ECG interpretations

Dr. Aly Abo-Elhoda

ECG Interpretation
What is your approach to reading an ECG?
Rate
Rhythm
Axis
Hypertrophy
Intervals
P wave
QRS complex
ST segment T wave
 Normal Impulse Conduction
Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

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Impulse Conduction & the ECG
Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

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LIMB LEADS

Bipolar leads
I II III

Augment leads
Avr Avl Avf

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CHEST LEADS
6 UNIPOLAR
LEADS
V1
V2
V3
V4
V5
V6

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 The ECG Paper
Horizontally
One small box - 0.04 s
One large box - 0.20 s
Vertically
One large box - 1 mV

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The ECG Paper (cont)
3 sec 3 sec

Every 3 seconds (15 large boxes) is

marked by a vertical line.
This helps when calculating the
heart rate.
NOTE: the following strips are not
marked but all are 6 seconds long.
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The PQRST

P wave - Atrial
depolarization

QRS - Ventricular
depolarization
T wave - Ventricular
repolarization
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 Rate
Square Counting: 300-150-100-75-60-50-42A

Count QRS in 10 second rhythm strip x 6

 Rhythm
Are P waves present?
Is there a P wave before every QRS complex
and a QRS complex after every P wave?

Are the P waves and QRS complexes regular?

Is the PR interval constant?
 Axis
Left or right axis deviation?
Look at limb leads I and aVF.
Normal: I +, aVF +
LAD: I +, aVF
RAD: I -, aVF +
 Hypertrophy

LVH: S in V1 or V2 + R in V5 or V6 35 mm.

RVH: V1 R/S ratio >1 or V6 S/R ratio >1.

 Intervals
What is the normal PR interval?
0.12 to 0.20 s (3 - 5 small squares).

What is the normal QRS?

< 0.12 s duration (3 small squares).

What is the normal QTc (QT/square root of RR)?

< 0.42 s.
 P Waves
Evaluate the shape, height and width of P
waves.
Multiple morphologies Wandering
pacemaker or Multifocal atrial tachycardia

Notched (M-shaped) P-wave in I and II, >

0.12 s P-mitrale seen in severe left
atrial enlargement
The P-Wave in Detail

The normal P-wave:

Has a smooth contour
Is monophasic in lead II
Is biphasic in lead V1
Has a duration 0f less than 0.12
seconds or 3 small boxes.
 QRS complex
Poor R Wave Progression in V1 to V6: suggests prior
anterior MI

Pathologic Q wave: previous MI. Q wave amplitude

25% or more of the subsequent R wave, OR > 0.04 s in
width + > 2 mm in amplitude in more than one lead
ST segment & T wave
 The PR Interval

Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)

(delay allows time for

the atria to contract
before the ventricles
contract)

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Rhythm Analysis

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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 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?

Interpretation? Normal P waves with 1 P

wave for every QRS
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The P-Wave

The normal P-wave:

Has a smooth contour
Is monophasic in lead II
Is biphasic in lead V1
Has a duration 0f less than 0.12
seconds or 3 small boxes.
P-wave Abnormalities Seen in Lead II
In lead II two types of P-wave
abnormalities can be seen.
Right atrial enlargement is seen as
a taller than normal P-wave(
increased amplitude)
Left atrial enlargement seen as a P-
wave with a notch in it.
Step 4: Determine PR interval

Normal: 0.12 - 0.20 seconds.

(3 - 5 boxes)

Interpretation? 0.12 seconds

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Step 5: QRS

Normal: 0.04 - 0.12 seconds.

(1 - 3 boxes)

Interpretation? 0.08 seconds

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Rhythm Summary

Rate 90-95 bpm

Regularity regular
P waves normal
PR interval 0.12 s
QRS duration 0.08 s
Interpretation? Normal Sinus Rhythm

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 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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Arrhythmias

Sinus Rhythms
Premature Beats

Supraventricular Arrhythmias

Ventricular Arrhythmias

AV Junctional Blocks

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Sinus Rhythms

Sinus Bradycardia
Sinus Tachycardia
Sinus Arrest

Normal Sinus Rhythm

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 Rhythm #1

Rate? 30 bpm
Regularity? regular
P waves? normal
PR interval? 0.12 s
QRS duration? 0.10 s
Interpretation? Sinus Bradycardia
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 Rhythm #2

Rate? 130 bpm

Regularity? regular
P waves? normal
PR interval? 0.16 s
QRS duration? 0.08 s
Interpretation? Sinus Tachycardia
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 Sinus Arrest

Etiology: SA node fails to depolarize and no

compensatory mechanisms take over
Sinus arrest is usually a transient pause in
sinus node activity
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Premature Beats

Premature
Atrial Contractions
(PACs)
Premature Ventricular
Contractions (PVCs)

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 Rhythm #3

Rate? 70 bpm
Regularity? occasionally irreg.
P waves? 2/7 different contour
PR interval? 0.14 s (except 2/7)
QRS duration? 0.08 s
Interpretation? NSR with Premature Atrial Contractions
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 Rhythm #4

Rate? 60 bpm
Regularity? occasionally irreg.
P waves? none for 7th QRS
PR interval? 0.14 s
QRS duration? 0.08 s (7th wide)
Interpretation? Sinus Rhythm with 1 PVC
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 Ventricular Conduction

Normal Abnormal
Signal moves rapidly Signal moves slowly
through the ventricles through the ventricles
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Supraventricular Arrhythmias

Atrial Fibrillation
Atrial Flutter
Paroxysmal Supra Ventricular
Tachycardia (PSVT)
MFAT

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 Rhythm #5

Rate? 100 bpm

Regularity? irregularly irregular
P waves? none
PR interval? none
QRS duration? 0.06 s
Interpretation? Atrial Fibrillation
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 Rhythm #6

Rate? 70 bpm
Regularity? regular
P waves? flutter waves
PR interval? none
QRS duration? 0.06 s
Interpretation? Atrial Flutter
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 Rhythm #7

Rate? 74 148 bpm

Regularity? Regular regular
P waves? Normal none
PR interval? 0.16 s none
QRS duration? 0.08 s
Paroxysmal Supraventricular Tachycardia
Interpretation? (PSVT)
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 Wolf Parkinson White

Delta Wave
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AV Nodal Blocks

1st Degree AV Block

2nd Degree AV Block, Type I
2nd Degree AV Block, Type II
3rd Degree AV Block

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 Rhythm #10

Rate? 60 bpm
Regularity? regular
P waves? normal
PR interval? 0.36 s
QRS duration? 0.08 s
Interpretation? 1st Degree AV Block
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 1st Degree AV Block

Deviation from NSR

PR Interval > 0.20 s

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 Rhythm #11

Rate? 50 bpm
Regularity? regularly irregular
P waves? nl, but 4th no QRS
PR interval? lengthens
QRS duration? 0.08 s
Interpretation? 2nd Degree AV Block, Type I
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 Rhythm #12

Rate? 40 bpm
Regularity? regular
P waves? nl, 2 of 3 no QRS
PR interval? 0.14 s
QRS duration? 0.08 s
Interpretation? 2nd Degree AV Block, Type II
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 Rhythm #13

Rate? 40 bpm
Regularity? regular
P waves? no relation to QRS
PR interval? none
QRS duration? wide (> 0.12 s)
Interpretation? 3rd Degree AV Block
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 Ventricular Fibrillation
Rhythm: irregular-coarse or fine, wave form varies in size
and 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,

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 Ventricular Tachycardia
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

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 IdioVentricular Rhythm
Escape rhythm (safety mechanism) to prevent ventricular
standstill
HIS/purkinje system takes over as the hearts pacemaker
Treatment: pacing
Rhythm: regular
Rate: 20-40 bpm
P wave: absent
QRS: > .12 seconds (wide and bizarre)

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 Right Bundle Branch Block

Right Bundle branch block is seen as 2

R-waves R and R prime with an
intervening S-wave in leads V1,V6 and
lead 1. The s wave is deep in lead 1 and
V1 . This is called R, S, R-prime.

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 Part II

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 Diagnosing a MI
To diagnose a myocardial infarction you
need to go beyond looking at a rhythm
strip and obtain a 12-Lead ECG.

Rhythm
Strip
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 The 12-Lead ECG

The 12-Lead ECG sees the heart

from 12 different views.
Therefore, the 12-Lead ECG helps
you see what is happening in
different portions of the heart.
The rhythm strip is only 1 of these
12 views.

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 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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Views of the Heart
Lateral portion
of the heart
Some leads get
a good view of
the:

Anterior portion
of the heart

Inferior portion
of the heart 56
ST Elevation

One way to
diagnose an
acute MI is to
look for
elevation of
the ST
segment.

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 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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 Anterior View of the Heart

The anterior portion of the heart is best

viewed using leads V1- V4.

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Anterior Myocardial Infarction

If you see changes in leads V1 -

V4 that are consistent with a
myocardial infarction, you can
conclude that it is an anterior
wall myocardial infarction.

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 Putting it all Together
Do you think this person is having a
myocardial infarction. If so, where?

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 Interpretation
Yes, this person is having an acute
anterior wall myocardial infarction.

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Other MI Locations

Now that you know where to look for

an anterior wall myocardial infarction
lets look at how you would determine
if the MI involves the lateral wall or
the inferior wall of the heart.

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Views of the Heart
Lateral portion
of the heart
Some leads get
a good view of
the:

Anterior portion
of the heart

Inferior portion
of the heart 68
 Other MI Locations
Second, remember that the 12-leads of the ECG look at
different portions of the heart. The limb and augmented
leads see electrical activity moving inferiorly (II, III
and aVF), to the left (I, aVL) and to the right (aVR).
Whereas, the precordial leads see electrical activity in
the posterior to anterior direction.

Limb Leads Augmented Leads Precordial Leads

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 Other MI Locations

Now, using these 3 diagrams lets figure

where to look for a lateral wall and inferior
wall MI.
Limb Leads Augmented Leads Precordial Leads

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 Anterior MI

Remember the anterior portion of the heart

is best viewed using leads V1- V4.

Limb Leads Augmented Leads Precordial Leads

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 Lateral MI
So what leads do you
think the lateral portion Leads I, aVL, and V5- V6
of the heart is best
viewed?
Limb Leads Augmented Leads Precordial Leads

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 Inferior MI
Now how about the
inferior portion of the Leads II, III and aVF
heart?

Limb Leads Augmented Leads Precordial Leads

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 Putting it all Together
Now, where do you think this person is
having a myocardial infarction?

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 Inferior Wall MI
This is an inferior MI. Note the ST
elevation in leads II, III and aVF.

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 Putting it all Together
How about now?

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 Anterolateral MI

This persons MI involves both the anterior wall

(V2-V4) and the lateral wall (V5-V6, I, and aVL)!

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ST depression

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Q-T Segment Abnormalities

Q-T segment analysis is very

complicated and complete
dissertation is out of the scope of
this presentation.
That being said the Q-T interval is
based on or corrected for the heart
rate. The equation is:
QT corrected=QT/the square root
of the R-R interval
in seconds.
Normal Q-T

The normal Q-T corrected interval is

different in males and females.
< 0.430 seconds in males and <
0.450 seconds in females.
Causes of Short Q-T Intervals

1) familial/genetic short Q-T

syndrome
2) Hypercalcemia
3) Hyperthermia
Causes of Prolonged Q-T Intervals

1) familial/genetic prolonged Q-T

syndrome
2) Hypocalcemia
3) Drugs
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Case #3 ECG
Case #4 ECG
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