A Comparison of Intravenous Propafenone and Flecainide in the Treatment of Tachycardias Associated with the Wolff-Parkinson-White Syndrome.

We compared the electrophysiological effects of intravenous propafenone and flecainide on accessory pathway conduction by a randomized crossover study in 16 patients with Wolff-Parkinson-White syndrome. The antegrade refractory period of the pathway increased from 256 ± 18 msec at baseline to 288 ± 13 msec on propafenone (P < 0.05) and to 296 ± 27 msec on flecainide (P = 0.075). The minimum preexcited RR interval during atrial fibrillation or incremental atrial pacing was prolonged from 225 ± 37 msec to 262 ± 22 msec by propafenone (P < 0.05) and to 301 ± 31 msec by flecainide (P < 0.005). The prolongation was significantly greater with flecainide than propafenane (P < 0.05). Both drugs increased tachycardia cycle length (TCL) from 310 ± 35 msec to 354 ± 37 msec (propafenone P < 0.005) and to 352 ± 37 msec (flecainide P < 0.01). Both propafenone and flecainide blocked antegrade conduction in the pathway in five patients, Both drugs rendered atrial fibrillation noninducible in seven patients and orthodromic tachycardia noninducible in five patients. Conclusions: (1) Flecainide causes a greater prolongation of minimum preexcited RR interval than propafenone; (2) There is no significant difference between propafenone and flecainide on the inducibility of arrhythmias, TCL, or incidence of antegrade conduction block. [ABSTRACT FROM AUTHOR]