Primary cardiac angiosarcoma initially presenting with sick sinus syndrome and pericardial effusion: a case report.

Background: Primary cardiac angiosarcoma is a rare and highly aggressive malignancy whose clinical presentation is primarily driven by local invasion and metastatic dissemination. Its rapid progression and frequent diagnostic delay contribute to a markedly poor prognosis. Case summary: We report a 64-year-old man who initially presented with pericardial effusion and symptomatic sick sinus syndrome, for which he underwent dual-chamber pacemaker implantation. A right atrial mass closely related to the pacing lead was subsequently detected and repeatedly interpreted as thrombus-like on transthoracic echocardiography, with markedly elevated D-dimer levels. Despite anticoagulation, the mass enlarged and multiplied, ultimately causing superior vena cava obstruction. Concurrent pulmonary nodules and ground-glass opacities developed. Surgical exploration and debulking revealed extensive tumour infiltration of the right atrium and venae cavae. Histopathology confirmed cardiac angiosarcoma. The patient remained haemodynamically unstable after surgery and was considered unsuitable for systemic antitumour therapy. He died 13 days after surgery. Discussion: This case highlights the diagnostic difficulty of primary cardiac angiosarcoma presenting with pericardial effusion and sick sinus syndrome, particularly when a right atrial mass is spatially related to a pacing lead and repeatedly appears thrombus-like on echocardiography. Progressive enlargement despite anticoagulation should prompt early reconsideration of malignancy and multidisciplinary evaluation.