Introduction
Atrial fibrillation (AF) is among the major risk factors for intracardiac thrombi that can lead to cerebral or systemic embolism.1 The majority of intracardiac thrombi are formed inside the left atrial appendage (LAA) due to turbulence and lower blood flow rates, particularly during AF.2,3Meanwhile, catheter ablation (CA) has become the first AF treatment choice in the last few decades. Prior to CA, when a thrombus is present in the LAA, safety evaluations must be performed, particularly in patients with persistent or long-standing persistent AF. Although the gold standard for the detection of intracardiac thrombi is transesophageal echocardiography (TEE), this method is associated with occasional technical and appraisal difficulties.
Contrast computed tomography (CT) is another standard method used for the detection of intracardiac thrombi and has the potential to replace TEE. Compared to TEE, CT is easier to perform and is related to lower levels of discomfort among physicians. Additionally, the level of difference observed in the evaluation of CT images is much lower than that in TEE. However, similar to TEE, CT can still show false-positive results under conditions of low blood flow or stasis in the LAA. In these situations, the contrast medium hardly fills the whole LAA, particularly the edge of LAA, at the time of CT. Some reports have shown that CT performed in the prone position is more useful in the differentiation of thrombi from stasis than scans performed in the supine position, as gravity can increase the spread of contrast dye into the top area of the LAA.4,5 It has been suggested that contrast CT conducted in the delayed or late phase yields improved accuracy in the detection of thrombi than that performed in the early phase.6-8 However, neither method is completely exclusive of false-positive results, and there is currently no known method that combines late-phase contrast CT and prone-position contrast CT (late-pCT) in this setting.
Therefore, with the aim of minimizing the rate of false-positive results, we sought to investigate the diagnostic accuracy of late-pCT in the detection of thrombi in the LAA among patients with persistent or long-standing persistent AF prior to CA and re-evaluated the LAA by intracardiac echocardiography (ICE) during CA.