Abstract
Atrial fibrillation (Af) is frequently seen in the emergency department (ED), and the main concern of which is the potential to lead to blockage of blood flow. Cardiac tumors can also present with Af, which are often overlooked due to the rarity but clinically significant. A 70-year-old woman presented at our ED with intermittent palpitation and dizziness for several weeks. She has an underlying disease of right thyroid follicular carcinoma status-post surgery many years ago, but no history of heart disease. Her electrocardiogram (ECG) showed Af, and the transthoracic echocardiography showed a huge mass occupying the left atrium. The patient underwent an open-heart surgery with tumor excision. The pathology revealed metastatic thyroid follicular carcinoma. The patient recovered smoothly, and her ECG showed normal sinus rhythm after the operation. Most cardiac secondary tumors remain clinically silent and are often diagnosed postmortem. These conditions are rare but clinically significant; therefore, the physician should always raise suspicion of metastatic cardiac tumor as the differential diagnosis when patient presents with an unexplained Af.