Primary cardiac lymphoma treated with R-CHOP resulting in rhythm recovery and avoidance of permanent pacing: a case report.

Background: Primary cardiac lymphoma (PCL) is a rare, aggressive extranodal lymphoma involving the heart and pericardium. It often presents with nonspecific symptoms and conduction disturbance, resulting in diagnostic delay. Multimodal cardiac imaging can characterize PCL tumours and guide biopsy, while histology is required for definitive diagnosis and treatment. Case Summary: A man in his 60s with well-controlled HIV presented with recurrent syncope preceded by fever, chest pain, and fatigue. He was found to have profound first-degree atrioventricular block (PR interval 414 ms). Transthoracic echocardiography revealed a large interatrial septal mass protruding into both atria with close association to the aortic root. Cardiac CT, MRI, and FDG PET-CT confirmed a metabolically active mass extending around the peri-aortic structures. Transoesopheal-guided biopsy confirmed PCL of B-cell origin. R-CHOP chemotherapy was commenced with continuous cardiac monitoring. Despite paroxysmal atrial flutter and intermittent higher-grade AV conduction disturbance, permanent pacing was deferred. After two cycles of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP), imaging showed substantial tumour regression, reduced FDG avidity, and improved AV conduction (PR 250 ms) and resolution of syncope. Discussion: PCL can present with cardiogenic syncope due to tumour-related involvement of the conduction system and mass effect. This case highlights the value of early multimodal imaging to rapidly characterize cardiac masses and monitor treatment response, while emphasizing the necessity of tissue diagnosis. In selected stable patients, early chemotherapy may reverse tumour-related conduction disease, allowing for deferral of permanent pacemaker implantation.