ECG
This Lecture Illustrated By Dr.Ahmed Emad Al-khafaji
College Of Medicine , University Of JIH
Department Of Physiology
What is ECG
The electrocardiogram (ECG) is a graphic recording of electric potentials generated by the
heart .
•The signals are detected by means of metal wire electrodes attached to the extremities and
chest wall and are then amplified and recorded by the electrocardiograph.
•ECG leads actually display the instantaneous differences in potential between these
electrodes.
•The clinical utility of the ECG derives from :-
- immediate availability
- noninvasive
- inexpensive
- highly versatile test
USES of ECG
-diagnosis of;
-arrhythmias
-conduction disturbances
-myocardial ischemia
-metabolic disturbances , increased susceptibility to - sudden cardiac death
(e.g., QT prolongation syndromes).
heart’s electrical system
consists of five structures:
1-SA node
2-AV node
3-bundle of His
4-right and left bundle branches
5-Purkinje fibers
Ecg Leads
Ecg Leads
Chest Leads
ECG limb Leads
+ - spetum blue V2-V4 Extending to V1
ECG paper
ECG PAPER AND TIME
•The normal EKG speed is 25 mm/second (5 large square per second)
•The EKG is recorded on special standardized paper that scrolls out of the machine at a specific
and controlled speed.
•Each large box is 5mm wide and represents 0.20 seconds.
•Each large box is equivalent to 5 smaller 1mm boxes, each representing 0.04 seconds.
•Measuring the width of any wave or interval from left to right, using the boxes as a scale,
determines the duration of that wave in seconds.
Constant speed of 25 mm/sec
Standardization (calibration)
To ensure that the EKG correctly measures and records the amplitude of waves above and below the baseline.
0.5 mv Normal calibration
0.5 mv
speed calibration
speed calibration
ECG Rules
1- an electrical impulse travelling directly towards the electrode produces an upright (“positive”) deflection
relative to the isoelectric baseline.
2- an impulse moving directly away from an electrode produces a downward (“negative”) deflection relative to
the baseline .
3- When the wave of depolarisation is at right angles to the lead, an equiphasic deflection is produced .
4- depolarization and repolarization deflections occur in opposite directions
ECG Rules
Voltage vector have the following
1-size (depending on muscle size)
2- angle of vector with lead axis
3-direction (towards positive or negative lead )
Comment on ECG paper
1-rhythm
2-rate
3-axis
4-p-wave
5-pr interval
6-QRS complex
7-ST segment
8-T wave
9-Q-T interval
10-u wave
Rhythm
Sinus or not
Regular or not
Sinus rhythms all originate in Distances between R waves
the sinoatrial (SA) node. are equals or not
Each p wave followed by QRS
Regular rhythm
Irregular rhythm
rate
If the rhythm is regular
300
Heart rate =
Number of large squares between two R waves
1500
Heart rate =
Number of small squares between two R waves
300 1500
Heart rate = =75 bpm Heart rate = =72 bpm
4 21
300
Heart rate = =35 bpm
8.5
If the irregular rhythm is irregular
Heart rate =number of (R) waves in 30 large square x 10
Heart rate =number of (R) waves in 15 large square x 20
30 large square
Heart rate =9 x 10 = 90 bpm
Axis
The axis of the ECG is the major direction of the overall electrical activity of the heart.
Normal axis is point to left and inferiorly (-30 to +90) due to left ventricle dominance
Normal axis
Lead 1 & aVF both are positive
Right axis deviation
Lead 1 negative & aVf positive
left axis deviation
Lead 1 positive & aVF negative
Extreme axis deviation
Both of lead 1 and aVF are negative
be patient , good things come to those who are waiting
