ECGs
AFMAMS Resident Orientation
March 26 2012
Lecture Outline
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ECG Basics
Importance of systematically reading ECGs
Rate
Rhythm
Axis
Hypertrophy
Intervals and Segments
Ischemia / Infarction
ECG Basics
• Measurements on ECG paper
Identify ECG Landmarks
Introduction
• Be systematic
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Rate
Rhythm
Axis
Chamber Hypertrophy
• Atrial
• Ventricular
– Intervals
– Ischemia / Infarction
• Read Every ECG the
same way!
How to Determine Rate
• Rhythm Strip
– 10 seconds
– Count QRS
complexes then
multiply by 6
• Count Big Blocks
between QRS
complexes
• 300-150-100-75-6050-43-37
Determining Rhythm
• Look for the P wave
– Leads II and V1
• Present vs. Absent
• Regular vs. Irregular
• Symmetric vs.
Asymmetric
• Normal Sinus
Rhythm is most
common
Normal P wave morphology
• P wave represents atrial activation
• The atria activate from right to left, so the first
half of the P wave usually represents right
atrial activation and the second half
represents the left atrium.
• The sinus node is the usual sight of atrial
activation.
Definition of Sinus Rhythm
• NOT “A P wave before every QRS”
ACTUAL DEFINITION OF SINUS RHYTHM
• Normal P wave axis
• Uniform P wave morphology
• Regular P-P interval
Rhythm
• P waves: normal sinus (NSR),
sinus bradycardia, sinus
tachycardia, multifocal atrial
tachycardia (MAT), atrial
flutter
• No P waves: atrial fibrillation,
junctional rhythm, ventricular
fibrillation, ventricular
tachycardia
• Regular: normal sinus, sinus
bradycardia, sinus tachycardia,
atrial flutter, junctional
rhythm, ventricular
tachycardia
• Irregular: atrial fibrillation,
multifocal atrial tachycardia,
ventricular fibrillation
Normal P wave morphology
• Normal P wave duration: 0.08 – 0.11 seconds
• Normal P wave amplitude: limb leads < 2.5mm;
V1 positive deflection < 1.5mm and negative
deflection < 1mm
• Normal P wave axis: 0-75 degrees
• Normal morphology: upright in I, II, aVF
Normal P wave morphology
• P wave duration (seconds): measured from
the beginning of the P wave to the end of the
P wave.
• Amplitude (mm): measured from the baseline
to the top (or bottom). Positive and negative
deflections are determine separately.
Question: Is this patient in normal sinus rhythm?
Axis
• Refers to the direction of the movement of
depolarization spreads through the heart
• Since left ventricle is the largest and thickest
chamber of the heart it undergoes most
depolarization
• Therefore, normal direction of depolarization
is from middle of the chest towards the left
hip
Axis
• Important in determining
– Prior myocardial infarction
– Ventricular Hypertrophy
– Intraventrcicular Conduction Delay
• Two methods to calculate axis
– Isoelectrical
– Short-cut
Isoelectrical Calculation
• Find the isoelectrical
QRS complex
• Axis is perpendicular to
isoelectrical axis
• Use other leads to
determine if positive or
negative
Short Cut Method
• Look at Lead I and II
• If QRS positive in Leads I
and II
– Normal axis
• If QRS negative in I and
positive in II
– Right Axis Deviation
• If QRS positive in I and
negative in II
– Left Axis Deviation
• If QRS negative in Leads I
and II
– Far Right Axis Deviation
Atrial Abnormalities
• Left Atrial Enlargement
– Terminal negative P wave in lead V1 >1mm deep
and 0.04sec in duration
– Notched P wave with a duration >0.12sec in limb
leads (I, II)
– Seen in: MS, MR, LVH
• Right Atrial Enlargement
– Tall P wave in inferior leads - >2.5mm
– Can be seen in: COPD, PE, Pulmonary HTN
LVH
• Cornell Criteria
– R in AVL + S in V3 >
28mm (>20mm in
females)
• Voltage Criteria
– S in V1 + R in V5/V6 >
35mm
– R in AVL > 11mm
– Largest R in limb leads
>20
• Supporting Criteria
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LAE
LAD
Prolonged QRS
Strain pattern
RVH
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Right axis deviation (>+90)
R V1 >7 mm
R V1 + S V5 or V6 >10 mm
R/S ratio in V1 >1
S/R ratio in V6 >1
Incomplete right bundle branch block
ST-T wave abnormalities ("strain") in inferior leads
Right atrial hypertrophy (P pulmonale)
S1- S2 - S3 pattern (particularly in children
Intervals
• PR interval
• QRS Complex
• QT Interval
The PR interval
• Normal interval: 0.12 – 0.20 seconds in length
• Short PR interval: < or = 0.11 seconds
• Long PR interval: > 0.20 seconds
Pericarditis
• Diffuse ST segment depressions
• PR depression
• Notching of the S wave
Wolf Parkinson White
• Short PR interval
• Wide QRS complex
• Presence of a delta
wave
• ST-T wave changes or
abnormalities
• Clinical association with
paroxysmal tachycardias
QRS Complex
• Normal QRS duration
– 80 – 120 ms
• Widened QRS
– RBBB
– LBBB
– Electrolyte abnormalities
RBBB
• Asynchronous activation of the two ventricles
increases the QRS duration (0.13 sec).
• Terminal forces are rightward and anterior due
the delayed activation of the right ventricle,
• Results in an rsR' pattern in the anteriorposterior lead V1 and a wide negative S wave
in the lead V6 and Lead I
• No significant association with risk factors for
or the presence of ischemic heart disease,
myocardial infarction, or cardiovascular deaths
RBBB Criteria
• QRS > 120 ms
• rSR’ or rsR’ in V1
• Wide S in I, V5 or V6
RBBB
LBBB Criteria
• QRS duration > 120 ms
• QS or rS complex in V1
• RsR’ in V6
• T wave deflection should be opposite QRS
complex (Discordance)
LBBB
QT Interval
• Normal
– Male < 440 ms
– Female < 460 ms
• Calculated
– QTc = QT / RR
• Prolonged
– Electrolytes
– Inherited
• Shortened
– Hypercalcemia
Long QT
Conclusions
• ECGs are a cheap and readily available
diagnostic test
• ECGs provide a tremendous amount of
information
• Properly interpreting ECGs requires a lot of
practice
Second Degree AV Block
• Mobitz Type I
– Progressive prolongation
of the PR interval until a
P wave is blocked
– RR interval containing
the nonconducted P
wave is less than two PP
intervals
– Usually narrow QRS
(block at the level of AV
node)
• Mobitz Type II
– Intermittent
nonconducted P waves
– Constant PR interval
– RR interval containing
the nonconducted P
wave is equal to two PP
intervals
– Often a wide QRS
complex
Third Degree AV Block
• Atrial and ventricular rhythms are
independent of one another
• PP and RR intervals are constant
• Atrial rate > ventricular rate