EKG INTERPRETATION CHAPTER 3

1. Basic EKG Interpretation
CHAPTER 3: EKG INTERPRETATION BASICS
Accompanying Textbook:
ECG Interpretation Made Incredibly Easy, 5th Ed.
© 2011 by Lippincott Williams & Wilkins. All rights reserved
Instructed by: Douglas J Michel, PMD

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EKG KEY ELEMENTS
E K G I N T E R P R E T A T I O N
The QRS complex illustrates the
contraction of the ventricles during the
cardiac cycle. The shape, width, and
deflection of the QRS are used to identify
the source of the electrical signal.
VENTRICULAR CONTRACTION
The P wave illustrates the simultaneous
contraction of the atria. The shape,
deflection, and PR interval can be used to
identify the source of the electrical
impulse.
ATRIAL CONTRACTION
The T wave represents the relaxation of
the ventricles, and can be used to identify
a range of cardiac abnormalities including
electrolyte imbalances, myocardial
infarction, and other heart abnormalities.
VENTRICULAR RELAXATION
P WAVE QRS COMPLEX T WAVE

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A normal P wave should be upright, precede the QRS complex, approximately 2-3
mm high, with a duration of 0.06-0.12 seconds. Their shape should be generally
rounded in appearance.
Inverted P waves – Indicate a junctional origin from AV node.
Retrograde P waves – indicate junctional origin from AV node below the septum.
Notched P waves – indicate a possible LAE or left atrial enlargement.
Peaked P waves – suggest right atrial enlargement or cor pulmonale.
Tall P waves – Hypokalemia or RAE
Biphasic / Flattened P wave – Myocardial ischemia or Hypokalemia
Multiform P waves – variable atrial pacemaker sites
P WAVE
FINDINGS
P Wave
Deflection AV Nodal
Rhythm
Negative Deflection
SA NODAL
RHYTHM
Positive Deflection

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The shape, size, and morphology of the QRS complex can indicate the origin of the
electrical impulse or conduction abnormalities within the ventricles.
Narrow QRS complex – indicates atrial origin
Wide QRS complex – indicates ventricular origin, junctional origin, or IVCD
Forked QRS complex – suggests a bundle branch block.
Malformed QRS – ventricular origin
Multiform QRS – rhythm changes or altered pacemaker site
Deep Q wave – ischemia or previous MI
Patterned QRS – (RSR, rsr, rSR, etc) Various heart abnormalities (advanced concept)
The QRS Complex
E K G I N T E R P R E T A T I O N

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The T wave can be observed to identify a number of abnormalities, however
is less useful in actual rhythm identification than the P wave or QRS complex.
Normal T Wave – found in most rhythms when ventricle relaxes
Tall Peaked T wave – indicates Hyperkalemia
Hyperacute T waves – early stages of MI, usually found with ST segment
changes.
Inverted T waves – MI, bundle branch block, ventricular hypertrophy, PE,
hypertrophic cardiomyopathy, raised intracranial pressure, etc.
Biphasic T waves – Ischemia or Hypokalemia
Humped T waves – Hypokalemia or heart block
Flat T waves – Ischemia or Hypokalemia
The T Wave
E K G I N T E R P R E T A T I O N

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PR INTERVAL
The normal PR interval measures
0.12-0.20
Greater than 0.20 indicates a
FIRST DEGREE AV BLOCK
QRS INTERVAL
The normal QRS interval measures
0.08-0.12
Greater than 0.12 may indicate
IVCD, BBB, junctional / ventricular
rhythm, or aberrant conduction.
QT INTERVAL
The normal QT interval measures
0.35-0.44
Greater than 0.44 indicates an
elevated risk for ventricular
tachyarrhythmias.
R-R INTERVAL
The normal R-R interval measures
60-100 BPM
Less than 60 bpm indicates
Bradycardia
Greater than 100 bpm indicates
Tachycardia.
INTERVALS
E K G I N T E R P R E T A T I O N

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The ST segment begins at the J point, or where the QRS returns to
the isoelectric line, and extends to the start of the T wave. In normal
findings, this segment should remain at the same amplitude level as
the isoelectric line.
ST segment changes when compared to the patients baseline
indicate a potential emergent patient condition.
ST segment depression is considered significant when the ST
segment deviates more than 0.5mm below the isoelectric line. This
may be an indicator of myocardial ischemia or digoxin toxicity.
ST segment depression is considered significant when the ST
segment deviates more than 1mm above the isoelectric line. This
may be an indicator of acute myocardial injury (such as with MI,
hence the term STEMI).
The ST Segment
Beyond the J Point
E K G I N T E R P R E T A T I O N

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Other Wave Forms
E K G I N T E R P R E T A T I O N
U waves are small flattened or rounded
waves found following the T wave with a
typically positive deflection. U waves are
not always apparent in every EKG as they
are commonly obscured by the T wave.
Prominent U waves may indicate an
electrolyte imbalance or digoxin toxicity.
Delta waves are found at the first upturn
of the QRS, giving a slanted appearance
to the Q wave. These waves are most
commonly found in patients who have
Wolf Parkinson White condition.
U Waves and Delta Waves
Delta waves are
often present
from birth.
U waves may or
may not be a
normal finding.

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Understanding how the different waves should appear in an
EKG is key to identifying dysrhythmias. Taking into account
the appearance, frequency, and interval measurements of
each type of waveform is key to rhythm identification. As
such, with skill refinement, an otherwise unknown rhythm
may be appropriately identified through process of
elimination.
The Process of Rhythm
Identification
E K G I N T E R P R E T A T I O N
Appearance
And Measurement
Know your Measurements!
The key to understanding EKG waveforms is in memorization of the normal
measurements and intervals, and knowing what is implied when
measurements fall outside of these ranges. As such, it is sometimes easier
to first figure out what a rhythm is NOT before making deductions as to
what that rhythm is.

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The Deductive Approach
E K G I N T E R P R E T A T I O N
STEP 1: RHYTHM
Measure the distance between R waves and
between P waves to determine REGULARITY.
In a regular rhythm, both of these distances
should remain relatively constant.
STEP 2: RATE
The Rate is measured between adjacent R
waves and is used to determine whether a
rhythm is Bradycardic or Tachycardic. Rates
on the low or high end may also provide a
clue as to the rhythm.
STEP 3: P WAVE AND PR INTERVAL
Evaluate the P waves and determine if most
have the same size, shape, and deflection,
as well as their distance from the QRS
complex, or PR interval.
STEP 4: QRS AND T WAVES
The shape and measurements of the QRS
and T waves provide the final key to
identifying the rhythm.
STEP 5: QT INTERVAL AND OTHER COMPONENTS
Take note of the QT interval and any other characteristics within
the EKG recording. Pay special attention to Ectopy, or intermittent
abnormal heartbeats that do not constitute a rhythm change,
but are more fleeting in nature. Other key features to note
include ST segment, U waves, delta waves, and abnormal
deflections.

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SINUS RHYTHM WITH BRADYCARDIA, A
FIRST DEGREE AV BLOCK, IVCD, PAC’S,
ATRIAL COUPLETS, PVC’S, AND
INTERMITTENT VENTRICULAR BIGEMINY.
Naming the Rhythm
E K G I N T E R P R E T A T I O N
Naming the rhythm strip should include all of your observations,
including the origin, rate, characteristics, ectopy, and any abnormal
patterns present. The most common naming conventions present all
of the information listed in this precise order. See the following
example:
Note that the first names identified the rhythm, followed by any rate
abnormalities. This is important to first show the underlying rhythm.
Third are any identified measured characteristics.
Lastly, you want to name any ectopy or ectopic patterns present.
Any additional findings not listed above can be placed after ectopy
identification.
Exception: Any critical finding should be listed early in the analysis,
generally right after the underlying rhythm. Critical findings include
anything potentially life threatening or with a higher degree of clinical
significance.

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Sinus Rhythm, aka Normal Sinus Rhythm or NSR, forms the basis of
comparison for all other rhythm types. It is critical to be able to identify
sinus rhythms before attempting to name abnormal alternatives.
The Basis of All Rhythms
Sinus Rhythm
E K G I N T E R P R E T A T I O N
REGULA
R
RHYTHM
60-100
RATE
WNL
INTERVALS
POSITIVE
T WAVES
NARROW
QRS COMPLEX
PRESENT
SIMILAR
UPRIGHT
P WAVES

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Augmented leads may naturally display
waveforms in a reversed or inverted view.
Be careful not to misanalyze rhythms
from these leads as having different
origins. (aVr is always negative)
AUGMENTED LEADS
PRECORDIAL LEADS
Each of the Precordial leads have specific
uses for which they are designed for.
Some of these include STEMI
identification, axial deviation, hypertrophy,
and more. These are the focus of 12 Lead
Interpretation courses.
These are the most commonly used leads
for primary analysis. Most waveforms
appear upright from this view.
LIMB LEADS
DIFFERING VIEWPOINTS
E K G I N T E R P R E T A T I O N
EKG waveforms will appear differently depending on the lead or view used to analyze
the rhythm. It is best to always conduct your primary analysis from Leads I, II, and III.
Then when available, use the augmented and precordial leads as appropriate to
identify the key abnormalities they were designed to display. Hence, it is important to
know what lead you are looking at before drawing any conclusions.

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Isolated early contractions of the atriums
falling out of sequence with the underlying
rhythm. PAC’s are narrow, have similar
morphology to sinus beats, and may or
may not have a visible P wave.
Premature Atrial Contractions PAC’S
Isolated early contractions originating in
the Ventricles and falling out of sequence
with the underlying rhythm. PVC’s will be
wide, highly varying QRS morphology,
and will NOT have P waves.
Premature Ventricular Contractions PVC’S
Isolated early contractions originating in
or around the AV Node and falling out of
sequence with the underlying rhythm.
PJC’s can be narrow or slightly wide
depending on origin, will have a slightly
differing QRS morphology, and may
display inverted P waves.
Premature Junctional Contractions PJC’S
Introducing Ectopy
E K G I N T E R P R E T A T I O N

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Ectopy that falls directly between two
normal beats is called Interpolated.
INTERPOLATED
Ectopy that falls before a normally
sequenced beat is called Premature.
PREMATURE
Ectopy that falls after the point where the
normal beat should fall is called Late.
LATE
Where the ectopy falls in relation to the underlying rhythm changes how the ectopy is identified. When
classifying ectopy, you must look at the preceding heartbeat as well as the following heartbeat to
determine what kind of ectopy is present.
Early, In Sequence, Late
Ectopy Identification
E K G I N T E R P R E T A T I O N

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Ectopy occurring in groups or patterns
should also be identified according to it’s
frequency of occurrence.
Groups and Patterns
A normal feature of ectopy is the presence of a compensation pause
following the abnormal heartbeats. This is NOT classified as a pause
for the purpose of analysis unless it exceeds 1 second in length.
Compensation Pauses
Other
Ectopic Features
Bigeminy
Trigeminy
Quadrigeminy
Every other heartbeat
Every third heartbeat
Every fourth heartbeat
Couplets
Triplets
Runs
Two ectopic beats together
Three ectopic beats together
Four or more ectopic beats
Fusion Beats
A ventricular ectopic beat that falls precisely where the normal
heartbeat should fall is commonly referred to as a Fusion beat.

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IDENTIFY RHYTHM AND RATE
Examples: Sinus rhythm, Sinus Tachycardia, Atrial Fibrillation1ST
IDENTIFY CHARACTERISTICS
Examples: First Degree AV Block, IVCD2ND
IDENTIFY ECTOPY AND PATTERNS /
GROUPINGSExamples: PVC’s, Atrial Couplets, Ventricular Trigeminy3RD
IDENTIFY OTHER ABNORMALITIES
Examples: Sinus pauses, delta waves, tall peaked T waves4TH
EKG QUICK ANALYSIS: RECAP
E K G I N T E R P R E T A T I O N