The document provides an overview of interpreting electrocardiograms (ECGs). It discusses the coronary circulation and electrical conduction system of the heart. It then covers the key elements of an ECG including the waveform and intervals in a normal reading. The document outlines how to interpret an ECG to identify lethal cardiac diseases by examining features such as the rate, rhythm, P waves, PR interval, and QRS complex. It provides guidance on evaluating the ECG for conditions like myocardial infarction by looking at changes in the ST segment across different electrode positions.

1. Interpreting ECG

2. 1. Coronary circulation.
2. Electrical conduction system of the heart
3. Electrocardiography elements
4. Electrical events & the waveform in a normal
ECG.
5. ECG interpretation
6. Identify lethal cardiac diseases
7. The learning

3. Coronary circulation

4.  Figure 1

5. Superior & Inferior Vena Cava
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonary Semi-lunar Valve

6. PulmonaryTrunk
Right & Left Pulmonary Arteries
Lungs
Left Atrium
PulmonaryVeins

7. MitralValve
LeftVentricle
Aortic Semi-lunarValve
Aorta
Body

8.  Supplies blood to:
 Right Atrium
 Right Ventricle
 The SA Node and in 55% of population the LV
inferior wall
 The LV posterior wall and ⅓ of the posterior
interventricular septum in 90% of the population

9.  Supplies blood to:
 the Left Atrium
 the LV lateral wall
 the SA Node in 45% of the population and to the LV
posterior wall
 ⅓ of the interventricular septum
 AV Node and Bundle of His in 10% of the population

10.  Supplies blood to:
 the LV anterior and lateral walls
 the Left and Right Bundle Branches
 the anterior ⅔ of the interventricular septum

11.  Recall:
 The Right Coronary Artery supplies both the Right
and Left heart.
 The Left Coronary Artery and its branches only
supply the Left heart.

12. Electrical conduction of
the heart

13.  The Conduction System of the Heart

14.  The SA Node is the primary pacemaker for the
heart at 60-100 beats/minute
 The AV Node is the “back-up” pacemaker of the
heart at 40-60 beats/ minute.
 The Ventricles (bundle branches & Purkinje
fibers) are the last resort and maintain an
intrinsic rate of only 20-40 beats/minute

15.  The normal conduction pathway:
SA Node AV Node
Bundle of
His
Right & Left
Bundle
Branches
Purkinje
Fibers
Myocardial
Contraction

16.  Correlation of the mechanical activity with the
electrical activity….

17.  Depolarization occurs when sodium channels
open fast and the inside of the membrane
becomes less negative (electrical stimulation).
 This is manifested as the P wave on an ECG,
which signifies atrial muscle depolarization.
 The plateau that immediately follows the P
wave represents atrial systole, when calcium
channels open slowly and potassium channels
close (at this time mechanical contraction of the
atria takes place).

18.  The PR interval on an ECG reflects conduction
of an electrical impulse from the SA node
through the AV node.
 PR = 0.12 – 0.20 seconds

19.  The QRS complex of an ECG reflects ventricular
muscle depolarization (the electrical impulse
moves through the Bundle of His, the left and right
bundle branches and Purkinje fibers).
 QRS = 0.08 – 0.10 seconds
 The QT interval measures the time from the start
of ventricular depolarization to the end of
ventricular repolarization.
 QT interval = < 0.43 seconds or ½ of the R-to-R interval.

20.  The ST segment reflects the early ventricular
repolarization and lasts from the end of the
QRS complex to the beginning of the T wave.
 The T-wave on an ECG reflects ventricular
muscle repolarization (when the cells regain a
negative charge - the “resting state”) and
mechanical relaxation, which is also known as
diastole.

21. ECG elements

22.  Myocardial Cells = the mechanical cells of the
heart. They contract when they receive an
electrical impulse from the pacemaker cells.
 Myocardial = Muscle
 Pacemaker Cells are very small cells within the
conduction system which spontaneously generate
electrical impulses.
 Pacemaker = Power Source
 Electrical Conducting Cells rapidly carry current to
all areas of the heart.
 Conducting Cells = Hard Wiring of Heart

23.  An electrocardiogram (ECG) is a graphic
recording of the electrical activity of the heart.
 The machine is called Electrocardiograph while
the recording is called Electocardiogram & is
used as a diagnostic tool to assess cardiac
function..

24.  ECG paper comes in a roll of graph paper
consisting of horizontal and vertical light and
dark lines.
 The horizontal axis measures time


 The vertical axis measures voltage.

25.  One small square = 0.04 seconds


 One large square = 0.2 seconds Or [One small
square(0.04)] x 5

26.  The light lines circumscribe small squares of 1 x 1
mm.
 One small square = 0.1 mV


 The dark lines delineate large squares of 5 x 5 mm
 One large square = 0.5 mV

27.  ECG is a painless procedure that is performed
by placing disposable electrodes on the skin of
a person’s chest wall, upper & lower
extremities.
 In the ECG, the 12 lead one is the most
commonly used tool to diagnose cardiac
conduction abnormalities, arrhythmias,
myocardial infarction and ischemia.

28.  The ECG represents the electrical impulses
that the heart transmits and are recorded as
wave tracings on specialized graph paper.

29.  6 limb leads
 6 precordial leads
 Positioning measures 12 perspectives or views
of the heart
 The 12 perspectives are arranged in vertical
columns
 Limb leads are I, II, III, AVR, AVL, AVF
 Precordial leads are V1, V2, V3, V4, V5, V6
 Horizontal marks time
 Vertical marks amplitude

30.  Each limb lead I, II, III, AVR, AVL, AVF records
from a different angle
 All 6 limb leads intersect and visualize a frontal
plane
 The 6 chest leads (precordial) V1, V2, V3, V4,
V5, V6 view the body in the horizontal plane to
the AV node
 The 12 lead ECG forms a camera view from 12
angles

31. I and AVL
II, III and AVF
V3 & v4
V1 & v2
V5 & v6
Where the positive electrode is positioned, determines what part of the heart is seen!

32.  Each positive electrode
acts as a camera looking
at the heart
 10 leads attached for 12
lead diagnostics. The
monitor combines 2
leads.
 Mnemonic for limb leads
 White on right
 Smoke(black) over fire(red)
 Snow(white) on
grass(green)

33.  Limb leads I, II, III are bipolar and have a negative
and positive pole
 Electrical potential differences are measured between the
poles
 AVR, AVL and AVF are unipolar
 No negative lead
 The heart is the negative pole
 Electrical potential difference is measured betweeen the lead
and the heart
 Chest leads are unipolar
 The heart also is the negative pole

34.  Anteroseptal: V1, V2, V3, V4
 Anterior: V1–V4
 Anterolateral: V4–V6, I, aVL
 Lateral: I and aVL
 Inferior: II, III, and aVF
 Inferolateral: II, III, aVF, and
V5 and V6

35.  Anteroseptal: V1, V2, V3, V4
 Anterior: V1–V4
 Anterolateral: V4–V6, I, aVL
 Lateral: I and aVL
 Inferior: II, III, and aVF
 Inferolateral: II, III, aVF, and
V5 and V6

38.  Yellow indicates V1, V2,
V3, V4
 Anterior infarct with ST
elevation
 Left Anterior Descending
Artery (LAD)
 V1 and V2 may also
indicate septal involvement
which extends from front to
the back of the heart along
the septum
 Left bundle branch block
 Right bundle branch block
 2nd Degree Type2
 Complete Heart Block

40.  Blue indicates leads
II, III, AVF
 Inferior Infarct with ST
elevations
 Right Coronary Artery
(RCA)
 1st degree Heart Block
 2nd degree Type 1, 2
 3rd degree Block
 N/V common, Brady
2004 Anna Story 40

42.  Red indicates leads
I, AVL, V5, V6
 Lateral Infarct with ST
elevations
 Left Circumflex Artery
 Rarely by itself
 Usually in combo

44.  Green indicates leads
V1, V2
 Posterior Infarct with ST
 Depressions and/ tall R
wave
 RCA and/or LCX Artery
 Understand Reciprocal
changes
 The posterior aspect of the
heart is viewed as a mirror
image and therefore
depressions versus
elevations indicate MI
 Rarely by itself usually in
combo

46.  No color for
SubEndocardial
infarcts since they
are not transmural
 Look for diffuse or
localized changes
and non – Q wave
abnormalities
 T-wave inversions
 ST segment
depression

48.  A combination of infarcts such as:
 Anterolateral yellow and red
 Inferoposterior blue and green
 Anteroseptal yellow and green

49.  Anteroseptal: V1, V2, V3, V4
 Anterior: V1–V4
 Anterolateral: V4–V6, I, aVL
 Lateral: I and aVL
 Inferior: II, III, and aVF
 Inferolateral: II, III, aVF, and
V5 and V6

53.  When an electrical current
moves toward a positive
electrode, the deflection on
the ECG strip will be positive
(up).
 When an electrical current
moves toward a negative
electrode, the deflection on
the ECG strip will be
negative(down).

54. Electrical events and
the waveform in ECG

55.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

56.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

57.  Rate
 What’s the normal heart rate for an adult human
being?
▪ 60 – 100 beats/ minute
 Remember:
 In terms of rate computation, heart rate generally
refers to the number of ventricular contractions that
occur in 60 seconds or one minute.
 When calculating rates, if there is a P-wave in front
of every R-wave, the atrial and ventricular rates will
be the same.

58.  Atrial rate can be calculated by measuring the
interval of time between P-waves (the P-to-P
intervals).
 Ventricular rate can be calculated by
measuring the time intervals between QRS
complexes (the R-to-R intervals).
 Check:
 Is the rate in the strip too fast or too slow?

59.  Why is it necessary to know both the atrial and
ventricular rates?
 There are instances, such as 2nd and 3rd degree
AV block, in which the atrial rate and ventricular
rates are different.
 This is why it is important to know how to
determine both atrial and ventricular rates.

60.  Rules
 Count the number of QRS’s in a 6 - second strip,
then multiply that number by 10.
 Determine the time between R-R intervals, then
divide that number by 60.
 For example:
▪ 40 (20 small boxes x 0.04 seconds each)
▪ = 50 beats per minute

61.  Rules
 Memorize these numbers:
 300, 150, 100, 75, 50
 Normal Heart rate for an adult = 60 -100 bpm
 This means that 3 to 5 large blocks should exist
between R – R intervals.
 Bradycardia = more than 5 large blocks
 Tachycardia = less than 3 large blocks.

62.  Rule of 300- Divide 300 by the number of
boxes between each QRS = rate
 HR of 60-100 = normal
 HR > 100 = tachycardia
 HR < 60 = bradycardia

64.  Let’s Practice with an Example:
 What is the rate based on Rule #1?
 If it is 50 bpm…., you are Correct!!!

65.  Let’s Practice with an Example:
 What is the rate based on Rule #1?
 300/6= 50 bpm

66.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

67.  Sinus
 Originating from SA
node
 P wave before every
QRS
 P wave in same
direction as QRS

68.  PR
 0.20 sec (less than one
large box)
 QRS
 0.08 – 0.10 sec (1-2
small boxes)
 QT
 450 ms in men, 460 ms
in women
 Based on sex / heart
rate
 Half the R-R interval with
normal HR

69.  Normal
 Men 450ms
 Women 460ms
 Corrected QT (QTc)
 QTm/√(R-R)
 Causes
 Drugs (Na channel
blockers)
 Hypocalcemia,
hypomagnesemia,
hypokalemia
 Hypothermia
 AMI
 Congenital
 Increased ICP

70.  AV blocks
1. First degree block
▪ PR interval fixed and > 0.2 sec
2. Second degree block, Mobitz type 1
▪ PR gradually lengthened, then drop QRS
3. Second degree block, Mobitz type 2
▪ PR fixed, but drop QRS randomly
4. Type 3 block
▪ PR and QRS dissociated

71.  Are the P waves regular or irregular?
 Are the R-to-R intervals regular or
irregular?

72.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

73.  Are there P-waves in the rhythm strip?
 Is there a P-wave for each QRS complex?
 Do all of the P-waves look the same?

74.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

75.  Is the PR Interval measurement normal?
 PR = 0.12 – 0.20 seconds
 Is the PR Interval measurement constant?

76.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

77.  Is the QRS wide? > 0.10
 Is it normal?
 QRS = 0.08 – 0.10 seconds
 Or is it narrow? < 0.08

78.  Is the T-wave peaked, inverted or flat?
 Is the ST segment elevated, depressed or
normal?
 Is the QT Interval < 0.43 seconds?
 Is there any ectopy present?

79.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

80.  Represents the overall direction of the
heart’s activity and Axis of –30 to +90
degrees is normal.

81.  QRS up in I and up in aVF = Normal

82.  Normal- QRS up in I and aVF

83.  Add the larger S wave of V1 or V2 in mm, to
the larger R wave of V5 or V6.
 Sum is > 35mm = LVH

84.  Rate
 Rhythm (including intervals and blocks)
 P - waves
 PR Interval
 QRS Complex
 Axis
 Hypertrophy
 Ischemia

85.  Ischaemia…..
 Usually indicated by ST segment changes
1. Elevation = Infarction
▪ Any elevation in the ST segment that is greater than 2 small boxes
is indicative of myocardial injury.
2. Depression = Ischemia
▪ Any ST segment depression greater than 2 small boxes indicates
myocardial ischemia.
 Can manifest as T wave changes
 Remote ischemia shown by Q waves

86.  T-wave inversion ( flipped T)
 ST segment depression
 T wave flattening
 Biphasic T-waves
Baseline

87.  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

88.  Significant Q-wave where none previously existed
 Why?
▪ Impulse traveling away from the positive lead
▪ Necrotic tissue is electrically dead
 No Q-wave in Subendocardial infarcts
 Why?
▪ Not full thickness dead tissue
▪ But will see a ST depression
▪ Often a precursor to full thickness MI
 Criteria
 Depth of Q wave should be 25% the height of the R wave
 Width of Q wave is 0.04 secs
 Diminished height of the R wave

89. 1 year
Q wave
ST Elevation
T wave inversion

90. ECG interpretation

91.  Let’s try an example…..
Is the rhythm regular or irregular?
Are the P-waves identical? Is there a P-
wave for each QRS complex?
Is the PR Interval 0.12 – 0.20?
Regular
Yes for both!
Yes, PR = 0.16

92.  Let’s try an example…..
Is the Is the QRS wide, normal or narrow??
Is the T-wave peaked, inverted or flat?
Is the ST segment elevated or depressed?
Is the QT Interval < 0.43?
Normal QRS = 0.08
No, it’s normal
No
Yes, QT Interval= 0.36

93.  Is there any ectopy present in this rhythm?
No

94.  So, the rhythm is …..
Normal sinus rhythm

95. Identify lethal cardiac
diseases

96.  The cardiac arrhythmias that are almost always
associated with death include:
1. Atrial Fibrillation
2. Atrial Flutter
3. Ventricular Fibrillation
4. Ventricular Tachycardia
5. 1st , 2nd and 3rd degree AV Block
6. Asystole
7. Ischaemia

97.  Atrial fibrillation…..
Rhythm
Rate
P-waves
PR interval
Atrial fibrillation is irregular + chaotic;
Ventricular rhythm is very irregular
Atrial is > 350 bpm; Ventricular is 120-
200 bpm
Not consistent (they are fine and
fibrillating)
Not measurable

98.  Atrial flutter…..
Rhythm
Rate
P-waves
PR interval
Atrial flutter is usually regular;
Atrial is 250- 350 bpm; Ventricular rate
depends on AV conduction
characterized by “saw tooth” pattern
cannot be determined; more flutter
waves than QRS complexes

99.  Ventricular fibrillation…..
Rhythm
Rate
P-waves
PR interval
Ventricular rhythm is totally erratic
Ventricular rate is 350-450 bpm
None
None

100.  Ventricular tachycardia….. Aka widow maker
Rhythm
Rate
P-waves
PR interval
Typically regular, but can be irregular
Ventricular rate is 100-220 bpm
can be present but have no correlation
to QRS complex
0.12 seconds with odd “tomb –stone”
shape

101.  Type 1st degree AV block
 PR is fixed and longer than 0.2 sec

102.  Type 1 - 2nd degree AV block [Wenckebach]

103.  Type 2 - 2nd degree AV block
Dropped
QRS

104.  3rd degree AV block….. Complete heart block
Rhythm
Rate
P-waves
PR interval
40-60 bpm (narrow QRS and junctional);
20-40 bpm (wide QRS and ventricular)
Normal, but usually more P-waves than
QRS’s

105.  Asystole…..
Rhythm
Rate
P-waves
PR interval
No rate as the person that belongs to
this rhythm is DEAD

106.  What is the diagnosis…..
Acute inferior MI with ST elevation in leads II, III, aVF

107.  What is the diagnosis…..
ST depression II, III, aVF, V3-V6 = ischemia

108.  What is the diagnosis…..
Anterior MI with lateral involvement
ST elevations V2, V3, V4
ST elevations II, AVL, V5

109.  What is the diagnosis…..
Anteroseptal MI
ST elevations V1, V2, V3, V4

110.  What is the diagnosis…..
Inferior MI
ST elevation 2,3 AVF

111.  What is the diagnosis…..
Inferior lateral MI
ST elevations 2, 3, AVF
ST elevations V5

112.  What is the diagnosis…..
Acute inferior MI
Lateral ischemia

113. Sample ECGs

115. Narrow complex, regular; retrograde P waves, rate <220

117.  (Wenckebach)
PR interval fixed, QRS dropped intermittently

118. Monophasic R wave in I and V6, QRS > 0.12 sec; Loss of R wave in precordial
leads; QRS T wave discordance I, V1, V6; Consider ischemia if a new finding

119. V1: RSR prime pattern with inverted T wave
V6: Wide deep slurred S wave

120. Ventricular escape rhythm, 40-110 bpm; Seen in AMI, a marker of reperfusion

121. Rate 40-60, no p waves, narrow complex QRS

122. Tall, narrow and symmetric T waves

123. U waves
Can also see PVCs, ST depression, small T waves

124. ST elevation & biphasic T wave in V2 and V3;Sign of large proximal LAD lesion

125. Short PR interval <0.12 sec; Prolonged QRS >0.10 sec; Delta wave
Can simulate ventricular hypertrophy, BBB and previous MI

126. RBBB or incomplete RBBB in V1-V3 with convex ST elevation

127.  Autosomal dominant genetic mutation of Na+
channels
 Causes syncope, v-fib, self terminating VT, and
sudden cardiac death
 Can be intermittent on ECG
 Most common in middle-aged males
 Can be induced in EP lab
 Need ICD

128. Trigeminy pattern

129. Sawtooth waves; Typically at HR of 150

130. Notice twisting pattern
Treatment: Magnesium 2 grams IV

132. Reciprocal changes

133. ST elevation II, III, aVF
ST depression in aVL, V1-V3 are reciprocal changes

134. Found in 1/3 of patients with inferior MI, Increased morbidity and mortality
ST elevation in V4-V6 of Right-sided ECG

135. LVH, AV junctional rhythm, bradycardia

136. S1, QIII, TIII in 10-15%; T-wave inversions, especially occurring in
inferior and anteroseptal simultaneously; RAD

152. 2004 Anna Story 152

153.  Twelve Lead Electrocardiography for ACLS Providers, D. Bruce Foster, D.O.
W.B. Saunders Company
 Rapid Interpretation of EKG’s , Dale Dubin, M.D., Cover Publishing Co. 1998
 ECG’s Made Easy, Barbara Aehlert, RN, Mosby, 1995
 The 12 Lead ECG in Acute Myocardial Infarction, Tim Phalen, Mosby, 1996
 Color Coding EKG’s , Tim Carrick, RN, H &H Publishing, 1994
 www.ecglibrary.com/ecghome.html
 www.urbanhealth.udmercy.edu/ekg/read.html
 www.ecglibrary.com/ecghome.html
 www.nyerrn.com/h/ekg.htm