Advanced ECG Interpretation
Dr. Jeffrey Elliot Field, HBSc. DDS,
Fellow, American Dental Society of Anesthesia
Diploma, the National Dental Board of Anesthesia.
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4/8/2015
OBJECTIVES
 To get a more in depth knowledge of ECG
interpretation.
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.
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.
P-Wave Abnormalities Seen In V1
 Biphasic P-Waves are seen for both left and right atrial
enlargement.
 For right atrial enlargement the initial portion of the
P-wave is larger than the distal portion.
 Alternatively for left atrial enlargement the initial
portion of the P-wave is smaller than the distal
portion.
P Pulmonale ( right atrial
enlargement)
Note the larger initial portion
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P Mitrale ( left atrial enlargement)
Note the larger terminal portion
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The QRS Complex in Detail
 As well as showing ventricular conduction defects, the
QRS complex along with ST segment analysis is used
to diagnose myocardial oxygen deficits and myocardial
infarctions.
 The QRS complex is also used to diagnose accessory
conduction pathways in the heart.
S-T Segment Analysis
 In order to assess the S-T segment we must first define
the J-point.
 The J point in the ECG is the point where the QRS
complex joins the ST segment. It represents the
approximate end of depolarization and the beginning
of repolarization.
The Isoelectric Point
 S-T segments can be elevated, depressed or isoelectric.
 The J-point is deemed to be isoelectric if the S-T
line/segment is not elevated or depressed with respect to
the P-Q line/segment. As in the diagram below. See
arrows 


S-T Changes
 You can see both S-T elevation and S-T depression on
ECG’s.
 S-T elevation is indicative of a myocardial infarction.
So in other words myocardial cell death is occuring.
 S-T depression is indicative of myocardial ischemia.
The myocardial cells are not getting enough oxygen
and are at risk of dying.
S-T Depression
S-T Elevation
Myocardial Infarction
 Myocardial infarctions can be categorized as follows:
 -Q-wave MI
 -Non Q-wave MI
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Q-Wave Myocardial Infarction
 This is the classic presentation for MI’s.
 The developing MI is seen as ST segment elevation




followed by deepening Q-waves
in the leads where ST
st
segment elevation was 1 seen.
Q waves are “significant” if they are greater than 1 box in
width (longer than 0.04 msec), or are larger than 1/4 of the
R wave.
Significant Q waves are indicative of myocardial infarction.
However signifigant Q-waves in lead III alone are
NOT diagnostic of an infarction, even they are
otherwise “significant” in size and width.
Therefore signifigant Q-waves in lead III are ignored
unless other abnormalities are seen.
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Note the large Q-waves.
Non Q-Wave Myocardial Infarction
 In this case you get classic signs and symptoms of an
MI(i.e elevated cardiac enzymes and markers and of
course physical signs of an MI ( chest pain ,nausea
,vomiting , etc)
But non of the usual ECG changes ( i.e. ST segment
elevation and deepening Q-waves). In fact
sometimes the only clue on the ECG are inverted
T-waves.
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Accessory Conduction
Pathways. Also Called PreExcitation Syndromes
Pre-excitation Syndromes
 These syndromes are characterized by an aberrant
conduction pathway that enters the ventricular
muscle in addition to the normal pathway. Since
these aberrant pathways are shorter they cause
ventricular depolarization prior to the normal
pathway.
 There are 2 pre-excitation syndromes
 Wolf –Parkinson-White
 Lown-Ganong-Levine
Both pathways show shortened P-R intervals of less than
0.20 sec.
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Wolf Parkinson White
 The abberant pathway is the bundle of Kent which
bypasses the AV node. This gives a shortened P-R
interval ( i.e. less than 0.20 seconds)
 There is a shoulder on the R-wave of the QRS
complex. This shouldered QRS complex is called a
Delta-wave and is the result of a fused ( fusion) beat
from the normal and aberant pathway.
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Wolf Parkinson White
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Delta Wave 
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Lown-Ganong-Levine
 The aberant pathway is the bundle of James which
joins the normal pathway above the AV node.
 Since the abnormal pathway joins the normal pathway
Above the AV node rather than within it there is no
delta wave but just a shortened PR interval (i.e. less
than 0.20seconds)
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Importance of Pre-Excitation
Syndromes
These can lead to severe
tachycardia's.
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Bundle Branch Blocks
In bundle branch blocks either the right or the left branch is partially (
hemiblocks) or totally blocked. If both right and left bundle branches are
blocked, this is termed complete or third degree heart block.
Normally both bundle branches depolarize simultaneously but with bundle
branch blocks the unblocked side depolarizes first and its impulse then
spread to the blocked ventricle . So depolarization of the ventricles is
sequential.
The major significance of a new BBB is that it may indicate the presence of a
previously unknown underlying cardiovascular disease.
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Right Bundle Branch Blocks
Conditions that cause this are :
-pulmonary embolism
-chronic lung disease
-cardiomyopathy
-atrial and ventricular septal defects
-However in some individuals RBBB is seen in
perfectly healthy individuals and is a variant of normal.
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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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Left Bundle Branch Block
In Contrast to RBBB LBBB is almost always indicative of
underlying cardiac pathology. There is no normal variant.
Conditions that cause this are :
-dilated cardiomyopathy
-hypertrophic cardiomyopathy
-hypertension
-aortic valve disease
-coronary artery disease
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Left
Bundle
Branch
Block
 Left Bundle branch blocks are seen in Leads 1
, V1 and V6 as 2 R-waves. R and R prime
without an intervening S-wave. The wave
between the R-waves is scooped. R-Rprime
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Clinical Considerations for Bundle
Branch blocks
 All patients with a bundle branch block should be
cleared by their physician prior to any in office
anesthesia.
 Fortunately it is uncommon for a stable right or left
bundle branch block to develop into complete heart
block. Therefore with physician approval in office
anesthesia can be safely performed
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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.
Shortened Q-T
Segment
Abnormalities
QT Interval Abnormalities
 Digoxin toxicity causes a shortened QT interval
with a scooping of the ST segment.
Note the Q-T segment is only 8 small boxes wide 0.32 seconds
divided by the square root of 1.16 ( 29 X 0.04)( the number of
small boxes X 0.04 seconds)= 1.07. So Q-T corrected is
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0.32/1.07=0.30
seconds
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 Although digoxin treatment toxicity is
outside the scope of this lecture suffice it to
say that under and over digitalization can
lead to severe arrhythmia's and cardiac
depression.
 So if your patient is on digoxin you have to
know their digoxin levels and get physician
approval to proceed with in office
ansthesia.As such these patients may be
inappropriate for in office anesthesia.
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Other Causes of Short Q-T Intervals
 1) familial/genetic short Q-T syndrome
 2) Hypercalcemia
 3) Hyperthermia
Prolonged Q-T
Segment
Abnormalities
Causes of Prolonged Q-T Intervals
 1) familial/genetic prolonged Q-T syndrome
 2) Hypocalcemia
Although calcium
abnormalities are also outside
the scope of this lecture
suffice it to say that they can
lead to severe arythmia’s and
cardiac depression.
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Potassium Induced ECG Changes
Including T-Wave Abnormalities
 Hyperkalemia as it evolves leads to tall peaked Twaves, prolonged P-R interval and a widened QRS
complex. Eventually the P-wave is lost and the
QRS becomes biphasic
 Hypokalemia leads to small biphasic flattened Twaves, S-T depression and a prominent U-waves
.The U-wave is an extra wave after the T-wave.
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Abnormalities in Serum
Potassium
 Potassium abnormalities are worth dwelling on for
a moment as we are likely to encounter them in our
day to day practice.
 Either hypo or hyperkalaemia can lead to severe
cardiac events and both need urgent treatment.
 Normal serum potassium is 3.0-5.0 milliequivalents
per litre of blood.
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The red flags to look
for are:
 patients on diueretics who loose potassium.
 Patients on exogenous potassium tablets who can
get hyperkalemia.
 In either of these groups it is worth getting preop
electrolytes done.
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ECG diagnosis does not
have to be difficult as long
as you take an orderly and
well thought out approach.
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PUTTING IT ALL TOGETHER
 1)
Look at the rhythm. Is it regular
or irregular.
2) Determine the rate. Is it normal,
fast or slow.
3) Determine the relationship ( if
any) between the P-wave and the
QRS complexes.
4) Look at the intervals , PR, QRS,
QT.
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PUTTING IT ALL TOGETHER
 5) Finally look at recognizable patterns to sort out
a difficult diagnosis:
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sawtooth P-waves in atrial flutter.
a missing QRS complexes in PAC’s.
irregularly irregular rhythm for atrial fibrillation.
delta waves for WPW.
RSR prime for RBBB.
RR prime with loss of S in LBBB.
Deep Q waves in MI , large T waves in hyperkalemia etc.
Missing P-waves in junctional rhythms.
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Categorizing Rhythms With
Respect To An Interventional
Hierarchy .
Know when to worry!
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Immediate Action Needed
Asystole
Ventricular Fibrillation
Pulseless Ventricular Tachycardia
Third degree heart block
Tachyarythmias in which
perfussion is compromised
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Action Required Within Minutes
( This group is also known as pre-arrest syndromes
)

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Significant Bradycardia.
Runs of unifocal PVC’s ( i.e. triplets , couplets etc.)
Multifocal PVC’s.
Second degree type 2 heart block ( because it often
is the precursor for third degree heart block.
 Tachyarrhythmia's in which perfusion is not yet
compromised.
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Referral Required ( prior to dental
treatment) With No immediate Action
Needed
Any other abnormality
noted which the patient
was unaware of in their
medical history.
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Summary
You hopefully now understand ECG interpretation.
 This can be applied in preoperative intraoperative and
post operative patient assessment.
 You can utilize this knowledge in courses designed to
teach arrhythmia treatment such as ILS and ALS and
in your emergency simulation courses.
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END OF PRESENTATION
 Thank you for your commitment to continuing
education