Demonstration of multiple antegrade and retrograde atrioventricular pathways.

A patient with paroxysmal supraventricular tachycardia had discontinuous antegrade (1a-A2, H1-H2) and retrograde (V1-V2, A1-A2) conduction curves suggesting dual A-V nodal pathways in both directions. Atrial echoes occurred with premature atrial pacing only at short A1-A2 coupling intervals after long antegrade (A2-H2) and retrograde (H2-A3) conduction intervals. Premature ventricular stimulation revealed ventricular echoes simultaneously with a sudden increase in the V2-A2 interval. The echo zone coincided with the slow pathway curve. Following atropine the echo zone was extended over the slow and fast pathway curves. Slow pathway conduction was observed at long and sort V1-V2 coupling intervals. Following isoproterenol ventricular stimulation initiated two cycles of ventricular echoes with relatively long retrograde (V2-A2, Ve-Ae) and short antegrade (A2-He, Ae-He) conduction times, the earliest atrial activation being observed in the low right atrium before the left atrium and the high right atrium. Antegrade fast and slow pathways as well as retrograde fast pathway conduction appeared to be confined to the A-V node. Retrograde slow pathway conduction may progress through a slow or fast A-V nodal pathway slowed by antegrade concealed conduction. However, an accessory pathway with long conduction times located near the septum cannot be ruled out entirely.