3. INTRODUCTION
ELECROCARDIOGRAPHY - the process of
producing recording of the heart's electrical activity
through repeated cardiac cycles.
ELECTROCARDIOGRAM - (ECG) is a representation of
the electrical events of the cardiac cycle.
EKG – A German version of the word, is a tool used to
visualize the electricity that flows through the Heart.
4. HISTORY
1842- Italian scientist Carlo Matteucci realizes
that electricity is associated with the heart beat.
1924 - The noble prize for physiology or
medicine is given to William Einthoven for his
work on ECG.
5. The importance of the ECG.
▪It is a vital test for determining –
Arrhythmias
Myocardial ischemia and infarction
Pericarditis Chamber hypertrophy
Electrolyte disturbances (i.e. hyperkalemia,
hypokalemia)
Drug toxicity
6. Fundamental Principles
Transmembrane ionic currents are ultimately
responsible for the potentials that are recorded as
an ECG.
An electrode senses positive potentials when an
activation front is moving toward it and negative
potentials when the activation front is moving
away from it.
7. Fundamental Principles
Contraction of any muscle is associated with
electrical changes called Depolarization.
A Phase of recovery/relaxation of any muscle
called Repolarization.
These changes can be detected by electrodes
attached to the surface of the body.
8. Conduction system of the Heart
THE SINO-ATRIAL (SA)
NODE.
THE ATRIO-VENTRICULAR
(AV) NODE.
THE BUNDLE OF HIS.
THE LEFT AND RIGHT
BUNDLE BRANCHES.
THE PURKINJE FIBRES.
9. ECG Leads
The standard ECG has 12 leads:
3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
Bipolar Leads: Two different points on the
body.
Unipolar Leads: One point on the body and
a virtual reference point with zero electrical
potential, located in the center of the heart
10. ▪ Limb leads are :
▪ I, II, II.
▪ Each of the leads are bipolar;
▪ There will be a positive end at one
electrode and negative at the other.
▪ The positioning for leads I, II, and
III were first given by Einthoven
(Einthoven’s triangle).
Augmented Unipolar leads
▪ aVR, Avl and aVF are unipolar;
▪ One limb with ‘O’ reference.
13. The ECG Paper
Horizontally
One small box - 0.04 s
One large box - 0.20 s
Vertically
One large box - 0.5 mV
•Speed = 25mm/sec
•VLimb Leads = 10mm/mV
•VChest Leads = 10mm/mV
14. NORMAL ECG
P wave
QRSComplex
T wave
U wave
PR interval
PR segment
ST segment
QT interval
16. P WAVE –
Represents the electrical depolarization of the atria of the
heart.
Always positive in lead I and II
Always negative in lead aVR
< 3 small squares ie 0.12sec in duration
< 2.5 small squares(2.5mm) in amplitude
Tall peaked ‘Pulmonale P’ in
Right atrial enlargement,
Pulmonary hypertension
and Right ventricular failure
17. Right atrial enlargement -The P waves are tall
(>2.5mm), especially in leads II, III and avF.
Left Atrial Enlargement - Notched/bifid (‘M’ shaped)
P wave (P ‘mitrale’) in limb leads
To diagnose LAE you can use the following criteria:
II > 0.04 s between notched peaks, or
V1 Neg. deflection > 0.04 s wide x 1 mm deep
18. PR interval-
.0.12 to 0.20 s (3 - 5 small squares).
.Short PR – Wolff-Parkinson-White
.Long PR – 1st Degree AV block
.means delay in AV junction, delay allows time for
the atria to contract before the ventricles contract
19. QRS COMPLEX –
Normal QRS duration is o.12sec
prolongation of the QRS complex indicates
Slow ventricular depolarization
Bundle branch block – duration exceeds 120
sec. with incomplete blocks the QRS interval is
between 110 to 120 sec.
Hypokalaemia
Exaggerated QRS – Ventricular hypertrophy,
Hyperkaleamia
20. RIGHT BUNDLE BRANCH
BLOCK
LEFT BUNDLE BRANCH
BLOCK
The wide QRS complex
assumes a unique, virtually
diagnostic shape in those
leads overlying the right
ventricle
MARROW
The wide QRS complex
assumes a unique,
virtually diagnostic shape
in those leads overlying
the right ventricle
WILLIUM
21. QT interval –
Beginning of the Q wave to end of the T wave
Normal duration 0.35 – 0.45 sec
Mrasured in lead aVl.
Abnormal prolongation – Ventricular arrhythmia,
Rheumatic fever, Hypokalaemia, Hypocalcemia ,Acute
myocarditis
Abnormal shortening – Hypercalcemia ,Hyperthermia
Vagal stimulation Hyperkalaemia, Digoxin therapy
22. St segment –
ST Segment is flat (isoelectric)
Elevation or depression of ST segment by 1 mm or more is
significant.
23. T wave –
Normal T wave is asymmetrical, first half having a gradual slope
than the second.
Abnormal T waves are symmetrical, tall, peaked, biphasic or
inverted.
•Peaked T waves
•Hyperacute T waves
•Inverted T waves
•Biphasic T waves
•‘Camel Hump’ T waves
•Flattened T waves
24. U WAVE –
U wave related to afterdepolarizations which follow
repolarization
Following flat T wave,
More prominent at slow heart rates
25. AXIS DEVIATION
▪ The QRS axis represents overall direction of the heart’s
electrical activity.
▪ Normal QRS axis from -30° to +90°.
▪ -30° to -90° is referred to as a left axis deviation (LAD)
▪ +90° to +180° is referred to as a right axis deviation (RAD)
▪ QRS complex in leads I and aVF
▪ Determine if they are predominantly positive or negative
27. RHYTHM
Evaluate the rhythm strip at the bottom of the 12-lead for the
following-
Is the rhythm regular or irregular?
Is there a P wave before every QRS complex?
Sinus Rhythm
is regular with normal P, Q-R-S, T deflections
and intervals.
Sinus Bradycardia
Sinus Tachycardia
AV Heart Block
Atrial Fibrillation
Atrial Flutter
Ventricular Tachycardia
Ventricular Fibrillation
Asystole
28. RATE
Large square method Count the number of “big boxes”
between two QRS complexes, and divide this into 300
for regular rhythm.
Small square method Similar to above, except 1500 is
divided by the number of SMALL squares between
consecutive R waves
R wave method Number of R waves (rhythm strip) X 6
•Useful for slow and/or irregular rhythms
29. Technical Errors and Artifacts
Artifacts that may interfere with interpretation can come
from movement of the patient or electrodes, electrical
disturbances related to current leakage and grounding
failure, and external sources such as electrical stimulators
or cauteries.
Misplacement of one or more electrodes is a common
cause for errors.
Significant misplacement of precordial electrodes.