Fifty-year-old woman with lightheadedness

Clinical introduction A 50-year-old woman presented to the emergency department with a 3-year history of worsening episodes of lightheadedness, anxiety and diaphoresis. She was otherwise healthy. Her cardiovascular physical examination was normal apart from an irregularly irregular pulse of 105 beats per minute. When she arrived in the emergency department, a 12-lead ECG was obtained (figure 1). Figure 1 Patient’s ECG. Question What is the most likely diagnosis? Atrial fibrillation (AF) Atrial premature beats Atrioventricular (AV) reciprocating tachycardia Dual AV nodal non-reentrant tachycardia (DAVNNT) AV nodal re-entrant tachycardia