Physiologic role of atrio-Hisian and nodo-Hisian bypass tracts in supraventricular tachycardia.

Atrio-Hisian bypass tracts are considered to be rare electrophysiologic curiosities. The prevalence and functional significance of these tracts are unknown. We examined the incidence of atrio-Hisian and nodo-Hisian bypass tracts, their electrophysiologic manifestations, and their physiologic role in supraventricular tachycardia in 200 consecutive patients referred for evaluation of supraventricular tachycardia. In one patient it was demonstrated for the first time that a concealed (retrograde only) nodo-Hisian bypass tract functioned as the retrograde limb of orthodromic reciprocating tachycardia. The VA interval was negative during tachycardia, similar to that sometimes observed in atrioventricular nodal reentry. In a second patient an anterograde and retrograde conducting pathway resulted in a pseudo Wolff-Parkinson-White electrocardiographic pattern and served as an "innocent bystander," permitting a rapid ventricular response during atrial flutter. In conclusion, although atrio-Hisian and nodo-Hisian bypass tracts are rare, they are sufficiently prevalent to make them observable in a larger referral series. Most importantly, they may participate as bystanders during supraventricular tachycardia or as either the anterograde or retrograde limbs of reciprocating tachycardia. They may possess features that mimic Wolff-Parkinson-White syndrome and/or AV nodal reentry.