title: Reversal of electrophysiologic effects of flecainide on the accessory pathway by isoproterenol in the Wolff-Parkinson-White syndrome.
abstract: To determine the reversibility of the effects of flecainide on accessory pathways, electrophysiologic studies were performed in the drug-free control state, after flecainide loading and with isoproterenol infusion during flecainide treatment in 12 patients with symptomatic preexcitation syndrome. After the baseline drug-free evaluation, oral flecainide was given in dosages of 50 to 200 mg twice daily (mean daily dose 282 +/- 75) for at least 4 days before the repeat electrophysiologic study. Isoproterenol infusion was given in dosages of 1 to 4 micrograms/min to increase the heart rate at rest by 50%. Anterograde block in the accessory pathway was observed in 3 patients with flecainide therapy, whereas in the other patients the anterograde refractory period increased from 243 +/- 20 to 315 +/- 23 ms (p less than 0.05). The shortest preexcited RR interval during atrial fibrillation lengthened from 234 +/- 27 ms before flecainide to 313 +/- 38 ms (p less than 0.05). Retrograde block occurred in 2 patients after flecainide, whereas the retrograde refractory period of the accessory pathway increased from 247 +/- 26 to 337 +/- 45 ms in the other patients. Orthodromic atrioventricular reciprocating tachycardia, inducible in 10 patients before therapy, became noninducible in 3 patients. Its rate was significantly slowed in the other 7 patients (from 346 +/- 50 to 471 +/- 81 ms). In 2 patients the tachycardia was nonsustained during flecainide treatment. Atrial fibrillation, inducible in all patients at baseline, was rendered nonsustained and more difficult to induce in 7 patients with flecainide. When isoproterenol was infused during flecainide treatment, complete anterograde (3 patients) or retrograde block (2 patients) persisted in the accessory pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, Tufts University School of Medicine, New England Medical Center, Boston, Massachusetts 02111.
authors.forename: A S
authors.initials: AS
authors.lastname: Manolis
authors.forename: N A
authors.initials: NA
authors.lastname: Estes
mesh_terms: D000293:Adolescent; D000328:Adult; D004594:Electrophysiology; D005260:Female; D005424:Flecainide / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D005500:Follow-Up Studies; D006801:Humans; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011433:Propranolol / Q000494:pharmacology; D014927:Wolff-Parkinson-White Syndrome / Q000188:drug therapy* / Q000503:physiopathology
chemical_list: D011433:Propranolol; D005424:Flecainide; D007545:Isoproterenol