[Proarrhythmic effect of propafenone in patients with atrial fibrillation and atrial flutter].

We present two cases of proarrhythmia after propafenone treatment. In the first case slowing of the flutter cycle length from 205 ms to 290 ms resulted in a change from well tolerated two to one atrioventricular conduction to one to one conduction with hypotension and presyncope. In the second case organization of atrial fibrillation to atypical atrial flutter and use-dependent left bundle branch block resulted in fast broad QRS tachycardia that mimicked ventricular tachycardia.