Changes in atrial effective refractory period and I(KACh) after vagal stimulation plus rapid pacing in the pulmonary vein.

INTRODUCTION AND OBJECTIVES Recent studies have shown that rapid atrial pacing causes atrial electrical remodeling. However, the influence of the vagus nerve on atrial electrical remodeling is not clear. METHODS This study involved 24 dogs divided into three groups. In the control group, the inducibility of atrial fibrillation (AF) during vagal stimulation (VS(1)) was investigated. In the pacing group, the atrial effective refractory period (AERP) was determined before and after pacing in the left superior pulmonary vein (LSPV). In the vagal stimulation (VS) plus pacing group, the LSPV was subjected to rapid electrical pacing after vagal stimulation (VS(2)), and the AERP was measured both before VS(2) and after pacing. The I(KACh) density was measured in LSPV and atrial myocardial cells in the three groups using the patch-clamp technique. RESULTS The duration of induced AF was greater in the pacing group than in the control or VS-plus-pacing group. In the pacing group, the AERP was markedly shortened and the AERP dispersion (dAERP) was significantly increased (P< .05). However, there was no significant change in AERP in the VS-plus-pacing group, though the dAERP increased significantly (P< .05). The I(KACh) density was increased in LSPV and atrial myocardial cells after pacing. However, there was no significant change in I(KACh) density after VS(2) plus pacing. CONCLUSIONS Although shortening of the AERP may play a fundamental role, it is not in itself responsible for cholinergically induced AF. Rapid pacing in the LSPV increased the I(KACh). However, VS before rapid pacing partly protected the atria against electrical remodeling.