A 23-year-old woman is referred to the Arrhythmia Clinic because of occasional brief episodes of palpitation, with sensation of anterior chest pounding, subsiding spontaneously:    

• Sinus rhythm
  
• Wolff Parkinson White (preexcitation)
• Anteroseptal accessory pathway

Comments: The location of the accessory pathway can be determined by the following step-wise approach:

• Is the the accessory pathway on the left? No, there are no q waves in I and aVL 
• Could the accessory pathway be posterior-inferior? No, the delta wave in positive in the inferior leads
• The delta wave is isoelectric in V1, the QRS is negative in V1 and V2 and positive in III and aVF. The accessory pathway is antero-septal

EP studies confirmed the presence of an anteroseptal accessory pathway. The pathway was very close to the His bundle. Atrial fibrillation was induced during the procedure and the ventricular rate was not above 150/min. Ablation was not carried out because of the mildness of the episodes of tachycardia, the low risk of sudden death and the high risk of the ablation inducing AV block.