Electrocardiographical case. Elderly man with acute breathlessness. Atrial tachycardia with variable AV conduction block and transient hyperkalaemia-induced aberrant conduction.

A 67-year-old Chinese man presented to the emergency department with a history of abdominal bloating and shortness of breath. Initial electrocardiogram (ECG) showed atrial tachycardia (AT) with 2:1 atrioventricular (AV) conduction block. Six days after admission, he developed acute dyspnoea and confusion. Repeat ECG demonstrated a regular wide-complex tachycardia. Serum analysis revealed hyperkalaemia secondary to acute on chronic renal failure. Emergency treatment with intravenous calcium gluconate, 50% dextrose solution and short-acting insulin was instituted. The ECG promptly reverted to a narrow-complex AT with 2:1 AV conduction block. The diagnosis and treatment of AT are discussed.