Right atrial thrombosis after upgrading to a biventricular pacing/defibrillation system.

A 56-year-old man under right ventricular pacing for atrial fibrillation and bradycardia had congestive heart failure. He received a cardiac resynchronization pacemaker with a defibrillator. Four months later, follow-up transthoracic echocardiography showed a right atrial mass although he had no symptom. Transesophageal echocardiography showed a large immobile round-shaped mass on the defibrillation lead, which was attached to the free wall of the right atrium. One month after the initiation of anticoagulant therapy, the mass disappeared, suggesting that it was thrombotic. During the 5 month follow-up, he remained in good condition without the recurrence of right atrial thrombosis.