The document discusses localization of accessory pathways using electrocardiography. It describes: - Accessory pathways are aberrant muscle bundles connecting the atria and ventricles outside the normal conduction system. - Algorithms have been developed to predict accessory pathway location based on delta wave morphology and other ECG criteria. Fitzpatrick's algorithm divides pathways into 8 anatomical locations. - Factors like precordial transition, delta wave polarity in various leads, and retrograde P wave morphology can provide clues about left vs. right, septal vs. free wall, and anteroseptal vs. posteroseptal localization. - Accurate localization guides patient counseling on ablation risks and assists planning the procedure

1. LOCALIZATION OF
ACCESSARY
PATHWAY BY ECG

2. INTRODUCTION
 First fully described by Wolf-Parkinson & White in 1930.
 It is the commonest variety of Pre-excitation Syndrome
associated with an accessory AV connection, called Kent
Bundle or Paladino tracts.
 The surface ECG is characterized by
1) Shortened PR interval for age (<120 milliseconds in
adults),
2)Prolonged QRS duration for age (>120 milliseconds),
with a slurred slow rising onset of the R wave upstroke
(Delta Wave).
3)Secondary ST and T wave changes which are directed
opposite to the major Delta wave and QRS vector.

3. • AV BTs are aberrant muscle bundles that connect the atria to the
ventricles outside of the normal AV conduction system.
• AV BTs are short and thin muscular strands (typically 5 to 10 mm in
length, with a maximal diameter of 0.1 to 7 mm)
• They can course through the AV groove at variable depths ranging
from subepicardial to subendocardial locations.

4. Direction of conduction
• 60% of AV BTs conduct both anterogradely and retrogradely
• AV BTs with only anterograde conduction are uncommon (less than 5%),
often cross the right AV groove, and frequently possess decremental
conduction properties.
• BTs that conduct only in the retrograde direction occur more frequently -
17% to 37%
• When the BT is capable of anterograde conduction, ventricular preexcitation
is usually evident during normal sinus rhythm (NSR), and the BT is referred to
as manifest.
• BTs capable of retrograde only conduction are referred to as concealed.
Orthodromic AVRT accounts for approximately 95% of AVRTs and 35% of all
paroxysmal SVTs, and 50% of the BTs that participate in orthodromic AVRT are
concealed

5. Decremental conduction across AV node
Vs
Non-decremental conduction across
bypass tracts

6. Need for localization of BT?
• Localisation provides the electrophysiologist with important
information that can guide patient counselling regarding the risks and
benefits of ablation.
• Eg - Guidance about the proximity of the BT to the normal
conduction system - Risk of AV block associated with an ablation
attempt
• The need for left heart catheterization and atrial septal puncture and
their potential complications.
• Can help in planning the ablation procedure, such as the use of
cryoablation for septal BTs or the need for special equipment for
atrial septal puncture for left-sided BTs.

7.  On the basis of large study of RF ablation of accessory
pathways in WPW syndrome, AP Fitzpatrick described
eight anatomical locations of pathways using
fluoroscopic landmarks
 Five of these accessory pathways are located on the
right side along the tricuspid valve annulus and three
left sided are located along the mitral valve annulus.

8. 1. Right anteroseptal
(RAS)
2. Right midseptal (RMS)
3. Right posteroseptal
(RPS)
4. Right anterolateral
(RAL)
5. Right posterolateral
(RPL)
6. Left anterolateral (LAL)
7. Left posterolateral
(LPL)
8. Left posteroseptal
(LPS)

10. LEFT SIDED
PATHWAYS
POSTERIOR
POSTEROLATERAL POSTEROSEPTAL
ANTERIOR
ANTEROLATERAL

11. RIGHT SIDED
PATHWAYS
SEPTAL
POSTERO
SEPTAL
MIDSEPTAL
ANTERO
SEPTAL
FREE WALL
ANTERO
LATERAL
POSTERO
LATERAL

12. 1. Left lateral (50 percent)
2. Left Posteroseptal (30
percent)
3. Right anteroseptal (10
percent)
4. Right lateral (10 percent).

13. Multiple bypass tracts
• Multiple AV BTs occur in 5% to 10% of patients.
• BTs are defined as multiple when they are separated by more than 1
to 3 cm at the AV junction.
• The most common combination of widely spaced multiple BTs is
posteroseptal and right free-wall BTs.
The incidence of multiple BTs is particularly high in patients with
• Antidromic AVRT (50% to 75%),
• Patients in whom AF resulted in VF
• Ebstein anomaly.

14. Localization of the accessory pathway
• Localization of the accessory
pathway
is
generally
of value
only
when considering catheter ablation.
• The pathway localization or the degree of preexcitation
otherwise does not predict the clinical course.
• Various algorithms (Chern – En Chiang’s, Ftizpatrick’s and
Xie’s algorithms) have been used for predicting accessory
pathway location using different electrographic criteria.

15. Localization Using the Delta Wave
Delta wave morphology reflects the ventricular insertion site of the BT
and, hence, is helpful in approximating the BT location
Retro grade p waves during orthodromic AVRT indicates the location of
atrial connection of the BT and can be used

16.  The height or the polarity of the
delta wave is measured on the
surface ECG in the first 40 msec
of QRS complex from the end of
P wave.
 On the basis of this it is
ISOELECTRIC, if it is on the
baseline or deflected above or
below the baseline but comes
back before the onset of QRS
complex.
 POSITIVE, if it is above the

17. • QRS duration is significantly increased in right sided
than the left sided accessory pathways (145±17, range
100-180 msec; versus 131±15, range 110-164 msec).

19. General concepts for localization of a bypass
tract
Precordial transition - Lead V1 is a unipolar lead positioned at the right
anterior chest wall.
• Therefore, as the BT location shifts progressively more to the left or
posteriorly, the precordial transition becomes sequentially earlier
• Earlier R/S transition in left sided BT
• Also left-sided BTs exhibit positive delta waves in lead V1, while right-
sided BTs exhibit negative delta waves

20. Frontal plane horizontal axis : Lead I primarily reflects the horizontal axis.
• BTs closer to the left axilla will produce a deeply negative complex in lead I
(i.e., rightward axis).
• Conversely, BTs closer to the right axilla are strongly positive in lead I (i.e.,
leftward axis).
• Leads II/ aVL and III/aVR also have net leftward and rightward vectors,
respectively.
• Hence, as the BT location moves progressively to the left (e.g., from anterior
to lateral mitral annulus), the delta wave assumes progressively less
positive/more negative deflection in lead I, a taller R wave in lead III than in
lead II, and a larger S wave in lead aVL compared to lead aVR.

21. Frontal plane vertical axis. The inferior leads (II, III, and aVF) reflect the
vertical axis.
• Therefore BTs located at the superior aspect of the tricuspid or mitral
annulus exhibit positive deflections in the inferior leads (i.e., vertical
axis).
• The magnitude of the inferiorly directed vector diminishes as the site
of origin shifts from superior to inferior regions of either annulus.

22. • Rosebaum in 1945 divided WPW into
 Type A left sided pathways (tall R wave in lead V1 with
a positive delta wave
 Type B. right sided pathways (QS complex in lead V1 with a a
negative delta wave)

23. Fitzpatrick algorithm
Right Sided Vs Left Sided
 If QRS transition is at or before V1 or dominant R wave in V1, then it
is Left
sided pathway.
 If transition is after V2, it is right sided pathway.
 If the transition is at V2 or between V1 and V2, then measure the
amplitude of R-wave and S wave in lead I.
 If R>S wave in lead I by 1 mV it is right sided otherwise it will be left
sided
accessory pathway.

25. Left Anterolateral Vs Left Posterior
 The most significant variable is delta wave polarities in the
inferior leads and the ratio of the R wave to the S wave in lead
avL.
 Two or more than two positive delta wave in inferior leads or S
wave larger than R wave in aVL indicates anterolateral location
of the accessory pathway.

26. Left Posterolateral vs. Left Posteroseptal
 The sum of the inferior delta wave polarities and the
amplitude of R wave to S wave in lead I are the best ECG
variables to differentiate the two sites.
 If the R wave is greater than S wave in lead 1 by 0.8 mV
and delta waves are negative in inferior leads, the
pathway is located at left posteroseptal site otherwise it
will be left posterolateral location of the accessory
pathway.

28. Right Septal vs. Right Free Wall
 QRS transition is the most significant variable and delta wave
amplitude in lead II can assist to discriminate where the first variable
is equivocal.
 QRS transition at or before V3 indicates a septal location, whereas
transition at or after V4 indicates free wall location (Anterolateral or
poserolateral) of the accessory pathways.
 If the transition is between V3 & V4 then look for the amplitude of
delta wave in lead II; if it is equal or more than 1 mV then septal
location otherwise lateral location (97% sensitivity & 95%
specificity).

33. Right Anteroseptal vs. Right Poster-oseptal
 Delta wave polarities in leads II, Ill and aVF is the most significant
variable.
 If it is greater than +2, the pathway is located at anteroseptal region;
if it is less than 1 then it is posteroseptal

37. Right anteroseptal accessory pathway.

41. Right posteroseptal accessory pathway. Atrial fibrillation is present.

43. Right free wall

44. Left lateral accessory pathway.

47. Chiang CE et al algorithm

48. Fox DJ, Klein GJ, Skanes AC, Gula LJ, Yee R, Krahn AD. How to identify the location of an accessory pathway by the 12-lead
ECG. Heart Rhythm. 2008;5:1763–1766.)

49. Taguchi N, Yoshida N, Inden Y, et al. A simple algorithm for localizing accessory pathways in patients with
Wolff-Parkinson-White syndrome using only the R/S ratio. J Arrhythmia. 2014;30:439–443.

50. Arruda aproach
An algorithm developed by Arruda et.al utilizing the
surface
ECG has an overall sensitivity of 90% and specificity
of 99%.

51.  Step 1: If the delta wave in lead 1 is negative or isoelectric or the R
wave is greater in amplitude than the S wave in V1 a left free wall
accessory pathway is present. If these criteria are fulfilled then lead
aVF is examined.
 If the delta wave in lead aVF is positive, a left lateral,
anterolateral
accessory pathway is identified.
 If the the delta wave in lead aVF is isoelectric or negative
then the
accessory pathway is located at the left posterior or posterolateral
region

53. Step 2: lead II is examined.
• A negative delta wave in lead II identifies the
subepicardial coronary sinus or middle cardiac vein
accessory pathway.
• If the delta wave in lead II is isoelectric or positive,
proceed to step 3.

55. Step 3:lead V1 is examined.
 A negative or isoelectric delta wave in lead Vi identifies a septal
accessory pathway.
If these criteria are fulfilled, lead aVf is examined.
 If the delta wave is negative, an accessory pathway is identified, which
is
located at the posteroseptal tricuspid annulus .
 If the delta wave is isoelectric in lead aVF, the accessory pathway may
be located to either the posteroseptal tricuspid annulus or the
posteroseptal mitral annulus.

56.  A positive delta wave in aVF identifies a pathway located within the
anteroseptal/right anterior paraseptal or midseptal tricuspid annulus
regions .
 If the delta wave in V1 is positive after having excluded patients with
a left free-wall accessory pathway in Step 1, a right free wall
accessory AV pathway is identified.
Proceed to Step 4.

58. Step 4: In patients with a right free –wall accessory pathways,
examine aVF.
 A positive delta wave in aVF identifies a right anterior/
anterolateral
accessory pathway.
 If the delta wave in aVF is isoelectric or negative, examine
lead II.
 A positive delta wave in lead II identifies a right lateral
accessory pathway , and an isoelectric delta wave in lead II
identifies a right posterior/posterolateral pathway.

61. Localization Using Polarity of the Retrograde
P Wave Morphology
• Left free-wall BTs have positive P
waves in lead V1 and negative P
waves in leads I and aVL.
• If the retrograde P wave is
negative in all three inferior
leads, the BT is located at the
inferoposterior mitral annulus.
• As the BT location moves to the
lateral mitral annulus, the P wave
becomes isoelectric or biphasic in
one of the three inferior leads.
• The P wave becomes positive in
all inferior leads for left
anterior/anterolateral BTs
Right free-wall BTs, the P wave is
negative in lead V1 and positive or
isoelectric in lead I.
If the P wave is positive in all inferior
leads, the BT is located in the anterior
wall.
If the P wave is negative in all inferior
leads, the BT is located in the
posterior wall.

62. Limitations of algorithms
They are inherently limited by
1. Biological variability in anatomy - (e.g., Rotation of the heart within the
thorax),
2. Variable degree of preexcitation and QRS fusion
3. The presence of more than one manifest BT
4. Intrinsic ECG abnormalities (such as prior MI and ventricular hypertrophy)
5. Patient body habitus
6. Technical variability in ECG acquisition and electrode positioning

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