Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
1
ECG – Electrocardiography
Practical Exercises in Physiology (Spring semester: 4th - 6th weeks)

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
2
Electrocardiography
̶Definition: recording the cardiac electrical activity from the surface of the body
(el. heart activity can also be obtained from the esophageal leads or the heart surface itself, but
these methods are used by other names)

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
3
Cardiac conduction system
Purkynje fibers
Sinoatrial node (SA)
Atrial preferential ways
Atrioventricular node (AV)
His bundle
Tawara (bundle) branches
SA node
Atrial myocyte
AV node
His bundle
Tawara branches
Purkynje fibers
Ventricular myocyte

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
4
Cardiac conduction system
̶Function: AP formation and preferential conduction
̶The atriums are separated from the chambers by a non-conductive fibrous septum - the only way is
through the AV
̶Sinoatrial node (SA) - natural frequency 100 bpm (mostly under parasympathetic damping effect),
conduction velocity 0.05 m/s
̶Preferred internodal atrial ways - conduction velocity 0.8 - 1 m / s
̶Atrioventricular node - single conductive connection between atria and ventricles, natural
frequency 40 - 55 bpm, conduction velocity only 0.05 m / s (nodal delay)
̶His bundle – conduction velocity 1–1,5 m/s
̶Tawara (bundle) branches – conduction velocity 1–1,5 m/s
̶Purkynje fibers – conduction velocity 3–3,5 m/s
̶
̶Sinus rhythm - AP starts at the SA node
̶Junction rhythm - AP is formed in the AV node or His bundle
̶Tertiary (ventricular) rhythm - AP is formed in bundle branches or Purkynje fiber
̶
̶Ventricular myocardial activation - from inside to outside, markedly synchronized, determined by
the onset of excitement
̶Repolarization of ventricular myocardium - in the opposite direction, less sharp, repolarization
isles
̶Note: natural frequency is the frequency of AP formation unaffected by neural and hormonal control
̶
natural frequencies of 20 - 40 bpm, they have slow spontaneous depolarization

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
5
Electric dipole
̶Electrode: records electrical potential (Φ)
̶Electrical lead: connection of two electrodes
̶It records the voltage between the electrodes
̶Voltage: difference of el. potentials
(V= Φ1- Φ2)
7354523
electrode
lead
Φ1
Φ2

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
6
Einthoven triangle
(standard, limb, bipolar leads)
̶Bipolar leads: both electrodes are active (variable electrical potential)
̶Electrode colors:
R: red, L: yellow, F: green
I
II
III
R
L
F

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
7
Goldberger leads
(augmented, limb, unipolar leads)
̶Unipolar leads: one electrode is active (variable electric potential) and the other is inactive
(constant electric potential, usually 0 mV)
̶The active electrode is always positive
aVF
aVL
avR
R
L
F

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
8
Wilsonova central terminal (W)
̶It is formed by the connection of limb electrodes through resistors
̶electrically represents the center of the heart (it is actually led out or it is calculated)
̶Inactive electrode (constant potential)
Central terminal
-
+
+
+
-
Real central terminal

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
9
Chest leads
̶Chest lead: connection of chest electrode and central terminal
̶
̶Unipolar leads: chest electrode is active (positive) and central terminal is inactive (0 mV
potential)
1
2
3
4
5
6
hrudní elektroda

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
10
Leads according to Cabrera
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°
+
-
+
R
L
F
aVR
-
+
-
+
aVL
aVF
–
–
+
+
–
I
III
II

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
11
Analysis of ECG
1.Heart action
2.Heart rhythm
3.Heart rate
4.Waves, segments and intervals
̶P wave
̶PQ interval
̶QRS complex
̶ST segment
̶T wave
̶QT interval
5.Electrical heart axis
P
Q
R
S
T
Atrial depolarization
Ventricular depolarization - QRS
Ventricular repolarization
Svod II

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12
Analysis of ECG
̶A millimeter grid of paper will help in fast analysis
̶See the paper speed (here 25 mm / s)v
̶How many ms is one mm?
̶It is good to know how much mV is one mm
Obsah obrázku text Popis byl vytvořen automaticky Obsah obrázku text Popis byl vytvořen automaticky

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
13
1) Heart action
̶Regularity of distances between QRS complexes - RR intervals
̶Calculate difference: RR – mean RR
(you only need to choose the shortest and longest RR in
the record)
̶
̶Regular action: difference < 0,16 s
̶Irregular action: difference > 0,16 s
̶Usually pathological
̶Beware of significant sinus respiratory arrhythmia - it is very physiological. If you are unsure,
ask the patient to hold their breath during recording
̶
̶Note: if one extrasystole is present, but otherwise the action is regular, it is called regular
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
RR

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
14
2) Heart rhythm
̶Heart rhythm is determined by the source of action potentials that lead to ventricular
depolarization
ventricular depolarization is crucial, because it determines cardiac output
̶Sinus rhythm
̶AP begins in SA node
̶On ECG: present P wave (atrial depolarization) before QRS
̶Junction rhythm
̶AP begins in AV node or His bundle, the frequency is usually 40-60 bpm
̶P wave is not before QRS, QRS is normal (narrow)
̶Heart rate is low (40-60 bpm)
̶Atrial depolarization can be present in the ECG if the ventricular impulses are transferred to the
atria - wave is after QRS and has opposite polarity because it runs in opposite direction
̶Tertial (ventricular) rhythm
̶AP begins in other parts of the conduction system, frequency 30-40 bpm
̶QRS has a strange shape (wider), because it spreads in a non-standard direction in the ventricles

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
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3) Heart rate (HR)
̶Frequency of ventricular contraction (because it determines cardiac output); on ECG - frequency of
ventricular depolarizations
̶HR = 1 / RR bpm
̶Physiological: 60 - 90 bpm at rest
̶
̶Tachycardia: > 90 bpm in rest
̶Can be sinus (increase sympathetic activity, medication, …)
̶Tachyarrhythmias: rhythm is not sinus
̶Bradycardia: < 60 bpm
̶Can be sinus (increase sympathetic activity, sport heart - physiological)
̶HR < 50 bpm, rhythm probably is not sinus
̶

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
16
4) Waves, segments, intervals
Name
Norm
wave P
80 ms
interval PQ (PR)
120-200 ms
segment PQ (PR)
50-120 ms
Q
-
complex QRS
80-100ms
R
-
S
-
segment ST
80-120 ms
interval QT
< 420ms
wave T
160 ms
P
R
T
Q
S
P wave
PQ interval
PQ segment
QRS complex
ST segment
T wave
QT interval

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
17
4) Waves, segments, intervals
name
Place and description
Physiological bacground
Norm
wave P
First round wave (negative or positive)
Atrial depolarization
80 ms
Interval PQ (PR)
Interval from beginning of P to beginning of Q (or R, if Q is not present)
Time interval from SA node activation to the Purkynje fibers activation
120-200 ms
segment PQ (PR)
From P wave end to beginning of Q (or R, if Q is not present)
Complete atrial depolarization, AP transfer from AV to ventricles
50-120 ms
Q
First negative deflection
Depolarization of septum and papilar muscles
-
complex QRS
From beginning of R to end of S
Ventricular depolarization
80-100ms
R
Positive deflection
Main ventricular depolarization
-
S
Negative deflection after positive deflection.
-
segment ST
Interval of isoelectric line between end of QRS and beginning of T wave
Complete depolarization of ventricles
80-120 ms
Interval QT
From beginning of Q (or R) to the end of wave T
Electrical systole
< 420ms
wave T
Second round wave (negative or positive)
Ventricular repolarization
160 ms

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
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4) Waves
Wave P:
-Is present?
-Is positive/negative, one-peak/two-peak, high(>0,25mV)/normal/low?
QRS:
Q:  first negative deflection
R:  first positive deflection
S:  negative deflection after positive deflection
-small deflection (pod 0,5 mV) – small letter
-Strong deflection – capital letter
-Second positive deflection  (‘)
-
Wave T:
-Is positive/negative/bipolar?
-Does it have the same polarity as the strongest QRS deflection?
-Yes: concordant (ok), No: discordant (pathology)
-Bipolar T:
-Preterminal negative (-/+)
-Terminal negative (+/-)
P
Q
R
S
T
Atrial depolarization
Ventricular depolarization - QRS
Ventricular repolarization
Lead II
RS
Examples:
qRs
rSr‘

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5) Electrical heart axis
Electrical heart axis: average direction of the electric heart vector during ventricular
depolarization (QRS complex)
(can also be determined for atrial depolarization: P, or ventricular repolarization: T, but in
practice we will analyse ventricular depolarization)
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°
Heart axis is physiologically directed down, left, back - refers to the real placement of the heart
in the chest.
- Here we solve only the frontal plane (limb leads)
Physiological range:
Middle type 0° – 90°
Left type -30° - 0°
Right type 90° - 120°
Pathological range:
Right deviation: > 120 ° (P ventricular hypertrophy, dextrocardia)
Left deviation: < -30° (L ventricular hypertrophy, pregnancy, obesity)
El. heart axis
vectocardiogram
the axis is also changed when Tawara branches are blocked or after IM, missing el. activity of part
of chambers

Adobe Systems
̶Calculate the sum of QRS oscillations in leads I, II, III.
When the oscillation is down, it is negative. When the oscillation is up, it is positive. Use a
millimeter grid
̶Lead I: QI=-1; RI=6; SI=0;
QRSI=5
̶
̶
̶Lead II: QII=-1; RII=17; SII=-1;
QRSII=15
̶
̶Lead IIII: QIII=0; RIII=10; SIII=-1;
QRSIII=9
̶
̶
Electrical heart axis - evaluation
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
̶Because the el. axis is related to ventricular depolarization in the frontal plane, use QRS in
limb leads: I, II, III.
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg

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Electrical heart axis - evaluation
̶Draw the Einthoven Triangle with Goldberger augmented Leads
̶Mark the angles around the triangle (in the circle)
̶Lead I:
̶0 at lead I is in the center of lead
̶QRSI = 5, so from 0, measure 5mm towards the positive electrode, make a mark (or any other units,
ratio is important)
̶If the sum of QRS is negative, you will go towards the negative electrode
̶Run a line from the mark perpendicular to the I lead (parallel to the aVF lead)
0°
30°
60°
90°
-30°
120°
I
II
III
–
+
–
–
+
+
0
0
0
15
9
5

Adobe Systems
Electrical heart axis - evaluation
̶Lead II:
̶0 at lead II is again in the center of lead
̶QRS II = 15, so from 0, measure 15 mm towards the positive electrode, make a mark (again, if the
sum of QRS is negative, you will go towards the negative electrode)
̶Run a line from the mark perpendicular to the II lead (parallel to the aVL lead)
0°
30°
60°
90°
-30°
120°
I
II
III
–
+
–
–
+
+
0
0
0
15
9
5
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg

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Electrical heart axis - evaluation
̶Lead III:
̶The same way draw line for QRS III = 9
̶Draw an arrow that starts at the center of the triangle and passes the cross of the drawn lines
̶This arrow shows the direction of the cardiac electrical axis in the frontal plane
̶
̶Note. logically, only lines from two leads are sufficient
0°
30°
60°
90°
-30°
120°
I
II
III
–
+
–
–
+
+
0
0
0
15
9
5
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
The cardiac electrical axis for ventricular depolarization in the frontal plane is 70 °

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24
Leads II a aVR
Note the appearance of the ECG in lead II and aVR. Both leads look at electrical cardiac activity
from a similar angle (deviation only 30 °), but the aVR has the opposite polarity (it looks at the
heart upside down compared to II).Therefore, leads II and aVR are similar, only mirror-inverted.
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
aVR usually has negative T and P
Due to its different appearance, QRS has different description in lead aVR and II.
qRs
rSr‘
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°

Adobe Systems
QRS in limb leads and axis
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
Q = -1
R = 6
S = 0
QRS = 5
Q = -1
R = 17
S = -1
QRS = 15
Q = 0
R = 10
S = -1
QRS = 9
Q = 1
R = -11
S = 0
QRS = -10
Q = 0
R = -3
S = 0
QRS = -3
Q = -1
R = 13
S = -1
QRS = 11
qR
qRs
Rs
rS
q
qRs
description of QRS
Sum of QRS
amplitudes of Q, R, and S

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26
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 1.jpg
Q = -1
R = 6
S = 0
QRS = 5
Q = -1
R = 17
S = -1
QRS = 15
Q = 0
R = 10
S = -1
QRS = 9
Q = 1
R = -11
S = 0
QRS = -10
Q = 0
R = -3
S = 0
QRS = -3
Q = -1
R = 13
S = -1
QRS = 11
Electric axis estimation
Find the lead with the largest and smallest sum of QRS (just by eye) - these leads will be
perpendicular to each other. The angle of lead with the largest sum of QRS will determine
approximately el. heart axis. It is not be perfectly accurate, but it is sufficient in practise.
I
aVR
II
aVF
aVL
III
0°
30°
60°
-30°
120°
90°
–
–
–
–
–
+
+
+
+
+
+
–
El. cardiac axis slightly more than 60 °
Sum of QRS
amplitudes of Q, R, and S

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27
C:\Users\Johanka\Desktop\výuka\seminář\EKG\EKG scan\EKG 3 vysledky.jpg
Electric axis calculation by software
72°
Electrical axis for atrial depolarization
Electrical axis for ventricular repolarization
Electrical axis for ventricular depolarization

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
28
Diagnostic use of ECG

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
29
ECG Holter
AEE89E4D
24-hour monitoring of ECG

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Fibrillation
Atrial – missing P, slightly irregular "serrated" isoline, irregular RR (usually), frequency 80 -
180 bpm. QRS is normaly shaped. It is not life threatening. Ventricular refraction time protects
ventricles from HR higher than 180 bpm, but it still exhausts the heart. Heart activity is not
regulated. Risk of trombembolia
Ventricular – the heart does not function as a pump (cardiac arrest), zero cardiac output, brain
damage after 3 - 5 minutes of fibrillation, without early defibrillation the cardiomyocytes become
exhausted → asystole
Fibrillation
Normal ECG
Fibrillation: unsynchronized cardiomyocyte activity. Cardiac muscle is „shaking“
Arrhythmia: a disorder of heart rhythm, formation or conduction of the excitation
Asystole – no electrical activity of cardiomyocytes, non-defibrillable
→ CPR and adrenalin
→ Cardio-Pulmonary Resuscitation (CPR), early defibrillation
(adrenalin and amiodaron)
Video: https://www.youtube.com/watch?v=lU3NHrjw-lA&ab_channel=NerdDoctor

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Atrioventricular block (heart block)
https://upload.wikimedia.org/wikipedia/commons/thumb/6/64/Afib_ecg.jpg/400px-Afib_ecg.jpg
http://www.qureshiuniversity.com/Ventricular%20Fibrillation.gif
https://ekg.academy/ekgtracings/313.gif
prolongation of the transfer of depolarization from the atrium to the ventricles, prolonged PQ
AV block: disorder of the transmission of depolarization from the atria to the ventricles
some atrial depolarizations do not transfere: occurrence of P, which is not followed by QRS
AV block II. degree
AV block III. degree
A complete blockage of the transfer of depolarization from the atria to the ventricles, P and QRS
are not synchronized
Pulse rate possibly very low → insufficient cardiac output
AV block I. degree

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
32
Artial flutter
C:\Users\Johanka\Desktop\výuka\seminář\EKG\obrázky\T0103.jpg
̶Regular „teeth“ between the QRS.
̶Regular RR, tachycardia.
̶The basis is the atrial re-entry.
̶The regularity is given by the number of "turns" of atrial depolarization per transfer to the
chambers (in the picture: 3 turns per 1 transfer to the chambers, ie 3:1).
̶If the flutter does not disappear, it changes into atrial fibrillation
̶Danger of the deblocked flutter 1:1 (each atrial turn is transfered in ventricles) – exhaustion of
ventricles
̶Risk of trombembolia

Adobe Systems
Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
33
Diagnostic use of ECG
Cardiac ischemia, myocardial infarction
normal
ST elevation,
sign of ischemia
Electrolyte dysbalance - hyperkalemia
Large QRS, hight T
A
B
C
D
E
Time
ischemia

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Fyziologický ústav, Lékařská fakulta Masarykovy univerzity
34
Extrasystoles - ectopic excitements
̶Supraventricular – atrial
̶normal shape of QRS (depolarization spreads normaly in ventricles),
̶P wave does not have a normal shape (it can be negative or covered by QRS),
̶may have a postextrasystolic pause
(re-propagation of depolarization through
the atria)
̶Ventricular
̶Large, non-normal shape of QRS
̶at a slow heart rate there is no compensatory pause (extrasystole is interspersed between normal
QRS)
̶or contains a compensating pause if the next depolarization coming from the SA node comes at a
time when the ventricles are still refractory
https://www.stefajir.cz/supraventrikularni-extrasystola-ekg
https://www.techmed.sk/predsienova-extrasystola/
https://thoracickey.com/atrial-ectopic-beats/
P
P
P
P
P
P
P
T+P
Atrial extrasystole

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35
PEA – pulseless electrical activity
̶PEA refers to cardiac arrest in which the electrocardiogram shows a heart rhythm that should
produce a pulse, but it does not. PEA can look almost like normal ECG activity. Pulseless
electrical activity is found initially in about 55% of people in cardiac arrest.
̶Under normal circumstances, electrical activation of muscle cells precedes mechanical contraction
of the heart (known as electromechanical coupling). In PEA, there is electrical activity but
insufficient cardiac output to generate a pulse and supply blood to the organs.
̶PEA is classified as a form of cardiac arrest.
̶non-defibrillable, therapy: Cardio-Pulmonary Resuscitation and adrenalin
̶Important !: Regular electrical activity on ECG does not mean maintained circulation. Always check
for a central arterial pulse.
https://www.researchgate.net/publication/334071817_Impact_of_Transitory_ROSC_Events_on_Neurological
_Outcome_in_Patients_with_Out-of-Hospital_Cardiac_Arrest/figures?lo=1,
https://www.stefajir.cz/bezpulzova-elektricka-aktivita-ekg,
https://medcourse.in/learn/lesson/asystole-and-pulseless-electrical-activity-pea/,
https://en.wikipedia.org/wiki/Pulseless_electrical_aktivity,
Bezpulzova elektricka aktivita na EKG Sinustachycardia scaled

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C:\Users\Johanka\Desktop\výuka\seminář\EKG\obrázky\Basic-EKG-ECG-Rhythms.png
https://www.medicalestudy.com/basic-ecgekg-rhythms-nclex-cheat-sheet/