3. Chest leads
QRS complex in the V
leads
Progression from lead
V1(predominantly d/w)
to lead V6 where
(predominantly u/w)
The ‘ transition point ’,
where the R and S wave
are equal , indicates the
position of the
interventricular septum
4. The Cardiac Axis
The cardiac axis is the
average direction of
spread of depolarization
as seen from the front and
is estimated from QRS
complex in leads I,II and
III
5. Normal axis
QRS complex
predominantly upward
in leads I and II and III;
Still normal if QRS
complex d/w in lead III
Minor degrees of right
and left axis deviation
are within the normal
range
6. Right axis deviation
QRS complex
predominantly d/w in
lead I
If the right ventricle
become hypertrophied, it
will have more effect on
QRS complex than left
ventricle average
depolarization wave swing
towards right
7. Left axis deviation
QRS complex
predominantly d/w in leads
II and III
When the left ventricle
become hypertrophied ,it
exerts more influence on
QRS complex than Rt
ventricle, axis swing to the
left
8. Inferior Changes in leads II, III and aVF
Anteroseptal V1 V2 V3
Anterolateral V4 V5 V6
Extensive Anterior V1 to V6
Lateral I, aVL
Posterior Associated increase in height of
R and upright T wave in V1
(ST depression in V1-V2 )
9.
10. Normal Cardiac Conduction
Cardiac conduction results in
the mechanical beating of the
heart.
Specific waves that appear on
an ECG correspond both to the
mechanical and the electrical
depolarization or repolarization
of a particular area of the
heart.
20. Label the ECG - Review
P – Wave: Atrial Depolarization.
• Can be positive, biphasic, negative.
QRS Complex: Ventricular Depolarization.
• Q – Wave: 1st negative deflection wave before R-Wave.
• R – Wave: The positive deflection wave.
• S – Wave: 1st negative deflection wave after R – wave.
T – Wave: Ventricular Repolarization.
• Can be positive, biphasic, negative.
21. One ECG period or one heartbeat
PR interval (containing P wave and PR segment)
QT interval (containing the QRS complex, ST segment and T wave)
22. Interval Measurement
Time between waves is an important characteristic in
determining a normal heart rhythm (measured in
milliseconds).
An interval outside of the normal duration can be an
indicator of heart problems.
Two key intervals in particular aid
in the interpretation of ECGs.
1. PR interval: Normal is 120 –
200ms
2. QRS interval: Normal is 60 –
100ms
23. ECG tracing showing QT interval
From 12 – lead ECG printout , choose Lead II, V 5 or V 6
QT interval – from the beginning of the QRS complex to the end of
the T wave
Measure at least 3 successive beats, with the maximum interval
taken, in case these three beats differ
24. Reading ECG Squares
Intervals and Timing
Horizontal axis – time:
Each small square = 40
ms
Each block = 200 ms (5
ea. 40 ms squares)
Converting this to a rate in
bpm:
1 min = 60,000 ms, so:
60,000/ms = bpm
– 60,000/600ms = 100
bpm
26. Rate – 6 second Rule
1) Count the # of complexes on a 6 second strip.
2) Multiply by 10 to get approx “bpm”
0 1 2 3 4 5 6 7
Approximately 70bpm
27. ECG Interpretations: Overview
ECG interpretation can be simplified if approached
one step at a time.
Understanding and practicing three basic steps will
aid in quickly and accurately identifying any given
rhythm.
Step 1—Calculate the RATE of an ECG tracing
Step 2—Determine the REGULARITY or irregularity of
a given ECG
Step 3—Analyze the RHYTHM of a given ECG by
describing the relationship between the P waves and
QRS complexes
28. ECG Interpretation: RATE
Rate generally refers to the ventricular rate or R-waves.
Resting rate is typically 60 – 100 bpm.
Focus is placed on the QRS complex.
29. ECG Interpretation: REGULARITY
The consistency of the interval
between each QRS complex.
PR intervals should remain
consistent.
PR interval should be 120-200ms.
The PR interval is the time from
beginning of the P-wave to the
beginning of the QRS complex.
30. ECG Interpretation: RHYTHM
PR ratio is the number of P-waves compared to
QRS complexes.
Every P-wave should have an associated QRS
complex.
32. Normal Sinus Rhythm
Rate 60-100bpm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal
33. Sinus Bradycardia
Rate Less than 60bpm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval
Normal, gradually lengthens with HR
decrease
QRS Width Normal
34. Sinus Tachycardia
Rate Greater than 100bpm, Gradual onset
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal, gradually shortens with HR increase
QRS Width Normal
35. Sinus Arrhythmia
Rate 60-100bpm
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal
36. Sinus Pause/Arrest
Rate Varies
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, except during pause
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal
37. Sinus Node Exit Block
Rate Varies
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, except during dropped beats
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal
38. Sinus Rhythm w/ PAC
(Premature Atrial Contraction)
Rate Depends on underlying sinus rate
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, may be different morphology during PAC
P:QRS Ratio 1:1, associated
PR Interval Normal, varies during PAC
QRS Width Normal
39. Atrial Tachycardia
Rate 100-180bpm, Sudden onset
P-P Regularity Regular
R-R Regularity Regular
P wave Morphology will differ from sinus p-wave
P:QRS Ratio 1:1, associated
PR Interval Interval of ectopic focus will differ from sinus PR
QRS Width
Normal, but can develop aberrant (wide)
complexes
40. Multifocal Atrial Tachycardia
Rate Greater than 100bpm
P-P Regularity Irregularly irregular
R-R Regularity Irregularly irregular
P wave At least 3 different p-wave morphologies
P:QRS Ratio 1:1, associated
PR Interval Varies
QRS Width Normal
41. Atrial Flutter
Atrial Rate
Ventricular Rate
Atrial Rate commonly 250-350bpm
Ventricular Rate will vary with conduction
P-P Regularity Regular
R-R Regularity Usually regular, but may be variable
P wave “Saw-tooth” p-wave morphology
P:QRS Ratio Varies, can be 1:1, 2:1, 3:1, 4:1, etc.
PR Interval Varies
QRS Width Normal
42. Atrial Fibrillation
Rate Varies, ventricular response can be fast or slow
P-P Regularity Chaotic atrial activity
R-R Regularity Irregularly irregular
P wave No discernable p-waves
P:QRS Ratio None
PR Interval None
QRS Width
Normal, but can develop aberrant (wide)
complexes
43. Junctional Rhythm
Rate 40-60bpm
P-P Regularity None, or Regular if antegrade or retrograde
R-R Regularity Regular
P wave Variable (none, antegrade, or retrograde)
P:QRS Ratio None, or 1:1 if antegrade or retrograde
PR Interval None, short, or retrograde
QRS Width Normal
44. Accelerated Junctional Rhythm
Supraventricular Tachycardia (SVT)
Rate
60-100bpm (Accelerated Junctional Rhythm)
Greater than 100bpm (Supraventricular
Tachycardia)
P-P Regularity None, or Regular if antegrade or retrograde
R-R Regularity Regular
P wave Variable (none, antegrade, or retrograde)
P:QRS Ratio None, or 1:1 if antegrade or retrograde
PR Interval None, short, or retrograde
QRS Width Normal
45. Sinus Rhythm w/ PVC
(Premature Ventricular Contraction)
Rate Depends on underlying sinus rate
P-P Regularity Irregular
R-R Regularity Irregular
P wave No P-waves with the PVC
P:QRS Ratio No P-waves with the PVC
PR Interval None
QRS Width Wide complex (>/= 0.12sec).
52. Sinus Rhythm
w/ 1st Degree AV Block
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present, Normal
P:QRS Ratio 1:1, associated
PR Interval Prolonged, > 0.20sec
QRS Width Normal
53. Sinus Rhythm
w/ 2nd Degree AV Block Type I (Wenckebach)
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regularly irregular
P wave Present
P:QRS Ratio Variable; 2:1, 3:2, 4:3, etc
PR Interval Variable, gradually lengthens until dropped
QRS Width Normal
54. Sinus Rhythm
w/ 2nd Degree AV Block Type II
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regularly irregular
P wave Present
P:QRS Ratio Variable; 2:1, 3:2, 4:3, etc
PR Interval Normal for conducted beats
QRS Width Normal
55. Sinus Rhythm
w/ 3rd Degree AV Block (Complete Heart Block)
Atrial Rate
Ventricular Rate
Atrial rate is the underlying rhythm (i.e, Sinus, Atrial Fib,
etc.)Ventricular rate is from the dissociated escape rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio Variable, dissociated
PR Interval Variable, No pattern
QRS Width Normal (Junctional escape rhythm)
Wide (Ventricular escape rhythm)
56. Sinus Rhythm w/ BBB
(Bundle Branch Block)
Rate Depends on the underlying sinus rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Wide (>0.12ms)
57. Atrial Fibrillation with BBB
(Bundle Branch Block)
Rate Depends on the underlying Atrial Fibrillation,
Ventricular rate can be fast or slow.
P-P Regularity Chaotic atrial activity
R-R Regularity Irregularly irregular
P wave Present
P:QRS Ratio None
PR Interval None
QRS Width Wide (>0.12ms)
