Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
1
ECG – Electrocardiography
Physiology II – practice
Spring, weeks 4-6

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
2
Electrocardiography
̶Definition: recording of the cardiac electrical activity from the surface of the body
(Recording of electrical heart activity can also be obtained from the esophageal leads or the heart
surface itself, but these methods are called differently)
̶Key words:
̶heart conduction system
̶tools for ECG recording
̶limb and chest leads
̶unipolar and bipolar leads
̶heart vector, the electrical axis of the heart

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
3
Cardiac conduction system
Purkinje fibers
Sinoatrial node (SA)
Internodal tracts
Atrioventricular node (AV)
His bundle
Tawara (bundle) branches
SA node
Atrial myocyte
AV node
His bundle
Tawara branches
Purkinje fibers
Ventricular myocyte

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
4
Cardiac conduction system
̶Function: AP formation and preferential conduction
̶Atria are separated from ventricles by a non-conductive fibrous septum - the only way is through
the AV node
̶Sinoatrial node (SA) – natural frequency 100 bpm (mostly under parasympathetic damping effect),
conduction velocity 0.05 m/s
̶Internodal tracts – conduction velocity 0.8 – 1 m/s
̶Atrioventricular node – a 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
̶Purkinje fibers – conduction velocity 3–3.5 m/s
̶
̶Sinus rhythm – AP is formed in 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 Purkinje fiber
̶
̶Ventricular myocardial activation – from inside to outside, synchronized, determined by the onset
of a stimulus
̶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
Department of Physiology, Faculty of Medicine, Masaryk University
5
Electric dipole
̶Electrode: records electrical potential (Φ)
̶Electrical lead: a connection between two electrodes
̶It records the voltage between the electrodes
̶Voltage: difference of el. potentials
(V= Φ1- Φ2)
7354523
electrode
lead
Φ1
Φ2

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
6
Einthoven’s 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
Department of Physiology, Faculty of Medicine, Masaryk University
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
Department of Physiology, Faculty of Medicine, Masaryk University
8
Wilson‘s central terminal (W)
̶It is formed by the connection of limb electrodes through resistors
̶Electrically represents the center of the heart (it is led out or it is calculated)
̶Inactive electrode (constant potential)
Central terminal
-
+
+
+
-
Real central terminal

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
9
Chest leads
̶A chest lead: a connection between a chest electrode and the central terminal
̶
̶Unipolar leads: the chest electrode is active (positive) and the central terminal is inactive
(potential = 0 mV)
1
2
3
4
5
6
chest electrode

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
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
Department of Physiology, Faculty of Medicine, Masaryk University
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
Lead 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)
̶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
Department of Physiology, Faculty of Medicine, Masaryk University
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 the 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
Department of Physiology, Faculty of Medicine, Masaryk University
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 the SA node
̶ECG: P wave (atrial depolarization) precedes QRS complex
̶Junction rhythm
̶AP begins in the AV node or His bundle, and the frequency is usually 40-60 bpm
̶P wave does not precede QRS complex, QRS shape 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 the opposite direction
̶Tertial (ventricular) rhythm
̶AP begins in other parts of the conduction system, frequency of 30-40 bpm
̶QRS has a strange shape (wider) because it spreads in a non-standard direction in the ventricles

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Sinus rhythm – P wave precedes each QRS complex – the impulse begins in the SA node, it is followed
by the depolarization of the ventricles
Junctional rhythm – normal P waves do not precede QRS – the impulse begins in the AV node or His
bundle, low heart rate, but normal QRS shape (the impulse spreads normally in the ventricle)
Tertiary (ventriclular) rhythm – there are no P waves bound to QRS, the impulse begins somewhere in
the ventricles – a deformed shape of QRS, very low heart rate, for example, 3rd-degree AV block
3rd-degree AV block – tertiary rhythm in ventricles, faster rhythm in atria determined by the SA
node, but the stimulus is not transferred to the ventricles
P – atrial depolarization
Atrial repolarization
2) Heart rhythm
Atrial depolarization
or

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
16
3) Heart rate (HR)
̶A frequency of ventricular contractions (it determines cardiac output); on ECG – a frequency of
ventricular depolarizations
̶HR = 1 / RR bpm (beats per minute)
̶Physiological values: 60-90 bpm at rest
̶
̶Tachycardia: > 90 bpm at rest
̶It can be sinus rhythm (due to increased sympathetic activity, medication, …)
̶Tachyarrhythmias: rhythm is not sinus rhythm
̶If higher than 180 bpm, it isnť probably sinus rhythm
̶Bradycardia: < 60 bpm
̶It can be sinus rhythm (increased parasympathetic activity, athlete‘s heart - physiological)
̶If HR < 50 bpm, it isnť probably sinus rhythm (but junctional or ventricular rhythm)
̶

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
17
4) Waves, segments, intervals
Name
Norm
P wave
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
Department of Physiology, Faculty of Medicine, Masaryk University
18
4) Waves, segments, intervals
name
Place and description
Physiological background
Norm
Wave P
First-round wave (negative or positive)
Atrial depolarization
80 ms
Interval PQ (PR)
The interval from the beginning of P wave to the beginning
of Q (or R, if Q is not present)
The time interval from SA node activation to the Purkinje fibers activation
120-200 ms
Segment PQ (PR)
From P wave‘s end to the beginning of Q (or R, if Q is not present)
Complete atrial depolarization, the AP transfer from the AV to ventricles
50-120 ms
Q
First negative deflection
Depolarization of septum and papillar muscles
-
Complex QRS
From the beginning of R to the end of S
Ventricular depolarization
80-100ms
R
Positive deflection
Main ventricular depolarization
-
S
Negative deflection after positive deflection.
-
Segment ST
The interval of isoelectric line between the end of QRS and the beginning of T wave
Complete depolarization of ventricles
80-120 ms
Interval QT
From the beginning of Q (or R) to the end of T wave
Electrical systole
< 420 ms
Wave T
Second round wave (negative or positive)
Ventricular repolarization
160 ms

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
19
4) Waves
P wave:
-Is it present?
-Is it positive/negative, one-peak/two-peak, high (>0,25 mV)/normal/low?
QRS:
Q:  first negative deflection
R:  first positive deflection
S:  negative deflection after positive deflection
-Small deflection (less than 0,5 mV) – small letter
-Strong deflection (5 mm and more) – capital letter
-Second positive deflection (‘)
-
T wave:
-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°
The heart axis is physiologically directed down, left, and back
- refers to the real placement of the heart in the chest.
-Here, we solve only the frontal plane (limb leads)
-The heart axis direction is influenced by bigger muscle mass. In a healthy heart, mostly the left
ventricule, in pathological hypertrophy, the direction of pathological muscle mass prevails
Physiological range:
Middle type   0° – 90°
Left type    -30° – 0°
Right type   90° – 120°
Pathological range:
Right deviation: > 120 ° (right ventricular hypertrophy, dextrocardia)
Left deviation: < -30° (left ventricular hypertrophy, pregnancy, obesity)
El. heart axis
vectocardiogram
The axis is also changed if Tawara branches are blocked or after a heart attack, el. activity of
part of chambers is missing

Adobe Systems
̶Calculate the sum of QRS oscillations in leads I, II, III.
When the oscillation goes downward, it is negative. When the oscillation is upward, 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 – calculation
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, for
calculation, 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

Adobe Systems
Electrical heart axis – calculation
̶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 5 mm towards the positive electrode, make a mark (or any other units,
a 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

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Electrical heart axis – calculation
̶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, and 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)
̶Draw an arrow that starts at the center of the triangle and passes the cross of the drawn lines
̶
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 – calculation
̶Lead III:
̶The same way, draw the 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, even lines from just 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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25
Leads II and aVR
Note the appearance of the ECG in the 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°

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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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27
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) - those 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 perfectly accurate, but it is sufficient in practice.
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, S

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28
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
Department of Physiology, Faculty of Medicine, Masaryk University
29
Diagnostic use of ECG
Arrhythmia: a disorder of heart rhythm, formation or conduction of the excitation

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
30
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

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
31
ECG Holter
AEE89E4D
24-hour monitoring of ECG

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Fibrillation
Atrial – missing P wave, slightly irregular "serrated" isoline, irregular RR (usually), frequency
80 - 180 bpm. QRS is normally 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 thromboembolia
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
Asystole – no electrical activity of cardiomyocytes, non-defibrillable
First aid:→ standard cardio-pulmonary resuscitation (CPR) and adrenalin

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
33
Artial flutter
C:\Users\Johanka\Desktop\výuka\seminář\EKG\obrázky\T0103.jpg
̶Regular “teeth“ between the QRS.
̶Regular RR, tachycardia.
̶The cause is 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, i.e. 3:1).
̶If the flutter does not disappear, it changes into atrial fibrillation
̶The danger of the deblocked flutter 1:1 (each atrial turn is transferred in ventricles) –
exhaustion of ventricles
̶Risk of thromboembolia

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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: a disorder of the transmission of depolarization from the atria to the ventricles
Some atrial depolarizations do not transfer: occurrence of P wave, which QRS does not follow
AV block 2nd degree
AV block 3rd 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 1st degree

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
35
Extrasystoles – ectopic pacemaker
̶Supraventricular – atrial or AV ectopic pacemaker
̶Normal shape of QRS (depolarization spreads normally in ventricles)
̶P wave does not have a normal shape (it can be negative or covered by QRS)
̶There may be a postextrasystolic pause
(re-propagation of depolarization through
the atria)
̶Ventricular
̶Large, abnormal shape of QRS
̶At a slow heart rate, there is no compensatory pause (extrasystole is interspersed between normal
QRS)
̶Or there may be 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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36
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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37
C:\Users\Johanka\Desktop\výuka\seminář\EKG\obrázky\Basic-EKG-ECG-Rhythms.png
https://www.medicalestudy.com/basic-ecgekg-rhythms-nclex-cheat-sheet/