Electrocardiography I and II
Exercise I:
a)
Monitor and record an ECG from 12 leads of your schoolmate.
b)
For the instantaneous values of potential in R peaks check the validity of following
relations: UII = UI + UIII (UI = UL-UR, UII = UF - UR, UIII = UF - UL).
c)
Construct and evaluate the mean electrical axis of the QRS complex.
Instrumentation: Electrocardiograph SEIVA PRAKTIK, ECG gel.
Procedure Ia:
1.
ECG unit is connected to PC. By double-clicking the icon SEIVA Database open the
database window.
2.
Press the button [Ins]. The New patient window appears. Fill the patient’s data and
confirm them by [Ctrl+Enter] or press button [OK].
Place electrodes to the limbs and chest according to the next figure and the table.
Moisture the places of connection with ECG-gel before the electrodes are attached.
After the measurement always clean, disinfect and dry electrodes. The person whose
EKG is being measured should remain calm and relaxed. Encourage the person to
breathe normally.
Fig. 1
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3.
Electrode Colour coding
Placement
R
red
right arm
L
yellow
left arm
F
green
left leg
N
black
right leg
Cl
red - white
4th interrib., right side from sternum
C2
yellow - white
4th interrib., left side from sternum
C3
green - white
between C2 and C4
C4
brown - white
5th interrib. in medioklav. line
C5
black - white
in the same level as C4 in the front ax. line
C6
Blue (purple) - white in the same level as C4 in the medial ax. line
By clicking the application icon ECG in the upper right corner of the database window
run the application.
4.
Start the monitoring by pressing [F5].
5.
Check parameters of monitoring by pressing [F7] or by right-clicking the corresponding
button, set AC filter for the elimination of 50/60 Hz noise and baseline (0.3 Hz).
6.
Press [F8] or right-click the corresponding button; set the speed of monitoring to 25
mm/s.
7.
Press [F9] or right-click the corresponding button; set the sensitivity of monitoring to
10 mm/mV.
8.
Press [F10] or right-click the corresponding button; set 2x6 leads+1rythm to be
displayed on the monitor.
9.
Stop monitoring, if necessary, by [Esc] or by pressing the button STOP. Save the last
10 seconds of ECG record into the database [F2].
10. Print out the record by pressing [F6].
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11. Open the analysis mode window [F11]. Select appropriate myofilter [F9]. Observe the
record in the Averaged and Zoom mode. Make some manual changes of intervals with
the aid of the measurement markers. (The intervals and the interpretation previously
saved are not changed after changing the position of the markers.)
12. Print out the table [F6] in the Averaged mode, if necessary.
13. Exit application [Alt+F4].
14. Exit Database
.
Data derived from the ECG record use for the drawing of the mean electrical axis of the
QRS complex.
Procedure Ib:
1. Use the records of the classical unipolar limb leads I, II, III for drawing the mean
electrical axis of the QRS complex. This construction represents the projection of
the heart vector to the frontal plane.
2. Design Einthoven's equilateral triangle. Label apexes as L, R, F. Mark
the conventional polarity of the standard lead I, II, III (Fig. 5).
3. Draw normal in the midpoint of each side of the triangle. The normal can be
considered as the intersection of isoelectric planes of records of leads I, II, III with
the frontal plane. Normals intersect in the isoelectrical point of the heart - a starting
point of an electrical vector of the heart, a special case of which is an electrical axis
of the heart.
4. Read the amplitudes of Q, R, S oscillations - the distance from the isoelectrical line
to the peak - for I, II, and III lead from ECG or the table of the analysis mode
window.
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5. Sum up the values of Q, R, S oscillations for I, II, and III lead, take care of the
correct polarity of oscillations. Draw them in corresponding polarity to the
respective sides of Einthoven's triangle.
6. Draw normals from the ends of abscissae corresponding to the sum of Q, R, S peaks.
Normals intersect in the ending point of the mean electrical axis of the QRS
complex. By connecting this point with the centre of Einthoven's triangle (the
starting point of the electrical axis), obtain the electric axis of the QRS complex.
7. To establish the direction of the heart electrical axis, regard the starting point as a
centre of the circle, the perimeter of which corresponds to the angular scale. The
positive direction of x-axis fits to 0o. The upper semicircle is divided from 0o to 180o, the lower from 0o to 180o (Fig. 58 in the textbook, page 122).
8. Compare the calculated value of the QRS complex with that of a healthy conducting
cardiac system.
Experiment II:
a) Monitor and record an ECG from 12 leads of your schoolmate.
b) Observe rate and rhythm changes in the ECG associated with the body position and
breathing.
Instrumentation: Electrocardiograph SEIVA PRAKTIK, ECG gel.
Procedure IIb:
1.
Make and save consequently the 10-second records of ECG of the volunteer in four
conditions (proceed as in the Procedure Ia):
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
lying down,

after sitting: have the subject quickly get up an sit in a chair, with arms relaxed. In
order to capture the heart rate variation, it is important that you resume the recording as
quickly as possible after the student sits, but avoid capturing motion artefacts,

breathing deeply: the student is seated (40-60 seconds). After the recording begins,
the student should start a series of slow, prolonged breaths, continuing for five cycles,

after exercise: have the student perform an exercise to elevate heart rate. To capture
the heart rate variation, it is important that you resume the recording as quickly as possible
after the student has performed exercise, but avoid capturing motion artefacts.
2.
Make a printout of the electrocardiograms.
3.
Complete Report´s Tables with the lesson data indicated.
BPM Results
Calculate the heart rate from the reciprocal (inverse) of the period of the heartbeat for each
condition. Convert the heart rate from beats per second to beats per minute:
–
Evaluate the time interval between two R waves in two successive QRS complexes. At
a chart speed of 25 mm per second, the time interval of 1 mm distance on the graph represents
0.04 second.
–
For example, suppose that the time interval from one R wave to the next is exactly 0.8
second. Then the cardiac rate in beats per minute:
1 beat x beats

0.8 sec 60 sec
x
1  60
 75 beats per min
0.8
Note: QT interval corresponds to ventricular systole; the end of T wave to subsequent R wave
corresponds to ventricular diastole.
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