We present a case of a 60 year old male who found to be in atrial
fibrillation during routine evaluation. Anticoagulation was initiated
for 36 hours and he was referred for TEE guided electrical
cardioversion. There was no thrombus identified in the left atrial
appendage, however the appendage was large and had a tongue like
accessory lobe along with spontanous contrast on the left atrium and its
appendage. TEE probe was not withdrawn, patient underwent successful
cardioversion with 200 joules and developed a thrombus in the left
atrial appendage immediately after cardioversion, which rapidly became
more dense. There was an associated marked decrease in appendage
velocities. Patient was hospitalized to initiate low molecular weight
heparin. This case highlights the need for vigilance in patients with
unknown duration of atrial fibrillation, who have received a short
duration of anticoagulant therapy and who have adverse appendage anatomy
as thrombus may develop immediately after cardioversion despite
anticoagulation.