Demonstration of dual A V nodal pathways in patients with paroxysmal supraventricular tachycardia

Abstract

Electrophysiological evidence suggestive of dual atrioventricular (AV) nodal pathways is presented in two patients with normal PR 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 AV nodal pathways in patients with normal PR interval and PSVT, as manifest by dual AV nodal conduction times and refractory periods. Antegrade failure of the fast pathway with subsequent availability for retrograde conduction could allow AV nodal reentry. These findings provide a basis for reentrance in some patients with reentrant PSVT.