This document provides an overview of electrocardiogram (ECG) interpretation. It begins by outlining the learning objectives, which are to recognize normal sinus rhythm, common rhythm disturbances on a 3-lead ECG, and how to interpret a myocardial infarction on a 12-lead ECG. The document then reviews ECG basics, how to analyze rhythms, defines normal sinus rhythm, and discusses common cardiac dysrhythmias and how to diagnose a myocardial infarction. It provides examples of various normal and abnormal rhythms.
crème de la crème basics to understand electrocardiographic analysis in an easy & simple way with some specifications to its use in Emergency medicine/clinical toxicology practice.
crème de la crème basics to understand electrocardiographic analysis in an easy & simple way with some specifications to its use in Emergency medicine/clinical toxicology practice.
An electrocardiogram (ECG or EKG) records the electrical signal from your heart to check for different heart conditions. Electrodes are placed on your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer
ECG is very important tool in diagnosis of various cardiovascular diseases ,it is important for every one dealing with cardiac patients to be aware about the basic information of electocardiogram, so my 1st lecture focused on conductiong system of the heart , the generation of deflection in ECG , and normal morphology of its waveform, and lastly focus oh method to determine heart rate and cadiac axis .
An electrocardiogram (ECG or EKG) records the electrical signal from your heart to check for different heart conditions. Electrodes are placed on your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer
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2. Marc Imhotep Cray, M.D.
Learning Objectives
2
• To recognize normal rhythm of heart
“Normal Sinus Rhythm (NSR)”
• To recognize 15 most common rhythm
disturbances (3-Lead ECG)
• To Interpret an acute myocardial infarction on a
12-Lead ECG, including: anterior, lateral,
anterolateral and inferior wall MIs
3. Marc Imhotep Cray, M.D.
Topics Outline
3
• ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Cardiac Dysrhythmias
• Diagnosing a Myocardial Infarction
4. Marc Imhotep Cray, M.D.
Features include:
Regular rhythm at 60-100 bpm
Normal P wave morphology and axis
(upright in I and II, inverted in aVR)
Narrow QRS complexes (< 100 ms
wide)
Each P wave is followed by a QRS
complex
The PR interval is constant
Review of ECG Basics
Normal ECG Morphology
5. Marc Imhotep Cray, M.D.
EKG Paper
Horizontal axis of EKG paper
records time, w black marks at
top indicating 3 second intervals
o Each second is marked by 5
large grid blocks thus each
large block equals 0.2 second
Vertical axis records EKG
amplitude (voltage)
o Two large blocks equal 1
millivolt (mV)
o Each small block equals 0.1 Mv
Within large blocks are 5 small
blocks each representing 0.04
seconds
ECG tracings are recorded on grid paper
6. Marc Imhotep Cray, M.D.
ECG Paper cont’d.
6
• Horizontally
– One small box - 0.04 s
– One large box - 0.20 s
• Vertically
– One large box - 0.5 mV
7. Marc Imhotep Cray, M.D.
ECG Paper cont’d.
7
• Every 3 seconds (15 large boxes) is marked by a
vertical line
• This Helps When Calculating Heart Rate
Note: Strip above and those that follow are not
marked but all are 6 seconds long
3 sec 3 sec
8. Marc Imhotep Cray, M.D.
Autorhythmicity
• Some heart cells (SA, AV node and Purkinje) show
automaticity ability to generate a heart beat
– These cells have an intrinsic rhythmicity which generates a
pacemaker potential
• Heart does not require nerve or hormonal input to
beat
– Heart transplant patients nerves are severed but heart
beats on
9. Marc Imhotep Cray, M.D.
Normal Impulse Conduction
9
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
10. Marc Imhotep Cray, M.D.
Impulse Conduction & the ECG
10
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
12. Marc Imhotep Cray, M.D.
PR Interval
12
Atrial depolarization + delay in AV
junction (AV node/Bundle of His)
delay allows time for atria to
contract before ventricles contract
13. Marc Imhotep Cray, M.D.
Pacemakers of Heart
13
• 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
16. Marc Imhotep Cray, M.D.
Step 1: Calculate Rate
16
Option 1 (6-second x 10 method)
• Count # of R waves in a 6 second
rhythm strip, then multiply by 10
Interpretation? 9 x 10 = 90 bpm
3 sec 3 sec
17. Marc Imhotep Cray, M.D.
Step 1: Calculate Rate cont’d.
17
Option 2 (300, 150, 100, 75, 60, 50 method)
– Find a R wave that lands on a bold line
– Count number of large boxes to next R wave
– If second R wave is 1 large box away rate is 300,
2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc. (cont.)
R wave
19. Marc Imhotep Cray, M.D.
Step 2: Determine regularity
19
• Look at 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
R R
20. Marc Imhotep Cray, M.D.
Step 3: Assess the P waves
20
• 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?
Interpretation? Normal P waves w 1 P wave for every QRS
25. Marc Imhotep Cray, M.D.
Basic Rhythm Analysis
• Rate – too fast or too slow?
• Rhythm – regular or irregular?
• Is there a normal looking QRS? Is it wide
or narrow?
• Are P waves present?
• What is relationship of P waves to QRS
complex?
26. Marc Imhotep Cray, M.D.
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
• A dysrhythmia
27. Marc Imhotep Cray, M.D.
Normal Sinus Rhythm
27
12 lead ECG in sinus rhythm
28. Marc Imhotep Cray, M.D.
Arrhythmia Formation
28
Arrhythmias can arise from problems in:
• Sinus node
• Atrial cells
• AV junction
• Ventricular cells
29. Marc Imhotep Cray, M.D.
SA Node Problems
29
SA Node can:
• fire too slow
• fire too fast
Sinus Bradycardia
Sinus Tachycardia*
*Sinus Tachycardia may be an appropriate response
to stress.
30. Marc Imhotep Cray, M.D.
Atrial Cell Problems
30
Atrial cells can:
• fire occasionally from a focus Premature
Atrial Contractions (PACs)
• fire continuously due to a looping re-
entrant circuit Atrial Flutter
31. Marc Imhotep Cray, M.D.
Atrial Cell Problems
25
Atrial cells can also:
• fire continuously from multiple foci Atrial Fibrillation
or
• fire continuously due to multiple micro re-entrant
“wavelets” Atrial Fibrillation
32. Marc Imhotep Cray, M.D.
Key Scientific Point
32
Atrial tissue
Multiple micro re-entrant
“wavelets” refers to wandering
small areas of activation which
generate fine chaotic impulses
Colliding wavelets can, in turn,
generate new foci of activation
33. Marc Imhotep Cray, M.D.
AV Junctional Problems
33
AV junction can:
• fire continuously due to a looping re-entrant circuit
Paroxysmal Supraventricular Tachycardia (PSVT)
• block impulses coming from SA Node AV Junctional
Blocks
34. Marc Imhotep Cray, M.D.
Ventricular Cell Problems
34
Ventricular cells can:
• fire occasionally from 1 or more foci Premature
Ventricular Contractions (PVCs)
• fire continuously from multiple foci Ventricular
Fibrillation (VF)
• fire continuously due to a looping re-entrant circuit
Ventricular Tachycardia (VT)
35. Marc Imhotep Cray, M.D.
Analyzing a Rhythm Table
Component Characteristics
Rate bpm is commonly ventricular rate. If atrial and ventricular rates
differ, as in a 3rd-degree block, measure both rates. Normal: 60–100
bpm. Slow (bradycardia): <60 bpm. Fast (tachycardia): >100 bpm
Regularity Measure R-R intervals and P-P intervals. Regular: Intervals consistent.
Regularly irregular: Repeating pattern. Irregular: No pattern
P Waves If present: Same in size, shape, position? Does each QRS have a P
wave? Normal: Upright (positive) and uniform
PR Interval Constant: Intervals are same. Variable: Intervals differ.
Normal: 0.12–0.20 sec and constant
QRS Interval Normal: 0.06–0.10 sec. Wide: >0.10 sec. None: Absent
QT Interval Beginning of R wave to end of T wave Varies with HR. Normal: Less
than half the R-R interval
Dropped
beats
Occur in AV blocks. Occur in sinus arrest.
39. Marc Imhotep Cray, M.D.
Rhythm #1
39
30 bpm• Rate?
• Regularity? regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s
• QRS duration?
Interpretation? Sinus Bradycardia
40. Marc Imhotep Cray, M.D.
Sinus Bradycardia
40
• Deviation from NSR
- Rate < 60 bpm
41. Marc Imhotep Cray, M.D.
Sinus Bradycardia cont’d.
41
• Etiology: SA node is depolarizing slower
than normal, impulse is conducted normally
(i.e. normal PR and QRS interval)
42. Marc Imhotep Cray, M.D.
Rhythm #2
42
130 bpm• Rate?
• Regularity? regular
normal
0.08 s
• P waves?
• PR interval? 0.16 s
• QRS duration?
Interpretation? Sinus Tachycardia
43. Marc Imhotep Cray, M.D.
Sinus Tachycardia
43
• Deviation from NSR
- Rate > 100 bpm
44. Marc Imhotep Cray, M.D.
Sinus Tachycardia cont’d.
44
• 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.
45. Marc Imhotep Cray, M.D.
Sinus Arrest
45
• Etiology: SA node fails to depolarize and no
compensatory mechanisms take over
• Sinus arrest is usually a transient pause in sinus
node activity
47. Marc Imhotep Cray, M.D.
Rhythm #3
47
70 bpm• Rate?
• Regularity? occasionally irreg.
2/7 different contour
0.08 s
• P waves?
• PR interval? 0.14 s (except 2/7)
• QRS duration?
Interpretation? NSR w PAC
48. Marc Imhotep Cray, M.D.
Premature Atrial Contractions
(PACs)
48
• Deviation from NSR
– These ectopic beats originate in atria (but not
in SA node) therefore, contour of P wave, PR
interval, and timing are different than a
normally generated pulse from SA node
49. Marc Imhotep Cray, M.D.
PAC cont’d.
49
• Etiology: Excitation of an atrial cell forms an
impulse that is then conducted normally
through AV node and ventricles
50. Marc Imhotep Cray, M.D.
Key Scientific Point
50
• When an impulse originates anywhere in atria
(SA node, atrial cells, AV node, Bundle of His)
and then is conducted normally through
ventricles QRS will be narrow (0.04 - 0.12 s)
51. Marc Imhotep Cray, M.D.
Rhythm #4
51
60 bpm• Rate?
• Regularity? occasionally irreg.
none for 7th QRS
0.08 s (7th wide)
• P waves?
• PR interval? 0.14 s
• QRS duration?
Interpretation? Sinus Rhythm with 1 PVC
52. Marc Imhotep Cray, M.D.
Premature ventricular
contractions (PVCs)
52
• Deviation from NSR
– Ectopic beats originate in ventricles resulting
in wide and bizarre QRS complexes
– When there are more than 1 premature beats
and they look alike, called “uniform”
– When they look different, called “multiform”
53. Marc Imhotep Cray, M.D.
PVCs cont’d.
53
• Etiology: One or more ventricular cells are
depolarizing and impulses are abnormally
conducting through ventricles
54. Marc Imhotep Cray, M.D.
Key Scientific Point
54
• When an impulse originates in a ventricle,
conduction through ventricles will be
inefficient and QRS will be wide and bizarre
55. Marc Imhotep Cray, M.D.
Ventricular Conduction
55
Normal
Signal moves rapidly
through ventricles
Abnormal
Signal moves slowly
through ventricles
58. Marc Imhotep Cray, M.D.
Atrial Fibrillation cont’d.
58
• Deviation from NSR
– No organized atrial depolarization so no normal P
waves (impulses are not originating from SA node)
– Atrial activity is chaotic (resulting in an irregularly
irregular rate)
– Common, affects 2-4%, up to 5-10% if > 80 years old
59. Marc Imhotep Cray, M.D.
Atrial Fibrillation cont’d.
59
• Etiology: due to multiple re-entrant wavelets
conducted betw R & L atria and impulses are formed
in a totally unpredictable fashion
• AV node allows some of impulses to pass through at
variable intervals (so rhythm is irregularly irregular)
61. Marc Imhotep Cray, M.D.
Atrial Flutter
61
• Deviation from NSR
– No P waves Instead flutter waves (note
“sawtooth” pattern) are formed at a rate of 250
- 350 bpm
– Only some impulses conduct through AV node
(usually every other impulse)
62. Marc Imhotep Cray, M.D.
Atrial Flutter cont’d.
62
• Etiology: Reentrant pathway in right atrium with
every 2nd, 3rd or 4th impulse generating a QRS
(others are blocked in AV node as node repolarizes)
63. Marc Imhotep Cray, M.D.
Rhythm #7
63
74 148 bpm• Rate?
• Regularity? Regular regular
Normal none
0.08 s
• P waves?
• PR interval? 0.16 s none
• QRS duration?
Interpretation? Paroxysmal Supraventricular
Tachycardia (PSVT)
64. Marc Imhotep Cray, M.D.
Paroxysmal Supraventricular
Tachycardia (PSVT)
64
• Deviation from NSR
–heart rate suddenly speeds up, often
triggered by a PAC (not seen here) and
P waves are lost
65. Marc Imhotep Cray, M.D.
AV Nodal Blocks
65
• 1st Degree AV Block
• 2nd Degree AV Block, Type I
• 2nd Degree AV Block, Type II
• 3rd Degree AV Block
66. Marc Imhotep Cray, M.D.
Rhythm # 8
66
60 bpm• Rate?
• Regularity? regular
normal
0.08 s
• P waves?
• PR interval? 0.36 s
• QRS duration?
Interpretation? 1st Degree AV Block
67. Marc Imhotep Cray, M.D.
1st Degree AV Block
67
• Deviation from NSR
–PR Interval > 0.20 s
68. Marc Imhotep Cray, M.D.
1st Degree AV Block cont’d.
68
• Etiology: Prolonged conduction delay in AV
node or Bundle of His
69. Marc Imhotep Cray, M.D.
Rhythm # 9
69
50 bpm• Rate?
• Regularity? regularly irregular
nml, but 4th no QRS
0.08 s
• P waves?
• PR interval? lengthens
• QRS duration?
Interpretation? 2nd Degree AV Block, Type I
70. Marc Imhotep Cray, M.D.
2nd Degree AV Block, Type I
Mobitz type I (Wenckebach)
70
• Deviation from NSR
– PR interval progressively lengthens, then impulse
is completely blocked (P wave not followed by
QRS)
71. Marc Imhotep Cray, M.D.
2nd Degree AV Block, Type I cont’d.
71
• Etiology: Each successive atrial impulse
encounters a longer and longer delay in AV
node until one impulse (usually 3rd or 4th)
fails to make it through AV node
72. Marc Imhotep Cray, M.D.
Rhythm # 10
72
40 bpm• Rate?
• Regularity? regular
nml, 2 of 3 no QRS
0.08 s
• P waves?
• PR interval? 0.14 s
• QRS duration?
Interpretation? 2nd Degree AV Block, Type II
73. Marc Imhotep Cray, M.D.
2nd Degree AV Block, Type II
Mobitz type II
73
• Deviation from NSR
– Occasional P waves are completely blocked (P
wave not followed by QRS)
– Progressive lengthening of PR interval until a QRS
is dropped
– Consistent ratio of conducted to dropped QRS
complexes
NB: Requires a pacemaker
74. Marc Imhotep Cray, M.D.
Rhythm #11
74
40 bpm• Rate?
• Regularity? regular
no relation to QRS
wide (> 0.12 s)
• P waves?
• PR interval? none
• QRS duration?
Interpretation? 3rd Degree AV Block
75. Marc Imhotep Cray, M.D.
3rd Degree AV Block
75
• Deviation from NSR
– P waves are completely blocked in AV junction
QRS complexes originate independently from
below junction
– Complete dissociation between atrial and
ventricular rates
NB: Requires a pacemaker
76. Marc Imhotep Cray, M.D.
3rd Degree AV Block cont’d.
76
• Etiology: There is complete block of conduction in
AV junction atria and ventricles form impulses
independently of each other
• Without impulses from atria, ventricles own
intrinsic pacemaker kicks in at around 30 - 45 bpm
77. Marc Imhotep Cray, M.D.
Remember
77
• When an impulse originates in a ventricle, conduction
through ventricles will be inefficient and QRS will be
wide and bizarre
78. Marc Imhotep Cray, M.D.
#12 Ventricular Tachycardia
78
• Ventricular cells fire continuously due to a looping re-entrant circuit
• Rate usually regular, 100 - 250 bpm
• P wave: may be absent, inverted or retrograde
• QRS: complexes bizarre, > .12
• Rhythm: usually regular
79. Marc Imhotep Cray, M.D.
#13 Ventricular Fibrillation
79
• Rhythm: irregular-coarse or fine, wave form varies in size & shape
• Fires continuously from multiple foci
• No organized electrical activity
• No cardiac output
• Causes: MI, ischemia, untreated VT, underlying CAD, acid base
imbalance, electrolyte imbalance, hypothermia etc.
80. Marc Imhotep Cray, M.D.
#14 Asystole
80
• Ventricular standstill, no electrical activity, no cardiac output
– no pulse!
• Cardiac arrest, may follow VF or PEA (Pulseless electrical
activity)
• Remember! No defibrillation with Asystole
• Rate: absent due to absence of ventricular activity
Occasional P wave may be identified
81. Marc Imhotep Cray, M.D.
#15 Idioventricular Rhythm
81
• Escape rhythm (safety mechanism) to prevent vent. standstill
• HIS/purkinje system takes over as heart’s pacemaker
• Treatment: pacing
• Rhythm: regular
• Rate: 20-40 bpm
• P wave: absent
• QRS: > .12 seconds (wide and bizarre)
83. Marc Imhotep Cray, M.D.
Diagnosing a myocardial infarction
83
To Dx a MI you need to go beyond looking at a rhythm
strip and obtain a 12-Lead ECG
Rhythm Strip
84. Marc Imhotep Cray, M.D.
The 12-Lead ECG
84
• 12-Lead ECG sees heart from 12 different views helps you
see what is happening in different portions of heart
– rhythm strip is only 1 of these 12 views
12 lead ECG in sinus rhythm
85. Marc Imhotep Cray, M.D.
Which coronary artery?
Site of infarct can be determined by correlating ECG
findings w knowledge of coronary circulation
o However, nml coronary vasculature varies widely from
individual to individual so only possible to make
generalizations
Idea is you should be able to look at a 12 lead ECG
pattern of ischemia or infarction and predict
coronary lesion location that will show at cardiac
catheterization
86. Two main coronary arteries are right coronary artery
and left anterior descending coronary artery
Tao Le T and Bhushan V, Cardiovascular, In: First Aid for the USMLE Step 1 2017.
New York, NY: McGraw-Hill ,2017; 271.
SA and AV nodes are supplied
by branches of RCA
• Infarct may cause nodal
dysfunction (bradycardia or
heart block)
Right-dominant circulation
(85%) = PDA arises from RCA
Left-dominant circulation
(8%) = PDA arises from LCX
Codominant circulation (7%)
= PDA arises from both LCX
and RCA
Coronary artery occlusion
most commonly in LAD
Coronary blood flow peaks in
early diastole
87. Taylor GJ. 150 practice ECGs: Interpretation and Review, 3rd ed. Malden, Mass: Blackwell Publishing, 2006.
Correlating ECG findings w knowledge of coronary circulation
89. Marc Imhotep Cray, M.D.
The 12-Leads
89
12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)
90. Marc Imhotep Cray, M.D.
Views of the Heart
90
Some leads get a good view of:
Anterior portion of heart
Lateral portion of heart
Inferior portion of heart
91. Marc Imhotep Cray, M.D.
Where do you see ST-T wave changes for
following areas of ischemia or infarction?
Diagram showing the contiguous leads in same color
92. Marc Imhotep Cray, M.D.
ST Elevation
92
• One way to diagnose an
acute MI is to look for
elevation of ST segment
93. Marc Imhotep Cray, M.D.
ST Elevation cont’d.
93
• Elevation of ST segment
(greater than 1 small box)
in 2 leads is consistent w a
myocardial infarction
94. Marc Imhotep Cray, M.D.
Anterior View of Heart
94
• Anterior portion of heart is best viewed
using leads V1- V4
95. Marc Imhotep Cray, M.D.
Anterior Myocardial Infarction
95
• If you see changes in leads V1 - V4 that are
consistent w a MI you can conclude
that it is an anterior wall myocardial
infarction
96. Marc Imhotep Cray, M.D.
Putting it all Together
96
Do you think this person is having a MI If so, where?
97. Marc Imhotep Cray, M.D.
Interpretation
97
Yes, this person in previous slide is having an
acute anterior wall myocardial infarction
98. Marc Imhotep Cray, M.D.
Other MI Locations
98
Now that you know where to look for an anterior
wall MI let’s look at how you would determine if
MI involves lateral wall or inferior wall of heart
99. Marc Imhotep Cray, M.D.
Other MI Locations
99
Remember 12-leads of ECG look at different portions of heart
– limb and augmented leads “see” electrical activity moving inferiorly (II, III
and aVF), to left (I, aVL) and to right (aVR)
– Whereas, precordial leads “see” electrical activity in posterior to anterior
direction
Limb Leads Augmented Leads Precordial Leads
100. Marc Imhotep Cray, M.D.
Other MI Locations
100
• Now, using these 3 diagrams let’s figure where to
look for a lateral wall and inferior wall MI
Limb Leads Augmented Leads Precordial Leads
101. Marc Imhotep Cray, M.D.
Anterior MI
101
• Remember anterior portion of the heart is best
viewed using leads V1- V4
Limb Leads Augmented Leads Precordial Leads
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Lateral MI
102
• So what leads do you think lateral portion of
heart is best viewed?
Limb Leads Augmented Leads Precordial Leads
Leads I, aVL, and V5- V6
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Inferior MI
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Now how about inferior portion of heart?
Limb Leads Augmented Leads Precordial Leads
Leads II, III and aVF
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Putting it all Together
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Now, where do you think this person is having a MI?
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Inferior Wall MI
105
This is an inferior MI. Note ST elevation in leads II, III
and aVF
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Anterolateral MI
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This person’s MI involves both the anterior wall (V2-V4) and
lateral wall (V5-V6, I, and aVL)!
108. Marc Imhotep Cray, M.D.
Next Module:
Reading 12-Lead ECGs
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Best way to read 12-lead ECGs is to develop a step-by-
step approach (just as we did for analyzing a rhythm
strip)
In next Module we present a 6-step and 9-step approaches:
1. Calculate Rate
2. Determine Rhythm
3. Determine QRS axis
4. Calculate Intervals
5. Assess for Hypertrophy
6. Look for evidence of Infarction
109. See next slide for links to tools and resources for further study.
THE END
110. Marc Imhotep Cray, M.D.
Companion study tools
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Video Playlist:
ECG Interpretation
Strong Medicine ECG Video Edu. , Dr. Eric Strong
Reading:
Olivieri , B et al. Ch. 28 ECG (Pgs. 820-28). In: USMLE Step 1
Secrets 3rd. Ed. (Eds. Brown TA and Shah SJ) Saunders, 2013.
ECG eBook:
Shade B. Pocket ECGs: A Quick Information Guide. New York, NY:
McGraw-Hill, 2008. (A good one for beginners.)