Module I

E.C.G. RHYTHM
INTERPRETATION















2007 Ontario Base Hospital Group

ONTARIO
BASE HOSPITAL GROUP
ECG Rhythm Interpretation OBHG Education Subcommittee 2














Reviewers

Rob Theriault EMCA, RCT(Adv.), CCP(F)
Paramedic Program Manager
Peel Base Hospital

Kim Arsenault AEMCA, ACP, BSc HK
Advanced Care Paramedic Coordinator
Peel Base Hospital












Authors

Mike Muir AEMCA, ACP
Paramedic Program Manager
Grey-Bruce-Huron Paramedic Base Hospital
Grey Bruce Health Services, Owen Sound

Kevin McNab AEMCA, ACP
Quality Assurance Manager
Huron County EMS
E.C.G. RHYTHM
INTERPRETATION
ECG Rhythm Interpretation OBHG Education Subcommittee 3
Table of Contents

Section 1 Electrophysiology

Cardiac Conduction System .............................................................................................. 4-7
Anatomy and Physiology ...................................................................................................... 4
Conduction Velocities and Times ......................................................................................... 5
Role of the AV Node ............................................................................................................ 5
Action Potential Purkinje Fibre ......................................................................................... 6
Action Potential Pacemaker Cell ....................................................................................... 7

Section 2 ECG Monitoring Equipment

ECG Paper ............................................................................................................................ 8
ECG Cables/Electrodes ........................................................................................................ 9
Rule of Electrical Flow ......................................................................................................... 9
Lead Placement Frontal Plane ........................................................................................... 10

Section 3 ECG Interpretation

P-QRS-T Configuration ........................................................................................................ 11
Five Steps For ECG Interpretation ....................................................................................... 13
Step 1 Rate ......................................................................................................................... 14
Step 2 Rhythm ................................................................................................................. 16
Step 3 P-R Interval ............................................................................................................ 17
Step 4 P-QRS-T Relationship ............................................................................................ 17
Step 5 QRS Duration ......................................................................................................... 18
Step 6 Anything Missing/Added ....................................................................................... 18
Aberrant Conduction ............................................................................................................ 19

Section 4 Cardiac Rhythms/Arrhythmias

Supra Ventricular Rhythms .............................................................................................. 20-27
Normal Sinus Rhythm .......................................................................................................... 20
Sinus Bradycardia ................................................................................................................. 20
Sinus Tachycardia................................................................................................................. 21
Multifocal Atrial Tachycardia .............................................................................................. 21
Supraventricular Tachycardia ............................................................................................... 22
Sinus Block ........................................................................................................................... 22
Sinus Arrest .......................................................................................................................... 23
Sinus Arrhythmia ................................................................................................................. 23
Premature Atrial Complexes ................................................................................................. 24
Premature J unctional Complexes ......................................................................................... 24
Atrial Flutter ................................................................................................................. 25
Atrial Fibrillation ................................................................................................................. 25
Wandering Atrial Pacemaker ................................................................................................ 26
J unctional Rhythm ................................................................................................................ 27

Heart Blocks ........................................................................................................................ 29-31
First Degree Heart Block ...................................................................................................... 29
Second Degree Heart Block Type I Wenkebach ............................................................... 29
Second Degree Heart Block Type II ..................................................................................... 30
Second Degree Heart Block Type II with 2:1 conduction .................................................... 30
Third Degree Heart Block .................................................................................................... 31
ECG Rhythm Interpretation OBHG Education Subcommittee 4
Table of Contents


Section 4 Cardiac Rhythms/Arrhythmias (contd)

Ventricular Rhythms .......................................................................................................... 33-38
Idioventricular ...................................................................................................................... 32
Premature Ventricular Complexes (PVC) ............................................................................ 33-35
Ventricular Tachycardia ....................................................................................................... 36
Torsades de Pointe (Polymorphic Ventricular Tachycardia) ............................................... 36
Ventricular Fibrillation Coarse .......................................................................................... 37
Agonal Rhythm ................................................................................................................. 37
Asystole ................................................................................................................................ 38

Pacemaker Rhythms ........................................................................................................... 39
Ventricular Pacemaker ......................................................................................................... 39
AV Sequential Pacemaker .................................................................................................... 39

Artifact ................................................................................................................................ 40
Baseline Artifact 31 ............................................................................................................. 40
60 Cycle Interference ........................................................................................................... 40

Notes .................................................................................................................................... 41

































ECG Rhythm Interpretation OBHG Education Subcommittee 5
Section I Electrophysiology

Cardiac Conduction System

Anatomy and Physiology

The cardiac conduction system is comprised of specialized tissues that unlike muscle tissue located elsewhere in the
body can 1: generate electrical impulses (automaticity) and 2: conduct electrical impulses (conductivity). The
cardiac muscle tissue is similar to other tissue in its ability to contract (contractility).

Specialized tissue located in the right atria known as the sinoatria node (SA) is the primary pacemaker of the heart
producing electrical impulses at a rate of 60 to 100 per minute in the normal resting heart. The generation of the
impulses results from the movement of electrolytes (Na
+
, Ca
++
and K
+
) across the cell membrane leading to the
depolarization of the cell. Other tissue similar in nature to the SA node, the atrioventricular node (AV) is capable of
producing the same impulses but at a slower rate, 40 to 60 per minute. Tissue located in the ventricles (bundle
branches and purkinje fibers) can also produce impulses at rates of 20 to 40 per minute.












In addition to the ability to automatically generate electrical impulses, the cardiac conduction system allows for the
transmission of the impulses throughout the heart in a coordinated manner, producing the rhythmic contraction
associated with normal cardiac output.

Impulses generated by the SA node travel along specialized tissue known as the conduction pathways. The impulse
travels to the AV node where it is delayed, allowing for the contraction of the atria. Once the impulse passes
through the AV node it transcends the Bundle of HIS, the Right and Left Bundle Branches and finally the Purkinje
Fibres.

Conduction Times & Velocities

Conduction times and velocities are important in that they co-ordinate the electrical system of the heart with its
mechanical function of a pump. The diagram below shows that the movement of the impulses through the atria
(right and left) is significantly slower that the movement through the ventricles. The larger mass of the ventricle
requires the rapid flow of the electrical impulses resulting in the complete depolarization and contraction of the
entire ventricle at almost the same time. This action results in the forceful contracting of the heart producing cardiac
output.

Notes:
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SA NODE
AV NODE
BUNDLE OF HIS
LEFT AND RIGHT
BUNDLE BRANCHES
PURKINJE FIBRES
ECG Rhythm Interpretation OBHG Education Subcommittee 6
Section I Electrophysiology

Cardiac Conduction System (contd)

Conduction Times & Velocities (contd)












Role of the AV Node

The AV Node plays a significant role in delaying the conduction of electrical impulses between the atria and the
ventricles. The delay provides sufficient time to allow the ventricle to fully fill with blood and stretch sufficiently
prior to the impulses entering the ventricle producing the contraction. The tissue of the AV Node becomes more
dense slowing the impulse then breaks through to enter the ventricle.












Because of the unique qualities of the AV nodal tissue and its ability to naturally slow the conduction of impulses,
when things go wrong, such as in the diseased or injured heart, the AV Node is responsible for the cardiac
arrhythmias involving the heart blocks of the 1
st
, 2
nd
, or 3
rd
degree type.





Notes:
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0.07 seconds
0.19 seconds
0.17 seconds
0.19 seconds 3-4 m/sec
0.16 seconds
0.5 m/sec
0.04 seconds
1.0 m/s
0.5 m/s
1.0 m/s
ECG Rhythm Interpretation OBHG Education Subcommittee 7
Section I Electrophysiology

Cardiac Conduction System (contd.)

Action Potential Ventricular Muscle

The action potential of ventricular muscle involves the movement of anions and cations across the cell membrane of
the cardiac muscle tissue. This movement results in the depolarization and subsequent repolarization of the cell with
corresponding contraction of the heart muscle.


Phase 0: Rapid Depolarization cell is stimulated by conducted impulse causing sodium ions to enter the cell
through slow channels. When polarity of cell becomes less negative (-65 mV) the fast sodium channels open and
the rapid influx of positively charged sodium enters the cell bringing the polarity of the cell to +20 mV.

Phase 1: Early Repolarization Fast sodium channels close. Chloride channels open allowing negatively charged
chloride to enter the cell, reducing the positive charge of the cell to neutral (0 mV). There is also a small efflux of
potassium at this stage, hence the dip in the action potential.

Phase 2: Plateau (Absolute Refractory Period) calcium channels remain open allowing the influx of positively
charged calcium ions to enter the cell. This period is slower allowing for the full depolarization and contraction of
the tissue.

Phase 3: Slope (Relative Refractory Period) potassium ions (+ve) leave cell (efflux) reducing the intracellular
polarity until it reaches 85 mV again.

Phase 4: Resting Membrane Potential constant efflux of potassium (K
+
) keeps intracellular polarity at 85 mV
until next impulse stimulates Phase 0 sodium channel opening.

Notes:
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Phase 0: Rapid Depolarization
Phase 1: Early Repolarization
Phase 2: Plateau (Absolute Refractory Period)
Phase 3: Slope (Relative Refractory Period)
Phase 4: Resting Membrane Potential
0
+20
- 100
0
- 85
- 65
MYOCARDIUM
Na
+

Ca
++
Na
+

-
Ca
++
K
+
K
+
K
+
K
+

4
4
1
2
3
mV
INSIDE CELL
OUTSIDE CELL
THRESHOLD
POTENTIAL
ECG Rhythm Interpretation OBHG Education Subcommittee 8
Section I Electrophysiology

1.0 Cardiac Conduction System (contd.)

1.4 Action Potential Pacemaker Cell

Automaticity is the hearts ability to generate its own electrical impulses. The SA Node is the primary pacemaker of
the heart depolarizing at a rate of 60 to 100 times per minute. Unlike ventricular muscle, the SA Node requires no
external stimulation to cause the sodium channels to open. The cell wall membrane of the pacemaker cell is
permeable to sodium allowing for the slow influx of this ion from outside to inside the cell. It is also believed that
slow calcium channels are present allowing the movement of Ca
++
inside the cell. The movement of the positively
charged Na
+
and Ca
++
ions into the cell results in the slow depolarization of the pacemaker cell.







































Notes:
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Phase 0: Slow Depolarization
Phase 1: Does not Apply
Phase 2: Plateau ( Absolute Refractory Period)
Phase 3: Relative Refractory Period
Phase 4: Spontaneous Phase 4 Rise constant influx of Na
+
- 100
- 85
- 65
0
+ 20
PACEMAKER
CELL
3 3
4 4 4
3

0 0 0
2 2 2
ECG Rhythm Interpretation OBHG Education Subcommittee 9
Section 2.0 ECG Monitoring Equipment

ECG Paper

ECG monitors provide both dynamic and static monitoring capabilities. ECG paper has been standardized
throughout the industry to maintain a running speed of 25 mm/second. It is the basis of this standard running speed
that creates the large boxes with corresponding time frames. The need to know how the math works out is of little
importance. The important information to remember is that each small square represents 0.04 second and each large
square represents 0.2 second.

























Formulas for paper speed and minute interval calculation.


25 mm/sec multiplied by 60 sec =1500 mm/min

60 (1 minute) seconds divided by 1500 mm =0.04 sec/mm

0.04 sec/mm x 5 =0.2 sec/5mm (large square)

1500 mm/min divided by 5 =300 large squared/min







Notes:
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1 mm
0.04 second
1 mm
5 mm
5 mm
0.2 second
ECG Rhythm Interpretation OBHG Education Subcommittee 10
Section 2 ECG Monitoring Equipment

ECG Cables/Electrodes

ECG cables are colour and letter coded: white (RA), red (LL), black/green (LA). The general rule for lead
placement is:


White (Right Arm) typically placed over right anterior chest, below clavicle
Red (Left Leg) placed at mid-axillary line below left nipple line
Black/Green (Left Arm) placed over left anterior chest, below clavicle
Ground lead (with 4 lead cable) generally placed over the right lateral chest


Factors affecting ECG quality:

Patient movement
ECG electrode directly over large muscle (e.g. bicep)
ECG electrode directly over bone
dried out electrodes
loose connections
frayed cables
improper lead selection


Rule of Electrical Flow

ECG complexes are the measurement of electrical flow registered on an oscilloscope (monitor) or plotted on a graph
(ECG Paper). The ECG machine measures the electrical current flowing between the negative and positive
electrodes. The diagram below describes the rule of electrical flow.



Notes:
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-
RA
LA
LL
IMPULSE
NEGATIVE
ELECTRODE
POSITIVE
ELECTRODE
If electricity flows toward the
negative electrode, the patterns
produced on the graph paper will
be negatively deflected.
If electricity flows toward the
positive electrode, the
patterns produced on the
graph paper will be positive.
Normally conducted
impulses travel the eleven to
five oclock vector
ECG Rhythm Interpretation OBHG Education Subcommittee 11
Section 2 ECG Monitoring Equipment


Lead Placement - Frontal Plane

Most lead II ECG monitoring machines have the ability to look at three different frontal leads. When the lead
selection is made by turning the switch to a specific lead, the polarity of the leads change amongst the white, red and
black leads as noted above.



Lead I monitoring atrial activity when difficult to see in lead II
Lead II monitoring of normal conduction vector from right atria to left ventricle
Lead III monitoring horizontal view of the heart with emphasis on left ventricle




















Notes:
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-
I
LEAD I

-
II
LEAD II
III
LEAD III
II
I III
II
I III
II
I III
-ve +ve
G
-ve
+ve
G
G
-ve
+ve
ECG Rhythm Interpretation OBHG Education Subcommittee 12
Section 3 ECG Interpretation

P-QRS-T Configuration

The P-QRS-T configuration of the ECG is the electrical activity representative of the depolarization and
repolarization of the atria and ventricles. The following diagram shows the correlation of the components of the
ECG and the location within the heart that the electrical activity occurs.























P Wave - depolarization of the atria
- usually SA node
- upright
P-R Interval - impulse conduction from SA Node to and through AV node
- from beginning of P wave to beginning of QRS complex
- delay allows atria to fully contract and expel its content into the ventricles
- 0.12 to 0.20 seconds
QRS Complex - depolarization of the ventricle
- 0.08 to 0.10 seconds (or <0.12)
- large amplitude due to large mass of ventricles producing more electrical activity
Q Wave - septal wall depolarization
- first negative deflection on ECG complex after P wave
R Wave - ventricular wall depolarization
- large mass of ventricles
- first upright deflection
S Wave - lateral wall depolarization
- downward deflection
T Wave - ventricular repolarization
U Wave - referred to as an after-depolarization. May result from electrolyte imbalance (e.g.
Hypokalemia) or other causes.

Notes:
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Ventricular Repolarization (T)
Ventricular Depolarization (QRS)
P Wave
Q Wave
P-R Interval
R Wave
S Wave
T Wave
U Wave
QRS
Duration
Atrial Depolarization(P)
ECG Rhythm Interpretation OBHG Education Subcommittee 13
Section 3 ECG Interpretation

QRS Morphology

The QRS complex of the ECG represents ventricular depolarization. The morphology or shape of the QRS complex
can vary depending on the lead from which youre viewing the ECG, the individual patient or abnormal pathology.
Although the QRS complexes below appear different, they may be normal for that individual or be suggestive of
an underlying conduction disturbance (especially QRSs >0.12 second).




































Notes:
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R
S
r
S Q
S Q
Q
R
R R

R
R
Q S Q S
R
S
R
Q
S
R
R
Q
Q
S
R
R QRSRS
QRS RS RSR
QRS QrSR QR
QRS QR
RS
Q or QS
ECG Rhythm Interpretation OBHG Education Subcommittee 14
Section 3 ECG Interpretation

Five Steps For ECG Interpretation

Listed below are the 5 steps to ECG interpretation. When interpreting the ECG it is important to follow the 5 steps
to avoid what is known as Pattern Recognition whereby the interpreter assumes a rhythm is of one type by just
looking at it whereas the rhythm would be identified correctly if the steps were followed.

Step 1 : Rate <60 Bradycardic
60 - 99 Normal
>100 Tachycardic

Step 2 : Rhythm Regular
Irregular

Step 3 : P-R Interval 0.12 - 0.20 Second

Step 4 : P-QRS-T Relation P Wave For Every QRS-t Complex

Step 5 : QRS Width 0.08 - 0.10 Second (or <0.12 second is considered narrow)

Step 6 : Missing Or Added Extra Beats Or Missing Beats


































ECG Rhythm Interpretation OBHG Education Subcommittee 15
S St te ep p O On ne e - - R Ra at te e

Method 1

Count the number of R waves for a six second interval and multiply by ten.












6 x 10 = 60/min


Points to consider:
- reliable only when rhythm is regular
- good for normal heart rates accuracy is diminished with fast or slow rates




Notes:
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______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
3 sec 3 sec
6 sec
1 2 3 4 5 6
ECG Rhythm Interpretation OBHG Education Subcommittee 16
Section 3 ECG Interpretation

Method 2:

Count the number of 5mm squares between each R wave and divide the number into 300. This will give you the
approximate rate/minute.












Points to consider:
- must be able to do division in your head

Method 3:

Using the following scale, where each number represents a 5mm square, count each 5 mm square between two R
waves.











The rate for the above is 60 based on method 3.




Points to consider:
- memorize the above numbers
- find a QRS complex that falls on a dark line
- count down from the next dark line as shown above
- reliable for regular rhythms
- recommended for brady and tachyarrhythmias
Notes:
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1 2 3 4 example 300 4 = 75

300
100
150
75
60
50
43
Start
300 150 - 100 - 75 - 60 - 50 - 43 37 - 33
37
33
ECG Rhythm Interpretation OBHG Education Subcommittee 17
Section 3 ECG Interpretation

Five Steps For ECG Interpretation (contd)

Step Two - Rhythm

Measure the R to R intervals to determine if the rhythm is regular in nature. It is acceptable to allow for a difference
of +/ one small square when determining regularity of the rhythm


Regular









Irregular











Irregularly Irregular










Points to consider:
- regular rhythms are produced by a single focus
- regularly irregular rhythms may occur with heart blocks or regular PVCs
- with very fast rhythms it is sometimes difficult to determine if a regular pattern exists
Notes:
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______________________________________________________________________________
______________________________________________________________________________

ECG Rhythm Interpretation OBHG Education Subcommittee 18
Section 3 ECG Interpretation

Step Three - P-R Interval

The P-R Interval is the time required for the impulse to travel from the SA node through the AV node. Impulses
generated in the atria should take between 0.12 to 0.20 seconds to travel through the AV node. Any delay of >0.20
seconds is considered a significant conduction delay.













Points to consider:
- measure PR Interval from beginning of P wave to beginning of QRS deflection regardless of
morphology
- must identify P wave over T wave

Step Four - P-QRS-T Relationship

Look for a marraige of P waves to QRS complexes. Normal complexes will always have the components as in the
diagram below. P waves with no corresponding QRS complexes or QRS complexes with no associated P wave will
signal heart block or ectopic beats.















Points to consider:
- fast rhythms may cause P waves to encroach on the preceding T wave
- more than one P wave per QRS may signal heart block or non-conducted PACs
Notes:
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______________________________________________________________________________
______________________________________________________________________________
0.12 - 0.20 second
1 Large Square or 5 Small Squares
<0.20 SEC
Normal P wave with no QRS complex
Normal
ECG Rhythm Interpretation OBHG Education Subcommittee 19
Section 3 ECG Interpretation

Five Steps For ECG Interpretation (contd)

Step Five - QRS Duration

Measure from the first deflection (+ve or ve) to where the QRS complex comes back to the isoelectric line (J
point). The normal range for the QRS width is <0.12 second or <3 small squares.













Points to consider:
- QRS widths of >0.12 are not always ventricular in origin, but can be supraventricular beats
with aberrant conduction as a result of a bundle branch block, drug effect, etc.

Step 6 Anything Missing/Added

This is the unofficial step that can help aid in the interpretation of any ECG. Look for missing beats where you
expect them to be, or added complexes where they werent expected. Look for premature beats or escape beats.

Premature Vs Escape

Premature








Extra QRS complexes which occur before the next expected beat are referred to as premature complexes. There are
multiple premature atrial (P waves present) beats in the above strip. Note how they occur prior to the next expected
beat.





Notes:
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______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
<0.12 second
<3 small squares
Premature
atrial complex -
ECG Rhythm Interpretation OBHG Education Subcommittee 20
Section 3 ECG Interpretation

Step 6 Anything Missing/Added (contd)

Escape











The above ECG is an example of a Sinus Arrest. Note that an escape beat (compensatory mechanism) occurs when
there is a missing complex. The complex that appears after the delay is referred to as an escape beat.

3.3 Aberrant Conduction

Aberrant conduction occurs when the QRS complex appears wider than normal (>0.12 second). The impulse may
follow the normal pathways in the atria but as it enters the ventricles it is blocked in either the left or right bundle
branches. This results in one ventricle depolarizing just prior to the other ventricle depolarizing. The delay can
occur in either the right or the left bundle branch. It is impossible to determine the exact location of the delay using
leads I, II or III and requires the use of modified chest leads or a 12 lead ECG to determine the location.























Notes:
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B
C
A
Example: A right ventricle depolarizes
B delayed conduction in left bundle branch
C left ventricle depolarizes
ECG Rhythm Interpretation OBHG Education Subcommittee 21
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms

Normal Sinus Rhythm (NSR)






















Sinus Bradycardia























Notes:
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Impulses generated by SA Node follow
normal conduction pathways.
Impulses generated by SA Node follow
normal conduction pathways. Rate less
that 60 per minute. Benign in nature
unless hemodynamically significant. Can
be normal in athletes.
Rate : <60
Rhythm : Regular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : Yes
Missing / Added : Nothing
Identifying Features : Rate less than 60,
otherwise normal.
Rate: 60 - 99
Rhythm: Regular
P-R Interval : <0.20 second
QRS Width: <0.12 second
P-QRS-T: Normal
Missing / Added : Nothing
Identifying Features: All criteria normal

ECG Rhythm Interpretation OBHG Education Subcommittee 22
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms

Sinus Tachycardia













Multifocal Atrial Tachycardia (MAT)












Notes:
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Impulses generated by SA Node follow
normal conduction pathways. Rate is equal or
greater than 100 per minute. Usually a sign of
hemodynamic compensatory response. Non
life threatening unless significant underlying
disease process exists.
Impulses generated by multiple sites
throughout atria. Rate equal or greater than
100 per minute. Results from atrial
irritability. Often confused with atrial
fibrillation but has definite P waves with
multiple morphologies. An uncommon
dysrhythmia, but is seen in COPD and CHF as
the result of atrial hypertrophy.
Rate : >100
Rhythm : Irregularly irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : Yes
Missing / Added : Nothing
Identifying Features : >100, P waves Present,
Irregular
Rate : >100, <160
Rhythm : Regular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : Yes
Missing / Added : Nothing
Identifying Features : all criteria normal, rate >100
and <160
ECG Rhythm Interpretation OBHG Education Subcommittee 23
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms

Supraventricular Tachycardia (SVT)






















Sinus Exit Block























Notes:
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Impulses generated from anywhere above the
bifurcation of the bundle branches. P waves are
absent or not clearly discernable and QRS is
generally narrow (unless theres a bundle
branch block present). Rate greater than 100
per minute, but generally >150 bpm. Indicative
of re-entrant focus or accessory bypass track
(e.g. Wolf Parkinson White Syndrome).
Sinus Exit Block occurs when the impulse
from the SA Node fails to exit the
surrounding tissue. The SA Node eventually
depolarizes when the next expected P wave
occurs in the cardiac cycle. There is a non
compensatory pause and the SA Node
depolarizes in sync with previous
P complexes. Can be caused by Sick Sinus
Syndrome, hypoxia or electrolyte
disturbances.
Rate : >100 (>140)
Rhythm : Regular
P-R Interval N/A
QRS Width : <0.12 second (usually)
P-QRS-T : P waves not clearly visible
Missing / Added : Nothing
Identifying Features : reg. narrow complex tachy
with no P waves
Rate : <100
Rhythm : Irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : Inconsistent
Missing / Added : Dropped P wave & QRS -
Next beat falls into
sequence
ECG Rhythm Interpretation OBHG Education Subcommittee 24
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms (contd)

Sinus Arrest
























Sinus Arrhythmia





















Notes:
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Rate : <100
Rhythm : Irregular
P-R Interval : <0.20
QRS Width : <0.12 second
P-QRS-T : Inconsistent
Missing / Added : Two or more PQRS missing
Identifying Features : Long pause (flat line). Next
beat is an escape pacemaker.
Rate : 60 - 100
Rhythm : Irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : Marriage
Missing / Added : Nothing
Identifying Features : Slowing of rhythm with
respiration
Sinus arrest occurs when the SA Node fails to
generate impulses. An escape pacemaker
generally resumes the function of pacing the
heart. Causes include Sick Sinus Syndrome,
hypoxia or electrolyte disturbances. This is a
potentially life-threatening dysrhythmia!
Sinus Arrhythmia is seen predominately in the pediatric
age group. The ECG shows normal sinus rhythm but the
rhythm has an accordion style irregularity that coincides
with the patients respiratory pattern. The rhythm speeds
up and slows down with ventilation. This is a benign
rhythm that is interpreted by watching the patients
breathing while simultaneously watching the changes in
heart rate.
ECG Rhythm Interpretation OBHG Education Subcommittee 25
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms (contd)

Premature Atrial Complex























Premature Junctional Complex






















Notes:
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Premature Atrial Complexes (PACs) are ectopic beats
that occur with an underlying sinus rhythm before the
next expected QRS complex. PACs are distinguished
by the presence of a P wave in front of the narrow
complex beat. The QRS in a PAC is identical in
morphology to the underlying QRS complexes as the
conduction follows normal pathways once the impulse
passes through the AV node. PACs are usually benign
and often result from atrial hypertrophy or excessive
stimulant ingestion (coffee or nicotine) and are
indicative of atrial irritability.
Rate : Can occur with any heart rate
Rhythm : Irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : P waves Present
Missing / Added : Narrow QRS
Identifying Features : PAC - narrow complex
occurring before next
expected QRS complex, P
wave present
Rate : Can occur with any heart rate
Rhythm : Irregular
P-R Interval: <0.20 second
QRS Width : <0.12 seconds
P-QRS-T : P waves present
Missing / Added : Narrow QRS with inverted P
wave before or after or no P
wave visible
Identifying Features : PJ C - Narrow complex
occurring before next
expected QRS complex
Premature J unctional Complexes (PJ Cs) are
ectopic beats that occur with an underlying sinus
rhythm before the next expected beat. PJ Cs are
distinguished by the presence of an inverted P
wave, the absence of a P wave with a narrow QRS
or the presence of an inverted P wave between the
QRS and T wave. The QRS is similar in
morphology to the underlying QRS as conduction
follows the normal pathways in the ventricles.
PJ Cs are usually benign and often caused by
stimulants (e.g. coffee or nicotine) and atrial
irritability.
ECG Rhythm Interpretation OBHG Education Subcommittee 26
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms (contd)

Atrial Flutter






















Atrial Fibrillation























Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Rate : Variable
Rhythm : Irregularly irregular
P-R Interval: N/A
QRS Width : <0.12 second
P-QRS-T : No P waves
Missing / Added : No P waves
Identifying Features : Irregularly irregular, no
discernible P waves, +/-
fibrillating baseline
Rate : May vary
Rhythm : Regular or irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : F waves present
Missing / Added : Flutter wave between
QRS complex
Identifying Features : Flutter waves replace P
waves
Atrial Flutter shows a sawtooth P wave pattern between
narrow complex QRS complexes. Seen in COPD or
CHF patients resulting from atrial enlargement. The
atrial impulses are generated at a rate of approximately
300 per minute but only travel through the AV node at
rates of usually 150 or less per minute. The AV node
remains in a refractory state allowing only a portion of
the impulses to travel through it. Can have a variable
conduction pattern of 2:1, 3:1 or 4:1 or any combination
as seen in the above strip.
Atrial Fibrillation is an irregularly irregular ECG
seen in CHF, AMI, and heart failure patients. The
isoelectric line is flat or chaotic in nature with no
discernable P waves before the usually narrow QRS
complex. Multiple ectopic foci in the atria
depolarize at rates exceeding 500 per minute but
only a limited number of impulses travel through
the AV Node.
ECG Rhythm Interpretation OBHG Education Subcommittee 27
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms (contd)

Wandering Atrial Pacemaker





































Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Rate : Variable
Rhythm : Irregular
P-R Interval : <0.20 second
QRS Width : <0.12 second
P-QRS-T : P waves
Missing / Added : Nothing
Identifying Features : Different morphology P
waves, irregular
Wandering Atrial Pacemaker occurs when there
are multiple pacemaker sites in the atria
producing an irregular rhythm with P waves of
different morphology. Similar to Multi focal
Atrial Tachycardia only slower in rate.
ECG Rhythm Interpretation OBHG Education Subcommittee 28
Section 4 Cardiac Rhythms/Arrhythmias

Supraventricular Rhythms (contd)

Junctional Rhythm

J unctional Rhythms are generated within the AV Node and are identified by the inverted P waves that occur before,
during (hidden from view) or after the QRS complex. The location within the AV Node of impulse generation
determines the unique characteristic of the junctional rhythm. The diagram below shows the correlation of the
location of the pacemaker and the location of the P wave in conjunction to the QRS complex.





























Inverted P wave before QRS complex










No visible P wave hidden in QRS complex
Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Impulse enters atria
and ventricle at same
time
Impulse enters ventricle
first then enters atria
second
Impulse enters atria
first then ventricle
second
AV Node
Impulse generated near
beginning of AV Node
Impulse generated near
middle of AV Node
Impulse generated near
end of AV Node
InvertedP wavebeforeQRS P wavehiddeninQRScomplex P waveafter QRSComplex
ECG Rhythm Interpretation OBHG Education Subcommittee 29
Section 4 Cardiac Rhythms/Arrhythmias

Supra Ventricular Rhythms (contd)

Junctional Rhythm (contd)









Inverted retrograde P wave after QRS complex









































Rate: 40 60
Rhythm : Regular
P-R Interval : Narrow if present
QRS Width : <0.12 second
P-QRS-T : Inverted P waves, no P waves
Missing / Added : retrograde P waves
Identifying Features : Regular, narrow complex, 40-
60, inverted P waves in front,
buried, or after QRS complex
J unctional Rhythms are identified by their slow,
regular rhythm and narrow QRS complex. Often
seen in post cardiac arrest patients and as an escape
rhythm in patients with SA Node failure. Inverted P
waves are seen before or after the QRS complex.
The P waves that occur before the QRS complex will
have a shortened P-R interval
ECG Rhythm Interpretation OBHG Education Subcommittee 30
Section 4 Cardiac Rhythms/Arrhythmias

Heart Blocks

Heart Blocks

Heart Blocks can be classified into 1
st
, 2
nd
and 3
rd
degree with additional differentiation for 2
nd
degree types. They
are indicative of conduction delays through the AV Node or surrounding tissue and can be of little clinical
significance or be life-threatening. The life threat increases as the heart block number increases.

First Degree Heart Block
















Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

Second Degree Heart Block Type I - Wenkebach






















Rate : May vary
Rhythm : Regular
P-R Interval : >0.20 second
QRS Width : <0.12 second
P-QRS-T : Marriage
Missing / Added : Nothing
Identifying Features : PR Interval >0.20 second

Rate : <100
Rhythm : Irregular
P-R Interval : Increases
QRS Width : <0.12 second
P-QRS-T : Inconsistent
Missing / Added : QRS Complexes dropped
Identifying Features : PR interval increases until
a QRS complex is
dropped after a P wave
1
st
Degree Heart Block is identified by the prolonged
( >0.20 second) P-R interval. Benign in nature and
normal in most patients.
2
nd
Degree Heart Block Type I Wenkebach is
characterized by the gradually increasing P-R
interval then a P wave with no associated QRS
complex. This pattern then repeats. Block occurs
higher in the AV Node. There is no change in the
P-P interval as the SA node is unaffected. Seen in
patients with increased parasympathetic activity or
hypoxia. Usually benign and does not lead to more
significant heart blocks.
ECG Rhythm Interpretation OBHG Education Subcommittee 31
Second Degree Heart Block Type II





















Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________


Second Degree Heart Block Type II with 2 : 1 conduction


























Rate : <60
Rhythm : Irregular
P-R Interval : Constant
QRS Width : <0.12 second
P-QRS-T : Inconsistent
Missing / Added : QRS complexes
Identifying Features : PR interval constant then
a QRS complex is
dropped after a P wave
Rate: <60 Bradycardic
Rhythm: Regular
P-R Interval: Constant
QRS Width: <0.12 second
P-QRS-T: Inconsistent
Missing / Added: QRS Complexes
Identifying Features: PR interval constant then
a QRS complex is
droppedafter aP wave
2
nd
Degree Heart Block Type II is characterized by
the constant P-R interval then a P wave with no
associated QRS complex. Block occurs further down
the AV Node. There is no change in the P-P interval
as the SA node is unaffected. Seen in patients with
AMI, degenerative nodal disease or hypoxia. May
deteriorate to 3
rd
Degree Heart Block.
2
nd
Degree Heart Block 2:1 is characterized by the
presence of a normal P-QRS-T complex then a P wave
with no associated QRS complex. This pattern repeats
at a 2:1 ratio ( two P waves for every one QRS
complex). Seen in patients with AMI, degenerative
nodal disease or hypoxia. May deteriorate to more
significant heart blocks specifically 3
rd
Degree Heart
Block.
ECG Rhythm Interpretation OBHG Education Subcommittee 32
Section 4 Cardiac Rhythms/Arrhythmias

Heart Blocks (contd)

Third Degree Heart Block


























Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________




















Rate : <60 bradycardic
Rhythm : Regular
P-R Interval : Varies
QRS Width : >0.12 second
P-QRS-T : No marriage
Missing / Added : Nothing
Identifying Features : P waves march through
QRS complex, no marriage
between P waves and QRS
complexes, regular
ventricular response
3
rd
Degree Heart Block is a bradycardic rhythm
characterized by a regular, wide QRS complex. P
waves are present but have no relationship with the
QRS complexes. The P waves appear to march
through the QRS complexes. The blockage between
the atria and ventricles is complete preventing the SA
Node generated impulses to pass through to the
ventricles. The wide QRS complex rhythm is
generated in the ventricle as an escape rhythm. Seen in
patients with AMI, degenerative nodal disease and
hypoxia.
ECG Rhythm Interpretation OBHG Education Subcommittee 33
Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms Cont


Idioventricular












































Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Rate : 20 40
P-R Interval : No P waves
Rhythm : Regular
P-QRS-T : N/A
QRS Width : >0.12 second
Missing / Added : P waves
Identifying Features : Wide and slow - Ps
absent
Idioventricular Rhythm is an escape rhythm that is
generated somewhere within the ventricle and at a
bradycardic rate. The pacemaker depolarizes at a
regular rate between 20 to 40 per minute. Wide
complex in nature. Seen in AMI, post arrest patients,
other pathologies. Patients generally present with
severe hemodynamic compromise.
ECG Rhythm Interpretation OBHG Education Subcommittee 34
Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms (contd)


Premature Ventricular Complexes (PVC)

Premature Ventricular Complexes (PVCs) are ectopic complexes that accompany a supraventricular rhythm such as
normal sinus rhythm. The PVCs are wide complex (>0.12 second) and can look similar or be of different
morphology. PVCs occur before the next expected beat.



Etiology of a PVC: Re-entry

Example A displayed below shows the re-entry of an impulse through the Purkinje fibre. Antegrade conduction is
stopped as it flows through ischemic or hypoxic tissue (A). Retrograde conduction flows through the tissue and
stimulates a depolarization as it escapes the damaged tissue. Example B shows normal antegrade conduction as it
flows through cardiac tissue (1) followed by the impulse slowing down through ischemic tissue (2). When the
impulse breaks out of the ischemic zone, the surrounding tissue which was stimulated by the wave of electrical
activity to depolarize, has reached the relative refractory period of repolarization and is ready to accept another
impulse. This results in the depolarization of the tissue and a PVC is generated.





























Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Muscle Fibre
Purkinje Fibre
A
Normal Cardiac
Tissue
Ischemic
Tissue
1
2
Example A Example B
ECG Rhythm Interpretation OBHG Education Subcommittee 35
Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms (contd)

Premature Ventricular Contraction (contd)

Unifocal





















Multifocal




















Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

Rate : 60 - 160
Rhythm : Irregular
P-R Interval : <0.20 seconds
QRS Width : normal and >0.12 seconds
P-QRS-T : Inconsistent
Missing /Added : Wide QRS complexes
Identifying Features : Wide QRS complexes without P
waves occurring before next
expected QRS interval, similar in
morphology
Rate : 60 - 160
Rhythm : Irregular
P-R Interval : <0.20 seconds
QRS Width : >0.12 seconds
P-QRS-T : Inconsistent
Missing / Added : Wide QRS complexes
Identifying Features : Wide QRS complexes without P
waves occurring before next
expected QRS interval, different in
morphology
Unifocal PVCs are the result of a single ectopic
foci originating in the ventricle. The presence of
PVCs was once thought to be of clinical
significance however recent clinical practice has
placed PVCs as a low treatment priority unless
there is significant hemodynamic compromise or
the patient is experiencing severe chest pain.
Unifocal PVCs are similar in nature. Caused by
hypoxia, MI, electrolyte imbalances.
Multi Focal PVCs are the result of multiple ectopic
foci originating in different locations within the
ventricle. Multifocal PVCs are different in
morphology. Multifocal PVCs are significant of
more severe disease process in the setting of hypoxia,
AMI and ischemia.
ECG Rhythm Interpretation OBHG Education Subcommittee 36


Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms (contd)

R on T PVC

R on T occurs when a PVC falls on the relative refractory period of the cardiac cycle. This period is the last half of
the repolarization phase of the T-Wave. If a strong enough electrical signal stimulates the cardiac tissue during the
relative refractory period, the tissue will depolarize and produce a QRS complex.











































Section 4 Cardiac Rhythms/Arrhythmias
Relative Absolute
T-Wave
PVC here
R on T
ECG Rhythm Interpretation OBHG Education Subcommittee 37

Ventricular Rhythms (contd)

Ventricular Tachycardia























Torsades de Pointes (Polymorphic Ventricular Tachycardia)























Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Rate : >100 (generally >120)
QRS Width: >0.12 seconds
Rhythm: Regular
P-QRS-T: No P waves
P-R Interval: None
Missing / Added: P waves missing
Identifying Features: Regular wide QRS complex
rhythm without P waves at rates
of >100/min
1
2
3
4
Rate : >100
QRS Width: >0.12 second
Rhythm: Irregular
P-QRS-T: No P waves
P-R Interval: None
Missing / Added: P waves Missing
Identifying Features: Wide QRS complex rhythm
that appears to twist
Ventricular Tachycardia (VT) is characterized by a
wide complex, rapid rate that is regular in nature.
There is a sawtooth pattern created by the opposite
deflection of the T wave to the QRS complex. May
spontaneously convert to NSR or may deteriorate
Ventricular Fibrillation unless corrected by chemical
or electrical cardioversion. Caused by hypoxia, MI,
electrolyte imbalances, electrical shock, etc.


Torsades de Pointe (Polymorphic Ventricular
Tachycardia) is characterized by a wide sawtooth pattern
that rotates on the graph paper. This results from
different sites in the ventricle depolarizing in a
systematic manner as shown in the diagram above. May
be caused by hypomagnesemia, prolonged Q-T or drug
effect.
ECG Rhythm Interpretation OBHG Education Subcommittee 38
Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms (contd)

Ventricular Fibrillation - Coarse
























Agonal Rhythm





















Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Rate : N/A
Rhythm: Irregular
P-R Interval: None
QRS Width: N/A
P-QRS-T: No P waves, no QRS or T
Missing / Added: No normal complexes
Identifying Features: Wide, chaotic electrical
activity greater than 1 large
square in height
Rate : <20
Rhythm: Regular or irregular
P-R Interval: N/A
QRS Width: >0.12 sec.(usually >0.20)
P-QRS-T: No P waves
Missing / Added: Normal QRS
Identifying Features: Slow, with long periods of
flatline

Ventricular Fibrillation (VF) presents with chaotic
electrical activity as the result of multiple ectopic foci
originating in the ventricles. There are no organized
QRS complexes. This lethal rhythm is seen in
approximately seventy percent of sudden cardiac
arrests. Fine and Coarse VF are differentiated by the
amplitude of the activity. Fine VF has an amplitude
of less than 5 mm (1 large square) whereas coarse VF
is greater that 5 mm in amplitude.
Agonal Rhythm is a low amplitude, wide complex
rhythm that has long periods of asystole. Treated
like asystole, this rhythm is seen as a terminal event
in cardiac arrest patients.
ECG Rhythm Interpretation OBHG Education Subcommittee 39
Section 4 Cardiac Rhythms/Arrhythmias

Ventricular Rhythms (contd)

Asystole













































Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

Rate : 0
Rhythm: None
P-R Interval: None
QRS Width: 0
P-QRS-T: No P-QRS-T
Missing / Added: Normal QRS
Identifying Features: Flatline
Asystole is a flat line indicative of no electrical activity
occurring anywhere in the heart. The baseline will
undulate in a wavelike pattern or remain completely flat.
Terminal event that has little chance of correction in
most cases
ECG Rhythm Interpretation OBHG Education Subcommittee 40
Section 4 Cardiac Rhythms/Arrhythmias

Pacemaker Rhythms

Ventricular Pacemaker






















AV Sequential Pacemaker























Notes:
_____________________________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________


Pacemaker
Pacemaker
Rate : 60 - 100
Rhythm: Regular
P-R Interval: None
QRS Width: >0.12 seconds
P-QRS-T: No P
Missing / Added: Pacemaker spikes
Identifying Features: Regular, wide complex
with pacer spike before
thecomplex
PACEMAKER
Rate : 60 - 100
Rhythm: Regular
P-R Interval: None
QRS Width: >0.12 seconds
P-QRS-T: Paced P, paced QRS
Missing / Added: Pacemaker spikes in front of P
waves and QRS complexes
Identifying Features: Regular, wide complex with
pacer spike before both P wave
and QRS
Ventricular Paced Rhythm is identified by a pacer
spike; a narrow vertical line that precedes a wide QRS
complex. The pacemaker electrode is embedded in the
right ventricle and when stimulated produces the wide
QRS. Seen in patients with history of implanted
defibrillator, heart block, sick sinus syndrome and
bradycardia.
Atrio-Ventricular Sequential Pacemaker is identified
by two pacemaker spikes followed by 1) a normal P
wave and 2) a wide QRS complex. Seen in patients
with history of implanted defibrillator, heart block,
sick sinus syndrome and bradycardia. Patients with
this type of pacemaker have the benefit of atrial
contraction or atrial kick to aid in cardiac output.
Not all pacemaker candidates qualify for a dual
chamber pacemaker.
ECG Rhythm Interpretation OBHG Education Subcommittee 41
Section 4 Cardiac Rhythms/Arrhythmias

Artifact

Baseline Artifact


Baseline artifact is seen on the ECG when there are problems with the recording of the electrical activity. The
artifact on the strip below distorts the baseline and can make P wave identification impossible. This results from
poor electrode contact, dried out electrodes, patient movement, damaged cables and improper electrode placement
such as over a boney area or large muscle mass.











60 Cycle Interference

60 Cycle Interference is seen when the patient is in close proximity to an electrical supply outlet or when electrical
appliances are operating in close proximity to the ECG machine. When encountering 60 Cycle Interference the
operator needs only to turn off the electrical appliance to elimate the interference.





























ECG Rhythm Interpretation OBHG Education Subcommittee 42
Notes: