Paradoxical preexcitation during cryoablation of a concealed parahisian accessory pathway.

ABSTRACT

A 16-year-old male presented with an orthodromic atrioventricular reentrant tachycardia over a concealed parahisian accessory pathway (AP). Cryoablation of the AP resulted in transient manifestation of a fully preexcited sinus rhythm of parahisian AP morphology. Potential causes for the paradoxical preexcitation include inadvertent atrioventricular nodal block, sourse-sink mismatch, as well as the activation of a dormant AP capable of anterograde conduction.