Demonstration of Dual A-V Nodal Pathways in Patients with Paroxysmal Supraventricular Tachycardia

Electrophysiological evidence suggestive of dual atrioventricular (A-V) nodal pathways is presented in two patients with normal P-R interval and reentrant paroxysmal supraventricular tachycardia (PSVT). His bundle recordings and atrial stimulation were used to obtain this electrophysiological evidence.Refractory periods were measured with the atrial extra-stimulus technique. Plotting of H1-H2 responses against A1-A2 coupling intervals revealed that as A1-A2 decreased, H1-H2 decreased appropriately. At a critical A1-A2, a sudden marked increase in H1-H2 occurred, suggesting failure of fast pathway, (defining the fast pathway effective refractory period ERP). Further shortening of A1-A2 defined a second H1-H2 curve. The longest A1-A2 with no H2 response was defined as the slow pathway ERP. Echo zones coincided with A1-A2 intervals equal to or less than the fast pathway ERP.These results provide the first electrophysiological demonstration of dual A-V nodal pathways in patients with normal P-R interval and PSVT, as manifest by dual A-V nodal conduction times and refractory periods. Antegrade failure of the fast pathway with subsequent availability for retrograde conduction could allow A-V nodal reentry. These findings provide a basis for reentrance in some patients with reentrant PSVT.