Does the ECG
in

**show evidence of**__Figure-1__*anterior*infarction__or__WPW?__IF__your answer is WPW —*Where*is the AP () likely to be?__A__ccessory__P__athway- Is AP localization on ECG clinically important?

12-lead ECG. Is there evidence of prior anterior infarction?Figure-1: |

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__Interpretation of Figure-1:__
The ECG in Figure-1
shows sinus rhythm (

*upright P wave in lead II*) — but the PR interval is short. Closer inspection reveals initial slurring of the R wave upstroke consistent with*delta***waves**in many leads (*red arrows in***). The patient has**__Figure-2__**WPW****(**__W__olff-__P__arkinson-__W__hite**)**. We highlight the following points:- All
**3**of theof*features***WPW**are present in__Figure-2__. These include:**i)***short*PR interval;**ii)**QRS widening;__and__**iii)***delta*waves. *Not*all leads show delta waves. For example — there is no delta wave in lead aVL. It is not uncommon in patients with WPW for delta waves to only be seen in a few of the 12 leads. Furthermore, because conduction may be*divided*between impulses passing over the**AP (**__A__ccessory__P__athway**)**and the normal AV nodal pathway — the QRS will not always be as wide as it is in__Figure-2.__- In addition to
positive delta waves — there are also
*negative***delta waves**in__Figure-2.__These*negative*delta waves in leads V1,V2,V3*simulate*anterior infarction. - The ECG in
__Figure-2__*also*simulates LVH (*given large amplitude of the R wave in V5,V6*) and LBBB (*monophasic slurred complex in lead I*). However, since the patient has WPW —can be said about the possibility of anterior infarction, LVH, or LBBB. Instead — all we can say is that there is__nothing__*sinus***rhythm**__with__**WPW**.

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**HOW to**

*Determine*the*Likely*Location of the AP?
Delta wave morphology
and orientation on 12-lead ECG may assist in surprisingly

*accurate*localization of the**AP (**__A__ccessory__P__athway**)**in the patient with WPW. This is of more than academic interest to the EP cardiologist — as it facilitates__and__*expedites*localization of the AP during EP (*) study. In addition — it helps in planning the procedure as well as in patient discussion, since risks of catheter ablation and likely success rates are based in part on localization of the AP.*__E__lectro__P__hysiology- We emphasize that ECG
localization of the AP is an
*advanced*topic beyond the clinical needs of the non-cardiologist. Practically speaking — it suffices to recognize WPW__and__IF there is need for referral. That said — ECG localization of the AP is not necessarily difficult if certain parameters are followed.

My

__Suggested__**to**__Approach__*ECG AP Localization*is based on my synthesis of material primarily derived from the following 2 references:- Das MK, Zipes DP:
*Electrocardiography of Arrhythmias*—*A Comprehensive Review*(*ePub book*). Elsevier-Saunders, Philadelphia, 2012. - Fitzpatrick AP Gonzales RP Scheinman
MM, et al:
*Algorithm for the Localization of Accessory Atrioventricular Connections Using a Baseline Electrocardiogram*. J Am Coll Cardiol 23:107-116, 1994.

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__The Basics of AP Localization:__
ECG localization of the AP is

*not*perfect. Accuracy of ECG localization is clearly*suboptimal*if there is less than maximum preexcitation — as may occur when the QRS is minimally widened because a substantial portion of ventricular activation is occurring by transmission of the impulse over the normal AV nodal pathway.*Approximate***distribution**of**AP sites**is the following:**i)**Lateral () Free Wall — ~50% of APs;__L__eft__V__entricular**ii)**Right or Left*PosteroSeptal*Area — ~20%;**iii)**RV (__R__ight) Free Wall — ~20%;__V__entricular__and__**iv)***AnteroSeptal*Area — ~10%.- On occasion —
*more*than a single AP may be present in a given patient. Together with variation in the*relative*amount of AP vs normal pathway conduction — this may account for*changing*delta wave morphology that can sometimes be seen from one ECG to the next in a given patient. - As a general rule — IF the
*delta***wave**(*first ~40msec of the QRS*) is**upright**(*positive*) in**lead V1**(*RBBB pattern*) — then there is a__LEFT__-sided**AP**(*as in*).__Step A-1__ - IF the
*delta***wave**is**downward**(*negative*) in**lead V1**(*LBBB pattern*) — then as a general rule there is a__RIGHT__-sided**AP**(*The major exception to this is when transition occurs between leads V1-to-V2*—*as described in*).__Step B-1__

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__Step A-1:__

*IF the QRS in Lead V1 is all UPRIGHT*
When the QRS complex is all

*upright*in lead V1 — then there is a “RBBB pattern”. In this case —**transition**(*where the R wave becomes taller than the S wave*) is said to occur*or*__before__*by*lead V1. This defines a__LEFT__-sided**AP**. Proceed as follows:**Measure**theof*sum**delta wave***polarities**in the**3**(*inferior*leads*II,III,aVF*) — giving a score of +1 if the delta (*first 40msec of the QRS*) is positive; 0 if the delta is isoelectric; and -1 if the delta is negative.__IF__Sum of*inferior*lead Polarities is +2 or +3 =*AnteroLateral***LV***Free*Wall AP.__IF__Sum of*inferior*lead Polarities is*less*than +2 — then the AP is*posterior.*__IF__Sum of*inferior*lead Polarities is -2 or -1 —__and__— the R wave in lead I is*at least*0.8mV (*8 mm*)*more*than the S wave in lead I =*PosteroSeptal***AP**. Otherwise = there is a*PosteroLateral***LV**.*Free*Wall AP

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__Step A-2:__*IF Transition Occurs Between Lead V1-to-V2*
IF the R wave in lead V1 is

*less*than the S wave in V1 —__but__by lead V2 the R wave*becomes*taller than the S wave in V2 (ie,*IF transition occurs*) — then the AP could be__between__V1-to-V2*left*__either____or__right-sided. Proceed as follows:__IF__the R wave in lead I isthan 1.0mV (__less__*10 mm*) greater than the S wave in lead I = then there is a__LEFT__-sided**AP**. In this case — Proceed as above () for when the QRS is UPRIGHT (__Step A-1__*beginning by measuring sum of delta polarity in the inferior leads to determine if the AP is anterolateral — posteroseptal — or**posterolateral*).- But
__IF__the R wave in lead I is*at least*1.0mV (*10 mm*)__more__than the S wave in lead I = then there is a__RIGHT__-sided**AP**. In this case — Proceed as described in__Step B-2__.

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__Step B-1:__*How to Tell IF the AP is RIGHT-sided?*
When the QRS complex is predominantly downward (

*negative*) in lead V1 —__and__—**transition**(*where the R wave becomes taller than the S wave*) occurs*lead V2 — then there is a*__after____RIGHT__-sided**AP.**- As stated above there can also be a
__RIGHT__-sided**AP**—__IF__transition occurs*between*V1-to-V2 —__and__— the R wave in lead I is*at least*1.0mV (*10 mm*)__more__than the S wave in lead I.

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__Step B-2:__*When the AP is RIGHT-sided*
Localization of a

*right-sided*AP will depend on**. There are***where*transition occurs**3 possibilities**. Transition may be:**i)***(*__before__*or by*) V2-to-V3 (**);**__Step B-3__**ii)***between*V3-to-V4 (**);**__Step B-4____or__**iii)***V4 (*__after__**).**__Step B-5__
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__Step B-3:__

**Right-Sided AP:**

*Transition before (or by) V2-to-V3*
IF the AP is

*right-sided*with transition*(*__before__*or by*) lead V2-to-V3 — then the AP is**. To determine**__Septal__*which*septal area is involved — Proceed as follows:**Measure**theof*sum**delta wave***polarities**in the**3**(*inferior*leads*II,III,aVF*) — giving a score of +1 if the delta (*first 40msec of the QRS*) is positive; 0 if the delta is isoelectric; and -1 if the delta is negative.__IF__Sum of*inferior*lead Polarities is -2 or -3 =*PosteroSeptal***AP**.__IF__Sum of*inferior*lead Polarities is -1, 0 or +1 =*MidSeptal***AP**.__IF__Sum of*inferior*lead Polarities is +2 or +3 =*AnteroSeptal***AP**.

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__Step B-4:__**Right-Sided AP:***Transition between V3-to-V4*
IF the AP is

*right-sided*with transition*lead V3-to-V4 — then the AP is*__between__*septal*__either____or__right ventricular free wall. To determine*which*— Proceed as follows:- Measure
*delta wave***amplitude**(*first ~40msec of the QRS*) in**lead II**. __IF__the delta wave in lead II is*at least*1.0mV (*10mm*) =*Septal***AP**. To then find out*which*septal area is involved — Proceed as above for when transition isV2-to-V3 (__between__).__Step B-3____IF__the delta wave in lead II is*less*than 1.0mV (*10mm*) =**RV**__Free__**AP**. To determine__IF__the AP is located on the*anterolateral*__or__*posterolateral*RV Free Wall — Proceed as below for when transition isV4 (__after__).__Step B-5__

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__Step B-5:__**Right-Sided AP:***Transition after Lead V4*
IF the AP is

*right-sided*with transition*lead V4 — then the AP is located in the*__after__**RV**. To determine*Wall*__Free____IF__the AP is located on the*anterolateral*__or__*posterolateral*RV Free Wall — Proceed as follows:- Measure the
*delta wave***frontal axis**(*looking at delta wave polarity in leads I and aVF*). __IF__the delta wave frontal axis is positive (=*more than 0 degrees*) =RV Free Wall__Anterolateral__**AP**.- But
__IF__the delta wave frontal axis is negative (=*less than 0 degrees*) — then look at the R wave in lead III. __IF__delta wave frontal axis is*negative*—__and__— the R wave in lead III is net*positive*=RV Free Wall__AnteroLateral__**AP**.__IF__delta wave frontal axis is*negative*—__and__— the R wave in lead III is net*negative*=RV Free Wall__PosteroLateral__**AP**.

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__Figure-3:__*Where is the AP likely to be?*
Let’s apply the above
approach to AP localization to the ECG from Figure-2 that we again show in

**.**__Figure-3__*Where is the AP likely to be?*

Sinus rhythm with WPW (Figure-3:ECG repeated from Figure-2). What is the likely location of the AP? (See text). |

__ANSWER to Figure-3:__

*Where is the AP?*
We begin by looking to
see

__IF__the**QRS**in**lead V1**of__Figure-3__is upright or negative:- Since the QRS complex
in V1 is negative — we
*skip*over Step A-1. **Transition (***where the R wave in precordial leads becomes taller than the S wave***)**isbetween V1-to-V2 — therefore we also skip over Step A-2.__not__- According to
— the__Step B-1__**AP**is(*right-sided**because the QRS is negative in V1 and transition occurs after lead V2*). **Transition**occurs*between***V3-to-V4**. Therefore we skip to. We are asked to measure__Step B-4__*delta wave***amplitude**in**lead II**. Realizing that it is*not*always easy to distinguish the precise end of slurring from the delta wave__vs__fusion with the remaining portion of the QRS — it looks like there is a*markedly*positive delta wave (*of at least 10mm*) in lead II. This suggests a*Septal***location**for the AP.- To determine the
likely part of the septum that is involved — We are asked to return to
. Delta wave polarities are clearly positive in__Step B-3__*each*of the inferior leads — therefore we suspect an__AnteroSeptal__**AP**location.

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__Figure-4:__*Where is the AP likely to be?*
Let’s apply the above
approach to the example of WPW shown in

**.**__Figure-4__*Where is the AP likely to be?*

Sinus rhythm with WPW. Figure-4:What is the likely location of the AP? (See text). |

__ANSWER to Figure-4:__

*Where is the AP?*
We begin by looking to
see IF the QRS in lead V1 of

__Figure-4__is upright or negative:- Since the QRS complex
in V1 is upright — we begin with
. Because the QRS is positive in lead V1 — we already know we are dealing with a__Step A-1____LEFT__-sided**AP**. - The sum of
*delta wave***polarities**is*at least*+2 (*decidedly positive delta waves in leads II,aVF — though no more than minimally positive in III, if not isoelectric in this lead*). Therefore —__AnteroLateral__**LV**.*Free*Wall AP

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**Realize that**

__Editorial Comment by the Author:__*many*algorithms have been proposed for ECG localization of the AP.

*None are perfect*—

__and__the “ultimate test” is precise localization by EP study. We hope the above proposed approach simplifies this topic for you and is helpful in allowing a rapid

*educated*guess as to AP localization based on ECG appearance.

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**My appreciation to**

__Acknowledgement:__

*Michael***Frease**for providing me with the ECG in Figure 4, and allowing me to publish this.

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- For more information – GO TO:

— for a pdf of our Section 05.36 on*CLICK HERE***WPW (***excerpted from ECG-2014-ePub***)**.- For an example of very rapid AFib with a wide QRS
*—**Check out*our**ECG Blog #37**.

very informative. I've been searching for this information a few times! very well explained. thank you Dr Grauer.

ReplyDeleteThank you for the kind words! I wanted to put a user-friendly approach on-line and readily available

DeleteHi Dr. Grauer,

ReplyDeleteI have read your article with great interest. I have a quick question regarding delta wave amplitude in step B-4. I couldn't imaging the delta wave amplitude as high as 10 mm in just 1 small box. Do you happen to have an EKG example of this?

Thanks in advance!

This comment has been removed by the author.

DeleteThanks for your comment Tim. I went back to the original article by Fitzpatrick et al from which I primarily derived the above system for AP localization. They provide 2 examples of tracings in which there is transition between V3-to-V4 - Please GO TO this link — http://tinyurl.com/WPW-V3-V4-Transition - You'll note in Figure 5 that they describe delta wave amplitude of 0.8 mV - which is 8 (not quite 10) mm ... Note how steep the incline of the R wave in lead II is! So I DO agree with your comment - and I'm afraid I don't have a specific example that attains 10 mm to provide ... but I think Figure 5 gives insight as to what we are looking for. THANKS again for your interest!

DeleteBottom Line: I think the definition of 40 msec for delta wave duration may be a bit arbitrary - and I might extend it a tad IF QRS morphology showed a monophasic R wave with steep upslope similar to that seen in Figure 5.

Thanks for this graet algoritm... I have two wuastion ; how can we diferantiate left anteroseptal accessory pathway and for a2 did you mean the R-S > 10 mm or R>S and R>10 mm

ReplyDeleteThanks for your comment. This algorithm places septal localization under right-sided APs ... Sorry if the wording of A-2 is confusing. It say if the R in lead I is less than 10mm more than the S in lead I. So, for example — if the R in lead I = 13, but the S in lead I = 4 — then 13-4 = 9, in which case the R in lead I will be less than 10mm more than the S in this lead. Hope that makes sense.

Delete