A 30 year old woman with a three year history of intermittent palpitations presented to the emergency department following a typical episode. She was known to have β thalassaemia minor and took no regular medication. A 12 lead ECG on presentation demonstrated sinus rhythm with a PR interval of 112 ms but without evidence of ventricular pre-excitation. During examination, syncope occurred and transient asystole was observed on a bedside monitor. Subsequent ambulatory ECG monitoring demonstrated …