Giant Left Atrial Thrombus After Left Atrial Appendage Occlusion: Surgery Reveals a Transseptal-Site Origin

Device-related thrombus (DRT) is a recognized complication of left atrial appendage occlusion. Persistent iatrogenic atrial septal defect (iASD) has not been described as a source of late left atrial thrombus.

An 84-year-old man with prior WATCHMAN FLX (Boston Scientific) implantation had a residual iASD on 45-day transesophageal echocardiography (TEE). Eighteen months later, transthoracic echocardiography revealed a large left atrial mass. TEE demonstrated a 5.4 × 4.0-cm mobile thrombus and a separate 2.4 × 1.0-cm device-adherent thrombus, interpreted as fragmented or partially separated DRT. After 2 weeks of therapeutic anticoagulation, both persisted. Surgery identified a dominant organized thrombus anchored to the interatrial septum at the iASD, with a separate fibrinous thrombus adherent to the device. Both were excised, and the device was preserved.

A persistent iASD may act as a late thrombotic nidus and coexist with true DRT. Surgery can clarify the diagnosis and permit device preservation.

A persistent iASD after left atrial appendage occlusion may serve as a late nidus for a giant left atrial thrombus and may coexist with true DRT, a distinction that TEE may not resolve. Surgical extraction of a large, highly mobile thrombus persisting despite anticoagulation can be diagnostic and therapeutic while permitting preservation of a stable device.