Download Lead I

ECG_for_6_c._p.I.docx
Олена Костянтинівна Редько
2015
Ключові терміни:
3
Зміст
Ключові терміни:
ECG Interpretation
ECG electrode system
Lead I
Lead aVF
Quadrant
Lead I
Lead aVF
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3
4
5
5
5
6
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ECG electrode system
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ECG Interpretation
ECG electrode system
Lead I
Lead aVF
Quadrant
Lead I
Lead aVF
Ключові терміни:
Abnormalities of the R wave, ECG Axis Interpretation, ECG Rate, ECG Rhythm, ECG Waves, Lead
positioning, Q Wave
ECG Interpretation
Lead positioning
3-electrode system
– Uses 3 electrodes (RA, LA and LL).
– Monitor displays the bipolar leads (I, II and III)
– To get best results – Place electrodes on the chest wall equidistant from
the heart (rather than the specific limbs)
5-electrode system
– Uses 5 electrodes (RA, RL, LA, LL and Chest)
– Monitor displays the bipolar leads (I, II and III)
– AND a single unipolar lead (depending on position of the brown chest lead
(positions V1–6))
12-lead ECG
– 10 electrodes required to produce 12-lead ECG.
– – Electrodes on all 4 limbs (RA, LL, LA, RL)
– – Electrodes on precordium (V1–6)
– Monitors 12 leads (V1–6), (I, II, III) and (aVR, aVF, aVL)
– Allows interpretation of specific areas of the heart
– – Inferior (II, III, aVF)
– – Lateral (I, aVL, V5, V6)
– – Anterior (V1–4)
The ECG is one of the most useful investigations in medicine. Electrodes attached to the chest and/or
limbs record small voltage changes as potential difference, which is transposed into a visual tracing
Lead I
ECG electrode system
ECG Axis Interpretation
The diagram below illustrates the relationship between QRS axis and the frontal leads of the ECG.
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Lead I
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Image reproduced from Chung
Normal Axis = QRS axis between -30 and +90 degrees.
Left Axis Deviation = QRS axis less than -30 degrees.
Right Axis Deviation = QRS axis greater than +90 degrees.
Extreme Axis Deviation = QRS axis between -90 and 180 degrees (AKA “Northwest Axis”).
There are several complementary approaches to estimating QRS axis, which are summarised below.
Method 1 – The Quadrant Method
The most efficient way to estimate axis is to look at leads I + aVF.
°°°°°
°°°°°
Lead Lead
Quadrant
I
aVF
Axis
Positive
Positive
Left lower quadrant
Normal (0 to +90 degrees)
Positive
Negative
Left upper quadrant
Possible LAD (0 to -90 degrees)
Negative
Positive
Right lower quadrant
RAD (+90 to 180 degrees)
Negative
Negative
Right upper quadrant
Extreme Axis Deviation (-90 to
180 degrees)
Method 2 – Leads I + II
Another rapid method is to look at leads I + II.
A positive QRS in lead I puts the axis in roughly the same direction as lead I.
Image reproduced from Chung
A positive QRS in lead II similarly aligns the axis with lead II.
Lead I
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Image reproduced from Chung
Therefore, if leads I and II are both positive, the axis is between -30 and +90 degrees (i.e. normal axis).
Image reproduced from Chung
Combining Methods 1 and 2
By combining these two methods, you can rapidly and accurately assess axis.
°°°°°
Lead I Lead aVF
Axis
Positive
Positive
Normal (0 to +90 degrees)
Positive
Negative
Possible LAD
Is lead II positive?
Yes -> Normal (0 to -30 degrees)
No -> LAD (-30 to -90 degrees)
Negative
Positive
RAD (+90 to 180 degrees)
Negative
Negative
Extreme Axis Deviation (-90 to 180 degrees)
Method 3 – The Isoelectric Lead
This method allows a more precise estimation of QRS axis, using the axis diagram below.
Reproduced from Chung
Key Principles
If the QRS is positive in any given lead, the axis points in roughly the same direction as this lead.
Lead I
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If the QRS is negative in any given lead, the axis points in roughly the opposite direction to this
lead.
If the QRS is isoelectric in any given lead (positive deflection = negative deflection), the axis is at
90 degrees to this lead.
Step 1. Find the isoelectric lead.
The isoelectric (equiphasic) lead is the frontal lead with zero net amplitude. This can be either:
A biphasic QRS where R wave height = Q or S wave depth.
A flat-line QRS with no discernible features.
Step 2. Find the positive leads.
Look for the leads with the tallest R waves (or largest R/S ratios).
Step 3. Calculate the QRS axis.
The QRS axis is at 90 degrees to the isoelectric lead, pointing in the direction of the positive leads.
This concept can be difficult to understand at first, and is best illustrated by some examples.
Example 1
Answer — Quadrant Method
Leads I + aVF are both positive.
This puts the axis in the left lower quadrant, between 0 and +90 degrees, i.e. normal axis.
Lead II is also positive, which confirms the normal axis.
Answer — Isoelectric Lead Method
Le a d aVL is isoelectric, being biphasic with similarly sized positive and negative deflections
(no need to precisely measure this).
From the diagram above, we can see that aVL is located at -30 degrees.
The QRS axis must be ± 90 degrees from lead aVL, either at +60 or -120 degrees.
With leads I (0), II (+60) and aVF (+90) all being positive, we know that the axis must lie
somewhere between 0 and +90 degrees.
This puts the QRS axis at +60 degrees.
Example 2
Lead I
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Answer — Quadrant Method
Lead I = negative.
Lead aVF = positive.
This puts the axis in the right lower quadrant, between +90 and +180 degrees, i.e. RAD.
Answer — Isoelectric Lead Method
Lead II (+60 degrees) is the isoelectric lead.
The QRS axis must be ± 90 degrees from lead II, at either +150 or -30 degrees.
The more rightward-facing leads III (+120) and aVF (+90) are positive, while aVL (-30) is negative.
This puts the QRS axis at +150 degrees.
This is an example of right axis deviation secondary to right ventricular hypertrophy.
Example 3
Answer — Quadrant Method
Lead I = positive.
Lead I
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Lead aVF = negative.
This puts the axis in the left upper quadrant, between 0 and -90 degrees, i.e. normal or LAD.
Lead II is neither positive nor negative (isoelectric), indicating borderline LAD.
Answer — Isoelectric Lead Method
Lead II (+60 degrees) is isoelectric.
The QRS axis must be ± 90 degrees from lead II, at either +150 or -30 degrees.
The more leftward-facing leads I (0) and aVL (-30) are positive, while lead III (+120) is negative.
This confirms that the axis is at -30 degrees.
This is an example of borderline left axis deviation due to inferior MI.
Example 4
Answer — Quadrant Method
Lead I = negative.
Lead aVF = negative.
This puts the axis in the upper right quadrant, between -90 and 180 degrees, i.e. extreme axis
deviation.
NB. The presence of a positive QRS in aVR with negative QRS in multiple leads is another clue to the
presence of extreme axis deviation.
Answer — Isoelectric Lead Method
The most isoelectric lead is aVL (-30 degrees).
The QRS axis must be at ± 90 degrees from aVL at either +60 or -120 degrees.
Lead aVR (-150) is positive, with lead II (+60) negative.
This puts the axis at -120 degrees.
This is an example of extreme axis deviation due to ventricular tachycardia.
Example 5
Lead I
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Reveal Answer
Causes of Axis Deviation
Right Axis Deviation
Right ventricular hypertrophy
Acute right ventricular strain, e.g. due to pulmonary embolism
Lateral STEMI
Chronic lung disease, e.g. COPD
Hyperkalaemia
Sodium-channel blockade, e.g. TCA poisoning
Wolff-Parkinson-White syndrome
Dextrocardia
Ventricular ectopy
Secundum ASD – rSR’ pattern
Normal paediatric ECG
Left posterior fascicular block – diagnosis of exclusion
Vertically orientated heart – tall, thin patient
Left Axis Deviation
Left ventricular hypertrophy
Left bundle branch block
Inferior MI
Ventricular pacing /ectopy
Wolff-Parkinson-White Syndrome
Primum ASD – rSR’ pattern
Left anterior fascicular block – diagnosis of exclusion
Horizontally orientated heart – short, squat patient
Extreme Axis Deviation
Ventricular rhythms – e.g.VT, AIVR, ventricular ectopy
Hyperkalaemia
Severe right ventricular hypertrophy
For a deeper understanding of axis determination, including a detailed explanation of the hexaxial
reference system, check out this excellent series of articles from EMS 12-lead.
http://www.ems12lead.com/2008/10/10/axis-determination-part-v/
http://www.ems12lead.com/2008/10/11/axis-determination-part-vi/
http://www.ems12lead.com/2014/09/11/the-360-degree-heart-part-i/
ECG Rate
The usual paper speed is 25mm/sec:
Lead I
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1mm (small square) = 0.04 sec
5mm (big square) = 0.2 sec
If a different paper speed is used, calculations will have to be modified appropriately.
Calculate atrial and ventricular rates separately if they are different (e.g. complete heart block).
There are multiple methods to estimate the rate:
For regular rhythms: Rate = 300 / number of large squares in between each consecutive R
wave.
For very fast rhythms: Rate = 1500 / number of small squares in between each consecutive R
wave.
For slow or irregular rhythms: Rate = number of complexes on the rhythm strip x 6 (this
gives the average rate over a ten-second period).
The machine reading can also be used and is usually correct — however, it may occasionally be
inaccurate in the presence of abnormal QRS/T-wave morphology, e.g. may count peaked T waves as
QRS complexes or miss QRS complexes with reduced amplitude.
Interpretation (adults)
60–100 beats/min
Normal
>100 beats/min
Tachycardia
<60 beats/min
Bradycardia
Normal Heart Rates in Children
Newborn: 110 – 150 bpm
2 years: 85 – 125 bpm
4 years: 75 – 115 bpm
6 years+: 60 – 100 bpm
ECG Rhythm
The rhythm is best analysed by looking at a rhythm strip. On a 12 lead ECG this is usually a 10 second
recording from Lead II. Confirm or corroborate any findings in this lead by checking the other leads. A
longer rhythm strip, recorded perhaps recorded at a slower speed, may be helpful.
A useful 7 step approach to rhythm analysis is described.
1. Rate —
Tachycardia or bradycardia?
Normal rate is 60-100/min.
2. Pattern of QRS complexes —
Regular or irregular?
If irregular is it regularly irregular or irregularly irregular?
3. QRS morphology —
Narrow complex — sinus, atrial or junctional origin.
Wide complex — ventricular origin, or supraventricular with aberrant conduction.
4. P waves —
Absent — sinus arrest, atrial fibrillation
Present — morphology and PR interval may suggest sinus, atrial, junctional or even retrograde
from the ventricles.
5. Relationship between P waves and QRS complexes —
AV association (may be difficult to distinguish from isorhythmic dissociation)
AV dissociation
complete — atrial and ventricular activity is always independent.
incomplete — intermittent capture.
6. Onset and termination —
Abrupt — suggests re-entrant process.
Gradual — suggests increased automaticity.
7. Response to vagal manoeuvres —
Sinus tachycardia, ectopic atrial tachydysrhythmia — gradual slowing during the vagal manoeuvre,
but resumes on cessation.
AVNRT or AVRT — abrupt termination or no response.
Lead I
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Atrial fibrillation and atrial flutter — gradual slowing during the manoeuvre.
VT — no response.
Differential Diagnosis
Follow links below for examples of individual rhythms.
Narrow Complex (Supraventricular) Tachycardias
Regular
Irregular
Sinus tachycardia
Atrial tachycardia
Atrial flutter
Inappropriate sinus tachycardia
Sinus node re-entrant tachycardia
Atrial
Atrioventricular
Atrial fibrillation
A t ria l flutter with variable
block
Multifocal atrial tachycardia
Atrioventricular re-entry tachycardia
(AVRT)
AV nodal re-entry tachycardia (AVNRT)
Automatic junctional tachycardia
Broad Complex Tachycardias
Regular
Ventricular tachycardia
Antidromic atrioventricular re-entry tachycardia (AVRT).
Any regular supraventricular tachycardia with aberrant conduction — e.g. due to bundle branch
block, rate-related aberrancy.
All regular BCTs should be considered to be VT until proven otherwise.
Irregular
Ventricular fibrillation
Polymorphic VT
Torsades de Pointes
AF with Wolff-Parkinson-White syndrome
Any irregular supraventricular tachycardia with aberrant conduction — e.g. due to bundle branch
block, rate-related aberrancy.
Bradycardias
P waves present
Each P wave is followed by a QRS complex (= sinus node dysfunction)
Sinus bradycardia
Sinus node exit block
Sinus pause / arrest
Not every P wave is followed by a QRS complex (= AV node dysfunction)
AV
AV
AV
AV
AV
block: 2nd degree, Mobitz I (Wenckebach)
block: 2nd degree, Mobitz II
block: 2nd degree, “fixed ratio blocks” (2:1, 3:1)
block: 2nd degree, “high grade AV block”
block: 3rd degree (complete heart block)
P waves absent
Narrow complexes
Junctional escape rhythm
Broad complexes
Ventricular escape rhythm
For escape rhythms to occur there must be a failure of sinus node impulse generation or transmission
by the AV node.
ECG Waves
The P wave
The P wave is the first positive deflection on the ECG
It represents atrial depolarisation
Lead I
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Characteristics of the Normal Sinus P Wave
Morphology
Smooth contour
Monophasic in lead II
Biphasic in V1
Axis
Normal P wave axis is between 0° and +75°
P waves should be upright in leads I and II, inverted in aVR
Duration
< 120 ms
Amplitude
< 2.5 mm in the limb leads,
< 1.5 mm in the precordial leads
Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF) and lead V1,
as the P waves are most prominent in these leads.
The Atrial Waveform – Relationship to the P wave
Atrial depolarisation proceeds sequentially from right to left, with the right atrium activated before
the left atrium.
The right and left atrial waveforms summate to form the P wave.
The first 1/3 of the P wave corresponds to right atrial activation, the final 1/3 corresponds to left
atrial activation; the middle 1/3 is a combination of the two.
In most leads (e.g. lead II), the right and left atrial waveforms move in the same direction, forming
a monophasic P wave.
However, in lead V1 the right and left atrial waveforms move in opposite directions. This produces
a biphasic P wave with the initial positive deflection corresponding to right atrial activation and the
subsequent negative deflection denoting left atrial activation.
This separation of right and left atrial electrical forces in lead V1 means that abnormalities
affecting each individual atrial waveform can be discerned in this lead. Elsewhere, the overall shape
of the P wave is used to infer the atrial abnormality.
Normal P-wave Morphology – Lead II
The right atrial depolarisation wave (brown) precedes that of the left atrium (blue).
The combined depolarisation wave, the P wave, is less than 120 ms wide and less than 2.5 mm
high.
Click image for source
Lead I
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Right Atrial Enlargement – Lead II
In right atrial enlargement, right atrial depolarisation lasts longer than normal and its waveform
extends to the end of left atrial depolarisation.
Although the amplitude of the right atrial depolarisation current remains unchanged, its peak now
falls on top of that of the left atrial depolarisation wave.
The combination of these two waveforms produces a P waves that is taller than normal (> 2.5
mm), although the width remains unchanged (< 120 ms).
Click image for source
Left Atrial Enlargement – Lead II
I n left atrial enlargement, left atrial depolarisation lasts longer than normal but its amplitude
remains unchanged.
Therefore, the height of the resultant P wave remains within normal limits but its duration is longer
than 120 ms.
A notch (broken line) near its peak may or may not be present (“P mitrale”).
Click image for source
Normal P-wave Morphology – Lead V1
The P wave is typically biphasic in V1, with similar sizes of the positive and negative deflections.
Normal P wave in V1
Right Atrial Enlargement – Lead V1
Right atrial enlargement causes increased height (> 1.5mm) in V1 of the initial positive deflection of
the P wave.
Click image for source
NB. This patient also has evidence of right ventricular hypertrophy.
Left Atrial Enlargement – Lead V1
Left atrial enlargement causes widening (> 40ms wide) and deepening (> 1mm deep) in V1 of the
Lead I
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terminal negative portion of the P wave.
Click image for source
Biatrial Enlargement
Biatrial enlargement is diagnosed when criteria for both right and left atrial enlargement are present
on the same ECG.
The spectrum of P-wave changes in leads II and V1 with right, left and bi-atrial enlargement is
summarised in the following diagram:
Reproduced from Wagner et al. (2007)
Common P Wave Abnormalities
Common P wave abnormalities include:
P mitrale (bifid P waves), seen with left atrial enlargement.
P pulmonale (peaked P waves), seen with right atrial enlargement.
P wave inversion, seen with ectopic atrial and junctional rhythms.
Variable P wave morphology, seen in multifocal atrial rhythms.
P mitrale
The presence of broad, notched (bifid) P waves in lead II is a sign of left atrial enlargement, classically
due to mitral stenosis.
Lead I
Bifid P waves (P mitrale) in left atrial enlargement
P Pulmonale
The presence of tall, peaked P waves in lead II is a sign of right atrial enlargement, usually due to
pulmonary hypertension (e.g. cor pulmonale from chronic respiratory disease).
Peaked P waves (P pulmonale) due to right atrial enlargement
Inverted P Waves
P-wave inversion in the inferior leads indicates a non-sinus origin of the P waves.
When the PR interval is < 120 ms, the origin is in the AV junction (e.g. accelerated junctional rhythm):
Accelerated Junctional Rhythm
When the PR interval is ≥ 120 ms, the origin is within the atria (e.g. ectopic atrial rhythm):
Ectopic Atrial Rhythm
Variable P-Wave Morphology
The presence of multiple P wave morphologies indicates multiple ectopic pacemakers within the atria
and/or AV junction.
If ≥ 3 different P wave morphologies are seen, then multifocal atrial rhythm is diagnosed:
Multifocal Atrial Rhythm
If ≥ 3 different P wave morphologies are seen and the rate is ≥ 100, then multifocal atrial
tachycardia (MAT) is diagnosed:
Multifocal Atrial Tachycardia
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Lead I
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Related Topics
Left Atrial Enlargement
Right Atrial Enlargement
Biatrial Enlargement
Accelerated junctional rhythm
Ectopic Atrial Rhythm
Multifocal atrial tachycardia
Q Wave
A Q wave is any negative deflection that precedes an R wave
Normal Q wave
Normal Q wave in V6
Origin of the Q Wave
The Q wave represents the normal left-to-right depolarisation of the interventricular septum
Small ‘septal’ Q waves are typically seen in the left-sided leads (I, aVL, V5 and V6)
Q waves in different leads
Small Q waves are normal in most leads
Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant
Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3)
Pathological Q Waves
Q waves are considered pathological if:
> 40 ms (1 mm) wide
> 2 mm deep
> 25% of depth of QRS complex
Seen in leads V1-3
Pathological Q waves usually indicate current or prior myocardial infarction.
Differential Diagnosis
Myocardial infarction
Cardiomyopathies — Hypertrophic (HOCM), infiltrative myocardial disease
Rotation of the heart — Extreme clockwise or counter-clockwise rotation
Lead placement errors — e.g. upper limb leads placed on lower limbs
Lead I
Examples
Inferior Q waves (II, III, aVF) with ST elevation due to acute MI
Inferior Q waves (II, III, aVF) with T-wave inversion due to previous MI
Lateral Q waves (I, aVL) with ST elevation due to acute MI
Lateral Q waves (V5-6) with T-wave flattening due to previous MI
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Lead I
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Anterior Q waves (V1-4) with ST elevation due to acute MI
Anterior Q waves (V1-4) with T-wave inversion due to recent MI
Loss of normal Q waves
The absence of small septal Q waves in leads V5-6 should be considered abnormal.
Absent Q waves in V5-6 is most commonly due to LBBB.
Abnormalities of the R wave
On this page we will discuss and provide examples of R wave abnormalities including
Dominant R wave in V1
Dominant R wave in aVR
Poor R wave progression
Causes of Dominant R wave in V1
Normal in children and young adults
Right Ventricular Hypertrophy (RVH)
Pulmonary Embolus
Persistence of infantile pattern
Left to right shunt
Right Bundle Branch Block (RBBB)
Posterior Myocardial Infarction (ST elevation in Leads V7, V8, V9)
Wolff-Parkinson-White (WPW) Type A
Incorrect lead placement (e.g. V1 and V3 reversed)
Lead I
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Dextrocardia
Hypertrophic cardiomyopathy
Dystrophy
Myotonic dystrophy
Duchenne Muscular dystrophy
Examples of Dominant R wave in V1
Normal paediatric ECG (2 yr old)
Paediatric ECG V1 R wave
Right Ventricular Hypertrophy (RVH)
Right Bundle Branch Block
Lead I
Right Bundle Branch Block (RBBB)
Right Bundle Branch Block MoRRoW
Posterior MI
Posterior AMI
WPW (type A)
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Lead I
WPW Type A
Leads V1 and V3 reversed
Note biphasic P wave (typically seen in only in V1) in lead “V3”
Leads V1 and V3 reversed
Muscular dystrophy
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Lead I
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Dominant R wave in aVR
Poisoning with sodium-channel blocking drugs (e.g. TCAs)
Dextrocardia
Incorrect lead placement (left/right arm leads reversed)
Commonly elevated in ventricular tachycardia (VT)
Poisoning with sodium-channel blocking drugs
Causes a characteristic dominant terminal R wave in aVR
Poisoning with sodium-channel blocking agents is suggested if:
R wave height > 3mm
R/S ratio > 0.7
Na Channel blockade with dominant aVR R wave
Dextrocardia
This ECG shows all the classic features of dextrocardia:
Positive QRS complexes (with upright P and T waves) in aVR
Negative QRS complexes (with inverted P and T waves) in lead I
Marked right axis deviation
Absent R-wave progression in the chest leads (dominant S waves throughout)
Lead I
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Left arm/right arm lead reversal
The most common cause of a dominant R wave in aVR is incorrect limb lead placement, with reversal
of the left and right arm electrodes. This produces a similar pattern to dextrocardia in the limb leads but
with normal R-wave progression in the chest leads.
With LA/RA lead reversal:
Lead I becomes inverted
Leads aVR and aVL switch places
Leads II and III switch places
Lead reversal
Lead reversal reversed
Ventricular Tachycardia
Lead I
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Poor R wave progression
Poor R wave progression is described with an R wave ≤ 3 mm inV3 and is caused by:
Prior anteroseptal MI
LVH
Inaccurate lead placement
May be a normal variant