Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
1
Cardiac Action Potential and Electrocardiography
Preclinical practice 17. 4. 2024
Mgr. Martin Král

Action potential – show different types (neuro, nodal, atrial ventricular…)
What cause that (ionic channels) – voltage gated, selectivity,
Nernst equation
their composition in different tissue
Action potential in nodal cell (how it starts)
Atrial
Ventrícular
Move to the tissue level
spreading through tissue (gap junction)
Diagram srdce
ECG
Leads
Electrical axis in vertical and horizontal layer
a zbytek z praktik
Ukazkové ECG

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
2
Action potential

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
3
Action potential
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
Ion channel
Pores and Selectivity Filters | LettsScience Ion Channels | GeneTex

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
5
Flow of ions
̶electrochemical gradient
̶Nernst eqation
̶
̶ electrochemical equilibrium potential for:
̶Na+ = +60 mV
̶K+ = -96 mV
̶Ca2+ = +134

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
6
Nodal cell SA
̶100 AP per minute
Pacemaker action potential

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
7
Atrial cell
̶
Human atrial action potential showing the principal currents that flow... | Download Scientific
Diagram

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
8
Ventricular cell
̶

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
9
Ventricular cell
̶
Example of an early after depolarization (EAD) and delayed after... | Download Scientific Diagram

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
10
Comparison of atrial and ventricular AP
̶
Phases of a prototypical atrial and ventricular action potentials (AP) and underlying currents. The
numbers refer to the five phases of the action potential. In each current profile the horizontal
line represents the zero current level; inward currents are below the line and outward ones are
above it.

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
11
ECG
̶
Electrical activity in the myocardium. Schematic of a human heart with illustration of typical
action potential waveforms recorded in five different regions, and their contribution to surface
electrocardiogram.

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
12
ECG
̶Definition: recording of the cardiac electrical activity from the surface of the body
̶
12-Lead ECG Placement Guide - CardiacDirect

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
13
Spreading of the signal
̶Cell to cell by gapjuctions
̶By conduction system
̶Sinoatrial node (SA) – natural frequency 100 bpm (mostly under parasympathetic damping effect),
conduction velocity 0.05 m/s
̶Internodal tracts – conduction velocity 1 m/s
̶Atrioventricular node – 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 3.5 m/s
Electrical activity in the myocardium. Schematic of a human heart with illustration of typical
action potential waveforms recorded in five different regions, and their contribution to surface
electrocardiogram.

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
14
ECG
̶1. Frequency (arrhythmias)
̶2. Conduction (blocks – SA, AV)
̶3. Rhythm
̶4. Ventricular gradient (relationship between depolarization and repolarization)
12-Lead ECG Placement Guide - CardiacDirect

examples - ischemia, hypertrophy, dilatation, cardiomyopathy, inflammations,
changes in electrolytes, drugs…)

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
15
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
16
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
17
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
18
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
19
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
20
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
21
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

Adobe Systems
22
Analysis of ECG
̶A millimeter grid of paper will help in fast analysis
̶See the paper speed (here 25 mm/s)
̶1 mm = 0,04 s
̶5 mm (big square) = 0,2 s
Obsah obrázku text Popis byl vytvořen automaticky Obsah obrázku text Popis byl vytvořen automaticky

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
23
1) Heart action
̶Regularity of distances between QRS complexes - RR intervals
̶
̶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
24
2) Heart rhythm
̶Heart rhythm is determined by the source of action potentials that lead to ventricular
depolarization
ventricul 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, with a frequency of 30-40 bpm
̶QRS has a strange shape (wider) because it spreads in a non-standard direction in the ventricles

Adobe Systems
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
26
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
̶
̶Bradycardia: < 60 bpm
̶

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
27
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
28
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‘

Adobe Systems
5) Electrical heart axis
Electrical heart axis: average direction of the electric heart vector during ventricular
depolarization (QRS complex)
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°
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

Adobe Systems
5) Electrical heart axis
Electrical heart axis: average direction of the electric heart vector during ventricular
depolarization (QRS complex)
I
aVF
aVL
+
+
+
–
–
90°
30°
0°
-30°
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
I

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, we 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
0°
30°
60°
90°
-30°
120°
I
II
III
–
+
–
–
+
+
0
0
0
15
9
5

Adobe Systems
33
Estimation of electrical heart axis
̶Leads II and aVR
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°

Adobe Systems
34
Estimation of electrical heart 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
I
aVR
II
aVF
aVL
III
0°
30°
60°
-30°
120°
90°
–
–
–
–
–
+
+
+
+
+
+
–
El. cardiac axis slightly more than 60 °

perpedicular

Adobe Systems
35
Estimation of electrical heart axis
Is deviation of QRS complex positive in I and aVF lead?
Yes
No
Physiological values between -30̊ to 110̊
Is deviation of QRS complex positive in I and negative in aVF lead
Is deviation of QRS complex negative in I and positive in aVF lead
Deviation to the left
Deviation to the right

Adobe Systems
36
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
Estimation of electrical heart axis in Horizontal plane
Obsah obrázku text Popis byl vytvořen automaticky

Adobe Systems
Department of Physiology, Faculty of Medicine, Masaryk University
38
Thank you for your attention!