Case:
A 64-year-old male presented with a 2-year history of palpitations and light-headedness. Referral for electrophysiological assessment was prompted by a Holter monitoring report of ‘frequent ventricular ectopic beats (>21,000/24hr) with repetitive runs of atrial fibrillation” (Fig 1A). Resting echocardiogram suggested low-normal left ventricular function, and stress testing was normal. Electrocardiogram (ECG) at baseline was normal. A 12-lead rhythm strip was recorded during a brief burst of tachycardia in clinic (Fig 1B). What are the differential diagnoses for the arrhythmia?