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

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.