U.S. patent application number 12/804758 was filed with the patent office on 2010-11-25 for method of examining dynamic cardiac electromagnetic activity.
Invention is credited to Herng-Er Horn, Chau-Chung Wu, Hong-Chang Yang, Shieh-Yueh Yang.
Application Number | 20100298691 12/804758 |
Document ID | / |
Family ID | 40096514 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100298691 |
Kind Code |
A1 |
Horn; Herng-Er ; et
al. |
November 25, 2010 |
Method of examining dynamic cardiac electromagnetic activity
Abstract
A method of examining cardiac electromagnetic activity over a
heart for diagnosing the cardiac functions of the heart is
disclosed. The method may include constructing a phase diagram of
electromagnetic signals over a heart by collecting sets of
time-dependent magnetic signals, determining the zeroth and the
first derivations of each set of the magnetic signals at a given
time, and categorizing the zeroth and the first derivations of the
magnetic signals in either of the four phases: (+, +), (-, -), (+,
-), (-, +). The method may also include monitoring a wave
propagation of the magnetic signals.
Inventors: |
Horn; Herng-Er; (Taipei,
TW) ; Wu; Chau-Chung; (Taipei, TW) ; Yang;
Hong-Chang; (Taipei, TW) ; Yang; Shieh-Yueh;
(Taipei County, TW) |
Correspondence
Address: |
J C PATENTS
4 VENTURE, SUITE 250
IRVINE
CA
92618
US
|
Family ID: |
40096514 |
Appl. No.: |
12/804758 |
Filed: |
July 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11811391 |
Jun 8, 2007 |
7805179 |
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12804758 |
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Current U.S.
Class: |
600/409 |
Current CPC
Class: |
A61B 5/243 20210101;
A61B 5/7239 20130101; G16H 50/50 20180101 |
Class at
Publication: |
600/409 |
International
Class: |
A61B 5/05 20060101
A61B005/05 |
Claims
1. A method of examining cardiac electromagnetic activity by
monitoring a propagation of a wave of magnetic signals of a
heart.
2. The method of claim 1, wherein the magnetic signals are either
two-dimensionally or three-dimensionally distributed over the
heart.
3. The method of claim 1, wherein the magnetic signals exhibit
features of a P-wave, a Q-wave, a R-wave, a S-wave and a T-wave
corresponding to an electrocardiography, and the propagation of the
P-wave, the Q-wave, the R-wave, the S-wave, the T-wave or a
combination thereof is monitored.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of and claims
the priority benefit of a prior application Ser. No. 11/811,391,
filed on Jun. 8, 2007, now allowed. This application relates to an
application Ser. No. 12/220,506, filed on Jul. 25, 2008, now
pending, which is a continuation-in-part of the prior application
Ser. No. 11/811,391, filed on Jun. 8, 2007, now allowed. The
entirety of each of the above-mentioned patent applications is
hereby incorporated by reference herein and made a part of
specification.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The invention relates to a method of examining dynamic
cardiac electromagnetic activity. More particularly, the invention
relates to a method of examining the magnetocardiographic signals
and a diagnosis of coronary artery diseases using the results
thereof.
[0004] 2. Description of Related Art
[0005] Each heart beat is originated from the development a small
pulse of electric current that spreads rapidly in the heart and
causes the myocardium to contract (depolarization and
repolarization). The electrical currents that are generated spread
not only within the heart, but also throughout the body, resulting
in the establishment of electric potentials on the body surface,
which are detectable as changes in the electrical potential with an
electrocardiograph (ECG). A typical ECG tracing of a normal
heartbeat (or cardiac cycle) consists of a P wave, a PR interval, a
QRS complex, a ST segment, a Q-T interval, a T wave and a U wave.
In brief, the P wave represents the wave of depolarization that
spreads from the SA node throughout the atria; the QRS complex
corresponds to the depolarization of the ventricles; the T wave
represents the repolarization (or recovery) of the ventricles; the
U wave, which normally follows the T wave, is not always seen and
is thought to represent the repolarization of the papillary muscles
or Purkinje fibers. The Q-T interval represents the time for both
ventricular depolarization and repolarization to occur; the ST
segment following the QRS complex is the time at which the entire
ventricle is depolarized. Any normal or abnormal deflections
recorded by the ECG depend upon the origin of this chain of
electrical activity. Hence, via the measurements of electrical
activity during a cardiac cycle, cardiac functions or pathologies
can be investigated.
[0006] Although electrocardiograph (ECG) provides information
related to cardiac electrical activity, the ECG signals crucially
depend on the contact between the electrodes and the body. Further,
in order to obtain two-dimensional signals via ECG, many electrodes
need to be placed on the body, which can be impractical and may
create interference between signals. Moreover, to obtain more
insightful results, it is often required to perform exercise
electrocardiography test, which may impose discomfort to the
patient. Therefore, alternative methods that are electrode-free,
contact-free and stress-free are being investigated.
[0007] Non-contact measurement technologies, such as thallium scan,
computer tomography, nuclear magnetic resonance imaging, etc. have
been developed, as a diagnostic tool for CAD. However, these
methods require the participants to the injection of isotopes or
contrast medium, or the subjection to X-ray or magnetic field,
which is invasive, uncomfortable and potentially dangerous for the
participants.
[0008] Many studies have demonstrated the benefit of
magnetocardiography (MCG) imaging over the existing methods for
certain clinical evaluation of cardiac functions and pathologies.
Magnetocardiography is a noninvasive, contact-free, risk-free
approach by measuring the magnetic fields of the heart generated by
the same electric current as the ECG and will be altered where the
electrical currents in the heart are disturbed. Although both MCG
and ECG measure the cardiac depolarization and repolarization
patterns, MCG may detect depolarization and repolarization in a
different manner.
[0009] The magnetic signals of a beating heart can transmit through
the body of a study subject and be sensed by sensors configured in
proximity to but not in direct physical contact with the body.
Hence, the problems in skin-electrode contact arising in ECG can be
obviated. Further, MCG is less affected by the conductivity
variations caused by other organs or tissues such as lung, bone and
muscles. Many studies have demonstrated that MCG is potentially
beneficial in various clinical applications.
[0010] However, one difficulty in obtaining the magnetocardiac
signals is the weakness of the signals, which are in the order of
tens of pico-Tesla for human. The superconducting quantum
interference devices (SQUIDs), which exhibit a noise level less
than the magnetocardiac signals by 2 to 3 orders in magnitude, have
been developed to record magnetocardiac signals with an improved
spatial-temporal signal resolution and a higher signal-to-noise
ratio. Currently, there are many commercially available SQUID
systems for detecting magnetocardiac signals. Some of these
systems, which are known as multi-channel SQUID systems, may
consist of many independent SQUID sensors (for example, more than
50 SQUID sensors) to allow the measurement of two-dimensional
magnetocardiac signals originating from various sites over the
heart. From a magnetocardiography, parameters such as .alpha.
angles, smoothness index, current dipole moments can be estimated.
Some reports have suggested that these parameters can be used as
indicators for diagnosing cardiac functions or pathologies.
However, other studies have indicated that these parameters overlap
between normal and abnormal hearts. Hence, the existing MCG
parameters are not adequate, in terms of sensitivity and
specificity, for diagnosing cardiac functions or pathologies.
SUMMARY OF THE INVENTION
[0011] In view of the foregoing, the invention provides a method of
examining cardiac electromagnetic activity, wherein differentiation
between a normally functioning and an abnormally functioning heart
is enhanced.
[0012] The invention also provides a method of examining cardiac
electromagnetic activity, wherein localization of an injured
myocardium can be achieved.
[0013] As embodied and broadly described herein, a method of
examining cardiac electromagnetic activity according to a first
embodiment of the invention includes constructing a phase diagram
of electromagnetic signals over a heart. According to one aspect of
the invention, a plurality of sets of spatially distributed,
time-dependent magnetic signals is collected. Thereafter, the
values of the zeroth and the first derivations of each set of the
magnetic signals at a given time are determined, followed by
categorizing the zeroth and the first derivations of each set of
the time-dependent magnetic signals in either of four phases: (+,
+), (-, -), (+, -), (-, +).
[0014] According to one aspect of the invention, the various parts
of the heart are mapped with the resulting phases to identify the
functional part and the dysfunctional part of the heart.
[0015] According to one aspect of the invention, wherein a normally
functioning part of the heart has the phases of (+, +), (-, -),
while an abnormally functioning part of the heart has the phases of
(+, -), (-, +).
[0016] According to one aspect of the invention, the abnormally
functioning part of the heart exists at the interface of parts of
the heart having phases (+, +) and (-, -).
[0017] According to one aspect of the invention, the given time of
each set of the magnetic signals is a turning point of a fitting
curve to the spatially distributed, time-dependent magnetic signals
at which a second derivation of the spatially distributed,
time-dependent magnetic signals is zero.
[0018] According to one aspect of the invention, each set of the
spatially distributed, time-varying magnetic signals is
representative of an intramyocardial, electrical behavior of the
subject and comprises features of at least a P-wave, a Q-wave, a
R-wave, a S-wave and a T-wave and the given time is at the turning
point during a ST segment of the magnetic signals.
[0019] According to one aspect of the invention, the first
derivation of the time-dependent magnetic signals is calculated at
about 0.01 to about 0.15 second after the turning point.
[0020] According to one aspect of the invention, a risk cutoff
value for screening injured myocardium can be defined with
resulting phases (+, +), (-, -), (+, -), (-, +).
[0021] According to one aspect of the invention, each set of the
spatially distributed, time-varying magnetic signals is offset
before the zeroth and the first derivations of the time-dependent
magnetic data at a given time are determined.
[0022] According to one aspect of the invention, the offsetting for
each set of the spatially distributed, time-varying magnetic
signals is accomplished by zeroing an interval of each set of the
magnetic signals before a P-wave.
[0023] According to one aspect of the invention, the magnetic
signals are either two-dimensionally or three-dimensionally
distributed over the heart.
[0024] According to the method of examining cardiac electromagnetic
activity of the first embodiment of the invention, by mapping the
resulting phases of the magnetic signals with the various parts of
the heart, the specificity of coronary artery diseases can be
identified. Moreover, the injured part of the heart can be
localized.
[0025] In accordance with a method of examining cardiac
electromagnetic activity of a second embodiment of the invention,
the method includes monitoring a wave propagation of the magnetic
signals.
[0026] According to one aspect of the invention, sets of spatially
distributed, time-dependent magnetic field data of the chest,
corresponding to a plurality of measurement positions, are
collected. A time corresponding to a local maximum (positive or
negative) intensity of the magnetic field of a wave of the magnetic
field data at each measurement position is then identified,
followed by plotting a temporal evolution of the local maximum
intensity of the magnetic field during a time interval of the
wave.
[0027] According to one aspect of the invention, the magnetic
signals are either two-dimensionally or three-dimensionally
distributed over the heart.
[0028] According to one aspect of the invention, each set of the
spatially distributed, time-varying magnetic field data is
offset.
[0029] According to one aspect of the invention, each set of the
spatially distributed, time-varying magnetic signals is
representative of an intramyocardial, electrical behavior of the
subject and comprises features of at least a P-wave, a Q-wave, a
R-wave, a S-wave and a T-wave.
[0030] According to one aspect of the invention, the offsetting is
accomplished by zeroing an interval of each set of the spatially
distributed, time-dependent magnetic field data before a P
wave.
[0031] According to one aspect of the invention, the temporal
evolution the local maximum intensity of the magnetic field during
a time interval of the T wave is plotted to obtain a propagation
behavior of the T wave.
[0032] According to one aspect of the invention, the propagation
behavior of a wave of a normally functioning heart and is different
form that of an abnormally functioning heart.
[0033] In accordance to a method of examining cardiac
electromagnetic activity of the invention, the propagation behavior
of a wave is useful in diagnosing coronary artery diseases and for
localizing an injured part of the heart.
[0034] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. The patent or
application file contains at least one drawing executed in color.
Copies of this patent or patent application publication with color
drawing(s) will be provided by the Office upon request and payment
of the necessary fee.
[0036] FIG. 1(a) is a diagram of B.sub.z-t curves, which are plots
of a collection of the spatially distributed magnetocardiac signals
along the direction normal to the body surface as a function of
time of a study subject using a SQUID MCG system.
[0037] FIG. 1(b) is a diagram the spatially distributed B.sub.z-t
curves after zeroing by using the B.sub.z's at the pre-P wave
segment.
[0038] FIG. 2(a) is a plot of one of the B.sub.z-t curves shown in
FIG. 1(b).
[0039] FIG. 2(b) is an enlarge view of the ST-segment of the
B.sub.z-t curve shown in FIG. 2(a).
[0040] FIG. 3 is an exemplary 2-dimensional phase diagram of
(B.sub.z, dB.sub.z/dt) at TP+0.06 for a normally functioning
heart.
[0041] FIGS. 4(a) and 4(b) are plots of MCG contour map showing the
distribution of the magnetic field B.sub.z at TP+0.06 and at
TP+0.06+.delta.t, respectively for a normally functioning heart.
The effective currents at TP+0.06 at TP+0.06+.delta.t, respectively
are respectively denoted with arrows.
[0042] FIGS. 5(a) and 5(b) are plots of MCG contour map showing the
distribution of the magnetic field B.sub.z at TP+0.06 and at
TP+0.06+.delta.t, respectively for an abnormally functioning heart.
The effective currents at TP+0.06 at TP+0.06+.delta.t, respectively
are respectively denoted with arrows.
[0043] FIG. 6 is an exemplary 2-dimensional phase diagram of
(B.sub.z, dB.sub.z/dt) at TP+0.06 an injured heart having stenosis
(>50%) at the right coronary artery (RCA).
[0044] FIG. 7(a) shows the statistical results for the risk of
injured myocardium based on the distribution probabilities of the
phases (+, -), (-, +) of the control group.
[0045] FIG. 7(b) shows the statistical results for the risk of
injured myocardium based on the distribution probabilities of the
phases (+, -), (-, +) of the CAD group.
[0046] FIG. 8 is a magnified view of the T curve of a collection of
B.sub.z-t curves shown in FIG. 1(b).
[0047] FIGS. 9a to 9d are diagrams showing a T-wave propagation of
a normal heart.
[0048] FIGS. 10a to 10e are diagrams showing a T-wave propagation
of a CAD patient.
DESCRIPTION OF THE EMBODIMENTS
Measurements of MCG
[0049] A multi-channel SQUID system, for example, a 64-channel
SQUID system or other type of sensitive superconducting
magnetometers, is positioned in a plurality of coordinates, for
example in a two-dimension or three-dimensional array slightly
above the thorax of a live specimen. Each sensor of the SQUID
system registers the local extracorporeal magnet field strength as
a function of time. A MCG system normally provides measurement of
the magnetic field components perpendicular (z-component) (B.sub.z)
to the body surface as a function of time (t). Magnetocardiograph
(MCG) has features similar to the P-wave, the QRS complex, the
T-wave and the U-wave of the ECG (electrocardiography). FIG. 1(a)
is a diagram of B.sub.z-t curves, which are plots of a collection
of the spatially distributed magnetocardiac signals along the
direction normal to the body surface as a function of time of a
study subject using a SQUID MCG system. The collection of the
magnetocardiac signals corresponds to the plurality of the
measurement positions. As shown in FIG. 1(a) the P, Q, R, S, and T
waves are clearly identified. However, it is worthy to note that at
the pre-P wave segment of the B.sub.z-t curves as indicated with
two arrows in FIG. 1(a), there is a broad variation in the B.sub.z
values at different positions. In principle, the value of B.sub.z
at the pre-P wave segment should be zero. The variation in
B.sub.z's at the different positions at the pre-P wave segment is
due to the background noise. Hence, in an embodiment of this
invention, the offset of each B.sub.z-t curve in FIG. 1(a) is
compensated by shifting the B.sub.z at the pre-P wave segment to
zero. The spatially distributed B.sub.z-t curves after zeroing by
using the B.sub.z's at the pre-P wave segment are shown in FIG.
1(b).
[0050] With the spatially distributed B.sub.z-t curves, several
diagnostic parameters such as .alpha. angles in MCG contour maps,
smoothness index for the QT interval, etc. can be extracted.
However, it has been identified that some patients having ischemia
with values of these parameters not significantly different from
those of normal individuals. Hence, relying on these conventional
parameters may lead to erroneous diagnosis. Accordingly, the
invention provides a method of examining the electromagnetic
activity, such as magnetocardiographic signals, wherein the
differentiation between a normally functioning heart and an
abnormally functioning heart is enhanced. Further, in accordance to
the methods of examining the electromagnetic activity of the
invention, localization of the abnormality can be achieved.
Phase Diagram Method
[0051] According to one aspect of the method of examining
electromagnetic activity of the invention, the method includes
constructing a phase diagram of magnetic signals, such as the
magnetocardiographic signals.
Construction of Phase Diagram of Turning Points at ST Segment
[0052] Although the disclosure herein refers to certain illustrated
embodiments on the construction of phase diagram of turning points
at the ST segment, it is to be understood that these embodiments
are presented by way of example and not by way of limitation. It
should be appreciated by a person of ordinary skill practicing this
invention that other intervals or waves can be used in the
construction of phase diagram of turning points.
[0053] Referring to FIG. 2(a), FIG. 2(a) is a plot of one of the
B.sub.z-t curves shown in FIG. 1(b). FIG. 2(b) is an enlarge view
of the ST-segment of the B.sub.z-t curve shown in FIG. 2(a). A
fitting curve of polynomial function to the data in the ST segment
is constructed, as presented with the yellow line in FIG. 2(b). A
time point on the fitting curve is defined as a turning point. The
turning point is set at which the second derivation of the fitting
curve is zero, for example d.sup.2B.sub.z/dt.sup.2=0. The
corresponding time to the turning point is referred as "TP". The
values of B.sub.z and dB.sub.z/dt around "TP", for example, about
0.01 to about 0.15 second after "TP", are analyzed for each
measurement position. In this embodiment, the values of B.sub.z and
dB.sub.z/dt around TP, for example, 0.06 second after TP (denoted
as TP+0.06), are analyzed for each measurement position.
[0054] As shown in FIG. 2(a), both B.sub.z and dB.sub.z/dt at
TP+0.06 are positive. Through analyzing the B.sub.z-t curves for
all measurement positions shown in FIG. 1(b), the zeroth and first
derivation of time-dependent magnetocardiac signals (B.sub.z and
dB.sub.z/dt) can be categorized in either of the four phases: (+,
+), (-, -), (+, -) and (-, +), and a two-dimensional phase diagram
of (B.sub.z, dB.sub.z/dt) at TP+0.06 can be constructed.
[0055] Referring to FIG. 3, FIG. 3 is an exemplary 2-dimensional
phase diagram of (B.sub.z, dB.sub.z/dt) at TP+0.06 for a normally
functioning heart. The phase (+, +) is presented in light blue, the
phase (-, -) is presented in green, the phase (+, -) is presented
in red, and the phase (-, +) is presented in purple. The various
parts of the heart including left atrium (LA), left ventricle (LV),
right atrium (RA), right ventricle (RV) and cardiac apex (C) are
mapped onto the phase diagram as labeled in FIG. 3. Categories of
(B.sub.z, dB.sub.z/dT).sub.TP+0.06 phase from the physiology point
of view
[0056] Normal Phases of (B.sub.z, dB.sub.z/dt).sub.TP+0.06
[0057] At the time of TP+0.06, which corresponds to the beginning
of the T wave, the electrical conduction along the ventricles for a
normally functioning heart should become enhanced. This is normally
expressed with an enhanced signal intensity of a T wave. Due to the
enhancement of the electrical conduction, the magnetic signals
generated by the electrical conduction are also enhanced. FIG. 4(a)
is a plot of a MCG contour map via SQUID MCG measurement. A MCG
contour map shows the distribution of the magnetic field obtained
at specific measurement positions and the precise moments of the
cardiac cycle, for example, the spatially distributed B.sub.z
signals at TP+0.06. From a magnetic field map, the magnetic field
extrema can be identified, and from the location of the magnetic
field minima and maxima, the excitation wavefront of the effective
current is determined. As shown in FIG. 4(a), a positive pole (N/+)
is located at the upper-left region, and a negative pole (S/-) is
located at the lower-right region. In between there exists an
effective current I.sub.TP+0.06 for the electrical conduction at
TP+0.06. The effective currents at TP+0.06 and TP+0.06+.delta.t are
respectively denoted with arrows. With an infinitesimal increase in
time by .delta.t, the intensity of the effective current at
TP+0.06+.delta.t should increase, for example,
I.sub.TP+0.06+.delta.t as plotted in FIG. 4(b). As a result, at
TP+0.06+.delta.t, the positive magnetic signals become more
positive, and the negative magnetic signals become more negative as
compared with those at TP+0.06. These results imply that at the
measurement positions having a positive/negative B.sub.z should
show a positive/negative dB.sub.z/dt. Therefore, for a normally
functioning heart, (B.sub.z, dB.sub.z/dt).sub.TP+0.06 over the
two-dimensional phase diagram should be mostly (+, +) or (-, -),
which is evidenced with the phase diagram shown in FIG. 3.
[0058] Injured Phases of (B.sub.z, dB.sub.z/dt).sub.TP+0.06
[0059] With an injured myocardium along the conduction path, the
electrical conduction could be depressed as time evolves from
TP+0.06 to TP+0.06+.delta.t. This implies that the effective
current I.sub.TP+0.06+.delta.t is weaker than I.sub.TP+0.06, as
illustrated in FIGS. 5(a) and 5(b). As a result, at
TP+0.06+.delta.t, the positive magnetic signals becomes less
positive, and the negative magnetic signals becomes less negative
as compared with those at TP+0.06. Accordingly, the measured
position having a positive/negative B.sub.z shows a
negative/positive dB.sub.z/dt. Therefore, for an injured heart,
(B.sub.z, dB.sub.z/dt).sub.TP+0.06 of (+, -) or (-, +) becomes more
prominently present in the two-dimensional phase diagram.
[0060] Notably, the regions in the phase diagram of (B.sub.z,
dB.sub.z/dt).sub.TP+0.06 showing (+, -) or (-, +) may correspond to
the injured parts of the myocardium. For example, a phase diagram
of (B.sub.z, dB.sub.z/dt).sub.TP+0.06 of an injured heart having
stenosis (>50%) at the right coronary artery (RCA) is shown in
FIG. 6. The function of RCA is to supply blood to the right side of
the heart including the right atrium (RA) and the right ventricle
(RV). If the RCA is stenotic, the myocardium at RA and RV would
become ischemic or even injured. As shown in FIG. 6, the (+, +)
phase is presented in light blue, the (-, -) phase is presented in
green, the (+, -) phase is presented in red and the (-, +) phase is
presented in purple. The various parts of the heart including left
atrium (LA), left ventricle (LV), right atrium (RA), right
ventricle (RV) and cardiac apex (CA) are mapped onto the phase
diagram as labeled in FIG. 6. In this example of an injured heart
with a stenotic RCA, (B.sub.z, dB.sub.z/dt).sub.TP+0.06 of (+, -)
or (-, +) are mainly present at the RV and RA regions, which
correspond to the injured parts of the myocardium at RV and RA. It
is also worth to note that the phases (+, -) and (-, +) normally
exist at the interface between the (+, +) phase and the (-, -)
phase.
[0061] Determination of a Risk Indicator for Injured Myocardium
[0062] The phase diagram results of the invention can be applied in
risk assessment for injured myocardium. With the phase diagram
results, a risk cutoff value can be defined for screening injured
myocardium. Phase diagrams of (B.sub.z, dB.sub.z/dt).sub.TP+0.06 of
53 control cases (C group) and 15 cases having stenotic (>50%)
coronary arteries (CAD group) are collected. For each phase
diagram, such as those shown in FIG. 3 or FIG. 6, the spatial
distribution probabilities of the (+, +)-phase, the (-, -)-phase,
the (+, -)-phase and the (-, +)-phase are analyzed respectively.
Then, the ratio of the sum of the area occupied by the (+, -)-phase
and the (-, +)-phase of each individual is calculated to determine
a risk indicator for injured myocardium. FIGS. 7(a) and 7(b)
respectively show the statistical results for risk of injured
myocardium for the C group and for the CAD group. The results
indicate that there is a significant difference in the distribution
of injured-myocardium risks between the control and the CAD groups.
Through analyzing the receiver operating characteristic (ROC)
curve, which reveals the inherent tradeoff between the sensitivity
and the specificity of a test, a risk cutoff value using the data
shown in FIGS. 7(a) and 7(b) was found to be 27%, which corresponds
to a sensitivity of about 86.7% and a specificity of about
83.0%.
[0063] According to the results shown in FIGS. 3 and 6, it is
apparent that the phase diagram of CAD patients is different from
that of the normal population. Hence, via the examination on the
phase diagram of the electromagnetic signals, an individual having
CAD can be diagnosed. In addition, this method of the invention
affords the possibility of localizing the abnormal regions of the
heart by mapping the injured phases to the regions of the heart.
The application of MCG phase diagram method is not only useful for
diagnostic purposes, it is also suitable for monitoring or
following-up the effect of coronary intervention therapy, such as
coronary artery bypass surgery, coronary angioplasty or stenting,
and even after cardiac transplantation.
Wave Propagation Method
[0064] The following disclosure is directed to another aspect of
the invention of examining cardiac electromagnetic activity. The
method includes monitoring a wave propagation of magnetic signals,
such as the magnetocardiographic signals.
Construction of Wave Propagation of MCG
[0065] The following is an exemplary illustration on how to
construct a wave propagation from the spatially distributed
B.sub.z-t curves. In this embodiment, the T wave propagation is
analyzed. However, it should be appreciated that these embodiments
are presented by way of example and not by way of limitation, and
the intent of the following detailed description is to cover all
modifications, alternatives, and equivalents as may fall within the
spirit and scope of the invention as defined by the appended
claims. For example, the wave propagation of other interval or wave
of the magnetocardiography signals may be examined.
[0066] Referring to FIG. 8, FIG. 8 is a magnified view of the
collection of B.sub.z-t curves shown in FIG. 1(b) at the T-wave
interval. The maximum of each B.sub.z-t curve at the T-wave
interval occurs at different time points. Each B.sub.z-t curve is
usually referred as magnetocardiac signals sensed by an independent
sensor channel or collected at a particular measurement position.
The time corresponding to the positive/negative maximum B.sub.z of
the N-th channel is defined as t.sub.max,chN. As shown in FIG. 8,
t.sub.max,chN of each channel varies in position in the x-y plane.
As time progresses in a cardiac cycle, the positive/negative
maximum B.sub.z of the N-th channel in the x-y plane at the time
equal to t.sub.max,chN is determined. Hence, as time progresses
through the T-wave interval, the two-dimensional propagation
behavior of the T-wave over a heart is registered.
T-Wave Propagation of a Normal Heart Beat
[0067] The MCG's of more than 30 people with a normal heart have
been collected. After analyzing the T-wave propagation of each MCG,
a common behavior is identified as shown in FIGS. 9a to 9d. The top
part of each of FIGS. 9(a) to 9(d) presents the collection of
spatially distributed B.sub.z-t curves at a particular time point,
while the low part of each of FIGS. 9(a) to 9(d) presents the
corresponding T-wave propagation. The red color refers to the
positive (or N) pole and the blue color refers to the negative (or
S) pole of MCG. Notably, the left/right side of the lower part of
FIGS. 9(a) to 9(d) is the right/left side of the heart under
detection. According to the evolutional behaviors shown in FIGS.
9(a) to 9(d), the positive pole of T wave appears earlier than the
negative pole and originates from nearly the center, slightly to
the left part of the heart. This point of origination is physically
close to the A-V node. Then, the positive pole propagates toward
the left ventricle, and continues to the left part of cardiac apex
as shown in FIGS. 9b and 9c. Finally, the T wave propagates in
terms of the negative pole from the right part of the cardiac apex
toward the central part through the right ventricle.
T-Wave Propagation of an Abnormal Heart Beat
[0068] The MCG's of more than 10 people with coronary artery
disease (CAD) have been collected. It has been discovered that the
T-wave propagations of CAD patients exhibit different behaviors
from that of a normal heart as shown in FIGS. 9(a) to 9(d).
Further, there are particular variations in the behaviors of the
T-wave propagation among CAD patients, depending on the ischemic
territory of CAD. Referring to FIGS. 10(a) to 10(e), FIGS. 10(a) to
10(e) display an example of the T-wave propagation of a CAD patient
having stenotic left anterior descending (LAD) artery. Due to the
stenotic LAD, some regions of the heart may become ischemic or
injured. As a result, the normal path of electrical conduction
through the myocardium is interrupted, which in turns modifies the
path or behavior of T-wave propagation. Referring to FIG. 10(b),
instead of originating from the point close to the A-V node, the
T-wave in this case originates from the left ventricle in positive
pole and the right ventricle in negative pole. The positive pole of
T wave then propagates to the left part of cardiac apex and
continues to the central part of the heart. Meanwhile, the negative
pole propagates toward the right part of the cardiac apex and
continues to the central part as shown in FIGS. 9(c) to 9(e).
[0069] According to the results shown in FIG. 9, it is apparent
that the T-wave propagation of CAD patients is different from that
of the normal population. Hence, via the examination on MCG T-wave
propagation or other wave's propagation, an individual having CAD
can be diagnosed. In addition, the invention affords the
possibility for localizing the abnormal regions, for example,
ischemic regions, of the heart. The application of MCG wave
propagation is not only useful for diagnostic purposes, it is also
suitable for monitoring or following-up the effect of coronary
intervention therapy, such as coronary artery bypass surgery,
coronary angioplasty or stenting, and even after cardiac
transplantation.
[0070] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
invention without departing from the scope or spirit of the
invention. In view of the foregoing descriptions, it is intended
that the invention covers modifications and variations of this
invention if they fall within the scope of the following claims and
their equivalents.
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