Introduction to ECG Interpretation
Electrocardiogram interpretation is an invaluable clinical skill that is taught in many different ways at medical
schools across the country. It is often informal and clinicians are expected to "pick it up" as they see patients
on the wards and in clinics. There are many "courses" which can be purchased off the shelves at the
bookstore -some of them too simplistic and others hopelessly detailed. In an effort to better meet the needs
of ecg interpretation this course started out at UW Madison as a self study manual with some workshops
where clinicians reviewed tracings with preceptors. The popularity of this course was immediate - we soon
had clinicians asking for it on other rotations and the workshops were often visited by an assortment of
clinicians from the health care fields. Reasons identified for the course's success was that it was directly
applicable to patient care, a skill that was enjoyable to master, of value as a lifelong career tool (ecg
interpretation content has been stable for years),and "adult learning" principles were respected.
This computerized version of the course has some significant improvements. At the end of each
content area is a quiz. This not only reinforces the material but the advanced clinician can try the
quiz first, if they already feel comfortable with the content material, and go on to another section, to
optimize their time. The tool bars at the bottom of the page allow this flexibility to go directly to any
section. The "guidelines" which summarize the ENTIRE interpretive process can be printed out on a
single page and carried in the lab coat pocket when seeing patients. The clinical cases at the end
are an assortment of real life cases to demonstrate that ecgs are always interpreted in the context
of patient care and not in a "vacuum". Differential diagnosis is emphasized to encourage thinking
about the "art" of interpretation, not just a cookbook mechanistic approach. In addition, this course
sets up the basic skills needed for interpretation in a self directed learning format, allowing clinicianpreceptor interaction to focus on more advanced patient specific ecg correlation
Primer on Basic Concepts
P wave = depolarization of the atria.
QRS = depolarization of the ventricle.
T wave = repolarization of the ventricle
1. Cardiac muscle cells depolarize with a
positive wave of depolarization, then repolarize
to a negative charge intracellularly.
2. Skin "leads" or electrodes have a positive and
negative end.
3. A positive wave form (QRS mainly above the
baseline) results from the wave of
depolarization moving towards the positive end
of the lead. A negative waveform (QRS mainly
below the baseline) is when a wave of
depolarization is moving away from the positive
4. electrode (towards the negative end of the
lead).
1. ECG paper has 1 millimeter small squares - so
height and depth of wave is measured in millimeters.
10 mm = 1.0 mVolt
2. Horizontal axis is time.
.04 seconds for 1 mm (1 small box).
.2 seconds for 1 large box = 5 small boxes = 5 x .04
seconds.
Positive QRS in Lead I.
Negative QRS in Lead aVR.
R wave = 7-8 mm high in Lead I.
QRS wave = .06 seconds long in Lead I.
1.Lead nomenclature.
Limb lead
Chest lead
Rhythm strip
I, II, III
aVR, aVF, aVL
V1 - V6 Located on the
bottom of the ECG
printout.
Selected to give the
best relationship of
the P wave to the
QRS
Figure 3: A normal ECG and rhythm strip
1.ECG interpretation: look at five areas, in order, on each ECG.
Rate
Rhythm (Intervals)
Axis
Hypertrophy
Infarct
Hypertrophy
Hypertrophy criteria are fairly straightforward; we will be looking for enlargement of any of the
four chambers.
1. LVH: (Left ventricular hypertrophy). Add the larger S wave of V1 or V2 (not both),
measure in mm, to the larger R wave of V5 or V6. If the sum is > 35mm, it meets
"voltage criteria" for LVH. Also consider if R wave is > 12mm in aVL. LVH is more
likely with a "strain pattern" which is asymmetric T wave inversion in those leads
showing LVH.
2. RVH: (Right ventricular hypertrophy). R wave > S wave in V1 and R wave
decreases from V1 to V6.
3. Atrial hypertrophy: (leads II and V1). Right atrial hypertrophy - Peaked P wave in
lead II > 2.5mm amplitude. V1 has increase in the initial positive deflection. Left atrial
hypertrophy - Notched wide (> 3mm) P wave in lead II. V1 has increase in the terminal
negative deflection.
Figure 32: Right ventricular hypertrophy and right atrial
enlargement.
Figure 33: Left ventricular hypertrophy (S wave V2
plus R wave of V5 greater than 35mm) and left
atrial enlargement (II and V1).
Take the hypertrophy quiz.
#1 Hypertrophy
Left ventricular and left atrial hypertrophy.
S wave in V2 plus R wave in V5 > 35.
The left atrial hypertrophy is noticaeable by a P wave that is long in lead II,
with an increase in the negative terminal deflection in lead V1.
[Done].
#2 Hypertrophy
Left ventricular and left atrial hypertrophy.
The R wave in aVL is greater than 12mm.
The left atrial hypertrophy is barely noticeable by a P wave that
is notched and wide in lead II and with an increase in the
negative terminal deflection in lead V1.
[Done].
#3 Hypertrophy
Right ventricular and right atrial hypertrophy.
The R wave is greater than the S wave in V1 and the R wave gets
progressively smaller from V1 to V6. Normally, the R wave should increase
from V1 to V6.
The right atrial hypertrophy is marked by peaked P waves in lead II and a
large intitial positive deflection of the P wave in lead V1.
Infarct
Accurate ECG interpretation in a patient with chest pain is
critical. Basically, there can be three types of problems ischemia is a relative lack of blood supply (not yet an infarct),
injury is acute damage occurring right now, and finally, infarct
is an area of dead myocardium. It is important to realize that
certain leads represent certain areas of the left ventricle; by
noting which leads are involved, you can localize the process.
The prognosis often varies depending on which area of the left
ventricle is involved (i.e. anterior wall myocardial infarct
generally has a worse prognosis than an inferior wall infarct).
V1-V2
anteroseptal wall
V3-V4
anterior wall
V5-V6
anterolateral wall
II, III, aVF
inferior wall
I, aVL
lateral wall
V1-V2
posterior wall (reciprocal)
Infarct
1. Ischemia
Represented by symmetrical T wave inversion (upside down).
The definitive leads for ischemia are: I, II, V2 - V6.
2. Injury
Acute damage - look for elevated ST segments. (Pericarditis
and cardiac aneurysm can also cause ST elevation; remember
to correlate it with the patient.
3. Infarct
Look for significant "patholgic" Q waves. To be significant, a
Q wave must be at least one small box wide or one-third the
entire QRS height. Remember, to be a Q wave, the initial
deflection must be down; even a tiny initial upward deflection
makes the apparent Q wave an R wave.
Figure 34: Ischemia: Note symmetric T wave inversions in leads I, V2-V5.
Figure 35: Injury: Note ST segment elevation in leads V2-V3 (anteroseptal/anterior wall).
Figure 36: Infarct: Note Q waves in leads II, III, and aVF (inferior wall).
For the posterior wall, remember that vectors representing depolarization of the
anterior and posterior portion of the left ventricle are in opposite directions. So,
a posterior process shows up as opposite of an anterior process in V1. Instead of
a Q wave and ST elevation, you get an R wave and ST depression in V1.
Figure 37: Posterior wall infarct. Notice tall R wave in V1. Posterior wall infarcts are often
associated with inferior wall infarcts (Q waves in II, III and aVF).
Two other caveats: One is that normally the R wave gets larger as you go to V1 to V6. If there is
no R wave "progression" from V1 to V6 this can also mean infarct. The second caveat is that,
with a left bundle branch block, you cannot evaluate "infarct" on that ECG. In a patient with
chest pain and left bundle branch block, you must rely on cardiac enzymes (blood tests) and
the history.
#1
Acute injury in the anterior, anterolateral, and lateral
wall (ST elevation in V2-V6, I and aVL).
#2
Infarct in the antereoseptal and anterior wall (Q waves in V2-V4 there is also
a probable inferior infarct (Q waves in II, III, and aVF)).
#3
Ischemia across the entire anterior and lateral wall (T wave inversions in V2V6, I and aVL). Also note, the injury pattern in V2 of ST elevation, the
prominent Q waves in V2 and V3 show that some of the myocardium has
also reached the infarct stage
Rate
Rate is cycles or beats per minute.
Normal rate for the SA node 60-100.
<60 bradycardia
>100 tachycardia
SA node is the usual pacemaker, other potential pacemakers (if SA node fails) are
atrial pacemakers with inherent rates of 60-80, AV node (rate 40-60), or ventricular
pacer (rate 20-40). In certain pathologic conditions ectopic (out of place) pacemakers
can go much faster at rates 150-250 cycles/minute. There are three methods of
calculating rate:
1. Most Common Method:
(Most rates can be calculated this way). Find an R wave on a heavy line (large box)
count off "300, 150, 100, 75, 60, 50" for each large box you land on until you reach the
next R wave. Estimate the rate if the second R wave doesn't fall on a heavy black line.
Rate calculation
Memorize the number sequence:
300, 150, 100, 75, 60, 50
1.Mathematical method:
Use this method if there is a regular bradycardia, i.e. - rate < 50. If the distance between the two
R waves is too long to use the common method, use the approach: 300/[# large boxes between
two R waves].
: Count number of large boxes between
first and second R waves=7.5. 300/7.5
large boxes = rate 40.
1.Six-second method:
Count off 30 large boxes = 6 seconds (remember 1 large box = 0.2 seconds, so 30 large
boxes = 6 seconds). Then, count the number of R-R intervals in six seconds and
multiply by 10. This is the number of beats per minute. This is most useful if you have
an irregular rhythm (like atrial fibrillation) when you want to know an average rate.
Figure 6: Count 30 large boxes, starting from the first R wave. There are 8 R-R
intervals within 30 boxes
Concentrate on the rate for the following unknown tracings.
#1 Rate
The rate is about 90.
The second R wave in the rhythm strip lands on a heavy line. Count "300-150100-75" over (four heavy lines) to the next R wave to determine the rate. You'll
have to estimate between 75 and 100 for this example.
#2 Rate
ANSWER 2
The rate is about 40.
Use the bradycardia method where 300 divided by the number of large boxes
between R waves is the rate. In this case, there are 7.5 large boxes between R
waves. 300 divided by 7.5 equals a rate of 40
#3 Rate
ANSWER 3
Rate about 70-80.
Use the six second strip method. There are 30 large boxes in six seconds.
Multiply the number of R-R intervals in six seconds by ten to get the rate.
Rhythm (to include intervals)
We will focus on the basic "core" of rhythms and measured "intervals" (PR, QRS, QT). Rhythms
are often the most challenging aspect of ECG's. You will see most rhythms several times over the
next few years of your training, and you will eventually recognize them at a glance.
Now for some basics - "arrhythmia" means abnormal rhythm.
The normal conduction pathway is: SA node --> AV node --> Bundle of HIS --> Bundle Branches.
Arrhythmia can be understood by realizing the existence of ectopic (out of place) foci
(pacemakers) and understanding the normal conduction pathway of the heart. Very simply put,
if the beat originates in the atria or AV node (supraventricular) the QRS is usually narrow
(normal), because it comes from above along the normal pathway.
Figure 6a: QRS is narrow (normal).
If the beat is ventricular in origin, the QRS is wide and bizarre
because it doesn't come down the normal pathway.
Figure 6b: QRS is wide.
Aberrancy is an exception to this rule - here it does actually follow the normal
pathway (atria - AV node - ventricle) but for some reason the pathway is refractory
to the beat and you get a wide QRS.
A reasonable way to group arrhythmias is in four general groups. Let us briefly review
these four groups, then we will develop some common sense principles for evaluating
rhythm (to include intervals).
Group 1 Irregular rhythms.
(main clue is QRS is not spaced evenly apart anywhere, total irregularity
of the beat).
A) Sinus arrhythmia.
P waves and P-R intervals are all identical because they originate from the
sinus node. Sinus rate may vary normally a bit (increase with inspiration,
decrease with expiration), but if the rate varies a lot, this term is used.
Figure 7: Sinus arrhythmia: P waves are identical.
B) Wandering atrial pacemaker.
Pacemaker discharges from different atrial locations - the clue here is the P waves are of
varying shape and differing PR intervals. PR interval is measured from the beginning of
the the Pwave to the beginning of the QRS - if the atrial pacemaker location varies it will
take different lengths of time to get to the ventricle - resulting in different PR intervals. If
the rate of the wandering atrial pacemaker is >100 it is descriptively called multifocal
atrial tachycardia.
Figure 8: Multifocal atrial tachycardia.
C) Atrial fibrillation.
You will frequently see this arrhythmia. There are no P waves,
only irregular or wavy baseline. The QRSs are irregularly
spaced, therefore it is included under irregular rhythms.
Figure 9: Atrial fibrillation.
Group 2 Escape (late) beats
and premature (early) beats.
The bottom line for Group 2 arrhythmias is that the rhythm is fairly regular - then you
will notice an early or late beat; try to figure out whether that beat is a premature atrial
contraction, premature ventricular contraction, etc.
A) Escape beats.
The usual pacemaker fails, so a slower pacemaker fires at its inherent rate.
Atrial escape
Different appearing and late P wave.
Figure 10: Atrial Escape Rhythm. Note differing appearance of the P waves for Sinus
Rhythm vs. Atrial Escape Rhythm.
Junctional escape
No P wave, normal QRS if not aberrant.
Figure 11: Note all beats are junctional escape
Ventricular escape
No P, wide, bizarre QRS.
Figure 12: Ventricular escape.
B) Premature Beats.
An ectopic pacemaker fires early before the next scheduled beat.
Premature atrial contraction
"PAC", early and differently shaped P wave, narrow QRS.
Figure 13: Premature Atrial Contraction noted by arrow.
Premature junctional
No P, normal QRS if not aberrant.
Figure 14: Note the two early, narrow beats at the arrow. These are probably
PJCs.
Premature ventricular contraction
No P, wide bizarre QRS. PVCs that occur three (3) or more in a row
(ventricular tachycardia), multifocal PVCs (different shapes), or PVCs that
land on a previous T wave (R on T phenomenon) can be dangerous ion a
patient with underlying heart disease.
Figure 15: Note: Every fourth beat is a PVC (beginning with the second beat).
rhythms.
Ectopic rate nomenclature:
So, the descriptives paroxysmal tachycardia, flutter, and fibrillation refer to the
"rates" of the arrhythmia, e.g. - it could be atrial fibrillation (wavy baseline refers
to the atria going >350 bpm.), or ventricular fibrillation (with the ventricle not
contracting in a coordinated fashion resulting in only an erratic line that isn't
possible to count).
[150-250]
Paroxysmal tachycardia
[250-350]
Flutter
[350+]
Fibrillation
So, the descriptives paroxysmal tachycardia, flutter, and fibrillation refer to the
"rates" of the arrhythmia, e.g. - it could be atrial fibrillation (wavy baseline refers
to the atria going >350 bpm.), or ventricular fibrillation (with the ventricle not
contracting in a coordinated fashion resulting in only an erratic line that isn't
possible to count).
Figure 16: Paroxysmal supraventricular tachycardia: note accelerated rate and narrow
QRS complexes.
Figure 17: Ventricular tachycardia: note fast rate and wide bizarre QRS.
Figure 18: Ventricular fibrillation: erratic and wavy baseline
Group 4 Atrioventricular heart blocks.
occur in three (3) degrees, like skin burns; third degree is the worst).
1st degree
PR interval > 0.2 seconds (1 large box), each P is followed by a QRS. PR interval is
measured from the beginning of the P wave to the beginning of the QRS.
(
Figure 19: The PR interval is approximately 0.28 seconds.
2nd degree block - type 1
Also called "Wenkebach". PR interval gets progressively longer each beat until finally
a QRS is "dropped" (missing).
Figure 20: Note the increasing PR interval before the QRS is dropped, then the
cycle is repeated.
2nd degree block - type 2
Also called "Mobitz II". Look out! A more serious conduction problem
than Type 1. PR intervals are constant and a QRS is "dropped"
intermittently.
Figure 21: Note the dropped QRS after the second and sixth P wave in lead II (the
rhythm strip).
3rd degree block
The atrial rate is independent of the ventricular rate (P wave and QRS march out separately.
The clue here is no relationship at all of the P-R intervals). The P-R interval is constantly
changing, the QRS is usually wide and bizarre because it is ventricular origin.
Figure 22: Note the P waves and QRS waves are independent of each other.
Intervals
An interval is a portion of the baseline and at least one wave. We measure an interval on the horizontal axis in
seconds. The PR, QRS, and QT are the intervals which should be routinely scanned on each ECG. For
measuring intervals, look at the widest form in any lead.
1.PR interval (beginning of P wave to the beginning of the next QRS). Normally, <
.2 seconds or one large box. If it is > .2 seconds, it is a first degree block. (Note: this
concept was introduced under blocks).
Figure 24: Note the prolonged PR interval (.28 seconds), especially at the second beat
QRS interval (beginning of Q to the end of the S wave) should be < .12
seconds (< 3 small boxes). If QRS is > .12, check for bundle branch block.
A QRS > .12 and RR (2 peaks or R waves in QRS) occurring in the right chest
leads (V1-V2) indicates a right bundle branch block.
Figure 25: RBBB.
If QRS is > .12 and RR occurs in the left chest leads (V5-V6), this indicates a left bundle
branch block.
Figure 26: LBBB.
Very important: For left bundle branch block, the ECG is often unreliable for identifying infarct. Infarct is a
concept explained later in this tutorial, but don't forget that with left bundle branch block, one cannot rely on
the ECG for diagnosis of infarct.
1.QT interval (beginning of QRS to end of T wave) should be less than half of the preceding RR interval - this varies
with the rate. For normal rates, QT < .4 seconds (2 large boxes). "QT prolongation" (too long) can lead to a refractory
form of ventricular tachycardia called torsades de pointes.
Figure 27: The QT interval is greater than half the preceding RR interval. Look at lead I.
Rhythm Guidelines
1. Check the bottom of the rhythm strip for regularity, i.e. - is it
completely regular, mostly regular with a few extra beats, or
totally irregular?
2. Check for a P wave before each QRS, QRS after each P.
3. Check RR interval (for AV blocks) and QRS interval (for bundle
branch blocks). Check for prolonged QT.
4. Continue to recognize "patterns" such as atrial fibrillation, PVCs,
PACs, escape beats, ventricular tachycardia, paroxysmal atrial
tachycardia, AV blocks and bundle branch blocks.
Rhythm and Intervals Quiz: Question 1
Match the tracings with the correct
interpretation:
A. First Degree Block
B. Sinus Arrhytmia
C. Third Degree Block
D. Atrial Fibrillation
Rhythm and Intervals Quiz: Question 1
The correct matches are:
C. Third Degree Block
The atrial rate is independent of the
ventricular rate so the P waves are
independent of the QRS's. The P waves are
regular and can be marched out with
calipers. The same can be done with the
QRS complexes.
D. Atrial Fibrillation
No P wave, irregular QRS with a wavy
baseline.
A. First Degree Block
PR interval is greater than .2 seconds (one
large box). Note that there is a P wave
before each QRS and a QRS after each P
wave.
Rhythm and Intervals Quiz: Question 2
Match the tracings with the
correct interpretation:
A. Second Degree Block Type 1
B. PAC
C. Second Degree Block Type 2
D. Paroxysmal Supraventricular
Tachycardia
Rhythm and Intervals Quiz: Question 2
The correct matches are:
C. Second Degree Block Type 2
PR intervals are the same, but every other
beat is dropped.
D. Paroxysmal Supraventricular Tachycardia
Regular narrow QRS. Often it's hard to
determine whether it's atrial or junctional as
it is going too fast to see P waves. Clinically it
doesn't matter since they are treated the
same.
B. PAC
The third beat is premature. It has a P wave
of different morphology than the sinus
beats. This defines it as a premature atrial
contraction.
Rhythm and Intervals Quiz: Question 3
Match the tracings with the
correct interpretation:
A. Ventricular Tachycardia
B. Second Degree Block Type 1
(Wenckebach)
C. Junctional Rhythm
D. Wandering Atrial Pacemaker
Rhythm and Intervals Quiz: Question 3
The correct matches are:
D. Wandering Atrial Pacemaker
(It's called Multi focal Atrial
Tachycardia if the rate is >100).
Strict definition is 3 different P
wave morphologies and 3
different PR intervals.
A. Ventricular Tachycardia
Fast, wide, regular, bizarre QRS.
B. Second Degree Block Type 1
(Wenckebach)
The PR gets progressively longer
until a beat is dropped.
Rhythm and Intervals Quiz: Question 4
Match the tracings with the
correct interpretation:
A. Normal Sinus Rhythm
B. Ventricular Fibrillation
C. Sinus Arrhythmia
D. Junctional Rhythm
Rhythm and Intervals Quiz: Question 4
The correct matches are:
A. Normal Sinus Rhythm
Normal appearing P waves and
QRS complexes.
D. Junctional Rhythm
Relatively narrow QRS, absence of
P waves.
C. Sinus Arrhythmia
Irregular, but note P wave
morphology and PR intervals are
identical, this identiies it as a sinus
rhythm.
Rhythm and Intervals Quiz: Question 5
For the following two 12 lead ECGs verify that the QRS is prolonged in each.
Which of the following 12 leads is a Right Bundle Branch Block and which is a
Left Bundle Branch Block?
Right Bundle Branch Block
There is a RR' in V1 and V2 with a QRS greater than .12 seconds (three small boxes). You can measure
the interval in the lead that shows the widest QRS. Also with right bundl branch block, the T wave is
often affected (at least partially inverted) as part of the bundle branch block.
Axis
Direction of depolarization (vector) of the QRS complex.
1.The left ventricle is thicker so the mean QRS vector is down and to the left. (The origin of
the vector is the AV node with the left ventricle being down and to the left of this).
2.The vector will point toward hypertrophy (thickened wall) and away from the infarct
(electrically dead area).
Figure 28: Axis nomenclature.
Normal axis
Left axis deviation
Right axis deviation
Indeterminate (extreme) axis deviation
-30 to +90 degrees
-30 to -90 degrees
+90 to +/-180 degrees
-90 to +/-180 degrees
Since lead I and aVF are perpendicular to each other, you can use
those two leads to quickly determine axis.
Lead I runs from right to left across a patient's body, positive at the
left hand:.
If the QRS in lead I is positive (mainly above the baseline), the
direction of depolarization will be in the positive half (right half) of
the circle above. You can make a diagram and shade in the positive
half of the circle.
Lead aVF runs from top to bottom across a patient's body, positive at the feet.
If the QRS in lead aVF is positive (mainly above the baseline), the direction of depolarization will be in the
positive half (lower half) of the circle above. You can make a diagram and shade in the positive half of the
circle:
To find the axis overlap the two circles. The common shaded area is the quadrant in which the axis lies. In
this example, the axis lies in the normal quadrant, which on a patient, points down and to the left.
You can repeat this process for any two leads, but I and aVF are the classic places to
look. If you realize that there are two leads to consider and a positive (+) or (-)
orientation for each lead, there would be four possible combinations. Memorize the
following axis guidelines.
1. Normal axis (0 to +90 degrees)
Lead I
Lead aVF
Positive
Positive
2. Left axis deviation (-30 to -90)
Also check lead II. To be true left
axis deviation, it should also be
Positive
down in lead II. If the QRS is
upright in II, the axis is still normal
(0 to -30).
Negative
3. Right axis deviation (+90 to
+180)
Positive
Negative
4. Indeterminate axis (-90 to -180) Negative
Negative
Normal axis.
Left axis deviation
Right axis deviation.
The bottom line is, if the axis is shifted out of the normal quadrant, evaluate the
reasons for this.
Differential Diagnosis
Left axis deviation
LVH, left anterior
fascicular block, inferior
wall MI
Right axis deviation
RVH, left posterior
fascicular block, lateral
wall MI
#1 Axis
Normal Axis.
Positive QRS in Lead I and aVF
#3 Axis
Left axis deviation.
Positive QRS in lead I, but negative QRS in leads II and aVF.
Right axis deviation.
Positive QRS in lead aVF, but negative QRS in lead I.
fascicular Blocks
fascicular blocks are blocks of part of the left bundle, either the posterior or
anterior division:
: Divisions of the bundles.
Anterior fascicular block - the most common.
You will see left axis deviation (-30 to -90) and a small Q wave in lead I and an S in
lead III (Q1S3). The QRS will be slightly prolonged (0.1 - 0.12 sec).
Anterior fascicular block.
Posterior fascicular block - less common.
You will see right axis deviation, an S in lead I and an Q in lead III (S1Q3).
The QRS will be slightly prolonged (0.1 - 0.12 sec).
Posterior fascicular block.
Bifascicular block.
This means two (2) of the three (3) fascicles (in diagram) are blocked. The most
important example is a right bundle branch block and a left anterior fascicular block.
Watch out for this. Only one fascicle is left for conduction, and if that fasicle is
intermittently blocked, the dangerous Mobitz 2 is set up!
: Right bundle branch block and left anterior fascicular block.
"fascicular Blocks" may seem a bit complicated simply remember that axis deviation is the clue.
In your differential, consider posterior fascicular
blocks with right axis deviation and consider anterior
fascicular blocks with left axis deviation. Fascicular
blocks cause axis deviations, like infarcts and
hypertrophy. If you see a left or right axis deviation,
first look for infarct or hypertrophy. If neither are
present, the remaining diagnosis of fascicular block is
usually correct. Review differential diagnosis of right
and left axis deviation.
#1 fascicular Block
Left anterior fascicular block (left axis deviation and Q1S3).
#2 fascicular Block
Left posterior fascicular block (right axis deviation and
S1Q3).
#3 fascicular Block
Bifascicular block RBBB and LAFB (right bundle branch block and left anterior
fascicular block).
One Last Differential Diagnosis
Four cases of an R wave taller than an S wave in
V1 (normally R wave always < S wave in V1.
1.Right bundle branch block.
2.Right ventricular hypertrophy.
3.Posterior wall myocardial infarction.
4.Wolff-Parkinson-White.
Case 1
A 60-year-old "walk-in" patient without a primary care physician arrives at your clinic
near the end of a busy afternoon clinic session. The patient is not on any medications
and has not seen a physician in years. The patient complains of several hours of severe
chest pressure and as he lives nearby he thought he would come to your clinic and try
to see a physician. Although the vital signs were remarkable only for some
bradycardia, the medical assistant is concerned that the patient appears ill. A stat ecg
was done and you are asked to see this patient immediately. The following ecg is
handed to you as you are on your way to see this patient.
Case 1 Answer
Rate - 50
Rhythm - sinus bradycardia
Intervals - PR and QRS intervals are not prolonged
Axis - normal
Hypertrophy - none
Infarct - acute injury pattern of ST elevation noted in V1-V4
Clinical correlation - An acute myocardial infarct can be one of the most dramatic emergencies in a primary
care clinic and most seasoned practitioners have seen it on an occasional basis. With the severe chest pain
and acute anterior injury pattern, this patient's situation is critical. Immediate medical stabilization is started
and stat (911) telemetry transport to the emergency room is arranged.
Case 2
A 55-year-old patient comes in to get your advice on starting a new exercise program to get back
into shape. The program involves heavy aerobic workouts and he needs a form filled out that he
is medically cleared to participate in this workout program. In talking to him you learn he has
cardiac risk factors for smoking, positive family history, high cholesterol and hypertension. He
has a sedentary lifestyle and has not participated in any strenuous physical activity for years.
Although his cardiorespiratory review of systems is negative, you are concerned that his activity
level is very limited and he has significant risk factors. As part of the workup you obtain the
following ecg to interpret:
Case 2 Answer
Rate - about 70
Rhythm - sinus rhythm with borderline first degree block
Intervals - PR is prolonged at .2 seconds, QRS is not prolonged
Axis - normal quadrant
Hypertrophy - left ventricular hypertrophy with strain pattern
Infarct - Q waves noted in V2 and V3 consistent with old myocardial infarct in the anterior septal
- anterior wall area
Clinical correlation - This patient should NOT be medically cleared at this time. He has significant
risk factors, a sedentary lifestyle and signs of previous infarction on ECG. He needs further
cardiac evaluation and testing.
Case 3
A 76-year-old patient, with a history of hypertension, comes to see you. She is
currently on a diuretic prescription and is complaining of a few days of "skipped heart
beats". She has felt slightly dizzy lately but does not have any other symptoms. Overall
she has been feeling well, her only medical issue has been hypertension. Previous
electrocardiograms in her chart show normal sinus rhythm and are otherwise
unremarkable. Her exam shows an irregular pulse in the 130 rate range but the rest of
the exam is unremarkable. You obtain the following electrocardiogram:
Case 3 Answer
Rate - about 130-150 range
Rhythm - atrial fibrillation
Intervals - no PR to measure, QRS is not prolonged
Axis - normal quadrant (aVF is downward but lead II is upward)
Hypertrophy - none
Infarct - none (nonspecific ST changes in lateral leads I and aVL
Clinical correlation - Atrial fibrillation is the most common sustained arrhythmia for which patients seek
treatment. It is more common in the elderly and is a major cause of thromboembolic events. This patient
will need a workup for the etiologies of atrial fibrillation and the usual therapeutic considerations of rate
control, anticoagulation and antiarrhythmic therapy.
Case 4
A 35-year-old man comes into your office as a new patient. He is concerned about his
elevated blood pressure. A year ago, in a physicians office, he had a reading of
150/100. A month ago, while being evaluated for bronchitis at a walk-in clinic, his
blood pressure was 150/105. At today's office visit his blood pressure is 155/105. He is
asymptomatic and currently takes no medications. His cardiac exam is remarkable for a
laterally displaced PMI and an S4. As part of the workup, you obtain the following
electrocardiogram:
Case 4 Answer
Rate - about 100
Rhythm - normal sinus
Intervals - no prolongation of the PR or QRS intervals
Axis - normal quadrant
Hypertrophy - left ventricle and left atrial
Infarct - none
Clinical correlation - This patient has three elevated blood pressure readings over different times
and findings of an S4 with hypertrophy on an ecg. He now needs evaluation and treatment for
hypertension.
Case 5
A pleasant, 75-year-old, man with no significant past medical history, comes in with
fatigue and feeling light headed. He denies any chest pain, current medication usage,
or syncope. He has had to limit his physical activity since this fatigue started about a
week ago. His vital signs are remarkable for a pulse of 40 and a blood pressure of
100/60 which he states is a bit low for him. Exam is unremarkable except for the
bradycardia. Because of the bradycardia an electrocardiogram is ordered as part of the
initial assessment.
Case 5 Answer
Rate -about 40
Rhythm - second degree block type 2
Intervals - prolonged qrs in V2 consistent with right bundle branch block
Axis - left axis deviation from anterior fascicular block
Hypertrophy - none
Infarct - none
Clinical correlation - This older patient has a bifascicular block combined with a Mobitz II block and this
setting often antedates complete heart block. Etiologies include conduction system disease, drug effects,
and myocardial ischemia. In this case the patient was admitted to the hospital with his symptomatci high
degree block. Cardiac enzymes were negative for myocardial infarct and a cardiac pacemaker was inserted
with excellent results - etilolgy was conduction system disease (presumed Lev's or Lenegre's disease).
Case 6
A 65-year-old, female patient comes in for a get acquainted visit. She
has a history of severe chronic obstructive pulmonary disease and is on
multiple medications and home oxygen. During the physical she is noted
to be tachycardic with an irregularly irregular pulse. An
electrocardiogram is taken for further evaluation.
Case 6 Answer
Rate -varies from 110 to about 140
Rhythm - multifocal atrial tachycardia
Intervals - differing PR intervals, QRS interval is not prolonged
Axis - normal
Hypertrophy - none
Infarct - none
Clinical correlation - By definition, MAT requires three or more consecutive P waves of different morphologies at rates
greater than 100 beats per minute. Most patients have severe associated illnesses, especially COPD. Treatment of the
underlying condition is the most effective approach. Atrial fibrillation and MAT are both irregularly irregular rhythms and a
12 lead ecg may be needed to tell them apart. It is clinically important to distinguish MAT from atrial fibrillation, as they are
treated differently.