Incessant tachycardia using a concealed atrionodal bypass tract.

A case of incessant supraventricular tachycardia continuing despite AV block is reported. Atrial tachycardia and AV nodal reentrant tachycardia were excluded, as was orthodromic tachycardia using a concealed accessory AV pathway. The earliest retrograde atrial activation was at the posterolateral tricuspid annulus, and the tachycardia was eliminated by ablation at this site. The findings in this case are explained only by a concealed atrionodal pathway.