Accessory pathway EP study

Supraventricular Arrythmias, Atrio-ventricular reentrant tachycardia

This is a typical EP study of a symptomatic accessory pathway.

History of the patient

A young women, 12 year old, had palpitations for years. She had a pattent short PR on the 12 leads electrocardiogram with a pre-excitation pattern. Echocardiography do not reveals any structural heart disease. 

During exercice test, PR interval remains short without abrupt loss of pre-excitation. An EP study is indicated to assess accessory pathway malignancy.


Full pre-excitation analysis  is the first step of an accessory pathway EP study. At baseline, PR is short and pre-excitation is difficult to analyse. While pacing from CS (wenckebach or premature beats) full pre-excitation allows us to localize AP (see Full pre-excitation algorythm page).

Ablation indication was confirmed by the sustainability of an orthodromic tachycardia. Otherwise we should induce atrial fibrillation as recommended in the last published guidelines (see : 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia, page e181).

During anterograde EP study, at accessory pathway anterograde refractoriness, an orthodromic AVRT starts. A CS excentric activation of CS rules out AVNRT. 

During retrograde EP study it is interesting to noticed CS activation. First concentric at baseline (S1), then excentric with echo beat on S2 unmasking the retrograde conduction through AP.

Ablation was performed.