A case of diffuse large B-cell lymphoma with cardiac tumor presenting tachycardia-bradycardia syndrome associated with atrial fibrillation.

We report a rare case of diffuse large B-cell lymphoma (DLBCL) presenting with both nasal and cardiac tumors. The patient was a 77-year-old man who initially visited a local clinic with a two-month history of right-sided nasal discharge and nasal obstruction. A tumor lesion was identified in the nasal cavity, and he was subsequently referred to our hospital. Blood tests revealed leukocytosis, and computed tomography demonstrated a right nasal tumor, multiple lymphadenopathies, and an irregular mass in the right atrium. A biopsy of the nasal lesion confirmed the diagnosis of DLBCL. Transthoracic echocardiography revealed a relatively immobile cardiac mass, approximately 50 mm in diameter, located in the right atrium, which was suspected to represent cardiac infiltration of lymphoma. Chemotherapy with polatuzumab vedotin in combination with rituximab, cyclophosphamide, doxorubicin, and prednisone was initiated. During the clinical course, the patient exhibited tachycardic atrial fibrillation and sinus pauses lasting up to approximately six seconds, suggesting tachycardia-bradycardia syndrome. With ongoing chemotherapy, the cardiac tumor showed a marked reduction in size over time. To date, the patient has been successfully managed without pacemaker implantation. This case suggests that careful management, including close monitoring, is crucial for arrhythmias associated with cardiac involvement of malignant lymphoma. Learning objective: We encountered a rare case of malignant lymphoma with a cardiac tumor complicated by tachycardia-bradycardia syndrome and atrial fibrillation. Tumor reduction was achieved through chemotherapy, and careful observation allowed management without pacemaker implantation. This case highlights the need for cautious and individualized clinical judgment in the management of arrhythmias associated with cardiac lymphoma.