ECG Basics
Clinical Part
Adult One Course
Prepared by:
MS.RN. Reem Ahmad Jarrad
Clinical Nursing Department
The Nursing School
The University of Jordan
2020
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Objectives
By the end of studying this ECG section the student is expected to:
1- Recognize ECG different waves and segments.
2Analyze an ECG strip reporting: heart rate, rhythm, intervals, segments, and
waves.
3Recognize significant ischemic myocardial changes as reflected on the ECG.
4- Recall the 12 ECG leads and the myocardial views which each group
reflects.
5- Define the characteristics of: normal sinus rhythm, sinus bradycardia, and
sinus tachycardia.
Definition of Electrocardiogram ( ECG )
ECG : is a visual representation of the sequence of cardiac electrical
depolarization and repolarization.
Definition of Heart Rhythm
Rhythm : refers to the part of the heart controlling the activation sequence,
which is normally the sinoatrial ( SA ) node.
Definition of Cardiac Axis
Axis: refers to the average direction of spread of depolarization wave through
the ventricles as seen from the front. Normally, the depolarization wave
spreads through the ventricles from 11 o clock to 5 o clock, so the deflections
in aVR are mainly downward ( negative ) and in lead II are upward ( positive ).
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Review of Normal Conduction System
ECG Paper
ECG paper is traditionally divided into 1mm squares. Vertically, ten
blocks usually correspond to 1 mV, and on the horizontal axis, the
paper speed is usually 25mm/s, so one block is 0.04s (or 40ms).
Always check the calibration voltage on the right of the ECG, and
paper speed. The following image shows the normal 1mV calibration
spike:
Each large square consists of five small squares.
Each large square equals 0.2 second.
Each small square equals 0.04 second.
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ECG Waves
- P wave: represents atrial depolarization . P duration < 0.12 seconds . P amplitude <
2.5 mm. It is upright in lead II.
-PR interval: represents the duration of time required for an electrical impulse to
spread from the SA node, through the atrial muscle and the AV node into the
ventricular muscle. Normal value: 3-5 small squares ( = 0.12- 0.2 second )
- QRS complex: represents ventricular depolarization. Width less than 3 small squares
(<0.12 second ).
- T wave: represents ventricular repolarization
-ST segment: segment extending from the end of the QRS complex to the beginning
of the T wave. Normally, on the isoelectric line
- Isoelectric line: is a reference line extending horizontally between the bases of the P
and T-waves.
- QT interval: is counted from the beginning of the R wave to the end of the T wave.
It is longer in females than in males for the same heart rate. QT relates conversely
with heart rate which means faster heart rate leads to shorter QTs.
For example: HR = 75 beat/ minute, QT interval upper limit would be: 0.36 sec in
men, and 0.39 in women. While for HR = 150 b/m, QT max = 0.25 sec in men, and
0.28 sec in women.
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Characteristics of Normal Sinus Rhythm
1- P: QRS = 1: 1; this means that every p wave is followed by R wave.
2- Every beat is constituted from P-QRS-T sequence.
3- PR interval ( 0.12-0.2 ) second which is constant beat to beat.
4- Regular R-R intervals ( equal distance between the R-R ).
5- P wave is present and has normal characteristics ( width, height, shape).
6- HR range ( 60 – 100 ) beat/ minute.
Characteristics of Sinus Bradycardia
They are similar to those of normal sinus rhythm except that HR is less than 60
beat/minute.
Characteristics of Sinus Tachycardia
They are similar to those of normal sinus rhythm except that HR is more than
100 beat/minute.
Heart Rate Calculation
1- Regular ECG
HR = 300/ number of large squares among R-R or:
HR = 1500/ number of small squares among R-R ( more precise )
HR = 1500/30 = 50 b/m ; HR = 300/6 = 50 b/m ( note R-R intervals are equal)
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2- Irregular ECG
- Take a rhythm strip for 6 seconds which corresponds to 30 large squares.
- Count the number of R waves in the 6 second strip
- Multiply the R wave's number by 10
HR = 8*10 = 80 beat/minute ( for the above rhythm strip).
ECG description and interpretation
ECG interpretation: indicates whether the record is normal or abnormal. If
abnormal the underlying pathology needs to be identified.
The ECG descriptive report should include:
1.Rhythm
2.Heart rate
3.Regularity
4.Conduction intervals: PR, QT.
5.Cardiac Axis
6.Description of the shape of the QRS ( narrow, wide, M shaped, peaked ,etc).
7.Description of the ST segment ( elevated; depressed or flat ).
8.Description of the T wave ( tented; flat; peaked, etc ).
9.Relationship between p waves and QRS complexes ( e.g., 1:1 ratio,
sequence, etc ).
10. P wave presence and characteristics.
ECG leads and their depolarization spread angles
Twelve Leads ECG
- Lead : is an electrical picture of the heart.
- Six leads are chest leads from V1 to V6 extending across the precordium.
- Three augmented voltage unipolar limb leads which are: aVR, aVL, aVF
- Three standard bipolar limb leads which are : I, II, III .
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10 bodily Electrodes placement
Chest Leads Placement
ECG ischemic Changes
* ST segment depression
* T inversion
* ST elevation
- Cardiac Ischemia: decreased coronary blood flow to the myocardium which
could lead to tissue injury and necrosis ( tissue death ).
ECG leads and Anatomic Groups
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ECG Rhythm Strips for ischemic change analysis
Question: determine what ischemic abnormalities are present in the upper
rhythm strips?