EFFECTS OF ENHANCED PARASYMPATHETIC TONE ON ATRIOVENTRICULAR NODAL CONDUCTION DURING ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

The effects of various physiologic and pharmacologic stimuli on the an terograde slow pathway in patients with atrioventricular nodal reentra nt tachycardia are well characterized, We sought to further characteri ze the nature of anterograde and retrograde conduction during tachycar dia and to define the differential input of the parasympathetic nervou s system to these pathways. A custom-made neck suction collar was plac ed to stimulate the carotid body baroreceptors during supraventricular tachycardia. Neck suction at -60 mm Hg was applied and changes in tac hycardia cycle length, AH, and ventriculoatrial intervals were measure d in 20 patients, These measurements were repeated after intravenous a dministration of 10 mg of edrophonium to enhance vagal tone. We observ ed a 15 +/- 6 ms increase in tachycardia cycle length from baseline (p < 0.0001) and a 14 +/- 6 ms increase in AH interval (p < 0.0001), but no change in the VA interval with neck suction alone, The tachycardia cycle length prolonged 26 +/- 55 ms (p < 0.0001) with edrophonium and an additional 12 +/- 43 ms (p < 0.001) with neck suction after edroph onium. There was no change in the VA interval before or after edrophon ium during neck suction. There were 10 tachycardia terminations in 8 p atients during anterograde slow pathway block during neck suction, wit h tachycardia cycle length prolongation and mean AH prolongation befor e termination of 45 +/- 37 ms (vs 15 +/- 7 ms increase in AH interval without tachycardia termination, p = 0.10), There were 12 tachycardia terminations in 4 patients with retrograde block during neck suction, only after edrophonium, without any preceding change in tachycardia cy cle length during 11 episodes. We conclude that anterograde slow pathw ay demonstrates gradual conduction slowing with parasympathetic enhanc ement, whereas retrograde fast pathway responds with abrupt block. (C) 1997 by Excerpta Medica, Inc.