Modern medicine sets itself the
challenges associated with the development of methods and devices, the goal of
which is to reduce the number of diseases through early diagnosis of
cardiovascular diseases.
One of the
most accurate ways to obtain information about condition of the heart‘s electrical field is
the registration of multiple leads for ECG mapping
[1,2,3].
This approach contains a high number of
electrodes that are located over the entire body surface.
Allowing you to record a cardiac signal with multi-electrode
leads
and to construct potential maps
along the epicardium surface, software, and hardware are required to solve a
current problem associated with receiving
the parameters
of the equivalent electric heart generator
(EEHG) and information about the heart electrical activity
[4, 5,
6, 7].
It’s also necessary to take into account the features of
the female bust. The current paper presents a working prototype of a women's
electrocardiographic vest and also presents test results.
The
mammary gland is a paired organ that belongs to the type of apocrine glands of
the skin.
There are many unstriated muscle fibers
in the
vicinity of the nipple. According to the type of its structure, the mammary
gland belongs to the complex alveolar-tubular glands [8].
Some
electrodes of the measuring
system
are located on the mammary glands, the
electrical conductivity of which makes it possible to estimate the density of
the tissue and take into account attenuation during subsequent processing.
While electrical resistance decreases, electrical conductivity tends to
increase over the years.. In addition, the density of breast tissue depends on many
factors such as age, menstrual cycle, lactation period, etc. (Stojadinovich et
al 2005; Korotkova et al 2007).
Figure 1 shows the location of
the electrodes for classical cardiography, which is the same for both male and
female patients. The cardiac signal in the elaborated system is recorded
from electrodes located on the mammary glands. We assume that this system
will
allow us to build higher quality and more detailed potential maps.
Figure 1.
Standard
electrode placement for classical cardiography
Research was carried out to
study the possibility of
getting
a cardiac signal from the mammary gland. For
this purpose, a series of experiments were
conducted.
In the first part, the electrode was installed
above the breast, which is the approximate position of V2, according to
Wilson's chest leads, and the second electrode was located near the center of
the chest. This position of electrodes helps to compare the influence of
tissue properties on the recorded signal.
The
results are presented in Figure 2.
Figure 2. Cardiac signals on and above the
breast. Red - the electrode is located above the mammary gland, blue - on it
The signal from the electrode
located above the mammary gland is shown in red, and on it in blue.
Note
that the amplitude in the signal on the mammary gland is smaller, despite its
proximity to the heart.
It can be seen that the blue graph is not
smaller in amplitude in all places. This is explained by the position of the
dipole in space [10, 11]. The signals are identical to each other and differ
only in amplitude.
In the second part, the electrode
was installed on the lower part of the chest,
and the second electrode was located
on the upper. The results are shown in Figure 3.
Figure 3. Cardiac signals on and below the
breast.
Red - the electrode is located above the mammary gland, and blue – is below it
The signal from the lower part
of the breast (blue, Fig. 3) is smaller in amplitude than the red one (above
the mammary gland). The difference in the signals is due to the attenuation of
the signal in the dense tissue of the breast. This can be seen in the previous
experiment.
The signal in the breast tissue
attenuates is slightly.
A cartographic signal
acquisition system is a vest with holes for electrodes.
Tight placement
of electrodes with their angle fixation is the major task.
Stretch
straps are used to ensure correct and constant positioning of the vest. Fig.4
exhibits
a vest prototype where 1 is a pair of shoulder straps, 2 is a pair of
stretch straps and 3 are holes for placing electrodes.
Figure
4.
Electrocardiographic vest model
A small area of the
current-collecting surface is the major requirement for electrodes(
units of square millimeters). The employ of conventional electrodes with an area of
170 mm2 is unacceptable, therefore MCScap-E electrodes from the manufacturer
«Medical Computer Systems» are utilized,
which are intended for studies that require frequent
installation and rapid removal.
MCScap-E has a universal 1.5 mm Touch Proof
connector that is suitable for most EEG amplifiers.
Since the electrode-skin
contact depends on the fixation on the patient’s body, fasteners
are
an important part of the
vest.
The designed vest has shoulder and back straps
that can be adjusted based on the patient.
Noise-reducing conductive gel
is
implemented
to ensure good contact between skin and the
electrodes.
To place the electrodes, it is
necessary to punch holes into the fixing rings which are inserted.
The
holes are placed at a specific angle on the patient's body, which is viewed as
an elliptical cone.
The map of electrodes is presented in Figure 5.
Figure 5.
Vest
electrode map
Two
NVX-24
biopotential amplifiers are used in the registration system.
The
neutral electrode
(GND)
is placed on the patient's right leg.
An
additional electrode is
mounted to the right hand for synchronizing
recordings. The first 24 electrodes are connected to the first amplifier,
electrodes from 25 to 48 to the second. Electrodes 24 and 48 are connected to
the “joint” electrode. Thus, each amplifier provides the operation of 23
monopolar leads. The 1st and 2nd rows contain 22 electrodes in total and are
fully serviced by the first amplifier. At the same time, the 2nd and 4th rows
of electrodes contain 24 electrodes in total, the last missing electrode 4.12
is connected to the free connector (O2) of the first amplifier.
At the first stage of the
recording algorithm, the upper rows are recorded. At the second stage: record
the bottom rows. This approach will allow increasing the number of monopolar
leads from 24 to 48.
Much attention has been paid to
the ability to measure over a wide dimensional range.
The
primary purpose is to
employ
a vest for a large range of sizes, however, it
is worth taking into account that the electrodes located at fixed angles are
displaced. It was previously noted that the patient’s body is considered as an
ellipse, so its stretch ratio changes for different torso parameters
(the
ratio of the length of the major semi-axis to the length of the minor semi-axis).
If the
ellipse stretch ratio changes, then the arc length also changes at the given
angles. Then, we consider how the angle changes when the ellipse stretch
ratio changes for a fixed arc length.
Since the maximum estimate of
the difference is important for the study, the difference in angles is
calculated at critical values of the ellipse stretch ratio
and in several intermediate cases
(Table 1).
Table 1.
Angle difference depending on the ellipse
stretch ratio.
|
Stretch ratio,
k
|
Angle,
φ°
|
Difference,
Δφ°
|
|
2
|
45
|
0
|
|
1.25
|
44.95
|
4
|
|
1.5
|
50.5
|
5.5
|
|
1
|
54.5
|
9.5
|
Table 1 shows that the
calculated error is small. In addition for most people, the ellipse
stretch ratio is in the range of 1.5-2. Minor differences will not affect
the results of the study, as correction angles are made in the software based
on the patient's size (a, b).
Minor differences will not affect the results of
the study, as correction angles are made in the software relying on the
patient's size (a, b). This minimizes error and makes it possible to cover a
larger number of patients, which makes the device more versatile.
The registration system
carries
out automated data capture, visualization, transmission, processing, and
storage of measurement information. Figure 6 demonstrates the algorithm for
recording ECG, which is divided into three stages.
Figure
6.
Registration system algorithm
The first stage is data capture
using a multi-channel recording system. The
second stage involves processing the received data and transforming
them to build potential distribution maps. The third stage involves
constructing static and dynamic images
relying
on
the obtained data,
which makes it possible to evaluate the heart
state.
To further develop the
recording system, it’s an appropriate to add animation of the propagation of heart
signals for continuous monitoring.
In addition, the ability to restore potentials
on the epicardium is required, as well as the selection of the most optimal
algorithms and methods for compressing and restoring information for storing
the results of multichannel recording and its transformations.
It is required to filter and interpolate signals, as well
as form a torso structure to visualize the distribution of the patient's
potential. Obtaining potential maps on the surface of the torso is not only an
intermediate stage in reconstructing potentials on the epicardium. These
distributions contain diagnostic information suitable for analysis; examples of
analysis of such maps are given in the work of I.P. Polyakov [3]. Figure 7
shows the results of constructing the potential distribution on the surface of
the torso, where here and below the distribution a dynamic color palette is
used, which shows the magnitude of the potential.
Figure
7.
The result of calculating the torso potentials
The construction of potential maps
occurs on the basis of the
potential
distribution
of the body. The construction
of the potential distribution is based
data from the ECS employing
a
women’s vest.
The results are presented in Figures 8 and 9 for R-wave apex moment.
Figure 8.
The potential distribution
on the surface of the heart epicardium
Figure 9.
The potential distribution
on the surface of the heart epicardium
The distribution of potentials
at each moment of the cardiac cycle on the surface of the chest
describes
the electrophysiological processes in the heart
that can be abnormal and normal. The color of the potential
value depends
on the sign and amplitude: the blue palette has negative
value, red
one
is positive;
the higher the amplitude, the higher the color saturation.
The distribution of potentials on
the heart surface reveals
localization
of arrhythmogenic areas and areas with impaired conductivity, which are typical
for cardiac ischemia.
This article considers
the
theoretical foundations of multichannel
ECG
recording. The
physiological characteristics of the female bust were analyzed. This stage was
fundamental for the development of the vest design in the registration system.
The elaborated multichannel
system is a promising direction for cardiac diagnostics. In the future, a
dynamic potential map helps to identify arrhythmogenic areas
on the surface of the myocardium, thereby providing early diagnosis of such
diseases associated with impaired conduction of heart tissue.
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