurring before and
after the center
60. As a result, the near field view 51 provides the ECG data corresponding to
the R-R interval
data at the center 60 (or other location) in a format that is familiar to all
physicians, while the
intermediate field view 52 enables presentation of the broader ECG data
context going beyond
the borders of the near field view 51. In a further embodiment, the center 60
can be slidably
adjusted backwards and forwards in time, with the near field view 51 and the
far field view 52
of the ECG data automatically adjusting accordingly to stay in context with
the R-R interval
data view 51. In a still further embodiment, multiple temporal points of
reference can be
identified with each temporal point of reference being optionally accompanied
by one or more
dedicated sets of ECG data views.
The collection of plots are conveniently arranged close enough to one another
to
facilitate printing on a single page of standard sized paper (or physical
paper substitute, such as
a PDF file), although other layouts of the plots are possible. The far field
view 53 is plotted
with time in the x-axis and heart rate in the y-axis. The R-R intervals are
calculated by
measuring the time occurring between successive R-wave peaks. In one
embodiment, the far
field view 53 presents R-R interval data (expressed as heart rate in bpm) that
begins about 20
minutes prior to and ends about 20 minutes following the center 60, although
other durations
are possible.
The near field view 51 and intermediate field view 52 present ECG data
relative to the
center 60 of the far field view 53. The near field view 51 provides a pinpoint
or short duration
view of the ECG data. In one embodiment, the near field view 51 presents ECG
data 55 that
begins about two seconds prior to and ends about two seconds following the
center 60,
although other durations are possible. The intermediate field view 52 provides
additional
contextual ECG information allowing the physician to assess the ECG itself and
gather a
broader view of the rhythm before and after a "blow-up" of the specific
arrhythmia of interest.
In one embodiment, the intermediate field view 52 presents ECG data 56 that
begins about 12
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seconds prior to and ends about 12 seconds following the center 60, although
other durations
are possible. For convenience, the eight-second interval of the ECG data 56 in
the interniediate
field view 52 that makes up the ECG data 56 in the near field view 51 is
visually highlighted,
here, with a surrounding box 57. In addition, other views of the ECG data,
either in addition to
or in lieu of the near field view 51 and the far field view 52 are possible.
Optionally, an ECG
plot presenting an extended far field view 54 of the background information
can be included in
the diagnostic composite plot 50. In one embodiment, the background
information is presented
as average heart rate with day and night periods 58 alternately shaded along
the x-axis. Other
types of background information, such as activity amount, activity intensity,
posture, syncope
impulse detection, respiratory rate, blood pressure, oxygen saturation (Sp02),
blood carbon
dioxide level (pCO2), glucose, lung wetness, and temperature, are possible.
Examples of the diagnostic composite plot as applied to specific forms of
cardiac
rhythm disorders will now be discussed. These examples help to illustrate the
distinctive
weightings that accompany different forms of rhythm disorders and the R-R
interval and ECG
waveform deflection context with which they occur. FIGURE 7 is a diagram
showing, by way
of example, a diagnostic composite plot 70 for facilitating the diagnosis of
sinus rhythm (SR)
transitioning into AF. SR is indicated through the presence of a reasonably
steady baseline, but
with subsidiary lines of premature beats and their compensatory pauses. SR
manifests as a
shadowing 71 of a high heart rate line and a low heart rate line AF is
characterized by
irregular heartbeats with a somewhat random variation of R-R intervals,
although within a
limited range and concentrating in a Gaussian-like distribution pattern around
a mean that
varies over time. Although AF can be diagnosed by viewing a near field view 51
of ECG data
showing heartbeats with reversed P-wave and irregular R-R intervals, this
approach may be
unclear when viewing "snippets" of ECG data, especially when associated with
poor quality
ECG signals. The presence of AF can also be confirmed through a far field view
53 of R-R
interval data, in which the R-R intervals assume superficially appearing
disorganized, spread-
out and decentralized scattered cloud 72 along the x-axis, in comparison to a
concentrated,
darkened line typical of a more organized cardiac rhythm.
FIGURE 8 is a diagram showing, by way of example, a diagnostic composite plot
80
for facilitating the diagnosis of 3:1 atrial flutter (AFL) transitioning into
SR with frequent
premature ectopic atrial beats. In the initial part of the R-R interval plot,
the R-R intervals have
a discernible aggregated line in the middle of the cloud 81 when the rhythm
has yet to stabilize
into a set pattern, not quite AF and not quite AFL. Immediately thereafter, a
dense line
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representing firm 3:1 atrial flutter stabilizes the rhythm prior to the
transition into SR associated
with the presence of two seesawing baselines that result from frequent atrial
ectopy causing
short coupling intervals and then compensatory long coupling intervals. SR is
indicated by the
middle of the three lines with a low heart rate line consistent with the
compensatory pause
(long coupling interval) and a high heart rate line with the shortest coupling
interval
representing the series of atrial premature beats 82, and thus, at a faster
heart rate.
FIGURE 9 is a diagram showing, by way of example, a diagnostic composite plot
90
for facilitating the diagnosis of atrial trigeminy. Atrial trigeminy is
characterized by three
heartbeat rates appearing intermittently yet reasonably regularly. Although
atrial trigeminy can
be diagnosed by viewing a near field view 51 of ECG data, the pattern is
significantly more
recognizable in a far field view 53 of R-R interval data, in which a repeating
pattern of three
distinct heartbeat lines are persistently present and clearly visible 91. This
view also provides
the physician with a qualitative feel for the frequency of the event troubling
the patient that is
not discernible from a single ECG strip.
FIGURE 10 is a diagram showing, by way of example, a diagnostic composite plot
100
for facilitating the diagnosis of maximum heart rate in an episode of AF
during exercise. In a
far field view 50 of R-R interval data, AF manifests through a dispersed cloud
of dots
(Gaussian-like distribution) without a discernible main heart rate line
representing regular
heartbeats 101. Under exercise, the maximum heartbeat can be located by an
increase in heart
rate clustered about the cloud 102. In addition, individual dots above the 200
bpm range
throughout the entire 40-minute range indicates the maximum heart rate during
exercise. The
very rapid rise in heart rate can be critical to patient management, as such
bumps in rate by
exercise can prove serious and even trigger cardiac arrest. Their very
presence is easily
visualized in the R-R interval data plot, thereby allowing the physician to
alter therapy
sufficiently to control such potentially damaging rises in heart rate.
FIGURE 11 is a diagram showing, by way of example, a diagnostic composite plot
110
for facilitating the diagnosis of SR transitioning into AFL transitioning into
AF. In a far field
view 53 of R-R interval data, SR manifests as an uneven main heart rate line
with a fluctuating
height 111. At the onset of AFL, the main heart rate line breaks away at a
lower heart rate than
the SR main heart rate line 112. The episode of AFL further evolves into AF as
characterized
by a dispersed cloud of irregular heartbeats without concentrated heart rate
lines 113. This
view provides critical information to the physician managing AF patients in
that, at a glance,
the view provides data that tells the physician that the patient's AF may be
the consequence of
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AFL. Such knowledge may alter both drug and procedure therapies, like catheter
ablation
details of intervention.
FIGURE 12 is a diagram showing, by way of example, a diagnostic composite plot
120
for facilitating the diagnosis of sinus tachycardia and palpitations that
occurred during exercise
accompanied by a jump in heart rate. In a far field view 50 of R-R interval
data, sinus
tachycardia is indicated by the presence of a baseline heart rate of about 60
bpm 121 that spikes
up to around 100 bpm 122 and gradually slopes down with a wide tail 123,
reflecting a sharp
rise of heart rates followed by a gradual decline. The associated ECG data in
the near field and
intermediate field views (not shown) can confirm the rhythm as sinus rhythm
and a normal
response to exercise. This rhythm, although superficially obvious, was
associated with
symptoms of palpitations and demonstrates a sensitivity to heart rate
fluctuations, rather than a
sensitivity to an arrhythmia. This common problem is often dismissed as merely
sinus
tachycardia, rather than recognizing the context of a changing rate that
generated the patient's
complaint, a problem, visible only in the R-R interval data plot.
FIGURE 13 is a diagram showing, by way of example, a diagnostic composite plot
90
for facilitating the diagnosis of bradycardia during sleep and a R-R interval
pattern
characteristic of sleep. Bradycardia refers to a resting heart rate of under
60 bpm. Bradycardia
during sleep is often tempered with occasional spikes of rapid heart rate,
which can be a
secondary compensatory response to dreaming, snoring or sleep apnea. In a far
field view 50
of R-R interval data, bradycardia manifests as the presence of a base line
heart rate in the range
of about 50 bpm 131, coupled with multiple spikes of dots 132 representing
intermittent
episodes of elevated heart rate. Such elevations in heart rate during a pre-
dominantly slower
rate may be signs of a cardio-respiratory disorder. Still other applications
of the diagnostic
composite plot 80 are possible.
The diagnostic composite plots are a tool used by physicians as part of a
continuum of
cardiac care provisioning that begins with ECG monitoring, continues through
diagnostic
overread and finally, if medically appropriate, concludes with cardiac rhythm
disorder
treatment. Each of these steps involve different physical components that
collaboratively allow
physicians to acquire and visualize R-R interval and ECG data in a way that
accurately depicts
heart rate variability over time. FIGURE 14 is a block diagram showing a
system 140 for
facilitating diagnosis of cardiac rhythm disorders with the aid of a digital
computer 150 in
accordance with one embodiment. Each diagnostic composite plot 151 is based on
ECG data
166 that has either been recorded by a conventional electrocardiograph (not
shown) or retrieved
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or obtained from some other type of ECG monitoring and recording device.
Following
completion of the ECG monitoring, the ECG data is assembled into a diagnostic
composite plot
151, which can be used by a physician to diagnosis and, if required, treat a
cardiac rhythm
disorder, or for other health care or related purposes.
Each diagnostic composite plot 151 is based on ECG data 166 that has been
recorded
over a period of observation, which can be for just a short term, such as
during a clinic
appointment, or over an extended time frame of months. ECG recordation and, in
some cases,
physiological monitoring can be provided through various types of ECG-capable
monitoring
ensembles, including a standardized 12-lead ECG setup (not shown), such as
used for clinical
ECG monitoring, a portable Holter-type ECG recorder for traditional ambulatory
ECG
monitoring (also not shown), or a wearable ambulatory ECG monitor.
One form of ambulatory ECG monitor 142 particularly suited to monitoring and
recording ECG and physiological data employs an electrode patch 143 and a
removable
reusable (or single use) monitor recorder 144, such as described in commonly-
assigned U.S.
Patent application, Serial No. 14/997,416, cited supra. The electrode patch
143 and monitor
recorder 144 are synergistically optimized to capture electrical signals from
the propagation of
low amplitude, relatively low frequency content cardiac action potentials,
particularly the P-
waves generated during atrial activation. The ECG monitor 142 sits centrally
(in the midline)
on the patient's chest along the sternum 169 oriented top-to-bottom. The ECG
monitor 142
interfaces to a pair of cutaneous electrodes (not shown) on the electrode
patch 143 that are
adhered to the patient's skin along the sternal midline (or immediately to
either side of the
sternum 169). The ECG monitor 142 has a unique narrow "hourglass"-like shape
that
significantly improves the ability of the monitor to be comfortably worn by
the patient 141 for
an extended period of time and to cutaneously sense cardiac electric signals,
particularly the P-
wave (or atrial activity) and, to a lesser extent, the QRS interval signals in
the ECG wavefolins
indicating ventricular activity.
The electrode patch 143 itself is shaped to conform to the contours of the
patient's chest
approximately centered on the sternal midline. To counter the dislodgment due
to
compressional and torsional forces, a layer of non-irritating adhesive, such
as hydrocolloid, is
.. provided at least partially on the underside, or contact, surface of the
electrode patch, but only
on the electrode patch's distal and proximal ends. To counter dislodgment due
to tensile and
torsional forces, a strain relief is defined in the electrode patch's flexible
circuit using cutouts
partially extending transversely from each opposite side of the flexible
circuit and continuing
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longitudinally towards each other to define in 'S'-shaped pattern. In a
further embodiment, the
electrode patch 143 is made from a type of stretchable spunlace fabric. To
counter patient
bending motions and prevent disadhesion of the electrode patch 143, the
outward-facing aspect
of the backing, to which a (non-stretchable) flexible circuit is fixedly
attached, stretches at a
different rate than the backing's skin-facing aspect, where a skin adhesive
removably affixes
the electrode patch 143 to the skin. Each of these components are distinctive
and allow for
comfortable and extended wear, especially by women, where breast mobility
would otherwise
interfere with ECG monitor use and comfort. Still other forms of ECG
monitoring and
recording assembles are possible.
When operated standalone, the monitor recorder 142 senses and records the
patient's
ECG data 166 and physiological data (not shown) into a memory onboard the
monitor recorder
144. The recorded data can be downloaded using a download station 147, which
could be a
dedicated download station 145 that permits the retrieval of stored ECG data
166 and
physiological data, if applicable, execution of diagnostics on or programming
of the monitor
recorder 144, or performance of other functions. To facilitate physical
connection with the
download station 145, the monitor recorder 144 has a set of electrical
contacts (not shown) that
enable the monitor recorder 144 to physically interface to a set of terminals
148. In turn, the
download station 145 can be operated through user controls 149 to execute a
communications
or data download program 146 ("Download") or similar program that interacts
with the monitor
recorder 144 via the physical interface to retrieve the stored ECG data 166.
The download
station 145 could alternatively be a server, personal computer, tablet or
handheld computer,
smart mobile device, or purpose-built device designed specific to the task of
interfacing with a
monitor recorder 144. Still other forms of download station 145 are possible.
In a further
embodiment, the ECG data 166 from the monitor recorder 144 can be offloaded
wirelessly.
The ECG data 166 can be retrieved from the download station 145 using a
control
program 157 ("Ctl") or analogous application executing on a personal digital
computer 156 or
other connectable computing device, via a hard wired link 158, wireless link
(not shown), or by
physical transfer of storage media (not shown). The personal digital computer
156 may also
execute middleware (not shown) that converts the ECG data 166 into a format
suitable for use
by a third-party post-monitoring analysis program. The personal digital
computer 156 stores
the ECG data 166 along with each patient's electronic medical records (EMRs)
165 in the
secure database 64, as further discussed infra. In a further embodiment, the
download station
145 is able to directly interface with other devices over a computer
communications network
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155, which could be a combination of local area and wide area networks,
including the Internet
or another telecommunications network, over wired or wireless connections.
A client-server model can be employed for ECG data 166 analysis. In this
model, a
server 62 executes a patient management program 160 ("Mgt") or similar
application that
accesses the retrieved ECG data 166 and other information in the secure
database 164 cataloged
with each patient's EMRs 165. The patients' EMRs can be supplemented with
other
information (not shown), such as medical history, testing results, and so
forth, which can be
factored into automated diagnosis and treatment. The patient management
program 160, or
other trusted application, also maintains and safeguards the secure database
164 to limit access
to patient EMRs 165 to only authorized parties for appropriate medical or
other uses, such as
mandated by state or federal law, such as under the Health Insurance
Portability and
Accountability Act (HIPAA) or per the European Union's Data Protection
Directive. Other
schemes and safeguards to protect and maintain the integrity of patient EMRs
165 are possible.
In a further embodiment, the wearable monitor 142 can interoperate wirelessly
with
other wearable or implantable physiology monitors and activity sensors 152,
such as activity
trackers worn on the wrist or body, and with mobile devices 153, including
smart watches and
smartphones. Wearable or implantable physiology monitors and activity sensors
152
encompass a wide range of wirelessly interconnectable devices that measure or
monitor a
patient's physiological data, such as heart rate, temperature, blood pressure,
respiratory rate,
blood pressure, blood sugar (with or without an appropriate subcutaneous
probe), oxygen
saturation, minute ventilation, and so on; physical states, such as movement,
sleep, footsteps,
and the like; and performance, including calories burned or estimated blood
glucose level.
Frequently, wearable and implantable physiology monitors and activity sensors
152 are capable
of wirelessly interfacing with mobile devices 153, particularly smart mobile
devices, including
so-called "smartphones" and "smart watches," as well as with personal
computers and tablet or
handheld computers, to download monitoring data either in real-time or in
batches through an
application ("App") or similar program.
Based on the ECG data 166, physicians can rely on the data as medically
certifiable and
are able to directly proceed with diagnosing cardiac rhythm disorders and
determining the
appropriate course of treatment for the patient 141, including undertaking
further medical
interventions as appropriate. The ECG data 166 can be retrieved by a digital
computer 150
over the network 155. A diagnostic composite plot 151 that includes multiple
temporal points
of reference and a plot of R-R interval data is then constructed based on the
ECG data 166, as
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discussed in detail supra with reference to FIGURE 3, and displayed or,
alternatively, printed,
for use by a physician.
In a further embodiment, the server 159 executes a patient diagnosis program
161
("Dx") or similar application that can evaluate the ECG data 166 to form a
diagnosis of a
cardiac rhythm disorder. The patient diagnosis program 161 compares and
evaluates the ECG
data 166 to a set of medical diagnostic criteria 167, from which a diagnostic
overread 162
("diagnosis") is generated. Each diagnostic overread 162 can include one or
more diagnostic
findings 168 that can be rated by degree of severity, such as with the
automated diagnosis of
atrial fibrillation. If at least one of the diagnostic findings 168 for a
patient exceed a threshold
level of tolerance, which may be tailored to a specific client, disease or
medical condition
group, or applied to a general patient population, in a still further
embodiment, therapeutic
treatment ("Therapy") to address diagnosed disorder findings can be generated
and, optionally,
programmed into a cardiac rhythm therapy delivery device, such as an IMD (not
shown),
including a pacemaker, implantable cardioverter defibrillator (ICD), or
similar devices.
While the invention has been particularly shown and described as referenced to
the
embodiments thereof, those skilled in the art will understand that the
foregoing and other
changes in form and detail may be made therein without departing from the
spirit and scope.
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