Key result
Continuous vagal enhancement using phenylephrine significantly prolonged the effective refractory period of the anterograde fast pathway (394 to 544 ms, P<0.001) in patients with AVNRT.
Why the study?
Does continuous vagal enhancement using phenylephrine infusion alter the electrophysiological properties of dual AV nodal and accessory pathways in patients with AVNRT and AV reciprocating tachycardia?
Does continuous vagal enhancement using phenylephrine infusion alter the electrophysiological properties of dual AV nodal and accessory pathways in patients with AVNRT and AV reciprocating tachycardia?
p-value: p=<0.001
Enhanced vagal tone disproportionately prolongs the refractoriness of the anterograde fast AV nodal pathway, creating conditions conducive to AVNRT induction.
Supports vagal role in AVNRT refractoriness; hypothesis-generating and should not yet change practice.
BACKGROUND: The aim of this study was to test the electrophysiological effects of continuous enhanced vagal tone on dual atrioventricular (AV) nodal and accessory pathways. METHODS AND RESULTS: This study included 10 patients with typical, slow-fast AV nodal reentrant tachycardia (AVNRT) and 10 patients with AV reciprocating tachycardia. Electrophysiological data were measured before and during continuous vagal enhancement by using phenylephrine infusion (0.6 to 1.5 microg/kg per min). For patients with AVNRT, during phenylephrine infusion, 1:1 conduction times over the anterograde fast and slow and retrograde fast pathways were prolonged (453+/-64 to 662+/-120 ms, P<0.001; 379+/-53 to 443+/-95 ms, P<0.05; 405+/-112 to 442+/-118 ms, P<0.05). The effective refractory period and functional refractory period of the anterograde fast pathway were prolonged with phenylephrine (394+/-73 to 544+/-128 ms, P<0.001; 454+/-60 to 596+/-118 ms, P<0.001). In contrast, the effective refractory period and functional refractory period of the anterograde slow and retrograde fast were not significantly changed. No significant change was observed in the conduction or refractoriness of the accessory pathways in patients with AV reciprocating tachycardia nor in atrial or ventricular refractoriness. CONCLUSIONS: Enhanced vagal tone produces disparate effects on the refractoriness of the slow and fast AV nodal conduction pathways, with the anterograde fast pathway being the most sensitive. These changes are conducive to induction of AVNRT with a premature atrial complex and may explain in part the relatively common occurrence of AVNRT during sleep or other periods of presumed increased parasympathetic tone.
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Chiou et al. (2003) studied Atrioventricular nodal reentrant tachycardia (AVNRT) and AV reciprocating tachycardia (n=20). Phenylephrine infusion vs. Baseline (before infusion) was evaluated on Electrophysiological properties including conduction times and refractoriness of AV nodal and accessory pathways (p=<0.001). Continuous vagal enhancement using phenylephrine significantly prolonged the effective refractory period of the anterograde fast pathway (394 to 544 ms, P<0.001) in patients with AVNRT.