RESUMO
A 71-year-old woman presented to a clinic with the chief complaint of facial edema and dyspnea; chest radiography showed mediastinal mass shadow and right pleural effusion. Computed tomography guided biopsy of the mediastinal mass had been performed by her previous doctor, and she was diagnosed with diffuse large B-cell lymphoma. She was referred to our hospital for chemotherapy. Electrocardiography performed before initiating chemotherapy showed sinus arrest for about 4 s, and Holter electrocardiography showed sinus arrest for up to about 7.4 s, which was repeatedly observed 6 times, indicating sick sinus syndrome (SSS). The mediastinal mass completely excluded the superior vena cava, and considering the risk of infection, an extracorporeal pacemaker was not inserted. We believed that the tumor effect was the cause of sinus arrest; hence, chemotherapy initiation was prioritized. R-CHOP therapy preceding vincristine and prednisolone was started, and sinus arrest was not observed after initial treatment. SSS may have been caused by carotid hypersensitivity syndrome that involved the exclusion of carotid artery pressure receptors by the tumor or the direct stimulation of the vagus nerve by microtumor infiltration.