VISHAL KUMAR 2021/2022
CLINICAL ECG
ECG Fundamentals
ECG (electrocardiogram):
- ECG is a test that checks for problems with the
electrical activity of the heart
- An ECG shows the heart’s electrical activity as line
tracings on paper
- The spikes and dips in the tracings are called waves
Dipole model of the heart:
- In a resting myocardial fiber, we have more
negativity in the inside and the membrane
potential of muscle cells at rest is -90mV
- When the resting cell is depolarized, the sodium
channels open and sodium flows in → as the
depolarization propagates, we can see a positive
deflection on an ECG
- During repolarization, we have a negative deflection
- The dipole is going to generate an electric field and
between these two fields we can measure the
potential difference
Depolarization and repolarization of the ventricle:
- Depolarization of the ventricle starts at the endocardium and goes
towards the epicardium → if we place an electrode on the surface of
the epicardium = record a very narrow and fast positive deflection
- Repolarization of the ventricle goes from the epicardium towards
the epicardium
Advantages and disadvantages of ECG:
Advantages:
- Non-invasive examination
- It is fast and widely available
- The registration can be made inexpensively
- In many cases, the diagnostic accuracy is good
Disadvantages:
- It does not provide direct information about the heart function
- Needing expertise → not so cheap (to train a physician)
- Many times, only the suspicion of the pathological condition can be detected
,VISHAL KUMAR 2021/2022
Anatomy of the intrinsic conduction system:
1. Every impulse is generated by the ‘’pacemaker center’’, the sinoatrial (SA) node.
These impulses are spread to the atrium
2. The internodal pathways are directly connected to the atrioventricular (AV) node,
which is located between the atrium and the ventricle. The AV node also has
pacemaker capability, however, the rate is slower compared to that of the SA node
3. The impulses pause (for 0,1 sec) at the AV
node, before entering the ventricle
4. The bundle of His connects the atria to the
ventricles
5. The bundle branches conduct the impulses
through the interventricular septum and
reach the Purkinje fibers
6. The Purkinje fibers cause a synchronized
depolarization of the contractile cells of
both ventricles
Action potential of nodal tissues:
Phase 1: Pacemaker potential
- This slow depolarization is due to both opening of Na+-channels
and closing of K+-channels
Phase 2: Depolarization
- The AP begins with the pacemaker channels
- Depolarization is due to Ca2+-influx through Ca2+-channels
Phase 3: Repolarization
- This is due to the Ca2+-channels inactivation and K+-channels
opening
- This allows K+-efflux, which brings the membrane potential back to its most negative
voltage
Sequence of depolarization and repolarization of the heart
1. Atrial depolarization is represented with a P-wave on the ECG
2. When the discharge goes through the AV junction, we just see the isoelectric line
(distance between the P-wave and QRS complex)
3. When the bundle branches activate the muscle
cells in the ventricles, we can observe the QRS
complex
4. When everything is depolarized, we can see the
isoelectric line (ST-segment)
5. When the repolarization starts, we can see the T-
wave
6. When everything is back to normal, we can see the
isoelectric line – before the cycle repeats again
,VISHAL KUMAR 2021/2022
ECG leads:
The standard ECG has 12 leads:
- 3 standard limb leads – Bipolar (Einthoven leads) – Frontal plane
- 3 Augmented limb leads – unipolar (Wilson-Goldberger) leads –
Frontal plane
- 6 precordial (chest) leads – Horizontal plane
➔ The axis of a particular lead represents the viewpoint from which it
looks at the heart
Hexa-axial reference system:
- An axis can be assigned to every one of the frontal leads in a natural way
- Drawing these axes from a single starting point creates the hexa-axial reference
system (MÅ SITTE FOR Å FINNE AXIS!)
Electrocardiogram:
- Normal P-wave has an amplitude of ≤ 0,25mV
- Q-wave is the first downward deflection after P-wave;
signals start of ventricular depolarization
- R-wave is the positive deflection after Q-wave
- S-wave is the negative deflection preceded by Q- or R-
waves
- T-waves follows QRS
, VISHAL KUMAR 2021/2022
Intervals and segments:
Intervals and segments are different:
- Intervals: time duration is measured
- Segments: shape and the offset from baseline (elevation/depression) is determined
Intervals:
PR-interval:
- Definition: from the beginning of the P-wave to the beginning of Q-wave (if missing,
the R-wave)
- Biological meaning: AV conduction time
- Reference value: 0,12 – 0,20 seconds (3 – 5 small squares)
QRS:
- Definition: from the beginning of the Q-wave (if missing, the R) to the end of S-wave
(if missing, the R)
- Biological meaning: duration of ventricular depolarization
- Reference value: <0,12 seconds (3 small squares)
QT:
- Definition: from the beginning of the Q-wave (if missing, the R) to the end of T-wave
- Biological meaning: duration of electric activation of the ventricles ‘’electric systole’’
- Reference value: frequency dependent, QTc < 0,44 sec
Activation of ventricle: (Precordial leads on ECG)
- The R-wave is getting bigger, while S-wave is
getting smaller from V1 to V6
- The transitional point is between V3 and V4,
when the R-wave is bigger than the S-wave
CLINICAL ECG
ECG Fundamentals
ECG (electrocardiogram):
- ECG is a test that checks for problems with the
electrical activity of the heart
- An ECG shows the heart’s electrical activity as line
tracings on paper
- The spikes and dips in the tracings are called waves
Dipole model of the heart:
- In a resting myocardial fiber, we have more
negativity in the inside and the membrane
potential of muscle cells at rest is -90mV
- When the resting cell is depolarized, the sodium
channels open and sodium flows in → as the
depolarization propagates, we can see a positive
deflection on an ECG
- During repolarization, we have a negative deflection
- The dipole is going to generate an electric field and
between these two fields we can measure the
potential difference
Depolarization and repolarization of the ventricle:
- Depolarization of the ventricle starts at the endocardium and goes
towards the epicardium → if we place an electrode on the surface of
the epicardium = record a very narrow and fast positive deflection
- Repolarization of the ventricle goes from the epicardium towards
the epicardium
Advantages and disadvantages of ECG:
Advantages:
- Non-invasive examination
- It is fast and widely available
- The registration can be made inexpensively
- In many cases, the diagnostic accuracy is good
Disadvantages:
- It does not provide direct information about the heart function
- Needing expertise → not so cheap (to train a physician)
- Many times, only the suspicion of the pathological condition can be detected
,VISHAL KUMAR 2021/2022
Anatomy of the intrinsic conduction system:
1. Every impulse is generated by the ‘’pacemaker center’’, the sinoatrial (SA) node.
These impulses are spread to the atrium
2. The internodal pathways are directly connected to the atrioventricular (AV) node,
which is located between the atrium and the ventricle. The AV node also has
pacemaker capability, however, the rate is slower compared to that of the SA node
3. The impulses pause (for 0,1 sec) at the AV
node, before entering the ventricle
4. The bundle of His connects the atria to the
ventricles
5. The bundle branches conduct the impulses
through the interventricular septum and
reach the Purkinje fibers
6. The Purkinje fibers cause a synchronized
depolarization of the contractile cells of
both ventricles
Action potential of nodal tissues:
Phase 1: Pacemaker potential
- This slow depolarization is due to both opening of Na+-channels
and closing of K+-channels
Phase 2: Depolarization
- The AP begins with the pacemaker channels
- Depolarization is due to Ca2+-influx through Ca2+-channels
Phase 3: Repolarization
- This is due to the Ca2+-channels inactivation and K+-channels
opening
- This allows K+-efflux, which brings the membrane potential back to its most negative
voltage
Sequence of depolarization and repolarization of the heart
1. Atrial depolarization is represented with a P-wave on the ECG
2. When the discharge goes through the AV junction, we just see the isoelectric line
(distance between the P-wave and QRS complex)
3. When the bundle branches activate the muscle
cells in the ventricles, we can observe the QRS
complex
4. When everything is depolarized, we can see the
isoelectric line (ST-segment)
5. When the repolarization starts, we can see the T-
wave
6. When everything is back to normal, we can see the
isoelectric line – before the cycle repeats again
,VISHAL KUMAR 2021/2022
ECG leads:
The standard ECG has 12 leads:
- 3 standard limb leads – Bipolar (Einthoven leads) – Frontal plane
- 3 Augmented limb leads – unipolar (Wilson-Goldberger) leads –
Frontal plane
- 6 precordial (chest) leads – Horizontal plane
➔ The axis of a particular lead represents the viewpoint from which it
looks at the heart
Hexa-axial reference system:
- An axis can be assigned to every one of the frontal leads in a natural way
- Drawing these axes from a single starting point creates the hexa-axial reference
system (MÅ SITTE FOR Å FINNE AXIS!)
Electrocardiogram:
- Normal P-wave has an amplitude of ≤ 0,25mV
- Q-wave is the first downward deflection after P-wave;
signals start of ventricular depolarization
- R-wave is the positive deflection after Q-wave
- S-wave is the negative deflection preceded by Q- or R-
waves
- T-waves follows QRS
, VISHAL KUMAR 2021/2022
Intervals and segments:
Intervals and segments are different:
- Intervals: time duration is measured
- Segments: shape and the offset from baseline (elevation/depression) is determined
Intervals:
PR-interval:
- Definition: from the beginning of the P-wave to the beginning of Q-wave (if missing,
the R-wave)
- Biological meaning: AV conduction time
- Reference value: 0,12 – 0,20 seconds (3 – 5 small squares)
QRS:
- Definition: from the beginning of the Q-wave (if missing, the R) to the end of S-wave
(if missing, the R)
- Biological meaning: duration of ventricular depolarization
- Reference value: <0,12 seconds (3 small squares)
QT:
- Definition: from the beginning of the Q-wave (if missing, the R) to the end of T-wave
- Biological meaning: duration of electric activation of the ventricles ‘’electric systole’’
- Reference value: frequency dependent, QTc < 0,44 sec
Activation of ventricle: (Precordial leads on ECG)
- The R-wave is getting bigger, while S-wave is
getting smaller from V1 to V6
- The transitional point is between V3 and V4,
when the R-wave is bigger than the S-wave
