This document provides an overview of electrocardiography (ECG) and how to interpret an ECG. It discusses the history and importance of ECG, the conduction system of the heart, how ECG leads work, what a normal ECG waveform looks like, how to evaluate rhythm and rate, and how to identify common abnormalities. Key aspects of a normal ECG that are described include the P wave, PR interval, QRS complex, ST segment, T wave, and QT interval. Common abnormalities that can be identified on an ECG include arrhythmias, myocardial infarction, chamber enlargement, and electrolyte imbalances.

1. UNDERSTANDING
E.C.G
DR. K. MALATHI
M.D. SCHOLAR.
DEPT OF KAYACHIKITSA

2. CONTENTS
 INTRODUCTION
FUNDAMENTAL PRINCIPLES
CONDUCTION SYSTEM OF HEART
LEADS
WHAT IS ELECTRO CARDIOGRAM
NORMAL ECG
RHYTHM, RATE, NORMAL INTERVALS
CLINICAL INTERPRETATION

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.

12. Precordial leads
The precordial leads lie in the
transverse (horizontal) plane,
perpendicular to the other six leads.

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

15. IMPORTANT POINTS TO
READ ECG PAPER…
Standardization (calibration)
P waves
PR interval/AV conduction
 QRS COMPLEX /interval
ST segments
T waves
Rhythm
Heart rate

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

26. Thumbs up
Romeo Juliet
REACHING towards
Thumbs down
LEAVING Away
each other

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.

30. Dr.K.Malathi
M.D.Scholar
Dept.Of kayachikitsa