Evaluation of normal ecg

1. Normal ECG Interpretation

2. 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.

3. 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.

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

5. 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)

8. 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.

10. 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.

11. 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

12. Normal QRS
V1
V6

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

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

16. 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.

17. 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

18. Intervals and segments

19. 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).

21. R-R interval - The RR interval represents the
amount of time between heart beats. Thus, the
RR interval is heart rate dependent.

22. • 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.

23. ECG Interpretation
What is your approach to reading an ECG?
•Rate
•Rhythm
•Axis
•Wave morpholo
•Intervals and
•Segment analys
gy
is

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

26. 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

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

28. 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
• yes
• Is the PR interval constant?
• yes
Yes to all these
• Are the P waves and QRS complexes regular? questions, so this is
normal sinus rhythm!

29. 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.

30. 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.

32. • 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

33. Normal R Wave
Progression
Transition Zone?

34. Normal ECG