SESSION TITLE: Medical Student/Resident Cardiovascular Disease Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: October 18-21, 2020 INTRODUCTION: While cardiac tamponade is unusual as the initial presentation of malignancy, malignant pericardial tamponade presenting as atrial fibrillation is even rarer. We present a case of atrial fibrillation with cardiac tamponade who was subsequently diagnosed with pulmonary adenocarcinoma CASE PRESENTATION: A 65-year-old woman presented with concerns of exertional shortness of breath for 1 week with dry cough, fatigue, and chest tightness, with a sudden worsening of respiratory symptoms and palpitations. She was hypotensive, tachycardic, and afebrile. Auscultation revealed muffled heart sounds and she had jugular venous distension. Her electrocardiogram showed atrial fibrillation with rapid ventricular response and no acute ST-segment changes. Chest x-ray showed blunting of her bilateral costophrenic angles with cardiomegaly, but no acute infiltrate. Computed tomography (CT) revealed moderate bilateral pleural effusions, moderate pericardial effusion (2-cm thickness), and bilateral noncalcified pulmonary nodules, with the largest measuring 1.7 x 2.4 cm at the left upper lobe (Image 1). Transthoracic echocardiogram revealed moderate to large pericardial effusion with early tamponade physiology (Image 2). She received emergent pericardial window surgery with drainage of exudative pericardial fluid. Cytological analysis revealed tumor cells positive for Ber-EP4, CK-7, and TTF-1 and negative for CK-20, PAX-8, and calretinin, consistent with metastatic adenocarcinoma likely from the lung. The patient had marked symptomatic improvement after the procedure, and her cardiac rhythm reverted to sinus rhythm. DISCUSSION: Nearly 18%–20% of autopsies performed on cancer patients show involvement of the heart or pericardium. Malignant pericardial effusions can occur by direct invasion of cancer or by metastatic invasion via the lymphatics or hematogenous spread. Tamponade physiology in patients with malignant pericardial effusion is associated with immediate mortality in up to 85% of cases. The association of atrial arrhythmias with cardiac tamponade is rare in the literature, and the association with malignant pericardial effusion is even rarer. Two cases in the literature report cardiac tamponade with atrial fibrillation as the first manifestation of malignancy—both were lymphoid in origin. This is the first case of newly diagnosed solid pulmonary tumor manifesting as atrial fibrillation with malignant pericardial tamponade. CONCLUSIONS: Despite its rarity, malignant pericardial tamponade with atrial fibrillation and rapid ventricular rate should be recognized and managed promptly to mitigate a potentially life-threating condition. Reference #1: Krisanda TJ. Atrial fibrillation with cardiac tamponade as the initial manifestation of malignant pericarditis. Am J Emerg Med. 1990;8(6):531–533. doi:10.1016/0735-6757(90)90157-u Reference #2: Refaat MM, Katz WE: Neoplastic pericardial effusion. Clin Cardiol. 2011;34:593–598. DISCLOSURES: No relevant relationships by Mohamed Elmassry, source=Web Response No relevant relationships by Amr Ismail, source=Web Response No relevant relationships by John Makram, source=Web Response No relevant relationships by Haneen Mallah, source=Web Response No relevant relationships by Ximena Solis, source=Web Response No relevant relationships by Victor Test, source=Web Response