A 62 years old man with carcinoma of lung presented to emergency depament with respiratory distress. His EKG showed electrical alternans. The most likely diagnosis is: (A) Pneumothorax., (B) Pleural effusion, (C) Cardiac tamponade, (D) Constrictive pericarditis.
Answer is C. Electrical alternans is an electrocardiographic phenomenon of alternation of QRS complex amplitude or axis between beats and a possible wandering base-line. It is seen in cardiac tamponade and severe pericardial effusionMassive pericardial effusion produces a triad of:Low QRS voltageTachycardiaElectrical alternansRef: Harrison's 18/e p1972