Objective-To determine the effect of changes in autonomic tone induced by phenylephrine infusion on atrial refractoriness and conduction. Design-Left and right atrial electrophysiological properties were measured before and after a constant phenylephrine infusion designed to increase sinus cycle length by 25%. Subjects-20 patients, aged 53 (SD 6) years, undergoing electrophysiological study for investigation of idiopathic paroxysmal atrial fibrillation (seven patients) or for routine follow up after successful catheter ablation of supraventricular tachycardia (13 patients). Main outcome measures-Changes in left and right atrial effective refractory periods, atrial activation times, and frequency of induction of atrial fibrillation. Results-Phenylephrine (mean dose 69 (SD 18) mg/min) increased mean blood pressure by 22 (12) 22'8 (19.4) ms in the five patients with induced atrial fibrillation after phenylephrine compared to 0 9 (16-2) ms in the 13 patients without induced atrial fibrillation after phenylephrine infusion (P = 0.02).Conclusions-Phenylephrine infusion increased left atrial refractoriness and intra-atrial conduction delay following a premature right atrial extrastimulus. Induction of atrial fibrillation during phenylephrine infusion was associated with non-uniform changes in atrial refractoriness. These data support the concept that changes in autonomic tone may precipitate atrial fibrillation in susceptible individuals.
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