A massive Pericardial effusion classically causes the triad of a short QRS complex, tachycardia and electrical alternans.See also: Pulmonary and Pericardial
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This ECG is from a middle-aged man who presented with chest pain, tachycardia 130 bpm and BP 50/30. He was alert but cool and clammy. His background was unclear, but he mentioned chronic dyspnoea, 'cancer' and 'chest'. Fluids were started. This ECG was recorded the next day, after the arrhythmia recurred and was treated with ibutilide.