Clinical introduction

A 39-year-old man presented to the Emergency Department (ED) with a 10-hour history of palpitations but denied any chest pain, breathlessness or syncope. His medical history and family history were unremarkable. On admission, he was tachycardic with an irregularly irregular pulse at 180 beats/min. ECG showed atrial fibrillation with fast ventricular response (figure 1A). Bed-side transthoracic echocardiogram demonstrated a structurally normal heart. Chemical cardioversion was therefore attempted with intravenous flecainide. A postcardioversion 12-lead ECG was obtained (figure 1B).