Classical response of antidromic atriofascicular tachycardia to premature atrial extrastimulus delivered during septal refractoriness.

A 23-year-old gentleman presented with a history of palpitations. The 12-lead electrocardiogram showed no manifest ventricular pre-excitation. Echocardiogram was within normal limits. A retrograde study showed concentric activation of the atrium with decremental conduction. Atrial pacing from right atrial free wall showed progressive pre-excitation. No anterograde nodal duality was documented.