Electrical Alternans as an Early Clue to a Rapidly Evolving Large Pericardial Effusion: The Role of Point-of-Care Ultrasound

Electrical alternans is an uncommon electrocardiographic finding classically associated with significant pericardial effusion and may raise suspicion for cardiac tamponade in the appropriate clinical context. We report the case of a 65-year-old man who presented with 3 days of progressive dyspnea 10 days after hospitalization for acute pericarditis, during which transthoracic echocardiography showed no pericardial effusion. On presentation, he was tachycardic at 110 beats/min and had jugular venous distension, while electrocardiography demonstrated prominent electrical alternans. Although he was not hypotensive and had no overt evidence of hemodynamic compromise, the combination of recent pericarditis, progressive dyspnea, venous congestion, and electrical alternans raised immediate concern for a rapidly evolving large pericardial effusion with clinical features suggestive of cardiac tamponade. Point-of-care ultrasound rapidly demonstrated a large pericardial effusion, prompting urgent transfer for definitive evaluation and management. Within minutes of transfer, the patient's respiratory distress worsened despite persistently preserved vital signs, and urgent pericardial drainage was performed. Approximately 1,200 mL of grossly hemorrhagic pericardial fluid was evacuated, resulting in rapid and marked clinical improvement. This case highlights electrical alternans as an important early clinical clue to significant pericardial effusion and emphasizes the value of immediate point-of-care ultrasound in the emergency department when cardiac tamponade is clinically suspected. It also demonstrates the dynamic nature of pericardial disease, showing that a large pericardial effusion with clinical features suggestive of cardiac tamponade may develop within a short interval after a previously negative echocardiographic examination. Integrating electrocardiographic findings with rapid bedside ultrasound assessment may facilitate earlier recognition of evolving clinically significant pericardial disease and timely definitive intervention.