(VII.) Electrocardiography
Physiology


Electrocardiography
Definition: the process of recording the electrical activity of the heart
Keywords
•Specialized excitatory and conductive system of the heart
•equipment for ECG recording
•limb and chest leads
•unipolar and bipolar leads
•heart vector, electrical axis of the heart

Purkyne fibers
Sinoatrial node (SA)
internodal pathways
Atrioventricular node (AV)
Bundle of His
Bundle branch
SA node
atrial myocard
AV node
bundle of His
bundle branch
Purkyne fibers
ventricular myocard
Specialized excitatory
and conductive system of the heart

Electric dipole
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Electrode: records electrical potential (Φ)
Elektric lead: connection of two electrodes
•Recordes voltage between electrodes
•Voltage: difference between el. potentials (V= Φ1- Φ2)
•
electrode
lead
Φ1
Φ2

Einthoven´s triangle
(standard, limb, bipolar leads)
I
II
III
R
L
F
Bipolar leads: both electrodes are active (variable potential en electrodes)

Augmented leads
(Goldberger´s, limb, unipolar leads)
aVF
aVL
avR
R
L
F
Unipolar leads:
one electrode is active  (variable el. potential) and the second one is indifferent (constant el.
potential)
Active electrode is always positive

Chest leads
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1
2
3
4
5
6
Wilson´s cental teminal
Chest electrode: connection of chest electrode and Wilson´s central terminal
Unipolar leads:
chest electrodes are active (positive) and Wilson´s central terminal is indifferent (el. potential
0 mV, electrically centre of the heart)
chest electrode

Leads acording to Cabrera
I
aVF
II
III
aVR
aVL
–
+
–
+
+
+
+
+
–
–
–
–
120°
90°
60°
30°
0°
-30°
+
-
+
R
L
F
aVR
-
+
-
+
aVL
aVF
–
–
+
+
–
I
III
II

ECG description
name
Norm
P wave
80 ms
Interval PQ (PR)
120-200 ms
Segment PQ (PR)
50-120 ms
Q
-
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

Electrical axis of heart
Untitled-1
1.  ORS of I,II and III lead
2. Sumation of QRS complex
I
II
III
Q = -1
Q = - 1
Q = 0
R = 5
R = 6
R = 4
S = -1
S = 0
S = 0
3
5
4
osa
+
R
L
F
–
–
+
+
–
I
III
II
3
5
3. Drawing in triangle
Physiological interval: -30° - 110°
Average deviation of QRS complex in each lead

Diagnostic use of ECG
Arrhytmia: irregular heartbeat
Atrial fibrillation
(absence of P, „jagged“ isolinia, irregular RR, HR 80 – 180 bpm)
Ventricular fibrillation
(heart cannot pump, brain damage after 3 – 5 min)
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
Fibrillation: is the rapid, irregular, and unsynchronized activity of cardiac muscle fibers
fibrillation
normal
AV block I. degree
Atrioventricular block: conduction between the atria and ventricles of the heart is impaired
AV block
II. degree
AV block
III. degree
P
P
P
P
P
P

Myocardial ischemia, heart-attack
A
B (ST elevation)
hyperkalaemia
Diagnostic use of ECG

AEE89E4D
24-hour monitoring of ECG (Holter)
Diagnostic use of ECG