Posts Tagged ‘arruda scheme’

If some body is struggling with same problem, say for over three decades , there is something seriously wrong with the way we deal with the problem. How do you localise accessory pathway in WPW syndrome from 12 lead ECG ? is one such entity, This question is asked exclusively in cardiology board exams. Now a 2023 paper from EUROPACE claims, it has come out with a simple algorithm bettering all the previous ones. Please check it for yourself.

One thing we can say with conviction is most of these embryological remnant pathways are posteriorly or laterally dragged in peri AV annular region or the para septal region. Very few appear anteriorly, if anterior it is more often placed on the right side.

Why should we take this question easy ?

Try asking any experienced EP specialist* to localise a pathway in given 12 lead ECG . Don’t get surprised by a long silence before they commit, because they know the truth, and how delicate this question might sound on quiet a few occasion, because of various anatomical and physiological reasons.

*Never fail to appreciate their hard long hours in cath lab to spot, analyse and shoot these tracts.(EP stuff is not like angioplasties, which, many can do even in half sleep!)

Final message

Yes, localising WPW can be either a fascinating or frustrating exercise depending on our understanding about the attitudinal cardiac anatomy, variable autonomic tone dependent morphological behaviour of delta waves, PR intervals, QRS axis ,the transition zones etc. Shrewd fellows may go through this 12 lead stress test. ,

For others just try to localise right from left , & then posterior or lateral Forget the anterior ones. This is more than suffice. Unlike drug trials, where statistics are often battered , here the Incident numbers are the key measure of truth. (Even without seeing a ECG you are likely to be correct in 80 % times, if you localise the pathway to posterior, para-septal or left lateral zones. )


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Localising  WPW syndrome is a favorite  time pass  for cardiologists in spite of  serious  limitations of surface ECG .Still , it is vital to generate a rough idea about the location of  these pathways ,  so that we can focus  our efforts  on  some sort of ablation procedure .

Arruda algorithm is probably a simple and fairly useful technique to remember. It asks us to climb 4 steps   and pause at each  step and look sideways   for the accessory  pathways !

Step 1 (Left free wall step )

Initially one need to look only two leads .

Look at lead 1  and  V1 for   delta wave and R/S ratio .After Identifying delta wave look for the polarity of delta wave (This can sometimes be really difficult ) .If there is iso-electric or negative delta it immediately  fixes the pathway  in left free wall . Similarly if V1 R >  S it also fixes in left free wall. To locate more precisely in left free wall  look  for  delta  wave polarity in  AVF  and proceed down*

If none of these finding are present then  Go to step 2 .

Step 2 (Coronary sinus step )

It is the most simple step . If negative delta  located in lead 2 (often mimic inferior MI)

Here the pathway is often located in coronary sinus /middle cardiac vein often as diverticulum.

After excluding left free wall and coronary sinus origin one has to look at possible septal  pathway  .

For this  go to step 3

Step 3  (Septal step ) And  again v1 lead  becomes important if v1 shows negative or iso-electric  go down  to septal  pathway decoding

After ruling out septal origin the scheme takes us to right free wall by default.

Step 4  (Right free wall step)  If the delta wave does not fit in  any   of the above three steps (Including  positive  delta in V 1 )  it  fixes  the right free wall  pathway

Arruda scheme summary

Arruda scheme  guides  us  to scan  systematically  for pathway from left free wall  to  septum and lastly  the right free  wall  (The key  to  locate  the APs is  to look at  delta waves in lead  1, 2  AVF and R/S ratio In V1 )

Here is a  simplified version for basic localization


  1. Arruda MS, McClelland JH and Wang X , et al. Development and validation of an ECG algorithm for identifying accessory pathway ablation site in Wolff-Parkinson-White syndrome. J Cardiovasc Electrophysiol 1998;9:2–12.

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