Rate-dependent flecainide effects on QRS duration in atrial fibrillation

Atrial fibrillation (AF) is an arrhythmia characterized by highly irregular atrial depolarization. Among various commonly used antiarrhythmic drugs, flecainide is known to decrease conduction velocity in a rate-dependent manner. The aim of this study was to establish a protocol to monitor flecainide’s rate-dependent conduction slowing, during physiologic increases in heart rate (HR) in patients with AF. QRS duration at rest and during symptom-limited bicycle exercise stress was measured in 9 patients with persistent AF before and during oral flecainide administration. Flecainide-induced QRS duration prolongation was more pronounced during exercise than at rest. In patients with AF, this characteristic can be monitored and quantified by measuring QRS duration under resting and exercise conditions, helping in determination of antiarrhythmic efficacy and preventing proarrhythmic effects in the individual patient.