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
- 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.