Electrophysiological effects of flecainide and propafenone on atrial fibrillation cycle and relation with arrhythmia termination

Objectives-(1) To investigate the electrophysiological effects of flecainide and propafenone during atrial fibrillation, and their relation to arrhythmia termination; (2) to investigate the effects of isoprenaline on atrial fibrillation in basal conditions and during treatment with class 1C drugs to evaluate the role of adrenergic stimulation on proarrhythmic events occurring during this treatment. Design-Prospective, single centre study. Setting-University hospital. Methods-10 patients with lone paroxysmal atrial fibrillation underwent an electrophysiological study. The dynamic behaviour of MFF (the mean of 100 consecutive atrial fibrillation intervals) was evaluated at two atrial sites after induction of atrial fibrillation either at baseline or after class 1C drug administration (flecainide or propafenone 2 mg/kg). The effects of isoprenaline on MFF and RR interval were also investigated both under basal conditions and during class 1C drug treatment. Results-After induction of atrial fibrillation, mean (SD) MFF shortened with time, and was further shortened by isoprenaline infusion (177 (22) v 162 (16) v 144 (11) ms, p < 0.05). The administration of class 1C drugs reversed this trend and significantly increased the MFF to an average of 295 (49) ms, leading to conversion to sinus rhythm within 10 minutes in all patients. Atrial fibrillation was then reinduced on class 1C drugs: isoprenaline shortened the MFF and RR interval with a trend to AV synchronisation (223 (43) v 269 (49) ms for the MFF, 347 (55) v 509 (92) ms for the RR, p < 0.05); 1:1 sustained AV conduction occurred in two patients, at 187 and 222 beats/min respectively. One of these patients underwent electrical cardioversion because of haemodynamic collapse. Conclusions-Class 1C drugs are effective at restoring sinus rhythm by increasing the MFF to a much greater extent than observed in self terminating atrial fibrillation episodes, and reversing the spontaneous atrial fibrillation behaviour (progressive shortening of MFF and self perpetuation of atrial fibrillation). MFF prolongation with 1:1 conduction at fast ventricular rates may lead to synchronisation during adrenergic stimulation, with a very short ventricular cycle; hence it is advisable to keep the patients at rest after acute class 1C drug loading or to consider pharmacological modulation of AV conduction for patients who are prone to a fast ventricular response.