EFFECT OF PHENYLEPHRINE INFUSION ON ATRIAL ELECTROPHYSIOLOGICAL PROPERTIES

Objective-To determine the effect of changes in autonomic tone induced by phenylephrine infusion on atrial refractoriness and conduction. De sign-Left and right atrial electrophysiological properties were measur ed before and after a constant phenylephrine infusion designed to incr ease sinus cycle length by 25%. Subjects-20 patients, aged 53 (SD 6) y ears, undergoing electrophysiological study for investigation of idiop athic paroxysmal atrial fibrillation (seven patients) or for routine f ollow up after successful catheter ablation of supraventricular tachyc ardia (13 patients). Main outcome measures-Changes in left and right a trial effective refractory periods, atrial activation times, and frequ ency of induction of atrial fibrillation. Results-Phenylephrine (mean dose 69 (SD 18) mg/min) increased mean blood pressure by 22 (12) mm Hg (range 7 to 44) and lengthened sinus cycle length by 223 (94) ms (20 to 430). Left atrial effective refractory period lengthened following phenylephrine infusion from 250 (25) to 264 (21) ms (P < 0.001) but th ere was no significant change in right atrial effective refractory per iod: 200 (20) v 206 (29), P = 0.11. There was a significant relation b etween the effect of phenylephrine on sinus cycle length and on right atrial refractoriness (r = 0.6, P = 0.005) with shortening of right at rial refractoriness in patients with the greatest prolongation in sinu s cycle length. During phenylephrine infusion, the right atrial stimul us to left atrial activation time at the basic pacing cycle length of 600 ms was unchanged, at 130 (18) v 131 (17) ms, but activation delay with a premature extrastimulus increased: 212 (28) v 227 (38)ms, P = 0 .002. Atrial fibrillation was induced by two of 58 refractory period m easurements at baseline and by 12 of 61 measurements during phenylephr ine infusion (P < 0.01). Phenylephrine increased the difference betwee n left and right atrial refractory periods by 22.8 (19.4) ms in the fi ve patients with induced atrial fibrillation after phenylephrine compa red to 0.9 (16.2)ms in the 13 patients without induced atrial fibrilla tion after phenylephrine infusion (P = 0.02). Conclusions-Phenylephrin e infusion increased left atrial refractoriness and intra-atrial condu ction delay following a premature right atrial extrastimulus. Inductio n 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 fibr illation in susceptible individuals.