The electrocardiogram (ECG) measures the electrical activity of the heart. There are 12 conventional ECG leads that measure the heart from different angles. The ECG uses electrodes placed on the limbs and chest to record the heart's electrical signals as waveforms on graph paper over time, showing deflections like the P, Q, R, S, and T waves. The ECG provides information about heart rate, rhythms, and time intervals to evaluate for conditions like arrhythmias or conduction delays.

1. ECG

2. Introduction
The electrocardiogram (ECG or EKG) is a
diagnostic tool that measures and records the
electrical activity of the heart

3. ECG Leads
There are 12 conventional leads
Limb leads or extremity leads : 6
Chest leads or precordial leads: 6

4. Limb leads
Electrodes are placed on the three limbs
namely right arm, left arm, left leg. Right leg
electrode is the grounding electrode
There are
Standard limb leads: 3
Augmented limb leads : 3

5. Standard limb leads
Measures electrical activity between two limbs
Lead
LeadLead

6. Augmented limb leads
Measures the electrical activity from one limb at
a time. Also called unipolar leads

8. Chest leads
• Electrodes are placed on the precordium.
• There are 6 chest leads namely V1, V2, V3, V4 V5,
V6

11. DIFFERENT VIEW
•Inferior leads, ( II, III and aVF) Inferior part of the heart.
•Lateral leads, (I, aVL, V5 and V6) lateral wall of left
ventricle.
•Septal leads, (V1 and V2) septal wall of the left ventricle.
They are often grouped together with the anterior leads.
•Anterior leads, (V1, V2, V3 and V4) anterior wall of the
left ventricle.
•Lead aVR offers no specific view of the left ventricle.
Rather, it views the endocardial wall from its perspective on
the right shoulder.

12. ECG Graph paper
• The output of an ECG recorder is a graph with
time represented on the x-axis and voltage
represented on the y-axis.

14. Time is measured from the L to the R —
one large box = 0.20 sec and one small one = 0.04 sec.
Voltage or current strength is determined from the
magnitude or height of the various waveforms and is
measured in mV or mm
one small box normally = 0.1 Mv or 1 mm
one large box = 0.5 mV or 5 mm.

15. Components of electrocardiogram
• ECG consists of:-
1. Waves/complexes: deflections that can be positive
/negative or both.
Waves: P,Q,R,S,T
Complex: QRS
2. Segments: period of time between a wave or complex
and other wave or complex
Eg: S-T
3. Interval: period of time between two points on the ECG
Eg: P-R,R-R

18. ECG WAVEFORMS
P wave
Represents atrial
depolarization
A measure of the
time required for
depolarization to
spread through the
atria
Normal duration:
less than 0.12 secs

19. Q wave
The initial negative
deflection of
ventricular
depolarization

20. R wave
The initial positive
deflection of
ventricular
depolarization

21. S wave
The first negative
deflection of
ventricular
depolarization that
follows the first R
wave

22. QRS Complex
Represents
ventricular
depolarization
Duration reflects the
intraventricular
conduction time
Duration of less than
0.11 seconds

23. T wave
The deflection
produced by
ventricular
repolarization

24. U wave
The deflection that
follows the T wave
but precedes the
subsequent P wave
Represent
repolarization of the
intramural Purkinje
conduction system

25. ST segment
The isoelectric
period between the
end of the S wave
and the beginning
of the T wave
Minor deviation
from baseline of
less than ± 1 mm

26. QT interval
Represents the total
duration of
electrical systole
Measured from the
beginning of the
QRS complex to the
end of T wave

27. PR Interval
Measures the AV
conduction time
Measured from the
onset of the P wave
to the onset of the
QRS complex
Normal value: 0.12-
0.20 secs

28. RR Interval
The distance
between the two
consecutive R
waves

29. PP Interval
The distance between
two consecutive P
waves
Normally should be
the same as the RR
interval unless certain
arrhythmias or AV
block are present

30. Approach to Reading the ECG
1. Rate
2. Rhythm
3. P wave: morphology and duration
4. PR interval
5. QRS complex: morphology and duration
6. ST segment
7. T wave
8. U wave
9. QT interval

31. Estimation of Heart Rate

32. Estimation of Heart Rate
Heart Rate No. of large boxes
between RR intervals
300 1
150 2
100 3
75 4
60 5
50 6
43 7