Termination of acute atrial fibrillation in the Wolff-Parkinson-White syndrome by procainamide and propafenone: Importance of atrial fibrillatory cycle length

Abstract

The effects of intravenous procainamide (n = 30) or propafenone (n = 25) were evaluated in 55 patients with acute atrial fibrillation and the Wolff-Parkinson-White syndrome. All patients received either procainamide (12 to 15 mg/kg body weight) or propafenone (1 to 2 mg/kg) during sustained (>10 min) atrial fibrillation or after termination of nonsustained atrial fibrillation. Termination of atrial fibrillation was attributed to a drug if it occurred ≤ 15 min after infusion. Measurements included mean cycle length of fibrillatory electrograms (mean AA interval) as measured at the high right atrium and shortest RR interval between pre-excited cycles during atrial fibrillation.Atrial fibrillation terminated more frequently after procainamide administration (65%) than after propafenone (46%), although this difference was not significant. Procainamide prolonged the shortest pre-excited RR interval (228 ± 41 to 339 ± 23 ms, p = 0.0001) as did propafenone (215 ± 40 to 415 ± 198 ms, p = 0.0001) and the magnitude of increase was greater for propafenone (p = 0.048). Patients with sustained atrial fibrillation had shorter mean AA intervals than did their counterparts with nonsustained atrial fibrillation (123 ± 25 versus 186 ± 35 ms, p = 0.0001). Termination of sustained atrial fibrillation by either drug was accompanied by prolongation of the mean AA interval but not necessarily by the shortest pre-excited RR interval. Termination of atrial fibrillation was heralded by a 68% increase in the mean AA interval after procainamide administration compared with a 30% increase when the arrhythmia persisted. For propafenone the increases were 90% and 68%, respectively.These data suggest that intravenous propafenone is superior to procainamide in immediately slowing the ventricular response during atrial fibrillation in patients with the Wolff-Parkinson-White syndrome, although procainamide may be more effective in terminating the arrhythmia. Termination of atrial fibrillation by either drug is heralded by prolongation of the cycle length of fibrillatory waves.