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A 21-year-old man presented with abdominal swelling, lower extremity edema, and progressive dyspnea of 1 month's duration. Physical examination was notable for mild respiratory distress, marked jugular venous distention, muffled heart sounds, a pulsus paradoxus of 30 mm Hg, and disappearance of the radial pulse with inspiration. A 12-lead electrocardiogram showed beat-to-beat variability in the amplitude of the QRS complexes (ie, electrical alternans). This prompted urgent transthoracic echocardiography that revealed a massive pericardial effusion with evidence of right ventricular diastolic collapse indicative of cardiac tamponade. Echocardiographic images obtained from consecutive cardiac cycles revealed a nearly 90° rotation of the heart from beat to beat (supplemental video online linked to this article), responsible for the electrical alternans seen on electrocardiography. Emergent pericardiocentesis resulted in removal of 1200 mL of fluid and immediate disappearance of the electrical alternans. The patient was subsequently diagnosed as having systemic lupus erythematosus; appropriate therapy was initiated, and he was discharged with no recurrence of pericardial pathology.
Electrical alternans is defined as alternating amplitude of the QRS complexes with every other beat. In the setting of a pericardial effusion, it is caused by the mechanical pendulum motion of the heart as it swings within the pericardial sac. The echocardiographic manifestation of marked beat-to-beat cardiac rotation is instructive in defining the genesis of this electrocardiographic phenomenon. Electrical alternans is an uncommon finding in patients with cardiac tamponade, with reported sensitivities of only 8% to 21%.1-3 However, electrical alternans is highly suggestive of pericardial effusion, with a specificity of 89% and a positive predictive value of 82%.1 In clinical practice, awareness of the presence of a pericardial effusion in a patient with cardiopulmonary symptoms is the critical first step in facilitating rapid diagnosis and treatment of cardiac tamponade.