ELECTROPHYSIOLOGIC EVIDENCE FOR SELECTIVE RETROGRADE UTILIZATION OF A SPECIALIZED CONDUCTING SYSTEM IN ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

In 12 patients with atrioventricular (A-V) nodal reentrant tachycardia, the existence and utilization of retrograde ventriculoatrial bypass tracts in the reentrant process were excluded, and the characteristics of the anterograde and retrograde limbs of the reentrant circuits were studied using His bundle electrograms, incremental atrial and ventricular pacing and atrial and ventricular extrastimulus techniques before and after the administration of 0.01 mg/kg of intravenous ouabain. Similar studies were also performed in five control patients without tachycardia. Paroxysmal supraventricular tachycardia could be induced in all 12 patients during atrial pacing-induced A-V nodal Wenckebach periods or premature atrial stimulation, or both. On the basis of conduction time in the retrograde limb during tachycardia and during retrograde studies, two groups were identified. Group I (seven patients) had (1) short (39 ± 10 msec) and constant conduction time in the retrogarde limb measured from the anterograde His bundle deflection to the retrograde atrial echo response (H-Ae interval), (2) no change in ventriculoatrial conduction time up to maximal ventricular pacing rates, (3) H2-A2 intervals during retrograde refractory period studies that were identical to the H-Ae intervals and that did not increase with decreasing V1-V2 intervals, and (4) increased conduction time of the anterograde limb (Ae-H intervals) after the administration of ouabain without any effect on retrograde limb conduction (H-Ae and H2-A2 intervals) and refractoriness. Group II (five patients) had (1) long and variable H-Ae intervals (60 to 180 msec), (2) a progressive increase in ventriculoatrial intervals during incremental ventricular pacing, (3) an increase in H2-A2 intervals in response to decreasing V1-V2 intervals, and (4) increased anterograde (Ae-H interval) and retrograde limb (H-Ae and H2-A2 intervals) conduction and refractoriness after the administration of ouabain. Changes in the H2-A2 interval corresponded to the changes in four of the five control patients. These findings suggest that (1) in group I the anterograde limb was the A-V node, whereas the retrograde limb was an A-V nodal bypass tract or an insulated intranodal tract physiologically unlike the A-V node; and (2) in group II the A-V node comprised both the anterograde and retrograde limbs of the reentrant circuit. © 1979.