The document provides information on normal ECG interpretation, including what an ECG measures, how it is recorded, the major waves and intervals of a normal ECG, and how to analyze ECGs. It describes the P wave, QRS complex, T wave, and other normal ECG components. It also outlines the normal rates, intervals, axes, and wave progression seen on ECG.

2. Normal ECG Interpretation

3. INTRODUCTION
• The electrocardiogram (ECG) is one of the
simplest and oldest cardiac investigations
available, yet it can provide a wealth of useful
information and remains an essential part of the
assessment of cardiac patients.
• With modern machines, surface ECGs are quick
and easy to obtain at the bedside and are based
on relatively simple electrophysiological
concepts.

4. What is an ECG?
An ECG is simply a representation of the electrical
activity of the heart muscle as it changes with
time, usually printed on paper for easier analysis.
Like other muscles, cardiac muscle contracts in
response to electrical depolarization of the muscle
cells. It is the sum of this electrical activity, when
amplified and recorded for just a few seconds that
we know as an ECG.

5. Recording the EKG
Basics:
• ECG graph:
 1 mm small squares
 5 mm large squares
• Paper speed
 25 mm/sec standard

6. The vertical lines measure amplitude or voltage
 Each small box represents 0.1 Mv
 Each large block (made up of 5 small boxes)
represents 0.5 mV
The horizontal lines measure time
 Each small box equals 0.04 seconds
 2. Each large block (made up of 5 small boxes)
equals 0.2 seconds (multiply 0.04 x 5 = 0.2)

9. Major waves of a single
normal ECG pattern
• P wave: Represents Atrial depolarization,
initiated by the SA node.
Characteristics:
1.width <3 small squares (0.12 sec) and height <2.5 mm
2.Upward in leads I,II and inverted in lead aVR. This is
called sinus’ P’ wave.
3.P wave after the QRS Complex(Retrograde P wave) or
inverted P wave indicates its origin from other source.

12. QRS complex
 It Represents ventricle depolarization This
also happens to coincide with the part of the cardiac
cycle when the myocardial cells in the atria are
repolarizing.
 The impulse is slightly delayed at the AV node
before entering the ventricles through the Common
AV Bundle.

13. Characteristics
• Completely negative in lead aVR, maximum
positivity in lead II
• Normal duration between 0.08 and 0.10 sec,
not more than 0.12 sec.
• Physiological Q wave not >0.03 sec.
• In a right ventricular lead (V1) the S wave is
greater than the R wave the height of the R wave
in the left ventricular leads (V5, V6) is less than
25 mm

14. Normal QRS
V1
V6

16. J-point
Is the end of the QRS complex and the beginning of
the ST segment.

17. Normal T wave
• It Represents Re polarization of
ventricles.
• Same direction as the preceding QRS
complex
• Height <5mm in limb leads and <10 mm in
precordial leads
• Smooth contours
• May be tall in athletes

18. The normal U Wave
It represents re polarization of purkinje fibers
and/or the ventricular septum.
The most neglected of the ECG waveforms
• U wave amplitude is usually < 1/3 T wave amplitude in
same lead.
• U wave direction is the same as T wave direction in that
lead.
• U waves are more prominent at slow heart rates and
usually best seen in the right precordial leads.

19. Intervals and segments
PR Interval: From the start of the P wave to the start of the
QRS complex
PR Segment :From the end of the P wave to the start of the
QRS complex
J Point:The junction between the QRS complex and the ST
segment
QT Interval: From the start of the QRS complex to the end of
the T wave
QRS Interval: From the start to the end of the QRS complex
ST Segment: From the end of the QRS complex (J point) to
the start of the T wave

20. Intervals and segments

21. Normal intervals
• PR interval: (measured from the beginning of
the P wave to the first deflection of the QRS
complex). Normally lasts 0.12 and 0.20 seconds.
(3 – 5 small squares on ECG paper).
• QRS Interval: (measured from first deflection of
QRS complex to end of QRS complex at
isoelectric line). Interval usually lasts between
0.08 and 0.12 seconds. (3 small squares on
ECG paper).

23. R-R interval - The RR interval represents the
amount of time between heart beats. Thus, the
RR interval is heart rate dependent.
 In fact, most of our methods for determining
heart rate from the EKG are dependent on
measuring the RR interval. For example if there
is 0.6 seconds between beats, and there are 60
seconds per minute, then the heart rate would be
100 beats per minute [(60 sec/minute / (0.6
sec/beat)].

24. • QT interval (measured from first deflection of
QRS complex to end of T wave at isoelectric
line). it is usually about 0.35 seconds in duration,
but the duration of the QT interval is very heart
rate dependent.
• ST segment - Is the segment between the J
point (the end of the QRS complex) and the
beginning of the T wave.

25. ECG Interpretation
What is your approach to reading an ECG?
•Rate
•Rhythm
•Axis
•Wave morphology
•Intervals and
•Segment analysis

27. The rule of 300
No of big
boxes
Rate (apprx)
1 300
2 150
3 100
4 75
5 60
6 50

28. 10 second rule
• As most ECG record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the ECG and multiply by 6 to get the
number of beats per seconds.
• Rate: (Number of waves in 10 second
strips)x6
• This method works well for irregular rhythm

29. Count QRS in 10 second rhythm strip x 6  use this
method to determine rate when rhythm is irregular
(e.g., atrial fibrillation)

30. Rhythm
Look at the rhythm strip below and answer the
questions
• Are P waves present?
• yes
• Is there a P wave before every QRS complex and a QRS
complex after every P wave?
• yes
• Are the P waves and QRS complexes regular?
• yes
• Is the PR interval constant?
• yes
Yes to all these
questions, so this is
normal sinus rhythm!

31. Normal Sinus Rhythm
ECG rhythm characterized by a usual rate
of anywhere between 60 and 100 beats per
min.
Every P wave must be followed by a QRS
And every QRS is preceded by P wave.
Normal duration of PR interval is 3-5 small
squares
• The P wave is upright in leads I and II.

32. Axis
Axis is the general flow of electricity as it
passes through the heart
The QRS axis represents the net overall
direction of the heart’s electrical activity.

33. Determining the Axis
• The quadrant approach
• The equiphasic approach

35. The Quadrant Approach
• Examine the QRS complex in Leads I and aVF to
determine if they are predominantly positive or
predominantly negative.
• The combination should place the axis into one of the 4
quadrants below.
I AVF Axis
+ + Normal
+ - LAD
- + RAD

38. • To determine cardiac axis look at QRS complexes
of lead II ,III.
AXIS LEAD II LEADIII
Normal Positive Positive/negativ
e
Right axis
deviation
Positive Positive
Left axis
deviation
Negative Negative

39. Normal R Wave
Progression
Transition Zone?

40. Transition Zone

41. Early & Delayed
Transition
• Figure 4-7
V1 V2 V3 V4 V5
V6

42. PRACTICE

43. No. Although there are P waves, they are negative.
negative P waves indicate a retrograde conduction
likely coming from the AV junction.

44. Normal ECG

45. CONCLUSION
ECG NORMAL VALUES:
 Heart rate 60 - 100 bpm
 PR interval 0.12 - 0.20 s
 QRS interval ≤ 0.12 s
 QT interval < half RR interval (males < 0.40 s;
females < 0.44 s) .
 P wave amplitude (in lead II) ≤ 3 mV (mm)
 P wave terminal negative deflection (in lead V1) ≤ 1
mV (mm)Q wave < 0.04 s (1 mm) and < 1/3 of R
wave amplitude in the same lead.