Residual contrast medium in the LAA
The prone position tends to lead to the congestion of contrast medium due to the influence of gravity. Therefore, in patients with impaired LAA function, the contrast agent may not be completely removed from the LAA even in the late phase of contrast CT. The presence of residual contrast medium in the LAA during late-pCT indicated the presence of LAA dysfunction. Patients with AF and an LAA blood flow velocity <20 cm/s, as estimated by TEE, have 2.6 times the risk of ischemic stroke compared to those with a higher LAA velocity.25 Moreover, the presence of spontaneous echo contrast (SEC) in the LA or LAA on TEE is related to thrombus formation and LAA velocities < 20–25 cm/s.25,26Although CT cannot aid in the measurement of the exact LAA velocity or SEC in the LA or LAA, our study suggested that the presence of residual contrast medium in the LAA during late-pCT was associated with a LAA velocity ≤ 15 cm/s. This cutoff value was lower than that for TEE. Therefore, the presence of residual contrast medium on late-pCT implies a higher risk for thrombotic events.