A 27-year-old female presenting palpitation without ECG documentation
underwent electrophysiology study. EP study revealed atrioventricular
accessory pathway with poor and unidirectional pathway conduction, and a
fasciculoventricular pathway. During isoproterenol infusion, delta wave
promptly became prominent, after which an antidromic AV reentrant
tachycardia was induced. When the pathway was mapped, widely split
double pathway potentials were observed at 12 o'clock site of tricuspid
annulus during mild preexcitation, demonstrating an example of
intra-pathway conduction delay, which can be reversed by isoproterenol.
Ablation at the site caused accelerated pathway rhythm and eliminated
the pathway, rendering the tachycardia non-inducible.