Automaticity with anterograde conduction of a concealed accessory pathway due to radiofrequency energy application.

We report a case of a patient with recurrent episodes of supraventricular tachycardia in which a concealed left-posterior accessory pathway-mediated orthodromic tachycardia was reproducibly induced during the EP study. Two interesting and very unusual electrophysiological phenomenon were observed at the same time during the ablation procedure of the accessory pathway: 1- Automaticity of the regular accessory atrioventricular pathway; 2- Emergence of manifest preexcitation following radiofrequency application exclusively during the automatic accessory pathway-mediated rhythm.