ECG localization of accessory pathways slideshare

ECG localization of accessory
pathway
Dr. Rajat Gupta

Overview
• Normal AV conduction
• Bypass pathway & Ventricular pre-excitation
• ECG findings of pre-excitation
• WPW syndrome
• ECG localization of accessory pathway
• Algorithms
• Arrhythmias associated with WPW syndrome
– AV reciprocating tachycardia or AVRT
• Orthodromic or narrow complex AVRT
• Antidromic or wide complex AVRT
– Atrial fibrillation
• Accessory pathway variants
• Summary

• WPW syndrome
• Algorithms
• Summary

Normal conduction
Pacing Clin Electrophysiol. 2010 Jun 01;33(6):754-62

Normal A-V conduction
• Normally the atria and ventricles are separated by a dense mass of
fibrous tissues.
• That prevent the spread of electrical impulses from atria to ventricles
• The only pathway by which the atrial impulse can reach the ventricles
is through the AV node and normal intra-ventricular conduction
system
Cardiovascular physiology concepts 3rd edition

Ventricular pre-excitation
The sinus impulse
activates the atria
and a P wave is
normally recorded.
Short PR interval
Initial portion of the QRS slurred
Impulse finally
emerges from
the AV node &
activates the rest
of the ventricles
normally
Wagner et al, Cardiac arrythmias, Newyork 1983:13

Bypass tract
• Extra piece of heart muscles connects directly atria & ventricles
– It does not contain cells that are specialized for conduction.
– May be left sided or right sided.
– May be single or multiple.
– Conduction may be constant or intermittent
– May be active or inactive.
– May conduct only anterogradely (from atrium to ventricle), only retrogradely
(from ventricle to atrium) or both.
Samuel et al Circulation: Arrhythmia and Electrophysiology. 2014;7:1268–1270

Bypass tract
Manifest or overt Concealed
If it is capable of
conducting anterogradely
from atrium to ventricle
Classical pattern of
preexcitation.
If it is capable of conducting
only retrogradely from ventricle to
atrium.
The baseline ECG will not show
any evidence of preexcitation
during normal sinus rhythm.
But the presence of a bypass
tract can potentially cause a
reentrant tachycardia to occur.
Samuel et al Circulation: Arrhythmia and Electrophysiology. 2014;7:1268–1270

ECG characteristics of WPW conduction
 Shortened PR interval
 Delta wave
 ST-T changes
•Atrial impulse reaches the ventricle faster through the bypass tract than
through the AV node.
•PR interval <120 ms during sinus rhythm
•In 25% of patients of WPW the PR interval may be normal
(more or equal to 120 ms)
•Slow, slurred initial deflection of the QRS complex.
•Represents myocardial conduction of the impulse through the
ventricle at the area of insertion of the bypass tract.
•QRS complex to be inscribed slowly and is widened (>120 ms)
because of direct myocardial spread of propagated impulse.
•Secondary to the abnormal activation of the ventricles.
•Generally directed in opposite direction to the major delta and
QRS vectors
Melissa et al Circulation. 2016;133:105–106

ECG findings

Ventricular Pre-excitation.
Short PR interval measuring 0.11 seconds
delta wave, and
ST-T abnormalities.

The PR interval - short
QRS complexes- wide
Delta waves- present
ST segments- depressed
Inverted T waves pointing away
from the direction of the delta wave.
Intermittent Preexcitation.
 No evidence of
preexcitation.
 The PR interval is
prolonged
 QRS complexes are
narrow.

Delta wave
• Size depends on:
– Amount of myocardium activated by the accessory pathway
– On the location of bypass tract
• A right-sided bypass tract is closer to the sinus node than a left-
sided bypass tract causing the ventricles to be activated earlier.
• A right-sided bypass tract therefore is expected to have a shorter
PR interval and a more prominent delta wave than a left-sided
bypass tract.
Significant delay of the
impulse at the AV node
Activation of larger portion of
myocardium through the
bypass tract
Longer, larger, and more
conspicuous delta wave.
Faster & efficient conduction
across the AV node
Amount of myocardium
activated by the bypass tract
will be small
Delta wave may be barely
noticeable

Delta wave is more prominent-
Larger amount of myocardium is
activated from the bypass tract. This is
often seen in right sided bypass tracts or
when there is delay in the conduction of
the impulse at the AV node
Delta wave is barely recognizable-
Smaller amount of myocardium
activated from the bypass tract.
This occurs when the bypass tract is
Left sided or conduction through
the AV node is enhanced.

WPW syndrome- Intro
• First fully described by Wolf- Parkinson & White in 1930.
• It is the commonest variety of pre-excitation syndrome.
• Associated with an accessory AV connection (bypass tract),
called Kent Bundle or Paladino tracts.
• The atrial impulse is able to reach the ventricles not only
through the AV node, but also through the bypass tract causing
premature activation of the ventricles.
• It can also serve as a pathway for reentry, which may result in
clinical symptoms of paroxysmal tachycardia.
Boersma et al, J Cardiovasc Electrophysiol 2002, 13: 1222

Historical perspective
• The earliest description of an accessory pathway was reported by
Stanley Kent in 1893.
• He suggested that impulses can travel from atrium to ventricle over a
tract other than the AV node.
• Cohn and Fraser reported the first case of preexcitation syndrome in
1913.
• In 1930, Louis Wolff, John Parkinson, Paul Dudley White described 11
young patients, suffered from attacks of tachycardia associated with
an ECG pattern of BBB with short PR interval
• Ohnell was the first to use the term “pre-excitation,”
• Seters described the initial slurred component of the QRS complex as a
“delta” wave. Boersma et al, J Cardiovasc Electrophysiol 2002, 13: 1222

N. Taguchietal./JournalofArrhythmia30(2014)439–443
Schematic diagram of the heart from the left anterior oblique projection shows the
relation among the tricuspid annulus(TA), mitral annulus (MA), His bundle(HIS),
coronary sinus (CS), and the anatomic locations of the accessory pathways.
Accessory pathway location
LA: left anterior
LL: left lateral
LP: left posterior
LPL: left postero lateral
MS: mid septal
PS: postero-septal
RA: right anterior
RAS: right antero-septal
RL: right lateral
RP: right posterior
RPL: right postero-lateral

Old and new nomenclature for localization of accessory pathway
Old
New
Cosio et al Cardiovasc Electrophysiol 1999,10:1162

N=93
Fitzpatrick et al JACC Vol. 23, No. 1, January 1994

Bypass tract

Distribution
• 50% to 60% at the free wall of the left ventricle
• 20% to 30% at the postero-septal area (left or right)
• 10% to 20% at the free wall of the right ventricle and
• 5% are located in the antero-septal area (mostly right sided)
• Left antero-septal pathways are very rare as this area is
occupied by the aortic root
Location of the Bypass Tract.
Baltazar Textbook basic and bedside ECG

• Preexcitation of the ventricles is an electrocardiographic diagnosis
characterized by the presence of a short PR interval and a delta wave
• This specific pattern of pre-excitation is also called the WPW ECG.
• Not all patients with the WPW ECG will develop symptoms of
tachycardia.
• When preexcitation of the ventricles is associated with symptoms of
tachycardia, the clinical entity is called WPW syndrome
Barunwald’s Heart disease eleventh edition

• Approximately 10% to 20% of patients with Ebstein’s anomaly has
WPW syndrome with more than one bypass tract commonly present.
• In Ebstein’s anomaly, the right ventricle is atrialized because of a
downward displacement of the tricuspid leaflets into the right
ventricle; thus, Ebstein’s anomaly should always be suspected when a
bypass tract is right sided.
• Other cardiac diseases associated with preexcitation include
hypertrophic cardiomyopathies and mitral valve prolapse.

D’avila, Pacing clinical electrophysiol 1995

WPW
Right sided pathway
Left sided pathway
Tall R wave in V1
Positive delta wave
QS complex in V1
Negative delta wave
Lowe et al Br Heart J. 1975 Jan; 37(1): 9–19.

Left-sided bypass tract
• When the bypass tract is left sided, the left ventricle is activated
earlier than the right ventricle.
• The impulse will travel from left to right ventricle in the direction
of V1, which is located on the right side of the sternum.
• During normal sinus rhythm, a positive delta wave or tall R or Rs
complex will be recorded in V1.
• This pattern of pre-excitation is also called type A.
• Tall R waves in V1 can be mistaken for RBBB, right ventricular
hypertrophy or posterior infarction.

Left-Sided Bypass Tract
tall R waves in V1.

Right-sided bypass tract
• When the bypass tract is right sided, the right ventricle is activated
earlier than the left ventricle.
• The impulse spreads from right ventricle to left ventricle away from
lead V1.
• This results in a negative delta wave with deep S or rS complex in V1
• This pattern of pre-excitation is also called type B.
• Because the S waves are deeper than the R waves in V1, the ECG may
be mistaken for left bundle branch block, left ventricular hypertrophy,
or anteroseptal myocardial infarction

Right-Sided Bypass Tract.
QS complexes in V1.
QS or rS complexes in V1.

Right-sided bypass tract
Early activation of right ventricles Delayed left ventricles activation
Softer first heart sound
Earlier closure of
the pulmonic
component of the
second sound
Single or paradoxically split
second heart sound.
On auscultation

Left-sided bypass tract
Early activation of left ventricles Delayed right ventricles activation
Wide split second heart sound
Delayed closure
of the pulmonic
component of the
second sound
Accentuated first heart sound.
On auscultation

Right sided vs left sided

Left sided accessory pathway
Dominant R in V1

Right sided accessory pathway
QRS transition after V2

QRS transition b/w V1 and V2
R>S by > 1 mv in lead 1

• WPW syndrome
• Algorithms
• Summary

Localizing the Bypass Tract.
Adapted from Olgin and Zipes.
Olgin JE, Zipes DP. Braunwald’s heart disease: a
textbook of cardiovascular medicine.

Left Ventricular Free Wall
•Tall R waves are present in V1 consistent with a left sided bypass tract.
•QS complexes are present in I and aVL resembling a lateral infarct.
•This suggests that the impulse is traveling away from the positive sides of leads I
and aVL consistent with a bypass tract at the lateral free wall of the left ventricle.

Left-Sided Postero-septal Bypass Tract
•Deep Q waves are present in leads II, III, and aVF resembling an inferior infarct.
•This is consistent with a posteroseptal bypass tract.
•The bypass tract is left sided because tall R waves are present in V1.

Right-Sided Posteroseptal Bypass Tract
•QS complexes are present in leads II, III, and a VF consistent with a posteroseptal
bypass tract.
•V1 shows a QS complex consistent with a right-sided posteroseptal bypass tract.

Right-Sided Anteroseptal Bypass Tract.
•QS complexes are present in V1 and V2 consistent with a right sided bypass tract.
•The axis of the QRS complex in the frontal plane is inferior (60).
•This is consistent with an anteroseptal bypass tract.

Right Ventricular Free Wall
•QS complexes are present in V1 consistent with a right-sided bypass tract.
•There is also left axis deviation of the QRS complexes of approximately 30
consistent with a bypass tract at the right ventricular free wall

Fitzpatric’ et al

Left anterolateral accessory pathway
•The QR transition was before lead V1 , indicating, left-sided pathway .
•The sum of the inferior lead delta wave polarities (lead II+1, lead III + 1,
lead aVF + 1) was +3, indicating left anterolateral location
•Monophasic S wave in Iead aVL

Transition b/w V3 and V4
Right free wall

The QRS transition was between leads V1 and V2
and the R wave amplitude in lead I (2.1 mV) > S wave (0 .01 mV), indicating aright-sided
pathway on the septum.
The inferior lead delta wave polarities were II positive, III isoelectric and aVF isoelectric
(i .e., a sum of +1), indicating a right midseptal location
QRS transition was between leads V1 andV2
R/S > 1mv
Right midseptal location

The QRS transition is between leads V3 and V.,
indicating a right-sided pathway.
The delta wave in lead II -0.2 mV, indicating a
free wall pathway.
The delta wave axis is in negative (<zero degre)
no R wave in lead III posterolateral pathway.

Aruda algorithm
Arruda et al 1998

(-) or (±) delta wave in lead I. or R > S in lead V1.
Delta wave polarity in lead aVf
sublocates these accessory pathways.
Positive Isolectric

Negative delta wave in lead II

Milstein Algorithm
•Milstein et al , pacing clin electrophysiol 1987 May;10(3 Pt 1):555-3.

Left lateral
accessory pathway

Left-Sided Postero-
septal Bypass Tract

QRS axis <+30
Right lateral
accessory pathway

Arrhythmias Associated with WPW Syndrome
• One of the clinical features of the WPW syndrome is its
predisposition to develop arrhythmias.
• The frequency of paroxysmal tachycardia apparently increases with
age, from 10/100 patients with WPW syndrome in the 20- to 39-year
age group to 36/100 in patients older than 60 years.
• Approximately
– 80% of patients with tachycardia have a
reciprocating tachycardia,
– 15% to 30% have atrial fibrillation
– 5% have atrial flutter
– VT (uncommon)
• There is an increased risk of SCD in asymptomatic children and
adults with electrocardiographic evidence of preexcitation

AV reciprocating tachycardia (AVRT)
• Most common arrhythmia associated with the WPW syndrome
• It is Supraventricular tachycardia that may have narrow or
wide QRS complexes

AV reciprocating tachycardia (AVRT)
Narrow complex AVRT
• Narrow QRS complexes
• Because atrial impulse enters the
ventricles anterogradely through
the AV node during tachycardia.
• The impulse follows the
intraventricular conduction system
and activates the ventricles,
normally resulting in QRS
complexes that are identical to that
during normal sinus rhythm.
• Also called orthodromic or narrow
complex AVRT.
Wide Complex AVRT:
• Wide QRS complexes
because the atrial impulse
enters the ventricles
through the bypass tract
during the tachycardia
which can be mistaken for
ventricular tachycardia.
• Also called antidromic
AVRT

(A) Orthodromic AVRT: During tachycardia, the impulse is conducted from
atrium to ventricle across the AV node resulting in narrow QRS complexes.
(B) Antidromic AVRT: During tachycardia, the atrial impulse is conducted from
atrium to ventricle across the bypass tract resulting in wide QRS complexes,
which can be mistaken for ventricular tachycardia.AVRT, atrioventricular
reciprocating tachycardia.

Orthodromic or Narrow Complex AVRT.
(A) PAC is conducted through the AV node but not through the bypass tract.
(B) ventricles are activated exclusively through the normal conduction system causing
the QRS complex to be narrow.
(C) The impulse is conducted from ventricles to atria across the bypass tract.
The atria are activated retrogradely allowing the impulse to be conducted back to the
ventricles through the AV node.
Delta waves are present only during normal sinus rhythm but not during tachycardia

In AVRT, the retrograde
P wave is inscribed
immediately after the
QRS complex with the R-
P interval shorter than the
PR interval
Atrioventricular Reentrant Tachycardia (AVRT
Atypical Atrioventricular Reentrant Tachycardia
(AVRT).
In atypical AVRT,the retrograde P waves are
inscribed in front of the QRS complexes with the
R-P interval longer than PR interval. Atypical
AVRT is associated with a slowly conducting
bypass tract resulting in a long R-P interval.

A narrow complex tachycardia with retrograde P waves in II,III,aVF,and in V4 to
V6 (arrows). The retrograde P waves are inscribed after the QRS complexes and
deform the ST segments or T waves of the previous complex with an R-P interval
shorter than PR interval
AVRT

In atypical AVRT retrograde P waves are in front of the QRS complex (R-P interval longer
than PR interval) because of the presence of a slowly conducting bypass tract. The
supraventricular tachycardia is terminated by a perfectly timed premature atrial complex
(arrow).

If the P waves are inverted in lead I during tachycardia (A),the bypass tract is left
sided. If the P waves are upright in lead I during the tachycardia (B),the bypass tract
is right sided. Arrows represent the direction of atrial activation.

The diagrams explain how a rate related BBB will slow down the ventricular rate during AVRT if the
bypass tract is on the same side as the BBB.
(A) Narrow complex AVRT with a right-sided bypass tract.
(B) If a rate-related LBBB develops during tachycardia, The circuit is not altered by the bundle branch
block and the rate of the tachycardia remains unchanged.
(C) If a rate-related right bundle branch block occurs the rate of the tachycardia will become slower if
the bypass tract is right sided because the right ventricle and bypass tract have to be activated
from the left bundle branch, resulting in a longer and slower circuit.

Algorithm for the
diagnosis of a narrow-
QRS tachycardia
ACC/AHA/ESC guidelines for
the management of
patients with supraventricular
arrhythmias Circulation
2003;108:1871.)

Antidromic or Wide Complex AVRT
(A)PAC is conducted through the bypass tract but not through the AV node.
(B)The QRS complex is wide because the ventricles are activated outside the
normal conduction system.
(C)The impulse is conducted retrogradely from ventricles to atria through the
atrioventricular conduction system. The atria are activated retrogradely
allowing the impulse to be conducted back to the bypass tract.

VA Conduction in Antidromic AVRT.
(A)In type I antidromic AVRT, the atrial impulse enters the ventricles through the
bypass tract and returns to the atria through the AV node. This type of antidromic
AVRT can be terminated by AV nodal blockers.
(B) In type II antidromic AVRT, the impulse enters the ventricles through the bypass
tract and returns to the atria through a second bypass tract. This type of antidromic
AVRT cannot be terminated by AV nodal blockers.
(C) Both wide complex tachycardia look identical and can be mistaken for ventricular
tachycardia.
Conduction Pathways in Antidromic AVRT

Localizing the Bypass Tract during Wide Complex AVRT
(A) When the bypass tract is left sided (bypass tract connects left atrium to left
ventricle), tall R waves are recorded in V1 during wide complex tachycardia. Because the
left ventricle is activated
first, the impulse will travel from left ventricle to right ventricle toward V1.
(B) If the bypass tract is right sided, the right ventricle is activated first and the impulse
is conducted from right ventricle to left ventricle causing deep S waves in V1.
Localizing the bypass tract during wide complex AVRT:

Baseline ECG Showing Preexcitation.
•Delta waves with short PR intervals are present in leads I, aVL,V2, and V3
consistent with preexcitation.
•The QRS complex is negative in V1 with deep S waves consistent with a right
sided bypass tract.

Wide Complex AVRT
•It shows a wide complex tachycardia with deep S wave in V1 suggesting that
the bypass tract is right sided.
•This wide complex tachycardia can be mistaken for VT.

Narrow complex tachycardia.
•The ECG shows narrow complex AVRT.
•The frontal leads are magnified to show that the P waves are upright in
leads I and aVL during SVT- Consistent with right sided bypass tract

• Narrow complex AVRT is the most common arrhythmia in
patients with the WPW syndrome occurring in approximately 85%
to 95% of patients who have symptoms of tachycardia.
• Wide complex AVRT is rare, occurring only in 5% to 10% of
patients with WPW syndrome.
• Wide complex AVRT is difficult to differentiate from VT because
both arrhythmias have wide QRS complexes.

• VT usually occurs in patients with history of myocardial
infarction or left ventricular systolic dysfunction.
• Wide complex AVRT occurs in patients who are younger with
known preexcitation and generally preserved left ventricular
systolic function.
• Wide or narrow complex AVRT is paroxysmal with abrupt
onset and sudden termination.

Major Features in D/D of Wide-QRS Beats vs Tachycardia

Algorithm for
diagnosis of
wide-QRS
tachycardia.
ACC/AHA/ESC guidelines for
the management of
patients with supraventricular
arrhythmias Circulation
2003;108:1871.)

Atrial fibrillation
• It one of the most catastrophic tachyarrhytmia in these subset of
patients.
• The arrhythmia can result in very rapid ventricular responses,
which can lead to hypotension, diminished coronary perfusion, and
ventricular fibrillation and can lead to sudden cardiac death.
• ~30% to 40% of patients with preexcitation with symptoms of
tachycardia will develop atrial fibrillation.
• The presence of AVRT increases the predisposition to develop
Afib, which (in the presence of preexcitation) may degenerate to
ventricular fibrillation.
Osmar et al J Atr Fibrillation. 2011 May-Jun; 4(1): 287.

ECG features
• Features include
– Irregularly irregular R-R intervals
– Varying morphology of QRS complexes
– Fast Ventricular rate

In patients with WPW syndrome with Afib , atrial impulses can enter the ventricles
through both bypass tract and AV node.
These impulses are conducted through the AV node.
The wide QRS complexes (arrows) are preexcited and are conducted through the
bypass tract.
Some QRS complexes are fusion complexes due to activation of the ventricles from
both bypass tract and AV node.
The R-R interval between two wide QRS complexes measure 250 milliseconds
(distance between the two arrows) making the patient high risk for ventricular
fibrillation.

From the same patient upon conversion to normal sinus rhythm.
ECG shows preexcitation.
•Afib in a patient with known WPW syndrome.
•Irregularly irregular R-R intervals and the presence of bizarre QRS
complexes of varying morphologies.
•The R-R interval between both preexcited complexes measures 250
milliseconds,making patient high risk for Vfib

Low risk factors for sudden death.
• Patients with preexcitation in the resting ECG, but are
completely asymptomatic.
• The preexcitation is noted only intermittently during routine
ECG.
• There is immediate disappearance of preexcitation during
stress testing.
• The delta waves disappear when procainamide is given
intravenously.

High risk factors for sudden death.
• Bypass tract has a short refractory period and is capable of
conducting atrial impulses rapidly.
• The delta wave persists during stress testing.
• The refractory period of the bypass tract is short measuring
250 milliseconds between preexcited complexes.
• This can be measured during spontaneously occurring atrial
fibrillation or it can be induced in the electrophysiology lab
during electrophysiologic testing.
• History of cardiac arrest from ventricular fibrillation.
• Presence of multiple accessory pathways.
• Presence of Ebstein anomaly.

(A) Preexcitation with a bypass tract connecting the atrium directly to the ventricles.
This is associated with the classic ECG of WPW syndrome.
(B) Mahaim fibers connecting the AV node directly to the ventricle (nodo-ventricular
fiber), bundle of His directly to ventricle (Hisioventricular fiber) and bundle branches or
fascicles directly to the ventricles (fasciculoventricular fiber)
(C) A bypass tract connecting the atrium directly to the bundle of His. This is often
associated with a Hisioventricular fiber resulting in pattern similar to WPW ECG (A)
(D) A small AV node resulting in a short PR interval and a normal QRS complex. ECG,
electrocardiogram;WPW,Wolff-Parkinson-White.
Accessory Pathway Variants

Accessory Pathway Variants

Take away message
• Successful ablation needs pre ablation proper identification in
accessory pathways.
• Algorithm based approach is very useful in correct localization
of accessory pathways.
• It can enlighten the necessary invasion intervention and reduce
time of fluoro exposure and discomfort to patients
• Aruda approach has maximum diagnostic accuracy.
• Ebstein’s anomaly should always be suspected when a bypass
tract is right sided.

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