Atypical response of class IC atrial flutter to adenosine.

We report the case of a 67-year-old female with a wide QRS complex tachycardia at 180 bpm. A diagnosis of class IC atrial flutter with aberrant ventricular conduction caused by flecainide therapy was formulated. Intravenous adenosine administration resulted in adequate slowing of the ventricular rate and normalization of QRS complexes. Restoration of sinus rhythm was achieved with intravenous amiodarone. The response to adenosine confirmed the diagnosis of supraventricular tachycardia with aberrant conduction, but the transition from arrhythmia onset to restoration of sinus rhythm showed interesting peculiarities.