An ECG provides a representation of the heart's electrical activity during each cardiac cycle. It displays distinct waveforms that can provide insight into a patient's cardiac pathophysiology. The ECG paper displays time and voltage measurements to analyze rate, regularity, P waves, PR interval, and QRS duration in order to identify normal sinus rhythm or potential arrhythmias originating from problems in the sinus node, atria, AV node, or ventricles. Arrhythmias can cause the heart to beat too slowly, too quickly, or irregularly compared to normal sinus rhythm.

2. What is an ECG?
The electrocardiogram (ECG) is a representation of
the electrical events of the cardiac cycle.
Each event has a distinctive waveform, the study
of which can lead to greater insight into a patient’s
cardiac pathophysiology.

3. The 12-Leads
The 12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)
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5. The ECG Paper
• Horizontally
– One small box - 0.04 s
– One large box - 0.20 s
– 5 Large squares = 1 second
• Vertically
– One large box - 0.5 mV
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7. Anatomy of Heart Conduction and ECG
signal

9. Pacemakers of the Heart
• SA Node - Dominant
pacemaker with an
intrinsic rate of 60 - 100
beats/minute.
• AV Node - Back-up
pacemaker with an
intrinsic rate of 40 - 60
beats/minute.
• Ventricular cells - Back-up
pacemaker with an
intrinsic rate of 20 - 45
bpm.

10. Rhythm Analysis
HOW TO ANALYSE THE RHYTHM?
• Step 1: Calculate rate.
• Step 2: Determine regularity.
• Step 3: Assess the P waves.
• Step 4: Determine PR interval.
• Step 5: Determine QRS duration.
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11. Step 1: Calculate Rate
1)Count the number large squares R wave
between two consecutive “R” waves
then devide the result by 300 → For regular H.R
i.E 300/4 = 75bpm
2) Count the number of “R” waves in 6 seconds strip(30 large squares) then multiply
the result by 10 → For irregular H.R
i.E 10×12=120bpm
Option 3
– Find a R wave that lands on a bold line.
– Count the # of large boxes to the next R wave. If the second R wave is 1 large box away
the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc.
– Memorize the sequence:
300 - 150 - 100 - 75 - 60 - 50
•
•
R-R interval is ventricular rate
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the same but not always

12. Step 2: Determine regularity
R
R
• Look at the R-R distances (using a caliper or markings on a
pen or paper).
• Regular (are they equidistant apart)? Occasionally
irregular? Regularly irregular? Irregularly irregular?
Interpretation?
Regular
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13. Step 3: Assess the P waves
• Are there P waves?
• Do the P waves all look alike?
• Do the P waves occur at a regular rate?
• Is there one P wave before each QRS?
Normal P waves with 1 P
Interpretation?
wave for every QRS
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14. Step 4: Determine PR interval
• Normal: 0.12 - 0.20 seconds.
(3 - 5 boxes)
Interpretation?
0.12 seconds
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15. Step 5: QRS duration
• Normal: 0.04 - 0.12 seconds.
(1 - 3 boxes)
Interpretation?
0.08 seconds

16. Rhythm Summary
• Rate
• Regularity
• P waves
• PR interval
• QRS duration
Interpretation?
90-95 bpm
regular
normal
0.12 s
0.08 s
Normal Sinus Rhythm
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17. NSR Parameters
• Rate
60 - 100 bpm
• Regularity
regular
• P waves
normal
• PR interval
0.12 - 0.20 s
• QRS duration
0.04 - 0.12 s
Any deviation from above is sinus tachycardia, sinus
bradycardia or an arrhythmia
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18. Arrhythmia Formation
Arrhythmias can arise from problems in the:
•Sinus node
•Atrial cells
•AV junction
•Ventricular cells
– AN ABNORMALITY OF THE RHYTHM OR RATE OF
THE HEARTBEAT CALLED ARRHYTHMIA CAUSED BY
DISTURBENCE IN THE ELECTRICAL IMPULSES IN THE
HEART
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19. SA Node Problems
The SA Node can:
• fire too slow
• fire too fast
Sinus Bradycardia
Sinus Tachycardia
Sinus Tachycardia may be an appropriate
response to stress.
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20. Sinus Bradycardia Rhythm #1
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
30 bpm
regular
normal
0.12 s
0.10 s
Sinus Bradycardia
SA node is depolarizing slower than normal, impulse is conducted
normally (i.e. normal PR and QRS interval).

21. Sinus Tachycardia Rhythm #2
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
130 bpm
regular
normal
0.16 s
0.08 s
Sinus Tachycardia
Etiology: SA node is depolarizing faster than normal, impulse is
conducted normally.
Remember: sinus tachycardia is a response to physical or psychological
stress, not a primary arrhythmia.

22. Atrial Cell Problems
Atrial cells can:
• fire occasionally from a
focus
Premature Atrial
Contractions (PACs)
• fire continuously due to a
looping re-entrant circuit
Atrial Flutter
• Atrial cells can also:
• fire continuously from
multiple foci
or
Atrial Fibrillation
• fire continuously due to
multiple micro reentrant “wavelets”
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23. Premature Atrial Contractions Rhythm #3
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
70 bpm
occasionally irreg.
2/7 different contour
0.14 s (except 2/7)
0.08 s
NSR with Premature
Atrial Contractions

24. Premature Atrial Contractions
• Deviation from NSR
– These ectopic beats originate in the atria (but not
in the SA node), therefore the contour of the P
wave, the PR interval, and the timing are
different than a normally generated pulse from
the SA node.
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25. Atrial Fibrillation Rhythm #4
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
100 bpm
irregularly irregular
none
none
0.06 s
Atrial Fibrillation
Impulses take Multiple, Chaotic, Random pathways through atria

26. Atrial Flutter Rhythm #5
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
70 bpm
regular
flutter waves
none
0.06 s
Atrial Flutter
Impulses take a circular course around the atria, setting up a flutter
waves

27. AV Junctional Problems
The AV junction can:
• fire continuously due
to a looping re-entrant
circuit
Paroxysmal
Supraventricular
Tachycardia
• block impulses coming AV Junctional Blocks
from the SA Node
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28. Paroxysmal Supraventricular Tachycardia
Rhythm #6
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
74 148 bpm
Regular  regular
Normal  none
0.16 s  none
0.08 s
(PSVT)
Impulses recycle repeatedly in the AV node ,
There are several types of PSVT but all originate above the
ventricles (therefore the QRS is narrow).

29. 1st Degree AV Block Rhythm #7
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
•Interpretation?
60 bpm
regular
normal
0.36 s Prolonged
0.08 s
1st Degree AV Block
Impulse conduction is slowed at AV node for a fixed interval

30. 2nd Degree AV Block, Type I Rhythm #8
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
50 bpm
regularly irregular
nl, but 4th no QRS
lengthens
0.08 s
2nd Degree AV Block, Type I
Impulse conduction is slowed at AV node, until one sinus impulse is
completely blocked and QRS complex fail to follow

31. 2nd Degree AV Block, Type II Rhythm #9
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
40 bpm
regular
nl, 2 of 3 no QRS
0.14 s
0.08 s
2nd Degree AV Block, Type II
Site of the block is often below the AV node at bundle of His or bundle
branches ( 2 dropped beats)

32. 3rd Degree AV Block Rhythm #10
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
40 bpm
regular
no relation to QRS
none
wide (> 0.12 s)
3rd Degree AV Block
Injury or damaged to cardiac conduction system

33. Ventricular Cell Problems
Ventricular cells can:
• fire occasionally from 1 Premature Ventricular
or more foci
Contractions (PVCs)
• fire continuously from
multiple foci
Ventricular Fibrillation
• fire continuously due to Ventricular Tachycardia
a looping re-entrant
circuit
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34. Sinus Rhythm with 1 PVC Rhythm #11
•
•
•
•
•
Rate?
Regularity?
P waves?
PR interval?
QRS duration?
Interpretation?
60 bpm
occasionally irreg.
none for 7th QRS
0.14 s
0.08 s (7th wide)
Sinus Rhythm with 1
PVC
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35. PVCs
• Deviation from NSR
– Ectopic beats originate in the ventricles resulting in wide
and bizarre QRS complexes.
– When there are more than 1 premature beats and look
alike, they are called “uniform”. When they look
different, they are called “multiform”.
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36. Ventricular Tachycardia Rhythm #12
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
160 bpm
regular
none
none
wide (> 0.12 sec)
Ventricular Tachycardia
Impulse conduction slowed around ventricular injury , or ischemia

37. Ventricular Tachycardia
• Etiology: There is a re-entrant pathway looping in a
ventricle (most common cause).
• Ventricular tachycardia can sometimes generate
enough cardiac output to produce a pulse; at other
times no pulse can be felt.
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38. Ventricular Fibrillation Rhythm #13
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
none
irregularly irreg.
none
none
wide, if recognizable
Ventricular Fibrillation
Ventricles consist of areas of normal myocardium alternating with areas of ischemic,
injured, or infarcted myocardium, leading to chaotic pattern of ventricular
depolarization

39. Ventricular Fibrillation
Coarse VF
Fine VF
• Etiology: The ventricular cells are excitable and
depolarizing randomly.
• Rapid drop in cardiac output and death occurs if not
quickly reversed
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40. Pulseless electrical activity Rhythm #13
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation?
none
Regular
present
Normal
0.10
PEA
Any organized rhythm without detectable pulse is “PEA”
Cardiac conduction impulses occur in organized pattern, but this fails to produce
myocardial contraction

41. Asystole Rhythm # 14
•Rate: no ventricular activity seen or ≤6/min; so-called “Pwave asystole” occurs with only atrial
impulses present to form P waves
• Rhythm: no ventricular activity seen; or ≤6/min
• PR: cannot be determined; occasionally P wave seen, but
by definition R wave must be absent
• QRS complex: no deflections seen that are consistent with
a QRS complex
Asystole: agonal complexes too slow to make this rhythm

42. Diagnosing a MI
To diagnose a myocardial infarction you need to go
beyond looking at a rhythm strip and obtain a 12-Lead
ECG.
12-Lead
ECG
Rhythm
Strip
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43. ST Elevation
One way to diagnose
an acute MI is to look
for elevation of the ST
segment.
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44. ST Elevation (cont)
Elevation of the
ST segment
(greater than 1
small box) in 2
leads is
consistent with a
myocardial
infarction.
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45. ECG Changes : Ischemia
•
•
•
•
T-wave inversion ( flipped T)
ST segment depression
T wave flattening
Biphasic T-waves
Baseline

2004 Anna Story
45

46. ECG Changes: Injury
• ST segment elevation of greater than 1mm in at least 2 contiguous
leads
• Heightened or peaked T waves
• Directly related to portions of myocardium rendered electrically
inactive
Baseline

2004 Anna Story
46

47. 
2004 Anna Story
47